RETICAL ORGANIC
-CHEMISTRY
COHEN
QV251
C6>1
THEORETICAL
ORGANIC CHEMISTRY
BY THE SAME AUTHOR
PRACTICAL ORGANIC CHEMISTRY
FOR ADVANCED STUDENTS
Globe 8v0. 4s.
CLASS BOOK OF ORGANIC
CHEMISTRY
Globe %vo.
Vol. I. 45. 6d. Vol. II. For Second Year
Medical Students and Others. 43. 6d.
LONDON : MACMILLAN & Co., LTD.
THEORETICAL
ORGANIC CHEMISTRY
BY
JULIUS B. COHEN, PH.D. B.Sc., F.R.S.
PROFESSOR OF ORGANIC CHEMISTRY, THE UNIVERSITY, LEEDS ; AND
ASSOCIATE OF THE OWENS COLLEGE.
MACMILLAN AND CO., LIMITED
ST. MARTIN'S STREET, LONDON
1920
COPYRIGHT.
First Edition, 1902.
Reprint, d) 1905, 1907 (with corrections), 1908 (twice}, 1910, 1911.
Second Edition, 1912. Reprinted, 1913, 1914, 1916, 1917,1918, 1919, 1920 (twice).
PREFACE
SOME apology for the appearance of a new text-book of
organic chemistry seems necessary ; for in face of the multitude
of its predecessors, the present volume can scarcely put forward
the customary claim of supplying a " long-felt want."
Whilst the study of general principles should form the ground-
work of every text-book, it is important, in a subject so essen-
tially practical as organic chemistry, to maintain a careful balance
between theory and practice. This has been my chief aim.
Organic chemistry has been so completely systematised so
few of the important links in the chain of facts are missing
that it offers great temptations to the teacher to place before the
student a series of equations, qualified by the statement that the
substances are acted upon by certain reagents, reduced with
nascent hydrogen^ treated with oxidising agents, &c., and other
vague directions which leave to the student the task of evolving
the practical details of the process for himself, and, what is
worse, transforming organic chemistry into a series of barren
formulas and bald equations.
To avoid this as far as possible, a description of the common
chemical reagents is introduced at the outset, and a number of
simple experiments are described in detail concurrently with an
account of many of the reactions.
The student is thus encouraged to study the reactions
practically a matter of very great consequence.
Another object of these experiments is to assist the teacher
in his class demonstrations ; for, with one exception (the pre-
paration of zinc ethyl, which cannot be conveniently carried out
in the class-room), they are devised so as to be completed
during the lecture, or occasionally in a second lecture, but,
vi PREFACE
in the majority of cases, to occupy not more than a few minutes.
For a reaction done in a test-tube is just as effective didactic-
ally as a more sensational experiment performed on a larger
scale, and involving a greater expenditure o.f time.
The book, including all these experiments, represents my
own course of about sixty lectures.
The production and uses of common materials, which come
under our daily observation, are frequently relegated in some
text-books of organic chemistry to a background of small
print ; in others they are entirely omitted. The reason for this
is not clear, unless it arises from our present ignorance of the
structural formulae and relations of some of these compounds,
and therefore from their lack of theoretical significance.
Whatever may be the cause, substances like lanoline, linseed
oil, gelatine, the tannins, turpentine, &c., are usually treated in
this stepmotherly fashion, and industrial processes, like tanning
and sugar-refining, the manufacture of varnishes, petroleum,
glycerine, soap, starch, &c., are dismissed with no more than
an honourable mention.
I make no shadow of a claim to having accomplished the task
of producing an ideal text-book. It is beset with many diffi-
culties. One difficulty arises from the very completeness of the
subject, for, to pursue the former metaphor, organic chemistry
forms not only a chain, but an endless chain of facts. At the
beginning, one is confronted with the difficulty that the simplest
organic compound involves a knowledge of others of greater
complexity. Certain assumptions have, in consequence, to be
made, which upset at once the natural development of theories,
and the gradual elaboration of the principles of structure, causing
the text to bristle with cross references, which cannot be avoided.
No attempt has been made to give anything like a complete set
of methods for preparing even the more important of the sub-
stances described ; on the contrary, the number has been care-
fully restricted to those which have a theoretical importance, or
practical value. For example, the numerous methods which are
generally introduced in describing the preparation of marsh-gas
are greatly curtailed, and the complex reactions involving the use
of zinc and magnesium alkyl compounds are grouped together in
a later portion of the book, where the close analogy, which they
PREFACE vii
exhibit, affords a better chance of their being understood and
remembered.
Another difficulty in compiling a text -book proceeds from the
introduction of theories, which cannot be exhaustively discussed
within the limits of a small volume. I do not regard this as a
real drawback ; for a suggestion, which arouses curiosity, is
better for the serious student, who will take a little trouble to
read for himself, than an elaborate and complete discussion of
the subject.
The idea of atomic space arrangement, which may now be
regarded as one of the corner-stones of organic chemistry
almost equalling in importance the theory of quadrivalent carbon
is introduced at an early stage and kept constantly in view.
The modern theories which are included under the head of
" physical chemistry " have at present only a subordinate interest
in organic chemistry, and have therefore been very briefly
mentioned with a reference to a text-book where the subject is
methodically developed and, therefore, more easily followed.
The time seems to have come when certain well-worn names,
which have done duty in the past, should now belong to history
and vanish from the text-book. We no longer think of esters as
compounds of ether with acids, as in the days of Berzelius, and
I make no apology for having discarded the terms ethereal salt
and ether applied in this sense.
The questions at the end of each chapter, many of which are
drawri from University B.Sc. pass-papers, and from the papers
of the Board of Education, South Kensington, are introduced
in response to the exigencies of the present universal system
of examination tests.
I wish to express my thanks to my friend and colleague,
Professor Smithells, for much valuable advice, and to Mr. A. T.
Simmons for his help in the correction of the proof sheets.
I am also indebted to many friends and former students for
details connected with technical processes with which they are
engaged.
J. B. COHEN.
THE YORKSHIRE COLLEGE,
October -, 1902.
PREFACE TO THE SECOND EDITION
SINCE the first appearance of this book, ten years ago,
new substances, processes, and reagents have been discovered,
some of which find a place in the present edition, so that, so
far as the elementary portions of the subject are concerned,
the book has been brought up to date. A number of new
experiments have also been added.
J. B. COHEN.
THE UNIVERSITY, LEEDS.
September, 1912.
CONTENTS
PAGE
INTRODUCTION i
The Growth of Organic Chemistry. The Scope of Organic
Chemistry. Reasons for the Distinction between Organic
and Inorganic Chemistry.
CHAPTER I. PURIFICATION OF SOLIDS AND LIQUIDS .... 5
Crystallisation. Sublimation. Melting- Point Determination.
Boiling- Point Determination. Fractional Distillation.
9
CHAPTER II. ANALYSIS OF ORGANIC COMPOUNDS 17
Qualitative Tests. Quantitative Analysis. Estimation of Car-
bon and Hydrogen. Estimation of Nitrogen. Estimation of
the Halogens. Estimation of Sulphur.
CHAPTER III. EMPIRICAL AND MOLECULAR FORMULA ... 30
Empirical Formula. Molecular Formula. Vapour Density
Methods of V. Meyer, Hofmann, Dumas. The Cryoscopic
Method. The Boiling- Point Method. Chemical Methods
for determining Molecular Weights.
CHAPTER IV. CLASSIFICATION 5
Reagents employed in Organic Chemistry. Classification of
Organic Compounds. Homologous Series.
ix
CONTENTS
PART I. ALIPHATIC COMPOUNDS.
PAGE
CHAPTER V. PARAFFINS, OR SATURATED HYDROCARBONS . 55
The Petroleum and Paraffin Industry. Addition and Substitu-
tion. Linking of Carbon Atoms. Methane. Ethane.
Propane. Butane. Pentane.
CHAPTER VI. HALOGEN DERIVATIVES OF THE PARAFFINS . 77
Ethyl Chloride. Ethyl. Bromide and Iodide. Reactions of
Methyl Iodide. Compound Radicals. Dihalogen Derivatives.
Ethylene and Ethylidene Compounds. Trihalogen Deriva-
tives. Chloroform. lodoform. Carbon Tetrachloride.
CHAPTER VII. THE ALCOHOLS 94
Constitution of the Alcohols. Primary, Secondary, and Tertiary
Alcohols. Methyl Alcohol. Fermentation. Theories of
Fermentation. Manufacture of Beer, Wines, and Spirits.
Alcoholometry. Ethyl Alcohol. Optical Activity.
CHAPTER VIII. THE ETHERS 116
Constitution of Ether. Metamerism. Ethyl Ether.
CHAPTER IX. ALDEHYDES AND KETONES 123
Constitution of Aldehydes and Ketones. Formaldehyde. Poly-
merisation. Acetaldehyde. Paraldehyde. Chloral. Acetone.
Condensation.
CHAPTER X. THE FATTY ACIDS 144
Constitution of the Fatty Acids. Formic Acid. Acetic Acid.
Vinegar. The Acetates. Propionic Acid. Butyric Acid.
Valeric Acid. Oils, Fats, and Waxes. Manufacture of
"Stearine" Candles. Soaps. Butter. Butter Substitutes.
CHAPTER XI. THE ACID CHLORIDES, THE ANHYDRIDES,
AND THE AMIDES 173
The Acid Chlorides. The Anhydrides. The Amides.
CONTENTS
CHAPTER XII. THE ESTERS
Esters of Organic Acids. Hydrolysis. Esters of Inorganic
Acids. The Nitro- paraffins.
CHAPTER XIII. SULPHUR COMPOUNDS !94
Mercaptans. Sulphonic Acids and Sulphonates. Thio-ethers.
CHAPTER XIV. THE AMINES 198
Primary, Secondary, and Tertiary Amines. Quaternary Am-
monium Compounds.
CHAPTER XV. THE CYANOGEN COMPOUNDS . 209
Cyanogen. Hydrocyanic Acid. The Metallic Cyanides. Cyanic
and Cyanuric Acids. Thiocyanic Acid and Thiocyanates.
Nitriles. Carbamines. Mustard Oils.
CHAPTER XVI. THE ALKYL COMPOUNDS OF PHOSPHORUS,
ARSENIC, AND SILICON, AND THE ORGANO-METALLIC
COMPOUNDS 231
The Phosphines. The Arsines. The Cacodyl Compounds.
Silicon Alkyl Compounds. Zinc Alkyl Compounds. Syn-
thetic Uses of the Zinc Alkyl Compounds. Magnesium Alkyl
Compounds.
CHAPTER XVII. THE UNSATURATED HYDROCARBONS . . . 245
The Olefmes. Ethylene. The Acetylenes. Acetylene.
CHAPTER XVIII. DERIVATIVES OF THE UNSATURATED
HYDROCARBONS 264
Allyl Compounds. Acrolein. Acrylic Acid. Oleic Acid.
Linseed Oil.
CHAPTER XIX. THE POLYHYDRIC ALCOHOLS 273
The Glycols. Ethylene Glycol. Ethylene Oxide. Choline.
Neurine. Taurine. Glycerol. Nitroglycerine.
xii CONTENTS
PAGE
CHAPTER XX. THE CARBOHYDRATES 287
Glucose. Fructose. Galactose. Mannose. Cane-sugar. Milk-
sugar. Maltose. Starch. Dextrin. Cellulose. Gun-cotton.
CHAPTER XXI. DERIVATIVES OF THE FATTY ACIDS . . . 314
The Hydroxy-acids. Glycollic Acid. Lactic Acid. Stereo-
isomerism of the Lactic Acids. The Amino-acids. Glycine.
Sarcosine. Betaine. Creatine. Creatinine. The Alde-
hydic and Ketonic Acids. Glyoxalic Acid. Pyruvic Acid.
Acetoacetic Ester Its Synthetic Uses. Levulinic Acid.
CHAPTER XXII. THE DIBASIC ACIDS AND THEIR DERIVA-
TIVES 332
The Dibasic Acids. Carbonic Acid. Carbonyl Chloride.
Urethane. Urea. Oxalic Acid. Malonic Acid. Synthetic
Uses of Malonic Ester. Succinic Acid. Malic Acid. Tar-
taric Acid. Stereoisomerism of the Tartaric Acids. Citric
Acid. The Unsaturated Dibasic Acids. Stereoisomerism of
the Unsaturated Compounds.
CHAPTER XXIII. THE UREIDES . . . 366
Uric Acid. Constitution of Uric Acid. Xanthine. Guanine.
Theobromine. Caffeine.
CHAPTER XXIV. THE PROTEINS 372
Composition of the Proteins. Classification of the Proteins.
Albuminoid Substances. Gelatine. Glue.
PART II.-AROMATIC COMPOUNDS.
CHAPTER XXV. THE AROMATIC HYDROCARBONS 375
Kekule's Theory. Properties of Aromatic Compounds. Distil-
lation of Coal-Tar. Benzene and its Properties. Toluene.
Friedel and Crafts' Reaction. Structure of Toluene.
Nucleus and Side-Chain. Action of Chlorine on Toluene.
The Xylenes. Oxidation of the Xylenes. Mesitylene.
Pseudocumene. Cumene. Cymene. Structure of Benzene.
Orientation.
CONTENTS
CHAPTER XXVI. AROMATIC HALOGEN COMPOUNDS .... 399
Halogen Substitution Products. Chlorobenzene. Bromo-
benzene. lodobenzene. Chlorotoluenes. Benzyl Chloride.
Benzal Chloride. Benzotrichloride. Properties of the
Halogen Derivatives.
CHAPTER XXVII. AROMATIC NITRO-COMPOUNDS 405
Nitrobenzene. Dinitrobenzene. Trinitrobenzene. Nitro-
toluenes. Dinitrotoluenes. Properties of the Nitro-Com-
pounds.
CHAPTER XXVIII. THE AMINO-COMPOUNDS OR AROMATIC
AMINES 411
Properties of the Amino-Compounds. Primary, Secondary, and
Tertiary Amino-Compounds. Aniline. Acetanilide. Nitrani-
lines. Chloranilines. Alkylanilines. Methylaniline. Di-
methylaniline. The Toluidines. Benzylamine. Diphenyl-
CHAPTER XXIX. THE DIAZO-COMPOUNDS 428
Reactions of the Diazo- Compounds. Phenylhydrazine. Diazo-
aminobenzene. Aminoazobenzene.
CHAPTER XXX. THE AZO-COMPOUNDS 43 6
Azobenzene. Hydrazobenzene. The A zo- Colours.
CHAPTER XXXI. THE SULPHONIC ACIDS 444
Benzenesulphonic Acid. Benzenesulphonic Chloride.
CHAPTER XXXII. THE PHENOLS 45
Properties of the Phenols. Ordinary Phenol. Phenol Ethers.
Nitrophenols. Picric Acid. Dihydric Phenols. Catechol.
Resorcinol. Quinol. Trihydric Phenols. Pyrogallol.
Phloroglucinol.
CONTENTS
CHAPTER XXXIII. AROMATIC ALCOHOLS, ALDEHYDES, KE-
TONES, AND QUINONES 467
Benzyl Alcohol. Aromatic Aldehydes. Benzaldehyde. Aro-
matic Ketones. Acetophenone. Benzophenone. Phenolic
Alcohols and Aldehydes. Saligenin. Salicylaldehyde. Van-
illin. Quinones. Benzoquinone.
CHAPTER XXXIV. THE AROMATIC ACIDS 479
Benzoic Acid. Benzoic Anhydride. Benzamide. Benzoic
Esters. Toluic Acid. Cumic Acid. Phenolic Acids. Sali-
cylic Acid. Anisic Acid. Protocatechuic Acid. Gallic
Acid. Tannins. Dibasic Acids. Phthalic Acid. Iso-
phthalic Acid. Terephthalic Acid. Phenylacetic Acid.
Mandelic Acid. Cinnamic Acid.
CHAPTER XXXV. THE TERPENES AND CAMPHORS 502
Pinene. Limonene. Camphor. Borneol. Menthol. Ole-
finic Terpenes and Camphors.
CHAPTER XXXVI. MULTINUCLEAR HYDROCARBONS AND
THEIR DERIVATIVES . . 508
Diphenyl. Benzidine. Tolidine. Diphenylmethane. Tri-
phenylmethane. Triphenylm ethane Colours. Malachite
Green. Rosaniline. Aniline Blue. Methyl Violets. Phenol-
phthalein. Eosin. Aurin and Rosolic Acid. Indigo.
CHAPTER XXXVII. NAPHTHALENE AND ITS DERIVATIVES . 527
Structure of Naphthalene. Halogen Derivatives. Nitro-
Derivatives. Naphthylamines. Naphthalenesulphonic Acids.
Naphthols. Naphthaquinones. Naphthoic Acids. Ace-
naphthene.
CHAPTER XXXVIII. ANTHRACENE AND ITS DERIVATIVES . . 542
Anthracene. Synthesis of Anthracene, Anthracene Hydride,
and Anthraquinone. Anthraquinone. Alizarin. Phenan-
threne. Phenanthraquinone.
CONTENTS
CHAPTER XXXIX. HETEROCYCLIC COMPOUNDS . : . . . 556
Furfurane. Furfurole. Thiophene. Pyrrole. Pyrazole. Anti-
pyrine. Pyridine. Homologues of Pyridine. Pyridine
Carboxylic Acids. Quinoline. Derivatives of Quinoline.-
Isoquinoline. Acridine. Carbazole.
CHAPTER XL. THE ALKALOIDS 574
Pyridine Alkaloids. Piperine. Conine. Nicotine. Atropine.
Cocaine. Quinoline Alkaloids. Cinchona Alkaloids. Opium
Alkaloids. Morphine. Strychnos Alkaloids. Strychnine.
Brucine.
INDEX ,..* 5^7
THEORETICAL ORGANIC
CHEMISTRY
INTRODUCTION
The Growth of Organic Chemistry. Organic chemistry is
a branch of the science of comparatively recent development.
Its real history begins about the year 1830. This statement
does not imply that either organic substances or processes were
unknown prior to that date. Numerous animal and vegetable
products, sugar, starch, oils, gums, resins, &c, had been familiar
commodities from the earliest times. Nations had long been
acquainted with the methods of soap-making and of dyeing
with vegetable dyes. A knowledge of fermentation and of dis-
tillation had produced alcohol, turpentine, essential oils, and
acetic acid. Towards the close of the eighteenth century
Scheele had added to the number of organic acids by the
separation of malic acid from apples, citric acid from lemons,
oxalic acid from sorrel, benzoic acid from gum benzoin, and
lactic acid from sour milk, and he had further obtained
glycerine from olive-oil. But, beyond the investigation of a
certain number of natural products, organic chemistry had
inspired as yet no sustained or systematic study. Indeed no
progress could be made until the phlogistic theory had been
abandoned, but with the dawn of the new century the true
nature of combustion and of the composition of organic com-
pounds were placed in their true light. It was Lavoisier who first
showed that organic compounds consisted of carbon, hydrogen,
3E B
2 THEORETICAL ORGANIC CHEMISTRY INTRO.
and frequently oxygen, to which Berthollet afterwards added
nitrogen. Even then the subject attracted little attention,
mainly for the following reasons. Inorganic chemistry included
mineral substances and their derivatives and inorganic com-
pounds were distinguished by simplicity of composition. A
substance consisting of two or three elements contained them
in one, sometimes in two, rarely in three proportions. There
was only one substance (common salt) consisting of sodium and
chlorine; only one substance (water) consisting of hydrogen
and oxygen ; only one compound (gypsum) containing calcium,
sulphur, and oxygen ; but, among organic compounds, sub-
stances so different in properties as alcohol, sugar, glycerine,
acetic acid, oils, and fats, contained the same three elements,
carbon, hydrogen, and oxygen, in different proportions. It was
inconceivable that such differences in character and complexity
could be evolved out of the same three elements without the
intervention of some special power, and this was termed vital
force. The living world, so it was held, laid aside the rules
which governed inorganic chemistry. It possessed its own
laws of combination and its own force of affinity. Its products
were called organic to denote their origin from living or organ-
ised matter. The improved method of organic analysis intro-
duced by Berzelius in 1814, by means of which he succeeded in
making accurate determinations of the composition of some
of the organic acids, revealed the simple atomic ratio of the
constituent elements, and so removed one distinction between
organic and inorganic compounds. But it was long before the
complete synthesis of purely organic substances from inorganic
materials shook the firmly-rooted belief in a vital force. It is
true that Scheele, as far back as 1776, had obtained oxalic acid,
hitherto only found in sorrel, from sugat and nitric acid ; that
Dobereiner, in 1822, had shown that tartaric acid on oxidation
yields formic acid, which had been previously obtained by the
distillation of ants with water ; that in 1826 Hennel, an English
apothecary, had synthesised alcohol, and that a little later
(1828) Wohler prepared urea, a purely animal product, from
lead cyanate and ammonium chloride ; but none of these
artificial substances was entirely independent of an animal or
vegetable origin. Even the cyanates were derived in the first
instance from potassium ferrocyanide, in the preparation of
INTRODUCTION
which animal matter was employed. But, as year by year new
synthetic products were added to the list of organic compounds,
this last barrier which separated organic from inorganic
chemistry was swept away, and organic chemistry became the
chemistry of carbon compounds.
It was when organic chemistry had reached this stage in its
history that it was stimulated into new life by the appearance
in 1832 of the classical research of Liebigand Wohler on " The
Radical of Benzoic Acid," which, they truly said, " might shed
a new light on the vast and unexplored region of organic
Nature. 551
Organic chemistry, which then comprised a few hundred
substances derived from animal and vegetable sources, now
includes some hundred thousand compounds, for the most part
artificial products of the laboratory. Through what agency
has this extraordinary development been accomplished? It
may be traced to two causes. One is the discovery of the laws,
first formulated by Kekule in 1858, which underlie the structure
of organic compounds. These laws have served not only to
co-ordinate and link together in a simple fashion the great mass
of organic substances ; but have enabled chemists to predict
with some certainty the existence of others yet unknown. The
other cause is the industrial application of discoveries in organic
chemistry (initiated by Perkin in 1856 by the introduction into
commerce of the first coal-tar colour) wherein theory and
practice have been happily blended to the great advantage of
both. The art of the dyer has been entirely revolutionised
by the introduction of artificial dye-stuffs, the skill of the
surgeon has been marvellously aided by the discovery of
anaesthetics and antiseptics. The photographer relies
on organic "developers. 55 Artificial drugs of established
purity are used in medicine, artificial essences in perfumery.
Moreover, the organic chemist controls such industries as
tanning and calico-printing, and the making of starch, soap,
paper, paraffin, ink, glue and gelatine, rubber, explo-
sives, &c.
The distinction between inorganic and organic chemistry,
though now purely arbitrary, is still retained for reasons
1 Vide Ladenburg's History of Chemistry -, trans, by L. Dobbin. Clay, Edin-
burgh, 1905.
B 2
4 THEORETICAL ORGANIC CHEMISTRY INTRO.
of convenience, but not because there exists any fundamental
difference between the two branches of the science.
Reasons for the Distinction between Organic and In-
organic Chemistry. The reasons for preserving this division
are, in the first place, the large number and complexity of
organic compounds. The number has already been referred to ;
the complexity of some of these compounds may be illustrated
by the following examples : -
Turpentine, C 10 H 16
Cane-sugar, C 12 H 22 O 11
Stearin, C 57 H 110 O 6
Starch (soluble), C 1200 H 2000 O 1000
In the second place, organic chemistry has its peculiar re-
agents and processes, arising from the nature of the compounds
and the variety of products to which they give rise. A solution
of ferrous sulphate may be oxidised by weak or strong nitric
acid, chlorine, bromine, potassium permanganate, hydrogen
peroxide, &c., and one product, ferric sulphate, results ; but the
effect of these reagents on an organic substance like grape-sugar
would probably be a different product in each case.
In the third place, the study of organic substances cannot be
limited to a knowledge of their composition. Sulphuric acid is
represented by the formula H 2 SO 4 , and that formula stands
for one substance only ; but the formula C 2 H 6 O stands both
for ethyl alcohol and dimethyl ether. Such substances, which
have different properties, but possess the same simple formula,
, are said to be isomeric (iVoy, equal or like ; pepos, a part), and
this is a striking characteristic of organic compounds. The
formula C 8 H 12 O 4 represents 66 compounds.
It is obvious that, if we wish to distinguish between isomeric
substances, we must learn something more than their mere com-
position. We must discover the different arrangement of the
atoms in the molecule upon which the properties of the various
isomeric compounds depend. We must determine, not only their
composition, but their structure or constitution. In other words,
we must find a 'structural or constitutional as well as a simple
formula. This is one of the chief objects of organic, chemistry.
It may be accomplished by disintegration, or cleavage, i.e.
breaking down the molecule into simpler parts ; or by synthesis^
INTRO. INTRODUCTION
i.e. building up the more complex substance from its simpler
constituents. As a rule, disintegration precedes synthesis.
When the former has revealed the structure of a compound, its
synthetic production has been only a question of time. In this
way many substances are now prepared artificially which were
formerly known only as natural products. This has been the
case with oil of bitter almonds, alizarin, indigo, Tyrian purple,
grape-sugar, caffeine, camphor, menthol, and a host of others.
It may come to pass that albumin, the universal constituent of
living matter, will one day be obtained synthetically ; but it
must be remembered that between the synthesis of the most
complex of individual organic substances and that of the
simplest living cell there exists, and probably always will exist,
an impassable gulf.
CHAPTER I
PURIFICATION OF SOLIDS AND LIQUIDS
BEFORE it is possible to determine the constitution of an
organic substance, it is first necessary to be assured that it
consists of one individual, or in other words, that it is a pure
substance. It is then analysed qualitatively and quantitatively,
the weight of its molecule is determined, and finally its
chemical behaviour is studied.
Crystallisation. If the substance under investigation is a
solid or mixture of solids, it may be purified by crystallisation.
The majority of organic substances can be obtained in the
crystalline form by employing a suitable solvent, or mixture
of solvents. A suitable solvent is one which dissolves much
more of the substance when hot than cold, so that the hot
saturated solution deposits a quantity of the solid on cooling.
The usual solvents are water, boiling-point (b.p.) 100 ; methyl
alcohol, b.p. 66 ; ethyl alcohol, b.p. 78 ; ether, b.p. 35 ; acetone,
b.p. 56 ; chloroform, b.p. 6i c ; benzene, b.p. 80; petroleum spirit,
b.p. 7o-9o ; ethyl acetate, b.p. 77 ; acetic acid, b.p. 119, &c.
It is sometimes convenient to use two miscible solvents, one
of which dissolves the substance readily, and the other only
slightly.
EXPT. I. Dissolve about 2 grams of acetanilide in 10 c.c. of
absolute alcohol. No separation takes place on cooling. Add to the
hot alcoholic solution 20 c.c. of hot water. On cooling crystals of
acetanilide separate and fill the liquid.
If more than one substance is present, one of the substances
may be soluble and the others insoluble in the solvent.
Separation is then partially effected by filtration. If they all
PURIFICATION OF LIQUIDS AND SOLIDS
dissolve, as more frequently happens, it is unlikely that they
will be equally soluble, and consequently the first crystals
which separate from the hot saturated liquid will represent
the least soluble portion. If the mother-liquors are now con-
centrated by evaporation, a second crop of crystals will be
deposited, which will contain a larger proportion of the more
soluble constituent. The mother-liquors from these will contain
a still greater proportion of the more soluble constituent
and so on. By a repetition of this process, which is termed
A
55
50
45
4O
35
SO
25
20
B-l?(
A-1C
B
55
50
45
40
35
30
25
2O
15
per
) cent
X
/
A
\
/
\
/
/
S
\
/
\
/
VI
3 1O 2O 3O 4O 5O 6O 7O SO 9O 1C
)O 90 SO 70 6O 5O 4O 3O 2O 1O <
FIG. i.
fractional crystallisation^ the mixture may be separated more /
or less completely into its constituents. Microscopic examina-
tion will often show if the crystals are homogeneous or not by
the difference in crystalline form. The process of crystallising
requires practice and skill, and is one of the most important
operations in organic chemistry.
Sublimation. Another method of purification, which is '
occasionally employed, is sublimation. The process may be
carried out in various ways. One method is to place the
substance in a large watch-glass on a sand-tray which is
heated by a small flame. The substance is covered with a
sheet of filter-paper, held in position by a second inverted
watch-glass or funnel. The volatile substance sublimes on the
8
THEORETICAL ORGANIC CHEMISTRY
filter-paper whilst the non-volatile compound remains on the
watch-glass.
Distillation in steam may be used occasionally for effecting
the separation of solids and liquids. An experimental illus-
tration of the process will be given later (p. 412).
Melting-Point Determination. It is well known that the
presence of a " foreign ingredient " lowers the melting-point of
a substance. Fusible metals are made on this principle. If
we made various mixtures of two substances A and B and
plotted their melting-points as
ordinates and the quantities as abscissae
we should obtain a curve something like
that in the accompanying Fig. I. The
melting-point of each would fall with
successive additions of the second sub-
stance until it reached a minimum
and would then rise until the second
pure substance alone was present.
Successive crystallisations would show
by a change or otherwise in melting-
point if the substance were pure. Slow
liquefaction is an indication that the
substance is impure for the following
reason : on cooling a mixture of two
substances, the one that predominates
would separate until the mixture of mini-
mum melting-point (eutectic point) is
attained, when the whole would solidify.
On heating a mixed solid the reverse occurs, and if the
process takes place slowly some of the more fusible mixture
will melt, leaving the purer and therefore higher melting
substance. Thus the melting is protracted and may take place
through a wide range of temperature. *
The apparatus used for determining the melting-point is shown
in Fig. 2. A small quantity of finely powdered substance which
has been carefully dried is introduced into a capilliary tube
sealed at one end. The tube is attached to a thermometer so
that the substance is level with the bulb. The attachment may
be made by a narrow rubber ring,. or by simply moistening the
side of the capillary tube by contact with the thermometer
bulb which has been dipped into the liquid in the large test-
FlG. 2.
I PURIFICATION OF SOLIDS AND LIQUIDS 9
tube. When pressed against the thermometer stem the
capillary tube adheres. The thermometer passes through a cork
inserted into a pear-shaped vessel with a long neck containing
concentrated sulphuric acid or castor-oil. The vessel fits into a
metal stand which can be placed upon a tripod, and is heated
very gradually by a small flame. When a certain temperature
is reached, the substance, if pure, melts suddenly within a range
of I or 2 degrees. When approaching the melting-point, it is
desirable to remove the flame, or turn it very low, so that the
rise of temperature is very gradual. As stated above, if the
liquefaction is protracted it is an indication that the substance
is not pure.
Some substances do not melt, but, on reaching a certain
temperature, decompose. The purity of such substances can
only be approximately gauged by repeated crystallisation and
careful microscopic examination. It is difficult to establish with
certainty whether substances like resins, dextrins, and proteins,
which do not crystallise, are single individuals or not, and
purification is rendered very troublesome.
Boiling-Point Determination. Pure volatile liquids have a
constant and definite boiling-point. This is ascertained by
FIG. 3. Apparatus for determining the boiling point.
distilling the liquid in the apparatus shown in Fig. It consists
of a flask with a side-tube (distilling-flask), which fs attached to
io THEORETICAL ORGANIC CHEMISTRY CHAP.
a condenser. A second flask (receiver) is placed below the end
of the condenser. A thermometer is inserted into the neck of
the distilling flask.
A standard thermometer must be used, and correction made for
barometric pressure, which is approximately o'O43 for every I mm.
below 760 mm. (Landolt). A further correction is required for the thread
of mercury which may project above the vessel. For this correction
the following formula may be used :
N(T - t) -000154,
where T = apparent temperature in degrees Centigrade.
/ = temperature of a second thermometer, the bulb of which is
placed at half the length N above the vessel.
N = length of the mercury column in degrees from above the
vessel to T.
0-000154 = apparent expansion of mercury in glass.
This correction may be avoided by using short (Anschiitz) thermo-
meters, in which the mercury thread is entirely immersed in the vapour.
FIG. 4. Distillation under diminished pressure.
A rough correction for points above 100 may be made by determining
the boiling-points of pure organic substances, such as naphthalene,
2 1 6 -6, c.
The liquid is then boiled, and the temperature noted
as the liquid distils. If the liquid is pure, the tempera-
ture, indicated by the thermometer, during the distillation
does not fluctuate. Some liquids of high boiling-point,
like glycerol (glycerine), which, under atmospheric pressure,
I PURIFICATION OF SOLIDS AND LIQUIDS n
undergo decomposition near the boiling-point, may be distilled
under diminished pressure, which naturally lowers the boiling-
point. The simplest apparatus for effecting this operation
is shown in Fig. 4. It consists of a distilling apparatus like
that described, but in place of an ordinary flask a second
distilling-flask serves for the receiver, the neck of which is
tightly attached to the condenser, and the side- tube to a gauge
and water-jet aspirator. Sometimes it is desirable to omit the
condenser, and the side-tube of the distilling-flask is then
inserted into the neck of the receiver.
Fractional Distillation. If the liquid is not a single sub-
stance, but a mixture, it is often possible to separate the
constituents by a single distillation, provided the boiling-points t
lie widely apart. The more volatile liquid first passes over,
the temperature quickly rises, and the liquid of higher boiling-
point distils. It is otherwise when a liquid consists of sub-
stances boiling at temperatures not very far removed from
one another, especially in the case of chemically related sub-
stances, such as constitute petroleum and coal-tar naphtha.
One distillation suffices only to produce a very incomplete
separation, a portion of the less volatile liquid being carried over
in the first distillate, together with the more volatile body, the
temperature gradually rising throughout the distillation. In
order to effect separation of the several substances, recourse is
had to the method of fractional distillation. The liquid is dis-
tilled in a round flask, which is surmounted with a fractionating '
column, holding the thermometer. Various forms of fractionating
columns are used (Fig. 5.)
The effect of the column may be explained as follows. The
vapour given off from a mixture ?>f liquids contains, as a rule,
a larger proportion of the more volatile constituent than the
liquid. If this vapour is partly condensed in its ascent, the
vapour above this condensed liquid will be still richer in the
more volatile constituent. If, by a series of constrictions or
diaphragms, the condensed liquid is obstructed in its return flow,
a momentary equilibrium between liquid and vapour is estab-
lished at each diaphragm, and the longer the column the greater
will be the amount of the more volatile constituent in the last
portion of vapour to undergo condensation. This passes off 'by
12 THEORETICAL ORGANIC CHEMISTRY CHAP.
the condenser, and is collected in the receiver. By this means
a partial separation is effected, and the portions distilling within
a range of a small number of degrees are collected in separate
flasks. Each of these portions or fractions is redistilled, and col-
lected within still narrower limits of temperature, until at length
k
B
FIG. 5 represents a series of simple and efficient fractionating columns or still-heads.
A is that of Vigreux, in which the constrictions are formed by indenting the
tube itself ; B is Hempel's column 'and consists of a long wide tube filled with
glass beads ; c, D, and E are columns devised by Young and Thomas, the last
being useful when large quantities of liquid have to be distilled, c contains
a series of glass discs fused on to a rod, which can be removed from the tube ;
D has a series of pear-shaped bulbs blown on the stem, and E is a wide tube
with a series of constrictions in each of which a small bent glass dripping tube
is suspended in a gauze cup.
the mixture is separated into certain portions, the boiling-points of
which are nearly constant, and these may be regarded as
pure.
The following tables, I. and II., illustrate two series of frac-
i PURIFICATION OF SOLIDS AND LIQUIDS i^
tional distillations of coal-tar naphtha containing a small quantity
of paraffin boiling below 80 ; benzene, b.p. 80 ; toluene, b'.p. 1 10;
and xylene, b. p. 140. In the first fractionation (Table I.)
the distillate is collected between every 5 degrees.
TABLE I.
A
B
C
D
E
F
G
7i'5-85
85-90
9-95
95-ioo e
loo'-ios"
105 -110
iio-ii5
19 c.c.
53 c.c.
26 c.c.
15 c.c.
13 c.c.
17 c.c.
21 C.C.
33 c.c.
In the second fractionation (Table II.) each of the first distillates
is redistilled and collected within a narrower range of tempera-
ture. Thus, the first fraction (A) is distilled until the thermometer
registers 79. Fraction B is then added, and the distillate divided
into two fractions, 79-8i and 8i-85. Fraction C is added, and
so forth. The new fractions, C and E', are again fractionated.
Ultimately, two fractions are obtained; B' consisting of nearly
pure benzene, and F' of nearly pure toluene.
TABLE II.
A'
below
B'
79 -8T
C'
8i-8 S
D'
8 5 -io 5
E'
1050-108
F'
io8-no
Residue
A
Added B . .
42 c.c.
(lOC.C.*)
c. .
fec.c.)
D, E
50 c.c.
F. .
(II C.C.*)
G. .
22 C.C.
42 c.c.
*RefractionatedC'
12 C.C.
7 c.c.
E'
,
6 c.c.
5 c.c.
5 c.c.
54 c.c.
7 c.c.
50 c.c.
6 c.c.
27 c.c.
42 c.c.
THEORETICAL ORGANIC CHEMISTRY CHAP.
EXPT. 2. Distil a
mixture of 20 c.c. of
alcohol, b.p. 78, and
50 c.c. of water, b.p.
100. The mixture will
not inflame. Collect
the first 10 c.c. of the
distillate. The liquid
now contains such a
large proportion of al-
cohol that it readily
takes fire.
If the fractional dis-
tillation has to be con-
ducted in vacua it is
undesirable to inter-
rupt the boiling in FlGt 6 . Receiver for fractional distillation under
Order tO remove the reduced pressure.
receivers containing different fractions. Various forms of
apparatus have been devised for continuous fractional dis-
tillation under reduced pres-
sure, one of which is shown
in Fig. 6.
The apparatus (Fig. 6) con-
sists of a double receiver, a
and b ; c and e are ordinary
two-way taps, whilst d is a
three-way tap pierced length-
wise and crosswise as shown
in section at f. The aspir-
ator is attached to the limb
marked with an arrow. Dur-
ing the distillation the taps
c and d connect the appar-
atus with the aspirator, whilst
e is closed. The distillate
collects in a. When this
fraction is to be removed, c is closed and e is opened. The
liquid is thereby transferred to the second receiver b ; e is
now closed, c is opened, and d turned so as to let air into b ;
b may now be removed and replaced by a similar vessel, and
FiG. 7. Receiver for fractional distillation
under reduced pressure.
PURIFICATION OF SOLIDS AND LIQUIDS
the process continued. Fig. 7 needs little explanation. There
are two or more receivers on one stem. By rotating the stem
I
Percentage
2
FIG. 8.
the distillate falls into one or other receiver. It should be
borne in mind that the method
of fractional distillation can
only be applied to those mix-
tures whose boiling-point curves
lie on a gradually ascending
slope, as shown in (i), Fig. 8,
where the quantities of the two
substances are plotted against
the boiling-points. But other
curves are conceivable and are
actually known where a given
mixture shows a minimum (2)
or maximum (3) boiling-point.
Complete separation by frac-
tional distillation is in such cases
impossible, because in the case
of (2) the lowest boiling portion,
which is a definite mixture of the
two constituents, will first distil.
As one of these diminishes in
quantity, the boiling-point will
rise to one side or other of the
curve according to the pro-
FIG. 9 .-Tap.funnel for separating portions of the remaining con-
non-miscibie liquids. stituents. In the case of (3), one
or other constituent, according to the proportion of the two
16 THEORETICAL ORGANIC CHEMISTRY CHAP.
present, will first distil, leaving behind a constant boiling
mixture, representing the highest point on the curve.
If, in a mixture of two liquids, one is soluble in water and the
other not, like benzene and alcohol, the insoluble constituent
may be separated by adding water and pouring the mixture into
a separating or tap-funnel (Fig. 9). The benzene will separate
and float above the water in which the alcohol remains dis-
solved. The aqueous layer is then drawn off and separated
from the benzene.
QUESTIONS ON CHAPTER I
1. Give reasons for retaining organic chemistry as a separate branch
of chemistry.
2. What is meant by fractional crystallisation and fractional distil-
lation ? With what object are these two processes employed ?
3. Explain the principle of the fractionating column. Can the
process of fractional distillation he employed in the separation of all
mixtures of volatile liquids of different boiling-points ?
4. How is the purity of organic liquids and solids ascertained ?
5. Devise methods for separating the constituents in the following
mixtures: (i) alcohol from water; (2) benzene from alcohol; (3)glycerol
(glycerine) from water.
CHAPTER II
ANALYSIS OF ORGANIC COMPOUNDS
QUALITATIVE TESTS
HAVING prepared the substance in a pure state, the next step
is to determine its constituent elements.
Carbon and Hydrogen. Compounds of carbon are frequently
inflammable, and when heated on platinum foil take fire or char.
A safer test for carbon is to heat the substance with some easily
reducible metallic oxide, the oxygen of which forms carbon
dioxide with the carbon present, which is detected by passing
the gas through lime-water.
Hydrogen, if present, is at
the same time converted
into water, which condenses
in drops on the cold part of
the apparatus.
EXPT. 3. Take a piece
of soft glass tube about 13
cm. long, and fuse it together
at one end. Heat a gram or
i two of fine copper oxide in a
porcelain crucible for a few
minutes to drive off the mois-
ture, and let it cool in a FIG. ic. Apparatus for detecting carbon,
desiccator. Mix it with about
f one-tenth of its bulk of powdered sugar in a mortar. Pour the
mixture into the tube, and draw out the open end, bending it at the
same time into the form shown in Fig. 10. Suspend it by a copper
wire to the ring of a retort stand, and let the open end dip into hme
i8 THEORETICAL ORGANIC CHEMISTRY CHAP.
or baryta water. Heat the mixture gently with a small flame.
! The gas which bubbles through the lime-water turns it milky.
Moisture will also appear on the sides of the tube, which, provided
that the copper oxide has been thoroughly dried beforehand, indicates
the presence of hydrogen in the compound.
Gases or volatile substances like ether and alcohol cannot of
course be examined in this way ; but the gases or liquids may
be burnt in a closed vessel, or the vapour led over a layer of red-
hot copper oxide and then through lime-water.
Nitrogen. When nitrogenous organic compounds are heated
with metallic potassium or sodium, potassium or sodium
cyanide is formed, and the subsequent test is the same as
for a cyanide (p. 214).
EXPT. 4- Pour about loc.c. of distilled water into a small beaker.
Place a fragment of gelatine or cheese in a small test-tube along with
a piece of metallic potassium or sodium the size of a coffee bean, and
heat them, at first gently, until the reaction subsides, and then
strongly, until the glass is nearly red-hot. Place the hot end of the
tube in the small beaker of water. The glass crumbles away, and any
residual potassium is decomposed with a bright flash ; all the cyanide
rapidly goes into solution, whilst a small quantity of carbon remains
suspended in the liquid. Filter through a small filter into a test-tube.
Pour into the clear solution about I c.c. of ferrous sulphate solution,
to which a drop of ferric chloride has been added, boil for a minute,
cool, and acidify with dilute hydrochloric acid. A precipitate of
Prussian blue indicates the presence of nitrogen.
; In many cases nitrogen may be detected by heating the
s.ubstance with soda-lime, when the nitrogen is evolved as
ammonia.
EXPT. 5- Grind up a small fragment of cheese with about four
times its bulk of soda-lime ; introduce the mixture into a test-tube,
and cover it with a shallow layer of soda-lime. Heat the test-tube
strongly, and at the same time hold a piece of moistened red litmus
at the mouth of the tube. If it is turned blue, nitrogen is present.
Halogens. Many halogen compounds impart a green fringe
to the outer mantle of the non-luminous flame. A more delicate
test is to heat the substance with copper oxide, which gives a
vivid green coloration.
ii ANALYSIS OF ORGANIC COMPOUNDS 19
EXPT. 6. Heat a fragment of copper oxide, held in the loop of a
platinum wire, in the outer mantle of the non-luminous flame, until
it ceases to colour the flame green. Let it cool down a little, and
then dust on some halogen compound. Now heat again. A bright
green flame, accompanied by a blue zone immediately round the
oxide, indicates the presence of a halogen.
The halogen in the majority of organic compounds is not
directly precipitated by silver nitrate. This may be seen by
adding silver nitrate solution to chloroform. Only those com-
pounds which, like the hydracids and their metallic salts, dis-
sociate in solution into free ions give this reaction. 1 If, how-
ever, the organic compound is first destroyed, and the halogen
converted into a soluble metallic salt, the test may be applied.
The substance is heated with pure lime, or with a fragment
of metallic sodium or potassium, as in the test for nitrogen
(Expt. 4, p. 1 8). The filtered solution is acidified with nitric
acid, and silver nitrate added. A curdy white or yellow preci-
pitate (provided no cyanide is present) indicates a halogen.
Sulphur. The presence of sulphur in organic compounds
may be detected by heating the substance with metallic sodium
or potassium. The alkaline sulphide, when dissolved in water,
gives a violet coloration with a solution of sodium nitro-
prusside.
EXPT. 7. Heat a fragment of cheese with a small piece 01
potassium in a test-tube until the bottom of the tube is red-hot, and
placed it in a small beaker of water, as described in the test for
nitrogen (Expt. 4, p. 1 8). Filter the liquid and add a few drops
of sodium nitro-prusside solution (p. 218).
Phosphorus and Arsenic. These elements are comparatively
rare constituents of organic substances. They may be detected
by fusion with an oxidising mixture of sodium carbonate and
potassium nitrate, which converts the phosphorus and arsenic
into phosphate and arsenate of the alkali. The fused mass is
dissolved in water, and the usual qualitative tests are applied.
Oxygen. There is no direct method for detecting the pre-
sence of oxygen in organic compounds.
1 Vide J. Walker, Introduction to Physical Chemistry, chap. xxvi. p. 296
(Macmillan).
C 2
THEORETICAL ORGANIC CHEMISTRY CHAP.
QUANTITATIVE ANALYSIS
The qualitative examination of an organic compound is fol-
lowed by a quantitative analysis.
Carbon and Hydrogen. The principle of the method for
the quantitative estimation of carbon and hydrogen is that
SCM
CuO
> BOAT
SCM
SPIRAL < .
I 1
ASBESTOS ASBESTOS
FIG. ii Arrangement of tube for the estimation of carbon and hydrogen.
described under the qualitative test (p. 17), but the substance
and the products of combustion, viz. carbon dioxide and water,
are weighed. The original form of the apparatus was devised
by Liebig (1831). A hard glass tube is filled two-thirds full of
coarse copper oxide, a small boat containing a weighed quantity
of the substance is then introduced, and behind it a roll of
oxidised copper gauze, as shown in Fig. n.
The tube is placed in a combustion furnace and the end
nearest to the boat is connected with two gas-holders, one con-
taining oxygen and the other air. The gases are purified by
passing them through U-tubes containing soda-lime and
concentrated sulphuric acid. The other end of the tube is
FIG. 12. Calcium chloride tube.
attached to a weighed U-tube containing calcium chloride (Fig.
12), and an apparatus, two forms of which are shown in Figs. 13
and 14, containing a strong solution of potash, which is also
weighed. The arrangement of the whole apparatus is shown
in Fig. 15.
ANALYSIS OF ORGANIC COMPOUNDS
21
The layer of copper oxide is made red-hot, and then the roll
of copper gauze, whilst a slow current of oxygen from the gas-
FIG. 13. Potash apparatus.
I 1 ic. 14. Potash apparatus.
holder is passed through the tube. The substance is then
gradually heated and burnt. 1 The water, which is formed,
collects in the calcium chloride tube and the carbon dioxide in
the potash apparatus.
When the substance is entirely burnt, the oxygen is cut off and
a current of air passed through the apparatus. The calcium
FIG. 15. Combustion apparatus for estimating carbon and hydrogen.
chloride tube and potash apparatus are then detached and
weighed.
The results are calculated in percentages of carbon and
hydrogen as follows :
iv is the weight of substance taken.
a is the increase in weight of the potash apparatus.
b is the increase in weight of the calcium chloride tube.
1 The full details of the process are described in the Author's Practical Organic
Cnemistry (Macmillan).
THEORETICAL ORGANIC CHEMISTRY
x 100 _ ,
= per cent, of carbon.
44 x w
2 X & X IOO
18 x w
= per cent, of hydrogen.
Example /. 0*1830 gram of substance gave 0*6118 gram of
CO 2 and 0*1315 gram of H 2 O.
12 x '6118 x loo
= 92*3 per cent, of carbon.
44 x '1830
2 X "1315 X IOO ri ,
1 8 x -1830 = 7 ' 9 per h y dr g en -
As the two quantities added together make, within the limits
of experimental error, 100 per cent., no oxygen is present.
Example II. 0*1510 gram of substance gave 0*1055 gram of
CO 2 and 0*068 gram of H 2 O.
12 x '1055 x 100 f ,
= 19-05 per cent, of carbon.
44 x -1510
2 x *o68 x loo = cem of hydrogen>
18 x -1510
Here the difference between 100 and the aggregate per-
centages of carbon and hydrogen is 75'95, and must be due to
the presence of oxygen, seeing that no other elements were
found.
Volatile liquids are inclosed in small bulbs (Fig. 16), which
are carefully weighed. The liquid is then introduced, and the
neck sealed. Before placing the bulb
in the tube, the neck is scratched
with a file and opened. If the
organic substance contains nitrogen, FIG. 16,
the latter may be liberated in the
form of one or other of its oxides. These would be absorbed in
the potash apparatus, and cause an error in the amount of
carbon. A spiral of metallic copper is therefore brought into the
front end of the combustion tube, which, when red-hot, reduces
the oxides of nitrogen. The free nitrogen then passes through
unabsorbed. ^ When halogens, or sulphur are present in the
organic compound, they are also liable to be absorbed either in
the free state, or in combination with oxygen in the potash
ii ANALYSIS OF ORGANIC COMPOUNDS 23
apparatus. In this case, fused lead chromate broken up into
small pieces must be used in place of the copper oxide in the
combustion tube. The halogens and sulphur are retained by
the lead, the former as halide salt, and the latter as lead
sulphate.
Nitrogen. Nitrogen is usually estimated by one of the fol-
lowing methods : by burning the substance with copper oxide
in an atmosphere of carbon dioxide, and collecting the free
nitrogen over potash solution (Dumas) ; by heating the sub-
stance with soda-lime, and estimating the ammonia evolved
(Will and Varrentrapp) ; or by decomposing the substance with
concentrated sulphuric acid at a high temperature, and con-
verting the nitrogen into ammonium sulphate (Kjeldahl). Whilst
Dumas' method is universally applicable, the other two pro-
cesses cannot always be employed, and only give trustworthy
results when the nitrogen in the compound is directly combined
with carbon and hydrogen.
DUMAS' METHOD. A combustion tube closed at one end is
filled as shown in Fig. 17. A layer of magnesite is first intro-
duced, then some coarse copper oxide. This is followed by
F,HE COARSE
SPIRAL COARSE CuO CuO CuO MAGNESITE
< J5 CM . >! < I3CM. X 8CM. > | < I3 C M. >
ASBESTOS ASBESTOS
. PLUG _ PLUS
FIG. 17. Arrangement of tube for nitrogen estimations.
the substance well mixed with fine copper oxide. The tube is
then partly filled with coarse copper oxide, and finally a spiral
of metallic copper is introduced. The copper spiral serves to
reduce any oxides of nitrogen, which would be otherwise absorbed
by the potash solution. The open end of the tube is attached
to a SchifTs asotometer (Fig. 18). It consists of a graduated
tube, surmounted with a tap and furnished with two side tubes,
one being attached to the combustion tube, and the other to a
reservoir containing potash solution. By opening the tap and
raising or lowering the reservoir, the solution may be introduced
into the graduated tube or removed into the reservoir. The
reservoir is first lowered, and the potash solution run out of the
THEORETICAL ORGANIC CHEMISTRY
tube. The magnesite is then
heated until the air is driven out
of the combustion tube. The
azotometer is then filled with
potash, and the combustion is
carried on in the manner de-
scribed in the estimation of car-
bon and hydrogen. Nitrogen
collects in the azotometer, and
when the evolution of gas
slackens, the magnesite is again
strongly heated to drive out the
last trace of nitrogen gas. In-
stead of using a closed tube
with magnesite for evolving
carbon dioxide, it is convenient
to use an open combustion
tube, and to attach it, either to
a second tube containing sodium
bicarbonate (Fig. 19), which is
heated in a second small furnace
or to an apparatus for evolving
carbon dioxide.
When the combustion is com-
plete, the liquid in the reservoir
of the azotometer is brought on
a level with that in the graduated
tube and the volume measured.
FIG. 18. SchifTs azotometer.
and the temperature are also noted.
The height of the barometer
FIG. 19. Open combustion tube for estimating nitrogen.
The percentage of nitrogen is calculated as follows :
v is the observed volume of nitrogen.
B is the height of the barometer in mms.
/ is the temperature.
ANALYSIS OF ORGANIC COMPOUNDS
f is the vapour tension of the potash solution, which may be
taken without serious error to be equal to that of water.
The volume, corrected to o c and 760 mms., will be given by
the following expression :
?/ x 273 x (B -/)',
(273 + /) 76o
As the weight of i c.c. of nitrogen at o and 760 mms. is
0*00126 gram, the percentage weight of nitrogen in the substance
iv will be given by the expression
v x 273 x (B-/") '00126 x 100.
(273 4- /) 760 ~u>
Example. 0*206 gram of substance gave 18*8 c.c. of moist N
at 17 and 756 mms. (/at 17 = 14*5 mms.).
iS*8 x 273 x (756 14*5) x "126 r .
L2 \L2 ^ >/ = 10*56 per cent, of N.
(273 + 17) x 760 x '206
KJELDAHL'S METHOD. The substance is boiled for a time
with concentrated sulphuric acid and potassium sulphate, a
little potassium per-
manganate or persul-
phate being subse-
quently added. The
acid, which at first
darkens in colour, then
becomes colourless.
The nitrogen is now
present as ammonium
sulphate. The liquid
is then made alkaline
with caustic soda and
boiled to drive off the
ammonia, the am-
monia being absorbed
in a receiver con-
taining a known vol-
ume of standard hydro-
chloric or sulphuric
acid. The apparatus
is shown in Fig. 20.
FIG. 20. Apparatus for estimating nitrogen by
Kjeldahl's method.
The flask a contains the ammonium
26
THEORETICAL ORGANIC CHEMISTRY
CHAP
sulphate, caustic soda is introduced, the liquid is boiled, and
the water and ammonia are condensed and collected in the
flask b containing the acid.
The quantity of ammonia is determined by titrating the acid
with standard alkali. The strength of the original acid being
known, the difference will give the amount of ammonia.
WILL AND VARRENTRAPP'S METHOD. This method, which
has been to some extent replaced by KjeldahPs process, depends
FIG. 21. Apparatus for estimating nitrogen by Will and Varrentrapp's method.
upon the fact, already mentioned, that nitrogenous substances
yield ammonia when heated with soda-lime. The operation is
conducted as follows : A combustion tube closed at one end is
filled with a short layer of soda-lime mixed with
zinc dust, a, then with the weighed substance
mixed with soda-lime, b. The remainder of the
tube is filled up with soda-lime, , and attached
to absorption bulbs containing a known volume
of standard acid. The tube is placed in a com-
bustion furnace. The long layer of soda-lime
is first heated to redness, then the substance,
and finally the zinc dust, which, in contact with
soda-lime, evolves hydrogen, and sweeps out
any residual ammonia. The arrangement of the
apparatus is shown in Fig.2i.
The Halogens. CARIUS' METHOD. The
method of Carius, which is usually employed,
consists in oxidising the substance with fuming
nitric acid under pressure in presence of silver
nitrate. The silver halide which is formed is FlG 22 .^- sealed
then separated by filtration and weighed. A t^ be used m
... , . . . . i -i /- Carius method.
thick-walled tube is sealed at one end, and a few
c.c. of fuming nitric acid introduced together with the silver
ANALYSIS OF ORGANIC COMPOUNDS
27
nitrate crystals. The substance is weighed in a narrow tube
and slipped in. The tube is then sealed before the blow-pipe in
such a way that a thick capillary is formed, which enables it to
be subsequently opened (Fig. 22). It is then placed in a hot-air
furnace, as shown in Fig. 23, and is heated for several hours at
200 or above, according to the nature of the compound. The
furnace is then allowed to cool, the pressure released by holding
FIG. 23. Hot-air furnace with a Carius' tube.
the capillary end in the flame until the glass softens and is per-
forated by the pressure within. The tube can then be safely
opened. The contents are washed out, and the silver halide
filtered, dried, and weighed.
PIRIA AND SCHI-FF'S METHOD. There are some substances
which are incompletely decomposed with fuming nitric acid
under the conditions described above, and the results are con-
sequently too low. In this case the substance is mixed with
quicklime and sodium carbonate in a small platinum crucible
which is inverted in a larger one, the space between the two
28 THEORETICAL ORGANIC CHEMISTRY CHAP.
being filled in with the mixture of sodium carbonate and lime.
The crucibles are heated over the blow-pipe, the contents allowed
to cool, and dissolved in excess of dilute nitric acid. The
halogen is then precipitated with silver nitrate and estimated in
the usual way.
Example. 0*151 gram of substance gave 0*134 gram AgBr.
0-134x80x100 of bromine.
188x0-151
Sulphur. CARIUS' METHOD. The process is essentially the
same as that just described.
The compound is oxidised in a sealed tube with fuming
nitric acid, but without the addition of silver nitrate. The
resulting sulphuric acid is then precipitated and weighed as
barium sulphate.
Example. 0-25.18 gram gave 0-2638 gram BaSO 4 .
0-2638 x 32 xioo =
233x0-2518
QUESTIONS ON CHAPTER II
1. How would you show that alcohol contains carbon, hydrogen, and
oxygen ?
2. Calculate the percentage composition of cane-sugar, C 12 Ho2O n .
3. Describe and explain the difference in the method employed in the
estimation of chlorine in chloroform and calcium chloride.
4. Calculate the weight of carbon dioxide and water, and the volume
of nitrogen under normal conditions, obtainable from 0*2 gram of urea,
CH 4 N 2 O.
5. Describe a method for the estimation of nitrogen in organic
compounds.
6. Calculate the percentage of nitrogen estimated by Kjeldahl's
method from the following data : 0*5 gram of the substance was decom-
posed and distilled with caustic soda, and the ammonia collected in
50 c.c. of normal sulphuric acid. The acid then required 33*6 c.c. of
normal caustic soda solution for neutralisation.
7. Calculate the percentage of carbon, hydrogen, and oxygen from
the following data : 0*2046 gram of substance gave, on combustion,
0-2985 gram of carbon dioxide and 0-1255 g^ am of water.
ii ANALYSIS OF ORGANIC COMPOUNDS 29
8. By what methods can a carbon compound be shown to contain.
(a) nitrogen, (b] chlorine, (c) phosphorus ?
9. Describe any method commonly used for the determination of
sulphur in an organic compound. ^
10. In the estimation of nitrogen by the soda-lime method, 0*2102
gram of benzamide was taken and the evolved ammonia absorbed in
25 c.c. of half-normal sulphuric acid solution ; the residual acid
required 21*52 c.c. of half-normal soda (NaOH) solution for neutralisa-
tion. What was the percentage amount of nitrogen in the benzamide ?
CHAPTER III
EMPIRICAL AND MOLECULAR FORMULAE
Empirical Formula. From the results of an analysis it is
possible to calculate the relative number of atoms of the
different elements present in an organic compound. This is
done by dividing the percentage weights by the atomic weights
of the elements. If we take the first example of an analysis of
carbon and hydrogen (p. 22), and divide the numbers repre-
senting the per cent, of carbon and hydrogen by the respective
atomic weights of these elements, we obtain approximately the
same quotient
The ratio of the number of carbon to hydrogen atoms is i : I,
and the substance may be represented by the formula CH. This
is known as the empirical formula. The real formula of the
substance is without doubt some multiple of the empirical
formula ; but an analysis can give no further information upon
this point. Let us now take the numbers in the second example,
\ and divide by the atomic weights. We obtain the following
quotients
oZfl-474.
in EMPIRICAL AND MOLECULAR FORMULA
To find the smallest whole numbers standing in the same ratio
as these quotients, we may divide by the smallest quotient of the
series
H -- = 3-14.
1-59
O 4 -^W 9 8.
1-59
The empirical formula is, therefore, approximately CH 3 O 3 .
By way of confirmation, the percentage composition of the sub-
stance is calculated from this formula and compared with the
analytical results. If the difference in the numbers falls within
experimental errors (o'2 to 0-3 percent.), the formula is accepted
as correct.
Found. Calculated for CH 3 O 3 .
C ..... I9'05 . . . 19*04
H ..... 5 -QO ... 476
O (by difif.) . 75*95 . . . 76*20
lOO'OO lOO'OO
The analytical numbers satisfy in this case the calculated per-
centages.
It is seldom that an analysis gives exactly theoretical results. It is
much more common to find the hydrogen o'l to O'2 per cent, too high,
the carbon the same amount too low, and the nitrogen 0*3 to 0*4 per
cent, too high. These discrepancies arise from various causes. In the
case of carbon and hydrogen, incomplete drying of the gases passing
from the gas-holders increases the weight of the calcium chloride tube,
and loss of moisture from the potash solution decreases that of the
potash apparatus. In the case of nitrogen, a small residual amount of
air, which cannot be displaced, adds to the volume of gas.
Molecular Formula. To find the molecular formula of an
organic compound we must determine the molecular weight of
the substance, or the weight of the molecule compared with
that of the atom of hydrogen as the unit. The methods may
be divided into physical and chemical.
THEORETICAL ORGANIC CHEMISTRY
PHYSICAL METHODS
There are several methods, all of which depend upon certain
hypotheses or laws.
Vapour Density Method. According to Avogadro's law,
equal volumes of all gases under the same conditions of tern*
perature and pressure contain the same number of molecules.
Suppose that an equal volume of hydrogen and of the substance,
X, of unknown molecular weight in the form of gas, be weighed
under the same conditions. If the volume of hydrogen contain
5 molecules, the volume of X will contain 5 molecules, or, in
other words, the ratio of the weight of these two volumes will be
the ratio of the weight of the molecule of hydrogen and of the
molecule of X.
CD
CD
(D
o o
o
o o
Volume of Hydrogen.
Volume of X.
But the ratio of the weights of equal volumes of the gas X and
hydrogen, is the density of the gas. It is represented by the
expression
in which W x and W h are the weights of equal volumes of sub-
stance and hydrogen, respectively. Now, as the molecule of
hydrogen consists of two atoms, the density, which is the mole-
cular weight of the substance compared with one molecule of
hydrogen, must be multiplied by 2 to make it represent the ratio
in respect of one atom of hydrogen.
W
M.W. = A X 2 = -f X 2.
"h
Seeing that the weight of any volume of hydrogen under
varying conditions of temperature and pressure is known (i c.c.
= 0*00009 gram at o and 760 mm.), it is only necessary to
ascertain the weight of a given volume of the vapour or gas,
from which the weight of the same volume of hydrogen may be
calculated. There are four methods for determining vapour
EMPIRICAL AND MOLECULAR FORMULAE
densities. In the case of permanent gases, the gas is weighed
in a large globe according to the method of Regnault. Victor
Meyer's method and Hofmann's method consist in ascertaining
the volume occupied by
a given weight of the
vaporised substance.
According to Dumas'
method, the weight of
substance occupying a
given volume is deter-
mined.
REGNAULT'S ME-
THOD. The method is
only used for permanent
gases, and has a very
limited application in
organic chemistry. It
consists in counterpois-
ing a large globe, first
evacuated, and then
filled with the gas and
finally with hydrogen,
against a similar globe
having the same capa-
city, the difference be-
ing adjusted by weights.
The second globe is em-
ployed to neutralise the
effects due to varying
temperature, pressure,
and moisture, which
would greatly alter the
buoyancy of the single
globe, whereas when
FIG. 24. The Victor-Meyer vapour density
apparatus.
two globes are em-
ployed, the changes
affect them in the same way, and do not interfere with the actual
weight of the gases. .
AIR DISPLACEMENT, OR VICTOR MEYER'S METHOD.-Tb,s
method is universally employed ; for, whilst yielding fairly
D
34 THEORETICAL ORGANIC CHEMISTRY CHAP.
accurate results, it is quickly performed and demands only small
quantities of material. It consists in rapidly vaporising a known
weight of the substance at a constant temperature at least 40-
50 above its boiling-point in a special form of apparatus, which
admits of the displaced air being collected and measured. The
volume occupied by a given weight of the substance under
known conditions is thus ascertained, and from these data the
density is calculated. The apparatus is shown in Fig. 24. It
consists of an elongated glass bulb with a narrow stem and a
capillary side-tube. It is provided with a well-fitting rubber cork.
The apparatus is clamped within an outer jacket of tin-plate or
copper (represented as transparent in the figure) which holds
the boiling liquid required to produce a constant temperature.
The substance, if liquid, is introduced into a small stoppered
glass bottle known as a Hofmann bottle (Fig. 25). The dry*
bottle with the stepper is carefully weighed
and then filled with liquid. The stopper is
inserted, and the bottle re-weighed. It should
hold about 0*1 gram of substance. The side-
tube of the apparatus dips under water con-
tained in a glass dish. The liquid in the
jacket is boiled, and when the temperature
J . ' ... FIG. 25. Hofmann
is constant, i.e. when no bubbles pass out bottle.
of the side-tube, a graduated tube filled with
water is inverted over the end of the side-tube and clamped.
The small bottle containing the substance is then dropped into
the apparatus, and the cork tightly inserted. A stream of air
bubbles passes into the graduated tube, and when they cease,
the tube is carefully transferred to a cylinder of water, and after
a time the volume, the temperature of the water, and the
barometric pressure are observed.
EXPT. 8. Thoroughly dry the apparatus by blowing air through
it, and introduce a small quantity of clean dry sand previously heated,
to break the fall of the Hofmann bottle. The bulb of the outer jacket
is filled two-thirds full of water. The burner below should be pro-
tected from draughts by a chimney. To avoid inconvenience arising
from the steam, a split cork, into which a bent glass tube is inserted,
is pushed loosely into the open end of the jacket. Whilst the water
is boiling steadily, the substance is weighed. Chloroform, b.p. 61, or
pure and dry ether, b.p. 34 '5, may be used for the experiment. Try
EMPIRICAL AND MOLECULAR FORMULAE
35
if the temperature is constant, and fix the graduated tube in position.
Remove the stopper of the Hofmann bottle before dropping it in.
Transfer the tube to a cylinder, and read off the volume, after
adjusting the level of the water within and without.
The density is calculated as follows :
If v is the volume, / the temperature, B the barometric pres-
sure, and/ the vapour tension of water at / 3 , then the corrected
volume is given by the formula
v x (B -/) x 273
760 X'(273 +
This multiplied by 0*00009, the weight of i c.c. of hydrogen,
gives the weight of hydrogen occupying the same volume as
the vaporised substance, from which the density, A ^rf^ is
obtained.
Example. 0*1146 gram gave 36*3 c.c. at 11 and 752 mm.
fio mm. at 11.
36-3 x (752 - 10) x 273 x 0-00009 = . 003o6 .
760 x 284
0-1146
0-00306 J/i -
Molecular weight = 37-4 x 2 = 74*8.
If substances of higher boil-
ing-point have to be vaporised,
the water in the outer jacket is
replaced by other liquids of
correspondingly higher boiling-
point, such as xylene, b.p. 140,
aniline, b.p. 182, ethyl benzoate,
b.p. 211, amyl benzoate, b.p.
260, diphenylamine, b.p. 310^,
&c.
A Lothar Meyer air-bath (Fig.
26) is, however, much more
convenient for obtaining con-
stant high temperatures. It
consists of three concentric
FIG. 6.-Lothar Meyer air-bath. metal cylinders, the outer one
D 2
THEORETICAL ORGANIC CHEMISTRY
being coated with non-conducting material. They are so
arranged that the heated air from a movable ring burner passes
between the two outer cylinders (shown in section in the
figure), and descends to the
bottom of the central cylinder,
into which it has access through
a ring of circular holes. The
hot air is thoroughly mixed by
this zig-zag flow and the tem-
perature is equalised. The bulb
of the displacement apparatus is
clamped in the interior cylinder,
and a thermometer is fixed be-
side it.
HOFMANN'S METHOD. This
method is very accurate, and
requires only small quantities of
material ; but it is troublesome
to manipulate. It consists in
vaporising at a constant tempera
ture a known weight of sub-
stance above the mercury column
of a barometer. The vapour is
under reduced pressure, and
substances may therefore be
vaporised below their ordinary
boiling-points. It admits also
of substances being vaporised,
which decompose under ordinary
pressure. A long tube marked
in millimetres, and calibrated so
that the volume corresponding to
the mm. divisions is known, is
filled with mercury and inserted
in a mercury trough. The height of the mercury is noted and
the weighed substance contained in a Hofmann bottle is in-
troduced. The tube is heated by an outer jacket, through which
the vapour of a liquid of constant boiling-point circulates. The
:ise of temperature drives the stopper out of the small bottle and
vaporises the contents, and this causes the mercury to descend
FIG. 27. Thorpe's Hofmann
apparatus.
in EMPIRICAL AND MOLECULAR FORMULAE 37
to a certain point where it remains stationary. The point is read
off on the scale, and from this the volume and pressure is as-
certained. The temperature is also noted. The apparatus
shown in section in Fig. 27 represents Thorpes modification of
Hofmann's apparatus.
It has a small mercury trough, #, from which the greater part
of the mercury may be withdrawn into the movable reservoir, ,
during the operation, and remain there unwetted by the sub-
stance (the mercury requires to be dried after each operation).
The tube is heated throughout its length, and the mercury in the
tube is therefore at one temperature. The upright, r, is hollow,
and serves the double purpose of a support and condenser,
returning the condensed vapour to the boiling vessel, d. The
barometer-tube is etched at one point only, which represents a
measured volume. It is calibrated from this point, and the
millimetres which correspond to a certain volume are measured
on an adjustable metal scale, e.
Example. 0*0518 gram of substance occupied 52*5 c.c. at
100 ; barometric height 752*5 mms. ; height of mercury column
484 mms. ; vapour tension of mercury at 100 074 mm. ; coefficient
of expansion of mercury 0*00018. The volume is reduced to o~
and 760 mms. as follows : The barometric pressure is the differ-
ence between the first and second readings of the mercury
column. But the second reading represents the column
at 100. This is corrected by taking the difference and mul-
tiplying by (100x0*00018). From this the vapour tension of
mercury at 100 = 0*74 must be deducted. The expression will
then be
760x373
0*00125
DUMAS' METHOD. In point of accuracy and simplicity ^ it
offers no advantage over Victor Meyer's method, and requires
a much larger amount of material. As a practical method, in
connection with organic chemistry, it is obsolete. A glass bulb is
used of about 200 c.c. capacity with a narrow neck (Fig. 28).
The weight of the bulb having been found, a few c.c. of the
liquid under investigation are introduced. The bulb is then heated
THEORETICAL ORGANIC CHEMISTRY
in a bath (water or paraffin) to
at least 4O-5O above the boiling-
point of the substance. As soon as
vapour ceases to issue, the narrow
neck is drawn out and sealed. The
temperature of the bath is noted.
As the pressure is practically con-
stant throughout the operation, it may
be omitted in the calculation. The
bulb is cooled and weighed with the
drawn out end of the neck. The
point is then broken off under water,
which rushes in and fills the bulb, with
the exception of a small bubble. The
bulb is then filled up and weighed,
and the capacity determined from the
weight of water.
Example. Weight of the bulb, temp. 1 5 -5
FIG. 28. Dumas' vapour density
apparatus.
23 '449 grams.
,, ,, ,, and vapour at 100 23-720 ,,
Capacity 178 c.c.
As the vapour has been weighed in air, the true weight will be the
apparent weight of the vapour plus that of the displaced air, just as the
true weight of mercury when weighed in water is the apparent weight
plus the volume of displaced water. W x will be
23720-23-4494-^ ^1^x0-001293 = 0-4892.
2oo
The weight of an equal volume of hydrogen at 100, W h , will be given
by the expression
178x273x0-00009^ 2
373
= = 4 1 '7.
0*01172
There are many substances which cannot be volatilised with-
out undergoing decomposition, and for which the above methods
are not adapted. The molecular weights of such substances
may be determined by the freezing- and boiling-point methods
of Raoult.
The Cryoscopic or Freezing-point Method (Raoult). The
freezing-point (cryoscopic) method and boiling-point (ebullio-
scopic) method of Raoult depend upon the general principle
that equimolecular solutions lower the vapour pressure to the
EMPIRICAL AND MOLECULAR FORMULA
39
FIG. 29.
same amount. Supposing we plot the change in vapour pres-
sure with temperature for ice and water in the form of a curve,
and then do the same after dissolving in it a small quantity of
substance. The new
curve will run nearly
parallel with the first 760tr
(Fig. 29). It will cut
the vapour pressure
curve for ice at some
point below o and
reach atmospheric
pressure above 100 ; TempT
in other words, the
addition of a soluble
substance will lower
the freezing-point and raise the boiling-point. Not only
so, but if an equal molecular proportion of another substance
were dissolved in the same quantity of water, precisely the same
effect would be observed.
EXPT. 9. This may be demonstrated by means of the following
apparatus :
The bottle of the capacity of about
I litre is furnished with a rubber cork
through which a T-piece carrying a
three-way tap is inserted, the horizontal
arm of which is attached lo a mercury
gauge. A small sealed tube containing
10 c.c. of ether is introduced into the
bottle, the tap turned in order to adjust
the pressure inside with that outside,
and then placed in communication
with the gauge. On shaking, the tube
containing the ether is broken and the
mercury in the ?ho."ter limb descends,
indicating roughly the vapour pressure
of the ether. Into a second similar
boUle, similarly fitted up, is introduced
a tube containing 4 grams of phenol
in 10 c.c. of ether, and into a third bottle another tube containing
10*8 grams of bromoform in 10 c.c. of ether. On breaking the two
latter an equal depression of the mercury occurs, which is, however,
less than in the first case,
Fig. 30.
40 THEORETICAL ORGANIC CHEMISTRY CHAP.
The above rule of Raoult does not, however, apply to salts,
acids, c., which appear to dissociate in certain solvents, nor
to substances which form molecular aggregates or associate
in solution. Supposing the freezing-point of 100 grams of a
solvent to be lowered i by dissolving I, 2, 3, and 4 grams
respectively of four different substances, the molecular weights
of these substances will be in the ratio of i : 2 : 3 : 4. In order
to convert these ratios into true molecular weights, the numbers
must be multiplied by a coefficient which depends upon the
nature of the particular solvent selected, and which may be
determined empirically by means of substances of known
molecular weight or by calculation from thermodynamical
data 1 according to the expression :
C = ' Q2T2
in which Tis the absolute temperature of the freezing-point and
L the latent heat of fusion of i gram of the solvent in calories.
If w is the weight of substance and W the weight of solvent,
d the depression of the freezing-point, and C the coefficient for
the solvent determined for the standard conditions (i.e. for the
weight of substance which produces i depression in 100 grams
of solvent) the molecular weight, M, is given by the following
expression :
100 Cw
The values of C for the common solvents in use are as
follows :
Water . . i8'8, Benzene . 50,
Acetic Acid 39, Phenol . 75.
The form of apparatus, known as the Beckmann apparatus,
is shown in the accompanying Fig. 31. It consists of a glass
jar furnished with a stirrer. The cover of the jar has a wide slit
to admit the stirrer, and a circular aperture with clips to hold
a wide test-tube.
Within the wide test-tube is a narrower one, which is held in
position by a cork. The narrow test-tube is sometimes
furnished with a side-tube for introducing the substance. It is
1 Vide van't Hofif, Zeitschr. Phys. Chem., i. p. 481 : Ostwald, Outlines of General
Chemistry, chap. vi. p. 139 (Macmillan) ; J. Walker, Introduction to Physical
Chemistry, chap, xviii. p. 176 (Macmillan).
in EMPIRICAL AND MOLECULAR FORMULAE 41
provided with a stirrer. A Beckmann thermometer completes
the apparatus. This is fixe'd through a cork so that the bulb
nearly touches the bottom of the tube, a wide slit being cut in
the side of the cork for moving the stirrer. The Beckmann
thermometer is of special construction, and requires explana-
tion. As the method involves
merely an accurate determination
of small differences of tempera-
ture, it is not requisite to know
the exact position on the thermo-
meter scale. The Beckmann
thermometer registers 6 degrees,
^hTch are divided into hun-
"ttfdclths. The little glass reser-
voir at the top (a, Fig. 31) serves
the purpose of adjusting the mer-
cury column to different parts of
the thermometer scale by adding,
or removing mercury from the
bulb. Eight to ten grams of sol-
vent are introduced into the inner
tube and weighed. The freezing-
point of the solvent is then deter-
mined by cooling the outer vessel
with water or ice below the freez-
ing-point of the solvent. The
solvent is slightly supercooled and
then stirred. As soon as crystals
begin to separate, the thermometer
rises, and reaches a maximum
which represents the freezing-
point of the solvent. The opera-
tion is repeated for confirmation,
and then a carefully weighed
amount of the substance intro-
duced. As soon as the substance
has dissolved, the freezing-point is again determined as before,
and this time a lower temperature will be indicated. A
further quantity of substance may be added, and a new deter-
mination made.
FIG. 31. Beckmann's freezing-point
apparatus.
THEORETICAL ORGANIC CHEMISTRY
Example. Using the same solvent (benzene), and adding
successively three quantities of substance (naphthalene), the
following numbers were obtained :
w
W
d
M
Mean.
I
0-0985
97
0-403
126
.
2
0-0729
97
0-305
123-2
125-3
3
0-1193
97
0-486
126-8
'
M, the molecular weight in the fifth column, is calculated as
follows :
It is first necessary to find the weight of substance which,
when dissolved in 100 grams of solvent, will lower the
freezing-point i.
The weight of substance w in 100 grams of solvent is
given by the expression
0*0985 x IQO
97
As the proportion between the substance and the solvent is
unchanged, no effect is produced on the freezing-point.
The weight of substance in 100 grams of solvent required to
lower the freezing-point i is
0*0985 x 100
97 x 0*403 *
Here it is. assumed that the depression of the freezing-point
is proportional to the weight of dissolved substance.
The above expression multiplied by 50, the coefficient for the
solvent (benzene), gives the molecular weight
= 0^0985 x icox 50
07x0*403
THE EIJKMAN DEPRESSIMETER. For rapid, but less accurate,
determinations, the apparatus of Eijkman may be used, which is shown
in. Fig. 32. It consists of a small vessel, into the neck of which a
thermometer is ground. The thermometer is of the Beckmann type,
but divided into twentieths of degrees. Phenol, melting-point (m. p.)
42, is usually employed as the solvent. The vessel and thermometer
are weighed. Phenol melted on the water-bath is poured in to within
M =
in EMPIRICAL AND MOLECULAR FORMULA 43
about 5 c.c. of the neck, the thermometer inserted, and the apparatus
weighed again. The melting-point of the phenol is then ascertained
by warming it until melted, and allow-
ing it to cool in the cylinder, where
it is occasionally shaken until crystalli-
sation sets in. The weighed substance
is now introduced, and the freezing-
point determined as before.
The Boiling-point Method
(Raoult.) The boiling-point of a
liquid is found to be affected like
the freezing-point by the presence
of a dissolved substance that
is, the boiling-point of a given
quantity of a liquid is raised the
same number of degrees by dis-
solving in it the same number of
molecules of different substances,
or, in other words, such weights
of these substances as represent
the ratio of their molecular weights.
These facts were first clearly de-
monstrated by Raoult One form
of apparatus for determining mole- Fic;> 2 ~
cular weights by this method is
that of Beckmann, shown in Fig. 33. Another is that of
Landsberger, shown in Fig. 34.
BECKMANN'S APPARATUS consists of a boiling tube furnished
with two side pieces, one of which is stoppered and serves to
introduce the substance, and the other acts as a condenser.
The boiling-tube stands on an asbestos pad and is surrounded
by two short concentric glass cylinders surmounted by a mica
plate. . A Beckmann thermometer is inserted through a cork
in the neck of the tube. The thermometer is similar in
construction to that used for freezing-point determinations,
but it has a smaller bulb. The boiling-point of the solvent
is first ascertained. The burner is lighted and the temperature
regulated so that the liquid boils briskly. The temperature
being constant, it is noted, and a weighed pellet of the solid
substance is dropped into the boiling tube through the side
44
THEORETICAL ORGANIC CHEMISTRY
piece without interrupting- the boiling. The boiling-point rises,
and after a short time will remain stationary. The temperature
is again noted. A second and third determination may be
made by introducing fresh pellets of the substance.
As in the freezing-point method, the molecular weight is cal-
culated from the weight of substance required to raise the
boiling-point of 100
grams of solvent i c ,
and the result is multi-
plied by a coefficient,
depending upon the
solvent. The follow-
ing is a list of
solvents commonly
employed, and their
coefficients :
Water 5*2
Alcohol 1 1 '5
Ether 21*1
Acetic Acid 25*3
Benzene 267
Aniline 32*2
Chloroform 36*6
Nitrobenzene 50*1.
The molecular
weight is determined
from the formula-
100 Cw
FIG. 33.
in which w is the
weight of substance, W that of the solvent, d the rise of boiling-
point, and C the coefficient. Although the method is able to
dispose of a greater number of convenient solvents than are
adapted for freezing-point determinations, it is never so
accurate, mainly on account of the difficulty of avoiding fluctua-
tions in the boiling-point, due to radiation, to the dripping of
cold liquid from the condenser, and to barometric fluctuations.
LANDSBERGER'S APPARATUS. The apparatus, modified by
Walker and Lumsden, and by McCoy, 1 is shown in Fig. 34.
1 American Chem, Journ. (1900), vol. 23, p. 353.
in EMPIRICAL AND MOLECULAR FORMULA
45
The pure solvent is contained in the outer jacket, , and the
solution in the inner vessel, b. On boiling the liquid in the outer
jacket, the vapour passes by the tube c, fused to the inside of
the inner vessel, into the solution. The temperature of the
solution is raised to the
boiling-point by the latent
heat given out by condensa-
tion of some of this vapour
when it reaches the inner
vessel. The vapour from the
inner vessel passes away to
a condenser. The boiling-
point of the solvent is first
determined, and a weighed
quantity of the substance is
then introduced. After the
boiling-pointhas become con-
stant, the contents of the inner
vessel are weighed, and
the weight of the solvent
estimated by deducting
the weight of substance.
If great accuracy is not
desired and a number of
consecutive readings is re-
quired, the inner vessel may
FIG. 34. Landsberger-McCoy apparatus.
be graduated in cubic centimetres, and the volume of solvent
read off by interrupting the boiling for a moment before the
introduction of each fresh portion of substance. When the
boiling is interrupted, the pinch-cock, d^ on the side-tube of the
jacket, must be opened to prevent the liquid running back from
the inner vessel, , into the outer jacket.
CHEMICAL METHODS
Molecular Weight of Organic Acids. The basicity of an
organic acid that is, the number of hydrogen atoms replaceable
by atoms of metal being known, the molecular weight can be
46 THEORETICAL ORGANIC CHEMISTRY CHAP.
determined by estimating the amount of metal in one of its
normal salts. The ratio of metal to salt will be that of the
atomic weight of the metal to the molecular weight of the salt.
The silver salts are usually selected for these determinations,
since they are, as a rule, normal, i.e. neither acid nor basic ;
they are only slightly soluble in water, and are consequently
readily obtained by precipitation, and finally they contain, as a
rule, no water of crystallisation. On the other hand, they are
very unstable, being quickly discoloured when exposed to light,
and often decompose with slight explosion when heated. The
silver salt is usually prepared by adding silver nitrate to the
ammonium salt of the acid. The ammonium salt is obtained
by boiling a solution of the acid with excess of ammonia until
the liquid is neutral. To the cooled solution silver nitrate is
added. The precipitate is carefully washed and dried. A portion
is then weighed and ignited, and the metallic residue of silver
weighed.
If W is the weight of salt, w the weight of silver, and n the
basicity of the acid, the molecular weight of the silver salt is
determined from the following formula :
W x 108^
IV
The molecular weight of the acid is then obtained by deduct-
ing n atoms of silver and adding n atoms of hydrogen.
Example. 0*3652 gram silver salt of a monobasic acid gave
0*172 gram of silver.
108x0-3652,
0*1720
This represents the molecular weight of the silver salt. As it
contains one atom of silver in place of one atom of hydrogen
(being a monobasic acid), 108, the atomic weight of silver must
be deducted and I added for the atom of hydrogen.
M = 229*3- 108+1 = 122-3.
Molecular Weight of Organic Bases. The organic bases
(B) form, like ammonia, crystalline chloroplatinates withplatinic
chloride, of the general formula, B 2 H 2 ,PtCl 6 . By estimating the
amount of platinum present in the salt, it is possible to calculate
the molecular weight of the platinum compound, and, con-
sequently, that of the base. The base is dissolved in a slight
in EMPIRICAL AND MOLECULAR FORMULA 47
excess of moderately strong hydrochloric acid, and platinic
chloride added. The chloroplatinate is precipitated as a yellow,
crystalline powder resembling the ammonium salt, and is care-
fully washed and dried. A portion is then weighed and ignited
in a crucible and weighed again. The molecular weight of the
salt is calculated from the weight w of the platinum and W of
the salt, according to the formula (the atomic weight of platinum
being 195)
Wx 195
w
To determine from this the weight of the base, it is necessary to
deduct from the molecular weight of the salt that of H 2 PtCl 6 ,
and as 2. molecules of the base are contained in the salt, the
result is halved.
Example. 07010 gram of a mono-acid salt gave 0-2303 gram
platinum.
07010 x 195
0-2303
This represents the molecular weight of the salt, from which the
weight of H 2 PtCl 6 must be deducted and the result halved.
One or other of the above physical and chemical methods for
determining molecular weights will be found applicable to the
majority of organic compounds. Only such substances are
excluded as, being neither acids nor bases, are non-volatile or
insoluble in any solvent. It is obvious that examples of this
kind are rare. The molecular weight can only be approximately
estimated by breaking up the compound into simpler constituents
of known molecular weight. Such is the case with the starch
molecule, which is non-volatile, and decomposes on dissolving
in water. The molecular weight of soluble starch (p. 307)
has been ascertained by the cryoscopic method. It follows
that the insoluble starch molecule from which soluble starch
is formed has not a smaller, but probably a larger, molecular
weight. Cellulose, which cannot be dissolved unchanged in
any solvent, is another example of a substance the molecular
weight of which cannot be determined. Its formula is therefore
written (C 6 H 10 O 6 ) n .
48 THEORETICAL ORGANIC CHEMISTRY CHAP.
QUESTIONS ON CHAPTER III
1. A substance gave the following analytical result: C = 54*5;
H = 9 -09 ; O = difference.
A vapour-density determination by V. Meyer's method gave the
following result: o* I gram of the substance displaced 27 c.c. of air
measured at 1 5 and 745 mm . pressure (vapour tension at 1 5 = 1 2 "j mm. ).
Determine the molecular formula.
2. The following two results were obtained with Landsberger's boiling-
point apparatus, using alcohol as solvent. Calculate the mean molecular
weight of the substance.
Weight of substance. Volume of solvent. Rise of b. p.
1*01 grm. 24-2 c.c. '535
1*01 grm. 25-3 c.c. 0*519
The sp. gr. of alcohol at the b.p. =07422.
3. 0-341 gram of the silver salt ofatribasicacid left on heating 0*2151
gram of silver. Calculate the molecular weight of the acid.
4. Calculate the molecular weight of a mono-acid base from the
following data: 0*3557 gram of the platinum salt gave 0*117 gram of
platinum,
5. What is the empirical formula of a compound having the following
percentage composition : C = 23*58, H = 3*28, Cl = 23*23, N = 18*40,
S= 21*00, O = 10*51 ? What precautions must betaken in the estima-
tion of carbon and hydrogen in the above substance ?
6. Find the empirical formula of the substance of which the analysis
is given in Question 7 on p. 28.
7. Calculate the molecular weight of grape-sugar determined by the
cryoscopic method from the following data : 10 grams of substance
dissolved in 73*12 grams of water lowered the freezing point i*45.
C = 1 8 -8.
8. Describe Hofmann's vapour density method. What are its
advantages and disadvantages ?
9. Describe three distinct methods of arriving at the molecular
weight of acetic acid.
10. Given a non- volatile, neutral, solid organic compound, how
would you proceed to determine its molecular weight ?
11. Calculate the empirical formula of a compound having the
composition : C = 85*71 per cent.; H = 14*29 per cent. Describe the
methods you would employ for the determination of the number of
carbon and hydrogen atoms in the molecule of the substance in the
event of its being (a) a gas, (b) a liquid, or (c) a solid.
ni EMPIRICAL AND MOLECULAR FORMULA 49
12. The percentage composition of a liquid, containing carbon,
hydrogen, and oxygen, was deduced from the following numbers : 0*300
gram when submitted to combustion with copper oxide gave 0*574
gram of carbon dioxide and 0-351 gram of water. The vapour density
was 23 compared with hydrogen as unity. What is the formula of the
liquid ?
13. A monacid organic base, containing only hydrogen, nitrogen, and
carbon, gave the following numberson analysis : 0*186 gram gave 0*528
gram of carbon dioxide and 0*126 gram of water: 0*596 gram of its
platinichloride yielded on ignition 0*195 gram of platinum. Calculate
the molecular formula of the substance (Pt = I94'3).
CHAPTER IV
CLASSIFICATION .
Classification. Having ascertained the molecular formula
of a substance from its analysis and molecular weight, some-
thing may be learned about its structure from its relation to
other compounds of known constitution. It is therefore desir-
able to adopt a system of classification which will bring into
prominence this relationship. The simplest and most natural
method is to group together all those compounds which contain
the same elements and which possess at the same time the
same chemical properties, i.e. which behave in the same manner
towards reagents.
Keagents employed in Organic Chemistry. The following are the
most important reagents used in organic chemistry :
OXIDISING AGENTS. (i) Nitric acid (dilute and strong)
2HNO 3 = 2NO + H 2 O + 30.
(2) Potassium permanganate in acid or alkaline solution
2KMnO 4 + 3H 2 SO 4 = K 2 SO 4 + 2MnSO 4 + sH 2 O + 50.
2KMnO 4 + H 2 O = *KOH + 2MnO 2 + 30.
(3) Potassium dichromate and sulphuric acid
K 2 Cr 2 O 7 4- 4H 2 SO 4 = K 2 SO 4 + Cr 2 (SO 4 ) 3 + 4H 2 O + 30.
(4) Chromium trioxide and glacial acetic acid
2CrO 3 + 6C 2 H 4 O 2 = Cr 2 (C 2 H 3 O 2 ) 6 + 3H 2 O + 30.
The use of a reagent in an organic solvent, like acetic acid, is of
advantage on account of the solubility of organic substances in such
solvents. ******
Hydrogen peroxide in presence of traces of iron (Fenton's reagent)
and bromine in presence of an alkali are also occasionally used.
CLASSIFICATION
REDUCING AGENTS. These may be divided into acid, neutral and
alkaline reducing agents.
Among the acid reducing agents are :
( i ) Hydriodic acid
2HI = I 2 + H 2 .
(2) Stannous chloride and strong hydrochloric acid
SnCl 2 + 2HC1 = SnCl 4 + H 2 .
(3) Tin or iron and hydrochloric acid
(4) Zinc dust and glacial acetic acid
Zn + 2C 2 H 4 O 2 = Zn(C 2 H 3 O 2 ) 2 + H 2 .
Neutral reducing agents are :
(i) The zinc-copper or aluminium-mercury couple
(2) Zinc dust and water
(3) Hydrogen in presence of finely divided nickel reduces many
organic compounds at temperatures which vary according to the nature
of the substance. The method was discovered by Sabatier and
Senderens. Hydrogen in presence of colloidal palladium and platinum
has a strong reducing action on substances dissolved or suspended in
water or other solvent. Electrolytic hydrogen evolved at the negative
electrode made of lead or cadmium is another important reducing agent.
Alkaline reducing agents are :
( I ) Sodium amalgam with alcohol or water
2NaIig + 2H 2 O = 2NaOH + Hg + H 2 .
(2) Sodium methylate
CH 3 ONa + O = HCO 2 Na -f H 2 .
Sodium formate.
(3) Zinc dust and caustic soda
Zn + 2NaOH = Zn(ONa) 2 + H 2 .
THE HALOGENS. The action of chlorine and bromine is in some
cases promoted by light, and by the presence of small quantities of
certain metals and their salts, such as iron and aluminium, the chloride
or bromide of iron and antimony, also by sulphur and iodine. Such
substances are called "halogen carriers," and their action is not fully
E 2
52 THEORETICAL ORGANIC CHEMISTRY CHAP.
understood. The chlorides and bromides of phosphorus are also
frequently used for introducing chlorine and bromine into organic com-
pounds, especially in place of oxygen or the hydroxyl (OH) group.
DEHYDRATING AGENTS. These agents are of two kinds. One
kind is employed for removing moisture from organic liquids. The
common reagents for this purpose are fused calcium chloride, potassium
carbonate, quicklime, or sodium sulphate. Another class of dehydrating
agents is used to remove the elements of water from organic substances,
thereby converting them into new compounds. The most useful sub-
stances of this class are concentrated sulphuric acid, phosphorus
pentoxide, and fused zinc chloride.
Classification based on Composition and Properties.
If we adopt a system of classification based on composition
and properties, we find that there are a number of families of
compounds, each member of a family behaving towards reagents
in a very similar manner to that of the other members. Three
such families are represented by the paraffins, the alcohols, and
the acids of the formic acid family.
PARAFFINS.
Formula. Name. Boiling-point.
CH 4 .... Marsh gas, or Methane ... - 164
C 2 H 6 .... Ethane
C 3 H 8 .... Propane - 38
C 4 H 10 . . . . Butane + i
C 5 H 12 . . . . Pentane +38
&c.
ALCOHOLS.
CH 4 O . . . Methyl alcohol 66
C 2 H 6 O . . . Ethyl alcohol ....... 78
C 3 H 8 O . . . Propyl alcohol 97
C 4 H 10 O . . . Butyl alcohol 117
C 5 H 12 O . . . Amyl alcohol 138
&c.
ACIDS.
CH 2 O 2 . . . Formic acid 101
C 2 H 4 O 2 . . . Acetic acid 118
C 3 H 6 O 2 . . . Propionic acid 141
C 4 H 8 O 2 . . . Butyric acid 162
C B H 10 Oo . . Valeric acid 185
&c.
CLASSIFICATION 53
The members of the first group, the paraffins, are indifferent
to most reagents ; those of the second, the alcohols, readily
undergo chemical change ; whilst the last group, " the acids," as
their name implies, are acids and form salts. Although the
chemical behaviour of each family is the same, the physical
properties, boiling-point, specific gravity, etc., vary from member
to member. With increasing molecular weight, the boiling-
point rises. It is customary to find the simplest member of a
family represented by a gas or by a low-boiling liquid, the one
with the largest molecule by a solid. In the case of the
paraffins, the first four members are gases at the ordinary
temperature, then follow a series of liquids, and at the bottom
of the list we find those solids of which paraffin-wax is composed
(p. 56).
Homologous Series. It will be further observed that each
member of a family differs from that which precedes or follows
it by the same number of carbon and hydrogen atoms, viz. CH 2 .
The explanation of this will be given later. It is only necessary
at present to state that families which fulfil the conditions just
set forth were named by Gerhardt homologous series. A
homologous series may therefore be defined as a family of
chemically related compounds, the composition of which varies
from member to member by one atom of carbon and two atoms
of hydrogen. The three series of homologues which have been
selected for illustration are by no means the only representa-
tives ; the number of such series is in fact very large, and each
will be considered in its turn.
The advantage of such a grouping will now be obvious, for
it will only be necessary to describe the chemical characteristics
of one member, when that of the whole series of homologues
may be inferred.
Aliphatic and Aromatic Series. A further division of
organic compounds into the two great groups of aliphatic
(aXet^ap, fat) and aromatic compounds is desirable. A natural
relationship exists between marsh gas, methyl alcohol, and formic
acid on the one hand, and marsh gas, ethane, propane, &c, oo.
the other, for they are mutually convertible ; but there is no such
natural connection between any member of the paraffins and
benzene, C 6 H 6 . Benzene, in fact, forms the starting-point of a
separate class of similarly-related homologous groups in the
54 THEORETICAL ORGANIC CHEMISTRY CHAP.
manner of the marsh gas, methyl alcohol, and formic acicl series.
These derivatives of benzene are called aromatic compounds, and
are treated in a special section of the book. They are known also
as the benzene series, or derivatives of benzene, to distinguish
them from the aliphatic, or marsh gas series, or derivatives of
methane.
QUESTIONS ON CHAPTER IV
1. Upon what system is the classification of organic compounds
based ? What special object does this classification serve ?
2. Give a list of three of each of the following reagents : (i) oxi-
djsing ; (ii) reducing ; (iii) dehydrating agents ; and describe their
action by equations where possible.
3. What is meant by " homologous series" ? Give an example.
4. Give examples of acid, neutral and alkaline reducing agents.
5. What substances are used as " halogen carriers " ?
PART I
ALIPHATIC COMPOUNDS
CHAPTER V
PARAFFINS, OR SATURATED HYDROCARBONS
WE shall begin with a study of the paraffins or saturated
hydrocarbons, because they have a simple composition. They
contain only carbon and hydrogen, being termed therefore
hydrocarbons. They occur in nature in large quantities, and
they form, moreover, the natural starting-point for the whole of
the aliphatic group of compounds. Table III., on the following
page, contains a. list of the paraffins, with their formula?,
melting-points, boiling-points, and specific gravities.
Nomenclature. The names of the first four members are
derived from those of the alcohols containing the same number
of carbon atoms, " methyl," " ethyl," " propyl," and " butyl " ;
the remainder are indicated by the Greek numeral correspond-
ing to the number of carbon atoms present. The names of all
the paraffins terminate in " ane" Several members, it will be
observed, are represented by two or more substances. These
.Have the same molecular formula, but a different grouping of
their atoms. They are therefore isomeric with one another, and
are termed isomers or isomerides. The difference in atomic
arrangement will be discussed later (p. 73).
The paraffins are formed by the natural process of decay of
vegetable and animal matter. Marsh-gas, which is found
bubbling up from stagnant water, is produced by the action 01
organisms on cellulose or woody fibre, and the reaction may be
represented by the following equation :
(C 6 H ]0 5 ) n + nII 2 = (3C0 2 ) a + (3CH 4 ) n .
Cellulose. Marsh-gas.
THEORETICAL ORGANIC CHEMISTRY
TABLE III.
PARAFFINS C n H 2n+2 .
Formula.
Name.
Melting
point.
Boiling
point.
Specific
gravity.
CH 4 .
C 2 H 6 .
C 3 H 8 .
C 4 H 10 .
C 6 H 14 .
C 8 H 18 .
c!fe
c&C
Qgiv
^23 "-48*
^24^50-
31^64-
32^66.
Methane
. Ethane
Propane .
-186
-172
1 8
22
28
32
37
40
44
48
60
68
70
75
-164
- 9
- 38
+ 1
- 17
+ 36
-f 28
+ 10
6 9
58
62
6 4
4 8
98 o
125
150
173
214
234
252
270
287
3^3
317
330
205 '
215
224
234
243
270
302
310
33 1 .
"s
B
415
446
'6OG
627.
677'
6/9
672
700
697
718
733
774
773
775
775
776
775
777
777
777
778
778
778
779
779
780
781
781
782
Atb.p.
\'!
13
o
'o
Cu
c
&
Normal Butane
Isobutane
Normal Pentane .
Dimethylethylmethane or\
Isopentane jf
Tetramethylmethane or "\
Neopentane /
Normal Hexane . . . .
Dimethylisopropylmethane ,
Dimethylpropylmethane . .
Methyldiethylmethane . . .
Trimethylethylmethane . .
Heptane
Isoheptane. . . .
Octane . .
Nonane
Decane . . . .
Undecanc
Dodecane . . . ...
Tridecane
Tetradecane .
Pentadecane ...
'Hexadecane
Heptadecane
Octadecane . . .
Eicosane
Heneicosane
Docosane
Tricosane .... . .
Tetracosane . ...
Heptacosane .......
Hentriacontane
Pentatriacontane
THE PARAFFINS
57
Paraffins are also formed by the decomposition of animal and
vegetable matter by heat, as in the destructive distillation of wood
and coal ; but the most plentiful source is the petroleum wells.
The Petroleum and Paraffin Industry. The oil deposits
found in different parts of the world yield what is known as
petroleum, earth oil, rock oil, or mineral oil. The origin of the
oil has been variously attributed to the action of steam on the
iron carbide of subterraneous mineral deposits (Mendelejeff),
which acts like water on aluminium carbide (see p. 68), and to
the decomposition at high temperatures and under pressure
of the remains of marine life. The latter view is supported
by the experiments of Engler, who heated the blubber of fish
under pressure, -and obtained a quantity of paraffins. It is an
interesting fact that Vhen acetylene mixed with hydrogen is
passed over finely divided nickel at about 200 a mixture of
hydrocarbons resembling petroleum is produced. (Sabatier).
The petroleum is found in sand or conglomerate known as
" sand rocks," and is obtained by boring and pumping.
AMERICAN PETROLEUM was discovered in 1859 by Colonel
Drake, in Pennsylvania. It has since been found in Ohio,
Colorado, California, Canada, and other places. The crude oil
is carried to the sea coast along iron pipes, some of which are
300 miles long. Here the oil is fractionally distilled in large
iron stills and purified. It is divided into the following fractions,
which are recognised in the trade by various names :
Name.
Fraction.
Specific
gravity at 15.
Constituents.
Per-
centage.
B.p.
o
) , .,
1 8
1 0-636
Petroleum ether, or Gasoline.
Petroleum naphtha,or Ligroin
Petroleum benzine, 1 or Ben-
zoline
4o-oo
90 -120
I2O 150
o'642-o'648
o'648-o'692
o'6g2-o*73o
CsHi2 CeH]4
C 6 H 14 -C 8 H 18
CgHjs CgHgo
16*5
Kerosene, Photogene, or
1 50 300
0*790-0*810
CjoH22 QlgH^
54'o
7*5
Vaseline
Solid paraffin, or paraffin wax
M.p.
45-65
-
-
2'0
Cymogen is liquefied by pressure, and by its rapid evaporation lowers
the temperature and is used for making ice ; rhigolene is used in
Not to be confused with coal-tar benzene.
58 THEORETICAL ORGANIC CHEMISTRY CHAP.
surgery to produce local insensibility by freezing ; petroleum ether and
ligroin are used for dissolving and extracting fats and oils ; and
benzine is employed for a similar purpose in dry cleaning. Petrol^
which is used in internal combustion engines, has a boiling-point of
70 140 and a specific gravity of 0705 0740.
The kerosene is purified after distillation by agitating it with
concentrated sulphuric acid and afterwards with caustic soda
solution and redistilling. The quantity of this fraction may be
increased by " cracking," that is, by heating to a high tempera-
ture the portions of higher boiling-point, which then break up
into products of lower boiling-point. The annual output is
about 2500 million gallons.
The American petroleum does not consist exclusively of
paraffins. There appear to be also present small quantities of
hydrocarbons of the benzene series (p. 383), and substances
termed naphthenes of the formula C n H 2n (p. 255).
RUSSIAN PETROLEUM is found in and around the town of
Baku, which stands on the peninsula of Apsheron on the Caspian
Sea. The so-called "eternal fires of Baku" attracted the fire-
worshippers as early as 600 B.C. Marco Polo described them,
and an English traveller, Han way, in 1754, gave an account of
the inflammable vapour with which the ground in the district
was saturated.
Systematic working for oil began in 1813, but the output was
restricted by Government monopoly, which was abolished in
1872, and in the following year Nobel Brothers started their
immense works. The total quantity of oil produced annually
is about 2250 million gallons. The oil differs from American
oil, both in its character and in the conditions under which it
occurs. It is contained under great pressure, so that in sinking
the bore-holes, the oil frequently is driven out to an enormous
height. The great Droojba well spouted for four months an oil
column from 100 to 300 feet high, which ran to waste, and caused
a loss of about 100 million gallons. Occasionally the wells take
fire and burn for many weeks. The oil is distilled and purified
like the American petroleum. Russian oil contains less of the
lower boiling portions than American oil. It consists on the
average of
30 per cent, illuminating oil. 30 per cent, lubricating oil.
35 solar oil, or ostatki, a heavy oil used for fuel.
THE PARAFFINS
59
The illuminating oil has a higher specific gravity than the
American oil (0*820 0*825) m consequence of the presence
of a large proportion of naphthenes (p. 255).
PARAFFIN INDUSTRY IN SCOTLAND. The origin of the
paraffin industry is due to James Young, who discovered a
petroleum spring in Derbyshire in 1848 ; but the spring shortly
afterwards becoming exhausted, he looked about for fresh
sources of supply, and found that a bituminous shale occurring
in Scotland the celebrated Torbanehill mineral would yield
paraffin oil on distillation.
The shale is distilled by a continuous process in long vertical
retorts, the upper portion of which
is of iron and the lower of fireclay,
the fresh shale being supplied
through the top, and the spent
shale withdrawn at the bottom.
Fig. 35 represents a vertical section
of a retort. The inflammable gases,
ammonia, and oil pass into the
hydraulic main, and thence into
coolers where the tar is deposited,
the ammonia being collected as in
a gas-works, and the inflammable
gases used for fuel and illumina-
tion. About 30 gallons of oil are
obtained from I ton of shale. The
viscid and tarry-looking oil is re-
distilled to remove the portions of
lower boiling-point, and purified by
treatment, first with strong sulphuric acid, and then with caustic
soda. It is again distilled, and the distillate is separated into -
Naphtha.
Burning, or paraffin oil.
Light mineral oil.
Residue.
The residue is treated for paraffin-wax or scale. It is first
frozen, when it becomes semi-solid, and then passed through
a filter press. The filtrate is a viscid liquid, and is used as
lubricating oil. The scale is pressed hot to remove adhering
oil, and finally sweated. This process consists in placing the
FIG. 35. Shale retort.
6o
THEORETICAL ORGANIC CHEMISTRY
FIG. 36. Terra-cotta lucerna, or
Roman lamp from Lanuvium.
wax in large cakes on a sloping table in a heated chamber,
whereby the lower melting portions run away, leaving behind
a much firmer material. The wax
is a mixture of paraffins, and melts
between 45 and 70. It is chiefly
used in the manufacture of candles.
About one-half of the 40,000 tons of
paraffin wax produced annually is
derived from Scotch shale.
The substance known as Ozo-
kerite is found in mines in Galicia, and consists mainly of
paraffins. It is used for medical purposes and a preparation of
it, resembling beeswax, is sold under the name of cerasine.
Petroleum and Paraffin Oil as Illuminants. The introduc-
tion of petroleum and paraffin oil as illuminants has effected a
revolution in the construction of
lamps. The old Roman lamps,
like the one represented in Fig.
36, in which vegetable . oil was
used, were always shallow vessels,
because the low capillarity of the
oil restricted its ascent of the wick.
If a deep vessel were used, the
oil, when exhausted to a certain
level, would cause the flame to be
extinguished. This is easily de-
monstrated by filling a separating
funnel with colza oil (rape seed
oil), and inserting a wick into the
neck. The wick is lighted, and the
oil allowed to trickle out below
(Fig- 37)- As the level of the oil
descends, the light is slowly ex-
tinguished. In consequence of this,
various mechanical contrivances
were introduced in more recent
times to maintain a constant level
in the oil reservoir. The intro-
duction of mineral oil permitted
the use of deeper reservoirs. The
luminosity of the flame has, more- FIG. 37.
THE PARAFFINS
61
over, been greatly intensified by the introduction of flat wicks
and of glass chimneys, which, by promoting a rapid current
of air round the flame, effect more complete combustion, raise
the temperature, and thereby increase the luminosity. In
consequence of the
large consumption of
paraffin oil for lamps,
and the danger of ex-
plosion from the use
of too volatile an oil,
which may form an
explosive mixture with
the air inside the re-
servoir, the Govern-
ment insist upon a
certain standard qual-
ity, which is deter-
mined by the "flash-
ing-point." The stand-
ard apparatus is shown
in Fig. 38, and the
method is known as
Abel's test. The ap-
paratus consists of a
cylindrical metal cup,
surmounted by a metal
cover, holding a slide,
which opens or closes
apertures in the cover.
In moving the slide so
as to uncover the cen-
tral hole, an oscillating , , , ,
lamp is caught by a LI \\
pin fixed in the slide, \A
and tilted in SUCh a FIG. 38. The Abel flashing-point apparatus.
way as to bring the
nozzle just below the surface of the lid. When the slide is
pushed back so as to cover the hole, the lamp returns to its
original position. The vessel is charged to a certain height
with the oil to be tested, and a thermometer inserted through
62 THEORETICAL ORGANIC CHEMISTRY CHAP.
the cover, the bulb of which is immersed in the oil. The
vessel is heated in a specially constructed water-bath, and
as the temperature of the oil rises, the slide is occasionally
withdrawn, so as to expose the interior of the cup to the jet of
flame. When the vapour ignites, the temperature is observed,
and this is the flashing-point.
The lowest flashing-point by Abel's apparatus permitted by
the Board of Trade is 73 F., but it is now generally recognised
that this minimum has been fixed too low.
One of the most common sources of danger in the use of
oil lamps is that arising from the burning down of a loosely-
fitting and short wick, the lower end of which is not immersed
in the oil. Such a wick may smoulder within the reservoir, and
occasionally fire an explosive mixture of paraffin vapour and air.
This danger is easily avoided by examining the wick occasionally,
and renewing it before it becomes too short.
EXPT. 10. Pour a few c.c. of paraffin oil into a large flask with a
wide neck, heat the oil strongly, and blow a little air through with a
bellows. If a piece of lighted wick, or roll of paper, be dropped in,
a vigorous explosion occurs.
Physical and Chemical Properties of Paraffins. The
paraffins are specifically lighter than water, and being insoluble,
they float on water. The lower and more volatile members
have a peculiar and not unpleasant smell.
Strong and dilute mineral acids have little action on the
paraffins, and they are unattacked by oxidising agents. It is
owing to this indifference to most reagents that the term
paraffin (parum, little ; affinis^ affinity) has been applied.
Fuming sulphuric acid and dilute nitric acid under pressure have been
found to react with some of the paraffins, the former giving sulphonic
acids, and the latter nitro-compounds (p. 405).
Addition and Substitution. Chlorine and bromine, but
not iodine, combine directly with the paraffins, and the action is
promoted by light. This combination is unlike that usually
denoted by the action of chlorine on carbon monoxide in the
formation of carbonyl chloride, or phosgene
CO + C1 2 = COClj.
Carbonyl chloride.
ADDITION AND SUBSTITUTION
Here the molecule of carbon monoxide unites with the mole-
cule of chlorine, without the separation of any part of either
molecule. Such a union of molecules produces what is known
as an additive, or addition compound. But when chlorine or
bromine acts upon a paraffin, hydrochloric, or hydrobromic acid
is invariably evolved. The action of
chlorine on methane is represented as
follows
CH 4
Monochloromethane,
or Methyl chloride,
and not by the equation
CH 4 + C1 2 = CH 4 C1 2 .
This action of chlorine on the paraffins
may be illustrated by taking a long, wide
glass tube closed at one end and filled
with strong brine. It is inverted in a
bath of brine, and sufficient chlorine is
introduced to fill it one-third full. This
is marked with a strip of paper. An
equal volume of marsh-gas is then passed
into the tube, and the volume indicated
by a fresh strip of paper. The apparatus
is shown in Fig. 39. The mixture is
left in diffused light (bright sunlight will
cause an explosion). After several hours
the mixed gases will occupy about one-
half the original volume. As equal
volumes of the two gases contain the same number of molecules,
the equation may be written
FIG. 39. Action of chlorine
on marsh-gas.
CH 4 4- CI 2 = HC1
CH 3 C1
i vol., i vol., i vol., T vol.,
or i mol. or i mol. or i mol. or i mol.
As the hydrochloric acid is absorbed by the brine, only the
methyl chloride remains, which occupies half the original
volume. Substances which, like the paraffins, lose hydrogen
in the form of hydracid when they enter into combination with
the halogens, are termed saturated compounds, and the process of
64 THEORETICAL ORGANIC CHEMISTRY CHAP.
replacement of hydrogen by a halogen is termed substitution.
The products obtained by substitution are known as substitution
products. The term substitution is not confined to the exchange
of hydrogen for chlorine or bromine. The exchange of hydrogen
for oxygen or any other element, or of one group of elements
for another, is sometimes termed substitution. The process has
now lost its original theoretical significance. It played an
important part in the overthrow of the dualistic theory. 1
This process of substitution effected by the action of chlorine
on the paraffins will continue, provided enough chorine is
present, until the whole of the hydrogen is replaced by chlorine.
For example, by the further action of chlorine on methyl
chloride, the following products are formed :
CH 3 C1 + C1 2 - HC1 + CH 2 C1 2
Dichloromethane, or
Methylene chloride.
CH 2 C1 2 + C1 2 = HC1 + CHC1 3
Trichloromethane,
or Chloroform.
CHC1 3 + C1 2 = HC1 + CC1 4
Tetrachloromethane, or
Carbon tetrachloride.
We have now to explain the existence of homologous series
and to discuss the cause which determines the constant
difference of CH 2 between each successive member of the
series.
Quadrivalent Carbon and the Linking of Carbon Atoms.
The explanation is founded on two theories, which are due
to Kekule. Carbon is quadrivalent that is, the atom of carbon
i
c
I
FIG. 40.
is capable of uniting with 4 atoms of a univalent element,
2 atoms of a bivalent element, or I atom of a tervalent and
I of a univalent element. The carbon atom may be re-
presented graphically as having 4 bonds or linkages (Fig. 40).
Marsh-gas, methyl chloride, methylene chloride, chloroform,
1 Vide E. von Meyer, History of Chemistry (Macmillan).
GRAPHIC FORMULAE
carbon tetrachloride, carbon dioxide, and hydrocyanic acid will
then be represented ty graphic formulas as follows :
H H . Cl Cl Cl
II C-H H C II H C H H C Cl C1-C-C1
I I I I I
H Cl Cl Cl Cl
Methane. Methyl Methylene Chloroform. Carbon
chloride. chloride. tetrachloride.
N
C ~!
u A
Carbon dioxide. Hydrocyanic acid.
Methylene chloride may also be represented by a second arrangement,
which will be referred to later (p. 86)
H
H C Cl.
I
Cl
Methylene chloride
(second arrangement).
liinking of Carbon Atoms. The second theory of Kekule,
that carbon atoms can not only attach themselves to other
elements by their bonds, but are capable of being linked to one
another, is sometimes termed the law of the linking of carbon
atoms. By the aid of these two theories, or principles, we are
able to account for the existence of all the members of the
paraffin family, and, indeed, of the majority of organic
compounds, as we shall presently see. Let us next take the case
of two atoms of carbon united or linked together ; I bond of
each is thereby utilised, leaving 6 bonds free for union with
other atoms
I !
C C
I I
If these bonds are united to hydrogen atoms, the formula
C 2 H 6 is* obtained, which is that of the second member of the
paraffin series. Three carbon atoms utilise 4 bonds in effect-
ing a linkage between themselves, leaving 8 bonds free. Hence
F
66 THEORETICAL ORGANIC CHEMISTRY CHAP.
the third member of the paraffins is represented by the
formula C 3 H 8
I I I
C C C
I I I
If we continue to build up chains of carbon atoms on this
principle, we shall find that each end carbon atom of the chain
has three available bonds, whereas each of the middle carbon
atoms possesses only two. If, therefore, n is the number of
carbon atoms present in the compound, there will be in bonds
available for each carbon atom and 2 extra for the two end
carbon atoms, making 2/2 + 2 available bonds. If, as in the
paraffins, these available bonds are attached to hydrogen, the
general formula for the paraffins will be C n H 2n + 2 .
The following univalent groups, which enter into the
structure of many organic compounds, are denoted by special
names, the significance of which will be explained later :
H
H C or CH 3 ' Methyl.
H
H H
H C C or C 2 H 5 ' Ethyl.
I I
H H
H H H
I I I
H C C C or C 3 H/ Propyl, &c.
I I I
H H H
It should be noted, however, that they are merely names, and
do not represent actual substances.
Having now reviewed the chief sources and principal
properties of the paraffin family, we will consider in greater
detail the characters of a few of the more important members.
Methane, marsh-gas, or fire-damp, CH 4 , is the only
hydrocarbon containing one atom of carbon. It is found rising
from stagnant water, and in the gases from oil wells. It is
frequently present in coal-pits, especially during a sudden fall
in atmospheric pressure, when it diffuses from crevices and old
METHANE
67
workings. It is also formed by the distillation of coal, and forms
about 40 per cent, by volume of coal-gas. It is an interesting
fact that methane can be obtained by the direct union of carbon
and hydrogen at 1200, or by means of an electrical discharge
between carbon poles in an atmosphere of hydrogen.
Methane can also be obtained by passing carbon monoxide,
or dioxide, mixed with hydrogen, over finely-divided nickel
heated to about 300.
CO + sH 2 = CH 4 + H 2 0.
Methane.
It is usually prepared by heating together fused potassium or
sodium acetate with soda-lime
C 2 H 3 O 2 Na -f NaOH = CH 4 + Na2CO 3 .
Sodium acetate. Methane.
This reaction has an important bearing on the structure of
acetic acid, and will be referred to again (p. 147).
FIG. 41. Preparation of Marsh-gas from Potassium acetate.
EXPT. II. Preparation of Methane. Powdered potassium acetate
(20-30 grams) is mixed with three times its weight of soda-lime. The
mixture is introduced into a glass or copper flask which is inclined as
in Fig. 41. The flask is closed with a cork, into which a delivery-
tube is inserted. The flask is strongly heated, and after the air has
F 2
68 THEORETICAL ORGANIC CHEMISTRY CHAP.
been expelled the gas is collected in a gas bottle over water, and,
the bottle, when full, is closed with a stopper. The gas is very far
from pure, and burns with a luminous flame. To remove the
luminous hydrocarbons the vaselined stopper is raised slightly and
a little concentrated sulphuric acid is poured in quickly and rinsed
round, followed by some fuming sulphuric acid, and the bottle is
quickly closed and left for an hour. The gas then burns with
a non-luminous flame.
Methane can be conveniently prepared by the action of
water on aluminium carbide
A1 4 C 3 + i2H 2 O = 3CH 4 + 4A1(OH) 8 .
EXPT. 12. The aluminium carbide is placed in a shallow layer over
a layer of sand in a large flask, furnished with a rubber cork having
two holes and carrying a dropping funnel and delivery tube. Dilute
hydrochloric acid is allowed to drop slowly on to the carbide where-
upon methane is evolved, and, after expelling the air, may be collected
over water. The gas may be liquefied, if liquid air is available, by
drying it through calcium chloride and then passing it through a
narrow U-tube, also furnished at the exit end with a drying tube, and
cooled in liquid air.
The gas is obtained in a pure state by the action of the
zinc-copper or mercury-aluminium couple on methyl iodide in
presence of water or alcohol. The couples act on the water
or alcohol, and liberate hydrogen, which reduces the methyl
iodide
Clljil" jH:H = CH 4 + HI.
Methyl iodide.
Exi'T. 13. Preparation of methane : another method. Fit up an
apparatus as shown in Fig. 42.
It consists of a wide U-tube, through one limb of which a small
separating funnel is fixed. The U-tube is then filled with the zinc-
copper or aluminium-mercury couple. The zinc-copper couple is pre-
pared by immersing granulated zinc (20 grams) in a solution of copper
sulphate until a film of metallic copper covers the surface of the zinc.
The couple is washed with water, and the water removed by pouring
fresh alcohol on and off two or three times. This can be done con-
veniently in a wide-necked tap-funnel. The aluminium-mercury couple
is prepared by immersing little rolls of sheet aluminium in mercuric
chloride solution until a film of mercury covers the surface of the
aluminium which is washed as described above. The couple is then
METHANE
69
placed in the U-tube and 50 c.c. of methyl alcohol containing 2 drops of
dilute sulphuric acid (if the zinc-copper couple is used) are poured in.
The limb of the U-tube containing the couple is closed by a cork and
delivery tube and the lower part cooled in water. The methyl
iodide is added gradually from the tap-funnel. After driving out the
air, the gas is collected over water.
Fic/42. Preparation of Marsh-gas from Methyl iodide.
The hydrogen is supplied by the methyl alcohol, and in the
case of the zinc-copper couple the reaction occurs according to
the equation
I
CH 3 iI + Zn + ~Cii,,O; H = Zn< + CH 4 .
X OCH 3
Zinc methoxyiodide.
Probably a similar reaction takes place in the case of the
aluminium.
There are other methods, which are less convenient than the
above, and will be referred to in connection with the substances
which yield the gas (p. 239).
THEORETICAL ORGANIC CHEMISTRY
CHAP
Properties of Methane. Methane is a colourless gas, without
smell. It condenses to a liquid at 164 under a pressure of 760
millimetres. When the pressure is suddenly released, the liquid
boils, and then solidifies, the temperature falling to 186. The
sp. gr. of liquid methane at o is 0*554. The gas burns with a
non-luminous flame, and explodes violently when mixed with air
FIG. 43. Hempel's apparatus.
or oxygen and fired. Methane shares the general properties of
the paraffins in being unaffected by most reagents. Substitution
takes place with chlorine and bromine, as already explained (p. 63).
Composition of Methane. The simplest way of determining
the composition of methane is to explode in a eudiometer a
measured volume of the gas with an excess of air. The con-
traction in volume determines the quantity of hydrogen, and
METHANE
the further contraction (on adding potash, to absorb the carbon
dioxide) gives the amount of carbon
CH 4 + 2O 2 = CO 2 + 2H 2 O.
I VOl., 2 VOls., I Vol., 2 VOls.,
or i mol. or 2 mols. or i mol. or 2 mols.
Now, water-vapour contains its own volume of hydrogen. If,
therefore, for I volume of methane taken, 2 volumes of gas
disappear after explosion, the diminution in volume corresponds
to 2 volumes of hydrogen = 2 molecules or 4 atoms of hydrogen.
In the same way, i volume, or molecule of carbon dioxide
contains i atom of carbon. As every volume of methane gives
i volume of carbon dioxide, the formula of methane will be
CH 4 . By this method both the composition and molecular
weight of methane are found without the weight of the
constituents or the density of the gas being known.
Hempel's apparatus (Fig. 43) furnishes a rapid method for esti-
mating the amount of methane and other paraffins in coal-gas,
or other mixture of gases. It consists of two upright tubes, a
and b, supported on stands, and connected below by rubber tubing.
One of the tubes, a, is finished with two taps, and holds from tap to tap
exactly loo c.c., graduated in tenths of a c.c. The other tube, , is
filled with mercury. The coal-gas is introduced into the graduated tube
by means of the lower three-way tap, and is allowed to stream through
until the air is displaced. The top tap is closed, and the lower tap turned
so that it places the two tubes a and b in communication. By letting in
the mercury from the tube b, the gas is driven over into "pipettes," con-
sisting of double bulbs containing various absorbents. In this way the
different constituents of the coal-gas are in turn removed and measured
by loss on the original volume, except hydrogen, marsh-gas, and nitrogen.
A portion of this residue, consisting of these three gases, is then passed
into the graduated limb of a similar apparatus. An excess of air is
introduced and measured, and the mixture passed into an " explosion
pipette," shown in Fig. 43, where it is fired by sparking through
platinum terminals. The gas is then passed back into the graduated
tube in which it was mixed with air and again measured, and from the
diminution in volume the total volume of hydrogen is determined. By
passing the gas into an absorption pipette containing potash, the carbon
dioxide is removed, and this further loss of volume gives the quantity
of carbon which is present as marsh-gas. The same method may be
applied to other gaseous hydrocarbons.
Ethane, or Dimethyl, CH 3 .CH 3 , occurs with methane in the
gases from petroleum wells, and, like methane, it is formed
72 THEORETICAL ORGANIC CHEMISTRY CHAP.
in minute quantities by sparking carbon terminals in an
atmosphere of hydrogen. It may be prepared by the action of
zinc (Frankland and Kolbe) or sodium (Wurtz) on methyl iodide.
The reaction is represented as follows :
H
I H
H-C H |
I H C H
ilTNa!
j (or Zn) =
jl + Nai
H C II J.
I
H
2NaI (or ZnI 2 ).
| H C II
*
Methyl iodide. Ethane.
This process represents not only a general synthetic method
by which many of the paraffins may be built up, but is one of
great theoretical importance. It affords strong evidence in
support of the theory of the linking of carbon atoms. As the
removal of an atom of iodine from each molecule of methyl
iodide leaves one carbon bond free, it must be by this single
residual bond that the carbon atoms are united.
As two methyl groups are represented as linked together, the
hydrocarbon may be called dimethyl. Ethane is most readily
prepared by the reduction of ethyl iodide with the zinc-copper
couple, as in the preparation of methane
C 2 H 5 I + Ho = C 2 H 6 + HI.
There are other methods of preparation, which will be referred
to in subsequent chapters (pp. 239, 242).
Ethane is a colourless ^as which can be liquefied at 4 under
a pressure of 46 atmospheres. It is acted upon by chlorine and
bromine, the final products being carbon hexachloride, C 2 C1 , and
carbon hexabromide, C 2 Br 6 , both of which are colourless, crystal-
line solids.,
Propane, or Ethyl methyl, CH 3 .CH 2 .CH 3 , is also a con-
stituent of petroleum gas. It may be prepared by the reduction
of propyl iodide, C 3 H r I, with the zinc-copper couple, or by the
action of sodium on a mixture of methyl iodide and ethyl iodide.
Both ethane, C 2 H 6 , and butane, C 4 H 10 , are formed at the same
time
ISOMERIC PARAFFINS 73
CH 3 .CH 2 !I ~+'Na7+'l!CH 3 = CH 3 .CH 2 .CH 3 *- 2 NaI.
Ethyl iodide. Methyl iodide. Propane.
As in the case of ethane, the structure of propane is confirmed
by this synthesis.
Butane, C 4 H 10 . If reference is made to Table III. (p. 56),
it will be noticed that there are two substances with the
formula C 4 H 10 , viz. normal butane and isobutane. The two
compounds are therefore isomeric. Their chief difference
lies in their boiling-points, normal butane being liquid at + 1,
whereas isobutane can only be liquefied at the ordinary pressure
a t -17. Moreover, the products obtained from each by the
action of chlorine and bromine have different properties. How
is this difference to be accounted for? It is a question of
atomic arrangement. The structure of normal butane is
determined by synthesis from ethyl iodide and sodium, and has
therefore a straight chain of carbon atoms
H H H H H H H H
! I 11 i 1 I I
H-C-C ! I + Nao + i:-C C-H = H C C-C-C H + 2 NaI.
I ! I I I 1 ! I
H H H H H H H H
Ethyl iodide. Ethyl iodide. Butane.
This substance may therefore be termed diethyl, C 2 H 5 .C 2 H 5 .
We may consider the formula of normal butane to be derived
from that of propane by the addition of a carbon atom, with its
accompanying hydrogen atoms, to an end carbon atom of
propane. But there is a second possible arrangement of 4
carbon atoms and 10 hydrogen atoms, forming, not a straight,
but a branched chain, thus
H
H C H
H
H
I
H C C C-H
I ! I
H H II
Isobutane.
This second formula may be derived from propane by attach-
ing a fourth carbon atom to the middle carbon atom of propane.
It represents a central carbon atom attached to 3 methyl groups,
74 THEORETICAL ORGANIC CHEMISTRY CHAP.
or methane in which 3 hydrogen atoms are replaced by 3
methyl groups. It may therefore be termed trimethylmethane,
CH(CH 3 ) 3 . The formula agrees with the synthesis of isobutane
from tertiary butyl iodide by reduction (p. 85)
(CH 3 ) 3 CI + Ho = (CH 3 ) 3 CH + HI
Tertiary butyl iodide. Isobutane.
Pentane, C 5 H 12 . This formula stands in Table III. (p. 56) for
three compounds, which corresponds exactly with the theoretical
number of combinations of 5 carbon atoms. One arrangement
is produced by adding a fifth carbon atom to one of the end
carbon atoms of normal butane
H H H H H
I I I I I
H -C C C C C H
I I I I I
H H H H H
Normal Pentane.
This structure is present in normal pentane. Again, the
additional carbon atom may be attached either to an end or
middle carbon atom of isobutane, and in each case a different
grouping will result
H II
f f
H C H H C H
H
H
I
H H II
I I I
H C C C C H H C C C H
I I I I I I
H H H H H H
H C H
H
Isopentane. Neopentane.
The first is called isopentane, or dimethylethylmethane,
C 2 H 5 ;H.C. (CH 3 ) 2 ; the second neopentane, or tetramethyl-
methane, C(CH 3 ) 4 .
Normal, iso-, and neo-paraffins. A normal paraffin repre-
sents a straight carbon chain, in which each middle carbon
atom is attached to 2 carbon atoms and 2 hydrogen atoms,
i.e. it contains the group n=CH 2 , sometimes called a primary
group; an iso-paraffin has at least one carbon atom attached
to 3 other carbon atoms, and contains the group EECH, some-
v ISOMERIC PARAFFINS 75
times called a secondary group; a neo-paraffin has at least
one carbon atom attached to 4 other carbon atoms, and has the
group E=C, termed a tertiary group '
CH 9 NCR c
X . |
Primary group Secondary group Tertiary group
of a of an ' of a
normal paraffin. iso-paraffin. neo-paraffin.
It should be noted that the normal paraffin has the highest
boiling-point, and the hydrocarbon with the largest number of
methyl groups, i.e. the largest number of branches, the lowest
boiling-point. This is seen in the case of the pentanes and of
the isomeric members of many other families.
Normal pentane, b.p. 36, and Isopentane, b.p. 28, are both
present in petroleum. Neopentane, b.p. 9, is obtained synthetic-
ally from tertiary butyl iodide (p. 86) and zinc-methyl (p. 227).
ZnI 2
Pentane, carefully fractionated from petroleum, is used in a
/amp of special construction as a standard illuminant for deter-
mining the illuminating power of coal-gas, &c.
Nomenclature of the Isomeric Paraffins. The simplest
method for distinguishing the isomeric paraffins is to regard
them as derivatives of some simpler paraffin, methane or
ethane, in which one or more hydrogen atoms are replaced by
" methyl/ 3 " ethyl," " propyl," &c. groups. The system will be
readily understood from what has been previously stated, and
by reference to the names of the isomeric paraffins in Table III.
(p. 56).
QUESTIONS ON CHAPTER V.
1. Discuss the theory which accounts for the existence of homo-
logues in the paraffin family.
2. Explain why the general formula of the paraffins is represented by
C n H 2 n4. 2 . What would n be if the vapour density of a 'paraffin were
found to be 57 ?
I
CH 8 -C-jI: +
r^tj '~7-n' c* tr _L 'T^ c* r^TT
l_/rl 3 . ;^H:. L/rl 3 T ;1; v>~ ^-^3
= 2CH 3 -C CH 3
I
CH 3
Tertiary butyl
iodide.
CH 3
Zinc methyl. Tertiary butyl
iodide.
CH 3
Neopentane.
76 THEORETICAL ORGANIC CHEMISTRY CHAP.
3. How would you determine the purity of a sample of methane ?
4. Calculate the proportion by volume of methane, hydrogen and
nitrogen in a mixture which gave the following data on analysis :
10 c.c. of gas were made up to 90 c.c. with air and exploded. The
volume then measured 7375 c.c., and after absorption by potash,
6975 c.c. Temperature and pressure were throughout constant.
5. What is meant by tib />
NaO C^ NaO.Cr' Sodium formate.
Caustic soda. Chloral.
Chloroform is usually manufactured by boiling ethyl alcohol,
or acetone, C 3 H 6 O, with bleaching-powder and water. The
reaction in either case is complex, and probably represents a
series of changes. The bleaching-powder may be considered as
furnishing both chlorine and lime. The alcohol is converted by
the chlorine into chloral, which is then decomposed by the lime,
as it is with an alkali, into chloroform and calcium formate
C 2 H 6 + 4 C1 2 = C 2 C1 3 HO + 5 HC1.
Chloral.
VI HALOGEN DERIVATIVES OF THE PARAFFINS 89
The acetone forms trichloracetone, which splits up when
heated with lime into chloroform and calcium acetate. The
structure of acetone and acetic acid must be assumed in order
to understand the course of the reaction.
CH 3 CC1 3
i ' I
C=O + 3C1 2 = C=O + 3HC1
CH 3 CH 3
Acetone. Trichloracetone.
H CC1 3 HCC1 3 Chloroform.
ca '6-fC=O = ca'O C=O
Calcium acetate. 1
CH 3 CH 3
Lime. Trichloracetone.
EXPT. 16. Preparation of Chloroform. A round 2-litre flask is
fitted with a cork, thiough which a bent tube passes, connecting the
flask with a long condenser and receiver. The flask is placed upon a
large sand-bath. The bleaching-powder (200 grams) is ground into
a paste with water (800 c.c. ). Fifty c.c. of acetone are now added,
and the contents heated cautiously until the reaction begins. The
flame is removed for a time until the reaction has moderated. The
liquid is then boiled until no more heavy drops distil with the water.
The distillate is purified by exactly the same process as that
described in the preparation of ethyl bromide (p. So).
Chloroform is a heavy, colourless liquid, b.p. 6i-62, m.p.
-63*2, and sp. gr. 1*525. It is non-inflammable. When pure,
dry chloroform is exposed to sunlight and air, especially when
calcium chloride is present, free chlorine and carbonyl chloride
are rapidly formed
2CHC1 3 -f 30 = H 2 O + 2COC1 2 + C1 2 .
The addition of about r per cent, of alcohol arrests this
change, but even then it is desirable to keep the liquid in the
dark, and the bottle filled to the neck.
The presence of the products of the above decomposition is
readily ascertained by adding silver nitrate solution, which has
1 By taking calcium as monovalent, or as representing a half atom, the equation
is simplified. Otherwise the number of molecules on both sides of the equation
would require to be doubled.
THEORETICAL ORGANIC CHEMISTRY CHAP.
no action on pure chloroform, but forms silver chloride when
either carbonyl chloride, or chlorine is present. For anaesthetic
purposes the presence of either impurity is extremely dangerous.
Chloroform should leave no residue on evaporation.
The presence of chloroform is detected by its smell. A more
delicate test is known as the phenyl carbamine, or isocyanide
reaction. This test depends upon the action of chloroform upon
aniline in the presence of caustic potash, which gives phenyl
carbamine, a compound with an intolerable smell
CHC1 3
Aniline.
= C 6 H 5 NC
Phenyl carbamine,
EXPT. 17. The following reaction should be performed in a fume
cupboard. Bring into a test-tube two drops of chloroform, one drop
of aniline, and I c.c. of alcoholic potash (caustic potash dissolved
in alcohol), and warm. Notice the smell of phenyl carbamine.
Chloroform may also be detected by-, boiling the substance
under examination (which must not contain free acid), with water,
and passing the vapour
through a heated tube.
The chloroform breaks
up, on heating, into
hydrochloric acid and
chlorine, which are in-
dicated by their action
on a piece of blue
litmus paper held at
the mouth of the tube.
EXPT. 18. A flask
furnished with a bent
delivery-tube may be
used (Fig. 47). Water
containing a few drops
of chloroform is intro-
duced into the flask
and gently boiled, the
delivery-tube being heated by a second burner. A piece of blue
litmus held at the end will be rapidly reddened and then bleached,
or potassium iodide and starch paper will be turned blue.
FIG. 47. Test for Chloroform.
vi HALOGEN DERIVATIVES OF THE PARAFFINS 91
lodoform, CHI 3 , is prepared from alcohol or acetone by
the action of iodine and an alkali. The process is probably
analogous to the formation of chloroform..
EXPT. 19. Preparation of lodoform. -Two parts of crystallised
sodium carbonate are dissolved in 10 parts of water ; one part of ethyl
alcohol is poured into the solution, and then one part of iodine
gradually added. The liquid is kept at 6o-8o, when iodoform
gradually separates out.
lodoform is decomposed, on boiling with caustic alkalis, into
potassium formate
/ X OH /QH
HCf-il + KjOH -> HC^-OH -> HC/ + H 2 O.
\|I KjOH \OH X)
lodoform. Ortho-formic acid Formic acid.
(not known).
Hence, in preparing^ iodcform with caustic alkali in place of
the carbonate, it is desirable not to boil the solution.
lodoform is also prepared commercially by the electrolysis of
a solution of potassium iodide in presence of alcohol or acetone.
EXPT. 20. Preparation of lodoform by Electrolysis. Twenty
grams of sodium carbonate (anhydrous) and 20 grams of potassium
iodide are dissolved in 200 c.c. of water and 50 c.c. of absolute alcohol
added, and poured into a beaker. The anode consists of a sheet of
platinum foil 8 x 10 cms., and the cathode of platinum wire wound into
a spiral of I cm. diameter. The solution is warmed to 60 70 and a
current of 3 amps, per sq. decimetre passed through the solution whilst
carbon dioxide is allowed to bubble into the liquid. In about 30
minutes a quantity of iodoform will have separated.
On electrolysis, iodine is liberated from the potassium iodide,
which, in presence of the alkaline carbonate, acts upon the
alcohol or acetone in the ordinary way and hydrogen is
evolved :
2KI + H 2 O + CO 2 = K 2 CO 3 + H 2 + I 2 .
lodoform crystallises in lemon-yellow hexagonal plates or
star-shaped crystals, which have a characteristic appearance
under the microscope. It melts at 119, and sublimes. It is
used in medicine and surgery as a strong antiseptic and dis-
92 THEORETICAL ORGANIC CHEMISTRY CHAP.
infectant ; but, on account of its peculiar and unpleasant smell,
other organic iodine compounds have been prepared as sub-
stitutes (p. 561).
Carbon Tetrachloride, CC1 4 , is now manufactured on a com-
mercial scale, and is used as a solvent. It is obtained by the
action of chlorine on carbon bisulphide in the presence of a
little metallic iron, which assists the reaction, as a " chlorine
carrier" :- CS 2 +3C1 2 =CC1 4
CS 2 +2S 2 C1 2 =CC1 4
Carbon tetrachloride is a colourless liquid, with a sweet smell
like chloroform. It boils at 76-77. It does not decompose
in sunlight like .chloroform.
QUESTIONS ON CHAPTER VI
1. Calculate the theoretical weight of bromine and hydrochloric acid,
respectively, required to convert 10 grams of ethyl alcohol into ethyl
bromide and ethyl chloride ; also the theoretical weights of the two
products.
2. Give the formulae for any two primary, any two secondary, and
any two tertiary, hexyl iodides.
3. What paraffins could be obtained from ethyl alcohol? Explain
the steps.
4. Formulate the action of metallic sodium, ammonia, potassium
cyanide, dilute caustic potash, and strong alcoholic potash on ethyl
bromide.
5. Explain the solvent action of boiling caustic potash on iodoform.
By analogy, what would be the action of the same alkali on chloroform
and carbon tetrachloride ?
6. How would you explain the isomerism and determine the structure
of ethylene and ethylidene chlorides ?
7. What is the meaning of the term compound radical? Give ex-
amples of a mono-, di-, and trivalent radical.
8. Explain the formation of chloroform from alcohol and acetone.
Give the tests for chloroform.
9. How would you determine the purity of a specimen of chloroform ?
What impurities is it likely to contain ?
10. Name the alky I groups in the following formulae : C 2 H 5 I ;
CH 3 .CHC1.CH 3 ; (CH 3 ). 2 CH.CH 2 Br.
11. Describe and explain the formation of iodoform. What are its
chief properties?
VI HALOGEN DERIVATIVES OF THE PARAFFINS 93
12. How is chloroform prepared ? What reactions prove it to be a
derivative of methane ? How can the presence of chlorine be shown ?
13. Suppose a small quantity of chloroform which contains some
water has been exposed to sunlight in a large colourless glass bottle,
would the chloroform be pure, and, if not, how would you test for the
impurities ?
14. How is ethyl bromide prepared ? How does ethyl bromide
react with (i) caustic potash, (2) ammonia, (3) sodium?
15. Describe a method for the preparation of methylic iodide.
How would you determine its vapour density ?
1 6. Two isomeric compounds having the composition C 2 H 4 C1 2 are
known ; how are these compounds obtained, and how has their con-
stitution been determined ?
17. What is iodoform ? Describe by equations how it is prepared?
What is produced on boiling it with a solution of caustic potash in
alcohol ?
18. What is the origin of the name " chloroform"?
CHAPTER VII
THE ALCOHOLS
THE alcohols may be looked upon as oxygen derivatives of
the paraffins. The general formula is C n H 2n+2 O, which repre-
sents a paraffin with an additional atom of oxygen. A list of
the more important alcohols, with their boiling-points and specific
gravities, is given in Table VI.
TABLE VI.
THE ALCOHOLS, C n H 2n + 2 O.
Methyl alcohol . ...
CHo(OH)
^
Sp. gr.
812
Ethyl alcohol
C 2 H 5 (OH)
78
806
Propyl alcohols
CsH^'OH)
Primary .
CH 3 .CH 2 .CH 2 (OH)
Q7
804
Secondary (Isopropyl) . .
Butyl alcohols ......
CH 3 .CH(OH).CH 3
C 4 II 9 (OH)
81
789
Normal primary ....
Normal secondary ....
Primary isobutyl ....
Tertiary , . . . .
C 2 H 5 .CH 2 .CH 2 (OH)
C 2 H 5 .CH(OH).CH,
(CH 3 ) 2 CH.CH 9 (OH)
(CHo)oC(OH) CHo
117
100
107
8V
810
806
786
Amyl alcohols
C 5 H U (OH)
Normal primary ....
Isobutyl carbinol ....
Secondary butyl carbinol .
Methyl propyl carbinol
Methyl isopropyl carbinol
Diethyl carbinol ....
Dimethylethyl carbinol . .
C 2 H 5 .CH 2 .CH 2 .CH 2 (OH)
(CH 3 ) 2 CH.CH 2 .CH 2 (OH)
CH 3 .CH.(C 2 H 5 ).CH 2 OH
C 2 li 5 .CH 2 .CH(OH).CH 3
(CH 3 ) 2 CH.CH(OH).CH 3
C 2 H 5 .CH(OH).C 2 H 5
(CH 3 ) 2 C(OH).C 2 H 5
138
131
128
119
112
117
102
815
810
(
94
CH. vii THE ALCOHOLS
95
General Properties of Alcohols. The alcohols are colourless
and neutral substances, having neither an acid nor alkaline
reaction. The lower members, viz. those with few carbon atoms
are liquids ; the higher members are solids. The lower members
have a burning taste and distinctive smell, and are more or less
soluble in water ; but taste, smell, and solubility in water rapidly
diminish with increasing molecular weight. Methyl, ethyl,
and propyl alcohol are miscible with water ; butyl alcohol
dissolves in 12 parts ; amyl alcohol, from fusel oil, requires 39
parts of water. The proportion of oxygen appears to determine
the solubility in water, and as it decreases with increasing
molecular weight, the general physical characters of the paraffin
gradually predominate. Cetyl alcohol, C 16 H 34 O, derived from
spermaceti, is a solid, quite insoluble in water, and greasy to the
touch like paraffin-wax.*
Constitution of the Alcohols. In spite of physical differ-
ences, the chemical behaviour of the alcohols persists through-
out the series. In certain reactions, the alcohols resemble
water ; in others, again, they show a closer similarity with
caustic soda. Like water, they are decomposed by sodium,
and hydrogen is liberated ; but, whichever alcohol is taken,
only one atom of hydrogen is liberated and replaced by
sodium.
EXPT. 21. Throw a small piece of sodium into methyl, or ethyl
alcohol. There is a vigorous effervescence, but the heat given out is
never sufficient to ignite the gas, as it may do when water is decomposed.
When the sodium has dissolved, evaporate the solution on the water-
bath to dryness. A white solid remains, which is very hygroscopic
and is decomposed by water. The solid has the formula CH 3 ONa,
or C 2 H 5 ONa, according to the alcohol taken. The product is a defi-
nite compound, known as sodium methylate (methoxide), or sodium
ethylate (ethoxide), or generally as sodium alcoholate.
We have already seen (p. 81) that an alcohol, like water,
decomposes the chloride, bromide, and iodide of phosphorus.
EXPT. 22. Add a small quantity of phosphorus pentachloride to a
few c.c. of methyl or ethyl alcohol. Notice the vigorous action and
the disengagement of hydrochloric acid fumes.
The relation between an alcohol and water may be illustrated
96 THEORETICAL ORGANIC CHEMISTRY CHAP.
by the following equations, in which methyl alcohol is taken as
the typical alcohol :
Water.
2H 2 O+Na 2 = 2 HONa-fH 2 .
H 2 O+PC1 5 = HC1 + HC1+POC1 3 .
3 HBr+H 3 P0 3 .
Methyl Alcohol.
2 CH 4 O-fNa 2 = 2 CH 3 ONa+H 2 .
CH 4 0+PC1 5 = CH 3 C1+HC1+POC1 3 .
3 CH 4 0-KPBr 3 = 3 CH 3 Br+H 3 P0 3 .
In these reactions the radical methyl plays the part of hydro-
gen (see p. 83). Some of the alcohols also enter into the
composition of certain crystalline inorganic salts, in which
relation they offer an analogy with water of crystallisation.
Examples of this character are the compounds of calcium
chloride with methyl alcohol and ethyl alcohol
CaCl 2 + 4CH 4 O, and CaCl 2 + 4C 2 H 6 O.
The correspondence subsisting between the alcohols and the
caustic alkalis is best observed in their behaviour with the acids.
Taking methyl alcohol as representative of the alcohols, the
following equations will explain the reactions which occur : :
Caustic Soda. I Methyl A Icohol
NaOH + HCl = NaCl + H 2 0.
NaOH+HNOs = NaNO 3 +H 2 O.
NaOH+H 2 SO 4 = NaHSO 4 +H 2 O.
CH 4 O+HC1 = CH 3 C1+H 2 O.
Methyl chloride.
CH 4 0+HN0 3 =CH s .N0 3 -fH 2 0.
Methyl nitrate.
CH 4 0-fH 2 S0 4 =CH 3 .H.S0 4 +H 2 O.
Methyl hydrogen
sulphate.
Here the radical, methyl, plays the part of sodium, and the
compounds formed from the alcohol may be regarded as salts
of the radical.
We may then build up the graphic formula for methyl alcohol
on the basis of the formula for water, o*- caustic soda
H
!
H O H Na O H H C O H.
I
H
The other alcohols will be similarly constituted. Ethyl alcohol
may be written, C 2 H 5 .OH ; propyl alcohol, C 3 H 7 .OH, &c. ; the
radicals methyl, ethyl, propyl, &c., playing the part of hydrogen
in water, or sodium in caustic soda. As caustic soda is also
termed sodium hydroxide, so the alcohol is sometimes denoted
THE ALCOHOLS 97
by the name of the hydroxide of the radical. Methyl hydroxide
is synonymous with methyl alcohol. It was in consequence of
the radicals being first recognised as constituents of the alcohols
that they were formerly known as the alcohol radicals^ a term
which is now replaced by the word alkyl.
The above graphic formula for the alcohols explains many
things which would not be apparent from the simple molecular
formula. Thus, only one atom of hydrogen is replaceable by
sodium. This atom of hydrogen possesses a different function
from the rest, and is evidently the one which is linked to oxygen.
Then, again, by the action of chloride or bromide of phos-
phorus, the oxygen atom and one atom of hydrogen are removed
together, and replaced by an atom of the halogen. The change
is readily explained by the above formula, which contains an
atom of oxygen and hydrogen linked together, forming the
hydroxyl group OH. This group, which often forms part of an
organic molecule, retains, in the majority of cases, its chemical
properties unchanged. Its presence may generally be deter-
mined by the action of sodium or phosphorus chloride, which
produces, as a rule, the same chemical change as in the
alcohols.
There are other methods for detecting the presence of the
hydroxyl group, which need not be discussed at present.
Other Chemical Properties of the Alcohols. In addition
to the reactions mentioned above, the alcohols undergo other
chemical changes of importance. Strong sulphuric acid com-
bines with the alcohols to form the alkyl hydrogen sulphates.
If these compounds are heated, sulphuric acid is separated,
and hydrocarbons of the general formula C n H 2n are formed.
The latter are termed olefines, and are treated more fully in
Chap. XVII. (p. 245). Ethyl alcohol gives ethyl hydrogen
sulphate and ethylene
C 2 H 5 OH + H 2 SO 4 = C 2 H 5 .H.SO 4 + H 2 O.
Ethyl alcohol. Ethyl hydrogen
sulphate.
C 2 H 5 .H.SO 4 = C 2 H 4 + H 2 SO 4 .
Ethylene.
The olefines are directly obtained by heating the alcohol to a
moderately high temperature with a large excess of concen-
trated sulphuric acid. The process is most simply explained
98 THEORETICAL ORGANIC CHEMISTRY CHAP.
by supposing that the elements of a molecule of water are
removed from the alcohol by the dehydrating action of the
sulphuric acid
C 2 H 6 O H 2 O = C 2 H 4 , Ethylene,
C 3 H 8 O H 2 O = CaH 6 , Propylene, &c.
Methyl alcohol does not form methylene, CH 2 , which is
unknown (see p. 82) ; but yields dimethyl sulphate, (CH 3 ) 2 SO 4 ,
by this reaction.
EXPT. 23. Put a little sand or anhydrous aluminium sulphate into a
round flask of about I litre capacity, pour in 60 c.c. of strong sulphuric
acid, and add gradually 20 c.c. of ethyl alcohol. Fit a long, wide,
upright tube by a cork to the neck of the flask, and heat the flask and
its contents on wire-gauze over a moderate flame. After a time the
mixture darkens and effervesces. Ethylene gas is evolved, and may
be ignited at the end of the upright tube, where it burns with a bright
luminous flame.
It should be noticed that the compounds prepared in this way
are identical with those obtained by- the action of alcoholic
potash on the alkyl halides (p. 82).
If, instead of an excess of strong sulphuric acid, an excess of
the alcohol is present, the reaction which occurs is of quite a
different character, and the products formed are termed ethers.
They will be considered in the following chapter. Thus, the
action of sulphuric acid upon an alcohol is of a threefold
character. At the ordinary temperature the two combine and
form the alkyl sulphate ; at high temperatures, with excess of
sulphuric acid, hydrocarbons are produced ; with excess of
alcohol, ethers are formed. This is one of many examples
which might be given of an organic reaction wherein a change
in the conditions produces a marked alteration in the nature of
the products.
The alcohols readily undergo oxidation.
EXPT. 24. Warm a solution of potassium dichromate, acidified
with dilute sulphuric acid, with a few drops of alcohol. The solution
soon becomes green from the reduction of the dichromate to chromic
sulphate, and, at the same time, a peculiarly penetrating smell is
evolved. The smell is that of the substance known as acetaldehyde y
and is the product of the oxidation of ethyl alcohol.
VIE THE ALCOHOLS 99
It is found that the different alcohols do not behave quite
alike on oxidation. Some, like ethyl alcohol, form substances
known as aldehydes, others form a class of compounds known as
ketones. The difference in the behaviour of the alcohols on
oxidation separates them into three well-defined groups, the
primary, secondary, and tertiary alcohols.
Primary, Secondary, and Tertiary Alcohols. These
names are used in the same sense as that applied to the alkyl
halides (p. 85). We have only to substitute a hydroxyl group
for the halogen atom in the alkyl halides.
A primary alcohol has the hydroxyl group linked to an end
carbon atom of the series, and contains the group .CH 2 (OH).
A secondary alcohol has the hydroxyl group attached to a
middle carbon atom of a straight chain, and contains the group
:CH(OH).
A tertiary alcohol contains the group j C(OH), i.e. the carbon
atom attached to the hydroxyl group is linked to three carbon
atoms.
CH 2 (OH), primary alcohol group.
:CH(OH), secondary alcohol group.
\ C(OH), tertiary alcohol group.
Examples of all three classes will be found in Table VI.
(p. 94).
The primary alcohols on oxidation first lose 2 atoms of
hydrogen and form aldehydes; but the latter can be further
oxidised, and, by taking up an additional atom of oxygen, are
converted into acids.
Thus, methyl alcohol first forms meth- or form-aldehyde, and
secondly formic acid (p. 124)
H H
! ! I
H C 0-j-H + O = H 0= O + H 2 0.
'- ; Formaldehyde.
H
II
I
HO C=O.
Formic acid.
H 2
ioo THEORETICAL ORGANIC CHEMISTRY CHAP.
Ethyl alcohol yields, by the same process, eth- or acet-alde-
hyde, and then acetic acid
CH 3 CH 3
H C 0--H + O = H 0=0 + H 2 0.
'l Acetaldehyde.
CH 3 CH 3
I i
H 0=0 + = HO C=0.
Acetic acid.
The secondary alcohols also lose two atoms of hydrogen in
the first stage of oxidation. The compounds which are formed
are termed ketones. Secondary or iso-propyl alcohol yields
dimethyl ketone, or acetone (p. 141)
CH 3 CH 3
CH(OH) + O = C=0 + H 2 0.
CH 3 CH 3
Secondary, or iso-propyl alcohol. Dimethyl ketone.
Further oxidation breaks up the ketone molecule into smaller
fragments, consisting of acids belonging to the formic acid family,
but containing fewer carbon atoms than the ketone. Dimethyl
ketone yields, on oxidation, acetic acid, carbon dioxide, and
water
CH 3 CH 3
0=0 + 20o = C/
| X OH
Acetic acid.
CH 3 C0 2 + H 2
Dimethyl ketone. Carbon Water,
dioxide.
The tertiary alcohols decompose on oxidation, forming
ketones, or acids with fewer carbon atoms than the original
.alcohol. Tertiary butyl alcohol gives dimethyl ketone, carbon
dioxide, and water
CH 3 CH 3
"CH 3 -j-C OH r 2O 2 = C=O + CO 2 + 2H 2 O.
CH 8 CH 3
Tertiary butyl alcohol. Dimethyl ketone.
THE ALCOHOLS
Nomenclature of the Alcohols. The division into primary,
secondary, and tertiary alcohols, is not sufficient to describe a
member belonging to a numerous family of isoiners like that
of the amyl or hexyl alcohols, which contain more than one
representative of each of the above groups. If they possess a
straight chain, they may be regarded as derivatives of a normal
paraffin, and the alcohol is termed a normal alcohol ; in the same
way an alcohol with a branched chain is termed an iso-alcohol,
i.e. a derivative of an iso-paraffin. Examples of this kind will
be noticed in Table VI. under the butyl alcohols. Another
system which is also in use was proposed by Kolbe. The carbon
group which contains the hydroxyl group, whether primary,
secondary, or tertiary, is termed the carbinol group. The
radicals attached to this group are then named in conjunction
with the word carbinol. To take a simple example, secondary
propyl alcohol, may also be called dimethyl carbinol ; tertiary
butyl alcohol may be termed trimethyl carbinol. The applica-
tion of this system is well illustrated in the case of the amyl
alcohols (see Table VI.).
Sources of the Alcohols. The alcohols are found in nature
as a constituent part of many vegetable and animal products of
very varied character, such as certain oils, fats, and waxes ; but
the chief source, especially of the lower members, is fermenta-
tion. Ethyl, propyl, butyl, and amyl alcohol are all obtained by
this process. Methyl alcohol is obtained by the distillation of
wood.
The artificial methods for the production of the alcohols are
very numerous. It has already been stated that aldehydes and
ketones are formed by the oxidation of the alcohols. By the
reverse process of reduction, aldehydes and ketones may be
converted into the corresponding alcohols. Acetone, which is
obtained from the products of distillation of wood, may be
reduced, by sodium amalgam and water, to secondary propyl
alcohol
CH 3 .CO.CH 3 + H 2 = CH 3 .CH(OH).CH 3 .
Acetone. Secondary propyl
alcohol.
On p. 96, the action of the various acids upon the
alcohols is explained. It was there pointed out that the
products might be regarded as salts of the radical, i.e. alkyl
102 THEORETICAL ORGANIC CHEMISTRY CHAP.
salts, or shortly esters. These reactions are all reversible, and
consequently, methyl chloride, nitrate, and sulphate may be
partially converted by water alone into the alcohol and free
acid. The presence of caustic alkali, by forming the stable
alkali salt with the free acid, usually accelerates this reaction
CH 3 C1 + HOH = CH 3 (OH) + HC1.
CH 3 .NO 3 + HOH = CH 3 (OH) + HNO 3 .
CH 3 .H.SO 4 + HOH = CH 3 (OH) + H 2 SO 4 .
The conditions, under which the different kinds of alkyl
salts decompose most readily, vary considerably, and must be
studied individually.
The more complex methods for preparing alcohols will be
dfscussed in later chapters (pp. 200, 240).
We will now consider in greater detail the production of a
few of the more important alcohols.
Methyl Alcohol, CH 3 .OH. The name methyl is derived
from /^'#v, wine, and v\rj, wood. It is known commercially as
wood-spirit or wood-naphtha. It was first prepared by Boyle in
1 66 1 by the distillation of wood, and this is the process by which
most of the methyl alcohol is at present manufactured. When
wood is subjected to destructive distillation, it yields in-
flammable gases, a strongly acid aqueous distillate, and a
quantity of tar. The residue is wood charcoal. The operation
is carried out in large iron retorts. The aqueous distillate contains
the methyl alcohol mixed with acetic acid and acetone and a
little methyl acetate, and is known as pyroligneous acid. The
tar, which consists of paraffins, phenols (p. 450), and other organic
substances, separates from the aqueous portion on standing,
and the latter is then withdrawn. It is neutralised with lime,
whereby the acetic acid is converted into the lime salt, and
distilled. The volatile methyl alcohol and acetone, together
with water, pass into the receiver. The crude wood-spirit is
purified by fractional distillation over quicklime, which removes
the greater part of the acetone (b.p. 56) and water.
Methyl alcohol is also produced by the destructive distilla-
tion of the by-products of the beet-root sugar industry (p. 301).
The molasses are fermented and the ethyl alcohol removed by
distillation. The residue is then dried and distilled like wood.
Commercial methyl alcohol always contains acetone, which
may be reduced in. amount by fractional distillation to i or 2 per
cent. : but the auantitv is frenuentlv greater. There are various
FERMENTATION 103
special methods for removing the last traces of acetone. Thus by
chlorination of the hot liquid and fractional distillation the acetone
remains as high boiling trichloracetone and the alcohol distils
unchanged. The presence of acetone is readily shown by the
iodoform reaction, which is described under ethyl alcohol (p. in).
To obtain methyl alcohol chemically pure, it is converted into
the solid crystalline compound with calcium chloride (p. 96).
EXPT. 25. A' mixture of 75 grams of methyl alcohol and 50 grams
of anhydrous calcium chloride is heated on the water-bath with
inverted condenser until solution is obtained. On cooling, the com-
pound CaCl 2 + 4CH 3 OH crystallises.
When the calcium chloride compound is heated, pure methyl
alcohol is driven off and is condensed and collected.
Methyl alcohol boils at 66. It is inflammable, and burns with
a blue flame. It is used in the manufacture of certain coal-tar
colouring matters, and for dissolving shellac and resins in the pre-
paration of varnishes. It is mixed withethyl alcohol in methylated
spirit (p. no), and is used for making formaldehyde.
Fermentation. When yeast (saccharomyces) is added to a
solution of grape, or cane sugar, the liquid shortly begins to
froth and has the appearance of boiling, although there is a
scarcely perceptible rise of temperature. The process is called
fermentation, from the Latin fervere, to boil. A fundamental
change occurs in the sugar, whereby it is broken up into ethyl
alcohol 1 and carbon dioxide.
EXPT. 26. Dissolve 10 grams of grape-sugar in 200 c.c. of water :
pour the solution into a large flask (2 litres), and add about an ounce
of brewers' yeast. Fit the flask with a cork and bent delivery tube,
dipping into lime-water. Warm the solution to about 25, and leave
the flask in a warm place. After a short time bubbles of gas appcai ,
and a considerable deposit of calcium carbonate will form in the Hire-
water. After twenty-four hours the presence of alcohol in the flask
may be readily ascertained by pouring out a small portion of the liquid
into a flask furnished with an upright tube. On gently boiling the
contents, the vapour of alcohol, which is more volatile than water, is
the first to pass out of the open end of the upright tube, and may be
ignited. Another portion of the contents of the flask may be dis-
tilled and the first few c.c. collected. Potassium carbonate (solid)
is added to the distillate, and the supernatant liquid, which is the
alcohol, separated. The liquid 'is then distilled over quicklime, and
is found to boil at 78.
1 The word ethyl is derived from alflrjp, ether ; vAry, substance ; as ordinary
ether contains the radical of ethyl alcohol (p. 117).
104 THEORETICAL ORGANIC CHEMISTRY CHAP.
This decomposition was first studied quantitatively by
Lavoisier. It may be expressed; in the case of grape-sugar,
by the following equation
C 6 H 12 O 6 = 2C 2 H 6 O + 2CO 2 .
Grape-sugar. Ethyl alcohol. Carbon dioxide.
But the reaction is not so simple as the equation represents ;
for, in addition to ethyl alcohol, there appear propyl and isobutyl
and the two amyl alcohols, viz. isobutyl carbinol and secondary
butyl-carbinol, which together constitute fusel oil. Moreover,
there is present about o'6 per cent, of succinic acid and 2*5
per cent, of glycerol. The process of fermentation is one of
great antiquity. It was well known that yeast, or the white
scum which forms in the fermenting liquid, is capable of setting
up fermentation in fresh. quantities of saccharine solution. The
yeast was first examined in 1680 by Leeuwenhoek, under the
microscope, shortly after that instrument had been invented,
and was observed by him to consist of numerous small
spherical granules ; but it was not until 1836
that de la Tour in France and Schwann in
Germany, independently, discovered the
living nature of yeast cells. These cells,
which are sometimes called the yeast plant,
are now recognised as a low form of veget-
able life. The cells are spherical, having,
under a high power, the appearance repre-
sented in Fig. 48. The cell has a thin outer
FIG. 48.- Yeast cells r ,, , , .
(highly magnified). envelope of cellulose, and its contents con-
sist of protoplasm. Reproduction takes place
by budding, and the bud, having attained a certain size, detaches
itself from the parent cell. The stages in the process are re-
presented in Fig. 48. If the liquid is undisturbed, the cells
remain clinging together in the form of branching clusters.
Theories of Fermentation. Various theories have been
advanced at different times to account for the chemical action of
the living cells. Our knowledge of the subject is largely due to
Pasteur, whose exhaustive researches have clearly shown that
the decomposition of sugar is dependent on the life and growth
of the yeast cell in the saccharine liquid. If the yeast is re-
xr.oved by filtration, or destroyed by boiling the liquid, fermenta-
VII FERMENTATION IO5
tion ceases. Pasteur has described fermentation as life without
air. According to his view, trie yeast, deprived of air by immer-
sion in the saccharine liquid, provides itself with the necessary
oxygen from the sugar molecule, which is broken up in the act.
The recent researches of Buchner have, however, entirely
modified our views on the whole subject of fermentation and
other kinds of chemical change accomplished by living
organisms. Buchner has shown that the contents of the dried
and pulverised yeast cells may be extracted by great pressure,
and that the liquid so obtained, and freed by filtration from ad-
hering cells, is capable of setting up fermentation like the living
ye^ast. This substance he has termed zymase. Fermentation is
-therefore a chemical process ; but it offers little analogy with any
"of the usual organic reactions with which we are acquainted.
Hydrolytic Ferments. When yeast is added to a solution of
grape-sugar, C 6 H 12 O 6 , fermentation soon begins ; but if cane-
sugar, C 12 H 2 2O n , is employed, the reaction is delayed. The
difference is due to the nature of the two sugars. Yeast cannot
ferment cane-sugar. The cane-sugar must be first decomposed
into fermentable sugar, viz. grape-sugar, or glucose, and fruit-
sugar, or fructose, and the decomposition is effected by the
presence of a soluble nitrogenous substance, which invariably
accompanies yeast and is known as invertase
C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 .
Cane-sugar. Grape-sugar. Fruit-sugar.
The decomposition is brought about by the addition of a
molecule of water. Such a decomposition is called hydrolysis,
and may be defined as a chemical change or decomposition
effected with the addition of the elements of water.
Invertase is known as a hydrolytic ferment or enzyme. It
differs from yeast, not only in the nature of the decomposition
which it induces, but by its solubility in water and by the fact
that it may be precipitated from solution by alcohol without
losing its fermentative or hydrolytic power. We are acquainted
with many enzymes, such as diastase, which occurs in leaves and
germinating grain, and ptyalin of the saliva, both of which
can convert starch into sugar ; pepsin, a constituent of the
digestive juices, which transforms insoluble albumin into soluble
albumin, known as peptone ; and mauy others.
106 THEORETICAL ORGANIC CHEMISTRY CHAP.
Both zymase and the enzymes belong to the complex group
of albuminoid substances and proteids, about the structure of
which little is at present known (p. 372).
It is very probable that the bacteria minute organisms
which are responsible for a great varety of chemical changes
among organic substances, such as the production of lactic and
butyric acids from sugar and starch, and acetic acid from alcohol
contain a nitrogenous principle, like zymase, within the living
cell, and that all these changes are purely chemical processes.
Manufacture of Beer, Wines, and Spirits. In the manu-
facture of beer, barley is steeped in water and then spread in
layers a few inches deep on large floors where a steady tem-
perature suitable for germination is maintained. During the
process, the hydrolytic enzyme, diastase, is formed in the grain,
and subsequently acts upon the starch present and converts it
into sugar. After germination has proceeded for a few days,
the grain is removed to a chamber where it is heated to a
sufficiently high temperature to arrest germination, and at the
same time to give the necessary flavour to the beer. The kiln-
dried grain is called malt. It is now steeped in water at 6o-65,
when the diastase rapidly acts upon the starch, decomposing il
into soluble dextrin and maltose, or malt-nugar, a sugar isomeric
with cane-sugar, C 12 H 22 O n . The extract, or wort, is then sepa-
rated from the insoluble portion of the malt and run into large
copper pans, where it is boiled with the addition of hops (the
dried flowers of the plant), which impart a slightly bitter taste,
and act at the same time as a preservative or antiseptic. The
liquid from the pans is rapidly cooled and drawn into vats
warmed to 15- 17, and yeast is added. The maltose alone
undergoes fermentation, and as this sugar constitutes only a
small portion of the extract, the quantity of alcohol is not large.
An additional quantity of alcohol is artificially introduced by
adding glucose (p. 291) to the boiling pan. After fermentation
has stopped, the liquid is run into casks and left to " brighten."
The wort is capable of nourishing other micro-organisms besides
the yeast plant, and if scrupulous cleanliness is not observed, or
if impure yeast is used, lactic, acetic, and other fermentations
may occur simultaneously, and produce what is known as the
" diseases of beer,' 7 which show themselves in acidity, or in
some other disagreeable flavour.
Wine is made from must or grape-juice, which contains grape-
vii FERMENTATION 107
sugar. The juice is left in open vats and undergoes spontaneous
fermentation, the quantity of alcohol depending upon the
amount of fermentable sugar present. It is unnecessary for
the wine-grower to add yeast like the brewer does, for the
natural acidity of the must excludes foreign organisms. The
yeast, necessary for fermentation, is derived from the dust, or
bloom, which covers the outside of the grape.
Spirits, like whisky and gin, are also made from barley by a
process which is nearly identical with that used in the brewing
of beer. The main difference consists in the length of time
during which the malt, or more frequently a mixture of malt
and un malted grain, is steeped in water. During the limited
time allowed for the diastase to act upon the starch
in brewing beer, the starch is transformed into dextrin and
into maltose. By the prolonged action of diastase, nearly
the whole of the dextrin is converted into maltose, so that in the
subsequent fermentation, the maximum amount of alcohol is
produced. Finally, the fermented liquor or wash is distilled
and the alcohol removed. The distillate is then redistilled or
rectified, care being taken not to push the distillation so far
that \hefusel oil (a mixture of the higher alcohols) distils.
If spirits of wine (ethyl alcohol) is required, the alcohol in the
fermented liquid is concentrated by fractional distillation. The
apparatus commonly used in this country is Coffees still, which
permits of the distillation being carried on continuously. The
still is drawn in section in Fig. 45. It consists of a boiler, #, into
which steam is admitted, and communicates with a column, ,
called the analyser, and a second column, c, called the rectifier.
These columns are made of wood, and are lined with copper.
The analyser is divided into compartments by horizontal plates
of copper perforated with holes and furnished with valves
opening upwards, and also with dropping tubes. The rectifier
has a construction very similar to b. It receives the vapour
passing from the analyser by the pipe d. The wash or fer-
mented liquor is pumped into the zig-zag column of pipes
within the rectifier c, which are heated by the surrounding
vapours, and is finally discharged above the top of the perforated
plate in the analyser b by the pipe e. Here it meets an ascend-
ing column of vapour from the boiler a, which deprives it of the
more volatile alcohol. This alcoholic vapour undergoes further ,
condensation in ascending the rectifier, so that on issuing from
io8
THEORETICAL ORGANIC CHEMISTRY
CHAP.
the pipe at the top of the rectifier it contains very little water,
and is then condensed and collected. The spent wash, or liquid
deprived of alcohol, collects in the boiler and is withdrawn from
time to time by the waste pipe.
The spirit obtained in this way, when diluted and flavoured
with various ingredients, is sold as British brandy, British rum,
FIG. 49. Coffey s still.
&c. In order to prepare pure alcohol from the rectified spiril
made with CofFey's still, the liquid is filtered through charcoal,
and is further fractionated. The first portions, or runnings, which
contain aldehyde, and the last, known as feints, which consist
of strong-scented fusel oil, are rejected. The alcohol is finally
distilled over quicklime, and is sold as absolute alcohol. It still
contains about a half per cent, of water, which can be removed
by adding a quantity of metallic sodium or calcium, necessary to
combine with the water present, and redistilling.
ALCOHOLOMETRY 109
Alcohol is also manufactured, especially on the Continent,
from potatoes and other materials, such as maize, rice, rye,
oats, c., which are rich in starch, and also by fermenting
molasses or treacle, that is, the uncrystallisable portion of the
sugar, and distilling the product. In the manufacture of potato
spirit, the potatoes are rasped, steamed, and crushed. Malt is
added, which converts the starch into maltose, and the wort is
then fermented and distilled.
Brandy or cognac is the alcoholic distillate from wine. Gin, like
whisky, is made from barley, and flavoured with juniper ; rum is
the distillate from fermented molasses ; hollands is prepared
from malt and rye. The following table gives the approximate
percentage of alcohol contained in various fermented liquors :
Per cent. | Per cent.
Whisky 40 | Burgundy 13
Brandy 40 Hock 9
Rum 40 Claret 7
Gin 3540 | Ale 6
Port 20 I Porter 56
Sherry 16 j Munich beer .... 4 5
Alcoholometry is the name given to the method of deter-
mining the quantity of alcohol in fermented liquors. All liquids
containing alcohol, or made from alcohol, pay an excise duty.
The excise duty on alcoholic liquids is at the rate of ten shillings
per gallon of proof spirit. The old proof spirit test was known
as the powder-test, and consisted in pouring the liquid on to gun-
powder, and then igniting it. If the alcohol contained so little
water that it burnt away, leaving the powder dry enough to
ignite, it was termed proof spirit ; but if the powder was too
damp to take fire, the spirit was under proof. The method
which is now employed is to take the specific gravity of the liquid.
Pure alcohol has a specific gravity of 0*806 at o, and 0793 at 15,
and it would appear a simple matter to determine by calculation
the quantity of alcohol in any mixture of water and alcohol.
This cannot, however, be done so readily ; because, when alcohol
and water are mixed, there is a considerable contraction in
volume. The contraction can be readily shown by pouring
down a long narrow tube, sealed at the end, a column of coloured
water, and gradually adding an equal volume of alcohol without
allowing the two columns of liquid to mix. The level of the
i io THEORETICAL ORGANIC CHEMISTRY CHAP.
liquid is marked with a rubber ring, and then the contents of
the tube are well shaken. In spite of the rise of temperature,
which the mixing of the two liquids occasions, a very consider-
able contraction is apparent.
Tables have been carefully compiled by Tralles, which give
the quantity of alcohol corresponding to different specific
gravities. The specific gravity is determined by a special form
of hydrometer known as Sikes's hydrometer. The duty is levied
on proof spirit which is defined by Act of Parliament as " such
as shall at a temperature of 51 F. weigh exactly ^jfths part of
an equal measure of distilled water." This corresponds to 49*3
per cent, by weight, or about equal weights of water and alcohol,
or 57*09 per cent, by volume of alcohol. All spirit is estimated
by its equivalent of proof spirit. Thus, every 100 gallons of spirit
25 over proof will be taxed as 125 gallons of proof, or 100 gallons
of spirit 25 under proof will pay duty on 75 gallons of proof. It
will be further observed, that the tax is payable on volume, not
on weight, so that a standard temperature must be fixed upon
to serve as a basis for calculation. The standard temperature
is taken at 51 F., and although the quantity of proof spirit is
estimated at that temperature, the volume of spirit, which is
taxed will vary with the prevailing temperature. Altogether the
system cannot claim the merit of simplicity.
In estimating the amount of alcohol in beer and wines, and in
liquors which contain other ingredients besides alcohol and
water, the hydrometer will not give a true indication of the
quantity of alcohol. The liquid is therefore distilled. A certain
volume is carefully measured and distilled in a flask connected
with a condenser and receiver until about one-half of the liquid r
which will contain all the alcohol, has passed over The dis-
tillate is then made up to the original volume, and its specific
gravity determined in the usual way.
The annual expenditure in the United Kingdom on alcoholic
beverages is about 160 million sterling, which pays a revenue of
about 32 million sterling to the Exchequer.
Methylated Spirit. Owing to the high duty on pure ethyl
alcohol (which amounts to about twenty shillings a gallon) methyl-
ated spirit is used in its place, being duty free. It is a mixture
of 90 parts of raw spirits of wine and io parts of crude wood-
spirit, with the addition of a little paraffin oil, which renders it unfit
for drinking, without affecting its value for many trade purposes.
vii
ETHYL ALCOHOL
The refinements which have been introduced into chemical pro-
cesses necessitate the use of pure alcohol, and the excise duty
places a serious obstacle in the way of the English chemical manu-
facturer in competing with Continental firms, which pay no duty.
Methylated spirit is used as a solvent for resins in the
preparation of varnishes, for the extraction of oils, for the puri-
fication of alkaloids, for the manufacture of chloroform, ether,
and for burning. The ordinary methylated spirit is very impure,
containing all the impurities of the original spirits. It may be
partially purified by distilling it over solid caustic potash.
Properties of Ethyl Alcohol. Pure ethyl alcohol is a colour-
less liquid, with a burning taste and fragrant smell, and boils at
78. It burns with a blue flame, and is miscible in all propor-
tions with water. The presence of small quantities of water in
ethyl alcohol may oe detected by adding anhydrous copper sul-
phate, which is tuined blue, or by pouring a few drops into paraffin
oil or benzene, which, if water is present, become turbid.
The usual test for ethyl alcohol is known as the iodoform test.
A crystal of iodine or a little iodine solution is added to the liquid,
together with a few drops of alkali, and the mixture is gently
warmed. Crystals of iodoform will separate, which can be readily
identified by their smell and by their crystalline form (p. 91 ).
Acetone gives the same reaction as alcohol.
The following table gives a summary of the most important
chemical changes which ethyl alcohol undergoes :
REAGENT. PRODUCT.
The Halogens and Acids.
1. Chlorine; bromine. j Chloral, CC1 3 .COH;
CBr 3 .COH.
2. Bleaching-powder and water. Chloroform, CHC1 3 .
3. Iodine and alkali.
4. The halogen acids, HC1,
HBr, HI.
5. Bromine or iodine and red
phosphorus.
6. Concentrated sulphuric acid.
7. Strong nitric acid.
bromal,
Iodoform, CHI 3 .
Ethyl chloride, C 2 H 5 C1 ; ethyl
bromide, C 2 H 5 Br ; ethyl iodide,
Ethyl bromide ; ethyl iodide.
Ethyl hydrogen sulphate,
C 2 H 5 HSO 4 ; ethylene, C 2 H 4 ;
or ether, C 4 H 10 O.
Ethyl nitrate, C 2 H 5 NO 3 .
THEORETICAL ORGANIC CHEMISTRY
REAGENT. PRODUCT.
Oxidising Agents.
8. Potassium dichromate and
sulphuric acid.
9. Chromium trioxide.
10. Red-hot platinum wire held in
the vapour of alcohol.
11. Platinum black and alcohol
exposed to the air.
Acetaldehyde, CH 3 .CHO.
The ethyl alcohol takes fire and
burns to carbon dioxide and
water.
Acetaldehyde, CH 3 .CHO.
Acetic acid, C 2 H 4 O 2 .
Optical Activity. Of the isomeric amyl alcohols, there are
two present in fusel oil, viz. isobutyl carbinol, which is the chief
constituent, and secondary butyl carbinol, which forms 10 to
20 per cent, of the mixture. The latter is also known as active
amyl alcohol. The term active, which we shall frequently have
occasion to use, has a special significance. It refers to the
action which certain substances produce upon plane-polarised
light.
When light is passed through a Nicol prism, only rays vibrating
in one plane are transmitted, and the light is said to be polarised.
A polarimeter is an instrument containing two Nicol prisms,
fixed at short distances apart. If we imagine rays passing
through the first prism to vibrate in a vertical plane, then, by
turning the second prism, so that rays can only traverse it in a
horizontal plane, the light from the first is totally extinguished
by the second prism. If the second prism is rotated, more
and more light is transmitted, until the planes of transmission
coincide, when the field is fully illuminated.
Supposing the Nicol prisms to be crossed, as in the first
case, so that the light after traversing the first prism is extin-
guished by the second prism, the introduction of a layer of
active amyl alcohol will allow some light to pass. The alcohol
has the property of turning the plane in which the polarised rays
vibrate from the normal direction to the left hand (laevo-rotatory),
so that some light now finds its way through the second Nicol
prism. In the case of other substances a right-handed (dextro-
rotatory) rotation is imparted. This will be more easily
understood by reference to Fig. 50.
VII
OPTICAL ACTIVITY
a represents the first Nicol prism and c the second, the plane
of vibration being indicated by the cross lines. On introducing
the alcohol, the plane of vibration of the polarised rays is twisted
through a certain angle indicated at b. This new position may
be regarded as the resultant of two forces, represented by vertical
and horizontal components, indicated by dotted lines. The
vertical component is extinguished when it reaches <:, but the
horizontal component passes through and produces a certain
FIG. 50.
degree of illumination of the field of view. A greater twist will
allow more light to pass, until the twist takes a horizontal posi-
tion, when the maximum amount of light will be transmitted.
The property of turning the plane of polarisation is also called
rotatory polarisation, and is synonymous with optical activity.
This property, possessed by certain liquids and solutions of
solids, is found to bear a close connection with their structure.
Optically active carbon compounds, without exception, contain
within the molecule at least one carbon atom, united by its 4
bonds to 4 different elements or groups of atoms.
FIG.
If we denote the carbon atom as a point from which 4 bonds
diverge at equal angles (Fig. 51), and ABCD as 4 different
groups attached to these bonds, such a grouping is present m
I
ii 4 THEORETICAL ORGANIC CHEMISTRY CHAP.
substances, which, like active amyl alcohol, exhibit optical
activity
CH 3
C 2 H 5 C-CH 2 OH.
H
In amyl alcohol the central carbon atom is linked to the
groups, H, CH 3 , CH 2 OH, and C 2 H 5 . This connection between
optical activity and atomic structure was discovered indepen-
dently by Le Bel and van J t Hoff (1874), who named the central
carbon atom of the group, an asymmetric carbon atom. Repre-
sented by the space formula (Fig. 52), the arrangement is
FIG. 52.
unsymmetrical in the sense that it cannot be divided in any
direction into. exactly similar halves.
The Higher Alcohols. The alcohols following amyl alcohol
are termed hexyl, heptyl, octyl alcohol, c., according to the
number of carbon atoms in the molecule. Th*e following
alcohols are solid at the ordinary temperature : Cetyl alcohol,.
C 16 H 31 .OH, which is combined with palmitic acid in spermaceti,
a wax-like substance found in the head of the sperm whale ;
ceryl alcohol, C 27 H 55 .OH, found in combination with cerotic
acid in Chinese wax. This wax is used in China for illumi-
nating purposes, and collected from the bark of certain trees,
where it is formed through the puncture of an insect ; mclissyt
or miricyl alcohol, C 30 H 6l .OH, which is combined with palmitic
acid in beeswax, and also occurs as a constituent of carnauba
\vax, a yellow brittle substance, found adhering to the leaves
of the Brazilian palm.
THE ALCOHOLS 115
QUESTIONS ON CHAPTER VII
1. Why is methyl alcohol sometimes called methyl hydroxide?
2. Give equations representing the action of chlorine, hydrochloric
acid, sodium, calcium chloride, and chromic acid mixture (potassium
bichromate and sulphuric acid) respectively upon ethyl alcohol.
3. Give the formulae for two primary, two secondary, and two tertiary
hexyl alcohols and name them. Give also the formulae and names of
their products of oxidation.
4. How would you prepare a specimen of pure ethyl alcohol from
grape-sugar ? How is the purity of the alcohol ascertained ?
5. Describe briefly the manufacture of beer, whisky, wine, and brandy.
How is the amount of alcohol estimated in these liquids ?
6. In what manner do the optical properties of certain organic sub-
stances give an indication of their structure ?
7. Describe the manufacture of methyl alcohol. What impurity may
it contain ? .
8. Give examples of hydrolysis produced by enzymes.
9. Discuss the meaning of the term alky I group.
10. Give an epitome of the action of reagents on ethyl alcohol.
11. Name the following : CH 3 .CH(OH).CH 3 ; (CH 3 ) 2 .C(OH).CH 3 ;
(CH 3 ) 2 .CH.CH(OH).CH 3 ; (CH 3 ) 2 .C(OH).C 2 H 5 . v
12. Give the modern explanation of the process of alcoholic fermenta-
tion. What are the chief products ?
13. Describe the action of hydrochloric, nitric, and sulphuric acids
on ethyl alcohol. Explain the application of the term reversible to
these reactions.
14. By what processes would you prepare pure methylic alcohol from
crude wood spirit ?
15. Under what ditferent conditions does sulphuric acid react with
alcohol, and what products are formed ii> the several cases ?
1 6. What are the principal chemical changes taking place (a) in
a brewery, (b) in a distillery ? What is methylated spirit ?
17. How would you estimate the percentage of alcohol in a sample
of wine ?
18. What is "methylated spirit"? How would you proceed to
detect methyl alcohol in the presence of ethyl alcohol ?
19. What products are formed when primary and secondary propyl
alcohols are gently oxidised? Compare and contrast their principal
properties.
I 2
CHAPTER VIIl
THE ETHERS
Physical and Chemical Properties of the Ethers. The
ethers have the same general formula as the alcohols, C n H 2D + 2 O.
A list of ethers is given in Table VII.
TABLE VII.
THE ETHERS, C n H 2n + 2 O.
Dimethyl ether
Diethyl ether
C 2 H 6
C,H 1ft O
R Po f
-23 6
74. '6
Sp. gr.
O'73i (A}
Dipropyl ether . .
GJLX)
QO'7
0*763 fo1
Di-isopropyl ether ....
Di-normal-butyl ether , .
Di-secondary-butyl ether .
Di-isobutyl ether
Di-isoamyl ether
Di-normal-octyl ether . . .
Dicetyl ether
C 6 H 14
C 8 H 18
C 8 H 18
C 8 H 18
CjoH^O
QeH^O
6 9
141
121
122
I70
280
M.p.
cc
0743 (o)
0784 (o)
0756 (21)
0762 (15)
0799 (o)
0-805 (17)
Like the alcohols, they are colourless and neutral substances.
When compared with the alcohols of the same molecular formula,
they are seen to be much more volatile. Dimethyl ether, C 2 H 6 O,
is isomeric with ethyl alcohol, but is a gas, which can be liquefied
at 23, whilst ethyl ether, C 4 H 10 O, which has the same mole-
cular formula as butyl alcohol, boils at 34. The ethers are
specifically lighter than water, in which they are much less
soluble than the alcohols. They offer a striking contrast to the
116
CH. VIII
THE ETHERS
117
alcohols in their chemical behaviour. Neither metallic sodium
nor phosphorus chloride in the cold have any action on the
ethers.
EXPT. 27. Add a few thin slices of metallic sodium to 100 c.c. of
ordinary ether contained in a distilling flask, cooled in water. Wait
until the effervescence slackens, and then add more sodium until,
after a few hours, the addition of fresh sodium produces no further
action. Then distil the ether from the water-bath. The distillate is
now free from water. Add to one portion a small piece of sodium,
and to another a little solid phosphorus pentachloride. In neither
case will there be any perceptible action.
The ether with which chemists are most familiar is diethyl
ether, commonly called ether. It will be taken as the repre-
sentative member of the family The discovery of ether is
FIG. 53. Preparation of Ether.
attributed to Valerius Cordus in 1544. It was obtained by
distilling pure spirits of wine with strong sulphuric acid. Boullay,
early in the last century, found that the residue left in the retort
after removing the ether, was able to furnish a fresh supply by
the addition of more alcohol. This discovery originated the
Ii8 THEORETICAL ORGANIC CHEMISTRY CHAP.
modern method of manufacturing ether, which is known as the
continuous etherification process.
EXPT. 28. Preparation of Ether. Fit up an apparatus like the
one in Fig. 53. It consists of a distilling flask (\ litre) furnished
with a tap-funnel and thermometer, the bulb of which is immersed in
the liquid in the flask. The liquid consists of a mixture of 80 c.c. of
concentrated sulphuric acid, and no c.c. of absolute alcohol. The
flask is heated on a sand-tray and kept at a temperature of 140-
145, whilst fresh alcohol is allowed to drop slowly in from the tap-
funnel. Ether and water collect in the receiver, which is cooled in
ice or cold water. The distillate is purified by shaking it with a
little dilute caustic soda to remove sulphurous acid, which is derived
from a slight decomposition of the sulphuric acid. The caustic soda
is drawn off, and a little strong solution of common salt added to
dissolve out any alcohol which may be present. The salt solution
is removed, and the ether first dehydrated over solid calcium chloride
and finally over metallic sodium, as described in Expt. 27.
A small quantity of sulphuric acid can convert a very large
amount of alcohol into ether. The explanation of this curious
reaction was at one period a subject of much controversy. The
action of the sulphuric acid as a dehydrating agent, which
was one of the first and most obvious suggestions, was not
long entertained, seeing tha^ both water and ether distil
simultaneously
2C 2 H 6 - C 4 H ]0 + H 2 0.
Ethyl alcohol Ether.
and it seemed highly improbable that the acid could remove
water from the alcohol and part with it at the same tem-
perature.
Constitution of Ether. In 1851, Williamson synthesised
ether by heating together sodium ethylate and ethyl iodide, and
he afterwards prepared other members of the class by a similar
process.
EXPT. 29. Dissolve 3 grams of sodium in 40 c.c. of pure alcohol
contained in a flask attached to an upright condenser. When the
sodium has dissolved, add 15 grams of ethyl iodide and heat the
mixture on the water bath. In a few minutes a deposit of sodium
/iodide will be formed, and if the contents of the flask be distilled,
ether and alcohol will collect in the receiver, from which the ether
may be separated by the addition of salt solution.
viii THE ETHERS
119
Williamson's synthesis furnished the key to the structural
formula of the ethers. We may explain the formation of
methyl ether according to this synthesis as follows
H H H H
1 I * \ \
H C I + Nai O-C H = H C O C H + Nal.
I III
H H H H
Methyl iodide. Sodium methylate. Dimethyl ether.
Dimethyl ether may be called oxide of methyl, just as methyl
alcohol is called the hydroxide of methyl. The relation is that
of sodium oxide to sodium hydroxide. Taking a general case,
and representing the radical by R, the two parallel series of
compounds will appear as follows
R O H R O R
Alcohol. Ether.
Na O H Na O Na.
Sodium hydroxide. Sodium oxide.
The formula for ethyl ether is usually represented in one of
the following ways
CH 3 .CHo C 2 H 5 C 2 H 5
\0 O/ ^>0 (C 2 H 5 ) 2 0.
CH 3 .CH 2 C 2 H 5 C 2 H 5
Whichever formula is adopted, it must be clearly recognised
that the characteristic group in the compound is the atom of
oxygen linked on either hand to carbon, \C O Cj . The
above structural formula offers a ready explanation of the
indifference of the ethers to sodium and phosphorus chloride.
There is neither hydrogen nor hydroxyl to replace.
As the ethers are insoluble in water, the solubility of the lower
alcohols in water must be attributed, not to oxygen alone, but
to the hydroxyl group. The low boiling-point of the ethers,
compared with the isomeric alcohols, is not exceptional. The
substitution of hydrogen in a hydroxyl group by a radical
frequently produces a lower boiling product. Ethyl acetate,
C 2 H 3 O 2 (C 2 H 5 ), boils at 78, whilst acetic acid, C 2 H 4 O 2 , with
nearly half the molecular weight, boils at 119. Yet the only
difference is the substitution of hydrogen in acetic acid for
ethyl in ethyl acetate.
THEORETICAL ORGANIC CHEMISTRY CHAP.
2.
Simple and Mixed Ethers. The formation of ether from
alcohol and sulphuric acid by the continuous process has yet to
be explained. The first action of sulphuric acid on alcohol is to
form ethyl hydrogen sulphate and water. When fresh alcohol
acts upon the sulphate at 140, ethyl ether is formed and sul-
phuric acid is regenerated. The sulphuric acid, liberated in
the second stage of the process, is capable of transform ing fresh
alcohol into ether. The sulphuric acid should thus be able to
convert an infinitely large quantity of alcohol into ether. In
practice this result is never attained, as some of the acid is
decomposed by carbonaceous by-products of the reaction. The
equations representing the reaction are as follows
I. C 2 H 5 OH + H 2 SO 4 = C 2 H 5 .H.SO 4 + H 2 O.
Ethyl hydrogen
sulphate.
C 2 H 5 HSO 4 + C 2 H 5 OH = C 2 H 5 .O.C 2 H 5 + H 2 SO 4 .
Diethyl ether.
No better evidence of the correctness of this explanation
could be found than the formation of ethers with dissimilar
radicals. They are obtained by running into the flask a
different alcohol from that forming the alky! hydrogen sulphate.
Thus, by adding amyl alcohol to ethyl hydrogen sulphate, amyl
ethyl ether, C 5 ll n .O.C 2 H^ is formed.
An ether with different radicals attached to the oxygen atom
is called a mixed ether to distinguish it from a simple ether,
like ethyl ether, with two similar radicals. Mixed ethers may
also be prepared by the action of an alkyl iodide on a sodium
alcoholate possessing a different radical from the alkyl iodide.
Metamerism. The word metameric was originally applied
by Berzelius to isomeric compounds, which could be meta-
morphosed one into the other. Since then, the meaning of the
word has undergone many changes, and it is at present applied
to a form of isomerism existing among compounds belonging
to the same family or class. These isomers contain different
radicals attached to the same polyvalent element or group.
Thus, diethyl ether is metameric with methyl propyl ether
/CsH. /CH 3
\ \
X C n H, X C,H-
THE ETHERS
In the one, two ethyl groups are present, and, in the other, a
methyl and a propyl group. We shall find similar cases of
metamerism among the ketones (p. 126), sulphides (p. 196),
amines (p. 205), &c.
The character of the radicals composing the ether may be
determined by heating the ether with strong hydriodic acid.
The ether is decomposed into the corresponding alkyl iodides.
Methyl propyl ether yields methyl and propyl iodides
I CH, CH 3 I
: H -.,X
! H + o;> + + H 2 o.
I C 3 H 7 C 3 H 7 I
Methyl propyl
ether.
They may be separated by fractional distillation and identified
by their boiling-points.
Properties of Ethyl Ether. Ethyl ether is a very volatile
and exceedingly inflammable liquid. It should therefore be
kept away from a flame. Its vapour is very heavy, and forms
with air an explosive mixture. It solidifies at 117*6.
EXPT. 30. The density of ether vapour can be readily demon-
strated by slightly tilting a beaker containing a little ether so that
the vapour descends an inclined trough of cardboard. At the lower
end a lighted burner is placed, and the vapour on reaching the burner
is ignited, and the flame travels up the trough.
Ether, when inhaled, produces unconsciousness, and was intro-
duced by Morton as an anaesthetic in 1846. It is also employed
in the form of a spray, for producing local insensibility. The
rapid evaporation of ether produces a low temperature, and
this property is employed for refrigerating purposes.
EXPT. 31. Pour a little ether into a beaker, and place it on a
narrow board moistened .with water. Blow a current of air through
the ether by means of bellows for a few minutes. Hoar frost will
form on the outside of the beaker, and the water below the beaker
will freeze and fix it firmly to the board.
Ether is largely used as a solvent for resins, fats, oils, and
alkaloids. It is frequently employed in the laboratory, for
extracting oils from water, especially when the oil is disseminated
122 THEORETICAL ORGANIC CHEMISTRY CH. viu
through the water in fine particles. When ether is shaken up
with such a liquid, it dissolves the oily globules and unites
them in a layer on the surface of the liquid. This layer is easily,
separated from the water by a tap-funnel, and when the ether
has been distilled off, the oil remains.
Methylated Ether is made like ethyl ether ; but, in place
of pure alcohol, methylated spirit is used. It is very impure,
containing water, alcohol, and resinous matters. It may be
purified by distilling it over solid caustic potash and then over
sodium.
QUESTIONS ON CHAPTER VIII
1. Describe the preparation and purification of diethyl ether by the
continuous process.
2. How would you determine the constitution of a liquid, the
molecular formula of which had been ascertained to be C 5 H 12 O ?
3. Why is ordinary ether termed " ethyl oxide " ?
4. Give two ways of preparing ethyl amyl ether from ethyl and
amyl alcohols.
5. Explain and illustrate the term metameric.
6. What is the action of strong sulphuric acid upon ethyl alcohol.
7. How has the structure of ethyl ether been ascertained ?
8. Wnat is methylated ether? What impurities does it usually
contain ?
9. Write the constitutional formulae for all the different bodies
having the molecular formula C 4 H 10 O, and indicate by what experi-
ments you would propose to distinguish them.
10. Explain the theory of the preparation of ordinary ether. What
bearing has the mode of preparation on the constitutional formula of
ether ?
11. How is ethyl iodide made, and what is the action of sodium
ethylate upon it ? Point out the theoretical importance of this reaction.
CHAPTER IX
ALDEHYDES AND KETONES
A LIST of the more important aldehydes and ketones is
given in Table VIII. It will -be observed that the general for-
mula of these substances is C n H 2n O. They therefore contain
2 atoms of hydrogen less than the alcohols and ethers. The
aldehydes (from alcohol dehydrogenatuni) are obtained by the
oxidation of the primary alcohols and the ketones by the oxida-
tion of secondary alcohols (p. 99). There are other methods
of preparation, which will be referred to later. The lowest
member of the aldehydes is therefore the one obtained by the
oxidation of methyl alcohol, viz., formaldehyde, CH 2 O ; the
lowest ketone is prepared from secondary or iso-propyl alcohol,
viz., dimethyl ketone, or acetone, C 3 H 6 O.
TABLE VIII.
ALDEHYDES, C n H 2n O.
Boiling-point.
Formaldehyde H.CHO . .
Acetaldehyde CH 3 .CHO . . 21
Propionaldehyde C 2 H 5 .CHO . . 49
Butyraldehyde C 3 H 7 .CHO . . 74
Isobutyraldehyde C 3 H 7 .CHO . . 63
Valeraldehyde C 4 H 9 .CHO . . 102
Isovaleraldehyde C 4 H 9 .CHO . . 92
Caprohaldehyde C 5 H U .CHO . . 128
Heptaldehyde, or (Enanthol . . . C 6 H 13 .CHO . . 155
KETONES, C n H 2n O.
Acetone, or Dimethyl ketone . . . CH 3 .CO.CH 3 . . 56
Propione, or Diethyl ketone . . . . C 2 H 5 .CO.C 2 H 5 . . 103
Butyrone, or Dipropyl ketone . . . C 3 H 7 .CO.C 3 II 7 . . 144
Isobutyrone, or Di-isopropyl ketone . C 3 H 7 .CO.C 3 H 7 . . 125
Isovalerone, or Di-isobutyl ketone . C 4 H 9 .CO.C 4 H . . 182
Caprone, or Diamyl ketone .... CsH u .CO.C 5 H)2 . . 227
Melting-point.
CEnanthone, or Dihexyl ketone . . C 6 H 13 . CO. C 6 H 13 . . 30 -5
123
124
THEORETICAL ORGANIC CHEMISTRY
Constitution of Aldehydes and Ketones. If phosphorus
pentachloride is added to an aldehyde or ketone in the cold,
an action ensues ; but, although phosphorus oxychloride is
formed, there is no evolution of hydrochloric acid. The action,
therefore, differs from that of phosphorus chloride *bn the
alcohols.
EXPT. 32. Add gradually 10 to 15 grams of phosphorus penta-
chloride to 5 grains of acetone, cooled in water. The pentachloride
dissolves, and the liquid turns yellow. Pour the product into ice-
cold water, and let it stand until the phosphorus oxychloride has
decomposed and dissolved. The heavy liquid which settles to the
bottom, and smells like chloroform, is dichloropropane. The dichloro-
propane distils at 70, and the distillate is purified like chloroform
(p. 89).
It is then found that the oxygen of the aldehyde or ketone
has been replaced by 2 atoms of chlorine. No hydrogen is
removed, and therefore no hydroxyl group is present as in the
alcohols
C 2 H 4 O + PC1 5 = C 2 H 4 C1 2 + POC1 3
Acetaldehyde. Ethylidene chloride.
C,H 6
Acetone.
PC1 5 = C 3 H 6 C1 2 + POC1 3
Dichloropropane.
This reaction, and the fact that aldehydes and ketones are
formed by the oxidation of alcohols, point to the existence of
a =C:O group in both classes of compounds.
As the primary alcohols alone give aldehydes, the CO group
jrrmst be present at the end of a carbon chain
II H
I
--H + O = H C=O + H 2 O.
H-
H
Methyl alcohol.
CH 3
H C-O--II + O
II
Ethyl alcohol.
Formaldehyde.
CH 3
= H C=O + H 2 O.
Acetaldehyde.
ix ALDEHYDES AND KETONES I25
In the ketones, the CO group must be in the middle of a
carbon chain
CH 3 CH a
CHo C O-
-H + O = CH 3 C=0 + H 2 O.
H
Secondary propyl alcohol. Dimethyl ketone, or Acetone.
The aldehydes are characterised by the group HCO, which
is called the aldehyde group, the ketones by CO, which is
termed the ketone group. The general formula for aldehydes
and ketones, where R stands for the radical, is therefore repre-
sented as follows
R \ R \
>CO >CO.
H/ R/
Aldehyde. Ketone.
We shall see by the various reactions of aldehydes and
ketones that the points of resemblance and difference are well
expressed by this structural relation.
The action of phosphorus chloride on acetaldehyde and
acetone can now be more correctly interpreted by the following
equations
CH 3 .CHO + PC1 5 = CH,.CHC1 2 + POC1 3 .
Ethylidene chloride.
CH 3 .CO.CH 3 + PC1 5 - CH 8 .CC1 2 .CH 3 + POC1 3 .
Dichloropropane.
The general formulae for aldehydes and ketones account,
moreover, in a satisfactory manner for the fact that aldehydes
can be oxidised without breaking the carbon chain, whereas the
ketones usually lose both hydrogen and carbon in the process.
Acetaldehyde gives acetic acid on oxidation ; acetone decom-
poses into acetic acid and carbon dioxide x (p. 100)
CH 3 CH 3
+ O =
CH:0
Acetic acid.
1 These reactions are probably brought about through the intervention of water,
and not by direct addition of oxygen
CH 3 .CO. :H"+ H..OH . + _.O""= CH 3 CO OH + H 2 O.
126 THEORETICAL ORGANIC CHEMISTRY CHAP.
CHg CH.j
I />
00 + 20 2 = C<; OH
J -f
CH 3 CO 2 + HoO.
It should be noted that the rapidity with which oxidation
occurs is much greater in the case of aldehydes (many of which
undergo oxidation on exposure to the air) than with ketones,
which are comparatively stable substances.
EXPT. 33. Attach a half-litre flask to an upright condenser, and
introduce 25 grams of potassium dichromate and looc.c. of dilute
sulphuric acid. Boil the mixture, and drop into the boiling liquid
from a tap-funnel, slipped into the top of the condenser, 10 c.c. of
paraldehyde, 1 and continue to boil for about an hour. Distil half the
contents, and neutralise the acid distillate with sodium carbonate.
On evaporating on the water-bath, sodium acetate remains.
Nomenclature of Aldehydes and Ketones. The aldehydes
are either designated by the name of the alcohol from which
they are derived or by the name of the acid to which they
give rise on oxidation. The compound H 2 C:O is obtained
by oxidising methyl alcohol, and is in turn converted by oxida-
tion into formic acid. It is therefore known as meth(yl)aldehyde
or form(ic)aldehyde, the syllable in brackets being omitted for
brevity
CH 3 OH <- H 2 CO _> HCO.OH.
Methyl alcohol. Methaldehyde, Formic acid,
or Formaldehyde.
The ketones are most simply described by the names of the
radicals linked to the ketone group. They were originally
named from the name of the acids, from which they were
obtained by distillation (see below), joined to the end syllable
" one." The following will serve as examples
CH, C 2 H 5 CH 3 C 3 H 7
I I I I
CO CO CO CO
I I I I
CHg C 2 H 5 C 3 H 7 C 3 H 7
Dimethyl ketone, Diethyl ketone, Methyl propy l)ipropyl ketone,
or Acetone. or Propione. ketone. or Butyrone.
1 Paraldehyde is more convenient to use for this experiment than acetaldehyde,
which is so volatile that it escapes oxidation.
ix ALDEHYDES AND KETONES 127
Diethyl ketone and methyl propyl ketone are metameric. On oxida-
tion, the ketones break down between the radical and the ketone group.
Thus, the division may and does occur at two points. For example,
methyl propyl ketone yields, by the oxidation of the methyl group,
butyric acid and carbon dioxide ; by the oxidation of the propyl group,
acetic and propionic acids, so that three acids are formed.
Preparation of Aldehydes and Ketones. Where the
corresponding alcohol is available, the common method of
preparing aldehydes and ketones is to oxidise the alcohol with
a mixture of potassium dichromate and sulphuric acid, or to
pass the alcohol vapour mixed with hydrogen over finely divided
copper heated to 300 (Sabatier). Although the aldehydes form
acids on oxidation, the reverse process of reducing acids to
aldehydes is not directly attainable. It may be effected, how-
ever, by distilling a dry mixture of the calcium or barium salt of
the acid with the same salt of formic acid.
The formation of acetaldebyde from calcium acetate and
calcium formate may be represented as follows (ca' = a half-
atom of calcium)
CH 3 .COjOca' CH 3 . iCO.Oca
or = CH 3 .CHO + CaCO 3 .
+ H ICO. Oca' H.COiOca'
The same reaction may be utilised for the preparation of
ketones, provided some other organic acid be substituted for
formic acid.
If calcium acetate be heated by itself, acetone is formed
CH 3 .CO.iOca'
- CH 3 .CO.CH 3 + CaCO 3 .
+ CH 3 .:CO.Oca'
If a mixture of two different calcium salts is taken, a
ketone with two different radicals will be formed. Calcium
acetate and calcium propionate yield methyl ethyl ketone-
CH 3 .CO ;0ca'
= CH 3 .CO.C 2 H 5 + CaCO 3 .
+ C 2 H 5 ;CO.Oca'
EXPT. 34. Preparation of Acetone. Distil 30 grams of dry cal-
cium acetate in a retort, attached to a condenser and receiver.
The retort must first be warmed and then strongly heated. A light
128 THEORETICAL ORGANIC CHEMISTRY CHAP.
brown liquid collects in the receiver. The liquid consists of acetone
mixed with other products. By adding a few c.c. of a saturated
solution of sodium bisulphite, a crystalline substance deposits on
standing, which is a compound of acetone with sodium bisulphite.
The acetone may be separated by distilling with sodium carbonate,
but the quantity is usually too small for this purpose.
Another and similar method is to pass a mixture of acids over
thorium oxide heated to 400 (Senderens)
CH 3 .COOH + C 2 H 6 .COOH = CH 3 .CO.C 2 H 5 + CO 2 + H 2 O.
Other methods for preparing ketones will be referred to in
subsequent chapters.
General Properties of Aldehydes and Ketones. The
chemical behaviour of these compounds depends upon two
characteristic properties of the doubly linked oxygen of the
C:O group : (i) the oxygen readily unites with the hydrogen of
the reacting substance and passes into thehydroxyl group ; this
is specially the case with aldehydes ; (2) the oxygen of the CO
group is removed with hydrogen of the reacting substance as
water. It is highly probable that the two processes are con-
nected, and that the first always precedes the second. There is
no doubt that the instability of this oxygen atom, or, more
correctly, of the CO group, is accountable for the diversity of
reactions which aldehydes and ketones undergo, and which is a
peculiar characteristic of these compounds.
Formation of the Hydroxyl Group.
(i) Aldehydes and ketones pass into alcohols on reduction -
\r.n -u TT \r/OH
Jrl 2 - /<-\H
Acetaldehyde, CH 3 .CHO, forms ethyl alcohol, CH 3 .CH 2 (OH) ;
acetone, CH 3 .CO.CH 3 , gives secondary propyl alcohol,
CH 3 .CH(OH).'CH 3 .
In addition to the secondary alcohol, ketones form substances known
as pinaconesf by the union of 2 ketone molecules, with the addition
of 2 hydrogen atoms. Acetone gives on reduction with sodium
amalgam a pinacone of the following formula
CH 3 .CO.CH 3 CH 8 .C(OH).CH 3
+ + H 2 = |
CH 3 .CO.CH 3 CH 3 .C(OH).CH S .
Tetramethyl pinacone.
IX ALDEHYDES AND KETONES
I29
(2) With hydrocyanic acid, an additive compound known as
the cyanhydrin of the aldehyde or ketone is formed
\ / OH
C:0 + HCN =
Acetaldehyde gives acetaldehyde cyanhydrin, CH 3 .CH(OH)CN.
Acetone forms acetone cyanhydrin, CH 3 .C(OH)(CN).CH 3 .
(3) A saturated solution of sodium bisulphite forms a crystal-
line additive compound with aldehydes and ketones. This can
be readily shown by shaking up a little acetaldehyde or
acetone with half the bulk of a saturated bisulphite
solution.
The compounds are known as bisulphite compounds of the
respective aldehyde or ketone, or as the sodium oxysulphonate of
the radical.
v /OH
::O + NaHSO 3 = >C<
^SO 3 Na
Acetaldehyde forms CH 3 .CH(OH)SO 3 Na, acetaldehyde
sodium bisulphite, or ethyl oxysulphonate of sodium.
Removal of Oxygen as Water
(1) With hydroxylamine, oximes are formed, which are known
as aldoximes when derived from aldehydes, and ketoximes
when prepared from ketones
\C:O + H 2 NOH = \C:N.OH + H 2 O.
Acetaldehyde forms acetaldoxime, CH 3 .CH:NOH ; acetone
yields acetoxime, CH 3 .C:(NOH).CH 3 .
EXPT. 35. Mix together in a flask 5 grams of hydroxylamine
hydrochloride dissolved in 10 c.c. of water, 3 grams of caustic soda
in 10 c.c. of water, and 7 c.c. of acetone. Crystals of acetoxime soon
begin to deposit, and the reaction is complete in a few hours.
(2) Hydrazine, NH 2 .NH 2 , phenylhydrazine, CgHgNH.NP^, 1
and other derivatives of hydrazine combine with aldehydes and
1 The aromatic radical, C 6 H 5 , of benzene, C 6 H 6 , is ^called phenyl, and bears the
same relation to benzene as ethyl, C2Hs, to ethane, \
130 THEORETICAL ORGANIC CHEMISTRY CHAP.
ketones with the removal of water, forming hydrazones, phenyl-
hydrazones, &c.(see p. 432)
\C:O + H 2 N.NH.C 6 H 5 = j>C:N.NH.C 6 H 5 + H 2 O.
Acetaldehyde gives acetaldehyde phenylhydrazone
CH 3 .CH:N.NH.C 6 H fi .
EXPT. 36. Add to a little phenylhydrazine rather more than an
equal volume of glacial acetic acid and dilute the solution with two to
three volumes of water. Mix the acetone with a little water, and add
the solution of phenylhydrazine acetate. A turbid liquid results, which
is due to the formation of acetone phenylhydrazone, an oily liquid in-
soluble in water. It may be extracted with ether by shaking and
separating the ether with a tap-funnel. When the ether evaporates,
acetone phenylhydrazone, (CH S ) 2 C:N.NHC 6 H 5 , remains. Bromo-
phenylhydrazine, C 6 H 4 BrNH.NH 2 , and nitrophenylhydrazine,
NO 2 .C 6 H 4 NH.NH 2 , used in the same way give crystalline products.
Special Properties of Aldehydes. Although the aldehydes
share some of the properties of ketones, they differ from the
latter in many important respects. They take up oxygen much
more readily, forming acids, and are therefore active reducing
agents. The aldehyde group is converted into what is known
as a carboxyl group, HO.C:O, about the structure of which
more will be said in the following chapter on acids.
When an alkaline solution of a copper salt, such as Fehling's
solution, is warmed with an aldehyde, the cupric oxide, which is
present in solution, is reduced to cuprous oxide, and acetic acid
is formed at the same time
2CuO + C 2 H 4 Oi = Cu 2 O + C 2 H 4 O 2 ;
or we may express the same reaction by structural formulae
CuO/ CH 3 CIK CH 3
/ + I = >0 + |
Cu/O HC:O CM/ HO.C:O
Acetaldehyde. Acetic acid.
EXPT. 37. Add a few drops of acetaldehyde to Fehling's solution
and boil. A red precipitate of cuprous oxide is formed. Fehling's
solution for qualitative tests is prepared by dissolving 3 to 4 grams of
copper sulphate together with 5 to 6 grams of Rochelle salt in 50 c.C.
ix ALDEHYDES AND KETONES 131
of water. This is mixed, when required for use, with about an equal
volume of caustic soda solution of 10 per cent, strength, when a clear
blue solution results. The Rochelle salt serves to keep the cupric
oxide in solution, when alkali is added.
A similar reaction occurs with an ammoniacal solution of
silver nitrate. This solution may be regarded as containing
dissolved silver oxide. When a few drops of aldehyde are
added to it and the liquid warmed, a metallic mirror of silver
is deposited and acetic acid is formed
Ag. 2 + C 2 H 4 - Ag + C 2 H 4 2 .
EXPT. 38. Add a few drops of acetaldehyde to half a test-tube
of ammonia-silver nitrate solution, and place it in hot water. In a
few minutes a mirror will cover the sides of the test-tube. The
silver solution is prepared by adding dilute ammonia to silver nitrate
until the precipitate of silver oxide just dissolves.
The aldehydes form a peculiar class of compounds with
ammonia, known as aldehyde- ammonias. They are colourless,
crystalline substances, formed by passing ammonia gas into an
ethereal solution of the aldehyde (see Expt. 45, p. 137). The
action takes place in the case of acetaldehyde as follows
/OH
CH 3 . CHO f NH 8 = CH 3 . CH<
X NH 2 .
Acetaldehyde-ammonia.
The aldehyde-ammonias give the reactions for aldehydes.
They are soluble in water and easily decomposed by acids,
ammonia being removed as the ammonium salt of the acid
and the aldehyde is regenerated. Formaldehyde is an exception,
and gives, with ammonia, hexamethylene tetramine, (CH 2 ) 6 N 4 ,
which is used medicinally under the name of aminoform or
urotropine (p. 136).
EXPT. 39. To a few c.c. of formaldehyde solution (40 per cent.)
add an equal bulk of cone, ammonia solution and evaporate on
the water-bath. Colourless crystals of (CH 2 ) 6 N 4 are deposited.
Caustic alkalis differ from ammonia in their effect upon alde-
hydes. The lower members of the series are transformed by the
caustic alkalis into brown resinous bodies of unknown constitution.
EXPT. 40. Boil a little acetaldehyde with caustic potash solution.
The liquid soon becomes yellow, and eventually deposits a brown
resinous substance known as aldehyde resin.
K 2
<7
132 THEORETICAL ORGANIC CHEMISTRY CHAP.
A further reaction for aldehydes is known as SchijjPs test.
If a little aldehyde is added to magenta solution, which has
been rendered colourless with sulphur dioxide, a violet colour
is produced.
EXPT. 41. Make a dilute solution of magenta (fuchsine or ros-
aniline) in water, and bubble sulphur dioxide through it until the
colour disappears. Add to the solution a few drops of aldehyde, and
observe the violet coloration.
Two other reactions for aldehydes illustrate the character-
istic properties of the CO group previously mentioned, viz.,
the readiness with which the oxygen passes into hydroxyl,
and the ease with which it is removed as water.
When a solution of potassium carbonate is added to well-
cooled acetaldehyde and the mixture left for some days, a
syrupy liquid known as aldol [from ald(ehyde-alcoh)ol] is
produced. It is formed by the union of two molecules of
aldehyde
CH 3 .CHO + CH 3 .CHO = CH 3 CH(OH).CH 2 .CHO.
Aldol.
Other aldehydes behave similarly. The process is usually
referred to as the "aldol condensation" (p. 139).
Aldehydes unite with alcohols in the presence of a little
dissolved hydrochloric acid gas or solid calcium chloride,
forming compounds known as acetals. Formaldehyde com-
bines with methyl alcohol, giving methylal, H 2 C(OCH 3 ) 2 ;
acetaldehyde and ethyl alcohol yield acetal, CH 3 .CH(OC 2 H 5 ) 2 ,
from which the generic name of the class is derived. The
reaction may be written as follows
Acetalde-
hyde.
CH 3 .CH O + I = CH 3 .CH(OC 2 H 5 ) 2 + H 2 O.
H:OC 2 H 5 Acetal. '
Ethyl
alcohol.
We shall now give a more detailed description of formalde-
hyde and acetaldehyde and their derivatives.
Formaldehyde is obtained by the oxidation of methyl
alcohol, by bringing the vapour, mixed with air, in contact with
heated platinum or copper. If a red-hot spiral of platinum is
ix ALDEHYDES AND KETONES 133
suspended near the surface of methyl alcohol, the wire continues
to glow, and the acrid smell of formaldehyde is soon apparent.
Oxidation takes place by means of the oxygen of the air, which
is occluded, or absorbed, by the platinum, and is then in a
much more active condition than free
oxygen
EXPT. 42. Make a spiral of platinum-
wire by wrapping it round a glass rod,
and leave one long end. Attach the long
end to a short glass rod, which serves to
suspend the spiral horizontally within a
small beaker. Pour in methyl alcohol
until the surface of the liquid rises to about
one-eighth of an inch from the spiral.
Gently warm the alcohol. Remove and FIG. 54.
heat the spiral red-hot, and replace it
quickly. It will continue to glow, evolving formaldehyde. The
arrangement of the apparatus is shown in Fig. 54. The above
property of metallic platinum of glowing in the vapour of methyl
alcohol and air is utilised in the form of cigar lighters, in which the
alcohol is ignited by the red-hot metal.
In order to collect the formaldehyde, the vapour from the
methyl alcohol, after passing a glowing platinum or copper
spiral, is absorbed in alcohol or water.
EXPT. 43. Preparation of Formaldehyde. The form of apparatus
is shown in Fig. 55. The flask a contains about 50 c.c. of methyl
alcohol. It is provided with a double-bored cork. Through one
hole a glass tube passes to the bottom of the flask ; and through the
second a bent glass tube connects the flask with the short combustion
tube b. Into the centre of this tube a loose plug of platinised asbestos
is inserted, which is kept in position by a short roll of copper gauze,
which in turn is held in its place by a slight constriction of the tube.
The platinised asbestos is prepared by soaking the loose fibrous
asbestos in platinic chloride and gently igniting. The open end of b
is attached, by a bent tube dipping to the bottom of the flask, to a
flask, c, cooled in ice. A second tube, d, which terminates below
the cork is joined to a water-jet aspirator. The flask a is warmed
in a water-bath to about 40, and a rapid current of air aspirated
through the apparatus. The platinised asbestos is then heated until
it begins to glow, after which the glowing will continue so long as the
air current is sufficiently rapid. The liquid which condenses in the
134
THEORETICAL ORGANIC CHEMISTRY
flask c is a strong solution of formaldehyde in methyl alcohol, and
may be used in Expts. 38 and 40.
Solutions of formaldehyde, on evaporation in vacuo, or in the
presence of a little concentrated sulphuric acid, yield a white,
crystalline powder, known as paraformaldehyde, which has the
same percentage composition as formaldehyde, but its molecular
weight is a multiple of that of formaldehyde. The molecular
weight of the solid substance has not been ascertained. On
FIG. 55. Preparation of Formaldehyde.
heating, it is volatilised and converted into formaldehyde vapour
which condenses again as paraformaldehyde.' The formula is
therefore denoted by (CH 2 O) n . Formaldehyde, CH. 2 O, is a gas
which liquifies at 21 and solidifies at 92.
Polymerisation. The change, which some organic com-
pounds undergo, in forming, by a union of their molecules, new
substances of higher molecular weight, but possessing the same
percentage composition as the original compound, is known as
polymerisation. Formaldehyde is said to undergo polymerisation
in forming paraformaldehyde. The latter is polymeric (770X1;?,
many ; pepos, a part) with, or a polymeride of, formaldehyde.
Polymerisation, moreover, usually implies that the polymeric
compound can be easily broken up again into its constituent
molecules. Though aldol is polymeric with acetaldehyde and
is formed from acetaldehyde (p. 139), it is not regarded as a
ix ALDEHYDES AND KETONES 135
true case of polymerisation, for the aldol cannot be readily
converted, like paraformaldehyde, into the original aldehyde.
The term polymerisation has, therefore, a somewhat restricted
meaning.
The term polymeric is used independently of the process
of polymerisation. It is sufficient for one substance to possess
a multiple of the molecular weight of another to be polymeric
with it, without any chemical relation existing between them.
Acetic acid, C 2 H 4 O 2 , is polymeric with formaldehyde, CH 2 O,
although the two compounds are chemically unconnected.
Technical Uses of Formaldehyde. Since the introduction
of formaldehyde as an antiseptic and disinfectant, and for
other technical purposes, its manufacture is conducted on a
commercial scale. Strong solutions, containing 40 per cent,
of the aldehyde dissolved in water containing about 15 per cent,
of methyl alcohol, known as formalin, as well as the solid
paraformaldehyde, or paraform are now sold. For disinfecting
rooms, the solution may be heated, or the solid paraform vola-
tilised over a lamp. A convenient formaldehyde lamp may be
constructed out of an ordinary >
acid has originated. The general formula of the fatty acids is
C n H 2n O 2 , and they therefore contain an atom more oxygen
than the aldehydes, or, compared with the alcohols, an atom of
oxygen in place of two atoms of hydrogen. A list of the
acids with their boiling-points and specific gravities is given in
Table IX., on the following page.
General Properties of the Fatty Acids. They are colourless
liquids or solids, the lower members possessing a sharp pungent
smell and sour taste, which are absent among the higher members.
As their names indicate, they are acids, and combine with bases
to form salts. They are all monobasic, containing one replace-
able hydrogen atom. If the electrical conductivity of an acid
is taken as the measure of its strength, 1 the lowest member,
formic acid, is twelve times as strong as acetic acid, after which
there is a gradual diminution in the strength of the acids with
increasing molecular weight. The solubility of the acids in water
and their specific gravities also decrease. Formic acid has a
specific gravity of 1*231, stearic acid of 0*845. Formic, acetic,
propionic, and butyric acids mix in all proportions with water ;
but propionic and butyric acid separate from the solution on
the addition of calcium or sodium chloride ; isobutyric acid
requires for solution 3 parts, and valeric acid about 30 parts
1 The electrical conductivity depends upon the number of free ions in the solution
of the acid, and the number of free ions is also found to determine the chemical
activity of the acid. Vide J. Walke*'* Introduction to Physical Chemistry
CMacmillan)> chap. xxiv.
144
THE FATTY ACIDS
146
THEORETICAL ORGANIC CHEMISTRY
of water. The higher members, though they dissolve in alkalis
and form soluble sodium and potassium salts, are insoluble in
water, and possess an oily or, if solid, a waxy consistency and
are greasy to the touch. All the acids are soluble in alcohol
and ether. It is somewhat curious that, among the higher
members, those. with an odd number of carbon atoms are rarely
met with in nature, and also possess a lower melting-point
than the next lower homologue with an even number of carbon
atoms.
It will be seen from Table IX. that the boiling-points differ
by about 20 between one member and the next in the series,
formic acid having about the same boiling-point as water.
Constitution of the Fatty Acids. A comparison of the boil-
ing-points of corresponding paraffin, alcohol, aldehyde, and acid
is instructive :
Paraffin.
Alcohol.
Aldehyde.
Acid.
CH 4
(Gas)
CH,(OH)
B.p. 66
CH 2 O
B.p. -21
CH 2 O 2
B.p. 100
C 2 H 6
(Gas)
CoH 5 (OH)
B.p. 78
C 2 H 4
B.p. 21
C 2 H 4 Oo
B.p. 118
It will be noticed that the CO group in the aldehyde lowers
the boiling-point below that of the corresponding alcohol. The
rise of boiling-point in the acid affords strong evidence of the
additional oxygen atom in the acid being present as hydroxyl.
We have already derived some knowledge of the structure of
formic acid from previous reactions. It is formed by heating
chloroform and iodoform with caustic alkalis (p. 91).
This change offers only one simple interpretation. The halo-
gen is first replaced by hydroxyl, and the trihydroxy-compound
being unstable, loses the elements of a molecule of water in the
same manner that phosphorus pentachloride yields phosphoric
acid
!C1 KiOH
HC^-iCl + KJOH ->
X ;C1 KjOII
ChltToform.
,OH
/OiHi ->
OH
HoO.
Intermediate
compound.
Formic acid.
THE FATTY ACIDS , 47
sHOH -> P(OH) 5
" (< )3
Phosphorus Intermediate Phosphoric
pentachloride. compound. acid.
Moreover, chloral decomposes rapidly and quantitatively into
chloroform and sodium formate on warming with caustic soda,
which clearly points to the same formula
H CC1 3
ONa
NaO C< C >?
X H
Chloral. Sodium formate.
The formula also explains the production of formic acid by
the oxidation of formaldehyde.
HC/ -f O = HC/
X H X OH
The Structure of Acetic Acid, C 2 H 4 O 2 , is a more complex
problem. The synthesis of ethane from methyl iodide and
sodium (p. 72), its conversion into ethyl chloride, and the decom-
position bf the latter by potash into ethyl alcohol, prove the
presence in the molecule of ethyl alcohol of two carbon atoms
directly united
CH 3 I CH 3 CHoCl CH 2 (OH)
-> I -> I -> I
CH 3 I CH 3 CH 3 CH 3
The oxidation of alcohol to acetic acid would not disturb the
union between the two carbon atoms, which must therefore be
linked together in acetic acid. The direct union of two carbon
atoms in acetic acid is proved, moreover, by the synthesis of the
acid from methyl iodide and potassium cyanide. Methyl
cyanide is formed, which readily yields the potassium salt of
acetic acid together with ammonia on boiling with caustic potash
solution
H H
H C \I'"+ KjCN = H C-CEEN + KI
Methyl cyanide.
T 2
148 THEORETICAL ORGANIC CHEMISTRY CHAP.
H H
H C C=N + HoO + KOH = H C CO. OK + NH 3 .
Potassium acetate.
We have therefore only to account for the grouping of the
hydrogen and oxygen atoms round the one carbon atom. By
analogy with the structure of formic acid in its relation to
formaldehyde, acetic acid should, by a similar relation to acet-
aldehyde, possess the following constitution
\ \
X H + O X OH
Acetaldehyde. Acetic acid.
Other evidence of the constitution of acetic acid may be briefly
summarised as follows : (i) The replacement of one hydrogen atom by
a metal differentiates that hydrogen atom from the remaining three.
(2) The replacement of one atom of hydrogen and one atom of oxygen
simultaneously by one atom of chlorine when phosphorus pentachloride
is allowed to act, indicates, by analogy with alcohol, the presence of a
hydroxyl group (p. 95)
C 2 H 4 2 + PC1 5 = C 2 H 3 OC1 + POC1 3 + HC1.
(3) That this hydroxyl contains the replaceable hydrogen of the salts is
shown by the action of chlorine on acetic acid. One, two, and finally
three atoms of hydrogen are replaced by chlorine, forming the following
three substitution-products in succession :
C 2 H 3 C1O 2 , Monochloracetic acid.
C 2 H 2 C1 2 O 2 , Dichloracetic acid.
C 2 HC1 3 O 2 , Trichloracetic acid.
All three compounds are acids, and form salts. If trichloracetic acid
is treated with phosphorus pentachloride, hydroxyl is removed and
replaced by chlorine. It is therefore the hydrogen of the hydroxyl
group which is replaced by a metal in the salts, which is the case with
the alcohols (p. 95). (4) That three of the hydrogen atoms in acetic
acid, or the corresponding three chlorine atoms in trichloracetic acid, are
THE FATTY ACIDS I49
attached, to one and the same carbon atom follows from the action of
caustic soda on the sodium salts of these two acids. In the former
case marsh-gas is formed (p. 67), in the latter, chloroform is produced
CH 3 H CH 4
I i !
CO.ONa ONa
CC1 3 H CHClo
............. + ...... ..... - +
CO.ONa ONa CO 3 Na 2
Thus, formic and acetic acid contain the same group CO.OH
united in the one case to hydrogen, in the other to the radical
methyl
H CH 3
I I
CO.OH CO.OH.
Formic acid. Acetic acid.
In the same way the other homologues may be shown to be
compounds of a radical united with the group
X OH.
This is known as the carboxyl group, and is the characteristic
group of most organic acids.
Nomenclature. The acids may be characterised as deriva-
tives of carboxyl, such as hydrogen carboxyl, H. CO.OH,
methyl carboxyl, CH 3 .CO.OH, c. ; but the names generally
employed are derived from the original sources of the acids.
Some of the higher members are denoted by the Greek
numerals corresponding to the number of carbon atoms in
the acid.
The acid without the hydroxyl group forms a monovalent
group, which has the properties of a radical, i.e. it is a con-
stituent group of many compounds. This group is denoted by
the general term acid radical or acyl, just as "alky!" is the
general term for the radical of the alcohols. The acyl like
the alkyl radicals are used for convenience to denote certain
groups, which do not exist as separate substances,
150
THEORETICAL ORGANIC CHEMISTRY
The following table contains the names of the first six acids,
their derivation, and the names of the acyl groups :
Name.
Derivation.
Acyl group.
Formic acid, H. CO. OH . .
formica^ an ant
formyl, H.OO.
Acetic acid, CH 3 .CO.OH .
acetuni^ vinegar
acetyl, CH^.OO.
Propionic acid, C 2 H 5 . CO. OH
TTpwros, first ;
propionyl,C 2 II 5 .C:O.
TriW, fat
Butyric acid, G>H 7 .CO.OH .
butyrum, butter
butyryl, C,H 7 .C:O.
Valeric acid, C 4 H 9 .CO.OH .
Valeriana offid-
valeryl, C 4 H 9 .C:O.
nalis, valerian
Capric acid, C 5 H n .CO.OH .
capra, a goat
caproyl, C 5 H n .C:O.
Chemical Properties of the Fatty Acids. The salts of the
lower members of the fatty acids are, for the most part, soluble
in water. The solubility of the salts diminishes with an in-
creasing molecular weight of the acid. The salts of the alkalis
are soluble both in water and alcohol.
In the formation of salts, the metal or metallic oxide interacts
with the carboxyl group. Acetic acid and caustic soda form
sodium acetate and water
/> />
CH 3 .C< = CH,.C< 4- HoO.
X Oiii -f HOiNa \ONa
Acetic acid.
Sodium acetate.
In this respect the alcohols resemble the bases. Alkyl salts,
or esters, are thus formed (p. 180). Acetic acid and methyl
alcohol form methyl acetate
HOiCH,
HoO.
Acetic acid. Methyl Methyl acetate,
alcohol.
As the process is reversible, the reaction with the alcohols is
never complete, unless other reagents are present.
Phosphorus trichloride and pentachloride replace the hydroxyl
group in the acid by chlorine. The substances thus formed are
x THE FATTY ACIDS 151
known as acid chlorides (p. 173). Acetic acid gives acetyl
chloride
// //
CPL.Cf + PC1 5 = CH 3 .C<; 4- HC1 + POC1 3 .
X OH \C1
Acetyl chloride.
Chlorine gas produces substitution in the alkyl group, but has
no action on the carboxyl group. Acetic acid forms chloracetic
acid
CHo.CO.OH + C1 2 - CH 2 C1.CO.OH + HC1. ,
Chloracetic acid.
Its action is accelerated by sunlight, or by the presence of a
carrier such as red phosphorus, sulphur, or iodine. Bromine
acts similarly, but iodine is without direct action. The action of
the halogens on the hydrocarbon radicals of the acids is there-
fore analogous to their behaviour with the paraffins (p. 63).
The analogy may be carried further, for, like the alkyl halides
(p. 82), the monohalogen derivatives of the acids exchange the
halogen for other groups when acted upon with various reagents.
Monochloracetic acid, for example, gives rise to the following
products by the action of water, ammonia, and potassium
cyanide respectively
1. CH 2 C1.COOH + H 2 O = CHo(OHj.COOH + HC1.
Hydroxyacetic acid.
2. CH 2 C1.COOH + 2NH 3 = CH 2 (NH 2 ).COOH + NH 4 C1.
Amidoacetic acid.
3. CH 2 C1.COOH + KCN = CH 2 (CN).COOH + KC1.
Cyanacetic acid.
The position of the halogen in the alkyl group of the higher fatty
acids is generally denoted by lettering the carbon atoms a, , 7, &c. ,
beginning with the carbon to which the carboxyl group is attached.
There are two, a and j8, chloropropionic acids.
CH,. CHo. COOH, Propionic acid.
ft * a
CH 3 .CHC1.COOH, a-Chloropropionic acid.
CH 2 C1.CH 2 .COOH, /8-Chloropropionic acid.
It should be noted that by direct chlorination, or bromination, the
halogen attaches itself to the a-carbon. The other halogen derivatives
(fl, 7, &c.) are obtained in a different manner (p. 269).
THEORETICAL ORGANIC CHEMISTRY CHAP.
The behaviour of the fatty acids on electrolysis was first
studied by Kolbe. He found that hydrogen is given off at the
negative electrode, whilst a mixture of carbon dioxide and a
paraffin is evolved from the positive electrode. Acetic acid
yields ethane, carbon dioxide, and hydrogen. The reaction may
be represented as follows :
f Electrode. - Electrode.
CH 3 -
CH,-
-COOjH
-COOiH
CH 3
I +
CH,
C0 2
+ I
H
Acetic acid.
Ethane. Car boa Hydro-
dioxide, gen.
EXPT. 48. Electrolysis of Potassium Acetate. As the pure acids
are bad conductors, it is usual to take the potassium salt. A strong
FIG. 57 Electrolysis of Potassium acetate.
solution of potassium acetate is used. The apparatus (Fig. 57) consists
of a porous cell, cemented to a wide glass tube, a. The cell is
provided with a cork through which a platinum wire attached to a
piece of platinum foil is inserted, which serves as the positive electrode.
Through a second hole in the. cork a delivery tube conducts the gases
to a series of bulbs, b, containing potash solution which absorbs the
carbon dioxide. The negative electrode consists of a platinum wire
welded to a sheet of copper, placed in the outer vessel, c. Both
vessels are filled with potassium acetate solution. On passing the
current, hydrogen is evolved at the negative electrode and ethane
X THE FATTY ACIDS 153
and carbon dioxide at the positive electrode, the carbon dioxide being
removed as the gases bubble through the bulbs. The ethane may be
collected over water.
Before concluding the account of the properties of the fatty
acids, the student is reminded of the behaviour of certain of the
fatty acids on heating with soda-lime (p. 67), and of the products
obtained by the distillation of their calcium salts (p. 127).
Sources of the Fatty Acids. The fatty acids are found in
combination with glycerol (glycerine) in fats and oils. Acetic and
a little propionic acid are formed by the destructive distillation of
wood, and a few of the lower members appear during the acid
fermentation of alcohol and carbohydrates (starch, sugar, c.).
Formic, acetic, propionic, and butyric acids are formed in this
way. Fatty acids are obtained by the oxidation of the alcohols
(p. 99), and by the action of moderately strong sulphuric
acid, strong hydrochloric acid, or caustic alkalis on the alkyl
cyanides. This reaction has already been referred to (p. 147).
The process is an example of hydrolysis (p. 105), in which
decomposition is effected by the addition of the elements of
water. Methyl cyanide forms acetic acid and ammonia
H-iOH, /OH
CH 3 .qN+Hjp = CH 3 .C^ + NH 3 .
The presence of the acid or alkali accelerates, the reaction
by uniting in one case with the liberated ammonia and in the
other with the free acid. There are many other methods for
preparing the acids, which will be considered in subsequent
chapters.
Methods for preparing Alcohols and Acids from
Alcohols and Acids of a Different Series. The above
reaction offers a simple method for passing from one member
of a series to the next. Methyl alcohol may be converted into
the iodide, the cyanide, and finally, by hydrolysis, into acetic
acid. On distilling calcium acetate with calcium formate, acet-
aldehyde is produced, which yields ethyl alcohol on reduction
HI KCN H 2 O HCO.ca'
CH 8 OH -> CH 3 I -> CH 3 CN - CH 3 .COOH ->
Ho
-> CH 3 .CH 2 OH.
154 THEORETICAL ORGANIC CHEMISTRY CHAP.
The reverse process may be effected by distilling the alkali
salt of the acid with soda-lime. Potassium acetate forms marsh
gas, which may be converted into 'methyl chloride, methyl
alcohol, and formic acid
NaOH C1 2 KOH O.,
CH 3 .COONa -> CH 4 ~ CH-jCl -> CH/)II -> HCO.OH.
Formic Acid, H.CO.OH, was obtained as early as the seven-
teenth century by distilling ants with water. It is present in sting-
ing nettles and in the sting of bees. The methods by which the
acid can be obtained are very numerous. We may refer to the
action of alkalis on chloroform (p. 146) and chloral (p. 147) and
to the oxidation of methyl alcohol (p. 99). Aqueous hydro-
cyanic acid is hydrolysed on standing, yielding, among other
products, ammonium formate
HOH
HCiN + Hi n = HCO.ONH 4 .
T-T
i ^j Ammonium formate.
This is an example of the general method mentioned on p. 153.
An interesting synthesis of formic acid was discovered by
Berthelot, and consists in the direct union of carbon monoxide
and caustic soda. The absorption takes place more rapidly if
the gas is introduced into a solution of sodium hydroxide at
1 60, a method which is now utilised in its manufacture
H H
CO + CO
ONa ONa
Sodium formate.
EXPT. 49. An apparatus is fitted up as shown in Fig. 58. It
consists of a tube of hard glass filled with soda-lime. One end is
connected with a gas-holder containing carbon monoxide, the other
with a pipette, dipping into coloured water. There is a glass tap at
each end of the tube, which lies in a furnace, and is gently heated to a
temperature of approximately i6o-i7o. When the temperature has
become constant, the tube is filled with carbon monoxide from the
gas-holder. On shutting off the supply of carbon monoxide, by
turning the tap, the coloured liquid will rapidly ascend the pipette,
indicating the absorption of the gas by the soda-lime.
THE FATTY ACIDS
155
Formic acid is found among the products formed by the
oxidation of many organic substances, and represents the final
stage before complete decomposition into carbon dioxide and
water has been reached. The acid also appears during certain
fermentative changes effected by the action of bacteria on the
carbohydrates (sugars, starches, &c.) and alcohols.
Formic Acid from Oxalic Acid. Formic acid is con-
veniently prepared in the laboratory by the decomposition of
FIG. 58. Synthesis of formic acid from carbon monoxide and soda-lime.
oxalic acid in presence of glycerol. Oxalic acid alone gives a
small quantity of formic acid on heating
C 2 H 2 O 4 = HCO 2 H + CO.,.
Oxalic acid. Formic acid.
When glycerol is present, the reaction occurs in two steps.
In the first, the acid oxalic ester of glycerol is formed and
water separates. The structure of glycerol as trihydroxy-
propane and of oxalic acid as dicarboxyl must, for the present,
be assumed.
CH 2 (OH)
CH(OH)
CH 2 (OH)
Glycerol.
CO. OH
CO. OH
Oxalic acid.
CH 2 (OH)
CH(OH)
CH 2 .O.CO.CO 2 H
Glycerol oxalic ester.
HoO.
The product breaks up into a compound known as glycerol
156 THEORETICAL ORGANIC CHEMISTRY CHAP.
monoformin and carbon dioxide. Fresh oxalic acid is now
added, which hydrolyses the monoformin into glycerol and
formic acid. The formic acid then distils. Each additional
quantity of oxalic acid produces fresh formic acid, the glycerol
being each time regenerated
CH 2 (OH) CH 2 (OH) CH 2 (OH)
CH(OH) , CH(OH) + CO 2 . CH(OH) + HCO 2 H.
I "** I "*" i
L CH 2 O.CO.C0 2 H CH 2 0;CH:0 CH 2 (OH)
Glycerol
monoformin.
The glycerol, in short, plays a similar part to that of sulphuric
acid in the ether process (p. 120).
EXPT. 50. Preparation of Formic Acid. Fifty grams of crystallised
oxalic acid and 50 grams of glycerol are heated in a retort (250 c.c.)
over wire-gauze, the retort being connected with condenser and
receiver. A thermometer with its bulb in the liquid is fixed through
the tubulus of the retort. The temperature is maintained at
io5-no until the evolution of gas has slackened, and the liquid
then distilled until the temperature reaches 120. If a larger quantity
of formic acid is required, 50 grams more of oxalic acid are added
before distilling, and decomposition effected at io5-uo as before.
This process may be repeated. The distillate is boiled with excess
of lead carbonate and filtered hot. On cooling, crystals of lead
formate, (HCO 2 ) 2 Pb, separate.
Pure formic acid is obtained by passing hydrogen sulphide
over the dry lead salt heated to about i io c
(HCOO) 2 Pb + H 2 S = 2H.CO.OH + PbS.
Lead formate. Formic acid.
The lead salt is contained in a wide tube plugged at each
end with asbestos. The tube dips downwards so that the free
acid runs down and collects in a receiver.
Properties of Formic Acid. Pure formic acid boils at
101 and melts at 8. It has a pungent and irritating smell
and is extremely corrosive, raising blisters on the skin.
All the salts are more or less soluble in water. Both acid
and salts are decomposed with effervescence by concentrated
sulphuric acid, yielding carbon monoxide. Pure carbon mon-
oxide is readily obtained in this way. The reaction is easily
shown by warming formic acid or a formate in a test-tube with
x THE FATTY ACIDS I57
strong sulphuric acid. On bringing a light to the mouth of
the tube, the escaping gas ignites and burns with a blue flame.
The sulphuric acid acts as a dehydrating agent
HCOOH H 2 O = CO.
Formic acid and the formates are strong reducing agents.
A solution of silver nitrate, when heated with the solution of
sodium formate, gives a black deposit of metallic silver ;
mercuric chloride is reduced to the insoluble white mercurous
salt, which is precipitated. This reducing action of formic acid,
which distinguishes it from all the other fatty acids, is to be
ascribed to the presence of the aldehyde group.
HO.C/
The compound may be described as a hydroxyaldehyde, which,
like other aldehydes, is a reducing agent, and in turn undergoes
oxidation to carbon dioxide and water
HCOOH + O = CO 2 + H 2 O.
When silver nitrate is added to a solution of sodium formate, the
silver formate, which is first produced, decomposes into silver, carbon
dioxide, and hydrogen. Part of the hydrogen is liberated in the free
state, and a part reduces some of the silver formate, giving metallic
silver and free formic acid
2AgO.COH = Ag 2 + 2CO 2 + H 2 .
Silver formate.
We have seen that oxalic acid is converted into formic acid.
The reverse process may be effected by heating dry sodium or
potassium formate. The alkali salt of oxalic acid is produced,
and hydrogen is at the same time evolved (p. 341). This
process is now used in the manufacture of oxalic acid
HiCO.ONa CO.ONa
i + = H 2 + I
HiCO.ONa CO.ONa.
Sodium formate. Sodium oxalate.
Acetic Acid, CH 3 .CO.OH, has long been known under the
name of vinegar, and is produced when wine becomes sour.
The name "acid" is derived from the Latin acetum, vinegar.
Acetic acid was first prepared in the pure state in 1720 by
Stahl, who noticed that its vapour was inflammable. If strong
158 THEORETICAL ORGANIC CHEMISTRY CHAP.
(glacial) acetic acid is boiled vigorously in a test-tube or flask,
the vapour may be ignited as it issues from the mouth of the
vessel, and burns with a blue, lambent, and very fugitive flame.
Acetic acid is found in very small quantities in the juices of
certain plants, in a few vegetable oils in combination with
glycerol (see Oils, Fats, and Waxes, p. 165), and in some animal
secretions. It is obtained by the hydrolysis of methyl cyanide
(p. 153), and by the oxidation of ethyl alcohol, either by pro-
longed heating with potassium dichromate and sulphuric acid
(p. 100), or by exposing the vapour of alcohol mixed with air
to the action of platinum black. The platinum black acts like
the platinum wire in Expt. 42, p. 133.
EXPT. 51. Fill a tube about a foot long with platinised asbestos.
The asbestos is prepared by soaking it in platinic chloride, and then
heating it until it turns black. A wash-bottle, containing ethyl
alcohol, is attached to one end of the tube, which is fixed horizontally.
The alcohol is gently warmed, and a current of air bubbled through
the alcohol, and then over the asbestos. Aldehyde and acetic acid
are formed, the latter being readily indicated by holding a piece of
blue litmus paper at the open end of the tube, when the paper soon
turns red.
Acetic acid is usually prepared either from the pyroligneous
acid obtained in the distillation of wood, or as vinegar by the
acetous fermentation of alcoholic liquids.
It has already been stated (p. 102) that in the destructive
distillation of wood, an aqueous distillate is produced, known as
pyroligneous acid, containing acetic acid, methyl alcohol, and
acetone.
EXPT. 52. To illustrate the process the following apparatus
may be used (Fig. 59). It consists of a copper retort or flask (a)
containing dry saw-dust which is attached to a round flask with
double tubulus (b}. The latter is connected with a condenser (c] and
a receiver (d] which consists of a bottle with a double neck.
Through one tubulus of the receiver a bent tube attaches it to the
condenser and through the other another bent delivery tube delivers
the evolved gas to a cylinder (e) standing over water. The receiver
contains caustic soda solution to absorb carbon dioxide. Tar and an
aqueous distillate collect in the round flask and also in the receiver.
The gas which collects in the cylinder is inflammable.
The aqueous distillate is neutralised with lime and the
THE FATTY ACIDS'
159
alcohol and acetone distilled off. The solution of the lime salt
is evaporated, tarry and resinous matters being removed from
the surface. The dry acetate of lime is gently heated to car-
bonise some of the impurities, and is then known as "grey
acetate." It is distilled in copper vessels with strong hydro-
chloric acid sufficient to decompose the lime salt
(CII 3 . COO) 2 Ca + 2HC1 = 2 CH 3 . COOH + CaCL.
Calcium acetate.
Acetic acid.
The distillate, which contains about 50 per cent, of acetic acid,
is further purified by a second distillation over a little potassium
dichromate. Glacial acetic acid is obtained by first converting
the acid into the sodium salt by neutralising with soda. The
FIG. 59.
sodium salt, C 2 H 3 O 2 Na + 3H 2 O, is then fused to expel the water
of crystallisation, and then distilled with concentrated sulphuric
acid. The pure acid solidifies on cooling, and forms a colour-
less, crystalline mass, from which the name glacial has
originated. It melts at i67 and boils at 119.
Vinegar. The souring of wine and beer when exposed to
the air is due to the vinegar organism, mother of vinegar, or
acetous ferment (Mycoderma aceti}. It consists of cells con-
stricted in the middle and often united in a chain (Fig. 60).
The activity of the organism is prevented by strongly alcoholic
liquids, such as spirits, port and sherry, and wines containing
more than 15 per cent, of alcohol, which consequently do not
turn sour. The methods used in the manufacture of vinegar are
essentially alike. An alcoholic liquid, containing not more
160 THEORETICAL ORGANIC CHEMISTRY CHAP.
than 10 per cent, of alcohol is added to vinegar from a
previous operation, containing the organism, and the liquid is
freely exposed to the air. The organ-
ism acts as a carrier of oxygen between
/>- V\ . the air and the alcohol. In the mann-
\ X^ltt"* n "*--~" % ~* - * facture of malt vinegar, the fermented
* \ **~r~ " wort, produced in the same manner
jj *,-""''* as whisky, is poured into casks con-
taining vinegar. The casks are aerated
^^?^^ 8 ^ by leavin S the bung-hole open and
magnification as yeast ( P . 104). perforating the ends near the top.
When the transformation is complete,
a portion of the vinegar is withdrawn, and the casks refilled with
fresh liquor. Wine vinegar is made in the wine-growing
districts of the Continent, and is produced from the poorer
qualities of wine, in much the same manner as malt vinegar.
It contains 6-8 per cent, of acetic acid, and owes its aroma to
ethyl acetate and other substances present in the wine.
Quick Vinegar Process. The vinegar generator or
" graduator " is a large cask with two perforated discs of wood
placed a little distance from the top and bottom. Short threads
are suspended through the holes in the top disc. To provide
for the circulation of air, holes are bored in the sides of the
cask above the lower disc. Birch twigs are packed in between
the two discs (Fig. 61). The twigs are first covered with the
mother of vinegar by pouring on strong vinegar. Weak spirit
containing 5-7 per cent, of alcohol is slowly run in from the
top and trickles over the twigs, in course of which the alcohol
is converted into vinegar. The liquor runs out below, and
having passed through a second time is finally clarified by
running it over beech-wood shavings. The operation is
conducted so that a constant temperature of 35 is maintained
within the cask. If too little air is admitted, acetaldehyde is
formed. If oxidation becomes too active or too prolonged, the
alcohol is oxidised to carbon dioxide and water.
Vinegar is never used in the preparation of pure acetic acid,
which is entirely derived from pyroligneous acid, as described
above.
Properties of Acetic Acid. Pure acetic acid is a useful
solvent for organic substances. It is little affected by oxidising
x THE FATTY ACIDS 161
agents, and is frequently used as a solvent for chromium trioxide,
where a powerful oxidising agent is required. The addition
of water to acetic acid produces contraction in volume, so that
an aqueous solution may have a higher specific gravity than the
pure acid.
The volatility of acetic acid renders its detection a compara-
tively simple matter. The liquid to be tested is distilled, and
the acid distillate neutralised with soda, and evaporated to dry-
FIG. 61. Quick vinegar process.
ness. On the addition ot concentrated sulphuric acid, the
strong smell of vinegar is at once apparent, or if a little alcohol
is added before the addition of the sulphuric acid, the fragrant
smell of ethyl acetate is observed
CH 3 .CO.OH + C 2 H 5 OH = CH 3 .CO.OC 2 H 5 + H 2 O.
Ethyl acetate.
Acetic acid is also detected by the red coloration which the
solution of a neutral salt gives with ferric chloride. The red
solution of ferric acetate loses acetic acid on boiling, and forms
an insoluble basic salt. Similar reactions are given by formic
M
162 THEORETICAL ORGANIC CHEMISTRY CHAP.
acid ; but acetic acid has no reducing action on silver and
mercuric saks.
The Acetates. Most of the normal salts of acetic acid are
soluble in water. Lead acetate, or sugar of lead, Pb(C 2 H 3 O 2 ) 2
-f 3H 2 O, is obtained by dissolving lead carbonate in acetic acid.
A solution of the normal salt dissolves lead oxide and forms
basic acetate of lead.
Acetic acid is used in the manufacture of white lead, by
exposing sheets of metallic lead to the combined action of
acetic acid and carbon dioxide. Verdigris, or basic acetate of
copper, (C 2 H 3 O 2 ) 2 Cu + Cu(OH) 2 , is used as a pigment, and is
obtained by placing cloths dipped in vinegar in contact with
sheets of copper. By contact with the air, a crust of the basic
acetate is formed on the surface of the copper, and is scraped
off and ground up.
Schweinfurt green, (C 2 H 3 O 2 ) 2 Cu + (AsO 3 ) 2 Cu 3 , is obtained
by precipitating a solution of copper acetate with sodium
arsenite, and is used as a pigment. Iron liquor and red liquor are
solutions of the acetates of iron and aluminium, and used as
mordants in calico printing and dyeing.
When the acetates, with which the cotton is impregnated, are heated,
acetic acid is driven off, and t'he aluminium and ferric oxides remain
firmly attached to the fibre, and fix the colouring matter with which
the cloth is printed, or dyed. A substance which serves to attach
colouring matter to cloth is termed a mordant (mordre, to bite).
Iron liquor is prepared by dissolving scrap iron in commercial
acetic acid ; red liquor is obtained by precipitating a solution of
lead acetate with aluminium sulphate and filtering off the lead
sulphate. The calcium salt of acetic acid is used in the manu-
facture of acetone.
Substitution Products of Acetic Acid. It has already been
mentioned that when chlorine is passed into acetic acid, the
hydrogen of the methyl group is replaced by chlorine. In this
way mono- di- and trichloracetic acids are formed successively
CH 3 .COOH + C1 2 = CH 2 C1.COOH + HC1.
Monochloracetic acid.
CH 2 C1.COOH + C1 2 = CHC1 2 .COOH + HC1.
Dichloracetic acid.
CHC1 2 .COOH + C1 2 = CC1 3 .COOH + HC1.
Trichloracetic acid.
x THE FATTY ACIDS 163
The action is promoted by sunlight, or by the presence of
red phosphorus, sulphur, or iodine, which act as carriers. The
chlorine is passed in, until the necessary addition in weight is
obtained and the product is fractionated. Di- and trichloracetic
acids are more conveniently obtained from chloral (p. 141).
They are all colourless substances, mono- and trichloracetic
acid being crystalline compounds, whereas dichloracetic acid is
a liquid. The following are their melting- and boiling-points
M.p. B.p.
Monochloracetic acid .... 62 . . . 185
Dichloracetic acid ... 190
Trichloracetic acid 52 . . . 195
Propionic Acid, C 2 H 5 .CO.OH, is most readily obtained by
the oxidation of propyl alcohol with potassium dichromate and
sulphuric acid, ft accompanies acetic acid in pyroligneous acid,
and is also found among the products of certain fermentative
processes. Although it mixes with water, the acid may be
separated from solution by the addition of calcium chloride
The acid then floats as an oily layer on the surface ; for which
reason it received the name of propionic acid (Trpwros-, first ;
TnW, fat).
Butyric Acid, C 3 H 7 .CO.OH, occurs in two isomeric forms,
both of which are found in nature. They may be obtained
synthetically by one of the general methods already described.
Normal butyric acid was discovered in 1814 by Chevreul as
a constituent of butter. It is present to the extent of about
7 per cent, as the glyceride, or glyceryl ester (p. 170). It occurs
as the free acid in perspiration and in certain animal secretions.
The principal source of the acid is the fermentation known
as the butyric fermentation^ effected by the combined action of
the lactic ferment and the Bacillus amylobaeter, consisting of
slender rods in active movement, on sugar, starch, and other
carbohydrates.
A solution of starch or glucose is prepared, and putrid cheese,
sour milk, and chalk, or zinc carbonate, together with a little
tartaric acid, ammonium phosphate, and magnesium sulphate,
are added, the temperature being maintained at 35-4o. The
cheese and sour milk contain the ferments, and at the same
time supply nutrient albuminoid matter for the growth of the
organisms, to which the tartaric acid and inorganic salts also*
164 THEORETICAL ORGANIC CHEMISTRY CHAP.
contribute ; the carbonate neutralises the free acid formed in
the process, which, if allowed to accumulate, would arrest
fermentation.
This process takes place in several stages. If starch is
employed, it is first converted into glucose. The glucose then
forms lactic acid (p. 319), and finally the lactic acid decomposes
into butyric acid
C 6 H 12 6 = 2C 3 H 6 3 .
Glucose. Lactic acid.
2C 3 H 6 3 = C 4 H 8 2 + 2C0 2 + 2H 2 .
Butyric acid.
Other changes also occur, and at the same time acetic,
caproic, and caprylic acid are formed.
The solution of the calcium or zinc salt obtained in the above
process is filtered, evaporated, decomposed with hydrochloric
acid, and the butyric acid separated by distillation.
Butyric acid is a liquid with the smell of perspiration and of
rancid butter. The disagreeable smell which rancid butter emits
is usually attributed to free butyric acid produced by the action
of certain micro-organisms.
Butyric acid is used in the manufacture of certain alkyl salts,
or esters, which are employed for flavouring essences (p. 180).
Isobutyric acid has not been observed in any process of
fermentation : but is found either as the free acid or ester in
many plants.
EXPT. 53. A simple method for distinguishing butyric and
isobutyric acids is by means of their calcium salts, that of butyric acid
being only slightly soluble in hot water, but soluble in cold water,
whereas calcium isobutyrate shows the reverse phenomenon. If
therefore a hot saturated solution of the isobutyrate and a cold
saturated solution of the butyrate be prepared, the first will deposit
crystals on cooling. If the two solutions are now placed in hot
water the isobutyrate will dissolve and give a clear solution and the
butyrate will deposit crystals.
Valeric Acid, Valerianic acid, C 5 H 10 O 2 , is known in 4
isomeric modifications. Two of the isomerides, isovaleric or
isopropy; acetic acid, (CH 3 ) 2 .CH.CH 2 .COOH, and methyl ethyl
acetic acid, (CH 3 )(C 2 H 5 )CH.COOH, are obtained by the oxida-
tion of the amyl alcohol of fusel oil. Isovaleric acid occurs as
x THE FATTY ACIDS 165
the glyceride in certain blubber oils. The two acids are found
together in valerian root and in angelica, from which they may
be removed by distilling with water. They are oily liquids, only
slightly soluble in water. Methylethyl acetic acid is optically
active and contains an asymmetric carbon atom (p. 114). It is
sometimes known as active valeric acid
CI-I, H
C 2 H 5 GOOH
Active valeric
acid.
Oils, 1 Fats, and Waxes. The nature of these substances
was first correctly described by Chevreul (1815-1823), who
showed that they were compounds of fatty acids with glycerol.
Beef and mutton tallow and lard consist chiefly of the glycerides
of stearic acid (ore'ap, tallow), C 18 H 36 O 2 , palmitic acid, C I6 H 32 O 2 ,
and oleic acid, C 18 H 34 O 2 . Oleic acid is not strictly a member
of this series of fatty acidst It is called an unsaturated fatty
acid, as it contains 2 atoms of hydrogen less than stearic acid,
which is a saturated acid (p. 269) ; but it is convenient to
include it here. The glycerides, as they occur in fat, are
known as stearin and palmitin (75 per cent.), which are solids,
and olein (25 per cent.), which is liquid at the ordinary tempera-
ture. At the body temperature all the fats are liquid
C W H M CO,0 CH 2
CifllggCG. C. CH
C 17 Il3 3 CO.O.CH 2
Formula of Stearin, the glyceride of stearic acid, or glyceryl stearate.
These substances are, however, not confined to the animal fats.
Palmitin is the chief constituent of palm oil, olein of olive oil, of
which it constitutes 75 per cent., whilst stearin is frequently found
in animal and vegetable oils. Butter and cocoa-nut oil contain,
in addition to the above, butyrin, the glyceride of butyric acid,
C 4 H 8 O 2 , whilst butter also contains the glycerides of caproic
acid, C 6 H 12 O 2 , caprylic acid, C 8 H 16 O 2 , and capric acid, C 10 H 20 O 2 .
1 The term oils used in the present sense implies the vegetable, non-volatile, or
fixed oils, which must be carefully distinguished from the very different class of
volatile, or essential oils (Part II. p. 502).
166 THEORETICAL ORGANIC CHEMISTRY CHAP.
It is difficult to draw any chemical distinction between oils and
fats. They consist mainly of glycerides of saturated fatty acids ;
but the acid may belong, like oleic acid, to a different series.
Linseed oil contains the glyceride of linoleic acid, C 18 H 32 O 2 ,
which has less hydrogen than oleic acid (p. 270). In the
waxes the glycerol is replaced by a higher alcohol of the methyl
alcohol series, like cetyl alcohol, C 16 H 33 (OH), which is combined
with palmitic acid in spermaceti.
The analysis of oils, fats, and waxes is technically of great
importance, and forms a special branch of commercial analysis,
which cannot be described here. 1 The saponification value, or
amount of alkali required to neutralise the fatty acids, in a given
weight of oil or fat, is estimated by heating a weighed amount
of the substance with a standard solution of alcoholic potash,
an excess of which is taken. The fatty acids unite with the
alkali, and form the potassium salts. The excess of alkali, and
consequently the quantity of alkali required for neutralisation
of the fatty acid, is ascertained by titration with standard
hydrochloric acid. The iodine value, or amount of iodine
absorbed, gives a measure of the amount of unsaturated acids
present, these substances possessing the property of forming
additive compounds with iodine (p. 270). A number of separate
estimations of both physical and chemical characters is needful
to arrive at a correct knowledge of the fats and oils, which are,
as a rule, very complex mixtures.
Saponification is a special case of hydrolysis (p. 105). The
term is applied to the breaking up of an ester into its two con-
stituent parts, the alcohol and the acid, by the addition of the
elements of water. To take a simple case, the hydrolysis of
methyl formate gives methyl alcohol and formic acid, and may
be represented by the following equation :
Methyl formate H.CO.JOCH 3
+ HCO.OH + CH 3 OH
Formic acid. Methyl alcohol.
The decomposition can be effected in some cases by water, in
others by a solution of caustic alkalis, or again by sulphuric acid.
Manufacture of "Stearine" Candles. The so-called
" stearine " used in the manufacture of candles is not glyceryl
fc 1 Vide Oils, Fats, and Waxes (II. Ed.), Lewkowitsch. (Macmillan.)j
x THE FATTY ACIDS 167
stearate, to which the name is usually applied, but the free acids
from fat, separated as far as possible from oleic acid. The
production of these acids from fat illustrates the variety of
reagents which may be employed in saponification. The old
process was to heat the fat with lime in open pans, and to
decompose the insoluble lime salt of the fatty acids with sul-
phuric acid. This was superseded by the action of steam alone
under pressure, or of superheated steam. Saponification is now
usually effected by strong sulphuric acid in the case of the
poorer qualities of fat, which are much discoloured and have a
strong smell (p. 282). Purer fats are hydrolysed by the action
of superheated steam in closed boilers, or autoclaves, under
pressure, with the addition of about 2 per cent, of lime to the
fat used. The following equation expresses the reaction in the
case of stearin
C 17 H 35 CO|OCH;"T"H!OPI
C 17 H 33 COOCH + HJOH = sQ^CO.OH -f C 3 H 5 (OH) 3 .
Stearic acid. Glycerol.
C 17 H 35 CO OCH 2 + HjOH
Stearin.
After saponification, the " sweet water," which contains the
glycerol, is drawn off, a little sulphuric acid is added to decom-
pose the lime salts, and the fatty acids, which float on the
surface, are removed, and may be purified by distillation with
superheated steam. The acids are pressed hot to remove the
liquid oleic acid and a firmer cake is thereby produced. The
cake is melted with the addition of a little paraffin wax, and
moulded into candles.
Soap Manufacture. The term saponification was originally
applied to the manufacture of soap. Hard soap is the sodium
salt, soft soap, the potassium salt, of the acids of fat. Conse-
quently, caustic soda and caustic potash are always used for the
saponification of the fat in soap-making. The reaction which
takes place may be illustrated in the case of stearin
(C 17 H 35 COO) 3 C 3 H 5 + 3NaOH = 3C l7 H 35 COONa + C 8 H 6 (OH),.
Stearin. Sodium stearate. Glycerol,
EXPT. 54. Thirty grams of tallow are placed in a beaker and
melted by steam passed in from a flask (with safety tube) containing
i6S THEORETICAL ORGANIC CHEMISTRY CHAP.
boiling water. After a short interval, 60 c.c. of a 10 per cent,
solution of caustic soda are added and steam driven through until a
clear brown solution is obtained. The soap is then separated by the
addition of salt. An alcoholic solution of caustic potash or soda for
saponifying oils and fats is much more rapid in its action than an
aqueous one, which does not dissolve the fat. Make a ten per cent,
solution of caustic soda in methyl alcohol. Place a little lard in a
porcelain basin on the water-bath, cover it with the alcoholic soda
solution, and stir. When the fat has dissolved, heat for a few minutes
to remove the alcohol. A hard mass will remain. It is the sodium
salts of the fatty acids mixed with glycerol. It readily dissolves in
water. Divide the solution into two portions. To one add dilute
hydrochloric acid, when a thick curdy precipitate of the fatty acids
separates, which on heating melts and floats on the surface ; on cooling,
it becomes a solid cake. To the other portion add strong sodium
chloride solution, when a precipitate of the sodium salts of the fatty
acids is formed.
The manufacture of soap is carried on in large iron pans,
which are heated by steam pipes. Fat, which has been pre-
viously " rendered," or melted and strained from cellular tissue,
or a mixture of fat and oil, is used. Beef and mutton tallow
and olive oil make the best hard, or curd soap. For cheaper
soaps, palm oil, palm-nut, cocoa-nut, cotton-seed, and various
otber vegetable oils, together with rosin (which contains an
acid, and forms a sodium salt), and oleic acid from the candle
industry, are employed. The fat and oil are mixed with
caustic soda solution, or " lye," and boiled until hydrolysis
is complete, and the materials have become converted into
the sodium salts of the fatty acids. Salt is now added, which
causes the sodium salts, or soap, to separate as a white granular
mass on the surface. The lower aqueous layer or " spent lyes,"
containing the glycerol, is drawn off and used for the production
of glycerol. The soap is again heated with the addition of a
little caustic soda to ensure complete saponification, and the
hot, pasty mass, after being allowed to settle two or three days,
is run or pumped into frames to cool and set.
In the cold process a strong solution of caustic soda is mixed
with cocoa-nut oil and tallow. Saponification occurs with rise
of temperature, and the mass sets to a hard soap.
A new and interesting commercial method of saponification
THE FATTY ACIDS 169
is that produced by the enzyme, lipase, which occurs in certain
seeds, especially castor oil seed. A very small amount has the
property of rapidly hydrolysing large quantities of fats and oils
at the ordinary temperature. In this way the free fatty acids
are obtained, which combine to form soap with sodium car-
bonate, thus dispensing with the more expensive caustic alkali.
Analysis of Soap. The quality of soap is determined by
estimating the amount of water, fatty acid, and alkali present.
The amount of water is estimated by heating a weighed quantity
of soap gradually to ioo-iio until the weight is constant. The
quantity of fatty acid and alkali are determined by dissolving a
weighed amount of the soap in water, adding excess of standard
hydrochloric, or sulphuric acid, and heating until the melted fatty
acids form a liquid layer on the surface. The fatty acids, on cool-
ing, set, as a rule, to a hard cake, which is removed, dried, and
weighed. If the acids remain liquid, a weighed amount of paraffin
or beeswax is added, which is melted with the fatty acids, and
gives the necessary consistency to the mass on cooling. The
quantity of alkali is found by adding standard alkali to the solu-
tion, from which the fatty acids have been removed, until neutrality
is reached. The difference between the amount of acid taken
and the alkali used, gives the quantity of alkali in the soap.
Free alkali in a toilet soap is very objectionable, and its amount
is estimated by dissolving the soap in alcohol, and adding a
drop or two of phenolphthalein solution as indicator. The
presence of free alkali produces a red colour, and the amount
may be estimated by adding standard acid until the red colour
disappears.
"Varieties of Soap. White curd soap is made from tallow ;
the different kinds of yellow soap usually contain some rosin ;
Castile soap consists largely of sodium oleate, and is made from
olive oil ; marine soap is prepared from cocoa-nut oil, and dis-
solves 'in salt water ; transparent soap is made by dissolving
ordinary yellow soap in methylated spirit, and, after driving off
the alcohol, pouring out the liquid, which, on cooling, forms a
transparent mass ; soft soap is made by saponifying oil, or fat,
with caustic -potash. The product forms a dark-coloured emul-
sion, which contains excess of alkali and all the glycerol of the
original materials ; lead soap, or lead plaster, is prepared by
boiling olive oil with litharge. Some so-called soaps, which are
i;o THEORETICAL ORGANIC CHEMISTRY CHAP.
used for cleaning rather than for washing in the ordinary sense,
consist chiefly of fine sand, pipe-clay, or fuller's earth, and little
real soap. Dry soap is made by drying ordinary soap and
grinding it with a certain amount of sodium carbonate.
The variety of materials used in the manufacture of soap is so great
that the mere proportion of water, alkali, and acid gives no very
definite information as to the real value of a soap. Good curd soap
for household purposes contains no free alkali, and not more than 30 per
cent, of water, which must be regarded as combined water. " Toilet"
or "milled" soap, made from compressed shavings of partially dried
soap, generally contains much less water. On the other hand, cheap
soaps made from cocoa-nut oil, &c., may contain as much as So per
cent, of water.
Wool-grease, or Yorkshire grease, is obtained from the scour-
ings of wool, and contains, in addition to fatty acids, the
alcohol, cholesterol, C 26 H 44 O. It is commonly separated from
the washings by "cracking" or adding sulphuric acid, which
causes the greasy matter to rise to the surface, and it is then
skimmed off. A more complete separation is effected by con-
centrating the wash liquors, and then separating the grease by
means of a centrifugal extractor. The grease, which is speci-
fically lighter, passes to the centre of the rotating cylinder,
whence it flows away. It forms a brown semi-solid mass, which
gives a colourless emulsion with water, and is used as an
ointment, known as lanoline.
Butter. Good cows' butter contains on the average about
90 per cent, of fat, i per cent, of curd, i per cent, of salt, and
8 per cent, of water. Butter fat consists mainly of stearin,
palmitin, and olein, with about 7 per cent, of butyrin, and 2 per
cent, of caproin, caprylin, and caprin. The purity of a butter
may be roughly determined by saponifying a weighed sample
with caustic soda, acidifying with sulphuric acid, and distilling.
The volatile fatty acids collect in the distillate and are esti-
mated by titration with alkali. The quantity of water is
determined by drying the sample in a steam oven ; the amount
of salt and curd, by melting, filtering on a weighed filter, and
washing the filter with ether until free from fat. The curd and
salt remain, and the salt is then estimated by igniting the filter
paper and burning off the organic matter.
THE FATTY ACIDS
Butter Substitutes, Margarine, Oleomargarine. Beef tallow
or suet is heated to a temperature of 35 and subjected to
pressure. The lower melting portion, which is expressed,
contains a large quantity of olein, and when mixed with certain
vegetable oils (cotton seed, sesame, arachis, cocoa-nut, or
other nut oils), and occasionally a little milk and genuine butter,
constitutes margarine. The quantity of volatile fatty acid
(butyric acid) present as butyrin is always considerably below
that in genuine butter. Nevertheless, margarine, if properly
prepared, is a perfectly wholesome article of diet.
EXPT. 55. The difference between butter and margarine may be
shown on a small scale by adding to a small quantity of each in a
test-tube a few c.c. of a methyl alcohol solution of caustic soda and
boiling until most of the alcohol is driven off. On cooling and
adding dilute hydrochloric acid, the unpleasant smell of butyric acid
is given by the butter, but is scarcely noticeable in the case of
margarine.
QUESTIONS ON CHAPTER X
1. Describe a method for separating the constituents of a mixture
consisting of methyl alcohol, acetone, and acetic acid.
2. By what series of reactions can ethyl alcohol be converted into
propionic acid ?
3. Discuss the structural formula of acetic acid.
4. Describe the reactions by which fatty acids may be converted into
paraffins, aldehydes, and ketones.
5. How would you obtain a specimen of pure acetic acid from
vinegar ?
6. Define "hydrolysis," and give examples. Name the different
ways in which fat may be hydrolysed.
7. Describe briefly the manufacture of soap. How is the water,
fatty acid, and alkali estimated in soap ?
8. What are the general characters of oils, fats, and waxes ?
9. What is the composition of butter and oleomargarine ? How can
they be distinguished ?
10. Give a list of methods for preparing the fatty acids.
11. Describe the "quick vinegar" process.
12. Give the formula for the acyl group in the first six members of the
fatty acids.
13. Explain the action of glycerol in the preparation of formic acid.
172 THEORETICAL ORGANIC CHEMISTRY CH. x.
14. Account for the action of formic acid on silver nitrate. How is
formic acid distinguished from acetic acid ? In what respects do these
acids resemble one another ?
15. Write precise instructions for the preparation of sodium
formate, using oxalic acid as the source.
1 6. How would you detect formic acid in acetic acid?
17. Starting from methyl alcohol, explain, illustrating your answer
by equations, how acetic acid can be produced. How can acetic acid
be reconverted into methyl alcohol ?
18. The ratio of carbon, hydrogen, and oxygen in acetic acid can be
expressed by the formula CH 2 O. What are the reasons that have led
to the formulae C 2 H 4 O 2 and CH 3 .COOH being used instead?
19. You are given the product of the distillation of wood. Describe
how a specimen of pure acetic acid could be obtained from it.
20. How has the constitutuion of the glycerides been determined ?
State the constitution and the chief constituents of the more important
natural fats.
CHAPTER XI
THE ACID CHLORIDES, THE ANHYDRIDES, AND
THE AMIDES
The Acid or Acyl Chlorides are prepared by the action of
phosphorus trichloride or pentachloride on the fatty acids.
Acetic acid and phosphorus trichloride give acetyl chloride,
phosphorus oxide, and hydrochloric acid ; when the penta-
chloride is used, phosphorus oxychloride and hydrochloric acid
are formed
3CH 3 .CO.OH + 2PC1 3 = 3CH 3 .CO.C1 + sHCl + P 2 O 3 .
Acetyl chloride.
CH 3 .CO.OH + PC1 5 = CH 3 .CO.C1 + HC1 + POC1 3 .
Formyl chloride, H.CO.C1, is unknown. It probably decom-
poses at once into carbon monoxide and hydrochloric acid.
EXPT. 56. Preparation of Acetyl Chloride. A distilling flask,
through the neck of which a tap-funnel is inserted, is attached to a
condenser and receiver. The receiver should be connected with
a tower of soda-lime, to absorb the hydrochloric acid evolved ;
otherwise, the operation must be conducted in a fume-cupboard.
Fifty grams of glacial acetic acid are placed in the flask, and 40 grams
of phosphorus trichloride are slowly added from the tap-funnel.
The flask is gently warmed in the water- bath to 4O-5o, until the
evolution of hydrochloric acid gas slackens. The water-bath is then
heated to boiling, when the acetyl chloride distils. It boils at 55.
These compounds are denoted as chlorides of the acid
radicals, or as acid, or acyl chlorides. Their structure repre-
sents them as substitution products of the aldehydes, and they
173
174 THEORETICAL ORGANIC CHEMISTRY CHAP.
yield aldehydes on reduction with sodium amalgam. Their
general formula is
R
^O
c*y
\a
Properties of Acid Chlorides. The acid chlorides are colour-
less liquids or solids with boiling-points lying between those of
the corresponding aldehyde and acid. They fume in moist
air, and are very quickly decomposed by water. Hydrochloric
acid is thereby evolved, and the original acid regenerated.
Acetyl chloride, when acted on by water, gives acetic acid
CH 3 .COiCl + HjOH = CH 3 .CO.OH + HC1.
EXPT. 57. Add a few drops of water to a few drops of acetyl
chloride in a test-tube. Decomposition takes place rapidly and the
liquid becomes hot.
The action of the alcohols on the acid chlorides is very
similar to that of water. The alkyl salts, or esters, are formed
and hydrochloric acid is evolved. Acetyl chloride and ethyl
alcohol in this way give ethyl acetate
CH 3 .CO:C1 + HjOC 2 H 5 = CH 3 .CO.OC 2 H 5 + HC1.
Ethyl acetate.
This reaction is of great importance as a means of detecting
the presence of a hydroxyl group in organic substances, and
is more convenient than that requiring the use of sodium or
of phosphorus pentachloride' (p. 95), as the acetyl derivatives
which are formed are usually easy to purify. Acetyl chloride,
being readily obtainable, is the most convenient acid chloride
to employ. In compounds in which the hydroxyl group occurs,
the hydrogen is replaced by acetyl^ and forms an acetoxyl group
OH + CH 3 COC1 = O.CO.CH 3 + HC1.
Acetoxyl.
EXPT. 58. To about I c.c. of ethyl alcohol in a test-tube add,
drop by drop, I c.c. of acetyl chloride and cool well under the tap.
Then add about I c.c. of a solution of common salt, in which ethyl
xi ACID CHLORIDES, ANHYDRIDES, AND AMIDES 175
acetate is only slightly soluble. Ethyl acetate separates out on the
surface of the liquid, and may be recognised by its fragrant smell.
Ammonia and the amines (p. 198) react with acid chlorides,
forming compounds known as amides (p. 176). Acetyl chloride
and ammonia yield acetamide. If excess of ammonia is used,,
ammonium chloride is formed as well
CH 8 .CO.j'Cf + H:NH 2 + NH 3 = CH 3 .CO.NH 2 + NH 4 C1.
Ammonia. Acetamide.
EXPT. 59. If ammonia solution is added to acetyl chloride, heat is
evolved ; but the acetamide, being very soluble in r water, does not
separate. If, however, a substituted ammonia, or amine, like phenyl-
amine (aniline), NH 2 .C 6 H 5 , be taken, the solid phenyl acetamide
(acetanilide), CH 3 .CO.NHC 6 H 5 , separates out. The experiment may
be performed with a drop or two of each substance.
The Anhydrides are obtained by the action of the acid
chloride on the sodium salt of the corresponding acid. Acetyl
chloride and sodium acetate yield acetic anhydride.
CH 3 .CO.:CFT~NaiO.CO.CH 3 = CH 8 .CO.O.CO.CH 8 + NaCl.
Acetic anhydride.
The reaction is similar to that by which ethers are prepared
(p. 119)5 an d as the ethers are also named alkyl oxides, these
compounds may be regarded as acyl oxides. By taking the
chloride of one acid and the sodium salt of another, mixed
anhydrides are formed, a process which resembles the method
of preparing mixed ethers (p. 120)
/CHa, X CO.CH 3 .
\ \
x:H 3 . xxx CH*
Alkyl oxide. Acyl oxide.
EXPT. 60. Preparation of Acetic Anhydride. A retort, through the
tubulure of which a tap -funnel is fixed, is attached to a condenser and
receiver. Fifty-five grams of fused sodium acetate are placed in the
retort, and 40 grams of acetyl chloride are slowly run in from the tap-
funnel, the retort being cooled in water. When the acetyl chloride
has been added, the contents of the retort are well stirred with a glass
rod and then distilled. Acetic anhydride distils at 130- 140.
The anhydrides possess a pungent smell, but do not fume.
They have a higher boiling-point than the acids from which
176 THEORETICAL ORGANIC CHEMISTRY CHAP.
they are derived. They closely resemble the acid chlorides in
chemical behaviour, being decomposed by water, alcohol, and
ammonia, but much less rapidly than the acid chlorides. Acetic
anhydride yields the same products as acetyl chloride with these
three reagents
CH.3.CO
OH
CH 3 .CO.OH
\/'
+ 1
/Xx O
H
+
/
Water.
CH 3 .CO
CH 3 .CO.OH.
Acetic anhydride.
Acetic acid.
CH 3 .CO
OCoH 5
CH 3 .CO.OC 2 H 5
>>0
+ i
H
Ethyl acetate.
4-
/
Alcohol.
CII 3 .CO
CH 3 .CO.OH.
CH 3 .CO
NH 2
CH 3 .CO.NH 2
\/
+ 1
Acetamide.
/So
H + NH 3 =
+
/
Ammonia.
CH 3 . CO CH 3 . CO. ONH 4 .
Ammonium acetate.
The Amides are formed by the action of ammonia on acid
chlorides (p. 175), on the anhydrides (see above), and on the
esters (p. 180). They may be prepared by the partial hydrolysis
of the alkyl cyanides with moderately strong sulphuric acid.
Complete hydrolysis converts the cyanide into the acid.
Methyl cyanide first forms acetamide and then acetic acid and
ammonia. The two reactions may be represented as follows :
1. CH 3 .CN + H 2 O = CH 3 .CO.NH 2 .
Acetamide.
2. CH 3 .CO.NH 2 + H 2 O = CH 3 .CO.ONH 4 .
Ammonium acetate.
One of the most convenient methods for obtaining the
amides is to heat or distil the ammonium salt of the acid.
The salt loses one molecule of water in the process. Ammonium
acetate gives acetamide
CH 3 .CO.ONH 4 = CH 3 .CO.NH 2 + H 2 O.
Ammonium acetate. Acetamide.
xi ACID CHLORIDES, ANHYDRIDES, AND AMIDES 177
All these reactions indicate that amides are derivatives of the
acids, in which the hydroxyl is replaced by an amido group
(NH 2 ).
EXPT. 61. Preparation of Acetamide. Melt 50 grams of
ammonium acetate by gently heating the salt and pour the liquid
into a distilling flask (200 c.c.) with the side-tube plugged with
a short piece of rubber tube and glass rod. Add 60 c.c. glacial
acetic acid and boil gently with reflux condenser for four hours.
The product is distilled as follows : insert a thermometer into the
neck of the flask and use a long, wide tube as a condenser (Fig. 62).
Heat the flask over wire gauze. A certain quantity of acetic acid and
water distils. When the temperature reaches 210, change the
receiver ; the distillate on cooling solidifies as a mass of colourless
FIG. 62. Preparation of Acetamide.
crystals consisting mainly of acetamide. Acetamide melts at 82
and boils at 222. The smell, which resembles that of mice,
proceeds from a minute trace of impurity.
Properties of the Amides. The amides, with the exception
of formamide, HCO.NH 2 , which is liquid at the ordinary tem-
perature, are colourless, crystalline solids with high boiling-
points. Formamide boUs at 2 1 2, acetamide at 222, propionamide
at2i 3 ,&c.
178 THEORETICAL ORGANIC CHEMISTRY CHAP.
The lower members are very soluble in water, and the solution
is neutral, to litmus. They form loose combinations with hydro-
chloric acid when the gas is passed into a solution of the amide
in ether ; but the compounds are quickly decomposed by water.
By the action of dehydrating agents (e.g. phosphorus pent-
oxide) the amides are converted into alkyl cyanides. Acetamide,
when mixed with phosphorus pentoxide and distilled, gives
methyl cyanide
CH 3 .CO.NH 2 -H 2 O = CH 3 CN.
Acetamide. Methyl cyanide.
When boiled with caustic alkalis, strong hydrochloric acid, or
moderately strong sulphuric acid, the amides are hydrolysed
and form a fatty acid and ammonia. Acetamide is converted
into acetic acid and ammonia
CH 3 .CO.NH 2 + H 2 = CH 3 .COOH + NH 3 .
EXPT. 62. Boil a small quantity of acetamide with caustic soda
solution in a test-tube, and smell the vapour given off, or test it
with red litmus. Ammonia is evolved, and sodium acetate is found in
solution
NaOH = CH 3 .CO.ONa + NH 3 .
Thus, the three classes of compounds, the ammonium salts
of the acids, the amides, and cyanides, are intimately related and
may be converted one into the other. Ammonium acetate, on
distillation, yields acetamide ; when distilled with a large quantity
of phosphorus pentoxide, it may be directly converted into methyl
cyanide. Acetamide, when distilled with phosphorus pentoxide,
forms methyl cyanide, whilst, on hydrolysis, it is converted into
acetic acid and ammonia. Methyl cyanide gives acetamide by
partial hydrolysis, and acetic acid and ammonia when the process
is carried to completion. These changes are indicated in the
following diagram :
CH 3 .CO.ONH 4 < > CH 3 .CO.NH 2 .
Ammonium acetate. Acetamide.
\\ %
CII 3 .CN.
Methyl cyanide.
xr ACID CHLORIDES, ANHYDRIDES, AND AMIDES 179
QUESTIONS ON CHAPTER XI
1. Describe the preparation of acetyl chloride.
2. In what manner can an acid chloride be employed to indicate the
presence of a hydroxyl group in an organic compound ? Illustrate this
by reference to propyl alcohol. What advantage has this reagent over
phosphorus chloride or sodium ?
3. Describe by means of equations the behaviour of propionyl chloride
with the following reagents : water, methyl alcohol, ammonia, sodium
amalgam, sodium propionate.
4. Compare the behaviour of alkyl and acyl oxides with different
reagents.
5. Describe two methods for the preparation of acetamide.
6. Explain the various stages in the process by which ( I ) acetic acid
is converted into methyl cyanide, and (2) methyl cyanide into acetic
acid.
7. Describe the method and apparatus you would employ for the
preparation of acetyl chloride. How is it acted upon by each of the
following substances : (i) sodium hydrate, (2) ethyl alcohol, (3)
ammonia, (4) zinc ethyl ? Give equations.
8. Describe the materials required and all the operations involved in
making acetic anhydride.
9. Starting with acetyl chloride, show how acetamide, acetic acid,
and acetic anhydride respectively may be obtained from it.
10. Describe two methods for the preparation of acetamide. How
would you convert it into (i) acetic acid, (2) methylamine ?
CHAPTER XII
THE ESTERS
Esters are formed by the action of an alcohol on an organic
or inorganic acid, just as salts are produced by the action of a
base on an acid (p. 150). Esters may therefore be termed alkyl
salts.
Methyl alcohol and formic acid, for example, give methyl
formate, just as caustic soda and formic acid yield sodium
formate
HCOiOH"T"H;OCH 3 = HCO.OCH 3 + H 2 O.
Methyl formate.
HCO[OH"T"H]ONa = H.CO.ONa + H 2 O.
Sodium formate.
The following are the formulas of a series of alkyl salts :
/CHO
/NO
/N0 2
/SCMOH)
Cl
\
\
\
\
1
X CH 3
X CH 3
\CH 3
X CH 3
CH 3
Methyl
Methyl
, Methyl
Methyl
Methyl
formate.
nitrite.
nitrate.
hydrogen sulphate.
chloride.
With the exception of the halide esters like methyl chloride, the
alkyl group in the ester is united by oxygen to the acid radical.
Esters of Organic Acids. The esters of the fatty acids,
which we shall consider first, were studied in 1782 by Scheele,
who discovered a method for their preparation which, with a
little modification, is still in general use.
Sources of the Esters. The esters form the sweet-smelling
constituents, or ethereal oils, of many plants, and on account of
their fragrant smell they are manufactured as a substitute for
CH. xir THE ESTERS 181
natural perfumes and fruit essences. They may be prepared by
the action of an alcohol on an acid chloride or anhydride (p. 174),
or by heating the silver salt of the acid with an alkyl iodide
dissolved in ether. Silver acetate and ethyl iodide yield ethyl
acetate
CH 3 .COO:Ag + IjC 2 H 5 = CH 3 .COOC 2 H 5 + Agl.
Eeversible or Balanced Reactions. The most common
method for preparing esters is to heat together the acid and
the alcohol. The reaction is. however, a reversible one (p. 78).
A condition of equilibrium is attained when a certain ratio
exists between the amount of ester and water and that of free
acid and alcohol. The point of equilibrium varies with the
conditions of the experiment, namely, the nature and relative
quantity of the alcohol and acid and the temperature. Ber-
thollet (1799) was the first to draw attention to the effect of
quantity. He showed that the amount of chemical change c is
proportional to the product of the quantity of the reacting
substances a and b and their affinity K. This is known as the.
law of mass action and is represented by the equation :
The only change introduced since Berthollet's time is in the
meaning of a and b, which now iitand for molecular proportions
and not actual weights. Guldberg and Waage (1867) showed
that K can be determined by studying the conditions of equi-
librium in the following way. Suppose a curve is drawn of the
action of an equal number of gram-molecules of ethyl alcohol
and acetic acid, the quantity transformed into ester and water
being plotted on the horizontal, and the time on the vertical.
This can be done by keeping the mixture in a thermostat and
removing a little from time to time, and titrating the amount of
free acid present. It will be found that, as the quantity of acid
and alcohol diminish, the velocity (quantity in equal times) also
diminishes until there is no further change. This is the
equilibrium point. If the reaction is begun from the other end
and a mixture of an equal number of gram-molecules of ester
ad water is taken, free acid will make its appearance, and
t$2 THEORETICAL ORGANIC CHEMISTRY CHAP.
the reaction will quickly slow down until the same equilibrium
point is reached. The following curves will be obtained
Equal gram, mots
or Alcohol + Acid
Time
Equal gram, mols
or Ester + Water
Alcohol + Acid transformed
gram, mols per cent
FIG. 63.
Ester -f- Water transformed
gram.inois percent*-
The equilibrium point is reached when two-thirds of a gram-
molecule of ester and water and one-third of a gram-molecule
of acid and alcohol are present. The reaction may be re-
presented by the following equation :
C 2 H 5 OH + CH 3 . COOH CH 3 . COOC 2 H 5 + H O.
4 i 8"
We may consider the subject in another way and suppose
that equilibrium is reached when the number of molecules of
acid and alcohol formed in unit time are exactly equal to the
number of molecules of ester and water decomposed, or, in
other words, when the velocities of the opposing reactions are
equal, that is, when
According to the kinetic theory the velocity of a reaction is
determined by the number of collisions between molecules ;
but the number of collisions in unit time is proportional to the
number of molecules in unit volume (concentration). For let
us take the following three cases, and let us suppose that in
the first case there is one molecule of alcohol and one molecule
of acid in unit volume and one collision in unit time. Now
double the number of each kind of molecule ; it is clear that,
without any change in their rate of movement, each molecule
has only half the distance to travel before meeting another
THE ESTERS 183
molecule and therefore hits two in unit time. As each has
two encounters there will be 4 (2 x 2) collisions. In the same
way, if the number is doubled again each molecule will hit 4 in
unit time, and there will be 16 (4x4) collisions. Therefore the
velocity of a reaction is proportional to the product (not the
sum) of the reacting molecules in unit volume.
Let a and b = number of molecules of reacting substances in
unit volume (concentration) and c and d number of molecules
of products in unit volume (concentration). The velocities of
the two reactions will be :
F 1 = A' 1 ^, and
When there is equilibrium, V l = F 2 ,
and
or -T^ I = ^I> replacing ^ by K
K 2 ab K
= ~ab'
In the above example,
/ ^ester X #water __3 ^ 3 __ .
^alcohol X acid \ X J
A', which is here represented by the number 4, is called the
equilibrium constant. It may be used for determining the
amount of ester produced for any known mixture of ethyl
alcohol and acetic acid at the same temperature.
If x required gram-mols. of ester( = water)
i = concentration (gram-mols.) of alcohol
m= acid
then (i^xWr 4 '
from which x can be determined.
Fischer and Speier found that the addition to the alcohol of
about 3 per cent, of hydrochloric acid gas, or the same quantity
of concentrated sulphuric acid, enables the reaction to be
completed on heating.
EXPT. 63. Preparation of Ethyl Acetate. METHOD' I. I Bubble
hydrochloric acid gas through 25 c. c. of ethyl alcohol cooled in water,
until the alcohol has absorbed 4-5 grams. Mix the alcohol with ap
equal volume of acetic acid, and boil the mixture in a flask (attached
to an inverted condenser) on the water-bath for half an hour. Pour
184 THEORETICAL ORGANIC CHEMISTRY CHAP.
the liquid into strong brine. The ethyl acetate separates as a layer
on the surface, and may be removed by means of a separating-funnel.
The liquid is then dehydrated with solid calcium chloride and
distilled from the water-bath. It boils at 77-78.
METHOD 2. Mix together equal volumes of concentrated sulphuric
acid and ethyl alcohol, and heat the mixture in a paraffin bath to 140,
using the form of apparatus shown in Fig. 53, p. 117. Drop in from
the tap-funnel a mixture of equal volumes of glacial acetic acid and
ethyl alcohol at the same speed as that at which the liquid distils.
The distillate contains the ester and also some acetic acid, alcohol
ether, sulphurous acid, and water. The distillate is shaken with a
strong solution of sodium carbonate, which is then drawn off and
replaced by strong brine. The brine, on shaking, dissolves the
alcohol, and is then separated from the ester, which is finally
dehydrated over solid calcium chloride and distilled.
The reaction is similar to that by which ether is prepared
C 2 H 5 (OII) + H 2 SO 4 = C 2 H 5 .H.SO 4 + H 2 O.
Ethyl hydrogen sulphate.
C 2 H 5 .H.SO 4 + CILj.CO.OH = CH 3 .COOC 2 H 5 + H 2 SO 4 .
Ethyl acetate.
The sulphuric acid can convert a large quantity of alcohol and acetic
acid into ethyl acetate.
Properties of the Esters. The esters are neutral and
colourless substances with a fragrant smell, and are for the most
part liquids which do not mix with water. The methyl and
ethyl esters have lower boiling-points than the acids from which
they are prepared. The esters in point of structure occupy an
intermediate position between the ethers and anhydrides
o o
\C 2 H 5 \CO.CH 3 X CO.CH 3
Ethyl ether. Ethyl acetate. Acetic anhydride.
Their relation to the ethers has given rise to the expression
compound e thers, and to names such as acetic ether , by which the
esters J|ere at one time known.
In chem/cal behaviour the esters stand midway between the
very stable ethers and unstable anhydrides. The esters are
slowly decomposed by water ; much more rapidly by caustic
alkalis in aqueous solution ; still more rapr-dly by alkalis in
alcoholic solution. The process is one of hydrolysis. The ele-
THE ESTERS
ments of water are taken up, and the ester is converted into acid
and alcohol. Ethyl acetate gives alcohol and acetic acid
CHoCO OH CH 3 .CO.OH
>>0 + i -
C 2 H 5 C 2 H 5 .OH.
The reaction is, in fact, identical with the saponification of
fats and oils (p. 166), the alcohol in the latter case being glycerol.
E*PT. 64. Hydrolysis of Ethyl Acetate. Heat 20 grams of ethyl
acetate with three times its volume of aqueous potash solution of about
30 per cent, strength. The mixture is placed in a distilling flask,
attached by the neck to an inverted condenser, and boiled over wire-
gauze. A piece of porous pot is placed in the flask to prevent bump-
ing, and the side-tube of the distilling flask is temporarily closed
with a stopper. When the layer of ethyl acetate has dissolved (the
potassium acetate and ethyl alcohol being both soluble in water),
the condenser is attached to the side-tube of the distilling flask and
the liquid distilled. The alcohol which passes over may be separated
from the water by the addition of potassium carbonate, which causes
the alcohol to float on the surface, and it may then be withdrawn.
The acetic acid remains in the distilling flask, as the potassium salt.
The alkali is carefully neutralised with sulphuric acid and the liquid
evaporated to dryness. The dry residue is then distilled with strong
sulphuric acid, when pure acetic acid passes over. The reaction
is expressed by the following equation
CH 3 .CO.OC 2 H 5 + KOH = CH 3 .CO.OK + C 2 H 5 .OH.
Ethyl acetate. ^ Potassium acetate. Alcohol.
The action of ammonia on the esters is essentially different
from that of caustic potash or soda ; in this case alcohol is
formed, but the ammonia remains attached to the acid radical,
forming an amide (p. 176). Ethyl acetate gives acetamide and
ethyl alcohol
CH 3 .CO NH 2
1 v + i
/\O H = CH 3 .CO.NH 2 + C 2 H 5 OH.
/ Acetamide. Alcohol.
C 2 H 5
EXPT. 65. The action of ammonia on ethyl acetate cannot be
used to demonstrate this change, as the resulting acetamide is too
186 THEORETICAL ORGANIC CHEMISTRY CHAP.
soluble to separate. If, however, ethyl oxalate is employed, the in-
soluble oxamide is at once precipitated on adding strong ammonia
CO.OCH 5 NH 3 CO.NH a
| + = | + 2C 2 H 5 OH.
CO.OC 2 H 5 NH 3 CO.NH a
Ethyl oxalate. Oxamide.
Isomerism of the Esters. The general formula of the esters
of the fatty acids is C n H 2n O 2 , i.e. the same as that of the fatty
acids. The esters are readily distinguished from the acids by
their neutral reaction, and, in the case of the lower members,
by their smell and insolubility in water. Moreover, the esters,
unlike the fatty acids, are insoluble in dilute solutions of the
alkalis. Among the esters themselves, isomerism may arise
from the presence of isomeric acids or alcohols forming the
constituent parts of the ester. Examples of this kind of isomerism
are ethyl butyrate and ethyl isobutyrate, and propyl and isopropyl
acetate. Finally, isomerism may be produced by the union of
acids and alcohols to form esters, in which both constituents
differ in the different isomers. A compound of the formula
C 4 H 8 O 2 may represent methyl propionate, ethyl acetate, or
propyl formate
C 2 H 5 CO.OCH 3 , Methyl propionate.
CH 3 .CO.OC 2 H 5 , Ethyl acetate.
H. CO. OC 3 H 7 , Propyl formate.
Such compounds may be readily distinguished by hydrolysis
followed by the separation of the alcohol and acid, according to
the method described in Expt. 64, p. 18$ . The alcohol is identified
by its boiling-point or other distinctive property ; the acid is
tested for in the residue left after removal of the alcohol.
Artificial Essences. It has already been stated that the
esters are manufactured as substitutes for natural essences.
The following compounds are commonly used for this purpose :
ethyl formate (rum), isoamyl acetate (pear), ethyl butyrate
(pine-apple), isoamyl isovalerate (apple).
The student is reminded that the constituents of butter (p. 171),
fats, oils (p. 165), beeswax, Chinese wax, and spermaceti (p. 114),
belong to the group of esters.
Ethyl Acetoacetate. If a small piece of sodium is added to
ethyl acetate, a gradual effervescence begins, which gains in
XII THE ESTERS 187
force as the action proceeds. The sodium dissolves and
hydrogen is evolved. The reaction was discovered by Geuther
(1863), and was further investigated by Frankland and Duppa
(1865). The product of the reaction is the sodium compound
of ethyl aceto-acetate, from which the free ester may be separated
by the addition of acetic acid followed by the fractional distil-
lation of the oil which separates. Acetoacetic ester is a colourless
liquid with a fruity smell. It has the formula
CH 3 . CO. CH 2 . CO. OC 2 H 5 .
Ethyl acetoacetate.
This formula represents ethyl acetate in which one hydrogen
atom of the methyl group is replaced by the acetyl group
CH 3 .CO. The properties of this important substance will be
discussed in a subsequent chapter (p. 326).
Esters of Inorganic Acids. These esters are prepared by
similar methods to those used in the preparation of the esters
of organic acids. The action of the alcohol on the acid
chloride may be illustrated in the case of dimethyl sulphite,
which is prepared from thionyl chloride, SOC1 2 , and methyl
alcohol
SOC1 2 + 2CH 3 OH = SO(OCH 3 ) 2 + 2HC1.
Thionyl Dimethyl sulphite,
chloride.
The action of the alkyl halide on the silver salt is used in the
preparation of diethyl sulphate from silver sulphate and ethyl
iodide (see p. 96)
Ag 2 S0 4 + 2C 2 H 5 I = S0 2 (OC 2 H 5 ) 2 + 2AgI.
Diethyl sulphate.
Ethyl Hydrogen Sulphate, Sulphovinic add. The most
common method for preparing the esters of inorganic acids is to
act upon the alcohol with the inorganic acid. Strong sulphuiic
acid, however, forms the acid, not the neutral sulphate. Ethyl
alcohol and sulphuric acid give, on heating, ethyl hydrogen
sulphate
C 2 H 5 OH + H 2 SO 4 = SO 2 (OH)(OC 2 H 5 ) + H 2 O.
Ethyl hydrogen sulphate.
The acid sulphates are very unstable. They are decomposed
on heating with both alcohol and water. With the former, ether
i88 THEORETICAL ORGANIC CHEMISTRY CHAP.
is produced, with the latter, hydrolysis occurs, and alcohol and
sulphuric acid are formed
C 2 H 5 .H.SO 4 + C 2 H 5 OH = (C 2 H 5 ) 2 O + H 2 SO 4 .
C 2 H 5 .H.SO 4 -f H 2 O = C 2 H 5 OH + H 2 SO 4 .
The acid sulphates form salts with metallic bases, which are
comparatively stable substances, being undecomposed by boiling
water or alkalis ; but they are hydrolysed by acids, which liberate
the unstable acid ester. The general formula of these salts is
RM'.SO 4 , in which R stands for the radical and M for the metal.
The calcium and barium salts are soluble, and the metal is not
immediately precipitated by sulphuric acid.
EXPT. 66. Preparation of Potassium Ethyl Sulphate. Forty c.c.
of pure ethyl alcohol and 10 c.c. of strong sulphuric acid are heated in
a flask on the water-bath for half an hour, then poured into a basin
containing 100 c.c. of water, and chalk added in excess. The
calcium salt is thereby formed. The mixture is boiled and filtered.
Potassium carbonate (about 25 grams) in solution is added, until the
liquid is alkaline. This precipitates tbe calcium as carbonate, and
the potassium salt remains in solution. The solution is filtered and
evaporated to a very small volume when potassium ethyl sulphate
crystallises out on cooling.
The following equations express the chemical reactions which
occur :
1. C 2 H 5 OH + H 2 S0 4 = C 2 H 5 .H.S0 4 + H 2 O.
Ethyl hydrogen sulphate.
2. 2C 2 H 5 .H.SO 4 + CaCO 3 = (C 2 H 5 SO 4 ) 2 Ca + H 2 O + CO,.
Calcium ethyl sulphate.
3. (C 2 H 5 SO 4 ) 2 Ca + K 2 CO 3 = 2C 2 H 5 .K.SO 4 + CaCO 3 .
Potassium ethyl sulphate.
Ethyl Nitrate. The nitrates are prepared by the action of
strong nitric acid on the alcohols. Ethyl alcohol and nitric acid
give ethyl nitrate and water
Ethyl nitrate.
But oxidation of the alcohol may occur at the same time, the
nitric acid being reduced to nitrous acid, which combines with
the alcohol to form a nitrous ester. To avoid the formation of
ethyl nitrite, a quantity of urea is added, which destroys any
THE ESTERS
nitrous acid that may be formed. The urea and nitrous acid
combine, with the production of free nitrogen, carbon dioxide,
and water (p. 337)
CON 2 H 4 + 2HNOo = CO., + 2N 2 + 3H O.
Urea.
EXPT. 67. Preparation of Ethyl Nitrate. Twenty c.c. of concen-
trated nitric acid (sp. gr. I -4) are poured into a retort attached to a
condenser and receiver. Five grams of urea are then introduced, and
50 c.c. of pure ethyl alcohol are gradually added from a tap-funnel.
The mixture is then slowly distilled from the water-bath. The ethyl
nitrate boils at 86. The substance is liable to explode when quickly
heated. When reduced with tin and hydrochloric acid, ethyl nitrate
yields hydroxylamine and ethyl alcohol
C 2 H 5 .O.NO 2 + 3H 2 = C 2 H 5 OH + NH 2 OH + H 2 O.
Amyl Nitrfte. The nitrites are obtained by passing nitrogen
trioxide into the alcohol, or more conveniently by adding sul-
phuric acid to a mixture of the alcohol and sodium nitrite,
whereby nitrous acid is liberated. Arnyl nitrite may be pre-
pared in this way
C 5 H n OH + HO. NO = C 5 H n .ONO -I- H 2 O.
Amyl alcohol. Amyl nitrite.
EXPT. 68. Preparation of Amyl Nitrite. Ten grams of amyl
alcohol and 10 grams of finely powdered sodium nitrite are mixed to-
gether in a flask and cooled in ice, whilst 6 grams of strong sulphuric
acid are added. A little water is then poured in, when the amyl
nitrite floats as a yellow liquid on the surface, and may be removed,
dehydrated over calcium chloride, and dhtilled. Amyl nitrite boils
at 96. It is used medicinally in cases of hear'; disease.
Sweet Spirits of Nitre is prepared by distilling a mixture
of alcohol, sulphuric acid, nitric acid, and copper turnings. The
reaction is a complex one, and gives rise to the formation of
ethyl nitrite, aldehyde, acetic ether, and acetic acid. The copper
probably attacks the nitric acid, forming nitrous acid, which
reacts with the alcohol, and gives ethyl nitrite, whilst the pro-
ducts of oxidation are produced by the action of nitric acid on
the alcohol. Spirits of nitre is used in medicine.
190 THEORETICAL ORGANIC CHEMISTRY CHAP.
EXPT. 69. Preparation of Sweet Spirits of Nitre. Mix together
2Oc.c. of alcohol and 2 c.c. of concentrated sulphuric acid, and cool.
Pour the mixture into a retort attached to a condenser and receiver,
and add 3 c.c. of nitric acid. Finally, introduce 4 grams of copper in
small pieces, and distil gently from the water-bath. The distillate,
diluted with about 3 times its volume of spirits of wine, forms sweet
spirits of nitre.
The Alkyl Halides. It should be remembered that the
alkyl halides, like ethyl chloride, bromide, and iodide, may be
regarded as esters of the halogen acids, both from the point of
view of their mode of preparation and from their behaviour with
alkalis.
THE NITRO-PARAFFINS
The nitre-paraffins are isomeric with the nitrites. They both
possess the general formula R.NO 2 . The nitrites are prepared,
as we saw above, by the action of nitrous acid on the alcohol ;
the nitre-paraffins are obtained by distilling a mixture of the
alkyl iodide with silver nitrite. Ethyl iodide and silver nitrite
give nitroethane, together with some ethyl nitrite
C 2 H 5 I + AgN0 2 = C 2 H 5 N0 2 + Agl.
ExPT. 70. Preparation of Nitroethane. The silver nitrite required
is prepared by adding a solution of silver nitrate to the equivalent
amount of pure sodium nitrite dissolved in water. The precipitate is
washed and thoroughly dried. The silver nitrite (5 grams) mixed
with its own weight of dry sand is placed in a small distilling flask,
attached to a condenser. The ethyl iodide (j grams) is added
gradually through a tap-funnel inserted tightly into the neck of the dis
tilling flask. When the ethyl iodide is added, a considerable rise of
temperature occurs. The contents of the flask are then distilled.
To show the formation of ethyl nitrolic acid (see below), the liquid
is dissolved in a little caustic potash solution, and a solution of
i potassium nitrite added. On cautiously adding dilute sulphuric
acid, a deep red coloration appears. If acid is added until the
i potassium salt of the nitrolic acid is decomposed, the colour vanishes
again.
The nitre-paraffins are colourless, pleasant-smelling liquids,
XII THE NITRO-PARAFFINS
191
the boiling-points of which are much higher than those of the
corresponding nitrous esters.
Boiling-point. Boiling-poinL
CH 3 NO 2 . . Methyl nitrite . - 12 . . Nitromethane . 101
C 2 H 5 NO 2 . . Ethyl nitrite . . 16 . . Nitroethane . 114
The difference in the structure of the two groups of com-
pounds is clearly indicated by their behaviour with caustic
alkalis and with reducing agents.
Caustic alkalis dissolve the primaiy nitro-parafrms (p. 182)
forming salts, whereas the alkyl nitrites are hydrolysed, and yield
the alcohol and salt of nitrous acid
C 2 H 5 NO 2 + KOH = C 2 H 4 KNO 2 + H 2 O.
Nitroethane. Potassium nitroethane.
C 2 H 5 N0 2 + KOH = C 2 H 5 OH + KNO 2 .
Ethyl nitrite.
With reducing agents the nitro-paraffins lose their oxygen,
which is replaced by two atoms of hydrogen, and are converted
into amines (p. 204) ; the alkyl nitrites are decomposed into
alcohol on the one hand, and into hydroxylamine or ammonia
on the other
C 2 H 5 NO 2 + 3lI 2 = C 2 H 5 NH 2 + 2H 2 O.
Nitroethane. Ethylamine.
C 2 H 5 NO 2 + 2H 2 = C 2 H 5 OH + NH 2 OH.
Ethyl nitrite.
These differences are accounted for by supposing that the
nitrogen in the nitro-paraffins is directly linked to the carbon
atom of the alkyl group, whilst in the nitrites the acid radical is
attached to the carbon atom of the alkyl group by oxygen. The
following formulae for nitroethane and ethyl nitrite will make
this evident
CH 3 .CH 2 .O.N:O.
Nitroethane. Ethyl nitrite.
It is a curious fact that both substances, when the vapour mixed with
hydrogen is passed over finely divided nickel or copper, yield the amine
(Senderens).
192 THEORETICAL ORGANIC CHEMISTRY CHAP.
Distinction between Primary, Secondary, and Tertiary
Alcohols. The action of nitrous acid on the nitro-paraffins is
used as a means of distinguishing the primary, secondary, and
tertiary alcohols, and is known as Victor Meyers method. By
converting the alcohols into the corresponding alkyl iodides, and
distilling the latter with silver nitrite, primary, secondary, and
tertiary nitro-paraffins are produced, containing the following
groups :
CH 2 .NO 2 =CH.NO 2 =C.NO 2 .
Primary. Secondary. Tertiary.
With nitrous acid the primary nitro-paraffins form acids
known as nitrolic acids, which dissolve in alkalis, forming salts
with a dark red colour. Nitroethane gives ethyl nitrolic acid
CH 3 .CiH 2 : .NO 2 CH 3 .C.NO 2
|| + H 2 0.
+ j OJNOH NOH.
Ethyl nitrolic acid.
The hydrogen indicated by thick type is replaceable by a metal.
The secondary nitro-paraffins, like secondary nitro-propane, form,
with nitrous acid, substances which dissolve in alcohol, ether, or
chloroform, with a blue colour, and are known as pseudo-nitrols.
They are not acids and form no salts.
(CH 3 ) 2 Ci"H"5NOo (CH 3 ) 2 C.NO a
+ 'HoO.
+ NO;OHj NO.
Isopropyl pseudo-nitrol.
The tertiary nitro-paraffins do not react with nitrous acid.
QUESTIONS ON CHAPTER XII
1. Describe a method for the preparation and purification of ethyl
acetate.
2. In what respect does the action of a metallic base (e.g. caustic
soda) on an acid differ from that of an alcohol on an organic acid ?
3. Explain the action of (i) caustic potash, (2) ammonia, and (3)
sodium on acetic ester.
4. How could you distinguish an acid from an ester, both of which
had the same molecular formula, C 4 H8O 2 ? How would you determine
xu THE KITRO-PARAFFINS
195
the nature of the acid and alcohol combined in an ester of the above
formula ?
5. Why is ethyl chloride to be regarded *as an ester ?
6. How would you distinguish between the following isomeric com-
pounds : nitroethane and ethyl nitrite ?
7. How is "sweet spirits of nitre " prepared? What substances does
it contain ?
8. Describe V. Meyer's method for identifying primary, secondary,
and tertiary alcohols.
9. Describe and illustrate three methods of preparing, (i) esters of
organic acids, (2) esters of inorganic acids. What is meant by
equilibrium constant applied to the process of esterification, how is it
determined, and how can the percentage amount of ester be ascertained
for any known mixture of acid and alcohol ?
10. Describe the action of water upon ethyl acetate, acetic anhydride,
acetyl chloride, and ethyl chloride.
11. By what reactions would you obtain the following derivatives
from -a.ce1.ic acid : acetyi chloride, acetamide, ethyl acetate, acetic
anhydride, monochloracetic acid ?
12. How is ethyl acetate prepared, and what is its constitutional
formula ? Explain clearly why the action of caustic soda on ethyl
acetate has been called saponifi cation.
13. Describe and explain V. Meyer's test for distinguishing primary,
secondary, and tertiary alcohols.
14. The nitrites and the nitro-compounds are regarded as isomeric ;
what is the ground for this? Contrast the chief reactions of one
member of each of these groups.
15. Explain the terms " mass law "and " equilibrium point." Given
the concentration of alcohol and acid how would you calculate the
amount of ester formed at a given temperature ?
CHAPTER XIII
SULPHUR COMPOUNDS
IN the list of reactions on p. 83 it will be seen (Reaction 9)
that the alkyl halides combine with potassium hydrosulphide,
and yield compounds similar in composition to the alcohols,
but containing sulphur in place of oxygen. These substances
are termed thio-alcohols or mercaptans. If potassium sulphide,
K 2 S, is used in place of the hydrosulphide, the alkyl sulphides
or thio-ethers are formed. A third class of compounds is known
as the disulphides, and corresponds to sodium disulphide, Na 2 S 2 ,
but they have no representative among the alkyl oxides. The
mercaptans, thio-ethers, and disulphides may be compared with
the alcohols and ethers on the one hand, and with the sulphur
compounds of sodium on the other.
The ethyl compounds may be taken as illustrating this
relation
C 2 H 5 OH
Ethyl alcohol.
C 2 H 5 SH
Ethyl hydrosulphide.
NaSH
Sodium hydrosulphide.
o/ 2 5
g/ C 2 H 5
/Na
s/
Ethyl ether.
Ethyl sulphide.
Sodium sulphide.
S C 2 H 5
S C 2 H 5
Ethyl disulphide.
S Na
1
S Na
Sodium disulphide.
Mercaptans. The mercaptans are prepared (i) by the action
of potassium hydrosulphide on the alkyl halide ; (2) by distilling
a solution of potassium alkyl sulphate with potassium hydro-
194
CH. xni SULPHUR COMPOUNDS 195
sulphide ; or (3) by acting on the alcohol with phosphorus penta-
sulphide. Ethyl mercaptan may be obtained by any of these
reactions, which are represented by the following equations :
QjHajCl + KiSH = C 2 H 5 SH + KC1
Ethyl mercaptan.
+ SHJK
= C 2 H 5 SH + K 2 SO 4 .
2. 2
X)K
3. sC 2 H 5 .OH + P 2 S 5 - 5C 2 H 5 .SH + P 2 O 5 .
Ethyl mercaptan is now used in the manufacture of sulphonal
(p. 276), and is prepared by heating ethyl chloride with a strong
solution of potassium hydrosulphide under pressure in closed
vessels. It boils at 36.
The mercaptans are volatile liquids (with the exception of
methyl mercaptan, which is a gas) and are insoluble in water.
They possess an intolerable smell. Sodium and potassium
liberate hydrogen from the mercaptans, forming mercaptides,
which correspond to the alcoholates of these metals. When
a mercaptan is added to mercuric oxide, or to an alcoholic
solution of mercuric chloride, a crystalline mercury mercaptide
is formed. This characteristic compound with mercury has
given rise to the name mercaptan (mercurium, mercury ; captans,
seizing).
The sodium, potassium, and mercury mercaptides of ethyl
have the following formulas :
C 2 H 5 SK (C 2 H 5 S) 2 Hg
Sodium mercaptide. Potassium mercaptide. Mercury mercaptide.
When exposed to the air, the mercaptans are converted into
disulphides
C,H B S:H~"--"-... c 2 H 5 s
; + o ";.: - I + H 2 o.
C 2 H 5 SjH .._.--"'" C 2 H 5 S
Ethyl mercaptan. Ethyl disulphide.
The same result is produced by the action of iodine on sodium
mercaptide
2C 2 H 5 SNa + I a = C 2 H 5 S.S.C 2 H 5 + 2NaI.
O 3
196 THEORETICAL ORGANIC CHEMISTRY CHAP.
Sulphonic Acids and Sulphonates. When the mercaptans
are oxidised with strong nitric acid, sulphonic acids are formed.
Ethyl mercaptan gives ethyl sulphonic acid
C 2 H 5 SH + 30 = C 2 H 5 SO 3 H.
Kthyl sulphonic acid.
The sulphonates of the alkalis are obtained by the action of
the alkyl halides on the alkaline sulphites
C 2 H 5 :I 4- K;SO 3 K = C 2 H 5 SO 3 K + KI.
Ethyl potassium sulphonate.
The sulphonic acids are strong monobasic acids, which are
very soluble in water, and form soluble salts with the metals. %
The aromatic hydrocarbons, like benzene, offer a great contrast to the
paraffins in their behaviour with strong sulphuric acid. The aromatic
hydrocarbons readily form sulphonic acids. Benzene yields benzene
sulphonic acid on heating with strong sulphuric acid
C 8 H 6 -f H,S0 4 = C 6 H 5 .S0 3 H + H 2 O,
Benzene. Benzene sulphonic acid.
whereas the paraffins are acted upon only in a few cases, and then very
slowly with fuming sulphuric acid.
The alkyl sulphonates are isomeric with the alkyl sulphites,
from which, however, they may be readily distinguished by
boiling with caustic potash. The sulphites are hydrolysed into
alcohol and potassium sulphite, whereas the sulphonates are
unchanged. For this reason the formulae of the two classes of
compounds are represented as follows : In the sulphonates, the
sulphur is directly linked to carbon, but in the sulphites the ac'd
radical is united by oxygen to the alkyl group which is charac-
teristic of the esters of all oxygen acids (p. 180).
/^ // Q
C. 2 H 5 .S~O C.H.O.SC
\ OK X OK
Potassium ethyl sulphonate. Potassium ethyl sulphite.
Thio-ethers. The alkyl sulphides, or thio-ethers, may be
prepared by the action of phosphorus sulphide on the ethers
5 (C 2 H 5 ),0 + P 2 S 5 = 5(C 2 H 5 ) 2 S + P 2 5 ,
Ethyl sulphide.
xin SULPHUR COMPOUNDS 197
or, by the action of potassium sulphide on the alkyl halide or
alkyl potassium sulphate
2C 2 H 5 I + K 2 S = (C 2 H 5 ) 2 S + 2KI.
OC 2 H 5
2S0 2 / + KgS = (CaHgkS + 2K 2 S0 4 .
Ethyl potassium sulphate. Ethyl sulphide.
The alkyl sulphides are insoluble in water, like the mercaptans,
and also possess a disagreeable smell.
They combine with the alkyl iodides and form compounds
known as sulphine iodides. Ethyl sulphide and ethyl iodide
form triethylsulphine iodide
(C 2 H 5 ) 2 S + C 2 H 5 I = (Call^SI.
Triethylsulphine iodide.
The iodine of the sulphine iodide may be exchanged for
hydroxyl by the action of moist silver oxide
(C 2 H 5 ) 3 S.I + AgOH = (CaH 5 ) 3 S.OH + Agl.
Triethylsulphine hydroxide. '
The sulphine hydroxides are hygroscopic crystalline substances
which are soluble in water, and the solution has an alkaline
reaction. They precipitate metallic oxides, from solutions of their
salts, absorb carbon dioxide from the air, and behave in fact like
the caustic alkalis or ammonia. By introducing three different
radicals into the sulphine iodide, asymmetric sulphur com-
pounds showing optical activity have been obtained (p. 112).
QUESTIONS ON CHAPTER XIII
1. Describe a method for the preparation of ethyl mercaptan.
2. What are the characteristic properties of mercaptans ? In what
respects do they resemble the alcohols ?
3. Compare the action of sulphuric acid on the paraffins and on
benzene. How are alkyl sulphonic acids prepared ?
4. How would you distinguish potassium ethyl sulphonate from
potassium ethyl sulphite ?
5. Which sulphur compounds resemble ammonia? How are they
prepared ?
6. How is mercaptan obtained and identified ? Describe the action
of nitric acid upon it, and state any facts which indicate the con-
stitution of the chief product.
CHAPTER XIV
THE AMINES
The Amines. The name amine is given to derivatives of
ammonia in which one or more atoms of hydrogen are replaced
by alkyl groups. They are also called substituted, or compound,
ammonias, and from their resemblance to ammonia and the
caustic alkalis generally, constitute one of the groups of organic
bases. If one, two, and three atoms of hydrogen in ammonia are
replaced by alkyl groups, the compounds are known as mono-, di-,
and tri-alkylamines, and also by the names, primary, secondary,
and tertiary amines. The methyl derivatives of ammonia have
the following structural formulas and names :
/H /CH 3 /CH 3 /CH,
N^-H N^-H N-CH S N^-CH;
MI Ml \H \CH 3
Methylamine Dimethylamine Trlmethylamine
(Primary amine). (Secondary amine). (Tertiary amine).
Although the existence of substituted ammonias was foretold
by Liebig as early as 1842, it was not until 1849 that Wurtz pre-
pared the first member, methylamine, by boiling the methyl ester
of cyanic acid, or methyl isocyanate (p. 227), with caustic potash.
He found that the gas evolved had a strong ammoniacal smell,
but differed from ammonia in being inflammable
CH 3 N:jCO + OjH 2 = CH 3 NH 2 + CO 2 .
Methyl isocyanate. Methylamine.
EXPT. 71. Mix together in a hard glass test-tube one part of
methylamine hydrochloride and two parts of quicklime or soda-lime
and heat. The methylamine gas which is evolved may be ignited,
and burns with a lambent bluish flame.
The carbon dioxide forms potassium carbonate with the potash
present, and the methylamine is liberated as a gas.
198
THE AMINES
199
Properties of the Amines. The amines have properties like
those of ammonia. The hydrochloride, nitrate, and sulphate
of methylamine have a similar composition to the salts of
ammonia
HC1
NH 2 .CH 3 .
Methylamine
hydrochloride,
NH 2 .CH 3 .HNO 3
Methylamine
(NH 2 .CH 3 ) 2 .H 2 S0 4
Methylamine
sulphate.
The amines also form double salts with the chlorides of
platinum, gold, and mercury. The platinum salts of the amines
are yellow, crystalline substances, closely resembling in appear-
ance ammonium chloroplatinate, and they are similarly
constituted. Methylamine chloroplatinate has the formula
(NH 2 CH 3 .HCl) 2 PtCl 4 .
The platinum salts are readily prepared by dissolving the
amine in moderately strong hydrochloric acid and adding
platinic chloride. These salts often serve for determining the
molecular weight of the amine (p. 46).
The lower members of the series of amines, like methylamine,
dimethylamine, and trimethylamine, are gases, which dissolve
in water ; the higher members are either colourless liquids or
solids, the solubility of which rapidly decreases with increasing
molecular weight. The more volatile amines have a strong
ammoniacal smell.
As the hydrochlorides and nitrates of the amines are very
soluble in water, amines, which are themselves insoluble,
dissolve readily on the addition of dilute hydrochloric or nitric
acid.
The following table contains a list of the first four members of
the series, from which it will be observed that the boiling-points
rise from the primary to the tertiary amines :
Amine.
Primary.
Boiling-point.
Secondary.
Boiling-point.
Tertiary.
Boiling-point.
-6
7
35
19
56
90
Propylamine
49
76
98
1 60
x 5 6 :
215
200 THEORETICAL ORGANIC CHEMISTRY
Primary, Secondary, and Tertiary Amines. It has already
been stated that the amines are divided into three classes, which
are termed primary, secondary, and tertiary amines, according
to whether one, two, or three hydrogen atoms in ammonia are
replaced by radicals.
Each of these classes possesses certain distinctive properties
by which it may be identified. The methods of identification
depend upon the presence of certain groups in reality, upon
the number of hydrogen atoms of ammonia "unsubstituted by
radicals.
These groups may be termed primary^ or amino groups,
secondary or imino groups, and tertiary groups
NH 2 =NH =N
Primary, or amino group. Secondary, or imino group. Tertiary group.
Nitrous acid is one reagent employed for distinguishing the
three groups.
The primary amines combine with nitrous acid and form
soluble nitrites, which resemble ammonium nitrite in being
rapidly decomposed in aqueous solution on heating. But,
whereas ammonium nitrite yields water and nitrogen, the
primary amine forms an alcohol, water, and nitrogen.
Methylamine nitrite decomposes in aqueous solution into
methyl alcohol, water, and nitrogen
HJNiH,
HOJNJO
Ammonium nitrite.
= CHo.OH + No 4- H 2 O.
HOiNjO
Methylamine nitrite.
This reaction is most conveniently carried out by dissolving
the amine, or its salt, in dilute hydrochloric acid, and then adding
a solution of sodium nitrite. Effervescence at once begins on
warming, and nitrogen is evolved. Alcohol is then found in
solution. If the same reaction is applied to a secondary amine,
THE AMINES
no effervescence occurs on addition of sodium nitrite, but a
yellow oil separates, which is called a nitros amine, and is volatile
in steam (p. 412). Dimethylamine forms dimethyl nitrosamine.
It is formed by the following reaction
(CH 3 ) 2 NJH ""+" HOiNO = (CH 3 ) 2 N.NO + H 2 O.
Dimethyl nitrosamine.
EXPT. 72. For this experiment methylaniline, C 6 H 5 NHCH 3 ,
may be used. Dissolve the base in dilute hydrochloric acid by
shaking, and add to the clear solution a few drops of sodium nitrite.
An emulsion consisting of oily drops of the nitrosamine,
C f) H 5 N(NO)CH 3 ,
is formed, which on shaking with ether dissolves and gives a yellow
solution.
Nitrous acid is without action on the tertiary amines. The
action of nitrous acid may therefore be employed for the
preparation of tertiary amines free from secondary or primary
compounds. If, after the addition of sodium nitrite to the
acid solution of the amines, the product is distilled in steam,
the alcohol derived from the primary amine and nitrosamine of
the secondary amine are removed, and the tertiary amine remains
as the hydrochloride in the distilling vessel. The nitrosamine
may be converted on boiling with strong hydrochloric acid into
the secondary amine
(CH 3 ) 2 N.NO + 2HC1 - (CH 3 ) 2 NH.HC1 + NOC1,
but the primary amine cannot be recovered. Another method
for separating the three groups of amines is described below.
Primary amines may also be identified by means of the
isocyanide, or carbamine reaction described on p. 90. In the
reaction referred to, chloroform is detected by the smell of
phenylisocyanide evolved on heating chloroform with aniline and
alcoholic potash. Any primary amine may be substituted for
aniline, with the formation of the corresponding alkyl isocyanide.
Methylamine forms, with chloroform and potash, methyl iso-
cyanide ; ethylamine gives ethyl isocyanide, and they all possess
the same disagreeable smell
CH 3 NiH 2 ' + C ; HGQ + 3 KOH = CH 3 .NC + 3KC1 + 3H 2 O.
Methyl isocyanide.
Secondary and tertiary amines do not form isocyanides.
The acid chlorides and anhydrides combine with primary and
202 THEORETICAL ORGANIC CHEMISTRY CHAP.
secondary amines, and form amides (p. 176) ; but have no action
on the tertiary amines. Acetyl chloride forms, with methyl-
amine and dimethylamine, methyl- and dimethylacetamide
CH 3 .CO.C1 + NH 2 .CH 3 = CHj,.CO.NH.CH 3 + HC1.
Methyl acetamide.
CHg.CO.Cl + NH(CH 3 ) 2 = CH 3 .CO.N(CH 3 ) 2 + IIC1.
Dimethylacetamide.
EXPT. 73. To show the action of acetyl chloride on primary and
secondary amines, aniline, C 6 H 5 NH 2 , and methylaniline, CgHgNHCHg,
may be used.
Quaternary Ammonium Compounds. Although tertiary
amines are unchanged by many of the reagents which react
with the primary and secondary amines, they possess the dis-
tinctive property of uniting with a molecule of an alkyl iodide
to form what are known as quaternary ammonium iodides.
The reaction resembles that by which alkyl sulphides are
converted into sulphine iodides (p. 197). The quaternary com-
pounds are solid substances, which are comparatively stable, and
are undecomposed by boiling caustic alkalis. Trimethylamine
and methyl iodide form tetramethyl ammonium iodide
N(CH 3 ) 3 + CH 3 I = N(CH 3 ) 4 I.
Tetramethyl
ammonium iodide.
EXPT. 74. To show this reaction dimethylaniline, C 6 H 5 N(CH 3 ) 2 ,
may be used. On warming a mixture of equal volumes of the base
and methyl iodide, the solid phenyl trimethyl ammonium iodide
separates.
By the action of moist silver oxide, which reacts like silver
hydroxide, on the quaternary ammonium iodide, the iodine
atom is exchanged for hydroxyl, and the resulting compound is
known as a quaternary ammonium hydroxide
N(CH 3 ) 4 I + AgOH = N(CH 3 ) 4 .OH + Agl.
Tetramethyl
ammonium hydroxide.
Tetramethyl ammonium iodide gives the corresponding
hydroxide. These substances are soluble in water, to which
they impart a strongly alkaline reaction. They behave, in fact,
like ammonia. The solutions precipitate metallic oxides from
solutions of metallic salts, and absorb carbon dioxide from
the air.
THE AMINES 2O3
When the quaternary hydroxides are heated, they are con-
verted into the original tertiary amines. Tetramethyl ammonium
hydroxide forms trimethylamine and methyl alcohol. The
tetrethyl compound gives triethylamine, ethylene, and water
N(CH 3 ) 4 OH = N(CH 3 ) 3 + CH 3 OH.
N(C 2 H 5 ) 4 OH = N(C 2 H 5 ) 3 + C 2 H 4 + H 2 O.
This is a convenient method for preparing the tertiary base in
a pure state and free from primary and secondary amines.
The value of this method, as well as of that described above,
will be evident when the following process for preparing the
amines has been explained.
Preparation of the Amines. In the same year in which
Wurtz discovered the first of the substituted ammonias,
Hofmann introduced an important process for preparing the
mono-, di, and trialkylamines. It consisted in heating the alkyl
halide with alcoholic ammonia (alcohol saturated with ammonia)
in sealed tubes under pressure. The three classes of amines,
as well as the quaternary compounds, are produced together.
In the case of methyl iodicle, the following series of reactions
occur
NH 3 + CH 3 I = CH 3 .NH 2 .HI.
Methylamine hydriodide.
CH 3 .NH 2 + CH 3 I = (CH 3 ) 2 NH.HI.
Dimethylamine hydriodide.
(CH 3 ) 2 NH + CH 3 I = (CH 3 ) 3 N.HI.
Trimethylamine hydriodide.
(CH 3 ) 3 N + CH 3 I = (CH 3 ) 4 N.I.
Tetramethyl ammonium iodide.
Separation of the Mono-, Di-, and Trialkylamines. The separation
of the four classes of amines, obtained in the above reaction, was effected
by Hofmann as follows : Caustic potash is added to the mixture,
which is distilled. The mono-, di-, and trialkylamines are liberated
from their salts and distil over. l The quaternary ammonium iodide is
non-volatile, and remains unchanged in the distilling vessel. The
amines are freed from water, and ethyl oxalate is then added to the
mixture, or, if the amines are gases, they are passed through liquid
ethyl oxalate. The monoalkylamine unites with the ethyl oxalate and
forms an amide, which is a solid ; the dialkylamine forms a liquid
oxamic acid, whereas the trialkylamine does not combine. The
mixture is distilled, when the trialkylamine passes over first, as its
boiling-point is much lower than that of the compounds of the mono-
1 The three ethylamines may be separated by fractional distillation.
204 THEORETICAL ORGANIC CHEMISTRY CHAP.
and di-alkylamine with oxalic ester. The solid amide is separated by
filtration from the liquid oxamic ester. The amide of methylatnine is
formed in the following way
COOC 2 H 5 CO.NHCH 3
| + 2NH 2 CH 3 = | + 2C 2 H 5 OH.
COOC 2 H 5 CO.NHCHj
Ethyl oxalate. Methylamine. Dimethyloxamide.
Two molecules of the amine combine with one molecule of ethyl
oxalate, the molecules of alcohol being liberated from the ester. The
formation of the oxamic acid of dimethylamine is represented as
follows
COOCoH 5 CO.N(CH 3 ) 2
| + NH(CH 3 ) 2 = | + C 2 H 5 OH.
COOC 2 H 5 COOC 2 H 5
Ethyl oxalate. Dimethylamine. Dimethyl oxamic ester.
Only one molecule of the amine combines with the ester. After
filtration, the oxamide and oxamic ester are separately decomposed with
caustic potash and distilled. The bases are liberated and distil over,
and, if gaseous, may be absorbed by dilute hydrochloric acid, placed in
the receiver. On evaporation the hydrochlorides are obtained.
CO.NH.CH 8
+ 2KOH = 2NHoCH 3 + C 2 O 4 K 2
CO.NH.CH 3
Dimethyl oxamide. Methylamine. Potassium oxalate.
CON(CH 3 ) 2
| 4- 2KOH - NH(CH,) a + C,O 4 K 2 + CoH 5 OH.
COOC 2 H 5
Dimethyl oxamic Dimethylamine. Potassium oxalate.
ester.
The difficulty involved in Hofmann's process for separating
the amines may be avoided by using methods of preparation in
which only one kind of amine is produced. The primary
amines are obtained either by the method of Wurtz already
referred to, or by the reduction of the nitro-paraffins (p. 191) with
tin and hydrochloric acid. Nitromethane yields methylarnine
CH,N0 2 + 3H 2 - CH 3 NH 2 + 2 H 2 O.
Nitromethane. Methylamine.
Or, by the reduction of the cyanides with sodium in alcoholic
solution ; methyl cyanide may be converted into ethylamine
CH 3 CN + 2H 2 = CH,CH 2 NH 2 .
Methyl cyanide. Ethylamine.
The readiest method is to add bromine to the amide of a fatty
xiv THE AMINES 205
acid, which is converted into the bromamide. Acetamide yields
acetobromamide
CHg.CONHo + Br 2 = CH 3 .CONHBr + HBr.
Acetamide. Acetobromamide.
If the acetobromamide is then warmed with excess of potash, it
is converted into methyl isocyanate, which further breaks up, on
boiling, into methylamine. In the first reaction the hydrobromic
acid is removed from the acetobromamide, which produces methyl
isocyanate by atomic rearrangement. The methyl isocyanate 'is
then hydrolysed, as previously described in Wurtz's reaction
(p. I9 8)_ w
CH 3 .CONJHBr + 7 KOH = CH 3 N.CO + KBr + H 2 O.
Acetobromamide. Methyl isocyanate.
CH 3 .N.CO + 2KOH = CH,NH 2 + K 2 CO 3 .
MethyJamine.
EXPT. 75. Mix together in a J litre flask 2 grams of acetamide
and 2 grams of bromine, and then cool and add dilute caustic potash
solution until the colour of the bromine vanishes. Now add 6 c.c. of a
strong potash solution and warm. There is a brisk effervescence and
evolution of methylamine, which has a strong smell of herring brine.
Another method is to pass the vapour of alcohol and ammonia
over heated thoria (Sabatier)
CH 8 OH + NH 3 = CH 3 NH 2 + H 2 O.
The secondary amines may be obtained pure by the decom-
position of certain aromatic bases which will be described
under the aromatic compounds (p. 424). Secondary amines
are also obtained in considerable quantity together with primary
amines by passing the vapour of oximes mixed with hydrogen
over heated nickel
CH 3 . CH :NOH = C 2 H 5 NH. 7
2C 2 H 5 NH 2 = (C 2 H 5 ) 2 NH + NH 3 .
Two of the methods for the preparation of primary amines
may be utilised for passing from one member of a homologous
series to the next.
For example, methyl alcohol may be converted into the iodide,
the cyanide, and, finally, by reduction, into ethylamine and ethyl
alcohol
HI KCN 2 H 2 HNO 2
CH 3 OH -> CH 8 I -> CH 8 CN -> CH 3 .CH 2 .NH 2 -> C 2 H 5 .OH.
Methyl Methyl Methyl Ethylamine. Ethyl
alcohol. iodide. cyanide. alcohol.
206 THEORETICAL ORGANIC CHEMISTRY CHAP.
In order to pass from a higher to a lower member of a series,
the second method may be introduced. Ethyl alcohol may be
converted into acetic acid, then into acetamide (p. 176), methyl-
amine, and methyl alcohol
O NH 3 Br 2 -fKOH HNO 2
C 2 H 5 OH->C 2 H 4 2 ->C 2 H 3 O.NH 2 > CH 3 .NH 2 -> CH 3 OH.
Ethyl Acetic Acetamide. Methylamine. Methyl
alcohol. acid. alcohol.
Metameric Amines. If a primary amine is treated by
Hofmann's method with an alkyl iodide in which the alkyl
group is different from that present in thfe amine, a mixed amine
is formed. A third alkyl group may be introduced, which is
again different from the other two. It is easy to conceive how,
by this means, metameric amines may result (p. 120). A
substance having the formula C 3 H 9 N represents three meta-
meric substances propylamine, ethylmethylamine, and tri-
methylamine
/C 3 H 7 /C 2 H 5 /CH 3
N^H ttf CH 3 N^CH 8
\H \H \CH 3
Propylamine. Ethylmethylamine. Trimethylamine.
Methylamine, CH 3 NH 2 , dimethylamine, (CH 3 ) 2 NH, and tri-
methylamine, (CH 3 ) 3 N, are gases. They are all present, but
chiefly dimethylamine, in the brine in which herrings have been
salted, and arise from the putrefaction of the fish.
Dimethylamine and trimethylamine are also present in
considerable quantity among the produces of the destructive
distillation of molasses residues from the beet-root industry,
together with other amines and methyl alcohol (p. 102). The
amines are separated by adding hydrochloric acid, distilling off
the alcohol, and evaporating the residue to dryness. When di- or
trimethylamine hydrochloride is heated in a current of hydro-
chloric acid gas, it yields methyl chloride and ammonium
chloride
NH(CH 3 ) 2 .HC1 + 2HC1 = 2CH 3 C1 + NH 4 C1.
N(CH 3 ) 3 .HC1 + 3HC1 = 3CH 3 C1 + NH 4 C1.
The methyl chloride obtained in this way from the beet-root
residues is liquefied by compression into steel cylinders, and is
used like ethyl chloride in surgery for producing insensibility
xiv THE AMINES 207
(p. 81). Its rapid evaporating causes intense cold. Under the
receiver of an air-pump the temperature may be reduced to 55.
The presence of the methylamine bases in herring brine and
molasses residues has its origin in the character of the nitro-
genous constituents of animal and vegetable matter, many of
which contain these basic groups, which become detached by
decomposition.
Methylamine and dimethylamine are conveniently prepared
by the action of formaldehyde on ammonium chloride
H.COH-f NH 4 C1 = CH 2 :NH(HC1) + H 2 O
CH 2 :NH(HC1) + H 2 O + H.COH = CH 3 NH 2 .HC1 + H.CO 2 H.
The methylamine hydrochloride then reacts in a similar
fashion, yielding the dimethylamine salt.
QUESTIONS ON CHAPTER XIV
1. Give two methods for preparing primary amines free from
secondary and tertiary amines.
2. How can a tertiary amine be obtained free from primary and
secondary amines ?
3. Give a method for distinguishing primary, secondary, and tertiary
amines. How would you obtain pure diethylamine from a mixture
containing monoethylamine ?
4. In what respects do the amines resemble ammonia ?
5. Write the formula for the hydrochloride, nitrate, sulphate, and
platinochloride of triethylamine.
6. Give the structural formula of metameric amines having the
molecular formula C 4 H n N.
7. Describe the preparation and properties of tetrethyl ammonium
hydroxide. What products does it yield on heating ?
8. What is the action of acetyl chloride on mono-, di-, and tri-
ethylamine ?
9. How can (i) acetic acid be converted into formic acid, and (2)
methyl alcohol into ethyl alcohol ?
10. Describe the technical process for preparing di- and trimethyl-
amine. For what purpose are they employed ?
11. Explain Hermann's method for separating primary, secondary,
and tertiary amines. Why is the method necessary ?
208 THEORETICAL ORGANIC CHEMISTRY CH. xiv
12. Describe the properties of methylamine, and show how it may
be prepared from methyl alcohol, formaldehyde, nitromethane, and
acetamide.
13. Starting with ethyl alcohol and with acetic aldehyde respectively,
show how ethylamine may be obtained.
14. If given acetamide, describe and explain the method by which
you would prepare from it methylamine. How would you convert
methylamine into trimethylamine ?
15. Describe the reactions by which primary, secondary, and tertiary
ethylamines have been obtained. How would you distinguish ethyl-
amine, diethylamine, and triethylamine from each other ?
1 6. Describe the chloroform test for a primary amine, and indicate
the nature of the reaction on which it depends.
17. Describe the reactions by which mono- and dimethylamine
can be obtained from formaldehyde.
CHAPTER XV
THE CYANOGEN COMPOUNDS
EARLY in the eighteenth century Diesbach, a German colour
maker, accidentally discovered Prussian blue by adding a salt of
iron to lixivium sangidnis (the aqueous extract of blood calcined
with potash). In 1782, Scheele obtained prussic, or hydrocyanic,
acid from the lixivium as well as from Prussian blue by distilling
them with a mineral acid ; but it was not until 1815 that Gay-
Lussac explained the composition of hydrocyanic acid and the
cyanogen compounds. He showed that these compounds con-
tain the group (CN) to which he gave the name cyanogen (KVOVOS,
blue ; ycvvaw, to produce), and pointed out that cyanogen plays
the part of an element like chlorine. It was, in fact, the first
example of a compound radical (p. 83). We shall see in the
course of the chapter the many points of similarity existing
between cyanogen and chlorine.
Cyanogen, (CN) 2 . Free cyanogen was obtained by Gay-
Lussac by heating mercury or silver cyanide
Hg(CN) 2 - Hg -f (CN) 2 .
Mercuric Cyanogen,
cyanide.
EXPT. 76. The mercuric cyanide for the experiment is prepared
' by dissolving mercuric oxide in aqueous hydrocyanic acid and con-
centrating the solution until it crystallises. Heat a few grams of
mercuric cyanide in a hard glass test-tube. A gas is evolved, which
may be ignited at the mouth of the tube, and burns with a purple
flame. A small quantity of a brown amorphous powder is left,
which is Jmown as paracyanogen^ and is a polymeride of cyanogen.
As cyanogen is soluble in water, it must be collected over mercury,
should this be necessary.
209 p
THEORETICAL ORGANIC CHEMISTRY
CHAP.
Cyanogen is a colourless gas with a peculiar smell and is
very poisonous. It burns with a purple flame, forming carbon
dioxide and nitrogen. Its density corresponds with the for-
mula (CN) 2 . Like chlorine, therefore, which in the free state
consists of molecules composed of two atoms, the molecule of
cyanogen is composed of two cyanogen groups, and the gas is
sometimes called di cyanogen. Cyanogen may be readily con-
densed, under a pressure of four atmospheres, to a liquid. Liquid
cyanogen boils at - 20 and solidifies at - 34. Cyanogen dissolves
readily in water ; but the solution gradually decomposes, form-
ing a brown flocculent precipitate, known as azulmic acid, whilst
ammonium oxalate is found in solution. The ammonium oxalate
arises from the hydrolysis of the cyanogen, a reaction which
resembles that which takes place when the alkyl cyanides are
hydrolysed (p. 153)
CN 4-
HjOH
/OH
NHo
CN
HJ
H:
HiOH
Cyanogen. Water.
+ NH 3
\OH
Oxalic acid. Ammonia.
Ammonium oxalate.
Just as methyl cyanide is obtained by dehydrating acet-
amide (p. 178), so, if oxamide is distilled with phosphorus
pentoxide, cyanogen is formed
CO.NH 2
CO.NH 2
Oxamide.
CN
= I
CN
Cyanogen.
+ 2H 2 0.
If cyanogen is passed into caustic potash solution, it is de-
composed into potassium cyanide, potassium cyanate, and water.
This reaction brings out clearly the similarity in the properties
of cyanogen and the halogens
(CN) 2 + 2KOH = KCN + KCNO + H 2 O.
Potassium Potassium
cyanide. cyanate.
C1 2 + 2KOH = KC1 + KC10 + H 2 0.
XV THE CYANOGEN COMPOUNDS 211
Hydrocyanic Acid, Prussic acid, occurs in certain plants ; it
is found in the leaves of the cherry laurel, in bitter almonds, and
in the kernels of cherry, peach, plum, and other stone fruits.
It is not usually present as the free acid in the plants named,
but in combination with glucose (grape-sugar) and benzaldehyde
(oil of bitter almonds, p. 469) in the form of a crystalline sub-
stance known as amygdalin. This crystalline compound is
termed x,glucoside, and is readily decomposed by dilute sulphuric
acid into its constituents. The process is one of hydrolysis
C 20 H 27 NO n + 2H 2 - C 7 H 6 + HCN + 2C 6 H 12 O 6 .
Amygdalin. Benzalde- Hydro- Glucose,
hyde. cyanic acid.
The same decomposition is produced by the action of an
enzyme (p. 105) known as emulsin, which is present in bitter
almonds. Emulsin acts only in the presence of water, so that
by grinding up bitter almonds with a little water, hydrolysis
takes place, and the smell of hydrocyanic acid, together with
that of benzaldehyde, is soon perceived. Dilute hydrocyanic
acid is usually made by distilling potassium ferrocyanide (see
below) with dilute sulphuric acid
2K 4 Fe(CN) 6 + 3H 2 SO 4 = 6HCN + K 2 Fe"Fe(CN) 6 + 3K 2 SO 4 .
Potassium Hydro- Potassium
ferrocyanide. cyanic acid, ferrous ferrocyanide.
The solution slowly decomposes, on standing, into ammonium
formate. The reaction is analogous to the formation of am-
monium oxalate from cyanogen (p. 210)
HCN + 2H 2 O = H.CO.ONH 4 .
Ammonium formate.
EXPT. 77. Preparation of Hydrocyanic Acid. As the acid vapours
are excessively poisonous, it is desirable to conduct the following
operation in a fume-cupboard. Ten parts of coarsely-powdered
potassium ferrocyanide are placed in a retort, and 7 parts of concen-
trated sulphuric acid, previously diluted with from 10-20 parts of
water, are added. The retort is connected with a well-cooled con-
denser and receiver. On distilling the mixture, aqueous hydrocyanic
collects in the receiver.
The pure anhydrous acid is prepared by distilling a mixture
of powdered potassium cyanide and moderately strong sulphuric
acid and passing the vapour, which is evolved, through U-tubes
P 2
212 THEORETICAL ORGANIC CHEMISTRY CHAP.
containing solid calcium chloride to remove the water. The
dry hydrocyanic acid vapour is then led into a U-tube surrounded
by ice, where it condenses to a colourless liquid.
Properties of Hydrocyanic Acid. Pure hydrocyanic acid
boils at 26 and solidifies at 14. It is inflammable, and burns
with a violet flame. It is excessively poisonous, even in the
minutest quantity, and the greatest care should be taken in pre-
paring and in using it.
Pure hydrocyanic acid is rapidly decomposed by strong
hydrochloric acid with a considerable rise of temperature, first
into formamide, and finally into formic acid and ammonium
chloride
HCN 4- H 2 - HCO.NHj.
Hydro- Formamide.
cyanic acid.
IICO.NH, + H 2 + HC1 = H.CO.OH -f NH 4 C1.
Formic acid.
Strong sulphuric acid probably effects the same change, but as
it decomposes formic acid at the same time into carbon monoxide
(p. 157), no formic acid is actually produced. This explains
why carbon monoxide alone is formed when either potassium
ferrocyanide or potassium cyanide is heated with strong
sulphuric acid. ?
As hydrocyanic acid yields formamide on hydrolysis, so the
reverse process may be effected by removing the elements of
water from formamide.
On distilling formamide with phosphorus pentoxide, hydro-
cyanic acid is produced
HCONH 2 -H 2 O = HCN.
When an alcoholic solution of hydrocyanic acid is reduced
with metallic sodium, methylamine is formed, just as methyl
cyanide is converted into ethylamine (p.2O4)
= CH 3 .NH 2 .
Methylamine.
The close analogy existing between the chemical behaviour
of hydrocyanic acid and the alkyl cyanides, indicates that the
acid is hydrogen cyanide, H.ClN, rather than a compound
having the isomeric form C:NH, corresponding to the class of
alkyl isocyanides, which will be referred to presently (p. 226).
xv THE CYANOGEN COMPOUNDS 213
The Metallic Cyanides. Potassium cyanide, KCN, and
sodium cyanide, NaCN, are two of the most important salts of
hydrocyanic acid. Potassium cyanide is formed by fusing
potassium ferrocyanide alone or with potassium carbonate _
I. K 4 Fe(CN) 6 = 4 KCN + FeC 2 + N 2 .
Potassium
cyanide.
2. K 4 Fe(CN) 6 + K 2 CO 3 = 5KCN + KOCN -f CO 2 4- Fe.
Potassium
cyanate.
Neither process is used commercially. The large quantity of
cyanide demanded for the extraction of gold from gold quartz
by the MacArthur-Forrest process (see below) has led to the
discovery of new and cheaper methods. When metallic sodium
is heated with sodium ferrocyanide, obtained in the coal-gas
manufacture, sodium cyanide is formed, and the whole of the
cyanogen is obtained as cyanide
Na 4 Fe(CN) 6 + N^ = 6NaCN 4- Fe.
The fused mass is then filtered from the finely-divided iron.
Another important method is to pass ammonia gas over a
heated or fused mixture of potassium carbonate and charcoal.
2NH 3 4- K 2 CO 3 + C = 2KCN + sH 2 O.
A third method is to pass ammonia over heated sodium. Sodium
amide, or sodamide, is formed, which is fused and run on to
red-hot charcoal. The product is sodium cyanide. The
formation of sodium cyanide actually occurs in two stages,
sodium cyanamide being first formed (p. 339). The following
equations express these reactions (see p. 340)
2NH 3 + Na 2 = 2NaNH 2 + H 2
Sodamide.
2NaNH 2 + C = CN. NNa 2 + 2H 2
Sodium cyanamide.
Sodium cyanide.
It has long been known that alkalis when heated with carbon
in the presence of free nitrogen form alkali cyanides. The
formation of cyanides in the products from blast furnaces is ex-
plained in this way. Attempts have been recently made to
produce cyanides from the nitrogen of the air by passing air
over fused calcium carbide. Calcium carbide, produced from
214 THEORETICAL ORGANIC CHEMISTRY CHAP.
a mixture of powdered limestone and coke, heated to the high
temperature of the electric furnace (p. 259), combines with
nitrogen and forms mainly calcium cyanamide. Barium
carbide, on the other hand, yields barium cyanide, from which
the alkali salts may be prepared
BaC 2 -r N 2 = Ba(CN) 2 .
Barium carbide. Barium cyanide.
About 10,000 tons of cyanide are produced annually, of
which about one-third is used in the Transvaal for gold
extraction.
Other methods are by the action of nitric acid on ammonium
thiocyanate (p. 222), giving hydrocyanic acid, which is passed
into potash solution and evaporated (Gelee's method), and the
distillation of beet-root residues, which yield a certain quantity
of hydrocyanic acid (Bueb). The nitrides of silicon and
aluminium which are formed at the temperature of the electric
furnace yield potassium cyanide on heating with potash.
In addition to the application of potassium and sodium cyan-
ides to gold extraction, potassium cyanide is employed in the
preparation of solutions of gold and silver for electroplating.
The cyanides of these metals form soluble double salts with
potassium cyanide (see below). The alkali cyanides are very
soluble in water, and the solutions undergo gradual decomposi-
tion. The action goes on more rapidly on boiling, ammonia
being evolved and formates of the alkalis produced. Potassium
and sodium cyanide are readily decomposed by the inorganic
and organic acids, and even by so weak an acid as carbonic
acid, giving off hydrocyanic acid. The smell which potassium
cyanide emits, when exposed to the air, is attributed to the
action of carbon dioxide. Hike hydrocyanic acid, the alkali
cyanides are strong poisons.
Detection of Hydrocyanic Acid and Cyanides. Owing to the
poisonous character of hydrocyanic acid and the soluble cyanides, the
detection of the presence of these substances is a matter of importance.
The volatility and peculiar smell of hydrocyanic acid render its separa-
tion and detection a comparatively simple matter. If nitric acid is
added to a soluble cyanide and warmed, hydrocyanic acid is evolved.
A drop of silver nitrate solution on a watch-glass or glass rod in con-
tact with the vapour becomes turbid from the formation of silver
xv THE CYANOGEN COMPOUNDS 215
cyanide. In the same way a drop of ammonium sulphide in contact
with hydrocyanic acid vapour is converted into ammonium sulpho-
cyanide, NH 4 CNS, If the liquid is somewhat concentrated by warming
and acidified with dilute hydrochloric acid, a blood-red stain is pro-
duced on the addition of a drop of ferric chloride (p. 223). A common
method of detecting hydrocyanic acid is to boil the liquid, which is
first made alkaline with potash, with a few drops of ferrous sulphate
and a drop of ferric chloride solution. On acidifying the solution, a
precipitate of Prussian blue is formed. If the cyanide is mixed with
other substances which would interfere with the reaction, it is first
separated by distilling the mixture with the addition of a little non-
volatile organic acid like tartaric acid. The distillate which contains
the hydrocyanic acid is then submitted to the above tests.
The Double Cyanides. When a solution of potassium or
sodium cyanide is added to the solution of a metallic salt, the
metal (with the exception of the alkalis, alkaline earths, and
mercury, which form soluble cyanides) is precipitated in the
form of the insoluble cyanide. A further addition of potassium
cyanide produces a solution of the metallic cyanide. A double
cyanide is formed. If a mineral acid is now added to the solution,
hydrocyanic acid is evolved, and the insoluble cyanide of the
metal is reprecipitated. In the case of silver, the addition of
potassium cyanide to a solution of silver nitrate produces a pre-
cipitate of silver cyanide, AgCN, very similar to silver chloride
in appearance, which redissolves on the further addition of
potassium cyanide, with the formation of a double cyanide,
AgCN.KCN. If nitric acid is now added, silver cyanide is re-
precipitated, and hydrocyanic acid is evolved
AgCN.KCN + HNO 3 = AgCN + HCN + KNO 3 .
Potassium Silver
silver cyanide. cyanide.
This reaction is utilised for the quantitative analysis of potassium
cyanide. A standard solution of silver nitrate is added to the cyanide
until a precipitate is just formed. At this point the amount of silver
solution added corresponds to the formation of the double cyanide of
silver and potassium ; for any additional amount of silver nitrate will
decompose some of the potassium cyanide and form a precipitate.
Hence, each atom of silver taken represents two molecules of potassium
cyanide.
The deposition of silver and gold in electroplating with the double
cyanides is explained by the breaking up of ihe compound into the
2i6 THEORETICAL ORGANIC CHEMISTRY CHAP.
positive K ions and negative Ag(CN) 2 ions. The K ions reduce ;i.e
double cyanide at the kathode, and silver is deposited
The Ag(CN) 2 ions dissolve fresh silver from the anode, and forui
2AgCN, which passes into solution as the double cyanide
K (cathode)
+ KAg(CN) 2
= (Ag) + 2KCN
Ag(CN) 2 (anode)
+ Ag
=2AgCN
= 2KAg(CN) 2 .
For this reason the double salts are sometimes regarded as salts
radicals Ag(CN) 2 and Au(CN) 2 .
In the extraction of gold, which occurs in a fine state of division in
gold-bearing rocks, and in residues or tailings, a very dilute solution of
potassium or sodium cyanide is used in presence of atmospheric oxygen,
or other oxidising agent
4KCN + 2Au + H 2 O + O = 2KAu(CN) 2 + 2KOH.
The gold is then deposited from the solution by electrolysis or by the
addition of metallic zinc
2KAu(CN) 2 + Zn = K. 2 Zn(CN ) 4 + 2 Au.
Nearly 2 million ounces of gold are extracted by this process annually.
There is another class of double cyanides in which the
metallic cyanide of the heavy metal is not precipitated from
solution by a mineral acid. The formation and properties of
this class of double cyanides may be illustrated by the following
experiment.
EXPT. 78. Make a fresh solution of ferrous sulphate and add
potassium cyanide solution until there is no further brown precipitate
of cyanide of iron ; boil and filter if necessary. A yellow solution is
obtained, which, after cooling, is to be divided into two portions. If
dilute hydrochloric acid is added to one portion, there is no pre-
cipitate of the original cyanide. If strong hydrochloric acid is added
to the second portion, a white precipitate is thrown down. The
yellow solution contains potassium ferrocyanide, and the addition of
strong hydrochloric acid to the second portion precipitates hydro -
ferrocyanic acid. The reactions which occur are expressed as
follows :
1. 2KCN + FeSO 4 = Fe(CN) 2 + K,SO 4 .
Ferrous cyanide.
2. Fe(CN) 3 + 4KCN - K 4 Fe(CN) 6 .
Potassium ferrocyanide.
3. K 4 Fe(CN) 6 + 4HC1 = H 4 Fe(CN) 8 + 4KC1.
Hydroferrocyanic
acid.
;
THE CYANOGEN COMPOUNDS 217
A similar reaction takes place when a solution of a cobalt salt is
boiled with excess of potassium cyanide and a few drops of acid.
Potassium cobalticyanide, K 3 Co(CN) 6 , is formed, from which cobalt
cyanide is not reprecipitated by acids. The separation of cobalt from
nickel depends upon this reaction. Nickel forms a double cyanide of
the first, cobalt of the second class, so that after boiling the double
cyanides of the two metals, and then acidifying, it is only the nickel
which is precipitated as cyanide.
It therefore appears that in the second class of double cyanides
the metallic cyanide forms an integral part of the acid. Hydro-
ferrocyanic acid, H 4 Fe(CN) 6 , contains the acid radical or
negative ion l ferrocyanogen, Fe(CN) 6 . Hydroferrocyanic acid
is a strong acid, and forms a series of salts, some of which, like
the zinc (white), copper (red), and ferric (Prussian blue) salts
are insoluble, and have a characteristic colour. They are ob-
tained by adding a solution of a salt of the particular metal to
a solution of potassium ferrocyanide. The most important salts
are potassium and sodium ferrocyanides.
Potassium Ferrocyanide, or Yellow prussiate of potash,
K 4 Fe(CN) 6 4- 3H L ,O, is the starting-point in the preparation of
nearly all the cyanogen compounds. Potassium ferrocyanide
was formerly manufactured by fusing in an iron pot, nitrogenous
animal refuse, such as horns, hoofs, blood, leather scraps, &c.,
with potassium carbonate. The mass is kept stirred during the
operation, and, after cooling, is lixiviated with water. On
evaporation, large tabular yellow crystals of potassium ferro-
cyanide are deposited. A satisfactory explanation of the
reaction has not yet been offered.
The salt is now obtained almost exclusively from coal gas. The
cyanogen derived from the coal, probably in the form of hydrocyanic
acid, is absorbed by alkaline ferrous hydrate before passing to the
purifiers, and is converted into sodium ferrocyanide
Na 4 Fe(CN) 6 +ioH 2 O.
In other gas-works it passes to the iron oxide of the "purifiers," and is
converted into insoluble iron ferrocyanide. Some thiocyanate (p. 222) is
also formed. The spent oxide is boiled with lime, and the soluble calcium
ferrocyanide, which is formed, is extracted and converted into the sodium
or potassium salt by treatment with an alkaline carbonate.
1 Vide J. Walker, Introduction to Physical Chemistry, chap. xxvi. p. 296
fMacmillan).
2i8 THEORETICAL ORGANIC CHEMISTRY CHAP.
Both sodium and potassium ferrocyanide, as well as certain
other salts, exist in two isomeric forms which are distinguished
by difference of colour and crystal habit. They may easily be
converted into one another, and the difference is therefore
attributed to a difference in space arrangement (Briggs).
When heated, potassium ferrocyanide first loses its water ot
crystallisation and becomes colourless ; it then blackens and
fuses, forming potassium cyanide and iron carbide (p. 213).
Ferric salts added to a solution of the ferrocyanide give a pre-
cipitate of ferric ferrocyanide or Prussian blue
Fe'" 4 [Fe(CN) G ] 3 ._
Ferric ferrocyanide, or Prussian blue.
When chlorine is passed into a solution of potassium ferro-
cyanide, the latter turns a deep red, and on evaporation red
crystals of potassium ferricyanide, or red prussiate of potash,
K 3 Fe(CN) 6 , are deposited
2K 4 Fe(CN) 6 + C1 2 = 2K 3 Fe(CN) 6 -f 2KC1.
Potassium ferricyanide.
EXPT. 79- The above reaction also takes place on the addition of
bromine. Add bromine water in excess to a solution of potassium
ferrocyanide and boil off the excess of bromine. The solution may
be evaporated, when red crystals of the ferricyanide are obtained. If
a drop of ferric chloride is added to the solution of the ferricyanide,
no precipitate of Prussian blue is formed ; but the solution turns
dark brown. The addition of a ferrous salt throws down a blue
precipitate, known as TurnbulFs blue, or ferrous ferricyanide,
Fe" 3 [Fe(CN) 6 ] 2 .
Potassium ferricyanide is occasionally used in alkaline solu-
tion as a mild oxidising agent. It decomposes the alkali and
liberates oxygen, forming at the same time potassium ferro-
cyanide, according to the following equation
2K 3 Fe(CN) 6 -f- 2KOH =. 2K 4 Fe(CN) 6 + H 2 O + O.
Potassium Potassium
ferricyanide. ferrocyanide.
When potassium ferrocyanide is heated with moderately
strong nitric acid, and then neutralised with caustic soda, sodium
nitroprusside, Na 2 NOFe(CN) 5 + 2H 2 O, crystallises out on evapo-
ration in the form of ruby red crystals. Sodium nitroprusside
solution is used as a test for sulphur. The sulphur, when present
in the form of a soluble sulphide in alkaline solution, produces a
xv THE CYANOGEN COMPOUNDS 219
deep violet coloration on the addition of sodium nitroprusside
solution (p. 19).
EXPT. 80. Heat together on the water-bath for half an hour 4
grams of powdered potassium ferrocyanide and 4 c.c. of strong nitric
.acid, previously diluted with 5 c.c. of water. Cool the mixture, and
add caustic soda solution until alkaline. Add a few drops of the
solution to a test-tube of water, and then a drop of ammonium
sulphide. A deep violet coloration is produced.
Cyanogen Chlorides. When chlorine is passed into hydro-
cyanic acid, a colourless liquid is produced, which has the
formula CNC1, and is known as liquid cyanogen chloride
HCN + C1 2 = CNC1 + HCi.
It polymerises on standing, forming a solid, C 3 N 3 C1 3 , known as
solid cyanogen chloride or cyanuric chloride.
When treated with potash the liquid cyanogen chloride is
converted into potassium cyanate, and the solid into potassium
cyanurate
CNC1 + 2KOH - CNOK + KC1 + H 2 O.
Cyanogen Potassium
chloride. cyanate.
C 3 N 3 C1 3 + 6KOH = C 3 N 3 O 3 K 3 + 3KC1 + 3 H 2 O.
Cyanuric Potassium
chloride. cyanurate.
Cyanic and Cyanuric Acids. Cyanuric acid, C 3 N 3 O 3 H 3
+ 2H 2 O, is obtained by a variety of reactions, such as heating
urea (see below), alone or in presence of chlorine
3CON 2 H 4 = C S N 3 O 3 H 3 + 3NH 3 .
Urea Cyanuric acid.
^6CON 2 H 4 + sC! 2 = 2C 3 N 3 3 II 3 + 4NH 4 C1 + 2HC1 + N 2 ,
or, it may be obtained by heating in a sealed tube a solution
of carbonyl chloride (in an inert solvent like benzene) with
ammonia
3COC1 2 + 3NH 3 = C 3 N 3 O 3 H 3 + 6HC1.
It is a very stable substance and dissolves unchanged in strong
sulphuric acid. When distilled and the vapours cooled in a
freezing mixture, it is converted into liquid cyanic acid, CNOH,
which is an extremely unstable substance ; for, when warmed to
the ordinary temperature, it polymerises with explosive violence,
and forms a compound known as cyamelide, which undergoes
slow transformation into cyanuric acid.
THEORETICAL ORGANIC CHEMISTRY CHAP.
EXPT. 8 1. The conversion of cyanuric acid into cyanic acid and
its reconversion into cyanuric acid was discovered by Wohler, and
offered the first example both of polymerism and of polymerisation
(p. 134). The experiment is readily performed as follows : Place a
few grams of powdered cyanuric acid, which must be previously
dehydrated on the water-bath, in a small retort made by blowing a
small bulb on the end of a piece of hard, wide glass tubing. The
open end of the tube dips to the bottom of a test-tube, which is
surrounded by a freezing mixture. The cyanuric acid is heated until
it has nearly all disappeared from the bulb. The test-tube is then
removed from the freezing mixture. It contains a little liquid cyanic
acid. After being exposed to the temperature of the air for a few
minutes, it polymerises with a succession of sharp cracks.
Although cyanic acid itself rapidly polymerises, many of its
salts are perfectly stable substances.
Potassium Cyanate, CNOK, is obtained by oxidising potas-
sium cyanide. This may be effected by fusing the cyanide with
some reducible metallic oxide, like lead or manganese peroxide,
or by adding permanganate solution to a solution of potassium
cyanide. The use of potassium cyanide as a reducing agent
for metallic oxides depends upon this reaction
KCN + O = KOCN.
Ammonium Cyanate, CNO(NH 4 ), may be prepared by bring-
ing together ethereal solutions of ammonia and cyanic acid,
cooled in a freezing mixture. It forms a white crystalline powder.
If the solid, or a solution in water or alcohol is heated, an " intra-
molecular" rearrangement, or change in the positions of the
atoms occurs, and the ammonium cyanate is transformed into
urea. The nature of tbis change will be discussed more^ully
later (p. 337). In the preparation of urea from potassium
cyanate, it is only necessary to add ammonium sulphate to the
solution of the cyanate in water and evaporate the mixture to
dryness. The ammonium cyanate, which is first formed, is
thereby converted into urea, which may be extracted from the
dried mass with alcohol. The alcohol dissolves the urea, but
not the potassium sulphate. The urea crystallises from the
alcoholic solution
2CNOK -f (NH 4 ) 2 SO 4 - 2CNO.NH 4 + K 2 SO 4 .
Ammonium
cyanate.
CNO.NH 4 = CO(NH 2 ) 2 .
Urea."
THE CYANOGEN COMPOUNDS
EXPT. 82. Preparation of Potassium Cyanate and Urea. Heat 50
grams of pure potassium cyanide in a small iron dish over a large
Bunsen burner, and, without waiting for the cyanide to fuse, add
gradually 140 grams of red lead. The addition of the lead produces
sufficient heat to melt the contents of the dish. When the red lead
has been added, and the mixture fuses quietly without effervescence,
pour it out on to a cold slab or iron tray
4 KCN + Pb a O 4 = 4CNOK + 3?b.
Powder up the mass, when cold, and separate the potassium cyanate
from lead and other impurities by leaving the mass in contact with
about 200 c. c. of water for an hour. The solution now contains the
potassium cyanate. Filter, and add to the filtrate 50 grams of
ammonium sulphate dissolved in water, and evaporate the mixture to
dryness on the water-bath. Boil up with about 50 c.c. of methylated
spirit on the water-bath, and filter into a crystallising dish. Long
prismatic crystals of urea deposit on cooling.
Mercury Fulminate, C 2 N 2 O 2 Hg + H 2 O, is formed by the
action of alcohol on a solution of mercuric nitrate in nitric acid.
EXPT. 83. Preparation of Mercury Fulminate. Three grams of
mercury are dissolved in 28 c.c. of strong nitric acid contained in a
large flask. The solution is then somewhat cooled, and 43 c.c. of
90 per cent, alcohol are added in two instalments. When the action,
which is sometimes very vigorous, has subsided, and the liquid has
cooled, colourless needles of mercury fulminate are deposited.
Mercury fulminate was formerly regarded as a nitro-derivative
of methyl cyanide ; but as it decomposes quantitatively with
strong hydrochloric acid into formic acid and hydroxylamine
and can be prepared from chloroformoxime, C1CH:NOH, and
nitroformoxime, or methyl nitrolic acid, NO 2 CH:NOH, it must
be regarded as the mercury salt of carbyloxime, and is
therefore isomeric with mercury cyanate
(C:NO),Hg.
Mercury fulminate.
The decomposition into hydroxylamine is represented as
follows
(CNO) 2 Hg + 2HC1 + 4H 2 O = 2NH*OH 4- 2liCO 2 H + HgCl,.
Mercury fulminate.
222 THEORETICAL ORGANIC CHEMISTRY CHAP,
The formation of fulminic acid from alcohol is supposed to
occur in the following series of steps (Wieland)
CH 3 .CH,>OH ->- CH 3 .CHO ->- CH:NOH.CHO ->
CHrNOH.COOH ->- C(NO 2 ):NOH.COOH ->- HC(NO 2 ):NOH ->
C:NOH + HNO a
Mercury fuminate, when dry, is a powerful explosive, and
is used as a detonator. The fulminate is placed in a metal cup
in contact with the explosive, and is fired either by a fuse, by
electricity, or by a sharp blow.
Other salts of fulminic acid are known, but the free acid has
not been isolated. The silver salt, CNOAg, was analysed by
Liebig (1823), and found to have the same composition as
Wohler's silver cyanate and cyanurate (p. 219). These three
salts constituted the first example of substances of the same
composition but possessing distinct properties, to which
Berzelius applied the term " isomerism."
Thiocyanic Acid and Thiocyanates. Thiocyanic acid, or
sulphocyanic acid, CNSH, is separated from its salts by the
addition of a mineral acid and is a gas which may be condensed
to a liquid in a freezing mixture. The liquid has an acrid and
penetrating smell. When removed from the freezing mixture it
quickly polymerises like cyanic acid. Ammonium and potassium
thiocyanate, or sulphocyanate, have a technical application in
cotton dyeing and printing. The potassium salt is obtained by
fusing potassium cyanide with sulphur
KCN + S = KCNS.
The ammonium salt is prepared by heating carbon bisulphide
and ammonia under pressure. Ammonium thiocarbamate is
thereby formed
NH 2
CSo + 2NH 3 = SC<
\SH.NH 3 .
Ammonium thiocarbamate.
When subjected to the action of steam, thiocarbamate is
decomposed into ammonium thiocyanate and hydrogen
sulphide
/NH 2
SC< = CNS(NH 4 ) + H 2 S.
X SHNH 3
Ammonium
thiocyanate.
THE CYANOGEN COMPOUNDS
A certain quantity of ammonium thiocyanate is obtained from
gas liquor and "spent oxide," where it is probably formed by the
action of sulphur upon ammonium cyanide
NH 4 CN + S = NH 4 SCN.
The soluble thiocyanates are used as a delicate test for iron in
the form of ferric salt. When a drop of ferric chloride is added
to a solution of potassium or ammonium thiocyanate, an intense
red coloration is produced. The colour is due to a compound,
resembling potassium permanganate in appearance, which has
the formula Fe(CNS) 3 .9KCNS + 4H 2 O. The colour disappears
if the iron is reduced to the ferrous state.
Mercuric thiocyanate is obtained by adding mercuric chloride
to a solution of potassium thiocyanate. The insoluble powder
when filtered and dried takes fire on ignition, and forms an ex-
ceedingly voluminous ash. When moulded into pellets, dried,
and ignited, it produces long snake-like tubes of ash known as
" Pharaoh's serpents." The vapour of the burning substance
contains mercury and is poisonous.
Esters of the Cyanogen Acids. Hydrocyanic, cyanic,
cyanuric, and thiocyanic acid form a series of esters. Each acid,
however, gives rise to, not one, but two isomeric esters, the
existence of which is accounted for by differences of structure,
which will be presently discussed.
Nomenclature of the Cyanogen Esters. It will be con-
venient to give at once the names and structural formulas of
the series of esters above referred to, taking the methyl esters
by way of illustration. From hydrocyanic acid are derived
methyl cyanide and methyl isocyanide.
As the alkyl cyanides, like hydrocyanic acid itself, are con-
verted on hydrolysis into the fatty acids (p. 154), they are
sometimes designated as the nitriles of the corresponding
acids.
Hydrocyanic acid is the nitrile of formic acid, methyl cyanide
of acetic acid, ethyl cyanide of propionic acid, &c.
H CH 3 C 2 H 5
I I I
CiN CiN CiN.
Hydrogen cyanide, or Methyl cyanide, or Ethyl cyanide, or
Formonitrile. Acetonitrile. Propionitrile.
224 THEORETICAL ORGANIC CHEMISTRY CHAP.
The alkyl isocyanides, which are converted into alkylamines
on hydrolysis, are also termed alkyl carbamines.
Methyl isocyanide is also known as methyl carbamine-
CH 3
NIC
Methyl isocyanide, or Methyl carbamine.
From cyanic acid are derived methyl cyanate and isocyanate
or carbimide
CH 3 CH,
I !
HOCN O.CjN N:C:O
Cyanic acid. Methyl cyanate. Methyl isocyanate.
Methyl carbimide.
From cyanuric acid, in the same way, methyl cyanurate and
isocyanurate are derived, to which the following structural
formulae have been assigned
C(OCH 3 ) CO
HAQN, N |fV
Cyanuric acid.
(CH 3 O)C'i JC(OCH 3 ) OCl JCO
N N(CH 3 )
Methyl cyanurate. Methyl isocyanurate.
Finally, thiocyanic acid gives rise to two esters, methyl
thiocyanate and methyl isothiocyanate. The latter is also
known as methyl mustard oil, seeing that the oil obtained from
mustard seed belongs to this class of compounds
CH 3 CH 3
HSCN S.CiN N:C:S
Thiocyanic acid. Methyl thiocyanate. Methyl isothiocyanate, or
Methyl mustard oil.
Attention is called to the fact that all the iso-esters contain
the carbon of the alkyl group linked to nitrogeti.
The Alkyl Cyanides or Nitriles. Certain methods of pre-
paration of the cyanides have already been described. The alkyl
cyanides may be obtained by the action of potassium cyanide
in aqueous alcoholic solution upon the alkyl iodide (p. 83)
CH 3 I + KCN = CH 3 CN + KI,
or by distilling the amides with phosphorus pentoxide (p. 178).
THE CYANOGEN COMPOUNDS
225
Acetamide is converted in this way into methyl cyanide
CH S .CO.NH 2 - H 2 = CHjCN.
EXPT. 84. Preparation of Methyl Cyanide or Acetonitrile.Wui
together 10 grams of dry acetamide and 15 grams of phosphorus
pentoxide in a small retort or distilling flask attached to a condenser
and receiver. Heat the mixture over a small flame. Collect the
liquid which distils, and add a few c.c. of water and then solid
potassium carbonate until no more dissolves. The upper layer of
liquid is removed and redistilled over fresh phosphorus pentoxide.
Methyl cyanide boils at 82.
The lower members of the series are colourless liquids with a
strong but not unpleasant smell. They are soluble to some ex-
tent in water. The higher members are less soluble in water,
and are solid crystalline substances.
The most important characteristics of the alkyl cyanides are
their rapid conversion into fatty acids on hydrolysis with
mineral acids or alkalis, and their reduction to the corresponding
amine by the action of sodium on the alcoholic solution of the
cyanide. Methyl cyanide is converted into ethylamine in the
same way that hydrocyanic acid is reduced to methylamine
( P . 212)
CH 3 CiN + 2H 2 = CH s .CH 2 .NHj.
Ethylamine.
The formation of acids and amines from the cyanides clearly
indicates that the carbon of the cyanogen group is directly linked
to the carbon of the alkyl group.
TJnsaturated Groups. The many reactions into which the alkyl
cyanides enter cannot be discussed here in detail. They resemble the
aldehydes and ketones in the variety of derivatives to which they give
rise. The resemblance is without doubt connected with the ketone group,
OO, in the one case, and the cyanogen group, C : N, in the other.
In both groups carbon is represented as linked to a second element by
more than one bond. The groups are termed umaturated because they
are capable of taking up additional atoms. They readily unite with
hydrogen : the aldehydes and ketones form alcohols in this manner ;
*.the cyanides yield primary amines. The elements of water, alcohol,
hydrogen sulphide, the halogen acids, hydroxylamme, and the halogens
all readily combine with the alkyl cyanides, and form additive com-
pounds in much the same way that hydrocyanic acid, sodium bisulphite,
and ammonia combine with aldehydes (p. 129). A multiple linkage,
similar to that which exists in the groups GO and C = N, is found to
occur between two carbon atoms in the compounds known as un-
Q
226 THEORETICAL ORGANIC CHEMISTRY CHAP.
saturated hydrocarbons and their derivatives, which are described in
Chap. XVII, p. 245. A further resemblance may be pointed out. The
presence of these groups gives to the organic compound in which they
occur a more strongly acid character. Reference to this point will be
again brought forward (p. 345).
For the present it is only necessary to mention the acid character of
the fatty acids, cyanic acid, and acetoacetic ester. In all these examples
the hydrogen of the hydroxyl group is replaceable by a metal
.CH.COOC 2 H 5
)H \)H X OH.
Formic acid Cyanic acid. Acetoacetic ester.
(Alternative formula, p. 329.)
The Alkyl Isocyanides, or Carbamines, are isomeric with
the cyanides. They are formed by the action of chloroform and
alcoholic potash on the primary amines (p. 201).
Methyl isocyanide is prepared by distilling a mixture of
methylamine, chloroform, and alcoholic potash
CH 3 N|H 2 [ + CiHCls + sKOH = CH 3 NC + sKCl + sH 2 O.
m Methyl
isocyanide.
The isocyanides are also obtained by distilling a mixture of alkyl
iodide and silver cyanide
CHsJl + AgiNC = CH 3 NC + Agl.
Methyl
isocyanide.
It would appear from this reaction that silver cyanide is differently
constituted from the potassium salt, which gives under similar condi-
tions the normal cyanide (p. 224) ; or, it may be that the higher tempera-
ture required to effect the decomposition in the case of the silver
compound may produce the change of structure. It is noteworthy that
although the amount of cyanide greatly predominates, some isocyanide
is always formed when a mixture of alkyl potassium sulphate and
potassium cyanide is distilled
(CH 3 CN
CHJoVSOsK'T KlCN * J + K 2 SO 4 .
tCH 3 NC
Methyl cyanide,
and isocyanide.
This fact would indicate that other conditions than the structure of
the metallic cyanide, determine the formation of one or the other isomer.
It is generally agreed that the metallic cyanides are isocyanides, whilst
xv THE CYANOGEN COMPOUNDS 227
hydrocyanic acid is regarded as a nitrile, though the evidence is
not conclusive.
The isocyanides are liquids with an intolerable smell. The
boiling-points are lower than those of the corresponding cyanides.
They are hydrolysed by hydrochloric acid into an amine and
formic acid, the reaction probably occurring in two steps.
In the first, the alkyl formamide is produced, which then
decomposes into amine and formic acid
I. CH 8 NC+ H. 2 O = CHjNH.CHO.
Methyl formamide.
2. CH 3 NH.CHO + H 2 O = CH 3 NH 2 + HCO.OH.
Methylamine. Formic acid.
Both the mode of formation from, and conversion into, the
primary amine indicate that in the alkyl isocyanides, nitrogen
is directly united to carbon of the alkyl group. As to whether
the group NC contains bivalent carbon, as some maintain, or
quadrivalent carbon, as others think, must be left an open
question
R_N=C or R N=C.
The Alkyl Cyanates and Isocyanates (Carbimides)> The
alkyl cyanates are prepared by acting on cyanogen chloride with
sodium alcoholate. Methyl alcoholate gives methyl cyanate
CNjCl +" NalOCHs = NC. OCH 3 .
Methyl cyanate.
They are colourless ethereal smelling liquids, which have not
yet been obtained in the pure state ; for they rapidly polymerise
and pass into alkyl cyanurates (see next page).
The isocyanic esters are much more readily obtained. They
were originally prepared by Wurtz (1854) by distilling an alkyl
potassium sulphate with potassium cyanate
CH 8 |OSO 8 K"+"KjNCO = CH 3 N:CO + K 2 SO 4 .
Potassium methyl Methyl
sulphate. isocyanate.
A more convenient method is to heat a mixture of silver
cyanate and alkyl iodide
CH 3 il TA^NCO = CH 3 N:CO + Agl.
Q2
228 THEORETICAL ORGANIC CHEMISTRY CHAP.
Another method is to warm the acyl azoimide (obtained from
the acyl chloride and sodium azoimide) which loses nitrogen,
thus
CH 3 CO.N 3 -> CH 3 N:CO + N 2 .
Acetyl azoimide gives methyl isocyanate.
The isocyanic esters are volatile liquids with a powerful and
suffocating odour. Like the cyanic esters they polymerise on
standing, forming isocyanuric esters. The most interesting
property of the isocyanic esters is their conversion into amines
on boiling with alkalis (p. 198)
CH 3 N:CO + H 2 = CH 3 NH 2 + C0 2 .
Methyl isocyanate. Methylamine.
They also unite with amino- and hydroxyl groups and are used as
reagents for these groups, thus
R. OH + CH 3 N :CO = RO. CO. NHCH 3
R.NH 2 + CH 3 N:CO = R.NH.CO.NHCH 3 .
In the first case a substance known as a urethane is obtained (p. 336)
and in the second a derivative of urea.
The Alkyl Cyanurates and Isocyanurates are formed by
the polymerisation of the corresponding cyanates and isocyanates.
The alkyl cyanurates are also obtained by acting upon cyanuric
chloride with sodium alcoholate
C 8 N 3 C1 3 + 3NaOCH 3 - N 3 C 3 O 3 (CH 3 ) 3
Methyl cyanurate.
The Alkyl Thiocyanates and Isothiocyanates. The thio-
cyanates are obtained by the action of an alkyl iodide on potas-
sium thiocyanate. Methyl iodide gives methyl thiocyanate-
CNSJK'T "liCH 3 = CNSCH 3 + KI.
Methyl
thiocyanate.
The structure of the thiocyanates is determined by their re-
duction to mercaptan and amine
CH 3 SCN + 3H 2 = CH 3 SH + CH 3 NH 2 ,
and by their oxidation to sulphonic acids
CH 3 S.CN > CH 3 .S0 3 H.
XV THE CYANOGEN COMPOUNDS 229
On prolonged heating the alkyl thiocyanates are converted
into the isomeric isothiocyanates.
The Mustard Oils, or Alkyl isothiocyanates, are most easily
obtained by the action of carbon bisulphide on the primary
amines. The method is analogous to the formation of ammonium
thiocyanate (p. 222). The compound first formed is the alkyl-
amine salt of an alkyl thiocarbamate
CS 2 + 2NH 2 CH 3 = CS<
Methylamine methyl thiocarbamate.
If this compound is now treated with mercuric chloride,
hydrogen sulphide is removed, and the thiocarbamate splits up
into the mustard oil and primary amine
/NjHjCHs
SC< -,---' = SC:NCH 3 + NH 2 .CH 3 + IIS.
NSH;NH 2 .CH 3
Methyl mustard oil.
The above reaction is occasionally used as a test for primary
amines (p. 201).
QUESTIONS ON CHAPTER XV
1. How is cyanogen most easily prepared? Compare cyanogen and
chlorine.
2. What products are obtained by the hydrolysis of cyanogen, hydro-
cyanic acid, methyl cyanide, methyl isocyanide, and methyl isocyanate ?
What reagent is required in each case ?
3. Describe a method for preparing potassium cyanide and sodium
cyanide. In what manner has atmospheric nitrogen been utilised in
the preparation of cyanides?
4. How is hydrocyanic acid detected? Describe a quantitative
method for analysing potassium cyanide.
5. What is meant by a dotible cyanide ? How may the two classes of
double cyanides be distinguished ?
6. How is yellow prussiate of potash converted into the red prussiate,
and vice versa ?
7. Describe and explain the formation of urea from potassium
cyanide.
230 THEORETICAL ORGANIC CHEMISTRY CH. xv
8. How may the following compounds be obtained from potassium
ferrocyanide : carbon monoxide, hydrocyanic acid, potassium cyanide,
hydroferrocyanic acid, and cyanogen ?
9. What is meant by the term mustard oil? How are the mustard
oils obtained ?
10. Discuss the structure of isomeric compounds of the formula
C 3 H 5 N (cyanide and isocyanide).
11. Explain the meaning of the term imsaturated group. Illustrate
your answer by reference to acetaldehyde and methyl cyanide.
12. Discuss the structure of hydrocyanic acid and the metallic
cyanides.
13. Give an account of the preparation and properties of cyanogen gas.
Why is cyanogen considered to be analogous to chlorine, and in what
respects does it differ from chlorine ?
14. How is potassium ferrocyanide manufactured ? How would you
prepare from potassium ferrocyanide (a) a dilute solution of prussic
acid, (b] urea, (c] carbon monoxide ?
15. How do you account for the different action of strong and
dilute sulphuric acid on potassium ferrocyanide ?
1 6. Starting from mercury and potassium ferrocyanide, how would
you prepare mercuric cyanide ? Describe its properties, and compare
them with those of potassium cyanide.
17. Describe the mode of preparation and properties of cyanic and
cyanuric acids. Point out the relation between the two substances.
1 8. Explain by examples the isomerism of carbamines and nitriles.
How is each class of bodies prepared? How can the formulae
ascribed to each be proved to be correct ?
19. What is a nitrile ? How can it be obtained from an ammonium
salt, and what transformation does it undergo when hydrolysed and
when reduced by nascent hydrogen ?
CHAPTER XVI
THE ALKYL COMPOUNDS OF PHOSPHORUS,
ARSENIC, AND SILICON, AND THE ORGANO-
METALLIC COMPOUNDS
The Phosphines. The alkyl compounds of phosphorus, which
correspond in composition to the amines (p. 198), are known as
phosphines. They may be regarded as derivatives of ordinary
phosphine or hydrogen phosphide, PH 3 . The methyl derivatives
have the following formulae
PH 3 CHjPH, (CH 3 ) 2 PH (CH 3 ) 3 P
Phosphine. Methyl Dimethyl Trimethyl
phosphine. phosphine, phosphine,
b. p. - 14. b. p. 25. b. p. 40 42.
Quaternary phosphonium compounds iodides and hydroxides
are also known
(CH 3 ) 4 PI (CH 3 ) 4 P.OH.
Tetramethyl phosphonium iodide. Tetramethyl phosphonium hydroxide.
By the action of an alkyl iodide on phosphine, PH 3 , only
tertiary alkyl phosphines are formed. In order to .obtain the
primary and secondary compounds, the alkyl iodide is heated
with phosphonium iodide in the presence of zinc oxide. Mono-
and di-methyl phosphine are formed according to the following
equations
2CH 3 I + 2PH 4 I + ZnO = 2CH 3 ,PH 2 .HI + ZnI 2 + H 2 O.
Methyl phosphine
hydriodide.
2CIT 3 I + PH 4 I + ZnO = (CH 3 ) 2 PH.HI + ZnI 2 + H 2 O.
Dimethyl phosphine
hydriodide.
231
232 THEORETICAL ORGANIC CHEMISTRY CHAP.
The tertiary phosphines are most conveniently prepared by
the action of the alcohol on phosplionium iodide in sealed tubes.
The phosphonium iodide and alcohol are converted into alkyl
iodide and phosphine, which then react upon one another.
Methyl alcohol and phosphonium iodide give trimethyl phos-
phine hydriodide
CH 3 OH + PH 4 I = PH 3 + CH 3 I + H 2 0.
3 CH 3 I + PH 3 = (CH 3 ) 3 P.HI 4- 2HI.
Trimethyl phosphine
hydriodide.
Properties of Phosphines. The phosphines are colourless
liquids (with the exception of mono-methyl phosphine, which
is a gas) with a penetrating and unpleasant smell. Even
the lower members are only slightly soluble in water. The
phosphines are much less basic than the corresponding amines ;
for, though they combine with acids and form soluble salts,
having a similar composition to those of the amines, the phos-
phines themselves are not alkaline, and the salts of the primary
phosphines are decomposed like phosphonium iodide, by water,
into the phosphine and acid.
The quaternary iodides and hydroxides are prepared in the
same manner as the ammonium compounds ; the phosphonium
hydroxides, like the ammonium hydroxides, dissolve readily in
water, forming strongly alkaline solutions, which absorb carbon
dioxide from the air and neutralise acids.
The phosphines readily undergo oxidation, the phosphorus
becoming pentavalent by uniting with an atom of oxygen, in
addition to which the hydrogen in the primary and secondary
phosphines is replaced by hydroxyl. Thus, the primary and
secondary phosphines are converted into phosphinic acids. The
following products are obtained by the action of nitric acid on
the three methyl phosphines
CH 3 v CH 3 v CH 3 v
HO-^PO CH 3 -^PO CHg-^PO
HO/ HO/ CH 8 /
Methyl phosphinic Dimethyl^phosphinic Trimethyl phosphonium
acid. acid. oxide.
The tendency to undergo oxidation exhibited by the phos-
phines (it has been observed in a few tertiary amines under the
influence of a powerful oxidising agent, e.g. hydrogen peroxide)
xvi THE ARSENIC ALKYL COMPOUNDS 2 33
is much more marked in the case of the alkyl compounds of the
more metallic elements, many 'of which oxidise in the air.
The Arsines. The primary, secondary, and tertiary arsines
are known. The corresponding chlorine derivatives have also
been obtained. The methyl compounds have the following
formulae
CH 3 v CH 3 v
ClAAs. CH 3 -^As.
Cl/ Cl/
Methyl arsine chloride. Dimethyl arsine chloride,
or Cacodyl chloride.
The tertiary arsines, and the quaternary arsonium iodides and
hydroxides, have the following formulae
(CH 3 ) 3 As * (CH 3 ) 4 As.I (CH 3 ) 4 As.OH.
Trimethyl arsine. Tetrarnethyl Tatramethyl
b. p 70. arsonium iodide. arsonium hydroxide.
The quaternary iodides and hydroxides are obtained by the
method employed in the case of the amines and phosphines.
The arsonium hydroxides resemble the ammonium and phos-
phonium compounds. They are freely soluble in water, have an
alkaline reaction, and neutralise acids.
The tertiary arsines are obtained when a zinc alkyl (p. 237}
acts upon arsenic trichloride or when an alkyl iodide is heated
with sodium arsenide. The formation of the methyl compounds
is represented by the following equations
1. 2AsCl 3 + 3Zn(CH 3 ) 2 = 2As(CH 3 ) s + 3ZnCl 2 .
Zinc Trimethyl
methj'l. arsine.
2. AsNa s + 3CH 3 I = As(CH 3 ) 3 + sNal.
The tertiary arsines are without basic properties and form no-
salts. They readily combine with the halogens and sulphur,,
and take up oxygen from the air, the arsenic thereby becoming
pentavalent. Trimethylarsine forms the following well-defined
compounds
(CH 3 ) 3 AsCl 2 . (CH 3 ) 3 AsS. (CH 3 ) 3 AsO.
Trimethyl Trimethyl Trimethyl
arsine dichloride. arsine sulphide. arsine oxide.
Cacodyl Compounds. When a mixture of equal parts of
potassium acetate and arsenious oxide is heated, a liquid distils
234 THEORETICAL ORGANIC CHEMISTRY CHAP.
which has an intolerable smell, is spontaneously inflammable
and excessively poisonous. It was first obtained by Cadet in
1760, and was known as "Cadet's fuming liquid." The com-
position of this substance was ascertained by Bunsen (1837-
1843) who named it cacodyl oxide (KaKco&y?, stinking) from its
smell. Bunsen showed that it was the oxide of the radical
cacodyl, AsC 2 H 6 [afterwards changed to As(CH 3 ) 2 ]. Like the
radical cyanogen CN, which plays the part of a halogen or
monovalent acid radical, so cacodyl plays the part of a mono-
valent metal, and may be termed a basic radical. Thus, cacodyl
chloride, As(CH 3 ) 2 Cl, platinochloride, [As(CH 3 ) 2 Cl] 2 PtCl 4 , and
cyanide, As(CH 3 ) 2 CN, &c., are known. The reaction by
which cacodyl oxide is formed is expressed by the following
equation
/As(CH 3 ) 2
AsgOg + 4CHo.COOK = O< + 2K CO 3 + 2CO 2 .
x As(CH 3 ) 2
Cacodyl oxide.
The reaction is used as a delicate test for arsenic or acetic
acid, a small quantity of either substance under appropriate
conditions giving the characteristic smell, which is easily
recognised.
When cacodyl oxide is exposed to the air or heated with
mercuric oxide, it takes up oxygen and water and is converted
into cacodylic acid
(CH 3 ) 2 As x ,>
>O + O 9 + HoO = 2(CH 3 ) 2 Asf
(CH 3 ) 2 As/ \OH.
Cacodylic acid.
Cacodylic acid is a crystalline substance, forming salts which
are for the most part insoluble in water and non-poisonous.
Some of the salts have been introduced into medicine.
When cacodyl oxide is distilled with hydrochloric acid, cacodyl
chloride is formed. The reaction resembles the formation of
sodium chloride from the oxide
(CH 3 ) 2 As x
^O + 2HC1 = 2(CH 3 ) 2 AsCl + H 2 0.
(CH 3 ) 2 As X Cacodyl chloride.
Na x
>0 + 2HC1 = 2NaCl + H 2 0.
Na/
KVI THE ARSENIC ALKYL COMPOUNDS 235
The chloride may be reconverted into the oxide by caustic
alkalis, a reaction which again resembles the behaviour of certain
metallic chlorides.
When cacodyl chloride is treated with metallic zinc in an at-
mosphere of carbon dioxide, cacodyl or more correctly dicacodyl
(tetramethyl diarsine) is formed
As(CH s ) 2 ;Cl" ""-... As(CH 3 )
I + Zn ""v = | -f ZnCl 2 .
As(CH 3 ) 2 ;Cl ....-" As(CH 3 ) 2
[..-"'" Cacodyl.
Cacodyl is a colourless, mobile, and highly refractive liquid,
which oxidises so rapidly in the air that it inflames spontane-
ously, giving off carbon dioxide and water and fumes of arsenic
trioxide.
Alkaline Alkyl Compounds. The frequent appearance among
organic compounds of derivatives of the most diverse elements possess-
ing marked alkaline characters is very striking. Elements belonging
to entirely different groups of the periodic system, such as iodine,
mercury, sulphur, and nitrogen (phosphorus or arsenic), form com-
pounds which have properties like ammonia. In these compounds,
the alkaline character is associated with the presence of hydrogen (in
ammonia) alkyl groups, or other hydrocarbon radicals, linked along with
hydrcxyl to a polyvalent element, the valency of which is, more or less,
saturated. The following examples will make these points clear
/N\
;n 3 ) 4 (p IOH.
\As/
(C 6 H 5 ) 2 LOH (C 2 H 5 )Hg.OH (CH 3 ) 3 S.OH (GIL
Diphenyl- Ethyl mercury Trimethyl Tetramethyl
iodonium hydroxide. sulphine ammonium, &c.,
hydroxide. hydroxide. hydroxide.
The above series of compounds possess the same general properties.
They dissolve in water forming strongly alkaline solutions, which can
be neutralised by acids and precipitate metallic oxides from their salts.
Recently, a compound, trianisyl carbinol, or carbonium hydroxide,
(CH 3 O.C 6 H 4 ) 3 C.OH, has been prepared, which has basic properties,
and forms well-defined salts.
It is interesting to compare these basic compounds with the organic
acids, which are also characterised by the presence of a hydroxyl
group. On referring to the paragraph on unsaturated groups (p. 225),
it will be observed that one essential difference in the structure of
alkaline and acid substances lies in the fact that in most acid compounds
236 THEORETICAL ORGANIC CHEMISTRY CHAP.
the hydroxyl group is associated with elements whose valencies
are unsaturated. Further speculation on the cause of alkalinity or
acidity lies beyond our present purpose.
Silicon Alkyl Compounds. Silicon, like carbon, is tetra-
valent, and stands nearest to carbon in the periodic system.
The alkyl compounds of silicon have in consequence a special
interest from the analogy which they might be expected to
offer with the paraffins. Silicon tetramethyl, or silico-pentane,
Si(CH 3 ) 4 , corresponds to neopentane, or tetramethyl methane,
C(CH 3 ) 4 (p. 74) ; silicon tetrethyl, or silico-nonane, Si(C 2 H 6 ) 4 ,
corresponds to tetrethyl methane, C(C 2 H 5 ) 4 . Silicon tetramethyl
is obtained from silicon chloride and zinc methyl, or by
Grignard's method with magnesium methyl bromide (see p. 243).
SiCl 4 + 2Zn(CH 3 ) 2 = Si(CH 3 ) 4 + 2ZnCl 2
Silicon
tetramethyl.
Silicon tetrethyl is prepared in the same manner from zinc
ethyl. Like the paraffins, the silicon alkyls are colourless
liquids, specifically lighter than water, in which they are inso-
luble. They are unattacked by strong sulphuric or strong nitric
acids. The boiling-points compared with those of the paraffins
are as follows :
Silico-pentane . . . 3O-3i norm, pentane . . . 37
neo-pentane .... 9
Silico-nonane . . . 151- 15 3 norm, nonane . . . 150
Silico-nonane, when chlorinated, forms a chlorine substitu-
tion product, SiC 8 H 19 Cl, which is a colourless liquid boiling at
185. The chlorine may be exchanged for hydroxyl, when
silico-nonyl alcohol, SiC 8 H 19 .OH, is produced, possessing many
of the properties of an alcohol.
By combining silicon with four different radicals, compounds have
been prepared containing an asymmetric silicon atom (p. 114), which,
like active amyl alcohol, exhibits rotatory polarisation (Kipping).
Organo-Metallic Compounds. The term is applied to the
alkyl compounds of the metals. They resemble certain of the
alkyl compounds of the non-metals, both in their mode of pre-
paration and properties. In fact, no sharp line can be drawn
between the two. There is the same gradual transition which
characterises the change from non-metals to metals.
xvi THE ZINC ALKYL COMPOUNDS 237
In this connection we may compare the alkyl with the hydro-
gen compounds of the elements. Thus, we find that, as the
metallic character of an element predominates, its affinity for
hydrogen diminishes. If such metallic hydrides exist, they are
very unstable, and, on heating, lose hydrogen. In the same
way the alkyl compounds of the metals are much less stable
than those of the non-metals. They unite with oxygen with
great avidity, frequently taking fire in the air, and decompose
water, alcohol, and other organic compounds containing oxygen.
The number of organo-metallic compounds is very large, and
for our present purpose a study of the zinc and magnesium
compounds must suffice.
Zinc Alkyl Compounds. The study of the zinc alkyl com-
pounds is closely linked with the history of organic chemistry.
It was with the object of isolating the organic radicals by
removing iodine from the alkyl iodides that Frankland dis-
covered the twofold action of zinc on the alkyl iodides (1849).
Frankland's radicals proved to be paraffins, and an important
synthetic method was thereby introduced, which has already
been described (p. 69). Methyl iodide and metallic zinc yield
ethane
2CH 3 I + Zn = C 2 H 6 + ZnI 2 .
If an excess of zinc is used, zinc alkyl compounds are formed.
The process actually occurs in two steps. When metallic zinc or
the zinc-copper couple (p. 82) is boiled with an alkyl iodide,
zinc alkyl iodide is formed
/CH 3
CH 3 I + Zn = Zn^
Zinc methyl iodide.
When the product of the first reaction is distilled, it is decom-
posed into zinc alkyl and zinc iodide
/CH 3
2Zn/ = Zn(CH 3 ) 2 + ZnI 2 .
M Zinc methyl.
EXPT. 85. Preparation of Zinc Ethyl. A round distilling flask, the
side-tube of which is temporarily closed, is attached to an inverted
condenser. Through a cork in the upper end of the condenser a bent
tube is tightly inserted, the lower end of which dips into mercury.
The object of this arrangement is to prevent the entrance of air, in
which the zinc ethyl readily takes fire. Equal weights of zinc-copper
THEORETICAL ORGANIC CHEMISTRY
couple (60 grams) and ethyl iodide (60 grams) are placed in the
flask attached to the condenser. The zinc-copper couple is made
by mixing zinc dust (50 grams) with fine copper oxide powder
(10 grams), previously reduced in a current of hydrogen. The mixture
in the flask is heated on the water-bath until the evolution of gas
(butane), which occurs at the beginning,
ceases (about 2 hours). The first re-
action is then at an end, and the
liquid is next distilled in an oil-, or
metal-bath in a current of dry carbon
dioxide. A small flask is used as the
receiver. The liquid, which passes
over, is zinc ethyl, boiling at 118.
The zinc ethyl is now introduced into
small bulbs for subsequent .experiments.
These bulbs have a capacity of 2-3 c. c. ,
and are made with long narrow stems,
or tubes, bent at right angles, and open
at the end. The bulbs are placed with
the open ends downwards in the flask
containing the zinc ethyl, as shown in
Fig. 64. The flask is quickly placed
in a vacuum desiccator filled with coal-
gas, which is then exhausted. On allowing coal-gas to enter, the
liquid enters the bulbs, which are removed and sealed.
When exposed to the air, the zinc alkyl rapidly oxidises, and
the heat developed is sufficient to inflame the substance, which
burns with a white luminous flame, evolving carbon dioxide and
water together with fumes of zinc oxide.
EXPT. 86. Break oft' the end of the stem of oneof the bulbs of zinc
ethyl prepared in Expt. 85 and shake out the contents. The liquid
takes fire on coming in contact with the air.
A similar change happens when the halogens act upon a zinc
alkyl compound. The substance takes fire, and the metallic
halide is formed. If the reaction is moderated by dissolving
the reacting substances in an inert solvent, zinc halide and alkyl
halide are formed. Zinc methyl and iodine form zinc iodide and
methyl iodide
Zn(CH 3 ) 2 + 2l 2 = ZnI 2 + 2CH 3 I.
FIG. 64. Method of filling bulbs
with Zinc ethyl.
xvi THE ZINC ALKYL COMPOUNDS 239
SYNTHETIC PROCESSES IN WHICH THE ZINC ALKYL
COMPOUNDS ARE .USED
Synthesis of Organo-metallic Compounds. The preparation
of arsenic and silicon alkyl compounds by means of zinc alkyls
has already been described (pp. 233, 236). Alkyl compounds of
different metals have been obtained in the same way by the
action of a zinc alkyl on the chlorides of antimony, bismuth,
tin, lead, mercury, c. The following methyl compounds of
these metals have been obtained. They are liquids which can
be vaporised unchanged, so that their molecular weights have
been correctly ascertained.
Hg(CH 3 ) 2 Sn(CH 3 ) 4
Bi(CH 8 ) 8 Pb(CH 8 ) 4
Sb(CH 3 ) 3
In comparing the alkyl compounds with the non-metallic compounds
of the elements, Frankland was struck with the correspondence in what
he called "saturation capacity," or, as we now term it, the "valency"
of the elements, and he was the first to draw attention to this
property, which has exercised so important an influence on chemical
theory.
Synthesis of the Paraffins. When the zinc alkyl comes in
contact with water, the water is decomposed, the hydrogen
attaching itself to the alkyl group and forming a paraffin, whilst
the oxygen combines with the zinc. Zinc methyl gives zinc
hydroxide and methane
/JCH 3 ...... Hi
Zn< i + !O + H 2 O = Zn(OH)o + 2CH 4 .
EXPT. 87. By means of pliers take one of the bulbs of zinc ethyl
(Expt. 85) by the long stem and introduce it below an inverted.
cylinder or gas-jar filled with water. Break the stem between the
pliers. A copious evolution of gas follows and partly fills the
cylinder, whilst at the same time a bulky white precipitate of
zinc hydroxide is deposited. By closing the mouth, the cylinder
may be brought into an upright position and the gas ignited by a
taper. Zinc ethyl yields ethane.
The synthesis of the paraffins may be simplified by heating
together in a sealed vessel, a mixture of zinc, alkyl iodide, and
240 THEORETICAL ORGANIC CHEMISTRY CHAP.
water. Probably the zinc alkyl is formed as an intermediate
product, which is decomposed in the presence of water. Methyl
iodide yields methane by this method
2CH 3 I + Zn 2 + 2H 2 O = 2CH 4 + ZnI 2 + Zn(OH) 2 .
A further synthesis of the paraffins is effected by the action
of the alkyl iodides on the zinc alkyl ; zinc methyl and methyl
iodide give ethane
:CH 3 CH 3 :i
Zni + j = ZnI 2 + 2C 2 H 6 .
;CH 3 ...... CHgjI
By a similar reaction neo-paraffins may be obtained. Acetone
bichloride and zinc methyl give neo-pentane (p. 75)
CH 3 CH 3 CH 3
I ............. L, I
C:C1 2 + Zni = CH 3 C CH 3 + ZnCl 2 .
CH 3 CH 3 CH 3
A very similar reaction to that produced by adding water to the zinc
alkyl occurs when the latter is decomposed by alcohol. Zinc alcoholate
is thereby formed, and the alkyl group takes up hydrogen and forms a
paraffin. Zinc methyl and methyl alcohol yield methane and zinc
methylate
/JCH 3 ...... HiOCHo
Zn< ! + = Zn(OCH 3 ) 2 + 2CH 4 .
NCH| HjOCHg
Zinc Methyl Zinc methylate
methyl. alcohol or methoxide.
The same product is obtained by the gradual absorption of oxygen by
the zinc alkyl, the reaction actually occurring in two steps
/CH 3 /CH 3 y OCH 3 .
Zn< + O = Zn< + O = Zn<
\CH 3 X OCH 3 X)CH^
Zinc methyl
methoxide.
Synthesis of Secondary and Tertiary Alcohols and
Ketones. From what has been already explained of the affi-
nity exhibited by the zinc alkyl compounds for oxygen and the
halogens, the following reactions will be readily understood. In
reactions with aldehydes and ke tones to be described, the zinc
XVI THE ZINC ALKYL COMPOUNDS 241
atom attaches itself to the oxygen atom of the unsaturated
group, CO, by one bond, losing at the same time an alkyl group,
which is transferred to the unsaturated carbon atom of the same
group. This represents the first stage in the reaction. The
product is subsequently decomposed with water, by which the
alcohol is produced. The following examples are given as
typical of this class of reactions
.CHO + Zri(CH 3 ) 2 ==CH 3 .CH ; , = CH 3 .CH
\O!ZnjCH 3 \OH
+ Hi O IH
Aeetalde- Intermediate Seconda
hyde. zinc compound. propyl al
lary
Icohol.
Acetaldehyde and zinc methyl yield secondary propyl alcohol.
In the same way acetone and zinc methyl form tertiary butyl
alcohol
>CO + Zn(CH 3 ) 2 =
CH/ CH/ X OiZn|CH 3
Acetone. Intermediate
zinc compound.
r^T-T C* W
^,n 3 \ x^n 3
>C< + ZnO + CH 4 . +
CH/ ^Oll
Tertiary butyl
alcohol.
With the esters a similar process takes place. Formic ester and zinc
methyl (two molecules) yield a zinc compound which is decomposed by
water, forming secondary propyl alcohol. Other fatty esters like acetic
ester will naturally yield tertiary alcohols by this process. The reaction
between formic ester and zinc methyl occurs in two steps
/OCH 3 X OCH 3
H.C< + Zn(CH 3 ) 2 = H.C< + Zn(CH 8 } a
^O I X OZnCH 3
Methyl formate. CH 3
= H.C< + Zn<
| \OZnCH 3 X CH 3 .
CH 3
242 THEORETICAL ORGANIC CHEMISTRY CHAR.
/CH 3 /CH 3
H.C< j I = H.COH + ZnO + CH 4 .
| X);ZniCH 3 \CH 3
CII 3 i + i Secondary propyl
HjOJH
Acid chlorides react in two ways. When one molecule of zinc alkyl
combines with one molecule of acid chloride and the product is de-
composed by water, a ketone is formed. Acetyl chloride and zinc
methyl yield acetone, according to the following equation
Cl /;Cl+"Hi.OH >;OHi
" + Zn(CH 3 ) 2 = CH 3 .C< i ; = CH 3 .C< i -- i
I x oiznicH 3 I NOJH
CH 3 j+j CII 3
HJOJH
Aoetyl chloride. Intermediate Acetone.
zinc compound.
The final product loses the elements of water and forms acetone.
If the intermediate zinc compound is allowed to react with a second
molecule of zinc alkyl, a tertiary alcohol is formed
JCli + CH 8 !ZnCH 3 /CH 3
CH 3 .C< = CH 3 .C< + ClZnCH 3 .
| \OZnCH 3 | \OZnCH 3
CH 3 CH S
/CH 3 /CH 3
aV.L j
CH 3 .
/CH 3
(CH 3 ) 2 C< -> (CH 3 ) 2 C(OH)CH 3 .
X)MgI
EXPT. 88. Add 3 grams of clean magnesium ribbon or filings to
75 c.c. of perfectly dry ether and then pour in 18 grams of methyl-
iodide, the flask being attached to a reflux condenser. The
magnesium rapidly dissolves. Cool and add to the solution 7 grams
of acetone. A white, bulky precipitate of the magnesium compound
is deposited. On dissolving in dilute sulphuric acid, the ether solution
of the alcohol separates, and may be withdrawn and distilled.
CH 3 .CO.OC 2 H 5 + 2C 2 H,MgBr ->
CH 3 .C(OMgBr)(C 2 H 6 ) 2 ^ CH 3 C(OH)(C 2 H 6 ) 2 .
R 2
244 THEORETICAL ORGANIC CHEMISTRY CH. xvi.
Ketones can be prepared from cyanides and amides :
CH 3 CN + C 2 H 5 MgBr ->
JSTMgBr CH 3 COC 9 H 5 +
CH C^ H2
\C 2 H 5 Mg(OH)Br+NH 3 '
NHMgl
+C 2 H 6 =
CH 3 .CO.C 2 H 5 + MgI 2 + Mg(OH) 2 +NH 3 .
The magnesium alkyl halides absorb carbon dioxide, and
form thereby compounds, which are decomposed by alkalis
and yield salts of the fatty acids. Methyl bromide gives acetic,
-ethyl bromide forms propionic acid
C 2 H 5 MgBr + CO 2 = C 2 H 5 CO.OMgBr.
C 2 H 5 CO.OMgBr + NaOH = C 2 H 5 CO.ONa + MgBr(OH).
The use of magnesium in the manner described is known as
GHgnard's reaction.
QUESTIONS ON CHAPTER XVI
1. How are the primary, secondary, and tertiary phosphine
prepared ?
2. Compare the properties of the alkyl compounds of nitrogen, pho
phorus, and arsenic.
3. Discuss the general structure of organic compounds possessing
alkaline properties.
4. Describe the preparation of cacodyl, cacodyl oxide and chloride.
Explain why cacodyl is to be regarded as a basic radical.
5. Compare the alkyl compounds of silicon with the paraffins. How
is silico-pentane prepared?
6. Compare the behaviour towards oxidising agents of the alkyl
compounds of the non-metals with those of the metals.
7. How is zinc ethyl obtained ? Describe the action of water, ethyl
alcohol, and the halogens on zinc ethyl.
8. Give examples of the uses of zinc ethyl in synthetic processes (pre
paration of paraffins and alcohols).
9. Explain the formation of secondary and tertiary alcohols fron
methyl magnesium iodide.
/ 10. How is zinc ethyl prepared? Give equations to illustrate it;
value in organic synthesis, and describe briefly the properties of the
substances obtained in the reactions you mention.
II. Describe the production and properties of the best known
organo-arsenic compounds.
CHAPTER XVII
THE UNSATURATED HYDROCARBONS
The Unsaturated Hydrocarbons. There are two important
families of unsaturated hydrocarbons the defines and acety-
lenes. They contain less hydrogen than the paraffins with the
same number of carbon atoms, and possess the character-
istic property of uniting with other elements, forming additive
compounds (p. 63). It is this property which has given rise to
the term unsaturated.
The defines, C n H 2n . A list of the members of this family is
given in Table X.
TABLE X.
THE OLEFINES, C n H 2n .
Ethylene . . . . . . . .
Boiling-
point.
- 103
Propylene
CH 3 .CH:CH 2
Butylene . .
C 4 H 8
.
Ethylethylene, or a-butylene . . .
Dimethylethylene (symm.) or
/8-butylene . . ....
C 2 H 5 .CH:CH 2
CH 3 .CH:CH.CH 3
~5
i
(CH 3 ) 2 C:CH 2
-6
Amylene . . ...
^5 10
Methylethylethylene
CH 3 .CH:CH.C 2 H 6
36
(CH 3 ) 2 CH.CH:CH 2
20-2I
Methylethylethylene (unsymm.) . .
(CH 3 )(C 2 H 5 )C:CH 2
(CH 3 ) 2 C:CH(CH 3 )
3i-32
36-38
246
THEORETICAL ORGANIC CHEMISTRY CHAP.
,
General Properties of the defines. The members of the
series with 2, 3, and 4 carbon atoms are gases, like the corre-
sponding paraffins. The higher members are colourless liquids
and solids. The defines are specifically lighter than water,
in which they are but slightly soluble. In physical pro-
perties, therefore, they resemble the paraffins. Chemically they
offer a marked contrast. They burn with a luminous and rather
smoky flame. They unite with hydrogen, halogen acids, halo-
gens, strong or fuming sulphuric acid (indirectly also with
water), hypochlorous acid, and finally they undergo oxidation
with potassium permanganate and other oxidising agents.
We may take the best known member of the series ethylene,
C 2 H 4 to illustrate the above reactions ; for the present we will
assign to it the formula CH 2 'CH 2 , indicating that the two
carbons are united by a double bond in the same way that the
union of oxygen and carbon is represented in l^etones and
aldehydes (p. 125).
Reactions of Ethylene. i. Ethylene burns with a luminous
and rather smoky flame as already shown in Expt. 23, p. 98,
2. When the olefines, mixed with hydrogen, are passed over
platinum black, colloidal palladium, or finely divided nickel,
they unite with the hydrogen and form paraffins. Ethylene
is converted into ethane
CH 2
"
CH 2
CH 3
= I
CH 3 .
Ethane.
3. The olefines combine with chlorine, bromine, and (though
less readily) with iodine, forming the chloride, bromide, and
iodide of the olefine. Ethylene forms with" chlorine, ethylene
chloride, and with bromine, ethylene bromide (p. 87)
CH 2
CH 2
II
CH 2
CH 2 C1
=
CH 2 C1.
Ethylene chloride.
Br 2 =
CH 2 Br
Ethylene bromide.
THE OLEFINES 247
EXPT. 89. Prepare ethylene as described in Expt. 23 (p. 98), but
collect the gas in gas bottles over water by means of a delivery tube
attached to the flask in which the alcohol and sulphuric acid are
heated. The gas bottles must then be stoppered and placed in an
upright position. Fill two other gas bottles of the same dimensions,
one with chlorine and the other with bromine vapour. Remove the
stoppers of the ethylene bottles and replace them by glass plates, and
invert over them the bottles of chlorine and bromine from which the
stoppers are also removed. On withdrawing the glass plate, the
gases mix, and the colour of the chlorine and bromine quickly dis-
appears. Colourless drops of oily liquid are then found on the sides
of the bottles ; they consist of ethylene chloride in one case and
ethylene bromide in the other.
4. The defines combine with hydrochloric, hydrobromic, and
hydriodic acids least readily with hydrochloric, most readily
with hydriodic acid forming alkyl halides. Ethylene passed
into a strong solution of hydriodic acid is absorbed and forms
ethyl iodide
CH 2 CH 2 I
II + HI = |
CHfj CH 3 .
Ethyl iodide.
In the case of unsymmetrical compounds like propylene,
CH 3 .CH:CH 2 , with which the hydracid may unite in two different
ways, the halogen atom attaches itself to the carbon with the fewest
hydrogen atoms. Propylene forms with hydriodic acid secondary
propyl iodide, CH 3 .CHI.CH 3 , and not the primary compound,
CH 3 .CH 2 .CH 2 I.
5. The defines combine wit'h strong (more quickly with
fuming) sulphuric acid, and form alkyl hydrogen sulphates.
Ethylene forms ethyl hydrogen sulphate (p. 187)
CH CH 3
|| " + H 2 S0 4 = |
CH 2 CH 2 .O.SO 2 .OH.
Ethyl hydrogen sulphate.
EXPT. 90. Pour a few c.c. of fuming sulphuric acid into a glass
tube about 25 cm. long closed at one end, introduce ethylene gas
until most of the air is displaced, and close with a corV f tted with a
glass tap (Fig. 65). On shaking and opening the tap under strong
sulphuric acid, the liquid rises nearly to the top of the tube.
248 THEORETICAL ORGANIC CHEMISTRY CHAP.
In this reaction the sulphuric acid dissociates into hydrogen and
the group O.SO 2 .OH, which distribute themselves between the
two unsaturated carbon atoms. In unsymmetrical olefines
the group O.SO 2 .OH usually attaches itself to the
carbon with fewest hydrogen atoms. In other words the
more negative group attaches itself to the more positive
carbon (viz. that linked with the larger number of alkyl
groups).
This reaction is used in estimating the amount
of olefines, or in removing them from a mixture with
other gases or liquids, which, like the paraffins, are
unabsorbed by the acid.
6. It has also been utilised for obtaining alcohol
from coal-gas by absorbing the ethylene as ethyl
"hydrogen sulphate and decomposing the latter with
water (see p. 188).
7. When the olefines are treated with a dilute solution of
potassium permanganate, they undergo oxidation ; in the first step
of the process hydroxyl groups are added to the two unsaturated
carbon atoms. Further oxidation converts the compounds thus
obtained into other products, which will be considered else-
where. Ethylene forms ethylene dihydroxide or glycol
CH 2 CH 2 .OH
|| + H 2 + 0=|
CH 2 CH 2 .OH.
Ethylene glycol.
8. The olefines combine with hypochlorous acid (prepared
from chlorine and water in presence of a copper compound) and
form chlorhydrins of the olefines
CH 2 CH 2 (OH)
|| + HC10 = |
CH 2 CH 2 C1.
Ethylene chlorhydrin.
9. They also unite with ozone to form ozonides
CH 2 CH 2 - O\
|| + 3 = I >0
CH 2 CH 2 - Q/
Ethylene ozonide.
Sources of the Olefines. The olefines are found among the
products of the distillation of wood and coal, and are conse-
quently present in coal-gas ; but they are most readily obtained
in a pure condition by the action of dehydrating agents (sul-
XVII
THE OLEFINES
249
phuric acid, phosphoric acid, or zinc chloride) on alcohols.
Ethyl alcohol yields ethylene
C 2 H 6 O - H 2 O = C 2 H 4 .
EXPT. 91. Preparation of Ethylene and Ethylene Bromide from
Ethyl Alcohol. The apparatus shown in Fig. 66 is convenient for
this preparation (Calam). It consists of a round flask of about
^-litre capacity with a wide neck furnished with a treble-bored cork.
A tube closed at the lower end for holding a thermometer is inserted
through one hole, a tube ending in a spiral-shaped capillary as shown
at a is inserted through a second hole, and a delivery tube through
the third. The upper end of the spiral outside the flask is attached
by rubber tubing to a long wide tube holding alcohol drawn out
below and provided with a screw clip to adjust the flow of alcohol.
A Woulff bottle is attached to the delivery tube which terminates
below the first tubulus ; through the second tubulus an open safety
tube is inserted with a side piece near the upper end, and through
the third tubulus a delivery tube which is attached to a wide bent
tube lying in a metal trough, through which cold water flows. The
upper end of this tube is connected to a wash-bottle. About 150 c.c.
of glacial phosphoric acid are poured into the round flask, about
FIG. 66. Preparation of Ethylene and Ethylene bromide.
50 c.c. of bromine and 10 c.c. of water are introduced into the wide
tube and 10 c.c. of bromine and 10 c.c. of water into the end wash-
bottle. The glacial phosphoric acid is heated to 190-200, and then
90-95 per cent, spirit is allowed to flow in slowly, the temperature
being maintained at 20 D. The phosphoric acid froths freely but does
not froth over, and ethylene comes off rapidly. Gradually the
bromine loses its colour, and finally a colourless liquid is obtained,
which is ethylene bromide
C 2 H 4 + Br 2 = C 2 H 4 Br 2 .
THEORETICAL ORGANIC CHEMISTRY
CHAP.
The ethylene bromide is then shaken up with a little carbonate of soda
solution, dehydrated over calcium chloride, and distilled. The
method of purification is that described in the preparation of ethyl
bromide (p. So). Ethylene bromide boils at 131 (p. 85).
The defines are also obtained by running the alkyl halide
into a strong solution of alcoholic potash. Ethyl iodide or
bromide and alcoholic potash yields ethylene (p. 82)
C 2 H 5 I + KOH = C 2 H 4 + KI + H 2 0.
EXPT. 92. Preparation of Ethylene from Ethyl Iodide. Make
a strong solution of caustic potash in methyl or ethyl alcohol (50 per
cent, solution), and pour 50 c.c. of the solution into a distilling flask
FIG. 67. Preparation of Ethylene from Ethyl iodide.
(250 c.c.). Attach the flask by the side-tube to an inverted con-
denser, and fix to the upper end of the condenser a bent delivery tube
passing into a gas trough of water. A tap funnel containing 10-20 c.c.
of ethyl iodide is inserted into the neck of the distilling flask. The
apparatus is shown in Fig. 67. Warm the potash solution in the
flask and then drop in the ethyl iodide. Gas is rapidly evolved and
potassium iodide is deposited. When the air in the flask has been
displaced, the ethylene may be collected and burnt.
xvii THE OLEFINES
251
In the reaction just described a certain amount of ether is formed,
the quantity of which depends upon the nature of the alkyl halide.
When methyl iodide is decomposed with methyl alcoholic potash,
the whole of the methyl iodide is converted into methyl ether.
Possibly methylene, produced in the nascent state, unites with a
molecule of methyl alcohol
CH 3 T + KOH = :CH 2 + KI + H 2 O.
CH 2 : + HOCH 3 = CII 3 .O.CH 3 .
Or, it may be that the alcoholic potash acts like potassium alcoholate,
as in the ordinary synthesis of ethers
CH 3 I + KOCH 3 = CH 3 .O.CH 3 + KI.
An interesting method for preparing defines is the electro-
lysis of salts of dibasic acids, i.e. acids which contain two
carboxyl groups (p. 333). Potassium succinate yields ethylene.
The reaction resembles the formation of ethane from potassium
acetate (p. 152)
CH 3 !COO;K CH 2 . jCOOfK
CHgjCOOJK CH 2 . JCOO;K
+ electrode. + electrode. .
Potassium acetate Potassium succinate
yields ethane. yields ethylene.
Structure of the defines. The readiness with which the
defines unite with other elements to form additive compounds
indicates that the full valency of the carbon atoms is not
brought into play, which is also the case with aldehydes, ketones,
and cyanides (p. 224). The question then arises : What is the
function of the unemployed bonds in an unsaturated compound,
and how should they be graphically represented ? Are they in-
active or free linkages (Formula I.) such as we usually associate
with the formulae of nitric oxide NO, and carbon monoxide,
=CO, or, on the other hand, is the residual valency of the
carbon atoms engaged in binding the two carbon atoms
together by forming a double bond (Formula II.) such as we have
tacitly assumed to exist between carbon and oxygen in alde-
hydes and ketones or between carbon and nitrogen in cyanic
and isocyanic esters (p. 227), mustard oils (p. 228), &c. ?
252 THEORETICAL ORGANIC CHEMISTRY CHAP.
Formula I. Formula II.
CH 2 CH 2
CH 2 CH 2
Ethylene with free bonds. Ethylene with double bonds.
The question at first sight seems to have little real signifi-
cance. Both formulae explain the transition from unsaturated to
saturated compounds, by the addition of new atoms or groups.
In the first, the free bonds are at once brought into action ; in
the second, one of the double bonds must first be severed. On
the other hand, the assumption of free bonds (Formula I.)
presupposes the existence of substances like methyl, CH 3 , or
methylene, =CH 2 , which are unknown, and of two sub-
stances having the formula C 2 H 4 , viz. ethylene and ethylidene
-CH 2 CH 3
CH 2 =CH.
Ethylene. Ethylidene.
Each of the latter would give rise to a different bromine
derivative, viz. ethylene and ethylidene bromide, whereas only
one compound, C 2 H 4 , exists, yielding ethylene bromide.
Theory of the Double Bond. The principal grounds upon
which the theory of the double bend rests are : firstly, the
defines and, in fact, all unsaturated compounds,
unite with an even number of monovalent
atoms or groups in other words, the saturation
of one unsaturated carbon atom necessitates
that of the other ; secondly, the unsaturated
carbon atoms invariably adjoin one another.
There is an evident connection of a special
kind between the two unsaturated carbon
atoms, for which the device of the double bond
is made to serve.
FIG. 68. We must be careful, however, to recognise
clearly that the method of indicating this
relationship is not taken to imply a firmer connection between
the unsaturated carbon atoms, but that, on the contrary, a
double bond is a point of weakness in the molecule rather
than of strength. For example, the heat of combustion of
ethane is 370 calories, that of the molecule of hydrogen 138
THE OLEFINES
253
calories. From this the heat of combustion of ethylene
should be 232 calories, whereas actually it is 333 calories
showing that less energy is expended in breaking up the
molecule, that is, in separating the two atoms of carbon
than in ethane. Various theories, giving prominence to this
idea, have been advanced, resting mainly on the space
arrangement of the carbon bonds (Fig. 51, p. 113). Thus, if we
suppose the bonds to diverge at equal angles (109 "5) from
the central carbon atom, and to retain their positions when
the two carbon atoms are doubly linked, the space arrangement
viewed in perspective will appear as in Fig. 68.
If a bond represents the direction in which a force acts, the
resultant of two forces acting at an angle of IO9*5 will not be
the equivalent of the same forces acting in a straight line.
According to another theory, if the result of double linking
tends to bend the two pairs of bonds from their original
positions into a straight line joining the two carbon atoms, a
condition of strain will be set up, which will be a cause of
instability (Baeyer's strain theory).
Nomenclature of the defines. The names of the olefines
are derived from those of the alkyl groups containing the
same number of carbon atoms, to which the end syllable -ene
is added (see Table X). The general term olefine is some-
times replaced by the word alkylene.
The isomeric olefines, such as the butylenes and amylenes,
are designated as derivatives of ethylene and are readily dis-
tinguished in this way. Where confusion might arise as
between the two methyl ethyl ethylenes, the word sym-
metrical or unsymmetrical is used, which implies that the
alkyl groups are distributed between the two carbon atoms
(symmetrical) or that both are attached to the same (unsym-
metrical). The Greek letters, a, /3, y, c., are also employed
to indicate the position of the double bond, the letter denoting
the one unsaturated carbon atom which lies nearest to the
end of the chain (the end carbon atom is a, the next 3, &c.).
Thus, ethyl ethylene, CH 3 .CH 2 .CH=CH 2 , is a-butylene, whilst
dimethyl ethylene, CH 3 .CH=CH.CH 3 , is /3-butylene.
Special Members of the Olefines. It has already been stated
that methylene, CH 2 , is unknown. It is probably formed in
the nascent state in many reactions, as in the decomposition of
254 THEORETICAL ORGANIC CHEMISTRY CHAR
methyl iodide with caustic potash in presence of alcohol (p. 251).
or, when the substance known as diazomethane, CH 2 N 2 , is
decomposed by water, or, when methylene iodide is acted upon
with copper, or zinc, and converted into ethylene
CH 2 jN 2 l 4- HOH = CH 3 OH + N 2 .
Diazomethane. Methyl alcohol.
CHJI 2 N \; CH 2
j + Zn 2 > = || + 2 Znl2.
CH 2 :I 2 ^,x' CH 2
Methylene Ethylene.
iodide.
Ethylene, Olefiant Gas, CH 2 :CH 2 . The name olefiant, or
oil-forming gas is connected with a property of the gas already
mentioned (and discovered by four Dutch chemists) of uniting
with chlorine to form an oily liquid (ethylene chloride). The
liquid was known at one time as Dutch liquid, and the term
olefiant has given rise to the word olefine, the present name of
the family. The chief methods of preparation and properties of
ethylene have already been fully described. Ethylene may be
liquefied at o under a pressure of 44 atmospheres, and boils at
103. When allowed to evaporate in a vacuum, the temperature-
falls to 150. It was by the aid of liquid ethylene that Dewar
succeeded in liquefying considerable quantities of oxygen and:
nkrogen. Ethylene and also a small quantity of other olefines.
are present, to the extent of 4-5 per cent., in coal gas. The
volume is readily ascertained by passing a measured quantity of
coal-gas into fuming sulphuric acid, by which ethylene is rapidly
absorbed. The Hempel apparatus is convenient to use for this
purpose, the fuming acid being contained in a pipette of a similar
construction to that shown in Fig. 43, p. 70.
Saturated Hydrocarbons which are Isomeric with the defines.
An important class of hydrocarbons, isomeric with the defines, has
been prepared and carefully studied in recent years. They are much,
more stable than the defines, and, with the exception of the lowest
member, C 3 H 6 , closely resemble the paraffins in physical and chemical,
properties. These substances are known as tri-, tetra-, penta-methylene s .
THE OLEFINES
255
&c. , or cyclo-propane, -butane, -pentane, &c. , and are represented as ring
compounds, with the following structural formulae : Hexamethylene, or
cyclohexane, and its alkyl derivatives are found in petroleum, and are
known as naphthenes
CH 2
CH 2
Trimethylene,
or Cyclopropane.
CH 2 CH 2
Tetramethylene,
or Cyclobutane.
&c.
CH
CH 2 V 'CH 2
Pentamethylene,
or Cyclopentane.
The highest member of the series is cyclononane, C 9 H 18 . For
further details a larger treatise must be consulted.
Diolefincs.
Isoprene, CH 2 :C(CH 3 ).CH:CH 2 , and butadiene, CH 2 :CH.CH:CH 2 ,
obtained respectively from butyl and isoamyl alcohol, polymerise in
presence of metallic sodium yielding synthetic rubber closely resembling,
if not identical with, the natural product.
The Acetylenes, C n H 2n _ 2 . A list of the lower members of
the series is given in Table XI.
TABLE XI.
THE ACETYLENES, CnH 2 n- 2 .
B.. P .
r Acetylene, or ethine
CHiCH
ffas 1
Methyl acetylene, propine, or allylene . .
Ethyl acetylene, butine, or crotonylene .
Propyl acetylene, pentine, or valerylene .
CHs.CiCH
C 2 H & .C;CH
C 3 H 7 .C!CH
18
4 8-5o
Nomenclature of the Acetylenes. The name of the group
is derived from that of the first and most important member,
acetylene, C 2 H 2 . The names of the individual members are
most conveniently designated as alkyl derivatives of acetylene,,
on the plan adopted in the nomenclature of the olefines.
Another method is to add the end syllable ine to the root
of the name of the paraffin with tne same number of carbon
atoms. Thus, acetylene is called ethine ; methyl acetylene,,
propine, &c. Some of the members have, in addition, certain
special names, which are derived from the names of unsaturated
radicals to which the acetylenes are related. Allylene, C 3 H 4 , is
4erived from the radical allyl, C 3 H 5 , &c. (p. 265).
256 THEORETICAL ORGANIC CHEMISTRY CHAP.
Structure of the Acetylenes. The acetylenes contain 2
hydrogen atoms less than the defines, or 4 hydrogen atoms less
than the paraffins. The relation of ethane, ethylene, and acetyl-
ene is represented as follows
n2n -f- 2
Paraffin. Olefine. Acetylene.
C 2 H 6 C 2 H 4 C 2 H 2 .
Ethane. Ethylene. Acetylene.
For similar reasons to those which have been advanced in the
case of the defines (p. 251), the unsaturated carbon atoms in
the acetylenes are assumed to be linked by a treble bond, like
carbon and nitrogen in hydrocyanic acid and the cyanogen
compounds (p. 22=;;-. Thus, each carbon atom of the group has
one bond free, which is united to hydrogen or an alkyl group.
The union of the unsaturated carbon atoms in the acetylenes is
still less stable than that of the double bond in the olefines, and
the space arrangement shown in Fig. 69 has the same signl
ficance as that represented in the case of the
olefines (Fig. 68).
In many respects the acetylenes resemble
the olefines, but the former undergo change
'more readily, and generally speaking show
less stability. Just as in the case of ethylene,
the heat of combustion of acetylene is higher
(3 locals.) than that obtained by deducting, the
value for a molecule of hydrogen from the
heat of combustion for ethylene (195 cals.).
FIG. 69. Acetylene, the most important member, serves
as a type of the whole group, and will alone be
considered in detail.
Acetylene, CHjCH. Acetylene was first observed by E.
Davy (1836), but was more carefully studied by Berthelot
(1859), who prepared it by the direct union of carbon and
hydrogen by sparking carbon electrodes in an atmosphere
of hydrogen. The apparatus used by Berthelot is shown in
Fig. 70. It consists of a pear-shaped bulb closed at each end
by a double-bored stopper. Carbon electrodes are inserted
through two opposite holes of the stopper, whilst, through the
XVII
THE ACETYLENES
257
other two holes, glass tubes are inserted for conducting a
current of hydrogen through the bulb. Acetylene is also formed
by the incomplete combustion of hydrocarbons ; coal-gas, for
example, produces acetylene when a Bunsen burner "strikes
back " and burns within the metal tube.
FIG. 70. Formation of Acetylene from Carbon and Hydrogen.
EXPT. 93. Arrange the apparatus shown in Fig. 71. It con-
sists of a glass funnel, bent twice at right angles, and dipping into
a cylinder containing an ammoniacal solution of cuprous chloride.
A Bunsen burner is lighted at the pinhole jet within the tube, and
' FIG 71. Acetylene formed by incomplete combustion of coal-gas.
placed below the funnel. A current of air is then aspirated through
the apparatus. In a short time a red precipitate of copper acetylide,
C 2 Cu 2 H 2 O, is deposited in the cylinder containing the copper
solution. The ammoniacal solution of cuprous chloride is prepared
S
258 THEORETICAL ORGANIC CHEMISTRY CHAP.
by boiling strong hydrochloric acid with copper oxide and metallic
copper until the liquid is transparent, and nearly colourless. The
solution is then poured into water, and the precipitate of cuprous
chloride is washed once or twice by decantation, and then dissolved
in a strong solution of ammonium chloride. When required, a little
of the liquid is taken, and sufficient ammonia is added to give a clear,
deep blue solution.
Acetylene is also obtained by tbe action of alcoholic potash
on ethylene bromide. The process occurs in two steps ; mono-
bromethylene, or vinyl bromide, is first formed, and the latter
then loses bydrobromic acid and forms acetylene
CH 2 Br CHBr
+ KOH = II + KBr -f H 2 O.
CH 2 Br CH 2
Vinyl bromide,
or Monobromethylene.
CHBr CH
-I- KOH = HI + KBr + H 2 O.
CH 2 CH
Acetylene.
EXPT. 94. Fit up an apparatus similar to that drawn in
Fig. 67 ; but instead of collecting the gas in a gas-trough, allow it
to bubble through an ammoniacal solution of cuprous chloride, con-
tained in a beaker. Pour 50 c.c. of a strong solution (50 per cent.,
made by dissolving 25 grams of KOH in a few c.c. of water and
making up to 50 c.c. with methyl alcohol) of alcoholic caustic potash
into the flask, and heat it gently. When ethylene bromide is dropped
in from the tap-funnel a rapid evolution of acetylene occurs, and
copper acetylide is deposited in the copper solution.
Acetylene is new used as an illuminant, and for this purpose
is obtained by the action of water upon calcium carbide
CaiCo +"H2O = C 2 H 2 + CaO.
Calcium carbide, or calcium acetylide, was first produced
commercially by Willson, an American (1892), and was also
obtained by Moissan by the aid of his electric furnace. It is
prepared by fusing a mixture of lime and coke by means of a
powerful electric current
3C + CaO = CaC 2 + CO.
Calcium
carbide.
ACETYLENE
The various electric furnaces in which carbide is manufactured are
constructed on the same principle. The heat of the arc produced by
the passage of the current between the bed of the
furnace which forms the positive electrode and a
carbon rod, or bundle of rods, which forms the
negative electrode, fuses the mixture of coke and
lime in which the electrodes are embedded.
Various forms of furnaces are used, in some of
which the charges are introduced and the product
removed intermittently ; in others the process is
continuous, and the fused carbide runs away as it
_ is formed. A carbide furnace in its simplest form
FIG. 7*.- Formation ls shown in Fi ^ ? 2 ' It consists of a graphite
of Calcium carbide. crucible in contact with a metal plate, a, which
forms the positive electrode, and a carbon rod, b,
which forms the negative electrode, the intermediate space being filled
up with the coke and lime mixture.
EXPT. 95. Add a few drops of water to some calcium carbide
contained in a test-tube. Rapid effervescence ensues, and the gas,
which is evolved, may be lighted at the mouth of the tube.
Acetylene burns with a white, intensely luminous and rather smoky
flame. The gas obtained from the carbide emits a smell of phosphine,
which is due to traces of phosphate in the limestone becoming
reduced to calcium phosphide. The latter is decomposed by water,
and forms phosphine. For obtaining larger quantities of the gas for
experimental illustration, a flask is furnished with a tap-funnel and
delivery tube. A layer of sand is placed on the bottom of the flask
and small pieces of carbide above this. Water is then added drop
by drop from the tap-funnel.
Properties of Acetylene. Acetylene is a colourless gas
which, in the pure state, has an unpleasant smell of garlic,
quite unlike the smell of a Bunsen burner when it is " burning
down,'' or of the gas given off from commercial carbide. Water
dissolves its own volume, and acetone 31 times its own volume,
of acetylene at o and 760 mm. and 300 times its own volume
at 12 atmospheres. This solution, unlike the liquid acetylene,
r may be safely stored in metal cylinders, and when burnt with
oxygen in a blow-pipe flame gives a temperature which readily
melts steel and is used for cutting that metal. Acetylene burns
with a smoky and very hot flame. For illuminating purposes,
complete combustion is effected by using fine pin-hole burners,
which produce a thin, flat flame, having a proportionately large
S 2
26o THEORETICAL ORGANIC CHEMISTRY CHAP.
surface. It has about 15 times the illuminating power of coal-
gas. Acetylene has been liquefied under a pressure of 26
atmospheres at o, and the liquid has a specific gravity of 0*45.
When mixed with air (from 3 to 65 per cent.) and fired, it
explodes violently. Even the pure gas when compressed or in
the liquid state, explodes on heating, or by detonation. For
illuminating purposes it is therefore necessary to have the gas
supply well-cooled. The principle upon which the various
forms of acetylene generators are constructed is to admit water
to the carbide, or to add carbide gradually to the water, and to
collect the gas in a gas-holder over water. By the first method
the gas-holder, on filling, automatically shuts off the supply of
water to the carbide, and so stops the evolution of gas. As the
gas-holder empties, fresh water enters the vessel containing the
carbide, and the process is repeated until the charge of carbide
is exhausted. By the second method, the carbide is added by
hand or automatically to a reservoir containing water, from
which the gas passes to a gas-holder. Traces of phosphine are
generally present in commercial acetylene, and produce, on
burning, fumes of phosphorus pentoxide. The phosphine is
removed by oxidising agents, such as bleaching powder, chromic
acid mixtures, c.
When acetylene is heated to a red heat, it is completely
decomposed into hydrogen and carbon, the latter being deposited
as soot. At lower temperatures acetylene appears to polymerise
and form benzene, according to the equation
This operation is most effectively conducted by passing the gas
over a long layer of finely divided nickel at a temperature of 1 50
and collecting the product in a U-tube surrounded by a freezing
mixture. The oily liquid which is condensed contains a small amount
of benzene. (Sabatier.)
A characteristic property of acetylene is the formation of
compounds with copper and silver known as acetylides of copper
and silver. They are deposited as amorphous precipitates by
passing the gas into ammoniacal solutions of cuprous chloride :
and silver nitrate respectively ; the copper compound is red,
that of silver, white. The substances have the formulae
C 2 Cu 2 H 2 O. C 2 Ag 2 H 2 O.
Copper acetylide. Silver acetylide.
xvn ACETYLENE 261
They are extremely explosive in the dry state, especially the
silver compound. When decomposed with potassium cyanide
or hydrochloric acid, acetylene is liberated.
Mono- and di-sodium acetylides, C 2 HNa and C 2 Na 2 , are also
known and are obtained by passing the gas over heated sodium.
The formation of copper and silver compounds is associated with the
presence of a =CH group. Methyl acetylene forms a compound,
CH 3 .C=CAg ; dimethylacetylene, CH 3 C^C.CH 3 , on the other hand,
forms no metallic derivative. The acid character of acetylene or its
property of forming metallic compounds may be connected with the
presence of an unsaturated carbon atom, such as we find to be the case
in hydrocyanic acid, HC^N (p. 211).
Additive Compounds of Acetylene. Acetylene, like cthyl-
ene, forms additive compounds with hydrogen, halogen acids,
the halogens, and water.
1. When acetylene mixed with hydrogen is passed over
platinum black or finely divided nickel at the ordinary tem-
perature, it is converted into ethylene and then into ethane
CH : CH + H 2 == CH 2 lCH 2 .
CH 2 :CH 2 + H 2 = CII 3 .CH 3 .
2. Acetylene unites with two molecules of halogen acid. The
addition occurs in two steps. The two halogen atoms attach
themselves to the same carbon atom, and thus form ethylidene
compounds
CH CH + HI = CH 2 :CHI.
Vinyl iodide.
CH 2 :CHI + HI = CH 3 .CHI 2 .
Ethylidene iodide.
3. Acetylene is rapidly absorbed by the halogens. Acetylene
and bromine form acetylene dibromide and then tetrabromide
CH : CH + Br 2 = CHBrtCHBr.
Acetylene dibromide.
CHBr.CHBr + Br 2 = CHBr 2 .CHBr 2 .
Acetylene tetrabromide.
EXPT. 96. Preparation of Acetylene Tetrabromide. -Fill a gas-
holder with acetylene, and bubble the gas through a U tube con
262 THEORETICAL ORGANIC CHEMISTRY CHAP.
taining bromine cooled in ice. After a time the bromine is decolorised.
The heavy, colourless liquid which is formed is acetylene tetrabromide.
It is purified like ethylene bromide in Expt. 91, p. 249. Acetylene
tetrachloride, C 2 H 2 C1 4 , and the trichloride, C 2 H 3 CI 3 , are now produced
as commercial products for use as solvents, &c.
4. Acetylene and its homologues containing a CH group may
be induced to combine with the elements of water by the action
of strong sulphuric acid, followed by the addition of water, or
by passing the gas into a mixture of mercuric oxide or a mer-
curic salt and dilute sulphuric acid according to the following
equation
CH : CH + H 2 = CH 3 .CHO.
The aldehyde prepared in this way has been utilised com-
mercially for the manufacture of acetic acid by oxidation and
ethyl alcohol by reduction.
Dipropargyl, C 6 H G , though not belonging strictly to the
acetylene series, has a special interest from the fact that it is
isomeric with benzene. Dipropargyl is prepared from diallyl,
CH 2 :CH.CH 2 .CH 2 .CH:CH 2 (p. 265), which contains two double
bonds, and therefore unites with 2 molecules of bromine. The
tetrabromide has the formula
CH 2 Br.CHBr.CH 2 .CH 2 .CHBr.CHoBr.
Diallyl tetrabromide.
When decomposed by alcoholic potash, it loses 4 molecules
of hydrobromic acid and forms dipropargyl, which consequently
has the following formula
CH : C.CH 2 .CH 2 .C : CH.
Dipropargyl.
It is a liquid which boils at 85, and has a specific gravity
of o'8i, whereas benzene boils at 81, and has a specific gravity
ofo*88o. Dipropargyl offers a marked contrast to benzene in
forming additive compounds with 4 molecules of the halo-
gens and halogen acids of the general formula, C 6 H 10 X 4 and
C 6 H 6 X 8 (X stands for the halogen), which may be regarded as
derivatives of hexane, C 6 H 14 . Benzene, on the other hand,
forms additive compounds only with the halogens ; not with
the halogen acids, and in the former case combines with not
more than 3 molecules. Benzene hexachloride has the formula
ETHYLENE 263
QUESTIONS ON CHAPTER XVII
1. Give a method for preparing ethylene. Name three of its charac-
teristic properties.
2. Devise a method for preparing alcohol from the elements carbon
and hydrogen.
3. Compare the properties of the paraffins, defines, and acetylenes.
4. Describe a method for preparing propylene. What products are
obtained when propylene is acted on by bromine, hydriodic acid, and
sulphuric acid ? Give the structural formulae of the products.
5. Give reasons for supposing that methylene exists in the nascent
state.
6. Why is ethylene represented as containing carbon atoms united by
a double bond ?
7. What class of saturated hydrocarbons are isomeric with the defines?
8. How would you separate ethylene from ethane in a mixture of the
two gases, and how would you identify ethylene ?
9. Describe a method by which ethyl iodide may be converted into
ethylene, and vice versa.
10. In what way can acetylene be distinguished from ethylene?
11. What is dipropargyl ? What relation does it bear to benzene ?
12. Explain what is meant by the term unsaturated compound.
How are such compounds identified ?
13. Given 10 c.c. of a gas which is either marsh gas or ethylene,
how would you experimentally determine the composition of the gas ?
14. State concisely the chemical reasons for concluding that ethylene
should be represented by the formula C 2 H4 and not by the formula
CH 2 .
15. Draw a diagram of the apparatus required in the preparation of
ethylene dibromide, and state the method of procedure.
1 6. Starting with acetylene, show how ethylene, ethyl alcohol,
and so-called cuprous acetylide may be obtained from it.
1 7. How is acetylene best obtained ? Compare the action of bromine
upon this compound with its action on marsh gas and ethylene
respectively.
CHAPTER XVIII
DERIVATIVES OF THE UNSATURATED
HYDROCARBONS
Compounds with Multiple Functions. We have up to the
present considered in some detail the properties of certain
families of compounds. It may have been observed that in their
behaviour towards reagents, the paraffins resemble hydrogen.
Both the paraffins and hydrogen are only acted upon (at the
ordinary temperature and in daylight) by chlorine and bromine.
In the same way the atom of hydrogen in certain compounds
resembles the alkyl groups, inasmuch as the one may replace
the other in the various homologous series without greatly
influencing the chemical character of the compound. This is
evident from a comparison of the lowest members of a series,
e.g., formaldehyde and acetaldehyde, formic acid and acetic
acid, ammonia and trimethylamine
H.CHO H.COOH H 3 N.
CH 3 .CHO CH 3 .COOH (CH 3 ) 3 N.
It is not therefore the hydrogen atom or the alkyl group (which
replaces it in these compounds) that determines the difference
in chemical properties which are the distinguishing features of
the various families of compounds, but the presence of such
elements or groups as the halogens, hydroxyl, aldehyde, ketone,
carboxyl, amino, cyanogen, olefine, and acetylene groups.
In this and subsequent chapters we shall treat of compounds
which contain more than one of the above groups. The study
of these compounds is facilitated by the knowledge that each
264
xvin THE ALLYL COMPOUNDS 265
group retains its specific characters for the most part unchanged
in the presence of other groups.
It follows, therefore, that a compound with more than one
group possesses, so to say, more than one set of properties. It
has, what we may term, a multiple function, which means that
it combines the properties of all the groups present. More-
over, if we know the character of the groups in the compound,
it is possible to predict with some certainty the chemical
behaviour of the compound.
The first examples which we shall study are the derivatives
of the unsaturated hydrocarbons. These hydrocarbons form,
like the paraffins, halogen derivatives, alcohols, aldehydes, acids,
c., and yet retain the property of forming additive compounds,
like the olefines and acetylenes.
Derivatives of the Olefines. We shall select for purposes
of illustration some of the derivatives of propylene. These
compounds may be either named after the olefines, from which
they are derived, or designated as compounds of an unsaturated
monovalent radical. The name allyl (from allium, garlic, which
contains allyl sulphide) is given to the radical CH 2 :CH.CH 2 ',
and the compound CH 2 :CH.CH 2 C1 is called allyl chloride;
whereas the isomeric substances CHC1:CH.CH 3 and
CH 2 :CC1.CH 3 are distinguished by the names a- and /3-chloro-
propylene respectively.
Allyl Compounds. All the allyl compounds are obtained
directly or indirectly from glycerol. Allyl chloride and bromide
are prepared from allyl alcohol, CH 2 :CH.CH 2 OH (see below),
by the usual methods for converting alcohols into halogen com-
pounds i.e. by the action of phosphorus chloride or bromide.
Allyl Iodide, CH 2 :CH.CH 2 I, is most readily obtained from
glycerol by the action of yellow phosphorus and iodine
C 8 H B (OH) 8 + I + P = C 8 H 5 I + P(OH) S .
Glycerol. Allyl iodide.
The glycerol and iodine are mixed in a retort attached to a
condenser, and the phosphorus is gradually added, whilst a
current of carbon dioxide is passed through the apparatus. A
violent reaction occurs and the allyl iodide distils. It is purified
in the same manner as ethyl bromide (p. 80). If more iodine
is. used, then isopropyl iodide is formed (p. 84). The two
266 THEORETICAL ORGANIC CHEMISTRY CHAP.
reactions are compared and explained under glycerol (p. 282).
Allyl iodide is a colourless liquid with an odour of garlic. It
boils at 101.
Being unsaturated, it combines with the halogens and halogen
acids. On the other hand, it undergoes reactions like an alkyl
iodide. It gives with potassium cyanide, allyl cyanide ; with
potassium sulphide, allyl sulphide ; and with potassium thiocyan-
ate, allyl thiocyanate, whilst with metallic sodium it forms diallyl,
OI"i2' C/ri.(^ri2v^ri2.Oxi' L/Jr^.
Allyl Sulphide, (C 3 H 5 ) 2 S, is a constituent of garlic (Allium
sativum\ to which it gives the characteristic odour, and is some-
times termed oil of garlic. It has been prepared in the manner
described above, by distilling allyl iodide and potassium
sulphide
2C 3 H 5 I -f K 2 S = (C 3 H 6 ) 2 S + 2KI.
Allyl iodide. Allyl sulphide.
Allyl Isothiocyanate, Oil of Mustard. The oil was first
obtained from black mustard seed, and gives its name to the
family of mustard oils (p. 229). It is present in the seed as a
glucoside, known as sinigrin or potassium myronate, associated
with a hydrolytic ferment, myrosin. The myrosin plays the part
of emulsin in bitter almonds (p. 211), t.e. 9 when the seed is
crushed with water, hydrolysis occurs and the glucoside is
broken up into glucose, potassium hydrogen sulphate, and allyl
isothiocyanate. The same decomposition is produced by dilute
mineral acids
C 10 H 16 NS 2 9 K + H 2 = C 6 H 12 6 + KHSO 4 + C 3 H 6 N.CS.
Potassium myronate. Allyl isothiocyanate.
Oil of mustard has been synthesised from allyl iodide and
potassium thiocyanate. Allyl thiocyanate is first formed, which
on distillation undergoes intramolecular change and yields the
isothiocyanate liquid, boiling at 151 and possessing a sharp and
pungent taste and smell.
Allyl Alcohol, CH 2 :CH.CH 2 .OH, is prepared by heating
glycerol with oxalic acid. This reaction resembles that by which
formic acid is obtained (p. 156), but it differs from it in certain
important respects. The compound first formed is the same in
both processes, viz. glycerol oxalic acid ester ; but the tempera-
ture at which the product is distilled is much higher (200 220)
XVIII THE ALLYL COMPOUNDS 267
in the case of allyl alcohol. At this temperature, the acid
oxalic ester is transformed into the neutral ester which decom-
poses into allyl alcohol and carbon dioxide
CH 2 .O.CO.C0 2 H CH 2 .O.CO CH 2
CH(OH) . CH.O.CO CH
I ["*"" I
:H 2 OH CH 2 OH CII 2 OH
Allyl alcohol.
V^A
c*
It will be Observed that it is the glycerol which yields the
allyl alcohol and not the oxalic acid, whereas in the preparation
of formic acid, the oxalic acid undergoes decomposition and the
glycerol is unchanged. The proportion of glycerol used in the
present case is consequently much larger.
Allyl alcohol is a colourless liquid with a pungent smell and
boils at 96. It combines the properties of an olefine and an
alcohol. On the one hand, it forms additive compounds with
the halogens, and may be converted by gentle oxidation with
potassium permanganate into glycerol, just as ethylene is con-
verted into glycol (p. 248). On the other hand, it shows the
characteristics of a primary alcohol, and with energetic oxidising
agents may be converted into an aldehyde, acrylaldehyde, or
acrolein, and then into a monobasic acid, acrylic acid
CH 2 CH 2 CH 2
CH CH CH
I I I
CH 2 .OII CH:0 CO.OH
Allyl alcohol. Acrolein. Acrylic acid.
EXPT. 97. Preparation of Allyl Alcohol Distil a mixture of
50 grams of oxalic acid and 200 grams of glycerol from a retort,
which is attached to a condenser and receiver. Continue heating
until the temperature reaches 180. Change the receiver and con-
tinue the distillation until 260 is reached. The first distillate
contains some formic acid, the second distillate consists of impure
allyl alcohol. The latter is redistilled until the temperature reaches
105. The distillate is dehydrated with solid potassium carbonate,
and the liquid removed and redistilled. Add bromine water to a
little of the allyl alcohol. It is immediately decolorised from the
formation of o-j8-dibromopropyl alcohol, CH 2 Br.CHBr.CH 2 OH.
268 THEORETICAL ORGANIC CHEMISTRY CHAP.
Acrolein, Acrylaldehyde, CH 2 :CH.CHO, is most easily
obtained by distilling a mixture of glycerol and potassium
hydrogen sulphate. The latter acts as a dehydrating agent
C 3 H 5 (OH) 3 - 2H 2 O = C 3 H 4 p.
Acrolein.
EXPT. 98. Mix together 10 parts of glycerol and I part of crystal-
lised potassium bisulphate in a test-tube and heat the mixture. The
vapour given off attacks the eyes and mucous membrane. If the
experiment is conducted on^a larger scale, a capacious retort must be
taken, as the mixture froths up on heating. A mixture of 250 grams of
glycerol and 10 parts of crystallised potassium bisulphate is introduced
and heated. The retort is connected with a condenser and receiver.
The distillate is fractionated and dehydrated over calcium chloride.
Acrolein is a colourless liquid which boils at 52. It has the
properties of an aldehyde, reducing alkaline solutions of silver
and copper and combining with sodium bisulphite to form an,
additive compound." It can be reduced to allyl alcohol and
oxidised to acrylic acid. Its olefinic character is shown by the
fact of its combining with the halogqns and halogen acids.
With bromine, dibromopropionaldehyde is formed
CH 2 :CH.CHO + Br 2 = CH 2 Br.CHBr.CHO.
Dibromopropionaldehj'de.
Acrolein has a penetrating smell, and attacks the eyes. The
unpleasant smell of burnt fat is due to the decomposition of the
glycerol of the fat, and the formation of acrolein.
Acrylic Acid, CH 2 :CH.CO.OH, is the simplest member of
the important group of unsaturated fatty acids. It is formed in
a variety of ways ; by the oxidation of acrolein ; by the action
of alcoholic potash on a or /3-bromopropiohic acid, and by heat-
ing hydracrylic acid, or hydroxypropionic acid, CH 2 (OH).CH 2 .
COOH, to which reference will be made later (p. 321)
CH 3 .CHBr.COOH + KOH = CH 2 :CH.COOH + KBr + H 2 O.
a-Bromopropionic acid. Acrylic acid.
CH 2 OH.CH 2 .COOH = CH 2 :CH.COOH + H 2 O.
Hydracrylic acid. Acrylic acid.
Acrylic acid is a liquid with a pungent smell, which boils at
140. It possesses the properties of an unsaturated compound.
On reduction, it yields propionic acid ; with bromine it forms
xviii UNSATURATED MONOBASIC ACIDS 269
dibromopropionic acid ; with hydrochloric acid it gives 0-chloro-
propionic acid. In the latter case it should be noted that the
halogen attaches itself to the carbon farthest from the carboxyl,
which is the general rule when halogen acids unite with un-
saturated acids
CH 2 Br. CHBr. CO. OH. CH 2 C1. CH 2 . COOH.
Dibromopropionic acid. , /3-Chloropropionic acid.
When acrylic acid is oxidised with permanganate, dihydroxy-
propionic acid (glyceric acid) is first formed, which on further
oxidation breaks up into carbon dioxide and oxalic acid
CH 2 CH 2 .OH C0 2
CH CH.OH COOH
CO. OH CO. OH COOH.
Acrylic Glyceric Oxalic acid and
acid - acid. Carbon dioxide.
Crotonaldehyde and Crotonic Add are the next homologues of acrolein
and acrylic acid.
Crotonaldehyde, CH 3 .CH:CH.CHO, is prepared by heating acet-
aldehyde with zinc chloride. Aldol (p. 132) is first formed, which
then loses a molecule of water
CH 3 .CH(OH).CH 2 .CHO = CH 8 .CH:CH.CHO + H 2 O.
Aldol. Crotonaldehyde.
Crotonaldehyde is a liquid which boils at 104.
Crotonic Acid, CH 3 .CH:CH.COOH, is obtained by the oxidation
of Crotonaldehyde ; also by the hydrolysis of allyl cyanide and by the
action of alcoholic potash on a-bromobutyric acid. Crotonic acid is
a solid which melts at 72 and closely resembles acrylic acid in its
chemical characters. It derives its name from croton oil, from which it
was originally obtained. An isomeric acid, known as isocrotonic acid,
has many of the properties of crotonic acid, but is a liquid at the ordinary
temperature.
Oleic Acid, C 18 H 34 O 2 , has already been -referred to under fats
and oils (p. 165) ; but belongs strictly to the acrylic acid series.
In animal fat, olive oil and other vegetable oils, it is present as
the glyceride or olein. Its lead salt is soluble in ether, and this
property is utilised for separating it from stearic and palmitic
acid, the lead salts of which are insoluble. Its relationship to
270 THEORETICAL ORGANIC CHEMISTRY CHAP.
stearic and palmitic acids as well as its unsaturated character are
clearly exhibited by the following reactions. It forms additive
compounds with iodine, bromine, and also with strong sulphuric
acid.
EXPT. 99. Add a few drops of a solution of bromine in carbon
tetrachloride to oleic acid or olein and shake up. The colour is at
once discharged.
It is oxidised by fusion with caustic potash to palmitic acid
and acetic acid
Ci H 34.2 + H 2 - C 18 H 36 O 2 .
Oleic acid. Stearic acid.
C 18 H 84 0, + 2KOH = C, 6 H 31 2 K + C 2 H 3 O 2 K + H 2 .
Potassium
palmitate.
It can also be reduced by nickel or nickel oxide at 200-250 in
presence of hydrogen to stearic acid. Olein in the same way
and many other liquid fats and oils are rendered solid (fat-
hardening process).
When the compound with sulphuric acid is distilled with
steam, it is converted into a solid isomer of oleic acid, known as
isoleic acid, which can be used like stearic and palmitic acid in
candle-making. This constitutes one of the advantages of the
sulphuric acid saponification process (p. 167), as by this means
a larger output of solid acids is obtained than by the other
saponification methods. Another solid isomer, elaidic acid, is
obtained by treating oleic acid with nitrous acid.
EXPT. loo. Pour u few c.c. of oleic acid into a test-tube and add
a small piece ot sod:- urn nitnte and a drop or two of strong nitric
acid. Nitrous acid is evolved, and in a few minutes the oleic acid is
converted into solid elaidic acid. A similar change occurs with
olive oil.
The formation of these isomers may be explained either by
a change produced in the position of the double bond in the
chain of carbon atoms or by some difference in the space
arrangement of the atoms ; but these points will be more fully
discussed in a subsequent chapter (p. 363).
Linoleic Acid, C 18 H 32 O 2 , is present as the glyceride, together
with the glycerides of linolenic acid, C 18 H3oO 2 , and other
xvni UNSATURATED MONOBASIC ACIDS 271
unsaturated acids, in the so-called drying oils, e.g. linseed,
cotton-seed, and rape-seed oils. These oils possess the property
of absorbing oxygen from the air and changing into transparent
resinous substances. The change is hastened by heating the
oil with certain metallic compounds known as driers, such as
lead oxide, manganese borate, etc. When linseed oil is thus
treated it is known as boiled linseed oil.
Linseed Oil. The boiled oil is used as a vehicle for pigments,
and forms, when dry, a hard, protective, and at the same time
transparent, covering. By pouring successive layers of the oil on
to cloth or canvas and freely exposing them to the air, the oil
hardens and forms the material known as oil-cloth. Linoleum
is produced in a similar manner by first oxidising the heated oil
by blowing a current of air or oxygen through the liquid,
thereby forcing it into a fine spray. The semi-solid gelatinous
product is melted and mixed with powdered cork and other
materials, and spread out in thin layers, which on cooling
become solid.
The absorption of oxygen by drying oils is generally
accompanied by a considerable rise of temperature, and fires
have been known to originate through the spontaneous ignition
of cotton waste which has become impregnated with oil in the
cleaning of machinery.
Varnishes are also made from boiled linseed oil, by mixing it
with certain gums or resins and diluting with turpentine or
spirits of wine.
Eicinoleic Acid, Cj 8 H 34 O 3 , is an unsaturated hydroxy-acid, i.e. an
unsaturated acid, which contains a hydroxyl group. It does not there-
fore belong to the acrylic series ; but it is convenient to consider it
here. It is present as the glyceride in castor oil ; the latter beinjr
Expressed from the seeds of the castor oilplant (Ricinus). When castor
oil is mixed with strong sulphuric acid, it forms a compound which
dissolves in water, and after neutralising with alkali is used in dyeing,
under the name of Turkey red oil.
The quantity of the glycerides of unsaturated acids present
in various oils is estimated by the amount of iodine with which
they combine, which is measured by adding a standard solution
of iodine and estimating the quantity absorbed. The measure
of this amount is known as the iodine value (p. 166).
THEORETICAL ORGANIC CHEMISTRY CH. xvni
QUESTIONS ON CHAPTER XVIII
1. Why is allyl alcohol termed an unsaturated primary alcohol?
How is it prepared ?
2. How do you explain the difference in the formation of (i) formic
acid and (2) allyl alcohol from glycerol and oxalic acid ?
3. Describe the preparation of allyl iodide from glycerol. What
other substance is obtained by the use of the same reagents ?
4. What are oil of mustard and oil of garlic ? What are the natural
sources of these compounds, and how have they been synthesised ?
5. How can oleic acid be obtained free from palmitic and stearic
acids ? What relation exists between these three acids ?
6. Describe the preparation of acrolein. In what respects may it be
said to possess mixed functions ?
7. Describe and explain the technical uses of linseed oil.
8. Give an account of the action of chlorine, hydriodic acid,
reducing and oxidising agents, upon acrylic acid. How is it prepared ?
9. Which classes of carbon compounds form " addition-products,"
and which of these classes would be termed unsaturated ?
10. Describe the method by which oil of mustard can be formed
from allyl iodide. Explain the action of ammonia on mustard oil.
11. Write the equations showing the conversion of glycerine into
acrolein and acrolein into acrylic acid.
CHAPTER XIX
THE POLYHYDRIC ALCOHOLS AND THEIR
DERIVATIVES
The Polyhydric Alcohols are, like methyl and ethyl alcohol,
hydroxy-derivatives of the paraffins, but contain more than one
hydroxyl group. According to the number of hydroxyl groups
present in the compound, they are known as mono-, di-, tri-,
etc., hydric alcohols. The names of all the alcohols terminate
in the syllable oL Thus ethyl alcohol, C 2 H 5 ,OH, is a mono-
hydric alcohol ; glycol, C 2 H 4 (OH) 2 , a dihydric alcohol ; glycerol,
C 3 H 5 (OH) 3 , a trihydric alcohol ; "erythritol, C 4 H 6 (OH) 4 , a tetra-
hydric alcohol, and so forth. The properties of the hydroxyl
group, which distinguish the monohydric alcohols as a class,
are exhibited by all the polyhydric alcohols, but as the latter
contain more than one hydroxyl group, and as each group retains
its alcoholic characters, a much greater variety of products is
necessarily formed by the action of reagents.
The Glycols, C n H 2n (OH) 2 , are so named from the first
member, C 2 H 4 (OH) 2 , now known as ethylene glycol, which was
prepared in 1859 by Wurtz, and which like most of the glycols
possesses a sweet taste (yAiWs-, sweet). The glycols are most
easily prepared from the dihalogen derivatives of the paraffins
by the action of water and metallic oxides, in much the same
way as the monohydric alcohols are obtained from the alkyl
halides (p. 82). Ethylene bromide, when boiled with water and
potassium carbonate, yields ethylene glycol. The product is then
distilled and fractionated
CHoBr CH 2 .OH
4- H 9 O + K COo = | + 2KBr + COo.
CH 2 Br CH 2 .OH
Ethylene glycol.
=73 T
274 THEORETICAL ORGANIC CHEMISTRY CHAP.
Another method, which has already been mentioned, but is
less common, is to oxidise the olefines with permanganate (p.
248). Neither methylene glycol, CH 2 (OH) 2 , ethylidene glycol,
CH 3 .CH(OH) 2 , nor, in fact, any dihydric alcohol with both
hydroxyls linked to one carbon atom are known in the free state.
This is due to the instability of these compounds, which, by the
removal of the elements of water, form aldehydes. This has
already been explained on p. 88. Chloralhydrate appears to
form an exception, and must be regarded as a trichlorethylidene
glycol (p. 139). Although ethylidene glycol and its homologues
are unknown, many of their derivatives have been obtained. The
ethers of these compounds have already been described under
the name of acetals (p. 132).
The glycols are colourless, rather viscid liquids resembling
glycerol, with a high boiling-point and a sweet taste. They are
very soluble in water.
Both the solubility in water and the high boiling-point
must be ascribed to the presence of hydroxyl groups.
Ethyl alcohol boils at 78, whereas ethylene glycol boils
at 195.
The glycols exhibit all the properties of alcohols, but in a
twofold degree. Ethylene glycol is a di-primary alcohol, and
by successive oxidation of the two carbinol groups to aldehyde
and carboxyl groups, the following series of products should be
obtainable
CH 2 OH CH 2 OH CHO CHO CO.OH
I I I I I
CHO COOH CHO CO.OH CO.OH
Glycollic Glycollic Glyoxal. Glyoxalic Oxalic
aldehyde. acid. acid. acid.
All these compounds are known, but only three of them, viz.
glycollic, glyoxalic, and oxalic acid, have been directly obtained
from glycol by oxidation. In regard to the action of other
reagents on glycol, metallic sodium forms a mono- and di-sodium
derivative ; two sets of ethers are produced by the action of
alkyl iodides on the sodium compounds, whilst two series of
esters are obtained by the action of one or two molecules of
acid chloride on the glycol. The following are the compounds
formed from ethylene glycol
THE POLVHYDRIC ALCOHOLS 275
CILONa
!
CH 2 .OC 2 H 5
CH 2 .OCO.CII 3
CH 2 OH
CH 2 OH
CH 2 OH
Sodium glycolate.
Glycol ethyl ether.
Glycol monoacetate.
t
CH.ONa
CH 2 .OC 2 H 5
CH 2 .O.CO.CH 3
CH 2 ONa
CH 2 .OC 2 H 5
CH 2 .O.CO.CH 3 .
Disodium glycolate.
Glycol diethyl ether.
Glycol diacetate.
When hydrochloric acid gas is passed into a glycol, only one
hydroxyl is replaced by chlorine, and the compounds which are
thus obtained are identical with the chlorhydrins formed by the
action of hypochlorous acid on the olefines (p. 247). Phosphorus
chloride and bromide replace both hydroxyls by halogens, and
form respectively ethylene chloride and bromide
CH.,OH CH 2 C1
I + HC1 = | + H 2 0.
CH 2 OH CH 2 OH
Ethylene
chlorhydrin. ,
CH 9 OH" CHoCl
j + 2PCI 5 = |
CHoOH CH 2 C1
Ethylene
chloride.
Ethylene Oxide, C 2 H 4 O. By the action of caustic alkalis on
the chlorhydrins, hydrochloric acid is removed and alkylene
oxides are formed. Ethylene chlorhydrin yields ethylene
oxide
Cl /CH 2
+ KOH=O<;| + KC1 + H 2 O.
CH 2 , H \CH 2
Ethylene oxide.
It is isomeric with acetaldehyde and is an ethereal-smelling
mobile liquid which boils at 14. Ethylene oxide may be re-
garded as dimethyl ether in which the two carbon atoms are
linked together. Such a combination is sometimes known as an
inner ether. Its properties, however, are very unlike those of
dimethyl ether. Although it is a saturated compound it readily
unites with halogen acids, water, nascent hydrogen, and many
T2
2 7 6
THEORETICAL ORGANIC CHEMISTRY
CHAP.
reagents whereby one link between oxygen and carbon is
broken. The following equations will explain these changes
CH
CH 2
>0
H CH 2 OH
Cl
H
CHoCl
Ethylene
chlorhydrin.
CHoOH
CH
2\
CH 2
OH
H
H
CH 2 OH
Ethylene
glycol.
CH 3
Ethyl
alcohol.
The affinity of ethylene oxide for hydrochloric acid is so
great that it takes up the acid from solutions of metallic
chlorides and precipitates the base. The same properties are
exhibited by other alkylene oxides.
Sulphonal, (CH 3 ) 2 C(SO 2 C 2 H 5 ) 2 . The acetals are formed, as
we have seen, by the union of aldehydes and alcohols (p. 132).
Aldehydes and ketones behave similarly with mercaptans.
Thus, acetone and ethyl mercaptan combine in presence of
hydrochloric acid or zinc chloride and form a mercaptol
CH 3
CJOH
CH""
CH 3
1
CH 3
Mercaptol.
H 2 0.
The latter when oxidised with permanganate solution yields
sulphonal, which is largely used in medicine a 3 a soporific
(see p. 196).
Trional) which is used for the same purpose, is obtained from methyl
ethyl ketone, (CH 3 )(C2H 5 )C(SO 2 C 2 H 5 ) 2 , and tetronal is the tetiaethyl
derivative, (C 2 H 5 ) 2 C(SO 2 C 2 H 5 ) 2 .
Xix THE POLYHYDRIC ALCOHOLS
277
CH 3 CH 3
C(SC 3 H 5 ) 2 + 20 2 = C(SO a C 2 H B ) a .
CH 3 CH 3
Sulphonal.
Diamines. When ammonia acts upon ethylene chloride it
combines with it as it does with an alkyl iodide, but both
halogen atoms in ethylene chloride are replaced by amino
groups and ethylene diamine is produced
CH 2 C1 CH 2 .NH 2
+ 4NH 3 = + 2NH 4 C1.
CH 2 C1 CH 2 .NH 2
Ethylene diamine.
The other alkylene halides behave similarly. These com-
pounds are called primary diamines^ and are basic substances
like the amines. They are also obtained by the reduction of
dicyanides by means of sodium in alcoholic solution. Tri-
methylene cyanide, which is prepared by the action of potassium
cyanide on trimethylene bromide, gives, in this way, penta-
methylene diamine
CN CH 2 .NH 2
(CH 2 ) 3 + 4 H 2 = (CH 2 ) 3
CN CH 2 .NH 2
Trimethylene cyanide. Petitamethylene diamine. 1
Tetramethylene diamine, or putrescine, and pentamethylene
diamine, or cadaverine, are found in the body after death among
the basic products formed by the putrefaction of albumin, and
are included in the group of compounds known as ptomaines.
Ammonia acts upon ethylene chloride in another manner than the
one described above. Two molecules of ammonia under certain
conditions combine with two molecules of ethylene chloride. The
product is a basic substance known as piperazine.
CT;CH 2 .CH 2 !Ci
W TT T-T 4- " i i TT
C1^CH 2 .CHJC1
r^TT r^T-T
NH = HN^ 2 \NH + 4 HC1.
\CH 2 -CH/
Pipeiazine.
1 The group (CH 2 ) 3 in the formulae is an abbreviated^ form of 'CH 2 .CHo.CH 2 '.
and is known as the trimethylene radical to distinguish it from CHs-CH'.CH^', or
propylene radical.
278 THEORETICAL ORGANIC CHEMISTRY CHAP.
Piperazine forms a soluble salt with uric acid, and is used in medicine.
The following three compounds, which are associated with products of
the animal and vegetable organism, and may be regarded as derivatives
of ethylene, are sufficiently important to be briefly mentioned. They
are known as choline, neurine, and taurine.
Choline is widely distributed in the animal organism, especially in
the brain and in egg yolk, forming a curiously complex compound
with glycerol, phosphoric acid, and stearic acid, known as lecithin.
CH 2 .OOC 17 H 35
CH.OOC 17 H 35
I
HO OCH 2 .CH 2 .N(CH 3 ) 3 OH
Lecithin.
Choline is also found in the seeds of many plants. It is obtained
synthetically by the action of trimethylamine on a strong solution of
ethylene oxide
CH 2X CH 2 OH
I >0 + H 2 + N(CH 3 ) 3 = |
CH/ CH 2 N(CH 3 ) 3 OH.
Choline.
Choline forms a hygroscopic crystalline mass, which has an alkaline
reaction.
Neurine is found among the ptomaines, and is a product of the
putrefaction of albumin. It has been obtained synthetically by acting
on ethylene bromide with trimethylamine and then treating the
product with silver hydroxide
CH 2 Br CH 2
| + 2AgOH = || + 2AgBr + H, O.
CH 2 .N(CH 3 ) 3 Br CH.N(CH 3 ) 3 OH
Neurine.
It may be described as trimethylvinylammonium hydroxide, and has
the basic characters of a quaternary ammonium hydroxide (p. 202).
Taurine is present in combination with cholic acid under the name
of taurocholic acid in the bile. From its synthesis from isetkionic
acid it must be regarded as aminoethylsulphonic acid, or, seeing that
it is a neutral substance, it may be supposed that the basic aminu-
group neutralises the acid sulphonic group. Its formula is thus
represented
xix THE POLYHYDRIC ALCOHOLS 279
CH 2 .NH 2 CH 2 .NH 3V
i or | >0.
CH 2 .SO 2 .OH CH 2 .SO/
Taurine.
Isethionic acid is obtained from ethyl alcohol and sulphur trioxide,
and is hydroxyethylsulphonic acid. By the action of phosphorus
pentachloride, the hydroxyl groups are replaced by chlorine, and when
the product is boiled with water, chlorethylsulphonic acid is formed.
Finally when the last product is heated with ammonia, taurine is
formed. These changes are represented as follows
3 20
> CH 2 .SO 2 C1 " * CH 2 SO 3 H ~~~ CH 2 SO 3 H.
Isethionic Chlorethyl Chlorethyl Taurine.
acid. sulphonlc chloride. sulphonic acid.
Glycerol, Glycerine, or Glyceryl alcolwl? C 3 H 5 (OH) 3 .-
Glycerol is the only representative of the trihydric alcohols. It
was discovered by Scheele in 1779, who found a sweet-tasting
liquid separated when olive oil was heated with litharge. It
was afterwards observed by Chevreul to be a common constituent
of natural fats and oils (p. 165). A small quantity of glycerol is
found among the products of alcoholic fermentation (p. 104).
Glycerol is a viscid, colourless liquid with a sweet taste, which,
when pure, crystallises slowly on cooling and then melts at 1 7. It
boils at 290 with very slight decomposition when pure, and it can
be readily distilled with superheated steam or under diminished
pressure. It is hygroscopic and mixes with water in all
proportions.
The constitution of glycerol has been determined by numerous
syntheses. Acetone gives isopropyl alcohol on reduction, and
the latter when heated with sulphuric acid forms propylene.
Propylene combines with chlorine, giving propylene chloride,
which iodine chloride converts into trichloropropane or glyceryl
trichloride. When glyceryl chloride is heated with water to 170
it yields glycerol
CH 3
CH,
CH,C1 CH 2 (OH)
|
1
CH
C1 2
CHCl
IClo
CHCl '3 H J? CH(OH)
CH 2
~~ >
4
CHoCl
1
CH 9 C1 (
:H,(OH).
Propylene.
Propylene chloride. Glyceryl trichloride.
Glycerol.
1 The term g lyceryl is applied to the trivalent radical CH 2 '.CH'.CHo'.
280 THEORETICAL ORGANIC CHEMISTRY CHAP.
Dioxyacetone, CH 2 OH.CO.CH 2 OH, has been obtained syn-
thetically, and gives glycerol on reduction. Allyl alcohol can also
be converted into glycerol by oxidation with permanganate (p. 265 ).
Chemical Properties of Glycerol. The chemical behaviour
of glycerol fully bears out the above constitution. It has the
properties of a trihydric alcohol. It forms esters by uniting
with i, 2, and 3 molecules of an acid radical. Thus, mono-, di-,
and tri-formyl and acetyl esters are known, which are named
respectively mono-, di-, and tri-formin and acetin.
CH 2 . 0. CO. CH ? CH 2 . 0. CO. CH, CH 2 . 0. CO. CH 8
CHOH CH.O.CO.CH 3 CH.O.CO.CH 8
I I !
CH 2 OH CH 2 OH CIL.O.CO.CHg
Mono-acetin. Di-acetin. Tri-acetin.
The glycerides of palmitic, stearic, and oleic acids, which occur
in fats, &c., are triacid esters, and should strictly be termed tri-
palmitin, tristearin, and triolein.
The mono-, di-, and tri-nitrates of glycerol are also known,
the latter, which is referred to below, being incorrectly named
nitroglycerine.
When hydrochloric acid gas is passed into glycerol it is
absorbed and forms glycerol a-monochlorhydrin ; if the
glycerol is dissolved in acetic acid and heated whilst the gas is
passed in, then the dichlorhydrin is produced ; the third hydroxyl
group can be replaced by chlorine by the action of phosphorus
chloride, the product being glyceryl trichloride, which smells
like chloroform. All three substances are liquids.
CH 2 OH CH 2 C1 CH 2 C1
CHOH CHOH CHC1
I I I
CH 2 C1 CH 2 C1 CH 2 C1.
Glycerol Glycerol Glyceryl
a-monochlorhydrin. aa-dichlorhydrin. trichloride.
The products of oxidation of glycerol, which are theoretically
possible, are very numerous, and many of them have been
obtained either directly or indirectly from glycerol. Glycerol
contains two primary and one secondary alcohol group. The
two primary groups should yield successively aldehyde and-
xix THE POLYHYDRIC ALCOHOLS 281
carboxyl groups ; the secondary, a ketone group. By the action
of dilute nitric acid on glycerol, glyceric and tartronic acids have
been obtained. On further oxidation oxalic is formed.
CH 2 OH CO. OH
! |
CHOH CH.OH
! I
CO.OH CO.OH.
Glyceric acid. Tartronic acid.
By the action of bromine in presence of sodium carbonate solu-
tion dihydroxyacetone is produced. A solution of caustic soda con-
verts a part of the dihydroxyacetone into the isomeric compound
glyceric aldehyde, and at the same time the alkali brings about
the aldol condensation (p. 139) between the two molecules with
the formation of an artificial sugar, which has been identified as
inactive fruit sugar, a-acrose, or fructose (p. 295)
CHoOH CHoOH CH 2 OH CH 9 OH
I I I ' I '
CHOH + CO = CHOH CO
I I I I
CHO CH 2 OH CHOH CHOH.
Glyceric aldehyde. Dihydroxyacetone. Fructose, or a-Acrose.
GLycerol undergoes fermentation with different ferments and
gives rise to various products. Certain bacteria produce butyl
alcohol, others ethyl alcohol, a third kind convert glycerol into
dioxyacetone, c.
Before discussing the industrial preparations and uses of
glycerol the student is reminded of the various reactions already
described in which glycerol plays a part.
Summary of Preparations in which Glycerol is used. By
distilling glycerol with potassium bisulphate, acrolein is formed
(p. 268). By heating glycerol with oxalic acid, either formic
acid (p. 156) or allyl alcohol (p. 266) is produced. By the
action of phosphorus and iodine, isopropyl iodide (p. 84), allyl
iodide (p. 265), or propylene is formed, according to the con-
ditions of the reaction. The formation of these different products
may be explained as the result of the action of hydriodic acid
282 THEORETICAL ORGANIC CHEMISTRY CHAP.
upon glycerol in varying proportions, as follows: We may
suppose in the first place that glyceryl triiodide is formed. This
loses iodine and forms allyl iodide. Allyl iodide may form pro-
pylene iodide by uniting with a molecule of hydriodic acid. If
at this point the temperature is raised, propylene is formed,
but if sufficient hydriodic is present to reduce the propylene
iodide, then isopropyl iodide is formed
CH 2 :OH Hjl C1LJ CH 2
I ! I II
CH,;OH + H I = CHI + sH 2 O = CH + L>.
Ill I
CHoOH HI CH 2 I CHJ
Glyceryl triiodide Allyl
(not isolated). iodide.
CHo H CH 3 CH 3
II I I
CH + I = CHI = CH + I 2 .
I I II
CH 2 I CH 2 I CH 2
Propylene Propylene.
iodide.
CH 3 CH 3
CHI = CHI + I 2 .
I I
CH 2 ji + I;H CH 3
Isopropyl iodide.
Manufacture of Glycerol. Glycerol is manufactured on a
large scale for a great variety of industrial purposes. The chief
sources are the fats and oils and spent lyes of the soap-works.
It has already been stated (p. 167) that the fats and oils are
usually hydrolysed either with a little strong sulphuric acid, or
by superheated steam, in the presence of a small quantity of
lime. In the sulphuric acid process, which is used for the
poorer qualities of fat and oil, some of the glycerol is decom-
posed by the acid, but the remainder is recovered from the
liquors from which the fatty acids have been separated. In the
lime process, the " sweet water " which contains the glycerol
is concentrated, filtered through animal charcoal to remove
colouring matter, and evaporated to the requisite specific gravity.
The spent lyes of the soap-works, containing 5 to 8 per cent, of
glycerol, were until recently a waste-product. At the present
xix THE POLYP1YDRIC ALCOHOLS 283
time they are the main source of the glycerol used in commerce.
The lyes contain large quantities of sodium chloride, free
alkali, and fatty and resinous matters, which have first to be
separated. The lyes are acidified, and filtered from the fatty
and resinous matters, then neutralised and concentrated under
diminished pressure, whereby the salts are deposited and
removed. By whichever 'process the glycerol is obtained, it is
usually purified by distillation with superheated steam. The
distillate, which contains water, is evaporated to the requisite
consistency in steam-heated vacuum pans, i.e. vessels from
which the air is partially exhausted. In this way evaporation
can be rapidly effected at a temperature at which no decom-
position or discoloration of the glycerol can occur. Glycerol
combines with metaphosphoric acid to form glycerolphosphoric
acid
the salts of which are used as a tonic in medicine. But the
greater part of the distilled glycerol is used in the manufacture
of nitroglycerine.
Nitroglycerine, Glyceryltrinitrate, NobePs oil, C 3 H 5 (ONO 2 ) 3 .
The formation of nitroglycerine by the action of nitric acid
on glycerol was discovered by Sobrero in 1846, but the prac-
tical application of this discovery to the manufacture of.
explosives is due to Nobel, a Swedish engineer (1862). Nitro-
glycerine is prepared by mixing 12 parts of fuming nitric acid
and 20 parts of sulphuric acid and injecting into the well-cooled
acid mixture a spray of glycerol (4 parts), which is forced in by
a current of air
C 3 H 5 (OH) 3 + 3 HN0 3 = C S H 6 (ON0. 2 ) S -f- 3H 2 O.
Glyceryl \ itrate, or
Nitroglycerine.
The sulphuric acid serves to unite ;vvth the water which is
formed in the reaction. The njlxtuie is allowed to stand, and
the nitroglycerine, which forms a layer on the surface, is run
into water, from which it separates as a heavy oil. It is well
mixed with the water and then with a solution of sodium
carbonate to remove all trace of acid, which, if present, renders
the substance liable to decompose and explode. It is finally
freed from water by filtering through flannel or felt covered with
a layer of salt.
284 THEORETICAL ORGANIC CHEMISTRY CHAP.
Properties of Nitroglycerine. Nitroglycerine is a heavy,
colourless liquid of specific gravity i'6, which solidifies at 8.
It has a sweetish, burning taste, and is poisonous. In minute
doses it is used in medicine. When spread in a thin layer over
a large surface, it may be ignited without danger, and burns
quietly ; but when suddenly heated, it explodes like most of the
nitric esters. A more violent explosion is produced by detonation.
The uncertainty which first attended the use of the oil as an
explosive led to the discovery that the admixture of inert absorb-
ent materials', whilst increasing the explosive force, rendered
the nitroglycerine less sensitive and more easily manipulated.
Dynamite is made by mixing 3 parts of nitroglycerine
with I part of kieselguhr, a fine siliceous earth which is very
light and porous, and can absorb considerable quantities
of nitroglycerine without becoming pasty. The mixture is
moulded and compressed into cartridges and fired by a
detonator (mercury fulminate). Blasting gelatine is made by
dissolving 7 parts of nitrated cellulose (p. 310) in 93 parts of
nitroglycerine, and forms a solid translucent mass. Cordite is
prepared from nitroglycerine (18 parts) and gun-cotton (73 parts)
made into a pulp with acetone, to which a little vaseline is added.
The pulp is squeezed through small holes into threads from which
the acetone evaporates, and the threads are cut up and used for
smokeless rifle cartridges. A great number of explosives are
prepared containing nitroglycerine mixed with such substances
as sawdust, charcoal, nitrates of potassium and ammonium, etc.,
and are known as/H) 2 is an abbreviated form for CH.OH.CH.OH .
287
288 TPIEORETICAL ORGANIC CHEMISTRY CHAP.
The existence of the large number of isomers in the examples
given above is due to the difference in space arrangement or
configuration of the atoms, which is discussed in a later
chapter (p. 355). '
The Carbohydrates. The most important members of the
family of hydroxy-aldehydes and ketones are the pentoses and
hexoses, which, together with certain related compounds of a
highly complex structure, are grouped together under the name
of carbohydrates.
The carbohydrates are among the chief products of plant life,
and are also found, but less extensively, in the animal kingdom.
Grape-sugar, fruit-sugar, cane-sugar, starch, cellulose, and the
gums are vegetable products, whilst milk-sugar, glycogen, and,
occasionally, grape-sugar are derived from the animal organism.
The study of their formation and decomposition in the living
organism belongs to the domain of plant and animal physio-
logy. Organic chemistry is concerned with their chemical
changes outside the body.
The wide distribution of the carbohydrates, their extensive
consumption as food, and their employment in various indus-
tries, as in the manufacture of fabrics and paper and in the
production of alcohol, have given them an interest and import-
ance possessed by few other groups of organic compounds.
Some of the carbohydrates,- like cane- and grape-sugar, are
crystalline, soluble in water, and sweet ; whilst others, like starch
and cellulose, are tasteless, insoluble in water, and possess an
organised structure. Although these two groups show marked
differences in physical properties, they are, nevertheless, closely
related chemically. The majority of them contain hydrogen
and oxygen in the proportion found in water, so that their com-
position may be expressed by the formula C x (H 2 O) y . This fact
has given rise to the name hydrate of carbon, or carbohydrate.
The more complex members are readily hydrolysed by acids
or hydrolytic ferments (p. 105) into one or more of the simpler
members. Thus, starch and cellulose, on boiling with dilute
sulphuric acid, are both converted into grape-sugar
(C 6 H 10 5 ) n + nH 2 = nC 6 H 12 6 .
Starch or Cellulose. Grape-sugar.
Classification of the Carbohydrates. The carbohydrates
fall naturally into two classes, as explained above ; the sweet
THE CARBOHYDRATES
289
and crystalline substances form one class, termed sugars, and
the tasteless and non-crystalline compounds belong to the other.
The sugars are further divisible into two principal groups of a
more and less complex molecular formula. There are three
groups, therefore which are distinguished by the names mono-
saccharoses^ with 5 and 6 carbon atoms, of the general formula
C 6 H 10 O 5 and C 6 H 12 O 6 ;?the disaccharoses, with 12 carbon atoms,
of the general formula C^H^On ; (there is also a trisaccharose of
the formula C 18 H 32 O 16 and a tetrasaccharose, C 24 H 42 O 21 ;) and the
poly saccharoses of unknown but high molecular weight, possessing
the empirical formula C 6 H 10 O 6 , usually written (C 6 H 10 O 5 ) n .
Table XII. contains a list of the more important natural
carbohydrates.
TABLE XII.
THE NATURAL CARBOHYDRATES.
THE SUGARS.
Monosaccharose ,
Disaccharoses,
Poly saccharoses,
Cl2 H 22ll
(C 6 H 10 5 ) n ,
PentoseSy
4- Cane - sugar, or
4- Starch
C 5 H 10 5 ,
Sucrose
4- Cellulose
4- Arabinose
4- Ribose
+ Xylose
4- Milk - sugar, or
Lactose
4- Malt - sugar, or
Maltose
L Inulin
' 4- Glycogen
4- Dextrin
The Gums
Hexoses,
C 6 H 12 O 6 ,
Trisaccharose,
4- Glucose, Grape-
sugar, or Dextrose
Fructose, Fruit-
4- Raffinose, or Meli-
triose
sugar, or Lsevulose
4- Galactose
Tetrasaccharose t
4- Mannose
^24"42^21>
4- Stachyose
Properties of the Carbohydrates. Most of the natural
carbohydrates are optically active in solution (p. 112) ; and in the
table, the character of the rotation, whether dextro (right-handed)
or laevo (left-handed), is indicated by the plus or minus sign,
U
290 THEORETICAL ORGANIC CHEMISTRY CHAP.
It will be observed that, with the exception of fruit-
sugar and inulin, all the natural carbohydrates are dextro-
rotatory.
Artificial Sugars. To complete the above list the artificial sugars
should be added. Their preparation has been effected by E. Fischer
(1887-90) in a series of brilliant researches, which constitutes one of
the most remarkable achievements in organic synthesis. The subject
cannot be entered into here; but it may be pointed out that a laevo-
rotatory compound, corresponding to dextro-rotatory grape-sugar, has
been obtained ; also a dextro-rotatory fruit-sugar, a Isevo-mannose, and a
laevo-galactose. In addition to these, Fischer has obtained pentoses,
hexoses, heptoses, octoses, and nonoses, which have no representatives
hitherto found in nature.
THE MONOSACCHAROSES
General Properties of the Monosaccharoses. The mono-
saccharoses possess strong reducing properties, causing the
separation of metallic silver from ammonia-silver-nitrate solution,
and precipitating cuprous oxide from an alkaline solution of
copper sulphate. They thus resemble aldehydes. Moreover,
like aldehydes and ketones, they form cyanhydrins with hydro-
cyanic acid, oximes with hydroxylamine, and phenylhydrazones
with phenylhydrazine (p. 129). The phenylhydrazones are, as
a rule, very soluble in water ; but, by the further action of
phenylhydrazine, they are converted into insoluble yellow
crystalline compounds known as osazones. The osazones are
nearly insoluble in water, and readily separate from a solution
containing the sugar. They have, moreover, a definite melting-
point, and seen under the microscope possess a characteristic
crystalline appearance. The reaction is therefore of consider-
able importance in detecting and identifying certain of the
sugars. The monosaccharoses are readily oxidised. The
aldoses yield mono- and dibasic acids containing the same
number of carbon atoms : the ketoses break up into acids with
fewer carbon atoms. They all yield oxalic acid when warmed
with strong nitric acid (p. 341). With strong hydrochloric acid
they form levulinic acid (p. 330). Finally, they undergo
xx THE CARBOHYDRATES 291
alcoholic fermentation with yeast (p. 104). These reactions
will be discussed in detail under glucose.
Glucose, Grape-Sugar, or Dextrose, is widely distributed
among plants, especially in the sweet-tasting parts, as in the nectar
of flowers and in ripe fruit, where it is usually associated with fruit
and cane-sugar. It has received the name grape-sugar from
its presence in ripe grapes, of dextrose from its dextro-rotation,,
and of glucose from its sweet taste (yXvKvs, sweet).
The discovery of a laevo-rotatory grape-sugar has led to the
substitution of the name dextro-glucose, or simply glucose, for
dextrose, although the latter name is still retained for the natural
sugar. Glucose is a constituent of many glucosides (p. 211)..
In cases of diabetes mellitus it is found in the urine, sometimes
to the extent of 8 to 10 per cent.
In small quantities pure glucose is most readily obtained from
cane-sugar. Cane-sugar is dissolved in 90 per cent, alcohol and
a little strong hydrochloric acid added. On gently warming the
mixture, the cane-sugar is hydrolysed, and breaks up into
glucose and fructose
CwHaAi + H 2 = C 6 H ]2 6 + C 6 H 12 O 6 .
Cane-sugar. Glucose. Fructose.
Glucose, being less soluble in alcohol than fructose, separates*
in anhydrous crystals.
Glucose is manufactured by boiling starch with very dilute
sulphuric acid. The starch is thereby hydrolysed and converted
into glucose (p. 305); The liquid is neutralised with chalk and
filtered, and the filtrate decolorised by filtration through animal
charcoal. The solution is evaporated to the requisite con-
sistency in vacuum-pans (p. 300). The product solidifies or*
cooling, and forms an amorphous-looking mass, which always
contains dextrin (p. 308). Commercial glucose is used as a
sweetening material in the manufacture of confectionery,
preserved fruit and jam, wines, liqueurs, and as a substitute for
malt in the brewing of beer.
Properties of Glucose. Pure glucose dissolves in 1*2 parts
of water. It crystallises from aqueous solution with .1 molecule
of water, and the crystals melt at 86, whilst from alcohol the
anhydrous compound separates, melting at 146. Glucose is
U 2
292 THEORETICAL ORGANIC CHEMISTRY CHAP.
dextro-rotatory in aqueous solution. Its specific rotation 1 - is
given by the expression [O]D= +52'$.
When lime or baryta solution is added to a solution of glucose,
and then alcohol, glucosates of calcium or barium are pre-
cipitated. These compounds are soluble in water, and are
decomposed by carbon dioxide into the original sugar and the
carbonate of the metal. Calcium glucosate has the formula
C 6 H 12 6 .CaO.
Glucose is converted, on oxidation, first into gluconic acid
and then into saccharic acid. These two acids have the
following formulae
CH 2 .OH CO. OH
(CH.OH) 4 (CH.OH) 4
CO. OH CO.CH
Gluconic acid. Saccharic acid.
Strong nitric acid converts glucose, as it does cane-sugar
and the other carbohydrates, into oxalic acid (p. 341). By
reducing glucose with sodium amalgam, sorbitol is formed
(p. 28 5 )._
Reactions of Glucose. Glucose gives the following series
of reactions : Caustic alkalis, added to a solution of glucose and
warmed, produce a brown solution.
EXPT. idi. Add a few drops of caustic soda solution to a dilute
solution of glucose, and warm gently. The colour of the liquid
changes to yellow and then to brown.
Glucose reduces an ammoniacal solution of silver nitrate,
metallic silver being deposited.
EXPT. 102. Add a few drops of a solution of glucose to half a
test-tube of ammonia-silver-nitrate solution, and heat the test-tube in
hot water. A mirror of silver will be deposited.
1 The term specific rotation is used to denote the deviation of polarised light
produced by a liquid or solution containing i gram of substance in i c.c. of liquid in
.a layer i decimetre in length. This is calculated from the strength of the solution
and the length of f^e column of liquid with which the deviation is determined ; the
deviation being proportional to the strength of the solution and the length of the
column of liquid. The specific rotation is icpresented by the symbol [a] D , the D
standing for monochromatic light produced by the sodium flame. The temperature
should also be indicated by writing it above the letter D, thus, [a]^
xx THE CARBOHYDRATES 293
An alkaline solution of copper sulphate is reduced, and
cuprous oxide is precipitated.
EXPT. 103. Add two or three drops of copper suiphate solution to
a solution of glucose, and then caustic soda solution, until a clear
blue solution is obtained. When the liquid is boiled, a yellow pre-
cipitate of cuprous oxide is formed, which rapidly turns red.
The rollowing reaction winch is given by all soluble carbo-
hydrates is known as MoliscWs test.
EXPT. 104. Add two or three drops of an alcoholic solution
of o-naphthol to the glucose solution and carefully pour down
the side of the test-tube some strong sulphuric acid. At the junction
of the two layers a blue or violet colour will be developed.
Analysis of GUucose. The above reaction _s utilised for the quantita-
tive estimation of glucose as well as other sugars. A standard solution
of copper sulphate is prepared by dissolving a carefully weighed quan-
tity of the salt (34*64 grams) in a measured volume of water (500 c.c.).
A second solution is prepared containing caustic soda (60 grams) and
Rocbelle salt (sodium potassium tartrate, 173 grams) in 500 c.c. of water.
Equal volumes of the two solutions are mixed before use. This alkaline
copper solution is known as Fehling's Solution. A measured volume of
Fehling's solution is run into a flask and boiled, and the sugar solution
is then added gradually from a burette until the whole of the copper is
exactly precipitated as cuprous oxide. The quantity of sugar solution
taken is a measure of the amount of glucose present. 10 c.c. of
Fehling's solution corresponds to 0*05 gram of glucose.
Phenylhydrazine in presence of acetic acid produces, en
heating, a yellow, crystalline precipitate of phenylglucosazone.
EXPT. 105. Dissolve about 0*5 gram of glucose in 5 c.c. of water,
and add a solution of phenylhydrazine acetate. The acetate is pre-
pared by dissolving about I gram of phenylhydrazine in the same
weight of glacial acetic acid and diluting to 10 c.c. Mix the two
solutions in a test-tube and heat in boiling water. In a few minutes a
yellow, crystalline mass of phenylglucosazone is deposited, seen under
the microscope in the form of crystalline tufts. The substance melts
at 204-5. The reaction occurs according to the following series of
equations. Glucose phenylhydrazone is first formed
THEORETICAL ORGANIC CHEMISTRY CHAP.
i. CH 2 OH CH 2 .OH
I I
(CH.OH) 4 = (CH.OH) 4 + H 2 O.
CH (O'T HjN. NH. C 6 H 5 CI,I:N. NHC 6 H 5
Glucose phenylhydrazone.
The glucose phenylhydrazone is oxidised by a second molecule of
phenylhydrazine and converted into a ketone, which is the phenyl-
hydrazone of glucosone, and the latter unites with a third molecule
of phenylhydrazine and forms the glucosazone
2. CH 2 OH
(CROH) 3
+NJL>.N:
CH.OH
CH:N.NH.C 6 H 5
3. CH 2 OH
(CH.OH) 3
| . =
CH 2 .OH
(CH.OH) 3
H.C 6 H 5 = | +NH 3 + NH 2 C 6 H 5 .
CO Aniline.
CH:N.NHC 6 H,
Phenylhydrazone of
glucosone.
CH 2 OH
(CH.OH) 3
= | + H 2 O.
CO + H 2 ;:N.NHC 6 H 5
C:N.NH.C 6 H 5
CH:N.NHC 6 H 5
CH:N.NHC 6 H 5
Phenylglucosazone.
Conversion of Glucose into Fructose. When phenylglucosazone is
hydrolysed with hydrochloric acid, glucosone and phenylhydrazine are
produced. When glucosone is reduced it yields fructose
4. CH 2 OH CH 2 OH
(CH.OH) 3 (CH.OH) 3
I +2H 2 0- |
C:N.NH.C 6 H 5 CO
CH:N.NH'C 6 H 5 CHO
Glucosone.
5. CH 2 OH CH 2 OH
(CH.OH) 3 (CH.OH) 3
CO CO
CHO CH 2 .OH
Fructose.
xx THE CARBOHYDRATES 295
Constitution of Glucose. Glucose forms a pentacetyl
derivative with acetic anhydride, and therefore contains 5
hydroxyl groups. Each hydroxyl group is probably attached to
a different carbon atom, seeing that the attachment of 2
hydroxyl groups to the same carbon atom would form a very
unstable arrangement (p. 88). The various reactions already
described stamp glucose as an aldehyde. The only point which
is left uncertain is whether or not the carbon atoms are linked
in a straight chain. This point is determined by the reduction
of glucose to sorbitol, and the conversion of the latter by means
of hydriodic acid into normal secondary hexyl iodide (p. 282).
It has also been shown that glucose combines with hydro-
cyanic acid, and forms a cyanhydrin which, on hydrolysis, yields
an acid. By the reduction of this acid with hydriodic acid,
normal heptylic acid is produced. These changes are represented
by the following formulas
CH 2 .OH
CH 2 .OH
CH 2 .OH
CH 3
|
I
I
I
(CH.OH) 4
(CH.OH) 4
(CH.OH) 4
(CH 2 ) 5
|
> 1 -3
* \ -'
> 1
CHO
CH.OH
CH.OH
CO. OH
1
1
CN
CO. OH
Glucose.
Glucose
Hydroxy-
Heptylic
cyanhydrin.
heptylic acid.
acid.
The formula for glucose is therefore that of a pentahydroxy-
aldehyde
CH 2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CHO.
Structural formula for Glucose.
Fructose, Fruit-Sugar, or Lsevulose, C 6 H 12 O 6 . It has
already been stated that fruit-sugar is associated with grape-sugar
in many fruits, and the mixture is probably produced by the
hydrolysis of cane-sugar, which is now known to precede the
formation of the other carbohydrates in plants. The name
laevulose, which was given to the natural sugar on account of
its Isevo-rotation, has been replaced by the word fructose, since
the discovery of a dextro-rotatory fruit-sugar. Fructose may be
obtained from cane-sugar by hydrolysis with dilute sulphuric
acid. The acid is removed by precipitation with barium
296 THEORETICAL ORGANIC CHEMISTRY CHAP.
carbonate, anr'-the filtrate is concentrated. Milk of lime is then
added, when the lime compound or calcium fructosate (corre-
sponding to calcium glucosate, p. 292), which is only slightly
soluble, separates out, and is filtered and washed. The calcium
compound is then suspended in water and decomposed by
carbon dioxide. The solution is again filtered from calcium
carbonate and evaporated. On introducing a crystal of fructose
into the syrup, the latter slowly crystallises. Fructose is also
prepared from inulin (p. 311) by hydrolysis with sulphuric acid.
Inulin is completely converted into fruit-sugar. After removal
of the acid, the liquid is evaporated, preferably under diminished
pressure, when a syrup is left which solidifies if a crystal of
the substance is added.
Fructose is now produced commercially for the use of diabetic
patients to replace cane-sugar. It appears to be assimilated,
whereas glucose is excreted unchanged. Fructose crystallises
in rhombic prisms which melt at 95. It is Isevo-rotatory,
[ajf = - 92. It has a sweet taste and gives many of the
reactions of glucose. Although fructose is not an aldehyde but
a ketone (see below), it nevertheless reduces alkaline copper
solution. This is due to the presence of the easily oxidisable
group CO.CH 2 (OH). With phenylhydrazine, fructose yields
an osazone, which is identical with glucosazone. Fructose also
undergoes fermentation with yeast, though less readily than
glucose, glucose being first removed when a solution of the two
sugars is fermented.
Constitution of Fructose. Fructose forms a pentacetyJ
derivative, like glucose. On reduction, it is converted into a
mixture of sorbitol and mannitol. On oxidation, it does not,
like glucose, form an acid with the same number of carbon
atoms, but breaks up into formic acid and trihydroxybutyric
acid. This decomposition points to the presence of a ketone
group in the molecule (p. 126), which is further confirmed by
the following reactions : Fructose forms a cyanhydrin with
hydrocyanic acid, which on hydrolysis yields an acid. The
latter, on reduction with hydriodic acid, is converted into methyl-
butylacetic acid. The reactions are readily explained on the
assumption that fructose is a hydroxy-ketone, in which the
ketone group adjoins one of the end carbon atoms
THE CARBOHYDRATES 297
CH 2 .OH
CH 2 .OH
CH 2 .OH
CH 3
1
1
(CH.OH) 3
(CH.OH),
(CH.OH) 3
(CH 2 ) 3
CO
" c< 01 ?
k-
1
:< OH
> 1
CH.COOH
I
| LJN
COOH
|
CH 2 .OH
CH 2 .OH
CH 2 .OH
CH,
Fructose.
Cyanhydrin of
fructose.
Hydroxy-acid.
Methylbutyl-
acetic acid.
The above formula for fructose agrees, moreover, with the
synthesis of inactive fructose from the mixture of glyceric alde-
hyde and dioxyacetone (p. 280), and with the production of the
same osazone as that obtained from glucose, a reaction in which
the two end carbon atoms of the chain are involved (p. 294)
CH 2 OH CH 2 OH
(CH.OH) 3 (CH.OH) 3
GO +H 2 ;N.NH.C 6 H 5 = C:N.NH.C 6 H 5 + H 2 O.
CH 2 OH CH 2 OH
Fructose
phenylhydrazcne.
CIIjOH
(CH.OH) 3 (CH.OH) 3
| +2C 6 H S NH.NH 2 = | +C 6 H 5 NH 2
C:N.NH.C 6 H 5 C:N.NH.C 6 H 5
CH 2 OH CH:N.NH.C 6 H 5
Phenylglucosazone.
Galactose, C 6 H 12 O 6 , is obtained from milk-sugar or lactose
(p. 304) by boiling with dilute sulphuric acid. The milk-sugar
decomposes into glucose and galactose in much the same way
that cane-sugar yields glucose and fructose
CjoH^On + II 2 O = C 6 H 12 O 6 + C 6 H 12 O 6 .
Milk-sugar. Glucose. Galactose.
To prepare galactose, milk-sugar is boiled with dilute sul-
phuric acid, the solution neutralised with baryta and concentrated
by evaporation. On the introduction of a crystal of grape-sugar,
galactose crystallises out, and the crystals are purified by washing
with dilute alcohol.
Galactose is less soluble in water than glucose or fructose.
-298 THEORETICAL ORGANIC CHEMISTRY CHAP.
It crystallises in microscopic hexagonal plates melting at 68.
It forms a pentacetyl derivative. On reduction it yields dulcitol
(p. 285), and on oxidation it forms the monobasic acid, galac-
Jonic acid, which is isomeric with gluconic acid, and the dibasic
acid, mucic acid, which is isomeric with saccharic acid. It
reduces alkaline copper sulphate solution, forms an osazone,
which melts at 193- 194, and undergoes fermentation by yeast,
but more slowly than either glucose or fructose. The proper-
ties of galactose point to the same structural formula as that of
glucose, and the difference between the two compounds must
be one of space arrangement or configuration of the atoms
{p. 355). It is dextro-rotatory a D = + 80.
Mannose, C 6 H 12 O 6 , was first obtained by the oxidation of mannitol
with bromine in presence of sodium carbonate ; but it has since been
identified as one of the products of hydrolysis of certain carbohydrates,
:such as the cellular tissue of the ivory-nut. Mannose, unlike the other
hexoses, forms an insoluble phenylhydrazone by which it may be identi-
fied. It has the same structural formula as glucose, and yields the
same osazone, but possesses a different configuration. It is dextro-
rotatory, and undergoes fermentation by yeast.
Sorbinose (Sorbose\ C 6 H 12 O 6 , is found in the juice of mountain-ash
berries after standing, and is formed by the oxidation of sorbitol, which
is always present in the berries, by the intervention of the sorbose
bacterium. Sorbinose is a ketone, like fructose.
DlSACCHAROSES
Cane-Sugar, C 12 H 22 O n , is found in the root, the tubers, and
in the stems and flowers of many plants, as well as in the sap
of certain trees. It is obtained chiefly from beet-root and sugar-
cane ; and in the United States, to a small extent, from the sugar
maple, maize, and sorghum, a plant belonging to the grass
family. Cane-sugar, known as jaggery, is made from a species
of palm.
The sugar-cane was originally grown in the East India and
Arabia and was introduced into Southern Europe by the Moors,
whence it was transplanted to the West Indies and other tropical
countries.
The Sugar-cane Industry. The sugar-cane contains 16-18
per cent, of cane-sugar. The canes are cut up and passed
between hot rollers, whereby the juice is expressed. The ex-
xx THE CARBOHYDRATES 299
tracted canes are known as begasse. The juice, which contains
19-20 per cent, of sugar, and small quantities of inorganic salts,
organic acids, and albuminoid substances, is run directly into a
copper vessel or darifier, mixed with milk of lime, and boiled.
The albuminoid substances are coagulated, and, together with
the lime salts of the acids, form a scum on the surface which is
removed. The juice is further concentrated until the point of
crystallisation is reached, when it is run into casks, the bottoms
of which are pierced with holes through which the molasses, or
treacle, drains, or the crystals are separated by a centrifugal
machine. The raw, or Muscovado, sugar is exported, and sub-
sequently undergoes a process of refining, which is described
further on.
The Beet-root Sugar Industry. The presence of sugar in
beet-root was observed in 1747 by the German chemist Marg-
graf, who suggested the cultivation of beet as a source of
sugar ; but the early attempts to utilise it commercially proved
unprofitable. The success of the industry dates from about the
year 1830, when important improvements began to be intro-
duced. Careful selection of seed, and improved cultivation,
nearly doubled the quantity of sugar in the beet The use of
steam-heated vacuum-pans gave a larger yield of crystallisable
sugar, and new mechanical appliances for saving labour lowered
the cost of production. Moreover, a method for revivifying the
charcoal used for decolorising the raw sugar (after being used
for a time it becomes inactive), and the introduction of a process
for separating crystallised sugar from the molasses, combined
to cheapen the product.
Beet-root contains about 13-14 per cent, of cane-sugar. The
other solid constituents are a sugar known as raffinosc, which
subsequently remains in the molasses, small quantities of citric,
oxalic, tannic, and tartaric acids, albumin, asparagine (p. 351),
betaine (p. 324), &c. The roots are washed and rasped into
very thin slices, and then macerated in warm water. The pro-
cess of maceration is known as diffusion. It is in reality a
process of dialysis, the cell-wall acting as a diaphragm through
which the sugar and the other crystalline substances pass, whilst
the albumin and non-crystalline contents of the cell are retained.
The maceration is conducted in a series, or battery, of tanks con-
taining the beet-root pulp, and filled up with hot water. The
3
THEORETICAL ORGANIC CHEMISTRY CHAP.
pulp in each tank is in a different stage of extraction, fresh pulp
being at one end of the series, and extracted pulp at the other.
The water is pumped through the tanks in succession, so that
fresh water comes in contact with the exhausted pulp, whilst
the highly charged juice, which has passed through the tanks,
is used for extracting the fresh beet. The juice, drawn from the
tanks, is then heated with the addition of lime, which precipitates
the acids, and coagulates the albumin. Carbon dioxide is
passed through the
liquid to decompose
the saccharosate of
lime which is
formed. The two-
processes, which
are usually com-
bined in one opera-
tion, are termed re-
spectively defeca-
tion and saturation.
The operation is
sometimes re-
peated, using sul-
phur dioxide in
place of carbon
dioxide to decolor-
ise the juice. The
mixture is now
pumped through a
filter-press to re-
move the insoluble
substances, and the
clear juice is eva-
porated in vacuum-pans, heated by steam from which the air
is partially exhausted. A form of vacuum-pan is shown in
section in Fig. 73. It consists of an iron pan, which is heated
by vertical steam coils placed in the lower part of the vessel.
Two or three pans are connected, so that the steam arising
from the evaporation of the liquid in the first pan is utilised for
heating the next, and its vapour passes on to the third. Between
the pans a small cylindrical vessel is interposed, which serves
FIG. 73. Vacuum-Pan.
XX THE CARBOHYDRATES
301
to collect any juice which " primes," or is carried over during
the boiling. The evaporation is continued until the liquid is so
far concentrated that it shows "grain," or commences to
crystallise. It is then run out and cooled, and the uncrystal-
lisable portion, or molasses, separated in a centrifugal extractor.
Extraction of Sugar from Molasses. The foreign sub-
stances in the molasses prevent its crystallisation. Among the
numerous processes proposed for separating crystallisable sugar
from molasses the strontia method is most commonly used.
By this method nearly the whole of the cane-sugar is separated
in the crystalline form. A hot saturated solution of strontium
hydrate is added to the molasses, which, when excess of strontia
is present, causes the separation of saccharosate of strontium,
C 12 H 22 O n .SrO. The latter is removed by filtration, dissolved
in water, and decomposed by carbon dioxide, which precipitates
strontium carbonate. The filtered liquid is evaporated, and the
sugar crystallises. The syrup which contains uncrystallisable
sugar is fermented and yields alcohol on distillation. By
evaporation and destructive distillation of the dry residues,
potash salts remain, some methyl alcohol distils, whilst ammonia
and hydrocyanic acid are recovered from the gases.
Sugar Refining. Raw sugar from the cane as well as from
beet-root has a brown or yellow colour, and requires refining,
which is usually carried on in separate factories. The raw
sugar is dissolved in water, and the solution heated with lime
and occasionally with other substances. It is then filtered and
the clarified juice passed through charcoal filters. These filters
consist of long cylindrical vessels filled with animal charcoal,
through which the saccharine liquid percolates and is de-
colorised. The juice is again concentrated in vacuum-pans
and crystallised. The charcoal is revivified by washing, drying,
and finally heating it in closed vessels.
EXPT. 1 06. Take a long wide tube open at the top and fitted at
the lower end with cork and glass tap. Fill the tube with fragments
of animal charcoal and allow a solution of caramel in water to trickle
through. The liquid which runs out at the bottom will be colourless.
The annual production of beet-root sugar in Europe is about
one-half of the total production of the world, which is estimated
at about 16 million tons. All European countries produce
beet-root sugar except Great Britain, although it has the largest
302 THEORETICAL ORGANIC CHEMISTRY CHAP.
consumption (2^ million tons or 83 Ibs. per head). A certain
amount is also produced in the United States.
Sugar Analysis. Cane-sugar is optically active and turns
the plane of polarisation to the right, [a] D = +66'5. The most
accurate method for estimating the amount of sugar present in
a commercial sample is to measure the rotation by means of a
polarimeter (p. 112), which, when applied for this purpose, is
usually termed a saccharimeter. A definite weight of sugar is
dissolved in water, the solution clarified with lead acetate, and
introduced into a tube 20 mm. in length closed at each end by
glass caps. It is then placed between the Nicol prisms of the
polarimeter. The amount of deviation measured on the vernier
gives directly the percentage of sugar in the sample. The
deviation in the so-called half-shadow instrument is determined
by an arrangement which produces an unequal illumination of
the two halves of the field of view when an active solution is
interposed between the Nicols. The eye-piece Nicol is then
turned until equality in shade, or tint, between the two halves is
restored. For an explanation of the arrangement a text-book
of physics must be consulted. Another method of analysis is
by determining the refractive index of the solution by means of
a refractometer.
Properties of Cane-Sugar. Cane-sugar crystallises from
aqueous solution in monoclinic prisms which melt at i6o-i6i c .
When allowed to deposit slowly on threads suspended in the
solution, large crystals known as sugar candy are formed.
Cane-sugar, like glycerol, glucose, and certain other hydroxy-
compounds, has antiseptic properties, and prevents the decay
of putrescible matter. The sugar in candied fruits and jam acts
as a preservative.
When cane-sugar is heated with a little water until it melts
and the liquid begins to turn yellow, it forms, on cooling, a hard
glassy mass, which is called barley-sugar. If sugar is heated
above its melting-point, it turns brown and forms caramel^ a
semi-solid amorphous substance which is used in confectionery
and for tinting spirits.
When sugar is heated in a retort, water, acetic acid, acetone,
and other products distil, and a very pure form of charcoal
known as sugar charcoal is left.
Dilute sulphuric acid hydrolyses cane-sugar and converts it
into equal proportions of glucose and fructose (p. 291). The
xx THE CARBOHYDRATES 303.
mixture is known as invert sugar, and the process as inversion.
The name has originated from the change of sign in the
rotation. Whereas cane-sugar is dextro-rotatory, when a
mixture of equal quantities of the two hexoses is present,,
the lasvo- rotation of fructose, [a] D = 92, more than neutralises
the dextro-rotation of glucose, [a] D = + 52*5, and consequently
the effect is laevo-rotatory.
Strong sulphuric acid gradually decomposes and chars cane-
sugar. The action is much more rapid if a little water is first
added to the sugar. The charred mass then froths up and
evolves carbon dioxide and sulphur dioxide.
Strong hydrochloric acid decomposes cane-sugar like the
hexoses, and yields levulinic acid. Strong nitric acid oxidises^
cane-sugar and forms oxalic acid (p. 341).
Cane-sugar forms saccharosates or sucrosates of the metals.
It combines with I, 2, and 3 molecules of strontia. The
compound with one molecule of stfontia has already been
mentioned in connection with the recovery of sugar from,
molasses.
Cane-sugar is not directly fermentable by yeast. Before
fermentation takes place the sugar undergoes inversion by-
means of the enzyme, invertase (p. 105). It has no reducing
action upon an alkaline copper solution until it has been,
hydrolysed.
EXPT. 107. Make a solution of cane-sugar and divide it into two
portions ; boil one portion with a drop or two of dilute sulphuric
acid. Add to each two drops of copper sulphate solution, and then
caustic soda solution, until a clear blue solution is obtained. On
boiling, cuprous oxide is precipitated by the hydrolysed sugar, but
not by the unchanged cane-sugar.
It would appear from this indifference to alkaline copper
solution that cane-sugar is not an aldehyde, and this view is
confirmed by its behaviour with phenylhydrazine, with which it
does not combine.
Constitution of Cane-Sugar. Although cane-sugar has
been synthesised by combining glucose and fructose, and its
general constitution known, some little doubt still exists in
regard to certain details of its structure, which cannot be
discussed here. The absence of the properties of aldehydes
and ketones renders it probable that the union of the two hexoses
is in the nature of an anhydride or ether, formed by the linking;
304 THEORETICAL ORGANIC CHEMISTRY CHAP.
of the aldehyde group of the one molecule to the ketone group
on the other
CH 2 .OH CH 2 .OH
CH.OH ^CH
xCH O<^ (CH.OH) 2
O<^ (CH.OH) 2 \C
O/ CHo.OH.
1 2-
Probable structure of Cane-sugar.
Milk-Sugar, Lactose, C 12 H 22 O n + H 2 O, is present in the
milk of mammals. An average sample of cows' milk has the
following composition:
Water 86'8 per cent.
Milk-sugar 4*8 ,,
Fat (butter) 3-6
Casein and soluble albumin 4*0 ,,
Mineral matter (calcium phosphate, &c.) 07 ,,
99*9
The milk-sugar is separated by coagulating the albumin of
the milk with rennet, or by the addition of a little acetic acid. The
liquid is filtered and evaporated. The residue is milk-sugar.
The whey which is obtained as a by-product in the manufacture
of cheese is used as a source of milk-sugar. Milk-sugar forms
large hard crystals containing one molecule of water of crystal-
lisation which it loses at 130. It is strongly dextro-rotatory,
[a]^= + 52 C *5. It reduces alkaline silver and copper solutions,
and forms an osazone of melting-point 200. Milk-sugar is
coloured yellow with alkalis. It is not directly fermentable
with ordinary yeast, but certain bacteria readily convert it
into lactic and butyric acids (p. 164). A ferment, or fungus,
consisting of yellow nodules known as kephir grains, and con-
taining bacilli and yeast, has the property of fermenting cows'
milk and converting the milk-sugar into alcohol and carbon
dioxide. Koumiss is a Russian beverage, and is made in a similar
way by fermenting mares' milk. Milk-sugar yields glucose and
galactose on hydrolysis (p. 297).
Maltose, Malt-Sugar, C l ^U 22 O n + H 2 O. Maltose is pro-
duced by the action of diastase on starch. It is the sugar
xx THE CARBOHYDRATES 305
whisky, when the malted grain is steeped in water, which
is ultimately fermented and converted into alcohol (p. 106).
Maltose is readily prepared in the following way : an extract of
malt is made by steeping the crushed grain in water for 24 hours
and adding a little of the solution, which contains diastase, to
starch-paste, and heating to a temperature of 6o-65 for an hour.
The paste, which has by this time become liquid, is boiled up and
filtered, and evaporated on the water-bath until the liquid becomes
syrupy. It is then extracted with 90 per cent, alcohol, which
removes the maltose. The extract is concentrated to a syrup
by evaporation, and a crystal of maltose added, which induces
the crystallisation of the mass. Maltose crystallises in fine
needles. It is strongly dextro-rotatory, [a] D = -f I4o c *6. It re-
duces alkaline copper solution, and forms, with phenylhydrazine,
maltosazone melting at 206, which has a characteristic crystal-
line appearance under the microscope. On boiling with dilute
sulphuric acid, maltose is hydrolysed, and is converted into
glucose CuHaOu + H 2 O = 2C 6 H M O 6 -
Maltose. Glucose
Maltose undergoes fermentation by yeast, the sugar being
probably first hydrolysed into glucose by the action of an
enzyme, maltose, which is contained within the yeast cell. It
seems, in fact, definitely proved that only the simple hexoses are
directly fermentable, and that the disaccharoses are all hydrolysed
before conversion into alcohol and carbon dioxide can take
place.
Isomaltose, C^H^On, has been obtained by synthesis from glucose
by the action of strong hydrochloric acid. Two molecules of glucose
combine with the elimination of water. Isomaltose is stated to be
identical with a substance formed, together with maltose, by the action of
diastase on starch, but some doubt has been thrown upon the state-
ment.
Raffinose, Melitriose, C 18 H 32 O 16 + 5H 2 O, is obtained from beet-root
molasses, and from other sources. It is strongly dextro-rotatory,
[o] D = + 104. It decomposes, on hydrolysis, into glucose, fructose,
and galactose.
POLYSACCHAROSES.
Starch, (C 6 H 10 O 5 ) n , is found in various parts of plants,
especially in the seeds and tubers, where it is stored as a
306 THEORETICAL ORGANIC CHEMISTRY CHAP.
reserve material to serve as nutriment for the young plant.
The chief sources of starch are the potato, rice, maize, and
wheat, which contain the following average percentages of
starch :
Potato 15-20 per cent.
Wheat, and other cereals 60-65 ?>
Maize 65 ,,
Rice 75-8o
Arrow-root starch is obtained from the tubers of certain
species of maranta, a plant which grows in the tropics ; sago
is derived from the pith of the sago-palm ; and tapioca is pre-
pared from the tubers of manihot or cassava. In the case of
sago, the starch is moistened and pressed through a sieve, the
grains being rounded and hardened by being rubbed together
and heated on hot metal plates. Sometimes potato starch is
given the form of sago or tapioca.
Manufacture of Starch. In England, starch is prepared
chiefly from rice, whilst potatoes are employed in Germany, and
maize, or Indian corn, in the United States. The process of
manufacture is mainly a mechanical one. The material is
softened and crushed, and then washed by a stream of water
through revolving cylinders covered with fine wire or silk,
which act as sieves, allowing the starch granules to pass,
but retaining the gluten, or vegetable albumin and cellulose, or
cell-wall. The starch is further washed on sloping troughs to
remove the lighter fibrous particles, and is then drained in a
centrifugal extractor and dried. Rice, maize, and wheat, in
which the starch is firmly cemented to the gluten of the grain,
is disintegrated before washing, either by fermentation or by the
action of dilute caustic soda, which dissolves the albumin.
EXPT. 108. Enclose a handful of flour in a small muslin bag and
knead it under water. The starch grains pass through the meshes of
the muslin into the water and produce a milky liquid, whilst the
gluten remains in the bag as a tough, sticky mass. Examine some
of the milky fluid under a good microscope, and notice the appear-
ance of the grains.
Properties of Starch. The appearance of different kinds of
starch under the microscope is characteristic. The grains may
be round, elliptical, or angular, and of different sizes. In
XX
THE CARBOHYDRATES
307
Fig. 74 is shown the microscopic appearance of wheat and
potato starch of the same magnification.
The grains consist of concentric rings, or layers, arranged round
a nucleus. Between crossed Nicols they present the appearance
of a doubly refracting crystal. Starch is insoluble in cold water,
Wheat starch (highly magnified). Potato starch (highly magnified).
FIG. 74.
but, when heated, the granules swell up and burst, forming a
slightly opalescent solution, which on cooling sets to a stiff
paste known as starch-paste. The soluble portion is termed
granulose, and the insoluble part which renders the liquid turbid
is known as starch cellulose. When starch is heated with water
under pressure, with glycerol, or with dilute acids, it dissolves
in hot water, and separates on cooling in the form of an
amorphous white powder. It is known as soluble starch. The
molecular weight of soluble starch has been determined by the
cryoscopic method, and found to correspond with the formula
Ci2ooH 2 oooOiooo- Wnen starcn i g heated below a point at which
it becomes discoloured, it is converted into dextrin (see below).
The most characteristic reaction for starch is its behaviour with
iodine. A solution of starch-paste in water is coloured blue by
free iodine. The colour disappears on warming, but returns
when the liquid cools. The reaction is very delicate, o'oc3
milligram of iodine being detected in this way. It has already
been stated that when extract of malt, in water or diastase
solution, is added to starch paste, and the mixture maintained at
a temperature of about 60, the starch soon liquefies and
becomes limpid. If iodine solution is added at intervals to
X2
3oS THEORETICAL ORGANIC CHEMISTRY CHAP.
portions of the solution, from the moment liquefaction occurs,
the following appearances will be observed : A blue solution
is first obtained. This is the ordinary reaction for starch or
soluble starch. The coloration of succeeding portions is
purple, then red, until, finally, no coloration is produced.
These changes are caused by the disintegration of the starch
molecule into simpler compounds known as dextrins, the latter
being ultimately decomposed and converted into maltose (p.
304), when the action ceases. Saliva and pancreatic juice,
which contain hydrolytic enzymes (ptyalin) resembling diastase,
produce a similar effect on starch. An analogous series of
changes is brought about by boiling starch with dilute sul-
phuric acid, but as the maltose is also hydrolysed, the. starch
is almost completely converted into glucose (p. 291).
EXPT. 109. Make a thin solution of starch paste by grinding up
about 2 grams with a little cold water and pouring the mixture
into 50 c.c. of boiling water. Divide the solution into three parts.
Add a few c.c. of malt extract to one portion, and warm to 60 ;
add a little saliva to another ; and boil a third portion with a few
drops of dilute sulphuric acid. Test a portion of each both with
iodine solution and alkaline copper solution from time to time. In
each case the blue colour will gradually give place to violet, then red,
and finally disappear, whilst the presence of maltose or glucose will
be indicated by the precipitation of cuprous oxide.
Uses of Starch. Starch is used for sizing and stiffening
paper and cloth, for laundry purposes and for the manufacture
of dextrin or British gum.
Dextrin, (C c H 10 O 5 ) n , is obtained from starch by the action of
a gentle heat or by partial hydrolysis with diastase or dilute
sulphuric acid. It is usually manufactured by moistening starch
with a mixture of dilute nitric and hydrochloric acid, and heating
to ioo-i25. It forms a yellowish powder with a peculiar
smell, which dissolves in water, forming a clear mucilage. It is
employed under the name of British gum.
Cellulose, (C 6 H 10 O 5 ) n , is a fundamental constituent of the
cell-walls of plants, and forms the framework, or skeleton, of
vegetable tissues. It is probably elaborated from simpler carbo-
hydrates secreted by the protoplasm of the cell. Cellulose in a
pure state is best known to us as cotton-wool, linen, and paper.
THE CARBOHYDRATES 309
The difference between cotton and linen is due rather to the
structure of the fibres, which consist of cylindrical tubes, than
to the chemical nature of the substance composing them.
Both kinds of fibre contain a small quantity of mineral matter,
which is left as ash on burning the organic matter. The
mineral matter is almost entirely removed by the action of
hydrofluoric acid. The best filter papers are prepared by
treatment with this acid, after which they are well washed with
water, alcohol, and ether. These papers, which are sometimes
known as Swedish filter papers, consist of cellulose in its purest
form. A careful study of the cellular tissues has shown that cel-
lulose does not represent one only, but several substances, which
may be differentiated by the products which they yield on
hydrolysis. Some, like cotton and linen, give glucose'; others
mannose ; and others, again, galactose and the pentoses, xylose
and arabinose (see p. 312).
Properties of Cellulose. We are most familiar with the
chemistry of the cellulose of cotton fibre. It is an unusually
inert substance compared with the other carbohydrates. It is
scarcely affected by chlorine, or bromine, or by boiling dilute
acids or alkalis. These reagents are consequently employed in
separating the fibre from encrusting matter, resin, gum, and
wax, with which it is usually associated. In the manufacture
of paper and in the cleaning and bleaching of cotton, both caustic
soda and hypochlorites are used. It is this inertness towards
the common reagents which renders paper so serviceable as a
filtering medium.
A strong solution of caustic alkalis produces a curious thicken-
ing and gelatinising of the walls of the fibre, which causes the
cellulose to shrink and become translucent. The effect of pour-
ing a strong solution of caustic soda on to filter paper is very
marked. It rapidly thickens and contracts. When applied to
cotton fibre and cloth the process is known, after its discoverer,
as mercerising, and is used for producing crinkled surfaces
on cotton fabrics. Strong sulphuric acid rapidly attacks and
dissolves cellulose. If the sulphuric acid is diluted with water
in the proportion of 2 volumes of sulphuric acid to I volume
of water, and a piece of filter paper dipped into the liquid, the
paper becomes immediately tough and translucent. When
freed from acid and dried, it is known as parchment paper.
310 THEORETICAL ORGANIC CHEMISTRY CHAI>.
Fuming hydrochloric acid or boiling dilute sulphuric acid breaks
up the cellulose molecule and yields glucose. The decom-
position is hastened by dissolving cellulose in strong sulphuric
acid, then diluting with water and boiling. Zinc chloride in
hydrochloric acid dissolves cellulose, and so also does a solu-
tion of cupric oxide in ammonia, known as Schweizer's
reagent. The latter solution is prepared by precipitating
copper sulphate with caustic soda in the cold, washing the
precipitate, and dissolving it whilst still moist in a little
strong ammonia solution. Cotton-wool rapidly gelatinises in
the solution and ultimately dissolves. The cellulose is thrown
down from the solution by the addition of acids, alcohol, or
even common salt, in the form of a gelatinous precipitate
resembling alumina. This reaction is utilised for producing
artificial silk (see next page) and also for preparing
Willesden paper. The surface of the paper is moistened
with the ammoniacal cupric oxide, which gelatinises tne
surface fibres, and, after drying, renders the paper impervious
to water. Cellulose is readily acted upon by strong nitric
acid, or a mixture of nitric and sulphuric acid, and yields a
series of cellulose nitrates, pyroxylins or nitro-celluloses. These
substances are not nitro-compounds, seeing that they are hydro-
lysed by alkalis and the nitrogen removed as nitrate of the
alkali. They must be regarded as nitric esters of cellulose.
The most important of these compounds is gun-cotton.
Gun-cotton, Cellulose hexanitrate, [C 12 H 14 O 4 (O.NO 2 ) 6 ] n .
Gun-cotton is prepared by steeping pure cotton-wool in a
mixture of 3 parts of fuming nitric acid and I part of strong
sulphuric acid for twenty-four hours at a temperature not
exceeding 10. It is then removed and carefully washed with
water until free from acid. When dry, the cotton, though still
preserving its fibrous texture, is much more inflammable and
burns with remarkable rapidity. When compressed into cart-
ridges and detonated, it forms a powerful explosive. Gun-
cotton is insoluble in a mixture of alcohol and ether, but
dissolves in acetone, forming a jelly. This solution is mixed
with nitro-glycerine in the preparation of cordite (p. 284). When
gun-cotton is dissolved in nitro-glycerine, it forms blasting
gelatine (p. 284). The lower nitrates of cellulose (tetra- and
penta-nitrates) are prepared by a modification of the above
reaction and are used for various purposes.
XX THE CARBOHYDRATES 311
Collodion is the solution of the lower nitrates in a mixture of
alcohol and ether. On evaporation of the solvent a transparent
film of considerable tenacity remains. It is used for producing
artificial silk (Chardonnet's process). The solution, to which
dilute sulphuric acid is added, is forced through a fine orifice
into water, where it is at once coagulated and forms a fine
transparent thread of considerable toughness. The threads
when wound on a reel, and twisted, produce a silky fibre, which
is rendered non-explosive by denitration with ammonium
sulphide.
Artificial silk is also prepared from the gelatinous mass obtained by
dissolving cotton in Schweitzer's reagent (Pauly), and also from the
viscous product (viscose) made by treating cellulose with a mixture of
carbon bisulphide and caustic alkali (Cross and Bevan). Cellulose acetate
is used for the same purpose. In all cases the viscid, transparent
liquid is squeezed through a fine aperture and subsequently rendered
insoluble.
Celluloid, Xylonite, consists of the lower nitrates of cellulose.
They are dissolved in acetone and camphor, and other sub-
stances added. The mixture forms a plastic mass, which can be
worked up for a variety of purposes. It is, naturally, extremely
inflammable.
Manufacture of Paper. A great variety of materials are
employed in the manufacture of paper, such as linen and cotton
rags, esparto grass, straw, and wood. The material is first
disintegrated by mechanical means. The fabrics are torn up
and the straw and wood cut into small pieces. The materials
are converted into pulp by boiling with caustic soda in closed
boilers heated by steam under pressure. Wood-pulp Is prepared
by using a strong solution of calcium bisulphite in place of
caustic alkalis. The pulp is run out, washed and bleached with
bleaching liquor, and again washed. It is then ready to be made
into paper.
Inulin, (C 6 H 10 O 5 ) n + H 2 O, is found in dahlia tubers and in the tubers,
bulbs, and roots of other plants, where it appears to take the place of
starch. It is a white powder, which does not give a blue colour with
iodine. On hydrolysis it yields fructose (p. 295).
Grlycogen, (C 6 H 10 O 5 ) n , is widely distributed in the animal kingdom, and
is sometimes known as animal starch. It appears to play the part of a
312 THEORETICAL ORGANIC CHEMISTRY CHAP.
reserve material, for it quickly disappears when food is not taken.
Glycogen is found in the liver and in small quantities in muscle. It is
also found in certain fungi, and is very plentiful in molluscs. Oysters
contain as much as 9 per cent, of glycogen. It is a white amorphous
powder, which dissolves in hot water, and is precipitated by alcohol.
Iodine colours it brown. It is strongly dextro-rotatory. Submitted to
the action of diastase, it yields dextrin, maltose, and glucose.
Gums are transparent, glassy, amorphous substances, which are exuded
from plants. They form a mucilage with water, from which the gum
is precipitated by alcohol. They do not reduce Fehling's solution, but
are hydrolysed by acids into monosaccharoses. The monosaccharoses are
not necessarily hexoses. The two pentoses, arabinose and xylose, are
obtained from certain gums. Gum arabic is an exudation from the bark
of several species of acacia. It consists of the calcium and potassium
salts of arabic acid. When hydrolysed with dilute sulphuric acid, it
yields arabinose, C 5 H 10 O 5 . Wood gum is widely distributed throughout
the vegetable kingdom. It is extracted from the wood of various trees
by digestion with caustic alkalis and precipitation by alcohol. It is a
white powder, which, on hydrolysis, yields xylose, C 5 H 10 O 5 .
&-Ribosc has been shown to be a constituent of the nucleic acid of
cell nuclei.
EXPT. no. The presence or pentoses may be shown by their
behaviour with a solution of phloroglucinol (p. 464) or orcinol in
strong hydrochloric acid. A pine shaving, or gum arabic, on gently
warming with the solution, turns a bright cherry-red with the former
and violet with the latter reagent, showing the presence of a pentose
in both cases.
QUESTIONS ON CHAPTER XX
1. Describe the system of classification adopted in the case of the
carbohydrates. How could you readily distinguish a carbohydrate
from a polyhydric alcohol ?
2. What are the chief reactions of the monosaccharoses ? Which of
the disaccharoses give similar reactions ?
3. Describe the preparation of glucose and fructose from cane-sugar.
How can the two sugars be distinguished ? How is fructose obtained
from glucose? Why are the names glucose and fructose used in
preference to the older names of dextrose and Icevulose ?
4. Give the products of hydrolysis of the three principal disaccharoses.
How is maltose prepared ? How is it distinguished from glucose ?
xx THE CARBOHYDRATES 313
5. How are the following compounds inter-related : starch, dextrin,
dextrose, mannitol, gluconic acid, and saccharic acid ?
6. What is the experimental evidence for the conclusion that dextrose
contains an aldehyde group and laevulose a ketone group ? How does
phenylhydrazine react with each of these sugars ?
7. How can the hydrolysis of starch, cellulose, cane-sugar, inulin, and
glycogen be effected ? State the properties of their hydrolytic products.
8. To what class of bodies does dextrose belong ? Where does it
occur ? From what sources is it made, and how can it be recognised ?
9. By what properties and reactions would you distinguish a
solution of cane-sugar from a solution of dextrose ?
10. How would you demonstrate the production of glucose from
cane-sugar and starch respectively ?
11. What effect is produced on starch by the action of (i) heat,
(2) dilute sulphuric acid, (3) nitric acid?
12. What are the principal differences between starch and cellulose?
What evidence exists as to the molecular weights of these substances ?
13. What is the action of (i) nitric acid, (2) sulphuric acid, and (3)
caustic soda, on cellulose ?
14. How are the following prepared : starch, British gum, gun-
cotton^ Willesden paper, celluloid, collodion, and cordite ?
15. Describe and explain the changes which starch undergoes
when acted on by malt extract. How could these changes be
demonstrated ?
CHAPTER XXI
DERIVATIVES OF THE FATTY ACIDS
i. THE HYDROXY-ACIDS
The Hydroxy-acids, or oxy-acids, are compounds which
combine the properties of alcohols and acids. They contain,
in other words, both hydroxyl and carboxyl groups. They
include some of the most important acids derived from the
vegetable and animal kingdoms. According to the number of
hydroxyl groups present in the compound, the acid is known as
a mono-, di-, tri-, &c., hydroxy-acid. Glycollic acid (see below)
is a monohydroxy-acid ; glyceric acid (p. 280) is a dihydroxy-
acid ; gluconic acid (p. 292) is a pentahydroxy-acid.
We shall begin with the study of the monohydroxy-monobasic
acids, that is to say, compounds which contain one hydroxyl
and one carboxyl group. They may be regarded as hydroxy-
derivatives of the fatty acids.
Formation of the Hydroxy-acids. They are obtained by
the careful oxidation of the glycols, whereby one carbinol group
is converted into a carboxyl group. The method is, however,
seldom used on account of the difficulty of preparing the glycols.
Ethylene glycol is converted by the action of dilute nitric acid
into hydroxyacetic or glycollic acid
CH 2 (OH) CH 2 (OH)
+ 2 = | + H 2 0.
CH 2 (OH) CO.OH
Glycol. ' Glycollic acid.
A more common method is to boil with water salts of mono-
halogen derivatives of the fatty acids. The chlorine is thereby
CH. xxi HYDROXY-ACIDS 315
replaced by hydroxyl. Potassium monochloracetate yields
glycollic acid (p. 318)
CH 2 iCl + HiOH CH 2 (OH)
I = | + KC1.
CO.OK CO.OH
Potassium Glycollic
monochloracetate. acid.
A third method is to hydrolyse the cyanhydrins of the alde-
hydes and ketones. In this manner the cyanogen group is
converted into a carboxyl group. Acetaldehyde cyanhydrin
forms hydroxypropionic acid ; acetone cyanhydrin yields hy-
droxyisobutyric acid
CH,
/OH
/OH
CH< + 2H 2 = CH< + NH 3 .
X:N X CO.OH
Hydroxy-
propionic acid.
CH, CH
/OH
3
/OH
+ 2H 2 O = C< + NH 3<
V CN
CH 3
Hydroxyisobutyric
acid.
It should be noted that by this method the hydroxyl and
carboxyl groups are necessarily linked to the same carbon atom.
Properties of the Hydroxy-acids. The hydroxy-acids are
more soluble in water than the corresponding fatty acids. This
may be ascribed to the additional hydroxyl group. For the
same reason they are less volatile, just as the glycols are less
volatile than the monohydric alcohols. Whereas acetic acid
melts at 16, glycollic acid melts at 80, and cannot be dis-
tilled unchanged. The hydroxy-acids form salts with the bases
in which the hydrogen of the carboxyl group is replaced by
a metal, whereas metallic sodium replaces hydrogen of the
hydroxyl as well as of the carboxyl group. Phosphorus
pentachloride likewise replaces both hydroxyl groups by
316 THEORETICAL ORGANIC CHEMISTRY CHAP.
chlorine. The action of sodium and phosphorus pentachloride
on glycollic acid produces the following compounds
CH 2 (ONa) CH 2 C1
CO.ONa CO.C1.
Disodium glycollate. Chloracetyl chloride.
Chloracetyl chloride is both an alkyl chloride and an acyl
chloride. Water rapidly attacks the acyl chloride group and
monochloracetic acid is formed
CH 2 .C1 CH a Cl
.1 =1 +HCL
co.jci + H;OH co. OH
On continued boiling the alkyl chlorine atom is also replaced
by hydroxyl as already explained.
The two hydrogen atoms of the hydroxyl and carboxyl groups
may be replaced separately or together by alkyl groups.
In the latter case a compound is formed which is both ether
and ester. Ethyl glycollic ester has the following formula
CH 2 .OC 2 H 5
CO.OC 2 H 5 .
Ethylglycolhc ester.
Hydrobromic acid attacks the alcohol hydroxyl and replaces
it by bromine ; hydriodic acid acts on the same group as a
reducing agent and replaces it by hydrogen. Glycollic acid
yields in the one case monobromacetic acid and in the other
acetic acid
CH.jOHTH"!Br CH 2 Br
I = | +H 8 0.
CO.OH CO. OH
Monobromacetic
acid.
CH 2 ;lTl':H CH 3
I - I + I
CO.OH CO.OH
Acetic acid.
On oxidation, the alcohol group is converted into an aldehyde
or ketone group, according to whether it is a primary 01
secondary alcohol group. Glycollic acid may be transformed
into glyoxalic and finally into oxalic acid by regulated oxidation.
xxi HYDROXY-ACIDS
317
CHO
CO.OH
CO.OH
> 1
CO.OH.
Glyoxalic acid.
Oxalic acid.
CH 3
CH 3
1
I
CO -*
CO.OH
CO.OH
C0 2
Pyruvic acid.
Acetic acid and
Carbon dioxide.
Hydroxypropionic acid or lactic acid forms a ketonic acid,
pyruvic acid, and then acetic acid
CO.OH
Glycollic acid.
CH 3
CH(OH) ->
CO.OH
Lactic acid.
Isomerism of the Hydroxy-acids. Among the hydroxy-
acids containing more than 2 carbon atoms it is clear that the
hydroxyl group may be attached to different carbon atoms of
the chain. Hydroxypropionic acid or lactic acid exists in two
isomeric forms
CH 3 .CH(OH).CO.OH CH 2 (OH).CH 2 .CO.OH
a-Hydroxypropionic acid. /3-Hydroxypropionic acid.
They are distinguished like the halogen derivatives of the
fatty acids (p. 151) by lettering the carbon atoms a, /3, y, c.,
beginning with the carbon atom next to the carboxyl group.
Properties of the a, #, 7, and 5 Hydroxy-acids. The position of the
hydroxyl group determines the character of the products obtained on
heating the different hydroxy-acids. When the o-hydroxy-acids are
heated, two molecules unite with the elimination of two molecules of
water. Hydroxypropionic acid gives lactide
CHg.CHO'H "+ "HOiOC CH 3 .CH O CO
i '::::::::::::::: i i i + 2H 2 o.
COO II + HO; . CII.CH 3 CO O CH.CH 3
Lactide.
The -hydroxy-acids lose a molecule of water and form unsaturated
acids. j8-hydroxypropionic acid forms acrylic acid (p. 268)
CH 2 (OH) CH 2
CHo = CH + H 2 O.
I I
CO.OH CO.OH
^Hydroxypropionic acid. Acrylic acid.
3i8 THEORETICAL ORGANIC CHEMISTRY CHAP.
The 7 and 5 hydroxy-acids also lose a molecule of water and form
what are known as inner esters or lactones. The product may be re-
garded as an ester formed by the union of an alcohol and acid ; but the
alcohol and acid are part of the same molecule. 7-Hydroxybutyric acid
forms 7-butyrolactone
CH 2 . CH 2 . CH 2 . CO CH 2 . CH 2 . CH 2 . CO
I i - \. -^ + H 2 0.
OjH OH: \O-^
y-Hydroxybutyric acid. y-Butyrolactone.
That the 7 and 8 hydroxy-acids form lactones rather than the o and $
hydroxy-compounds has been explained by the space arrangement of
the carbon linkages (p. 86). If a number
of carbon atoms are linked together, they
do not form a straight chain as usually
represented ; but as the linkages diverge at
an angle of about 109, the tendency will
be to form a closed chain when the num-
ber of carbon atoms exceeds 3. This is
shown in the diagram, (Fig. 75).
In other words, the groups attached to
the end carbon linkages of a chain of 4 or
5 carbon atoms are brought within closer
range than when fewer carbon atoms are
present in the compound. Thus, mutual
action can occur, and new combinations are FIG. 75. Space arrangement
formed between the end groups of the chain. f iour Carbon groups.
Carbonic acid, (OH)CO.OH, which, though non-existent in
the free state, forms salts and esters, might be regarded as the
first representative of the monohydroxy-acids ; but it is distinctly
a dibasic acid, for it contains 2 hydrogen atoms replaceable by
metals in the salts and by alkyl groups in the esters. It must,
therefore, be classed with the dibasic or dicarboxylic acids (p. 333).
Glycollic Acid, Hydroxyacetic acid, CH 2 (OH).COOH, is the
first member of the series. It is found in unripe grapes, and in
the leaves of the Virginian creeper. It is most readily obtained
by boiling potassium chloracetate with water. The liquid is
evaporated and the glycollic acid extracted with acetone, in which
it readily dissolves, leaving the potassium chloride undissolved
CH 2 C1.CO.OK + H 2 = CH 2 (OH).COOH + KC1.
Glycollic acid.
It is a colourless, crystalline substance, which melts at 80.
HYDROXY-ACIDS 319
Crlyoxal, CHO.CHO, is the dialdehyde of glycol, and may be re-
garded as the intermediate product between glycol and glyoxalic acid,
CHO.CO.OH (p. 325). It is prepared by oxidising acetaldehyde
with nitric acid. Equal parts of aldehyde and water are mixed together
and poured into a cylinder. A layer of water is formed below the
aldehyde solution by pouring the water carefully down a thistle funnel.
Below this a layer of strong nitric acid is poured, and the three layers
allowed to diffuse slowly. A polymer of glyoxal is formed and may be
separated by evaporation, as a colourless amorphous mass. It exhibits
the properties of an aldehyde, but in a twofold degree, uniting with two
molecules of hydroxylamine and phenylhydrazine, forming a bisulphite
compound with two molecules of sodium bisulphite and a cyanhydrin
with two molecules of hydrocyanic acid (p. 129). Glyoxal itself may
be obtained from the polymeric form by distilling with phosphorus
pentoxide, and forms yellow crystals, m. p. 15.
Lactic Acid, Ethylidene lactic acid^ a-Hydroxypropionic acid>
CH 3 .CH(OH).CO.OH. The a-hydroxy-acid or ordinary lactic
acid is present in sour milk, from which it was first isolated by
Scheele in 1780. It is produced in milk by the lactic fermenta-
tion of milk-sugar (p. 304). The ferment consists of chains of
cells resembling the acetic ferment (p. 160). Lactic acid is more
readily prepared from cane-sugar or starch, the operation being
practically the same as that used in the preparation of butyric
acid (p. 164) ; but the decomposition is arrested before the
butyric fermentation sets in. Cane-sugar is dissolved in water,
and a little tartaric acid is added together with zinc or calcium
carbonate to neutralise the free lactic acid. The ferment is
added in the form of decayed cheese and sour milk, and the
mixture is kept at a temperature of 4o-5o for several days.
Crystalline crusts of zinc or calcium lactate separate, and are
removed and recrystallised. The acid is obtained by decom-
posing the salts with sulphuric acid and extracting with ether.
On evaporating the ether, the lactic acid remains as a colour-
less viscid liquid which possesses a sour smell and taste. It is
also obtained from a-chloro- or bromopropionic acid by boiling
with water (p. 151), and by the hydrolysis of acetaldehyde cyan-
hydrin (p. 129). When pure, it melts at 18 and distils at I mm.
pressure unchanged. At the ordinary pressure it is converted
into lactide (p. 317). Boiled with dilute sulphuric acid, it decom-
poses into acetaldehyde and formic acid
CH 3 .CH(OH).CO.OH = CH 3 .CHO + H i COOH.
The calcium and zinc salts of lactic acid readily crystallise
320 THEORETICAL ORGANIC CHEMISTRY CHAP.
from hot water, and are characteristic of the acid. The calcium
salt has the composition (CH 3 .CH(OH).COO) 2 Ca + 5H 2 O ; the
zinc salt has the formula (CH 3 .CH(OH).COO) 2 Zn + 3H 2 O.
Para-, or Sarcolactic Acid, CH 3 .CH(OH).CO.OH. The
acid is found in muscle, to which it imparts an acid reaction,
and is consequently present in the juice of flesh. A convenient
source of the acid is Liebig's extract of meat. The extract is
dissolved in water, and the albumin precipitated by alcohol.
The alcohol is then driven off, the liquid acidified, and the
sarcolactic acid extracted with ether. It is optically active,
turning the plane of polarisation to the right, and in this
respect it differs from the sour milk acid, which is inactive.
Moreover, the zinc salt of sarcolactic acid contains only two
molecules of water of crystallisation. In all other chemical
properties the two acids appear to be identical
The optical activity of the acid implies the presence of an
asymmetric carbon atom (p. 114). This is readily explained
by the following formula (the asymmetric carbon atom is in
thick type)
CH 3
I
H C OH
CO.OH.
Sarcolactic acid.
But this formula is also that of the sour milk acid. How
are we to bring these facts into harmony? The explanation
is based on the speculations of Pasteur (1860), further de-
veloped by Van 't Hoff and Le Bel (1874) into the present
theory of space or stereo-isomerism.
Theory of Space- or Stereo-isomerism. A brief reference
has already been made to the meaning of the term asym-
metric applied to the central carbon atom of a group (p. 114),.
Now every asymmetric or imsymmetrical object like a hand
or foot has its fellow, but the two do not precisely overlap ;
in the same way every substance containing an asymmetric
carbon atom, round which the four different groups are dis-
tributed in three-dimensional space, is capable of existing in
two forms, which correspond to a left and right hand or to an
object and its reflected image. The two forms will then
HYDROXY-ACIDS 321
appear as in Fig 76. The one is the mirror-image of the
other.
CH, CH,
COOH COOH
OH OH
FIG. 76. Stereo-isomeric forms of Lactic acid.
When using actual models in which the different groups are
represented by coloured sticks or balls, it will be found that
the two models cannot be turned so as to coincide until two of
the groups in one model have been interchanged. It has been
shown that the only difference between two substances having
a space arrangement of their atoms corresponding to object
and image lies in their action on polarised light, the one turn-
ing it to the right (dextro-rotatory) and the other the same
amount to the left (laevo-rotatory) when in the dissolved or
liquid state.
Although every optically active substance, like active amyl
alcohol (p. 114), and sarcolactic acid, contains at least one
asymmetric carbon atom, the converse does not hold ; for there
are compounds like sour milk lactic acid which possess an
asymmetric carbon atom and show no rotation.
How is this explained ? The substance may be a mixture
of equal quantities of the two forms, the dextro-rotation of the
one form neutralising the Isevo-rotation of the other.
This is the case with the sour milk acid. It has, in fact, been
resolved into its two active components, a laevo- and a dextro-
rotatory acid, the latter being identical with sarcolactic acid.
The methods used for resolving inactive compounds into their
active components will be referred to under tartaric acid
(p- 358)-
Hydracrylic Acid, Ethylene lactic acid, $-Hydroxypropionic
acid, CH 2 (OH).CH 2 .CO.OH. This represents a third lactic
acid, which, however, has a different structure from either of
the previous acids. It is named hydracrylic acid from the fact
'of its losing a molecule of water on heating, a property of all
322 THEORETICAL ORGANIC CHEMISTRY CHAP.
/3-hydroxy-acids (p. 317), and forming acrylic acid. It is termed
also ethylene lactic acid to denote that the acid contains the
radical ethylene CH' 2 .CH' 2 , thereby distinguishing it from or-
dinary lactic acid or ethylidene lactic acid, which contains the
ethylidene radical CH 3 .CH". The designation /3-hydroxypro-
pionic acid has already been explained (p. 317). Hydracrylic
acid has been obtained synthetically by boiling the /3-chloro- and
bromo-propionic acids with water, or by acting upon ethylene
chlorhydrin (p. 248) with potassium cyanide. The cyanhydrin,
thus formed, yields the acid on hydrolysis. These changes are
represented as follows :
*W KCN ^(OH) H 2 CH 2 (OH)
CH 2 C1 CH 2 .CN CH 2 .CO.OH.
Ethylene Ethylene Ethylene
chlorhydrin. cyanhydrin. lactic acid.
Hydracrylic acid is a thick, syrupy liquid resembling ordinary
lactic acid.
2. THE AMINO-ACIDS
The Amino-Acids derive their interest from their occurrence
among the decomposition products of albuminoid substances
and proteids (p. 373). The amino-derivatives of the fatty acids
are fatty acids in which one atom of hydrogen of the alkyl
group is replaced by the amino (NH 2 ) group. They are conse-
quently both amines and acids, the result being that they are
neutral substances.
Glycine, Glycocoll, Ammo-acetic acid^ CH 2 (NH 2 ).CO.OH.
This compound was originally prepared by boiling gelatine, or
glue with dilute sulphuric or hydrochloric acid, or caustic soda.
It crystallises in large four-sided prisms which have a sweet
taste. Hence, it received the name of glycocoll (yXvKvs, sweet ;
Ko'XXa, glue) or gelatine-sugar. It is most conveniently prepared
by mixing chloracetic acid and ammonia solution
CH 2 C1 CH 2 (NH 2 )
+ 3NH 3 = | + NH 4 C1.
CO. OH CO.ONH 4
. Chloracetic acid. Glycine ammonia.
After standing, the solution is concentrated and the glycine
converted into the crystalline copper salt by boiling with copper
carbonate.
xxi AMINO-ACIDS 323
The copper salt, (C 2 H 4 NO 2 ) 2 Cu + H 2 O, is then separated, dis-
solved in water, and decomposed by hydrogen sulphide. The
sulphide of copper is removed by filtration, and the solution
concentrated until the glycine begins to crystallise. The copper
salt of glycine as well as of certain other amino fatty acids has
a deep blue colour.
EXPT. in. Dissolve a crystal of glycine in water and add a single
drop of copper sulphate solution. A blue colour is at once produced,
which is of a different shade from that of copper sulphate and is much
more intense. Ferric chloride gives a deep red colour with glycine.
Glycine exhibits the property of a primary amine in its
behaviour with nitrous acid. The amino group is replaced by
hydroxyl, nitrogen is evolved, and glycollic acid is formed
CH 2 NH 2 CH 2 (OH)
+ HNO 2 =| + N 2 + H 2 O.
COOH COOH
It differs from an amide inasmuch as it does not evolve am-
monia when heated with a solution of caustic soda.
Derivatives of Glycine. Hippuric Acid, or benzoyl glycine, is glycine
in which a hydrogen atom of the amino group is replaced by the
aromatic acid radical benzoyl (p. 480). The formula of hippuric acid
CH 2 .NH(CO.C 6 H 5 )
CO. OH
Hippuric acid, or
Benzoyl glycine.
It is found in the urine of herbivorous animals, and crystallises in long
white prisms, which readily decompose on boiling with strong hydro-
chloric acid into benzoic acid and glycine
CH 2 .NH\ CO.C 6 H 5 CH 2 .NH 2
| ,\ + = | +C 6 H B CO.OH.
CO. OH H\OH CO. OH Benzoic acid.
EXP. 112. Boil a few crystals of hippuric acid with strong hydro-
chloric acid. Cool and filter off the crystals of benzoic acid, add a
slight excess of ammonia to the filtrate, and boil until the solution is
neutral and the excess of ammonia driven off. The addition of a few
drops of copper sulphate solution will produce the characteristic deep
blue colour of copper glycine.
Y2
324 THEORETICAL ORGANIC CHEMISTRY CHAP.
Sarcosine, Methyl glycine, (CH 3 NH)CH 2 .COOH, is obtained by
boiling creatine (see below) with baryta solution. It may be prepared
synthetically by the action of methylamine on chloracetic acid
CH 2 ;C1 + H:NHCH 3 CH 2 .NHCH 3
| = | + HC1.
COOH COOH
Betaine, Trimethyl glycine, HO(CH 3 ) 3 N.CH 2 .COOH, is present in
beetroot molasses (p. 301), and is the probable source of trimethylamine,
which the dry beet residues yield on distillation (p. 206). It is closely
related to choline, from which it may be obtained by oxidation (p. 278).
Its synthesis from chloracetic acid and trimethylamine establishes its
constitution
N(CH 3 ) 3 OH N(CH 3 ) 3
CH 2 .COOH CH 2 . CO
Betaine. Betaine anhydride.
When heated to 100 it loses a molecule of water and forms the
anhydride.
Creatine, Methylguanidine acetic acid, C 4 H9N 3 O 2 , is present in small
quantity in the juice of meat together with sarcolactic acid. It is
readily obtained by precipitating the albumin from meat extract with
basic lead acetate. The liquid is filtered and the lead removed
with hydrogen sulphide. On concentrating the filtrate on the water-
bath, a brown, viscid liquid remains, from which, on cooling, creatine
crystallises in long prisms. When boiled with baryta water creatine is
hydrolysed, and yields urea and sarcosine
(CH 3 )HN.CH 2 .COOH.
Sarcosine.
Creatinine, C 4 H 7 N 3 O, is the anhydride of creatine
. HN:C N(CH 3 ).CH 2
NH CO.
Creatinine.
It is a normal constituent of urine, but the quantity is usually very
small. It crystallises in colourless prisms, having a characteristic,
lenticular form.
HN:C-
-N(CH 3 ).CH 2 .COOH
= CO(NH 2 ) 2
Creatine.
Urea.
+ HO
H
XXI KETONIC ACIDS 325
Among the better-known amino-acids, found among the decomposition
products of albuminoid substances, are Alanine, or a-amino-propionic
acid, CH 3 .CH(NH 2 ).COOH, a product of the decomposition of silk,
and Leucine, or a-amino-isobutyl acetic acid, (CH 3 ) 2 .CH.CH 2 .CH(NH 2 ).
CO. OH, which is obtained, together with glycine and other substances
by the decomposition of gelatine, glue, and other albuminoid substances
by boiling them with mineral acids or caustic alkalis. Leucine is also
formed during the digestion of proteids by trypsin, an enzyme derived
from the pancreas.
3. ALDEHYDIC AND KETONIC ACIDS.
The Aldehydic and Ketonic Acids, as their name implies,
combine the properties of aldehydes or ketones with those of
acids.
Glyoxalic Acid, Glyoxylic add, CHO.CO.OH + H 2 O, may be
taken as the representative of an aldehydic acid. It is obtained
by the oxidation of ethyl alcohol, glycol, or glycollic acid with
nitric acid (p. 318), or by the reduction of oxalic acid on electro-
lysis or by means of magnesium powder.
EXPT. 113. Place 10 grams of magnesium powder in a flask, cover
with water and cool well in ice. Pour on 250 c.c. of a saturated
solution of oxalic acid. After it has stood for a time, filter. The
solution may be used for the test for proteins (p. 372). Add a little
glacial acetic and strong sulphuric acid to a few drops of glyoxalic
acid solution, and then a solution of egg albumin ; a violet coloratior
is produced.
Another method is to boil dichlor- or dibrom-acetic acid with
water
CHC1 2 CH(OH)o CHO
| +2H 2 0= | "+2HC1= | +H 2 0.
COOH COOH COOH
Dichloracetic Intermediate Glyoxalic
acid. product. acid.
The latter reaction resembles the formation of aldehyde from
ethylidene chloride (p. 88). The acid is found in unripe fruits
but disappears as the fruit ripens. It appears to be formed in
small quantities when acetic acid is exposed to the air. Gly-
oxalic acid is usually obtained as a syrupy liquid which slowly
crystallises on standing. It is very soluble in water and
volatilises in steam. Whilst it forms salts with bases, it also
reduces ammoniacal silver solution, producing a mirror, and
326 THEORETICAL ORGANIC CHEMISTRY CHAP.
combines with hydroxylamine and phenylhydrazine like an
aldehyde.
Pyruvic acid, CH 3 .CO.CO.OH, is the simplest of theketonic
acids. It is most readily prepared by distilling tartaric acid
with acid potassium sulphate, which acts as a dehydrating
agent.
C 4 H 6 O fi = C 3 H 4 p s + C0 2 + H 2 0.
Tartaric Pyruvic
acid. acid.
Pyruvic acid is a colourless liquid which boils at 165. It
yields lactic acid on reduction, and acetic acid and carbon
dioxide on oxidation
CH 3
CH(OH)
COOH
CH 3
4- CO
COOH
CH 3
-> COOH
C0 2 .
The latter reaction occurs readily on warming with ammonia
silver solution, the metal being deposited as a mirror. The
reduction of silver nitrate solution is therefore not limited to
aldehydes alone, but is brought about both by ketonic alcohols,
like fructose (p. 296), and ketonic acids. The ketonic properties
of the acid are exhibited in the compound which it forms with
sodium bisulphite and the yellow crystalline phenylhydra-
zone, which is precipitated on adding a solution of phenyl-
hydrazine acetate to the acid.
Acetoacetic Acid, CH 3 .CO.CH 2 .COOH, only exists in the
form of its esters. Ethyl acetoacetate has already been re-
ferred to (p. 186) as being formed by the action of sodium
upon ethyl acetate. The process is conducted as follows :
Metallic sodium, in thin slices, or as wire, is introduced into ten
times its weight of pure ethyl acetate. The action, which
begins slowly, becomes more vigorous after a time, and the
liquid boils. The flask containing the mixture is then
attached to an inverted condenser. To decompose the undis-
solved sodium, the liquid is finally heated on the water-bath.
The sodium compound of ethyl acetoacetate is thus formed,
from which dilute acetic acid liberates the ester as an oil, which
xxi KETONIC ACIDS 327
floats on the surface of the liquid. The oil is removed and
fractionated, the portion boiling at i75-i85 being separately
collected.
Formation of Ethyl Acetoacetate. The action of sodium on ethyl
acetate has been carefully studied by Claisen, who has shown that the
process is not a simple one, but involves four distinct reactions. Sodium
only reacts in the presence of a little alcohol, with which it forms sodium
alcoholate. The alcoholate is the active agent, uniting with a molecule
of ethyl acetate to form an additive compound. The latter then com-
bines with a second molecule of ethyl acetate, forming the sodium
compound of the new ester, and alcohol is then split off to form fresh
sodium alcoholate with the metallic sodium. The addition of acetic
acid replaces the sodium of the sodium compound by hydrogen. These
reactions are represented as follows :
i. 2C 2 H 5 OH + Na 2 = 2C 2 H 5 ONa + H 2 .
/ONa
2. CH 3 .CO.OC 2 H 5 + NaOC 2 H 5 = CH 3 C^-OC 2 H 5 .
\OC 2 H 5
Additive compound
(not isolated).
3. CH 3 .C(ONa)(OC 2 H 5 ) 2 + CH 3 .CO.OC 2 H 5
= CH 3 .C(ONa):CH.COOC 2 H 5 + 2C 2 H 5 OH.
Sodium acetoacetic ester.
4. CH 3 .C(ONa):CH.COOC 2 H 5 + C 2 II 4 O 2
= CH 3 .CO.CH 2 .COOC 2 H 5 + CH,.COONa.
Acetoacetic ester.
The formula of the sodium compound may also be written
CH 3 .CO.CHNa.COOC 2 H 5 , and this will be the one adopted to explain
subsequent reactions. The double formula for sodium acetoacetic ester
represents a case of Tautomerism> to which a brief reference is made
on p. 329.
Properties of Ethyl Acetoacetate. Ethyl acetoacetate is a
colourless liquid with a fruity smell, which boils at 182. It
gives a characteristic violet coloration with ferric chloride, and
forms, on adding an alcoholic solution of ciupric acetate to the
ester, a crystalline copper compound which has the formula
(C 6 H 9 O 3 ) 2 Cu, corresponding to the sodium compound. Ethyl
328 THEORETICAL ORGANIC CHEMISTRY CHAP.
acetoacetate has a peculiar interest in organic chemistry from
the extraordinary number and variety of synthetic products to
which it gives rise. There is probably no other single organic
compound which has been so extensively employed in organic
synthesis. We must confine our attention to a few of its more
important properties.
Synthetic Uses of Acetoacetic Ester. When the calcu-
lated quantity (i atom) of sodium dissolved in alcohol (i.e. an
alcoholic solution of sodium alcoholate) is added to aceto-
acetic ester, the sodium compound of the ester is formed. If
an alkyl iodide is now boiled with the sodium compound, an
alkyl derivative of acetoacetic ester is formed. In this way
methyl iodide gives methyl acetoacetic ester
CH 3 .CO.CH!Na.COOC 2 H 5 = CH 3 .CO.CH.COOC 2 H 5 + Nal.
CH 3 !I CH 3
Methylacetoacetic ester.
A second atom of hydrogen of the acetoacetic ester may now
be replaced by sodium as before, and by the action of another
molecule of the alkyl iodide, a second alkyl group may be
introduced. The alkyl group may be the same as the previous
one or different. A second molecule of methyl iodide yields
dimethylacetoacetic ester
CH 3
CH 3 .CO.C iNa!(CH 3 ).COOC 2 H 5 = CH 3 .CO.C.COOC 2 H 5 + Nal.
+ ! i I
fT_j IT : r^PT
^n. 3 ;i v^n. 3
Dimethylacetoacetic ester.
The two atoms of hydrogen cannot, however, be replaced
simultaneously by sodium : the reaction must be performed in
two steps, as described.
Acetoacetic ester and its alkyl derivatives undergo decom-
position in two ways, according to whether dilute alkalis or
acids or, on the other hand, strong alkalis are employed.
With dilute aqueous or alcoholic caustic alkalis or baryta, a
ketone is formed (ke tonic hydrolysis]
CH 8 .CO.CH .iCOiOC 2 H 5
= CH 3 .CO.CH 3 + CO 2 + C 2 H 5 OH.
+ H; O IH Acetone.
xxi KETONIC ACIDS 329
Concentrated alcoholic potash decomposes the ester into
2 molecules of acid (acid hydrolysis]
CH 3 .COJCH 2 .CO!OC 2 H 5
= CH 3 .CO.OH + CH 3 .CO.OH + C 2 H 5 OH.
+ HOjH+HOjH
If the alkyl derivatives of the ester are employed, it is possible
to effect the synthesis of a series of ketones by the ketonic de-
composition, or a series of fatty acids by the acid decomposition.
Thus the monomethyl derivative of acetoacetic ester would
yield, by the first process, methyl ethyl ketone ; by the second,
a mixture of acetic acid and propionic acid ; whilst the dimethyl
derivative would give, in the first case, methyl isopropyl ketone,
and in the second a mixture of acetic and isobutyric acid. These
are two of the most important synthetic processes for preparing
ketones and acids, and should be included among the methods
given on p. 127 and p. 153.
Tautoraerism, dynamic isomerism. It has already been stated that,
according to its mode of formation, the sodium compound of ethyl
acetoacetate must be Derived from an ester having the following
formula, which is that of an unsaturated hydroxy-acid
CH 3 .C(OH):CH.COOC 2 H 5 ,
whilst the various reactions enumerated above point to the formula
of a ketonic ester
CH 3 . CO. CH 2 . COOC 2 H 6 .
Two 'formulae are therefore representative of the same substance.
Which is correct ?
Our previous experience of the behaviour of the hydroxyl group in
alcohols and acids towards metallic sodium would naturally suggest
the hydroxyl form for the ester ; but there is strong evidence in support
of the ketone form. Thus, acetoacetic ester gives -hydroxybutyric
ester on reduction ; that is, the ketone group becomes a secondary
alcohol group
CH 3 . CH(OH). CH 2 . COOC 2 H 5 .
/3-Hydroxybutyric ester.
Moreover, like a ketone, it unites with phenylhydrazine and hydro-
xylamine. The present position of this much-debated question is that
the liquid is a mixture of both forms, one or other form predominating
according to the temperature and the action of different reagents. By
330 THEORETICAL ORGANIC CHEMISTRY CHAP.
freezing the liquid at - 79 the pure ketonic form has been obtained in
the crystalline form and constitutes about 98 per cent, of the mixture.
It gives no colour reaction with ferric chloride.
The term tautomerism (ravrb, the same ; /ie'pos, a part) or desmo-
tropism (Seo-^s, a bond ; rpeireiv, to change) has been applied to
this and similar cases where one substance appears to do duty for two
different isomers. In the majority of tautomeric substances, the change
in properties is due to the wandering of a hydrogen atom from one
polyvalent element to another, accompanied by a change in the
character of the linkage. In the case of ethyl acetoacetate the hydrogen
of the hydroxyl group passes from the oxygen atom to the adjoining
carbon atom or the reverse
C(OH):CH ^T CO.CH 2
Seeing that both isomeric forms may, and frequently do, exist side
by side, the substances which exhibit this property represent a
peculiarly labile form of isomerism, and the term dynamic isomerism is
a more satisfactory term for the phenomenon.
Levulinic Acid, Acetylpropionic acid, CH 3 .CO.CH 2 .CH 2 .
CO.OH, is formed by heating with dilute hydrochloric acid
either the hexoses, or such substances as starch and cane-sugar
which yield hexoses on hydrolysis. The product is filtered,
evaporated and distilled in vacua. Levulinic acid is a crystalline
solid which melts at 33. Neither the acid nor its ester forms a
sodium compound like acetoacetic ester. This property is
usually connected with the group CO.CH^CO (p. 345), which is
absent in levulinic acid.
QUESTIONS ON CHAPTER XXI
1. Describe the methods of preparing the hydroxy-acids of the
fatty series. Give some account of their properties.
2. What is the action of hydrogen cyanide on ketones and alde-
hydes ? Mention two examples in which this action has been utilised
in effecting the synthesis of important organic compounds.
3. Show how lactic acid may be produced from propionic acid
and from aldehyde, and how these substances may be obtained from
lactic acid.
4. Describe the properties of the hydroxy-acids. What is the action
of phosphorus chloride, hydrobromic acid, hydriodic acid, and nitric
acid on glycollic acid ?
KETONIC ACIDS 331
5. Several acids are known having the composition expressed by the
formula C 3 H 6 O 3 . Expand this into the several constitutional formulae.
What facts go to prove that lactic acid is both acid and alcohol ?
6. Describe how a- and ^3-lactic acids may be obtained synthetically.
What is the result of heating each variety? Which exhibits optical
isomerism? Give a brief account of the theory which is generally
accepted as accounting for this kind of isomerism.
7. Give an account of the behaviour of different kinds of hydroxy-
acids on heating. Explain the theory which accounts for the formation
of lactones.
8. What is meant by the term amino-acid ? What are its properties ?
In what respect does it differ from an amide ?
9. Describe the preparation of glycine. How can it be converted
into glycollic acid ?
jo. What is hippuric acid? How is its constitution determined?
Name any other derivatives of glycine obtained from natural sources,
and give their formulae.
11. Give an example of an aldehydic and a ketonic acid, and
describe some of their characteristic properties.
12. What is the action of sodium on ethyl acetate? Indicate how
the resulting product may be made the means of obtaining (a) a
substituted acetic acid, (b) a substituted acetone.
13. Describe and explain the formation of ethyl acetoacetate, and
give an account of the various syntheses in which it has been
employed.
14. Explain the meaning of the term tautomerism.
CHAPTER XXII
THE DIBASIC ACIDS AND THEIR DERIVATIVES
The Dibasic Acids contain two carboxyl groups and conse-
quently two replaceable hydrogen atoms. According to whether
one or both hydrogen atoms are replaced, they form acid and
neutral salts and esters in some cases salts with two different
metals and salts containing a metal and an alkyl group. They
may be regarded as paraffins in which two hydrogen atoms are
substituted by carboxyl groups, or fatty acids in which one alkyl
hydrogen is so replaced. Oxalic acid may be taken as repre-
sentative of the group of dibasic acids. It forms the following
series of compounds
CO. OH CO. OH CO. OK fCO.O~l(K 2 )
CO.OH CO. OK CO. OK LcO.oJ 2 Fe"
Oxalic acid, or Potassium Potassium Potassium ferrous
Dicarboxyl. hydrogen oxalate. oxalate. oxalate.
CO.OH CO.OC 2 H 5 CO. OK
CO.OC 2 H 5 CO.OC 2 H 5 CO.OC 2 H 5 .
Ethyl oxalic Diethyl Ethyl potassium
acid. oxalate. oxalate.
The dibasic acids are colourless, crystalline substances (with
the exception of carbonic acid, which is known only in the form
of its salts and esters). They dissolve in water, to which they
impart a strongly acid reaction. The lower members cannot be
distilled without decomposition.
CH. xxn DIBASIC ACIDS AND THEIR DERIVATIVES 333
The following table contains a list of the more important
members of the group :
TABLE XIII.
THE DIBASIC ACIDS, C n H 2n _ 2 O 4 .
Carbonic acid
HO.CO.OH
Melting-point.
Oxalic acid . . .
COOH COOH
1 80
Malonic acid .
COOH CH 2 COOH
loy
I7A
Succinic acid ....
COOH CH 2 CH 2 COOH
!&
Glutaric acid
COOH (CH 2 ) 3 COOH
Q7
Adipic acid
COOH.(CH 2 ) 4 COOH
ICO
Pimelic acid
COOH. (CH 2 ) 5 . COOH
"
IO^
Preparation of the Dibasic Acids. The dibasic acids are
prepared by processes which recall the formation of the fatty
acids. The glycols with two primary alcohol groups yield
dibasic acids on oxidation. Ethylene glycol forms oxalic acid
CH 2 OH
CH 2 OH
CO. OH
= I
CO. OH
Oxalic acid.
The dicyanides form dibasic acids on hydrolysis. Cyanogen
gas when dissolved in water and allowed to stand gives ammo-
nium oxalate (p. 210). A third method is to form the cyanogen
derivative of the fatty acid by acting upon the halogen substi-
tution product with potassium cyanide and hydrolysing the
product with alkali or mineral acids in the usual way. Mono-
chloracetic acid can, in this way, be converted into cyanacetic
acid and malonic acid
CH 2 C1
CO. OH
Chloracetic
acid.
KCN
CH 2 .CN
CO. OH
Cyanacetic
acid.
H 2
CH 2 .CO.OH
CO. OH
Malonic
acid.
An interesting method for preparing the higher dibasic acids is by
the electrolysis of the potassium alkyl salts of the lower dibasic acids.
334 THEORETICAL ORGANIC CHEMISTRY CHAP.
Potassium ethyl malonate, on electrolysis, decomposes in the following
way
C 2 H 5 O.CO.CH 2 JCO.OJK C 2 H 5 O.CO.CH 2 CO 2 K
I + +
C 2 H 5 O.CO.CH 2 .:CO.OjK C 2 H 5 O.CO.CH 2 CO 2 K
+ Electrode. - Electrode.
The product is the higher homologue, succinic ester, which separates
at the positive electrode ; the reaction resembles the production of
ethane from potassium acetate (p. 152).
Carbonic Acid, HO.CO.OH (?). Apart from the fact that
the salts and esters of carbonic acid contain only one carboxyl
group, the compounds are those of a dibasic acid. The metallic
salts are usually described among the metals in text-books of
inorganic chemistry. The alkyl salts are obtained by boiling
silver carbonate with the alkyl iodide. Ethyl iodide forms
ethyl carbonate, which is a liquid, boiling at 126
/ i|c 2 H 5
OOQ + j = OC(OC 2 H 5 ) 2 + 2AgI.
\OjAg I|C 2 H 5 Ethyl carbonate.
On passing carbon dioxide into alcoholic potash, the potas-
sium alkyl carbonate is precipitated as a white crystalline powder.
Ethyl alcoholic potash gives ethyl potassium carbonate
/OC 2 H 5
C 2 H 5 OH + KOH + CO 2 = OG/ + H 2 O.
Ethyl potassium
carbonate.
EXPT. 114. Boil powdered caustic potash with ethyl alcohol
on the water-bath, cool, and decant the clear solution. Pass a
rapid current of carbon dioxide through the solution. The crystal-
line ethyl potassium carbonate is rapidly precipitated with evolution
of heat.
Carbonyl Chloride, 1 Carbon oxy chloride, Phosgene , is ob-
tained by the direct union of carbon monoxide and chlorine
1 The term carbonyl, or carbonyl group, stands for the radical of carbonic acid,
CO. It is sometimes used as synonymous with ketone group. It might be desirable
to retain the name carbonyl for the group CO when ketone or aldehyde properties
are absent, as in the present case, and generally in the case of acyl chlorides, anhy-
drides, and amides. We have refrained for this reason from using the term carbonyl
group in reference to ketones and aldehydes.
xxii DIBASIC ACIDS AND THEIR DERIVATIVES 335
in sunlight. The discovery is due to J. Davy (1811), who gave
the name phosgene ($$, light ; yei/i/aco, I produce) to the gas
to describe its mode of production. Carbonyl chloride is also
formed by the oxidation of chloroform in presence of oxygen
and light (p. 89), or by the aid of potassium dichromate
and sulphuric acid. It is most conveniently prepared on a small
scale by the action of sulphur trioxide on carbon tetrachloride,
CC1 4 +2SO 3 = COC1 2 + SO 2 C1 2 .SO 3 .
EXPT. 115 One hundred
c.c. of carbon tetrachloride
are placed in a flask which is
attached to a reflux con-
denser, shown in Fig. 77,
and heated on the water-bath.
When the carbon tetra-
chloride has been heated
until it boils briskly, 120 c.c.
of 80 per cent, fuming sul-
phuric acid are slowly dropped
in through the tap-funnel,
which is attached to the top
of the condenser. Any carbon
tetrachloride which escapes
decomposition is condensed
in the U-tube surrounded by
cold water, whilst the carbonyl
chloride passes on and is con-
densed in a second vessel
surrounded by a good freez-
ing 'mixture. If liquid air
is available, the carbonyl
chloride may be obtained as
a colourless solid.
It is produced on the large scale by passing a mixture of
carbon monoxide and chlorine through charcoal, combination
between the gases being effected by contact action, or catalysis.
Carbonyl chloride is used in the manufacture of certain organic
colouring matters (p. 518). It readily condenses to a liquid at 8
and has a peculiarly suffocating and pungent smell. The solution
of the gas in benzene or toluene, which absorb as much as 20
per cent, of carbonyl chloride, is convenient for experimental
FIG. 77
336 THEORETICAL ORGANIC CHEMISTRY CHAP.
purposes. Carbonyl chloride has the properties of an acid
chloride, and may be regarded as the acid chloride of carbonic
acid. The gas fumes in moist air, decomposing into hydrochloric
acid and carbon dioxide
...... HiOH
+ = CO 2 + 2HC1 + H 2 O.
HJOH
It is also decomposed by alcohol, and gives chloroformic ester
according to the following equation
/Cl 7 C\
OC< = OC( + HC1.
Na+"HjOC 2 H 5 X OC 2 H 5
Chloroformic
ester.
Urethane, Ethyl carbamate, NH 2 .CO.OC 2 H 5 , is the product
formed by the action of ammonia on chloroformic ester, and is
used as a hypnotic
/NH 2
OC< : + NH 3 = OC< + NH 4 C1.
X OC 2 H 5 X OC 2 H 5
Urethane.
A variety of similar hypnotics are produced by replacing the
amino-group by substituted amino-groups and ethoxy-groups
by other alkoxy-radicals. Hedonal, NH 2 .COOC 6 H n , is an
example. Hedonal is also used as an anaesthetic.
Urethane is the ethyl ester of carbamic acid. The acid itself is
unknown in the free state, but the ammonium salt is a common
constituent of commercial ammonium carbonate. Ammonium
carbamate is readily obtained by passing carbon dioxide into
an alcoholic solution of ammonia
/
2NH 3 + C0 2 =--OC/
'NH 9
' a r-^ 0/
V ONH 4 .
EXPT. 1 1 6. Pass ammonia gas into ethyl alcohol until the alcohol
is saturated, then bubble carbon dioxide through the liquid. Am-
xxii DIBASIC ACIDS AND THEIR DERIVATIVES 337
monium carbamate is precipitated in the form of a white crystalline
powder.
Urea, Carbamide, CO(NH 2 ) 2 . When ammonia is added to
carbonyl chloride, urea is formed, just as acetamide is obtained
when ammonia acts uponacetyl chloride (p. 175)
CH 3 .COiCl + HJNH 2 + NH 3 = CH 3 .CONH 2 + NH 4 C1.
Acetamide.
id HiNH 2 /NH 2
/
X I
NCI H!NH 2 X NH
2NH 4 C1.
X
Urea.
This reaction determines the constitution of urea, as the amide
of carbonic acid. Hence the name carbonic amide, or shortly
carbamide, which is synonymous with urea.
That the substance is an amide is further seen from its
behaviour with boiling caustic alkalis, which decompose it into
ammonia and a salt of carbonic acid (p. 178)
OC/ 2 4- 2NaOH = Na^Og + 2NH 3 .
X NH 2
The presence of amino groups is also shown by the action of
nitrous acid, which liberates nitrogen ; at the same time carbon
dioxide is evolved
HO JNJO
+ ; \
CO<1 I 2 = C0 2 + H 2 + 2N 2 + 2H 2 0.
HO JNJO
EXPT. 117. Add to a solution of urea in water, a little sodium
nitrite solution and a few drops of hydrochloric acid. Effervescence
occurs and nitrogen and carbon dioxide are evolved.
The usual method for obtaining urea has already been de-
scribed (p. 221). Urea is a colourless substance which crystal-
lises in long prisms, melting at 132. It is very soluble in water
z
338 THEORETICAL ORGANIC CHEMISTRY CHAP.
and in hot alcohol. When heated, it decomposes into ammonia,
biuret (see below), and cyanuric acid.
The ehief interest attaching to urea is its presence in normal
human urine, about 30 grams being excreted daily. Urea
may be regarded as the final decomposition product of the
waste nitrogenous materials of the body. It is obtained from
urine by concentration and extraction with alcohol, which dis-
solves out the urea. The alcoholic extract is allowed to evaporate
and the urea then crystallises.
When urine is exposed to the air, fermentation sets in, the
urea being converted into ammonium carbonate
CO(NH 2 ) a + 2H 2 O = (NH 4 ) 2 CO 3 .
Detection and Estimation of Urea. The presence of urea may
be detected by a variety of reactions, which are described in the
following experiments :
EXPT. 118. I. Pleat a few crystals of urea over a very small flamt
until they melt and slowly evolve bubbles of ammonia gas. Con-
tinue to heat for a minute or two, then cool and add a few drops
of water, a drop or two of copper sulphate solution, and finally caustic
soda solution, until a clear solution is obtained. A violet, or pink,
solution is produced, which is a compound of biuret with copper.
The formation of biuret from urea takes place according to the
following equation
NH 2 .CO.NH|HT"NH2;.CO.NH 2 = NH 2 .CO.NH.CO.NH 2 + NH 3 .
Urea. Urea. Biuret.
Two molecules of urea combine with the elimination of one molecule
of ammonia.
2. Add to a solution of urea a few drops of a neutral solution
of mercuric nitrate. A white curdy precipitate is thrown down, which
is a basic compound of mercuric nitrate and urea
[CO(NH 2 ) 2 ] 2 .Hg(N0 3 ) 2 .3HgO.
3. Add to a strong solution of urea in water a few drops of
strong nitric acid, and to another portion a strong solution of oxalic
acid. In one case urea nitrate and in the other urea oxalate is
precipitated in crystals which have a characteristic appearance
under the microscope
CO(NH 2 ) 2 .HN0 3 [CO(NH 2 ) 2 ] 2 C 2 H 2 4 + H 2 O.
Urea nitrate. Urea oxalate.
4. Add to a solution of urea a few drops of an alkaline solution
xxn DIBASIC ACIDS AND THEIR DERIVATIVES
339
of sodium hypochlorite or hypobromite. Effervescence occurs, and
free nitrogen is evolved, the alkali retaining the carbon dioxide,
which is liberated at the same time
!H 2 JN jCOj N!H 2 !
: + ! i + : 1+1
Na; O :C1 Na! O |C1 Naj O JCI
4- 2 H 2 O + CO 2 -f N.
This reaction is utilised for the quantitative estimation of urea in
urine. It may be performed by the aid of Lunge's nitrometer (Fig. 78)
or other convenient apparatus. A solu-
tion of sodium hypobromite is prepared
by dissolving 100 grams of caustic soda in
250 c.c. of water and adding 25 c.c. of
bromine.
25 c.c. of this solution is introduced
into the flask a together with a small tube
containing 5 c. c. of urine. The graduated
vessel b is filled with water by raising
the reservoir c. The pressure in the
flask is adjusted by turning the three-
way tap d so that the vessel is for a
moment in communicatio*n with the air.
The tap is then turned so that a connec-
tion is made between the flask and the
graduated tube, and the small tube con-
taining the urine is then allowed to drop
into the hypobromite solution. Nitrogen
is evolved, and the liquid in b descends.
When gas ceases to be evolved, the
pressure in the graduated tube is adjusted
by means of the reservoir, and the volume
of gas is read off. The volume of gas
corresponding to the urea present is
always about 7 per cent, below the
theoretical amount, and a correction to
this extent must be introduced. In
analysing urine it is customary to
estimate, in addition to the urea, the total nitrogen by Kjeldahl's
method.
Cyanamide, NC.NH 2 , is prepared by the action of mercuric oxide on
thiourea, which removes from the latter hydrogen sulphide
SC(NH 2 ) 2 -H 2 S = NiC.NH 9 .
Thiourea. Cyanamide.
Z2
FIG. 78. Lunge's Nitrometer
for the estimation of Urea.
340 THEORETICAL ORGANIC CHEMISTRY CHAP.
The disodium and calcium compounds are formed as intermediate
products in the manufacture of sodium cyanide from sodamide and oi
calcium cyanide from the carbide (p. 213)
2NaNH 2 + C = CN.NNaa + 2H 2 .
Disodium
cyanamide.
CaC 2 + N 2 = NCNCa + C
Calcium cyanamide.
Cyanamide is a colourless, deliquescent substance, which melts at 40
and is soluble in water and alcohol. By the action of mineral acids
it takes up water and forms urea. The reaction resembles the formation
of formamide from hydrocyanic acid (p. 212)
NH 2 .CN + H 2 = OC(NH 2 ) 2 .
The calcium compound has been found useful as a manure in place of
nitrates and ammonium salts.
Guanidine, (NH 2 ) 2 C:NH. Ammonia combines with cyanamide
and forms guanidine
,NH
NH 2 .CN + NH 3 = NHg.cC
"NH 2 .
Guanidine.
It is more conveniently prepared by heating ammonium thiocyanate
(p. 222) to 1 80. The formation of guanidine depends on that of
Hhiourea and cyanamide as intermediate products. Cyanamide combines
with ammonium thiocyanate to produce the thiocyanate of guanidine
(NH 4 )SCN"1
X \ = NH 2 .C:NH.NH 2 .HSCN.
SC(NH 2 ) 2 -> NH 2 CN J Guanidine thiocyanate.
Guanidine is a deliquescent, crystalline compound with strongly
alkaline properties, which combines with carbon dioxide and other
acids, forming crystalline salts. Guanidine is found among the
products of oxidation of certain proteid substances, such as egg albumin
and the albumin of lupine seedlings, as well as of guanine (p. 369).
Guanidine may be regarded as a constituent of creatine (p. 324). It
is intimately associated with the nitrogenous products of the animal
and vegetable organism.
Oxalic Acid, CO.OH.CO.OH + 2H 2 O. Oxalic acid is found
in wood sorrel (Oxalis acetosella) and other plants, as the acid
potassium salt. The salt is sometimes called salts of sorrel.
The calcium salt is frequently found crystallised in plant cells.
Certain lichens growing on limestone consist largely of this
salt. It is also 'present in urine and in urinary calculi. It is
xxii DIBASIC ACIDS AND THEIR DERIVATIVES 341
produced by a peculiar fermentation of sugar caused by certain
species of yeast and fungi. Scheele, in 1776, first obtained oxalic
acid artificially by heating sugar with nitric acid.
EXPT. 119. Pour 1 80 c.c. of strong nitric acid into a large flask
(2 litres) and warm the acid on the water-bath. Remove the flask
to the fume cupboard and add 50 grams of cane-sugar. Torrents of
brown fumes are evolved. When the reaction has ceased, evaporate
the liquid on the water-bath to one-quarter its bulk. On cooling,
large, colourless, prismatic crystals of oxalic acid separate.
Oxalic acid is at present manufactured either from sodium
formate (p. 157) or from pine sawdust, which is oxidised by
2HCOONa = C 2 O 4 Na 2 + H 2 .
Sodium Sodium
formate. oxalate.
fusion with caustic alkalis. The sawdust is stirred into a stiff
paste with a mixture of strong caustic potash and soda solution,
and the paste is heated on iron plates. The temperature is
gradually raised, care being taken to avoid charring. The dry,
brown mass is lixiviated with a small quantity of warm water
which removes the excess of alkali and leaves the less soluble
sodium oxalate. The waste alkali is recovered and used again.
The sodium oxalate is dissolved in water, and converted into
the insoluble lime salt by boiling witb milk of lime, and the
lime salt is separated and decomposed with sulphuric acid.
The liquid, separated from the calcium sulphate, is evaporated,
when the oxalic acid crystallises in long prisms, containing two
molecules of water of crystallisation. There are various
methods by which oxalic acid has been synthesised, some of
which have already been mentioned. A solution of cyanogen
in water changes into ammonium oxalate (p. 210).
EXPT. 1 20. Heat a few grams of sodium formate in a test-tube.
The gas which is evolved can be ignited at the mouth of the tube.
If the residue is dissolved in water and filtered, the solution gives
the reactions for oxalic acid (see below).
Properties of Oxalic Acid. Oxalic acid crystallises in long,
colourless prisms containing two molecules of water of crystal-
lisation. When heated to 100, the water of crystallisation is
driven off. Above this temperature part of the acid melts, a
342 THEORETICAL ORGANIC CHEMISTRY CHAP.
part sublimes, and a certain amount decomposes into carbon
dioxide and formic acid. When warmed with strong sulphuric
acid, oxalic acid breaks up into carbon dioxide and carbon
monoxide
C 2 4 H 2 -H 2 = C0 2 + CO.
EXPT. 121. Heat a few grams of oxalic acid, or an oxalate, with
an equal bulk of strong suphuric acid. Effervescence ensues without
charring, and the gas, which is evolved, may be ignited.
Oxalic acid, in presence of dilute sulphuric acid, is rapidly
oxidised by potassium permanganate, on warming, to carbon
dioxide and water. The process is utilised in volumetric
analysis.
5C 2 O 4 H 2 + 2KMnO 4 + 3H 2 SO 4 = 5CO 2 + 5H 2 O + K 2 SO 4 + 2MnSO 4 .
EXPT. 122. Dissolve a few crystals of oxalic acid, or an oxalate in
water ; add dilute sulphuric acid and warm gently. Add potassium
permanganate, drop by drop. It is at first decolorised ; but when
the oxalic acid is all oxidised the pink colour remains.
Phosphorus pentachloride converts oxalic acid into oxalyl
Moride. It is a colourless liquid which boils at 64
C 2 H 2 O 4 + 2PC1 5 =C 2 O 2 C1 2 + 2POC1 3 + 2HC1.
Salts of Oxalic Acid. The following are the most im-
portant salts of oxalic acid. Potassium oxalate, C 2 O 4 K 2 + H 2 O,
is soluble in water ; the acid salt, C 2 O 4 HK, is less soluble and has
been referred to as a constituent of many plants. Acid potas-
sium oxalate combines with oxalic acid and forms what is known
as potassium quadroxalate, C 2 O 4 HK.C 2 H 2 O 4 + 2H 2 O, which is
sometimes used for removing ink-stains and iron-moulds, under
the name of salts of sorrel, or lemon. The calcium salt, C 2 O 4 Ca,
is found in plants ; the precipitated salt, which is thrown down
when calcium chloride is added to a solution of an oxalate, con-
tains one molecule of water of crystallisation. Ferrous oxalate,
C 2 O 4 Fe-f-2H 2 O, is precipitated as an insoluble, yellow powder
when a ferrous salt is added to an oxalate in solution. Potas-
sium ferrous oxalate, (C 2 O 4 ) 2 K 2 Fe + H 2 O, has strong reducing
properties, and is used as a developer in photography. It is
obtained by mixing solutions of ferrous sulphate and potassium
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 343
oxalate in certain proportions. The ferric alkali salts have
a green colour. The alkyl salts, or esters, of oxalic acid are
obtained by boiling the alcohol with anhydrous oxalic acid and
distilling the product. Methyl oxalate is a solid, which melts at
51 and boils at 162 ; ethyl oxalate is a liquid boiling at 186.
Both esters are rapidly hydrolysed by alkalis, in the cold.
Oxamide, CONH 2 .CONH 2 , is obtained by heating ammo-
nium oxalate, or, more readily, by adding strong ammonia to
methyl, or ethyl, oxalate, when oxamide is precipitated as a white
crystalline powder (p. 185)
CO.OC 2 H 5 CO.NH 2
+ 2NH 3 = | + 2C 2 H 5 OH.
CO.OC 2 H 5 CO.NH 2
Oxamide.
Oxamide is converted on the one hand into cyanogen, by
heating with phosphorus pentoxide ; and on the other into
crxalic acid and ammonia, by hydrolysis with alkalis,
CN CO.NH 2 CO.OH NH 3
I -2H 2 O I +2H2O I _j_
CN CO.NH 2 CO.OH NH 3 .
EXPT. 123. Bring into a hard glass test-tube some phosphorus
pentoxide to a depth of about f inch and immediately add about
half its bulk of oxamide. Mix thoroughly by shaking and stirring
with a glass rod, and then heat. The cyanogen can be ignited at the
mouth of the tube.
Malonic Acid, CH 2 (CO.OH) 2 , is found as the calcium salt
in beetroot. It was originally prepared by the oxidation of
malic acid (p. 349) with potassium dichromate and sulphuric
acid, a process which gave rise to the name ; but it is now
usual to obtain it from monochloracetic acid. Potassium
chloracetate is boiled with potassium cyanide. The cyanacetate
of potassium is then hydrolysed with strong hydrochloric
acid ; the product is evaporated to dryness and extracted
with ether. When the ether has evaporated, malonic acid
remains.
It is a colourless, crystalline substance, which melts at 132,
and dissolves readily in water, alcohol, and in ether.
Malonic acid loses carbon dioxide on heating to 140-! 50,
344 THEORETICAL ORGANIC CHEMISTRY CHAP.
whereby it is converted into acetic acid. This is a characteristic
property of all polybasic acids^ having two carboxyl groups
attached to the same carbon atom.
CH 2 .;COO;H CH 3
I = I +C0 2 .
COOH COOH
Malonic acid. Acetic acid.
EXPT. 124. Heat a little malonicacid in a test-tube until it melts
and effervesces, and decant the gas given off into lime-water. The
presence of carbon dioxide is shown by the turbidity of the lime-
water, whilst the liquid which remains has the smell of acetic
acid.
When malonic acid is heated with phosphorus pentoxide a
gas escapes which can be condensed to a solid in liquid air. It
has the formula C 3 O 2 , and is termed carbon suboxide. It is
formed according to the equation :
CH 2 (COOH) 2 - 2H 2 O = C 3 O 2 .
It re-unites with water to form malonic acid and with ammonia
to form malonamide, and probably has the constitution : r
Malonic ester is prepared from cyanacetic acid by heating it
with a mixture of alcohol and sulphuric acid. The hydrolysis
of the cyanogen group to carboxyl and the formation of the
ester proceed simultaneously
CH 2 CN CH 2 .COOH CH 2 .COOC 2 H 5 .
! -> I -> I
COOH CO. OH CO.OC 2 H 5 .
Cyanacetic acid. Malonic acid. Diethyl malonate.
The esters are fragrant-smelling liquids, which are insoluble
in water and can be distilled.
Synthetic Uses of Malonic Ester. Malonic ester shares
the property of acetoacetic ester in forming a sodium compound
xxii DIBASIC ACIDS AND THEIR DERIVATIVES 345
when a solution of sodium alcoholate in alcohol is added to the
ester (p. 328)
CH,(COOC 2 H 5 ) 2 + NaOC 2 H 5 = CHNa(CO. OC 2 H 5 ) 2 + C. H 5 OH.
Malonic ester. Sodium malonic ester.
Cyanacetic ester behaves similarly.
This property is associated with the groups CO.CH 2 .CO and
CO.CH 2 .CN ; that is to say, a methylene group, situated between
ketone, cyanogen or certain other acidic groups
!"CO"iOC 2 H 5 fOXiCHg i"CN"!
Mi II 1 ' II
I CH 2 ; CH 2 j i CHJ
I ! Mi I
[ CO. !OC 2 H 5 ICO. JOC 2 H 5 j CO. |OC 2 H 5 .
Malonic ester. Acetoacetic ester. Cyanacetic ester.
If the equivalent of one molecule of alkyl iodide is added
to the sodium compound of malonic ester in alcoholic solution,
and the mixture boiled, sodium iodide separates, and at the
same time the alkyl malonic ester is formed. Methyl iodide
gives methyl malonic ester. The product is poured into water,
and the ester, which is insoluble, is separated and distilled
CH:Nai(CO.OC 2 H 6 ) 2
= CH 3 .CH(CO.OC 2 H 5 ) 2 + Nal.
-f- CH 3 I Methyl malonic ester.
A second alkyl group (it may be the same, or a different
one), can then be introduced by repeating the above operation.
Methyl iodide will give dimethyl malonic ester
CH 3 .C!N(CO.OQH B ) a
= (CH 3 ) 2 C.(CO.OC 2 H 5 ) 2 .
4- CH 3 |I ! Dimethyl malonic ester.
Ethyl iodide forms methyl ethyl malonic ester
CH 3 .C|Na(CO.OC 2 H 5 ) 2 CH,
=
+ C 2 H 5 ;I C 2 H/
Methyl ethyl malonic ester.
If the above esters are now hydrolysed with caustic potash
and the free acids separated by the addition of hydrochloric
346 THEORETICAL ORGANIC CHEMISTRY CHAP.
acid and extraction with ether, new dibasic acids are obtained.
The method is therefore important for obtaining homologues
ofmalonic acid. As all the acids necessarily have, like malonic
acid, two carboxyl groups linked to the same carbon atom,
they lose carbon dioxide on heating, and pass into monobasic
acids ; methyl malonic acid gives propionic acid ; dimethyl
malonic acid forms isobutyric acid ; methyl ethyl malonic acid
produces methyl ethyl acetic acid
CH 3 .CH(COOH) 2 = CH 3 .CH 2 .COOH + CO 2 .
Methyl malonic acid. Propionic acid.
(CH 3 ) 2 C(COOH) 2 = (CH 3 ) 2 .CH.COOH + CO 2 .
Dimethyl malonic acid. Isobutyric acid.
CH 3 \ CH 3 x\
>C(COOH) 2 = >CH.COOH + CO 2 .
C 2 H/ C 2 H/
Methyl ethyl malonic Methyl ethyl acetic
acid. acid.
In this way the fatty acids may be synthesized.
Malonic ester may also be employed in the synthesis of
saturated ring compounds referred to on p. 255. To give one
illustration : ethylene bromide and sodium malonic ester
yield trimethylene dicarboxylic ester
CH a jBr CH 2V
; + Na 2 : C (COOC 2 H 5 ) 2 = | >C(COOC 2 H 5 ) 2 + 2 NaBr.
CH 2 ;Br i CH/
Trimethylene
dicarboxylic ester.
Simultaneously with the above reaction, there is formed butane
tetracarboxylic ester
CH 2 ; Br + NaiCH(COOC 2 H 5 ) 2 CH 2 .CH.(COOC 2 H 5 ) 2 .
= | + 2NaBr.
CH 2 iBr_Na:CH(COOC 2 H 5 ) 2 CH 2 .CH.(COOC 2 H 5 ) 2
Butane tetracarboxylic ester.
The free acid, obtained by hydrolysis from butane tetracarboxy-
lic ester, contains two pairs of carboxyl groups, each pair being
linked to the same carbon atom, and consequently, on heating,
two molecules t of carbon dioxide are evolved. The resulting
acid is a dibasic acid (adipic acid) of this series. In this way
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 347
the synthesis of dibasic acids may be effected by the aid of
malonic ester.
(COOH) 2 CH.CH 2 .CH 2 .CH(COOH) 2 = COOH.(CH 2 ) 4 COOH + 2CO 2 .
Butane tetracarboxylic acid. Adipic acid.
Succinic Acid, COOH.CH 2 .CH 2 .COOH, is mentioned by
Agricola (1550) as being obtained from amber (Lat. succinuni)
by distillation, and the method is still used in its preparation.
When amber is distilled in iron retorts, the acid collects in the
receiver partly in the solid form and partly in solution, together
with an oil, known as amber oil. The distillate is then filtered
from the oil and evaporated. Succinic acid occurs in certain
lignites and fossil wood, and in lettuces, unripe grapes, and
wormwood. It is also obtained by the fermentation of calcium
malate or ammonium tartrate by yeast or putrid cheese. The
process is one of reduction, and may be imitated by the action
of strong hydriodic acid.
CH(OH).CO.OH CH(OH).CO.OH CH 2 .CO.OH
CH(OH).CO.OH CH 2 .CO.OH CH 2 .CO.OH
Tartaric acid. Malic acid. Succinic acid.
When either tartaric or malic acid is heated with strong
hydriodic acid, it is converted into succinic acid, just as
glycollic acid under the same conditions forms acetic acid
(p. 316). Succinic acid has also been synthesised by a method
which leaves no doubt as to its constitution. When ethylene di-
bromide is boiled with potassium cyanide, ethylene cyanide is
formed. The latter, on hydrolysis, gives succinic acid. As
ethylene dibromide is prepared from ethylene and ethylene
may be obtained from acetylene, which is formed by the direct
union of carbon and hydrogen, succinic acid can be synthesised
from its elements
H 2 C H * Br 2 ^Br KCN CH 2 CN ^ CH,CO.OH.
" " " " " " " "
CH " " CH 2 " " CH 2 Br " " CH 2 CN " " CH 2 .CO.OH.
Acetylene. Ethylene. Ethylene Ethylene Succinic acid.
bromide. cyanide.
Succinic acid can also be obtained from /3-iodopropionic acid
by the action of potassium cyanide and by hydrolysing the
348 THEORETICAL ORGANIC CHEMISTRY CHAP.
resulting cyanopropionic acid. There are many other methods
of preparation, which are of less importance
ICH 2 .CH 2 .COOH -> CN.CH 2 .CH 2 .COOH
jB-Iodopropionic acid. /3-Cyanopropionic acid.
> COOH.CH 2 .CH 2 .COOH.
Succinic acid.
Succinic acid crystallises in prisms, or plates, which melt at
182. When distilled it is converted into the anhydride, a white
crystalline substance, which melts at 120. The fact that
succinic acid alone among the simple dibasic acids gives an
anhydride is explained on the same grounds as those which
determine the formation of the lactones from the y and d
hydroxy-acids (p. 317).
CO. CH 2 . CH 2 . CO CO. CH 2 . CH 2 . Co'
I. I = X +HA
OjH OH; NO/
Succinic anhydride.
Succinic anhydride, like acetic anhydride, is converted into
the acid by boiling with water or alkalis
CH 3 .CO CH 3 .CO.OH
^>0 + H 2 = +
CH 3 .CO CH 3 .CO.OH.
Acetic anhydride. Acetic acid.
CH 2 .CO CH^CO.OH
\r
CH 2 .CO CH 2 .CO.OH.
Succinic anhydride. Succinic acid.
When succinic anhydride is heated in a current of ammonia,
succinimide is formed
CH 2 .CO CH 2 CO
No + NH 3 = | \NH + H 2 O
CH 2 .CO CH 2 CO
Succinimide.
Succinimide is a crystalline substance which has the properties
of weak acid, inasmuch as the hydrogen of the NH group is
replaceable by certain metals, and forms salts of the general
formula
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 349
CH 2 CO
X >NM'
CH 2 CO
General formula of
Succinimide salts.
Succinic acid forms a series of well-defined salts, among
which the calcium and basic ferric salts are characteristic. The
latter is thrown down as a light brown, gelatinous precipitate on
adding ferric chloride to a solution of a succinate. Iron may
be separated from other metals by this means.
Isosuccinic Acid, Methyl malonic acid, CH 3 .CH(CO.OH) 2 , isisomeric
with succinic acid and is obtained from malonic ester by the action of
methyl iodide on sodium malonic ester. The free acid loses carbon
dioxide on heating, and yields propionic acid (p. 344).
Pyrotartaric Acid, Methyl succinic acid, CH 3 .CH(COOH).CH 2
(COOH), is isomeric with glutaric acid and dimethyl malonic acid. It
is obtained by the dry distillation of tartaric acid. Like succinic acid
it forms an anhydride.
Adipic Acid, CO.OH(CH 2 ) 4 CO.OH, was first obtained by the
oxidation of fat (Lat. adeps}. It has been synthesised by various
methods ; by the electrolysis of potassium ethyl succinate (p. 334) ;
by the action of ethylene bromide on sodium malonic ester (p. 346) ;
and by decomposing 0-iodopropionic acid with finely divided metallic
silver
ICH 2 . CH 2 . COOH CH 2 . CH 2 . COOH
Ag 2 + = 2AgI + |
ICH 2 . CH 2 . COOH CH 2 . CH 2 . COOH
/3-Iodopropionic acid. Adipic acid.
HYDROXY-DIBASIC ACIDS
Malic Acid, Hydroxy succinic acid, COOH.CH(OH).CH 2 .
COOH. The acid was isolated by Scheele, in 1785, from the
juice of unripe apples (Lat. malum\ and it frequently accom-
panies tartaric and citric acid (see pp. 352, 359) in fruits, partly
in the free state and partly as the potassium or calcium salt.
In currants, cherries, and in the leaves and stems of rhubarb, it
is present as the acid potassium salt ; in the tobacco plant, as
the acid calcium salt.
It is usually prepared from the unripe berries of the mountain
ash. The juice is boiled with milk of lime which precipitates
350 THEORETICAL ORGANIC CHEMISTRY CHAP.
the neutral calcium salt, C 4 H 4 O 6 Ca. The precipitate is
collected and washed, and recrystallised from hot, dilute nitric
acid, from which the acid salt separates, (C 4 H 6 O 6 ) 2 Ca+6H 2 O.
This is decomposed with the theoretical quantity of oxalic or
sulphuric acid, and the liquid, filtered from the calcium oxalate
or sulphate, is concentrated by evaporation. Malic acid is a
crystalline substance which melts at about 100. It is very
hygroscopic, and deliquesces on exposure to moist air. When
heated it loses water, and is converted into two isomeric acids,
known as fumaric and maleic acids, which will be described
later (p. 361)
C 4 H 6 5 - H 2 = C 4 H 4 4 .
Fumaric and
Maleic acid.
The structure of malic acid has been determined in various
ways. It is readily reduced by hydriodic acid to succinic acid,
and is therefore a derivative of succinic acid. When mono-
bromosuccinic acid is acted upon with moist silver oxide, it
is converted into malic acid. It is therefore hydroxysuccinic
acid
OHiAg + BrjCH.COOH = (OH)CH.CO.OH
"" I I + AgBr
CH 2 . COOH CH 2 . COOH.
Monobromosuccinic acid. Malic acid.
Moreover, hydrobromic acid yields monobromosuccinic acid ;
phosphorus chloride, monochlorosuccinic acid ; and acetyl
chloride, acetyl malic acid
C 2 H 3 O.OCH.CO.OH
CH 2 .CO.OH.
Acetyl malic acid.
All these reactions give evidence of the presence of a hydroxyl
group in the acid. The natural acid from berries is laevo-
rotatory in dilute solution, which points to the existence of an
asymmetric carbon atom. The corresponding dextro-rotatory
acid is obtained by the partial reduction of ordinary tartaric
acid (see p. 357) with hydriodic acid. The existence of these
two acids receives the same on explanation as that of the two
lactic acids. The space configuration of the two isomers is
represented in Fig. 79.
xxii DIBASIC ACIDS AND THEIR DERIVATIVES 351
The synthetic malic acids obtained from bromosuccinic acid
and by the reduction of inactive racemic acid (p 354) are
inactive, and consist of a mixture of equal quantities of the two
active components. It is usual to find the artificial products of
the laboratory, prepared from inactive materials, to be themselves
CH 2 -COOH
COOH
COOH
COOH
FIG. 79. Space configuration of isomeric Malic acids.
inactive ; and this is readily understood when we consider that
there is only a single property, the action on polarised light,
which distinguishes the two components. Chemically they are
identical, and therefore, in any chemical change, the formation
of the one isomer necessitates, under ordinary conditions, the
production of an equal quantity of the second.
Asparagine, Aminosuccinamide, COOH.CH(NH 2 ).CH 2 .CO(NH 2 ),
receives its name from having been first found in asparagus (1805) ; but
it is very widely distributed in the vegetable kingdom, and is present in
the parts of the plant which afford a store of reserve material, such as
bulbs, tubers, and seedlings. The dried seedlings of lupines contain
20-30 per cent, of asparagine. It yields aspartic acid on hydrolysis
with caustic potash solution
CH(NH 2 ).COOH
CH 2 .CO|NH 2
+ HOjH
Asparagine.
CH(NH 2 ).COOH
| +NH 3
CH 2 .COOH.
Aspartic acid.
Aspartic Acid, Aminosucdnic acid, COOH.CH(NH 2 ).CH 2 .COOH,
occurs in beet-root molasses, and is formed from albuminoid substances
by the action of mineral acids. It is converted into malic acid by the
action of nitrous acid. The reaction resembles the conversion of a
Drimary amine into an alcohol, or of glycine into glycollic acid (p. 323).
352 THEORETICAL ORGANIC CHEMISTRY CHAP.
Glntamic Acid, Aminoglutaric acid, COOH.CII(NH 2 ).CH 2 CH 2 .
COOH, frequently accompanies aspartic acid, and is chiefly interesting
from its occurrence among the products of decomposition of albumin,
formed by boiling with mineral acids.
Tartaric Acid, Dihydroxysuctinic acid, COOH.CH(OH).
CH(OH).COOH. Tartaric acid in the form of theacid potassium
salt has been known since wine was made from grapes. It is
deposited during fermentation as a brown, crystalline crust, known
as argol, or wine-lees. The term tartar was given by the
alchemists to both animal and vegetable concretions, and wine
lees, stone, gravel, and the deposit on teeth being attributed to
the same cause received the same name. Tartaric acid was
isolated and recognised as a distinct acid by Scheele in 1769,
who described it in his first scientific paper. As the free acid
and as the acid potassium salt it is widely distributed throughout
the vegetable kingdom. It is found with malic acid in the
berries of the mountain ash, and in other berries and fruits, but
the chief source is grape iuice. During fermentation the acid
potassium salt in the juice is rendered insoluble by the alcohol,
and gradually separates in minute crystals which carry down
some of the colouring matter of the wine/ The brown powder,
or argol, is recrystallised for the production of the pure salt
which is known as cream of tartar.
In order to prepare tartaric acid, the argol is dissolved in water,
and chalk is added until the solution is nearly neutralised. The
insoluble calcium tartrate, which is deposited, is separated by
filtration from the neutral potassium tartrate which is in solution.
A further quantity of calcium tartrate is obtained from the
filtrate by adding calcium chloride. The process is represented
by the following equations
2C 4 H 5 6 K + CaC0 3 = C 4 H 4 O 6 Ca + C 4 H 4 O 6 K2 + CO 2 + H 2 O.
Acid potassium Calcium Potassium
tartrate. tartrate. tartrate.
C 4 H 4 O 6 K 2 + CaCl 2 = C 4 H 4 O 6 Ca + 2KC1.
The calcium tartrate is then decomposed by the addition of
sulphuric acid, and the solution, filtered from calcium sulphate,
is concentrated and allowed to cool, when crystals of tartaric
acid separate. The potassium chloride is recovered and used
in the manufacture of potash salts.
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 353
Tartaric acid crystallises in large, transparent prisms, which
dissolve in water and alcohol and melt at 205. It is dextro-
rotatory in aqueous solution. When heated by itself it forms
pyrotartaric acid (p. 349) ; with potassium hydrogen sulphate, it
yields pyruvic acid (p. 326).
Salts of Tartaric Acid. Tartaric acid forms acid and neutral
salts and salts with two different bases. The acid salts of
potassium and ammonium are sparingly soluble in cold water.
EXPT. 125. Add a little potassium nitrate, or acetate, solution and
a few drops of dilute acetic acid to a strong solution of tartaric acid,
and stir with a glass rod. The acid potassium salt of tartaric acid is
precipitated. A similar precipitate is formed when an ammonium salt
is used in place of the potassium salt.
The neutral salts of the alkalis are all readily soluble in water.
Rochelle salt, or potassium sodium tartrate, C 4 H 4 O 6 KNa
+ 4H 2 O, so called after its discoverer, Seignette de la Rochelle,
is prepared by neutralising a solution of cream of tartar with
sodium carbonate solution. The solution is then evaporated, and
deposits, on cooling, large transparent crystals. Tartar emetic,
C 4 H 4 O 6 K(SbO) + ^H 2 O, is prepared by dissolving antimonious
oxide in a solution of cream of tartar. It crystallises in rhombic
octahedra. It dissolves in water, and is used in medicine as an
emetic and in cotton dyeing as a mordant (p. 440).
Detection of Tartaric Acid. Tartaric acid is detected by the
formation of the insoluble calcium salt, C 4 H 4 O 6 Ca + 4H 2 O, on the
addition of calcium chloride to the neutral solution. The calcium
salt is distinguished from calcium oxalate by its solubility in caustic
alkalis and acetic acid. It may also be detected by Fenton's reagent
(P- So)-
EXPT. 126. Dissolve a neutral salt of tartaric acid in water. Add
a drop of ferrous sulphate solution, a few drops of hydrogen peroxide
solution, and make alkaline with caustic soda. A violet solution
is obtained.
When tartaric acid or its salts are strongly heated they char and emit
an odour of burnt sugar.
A further test is the reduction of silver tartrate in alkaline solution as
follows :
EXPT. 127. Dissolve some Rochelle salt or other neutral salt in
water, and add a solution of silver nitrate. A white precipitate ui
A A
354 THEORETICAL ORGANIC CHEMISTRY CHAP.
jllver tartrate is thrown down. Add dilute ammonia solution drop
by drop until the precipitate nearly vanishes, and place the vessel in
a beaker of hot water. A mirror of silver is deposited.
Structure of Tartaric Acid. The salts described above
show tartaric acid to be a dibasic acid. Moreover, tartaric acid
readily forms mono- and dialkyl esters viscid liquids, which can
be distilled without decomposition under reduced pressure.
These esters combine with acid chlorides and form mono- and
diacyl esters ; whilst strong nitric acid gives a dinitroxy-ester.
Taken in conjunction with the fact that tartaric acid undergoes
reduction to malic and succinic acids (p. 347), the formation of
acyl esters affords additional evidence of the acid being a
dihydroxy-succinic acid
CH(OH).COOC 2 H,
i
CH(OH).COOC 2 H 5
Diethyl tartrate.
(C 2 H 3 O). OCH. COOC 2 H,
(C 2 H 3 0).OCH.COOC 2 H 5
Diacetyl tartaric ester.
(N0 2 )O.CH.COOC 2 H 5
).CH.
(NO 2 )O.CH.COOC 2 H 5
Dinitroxy-tartaric ester.
Racemic Acid, C 4 H 6 O 6 . A second acid, isomeric with
ordinary tartaric acid, is sometimes found in the mother liquors
from cream of tartar, and can be obtained by heating tartaric
acid with water in a sealed tube to 175 or by boiling with
strong caustic soda solution. It is known as racemic acid and
melts at 205. It has been synthesised from glyoxal by forming
the dicyanhydrin and hydrolysing the product
CHO CH(OH)CN CH(OH).COOH
I > I > I
CHO CH(OH)CN CH(OH).COOH.
Glyoxal. Glyoxal cyanhydrin. Racemic acid.
Some of the salts of racemic acid have a different crystalline form and
contain a different amount of water of crystallisation from those of the
ordinary acid, and the calcium salt is less soluble in water, but, like
tartaric acid, it yields succinic acid on reduction. The main point of
distinction is that racemic acid is optically inactive in solution. It is
clear that we are dealing with a case of stereo-isomerism.
Mesotartaric acid, C 4 H 6 O 6 . A third acid, isomeric with
tartaric and racemic acid, is formed together with racemic acid
by heating ordinary tartaric acid with water to 165 or with
caustic soda. It has been obtained synthetically by the action
of silver hydroxide on dibromosuccinic acid.
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 355
AgOH
BrCH.COOH
(OH)CH.COOH
AgOH
h I
BrCH.COOH
= +2 AgBr.
(OH)CH.COOH
Dibromosuccinic
Mesotartaric
acid.
acid.
Mesotartaric acid crystallises in rectangular tables, with one molecule
of water. It melts at 140 and is more soluble than racemic acid.
The most characteristic salt of this acid is calcium mesotartrate,
C 4 H 4 O 6 Ca + 3H 2 O, which is insoluble in acetic acid and much less
soluble in water than ordinary calcium tartrate. It is optically inactive.
Stereo-isomerism of the Tartaric Acids. The relationship
of the three tartaric acids was first explained by Pasteur (1860).
In examining* the crystalline form of sodium ammonium
tartrate, Pasteur observed that the crystals exhibited hemihedral
facets that is, facets of which only half the full number required
by the symmetry of the crystal form are present. Assuming
that optical activity in ordinary tartaric acid was in some way
related to the presence of these facets, he crystallised the same
FIG. 80. Enantiomorphous crystal forms of Sodium ammonium tartrate.
salt of racemic acid which is inactive, anticipating that the
inactive salt would exhibit a symmetrical crystalline structure.
The crystals, however, showed the unsymmetrical facets of the
ordinary acid ; but the crystals were not identical, some having
their facets situated on one side, some on the opposite side of
the crystal. Crystals which bear the relation of object and
image are known as enantiomorphous forms. The two kinds of
crystals are drawn in Fig. 80, in which the hemihedral facets
are indicated by shading.
Pasteur separated the two kinds of crystals, dissolved them
A A 2
356 THEORETICAL ORGANIC CHEMISTRY CHAP.
in water, and examined them in the polarimeter. They were
found to deviate the plane of polarisation in opposite directions,
and to the same amount. The dextro-rotatory variety was
identical with the salt of ordinary tartaric acid ; the laevo-
rotatory crystals represented a new and fourth variety. Laevo-
tartaric acid is identical with the dextro-compounds in all
respects except in its action on polarised light. Racemic acid,
like lactic acid, therefore represents a mixture, or, more correctly,
a compound, of an equal number of molecules of the dextro- and
laevo-forms. That crystallised racemic acid and its salts must
be regarded rather as compounds than mixtures is shown from
their chemical and physical properties, which are distinct from
those of either of the components. The same thing holds with
regard to the salts of ordinary and sarco-lactic acids (p. 321).
Under certain conditions these acids and salts may be resolved
into their active components (see below). An inactive substance
which shows physical characters distinct from its constituent
active components is known as a racemic compound.
We have still to account for the isomerism of mesotartanc
acid. If we examine the structural formula of tartaric acid, it
will be seen that it possesses two asymmetrical carbon atoms.
The asymmetrical carbon atoms are denoted by thick type
H
COOH
OH C COOH
OH C '
Each asymmetrical carbon atom is surrounded by the same
groups. Let us suppose that each asymmetrical carbon with its
associated groups produces a certain rotation in a given
direction, we may imagine the following combinations of two
similar asymmetric groups. Both produce dextro -rotation or
both produce lasvo-rotation. These will represent the dextro-
and laevo-varieties, and the mixture of the two will produce
inactive racemic acid. Racemic acid is said to be inactive by
external compensation. Suppose, finally, the two asymmetric
groups produce rotation in opposite directions. They will
neutralise one another. The res;lt \ir:U be a compound which
DIBASIC ACIDS AND THEIR DERIVATIVES 357
is inactive by internal compensation. Such a compound cannot
be resolved by any process into its active components. This
represents mesotartaric acid, which is permanently inactive, never
having been resolved. The explanation is more easily followed
by means of models. Suppose that Fig. 81 represents the two
asymmetric carbon atoms, and that the bonds lettered X, Y, Z,
stand for the three groups H, OH, and CO. OH, for which
coloured sticks may be employed. Join together two identical
X
I. II. .
Dextro-tartaric acid. Laevo-tartaric acid.
in.
Meso-tartaric acid.
Racemic acid.
FIG. 82.
models by bringing the one on to the top of the other (Fig. 81).
If we suppose each model to be dextro-rotatory, the combina-
tion will also be dextro-rotatory, and may stand for the dextro-
acid, I., Fig. 82.
358 THEORETICAL ORGANIC CHEMISTRY CHAP.
The mirror image of this is shown at II., Fig. 82, and will
stand for the kevo-acid. It is impossible, of course, to establish
any direct connection between the character of the rotation and
the particular grouping. All we can do is to make an arbitrary
choice, and let I. stand for the dextro-, then II. represents the
lasvo-acid. The mixture represents racemic acid. In meso-
tartaric acid (III.) the top and bottom asymmetric groups stand
in the relation of object and mirror image, and consequently
their rotations are opposed and neutralised.
Stereo-isomerism in relation to the Number of Asym-
metric Carbon Atoms. From the foregoing it will be seen that
every additional asymmetric carbon atom produces a rapidly-
increasing number of possible stereo-isomers, which may be
easily determined by a simple calculation. Sorbitol, dulcitol,
and mannitol (p. 285) contain 4 asymmetric carbon atoms, and
represent 3 out of 10 possible stereo-isomers. In the same
way, saccharic acid (p. 292) contains 4 asymmetric carbon
atoms, and is one of 10 stereo-isomers, all of which are
known. In glucose, which also contains 4 asymmetric carbon
atoms, the theoretical number is larger, as the end groups of
the chain are different, and 16 stereo-isomers are possible, of
which 14 are known, mannose and galactose being among this
number.
The Resolution of Externally-Compensated Compounds*
The principal methods for resolving inactive substances into
their active components are due to Pasteur. The separation by
the aid of the enantiomorphous crystalline forms of the salts
has already been explained in the case of racemic acid ; but
the method is limited in its application by the fact that well-
defined crystals which exhibit hemihedral facets cannot always
be obtained. A more serviceable method is to combine the in-
active substance, which is to be resolved, with an optically active
compound : if a base, with an active acid ; or, if an acid, with
an active base. The solubilities of the salts of dextro- and laevo-
tartaric acid with the same active base, such as strychnine or
brucine (Part II) are not the same, andean be separated by frac-
tional crystallisation. For resolving racemic acid, the racemate
of an active base is prepared, and the salt crystallised. The least
soluble portion, which first crystallises, is the salt of the one
acid, and the most soluble that of the other. This process has
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 359
been applied successfuly to the resolution of inactive lactic acid,
and to many other cases. A third method, also employed by
Pasteur, is to cause a solution of the inactive substance to fer-
ment, by introducing certain low vegetable organisms, such as
yeast, moulds, or bacteria ; one of the two active forms is, as
a rule, more easily assimilated than the other, and the liquid
shows increasing optical activity as the fermentation proceeds.
Artificial fructose, like most laboratory products obtained
from inactive materials, is inactive ; but, when fermented
with yeast, the natural fructose is assimilated whilst the
dextro-rotatory sugar remains. In this way a dextro-rotatory
fructose has been prepared.
Citric Acid, C 6 H 8 O 7 + H 2 O, is present as the free acid in
lemon juice, and in the juice of oranges, limes, sloes, &c. It is
found with malic acid in gooseberries, currants, and other fruits
and with malic and tartaric acids in mountain-ash berries. It
also occurs as the calcium and potassium salts in many plants.
It is obtained from lemon juice, which contains 7-8 per cent,
of the acid, by neutralising with chalk or lime, and boiling the
liquid. The calcium salt, which is insoluble in hot water, is
thrown down and filtered. It is then decomposed with sulphuric
acid. On evaporating the filtrate from calcium sulphate, citric
acid crystallises in large transparent crystals containing I mole-
cule of water. Lemon juice, which contains the acid, should
not be confounded with oil of lemons, which is obtained from
the rind, and contains substances belonging to the family of
terpenes (p. 502).
Citric acid is now prepared on an industrial scale by the citric
fermentation of glucose, whereby 50 per cent, of the glucose is
converted into citric acid. The ferment is a fungus which breaks
up the glucose into citric acid and carbon dioxide. Citric acid
is a tribasic acid, and forms three series of salts. The potas-
sium and sodium salts of citric acid can be prepared containing
i, 2, and 3 atoms of the metal in place of hydrogen. The
calcium salt, (C 6 H 5 O 7 ) 2 Ca 3 + 4H 2 O, is characteristic of the
acid. It is not precipitated on adding lime-water to a cold
solution of citric acid, or calcium chloride to a citrate ; but
on boiling, the calcium salt, which is less soluble in hot water
than cold, is thrown down. In this way the acid may be dis-
tinguished from some of the other acids derived from vegetable
sources.
360 THEORETICAL ORGANIC CHEMISTRY CHAP.
Ferric ammonium citrate is prepared for medicinal purposes
in thin transparent flakes, by evaporating a solution of ferric
citrate in ammonia on glass plates, and breaking up the hard
film which remains.
Structure of Citric Acid. When citric acid is heated to
175, it loses a molecule of water, and gives aconitic acid, an
acid which is also found in aconite
C 6 H 8 7 - H 2 = C 6 H 6 6 .
Aconitic acid.
Aconitic acid is tribasic, and is unsaturated ; for, by the action
of sodium amalgam, it takes up 2 atoms of hydrogen, and forms
tricarballylic acid, which is also tribasic
C 6 H 6 6 + H 2 = C 6 H 8 Og.
Tricarballylic acid.
Tricarballylic acid, being tribasic, contains 3 carboxyl groups.
Each of these groups will probably be united to 3 different
carbon atoms of a chain. This accounts for 6 carbon, 6 oxygen,
and 3 hydrogen atoms. By distributing the remaining 5 hydrogen
between the 3 carbon atoms of the chain, we arrive at the
following formula for tricarballylic acid
CH 2 .COOH
CH. COOH Tricarballylic acid.
CH 2 .COOH.
What is the relationship of tricarballylic acid to aconitic and
citric acids ? Aconitic acid contains 2 hydrogen atoms less than
tricarballylic acid. It will probably have the formula
CH.COOH
C.COOH Aconitic acid.
CH 2 .COOH.
The addition of the elements of a molecule of water to aconitic
acid will offer a choice between the following formulae for citric
acid
xxii DIBASIC ACIDS AND THEIR DERIVATIVES 361
CH(OH). CO. OH CH 2 . COOH
CH.CO.OH C(OH).COOH
I I
CH 2 . CO. OH CH 2 . COOH.
Probable formulae of Citric acid.
The presence of a hydroxyl group, which is assumed in these
formulae, is confirmed by the formation of an acetyl derivative of
citric acid by the action of acetyl chloride on the ethyl ester.
The position of the hydroxyl group has been determined by
synthesis.
Synthesis of Citric Acid. Glycerol dichlorhydrin (p. 280)
gives dichloracetone on oxidation. The latter forms a cyanhydrin
with hydrocyanic acid, arid the cyanhydrin yields a hydroxy-
acid on hydrolysis. The two atoms of chlorine may now be
replaced by cyanogen groups by the action of potassium cyanide
on the potassium salt of the acid. The dicyano-derivative is
then converted into citric acid by boiling with hydrochloric
acid. The series of processes may be represented as
follows :
CH 2 C1 CH 2 C1 CH 2 C1 CH 2 C1
CH(OH) -> CO -> C(OH)CN -> C(OH).COOH
III I
CH 2 C1 CH 2 C1 CH 2 C1 CH 2 C1
Glycerol Dichlor- Dichloracetone Dichlor-a-pxybutyric
dichlorhydrin. acetone. cyanhydrin. acid.
CH 2 CN CH 2 .CO.OH
> C(OH).COOH -> C(OH).CO.OH
CH 2 CN CH 2 .CO.OH
Dicyan-a-oxybutyric Citric
acid. acid.
UNSATURAfED DIBASIC ACIDS
Fmnaric and Maleic Acids, C 4 H 4 O 4 . It has already been
stated that when malic acid is heated it loses water, and forms
two new acids which are isomeric (p. 350). If the process is
conducted in a retort, maleic acid sublimes as the anhydride
-362 THEORETICAL ORGANIC CHEMISTRY CHAP.
into the neck, whereas fumaric acid remains in the body of the
retort, and may be extracted with water. Fumaric acid is also
found in certain fungi, and in a few plants, the name being
derived from the botanical name of fumitory (Fumaria officinalis\
in which it occurs.
Maleic acid crystallises in rhombic prisms which are very
soluble in water. It melts at 130, and at a higher temperature
is converted into the anhydride. Fumaric acid crystallises in
needles. It is sparingly soluble in water. When heated strongly
it does not melt, but sublimes, and is converted into maleic
anhydride. Apart from differences in properties, the two acids
are closely related chemically ; they both yield succinic acid
on reduction with sodium amalgam ; monobromosuccinic acid
with hydrobromic acid ; and inactive malic acid on heating with
water. On oxidation with potassium permanganate one forms
racemic acid, the other mesotartaric acid. These changes find
a simple expression in the following formula
CH.COOH
II
CH.COOH.
Fumaric and maleic acid.
A further peculiarity in the relation of the two acids is the
ease with which they change one into the other. As mentioned
above, fumaric acid is converted into the anhydride of maleic
acid on heating. On the other hand, the addition of a little
strong hydrochloric, hydrobromic, or hydriodic acid will trans-
form maleic into fumaric acid.
Mesaconic and Citraconic Acids, C 5 H 6 O 4 . A similar rela-
tionship to that just described exists between mesaconic and
citraconic acids. The anhydride of citraconic acid is obtained
by distilling citric acid. It is a viscid liquid which readily
combines with water, and forms a crystalline acid, m.p. 86.
Citraconic acid is readily transformed into mesaconic acid by
dissolving the former in a mixture of ether and chloroform, adding
a little bromine, and exposing the solution 1 to sunlight or the
electric arc. The mesaconic acid, which is insoluble in the
mixture of ether and chloroform, rapidly crystallises. It melts
at 199. Both acids yield pyrotartaric acid on reduction, and
must be represented by the same formula
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 363
CH 3 .C.COOH
CH.COOH
Mesaconic and Citraconic acid.
Stereo-isomerism of Unsaturated Compounds. The theory
of Le Bel and van 't Hoff has been extended to unsaturated
compounds like the above two pairs of acids. The explanation
is as follows : Assuming the four bonds of the carbon atom to
diverge at equal angles, and that in unsaturated compounds two
bonds of each carbon atom are united (Fig. 68, p. 252), then it
follows that the position of the remaining two bonds of one
carbon atom are fixed relatively to the two bonds of the other
carbon atom. Suppose, moreover, that two different groups,
A and B, are attached to the free bonds of each carbon atom,
two isomers can be formed by interchanging the positions of
one pair of groups as in Fig. 83 (A and B being viewed in
perspective).
B
A
B
FIG. 83. Stereo-isomeric forms of unsaturated compounds.
This may for simplicity be represented thus
A C B A C B
A C B B C A
The isomerism of fumaric and maleic, and of mesaconic and
citraconic acid, will then be represented by the formulae
COOH.C.H H.C.COOH COOH.C.CH 3 CH 3 .C.COOH
H.C.COOH H.C.COOH H.C.COOH H.C.COOH
Fumaric acid. Maleic acid. Mesaconic acid. Citraconic acid.
364 THEORETICAL ORGANIC CHEMISTRY CHAP.
The acids (maleic and citraconic) which form anhydrides are
supposed to have the carboxyl groups on the same side of the
molecule and therefore in closer proximity, and are known as
cis compounds. The other pair (fumaric and mesaconic acid)
are called trans compounds. It should be noted that isomerism
in this case, although determined by space arrangement, is not
characterised by optical activity, for the groups lie in one plane
(in Fig. 75 it is in a plane at right angles to that of the paper)
and no structural asymmetry is possible. Isomerism is exhibited
by such physical differences as solubility, melting-point, electrical
conductivity, and by the fact that in the case of dibasic acids
only one of the pair yields an anhydride. The isomerism of
crotonic and isocrotonic acids (p. 269) and of oleic and elaidic
acids (p. 270) has been explained in the same manner.
QUESTIONS ON CHAPTER XXII
1. By what means are acids of the succinic series prepared from acids
of the acetic series ?
2. Describe any method by which an acid of the succinic series may
be converted into a higher homologue of the same series.
3. How is carbonyl chloride obtained ? Why is it regarded as the
acid chloride of carbonic acid ? Illustrate your answer by reference to
its action on water, alcohol, and ammonia.
4. Why is urea called carbamide ? Mention two analytical and two
synthetical experiments which support this view of its composition.
Calculate the quantity of urea in a specimen, which gave the following
results on analysis: 0*0884 gram gave 32*8 c.c. of moist nitrogen at
19 and 753 mm. Make the necessary correction for deficiency in
volume.
5. How would you proceed in order to prepare urea from ( I ) carbon
monoxide, (2) uric acid, (3) ammonium carbonate ? Explain the
changes which are induced in urea by (i) heat, (2) nitrous acid, (3)
aqueous alkalis, (4) nitric acid.
6. The formula for urea is CO(NH 2 ) 2 : give an account of how it
might be obtained (a) from urine, (b) synthetically. Explain the
reactions used in its detection, and enumerate the reasons why the
above formula is given to it.
7. How would you proceed to make oxalic acid from (a) common
sugar, (b) oxamide, (c) formic acid ?
xxn DIBASIC ACIDS AND THEIR DERIVATIVES 365
8. How is oxalic acid made on the large scale ? What reactions occur
between oxalic acid and (a] alcohol, (b) sulphuric acid, (c) phosphorus
pentachloride ?
9. What is the formula of oxalic acid ? How is it made ? How can
ammonium oxalate be prepared ? What is its relationship to cyanogen ?
10. Starting from acetic acid, how would you prepare the diethyl
ester of malonic acid, and how would you obtain acetic acid from the
ester ?
11. Give examples of the synthesis of various compounds from
malonic ester.
12. An acid which contains only carbon, hydrogen, and oxygen gave
on analysis 407 per cent, of carbon and 5*08 per cent, of hydrogen.
The silver salt contained 65 per cent, of silver. The acid on heating
evolved carbon dioxide, leaving a strongly acid liquid. What is the
probable composition of the acid and of the product formed on heating,
and how is the former most easily prepared ?
13. What are the chief natural sources and chemical relationships of
succinic, malic, and tartaric acids ? How may these acids be changed
into each other ?
14. How many tartaric acids are known? How are they obtained ?
How do you account for their existence ?
15. Starting from ethylene, show by what series of operations tartaric
acid may be built up. In what respect does the acid so formed differ
from tartaric acid obtained from grapes ?
1 6. Tartaric acid contains six atoms of oxygen, but is only dibasic,
In what forms does the oxygen exist in this acid, and how is such a
question determined ?
17. What is the common source and mode of manufacture of citric
acid ? How has it been synthetically prepared and its constitution
determined ?
1 8. Explain the isomerism of maleic and fumaric acids. By what
means can they be changed into tartaric acids, and how are they related
to the different modifications of the latter ?
CHAPTER XXIII
THE UREIDES
THE ureides are compounds of urea with acids and belong to
the class of amides. The ureide of oxalic acid or oxalyi urea
may be compared with oxamide
OC.NH 2 C'NH
I >CO.
OC.NH 2 . Q( l / H
Amide of Oxalic acid, Ureide of Oxalic acid,
or Oxamide. Oxalyi urea, or Parabanic acid.
A large number of ureides of the dibasic acids are known, of
which the following are examples
NH CO NH CO
CO CH 2 CO CO
I I I
NH CO NH CO.
Malonyl urea, or Mesoxalyl urea, or
Barbituric acid. Alloxan.
Certain derivatives of malonyl urea have received important applica-
tions in medicine.
Veronal) the diethyl derivative, is an important hypnotic
/NH CO.'
OC< >C(C 2 H 5 ) 2
X NH CO/
Veronal.
The dipropyl derivative or propional is used for the same purpose.
The most important of the more complex ureides, known as
diureideS) is uric acid.
Uric Acid, C 6 H 4 N 4 O 3 . The composition of chalk stones
and urinary calculi attracted the attention of physicians and
alchemists at a very early period, and they speculated freely on
their origin, submitting them to the usual process of dry dis-
tillation without eliciting much information. It is interesting to
learn that Paracelsus looked upon them as deposits originating
in the same manner as the lees, or tartar of wine. The dis-
covery of uric acid, or, as it was then termed, lithic acid, in
366
THE UREIDES 367
urinary concretions is due to Scheele, who in 1776 isolated the
acid and observed the red colour which it produces with nitric
acid on evaporation. Prout subsequently noticed the change to
violet which ammonia produces, now known as the murexide
test. It is the principal test for uric acid.
EXPT. 128. Evaporate a minute quantity of uric acid with a few
drops of dilute nitric acid to dry ness on the water-bath, then add to
the red residue, when cold, a few drops of ammonia. A deep red
coloration is produced.
Uric acid is the chief constituent of the excreta of birds and
reptiles. The excrement of snakes is nearly pure ammonium
urate, C 5 H 3 N 4 O 3 (N H 4 ). Guano contains a considerable quantity
of uric acid together with guanine, which will be described later.
The amount excreted by mammals is very small, not more than
o'2-i gram being found in human urine in 24 hours. It is
usually present in the urine as the acid ammonium salt ; in the
blood and calculi of gouty patients as the acid sodium salt,
C 5 H 3 N 4 O 3 Na. It is precipitated from urine by adding
2 to 3 per cent, of strong hydrochloric acid and allowing the
liquid to stand for a few days. Uric acid is usually obtained
from snakes' or fowls' excrement or from guano. The material
is boiled with caustic soda or potash until ammonia ceases to
be evolved. The uric acid dissolves as the sodium salt, and the
liquid is then filtered and the uric acid precipitated by the
addition of a mineral acid.
Uric acid and the urates have a characteristic crystalline
appearance, which is readily recognised under the microscope.
Uric acid is very slightly soluble in water, but dissolves in
caustic alkalis and in strong sulphuric acid without decompo-
sition. It decomposes on dry distillation without fusion into
ammonia, cyanuric acid, and urea.
Constitution of Uric**A.cid. On oxidation with nitric acid,
uric acid decomposes into alloxan and urea
C 5 H 4 N 4 O 3 + H 2 O + O = C 4 H 2 N 2 O 4 + CON 2 H 4 .
Uric acid. Alloxan. Urea.
Now the structure of both alloxan and urea is known, and
therefore the structure of uric acid must be represented by
linking these two molecules together with the removal of two
atoms of oxygen and hydrogen. This can be effected in several
368
THEORETICAL ORGANIC CHEMISTRY
CHAP.
ways, but the following structural formula has, for various
reasons, been adopted
NH CO
CO C NH
ii >
NH C NH
Formula of Uric acid.
It explains the existence of four different monomethyl uric
acids, of di- and trimethyl uric acids and of one tetramethyl uric
acid. From the latter, all the nitrogen is liberated as methyl-
amine by heating with strong hydrochloric acid, and it follows
that the 4 hydrogen atoms in uric acid are probably attached to
nitrogen. This view of the structure of uric acid is supported
by various syntheses, especially by that of E. Fischer. The
steps in the synthesis are briefly the following. Alloxan and
ammonium sulphite form thionuric acid, which is decomposed
by hydrochloric, or sulphuric acid, into uramil
i. NH CO NH CO
CO CO + (NH 4 )HSO 3 = CO C
NH CO
Alloxan.
NH CO
i
I CO
NH 2
S0 3 H
H 2 O.
/NH,
CO C<
NH-
Thionuric acid.
NH CO
+ H 2 = CO CH(NH 2 ) + H 2 SO,.
NH CO
Uramil and potassium
pseudo-urate
3. NH CO
NH CO
Uran|il.
cyanate unite to
form potassium
I
C
I
:O CH.NH 2 + OC.NK
NH CO
NH CO
= CO CH.NH.CO.NHK
NH C
-CO
Potassium
pseudo-urate.
THE UREIDES
369
When the pseudo-uric acid is heated with 20 per cent, hydro-
chloric acid, it yields uric acid
NH CO
4. NH CO
CO CH.NH.CO.NH 2 = CO C NH + H 2 O.
II x co
NH CO NH C NH
Pseudo-uric acid. Uric acid.
The question naturally arises : Why is uric acid an acid,
seeing that it contains no carboxyl groups ? Examples have
already been given of organic substances, like acetoacetic ester
and malonic ester, which contain hydrogen not forming part
of a carboxyl group, being replaceable by metals. The present
case resembles that of succinimide (p. 348). The hydrogen of
the NH groups, probably from their proximity to carbon yl
groups, become acidic and replaceable by metals. By the
action of methyl iodide on these metallic compounds, the
various methyl uric acids have been prepared.
Xanthine, C 5 H 4 N 4 O 2 , is common to the vegetable and animal
kingdom. It is present in extract of meat, in lupine seedlings,
in malt, and in tea. It is closely related to uric acid ; for
though it contains one atom of oxygen less than uric acid, it
yields the same products on oxidation, viz. alloxan and urea.
It has therefore received the following structural formula
NH CO
CO C NH
ii \
>CH.
NH C N
Xanthine.
Guanine, C 5 H 5 N 5 O, is obtained from guano by first extracting
with boiling milk of lime. The residue is then heated with
sodium carbonate, which dissolves the guanine. After pre-
cipitation with acetic acid, the guanine is purified by crystallis-
ing the hydrochloride from hot dilute hydrochloric acid. On
6 B
370
THEORETICAL ORGANIC CHEMISTRY
CHAP.
oxidation it yields guanidine (p. 340) and parabanic acid. With
nitrous acid it is converted into xanthine.
NH CO
HN=C C NH
NH C N
Guanine.
Theobromine, Dimcthylxanthint, C 7 H 8 N 4 O 2 , is present in
cocoa beans (Theobroma cacao) to the extent of 1-2 per cent. It
has been synthesised from xanthine by acting with methyl iodide
on the silver compound of xanthine.
Caffeine, Theine, Trimethylxanthine^ C g H 10 N 4 O 2 , is present
in coffee and tea. Coffee beans contain about i per cent., tea
leaves from 1*5 to 2*5, or sometimes 3 per cent of caffeine. It
is readily prepared from tea as follows : The tea is extracted
with hot water, the albuminoid substances and tannin are pre-
cipitated with basic acetate of lead and removed by filtration.
The excess of lead is then precipitated in the filtrate with sul-
phuric acid, and the caffeine extracted with chloroform. On
evaporating the chloroform, the caffeine remains in the form
of long silky needles. Caffeine has been synthesised from
theobromine by forming the silver compound of the latter, and
acting upon it with methyl iodide. In this way a third methyl
group is introduced into xanthine. The following are the
structural formulas of theobromine and caffeine
NH CO
CO C N(CH 3 )
(CH 3 )N CO
(CH 3 )N C-N
Theobromine.
(Dimethyl xanthine.)
CO C N(CH 3 )
! \CH
I /- CH -
(CH 3 )N C-N
Caffeine.
(Trimethyl xanthine.)
Both theobromine and caffeine have been prepared from uric
acid by reducing the corresponding di- and trimethyl uric
acids. In the case of caffeine the process is as follows :
Trimethyl uric acid, obtained by methylating uric acid, is acted
XXIII
THE UREIDES
371
upon with a mixture of phosphorus pentachloride and oxychloride.
ChlorocafTeine is thus formed, which is then reduced with
hydriodic acid
(CH 8 )N CO
'(CH 3 )N CO
CO C N(CH 3 ) >
Sco
(CH 3 )N-
: NH
Trimethyluric acid.
(CH 3 )N CO
CO C N(CH 3 )
(CH 8 )N - C N
Chlorocaflfeine.
CO C N(CH 3 )
^CH
(CH 3 )N C N
Caffeine.
QUESTIONS ON CHAPTER XXIII
1. Explain and illustrate by examples the meaning of the term
ureide.
2. How do you obtain pure uric acid ? What is the action of nitric
acid upon uric acid ?
3. Give the graphic formula for uric acid, and show how, by oxidation
with nitric acid, it yields alloxan and urea.
4. What is the nature of the bodies included in the uric acid group?
Give a short sketch of the more important of these.
5. How is caffeine usually obtained? Describe its synthesis from
uric acid.
6. Discuss the constitution of uric acid, including its synthesis. Hew
do you account for its acid properties ?
7. Explain the relations of xanthine, theobrorn ine, and caffeine.
B B 2
CHAPTER XXIV
THE PROTEINS
The term albumin or protein is given to certain colourless
amorphous substances composing the solid constituents of
animal tissues, plant cells and other products of animal and
plant life. They are identified by certain reactions, which,
however, are probably due to certain groups present in the
molecule, rather than to the molecule as a whole. It is certain
that many of the substances giving the reactions vary much in
complexity as well as in chemical behaviour.
Eeactions of the Proteins. i. A solution of mercury in
excess of nitric acid (Millon's reagent), added to a protein, gives
a precipitate which turns red on heating.
2. A few drops of copper sulphate and an excess of caustic
soda produce a violet colour, which becomes deeper in tint on
boiling (biuret reaction).
3. A violet coloration is produced by adding a few drops of
glyoxalic acid (p. 325) and strong sulphuric acid (Adamkiewicz's
reaction).
Composition of the Proteins. The percentage composition
of the proteins varies very little. The following represents the
minimum and maximum amounts in parts per hundred, found in
different proteins :
C 5055
H 6-9- 7'3
N 15 19
O 19 24
S 0*3 2 '4
372
CH. xxiv THE PROTEINS 373
Although egg and serum albumin have been prepared in the
crystalline form, from which it may be concluded that they are
single substances, no trustworthy information as to the molecular
weight is at present forthcoming. There is no doubt that even
the simplest of the proteins consist of highly complex molecules
about the structure of which little is known. They may be
compared with the polysaccharose group of carbohydrates,
which possess a complex structure and high molecular weight,
but readily break up into fragments of comparatively simple
constitution. These simple constituents of the proteins, which
are produced by the action of acids and alkalis, are, for the most
part, ammo-adds, glycine (p. 322), alanine (p. 325), leucine
(p. 322), aspartic acid (p. 351), glutamic acid (p. 352), and the
guanidine acids, like creatine (p. 324) and arginine, or guanidine
a-aminovaleric acid^
NH 2
HN:C NH.CH 2 .CH2.CH 2 .CH(NH 2 ).COOH.
Arginine.
The latter substance is one of the first products of decom-
position of the simplest albumins, or protamines, found in the
spermatozoa (milt) of fishes. Among the more complex con-
stituents of the protein molecule composing the nucleus (nuclein)
of cells are xanthine and guanine and other closely-related
ureides. A few aromatic compounds and derivatives of indole
(p. 525) and pyrrole (p. 560) also occur among the products of
decomposition of proteins.
It is found convenient to divide the proteins into groups,
according to certain differences in physical and chemical
properties, but the line of demarcation is not sharp, and the
classifications of different authors vary. Some proteins known
as albumins, such as egg and serum albumin, are soluble in water
and are coagulated by heat ; others, the globulins, like inyosin of
muscle and fibrinogen of blood, are insoluble in water, but soluble
in saline and dilute acid and alkaline solutions. The phospho pro-
teins, such as casein of milk and vitellin of egg-yolk, are soluble in
acids and alkalis, but insoluble in water. The proteides are separ-
able into two constituents, of which one is a simpler protein. Such
are the micleo proteins composing the nuclein of cells and the
chromo proteins of which haemoglobin of the blood is an example.
374 THEORETICAL ORGANIC CHEMISTRY CH. xxiv
The proteoses and peptones are extremely soluble in water, in
acids, and alkalis, and are not coagulated on heating. They are
formed by the action of digestive enzymes, pepsin or trypsin,
on the other proteins, and probably represent simpler molecular
complexes, corresponding to the dextrins formed in the dis-
integration of starch.
Albuminoid Substances. In addition to the above, there
exists a group of amorphous nitrogenous substances resembling
the proteins in many of their properties, but differing more
widely among themselves than the proteins. They are included
with the former in the general term albuminoid substances.
Such substances are mucin^ which gives the ropy consistency
to many animal secretions \gelatine or glutin, which is obtained
from connective tissue, &c. ; keratin, of which hair, nails, horn,
&c., are chiefly composed; and chitin^ which is present in the
hard covering of invertebrates such as crabs and lobsters.
Gelatine, or glue, is obtained from bones by dissolving out
the inorganic matter (calcium phosphate, &c.) with dilute
hydrochloric acid, and heating the elastic mass which retains
the shape of the bone with water or with water under pressure.
The substance is dissolved, and, on cooling, solidifies to a jelly.
Skins heated with water also produce gelatine. Gelatine does
not give the reaction for proteins, but yields much the same
products on hydrolysis with acids and alkalis, and by the
action of the digestive ferments. It forms an insoluble com-
pound with tannin, a property which is utilised in the pro-
duction of leather (p. 490). When mixed with potassium
dichromate, and exposed to light, 'gelatine becomes insoluble
in water. A number of photographic processes depend upon
this property.
QUESTIONS ON CHAPTER XXIV
i. Give the reactions for the proteins. Describe some of their
decomposition products.
i2. Name some of the chief groups of proteins and their characteristic
properties.
3. What is meant by the term albuminoid substance ?
4. How is gelatine obtained ? Name some of its properties. How
could it be distinguished from egg albumin ?
PART II
AEOMATIC COMPOUNDS
CHAPTER XXV
THE AROMATIC HYDROCARBONS
The Meaning of "Aromatic." The name aromatic was
originally applied to a small group of compounds which could
not be classed among existing families of the better-known
aliphatic series. The members of this group, which included
the balsams and resins, and products derived from them, essen-
tial oils, like bitter almond oil, turpentine oil, oil of wintergreen,
of cloves, and of lemon, &c., possessed in common an aromatic
smell.
On closer study, many were found to possess properties not
very dissimilar from those of aliphatic compounds, and to be
similarly related among themselves. For example, toluene is
a liquid hydrocarbon originally obtained from tolu balsam ; oil
of bitter almonds is an aldehyde ; and benzoic acid is an acid,
derived from gum-benzoin. They can be converted into one
another, and stand in the relation of paraffin, aldehyde, and
acid.
C 7 H 8 C 7 H 6 C 7 H 6 2 .
Toluene. Oil of bitter almonds. Benzoic acid.
C 2 H 6 C 2 H 4
Ethane. Acetaldehyde. Acetic acid.
But notwithstanding this parallelism which appeared among
members of the two series, a sharp line divided the aliphatic
from the aromatic compounds. Indeed, some years elapsed
before any direct synthesis of a member of the one group from
that of the other served as a connecting link between them.
37S
376 THEORETICAL ORGANIC CHEMISTRY CHAP,
The aromatic compounds contain a higher percentage of
carbon; hexane, C 6 H 14 , contains 837 per cent., whereas benzene,
C 6 H 6 , which is the simplest hydrocarbon of the aromatic series,
contains 93*6 per cent, of carbon.
EXPT. 129. Burn some hexane and benzene side by side on two
inverted porcelain lids, and note the much larger separation of soot
in the flame of benzene.
The more complex members of the aromatic series may be
broken up by the action of various reagents into simpler sub-
stances, such as benzene, C 6 H 6 , phenol, C 6 H 6 O, picric acid,
C 6 H 3 N 3 O r , &c. ; but any attempt to pass beyond this point, and
to form substances with 5 or fewer carbon atoms, generally
results in the complete disintegration of the molecule. Toluene
may be oxidised to benzoic acid (see above) ; and benzoic acid,
when distilled with soda-lime, loses carbon dioxide and yields
benzene
C 7 H 6 2 - C 6 H 6 + C0 2 .
Benzoic Benzene,
acid.
But if benzene is decomposed by oxidation, it forms carbon
dioxide and water, and no intermediate products are obtained.
Kekule*'s Theory. It was upon the existence of this residual
nucleus of 6 carbon atoms, which appeared in the ultimate
products of decomposition of aromatic substances, that Kekule
founded his celebrated benzene theory. The aliphatic com-
pounds are open-chain compounds ; benzene, which is the
fundamental hydrocarbon of the aromatic series, as methane is
of the aliphatic series, possesses a closed-chain or ring of carbon
atoms.
Let us suppose the 6 carbon atoms of benzene to be arranged
in a horizontal row, and a hydrogen atom attached to a bond of
each of the carbon atoms
CH. CH. CH. CH. CH. CH
The number of carbon and hydrogen atoms corresponds to
the formula of benzene. Let us now modify the above arrange-
ment by attaching the two end carbon atoms
CH.CH.CH.CH.CH.CH.
I .1
xxv THE AROMATIC HYDROCARBONS 377
A closed chain or ring results, which is usually represented
in the form of a regular hexagon J
CH
HC
H
CH
The existence of such a closed system of atoms presents
nothing unusual, when we consider the structure of lactones
(p. 318) and anhydrides of dibasic acids (p. 348) from a stereo-
chemical point of view, as previously explained. This arrange-
ment furnishes an explanation of many well-known properties
of benzene. It explains its unusual stability towards reagents.
It accounts for the existence of only one mono-derivative of
benzene (that is, a derivative obtained by replacing one of the
hydrogen atoms by another element or group) ; for the hydro-
gen atoms being symmetrically distributed, the 6 positions are
identical. It explains, moreover, the occurrence of three iso-
meric di-derivatives. Isomeric di-derivatives of benzene are
very common, but the maximum number is always three. There
are three dichlorobenzenes, C 6 H 4 C1 2 , three dibromobenzenes,
C 6 H 4 Br 2 , three dinitrobenzenes, C 6 H 4 (NO 2 ) 2 , &c.
Suppose we number the carbon atoms of the benzene ring
from i up to 6, and represent the two new elements or groups
by X. The positions which they can take are i, 2 ; i, 3 ; i, 4 ;
i, 5, and i, 6.
It is clear, however, that positions i, 2 and i, 3 are identical
with i, 6 and i, 5. Three positions, therefore, remain, which
1 The hexagon is elongated in the figures, partly to economise space when a
number of them are drawn side by side, partly to assist the memory in retaining the
relative positions of substituted hydrogen atoms by giving the figure somewhat
different dimensions in horizontal and vertical directions.
378 THEORETICAL ORGANIC CHEMISTRY CHAP.
will be those of the three isomers referred to above. These
positions are known as ortho-, meta-, and /tf
X
) x
X
Ortho- Meta- . Para-
Positions of the groups in the three isomeric di-derivatives of Benzene.
It will be seen from the above formula for benzene that only
three bonds of each carbon atom are appropriated ; two for
union with the adjoining carbon atoms and one for attaching
the hydrogen atom. What is the function of the fourth carbon
bond ? In Kekule's original formula the carbon bonds were
linked alternately by double and single bonds
CH
HOrJCH
CH
Kekule's formula for Benzene.
This formula represents an unsaturated hydrocarbon of the
olefine family (p. 246). Benzene, in fact, possesses the properties
of an olefine, inasmuch as it forms the following additive com-
pounds with hydrogen, chlorine, bromine, and hypochlorous
acid
C 6 H 12 C 6 H 6 C1 6 C 6 H 6 Br 6 C 6 H 6 (HC1O) 3
Hexahydro- Benzene Benzene Benzene
benzene. hexachloride. hexabromide. trichlorhydrin.
The fact that the maximum number of monovalent atoms
which are required to saturate benzene is 6 and no more, is
taken as strong evidence of the existence of 3 double linkages,
and consequently of a closed chain. The isomeric compound
1 The names orthn, meta, and para will be occasionally indicated by the initial
letters o-, m-, p~ before the name of the substance. The numbers will be also used
to denote the relative positions of atoms, or groups, in the ring.
THE AROMATIC HYDROCARBONS
379
dipropargyl) which has already been described (p. 262), offers
a great contrast to benzene in chemical properties, in so far
as it requires 8 monovalent atoms for saturation, yielding
a parallel series of additive products with the following
formulae
C 6 H 14
Hexane.
Octachloro
hexane.
C 6 H 6 Br 8 .
Octabromo-
hexane.
Moreover, dipropargyl is very sensitive to oxidising agents
whereas benzene is marked by great stability.
On the other hand, Kekule's formula for benzene fails to
account for some of the characteristic properties of the defines,
which possess double linkages. Benzene and its derivatives
form no additive compounds with the halogen acids, or
strong sulphuric acid ; nor are they, as a rule, oxidised by a
solution of potassium permanganate in the cold, which rapidly
attacks the olefines and their derivatives. Furthermore, the
positions i, 2 and I, 6 are not strictly identical, for a double
link is interposed between one pair of carbon atoms and a
single link between the other pair
Consequently, 4 and not 3 di-derivatives should exist, and no
example of the kind is known.
Kekuld's formula has therefore met with some opposition.
The fate of the fourth carbon bond has been a long-debated
problem. In order to sever the connection of benzene with the
olefines, the fourth carbon bond has been described as a centric,
potential, or residual valency, which signifies a modified bond
of a somewhat ill-defined character. What is known as the
centric formula for benzene was suggested by Armstrong and
supported by the experimental evidence of Baeyer, but
cannot be discussed here. The fourth or centric bond is
2 8o THEORETICAL ORGANIC CHEMISTRY CHAP.
represented as an arrow directed towards the centre of the
hexagon.
HC< N
CM
FIG. 84. Armstrong and Baeyer's centric formula for Benzene.
For practical purposes the fourth carbon bond may be omitted
irom the formula, and until something more definite transpires
concerning it, the simple hexagon formula will suffice. Before
entering upon a more elaborate discussion of the evidence upon
which the hexagon formula rests that is to say, the symmetrical
distribution of carbon and hydrogen atoms in the molecule it
will be necessary to study in greater detail the properties of the
aromatic hydrocarbons.
THE AROMATIC HYDROCARBONS
Distillation of Coal-Tar. The principal source of benzene
and its homologues is coal-tar. Coal-tar is produced in the
manufacture of coal-gas by the destructive distillation of coal in
fire-clay retorts. The gases from the retorts pass through a
series of upright pipes or air-condensers, which rise from a long
trough in which the tar collects, whence it is drawn into a tank,
or tar-well. Tar is also produced in considerable quantities in
the manufacture of coke in coke-ovens. The quantity of tar
varies with the character of the coal employed, 10 to 20 gallons
being usually obtained from each ton of coal. When the tar is
submitted to fractional distillation, it yields a variety of volatile
products of different boiling-points, which form the material
from which the majority of aromatic compounds are prepared.
Coal-tar is distilled in large wrought-iron stills, holding from 20
to 30 tons. Fig. 85 represents a section of a tar still. It is
surrounded by brick-work, and heated by a fire below. The
still-head is connected with a condensing worm (not shown in
XXV
THE AROMATIC HYDROCARBONS
the drawing), from which the condensed products are conducted
into different receivers.
FIG. 85. Tar Still.
The distillate is usually divided into the following fractions,
although different works vary slightly in their mode of
working :
Distillate.
Distilling
temperature.
Constituents of the fraction.
Light oil, or Crude
to 170
Benzene and homologues.
Naphtha
Middle, or Carbolic
to 230
Carbolic acid and Naphthalene.
oil
Heavy, or Creosote
to 270
Constituents not usually sepa-
oil
rated.
Anthracene oil
above 270
Anthracene.
Pitch
residue in the
.
still
3 8 2 THEORETICAL ORGANIC CHEMISTRY CHAP.
The terms "light," "middle," and " heavy " oil, denote the
specific gravity of the distillate. During the distillation a
sample is run into water. If it floats it is known as light oil, if
it sinks it is called heavy oil. A certain quantity is collected
after the light oil ceases to distil, and this is the middle oil. The
separation of the fractions is often determined by the boiling-
point of the distillate, which is indicated by a thermometer fixed
in the still. Each of the fractions is worked up and separated
into its constituents, except the creosote oil, which is employed
as it comes from the still for preserving timber. 100 parts of
tar yield the following approximate quantities of commercial
products :
Benzene and homologues I '40
Carbolic acid 0*20
Naphthalene . 4*00
Creosote oil 24*00
Anthracene .* O'2O
Pitch 55 'oo
Water 15-00
99-80
The separation of the constituents from the different fractions
will be dealt with later, when the substances themselves are
described. We shall confine our attention at present to the first
fraction, or light oil. This fraction is usually redistilled, and the
portion boiling between 80 and 150 is worked up for benzene
and its homologues. It contains basic substances aniline,
(p. 418), pyridine(p. 563),*c. which are dissolved out by agita-
tion with strong sulphuric acid. The acid is then withdrawn, and
the oil treated with caustic soda solution, which removes any
residual sulphuric acid as well as carbolic acid. This is fol-
lowed by agitation with water, after which the purified oil is
fractionated. A special form of still is used, which is heated by
steam, and is furnished with a long fractionating column. The
fraction, which is first collected, is known as fifty per cent.
or ninety per cent, benzene. The names signify a mixture of
benzene and its higher homologues, toluene and xylene. In the
case of 50 per cent, benzene, 100 c.c. of the liquid yield on
distillation 50 c.c. when the boiling-point reaches 100 ; 90 per
cent, benzene gives 90 c.c. at 100. The higher-boiling fractions
xxv THE AROMATIC HYDROCARBONS 383
are known as solvent naphtha, which is used for dissolving
rubber in the preparation of waterproof fabrics, and burning
naphtha^ for illuminating purposes.
The 50, or 90 per cent, benzene, by a second distillation, is
separated into benzene, toluene, and xylene. 1
Benzene, C 6 H 6 , was discovered by Faraday (1825). Before
the introduction of coal-gas, a little illuminating gas was
manufactured from oil, and delivered to consumers compressed
into cylinders. By cooling the gas from these cylinders in a
freezing mixture, a liquid was obtained from which Faraday
separated benzene by distillation. Benzene was afterwards
obtained by distilling calcium benzoate with slaked lime. The
benzoate decomposes into benzene and calcium carbonate, a
process which recalls the formation of marsh-gas from sodium
acetate
CeHjCOOcay+'ca'O H = C 6 H 6 + CaCO 3 .
Calcium benzoate. Benzene.
EXPT. 13. Grind together 30 grams of calcium benzoate with
twice its weight of soda-lime, and distil the mixture from a retort,
which must be attached to a condenser and receiver. Water and
a light brown oil distil, smelling strongly of benzene. The benzene
can be separated from the water by a small tap-funnel. It is then
dried over calcium chloride, and redistilled.
Benzene has been synthesised by Berthelot from acetylene
(p. 260), by heating the gas in a closed vessel at a moderately
low temperature. The acetylene polymerises, and forms
benzene
3C 2 H 2 = C 6 H 6 .
Acetylene. Benzene.
Benzene is now exclusively obtained from coal-tar in the
manner already described.
The commercial product always contains a small quantity of an
organic sulphur compound, known as thiophene^ C 4 H 4 S, which is a
colourless liquid and has nearly the same boiling-point as benzene
(p. 559). The presence of thiophene may be shown in the following way :
Dissolve a crystal of isatin (p. 523) in the cold in a few c.c. of strong
sulphuric acid and add about the same volume of coal-tar benzene.
On shaking, a deep blue coloration (indophenin) is produced. If the
1 The commercial names are benzol, toluol, and xylol.
384 THEORETICAL ORGANIC CHEMISTRY CHAP.
benzene obtained from calcium benzoate is treated in the same mannet
no blue colour is developed.
ExPT.131. The distillation of coal on a small scale may be shown
by means of the apparatus, Fig. 59, p. 1 59. A copper vessel a con-
taining coal in small lumps is fixed to a doubly tubulated vessel b,
which is in turn attached to a condenser c, and wash-bottle containing
caustic soda solution d. A delivery tube conducts the inflammable
gases into an inverted cylinder e. The tar and water accumulate in b.
Properties of Benzene. Benzene is a colourless liquid with a
peculiar smell. It boils at 8o*5, solidifies at 5'4, and has a specific
gravity of 0*874 at 20. It is very inflammable, and burns with a
luminous and smoky flame. It is insoluble in water, and, having
a lower specific gravity, floats on the surface. It is sometimes
used like ether for separating organic liquids when mixed with
water, also for extracting fats, c., and for dry cleaning.
The chemical properties of benzene may be taken as typical
of the family of aromatic hydrocarbons. Benzene resists the
action of all the ordinary oxidising and reducing agents. Strong
hydriodic acid, at a high temperature, and after prolonged heat-
ing, or hydrogen in presence of colloidal platinum at the ordinary
temperature, or finely divided nickel at about 160, converts
it into the hexahydride, C 6 H 12 . When benzene is exposed to
the action of chlorine or bromine in sunlight, crystals
of benzene hexachloride, C 6 H 6 C1 6 , or hexabromide, C 6 H 6 Br 6 ,
slowly deposit. Both substances are very unstable, and emit a
smell of chlorine or bromine. Potash decomposes them at once
into trichloro- and tribromo-benzene
C 6 H 6 C1 6 + sKOH = C 6 H 3 C1 3 + 3KC1 + 3H 2 O.
Benzene hexachloride. Trichlorobenzene.
If chlorine or bromine acts upon benzene in presence of a
" carrier," substitution occurs, and a series of chlorinated, or
brominated products is formed, containing from one up to six
atoms of the halogen in place of hydrogen
C 6 H 6 + C1 2 = C 6 H 5 C1 + HC1, C 6 H 5 C1 + C1 2 = CeH 4 Cl 2 + HC1,
Monochloro- Dichloro-
benzene. benzene.
and so forth.
EXPT. 132. Pour a few c.c. of benzene into four test-tubes, and
add a few drops of bromine to each. Into one of the test-tubes drop
a small piece of aluminium-mercury couple (p. 68), into a second
pour a few 'drops of pyridine and warm gently, and to a third add
some iron filings. Notice the difference in the action as indicated by
the evolution of hydrobromic acid from the four test-tubes.
xxv THE AROMATIC HYDROCARBONS 385
Iodine has no direct action on the aromatic hydrocarbons
unless at a high temperature and with the addition of iodic
acid or sodium persulphate, NaSO 4 . The latter serves to
decompose the hydriodic acid formed in the reaction, which
would otherwise produce a reversal of the process
SHI * HI0 3 - sI 2 + 3 H 2 0.
The above action of the halogens on benzene recalls their
behaviour with the paraffins (p. 63).
Dilute nitric acid has no action on benzene, but strong nitric
acid rapidly attacks it, and forms nitro-derivatives. The action
is assisted by the presence of strong sulphuric acid, which
absorbs the water formed in the process
C 6 H 6 + HN0 3 - C 6 H 5 .N0 2 + H 2 O.
Nitrobenzene.
C 6 H 5 NO 2 + HNO 3 = C 6 H 4 .(NO 2 ) 2 + H 2 O.
Dinitrobenzene.
EXPT. 133. Mix together 20 c.c. of strong sulphuric acid and
15 c.c. of strong nitric acid in a graduated cylinder. Add half the
volume of the mixed acid (17 c.c.) gradually to 5 c.c. of benzene,
contained in a small flask ; cool and shake well. Heat is evolved
and nitrobenzene is formed. When the acid has been added, pour a
little into water and notice that the liquid has a yellow colour, and,
instead of floating on the surface like benzene, sinks in the water.
Add the remainder of the acid at once to the remaining liquid in the
flask, and heat for a quarter of an hour on the water-bath ; then pour
into a cylinder of water. The substance which now separates is no
longer liquid ; but a yellow, crystalline solid, which is the dinitro-
compound.
Strong sulphuric acid, on warming, gradually dissolves ben-
zene, and forms benzene sulphonic acid. Fuming sulphuric
acid converts the latter into benzene disulphonic acid
C 6 H 6 + H 2 SO 4 = C 6 H 5 .SO 3 H + H 2 O.
Benzene sulphonu*
acid,
C 6 H 5 .S0 3 H + H 2 S0 4 = C 6 H 4 (S0 3 H) 2 + H 2 O.
Benzene disulphonic
acid.
EXPT. 134. Mix together in a boiling-tube about 3 c.c. of benzene
and 10 c.c. of strong sulphuric acid, and heat gentlv with constant
C C
386 THEORETICAL ORGANIC CHEMISTRY CHAP.
shaking. The benzene, which at first floats on the acid, gradually
dissolves with rise of temperature. When a little of the mixture is
poured into water, a clear solution of benzene sulphonic acid is
obtained. If another portion is poured into about four times its.
volume of saturated salt solution, crystalline plates of sodium benzene
sulphonate, C 6 H 5 .SO 3 Na ; separate.
The action of strong nitric and sulphuric acids on benzene,
in producing nitro-derivatives in the one case, and sulphonic '
acids in the other, is a characteristic property of aromatic com-
pounds. The homologues of benzene, as well as the majority
of benzene derivatives, combine with these two acids in the
manner described. In this respect the aromatic compounds,
offer a marked contrast to the paraffins, and the other aliphatic
hydrocarbons. Reference should be made to the methods by
which nitro-paraffins (p. 190), and the aliphatic sulphonic acids
(p. 196), are produced.
Toluene, Methyl benzene, Phenyl methane, C 6 H 5 .CH 3 .
Toluene received its name from a resin, known as tolu balsam r
from which it is obtained by distillation. It is now separated
by fractional distillation from coal-tar naphtha by the method
already described. Toluene closely resembles benzene in pro-
perties. It is a colourless liquid with an odour resembling ben-
zene. It boils at 110, solidifies at 98 and has a sp. gr.
0*869 at J 6 . The relation of toluene to benzene has been
determined by analysis and synthesis. It has already been
stated that toluene may be oxidised to benzoic acid, and the
latter converted by distillation with lime into benzene. The
synthetic processes used in its preparation are known as the
methods of Fittig, and of Friedel and Crafts.
Fittig's method recalls that employed by Wurtz in the syn-
thesis of the paraffins (p. 72). It consists in mixing together
bromobenzene and methyl iodide, diluted with dry ether, ancfe
adding sodium in thin slices. The action commences spon-
taneously, and, when it ceases, the liquid is decanted from the
sodium salts, and the toluene separated by fractional distillation
QH 5 Br + CH 3 I + Na^ = C 6 H 5 .CH 3 + NaBr + Nal.
Bromo- Methyl Toluene,
benzene. iodide.
The Friedel-Crafts' Reaction. In this reaction anhydrous,
aluminium chloride is added to benzene, and methyl chloride
Xxv THE AROMATIC HYDROCARBONS 387
passed in, or methyl bromide added to the mixture. Hydro-
chloric, or hydrobromic, acid is rapidly evolved, and toluene is
formed. The product is poured into water, and the upper layer
removed and fractionated. The action of the aluminium chloride
is not fully understood, but is usually accounted for by the
formation of an intermediate compound of benzene and aluminium
chloride, which is decomposed by the alkyl halide. The reaction
may be expressed as follows
C 6 H 6 + CH 3 C1 [+ A1C1 3 ] - C 6 H 5 .CH 3 + HC1.
By prolonging the action, additional methyl groups are intro-
duced into benzene, and a series of di-, tri-, &c., methyl benzenes
are formed.
Both Fittig's and Friedel and Crafts' reactions can be applied
to the synthesis of a large number of aromatic hydrocarbons by
substituting different alkyl halides for the methyl compounds.
Friedel and Crafts' method in particular has a very wide and
varied application, for its action is not limited to the production
of hydrocarbons alone. Many other substances containing
chlorine, such as the acid chlorides, unite in presence of alumi-
nium chloride with benzene and its homologues, with the evo-
lution of hydrochloric acid and the formation of new products.
The acid chlorides yield ketones. Benzene, acetyl chloride, and
aluminium chloride form phenyl methyl ketone
C 6 H 6 + CH 8 .CO.C1[+ A1C1 3 ] = C 6 H 5 .CO.CH 3 + HC1.
Phenyl methyl
ketone.
It appears that only hydrocarbons of the aromatic series can
enter into these reactions. Neither the paraffins nor defines
possess the property. Friedel and Crafts' reaction is, therefore,
recognised as a distinctive feature of the aromatic hydrocarbons.
EXPT. 135. Pour a few c.c. of benzene into a test-tube ; add
about a gram of anhydrous aluminium chloride and then a few drops
of ethyl bromide. Hydrobromic acid is at once evolved. If the
product is poured into water, the upper layer contains ethyl benzene,
which, on a larger scale, would be separated by fractional distillation.
Repeat the experiment, using acetyl chloride in place of ethyl
bromide, and pour the product into caustic soda solution. The
upper layer contains methyl phenyl ketone, which possesses a
characteristic smell.
C C 2
I w, THEORETICAL ( > .' CJU '-
Structure of Toluene. The synthesis of toluene from
benzene cl' ' i txplatiM its structure. Toluene is tin: methyl
five of benzene, the graphic formula of which is i <
leu
5H
Structural formula for Toluene.
Tohi. nr i . .,1 ,o I.I.O-.MI .1 . phenvl inrihaiir. The term phenyl
d i. .I!M monovalent radical (\,l 1,,' ol bmzene, just as ethyl,
( ,1 l r /, stands for Ihr iadia>, to illuminate, from the connection of
bemene with the coal-gas manufacture. 1 It is equally correct to
represent toluene as methane in which a phenyl group replaces
an atom ol hvdroj;cn
II
II (' II
I
Toliirnc, ,,t I'hrnyl inrdmiio
Nucleus and Sale cha.in. It is found convenient to draw a
dr. hm lion lrt\vrrn the | >ti i el \ a i 01 ua t ic p. lit, or nil!', and the
ahphalu pail, 01 alkvl j'.icuip, m a \ oxidismv; a>;ents. This has aheatlvbeen icli-i i cil to. Thi'
side-chain is converted into a cwboxvl j;ioup, the nucleus re-
mamm:; mtact. Toluene forms benzole acid. The same result
is puulnced it the side chain is an ethyl, propyl, or other alky!
t;roup, ontamm:: several carl>on atoms; it breaks iKnvn on
oxulatuMi m the au\e maimei as toluene, and torms i\\c same'
i I 1 ,,, . .. . i. t.nnt.M t!u rti.'in.itu i.ulu.\l-- is .i 1.', M!IU h wiu'si>oiuls to .jlk\l
xxv THE AROMATIC HYDROCARBONS ;So
product, viz. benzole acid. The value of this property in s:
ing the structure of aromatic hydrocarbons and their c
is very considerable, and is well illustrated in the case of the
xylenes (p. 391).
Action of Chlorine on Toluene. Toluene, like benzene,
undergoes substitution by chlorine and bromine. Substitution
is not, however, limited to the nucleus. Hydrogen may be
replaced in the side-chain. Substitution takes place in the side-
chain if chlorine is passed into boiling toluene, and the following
three products are successively produced
C 6 H 8 .CH 2 C1 C 6 H 5 .CHC1 2 C 6 H 5 .CG 8 .
Benzyl chloride. Benzylidene, or Benzenyl chloride, or
Benzal chloride. Benzotrichloride.
The first contains the monovalent radical benzyl, C 6 H 5 .CH 2 ',
corresponding to ethyl ; the second benzylidene, C 6 H fi .CH",
corresponding to ethylidene ; the third, the radical benzenyl,
C 6 H 6 .C'".
If, on the other hand, chlorine is passed into cold toluene
to which a little antimony chloride, aluminium-mercury couple,
iodine, or other carrier, is added, substitution is confined to the
nucleus, and mono-, di-, tri-, &c., chlorotoluenes are formed.
There are three monochlorotoluenes, the ortho-, meta-, and
para-compounds, which are isomeric with benzyl chloride, so
that there are in all four compounds of the formula C 7 H 7 CL
In the following formulae the carbon and hydrogen atoms of
the nucleus are omitted
CH 3 CH 3 CH 3 CH 2 C1
-' /Cl
Ortho- Meta- Para- Benzyl
chlorotoluene. chlorotoluene. chlorotoluene. chloride.
There is a marked difference in the properties of the halogen
derivatives of the aromatic hydrocarbons containing the halogen
390
THEORETICAL ORGANIC CHEMISTRY
in the side-chain, and those which are substituted in the nucleus :
but the subject will be reserved for a later chapter (p. 401).
Hydrocarbons of the Formula C 8 H 10 . Theory requires
four isomeric hydrocarbons of the formula C 8 H 10 , viz. ortho-,
meta-, and para-dimethylbenzene and an ethyl benzene
CH f
CH 3
I
CH 3
C 2 H 5
Ortho-
dimethylbenzene.
CHo
Meta-
dimethylbenzene.
\/
CH 3
Para-
dimethylbenzene.
Ethyl-
benzene.
The three dimethylbenzenes, which are termed xylenes, are all
present in coal-tar, the meta-compound largely predominating.
They cannot be separated by fractional distillation, as the
boiling-points lie too close together, and commercial xylene is
therefore a mixture of the three isomers.
Boiling-
point.
Ortho-xylene ..... ..... 142
Meta-xylene .......... 137
Para-xylene ........... 137*
Meta-xylene is readily separated from the other two compounds by
boiling with dilute nitric acid, which oxidises the ortho- and para-
compounds more rapidly than the meta-, and converts them into acids.
The acids are then removed by shaking with caustic soda solution.
The para-compound is separated by shaking with strong sulphuric acid,
which dissolves the ortho- and meta-compounds in the form of their
sulphonic acids. A simpler process for obtaining pure para- and ortho-
xylene is by synthesis.
The constitution of all four compounds has been determined
by synthesis. The ortho- and para-xylenes have been prepared
by Fittig's reaction from ortho- and para-bromotoluene, methyl
iodide, and sodium
QH 4 Br(CH 3 )
Na 2 = C 6 H 4 (CH 3 ) 2 + NaBr + Nal.
xxv THE AROMATIC HYDROCARBONS 391
By means of Friedel and Crafts' reaction, using benzene
methyl chloride and aluminium chloride, the same two com-
pounds are formed, but the ortho-compound predominates
Pure meta-xylene cannot be prepared by either of these methods,
but is obtained from mesitylene (p. 392), which on oxidation
gives mesitylenic acid. The acid, when distilled with lime, yields
meta-xylene
C 6 H 3 (CH 3 ) ? COOH = C 6 H 4 (CH 3 ) 2 + CO 2 .
Mesitylenic acid. Meta-xylene.
Ethyl benzene is readily prepared from bromobenzene, ethyl
iodide, and sodium, or by Friedel and Crafts' method from
benzene, ethyl bromide, and aluminium chloride (Expt. 135,
P- 387)-
Oxidation of the Xylenes, &c. The behaviour of the four
compounds on oxidation is instructive, as illustrating the manner
in which the constitution of an aromatic hydrocarbon may be
studied. When the hydrocarbon is oxidised, the side-chains
are converted into carboxyl groups as already explained. Ethyl
benzene gives benzoic acid, and consequently contains one side-
chain. The xylenes, on the other hand, yield dibasic acids
containing two carboxyl groups. The process occurs in two
stages ; the two methyl groups being converted successively
into carboxyl groups. The first products are known as toluic
acids
CH 3 CH 3 CH 3
/NcooH
/COOH
COOH
Ortho-toluic acid. Meta-toluic acid. Para-toluic acid.
Each of these gives rise to a dibasic acid, known respectively
as phthalic, isophthalic, and terephthalic acids
COOH COOH COOH
^COOH
/COOH
COOH
Phthalic acid. Isophthalic acid. Terephthalic acid
392 THEORETICAL ORGANIC CHEMISTRY CHAP.
The three toluic acids and the esters of the three phthalic
acids l have different melting-points, by which they may be
readily identified. Let us suppose that a hydrocarbon of un-
known composition yields benzoic acid on oxidation ; the
natural inference is that it contains a single side-chain. The
formation of one of the phthalic acids implies the presence of
two side-chains, whilst the melting-point of the acid will indicate
their relative positions. Moreover, by this process of oxidation
the side-chains may be successively removed. The three toluic
acids, by distillation with lime, give toluene ; the three phthalic
acids form benzene. In this way the nature, the position, and
the number of the side-chains may be determined.
It must not be inferred that the process of oxidation of side-chains
takes place with equal facility in the case of the three xylenes or other
group of isomeric hydrocarbons. Considerable differences have been
observed, not only in the case of different isomers, but in the effect upon
them of different oxidising agents. Dilute nitric acid is the least active
oxidising agent of those usually employed. The three xylenes are
converted by nitric acid into toluic acids, whilst chromic acid solution
oxidises meta- and para-xylene to the corresponding phthalic acids.
On the other hand, the ortho-compound is completely decomposed by
chromic acid, whilst potassium permanganate oxidises it to phthalic
acid. These results are intimately related with the protective influence
which groups in close proximity exert upon one another. The
presence of groups in the ortho-position to the methyl group renders
oxidation more difficult. We shall be frequently confronted with
similar cases of protective influence, or, as it is sometimes termed,
space interference or steric hindrance exercised by adjoining groups in
arresting, or impeding chemical change (p. 484).
Hydrocarbons of the Formula C 9 H 12 . Isomeric hydro-
carbons of the formula Q,H 12 include three trimethylbenzenes,
three methylethylbenzenes, a propyl- and an isopropylbenzene.
Mesitylene, or i-^-THtnethylbenzene. The formation of
mesitylene from acetone and sulphuric aeid has already been
described (p. 142). A similar reaction occurs with methyl
acetylene, CH 3 .C \ CH, which polymerises in presence of
1 The acids themselves either decompose, or sublime on heating (p. 49 r).
xxv THE AROMATIC HYDROCARBONS
393
sulphuric acid. The latter reaction resembles the formation of
benzene from acetylene (p. 383)
3 CH 3 .C ; CH = C C H 3 (CH 3 ) 3 .
Methyl acetylene. Mesitylene.
These reactions are of interest as affording grounds for the
assumption of a symmetrical formula for mesitylene, a view
which is confirmed by experimental evidence. Mesitylene
yields a series of acids on oxidation, which are known as
mesitylenic, uvitic, and trimesic acids
CH 3
/\
COOH
CH, COOHl /COOH
Mesitylene. Mesitylenic acid.
COOH
COOHl , COOH
Trimesic acid.
Each of the acids loses carbon dioxide on distillation with
lime, so that mesitylene may be converted in succession into
w-xylene, toluene, and benzene. Mesitylene is a colourless
liquid which boils at 165.
Pseudocumene, or 1-2-4- Trtmetfylfenzene, is one of the con-
stituents of solvent naphtha (p. 383), from which it may be
separated first by fractional distillation and then by treatment
with sulphuric acid, which dissolves the pseudocumene. The
sulphuric acid solution is then distilled in steam (p. 412),
when the pseudocumene passes over. It is a colourless liquid
which boils at 169.
Cumene, or Isopropylbenzene, C 6 H 5 .CH(CH 3 ) 2 , is prepared
from cumic acid, COOH.C fi H 4 .CH(CH 3 ) 2 , by distillation with
lime or by one of the synthetic methods described above
(P- 38;).
394 THEORETICAL ORGANIC CHEMISTRY CHAP.
Cymene, p-Cymene, or p-Methylisopropylbenzene, CH^.C 6 H 4 .
CH(CH 3 ) 2 , is the only important hydrocarbon of the formula
C 10 H 14 . It is found in certain essential oils, such as oil of
thyme and eucalyptus oil, and it is closely related to camphor,
C 10 H 16 O, and to the group of hydrocarbons of the formula
C 10 H 10 , known as terpenes, of which turpentine oil is the best
known example. Cymene is usually obtained from camphor by
distillation with phosphorus pentoxide or pentasulphide, which
act as dehydrating agents
Qio^ieO = C 10 H 14 + H 2 O,
Camphor. Cymene.
or from turpentine by the action of iodine or strong sulphuric
acid, whereby the oil is oxidised
C 10 H 16 + O = C 10 H 14 .+ H 2 0.
Cymene boils at 175. On oxidation it yields /-tolaic and
terephthalic acid. There are consequently two side-chains
in the para-position, one of which is a methyl group. The
character of the other group has been determined by synthesis.
;;z-Cymene is also known, and appears to be the parent-
substance of a certain number of terpenes.
Symmetrical Structure of Benzene. It has already been *
pointed out (p. 376) that Kekule's theory of the structure of
benzene rests mainly on evidence of an indirect or negative
character the non-existence of more than one mono-derivative ;
the occurrence of not more than three di-derivatives. The
theory is in so far inconclusive, that future research might bring
to light a second mono- or an additional di-derivative, when the
theory would fall to the ground. The symmetrical structure of
benzene, however, rests upon the firmer basis of direct experi-
ment. The experimental method involves a principle, first
employed by Hiibner and Petermann, which the following
^example may serve to illustrate. By the action of nitric
acid on benzoic acid, the three isomeric compounds o-, ;-,
and /-nitrobenzoic acids are formed. When each of these is
distilled with lime, the same nitrobenzene is produced. The
difference in the three nitrobenzoic acids must be ascribed
to a different position of the three nitro-groups in the benzene
XXV THE AROMATIC HYDROCARBONS 395
f ing ; but seeing that the products obtained by removal of the
'carboxyl group are identical, the three positions of the nitro-
groups must be identical. The structure of benzene must
therefore be symmetrical as regards the three carbon atoms to
which the nitro-groups are attached. The same process has
been applied to all six carbon atoms with the same result,
and the complete symmetry of the molecule has thus been
established.
Orientation. The existence of three di-derivatives, the ortho-,
meta-, and para-compounds of benzene, has been repeatedly
mentioned. They are distinguished by differences of melting or
boiling-point, sometimes by chemical properties, and occasionally,
if solid, by their crystalline form. Tri-derivatives in which the
three substituting elements or groups are the same, as in the
trimethylbenzenes, likewise form three isomers ; if two of the
groups are the same and the third different, six isomers are
possible and in many cases known, whilst, if all three groups are
different, the number of possible isomers rises to ten and so
forth. *
Is there any means of assigning to the different isomers the
relative positions in the nucleus of the substituting elements or
groups ? To take the simplest case, that of the di-derivatives :
Is there any means of determining which of the three isomers is
the ortho-, which the meta-, and which the para-compound ?
The process by which this is accomplished is known as orienta-
tion (French, orient^ situated).
Provided the position of the groups in certain fundamental
compounds is known, the structure of substances directly
related to them would naturally follow. If, for example, the
positions of the carboxyl groups in the three phthalic acids could
be ascertained, that of the methyl groups in the three xylenes
would be known (p. 391). At first the structure of certain
fundamental compounds rested largely upon assumptions, which,
"being frequently incorrect, led to much confusion. The process
known as Kbrner's absolute method of orientation is free from any
such objection. It is based upon the following principle. A
di -derivative will yield a different number of tri -derivatives
according to whether the original substance is an ortho-, meta-,
or para-compound. If it can be shown, for example, that one
of the three isomeric di-chlorobenzenes can be converted into
396
THEORETICAL ORGANIC CHEMISTRY
CHAP.
three trichlorobenzenes or three dichloro-nitrobenzenes, it can
only happen if the original dichlorobenzene is a meta-compound.
In the same way, if the di-derivative can only give two tri-
derivatives, it is an ortho-compound, whilst a para-compound is
only capable of yielding one tri-derivative. This will be under-
stood from the following scheme, in which A stands for the
element or group
Ortho gives two tri-
derivatives.
n
A M*
A
Meta gives three tri-derivatives.
A
A
Para gives one
tri-derivative.
It is immaterial whether the new element or group is the
same as the other two or not ; the rule still holds. The only
difference lies in this, that if all three groups are the same,
the total number of isomeric tri-derivatives is three ; if the new
group (B) is different from the other two, each of the six products
represents a different substance
A
/\
In practice, the above method of determining the structure of
aromatic compounds is difficult to carry out, as the whole series
of derivatives cannot always be directly prepare^ The reverse
process may sometimes be adopted with advantage. There are,
for example, six dichlorobenzoic acids, which when distilled with
lime give three dichlorobenzenes. The dichlorobenzene obtained
from three of the dichlorobenzoic acids is a meta-compound ;
THE AROMATIC HYDROCARBONS
397
that obtained from two of the acids is an ortho-compound. The
sixth dichlorobenzoic acid gives a para-compound.
Cl
'
fcOGH
Cl
COOH
0-Dichlorobenzene.
Cl Cl Cl
COOH /
Cl
ci cooHl
COOH
Cl
Cl
w-Dichlorobenzene.
COOH
/-Dichlorobenzene.
QUESTIONS ON CHAPTER XXV
1. Explain the origin and present meaning of the term aromatic
compotinds. Name some of the facts which originated the view of a
common nucleus in these compounds.
2. Explain why benzoic acid is said to be a benzene derivative.
What relation does oil of bitter almonds bear to benzoic acid ?
3. Discuss the merits and demerits of Kekule's formula for benzene,
and those of any alternative formula.
4. Give an outline of the production of aromatic hydrocarbons from
coal-tar.
5. By what physical and chemical properties are benzene and its
homologues distinguished from all other hydrocarbons?
393 tfHEO&fiffCAL ORGANIC CHEMISTRY CH. xxv
6. Discuss the 1 structural formula of toluene.
7. Give art account of the principal reactions of toluene which prove
that it contains both a benzenoid and a paraffinoid residue. Describe
precisely how you would conduct the operations and isolate the
products.
8. Describe the Friedel- Crafts and Fittig reactions for obtaining
benzene hydrocarbons. Give at least one other example of the
application of each of these important general methods of preparation.
9. How would you proceed to (i) identify an aromatic hydrocarbon?
(2) remove it from a mixture with petroleum ?
10. State how you would distinguish the isomeric hydrocarbons of
the formula C$H 10 . How would you show that they are ail derivatives
of benzene ?
11. Give the formulae of the isomeric xylenes, and state how one of
them may be converted into phthalic acid and how another may be:
made from mesitylene.
12. Give the structural formula of mesitylene: explain the evidence
upon which this formula is based and its significance in ascertaining the
constitution of derivatives of benzene.
13. By what means has orientation in benzenoid compounds been,
determined ?
14. Three dichlorobenzoic acids, when distilled with lime, yield the
same dichlorobenzene. Formulate the reaction and deduce from it
the structure of the dichlorobenzene produced.
15. What experimental proof exists that the hydrogen atoms in
benzene are of equal value and have similan functions,?
CHAPTER XXVI
AROMATIC HALOGEN COMPOUNDS
The Halogen Substitution Products. The action of the
halogens on the aiv .atic hydrocarbons in producing substitu^
tion has already been described (p. 389), and it was then
pointed out that, by modifying the conditions, the replacement
of hydrogen by chlorine, or bromine, may occur in the side^
chain or be confined to the nucleus. The process of sub-
stitution by chlorine, or bromine, is usually termed chlorination
or bromination.
In addition to this method, the action of phosphorus penta*
chloride, or pentabromide, on hydroxy-compounds may be
employed, though rarely used. The method resembles thq
action of the phosphorus halides on the aliphatic alcohols.
Hydroxybenzene, or ordinary phenol, gives chloro- or bromo*
benzene
C 6 H 5 (OH) + PC1 6 = C 6 H 5 C1 + POC1 3 + HC1. ,
Phenol. Chlorobenzene.
The same reaction occurs if the hydroxyl group is in the side~
chain, as in benzyl alcohol, which forms benzyl chloride
C 6 H 5 .CH 2 (OH) + PC1 5 = C 6 H 5 .CH 2 C1 + POC1 3 + HCL
Benzyl alcohol. Benzyl chloride.
A much more important means of introducing all three
halogens into the nucleus is by replacing the amino-group of'
the aromatic amines by the aid of the diazo-reaction, a process
which is of sufficient importance to merit a chapter to itself
399
4 oo THEORETICAL ORGANIC CHEMISTRY CHAP.
(p. 429). It is therefore postponed for the present. The following
examples are selected in order to illustrate the formation of the
halogen derivatives by direct substitution.
Monochlorobenzene, Phenyl chloride, C 6 H 5 CL Dry chlorine
is passed into benzene, to which a small piece of aluminium-
mercury couple (p.68) is added as carrier. Hydrochloric acid
is evolved, and when the additional weight corresponding to the
replacement of one atom of hydrogen by chlorine has been
gained, the operation is stopped. The liquid is shaken with a
solution of caustic soda, then dehydrated over calcium chloride,
and finally distilled, the portion boiling at 130-! 35 being
collected. Chlorobenzene is a colourless liquid, which boils
at 132. Like benzene, it forms nitro- and sulphonic acid
derivatives when acted upon with strong nitric or sulphuric
acid.
Bromobenzene, or Phenyl bromide, C 6 H 5 Br, is formed in the
same way, the bromine being added slowly to the benzene
containing the aluminium-mercury couple. Both chloro- and
bromobenzene may be prepared by the diazo-reaction from
amino-benzene, C 6 H 5 NH 2 . This method is the only available
one for the preparation of iodobenzene, C 6 H 5 I, as direct sub-
stitution by iodine is difficult to effect (p. 385).
The following are the boiling-points and specific gravities of
the three compounds, from which it will be seen that with
increasing molecular weight there is a rapid rise in both
boiling-point and specific gravity :
Boiling- Specific
point. gravity.
Chlorobenzene . . C 6 H 5 C1 ... 132 . . 1-128
Bromobenzene . . C 6 H 5 Br ... 155 . . 1*517
lodobenzene . . C 6 H 5 I .... 188 . . i'86i
Chlorotoluenes, Tolyl chlorides, C 6 H 4 (CH 3 )C1, exist in three
isomeric forms, the ortho-, meta-, and para-compounds. The
ortho- and para-compounds are formed by chlorinating toluene
in presence of a carrier. They are all obtained in a pure state
from the corresponding amino-toluenes, C 6 H 4 (CH 3 )NH 2 , by the
diazo-reaction already referred to. They are colourless liquids,
resembling Chlorobenzene.
The chlorotoluenes are rapidly converted, on oxidation, into
AROMATIC HALOGEN COMPOUNDS
401
the corresponding chlorobenzoic acids, by the melting-points
of which they are easily identified.
0 I!
C 6 H 5 NO 2 C 6 H 5 N/ C 6 H 5 N QH B NH
Nitrobenzene. Azoxybenzene. Azobenzene. Hydrazobenzene.
The action of the alkaline reducing agent is no doubt due to the
simultaneous formation of phenylhydroxylamine and nitrosobenzene,
which interact in alkaline solution, giving azoxybenzene
C 6 H 5 NHOH + NOC 6 H 5 = C 6 H 5 N NC 6 H 5 + H O
\/
O
QUESTIONS ON CHAPTER XXVII
1. Write a precise account of the method of preparing and purifying
nitrobenzene, in order to obtain a specimen of the pure substance.
2. Describe the course of the reaction in the nitration of benzene
and toluene, and the structure of the products obtained. What empiric
rule may be deduced from these reactions ?
3. Discuss the general laws of substitution. What products will
predominate in the following reactions : ( I ) nitration of chlorobenzene,
(2) chlorination of nitrobenzene, (3) chlorination of aniline, (4) nitra-
tion of aniline, (5) nitration of benzene sulphonic acid ?
4. Compare and contrast the properties of the nitre-paraffins with
the aromatic nitre-compounds.
5. What products can be obtained by the reduction of nitrobenzene
-and by what methods ?
CHAPTER XXVIII
THE AMINO-COMPOUNDS, OR AROMATIC AMINES
Amino-compound is the name usually given to those aromatic
compounds in which the hydrogen of the nucleus is replaced by
the amino-group. They correspond in structure to the aliphatic
amines. Aminobenzene, or phenylamine, C G H 5 .NH 2 , is the
analogue of ethylamine, C 2 H 5 .NH 2 . The term ammo-compound
rather than amine is preferred, inasmuch as the aromatic amino-
compounds differ in many important respects from the aliphatic
amines.
The amino-compounds cannot be obtained, as a rule, by
the direct action of ammonia on the halogen substitution
products of benzene and its homologues (p. 203), nor by any of
the usual reactions which yield the aliphatic amines. The
common 'method is one already referred to, viz. the reduction of
the nitro-compounds in acid solution. The agents usually
employed are the metals, iron, tin, and zinc, together with hydro-
chloric or acetic acid, stannous chloride dissolved in strong
hydrochloric acid, or, in certain special cases, ammonium
sulphide.
EXPT. 138. Preparation of Aniline from Nitrobenzene. 45 grarrs
of granulated tin and 25 grams of nitrobenzene are placed in a
round flask (i litre). The contents are warmed for a few minutes c:>
the water-bath. The flask is removed, and 90 c.c. of strong hydro-
chloric acid are gradually added in quantities of 5 to 10 c.c. at a
time. The mixture sometimes boils up violently, in which case the
flask should be immersed in cold water for a few minutes. In the
course of half an hour all the acid should have been added. The flask
411
412
THEORETICAL ORGANIC CHEMISTRY CHAP.
is then heated on the water-bath for an hour to complete the re-
duction. The reduction takes place according to the following
equation
2C 6 H 5 N0 2 + 3 Sn
i 4 HCl = 2C 6 H 5 NH 2 HC1 + sSnCl 4
Aniline hydrochloride.
If the liquid is allowed to cool at this stage, the double salt of aniline
hydrochloride and stannic chloride, (C 6 H 5 NH 2 HCl) 2 SnCl 4 , crystal-
lises. Water is at once added, therefore, and a strong solution of
caustic soda (70 grams in 100 c.c. of water). The aniline, which is
liberated and floats on the surface as a dark-coloured oil, is separated
by distillation in steam.
Distillation in Steam. The apparatus used in this operation is
shown in Fig. 86.
it
JMG. 86. Distillation in steam.
The vessel a, which is an ordinary oil-can, is used to generate steam,
and is partly filled with water. It is furnished with two tubes
inserted through the cork. One tube, which is long and straight and
open at both ends, serves as a safety-tube, by preventing liquid being
drawn from the flask b in case the flame under a is accidentally
removed. The second tube is bent, and terminates just below the
cork. It is attached by rubber tubing to the bent tube, which passes
to the bottom of flask b containing the aniline. The flask b is
connected with a condenser and receiver by a bent tube. The vessel
a is heated directly by the flame, and the steam passes into b, which
is heated on a sand-tray or wire-gauze, and is sloped to prevent the
contents being splashed over into the condenser. The steam carries
xxvui THE AMINO-COMPOUNDS 413
with it the vapour of aniline, which condenses and collects along with
water in the receiver. The aniline in the receiver is separated by
shaking with ether, which dissolves the aniline. The ethereal layer
is then removed, and dehydrated over solid caustic potash. The
ether is distilled off on the water-bath, and the residual liquid is then
distilled over the flame. Aniline boils at i8i-i82. The process of
distillation in steam is one of great practical value, and is frequently
employed where the substance is mixed with organic or inorganic
impurities which do not volatilise. It may appear strange at first
sight that aniline, which boils at 182, can be distilled by passing in
steam at a much lower temperature. The boiling-point of mixed
liquids, which do not dissolve in one another, is determined by their
combined vapour pressures. When this is equal to the external
(atmospheric) pressure, both liquids distil. It follows, therefore, that
aniline can be distilled much below its own boiling-point. 1
The conversion of a nitro- into an amino-group takes place in
the presence of other groups, or, if there is more than one
nitro-group in the nucleus, they all undergo reduction. Thus,
dinitrobenzene gives diaminobenzene
/NO, /NH 2
Dinitrobenzene. Diaminobenzene.
It is possible to effect the reduction of the two nitro-groups in
succession by using an alcoholic solution of ammonium sulphide.
The dinitro-compound is dissolved in alcohol, strong ammonia
is added, and hydrogen sulphide is passed through the solution
until saturated. The reduction is effected by the hydrogen of
the hydrogen sulphide, and sulphur is deposited
H 2 S = H a + S.
The reaction in the case of dinitrobenzene is represented as
follows
o
C 6 H 4 < + 3NH 4 HS = C 6 H 4 < + 3 NH 3
X NH 2
Nitroaminobenzene,
or Nitraniline.
Meta-nitraniline is readily prepared in this way from meta-dinitro-
benzene. The reduction is effected as described above ; the product is
1 Vide J. Walker, Introduction to Physical Chemistry, chap. ix. p. 82.
(Macmillan.)
414 THEORETICAL ORGANIC CHEMISTRY CHAP.
then poured into water, which precipitates the nitraniline mixed with
sulphur. The whole is filtered, and the nitraniline dissolved out with
dilute hydrochloric acid. The acid solution, separated from sulphur, is
made alkaline with ammonia, which again precipitates the nitraniline.
This is finally filtered and recrystallised from hot water. It crystallises
in long golden needles which melt at 114.
Properties of the Amino-Compounds. The amino-com-
pounds of the aromatic hydrocarbons are colourless liquids, or
solids which are sparingly soluble in water, but dissolve in the
common organic solvents. They may be distilled over the
flame without decomposition, and are volatile in steam. They
have a faint and not unpleasant smell, which, however, is not in
the least ammoniacal. If other groups accompany the ammo-
group, the compound partakes of their physical characters.
The amino-compounds are bases. They form well-crystallised
salts with acids and double salts with platinic chloride.
Aniline forms the following series of salts
CeH 5 NH 2 . HC1. C 6 H 5 NH 2 . HNO 3 . (C 6 H 5 NH 2 ) 2 H 2 SO 4 .
Aniline hydrochloride. Aniline nitrate. Aniline sulphate.
(C 6 H 5 NH 2 .HCl) 2 PtCl 4 .
Aniline platinochloride.
The hydrochlorides and nitrates of the bases are usually very
soluble, the sulphates less soluble, in water. So far the com-
pounds resemble the aliphatic amines. The bases, however,
are not alkaline to litmus, nor are the salts neutral substances,
but exhibit a strongly acid reaction with litmus. If a few
crystals of pure aniline hydrochloride are dissolved in water,
the solution will redden blue litmus. There are certain other
organic colouring matters (methyl violet, magenta, etc.) which
are unchanged unless free acid is present, and are used for
indicating neutrality when an acid is added to an aromatic base.
This weakening of the basic properties of the amino-compounds
is ascribed to the negative, or acid character of the benzene
nucleus, which partially neutralises the basic properties of the
amino-group. Diphenylamine, NH(C 6 H 5 ) 2 , which contains two
phenyl groups, forms salts which are decomposed by water.
Triphenylamine, N(C 6 H 5 ) 3 , does not combine with acids and
forms no salts. We shall presently see that the negative
character of the nucleus finds further expression in the enhanced
xxviii THE AMINO-COMPOUNDS 415
acidic character of the hydroxy-compounds like phenol,
C 6 H 5 (OH), which forms salts with the caustic alkalis.
The amino-compounds form secondary and tertiary bases,
like the amines, by replacement of the hydrogen atoms of the
ammo-group by radicals. The radical may be an alkyl
group-
Primary. Secondary. Tertiary
X H \H
Aniline. Methylaniline. Dimethylamline.
or, an aromatic radical like phenyl
.
Aniline, or Phenylamine. Diphenylamine. Triphenylamine.
The formation of these substances, many of which are of
great commercial importance, is described in detail below
(p. 422).
Distinction between Primary, Secondary, and Tertiary
Ammo-Compounds. The same reagents may be employed
for distinguishing the three classes of amino-compounds, as are
used for the aliphatic amines, with similar, though not identical,
results (p. 200).
If a solution of nitrous acid is added to a primary amino-
compound and the liquid is warmed, effervescence occurs, and
the amino-group is replaced by hydroxyl. Aniline yields
hydroxybenzene, or ordinary phenol
C 6 H 5 NH 2 + HNO 2 = C 6 H 5 (OH) + N 2 + H 2 O.
Phenol.
The process actually takes place in two steps, as will be seen
from the following experiment.
EXPT. 139. Dissolve a few drops of aniline in excess of dilute-
hydrochloric acid (test with methyl violet paper), cool the solution,
and add a few drops of sodium nitrite solution. The liquid turns
yellow, but no effervescence occurs. There is present diazobenzene.
chloride, which is very soluble in water
C 6 H 5 NH 2 .HC1 + HNO 2 = C 6 H 5 N 2 .C1 + 2H 2 O.
Diazobenzene
chloride.
416 THEORETICAL ORGANIC CHEMISTRY CHAP.
Divide the liquid into two parts, and warm one portion. Effer-
vescence occurs and nitrogen is evolved. The smell of phenol, or
carbolic acid, is then perceived
C 6 H 5 N 2 C1 + H 2 - C 6 H S (OH) + N 2 + HC1.
Phenol.
Pour the other portion into a solution of phenol in caustic soda.
A deep orange-red colour is at once produced. This is an azo-colour,
the structure and properties of which will be described later (p. 438).
The two reactions serve to identify a primary aromatic amino-
compound.
If nitrous acid is added to a secondary base, a nitrosamine
is formed, which is a yellow substance, insoluble in water.
Methylaniline yields nitrosomethylaniline
C 6 H 5 NH(CH 3 ) + HN0 2 = C 6 H 5 N(NO)CH 3 + H 2 O.
Nitrosomethylaniline.
EXPT. 140. Dissolve a few drops of methylaniline in dilute
hydrochloric acid, and add sodium nitrite solution as above. A
precipitate consisting of fine drops of nitrosomethylaniline is formed,
which may be removed by extraction with ether. It possesses a
fragrant smell and yellow colour. If a few crystals of phenol are
dissolved in strong sulphuric acid (2 c.c.) and a drop of nitroso-
methylaniline added, a blue colour is developed on warming, which
changes to red on dilution with water. This reaction for "nitroso "
compounds is known as Liebermann 's nitroso-reaction. Together,
the above two reactions serve to identify a secondary ammo-
compound.
In their behaviour with nitrous acid, the tertiary amino-com-
pounds offer no analogy with the tertiary aliphatic amines.
When nitrous acid is added to dimethylaniline, a deep red
solution is obtained, from which yellow crystals separate. This
is the hydrochloride of a new base, nitrosodimethylaniline. The
nitrous acid, here, attacks the nucleus
C.N(CH 3 ) 2 C.N(CH 3 ) 2
HCCH
Iicl JcH HCv.CH
CJH ..... | C.NO
Nitrosodimethylaniline.
-f-JHONO.
xxvin THE AMINO-COMPOUNDS 417
EXPT. 141. Dissolve a few drops of dimethylaniline in dilute
hydrochloric acid. Notice that it is necessary to shake the mixture
before a clear solution is obtained. Cool the liquid, and add
cautiously a solution of sodium nitrite. Yellow crystals of the
hydrochloride of the nitroso-compound soon begin to separate. If a
portion of the liquid is made alkaline with caustic soda, a bright green
precipitate is formed, which is the nitrosodimethylaniline base.
Tertiary aromatic bases, like the aliphatic tertiary amines,
combine with alkyl iodides and form quaternary ammonium
iodides (p. 202). Dimethylaniline, when warmed for a minute
with methyl iodide, forms a crystalline trimethylphenylam-
monium iodide
C 6 H 5 N(CH 3 ) 2 + CH 3 I = C 6 H 5 N(CH 3 ) 3 I.
Trimethylphenyl-
ammonium iodide.
The primary and secondary bases do not yield compounds of
this character.
Acetyl chloride, or acetic anhydride, may be used for dis-
tinguishing the primary and secondary from the tertiary bases.
The primary and secondary amino-compounds form acetyl
derivatives, but not the tertiary base.
Aniline and methylaniline give respectively acetanilide and
methyl acetanilide
C 6 H 5 NH 2 + CH 3 .COC1 = C 6 H 5 NH.COCH 3 + HC1.
Acetanilide.
C 6 H 5 NH(CH 3 ) + CH 3 .COC1 = C 6 H 5 N(CH 3 )CO.CH 3 + HC1.
Methylacetanilide.
EXPT. 142. Add a few drops of acetyl chloride or acetic anhydride
separately to aniline, methylaniline, and dimethylaniline. Warm for
a minute over a small flame and pour into water. In the case of
aniline and methylaniline, solid crystalline precipitates will be formed
on rubbing with a glass rod, which are the acetyl derivatives of the
two bases ; but dimethylaniline is unchanged and remains liquid.
The primary aromatic amines are further distinguished by
the carbamine reaction, which is described on p. 90, and also
by their behaviour with carbon bisulphide. If aniline is boiled
with carbon bisulphide, diluted with alcohol in a flask provided
with an inverted condenser hydrogen sulphide is evolved, and
EE
41 8 THEORETICAL ORGANIC CHEMISTRY CHAP.
a colourless, crystalline substance known as thiocarbanilide is
formed
! HJNH.C 6 H 5 y NH.C 6 H 5
SOS + = SC/ + H 2 S.
j HJNH.C 6 H 5 X NH.C S H 5
Thiocarbaniiide.
Aniline, Aminobenzene, Phenylamine, C 6 H 5 NH 2 . Aniline
was discovered in 1826 by Unverdorben among the products of
the distillation of indigo. Later, Fritsche obtained it from the
same source by distilling with strong potash, and called it
aniline from the Portuguese word anil, indigo. It was found in
coal-tar by Runge, who discovered the reaction with hypo-
chlorites, and named it kyanoL Its production from nitro-
benzene by reduction is due to Zinin. Since the discovery of
the aniline dyes, its manufacture has attained very large
dimensions. It is prepared by the reduction of nitrobenzene,
with tin and hydrochloric acid as already described (p. 412) ; but
on the industrial scale the reducing agent is iron borings and
strong hydrochloric acid. The nitrobenzene and a little hydro-
chloric acid are heated by means of steam in an iron pan, which
is provided with a condenser, so that the escaping vapours may
be either returned to the pan, or, when required, conducted to a
receiver. Iron borings are added to the mixture of nitrobenzene
and hydrochloric acid, which is kept in agitation by a revolving
stirrer. The action, once started, continues without the applica-
tion of heat, until the reduction is complete. Lime is then
added to neutralise the acid, and the aniline is removed by
distillation with steam.
As the amount of acid employed is much below the theoretical
quantity required by the equation Fe + 2HC1 = FeCl 2 + H 2 , the
main reaction is probably represented as follows
C 6 H 5 .NO 2 + 2Fe + 4H 2 O = C 6 H 5 .NH 2 + 2Fe(OH) 3 .
Freshly distilled aniline is a colourless, oily liquid, which
rapidly darkens on exposure to light and air. It boils at
i82-i83and solidifies at -8. Its specific gravity is ro24at 16,
and, being sparingly soluble, it sinks when poured into water.
The salts of aniline have already been mentioned (p. 414).
They are prepared by dissolving aniline in the respective acids,
which, in the case of nitric and sulphuric acids, must be diluted.
The mixture is then allowed to cool, when the salts crystallise.
xxviii THE AMINO-COMPOUNDS 419
They become discoloured after a time if exposed to the air.
The term aniline salt is applied technically to the hydro-
chloride.
Reactions of Aniline. The presence of aniline is readily
detected by pouring a drop of the base into a solution of
bleaching powder or sodium hypochlorite. An intense violet
coloration is produced, which slowly turns brown and fades.
Another test for aniline is as follows : A few drops of strong
sulphuric acid are added to a drop of aniline in a basjn, and the
pasty mass is stirred with a glass rod. On the addition of a
few drops of potassium dichromate solution, an intense blue
colour is produced.
When aniline is oxidised with a cold solution of potassium
dichromate and dilute sulphuric acid, it turns black, and the
solution contains, among other products, 'benzoquinone^ C 6 H 4 O 2 ,
which is described later (p. 476).
Aniline undergoes the following reactions with the acids and
halogens.
Chlorine and bromine act vigorously on aniline and form the
2-4-6-trichlor- and tribromaniline
NH 2 NH 2
Cl Br
Trichloraniline. Tribromaniline.
When aniline, or aniline sulphate, is heated with strong
sulphuric acid, aniline /-sulphonic acid or sulphanilic acid is
formed
X NH 2
C 6 H 5 NH 2 + H 2 S0 4 = C 6 H 4 < + H 2 O.
\S0 3 H
Sulphanilic acid.
When aniline arsenate is heated, ^-aminophenylarsenic acid is formed,
the sodium salt of which has been used under the name of atoxyl as
a specific against sleeping sickness. Its acetyl derivative or arsacetin is
also used. By reduction of ^-hydroxy-w-aminophenylarsenic acid,
a-diaminodihydroxyarsenobenzene is obtained
HO/ \As = As/Nori.
NH7 S NH 2
E E 2
420 THEORETICAL ORGANIC CHEMISTRY CHAP.
the hydrochloride of which is known as salvarsan, and is a still more
effective drug.
The action of nitric acid on aniline is sufficiently vigorous to
decompose the substance completely, unless the amino-group
is " protected " by introducing an acid radical (see below).
On boiling aniline with glacial acetic acid, acetanilide is
formed
C 6 H 5 NII 2 -h C 2 H 4 O 2 = CgHgNH.QHaO + H 2 O.
Acetanilide.
Acetanilide, Phenylacetamide, Antifebrin, C 6 H 5 NH.C 2 H 3 O,
is obtained, as already mentioned, by the action of acetyl
chloride, or acetic anhydride, on aniline, but is more economically
prepared by boiling 'aniline with glacial acetic acid.
EXPT. 143. Mix 5 c.c. of aniline with 10 c.c. of glacial acetic
acid in a flask provided with a straight, upright tube about 2. feet long
to condense the acetic acid vapour, which is given off. Boil gently for
about an hour and pour the contents into water. The acetanilide is
precipitated as a crystalline mass, which may be purified by
recrystallisatioiv from water.
The anilides of other acids are prepared in a similar way, of
which the following are examples
Formanilide ..... C 6 H 5 NH.CHO
Propionanilide .... C 6 H 5 NH.CO.C 2 H 5
Oxanilide ...... C 6 H 5 NH.CO.CO.NHC 6 H 5 .
Acetanilide serves as the type of an acyl derivative of an
aromatic amino-compound. It crystallises from water or dilute
alcohol, and melts at 114. It is used in medicine as a febrifuge
under the name of antifebrin. When boiled with a strong
solution of caustic alkalis, or with strong hydrochloric acid, or
with moderately strong sulphuric acid, it is hydrolysed and
converted into aniline and acetic acid, a reaction which recalls
the behaviour of acetamide (p. 178)
= C 6 H 5 NH 2 + CH 3 .COOH.
HOH
xxvin THE AMINO-COMPOUNDS 421
EXPT. 144. Boil 0*5 gram of acetanilide with a few c.c. of strong
hydrochloric acid for a minute, and pour into water. A clear
solution containing aniline hydrochloride is obtained, from which the
aniline may be separated by adding caustic soda and extracting with
ether in the usual way.
Nitranilines. When acetanilide is added gradually to well-
cooled, fuming nitric acid, a mixture of o- and /-nitracetanilide
is produced. The nitracetanilides are precipitated by pouring
the mixture into water, and after being filtered, washed, and
dried, they can be separated with chloroform, which dissolves
the ortho- but not the par^-compound. From each of these, on
hydrolysis, the corresponding nitraniline is obtained. The
hydrolysis is performed, as described in Expt. 144, by boiling
with strong hydrochloric acid. The product is then poured
into water, made alkaline with soda (or ammonia), and the
solid nitraniline filtered. The meta-compound is most readily
prepared by the partial reduction of 7;z-dinitrobenzene with
alcoholic ammonium sulphide (p. 413). It is an interesting fact
that if aniline is nitrated in strong sulphuric acid solution, the
chief product is ;/z-nitraniline, and not the ortho- or para-
compounds. The same influence of sulphuric acid has been
observed in other cases (see below).
The three nitranilines are yellow, crystalline substances, which
differ considerably in their melting-points. The para-compound
has a technical value, being used for producing a brilliant red dye.
known as paranitraniline red (see p. 439). Each nitraniline
yields the corresponding diamino-compound, or phenylene-
diamine, C 6 H 4 (NH 2 ). 2 , on reduction (the phenylene radical is
C 6 H 4 "). Tetranitraniline (NO 2 ) 3 C 6 H 2 NH.NO 2 is a powerful
explosive.
m-Phenylenedtamme is usually prepared directly by the
reduction of w-dinitrobenzene, and is employed commercially
in the production of a brown colouring matter, known as
Bismarck brown (p. 439).
Melting-
point.
/NH 2 0-nitraniline ...... 7 J
C 6 H 4 < m- ...... 114
X N0 2 /- ...... 147
/NH 2 0-phenylenediamine .... 103
C 6 H 4 < m- .... 63
\NH 2 /- .... 140
422 THEORETICAL ORGANIC CHEMISTRY CHAP.
Chloranilines. If chlorine is passed into acetanilide dissolved
in acetic acid, or bromine is added to the same solution, a
mixture of o- and ^-monochlor- or monobrom-acetanilide is
first formed. If the operation is continued, these pass into the
2-4 (NH 2 = i) disubstitution products. If the aniline is dissolved
in strong sulphuric acid, the chlorine, or bromine, enters the
meta-position to the amino-group.
A recent study of these reactions shows that when acetanilide is
chlorinated or brominated by hypochlorous or hypobromous acid,
chlorine and bromine first replace the hydrogen of the amino-group,
from which, by intramolecular exchange, the chlorine, or bromine,
enters the ortho- and para-position of the nucleus.
C 6 H 5 NH.C 2 H 3 O + HC10 = C 6 H 5 NC1.C 2 H 3 O + H 2 O.
Acetchloranilide.
C 6 H 5 NC1.C 2 H 3 = C 6 H 4 C1.NH.C 2 H 3 0.
o- and /-Chloracetanilide.
A similar thing occurs with nitric acid. If nitrogen pentoxide is
added to well-cooled aniline, the compound which is formed is
phenylnitramine, and the nitro-group replaces hydrogen of the amino-
group.
C 6 H 5 NH 2 + N 2 5 = C 6 H 5 NH.N0 2 + HNO 3 .
Phenylnitramine.
From this position, in the presence of mineral acids, the nitro-group
passes into the ortho- and para-position of the nucleus. The action of
sulphuric acid in producing meta-derivatives has so far received no
satisfactory explanation.
Alkylaniiines are obtained by the action of the alkyl halide
on aniline. If methyl chloride is passed into aniline, heated under
pressure, methyl and dimethylaniline are formed
C 6 H 5 NH 2 + CH 3 C1 = C 6 H 5 NH(CH 3 ) + HC1.
Methylaniline.
C 6 H 3 NH(CH 3 ) + CH 3 C1 = C 6 H 5 N(CH 3 ) 2 + HC1.
Dimethylaniline.
A similar reaction occurs if the aniline is boiled with methyl
bromide or iodide. The manufacturing process is to heat aniline
hydrochloride, or sulphate with the alcohol to i8o-2oo in closed
vessels.
THE AMINO-COMPOUNDS
423
i.
2.
If methyl alcohol is used, it is converted into methyl chloride,
or methyl sulphate (if the sulphate of aniline is used), whictfi
then acts upon the aniline.
C 6 H 5 NH 2 .HC1 + CH 3 OH = C 6 H 5 NH 2 + CH 3 C1 + H 2 O.
C 6 H 5 NH 2 + CH 3 C1 = C 6 H 5 NHCH 3 .HC1.
Methylaniline hydrochloride.
3. C 6 H 5 NH(CH 3 )HC1 + CH 3 OH = C 6 H 5 N(CH 3 ) 2 .HC1 + H 2 O.
Dimethylaniline hydrochloride.
In this reaction, as in Hofmann's method for preparing the
aliphatic amines, both secondary and tertiary bases are formed.
The separation of the tertiary base, which has the greater
technical value, is effected by converting the primary and
secondary bases present into acyl derivatives. For example, by
boiling the mixture with acetyl chloride, or acetic anhydride,
acetyl derivatives of aniline and methylaniline are formed,
which have a sufficiently high boiling-point to permit of the
unchanged dimethylaniline being removed by distillation.
The alkyl anilines undergo a curious intramolecular change on
heating, whereby the alkyl group leaves the amino-group to enter
the nucleus. The process resembles in some respects the trans-
ference of the halogens and nitro-group from the amino-group
to the nucleus (p. 422). When the hydrochloride of methyl, or
dimethylaniline, is heated in closed vessels to 25o-35o, toluidine
(aminotoluene) and 2-4-xylidine (aminoxylene) are formed, the
methyl group entering the oftho- or para-position, or both, to
the amino-group.
NH(CH 3 ).HC1
NH^HCl
o-Toluidine.
NH(CH 3 ). HC1 NH(CH 3 ). HC1
~ I, /\
\/
NH 2 .HC1
,CH 3
V
CH 3
2-4-Xylidine.
424 THEORETICAL ORGANIC CHEMISTRY CHAP.
This process is of great technical importance, and is used in
the manufacture of xylidine.
The alkylanilines are oily liquids, which can be distilled with-
out decomposition. They possess a smell which recalls that of
aniline with something of the fishy odour of methylamine.
Methylaniline, C 6 H 5 NH(CH 3 ), is a colourless liquid of sp. gr.
0*976, which boils at 193. It is prepared by the method
described above. In this process it is separated from the
dimethylaniline by conversion into the acetyl derivative, and
remains when the dimethylaniline is distilled off. In order to
regain the methylaniline, the acetyl derivative is hydrolysed
with caustic potash and the base separated and distilled. The
acetyl derived is occasionally used as a febrifuge under the
name of exalgine.
Dimethylaniline, C 6 H 5 N(CH 3 ) 2 , has the same boiling-point
as monomethylaniline, but is readily distinguished from it by
its behaviour with acetic anhydride, nitrous acid, or methyl
iodide (p. 415). Dimethylaniline is manufactured on a commer-
cial scale for the production of a variety of colouring matters,
some of which will be described later.
Nitrosodimethylaniline, (NO)C 6 H 4 N(CH 3 ) 2 , the preparation
of which has already been described, is also employed in the
colour industry. Methylene blue is prepared from this com-
pound.
EXPT. 145. Warm a very small quantity of nitrosodimethyl-
aniline with a few c.c. of ammonium sulphide solution until the
substance dissolves. Cool and acidify with hydrochloric acid. Then
add ferric chloride solution until the blue colour appears. The
colour is known as methylene blue.
When boiled with dilute caustic soda solution, nitrosodimethyl-
aniline is decomposed into quinonoxime (/-nitrosophenol) and
dimethylamine. In this manner pure dimethylamine can be
obtained (p. 205).
(NO)C 6 H 4 N(CH 3 ) 2 +H 2 = (HON).C 6 H 4 O + NH(CH 3 ) 2 .
Nitrosodimethylaniline. Quinonoxime. Dimethylamine.
The Toluidines, CH 3 .C C H 4 .NH 2 . The three toluidines are
prepared by the reduction of the corresponding nitrotoluenes.
xxvin THE AMINO-COMPOUNDS 425
Ortho- and meta-toluidine are liquids which boil at 199 ; para-
toluidine is a solid, which melts at 43, and boils about the same
temperature as its isomers. Although the three toluidines
possess the same boiling-point, the melting-points of their
respective acetyl derivatives show a remarkable difference
Melting-
point.
0-Acetotoluide 110
m- 63
P- 153
Benzylamine, C 6 H 5 .CH 2 NH 2 , is isomeric with the toluidines,
but offers a marked contrast to them both in its mode of
^preparation and in its properties.
"'It exhibits, in fact, a much closer relation to the aliphatic
amines, and is prepared by similar methods. It is obtained by
the action of ammonia on benzyl chloride (p. 402)
C 6 H 5 CH 2 C1 + NH 3 = C 6 H 5 CH 2 NH 2 + HC1.
Benzylamine.
Also, by the action of bromine and caustic potash on the
amide of phenylacetic acid, or benzyl formamide
C 6 H 5 .CH 2 .CONH 2 + Br 2 + 4KOH
Benzyl formamide.
= C fi H 5 .CH 2 NH 2 +2KBr I- 2 H 2 O + K 2 CO 3 .
It is further obtained by the reduction of phenyl cyanide
C 6 H 5 CN + 2H 2 = C 6 H 5 .CH 2 NH 2 .
Phenyl
cyanide.
Benzylamine is an alkaline liquid, which boils at 185, and
possesses an ammoniacal smell and strongly basic properties.
It behaves like a primary amine of the aliphatic series towards
nitrous acid, giving the nitrite, which, on boiling with water,
immediately forms the alcohol without the production of a
diazo-compound
C 6 H 5 .CH 2 NH 2 .HN0 2 = C 6 H 5 CH 2 (OH) + N 2 + H 2 O.
Diphenylamine, (C 6 H 5 ) 2 NH, is prepared by heating aniline
hydrochloride and aniline to about 240 in a closed vessel
426 THEORETICAL ORGANIC CHEMISTRY CHAP.
C 6 H 5 NH 2 . HC1 + C 6 H 5 NH 2 = (C 6 H 5 ) 2 NH + NH 4 C1.
Diphenylamine.
It is a colourless, crystalline compound, with a faint and not
unpleasant smell. It melts at 54 and boils at 310. The salts
are decomposed by water, and the base, being insoluble, does
not dissolve in dilute acids. Uiphenylamine is employed in the
manufacture of certain blue colouring matters. It is occasionally
used to detect the presence of nitrous acid.
EXPT. 146. Dissolve a crystal of diphenylamine in a few c.c. of
strong sulphuric acid, and add a single drop of a dilute solution of a
nitrite. On warming gently, a blue colour is developed.
Diamino-compounds or Diamines. The reduction products of the
three dinitrobenzenes are known as phenylenediamines (p. 421). Each
of the isomers is characterised by certain properties which distinguish it
from the others, and which depend upon the relative positions of the
two amino-groups. These properties are shared by other diamines.
The ortho-diamines, from the proximity of the two amino-groups, readily
undergo condensation With acetic acid they form so-called anhydro-
bascs or amidines.
/NH 2 /NH V
C 6 H 4 < + CH 3 .COOH = C 6 H 4 < >C.CH 3 + 2 H 2 O.
\NH 2 X -N=^
0-Phenylene acetamidine.
Nitrous acid produces azimino- compounds.
/NH 2 /NH\
C 6 H 4 / + HN0 2 - C 6 H 4 / J)N + 2H 2 0.
Aziminobenzene.
The ortho-diamines also combine with phenanthraquinone in presence
of acetic acid, giving yellow, crystalline precipitates (p. 554).
The meta-diamines form brown colouring matters with nitrous acid,
e.g. w-phenylenediamine yields Bismarck brown (p. 439).
The para-diamines give rise to a variety of red and blue colouring
matters when they are submitted to oxidation in presence of a primary
amino-compound (saffranines, indamines). When oxidised alone, they
are converted into quinones (p. 476).
xxvm THE AMINO-COMPOUNDS 427
QUESTIONS ON CHAPTER XXVIII
1. Describe and explain the process of steam distillation. How is it
applied in the preparation of aniline ? What other method could be
used on a small scale for separating the aniline ?
2. What reagents are usually employed for reduction of nitro-
compounds to amino-compounds ? Illustrate their use in reference to
dinitrobenzene.
3. What are the principal reactions which distinguish aniline and its
homologues from ethylamine and its homologues? (Lond. Int. M.B.
1897.)
4. How was aniline originally obtained ? From what other sources
is it procurable, and how is it now manufactured ?
5. How is dimethylaniline prepared from benzene ? Compare and
contrast the behaviour of fatty and aromatic amines towards nitrous
acid.
6. Describe the action of reagents, other than nitrous acid, on the
primary, secondary, and tertiary amino-compounds.
7. What is the action of the following reagents on aniline : ( i ) sodium
hypochlorite, (2) potassium dichromate and sulphuric acid, (3) the
mineral acids, (4) the halogens ?
8. What is acetanilide, how is it prepared, and for what purpose
is it used ? In what respects does it resemble acetamide ? Describe
the action of the halogens on acetanilide, and explain the probable
course of these reactions.
9. How are three isomeric nitranilines obtained, and what products
do they yield on reduction ?
10. How are the alkylanilines obtained ? Give two methods.
What intramolecular changes do they undergo ?
11. How is dimethylaniline separated from monomethylaniline and
aniline ? Why is this separation necessary ? In what manner can
dimethylaniline be utilised for the preparation of pure dimethylamine ?
12. Contrast the isomeric amino-compounds of the formula GjHgN.
13. What is the structure of the three phenylenediamines, and how
may they be prepared from benzene ? Name some of the characteristic
properties of ortho-, meta-, and para-diamines.
14. Three isomeric phenylenediamine carboxylic acids have been
found to yield, on distillation with lime, the same phenylenediamine.
What is the constitution of the latter, and how is it most readily
obtained ?
CHAPTER XXIX
THE DIAZO-COMPOUNDS
Diazo-compounds. In 1860, Griess, a German chemist,
discovered what is known as the diazo-reaction, a process of
fundamental importance, not only as an aid to organic synthesis
among the aromatic compounds, but as the .source of a large
class of artificial dye-stuffs, known as the azo-dyes. It has already
been stated (p. 415) that if aniline is dissolved in hydrochloric acid
and cooled, and sodium nitrite solution is then added, nothing
is observable but a slight change in the colour of the solution,
which becomes yellow. A new substance is, however, present,
viz. the hydrochloride of a strong base. It is termed diazo-
benzene chloride, and the process is called diazotising.
The process is usually conducted by dissolving the equivalent
of one molecule of the base in two molecules of hydrochloric
acid, and adding one molecule of sodium nitrite.
C 6 H 5 N!H 2 H J C1
= C 6 H 5 N 2 .C1 + 2H 2 0.
+ N;O OH; Diazobenzene chloride.
The group C 6 H 5 N 2 is a basic group which may be compared
with ammonium, NH 4 . Like ammonium, it does not exist in
the free state, but forms a very unstable hydroxide, which is an
oil, and a series of well-crystallised salts, which are extremely
soluble in water, but not in alcohol or ether
C 6 H 5 N 2 . OH. C ? H 5 N 2 Cl. C 6 H 5 N 2 . NO 3 . C 6 H 5 N 2 . SO 4 H.
Diazobenzene Diazobenzene Diazobenzene Diazobenzene
hydroxide. chloride. nitrate. sulphate.
428
CH. xxix THE DIAZO-COMPOUNDS 429
All the salts, in the dry state, explode on heating, or by shock,
especially the nitrate, which detonates violently with a slight
blow. The formation of diazo-compounds is a property of the
majority of the aromatic amino-compounds.
Structure of the Diazo-compounds. The formula for the
diazo-compounds, proposed by Kekule, contains two doubly-
linked nitrogen atoms. Diazobenzene chloride is represented
by the following formula
C 6 H 5 N:N.C1.
Kekul's formula.
The basic character of the diazo-group has suggested an
alternative formula, which is known as Blomstrand's formula.
The nitrogen attached to the acid radical is pentavalent, as in
the ammonium salts ; hence the compounds are sometimes
called diazonium salts
C 6 H 5 N=N
Cl.
Blomstrand's formula.
For present purposes, Blomstrand's formula will be adopted,
as it probably affords a more correct interpretation of most
reactions of the diazo-salts.
Reactions of the Diazo-compounds. Diazobenzene chloride
may be taken as typical of the diazo-salts. It undergoes the
following series of changes :
1. When boiled with alcohol, effervescence due to liberated
nitrogen occurs. At the same time reduction of the phenyl
group to benzene takes place at the expense of the alcohol,
which loses hydrogen, and is oxidised to aldehyde
. ;
C 6 HJNJC1
j|||! =C fl H 6 + N a + HCL
+ H;N!H
i
An alkaline solution of stannous hydrate can also be used.
2. If the aqueous solution of diazobenzene chloride is boiled,
nitrogen is evolved as before, and phenol is formed (p. 416)
C 6 H 5 :N;C1
ii i ;
+ OH
illlj = C 6 H 6 (OH) + N 2 + HCL
iN C 6 H 5 SO.OH -> C 6 H 5 SH
Benzenesulphonic Benzenesulphinic Phenyl
acid. acid. mercaptan.
The sulphur in the mercaptan is linked to the carbon of the
radical, or nucleus. Hence, the structural formula of benzene-
sulphonic acid must be represented by the following formula
C B H a .S.OH
O
Structural formula cf benzenesulphonic acid.
Benzenesulphonic Chloride, C 6 H 5 .SO 2 CL The mode of
preparation of benzenesulphonic chloride may be taken as
typical for this class of compounds. Benzenesulphonic acid, or,
usually, one of its salts, is heated on the water-bath with
phosphorus pentachloride until the evolution of hydrochloric
acid nearly ceases. The product is poured into water and
extracted with ether. On removing the ether, the sulphonic
448 THEORETICAL ORGANIC CHEMISTRY CHAP.
chloride remains as an oil, which must be distilled under
diminished pressure to avoid decomposition. Many of the
sulphonic chlorides are crystalline solids, but their melting-points
are usually low. The sulphonic chlorides have the general
characters of other acid chlorides, although they do not fume in
the air, nor are they very rapidly decomposed by water or dilute
alkalis. On the other hand, they combine directly with
ammonia and with primary and secondary amines like ethyl-
amine, or diethylamine, aniline, or methylaniline ; but not with
tertiary amines
C 6 H 5 .S0 2 C1 + 2NH 3 = C 6 H 5 .S0 2 .NH 2 + NH 4 C1.
Benzene-
stilphonaraide.
C 6 H 5 .S0 2 C1 + 2NH 2 C 6 H 5 = C 6 H 5 .S0 2 .NHCeH 5 + C 6 H 5 NH 2 .HC1.
Benzenesulphonanilide.
Both sulphonamides and sulphonanilides are sparingly
soluble in water, and are therefore easily separated from the
other products of the reaction (in the above example, ammonium
chloride and aniline hydrochloride). They are purified by
crystallisation from alcohol. The sulphonic chlorides also
combine with alcohols and phenols (hydroxybenzenes) in
presence of caustic soda solution. Ethyl benzenesulphonate
is obtained by warming a mixture of benzenesulphonic chloride
and ethyl alcohol with a solution of caustic soda. It is then
extracted with ether, and the ether evaporated
C 6 H 5 SO 2 C1 + C 2 H 5 OH + NaOH = C 6 H 5 .SO 2 .OC 2 H 5 + NaCl + H 2 O.
Ethyl benzene-
sulphonate.
When benzenesulphonic chloride is heated with phosphorus
pentachloride, chlorobenzene is produced. Other sulphonic
chlorides behave similarly.
C 6 H 5 S0 2 C1 + PC1 5 = C 6 H 5 C1 + SOCLj + POC1 3 .
We thus see that by the aid of sulphonation, the hydrogen of
the benzene nucleus may be replaced by hydroxyl, cyanogen, and
chlorine ; that insoluble substances may be rendered soluble in
water ; and that isorneric hydrocarbons in a mixture may be
separated from one another.
THE SULPHONIC ACIDS 449
QUESTIONS ON CHAPTER XXXI
1. Describe the preparation of benzenesulphonic acid. How are
the sodium, potassium, and calcium salts obtained?
2. In what manner has the process of sulphonation been of
advantage technically ?
3. What is the result of sulphonation of (i) benzenesulphonic
acid, (2) aniline, (3) phenol, and (4) nitrobenzene ? State what you
consider will be the probable positions taken by the sulphonic
group.
4. Describe some of the properties of the sulphonic acid. Explain
how benzene, chlorobenzene, phenol, and phenyl cyanide may be
obtained from benzenesulphonic acid.
5. Explain and illustrate the use of sulphonation in separating
mixtures of hydrocarbons.
6. How is benzenesulphonic chloride obtained ? Compare its
behaviour as an acid chloride with acetyl chloride.
7. Discuss the structural formula of the sulphonic acids.
CHAPTER XXXI I
THE PHENOLS
Phenols. The name is given to the hydroxy-derivatives of the
aromatic hydrocarbons, in which the hydrogen of the nucleus is
replaced by hydroxyl. The simplest member of the group is
ordinary phenol, or carbolic acid, C 6 H 6 (OH). It is called a
monohydric phenol, by which is meant a phenol with one
hydroxyl group, and conveys the same idea as monohydric
applied to ethyl alcohol (p. 273). If more than one hydrogen
atom in benzene is replaced by hydroxyl, the compounds are
known as di- and trihydric phenols, &c.
C 6 H 4 (OH) 2 . C 6 H 3 (OH) 3 .
Dihydric phenol. Trihydric phenol.
Structurally, the phenols are analogous to the alcohols, but,
as the name carbolic acid implies, they possess a distinctly acid
character, inasmuch as they form salts with metallic hydroxides.
Ordinary phenol, though sparingly soluble in water, dissolves
readily in caustic soda, and on evaporating the solution yields a
[solid sodium compound. This is sodium phenate or carbolate,
;C 6 H 6 (ONa).
Amyl alcohol, which may be taken for comparison with phenol,
is, like phenol, sparingly soluble in water ; but the addition of
caustic soda produces no change.
It should be remembered that the true analogues of the phenols
are the tertiary alcohols containing the group ;C(OH) ; but they ex-
liiitit the same indifference to alkalis as the other alcohols.
450
THE PHENOLS 451
If we accept Kekule's formula for benzene, ordinary phenol will
ihave the following structure :
C(OH)
HC/^CH
HC
CH
The acidic character may be connected with the group CH:C(OH),
ailso present in acetoacetic ester, which has the property of forming a
sodium compound (p. 327).
There is another class of hydroxy-derivativesSpf the aromatic
hydrocarbons which possess the properties oT true alcohols.
The aromatic alcohols, as they are termed, differ in structure
from the phenols, inasmuch as they contain the hydroxyl group
in the side-chain. Benzyl alcohol, C 6 H 5 .CH 2 (OH), is a typical
aromatic alcohol. The aromatic alcohols will be described in
the following chapter (p. 467). Theory demands one mono-
hydroxy-benzene, three dihydroxy-benzenes (ortho, meta, and
para), and three trihydroxybenzenes. These are all known,
as well as the hydroxy-derivatives of toluene, termed cresols,
and of xylene, called xylenols, and many more. They all
possess similar properties.
CH 3 .C 6 H 4 (OH). (CH 3 ) 2 .C 6 H 3 (OH).
Cresols. Xylenols.
Sources of the Phenols. Many of the phenols are formed
t>y the destructive distillation of organic matter, e.g. wood and
coal. Wood-tar and coal-tar are rich in phenols, coal-tar being
the main source of ordinary phenol-. They are also formed, more
especially the di- and tri-hydric phenols, by fusion with caustic
potash of resins, tannins (p. 490), and the colouring matters
associated with them. Two synthetic methods for the prepara-
tion of phenols have been described, one of which, viz. the fusion
of the sulphonates with caustic alkalis, has an important
technical application (p. 446).
C 6 H 5 SO 3 Na 4- NaOH = C 6 H 5 (OH) -f Na 2 SO 3 .
The second method is the decomposition of diazo-salts with
-water (p. 429).
C 6 H 5 N:NC1 + H 2 O = C 6 H 5 (OH) + N 2 + HCI-
G 3 2
452 THEORETICAL ORGANIC CHEMISTRY CHAP.
By the second method all amino-compounds are available for
the preparation of phenols. A little reflection will show that
both reactions offer ready means of obtaining phenols from the
hydrocarbons (p. 442).
Properties of the Phenols. The phenols are generally
colourless, crystalline compounds of low melting-point, many of
which may be distilled without decomposition, or are volatile in
steam. They often have a characteristic smell, and possess a
strong antiseptic action. The solubility of the phenols in water
depends on the proportion of carbon to hydroxyl groups.
Ordinary phenol requires 1 5 parts of water for solution, whereas
hydroxy-cymenl, C 10 H IS (OH) is nearly insoluble ; on the
other hand, the di- and trihydric phenols are very soluble. They
all dissolve in alcohol and ether. With caustic alkalis they
form salts or phenates, as already explained ; but the phenols
being very weak acids, the phenates of the alkalis are strongly
alkaline to litmus, and are decomposed even by so feeble an acid
as carbonic acid.
EXPT. 154. Add a few c.c. of water to a few grams of ordinary
phenol. Little of the phenol dissolves ; but the addition of caustic
soda rapidly effects solution. Divide the solution into two parts and
add dilute sulphuric acid to one and pass carbon dioxide through
the other portion. Provided the solution is sufficiently concen-
trated, phenol will be precipitated as an oil from both solutions.
The decomposition of the phenates by carbon dioxide is used
in the separation of phenols from acids, the sodium salts of
which are not affected by carbon dioxide. After saturating the
alkaline solution with carbon dioxide, the phenol is separated
frorn the mixture by extraction with ether or distillation in steam,
whilst the acid remains as the sodium salt in the alkaline
solution.
Phenol Ethers and Esters. When the phenates of the alkalis
are boiled with the alkyl halides, phenol ethers, or alkyl
phenates, are obtained.
Sodium phenate and methyl iodide yield methyl phenate,
phenyl methyl ether, or methoxy-benzene
C 6 H 5 ONa + CH 3 I = C 6 H 5 OCH 3 + NaL
Methyl phenate.
xxxn THE PHENOLS 453
The methyl ethers are most conveniently prepared by warrn-
ing the phenol with dimethyl sulphate in alkaline solution
C 6 H 5 ONa + (CH 8 ) 2 S0 4 = C 6 H 5 OCH 3 + CH 3 NaSO 4 .
EXPT. 155. Mix I gram of phenol with I c.c. of dimethyl sulphate l
and add 4 c.c. of a 10 per cent, solution of caustic soda. Warm
and shake. The odour of phenol is replaced by that of anisole, which
can be extracted from the liquid by ether (Ullmann's reaction).
The phenol-ethers are fragrant smelling liquids or solids,
which are insoluble in water. Like the aliphatic ethers they
are decomposed by strong hydriodic acid (p. 121). Phenyl
methyl ether yields methyl iodide and phenol
C 6 H 6 OCH 3 -*- HI = C 6 H 5 OH + CH J.
Zeisel's Method. The reaction, just described, has been utilised for
the identification and estimation of the so-called methoxyl, .OCH 3 ,
and ethoxyl, .OC 2 H 5 , groups in phenol ethers and their derivatives.
Compounds of this nature frequently occur among the aromatic con-
stituents of vegetable products and their identification is a matter
of importance. The method is known by the name of Zetsel, the
discoverer, and consists in heating a weighed amount of the substance
in a distilling flask with a long neck with strong hydriodic acid in
a current of carbon dioxide. The methyl or ethyl iodide which is
evolved is passed through an alcoholic solution of silver nitrate,
whereby the alkyl iodide is decomposed and silver iodide deposited..
The weight of silver iodide represents the weight of alkyl iodide, and
consequently determines the presence and number of methoxyl, or
ethoxyl, groups in the compound.
Reactions of the Phenols. Phenols play the part of
alcohols not only in giving ethers but in forming esters with
acids. When phenol is heated with acetyl chloride and acetic
anhydride, the phenyl ester of acetic acid is formed
C 6 H 5 OH + CLCOCHs = C 6 H 5 O.CO.CH 3 + HCI.
Phenyl acetate.
In the behaviour of the phenols with nitric and sulphuric acids,
the benzenoid predominates over the alcoholic character, and in
place of nitric and sulphuric esters, such as the alcohols form
(p. 187), nitro-derivatives and sulphonic acids are produced;
indeed, the presence ofhydroxyl greatly facilitates the formation
of these compounds. Phenol yields mono-, di-, and trinitro-
1 The vapour of dimethyl sulphate is very poisonous and care should be taken
not to breathe it.
454 THEORETICAL ORGANIC CHEMISTRY CHAP.
phenols with nitric acid, and phenolsulphonic acid witi
sulphuric acid
C 6 H 5 OH -f HN0 3 = (OH)C 6 H 4 (N0 2 ) + H.,O.
Nitrophenol.
C 6 H 5 OH + H 2 S0 4 = (OH)C 6 H 4 .S0 3 H + H 2 O.
Phenolsulphonic acid.
The amino-phenols are obtained by the reduction of the
nitro-compounds, and certain of them have found application in
photography as developers. Metol is ^-methylaminophenol sul-
phate. Many of the reactions of the phenols have already been
mentioned. The hydroxyl group may be replaced by chlorine
or bromine by the action of phosphorus pentachloride or penta-
bromide (p. 399). The phenols unite with diazo-salts to form
important azo-dyes (p. 438). Furthermore, by heating phenol
with the compounds of zinc chloride, or calcium chloride and
ammonia, the hydroxyl is replaced by the amino-group and
aromatic amino-compounds result. Phenol yields aniline
C 6 H 5 OH + NH 8 - C 6 H 5 NH 2 + H 2 O.
The reaction has a technical value in connection with the
preparation of amino-naphthalene, or naphthylamine (p. 536),
which will be referred to again.
When phenols are distilled over hot zinc dust, the hydroxyl
is replaced by hydrogen. Ordinary phenol forms benzene
C 6 H 5 OH + Zn = C 6 H 6 + ZnO.
The phenols are frequently characterised by colour reactions
with ferric chloride. Some phenols (ordinary phenol and
resorcinol) give a violet colour, others (the cresols and phloro-
giucinol) a blue colour, others again (catechol) a green colour.
Another colour reaction of the phenols is known as Liebermann's
reaction, and has already been described as a test for nitroso-
compounds (p. 416). The same reaction may be used as a test for
phenols, using sodium or potassium nitrite as the nitroso-com-
pound.
EXPT. 156. Liebermanns reaction. Add a small fragment of
solid sodium nitrite to 5 c.c. of strong sulphuric acid, and warm very
gently until it is dissolved. Add now about 0*5 gram of phenol. A
brown solution is obtained, which, on warming, rapidly changes to deep
blue. If the blue solution is poured into water, a cherry red coloration
is produced, which changes to blue again on the addition of caustic soda.
THE PHENOLS 455
In presence of alkalis, the phenols undergo oxidation,
more or less readily, by absorbing oxygen from the air. A
solution of a trihydric phenol in alkalis causes immediate
absorption of oxygen ; and even ordinary phenol, which
is comparatively stable in alkaline solution, is converted into
di- and tri-hydric phenols on fusion with caustic alkalis
(p. 464).
Many of these reactions will be referred to again in the
description which follows of the more important individuals of
the phenol group.
Ordinary Phenol, Carbolic acid, Phenic acid, Hydroxy-
benzene, C 6 H 5 (OH). Phenol was discovered by Runge in 1834
in coal tar, which is the present sou/ce of the substance. The
middle or carbolic oil (p. 381), obtained in the distillation of
coal-tar, contains the greater part of the phenol. It is shaken
up with just sufficient caustic soda solution to dissolve the
phenol. The alkaline liquid is then removed from the un-
dissolved oil (which is subsequently worked up for naphthalene
(p. 527) and acidified with sulphuric acid. The crude phenol
separates on the surface as a dark-coloured oil, and, after
standing, is carefully removed and distilled. The distillate
constitutes the crude carbolic acid of commerce. In order to
obtain the colourless crystals of the pure substance, the crude
carbolic acid is fractionated, when the greater part of the distil-
late solidifies on cooling or freezing, and any residual liquid is
drained off. One ton of coal yields about \\ Ib. of
phenol. Phenol is also made synthetically from benzene
through the sulphonate (p. 451), and from aniline by the diazo-
reaction (p. 429).
Phenol forms large, colourless crystals, which melt at 42 and
boil at 183. On exposure to air and light it turns a pink colour.
Phenol has the well-known smell associated with sanitary
disinfecting preparations, for which it is largely used. Carbolic
powders are made by mixing phenol with a variety of ingredients,
such as china clay, &c. Pure phenol has a strongly corrosive
action on the skin, producing sores which heal with difficulty.
A very dilute solution (3 per cent.) is therefore used for washing
wounds or cleansing the skin. Taken internally it acts as a
strong poison.
Phenol is used in the manufacture of salicylic acid (p. 487).
salol (p. 488), picric acid (p. 458), phenacetin (p. 457), and for
other purposes, which will be described later.
456 THEORETICAL ORGANIC CHEMISTRY CHAP.
Reactions of Phenol. When phenol is chlorinated or
brominated, it forms the 2-4-6 -trichloro- or tribromo-compounds,
following the ortho-para-law of substitution (p. 408).
The formation of the insoluble tribromophenol, when bromine is
added to phenol, is utilised in its analysis. A standard solution is
prepared, containing sodium bromide and bromate in the proportion of
5 molecules to I molecule, by dissolving bromine in hot caustic soda
6NaOH + 3Br 2 = $NaBr + NaBrO 3 + 3H 2 O.
When the solution is acidified, bromine is liberated
SNaBr + NaBrO 3 + 6HC1 = 6NaCl + 3Br 2 + sH 2 O.
If phenol is present, the tribromo-compound is precipitated, and the
free bromine, which should always be in excess, is estimated by adding
potassium iodide and titrating the free iodine with sodium thiosulphate
solution in the ordinary way.
When oxidised with hydrochloric acid and potassium chlorate,
phenol is converted into tetrachloroquinone or chloranil,
C 6 C1 4 2 (p. 477).
Phenol gives colour reactions with ferric chloride and
Liebermann's reaction, which, however, are shared by other
phenols and are not distinctive tests (p. 454). If ammonia is
added to phenol and a few drops of sodium hypochlorite,
a blue colour is developed on warming.
Phenol Ethers. The general formation of phenol ethers has
been briefly mentioned (p. 452). Methyl phenate, or anisole,
C 6 H 6 OCH 3 , is obtained by adding the equivalent of one atom
of sodium dissolved in alcohol to phenol (i mol.)and boiling for
some time with methyl iodide (i mol.) The product is poured
into water, in which the anisole is insoluble, and the anisole is
removed and fractionated
C 6 H 5 ONa + CH 3 I = C H 5 OCH 8 + Nal.
Anisole.
Ethyl phenate, or phenetole, C 6 H 5 OC 2 H 5 , is obtained in a
similar way. They are both fragrant smelling liquids. Anisole
was originally obtained from anisic acid, which in turn was pre-
pared by the oxidation of anethole, the sweet-smelling constituent
of oil of aniseed. The relation of the three compounds is
represented by the following formulas :
THE PHENOLS 457
OCH 3 OCH 3
/\
\/
CH:CH.CH 3 COOH
Anethole. Anisic acid. Anisole.
Nitrophenols. Strong nitric acid attacks phenol vigorously
and forms resinous products. In order to obtain the mono-
nitro-derivatives, the nitric acid is somewhat diluted with water
and the phenol is slowly added. Both ortho- and para-nitro-
phenol are formed, in accordance with the law of substitution
(p. 407). The two substances are separated by distillation in
steam. The ortho-compound distils, whereas the para-com-
pound is non-volatile and remains in the distilling flask, from
which it is extracted with water. The two isomers present a
curious contrast in properties.
The ortho-compound has a bright yellow colour, melts at
45 and has a peculiar tarry smell. The para- compound is
colourless and odourless and melts at 114. They both form
well-crystallised sodium and potassium salts, which are not
decomposed by carbon dioxide, The substances are, in fact,
stronger acids than phenol, and the property is enhanced with
each additional nitro-group (see Picric Acid, below).
/-Nitrophenol is also prepared from /-nitracetanilide, which
is obtained by nitrating acetanilide in presence of acetic
acid. ^-Nitracetanilide is hydrolysed and converted into
^-nitraniline, which is then diazotised in the usual way,
whereby the amino-group is exchanged for hydroxyl (p. 429).
^-Nitrophenol is prepared in the same way from m-
nitraniline (p. 432). ^-Nitrophenol is used in the prepara-
tion of phenacetin, or ^-acetaminophenetol, (C 2 H 5 O)C e H 4 .
(NH.CO.CH 3 ), which is used in medicine for neuralgia and
headache. The nitrophenol is converted into the nitrophenyl
ethyl ether, then reduced to aminophenol, and acetylated
(OH)C 6 H 4 (N0 2 ) -> (C 2 H 5 0)C 6 H 4 (N0 2 ) -> (C 2 H 5 O)C 6 H 4 (NH 2 )
/-Nitrophenol. /-Nitrophenyl ethyl ether. /-Aminophenetole.
-> (C 2 H 5 0)C 6 H 4 (NHC 2 H 3 0).
Phenacetin.
Other derivatives of ^-aminophenetole are also used as antipyretics ;
such are the glycocoll compound, (C 2 H 5 O)C 6 H 4 NH.CO.CH 2 .NH 2 ,
or phenocoll, and the lactyl derivative or lactophenin.
458 THEORETICAL ORGANIC CHEMISTRY CHAP.
w-Aminophenol and its derivatives are largely used in the
manufacture of the important dyes, known as rhodamines (p. 521).
Picric Acid, 2-4-6-Trinitrophenol, C 6 H 2 (OH)(NO 2 ) S , is the
final product of the direct nitration of phenol, and is also formed
when nitric acid acts on many organic substances, such as silk,
wool, leather, &c.
In the manufacture of picric acid phenolsulphonic acid is
nitrated in place of phenol, and the formation of tarry and
resinous by-products is thereby avoided.
Phenolsulphonic acid is obtained by warming phenol with
sulphuric acid on the water-bath (both ortho- and para-sul-
phonic acids are formed, the ortho-compound predominating
when the action occurs at a low temperature, and becoming
gradually transformed into the para-compound at 100). The
phenolsulphonic acid is then added slowly to strong nitric acid
and subsequently heated.
C 6 H 4 (OH)S0 3 H + sHNO s = C 6 H 2 (OH)(NO 2 ) 3 + H 2 SO 4 + sH 2 O.
Phenolsulphonic acid. Picric acid.
EXPT. 157 . Preparation of Picric Acid. Dissolve about 2 grams
of phenol in 2 c.c. of strong sulphuric acid by gently warming ; cool,
and pour the solution slowly into 6 c.c. of strong nitric acid. Red
fumes are evolved. When the action has abated, heat the product on
the water-bath for a quarter of an hour with the addition of a little
fuming nitric acid, and then pour into cold water. Yellow crystals of
picric acid immediately separate.
Picric acid is a lemon-yellow, crystalline compound, melting
at I22'5. It dissolves in water very sparingly with a yellow
colour. The petroleum solution, on the other hand, is colourless. 1
The presence of the nitro-groups has the effect of converting
phenol into a strong acid ; for picric acid decomposes carbonates
of the metals, and forms a series of well-crystallised salts or
picrates. Moreover, picryl chloride^ C 6 H 2 (NO 2 ) 3 C1, which is
obtained by the action of phosphorus chloride on picric acid, is
an acid chloride, and forms picramide, or trinitraniline, with
ammonia. Many of the picrates explode on percussion, although
picric acid itself burns quietly when ignited. The fused acid,
however, becomes a violent explosive when detonated, and enters
1 The yellow colour of the aqueous solution is attributed to the dissociation of
picric acid into its electro-negative ion, CsH^NOo^O, which is yellow, and
hydrogen, the positive ion. In petroleum no dissociation takes place, and the liquid
is therefore colourless.
THE PHENOLS 459
into the composition of lyddite and melinite. It also explodes
when mixed with lead peroxide and heated.
EXPT. 158. Mix cautiously a quantity of picric acid, sufficient to
be heaped upon a threepenny piece with rather more than its bulk of
red lead ; place the mixture in the centre of a metal tray, and heat
it with a small flame. The mixture explodes with great violence.
Picric acid is used as a dye for wool and silk. It
has the property of uniting with aromatic hydrocarbons and
ammo-compounds and forming well-crystallised compounds.
The picrate of benzene, C 6 H 6 .C 6 H 2 (OH)(NO 2 ) 3 , is colour-
less ; naphthalene picrate, C 10 H 8 .C 6 H 2 (OH)(NO 2 ) 3 , is yellow.
Anthracene and many of its homologues form compounds which
have a brilliant red colour (p. 520). The compound with aniline
has the formula C 6 H 5 NH 2 .C 6 H 2 (OH)(NO 2 ) 3 .
The presence of picric acid is sometimes detected by its
affinity for wool and silk, which are rapidly dyed a yellow
colour in a warm solution without any mordant. When a
solution of picric acid is warmed with a solution of potassium
cyanide, the liquid becomes a deep violet colour, and deposits,
on cooling, a crystalline compound, known as isopurpuric acid.
When nitrous acid acts upon phenol it forms a compound,
which is known as nitrosophenolm quinonoxime. The compound
is an example of tautomerism. It behaves, on the one hand,
like a nitroso-compound, giving Liebermann's reaction and
aminophenol on reduction. On the other hand, it is prepared
like an oximeby the action of hydroxylamine on quinone (p. 4 76).
C(OH) C:0
C(NO) ONOH
Tautomeric forms of Nitrosophenol.
Cresols, Cresylic acids, Hydroxy toluenes, C 6 H 4 (CH 3 )OH.
The three isomers o- m-, and /-cresol are present in
coal-tar. The crude cresylic acid is the higher-boiling portion
(198 203) of the coal-tar phenol which is separated during
fractional distillation, or drained from the crystals of phenol.
When emulsified with oil or soap, it is used without further
4 6o THEORETICAL ORGANIC CHEMISTRY CHAP.
treatment as a disinfectant and cheap substitute for phenol.
The pure cresols may be obtained by one of the general
synthetic methods already described. They give a blue colora-
tion with ferric chloride.
Among the higher monohydric phenols are the hydroxy-
cymenes, carvacrol and thymol, both of which are vegetable
products
CH 3 CH 3
/\ /\OH
/OH
v^ 3 n 7 Q 3 H>7
Thymol. Car vac. ol.
Thymol is a crystalline compound, which is present with
cymene in oil of thyme, to which it imparts its fragrant smell.
It is used as an antiseptic, and so is its iodine derivative, known
as aristol. Carvacrol is found in origanum oil (Origanum
hirtuni). It is also obtained from carvone, C 10 H 16 O, a con-
stituent of caraway oil, by heating with phosphoric acid, and
from camphor by distilling with iodine.
THE DIHYDRIC PHENOLS
The dihydroxy-benzenes exist in three isomeric forms ; the
ortho-compound is called catechol, the meta, resorcinol, and the
para, quinol
OH OH OH
AOH
\/ \/ w XX
OH
Catechol. Resorcinol. Quinol.
Catechol, C 6 H 4 (OH) 2 , was originally obtained by distilling
catechu (the extract of the Indian Acacia catechu}^ and by
fusing certain natural resins with potash. It is also prepared
from 0-phenolsulphonic acid by fusing the potassium salt with
potash
C 6 H4(OH)SO 3 K + KOH = C 6 H 4 (OH) 2 + K 2 SO 3 .
Potassium-0-phenol- Catechol.
sulphonate.
1 Catechu, or cutch, consists mainly of catechin and a tannin (p. 400), which
appear to be chemically related ; for they both contain a catechol group in the
molecule.
THE PHENOLS 461
A convenient method for obtaining catechol is by the action
of hydriodic acid on guaiacol or methyl catechol, a colourless
liquid which is present in beech-wood tar
C 6 H 4 (OH)OCH 3 + HI = C 6 H 4 (OH) 2 + CH 3 I.
Guaiacol. Catechol.
The best method, however, is to oxidise 0-hydroxybenzalde-
hyde with an alkaline solution of hydrogen peroxide
C 6 H 4 (OH).CHO 4- H 2 O 2 = C 6 H 4 (OH) 2 + H.COOH.
Catechol crystallises in colourless plates which melt at 104.
It gives a green coloration with ferric chloride, which changes
to red on the addition of sodium bicarbonate solution. This
reaction is characteristic of all ortho-dihydric phenols. Catechol
reduces Fehling's solution.
Resorcinol, C 6 H 4 (OH) 2 . Resorcinoi can be obtained by a
variety of synthetic methods. The industrial process is to fuse
the sodium salt of w-benzenedisulphonic acid (p. 428) with
caustic soda
C 6 H 4 (S0 8 Na) a + 2NaOH = C 6 H 4 (OH) 2 + 2^803.
Sodium-w-benzene- Resorcinoi.
disulphonate.
Resorcinoi crystallises in colourless needles which melt at
119. It has a sweetish taste, and is very soluble in water.
The reactions of resorcinol resemble those of phenol.
With bromine, tribromoresorcinol is precipitated. Ferric
chloride gives a violet coloration. It reduces Fehling^s solution
and ammonia-silver nitrate like a sugar. Resorcinoi is used in
the preparation of fluorescein and the eosin dyes (p. 520). The
fluorescein reaction is characteristic of meta-dihydric phenols
on the one hand, and of anhydrides of dibasic acids, such as
succinic acid (p. 347) of the aliphatic series, and phthalic acid
(p. 492) of the aromatic series, on the other. Ordinary
fluorescein is formed by fusing at 200 a mixture of resorcinol
and phthalic anhydride C 6 H 3 (OH)
/ C \ >
X CO V */ | X C 6 H 3 (OH)
C 6 H/ >0 + 2C 6 H 4 (OH) 2 = C 6 H 4 <; O
\ |
x co
Fiuores'cein.
462 THEORETICAL ORGANIC CHEMISTRY CHAP.
Fluorescein dissolves in dilute caustic alkalis and in alcohol
with a brilliant green fluorescence.
EXPT. 159. Heat together over a small flame about 0*25 gram of
phthalic anhydride and 0-5 gram of resorcinol for a minute, taking care
not to raise the temperature too high. It is advisable to hold the
test-tube a little above the flame. Let the mixture cool, dissolve it
in a little caustic soda solution, and pour it into water. The liquid
shows a brilliant green fluorescence.
Orcinol, m-Dihydroxytoluene, CH 3 .C 6 H 3 (OH) 2 , is obtained
from Orcina and other lichens. Orcinol resembles resorcinol,
and gives the fluorescein reaction.
Quinol, Hydroquinone, C 6 H 4 (OH) 2 . Quinol is occasionally
found among vegetable substances. It is present in bearberry
in combination with glucose, as the glucoside, arbutin. It is
usually obtained from quinone, C 6 H 4 O 2 (p. 4/6), by reduction
with sulphurous acid, and extraction with ether
C 6 H 4 2 + H 2 + H 2 S0 3 = C 6 H 6 2 + H 2 SO 4 .
Quinone. Quinol.
EXPT. 1 60. Dissolve a few of the yellow crystals of quinone in
water, and add sulphurous acid. The solution is decolorised.
Extract with a little ether and decant the ethereal solution on to a
watch-glass. On evaporation, colourless crystals of quinol are
deposited.
Quinol is readily oxidised to quinone by ferric chloride and
other oxidising agents.
EXPT. 161. Dissolve a few crystals of quinol in water, and add
a few drops of ferric chloride. The solution turns yellow and con-
tains quinone. The dirty-green coloration, which is observed on
first adding the ferric chloride, is due to the formation of a compound
of quinol and quinone, known as quinhy 'drone , C 6 H 4 O 2 .C 6 H 4 (OH) 2 .
Quinol crystallises in colourless needles which melt at 169.
It is very soluble in water, and its reducing properties in alkaline
solution render it a useful photographic developer.
XXXII
THE PHENOLS
463
THE TRIHYDRIC PHENOLS
The three trihydroxybenzenes have the following structural
formulae and names :
OH
t OH
OH
OH
;OH
Pyrogallol.
X)H
Phloroglucinol.
OH
OH
1-2-4-Trihydroxy benzene.
Pyrogallol, Pyrogallic acid, C 6 H 3 (OH) 3 . Pyrogallol was
first obtained by Scheele in 1786 by heating gallic acid, and the
process is still used for its preparation. When gallic acid is
heated it loses carbon dioxide
C 6 H 2 (OH) 3 COOH = CH 3 (OH) 3 + CO 2 .
Gallic acid. Pyrogallol.
Pyrogallol melts at 132 and is very soluble in water. In
alkaline solution it rapidly absorbs oxygen
and darkens in colour. Among the pro-
ducts of oxidation, acetic acid, carbon
dioxide, and a little carbon monoxide have
been detected. The property is utilised
in gas analysis for estimating oxygen.
EXPT. 162. Take a long tube closed at
one end and furnished with a cork holding
a glass tap (Fig. 87). Introduce a few
grams of pyrogallol, and then fill the tube
with oxygen from a cylinder. Quickly
introduce a little solution of caustic soda,
close the tube and shake for a minute. On
opening the tap under water, water rapidly -M
ascends the tube, indicating absorption of H
oxygen gas.
FIG. 87.
Pyrogallol reduces gold, silver, and
mercury solutions, and is extensively used as a photographic
developer.
It gives a red coloration with ferric chloride, and a blue
464 THEORETICAL ORGANIC CHEMISTRY CHAP.
coloration with ferrous sulphate containing a little ferric
chloride,
Phloroglucinol, symm. Trihydroxybenzene, C 6 H 3 (OH) 3> is a
constituent of certain resins (gamboge, dragon's blood), some of
the tannins (p. 490), and certain natural yellow colouring matters,
from all of which it is separated by fusion with potash. It is
most conveniently prepared from resorcinol by fusion with
caustic soda, whereby the resorcinol takes up an additional
atom of oxygen from the air
C 6 H 4 (OH) 2 + O = C 6 H 3 (OH) 3 .
Resorcinol. Phlorglucinol.
It has also been obtained by synthesis from malonic ester,
the details of which cannot be given here.
Phlorglucinol crystallises with two molecules of water. It
gives a blue-violet coloration with ferric chloride, it reduces
Fehling's solution, and absorbs oxygen in presence of caustic
alkalis. It is used as a reagent for the pentoses (p. 312).
Dissolved in strong hydrochloric acid, it turns pink on warm-
ing in presence of a pentose, a reaction which is readily
demonstrated with a piece of match-wood containing xylose.
Phloroglucinol yields phloroglucitol, C 6 H 9 (OH) 3 , on reduction.
Phloroglucinol offers an interesting example of tautomerism (p. 327).
On the one hand, it behaves as a trihydric phenol, forming trialkyl and
triacyl derivatives. On the other hand, it exhibits the properties of
ft triketone, and yields a trioxime with hydroxylamine. The two
structural forms will be represented as follows
C(OH)
HC\CH H 2 C
CH
Tautomeric forms of Phloroglucinol.
The third isomer, or 1-3-4-trihydrozybenzene, has little specia\
interest. It is obtained by fusing quinol with caustic soda, ii;
the same way that resorcinol is converted into phlorglucinol.
Other Hydroxybenzenes. The potassium salt of hexahydroxy benzene,
C 6 (OK) 6> is formed when carbon monoxide is passed over heated
xxxii THE PHENOLS 465
potassium. It is in itself quite stable, but, on standing, under-
goes a change and becomes extremely explosive. The compound is a
constituent of the black mass, which is formed during the distillation of
potassium in the course of manufacture. An interesting class of com-
pounds, which have certain points of resemblance with the hexahydric
alcohols (p. 285), and hexoses (p. 287), are the hydroxy-derivatives of
hexahydrobenzene, C 6 H 12 . Qttercttol, C 6 H 7 (OH) 5 , is found in acorns.
It is a crystalline substance with a sweet taste, and dissolves in water,
but does not ferment. Inositol, C 6 H 6 (OH) 6 , of which two active forms
and one inactive form are known, is contained in unripe peas^and beans.
These substances appear to take the place of the vegetable carbo-
hydrates.
QUESTIONS ON CHAPTER XXXII
1. Explain the meaning of the term phenol. Compare and contrast
arnyl alcohol and ordinary phenol. Is this comparison with amyl alcohol
a legitimate one ?
2. Give examples of mono-, di-, and trihydric phenols. Name any
properties by which a phenol may be distinguished from a member of
any of the previous groups of compounds, and devise a method for
separating ordinary phenol from (i) benzene, (2) chlorobenzene,
(3) nitrobenzene, and (4) aniline.
3. Give a list of the natural sources of the phenols, and describe the
preparation of carbolic acid from coal-tar.
4. In what manner may the phenols be obtained from the hydro-
carbons ? Mention two methods.
5. Describe a method for separating the phenols from organic acids.
Illustrate this in the case of a mixture of acetic acid and carbolic
acid.
6. Describe and explain Zeisel's method for estimating methoxyl and
ethoxyl groups in phenol ethers. Ca culate the number of methoxyl
groups in a compound of the formula C 8 H 8 O 3 from the following data :
0*2338 gram of substance gave 0*3598 gram of silver iodide.
7. How can phenol be (l) obtained from benzene and aniline ; and
(2) converted into benzene and aniline ? Describe the action of the
following reagents on phenol : (i) caustic soda, (2) bromine, (3) phos-
phorus pentabromide, (4) nitric acid, (5) sulphuric acid, and (6) acetyl
chloride.
8. Describe Liebermarm's test for phenols. What other reactions
are characterististic of the phenols as a class?
9. Describe methods of preparing and distinguishing the three
isomeric dihydroxy benzenes.
H H
4 66 THEORETICAL ORGANIC CHEMISTRY CH. xxxn
10. Mention some of the properties of pyrogallol. How is it dis-
tinguished from phloroglucinol ?
11. How are the three mononitrophenols obtained ? How are the
ortho- and para-compounds distinguished, and for what purpose is the
para-compound employed ?
12. Describe the preparation of picric acid. Why is it termed an
acid ? Compare it with carbolic acid. What are its technical uses ?
13. What is anisole ? In what relation does it stand to aniseed oil r
How can anisole be synthesised ?
CHAPTER XXXIII
AROMATIC ALCOHOLS, ALDEHYDES, KETONES,
AND QUINONES
*
AROMATIC ALCOHOLS
IF hydrogen in the side-chain of an aromatic hydrocarbon
is replaced by hydroxyl, the aromatic alcohols result. Little
more need be said about these compounds than that they
resemble the aliphatic alcohols, both in their method of pre-
paration and in their chemical properties (p. 94). They are
naturally less soluble in water than the simpler members of the
aliphatic series by reason of the large proportion of carbon to
hydroxyl ; their higher boiling-point is owing to their higher
molecular weight ; but they form esters with acids and undergo
oxidation to aldehydes, ketones, and acids, after the usual
manner of alcohols. The most important features of the
aromatic alcohols may be best illustrated by studying benzyl
alcohol, the simplest member of the group.
Benzyl Alcohol, C 6 H 5 .CH 2 (OH), is isomeric with the cresols.
It is found in Peru and Tolu balsam and in storax (the exudation
from Styrax offitinalis, a shrub which grows in the East) as the
benzyl ester of benzoic and cinnamic acids (p. 496).
Benzyl alcohol is most easily prepared by boiling benzyl
chloride with a solution of potassium carbonate, until the
pungent smell of the chloride vanishes.
2C 6 H S .CH 2 C1 + KjjCa, -f H 2 O = 2C 6 H 5 .CH 2 (OH) + 2KC1 + CO 2 .
Benzyl alcohol.
The product is extracted with ether, which dissolves the
alcohol ; the ether is removed and the benzyl alcohol distilled.
467 H H 2
468 THEORETICAL ORGANIC CHEMISTRY CHAP.
Benzyl alcohol is also obtained by the action of caustic potash
solution on benzaldehyde. Two molecules of benzaldehyde
take part in the reaction, one molecule being oxidised to
benzoic acid at the expense of the other, which is reduced to
benzyl alcohol
C 6 H 5 C!HjO"+"C 6 H 5 CHOi
1 = C 6 H 5 COOK + C 6 H 5 .CH 2 (OH).
+ OK H Potassium Benzyl alcohol,
benzoate.
The semi-solid product is dissolved in water and extracted
with ether, which separates the benzyl alcohol from the potas-
sium benzoate.
This reaction is specially characteristic of aromatic aldehydes
which contain the aldehyde group in the nucleus, and is not
shared by the lower aldehydes of the aliphatic series (p. 131),
although some of the higher members behave in a similar
fashion. Benzyl alcohol can also be prepared by the hydrolysis
of its esters.
It is a colourless liquid with a faint aromatic smell, which
boils at 206 and is moderately soluble in water. It is readily
distinguished from the isomeric cresols by its smell, and by
its behaviour with caustic soda, hydrochloric and nitric acids.
Benzyl alcohol, unlike the cresols, does not dissolve in caustic
soda more readily than it does in water ; on warming benzyl
alcohol with strong hydrochloric acid, the liquid, which is at
first clear, becomes turbid from the separation -of fine drops of
benzyl chloride which gradually rise and form a layer on the
surface.
C 6 H 5 CH 2 OH + HC1 = C 6 H 5 CH 2 C1 + H 2 O.
When strong nitric acid is added slowly to benzyl alcohol,
heat is developed and nitrous fumes are evolved. When the
action has ceased and a little alkali added to neutralise the acid,
the smell of benzaldehyde is at once perceived.
2C 6 H 5 CH 2 OH + 2HNO 3 = 2C 6 H 5 CHO + sH 2 O + N 2 O 3 .
AROMATIC ALDEHYDES
The aldehydes, like the hydroxy-compounds, may be divided
into two classes, those which contain the aldehyde group in the
side-chain and those in which it is present in the nucleus. There
xxxm AROMATIC ALDEHYDES 469
is not, however, that marked difference in the properties of the
two classes of compounds which separates the aromatic alcohols
from the phenols. There aie certain minor differences to which
attention will be drawn ; but, broadly speaking, they resemble
one another as well as the aliphatic aldehydes. Like the ali-
phatic compounds, the aromatic aldehydes undergo an unusual
variety of chemical changes, many of which must be omitted
for want of space. As in the foregoing chapters, we shall study
the group by selecting from it a common and typical member.
Benzaldehyde, Oil of Bitter Almonds, C 6 H 5 .CHO. Few
compounds have played so important a role in the development
of organic chemistry as benzaldehyde ; whether we consider it
historically, as affording by its chemical changes the first clear
conception of the term compound radical (p. 83), or chemically,
as marking the rapid progress of synthetic organic chemistry.
Benzaldehyde was originally obtained from bitter almonds,
in which, as Wohler showed, it is present as the glucoside,
amygdalin (p. 211). When amygdalin is boiled with dilute acids,
it is hydrolysed and yields benzaldehyde, hydrocyanic acid, and
glucose. The same change occurs if the almonds are crushed
in a mortar with a few drops of water. In the second case,
the ferment emulsin which is present in the almonds is the
hydrolytic agent. The benzaldehyde may be removed by dis-
tilling in steam, and purified by the method described below.
EXPT. 163. Grind up a few bitter almonds with a little water in
a mortar, and leave them for half an hour. The smell of the alde-
hyde and of hydrocyanic acid will be perceived.
Benzaldehyde is prepared by the oxidation of benzyl alcohol
with strong nitric acid or nitrogen tetroxide (p. 467), or by
distilling a mixture of calcium benzoate and calcium formate
(p. 127),
C 6 H 5 :COOca'
- C 6 H 5 CHO + CaC0 3 .
+ H COjOca' Benzaldehyde.
Another method is to oxidise toluene, diluted with carbon
bisulphide, by means of chromium oxychloride. A brown
precipitate is formed, which is separated by filtration and
decomposed with water. The composition of the precipitate is
net known, but, on adding water, it yields benzaldehyde and
470 THEORETICAL ORGANIC CHEMISTRY CHAP.
chromic chloride. The laboratory method of preparing benz-
aldehyde is to oxidise benzyl chloride by boiling it with a
solution of copper nitrate
2C 6 H 5 .CH 2 C1 + Cu(NO 8 ) a = 2C 6 H 5 CHO + CuG 2 + 2HNO,.
The product is distilled in steam, and the distillate, which
contains the aldehyde, is extracted with ether.
It is manufactured on a large scale from benzal chloride by
heating it with milk of lime under pressure in an iron vessel
C 6 H 5 CHC1 2 + H 2 O + CaO = C fi H 5 CHO + CaCl 2 + H 2 O.
Benzaldehyde can be readily purified by converting it into the
crystalline bisulphite compound, which is washed with ether to
remove impurities, and then decomposed with dilute sulphuric
acid in a current of steam
C 6 H 5 CH(OH)SO 3 Na + H 2 SO 4 = C 6 H 5 CHO + Na 2 SO 4 + H 2 O + SO 2 .
EXPT. 164. Shake up a few c.c. of benzaldehyde with an equal
volume of a strong solution of sodium bisulphite. It immediately
solidifies to a mass of crystals of the bisulphite compound.
Properties of Benzaldehyde. Benzaldehyde is a colourless
liquid, which boils at 179 and possesses a fragrant smell of
bitter almonds. It quickly oxidises on exposure to the air ana
forms benzoic acid. A bottle of benzaldehyde will generally
contain crystals of benzoic acid in the neck.
The process is not one of ordinary oxidation ; for it is a remarkable
fact that strong nitric acid does not oxidise benzaldehyde in the
cold ; but forms the nitro-derivative (p. 472). It appears that
during oxidation in air benzaldehyde first takes up a molecule of
oxygen and forms the peroxide of benzoic acid, QH 5 .CO 2 .OH,
which acts as the oxidising agent in the process, yielding atomic
oxygen to another benzaldehyde molecule and becoming itself con-
verted into benzoic acid.
Benzaldehyde gives SchifFs reaction (p. 132). It slowly
reduces ammonia-silver nitrate, and alkaline copper solution,
which may be in part accounted for by its insolubility in water.
It forms a bisulphite compound described in Expt. 144, and a
cyanhydrin with hydrocyanic acid
C fi H 5 CHO + HCN = QH 5 CH(OH)CN.
Benzaldehyde cyanhydriu.
xxxin AROMATIC ALDEHYDES 47E
With phenylhydrazine, benzaldehyde forms a phenylhydrazone,
C 6 H 5 CH:N.NHC 6 H 5 .
EXPT. 165. Make a dilute solution of phenylhydrazine acetate
(p. 130), and add it to a drop of benzaldehyde. A yellow,
crystalline precipitate of the hydrazone is thrown down.
With hydroxylamine, benzaldehyde yields benzaldoxime,
ff:N.OH.
C 6 H 5 CHJOTH ? JNOH = C 6 H 5 .CH:NOH + H 2 O.
Benzaldoxime.
In reality, two oximes of benzaldehyde are known ; one is obtained
by adding hydroxylamine hydrochloride to the benzaldehyde mixed
with caustic soda, and extracting the benzaldoxime with ether. The
second is prepared by passing hydrochloric acid into the ethereal
solution of the first aldoxime ; the hydrochloride of the second
benzaldoxime is formed, from which the oxime is liberated by the
addition of alkali and extraction with ether. The first melts at 34 ;
the second melts at 130, becoming slowly transformed into the lower-
melting compound. The difference between the two compounds is
attributed to a space arrangement of the atoms, of the same character
as that described under fumaric and maleic acid (p. 363). The two
stereo-isomers are usually represented by the following formulae, and
are distinguished by the names syn and anti, which correspond to
cis and trans among the stereo- isomeric acids.
C 6 H 5 .CH C 6 H 5 .CH
II l|
N.OH. HO.N
/3 or Benzjj'Tzaldoxime, a or Benza//aldoxime,
m. p. 130. m. p. 34.
This theory of the isomerism of the benzaldoximes is due to
Hantzsch and Werner. Similar relations exist among the isomeric
oximes of the aromatic ketones (p. 474).
So far benzaldehyde exhibits a close correspondence with the
aliphatic aldehydes. It is distinguished from them by its be-
haviour with the caustic alkalis, ammonia, and potassium cyanide.
The action of caustic potash on benzaldehyde in producing
benzyl alcohol and benzoic acid has already been described
(p. 468). When strong ammonia solution is added to benz-
aldehyde, a crystalline compound is gradually deposited, which
472 THEORETICAL ORGANIC CHEMISTRY CHAP.
is not an aldehyde-ammonia, but a substance known as
hydrobenzamide, which is formed as follows
3 C 6 H 5 CHO + 2NH 3 = (C 6 H 5 CH) 3 N 2 + 3 H 2 O.
Hydrobenzamide.
At a low temperature an aldehyde-ammonia of the formula
(C 6 H 5 CHO) 2 NH 3 is formed.
When benzaldehyde is boiled with an aqueous-alcoholic
solution of potassium cyanide, condensation of two molecules
of the aldehyde occurs, resembling the aldol condensation
(p. 132). The product is called benzoin, and is a colourless,
crystalline compound melting at 137
C 6 H 5 CHO C 6 H 5 .CH(OH)
C 6 H 5 CHO ~ C 8 H 8 .CO
Benzoin.
Benzoin is an alcoholic ketone, which, like fructose, readily
takes up oxygen and reduces Fehling's solution. The product
of oxidation is the diketone, benzil, C 6 H 5 .CO.CO.C 6 H 5 . It is
more conveniently prepared by boiling benzoin with nitric acid.
Benzaldehyde is used in the manufacture of benzaldehyde
(malachite] green and other colours ; in the preparation of
cinnamic acid, and for a variety of synthetic processes, some of
which will be referred to in later chapters.
When benzaldehyde is added to strong nitric acid it dissolves,
and, following the rule laid down on p. 408, forms mainly the
meta-compound. The ortho-compound is obtained by oxidising
0-nitrobenzyl alcohol with nitrogen tetroxide. 0-Nitrobenz-
aldehyde has a special interest from the ease with which it is
converted into indigo (p. 524). The para-compound is formed
by the oxidation of /-nitrotoluene.
Among the other aromatic aldehydes, cuminol, or/-isopropyl-
benzaldehyde, and cinnamic aldehyde, or phenyl acrolein, are of
interest. Cuminol is present in cumin oil ; cinnamic aldehyde
is the chief constituent of cinnamon and cassia oil. Cinnamic
aldehyde is also obtained by the action of a solution of caustic
soda on a mixture of benzaldehyde and acetaldehyde. This
reaction, which takes place between aromatic aldehydes and
many aldehydes and ketones containing the group CH 2 .CO, is
known as Claisen's reaction, and recalls the formation of croton-
aldehyde from acetaldehyde (p. 269).
C 6 H 5 . CHO + CH 3 . CIIO = C 6 H 5 . CH :CH. CHO + H 2 O.
Cinnamic aldehyde.
xxxin AROMATIC KETONES 473
On oxidation, cinnamic aldehyde is first converted into
cinnamic acid (p. 496), the side-chain then breaks down and
benzoic acid is formed.
AROMATIC KETONES
The aliphatic ketones contain two alkyl radicals linked by a
ketone group. In the aromatic ketones, one radical is aromatic,
the other may be aliphatic or aromatic. Acetophenone, or phenyl-
methyl ketone, and benzophenone, ordiphenyl ketone, are two
typical examples of aromatic ketones
C 6 H 5 . CO. CH 3 . C 6 H 5 . CO. C 6 H 5 .
Acetophenone, or Benzophenone, or
Phenylmethyl ketone. Diphenyl ketone.
The aromatic ketones are usually crystalline substances with
a pleasant smell, which in chemical characters resemble the
aliphatic ketones. The methods of preparation will be illus-
trated in the case of acetophenone and benzophenone.
Acetophenone, Phenylmethyl ketone, C 6 H 5 .CO.CH 3 , is
obtained by distilling a mixture of calcium benzoate and
acetate
C 6 H 5 !COOca'
""", f = C 6 H 5 .CO.CH 3 . + CaCO 3 .
CH 3 .COjOca' Acetophenone.
A more convenient method is that of Friedel and Crafts
already referred to (p. 386), in which a mixture of benzene,
acetyl chloride, and aluminium chloride are allowed to react
C 6 H 6 + C1CO.CH 3 [+ A1C1J = C 6 H 5 .CO.CH 3 + HC1.
When the reaction, which proceeds spontaneously, ft complete,
the product is shaken with caustic soda solution, and the
undissolved oil removed and distilled.
Acetophenone is a colourless, crystalline compound with a
fragrant smell, which melts at 20 and boils at 202. It is some-
times used as a hypnotic, under the name of hypnone. On
reduction it yields the secondary alcohol, phenylmethyl
carbinol, C 6 H (V CH(OH).CH 3 , and on oxidation, benzoic acid,
the aliphatic side-chain being removed. Acetophenone forms
an oxime and a phenylhydrazone, and possesses the general
characters of an aliphatic ketone.
474 THEORETICAL ORGANIC CHEMISTRY CHAP.
Benzophenone, Diphenyl ketone, C 6 H 5 .CO.C 6 H 5 , is obtained
by distilling calcium benzoate, and by the action of benzoyl
chloride, or carbonyl chloride, on benzene in presence of
aluminium chloride.
C 6 H 6 + C1CO.C 6 H 5 [+ A1C1 3 ] = C 6 H 5 .CO.C fi H 5 + HC1.
2C 6 H 6 + COC1 2 [+ A1C1 3 ] = C 6 H 5 .CO.C 6 H 5 + 2HC1.
It is a fragrant-smelling, crystalline substance, which melts at
48 and boils at 162. On reduction with sodium amalgam it
gives the secondary alcohol, benzhydrol, C 6 H 5 .CH(OH).C H 5 ,
and also benzpinacone, (C 6 H 5 ) 2 C(OH).C(OH)(C G H5) 2 (p. 124).
By using a stronger reducing agent, such as hydriodic acid, ben-
zophenone is converted into diphenylmethane, C 6 H 6 .CH 2 .C 6 H 5 .
Examples of stereo-isomeric ketoximes similar to those of the benz-
aldoximes (p. 471) are not uncommon, where the two radicals attached
to the ketone group are different. Chlorobenzophenone, when con-
verted into the oxime, yields two products of different melting-
points, which are represented by the following space formulae
C1C G H 4 .CC 6 H 5 C1C 6 H 4 .C.C 6 H 5
HO.N. N.OH.
PHENOLIC ALCOHOLS AND ALDEHYDES
A number of substances are known which possess the double
function of phenol and alcohol as well as of phenol and
aldehyde. In one group the properties are determined by
the presence of hydroxyl groups, both in the side-chain and
nucleus ; in the other by the presence of an aldehyde group
together with a nuclear hydroxyl. Many of these compounds
possess an agreeable aroma, and derive an interest from their
occurrence among plant products. It is to these especially that
attention will be directed.
Saligenin, o-Hydroxybenzylalcohol, C 6 H 4 (OH)CH 2 OH, is
found combined with glucose in the glucoside, salicin, which
occurs in the bark of the willow (Salix] and in poplar buds. It
is prepared synthetically by the reduction of salicylic aldehyde
(see below). It is a crystalline substance, which melts at 82,
and gives a deep blue colour with ferric chloride.
Salicylaldehyde, o-Hydroxybenzaldehyde, C 6 H 4 (OH)CHO, is
found in the volatile oil of certain kinds of spiraea, and is also
xxxin AROMATIC KETONES 475
obtained by the oxidation of saligenin. An interesting synthetic
method is that known as Eeimer's reaction, by which both the
o- and ^-hydroxybenzaldehydes are formed It consists in
heating together a mixture of phenol, chloroform, and sodium
ethoxide or caustic potash
C 6 H 5 OH + CHC1 3 + 4KOH = KO.C 6 H 4 .CHO + sKCl + 3H 2 O.
The product is acidified, to liberate the hydroxyaldehydes
from the potassium salts, and distilled in steam. The ortho-
compound, which is a volatile oil, distils ; the para-compound,
which is a solid, remains in the distilling flask, and is extracted
with water.
Another interesting method for preparing aldehydes of the phenol
ethers is to act on the phenol ether with the hydrochloride of hydro-
cyanic acid, HCN.HC1, in presence of aluminium chloride. The
imide is first formed, which decomposes on warming into the aldehyde
and ammonia* The two stages in the reaction are represented as
follows
1. C 6 H 5 OCH 3 + HCN.HC1 = C 6 H 4 (OCH 8 )CH:NH + HC1.
2. C 6 H 4 (OCH 3 )CH:NH + H a O = C 6 H 4 (OCH 8 )CHO + NH 3 .
Anisaldehyde.
Anisol gives anisaldehyde, or /-methoxybenzaldehyde.
Vanillin, m-Methoxy-p-hydroxybenzaldehyde, C 6 H 3 (OH)
(OCH 3 ).CHO, is the sweet-smelling constituent of the vanilla-
pods, and sublimes from the pods on heating, in fine colourless
needles which melt at 80^. It was first obtained synthetically
from coniferyl alcohol, which is present in combination with
glucose, as the glucoside, coniferin, in the cambium sap of
certain conifers. It is now prepared from eugenol, the chief
constituent of oil of cloves. Both coniferyl alcohol and eugenol
yield vanillin on oxidation.
HO
CH,0
nor >
CHO CH 3 Ol JcH:CH.CH 2 (OH)
Vanillin. Coniferyl alcohol.
HO/
CILOl JCH 2 .CH:CH a .
Eugenol.
476
THEORETICAL ORGANIC CHEMISTRY
Vanillin has also been obtained from guaiacol (p. 461) by
means of Reimer's reaction. When oxidised, the aldehyde
group becomes a carboxyl group, and vanillic acid is formed.
QUINONES
The quinones form a peculiar class of substances which have
no representatives among the aliphatic compounds. They are
obtained by the oxidation of para-hydroxy- and amino-derivatives
of benzene and its homologues.
Benzoquinone, Quinone, C G H 4 O 2 , was originally obtained by
the oxidation of quinic acid (p. 491), which is found in cinchona
bark associated with the cinchona alkaloids (p. 579), but has
chemically no connection with the alkaloid, quinine. It is
formed when quinol, ^-aminophenol, or /-phenylenediamine
is oxidised ; but it is usually prepared by the oxidation of
aniline in the cold, with potassium dichromate and sulphuric
acid. The dark product is extracted with ether, which dissolves
the quinone, and on removing the ether, benzoquinone crystallises
in golden-yellow prisms, which melt at 116 and sublime without
decomposition, emitting a peculiar smell and acrid vapours. The
course of this somewhat complex chemical change will be better
understood when the structure of quinone has been discussed.
Structure of Quinone. The constitution of quinone is derived from
a study of its various reactions, and especially from its close relationship
to quinol (p. 462).
It was stated on p. 462 that quinol gives quinone on oxidation. The
process may occur in two ways, represented by the following formulae
I. II.
C O CO
/\
HC/
HC
CH
CH
,c
HC
,CH
I'CH
C 6 C:O
Quinone.
Formula I. represents a peroxide, examples of which are known
among the derivatives of the acids, e.g. benzoyl and acetyl peroxide,
which have the general formula
R'.CO.O
R'.CO.O.
QUINONES 477
These substances agree with quinone in so far as they are all
oxidising agents ; but, on the other hand, the fact that quinone
combines with hydroxylamine and forms both a mono- and a di-
oxime, is strongly in favour of the diketone formula represented in
Formula II.
O:C 6 H 4 :NOH HON:C 6 H 4 :NOH
Quinone monoxime. Quinone dioxime.
Moreover, the existence of the pair of double bonds, which the
second formula necessitates, is supported by the fact that quinone
forms a di- and tetra-chloride with chlorine, C 6 H 4 O 2 C1 2 , C 6 H 4 O 2 C1 4 ,
and similar compounds with bromine.
The formation of quinone by the oxidation of aniline is
represented by the following series of changes :
,H 2 /NH 2
C 6 H 5 NH 2 -> C 6 H 5 N^ -> C 6 H 5 NH.OH -> C 6 H 4 < -> C 6 H 4 O 2 .
^O X OH
Aniline. Phenyl- Phenylhydroxyl- /-Amino- Quinone.
ammonium oxide. amine. phenol.
Aniline first takes up oxygen and passes into an oxide,
phenylammonium oxide, which changes into phenylhydroxyl-
amine. The latter also undergoes intramolecular change, and
forms /-aminophenol, which, as is well known, gives quinone
on oxidation.
Chloranil, Tetrachloroquinone, C 6 C1 4 O 2 , has already been
referred to (p. 456) as a product obtained by oxidising phenol
with potassium chlorate and hydrochloric acid. It is also
obtained in a similar way from aniline, /-phenylenediamine,
and other substances. Chloranil is occasionally employed as
an oxidising agent for organic substances.
Ortho-quinone, prepared by oxidising catcchol dissolved in
ether with dry silver oxide, is a red crystalline substance with-
out smell and non-volatile (see p. 539).
C:O
Hc/Noo
HC
CH
CH
Ortho-quinone.
478 THEORETICAL ORGANIC CHEMISTRY CH. xxxm
QUESTIONS ON CHAPTER XXXIII
1. Describe two methods of obtaining benzyl alcohol. How would
you distinguish benzyl alcohol from the isomeric phenols ? Give the
formulae of the latter compounds.
2. Describe two methods by which benzaldehyde is prepared. Give
details of the process, including the method of purification.
3. How would you prove by its properties and reactions that the
chief constituent of bitter almond oil is an aldehyde ? In what respect
do such aldehydes differ from acetic aldehyde ?
4. Explain the theory which accounts for the existence of two benz-
aldoximes.
5. Describe the action of the following reagents on benzaldehyde :
(i) potassium cyanide, (2) caustic potash, (3) ammonia, (4) nitric acid.
Explain the conditions of each reaction, and the method you propose for
isolating the products.
6. What is Claisen's reaction ? Describe the artificial preparation of
cinnamic aldehyde. What products does cinnamic aldehyde yield on
oxidation ?
7. Describe a method for preparing aromatic ketones, and give an
example of their behaviour with reducing agents.
8. What is meant by " Reimer's reaction"? Describe the pre-
paration of (i) salicylaldehyde from phenol, and (2) vanillin from
guaiacol by this reaction.
9. How is quinone prepared ? What evidence is there that this
compound does not contain hydroxyl, and how is it converted into a
substance which does ?
CHAPTER XXXIV
THE AROMATIC ACIDS
The Aromatic Acids derive their properties as acids from
the presence of the carboxyl group, which may be either in the
nucleus or side-chain of the aromatic compound. The isomers,
toluic and phenylacetic acid are examples of the two classes of
compounds
(CH 3 )C 6 H 4 .COOH.
Toluic acid.
C 6 H 5 .CH 2 .COOH.
Phenylacetic acid.
The general properties of both classes resemble those of the
aliphatic acids. They form salts with metals, esters with the
alcohols, acid chlorides, anhydrides, and amides by similar
methods. The following derivatives of benzoic may be taken
by way of illustration, by the side of which the corresponding
derivatives of acetic acid are placed for comparison :
C 6 H 5 . CO. ONa Sodium benzoate.
CHg.CO.ONa Sodium acetate.
C 6 H 5 .CO.OC 2 H 5 Ethyl benzoate.
CH 3 .CO.OC 2 H 5 Ethyl acetate.
C 6 H 5 . CO. Cl Benzoyl chloride.
CH 3 . CO. Cl Acetyl chloride.
C 6 H 5 .CO
CH 3 .CO
\ n Benzoic anhy-
dride.
~/O Acetic anhydride.
C 6 H 5 .CO
CH 3 .CO
C 6 H 5 . CO. NH 2 Benzamide.
CH 3 . CO. NH 2 Acetamide.
Any difference in properties between the aromatic and
aliphatic acids may generally be ascribed (i) to the larger
proportion of carbon to carboxyl in the aromatic acids, which
decreases the solubility in water ; (2) to the higher molecular
weight, which renders the substance less volatile (the aromatic
480 THEORETICAL ORGANIC CHEMISTRY CHAP.
acids are crystalline solids) ; (3) to the presence of the benzene
nucleus, which increases the strength of the acid, as determined
from its augmented dissociation constant (p. 144).
The aromatic acids, like the hydrocarbons, are acted upon
by chlorine, bromine, and nitric and sulphuric acids, and give
substitution products from which ammo-acids, hydroxy-acids,
and other derivatives may be obtained by means of the reactions
already studied.
C 6 H 5 .COOH
Benzoic acid.
\
(HN0 3 )
yN0 2
c 6 H/
XX)OH
Nitrobenzoic acid.
(H 2 S0 4 )
/S0 8 H
C 6 H 4 <(
XX)OH
Sulphobenzoic acid.
(C1 2 )
/Cl
4 \COOH
Chlorobenzoic acid.
By replacing more than one hydrogen atom by carboxyl,
either in the nucleus or side-chain, polybasic acids are Obtained.
Examples of dibasic acids are the three phthalic acids (p. 391).
The carboxyl is readily replaced by hydrogen by distilling the
acid, or its calcium salt with lime, or, in some cases, by the
action of heat alone. An example of the first is benzoic acid,
which gives benzene on distillation with lime (p. 383) ; of the
second, gallic acid, which loses carbon dioxide on simply heating,
forming pyrogallol (p. 463).
Many of the acids are found in nature as constituents of
plants and, occasionally, of animal products. As a rule, they
are more readily prepared by one or other of the numerous
synthetic methods, which are described under benzoic acid.
Benzoic Acid, C 6 H 5 .COOH, has long been known, and was
originally obtained by heating gum-benzoin, a resin obtained by
incisions made into the stem of Styrax benzoin, a tree which is
indigenous to Sumatra and Java. The true composition of
benzoic acid was determined by Liebig and Wohler in 1832.
They discovered some of the derivatives enumerated above
(p. 479) and many others, and showed that the same group of
elements, C 7 H 5 O (now written, C 6 H 6 .CO), which they termed
benzoyl, ran through the whole series of compounds. These
were the facts which they embodied in their classical research
on "The Radical of Benzoic Acid" (p. 3), wherein they placed
xxxiv THE AROMATIC AGIDS 481
the theory of the compound radical for the first time on a secure
foundation.
EXPT. 166. The formation of benzoic acid from gum-benzoin is
readily shown as follows : Place a little of the resin in a porcelain
basin, cover it with a cone made out of filter paper, and heat it
gently on a sand-bath over a small flame. The resin fuses, and
crystals of benzoic acid sublime into the paper cone, emitting at
the same time a smell resembling incense.
Benzoic acid is present in the resin chiefly in the form of the
ester of benzyl alcohol. A small amount of the same ester is
also found in Peru and Tolu balsam. Another source of
benzoic acid is Mppuric acid, which is present in the urine of
horses and cattle and other herbivorous animals, and has already
been referred to under glycine (p. 323).
Preparation of Benzoic Acid. Benzoic acid is obtained
by the following general synthetic methods, which may be applied
to the preparation of other acids of the series :
1. By hydrolysis of phenyl cyanide, or benzonitrile, usually
by boiling with moderately strong sulphuric acid (p. 154).
C 6 II 5 CN + 2H 2 O = C 6 H 5 .COOH + NIL,.
Benzonitrile. Benzoic acid.
As the cyanides are easily obtained from the ammo-compounds
by means of the diazo-reaction, as well as from the sulphonic
acids, the method is available both for preparing the acid and
its derivatives.
2. By the oxidation of aromatic compounds containing one
side-chain, and even more readily, if the side-chain is substituted.
Toluene can be oxidised to benzoic acid by heating it with
dilute nitric acid in a sealed tube ; but if benzyl chloride,
benzyl alcohol, benzaldehyde, or acetophenone is taken, the
reaction is facilitated, and boiling with potassium permanganate
is sufficient to effect oxidation.
Derivatives of toluene, which are substituted in the nucleus,
undergo a similar change, and yield the corresponding deriva-
tives of benzoic acid (p. 391). Chlorotoluene gives chlorobenzoin
acid
C1.C 6 H 4 .CH 3 + 30 = C1.C 6 H 4 .COOH + H ? O.
Chlorobenzoic acid.
482 THEORETICAL ORGANIC CHEMISTRY CHAP.
3. The Friedel-Crafts reaction is the basis of two methods for
preparing aromatic acids. When benzene and carbonyl chloride
react in presence of aluminium chloride, benzoyl chloride
is formed, which yields the acid when decomposed by water
(p. 483)-
C 6 H e + COC1 2 [ + A1C1J = C 6 H 5 .COC1 + HC1.
Benzoyl chloride.
The materials are the same as those used in preparing benzo-
phenone, but the reaction is arrested before the ketone is
formed (p. 474).
If chloroformamide, C1CO.NH 2 , which is obtained by heating
cyanuric acid in a current of hydrochloric acid gas, is passed
into benzene containing aluminium chloride, benzamide is formed,
which can be hydrolysed and converted into benzoic acid
(p. 483)
CONH + HC1 = C1CO.NH 2 .
Chloroformamide.
C 6 H 6 + C1CO.NH 2 [+ A1C1J = C 6 H 5 .CO.NH 2 + HC1.
Benzamide.
There are other general methods for preparing aromatic acids,
but they are of less importance and need not be described.
Benzoic acid is manufactured on a large scale from benzo-
trichloride by heating with milk of lime
2C 6 H 5 .CC1 S + 4CaO = (C 6 H 5 COO) 2 Ca + 3CaCl 2 .
Calcium benzoate.
The lime salt is decomposed by acid, and the benzoic acid
crystallises out. It forms colourless needles, which melt at
I2i-i22 and boil at 250. Benzoic acid is volatile in steam, and
its vapours affect the throat and nose, producing coughing and
sneezing. It is soluble in hot, but sparingly in cold water, and it
dissolves in alcohol and ether. The insolubility of the majority
of aromatic acids in water and their solubility in ether enable
them to be separated and distinguished from many of the
simpler aliphatic acids and hydroxy-acids. Benzoic acid forms
weil-defmed salts. The calcium salt crystallises in long needles.
Ferric benzoate is precipitated as a brown amorphous . powder
from neutral solutions with ferric chloride. The acid is
separated and precipitated from the salts on the addition of
hydrochloric acid.
THE AROMATIC ACIDS
Benzoyl Chloride, C 6 H 5 .COC1, is prepared, like other acid
chlorides, by the action of phosphorus tri- or penta-chloride on
benzoic acid (p. 173)
C 6 H 5 .COOH + PC1 5 = C 6 H 5 .COC1 + POC1 3 + HC1.
Benzoyl chloride.
The product is fractionated, the benzoyl chloride being readily
separated from the phosphorus oxychloride by reason of its
higher boiling-point.
EXPT. 167. Add a little benzoic acid to double its bulk of
phosphorus pentachloride in a test-tube. The mixture becomes
hot and liquefies, whilst clouds of hydrochloric acid fumes are
evolved.
Benzoyl chloride is a colourless liquid which boils at 198 and
fumes in moist air. It possesses the general characters of the
aliphatic acid chlorides, and, like acetyl chloride, it combines
with water, alcohols (though more slowly), and also with phenols.
ammonia, and the amines (p. 173). These reactions are
described in detail below.
Benzoic Anhydride, C 6 H 5 CO.O.COC 6 H 5 , is prepared, like
acetic anhydride, by heating a mixture of benzoyl chloride and
dry sodium benzoate. It is a crystalline compound which
melts at 42, and combines with phenols and alcohols like benzoyl
chloride.
Benzamide, C 6 H 5 .CONH 2 , is readily obtained by adding
ammonia or ammonium carbonate to benzoyl chloride, washing
out the ammonium chloride with cold water, and crystallising
from hot water the benzamide which is left
C 6 H 5 .COC1 + 2NH 3 = C 6 H 5 .CONH 2 + NH 4 C1.
Benzamide.
EXPT. 168. Add a few drops of strong ammonia solution to a drop
of benzoyl chloride. There is a violent reaction, and a white deposit
of benzamide and ammonium chloride is formed. Add a little
water to dissolve the ammonium chloride, and crystallise the residue
from hot water. The formation of benzanilide from aniline and
benzoyl chloride may be shown in the same way.
Benzamide is also obtained, like acetamide, by heating am-
monium benzoate in a sealed tube (p. 177), and by Friedel and
Crafts' method described on p. 482. It is a colourless, crystalline
I I 2
484 THEORETICAL ORGANIC CHEMISTRY CHAP.
substance which melts at 128, and gives benzoic acid on
hydrolysis like other amides.
Benzonitrile, Phenyl cyanide, C 6 H 5 .CN, is prepared from aniline
by Sandmeyer's reaction (p. 430), and from benzene sulphonic acid
by fusion of the potassium salt with potassium cyanide (p. 447). A
useful method of preparation is to distil benzoic acid with potassium,
or lead sulphocyanide
2 C 6 H 5 COOH + KCNS = C 6 H 5 CN + C 6 H 5 COOK + CO 2 + H 2 S
Benzonitrile.
Benzonitrile is a colourless liquid with a smell resembling nitrobenzene,
or benzaldehyde. It boils at 191. On hydrolysis it yields benzoic acid.
Expt. 169. Mix 3 c.c. of cone, sulphuric acid with 2c.c. of water,
add I gram of benzonitrile, and boil gently until complete solution is
effected. On adding a little water and cooling, benzoic acid
separates in needles.
Benzoic Esters. The simplest method for obtaining the alkyl
benzoates is that described in Expt. 63 (p. 183). Hydrochloric
acid gas is passed into the alcohol until it has absorbed 4 to 5 per
cent, by weight, and then boiled with benzoic acid. The product
is poured into water, which is made alkaline to dissolve any
unchanged benzoic acid, and the ester, which falls to the bottom
as an oil, is removed and distilled.
Victor Meyers Ester Law. A reference has been made on p. 392
to the differences exhibited by the dimethyl derivatives of toluene
on oxidation, and it was pointed out that the protective influence
exercised by the proximity of certain groups, to the group submitted
to the reaction, was not an 'uncommon occurrence. The most striking
example of this protective influence is that afforded by the di-ortho-
substituted benzoic acids. They cannot be converted into esters by the
method just described, whereas a theoretical yield of the isomeric esters
is obtained. And this does not depend on the character of the sub-
stituting groups, which may be entirely unlike one another. The pre-
sence of methyl, nitro- and halogen groups in the two ortho-positions
arrest esterification with equal effect. The following di-ortho-deriva-
tives of benzoic acid form no esters when boiled with alcohol in pre-
sence of hydrochloric acid
COOH COOH COOH
CH
V
Yet the esters may be obtained by the action of the alkyl iodide on
CH 3 Brf >Br NO,
xxxiv THE AROMATIC ACIDS 485
the silver salts. The phenomenon does not arise, therefore, from any
intrinsic inability on the part of the acid to form these compounds.
It is attributed by V. Meyer to the space occupied by the element or
group adjoining the carboxyl, which prevents the alcohol molecules
coming within the sphere of action of the carboxyl group. The pheno-
menon is sometimes described as steric hindrance. The indifference of
di-ortho-derivatives of phenylcyanide, benzamide, and benzoic esters
to the action of hydrolytic agents is attributed to the same cause.
A simple and rapid method for preparing small quantities of
esters, including phenolic esters, is that known as Schotten-
Baumanris reaction, and consists in mixing the alcohol, or
phenol, with benzoyl chloride, or other acid chloride, in presence
of caustic soda solution
C 6 H 5 .COC1 + C 2 H 5 OH + NaOH = C 6 H 5 CO.OC 2 H 5 + NaCl + H 2 O.
Ethyl benzoate.
The reaction is used to detect the presence of alcoholic or
phenolic hydroxyl as well as of amino-groups, which form
amides of the acid radical.
EXPT. 170. Mix together I c.c. of benzoyl chloride and 2 c.c. of
ethyl alcohol, and add caustic soda solution until alkaline. Shake
well and warm gently, keeping the liquid alkaline. The smell of the
benzoyl chloride eventually disappears, and an oil with a fragrant
smell collects at the bottom of the tube. This is ethyl benzoate.
Repeat the reaction with phenol in place of ethyl alcohol. Solid
phenyl benzoate is formed.
The alkyl benzoates are fragrant-smelling liquids, which are
specifically heavier than water (compare ethyl acetate). The
methyl ester boils at 199, the ethyl ester at 213. The phenyl
ester is a crystalline compound, which melts at 71.
Substituted Benzoic Acids. Following the law of substitu-
tion (p. 407), the main product of the action of chlorine,
bromine, sulphuric and nitric acids on benzoic acid is in each
case the meta-compound. It should be noted, however,
that with nitric acid all three isomeric nitro-compounds are
formed, which yield ammo-compounds on reduction. These
amino-benzoic acids may be in turn diazotised and converted
into the different derivatives to which the diazo-reaction gives
rise. Another method for obtaining substituted benzoic acids is
to oxidise the substituted toluene. For example, ortho- and
para-chlorotoluene yield ortho- and para-chlorobenzoic acid,
4 86 THEORETICAL ORGANIC CHEMISTRY CHAK
whilst direct chlorination of benzoic acid gives the meta-com-
pound. In this way all three isomers may be obtained.
Methods may be readily devised for the preparation of most
of the simpler substituted benzoic acids.
Anthranilic Acid, o- Anrinobenzoic acid, C 6 H 4 (NH 2 ). COOH, may be
obtained by one of the methods described above ; but in practice, where
large quantities are required for the manufacture of artificial indigo, it
is produced from naphthalene. The process is described on p. 475.
The methyl ester is the sweet-smelling constituent of the oil (neroli
oil) extracted from orange blossom.
/ C \
Saccharin, Sulphobenzolnide, C 6 H 4 ^ /NH, is obtained from
toluene. The toluene is converted by sulphonation into a mixture of
p- and 0-sulphonic acid which are partly separated. From the ortho-
compound the sulphochloride and sulphonamide are prepared. The
latter is then oxidised to the corresponding benzoic acid derivative and
saccharin is thus formed.
/COOH /CO x
= C 6 H / >NH + H 2 0.
NSOaNHg X SO/
0-Suiphon- Saccharin,
amide of benzoic acid.
Saccharin is a colourless, crystalline compound, which, when dis-
solved in water, has an intensely sweet taste, and is used in cases of
diabetes and other disorders to replace cane-sugar in the patients' diet.
Its sweetness is estimated at 4-500 times that of cane-sugar.
Toluic Acids, Methylbenzoic acids, CH 3 .C 6 H 4 .COOH, exist
in three isomeric forms, and are prepared by one or other of
the general methods described under benzoic acid. They are
crystalline substances resembling benzoic acid, and are readily
identified by their melting-points. The ortho-acid melts at
103, the meta-acid at ITO, and the para-acid at 180. They
yield the three phthalic acids on oxidation (p. 391).
Cumic Acid, p-hopropylbenzoic acid, C 3 H 7 .C 6 H 4 .COOH, is
prepared by the oxidation of cuminol (p. 472).
PHENOLIC ACIDS
Phenolic acids are derivatives of the aromatic acids in which
one or more hydrogen atoms of the nucleus are replaced by
hydroxyl. They combine the characters of phenols and acids.
Many possess antiseptic properties, and give Ihe colour
THE AROMATIC ACIDS
reactions of the phenols with ferric chloride. They frequently
occur among plant products, and many of them have found a
technical application. Some of the amino-derivatives of
hydroxy-esters are employed as local anaesthetics.
Salicylic Acid, o-Hydroxybenzoic. acid, C 6 H 4 (OH).COOH, is
found as the methyl ester, C 6 H 4 (OH).COOCH 3 , in oil of
wintergreen, a fragrant liquid which is extracted from a heath
{Gaultheria procumbens] grown in the United States and Canada.
It is used for flavouring confectionery. It readily yields the
acid on hydrolysis. A variety of synthetic methods exists for
preparing salicylic acid, which a little reflection will suggest;
but the manufacturing process, which is known as Kolbe's
reaction, after -its discoverer, is a peculiar one and unlike any
previously described.
It consists in heating to 1 20- 130 dry sodium phenate with
carbon dioxide in closed vessels under pressure. The process
actually occurs in two steps. In the first reaction, sodium
phenyl carbonate is formed
C 6 H 5 ONa + CO 2 = C 6 H 5 O.CO.ONa.
Sodium phenyl
carbonate.
Then, at the high temperature of the reaction, an intramole-
cular change occurs, whereby the carboxyl group replaces
hydrogen of the nucleus in the ortho-position to the hydroxyl
group.
X O.iCO.ONa /\OH
H"! v xCO.ONa.
Sodium phenyl carbonate. Sodium salicylate.
It is an interesting fact that if potassium phenate is heated
to 220 in carbon dioxide, the product is exclusively the para-
compound, or if potassium salicylate is heated to the same
temperature, it is converted into /-hydroxybenzoic acid.
Another method by which salicylic acid, together with
/-hydroxybenzoic acid, is formed, is analogous to Reimers
reaction for preparing hydroxy- aldehydes (p. 474). A mixture
of phenol, carbon tetrachloride, and caustic soda solution is
heated together ONa
C G H 5 OH + CC1 4 + 6NaOH = C 6 H 4 <
\COONa
4 88 THEORETICAL ORGANIC CHEMISTRY CHAP.
The product, after removing excess of carbon tetrachloride,
is saturated with carbon dioxide and shaken with ether to
extract unchanged phenol. The hydroxybenzoic acids are then
precipitated with hydrochloric acid and filtered.
Salicylic acid crystallises in colourless needles, which melt at
155. Its vapour has an irritating effect on the throat. It is
very sparingly soluble in cold water, but dissolves readily in hot
water. Like phenol and resorcinol, it gives an intense violet
coloration with ferric chloride, and may be distinguished in
this way from the isomeric meta- and para-compounds which
give no colour reactions. On heating with soda-lime, salicylic
acid loses carbon dioxide and is converted into phenol
C 6 H 4 (OH).COOH = C 6 H 5 OH + CO 2 .
EXPT. 171. Grind up some salicylic acid, or its calcium salt, with
double its bulk of soda-lime and heat over the flame. The smell of
phenol is quickly detected.
Salicylic acid is a powerful antiseptic, and is frequently used
as a substitute for phenol. Salol, the phenyl ester, and betol, the
naphthyl ester (p. 537), of salicylic acid, are also used as
antiseptics. They are obtained by the action of salicylic acid
on phenol, or naphthol, in presence of an acid chloride (phos-
phorus oxychloride, or carbonyl chloride)
C 6 H 4 (OH)COOH + C 6 H 5 OH = C 6 H 4 (OH)COOC 6 H 5 + H 2 O.
Salicylic acid is also an antipyretic and the sodium salt is used in
cases of rheumatism. The acetyl derivative, aspirin, has a similar
effect, but is less of an irritant.
Anisic Acid, p-Methoxybenzoic acid, CH 8 O.C 6 H 4 .COOH, is
obtained by the oxidation of anethole (p. 456). It is isomeric
with methyl salicylate.
Protocatechuic Acid, C 6 H,(OH) 2 COOH + H 2 O, is one of six
isomeric dihydroxybenzoic acids. It is a common constituent
of aromatic compounds, which are present in certain resins,
alkaloids, tannins, and yellow colouring matters associated with
them. It has the following structure
HO
HO
Protocatechuic acid.
:OOH.
THE AROMATIC ACIDS 489
It loses carb6n dioxide, and is converted into catechol on
heating-. The tannins, which yield catechol on distillation, and
are called catechol-tannins (see p. 490), probably contain proto-
catechuic acid as a constituent of the tannin molecule. Proto-
catechtiic acid crystallises from water with one molecule of
water of crystallisation, which it loses at 100, and then melts at
199. It gives a similar reaction to catechol with ferric chloride
(p. 461), and like catechol reduces ammonia-silver nitrate but not
Fehling's solution. The position of the groups in protocatechuic
acid should be compared with those in vanillin and its allied
compounds.
Piperonylic Acid is closely related to protocatechuic acid, not only
1 in structure, but in its connection with the products of plant life. It may
be termed methylene protocatechuic acid, and is readily converted into
protocatechuic acid by heating with strong hydrochloric acid. Piperonal
is the corresponding aldehyde, and is obtained by the oxidation of safrol
(oil of sassafras). It has the scent of heliotrope, and is used as a
perfume by the name of heliotropin. It bears the same relation to
safrol that vanillin does to eugenol (p. 475).
CH,
CHo<
/O
CH 2 .CH:CH 2 X)
Safrol. Piperonal.
1CHO
/COOH
Piperonylic acid.
Gallic Acid, i-2-^-Trihydroxybenzoic acid, C 6 H 2 (OH) 3
COOH, is one of six possible isomers. It is found associated
with certain tannins (see p. 490) from which it is separated by
digestion with aqueous ether. The gallic acid dissolves in the
ether, whereas the tannin substances are insoluble, but dissolve in
the water present, and form a lower aqueous layer which can be
separated. Gallic acid is also obtained by the hydrolysis of gallo-
tannic, or digallic acid, which is the chief constituent of sumach
and of galls, the round excrescences formed on oak leaves and
twigs by the puncture of the gall-fly.
Gallic acid crystallises in colourless needles, which lose
carbon dioxide on heating, forming pyrogallol (p. '463). It
490 THEORETICAL ORGANIC CHEMISTRY CH \p.
.gives a deep blue coloration or precipitate with ferric chloride,
and a pink solution when shaken with potassium cyanide, which
fades on standing, but reappears on shaking. In alkaline solution
it rapidly darkens in the air by oxidation. It does not precipitate
gelatine, and can by this means be distinguished from the tannins.
Ellagic Acid, C 14 H 8 O 9 , is a substance of unknown constitution
closely related to gallic acid. It is frequently found associated with
the tannins (in sumach) and may be obtained from gallic acid by oxida-
tion with arsenic acid, or iodine. It is a yellow crystalline substance,
which is insoluble in water and can therefore be readily separated from
gallic acid and the tannins.
The Tannins is the name given to the active constituents of
those substances which are used in tanning skins. The object
of tanning is to prevent putrefactive changes, and to render the
skin permanently flexible and porous. The hair is first removed
from the skin, usually by the action of milk of lime, which at the
same time causes the skin to swell. The lime is then dissolved out
as far as possible by soaking the skins in fermenting dung, bran
or old tan liquor, which contain organic acids (acetic, lactic, etc.)
produced by fermentation. The skins are then steeped in tan
liquor, which is the aqueous extract of a variety of vegetable
substances, of which the following- are among those commonly
employed :
Oak bark.
Myrabolans (dried fruit of Terminalia chebula, India).
Valonia (acorn cup of Quercus sEgilops^ Asia Minor).
Sumach (leaf of Rhus coriaria, Sicily).
Cutch (extract of wood of Acacia catechu, India).
Divi-divi (pod of Ccesalpina coriaria, S. America).
Hemlock bark (Abies canadensis^ N. America).
Although the tannins differ widely in chemical constitution,
and produce different effects on skins, they have the common
property of precipitating gelatine from solution and forming
insoluble compounds with it. It is this property, which is
effective in producing leather ; for the process of tanning has
been succesfully imitated by the use of formaldehye, or inorganic
compounds like chromic salts and alum, all of which render
gelatine insoluble.
xxxiv THE AROMATIC ACIDS 491
The tannins are astringent substances, which give dark blue
or green colorations, or precipitates with ferric salts, and are
precipitated by lead acetate, tartar emetic, and the alkaloids. The
use of tannin and tartar emetic as a mordant has been explained
(p. 441). The tannins turn dark brown in presence of alkalis,
and give a deep red coloration with potassium ferricyanide
and ammonia. They are all very soluble in water, and insoluble
in ether, but do not crystallise.
The tannins vary much in character, and little is known of
their structure. Some appear to be glucosides of gallic acid, in
which the hydroxyl groups of glucose are combined with gallic
acid in the form of an ester, and decompose with acids into
glucose and gallic acid ; others appear to contain phloroglucinol
in place of glucose, and protocatechuic acid in place of gallic
acid. Tannic acid, from oak galls and sumach, decomposes
into gallic acid and glucose on hydrolysis, and is probably a
pentadigalloyl-glucose (Fischer).
Quinic Acid, C 6 H 7 (DH) 4 .COOH, already referred to (p. 476) as
occurring in cinchona bark combined with the alkaloids, is the tetra-
hydroxy-derivative of hexahydrobenzoic acid. It is a crystalline
compound which melts at 162 and is optically active.
THE DIBASIC ACIDS
The most important dibasic acids are the three isomers,
phthalic, isophthalic, and terephthalic acids, already mentioned
as representing the final products of oxidation of the three
isomeric xylenes
COOH COOH
/NCOOH
/ICOOH IJCOOH
COOH
Phthalic acid. Isophthalic acid. Terephthalic acid.
The acids correspond to the aliphatic acids of the succinic
acid series (p. 332) inasmuch as they form acid and neutral salts
and esters.
492 THEORETICAL ORGANIC CHEMISTRY CHAP.
Phthalic Acid, Benzene-o-dicarboxylic acid, C 6 H 4 (COOH) 2 , is-
made in large quantities for the preparation of fluorescein and
the eosin dyes (p 520), and for conversion into anthranilic acid,
now extensively used in the manufacture of artificial indigo-
(p. 521). It is obtained by oxidising naphthalene with fuming
sulphuric acid in presence of mercury, which acts as a contact,
or catalytic, agent. The product is converted into phthalic
anhydride by sublimation
C 10 H 8 + 90 - C 6 H 4 (COOH) 2 + 2C0 2 + HoO.
Naphthalene. Phthalic acid.
/ C \
C 6 H 4 (COOH) 2 - C 6 H 4 < >0 + H 2 0.
XXX
Phthalic anhydride.
The conversion of naphthalene into phthalic anhydride is
adduced as affording valuable evidence of the structure of
naphthalene, by indicating the probable existence in naphthalene
of a benzene nucleus (p. 528).
In order to obtain anthranilic acid from phthalic anhydride, ft
is heated with ammonia, which converts it into phthalimide
O + NH 3 = C 6 H 4 / ^>NH + H 2 0.
Phthalimide.
Phthalimide is then warmed with bromine and potash, or
potassium hypobromite. The alkali hydrolyses the phthalimide,
yielding phthalaminic acid, and the subsequent reaction is the
same as that by which acetamide is converted into methylamine
(p. 204). The following scheme represents the series of
changes
XXX' /CONH 2
C 6 H 4 < >NH ^|? C 6 H 4 <
XXX \COOH
Phthalimide. Phthalaminic acid.
H 2 0--/ NH *
OOH \COOH " XX)OH.
Intermediate products. Anthranilic acid-
CH
HC/NcCOv
/ NH
HC^/C.CO
CH
CK
HC/\
HC \/
CK
[
C.COC1
C.COC1
[
Phthalimide.
Phthalyl chloride.!
CH 2 .C(X
>NH
CH 2 .C(K
CH 2 .
CH 2 .
COC1
COC1
xxxiv THE AROMATIC ACIDS 493
Phthalic acid, when heated quickly, melts at 213, and at the
same time passes into the anhydride.
Phthalic Anhydride sublimes in long colourless needles
which melt at 128. Heated with phenol and sulphuric acid,
it gives phenolphthalein (p. 518) ; heated with resorcinol alone,
fluorescein is formed (p. 46 1 ). The anhydride yields phthalimide
with ammonia, and phthalyl chloride with phosphorus penta-
chloride. Each of these compounds has its representative
among the derivatives of succinic acid (p. 348).
CH
HC/Nc.CO
net ;c.co
CH
Phthalic anhydride.
CH 2 .CO X
I >o
CH 2 .C(X
Succinic anhydride. Succinimide. Succinyl chloride.
A much closer resemblance than that just described, subsists between
dimethylsuccinic acid and hexahydrophthalic acid, which is obtained by
the reduction of phthalic acid. Each of these acids exists in two stereo-
isomeric forms, and each of the isomers yields a different anhydride.
The space arrangement of the isomers is represented in the diagram
(p. 494), from which it will be seen that there are two asymmetric carbon
atoms present as in tartaric acid, indicated in the diagram by the point
of intersection of the cross lines. Possibly the two isomers correspond
to the racemic and meso-forms, for they are both inactive ; but the
point cannot be decided until one of them has been resolved into its
active components, which has not yet been accomplished. They are
usually distinguished by the terms cis and trans ; in the cis-compound
the two carboxyl groups are close together, and in the trans-compound,
diagonally opposite.
If it is a question of asymmetry, the trans-compound in the diagram
represents only one of the racemic components (see p. 357). The
1 There is some doubt as to whether the constitution of phthalyl and succinyl
xCCla ,CC1 2
chloride is represented by the above formulae, or by CgH^ /Q and C 2 H4O.
CO CO
A number of facts lend support to the second formula.
494
THEORETICAL ORGANIC CHEMISTRY CHAP.
second will be its mirror-image. The cis-compound is the meso-
form, i.e. it is inactive by inner compensation.
CH,
CH S
H
COOH
H COOH
H
COOH
COOH H
(
(
CI
H 2 Cf / H-
H 2 ci H-
\/
CI
;H S CH 3
?tt. Trans.
Dimethylsuccinic acids.
CH 2
i.
\ COOH H r// u ^ r^r\r\\y
POOTT H
r pnnTT TJ
~ \j\J\JLl. J.l 2 v^v v^v-'v/ J. J.-~7 J.A
fc
Cis. Trans.
Hexahydrophthalic acids.
Both hexahydroisophthalic and hexahydroterephthalic acids are re-
presented by stereo-isomers.
Isophthalic Acid, Be
is prepared by a variety of synthetic processes. It is obtained
from ;;z-xylene, ?;z-toluic acid, ;/z-toluidine, &c. It is a crystal-
line substance, which melts above 300 and sublimes.
Terephthalic Acid, Benzene-p-dicarboxylicacid, C 6 H 4 (C OO H ) 2 ,
is prepared by similar methods to those which yield the other
two dibasic acids, e.g. from /-xylene, /-toluic acid, cuminol,
and cymene, by oxidation, and further from ^-toluidine and
/-nitraniline. A little reflection, and a knowledge of the
structure of the substances, will suggest the course of each
reaction. Terephthalic acid sublimes on heating, but forms no
anhydride.
ACIDS CONTAINING CARBOXYL IN THE SlDE-CHAIN
These acids are the true representatives of the aliphatic acids
among the benzene derivatives. They possess similar properties
and are prepared by similar methods. The analogy is further
maintained in the system of nomenclature, which represents the
xxxiv THE AROMATIC ACIDS 495
acid as a phenyl derivative of the corresponding aliphatic acid.
A few examples will suffice.
Phenylacetic Acid, C 6 H 5 .CH 2 .COOH, is prepared from
benzyl chloride, which is first converted, by boiling with an
aqueous-alcoholic solution of potassium cyanide, into benzyl
cyanide. The product is fractionated, and the cyanide, which
boils at 232, is collected. The cyanide is finally hydrolysed
with moderately strong sulphuric acid, when the phenylacetic
acid crystallises
C 6 H 5 .CH 2 C1 -> C 6 H 5 .CH 2 CN -> C 6 H 5 .CH 2 .COOH.
Benzyl chloride. Benzyl cyanide. Phenylacetic acid.
Phenylacetic acid is a colourless, crystalline compound which
melts at 76 and boils at 262. When the acid is chlorinated or
brominated by the direct action of the halogen, the halogen
replaces the hydrogen of the a-carbon (the carbon atom next to-
the carboxyl group) of the side-chain as in the fatty acids
(p. 151) ; in the cold it enters the nucleus. On oxidation benzoic
acid is formed.
Mandelic Acid, Phenylhydroxy acetic acid, Phenylgly collie
acid, C 6 H 5 CH(OH).COOH. Mandelic acid is isomeric with the
nydroxytoluic acids. It was originally prepared from amygdalin
of bitter almonds by boiling with mineral acids. The benzalde-
hyde and hydrocyanic acid of the amygdalin, which are doubt-
less present in combination, are hydrolysed. The process has
been imitated by forming the cyanhydrin of benzaldehyde, or
mandelic nitrile (p. 470), and hydrolysing the product with
strong hydrochloric acid.
C 6 H 5 CH(OH)CN + 2H 2 O = C 6 H 5 CH(OH).COOH + NH 3 .
Mandelic nitrile. Mandelic acid.
Mandelic acid bears a certain resemblance to lactic acid (p. 319),
On oxidation with nitric acid, it yields benzoyl formic acid, and r
on reduction with hydriodic acid, phenylacetic acid. Hydro-
chloric and hydrobromic acid give respectively chloro- and
bromo-phenylacetic acid
(HN0 3 )
(HI)
C 6 H 5 .CO.COOH.
Benzoyl formic acid.
C 6 H 5 .CH 2 .COOH.
Phenylacetic acid.
(HC1)
(HBr)
C 6 H 5 .CHC1.COOH.
Phenylchloracetic acid.
C 6 H 5 .CHBr.COOH.
Phenylbromacetic acid.
496 THEORETICAL ORGANIC CHEMISTRY CHAP.
Like lactic acid, mandelic acid contains an asymmetric carbon
atom, and exists in two optically active forms.
The acid of bitter almonds is laevo-rotatory ; the artificial
product, which is necessarily inactive (p. 351), has been resolved
into active components by fractional crystallisation of the salts
of the active alkaloids, and also by sowing penicillium (green
mould) in the solution of the ammonium salt, which destroys
the lasvo-acid and liberates the dextro-compound.
Mandelic acid melts at 133. It dissolves in six times its
weight of water at the ordinary temperature. Its solubility is
such as might be anticipated from a hydroxy-acid.
Phenylpropionic Acid, Hydrocinnamic acid, C 6 H 5 .CH 2 .CH 2 .
COOH, is most conveniently obtained from cinnamic acid (see
below) by reduction with sodium amalgam
C 6 H 5 .CH:CH.COOH + H 2 = C 6 H 5 .CH 2 .CII 2 .COOH.
Cinnamic acid. Hydrocinnamic acid.
It crystallises in needles and melts at 47.
Cinnamic Acid, Phenylacrylic add, C 6 H 5 .CH:CH.COOH.--^
The acid is found as the benzyl ester in Peru and Tolu balsam
(p. 467), in storax (p. 480), and in some gum-benzoins (p. 467).
The usual method of preparation illustrates an important
synthetic method, which is known as Perkin's reaction
Perkin's reaction consists in heating together a mixture of an
aldehyde (either aliphatic or aromatic), the sodium salt of a
fatty acid and its anhydride, or some other anhydride. In the
preparation of cinnamic acid, the materials are benzaldehyde,
sodium acetate, and acetic anhydride, which are heated for
several hours to 180. Condensation occurs between the alde-
hyde and the fatty acid with the elimination of water, which is
taken up by the anhydride. The anhydride is converted into
the acid, which liberates the cinnamic acid from its sodium salt
as folio v/s
C 6 H 5 CH;O' TH 2 iCH.~COONa = C 6 H 5 .CH:CH.COONa + H 2 O.
Sodium cinnamate.
(CH 3 CO) 2 O + H 2 O = 2CH 3 .COOH.
C 6 H 5 .CH:CH.COONa + CH 3 .COOH
= C 6 H 5 .CH:CH.COOH + CH 3 .COONa.
Cinnamic acid.
xxxiv THE AROMATIC ACIDS 497
The cinnamic acid is separated from benzaldehyde by pouring
the product into water, adding alkali, and distilling in steam.
The benzaldehyde distils, and the cinnamic acid in the residual
liquid is precipated with hydrochloric acid,'removed by filtration,
and recrystallised from water.
Cinnamic acid forms colourless crystals which melt at 133.
It yields hydrocinnamic acid on reduction (p. 496) and benzalde-
hyde and benzoic acid by oxidation.
Fittig's Researches. The explanation of the course of Perkin's re-
action, about which some difference of opinion at one time existed, is
due to Fittig. He showed that the process is analogous to the forma-
tion of aldol (p. 132) and crotonaldehyde from acetaldehyde (p. 269).
The aldehyde first forms an additive compound with the acid, the
carbon of the aldehyde group attaching itself to the o-carbon of the acid.
A hydroxyacid is formed, which is stable, if, as in isobutyric acid, the
a-carbon has only one hydrogen atom attached. The process resembles
the aldol condensation.
CH 3 .CHO + CH 3 .CHO = CH 3 .CH(OH).CH 2 .CHO.
Aldol.
CH 3 CH 3
I I
C 6 H 5 .CHO + CH.COOH = C 6 H 5 .CH(OH).C.COOH.
CH 3 CH 3
If, as in acetic and propionic acid, the group CH 2 is present in the a
position, water is simultaneously removed and an unsaturated acid
results. This process corresponds to the formation of crotonaldehyde
(p. 269), or cinnamic aldehyde (p. 472).
CH 3 .CHO + CH 3 .CHO = CH 3 .CH(OH).CH 2 .CHO
= CH 3 .CH:CH.CHO + H 2 O.
Crotonaldehyde.
CH 3 CH 3
C 6 H 5 .CHO + CH 2 .COOH = C 6 H 5 .CH(OH).CH.COOH
Intermediate compound.
CH 3
= C 6 H 5 .CH:C.COOH + H t O.
a-Methylcinnamic acid.
It should be noted, that the aldehyde carbon attaches itself always to
the a-carbon atom, and that in the above reaction between benzaldehyde
K K
498 THEORETICAL ORGANIC CHEMISTRY CHAP.
and propionic acid, phenylisocrotonic acid is not formed, as might be
anticipated.
C 6 H 5 .CH:CH.CH 2 .COOH.
Phenylisocrotonic acid.
Phenylisocrotonic acid can, however, be prepared by Perkin's reaction
from benzaldehyde and succinic acid
COOH
C 6 H 5 CHO + CH 2 .CH 2 .COOH
= C 6 H 5 CH:CH.CH 2 .COOH + CO 2 + H 2 O.
From phenylisocrotonic acid, a-naphthol has been synthesised (p. 530).
Perkin's reaction and the formation of crotonaldehyde bear a close
resemblance to Claisen's method for preparing cinnamic aldehyde. It
is probable that in this, as in Perkin's reaction, the formation of a
hydroxy-additive compound precedes that of the unsaturated product.
In reviewing these processes, it may be observed that the conditions
of the reaction are determined by the presence of an aldehyde group on
the one hand and a group CH 2 . CO on the other. The general equation
may be abbreviated in the following way
CO + CH 2 .CO = C(OH).CH.CO = CO. CO + H 2 O.
II II II II II II
It is obvious that the number of unsaturated compounds of both the
aromatic and aliphatic series may be multiplied almost indefinitely by
means of these reactions. The unsaturated aromatic acids have the
following properties in common. They form additive compounds with
nascent hydrogen, halogen acids, and the halogens. On oxidation with
alkaline permanganate in the cold, they take up two hydroxyl
groups to form a dihydroxy-derivative, and, on further oxidation,
ultimately divide at the double link. Cinnamic acid may be taken by
way of illustration. On reduction it forms phenylpropionic acid ; with
hydrobromic acid, phenyl-j8-bromopropionic acid (the bromine
attaches itself to the 0-carbon, see p. 256) ; with bromine, phenyl-
a)3-dibromopropionic acid ; on oxidation with permanganate, phenyl-
glyceric acid, and then benzaldehyde and benzoic acid
(H 2 ) C 6 H 5 .CH 2 .CH 2 .COOH.
Phenylpropionic acid.
(HBr) C 6 H 5 . CHBr. CH 2 . COOH.
Phenyl-j3-bromopropionic acid.
(Br 2 ) C 6 H 5 . CHBr. CHBr. COOH.
Phenyl-aj3-dibromopropionic acid.
(H 2 + O) C 6 H 5 .CH(OH).CH(OH).COOH.
Phenylglyceric acid.
xxxiv THE AROMATIC ACIDS 499
The above reactions should be compared with those of ethylene and
acrylic acid.
afi and 07 Unsaturated Acids. These two kinds of unsaturated
acids are represented by cinnamic and phenylisocrotonic acid, and are
denoted by the position of the double bond which lies between the a
and /3 carbon atoms in cinnamic acid and the # and 7 carbon atoms in
phenylisocrotonic acid.
The chief difference lies in the behaviour of the additive compounds
which they form with hydrobromic acid. In the case of the aj8-acids,
the hydrobromide of the acid, on boiling with water, yields the cor-
responding /3-hydroxy-acid (i), and, on boiling with alkalis, a mixture of
the original acid (2) and the unsaturated hydrocarbon (3) formed by the
elimination of carbon dioxide and hydrobromic acid
1. C 6 H 5 .CHBr.CH 2 .COOH + H 2 O
= C 6 H 5 .CH(OH).CH 2 .COOH + HBr.
Phenyl--hydroxypropionic acid.
2. C 6 H 5 .CHBr.CH 2 .COOH + NaOH
= C 6 H 5 .CH:CH.COOH + NaBr + H 2 O.
Cinnamic acid.
3. C 6 H B . CHBr. CH 2 . COOH + NaOH
= C 6 H 5 .CH:CH 2 + CO a + NaBr + H 2 O.
Styrene.
The hydrobromides of #7 unsaturated acids, like phenylisocrotonic
acid, behave quite differently. On boiling with water, the hydroxy-
acid, which is first formed, loses water and yields a lactone (p. 318)
C 6 H 5 CH.CH .CH 2 .
C 6 H 5 CHBr.CH 2 .CH 2 .COOH ->
O CO.
Phenyl-y-bromobutyric acid. Phenylbutyrolactone.
The readiest method for distinguishing a (By-acid is to heat the acid
with a mixture of equal volumes of strong sulphuric acid and water to
about 140. The lactone is formed if a fty-acid is present, whereas an
a/8-acid remains unchanged. By diluting, neutralising with sodium
carbonate, and extracting with ether, the lactone is separated, the ct-
acid remaining in solution as the alkali salt.
An interesting relation exists between the two groups of acids. It
has been found that, on heating #7-acids with caustic soda solution, a
shifting of the double link to the apposition takes place
C 6 H 5 CH:CH.CH 2 COOH = C 6 H 5 CH 2 .CH:CH.COOH.
y ft * y p a
K K 2
500 THEORETICAL ORGANIC CHEMISTRY CHAP.
The behaviour of these acids has played an important rdle in the
study of chemical structure.
^-Nitrophenylpropiolic Acid, C 6 H 4 (NO 2 ).C:C.COOH. This acid
is readily converted into indigo-blue (p. 524), and was at one time
manufactured as a source of the dye. It is obtained from cinnamic acid
by nitration. Ortho- and para-nitrocinnamic acid are formed together,
and are separated by conversion into the ethyl esters, which have very
different solubilities in alcohol, the para-compound being very sparingly,
the ortho-compound easily soluble. The ester is then hydrolysed and
the free acid brominated. By treatment with strong caustic potash in
the cold, 0-nitrophenylpropiolic acid is obtained
C 6 H 5 .CH:CH.COOH + HNO 3 = C 6 H 4 (NO 2 )CH:CH.COOH.
Nitrocinnamic acid.
C 8 H 4 (NO 2 ).CH:CH.COOH + Br 2 = C 6 H 4 (NO 2 )CHBr.CHBr.COOH.
0-Nitrophenyl-a/3-dibromopropionic acid.
C 6 H 4 (NO 2 )CHBr.CHBr.COOH + 2KOH
= C 6 H 4 (NO 2 )C:C.COOH + 2KBr + 2H 2 O.
0-Nitrophenylpropiolic acid.
It is a crystalline compound which melts at 156. On warming with
alkalis in presence of grape-sugar it is converted into indigo (p. 524).
,CH:CH
Coumarin, C 6 H 4 by the same process by which cinnamic acid
is obtained from benzaldehyde. The hydroxy-cinnamic acid, which
is formed, passes spontaneously into the lactone, when liberated from
its sodium salt.
It is a colourless, crystalline compound, which melts at 67 and has
a pleasant aroma.
QUESTIONS ON CHAPTER XXXIV
1. How may benzoic acid be prepared from each of the following
substances : benzene, toluene, phenylcyanide, benzaldehyde, and benzyl
alcohol ? Which of these methods is of general application, and might
be employed for the preparation of acetic acid ?
2. Compare the physical and chemical properties of the aliphatic and
aromatic acids by reference to acetic and benzoic acid.
xxxiv THE AROMATIC ACIDS 501
3. Describe the preparation of benzoyl chloride and the action upon
it of (i) ammonia, (2) aniline, (3) alcohol, (4) sodium benzoate. Give
equations.
4. Describe a common method for obtaining benzoic esters. Does
the preparation of the derivatives of benzoic ester offer any difficulty ?
5. How can 0-chlorobenzoic acid be obtained from 0-chloronitro-
benzene, w-chlorobenzoic acid from benzoic acid, and /-chlorobenzoic
acid from /-chlorotoluene ?
6. What is anthranilic acid ? How may it be converted into
salicylic and 0-chlorobenzoic acid ?
7. Describe the preparation of saccharin from toluene. What is its
chemical name, and for what purpose is it used ?
8. Explain Kolbe's reaction by reference to the synthesis of salicylic
acid. Mention any reactions by which salicylic acid may be identified
and distinguished from the o- and w-hydroxy-benzoic acids. How is
salicylic acid converted into phenol, benzene, and benzoic acid ?
9. Explain the structural relations which exist between proto-
catechuic acid, vanillin, and piperonylic acid.
10. How is gallic acid obtained ? Name those reactions by which it
is distinguished from gallotannic acid on the one hand and pyrogallol
on the other.
11. Give an account of the tannins and their use in the preparation
of leather. Name some tannin-containing products.
12. Describe the preparation of phthalic acid from naphthalene,
isophthalic acid from ;-xylene, and terephthalic acid from /-toluidine.
How can these three acids be distinguished ?
13. Compare phthalic and succinic acids.
14. How is phthalic acid prepared ? Describe its constitution and
state how it may be transformed-into benzoic acid and benzene.
15. In what manner do mandelic and lactic acids resemble one
another ?
1 6. Describe and explain Perkirfs reaction. How are isomeric
Compounds of the formula C 6 H 5 .C 3 H 4 .COOH obtained? By what
characteristic properties are they distinguished ? Draw a comparison
between Perkin's and Claisen's reactions.
17. Give examples of the application of Perkin's reaction to the pre-
paration of coumaric and 0-nitrophenylpropiolic acid.
CHAPTER XXXV
THE TERPENES AND CAMPHORS
The Terpenes and Camphors include a variety of aromatic
compounds which are common constituents of the essential oils,
or sweet-smelling oils, of plants. It is rarely that these oils con-
sist of one substance. As a rule they contain a number of
closely related compounds, among which are hydrocarbons of the
formula C 10 H 16 . These hydrocarbons are called terpenes, and
have many properties in common. The camphors, which are
frequently associated with them, are ketones of the formula
C 10 H 16 O. Both classes of compounds are related to p- (also
;-) cymene (methyl isopropyl benzene, p. 394).
^10^14 ^10^16 ^10^16^
Cymene. Terpene. Camphor.
Essential oils of plants contain in addition to these the
alcohols terpineol) C 10 H 1C O, borneol, C 10 H 18 O, and menthol,
C 10 H2oO, and certain isomeric compounds belonging to the
aliphatic series, which are described below under olefinic
camphors and terpenes. The following are some of the more
important members of the group.
Pinene, C 10 H 16 , is the chief constituent of oil of turpentine.
It is obtained from rosin, the exudation from the stems of
conifers, by distillation with water. It is also present in varying
quantities in many of the essential oils. It boils at 155, and
has a specific gravity of 0-858. Pinene is found in two optically
active forms : the dextro-compound, or australene, is contained
in American turpentine (Pinus australis) ; the Isevo-compound,
or terebenthene, in French turpentine (Pinus maritima). When
hydrochloric acid gas is passed into pinene, a solid crystal-
line compound, pinene hydrochloride, or artificial camphot 7
10 H 16 .HC1, is formed. With iodine or sulphuric acid, pinene
is converted into cymene (p. 394). Its constitution is not fully
CH. xxxv THE TERPENES AND CAMPHORS
503
established, but is probably represented by the following
formula
C.CH 3
H 2 C
I
CH3.C/
CH.
CH
Probable formula of Pinene.
Turpentine oil is used as a solvent in the preparation of
varnishes, for mixing with pigments, as an embrocation, &c. It
absorbs oxygen, when heated in presence of water, and the
oxygenated water is employed as a disinfectant and deodoriser.
Limonene, C 10 H 16 , is one of the constituents of oil of lemons,
limes, citrons, &c., and is extracted from the rind. Like pinene,
it is optically active, and is found in dextro- and laevo-forms,
which stand in the relation of the two active tartaric acids.
Dipentene is the inactive and probably the racemic form, for its
properties differ somewhat from those of the limonenes. It is
obtained by mixing together equal quantities of the two active
limonenes ; but it is also frequently found in different essential
oils, and in turpentine. Dipentene has been obtained synthetic-
ally and its structure, as well as that of the limonenes, is re-
presented by the following formula
CH,
c
CH 2
CH
CH 3 CH 2
Limonene (Dipentene).
Limonene boils at 175, and has a specific gravity of 0*846.
It combines with 2 molecules of the halogens and halogen
acids, and forms crystalline additive compounds of the formulae
504
THEORETICAL ORGANIC CHEMISTRY
CHAP,
C 10 H ]6 Br 4 , C 10 H l8 Br 2 , which are explained by the presence of
two double bonds.
Camphor, C 10 H 16 O, is obtained from the camphor tree (Laurus
camphora) by boiling the wood with water in a vessel covered
with a perforated^dome, into which the camphor sublimes. It is
a colourless, crystalline substance, with a characteristic smell.
It melts at 175, and boils at 204. In spite of its high
melting- and boiling-points, it vaporises appreciably at ordinary
temperatures. Ordinary or Japan camphor is dextro-rotatory ;
matricaria camphor (Matricaria partkeniuni) is laevo-rotatory.
Camphor is a ketone, for it gives an oxime, camphor oxime,
C 10 H 16 :NOH, with hydroxylamine, and a secondary alcohol,
borneol) C 10 H 17 (OH), on reduction. When oxidised with nitric
acid, it yields camphoric acid, C 8 H 14 (COOH) 2 , which is a
dibasic acid. When distilled with phosphorus pentoxide, or
pentasulphide, it forms cymene.
Both camphoric acid and camphor have been synthesised
and their formulae are well established.
CH,
CH 3
-C COOH
CH 2
CH 3 . C. CH 3
CH 3
-c
CH 3 .C.CH 3
-CO
CH 2 CH
Camphor.
-CH 2
CH 2 CH COOH
Camphoric acid.
The synthetic camphor of commerce is made from pinene,
which by the action of hydrogen chloride at a low temperature
produces by intramolecular change isobornyl chloride (pinene
hydrochloride). This, by heating with sodium acetate and
acetic acid, is converted into isobornyl acetate, which on
hydrolysis gives isoborneol, closely related to borneol, and
finally isoborneol on oxidation yields camphor.
C'CHo
C.CH,
CIIC1
H 2
X ,CH.O.COCH 3
CH
Bornyl chloride.
CH 3 .C.CH,|
\
CH
Bornyl acetate.
THE TERPENES AND CAMPHORS
505
C.CH 3
H 2 C/'
\
CH.OH
CH,.<
:.CH 3
HCI
/
CH 2
\
"H
liorneot.
Borneol, Borneo camphor, C 10 H 17 (OH), is found in nature in
the dextro-, laevo-, and inactive forms. The common or Borneo
camphor, which is dextro-rotatory, is obtained from a tree,
Dryobalanops camphora, growing in Borneo and Sumatra. It is
a crystalline compound, which melts at 203, and boils at
212. It is prepared from camphor by reduction with sodium
in alcoholic solution, which gives isoborneol at the same
time.
Menthol, C 10 H 19 (OH), is the chief constituent of peppermint
oil, to which it lends the characteristic smell. It is the crystalline
residue left on distillation, after removal of the terpenes. It is a
colourless, crystalline substance, which melts at 42 and boils at
212. It is a secondary alcohol, and yields the ketone, menthone,
C 10 H 18 O, on oxidation, and menthyl chloride, C 10 H 19 C1, by the
action of phosphorus pentachloride. Its structure is known,
and is represented as a hydroxy-hexahydrocymene.
CH 3
CH
H 2 C
CH(OH)
CH
CH 3 CH 3
Menthol.
Olefinic Terpenes and Camphors. These substances are
associated with the terpenes and camphors in essential oils, and
506
THEORETICAL ORGANIC CHEMISTRY
are closely related to them chemically, although they strictly
belong to the aliphatic series. The olefinic terpenes have
acquired in recent years a special interest, from the discovery of
their value as perfumes. They constitute the true perfume of
many essential oils.
The scent of geranium oil, oil of lemons, lavender, bergamot,
coriander, linaloes, and attar of roses is derived from these
substances. Two examples will be given.
Greranial, Citral, C 10 H 16 O, is isomeric with camphor. It is an
aldehyde, which gives on reduction the alcohol, geraniol. It is
readily converted into cymene by heating with potassium
hydrogen sulphate
CH 3
C
HCO /v
CH
CH 3
C
HG
HO
Y
CH
CH
CH 3 CH 3
Geranial.
CH 3 CH 3
Cymene.
Geranial is present in lemongrass oil, oil of lemons, and in
citron oil ; geraniol gives the perfume to rose oil, oil of lavender,
ylang ylang, and many other essences. It is converted into
linalol when heated with steam under pressure.
Linalol, C 10 H 18 O, is an alcohol, which has the following
structural formula
HC. CH 2 . CH 2 . C(OH ). CH :CH 2 .
/ c \
CH 3 CH 3
I
CH,
Linalol.
It is found, occasionally with linalyl acetate, in linalol oil, in
bergamot, coriander, and lavender oils. Heated with formic acid
it is converted into dipentene.
THE TERPENES AND CAMPHORS 507
QUESTIONS ON CHAPTER XXXV
1. Give a general account of the constituents of the essential oils.
2. Explain the relationship of the following : pinene, camphor, and
cymene. What are the chief sources of pinene and camphor, and how
are they obtained ?
3. From the formula of limonene, explain the existence of two
optically active forms. What relation do they hold to dipentene ?
What are the sources of limonene ?
4. Why is camphor regarded as a ketone ? What is its relation to
borneol ?
5. Explain the formation of menthyl chloride and menthone from
menthol.
6. Give a short account of the olefmic terpenes and camphors. Why
are they classed among the terpenes and camphors ? What relation do
they bear to cymene and the terpenes ?
CHAPTER XXXVI
MULTINUCLEAR HYDROCARBONS AND THEIR
DERIVATIVES
Multinuclear Hydrocarbons are formed by the linking
together of two or more benzene nuclei. The simplest example
is diphenyl, in which the carbon atoms of two benzene nuclei are
united, or, in other words, a hydrogen atom of benzene is
replaced by phenyl. Theoretically, each hydrogen of the
nucleus might be so replaced, and each new nucleus might be
the centre of a new series of phenyl derivatives. In reality, the
number of such compounds is small, and is limited to two
isomenc diphenyl and two isomeric triphenyl benzenes.
C 6 H 5 . C 6 H 5 . C 6 H 4 (C G H 5 ) 2 . C 6 H 3 (C 6 H 5 ) 3 .
Diphenyl. Diphenylbenzene. Triphenylbenzene.
Again, the phenyl groups, instead of being directly linked,
may be united by one or more carbon atoms. Diphenyl- and
triphenylmethane and dibenzyl are well-known instances.
C 6 H 5 . CH 2 . C 6 H 5 . (C 6 H 5 ) :1 CH. QH 5 . CH 2 . CH 2 . C 6 H 5 .
Diphenylmethane. Triphenylmethane. Dibenzyl, or Diphenylethane.
It is unnecessary to multiply examples. We shall confine our
attention to the better known members of the group, which form
the basis of important colouring matters.
Diphenyl, C 6 H 5 .C 6 H 5 , is found in small quantities in coal-tar.
It may be prepared by passing benzene through a red-hot tube,
or by Fittig's method by acting upon bromobenzene with
sodium. Another good method of preparation is by the action
of finely divided copper on diazobenzenesulphate dissolved in
CH. xxxvi MULTINUCLEAR HYDROCARBONS 509
acetic anhydride. In the reaction nitrogen is evolved, and the
two phenyl groups which are set at liberty unite ; but the
process has received no complete explanation.
Diphenyl is a colourless, crystalline substance, which melts at
71 and boils at 254. In its behaviour with nitric and sulphuric
acids and the halogens it resembles benzene. The only
derivative of importance is diaminodiphenyl or benzidine, which
may be obtained by the reduction of dinitrodiphenyl, but is
more readily prepared from nitrobenzene (see below)
Benzidine, p- Diaminodipheny^ NH 2 .C 6 H 4 .C 6 H 4 .NH 2 . The
manufacturing process for obtaining benzidine is by the
reduction in alkaline solution of nitrobenzene to hydrazo-
benzene. The hydrazobenzene is then boiled with strong
^ hydrochloric acid and converted into benzidine (p. 437). Or,
azobenzene may be first prepared, and by reducing it in acid
solution, converted into hydrazobenzene, which is changed by
the acid into benzidine.
Tolidine, Diaminoditolyl, is prepared in the same way from
o- and ;;z-nitrotoluene. The para-compound cannot be obtained
by this method, for it is the carbon atom in the para-position
to the amino-group, which serves as the link between the two
nuclei and in /-nitrotoluene the position is already ap-
propriated.
Benzidine and 0-tolidine have already been referred to as
forming important azo-dyes, which are known as Congo reds
and benzopurpurins (p. 441).
Diphenylmethane, C 6 H 5 .CH 2 . 6 CH 6 , is most readily obtained
from benzyl chloride and benzene in presence of aluminium
chloride or the aluminium-mercury couple
C 6 H 5 CH 2 C1 + C 6 H 6 = C 6 H 5 .CH 2 .C 6 H 5 + HC1.
Diphenylmethane.
It has a pleasant smell ; it melts at 26 and boils at 263.
When oxidised it yields benzophenone. The reaction is with-
out analogy among the paraffins, and must be ascribed in the
case of diphenylmethane to the influence of the benzene nuclei,
just as the presence of hydroxyl in the alcohols facilitates the
further replacement of hydrogen by oxygen. Benzophenone by
the reverse process of reduction forms diphenylmethane (p. 473).
Triphenylmethane, CH(C 6 H 5 ) 3 , is the mother substance of a
5 io
THEORETICAL ORGANIC CHEMISTRY CHAP,
great variety of dyes, which are generally included under the
name of triphenylmethane colours.
Triphenylmethane itself is a colourless, crystalline compound,
which melts at 92, and forms a molecular compound with one
molecule of benzene, melting at 75. It is obtained by the
action of aluminium chloride on a mixture of chloroform and.
benzene by the ordinary process of Friedel and Crafts.
CHC1 3 + 3C 6 H 6 [+ A1C1 3 ] = CH(C 6 H 5 ) 3 + 3 HC1.
Triphenylmethane.
On oxidation it yields triphenylcarbinol, (OH)C(C 6 H 5 ) 3 , which
appears to possess the properties of a weak base, and may be
termed tripheryl carbonium hydroxide, for it forms an unstable
chloride and sulphate with hydrochloric and sulphuric acids
(p. 235)
(C 6 H 5 ) 3 C.C1. (C 6 H 5 ) 3 C.S0 4 H.
Triphenylmethyl chloride. Triphenylmethyl sulphate.
Colour and Structure. It has already been stated (p. 442 }
that the azo-group is a chromophor forming a part of the
chromogen, azobenzene, which is a highly coloured substance.
According to the theory of Witt the following unsaturated
groups may also act as chromophors
C = C; C = 0; C = N;N/ ; and N = O, '
^O
and when they enter into a compound form a chromogen,
which may or may not be coloured. The manifestation of
colour is usually associated with one or more aromatic nuclei,
and, according to one view, is due to the reduplication of
double linkages ; according to another it is due to the selective
absorption of the aromatic nucleus. The colour of a substance
arises from its power of absorbing certain of the light rays of
the visible spectrum and reflecting others. Solutions of
coloured substances placed in the path of a beam, which is
refracted through the prism of a spectroscope, show a series
of absorption bands. Benzene, though it does not absorb in
the visible spectrum, shows bands in the ultra-violet (or that
portion of the invisible spectrum lying beyond the violet) and
which, though it does not affect the eye, will affect a photo-
graphic plate. These bands of benzene lie on the border of the
visible spectrum and the effect of the chromophor is to slow
xxxvi TRIPHENYLMETHANE COLOURS 511
down the vibrations and thus shift the absorption to the visible
region, which then manifests itself as colour. Thus, the single
chromophor CO in benzophenone produces a colourless product ;
but the diketone, benzil, is yellow, and the triketone is orange.
Benzophenone . C 6 H 5 .CO.C 6 H 5 colourless
Benzil .... C 6 H 5 .CO.CO.C 6 II 5 yellow
Diphenyltriketone C 6 H 5 .CO.CO.CO.C 6 H 5 orange
The same applies to ortho- and para-benzoquinone, in which
the ketone groups are associated with two pairs of double
bonds ; the ortho-compound, in which the ketone groups rein-
force one another, is the more deeply coloured
O O
II II
c c o
HC'.iCH HC'l JCH
C CH
II
O
Yellow. Orange.
In certain classes of dyes, which are basic or acid, it is found
that the substances themselves are colourless, and that
the colour is cnly produced on their conversion into salts ; that
others again change their colour. These changes are usually
explained by a change of structure, in which an arrangement of
double bonds similar to that in quinone, known as a quinonoid
structure, is supposed to take place. We shall see presently
that the free base of malachite green, magenta and other basic
dyes are colourless, and only their salts are coloured. Again r
aminoazobenzene(p.434) is orange in colour, but its salts are violet.
The change is again accompanied by a change of structure.
Aminoazobenzene . NH 2 .C 6 H 4 N = N.C 6 H 5 orange
Hydrochloride . . HC1.NH = C 6 H 4 = N.NHC 6 H 5 violet
A similar kind of change is supposed to occur when colour-
less j^-nitrophenol is dissolved in caustic soda solution
O
OH I
.0
\QAj
Colourless /-nitrophenol. Orange sodium nitrophenate.
5 i2 THEORETICAL ORGANIC CHEMISTRY CHAP.
Malachite green, Betuealdehyde green, js one of the simplest of
the triphenylmethane colours. The first step in its preparation
is to heat together a mixture of benzaldehyde (i mol.), dimethyl-
aniline (2 mols.), and solid zinc chloride. The benzaldehyde and
dimethylaniline combine with 'the elimination of a molecule of
water, which is absorbed by the zinc chloride. The product,
tetramethyldiaminotriphenylmethane, is a colourless, crystalline
substance, which is usually called the leuco-base of malachite green,
and is insoluble in water. I ts formation is represented as follows
A HiC 6 H 4 N(CH 3 ) 2 K /QH 5
HCO + \ = Hfc^QH 4 N(CH 3 ) 2 -fH 2 0.
I HC 6 H 4 N(CH 3 ) 2 X C 6 H 4 N(CH 3 ) 2
Leuco-base of Malachite green.
The second step is to oxidise the leuco-base by means of
lead peroxide and hydrochloric acid. The triphenylmethane
derivative is converted into the carbinol, or base of malachite
green, which, like the leuco-base, is a colourless substance,
insoluble in water ; but, in the presence of the acid, it forms the
soluble chloride, which constitutes the dye.
EXPT. 172. Dissolve a little of the leuco-base in very dilute hydro-
chloric acid, add a minute quantity of lead peroxide, shake up for a
minute, and pour into a large volume of water.
These changes are represented as follows
/C H f TT
HCeC6H 4 N(CH 3 ) 2 (HO)C^QH^
\C 6 H 4 N(CH 3 ) 2 \C 6 P_
Leuco-base of Base of
Malachite green. Malachite green.
HC1 /QH 5
\QH 4 N(CH 3 ) 2 '
Malachite
green.
The constitution of the salts of malachite green is at present
undetermined. The general consensus of opinion is in favour
of what is termed a quinonoid structure for many colouring
matters ; that is, a structure containing one or more double
links of the kind that occur in quinone between carbon and
oxygen. The quinonoid structure for malachite green is repre-
sented as follows
xxxvi TRIPHENYLMETHANE COLOURS 513
N(CH 3 ) 2 .C1.
Quinonoid structure of Malachite green.
In this formula the only position available for the acid radical
n the salts is with the doubly-linked nitrogen atom, which
>ecomes thereby pentavalent.
Rosaniline, Magenta, Fuchsine, was one of the earliest of the
irtificial dyes, and was originally obtained by oxidising with
irsenic aQd a mixture of aniline, o- and /-toluidine.
EXPT. 173. Mix together in a boiling tube about 2. grams each of
aniline, o- and/ toluidine \vithtwice the weight (12 grams) of syrupy
arsenic acid, and heat the mixture in a fusible-metal bath to i8o-i9O
for an hour. The product, which r the arsenate of rosaniline,
dissolves in water with a bright magenta colour.
When the product is extracted with water and treated with
:ommon salt, the rosaniline, which is present as the arsenate, is
converted into the hydrochloride of rosaniline, and, on evapora-
lon, green iridescent crystals are deposited.
To avoid the use of arsenic in the preparation, nitrobenzene,
lydrochloric acid, and iron filings have been introduced as the
>xidising materials. The oxidising agent is the nitrobenzene,
nid the ferrous chloride, which is formed when the iron
lissolves in the hydrochloric acid, acts as carrier, becoming
ilternately oxidised to ferric and reduced to ferrous
alt.
Rosaniline base is, when pure, a colourless substance like the
>ase of malachite green, and is precipitated from a solution of
nagenta by the addition of ammonia.
EXPT. 174. Dissolve a few crystals of magenta in water, and whilst
carbon dioxide is passing through the solution add ammonia.
Magenta base is precipitated in a nearly colourless form. If a skein
of wet wool or silk is steeped in the colourless liquid, it takes up the
colour and is dyed, showing that a salt of the base is formed with a
constituent of the fibre
It dissolves in strong hydrochloric acid with a brown colour,
L L
514 THEORETICAL ORGANIC CHEMISTRY CHAP,
which changes to magenta on pouring into water. Wher
sulphur dioxide is passed through a solution of magenta, the
colour vanishes owing to the formation of the hydrochloride o:
the colourless leuco-base.
Para-rosaniline is prepared, like rosaniline, from a mixture
containing, however, only aniline and ^-toluidine. More
important is the synthesis from triphenylmethane, which, in the
skilful hands of E. and O. Fischer, served the double purpose
of explaining the structure of magenta and the course of the
reaction by which it is obtained.
EXPT. 175. Synthesis of Para-rosaniline. Dissolve a gram o:
triphenylmethane in about 5 c - c - f cold fuming nitric acid, poui
into water, filter, wash, dry on a porous plate, and dissolve in 5 c. c.
of glacial acetic acid. Add gradually a gram of zinc dust from the
point of a knife, and shake up. The colour changes to brown
and the leuco-base of para-rosaniline is formed. It is diluted with
water and precipitated with ammonia, and it is then filtered and
dried. On gently warming the dry precipitate with a few drops
of strong hydrochloric acid in a porcelain basin and adding a little
water, a magenta coloration is produced, from the formation of para-
rosaniline hydrochloride.
The series of reactions described in the above experiment, b}
which triphenylmethane is converted into para-rosaniline, is
represented as follows
,C,H 5 /C 6 H 4 N0 2 /C 6 H 4 NH 2
HC< C 6 H 5 -> HC^-C 6 H 4 NO 2 -> HC^C 6 H 4 NH 2
\C 6 H 5 \C 6 H 4 N0 2 \C 6 H 4 NH 2
Triphenyl- Trinitrotriphenyl- Para :
methane. methane. leucaniline.
/C 6 H 4 NH 2
> (HO)C<-C 6 H 4 NH 2
\C 6 H 4 NH 2
Para-rosaniline
base.
By the action of hydrochloric acid on the base, the hydro-
chloride of para-rosaniline is formed, which is the solubk
colouring matter
HO.C(C 6 H 4 NH 2 ) 3 + HC1 = C(C 6 H 4 NH 2 ) 3 C1 + H 2 O.
As in malachite green, the constitution of the hydrochloride
is doubtful ; but the quinonoid structure is generally accepted
TRIPHENYLMETHANE COLOURS 515
HO
C(C 6 H 4 NH 2 ) 2 .
CH
CH
V
NH.HC1.
Para-rosaniline hydrochloride.
The formation of rosaniline from the mixture of aniline, o- and
/-toluidine is represented by assuming that the methyl group
of /-toluidine acts as the link which connects the nuclei of
aniline and 0-toluidine.
C 6 H 4 NH 2
/C 6 H 4 NH 2
HCJH HiC 6 H 4 NH 2
NH + 30 - HO.C< C 6 H 4 NH 2 + 2H 2 0.
JH H;C 6 H 3 /^ \CH/ NH2
CH 3 6 3 \CH 3
Rosaniline
base.
Aniline Blue. By replacing a hydrogen atom in each of the
three amino-groups of rosaniline by phenyl groups, triphenyl-
rosaniline, or aniline blue, is produced. The discovery was made
by Girard and de Laire, and is effected by heating rosaniline
base with aniline in presence of a small quantity of an organic
acid, such as acetic or benzoic acid
HO.C(C 6 H 4 NH 2 ) 3 + 3C 6 H 5 NH 2 + 4 C 2 H 4 O 2
= (C 2 H;A).C(C 6 H 4 NH.C 6 H 5 ) + 3NH 4 .C 2 H 3 O 2 + H 2 O.
Triphenylrosaniline acetate.
EXPT. 176. Mix together in a boiling tube I gram of rosaniline
base, 5 grams of aniline, and a few drops of glacial acetic acid,
and heat for a quarter of an hour in a metal bath to 180.
Extract the colouring matter with methylated spirit. The solution
is deep blue.
The salts of triphenylrosaniline are insoluble in water but
soluble in alcohol. For this reason the hydrochloride of the
base is sometimes known as spirit blue. It may be rendered
L L 2
516 THEORETICAL ORGANIC CHEMISTRY CHAP.
soluble in water by sulphonation (p. 446), a fact discovered by
Nicholson, and the soluble sulphonates are sometimes called
Nicholsons blues. The sodium monosulphonate is usually
termed alkali blue. It is used in a faintly alkaline solution for
dyeing wool.
EXPT. 177. Make a solution of alkali blue in water faintly alkaline
with sodium carbonate, heat gently, and steep in it a skein of wool for a
few minutes. Squeeze out the wool and introduce it into water acidified
with hydrochloric acid. The blue colour is at once developed.
The colouring matter is absorbed by the fibre as the colour-
less sulphonate, and the blue is only developed after placing the
wool in dilute acid. The sodium disulphonate dissolves in water
with a deep blue colour, and is known as cotton blue or water
blue.
EXPT. 178. To dye cotton with cotton blue, the cotton must first
be mordanted by steeping the cotton for a few hours previously in a
5 per cent, solution of tannin. The cotton is then squeezed out and
placed in a similar solution of tartar emetic for a few minutes and
rinsed in water. The cotton is now impregnated with tannin, which,
in an insoluble form, adheres to the fibre, and on bringing it into a
warm solution of the blue it will take up the colour.
Methyl Violets. The discovery of the aniline blues suggested
the introduction of alkyl radicals into the amido-groups of
rosaniline, and resulted in Hofmann's discovery of the methyl
violets. He obtained the first of these dyes by heating rosani-
line with methyl and ethyl iodide. The colours were known as
Hofmanrts violets, and were probably mixtures of tetra- and
pentamethyl- and ethyl-rosanilines. He found in the mother-
liquors from the violet a green colouring matter, which was
separated and used under the name of iodine green. It is the
quaternary methyl-ammonium iodide of the tetramethyl com-
pound of rosaniline.
X C 6 H 3 (CH 8 )N(CH 3 ) 2 .CH 3 L
I.C^C 6 H 4 .NHCH 3
\C G 1I 4 .NHCH 3
Iodine green.
Neither the Hofmann violets nor iodine green are any longer
employed for dyeing. They were soon replaced by similar
colours, but prepared in a different and less expensive fashion,
known as methyl violet and methyl green-
xxxvi TRIPHENYLMETHANE COLOURS 517
Methyl violet is obtained by oxidising dimethylaniline with
cupric chloride. It is a mixture consisting mainly of tetra- and
penta-methyl pararosaniline. It is probably formed by the
oxidation of one of the methyl groups of dimethylaniline, which
is removed as formaldehyde and serves as the link to the three
dimethylaniline molecules.
H;C 6 H 4 N(CH 3 ) 2
X C 6 H 4 N(CH 3 ),
H.CHO + HiC 6 H 4 N(CH 3 ) 2 + O 2 = HO.C-C 6 H 4 N(CH 8 ) 2 + 2H 2 O.
\C 6 H 4 NHCH 3
HjC 6 H 4 NHCH 3
Base of Pentamethyl
para-rosaniline.
EXPT. 179. Place in a porcelain basin about 40 grams of
common salt, mix it well with 0*3 gram of powdered cupric
chloride, pour in about I c.c. of dimethylaniline and a few drops
of glacial acetic acid, and mix. Warm the basin gently over a small
flame with constant stirring. After a minute or two the violet
colour of methyl violet appears, and in a short time the whole mass
changes to a bronze-coloured powder. This is a double chloride of
the colour base with cupric chloride, from which the colouring matter
is separated by precipitating the copper with hydrogen sulphide.
The violet colour of the substance is shown by mixing some of the
product with water acidified with a little dilute hydrochloric acid to
which sodium acetate solution is then added.
Methyl green is formed from methyl violet by acting upon the
violet with methyl chloride. The compound has a similar com-
position to that of iodine green, the methyl chloride replacing
the methyl iodide. Methyl green quickly loses the molecule
of methyl chloride on heating, and is converted into the original
violet compound.
EXPT. 1 80. Dye a strip of filter paper in methyl green, and
warm it cautiously over a small flame, The colour soon changes
to violet.
The formation of the green colour in the quaternary compounds
is attributed to the formation of a quaternary ammonium group,
which neutralises one of the basic groups, whereby the compound
is practically converted into a derivative of malachite green.
Crystal Violet is the hexamethyl derivative of para-rosaniline.
It was the first of the violets to be obtained in a pure and
5 i8 THEORETICAL ORGANIC CHEMISTRY CHAP.
crystalline form. It is prepared by the action of dimethylani-
line on tetramethyldiamino-benzophenone. The benzophenone
derivative, or Michler's ketone, is formed by the action of
carbonyl chloride on dimethylaniline
X C 6 H 4 N(CH 3 ) 2
COC1 2 + 2C 6 H 5 N(CH 3 )o = C0( + 2HC1.
X C 6 H 4 N(CH 3 ) 2
Michler's Ketone.
(Tetramethyldiaminobenzophenone.)
When equivalent molecules of the ketone and dimethylaniline
react in presence of an acid chloride (phosphorus tri- or oxy-
chloride), the hydrochloride of hexamethyl pararosaniline is
formed.
CO[C 6 H 4 N(CH 3 ) 2 ]. 3
+ = HO.C[C 6 H 4 N(CH 3 ) 2 ] 3 .
H |C 6 H 4 N(CH 3 ) 2 Base of crystal violet.
The base is converted into the hydrochloride by the phos-
phorus chloride.
EXPT. 181. Take about 0*25 gram each of Michler's compound and
dimethylaniline, and add a few drops of phosphorus tri- or oxy-chloride.
In a few moments the colour changes to a deep blue. Pour into a
large volume of water. The colour now assumes a blue-violet tint.
Auramine, which is an important yellow dye, is also prepared
from Michler's ketone by fusing it with ammonium chloride and
zinc chloride
X C 6 H 4 N(CH 3 ) 2 X C 6 H 4 N(CH 3 ) 2
OC< +NH 3 = HN:C< +H,O.
C 6 H 4 N(CH 3 ) 2 C 6 H 4 N(CH 32
Auramine.
EXPT. 182. Take about 0*5 gram each of Michler's ketone,
ammonium chloride, and powdered zinc chloride, and heat over a small
flame until the mass fuses quietly. The deep orange-coloured
product dissolves in alcohol or hot water with a yellow colour.
PHTHALEINS
The compounds which are known as phthaleins are obtained
by heating phthalic anhydride with the phenols. The simplest
of these compounds is phenolphthalein. The phthaleins form
soluble salts with the alkalis, which possess a brilliant and
frequently a fluorescent colour.
Phenolphthalein. When two molecules of phenol and one
molecule of phthalic anhydride are heated together to 115,
xxxvi TRIPHENYLMETHANE COLOURS 5 '9
with the addition of strong sulphuric acid, phenolphthalein is
formed
/CO /C(C 6 H 4 OH) 2
2C 6 H 5 (OH) + C 6 H/ *>0= C 6 H/ yo + H 2 O.
X CO X CO
Phenolphthalein.
It is a white, crystalline substance which melts at 25o-253; it
is very slightly soluble in water, but dissolves readily in hot
alcohol. It retains its character as a phenol, and dissolves in
caustic alkalis with a crimson colour. It is used in alkalimetry
and acidimetrv as an indicator for the titration of weak (organic)
acids with caustic alkalis and alkaline earths, but cannot be used
with ammonia. It also gives a pink colour with the alkaline
carbonates, but not the bicarbonates, and can be employed for
determining the point of conversion of the neutral into the acid
carbonate on the addition of acids.
The constitution of phenolphthalein has been determined by
its synthesis from phthalyl chloride and benzene by means
of Friedel and Crafts' reaction. Phthalyl chloride (p. 476) and
benzene in presence of aluminium chloride form phthalo-
phenone
HjC 6 H 5 ^^CgHjj
CJCla HJC 6 H 5 = C 6 H 4 /\0 6
C 6 H 4 /^>O CO
CO Phthalophenone.
Phthalophenone is then converted successively into dinitro-
diamino-, and, finally, by the action of nitrous acid, into
dihydroxy-phthalophenone, or phenolphthalein
r C^H/Sd ]
CO
Diamino-phthalophenone. Phenolphthalein.
520 THEORETICAL ORGANIC CHEMISTRY CHAP.
The relation of phenol phthalein to triphenyl methane will be
easily realised by a slight change in the manner of writing
the formula (I.). The quinonoid structure is not so readily
formulated. It has been represented by giving to the compound
the form of an acid (II.).
I. II.
/C 6 H 4 OH /C 6 H 4 OH
Cf-C 6 H 4 OH * or C^=C 6 H 4 =0.
I \C 6 H 4 . CO \C 6 H 4 . COOH
Phenolphthalein. Phenolphthalein.
(Quinonoid formula.)
Fluorescein. A more important substance than phenol-
phthalein is fluorescein, which is used in the manufacture of the
eosin dyes. Fluorescein is obtained as already explained
(p. 493) by heating together to 200 (without the aid of sulphuric
acid) phthalic anhydride and resorcinol. It is formed in the
same manner as phenolphthalein.
A C 6 H 3 (OH) 2
2C 6 II 4 (OH) 2 = QH/No
CO CO
At the same time, the tetrahydroxy-compound loses water
and forms fluorescein
: 6 H 3 (OII)
>o
x;o
Fluorescein.
Fluorescein forms a red powder, which is insoluble in water,
but dissolves in alcohol and dilute alkaline solutions with abrilliant
green fluorescence. It is occasionally used as a dye for silk and
wool, and imparts to the fibre a yellow fluorescent effect.
Eosin. By the action of the halogens on fluorescein,
dissolved in acetic acid or alcohol, the eosins are obtained,
colouring matters which are characterised, like fluorescein, by
xxxvi TRIPHENYLMETHANE COLOURS 521
their fluorescence in alkaline, or alcoholic solution, but they
possess a pink instead of a green colour. The formula for the
sodium salt of tetrabromofluorescein, or ordinary eosin, is
represented thus
xC 6 HBr 2 ONa
UC
C 6 HBr 2 ONa
o.
Eosin.
Erythrosin is the corresponding tetriodo-compound.
EXPT. 183. Dissolve about 0*25 gram of fluorescein in alcohol ;
cool, and add a little bromine water. If the solution is now made
alkaline with caustic soda, a deep red-green fluorescent solution is
obtained, which has a pink colour when diluted with water.
An important group of brilliant red dyes, known as the
rh.odami.nes, is obtained from phthalic anhydride and meta-amino-
phenol and its derivatives. They have a constitution similar to
that of fluorescein. The simplest of these compounds is
represented by the following formula
' c \ .
: 6 II 3 NH 2
1 '
Rhodamine.
Aurin and Rosolic Acid. Rosolic acid was originally
obtained from coal tar. It has been synthesised by oxidising a
mixture of phenol and cresol with arsenic acid and sulphuric
acid. Aurin is prepared by heating together phenol, oxalic and
strong sulphuric acids. Rosolic acid and aurin dissolve in
alkalis and alcohol with a bright red colour, but they are now
little used as dyes. Their close connection with para-rosaniline
has been shown in the following way. By heating aurin with
ammonia under pressure, para-rosaniline is formed ; by diazo-
tising para-rosaniline and rosaniline and boiling the product
with water, the ami no-groups in both cases are replaced by
522 THEORETICAL ORGANIC CHEMISTRY CHAP.
hydroxyls, and aurin and rosolic acid are produced. The
formulae of the two compounds are therefore represented as
follows
/QH 4 OH /QH 3 (CH 3 )OH
Aurin. Rosolic acid.
Indigo is the blue colouring matter obtained from the leaves
of the indigo-plant {Indigo/era Sumatrana and arrecta), which
grows in India and Java. The blue colour from woad (Isatis
tinctoria\ a European plant, appears to be a distinct substance.
The indigo is not present as such in the plant, but as indoxyl
gliicoside or indican, which undergoes hydrolysis during
spontaneous fermentation, which sets in when the leaves are
steeped in water
C 14 H 17 6 N + H 2 = C 8 H 7 ON + C fi H 12 O 6 .
Indican or Indoxyl. Glucose.
Indoxyl glucoside.
The indoxyl becomes oxidised by exposure to the air (see
p. 524) and the indigo then separates as a blue, insoluble
powder, which is washed and dried. It comes into the market
in the form of irregular lumps, which, when rubbed against
a hard surface, show a coppery lustre. The sugar with which
the indigo is combined is dextro-glucose.
Commercial indigo is not a pure substance, but contains
varying quantities of other colouring matters (indirubin, indigo
brown), as well as indigo gelatine, etc. Indigo is purified by
crystallisation from aniline and other solvents or by sublimation.
Pure indigo. blue is known as indigotin.
EXPT. 184. Place a few grams of powdered' indigo in a small
porcelain basin, and, nearly in contact with it, a circular sheet of
asbestos paper which is kept in position by a funnel placed on the
top. The basin is heated to a high temperature on a sand-bath. In
the course of about half an hour needle-shaped crystals with a brilliant
coppery lustre will he found attached to the asbestos paper.
For dyeing wool the insoluble indigo is sulphonated and con-
verted into the soluble disulphonic acid, or indigo carmine (p 446).
EXPT. 185. Add strong sulphuric acid to a little indigo, and warm
gently. If the liquid is poured into water a clear blue solution is
obtained, showing that the indigo, which is itself insoluble in water,
has formed a soluble sulphonic acid. A small skein of wool, previously
moistened, when left in the hot, dilute solution for a short time takes
up the colouring matter and is dyed blue.
xxxvi INDIGO 523
For dyeing cotton, indigo carmine is not employed, but an
indigo-vat is prepared, in which the indigo is present in the dis-
solved state. The solubility of the indigo in this case depends
upon the reduction of indigo to indigo white, a colourless substance
which forms soluble salts with the caustic alkalis and alkaline
earths. The reduction is usually effected with alkaline reducing
agents, and the resulting solution is called an indigo-vat. The
reducing agents commonly employed are ferrous sulphate and
lime, or zinc dust and sodium bisulphite. This solution rapidly
oxidises on exposure to air, and indigo blue is precipitated.
When the cotton is immersed in the liquid, it absorbs the indigo
white which on removal from the liquid changes to blue, and
remains firmly attached to the fibre. Indigo blue is one of the
fastest of the organic dyes, and resists the action of soap and
light.
EXPT. 186. Heat a little finely powdered indigo with zinc dust
and caustic soda solution. The indigo dissolves and gives a dark
yellow solution, the yellow colour being due to impurities. Pour
a little of the solution into water. As soon as the liquid falls into the
water it instantly forms a blue precipitate. Place a skein of wet
cotjton in the remainder of the liquid, withdraw it and expose it for
a few seconds to the air, and then wash it in water. The cotton is
permanently dyed.
When indigo is oxidised with nitric acid it forms isatin. The
structure of isatin is known from its synthesis, which need not
be discussed
/ C0 \
C 6 H 4 <( >C(OH).
\N=^
Isatin.
Isatin chloride is obtained from isatin by the action of
phosphorus chloride. The first synthesis of indigo was by the
action of zinc dust and acetic acid on isatin chloride, and is
formulated as follows :
/ C0 \ / co \
CH 4 < >C;C1 + Zn + Cl!C< >C 6 H 4 .
Isatin chloride. J, Isatin chloride.
C0- x
>C 6 H 4 .
H/
Indigo blue.
524 THEORETICAL ORGANIC CHEMISTRY CHAP.
Two molecules of isatin chloride combine, chlorine being
removed and hydrogen taken up by the two nitrogen atoms.
Another synthetic method is the action of grape-sugar and
caustic soda solution on 0-nitrophenylpropiolic acid (p. 500)
+ 2H 2 = C 10 H 10 N 2 2 + 2H 2 + 2 CO 2 .
EXPT. 187. Dissolve a few grams of grape-sugar in a beaker of
warm water, add a little 0-nitrophenylpropiolic acid on the end of
a glass rod, and then a little caustic soda solution. Provided the
water is warm, the formation of indigo takes place rapidly.
A third synthesis is by using 0-nitrobenzaldehyde (p. 472),
acetone, and dilute caustic soda solution.
/CHO
2C 6 H / + 2CH 3 . CO. CH 3 = C 16 H 10 N S O 2 + 2CH 3 . COOH + 2' H 2 O.
\NO 2
EXPT. 188. Dissolve 0-nitrobenzaldehyde in a little acetone, add
a few drops of a dilute solution of caustic soda, and warm gently.
Indigo blue is deposited.
The present method of manufacture is from anthranilic acid
and chloracetic acid. When heated they combine and form
phenylglycine-0-carboxylic acid
/COOH /COOH
f^ TT / _ f~* T T /
^NHJH'T'CijCHfrCOOH l \NH.CH a .COOH + HC1.
Phenylglycine-
0-carboxylic acid.
On fusion with potash, indigo is formed. The process
takes place in two steps. In the first, a substance known as
indoxyl is produced, which in the alkaline melt, oxidises and
forms indigo
/COOH ,CO-\
i. C 6 H 4 / = C 6 H 4 < >CH 2 + C0 2 + H.,0.
X NH.CH 2 .COOH \NH/
Indoxyl.
/CO-. x c -\
= C 6 H 4 < >0=C< >C 6 H 4 + 2H 2 0.
X / XX
Indigo.
xxxvi MULTINUCLEAR HYDROCARBONS 525
EXPT. 189. Mix in a hard glass test-tube 2 grams of phenylglycine
0-carboxylic acid and 5 grams of coarsely powdered caustic potash and
close the tube loosely with a cork. Heat for a minute or two until
the mass fuses and turns to a deep orange colour. On dissolving in
water and exposing the liquid to the air, a precipitate of indigo blue
is thrown down.
I satin and mdoxyl may be looked upon as derivatives of the
parent substance indole, which is obtained by distilling isatin
with zinc dust
CH.
C 6 H 4 <
Indole.
QUESTIONS ON CHAPTER XXXVI
1. What is meant by multinuclear hydrocarbons ? Give examples.
2. Describe the preparation of diphenyl. How would you propose
to prepare benzidine from it ? What is the customary process ?
3. Give an example of the use of benzidine for the preparation of
dyes.
4. Explain why/-nitrotoluene cannot be converted into tolidine.
What is the structure of the tolidines that are known ?
5. Describe the preparation of diphenylmethane and triphenyl-
methane. What products do they give on oxidation ? Contrast this
reaction with the behaviour of the paraffins.
6. Give the alternative formulae for malachite green. Explain the
relation of the colouring matter to the leuco-base and the base. How is
the leuco-base obtained ?
7. Describe the synthesis of para-rosaniline, and explain by means of
it the formation of rosaniline. What is the nitrobenzene process for
preparing rosaniline t
8. What is aniline blue ? How is it prepared and in what form is
it used as a dye ?
9. Give a short account of the development qf the methods for
obtaining violet dyes. How do you explain the formation of methyl,
violet and crystal violet ? How are these substances converted into
green colouring matters and what explanation has been given of the
change ?
10. Discuss the structure of phenolphthalein. Explain its use as an
indicator.
526 THEORETICAL ORGANIC CHEMISTRY CH. xxxvi
11. Give a general description of the manufacture of eosin from
phthalic acid and resorcinol.
12. What is aurin, and what is its relation to para-rosaniline ?
13. How does indigo occur in nature, and how is it obtained from the
natural source ?
14. Describe those properties of indigo which render it available for
dyeing wool and cotton.
15. What product does indigo yield on oxidation, and how
be obtained from that product }
1 6. Name any method by which indigo has been synthesised.
CHAPTER XXXVII
NAPHTHALENE AND ITS DERIVATIVES
Condensed Nuclei. In previous chapters a variety of
hydrocarbons and their derivatives have been described, some
containing one, others more than one, benzene nucleus, linked
together in different ways. Naphthalene affords an example of
an aromatic hydrocarbon of a somewhat different type. Ac-
cording to present views, naphthalene contains two benzene
nuclei which are not distinct, but have two carbon atoms in
common. In anthracene (p. 542) and phenanthrene (p. 553)
three nuclei are fused together, or condensed, in a similar way.
They are examples of condensed nuclei.
Naphthalene, C 10 H 8 , is contained in the middle oil distillate
of coal-tar (p. 38 [), from which, on standing, a portion frequently
crystallises. A further quantity is obtained by fractionating the
same oil after the phenol has been separated with caustic soda
(p. 455). When the uncrystalli sable oil, which first distils, is
removed, the subsequent distillate solidifies. This is impure
naphthalene. It is purified by treatment with a little strong
sulphuric acid, which forms soluble sulphonic acids with the
impurities, so that on washing with water they are dissolved out.
The naphthalene is then sublimed or distilled in steam. It
crystallises in plates, which melt at 79 and boil at 218.
Naphthalene is extremely volatile, even far below its boiling-
point, so that in the coal-gas manufacture a little of it passes
through the scrubbers and purifiers and finds its way into
the gas-pipes, where it occasionally accumulates in sufficient
quantity to obstruct the flow of gas. It burns with a luminous,
527
528 THEORETICAL ORGANIC CHEMISTRY CHAP.
smoky flame, and is utilised for increasing the illuminating
power of (i.e. carburetting) coal-gas. This is well illustrated in
the albo-carbon lamp, where the coal-gas in its passage to the
burner can be directed into a small metal chamber containing
solid naphthalene, which is warmed by the heat of the gas flame.
A little naphthalene volatilises and mixes with the coal-gas,
adding considerably to its luminosity.
Naphthalene acts as a vermin killer and as a mild antiseptic ;
but its chief industrial use is in the manufacture of indigo
(p. 492) and of certain azo-dyes (p. 428).
The formula of naphthalene is C 10 H 8 , and in its chemical
properties it resembles benzene. It can be chlorinated, bromin-
ated, nitrated, and sulphonated in the same way, and gives very
similar products. The following are the formulas of some of
these products
C 10 H 7 C1. C 10 H 7 N0 2 . C 10 H,.S0 3 H.
Chloronaphthalene. Nitronaphthalene. Naphthalene sulphonic acid.
C 10 H 6 CL, Q H 6 (N0 2 ) 2 . C 10 H ( .(S0 3 H) 2 .
Dichloronaphthalene. Dinitronaphthalene. Naphthalene disulphonic acid.
Naphthalene forms ami no-compounds (naphthylamines),
which, like the amino-derivatives of benzene, can be diazotised.
The sulphonic acids can be converted into phenols (naphthols)
by fusion with caustic alkalis ; or into cyanides (naphthyl
cyanides) by distillation with potassium cyanide.
Naphthalene also forms additive products with hydrogen and
chlorine. Tetrahydronaphthalene, C 10 H 12 , is obtained by the
reduction of naphthalene with sodium in a solution of amyl
alcohol. Naphthalene dichloride is prepared by adding hydro-
chloric acid to a mixture of naphthalene and potassium chlorate
(prepared moist and dried) ; naphthalene tetrachloride is formed
by passing chlorine into a chloroform solution of naphthalene.
The first is a yellow liquid, the second, a solid melting at 182.
C 10 H 8 C1 2 . C ]0 H 8 C1 4 .
Naphthalene dichloride. Naphthalene tetrachloride.
Structure of Naphthalene. From the close analogy existing
between naphthalene and benzene, one is naturally led to infer
that naphthalene contains a benzene nucleus, and this view
is apparently confirmed by the behaviour of naphthalene on
xxxvn NAPHTHALENE AND ITS DERIVATIVES
529
oxidation ; for it readily yields phthalic acid (p. 492) when heated
with sulphuric acid in presence of mercuric sulphate.
Now, phthalic acid contains a carbon skeleton of 8 atoms, 6 in
the benzene ring and two in the ortho-position outside it
Yet, the additional 4 carbon and 4 hydrogen atoms of naphtha-
lene outside the benzene nucleus cannot represent two side-
chains such as would yield phthalic acid on oxidation ; for
the stability of naphthalene towards oxidising agents, as well
as the difficulty of distributing the group C 4 H 4 between two
(even unsaturated) side-chains would be directly opposed to
this view. A skeleton of 10 carbon atoms of the following
character must, therefore, be rejected
C C C
: C
But, if the carbon atoms of naphthalene outside the benzene ring
are joined so as to complete a second ring of 6 carbon atoms,
and, if to each of the 8 outlying carbon atoms of the two rings,
a hydrogen atom is attached, such a structure would give the
necessary number of carbon and hydrogen atoms required by the
formula for naphthalene
HO
M M
530
THEORETICAL ORGANIC CHEMISTRY
It would account, moreover, for the stability of the compound
and its similarity to benzene. This structural formula represents
two benzene rings, yet different from any previous combination,
inasmuch as two carbon atoms are common to the two nuclei.
It is commonly called the double-hexagon formula.
Let us now examine the experimental evidence upon which
this structure rests.
We may first refer to an interesting synthesis of naphthol
(hydroxynaphthalene) discovered by Fittig by heating phenyl-
isocrotonic acid (p. 498)
CH
/\
COiOH CO
Phenylisocrotonic acid. (Intermediate compound.)
Another synthesis has been effected by passing phenylbutylene,
or phenylbutylene bromide, over red-hot soda-lime
/CH 2 CH 2 /CH=:CH
C 6 H/ | =C 6 H/ | +2H 2 .
CH^CH \CH=CH
Phenylbutylene. Naphthalene.
Both syntheses, however, only point with certainty to the
presence of one benzene ring in the compound.
More conclusive and complete is the experimental evidence of
Graebe..
It has been stated that when naphthalene is oxidised, it forms
phthalic acid, which is a benzene derivative. In the same way
if nitro-naphthalene is oxidised it yields nitro-phthalic acid. The
benzene ring (A) (p. 531), stamped, as it were, with the nitro-
group, remains intact. If, however, the nitro-compound is
reduced, the product, naphthylamine (ammo-naphthalene), gives
phthalic acid on oxidation. In this case it is the stamped
benzene ring (A) which has been destroyed ; the second.benzene
ring (B) has been preserved. Two benzene rings are con-
sequently present in naphthalene. These changes are repre-
sented as follows
xxxvii NAPHTHALENE AND ITS DERIVATIVES
531
NO,
2/COOII
NO,
NH 9
COOH,
Nitrophthalic acid. Nitronaphthalene. Naphthylamine.
Phthalic acid.
It must be carefully borne in mind that the above proof is not quite
conclusive ; for though it demonstrates clearly the existence of two
separate and distinct benzene rings in the products of oxidation, it fails
to afford actual evidence of their presence in naphthalene itself. This
point has been strongly insisted on by Bamberger, who has suggested
an alternative formula which is discussed below.
In naphthalene, as in benzene, we are met by the difficulty of
disposing of the fourth carbon bond. The formula with alter-
nate double bonds, proposed by Kekule for benzene, was applied
by Erlenmeyer, to naphthalene, and seems a natural and logical
consequence of the relation of the two hydrocarbons
CH CH
HC
HC
CH
CII
CH CH
Erlenmeyer's formula for Naphthalene.
But a similar set of objections to those advanced against the
olefinic (Kekule) formula for benzene may be brought against
Erlenmeyer's formula for naphthalene.
Bamberger has suggested in its place a centric formula of the
following character
CH CH
HC<'
HC
ICH
\l/ c
CH CH
Bamberger's centric formula.
This formula converts naphthalene into a ring of 10 carbon atoms
with 1 2. potential valencies distributed among them, and consequently
M M 2
$32
THEORETICAL ORGANIC CHEMISTRY CHAP.
it contains no benzene ring. This result has been arrived at by
studying the reduction products of naphthylamine and naphthol. The
subject cannot be discussed at length, but one example may suffice. If
naphthylamine, or naphthol in amyl alcohol, is submitted to the action
of sodium, 4 atoms of hydrogen are taken up and tetrahydro-derivatives
are formed. But there are actually produced two derivatives of each
substance, one containing the 4 hydrogen atoms in the substituted, the
other in the unsubstituted, nucleus. The two tetrahydronaphthols may
be represented as follows
I.
CH C'H(OH)
\-s
HC
II.
CH 2 C(OH)
/\ C /\
\CH
CH 2
B
CH
/\
C
CH
Tetrahydronaphthol
VsuDSULiited nucleus).
CH 2 CH
Tetrahydronaphthol
(unsubstituted nucleus).
This difference in the position of the 4 additional hydrogen atoms
produces a very remarkable difference in the properties of the two
compounds. Substance of Formula I., instead of exhibiting the phenolic
properties of the original compound, resembles an aromatic alcohol like
benzyl alcohol. In short, the substituted nucleus acquires aliphatic
properties. It has been termed an alicyclic (ac.} ring, to indicate the
aliphatic properties of the ring^or cyclic portion of the compound.
Now naphthol differs from ordinary phenol in forming naphthyl
ethers by the action of alcohols in presence of strong sulphuric acid, and
in a few other unimportant respects. If the 4 hydrogen atoms enter
the unsubstituted nucleus (Formula II.), naphthol acquires the properties
of ordinary phenol, and loses the power of forming ethers in the above
manner. The substituted nucleus becomes a true benzene ring,
which is indicated by the abbreviation ar. (aromatic). It may be con-
cluded, therefore, that by the process of reduction, nucleus A in Formula
I. and nucleus B in Formula II. are transformed into true benzene
rings. Reference to Bamberger's formula will indicate how this will
occur. By adding 4 hydrogen atoms to either nucleus, four centric
bonds will vanish. The two which project from the middle carbon
atoms into the reduced nucleus, join up and complete a benzene ring of
the centric type (p. 380). By applying this to the case under con-
sideration, the following formulae will represent the two tetrahydro-
xxxvn NAPHTHALENE AND ITS DERIVATIVES
533
haphthols, against which are placed the benzene derivatives they most
closely resemble
CH CH(OH) CH
/i\ C /\
HC/ I V \CH,
J.J.V_/
\ /I
\^JLJ. 2 AAV-/ v
/
HC
ac.
\\A
CH
Tetrahy
> /
CH
dronapht
/^TT "HT^ /
LH 2 WC<^ 1
2 Ct
lol. Benr
/ Crl
[
^1 alcohol.
H 2 C
CH,
/\ (
(
\
\CH V
XT" \
C(OII)
^
H 2 C
\ /
\
/
CH
\ C J
\/ C \\/
CH 2 CH
ar. Tetrahydronaphthol.
CH ::
/ C -,
CH
Xylenol.
The same thing occurs with naphthylamine ; the one compound
resembles benzylamine and the other xylidine
HC
CH.NH 2
CH
HC
HC
X CH 2 .NH 2
CH,
\l/ C V
CH CH 2
a^-. Tetrahydronaphthylamine.
H 2 C
H 2 C
CH 2 C.NH 2
/
I > CH
N / \ /
V c \l/
CH 2 CH
ar. Tetrahydronaphthylamine. Xylidine.
Isomerism of Naphthalene Derivatives. If we number the
positions of the 8 hydrogen atoms arranged round the double
hexagon I, 2, 3, 4 and i', 2', 3', 4', we notice that they may b^
divided into two sets of 4 each, which are symmetrically situated.
534 THEORETICAL ORGANIC CHEMISTRY CHAP.
viz. i, 4, i', 4' (these adjoin one of the central carbon atoms) and
2, 3, 2', 3' (these are separated by one carbon atom from one of
the central carbon atoms)
It follows that two mono-derivatives of naphthalene should
exist, in which one of the first set, or one of the second set of
positions is occupied by the new element or group. This is
actually the case.
Two isomers of most of the mono-derivatives of naphthalene
are known. There are 2 monochloro-, monobromo-, and mono-
nitronaphthalenes, 2 naphthylamines, and 2 naphthols, &c. The
first series is known as a-, the second as /3-compounds. The
number of di-derivatives is easily estimated. Theoretically there
are ten, which number also agrees with the experimental results,
although the complete set has only been obtained in a few cases.
They are indicated by the above numbers, or by "the Greek letters
a i 2 a s 4 an d #1 ft% 3 )3 4 . The i, 2 ; i, 3, and i, 4 positions in
the same ring are sometimes referred to as ortho-, meta-, and
para-positions ; the position I, i' is termed the proposition, and
resembles an ortho-position ; for, if carboxyl groups occupy
these two positions, the substance behaves like phthalic acid,
and forms an anhydride (p. 493).
In the following pages a brief account is given of the more
important naphthalene derivatives, their method of preparation,
properties and uses.
Homologues of Naphthalene. Some of the alkyl derivatives
of naphthalene are found in small quantities in coal-tar. They
are also obtained by Fittig's method from bromonaphthalene,
the alkyl halide, and metallic sodium (p. 386), or by the Friedel-
Crafts reaction from naphthalene and the alkyl halide in
presence of aluminium chloride (p. 386).
There are two methyl and two ethyl naphthalenes of which
only the #-methyl compound is a solid at the ordinary tempera-
ture ; it melts at 32. The other three are liquids with high
boiling-points.
xxxvn NAPHTHALENE AND ITS DERIVATIVES 535
Halogen Derivatives of Naphthalene. They are obtained
by precisely the same methods as the corresponding benzene
derivatives. a-Chloronaphthalene is prepared by passing chlorine
through boiling naphthalene, or by heating naphthalene a-
sulphonic chloride with phosphorus pentachloride (p. 448). It is
a colourless liquid which boils at 263.
C ]0 H 7 S0 2 C1 -f PC1 5 =.C, H 7 C1 + POC1 3 + SOC1 2 .
Naphthalene a-Chloro-
sulphonic chloride. naphthalene.
The $-chloronaphthalene cannot be prepared by direct chlor-
ination but is obtained from /3-naphthylamine (p. 414) by means
of the diazo-reaction
1. C 10 H 7 NH 2 -> C 10 H 7 N:NC1 -> C 10 H 7 C1.
/3-Naphthyl- /3-Diazonaphthalene /3-Chloro-
amine. chloride. naphthalene.
or by the action of phosphorus chloride on /3-naphthol
2. C 10 H 7 OH + PC1 5 = C 10 H 7 C1 + POC1 3 + HC1.
/3-Naphthol. /3-Chloro-
naphthalene.
/3-Chloronaphthalene is a solid which melts at 56 and boils at
265. All the ten dichloronaphthalenes are known.
The halogen atoms as well as the nitro-, sulphonic, and hydr-
oxyl groups are less firmly fixed in the molecule of naphthalene
than in that of benzene, and undergo changes more readily. An
example of this, among others to be presently mentioned, is the
conversion of a-nitronaphthalene into a-chloronaphthalene by
the action of phosphorus pentachloride.
Nitro-Derivatives of Naphthalene. Only a-nitronaphtha-
lene, m.p. 61, is obtained by direct nitration of naphthol with
strong nitric acid.
The second nitro-groups likewise enter the a-positions(i'and
4'). /3-Nitronaphthalene consequently cannot be prepared by
any direct method. It is obtained from /3-naphthylamine by a
curious application of the diazo-reaction. The /3-naphthylamine
is converted into diazonaphthalene nitrite by adding sodium
nitrite to the nitrate of the base. Finely divided cuprous oxide
is then added, when effervescence occurs from the evolution
536 THEORETICAL ORGANIC CHEMISTRY CHAP.
of nitrogen, and /3-nitronaphthalene is formed. It melts
at 79.
CH 7 :N 2 ONO=C 10 H 7 N0 2 -fN a .
/3-Diazonaphthalene /3-Nitro-
nitrate. naphthalene.
Naphthylamlnes. The two a- and /3-naphthylamines re-
semble aniline, and are prepared by similar methods.
a-Naphthylamine is obtained by the reduction of a-nitronaph-
thalene, or by heating a-naphthol with the compound of ammonia
with zinc chloride, or calcium chloride, to 250.
C 10 H 7 OH+NH 3 = C 10 H y NH 2 -{-H 2 0.
The latter reaction has been applied to ordinary phenol (p. 454),
but, in the case of the naphthols, the change is much more easily
accomplished (see below), and is another instance of the mobility
of the groups in naphthalene derivatives.
a-Naphthylamine crystallises in colourless needles, which melt
at 50 and boil at 300.
EXPT. 190. Reactions for a-Naph thy famine. I. Add to a few
grams of a-naphthylamine a solution of dilute hydrochloric acid, in-
sufficient to dissolve the base on shaking. Pour off the solution and
add FeCl 3 . A blue coloration of the liquid slowly develops. 2.
Dissolve a very small quantity of the base in dilute alcohol, add a
little glacial acetic acid, and then drop by drop sodium nitrite
solution. A yellow solution is obtained, which on the addition of
dilute hydrochloric acid changes to violet.
$-Naphthylamine cannot be prepared from nitronaphtha-
lene, as the preparation of the base involves that of the nitro-
compound (p. 535) ; but the action of ammonia under pressure
on /3-naphthol can be applied and is commercially used as the
source of this compound. /3-Naphthylamine melts at 112 and
boils at 294.
Sulphonic Acids of Naphthalene. When naphthalene is
heated with strong sulphuric acid, both the a- and .^-naphthalene
monosulphonic acids, C 10 H 7 .SO 8 H, are formed, which vary in
relative quantity according to the temperature of the reaction.
The a-compound predominates at a low temperature (80) ; the
/^-compound at the higher temperature (160).
The sulphonic acids resemble in properties the corresponding
derivatives of benzene. They are very so'uble and form
soluble salts. By fusion with potash they form naphthols, and by
distillation with potassium cyanide yield cyanides. Phosphorus
xxxvii NAPHTHALENE AND ITS DERIVATIVES 537
pentachloride converts them into sulphonic chlorides, which
have the properties of the corresponding benzene compounds
(p. 448). Di- and tri-sulphonic acids of naphthalene are obtained
by using fuming sulphuric acid containing different quantities
of sulphur trioxide.
Naphthylamine sulphonic acids are important industrial
products, being largely applied in the manufacture of azo-dyes.
Among these may be mentioned naphthionic acid, or 1-4-
naphthylamine sulphonic acid, C 10 H 6 (NH 2 )SO 3 H, which is
obtained by heating a-naphthylamine sulphate in vacuo to
130. It is .the analogue of sulphanilic acid (p. 448) among
the naphthalene compounds, and is used in the production of
Congo-red and the benzopurpurin colours (p. 441).
EXPT. 191. To show the similarity in properties of sulphanilic
acid and naphthionic acid, take about 0*5 gram of each acid in
separate test-tubes, add a few drops of sodium nitrite solution and a
few c.c. of dilute hydrochloric acid, and pour a little of each solution
into test glasses containing about I gram of j8-naphthol dissolved in
caustic soda and diluted with water. Bright red azo-colours of
different shades will be produced.
/3- Naphthylamine gives, according to the temperature of the
reaction, one or 'other of four isomeric sulphonic acids. Many of
the disulphonic acids are also commercial products.
Naphthols are the naphthalene representatives of the phenols,
and share their general characters, although they exhibit some
minor differences in chemical behaviour. The hydroxyl group
is more readily replaced by ammonia, as we have seen in the
formation of the naphthylamines (p. 536), and the ethers are
prepared by the combined action of alcohol and sulphuric acid
after the fashion of ethyl ether. A number of the a- and /3-
naphthol monosulphonic acids, as well as disulphonic acids, are
used in the manufacture of azo-dyes.
a-Naphthol, C 10 H 7 (OH), is obtained by fusing naphthalene
monosulphonic acid with caustic soda (p. 456), or from a-naphthyl-
amine by means of the diazo-reaction (p. 428). Its synthesis
from phenylisocrotonic acid has already been described (p. 530).
a-Naphthol is sparingly soluble in water. It has a phenolic smell
and is volatile. Ferric chloride gives a violet precipitate of
dinaphthol, which is an oxidation product, and has the following
structure
OH.C 10 H 6 .C ]0 H 6 OH.
Dinaphthol.
538 THEORETICAL ORGANIC CHEMISTRY CHAP.
EXPT. 192. I. Reactions for a- Naphthol. Dissolve a little
a-naphthol in very dilute alcohol and to the hot solution add
FeCl 3 . A flocculent violet precipitate of dinaphthol is thrown
down. 2. To another portion of the same solution, when cold,
? per cent, anthracene. This forms the raw material which
is used on an extensive scale in the manufacture of alizarin and
allied colouring matters (p. 549). The crude anthracene may
be purified by distillation with the addition of a little solid
caustic potash, which combines with the carbazole, forming
potassium carbazole. The phenanthrene is removed with
carbon bisulphide, in which it is much more soluble than
anthracene.
Pure anthracene crystallises from benzene and other solvents
in colourless plates with a lustrous surface and blue fluorescence.
It melts at 213 and boils at 351, and forms a compound with
picric acid which crystallises in red needles.
EXPT. 193. Dissolve picric acid and anthracene in about equal
molecular proportions in glacial acetic acid, and pour them together.
Red crystals soon deposit, and melt at 138.
The majority of oxidising agents convert anthracene into
anthraquinone.
Ci 4 H 10 + 30 = C 14 H 8 2 + H 2 0.
Anthracene. Anthraquinone.
CH. xxxvin ANTHRACENE AND ITS DERIVATIVES 543
EXPT. 194. Estimation of Anthracene. The last reaction affords a
simple means of estimating anthracene quantitatively. Dissolve one
gram of crude anthracene in 45 c.c. of glacial acetic acid, and whilst
boiling with a reflux condenser attached to the flask, add 1 5 grams of
chromic acid (CrO 3 ) dissolved in 10 c.c. of glacial acetic acid, diluted
with an equal volume of water. Boil for an hour ; then pour and
rinse the contents into water. Filter, wash with a little dilute caustic
soda and then with water, and dry. Dissolve the crude anthra-
quinone in strong, or slightly fuming, sulphuric acid at 100, and
expose the surface to a jet of steam until crystals begin to form ;
then pour into water, filter, wash, dry, and weigh. 'Sublime the
anthraquinone by heating it in a basin, and estimate the loss of
weight, which is that of pure anthraquinone. The anthracene is
calculated from the amount of anthraquinone.
Properties of Anthracene. Anthracene exhibits certain
points of resemblance to benzene, and more particularly to
naphthalene. It is converted by sulphuric acid into a mono-
and disulphonic acid. By the action of sodium amalgam in
alcoholic solution, it forms anthracene hydride, C 14 H 12 , which
readily passes back into anthracene on oxidation.
With chlorine both addition and substitution products are
formed. The addition compound, anthracene dichloride,
C 14 H 10 C1 2 , is obtained by passing chlorine into a cold solution of
anthracene in carbon bisulphide, whilst the substitution product,
mono chl or anthracene, C 14 H 9 C1, is prepared by the action of
potash on the dichloride
C 14 H 10 C1 2 4- KOH = C 14 H 9 C1 + KC1 + H 2 O.
Mono-
chloranthracene.
Dichloranthracene, C 14 H 8 C1 2 , is produced from anthracene
by the action of chlorine at 100. Both the mono- and dichlor-
anthracenes are yellow, crystalline compounds, which melt at
103 and 209 respectively, and give anthraquinone on oxidation.
It has already been stated that anthracene is readily oxidised to
anthraquinone. The action resembles the oxidation of naphtha-
lene to naphthaquinone, but in the case of anthracene the
process is much more easily accomplished. The resemblance
between the substances themselves is only apparent, for we
shall see presently that anthraquinone has few of the properties
of a true quinone.
544 THEORETICAL ORGANIC CHEMISTRY CHAP.
Anthracene yields no nitro-derivatives when nitrated in the
ordinary way, but is oxidised to anthraquinone. Anthraquinone
is a remarkably stable substance and resists the action of the
ordinary oxidising agents ; but some of its derivatives yield
phthalic acid, and anthraquinone itself is converted into benzoic
acid by the action of fused potash.
In reviewing the above reactions, it must be admitted that
they afford little knowledge of the structure of anthracene. Much
more valuable is the information derived from the synthesis of
anthracene, anthracene hydride, and anthraquinone, which will
now be described.
Synthesis of Anthracene. Anthracene is obtained by the
action of benzene on acetylene bromide (p. 386) in presence of
aluminium chloride
C 6 H 6 + C 2 H 2 Br 4 + C 6 H 6 = C 6 H 4 . C 2 H 2 . C 6 H 4 + 4 HBr.
Anthracene.
It is also obtained by heating C 6 H 4 + 2HC1.
CH,CK \CH/
CH 2 C1
,
Benzyl chloride. Anthracene hydride.
Hjv
4 \C 6 H 4 + 2C 6 H 5 CH 2 Ci
/CH X
= C J ] 4\ ( / C 6 H 4 + 2CH 5 CH 3 + 2HC1.
Anthracene. Toluene.
A second and very important synthesis is effected by boiling
0-bromobenzyl bromide with sodium, for it indicates that the
two central carbon atoms of the molecule of anthracene are
linked to both benzene nuclei in the ortho-positions, though it
xxxvni ANTHRACENE AND ITS DERIVATIVES
545
remains uncertain in which of two ways the combination
occurs
/CHo .-'''Br Br /\
C 6 H 4 < / + 4 Na+ / >
\/Br Br/CH/
0-Bromobenzyl bromide.
C 6 H 4 + 4 NaBr.
xCrLj/Br Br\CH 2X
/ +4Na+ \
VBr BrX
CIIo.CH
-
-S
C 6 H 4 + 4NaBr.
The second formula is excluded by the fact that anthracene is
obtained from 0-tolylphenylketone (see p. vi4). The second
reaction does nevertheless occur at the same time, and gives rise
to phenanthrene described on p. 552.
Synthesis of Anthraauinone. Anthraquinone has been
obtained synthetically by heating #-benzoylbenzoic acid with
phosphorus pentoxide
/CO x /CCk
C 6 H/ \C 6 H 5 = C 6 II 4 <( >C 6 H 4 + H 2 O.
\COOH \CO/
<7-Benzoylbenzoic acid. Anthraquinone.
The various syntheses just described point unmistakably to
the existence in anthracene and its derivatives of a framework
of two benzene nuclei, joined together by two central carbon
atoms, which are attached to adjacent or ortho-carbon atoms of
the nuclei.
Seeing that anthracene is converted by reduction into
anthracene hydride, and that anthracene is changed by oxida-
tion into anthraquinone, the relation of the three is very simply
expressed by the following formulae
CH 2 CII CO
CH 2
Anthracene hydride.
CH
Anthracene.
CO
Anthraquinoee
*T N
546 THEORETICAL ORGANIC CHEMISTRY CHAP.
Moreover, as mono- and dichloranthracene both yield anthra-
quinone on oxidation, the chlorine atoms, which disappear
from the compound, must be attached to the central carbon
atoms
/CCk * /CCk
Monochloranthracene. Dichloranthracene.
A centric formula has also been suggested for anthracene
CH CH
/|\C /i\ C
HC< :
Hd> - x i x y
\l/ c \l/c \/
CH CH CH
Centric formula for Anthracene.
In both formulas for anthracene the disposition of the two
central CH groups differentiates them from the other eight, and
may account for the greater mobility of these two groups.
It is at least noteworthy that reagents first attack the molecule
at these points.
Isomerism of Anthracene Derivatives. We are now in a
position to compute the number of possible isomers which the
derivatives of anthracene can give, and to adopt a system for
distinguishing them. This system consists in numbering or
lettering the carbon atoms as follows
As in naphthalene, the eight outlying carbon atoms form two
series of symmetrical positions of four each, which are dis-
tinguished as a- and )3- positions, or numbered I, 2, 3, 4, and
i', 2', 3', 4', as in naphthalene. There are, in addition, two central
carbon atoms representing a third symmetrical series, which are
distinguished as y l and y 2 positions. There are consequently
xxxvui ANTHRACENE AND ITS DERIVATIVES 547
three mono-derivatives of anthracene, viz. a, /3, and y, and
fifteen di-derivatives. Few of the second series are complete.
Anthraquinone, C 4 H 8 O 2 , is one of the most important of the
anthracene derivatives, and is obtained, as already described, by
the oxidation of anthracene. The manufacturing process is
carried out by heating 50 per cent, anthracene with sodium
dichromate and sulphuric acid. The anthraquinone is digested
with strong sulphuric acid at 100, whereby the impurities are
converted into soluble sulphonic acids, which remain in solution
when the product is poured into water. The purified anthra-
quinone is filtered, and is then ready for conversion into
alizarin.
Anthraquinone prepared in this way is not pure, but may be
further purified by sublimation. Anthraquinone crystallises in
yellow needles, which melt at 277 and sublime at 250 ; it is
insoluble in water, but dissolves in glacial acetic acid and other
organic solvents.
Structure of Anthraquinone. The synthesis of anthra-
quinone from 0-benzoylbenzoic acid has already been described.
As 0-benzoylbenzoic acid is prepared from phthalic anhydride
and benzene in presence of aluminium chloride
CO\ /CO v
O + C 6 H 6 = C 6 H 4 / \C 6 H 5 ,
CO/ X COOH
it follows that the central pair of carbon atoms is linked to at
least one nucleus in the ortho-position. By a similar series of
reactions bromophthalic anhydride can be converted into
bromanthraquinone
/CO-
BrC 6 IL/ \O + C 6 H 6 = m
X OX X COOH
/ /CC \C H + H O
3 \co/
In this case the central pair of carbon atoms is attached to
the substituted nucleus in the ortho-position.
Now, bromanthraquinone, when fused with potash, gives
hydroxyanthraquinone, which on oxidation yields phthalic acid,
the substituted nucleus being destroyed.
N N 2
548 THEORETICAL ORGANIC CHEMISTRY CHAP.
Consequently, the central carbon atoms are also linked to the
unsubstituted nucleus in the ortho-position
HOCO
Hydroxyanthraquinone. Phthalic acid.
Anthraquinone exhibits the properties of a ketone in its
behaviour with hydroxylamine, with which it forms an oxime.
Moreover, on reduction with zinc dust and caustic soda, it
yields a secondary alcohol, oxanthranol^ which forms a red
sodium compound, thus affording a delicate test for the
detection of anthraquinone
/ C0 \ / C0 - \
C 6 H 4 < >C 6 H 4 -f NaOH -f Zn = C 6 H 4 < >C 6 H 4 + ZnO.
\CCK \CH(ONa)/
Sodium oxanthranolate.
EXPT. 195. Add a little caustic soda to a small quantity of
anthraquinone, and then a little zinc dust. On heating to boiling, an
intense red coloration is produced, which disappears on shaking.
This arises from the sodium oxanthranolate becoming oxidised to
anthraquinone on exposure to air.
With tin and hydrochloric acid, anthranol is formed ; it is a
substance possessing weak phenolic properties
XXX X C(OHK
C 6 H 4 +2H 2 = C 6 H 4 <^^ H _ \QH 4 + fI 2 O.
Anthranol.
With a more vigorous reducing agent, as, for example, distilling
with zinc dust, anthracene is formed.
The term anthraquinone is somewhat of a misnomer, for,
although similar in structure, it possesses few of the
characteristics of benzoquinone or naphthaquinone. It has nc
smell, nor does it sublime readily. Moreover, it cannot be
reduced with sulphurous acid, although stronger reducing
agents act upon it in the manner already explained.
Alizarin, D iky droxy anthraquinone, C 14 H 6 O 2 (OH) 2 , is the
principal colouring matter of madder (Rubia tinctorid]. Madder
root has been used as a dyestuff in India and Egypt from the
earliest times, and the process of dyeing cotton with a mordant
xxxvin ANTHRACENE AND ITS DERIVATIVES 549
is mentioned by Pliny. Madder owes its properties as a dye to
alizarin and purpurin, which are present in the root as glucosides.
The glucoside of alizarin is known as ruberythric acid, which is
hydrolysed by acids or ferments, and breaks up into glucose and
alizarin
CajHagOu + 2H 2 O - 2C 6 H 12 O 6 + C 14 H 8 O 4 .
Ruberythric acid. Glucose. Alizarin.
Madder root and the various extracts, which until fifty years
ago were extensively employed in the production of Turkey red
cloth and other dyed and printed fabrics, has been entirely
superseded by artificial alizarin, purpurin, and similar colouring
matters. The first important step in the synthesis of alizarin
was made by Graebe and Liebermann in *i 868, who found that
when alizarin is heated with zinc dust it is converted into
anthracene
C 14 H 8 O 4 + Zn(OH) 2 + 5Zn = C 14 H 10 + 6ZnO.
Alizarin. Anthracene.
Anthracene, well known as a constituent of coal-tar,
was recognised for the first time as the parent substance of
alizarin. Now, alizarin contains two atoms of oxygen more than
anthraquinone, which, from the solubility of alizarin in caustic
soda, are probably present as hydroxyl groups. In order to
introduce two hydroxyl groups into anthraquinone, Graebe and
Liebermann converted it into dibromanthraquinone by bromin-
ation, and then fused the product with potash. They were
fortunate in obtaining the one dihydroxy-derivative, out of ten
possible isomers, identical with alizarin
C 6 H 4 < >C 6 H 2 Br 2 + 2KOH - C 6 H 4 >C 6 H 2 (OH) 2 + 2KBr.
XXX XXK
Dibromanthraquinone. Alizarin.
Manufacture of Alizarin. The somewhat costly process of
Graebe and Liebermann, was soon relinquished in favour of a
method discovered simultaneously by these two chemists and
by Perkin. The anthraquinone is heated with fuming sulphuric
acid (containing 40 per cent, of sulphur trioxide) to 160, and
is converted into anthraquinone-/3-monosulphonic acid. The
550 THEORETICAL ORGANIC CHEMISTRY CHAP.
sodium salt is then prepared by neutralisation of the sulphonic
acid with sodium carbonate
X CO \ X CO \
C 6 H 4 < >C 6 H 4 + H 2 S0 4 = C 6 H/ >C 6 H 3 .S0 3 H + H 2 O.
Anthraquinone-/3-sulphonic acid.
The crystals of the sodium salt are fused in a closed vessel
with caustic soda and a little potassium chlorate. The chlorate
furnishes the necessary oxygen required by the reaction
X CO \
C 6 H 4 < >C 6 H 3 S0 3 Na + NaOH + O
XXX
/ C0 \
= C 6 H 4 < >C 6 H 2 (OH) 2 + Na2S0 3 .
\CO/
Alizarin.
The alizarin, present as the deep violet sodium compound,
is extracted with water, in which it readily dissolves, and
digested with milk of lime.
X CO \
C 6 H 4 / ^>C 6 H 2 (ONa) 2 .
Sodium alizarate.
Insoluble calcium alizarate is thus formed, whilst the impurities
remain in solution. The calcium alizarate is filtered and de-
composed with hydrochloric acid, whereby the alizarin is pre-
cipitated in the form of a light brown amorphous powder. It
comes into commerce mixed with water in the form of a paste
containing 10 or 20 per cent, of alizarin. In order to obtain
alizarin in crystals, it may be sublimed or crystallised from
cumene. It forms ruby-red prisms, which melt at 290 and
sublime without decomposition.
EXPT. 196. The formation of alizarin from anthraquinone sulphonic
acid may be shown on a small scale in the following way. Fuse in a
hard glass tube a little sodium 3-anthraquinone sulphonate with a
little powdered caustic soda and a crystal of potassium chlorate until
a violet-coloured mass is obtained. The test-tube should be turned
round over the flame during the fusion. When cool, the melt of sodium
alizarate is extracted with water, in which it dissolves with a deep violet
colour. On the addition of acid the insoluble alizarin is precipitated
as a buff-coloured oowder.
xxxvin ANTHRACENE AND ITS DERIVATIVES 551
Alizarin is insoluble in water, but dissolves in the caustic alkalis
with a violet colour, forming alizarates of sodium and potassium.
Many of the metallic compounds are insoluble and are differently
coloured. The aluminium alizarate is bright red, the ferric salt
violet, and the chromic compound has a chocolate colour. A
solution of sodium alizarate poured into a solution of one of the
above metallic salts precipitates the insoluble alizarate, called
a lake, and when washed and dried it is used as a pigment.
EXPT. 197. Make moderately strong solutions of alum, ferric
chloride, a mixture of alum and a few drops of ferric chloride and
chromic chloride in separate cylinders, and pour into each a little
alizarin dissolved in a few c.c. of caustic soda solution. The metallic
oxide precipitated by the alkali combines with the alizarin to form an
insoluble lake (or metallic alizarate) which has a different colour in
each case.
The formation of lakes explains the application of alizarin in
the dyeing of cotton. Alizarin is insoluble in water, and has,
moreover, no natural affinity for vegetable fibres. In order to
attach it to cotton, the cloth or yarn is first impregnated with a
salt, usually the acetate, of aluminium, iron, or chromium. It is
then submitted to the action of heat, whereby the acetic acid is
driven off, and the metallic oxide left attached to the fibre. The
cotton is said to be mordanted (p. 441). When steeped in water
containing alizarin in suspension, the oxide unites with the
colouring, and the cotton is permanently dyed. By using
different mordants or mixtures of them, a variety of tints is
produced. In printing cotton cloth, the metallic salt is thickened
with gum, or starch paste, and printed on the fabric, after which
it is decomposed by passing over steam-heated iron plates.
The cloth is then washed and dyed in alizarin, when the
colour adheres to the pattern printed with the metallic salt.
EXPT. 198. Cloth mordanted with stripes' of different metallic
oxides when moistened and left in a beaker of hot water containing a
little alizarin in suspension takes up the dye and after a few minutes
each stripe, according to the nature of the mordant, exhibits a different
colour.
Structure of Alizarin. Alizarin has been prepared syn-
thetically by heating together a mixture of phthalic anhydride
and catechol with sulphuric acid to 150.
552
THEORETICAL ORGANIC CHEMISTRY
C0
CO
- X\
+ C 6 H 4 (OH) a - C 6 H / >C 6 H 2 (OH) 2 + H 2 O.
\ro/
It follows that the two hydroxyl groups are attached to adjacent
carbon atoms in the same nucleus, but leaves undecided which
of the following two structures, I. or II., is correct.
OH
OH
The true formula has been ascertained in the following way.
If phthalic anhydride and phenol are heated with sulphuric acid
two monohydroxyanthraquinones are formed, each of which
can be converted into alizarin. This could only happen if
the hydroxyl groups occupy the a-/3-positions as represented
in Formula I., which is the generally accepted formula for
alizarin.
In addition to alizarin a number of trihydroxyanthraquinones are
prepared and used as dyes.
Purpurin, i-2-<(.>Trihydroxyanthraqtiinone, accompanies alizarin in
madder, but is now prepared synthetically by oxidising alizarin with
sulphuric acid and manganese dioxide.
Anthrapurpurin, \-2-2' -Trihydroxyanthraquinone, is obtained from
the anthraquinone- 1 -2'-disul phonic acid by fusion with caustic soda and
potassium chlorate in the same manner that alizarin is obtained from the
monosulphonic acid.
Flavopurpurin, \-2-TJ-Trihydroxyanthraquinone, is formed like
anthrapurpurin from i-3'-anthraquinone-disulphonie acid.
The structural formulae of the three compounds is represented as
follows :
CO OH
CO OH
CO OH
,OH
HO
CO
Anthrapurpurin.
OH
CO
Flavopurpurin.
xxxvin ANTHRACENE AND ITS DERIVATIVES 553
All these compounds dye a brilliant red with alumina mordants, but
of a slightly yellower shade than alizarin. They are the chief con-
stituents of commercial alizarin sold under the name of yellow shade
alizarin.
It is an interesting fact that among the ten dihydroxyanthraquinones
and the numerous trihydroxy-compounds which have been prepared,
only those can be used as dyes, which contain the two hydroxyl groups
in the a-/8-position in the same nucleus.
Phenanthrene, C 14 H 10 , is isomeric with anthracene, and
accompanies it in coal-tar. It is present in considerable
quantity in crude anthracene, and is removed as already
described (p. 542) ; but it has no commercial value. It crystal-
lises in -colourless needles, melts at 99 and distils at 340. Its
interest is mainly derived from its relation to anthracene.
Phenanthrene has been prepared synthetically by boiling
0-bromobenzyl bromide with metallic sodium, which also yields
anthracene hydride in the manner already explained (p. 545).
The phenanthrene hydride, which is probably first formed in
the reaction, loses hydrogen and gives phenanthrene
/CHo/Br Br\CH 2
C 6 H/ / +4N a
/Br
/CH:CH\
= C 6 H 4 /_ -^C 6 H 4 + 4 NaBr + H 2 .
Phenanthrene.
The structure of phenanthrene is further determined by its
formation from dibenzyl and 0-ditolyl by passing them through
red-hot tubes, and in other ways
C 6 H 5 .CH 2 C 6 H 4 .CH C 6 H 4 .CH 3
C 6 H 5 .CH a C 6 H 4 .CH C 6 H 4 .CH 3
Dibenzyl. Phenanthrene. Ditolyl.
Phenanthrene must therefore be regarded as a derivative of
diphenyl in which the two ortho-positions of the nuclei are
slinked by the group CH:CH
554
THEORETICAL ORGANIC CHEMISTRY
CH
HC/
CH=CH
c/ \c
CH
~\
/
SCH
xc
c\
HC
CH CH
Phenanthrene.
CH
Phenanthrene forms a diketone, or phenanthraquinone,
C 14 H 8 O 2 , on oxidation with chromic acid, which bears a close
resemblance to /3-naphthaquinone. It crystallises in orange
needles, which melt at 198 ; it has no smell, and is not volatile
in steam. It is reduced by sulphurous acid, forms a dioxime
and a bisulphite compound. When phenanthraquinone is
further oxidised with chromic acid, it is converted into a dibasic
acid, diphenic arid, C 14 H 10 O 4 , which forms an anhydride. The
formation of the anhydride recalls that of naphthalic anhydride
(p. 540). The formulae of these compounds is represented as
follows
COOH COOH
I
Phenanthraquinone. Diphenic acid.
CO O CO
Diphenic anhydride.
Phenanthraquinone combines with 0-diamines in presence of
acetic acid and forms yellow crystalline substances, a reaction
which serves to distinguish 0-diamines from other amines
(p. 426)
C 6 H 4 .CO H 2 N
I I +
C 6 H 4 .CO H 2 N
C 6 H 4 C:N X
,H 4 = | | \C 6 H 4
C 6 H 4 ON/
2H 2 0.
QUESTIONS ON CHAPTER XXXVIII
1. Explain the commercial process for obtaining anthracene. What
substances accompany it in coal-tar, and how are they removed ?
2. Give an account of the properties of anthracene. What con-
xxxvin ANTHRACENE AND ITS DERIVATIVES 555:
elusions would you draw as to its structure from a consideration of the
chemical properties of anthracene ?
3. Describe one synthesis of each of the following : ( i ) anthracene,
(2) anthracene hydride, (3) anthraquinone. From these syntheses-
describe the relation of the three compounds by means of structural
formulae.
4. In what respects do the central carbon groups of anthracene
differ from the other carbon groups ? Indicate by numbers or letters
their relative positions in the isomeric di-derivatives of anthracene.
5. Discuss the structure of anthraquinone. How is it obtained in
the pure state ? Why is it called a quinone, and is the appellation a-
correct one ?
6. Describe the production of alizarin. How is the dye applied to-
cotton ? What is the meaning of the terms lake and mordant ?
7. How has the structure of alizarin been ascertained ? What other
derivatives of anthraquinone are used as dyes ?
8. Give an account of the phenanthrene and some of its more im-
portant derivatives.
CHAPTER XXXIX
HETEROCYCLIC COMPOUNDS
FURFURANE, THIOPHENE, PYRROLE, &C.
Heterocyclic Compounds. The term heterocyclic is applied
to ring compounds, not composed wholly of carbon atoms, like
those which have been described in preceding chapters
(homocyclic compounds) ; but in which one or more of the links
in the closed chain are supplied by other polyvalent elements,
such as oxygen, sulphur, or nitrogen. We have already met
with examples of this type of compound in the lactones (p. 318)
and the anhydrides of dibasic acids (p. 348), in which oxygen is
an element in the ring ; also in succinimide and phthalimide
(p. 493), which contain an atom of nitrogen, and in piperazine
(p. 277), which has two atoms of nitrogen in the ring ; and again
in uric acid (p. 368) and xanthine (p. 369) which form con-
densed, or double rings, consisting of a carbon and nitrogen
skeleton. Such heterocyclic compounds are very common, and
their synthesis forms an interesting chapter in recent research.
It would cover too much ground, and exceed the scope of the
present volume, to give even a summary of all the different
known classes of heterocyclic compounds. Some idea of their
number and variety may be gathered from the examples which
are given below. It should be pointed out that the most
common kinds of ring compounds are those consisting of nuclei
of 5 and 6 atoms, or condensed nuclei of the type of naphtha-
lene and anthracene. Ring compounds composed of a larger
or smaller number of atoms are less common.
556
CH. XXXIX
HETEROCYCLIC COMPOUNDS
557
An explanation of these facts has already been indicated, and
is based upon stereochemical considerations (p. 318). We
have selected for illustration three examples of heterocyclic
compounds containing oxygen, sulphur, and nitrogen in a ring
skeleton of 5 atoms. They are known as furfurane, thiophene,
and 'pyrrcle, and their structure is usually expressed by the
following formulse
HC CH HCCH
HCCH
II II
HC CH
O
Furfurane.
Y
Thiophene.
YH
Pyrrole.
Pyrazole, Triazole, and Tetrazole represent 5 -atom rings, con-
taining 2, 3, and 4 nitrogen atoms
HCCH
NH
Pyrazole.
HC CH
II II
N N
NH
Triazole,
HC N
H
Tetrazole.
Examples of 6-atom rings are furnished by pyridine, quinoline,
and isoquinoline, which may be compared with benzene and
naphthalene, wherein an atom of nitrogen replaces one of the
CH groups of the ring
CH
HC
H
CH
CH CH
/\C/\
HC/ V \CH
\
\s
N
Pyridine.
CH
CH HC
Isoquinoline.
These three substances may be regarded as the parent com-
pounds of the alkaloids, which are described in the succeeding
chapter. Acridine, which corresponds to anthracene in structure,
and carbazole, which is a dibenzopyrrole, or condensed nucleus
of pyrrole and benzene, are other well-known examples of
heterocyclic compounds.
5S 8
THEORETICAL ORGANIC CHEMISTRY CHAP.
CII cA H c
CH
CH
CH
HQ
HO
CH
HO
CH
Carbazole.
The structure and properties of the more important of these
compounds will be discussed in the following pages.
Furfurane, C 4 H 4 O, is found in the distillate of pine-wood tar.
It is also obtained by distilling the barium salt of pyromucic
acid (obtained by heating mucic acid) with soda-lime
C 4 H 3 O.COOH = C 4 H 4 O + CO 2 .
Pyromucic acid. Furfurane. I
An interesting synthesis of furfurane derivatives is effected
fay the action of dehydrating agents, like acetyl chloride, on
diketones (known as i-4-diketones from the number of carbon
atoms which separate the oxygen atoms) of the general formula
R.CO.CH 2 .CH 2 .CO.R. This reaction is explained by supposing
a tautomeric change (p. 329) to take place in the structure of
the diketone, which then loses a molecule of water. Acetonyl
acetone, CH 3 .CO.CH 2 .CH 2 .CO.CH 3 , gives dimethylfurfurane -
CH 3 .C:CH.CH:C.CH 3
I.
OiH
OH;
Acetonyl acetone.
CH 3 .C:CH.CH:C.CH 3
I Q
Dimethylfurfurane.
Furfurane is a liquid which boils at 32. No hydrogen is
evolved when sodium is added to it, nor does it combine with
hydroxylamine or phenylhydrazine. The oxygen is therefore
not present as a hydroxyl, or ketone group, which is in agree-
ment with the theory of a ring structure. The vapour of fur-
furane reddens a pine shaving moistened with hydrochloric acid,
and it gives a violet colour with isatin, or with phenanthra-
quinone dissolved in strong sulphuric acid (see reactions for
thiophene and pyrrole). '
Furfurole, Furfuraldehyde, C 4 H 3 O.CHO. The most im-
portant derivative of furfurane is the aldehyde, furfurole, which is
found in the distillate when the pentoses are boiled with strong
xxxix HETEROCYCLIC COMPOUNDS 559
hydrochloric acid. The reaction is used for the quantitative
estimation of pentoses in the following manner : Phenyl-
hydrazine is added to the distillate, and the solid phenyl-
hydrazone of furfurole is then collected and weighed
JHOiHC CiOHJH HC CH
I 1 1 = II II + 3 H 2 0.
j HJHC CjH JCHO HC C.CHO
\)JHOHJ ^
Pentose. Furfurole.
Furfurole is also obtained by distilling bran, or carbohydrates
with dilute sulphuric acid. When freshly distilled and pure, it
is a colourless liquid with an empyreumatic smell, which boils
at 162 ; but it soon darkens on standing. It possesses in
a very marked degree the characteristics of an aromatic
aldehyde.
It yields furfuralcohol on reduction, and pyromucic acid by
oxidation
'CH 2 OH
6
Furfuralcohol. Pyromucic acid.
v/COOH
O
With ammonia it forms hydrofurfuramide, corresponding to
hydrobenzamide (p. 472), and furoin with potassium cyanide,
corresponding to benzoin (p. 472) ; it gives Perkin's (p. 496)
and Claisen's reactions (p. 472), and forms furfuraldehyde green
with dimethylaniline and zinc chloride (p. 512). A delicate
test for furfurole is to expose to its vapour a piece of filter paper
dipped in a solution of aniline hydrochloride, which immediately
turns pink.
Thiophene,C 4 H 4 S. The blue colour, or indophenine reaction
(p. 383), which coal-tar benzene (as distinguished from synthetic
benzene from benzoic acid or aniline) gives with isatin dissolved
in strong sulphuric acid, was traced by V. Meyer to the pre-
sence of a small quantity (about 0*5 per cent.) of a liquid,
to which he gave the name of thiophene.
Thiophene has since been obtained by a variety of synthetic
processes, which for the most part consist in heating mono-
and di-basic acids, or alcohols containing 4 carbon atoms with
560 THEORETICAL ORGANIC CHEMISTRY CHAP.
phosphorus sulphide. Sodium succinate and phosphorus tri-
sulphide, when distilled, afford the best yield of thiophene. Its
homologues are obtained from the i-4-diketones (which yield
furfuranes) by heating them with phosphorus sulphide. The
explanation of the course of the reaction is similar to that given
in describing the process for obtaining furfurane derivatives,
the sulphide of phosphorus furnishing in the present instance
the necessary hydrogen sulphide
R.CH:CH.CH:C.R R.CH:CH.CH:C.R
I I = I I + 2H 2 O.
jOH HjSjH OHj I S 1
Thiophene is a colourless liquid with a faint smell resembling
benzene, and boils at about the same temperature as benzene
(8 4 C ).
Thiotolene, or methylthiophene, and thioxene, or dimethyl-
thiophene, are found in small quantities in the toluene and
xylene fractions of coal-tar naphtha.
All these substances possess the distinctive benzenoid
characters of ring compounds, viz. the property of forming
sulphonic acids and nitro-derivatives with sulphuric and nitric
acids. Moreover, the side-chains of the alkyl thiophenes are
oxidised, like the benzene homologues, to carboxyl groups, and
form acids.
Pyrrole, C 4 H 5 N, is found in small quantities in coal-tar and to
a larger extent in bone-oil or DippePs oil. Dippel's oil, so called
from its discoverer, who used it as a medicine, is obtained by
distilling bones. The glutin (p. 373) of the bone is decomposed
and converted into volatile nitrogenous substances, the majority
of which possess basic characters. Pyrrole is separated from the
black oily distillate by conversion into the solid potassium
pyrrole, C 4 H 4 NK, which it forms on boiling with solid caustic
potash. The potassium compound is separated and decomposed
by water into pyrrole and potash
HC CH IIC CH
II II = II II + KOH.
HC CH HC CH
NiK + HOjH NH
Potassium pyrrole. Pyrrole.
HETEROCYCLIC COMPOUNDS
561
Pyrrole is also obtained by distilling succinimide with zinc
dust
CH 2 .CO X CH=CH X
>NH -> | >N.
CH 2 .CO/ CH=CH/
Succinimide. Pyrrole.
The homologues of pyrrole are prepared from the same class
of diketones, which yield furfurane and thiophene compounds,
by heating them with ammonium acetate, and the reaction may
be explained in a similar fashion
R.C : CH . CH :C.R
!OH"HiNHiH"OHj
R.C:CH.CH:C.R
_NH
2H 2 0.
Pyrrole is a colourless liquid, which boils at 131. It received
its name from the characteristic property of reddening a pine
shaving moistened with hydrochloric acid (Trvppos, fire). It
possesses the characters of a secondary amine and forms a
nitrosamine and an acetyl derivative ; but it is a weak base and
dissolves slowly in dilute acids. When the acid solution is
warmed, it deposits a red amorphous powder, known as pyrrole
red.
lodoie, Tetriodopyrrole, C 4 I 4 .NH, is obtained by the action of
iodine and potash on pyrrole, and, being without smell and a
strong antiseptic, is used as a substitute for iodoform.
Pyrazole, C 3 H 4 N 2 , has only been obtained by direct synthesis.
It is formed by the action of hydrazine on epichlorhydrin in
presence of zinc chloride, when condensation occurs and a ring
compound is formed. At the same time two atoms of hydrogen
are removed by the reducing action of the hydrazine, which is
thereby converted into ammonia
CH 2 . CH
CH 2 CH CH CH
I ^\ II II
-> N^CH 2 -> N CH
NiH 2 ' CH 2 \/ \/
\ NH NH
X NH!HCi!
Epichlorhydrin Intermediate Pyrazole.
+ hydrazine. product.
O O
562 THEORETICAL ORGANIC CHEMISTRY CHAP.
Many of the derivatives of pyrazole are obtained by the action
of hydrazine or its derivatives on i-3-diketones, of the general
formula R.CO.CH. 2 .CO.R. The diketone undergoes tautomeric
change and condensation in the following way
R.Ci"OlCH:C!OH!.R. R.C.CH:C.R
! ! = II I +2H 2 o.
Nj H ;H N - NH
Pyrazole is a crystalline compound which melts at 70 and
boils at 187 and possesses the properties of a weak base.
Antipyrine. The most important of the pyrazole derivatives
is antipyrine, which has a very extensive use in medicine as a
febrifuge and antiseptic. It is obtained by heating together
acetoacetic ester and phenylhydrazine. Condensation occurs,
and the product, which contains one of the carbon atoms in the
form of a ketone group, is known as phenylmethylpyrazolone.
It is formed in the following manner
CH 3 . Ci 6 I CH 2 CH S . C CH 2 .
|| | + H 2 + C 2 H 5 OH
N;H 2 ; CO/OQH, N CO
\ /
N;H
I
C 6 H 5
Phenylmethylpyrazolone.
When the product is heated with methyl iodide and potash, a
tautomeric change occurs in the position of one hydrogen atom,
which wanders to the doubly-linked nitrogen and is replaced by
a methyl group
CH 3 .C=CH
I I
CH S .N CO
N
Formula of Antipyrine.
Antipyrine is a colourless, crystalline compound, which melts
at 113 and dissolves in water. It is a base, and forms soluble
salts. The aqueous solution gives a red colour with ferric
chloride and a bluish-green with nitrous acid.
PYRIDINE 563
PYRIDINE, QUINOLINE, ISOQUINOLINE.
Pyridine, C 5 H 5 N. Pyridine is found in the light-oil
distillate from coal-tar, from which it is separated by treatment
with sulphuric acid in the ordinary course of purification. If
an alkali is added to the acid liquid, a dark-coloured oil separates,
containing pyridine and its homologues, together with quinoline,
isoquinoline, aniline, &c., the constituents of which may be
partially separated by fractional distillation. Pyridine and
its homologues, together with quinoline, are also present in
considerable quantities in bone-oil (p. 560).
Pyridine is a colourless liquid, which boils at 115 and mixes
in all proportions with water. It has a strongly alkaline reaction
towards litmus, and possesses a peculiar smell, which is charac-
teristic of both pyridine and quinoline and many of their homo-
logues. Pyridine is very indifferent to most reagents. It is
unaffected by boiling strong nitric acid or chromic acid.
Sulphuric acid only attacks it at a high temperature, forming a
sulphonic acid. In the same way the halogens have little
action on pyridine under conditions which in the case of
benzene give rise to substitution products. With strong re-
ducing agents, like strong hydriodic acid, nitrogen is eliminated
in the form of ammonia, and the remainder of the molecule is
reduced to pentane
C 5 H 5 N + 5H 2 - C 5 H 12 + NH 3 ,
Pyridine. Pentane.
Pyridine is a base, and forms salts with acids, which are
usually soluble in water. It gives also a yellow, crystalline
double salt with platinic chloride like other organic bases.
C 5 H 5 N. HC1 (CsH 5 N. HCl) 2 PtCl 4 .
Pyridine hydrochloride. Pyridine platinochloride.
It is, moreover, a tertiary base, for it neither combines with
acetyl chloride to form an acetyl derivative, nor with nitrous
acid to form a nitrosamine ; but it unites with methyl iodide,
and gives the quaternary ammonium compound, or pyridinium
methyl iodide, C 5 H 5 N.CH 3 I, which is a crystalline compound.
EXPT. 199. Warm a mixture of equal volumes of pyridine and
methyl iodide ; a reaction sets in and the liquid boils. When cold,
the crystalline quaternary compound is deposited.
P O 2
564 THEORETICAL ORGANIC CHEMISTRY CHAP.
Structure of Pyridine. The stability of pyridine towards
reagents, and the fact that the alkyl pyridines are oxidised to
pyridine carboxylic acids (p. 388), is an indication that we are
dealing with a ring compound, and this view is supported by
numerous syntheses, of which the following are the most
instructive.
Allylethylamine passed over heated lead oxide gives pyri-
dine
CH 2 CH
CH,\H HC/Vll
J + 3?bO = + 3H 2 O + 3?b.
.
CH 2 CH
2 y.L 2 HC
CH
NH N
Allylethylamine. Pyridine.
More important from the point of view of structure is the
relation of pyridine to piperidine or hexahydropyridine, C 5 H n N.
Piperidine is a constituent of black pepper (p. 576), and is a
liquid with a strong ammoniacal smell. It gives pyridine
on oxidation with strong sulphuric acid, or nitrobenzen'e ; and
pyridine, on the other hand, is reduced to piperidine by the
action of sodium on the alcoholic solution
C 5 H 5 N ; C 5 H n N.
Pyridine. Piperidine.
The relation of the two substances is that of benzene to
hexamethylene or hexahydrobenzene (p. 378).
Now piperidine has been synthesised by the dry distillation
of pentamethylenediamine hydrochloride (p. 277)
/CH 2 .CH 2 .NHiHHCl /CH 2 .CH 2X
H,C< = H 2 C< >NH + NH 4 C1.
X CH 2 . CH 2 . JNH 2 X CH 2 . CH/
Piperidine.
Also, by heating an aqueous solution of chloramylamine
**v
\TMT
/CH 2 .CH 2 .NH 2 /CH a ..CH*
H 2 C< = H 2 C< >NH.HQ.
. CH 2 . Cl X CH Q . CH 2
Chloramylamine.
xxxix PYRIDINE 565
It follows, therefore, that pyridine is a ring compound
composed of a skeleton of 5 carbon atoms and I nitrogen atom.
By attaching a hydrogen atom to each carbon atom the formula
C 5 H 5 N is arrived at. We may dispose of the fourth bond of
carbon and the third bond of nitrogen, which remains un-
accounted for, by adopting the alternate double linkage of
Kekule, which was suggested by Korner, or by accepting the
centric arrangement proposed by Bamberger.
N N
Korner's formula. Centric formula.
Isomerism of Pyridine Derivatives. The number of
mono-derivatives, which would be anticipated from a compound
of the structure of pyridine, is three ; for the substance may be
compared with a mono-derivative of benzene, inasmuch as one
position in the ring, viz. that occupied by the nitrogen atom, is
differentiated from the rest, and this is in perfect agreement
with the experimental facts. The three positions are indicated
by the Greek letters a, f, and y.
N
There are three methyl pyridines, three hydroxypyridines,
three pyridine-carboxylic acids, &c.
Homologues of Pyridine. The three methyl pyridines are
known as picolines, the dimethylpyridines as lutidines, and the
trimethylpyridines as collidines. They possess the general
characters of pyridine. On oxidation, the side-chains are
converted into carboxyl groups and mono-, di-, and triba sic acids
are formed after the manner of the methyl derivatives oi
benzene (p. 391) ; but the acids are necessarily weaker, for they
re partly neutralised by the basic character of the nucleus.
566 THEORETICAL ORGANIC CHEMISTRY CHAP.
There are various means of obtaining the homologues of
pyridine. They occur in coal-tar and bone-oil, but they are also
formed synthetically. An interesting process for obtaining the
a-alkylpyridines is the action of heat on quaternary alkyl-
pyridinium iodides. Pyridine methyl iodide heated to 300 gives
a-picoline hydriodide. The method recalls the conversion of
methylaniline into toluidine (p. 423).
N.CH 8 I N.HI
Pyridinium methyl a-Picoline
iodide. hydriodide.
Pyridine-carboxylic Acids. The a-/3-and y-monocarboxylic
acids of pyridine are known as picolinic, nicotinic, and iso-
nicotinic acids, respectively.
COOH
\/ COOH v V
N N N
Picolinic acid. Nicctinic acid. Isonicotinic acid
They can be obtained by the oxidation of the respective alkyl
pyridines, as already mentioned. Of greater interest is their
appearance among the products of oxidation of certain alkaloids.
Thus, Conine (p. 576) yields picolinic acid, whereas nicotine forms
nicotinic acid. For this reason the identification of the three
acids, which is easily effected from a determination of their
melting-points, and from other specific characters, is often of
fundamental importance in arriving at the structure of the
alkaloid under examination. Picolinic acid melts at 136. It
loses carbon dioxide when heated, and gives an orange colour
with ferrous sulphate. The colour reaction with ferrous sulphate
and the loss of carbon dioxide on heating are characteristic of
all the pyridine derivatives containing carboxyl in the n-position.
Nicotinic acid melts at 229 and isonicotinic acid at 304. They
QUINOLINE 567
are all crystalline substances, which dissolve more or less readily
in water.
Quinolinic and Cinchomeronic Acids, C 5 H 3 N(COOH) 2 , are
pyridine-dicarboxylic acids. Quinolinic acid, or pyridine-a/3-
dicarboxylic acid, is obtained by oxidising quinoline (see below) ;
cinchomeronic acid, or pyridine-/3y-dicarboxylic acid, by oxidising
isoquinoline (p. 571).
COOH
M:OOH /NcooH
;COOH . '^
N N
Quinolinic acid. Cinchomeronic acid.
Both acids give anhydrides like phthalic acid by boiling with
acetic anhydride ; but if heated alone they lose carbon dioxide.
Quinolinic acid is readily converted into nicotinic acid, whereas
cinchomeronic acid forms, though at a much higher temperature,
isonicotinic acid.
Quinoline, C 9 H 7 N, was originally obtained by Gerhardt
(1842) by distilling quinine, strychnine, and other alkaloids with
caustic potash. The oil which distilled received the name of
quinolein, which was changed to quinoline. Shortly afterwards
(1846) Anderson isolated the same compound and many of its
homologues from bone-oil. It is also present in coal-tar.
The most convenient source of quinoline is the synthetic method
discovered by Skraup, to be presently described. Quinoline is a
colourless liquid with a smell resembling pyridine ; but differs
from pyridine in not being miscible with water, and it boils at a
much higher temperature (236). In chemical properties the two
substances correspond closely. Quinoline is a tertiary base, and
forms well-defined salts. The acid chromate, (C 9 H 7 N) 2 H 2 CrO 4 ,
is sparingly soluble in water, and is precipitated in the form
of yellow needles on the addition of potassium chromate to a
solution of a salt of quinoline.
Structure of Quinoline. The structure of quinoline is
derived from its synthesis, and from the nature of its de-
composition products. It is obtained by passing the vapours of
allylaniline over heated lead oxide, a reaction which recalls the
formation of pyridine from allylethylamine (p. 564).
568
THEORETICAL ORGANIC CHEMISTRY
CHAP.
/\
CH 2
CH
CH 2
2PbO =
2H 2 O + 2Pb.
yv
NH
Allylaniline.
Skraup's Synthesis consists in heating a mixture of aniline,
glycerol, strong sulphuric acid, and nitrobenzene. The action
is a vigorous one, and when complete the product is made
alkaline and distilled in steam. The quinoline distils over
and is purified by fractionation. The process may be ex-
plained as follows. The glycerol is converted into acrolein,
which forms acrylaniline with the aniline. The nitrobenzene
then oxidises the acrylaniline to quinoline
i. C 6 H 5 NH 2 + OCH.CH:CH 2 = C 6 H 5 N:CH.CH:CH 2 + H 2 O.
Acrylaniline.
joj
?H'CH
. N
Acrylaniline.
N
Quinoline.
Baeyer has also synthesised quinoline in a very simple and
suggestive manner by the reduction of 0-nitro-cinnamic
aldehyde. The nitro-compound on reduction yields the corre-
sponding amino-compound, which undergoes condensation with
the aldehyde group in the side-chain.
CH
^CH
CH:O
\NjHa
0-Aminocinnamic aldehyd.-.
/\
CH
CH
\
CH
N
Quinoline.
QUINOLINE
569
A clear insight into the structure of quinoline is afforded by
the production of quinolinic acid (p. 567) when quinoline is
boiled with potassium permanganate. The reaction is precisely
analogous to the formation of phthalic acid from naphthalene.
In this case, what may be termed the benzene nucleus (B) is
destroyed, and the pyridine nucleus (Py) remains
COOHv
COOH
By converting quinoline into a quaternary ammonium com-
pound with benzyl chloride, the pyridine nucleus is weakened,
and when the product is submitted to oxidation the pyridine
nucleus is destroyed and the benzyl derivative of anthranilic acid
is formed
/COOH
Py!
/\
\/
N.C 7 H 7 C1
Benzylanthranilic acid.
It follows, therefore, that quinoline contains a benzene and
pyridine nucleus, and its structure, like that of naphthalene,
may be interpreted by the aid of Korner's or Bamberger's
formula
XV\
Krrner's formula.
/ x/ \i
\\/\\/
N
Bamberger's formula.
The centric formula proposed by Bamberger rests upon experi-
mental evidence derived from the study of the reduction products of
quinoline, which cannot be described at length. It may, however, be
pointed on*" that the evidence is of the kind which led to the adoption
570
THEORETICAL ORGANIC CHEMISTRY
CHAP.
of the centric formula for naphthalene (p. 379). Quinoline, like the
naphthalene compounds, gives two tetrahydro-derivatives on reduction.
One compound, in which the pyridine nucleus is reduced, resembles
methylaniline in a very remarkable degree, whilst the second compound,
in which the benzene nucleus is reduced, corresponds very closely with
xylidine. A reference to the paragraph relating to naphthalene will
make these points clear (p. 532).
CH 9
Py-tetrahydroquinoline.
CH 2
/\ /\
/CH 3
\/
NH
Methylaniline.
B-tetrahydroquinoline.
Xylidine.
Isomerism of Quinoline Derivatives. The number of
isomeric mono-derivatives of quinoline is obviously very large.
They are distinguished by lettering the three positions of the
pyridine nucleus with the Greek letters a, ft 7, and indicating the
four positions of the benzene nucleus by ortho, meta, para, and
ana^ or by simply numbering the positions in the two nuclei
and attaching the symbols B and Py to distinguish them.
Derivatives of Quinoline. Skraup's reaction has a general
application, i.e. it can be employed not only for converting
aniline into quinoline, but aromatic ammo-compounds in general
into quinoline derivatives. It necessarily follows that such
quinoline derivatives are substituted in the benzene nucleus.
XXXIX
ISOQUINOLINE
571
Thus, 0-aminophenol, when heated with glycerol, sulphuric
acid, and nitrobenzene, is converted into hydroxyquinoline.
When hydroxyauinoline is reduced with tin and hydrochloric
acid, it gives Py-tetrahydro-B-hydroxyquinoline, and the product,
when methylated with methyl iodide, yields kairine, which was
formerly much used in medicine as a febrifuge. Kairine is a
crystalline base, and forms a soluble hydrochloride.
CH 2
S CH 2
-> I I I >
OH
0-AminophenoL
B-0-hydroxyquinoline.
When /-methoxyaniline is submitted to a similar process, it
gives methoxyquinoline, and the tetrahydro-derivative has also
been used in medicine under the name of thalline.
In addition to Skraup's reaction many other synthetic pro-
cesses are available for obtaining quinoline derivatives. The
action of ketones and aldehydes on 0-aminophenol affords a
simple example. Acetone forms a-methyl quinoline
+ 2H 2 O
0-Aminophenol. Acetone. a-Methyl quinoline.
Isoquinoline, C 9 H 7 N, is isomeric with quinoline, and was first
separated by Hoogewerff and van Dorp from the crude coal-tar
quinoline by fractional crystallisation of the sparingly soluble
sulphate. It is a colourless, crystalline substance, which melts at
21 and boils at 237. It resembles quinoline in properties.
Isoquinoline has increased in interest since its recognition as the
parent substance of several alkaloids, such as berberine, the
alkaloid of barberry, and the alkaloids narcotine, papaverine,
and hydras tine, which accompany morphine in opium. Iso-
quinoline has been synthesised in several ways ; but its structure
is most clearly and simply determined by the products which
it yields on oxidation. It is broken up into phthalic acid and
cinchomeronic acid (p. 567) in the following way
572
THEORETICAL ORGANIC CHEMISTRY
CHAP,
COOH
Phthalic acid.
Isoquinoline.
COOH
N
COOH/
Cinchomeronic acid.
In one case the pyridine nucleus is destroyed and phthalic
acid is formed ; in the other, it is the benzene nucleus which
suffers extinction and cinchomeronic or /3y-pyridine-dicarboxylic
acid is produced.
Acridine, C 13 H9N, is found in crude coal-tar anthracene. Its
structure (p. 558) is proved by its synthesis from formyl-diphenylamine
and zinc chloride.
CHO
C 6 H B = C 6 H 4 <
H 4
N
Acridine
Moreover, on oxidation with permanganate it forms quinoline-a-
/8-dicarboxylic acid. Acridine is the mother substance of several
important colouring matters.
Carbazole, C^HgN, accompanies anthracene in anthracene oil, and
is separated from the crude anthracene by distillation with a small
quantity of caustic potash which retains the carbazole in the form of
the potassium compound (p. 542). This compound of carbazole cor-
responds with that of pyrrole, of which it may in fact be regarded as a
derivative (p. 560).
NK
Potassium carbazole.
Like pyrrole also, it gives the red colour with a pine shaving moistened
with hydrochloric acid, and a blue colour to a sulphuric acid solution of
isatin (p. 561). It has been obtained synthetically bypassing diphenyl-
amine through a red-hot tube and in other ways
NH
Diphenylamine.
C 6 H 4
NH
Carbazole
H 2 .
It is a crystalline compound, possessing feebly basic properties ; it
melts at 238 and boils at 351.
ISOQUINOLINE 573
QUESTIONS ON CHAPTER XXXIX.
1. Explain the meaning of heterocyclic compounds. Give examples
drawn from the aliphatic series. Name some heterocyclic compounds
composed of 5 atoms, and give their formulae.
2. Compare the mode of preparation and properties of furfurane,
thiophene, and pyrrole, and their derivatives. Give your reasons for
regarding them as ring compounds.
3. What is furfurole ? Plow is it most readily obtained ? How is it
detected and estimated? Compare its properties with those of
benzaldehyde.
4. Describe the preparation of antipyrine. "What is its relation to
pyrazole ?
5. Give an account of those properties of pyridine which indicate its
ring structure, and any synthesis which points in the same direction.
6. How are the pyridine monocarboxylic acids obtained, and how are
they distinguished ? Why is their identification of importance ?
7. Give an account of the chemical and physical properties of
quinoline. Discuss its structure and its relation to pyridine.
8. Describe and explain Skraup's synthesis of quinoline, and name
any quinoline derivatives, which have been prepared by this reaction.
9. What is isoquinoline and where is it found ? How has its
structure been determined ? What special interest attaches to it ?
10. Compare pyrrole and carbazole in structure and properties.
CHAPTER XL
THE ALKALOIDS
The Alkaloids. The medicinal properties, as well as the
poisonous characters of certain plants have long been recognised.
Early in the nineteenth century Sertiirner, a German apothecary,
isolated the active principle of opium in the crystalline form and
gave it the name of morphium. This discovery quickly led to
others, and before long a large number of similar substances
had been separated in the pure state from a variety of plants.
They possessed basic properties, and were called alkaloids or
vegetable bases ; but whilst the name alkaloid is now applied to
those compounds which have been shown to contain a pyridine,
quinoline, or isoquinoline nucleus, the term vegetable base has
a wider sense, and includes substances like caffeine, theo-
bromine, betaine, c. The alkaloids, then, are complex nitro-
genous substances, possessing basic properties and a pyridine,
or condensed pyridine nucleus. The structure of the majority
of them is still unknown. Although the different individuals
possess distinctive characters, they have many properties in
common. They are optically active and usually lasvo- rotatory
in solution. They form insoluble compounds with many of the
reagents which precipitate the proteins (p. 372), such as tannin,
phosphomolybdic acid, and potassium mercuric iodide. They
also give amorphous brown precipitates with iodine solution.
They have an alkaline reaction, possess for the most part a
bitter taste, and many of them are extremely poisonous. A
few of the alkaloids (conine, nicotine) are liquids, but the
majority are crystalline solids, which are insoluble in water, but
dissolve in most of the organic solvents, such as ethyl and
CH. XL THE ALKALOIDS 575
amyl alcohol, ether, chloroform, &c. The salts, especially the
chloride and nitrate, are very soluble in water, and from the
solution the insoluble base is precipitated by alkalis. The
platinochlorides are yellow, crystalline, and sparingly soluble
substances. Most of the alkaloids are tertiary bases and form
additive compounds with the alkyl iodides. As a rule they are
present in the plant combined with organic acids, such as
malic, citric, and lactic acid, or an acid peculiar to the alkaloid
with which it is associated. In cinchona bark, for example, the
alkaloids are combined with quinic acid, in aconite with aconitic
acid, &c. With the salts of the alkaloids are frequently
associated proteiis, tannins, resins, essential oils, and other
vegetable products, which have to be dealt with in the process
of extraction.
For each alkaloid a special process of extraction is employed,
and for costly pharmaceutical preparations the estimation of the
amount of alkaloid present in the raw material is" effected by a
recognised and carefully elaborated analytical method. A
general scheme for extraction may be briefly indicated. The
carefully ground material is digested with water, which dis-
solves out the salt of the alkaloid, and the solution is then
precipitated with an alkali or lime. If the alkaloid is volatile,
like conine, it is separated by distillation in steam ; otherwise it
is either extracted with a volatile solvent like ether, chloroform,
amyl alcohol, c., or filtered. The solvent in the first case is
evaporated or shaken up with acid, which dissolves the alkaloid
as the soluble salt ; in the second case, the precipitate or its
salt is recrystallised. It is seldom that a single alkaloid occurs
in the plant ; more frequently several are associated, and being
chemically related, they are often difficult to separate.
The free alkaloids belong to different classes of compounds,
such as amides or esters of organic acids in which the basic
character predominates. The amides and esters are separable
into a basic and acid constituent by hydrolysis. The basic portion
often contains a hydroxyl, methoxyl, or carboxyl, or all three
groups. Piperine is an amide, and breaks up on hydrolysis
into the base piperidine and piperic acid (p. 576) ; atropine is
an ester, and yields the base tropine and tropic acid (p. 578).
Cocaine represents a still more complex type, for the basic
portion contains both a hydroxyl and carboxyl group in the
576 THEORETICAL ORGANIC CHEMISTRY CHAP.
form of a double ester, with methyl alcohol in union with the
carboxyl group, and benzoic acid combined with the hydroxyl
group (p. 579)-
In the following pages a short account of some of the better
known alkaloids is given, together with their distinctive re-
actions. They are divided into two classes, viz. those containing
a pyridine and those containing a quinoline nucleus. The
derivatives of isoquinoline, which are of less importance, are
omitted.
PYRIDINE ALKALOIDS
Piperine, C 17 H 19 NO 3 . The fruit and seeds of different kinds
of pepper contain from 7 to 9 per cent, of piperine, which is
extracted by heating with milk of lime, evaporating to dryness,
and extracting the residue with ether.
Piperine is a colourless, crystalline substance which melts at
129. It breaks up, on hydrolysis with caustic alkalis or acids,
into piperidine and piperic acid
C 17 H 19 N0 3 + H 2 * C 5 H n N + C 12 H 10 O 4 .
Piperidine. Piperic acid.
The structure of piperidine has already been explained
(p. 564) ; that of piperic acid is determined by its conversion
into piperonylic acid (p. 489) on oxidation. It is represented
by the following formula
\
^>C 6 H 3 .
CII:CH.CH:CH.COOH.
Piperic acid.
The structure of piperine is that of an amide of piperic acid
in which piperidine is the basic constituent. This agrees with
the fact that piperic chloride and piperidine combine to form
piperine.
Conine, C 8 H 17 N, is the poisonous constituent of hemlock
(Conium maculatum), to which it imparts its unpleasant smell.
The alkaloid is readily obtained by distilling the plant with a
solution of caustic soda. The conine is extracted from the
distillate. It is an oil which boils at 167, and is extremely
XL
THE ALKALOIDS
577
poisonous. The structure of conine was first clearly demon-
strated by Hofmann (1884) who showed it to be a-propyl-
piperidine. Its synthesis was shortly afterwards achieved by
Ladenburg (1886) in the following manner.
a-Picoline undergoes condensation with acetaldehyde and
forms a-allylpyridine
'CHjH 2 + OjCH.CHo
N
a-Picoline.
N
a-Allylpyridine.
H 2 C
H 2 C
Allylpyridine, on reduction, is converted into a-propyl-
piperidine
CH 2
CH 2
CH. CH 2 . CrI 2 . Crlg
NH
a-Propylpiperidine.
The compound is, however, inactive, whereas conine is dextro-
rotatory. Ladenburg succeeded in resolving the inactive com-
pound into its active components by crystallising the inactive
conine tartrate. The dextro-conine tartrate is less soluble than
the laevo-compound, and is the first to crystallise (p. 358).
The substance obtained in this way is identical in every respect
with the natural alkaloid.
Nicotine, C 10 H 14 N 2 , is found in combination with malic and
citric acids in tobacco leaves in quantities varying from o'6 to 8
per cent., from which it is removed by distilling with milk of
lime. The alkaloid passes into the distillate, which is extracted
with ether. Nicotine is an oil which boils at 247, and is laevo-
rotatory. It is very soluble in water, has a strong and dis-
agreeable smell, possesses a burning taste, and is a powerful
poison. It is converted into nicotinic acid on oxidation with
potassium permanganate or chromic acid (p. 566).
It has recently been prepared synthetically, and both the
dextro- and lasvo-modifications are known. It is an interesting
fact that the natural, laevorotatory alkaloid is much the stronger
P P
578 THEORETICAL ORGANIC CHEMISTRY CHAP.
poison. The substance is represented by the following
formula
HX
CH
HQ
H( V
C HC
CH
CH 9
\/
NCH 3
N
Atropine, C 17 H 23 NO 3 , is a constituent of deadly nightshade
(Atropa belladonna)^ henbane (Hyoscyamus niger\ and thorn-
apple (Datura strammonium\ in which it is associated with
hyoscyamine^ hyoscine^ and several other alkaloids. The ex-
tracted juice is mixed with caustic potash and shaken up with
chloroform. The chloroform solution of the alkaloids is
evaporated, and the residue extracted with dilute sulphuric
acid, which dissolves the atropine as the sulphate, from which
the base is precipitated by alkalis. Atropine crystallises in
prisms, which melt at 115. It is a strong base and forms
well-defined salts. Atropine sulphate is used in ophthalmic
cases for dilating the pupil of the eye. It is a strong poison.
When hydrolysed it breaks up into a base, tropine, and an acid,
tropic acid
CtfH^NO, + H 2 = C 8 H 1? NO + C 9 H 10 O 3 .
Atropine. Tropine. Tropic acid.
When tropic chloride is combined with tropine, atropine is
regenerated. Other acids may replace tropic acid, and the
various compounds thus obtained are known as tropeines.
The tropeine of mandelic acid is used as a substitute for
atropine in medicine, and is known as homatropine. Tropic
acid has been synthesised, and its structure is known. The
structure of tropine is probably represented by the following
formula, which is that of a condensed pyridine and pyrrol
nucleus. Tropic acid is probably united to the hydroxyl group
of the base in the form of the ester.
CH 2 CH CH 2
| | ,CH 2 OH
N.CH, CH(OH) C 6 H 5 .CH<;
| | \COOH
CH 2 CH CH 2
Tropine. Tropic acid.
XL THE ALKALOIDS 579
EXPT. 200. Test for Atropine. Moisten a minute quantity of
atropine with strong nitric acid, and evaporate it to dryness *n the
water-bath. Add to the yellow residue a few drops of alcoholic
potash. A violet solution is obtained.
Cocaine, C 17 H 21 NO 4 . The alkaloid is obtained from the
leaves of Erythroxylon coca, in which several closely related
alkaloids occur. The leaves are extracted with water, lead
acetate is added to precipitate tannin and other substances ;
the filtered solution is then freed from lead by means of
hydrogen sulphide ; the filtered liquid is made alkaline, and
the cocaine extracted with ether. Cocaine is a crystalline sub-
stance, which melts at 98. The hydrochloride, C l7 H 21 NO 4 .HCi,
is soluble in water, and is used in medicine as a powerful local
anaesthetic. Taken internally, it acts as a strong poison.
Cocaine breaks up on hydrolysis into a base, ecgonine, methyl
alcohol, and benzoic acid
C 17 H 21 NO 4 + 2H 2 O = C 9 H 15 NO 3 -f C 6 H 5 COOH + CH 3 OH.
Cocaine. Ecgonine.
Ecgonine is closely related to tropine, and is probably repre-
sented by the following formula
CH 2 CH CH.COOH
N.CH 3 CH.OH
I I
CH 2 CH CH 2
Probable formula of Ecgonine.
The benzoic acid and methyl alcohol are united to the
hydroxyl and carboxyl groups respectively.
QUINOLINE ALKALOIDS
Cinchona Alkaloids. The different varieties of cinchona
bark which are grown in India, Ceylon, and South America are
distinguished by the names of red, yellow, and pale bark, and
contain a great number of alkaloids (amounting to 2 to 3 per
cent, of the bark) united with quinic acid (p. 491) and a peculiar
tannin, known as cinchotannic acid. The following are the
most imDortant members of the group
P P 2
580 THEORETICAL ORGANIC CHEMISTRY
Quinine. Cinchonine.
The well-ground bark is mixed with milk of lime and
evaporated to dryness. The mass is extracted with chloroform
or petroleum, and the extract shaken with dilute sulphuric acid,
which dissolves out the alkaloids as sulphates. The acid
solution is neutralised with ammonia and concentrated.
Quinine sulphate first separates, whilst cinchonine sulphate
remains in the mother-liquors.
Quinine, C 20 H 24 N 2 O 2 . When the sulphate of quinine obtained
as described above is dissolved in water and alkali added, the
free alkaloid is precipitated, and may be purified by crystallisa-
tion from alcohol. It forms glistening white needles which,
when anhydrous, melt at 177. It has an alkaline reaction, a
bitter taste, and is a feeble diacid base, forming a hydrochloride
and sulphate of the following formulae
_ J 2 2 .H 2 S0 4 + 8H 2 0. C 2 oH 24 N 2 2 .2HCl + 2H 2 O.
Quinine sulphate. Quinine hydrochloride.
Quinine sulphate is the salt commonly used in medicine. It
has the property of lowering the temperature, and is a valuable
remedy in cases of fever.
The structure of quinine is still unknown. It is a tertiary
diamine, for it combines with 2 molecules of methyl iodide. It
yields quinoline when distilled with potash, and quininic acid
when oxidised with chromic acid. The structure of quininic
acid is represented by the following formula
COOH
N
Quininic acid.
Quinine will probably be represented by the formula
CH S
C 10 H 15 (OH)N
N
Formula of Quinine.
XL
THE ALKALOIDS 581
The structure of the second half of the molecule still remains
undetermined.
EXPT. 20 1. Tests for Quinine. Quinine is detected by the
following tests. Use a solution of the hydrochloride prepared by
adding a few drops of hydrochloric acid to the sulphate mixed with
water. I. Add to a little of the solution a few drops of iodine solu-
tion ; a brown amorphous precipitate is formed. This reaction is
also given by other alkaloids (p. 574). 2. Add chlorine water and
then ammonia in excess. An emerald-green colour is produced.
3. Add sodium carbonate solution and then a little ether. The free
base is first precipitated, and then dissolves in the ether. Decant the
ether on to a watch-glass and let it evaporate. Crystals of the base
remain. 4. Dissolve a little quinine sulphate in a large volume of
water, or add a few drops of glacial acetic acid and then a large
volume of water. A blue fluorescent liquid is obtained.
Cinchonine, C 19 H 22 N 2 O, accompanies quinine in cinchona
bark, and is especially abundant in the bark of Cinchona huanoco,
which contains 2*5 per cent. It crystallises from alcohol in
colourless prisms, and sublimes in a current of hydrogen in
needles which melt at 250. Its physiological action is similar
to that of quinine, but less potent. On oxidation, cinchonine
gives cinchoninic acid, or y-quinoline-carboxylic acid
COOH
N
Cinchoninic acid.
The other part of the molecule appears to be identical with
that of quinine.
Cinchonine affords few distinctive tests. It may be dis-
tinguished from quinine by the absence of any colour reaction
with chlorine and ammonia and the non-fluorescent character
of its solutions.
Opium Alkaloids. The milky juice of the poppy capsule
(Papaver somniferum\ when dried, constitutes opium, and is a
complex mixture of a very large number of alkaloids, resins,
proteids, mineral salts, and organic acids. The alcoholic
solution of onium is known as laudanum.
582
THEORETICAL ORGANIC CHEMISTRY
CHAP.
The following is an average analysis of opium, only the more
important alkaloids being given :
Per
cent.
Morphine 10
Narcotine 6
Papaverine I
Codeine 0*5
Per
cent.
Thebaine 0-3
Narceine O'2
Meconic acid 4
Lactic acid I '25
In order to separate the alkaloids, the opium is extracted with
hot water and boiled with milk of lime, which dissolves the
bases, but precipitates the meconic acid. t The liquid is filtered
from the insoluble calcium meconate, and the filtrate boiled with
ammonium chloride until ammonia ceases to be evolved,
whereby the lime is converted into calcium chloride and
the morphine is precipitated together with other alkaloids.
Morphine, C^H^NOg + HgO, is a colourless crystalline com-
pound, which melts at 230 and decomposes at the same time.
It is very slightly soluble in water, is without smell ; it has a
bitter taste, and is a strong narcotic. It has an alkaline reaction,
and is a tertiary monacid base. The hydrochloride has the
formula C ir H 19 NO 3 .HCl + 3H 2 O. Morphine may be distin-
guished from many of the alkaloids by its solubility in caustic
alkalis. There is little of a definite nature known about its
structure. When distilled with zinc dust, it yields pyrrole
pyridine, quinoline, and phenanthrene.
EXPT. 202. Tests for Morphine. -I. Add a few drops of ferric
chloride to a solution of morphine chloride. A violet-blue colour is
developed. 2. Add a little starch solution to a solution of morphine
hydrochloride, and then a few crystals of iodic acid. Iodine is
liberated by the morphine, and the starch turns blue. 3. Heat a
little morphine with a few drops of strong sulphuric acid on the
water-bath for half-an-hour. Cool the liquid, and add a drop of
nitric acid. A violet colour is produced.
Strychnos Alkaloids. The seeds of nux vomica (Strychnos
nux-vomica) and St. Ignatius' beans (Strychnos Ignatit) contain
the three alkaloids strychnine, brucine, and curarine, which are
remarkable for their excessively poisonous character. At pre-
sent little is known about their structure. On distillation with
potash they yield quinoline.
XL THE ALKALOIDS 5^3
To obtain the alkaloids from nux vomica, the seeds are
powdered and extracted with alcohol. The extract is con-
centrated, and lead acetate added to precipitate tannin. The
excess of lead is removed from the filtrate with hydrogen
sulphide, and the alkaloids are then thrown down from the
filtrate with ammonia. Brucine is separated from strychnine
by its greater solubility in alcohol.
Strychnine, C 21 H 22 N 2 O 2 , crystallises in colourless prisms,
which melt at 284. It is nearly insoluble in water, but dis-
solves readily in acids. The hydrochloride has the formula
C 21 H 22 N 2 O 2 .HC1, and the alkaloid is therefore a monacid base.
EXPT. 203. Test for Strychnine. A characteristic test for strych-
nine is the following : Dissolve a crystal of strychnine in strong
sulphuric acid, and add a little solid potassium dichromate, lead
peroxide, or manganese dioxide. A violet colour is produced,
which soon fades.
Brucine, C 2 3H 26 N 2 O 4 + 4H 2 O, crystallises in colourless needles,
which in the anhydrous state melt at 178. When fused with
potash, tetrahydroquinoline together with lutidine and collidine
distil. It is a monacid base like strychnine, but is less
poisonous.
EXPT. 204. Test for Brucine. Brucine is detected as follows :
Dissolve a little brucine in strong sulphuric acid, and add a crystal of
potassium nitrate or a drop of nitric acid. A deep orange colour is
developed, which changes to violet on the addition of a solution of
stannous chloride. The presence of nitric acid is easily detected by
this reaction.
QUESTIONS ON CHAPTER XL
1. Name some of the characteristic features of the alkaloids. What
is the origin of the name ?
2. How would you show the relation of certain of the alkaloids to
pyridine and quinoline ? Give examples.
3. Give either a general scheme or some special method for extracting
the alkaloids from plants, and explain the object of the different steps.
4. What is piperine? What products does it yield on hydrolysis?
Give a method for preparing pyridine from piperine.
584 THEORETICAL ORGANIC CHEMISTRY CH.
5. Describe the synthesis of conine from pyridine.
6. How is nicotine prepared from tobacco ? Name some of its pro-
perties. How would you show its relationship to pyridine ?
7. What is tropine? How is it related to atropine ? Name the
plants in which atropine is found.
8. Describe a method for separating the cinchona alkaloids from bark.
Compare the structure and reactions of quinine and cinchonine.
9. Name some of the constituents of opium. How are the alkaloids
separated ? What are the distinctive reactions for morphine ?
10. How would" you distinguish strychnine from brucine ?
ANSWERS TO QUESTIONS
CHAPTER II
2. C, 42*13 ; H, 6*42 ; O, 51*45 per cent.
4. CO 2 , 0*146; H 2 O, 0-12 ; N, 74-66 c.c.
6. N, 45*92 per cent.
7. C, 3978; H, 6*79 per cent.
10. N, 11*58 per cent.
CHAPTER III
1. C 4 H 8 2 .
2. 120*05, M.W.
3. 192*7, M.W.
4. 91*45, M.W.
5. C 3 H 5 ON 2 C1S.
6. CH 2 O.
7. 177-3, M.W.
11. CH 2 .
12. C 2 H 6 O.
13. C 6 H 7 N.
CHAPTER V
2. n = 8.
4. CH 4 , 40 ; H, 55 ; N, 5 per cent.
17. CH 4 , 42*25 ; H, 53*52 ; N, 4*23 per cent.
CHAPTER VI
I. 17*4; 7*9; 23*7; 14 grams.
CHAPTER XXII
4. 99 per cent.
12. C 2 H 4 (COOH) 2 , C 3 H 6 2 .
CHAPTER XXXII
6. 20*32 per cent., or one methoxyl group
585
INDEX
INDEX
(Names of persons are printed in italics.)
AbeVs flashing-point apparatus, 61
Acenaphthene, 540
Acetal, 132 ; acetals, 132, 276
Acetaldehyde, 87, 100, 123, 137
Acetaldehyde fCyanhydrin, 129 ; phenyl-
hydrazone, 130 ; preparation of, 130
Acetaldpxime, 129
Acetamide, 177
/>-Acetamidophenetol, 457
Acetanilide, 417, 420
Acetates, 162
Acetic acid, 157 ; electrolysis of, 152 ; pro-
perties of, 161 ; salts of, 162 ; structure
of, 147
Acetic acid, glacial, 158
Acetic anhydride, 175
Acetic ether, 184
Acetins, 280
Acetoacetic acid, 187, 326
Acetoacetic ester, 326 ; acid hydrolysis of,
329 ; ketonic hydrolysis of, 328
Acetobromamide, 205
Acetochloranilide, 422
Acetone, 100, 123, 127, 141, 242
Acetone cyanhydrin, 129 ; phenylhydr-
azone, 130 _,
Acetonitrile, 223
Acetonylacetone, 558
Acetophenone, 473
Acetoxime, 129
Acetoxyl radical, 174
Acetyl chloride, 173
Acetyl radical, 150
Acetylene, 256, 383 ; properties of, 259
Acetylene dibromide, 261 ; tetrabromide,
261
Acetylenes, 255
Acetylides of the metals, 260
Acetyl malic acid, 350
Acetyl propionic acid, 330
Acid amides, 176
Acid anhydrides, 175
COHEN'S THEOR. ORG. CHEM. B.D. 589
Acid chlorides, 151, 173
Acid hydrolysis of acetoacetic ester, 3 2'
Acid radicals, 149
Acids, aromatic, 479
Acids, fatty, 144
Acids, aldehydic, 325 ; amino-, 322 ; diba
sic, 332; hydroxy-, 314; ketonic, 325
phenolic, 486
Aconitic acid, 360
Acridine, 557, 572
Acrolein, 268
Acrylaldehyde, 268
Acrylaniline, 568
Acrylic acid, 268
Active amyl alcohol, 112
Active valeric acid, 165
Acyl radicals, 149
Additive compounds, 63
Adipic acid, 333, 349
Adjective colours, 441
Air-displacement method, 34
Alanine, 325
Albo-carbon lamp, 528
Albumin, 372
Albumin ates, 373
Albuminoid substances, 374
Albumoses, 373
Alcohol, absolute, 108 ; properties of, u:
Alcohol, manufacture of, 105
Alcoholic aldehydes, 287 ; ketones, 287
Alcoholic liquors, 109
Alcoholometry, 109
Alcohols, 94 ; monphydric, 94 ; nomen
clature of, 101 ; oxidation of, 99 ; polyhy
dric, 273 ; sources of, 101 ; structure of
95 ; synthesis of, 240, 243
Aldehyde-ammonias, 131, 1318
Aldehyde resin, 131
Aldehydes, 123 ; nomenclature of, 126
oxidation of, 125 ; preparation of, 127
properties of, 128 ; reactions of, 131
structure of, 124
590
INDEX
Aldehydic acids, 325
Aldol, 132
Aldoses, 287
Aldoximes, 129
Alley clic compounds, 532
Aliphatic series, 53, 55
Alizarates, 550
Alizarin, 548
Alizarin, manufacture of, 549 ; structure
of, 55i
Alkali blue, 516
Alkaline alkyl compounds, 235
Alkaloids, 574
Alkaloids in cinchona, 579 ; opium, 581 ;
strychnos, 582 ; derived from pyridine,
576 ; derived from quinoline, 579
Alkylamines, 198 ; separation of, 203
Alkylanilines, 422
Alkyl carbamines, 224
Alkyl compounds of arsenic, 233 ; magne-
sium, 242 ; phosphorous, 231; silicon, 236-;
zinc, 237
Alkyl cyanates, 227
Alkyl cyanides, 223
Alkyl cyanurates, 228
Alkylene oxides, 275
Alkylene radicals, 86, 253
Alkyl halides, 84, 190
Alkyl hydrogen sulphates, 97
Alkyl isocyanates, 227
Alkyl isocyanides, 226
Alkyl isocyanurates, 228
Alkyl isothipcyanates, 228
Alkyl pyridines, 566
Alkyl radicals, 84, 97
Alkyl thiocyanates, 228
Alloxan. 366, 367
Allyl alcohol, 266
Allyl compounds, 265
Allyl ethylamine-, 564
Allyl iodide, 265, 281
Allyl isothiocyanate, 266
Allyl mustard oil, 266
Allyl pyridine, 577
Allyl radical, 265
Allyl sulphide, 266
Aluminium-mercury couple, 68
Amber oil, 347
American petroleum, 57
Amides, 176
Aminoacetic acid, 322
Amino-acids, 322, 373
Aminoazobenzene, 434
Aminobenzene, 418
Aminobenzoic acid, 486
o-Aminocinnamic aldehyde, 568
Ammo-compounds, 411
Aminoglutaric acid, 352
Amino-group, 200
Aminoisobutylacetic acid, 325
-Aminophenetole, 457
Aminpphenols, 457
/>-Aminophenol, 477
Aminosuccinamide, 351
Aminosuccinic acid, 351
Amines, 198 ; properties of, 199 ; prepara-
tion of, 203 ; separation of, 203
Amygdalin, 211
Amyl alcohol, 52, 112
Amyl nitrite, 189
Amylenes, 245
Analysis of alcoholic liquors 109 ; butter,
170; fats and oils, 165; glucose, 292;
methane, 70 ; organic compounds, 17 \
soap, 168 ; sugar, 301 ; urea, 338
Anethole, 456
Aniline, 409, 411, 418
Aniline, reactions of, 419 ; salts of, 414
Aniline blue, 515
Aniline yellow, 434
Animal starch, 311
Anisaldehyde, 475
Anisic acid, 457
Anisole 456
Anthracene, 542 ; analysis of, 543 ; iso-
merism of derivatives, 546 ; properties of,
543 ; synthesis of, 544
Anthracene dichloride, 543
Anthracene hydride, 543 ; synthesis of,
544
Anthracene oil, 381
Anthracene picrate, 542
Anthranilic acid, 486, 492
Anthranol, 548
Anthrapurpurin, 552
Anthraquinone, 547 ; structure of, 547 ;
synthesis of, 545
Anthraquinone-/3-sulphonic acid, 550
Antifebrin, 420
Antipyrine, 433, 562
Arabinose, 312
Arabitol, 284
Arbutin, 462
Arginine, 373
Argol, 352
Armstrong's centric formula, 379
Aromatic acids, 479 ; alcohols, 467 ; alde-
hydes, 468 ; amino-compounds, 411 ;
halogen compounds, 399 ; hydrocarbons,
380 ; ketones, 473 ; nitre-compounds,
405
Arrowroot starch, 306
Arsenic, estimation of, in organic com-
pounds, 20
Arsines, 233
Artificial camphor, 504; silk, 310; sugars,
289
Aryl radicals, 388
Asparagine, 351
Aspartic acid, 351
Asymmetric carbon atom, 114
Atropine, 578
Atropine, test for, 578
Aurin, 521
Auxochrome, 442
Azobenzene, 410, 436
Azo-colours, 428
Azo-compounds, 436
INDEX
591
Azoxybenzene, 410, 436
Azulmic Acid, 210
Beaeyer's centric formula, 380
Baeyer's strain theory, 253
Bamberger's formula^for naphthalene, 531 ;
for quinoline, 569
Barbituric acid, 366
Barley sugar, 302
Base of malachite-green, 512
Bases, organic^ 198, 574
Beckmann's apparatus for freezing-point,
40 ; for boiling-point, 43
Beer, manufacture of, 106
Beeswax, 114
Beetroot sugar industry, 299
Begasse, 299
Benzal chloride, 389, 401
Benzaldehyde, 403, 469
Benzaldehyde cyanhydrin, 470 ; sodium
bisulphite, 470 ; phenylhydrazone,47i
Benzaldehyde green, 512
Benzaldpximes, 471
Benzamide, 483
Benzene, formula of, 376 ; properties of,
383 ; production of, 380 ; structure of,
376, 394
Benzene dicarboxylic acids, 492
Benzene-w-di?ulphpnate of sodium, 445
Benzene disulphonic acid, 385, 444
Benzene hexabromide, 378, 384
Benzene hexachloride, 378, 384
Benzene hexahydride, 378
Benzene picrate, 458
Benzene sulphinic acid, 447
Benzene sulphonamide, 448
Benzene sulphonanilide, 448
Benzene sulphonates, 445
Benzene sulphonic acid, 445
Benzene sulphonic chloride, 448
Benzenyl chloride, 389
Benzidine, 437, 440
Benzidine conversion, 437
Benzhydrol, 474
Benzil, 472
Benzine, 58
Benzoic acid, 403, 480
Benzoic acid, derivatives of, 485
Benzoic anhydride, 483
Benzoic esters, 484
Benzoin, 472
Benzoline, 57
Benzonitrile, 425, 447, 484
Benzophenone, 473, 474
Benzopurpurins, 441
Benzoquinone, 419, 476
Benzotrichloride, 389, 401, 482
o-Benzoylbenzoic acid, 545
Benzoyl chloride, 482, 483
Benzpinacone, 474
Benzyl alcohol, 467
Benzylamine, 402, 425
Benzylanthranilic acid, 569
Benzyl chloride, 389, 399, 401, 467
Benzyl cyanide, 402
Benzylformamide, 425
Benzylidene chloride, 389, 401
Benzylidene radical, 389
Berberine, 571
Betaine, 324
Betol, 488
Biebrich scarlet, 440
Bioses, 287
Bismarck brown, 439
Bisulphite compounds of aldehydes and
ketones, 129
Biuret reaction, 337
Blasting gelatine, 284
Blomstrand's formula for diazo-salts, 429
Boiling-point, correction for, 10 ; deter-
mination of, 9
Bone-oil, 560
Borneo camphor, 505
Borneol, 502, 505
British gum, 308
Bromacetic acid, 316
Bromal, 141
Bromanthraquinone, 547
Bromethane, 77
Broraethylene, 258
Bromine, estimation of, 19 ; detection of, 27
Bromobenzene, 400
o-Bromobenzylbromide, 545
Bromomethane, 77
Bromopropane, 77
Bromosuccinic acid, 350
Brucine, 583
Brucine, test for, 583
Burning naphtha, 383
Burning oil, 57
Butane, normal, 52, 56, 73
Butane tetracarboxylic ester, 346
Butter, 170
Butter substitutes, 171
Butyl alcohols, 94, 281
Butyl halides, 84
Butylenes, 245
Butyraldehyde, 123
Butyric acid, 52, 163
Butyric fermentation, 164
Butyrin, 165, 170
Butyrolactane, 318
Butyrone, 123, 126
Butyryl radical, 150
Cacodyl, 234
Cacodyl chloride, 234
Cacodyl compounds, 233
Cacodyl cyanide, 234
Cacodylic acid, 234 -
Cacodyl oxide,f 234
Cadaverine, 277
Caffeine, 370
Calcium carbide, 258
592
INDEX
Camphor, 394. 504
Camphoric acid, 504
Camphoroxime, 504
Camphors, 502
Cane-sugar, 298 ; analysis of, 301 ; ex-
traction from molasses, 301 ; manufac-
ture of, 298 ; refining of, 301 ; structure
of, 303
Capric acid, 165
Caprin, 170
Caproic acid, 165
Caproin, 170
Capronaldehy de, 123
Caprone, 123
Caproyl radical, 150
Caprylic acid, 165
Caprylin, 170
Caramel, 302
Caraway oil, 460
Carbamide, 337
Carbamine reaction, 90
Carbamines, 226
Carbazole, 542, 557, 572
Carbimides, 227
Carbinol group, 101
Carbohydrates, 287
Carbolic acid, 381, 455
Carbolic oil, 381
Carbon detection of, 17 ; estimation of,
21
Carbon hexabromide, 384
Carbon hexachloride, 384
Carbon monoxide, 212
Carbon ox y chloride, 334
Carbon tetrachloride, 64, 65, 92
Carbonic acid, 318, 334
Carbonyl chloride, 89, 334
Carbonyl group, 334
Carboxyl group, 149
Carius' method of analysis, 26, 28
Carvacrol, 460
Casein, 304, 373
Castor oil, 271
Catechol, 460
Catechu, 460
Celluloid, 311
Cellulose, 308
Cellulose hexanitrate, 310
Centric formula for benzene, 379
Cerasine, 60
Cerotic acid, 114
Ceryl alcohol, 114
Cetyl alcohol, 114, 166
Cetyl palmitate, 114, 166
Chinese wax, 114
Chitin, 374
Chloracetanilides, o, p, 422
Chloracetyl chloride, 316
Chloral, 88, 139
Chloral alcoholate, 140
Chloral hydrate, 140
Chloramylainine, 564
Chloranil, 456, 477
Chloranilines, o, m t p, 422
Chlorethane, 77
Chlorethylsulphonic acid, 279
Chlorhydrins, 248
Chlorine carrier, 51, 163, 389
Chlorine, detection of, 19 ; estimation of,
27
Chlorobenzenes, 384, 400
Chlorobenzoic acids, 401
Chlorocaffeine, 371
Chloroform, 65, 88
Chloroform, tests for, 90
Chloroformamide, 482
Chloroformic ester, 336
Chloromethane, 77
Chloronaphthalenes, a, /3, 535
Chloropropane, 77
a-Chloropropionic acid, 151
/3-Chloropropionic acid, 151, 169
Chloropropylene, 265
Chlorotoluenes, o, m, p, 389, 400
Cholesterol, 170
Choline, 278
Chromogenic compound, 442
Chromophoric group, 442
Chrysoidine, 439
Cinchomeronic acid, 567
Cinchona alkaloids, 579
Cinchona bark, 579
Cinchonine, 580, 581
Cinch oninic acid, 581
Cinnamic acid, 496
Cinnamic aldehyde, 472
Cinnamon oil, 472
Citraconic acid, 362
Citral, 506
Citric acid, 359 ; structure of, 360 ; syn-
thesis of, 361
Citron oil, 303
Claisen's reaction, 472, 498
Classification of organic compounds, 50
Closed-chain compounds, 254, 376
Coal-tar, 380
Coca, alkaloids of, 579
Cocaine, 579
Codeine, 582
Coffey's still, 107
Collidines, 565
Collodion, 311
Combustion apparatus, 22
Compound ammonias, 198
Compound ethers. 180
Compound radicals, 83
Condensation, 139, 142
Condensed nuclei, 527
Congo red, 441
Coniferin, 475
Coniferyl alcohol, 475
Conine, 576
Constitutional formulae, 8
Continuous ether process, 118
Copper acetylide, 260
Cordite, 284
Correction for boiling-point, 10
Cotton-seed oil, 270
INDEX
593
Coumarin, 500
Cracking of oils, 60, 170
Cream of tartar, 352
Creatine, 324
Creatinine, 324
Creosote oil, 381
Cresols, 451, 459
Croceins, 440
Croton oil, 269
Crotonaldehyde, 269
Crotonic acid 269
Crude naphtha, 381
Cryoscopic method, 38
Crystal violet, 517 ; base of, 518
Crystallisation, 6
Cumene, 393
Cumic acid, 393, 486
Cuminol, 472
Cutch, 460, 490
Cyamelide, 219
Cynamide, 339
Cyanates, 220
Cyanhydrins, 129
Cyanic acid, 219
Cyanides, 213
Cyanides, double, 215
Cyanogen, 209
Cyanogen chlorides, 219
Cyanogen compounds, 209
Cyanuric acid, 219
Cyanuric chloride, 219
Cyclobutane, 255
Cyclopentane, 255
Cyclopropane, 255
Cymene, m, p, 394, 502
Cymogene, 57
Decane, 56
Dehydrating agents, 51
Depressimeter of Eijkman, 42
Desmotropism, 330
Detection of carbon and hydrogen, 17 ;
halogens, 18 ; nitrogen, 18 ; oxygen, 19 ;
phosphorus, 19 ; sulphur, 19
Determination of boiling-point, 9
Determination of melting-point, 8
Dextrin, 307, 308
Dextro-rotatory, 112
Dextro-tartaric acid, 357
Dextrose, 291
Diacetin, 280
Diacetyl tartaric ester, 354
Diallyl, 262, 266
Diallyl tetrabromide, 262
Diamino-compounds, 426
Diaminoazobenzene hydrochloride, 439
Diaminobenzenes, 413, 421
Diaminodiphenyl, 509
Diaminoditolyl, 509
Diaminophthalophenone, 5 19
Diamines, 277
Diamines, reactions of, 426
Diastase, 105
Diazo-compounds, 428 ; reactions of, 429
Diazoaminobenzene, 433
Diazobenzene chloride, 428 ; hydroxide,
428 ; nitrate, 428 ; sulphate, 428, 431
Diazobenzene perbromide, 430
Dibasic acids, 251, 332 ; electrolysis of, 334
Dibenzyl, 508, 553
Dibromanthraquinone, 549
Dibromethane, 85
Dibromopropionic acid, 269
Dibromosuccinic acid, 355
Dichloracetic acid, 141, 163
Dichloracetone, 361
Dichloranthracene, 543
Dichlorethane, 85
Dichlorhydrin, 280
Dichlorobenzenes, 384, 397
Dichloromethane, 64, 85
Dichloronaphthalenes, 528
Dichloropropane, 124
Dicyanogen, 210
Diethyl, 73
Diethyl ether, 117
Diethyl ketone, 123, 126
Diethyl tartrate, 354
Diethylamine, 199
Digallic acid, 489
Dihalogen derivatives of the paraffins, 86
Dihydric alcohols, 273
Dihydric phenols, 450, 460
o-Dihydric phenols, 460
Dihydroxyanthraquinone, 548
Dihydroxybenzoic acid, 488
Dihydroxyphthalophenone, 5 19
Dihydroxysuccinic acid, 352
i-4-Diketones, 558, 559, 560
Dimethyl, 71
Dimethylacetamide, 202
Dimethylacetoacetic ester, 328
Dimethylaminoazobenzene hydrochloride,
438
Dimethylamine, 199, 203, 205, 424
Dimethylaniline, 415, 422, 424
Dimethylarsine, 233
Dimethylarsine chloride, 233
Dimethylbenzenes, 390
Dimethylcarbinol, 101
Dimethyl ethyl methane, 56
Dimethylfurfurane, 558
Dimethyl isopropyl methane, 56
Dimethyl ketone, 100, 141
Dimethylmalonic ester, 345
Dimethylnitrosamine, 201
Dimethyl oxamic ester, 204
Dimethyl oxamide, 204
, Dimethylphosphine, 231
Dimethylphosphinic acid, 232
Dimethyl propyl methane, 56
Dimethylpyridines, 565
Dimethyl sulphate, 98
Dimethyl sulphite, 187
Dimethylxanthine, 370
Dinaphthol, 537
Dinitrobenzene, 385, 406
594
INDEX
Diaitronaphthalene, 528
Dinitro-a-naphthol, 538
Dinitrophthalophenone, 5 19
Dinitrotoluene, 407
Dinitroxytartaric ester, 354
Dioxyacetone, 280
Dipentene, 503
Diphenic acid, 554
Diphenic anhydride, 554
Diphenyl, 508
Diphenylamine, 425
Diphenylbenzene, 508
Diphenylethane, 508
Diphenylketone, 474
Diphenylmethane, 509
Dippel's oil, 560
Dipropargyl, 262, 379
Distillation in vacua, 10 ; in steam, 8, 406
Distillation of coal-tar, 380 ; of wood, 102
Ditolyl, 553
Diureides, 366
Dodecane, 56
Double bond, theory of, 252
Double cyanides, 214
Driers, 271
Drying oils, 271
Dulcitol, 285
Dumas' method for estimating nitrogen, 23
Dumas' method for vapour density, 37
Dutch liquid, 254
Dynamite, 284
Earth oil, 57
Ecgonine, 579
Eijkman depressimeter, 42
Elaidic acid, 270
Electroplating solutions, 215
Ellagic acid, 490
Erlenmeyer's formula for naphthalene, 531
Empirical formulas, 30
Emulsin, 211
Enantiomorphous crystals, 355
Enzyme, 105
Eosin, 520
Erythrosin, 521
Essence of mirbane, 406
Essences, artificial, 186
Essential oils, 502
Esters, 102, 150, 180
Esters, isomerism of, 186 ; properties of,
184 ; sources of, 180
Esters of inorganic acids, 187
Esters of organic acids, 187
Estimation of carbon and hydrogen, 20 ;
nitrogen, 23.; halogens, 26; sulphur, 28
Ethane, 50, 71, 152, 240
Ethereal oils, 180
Etherification process, 118
Ethers, 116 ; constitution of, 118 ; simple
and mixed, 120
Ethoxyl group, 453
Ethyl, 66
Ethyl acetate, 183
Ethyl acetoacetate, 186
Ethyl alcohol, 52, 103, in
Ethyl alcohol, properties of, in ; oxidation
of, 137
Ethyl benzene, 387, 390
Ethyl benzene sulphonate, 448
Ethyl benzoate, 485
Ethyl bromide, 77, 80
Ethyl carbamate, 336
Ethyl carbonate, 334
Ethyl chloride, 77, 78
Ethyl cyanide, 223
Ethyl disulphide, 195
Ethyl ether, 121 ; synthesis of, 118 ; methyl-
ated, 122
Ethyl glycollic ester, 316
Ethyl hydrogen sulphate, 187
Ethyl iodide, 77, 80
Ethyl malonate, 344
Ethyl mercaptan, 195
Ethyl methyl, 72
Ethyl naphthalenes, 534
Ethyl nitrate, 188
Ethyl nitrite, 189
Ethyl riitrclic acid, 192
Ethyl oxalate, 343
Ethyl phenate, 456
Ethyl potassium carbonate, 334
Ethyl potassium sulphate, 188
Ethyl potassium sulphite, 196
Ethyl potassium sulphonate, 196
Ethyl sulphide, 196
Ethyl sulphonic acid, 196
Ethyl tartrate, 354
Ethylamine, 199
Ethylate of sodium, 95
Ethylene, 82, 86, 246
Ethylene bromide, 85, 249
Ethylene chlorhydrin, 248, 275
Ethylene compounds, 87
Ethylene cyanhydrin, 322
Ethylene diamine, 277
Ethylene dibromide, 85, 249
Ethylene dichloride, 85, 275
Ethylene glycol, 87, 273
Ethylene iodide, 85
Ethylene lactic acid, 321
Ethylene oxide, 275
Ethylidene bromide, 85
Ethylidene chloride, 85, 125
Ethylidene compounds, 87
Ethylidene iodide, 85
Ethylmethylamine, 206
Eugenol, 475
Exalgine, 424
Externally compensated compounds, 356
Fats, 165
Fatty acids, 144
Fatty acids, chemical properties of, 150 ;
constitution of, 146 ; electrolysis of, 152 ;
nomenclature of, 149 ; properties of, 144 ;
sources of, 153 ; syntheses of, 243, 328,
346
INDEX
595
Fehling's solution, 293
Fermentation, 103
Fermentation, acetous, 158
Fermentation, butyric, 163
Fermentation, theories of, 104
Ferments, hydrolytic, 105
Fittig's reaction _, 386
Fittig's researches, 497
Flashing-point, 61
Flavopurpurin, 552
Fluorescein, 461, 520
Formaldehyde, 123, 132
Formaldehyde, analysis of, 136 ; prepara-
tion of, 132 ; polymerisation of, 134 ;
uses of, 135
Formalin, 135
Formamide, 177, 212
Formanilide, 420
Formic acid, 146, 154, 212
Formic acid, preparation of, from oxalic
acid, 155 ; structure of, 145 ; tests for,
Formonitrile, 223
Formose, 136
Fcrmyl radical, 150
Formyldiphenylamine, 572
Fractional crystallisation, 7
Fractional distillation, 12
Fractionating columns, iz
Freezing-point method, 38
Friedel-Crafts' reaction, 386, 473
Fructose, 295
Fructose phenylhydrazone, 296
Fructose, structure of, 296
Fruit-sugar, 295
Fuchsine, 513
Fulminate of mercury, 221
Fumaric acid, 356, 362
Furfuralcohol, 559
Furfur aldehyde, 558
Furfurane, 557, 558
Furfurole, 558
Furoin, 559
Fusel oil, 104, 107
Galactonic acid, 298
Galactose, 297
Gallic acid, 463, 489
Gallotannic acid, 491
Gelatine, 374
Geranial, 506
Geraniol, 506
Glacial acetic acid, 158
Globulins, 373
Glucosates, 292
Glucosazone, 293
Glucose, 291
Glucose, analysis of, 293 ; reactions of, 292 ;
structure of, 291
Glucose phenylhydrazone, 294
Glucosides, 211, 462, 474, 475
Glucosone, 294
Glue, 374
Gluten, 306
Glutin, 374
Glyceric acid, 269, 281
Glycerine, 279
Glycerol, 267, 279
Glycerol chlorhydrins, 280
Glycerol, manufacture of, 282
Glycerol, mono-, di-, and tri-acetin, 280
Glycerol monoformin, 155-156
Glyceryl alcohol, 279
Glyceryl trichloride, 279, 280
Glyceryl trinitrate, 283
Glycine, 322
.Glycocoll, 322
Glycogen, 311
Glycol, 87
Glycol acetate, 275
Glycol ether, 275
Glycols, 273
Glyoxal, 274, 319
Glyoxalic acid, 274, 325
Grape-sugar, 290
Graphic formula?, 65
Griess's reaction, 428
Guaiacol, 461
Guanidine, 340
Guanidine thiocyanate, 340
Guanine, 369
Gum arabic, 312
Gums, 3i2<
Gun-cotton, 310
Halogen carriers, 51
Halogen derivatives of the aromatic hydro-
carbons, 399
Halogen derivatives of the paraffins, 77
Halogens, detection of, 18 ; estimation of, 26
Hard soap, 167
Heavy oil, 381
Helianthin, 439
Heliotropin, 489
Hemlock, alkaloid of, 576
HempeVs apparatus, 70
Heptadecane, 56
Heptaldehyde, 123
Heptane, 56
Heptoses, 287
Heptylic acid, 295
Heterocyclic compounds, 556
Hexadecane, 56
Hexahydric alcohols, 285
Hexahydrobenzene, 378
Hexahydrophthalic acids, 494
Hexamethylene, 255
Hexamethylene tetramine, 131
Hexane, 56
Hexoses, 287
Hexyl iodide, 287, 295
Hippuric acid, 323, 481
Hofmann's bottle, 34
Hofmann's carbamine reaction, 90
Hofmann's separation of the amines, 203
Hofmann's vapour density method, 36
596
INDEX
Hofnumn's violets, 516
Homatropine, 578
Homologous series, 53
Hydracrylic acid, 321
Hydrastine, 571
Hydrazobenzene, 410, 437
Hydrazones, 130
Hydrobenzamide, 472
Hydrocinnamic acid, 496
Hydrocyanic acid, 211
Hydrocyanic acid, properties of, 212 ; tests
for, 214
Hydroferrocyanic acid, 216
Hydrofurfur amide, 559
Hydrogen, detection of, 17 ; estimation of,
20
Hydrolysis, 105, 153, 166, 184
Hydrolytic ferments, 105
Hydroquinone, 462
Hydroxyacetic acid, 318
Hydroxy-acids, 314
Hydroxy-aldehydes, 287
Hydroxyanthraquinone, 548
Hydroxybenzaldehydes, 474
Hydroxybenzene, 455
Hydroxybenzoic acid, 487
Hydroxycinnamic acid, 500
Hydroxyisobutyric acid, 315
Hydroxy-ketones, 287
Hydroxyl group, 97, 174
Hydroxyquinoline, 571
Hydroxysuccinic acid, 349
Hydroxy toluene, 459
Hyoscine, 578
H yoscy amine, . 5 78
Hypnone, 473
Immo-group, 200
Indican, 522
Indigo, $22
Indigo carmine, 522
Indigo vat, 523
Indigo white, 523
Indigotin, 522
Indirubin, 522
Indole, 525
Indophenin, 383
Indoxyl, 522, 524
Inositol, 465
Internal compensation, 357
Inulin, 311
Inversion, 303
Invert-sugar, 303
Invertase, 105
lodal, 141
Iodine green, 516
Iodine value, 166, 271
lodobenzene, 400
lodoform, 91
lodoform test, n-i
lodole, 561
Iron liquor, 162
Isatin, 523
Isatin chloride, 523
Isethlonic acid, 278
Isobutane, 56, 73
Isobutyraldehyde, 123
Isobutyrone, 123
Isocrotonic acid, 269
Isocyanide reaction, 90
Isoheptane, 56
Isoleic acid, 270
Isomaltose, 305
Isonicotinic acid, 566
Isopentane, 56, 74
Isophthalic acid, 391
Isopropyl alcohol, 94, 101
Isopropyl bromide, 77
Isopropyl chloride, 77
Isopropyl halides, 84
Isopropyl iodide, 77
Isopropyl pseudonitrol, 192
Isopropylbenzaldehyde, 472
Isopropylbenzene, 393
Isopropylbenzoic acid, 486
Isopurpuric acid, 459
Isoquinoline, 571
Isosuccinic acid, 349
Isovaleraldehyde, 123
Isovalerone, 123
Jaggery, 298
Kairine, 571
Kekule's formula for benzene, 379 ; for
diazo-compounds, 429
Kekule's theory, 376
Kephir grains, 304
Keratin, 374
Kerosene, 57, 58
Ketones, 99, 123
Ketones, constitution of, 124 ; nomencla-
ture of, 126 ; oxidation of, 127 ; prepara-
tion of, 127 ; properties of, 128 ; synthesis
of, 240, 328
Ketonic acids, 325
Ketonic hydrolysis, 328
Ketoses, 287
Ketoximes, 129
KjeldahVs method for estimating nitrogen,
25
Kolbe's reaction, 487
Korner's formula for pyridine, 565
Korner's method of orientation, 395
Koumiss, 304
Lactic acid, 319
Lactide, 317
Lactones, 318
Lactose, 304
La3vo-tartaric acH, 356
Laevulose, 295
Lakes, 551
Landsberger's boiling-point apparatus, 44
INDEX
597
Lanoline, 170
Lard, 165
Laudanum, 581
Laws of nuclear substitution, 407
Lead acetate, 162
Le Bel and van't Hoff's theory, 320
Lecithin, 278
Leucine, 325
Leucobase of malachite green, 512
Levulinic acid, 330
Liebermann's " nitroso " reaction, 416, 454
Liebig's apparatus, 20
Light mineral oil, 59
Light oil, 381
Ligroin, 57
Limonene, 503 4
Linalol, 506
Linalol oil, 506
Linalyl acetate, 506
Linking of carbon atoms, 65
Linoieic acid, 270
Linoleum, 271
Linseed oil, 271
Lubricating oil, 57, 58
Lutidines, 565
Lyddite, 459
Madder, 548
Magenta, 513
Malachite green, 512
Maleic acid, 350, 361
Maleic anhydride, 361 *
Malic acid, 349
Malonic acid, 343
Malonic ester, 344
Malonyl urea, 366
Malt, 1 06
Malt sugar, 304
Maltase, 305
Maltose, 304
Manna, 285
Mandelic acid, 495
Mandelic nitrile, 495
Mannitol, 285
Mannose, 298
Margarine, 171
Marsh-gas, 52, 66
Martius' yellow, 538
McCoy's boiling-point apparatus, 44
Meconic acid, 582
Melinite, 459
Melissyl alcohol, 114
Melitriose, 305
Melting-point, determination of, 8
Menthol, 505
Menthone, 505
Menthyl chloride, 505
Mercaptans, 194
Mercaptides, 195
Mercaptpls, 276
Mercerising, 309
Mercuric cyanide, 209
Mercuric thiocyanate, 223
Mercury fulminate, 221
Mesaconic acid, 362
Mesitylene, 142, 392
Mesitylenic acid, 393
Mesotartaric acid, 354
Mesoxalyl urea, 366
Meta-compounds, 378
Metaldehyde, 139
Metameric, 120
Metameric amines, 206
Metameric ethers, 120
Metamerism, 120
Methaldehyde, 126
Methane, 52, 56, 66, 240
Methoxybenzene, 452
^-Methoxybenzaldehyde, 475
ra-Methoxy--hydroxybenzaldehyde, 475
Methoxyl group, 453
Methoxyquinoline, 571
Methyl alcohol, 52, 82, 102
Methyl anthranilate, 486
Methyl benzoic acids, 486
Methyl bromide, 77, 81
Methyl carbamine, 224
Methyl catechol, 461
Methyl chloride, 64
Methyl ether, 119
Methyl green, 516
Methyl hydrogen sulphate, 96
Methyl iodide, 77
Methyl isocyanide, 201, 225
Methyl mustard oil, 229
Methyl nitrate, 96
Methyl nitrite, 191
Methyl orange, 439
Methyl oxalate, 343
Methyl phenate, 456
Methyl propyl ether, 121
Methyl radical, 66, 83
Methyl salicylate, 487
Methyl violet, 516
Methylacetamide, 202
Methylacetanilide, 417
Methylacetoacetic ester, 328
Methylacetylene, 393
Methylal, 132
Methylamine, 82, 198, 205, 212
Methylamine nitrite, 200
Methylaniline, 415, 422
Methylarsine, 233
Methylarsine chloride, 233
Methylated ether, 122
Methylated spirit, no
Methylbenzene, 386
Methylbenzoic acid, 486
Methylbutylacetic acid, 297
a-Methylcinnamic acid, 497
Methyldiethylmethane, 56
Methylene, 82, 86
Methylene blue 424
Methylene bromide, 85
Methylene chloride, 65, 85, 8^
Methylene iodide, 85
598
INDEX
Methylethylacetic acid, 346
Methylethylketone, 329
Methylethylmalonic acid, 345
Methylethylmalonic ester, 345
Methylglycine, 324
Methylguanidine acetic acid, 324
/j-Methylisopropylbenzene, 394
Methylisopropylketone, 329
Methylmalonic acid, 346
Methylmalonic ester, 345
Methylphosphines, 231
Methylphosphinic acid, 232
Methylpyridine, 565
Methylquinoline, 571
Methylsuccinic acid, 349
Metol, 454
Meyer, L., air-bath of, 35
Meyer, V., ester-law of, 484
Meyer, V., vapour density method of, 33
Michler's compound, 518
Middle oil, 381, 455
Milk, composition of, 304
Milk-sugar, 304
Mineral oil, 57, 59
Mirbane, essence of, 406
Miricyl alcohol, 114
Mixed amines, 205
Mixed anhydrides, 175
Mixed ethers, 120
Molasses, sugar from, 301
Molecular formula, 31
Molecular weight, 3 z
Mono-acetin, 280
Monobromacetic acid, 162, 316
Monochloracetic acid, 148, 163
Monochloracetic acid, reactions of, 151
Monochloranthracene, 543
Monochlorobenzene, 384, 400
Monochloronaphthalene, 534
Monoformin, 280
Monohalogen derivatives of the paraffins,
77
Monohydric alcohols, 94
Monohydric phenols, 453
Monosaccharoses, 289, 290
Mordants, 162, 441
Morphine, 582
Morphine, tests for, 582
Mucic acid, 298
Mucin, 374
Multinuclear hydrocarbons, 508
Multiple functions of compounds, 264
Murexide, 367
Muscovado sugar, 299
Mustard oils, 229
Mycoderma aceti, 160
Myrosin, 266
Naphtha, 59
Naphtha, coal-tar, 381
Naphtha, solvent, 383
Naphthalene, 527
Naphthalene, amido-derivatives of, 536 ;
halogen derivatives of, 535 ; homologues
of, 534 ; nitro-derivatives of, 535 ;
structure of, 528 ; sulphonic acids of, 536 ;
synthesis of, 530
Naphthalene carboxylic acids, 539
Naphthalene dichloride, 528
Naphthalene disulphonic acid, 528
Naphthalene formula, 531
Naphthalene picrate, 459
Naphthalene sulphonic acids, a, /3, 536
Naphthalene tetrachloride, 528
Naphthalic acid, 540
a-Naphthaquinone, 539
/3-Naphthaquinone, 539
Nachthaquinones, 539
Naphthaquinonoximes, 538, 539
Naphthenes, 58, 59, 255
Naphthionic acid, 537
Naphthoic acids, 539
a-Naphthol, 537
/3-Naphthol, 538
Naphthol yellow, 538
Naphthols, 537
a-Naphtholtrisulphonic acid, 538
Naphthylamines, a, 6, 536
Naphthylaminesulphonic acids, 537
Narceine, 582
Narcotine, 571, 582
Native albumins, 373
Neopentane, 56, 74, 240
Neurine, 278
Nicotine, 577
Nicotmic acid, 566^ 577
Nitracetanilide, 421
Nitraniline, m, 413, 421
Nitranilines, o, p, 421
Nitriles, 223
w-Nitro--acetotoluide, 432
Nilrobenzaldehyde, 472, 524
Nitrobenzene, 385, 405
Nitrocellulose, 310
Nitrocinnamic acids, 500
Nitro-compounds, 405
Nitro-ethane, 191
Nitrogen, detection of, 18 j estimation of, 23
Nitroglycerine, 283
Nitrolic acids, 192
Nitromethane, 83, 191, 204
Nitronaphthalenes, 535
Nitro-paramns, 190
Nitrophenols, o, m, p, 45 1
o-Nitrophenyl-a-j8-dibromopropionic acid,
500
/j-Nitrophenyl ethyl ether, 457
o-Nitrophenyl propiolic acid, 500, 524
Nitrophthalic acid, 531
Nitrosamines, 201
Nitrosodimethylaniline, 416, 424
Nitrosomethylaniline, 416
a-Nitroso-a-naphthol, 538, 539
/3-Nitroso-a-naphthol, 538, 530
Nitrosonaphthols, 538, 539
Nitrosophenols, 459
INDEX
599
Nitrotoluene, m, 432
Nitrotoluenes, o, p, 407
Nobel's oil, 283
Nomenclature of acetylenes, 255 ; alcohols,
in ; aldehydes, 120 ; carbohydrates, 287 ;
fatty acids, 149 ; halogen compounds, 84 ;
ketones, 126 ; olefines, 253 ; paraffins, 55
Nonane, 56
Nonoses, 287
Normal alcohols, 101
Normal paraffins, 74
Nuclear substitution, 407
Nucleus and side-chain, substitution pro-
ducts, 402
Nucleus, meaning of, 388
Nucleus, position of groups in, 405, 407
Nux vomica, alkaloids of, 583
Octadecane, 56
Octane, 56
Octoses, 287
(Enanthol, 123
(Enanthone, 123
Oil of bergamot, 506 ; bitter almonds, 211,
469 ; bitter almonds, artificial, 406 ;
aniseed. 456 ; caraway, 460 ; cinnamon,
472 ; citron, 503 ; eucalyptus, 394 ; fusel,
107, 112; geranium, 506; garlic, 266;
lavender, 506 ; lemons, 503, 506 ; linalol,
506 ; mirbane, 406 ; mustard, 266 ; ori-
ganum, 460 ; roses, 506 ; thyme, 460 ;
turpentine, 503 ; wintergreen, 487
Oil-cloth, 271
Oils, drying, 271
Oils, essential, 502
Oils, fixed or vegetable, 165
Olefiant gas, 254
Olefines,.-8 2, 97, 245
Olefines, properties of, 246 ; nomenclature
of, 253 ; structure of, 251
Olefinic camphors, 505
Olefinic terpenes,5O5
Oleic acid, 165, 269
Olein, 165
Oleomargarine, 171
Opium alkaloids, 581
Optical activity, 112
Orcinol, 462
Organic compounds, classification of, 50
Organic reagents, 50
Organo- metallic compounds, 236, 239
Orientation, 395
Origanum oil, 460
Ortho-compounds, 378
Ortho-diketones, 539
Ortho-quinones, 477, 539
Osazones, 290
Ostatki, 58
Oxalates, 342
Oxalic acid, 274, 340
Oxalyl urea, 366
Oxamide, 343
Oxanilide, 420
Oxanthranol, 548
Oxidising agents, 50
Oxysulphonates, 129
Ozokerite, 60
Palmitic acid, 165
Palmitin, 165
Papaverine, 571, 582
Paper, 310
Parabanic acid, 366
Para-compounds, 378
Paracyanogen, 209
Paraffin industry, 59
Paraffin oil, 59
Paraffin scale, 59
Paraffin- wax, 57
Paraffins, 55
Paraffins, properties of, 62 ; synthesis of,
239
Paraform, 135
Paraformaldehyde, 135
Paralactic acid, 320
Paraldehyde, 139
Paraleucaniline, 514
Paranitraniline red, 421
Para-quinone, 476, 539
Pararosaniline, 514
Pararosaniline, base, 514 ; hydrochloride,
515 ; synthesis of, 514
Parchment paper, 309
Pentadecane, 56
Pentamethyl pararosaniline, 517
Pentamethylene, 254
Pentamethylenediamine, 277
Pentane, normal, 56, 74
Pentoses, 287, 312
Pepper, alkaloid of, 576
Pepsin, 105
Peptones, 374
Peri-position, 534
Perkin's reaction, 496
Peru balsam, 467
Petroleum, 57
Petroleum, American, 57 ; Russian, 58
Petroleum benzine, 57
Petroleum ether, 57, 58
Petroleum industry, 57
Petroleum naphtha, 57
Pharaoh's serpents, 223
Phenacetin, 457
Phenanthraquinone, 554
Phenanthrene, 542, 553
Phenetole, 456
Phenic acid, 455
Phenol, 415, 455
Phenol esters, 452
Phenol ethers, 452, 456
Phenolic acids, 486
Phenolic alcohols, 474
Phenolic aldehydes, 474
Phenolphthalein, 518
Phenols, 450
Phenols, properties of, 452 ; reactions of, 453
Goo
INDEX
Phenolsulphonic acids, 454, 458, 460
Phenyl benzoate, 485
Phenyl bromide, 400
Phenyl chloride, 400
Phenyl chloroform, 401
Phenyl cyanide, 425, 447
Phenyl ethyl ether, 457
PhtMiyl mercaptan, 447
Phenyl methyl ether, 453
Phenyl radical, 388
Phenylacetamide, 420
Phenylacetate, 453
Phenylacetic acid, 495
Phenylacrylic acid, 496
Phenylamine, 418
Phenylbromacetic acid, 495
Phenyl-y-bromobutyric acid, 499
Phenyl- /3-bromopropionic acid, 498
Phenyl-aj8-dibromoprop ionic acid, 498
Phenylbutylene, 530
Phenylbutyrolactone, 499
Phenylcarbamine reaction, 90
Phenylcarbonate of sodium, 487
Phenylchloracetic acid, 495
Phenylene radical, 421
w-Phenylenediamine, 421
^-Phenylenediamine, 434
Phenylglucosazone, 293
Phenylglyceric acid, 498
Phenylglycine-o-carboxylic acid, 524
Phenylgly collie acid, 495
Phenylhydrazine, 432
Phenylhydrazones, 130
Phenylhydroxy acetic acid, 495
Phenylhydroxylamine, 409, 477
Phenyl-/3-hydroxypropionic acid, 499
Phenylisocrotonic acid, 498
Phenylisocyanide reaction, 90
Phenylmethane, 386
Phenylmethyl carbinol, 473
Phenylmethyl ketone, 387, 473
Phenylmethypyrazolone, 562
Phenylmethylpyrazolone, 562
Phenylnitramine, 422
Phenylnitromethane, 409
Phenylpropionic acid, 498
Phenyl trimethylammonium iodide, 417
Phloroglucinol, 464, 491
Phloroglucitol, 464
Phosgene, 334
Phosphines, 231
Phosphinic acids, 232
Phosphorus, estimation of, 19
Photogene, 57
Phthalaminic acid, 492
Phthaleins, 518
Phthalic acids, 391, 491
Phthalic anhydride, 493
Phthalimide, 492, 493
Phthalophenone, 519
Phthalyl chloride, 493
a-Picoline hydriodide, 566
Picolines, 565
Picolinic acid, 566
Picramide, 458
Picrates, 458
Picric acid, 458 "
Picryl chloride, 458
Pinacones, 128, 474
Pinene, 502
Piper azirie, 277
Piperic acid, 576
Piperidine, 564
Piperine, 576
Piperonal, 489
Piperonylic acid, 489
Piria and Schiff's method of analysis, 27
Pitch, 381
Polyhydric alcohols, 273
Polymeric, 134
Polymeride, 134
Polymerisation, 134
Polysaccharoses, 289, 305
Potassium benzene sulphonate, 445
Potassium cyanate, 210, 219; preparation
of, 220
Potassium cyanide, 210, 213
Potassium ethyl carbonate, 334
Potassium ethyl sulphate, 188
Potassium ferricyanide, 217
Potassium ferrocyanide, 216
Potassium myronate, 266
Potassium pyrrol, 560
Preparation of : acetaldehyde, 137 ; acet-
amide, 177 ; acetanilide, 420 ; acetic an-
hydride, 175 ; acetone, 127; acetonitrile,
225 ; acetylene tetrabromide, 261 ; allyl
alcohol, 267 ; amyl nitrite, 189 ; aniline,
418 ; chloroform, 89 ; diazobenzene sul-
phate, 431 ; ethyl acetate, 183 ; ethyl
alcohol, 103 ; ethyl bromide, 80 ; ethyl
chloride, 78; ethyl ether, 118 ; ethyl
nitrate, 189 ; ethylene, 249, 250 ; ethyl-
ene bromide, 249 ; formaldehyde, 133 ;
formic acid, 156 ; hydrocyanic acid,
211 ; iodoform, 91 ; methane, 67, 68 ;
methyl cyanide, 225 ; mercury fulminate,
221 ; nitroethane, 190; picric acid, 458 ;
potassium cyanate, 221 ; potassium
ethyl sulphate, 188 ; spirits of nitre,
190 ; urea, 221 ; zinc ethyl, 237
Primary alcohols, 99, 192
Primary amines, 200
Primary amino-compounds, 415
Primary diamines, 277
Primary halogen compounds, 85
Primary paraffin group, 74
Proof spirit, no
Propane, 52, 56, 72
Propionaldehyde, 123
Propionanilide, 420
Propione, 123, 126
Propionic acid, 52, 163
Propionyl radical 150
Propyl alcohol, 52
Propyl bromide, 77
Propyl chloride, 77
Prcpyl halides, 84
INDEX
60 1
Propyl iodide, 77
Propyl radical, 66
Propylene, 82, 86, 245, 281
Propylene chloride, 279
Propylene radical, 277
a-Propylpiperidine, 577
Proteins, 372
Protocatechuic acid, 488
Prussian blue, 217
Prussiate of potash, 217
Prussic acid, 211
Pseudocumene, 393
Pseudonitrols, 192
Pseudouric acid, 369
Ptomaines, 277
' Ptyalin, 105, 308
Purification of organic compounds, 6
Purpurin, 552
Putrescme, 277
Pyrazole, 5 5 7, 561
Pyridine, 563
Pyridine alkaloids, 576
Pyridine carboxylic acids, 566
Pyridine dicarboxylic acids, 567
Pyridine, homologues of, 565 ; isomerism
of derivatives, 565 ; structure of, 564
Pyridinium methyl iodide, 560
Pyrogallic acid, 463
Pyroa;allol, 463
Pyroligneous acid, 102
Pyrcmucic acid, 558, 559
Pyrrole, 557, 560
Pyrrole, red, 561
Pyrotartaric acid, 349
Pyroxylins, 310
Pyruvic acid, 326
Quadrivalent carbon, 64
Qualitative tests for arsenic, 19 ; carbon, 17 ;
halogens, 18 ; hydrogen, 19 ; nitrogen,
1 8 ; oxygen, 19 ; phosphorus, 19 ; sul-
phur, 19
Quantitative estimation of carbon and
hydrogen, 20 ; halogens, 26 ; nitrogen,
23 ; sulphur, 28
Quaternary ammonium compounds, 202,
41?
8uaternary phosphonium compounds, 231
^uercitol, 465
Quick vinegar process, 160
Quinhydrone, 462
Quinic acid, 491
Quinine, 580
Quinine, salts of, 580
Quinine, tests for, 581
Quininic acid, 580
Quinol, 462
Qumoline, 567
Quinoline, derivatives of, 570 ; isomerism
of derivatives, 570 ; structure of, 567 ;
synthesis of, 568
y-Quinoline-carboxylic acid, 581
Quinolinic acid, 567
^uinones, 476
2uinonoid structure, 512
2uinoneoximes, 477
Racemic acid, 354
Racemic compound, 356
Radicals, 83
Raffinose, 299, 305
Rapeseed oil, 271.,
Reagents used in organic chemistry, 50
Red liquor, 162
Red prussiate of potash, 218
Reducing agents. 51
RegnauWs method, 33
Reimer's reaction, 476
Rennet, 304
Resolution of inactive compounds, 358
Resorcinol, 461
Reversible reactions, 78, 181
Rhigolene, 57
Rhodamines, 458, 521
Ricinoleic acid, 271
Ring compounds, 255
Rochelle salt, 353
Rock oil, 57
Rosaniline, 513
Rosaniline base, 515 ; arsenate, 513 ; hydro
chloride, 513
Rosolic acid, 521
Rotatory polarisation, 113
Ruberythric acid, 549
Rules of substitution in the benzene nucleus,
407
Russian petroleum, 58
Saccharic acid, 292
Saccharimeter, 302
Saccharin, 486
Saccharomyces cerevisiae, 104
Saccharoses, 289
Safrol, 489
Sago starch, 306
Salicin, 474
Salicyl alcohol, 474
Salicylaldehyde, 474
Salicylic acid, 487
Saligenin, 474
Salol, 488
Salts of lemon, 342
Salts of sorrel, 340, 342
Sandmeyer's reactions, 430
Saponification, 166
Saponifi cation value, 166
Sarcolactic acid, 320
Sarcosine, 324
Saturated compounds, 63
Saturated hydrocarbons, 55
Saturated ring compounds, 255
Scale, paraffin, 59
Schiff's azotometer, 23
Sclriff's test for aldehydes, 132
Schotten-Baumann's reaction, 485
RR
Schweinfurt green, 102
Schweizer's reagent, 310
Sealed tube, 26
Secondary alcohols, 99
Secondary amines, 200
Secondary aromatic bases, 415
Secondary butyl carbinol, 104, 112
Secondary halogen compounds, Si-
Secondary paraffin group, 75
Secondary propyl alcohol, 94, 101, 241
Shale, bituminous, 59
Shifting of the double link, 499
Side-chain, 388
Silico-nonane, 236
Silico-nonyl alcohol, 236
Silico-nonyl chloride, 236
Silico-pentane, 236
Silicon alkyl compounds, 236
Silicon tetramethyl, 236
Silicon tetrethyl, 236
Silver acetylide, 260
Simple ethers, 120
Sinigrin, 266
Skraup's reaction, 568
Soap, 167
Soap, analysis of, 169 ; manufacture of,
167 ; value of, 170 ; varieties of, 170
Sodamide, 213
Sodium alcohblate, 95
Sodium alizarate, 550
Sodium benzene sulphonate, 445
Sodium cyanide, 213
Sodium ethylate, 95
Sodium ferrocyanide, 217
Sodium glycolate, 275 .
Sodium hydroxyazobenzene, 438
Sodium hydroxynaphthaleneazobenzene,
438
Sodium methylate, 95
Sodium nitroprusside, 218
Sodium phenate, 450
Sodium phenyl carbonate, 487
Soft soap, 167, 169
Solar oil, 58
Solid paraffin, 57
Solvent naphtha, 383
Solvents, 6
Sorbinose, 298
Sorbitol, 285
Sorbose, 298
Space configuration, 86
Space interference, 485
Space isomerism, 320
Specific rotation, 292
Spermaceti, 114
Spirit blue, 515
Spirits, manufacture of, 106
Spirits, methylated, no
Spirits of nitre, 189
Spirits of wine, 107
Starch, 305
Starch cellulose, 307
Starch granulose, 307
Starch, soluble, 307
Stearic acid, 165, 167
Stearin, 165
Stearine, 166
Stereoisomerism, 320
Stereoisomerism of aldoximes, 4/1 ; ket-
oximes, 474; lactic acids, 321; malic-
acids, 249 ; tar tar ic acids, 352 ; un-
saturated compounds, 361
Storax, 467
Strohtia method of sugar extraction, 300
Strontium saccharosate, ",oo
Structural formula?, 4
Strychnine, 583
Strychnine, test for, 583
Strychnos alkaloids, 582
Styrax benzoin, 480
Styrene, 499
Sublimation, 7
Substantive colours, 440
Substituted ammonias, f 98
Substitution, 62, 64
Substitution in side-chain and nucleus, 402
Substitution, rules of, 403
Succinic acid, 347
Succinic anhydride, 348
Succinimide, 348
Sugars, 288
Sugars, analysis of, 302
Sugar-candy, 302
Sugar-cane, 298
Sugar-charcoal, 302
Sugar of lead, 162
Sugar refining, 301
Sulphanilic acid, 419, 444
Sulphides, 196
Sulphine compounds, 197
o-Sulphobenzoic acid, 486
Sulphobenzoimide, 486
Sulphonal, 276
Sulphonamides, 448
Sulphonates, 196
Sulphonanilides, 448
Sulphonation, 444
Sulphonic acids, 196, 444
Sulphonic acids, properties of, 446 ; struc-
ture of, 447
Sulphovinic acid, 187
Sulphur compounds, 194
Sulphur, detection of, 19 ; estimation of, 28
Sweet spirits of nitre, 196
Sweet water, 167, 282
Synthesis with acetoacetic ester, 327
Synthesis with malonic ester, 344
Synthesis with zinc alkyl compounds, 239
Tallow, 165, 1 68
Tannins, 490
Tapioca, 306
Tartar emetic, 353
Tartaric acid, 352
Tartaric acid, detection of, 353 ; salts of,
353 ; Stereoisomerism of, 355 ; structure
of, 354
INDEX
603
Tartrates, 353
Tartronic acid, 281
Taurine, 278
Tautomensm, 329
Terephthalic acid, 391
Terpenes, 502
Terpineol, 502
Tertiary alcohols, 99
Tertiary amines, 200
Tertiary aromatic bases, 415
Tertiary butyl alcohol, 100, 241
Tertiary butyl halides, 85
Tertiary halogen compounds, 85
Tertiary paraffin group, 75
Tetrabromofluorescein, 521
Tetrachloromethane, 64
Tetrachloroquinone, 456, 477
Tetrahydrohydroxyquinoliue, 571
Tetrahydronaphthalene, 528
fetrahydronaphthol, 532,
Tetrahydronaphthylamine, 533
Tetrahydroquiriolines, 5/0
Tetramethylammonium iodide, 202 ;
hydroxide, 202
Tetramethylarsonium iodide, 233
Tetramethyldiaminobenzophenbne, 518
Tetramethyldiarsine, 235
Tetramethylene, 255
Tetramethylenediamine, 277
Tetramethylmethane, 56, 74
Tetramethylphosphonium iodide, 231 ;
hydroxide, 231
Tetrazole, 557
Tetriodofl uorescein, 521
Tetriodopyrrole, 561
Thebame, 582
Theine, 370
Theobromine, 370
Thio-alcohols, 194
Thio-ethers, 196
Thiocarbanilide, 418
Thiocyanic acid, 222
Thiocyanates, 222
Thiocyanates, alkyl, 228
Thionuric acid, 368
Thiophene, 383, 559
Thiotolene, 560
Thiourea, 339
Thioxene, 560
Thorpe's Hofmann apparatus, 36
Thymol, 460
Tobacco, alkaloid of, 577
Tolidiae, 438
Tolu balsam, 386, 467
Toluene, 386
o-Toluenesulphonamide, 486
Toluic acids, o, m, p, 391, 486
Toluidines, o, m, p, 423, 424
Tolyl chlorides, 400
o-Tolylphenylketone, 545
Triacetin, 280
Triazole, 557
Tribromaniline, 419
Tribromophenol, 456
Tribromoresorcinol, 461
Tricarb ally lie acid, 360
Trichlor acetic acid, 141, 162
Trichloracetone, 89
Trichloraldehyde, 139
Trichloraniline, 419
Trichlorobenzene, 384
Trichloromethane, 64
Trichloroprppane, 279
Triethylamine, 199
Triethylsulphine compounds, 197
Trihalogen derivatives of the paraffins,
88
Trihydric alcohols, 279
Trihydric phenols, 456, 463
Trihydroxyanthraquinones, 552
Trihydroxybenzenes, 463
Trihydroxybenzoic acid, 489
Trimesic acid, 393
Trimethylamine, 199, 206
Trimethylarsine, 233
Trimethylarsine dichloride, 233
Trimethylarsine oxide, 233
Trimethylarsine sulphide, 233
Trimethylbenzene, 392
Trimethylcarbinol, 101
Trimethylene, 254
Trimethylene bromide, 277
Trimethylene cyanide, 277
Trimethylene dicarboxylic ester, 346
Trimethylene radical, 277
Trimethylethylmethane, 56
Trimethyl^lycine, 324
Trimethylphenylammonium iodide, 417
Trimethylphosphine. 231
Trimethylphosphonium oxide, 232
Trimethylpyridines, 565
Trimethyluric acid, 370
Trimethyixan thine, 370
Trinitraniline, 458
Trinitrobenzene, 407
Trinitrobutyltoluene, 407
Trinitrophenol, 458
Trinitroluene, 407
Trinitrotriphenylmethane, 514
Triolein, 280
Tripalmitin, 280
Triphenylainine, 415
Triphenylbenzene, 508
Triphenylcarbinol, 5x0
Triphenylcarbonium hydroxide, 510
Triphenylmethane, 509
Triphenylmethane colours, 5 10
Triphenylmethyl chloride, 510; sulphate,
510
Triphenylrosaniline, 515
Trisaccharose, 289
Tristearin, 280
Tropaeolin, 439
Tropemes, 578
Tropic acid, 578
Tropine, 578
Turkey red, 549
Turkey red oil, 271
604
INDEX
Turnbull's blue, 218
Turpentine, 394, 603
Turpentine, American, 502 ; French, 502
Unsaturated acids, 268
Unsaturated dibasic acids, 361
Unsaturated groups, 225
Unsaturated hydrocarbons, 245
Uramil, 368
Urea, 337
Urea, detection of, 338 ; estimation of, 338 ;
preparation of, 221
Urea nitrate, 338
Urea oxalate, 338
Ureides, 366
Urethane, 336
Uric acid, 366
Uric acid, test for, 367 ; structure of, 367 ;
synthesis of, 368
Uvitic acid, 393
Vacuum-pan, 300
Valency of carbon, 64
Valeraldehyde, 123
Valerianic acid, 164
Valeric acid, 164
Valeryl radical, 150
Vanillic acid, 476
Vanillin, 475
Vapour density, determination of, 32
Varnishes, 271
Vaseline, 57
Vegetable bases, 574
Vegetable oils, 168
Verdigris, 162
Vinegar, 159
Vinegar, malt, 160 ; wine, 160
Vinegar organism, 160
Vinegar, quick process, 160
Vinyl bromide, 258
Vinyl iodide, 261
Water blue, 516
Waxes, 165
Will and Varrenlrapp's method for nitrogen,
26
Willesden paper, 310
Wines, manufacture of, 106
Wintergreen oil, 487
Wood-gum, 312
Wood-naphtha, 102
Wood-spirit, 102
Wool -grease, 170
Wurtz's reaction, 72
Xanthine, 369
Xylenes, o, m, p, 390
Xylenes, oxidation of, 391
Xylenes, separation of, 446
Xylenols, 451
Xylidines, 423
Xylitol, 284
Xylonite, 311
Xylose, 312
Yeast-cells, 104
Yellow prussiate oi potash, 217
Yorkshire grease, ? 7c
ZeiseFs method, 453
Zinc alkyl compounds, 2
Zinc- copper couple, 69
Zinc ethyl, 237
Zinc methoxyiodide, 69
Zinc methyl, 75, 237
Zinc methyl iodide, 237
Zymase, 105
THE END.
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