;-NRLF E77 fllE INTRODUCTION TO ORGANIC CHEMISTRY STODDARD INTRODUCTION TO ORGANIC CHEMISTRY BY JOHN TAPPAN STODDARD PROFESSOR OF CHEMISTRY IN SMITH COLLEGE SECOND EDITION PHILADELPHIA P. BLAKISTON'S SON & CO. 1012 WALNUT STREET COPYRIGHT, 1918, BY P. BLAKISTON'S SON & Co. THE. MAPLE- PBJSBS. YORK- PA PREFACE TO THE SECOND EDITION The favorable reception accorded to this text has encouraged me to take advantage of this year's reprinting to make a number of corrections and changes that have been suggested during the four years since it first appeared. Many minor alterations will be found, and a few portions have been entirely rewritten. Among the latter are the sections on the Natural Oils and Fats, on Uric Acid and the Purine Bases, and on the Proteins. I trust that the revision will be found to have measurably improved the book and that its efficiency as an aid to the instruc- tion of college students who are beginning the subject has been increased. It gives me great pleasure to acknowledge my indebtedness to the friends whose criticisms and suggestions have aided me in my task, and I am under especial obligation to Professor Cook of Smith College and Dr. Harry L. Fisher of Columbia University who placed in my hands the corrections and notes they had mlade while using the book with their classes. J. T. S. NORTHAMPTON, MASS. 574256 PREFACE TO THE FIRST EDITION This book is intended to be used in connection with lectures, recitations, and laboratory work in the first course of Organic Chemistry in college. The author has endeavored to present the subject simply, directly, and connectedly, so that the student may gain a clear idea of the principles of organic chemistry and its relations to general chemistry. The fundamentally important questions of the constitution of organic compounds are discussed at some length in many typical cases. In these discussions, the facts in regard to the behavior of the substances are given first, and then the arguments by which the formulas are established. The student in this way is trained in the method of deriving constitutional formulas, and should soon be able to work out simple problems from a given statement of facts. Emphasis is laid on general reactions and characteristics, rather than on special facts relating to particular compounds; and the text is relieved from much detail by the use of tables giving names, formulas and properties of many groups of compounds. Many applications of organic chemistry to practical life are given so that the student may realize, in some measure, the part which the science of organic chemistry plays in ordinary life and in our industries. The book is considerably smaller than many of the text-books on the subject, but it is believed that it is none the less complete in all the essential matter which is properly presented in a first course. The larger text-book is apt to bewilder the student by brief descriptions of too many compounds of minor importance, or to fill too many pages with discussions which can be conducted to better advantage by the lecturer. The student often finds his course in organic chemistry at vii Vlll PREFACE first difficult and confusing. It is so different from the inor- ganic chemistry that it takes him some time to get the new point of view. This is, perhaps, to some extent inevitable; but a good deal depends on the manner in which the subject is intro- duced. If details are subordinated and the fundamental princi- ples are presented logically and with a f ew well-chosen illustrations of their applications, the first difficulties are soon overcome. The order in which the various groups of compounds are to be treated is a more or less open question. The choice depends largely, in several instances, on the particular relations which it seems desirable to emphasize. What appears a logical sequence from one point of view, is, from another, illogical. No claim is made that the order given in this book is the best; and it should be said that it is not necessary that this order be strictly followed by those who use the book. Numerous cross-references are given to help in binding the discussions into a coherent whole. Some references are made to books in which fuller treatment of certain subjects will be found, and a short list of books for collateral reading is given at the end of the volume. I wish to express my sincere thanks to Professor H. W. Doughty of Amherst College and Professor E. P. Cook of Smith College, who have read the book in manuscript and have made many helpful suggestions. Professor Cook has also rendered great assistance in reading the proofs. CONTENTS CHAPTER PAGE I. PRELIMINARY DISCUSSION i II. THE PARAFFINS OR HYDROCARBONS OF THE METHANE SERIES , . 15 III. HALOGEN SUBSTITUTION PRODUCTS OF THE PARAFFINS . 31 IV. UNSATURATED HYDROCARBONS 42 V. THE ALCOHOLS 57 VI. THE ETHERS , . 70 VII. ALDEHYDES AND KETONES 76 VIII. SIMPLE MONOBASIC ACIDS 94 IX. ACID CHLORIDES ANHYDRIDES ESTERS 114 X. AMINES AND AMIDES NITRO-COMPOUNDS . . . . 127 XI. CYANOGEN AND CYANOGEN COMPOUNDS 144 XII. POLYHYDROXYL ALCOHOLS 155 XIII. OXIDATION DERIVATIVES OF POLYHYDROXYL ALCOHOLS STEREOCHEMISTRY 161 XIV. POLYBASIC ACIDS AND ALCOHOL-ACIDS 177 XV. CARBOHYDRATES FERMENTATION ENZYMES . . . 198 XVI. DERIVATIVES OF CARBONIC ACID 227 XVII. COMPOUNDS CONTAINING SULPHUR 236 XVIII. SOME HALOGEN AND AMINO DERIVATIVES .... 245 XIX. CYCLO-PARAFFINS 257 XX. AROMATIC HYDROCARBONS ORIENTATION .... 265 XXI. HALOGEN DERIVATIVES SULPHONIC ACIDS NITRO-COM- POUNDS INFLUENCE OF SUBSTITUENTS ON EACH OTHER. 284 XXII. AROMATIC AMINES 301 ix X CONTENTS CHAPTER PAGE XXIII. DIAZO COMPOUNDS . 313 XXIV. Azo AND OTHER NITROGEN COMPOUNDS DYES . . .321 XXV. PHENOLS AROMATIC ETHERS ALCOHOLS . . . .327 XXVI. AROMATIC ALDEHYDES KETONES AND QUINONES . . 343 XXVII. AROMATIC ACIDS 353 XXVIII. HYDROAROMATIC HYDROCARBONS AND THEIR DERIVA- TIVES TERPENES AND CAMPHORS 371 XXIX. NAPHTHALENE AND ANTHRACENE . . . ... . . 382 XXX. HETEROCYCLIC COMPOUNDS 393 XXXI. ALKALOIDS PROTEINS . ' 402 INDEX 413 TABLES PAGE ACIDS, AROMATIC 356 DIBASIC i 77 HYDROXY (ALIPHATIC) 197 HYDROXY (AROMATIC) 363 MONOBASIC (NORMAL) 101 SULPHONIC 292 ACID AMIDES 142 ANHYDRIDES 117 CHLORIDES 117 ALCOHOLS, AMYL 68 PRIMARY 67 ALDEHYDES 87 AMINES, ALKYL 136 AROMATIC 312 CYCLO-PARAFFINS 258 ESTERS OF INORGANIC ACIDS 122 ETHERS 75 ETHYL ESTERS OF ORGANIC ACIDS 123 HYDROCARBONS, AROMATIC 276 UNSATURATED 45 IONIZATION CONSTANTS 407 KETONES 88 NITRO COMPOUNDS (AROMATIC) 297 PARAFFINS, NORMAL 17 HALOGEN DERIVATIVES 33, 40 PHENOLS 331 SPECIFIC ROTATIONS 406 XI INTRODUCTION TO ORGANIC CHEMISTRY CHAPTER I PRELIMINARY DISCUSSION Organic chemistry is the chemistry of the compounds of carbon. Although the fundamental laws and theories of chemistry are as applicable to these compounds as to all others, there are several reasons for their separate treatment. In the first place, the number of compounds that contain carbon j is extraordinarily large. The only other elements that enter into the composition of any very large number of substances are hydrogen and oxygen; and we shall see that hydrogen and oxygen are quite usually associated with carbon in the organic compounds. The association, however, is of such a nature that carbon is the dominant element, so to speak, remaining intact in very many of the chemical changes that occur, while hydrogen and oxygen are added, subtracted, or exchanged for other elements or groups of elements. The great number and variety of the compounds in which carbon is a constituent is of itself a sufficient ground for making their discussion a separate branch of study. In the second place, there are certain general characteristics which distinguish the organic substances from the inorganic. Most of the compounds of carbon are decomposed at temperatures / which are below a red heat, while many inorganic compounds with- stand much higher temperatures; and organic compounds are more liable to change when exposed to the light and air than are i INTRODUCTION ( TO ORGANIC CHEMISTRY the inorganic. The majority of organic substances are practically insoluble in water, which is the solvent of so many inorganic compounds, and are usually soluble in such liquids as ether, chloroform, alcohol, carbon disulphide, and benzene, in which few of the inorganic compounds dissolve. Again, while the greater number of inorganic compounds * with which we deal in aqueous solution react almost instan- taneously with each other, if at all, the reactions between dissolved or liquid organic compounds, though occasionally rapid, are more frequently very slow, often requiring heat, and hours or even days for completion. This difference in behavior is explained by the fact that the inorganic compounds are electrolytes and the reactions are the realiojas__of_ians, while comparatively few organic compounds are ionized, and their reactions are those of undissocjaleji^mjolecules. These distinctions must not be understood to be absolute. Some carbon compounds, such as the carbides of the metals, the oxides of carbon, and others withstand very high temperatures, while a considerable number of inorganic compounds are decom- posed at a moderate heat; and a number of organic substances dissolve in water and are electrolytes, while some inorganic compounds dissolve in the non-aqueous solvents which were named, and usually without ionization. The differences, however, are sufficiently general to justify the separate treatment. Another peculiarity of organic substances is that among them we find many large groups of closely related substances the relation being much closer than that which exists between the members of the inorganic classes of bases, acids and salts. The members of each of these organic groups not only give similar reactions with a given reagent, yielding similar products, but show a nearly uniform gradation in all their physical and chemical properties. This very much simplifies our study; for when we have learned the characteristics of one or two members of a group, detailed examination of the others becomes unnecessary. PRELIMINARY DISCUSSION 3 A complete discussion of the compounds of carbon would include carbon monoxide, carbon dioxide, carbon disulphide, certain carbides, carbonic acid, and the carbonates substances which are usually treated in inorganic chemistry on account of their close relations to inorganic compounds. All of these compounds, however, have also certain relations to other compounds of carbon, so that some reference to them which will bring out this relation should be made in organic chemistry. Sources of Organic Compounds. Carbon combines directly with hydrogen at high temperatures, and the hydrocarbons which are formed may be employed as the starting point for the prepara- tion of a great variety of other organic compounds. Some simple organic substances may be made by the use of the oxides of car- bon, its sulphide, chloride, and one or two carbides of the metals, and these may then be built up into more complex compounds by laboratory methods. But in actual practice the chief sources of organic compounds are in the products elaborated in plants and animals. These substances were the first to receive the name "organic," and for a long time it was believed impossible to pro- duce any of them artificially from the elements or from so-called inorganic material. Among the important organic compounds which are found already formed in plants are starch, cellulose, the sugars; acids or salts of acids, such as oxalic, citric, tartaric acids; the alkaloids, such as quinine and strychnine, and many other substances of greater or less complexity. Petroleum con- tains many compounds of carbon and hydrogen. Many organic substances are also produced by the destructive distillation of coal, wood, and bones those which are contained in the coal tar being of the greatest interest and practical value. Furthermore, fermentative processes produce ordinary alcohol from sugar, acetic acid from alcohol, and a number of other compounds. It is interesting to note that we may trace the source of the natural organic substances to the carbon dioxide of the air, which, in turn, is supplied to the air by the combustion, decay, fermenta- 4 INTRODUCTION TO ORGANIC CHEMISTRY tion, etc., of plant and animal matter. All of the carbon in plants and it is the chief element they contain is derived from this gas which forms only about three ten-thousandths of the vol- ume of the air. Under the influence of solar energy, carbon dioxide, water, and small quantities of other simple inorganic com- pounds taken up through the roots from the soil, are built up into the structure of the plant or vegetable, oxygen being returned to the air. The chemical processes in the growing plant are, in gen- eral, of a synthetic character, and " endothermic " or such as require the expenditure of energy (furnished by the sun) to produce them. But at the same time, processes of the opposite character, or analytic processes which are " exothermic, " go on to some extent, as is shown by the fact that plants exhale carbon dioxide. Since the food of animals is either directly or indirectly of vegetable origin, the compounds which are formed in their bodies owe their principal constituent, carbon, to the same original source. But the chemical changes in the living animal are more largely of an analytic character than those in the growing plant. While new complex substances are built up from the food materials, the resolution of these into simpler compounds is all the time proceed- ing. These latter reactions, being exothermic, supply the energy which maintains the temperature and varied activities of the animal body. In the greater number of these natural substances and in those directly obtained from them in the ways which have been men- tioned, we find only three elements beside carbon, viz., hydrogen, oxygen, and nitrogen. Many contain only carbon and hydrogen; a large number, carbon, hydrogen and oxygen; and a compara- tively small number, carbon and nitrogen with either hydrogen, or both hydrogen and oxygen. A still smaller number of definite organic compounds containing sulphur or phosphorus are found in nature, and certain metals chiefly potassium, sodium, and cal- cium are present in the natural salts of organic acids. While the number of elements that enter into the composition PRELIMINARY DISCUSSION 5 of the natural organic compounds is thus limited, many other elements may be introduced by laboratory methods. The chem- ist has by no means succeeded in making in his laboratory all the organic compounds which are found in nature, and where he has succeeded, it is very seldom that the steps of his processes are those followed by nature. Natural compounds are formed in living organisms at ordinary temperatures, while the laboratory products are usually obtained by the use of higher temperatures and under other conditions quite dissimilar to those which prevail in the plant or animal. The immense number of compounds which carbon forms with four or five other elements must mean that the molecules of many of them are of great complexity; and in fact the evidence indicates that the carbon atoms possess the unusual property of combining with each other in what we picture to be chains or rings of atoms united by one or more of their valencies, while the remaining valencies serve to hold the other elements of the compound. Not only is this the case, but a given number of atoms of carbon and of one or two other elements often combine in varied relations, giving compounds of distinct properties. The molecules of such compounds of the same composition but different properties may be regarded as analogous to the patterns which may be made by putting together a definite number of colored or differently shaped blocks in various ways; and indeed the graphic formulas which the organic chemist uses to explain the variety he finds resemble such patterns with the atomic symbols used instead of blocks. It is thus seen that valency and the combinations which it per- mits must play an immensely greater part in the discussions of organic chemistry than it usually does in those of inorganic compounds. Identification of a Substance as Organic. This resolves itself into a test for carbon. Most organic substances burn, and if the substance chars or if the flame deposits lampblack on a cold 6 INTRODUCTION TO ORGANIC CHEMISTRY surface which is brought into it, no further test is necessary. Many organic compounds show the presence of carbon by charring when heated in an ignition tube; but the most general test for carbon is the formation of carbon dioxide and its detection by lime water. The substance is heated with copper oxide in a test tube and any gases that are formed are led into lime water; or if the substance is a gas, or one which sublimes or distils before reacting with the copper oxide, its vapor is led through a tube containing hot copper oxide. Test for Elements Combined with Carbon. Hydrogen is usu- ally indicated by the water produced in the test for carbon; but, as practically all organic substances contain hydrogen, a test for this element is seldom necessary Nitrogen. If, in the burning or charring of the substance, an odor like that of burning wool is noticed, this shows that nitrogen is a constituent of the substance. Many organic compounds, however, which contain nitrogen do not give this odor. In this case, the substance is ignited with sodium (or with a mixture of magnesium powder and sodium carbonate) in a test tube, and if nitrogen is present it forms a cyanide, which, when brought into solution, and digested with a few drops of a mixture of ferrous and ferric salts, gives a precipitate of Prussian blue when acidu- lated with hydrochloric acid. Certain substances which contain nitrogen fail, however, to give this test, since the nitrogen is dis- engaged as gas at a temperature below that at which the reaction with the metal occurs. In these cases it is necessary to prove that nitrogen is one of the gases evolved when the substance is heated, or when it is oxidized as in the quantitative determina- tion of nitrogen. The other elements which may be present, such as sulphur, phosphorus, and the halogens, may be detected in the soluble product formed by the ignition of the substance with sodium, where they appear as sodium compounds and respond to the usual tests of inorganic chemistry. Halogens may be detected more simply by bringing a bit of the substance on a clean PRELIMINARY DISCUSSION 7 copper wire into the Bunsen flame; if a halogen is present it forms a volatile copper halide which colors the flame green. Or the sub- stance may be ignited with calcium oxide, when the calcium halide is produced together with the carbonate, and after dissolving in dilute nitric acid the halogen is detected by adding silver nitrate. Metals which may be present are detected in the residue from ignition by the usual procedure of qualitative analysis. Tests for Purity. Before the quantitative composition of a compound can be determined, it is, of course, necessary to obtain it in a state of purity. The usual tests for the purity of solid and liquid organic compounds are the melting and the boiling points. If a solid melts abruptly at a certain temperature (01 witEin a range of 0.5) it is considered pure enough for most purposes. Impurities cause a more gradual melting, and at a temperature which is lower than that of the pure substance. Pure liquids have a constant boiling point, while in the case of mixtures the temperature generally rises as the distillation pro- ceeds. There are, however, some mixtures of definite composi- tion, such as alcohol and water, which have a constant boiling point under a given pressure. A change of pressure (distillation in a partial vacuum) reveals their character, for while the boiling point of a pure substance would still be constant, though different, under the new pressure, the boiling point of the mixture becomes inconstant until a new equilibrium is established with a different proportion of the components. 1 Methods of Purification. The general method for the purifica- tion of solid organic compounds is by fractional crystallization from an appropriate solvent. Organic liquids are purified by fractional distillation, the distillate being collected in sepa- rate portions or "fractions" for small ranges of temperature as shown by a thermometer suspended -in the vapor. A partial 1 Refer to the behavior of mixtures of hydrochloric and of nitric acids with water. For a discussion of the boiling points of mixtures see some Physical Chemistry. 8 INTRODUCTION TO ORGANIC CHEMISTRY separation of the constituent liquids is effected in this way, and the separation is made more complete by redistilling the fractions a sufficient number of times. When the substance is one which decomposes at or below its boiling point under ordinary atmos- pheric pressures, it may be distilled at a lower temperature with- out decomposition in a partial vacuum, (e.g., in the preparation of glycerine). A method which is successful in a number of instances is by distillation' in a current of steam, as in the preparation of aniline and nitrobenzene. Mixtures of solids or of liquids can frequently be separated into the individual con- stituents, or one constituent can be extracted in a state of purity, by taking advantage of the different solubilities in various solvents. A pure solid compound may sometimes be obtained from a mixture by sublimation (cf. benzoic acid). No general methods are known for the purification of gases. Most frequently it is effected by absorbing one or more of the constituents of the mixture in certain liquids or solids. But usu- ally it is necessary to prepare the gas as pure as possible from pure materials by a definite chemical action. Even then, in most cases, there are impurities of small amount which must be removed by absorption in some substance. Quantitative Analysis. Carbon and hydrogen are always determined in one operation, which consists in the complete oxidation of a weighed portion of the pure compound (usually by means of copper oxide) and absorbing the water in solid calcium chloride, and the carbon dioxide in a strong solution of potassium hydroxide. From the increase in weight of these sub- stances, the amounts of hydrogen and carbon are calculated. The weight of the nitrogen may be determined (by the Dumas method) from the volume of gas collected over potassium hydroxide solu- tion when the substance is oxidized by copper oxide in an appara- tus from which the air has been displaced by carbon dioxide. This is often called the " absolute method." By the method of Kjeldahl, which is the one generally used in the analysis of foods PRELIMINARY DISCUSSION 9 and other complex mixtures, the nitrogen is converted into am- monium sulphate by heating the substance with concentrated sulphuric acid, and from this compound ammonia is set free by sodium hydroxide and absorbed in a measured quantity of stand- ard acid. The amount of acid neutralized by the ammonia is determined by titration, and from these figures the amount of ammonia and hence of nitrogen is readily calculated. No satis- factory method for the direct determination of oxygen has been found, and the percentage of this element is usually estimated by subtracting the sum of the percentages found for the other elements from one hundred. For the determination of sulphur or phosphorus, the substance is oxidized usually by heating with fuming nitric acid in a sealed tube so that these elements are converted into sulphuric or phosphoric acid, from which the amount of each is found by the ordinary methods of inorganic quantitative analysis. The halo- gens are determined as silver halides, being converted into this form by oxidizing the substance as above in the presence of silver nitrate. If metals are present in organic compounds, as in the case of organic salts, it is usually sufficient to ignite a weighed amount of the substance, when the carbonate or oxide of the metal is left, and can be weighed as such, or the metal determined in the usual ways. Such metals as silver and platinum are, of course, left from the ignition in the metallic state. The Empirical Formula. Since the empirical formula of a compound is simply a record of the quantitative composition in terms of atomic weight units, it is found by translating the parts by weight, or the percentages obtained from the quantitative analysis, into these terms. The student is familiar with the method from his work in inorganic chemistry. The symbol of an element represents a definite number of atomic weight units, and the relative numbers of atoms of the several elements that make up the compound are found by dividing the percentages or proper- 10 INTRODUCTION TO ORGANIC CHEMISTRY tional weights of the elements by their respective atomic weights. The quotients thus obtained are compared, and their ratios to each other expressed in the smallest whole numbers. For in- stance: A certain compound is found to have the following per- centage composition: C = 40.00, H = 6.67, O = 53.33, 40.00-5-12=3.33 6.67 -5- I = 6.67 53-33 -M6 = 3-33 Therefore the composition in atomic weight units is most simply expressed in the formula CH 2 O. Since the methods of quanti- tative analysis are always subject to small errors, the ratios of the quotients often cannot be expressed in exact whole numbers; in these cases, the values which are the nearest possible to whole numbers are taken as representing those numbers. Molecular Formulas. Since the empirical formula is merely an expression in chemical notation of the quantitative composition, any formula which is the multiple of the simplest one would express this fact with the same accuracy. Now it happens very often in organic chemistry that there are two or more distinct com- pounds of different properties which have the same percentage composition, and consequently the same empiricial formula. There are, for example, several different compounds which have the same composition and hence the same empirical formula as that taken for illustration above. This fact suggests that the molecules of these compounds are probably of different weights, and that while one of them may be properly represented by the formula CH 2 O, the others have such formulas as: C 2 H 4 O 2 , C 3 H 6 O 3 , C 4 H 8 O 4 , C 6 Hi 2 O 6 , etc. We must, therefore, find the molecular weight of the compound in order to decide which of the possible multiple formulas belongs to it. The student probably remembers the relation between the densities of gases or vapors and molecular weights: By the hy- pothesis of Avogadro, equal volumes of all gases, when measured PRELIMINARY DISCUSSION II under the same conditions of temperature and pressure, contain equal numbers of molecules. It follows that since density is the weight of a unit volume, the molecular weight of a gas or vapor can be found by comparing its density with the density of some gas whose molecular weight is known, such as hydrogen (2), oxygen (32), or air (whose average molecular weight is 28.96). This method can be employed only with substances" which are gases, or are converted into vapor without decomposi- tion. The densities of gases and of vapors can be determined by direct or indirect weighing, and measuring the volume. The vapor densities of volatile liquids or solids are usually found by the method of Victor Meyer, which consists in causing the vapor from a known weight of substance, formed suddenly at a temperature much above its boiling point, to displace its own volume of air. The apparatus is arranged so that this air is collected over water and measured at room temperature. By this method the molecu- lar weight of one of the compounds whose empirical formula is CH 2 O is found to be 30; hence the molecular formula is at once picked out from the possible multiples as CH 2 O, since here the sum of the atomic weights is 30. It is obvious that the density determination, and hence the molecular weight calculated from it, need not be very exact, since the possible molecular weights which correspond to a given empirical formula are usually quite far apart; in the case taken for illustration, they would be 30, 60, 90, etc., and a determination which was within five units of the true value would be conclusive. The molecular weights of substances which cannot be vapor- ized without decomposition are generally found from the effect which a given weight of the substance has in lowering the freez- ing point, or in raising the boiling point of some solvent. 1 Another method for determining molecular weights in certain cases depends on an argument which may be made from the com- position of the substance as compared with that of some substi- 1 For these methods see Ostwald-Luther's Physico- Chemical Measurements. 12 INTRODUCTION TO ORGANIC CHEMISTRY tution product. This is best shown by an example. One of the compounds whose empirical formulas are all CH 2 O is an acid. If we make the silver salt of this acid and determine the silver, we find that it amounts to 64.64 per cent, of the salt; the rest of the salt the acid radical making up the remaining 35.36 per cent. Since 64.64 : 35.36 = 107.88 (atomic weight of silver): 59, for every atomic weight of silver there are 59 atomic weight units of the radical which contains all the carbon and oxygen of the acid, with any hydrogen which has not been displaced by the silver in the formation of the salt. Now we know that silver has a valence of one, and therefore each atomic weight of silver takes the place of one atomic weight of hydrogen. If we add the weight of one atom of hydrogen to the atomic weight units of the acid radical, we have the probable molecular weight of the acid, that is, 60. The simplest formula which agrees with this is C 2 H 4 O2, that of the silver salt being C 2 H 3 AgO 2 . But here, as in the case of the empirical formula, any multiple of this would satisfy the facts equally well, for the silver salt might be C4HeAg 2 O4, or any multiple of C 2 H 3 AgO 2 . If the salt which we analyzed really had one of these formulas, we should expect that an acid salt, containing only one atom of silver, could be obtained, and since we find in this case that such a salt cannot be made, the simple formula, C 2 H 3 AgO 2 , is, in all probability, the correct one. Structural Formulas. In organic chemistry we not only find many instances of different compounds which have the same empirical formulas, and which must be distinguished by a knowl- edge of their molecular formulas, but there are also frequent cases in which two or more compounds have the same molecular formulas and are yet very different substances. There is only one way in which we can imagine the occasion of such differences, and that is by different relations of the elements to each other in the molecule. These we represent by formulas which are known as constitutional, structural, or graphic formulas, and with which the student is familiar to some extent in inorganic chemistry, PRELIMINARY DISCUSSION 13 In such formulas, the atomic symbols are connected in different ways and in different groups. Compounds of the same mole- cular formula but of different properties are called isomeric compounds or isomers, and the phenomenon is known as isomer- ism. The subject will be discussed in connection with the various cases of isomerism which we shall meet in the course of our study. Classification of Organic Compounds. For reasons that need not be formally discussed at this point, the organic compounds are usually treated under two general classes: the Aliphatic and the Aromatic compounds. These names, like that of Organic Chemistry, have lost much of their original significance many of the aliphatic compounds have no direct relationship to the fats and their derivatives, from which the name is taken, and many of the aromatic compounds are unlike the fragrant substances which suggested their name. There are, however, broad lines of dis- tinction between the two groups of compounds, which justify the classification. In each of these two main classes, we shall find a number of well-defined smaller groups each containing compounds which are closely related to each other in both their physical and chemical properties, such as the several groups of the hydrocarbons, the alcohols, the acids, the carbohydrates, the phenols, etc. Laboratory Operations. Many of the reactions for the prepara- tion of organic substances proceed very slowly as compared with those familiar in inorganic chemistry. The principal reaction is also more often complicated by secondary reactions, and therefore the yield of the desired product is frequently far below that indicated by the equation which represents the reaction. Solvents are often necessary to bring about the intimate contact which is necessary for the reaction, and where, as is generally the case, one or more of the substances is insoluble in water, various organic solvents are employed, such as alcohol, acetone, acetic acid, chloroform, ether, benzene, phenol, etc., and in some 14 INTRODUCTION TO ORGANIC CHEMISTRY instances, sulphuric, hydrochloric, or nitric acid. Frequently the solvent acts also as a necessary diluent. The temperatures for organic reactions are usually not very high. In some cases, where heating is necessary, it is sufficient to distil the mixture, either immediately or after more or less prolonged preliminary boiling with a reflux condenser; or the substances may be dissolved in a high boiling solvent. Higher temperatures than those permitted by the boiling points are obtained by heating under pressure, ordinarily in sealed glass tubes. In many instances, reactions succeed only when the tem- perature is kept low, on account of the instability of the desired product (as in the preparation of the diazo compounds, p. 313), or because other products are formed at higher temperatures. The heat developed in the reactions is often considerable, and its ill effects may be avoided by gradual addition of the reacting sub- stances to each other and external cooling (cf. pp. 159, 294), or by dilution with indifferent solvents such as water, glacial acetic acid, alcohol, ether, or benzene. CHAPTER II THE PARAFFINS OR HYDROCARBONS OF THE METHANE SERIES Among the hundreds of compounds which contain only carbon and hydrogen, there is a considerable group whose members resemble each other in a remarkable manner. Some of them are gases, some are liquids, and others solids; but they are all color- less, all insoluble in water, and are all characterized by great chemical indifference. Even such powerful agents as concen- trated sulphuric acid, chromic acid, and fuming nitric acid, fail to attack them at ordinary temperatures. At higher temperatures these agents act very slowly with the production of carbon dioxide and water, and only very small amounts of intermediate com- pounds. Chlorine is the only agent which acts on these substances at all readily in the cold. It acts more rapidly in sunlight or when the temperature is raised, and the result of its action is a step-by-step replacement of hydrogen by chlorine. This may proceed until all of the hydrogen is replaced and compounds are formed which consist of carbon and chlorine alone. Bromine reacts in sunlight with the liquid and gaseous hydrocarbons with the production of similar substituted compounds. These hydrocarbons have received the name of paraffins (parum and affinis) on account of their chemical indifference or "little affinity." The results of analyses and molecular weight determinations show that their formulas can be arranged in a regular series. The - 15 1 6 INTRODUCTION TO ORGANIC CHEMISTRY hydrocarbon of the lowest molecular weight, 16, has the composi- tion Qj^JNj, H = 25, and these data lead to the molecular for- mula, CH 4 . The next in molecular weight contains C = 80, H = 20 and as its molecular weight is 30 its formula is C 2 He. The third with the molecular weight of 44 has C = 8i.82,H = 18.18, and the formula C 3 H 8 . These molecular weights increase from the first to the second, and from the second to the third, by 14 atomic weight units, and the formulas by an increment of CH 2 . The other paraffins have molecular weights and formulas which stand in a like relation to these and to each other, so that the mo- lecular weight of any one of them can be expressed by 16 + I4n, and their composition by CH 4 + nCH 2 , where n is any number from o to 59. The last expression may be given the more com- pact form, C n H 2n + 2, in which n is any number from i to 60. CnH 2n + 2 is, therefore, a general formula for the paraffins. Com- pounds having such relations as this, which can be expressed by a general formula, are said to form an homologous series. The per- centage of hydrogen decreases rapidly at first, and then more and more slowly as we pass from CH 4 to the higher members of the series; but here, again, a general expression may be formu- lated for the percentage of hydrogen in any of the paraffins. This , , ioo(n + i).i is : per cent, of hydrogen = - 7n + i With this orderly relationship in composition and molecular weight there is also found a generally uniform gradation in such physical properties as the boiling and the melting points. Many of the series from n = i to n = 60 are known and have been investigated, and the others could, undoubtedly, be made if there was any special object in so doing. Some of the formulas with the names and the melting and boiling points are given in the following table. 1 In this discussion, for the sake of greater clearness, the atomic weight of hydrogen has been taken as i instead of 1.008. The more exact formula for the percentage of hydrogen is I00 - 8 ( n + I )_. 7.oo8n + 1.008 PARAFFINS OR HYDROCARBONS OF METHANE SERIES 17 NORMAL PARAFFINS Boiling Point -160 - 93 37 0.6 36.4 70 98.4 125.6 149-5 173 194 214-5 252.5 287.5 205 l 2I5 1 2341 302! 33I 1 But the number of hydrocarbons in the group is very much larger than indicated by this list. While there is only one com- pound of the formula CH 4 , and only one for each of the formulas CzH-e and C 3 Hs, there are two hydrocarbons of the formula C4Hio, three whose composition and molecular weights correspond to CsH^, and a rapidly increasing number for each of the following members of the series. As was stated in the first chapter, the explanation of such "iso- meric" compounds is found in the theory that the same number of atonis is differently combined in molecules of the same com- position and weight. In the theory of valency, as the student knows, the atoms of a compound are supposed to be bound together by the force of x At 15 mm. pressure. 2 Formula Name Melting Point CH 4 Methane -184 C 2 H 6 Ethane -172 C 3 H 8 Propane C4Hio Butane -135 CsHi2 Pentane CeHu Hexane C 7 H 16 Heptane CgHig Octane CgH^o Nonane -51 CloH22 Decane -31 CnH24 Undecane -26 Ci2H26 Dodecane 12 CuHso Tetradecane 4 CieH34 Hexadecane 18 C 2 oH 42 Eicosane 37 C2lH44 Heneicosane 40 C23H48 Tricosane 48 CsiH64 Hentriacontane 68 C35H72 Pentatricontane 75 CeoHi22 Hexacontane 101 1 8 INTRODUCTION TO ORGANIC CHEMISTRY chemical affinity acting at certain points or through certain lines of union which are called ''valencies." The number of valencies depends on the nature of the element, and is determined by the study of the simpler compounds which it forms with other ele- ments the valence of hydrogen being, taken as the unit. Carbon is tetravalent in such simple compounds as CH 4 , CGU, CO 2 ; and the formulation of the vast majority of its compounds is satis- factorily accomplished by the use of the tetrad carbon atom. (In CO, and a few other compounds carbon acts as a dyad and in one instance, at least, carbon appears to be a triad.) Of the other "organic elements," hydrogen is, of course, monovalent, oxygen divalent, and nitrogen either trivalent or pentavalent. The theory of valency is the basis on which organic chemistry has been developed, and its value as a working hypothesis has been abundantly demonstrated by the results, which prove it to have been one of the most fruitful theories of natural science. By the linking of atomic symbols in accordance with the valence theory we can represent in graphic or structural formulas arrange- ments which clearly differentiate and, in a way, explain the various organic compounds. For instance, in the case of C 4 Hi two different arrangements can be made: H H H I I I H C H CH 3 H C H H CH CH 3 CH 3 I I \/ H C EL CH 2 C H CH or | and or H C H CH 2 H C H CH 3 I I I H C H CH 3 H PARAFFINS OR HYDROCARBONS OF METHANE SERIES IQ and for C 5 Hi 2 , the three arrangements: CH 3 CH 3 CH 3 CHs I \/ I CH 2 CH CH 3 C CH 3 I I I CH 2 CH 2 CH 3 I I CH 2 CH 3 CH 3 Moreover, these groupings are the only ones which can be made in which actual differences in the relations of the atoms are indi- cated. Now it happens that there are only two different com- pounds of the formula C-iHio, and only three of the formula CsHi 2 known, in spite of all attempts to make others; and this agreement between the number of theoretical formulas and the facts is found to extend to all such cases of chemical isomerism that is, in no instance is a larger number of isomers known than is predicted by the possible structural formulas, and, though in many cases the whole number of isomers is not known, the validity of this ex- planation has been abundantly proved. It should be noticed, incidentally, that only one distinct grouping is possible for the formulas of the first three members of this series. It is one thing, however, to find that for the observed differences of several compounds of the same molecular formula there is an equal number of possible structural formulas, and quite another to decide which particular grouping is the proper representation of each of these compounds. The problem can, however, be solved by studying the reactions by which the compounds are synthesized and those by which they are converted into other compounds. Illustrations of the methods and the reasoning employed for the selection of a definite arrangement for a particu- lar compound will be given in a number of individual instances. It is very important that the student should clearly understand 20 INTRODUCTION TO ORGANIC CHEMISTRY that a formula of any sort is only a short-hand or pictorial record of observed facts. Hypothetical structural or graphic formulas are often useful as suggestions and incentives for investigation; but no formula of any kind should be accepted unless it is found to be in accordance with all the experimental facts. It may not accurately explain all these facts, and indeed few if any of our formulas do; but it must, at least, not be in contradiction with any of them. The empirical formula records only the elementary composition ; the molecular formula adds to this the numbers of the several atoms in the molecule; and the graphic, constitutional, or struc- tural formula is an attempt to represent the relations of these atoms to each other. It should, perhaps, be pointed out, in order to prevent any possible misunderstanding later, that the relative positions which are given the symbols in the usual structural formulas are entirely without significance. It makes no difference in the meaning of the formula for methane, for instance, whether we write CH 4 or H M H C H Of <-CTT H H In all three cases the one essential fact is that all four hydrogen atoms are directly united to one atom of carbon. In other words, in the usual formula no attempt is made to indicate the actual positions or space relations of the atoms of the molecule. In more complex formulas the position of the symbols is fre- quently varied for the purpose of bringing out some special point or to emphasize certain facts in the behavior of the compound; and the student should accustom himself to recognize the iden- tity of relationship or essential "structure" of these different arrangements. PARAFFINS OR HYDROCARBONS OF METHANE SERIES 21 We shall find, however, that there are a number of instances where isomeric compounds show differences, usually in their physical properties, for which the ordinary method of formulation can render no account; and that here a satisfactory explanation may be given for their differences by formulas which indicate the relative positions of the atoms and groups in space. It is obvious that empirical and simple molecular formulas are of little use in organic chemistry, except as the first expression of composition and the basis for structural formulas. They are so similar in form that it is very difficult to remember them; and in many instances, as has been said, one formula often applies to a number of substances which are entirely distinct in physical and chemical properties, and therefore fails to represent an individual compound. On the other hand, the structural formula is of the greatest importance, for by this mode of representation we can form a clear picture of the differences in molecular arrangement which explain the differences in the behavior of the compounds. In inorganic chemistry where the number of compounds consisting of the same two or three elements is never large, such formulas are interesting, but by no means so necessary for our study. A good exercise for the student at this point is to write all of the possible formulas for a few of the paraffins higher than CsH^. He will find that while there are five arrangements for CeHn, there are nine for C 7 Hi 6 and eighteen for C 8 H 18 . Indeed, the number of combinations and hence of the possible isomers must, from the nature of the case, increase very rapidly. There are 75 for CioH 22 , 355 for Ci 2 H 2 6, and 802 for Ci 3 H 28 . The paraffins which are represented by formulas in which the carbon atoms are united in unbranched chains, that is, where no carbon atom is in combination with more than two other carbon atoms, are termed normal paraffins. It is these which are given in the table on page 17. The isomers or iso-hydrocarbons have branching chains of carbon atoms. 22 INTRODUCTION TO ORGANIC CHEMISTRY Nomenclature. The first four of the normal paraffins have arbitrary names; the higher members of the series are named numerically by the use of the Greek numerals. The names of all paraffins, normal and isomeric, end in ane. Since ethane is composed of two CH 3 groups, CH 3 .CH 3 , propane of a CH 3 group and a C 2 H 6 group (CH 3 .CH 2 ), butane of a CH 3 group and a CsHy group (CH 3 .CH 2 .CH 2 ), etc., and as these groups appear in many compounds, it is convenient to have simple names for them. They are, therefore, named from the corresponding hy- drocarbon containing one more atom of hydrogen by substituting the termination yl for ane; thus CH 3 is methyl, C 2 H 5 is ethyl, CzH.7 is propyl, etc. Compounds which contain these groups are very commonly named from the groups, so that the names become descriptive of the composition. Thus ethane is di- methyl, propane is ethyl-methane, butane is propyl-methane or di-ethyl, etc. The general name of alkyl is given to these groups. The iso-paraffins are, perhaps, most satisfactorily named on a similar principle, as substituted methanes, taking the carbon atom which is united to the largest number of other carbon atoms as the carbon of the original methane. Thus the two iso- meric pentanes whose formulas are given on page 19 would be called dimethyl-ethyl-methane and tetramethyl-me thane; iso- butane would be trimethyl-methane. The formulas of these compounds may be written in a more compact manner on one line with points to separate the groups and indicate the valences instead of lines: dimethyl-ethyl-methane (CH 3 ) 2 :CH.CH 2 .CH 3 or (CH 3 ) 2 :CH.C 2 H 5 , tetramethyl-methane (CH 3 ) 2 :C:(CH 3 ) 2 , trimethyl-methane (CH 3 ) 3 ;CH. Occurrence of the Paraffins. Petroleum consists almost wholly of mixtures of hydrocarbons, often with small amounts of compounds containing sulphur, nitrogen, and occasionally phosphorus. In the Pennsylvania oils the hydrocarbons are almost exclusively members of the paraffin series, while other PARAFFINS OR HYDROCARBONS OF METHANE SERIES 23 oils, such as the Russian, are chiefly mixtures of other hydro- carbons. From the Pennsylvania petroleum the individual paraffins from CH 4 to C 3 oHe2 have been isolated. The process of separating the single hydrocarbons from such mixtures is, however, a difficult and tedious matter, so that petroleum cannot be regarded as a practical source for their preparation. Crude petroleum finds considerable employment as fuel, but much of it is separated by distillation into "fractions," which are characterized by a certain range of the boiling point and have a specific gravity lying between certain limits. Each of these fractions contains more than one hydrocarbon, and in the order of their boiling points and increasing specific gravities are known by the commercial names given in the table: Boiling Specific Contains Between Gravity Chiefly Petroleum ether ..... 4o-6o 0.665-0.670 CsH^-CeHu p .. f Benzine or naphtha .. 7o-go 0.680-0.720 C6H 14 -C 7 Hi 8 \ Ligroin ............. Qo-i2o ........... Kerosene ........... i5o-3oo o. 780-0.820 Lubricating oils ...... above 300 Paraffin ....... melts 38-56 o . 87-0 . 93 These products are purified by washing successively with sulphuric acid and caustic soda, to remove basic and acid im- purities. Sulphur is removed by treatment with copper oxide. From the last fraction, solid "paraffin" is separated by cooling. The yield of the more valuable light oils is increased by carrying out the distillation of the heavier oils in such a way that part of the condensing vapors run back into the boiling oil. The tem- perature is so high that the condensed hydrocarbons are decom- posed, or "cracked," as it is technically termed, into others of smaller molecular weight. Distillation under pressure is also effective. Vaseline or petrolatum is obtained from the residuum of the heavier oils, when these are distilled in a partial vacuum. Since all inflammable gases and vapors form explosive mixtures when mixed in certain proportions with air, the lighter and more 24 INTRODUCTION TO ORGANIC CHEMISTRY volatile oils must always be used with great care to avoid the ignition of such mixtures by a flame or electric spark. The occa- sional explosion of kerosene lamps is due to the presence of some of these lighter oils, which should have been removed in its preparation. The quality of kerosene is tested by finding at what tem- perature it gives vapors which "flash" on its surface when it is slowly heated and a small flame brushed over it Jrom degree to degree. This " flashing point" should be above the temperature which the oil in a lamp can reach. A "fire test" is also made, and consists in determining the temperature at which the oil takes fire and burns. Both the flashing point and the fire test depend somewhat on the apparatus employed. Each of the United States has its own specification and method of testing pre- scribed by the law. The uses of the various petroleum products as solvents, for cleansing, etc., as fuels and illuminants, as in gasoline engines and kerosene lamps and stoves, as lubricating- oils, and, in the case of paraffine, for candles, etc., are well known. While petroleum is the chief natural product in which the paraffins occur, some of the gaseous members of the series, notably methane, are constituents of natural gas, and of the "fire-damp" of coal mines; and some of the solid members occur in earth wax or ozokerite. Considerable amounts of gasoline are obtained from natural gas. Various paraffins are products of the natural decomposition of organic matter, or are produced in the processes of destructive distillation of coal, wood, etc. ; but these are mostly the first members of the series or those of large molecular weight which form the solid paraffins. Although the mixtures of the various hydrocarbons of the methane series, which are obtained from petroleum and other sources, are of very great importance, no practical application whatever has been made of any member of the series by itself. The individual paraffins are, however, of great interest to the PARAFFINS OR HYDROCARBONS OF METHANE SERIES 25 chemist, not only in themselves and in the relationship they have to one another, but also because many other organic com- pounds may advantageously be viewed as derived from them by the substitution of various elements or groups for part or all of the hydrogen they contain, and can be made in the laboratory in this way. Since the same remarks apply to the other series of hydrocarbons, organic chemistry is sometimes denned as the "chemistry of the hydrocarbons and their derivatives" Methane, CH 4 , with other gaseous paraffins, escapes from petroleum as it issues from the ground; and it is the chief compo- nent of natural gas and of the "fire-damp" which finds its way into coal mines from fissures in the coal,' and often occasions disastrous explosions. It is a frequent product of the decomposi- tion of organic matter under certain conditions, as when vege- table matter dead leaves, etc. decays under water, and hence is contained in the gas which is disengaged on stirring the bottom of stagnant pools. On this account it has sometimes been called "marsh gas." It is always formed in the destructive distillation of coal, wood, etc.; and is present in coal gas to the amount of 30-40 per cent. Methane can be made in the laboratory by several methods, some of which may be used for its actual preparation, while others are chiefly of theoretical interest. We shall here, and in the future, designate the former "methods of preparation," the latter "methods of formation." Formation. (a) Methane is produced in small amounts, but mixed with hydrogen and other hydrocarbons, when an electric arc between carbon electrodes is formed in an atmosphere of hydrogen. It is also formed: (b) when the vapor of carbon disul- phide mixed with hydrogen sulphide or with steam is passed through a tube containing heated copper. The reactions are : CS 2 + 2H 2 S + 8Cu = 4 Cu 2 S + CH 4 CS 2 + 2H 2 O + 6Cu = 2 Cu 2 S + 2 CuO + CH 4 26 INTRODUCTION TO ORGANIC CHEMISTRY (c) When mixtures of carbon monoxide or carbon dioxide and hydrogen are passed over finely divided nickel (obtained by reduc- tion of the oxide with hydrogen) which is heated to about 250, the nickel acting as a contact agent. If the gases are mixed in the proportion indicated by the equations, the reaction is complete and the methane is pure: CO + 3 H 2 = CH 4 + H 2 O C0 2 -f 4 H 2 When aluminium carbide is brought into water: A1 4 C 3 + i2H 2 O = 4A1(OH) 3 (e) When halogen substitution products of methane are re- duced by " nascent" hydrogen. The first four of these methods show that methane, and there- fore the great variety of compounds which can be made from it, can be synthesized from the elements; for carbon disul- phide, water, both of the oxides of carbon, and aluminium carbide can be produced by the direct union of their constituent elements. Preparation. Some of the methods of formation can, of course, be used for the preparation of methane, but the methods chosen for the preparation of substances are naturally selected on ac- count of the simplicity of the apparatus and conduct of the proc- ess, and the yield of the resulting product, (i) The most usual method of preparing methane is by heating a mixture of sodium acetate and soda-lime (a mixture of sodium and calcium hydroxides)/ Sodium acetate has the formula C 2 H 3 NaO 2 , and the reaction is: C 2 H 3 O 2 Na + NaOH = Na 2 CO 3 + CH 4 The methane made in this way is not quite pure and cannot be freed from small amounts (up to 8 per cent.) of hydrogen which, with other substances, is formed by the action of heat on sodium PARAFFINS OR HYDROCARBONS OF METHANE SERIES 27 acetate alone. (2) Pure methane is most readily prepared from methyl iodide, CH 3 I (made from methyl alcohol), by placing in an alcoholic solution of this substance some zinc which has first been coated with copper by treatment with a dilute solution of copper sulphate. A compound of the metal with the methyl iodide is first formed, CH 3 ZnI, and then this reacts with the alcohol or the water which is mixed with it as follows: CH 3 ZnI + HOH = CH 4 + Znl(OH) Properties. Methane is the lightest compound gas that is known, being a little lighter than ammonia and having the spe- cific gravity of 0.557 ( a * r = I )- Its flame is almost colorless, and like every combustible gas and vapor, it forms explosive mix- tures with oxygen or with air. In common with the other paraffins, methane is hardly acted on at ordinary temperatures by any agent except chlorine or bromine. The action is slow in diffused daylight, but more rapid in sunlight. The chlorine replaces the hydrogen of methane, with the production of hydrogen chloride and the successive formation of CH 3 C1, CH 2 C1 2 , CHC1 3 , CC1 4 . When mixed with twice its volume of chlorine, methane explodes in direct sunlight with the separation of finely divided carbon: CH 4 + 2C1 2 = 4HC1 + C By reactions with methyl chloride, CH 3 C1, the synthesis of organic substances can be carried on from the elements. As it has proved impossible to obtain more than one com- pound of the formula CH 3 C1, and only one of the formula CH 2 Cl2, the four hydrogen atoms of methane must all be similarly related to the carbon atom. Ethane, C 2 He, occurs in petroleum and natural gas. It may be formed (i) by the reaction of sodium or zinc on methyl iodide: 2 CH 3 I + 2Na = 2 NaI + C 2 H 6 28 INTRODUCTION TO ORGANIC CHEMISTRY This reaction leads to the conclusion that ethane is di-methyl with the constitutional formula, CH 3 .CH 3 . Ethane may be pre- pared, like methane, (2) by the reduction of its halogen substi- tution products by the action of coppered zinc on an alcoholic solution of ethyl iodide, C 2 H 5 I, and (3) by heating the sodium salt of propionic acid, C 3 H 5 O 2 Na, with soda-lime, the reaction being like that for the preparation of methane from sodium ace- tate. Ethane is similar to methane in its properties, but is more easily liquefied and burns with a slightly luminous flame. General Methods for the Formation of Paraffins. i. The first method just given for the production of ethane (i) may be used for the formation of the other hydrocarbons of this series. When two different alkyl halides are employed, however, a mix- ture of products results. For instance, from the action of sodium on a mixture of methyl and ethyl iodides in ethereal solution, propane, CH 3 .CH2.CH 3 ,is formed by the union of the methyl and ethyl radicals: CH 3 I + CH 3 .CH 2 I + 2 Na = CH 3 .CH 2 .CH 3 + 2 NaI but at the same time ethane is formed from the union of methyl to methyl, and butane from the union of two ethyl radicals. Since the mixed products are not easily separated, this method is chiefly useful in syntheses from single alkyl halides, which yield hydrocarbons containing double the number of carbon atoms of the halide. The paraffins may also be formed: 2. From halides containing the same number of carbon atoms (a) By reduction with "nascent" hydrogen (sodium amalgam, zinc and hydrochloric acid, or concentrated hydriodic acid), (b) By the formation of zinc alkyls and their reaction with water (p. 36). (c) By means of the Grignard reaction (p. 37). The iodides and bromides are most suitable for these reactions. 3. By distilling the sodium salts of acetic acid or its homologues with soda-lime. The product is a hydrocarbon whose molecule contains one less carbon atom than the salt: PARAFFINS OR HYDROCARBONS OF METHANE SERIES 2Q CH 3 .CH 2 .CO.ONa + NaOH = CH 3 .CH 3 + Na 2 CO 3 4. Another reaction by which two like alkyl groups may be combined to a paraffin hydrocarbon occurs in the electrolysis of the organic acids or salts which contain these groups. By the electrolysis of acetic acid, for instance, the CH 3 groups which it contains unite in pairs forming ethane, which is evolved at the positive pole together with carbon dioxide, while hydrogen escapes at the negative pole: CH 3 .CO 2 H CH 3 = | + 2 C0 2 + H 2 CH 3 .CO 2 H CH 3 This reaction is, however, often accompanied by other reactions, giving different products from those indicated by the equation above. 5. By the addition of hydrogen to unsaturated hydrocarbons: CH 2 :CH 2 + H 2 = CH 3 .CH 3 This reaction takes place readily in the case of the lower members of the series in the presence of platinum black, and may be effected for the higher members by heating the unsaturated hydrocarbon with hydriodic acid in a sealed tube. The possibility of isomeric paraffins begins with the fourth, butane, C 4 Hi , as has already been shown (p. 18); but the con- stitutional formula for propane, CH 3 .CH 2 .CH 3 with a CH 2 and two CH 3 groups, shows that two different mono-substitution products are possible, CH 3 .CH 2 .CH 2 C1 and CH 3 .CHC1.CH 3 ; and these compounds are readily prepared. They correspond to the two butanes which may be regarded as propane in which one hydrogen atom is replaced by a CH 3 group. Very few of the iso-hydrocarbons can be successfully prepared by the sodium synthesis, because of the mixture of products which is formed. They are best made by reduction of the corre- sponding halides, which in turn are prepared from the correspond- ing alcohols by methods which will be discussed further on. 30 INTRODUCTION TO ORGANIC CHEMISTRY We may add to the properties of the paraffins, that as the molec- ular weights increase they burn with a more luminous, and pres- ently with a smoky flame, and that the higher members cannot be distilled at ordinary pressure, but undergo decomposition into other lighter hydrocarbons, often with separation of carbon. The iso-hydrocarbons have boiling points which are lower than those of the corresponding normal paraffins, and different from each other. In general, a higher boiling point and a longer unbranched chain of carbon atoms are found to go together. Thus the boiling point of normal pentane with a chain of five carbon atoms is 36.4, that of dimethyl-ethyl-methane (isopen- tane) with a chain of four atoms is 30, and that of tetra-methyl- methane, 9. Identification of the Paraffins. An organic substance which is lighter than water and insoluble in it but soluble in ether and benzene, which is not attacked in the cold by fuming nitric acid or concentrated sulphuric acid, and reacts very slowly with bro- mine, is probably a paraffin. Many commercial mixtures, such as the products of petroleum, when subjected to these tests do show some reaction, but this is because of the presence of small amounts of hydrocarbons of other series, and after the partial reaction is over, the pure paraffins remain. They may therefore be purified in this way. The individual paraffins are identified by their melting or boiling points, and by the results of quantita- tive analysis. The iso-compounds are distinguished not only by melting and boiling-point determinations but also by the substitution products which can be obtained from them. CHAPTER III THE HALOGEN SUBSTITUTION PRODUCTS OF THE PARAFFINS The chlorine and bromine substitution products of the par- affins are, as already indicated (p. 15), the only halogen deriva- tives which can be made directly from the hydrocarbons; but since this action gives a mixture of products, it is not a very practical method for their preparation. The action of chlorine and bro- mine is increased by heat or sunlight, and also by the presence of certain substances, such as ferric chloride, aluminium or antimony chloride, or iodine, which act as "halogen carriers." Alkyl chlor- ides, bromides, and iodides are usually prepared from the corre- sponding alkyl hydroxides known as alcohols, which have the general formula, C n H 2n + iOH. The replacement of the hy- droxyl group by the halogen is effected, in the case of the lower members of the series, by the action of the gaseous hydrogen halides on the alcohol in the presence of anhydrous zinc chloride which acts as a water-absorbing agent. For instance: C 2 H 5 OH + HC1 5 C 2 H 5 C1 + H 2 O Ethyl Ethyl alcohol chloride Zinc chloride cannot be employed when the higher alcohols of the series are used, since it acts directly on the alcohol and gives rise to other products. The bromides and iodides (but not the chlorides) can be pre- pared by distilling the alcohols with an excess of an aqueous solu- tion of hydrobromic or hydriodic acid. In some instances a halide 32 INTRODUCTION TO ORGANIC CHEMISTRY salt is mixed with the alcohol and the halogen acid set free by treatment with sulphuric acid. Ethyl bromide, C 2 H 5 Br, for example, is readily made by distilling a mixture of alcohol, potas- sium bromide, and sulphuric acid. In every case a large excess of the hydrogen halide is necessary, since the reaction, as indicated in the above equation, is a reversible one. The method of most general applicability is the treatment of the alcohol with a phosphorus halide: 3 C 3 H 7 OH + PC1 3 = 3C 3 H 7 C1 + P(OH) 3 Propyl Propyl alcohol chloride This method is the one almost always used in the preparation of alkyl bromides and iodides. It is not necessary, however, to employ the phosphorus halides themselves, but simply to add bromine or iodine, a little at a time, to the alcohol in which red phosphorus has been placed. After standing for some time the alkyl halide is obtained by distillation. General Properties. Methyl chloride, methyl bromide, and ethyl chloride, are gases at ordinary temperatures. The other alkyl halides up to those of high molecular weight are liquids which are almost insoluble in water, but very soluble in alcohol or in ether. The lower alkyl halides burn, and methyl and ethyl chlorides give a green-edged flame. All of them are colorless, though the iodides become brown after a time, on account of iodine which is separated by slight spontaneous decomposition and dissolves in the unchanged iodide. As shown in the follow- ing table the boiling points are higher as the molecular weights increase; and, for corresponding halides, are highest for the iodides and lowest for the chlorides. The specific gravities of the compounds of a given halogen decrease as the -molecular weight is larger, and the specific gravities of the different halides of the same alkyl show the same gradation as the boiling points, in- creasing from the chlorides (which are all lighter than water) to the iodides. HALOGEN SUBSTITUTION PRODUCTS OF PARAFFINS 33 SOME NORMAL ALKYL HALIDES (Primary) CHLORIDE BROMIDE IODIDE Boiling Specific Boiling Specific Boiling Specific Point Gravity Point Gravity Point Gravity Methyl 23.7 0.952 (o) 4-5 i.73 (o) 45 2.293 (18) Ethyl 14 0.918 (8) 38.4 1.468 (13) 72.3 1.994 (14) Propyl 46.5 0.912(0) 71 Butyl 78 0.907 (o) 101 Amyl 107 0.901 (o) 129 Hexyl 133 0.892 (16) 156 Heptyl 159 0.881 (16) 179 Octyl 180 0.880 (16) 199 .383 (o) 102.5 1.786 (o) .305 (o) 130 1.643 (o) .246 (o) 156 1.543 (o) .193 (o) 182 1.461 (o) .113 (16) 201 1.386 (16) .116 (16) 221 1.345 (16) The relation between structure and physical properties is illustrated by the following table of the boiling points and specific gravities of the isomeric butyl halides: CHLORIDE BROMIDE IODIDE Boiling Specific Boiling Specific Boiling Specific Point Gravity Point Gravity Point Gravity Normal butyl 78 0.907(0) 101 1.305(0) 130 1.643 (o) CH 3 .CH 2 .CH 2 .CH 2 X Iso-butyl 68.5 0.895(0) 92 1.204X16) 119 1.640(0) (CH 3 ) 2 CH.CH 2 X Secondary butyl 67.5 0.871(20) 91.3 1.250(25) 119 1.626(0) CH 3 .CH 2 .CHX.CH 3 Tertiary butyl 55 0.866(0) 72 1.215(20) 100 1.571(0) (CH 8 ) 2 CX.CH 3 The chemical reactivity of the normal halides is greatest in the iodides and least in the corresponding chlorides; it also increases from the higher members to the lowest. Methyl iodide is, there- fore, the alkyl halide of greatest activity. Alkyl iodides are converted into bromides or chlorides by bromine or chlorine. Bromine is not displaced by chlorine, but a bromide may be changed into a chloride by antimony pentachloride. The halides react more or less readily with many substances, and are consequently of great importance in organic synthesis. The following are typical reactions: i. With Hydroxyl Compounds. With water or alkalies the 3 34 INTRODUCTION TO ORGANIC CHEMISTRY halogen is exchanged for the hydroxyl group and alcohols are formed: CH 3 I + HOH <= CH 3 OH + HI Methyl Methyl iodide alcohol C 2 H 5 Br + KOH = C 2 H 5 OH + KBr Ethyl Ethyl bromide alcohol The reaction with water is reversible, and to render it complete, heat and a considerable excess of water are necessary, while that with the base goes more readily. Moist silver oxide, which reacts like a hydroxide, effects the exchange still more easily, and usually without heating: C 2 H 5 C1 + AgOH = C 2 H B OH + AgCl Ethyl Ethyl chloride alcohol This replacement of the halogens by hydroxyl takes place most easily with the alkyl iodides and least rapidly with the chlorides. If, however, potassium hydroxide acts in an alcoholic instead of an aqueous solution, the character of the reaction is altered: the replacement by hydroxyl does not occur, but instead, the halogen and an atom of hydrogen are withdrawn from the halide with the production of an " unsaturated " hydrocarbon (p. 42): CH 3 .CH 2 Br + KOH = CH 2 :CH 2 + KBr + H 2 O Ethyl bromide Ethylene 2. With Certain Salts. The inorganic salts most employed in the reactions are those of silver. With these a fairly ready reac- tion usually takes place, with the formation of the insoluble silver halide and compounds in which the alkyl group is united to the acid radical of the silver salt, thus: CH 3 I + AgN0 3 = CH 3 NO 3 + Agl Methyl Methyl iodide nitrate 2 C 2 H 5 Br + Ag 2 S0 4 = (C 2 H 5 ) 2 SO 4 + 2AgBr Ethyl Ethyl bromide sulphate HALOGEN SUBSTITUTION PRODUCTS OF PARAFFINS 35 Organic salts of sodium and potassium act in a similar way, CH 3 C1 + KCN = CH 3 CN + KC1 Methyl Methyl chloride cyanide C 2 H 5 I + C 2 H 3 O 2 Na = C 2 H 3 O 2 C 2 H 5 + Nal Ethyl Sodium Ethyl iodide acetate acetate The alkyl compounds formed in these reactions are named as alkyl salts of the several acids, and are given the group name of "esters" or "ethereal" salts. The alkyl halides themselves obviously belong to this same group. 3. With ammonia, the halogen is replaced by NH 2 , the " amino" group, C 2 H 5 Br + NH 3 = C 2 H 5 NH 2 .HBr Ethyl Ethyl amine bromide hydrobromide 4. The alkyl halides, as well as all halogen substitution products of the paraffins, are converted into the respective hydrocarbons by "nascent" hydrogen: C 2 H 6 I + HH = C 2 H 6 + HI Attention should be called to the fact that the metathetical reactions with alkyl halides, which have been described, progress slowly as compared with the almost instantaneous reactions of this kind which occur between inorganic salts and ba,ses. The explanation given for this is that the organic halides are iC*iized very slightly, if at all. 5. With Metals. The reaction of alkyl halides with sodium has already been given (p. 28) as a means of synthesizing the paraffins. A compound containing zinc was also used for the same purpose. Zinc, magnesium, and some other metals react with the alkyl halides as follows: C 2 H 6 I + Zn = C 2 H 6 ZnI When this zinc ethyl iodide is boiled for some time it is converted into zinc ethyl (C 2 H 5 ) 2 Zn: 2C 2 H 5 ZnI =- (C 2 H B ) 2 Zn -f ZnI 2 36 INTRODUCTION TO ORGANIC CHEMISTRY Zinc ethyl iodide is a solid, but the zinc alkyls are liquids of repugnant odor, which take fire spontaneously in the air, so that their preparation and their use as reagents must all be conducted in an atmosphere of an indifferent gas, usually carbon dioxide. They are immediately decomposed by water with the produc- tion of hydrocarbons: (C 2 H 5 ) 2 Zn + 2 H 2 = 2 C 2 H 6 + Zn(OH) 2 The Grignard Synthesis. The use of zinc alkyls and their halide salts has been generally displaced by the employment of corresponding magnesium compounds; since it has been found that these are more easily prepared, and have the further advantage of not igniting spontaneously in the air. Clean dry magnesium turnings are covered with anhydrous ether and the organic halogen compound is gradually added. Absence of moisture is essential to success. After the reaction, evaporation of the ether leaves the magnesium compound in combination with one molecule of ether, e.g., C 2 H 5 MgI, (C 2 Hs) 2 O. Other solvents besides ether, such as benzene, can be used, if a little ether or anisol is added as a catalyzer, and in this case the magnesium compound is obtained free from ether. In many instances the preliminary preparation of the magnesium com- pound is not necessary, the two organic substances which are to be synthesized being brought together in the presence of mag- nesium and ether. Almost all the halogen derivatives of organic compounds, ex- cept acyl halides (p. 114), form addition compounds .with magne- sium, and these substances, which are called Grignard reagents, are of the greatest service to the organic chemist on account of the wide variety of syntheses which can be effected by their means. Some of the reactions with Grignard reagents are given here for convenience in future reference. i. With water and other hydroxyl compounds, they yield hydrocarbons: CH 3 MgBr + H 2 O = CH 4 + MgBrOH C 6 H 5 MgBr + H 2 = C 6 H 6 + MgBrOH HALOGEN SUBSTITUTION PRODUCTS OF PARAFFINS 37 2. They absorb carbon dioxide, forming products which yield organic acids when treated with inorganic acids: C 2 H 6 MgI + CO 2 = C 2 H 5 CO.OMgI C 2 H 5 CO.OMgI + HC1 = C 2 H 5 CO.OH + MglCl 3. They absorb dry oxygen and the products yield primary alcohols or phenols when treated with an acid: 2RMgBr + O 2 = 2RO.MgBr RO.MgBr + HC1 = R.OH + MgBrCl 4. They form additive compounds with most substances which contain a carbonyl group (CO), and these yield alcohols when acted on by water or an inorganic acid. In this way primary alcohols may be prepared by means of formaldehyde: C 2 H 5 MgI + HCHO = C 2 K & ^ X X)MgI C 2 H 6 C^ + HC1 = C 2 H 5 CH 2 OH + MglCl \)MgI With other aldehydes secondary alcohols are formed: H /H Mgl CH 3 MgI = (CH 3 ) 2 C< X)] Aldehyde /H (CH 3 ) 2 C<; + HC] = (CH C ) 2 CH.OH + MglCl X)MgI Ketones, e.g., CH 3 .CO.CH 3 , and esters, in a similar manner give tertiary alcohols. 5. Aldehydes can be prepared from formic esters, and ketones from cyanogen, cyanides, and amides. 6. With many halides of metals and non-metals they enter into reaction with the production of the alkyl, or alkyl-halogen derivatives of these elements: 38 INTRODUCTION TO ORGANIC CHEMISTRY SnBr 4 + 4C 2 H 5 MgBr = ( SiCl 4 + C 2 H 5 MgBr = C 2 H 5 SiCl 3 + MgBrCl Methyl chloride is a commercial product made from trimethyl- amine hydrochloride (p. 132), which is obtained as a by-product in the beet-sugar industry. It is compressed to a liquid and used for the production of cold (like ammonia), and is extensively employed in the manufacture of various coal tar dyes. Ethyl chloride is also made on the large scale and used in the prepara- tion of ethyl mercaptan, C 2 H 5 SH (p. 238) which is employed in making "sulphonal" (p. 240). While there is only one methyl and one ethyl chloride, bromide, or iodide known or possible, isomeric alkyl halides begin with the two propyl halides, CH 3 CH 2 CH 2 C1, CH 3 .CHC1.CH 3 , and in- crease rapidly in number as we go higher in the series. There are four butyl bromides, CH 3 .CH 2 .CH 2 .CH 2 Br, (CH 3 ) 2 CH.- CH 2 Br, CH 3 .CH 2 .CHBr.CH 3 , and (CH 3 ) 3 CBr; and eight pentyl bromides. Among the halogen substitution products of the paraffins, which contain more than one halogen atom, may be mentioned: Methylene iodide, CH 2 I 2 , which is one of the heaviest known liquid compounds (specific gravity 3.292 at 1 8). By mixing with benzene, liquids of any specific gravity between 0.8736 (benzene) and 3.292 can be prepared, and may be used for the indirect spe- cific gravity determination of solids, and for the separations of solids of different specific gravities. It is made by the reduction of iodoform, or tri-iodomethane, by hydriodic acid in the presence of phosphorus: CHI 3 + HI = CH 2 I 2 + Is This is a typical instance of the use of hydriodic acid as a reduc- ing agent. The student will recall from his study of inorganic chemistry that hydrogen iodide is an endothermic and hence an unstable compound, separating easily into hydrogen and iodine. The phosphorus facilitates the reaction by uniting with the iodine HALOGEN SUBSTITUTION PRODUCTS OF PARAFFINS 39 as it is set free; the phosphorus iodide then reacts with the water which is present, giving phosphorous acid and hydriodic acid again. Tri-iodomethane, CHI 3 , commonly known as iodoform, is a yellow crystalline substance, which is prepared by warming an aqueous solution of alcohol and sodium carbonate with iodine. Its formation is often used as a test for alcohol, but several other organic substances give iodoform under similar conditions. It is used as an antiseptic in surgery, often in preparations where it is mixed with other substances to disguise its peculiar odor. Tri-chlormethane, CHC1 3 , or chloroform, is the well-known anaesthetic which was discovered in 1831 and first used for this purpose in 1848. It is prepared by the action of bleaching powder on alcohol or acetone or from chloral hydrate by reactions which will be discussed under those topics. Chloroform is a colorless liquid of ethereal odor and a sweetish taste. It is slightly soluble in water to which it imparts its odor and taste. It is readily volatile, but not inflammable. Chloroform is an excellent solvent for many organic compounds; it dissolves rubber and fats, and is a useful cleansing agent. In the air and light chloroform under- goes a slow decomposition with the formation of chlorine, hydro- gen chloride, and carbonyl chloride, COCU. Consequently great care must be taken in regard to its purity when it is used for anesthesia. When heated with an alcoholic solution of potas- sium hydroxide, chloroform is decomposed with the formation of potassium formate: CHC1 3 + 4KOH = HCO.OK + 3 KC1 + 2 H 2 O Chloro- Potassium form formate If ammonia is added to the mixture of alcoholic potash and chloroform, potassium cyanide is produced: CHC1 3 + NH 3 + 4KOH = KCN + 3KC1 + 4 H 2 O INTRODUCTION TO ORGANIC CHEMISTRY A similar reaction occurs when a primary amine (p. 127) is used in place of ammonia, and the unmistakable odor of the prod- uct serves as a test for chloroform and for the primary amines (cf. p. 132). Tetra-chlormethane, CCU, or carbon tetrachloride, is the final product when chlorine acts on methane. It is prepared commer- cially by passing the vapor of carbon disulphide mixed with chlo- rine through red-hot porcelain tubes, or by leading chlorine into the liquid disulphide in which a little iodine has been dissolved, and which acts as a catalyzer: CS 2 = CC1 4 + S 2 C1 2 Carbon tetrachloride is a heavy liquid which is not inflammable and is an excellent solvent for fats. It is sold for extinguishing fire as "pyrene," and is much used for cleansing purposes, often mixed with benzine or gasoline, under the name of "carbona." It is hydrolyzed by a hot solution of potassium hydroxide with the production of potassium carbonate: CC1 4 + 6KOH = K 2 CO 3 + 4KC1 + 3H 2 O On heating with "molecular" silver, tetrachlor-methane is con- verted into hexachlorethane, CCls.CCls, a crystalline substance of camphor-like odor, which is hydrolyzed by potash at 200 into potassium oxalate. SOME POLYHALOGEN DERIVATIVES CHLORIDE Boiling Specific j Point Gravity Methylene, CH 2 X 2 4i.6 1.38 Methenyl, CHX 3 61 1.50 Carbon tetrahalide, . BROMIDE -IODIDE Boiling Specific Boiling Specific Point Gravity Point Gravity 1 80 CX 4 Ethylene, CHaXCHaX Ethylidene, CH 3 .CHX 2 76.8 1.63 83.7 57-5 1.27 98-5 i8 9 129 112.5 2.50 2.90 2.18 3-33 melts 119 4.01 unstable 2.07 178 2.84 HALOGEN SUBSTITUTION PRODUCTS OF PARAFFINS 41 While the chlorine substitution products of the paraffins, which contain two or more chlorine atoms, can be formed by direct step-by-step replacement of hydrogen with chlorine, this method is not a practical one for the preparation of the individual members, because of the mixtures it gives. Hence other methods are em- ployed for making the chlorides and other polyhalogen derivatives. Besides such special methods as have just been given for the methane derivatives, there are certain methods of general ap- plication for the derivatives of the higher paraffins. Dihalogen compounds, in which the two halogen atoms are united to one carbon atom, are obtained by the action of phosphorus pentahal- ides on aldehydes and ketones: CH 3 .CHO + PC1 5 = CH 3 .CHC1 2 + POC1 3 Aldehyde Ethylidene chloride CH 3 .CO.CH 3 + PC1 5 = CH 3 .CC1 2 .CH 3 + POC1 3 Acetone Dichlorpropane (2.2) The isomeric dihalogen derivatives with the halogen atoms united to different carbon atoms can be made from the correspond- ing dihydroxyl alcohols glycols as the monohalogen com- pounds are from the simple alcohols the reaction involving two steps: CH 2 OH.CH 2 OH -> CH 2 Br.CH 2 OH -> CH 2 Br.CH 2 Br Glycol Glycolbromhydrin Ethylene bromide These halides are also the product of the direct addition of halogen to unsaturated hydrocarbons of the olefine series (p. 44) : CH 2 :CH 2 + Br 2 = CH 2 Br.CH 2 Br Ethylene Ethylene bromide Compounds of this type are useful in synthetic work, since they may form a step in the conversion of a monosubstituted compound to various disubstituted compounds. We shall meet with illustrations of such transformations. It should be remarked that isomerism in the alkyl polyhalides begins with the derivatives of ethane. Thus there are two di- 4ia INTRODUCTION TO ORGANIC CHEMISTRY halides of ethane represented by the formulas, CH 2 C1.CH2C1, eth- ylene chloride, and CH 3 .CHC1 2 , ethylidene chloride. Similarly there are two tri-halides, two tetra-halides, but only one penta- and one hexa-halide. As we go higher in the series the number of halogen substituted isomers increases rapidly. Hydrolysis of Halogen Derivatives. All the halogen deriva- tives of the paraffins are subject to hydrolysis. The normal course of the hydrolysis is the replacement of each halogen atom by an hydroxyl group (cf. p. 34). When the compound contains only one halogen atom attached to any one carbon atom, the product is the corresponding hydroxyl compound a simple or a polyhydroxyl alcohol (p. 59). But when the halogen derivative contains groups of the types: CHX 2 , CX 2 , or CX 3 , which would give two or three hydroxyl groups united to the same carbon atom, such products being unstable pass at once into stable forms by splitting off water. Thus from R.CHX 2 we get an aldehyde, R.CHO (p. 77); from R.CX 2 .R, a ketone, R.CO.R (p. 89); and from R.CX 3 , an acid, R.CO.OH (pp. 98, 99, 103). CHAPTER IV UNSATURATED HYDROCARBONS There are two other series of hydrocarbons, which are so re- lated to the paraffins and to each other that a brief considera- tion of them may properly be given at this point. In each of these series the members show a constant difference of 14 between their molecular weights and consequently, like the paraffins, a formula difference of CH 2 . The percentage of hydrogen is, however, less than in the corresponding paraffins which have the same number of carbon atoms, and less in one series than in the other; the difference expressed in their formulas being that of two atoms of hydrogen in each case. The general formulas for these series are, therefore, C n H 2n and C n H 2 n _ 2 . In neither of these series is a compound known which contains only one carbon atom. Such compounds would have the formulas, CH 2 and CH, with carbon acting as a divalent element in one, and as a monovalent element in the other. Both series begin with compounds con- taining two atoms of carbon: C 2 H 4 , ethylene, and C 2 H 2 , acetylene; and the series are called from these first members the ethylene series and the acetylene series, respectively. It is characteristic of the hydrocarbons of both series that they absorb chlorine and bromine, uniting additively with these halogens to form compounds of the types, C n H 2n Cl 2 and C n H 2n _ 2 Cl4, substances which can be formed from the corresponding paraffins by substitution, and which can be converted into these paraffins by nascent hydrogen. On account of this behavior, the hydrocarbons of these series are termed " unsaturated" hydrocarbons. In making a graphic formula for ethylene, with the assumption that carbon is here, as 42 43 UNSATURATED HYDROCARBONS H-C-H usually, tetravalent, we must write II , with a double bond H-C-H between the carbon atoms. Any other formula would require an unusual valency for carbon. With a very few exceptions, such as CO, carbon appears everywhere to be tetravalent, and there seems to be no good reason for believing that its valency in these compounds is an exception to the general rule. On the contrary, the facts that a hydrocarbon of the formula CH 2 cannot be ob- tained, and that only one compound of the type CH 2 .CHC1 can be made, are in favor of the tetravalency of carbon in ethylene and the symmetrical formula, CH 2 :CH 2 . Again, if carbon was here trivalent, we might expect to find hydrocarbons containing a single trivalent atom, such as C=H 3 .C = H 2 , which must then of necessity have an odd number of hydrogen atoms. But no such compounds are known, and on the contrary, all formulas oj known hydrocarbons contain an even number oj hydrogen atoms. CH 2 The symmetrical formula II with the double bond is, there- CH 2 fore, usually accepted for ethylene and similar formulas for its homologues; but it must be remarked that the double bond, instead of denoting a firmer union, indicates a weak point in the molecule. It readily gives place to a single linkage, as in the reaction with bromine: C = H 2 * CH 2 Br II + Br 2 = | C = H 2 CH 2 Br and in oxidation processes is the point where the compound breaks down most easily with the production of substances which have a smaller number of carbon atoms in the molecule. The members of the ethylene series have only one double bond, INTRODUCTION TO ORGANIC CHEMISTRY 44 as for instance, propylene CH 3 .CH:CH2, and the isomeric butylenes, av CH 3 .CH 2 .CH:CH 2 , CH 3 .CH:CH.CH 3 , and >C:CH 2 . CH/ In acetylene, C 2 H 2 , a triple bond between the two carbon atoms is indicated for reasons of the same kind as those given for the double bond in the ethylene series, and this triple bond is weaker C H than the double bond. Acetylene is III ; allylene, or methyl- C H acetylene, the next number of the series, is CH 3 .C ! CH. The acetylene series contains two groups the acetylene group proper, in which there is one triple bond; and the di-olefines, which are isomeric with the acetylenes, but have two double bonds instead of one triple bond. Thus, allene, CH2iC:CH 2 , a di-olefine, is isomeric with allylene given above. The name olefine (oil-forming) was given to ethylene because this gas forms an oil by its additive reaction with chlorine. From this the general name of olefines was given to the members of the ethylene series; and the isomers of the acetylenes, which have two double bonds, are known, by analogy, as di-olefines. A more systematic mode of naming these unsaturated compounds is to use the ending ene to indicate the ethylene state with one double bond, diene for the di-olefines with two double bonds, and ine for compounds, like acetylene, which have one triple bond. These endings are added to the stem of the name for the paraffin with the same number of carbon atoms. Thus, cor- responding to ethane, C2H 6 , we should have ethene, C 2 H 4 , and ethine, C 2 H 2 ; and in the next group, propane, C 3 Hg; propene, CH 3 .CH : CH 2 ; propadiene, CH 2 : C : CH 2 ; and propine, CH 3 .C : CH. 45 UNSATURATED HYDROCARBONS UNSATURATED HYDROCARBONS Boiling Point Ethylene Series CnHzn Ethylene, CH2:CH 2 -103 Propylene, CH 3 .CH: CH 2 . ... -48 Butylene, C 2 H 5 .CH: CH 2 .. . . -5 Butylene, CH 3 .CH:CH.CH 3 * i Butylene, (CH 3 ) 2 C: CH 2 .. . . -6 Amylene, C 2 H 5 CH: CH.CH 3 36 Amylene, (CH 3 ) 2 CH.CH:CH 2 20-21 Amylene, (CH 3 ) (C 2 H 5 )C: CH 2 3.1-32 Amylene, (CH 3 ) 2 C: CH.CH 3 36-38 Hexylene, C 4 H 9 .CH:CH 2 68-70 Heptylene, C 5 Hn.CH:CH 2 96-99 Octylene, C 6 Hi 3 .CH:CH 2 122-123 Acetylene Series Boiling CnHjn_2 Point Acetylene, CH : CH -83.8 Allylene, CH 3 .C:CH Dimethyl- Acetylene, CH 3 .C 1C. CH 3 . 27-28 Ethyl- Acetylene, C 2 H 5 .C : CH. . 1 8 Methyl-Ethyl- Acetylene C 2 H 5 .C:C.CH 3 55-56 Propyl- Acetylene (n),C 3 H 7 .C : CH 48-49 Iso-Propyl- Acetylene, (CH 3 ) 2 CH.C H 28-29 C n H 2 n - 4 Series (CH 3 )2CH.CH 2 .CH:CH.C(CH 3 ):C:CH 2 Boils I 7 2 -i 7 6 Diacetylene Dipropargyl Cn H Z n - e Series CHiC.CiCH CHiC.CH 2 .CH 2 .CiCH 85' Formation. Various unsaturated hydrocarbons, chiefly ethy- lene and acetylene are formed in small amounts in the destructive distillation of organic substances and are consequently found in coal gas. They are formed, theoretically, by the removal of pairs of hydrogen atoms from the paraffins: C 2 H 6 - 2H -> C 2 H 4 - 2H - C 2 H 2 - 2H -* 2C These changes probably occur in gas retorts, and account for the large percentage of hydrogen (up to 50 per cent.) and the small amounts of saturated hydrocarbons found in coal gas, as well as for the deposits of carbon in the compact form of "gas carbon," in the outlet of the retorts. The preparation of the ethylene hydrocarbons may be effected: INTRODUCTION TO ORGANIC CHEMISTRY 46 1. By removal of the halogen from alkyl dihalides by means of a metal acting on an alcoholic solution: CH 2 Br.CH 2 Br + Zn = CH 2 :CH 2 + ZnBr 2 2. By heating an alkyl monohalide with potassium hydroxide in an alcoholic solution: CH 3 .CH 2 Br + KOH = CH 2 :CH 2 + KBr + H 2 (The use of an alcoholic solution of the hydroxide is important, since in aqueous solution the presence of the water causes the replacement of the halogen by hydroxyl: CH 3 .CH 2 Br + KOH = CH 3 .CH 2 OH + KBr.) 3. From alkyl hydroxides (alcohols) by withdrawing the ele- ments of water: CH 3 .CH 2 OH - H 2 O = CH 2 :CH 2 This may be effected by anhydrous zinc chloride, phosphorus pentoxide, syrupy phosphoric acid, or by concentrated sulphuric acid. In the reaction with sulphuric acid intermediate products are formed. Ethylene or ethene, C 2 H4. Ethylene is usually prepared by heating alcohol with about six times its weight of concentrated sulphuric acid to about 170. (Syrupy phosphoric acid may be advantageously substituted for sulphuric acid.) It is a colorless gas of peculiar, somewhat sweetish odor, which burns with a luminous flame. It is one of the most important of the illu- minating constituents of coal gas. It decomposes at about 400 with the production of hydrocarbons of the paraffin, acetylene, and benzene series. By the electric spark discharge it is decom- posed first into acetylene and hydrogen, and then into carbon and hydrogen. Reactions, i. Ethylene combines directly with the halogens, most energetically with chlorine and least readily with iodine. CH 2 :CH 2 + Br 2 = CH 2 Br.CH 2 Br Ethylene Ethylene bromide 47 UNSATURATED HYDROCARBONS In chlorine it burns with a smoky flame. 2. A mixture of ethyl- ene and hydrogen is synthesized to ethane at about 300 by finely divided nickel as contact agent. 3. Not only does ethylene unite with the halogens, but it also combines additively with hydrogen bromide and iodide forming ethyl halides: CH 2 :CH 2 + HBr = CH 3 .CH 2 Br Ethyl bromide The reaction is more energetic with hydrogen iodide than with hydrogen bromide, and hydrogen chloride does not react at all. 4. With hypochlorous acid, HC1O (in aqueous solution), ethylene combines directly, forming monochlor- alcohol or ethyl- ene chlorhydrin: CH 2 :CH 2 -f HOC1 = CH 2 C1.CH 2 OH Ethylene chlorhydrin We shall find later that the chlorhydrins form important steps in certain syntheses. 5. A similar reaction occurs between ethylene and sulphuric acid, ethylene being slowly absorbed by the concentrated acid with the formation of ethyl sulphuric acid (cf. p. 120): C 2 H 4 + H 2 SO 4 = (C 2 H 6 )HSO 4 Ethyl sulphuric acid 6. Organic acids also react slowly with the f ormation of analogous compounds. 7. Oxidizing agents act on ethylene very readily. This description of the properties and reactions of ethylene applies in a general way to the other members of the series. The first of these "alkenes" are gases, then come a number of hydro- carbons which are liquids, insoluble in water but soluble in alcohol and in ether. The higher members of the series are crystalline solids. Acetylene, C 2 H 2 , is formed in small amounts when an electric arc is produced between carbon poles in an atmosphere of hydro- gen. This gives another method for the synthesis of organic com- INTRODUCTION TO ORGANIC CHEMISTRY 48 pounds from the elements (cf. p. 26), since acetylene is readily converted into other hydrocarbons from which the greatest variety of derivatives can be made. Acetylene is also formed as one of the products of the incomplete combustion of other hydro- carbons, which occurs when the supply of oxygen is limited. The gases that come from a Bunsen burner, when the flame has "struck back" and is burning at the bottom of the tube, contain acetylene, though in small amounts (less than i per cent, of the gases). Methods of formation similar to those given for ethyl- ene may be employed for acetylene and its homologues: CH 2 Br.CH 2 Br + 2 KOH = CH i CH + 2 KBr + 2 H 2 O CHBr 2 .CHBr 2 + 2Zn = CH I CH + 2ZnBr 2 But since the manufacture of calcium carbide has become com- mercial, the common mode of preparation is through the reaction of this substance with water: C 2 Ca + 2 H 2 O = C 2 H 2 + Ca(OH) 2 This may be regarded as another elementary synthesis; for while calcium carbide is actually made from lime, CaO, and coke (C) in the electric furnace, the calcium oxide can be made from the metal calcium and oxygen. Properties. Acetylene is a gas of garlic-like odor. When made from commercial carbide it is contaminated with small amounts of ill- smelling gases, such as phosphine, and hence the odor of the ordinary gas is not that of pure acetylene. It burns with an exceedingly bright flame, which gives much smoke unless the gas is burnt in special burners whose tips deliver about one-half of a cubic foot per hour. It can be liquefied quite readily (by a pressure of 83 atmospheres at 18), but cannot be safely used in the liquid state or even under a pressure of more than two at- mospheres, since under these circumstances it is liable to explode violently with the production of hydrogen and finely divided carbon. This instability indicates that acetylene possesses an 49 UNSATURATED HYDROCARBONS unusual amount of stored or potential energy. It is in fact an endothermic compound which absorbs 58.7 calories in its forma- tion (cf. p. 53). It is slightly soluble in a number of liquids, and dissolves quite freely in acetone (24 vols. of acetylene in i vol. acetone under atmospheric pressure) forming a solution in which, even under considerable pressure, it is not explosive. Such solutions are used as a convenient source of the gas for lighting purposes. Otherwise it is generated as it is used, as in bicycle and automobile lamps, or is stored in small gas holders under slight pressure for household lighting. Mixtures of acetylene and air are explosive through a remarkably wide range of proportions: beginning with only 3.5 per cent, of acetylene by volume and end- ing with 82 per cent. For comparison it may be stated that the range for hydrogen is from 5 to 72 per cent.; for carbon monoxide, *3 to 75 per cent.; for water gas, 9 to 55 per cent; coal gas, 6 to 29 per cent. ; and for methane, 5 to 13 per cent. When acetylene is passed through a tube heated to dull red- ness, it "polymerizes" by the union of its molecules, and forms, among other compounds, benzene, CeH 6 , which is the most im- portant hydrocarbon of the aromatic series. Acetylene and its homologues unite additively with the halo- gens, with hydrogen (in the presence of platinum black), and with the halogen acids. They are readily oxidized by oxidizing agents in solution (e.g., KMnO^, showing reactions which are analogous to those of ethylene and its homologues. All compounds of the acetylene series that have a triple bond between two carbon atoms at the end of the chain give a distinctive reaction with ammoniacal solutions of silver or cuprous chloride. This con- sists, in the case of acetylene, in the precipitation of carbides of these metals, C2Ag 2 and C2Cu 2 , compounds in which the metal has taken the place of the hydrogen of the acetylene, and which are consequently called " acetylides." When dry, these com- pounds explode when struck or when heated to 100. With hydrochloric acid, copper acetylide gives acetylene. INTRODUCTION TO ORGANIC CHEMISTRY 50 CH 2 = C - CH = CH 2 , Of the di-olefines, isoprene, CsHs or CH 3 is of special interest, because of the recent discovery that it can be converted into India rubber. Isoprene is a liquid, boiling at 37. It is one of the products of the destructive distillation of rubber, and is formed when turpentine is passed through a red hot tube. Its conversion into India rubber is the effect of a polymerization, or union of several molecules to a more com- plex one of the same composition. Hydrocarbons of the Formulas, CnH 2n -4, C n H 2n -6. The compound of the lowest molecular weight corresponding to the general formula C n H 2n -4 which is theoretically possible would be C 4 H 4 , and this might have the structure CH 2 :C:C:CH 2 or CH; C.CH: CH 2 . The higher members of the series would have similar constitutions with either three double linkages or one double and one triple linkage, on the assumption that the carbon atoms of each compound form open chains. One such hydro- carbon with three double bonds has been obtained by the with- drawal of the elements of water from the natural di-olefine alcohol geraniol (p. 87) and has the formula (CH 3 ) 2 CH.CH 2 .CH:CH ? - C(CH 3 ):C:CH 2 = CioHi 6 . This hydrocarbon unites additively with six atoms of hydrogen or of bromine with the formation of saturated compounds, CioH 22 and CioHi 6 Br 6 . Other open-chain hydrocarbons of this series are practically unknown. A large number of hydrocarbons known as terpenes which occur in the vegetable kingdom have the same composition, but are proved to be cyclic compounds in which the carbon atoms form closed chains or rings (p. 257). In the series of open-chain hydrocarbons of the formuia C n H 2n _6 the simplest is diacetylene, CHiC.C-CH, which can be made from propiolic acid (p. in), CHlC.CO.OH, through di- acetylene-dicarboxyKc acid, CO.OH.CiC.C-C.CO.OH. Dipro- pargyl, CHlC.CH 2 .CH 2 .GCH, = C 6 H 6 , can be made from the 51 UNSATURATED HYDROCARBONS tetrabromide of diallyl, CH 2 Br.CHBr.CH2.CH2.CHBr.CH 2 Br, by splitting off hydrogen bromide by means of alcoholic potassium hydroxide. This mode of formation and its acetylene-like proper- ties establish its constitution as given in the formula. This hydrocarbon is of especial interest because it is isomeric with benzene, the most important of the cyclic hydrocarbons. It is a liquid boiling at about 85, having a specific gravity of 0.8 1. It slowly changes to a shellac-like mass, which decrepitates when heated. No open-chain hydrocarbons with more than three double or two triple linkages are definitely known. Heats of Combustion and of Formation Knowledge of the amount of heat which is produced by a given weight of a substance used for fuel, such as the different kinds of coal, petroleum, water gas, and coal gas, is, of course, of practical importance. Since the gaseous and liquid fuels are composed largely of hydro- carbons, the heating value of individual hydrocarbons as well as that of the hydrogen and carbon monoxide, which are usually present in fuel gases, is also important. To the chemist, the heating value of these compounds is of 'special interest, because by its aid he can find the "heat of formation" of the compounds, which gives information in regard to their stability and, to some extent, to their reactivity with other compounds. It is assumed that the student is familiar with the units of heat measurement, the small or gram-calorie and the large or 1000 gram-calorie. The latter is used in the following discussion. By the heat of formation is understood the number of heat units which are given out or absorbed in the formation of a gram- molecular weight of the compound from its elements. This is readily determined when the compound can be made by the direct union of its elements, as in the case of water, carbon dioxide, INTRODUCTION TO ORGANIC CHEMISTRY 52 etc., but in other cases it must be arrived at by an indirect method. The method depends on the fact that the same amount of energy is required to separate the elements of a compound as is set free in their union. The product of a reaction which is at- tended with the production of heat an exothermic reaction has less potential energy and hence greater stability in proportion to the amount of heat evolved, and, similarly, the instability of a compound is greater the greater the heat which is absorbed in its formation, and the greater the potential energy which it therefore possesses. Now, the heat of formation of a compound must be equal to the heat which its elementary constituents would produce on oxida- tion, less the heat of combustion of the compound. For the amount of energy which is necessary to break the union of the elements will fail to appear as heat when the compound is burned. If, therefore, we know the heats of combustion of the con- stituent elements and of the compound, the heat of formation is their difference. In the table are given the heats of combustion and of formation of a number of hydrocarbons which we have been studying, as well as those of their constituents, carbon and hydrogen. For use in determining the heats of formation both are given for \the gram-molecular weight of the compounds, but in the first column, the heats of combustion for one gram are also given as is usual in the practical evaluation of fuel substances. HEAT OF FORMATION One Gram- molecule Hydrogen Carbon Paraffins CH 4 13.3 213.5 18.5 158-8 C 2 H 12.4 372.3 22-7 156.1 C 3 H 8 12.0 528.4 29.6 HEAT OF COMBUSTION One Gram- One Gram molecule 34-2 69.0 7.83 94.0 Difference 13-3 213-5 158.8 12.4 372.3 156.1 12.0 528.4 158.8 S3 UNSATURATED HYDROCARBONS Paraffins C 4 H 10 HEAT OF COMBUSTION One Gram- One Gram molecule Difference ii. 8 HEAT OF FORMATION One Gram- molecule II. 7 Unsaturated Hydrocarbons C 2 H 4 C 3 H 6 C 4 H 8 C 2 H 2 C 3 H 4 687.2 847.1 341. 1 499-3 650.6 315.7 473-6 33.8 159-9 158.2 157-9 -10.3 1.4 -58.7 -53.6 It will be noticed that while the heat of combustion for the same weight of different hydrocarbons decreases as the molecular weights increase, the figures for the gram-molecular quantities show a fairly constant increase of about 158 calories for each addition of CH 2 . We may, therefore, reckon the gram-molecular heat of combus- tion for any hydrocarbon if we know what it is for one member of an homologous series. For instance, knowing the heat of combus- tion of methane (213.5) we ma y ^ u ^- th at ^ CnH24 as ^ o ^ ows: CnH 2 4 = CH 4 + ioCH 2 ; hence, 213.5 + ( I0 X 158) = 1793-5 which is the gram- molecular heat of combustion of CnH24- As this is the heat from 156.192 grams (gram-molecular weight) of undecane, the heat obtainable from one gram would be 1793.5 + 156.192 = 11.48 cal. To find the heat of formation of a hydrocarbon, the procedure is as follows: Ethane has as its heat of combustion 372.3 cal. The gram-molecule of ethane contains 24 grams of carbon and 3 g-mols. of hydrogen, and the heat which would be developed by burning these amounts of carbon and hydrogen is 7.83 X 24 = 1 88 cal. and 69 X 3 = 207, or in all, 395; the heat of INTRODUCTION TO ORGANIC CHEMISTRY 54 formation of ethane is, therefore, 395 372.3 = 22.7 cal. For acetylene (7.83 X 24) + (69 X i) - 315.7 = - 58.7 cal- ories. (For further discussion of thermochemistry the student is referred to a Physical Chemistry. Halogen Derivatives of Unsaturated Hydrocarbons There are two types of these derivatives which are quite dif- ferent in then* behavior: those in which the halogen is united to an unsaturated carbon atom, one that is linked to another carbon atom by a double or triple bond, as CH 2 :CHBr, or CIiC.CH 3 ; and those where the halogen is joined to a saturated carbon atom, or one linked to another carbon atom by a single bond, as CH 2 :CH.CH 2 Br or CHiC.CH 2 Cl. In compounds of this second type, the halogen is readily re- placed by hydroxyl, cyanogen, and other groups as in the case of the alykl halides; while with halogen derivatives of the first type these reactions do not take place, i. Compounds of the first type where the halogen is united to a carbon atom with a double bond may be made by the action of alcoholic potassium hydroxide on dihalogen derivatives of the saturated hydrocarbons: CH 2 Br.CH 2 Br + KOH = CH 2 :CHBr + KBr + HOH Ethylene bromide Vinyl bromide CH 3 .CH 2 .CHC1 2 + KOH = CH 3 .CH:CHC1 + KC1 + H 2 O Propylidene chloride Chlorpropylene Their formation also takes place by direct addition of the hydro- gen halide to hydrocarbons of the acetylene series: CH : CH+HBr = CH 2 : CHr But with another molecule of the hydrogen halide this gives an alkyl dihalide: CH 2 :CHBr + HBr = CH 3 .CHBr 2 55 UNSATURATED HYDROCARBONS Vinyl chloride, CH 2 : CHC1, is a gas; the bromide, CH 2 : CHBr, is a liquid of ethereal odor, boiling at 16; vinyl iodide, CH 2 : CHI, is also a liquid, which boils at 56. The chloride and bromide change to white solids when exposed to sunlight, being "poly- merized" (several molecules combined to one). Reagents such as potassium hydroxide, sodium ethylate, or sodium acetate do not give substitution products, but cause the compounds to break down into acetylene and the halogen acid. The hydrocarbon radical, CH2:CH , in these compounds is called vinyl and ap- pears in other derivatives. Bromacetylene, CBr-CH, is made from bromethylene by means of alcoholic potash: CHBr: CHBr - HBr = CBr-CH Bromacetylene is a gas which condenses to a liquid in a freez- ing mixture, and polymerizes to a solid in the light. lodoace- tylene. CI i CH, is a crystalline solid, of disagreeable odor, and apparently very poisonous. 2. Compounds of the second type in which the halogen is united to a saturated carbon atom have the characteristics both of unsaturated hydrocarbons and of alkyl halides. The best known halogen compounds of this class are obtained from allyl alcohol, CH 2 :CH.CH 2 OH, and from propargyl alcohol, CHi C.- CH 2 OH (cf. p. 69), by the action of phosphorus halides. Allyl chloride, CH 2 : CH.CH 2 C1, and the corresponding allyl bromide and iodide are liquids boiling at 46, 70, and 103, respectively. They have an odor resembling that of mustard. The propargyl halides are also liquids and give metallic derivatives such as are characteristic of the acetylene grouping. The reactions on page 54 show how various saturated and unsaturated halogen derivatives may be made from each other. The splitting off of halogen and hydrogen by alcoholic alkali, and the addition of halogens or hydrogen halides to the resulting unsaturated compounds give means for making halogen deriva- INTRODUCTION TO ORGANIC CHEMISTRY 56 tives of almost any type. From ethyl bromide, for instance, all possible halogen derivatives of ethane, ethylene, and acetylene, as well as ethylene and acetylene themselves, may be obtained: - HBr + Br 2 - HBr CH 3 .CH 2 Br > CH 2 :CH 2 > CH 2 Br.CH 2 Br- -f Br 2 - HBr + Br 2 CHBr:CH 2 > CHBr 2 .CH 2 Br > CBr 2 :CH 2 > - HBr + Br 2 - HBr CBr 3 .CH 2 Br > CBr 2 :CHBr > CBr 3 .CHBr 2 - > CBr 2 .CBr 2 _^ CBr 3 .CBr 3 . CHAPTER V THE ALCOHOLS HYDROXYL DERIVATIVES OF THE ALIPHATIC HYDROCARBONS Among the many organic compounds which contain hydrogen and oxygen, there are several important groups of substances, the members of each of which show general characteristics, and a similarity in behavior such as marks the different series of hydrocarbons which we have studied; and we shall find here, as in the case of the hydrocarbons, that the members of ea.ch group form an homologous series, with a general formula. One of these groups is that of the alcohols, of which the well- known "wood alcohol" and ordinary alcohol are the most im- portant members. These two alcohols will now be studied as typical of the group. Formula of an Alcohol. Neither of the commercial alcohols is quite pure, or free from water, but the anhydrous pure alcohols can be obtained from them. Pure wood alcohol is a liquid boiling at 66. Its percentage composition is C = 37.46, H = 12.59, O = 49.95, and its vapor density is 1.106 (air = i); hence the molecular formula is CH 4 O. From the corresponding data for ordinary alcohol, its formula is found to be C 2 HO. It is impossible, with tetravalent carbon, to write graphic formulas for these alcohols in which the oxygen is united by both of its valencies with a carbon atom. For CH 4 O, only one graphic H formula can be written, namely, H C O H, in which the H 57 INTRODUCTION TO ORGANIC CHEMISTRY 58 oxygen atom and one hydrogen atom form a hydroxyl group. For C 2 H 6 O there are two arrangements which account for the H H H H II II valencies, H C C O H and H C O C H. The II II H H H H first, containing an hydroxyl group, would seem the more prob- able, because of the similarities in the properties of the two alcohols. The matter can, however, be settled in the following manner: Anhydrous alcohol acts on sodium with the evolution of hydrogen and the formation of a compound whose formula is found to be C 2 H 5 NaO, in which sodium has replaced one atom of hydrogen in the alcohol molecule. As no other compound containing a larger proportion of sodium can in any way be produced from alcohol and sodium, we conclude that one of the six hydrogen atoms in alcohol stands in a different relation from the other five. This can only be accounted for by the first of the two possible formulas, and decides in its favor as the one which represents the constitution of alcohol. This conclusion is confirmed by the result of the reaction which alcohol undergoes with phos- phorus chlorides: C 2 H 6 + PC1 5 = C 2 H 5 C1 + POC1 3 + HC1 3C 2 H 6 O + PC1 3 = 3C 2 H 5 C1 + H 3 P0 3 The formula of the chlorin,e substitution product is determined in the usual way and shows that one atom of chlorine has taken the place of the oxygen and one hydrogen atom; and this clearly indicates that these two atoms were acting as the monovalent group hydroxyl. Wood alcohol gives exactly similar reactions, and therefore we consider these alcohols to be alkyl hydroxides. They can, in fact, be made by a reaction which this view of their character suggests, namely, by the reaction of the alkyU 59 THE ALCOHOLS halides with potassium hydroxide in aqueous solution, or with silver hydroxide (p. 34) : CH 3 I + KOH = CH 3 OH + KI C 2 H 5 Br + KOH = C 2 H 5 OH + KBr (Compare these reactions with those which occur between the alkyl halides and potassium hydroxide in alcoholic solutions (p. 46). Finally, all the facts that we know about these compounds agree with this conclusion that they are hydroxyl derivatives of the hydrocarbons, and all other such compounds are grouped with them as alcohols. The general formula of an alcohol is, there- fore, CnH 2n + iOH. Methyl alcohol, CH 3 OK, commercially known as "wood alcohol," is one of the products of the destructive distillation of wood. The process is carried out in iron retorts, and yields first a watery distillate called "pyroligneous acid," and then gases (methane, ethane, ethylene, carbon dioxide, etc.) and tar, leav- ing a residue of charcoal in the retort. The pyroligneous acid contains methyl alcohol, acetic acid, and acetone in aqueous solution, together with smaller amounts of many other substances. The yield of the various products depends on the kind of wood used, and also on the manner of heating. Quick heating to a high temperature gives the greatest amount of gas, and prolonged heating at lower -temperatures increases the proportion of pyro- ligneous acid and tar. From birch, beech, and oak about 30 per cent, of the weight of the wood is obtained in the watery distillate. Of this about 10 per cent, is acetic acid, i per cent, methyl alcohol, and o.i per cent, acetone. On distilling the pyroligneous acid, the alcohol and acetone, whose boiling points are not very far apart and much lower than that of acetic acid, are separated from the latter, the separation being often made more complete by passing the vapors through milk of lime which fixes the acid as calcium acetate. INTRODUCTION TO ORGANIC CHEMISTRY 60 A second distillation from quicklime gives an alcohol of 99 per cent., which still contains some acetone. This is not ob- jectionable for most of the commercial uses of the alcohol. The alcohol may be obtained in a state of purity as follows. By add- ing anhydrous calcium chloride to the impure alcohol a crystalline compound is formed in which the alcohol plays the part of "water of crystallization." When this is heated to 100, the volatile impurities are driven off, and then, on adding water, the pure alcohol is distilled. Absolutely pure methyl alcohol may be obtained from the methyl ester of oxalic acid (p. 179), by boiling it with water. The disagreeable odor of most commercial wood alcohol is due to impurities; the pure alcohol has only a slight odor resembling that of ethyl alcohol. Ethyl alcohol, CH 3 .CH 2 OH, commercially known as grain alco- hol and ordinarily as "alcohol," is the chief product of the ordin- ary fermentation of certain sugars. This fermentation is brought about in the technical manufacture of alcohol by the addition of yeast, and it occurs naturally in the sweet juices of fruits, such as grapes, apples, etc., and in sugar solutions which are exposed to the air, because of the almost universal presence of yeast spores in the atmosphere. Much alcohol is produced from molasses (p. 213); and much has its source in the starch of various grains such as maize, rye, etc. in the United States, while in Europe the starch of potatoes is used. The starch is first converted into fermentable sugars, and yeast is then added to their solutions. Alcohol has also been made to some extent from saw-dust (cellu- lose) from which a fermentable sugar can also be obtained. The conversion of starch and cellulose into sugars and the fermenta- tion of the latter are discussed in a later chapter. It is sufficient here to note that the fermentation requires a rather dilute solution of the sugars, and that the immediate product contains not more than about 12 per cent, of alcohol in aqueous solution, and in the case of cider, wines and beer, often much less. No alcoholic solution containing more than about 14 per cent, of alcohol can 6 1 THE ALCOHOLS be obtained by fermentation alone, since alcohol of this strength inhibits the fermentation. When the purpose of the fermentation is to produce such beverages as those just named, no distillation is necessary; but for making liquors such as whiskey, brandy, rum, etc., or for the preparation of commercial alcohol, the dilute solu- tion is distilled with the production of stronger alcoholic solutions. The wines, beers, etc., are, therefore, dilute alcoholic solutions which contain various amounts of substances extracted from the materials out of which they are made, and which give them their "body," flavor, and color; while the distilled liquors are, of course, freed from all non-volatile substances, and are solu- tions containing 40-60 per cent, of alcohol, with minute amounts of volatile matters which impart an aroma and taste depending on the original material employed. In some instances, as in gin, a peculiar taste and odor are imparted by the addition of aromatic substances before the distillation. The distillates are all colorless, and the color which many liquors have is given them by standing in casks of charred wood as in the case of some whiskeys, or by addition of caramel, etc. Brandies are made by distilling wine or the fermented juices of various fruits, such as apples, peaches, etc.; whiskey is made from Indian corn or rye; rum, from molasses. For the preparation of commercial alcohol, a more efficient apparatus is employed for the separation of the alcohol and water by distillation than that used in making the distilled liquors, with the result that there is only about 4 per cent, of water in the distillate. The rectification cannot go farther than this, since 96 per cent, of alcohol and 4 per cent, of water form a mix- ture which has a constant boiling point under ordinary pressure. Commercial alcohol is usually from 93-95 per cent. In order to get anhydrous alcohol it is necessary to use some dehydrating agent. By allowing 95 per cent, alcohol to stand in contact with quicklime for some time and then distilling, most of the water is retained by the lime in the form of calcium INTRODUCTION TO ORGANIC CHEMISTRY 62 hydroxide, and the distillate does not contain more than 0.5 per cent. This is often called "absolute alcohol," though the name prop- erly belongs only to a perfectly water-free product. The last amounts of water can be removed by means of anhydrous copper sulphate or by sodium or calcium. It is, however, very difficult to keep alcohol free from water, as it is very hygroscopic and takes up water from ordinary air. Traces of water are detected by the blue color which white anhydrous copper sulphate assumes when shaken with the alcohol, or by the yellow color imparted to the alcohol when barium oxide is added (barium oxide dis- solves only in anhydrous alcohol). Properties. Methyl alcohol boils at 66, ethyl alcohol at 78. Both mix with water in all proportions and the mixing is attended with a rise in temperature and a contraction in volume. Both are solvents of wide application and burn with a hot, almost colorless flame. Both are intoxicating, and are poisonous, at least when pure or but slightly diluted. The poisonous char- acter of methyl alcohol is much more pronounced than that of ethyl alcohol, and prolonged exposure to its vapor is attended with serious consequences, and has been followed by loss of sight. On this account ethyl alcohol is preferable as a solvent and has largely displaced wood alcohol in making shellac varnish since the introduction of the tax-free " denatured alcohol," which is ordinary alcohol rendered unfit for internal use by the addition of wood alcohol, benzene, and various other substances. " Proof spirit" contains 50 per cent, of alcohol by volume. The amount of alcohol in pure aqueous solutions is found by determining the density and using "alcohol tables" that give the percentages of alcohol corresponding to the densities. Reactions. Both alcohols are neutral substances. They undergo the following reactions, i . The hydrogen of the hydroxyl group is replaced by sodium, which acts on the alcohols much more moderately than on water. The alcoholates thus formed are 63 THE ALCOHOLS solid substances which crystallize with "alcohol of crystalliza- tion" (e.g., C2H 5 ONa.2C2H 6 OH), which can be removed by heat- ing. The alcoholates of sodium and potassium are decomposed by water* C 2 H 6 ONa + HOH + C 2 H 5 OH + NaOH The reaction is reversible to some extent, and hence a solution of sodium hydroxide in alcohol, such as is employed in some organic reactions (cf. p. 46), contains some alcoholate. Since the alcohols react only with the most positive metals, and no alcoholates of such metals as zinc or silver can be made, these compounds cannot be regarded as salts in the proper sense of the term, but rather as mixed alkyl and metal oxides, and the names of sodium methoxide and ethoxide are therefore preferable to the salt-suggesting term alcoholate. 2. The alcohols show a certain analogy to the inorganic bases by reacting, as these do, with acids with the production of water and compounds in which the hydroxyl group of the alcohol is replaced by acid radicals: C 2 H 5 OH + HC1 * C 2 H 5 C1 + H 2 O CH 3 OH + H 2 SO 4 ^ CH 3 .H.SO 4 + H 2 O Similar reactions take place between the alcohols and organic acids, and, since they are reversible reactions, are in all cases furthered by an excess of the acid or by the presence of some water-withdrawing substance. The compounds formed with acids, while not well-defined salts, show some marked analogies to salts, and are called "ethereal salts" or esters (cf. p. 119). 3. The characteristic action of the phosphorus halides on alco- hols, resulting in the replacement of the hydroxyl group by the halogen, has been given (p. 32). 4. By means of water-absorbing agents, such as zinc chloride or concentrated sulphuric acid, the elements of water may be withdrawn from alcohols with the production of unsaturated INTRODUCTION TO ORGANIC CHEMISTRY 64 hydrocarbons or of ethers. Methyl alcohol, however, can yield n unsaturated hydrocarbon, though it gives an ether. When sulphuric acid is used, the alkyl sulphuric acid is first formed (e.g., C2H5.HSO 4 ), and then this breaks up at 170 or 180 in the presence of a large excess (5:1) of concentrated acid into sul- phuric acid and the alkene: C 2 H 5 .HSO 4 = C 2 H 4 + H 2 S0 4 Under other conditions (i3o-i4o and a smaller proportion (1.5: i) of acid), ethers or alkyl oxides are formed (cf. p. 70): C 2 H 5 .HSO 4 + C 2 H 5 OH = (C 2 H 5 ) 2 O + H 2 S0 4 similarly: C 2 H 5 I + C 2 H 5 OH = (C 2 H 5 ) 2 + HI 5. Alcohols are not only readily burned to carbon dioxide and water, but are also easily oxidized in dilute solution to inter- mediate compounds. 1 By means of a mixture of dichromate of potassium and dilute sulphuric acid, for instance, ethyl alcohol is oxidized as follows: C 2 H 5 OH + O - C 2 H 4 O (aldehyde) and C 2 H 4 O + O = C 2 H 4 O 2 (acetic acid) The higher homologues of ethyl alcohol give similar reactions, but methyl alcohol is oxidized much more readily than the other alcohols so that the reaction hurries through the aldehyde to the acid and even to the end products, carbon dioxide and water. The vapor of methyl alcohol mixed with air is, however, partially oxidized to the corresponding aldehyde when brought in contact with a heated spiral of platinum wire. These reactions will be discussed in connection with our study of the aldehydes, ketones, and acids. 6. Chlorine acts on alcohols first as an indirect oxidizing agent 1 The oxidizing agents usually employed in organic chemistry are nitric acid, chromic acid (K 2 Cr 2 O7 + H 2 SO4), potassium permanganate, manganese dioxide and sulphuric acid, and, occasionally, chlorine or bromine. 65 THE ALCOHOLS with the production of aldehyde, and then replaces hydrogen (cf. p. 92). Isomeric Alcohols. It is evident from the principles of isom- erism which we have studied, that beginning with propane, different hydroxyl derivatives of the hydrocarbons, or different alcohols, of the same molecular weight, are possible. We find here, as in the other cases, that the facts agree with the theory; there are two propyl alcohols, CH 3 .CH 2 .CH 2 OH and CH 3 .CHOH.CH 3 ; four butyl alcohols, CH 3 .CH 2 .CH 2 .CH 2 OH, (CH 3 ) 2 :CH.CH 2 OH, CH 3 .CH 2 .CHOH.CH 3 , and (CH 3 ) 3 iC.OH; etc. The formulas of these alcohols are, of course, arrived at by the consideration of the reactions of the various alcohols and by the manner in which they can be formed; and it will be noticed that the hydroxyl appears in three different groups : - CH 2 .OH, = CH.OH, and = COH, and that these are all the varieties possible. Ethyl alcohol and all those which on oxidation first yield alde- hydes and then acids containing the same number of carbon atoms as the alcohol, are, in consequence, given formulas with the group CH 2 OH. In ethyl alcohol and its higher homologues, this group is united to an alkyl group; in methyl alcohol we as- sume, by analogy, the presence of the same alcohol group, here united with hydrogen. This difference probably explains the readier oxidation of methyl alcohol. Alcohols which give ketones as the first oxidation product, and then, on further oxidation break down into acids with a smaller number of carbon atoms, are characterized by the group = CH.OH; and, finally, those which are converted at once into ketones or acids of a less number of carbon atoms have = C OH as their characteristic group. The first variety of alcohols, containing CH 2 .OH, are called primary INTRODUCTION TO ORGANIC CHEMISTRY 66 alcohols; those with = CH.OH, united with two alkyl groups, secondary; and those with = C OH, with three alkyl groups, tertiary alcohols. Some of the experimental evidence for the assignment of these groups will be given in Chapter VIII. Here we will only state that the primary and secondary alcohols can be formed by reduction (nascent hydrogen) of aldehydes and ketones, respectively. Methods of Formation. The principal laboratory methods for forming primary alcohols are: 1. Substitution of hydroxyl for a halogen atom or other acid radical in alkyl halides or other esters by the action of hydroxides of the metals or water (for the halides, moist silver oxide, which acts as silver hydroxide, is especially good; cf. p. 34). 2. From alkyl amine nitrites (cf. p. 131) on heating their aqueous solutions: CH 3 (NH 2 ).HNO 2 = CH 3 OH + N 2 + H 2 This reaction is analogous to that of ammonium nitrite when heated. 3. By reduction (with sodium amalgam) of aldehydes and ketones: CH 3 .CHO + 2H = CH 3 .CH 2 OH Aldehyde Ethyl alcohol CH 3 .CO.CH 3 + 2H = CH 3 .CHOH.CH 3 Acetone Sec. propyl alcohol 4. The Grignard reactions for secondary and tertiary alcohol. It is not necessary to give here other special reactions for the formations of the three classes of alcohols. Although the alcohols are often spoken of as derivatives of the hydrocarbons, it must not be forgotten that the direct substitution of OH for H in a hydrocarbon is always impossible. In some discussions, methyl alcohol is called "carbinol" and the other primary alcohols are considered as derivatives of it by the replacement of hydrogen by alkyl groups: thus ethyl alcohol is methyl carbinol; secondary butyl alcohol, CH 3 .CH 2 .- CHOH.CH 3 , is methyl-ethyl-carbinol, etc. Fusel oil, which is formed in small amounts in the fermenta- 6 7 THE ALCOHOLS tion which produces ethyl alcohol, is composed chiefly of two of the eight possible amyl alcohols: CH 3 v (CH 3 ) 2 : CH.CH 2 .CH 2 OH, isoamyl alcohol, and >CH.CH 2 OH, active amyl alcohol. The former comprises 70-80 per cent, of the fusel oil. The latter has the property of "optical activity" or power of rotating the plane of polarized light (cf. p. 1 69) . Normal propyl alcohol and isobutyl alcohol isopropylcarbinol are also found in fusel oil. Fusel oil has a characteristic odor, and is poi- sonous. It distils with the ethyl alcohol, though having a much higher boiling point, and is, therefore, found in crude spirituous liquors, and is responsible in part for their specially disagreeable effects. It is destroyed more or less completely by the "aging" of the liquor. Fusel oil is used as the source of iso-amyl alcohol and various esters derived from it, such as the acetate ("pear oil"), the iso- valerate ("apple oil"), and the nitrite, which find a number of uses Amyl alcohol itself is employed occasionally as a solvent for alkaloids, etc. None of the other alcohols, except methyl and ethyl alcohols, are of any especial practical importance. NORMAL PRIMARY ALCOHOLS Name Formula Melting Point Boiling Point Specific Gravity Methyl CH 3 OH 97.8 66.7 0.812 Ethyl C 2 H 6 OH 117.6 78.4 0.806 Propyl C 3 H 7 OH 97 0.817 > Butyl C 4 H 9 OH 117 0.823 rt- Pentyl (Amyl) C 6 HnOH 138 0.829^ Rg" Hexyl CeHiaOH I 57 0-833 0* Heptyl C 7 H 16 OH 176 0.836 1 Octyl C 8 H 17 OH 195 0.839 Nonyl C 9 H 19 OH -5 213 o.8 42 J ^ Decyl C 10 H 21 OH + 7 231 0.839 IB Dodecyl C 12 H 25 OH 24 143 ^ > 0-831 II Tetradecyl C 14 H 29 OH 38 167 fl>M 0.824 Cetyl C 18 H 33 OH 50 190 S3 0.818 si Octadecyl C t8 H 37 OH 59 211 P - 3 0.813 J l Myricyl CsoHdOH 86 0.808 INTRODUCTION TO ORGANIC CHEMISTRY 68 It will be noticed that the boiling points of these alcohols from ethyl alcohol to decyl alcohol increase with approximate regu- larity, the average increment being 19. The boiling points of the last four are not comparable with those of the first ten since they are determined under reduced pressure, but when compared with each other it is seen that the differences are less. A similar decrease in boiling-point differences is observed in the normal paraffins (cf. table on page 17) and in other homologous series; and in general, in the higher members of a series, the uniform increase of molecular weight by the addition of CH 2 has less and less effect on the physical properties of the members. The dif- ference between the boiling points of methyl and ethyl alcohols is 12 instead of 19, and the specific gravity of methyl alcohol is greater than that of ethyl alcohol instead of less as it should be to conform with the general changes in specific gravity of the other members. Such irregularities are found in other series, and correspond to the somewhat different chemical behavior often observed in the derivatives of methane as compared with their homologous compounds. The effect of structure on the boiling point is shown in the following table of the amyl alcohols. ISOMERIC AMYL ALCOHOLS Formula Boiling Point i.CH 2 .CH 2 .CH 2 OH 138' Primary (CH 3 ) 2 CH.CH 2 .CH 2 OH _i 131 Secondary f CH 3 .CH 2 .CH 2 .CH 2 .CH 2 OH 138 CH 3 .CH(C 2 H 5 ).CH 2 OH 128 CH 3 .CH 2 .CH 2 .CHOH.CH 3 up (CH 3 ) 2 CH.CHOH.CH 8 112.5 CH 3 .CH 2 .CHOH.CH 2 .CH 3 117 Tertiary (CH 3 ) 2 COH.CH 2 .CH 3 102 Unsaturated Alcohols These are hydroxyl compounds in which a double or triple bond between two carbon atoms occurs. A number of alcohols 69 THE ALCOHOLS of the general formula CnHan^OH are known, but the first member of the series, Vinyl alcohol, CH 2 :CHOH, has not been isolated the reactions which should produce it resulting in the formation of acetaldyde, CH 3 .CHO, which is isomeric with it. No simple alcohol, in fact, has a stable existence in which the carbon atom carrying the hydroxyl group is combined with another carbon atom by a double or triple bond. The first and best known of the unsaturated alcohols is allyl alcohol, CH 2 : CH.CH 2 - OH. It occurs in small amounts in crude wood alcohol, and can be made, mixed with other products, from glycerol and oxalic acid. The reaction, which is a somewhat complicated one, will be discussed under formic acid (p. 105). Allyl alcohol is a colorless liquid of very sharp odor, which boils at 96.6, and mixes with water in all proportions. It gives reactions which are characteristic of a primary alcohol, and also such as belong to an unsaturated hydrocarbon. Propargyl alcohol, CH = C.CH 2 OH, is the chief representa- tion of alcohols with a triple bond, and which have the general formula, C n H 2n _ 3 OH. It is made by reactions of the kind which have been given for the production of members of the acetylene series and for the introduction of the hydroxyl group. It is a liquid boiling at 1 15 and gives reactions in accord- ance to the structure which is attributed to it. Quite a number of alcohols with two double bonds have' beer made in the laboratory and some representations of this grouf have been found in nature. The general formula of these alco hols is the same as that for the alcohols with a triple bond. CHAPTER VI THE ETHERS Ethyl Ether. Ordinary ether is obtained by the action of sul- phuric acid on alcohol, and is often called "sulphuric ether" for that reason, though it contains no sulphur or sulphur-oxygen group. Alcohol and concentrated sulphuric acid are mixed in the proportion of about one to two, so that distillation begins at about 140, and then alcohol is gradually added so that the boiling point is kept nearly constant. Some sulphur dioxide from the reduction of sulphuric acid, and other products from alcohol besides ether are formed at the same time. The ether formation, which, theoretically, should continue indefinitely, comes to an end when alcohol to the amount of about four times the weight of the sulphuric acid has been used. It will be recalled that a mixture of concentrated sulphuric acid and alcohol is used for the preparation of ethylene (p. 46). The chief product is seen to depend on the proportions of acid and alcohol and the tempera- ture at which the reaction is carried on. This is an illustration of the greater flexibility of organic reactions as compared with the usual inorganic reactions. The distillate contains water, alcohol, and some sulphur dioxide, mixed with the ether. The addition of sodium carbonate neu- tralizes and fixes the sulphurous acid, and renders the ether less soluble. The ether forms a layer on top of the solution, and, after separation from the aqueous solution, most of the water and some of the alcohol which is still mixed with it is absorbed by calcium chloride or quicklime, and the ether is distilled. It still contains small amounts of water and alcohol which may be removed by shaking it with shavings of bright sodium, and again distilling. 70 71 THE ETHERS Properties. Ether is a colorless, very thin liquid of the well- known characteristic odor. It is very volatile, giving a vapor which is two and a half times heavier than air; boils at 34.6 and has a specific gravity of 0.718 at 15.6. It dissolves in about eleven times its volume of water at 25, and in turn dissolves about 2 per cent, of its volume of water. It and its vapor are very easily inflammable and all operations with it must be con- ducted with great care to avoid its ignition. Chemically, it is a neutral substance and rather inert. Unlike alcohol, it is not acted on by sodium or potassium, nor by phosphorus chlorides in the cold. When heated with phosphorus pentachloride, ethyl chloride is formed. Formula. The molecular formula of ether derived from its analysis and vapor density is C4HioO. The formation of ethyl- ene from alcohol was explained by the abstraction of the ele- ments of one molecule of water from one molecule of alcohol. The ether reaction goes on at a lower temperature, and is hence presumably less drastic. The withdrawal of a molecule of water would presumably take place more readily from two molecules of alcohol than from one, and this would give us the formula of ether: 2 C 2 H 5 OH - H 2 O = C4H 10 O Knowing that alcohol is the hydroxide of ethyl, the probable structure of ether is, therefore, (2115)20, or ethyl oxide. That it does not contain a hydroxyl group is shown by the failure of sodium to act on it. The reaction is not, however, quite as simple as indicated by the above equation. Ethyl sulphuric acid is first formed and then reacts with a second molecule of alcohol: C 2 H 5 OH + H 2 SO 4 = C 2 H 5 .HSO 4 + H 2 O C 2 H 5 .HSO 4 + C 2 H 5 OH = (C 2 H 6 ) 2 + H 2 SO 4 The constitution given to the ether molecule is confirmed by the other methods of its formation and by all of its chemical INTRODUCTION TO ORGANIC CHEMISTRY 72 behavior. Thus, ether is formed when ethyl bromide or iodide reacts with certain oxides. The iodide and dry silver oxide react at once with evolution of heat: 2 C 2 H 5 I + Ag 2 = (C 2 H 5 ) 2 + 2AgI A similar reaction with sodium oxide takes place at 180, and ether is formed even when the iodide is sufficiently heated with a small amount of water. The temperature required for these last two reactions makes it necessary to carry them out in sealed tubes. Attention has been called to the fact that the reaction between alcohols and acids with the formation of esters and water is a reversible reaction. Now, when ethyl iodide (an ester) and water react, the first products are alcohol and hydrogen iodide: C 2 H 5 I + H 2 O * C 2 H 5 OH + HI and under proper conditions the alcohol and the still unchanged ethyl iodide form ether and hydrogen iodide: C 2 H 5 OH + C 2 H 5 I ? (C 2 H 5 ) 2 + HI An excess of water would transform almost all of the iodide into alcohol, so only a small amount must be used if ether is to be produced. Ether is also formed when sodium ethoxide and ethyl iodide are brought together in alcoholic solution: C 2 H 5 ONa + C 2 H 5 I = (C 2 H 5 ) 2 + Nal This synthesis of ether is of great historical importance, as it not only served to establish the structure of ether, but also had a far-reaching effect in clearing up the structural formulas of many other compounds. It was made by Williamson in 1850. The student should read his papers on etherification in the Alembic Club Reports, No. 16. Reactions. All the reactions of ether are in accordance with this view of its molecular structure. The production of ethyl 73 THE ETHERS chloride when ether is heated with phosphorus pentachloride shows that two chlorine atoms have replaced the one oxygen atom which unites two ethyl groups: C 2 H 6 C1 2. Ethyl halides are formed when the halogen acids react with ether, hydrogen iodide acting more readily than the others. At o hydrogen iodide produces ethyl iodide and ethyl alcohol: (C 2 H 5 ) 2 + HI = C 2 H 6 I + C 2 H 6 OH but when heated with the strong acid the products are ethyl iodide and water: (C 2 H 5 ) 2 O + 2HI = 2C 2 H 5 I + H 2 O 3. Ether dissolves in cold concentrated sulphuric acid and can be separated unchanged from the solution by pouring the acid solution into water. When the solution of ether in the acid is warmed, however, ethyl sulphuric acid is formed: (C 2 H 5 ) 2 O + 2 H 2 SO 4 = 2(C 2 H 5 )HSO 4 + H 2 O 4. When heated with water containing a little sulphuric acid to 150-180 ether is hydrolyzed into alcohol: (C 2 H 5 ) 2 O + H 2 O = 2 C 2 H 5 OH 5. Oxidation by means of nitric or chromic acid produces the same products as those obtained by the oxidation of alcohol aldehyde and acetic acid: (C 2 H 5 ) 2 O + 20 = 2 CH 3 .CHO + H 2 O (C 2 H 6 ) 2 O -f 40 = 2CH 3 .CO.OH + H 2 O 6. Chlorine replaces the hydrogen step by step, with the final formation of (C 2 C1 5 ) 2 O, a solid compound melting at 69 and having a penetrating camphor-like odor. Uses. Besides its use as a valuable anaesthetic, ether is much INTRODUCTION TO ORGANIC CHEMISTRY 74 employed in the laboratory and in the arts and manufactures as an excellent solvent for many substances. These are readily recovered from their solutions in it, on account of its great vola- tility and low boiling point. Thus it is used for the extraction of fats, oils, etc., from mixtures. It not only dissolves many organic compounds, but also a number of inorganic substances, such as iodine, chromic acid, and chlorides of iron, mercury, and tin. In its rapid change into vapor, ether produces such a lowering of temperature that it has been used to manufacture ice; and in the form of a fine spray on the skin to produce local anaesthesia. Other Ethers. By methods similar to those which produce ethyl ether, many other ethers can be made whose reactions are like those of this ether and whose properties have the relation- ship and show the gradation which are familiar to us in com- pounds forming a homologous series. The general formula of an ether is C n H 2n+2 O, in which, however, n cannot be less than two. For if n = o, we have H 2 O, and if n = i, CH 4 O or methyl alcohol. Both of these substances may be considered of the ether type, since ether, water, and methyl alcohol are all oxides. But an ether is an alkyl oxide, while water is hydrogen oxide, and methyl alcohol, methyl-hydrogen oxide. The first ether, then, is methyl ether (CH 3 ) 2 O. Methyl and ethyl ether each contain two like alkyl groups. But from the methods of ether formation we should expect it possible to make ethers containing two dissimilar groups, and this can, in fact, be readily done. When a mixture of two alcohols is treated with sulphuric* acid, as in the preparation of ethyl ether, a mixture of ethers results: from methyl and ethyl alcohols there is formed methyl ether, (CH 3 ) 2 0; ethyl ether, (C 2 H 5 ) 2 O; and methyl-ethyl ether, CH 3 .O.C 2 H 5 . A definite single mixed ether is obtained by the reaction of a sodium alkoxide and an alkyl iodide: CH 3 ONa + C 2 H 5 I = CH 3 .O.C 2 H 5 +NaI 75 THE ETHERS This formation of a mixture of ethers and of single mixed ethers was used by Williamson to confirm his theory of the structure of ether and alcohol. The ethers with two like alkyl groups are called simple ethers, the others mixed ethers. The first two ethers which correspond to the general formula, namely, (CHa^O and CH 3 .O.C2H 5 , are gases at ordinary temperature. All the other ethers, except those of high molecular weights, are liquids, lighter than water. A few unsaturated ethers are known, e.g., divinyl ether (CHa : CH) 2 O, and ethyl-propargyl ether, CH : .C.CH 2 .O.C 2 H5. ETHERS Boiling Specific Names Formulas Points Gravity Dimethyl Ether (CH 3 ) 2 O -23.6 Diethyl (C 2 H 6 ) 2 O 34-6 0.731 (4) Dipropyl (C 3 H 7 ) 2 O 90.7 0.763 (o) Dibutyl (normal) (C 4 H 9 ) 2 O 141 0.784 (o) Dioctyi (normal) (C 8 Hi 7 ) 2 O 280-282 0.805 (17) Methyl-ethyl CH 3 OC 2 H 6 n Ethyl-propyl C 2 H 6 OC 3 H7 63-64 0.739(20) Ethyl-butyl (norm.) C 2 H 5 OC 4 H9 92 0.769 (o) Ethyl-octyl (norm.) CsHsOCgHn 182-184 0.794(17) CHAPTER VII OXIDATION PRODUCTS OF ALCOHOLS ALDEHYDES AND KETONES Aldehydes Ethyl alcohol reacts readily with a dilute solution of chromic acid (potassium dichromate and sulphuric acid). Heat is devel- oped and the first portions of the distillate contain a substance called aldehyde, which has a peculiar and suffocating odor. When separated from the water, alcohol, and small amounts of other substances with which it is mixed, the pure aldehyde is obtained as a liquid which boils at 21. Its analysis and vapor density lead to the molecular formula, C 2 H 4 O. The oxidation of alcohol to aldehyde consists, therefore, in the removal of two hydrogen atoms from the alcohol molecule C2H 6 O, and it is from this fact that the name aldehyde alcohol dehydrogena.tus was given it: CH 3 .CH 2 .OH + O = C 2 H 4 + H 2 O There are three possible arrangements of the atoms in this formula: CH 3 CH 2 2 , =O C O H and >O I I CH/ H H Two reactions will help us to decide which of these arrange- ments properly represents the structure of the alehyde molecule, i. Phosphorus pentachloride acts on aldehyde with the pro- 77 ALDEHYDES AND KETONES duction of a compound whose formula is C2H 4 Cl2, and whose structure must be CH 2 C1.CH 2 C1 or CH 3 CHC1 2 . This cuts out the second of the possible aldehyde formulas, which contains a hydroxyl group, and from which we should consequently expect phosphorus pentachloride to produce CH 2 : CHC1. 2. Aldehyde is readily oxidized to a monobasic acid, C 2 H 4 O 2 , three of whose hydrogen atoms only can be replaced by chlorine by the direct action of this halogen, giving C 2 ClsHO 2 , which is still a monobasic acid. We may conclude, therefore, that in the acid, and in the aldehyde from which it is made, there is a CH 3 group. The structural formula of the aldehyde ap- pears, therefore, to be the first one of the three, All the reactions by which aldehyde is formed, and all of the reactions it gives, afe in accord with this view of its structure. Acetaldehyde, CH 3 .CHO, is usually prepared by oxidizing alcohol in the way stated above. It is also produced when a mixture of calcium acetate and calcium formate is heated: CH 3 = | + CaCO 3 HCOaca 1 CHO Acetaldehyde can also be formed from ethylidene chloride or bromide (p. 40) by heating with water in sealed tubes, or by boil- ing with alkalies: CH 3 CHBr 2 + H 2 O = CH 3 CHO + 2 HBr This reaction is of interest, but of no practical importance as a method of preparation, since these halides themselves are usually made from aldehyde by phosphorus halides. Another method of formation of theoretical interest is from unsaturated hydrocarbons of the acetylene series, by the addition of the elements of water. This occurs when the hydrocarbon is 1 For the sake of greater simplicity in the equation, ca = \ Ca. INTRODUCTION TO ORGANIC CHEMISTRY 78 dissolved in strong sulphuric acid which is then largely diluted and distilled: CH : CH + H 2 O = CH 3 CHO Properties and Reactions. Acetaldehyde is a very volatile liquid which boils at 21, and mixes with water in all proportions. It dissolves sulphur, phosphorus and iodine. It is easily inflam- mable and burns with a bright flame. 1. It is very readily oxidized to acetic acid, even in dilute solutions, and this change goes on slowly when it is in contact with air. Hence it is a powerful reducing agent. When warmed with an alkaline solution of copper sulphate (Fehling's Solution) it precipitates red cuprous oxide. Even very dilute solutions (1:4000) reduce ammoniacal solutions of silver nitrate, sepa- rating the silver in a finely divided state and giving to the solu- tion a violet color. Stronger solutions precipitate most or all of the silver as a mirror on the walls of the vessel. 2. When sodium amalgam is put into its aqueous solution, aldehyde is "reduced" to alcohol by the direct addition of hydrogen: CH 3 .CHO + 2 H = CH 3 .CH 2 .OH 3. A number of other addition products are formed with various substances, in which, as in this instance, the double bond which unites oxygen to carbon in the CHO group is changed to a single bond so that the oxygen becomes a linking atom. Such reac- tions occur with ammonia, acid sodium sulphite, and hydrocyanic acid: /OH CH 3 .CHO + NH 3 = CH 3 .CH< X NH 2 /OH CH 3 .CHO + NaHSO 3 = CH 3 .CH< X S0 3 Na /OH CH 3 .CHO + HCN = CH 3 CH< X 79 ALDEHYDES AND KETONES The ammonia addition product is precipitated in crystals when dry ammonia gas is led into a cold solution of aldehyde in anhydrous ether. It is very soluble in water. In air it slowly decomposes into resinous substances. The sodium sulphite compound is also a solid crystalline sub- stance which is obtained by shaking aldehyde with a saturated solution of the sulphite. Aldehyde is recovered from both of these compounds when they are heated with dilute acids, and on this account they are some- times made as a means of isolating and purifying aldehyde. The hydrocyanic compound is the nitrile of lactic acid (p. 165), into which it is converted by hydrolysis. 4. With anhydrides of organic acids (cf. p. 117) addition prod- ucts are also formed: CH 3 .CHO + (CH 3 .CO) 2 = CH 3 .CH(CH 3 .CO.O) 2 These compounds are decomposed by water into aldehyde and .acid, or more readily by an alkali into aldehyde and a salt of the acid. 5. Another reaction which is common to the aldehydes is one in which they react with hydroxyl compounds with elimination of water. Thus, with alcohol, an acetal is formed: CH 3 .CHO + 2C 2 H 5 OH * CH 3 .CH(OC 2 H 5 ) 2 + H 2 O Diethylacetal The reaction is aided by the presence of a little acetic acid as a catalyser. It is reversed when the acetals are boiled with acids and water. 6. With hydroxylamine (p. 122) aldehydes react to form ald- oximes: /H CH 3 .CHO + NH 2 OH = CHa.C^ + H 2 O Acetoxime INTRODUCTION TO ORGANIC CHEMISTRY 80 Similar products from ketones are called ketoximes. Oximes from the lower members of the aldehyde and ketone series are liquids that can be distilled without decomposition. The hydrogen of their hydroxyl groups can be replaced by alkali metals, and with acids they form addition compounds such as, CH 3 .CH:N(OH)HC1. On heating with acids they are hydro- lyzed into hydroxylamine and the corresponding aldehyde or ketone. Energetic reduction (sodium amalgam in weak acid solution) converts them into primary amines. 7. A somewhat similar reaction occurs with hydrazine and hydrazine derivatives, with the formation of hydrazones: CH 3 .CHO + H 2 N - NH 2 = CH 3 . CH.CHO 63 0.794(20) / Valeric CH 3 .CH 2 .CH 2 .CH 2 .CHO 103 0.818(11.2) CH 3V Isovaleric > CH.CH 2 .CHO 92 0.798(20) CH 3 7 Caproic CH 3 (CH 2 ) 4 .CHO 128 0.834 (20) Acroleln CH 2 :CH.CHO 54.2 ........ Crotonic CH 3 .CH:CH.CHO 103 0.856 (17) Geranial (citral) C 9 Hi 6 .CHO 224-228 ........ Chloral CCl^.CHO 97 1.512(20) INTRODUCTION TO ORGANIC CHEMISTRY 3 KETONES Formula Acetone CH 3 .CO.CH 3 56. 0.812 (o) Methyl-ethyl Ketone CH 3 .CO.C 2 H 6 79.6 0.825(0) Diethyl Ketone C 2 H 6 .CO.C 2 H6 102.7 0.833(0) Methyl-propyl (n) Ketone CH 3 .CO.C 3 H 7 102 0.808(20) Methyl-isopropyl Ketone CH 3 .CO.CH(CH 3 ) 2 94-96 0.815(15) Methyl-butyl (n) Ketone CH 3 .CO.C 4 H 9 127-128 0.830(0) Methyl-butyl (iso) Ketone CH 3 .CO.CH 2 .CH(CH 3 ) 2 116 0.819 (o) Methyl-butyl(ter.) Ketone CH 3 .CO.C(CH 3 ) 3 106 0.826(0) Ethyl-propyl (n) Ketone C 2 H 5 .CO.C 3 H 7 122-124 0.833(0) Ethyl-propyl (iso) Ketone C 2 H 6 .CO.CH(CH 3 ) 2 117-119 0.830(0) Dipropyl (n) Ketone C 3 H 7 .CO.C 3 H 7 144 0.820(20) Methyl-amyl (n) Ketone CH 3 .CO.C 6 Hu 155-156 0.813 (o) Ethyl-butyl (iso) Ketone C 2 H 5 .CO.C 4 H 9 135 0.829(0) Ketones Ketones are the first oxidation products of secondary alcohols. The simplest ketone possible, therefore, is that derived from isopropyl alcohol, CHs.CH.OH.CHa and has the molecular for- m.ula, CsHeO. From our knowledge of the structure of secondary alcohols and the discussion of the structural formula of aldehyde, we should naturally give this ketone the formula, CH 3 .CO.CH 3 . This is determined to be the correct formula by its reactions, especially that with phosphorus pentachloride which substitutes two atoms of chlorine for one of oxygen. Other ketones give similar reactions; hence the characteristic group of a ketone is the divalent group = C = O uniting two alkyls, and the general formula for simple ketones of this series is C n H2 n +2CO, in which n is not less than two. The group = CO is called carbonyl. It should be noticed that the carbonyl group is common to both ketones and aldehydes, the only difference in their formulas being that in the ketones carbonyl unites two alkyls, and in the alde- hydes, an alkyl and a hydrogen atom. 89 ALDEHYDES AND KETONES Acetone, CH 3 .CO.CH 3 , is the first member of the series of saturated ketones and is typical of all the others. It is ob- tained commercially from the products resulting from the dis- tillation of wood (p. 59), and also from calcium or barium acetate. Pure acetone is made by distilling the crystalline addition product it forms with sodium sulphite with a solution of sodium carbonate. It is a colorless liquid of a characteristic and not unpleasant odor. It mixes in every proportion with water and can be separated from water by fractional distillation. It boils at 56.5. Acetone is a good solvent for many organic compounds, and for gums, resins, etc. It is used as a solvent, and also in the preparation of chloroform, iodoform, sulphonal (p. 240), and other compounds used in medicine. Acetone occurs in normal urine in small amounts, and is present in larger quantities in certain diseases, especially in diabetes. Acetone and other ketones can be formed: i. From the corresponding alkyl dihalides, as the aldehydes are: CH 3 .CC1 2 .CH 3 + H 2 O = CH 3 .CO.CH 3 +' 2 HC1 2. From acid chlorides (p. 114) by zinc alky Is or magnesium alkyl halides: 2 CH 3 .CO.C1 + 2C 2 H 5 MgI = 2 CH 3 .CO.C 2 H 5 + MgCl 2 -f MgI 2 Acetyl chloride Methyl-ethyl ketone This reaction gives a method by which mixed ketones, contain- ing two different alkyl groups can be made. 3. By oxidation of secondary alcohols (p. 66): CH 3 .CHOH.CH 3 + O -> CH 3 .CO.CH 3 + H 2 O 4. From calcium salts of organic acids by distillation: CH*COxS " CHa.CO.CH, + CaCO, " CH,CO.C 2 H 6 + CaCO, But in the second reaction the two simple ketones, acetone CH 3 .CO.CH 3 , and diethylketone C 2 H 5 .CO.C 2 H 5 , are also formed. We have seen that when calcium formate is heated with the INTRODUCTION TO ORGANIC CHEMISTRY 90 salt of a higher acid, the chief product is an aldehyde (p. 77). Aldehydes may, indeed, be viewed as mixed ketones in which hydrogen replaces one of the alkyl groups. In fact, the first substance corresponding to the general formula C n H 2n +2CO is CH 4 CO = CH 3 .CHO or acetaldehyde. The general formulas for ketones and for aldehydes show that these compounds, when the number of carbon atoms is the same, are isomeric, both being C n H 2n +2CO, and are only distinguished by formulas containing the groups characteristic of each. Nomenclature. Acetone was the first ketone known and its name indicated its relation to the acetates. The individual ketones are named descriptively from the alkyl groups they con- tain thus acetone is dimethyl ketone; CH 3 .CO.C2H 5 , methyl- ethyl ketone, etc. Ketones are also systematically named by adding on to the name of the hydrocarbons from which they are theoretically derived: thus CH 3 .CO.CH 3 is propanon, CH 3 CO.C 2 H 5 , butanon, etc. The reactions of acetone and the other ketones are not as varied as those of the aldehydes. Like the aldehydes, their oxygen atom is replaced by two atoms of chlorine or bromine through the action of phosphorus pentahalides; they form addition products with hydrocyanic acid and acid sodium sulphite (but only when they contain the group CH 3 .CO), and with nascent hydrogen (giv- ing secondary alcohols); with Grignard's reagent they yield tertiary alcohols (p. 37); and they react with hydroxyiamine and hydrazines, forming ketoximes and hydrazones. But unlike the aldehydes, the ketones are not easily oxidized, and hence are not reducing agents. When oxidation occurs, acids of a less number of carbon atoms are formed, the chain of carbon atoms breaking at the carbonyl group. When reduced by sodium amalgam, together with the secondary alcohol appreciable amounts of dihydroxyl tertiary alcohols are formed, called pinacones: 2CH 3 .CO.CH 3 + HH = (CH 3 ) 2 C.C(CH 3 ) 2 I I HO OH 91 ALDEHYDES AND KETONES Ketones give no addition product with ammonia, but form a number of complex condensation products from reaction between two or more molecules and ammonia, e.g. : /CH 3 2 CH 3 .CO.CH 3 + NH 3 = CH 3 .CO.CH 2 .C(-CH 3 -f H 2 O \NH 2 Diacetonamine Ketones do not react with alcohols and acid anhydrides as aldehydes do, they do not polymerize, nor do they give resins with alkalies. The agreements in the reactions of ketones and aldehydes are conditioned by the presence of the carbonyl group, =C = O, which is common to both classes of compounds; the differences are due to the fact that in ketones both valencies of this group are united to alkyl groups, while in aldehydes (except formaldehyde which shows individual peculiarities), one valence is satisfied with hydrogen and the other with an alkyl group. Identification. Ketones are identified by the formation of an oxime (ketoxime) or phenylhydrazone, or a crystalline additive product with acid sodium sulphite (if they contain the CH 3 .CO group), while they do not reduce Fehling's solution, or silver nitrate, or produce an immediate color with S drift's reagent. Halogen Derivatives of Aldehydes and Ketones Chloral, CC1 3 .CHO (trichloraldehyde), and chloral hydrate, CC1 3 .CHO.H2O, are the most important of the halogen deriva- tives of the aldehydes. Chloral can be made by the direct action of chlorine on aldehyde in dilute solution; but the best method for its preparation is by leading chlorine into alcohol. The alcohol is at first kept cool and afterward warmed to about 60, and the current of chlorine is continued until it is no longer absorbed, the operation lasting several days. The product, when cool, forms a crystalline mass from which, on treatment with concentrated INTRODUCTION TO ORGANIC CHEMISTRY 9 2 sulphuric acid, the chloral separates as an oil, and is purified by distillation from calcium carbonate. The action of the chlorine on alcohol is first that of an oxidizing agent, producing aldehyde: CH 3 .CH 2 OH + C1 2 = CH 3 .CHO + 2HC1 Then the chlorine replaces hydrogen in the methyl group: CH 3 .CHO + 3 C1 2 = CCla.CHO + 3HC1 Secondary reactions, however, occur, so that the product contains trichloracetalj CCl3.CH(OC 2 H 5 )2, from reactions of aldehyde and chlorine with unchanged alcohol; ethyl chloride, C 2 H 5 C1, and /OH chloral alcoholate, CC1 3 .CH , from decomposition of tri- \OC 2 H 5 chloracetal by the hydrochloric acid which is formed; and chloral hydrate by union of chloral with the water present. The sul- phuric acid which is added sets chloral free from its compounds. Properties and Reactions. Chloral is an oily liquid of penetrat- ing odor; it boils at 97.7 and its specific gravity is 1.513 (20). It does not dissolve in water, but reacts with it with the develop- ment of much heat and the formation of the hydrate. Chloral hydrate, which is the form in which chloral is usually employed, is given the formula, CC1 3 .CH(OH) 2 , indicating that it is not prop- erly a hydrate, or compound with water of crystallization, but a definite compound with two hydroxyl groups. In support of this view are the facts of the heat produced in its formation, and that it does not give the aldehyde reaction with Scruff's reagent (p. 86). Chloral hydrate forms large crystals, which melt at 57. At 96-98 it boils with decomposition into chloral and water. It is well known as a soporific. Chloral and chloral hydrate are oxidized by nitric acid to tri- chloracetic acid, CC1 3 .CO.OH; and when treated with alkalies give chloroform and a formate: CC1 3 .CHO + KOH = CHC1 3 + HCO.OK 93 ALDEHYDES AND KETONES Chloral is probably formed as an intermediate step in the manu- facture of chloroform from alcohol by means of bleaching powder. The course of this reaction is commonly represented as follows: (i) Oxidation of alcohol to aldehyde, (2) chlorination of aldehyde to chloral, and (3) reaction of the chloral with the calcium hydrox- ide present in bleaching powder with the formation of chloroform and calcium formate: 1. 2CH 3 .CH 2 OH + Ca(OCl) 2 =2CH 3 .CHO +CaCl 2 + 2H 2 O 2. 2 CH 3 .CHO + 3Ca(OCl) 2 = 2 CCl 3 .CHO+3Ca(OH) 2 3. 2 CC1 3 .CHO +Ca(OH) 2 = 2 CHC1 3 +(HCO.O) 2 Ca Halogen derivatives of ketones are readily made by direct sub- stitution; but here, as generally in direct replacements of hydrogen in compounds containing two or more carbon-hydrogen groups, it is impossible to obtain all of the possible chlorine or bromine deriva- tives by the action of these elements on the ketone. Sym- metrical dichloracetone, CH 2 C1.CO.CH 2 C1, is not formed in this way, though the isomeric compound, CH 3 .CO.CHC1 2 , is readily made. Trichloracetone is decomposed by alkalies into chloroform and an acetate, and this reaction is probably the last step in the preparation of chloroform from acetone by the action of bleaching powder: 2 CH 3 .CO.CH 3 + 3Ca(OCl) 2 = 2CC1 3 .CO.CH 3 + 3Ca(OH) 2 2CC1 3 .CO.CH 3 + Ca(OH) 2 = 2 CHC1 3 + (CH 3 .CO.O) 2 Ca CHAPTER VIII SIMPLE MONOBASIC ACIDS Acetic acid is one of the best-known organic acids, and since it is one of the simplest in composition and structure we will begin our discussion of the organic acids by considering its prop- erties and reactions. Both the acid and its salts occur in small amounts in certain plants. Vinegar, of which acetic acid is the chief acid constituent, has been known from the earliest times. The two chief sources of acetic acid are alcohol and wood. The acid is obtained in many instances from ethyl alcohol as the result of an oxidation effected by means of a bacterial ferment (Bacterium aceti). These bacteria are usually present in the air, and, consequently, dilute solutions of alcohol such as cider, wines, etc., produced by the alcoholic fermentation of fruit juices, usu- ally become sour after a time from the conversion of their alcohol into acetic acid, and are thus changed into vinegar. The slimy substance which is found in vinegar barrels contains the bacteria and is called " mo ther-of- vinegar." The oxygen neces- sary for the change is supplied by the air. Solutions containing more than about 10 per cent, of alcohol do not ferment, nor does fermentation occur in dilute solutions unless they contain small amounts of certain substances phosphates and nitrogen com- pounds which are essential for the growth of the organisms. This method of making acetic acid is carried on commercially by the so-called "quick vinegar process." In this, dilute alcohol, mixed with vinegar, and to which malt or beer is often added, is allowed to trickle slowly through tall vats nearly rilled with beech- 94 95 SIMPLE MONOBASIC ACIDS wood shavings which have been covered with the necessary bac- teria by previous soaking in vinegar. The heat produced by the oxidation of the alcohol causes a current of air to enter by perfora- tions in the bottom, and draw up through the vats; and the tem- perature, which should be about 30, is regulated by controlling the temperature of this entering air. The solutions are usually passed through several vats in succession, the operation taking eight to twelve days, until most of the alcohol is changed into acid. A little alcohol is, however, always left unchanged, be- cause with its total disappearance the acetic acid would begin to be itself oxidized into carbon dioxide and water. The vinegar thus obtained usually contains from 4 to 6 per cent, of acid, though it is sometimes a little stronger. It is used as table vinegar, and to some extent in making white lead by the Dutch process. Table vinegar contains vari- ous substances besides acetic acid, which give it its aroma and flavor and which vary with the source. Thus cider vinegar, wine vinegar, and malt vinegar, each have distinctive qualities. Spirit vinegar, made from dilute alcohol, is often colored with caramel and given its odor and flavor by adding cer- tain esters. Acetic acid for other uses than the above is mostly obtained from the "pyroligneous acid" produced in the dry distillation of wood. The acid in the distillate is first converted into calcium acetate, and from this the commercial acid is obtained by distil- lation with sulphuric acid from cast iron retorts, or with concen- trated hydrochloric acid from copper retorts. An excess of hydro- chloric acid must be avoided so that none of it shall distil with the acetic acid. The acid thus obtained is purified by redistilla- tion from a little potassium dichromate (to oxidize impurities) and by filtering through charcoal. The ordinary commercial acid contains about 30 per cent, of the pure acid. For the purpose of preparing the pure anhydrous acid, sodium INTRODUCTION TO ORGANIC CHEMISTRY 96 acetate is made, purified by recrystallization, heated to drive off its water of crystallization, and then mixed with concentrated sulphuric acid and distilled. A nearly anhydrous acid is thus obtained, and from it an acid entirely free from water is prepared by crystallization. Its molecular formula is found to be C2H 4 O 2 . Uses. Acetic acid is used in making white lead, as stated above, in the dye-stuff industry, and for making a number of salts of practical value: lead acetate or "sugar of lead," "verdigris," a basic acetate of copper, "Paris green," a double salt of copper acetate and arsenite, and the acetates of iron, chromium, and aluminium, which are extensively used as mordants in dyeing and calico printing. In the laboratory the pure acid is used as an excellent solvent for many carbon compounds. Properties of Acetic Acid. Pure anhydrous acetic acid is a color- less liquid at temperatures above 16.675, which is the melting point of the crystalline solid formed at lower temperatures. From the resemblance of the solid acid to ice the anhydrous acid is often called "glacial" acetic acid. The boiling point is 118. The anhydrous acid and mixtures with small amounts of water show in a pronounced degree, the phenomenon of supercooling, which is common to many liquids and solutions. The addition of a crystal of the acid is usually necessary to cause the crystalli- zation to take place, and when it occurs the temperature rises to the "freezing point." The freezing point of mixtures of acid and water (the temperature at which some separation of solid occurs) is lower as the proportion of water increases, until with 40 per cent, of water a minimum is reached at 26.75. From solu- tions less dilute than this, the anhydrous acid separates at the freezing point, while from more dilute solutions ice is formed. From the mixture containing 40 per cent, of water, acid and water crystallize together and the temperature remains unchanged till the whole is solid. 1 When the anhydrous acid is mixed with 1 See a Physical Chemistry for discussion of cryohydrates. 97 SIMPLE MONOBASIC ACIDS water there is contraction of volume and tjie temperature rises. The specific gravity increases as the acid is diluted, until (at 15) with 77-80 per cent, of acid a maximum is reached. A solution containing 43 per cent, has the same specific gravity at 15 as the anhydrous acid; and there are two solutions of different strengths for all specific gravities between this (1.055) an d the maximum (1-075). Acetic acid does not form a constant boiling-point mixture with water as the halogen acids (and formic acid) do, but the distillate becomes more and more dilute, while a stronger and stronger acid remains in the flask. Glacial acetic acid blisters the skin, and has a penetrating and characteristic odor. It is not inflammable until heated nearly to the boiling point, when the vapor burns wjth a pale blue flame. The acid mixes with water, alcohol and ether in all proportions, and its aqueous solutions are sharply acid. Acetic acid dissolves very many organic compounds (without acting on them chem- ically) and some inorganic substances which are insoluble in water, as, for instance iodine and sulphur. It acts on certain metals and dissolves the hydroxides of metals, readily forming acetates. Acetic acid is an unusually stable organic compound. Its vapor is hardly decomposed when led through a red-hot tube; it withstands oxidizing agents to a re- markable degree, and is hence a frequent product of the oxidation of more complicated compounds. On this account it may be employed as a solvent for chromic acid when this is to be used to oxidize a substance insoluble in water. Structure of Acetic Acid. From the molecular formula of acetic acid, C2H4O2, we can make three simple structural formulas: CH 3 CH 3 CH 2 OH CH.OH I or | ,| , and || C=O C=O.OH C=O CH.OH \OH \H INTRODUCTION TO ORGANIC CHEMISTRY 98 The third formula is that of an unsaturated dihydroxyl alcohol, and the second is a mixed alcohol and aldehyde. Acetic acid shows none of the properties of such compounds: it does not give the reactions peculiar to unsaturated compounds, it has no alcohol characteristics, and it is not a reducing agent as it should be if it contained an aldehyde group. As it is formed by the oxidation of ethyl alcohol, CH 3 .CH 2 OH, or of its first oxidation product aldehyde, CH 3 .CHO, the first formula is the one naturally suggested, i. Analysis of its salts show that it is a monobasic acid, which means that one hydrogen atom is differently combined from the other three. 2. Chlorine replaces, one after the other, three and only three of the hydrogen atoms. This indicates the methyl group, CH 3 . 3. Phosphorus chlorides substitute one chlorine atom for one atom each of hydrogen and oxygen; hence an hydroxyl group is present. The only possible structure with a methyl and a hydroxyl group is CH 3 .C = O.OH. Further, acetic acid may be made by the action of potassium hydroxide in alcoholic solution on trichlor-ethane, CH 3 .CC1 3 . We may picture this reaction as first giving CH 3 .C(OH) 3 followed by the breaking down of this unstable compound into acetic acid and water: /OH - = CH 3 .CO.OH + H 2 O. \OH This structure accords with all the reactions of acetic acid and all the methods of its formation. The monad group C = O.OH which contains the acid hydrogen atom of acetic acid is called the carboxyl group (carbonyl and hydxoxyl) and is the charac- teristic group of all organic acids. Laboratory Methods for the Formation of Acetic Acid and its Homologues. The most important reactions which result in the formation of acetic acid and which are also general reactions for the formation of its homologues, are: Q9 SIMPLE MONOBASIC ACIDS 1. Oxidation of the primary alcohols or aldehydes (already described). 2. Hydrolysis of an alkyl cyanide (acid nitrile) (p. 153) : CH 3 .CN + 2 H 2 = CH 3 .CO.OH + NH 3 Methyl cyanide Acetic acid The alkyl cyanides are produced by the action of potassium cyan- ide and alkyl iodides: CH 3 I + KCN = CH 3 .CN + KI The hydrolysis of the alkyl cyanide is effected most rapidly by boiling the cyanide with dilute sulphuric or hydrochloric acid, or a dilute alkali (cf. the formation of formic acid p. 102). 3. From esters by hydrolysis with water or caustic alkalies: CH 3 .CO.OC 2 H 5 + H 2 O CH 3 .CO.OK + 3KC1 + 2H 2 O 5. By heating dibasic acids which contain two carboxyl groups united to the same carbon atom: CH 2 :(CO.OH) 2 = CH 3 .CO.OH + CO 2 Malonic acid 6. From alkyl halides by the Grignard reaction (p. 37). Reactions of Acetic Acid. The hydrogen of the hydroxyl group can be replaced: 1. By metals with the formation of salts. 2. By alkyl groups, giving esters, CH 3 .CO.OH+ C 2 H 6 OH <= CH 3 .CO.OC 2 H 6 -fH 2 O Ethyl acetate 3. The hydroxyl group may be replaced by chlorine or bromine (by phosphorus halides) giving the acid halides: 3CH 3 .CO.OH + 2 PC1 3 = 3CH 3 .CO.C1 + 3HC1 + PiO CH 3 .CO.OH+ PC1 6 = CHa.CO.Cl + POClj + HC1 Acetyl chloride INTRODUCTION TO ORGANIC C 4. The hydrogen of the methyl group can be directly replaced by chlorine or bromine, yielding mono-, di-, and tri-halogen acetic acids: CH 2 C1.CO.OH, CHC1 2 .CO.OH, CC1 3 .CO.OH Reactions of Acetates. Among the important reactions into which acetates enter are: 1. The formation of the acid amide (p. 137) by heating ammo- nium acetate: CH 3 .CO.ONH 4 = CH 3 .CO.NH 2 + H 2 O Acetamide By distillation of the acid amide with phosphorus pentoxide the nitrile of the acid (an alkyl cyanide) is formed: P 2 5 CH 3 .CO.NH 2 -> CH 3 .CN + H 2 O 2. The formation of aldehyde by heating a mixture of calcium acetate and formate ; or of a ketone when calcium acetate is heated alone or with homologous calcium salts of higher atomic weights (pp. 77, 89). 3. The formation of methane by replacement of the carboxyl group with hydrogen, when sodium acetate is heated with sodium hydroxide or soda-lime (p. 26): CHs.CO.ONa + NaOH = CH 4 + Na 2 CO 3 4. The formation of ethane by electrolysis (p. 29). Other Acids of the Type of .Acetic Acid. A large number of organic acids are known, in each of which one carboxyl group is united to an alkyl group (or hydrogen). They form an homologous series, whose general formula is C n H 2n+I CO.OH. General Properties of the Acids. The acids of this series, which contain less than ten atoms of carbon, are liquids at ordinary temperatures, and those of greater molecular weight solids. As the molecular weight increases, the liquid acids become oily and less soluble in water, and the specific gravity decreases. All except the first three are lighter than water. The solid acids IO1 'SIMPLE MONOBASIC ACIDS have a waxy or fatty consistency and are insoluble in water but are all soluble in alcohol and in ether. All except the highest boil without decomposition, and the boiling points are higher with greater molecular weights. The melting points of the acids exhibit an interesting periodicity, alternately rising and sinking as the molecular weights become larger; the acids with an even num- ber of carbon atoms always having higher melting points than the acids containing an odd number of carbon atoms which are next above them in the series. The acids containing from four to nine carbon atoms have a disagreeable odor like that of rancid butter. The acid character becomes less and less pronounced as the molec- ular weight is greater, and the higher members of the series show that they are acids only by the formation of salts. The salts of the lower members are all soluble in water, but with the higher members only the alkaline salts dissolve. Their reactions are similar to those of acetic acid and the ace- tates. It should be remarked, however, that chlorine and bro- mine replace the hydrogen nearest the carboxyl group, thus giving a-substitution products. NORMAL MONOBASIC ACIDS Name Radical with CO. OH group Melting Point Formic H 8.6 Acetic CH 3 I6. 7 Propionic C 2 H 6 22 Butyric C 3 H 7 - 7-9 Valeric C 4 H 9 -58.5 Caproic CsHn 1.5 Heptylic C 6 H 13 -10.5 Caprylic C 7 H 15 16.5 Pelargonic C 8 Hi7 12.5 Capric C 9 Hi 9 31.4 Laurie C U H 2 3 48 Palmitic Ci 5 H 31 62.6 Margaric Ci 6 H 33 60 Stearic CnH 3 5 69-3 Cerotic C 26 H 63 78 Boiling Point Specific Gravity 101 I 231 ( 10) Il8.5 I .0515 dS) 141 .9985 (14) 162 O 9599 (i9-i) 186 .9560 (o) 205 o 9450 (o) 223 o .9186 (17.2) 237-5 o .9100 (20) 254 o .9110 (m.p.) 260 wy 225 H 268 l> 8527 (m.p.) 277 3 3 287 . o 8454 (m.p.) INTRODUCTION TO ORGANIC CHEMISTRY IO2 All the normal acids up to Ci9H 39 .CO.OH are known. The acid of largest molecular weight which is known is C 33 H67.CO.OH. Isomeric acids corresponding to the isomeric primary alcohols can all be made. Nomenclature. The usual names of the acids of this series are the original names which are often suggested by the sources from which the acids were first obtained. Thus formic acid from ants (formica), acetic from vinegar (acetum), butyric from butter, palmitic from palm oil, stearic from tallow (STX,/O), oleic from oils, etc. A systematic method of naming which is of ten' employed, and which has the advantage of being descriptive of the structure, is one which regards them (except formic acid) as derivatives of acetic acid: thus propionic acid, CH 3 .CH 2 .CO.OH, is methyl acetic acid; normal butryic acid, CH 3 .CH 2 .CH 2 .CO.OH is ethyl acetic acid; and iso-butyric acid (CH 3 ) 2 CH.CO.OH, is dimethyl acetic acid. Another systematic nomenclature changes the name of the hydrocarbon of the same number of carbon atoms, of which the acid is a theoretical derivative, by substituting oic for the final e; thus acetic acid is ethanoic acid, etc. The name of fatty acids is often given to the series, from the fact that esters of some of the higher members occur in the fats, and many of the acids themselves resemble fats. Formic acid, HCO.OH, the first member of the series, is found in ants (formica), bees, and in stinging nettles. The irritation from the sting of these is probably due to the formic acid which they deliver. Formic acid occurs also in many insects and plants, and is frequently one of the products formed in the destructive distillation and oxidation of many organic substances. Formic acid, or its alkaline salts (from which the acid is readily set free by hydrochloric acid) can be made in the laboratory by many reactions. Some of them are: 1. By the oxidation of a solution of methyl alcohol. 2. By the hydrolysis of hydrocyanic acid by means of dilute alkalies or acids: HCN + 2H 2 O = H.CO.OH + NH 3 103 SIMPLE MONOBASIC ACIDS If an acid is employed the products are formic acid and the am- monium salt of the acid; with an alkali, the alkaline formate and ammonia are produced. 3. By warming chloroform with an alkali, CHC1 3 + 4KOH = H.CO.OK + 3 KC1 + 2 H 2 O This reaction may be regarded as taking place in three steps: /OH CHC1 3 + 3KOH = 3 KC1 + CH^OH; \OH /OH CH^-OH = HCO.OH + H 2 O; \OH HCO.OH + KOH = HCO.OK + H 2 O. Two further reactions by which salts of formic acid can be formed from the elements are of special interest. These are: 4. By the action of moist carbon monoxide on solid potassium or sodium hydroxide at a temperature of about 200: CO + NaOH = HCO.ONa This reaction is employed in the commercial preparation of sodium formate, the carbon monoxide from generator gases being used under pressure. 5. Moist carbon dioxide acts slowly on potassium, forming a mixture of the acid carbonate and the formate: 2 CO 2 + 2K + H 2 O = HCO.OK + KHCO 3 6. Formates are also produced by the reduction of solutions of ammonium carbonate or of acid carbonates by means of sodium amalgam. Preparation. None of the above -reactions are, however, usually employed for laboratory preparation of formic acid; but the acid is made by distilling a mixture of glycerol (glycerine) and INTRODUCTION TO ORGANIC CHEMISTRY 104 oxalic acid. Oxalic acid when heated alone gives a small amount of formic acid together with carbon dioxide: C 2 H 2 O 4 = HCO.OIJ + CO 2 but most of the oxalic acid sublimes unchanged. When mixed with glycerol, however, the reaction goes on quite readily and completely. The glycerol prevents the sublimation of the oxalic acid through the formation of a formic acid ester of glycerol, which then breaks down through hydrolysis with the water present into formic acid and glycerol. The reactions which occur at about 120 with a mixture of equal parts of glycerol and crystallized oxalic acid are: CH 2 OH CH 2 O.OCH CHOH + CO.OH = CHOH + CO 2 + H 2 O I I I CH 2 OH CO.OH CH 2 OH Glycerol Oxalic acid Glyceryl monoformate Very little formic acid distils until another portion of oxalic acid is added, when by the reaction between the monoformate and the crystallization water of the oxalic acid formic acid is set free and at the same time the monoformate is reproduced: CH 2 O.OCH CH 2 OH CHOH + H 2 O = CHOH + HCO.OH I I CH 2 OH CH 2 OH By adding fresh portions of oxalic acid from time to time the production of formic acid goes on indefinitely. When oxalic acid and four times its weight of glycerol are heated and the temperatures brought up to 22o-26o, a deeper-seated decomposition of the formic acid ester occurs with the formation and distillation of ally! alcohol (p. 69): 105 SIMPLE MONOBASIC ACIDS CH 2 O.OCH CH 2 I II CHOH = CH -f CO 2 + H 2 O I I CH 2 OH CH 2 OH Glycerol monoformate Allyl alcohol Anhydrous formic acid cannot be obtained by distillation. It can be prepared from anhydrous lead formate by the action of hydrogen sulphide; but more conveniently by using anhydrous oxalic acid as a dehydrating agent. The structure shown by the formula which has been used in the description of the methods for making formic acid is directly indicated by some of these reactions, and is in accord with all the known facts about the acid. The characteristic acid group, CO.OH, is here combined with hydrogen instead of an alkyl group as in acetic acid and the other acids of this series, and in this fact we have an explanation of some methods of formation and some reactions which differ from those of the other acids of this series. Attention is called especially to the presence of the aldehyde group shown in the structural formula, H = o OH Formic acid is thus both an acid and an aldehyde. Properties. Formic acid is a colorless liquid which fumes slightly in the air and is hygroscopic. It is heavier than water, solid below 8. 6 and boils at 101. When mixtures of the acid and water are distilled, they behave like solutions of hydrochloric acid, both strong and weak solutions giving finally a mixture whose boiling point (about 107) and composition (about 77 per cent, acid) are constant while the pressure remains unchanged. The acid has an irritating odor, and the pure acid in contact with the INTRODUCTION TO ORGANIC CHEMISTRY 106 skin causes blisters and painful wounds. It mixes with water and with alcohol in, all proportions, and its solutions show a strong acid reaction with litmus. Formic acid is, in fact, the strongest of the organic acids. The liquid acid does not burn, but its vapor burns readily with a blue flame into water and carbon dioxide; and solutions of the acid are easily oxidized by various agents and yield the same products. Formic acid is, therefore, a strong reducing agent. It precipitates silver and mercury when warmed with neutral solutions of their salts. This reducing power, which is not shown by the other acids of this series, is like that shown by the aldehydes (p. 78); and as has been pointed out, the acid contains an aldehyde group united with hydroxyl. Formic acid, from this point of view, may be regarded as an aldehyde deriva- tive of carbonic acid: OH OH OH H Carbonic acid Formic acid The production of formates by the reduction of carbonates (p. 103) agrees with this view, since the aldehydes may be regarded as derived from the corresponding acids by the withdrawal of an atom of oxygen. Reactions. Formic acid is decomposed into carbon dioxide and hydrogen when heated to 160 in a closed vessel; and with concentrated sulphuric acid the acid (and of course, its salts) decompose readily into carbon monoxide which is evolved, and water which is held by the sulphuric acid. Some contact agents such as finely divided rhodium, cause a spontaneous decomposi- tion of the same sort. The salts of formic acid the formates are all soluble in water, though some, such as the silver and lead formates, do not dissolve very freely. 107 SIMPLE MONOBASIC ACIDS Formates are decomposed by heating. The alkali salts when carefully heated, and the salts of the alkaline earths under all conditions, give carbonates: **,, + H, + CO though by rapidly raising the temperature to 400, in the absence of air, the alkali formates yield oxalates and hydrogen : HCO.ONa HCO.ONa = Ammonium formate gives neither carbonate nor oxalate when heated, but at 230 loses the elements of water with the pro- duction of formamide HCO.NH 2 . Formic acid and formates may be identified by the reactions with concentrated sulphuric acid, and with an ammoniacal solution of silver nitrate. Either alone is inconclusive, because given by other substances, but if in the first the substance does not blacken and a gas is obtained which burns with a blue flame; and silver is precipitated in the second, formic acid or a formate is present. Higher Fatty Acids These may be made by the general methods which have been given. The three normal acids which follow acetic acid in the series are also formed by processes of fermentation. Propionic Acid, CH 3 .CH 2 .CO.OH (methyl acetic acid or propanoic acid). The original name of this acid was -given it as the first 01 the series which showed fat-like properties (TTP&TOS and iriov). It is found in small quantities in wood vinegar, and is formed in a fermentative process which takes place in solu- tions of the calcium salts of malic and lactic acids. It is also a reduction product of lactic, glyceric, acrylic and propargylic acids. INTRODUCTION TO ORGANIC CHEMISTRY 108 Butyric Acids. Normal butyric acid, CH 3 .CH 2 .CH 2 .CO.OH, ethyl acetic acid, is found in rancid butter. Its glyceryl ester forms about 5 per cent, of butter fat, which is made up of this and of esters of several other acids of this series. The acids may be set free from these esters by hydrolysis; but on account of the difficulty of separation this is not a favorable method for obtain- ing butyric acid. It is produced by the action of a special ferment (butyric fer- ment) contained in old Limburger cheese (which also contains the acid), on sugars, lactic acid, and other substances. This fermenta- tive process is the one usually employed for its preparation. Isobutyric acid (CH 3 ) 2 :CH.CO.OH, dimethyl acetic acid, is apparently not formed by fermentation. It occurs in consider- able quantities in the juices of "St. John's bread," the fruit of the carob tree, and can be obtained from this source by distillation with water. Both the acid and an ester occur in aconite root, and in some other substances. Isobutyric acid is much less soluble in water than the normal acid, and, as is the rule with iso-compounds, its boiling point is lower. Valeric Acid. -There are four valeric acids, C^g.CO.OH, known, all that are structurally possible. The normal acid is in wood vinegar in small amounts and is formed in a fermentation of calcium lactate solution. One of the iso-acids is found in the roots of valerian (hence the name), and angelica, and may be obtained from these by distillation with water. It is optically active. Palmitic Acid,Ci5H 3 iCO.OH, and Stearic Acid,Ci 7 H 35 CO.OH. Glyceryl esters of the normal acids, together with that of oleic acid (p. no), are the chief constituents of animal fats, and are contained in many vegetable fats and oils. The acids are ob- tained from these sources, commercially, by hydrolysis of the esters (p. 124). After the crystallization of the two solid acids, the liquid oleic acid is removed from them by hydraulic pres- SIMPLE MONOBASIC ACIDS sure. The mixture of palmitic and stearic acids thus obtained is known by the trade name of "stearin" (not to be confused with stearin as used in chemistry, which is the name given to the glyceryl ester of stearic acid). This " stearin," mixed with paraffin to prevent crystallization and consequent brittleness, is largely used for making candles. Palmitic and stearic acids are colorless, waxy solids which melt at 63 and 69 respectively, and can be distilled without decompo- sition only in a partial vaccuum. Soaps. The salts of the three acids whose esters form the fats are called soaps, though in the common use of the word, only the alkali salts are meant. Soap is made by the decomposition of the esters (fats) by solutions of the alkalies, the alkali salts and glycerol being produced in equivalent amounts: Stearin Potassium stearate Glycerol When potassium hydroxide is used, the salts with the glycerol form a jelly-like mass which is known as soft-soap; when the fats are boiled with sodium hydroxide, a hard soap is formed, which is precipitated from the solution by adding common salt and cool- ing, while the glycerol is left in solution. Transparent soaps are made by dissolving a hard soap in alcohol and evaporating the clear solution. Common soaps are made from many different materials and often contain various additions. Pure soaps are soluble in alcohol, and dissolve in water with some hydrolysis or separation into alkali and insoluble acid. The soaps of the alka- line earths and of other metals are insoluble; hence a precipitate of calcium and magnesium salts is produced when soap is used with hard water and the formation of a lather is prevented until the precipitation is complete. The method for determining the hardness of a water is based on this reaction a soap solution of known strength being added to a measured quantity of water, till a permanent lather is produced on shaking. The cleansing action of soap has been the subject of such dispute. It appears INTRODUCTION TO ORGANIC CHEMISTRY IIO to be due chiefly to the power which soap solutions have of emulsi- fying oily substances, of wetting and penetrating into oily textures, and of lubricating texture and impurity so that the impurity is readily removed. 1 Unsaturated Acids Olei'c acid, whose glyceryl ester occurs in fats and oil, is an unsaturated acid with a double bond between two of its carbon atoms: Ci 7 H 33 .CO.OH, or CH 3 (CH 2 ) 7 CH :CH(CH 2 ) 7 CO.OH. The position of the double bond is indicated by the study of the compounds (acids) obtained by its oxidation, on the assump- tion that the break caused by oxidation occurs at this place. Oleic acid is an oily, odorless liquid, insoluble in water. When cooled it crystallizes, and melts at 14. It readily oxidizes in contact with air, becoming brown and rancid. Both ole'ic acid and its glyceryl ester are changed into solids by a small amount of nitrous acid. These solids have the same composition as the original substances, and are called ela'idic acid and ela'idin, respectively. The reaction is used in the examination of oils as an indication of the amount of plein they contain. Acrylic acid, CH 2 : CH.CO.OH, is to be regarded as the oxida- tion product of allyl alcohol (p. 69) or of acrylic aldehyde (acrolein, p. 86). It is the first acid of the series of acids with a double bond, as allyl alcohol is the first alcohol. It can be formed from the corresponding saturated acid, propionic acid, by substituting a halogen atom or a hydroxyl group for hydrogen, and then employing the reactions used for making the unsaturated hydro- carbons from similar substitution products (p. 45) : CH 2 LCH 2 .CO.OH + KOH = CH 2 :CH.CO.OH + KI + H 2 O. CH 2 OH.CH 2 .CO.OH - H 2 O = CH 2 :CH.CO.OH In the first reaction the potassium hydroxide must be used in alcoholic solution ; the second occurs on distillation. Since the 1 See Journal of American Chemical Society, XXV, 511. Ill SIMPLE MONOBASIC ACIDS corresponding nitrile, CH 2 :CH.CN, does not exist, the general reaction for making acids from their nitriles cannot be employed in this case. Acrylic acid is not unlike acetic acid in many of its properties, but it gives the reactions which are characteristic of an unsatu- rated compound, uniting directly with chlorine and bromine, with halogen acids, and with hydrogen (nascent) to form saturated compounds. When oxidized, it breaks at the double bond. The structural formula given it is based on a study of the methods of its formation and its reactions. Crotonic acids, C 3 H 6 CO.OH. Four acids of this formula are known, two of which have a special theoretical interest, since they have the same constitutional formula, and yet differ widely in their physical characteristics. Crotonic acid (first obtained from croton oil) is a solid, melting at 72 and boiling at 181, and resembles acrylic acid in its general behavior. Isocrotonic acid is an oily liquid boiling at 172, with an odor which recalls that of butyric acid. Both acids are present in crude wood vinegar and both can be made synthet- ically. Both can be converted into butyric acid by addition of hydrogen halides followed by reduction with nascent hydrogen; and isocrotonic acid is transformed into cro tonic acid by continued heating to 170-180. The constitutional formula given to these acids is CH 3 .CH:CH.CO.OH, and the differences in the two acids is explained as the result of so-called geometrical isomerism which will be discussed later (p. 186). Propiolic acid, CHiC.CO.OH, is an illustration of a small group of acids which have a triple bond. It is related to propargyl alcohol (p. 69) as acetic acid is to ethyl alcohol, but cannot be made from this by oxidation. It is a liquid. When cooled it freezes, and the crystalline solid melts at 6. It is partly de- composed when distilled under ordinary pressure, but distils unchanged in a partial vacuum. It unites the properties of an organic acid with those which are characteristic of acetylene, and in every way justifies the structural formula given it. INTRODUCTION TO ORGANIC CHEMISTRY 112 Acids with Two or More Double Bonds. Very few acids of these classes are known. An acid with two double bonds is sorbic acid, CH 3 .CH:CH.CH:CH.CO.OH, which is found in the unripe berries of the mountain ash. It is an odorless, crystalline solid, melting at 134.5. Linolic acid, CiyHsi.CO.OH, whose glyceryl ester is an important constituent of several "drying oils" (cf. p. i6oa), has also probably two double bonds. Two acids with three double bonds are linolenic and isolinolenic acids, CnH29.CO.OH, whose glyceryl esters are in linseed oil. Further Study of Oxidation We have learned that the saturated hydrocarbons are not oxidized easily, and that oxidation, when it takes place, usually results in producing the end products, carbon dioxide and water, without such intermediate compounds as alcohols, aldehydes, and acids. When, however, the hydroxyl group is present, as in alcohols, oxidation is easily effected and controlled, so that these compounds may be prepared. How shall we picture the progress of these oxidations? When alcohol is oxidized into aldehyde, the net result is the removal of two atoms of hydrogen from the primary alcohol group, OH with the formation of water and the aldehyde group, CHO. The first suggestion is that the two atoms of hydrogen united to the carbon atom have been simply burned out of the group. This, however, would leave = C O H, a group still contain- O ing hydroxyl, while in the aldehyde group, C CH 3 .C(OH) 2 CH 3 - CH 3 .CO.CH 3 + H 2 O while the oxidation of an aldehyde into an acid evidently consists simply in the formation of a hydroxyl group in the manner just described: -CO.H + O = -CO.OH Further, unsaturated hydrocarbons, which are readily oxidized, yield hydroxyl derivatives. This is the view of the course of oxidation which is generally accepted, and it is applicable to all oxidations of organic substances. We may sum the matter up as follows: i. Saturated hydrocarbons are not readily oxidized except into the end products, carbon dioxide and water. Un- saturated hydrocarbons, on the contrary, are easily oxidized and give hydroxyl derivatives. 2. Saturated compounds already INTRODUCTION TO ORGANIC CHEMISTRY containing oxygen in a hydroxyl group, or an aldehyde group, are easily oxidized, and the oxidation affects first the hydrogen atoms united to the carbon atom already in combination with oxygen. 3. The immediate result of the oxidation is the formation of hydroxyl groups. 4. If two hydroxyl groups are united to a single carbon atom, the system is unstable, and breaks down into oxygen, which remains combined with the carbon by both valen- cies, and water. CHAPTER IX ACID CHLORIDES; ANHYDRIDES; ESTERS Acyl Chlorides When phosphorus trichloride is mixed with glacial acetic acid and the mixture gently heated, hydrogen chloride is copiously evolved, and on distillation of the remaining liquid a compound is obtained which boils at 51 and has the molecular formula, C2H 3 OC1. It reacts readily with water, forming acetic and hydrochloric acids. It appears from these reactions that the hydroxyl group of acetic acid is replaced by chlorine, and then restored; so that the structure of the compound first formed is CH 3 .CO.C1. This is acetyl chloride the group, CH 3 .CO being named the acetyl group. With the exception of formic acid, similar compounds can be obtained from all organic acids, and are called, generally, acyl chlorides, acyl being a general name for the organic acid radical or group, C n H 2n+ iCO. All attempts to make formyl chloride have failed, as it breaks up at once into carbon monoxide and hydrogen chloride: HCO.C1 = CO + HC1. The general formula for the acid chlorides of the acetic acid series is C n H 2n +iCO.Cl. Preparation. i. The reaction by which acetyl chloride is prepared, as above, is: 3 CH 3 .CO.OH + 2PC1 3 = 3CH 3 .CO.C1 + 3 HC1 + P 2 O 3 . 2. Phosphorus pentachloride gives the same product together with phosphorus oxy chloride: CH 3 .CO.OH + PC1 5 = CH 3 .CO.C1 + POC1 3 + HC1. 114 ACID CHLORIDES; ANHYDRIDES; ESTERS 115 These are general reactions for making the acid chlorides. For the lower members of the acetic acid series the reaction with phosphorus trichloride is preferred, since it avoids the formation of the phosphorus oxychloride (boiling point 107) from which the acyl chloride is separated with some trouble. Other general reactions for the formation of acid chlorides are the following: 3. By the action of phosphorus chlorides or oxy- chloride on the sodium salts of the acids, and 4. By withdrawal of the elements of water from a mixture of the acid and hydro- gen chloride, which is effected by leading hydrogen chloride into a mixture of the acid and phosphorus pentoxide: CH 3 .CO.OH + HC1 = CH 3 .CO.C1 + H 2 O In the commercial preparation of acetyl chloride (for laboratory use) a mixture of sulphur dioxide and chlorine is passed over an- hydrous sodium acetate. Sulphuryl chloride, SO2C12, appears to be first formed, and this reacts with the acetate as follows: 2CH 3 .CO.ONa + S0 2 C1 2 = 2CH 3 .CO.C1 + Na 2 SO 4 Properties and Reactions. The lower members of the series are liquids of penetrating odor, which fume in the air, because of the hydrogen chloride formed by the aqueous vapor present. The boiling points of the acyl chlorides are lower than those of the cor- responding acids, an effect of the substitution of chlorine for hydroxyl like that found in the boiling points of alcohols and the corresponding alkyl chlorides. The acyl chlorides react readily with hydroxyl and amido compounds, and acetyl chloride is fre- quently employed as an organic reagent (cf. pp. 124, 138, 329, etc.). i. The acyl chlorides are insoluble, as such, in water, but are decomposed by it with the formation of the organic acid and hydro- chloric acid: CHa.CO.Cl + H 2 O = CH 3 .CO.OH + HC1 Il6 INTRODUCTION TO ORGANIC CHEMISTRY This reaction occurs very readily and violently in cold water with acetyl chloride and a few of the next higher homologues, but more slowly as the molecular weight increases. Similar reactions take place with other hydroxyl compounds. 2. With sodium hydroxide the acetate and chloride of sodium are formed. 3. With alcohols, an ester and hydrogen chloride are formed 1 , CHa.CO.Cl + C 2 H 6 OH = CH 3 .CO.OC 2 H 6 + HC1 This reaction with acetyl chloride is a valuable one for determin- ing whether a compound contains the hydroxyl group of an alcohol. The facility with which these reactions of the acyl chlorides with water and alcohols take place stands in sharp contrast with the behavior of the alkyl chlorides. 4. With organic acids a reaction occurs which is slow and incomplete, but their salts react readily with the formation of simple or mixed acid anhydrides (p. 117): CH 3 .CO.C1 + CH 3 .CO.OK = (CH 3 CO) 2 O + KC1 5. With ammonia the acid chloride reacts easily with the for- mation of acid amides (p. 137), and similar reactions occur with substituted ammonias, such as aniline: CHa.CO.Cl + NH 3 = CH 3 .CO.NH 2 + HC1 The acyl chlorides, unlike the alkyl chlorides, do not react directly with sodium or other metals. The acid bromides and iodides are of much less importance than the chlorides. The bromides are sometimes used in pre- paring bromine substituted acids, as a-brompropionic acid, CH 3 .CH.Br.CO.OH, since replacement by bromine occurs more readily in the acid bromide than in the acid. They can be made by the action of the phosphorus bromide (red phosphorus and bromine) on the acids or their salts. ACID CHLORIDES; ANHYDRIDES; ESTERS 117 ACID CHLORIDES AND ANHYDRIDES Name of Formula ACID CHLORIDE : RC1 ACID AN Acid of Radical Melting Boiling Melti Point Point Poin Acetic CH 3 .CO 51 Propionic C 2 H 6 .CO 78 Butyric (norm.) C 3 H 7 .CO 101 Butyric (iso) C 3 H 7 .CO 92 Valeric (iso) C 4 H 9 .CO "5 Heptylic C 6 H 13 .CO Caprylic C 7 H 15 .CO 83 Pelargonic C 8 H 17 .CO 98 " 5 Capric C 9 H 19 .CO 114 IB Palmitic Ci 5 H 31 .CO 12 192-5 33 64 Stearic Ci 7 H 35 .CO 23 215 Boiling Point 136 I6 7 I 9 2 182 215 268-271 Acid Anhydrides We have seen that by the action of acetyl chloride on sodium acetate a compound is produced with the formula (CHs.CO^O. This is the anhydride of acetic acid, which may be regarded as two acid radicals united by oxygen, and derived from two molecules of the acid by the withdrawal of the elements of water. It corre- sponds, therefore, to the inorganic anhydrides, SO 3, ^Os, etc. This view of its constitution follows immediately from the method of its formation, since we know the structure of the acid chloride and of the sodium acetate. In confirmation of this formula is the fact that it is formed (though not readily and only in small amounts) by the action of phosphorus pentoxide on glacial acetic acid: 2 CH 3 .CO.OH + P 2 O 5 = (CH 3 .CO) 2 O + 2HPO 3 Similar compounds are obtained corresponding to the other acids of this series, except in the case of formic acid. Formic anhy- dride (HCO) 2 O, like its chloride, is too unstable to exist. Formation. In addition to the methods already given, the anhydrides can be formed by the action of the acid chlorides OP Il8 INTRODUCTION TO ORGANIC CHEMISTRY the anhydrous acids; but the reaction, like that of the direct with- drawal of water from the acid, is slow and incomplete. The anhy- drides can also be formed from the salts of the acids by heating them with carbonyl chloride: 2 CH 3 .CO.ONa + COC1 2 = (CH 3 CO) 2 O + C0 2 + 2NaCl They are almost always prepared, however, by the interaction of the sodium salt of the acid and its chloride. Properties. Acetic anhydride, or acetyl oxide, and its next homologues are liquids whose boiling points are higher than those of the acids from which they are derived. The anhydrides of greater molecular weight are solids. They are all insoluble in water, but soluble in ether. Acetic anhydride is the most impor- tant of this group. Reactions. The anhydrides react with hydroxyl compounds in a manner similar to the acid chlorides, but less vigorously, and, like the chlorides, they are much used to identify the alcoholic hydroxyl group. 1. Like the inorganic anhydrides, the organic anhydrides are converted into acids by water. The reaction, however, even with acetic anhydride, is very slow in cold water; and some of the higher anhydrides can be boiled in water for a considerable time without being completely changed. With solutions of alkalies the reaction takes place easily with the formation of the salt of the acid. 2. With alcohols, the anhydrides give an ester and the acid: (CH 3 .CO) 2 O + C 2 H 5 OH = CH 3 .CO.OC 2 H 5 + CH 3 .CO.OH 3. With organic acids, the anhydrides act only when heated, and then slowly. This reaction gives a method for making mixed anhydrides, for instance, with propionic acid: CH 3 .CO\ (CH 3 .CO) 2 O + C 2 H 5 .CO.pH = yo + CH 3 .CO.OH Acetic anhydride Propionic acid C2Hs.CC) ACID CHLORIDES; ANHYDRIDES; ESTERS 119 Such mixed anhydrides are decomposed by distillation into the simple anhydrides. 4. With hydrochloric acid, a reaction of the same kind occurs: (CH 3 .CO) 2 O + HC1 = CH 3 .CO.C1 + CH 3 .CO.OH Acetyl chloride may be thus regarded as a mixed anhydride of acetic and hydrochloric acids. 5. With ammonia, acid amides are formed: (CH 3 .CO) 2 O + 2NH 3 = 2 CH 3 CO.NH 2 + H 2 O Acetamide 6. Chlorine and bromine act very readily on the anhydrides, substituting for one hydrogen atom, while the hydrogen halide which is formed reacts on the substituted anhydride, so that the final products are the acyl halide, and the monohalogen substi- tuted acid; e.g., CH 3 .CO.C1 and CH 2 C1.CO.OH. 7. Nascent hydrogen (sodium amalgam) reduces anhydrides to aldehydes and alcohols, but the reaction yields other products as well. The student should compare the reactions of the anhydrides with those of the acyl halides (and esters) and decide how an anhydride may be identified. Esters of Inorganic Acids Both inorganic and organic acids react with alcohol with the formation of compounds which are called esters. Esters of Sulphuric Acid. When concentrated sulphuric acid is mixed with ethyl alcohol and the mixture heated for some time on a water bath, an acid compound is formed which gives with barium carbonate a soluble barium salt, and thus may be sepa- rated from any unchanged sulphuric acid. If just enough sul- phuric acid is added to the solution of this barium salt to exactly precipitate the barium, there is obtained, on evaporation of the 120 INTRODUCTION TO ORGANIC CHEMISTRY filtrate, a thick acid liquid which cannot be distilled without decomposition into ethylene and sulphuric acid. Most of the salts of this acid compound are soluble in water and can be obtained pure by crystallization. Analysis of these salts shows that they may be regarded as derived from an acid whose composi- tion is H(C2H 5 )SO 4 , ethyl hydrogen sulphate. The normal ethyl sulphate or diethyl sulphate, may be made by the reactions of silver sulphate and ethyl iodide: Ag 2 S0 4 + 2C 2 H 5 I = (C 2 H 5 )2S0 4 + 2AgI This reaction gives conclusive evidence as to the structure of this compound. It is a liquid of pleasant peppermint-like odor, which boils at 208 with only slight decomposition. Ethyl hydrogen sulphate, or ethyl sulphuric acid, is an interme- diate product in the reactions by which ethylene and ether are prepared (pp. 46 and 70). Although the final result of these reactions may be expressed as due to the withdrawal of the elements of water from one or from two molecules of alcohol, the actual progress of the reactions is represented by the following equations. For ethylene: C 2 H 5 OH + H 2 SO 4 *=* H(C 2 H 5 )SO 4 + H 2 O and H(C 2 H 5 )SO 4 = CH 2 : CH 2 + H 2 SO 4 In the ether formation, ethyl sulphuric acid is formed as above, and then reacts with another molecule of alcohol: H(C 2 H 5 )S0 4 + C 2 H 5 OH = (C 2 H 5 ) 2 + H 2 SO 4 The course of the principal reaction is determined, as has been stated, by the proportions of acid and alcohol which are used, and the temperature. Ethyl sulphuric acid is also formed when ethylene is led into the concentrated acid. This gives an interesting method for making ACID CHLORIDES; ANHYDRIDES; ESTERS 121 ethyl alcohol from inorganic materials. For from calcium car- bide (lime and coke), acetylene is obtained by the action of water, and acetylene is readily converted into ethylene by hydrogen in the presence of platinum black. When heated with water, ethyl sulphuric acid is converted into alcohol and sulphuric acid: H(C 2 H 5 )S0 4 + H 2 O + C 2 H 5 OH + H 2 SO 4 Ethyl sulphuric acid or its salts are frequently used in preparing other ethyl compounds by such reactions as: K(C 2 H 5 )SO 4 + KBr = C 2 H 6 Br + K 2 SO 4 K(C 2 H 5 )SO 4 + KCN = C 2 H 5 CN + K 2 SO 4 Sulphuric acid esters containing other alkyl groups may be obtained by the methods given for making the ethyl compounds, and resemble these in their properties. Esters of Other Inorganic Acids. The hydrogen of other inorganic acids may be replaced by alkyl groups with the forma- tion of esters. These esters are mostly oily liquids which are more or less easily hydrolyzed into alcohol and acid by water, and are in all cases decomposed by boiling solutions of alkalies into alcohols and salts. The normal esters are insoluble or only slightly soluble in water, but the acid esters are soluble; an illustration of the influence of the presence of the hydroxyl group on solubility in water. (Com- pounds containing this group are mostly more or less soluble in water, while those in which the group is absent are usually insol- uble or nearly insoluble. Among the compounds we have so far considered this is seen to be true, except in the case of the alde- hydes and ketones.) In the formation of the esters by the direct action of the acids on the alcohols, the reaction is never complete, and when the acid is polybasic an acid ester (or alkyl acid) is formed. The best 122 INTRODUCTION TO ORGANIC CHEMISTRY general method for making the normal esters is by the reaction between the silver salt of the acid and the alkyl halide as in the case of ethyl sulphate. For instance: Ag 3 As0 3 + 3C 2 H 5 I = (C 2 H 5 ) 3 AsO3 The acid esters are, as a rule, less stable than the normal ones. They are odorless and decompose when distilled. Their salts, however, are more stable than the esters themselves. The normal esters often have a pleasant fruity odor, and can usually be distilled without decomposition. The nitric and nitrous esters of methyl and ethyl are readily hydrolyzed to acid and alcohol; the nitric esters are converted by nascent hydrogen (tin and hydrochloric acid) into hydroxyl- amine and alcohol: C 2 H 5 ON0 2 + 6H = NH 2 OH + C 2 H 5 OH + H 2 O. Hydroxylamine The nitric ester of glycerol, a polyhydroxyl alcohol, is de- : scribed on page 159. Ethyl nitrite, C 2 H 5 ONO known in alcoholic solution as "sweet spirit of nitre," and isoamyl nitrite are used in medicine. The alkyl halides are esters of the halogen acids, but on account of their importance in various reactions and the fact that many of them can be made directly from the hydrocarbons by the action of halogens, have been already discussed (p. 31). ESTERS Nitrite Nitrate Sulphate Acetate B.p. B.p. (neutral) B.p. B.p. Methyl -12 66 187 57.3 Ethyl 17 87 208 77.5 Propyl 57 110.5 101.8 Isopropyl 45 101 . 5 c. 90 Butyl (norm.) 75 ..... 124.5 Isobutyl 67 123 116.3 ACID CHLORIDES; ANHYDRIDES; ESTERS 123 Boiling Point Formic acid 55 Acetic 77-5 Propionic 98.8 Butyric (norm.) 120.9 Butyric (iso.) IIO. I Valeric (norm.) 144.7 Valeric (iso.) 134-3 ETHYL ESTERS Caproic Heptylic Caprylic Pelargonic Capric Palmitic Stearic Boiling Point 166.6 187.1 205.8 227-228 243-245 Melting Point 24 34-34 Esters of Organic Acids Ethyl acetate, which makes its presence known, when ethyl alcohol and acetic acid or an acetate are heated with sulphuric acid, by the agreeable fruity odor which serves as a test for the acetic acid radical, is a typical member of a large group of similar compounds. Several reactions into which it enters have already been given (pp. 35 and 99). It is formed when alcohol and acetic acid are mixed and heated; but the reaction goes on very slowly and, as it is rather readily reversible, an equilibrium is established far short of completion. An excess of either acid or alcohol causes a larger proportion of the one present in smaller amount to be changed into the ester; and in the presence of a water- withdrawing agent the conversion may be nearly complete. When the ester, already made, is mixed with water it is slowly transformed into acid and alcohol. The reaction by which it is formed appears, thus, to consist in the separation of the elements of water from acid and alcohol: CH 3 .CO.OH Acetic acid C 2 H 5 OH Alcohol H 2 O CH 3 .CO.OC 2 H 5 Ethyl acetate and (since the formulas of the acid and alcohol are known), the formula given in the above equation for the ester is plainly indi- cated. This is proved to be the right formula by other reactions 124 INTRODUCTION TO ORGANIC CHEMISTRY in which the ester is made from substances with known formulas, as from acetic acid or an acetate with ethyl halide, or from acetyl chloride with sodium ethoxide. CH 3 .CO.ONa + C 2 H5l = CH 3 .CO.OC 2 H 6 + Nal CH 3 .CO.C1 + C 2 H 5 ONa = CH 3 .CO.OC 2 H 6 + NaCl In the usual method for the preparation of ethyl acetate from alcohol and acetic acid with the addition of sulphuric acid, ethyl sulphuric acid is first formed, and then reacts with the acetic acid: In another procedure hydrogen chloride is led into the mixture of acid and alcohol. One explanation of the effect of the hydrogen chloride is that it acts as a water-withdrawing substance, while according to another interpretation of the reaction, acetyl chlo- ride is an intermediate product which then reacts as follows: CH 3 .CO.C1 + C 2 H 5 OH <= CH 3 .CO.OC 2 H 5 + HC1 Ethyl acetate is also formed from alcohol and acetic anhydride (p. 118). Properties and Reactions. Ethyl acetate is a liquid which boils at 77 and is soluble in about 17 parts water. It enters readily into a number of reactions. 1. With water it is partly hydrolyzed. The hydrolysis is aided by the presence of a small amount of an inorganic acid and boiling. 2. With caustic alkalies, complete decomposition is readily effected with the production of alcohol and an acetate: CH 3 .CO.OC 2 H 5 + NaOH = CH 3 .CO.ONa + C 2 H 6 OH This reaction, which can be carried out with all esters, is called " saponification " from the fact that soap is made in this way from fats, which are esters of glycerol (p. 160). The term is often ACID CHLORIDES; ANHYDRIDES; ESTERS 125 extended to the decomposition by water, in which no salts are produced, and the saponification process is often termed hydrolysis. The rate at which the hydrolysis proceeds depends on the temperature and concentration of the solution as well as on the nature of the hydrolyzing agent and of the ester. 3. Concentrated halogen acids when heated with ethyl acetate form acetic acid and ethyl halide: CH 3 .CO.OC 2 H 5 + HC1 = CH 3 .CO.OH + C 2 H 5 C1 The action is more rapid the higher the molecular weight of the acid; thus hydriodic acid acts most quickly and hydrofluoric acid the most slowly. 4. Ammonia converts ethyl acetate into acetamide (p. 138): CH 3 .CO.OC 2 H 5 + NH 3 = CH 3 .CO.NH 2 + C 2 H 6 OH Acetamide Other esters of organic acids may be made by the methods used for ethyl acetate, and their reactions are of the same kind. Many organic esters are found in nature, and a considerable number are manufactured as artificial fruit essences. Isoamyl acetate has the odor of pears; octyl acetate , that of oranges; ethyl butyrate, that of pineapples; isoamyl isovaleriate that of apples, etc. The natural fats, as we have seen (p. 108), are esters of glycerol, and various waxes are composed chiefly of esters of the higher homologues of acetic acid and the higher alcohols. Spermaceti is mostly cetyl palmitate; beeswax contains myricyl palmitate; etc. (See also p. 160.) Esters of both inorganic and organic acids are named as alkyl salts of the acids, and sometimes called ethereal salts. Most of their reactions are analogous to those of inorganic salts formed from weak bases and weak acids, and which are readily hydrolyzed. There is, however, this difference, that the hydrolysis of the salts takes place quickly, while that of the esters is slow. In other words, the esters are ionized very slightly, while the salts are usu- ally more or less highly ionized. The rate at which esters are formed from the alcohol and the 126 INTRODUCTION TO ORGANIC CHEMISTRY acid, and the progress of their hydrolysis are both so slow that these processes have proved very valuable to theoretical chemistry . Their quantitative study has given information as to the influence of different conditions on the velocity of reactions: such as the effect of mass or molecular concentration, of temperature, and of ionic concentration (influence of acids and bases on hydrolysis). In the esters of organic acids two carbon atoms are united by oxygen. We find a similar linkage in the ethers and in the acid anhydrides. In the ethers two alkyl groups are linked, in the anhydrides two acyl groups. In the esters the two groups held together by oxygen are an alkyl and an acyl group, and we find in comparing the reactions of these three classes of compounds that the esters are in some respects intermediate between the ethers and the anhydrides. CHAPTER X AMINES AND AMIDES. NITRO -COMPOUNDS In several reactions which we have studied, ammonia has been represented as acting in such a. way as to produce compounds containing the group NH 2 . When this group is united to an alkyl radical, as in CH 3 .NH 2 , the compound is called an amine; when combined with an acyl radical, as in CH 3 .CO.NH 2 , an amide. The group NH 2 itself receives a correspondingly different name in the two classes of compounds, being termed the amino group in amines, and the amido group in amides. Both amines and the amides may be regarded as substituted ammonias, and their behavior, especially that of the amines, abundantly justifies this view. There are, also, related compounds in which two or all three hydrogen atoms of the ammonia molecule are replaced by alkyl or acyl radicals; and the three classes of substituted ammonias are distinguished by the names of primary, secondary, and tertiary, according as one, two, or three hydrogen atoms have been replaced. The Amines The amines show their relationship to ammonia by combining directly and additively with acids to form salts which are like the ammonium salts, and from which the amines are liberated by alkalies, just as ammonia is from ammonium salts. Formation. i. By the action of ammonia in alcoholic solution on alkyl halides. This reaction does not take place readily, requiring a temperature which can be attained with these volatile 127 128 INTRODUCTION TO ORGANIC CHEMISTRY substances only by heating them in sealed tubes. The product is a mixture of the three classes of amines together with quaternary compounds which are completely substituted ammonium halides. The reactions for the methyl compounds are: *NH 3 + CH 3 I = CH3NH 2 .HI CH 3 NH 2 .HI + GH 3 I = (CH 3 ) 2 NH.HI + HI (CH 3 ) 2 NH.HI + CH 3 I = (CH 3 )3N.HI + HI (CH 3 )3N.HI + CH 3 I = (CH 3 )4N.I + HI The formation of a single product cannot be assured by using definite proportions of ammonia and the alkyl halide, and the amounts of the four compounds which are produced depend on the nature of the alkyl group. The alkyl ammonium salts, with the exception of the tetra- amine salt, are all decomposed by caustic alkalies, yielding ammonia-like amines; in the cases taken for illustration, CH 3 .NH 2 , (CH 3 ) 2 NH, and (OH,),**. The mixture of amines, obtained by distillation of the salts with caustic alkali, is separated with some difficulty. Fractional distillation is not usually successful, and no entirely satisfactory general method can be given. When dealing with considerable quantities, the following procedure is often employed for the methyl and the ethyl amines: The greater part of the primary amine is obtained as chloride or oxalate by fractional crystalliza- tion of these salts. Then by the action of nitrous acid on the residue, the remaining amount of primary amine is decomposed into alcohol, water, and nitrogen, while the tertiary amine is unchanged; and the secondary amine is converted in to a nitroso- amine (p. 131) which is an oil and readily separated from the unaltered tertiary amine. Finally from the nitroso-amine the secondary amine in the form of its chloride is obtained pure by treatment with concentrated hydrochloric acid. Other Methods for Making the Amines. Among the other meth- AMINES AND AMIDES; NITRO-COMPOUNDS 1 29 ods by which primary amines can be formed, the following are the more important. 2. By treating an ester of isocyanic acid (p. 154) with potassium hydroxide: C 2 H 5 .N:C:0 + 2KOH = C 2 H 5 NH 2 + K 2 CO 3 . This method is of especial interest as it is the one by which the first amine was discovered (Wurtz, 1848). The resulting gaseous amine was believed to be ammonia until, by chance, it was found to be inflammable. 3. From amides (p. 1*37), by treatment with bromine and sodium hydroxide (or sodium hypobromite) ; Hofmanri's reaction.*/ The reaction, whose net result is the removal of CO from the acetamide, proceeds by the following steps: CH 3 .CO.NH 2 + Br 2 + NaOH = CH 3 .CO.NHBr + NaBr + H 2 O CH 3 .CO.NHBr + NaOH = CH 3 .N:C:O + NaBr + H 2 O CH 3 .N:C:O + 2 NaOH = CH 3 .NH 2 + Na 2 CO 3 . The last step in this method is the Wurtz reaction given above (2). This reaction furnishes a means of "building down" from higher to lower hydrocarbon derivatives. For instance, starting with propyl alcohol, ethyl alcohol may be made by the following steps: CH 3 .CH 2 .CH 2 .OH - CH 3 .CH 2 .CO.OH -> CH 3 .CH 2 .CO.NH 2 -> CH 3 .CH 2 .NH 2 -> CH 3 .CH 2 .OH. The last step is effected by decomposition of the amine nitrite (p. 131). (Compare this method of going from one compound to another with a less number of carbon atoms with the formation of hydrocarbons from the salts of the higher acids.) 4. By reduction of various nitrogen compounds nitro-com- pounds, alkyl cyanides, oximes, and hydrazones. From the alkyl cyanide (nitrile), for example, by "nascent" hydrogen: CH 3 .CN + 4H = CH 3 .CH 2 .NH 2 This is best effected by the action of sodium in alcoholic solution. 130 INTRODUCTION TO ORGANIC CHEMISTRY Since the formation of an alkyl cyanide adds an atom of carbon to the original compound, its conversion into an amine may be employed as a means of passing from one alcohol to the next higher in the series. For instance, CH 3 OH - CH 3 I > CH 3 .- CN-> CH 3 .CH 2 NH 2 - CH 3 .CH 2 OH. The last step is effected by the decomposition of the amine with nitrous acid. 5. From alkyl esters of inorganic acids by the action of am- monia. The reaction with the esters of the halogen acids (alkyl halides) has already been discussed. The nitric and sulphuric acid esters react in a similar manner. The action of ammonia on the esters of organic acids produces acid amides and alcohol. In spite of the numerous methods for forming amines, there is no way by which the pure substances may be easily prepared in any quantity. Properties. The primary, secondary, and tertiary methyl amines, and primary ethyl amine are gases at ordinary tempera- tures. The amines of higher molecular weight are liquid and fi- nally solid. The lower amines have odors unpleasantly resembling that of ammonia, and are freely soluble in water. The odor grows less and the solubility decreases with an increase in the number of the carbon atoms, and the highest amines are odorless and insoluble. They are all lighter than water. The solutions of the lower amines are strongly alkaline, and like that of ammonia probably contain the unstable hydroxides of the alkyl ammoniums. The ionization of these hydroxides is shown by their alkaline reac- tion, by the precipitation of hydroxides of metals from their salt solutions, and by the readiness with which they form ammonium- like salts. Their electrical conductivity indicates that the lower amine hydroxides are more highly dissociated than ammonium hydroxide, the bacisity being least in the tertiary, and greatest in the secondary amines (cf. p. 410). The halide salts of amines are soluble in alcohol and may be thus separated from ammonium halides which are insoluble. Like ammonium chloride, however, the amine chlorides form dou- AMINES AND AMIDES; NITROCOMPOUNDS 131 ble salts with platinum. chloride, which are sparingly soluble in alcohol. Methyl and ethyl amines differ from ammonia most markedly by their inflammability; and their hydroxides, unlike solutions of ammonia, dissolve aluminium hydroxide. Reactions. i. On oxidation of the amines, the alkyl groups are split off and converted into the corresponding aldehydes or acids. The other reactions of the amines differ with the number of alkyl groups they contain. The tertiary amines are rather indif- ferent to reagents, while the primary amines are more readily acted on than the secondary. 2. An important reaction which serves to distinguish the three classes is that with nitrous acid. A primary amine in acid solu- tion, when warmed with sodium nitrite, decomposes with the pro- duction of nitrogen, alcohol, and water: C 2 H 5 .NH 2 -h HNO 2 = N 2 + C 2 H 6 OH + H 2 O We may suppose that the nitrite of the amine, C 2 H 5 NH 2 .HNO 2 , is first formed and then decomposes like ammonium nitrite, where, however, as no alkyl group is present, nitrogen and water, instead of alcohol and water, are formed: NH 4 NO 2 = N 2 -f HOH -f H 2 O On secondary amines, nitrous acid acts less vigorously, and gives insoluble nitroso-amines, compounds in which the fiydrogen of the amine is replaced by the nitroso-group NO: (C 2 H 5 ) 2 :NH + HONO = (C 2 H 5 ) 2 :N.N:O + H 2 O When a nitroso-amine is treated with phenol and concentrated sulphuric acid, it gives a dark green solution which becomes red when diluted with water, and with an excess of alkali assumes an intense blue or green. This reaction (Liebermann's) serves for the detection of nitroso-amines and hence of secondary amines. On tertiary amines, nitrous acid hardly acts at all, and if action 132 INTRODUCTION TO ORGANIC CHEMISTRY occurs it is usually with the production of oxidation products and oxides of nitrogen. Since the secondary amines can be recovered from their nitroso- compounds by means of concentrated hydrochloric acid, the reac- tion gives a means for obtaining them from mixtures with the other two: (C 2 H 5 )2:N.N:O + 2HC1 = (C 2 H 5 ) 2 :NH.HC1 + NOC1 3. Primary amines give a characteristic reaction with chloro- form and caustic alkali. When warmed with chloroform and an alcoholic solution of potassium hydroxide, an isocyanide (formerly called carbylamine) is formed which is recognized by its charac- teristic and unendurable odor (carbylamine reaction): C 2 H 5 .NH 2 + CHC1 3 + 3KOH = C 2 H 6 .NC + 3KC1 + 3 H 2 O. Ethyl isocyanide 4. With both primary and secondary amines, acetyl chloride reacts at once without warming, forming compounds by the with- drawal of hydrogen chloride. With tertiary amines no reaction occurs. With alkyl halides, primary amines combine additively, forming the halide salt of the secondary amine. Secondary amines, in like manner, give the tertiary; and the tertiary, the quaternary amine salt. Some Individual Amines. All three of the methyl amines occur in herring brine, the tertiary amine in the largest proportion. They are all gases. The primary amine has an odor very like that of ammonia, but with a fishy suggestion. In the secondary and tertiary amines the fishy character of the odor becomes very pro- nounced. Monomethyl amine also occurs in Mercurialis perennis, and is one of the products of the destructive distillation of wood, bones, and other natural substances. Trimethyl amine is found in a number of plants, and can be obtained from wine by dis- tilling with caustic alkali. Commercial "trimethyl amine," obtained as a product of the dry distillation of residues left after AMINES AND AMIDES; NITRO-COMPOUNDS 133 making alcohol from beet-root molasses, is chiefly dimethyl amine (50 per cent.) with monomethyl and several higher amines, and only about 5 per cent, of the trimethyl amine. It is used as a source of methyl chloride and ammonia: (CH 3 ) 3 N + 4HC1 = 3CH 3 C1 + NH 4 C1 The best method for the laboratory preparation of trimethyl amine is by the distillation of tetramethyl amine hydroxide (p. 135). It is curious that trimethyl amine, which has a most offensive odor when diluted with other gases, is almost indistin- guishable from ammonia when concentrated,, Hexamethylene tetramine, CeH^N^ formed by the action of ammonia on formaldehyde (p. 84), is a weakly basic crystalline substance which under the name " urotropin," and in the form of the ethyl bromide. " bromalin," and of the salicylate, " sal- formin," has found some use in medicine. When heated with acids, it breaks up into formaldehyde and ammonia, some methyl amine being formed at the same time. Its constitution is unknown. Vinyl amine, either CH 2 :CH.NH 2 or yNH, is often cited CH/ as an unsaturated amine; but as it does not decolorize potassium permanganate as an unsaturated compound should, the second, cyclic formula, is the more probable one. The amine is known only in its strongly alkaline (hydroxide) aqueous solution and in its salts. It is made from bromethyl amine, CH 2 Br.CH 2 NH 2 , by means of moist silver oxide or potassium hydroxide. It com- bines with sulphurous acid to form taurine, CH 2 (SO 3 H).CH2NH 2 , which in combination with cholic acid is the chief constituent of bile. /CH:CH 2 Neurine, (CH 3 ) 3 N\ is a mixed quaternary amine X OH hydroxide which contains the vinyl radical. It has been synthe- sized, and is a substance of physiological importance, being 134 INTRODUCTION TO ORGANIC CHEMISTRY formed in the putrefaction of meat and in other fermentative proc- esses. It is very poisonous, belonging to the class of basic com- pounds formed in the decay of animal substances which are known as ptomaines, many of which are also poisonous. Neurine is a strong base and gives well-characterized salts. X CH 2 .CH 2 OH Choline, (CH 3 ) 3 N^ , ethylol-trimethyl-ammo- nium hydroxide, is a mixed quaternary base in which hydroxyl has been substituted in the ethyl group. The constitution of choline as represented in the formula has been established by its synthetical formation. It is obtained as one of the products of the hydrolysis of compounds called lecithins (Xejo0os, egg-yolk) which are found in all animal and vegetable tissues. Lecithins are complex compounds which may be regarded as mixed glycerol esters of palmitic, stearic, or ole'ic, and phosphoric acids, combined with choline. The formula for stearin-lecithin, which occurs in egg-yolk, is CH 2 O.OC.Ci 7 H 35 CHO.OC.CnH 35 >^OH \O.CH 2 .CH 2 .^\ X OH When boiled with barium hydroxide, barium stearate, (Ci 7 H 3 5- CO.O) 2 Ba, is precipitated, choline is set free, and the barium salt of glycero-phosphoric acid, CH 2 OH.CHOH.CH 2 .OPO(O 2 Ba), is formed. The importance of the lecithins in the functions of life is evi- dent from their universal occurrence in the tissues and especially in the nervous tissue; and from the fact that they form a constant constituent of milk. The lecithins are wax-like, hygroscopic substances, which swell AMINES AND AMIDES J NITRO-COMPOUNDS 135 up in water to gelatinous masses. They are soluble in alcohol, ether and chloroform, and crystallize with difficulty. Cephalin, closely related to lecithin and probably as gener- ally present in the tissues, is a derivative of amino ethyl alcohol as lecithin is of choline. Tetraalkylammonium Hydroxides. The quaternary halides are obtained by the direct union of a tertiary amine and the alkyl halide, and therefore appear in the mixture of amine salts formed by the reaction of ammonia on alkyl halides. It has been already stated that the tetraalkyl amines cannot be set free from their salts, like other amines, by caustic alkalies. When, however, solutions of the halide salts are digested with silver oxide, silver halide is formed and the solution becomes strongly alkaline. By evaporation in a vacuum, a white crystalline mass is obtained which is believed to be the hydroxide of the amine: (CH 3 ) 4 NI + AgOH = (CH 3 ) 4 NOH + Agl The tetraalkyi ammonium hydroxides are very strong bases, resembling the caustic alkalies in their behavior. For this reason the caustic alkalies do not react with their salts in aqueous solu- tion; such a reaction would be like one between sodium hydroxide and potassium chloride with the formation of potassium hydrox- ide. The reaction with silver hydroxide is in consequence of the insolubility of silver iodide. Similarly, the hydroxides may be obtained from the chlorides by using potassium hydroxide in alcoholic solution, since potassium chloride is insoluble in alcohol. These substituted ammonium hydroxides in solution absorb carbon dioxide from the air with the formation of carbonates, corrode the flesh, and saponify fats. When heated, they decom- pose with the formation of tertiary amines. Tetramethyl ammonium hydroxide, for example, gives trimethyl amine and alcohol: (CH 3 ) 4 NOH = (CH 3 ) 3 N + CH 3 OH but the homologous compounds give an olefine and water: (C 2 H 6 )4NOH = (C 2 H 5 ) 3 N + C 2 H 4 + H 2 O 136 INTRODUCTION TO ORGANIC CHEMISTRY AMINES Methyl PRIMARY Melting Boiling Point Point -6 SECONDARY Boiling Point 7 TERTIARY Boiling Point 1 S Ethyl + 16.2 / *6 3O OO Propyl Propyl (iso) Butyl Butyl (iso) Butyl (sec.) 49 32 76 66 63 *J W 98 84 1 60 136 yvj 156 215 187 Butyl (tert.) 46 Amyl (iso) Hexyl Dodecyl Tridecyl Heptadecyl 95 129 27 248 27 265 49 335-340 187 235 260 Phosphines and Arsines Alkyl derivatives of phosphine, PH 3 , and of arsine, AsH 3 , are known which are analogous to the amines. All of the classes of the amines are represented in the phosphines. The primary, secondary, and tertiary phosphines are weakly basic, but the alkylphosphonium hydroxides (e.g., (CH 3 ) 4 POH) are strong bases. Primary and secondary arsines in their chlorine and oxygen derivatives, such as CH 3 AsCl2, (CH 3 ) 2 AsCl, and (CH 3 )2As.O.As(CH 3 )2 have been long known, and more recently the arsines themselves have been prepared and investigated. (CH 3 )AsH 2 boils at 2, (CH 3 ) 2 AsH boils at 36 and is spontane- ously inflammable. The tertiary arsines such as (CH 3 ) 3 As have no basic properties, but the quaternary arsine hydroxide, (CH 3 ) 4 AsOH, forms salts like the corresponding phosphorus and nitrogen compounds. We notice here a gradation in the behavior of amines, phosphines, and arsines which tallies with that which appears in comparing the other compounds of nitrogen, phosphorus, and arsenic. AMINES AND AMIDES; NITRO-COMPOUNDS 137 Cacodyl Oxide, (CH 3 )2As.O.As(CH 3 ) 2 , is a liquid of frightful odor, which is formed by distilling arsenious oxide with an acetate: As 2 O 3 + 4CH 3 CO.OK = (CH 3 ) 2 As.O.As(CH 3 ) 2 + 2 K 2 CO 3 + 2CO 2 This substance reacts with hydrochloric acid to form cacodyl chloride, (CH 3 ) 2 AsCl; and from this, by the action of zinc, free cacodyl, (CH 3 ) 2 As.As(CH 3 ) 2 , is produced, as a spontaneously in- flammable liquid. The cacodyl radical, (CH 3 ) 2 As, enters into many combinations, and is readily transferred by simple reactions from one compound to another. Cacodyl and its compounds are of great historical interest in the theory of organic radicals through their investiga- tion by Bunsen (1837-1843). The compounds of cacodyl have very repulsive odors and are poisonous. The Amides The amides may be denned as ammonias in which hydrogen is replaced by acyl groups, or as acids whose hydroxyl is replaced by the NH 2 group. As in the case of amines, we have primary, secondary, and ter- tiary amides, but quaternary amides, or compounds of them, are not known. Formation. Primary amides can be made: i. From the am- monium salts of the acids by the removal of the elements of water through heating: CH 3 . CO.ONH 4 * CH 3 .CO.NH 2 + K) Acetamide But since the ammonium salts of the fatty acids dissociate to a considerable degree into the acids and ammonia, when heated under ordinary pressure, this reaction is usually carried out at a high temperature (2oo-25o) in sealed tubes. It is a reversible reaction and hence only a partial conversion into amide occurs 138 INTRODUCTION TO ORGANIC CHEMISTRY under the above conditions some 75 per cent, of the theoretical amount is obtained. A more convenient way which has been used for making aceta- mide, in which the use of sealed tubes is avoided, is by boiling dry ammonium acetate with rather more than its weight of glacial acetic acid for several hours with a reflux condenser. The water is thus removed, and the acetic acid on the principal of mass action inhibits the dissociation of the salt into acid and ammonia. 2. From esters, by the action of ammonia: CH 3 .CO.OC 2 H 6 + NH 3 = CH 3 .CO.NH 2 + C 2 H 5 OH With esters which are quite soluble in water this reaction goes easily. The alcohol and water are readily removed by distilla- tion. 3. From acid chlorides or anhydrides: CH 3 .CO.C1 + 2 NH 3 = CH 3 :CO.NH 2 + NH 4 C1 (CH 3 .CO) 2 O + 2NH 3 = 2 CH 3 .CO.NH 2 + H 2 O The reaction with acid chlorides is analogous to that for making amines from alkyl chlorides, but takes place much more easily in the case of acetyl chloride, at room temperature. The differ- ence is due to the presence of an acid group (acyl) instead of a basic group (alkyl). For the same reason, the reaction of ammonia with acid anhydrides is readily effected, while the anal- ogous reaction for the formation of an amine from ether and ammonia does not take place at all. 4. From nitriles (alkyl cyanides) by partial hydrolysis. This is accomplished by dissolving the nitrile in concentrated sulphuric acid or by treatment with concentrated hydrochloric acid; also by means of hydrogen peroxide in alkaline solution: CH 3 CN + H 2 O = CH 3 CO.NH 2 C 5 HnCN + 2H 2 O 2 = C 5 H U CO.NH 2 + O 2 + H 2 O Secondary amides are formed by reaction between primary AMINES AND AMIDES; NITRO-COMPOUNDS 139 amides and acid anhydrides, the acid being formed at the same time: CH 3 .CO.NH 2 + (CH 3 .CO) 2 O = (CH 3 CO) 2 NH + CH 3 .CO.OH or by heating nitriles with organic acids: CH 3 .CN + CH 3 .CO.OH = (CH 3 .CO) 2 NH Tertiary amides can be made by heating nitriles with acid anhy- drides: CH 3 .CN + (CH 3 .CO) 2 = (CH 3 .CO) 3 N Neither of these classes of amides is of special importance. Properties. Formamide, HCO.NH 2 is a liquid. The other amides are crystalline solids. The amides of the lower acids are deliquescent and very soluble in water. They distil without de- composition at temperatures which are higher than the boiling points of the corresponding acids; formamide, however, suffering partial decomposition into ammonia and carbon monoxide. It may be noted that the boiling points of the amines are much lower than those of the hydroxyl compounds (alcohols) to which they bear the same relation as that of the amides to the acids. The amides usually have a disagreeable odor, which, however, is in most instances due to certain impurities. Acetamide, for example, when carefully purified, is odorless. Amides of highest molecular weight are almost insoluble in water, but they all dissolve in alcohol or ether. Reactions. Certain differences between amides and amines have been noted in respect to the reactions for their formation; and similar differences, also due to the presence of an acyl group instead of an alkyl group, are observed in the various reactions into which they enter. In the amides the basic and acidic proper- ties are balanced so that they are neutral substances, while the amines are strong bases. i. With strong acids amides form rather unstable salts, such as H 3 .CO.NH 2 HC1. 140 INTRODUCTION TO ORGANIC CHEMISTRY 2. On the other hand, the hydrogen atoms of the NH 2 group can be replaced by some metals. With mercuric oxide, for in- stance, the compound, (CH 3 .CO.NH) 2 Hg, is formed, whose alcoholic solution yields colorless crystals, melting at 195. 3. The most characteristic reaction of the amides, and that in which their difference from the amines is most striking, is their ready hydrolysis, by which the bond between the nitrogen and carbon is broken, with the formation of ammonia and the- cor- responding acid (or the ammonium salt) : CH 3 .CO.NH 2 + H 2 O = CH 3 .CO.OH + NH 3 This hydrolysis is a reversal of the first reaction given for their formation (p. 137), and occurs when they are heated with water alone, but more rapidly when an inorganic acid or alkali is present (cf. hydrolysis of esters, p. 124). Amines do not enter into an analogous reaction with water with the formation of ammonia and an alcohol ; but at high temperatures amides act on alcohols, giving either an ester and ammonia, or the acid and a primary amine: CH 3 .CO.NH 2 + CH 3 .OH = CH 3 .CO.OCH 3 -jr NH 3 CH 3 .CO.NH 2 + CH 3 .OH = CH 3 .CO.OH + CH 3 NH 2 4. By the action of phosphorus pentoxide, the elements of water are withdrawn from amides, with the production of nitriles, thus reversing the reaction by which they are formed from these compounds. 5. Like the primary amines, the amides are changed into the corresponding hydroxyl compounds (acids) by the action of nitrous acid: CH 3 .CO.NH 2 + HN0 2 = CH 3 .CO.OH + N 2 + H 2 O 6. The reaction of amides with bromine and caustic alkalies has already been given (p. 129). AMINES AND AMIDES; NITRO-COMPOUNDS 141 7. Amides are decomposed by concentrated nitric acid with evolution of nitrous oxide: CH 3 .CO.NH 2 + HNO 3 = CH 3 .CO.OH + H 2 O + N 2 O. In this reaction the nitrate of the amide, CH 3 .CO.NH 2 HNO 3 ,is first formed and its decomposition is like that of ammonium nitrate: NH 4 N0 3 = N 2 O + 2H 2 0. Structure of Amides. We have assumed, in discussing the amides, that the structure of their characteristic group is The only other arrangement possible would be / OH ~ The facility with which an amide is formed from an ammonium salt, and the easy exchange of the amido-group for the hydroxyl are in favor of the first formula. The second formula with its hydroxyl group calls for an alcoholic character which is not indi- cated by most of the behavior of the amide. In the compound which acetamide forms with mercury, however, there is reason for believing that the metal is linked to carbon by oxygen, so that this substance is probably derived from a compound with the second formula. Unfortunately this question cannot be settled, as in other cases, by studying chlorine replacement products formed by the action of phosphorus pentachloride, because these products, if formed at all, are very unstable, breaking down almost at once into nitriles. Since the first formula agrees with most of the facts, it is taken as representing the ordinary structure of amides. INTRODUCTION TO ORGANIC CHEMISTRY AMIDES Melting Boiling Point Point Formamide HCO.NH 2 -i 200-212 Acetamide CH 3 .CO.NH 2 83 222 Propionamide C 2 H 5 .CO.NH 2 79 213 Butyramide C 3 H 7 .CO.NH 2 115 216 Butyramide (iso) C 3 H 7 .CO.NH 2 128-129 216-220 Valeramide C 4 H 9 .CO.NH 2 u 4 -n6(?) Capronamide C 6 H U .CO.NH 2 100 255 Heptylamide C 6 Hi 3 .CO.NH 2 95 250-258 Caprylamide C 7 Hi 6 CO.NH 2 105-106 Pelargonamide C 8 Hi 7 .CO.NH 2 99 Capramide C 9 H 19 .CO.NH 2 98 Palmitamide Ci 6 H 3 i.CO.NH 2 106-107 Stearamide CnH 36 .CO.NH 2 109 Nitre-paraffins Hydrocarbons in which one or more hydrogen atoms have been replaced by the NO 2 group, with a direct linkage of nitrogen to carbon, are called nUro-compounds. In the benzene series of hydrocarbons, these compounds are of great importance, and are readily made by the action of nitric acid upon the hydrocarbons; but the nitre-paraffins are seldom formed, and then in small amount, when nitric acid is forced to act on the indifferent hydro- carbons. They are relatively unimportant and were not known until 1872. They are briefly described here because of their relation to the amines. Formation. The most important method for making the nitro- paraffins is by adding an alkyl iodide gradually to solid silver nitrite: CH 3 .CH 2 I + AgNO 2 = CH 3 .CH 2 .NO 2 + Agl Except in the case of the methyl compound, the distillate from this reaction contains two substances which are readily separated by redistillation, as their boiling points are widely different. Both AMINES AND AMIDES; NITRO-COMPOUNDS 143 of the ethyl derivatives have the percentage composition and the molecular weight indicated by the formula given above. The one with the lower boiling point is readily hydrolyzed with the for- mation of alcohol and nitrous acid; and by nascent hydrogen it is reduced to alcohol and ammonia or hydroxylamine (cf. p. 122). It is evidently ethyl nitrite or nitrous ester, with the formula CH 3 .CH 2 O.N:O. The isomeric, higher boiling compound, is not hydrolyzed, and on reduction gives an amine, CH 3 .CH2-NH 2 . We conclude from these facts that this is a true nitro-compound with the nitrogen directly united to carbon; while in the ester it is linked to carbon by oxygen. The structure of the nitro-compound is, therefore, CH 3 .CH 2 . // N^t Nitro-compounds are not produced from alkyl halides by the action of other nitrites, such as NaNO 2 or KNO 2 . Silver nitrite appears therefore to have a different constitution from other nitrites and to be Ag.NO 2 with some Ag.O.NO. Properties. The nitro-paraffms are liquids of pleasant odor, which distil without decomposition, and are almost insoluble in water. The lower ones are heavier than water, but the specific gravity grows less as the number of carbon atoms increases, that of nitrobutane being already lighter than water. The lower nitro-paraffins have acid characteristics, due to the strongly nega- tive nature of the NO 2 group. They dissolve in aqueous solutions of alkalies, and are precipitated from these solutions by acids. From an alcoholic solution of sodium hydroxide a sodium salt, CH 3 .CHNa.NO 2 is precipitated. These salts decompose explo- sively when heated. The most important reaction of the nitropar- afnns is that of their reduction to amines by "nascent" hydrogen. The introduction of more than one nitro group cannot usually be effected directly, and only a few of the more highly nitrated paraf- fins have been made. Dinitromethane, CH 2 (NO 2 ) 2 , and trinitro- methane, CH(NO 2 )3, " nitroform," are unstable oils, the latter ex- ploding violently when heated. Tetranitromethane, C (NO 2 ) 4 , how- ever, is a stable liquid that can be distilled without decomposition. CHAPTER XI CYANOGEN AND CYANOGEN COMPOUNDS The student has already learned, in inorganic chemistry, some- thing about cyanogen, and has become acquainted with certain cyanogen compounds, particularly with potassium cyanide, and potassium ferro and ferricyanides, which are used as reagents in analysis. In the first chapter of this book the formation of sodium cyanide, on heating a nitrogen-containing organic sub- stance with sodium, was given as a means for the detection of nitrogen. Nearly all nitrogenous organic substances react in this way with sodium or potassium, and on digestion of the soluble cyanide with a ferrous salt, the f errocyanide of sodium or potassium is formed. The chief sources of the cyanogen compounds are : 1. Potassium f errocyanide, which is made commercially by heating a mixture of crude potash (K 2 CO 3 ), scrap iron, and refuse animal substances, such as clippings of leather or horn, or dried blood, and treating the mass, after cooling, with water. Yellow crystals of the ferrocyanide are obtained from this solution. From the ferrocyanide, potassium cyanide, KCN, is obtained by heating it alone or with potassium carbonate. 2. Sodium cyanide, NaCN, is made in large quantities by pass- ing ammonia over sodium at 3oo-4oo, and decomposing the sodium amide, NaNH 2 , thus formed, by carbon at a red heat: 2 Na + 2NH 3 = 2NaNH 2 + H 2 NaNH 2 + C = NaCN -f- H 2 Sodium cyanide may also be successfully manufactured by a 144 CYANOGEN AND CYANOGEN COMPOUNDS 145 method recently described by J. E. Bucher 1 in which nitrogen reacts with a mixture of sodium carbonate and powdered coke at a red heat in the presence of finely divided iron as a catalyst: Na 2 C0 3 + 4C + N 2 (+ Fe) - 2 NaCN + 3 CO (+ Fe) Producer gas may be used to furnish the nitrogen, and in this case the carbon monoxide of the gas, under the catalyzing effect of the iron, yields a continuous supply of finely divided carbon: CO + C <= CO 2 + 38,080 calories Compounds containing cyanogen are also obtained by heating the carbides of calcium or barium in nitrogen. The calcium com- pound, CN.NCa, calcium cyanamide, " nitrolime," is manu- factured on a large scale from calcium carbide and nitrogen from liquid air. It slowly decomposes in the soil, producing ammonia: CN.NCa + 3H 2 O = 2NH 3 + CaCO 3 and is used, on this account, as a fertilizer, thus making atmos- pheric nitrogen available for plant life. With superheated steam all the nitrogen of cyanamide is converted into ammonia which is now prepared commercially in this way. Cyanamide on fusion with salts of alkalies and carbon yields the alkali cyanide: CN.NCa + C H- 2NaCl = NaCN + CaCl 2 Cyanogen (CN) 2 . The cyanogen radical, CN, can be trans- ferred from one compound to another like the halogen atoms; and like them it is incapable of independent existence, but when forced from combination unites with itself forming molecules of (CN) 2 , similar to the diatomic molecules of chlorine, etc. The evidence for this is its molecular weight as found from its density. Cyanogen is formed when ammonium oxalate is strongly heated with phosphorus pentoxide : CO.ONH 4 CN | - 4 H 2 = | or (CN) 2 CO.ONH 4 CN 1 Journal of Industrial and Engineering Chemistry, IX, 233 (1917). 146 INTRODUCTION TO ORGANIC CHEMISTRY This reaction, and the fact that an intermediate product, oxamide, CO.NH 2 | , can be made both from ammonium oxalate and from CO.NH 2 cyanogen, are evidence that cyanogen is the nitrile of oxalic acid, and from the known structure of oxalic acid (p. 178) we C=N N=C conclude that that of cyanogen is | and not | , which C=N N=C would be the other possible arrangement with tetrad carbon. Preparation. Cyanogen is prepared by heating mercuric cyanide: Hg(CN) 2 = (CN) 2 + Hg or more conveniently by slowly adding a solution of copper sul- phate to a warm solution of potassium cyanide. The cupric cyanide first formed decomposes readily into cuprous cyanide, CuCN, and cyanogen. Cyanogen is also a product of the electro- lysis of sodium cyanide. Properties. Cyanogen is a poisonous gas of characteristic pungent odor. It burns with a purple-fringed flame. It is somewhat soluble in water, but the solution is unstable. A brown solid separates, and the solution contains oxalate and carbonate of ammonia, hydrocyanic acid, and urea. A polymeric form of cyanogen of unknown molecular weight is produced in the form of a brown solid as a by-product in making cyanogen from mercuric cyanide; and in the electrolysis of potassiun cyanide all of the cyanogen is converted into this modification, which is called paracyanogen. At 860 this changes to cyanogen. Cyanogen is readily converted into oxamide (p. 180) when led nto hydrochloric acid containing 44 per cent, of hydrogen chlo- ride. On heating the oxamide with the concentrated acid, the hydrolysis to oxalic acid is quickly completed (Bucher). When led into solutions of potassium hydroxide, cyanogen forms com- pounds analogous to those given by chlorine or bromine, namely, potassium cyanide, KCN, and cyanate, KOCN. CYANOGEN AND CYANOGEN COMPOUNDS 147 Hydrocyanic acid, HCN, commonly known as prussic acid, occurs in all parts of a tree, Pangium edule, which is native in Java. The seed-kernels of this tree are a deadly poison, but by soaking in flowing water the hydrocyanic acid is removed, and they are then used by the Malays as food. A substance called amygdalin which occurs in the leaves of laurel and cherry, and in the kernels of peach-stones, in bitter almonds, and other sub- stances, when softened by water, usually undergoes a fermentation, one of whose products is prussic acid. Hydrocyanic acid is readily made by distilling potassium cyan- ide or potassium ferrocyanide with dilute sulphuric acid: 2K 4 Fe(CN) 6 + 3H 2 S0 4 = 6HCN + 3 K 2 SO 4 + FeK 2 Fe(CN) 6 Ferrous potassium ferro-cyanide (Concentrated sulphuric acid with the ferroeyanide yields no hydrocyanic acid, but carbon monoxide.) The distillate is a dilute solution of hydrocyanic acid. The anhydrous acid is obtained by drying the vapors from this reaction by means of calcium chloride and condensing them by a freezing mixture. Properties. The anhydrous acid is a volatile liquid, boiling at 26. It has the odor of bitter almonds, and burns with a violet flame. When unmixed with water the acid can be kept without change, but its solutions are unstable, depositing a brown sub- stance with the production of ammonium formate and other compounds. This decomposition is retarded by the presence of a very small amount of an inorganic acid. Hydrocyanic acid is a very weak acid, hardly reddening litmus paper. It does not decompose carbonates, but, on the contrary, is set free from its salts by carbonic acid; and, in consequence, potassium cyanide always smells of prussic acid when exposed to the air. Hydro- cyanic acid and the cyanides which contain the ion CN are very powerful and rapidly acting poisons. Complex ions containing cyanogen, like Fe(CN) 6 , in solutions of potassium ferro- and ferricyanides, are not poisonous. 148 INTRODUCTION TO ORGANIC CHEMISTRY Structure. Two structural formulas for hydrocyanic acid can be written: H-C=N, and H-N = C, or H-N=C. 1 'From the structure agreed on for cyanogen, N = C C = N, the first of these, H C = N, is indicated. Some reactions are better explained by this formula, some by the second, and some are equally well explained by either. The first formula is that of a nitrile of formic acid, and hydrocyanic acid can be hydrolyzed to formamide and to formate of ammonium, and the reverse reac- tions can also be carried out: HC ^N -f H 2 < HC< + H 2 + HC By nascent hydrogen hydrocyanic acid is converted into methyl amine: H-C=N + 4H = CH 3 .NH 2 As nitrogen readily changes its valence from three to five and from five to three, these reactions might be written with the second formula. When potassium cyanide acts on an alkyl halide, a nitrile is formed in which the carbon of the cyanogen group is certainly united to the CH 3 group: CH 3 I + KCN = CH 3 CN + KI But this again could be explained, through change of valence, by the other formula. Silver cyanide, however, with an alkyl halide, gives an isomeric compound whose . structure has been proved to be CH 3 .N = C, or CH 3 .N = C. The cyanogen group appears, therefore, in both arrangements, C = N and N = C or N = C. The former is that usually adopted as that of hydrocyanic acid, whose formula is therefore written, H C=N; while the isomeric form, H N = CorH N=C, is called isohydrocyanic acid; the group N = C or N = C being 1 In this formula, and others which will be discussed, carbon is represented as divalent or unsaturated, as it is in CO. CYANOGEN AND CYANOGEN COMPOUNDS 149 called the isocyanogen group. Both of the possible forms may be present together. The great difficulty in deciding this question is the absence of an alkyl group. When such a group, instead of hydrogen, is combined with cyanogen, the decision is easily made by finding whether, in reactions by which the molecule is broken up, the carbon or the nitrogen atom of the CN group remains attached to the alkyl. For the properties anfl uses of the salts of hydrocyanic acid, and of the ferro and ferricyanides of the metals the student is referred to his text-book on inorganic chemistry. Cyanogen chloride, CN.C1, is a very poisonous compound which is formed when chlorine is brought into a solution of hydrocyanic acid. It boils at 15.5, and is somewhat soluble in water. On keeping, it partly polymerizes to cyanuric chloride, C 3 N 3 Cl3. With ammonia it gives cyanamide, CN.NH 2 . With potassium hydroxide, potassium cyanate, CN.OK, is formed: CN.C1 + 2KOH = CN.OK + KC1 + H 2 O Cyanamide, CN.NH 2 , is a colorless, crystalline solid, melting at 40. It is readily soluble in water, alcohol, and ether. The hydrogen of its amido-group is replaceable by metals. Silver cyanamide, CN.NAg 2 , which, unlike most silver salts, is almost insoluble in ammonia, is precipitated from an ammoniacal solution of silver nitrate by cyanamide. The industrial manufacture of calcium cyanamide, CN.NCa,has already been referred to (p. 145). Cyanuric acid, (CNOH) 3 , is formed when cyanuric chloride is boiled with water, and is also one of the products obtained when urea, CO(NH) 2 , is heated: 3 CO(NH 2 ) 2 = (CNOH) 3 + 3 NH 3 It crystallizes from water, in which it is sparingly soluble, with two molecules of water of crystallization, and forms well characterized salts. Cyanic acid, (H O C=N, is made by heating anhydrous 150 INTRODUCTION TO ORGANIC CHEMISTRY cyanuric acid in a current of carbon dioxide, and condensing the gas which is formed in a receiver surrounded by a freezing mixture. It is a very volatile liquid, and unstable, polymerizing rapidly at o to cymelide, (HOCN) X , a solid of unknown molecular weight, which regenerates cyanic acid on heating. In aqueous solution, cyanic acid decomposes at temperatures above o into carbon dioxide and ammonia: HOCN + H 2 O = C0 2 + NH 3 Potassium cyanate, K O C =N, is formed by the reaction of cyanogen chloride and potassium hydroxide (p. 149); but is usually prepared by the oxidation of potassium cyanide through heating it with lead oxide, or by heating a mixture of potassium ferrocyanide and dichromate. The readiness with which potas- sium cyanide is oxidized to the cyanate explains its use as a reduc- ing agent in inorganic chemistry. The cyanate is extracted from the resulting mass by boiling with 80 per cent, alcohol, and is obtained on evaporation of the solvent as a white crystalline pow- der. It is very soluble in water, and is slowly hydrolyzed in solution into ammonium and potassium carbonates. When hydrochloric acid is added to its solution, the cyanic acid set free decomposes at once into carbon dioxide and ammonia. From the potassium cyanate other cyanates can be formed by dou- ble decomposition. The ammonium salt NH 4 OCN is of especial interest because of its ready transformation into urea (p. 231). Ammonium Cyanate may be prepared from sodium cyanide by leading carbon dioxide and ammonia in to its solution; the reaction being exactly similar to that of the ammonia-soda process, the radical CNO taking the place of chlorine in the sodium chloride (Bucher): NaOCN + NH 3 + CO 2 + H 2 O = NaHCO 3 + NH 4 OCN Esters of cyanic acid have not been isolated, the reactions which should give them yielding the polymeric cyanuric esters. CYANOGEN AND CYANOGEN COMPOUNDS These exist in two isomeric forms, in one of which the alkyl group is linked to the CN group by oxygen, and in the other is directly united to the nitrogen of the group. These relations are proved by the products of hydrolysis: one form of ester giving cyanuric acid and an alcohol, and the other producing primary amines and carbon dioxide: (CH 3 .OCN) 3 + 3H 2 O = 3CH 3 OH + (HOCN) 3 (CH 3 .NCO) 3 + 3 H 2 = 3 CH 3 NH 2 There thus appear to be at least two isomeric cyanuric acids one containing a hydroxyl group, called cyanuric acid; and an- other in which there is no hydroxyl group and where the hydrogen is united directly with nitrogen the isocyanuric acid. Two cyanic acids: normal, HOC = N and iso, HN = C = O, correspond to these. Both forms may be present together in some of the compounds. Fulminic Acid and Fulminates. When ethyl alcohol is added to a mixture of mercuric nitrate and nitric acid a rather violent reac- tion occurs, with danger of explosion unless precautions are taken. After the reaction is finished, and as the solution cools, white crystals are precipitated which have the composition Hg(CNO)2. A corresponding silver salt is formed under similar conditions. These salts, when dry, explode with great violence when heated or struck; and the mercury compound is the substance used in percussion and fulminating caps for firing gunpowder, dynamite and smokeless powders. The composition of these fulminates shows them to be salts of fulminic acid, which is a third isomer of cyanic acid. When sodium fulminate (formed by the action of sodium amalgam on the mercury salt) is treated with hydrochloric acid at o, an unstable crystalline compound is produced whose /H structure has been shown to be HO . N = C\ This substance is regarded as an addition product of fulminic and hydrochloric acids, and the formula of fulminic acid is inferred to be H O N = C, in which the carbon atom acts as a dyad. 152 INTRODUCTION TO ORGANIC CHEMISTRY Fulminic acid is too unstable to be isolated, though it probably can exist in vapor and in solution. When fulminates are treated with hydrochloric acid, a prussic acid odor is perceived, which is evidently due to traces of fulminic acid. The fulminates are nearly if not quite as poisonous as hydrocyanides. A special historical interest attaches to the fulminates, because of Liebig's demonstration in 1823 that the two different com- pounds, silver cyanate and silver fulminate had the same composi- tion. This was the first case discovered of two different sub- stances with the same composition; and it was to designate this phenomenon that Berzelius proposed the name isomerism. It is seen that it is not a simple matter to determine the struc- ture of the cyanogen compounds, and the task is complicated by an apparent mobility in the arrangement of the atoms, so that in some cases, at least, we must assume two forms to be present in the same compound, or to shift easily in the course of the reactions. The possible arrangements of HCNO are four: i. H O C = N; 2. H O N = C(orH O N = C); 3. H C = N = O; 4. H N = C = O. The generally accepted view is that the first represents cyanic acid, the fourth, isocyanic acid, and the second fulminic acid. Thiocyanic Acid and Thiocyanates. Sulphur combines directly with cyanides of the metals forming thiocyanates. For instance, when a solution of potassium cyanide is boiled with sulphur, the salt, K S C = N, is produced. The acid, H S C = N, is obtained in dilute solution by distilling this or the barium salt with sulphuric acid. The anhydrous acid is a very volatile liquid of sharp odor, which, like the cyanic acid, polymerizes very readily. In dilute solutions the acid is stable, but in strong solutions it decomposes into hydrocyanic acid and persulphocyanic acid, H 2 C 2 N2S 3 . The strength of thiocyanic acid approaches that of the halogen acids. Thiocyanates are converted into cyanides by melting them with zinc. The salts of thiocyanic acid are obtained as a by-product in the CYANOGEN AND CYANOGEN COMPOUNDS 153 coal gas industry, and are used as mordants. With the exception of the copper, mercury, and silver salts, the thiocyanates are sol- uble in water. Potassium and ammonium thiocyanates solutions are well-known reagents for ferric salts, giving a blood-red color even in very dilute solutions. Mercury thiocyanate, when hea'ted, decomposes with the production of an extraordinarily voluminous ash, and is used in making the "Pharaoh's serpents." The ammonium salt, when melted, is partly transformed into thio-urea, CS(NH 2 ) 2 . Esters of thiocyanic acid are obtained by the action of alkyl iodides on the thiocyanates: K-S-C = N + CH 3 I= CH 3 -S-C = N + KI These alkyl thiocyanates are converted into isothiocyanates, such as CH 3 N = C = S, by heating. Thus, distillation of allyl thiocyanate, CH 2 :CH.CH 2 S C = N, causes the change into CH 2 :CH.CH 2 -N = C = S. This compound, allyl iso- thiocyanate, was first obtained as an oil from mustard seeds where it is present as a glucoside, and the name of mustard oils is given to the group of isothiocyanic acid esters on this account. ALKYL CYANIDES AND ISOCYANIDES In the discussion of the structure of hydrocyanic acid it was stated that the action of silver cyanide on an alkyl halide gave a different compound from that obtained when potassium cyanide was used. The two compounds are isomeric, that produced by potassium cyanide probably having the structure of the cyanide or nitrile, CH 3 C = N, while the other is an isocyanide with the formula, CH 3 .N = C or CH 3 .N = C. Alkyl Cyanides or Nitriles. These compounds are esters of hydrocyanic acid, as the first name indicates, but their ready hydrolysis into ammonium salts or acids is their most interesting characteristic, and hence they are more often designated as nitriles. Thus, CH 3 .CN is methyl cyanide or acetonitrile. They are formed i. by the withdrawal of the elements of water from the 154 INTRODUCTION TO ORGANIC CHEMISTRY ammonium salts of acids, the acid amide being an intermediate product (p. 100); 2. By the action of potassium cyanide on alkyl halides (p. 35); or by distilling the potassium salt of an alkyl sulphuric acid with potassium cyanide: C 2 H 6 .KSO 4 + KCN = C 2 H 5 .CN + K 2 SO 4 In these reactions small amounts of the isocyanide (or isonitrile} are formed. There are also other less important methods by which nitriles can be formed. The nitriles show the gradation in physical properties which is familiar in all homologous series of compounds. The lower members are liquids of not unpleasant odor, and are soluble in water. The hydrolysis of the nitriles into acid amides and ammonium salts, and their conversion into primary amines by nascent hydro- gen, have already been sufficiently discussed. Alkyl isocyanides or isonitriles are formed, as has been stated, by treatment of an alkly halide with silver cyanide. Some nitrile is produced at the same time. Another reaction for making the isocyanides is carried out by heating a primary amine with an alcoholic solution of chloroform and potassium hydroxide: C 2 H 5 .NH 2 + CHC1 3 + 3KOH = C 2 H 6 .NC + 3KC1 Since in this reaction, a carbon atom replaces the two hydrogen atoms of the amino-group, the compounds are often given a third name, carbylamines, which indicates this relation. This reaction is employed as a test for primary amines (p. 132). The isonitriles are volatile liquids of an almost unbearable odor, lighter than water and soluble in it. They are readily decomposed by water in the presence of inorganic acids into amines and formic acid: C 2 H 5 .NC + 2H 2 O = C 2 H 5 .NH 2 -f H.CO.OH Both the formation of these compounds and the mode of their CYANOGEN AND CYANOGEN COMPOUNDS 1540 hydrolysis justify the name of carbylamine, and are evidence for the structure which is assigned to them: C 2 H 5 .N = C or C 2 H 5 .N = C Alkyl Isocyanates such as C 2 H 5 NCO, are volatile liquids of penetrating and very disagreeable odor. They are formed by the action of silver cyanate on alkyl halides, and by oxidation of isonitriles with mercuric oxide. When heated with alkalies, they give primary amines and alkali carbonate (p. 129). With ammonia or amines they produce alkyl-substituted ureas: /NH.C 2 H 5 Hence, when boiled with water, they yield symmetrical dialkyl ureas, the amine formed at first reacting with excess of ester: C 2 H 5 .NCO + H 2 O = CO 2 + C 2 H 5 .NH 2 and C 2 H 5 .NCO + C 2 H 5 .NH 2 = CO(NH.C 2 H 5 ) 2 CHAPTER XII ALCOHOLS WITH MORE THAN ONE HYDROXYL GROUP Besides the alcohols with one hydroxyl group, which have been studied, there are many compounds known which are shown by their reactions to contain two or more hydroxyl groups. These polyhydroxyl compounds show the characteristic alcohol reactions and hence belong to the general group of alcohols. The simplest formula which can be written for a dihydroxyl derivative of a paraffin is CH 2 (OH) 2 . Such a compound, however, cannot be made, nor can other similar compounds, such as CH 3 .CH(OH) 2 , be obtained. Methods which should give these compounds in which two hydroxyl groups are united to a single carbon atom, such as: CH 3 .CHI 2 '+ 2 AgOH = CH 3 .CH(OH) 2 + 2AgI always result, as we have seen (p. H3a), in the formation of the aldehyde group C = O.H, instead of the group CH.(OH) 2 . The Glycols. The simplest polyhydroxyl derivative is, there- fore, CH 2 OH.CH 2 OH. This is called glycol, ethylene glycol, or ethylene alcohol. It is the first member of a series of "glycols" which have the general formula C n H 2n (OH) 2 . The isomeric higher glycols are distinguished as a, /3, 7, 5, etc., glycols accord- ing as the hydroxyl groups are united to adjacent carbon atoms or to those farther apart. Thus, of the butylene glycols, CH 3 .- CH 2 .CHOH.CH 2 OH is the a-compound, CH 3 .CHOH.CH 2 .- CH 2 OH, the ft and CH 2 OH.CH 2 .CH 2 .CH 2 OH, the 7 glycol. (This notation is also employed to designate the positions of other substituting radicals or atoms in hydrocarbon derivatives.) 155 INTRODUCTION TO ORGANIC CHEMISTRY 156 Since in the higher glycols derived from the normal hydro- carbons the alcohol groups may both be primary, both secondary, or one primary and one secondary, and in isomeric derivatives we may have both primary, both secondary, or both tertiary, or any combination of the three, the number of glycols which are theo- retically possible is exceedingly great far greater than the number of possible hydrocarbons. Very few of them, however, have been made. Preparation. i. The glycols may be made by replacing the halogen in paraffin dihalides with hydroxyl, as in the making of monohydroxyl alcohols; but the action of potassium hydroxide is usually so vigorous that unsaturated monohalide compounds or acetylene hydrocarbons are formed: (CH 2 C1.CH 2 C1 + 2KOH = CH 2 OH.CH 2 OH + 2 KC1) CH 2 C1.CH 2 C1 + KOH = CHC1:CH 2 + KC1 + H 2 O, and CHC1 : CH 2 + KOH = CHi CH + KC1 + H 2 O The reaction succeeds, however, when sodium carbonate is used^ or when organic acid radicals are first substituted for the halogen, and these compounds are hydrolyzed. 2. Another method of formation is by first forming a compound containing one hy^ droxyl group and chlorine, a chlorhydin, through the union of an ethylene hydrocarbon and hypochlorous acid: CH 2 :CH 2 + HOC1 = CH 2 C1.CH 2 OH Glycol chlorhydrin and then replacing the chlorine with hydroxyl by means of moist silver oxide: CH 2 C1.CH 2 OH + AgOH = CH 2 OH.CH 2 OH + AgCl 3. The glycols are also formed by the oxidation of olefines by means of an alkaline solution of potassium permanganate or by hydrogen dioxide: CH 2 :CH 2 + O + H 2 O = CH 2 OH.CH 2 OH I$7 POLYHYDROXYL ALCOHOLS 4. Diamines are converted into glycols by nitrous acid (cf. p. 131), CH 2 .NH 2 .HNO 2 CH 2 OH CH 2 .NH 2 .HNO 2 CH 2 OH Properties. Ethylene glycol is typical of all the glycols, and will be alone described. It is an oily, sweetish liquid, which like most hydroxyl compounds is soluble in water and only slightly soluble in ether. It boils at 195. Its chemical reactions are those of a double primary alcohol. Thus its hydroxyl hydrogen is replaceable by sodium, and its hydroxyl groups by halogens by means of phosphorus halides or halogen acids; it forms single and double esters with inorganic and organic acids, and its alcohol groups are oxidized to aldehyde and acid groups, with the final production of oxalic acid before breaking down into carbon dioxide and water. When the higher glycols contain secondary or tertiary alcohol groups, their behavior on oxidation is in part that of secondary or tertiary alcohols. Alkylene Oxides. Closely related to the glycols are the alkyl- ene oxides, which may be regarded as glycols from which the elements of water have been subtracted. This cannot, however, be directly accomplished in most cases, but the compounds may be made by the action of potassium hydroxide on the correspond- ing chlorhydrines: CH,. CH 2 C1.CH 2 OH + KOH = j >O + KC1 + H 2 O CH/ Alcohols with More than Two Hydroxyl Groups Derivatives of the paraffins containing four, five, six, and seven hydroxyl groups are known. Certain hexahydroxyl alcohols occur in the sap of various trees; mannitol or manna, CH 2 OH(CHOH) 4 CH 2 OH, being obtained from the mountain ash. As the number of hydroxyl groups increases, the compounds are sweeter and become more like sugars, to which they are closely INTRODUCTION TO ORGANIC CHEMISTRY 158 related; and the tendency to decompose when heated, with the loss of the elements of water, becomes greater. Among the poly- hydroxyl alcohols the only one of practical importance is that commonly known as glycerine or glycerol Glycerol, CH 2 OH.CHOH.CH 2 OH, or "glycerine," is the sim- plest possible trihydroxyl alcohol. It may be formed by methods like those used for the formation of glycol; and is produced in large quantities from fats (which are glyceryl esters of certain of the higher paraffin or fatty acids) by replacement of the acid radi- cals with hydroxyl. This is effected by alkali hydroxides with the production of soap (p. 109) and glycerol, or by the action of superheated steam, when the products are glycerol and the fatty acids. The watery liquid containing the glycerine is purified by filtration through animal charcoal and the water removed by evapo- ration in a partial vacuum. The product, which is still impure, is refined for medical purposes and for making nitroglycerine, by distillation in a current of superheated steam, and treatment again with animal charcoal. It is finally concentrated in a vacuum. Glycerine is always formed in small amounts in the alcoholic fermentation of sugars, so that it is present in all undistilled alcoholic beverages. Glycerol is a syrupy liquid, colorless and odorless, heavier than water (specific gravity 1.265 at 15), miscible with water or alco- hol in all proportions, but insoluble in ether and chloroform. It boils at 290 with very slight decomposition. It dissolves many inorganic and organic substances. It is very hygroscopic, and this property together with its non-volatility leads to an extensive use in non-drying Inks, such as copying inks and those employed on typewriter ribbons and the pads for rubber stamps. Other uses are in pharmacy, in the preparation of tobacco, in confec- tionery, preserves, and cosmetics; but the largest amount is employed in making "nitroglycerine." The formula given to glycerol is the only one that can explain the methods of its formation and the products which are obtained 159 POLYHYDROXYL ALCOHOLS from it in various reactions. Its oxidation products show the presence of two primary and one secondary alcohol groups. On heating glycerol with dehydrating substances, (P 2 Os) acrolein is formed (p. 86). Glycerol can undergo fermentation, and yields different products according to the nature of the ferment. One bacillus converts it chiefly into butyl alcohol, which is often pre- pared in this way. Glycerol, like all alcohols, forms esters with acids, and since it contains three hydroxyl groups, it can form three different esters with a monobasic acid, according as one, two, or all three of the hydroxyls are replaced by acid radicals. The most important of its esters are those that occur in the natural fats and oils (p. 160) and nitroglycerine. Nitroglycerine is the common name of the trinitrate of glycerol, CH 2 (O.NO 2 ).CH(O.NO 2 ).CH 2 (O.NO 2 ), and is not a nitro-com- pound as the name implies. It is made by adding glycerine slowly to a well-cooled mixture of concentrated nitric and sulphuric acids, so long as it dissolves. On pouring the solution thus obtained into a large quantity of water, the nitroglycerine sepa- rates, as a heavy oil. It is thoroughly washed with a solution of sodium carbonate to remove all acid, and then with water, and finally dried by chloride of calcium. Pure nitroglycerine is color- less and odorless. Its specific gravity is 1.6 at 15. It is almost insoluble in water but dissolves somewhat in alcohol and mixes in every proportion with ether, chloroform and benzene. A com- parison of its solubility with that of glycerol is a good illustration of the influence of hydroxyl groups on this property. Nitrogly- cerine is poisonous, but is a valuable remedy in heart disease. It is saponified by caustic alkalies, but the reaction is accompanied by the production of some oxidation products of glycerol and reduc- tion of the alkali nitrate to nitrite. Pure nitroglycerine keeps without change, but if impure, it slowly decomposes. Hence it is important to use pure glycerol in its manufacture, and to remove from it all traces of acid. Nitroglycerine is best known as a pow- INTRODUCTION TO ORGANIC CHEMISTRY l6o erful explosive. It is used largely in the form of "dynamite," which is nitroglycerine absorbed in infusorial earth or some other substances. By this device it is brought into solid form which can be conveniently used. The most powerful dynamite contains 75 per cent, of nitroglycerine. It is also converted into a jelly- like solid by dissolving in it a small quantity (7-8 per cent.) of gun-cotton (p. 223), and in this form is known as " explosive gel- atine." Small amounts of nitroglycerine may be kindled without exploding, and considerable quantities of dynamite burn quietly. Dynamite is not very sensitive to shocks, and is transported with little danger, but nitroglycerin is readily exploded by shock. All forms are exploded by a detonating substance such as mercury fulminate (p. 151), which is usually "fired" by electricity. Natural Oils and Fats. Besides the petroleum oils, whose origin is still in question, and ozokerite or earth wax, there are many oils and fats and a few waxes that are obtained from plants and ani- mals. Two classes of oils are recognized : the fixed or fatty oils and the essential oils. The essential oils are practically all of vegetable origin, and are characterized by strong and individual odors. They can usually be distilled without decomposition and evaporate from paper without leaving a permanent oily stain. Most of them are not sensibly soluble in water but impart to it their characteristic odors. Their composition is very varied, including hydrocarbons such as cymene, pinene (in turpentine oil), camphene, and limonene; alcohols benzyl alcohol in balsam of Peru and menthol in peppermint oil; phenols thymol in oil of thyme; esters of acetic, butyric, valeric, benzoic, salicylic, and and other acids; many aldehydes such as benzaldehyde in oil of bitter almonds, cinnamic aldehyde in cinnamon oil) and vanillin (p. 347) in vanilla; ke tones such as camphor; and others. The fixed oils and fats are insoluble in water, leave a permanent oily stain on paper, and decompose when heated, giving acrolein (p. 86) as one of the decomposition products. They are found in both plants and animals, and most commonly consist of tri- l6oa POLYHYDROXYL ALCOHOLS glyceryl esters of organic acids. The esters most frequently present are the glycerides of palmitic, stearic, and oleic acids, known as palmitin, stearin, and ole'in. The first two of these esters are solids and ole'in a liquid; and when these three are the principal constituents as is the case with many of the animal fats especially, their proportions determine the con- sistency of the fat. Thus, olive oil contains about 75 per cent, of ole'in; lard which melts at 35-38, about 60 per cent.; and tallow, melting at 47-48, about 25 per cent. Among the con- stituents of some of the fats and oils are also glyceryl esters of a number of other fatty acids, such as butyric, caproic, caprylic, lauric, and myristic of the saturated series; cro tonic, physetoleic, and ricilinoleic (hydroxyoleic) of the oleic series; linolic, an acid with two double bonds; linolenic and isolinolenic (p. 112), acids with three double bonds. Butter fat differs from all other fats and oils by containing about 7.7 per cent, of triglyceryl butyratein addition to stearin, palmitin, ole'in, and -traces of other glyceryl esters. Oils like linseed oil, that consist chiefly of glycerides of the highly unsaturated acids, linolic,' linolenic, and isolinolenic, are called "drying" oils because they absorb oxygen from the air and be- come dry and hard. Such oils, on this account, are extensively used in paints and varnishes. Linseed oil dries more rapidly if it has been "boiled," a process in which the oil is heated to about 150 with certain oxides or salts such as litharge or borate of manganese that are called "driers" and probably act as contact agents. Much heat is developed in the drying of these oils and occasions the danger of spontaneous combustion in the oily rags and waste used by painters. Some oils, such as cotton seed oil, that con tain small amounts of linolic acid ester are semi-drying, while many such as olive and rape oils are non-drying. These oils generally become rancid from exposure to air, apparently because of a partial hydrolysis occasioned by bacterial action followed by oxidation of the fatty acids that are set free. INTRODUCTION TO ORGANIC CHEMISTRY l6ob In the last few years the production of "hardened" oils has developed into an industry of considerable importance. The chemical change involved consists in " hydrogenation " or~ addi- tion of hydrogen to the unsaturated esters in the oils, by which they are converted into saturated compounds. The reaction is effected by leading hydrogen into the moderately heated oil after the addition of a substance that acts as a catalyst. The most important of these catalysts is finely divided nickel (Sabatier and Senderens), though palladium, platinum, and other metals are also employed. A large variety of oils can be thus hardened vegetable, animal, train, fish, and whale oils and the resulting fats are of great commercial importance, being largely used in soap and candle making, and also providing edible fats from oils. One of the latter products is "crisco," a substitute for lard. A method of saponifying fats for soap-making has recently been introduced into the industry by Twitchell, in which an aromatic sulphonic acid acts as a catalyzer. The exact nature of the com- pound is not disclosed, but it is prepared by the action of sulphuric acid on a solution of olei'c acid in an aromatic hydrocarbon: and 1-2 per cent, of it is effective in producing saponification. CHAPTER XIII OXIDATION DERIVATIVES OF POLYHYDROXYL ALCOHOLS A large number of compounds may be regarded as oxidation derivatives of the alcohols discussed in the last chapter. The compounds may contain unchanged alcohol groups primary, secondary, and tertiary with aldehyde groups, ketone groups, or carboxyl groups, in every possible combination. From glycol, for example, the derivatives are: CH 2 OH CH 2 OH CH 2 OH CHO CHO CO.OH CH 2 OH CHO CO.OH CHO CO.OH CO.OH m,i Glycollic Glycollio pu rrivQ i Glyoxylic Oxalic G1 y co1 aldehyde acid Glyoxal ad( f &cid From glycerol and the higher polyhydroxyl alcohols ketone derivatives may also be obtained such as dihydroxy-acetone, CH 2 OH.CO.CH 2 OH. But while many of these substances are formed by the actual oxidation of the corresponding glycols, etc., this method is not often used for their preparation, because of the difficulty of controlling the reaction so as to obtain a good yield of the individual products. Glyceric acid is, however, usually made by oxidizing glycerol with nitric acid, but, in general, the compounds which form the subject of this chapter are prepared by indirect methods. The student will recall that the most important general methods for the introduction of the hydroxyl groups are: By replacement of a halogen atom through the action of water, alkali hydroxide, or silver hydroxide; by saponification of an ester; for a primary 161 INTRODUCTION TO ORGANIC CHEMISTRY 162 alcohol group, the reaction of nitrous acid on a primary amine group, and for a secondary alcohol group, the reduction of a carbonyl group. For the general methods of introducing the aldehyde, ketone, (CO), and carboxyl groups, reference should be made to the methods of forming aldehydes, ketones and acids. Aldehyde-alcohols and Ketone-alcohols The simpler compounds of these classes are of interest chiefly because of the fact that some of the sugars are aldehyde or ketone- alcohols, while other so-called carbohydrates are converted into aldehyde or ketone-alcohols by hydrolysis. The carbohydrates themselves form the subject of a separate chapter. Only a few of the simpler aldehyde-alcohols and ketone-alcohols have been made, and these are of no especial practical importance. Glycollic aldehyde, CH 2 (OH).CHO, or hydroxy-acetaldehyde, is formed in the oxidation of glycol. It can be prepared from acetal, CH 3 .CH(OC 2 H5) 2 , by appropriate reactions. Chlorine is sub- stituted in the CH 3 group, and replaced by hydroxyl, making CH 2 OH.CH(OC 2 H 5 )2; and then by the action of a dilute acid, this glycolacetal is hydrolyzed into glycollic aldehyde and alcohol (cf. p. 79). It is known only in solution. Its aldehyde character is marked. It reduces Fehling's solution at room temperature, is colored yellow when heated with alkalies, and is oxidized by bromine water to glycollic acid. On standing at o with dilute alkali it suffers "condensation" like that of acetaldehyde, with the formation of a tetrose, CH 2 (OH).CH(OH).CH(OH).CHO. Aldol or fchydroxybutyric aldehyde, CH 3 .CH(OH).CH 2 .CHO, is formed by the polymerization of acetaldehyde (p. 82), and was the first known case of this characteristic aldehyde reaction f " aldol condensation ") . Ketoles. A number of compounds with a ketone group and a hydroxyl group are known, such as hydroxyl acetone or acetocarbinol, CH 3 .CO.CH 2 (OH), and acetobutyl alcohol, CH 3 .CO.(CH 2 ) 3 .CH 2 (OH). 163 DERIVATIVES OF POLYHYDROXYL ALCOHOLS Dialdehydes and Diketones CHO Glyoxal, | , is one of the several products formed by the CHO oxidation of glycol or ethyl alcohol or aldehyde with nitric acid. A solution of it may be prepared in this way from aldehyde or paraldehyde, and on evaporation the glyoxal is obtained as an amorphous, hard mass, not entirely free from water. Its aldehyde character is shown by the formation of a silver mirror with am- moniacal silver nitrate, and the presence of two aldehyde groups by the composition of the crystalline addition products with acid sodium sulphite. By dilute alkalies it is converted into a glycollic acid salt, CH 2 (OH).CO.ONa, one aldehyde group being reduced, and the other oxidized. Acetonylacetone, CH 3 .CO.CH 2 .CH2.CO.CH3, is an example of a diketone, which may be regarded as an oxidation product of a 7-hexylene glycol. It is made, however, in an indirect way. It is a liquid of pleasant odor, which boils at 194. Aldehyde -ketones The simplest representative of this class is the methylglyoxal, CH 3 .CO.CHO, and may be looked on as a derivative of propylene glycol. Alcohol-acids Carbonic acid t HO.CO.OH, may be considered as hydroxy- formic acid. It and its derivatives will be discussed later. Glycollic acid, CH^OH.CO.OH, or hydroxyacetic acid, is (with the exception of carbonic acid) the simplest of these compounds. Its structure is shown by its formation from monochloracetic acid, when this is boiled with water: CH 2 C1.CO.OH + HOH - CH 2 OH.CO.OH INTRODUCTION TO ORGANIC CHEMISTRY 164 It occurs in unripe grapes. It is formed by the oxidation of glycol or of ethyl alcohol with nitric acid, by reduction of oxalic acid, and by the action of dilute alkalies on glyoxal (p. 163.) Glycollic acid is a crystalline substance, which melts at 80 and dissolves readily in water. Nitric acid converts it into oxalic acid. Hydroxypropionic Acids. There are two chemically different acids of this name whose formulas are, CH 3 .CHOH.CO.OH, and CH 2 OH.CH 2 .CO.OH. They may be made from other compounds such as iodo- or amino-propionic acids by the usual methods of hydroxyl substitution. That they are monobasic acids is proved by the composition of their salts; and that they contain one hydroxyl in addition to that of the carboxyl, is shown by the fact that sodium acts on them with the formation of com- pounds in which it takes the place of two hydrogen atoms those of the hydroxyl and carboxyl group. Both acids form thick, sour syrups. Their diversity is shown by a great difference in the solubility of their zinc salts, and by the following reactions which serve to decide which of the two formulas represents the structure of each. One of them when oxidized with potassium permanga- nate is converted into a ketone acid, acetylformic acid, CH 3 .CO.- CO.OH. This result is evidence of the presence of a secondary alcohol group in the acid, the reaction being: CH 3 .CHOH.CO.OH + O = CH 3 .CO.CO.OH +H 2 O The formula given the acid in this equation is also indicated by the fact that when heated with dilute sulphuric acid, it breaks up into aldehyde and formic acid, a reaction which is characteristic of many a-hydroxy acids: CH 3 .CHOH.CO.OH = CH 3 .CHO + HCO.OH and that its nitrile may be made by direct combination of aldehyde and hydrocyanic acid: CH 3 .CHO + HCN = CH 3 .CHOH.CN This acid is, therefore, a-hydroxypropionic acid. 165 DERIVATIVES OF POLYHYDROXYL ALCOHOLS The other must, then, be /3-hydroxypropionic acid,CH 2 OH.- CH 2 .CO.OH; and this formula is confirmed by its oxidation into the corresponding dibasic malonic acid, CO.OH.CH 2 .CO.OH, showing the presence of a primary alcohol group; and also by its breaking up when heated into the unsaturated acrylic acid, CH 2 :CH.CO.OH (p. no). a-Hydroxypropionic acid, CH 3 .CHOH.CO.OH, is the acid of sour milk, being formed by the action of certain bacteria on the milk sugar. Hence it is known as lactic acid. (Tablets contain- ing pure cultures of lactic acid bacteria are sold under the name of "lactone" or "butter-milk tablets.") Lactic acid is also the product of special fermentations of other sugars, and is found in "sauerkraut" and in the gastric juice, and is present in "beef- extract." But the lactic acid obtained from the last source differs from that from most other sources and from the synthetic lactic acid, by being "optically active;" that is, its solutions rotate the plane of polarized light. On fermentation of cane-sugar by means of a special culture of bacteria, an active lactic acid is formed which also rotates the plane of polarized light, but in the opposite direction from that which is made from beef-extract. The latter turns the plane to the right, the former to the left. The salts of these two acids give optically active solutions which rotate the plane in a sense opposite to the rotation by the respec- tive acids. The ordinary salts of both these acids have the same solubility, but the strychnine salt of the levo-rotatory acid is less soluble than that of the dextro-rotatory, and from a solution of the strychnine salt of the ordinary lactic acid, which is "inac- tive," two lots of crystals can be obtained by fractional crystal- lization, and from these the two optically active acids may be set free. The dextro-acid may be also made from the ammonium salt of the inactive acid by means of a mould, penicillium glaucum, which destroys the levo form. Special ferments determine the formation from sugars of one or the other of the active acids. When the zinc salts of the two active acids in solution are mixed INTRODUCTION TO ORGANIC CHEMISTRY 1 66 in equal proportions, the less soluble salt of the inactive acid crystallizes out. It appears, therefore, that the inactive acid is a mixture in equal parts of the two oppositely active acids. The three acids differ in no chemical way, and this "physical isomerism" which is found cannot be represented by such structural formulas as we have thus far employed. A satisfactory explanation is, however, found in formulas which give arrangements of atoms and groups in space of three dimensions, instead of the representa- tions in a single plane such as have served in our discussions up to this point. Stereochemistry In methane we saw that each of the four hydrogen atoms bore the same relation to the other three and to the carbon atom; at least, it has not proved possible to make different monosubsti- tution products of methane. This symmetry of the methane molecule is satisfactorily indicated by the usual plane graphic for- H mula, H C H. If chlorine replaces any one of the hydrogen H atoms, we have formulas which may be considered identical. B ut when two atoms of hydrogen are replaced there are two formulas possible which are not strictly identical in this mode of representa- tion; for in one the hydrogen and chlorine atoms alternate as we go round the carbon atom, and in the other the two chlorine atoms are next each other : H H Cl C Cl and H C Cl I I H Cl And yet only one dichlormethane has ever been obtained. Such differences in arrangement have been hitherto disregarded i6 7 DERIVATIVES OF POLYHYDROXYL ALCOHOLS in our discussions. The phenomena of optical activity or physical isomerism, however, has led to the development of spatial repre- sentations, which account for the existence of but one dichlor- methane and other similar failures of the plane formula; and also gives a good explanation of the facts of optical activity. There is, of course, every reason to believe that the molecular arrangement is never confined to bi-dimensional space, but that the atoms and groups form tri-dimensional structures; and the graphic formulas have been regarded as giving merely a plan or diagram with no attempt to represent the actual relative positions. The tetrahedron, the simplest regular solid, is the only form that can give full expression to the symmetry of methane, and this was taken by Van't Hoff andLe Bel as the basis for their formulation of spatial relations. The carbon atom is placed at the center of the tetrahedron, its four valencies being directed to the four solid angles. H ci 2. Monochlormethane H 3. Dichlormethane 4. Dichlormethane The diagrams show the tetrahedral formulas for methane, mono- chlormethane, and dichlormethane. They are all symmetrical, and formulas 3 and 4 are identical; for 3 may readily be turned so INTRODUCTION TO ORGANIC CHEMISTRY 168 that the chlorine and hydrogen atoms coincide, or, in other words, the two figures are superposable. This symmetry holds good for all compounds in which a carbon atom is combined with four elements or groups of the same kind, or any combination of elements or groups except that of four differ- ent ones. In this case there are possible two arrangements which are unsymmetric or asymmetric and which cannot be turned into coincidence or superposed. On this account, a carbon atom united to four different atoms or groups is called an asymmetric carbon atom. ,The two asymmetric arrangements bear the rela- tion to each other of an object and its image in a plane mirror, as may be seen by study of the diagrams, or better by tetrahedral forms. The relations shown in the tetrahedral formulas may also and more conveniently be indicated by formulas like those below, which are projections of the tri-dimensional arrangements on the plane of the paper: a a i i d C b b C d I I It will be noticed that the configurations cannot be made to coin- cide by turning one of them in the plane of the paper. This will be found true of all such projections of asymmetrical tetrahedral formulas, and we shall make use of this mode of representation in future instances of physical isomerism. By these formulas, we have a means of recording the physical 169 DERIVATIVES OF POLYHYDROXYL ALCOHOLS difference which we are discussing, while the chemical identity is still preserved. A large number of optically active organic substances is known. When the plane of polarized light is rotated on passing through a solid substance, it can be assumed that the effect is due to the arrangement of the molecules, as in the various crystal forms; but in the case of the lactic acids and other so-called optically active chemical compounds, the activity is shown in solution, where free motion of the molecules is probable, and where they certainly do not assume any fixed relations to each other; and camphor and certain terpenes retain their optical activity unim- paired in the state of vapor. In all the optically active compounds, we find on examining their ordinary structural formulas that there is an asymmetric carbon atom. In lactic acid, CH 3 .CH(OH).CO.OH, the four different groups CH 3 , H, OH, and CO. OH are in combination with the carbon atom which is printed in blacker type. The formulas of the two optically active lactic acids are: CO.OH CO.OH or d-Lactic acid CO.OH H C OH CH 3 The choice of one formula rather than the other to represent the dextro- or levo-compound is arbitrary. When a compound contains an asymmetric carbon atom, and is optically inactive, the explanation is that equal amounts of the INTRODUCTION TO ORGANIC CHEMISTRY 170 two oppositely active substances are probably present: and this, as we have seen, agrees with the facts which have been stated as to the separation and the mixing of the two active lactic acids. In case of compounds with two asymmetric carbon atoms, as in mesotartaric acid (p. 193), the optical inactivity may be due to a different cause. Optically active compounds which have been previously 3 v mentioned are: active amyl alcohol, ^>CH.CH 2 OH (p. 67), C 2 H/ and one of the four valeric acids (p. 108) which has the av formula, ^>CH.CO.OH. Each formula contains an asynv C 2 H/ metrical carbon atom. The active alcohol from fermentation is levo-rotatory; on oxidation it yields dextro-rotatory valeric acid. An inactive modification of the acid has been synthe- sized, and resolved by its brucine salts into dextro and levo components. It is of great interest to note that this theory of the relation of optical activity to the asymmetric tetravalent carbon atom has been found to explain in a similar manner the phenomena of optical activity recently discovered in compounds of other tetravalent elements. These are compounds of tetravalent tin, silicon, sulphur, and selenium, in all of which four different groups or atoms are directly united to these elements, and can be repre- sented as tetrahedral arrangements. Lactic acid is made commercially by fermentation of sugar, and is used in dyeing and calico printing as a substitute for tartaric and citric acids, and its antimony salt is used in place of tartar emetic as a mordant. The lactic-acid fermentation is often induced in making grain alcohol, as a i per cent, solution of the acid inhibits the action of other bacterial ferments, while having little effect on yeast. When distilled, lactic acid is decomposed into aldehyde, water, carbon monoxide and other products. Since lactic acid is both an 1 71 DERIVATIVES OF POLYHYDROXYL ALCOHOLS alcohol and an acid, two molecules of it may react to form an xO.OC.CHOH.CH 3 ester, CH 3 .CH ^ , and this by a second \CO.OH reaction of the same kind may give a compound called lactide xO.OC.CH.CHa and having the constitution CH 3 .CH <^ / . The \co.o lactide is formed when the acid is heated to 150 in a current of dry air. Lactide is an indifferent substance, and in contact with water slowly changes back to lactic acid. 0-Hydroxypropionic acid, CH 2 OH.CH 2 .CO.OH, is also called hydracrylic add, on account of its relation to acrylic acid. To the evidence for its structure already given, may be added the fact of its synthesis from ethylene through ethylene chlorhydrin. Ethylene unites directly with hypochlorous acid, when led into its dilute solution, giving ethylene or glycol (chlorhydrin: CH,:CH 2 + HOC1 = CH 2 OH.CH 2 C1, and the chlorhydrin, which is a liquid, boiling at 128, reacts with potassium cyanide forming hydracrylic nitrile, from which the acid is readily obtained by hydrolysis: CH 2 OH.CH 2 C1 + KCN = CH 2 OH.CH 2 CN + KC1 CH 2 OH.CH 2 .CN + 2H 2 O = CH 2 OH.CH 2 .CO.OH + NH 3 It will be noticed that hydracrylic acid contains no asymmetric carbon atom". Dehydration of Hydroxy-acids. By this is meant the removal of the elements of water from the acids. This is readily effected, and the nature of the compounds which result depends on the relative positions of the hydroxyl and carboxyl groups. a-Hydroxy-acids form various complex compounds by the loss of the elements of water from hydroxyl and carboxyl groups, and the union of two molecular residues, as in the case of lactic INTRODUCTION TO ORGANIC CHEMISTRY 172 acid (p. 171). From gly collie acid, for example, the following compounds have been obtained: X CH 2 .CO.OH X CH 2 .CO V o< a( X CH 2 .CO.OH X CH 2 .O HO.CH 2 .CO X X CH 2 .CO\ >0, 0< >0 HO.OC.CH/ X)C.CH 2 / The last is glycollide, corresponding to lactide. Compounds of this constitution have received the general name of lactides. When heated with dilute sulphuric acid, a-hydroxy acids often split off formic acid (or its equivalent, CO and H 2 O), as in the case of lactic acid. 0-Hydroxy acids when heated give unsaturated acids, as in the case of hydracrylic acid which produces acrylic acid : CH 2 OH.CH 2 .CO.OH = CH 2 rCH.CO.OH 5- and y-hydroxy- acids lose the elements of water very easily from the hydroxyl and carboxyl groups of a single molecule, forming lactones: CH 2 OH.CH 2 .CH 2 .CO.OH = CH 2 .CH 2 .CH 2 .CO L _ -J The tendency of the 7-acids to form lactones is so great, that when the acids are in solution it occurs in most cases slowly at ordinary temperature, and immediately on boiling. The y-lac- tones are neutral compounds which distil without decomposition. On boiling with water the acid is reproduced to a small extent. Glyceric acid, CH 2 OH.CHOH.CO.OH, is an example of a dihydroxy-acid. It may be made by careful oxidation of glycerol, preferably with nitric acid. Its constitution as a dihydroxy- propionic acid is determined by its formation from chlorlactic acid, CH 2 C1.CHOH.CO.OH, by reaction with silver hydroxide. Glyceric acid is a thick syrup which mixes in all proportions with 173 DERIVATIVES OF POLYHYDROXYL ALCOHOLS water and alcohol, but is insoluble in ether (alcohol -hydroxyl groups). It is seen that this acid contains an asymmetric carbon atom. As usually prepared its solutions have no effect on polar- ized light; but a special bacillus produces a dextro-rotatory acid from it, and by the action of penicillium glaucum on th/e solutions of the ammonium salt of the inactive acid, a levo-rotatory acid may be obtained. Aldehyde and Ketone Acids Glyoxylic acid, CHO.CO.OH, is the simplest aldehyde acid. It is a product of the oxidation of alcohol, glycol, or glycollic acid with nitric acid, and can be prepared from dichlor or dibrom- acetic acid by heating with water. It shows itself to be an alde- hyde by its reducing power (being itself oxidized to oxalic acid), its reduction to glycollic acid, and its reactions with acid sodium sulphite and hydroxylamine. It forms a syrup from which crystals separate on long standing. These crystals, however, do not have the composition of the acid, but contain an additional molecule of water which cannot be driven off without decomposi- tion of the acid. Its salts also, except the ammonium salt, con- tain water and cannot be obtained in the anhydrous condition. Consequently its composition is sometimes considered to be CH(OH) 2 .CO.OH, analogous to that of chloral hydrate (p. 92). But its reactions are best explained by the formula CHO.CO.OH. Pyroracemic acid, pyruvic acid, or acetyl formic acid, CH 3 .CO.- CO-OH, is a ketone acid, which owes its first name to its forma- tion by heating racemic (tartaric) acid. This is the usual way for preparing it. The yield is increased by distilling the acid with acid potassium sulphate. The structure of pyroracemic acid is evident from its formation by oxidizing lactic acid: CH 3 .CHOH.CO.OH + O - CH 3 .CO.CO.OH, and also from its production by the following methods : from a dibrompropionic acid, CH 3 .CBr 2 .CO.OH, by the action of silver INTRODUCTION TO ORGANIC CHEMISTRY 174 oxide; and from acetyl chloride by means of potassium cyanide, and subsequent hydrolysis: CHs.CO.Ci + KCN = CHa.CO.CN + KC1 CH 3 .CO.CN + 2H 2 O = CH 3 .CO.COONH 4 Pyroracemic acid gives the characteristic reactions of a ketone and of an acid. It is a liquid, boiling with little decomposition at about 165, and when frozen at a low temperature, melts at 9. Acetoacetic acid, CH 3 .CO.CH 2 .CO.OH, is not known in the anhydrous condition. It may be obtained by the evaporation of its solutions as a syrup, but decomposes when warmed to some- what below 1 00 into acetone and carbon dioxide. Acetoacetic acid is formed by the oxidation of butyric acid with hydrogen peroxide, and is also a product of the oxidation of fats and proteins in the body. By the splitting off of carbon dioxide it is converted into acetone: CH 3 .CO.CH 2 .CO.OH = CH 3 .CO.- CH 3 + CO 2 ; and in the enol form, CH 3 .COH:CH.CO.OH, 0- hydroxycrotonic acid, is reduced to /3-hydroxybutyric acid, CH 3 .- CHOH.CH 2 .CO.OH. These three substances, acetoacetic acid, /3-hydroxybutyric acid, and acetone are present in considerable quantities in the urine in severe cases of diabetes mellitus. Acetoacetic ethyl ester is a more stable compound, and, as it readily reacts with many substances, is an important aid in various organic syntheses. It is prepared by the action of sodium on ethyl acetate. The reaction is believed to proceed in the following way: Sodium acts first on traces of alcohol, which are present in the acetate, forming sodium ethoxide, and then this forms an addition product with the acetate: X)Na CH 3 .CO.OC 2 H 5 + C 2 H 5 ONa = )C 2 H 5 This immediately reacts with another molecule of the acetate, forming a sodium compound of acetoacetic ester, and alcohol: 175 DERIVATIVES OF POLYHYDROXYL ALCOHOLS Na 2 H 5 + CH 3 .CO.OC 2 H 5 = \OC 2 H 5 CH 3 .C(ONa):CH.CO.OC 2 H 6 + 2C 2 H 5 OH Finally on adding acetic acid to the sodium compound thus formed, the ester, CH 3 . COH : CH . CO . OC 2 H 5 or CH 3 . CO . CH 2 CO . OC 2 H 5 , is set free. It will be noticed that two alternate formulas have just been given for the ester. The first is the formula of an unsaturated hydroxy ester, the second of a saturated ketone ester. The explanation of its formation leads most naturally to the first formula and some of its reactions accord with this view; but, on the other hand, many of its reactions are those of a ketone com- pound. It is probable that it exists in both forms, and that they are both present in varying proportions in it and in its substitution products, and change readily into each other. We have noticed before in the acid amides a similar case, where the compound probably exists in two forms which are structurally different. This double behavior is found in a number of compounds and is called tautomerism, tautomeric compounds being such as possess a double function though usually represented as a single sub- stance. In this way they differ from the usual cases of isomerism in which, when the structure is once determined by the reactions of formation, the arrangement is a stable one. The hydroxy form is known as the enol modification, and the other the keto form. Acetoacetic ester is a liquid of pleasant strawberry-like odor, which boils at 181. It is only slightly soluble in water, and is col- ored violet by a solution of ferric chloride. This color reaction is common to compounds having an unsaturated alcohol group, and is evidence of the presence of some, at least, of the ester repre- sented by the first formula. Treated with cold, dilute alkali,the ester is saponified into the alkali salt of acetoacetic acid and alco- hol. Heated with stronger solutions of alkalies, it is partly con- certed into alkali acetate and alcohol: INTRODUCTION TO ORGANIC CHEMISTRY 176 CH 3 .CO.CH2.CO.OC 2 H5 + 2KOH = 2 CH 3 .CO.OK + C 2 H 5 OH and partly hydrolyzed into acetone, alcohol and carbon dioxide: CH 3 .CO.CH2.CO.OC 2 H5+H 2 O = CH 3 .CO.CH 3 +C 2 H 5 OH+CO 2 . This latter reaction occurs completely when it is heated with dilute acids. There are, therefore, two distinct varieties of hy- drolysis possible which may be distinguished as ketone hydrolysis and acid hydrolysis. The most notable property of acetoacetic ester is that of forming compounds with metals, which are either of the type, CH 3 .CONa:CH.CO.OC 2 H 5 , or CH 3 .CO.CHNa.CO.OC 2 H 5 . By treating the sodium compound with alkyl halides, alkyl groups are introduced in place of the metals, and since the sub- stituted esters undergo decompositions of the same character as the ester itself, many substitution derivatives of acetone and acetic acid may be prepared in this way. In general the ester shows the characteristic ketone reactions: By nascent hydrogen it is converted into /3-hydroxybutyric acid, CH 3 . CHOH . CH 2 CO . OH; it forms a crystalline addition product with acid sodium sulphite, etc. Further, acetyl substitution products are not formed by acetic acid, or its chloride or anhy- dride, substances which always react with hydroxyl groups. Reactions of acetoacetic ester that are characteristic of ketones are: the formation of /3-hydroxybutyric acid on reduction; the production of additive compounds with hydrogen cyanide and with acid sodium sulphite; and the hydrolysis of the ester and of its alkyl derivatives by alkalies and acids into acetone and its homologues. Further, with acetic anhydride the ester yields so little of an acetyl derivative that the presence of an hydroxyl group seems very improbable, and acetyl chloride acting on the sodium compound gives mainly diacetoacetic ester: CH 3 .CO.CHNa.CO.OC 2 H 5 + CH 3 .CO.C1 = (CH 3 .CO) 2 CH.CO.OC 2 H 5 + NaCl Ij6a DERIVATIVES OF POLYHYDROXYL ALCOHOLS On the other hand, the acidic character of the ester indicates the hydroxyl form, and ammonia and amines yield amino and alkyl- amino crotonic esters of the general formula: CH 3 .C(NR 2 ):- CH.CO.OC 2 H 5 . It is now generally agreed that the free acetoacetic ester con- sists chiefly of the ketonic form, while the solid sodium compound must be represented by the isomeric formula as a derivative of 0-hydroxycrotonic acid. CHAPTER XIV POLYBASIC ACIDS AND ALCOHOL-ACIDS SOME DIBASIC ACIDS Name Formula Melting Point Oxalic CO.OH.CO.OH 189 -(Anhydrous) Malonic CO.OH.CH 2 .CO.OH 132 Succinic CO.OH.(CH 2 ) 2 .CO.OH 184 Glutaric CO.OH.(CH 2 ) 3 .CO.OH 98 Adipic CO.OH.(CH 2 ) 4 .CO.OH 153 Pimelic CO.OH.(CH 2 ) 5 .CO.OH 105.5 Suberic CO.OH.(CH 2 ) 6 .CO.OH 141 Azelaic CO.OH.(CH 2 ) 7 .CO.OH 108 Sebacic CO.OH.(CH 2 ) 8 .CO.OH 134.5 Oxalic acid, (CO.OH) 2 , one of the well-known organic acids, is one of the products formed when ethyl alcohol or glycol is oxidized by nitric acid, and also results from the oxidation of many more complex organic substances. When sugar, for instance, is warmed with concentrated nitric acid, a strong reaction occurs, and oxalic acid crystallizes from the resulting solution as it cools. It is prepared commercially from saw-dust by mixing it with a strong solutionof potassium hydroxide and heating to about 250; or, more usually now, by heating an alkali formate (see p. 106, and below). The potassium oxalate produced is extracted with water, changed into the insoluble calcium oxalate by milk of lime, and the acid set free by sulphuric acid. The white crystalline solid which is obtained from solutions of oxalic acid contains two molecules of water of crystallization. It begins to lose water at 30 and becomes anhydrous at 100. On further careful heating, the an- hydrous acid sublimes, and this fact is employed for its purifica- tion, as it is thus readily freed from the small amount of its salts which crystallize with it The acid is moderately soluble in water, 177 178 INTRODUCTION TO ORGANIC CHEMISTRY more readily soluble in alcohol, and nearly insoluble in ether. When strongly heated, it breaks down into carbon dioxide, carbon monoxide, and water, with the production of some formic acid as an intermediate step: CO.OH = HCO.OH + CO 2 = CO 2 -f CO + H 2 O CO.OH Heated with concentrated sulphuric acid, it gives the end products of water and the oxides of carbon at once. The relation of oxalic acid to formic acid is of interest. As stated, some formic acid is produced when oxalic acid is heated, and the usual method for the preparation of formic acid is by heating oxalic acid with glycerol (p. 104); on the other hand, when an alkali formate is sharply heated (400) with exclusion of air, the alkali oxalate is produced: HCO.OK CO.OK = | + H 2 HCO.OK CO.OK From two molecules of formate one molecule of oxalate is formed, with hydrogen as a by-product; and one molecule of oxalic acid yields one molecule of formic acid with carbon dioxide as a by- product; the two by-products being equivalent to the one mole- cule of formic acid which is lost in completing the cycle. Besides this formation of oxalic acid from formic acid, two other methods of theoretical interest may be given: An alkali oxalate is obtained when carbon dioxide is led over sodium or potassium heated to 360: 2Na + 2CO 2 = (CO.ONa) 2 By hydrolysis of cyanogen, the acid or its salts are formed, cyan- ogen thus showing itself to be the nitrile of oxalic acid: CN CO.NH 2 CO.ONH 4 | + 2 H 2 = | + 2H 2 = | CN CO.NH 2 CO.ONH 4 POLYBASIC ACIDS AND ALCOHOL-ACIDS 179 Oxalic acid resists the oxidizing action of nitric acid, as is evi- dent from its preparation by means of this acid; but it is readily oxidized in sulphuric acid solutions by potassium permanganate, and is used in volumetric analysis to standardize permanganate solutions. The reaction is, at first, slow, but soon becomes instan- taneous, being accelerated by the catalytic effect of the manganous sulphate which is formed. When manganous sulphate is added before the titration begins, the permanganate is instantly de- colorized. Salts and Esters of Oxalic Acid. Oxalic acid is a strong dibasic acid, being highly ionized in its solutions. Its salts, chiefly the acid potassium oxalate and calcium oxalate, are found in many plants, such as sorrel and rhubarb, and crystals of calcium oxalate are found generally in the cell- walls of plants. Ammonium oxa- late is a well-known laboratory reagent. Besides the acid and normal potassium salts, another salt called potassium tetroxalate, (CO.O) 2 HK.(CO.OH) 2 .2H 2 O, is readily obtained pure. It is sometimes used as a standard substance in volumetric analysis and is sold as "salt of sorrel" for removing rust and ink stains (of iron inks) . The insolubility of calcium oxa- late in acetic acid serves as a test for calcium and for oxalic acid. Many double oxalates are known. Potassium- ferrous oxalate, K2Fe(C 2 O 4 )2, made by mixing solutions of ferrous sulphate and potassium oxalate, is a powerful reducing agent, and used as a developer in photography. The corresponding ferric salt, K 3 Fe- (C 2 O 4 )s, is reduced to the ferrous compound by light, and this reaction is the basis for making platinum prints. The paper coated with the double salt is exposed under a negative and then treated with a solution of platinum salt. The platinum is reduced and deposited in proportion to the change which the light has produced. Oxalic acid and some of its salts are used as mordants. Of the esters of oxalic acid, the dimethyl ester, C 2 O 4 (CH 3 )2, is used for preparing pure methyl alcohol. It is prepared by dissolving anhydrous oxalic acid in the alcohol and heating. l8o INTRODUCTION TO ORGANIC CHEMISTRY Methyl oxalate is a solid which melts at 54. Ethyl oxalate, made in a similar manner, is a pleasant smelling liquid, boiling at 186. Other Derivatives. The acid chloride, C1.CO.CO.C1, cannot be made. Phosphorus pentachloride acts as a dehydrating agent in this case, and gives carbon dioxide, carbon monoxide, phos- phorus oxychloride, and hydrogen chloride. CO.NH 2 Oxalic acid amide or oxamide, , is formed when am- CO.NH 2 monium oxalate is heated; when a neutral oxalic ester is shaken with aqueous ammonia; or from cyanogen by the action of water in the presence of a trace of aldehyde. It is a white crystalline substance, almost insoluble in water, alcohol or ether. When heated it partly sublimes unchanged and partly decomposes into cyanogen and water. When heated to 200 with water it is converted into ammonium oxalate. When acid ammonium oxalate is heated, the first product is oxamic acid, NH2.CO.CO.OH. The anhydride of oxalic acid does not exist. Malonic acid, CO.OH.CH 2 .CO.OH, may be looked at as acetic acid in which carboxyl has been substituted for one hydro- gen atom in the CH 3 group. It is, in fact, made from acetic acid by such substitution. Monochloracetic acid, CH 2 C1.CO.OH, is first made, and after conversion into the potassium salt, is changed into the cyanacetate, CH 2 .CN.CO.OK, by means of potassium cyanide. This is the nitrile of malonic acid, and from it the acid (or its salt) is obtained in the usual way by hydrolysis. This method of formation is satisfactory evidence of the consti- tution of the acid. Malonic acid was first observed as an oxidation product of malic acid (p. 185), and its name was given it on account of this origin. It is a solid, melting at I33-I34, and very soluble in water and in alcohol. POLYBASIC ACIDS AND ALCOHOL-ACIDS l8l Heated a little above its melting point, malonic acid breaks up quantitatively into carbon dioxide and acetic acid: CO. OH CH 2 = CHa.CO.OH-f CO 2 I CO.OH This is a typical general reaction which takes place on heating compounds containing two carboxyl groups united to the same carbon atom. We have here an unstable arrangement, which is like that already noticed in the case of hydroxyl groups; but while, in general, the dihydroxyl combination is unstable under all conditions, the dicarboxyl compounds decompose only when heated to their melting point or above. When a compound contains two carboxyl groups which are not immediately united to the same carbon atom, it decomposes on heating with the loss of the elements of water and formation of an anhydride. Thus in the case of succinic acid (p. 184): CH 2 .CO.OH CH 2 .CO\ | =| >0 -f H 2 CH 2 .CO.OH CH 2 .CCK Ethyl malonate, CH 2 (CO.OC 2 H 5 ) 2 , has a special interest because of the fact that one or both of the hydrogen atoms of the CH 2 group can be replaced by sodium. The ester itself may be made by the reaction of malonic acid with alcohol, but is usually prepared by treating a mixture of cyanacetate of potassium (made as above) and alcohol with hydrogen chloride. It is a liquid, boiling at 198. When sodium is added to it, hydrogen is evolved and CHNa(CO.OC 2 H 5 ) 2 or CNa 2 (CO.OC 2 H 5 )2 is formed according to the proportion of sodium used. These sodium compounds are also formed by the action of sodium ethoxide on the ester. In this case intermediate addition prod- ucts are probably formed as in the case of acetoacetic ester 1 82 INTRODUCTION TO ORGANIC CHEMISTRY (p. 174). The structure of the resulting sodium compounds, as in that case, is in doubt. Most of the reactions, however, are in agreement with the formulas given above. These sodium com- pounds react readily with alkyl halides and with acetyl chloride, giving replacements of the sodium by alkyl groups or by the acetyl group. By hydrolysis of these substituted esters the substituted dibasic acids are obtained; and from these, on heating, carbon dioxide is split out as in the decomposition of malonic acid by heat and the corresponding substituted monobasic acid is made. For instance, the sodium compound, CHNa(CO.OC 2 H 5 ) 2 with CO.OC 2 H 5 CO.OH I I C 2 H 5 I gives CH(C 2 H 5 ) , and this on hydrolysis yields CH(C 2 H 5 ), CO.OC 2 H 5 CO.OH H which on heating = CH.(C 2 H 5 ) or CH 3 .CH 2 .CH 2 .CO.OH, CO.OH ethyl acetic acid or normal butyric acid. This method of malonic acid synthesis is, therefore, a very useful means for making a great variety of compounds, and is especially employed for the synthesis of isomonobasic acids. A step-by-step replacement makes it possible to substitute two different alkyl groups for the two hydro- gen atoms in the CH 2 group of malonic acid. Other Derivatives of Malonic Acid Among other derivatives the hydroxyl substitution products have the most interest. Tartronic acid, CO.OH.CHOH.CO.OH, or monohydroxy- malonic acid, can be made by the usual method for replacing hydrogen by hydroxyl : formation of brommalonic acid by direct action of bromine, and treatment of this with silver hydroxide. The name of this acid is derived from tartaric acid, from which POLYBASIC ACIDS AND ALCOHOL-ACIDS 183 it was first prepared by oxidation. It is a solid, melting at 187. Dihydroxymalonic acid, CO.OH.C(OH) 2 .CO.OH, can be made from dibrommalonic acid by boiling it with barium hydroxide. Although this acid can be melted without loss of water, and forms salts which correspond to the formula given for the acid, it deports itself in reactions like a ketone-acid, mesoxalic acid, CO .OH. CO. CO. OH. Esters of both forms are known. Dihydroxymalonic acid is interesting as one of the very small number of compounds which appear to contain two hydroxyl groups united to a single carbon atom (cf. p. 113). It is evident, however, from the ketone reactions it gives, that the combination is rather unstable. The acid melts at 115, and at higher temperatures decomposes into carbon dioxide, water, and glyoxylic acid: CO.OH.C(OH) 2 .CO.OH = CHO.CO.OH + CO 2 + H 2 6 and on evaporation of its aqueous solution it breaks up into carbon monoxide, oxalic acid, and water: CO.OH.C(OH) 2 .CO.OH = (CO.OH) 2 + CO + H 2 O The appearance of carbon monoxide in this reaction causes it to reduce ammoniacal silver nitrate with evolution of carbon dioxide. By sodium amalgam it is reduced to tartronic acid, and it unites with acid sodium sulphite like a ketone. Succinic acid, CO.OH.CH 2 .CH 2 .CO.OH, occurs in many plants, in fossil wood, and derives its name from the fact that it is a prod- uct of the distillation of amber (succinum). It is prepared for medicinal purposes from amber, but may also be made by the fermentation of calcium malate or ammonium tartrate; or syn- thetically from propionic acid, or from ethylene by the usual method of forming the corresponding cyanogen compounds (nitriles). It is produced in small amounts in the alcoholic fer- mentation of sugar, and is frequently one of the products of the oxidation of fatty acids, etc., of higher molecular weight, by nitric 184 INTRODUCTION TO ORGANIC CHEMISTRY acid. The structure of succinic acid is clear from the methods of its synthetic formation. It melts at 182, and boils at 235, decomposing in great part into its anhydride. Dehydrating agents also produce the anhydride, CH 2 .C< CH 2 .C( CH 2 .CO.NH 2 Succinamide. The amide of succinic acid, | , can CH 2 .CO.NH 2 be prepared, like other acid amides, by the reaction of an ester of succinic acid with ammonia. It behaves, in general, like other acid amides, but when strongly heated does not give the corresponding CH 2 .CN nitrile, | , with loss of the elements of water, but loses one CH 2 .CN molecule of ammonia with conversion into a compound whose CH 2 .C = O structure appears to be, I ^r^NH, succinimide (NH being CH 2 .C = the imido group). This compound is also formed by distilling ammonium succinate, and by heating succinic anhydride in a current of ammonia. Succinic anhydride and the imide both have formulas in which there is a closed ring of atoms instead of the open single or branched chains which represent the structure of most of the ali- phatic compounds. The tendency to form such closed rings, or cyclic compounds, is most pronounced where the ring contains five or six connected atoms; others with a smaller or larger num- ber are formed, but are less stable (cf. p. 257). Succinamide melts at 242-243 and is somewhat soluble in water. Succinimide melts at 1 26, boils at 287-288 and is readily soluble in water. Its reaction is neutral, but the hydrogen of the imido group is replaced by metals more readily than that of the amido group in acid amides. POLYBASIC ACIDS AND ALCOHOL-ACIDS 185 Isosuccinic acid, CH 3 .CH(CO.OH) 2 , is a methyl derivative of malonic acid, and decomposes like this, when heated, giving pro- pionic acid and carbon dioxide: CH 3 .CH(CO.OH) 2 = CH 3 .CH 2 .CO.OH + CO 2 Hydroxyl Derivatives of Succinic Acid CH.OH.CO.OH Malic acid, | , is monohydroxy-succinic acid. CH 2 .CO.OH It was first obtained from unripe apples (malum) and owes its name to that fact. It occurs very generally in acid fruits, such as gooseberries and currants, and is found in the roots, leaves and seeds of many plants and vegetables. It is readily prepared from the berries of the mountain ash. The juice of the berries is neutralized with calcium hydroxide, and the acid obtained from the difficultly soluble calcium salts by means of sulphuric acid. Another good source of malic acid is the so-called "maple sugar sand" formed in the making of maple sugar. The acid may also be made by the usual synthetic methods. It melts at 100, and at a somewhat higher temperature begins to decompose. Instead of forming an anhydride by loss of water from the carboxyl groups, however, the decomposition is similar to that of the /?- hydroxy-monocarboxylic acids with the production of an un- saturated acid (p. 172). At I4o-i5o the chief product is fumaric acid. When heated rapidly to 180, male'ic anhydride is a considerable product which is readily converted into maleic acid by water. The malic acid obtained from fruits is optically active, but its solutions show a somewhat unusual behavior in that the rotatory power changes with their concentration, so that dilute solutions are levo-rotatory, while concentrated solutions are dextro-rota- tory. From the synthetic malic acid, which is inactive, two oppo- sitely active acids can be obtained by means of the cinchonine 1 86 INTRODUCTION TO ORGANIC CHEMISTRY salts. It will be noticed that the formula of the acid contains an asymmetric carbon atom. Fumaric and maleic acids, which are formed by heating malic acid and can be made in other ways, present an interesting case of phy- sical isomerism. The simple formula which stands for either is CH.CO.OH || . There is no asymmetric carbon atom and no op- CH.CO.OH tical activity, but the two acids differ widely in their solubility, their crystalline form, and their behavior when heated. Fumaric acid which occurs in many plants, in Iceland moss, and in some fungi, is the more stable of the two isomers. It is very sparingly soluble, and volatilizes at 200, without melting. When heated higher it decomposes into water and maleic anhydride, CH.COv yO with partial charring. Maleic acid is exceedingly CH.CCX soluble, melts at 130, and at 160 boils and decomposes into water and its anhydride. It is converted into fumaric acid when heated with water at 130, and under several other conditions. Maleic acid solutions are precipitated by barium hydroxide, fumaric acid solutions are not. Other instances of similar isomeric pairs are known among unsaturated compounds. Stereo-isomerism of Unsaturated Compounds. Fumaric and maleic acids present a case of isomerism like that of crotonic and isocro tonic acids (p. in), in which decided differences in physical behavior are to be accounted for. An explanation given by stereochemistry is, in brief, as follows: When a compound contains two carbon atoms united by a single bond, the tetrahedral formula is that shown in i. When each of the carbon atoms is joined to four different atoms or groups (is asymmetrical), we may have such optical isomerism as is shown by lactic or tartaric acid (pp. 165 and 193). But in any other case the free rotation possible to the carbon atoms about their common axis is unattended by isomerism of any kind POLYBASIC ACIDS AND ALCOHOL-ACIDS I8 7 except that provided for by the usual structural formulas. If, however, the carbon atoms are united by a double bond, it is as- sumed that their rotation is no longer possible, and the condition is represented by 2, where the two tetrahedra are shown with one H [. Ethane 2. Ethylene edge in common, indicating the double bond. Diagram i is the stereochemical formula of ethane, 2 that of ethylene. If two different atoms or groups are united to each of the carbon CO.OH CO.OH, CO.OH CO.OH 3. Maleic acid 4. Pumaric acid atoms joined by a double bond, two distinct arrangements can be made, as shown in 3 and 4, which give the stereochemical 1 88 INTRODUCTION TO ORGANIC CHEMISTRY formulas of male'ic and fumaric acids. In these diagrams, as in those for the lactic acids and tartaric acids, the two forms cannot be superposed, but, unlike the cases of optical isomers, one is not the mirror image of the other. This type of isomer- ism which is shown by fumaric and maleic acids, and by cro- tonic and isocrotonic acids, as well as by other unsaturated compounds, is called geometric isomerism, since the four atoms or groups united to the carbon atoms are represented as ly- ing in the same plane. The two configurations may also be shown in diagrams which present the tetrahedral axes, as follows: CO.OH CO.OH CO.OH CO.OH 5. Fumaric acid 6. Maleic acid The corresponding projection formulas which are commonly used for these representations are: HC CO.OH II HC CO.OH Maleic acid CO.OH CH II CH 3 C H Isocrotonic acid CO.OH CH II HC CO.OH Fumaric acid CO.OH CH II H C CH 3 Crotonic acid POLYBASIC ACIDS AND ALCOHOL-ACIDS 1 89 The assignment of the formulas to the maleic and fumaric acids, as above, is based on the assumption that the positions of the carboxyl groups in the maleic acid formula is the more favorable one for the formation of the anhydride which maleic acid forms more readily than fumaric acid. This arrangement with like groups on the same side is called the cis or malemoid form, and the other, with opposed positions, the trans or fumaroid form. The latter is always given to the more stable isomer, as in the case of the cro tonic acids (p. in). Tartaric acid, CO.OH.CHOH.CHOH.CO.OH, is dihydroxy- succinic acid. This well-known acid is widely distributed in na- ture both as free acid and in the form of potassium and calcium salts. Acid potassium tartrate, especially, is found in many fruits, and is present in considerable amount in the juice of grapes. As this salt is even less soluble in alcohol than in water, it is pre- cipitated in wine casks as alcohol is formed by the fermentation of the grape-juice. Tannin and other substances are deposited with it, forming crystalline crusts which are known as argol, and from this the pure acid tartrate and the acid are prepared. Preparation. To obtain the pure salt, the crude argol is boiled with water and bone black, the solution filtered, and then evapo- rated to crystallization. For the preparation of the acid, the nearly insoluble calcium tartrate is precipitated from a solution of argol by chalk (or gypsum), and after filtration the acid is set free by sulphuric acid (with precipitation of calcium sul- phate), and the tartaric acid is then crystallized from the clear solution. Uses. Tartaric acid and the acid potassium salt are used in medicine, in dyeing and calico printing, and for other purposes. Under the name of "cream of tartar" acid potassium tartrate is largely used as an ingredient of one class of baking powders. Potassium sodium tartrate, known as "Rochelle salt," has long been used in medicine, especially in Seidlitz powders which con- tain (i) this salt with sodium bicarbonate and (2) tartaric acid. I QO INTRODUCTION TO ORGANIC CHEMISTRY In the laboratory it is used in the preparation of Fehling's solution. Tartar emetic, potassium antimonyl tartrate, CO.OK.CHOH. CHOH.CO.O(SbO), is used as a mordant, and was formerly considered an important remedy. Properties. Tartaric acid crystallizes in long monoclinic prisms. It melts at i68-i7o, and when heated somewhat above its melting point, loses the elements of water with the formation of several substances which may be considered as anhydrides, since they are converted into tartaric acid again by boiling with water. At higher temperatures a more profound decomposition occurs; the acid becomes brown and chars, giving an odor like burnt sugar, and a distillate may be obtained which contains pyrotartaric (methyl succinic) and pyroracemic (p. 173) acids. When heated with concentrated sulphuric acid, tartaric acid chars, and carbon monoxide, dioxide, and sulphur dioxide are evolved. Tartaric acid is readily soluble in water and in alcohol, but insoluble in ether. When its solution is boiled alone or with addition of hydrochloric acid, tartaric acid is partly converted into the isomeric racemic acid. Tartaric acid is readily oxidized in solution. Ammoniacal silver nitrate solutions are reduced by it, and it is used in making silver mirrors. Solutions of the acid and of its salts are subject to change through the action of moulds and bacteria, and consequently do not keep well when exposed to the air. Succinic acid may be prepared from am- monium tartrate by bacterial fermentation. Calcium tartrate, on the other hand, yields no succinic acid, but gives volatile fatty acids, acetic, propionic, and butyric. Solutions of tartaric acid and its salts are optically active, being dextro-rotatory. Tartaric acid is readily proved to be a dibasic acid, and its constitutional formula, which represents it as dihydroxy succinic acid, is established by its reduction (by HI) to malic and then to succinic acid. Other evidence to the formula is found in the synthesis of racemic acid whose relation to tartaric acid will now be discussed. POLYBASIC ACIDS AND ALCOHOL-ACIDS IQI Racemic acid is an acid of the same composition as tartaric acid, but which differs from the latter in several particulars. It crystallizes in a different form (triclinic) and with one molecule of water of crystallization which is lost at 110, and the acid melts with decomposition at 205-206. It is much less soluble in water than tartaric acid, and the solutions are optically inactive. Its salts, the racemates, often differ from the tartrates of the same metals both in their crystalline form and in their water of crystal- lization and solubility. The calcium racemate is still less soluble in water than the calcium tartrate, while the acid potassium racemate is more soluble. These differences led to its recognition and separation in the preparation of tartaric acid from argol. Racemic acid is formed in tartaric acid solutions under certain conditions, and this probably accounts for its appearance as a by-product in the working up of argol, though it or its salts may be a natural product. Berzelius proved the identity of its com- position with that of tartaric acid in 1830, and it is of interest to note that this fact together with the earlier discovery, that the fulminate and cyanate of silver had the same composition (Liebig, 1823), and some other similiar instances, led to the introduction of the word and idea of isomerism into chemistry. Formation.' Racemic acid is formed from tartaric acid by boiling it for some time with water or with solutions of hydro- chloric acid or sodium hydroxide. The conversion is, however, under these conditions, only partial; but when tartaric acid is heated with about one-ninth its weight of water to 125 (in a sealed tube) for some 30 hours, the change is almost complete. Racemic acid, together with mesotartaric acid, can be made from dibromsuccinic acid by substitution of hydroxyl for bromine: CO.OH.CHBr.CHBr.CO.OH + 2AgOH = CO.OH.CHOH.CHOH.CO.OH + 2 AgBr This reaction, which gives evidence for the structural formula of IQ2 INTRODUCTION TO ORGANIC CHEMISTRY racemic acid, may be made the final step for its synthesis from the elements, as follows: 2 C + sH 2 -* CH 2 :CH 2 - CN.CH 2 CH 2 CN -> CO.OH.CH 2 .CH 2 .CO.OH, etc. Resolution of Racemic Acid into Optically Active Tartaric Acids. In 1848, Pasteur found that the sodium ammonium salt of racemic acid gave two sets of crystals differing slightly in the disposition of their faces, and in such a way that one form corre- sponded to the mirror image of the other. On separating the two kinds, he found that the solution of one kind turned the plane of polarized light to the right, while that of the other was levo- rotatory. When the acids were set free from these salts, one proved to be the ordinary dextro-rotatory tartaric acid, and the other an isomeric, levo-rotatory acid. On mixing solutions con- taining equal weights of the two acids, and crystallizing, racemic acid is obtained. Pasteur also resolved racemic acid into the two active tartaric acids by taking advantage of the different solubilities of compounds which the two acids, mixed in racemic acid, form with certain optically active bases, such as cinchonine. By a third method, consisting in the action of certain organisms, one modification may be destroyed, leaving the other. Thus penicillium glaucum in a solution of ammonium racemate causes the dextro-tartrate to disappear, and ammonium levo-tartrate re- mains alone in solution. Racemic acid, like ordinary lactic acid, is, therefore, a com- bination of two optically active isomeric acids whose power on polarized light is equal, but opposite. The work of Pasteur by which these facts were brought out is of great historical interest, as it gave the first explanation of the relation of tartaric and racemic acids, and was the first time that an inactive substance was resolved into optically active com- pounds. * Racemic is now used as a general term to designate an 1 See Pasteur's " Researches on The Molecular Asymmetry of Natural Organic Products," in Alembic Club Reprints, No. 14. POLYBASIC ACIDS AND ALCOHOL-ACIDS 1 93 inactive substance which consists of a mixture of dextro and levo forms. Mesotartaric acid, also has the same composition as tartaric acid, and is formed together with racemic acid when ordinary tartaric acid is heated with water or sodium hydroxide; but its formation takes place more slowly than that of racemic acid, so that the yield is increased by prolonging the heating. It is also formed with racemic acid by the synthesis from dibromsuccinic acid. It is separated from ordinary tartaric and racemic acids by taking advantage of the much greater solubility of its acid potassium salt. 'It crystallizes with one molecule of water of crystallization in a form differing from those of the other acids, and the anhydrous acid melts at 140. Its solubility is about the same as that of tartaric acid, but its solutions are optically inac- tive, and it is not possible to resolve the acid into active com- ponents. It can, however, be partly converted into racemic acid by heating, and thus indirectly into the active tartaric acids. Its structural formula is the same as that of racemic acid and tartaric acid, as is shown by its formation from dibromsuccinic acid. We have, therefore,/0w dihydroxysuccinic acids: two of these are optically active, turning the plane of polarized light to an equal degree in opposite directions, and differing in no other respect except in the modifications of their crystalline forms, in the solubility of the compounds they form with optically active organic bases, and in their behavior toward certain organisms. The other two inactive acids differ from the active acids and from each other in crystalline form, in their melting points, the solubility of their salts, etc., as well as by the fact that one of them can be resolved into active components, while the other cannot. Stereochemistry of the Tartaric Acids. The student has noticed that the structural formula for these acids contains two asymmetric carbon atoms. One such atom accounts for the existence of two oppositely active and one inactive compound, as we have seen in a former discussion (p. 169). When there are 194 INTRODUCTION TO ORGANIC CHEMISTRY two or more asymmetric carbon atoms in the molecule the prin- ciples of stereochemistry admit the possibility of a larger number of physical isomers. With two as in this case, and two which are each combined with the same groups, there is but one additional arrangement. The formulas for the tartaric acids are: OH HO CO.OH i. d-Tartaric acid. OH HO. OH CO.OH 3. Mesotartaric acid. CO.OH CO.OH H--C OH HO C H I H C OH CO.OH 2 CO.OH 4. Mesotartaric acid. HO.OC HO C H CO.OH i H-C OH H C OH I CO.OH 3 CO.OH HO C H HO C H CO.OH 4 POL YB ASIC ACIDS AND ALCOHOL-ACIDS 1 95 The lower and upper halves of formula i or 2 can be exactly superposed, and we may suppose that each half therefore sup- plements the optical activity of the other. One molecule will then be wholly dextro-rotatory, the other wholly levo-rotatory. A mixture of the two in equal amounts will be inactive through external or intermolecular compensation. This accounts for the two active tartaric acids and for racemic acid. But in the arrange- ments 3 or 4 the lower and upper halves of the figure cannot be superposed; one half of each formula is identical with one of the two halves of i, and the other with one of the two halves of 2, so that both levo and dextro arrangements are present in the same molecule, and there is, therefore, optical inactivity through in- ternal or intramolecular compensation. This is the representation of mesotartaric acid. Formula 4 differs in no essential feature from formula 3. CO.OH I Citric acid, CO.OH.CH 2 .C.CH 2 .CO.OH, occurs in many acid OH fruits often together with malic and tartaric acids. The juice of unripe lemons contains 6-7 per cent, of citric acid, and the acid is prepared commercially from this source. It is first precipitated as the calcium salt from the hot clarified juice by adding powdered chalk until no more carbon dioxide is evolved, and then milk of lime. The calcium citrate, after thorough washing with hot water, is decomposed by the calculated amount of sulphuric acid which precipitates the calcium as calcium sulphate. The acid is finally purified by recrystallization. It is readily soluble in water and in alcohol. It ordinarily crystallizes with one mole- cule of water, which is lost at about 130. The anhydrous acid melts at 153, and recrystallizes from cold water without water of crystallization. When the solid acid is heated, it chars and gives irritating vapors, but no 'odor of burnt sugar as in the case ig6 INTRODUCTION TO ORGANIC CHEMISTRY of tartaric acid. It differs from tartaric acid also by charring much less readily when heated with concentrated sulphuric acid, and by the fact that its calcium salt is more soluble in cold than in hot water. Like tartaric acid and some other organic acids, it prevents the precipitation of certain hydroxides of metals from solutions of their salts. The acid is used for making lemonade, and is employed in medicine and in dyeing and calico printing. Magnesium citrate, (CeHsOT^Mgs^HjjO, is a readily soluble salt which is used in medicine and, mixed with acid sodium carbonate and sugar, forms the well-known "effervescing citrate of magnesia" or " fruit salts.' 7 Ferric ammonium citrate is used in making " blue- , print" paper. Structure of Citric Acid. The acid is readily proved to be a tribasic acid and to contain one hydroxyl group by the usual methods. The positions of the hydroxyl and carboxyl groups is demonstrated by the synthesis of the acid from symmetrical dichloracetone by the following steps: CH 2 C1 CH 2 C1 CH 2 C1 CH 2 .CN CH 2 .CO.OH HCN :o ->( < CN /OHxcN or ->( XJO.OH /OH HOH :< ->( X CO.OH /OH ^s ^\CO.OH :n 2 ci ( :H 2 ci ( :n 2 ci ( :H 2 .CN C H 2 .CO.OH Dichloracetone Citric acid Also, when carefully heated with concentrated sulphuric acid the first reaction is the general one for the a-hydroxy-acids the splitting off of formic acid (p. 171) with the formation of acetone-dicarboxylic acid, followed by the decomposition of this acid into acetone and carbon dioxide: POLYBASIC ACIDS AND ALCOHOL-ACIDS CH 2 .CO.OH CH 2 .CO.OH CH g /OH '/ 197 \CO.OH CH 2 .CO.OH Glycollic Lactic Hydracrylic Glyceric o-Hydroxybutyric /3-Hydroxybutyric 7-Hydroxybutyric Trihydroxy-isobutyric Malic Tartaric Racemic Mesotartaric Citric HYDROXY-ACIDS CH 2 (OH).CO.OH CH 3 .CH(OH).CO.OH CH 2 (OH).CH 2 .CO.OH CH 2 (OH).CH(OH).CO.OH CH 3 .CH 2 .CH(OH)CO.OH CH 3 .CH(OH).CH 2 .CO.OH CH 2 (OH).CH 2 .CH 2 .CO.OH (CH 2 OH) 2 .C(OH).CO.OH CO.OH.CH 2 .CH(OH).CO.OH CO.OH.CH(OH) .CH(OH) . CO.OH CO.OH.CH(OH).CH(OH).CO.OH CO.OH.CH(OH).CH(OH). CO.OH CO.OH I CO.OH.CH 2 .C.CH 2 .CO.OH Melting Point 79-80 (Syrup) (Syrup) (Syrup) 42-44 (Syrup) (Unstable) 116 c.ioo 168-170 205-206 140 153 OH CHAPTER XV THE CARBOHYDRATES The compounds which are produced most abundantly, by growing plants, and which are the most important products of vegetation, are substances which contain hydrogen and oxygen, in the proportion in which they form water, combined with carbon. For this reason they were called carbohydrates. They do not con- tain water as such, and they are in no sense hydrates of carbon, as the name implies. Other compounds of carbon, hydrogen, and oxygen, in which the hydrogen and oxygen atoms are in the proportion of two to one, such as formaldehyde, acetic acid, or dihydroxyl acetone, might with equal reason be called carbohy- drates. But, as in other cases, the old name has been retained, in spite of its erroneous suggestion, as a convenient designation of a group of substances which are definitely related to each other. The study of the structure of the carbohydrates has shown that the simpler ones are aldehyde-alcohols or ketone-alcohols, and the more complex are converted into such compounds by hydrolysis. The most important and best known members of the group are the sugars, starches, and celluloses. Our knowledge of the struc- ture of the sugars has been greatly extended in the last twenty- five years, especially by the investigations of Emil Fischer, who has succeeded in adding a considerable number of new synthetic sugars to those found in nature. The starches and celluloses are much more complex substances than the sugars and we have no definite knowledge of their structure except through the fact that they all yield simple sugars on hydrolysis. This indicates that 198 THE CARBOHYDRATES 1 99 they, as well as the more complex sugars, may be regarded as anhydride-like derivatives of the simple sugars. Their mole- cular weights cannot be determined with any certainty, but they appear to be very large. Unlike the sugars, they cannot be crystallized, have no characteristic taste, and in some cases are entirely insoluble in water. The sugars, and the other carbohydrates from which sugars are derived by hydrolysis, are called saccharoses and are divided into two classes: the mono ^saccharoses, which do not undergo hydrolysis; and the poly saccharoses, which can be converted by hydrolysis into monosaccharoses. The Monosaccharoses These sugars have names that end in ose. Those which are aldehyde-alcohols are known as aldoses, and those that are ketone- alcohols are called ketoses. They are further distinguished .ac- cording to the number of carbon atoms they contain as dioses, trioses, etc. Except in one instance, the rhamnose, the molecules contain no unsubstituted alkyl groups, but only primary or secondary alcohol groups with one aldehyde or ketone group. Further, their carbon atoms are united in open, unbranched chains, so that they are all derivatives of normal hydrocarbons. When the aldehyde group is present it is a terminal group, and the ketone group is always next to a terminal alcohol group. Compounds of this structure have been met with in glycollic aldehyde (p. 162), glyceryl aldehyde, and dihydroxyl acetone, (p. 161). These represent the classes of dioses and trioses and may properly be included in the group of sugars. The student will recall that glycollic aldehyde is "condensed" by the action of dilute alkali into a tetrose (p. 162). All of the aldoses and ketoses, with the exception of glycollic aldehyde, and dihydroxyl acetone, contain one or more asymmetric carbon atoms. Hence stereochemical isomerism is possible, 200 INTRODUCTION TO ORGANIC CHEMISTRY with an increase in the number of groupings as the number of the asymmetric carbon atoms is greater. The rule for the number of isomers is given by the formula 2 n , n being the number of asymmetric carbon atoms. The aldohexoses contain four such atoms, and hence there are sixteen stereo-isomers; the ketohexoses have three asymmetric carbon atoms and hence their possible number is eight. We find that the sugars are all optically active when they are not in the "racemic" form. The structure of these compounds is determined by the methods with which we have become familiar in the study of simpler sub- stances. The presence of hydroxyl groups and their number is found by examination of the acetyl substitution products which are obtained when the sugar is treated with acetic anhydride in the presence of zinc chloride; and the presence of the aldehyde or ketone group is determined by the products of careful oxidation and by their reactions. An aldehyde group, being monovalent, must always be at the end of the chain of carbon atoms, and the position of the divalent ketone group is inferred from the numbers of carbon atoms in the first oxidation products (cf. p. 90). The monosaccharoses are all colorless and odorless substances. They dissolve readily in water, with difficulty in absolute alcohol, and are insoluble in ether. Their solutions are sweet, and are neutral to litmus. Those which contain five or more carbon atoms are mostly solids which usually crystallize well from pure solu- tions, but the crystallization is often very slow, and is retarded or prevented by the presence of other substances. When heated above their melting point, they are decomposed, turning brown, and finally charring. Glycerose (glyceryl aldehyde) and the natural hexoses are fermented by yeast with the production of alcohol. The pentoses do not enter into alcoholic fermentation, and the property of such fermentation appears to be restricted to sugars which contain three, or a multiple of three, carbon atoms. Monosaccharoses with Less than Six Carbon Atoms. Gly collie aldehyde, CH 2 OH.CHO, is the simplest possible aldose; THE CARBOHYDRATES 2OI glyceryl aldehyde, CH 2 OHCHOH.CHO, is the next aldose, and dihydroxylacetone, CH 2 OH.CO.CH 2 OH, is the simplest of the ke- tones. Erythrose, C 4 H 8 O 4 , or CH 2 OH.CHOH.CHOH.CHO, is the first product of the oxidation of erythritol, the normal tetra- hydroxyl alcohol, and is probably identical with the tetrose which is formed by the aldol condensation of glycollic aldehyde. Tet- roses are also formed by oxidation of pentonic acid (tetrahy- droxy valeric acid, CH 2 OH(CHOH) 3 .(CO.OH) in the form of its calcium salt. Pentoses. Arabinose and Xylose are both aldoses with five carbon atoms and have the formula CH 2 .OH(CHOH) 3 .CHO. They are obtained by the hydrolysis of natural polysaccharoses arabinose from gum-arabic or cherry gum, and xylose (wood sugar) from wood gum, by boiling beech- wood, jute, etc., with dilute acids. Rhamnose is a methyl substituted pentose, CH 3 .- (CHOH) 4 .CHO, which is a product of the hydrolysis of certain glucosides. These three pentoses are all dextro-rotatory. They are oxi- dized by bromine to corresponding monocarboxylic acids, and by nitric acid to trioxyglutaric acid, CO.OH(CHOH) 3 .CO.OH. They can all be reduced by sodium amalgam to the corresponding pentahydroxyl alcohols. Hexoses Two natural sugars, glucose and fructose, are hexoses. They are widely distributed in the vegetable kingdom, occurring to- gether in the juices of many sweet fruits, in the roots, leaves, and flowers of plants, and in honey. These two sugars are formed in equal amounts by the hydrolysis of cane sugar, and isomers, identical in every respect except in the matter of optical activity, have been made synthetically from formaldehyde and from glycerol. They crystallize less readily than cane sugar. In solution both undergo alcoholic fermentation with yeast but the rate of the fermentation is usually not the same, and depends 202 INTRODUCTION TO ORGANIC CHEMISTRY on the yeast that is used. Both reduce Fehling's solution to the same extent, the fructose here acting more rapidly than the glucose; both give silver mirrors with ammoniacal silver nitrate; and neither when pure is discolored by cold concentrated sulphuric acid. Their solutions are both optically active, glucose being dextro-rotatory, and fructose (levulose) levo-rotatory. The action of fructose on polarized light is more powerful than that of glucose; and hence a solution containing equal amounts of the two sugars (invert sugar) is levo-rotatory. (See table of Specific Rotations p. 408). Both sugars form compounds with calcium and barium when treated with the hydroxides of these metals. d-Glucose, CeH^Oe, is also known as dextrose and grape- sugar. The name of dextrose was given this sugar because it is dextro-rotatory; but with the discovery of other dextro-rotatory hexoses, and of a levo-rotatory glucose, the name is no longer distinctive, and is little used. Glucose is present in considerable quantities in ripe grapes, and forms the brownish nodules which are seen in raisins. Certain natural substances known as glucosides are esters of glucose, and yield this sugar as one of the products of hydrolysis. Among these are: amygdalin (p. 147), asculin (in horse-chestnut bark), and the tannins (p. 367). Glucose appears in diabetic urine, sometimes to the amount of 8-10 per cent. Formation and Preparation. Glucose is a product of the hydrolysis of a number of poly saccharoses, which occurs when they are heated with water with the addition of a little inorganic acid. Starch, dextrin, and maltose can in this way be completely converted into glucose. Cellulose is soluble in concentrated sulphuric acid, and when the solution is largely diluted with water and boiled, soluble carbohydrates are formed, the final product of the hydrolysis being glucose. It is thus possible to make wood and other vegetable fibers into a sugar, and through this into alcohol. Certain other carbohydrates on hydrolysis yield glucose with THE CARBOHYDRATES 203 some other hexose. Cane sugar gives equal amounts of dextrose and levulose (invert sugar), milk sugar is converted into dextrose and galactose, and raffinose into glucose, fructose, and galactose. Glucose may be prepared in the laboratory by hydrolysis of cane sugar in alcoholic solution by means of hydrochloric acid. Since glucose is less soluble in alcohol than the fructose which is simultaneously formed, a considerable part of it will crystallize from the solution. Commercial glucose or "grape-sugar" is made from starch by heating it with very dilute acid. In Europe the starch of pota- toes, rice and sago is used and sulphuric acid is employed as the hydrolytic agent. In this country corn starch is the source of "dextrose" and the syrup known as "glucose." The starch is heated with a i to 3 per cent, solution of hydrochloric acid, usually under pressure. For the production of "glucose," the heating is stopped when iodine no longer gives a blue color (starch) with the solution. The solution is then nearly neutralized with sodium carbonate, clarified by bone-black and evaporated in vacuum pans to a specific gravity of 1.375-1.43. This "glucose" contains d-glucose with maltose, and considerable amounts of dextrin which is an intermediate product. In the manufacture of grape-sugar, the heating is prolonged a little beyond the point at which alcohol fails to produce a precipitate in a sample of the solution (absence of starch and dextrin). The solution is then neutralized, clarified, and evaporated so far that it solidifies on cooling. Grape-sugar forms a mass of waxy texture, and con- tains a small .amount of dextrin. Glucose is also obtained when cellulose (wood fiber) is heated with dilute acids under pressure of six or eight atmospheres. In a recent process for making alcohol from wood waste such as saw-dust, sulphurous acid is used under pressure to cause the conversion into glucose. Uses of "Glucose" Glucose is largely used as a table syrup, in making confectionery, jellies, and preserves; as an addition to wine and beer wort before fermentation in order to increase the 204 INTRODUCTION TO ORGANIC CHEMISTRY amount of alcohol; as an adulterant for thick liquids, such as extracts of logwood, etc.; and as a reducing agent in indigo dyeing. Properties of Glucose. Glucose crystallizes from water at or- dinary temperatures with one molecule of water, but from alcohol or concentrated aqueous solutions at 3o-35, anhydrous crystals are formed which melt at 146. It is much less sweet than fructose or cane sugar. It is not charred by concentrated sul- phuric acid, as cane sugar is, but like cane sugar is oxidized to oxalic acid by nitric acid. Heated with alkalies it turns brown. Structure. By the acetyl reaction glucose is shown to contain five hydroxyl groups. Reduction by sodium amalgam in aqueous solution converts it into sorbitol, a normal hexahydroxyl alcohol, which shows that the carbon atoms in glucose are linked in an unbranched chain. By careful oxidation it forms gluconic acid, C 6 Hi 2 O 7 or CH 2 OH(CHOH) 4 .CO.OH, by the addition of one oxygen atom, which indicates that glucose contains an aldehyde group. Gluconic acid cannot be crystallized, as on concentrating its solution it is dehydrated and forms gluconic lactone (cf. p. 172), a crystalline substance that is reconverted into glucose on reduction with sodium amalgam in slightly acid solution. This is a reaction of great synthetical importance (p. 207) . Further oxi- dation of glucose gives saccharic acid, CeHioOs, HO.OC(CHOH) 4 .- CO.OH. This is a dibasic acid and a comparison of its formula with that of gluconic acid shows that both gluconic acid and glucose contain a primary alcohol group. We arrive thus at the following constitutional formula for glucose as an aldose: CH 2 OH.CHOH.CHOH.CHOH.CHOH.CHO d-Fructose, C 6 Hi 2 O6, also known as fruit sugar, and levulose. We have seen that fructose frequently occurs in nature with glucose, and is formed with it in the hydrolysis of certain poly- saccharoses. Honey contains about 80 per cent, of invert sugar, and cane sugar is completely hydrolyzed into this mixture of glucose and fructose. From such mixtures fructose can be sepa- THE CARBOHYDRATES 205 rated in the form of an insoluble calcium compound which yields fructose when treated with carbon dioxide; but it is best prepared by the hydrolysis of inulin, a polysaccharose which occurs in the tubers of the dahlia and some other plants, and yields only fructose. Properties. Fructose is somewhat less soluble in water than glucose, but crystallizes with greater difficulty. Anhydrous crystals are obtained from its alcoholic solution which melt at 95. It is sweeter than glucose. Structure. As in the case of glucose, five hydroxyl groups may be proved to be present; but on oxidation it gives two acids, one with four carbon atoms, and one with two, instead of a single acid with six carbon atoms. When boiled with mercuric oxide it gives a mixture of trihydroxy-butyric acid and glycollic acid; carefully oxidized with nitric acid, it yields tartaric and glycollic acids: C 6 Hi 2 O 6 + 2O = CH 2 OH.(CHOH) 2 .CO.OH + CH 2 OH.CO.OH Trihydroxy-butyric acid Glycollic acid C 6 H 12 O 6 + 40 -> CO.OH.(CHOH) 2 .CO.OH + CH 2 OH.CO.OH Tartaric acid Glycollic acid These reactions are those of a compound with a ketone struc- ture (p. 90) and show that fructose is a ketose with the formula, CH 2 OH. CHOH. CHOH. CHOH. CO. CH 2 OH. d-Galactose, CeH^Oe, is a sugar which is formed together with glucose by the hydrolysis of milk sugar. A number of other carbohydrates, such as certain gums, also yield galactose as one of the products of their hydrolysis; and it is formed by the careful oxidation of dulcitol, a hexahydroxyl alcohol which occurs in cer- tain plants. It is less soluble in water than either glucose or levulose, and its solutions are fermented by yeast, though more slowly than those of these sugars. It is strongly dextro-rotatory and forms minute hexagonal crystals which melt at 168. d-Mannose, CeHujOe, is produced together with fructose by the careful oxidation of the natural hexahydroxyl alcohol, mannitol, and is also formed by the hydrolysis of certain carbohydrates, 206 INTRODUCTION TO ORGANIC CHEMISTRY especially from one contained in vegetable ivory. It is a hard amorphous substance which is hygroscopic and very soluble in water, but difficultly soluble in alcohol, even when hot. It is dextro-rotatory and readily fermented by yeast. Both galactose and mannose are aldoses with the same struc- tural formulas as glucose, as is shown by their conversion by careful oxidation into galactonic and mannonic acids which are physical isomers of gluconic acid, and then into mucic and manno- saccharic acids, which stand in similar relation to saccharic acid. Sorbose, CeH^Oe, is found in the juice of mountain ash berries after standing, being apparently formed by bacterial oxidation of the hexahydroxyl alcohol, sorbitol, which is present in the berries. It is a ketose, a stereo-isomer of fructose. Formation and Synthesis of the Monosaccharoses. Besides the method of formation which consists in the hydrolysis of polysaccharoses, and which is applicable to both pentoses and hexoses, the members of this group can be made in other ways, of which the following are the most important: 1. Oxidation of the corresponding polyhydroxyl alcohols. The products obtained by ordinary oxidizing agents (nitric acid) are aldoses, while the sorbose bacteria (bacterium xylinum) cause the formation of ketoses not only from sorbitol, but also from glycerol and other polyhydric alcohols. 2. Through the addition product which hydrocyanic acid forms with aldehydes, one aldose may be converted into another with one more atom of carbon in the molecule. For example, an aldohexose forms with hydrocyanic acid a cyanhydrin, /OH CH 2 OH.CHOH.CHOH.CHOH.CHOH.CH< . This is con- X CN verted on hydrolysis into a seven-carbon-atom monobasic acid, CH 2 OH.CHOH.CHOH.CHOH,CHOH.CHOH.CO.OH, which THE CARBOHYDRATES 207 readily loses the elements of water with the production of a 7- lactone (cf. p. 172). CH 2 OH.CHOH.CHOH.CH.CHOH.CHOH.CO; and finally, the lactone in aqueous solution is reduced by sodium amalgam to the corresponding aldehyde, which is an aldoheptose, CH 2 OH(CHOH) 5 CHO. By this method heptoses, octoses and nonoses have been prepared. 3. One of the methods for descending from one sugar to another with one less carbon atom is the following: the oxime (p. 79) is made, and this on heating with concentrated sodium hydroxide gives the nitrile, which on further heating loses hydrocyanic acid and gives the lower sugar. The transformations in the groups affected are: CHO CH:N.OH CN CHO (CH.OH) 4 -> (CHOH) 4 -> (CHOH) 4 -> (CHOH) 3 +HCN I I I I CH 2 OH CH 2 OH CH 2 OH CH 2 OH Glucose Oxime Nitrile Arabinose 4. The formation of a tetrose from glycollic aldehyde and of a hexose from formaldehyde and from glyceric aldehyde by aldol condensation have already been referred to, as has also the significance of the synthesis of a sugar from formaldehyde with its suggestion of the mode by which the natural carbohydrates may be built up in plants from the carbon dioxide and water (p. 86). 5. Aldoses can be converted into the isomeric ketoses by means of the osazones which can be made from them (see below). 6. Ketoses can be changed into the corresponding aldoses by the following steps : the ketone is reduced by sodium amalgam to the polyhydroxyl alcohol; this may be converted into the aldose by careful oxidation (method i); or is oxidized into a monobasic 208 INTRODUCTION TO ORGANIC CHEMISTRY acid which is then changed to the aldose by the lactone reaction (method 2). Inactive fructose is of especial historic interest as it is the first sugar which was produced from substances which are themselves capable of synthetic formation. It results from the polymeriza- tion of formaldehyde by bases (p. 85); from glyceric aldehyde by aldol condensation; from glycerose (formed by oxidation of glycerol) by the action of dilute alkalies. It was originally called acrose. It has all the properties of natural fructose, ex- cept optical activity. It ferments with yeast, but the fermenta- tion is partial, destroying the levo-rotatory component and leav- ing a dextro-rotatory fructose. By a series of reactions, mostly of the kind which have been discussed, the synthetic inactive fructose can be converted into the natural sugars mannose, glucose and fructose. Another interesting fact is that glucose, fructose and mannose are each partially converted into both of the others under the influence of dilute alkalies, an equilibrium being established which may be thus represented; Glucose <=* Fructose ^ Mannose The study of the sugars has been greatly facilitated by the fact that they form compounds called osazones which, unlike the monosaccharoses themselves, are sparingly soluble in water, are readily obtained in the pure state by crystallization, and have characteristic melting points. Through these properties of the osazones, the sugars, which by themselves are separated with great difficulty, may be distinguished and identified. We have seen (p. 80) that hydrazine and its derivatives react with the aldehydes and ketones to form hydrazones. By reac- tion with phenyl (C 6 H 5 ) hydrazine, C 6 H 6 NH:NH 2 , both the aldoses and the ketoses form hydrazones, which, when an excess of the phenyl hydrazine is present, react with it with the final THE CARBOHYDRATES 2OQ production of double hydrazones called osazones. The steps in the case of an aldose are: - CHOH.CHOH.CHO + C 6 H 5 .NH.NH 2 - Aldose -CHOH.CHOH.CH:N.NH.C 6 H 5 Hydrazone - CHOH.CHOH.CH:N.NH.C 6 H 5 + C 6 H 5 NH.NH 2 - Hydrazone NH 3 + CeHs.NH, + - CHOH.CO.CH:N.NH.C 6 H 5 , Carbonyl compound and this + C 6 H 5 .NH.NH 2 -> - CHOH.C.CH:N.NH.C 6 H 5 II N.NH.C 6 H 5 Osazone With a ketose the steps are: -CHOH.CO.CH 2 OH -CHOH.C.CH 2 OH > Ketone y N.NHC 6 H 6 Hydrazone -CHOH.C.CHO > -CHOH.C.CH:N.NHC 6 H 6 II II N.NHC 6 H 5 N.NHC 6 H 5 Aldehyde Osazone compound The osazones of the aldoses and of corresponding ketoses are identical. On treatment of an osazone with strong hydrochloric acid it is decomposed with the formation of a ketone-aldehyde, CO.CHO, called an osone, and this is reduced by nascent hydrogen into a ketose. Thus it is possible to convert an aldose into its isomeric ketose, as for instance, glucose into fructose. By the reactions which have just been discussed, many synthet- ical sugars have been made and definitely distinguished. All of the sixteen possible aldolhexoses are known and five of the eight ketohexoses, including the natural sugars. The synthetical sugars which have been made are stereo-isomers of the natural sugars, having a different optical activity or being inactive. 1 1 For further discussion of the methods of sugar synthesis and for the stereochemistry of the sugars, see: "The Simple Carbohydrates and the Glucosldes" by E. Frankland Armstrong, and "Modern Organic Chemistry" by C. A. Keane. 210 INTRODUCTION TO ORGANIC CHEMISTRY Stereochemistry of the Hexoses. The configurations, or stereo-formulas of all of the possible sixteen aldo-hexoses have been determined by Fischer, as well as those of many of the related alcohols and acids; and the following projection formulas of the three aldo-hexoses which we have considered, and of the two fructoses (ketohexoses) are given here as illustrations: d-Glucose d-Galactose d-Mannose CHO CHO CHO HCOH HCOH HOCH I I I HOCH HOCH HOCH I I I HCOH HOCH HCOH I I I HCOH HCOH HCOH CH 2 OH CH 2 OH CH 2 OH d-Fructose l-Fructose CH 2 OH CH 2 OH I I CO CO I I HOCH HCOH I I HCOH HOCH I I HCOH HOCH CH 2 OH CH 2 OH In the systematic nomenclature of sugars which the synthetic additions to the group have made necessary, all monosaccharoses derived from a dextro-, levo-, or inactive hexose are designated by the letter d, I, or i, without reference to the rotatory power they may actually possess. Thus ordinary fructose which is levo-rotatory is called d-fructose because it can be obtained from "d-glucose." The same method of classification is adopted for the THE CARBOHYDRATES 211 hexahydroxyl alcohols and other derivatives of the hexoses. This has not been emphasized in the brief discussion of the sugars in this book, but is necessary in any extended study of the litera- ture of the subject. The Polysaccharoses We may divide this group into the disaccharoses, of which cane sugar is the most important member, the trisaccharoses, and the carbohydrates of unknown molecular weight the starches and the celluloses to which the name of polysaccharoses is often re- stricted. Disaccharoses These sugars have the molecular formula, Ci 2 H 22 On, equal to a double hexose less a molecule of water; and they are readily con- verted into hexoses by hydrolysis: C 12 H 22 O n + H 2 = 2C 6 H 12 6 From the ease with which this conversion occurs, it is inferred that the hexose residues in the disaccharoses are not united by the linkage of carbon atoms, but by oxygen; so that the disac- charoses are, in a sense, anhydrides of the hexoses. They can- not, however, be obtained from the hexoses by means of water- withdrawing agents, as many anhydrides are made; but by in- direct methods in which acetyl substitution products of the hexoses play a part, artificial disaccharoses have been made. Saccharose, sucrose, or cane sugar, Ci 2 H 22 On, is our common sugar and commercially much the most important of all the sugars. It is widely distributed in nature, occurring in the juice of the sugar cane, sorghum and many other species of grass, in beets and many other roots, in the sap of the sugar maple and other trees, and in many fruits, and in seeds such as walnuts, almonds, and coffee, and in the nectar of flowers. Nearly all of the world's supply is obtained from the sugar cane and the sugar beet. In the growing cane the only sugar present 212 INTRODUCTION TO ORGANIC CHEMISTRY is dextrose, but this disappears as the plant matures and the ripe cane contains only a trace of it with about 18 per cent, of sac- charose. The sweet juice is usually expressed from the cane by crushing it between heavy rolls. Beets contain from 12 to 15 per cent, of sugar. They are cut into thin slices or rasped to a pulp, and digested with warm water, into which the crystallizable sugar passes by diffusion, leaving the colloids albuminoids, gums etc., for the most part in the root cells. This diffusion process, consequently, gives a purer juice than can be obtained by other means. The subsequent processes are much the same in both the sugar cane and the beet industries. The juice is boiled with milk of lime with the result that calcium salts of the acids which are present, together with coagulated albuminous substances and gum, are separated as a scum. The clarified juice is finally concentrated by evaporation, usually in vacuum pans, allowed to crystallize, and separated from the mother-liquor or "molasses" by draining from hogsheads with perforated bottoms, or more commonly by centrifugal machines. The product is a raw sugar of a more or less brownish color, containing a number of im- purities. White granulated sugar is obtained from it by a refining process which consists essentially in dissolving the sugar in water, decolorizing- by bone black and recrystallizing. The molasses contains 40 to 50 per cent, of sugar. This is diluted, clarified and boiled down for a "second sugar." The " second molasses" from this sugar, when obtained from the sugar cane, still contains about 40 per cent, of sugar which it does not pay to recover. It is sometimes fermented for making rum or alcohol, and sometimes used as fuel. It is not suitable for table use or cooking, but a little of the first molasses from cane sugar is used in this way. Beet sugar molasses is unfitted for table use, by its very unpleasant odor and taste from, the pres- ence of certain nitrogenous substances. Much of the . sugar re- maining in the second molasses from beet sugar is recovered by changing it into an insoluble calcium or strontium sucrate by THE CARBOHYDRATES 213 treatment with lime or strontium hydroxide. After separation and washing, the sucrate is mixed with water and decomposed into sugar and insoluble calcium or strontium carbonate by carbon dioxide. The final molasses from beet sugar contains a large amount of organic salts of potassium together with the nitrogenous substances which have been mentioned. This molasses is usually fermented and the alcohol distilled, leaving these substances in the residue, which is called mnasse. If this is evaporated and calcined, the ash contains about 35 per cent, of potassium carbonate. If the residue from evaporation is destruc- tively distilled, methyl alcohol, ammonia and "trimethyl amine" (p. 132) are obtained as valuable products, and the potassium products are recovered from the cinder left in the retort. Properties. Cane sugar is soluble in about half its weight of cold water. It crystallizes well from concentrated solutions (syrups) in large, transparent crystals known as "rock-candy." It melts at 160 and solidifies, on cooling, to an amorphous, glass- like mass, which after a time becomes crystalline. On stronger heating, it turns brown, being converted into "caramel," an amorphous substance, much used as a flavoring and coloring material. At a high temperature it is completely decomposed, with the evolution of gases and vapors, leaving a residue of nearly pure, porous charcoal (sugar charcoal). Among the products of its destructive distillation are the oxides of carbon, hydro- carbon gases, aldehyde, acetic acid, etc. When moistened and treated with concentrated sulphuric acid it turns brown and finally chars. Sugar is oxidized easily by such agents as chromic acid, potas- sium chlorate, or nitric acid. With the first two the reaction is explosive; with concentrated nitric acid, a considerable product is oxalic acid (cf. p. 177). Caustic alkalies do not turn cane- sugar solutions brown as they do solutions of dextrose. Cane-sugar solutions are strongly dextro-rotatory. In the presence of acids, the sugar is hydrolyzed into a mixture of equal 214 INTRODUCTION TO ORGANIC CHEMISTRY amounts of glucose and fructose (invert sugar), which is levo- rotatory because of the stronger optical effect of fructose. The hydrolysis takes place slowly in cold solutions and more rapidly when they are heated. Even carbonic acid effects the con- version. Cane sugar is not fermented by zymase, the enzyme of yeast, which produces alcoholic fermentation in glucose and fructose; but ordinary yeast causes alcoholic fermentation, though not as quickly as with the hexoses, because it contains another enzyme, called invertase, which first converts the saccharose into invert sugar. Strong syrups, however, do not ferment, and sugar is used in the preserving of fruit and in jellies. Sugar combines with various oxides and hydroxides of metals, which are resolved into sugar and the metal carbonate by carbon dioxide. The calcium and strontium sucrates, as has been noted, play a part in the recovery of sugar from molasses. Structure of Saccharose. Saccharose is shown by its acetyl substitution products to contain eight hydroxyl groups, and its reactions indicate the absence of aldehyde and ketone groups. In the natural synthesis of cane sugar, which appears to be effected from the hexoses, these groups must be involved in the change. We have seen in the case of the polyhydroxy -acids that lactones are readily formed by the loss of the elements of water from the carboxyl and -y-hydroxyl group; and while the structure of saccharose has not been definitely established, it is probable for this and other reasons that it is represented by the following formula: O CH 2 OH.CHOH.CH.CHOH.CHOH.CH Glucose residue r J CH 2 OH.CH.CHOH.CHOH.C.CH 2 OH Fructose residue THE CARBOHYDRATES 215 Lactose, milk sugar, Ci 2 H 22 Oii is present to the amount of 3 to 5 per cent, in the milk of mammals. When the fats (cream) have been removed from milk and the casein (curds) has been precipitated, as by rennet in cheese-making, the whey or watery solution c ntains most of the milk sugar, which is readily obtained by evaporation, and purified by recrystallization. It crystallizes with one molecule of water, Ci 2 H 22 On, H 2 O. It is much less soluble, and much less sweet than cane sugar. Lactose is not affected by cold concentrated sulphuric acid. Solutions of lactose are dextro-rotatory. It differs from cane sugar and resembles dextrose by turning brown when heated with solutions of caustic alkalies, by reducing Fehling's solution and ammoniacal silver nitrate, by forming a phenyl osazone, and in being reduced to polyhydroxyl alcohols by sodium amalgam. It differs from both cane sugar and the hexoses by not fermenting with yeast. It is converted into lactic acid by the lactic acid ferment, and is hydrolyzed by dilute acids into a mixture of glucose and galactose, both of which are aldoses. Structure. The reactions of lactose indicate the presence of an aldehyde group, and reasons similar to those given for the con- stitution of saccharose point to the following as the probable formula for lactose: O CH 2 OH.CHOH.CH.CHOH.CHOH.CH Glucose residue O CHO.CHOH.CHOH.CHOH.CHOH.CH 2 Galactose residue Maltose Ci 2 H 22 On, is produced from starch by the action of diastase, an enzyme present in malt, by an enzyme contained in saliva, and by other ferments, and is an intermediate product in the hydrolytic conversion of starch and dextrin into dextrose. Its formation from starch is a important factor in the manufac- ture of beers and other alcoholic beverages, and of alcohol. 2l6 INTRODUCTION TO ORGANIC CHEMISTRY Maltose is very readily soluble in water and its solutions are more strongly dextro-rotatory than those of any other sugar. It reduces Fehling's solution, and is readily and completely fer- mented by yeast into alcohol and carbon dioxide. It forms a phenyl osazone. From dextrose, which it so greatly resembles in its behavior, it is distinguished by its stronger rotatory power, by being less soluble in water and in alcohol, and by not reducing a weak acetic acid solution of copper acetate. Its reduction of Fehling's solution, too, is slower and less in amount than that of glucose. Maltose yields only glucose when hydrolyzed. As the anhydride from two molecules of an aldose, glucose, it is given the same structural formula as lactose. Trisaccharoses Raffinose, Cigl^Oie, is the only one of this group which has any importance. It occurs in small amounts in the sugar beet and is obtained from the molasses. It is also found in cotton seed and in barley. It is much less soluble in water than cane sugar and crystallizes with five molecules of water. The crystals lose their water at 100, and the sugar melts atii8-ii9. The solutions are strongly dextro-rotatory. It is indifferent toward alkalies and Fehling's solution, but is completely fermented by yeast. On hydrolysis it yields first fructose and melebiose (melebiose being a disaccharose) which breaks down into glucose and galactose. Two or three crystallizable carbohydrates obtained from various roots seem to belong between the well-characterized sugars and the amorphous carbohydrates of much higher molecular weight. Their molecular weights are not known with certainty but are possibly expressed in the formula CaeH^Oai. They are readily soluble in water, are dextro-rotatory and give mixtures of sugars on hydrolysis. THE CARBOHYDRATES 217 Carbohydrates of Unknown Molecular Weight Polysaccharoses Most of these carbohydrates are amorphous substances and have no distinctive taste. The most important members of the group the starches and celluloses are insoluble in water, and those which appear to dissolve form " colloidal solutions." Like other amorphous and colloidal substances they have no definite melting points. Their composition is represented by the formula CeHioOs, but their molecular weights are unknown though there is evidence that they must be very large. The formula usually given them is, therefore (CeHioOs) . Since these carbohydrates give simple sugars on hydrolysis, we may infer that they are built up of monosaccharose residues united, as in the disaccharoses, by linking oxygen atoms. If this is the case their relation to the simple sugars would be represented by xC 6 Hi 2 O 6 - (x-i)H 2 O It would be practically impossible to determine by analysis the differences between the composition represented by this last formula and that shown by (CeHioOs)*, if x is very large. For instance, if x = 100, the percentages of carbon, hydrogen, and oxygen corresponding to the two formulas would be: For (C 6 HioO 6 )ioo For C 60 oHioojO 60 i C = 44.42 44.37 H = 6.22 6.23 O = 49-36 49-40 100.00 100.00 Most of these carbohydrates are the products of plant life, nd together with the natural sugars are built up from the carbon dioxide of the air and water, probably through the formation of 2l8 INTRODUCTION TO ORGANIC CHEMISTRY formaldehyde and subsequent polymerizations. Cane sugar ap- pears to be the first definite carbohydrate formed which can be isolated, though fructose, glucose, and maltose are also present in the green leaf. The more complex starches and celluloses are the final products of the plant synthesis. Starch occurs in nearly all plants, and is utilized by the plant for the elaboration of other substances. It is stored in consider- able quantities in the seeds, tubers, and many roots, where it forms an important reserve material for the nourishment of the future plant until it can become self-supporting from atmospheric supplies. The chief industrial sources of starch are potatoes, wheat, corn, rice, arrowroot and certain palms. In this country corn and wheat are used; in Europe, potatoes, rice and wheat are mainly employed. The manufacture of starch is essentially a mechanical separation from the gluten, fats, etc., which accompany it in the original material. In making corn starch, for instance, one proc- ess is in outline as follows: Much of the oil is removed and the gluten softened by first steeping in warm water for some days. Next, the grain is ground, while a current of water carries the product to revolving sieves and then to bolting cloth strainers, through which the starch passes in suspension in the water. On standing, the crude starch is deposited, and after being washed with fresh water is stirred up in vats with a dilute solution of caustic soda. After several hours the suspended matters are allowed to settle, and the solution containing much of the im- purity is drawn off. The sediment is again stirred up with water, and allowed to stand until the gluten is deposited, while the starch, still in suspension, is drawn off and deposited in other tanks. By several repetitions of this process the starch is mostly removed from the gluten and at the same time separated into several grades. Modifications of this process are also employed, and centrifugal machines are sometimes used to separate the starch from the wash water. Corn contains about 58 per cent. THE CARBOHYDRATES 2 19 of starch and about 50 per cent, is actually obtained, and, at the same time, over 20 per cent, of gluten suitable for cattle food. Properties. Starch is a white, glistening powder, consisting of micr .scopic granules which have a concentric structure and are doubly refracting. The form, size and markings of the granules vary with the source, so that this is readily determined by a microscopical examination. Starch is very hygroscopic, and ordinary starch contains from 16-18 per cent, of water, which can be driven off by careful heating up to 110. The granules are enveloped in a cellulose membrane which completely protects them from the action of cold water, but when heated with water the granules swell up and burst, forming starch paste, and on longer heating some of the starch goes into colloidal solution. If treated for some days with a cold dilute inorganic acid, "soluble starch" is produced which dis- solves in hot water without forming a paste. When heated to 2oo-25o starch is changed into dextrin, and a similar change is effected at a lower temperature, when the starch has first been moistened with hydrochloric or nitric acid, dried at 50, and then heated to 140-! 70. Starch is hydrolyzed to dextrin, maltose, and glucose, by dilute acids, and also by diastase, an enzyme contained in barley sprouts, and by ptyalin, the characteristic enzyme of saliva. It does not form an -osazone, and its solutions do not reduce Fehling's solution or ferment with yeast. Starch is readily detected by the intense blue color which it gives when brought in contact with free iodine. The nature of this " starch iodide," is not known. It usually contains 18 to 20 per cent, of iodine. Uses. Starch is a very important food, both in natural sub- stances and when prepared from them, being first hydrolyzed and then supplying the chief fuel material for the maintenance of the temperature of the body. It is used in the preparation of 220 INTRODUCTION TO ORGANIC CHEMISTRY glucose and dextrin, and is employed in laundry work, in finish- ing cotton cloth, in sizing paper, for making paste, etc. Different starches vary in their properties to some extent and are adapted to different purposes. Sago, tapioca, arrowroot, and some other starches are used chiefly for food. Wheat starch makes the best paste, rice starch is preferred for toilet powders, while potato and corn starch are most largely employed in the glucose and dextrin industries, and are also used for other purposes. Inulin (CeHioOs)*, occurs in many composite and some other plants in a swollen or dissolved state. It differs from ordinary starches by being readily soluble in warm water, and giving solutions which are not colored by iodine, and do not form a jelly. The solutions are levo-rotatory, and the inulin is easily hydrolyzed by dilute acids with the formation of fructose as the sole product (cf. p. 204). Inulin is not affected by diastase. When dried, it forms a white powder, consisting of minute spherical granules. * Glycogen (CeHioOs)*, is a starch-like substance found in the animal organism, being especially abundant in the liver. It also occurs in mollusca, and in moulds and other fungi. It resembles starch in appearance, but dissolves in warm water to an opalescent solution from which it can be precipitated by alcohol. Its solutions are colored red by iodine. They are dextro-rotatory, and are hydrolyzed by acids, and by diastase and ptyalin, into the products similar to those given by starch. Dextrin is produced, as already stated, when starch is heated alone, or after it has been moistened with acids. It is of a brownish color, which is lighter when the acid process is used; but in this case the dextrin contains some sugar and its adhesive power is less. It is also the first product of the hydrolysis of starch. Dextrin is readily soluble in water and is precipitated from its solutions by alcohol. The solutions reduce Fehling's solution, and give a red to violet color with iodine. They are dextro-rotatory and are hydrolyzed to maltose and glucose. THE CARBOHYDRATES 221 Dextrin is not directly fermentable by yeast. It is used for making mucilage, and is also employed in calico printing and tanning to thicken the colors and extracts, in brewing and in confectionery. GuiuS. This name is given to certain products of plants which sometimes occur as translucent amorphous masses, and in other cases are precipitated from alkaline extracts of plant substances by hydrochloric acid and alcohol. They go into colloidal solu- tion in water, forming sticky liquids, and are precipitated from these solutions by alcohol. They appear to be mixtures, but contain certain carbohydrates, which, unlike any we have so far considered, often yield pentoses on hydrolysis. Gum arabic, and the gums which appear on cherry and peach trees, give arabinose; xylan, a gum frequently found in tree bark, and a gum obtained from grains, give xylose. Galactose is formed at the same time in most cases. Cellulose forms the cell membrane in all plants, and is their chief solid constituent. It is, however, almost always incrusted with other substances (lignin, resins, etc.). These substances can be removed more or less completely by treatment with various reagents which act on them more readily than on the cellulose. Thus paper pulp is made from wood, and the textile fibers of linen, hemp, and jute are prepared by a bacterial fer- mentation in water ("retting") which softens and partly destroys the gummy and resinous matters. Cotton, linen, and various piths are almost pure cellulose, and the best "washed" filter paper is cellulose with only a trace of impurity. Properties. Cellulose is a stable substance, insoluble in all ordinary solvents; but it is dissolved by an ammoniacal solution of copper hydroxide ("Schweitzer's reagent" made by forcing a current of air through a solution of ammonia in which copper turnings are placed) ; and is precipitated from this solution by acids and salts. The precipitated cellulose, when washed with alcohol and dried, forms a white amorphous powder. A water- proof paper can be prepared by passing unsized paper through 222 INTRODUCTION TO ORGANIC CHEMISTRY a strong solution of Schweitzer's reagent and then pressing several sheets together without washing. Strong sulphuric acid (4:1) dissolves cellulose, and if the fresh solution is poured into water a colloidal substance is precipitated, which, so long as it is in contact with the acid, is colored blue by iodine, as starch (amylum) is, and is hence called amyloid. The blue color also appears when cellulose is moistened with a solution containing free iodine (iodine in potassium iodide) and then treated with concentrated sulphuric acid or zinc chloride solution (test for cellulose). "Parchment paper" is paper coated with amyloid by dipping unsized paper into sul- phuric acid (4:1) and washing it immediately with water. A strong solution of zinc chloride acts in the same way as sulphuric acid. If the colloidal solution of cellulose in sulphuric acid is allowed to stand for some time before diluting it, and is then boiled, solu- ble carbohydrates are formed, among which glucose is usually present in considerable quantity. Dilute alkalies do not affect cellulose, but strong solutions form compounds which are decomposed when washed with water, leaving a hydrate of cellulose. When cotton cloth is treated in this way (under tension to prevent shrinking) the fibers acquire a silky luster, and the cloth is known as "mercerized" cotton. 1 When the compound formed by the action of the alkali on cellulose is treated with carbon disulphide it produces a substance, cellulose xanthate (p. 243) which, when beaten with water, forms a thick solution known as "viscose." This is easily de- composed with the formation of a cellulose hydrate. By squirting viscose through fine tubes into a solution which causes this decom- position, lustrous threads of artificial silk are formed. Artificial silks are also made from nitrocellulose, and by treatment of cellulose with ammoniacal copper solutions. Viscose is also employed in making photographic films, in sizing paper, and for other purposes. The presence of alcohol groups in cellulose can be proved by the 1 Process discovered by John Mercer about 1850. THE CARBOHYDRATES 223 usual method. It can therefore form esters, and among the esters of cellulose is a cellulose triacetate which on evaporation of its chlor form or other solution leaves a tough water -proof film. Such films are non-inflammable and used in photography, for water-proofing, insulation of wires, etc. The esters which are formed by reaction with nitric acid are, however, the most im- portant ones. The number of acid radicals introduced depends on the strength of the acid used, the temperature, and the time allowed the reaction. These esters are called " nitrocelluloses," just as the glyceryl nitrate is called" nitroglycerine." A mixture of the lower nitrates, in which two to five nitric acid radicals have replaced hydroxyl in Ci2H 2 oOio is called "pyroxylin" and its solution in alcohol and ether is "collodion." "Celluloid" is an intimate mixture of pyroxylin with camphor. These sub- stances burn with a quick flare, but are not definitely explosive. When cellulose is nitrated further by means of a mixture of con- centrated nitric and sulphuric acids the explosive hexanitrate is produced [C^H^O^NOsJelx- This is used in making smokeless powder. "Gun-cotton" made by this treatment from cotton fiber resembles closely in appearance the cotton from which it is made. It is insoluble in alcohol and ether as well as in water. It burns rapidly but without explosion, when unconfined. When confined, it explodes violently on detonation. 1 Storage of Energy in Plants. In connection with this study of carbohydrates, the amount of energy stored by plants in the form of carbohydrates is of interest. In the building up of the amount of these substances which is represented by the gram-molecular weight of the simple composition formula of starch or cellulose (162 grams), about 670 large calories are required. Roughly indicated, the change is shown as follows: 6CO 2 + sH 2 = CeHioOs + 6O 2 - 670 calories The necessary energy for this process comes from sunlight, which 1 See J. B. Bernadou, "Smokeless Powder, Nitrocellulose, etc." 224 INTRODUCTION TO ORGANIC CHEMISTRY is the source of almost all of the energy at man's disposal, since that obtained from water power and wind is also the result of solar radiation. The storage of energy in the formation of car- bohydrates, it should be noted, is not only through the synthesis of these substances, but also in the release of oxygen with its potential chemical energy. In the various processes of utiliza- tion of this energy, in the use of fuels, of food, etc., the potential energy of the organic materials and of oxygen .is transformed into kinetic energy which largely appears as heat. Fermentation and Enzymes 1 The term fermentation originally signified the effervescent action which occurs when sugars are converted into alcohol by yeast. It has since come to include a great variety of changes in which more or less complex organic substances are resolved into simpler ones under the influence of certain living organisms or of substances contained in them. While it was long believed that the living yeast cells were essential to the process of alcoholic fermentation, other changes, like that of starch into glucose by means of malt, were found to be due to "unorganized ferments" or substances which, like the diastase in malt, are not living organisms, though formed by such organisms. Such unorganized or "unformed" ferments are known as enzymes. The inversion of cane sugar which is effected by yeast before alcoholic fermen- tation sets in is effected by such an enzyme known as invertase. In 1898 Buchner demonstrated that the living yeast was not necessary for alcoholic fermentation, but that this change can be brought about by means of a substance in the juice expressed from yeast and freed from all living organisms. This enzyme is called zymase. The present view in regard to all the reactions which are classed as fermentations is that they are the result of the action of 1 See W. M. Bayliss, "The Nature of Enzyme Action," and Cohnheim, " Enzymes." THE .CARBOHYDRATES 225 enzymes which probably act as catalytic agents. Some of them cause the splitting of the complex substance into simpler ones, as in the jreaking down of glucose into alcohol and carbon dioxide; others bring about hydrolysis, as in the conversion of starch into glucose by diastase, and the production of various hexoses from the disaccharoses; others, still, effect oxidations with the aid of the oxygen of the air, as in the fermentation processes by which acetic acid is formed from alcohol, and lactic and butyric acids from sugars. Certain reductions, also, are apparently the result of enzymic action. The enzymes, like other catalyzers, show a very definite select- ive power in their action. We have had a number of instances showing this fact, and may recall as an illustration the destruc- tion of one of the two optically active components in racemic acid by certain bacteria, while the other is untouched (p. 192). The enzymes are probably asymmetric substances, and we may imagine that that selective action is due to some relation between their (unknown) structure and that of the compound on which they act. As Emil Fischer suggests, the enzymes and the com- pounds may possess complementary configurations like those of a lock and its key. None of the enzymes have been obtained in a state of complete purity. They are very complex substances of a protein character, and efforts to isolate them from the other proteins with which they are associated cause a loss of their activity. They occur chiefly in moulds, yeasts, bacteria, and living tissues, and these organisms are usually employed to bring about the fermentations without attempting to separate the enzymes from them. In a few instances, powders are prepared which contain the enzymes, such as diastase, pepsin, and rennin. While some of the reactions which are effected by enzymes can also be brought about by inorganic catalyzers (notably those of hydrolysis of sugars, starch, and glucosides), and alcohol can readily be converted into acetic acid by ordinary oxidizing 226 INTRODUCTION TO ORGANIC CHEMISTRY agents, many other transformations, such as the production of alcohol and of lactic acid from sugars, cannot be realized by the usual chemical means. Very many of the chemical changes which go on in living plants and animals are now known to be dependent on the presence of enzymes. We have spoken of enzymes as catalytic agents. They at least resemble them, as appears from the facts that, like the in- organic catalysts, they are not used up in the processes which they conduct, they do not enter into the products of the reactions, and their amount in proportion to the quantity of substance transformed is often infinitesimally small. It is probable that no catalyst is capable of starting a reaction; but that it acts rather as an accelerator of actions which are already proceeding, though often with such slowness that we are quite unable to note their progress. It is believed that enzymes, or substances of the nature of enzymes, are generated abundantly in the tissues of both plants and animals, and that the secretions which are so intimately associated with digestion and other functions of the body owe their special effectiveness to the presence of these substances. CHAPTER XVI DERIVATIVES OF CARBONIC ACID Carbonic acid, CO (OH) 2, which is assumed to be present in solutions of carbon dioxide, carbon dioxide its anhydride, and the carbonates, are always treated in inorganic chemistry; but these compounds, as well as carbon monoxide, belong also to organic chemistry if we define it broadly as the chemistry of the com- pounds of carbon. As these compounds have been sufficiently presented in inorganic chemistry, it is only necessary for us here to recall the part which they play in the synthesis of some organic compounds and to call attention to the fact that carbonic acid may be regarded as hydroxyl formic acid, HO. CO. OH, and may indeed be reduced to formic acid (and carbonates to formates). There are certain compounds, however, which may be regarded as derivatives of carbonic acid, in the sense in which this term has been employed, and which from their character are usually classed with the organic substances. Some of these compounds are briefly discussed in this chapter by themselves, because of the unusual character of carbonic acid as compared with other organic acids. Carbonyl chloride, COC1 2 , may be considered as the dichloride of carbonic acid. It is, in fact, formed, though in small amount, by the action of phosphorus pentachloride on sodium carbonate, just as chlorides of other organic acids are from their salts. It is also formed from carbon tetrachloride when this is heated with sulphur trioxide or phosphorus pentoxide; and when a mixture of carbon dioxide and carbon tetrachloride vapor is led over pumice heated to 350: C0 2 + CC1 4 = 2COC1 2 227 228 INTRODUCTION TO ORGANIC CHEMISTRY It is also one of the products of the oxidation of chloroform (cf. p. 39); and carbon monoxide and chlorine unite directly under the influence of sunlight to carbonyl chloride. The compound was first obtained in this way and was given the name of phosgene, as a product formed by the action of light. Carbonyl chloride is prepared commercially by passing a mixture of chlorine and carbon monoxide over charcoal, which acts as a catalyzer. Carbonyl chloride is a gas (boiling point 8.2) which dissolves readily in benzene and toluene. It has a stifling odor, and is very irritating to the throat and lungs. It is sold in liquid form in cylinders and in solution in toluene, and is employed in synthet- ical work, both in laboratories and in the making of coal tar dyes. Reactions. Carbonyl chloride gives the reactions which are characteristic of acyl chlorides with water, alcohol, and am- monia (cf. p. 115); but in some respects is a more powerful agent than acetyl chloride, as is seen by the fact that it reacts with acetic acid at 120 with the production of acetyl chloride, and converts the sodium salts of the fatty acids into their acid anhydrides. A monochloride of carbonic acid would be chloroformic acid, C1CO.OH; but this, like formyl chloride, HCO.C1, has not been obtained. Both these compounds, if formed, must be very un- stable, breaking down into hydrogen chloride and carbon dioxide or carbon monoxide. Esters of Carbonic Acid. By the action of alcohols on car- bonyl chloride, esters are formed. The first product is an ester of chlorcarbonic (or chlorformic) acid: C1CO.C1 + C 2 H 5 OH = C1CO.OC 2 H 6 + HC1 By further action of alcohol or of alkali alkoxide on the chlor- carbonic ester, the neutral ester, CO(OC 2 H 6 )2, is produced. In DERIVATIVES OF CARBONIC ACID 2 29 this way both simple esters, and mixed esters, such as CH 3 O.CO.- OC 2 H5, can be made. The chlorcarbonic esters are liquids of tear-compelling odor. They are used in synthetic reactions for the purpose of introducing the carboxyl group. For instance, by reaction with the sodium compound of ethyl malonic ester (cf. p. 181), ethyl chlorcarbonate gives the ethyl ester of methane-tricarboxylic acid. CHNa(CO.OC 2 H 5 ) 2 + C1CO.OC 2 H 5 = CH(CO.OC 2 H 5 ) 3 + NaCl In many reactions these esters split into carbon dioxide and the alkyl chloride; e.g., with ZnCl 2 : C1CO.OC 2 H 5 = C0 2 + C 2 H 5 C1; and by nascent hydrogen they are converted into esters of formic acid. The neutral esters are liquids of ethereal odor, insoluble in water, and readily saponified. When heated with an alcohol which contains a higher alkyl group, this is substituted for the lower one in the ester: CH 3 O.CO.OC 3 H 7 + C 3 H 7 OH = CO(OC 3 H 7 ) 2 + CH 3 OH Acid esters of carbonic acid, such as C 2 H5O.CO.OH, are too unstable to exist, but their alkali salts, C 2 H 5 O.CO.ONa, are formed by leading carbon dioxide into an alcoholic solution of an alkoxide. These ester-salts are decomposed by water with the production of alcohol and alkali carbonate. Amides of Carbonic Acid As in the case of the carbonic acid chlorides, the diamide is a stable compound while the monamide cannot be isolated. Carbamic acid, NH 2 .CO.OH, the monamideof carbonic acid, exists only in its salts, esters, and chloride. Ammonium car- 230 INTRODUCTION TO ORGANIC CHEMISTRY bamate, the ammonium salt of the monamide, NH 2 CO.ONH 4 , is formed when carbon dioxide and ammonia gas are brought to- gether. Commercial ammonium carbonate, which is prepared by sublimation from a mixture of ammonium sulphate and cal- cium carbonate, contains both ammonium carbamate and acid ammonium carbonate. The carbamate is precipitated when ammonia and carbon dioxide are led into cool, absolute alcohol, and may be prepared in this way. In solution in water it is partly converted into the carbonate: /ONH 4 CO + H 2 = CO \)NH 4 \)NH 4 Acids decompose it into carbon dioxide and the ammonium salts of the acid: NH 2 CO.ONH 4 + 2HC1 = 2 NH 4 C1 + CO 2 At 60, the solid carbamate breaks up into ammonia and carbon dioxide; and when it is heated in sealed tubes to 130 140, it is largely converted into urea: NH 2 .CO.ONH 4 = NH 2 .CO.NH 2 -f H 2 O Urea, CO(NH 2 ) 2 , was discovered in urine in 1773, and is of great physiological interest as it is the most important nitrogen end-product of the metabolism of protein substances in man and the carnivora. The average amount of urea excreted by an adult person in health, is about 30 grams a day, representing about 84 per cent, of the total nitrogen eliminated from the system. In disease, the proportions of urea and other nitrogen compounds may be markedly different. Preparation from Urine. Urea may be obtained from urine in the form of its nitrate by evaporating the urine to small bulk and adding nitric acid, Urea nitrate, CO(NH 2 ) 2 .HN0 3 , is DERIVATI/ES OF CARBONIC ACID 23! precipitated, and purified by oxidizing agents (nitric acid or potas- sium permanganate) and recrystallization. Urea is set free from the nitrate by decomposing the salt in a warm solution with barium carbonate. On evaporating the solution of urea and barium nitrate to dryness and extracting with hot alcohol, the urea alone is dissolved. Formation and Preparation from Other Substances. i. Urea was first made in the laboratory by Wohler in 1828. He obtained it as a result of evaporating an aqueous solution of ammonium cyanate: NH 2 Ammonium cyanate (p. 150) had not then been prepared from its elements, but it was considered to be essentially an inorganic sub- stance. Up to this time no organic substance had been made from inorganic material and it had been generally thought that* transformations of this sort were impossible. Wohler's discovery is, therefore, of great historical importance, though it was many years before synthetical methods of producing organic substances became a well-established laboratory procedure. The formation of urea from ammonium cyanate evidently involves a considerable rearrangement within the molecule, but we have already noted that the atoms in hydrocyanic and cyanic acids appear to be unusually mobile (p. 151). The reaction is not a complete one, as it is reversible. Other ways of forming urea are: 2. By leading a mixture of carbon dioxide and ammonia through a tube heated to a faint red, cyanic acid being an intermediate product. 3. From ammon- ium carbamate at i3o-i4o, also essentially a synthesis from carbon dioxide and ammonia. 4. By passing carbonyl sulphide, CO.S (p. 242), into a strong solution of ammonia. Ammonium thiocarbamate, NH^.CO.SNHU, is first formed but readily breaks down into hydrogen sulphide and urea, especially when shaken with lead carbonate. 232 INTRODUCTION TO ORGANIC CHEMISTRY 1. Like other acid amides, urea is hydrolyzed when its solutions are heated with acids or alkalies, the products being ammonia and carbon dioxide (carbonic acid) : CO(NH 2 ) 2 + H 2 O = CO 2 + 2NH 3 This hydrolysis occurs in urine through the action of certain organisms, so that the urine that is normally acid becomes alkaline, and smells of ammonia. 2. Urea, like other amides, forms salts with strong acids, such as the nitrate, whose formula has been given, and the difficultly soluble oxalate, 2CO.(NH 2 ) 2 ,(CO.OH) 2 , only one of the amido groups reacting with acids. 3. Nitrous acid acts on urea, as on the amides and primary amines, with the production of nitrogen and carbonic acid : CO(NH 2 ) 2 + 2 HN0 2 = 2 N 2 + C0 2 + 2H 2 O 4. A solution of sodium hydroxide and bromine (in which sodium hypobromite is present) effects a like reaction with formation of sodium carbonate and nitrogen. This is often em- ployed for the determination of the amount of urea in solution by measurement of the nitrogen, but in the case of urine it is not a very exact method: CO(NH 2 ) 2 + 3 NaOBr = N 2 + 3NaBr + CO 2 + 2 H 2 O A test for urea (also given by proteins) is made by heating the solid substance and then treating it with a solution of alkali con- taining a little copper sulphate. A reddish- violet color is pro- duced. (Biuret test.) 5. By reaction of ammonia with carbonyl chloride a general reaction of acid chlorides. If instead of carbonyl chloride, di- phenyl carbonate, CO(OC 6 H 5 ) 2 , is first made by the action of the sodium salt of phenol on carbonyl chloride, and this is then treated with ammonia, the reaction is especially successful. 6. Cyanamide (p. 149) is hydrolyzed in the presence of a little inorganic acid to urea: CN-NH 2 + H 2 = CO(NH 2 ) 2 DERIVATIVES OF CARBONIC ACID 233 The composition of urea and its formation from carbonyl chloride are sufficient evidence for the structure which is repre- sented by its formula. Properties and Reactions. Urea crystallizes in a form resembling that of saltpeter. It melts at 13 2 and at a higher temperature de- /NHa composes first into ammonia and biuret, CO ; and \NH.CO.NH 2 gives as a final product cyanuric acid (p. 149). Urea is readily soluble in water and in alcohol. Derivatives of Urea and Related Substances. Guanidine, HN: C(NH 2 ) 2 , was first obtained from guanine, a purine base (see p. 235) of complicated structure. Guanidine can be made by heating ammonium thiocyanate to i8o,or by heating an alcoholic solution of cyanamide with ammonium chloride: /NH 2 .HC1 CN.NH 2 + NH 3 .HC1 = NH:C< X NH 2 It is a crystalline substance of strong basic properties, which is converted into urea by baryta water. or urea chloride is half carbonyl chloride and half amide. It can be made by leading carbonyl chloride over heated ammonium chloride. It reacts vigorously with water to form ammonium chloride and carbon dioxide; with ammonia or amines it gives urea or alkyl-substituted ureas; with alcohols it forms amido-carbonic or carbamic acid esters: CO + C 2 H 6 OH = CO + HC1 \NH 2 \NH 2 These esters of carbamic acid are called urethanes. 234 INTRODUCTION TO ORGANIC CHEMISTRY Alkyl derivatives of urea, in which the hydrogen is partly or wholly replaced by alkyl groups, are known in large number, Uric acid, C 5 H 4 O 3 N4, is a white, crystalline substance, without odor or taste. It is present in small amount in normal human urine, and occurs in large quantities in the excrement of birds (guano) and of reptiles in the form of ammonium urate. It is conveniently prepared from these Jatter sources. Uric acid is almost insoluble in water. It is a feeble dibasic acid (though containing no carboxyl group). Its alkali salts are sparingly soluble, the lithium salt dissolving more freely than the others. When heated with acids uric acid gives glycocoll (p. 254), ammonia, and carbon dioxide. On oxidation with cold nitric acid there are formed urea and alloxan, NH CO I I CO CO I I NH CO and with alkaline permanganate the product is allantoin whose formula has been shown to be NH.CH.NH.CO.NH 2 CO \ NH.CO On the basis of these reactions Medicus proposed a formula for uric acid which was long in dispute but after many years of investigation by E. Fischer and others was confirmed by success- ful syntheses. This formula is: NH - CO I I CO C NH I II >co NH - C NH DERIVATIVES OF CARBONIC ACID 23$ A reaction of the acid with phosphorus oxychloride by which the three oxygen atoms and three hydrogen atoms are replaced by three chlorine atoms suggests an enol tautomeric structure: N=COH I I HOC C - NH || > COH N C - N Uric acid and a number of other important natural products such as caffeine, theobromine, xanthine and guanine all contain the same carbon and nitrogen skeleton in their structural formu- las, and may be regarded as derivatives of a hydrogen compound which Fischer called purine (from purum and uricum) and suc- ceeded in preparing in 1898. Purine Bases. Guanine occurs in animal tissues and in guano, and in the form of a calcium salt in fish scales. It is a colorless powder very slightly soluble in water, and combines with both acids and bases. On oxidation it gives guanidine (p. 233) and parabanic acid which hydrolyzes into urea and oxalic acid. Heated with hydrochloric acid it decomposes into glycocoll, formic acid, ammonia, and carbon dioxide. By nitrous acid it is converted into xanthine. Xanthine is found in all tissues of the body. It unites with both acids and bases. When oxidized it yields alloxan and urea. Theobromine is formed by the reaction of its lead salt with methyl iodide. Theobromine occurs in cocao, beans. It is a white crystalline powder, and is amphoteric in its behavior. Its oxidation prod- ucts are methyl alloxan and methyl urea. Its silver salt with methyl iodide gives caffeine. Caffeine or theme is a ingredient of coffee and tea and occurs in the cola nuts, etc. It crystallizes with one molecule of water in silky needles, and is weakly basic. It can be oxidized into dimeth- 23 5* INTRODUCTION TO ORGANIC CHEMISTRY ylalloxan and monomethylurea. When decomposed by hydro- chloric acid, its nitrogen appears partly as ammonia and partly as methylamine. N= CH CH C - NH II II >CH N C-N Purine N(CH 3 ) CO CO C - N(CH 3 ) I II >CH N(CH 3 ) C - N N Caffeine COH C - NH 2 C - NH N C-N Guanine CO NH- I I CO C - N(CH 3 ) I II >CH N(CH 3 ) C-N Theobromine NH CO I I CO C - NH I II >CH NH - C - N Xanthine CHAPTER XVII COMPOUNDS CONTAINING SULPHUR Sulphur is found in only a few natural organic compounds of established chemical constitution, as for instance in the mustard oils (p. 153); but it is usually present in the protein substances which are essential constituents of all living cells, and of whose chemical structure comparatively little is yet known. Many organic compounds containing sulphur have, however, been made by laboratory methods. Some of these in which sulphur is linked to carbon by oxygen, such as the alkyl sulphates, have already been described. We have also noticed a few others where carbon and sulphur are directly united, as in thio and isothiocyanic acids and their esters. In inorganic chemistry we have learned that sulphur and oxygen form many similar compounds, the sulphides and hydro- sulphides generally having formulas which find their analogies in those of the oxides and hydroxides. The same is true in organic chemistry; and sulphur alcohols, esters, aldehydes, ketones, and acids can be readily made in which sulphur takes the place of oxygen in the ordinary compounds of these names. In all these substances sulphur is, like oxygen, divalent. But sulphur in in- organic compounds is also, on occasion, tetravalent or hexavalent, these higher valencies appearing especially in compounds in which it is combined wholly or partly with oxygen, as in its oxides and acids. Similarly, in organic chemistry, tetravalent or hexavalent sulphur appears, often as a linking element between oxygen and alkyl groups. Sulphur atoms also show a tendency to link with each other as oxygen seldom does. Consequently, there 236 237 COMPOUNDS CONTAINING SULPHUR are many thio-organic compounds which find no analogies among those of oxygen. Almost all of the organic sulphur compounds are laboratory products, as already indicated. Those which are of the type of oxygen compounds are made by analogous methods. They are, in general, less stable than the corresponding oxygen com- pounds, which accords with our knowledge of the inorganic sulphur compounds; and those which are volatile are characterized by most objectionable odors. When alcohols and ethers are oxidized, the hydrogen of the alkyl groups is at once affected with the production of aldehydes, acids, and ketones. The corresponding sulphur compounds, on the other hand, give a series of oxidation products in which the hydrogen combined with sulphur may be removed, or oxygen added to the sulphur. The thioalcohols, C n H 2n + i.SH, give as their first oxidation product disulphides, C n H 2n + i.S S.C n H 2n + i. On more ener- getic oxidation, the valence of the sulphur is increased, and sul- phonic acids are formed, whose formula is probably, CH s4 + \OH In like manner, the thioethers, (C n H 2n + i) 2 S, are oxidized first to sulphoxides (C n H 2n + i) 2 S = O, in which sulphur is tetra- valent, and then to sulphones, (C n H 2n + i) 2 S^ , where the valence has become six. 1 The disposition of sulphur to change from divalency to a higher valence is also shown by the formation of addition compounds. 1 The structure of the sulphur oxygen groups in the sulphonic acids and sulphones is not entirely certain. It may be = S \t t in which case sulphur is tetravalent. INTRODUCTION TO ORGANIC CHEMISTRY 238 The alkyl sulphides unite with alkyl halides forming such com- pounds as (CnH 2 n+l)3SI. Thioalcohols are prepared by the action of alcoholic potassium hydrosulphide on alkyl halides or potassium alkyl sulphates: C 2 H 5 C1 + KSH = C 2 H 5 SH + KC1 C 2 H 6 O.SO 2 .OK + KSH = C 2 H 6 SH + K 2 SO 4 These reactions are exactly analogous to those for making alcohols. The first is carried out by heating under pressure, the second takes place on distillation. The thioalcohols are volatile liquids whose boiling points are much lower than those of the corresponding alcohols (methyl thioalcohol boils at 6). They are almost insoluble in water, but dissolve easily in alcohol and in ether. The products of their oxidation have already been given. As in the case of the alcohols, the hydrogen of the SH-group can be replaced by metals, with the formation of salt-like compounds. But these compounds are more stable than the alcoholates, and are formed with heavy metals such as lead, copper, and mercury. With mercuric oxide, for instance, thioethyl alcohol readily forms (C 2 H 5 S) 2 Hg, which can be crystallized from alcohol. On account of the formation of these mercury compounds, the thioalcohols were called mer- captans (corpus mercuiio aptum), a name which is still commonly used, and the salts are called mercaptides. The odor of ethyl mercaptan is not only very disagreeable but so intense that it is said that 0.000,000,002 mg. can be detected, an amount about 250 times less than that of sodium which can be recognized by the spectroscope. Ethyl mercaptan is made commercially, and used in the preparation of sulphonal (p. 240). Thioethers may be made in a manner analogous to that for making ethers, by the reaction of alkyl halides, or alkali alkyl sulphates with sodium mercaptides: C 2 H 6 O.S0 2 .OK + CH 3 SK = C 2 H 6 .S.CH 3 + K 2 SO 4 239 COMPOUNDS CONTAINING SULPHUR Both simple and mixed thioethers may be thus prepared. The thioethers are also made by the action of potassium sulphide on the above alkyl compounds: 2 C 2 H 5 I + K 2 S = (C 2 H 5 ) 2 S + 2KI The. analogous reaction with the alkali oxide does not take place, but can be carried out with dry silver oxide and alkyl halide. The thioethers are liquids insoluble in water, and having higher boiling points than the corresponding mercaptans. (Compare this with the boiling points of alcohols and ethers.) As has already been stated, they are readily oxidized. They form addition products not only with alkyl halides, but also combine with halogen salts of metals, and with bromine and iodine, with the production of crystalline compounds. Sulphonium Bases and Salts. The addition products which the thioethers or alkyl sulphides form with alkyl halides, such as (C2H 5 ) 3 SI, are salt-like compounds, from whose aqueous solutions other salts may be made by reaction with silver salts: (CH 3 ) 3 SI + AgN0 3 = (CH 3 ) 3 SN0 3 + Agl By the action of silver hydroxide, strongly alkaline solutions are obtained, which yield on evaporation deliquescent crystals of sulphonium hydroxide: . (CH 3 ) 3 SI + AgOH = (CH 3 ) 3 SOH + Agl The sulphonium hydroxide solutions are strongly basic and precipitate hydroxides of metals, set ammonia free from its salts, and absorb carbon dioxide from the air, as do the hydroxides of potassium and sodium. In the manner of their formation and their behavior they are analogous to the tetra-alkyl ammonium bases (p. 135). On heat- ing, the sulphonium halides decompose into the alkyl sulphides INTRODUCTION TO ORGANIC CHEMISTRY 240 and alkyl halides, reversing the reaction by which they are formed, and behaving in this respect like % the tetra-alkyl ammonium salts. Bisulphides, such as C 2 H 5 .S S.C 2 H 6 , are formed by careful oxidation (often through oxidation in the air) of the mercaptans. They are also formed by distilling potassium ethyl sulphate with potassium disulphide; and when mercaptans are treated with concentrated sulphuric acid, the product is not the thioether (analogous to ordinary ether formation) but the disulphide. The disulphides are liquids which boil higher than the corre- sponding sulphides. They are easily reduced to mercaptans. Thioacids, in which the SH-group appears in place of the hydroxyl group, can be made by heating oxygen acids with phos- phorus pentasulphide, or through the action of potassium hydrosulphide on the acid chlorides. The thioacids have lower boiling points and are less soluble than the corresponding oxygen acids. Their salts with the heavy metals are mostly difficultly soluble and are easily decomposed with the formation of metal sulphides. Thioaldehydes, and thioketones are formed when hydrogen sulphide is passed into solutions of aldehydes or ketones to which hydrochloric acid is added; but these compounds polymerize so readily (the ketones as well as the aldehydes) that the monomo- lecular substances have not been prepared in the pure state. Alkyl sulphoxides, such as C2H 5 .SO.C2H 5 , are the first product of oxidation of the thioethers by nitric acid. They cannot be distilled without decomposition, and are readily reduced to thioethers again. Sulphones, of the type of C2H B .SO2.C2HB, are formed by vigorous oxidation of thioethers or the alkyl sulphoxides. They are not reduced by nascent hydrogen. Sulphonal, which is employed in medicine as a soporific, is a disulphone, (CH 3 ) 2 C(SO2.C2H5)2, diethyl-sulphon-dimethyl methane. It is made by " condensation " of acetone and ethyl 241 COMPOUNDS CONTAINING SULPHUR mercaptan through the influence of hydrochloric acid, and oxidation of the product: CH 3 .CO.CH 3 + 2C 2 H 5 SH = (CH 3 )2C.(SC2H 6 )2 + H 2 O Acetone (CH 3 ) 2 C(SC 2 H 5 )2 + 40 = (CH 3 )2C.(S0 2 .C2H 5 )2 Sulphonal Other analogous compounds are made in a similar manner. Sulphonic acids are compounds in which one hydroxyl group in sulphuric acid is replaced by a hydrocarbon radical. They are formed by vigorous oxidation of mercaptans by nitric acid, and their salts can be made by the action of alkyl iodides on an alkali sulphite: C 2 H 5 I + KSO 3 K = C 2 H 5 .SO 3 K + KI By phosphorus pentachloride the sulphonic acids are converted into acid chlorides, e.g., C 2 H 5 .SO 2 .C1, and these are reduced to mercaptans by nascent hydrogen. This fact together with the formation of the sulphonic acids by oxidation of mercaptans, indicates that in them, as in the mercaptans, sulphur is directly united to carbon. Their structure 1 is, therefore, probably H The sulphonic acids are stable, strongly acid compounds which are very soluble in water and give deliquescent crystals. They form alkali salts with solutions of caustic alkalies, but are other- wise unaffected, even on boiling, and they are not acted on by boiling acids. When melted with solid alkalies, however, they are decomposed with the formation of alcohols and alkali sulphites : C 2 H 5 .SO 2 OH + 2KOH = C 2 H 5 OH + K 2 S0 3 + H 2 O 1 This conclusion as to the structure of the sulphonic acids, and the fact that they can be made by the reaction of alkali sulphites and alkyl iodide, indicates that the structure of the sulphites is KSO 2 . OK, rather than KO . SO. OK, and that a similar constitution should be assigned to the unstable sul- phurous acid. INTRODUCTION TO ORGANIC CHEMISTRY 242 Esters of sulphonic acids, such as C2H 5 .SO2.O.CH 3 are made by the usual methods of ester formation. The aliphatic sulphonic acids are of comparatively little importance; but the sulphonic acids of the aromatic compounds are extensively employed in synthetical operations both in the laboratory and in chemical manufactures. Sulphur Compounds Related to Carbonic Acid Carbon disulphide, CS 2 , is the analogue of carbon dioxide, and, like it, is made by the direct union of the elements, when sulphur vapor is passed over red-hot carbon. It is, however, an endother- mic compond, absorbing about twenty-five large calories in the formation of the gram-molecular weight, while the formation of the gram-molecular weight of carbon dioxide is attended with the production of about ninety-six calories. Carbon disulphide is a strong refracting liquid, which boils at 46, and which usually has a very disagreeable odor, due to slight impurities. It is an excellent solvent for phosphorus, iodine, oils, fats, and rubber, and is largely used. Carbon oxysulphide, CO.S, is formed when a mixture of carbon monoxide and sulphur vapor is passed through a tube heated to a faint red heat. It is also produced by the action of hydrogen sulphide on isocyanic esters: 2C 2 H 5 NCO + H 2 S = CO.S + (C 2 H 5 .NH) 2 CO Ethyl isocyanate Substituted urea It may also be prepared by the action of strong sulphuric acid on ammonium or potassium thiocyanate: HSCN + H 2 O = CO.S + NH 3 Carbon oxysulphide is an inflammable gas of faint peculiar odor. It is decomposed by alkalies as follows: CO.S + 4 KOH = K 2 CO 3 + K 2 S + 2 H 2 O 243 COMPOUNDS CONTAINING SULPHUR Sulphur Derivatives of Carbonic Acid. By the replacement of oxygen in carbonic acid it is easily seen that five different sulphur acids might be formed. The acids, themselves, like carbonic acid, are very unstable, and with one exception, CS(SH) 2 , are not known in the free state; but fairly stable neutral or acid esters, and salts of all of the acid esters have been prepared. /SH Salts of the acid esters of thiocarbonic acid. CO\ , for in- NDH stance, may be prepared by leading carbon oxysulphide into alcoholic solutions of the alkalies, or by the action of carbon dioxide on mercap tides: /SK CO.S + C 2 H 5 OK = CO< X OC 2 H 5 /SK CO 2 + C 2 H 5 SK = C0< ; X OC 2 H 6 /SH and the neutral esters of the dithiocarbonic acid, CO CH 3 .CO.CH 3 + HC1 Further action of chlorine causes replacement of hydrogen in the associated alkyl group or groups. Therefore, the product actually obtained is a chloraldehyde (cf. chloral, p. 91), from a primary alcohol, or a chloracetone, if a secondary alcohol is used. Although chloralcohols with chlorine and hydroxyl united to the same carbon atom do not exist, the corresponding esters in which the hydroxyl hydrogen is replaced by an alkyl group are 245 INTRODUCTION TO ORGANIC CHEMISTRY 246 comparatively stable. Thus by the action of chlorine on ethyl ether (kept cool and in the dark to avoid explosive action), there may be obtained as the first product, CH 3 .CH xa Substances of this type are called chlorethers. The constitution indicated by the formula is proved by the products of hydrolysis with sulphuric acid as a catalytic agent, viz., alcohol, aldehyde, and hydrogen chloride: /OC 2 H 5 CH 3 .CH< + H 2 O -* C 2 H 5 OH + (CH 3 .CH -> CHaCHO + HC1 Halogenhydrins. Halogen-substituted alcohols in which the halogen and hydroxyl are united to different carbon atoms can be obtained indirectly in several ways. They are called halogen- hydrins. Chlorhydrins are formed: 1. By the action of hydrogen chloride on glycols: CH 2 OH.CH 2 OH + HC1 = CH 2 C1.CH 2 OH + H 2 O 2. From defines by addition of hypochlorous acid (p. 47): CH 2 :CH 2 + HC1O = CH 2 C1.CH 2 OH From alkylene oxides (which are themselves, however, prepared from the chlorhydrins p. 157), by addition of hydrogen chloride: CH 2 \ CH 2 C1 | >0 + HC1 = | CH/ CH 2 OH 247 SOME HALOGEN AND AMINO DERIVATIVES The bromhydrins are made by the same methods, but the meth- ods are not effective for iodohydrins. These may be prepared by the action of potassium iodide on the chlorhydrins: CH 2 .C1.CH 2 OH.+ KI = CH 2 LCH 2 OH + KC1 Properties and Reactions. The halogenhydrins have the prop- erties and give the reactions of both alkyl halides and alcohols. Since they can be made directly from the polyhydroxyl alcohols, they serve as a means for passing from one such alcohol to others with fewer hydroxyl groups. Both the hydroxyl group and the halogen are affected when a halogenhydrin is treated with alkalies, and alkylene oxides are formed: CH2V CH 2 C1.CH 2 OH + KOH = | >O + KC1 + H 2 O CH/ Of the halogen-substituted aldehydes, chloral, CC1 3 .CHO, is the most important representative (cf. p. 91). The formation of halogen ketones and ethers has already been alluded to. The chlor and brom-ketones as well as the ethers may be made by direct action of the halogen. Halogen-substituted Acids. Chlorine and bromine do not act very readily on the saturated acids, but the action is assisted by sunlight, or by the presence of a catalytic agent, such as iodine or sulphur. The substitution takes place much more rapidly in the acid chlorides or bromides, or the acid anhydride, and is more easily effected the higher the molecular weight of the acid. Since the substituted acid halides or anhydrides are readily converted into the corresponding acids, they are usually employed in making the chlor and brom-acids. Iodine is usually introduced by reac- tion of the chlor-acids with potassium iodide. Direct chlorina- tion or bromination gives generally a-substitution products, or products in which the halogen is united to the car-bon atom standing next to the carboxyl group. /3-, 7,- and 6-compounds are usually formed by the addition of INTRODUCTION TO ORGANIC CHEMISTRY 248 the hydrogen halide to unsaturated acids, the halogen in this case usually entering at a point as far removed from the carboxyl group as possible : CH3.CH:CH.CH 2 .CO.OH. + HBr = Ethylidene-propionic acid CH 3 .CHBr.CH 2 .CH 2 .CO.OH y-brompropylacetic acid CH 2 : CH.CH 2 .CH 2 .CO.OH + HBr = Ally lace tic acid CH 2 Br.CH 2 .CH 2 .CH 2 .CO.OH 5-brompropylacetic acid More than one atom of chlorine or bromine can be substituted by further direct action of the halogen on the monosubstituted acid. Chlorine is allowed to act in solution in carbon tetra- chloride when possible, while bromine often acts without a solvent. It is also possible to obtain the halogen-substituted acids by introduction of the carboxyl group into other halogen-substituted compounds or by oxidation 'of the substituted alcohols or alde- hydes. Thus trichloracetic acid is prepared by oxidizing chloral by means of nitric acid : CC1 3 .CHO + O = CC1 3 .CO.OH Other methods for introducing the carboxyl group may be employed as, for instance, through the cyanogen group. Chlorformic add, Cl.CO.OH, can exist only in the form of its esters. Chloracetic Acids. Monochloracetic acid, CH 2 C1.CO.OH, may be prepared by the direct action of chlorine on boiling acetic acid to which some sulphur has been added. It forms crystals which melt at 63. It is a stronger acid than acetic acid. Di- Mor acetic acid, CHC1 2 .CO.OH, can be made by further action of chlorine on acetic acid or on the monochloracid, but, as this gives a mixture of chloracetic acids, it is best prepared by boiling chloral hydrate with a solution of potassium cyanide. The reac- tion occasions a rearrangement which is rather unusual: CC1 3 .CH(OH) 2 + KCN = CHC1 2 .CO.OH + HCN + KC1 249 SOME HALOGEN AND AMINO DERIVATIVES This acid is liquid at ordinary temperatures, having a melting point of 4. Trichloracetic acid is made by the oxidation of chloral, as given above. It is a solid, melting at 55. Though it stands so near to chloral in its structure, it has no trace of the physiological effect of this substance. The discovery of trichloracetic acid by Dumas in 1839 had a very important influence on chemical theory, the fact that the strongly negative element chlorine could be substituted for hydrogen without changing the essential nature of the compound leading to the overthrow of the dualistic theory of Berzelius. Trichloracetic acid has also a further historical interest through the demonstration in 1845 by Kolbe of a method of its synthesis from the elements. As the reduction of the trichlor- acetic acid to acetic acid by potassium amalgam in aqueous solu- tion had already been effected, the synthesis of acetic acid from its elements for the first time was accomplished. Kolbe's syn- thesis was as follows: Q. Heat CC1 2 C1 2 ,H 2 CO.OH C + 28 - CS 2 >CC1 4 || > CC1 2 Sunlight CC1 3 The chloracetic acids are all soluble in water. The mono- chloracetic acid is decomposed by boiling its solutions, with the production of glycollic acid, CH 2 OH. CO.OH. Dichloracetic acid in solution is decomposed slowly at 100, more rapidly when heated in a sealed tube to higher temperatures, and yields gly- oxylic acid, CHO.CO.OH. Trichloracetic acid is more unstable, and on boiling its solution gives chloroform and carbon dioxide: CC1 3 .CO.OH = CHC1 3 + CO 2 These reactions are effected more rapidly by alkalies or silver hydroxide. General Properties of the Halogen-substituted Acids. The substitution of halogen atoms for hydrogen increases the acid character; the influence of chlorine being greater than that of INTRODUCTION TO ORGANIC CHEMISTRY 250 bromine, and that of bromine greater than that of iodine. The position of the substituted halogen also has an influence on the acidity; being less effective the further it is removed from the carboxyl group. The activity of acids is measured by their dis- sociation-constants, and from determinations of these it appears that the strength of monochloracetic acid is about eighty-six times that of acetic acid. Introduction of a second chlorine atom multiplies this strength by 33, and trichloracetic acid is about 23 . 5 times as strong as the dichlor-acid, or nearly 67,000 times as strong an acid as acetic acid. While the presence of the halogen thus influences the acid character, the carboxyl group has a reciprocal influence on the stability of the halogen. In the alkyl halides the hatogen can be replaced by hydroxyl, or an unsaturated hydrocarbon produced, by means of alkali hydroxides, but the reaction is slow, and usu- ally requires heating to a high temperature (in sealed tubes) for hours. With the halogen-substituted acids, however, the same reaction takes place much more readily. The influence of the carboxyl group on the reactivity of the halogen, like that of the halogen on the acidity, depends upon the relative position of the halogen and carboxyl in the molecule. With a-compounds, there is substitution of hydroxyl for the halogen; with /3-compounds and alcoholic solutions of alkalies the chief product is an unsaturated acid; with y-compounds, the hydroxyl acids which are first formed break down easily into lactones (p. 172). The j8-halogen-substituted acids enter into a characteristic reaction with sodium carbonate by which the sodium salt which is first formed is decomposed with the formation of an unsaturated hydrocarbon : Na2COs CH 3 .CHBr.CH(CH 3 ).CO.ONa >CH 3 .CH:CH.CH 3 /3-brommethylethyl acetic acid Butylene + NaBr + CO 2 By means of potassium cyanide, the halogen in all monohalogen acids is replaced by cyanogen and the compound thus becomes 251 SOME HALOGEN AND AMINO DERIVATIVES the half-nitrile of a dibasic acid. Hence the monohalogen acids are a means for building up dicarboxylic acids from monocarboxy- lic acids. Ammonia reacts with the monohalogen acids with the produc- tion of amino-acids. Ammo -compounds Ammo-alcohols. We have already met with compounds in which the amino-group and hydroxyl are united to the same carbon atom the aldehyde-ammonias. Amino-alcohols or hydramines in which hydroxyl and the amino group are combined with different carbon atoms of a hydrocarbon radical can be made by the action of ammonia on halogen hydrins or alkylene oxides: CH 2 OH.CH 2 C1 + NH 3 = CH 2 OH.CH 2 NH 2 + HC1 CH2V | >O + NH 3 = CH 2 OH.CH 2 NH 2 CH/ These reactions may give secondary and tertiary derivatives, e.g., (CH 2 OH.CH 2 ) 2 NH and (CH 2 OH.CH 2 ) 3 N, as in the forma- tion of amines (p. 128). The amino-alcohols are bases which form salts, as the amines do, by direct addition of acids; and the hydrogen of the amino- group may be replaced with alkyl groups as in the amines. Aminoethyl alcohol, whose formula is used above as an illustra- tion, is of interest as the compound from which the physiologically important choline (p. 134) may be considered a derivative. Ammo-aldehydes, the simplest of which is aminoacetaldehyde, CH 2 NH 2 CHO, and amino-ketones, have been made, but in small number. Muscarin, a very poisonous substance, which is found in toad-stools and certain other plants, is apparently a quaternary base related to aminoacetaldehyde, and having the formula, /N(CH 3 ) 3 OH CH< , H 2 X CHO INTRODUCTION TO ORGANIC CHEMISTRY 252 Amino-acids Acids in which the amino group has replaced hydrogen in the alkyl radical of the acid are of great physiological importance, since many of them are natural decomposition products of the pro- teins (cf. p. 405). They may be considered as amines in which alkyl hydrogen has been replaced by the carboxyl group, and, in fact, they show amine as well as acid characteristics: but on the whole it is simpler to view them as substituted acids. Formation. They may be made: i. By the action of ammonia on the monohalogen acid. Thus chloracetic acid yields NH 2 . CH 2 .- CO.OH, NH(CH 2 .CO.OH) 2 , and N(CH 2 .CO.OH) 3 . The reac- tions are like those for forming amines from the alkyl halides, and, as in that case, the immediate products are substituted ammo- nium salts from which the amino-acids are set free by the action of alkalies. If amines (substituted ammonias) are used instead of ammonia, the products are correspondingly substituted amino-acids, thus: CH 3 NH 2 + CH 2 C1.CO.OH = (CH 3 .NH)CH 2 CO.OH Methyl ammo-acetic acid 2. a- Amino-acids are also produced from aldehydes or ketones by forming first the hydrocyanic acid addition product of these compounds (p. 78), replacing the hydroxyl group with the amino group by ammonia, and finally converting the cyanogen group into the carboxyl group by hydrolysis: CH 3 HCN CH 3 NHs CHs 2HaO I - > I /OH - > | /NH 2 -- > | CHO CH< CH< (HC1)CH(NH 2 ) X CN X CN | CO.OH Acetaldehyde Lactonitrile o-Amino- ot-Amino- propionitrile propionic acid (alanine) 253 SOME HALOGEN AND AMINO DERIVATIVES The amino-acids may be obtained in a pure state by means of their copper salts. These are made by boiling the solutions of the acids with copper carbonate, and crystallize from the hot solu- tions. The copper is replaced by hydrogen by treatment with hydrogen sulphide. Properties. The amino-acids are crystalline substances, most of which are readily soluble in water, but insoluble or sparingly soluble in alcohol or ether. Some of them have a sweet taste. While, as we have seen, the presence of the strongly negative halogens greatly increases the acid character of acids, the decidedly positive amino group opposes the acidity, so that the amino-acids are neutral compounds, forming salts both with bases and with acids. With oxides or hydroxides of the heavy metals they give salts in which the hydrogen of carboxyl is replaced by the metal; but no crystallizable salts with sodium, potassium, or barium are formed. With acids the salts are like those of the amines sub- stituted ammonium salts. It also appears probable from some of their behavior that the amino-acids may form cyclic salts by reaction between the carboxyl and amino groups: /NH 2 / CH 3 .CH< = CH 3 .CH< O X CO.OH ^CQ / Reactions. The amino-acids give most of the reactions of the amines. Thus with nitrous acid the amino-group is replaced by hydroxyl as in the case of primary amines (p. 131), and alkyl and acyl chlorides replace the hydrogen of the amino-group with their radicals. Esters of the amino-acids are made by the ordinary method of leading hydrogen chloride into a mixture of the acid and alcohol. The hydrochloride of the amino-ester which is thus produced gives the ester by treatment with a solution of potas- sium hydroxide at a low temperature and immediately extracting the ester with ether. In other reactions the relative positions of the amino and carboxyl groups influence the result, as in the cases INTRODUCTION TO ORGANIC CHEMISTRY 254 of the hydroxyl and halogen-substituted acids. The a-compounds readily give anhydride compounds by the loss of water from two molecules: CH 2 NH 2 .CO.OH ,NH - CO - 2 H 2 O = ; CH 2 NH 2 .CO.OH X CO - NET The /3-acids easily lose ammonia with the formation of unsat- urated acids: CH 2 NH 2 .CH 2 .CO.OH = CH 2 :CH.CO.OH + NH 3 /3-Amino-propionic acid Acrylic acid The 7-amino-acids, like the 7-amino-hydroxy acids give inner anhydrides called lactams, on account of their similarity to the lactones (p. 172). CH 2 NH 2 .CH 2 .CH 2 .CO.OH = CH 2 NH.CH 2 .CH 2 CO + H 2 O -y-Amino-butyric acid j _ [ Lactam Among the amino-acids and their derivatives the following may be given as examples. Aminoacetic acid, CH 2 NH 2 . CO .OH, which is also called glycine and glycocoll, may be made from monochloracetic acid and ammo- nia. It is obtained from glue and other proteins by boiling with di- lute sulphuric acid, and from hippuric acid (p. 359) by hydrolysis. From its aqueous solution crystals are obtained, which melt with decomposition at 232. Glycine has a sweet taste, which together with its production from glue, was the occasion for the name gly- cocol (y\vKvs and KoXXa). Like many amino-acids it forms a blue copper salt when its solution is boiled with copper carbon- ate. This salt is very sparingly soluble in water, and crystallizes with one molecule of water. Sarcosine is methylaminoacetic acid, CH 2 NH(CH 3 ).CO.OH, which was first obtained from creatine /NH 2 HN C< X N(CH 3 ).CH 2 .CO.OH t 255 SOME HALOGEN AND AMINO DERIVATIVES a subtance contained in meat extract, and related to guanidine (p. 233). It can also be obtained from caffeine, and can be synthe- sized from methylamine and monochlor-acetic acid. Betame, which is found in the molasses of beet sugar, is a derivative of trimethyl glycine, being an inner ammonium salt, N(CH 3 ) 3 .CH 2 .CO.O j [ Betame is the source of the "trimethyl amine" obtained by the destructive distillation of vinasse (cf. p. 213). Alanine, CH 3 .CHNH 2 .CO.OH, or a-amino-propionic acid; leucine, CH(CH 3 ) 2 .CH 2 .CHNH 2 .CO.OH, or a-amino-isobutyl- acetic add', ly sine, CH 2 NH 2 .(CH 2 ) 3 .CHNH 2 .CO.OH, a,ediamino caproic acid, are illustrations of amino-acids obtained by the hydrolysis of proteins. Asparagine, which is found in asparagus and often is present in sprouting seeds and in many plants, is at once an amino- and an amido-compound, being amino-succinic acid amide. CH 2 .CO.OH HNH 2 .CO.NH 2 That this is the structure of asparagine is shown by the fact that on hydrolysis it gives aspartic acid, CH 2 .CO.OH , CH.NH 2 .CO.OH whose structure is proved by its conversion into malic acid, (p. 185), CH 2 .CO.OH CHOH.CO.OH by nitrous acid. Like many amino-acids and their derivatives, these compounds all contain an asymmetric carbon atom and are optically active. INTRODUCTION TO ORGANIC CHEMISTRY 256 Asparagine from most natural sources is levo-rotatory; but from one source (the sprouts of vetches) two sets of asparagine crys- tals are obtained whose solutions have opposite rotatory power. No crystalline racemic form has been obtained. It is note- worthy that the dextro-asparagine has a sweet taste, while that of the levo-compound is disagreeaable and cooling. CHAPTER XIX CYCLO-PARAFFINS In several instances in inorganic chemistry and also among the organic substances already studied, the student has met with formulas in which the atoms are united in closed rings, such as, O N v CH2v CH 2 .C(X 'X, || >0, | >>, | >0 O N/ CH/ CH 2 .C(X /\ O - O Ozone Nitrous Ethylene Succinic oxide oxide anhydride CH2.CO 2\ / \ >NH , (X( >0 CH,CH Succinic Glycollide imide But no compounds have thus far been discussed whose formulas contain a ring of carbon atoms alone. Such compounds, however, are known, and among them are a very large number of the most important substances of organic chemistry those which form the subject of the second part of this book under the title of the Aromatic Compounds. Compounds which have the closed-ring structure are called cyclic compounds isocyclic when the ring is composed of atoms of one element alone as in ozone, and heterocyclic if the elements are different as in the other illustrations given above. Certain carbocyclic (isocyclic) compounds which are inter- mediate in their deportment between the open-chain aliphatic compounds and those of the aromatic group will be briefly con- sidered here. These carbocyclic hydrocarbons are composed of methylene radicals, CH 2 , and are known as the cycloparaffins. Their names, formulas, and boiling points are given in the following table, which also includes for comparison the boiling points of the paraffins and defines having the same number of 257 INTRODUCTION TO ORGANIC CHEMISTRY 258 carbon atoms. It will be noticed that in every case the boiling point of the cyclic compound (polymethylene) is the highest of the three. Trimethylene or cyclopropane | 2 \CH 2 CH/ Tetramethylene, cyclobutane CH 2 .CH 2 1 1 CH 2 .CH 2 Pentamethylene, cyclopentane CH 2 . CH 2 x 1 >ci CH 2 .CH/ Hexamethylene, CH 2 .CH 2 .CH 2 Poly- methylene -35 cyclohexane Heptamethylene, cycloheptane CH 2 .CH 2 .CH 2 CH 2 .CH 2 .CH2v I CH 2 .CH 2 .CH/ CH 2 .CH 2 .CH 2 .CH 2 CH 2 49 81 117 Olefine Paraffin - 48 - 45 C - 5 40 69 95 98 Nonomethylene, cyclononane >CH 2 146 171 126 150 Octomethylene, cyclooctane | | CH 2 .CH 2 .CH 2 .CH 2 CH 2 .CH 2 .CH 2 .CH 2V 1 / ( CH 2 .CH 2 .CH 2 .CH/ The cycloparaffins are isomeric with the unsaturated hydro- carbons of the ethylene series (olefines), but differ from them in not being readily oxidized by potassium permanganate, and in forming substitution rather than addition products, so that their conduct in general resembles that of the paraffins. Unlike both paraffins and defines, the series of polymethylenes is apparently limited to the small number given in the table, and there are theo- retical considerations which make the existence of larger rings improbable. Much larger heterocyclic rings are, however, known. The argument for the ring formula of trimethylene is as follows. It is formed by the action of sodium on (i,3)-dibrompropane (tri- 259 CYCLO-PARAFFINS methylene bromide) whose formula is known to be that used in the following equation: CH 2 Br.CH 2 .CH 2 Br + 2 Na = CH 2 .CH 2 .CH 2 + 2 NaBr Trimethylene bromide Trimethylene Chlorine forms a substitution product, C3H 4 C1 2 . Trimethylene is more stable toward bromine than is its isomer propylene, but in sunlight bromine acts additively, forming, however, trimethyl- ene bromide again, instead of propylene bromide, CH 2 Br . CHBr . - CH 3 , which would be the product of bromine on propylene. Pentamethylene can be made by the following steps which indi- cate its structure: CH 2 .CH 2 .CO.(X CH 2 .Ctf2\ HH CHa.CH^ | \ Ca | >CO >| >CH 2 CH 2 .CH 2 .CO.CK CH 2 .CH/ HH CH 2 .CH/ Calcium Adipate Ketopentamethylene Pentamethylene Hexamethylene will be discussed later under the aromatic compounds, because of its relationship to benzene. Many deriva- tives of this hydrocarbon occur in nature, particularly in the ter- penes and in camphor. Numerous derivatives of the cycloparaffins have been prepared and investigated, most of them being made much more readily than the hydrocarbons themselves. The preparation of the tetra-, octo-, and nonohydrocarbons has proved especially troublesome, and it is only quite recently that they have been obtained. The penta- and hexamethylenes are the most stable of the group, and the stability decreases from this maximum, whether the number of carbon atoms in the ring is increased or diminished. Stereochemistry of the Cycloparaffins. An explanation of the different degrees of stability of the poly methylene compounds and of the non-existence of rings of more than nine carbon atoms is offeredin the "strain theory "of A. v.Baeyer (1885). This theory is in brief as follows: In the tetrahedral structure of which the carbon atom is the center, the valencies or affinities of that atom are supposed to be directed to the solid angles of the figure, along the axes of the tetrahedron. When several carbon atoms are INTRODUCTION TO ORGANIC CHEMISTRY 260 united in chains or in rings, the condition for the greatest stability is when the valencies connecting each pair of neighboring carbon atoms are in a straight line. If this condition is unfulfilled and the directions of the valencies make an angle with each other, the con- figuration becomes less stable as this angle (of 180) becomes less, because of the "strain" which results from the deflection that the valencies suffer in coming together. In open-chain compounds the paraffins the linkages occur without deflection of the valencies from their normal directions, but the result is that in these compounds the carbon atoms do not lie in a straight line (as represented in the usual formulas), but in a regular zigzag whose equal angles are those which the edges of a regular tetrahedron subtend at its center, or 109 28'. Thus the formula for normal pentane would be HI K H FIG. i. Normal pentane. FIG. 2. Baeyer's strain theory. 2 6 1 C YCLO-P ARAFFINS Figure 2 gives the normal directions of valencies in ring for- mations of from three to five atoms of carbon. Supposing that in trimethylene the centers of the three carbon atoms lie in the angles of an equilateral triangle, the directions of the linking valencies from each carbon atom must be at an angle of 60 with each other. Since the normal directions of the valencies would make an angle of 109 28', this configuration requires that each valence shall be "strained" 24 44' from its normal direction since 109 28' 60 = 4928' = 2 X 24 44'. In the tetramethylene ring with the four carbon atoms at the angles of a square, the deviation of each of the valencies is 9 44' (109 28' 90 = 19 28' = 2 X 9 44') . In pentamethylene the angle of strain would be o 44'; in hexamethylene, 5 i6';and becomes larger in the higher cycloparaffins. Thus the greater stability of the five- and six-carbon atom rings is "explained." This theory also accounts for the non-existence of anhydrides of oxalic and malonic acids, and the ready formation of succinic and glutaric anhydrides with chains of four and five atoms of carbon linked into rings by an atom of oxygen. In accord with the the- ory, too, is the fact that no anhydrides of adipic acid, (CH 2 )4- (CO.OH) 2 , or of higher dicarboxylic acids exist. The readiness with which 7- and 5-lactones and lactams are produced is also in agreement with the theory. PART II AROMATIC COMPOUNDS AND RELATED SUBSTANCES CHAPTER XX AROMATIC HYDROCARBONS Benzene and Its Homologues The substances that belong to the so-called aromatic group comprise the majority of those known to organic chemistry. The name of the group was first applied to certain natural vegetable substances which possess an agreeable, aromatic odor, such as the oil of bitter almond and of wintergreen. It has persisted like many of the older names, being the common designation of a large group of compounds which, though often without the charac- teristic aromatic odor, are chemically related to those first classed under this name. Certain well-marked peculiarities in chemical deportment, in which the aromatic compounds differ from those of the aliphatic group, justify a separate classification and treatment. Every aromatic compound contains at least six carbon atoms; and one of the most significant of the peculiarities of these compounds is that, when one of them has more than six carbon atoms, it can be broken down into one which contains six, and at this point farther decomposition is resisted. Benzene, CeHe, is the simplest of the hydrocarbons of this group and may be regarded as the parent substance from which all the others are derived. It was discovered in 1825 by Faraday in the liquid found in compressed oil gas, and found by A. W. Hofmann twenty years later in the mixture of light oils distilled from coal tar, and is obtained from this latter source. 266 INTRODUCTION TO ORGANIC CHEMISTRY Coal tar is formed in the destructive distillation of bituminous coals in the coal gas and coke industries, which is carried out at temperatures from Q8o -iioo. It is a black, viscous oil, owing its color chiefly to the presence of finely divided carbon. When distilled, less than half of it is volatilized, leaving a residue of pitch which is used as a black varnish for metals and, mixed with asphalt, for making pavements. The distillate is collected in separate fractions, the temperature being carried up to about 300. The substances obtained in this way are of three classes: indifferent hydrocarbons not affected by dilute acids or alkalies, acid compounds which dissolve in alkalies, and bases which dis- solve in acids. By successive treatment with alkalies and acids a separation of these classes is effected, and by further operations, more limited groups of substances, or individual compounds are obtained. Of the many compounds contained in the coal tar distillates, only a few benzene, toluene, naphthalene, anthracene, and phenol are produced commercially in a pure, ore vqn approxi- mately pure, condition. Mixtures of isomeric compounds are also obtained, known as xylols and cresols; and mixtures of homo- logues the pyridine and other bases. Small amounts of other compounds containing oxygen, sulphur, and nitrogen, are also obtained. The amount of benzene and toluene is usually about 1-1.5 P er cent, of the tar, of anthracene 0.25-0.45 per cent., of phenol 0.4-0.5 per cent., of cresols 2-3 per cent., and of naphtha- lene o-io per cent. Benzene obtained from this source contains very small amounts of thiophene (p. 394), which cannot be removed by distillation, but is extracted by shaking the benzene with concentrated sul- phuric acid. - The final purification of the benzene is effected by crystallizing it in a freezing mixture. Benzene is a thin oil, lighter than water, which has a slight, not unpleasant odor, melts, when frozen, at 5. 4, and boils at 80.4. It is insoluble in water. Formation. Benzene is formed, together with some related AROMATIC HYDROCARBONS 267 hydrocarbons, when acetylene is led through tubes heated to a dull red. Benzene can in this way be synthesized from the ele- ments, and another synthesis of this sort can be made through mellitic acid (p. 370). In these ways and others, it is possible to convert simple aliphatic compounds into substances of the aro- matic group. Benzene can also be made: i. From benzoic acid, CeH 5 .CO.OH, by heating sodium benzoate with sodium hydrox-j ide or soda-lime, a reaction similar to that by which aliphatic hydrocarbons are formed from acids: C 6 H 5 .CO.ONa + NaOH = C 6 H 6 + Na 2 CO 3 2. From phenol, CeHs.OH, by distillation with zinc dust. 3. From benzene sulphonic acid, C 6 H 6 .SO 3 H, by superheated steam, or boiling with hydrochloric acid. 4. From amidobenzene (ani- line), C6H 5 NH 2 , by conversion into the corresponding diazo compound (p. 315) and boiling with alcohol. 5. From halogen derivatives by the Grignard reaction (cf. p. 274). These four methods are general ones for the exchange of these different groups for hydrogen in the aromatic compounds. Formula of Benzene. The molecular formula for benzene, established by analysis and the determination of its vapor density, is CeHe. This means that of the twenty-four valencies of the six carbon atoms only sixteen are necessary for the single linkage of these atoms if the atoms form an open chain, or eighteen if the compound is cyclic, and suggests a high degree of unsaturation. The same thing is true of dipropargyl which is also C 6 He. But while dipropargyl shows itself to be a highly unsaturated com- pound (p. 50) benzene differs markedly in its chemical conduct from this substance and the other unsaturated compounds we have studied. It is exceedingly indifferent toward oxidizing agents, not decolorizing permanganate, and resisting attacks which would break down ordinary unsaturated hydrocarbons into compounds of a less number of carbon atoms. Further, it does not unite additively with certain reagents as the unsaturated compounds 268 INTRODUCTION TO ORGANIC CHEMISTRY do so readily; for instance, with hydrogen bromide, or hypochlor- ous or sulphuric acid. With the free halogens, however, it does form addition products in sunlight, but much less readily than the hydrocarbons of unsaturated groups; and hydrogen can also be added to it under certain conditions. But the maximum num- ber of added atoms in either case is six, giving CeHeBre and CcHi 2 , while the corresponding aliphatic compounds from unsaturated hydrocarbons are CeHeBrg, and CeHu. In this last respect, there- fore, benzene differs both from the unsaturated hydrocarbons, and from the paraffins which form no addition products. It differs from the paraffins also by the readiness with which nitro- substitution products are made by the action of concentrated nitric acid: HONO 2 = C,H.^O 2 + H 2 O Nitrobenzene and sulphonic acids by concentrated sulphuric acid: CeHe+HO.SCVOH = CeH^SCVOH + H 2 O Benzene sulphonic acid And, further, the behavior of the various derivatives of benzene is quite unlike that of corresponding substitution products of the open-chain hydrocarbons we have studied. The stability and per- sistence of the benzene nucleus of six carbon atoms in aromatic compounds led Kekule in 1865 to propose a closed-ring forma- tion in explanation of its peculiarities and its differences from the open-chain aliphatic compounds. Facts helpful in suggesting the structure of the benzene mole- cule are found in the number of substitution products it forms with a given element or group, i. It has proved impossible to obtain more than one monosubstitution product, and the results of elaborate experiments have shown that each of the six hydro- gen atoms bear the same relation to the rest of the molecule. A AROMATIC HYDROCARBONS 269 formula in which the six carbon atoms are linked in a closed ring is the only one by which this symmetry can be expressed. H C /\ HC CH I I HC CH Y H 2. If more than one hydrogen atom in benzene is replaced by the same element or group, it is found that three a^id only three isomeric substitution products can be obtained when two, three, or four atoms of hydrogen are replaced; and only one product when five or six are replaced. These facts are accounted for by the symmetrical ring formula. In the following formulas which show this, we adopt the conventional expression for the benzene molecule as an unlettered hexagon. At each angle the group CH is assumed unless some symbol appears,- and in this case it indi- cates the replacement of the hydrogen alone by some atom or group. The angles (carbon atoms) are numbered for readier ref- erence in the discussion. The five possible arrangements with two substitutes are: X X X X X It is evident that the positions i, 2 and i, 6 are identical so far as relations of the substituents to each other and the rest of the 270 INTRODUCTION TO ORGANIC CHEMISTRY molecule are concerned. The same is true of the positions i, 3 and i, 5. Formulas i and 5 are therefore the same, and formulas 2 and 4 also represent the same compound, leaving three different disubstitution products shown by formulas i or 5, 2 or 4, and 3. The three types of disubstitution products are designated as ortho, when the substituents are on adjacent carbon atoms, i, 2 or 1,6; meta, when in the positions i, 3 and i, 5, and para when on opposite carbon atoms, i, 4. With three like substituents the student will readily see that, again, only three distinct structures can be formulated. These are shown in the following formulas with the names which are given them: X Adjacent i, 2, 3 Unsymmetrical i, 2, 4 Symmetrical i, 3, 5 When there are four like substituents, there are also three and only three isomers possible. If in this case we may regard the two remaining hydrogen atoms as the substituents in a molecule of CeXe, the demonstration becomes identical with that for the disubstitution products. With five like substituents, it is evident that there can be but one arrangement, and the same is, of course, true when all the hydrogen is replaced by like atoms or groups. If, however, the substituting atoms or groups are different, it is obvious that the numbers of isomers may be much larger when three or more hydrogen atoms are replaced. A symmetrical ring formula is thus seen to allow the successful representation of the possibilities and limitations of the isomerism which is established by experiment. The student has probably noticed that the formulas which have been given have represented AROMATIC HYDROCARBONS 271 carbon as a triad, or at least have not indicated the disposal of its fourth valency. In fact, this is still an open question, but in the great majority of aromatic compounds it is a matter of compara- tively little importance, since in most of the reactions, the fourth bond, whatever its nature, remains undisturbed. It is only in the halogen and hydrogen addition products that it must be reckoned with, and here it is only necessary to assume that each carbon atom has one additional valence which is disposable under certain conditions. From a theoretical point of view, however, the question is of great interest, and many suggestions have been made, none of which are free from objections. The first struc- tural formula for benzene was proposed by Kekule in 1865 in the form shown in i, with alternate double and single bonds, H C HC CH I II HC CH V c H i Kekute The chief objection to this is that the positions i, 2 and i, 6 are not identical and that there should therefore be two ortho com- pounds. To meet this criticism Kekule assumed that the linkages between the carbon atoms were dynamic instead of static, and that the double and single unions are continually shifting their places. In the Claus formula the fourth valencies are utilized in binding opposite atoms, while in the "centric" formula of Baeyer, they "neutralize" each other without actually uniting, and thus render no service in holding the ring together, but may be utilized in the case of addition products. The objec- 272 INTRODUCTION TO ORGANIC CHEMISTRY tions to these, and to other formulas which have been proposed, gain in force when the spatial arrangement of the atoms is considered. The solution of the problem of the structure of the benzene molecule, which Kekule gave in 1865, in his hexagonal formula, has had the most profound influence on the development of organic chemistry. It led at 'once to an understanding of the relations of the aromatic compounds to benzene and to each other, and has guided the wonderful synthetic achievements in this group of substances. It is probably the most fruitful single idea in the history of chemistry since Dal ton's atomic theory. It has been stated that benzene reacts directly with nitric acid, sulphuric acid, chlorine, and bromine, with the formation of compounds in which one or more hydrogen atoms of the benzene molecule are replaced by the nitro group, NC>2, the sulphonic acid group, SO 3 H, or by the halogens. If we add to this that halogen derivatives of the aliphatic hydrocarbons react with benzene in the presence of aluminium chloride with the substitution of the aliphatic radical for hydrogen, the list of direct substitutions is practically exhausted. Other products in which amido, hydroxyl, carboxyl, and other groups are present, may be made from these directly substituted compounds. The monad group, CeH 5 , which appears in all monosubstituted benzenes, is called phenyl (from phenol, CeHe.OH, in which it is united to hydroxyl), and this term is commonly employed in the naming of compounds; thus, CeH^Cl is phenyl chloride, C^R^C^H.^ is diphenyl, etc. The general name aryl is used for phenyl and the other homologous monad radicals of the aromatic group. For the sake of convenience in .our discussions we will further desig- nate the divalent, trivalent, etc., groups, CeH 4 , CeHs, etc., and those in which partial substitution has occurred, such as Br.C 53 139 0.881(0) CsHi.0 ' v^ii3 \3/ p-Xylene /CH 3 (i) C6H CeH/ -> C 6 H 4 < - C 6 H 4 < X NO 2 X NH 2 x N:NBr Toluene Nitrotoluene Toluidine Diazo compound X CH 3 C 6 H 4 / . X Br Bromtoluene 286 INTRODUCTION TO ORGANIC CHEMISTRY When two chlorine or bromine atoms are substituted in the benzene nucleus by direct reaction on benzene, the chief product is the para compound, a small amount of ortho compound being formed at the same time. Similarly, when mono-chlor or brom- toluene is made by direct substitution, the product is mainly the para compound with a little of the ortho derivative. The influ- ence of groups already present on the entrance of other substitu- ents, and how these may be directed to certain positions will be taken up later (p. 298). In the preparation of the halogen derivatives by the direct action of the halogen, the theoretical amount of the halogen necessary to give the special derivative, or a slight excess of it, is added. Bromine is weighed directly before adding it, but the weight of chlorine is usually determined by noting the increase in the weight of the flask in which the reaction takes place. SOME TYPICAL HALOGEN COMPOUNDS Name Chlorbenzene, Phenyl chloride Hexachlorbenzene Brombenzene o-Dibrombenzene m-Dibrombenzene p-Dibrombenzene Adj-Tribrombenzene Unsym-Tribrombenzene Sym-tribrombenzene lodobenzene p-Di-iodobenzene o-Chlortoluene p-Chlortoluene Benzylchloride, Chlor- methylbenzene Benzalchloride, Dichlor- methylbenzene Phenylchloroform, Tri- chlormethylbenzene Formula CeHsCl C 6 H 6 Br C 6 H 4 Br 2 (i, : C 6 H 4 Br 2 (i, - C 6 H 4 Br 2 (i, < C 6 H 3 Br 3 (i, : C 6 H 3 Br 3 (i, : C 6 H 3 Br s (i, . C 6 H 6 I :,4) C 6 H 4 C1.CH 3 C 6 H 6 .CH 2 C1 C 6 H 6 .CH.C1 2 C 6 H 6 CC1 3 Melting point -44-9 227 Boiling point 132 326 f Specific gravity I.I06 (20/4) -30.5 I + 1-2 89-3 ) 87 157 22 4 22O 2I 9 1.491 (20/4) 2.003 (o) 1.955(19) 1.841 (89) ) 44 \ 1 20 278 -28.5 1 88 28* 1.861 (o) 2) ^ 4) 74- 162 -43-2 -16.1 179 204 1.113(15) 1.295 (16) 22.5 213-214 1.38 (14) HALOGEN DERIVATIVES 287 Properties and Reactions. Some of the halogen derivatives are liquids, but most of them are solids. They are readily soluble in alcohol, ether, etc., but are usually insoluble or only slightly sol- uble in water. The compounds containing a halogen in the side chain generally have a pungent and irritating odor, while those in which the halogen is in the nucleus have a much weaker and not unpleasant smell. Like all other organic halogen derivatives they are less inflammable than the corresponding hydrocarbons. When the halogen is in the nucleus, it is held, as a rule, so firmly that it does not readily enter into reaction. Compounds of this kind may be boiled with alkalies, silver hydroxide, ammonia, potassium cyanide, or acid sulphites without being sensibly affected. But the halogen atom shows a greater reactivity when certain other substituents are present for instance, o- and p- nitrochlorbenzene, C6H 4 C1.NO 2 , give with alcoholic potash the corresponding nitrophenols, C6H 4 (OH)NO 2 . Sodium, however, removes the halogen, and usually at ordinary temperatures (Fittig's reaction, p. 273), e.g., the syntheses of diphenyl and toluene: 2 C 6 H 6 Br + 2 Na = C 6 H 5 .C 6 H5 + 2NaBr Diphenyl C 6 H 5 Br + CH 3 Br + 2Na = CeH^CHa + 2NaBr Magnesium also reacts with the halogen compounds as de- scribed under Grignard's synthesis (p. 36). When the halogen is in the side chain it is readily replaced by the hydroxyl, amino, cyanogen, and other groups by the reactions employed with aliphatic halogen compounds. Thus benzyl- chloride, C6H 5 .CH 2 C1, may be converted into benzylalcohol, C 6 H 5> CH 2 OH, benzylamine, C 6 H 5 .CH 2 NH 2 , or benzylcyanide, CcHs.CH^CN, by the action of water or alkalies, ammonia, or potassium cyanide, as in the case of the aliphatic halides. This difference in reactivity according to the place occupied by the halogen may frequently be made the basis for determining whether the halogen is in the ring or in the side chain. If the 288 INTRODUCTION TO " ORGANIC CHEMISTRY substance is boiled with alcoholic potash and the solution is then acidified with nitric acid and tested with silver nitrate, a precipi- tate of silver halide shows that the halogen has been displaced from the organic compound and hence was probably present in the side chain; while no precipitation indicates that the halogen was in the ring. Benzalchloride, CeHB.CHC^, and benzotrichloride (phenyl- chloroform), C 6 H 5 .CC1 3 , are made commercially by the action of chlorine on toluene, and are employed in the preparation of benzaldehyde, C 6 H 5 .CHO, and benzoic acid, C 6 H 5 .CO.OH, respectively. Sulphonic Acids The action of sulphuric acid on aromatic compounds is one of the most striking characteristics of this group of compounds. All aromatic compounds dissolve in concentrated or fuming sul- phuric acid with greater or less readiness, and from these solutions compounds are obtained in which hydrogen of the nucleus is found to be replaced by the sulphonic acid group, S0 3 H: C 6 H 5 .CH 3 + H 2 SO 4 = CH 3 .C 6 H 4 S0 3 H + H 2 O Toluene Toluenesulphonic acid Aliphatic compounds react with sulphuric acid much less readily; and prolonged heating results in only a partial and un- satisfactory production of sulphonic acids (p. 241). Aromatic sulphonic acids may also be made, as the aliphatic sulphonic acids are, by the oxidation of the corresponding sulph- hydrogen compounds (thiophenols), and the sulphonic acid group may be introduced by other methods; but the preparation of the sulphonic acids is almost aways effected by the direct action of sulphuric acid. The ease with which this reaction proceeds is markedly influenced by the presence of other substituting groups. In general, alkyl or other positive groups favor the reaction, while carboxyl and other acid groups render it more difficult; and the SULPHONIC ACIDS 289 successive replacement of hydrogen atoms by the sulphonic acid group becomes impossible after three such groups have been introduced. The process of making sulphonic acids is called sulphonation. Preparation. In the preparation of sulphonic acids the aro- matic hydrocarbon or other compound is boiled for some time with concentrated sulphuric acid, or gently heated for a shorter time with fuming acid, and then the mixture of sulphonic acid with the excess of sulphuric acid is poured into water. The sulphonic acids of the hydrocarbons are mostly very soluble in water and may be separated from sulphuric acid in the following way: By neu- tralizing the mixture with carbonate of calcium, barium or lead, the sulphuric acid is precipitated as an insoluble sulphate, while the calcium, barium, or lead salt of the sulphonic acid remains in solution, and may be obtained by evaporation or converted into other salts by double decomposition, as, for instance, into the sodium salt by adding sodium carbonate. The free acid may be obtained from the calcium or barium salt by exact precipitation with sulphuric acid, or from the lead salt by decomposition with hydrogen sulphide. Another method depends on the fact that many of the sodium salts are difficultly soluble in a solution of sodium chloride, and hence are precipitated when the product of the reaction is poured into a saturated solution of common salt a result of the changed ionic concentration. The sulphonic acids of some aromatic compounds are precipi- tated by ice-water and, in a number of cases, by concentrated hydrochloric acid. Properties. 'Aromatic sulphonic acids are solids which crystal- lize from water, in which many of them are very soluble. The sulphonic acid salts are also mostly soluble in water and many of them crystallize well. Reactions. i. The sulphonic acids are strong acids, forming salts by the replacement of the hydrogen of the SOsH group by metals; and esters, such as C6H 6 .S03C2H 5 , with alcohols. 2 90 INTRODUCTION TO ORGANIC CHEMISTRY 2. Phosphorus pentachloride converts the sulphonic acids or their salts into sulphonic acid chlorides: CeHe.SOaH + PC1 5 = CH 6 .SO 2 C1 + POC1 3 + HC1 3. Melted with alkalies, the alkali salts of sulphonic acids have their sulphonic acid group replaced by hydroxyl: C 6 H 6 .S0 3 Na + NaOH = C 6 H 6 .OH + Na 2 SO 3 Phenol This reaction serves as the best practical method for making certain commercial phenols such as, resorcinol, C6H 4 (HO) 2 , naphthol, CioH 7 .OH, alizarin, Ci4H 6 O 2 (OH) 2 , etc. 4. Melted with potassium cyanide, the alkali salts give aromatic cyanides (nitriles) which may be hydrolyzed to acids: C 6 H5.S0 3 K + KCN = CeHs.CN + K 2 SO 3 5. Melted with sodium formate, the alkali salts form salts of carboxyl acids, CeHe.SOaNa + HCO.ONa = C 6 H 6 .CO.ONa + NaHSO 3 Sodium benzoate 6. Heated with sodium amide, the alkali salts give aromatic amines: OaNa + NaNH 2 = CeHs-NI^ + Na 2 SO 3 Aniline 7. The sulphonic group is replaced by the nitro group in some sulphonic acids by treatment with strong nitric acid. 8. The sulphonic acid group is replaced by hydrogen by dis- tillation of the acid, or most effectively by means of steam under pressure: CH 3 .C6H 4 .SO 3 H + H 2 = CH 3 .C6H 5 + H 2 SO 4 Toluenesulphonic acid Toluene This reaction following the sulphonation. of a mixture of hydro- carbons and separation of the sulphonic acids is sometimes used for the preparation of pure hydrocarbons; for the sulphonic acids can be separated by crystallization more readily and completely than the hydrocarbons by distillation. SULPHONIC ACIDS 2QI 9. Sulphonic acid chlorides react: (a) Slowly with water or alkalies, forming the sulphonic acid or its salts, (b) With am- monia or primary or secondary amines with the formation of sim- ple or substituted acid amides: OsCl + CH 3 NH 2 = C6H 5 .SO 2 .NH.CH 3 + HC1 (c) With alcohols, the chlorides give sulphonic acid esters: C6H 5 .SO 2 C1 + C 2 H 6 OH = C 6 H6.S02.OC 2 H 6 + HC1 (d) Nascent hydrogen reduces the chlorides to thiophenols, e.g., CeHe.SH. (e) When distilled with phosphorus pentachloride the sulphonic acid group is replaced by chlorine. The structure of the aromatic sulphonic acids is inferred from the reactions common to these compounds and the sulphonic acids of the aliphatic series (p. 241). The reaction with phos- phorus pentachloride shows the presence of the hydroxyl group, and the reduction of the acid chloride to a thiohydride proves that the sulphur atom is united directly to nucleus carbon. The structure is therefore R - S0 2 . OH and probably R - S^= O . \OH The sulphonic acids may thus be regarded as sulphuric acid in which one hydroxyl has been replaced by an aromatic radical. Uses. On account of the many reactions which they give, and their own ready preparation, the sulphonic acids are largely employed in chemical work. Sulphonation serves also to bring insoluble substances into a soluble condition, so that insoluble dyes, for instance, which cannot be directly employed on account of their insolubility, are made available for dyeing in the form of their sulphonic acids. Further, the sulphonic acid salts, the acid chlorides, and amides are used for the identification of aromatic 2Q 2 INTRODUCTION TO ORGANIC CHEMISTRY hydrocarbons. The amides are especially good for this purpose, since they crystallize well from hot water and have well-defined melting points. Benzenesulphonyl chloride, CeEU.SC^C^maybe used to distinguish the three classes of amines. It does not react with tertiary amines; but with primary and secondary amines forms substituted acid amides which are distinguished by the fact that the product from the primary amine is soluble in sodium hydroxide, while that from the secondary amine is insoluble. This difference in solubility is due to the presence in the former compound of hydrogen which is replaced with sodium by the action of sodium hydroxide: C6H 5 .SO 2 NH.CH 3 + NaOH -^CeHs.SOaNNa.CHa while in the secondary product there is no replaceable hydrogen in the acid amido group : C6H B .SO2N(CH 3 )2. In the following table are given a few typical sulphonic acids with the melting points of their chlorides and amides. " Sulph- onic acid" is to be added in each case to the name which is given. SULPHONIC ACIDS Melting Points Name Formula Chlorides Amides Benzene C 6 H 6 .SO 2 OH 14 -5 *S m-Benzenedi- C 6 H 4 .(SO 2 OH)2 (i, 3) 63 229 p-Benzenedi- C 6 H 4 .(SO 2 OH) 2 (i, 4) 131 Benzenetri- C 6 H3(SO 2 OH) 3 (i, 3, s) l8 4 306 o-Toluene- CeH (i. 2) liquid 153 SO 2 OH p-Toluene- C 6 H (i, 4) 96 X S0 2 OH 136 /CHa (i) o-Xylene- C 6 H 3 .CH 8 (2) 51-52 144 \S0 2 OH (4) NITRO COMPOUNDS 293 A substance may be identified as a sulphonic acid or a sulphonic- acid salt by fusing it with sodium hydroxide and treating the product with water and a dilute acid. If the sulphonic-acid group is present, sulphur dioxide is evolved, and a phenol remains in solution which is detected by adding ferric chloride, or bromine water (cf. p. 330). Compounds containing the sulphonic group in the side chains of aromatic compounds may be made by the methods given for forming the alkyl-sulphonic acids (p. 241). Nitro Compounds The action of nitric acid on aromatic hydrocarbons has already been noted. The dilute acid when heated with homologues of benzene usually oxidizes one or more of the side chains to the carboxyl group. Occasionally, under certain conditions, hydro- gen of the alkyl groups is replaced by the nitro group, NO 2 , producing such compounds as CeHs.CH^.NC^; and usually small amounts of compounds are produced which contain the nitro group in place of nucleus hydrogen. With concentrated nitric acid this last reaction becomes the chief one; one, two, or three nitro groups being introduced into the aryl radical. This reaction is called nitration, and the resulting substances are nitro com- pounds: C 6 H 5 .CH 3 + HNO 3 = C6H 4 (CH 3 )NO2 + H 2 O Toluene Nitrotoluene In nitrating the homologues and other derivatives of benzene, the ease of the reaction is, of course, influenced by the character of the groups which are present- and since the nitro group is a strongly acid group, the statements made in regard to sulphona- tion (p. 288), apply in general to nitration. It has proved impos- sible to introduce in this way more than three nitro groups into a compound. In many cases, fuming nitric acid is necessary to effect nitration, and very commonly a mixture of concentrated or 2Q4 INTRODUCTION TO ORGANIC CHEMISTRY fuming nitric acid with sulphuric acid is used, the sulphuric acid uniting with the water formed in the reaction and thus preventing the dilution of the nitric acid. On the other hand, some sub- stances are readily nitrated by dilute acid. Phenol, for instance, can be nitrated by a mixture of concentrated nitric acid with twice its volume of water. The number of nitro groups introduced depends in each case upon the strength of the acid, the tempera- ture, and the nature of the aromatic compound. Nitrobenzene, C6H 5 .NO 2 , is manufactured in large quantities by allowing a mix- ture of concentrated nitric and sulphurjc acids to flow into ben- zene which is continually stirred and cooled. Dinitrobenzene, C6H 4 (NO 2 ) 2 , results if the mixture is not cooled but allowed to heat from the effect of the reaction; while the formation of trinitrobenzene, C6H 3 (NO 2 )3, requires fuming acid and a higher temperature (180). In general, it is advantageous to carry on the nitration at as low a temperature as is effective, espe- cially when the compounds contain groups subject to oxidation. Nitro compounds can also be formed from aromatic amines by oxidation or by the replacement of the amino group by the nitro group through diazo compounds; but these methods are only of theoretical interest, practically all nitro compounds being pre- pared by direct nitration, as the sulphonic acids are by direct action of sulphuric acid. The introduction of the nitro group into side chains cannot be effected, as one might expect, by the reaction between the halogen compound and silver nitrite (cf. p. 142). But the nitration of saturated side chains can be accomplished directly by dilute nitric acid under certain conditions. For example, when ethyl- benzene is heated in a sealed tube with weak nitric acid (sp. grav. 1.076) to io5-io8, a good yield of phenylnitroethane, C 6 H 6 .- CHNO 2 .CH 3 , is obtained. Nitro compounds with the nitro groups in unsaturated side chains may often be made: i. by the action of nitric or nitrous acid or nitrogen tetroxide on the unsatu- rated hydrocarbon. Styrene, for example, CeEU.CH : CH 2 , NITRO COMPOUNDS 2Q5 in ethereal solution reacts with nitrous acid to form phenylnitro- ethylene, C6Hs.CH:CHNO 2 . 2. Similar compounds can also be made synthetically from nitro paraffins and benzaldehyde, , in the presence of zinc chloride: ZnCli C 6 H 6 .CHO + CH 3 NO 2 = C 6 H 5 .CH:CHNO 2 + H 2 O ZnCl. C 6 H 5 .CHO + CH 3 .CH 2 NO 2 = C 6 H 5 .CH:C.NO 2 + H 2 O I CH 3 The compounds with nitro groups in side chains are, however, of very minor interest, while the importance of the nitro com- pounds containing the nitro groups in place of nucleus hydrogen can hardly be over-estimated. Their importance lies chiefly in the fact that these nitro compounds form the first step in the intro- duction of other groups into the cyclic radicals, for the nitro compounds, as such, find only a limited use. In the following, only those compounds which have nitro groups in the ring will be considered. Properties. The mononitro derivatives of the lower aromatic hydrocarbons are liquids or crystalline solids having an odor like that of bitter-almond oil. The liquid compounds are pale yellow, and the solids yellow or colorless. They are heavier than water and insoluble in it. They are volatile with steam and can in most cases be distilled without decomposition. Compounds with two or three nitro groups, on the contrary, in most cases do not distil at ordinary pressure without decomposition, and the decomposition is usually the occasion of a more or less violent explosion. They are, however, stable beyond their melting points, and these are often determined for purposes of identification. Reactions. i. The most important reaction of the nitro com- pounds is the reduction they undergo with active reducing agents, with the conversion of the nitro group into the amino group. In the laboratory the reduction is usually effected by means of tin 296 INTRODUCTION TO ORGANIC CHEMISTRY and hydrochloric acid, while iron filings and hydrochloric acid are commonly employed in technical operations (cf. p. 303). Various other reducing agents may, however, be used: C 6 H 5 .NO 2 + 6H = C 6 H 5 .NH 2 + 2 H 2 O Nitrobenzene Aniline The amines which are products of these reductions form the sec- ond step in the introduction of various groups in place of nucleus hydrogen, the third being the conversion of the amine into a diazo compound (p. 313). 2. By the use of milder reducing agents several intermec[iate reduction products can be produced (p. 321). All of these sub- stances are converted into amines, e.g., aniline, by further reduc- tion, and some of them at least, form transition steps in the active reduction which yields the amines directly, and are also produced by oxidation of the amines. 3. The direct replacement of the nitro group by other groups cannot usually be effected. This is especially true of the mono- nitro compounds. When two nitro groups are present in the ortho or para position to each other, one of them can be exchanged for hydroxyl by boiling with a solution of sodium hydroxide; or for the amino group when heated with an alcoholic solution of ammonia. These reactions do not occur when the groups have the meta positions. Trinitro compounds, however, give similar reac- tions whatever the positions. Thus symmetrical trinitrobenzene (i, 3, 5) is converted slowly at ordinary temperature by sodium methoxide, CH 3 ONa, into dinitro anisol, C 6 H 3 (NO)2(O.CH3). 4. The influence of the presence of the nitro group is seen in many reactions, and we may note here that hydrogen situated in the ring between nitro groups is rendered more active, so that, for instance, symmetrical trinitrobenzene is oxidized by potassium ferricyanide to trinitrophenol, CgHWOHXNC^a. Structure of Nitro Compounds. Two facts indicate that the nitro group is NOg and not the nitrous acid radical ONO. NITRO COMPOUNDS 2Q7 These are: i. That the mononitro compounds cannot be saponi- fied as a nitrous ester would be, and 2. The reduction of the group to an amino group, instead of to hydroxyl, which would be the probable result if the compound had the ester formation. Hence the nitrogen of the nitro group is directly united to the ring car- bon, and the structure is NITRO COMPOUNDS Name Formula Melting point Boiling point Specific gravity Nitrobenzene o-Dinitrobenzene m-Dinitrobenzene p-Dinitrobenzene unsym.-trinitrobenzene sytn-trinitrobenzene o-nitrotoluene C 6 H 6 .NO 2 C 6 H 4 (N0 2 ) 2 (i, 2) C 6 H 4 (N0 2 ) 2 (i, 3) C 6 H 4 (N0 2 ) 2 (i, 4) C 6 H 3 (N0 2 ) 3 (i, 2, 4) C 6 H 3 (N0 3 ) 3 (i, 3, 5) /CH 3 (i) CeH4 \N0 2 (2) 5-7 "7 90 172 57-5 122 -13-8 210. 9I. 319 -. 303 I. 2OO 204 (20) 369 (98) 222. 3 I. 168 (15) m-nitrotoluene /CH,(i) CeH4 \N0 2 (3) 16 230 I .168 (22) p-nitrotoluene /CH 3 (i) CeH4 \N0 2 (4) 54 237. 7 i. 123 (54) Dinitrotoluene /CH 3 (i) [ "\(N0 2 ) 2 (2, 4) 70 .... I ., 32i ( 7 o) Trinitrotoluene (T.N.T.; )CeH2 /CH 3 (i) 82 Nitroorthoxylene 2 9 ^58 1.139(30) Dinitrometaxylene . (2, 4) 82 298 INTRODUCTION TO ORGANIC CHEMISTRY NITRO COMPOUNDS (Continued) KT TO i Melting Boiling Specific Name Formula point point gravity 'CH 3 (i) 'N0 2 (2) Trinitrometaxylene C 8 H ^ ( CH 3 (3) 182 -N0 2 (4) (6) ,CH 3 (i) Nitromesitylene C 6 H 2 <^* ^ 44 255 3 (5) (i) Nitrocymene C 6 H 3 f NO 2 (2) liquid 1.085(15) N CH(CH 3 ) 2 (4) Nitrobenzene, CeHs.NC^, is technically the most important of the nitro compounds of the aromatic hydrocarbons. It was dis- covered by Mitscherlich, in 1834. Its first practical use was as a substitute for oil of bitter almonds in perfumery. While it is still used to scent many commercial substances, this is of quite minor importance as compared with the employment of nitro- benzene for making aniline for the manufacture of coal tar dyes. The Influence of Substituents on Each Other The fact that the presence of a substituent in the benzene ring influences both the readiness with which a second atom or group can be introduced, and the position which it occupies, has been noticed. Sulphonation and nitration proceed more easily with compounds which contain alkyl or hydroxyl groups than with benzene or derivatives in which a nitro or sulphonic group is already present; and not only is the position of the entering group affected by the character of the group attached to the nucleus, but also the reactivity of both groups in the resulting compound. A second nitro or sulphonic group enters chiefly in the meta posi- RULES FOR SUBSTITUTION 2QQ tion to the first, while a second chlorine or bromine atom gives principally a para compound. The following rules are found to be generally applicable: 1. When an alkyl group, a halogen atom, or either of the groups NH2 or OH, is present, a second alkyl group (by Friedel and Craft's synthesis), halogen atom, or the sulphonic or nitro group, enters in the para or ortho position, the chief product being generally the para compound. 2. Compounds containing one of the groups, NC>2, SOsH, CN, CO.OH, or CHO give on a second substitution chiefly meta compounds. These statements may conveniently be put in the form of a table, in which the positions are indicated by the conventional numbers, bracketed numbers meaning that these compounds are produced in relatively small amounts. Element or group Positions of substitutes in position i Alkyl Cl Br I SOsH NO 2 Alkyl Cl Br I OH NH 2 S0 3 H 4(2) .... 3 .... 3(4) 3(2,4) N0 2 4(2) 3 ... 3(2,4) 3(2,4) CO.OH 4 (2) 3 3 3 3 (4) 3 (2, 4) CN 4 3 To the illustrations already given may be added the great readi- ness with which phenol, CeHs-OH, reacts with bromine, giving symmetrical tribromphenol; and with nitric acid, with the produc- tion of ortho and para nitrophenol, ortho-para and diortho-nitro- phenol, and para diorthonitrophenol (p. 337). As regards the activity of the products, the meta compounds, as a class, are more stable toward reagents than the ortho or para 4(2) 4(2) 4(2) 4(2) 4(2) 4(2) 4 4(2) 4 4(2) 4 4 4(2) 4(2) 4(2) 4 (2) 4(2) 4(2) 4(2) 4 4(2) 4 4(2) 4 4(2) 4 *T \ *" f 4(2) 4(2) 300 INTRODUCTION TO ORGANIC CHEMISTRY compounds. Ortho and para bromnitrobenzene, react with ammonia to form the corresponding nitranilines, NH2.CeH4.NO2, while meta bromnitrobenzene, and brombenzene itself, are not affected by ammonia. Many further illustrations of the reciprocal influence of substituents on reactions will be met with in the course of our study. CHAPTER XXII AROMATIC AMINES All aromatic amines contain, of course, one or more aryl (or substituted aryl) radicals. Considering them as substituted ammonias, we may distinguish the following types of simple aro- matic amines: i. Those in which one or more cyclic radicals are substituted for hydrogen in NH 3 , nitrogen being united to nucleus carbon. Of this type are aniline CeHsNH^, triphenylamine (C 6 H 5 ) 8 N, toluidine C 6 H 4 < , etc. X NH 2 2. Those in which the nitrogen of the substituted ammonia is combined with carbon in a side chain, such as CeH5.CH 2 NH 2 , etc. 3. Mixed amines which contain both phenyl and alkyl groups combined directly with nitrogen as in CeH^.NH.CHs; phenyl and phenyl-alkyl groups, such as C6H 5 .CH 2 .NH.C6H 5 ; and, finally, amines containing alkyl and phenyl-alkyl groups such as CeHs-CHij.NH.CHa. These mixed amines are necessarily second- ary and tertiary amines, while all three classes, primary, second- ary, and tertiary may be represented in the first two types. 4. Aromatic amines containing two or more amino groups are ,'CH; also known, and may be of the type of C6H 4 (NH 2 ) 2 , etc., with the amino groups all united to nucleus carbon; or such as CeH , with an amino group in the side chain as well X NH 2 as in the nucleus. 301 302 INTRODUCTION TO ORGANIC CHEMISTRY There is, therefore, rather a bewildering variety of aromatic amines; but we need consider here only the general characteristics of the several types and give special attention to a few individuals which illustrate these types and are of practical importance. In the first place, we may observe that in contrast with the aliphatic amines, the aromatic amines, in which the amino group is united with nucleus carbon, are neutral in reaction instead of strongly alkaline, and do not absorb carbon dioxide. The amines containing one or two phenyl groups form additive salts with acids, but these salts are less stable than the salts of the aliphatic amines, being more or less hydrolyzed in solution so that the reaction of then- solutions is acid; and tertiary amines like triphenylamine have no basic properties at all. The aliphatic amines, on the contrary, form stable salts, and their alkalinity and basicity is greater with the increase in the number of alkyl groups. These differences between the aromatic nucleus amines and the alkyl amines show that the phenyl radical has a negative character as compared with the rather strongly positive alkyl radicals. This is again very markedly in evidence in the aromatic hydroxyl com- pounds the phenols (p. 327) which have distinctly acid proper- ties as compared with the alkyl hydroxides the alcohols; and is also more or less marked in all the aromatic derivatives. Aromatic amines which have the amino group in side chains are very similar to the alkyl amines in their properties, and may be regarded as alkyl amines in which aryl groups have been sub- stituted for hydrogen in the alkyl radical. The presence of the positive amino group in the nucleus increases the reactivity of the hydrogen atoms of the ring, which are now readily replaced by chlorine or bromine and yield easily to sul- phonation and nitration. Primary Amines Preparation. i. Aromatic amines with the amino group united with nucleus carbon aryl amines -cannot usually be made, like AROMATIC AMINES 303 the alkyl amines, by the action of ammonia on the halogen deriva- tives of the aromatic hydrocarbons the halogen in this position having, as we have seen, little reactivity. The reaction becomes possible, however, when the nitro group is also present in the ortho or para position relative to the halogen; and ortho-dinitrobenzene, and ortho and para nitrophenols also give nitro-amido com- pounds when heated with ammonia. Meta compounds do not react. Some phenols also are converted into amines by heating to 3oo-35o with ammonia-zinc chloride. But the method generally employed for the preparation of these amines is by the reduction of the corresponding nitro compounds. The reduction is usually effected by means of tin or iron and hydro- chloric acid, though quite a variety of other reducing agents are sometimes employed. Among these ammonium sulphide in alcoholic solution is especially useful for the reduction of a single nitro group in a compound containing two or three such groups. 2. Aromatic aryl-alkyl amines with the amino group in the side chain are prepared by the methods used for alkyl amines (cf.p. 128). Aniline, CeH 5 .NH 2 , received its name from the Spanish term for indigo, anil, as it was first obtained by the destructive dis- tillation of this substance in 1826. In 1834 it was discovered in coal tar, and shortly before had been made by the reduction of nitrobenzene. It was not till 1843, however, that the identity of these products with that from indigo was established. Its con- stitution is determined by its formation from compounds of known structure and by the products of its reactions. The amount of aniline in coal tar is too small to make this source of any importance. The very large amounts that are used, chiefly in the dye-stuff industry, are obtained from coal tar ben- zene through nitrobenzene. The reduction of the nitrobenzene is effected by means of iron-filings and hydrochloric acid : C6H 5 .N0 2 + 3 Fe + 7HC1 = Nitrobenzene CeHs-NH^HCl + 3Fefcl 2 + 2H 2 O Aniline hydrochloride 304 INTRODUCTION TO ORGANIC CHEMISTRY This reaction is accomplished, however, with the use of a very much smaller amount (about A) of hydrochloric acid than is indi- cated in the above equation. The probable explanation of this fact is that iron filings and water effect the reduction, the small amount of ferrous chloride formed at first acting as a catalyzer. C 6 H 5 .NO 2 + 2Fe + 4H 2 O = C 6 H 5 .NH 2 + 2 Fe(OH) 3 When the reduction is ended, lime is added and the aniline is distilled with steam. Since the aniline is only slightly soluble in water and is a little heavier, the greater part of it separates as an oil and is purified by redistillation, while the "aniline-water" is used in the boiler which furnishes steam for the first distillation. In the laboratory, tin and strong hydrochloric acid are usually employed for the reduction. In this case double salts of tin and aniline are formed, which are decomposed by adding caustic soda before distilling with steam. Common salt added to the distillate reduces the solubility of the aniline, which is then extracted with ether and distilled. Properties. Aniline is an oily liquid of a slight and characteris- tic odor, and is poisonous. When freshly distilled it is colorless, but turns yellowish-brown on exposure to light and air. This change in color is apparently due to the presence of traces of sulphur compounds, which can be removed by heating with ace- tone. Aniline thus treated remains colorless. Its specific gravity is 1.024 (16). It boils at 183.7. I* 1 water it dissolves in the proportion of about one part to 30 of water; and it dissolves water in a slightly larger proportion. Aniline is dried by means of solid potassium hydroxide or carbonate (calcium chloride com- bines with ammonia and amines, and is consequently not suitable for drying these compounds). Aniline is miscible in every pro- portion with alcohol, ether, benzene, etc. It is readily volatile (vith steam. Reactions. i. Aniline, like most amines, unites additively with acids, forming crystalline salts which are mostly soluble in water. AROMATIC AMINES 305 The normal sulphate, (C6H 5 .NH 2 )2.H 2 S04, and the oxalate, (C6H 5 .NH 2 ) 2 .H 2 O 4 C2, however, are only slightly soluble in cold water. The solutions have an acid reaction from hydrolysis ; and the salts with fatty acids are converted by heating into the more stable substituted acyl amides (anilides) : C 6 H 5 NH 2 .HO.OC.CH3 = C 6 H 5 NH.OC.CH 3 + H 2 O-MIC1 Aniline also forms double salts such as (C6H 5 .NH 2 ) 2 ZnCl 2 , (C 6 H 5 .NH 2 .HCl) 2 PtCl4, and (CeHe.NHa.HCl^SnCU. 2. Like ammonia and the alkyl amines, aniline enters into re- action with alkyl halides with the formation of mono- and dialkyl anilines, such as C 6 H 5 .NH.CH 3 and C6H 5 N(CH 3 ) 2 ; and with alkyl iodides the reaction proceeds to the formation of the salt of the quaternary ammonium base, e.g., trimethylphenylammonium iodide, C6H 5 (CH 3 ) 3 NI, which is not decomposed by cold solutions of alkalies, and from which silver hydroxide sets free the strongly alkaline base, C 6 H5(CH 3 ) 3 NOH. 3. Aniline reacts with acid chlorides with the formation of anilides corresponding to the amides: C 6 H 5 .NH 2 + CH 3 .CO.C1 = C 6 H 5 .NHOC.CH 3 + HC1 Aniline Acetanilide 4. When warmed with nitrous acid, solutions of salts of aniline and other primary aryl amines evolve nitrogen with the exchange of the amino group for the hydroxyl group, as in the case of the alkyl amines; but at room temperature or in ice water no nitrogen is set free, but a diazo compound is formed which contains two atoms of nitrogen: C 6 H6.NH 2 .HC1 + HNO 2 = CeHg.NaCl + 2H 2 O Benzenediazonium chloride The diazo compounds are quite unstable, as is indicated by the statements just made in regard to their preparation, and they enter into many important reactions (p. 315). 306 INTRODUCTION TO ORGANIC CHEMISTRY 5. The nucleus hydrogen of aniline is more readily replaced than that of benzene by halogens, and by the sulphonic acid and nitro groups. In an aqueous solution of an aniline salt, chlorine or bromine readily give trichlor or tribromaniline, (i, 2, 4, 6). 6. Aniline like all primary amines gives the carbylamine test (cf. p. 132). 7. Special tests for aniline are: Dilute solutions of aniline or its salts give (a) a violet color with a solution of bleaching powder; (b) a precipitate of tribromaniline with bromine water; (c) a green, blue, or black precipitate when treated with sulphuric acid and a little potassium dichromate. Some Derivatives of Aniline Acetanilide, C 6 H 5 NH.OC.CH 3 , is the most important of a group of compounds which may be regarded as amides in which hydrogen of the amido group is replaced by aromatic radicals in this case by phenyl. Acetanilide (or phenyl-acetamide) is usually prepared by boiling a mixture of glacial acetic acid and aniline for some hours. The aniline acetate first formed loses the elements of water under this treatment, leaving the acetanilide: C 6 H 6 .NH2.HO.OC.CH 3 =C 6 H 5 .NH.OC.CH 3 + H 2 O It may also be made by the other methods used for the forma- tion of amides (p. 137): treatment of aniline with acetyl chloride, acetic anhydride, or acetic esters. Acetanilide melts at 116 and boils at 304. It is much more soluble in hot water than in cold, and crystallizes well from its solution in glistening plates. It is not hydrolyzed by water alone, but when boiled with alkalies or acids is converted into its components, aniline and acetic acid (or acetate) : CeH 5 .NH.OC.CH 3 + KOH = C 6 H 5 .NH 2 + CH 3 CO.OK The hydrogen of the amido group can be replaced by a second acetyl group by the action of acetyl chloride at 170-! 80, giving AROMATIC AMINES 307 diacetanilide, C 6 H 5 .N(OC.CH 3 ) 2 . This melts at 37, is decom- posed on boiling, and is readily hydrolyzed to acetanilide and acetic acid by very dilute alkalies or acids. Acetanilide and the corresponding derivatives of other aromatic amines are often employed in the preparation of aryl amine sub- stitution products, since the presence of the negative acetyl group renders the nucleus hydrogen less reactive and so makes it possible to control the reaction to some extent. Thus, while with aniline, bromine water produces principally tribromaniline, acetanilide yields monobromacetanilide (para) from which monobromaniline can be obtained by hydrolysis. Acetanilide, formerly known as "antifebrine," is used in medi- cine, especially in headache tablets. "Antipyrine" is a derivative of aniline whose formula is / N(CH 3 ).C.CH 3 C 6 H 5 N/ || X CO - CH Sulphanilic Acid, NH 2 .C6H 4 .SO 3 H(i, 4), or para aminoben- zenesulphonic acid, is prepared by heating aniline and concen- trated sulphuric acid to i8o-i9o for four or five hours. Sulph- anilic acid separates from its solution in hot water in crystals which contain two molecules of water and are efflorescent It has no definite melting point, and chars when heated to about 300. Sulphanilic acid, unlike the sulphonic acids of the hydro- carbons, is only slightly soluble in cold water. It dissolves readily, however, in alkaline solutions from the formation of alkali salts. It forms no salts with acids, the basic character of the amino group being neutralized by the negative sulphonic group. It is oxidized by chromic acid into quinone, CeH 4 O2 (i, 4) (p. 3 50) . When fused with caustic potash, instead of yielding amino- phenol, HO.C6H 4 NH 2 , it gives aniline. The diazo compound formed from it by the action of nitrous acid is used in the prepara- tion of certain dyes. 308 INTRODUCTION TO ORGANIC CHEMISTRY The ortho and meta isomers of sulphanilic acid can be made by the reduction of the corresponding nitrosulphonic acids. Nitranilines, NCfe.CeH^NEk. It is difficult to control the reac- tion of concentrated nitric acid on aniline so as to obtain a mono- nitraniline, but nitration of acetanilide gives a mixture of para and ortho nitroacetanilide from which the para and ortho nitranil- ines are obtained by hydrolysis. The nitro group may be directed to the ortho position by first sulphonating acetanilide. This gives the para sulphonic acid, and when this is nitrated the nitro group enters the position which is ortho to the acetylamino group ; and then by splitting off the sulphonic and acetyl groups, ortho- nitraniline is obtained: NH.OC.CHa NH.OC.CH 3 NH.OC.CH 3 NH 2 jN0 2 _ SO 3 H SO 3 H Meta nitraniline is readily prepared by partial reduction of meta dinitrobenzene (p. 294) by means of ammonium sulphide, or stannous chloride and hydrochloric acid in alcoholic solution: NO 2 .C6H 4 .NO 2 m-Dinitrobenzene m-Nitraniline The nitranilines are yellow solids which crystallize well and are very slightly soluble in water, but dissolve readily in alcohol. They are weak bases, the presence of the nitro group not quite neutralizing the basicity of the amino group. The basic character varies with the relative positions of the nitro and amino groups: being least in the ortho compound and greatest in the meta nitraniline. Their melting points are 71.5, 114, and 147 for the ortho, meta, and para, respectively. Para nitraniline, and to a less extent, meta nitraniline, are employed in the manufacture of azo-dyes. Tetranitro-aniline is one of the most powerful explosives known, and another similar compound, tetranitro-methylaniline, AROMATIC AMINES 309 called "tetryl," is used for detonators in place of mercuric ful- minate. Alkyl Derivatives of Aniline. By the replacement of one or both hydrogen atoms of the amino group in aniline by alkyl groups, mixed secondary and tertiary amines are produced. These may be prepared by the direct action of alkyl halides on aniline; but in the technical manufacture they are made by heating aniline with hydrochloric or sulphuric acid and the appropriate alcohol to about 200: C 6 H5.NH 2 .HC1 + CH 3 OH = CeHs.NH.CHa.HCl + H 2 O C 6 H 5 .NH.CH 3 .HC1 + CH 3 OH = C6H 6 .N(CH 3 ) 2 .HC1 + H 2 O These alkyl derivatives are oily liquids which smell like aniline. They are neutral in reaction, but are stronger bases than aniline, as one would expect from the presence of the positive alkyl groups, and are very similar to the secondary and tertiary alkyl amines. Many of these tertiary amines differ, however, from the tertiary aliphatic amines, in reacting very readily with nitrous acid forming paranitroso derivatives which are of importance as intermediate compounds in the preparation of certain dyes: N(CH 3 ) 2 C 6 H 5 .N(CH 3 ) 2 + HONO = C 6 H 4 %O +H 2 O N Dimethyl-aniline p-Nitroso-dimethyl-aniline Another peculiar reaction of these amines is that which occurs when their hydrochloric acid salts are heated to about 300. Under these conditions the alkyl groups are transferred from the amino group to the nucleus, with the formation of homologues of aniline, aniline and alkyl chloride being perhaps intermediate products: C 6 H5.NH(C2H 5 ).HC1 -C 6 H 5 .NH 2 + C 2 H 5 C1 Ethyl-aniline hydrochloride _> C 2 H5.C 6 H 4 .NH 2 .HC1 Aminoethylbenzene chloride This is an important technical method for preparing the homo- logues of aniline. 310 INTRODUCTION TO ORGANIC CHEMISTRY The quaternary ammonium salts undergo a like transformation: C6H 5 .N(CH 3 ) 3 I -> CH 3 .C6H4.N(CH 3 )2.HI -> Trimethyl-phenylam- monium iodide (CH 3 ) 2 .C6H3NH.(CH 3 )HI - (CH 3 ) 3 .C6H 2 .NH 2 .HI Tri-methyl-animoben- zene iodide 1:2:4:6 By this reaction it has proved possible to prepare a homologue of aniline in which all five of the nucleus hydrogen atoms are replaced by methyl, (CH 3 ) 5 C6NH 2 . The most important of these alkyl derivatives is dimethylani- line, CeH5.N(CH 3 ) 2 , which is employed in the manufacture of a number of dyes. Monomethyl, monoethyl, and diethyl anilines are also prepared in the industry, but their use is far less than that of the dimethylaniline. Novocaine, a local anaesthetic, is the hydrochloride of diethyl- ammo-ethyl-p-aminobenzoate : NH 2 .C 6 H4.CO.OC2H4.N(C 2 H5) 2 HC1 Homologues of Aniline. These are usually prepared from the corresponding nitro compounds when the hydrocarbon is obtain- able for nitration. In many instances they are conveniently made from the phenols, whose hydroxyl group is replaced by the amino group by heating with ammonia in the presence of zinc chloride, etc: ZnCh (CH 8 ) (C 3 H 7 )C6H 3 OH + NH 3 = (CH 3 )(C 3 H 7 )C6H 3 .NH 2 + H 2 O Thymol Thymylamine A third method is by heating the halogen salts of the alkyl- anilines (p. 309). The homologues of aniline have the same general characteristics as that substance and require no further description here. Impor- tant from a practical standpoint on account of their employment in the color industry are: the three toluidines, CH 3 .CeH4NH 2 , ortho and para toluidines being used almost as much as aniline itself. The xylidines, (CH 3 ) 2 .C6H 3 .NH 2 , and pseudocumidine, (CH 3 ) 3 .CeH 2 .NH 2 (1,2,4,5), are al so employed. AROMATIC AMINES 311 Secondary and Tertiary Aromatic Amines. Diphenylamine, (C6H 5 ) 2 NH, is made on a large scale for the color industry by heating aniline with aniline hydrochloride to about 200; C6H 5 .NH 2 + C 6 H 5 NH 2 .HC1 = (CH 5 )>NH + NH 4 C1 It can also be made by heating phenol with aniline in the presence of zinc chloride: ZnCl 2 CeHg.NH, + CeKU.OH = (CeHs^NH + H 2 O The tertiary triphenylamine (CeH^sN, cannot be made by these methods. It is formed, but in small amount, when the sodium compound of diphenylamine is heated with brombenzene: N.Na + CeHsBr = (C 6 H 5 ) 3 N + NaBr The basic character of aniline is much weakened by the intro- duction of the negative phenyl group. Diphenylamine forms salts with strong acids, but they are at once decomposed by water; while in triphenylamine the basic properties have wholly dis- appeared. A solution of diphenylamine in concentrated sulphuric acid serves as a delicate test for nitric acid, giving a blue color with traces of this acid. Benzylamines Aromatic amines which have the amino group in a side chain have received the name of benzylamines from the simplest mem- ber of this type, C6H 5 .CH 2 .NH 2 (CeHs.CH, = benzyl). They can be made by the methods for forming the aliphatic amines, and show the general behavior of these amines, modified, of course, by the presence of the phenyl group. Benzylamine, and the other primary amines of this class, are isomeric with the homologues of aniline. They are of comparatively little importance. Benzylamine, CeH5.CH 2 NH 2 , isomeric with toluidine, is an alkaline liquid which absorbs carbon dioxide from the air. It boils at 185, and is miscible with water in every proportion. 3 I2 INTRODUCTION TO ORGANIC CHEMISTRY Dibenzylamine, (C6H 5 .CH 2 )2NH, is a liquid which boils above 300 but decomposes when slowly distilled. It is insoluble in water and does not absorb carbon dioxide. Tribenzylamine, (CeHs.CH^sN, crystallizes from hot alcohol, melts at 91, and combines with methyl iodide to tribenzyl- methyl-ammonium iodide. Derivatives of these amines, such as benzyl aniline, CeH 6 . CH2 . - NH.CeHs, and dibenzylaniline, (Cel^.CHa^N.CeHB, can also be obtained. SOME AMINO DERIVATIVES OF BENZENE Aniline o-Toluidine m-Toluidine P-Toluidine p-E thylphenylamine Benzylamine Methylaniline Dimethylaniline o-Phenylene diamine m-Phenylene diamine p-Phenylene diamine Toluylene diamine Diphenylamine Triphenylamine Acetanilid Diacetanilide C 6 H 6 .NH 2 CH 3 .C 6 H4.NH 2 (i, 2) CH 3 .C 6 H 4 .NH 2 (i, 3) CH 3 .C 6 H4.NH 2 (i, 4) C 2 H 6 .C 6 H4.NH 2 (i, 4) C 6 H 5 .CH 2 .NH 2 C 6 H 5 .NH(CH 3 ) C 6 H 5 .N(CH 3 ) 2 C 6 H 4 (NH 2 ) 2 (i, 2) C 6 H 4 (NH 2 ) 2 (i, 3) C 6 H 4 (NH 2 ) 2 (i, 4) CH 3 .C 6 H 3 (NH 2 ) 2 (1,3,4) (C 6 H 6 ) 2 NH (C 6 H 6 ) 3 N C 6 H 5 .NH.CO.CH 3 C 6 H 6 .N(CO.CH 3 )2 Melting Boiling point point -6.2 183-184 liquid 199.7 liquid 203.3 45 200.4 -5 214 185 o IQ7 , r 2-5 * vo * o 193 1 02- J 03 257 63 283 140 267 1 88.5 265 54 302 127 116 304 37 145 (15 mm.) CHAPTER XXIII DIAZO COMPOUNDS Attention has already been called to the existence of a class of compounds which are formed by the action of nitrous acid on the salts of the primary aromatic amines (cf. p. 305). The immediate products of this reaction are unstable, very reactive substances whose composition is of the type, CeHU.^Cl or CeHs.^NOa. They were called diazo compounds from the fact that they con- tain two united atoms of nitrogen (French, azote). These com- pounds were discovered in 1858 by Peter Griess, and the many useful reactions which they give quickly established their im- portance in synthetic and technical chemistry. Preparation. Although diazo compounds can be made in other ways, the method which is of the first importance is by means of nitrous acid acting on the salt of the amine: C 6 H 5 .NH 2 .HC1 + HONO = CeH^Cl + 2 H 2 O Aniline hydrochloride Phenyldiazonium chloride The reaction is carried out by adding sodium nitrite or amyl nitrite to an acid solution of the amine; or less often by leading into a solution of the amine salt oxides of nitrogen evolved by the action of nitric acid on arsenic trioxide or starch. The operation is conducted in solutions cooled by ice on account of the instability of the diazo compounds at higher temperatures. The diazo compounds made in this way are usually not isolated, but im- mediately employed in solution for various reactions. The solid compounds can, however, be prepared by taking advantage of their small solubility in alcohol and their insolubility in ether. Properties. Since the isolation of these substances is seldom 313 314 INTRODUCTION TO ORGANIC CHEMISTRY necessary, for the purposes to which they are applied, compara- tively little is known of their individual properties, in spite of the fact that almost every known primary aromatic amine has been "diazotized." They are colorless, crystalline solids which are easily soluble in water. In the dry solid state they are very explo- sive when heated, and in some cases when struck. Diazo- benzenenitrate, in particular, is more violently explosive than nitrogen iodide or mercury fulminate. They are well characterized salts, and they form double salts, such as (CeHe^^PtCle, which are analogous to those of the alkalies. The chlorides and nitrates are not hydrolyzed in solu- tion, as is shown by their neutral reaction, and they are ionized to the same high degree as potassium chloride and nitrate. The carbonates, which are formed in solution by digesting diazo- nium halides with silver carbonate, are, like potassium carbonate, soluble, and have a strong alkaline reaction. On treatment of a solution of the chlorine compound with silver oxide, silver chloride is precipitated and the solution becomes strongly alkaline from the formation of the diazonium hydroxide. Structure. 'The facts that have just been stated show that the solutions of these compounds contain a highly positive ion, CeH 5 N2, resembling in character the potassium or ammonium ion, and in which one nitrogen atom probably has the valence of five, as in ammonium. This ion or radical is, by analogy, called diazonium and the structure of the diazonium salts is represented by the formula, Ar.N\ (in which Ar stands for the aryl X X radical). The strong base which is produced by the action of ^ N silver oxide (hydroxide) on a diazonium salt is Ar.N v \OH analogous to ammonium hydroxide. This structure of the diazo- nium compounds accords with the simplest explanation of the reaction by which they are formed: DIAZO COMPOUNDS 315 Ar.N/ ' 3 + H O-- N = O = Ar.N/ + 2H 2 O \x NX Amine salt Diazonium salt The nitrogen atom in the amine salt has the valence of five, that in nitrous acid is a triad, and the formation of the diazonium salt is the result of simple replacement of three hydrogen atoms by triad nitrogen. Reactions. The diazo group can be replaced by: 1. Hydroxyl. This usually takes place on warming the aqueous solution of a diazonium salt, or allowing it to stand at ordinary temperature: C6H 5 .N 2 C1 + H 2 O = CeHs.OH + N 2 + HC1 If a diazonium nitrate is used, the resulting phenol is liable to be nitrated by the nitric acid liberated in the reaction. 2. Alkoxyl. In many cases an alkoxyl group may be substi- tuted by boiling the dry diazonium salt with absolute alcohol: (CH 3 )3C6H 2 .N 2 .SO 4 H + C 2 H 5 OH = (CH 3 ) 3 C 6 H 2 .OC 2 H5 + N 2 +H 2 SO 4 The reaction with alcohol in other cases results in the substitution of: 3. Hydrogen. In this reaction the alcohol is oxidized to alde- hyde: C6H 5 .N 2 C1 + C 2 H 6 OH = C 6 H 6 + N 2 + CH 3 .CHO + HC1 Which of these two reactions with alcohol occurs, depends on the nature of the diazonium compound and of the alcohol, as well as on the conditions of the reaction. The hydrogen replacement is favored by the presence of negative groups in the aryl ring, espe- cially if they are in the ortho position. Hydrogen can also be substituted for the diazo group by treatment of the diazonium salt with an alkaline stannous solution; or indirectly, by formation 316 INTRODUCTION TO ORGANIC CHEMISTRY of diazonium iodide and reduction of this by distillation from zinc dust; or through the hydrazine (p. 318). 4. Halogens can be introduced in place of the diazo group in several ways: (a) By heating with the halogen acids, (b) By distilling the platinum double salt with sodium carbonate, (c) By treating the solution of the corresponding diazonium halide with finely divided copper, which usually decomposes it in the cold (Gattermann's reaction), (d) Most conveniently by heating the diazonium chloride or bromide with cuprous chloride or bro- mide (Sandmeyer's reaction), (e) Iodine is introduced most simply by pouring a strongly acid solution of diazonium sul- phate into a solution of potassium iodide. 5. Cyanogen is substituted by means of Sandmeyer's reaction, using a hot solution of potassium cuprous cyanide. Since the resulting cyanide (nitrile) is readily hydrolyzed to the correspond- ing acid, this reaction serves as a useful method for introducing the carboxyl group into aromatic compounds. 6. Aromatic hydrocarbon groups, such as toluyl, can be intro- duced by warming the dry diazonium salt with an excess of the corresponding hydrocarbon the reaction being aided, if neces- sary, by the presence of aluminium chloride: C 6 H 5 N 2 C1 + CeHs.CHs = CeHs.CeH^CHg + N 2 + HC1 7. Nitro Group. This replacement is seldom made, but is occasionally useful, as in making /3-nitronaphthalene which can- not be obtained by direct nitration, while the corresponding amine is easily prepared. The nitro group is introduced t by treating the diazonium solution with an equivalent amount of sodium nitrite and then decomposing the diazonium nitrite with cuprous oxide. Other replacements can be made, but these which have been described are the most important ones. Reactions in which the diazo group is not replaced are: 8. The formation of diazoamino and aminoazo compounds. DIAZO COMPOUNDS 317 By the action of a diazonium salt on amines (aromatic or aliphatic) the first product is a diazoamino compound: C6H 5 N 2 C1 + C 6 H 5 .NH 2 = CeHs.Na.NH.CeHs + HC1 Diazoaminobenzene These compounds are very weak bases. They are converted into diazonium chlorides or bromides and the corresponding amine salts by the action of concentrated hydrochloric acid, or by hydrobromic acid in ethereal solution : NO 2 .C6H4.N 2 .NH.C6H 4 .NO 2 +HC1 = Diazoaminonitrobenzene N0 2 .C6H 4 .N 2 C1 + NO 2 .C 6 H 4 .NH 2 .HC1 Nitrobenzene diazonium Nitraniline hydrochloride chloride The most remarkable property of the diazoamino compounds is that of molecular rearrangement which occurs in their solu- tions in the free amines when a little of the amine salt is also present, and under some other conditions. If the para position in the amine group is unsubstituted, a para aminoazo compound is formed: NH.N = N N = N NH 2 Diazoaminobenzene p-Aminoazobenzene The aminoazo compounds are of great importance in the dye- stuff industry. 9. Diazonium salts react with phenols in alkaline solutions to form para hydroxyazo compounds: C6H 5 .N 2 C1 + CeHsOH = CeH^.CeKU.OH + HC1 Hydroxyazobenzene A great variety of dyes are made by similar reactions. 10. By partial reduction of diazonium salts hydrazines are 318 INTRODUCTION TO ORGANIC CHEMISTRY produced, which may be regarded as hydrazine, NH 2 .NH 2 , in which a hydrogen atom is replaced by an aryl group. Phenyl- hydrazine hydrochloride, CeH5.NH.NH2.HCl, for instance, can be made by treating benzenediazonium chloride with the proper amount of stannous chloride and hydrochloric acid: C6H 5 .N 2 C1 + 4H = C 6 H 5 .NH.NH 2 .HC1 The hydrazines are pronounced mono-acid bases. They are set free from their salts by sodium hydroxide in the form of oils or solids which are sparingly soluble in water and nearly insoluble in strong alkalies; but they dissolve readily in alcohol and ether. They are very sensitive to oxidizing influences, and hence are strong reducing agents, even dilute solutions reducing Fehling's solution in the cold. The first product of the oxidation of primary hydrazines is the corresponding diazo compound. Treatment with copper sulphate or ferric chloride under certain conditions results in the replacement of the hydrazine group by hydrogen, and this reaction serves as a means for converting amines into the corresponding hydrocarbons, and also for the quantitative deter- mination of the hydrazine by measurement of the nitrogen which is evolved: C6H 5 .NH.NH 2 + 2 CuSO 4 + H 2 O = CeH 6 + Cu 2 O + N 2 + 2H 2 SO 4 Phenylhydrazine is a poisonous oil. It is made commercially for the preparation of "antipyrine" and certain dyes. The hydrazines react with compounds containing the carbonyl group, forming with aldehydes and ketones, hydrazones, whose service in the characterization of carbonyl compounds espe- cially the sugars has already been noticed (p. 208). Further Discussion of the Structure of Diazo Compounds. We have seen that diazonium hydroxide is a strong base whose constitution is like that of ammonium hydroxide. Its solutions, nevertheless, react with potassium hydroxide forming a potassium diazoate by replacement of the hydroxyl hydrogen by potassium. DIAZO COMPOUNDS 319 In this relation, therefore, it behaves as an acid. Now while we know several metal hydroxides which play the double part of base and acid, such as the hydroxides of zinc, aluminium, and tin their compounds are weak bases and very weak acids, and the alkali salts they form are usually very unstable. But here we have a very strong base which also forms a distinct alkali salt. The explanation is found in a probable rearrangement of the diazo group, so that in acting as a weak acid toward potas- sium hydroxide its structure becomes Ar.N:N OH, isomeric with the base, Ar.N^ . The hydroxyl group has shifted, and X)H the valence of the pentad nitrogen atom has dropped to three, with the change from strong base to weak acid. Potassium benzenediazoate, CeH 5 N:NOK, when heated with strong potassium hydroxide is changed to a more stable iso-form which is considered to be a stereoisomer of the first. The arrange- ments of the groups in these two salts may be represented by pro- jection formulas which are similar to those for maleic and fumaric acids (p. 186), the "anti" arrangement being the stable one, C 6 H 5 .N C 6 H 5 .N II II KO.N N.OK Normal or syn-diazoate Iso- or anti-diazoate The only hydroxide which can be isolated is the anti-diazo it hydroxide, which is obtained in the form of unstable crystals by nprecipitating an anti-diazoate with acetic acid at a low tempera- ture. On dissolving in water it changes into another isomeric iform, nitrosamine, C 6 H 5 .NH N=O This theory as to the structure of the diazo compounds explains pie reactions which result in the replacement of the diazo group as 32O INTRODUCTION TO ORGANIC CHEMISTRY follows: The diazonium salts first form addition products with the reagent employed, and then these break down into syn-diazo compounds, which in turn decompose with loss of nitrogen. In the replacement by hydroxyl, for instance, the steps would be: Ar Ar OH Ar OH | OH | | -II Ar.OH N = N + | -+N=N -> N = N - + | H | | N = N Cl Cl H + C1H In the case of the reaction with alcohol, which sometimes sub- stitutes alkoxyl and sometimes hydrogen, two different addition Ar Ar O.C 2 H 5 Ar O.C 2 H 5 ArO.C 2 H 6 I O.C 2 H 6 || |.| + (i)N = N+| ->N = N ->N = N ->N = N I H | | + Cl Cl H HC1 products can be formed, and the formation of one or the other determines the final product. Ar Ar H Ar H I H | | || ArH ( 2 )N s N + | -* N = NH - N = N + O.C 2 H 5 || + N^N. Cl Cl O.C 2 H 5 C1H + CH 3 CHO The other reactions may be explained in a similar way. l 1 For a good exposition of Hantzsch's theory of the structure of diazo com- pounds, see Sidgwick's "Organic Chemistry of Nitrogen." CHAPTER XXIV AZO AND OTHER NITROGEN COMPOUNDS DYES In discussing the reactions of the nitro compounds, we have noticed that while the amines anilines are the final products of the reduction of these substances, the reduction can be controlled by the use of certain mild reducing agents, so that intermediate compounds are obtained. These are illustrated by the following, which are products of different reductions of nitrobenzene: Phenylhydroxylamine, C 6 H 5 .NH.OH Azoxybenzene, C 6 H 5 .N - - N.C 6 H 5 Azobenzene, Hydrazobenzene, All of these substances are converted into the corresponding amines e.g., aniline by strong reducing agents, and they usually do not appear at all when acid reducing agents act on the nitro compounds. Phenylhydroxylamine is formed when nitrobenzene is reduced by a neutral reducing agent, such as aluminium amalgam or zinc dust and hot water. It forms white crystals which melt at 81. It reduces an ammoniacal solution of silver nitrate and Fehling's solution in the cold, and in aqueous solution is quickly oxidized by the air into azoxybenzene. By chromic acid it is oxidized to nitrosobenzene, CeHs.NO, which is readily reduced to aniline. Phenylhydroxyl- amine acts toward acids as a base, but when warmed with inor- 21 321 322 INTRODUCTION TO ORGANIC CHEMISTRY ganic acids suffers a transformation by rearrangement, into the isomeric p-aminophenol, NEk.CeH^OH. Azoxy compounds are formed by reduction of the nitro com- pounds with weak alkaline reducing agents, such as an alcoholic solution of sodium hydroxide. Azoxybenzene, CeHs.N - N.C 6 H 6 \0/ is a light yellow crystalline substance, which melts at 36. Azo compounds can be prepared from the nitro compounds by the use of somewhat stronger alkaline agents sodium amal- gam, alcoholic solutions of an alkali with zinc dust, or stannous chloride with an excess of sodium hydroxide. The azo compounds can also be prepared by further reduction of the azoxy compounds by the agents just mentioned, or, very conveniently, by their distillation from iron filings; or by oxidation of the primary aromatic amines (by alkaline permanganate or hydrogen peroxide) : C 6 H 6 NH 2 + H 2 N.C 6 H 5 + 2O The azo compounds are strongly colored substances. They are insoluble in water, acids, and alkalies, but dissolve in ben- zene, alcohol and ether. They are very stable, and in this re- spect form a striking contrast to the diazo compounds, which also contain two united nitrogen atoms. By reducing agents, however, the azo compounds are readily changed, being con- verted, according to the conditions, into hydrazo compounds or into the amines. Azobenzene forms orange red crystals, melts at 68 and boils at 295. While the azo hydrocarbons are not them- selves dyes, a large number of the most important dyes are derivatives of these compounds and are known as the azo dyes (P- 325). Hydrazo compounds, such as hydrazobenzene, CeH 5 .NH.NH.- CeHs, are formed in the last step before the amine in the reduc- tion of nitro compounds. They are formed by the reduction AZO AND OTHER NITROGEN COMPOUNDS 323 of nitro, azoxy, or azo compounds by an alcoholic solution of ammonium sulphide, or other alkaline reducing agents, and also by electrolytic reduction of the nitro compounds in the presence of an alkali. The hydrazo compounds are colorless substances, which are neutral in character. In the air they suffer a partial oxidation, especially when moist, into the strongly colored azo compounds, and this change occurs readily with other mild oxidizing agents. When strongly heated they are converted into a mixture of azo compounds and amines: 2C 6 H 5 .NH.NH.C6H 5 = C6H5.N:N.C 6 H5+ 2C 6 H 5 NH 2 . Strong acids cause a molecular rearrangement, hydrazobenzene being transformed into benzidine with some of the isomeric diphenyline, and X_X Hydrazobenzene Benzidine NH 2 Diphenyline Benzidine, p-diaminodiphenyl, crystallizes in colorless plates which melt at 122. It is a diacid base, and is the starting point for the manufacture of a large group of dyes of the Congo series. Dyes The azo dyes exceed in number those of any other class, and are perhaps the most important of the manufactured dyes. The first commercial dye made from coal tar. products was prepared by W. H. Perkin in 1857 by the oxidation of an impure aniline sulphate with chromic acid. The manufacture of this dye, " mauve," and, soon after, of a number of others from aniline and its homologues, led to their designation as "aniline dyes," a term 324 INTRODUCTION TO ORGANIC CHEMISTRY which is now often used for all of the dyes which are made from the aromatic substances distilled from coal tar. Many of these dyes, however, are in no way derived from, or related to, aniline, so that the general name of "coal tar dyes" is a more appropriate one. A dye must be soluble in water, or readily brought into a soluble form, and have the property of adhering to the fiber either directly, or after the fiber has been treated with certain agents called "mordants." Dyes which color the fiber permanently without a mordant are called "direct" or "substantive" dyes, while those which require a mordant are "mordant" or "adjective" dyes. Many dyes are either substantive or adjective according to the character of the fiber. Substantive dyes for wool or silk are more common than for cotton and linen. Many different substances serve as mordants; those most used being, for basic dyes, tannic acid and compounds of it with antimony; and for acid dyes, acetates of aluminium, chromium, or iron, from which the hydroxides of the metals are separated on the cloth by pass- ing through a weak basic bath or steaming. The cloth prepared by treatment with the mordant is dyed by the formation of in- soluble compounds of the dye with the hydroxides. The mordant frequently modifies the color produced by the dye. In some cases, a fabric is dyed by developing the dye on the fibers by the use of appropriate reagents in the dye-bath. The results are called "ingrain" colors and are remarkably "fast," i.e., resistant to washing and acids. There are certain groups which are almost always present in colored organic compounds. The most important of these "chromophore" groups are: The nitro group, NO 2 , the azo group, N = N , and the quinoid group (p. 352): /c - c x = c c = \c-c/ AZO AND OTHER NITROGEN COMPOUNDS 325 The colors of the compounds containing these groups are often much modified by the further introduction of atoms or groups which of themselves produce no color; such as phenyl, alkyl groups or bromine. With the increase in molecular weight which is brought about in this way there is in general a deepen- ing of the shade, or a change in color, usually in the order yellow, orange, red, violet, blue, black. But the presence of a chromophore group does not of itself make the compound a dye. There must be also a basic or acid group which will enable it to combine with the fiber or mordant. Such groups are called "auxochrome" groups, and the most im- portant of them are the amino and hydroxyl (phenol) groups. Thus nitrobenzene, which is pale yellow, is not a dye, but p-nitraniline, NO 2 .C 6 H 4 .NH 2 , and p-nitrophenol, NO-j.CgHs.OH, are dyes; and azobenzene, though deeply colored, is incapable of dyeing cloth, while aminoazobenzene and derivatives of it form a large number of well-known dyes. The acid groups - CO.OH and - S0 3 H do not have the power of changing a colored compound into a dye, but the sulphonic group is often introduced to give an insoluble dye the solubility necessary for use in dyeing. Azo dyes are aminoazo or oxyazo compounds and are made by treating diazonium salts with aromatic amines or phenols: C 6 H 5 .N/ + C 6 H 4 (NH 2 ) 2 = CeHs.NH.OH -> HO.CeKU.NH-, The aminophenols are basic through the presence of the amino group and form stable salts with acids; and the acidity of tfre hydroxyl group is so weakened that although they dissolve in caustic alkalies, they do not form definite alkali salts. The aminophenols are mostly quite soluble in water, and their solutions oxidize in the air and consequently are reducing agents. A number of them are employed as photographic developers: "Rodinal" is the hydrochloric acid salt of p-aminophenol; "Amidol" a salt of o-p-diaminophenol; "Reducin," a salt of di- PHENOLS AROMATIC ALCOHOLS ETHERS 339 ortho-para triaminophenol; and "Metol," the sulphate of methyl- aminophenol, C 6 H 4 (OH)NH(CH 3 ). Salvarsan, or 606, recently introduced into medicine as a speci- fic for syphilis, is the dihydrochloride of a derivative of amino- phenol containing arsenic, As - C 6 H 3 (NH 2 )OH I As - C 6 H 3 (NH 2 )OH Esters of Phenols. Of these only certain phenylsulphuric acids need be mentioned, which occur as sodium salts in urine. Bakelite. By a "condensation" of phenols and formaldehyde under certain conditions, a hard, infusible product is obtained, which under the name of " bakelite " is finding many applications. It resembles amber in appearance, burns with difficulty, is insoluble in all solvents and withstands almost all chemical reagents. If made from phenol its formula is represented by C43H3 8 O7, and it has received the chemical name of oxybenzylmethylene- glycolanhydride. In the form of a transition product it is softened by heat and can be molded. It is mostly used com- pounded with other substances such as wood pulp, for the manufacture of a great variety of articles for which celluloid, hard rubber, and amber have been employed, for insulating purposes, etc. Aromatic Alcohols The aromatic compounds which contain hydroxyl in a side chain can be made by the synthetic methods employed for the preparation of the aliphatic alcohols. When the corresponding aldehydes are available, as in some cases, the primary alcohols are conveniently prepared from them by the usual methods of reduction, or by shaking the aldehyde with an aqueous solution of an alkali. Aliphatic aldehydes (except formaldehyde) are 340 INTRODUCTION TO ORGANIC CHEMISTRY converted into resins by alkalies, but aromatic aldehydes undergo a reaction of a different nature in which one half of the aldehyde is reduced to alcohol and the other half oxidized to an acid (salt) (cf. p. 84): KOH = C6H 6 .CH 2 OH + C 6 H 5 .CO.OK Benzaldehyde Benzyl alcohol Potassium benzoate Alcohols in which the group CH 2 OH is directly united to ring carbon can also be obtained by reduction of the correspond- ing acid amides : CeH6.CO.NH2 + 4H = C6H 6 .CH 2 OH + NH 3 The aromatic alcohols completely resemble the aliphatic alco- hols, and differ from the phenols in the greater readiness with which they form esters, and are oxidized to aldehydes, acids or ketones, as well as by the fact that they do not form stable salts with bases. Benzyl Alcohol, C 6 H 5 .CH 2 OH (phenylcarbinol), occurs as benzoic and cinnamic esters in the balsams of Peru and Tolu, and in liquid storax. It is a liquid of faint aromatic odor, boiling at 204. On oxidation it gives benzaldehyde and benzoic acid and it can be reduced to toluene. Benzyl alcohol may be considered as methyl alcohol in which one hydrogen atom of the CH 3 group is replaced by phenyl. If two of these atoms are thus replaced the compound is diphenylcarbinol (or benzhydrol) (CeHs^CHOH, a secondary alcohol. This alcohol may be made, like the secondary alcohols of the aliphatic series, by reduction of the corresponding ketone, benzophenone or diphenyl- ketone C^.CO.CeHs. It is a solid, melting at 68 and boiling at 298. Triphenylcarbinol, (CeHs^COH, is a tertiary alcohol, which can be obtained by the oxidation of triphenylmethane, (C6H 5 )3CH, a reaction peculiar to aromatic compounds. It is a solid, melting at 159. Cinnamyl Alcohol, C 6 H 5 .CH:CH.CH 2 OH, (7-phenyl-allyl alco- hol), occurs in storax as the ester of cinnamic acid, and serves as an illustration of an unsaturated aromatic alcohol. It melts at PHENOLS AROMATIC ALCOHOLS ETHERS 341 33, boils at 254, and has the odor of hyacinths. It may be reduced to phenylpropyl alcohol, C6H5.CH2.CH 2 .CH 2 OH, and when oxidized gives cinnamic aldehyde, CeHs.CHiCH.CHO, cin- namic acid, CeHs.CHrCH.CO.OH, or benzoic acid, CeHs.CO.- OH according to the oxidizing agent employed. Phenol-Alcohols. Certain compounds which are hydroxy aro- matic alcohols, or phenol-alcohols, since they contain hydroxyl both in the ring and in a side chain, occur as glucosides in nature. The simplest of these is o-hydroxybenzylalcohol, or salicyl alcohol, HO.CeH^.CH^OH, whose glucoside is salicin which is found in the bark of the willow. The alcohol can be obtained by splitting off the sugar of the glucoside with mineral acids or emulsin. Salicyl alcohol melts at 86, and is quite soluble in water. It gives a blue color with ferric chloride, and it shows both phenol and alcohol reactions. Aromatic compounds containing sulphur in place of oxygen can be prepared, but these thiophenols, aromatic mercaptans, thioethers, etc., present no very important points of interest. Aromatic Ethers Diphenyl Ether, C 6 H5.O.C 6 H5, is the simplest ether contain- ing two aryl groups. It can be made by heating phenol with anhydrous zinc chloride, or by the dry distillation of aluminium phenolate, A1(O.C 6 H 6 )3. It has a geranium-like odor, and melts at 28 and boils at 252. Anisol, CeHs.OCHs, phenyl-methyl ether, is produced by dis- tilling anisic acid, CO.OH.C 6 H 4 .OCH 3 (which is obtained by oxidation of anethol, the chief constituent of anise oil) with lime, or by heating guaiacol with zinc dust. . Anisol, and other ethers of this type, can be made by the action of alkali phenolates on alkyl halides: C 6 H 6 .ONa + CH 3 I = C 6 H 5 .OCH 3 + Nal Their formation from aryl halides and sodium alkoxides is also possible, but more difficult, because of the smaller reactivity of the halogen atom when united to a cyclic radical. 34 2 INTRODUCTION TO ORGANIC CHEMISTRY Guaiacol,C 6 H 4 (OH)(OCH 3 )(i,2), was first obtained from gum guaiacum. It is among the products of wood tar, and can be made from catechol (p. 333) of which it is the methyl ether. Eugenol, or allyl-guaiacol, C 6 H3(OH)(OCH 3 )(CH 2 .CH:CH 2 ) (i, 2, 4), occurs in oil of cloves which is obtained by distilling cloves with steam, and in other essential oils. In oil of cloves it is associated with a terpene of the formula, Ci5H 24 , and it is separated from this as an alkali salt by its solubility in an alkaline solution. It has a strong odor of cloves, and unites the properties of a phenol, an ether and an unsaturated compound. It is a colorless oil which boils at 247, and is used for perfumery and for making vanillin (p. 347). Safrol, the chief constituent of sassafras oil, has the constitution, O CH 2 :CH.CH 2 .C 6 H 3 <^>CH 2 (i, 3, 4) O which is that of methylene ether of propylene dihydroxybenzene. It is very poisonous, but has been used to cover the unpleasant fatty odor of soaps. It also serves for the preparation of pipero- O nal, CHO.C 6 H 3 < >CH 2 , the methylene ether of dihydroxy- O benzaldehyde (i, 3, 4) which is a product of its oxidation; and is employed, on account of its heliotrope odor, in perfumery under the name of "heliotropin." Safrol melts at 8 and boils at 232, piperonal at 37 and 263. Phenacetin, the well-known drug, is an ethereal derivative of p-hydroxyacetanilide, having the formula, C6H 4 (OC 2 H 5 )- (NH.OC.CH 3 ) (1,4). It forms colorless crystals which melt at 135, and is very slightly soluble in cold water. It is made by boiling the ethyl ether of p-aminophenol with glacial acetic acid. CHAPTER XXVI AROMATIC ALDEHYDES, KETONES AND QUINONES Aldehydes The aldehyde group, C\ , requiring two valencies for oxygen and one for hydrogen, cannot be developed on nucleus carbon. The aromatic aldehydes are, therefore, compounds in which this group is directly or indirectly united to an aryl radical in place of hydrogen. There are thus two varieties of aromatic aldehydes, both of which may be regarded as aliphatic alde- hydes in which aryl groups have been substituted for hydrogen in formaldehyde, or in the radicals of higher aldehydes. Preparation. Aromatic aldehydes can be made from the alcohols, as in the case of formaldehyde and acetaldehyde, but the corresponding alcohols are generally not readily accessible. In the aromatic series, as we have seen, the hydrocarbons form the most important sources for the preparation of other compounds, hence a method much employed for making aldehydes which have the aldehyde group immediately attached to the benzene ring, is by first forming, directly from the hydrocarbons, deriva- tives having chlorine in a side chain, and then converting the alkyl halogen group into the aldehyde group. In this way benzalde- hyde is prepared commercially from toluene. The toluene is chlorinated with the production of benzalchloride, CeHs.CHC^, as the chief product, and then the chlorine is replaced by oxygen by heating under pressure with milk of lime: C6H 6 .CHC1 2 + Ca(OH) 2 = CeHs.CHO + CaCl 2 + H 2 O 343 344 INTRODUCTION TO ORGANIC CHEMISTRY The reaction can be effected with other agents, even with water. Benzaldehyde may also be made from benzylchloride, CeHs.- CH 2 C1, by oxidation with lead or copper nitrate; or direct from toluene by an oxidation effected by chromyl chloride, CrO 2 Cl 2 (Etard's method). This method of oxidizing a methyl group to an aldehyde group may also be used for the preparation of other aromatic aldehydes. The aldehyde group may also be introduced in place of a hydrogen atom of the aryl nucleus by Gattermann's reaction. Thus benzaldehyde is prepared directly from benzene by passing into it a mixture of hydrogen chloride and carbon monoxide in the presence of anhydrous cuprous chloride and aluminium chloride. It may be assumed that the unstable formyl chloride, HCO.C1 is an intermediate product: + HCO.C1 = CeHB.CHO + HC1 Aldehydes, in which the aldehyde group is linked to the cyclic radical by other groups, are made by distillation of a mixture of calcium formate and the calcium salt of the corresponding acid a general method for both aliphatic and aromatic aldehydes: C6H 5 .CH 2 .CO.Oca + H.CO.Oca = C 6 H 5 .CH 2 .CHO + CaCO 3 Properties. The aromatic aldehydes are very like the ali- phatic aldehydes in behavior, but differ from these in some respects. They form no addition products with ammonia, though they unite with acid sodium sulphite and hydrocyanic acid; they do not reduce Fehling's solution, though ammoniacal silver nitrate is reduced; and they do not polymerize in the manner characteristic of the aliphatic aldehydes, or form resins when treated with caustic alkalies. With ammonia, they form con- densation products such as hydrobenzamine, (C6H 5 .CH 3 )N 2 , from benzaldehyde, resembling in this respect formaldehyde (p. 84); and again like formaldehyde, they are converted by concentrated alkalies into a mixture of the corresponding alcohol and the alkali salt of the corresponding acid: AROMATIC ALDEHYDES 345 2C 6 H 5 .CHO + KOH = C 6 H 5 .CH 2 OH + C 6 H 5 .CO.OK Benzaldehyde Benzyl alcohol Potassium benzoate With chlorine the aromatic aldehydes, unlike the aliphatic aldehydes, yield the corresponding acid chlorides (cf. p. 358); but like the aliphatic aldehydes they form hydrazones with phenyl- hydrazine (cf. p. 80). Although the aldehyde group is, in general, readily oxidized to the carboxyl group, aromatic aldehydes can be successfully nitrated without such oxidation by working at temperatures below o. Aromatic aldehydes form condensation products with many varieties of aliphatic and aromatic compounds, the combina- tion taking place with the loss of the elements of water, thus-. C 6 H 5 .CHO + 2C 6 H 6 .CH 3 = C 6 H 5 .CH(C 6 H4.CH 3 )2 + H 2 O C 6 H 5 .CHO + CH 3 .CO.ONa = C 6 H 5 .CH:CH.CO.ONa + H 2 O Benzaldehyde, C 6 H 5 .CHO, is one of the products of the hydrolysis of amygdaline, a glucoside which is present in bitter almonds and the kernels of other fruits, hydrocyanic acid and glucose being formed at the same time. Some of the many methods proposed for its commercial preparation have been de- scribed above. 1 It is commonly called "oil of bitter almonds," and is used for flavoring, and for making dyes. Benzaldehyde is a colorless oil which boils at 179 and is slightly heavier than water. It is very easily oxidized to benzoic acid, the change taking place slowly in contact with air. In the atmospheric oxidation of benzaldehyde it has been found that an intermediate product, benzoyl-hydrogen peroxide, is formed. This is an active oxidizing agent, X)-OH and in oxidizing other substances, e.g. unchanged benzaldehyde, is itself reduced to benzoic acid. This conversion of half of the absorbed oxygen to the " active" state is observed in the atmos- pheric oxidation of various other substances (e.g. turpentine). 1 For an account of the various methods by which benzaldehyde can be made see Thorpe's Dictionary of Applied Chemistry. 346 INTRODUCTION TO ORGANIC CHEMISTRY When chlorine is led into benzaldehyde it converts it into benzoyl chloride, CeHs.CO.Cl. Derivatives which contain a halogen atom in the benzene ring are made from the corre- sponding derivatives of benzalchloride (cf. p. 288). Sulphuric and nitric acids act on benzaldehyde with the formation of the meta sulphonic acid and meta nitrobenzaldehyde. The only other aromatic aldehydes of special interest are -the following : /CHO (i) Cuminic Aldehyde, C 6 H 4 <( p-isopropyl ben- \CH(CH,), (4), zaldehyde, occurs in caraway oil and other essential oils. Its constitution is proved by its oxidation to terephthalic acid (p. 368). It can be obtained from the essential oils which con- tain it by taking advantage of the small solubility of the addition product it forms with acid sodium sulphite, and then distilling this product with a solution of sodium carbonate. This is a general method for isolating naturally occurring aldehydes. Cinnamic Aldehyde, C 6 H 5 .CH:CH.CHO, is found in oil of cinnamon, oil of cassia, and other oils, and can be isolated by the method just described. It is formed by the oxidation of cin- namyl alcohol (p. 340), and can be prepared by condensing ben- zaldehyde and acetaldehyde (p. 82), a reaction which takes place in the presence of a dilute solution of sodium hydroxide. Cinna- mic aldehyde is an oil of aromatic odor which is volatile with steam, but cannot be distilled alone at ordinary pressures without decomposition. yCHO (l) Salicylic Aldehyde, CeH 4 H (2) from varieties of spiraea, and can be obtained by the oxidation of salicin (a glucoside found in willow bark) or salicyl alcohol. It is prepared by the action of chloroform on phenol when this is dissolved in an excess of potassium hydroxide: AROMATIC ALDEHYDES 347 /CHO C 6 H 6 .OK + CHC1 3 + 3KOH = C 6 H 4 < + 3KC1 + 2H 2 O. X OK This reaction, which is known as the Reimer-Tiemann reaction, serves to introduce the aldehyde group into phenol in the ortho and para positions. Probably an intermediate product contain- ing the group CHC1 2 is first formed, which is then converted into the aldehyde group, as in the making of benzaldehyde (p. 343). Salicylic aldehyde is a pleasant smelling liquid which boils at 196.5. It gives an intense violet with ferric chloride, and has the general properties of a phenol and an aldehyde, but does not reduce Fehling's solution. Anisaldehyde is the methyl ether of p-hydroxybenzaldehyde, (i) X)CH 3 (4) ,CH:CH.CH 3 It is prepared by oxidation of anethol, CeH^ , which X OCH 3 is the chief constituent of oil of aniseed. Anisaldehyde has an agreeable aromatic odor and is used in perfumery. It is an oil which boils at 245. Vanillin is the principal substance in the much-used extract of vanilla which is extracted from vanilla beans by alcohol. Its formula is /CHO (i) (3). (4) It may be made from guaiacol (p. 342) by the Reimer-Tiemann reaction, and is prepared commercially chiefly from eugenol (p. 342) by oxidation. Vanillin, thus prepared, has largely sup- planted the natural extract. Vanillin forms white crystals which melt at 81, and is sparingly soluble in cold water. It has a strong vanilla-like odor and taste. Its solutions have an acid reaction and are colored blue by ferric 348 INTRODUCTION TO ORGANIC CHEMISTRY chloride. If the solution containing ferric chloride is heated, a characteristic white crystalline precipitate is formed. Aromatic Ketones The compounds of this class may be divided into two groups: Those in which the ketone group carbonyl unites an aryl and an aliphatic radical, and those in which two aryl radicals are thus linked. Ketones of both groups can be obtained by the general method for making aliphatic ketones the distillation of the calcium salts of the corresponding acids; or more advantageously, from the aromatic hydrocarbon and the appropriate acid chloride by the Friedel and Crafts method (p. 274). Acetophenone, CeHs.CO.CHs, the simplest of the mixed aryl- aliphatic ketones, will serve as an illustration of this group. It is best prepared by the condensation of benzene and acetyl chloride by the Friedel and Crafts reaction : Aids O.Cl + C 6 H 6 -CH 3 .CO.C6H 5 + HC1 Acetophenone melts at 20.5 and boils at 202. It is used as medicine under the name of " hypnone," as a hypnotic. Its general chemical behavior is like that of the aliphatic ketones, but it does not unite with acid sodium sulphite. By reduction with sodium amalgam, it yields, in part, methylphenyl carbinol CH 3 .CHOH.C 6 H 5 , a secondary alcohol. When oxidized with alkaline permanganate it is converted into a ketone-acid, phenylglyoxylic acid, C 6 H 5 .CO.CO.OH, and then into benzoic acid, CeHs.CO.OH. Chlorine under all conditions (temperature, light, chlorine carriers) acts almost entirely on the methyl group with replace- ment of its hydrogen, and not on the phenyl radical. Benzophenone, CeHs.CO.CeHs, the first of the diaryl ketones, can be made by heating calcium benzoate, (CeHs.CO.O^Ca; or AROMATIC KETONES 349 from benzene and benzoyl chloride, CeHs.CO.Cl by the Friedel and Crafts reaction. It melts at 48 and boils at 306. Under certain conditions benzophenone is obtained in an unstable form which melts at 27. This variety slowly changes to the other on standing, and in contact with a trace of the stable form the change takes place rapidly with evolution of heat. This appears to be a case of allotropy due to molecular arrangement, as with phos- phorus and sulphur. Benzophenone is reduced by sodium amalgam to diphenyl- carbinol, (CeHs^CH.OH, or by zinc and sulphuric acid to a pinacom, (C6H5) 2 C(OH)C(OH)(C6H 5 ) 2 , and by hydriodic acid to diphenylmethane, (C eH 5 ) 2 CH 2 . Benzoin, CeHs.CH.OH.CO.CeHg, is a ketone-alcohol, formed by the union of two molecules of benzaldehyde, which occurs with molecular rearrangement when the aldehyde is heated in dilute alcoholic solution with potassium cyanide: 2C 6 H 5 .C< Benzaldehyde Benzoin Benzoin melts at 137. In virtue of the group, CHOH.CO, which it contains, it is, like certain ketoses (p. 199) which contain the same group, easily oxidized by Fehling's solution even in the cold, and forms a hydrazone and an osazone with phenyl- hydrazine. It is oxidized by nitric acid to benzil (diphenyldiketone), Ce^.CO.CO.C&Hs (melting point 95), and can be reduced by suitable agents to desoxybenzoi'n (phenylbenzylketone), CeH5.CH2.CO.C6H5, hydrobenzoin, CeHs.CH.OH.CH.OH.CeHe, or dibenzyl C6H 5 .CH 2 .CH 2 .C6H 5 . Quinones A considerable number of para derivatives, such as diamines, dihydroxyl compounds (hydrochinones), aminosulphonic acids, phenolsulphonic acids, aminophenols, when oxidized with chromic 35O INTRODUCTION TO ORGANIC CHEMISTRY acid or certain other acid oxidizing agents, are converted into well-crystallizing compounds of an intense yellow color, and a pungent, characteristic odor. These substances, which are called quinones, withstand the action of acid oxidizing agents as is evident from the manner of their formation, but are readily re- duced with the production of hydrochinones. Benzoquinone, usually called simply quinone, C 6 H 4 O2, is the simplest representative of the quinones. It was discovered in 1838 as the oxidation product of quinic acid, a by-product obtained in the extraction of quinine and allied alkaloids from cinchona bark. Structure. Quinone is a para derivative of benzene, as its formation from many para compounds and its relation to quinol (hydrochinone) indicates. It behaves like a diketone in forming both a monoxime and a dioxime with, hydroxylamine; but on reduction, the carbonyl groups are converted into = C.OH group (quinol) instead of = CH.OH groups as in the case of ordinary ketones. Further, by phosphorus pentachloride, quinone, CeH 4 O2, is changed into C 6 H 4 Cl2, one chlorine atom taking the place of each oxygen atom, instead of a replacement with two chlorine atoms, as in ketones. Two structures are suggested by these reactions which in the Kekule formulation are: O HC CH II I HC CH \l O and HC CH II II HC CH \C/ O I. 2. The first formula shows the usual benzene ring with two link- ing atoms of oxygen replacing two hydrogen atoms. In the QUINONES 351 second, two carbonyl groups appear, and the valence require- ments are met by the omission of one of the double linkages, and the shifting of a second one. The first formula explains in a simple manner the reduction OH Cl /\ /\ to quinol || |, and the formation of para-dichlorbenzene, 1 1 I, \/ \/ OH Cl by the action of phosphorus pentachloride; while the second form- ula requires rearrangement of valencies in the benzene ring. On the other hand the formulas for the oximes, O NOH and NOH NOH are derived naturally from the second formula. Further, in a chloroform solution of quinone, two or four atoms of bromine may be added, forming C6H 4 Br 2 O2, and C 6 H 4 Br 4 02. This is a reaction characteristic of an unsaturated compound, and is ex- plained by assuming that the two double bonds between -carbon atoms in the second formula are like the double bond in ethylene, and are easily resolved into single bonds: O O H BrH/\HBr + 2Br 2 = | H\/H BrH\/HBr O O These and other considerations have led to the adoption of the diketone formula the second one for the quinones. Quinone is usually prepared by oxidizing aniline with potassium dichromate and sulphuric acid, and extracting with ether. It 35 2 INTRODUCTION TO ORGANIC CHEMISTRY is purified by distillation with steam. The golden-yellow crystals melt at 116, and are quite soluble in hot water. H/\H The "quinoid configuration," I | ,is a " chromophore " group, since all of the quinones and their derivatives are colored compounds. The most important dyes containing this group are, however, derivatives of aromatic hydrocarbons with two or more "condensed" benzene rings, such as naphthalene and anthracene, and among them are both natural and artificial dyes. Quinone is easily converted into quinol by sulphurous acid and other reducing agents. Hydrogen chloride and hydrogen bromide effect a peculiar reaction, changing quinone into chlor or brom- quinol, C6H 3 Br(OH) 2 . The steps in this reaction and the rear- rangements involved are probably, OH H OH Tetrachlorquinone or chloranil, C 6 C1 4 O 2 , is produced by the chlorination of quinone, but is usually prepared by the simultane- ous oxidation and chlorination (potassium dichromate or chlorate and hydrochloric acid) of many aromatic substances. It is a yellow substance which melts at 290, and is insoluble in water. It is readily reduced to tetrachlorquinol, C 6 Cl4(OH) 2 , and is hence a strong oxidizing agent, and employed as such in the production of certain dyes. CHAPTER XXVII AROMATIC ACIDS The carboxyl group which is characteristic of all organic acids cannot be developed on an atom of nucleus carbon, and hence, as in the case of the aldehydes, the aromatic acids are compounds in which the carboxyl group is united directly or by linking groups to the aryl radical. Of these two classes of acids, those with directly united carboxyl groups are much the more important. Many of the aromatic acids occur in nature in the free condition, or as esters, 'in resins, balsams, and essential oils. The acids are solid crystalline substances, which are generally somewhat soluble in hot water, but almost insoluble at ordinary temperatures. Many of them are volatile with steam, and those of smaller molecular weight can be distilled without decomposition. In solution they are ionized to some extent and usually redden litmus. They decompose carbonates, and are, in general, "stronger" than the aliphatic acids. Preparation. i. Both classes of aromatic acids can be made by the methods employed for the formation of aliphatic acids: oxidation of alcohols, or hydrolysis of nitriles or esters. 2. A more important method for the preparation of many acids with carboxyl united to the nucleus is by oxidation of the hydro- carbons with side chains. All side chains can be oxidized to carboxyl groups. When side chains of different lengths are present the longer is usually oxidized first, and it is possible to control the oxidation so that one or more carboxyl groups shall be formed. 3. A useful method is by the oxidation of aryl-alkyl ke tones 23 353 354 INTRODUCTION TO ORGANIC CHEMISTRY (p. 348), which are readily formed from the aromatic hydrocar- bons and acyl chlorides by the Friedel-Craf ts reaction. Thus from mesitylene and acetyl chloride, acetomesitylene, (CH 3 ) 3 C6H 2 .CO.- CH 3 , is made, and then oxidized to the corresponding acid, (CH 3 ) 3 C6H 2 .CO.OH. 4. The carboxyl group can be introduced into the hydrocarbon in place of hydrogen by the action of carbonyl chloride in the presence of aluminium chloride (Friedel-Crafts) and hydrolysis of the resulting chloride; or, with better results, by carbonyl chloramide (p. 233), followed by hydrolysis: AlCli CHs.CeHs + C1.CO.NH 2 -> CH 3 C 6 H4.CO.NH 2 + HC1 5. The aromatic acids can also be prepared by the Grignard reaction (p. 37). The immediate product of the reaction, e.g., CeH 5 .MgBr, absorbs carbon dioxide giving CeH 6 .CO.OMgBr, and this on treatment with hydrochloric acid yields the aromatic acid, C 6 H 5 .CO.OH, and MgBrCl. The yield is nearly that in- dicated by the equation. 6. Halogen can be replaced by carboxyl by the action of carbon dioxide in the presence of sodium: C 6 H 5 Br + CO 2 + 2Na = C 6 H 5 .CO.ONa + NaBr Acids which have the carboxyl group in a side chain may be prepared by the acetoacetic ester synthesis (p. 174). Reactions. Salts are of course formed by the action of the acids on hydroxides or carbonates. The alkali salts are readily soluble in water, and the acids are precipitated from them by inorganic acids. The silver salts are frequently employed in determining the molecular weight of the acid, since on ignition the silver is left in a pure state. The formation of esters, acid chlorides, amides and anilides, and the replacement of the carboxyl group by hydrogen, are accomplished by reactions similar to those employed with the aliphatic acids (p. 99). AROMATIC ACIDS 355 Chlorine or bromine, or the sulphonic acid or nitro group can be introduced into the aryl radical of acids directly, and these nega- tive substituents enter chiefly the meta position with reference to the carboxyl group. Other derivatives may be made by the usual methods. An unusual reaction is that which produces hydrogen addition products of the acids. In alkaline solution into which carbon dioxide is led, sodium amalgam converts benzoic acid into tetra- hydrobenzoic acid, CeHg.CO.OH, and in boiling amyl alcohol, benzoic acid is reduced to hexahydrobenzoic acid, CeHn.CO.OH. Such additions of hydrogen take place more easily as the number of carboxyl groups is larger. These hydroaromatic compounds are discussed in Chapter XXVIII. Benzoic acid, CeHs.CO.OH (phenylformic acid), has been known since the beginning of the seventeenth century, having been originally obtained as a sublimate from gum benzoin. It is present in gum benzoin chiefly in the form of esters, and is also found in other plant products, such as balsams of Peru and Tolu, and in cranberries. A derivative of benzoic acid, the hippuric acid (p. 359), is present in the urine of herbivora. While it may be made by any of the methods which have been given, it is usually prepared for pharmaceutical purposes by sublimation from gum benzoin; and manufactured on a large scale from toluene by converting this hydrocarbon into benzyl chloride, C6H 6 .CH 2 C1, and then oxidizing the latter with nitric acid. The direct oxidation of toluene gives the acid, but in such small amounts that its preparation through the chlorine deriva- tive is more advantageous. Benzoic acid is also made from benzotrichloride, CeHs.CCla, which is a by-product in the production of benzaldehyde, by heating this with milk of lime: 3Ca(OH) 2 = 2 C6H 5 .CO.OH + 3CaCl 2 + 2 H 2 O Benzoic acid is nearly odorless when perfectly pure, but that 356 INTRODUCTION TO ORGANIC CHEMISTRY made from gum benzoin has a slight odor of the aromatic gum. It sublimes readily and its vapors are very irritating to the nose and throat. Benzoic acid is used in medicine, in the preparation of dyes, aniline blue and anthragallol. The latter is an anthracene derivative formed from benzoic and gallic acids by elimination of water: H OH H CO OH H/\CO.OH H/\OH HX\/\/\OH HO.OC\/OH HX/\/\/OH H H H CO H Benzoic acid Gallic acid Anthragallol o H\/] Sodium benzoate is well known as a food preservative. 2 H 2 Name Benzoic o-Toluic m-Toluic p-Toluic Cuminic Phenylacetic Cinnamic o-Phthalic m-(Iso)Phthalic p-(Tere)Phthalic Trimellitic Pyromellitic B enzenepentacarboxy lie Mellitic AROMATIC ACIDS Formula . C 6 H 5 .CO.OH 3 (i) CO.OH (2) I. d) ).OH (3) /CH 3 (i) CeH4 \CO.OH (4) C 6 H 4 < CH(CH 3 ) 2 (i) .CO.OH (4) C 6 H 6 .CH 2 .CO.OH C 6 H 5 .CH:CH.CO.OH C 6 H 4 (CO.OH) 2 (i, 2) C 6 H 4 (CO.OH) 2 (i, 3) C 6 H 4 (CO.OH) 2 (i, 4) C 6 H 3 (CO.OH) 3 (i, 2, 4) C 6 H 2 (CO.OH) 4 (i, 2, 4, C 6 H(CO.OH) 6 C 6 (CO.OH) 6 Melting point 121.4 104 109 180 116 76 133 231 330+ sublimes 228 265 287 AROMATIC ACIDS 357 Toluic acids, CHs.CeH^.CO.OH. The three isomeric acids of this formula can be made by partial oxidation of the three xylenes with nitric acid, or from the toluidines by conversion into nitriles by the diazo reaction and subsequent hydrolysis. Para- toluic acid is also readily prepared from cymene CH 3 .C6H 4 .C 3 H7, by oxidation of the isopropyl group. These acids present no especial points of interest, nor is it necessary to discuss further the homologues of benzoic acid. Phenylacetic acid, C6H 5 .CH 2 .CO.OH, which is isomeric with the toluic acids, is best obtained by the hydrolysis of benzylcyan- ide, C6H 5 .CH 2 .CN, its nitrile, which is made by the reaction of benzylchloride, CeHs-CH^Cl, with potassium cyanide. It is a slightly weaker acid (less ionized) than benzoic acid, though stronger than acetic acid; and illustrates the general fact that with wider separation of the phenyl and carboxyl groups by in- termediate hydro-carbon groups the acids become weaker. Phenylacetic acid can yield, of course, two classes of derivatives, according as substitution takes place in the nucleus or in the side chain. On oxidation it gives benzoic acid, while the toluic acids give dibasic phthalic acids. Cinnamic acid, CeHs.CHiCH.CO.OH, /3-phenylacrylic acid, is a type of the unsaturated aromatic acids and the most important of the group. It occurs free, and in esters of various aromatic alcohols, in many gums and balsams, and in the leaves of certain plants. It has been known for a long time, and was formerly confused with benzoic acid. It is prepared from storax, or is synthesized by Perkin's reaction. This reaction, which is the most important method for making many unsaturated aromatic acids (and also applicable to the formation of unsaturated aliphatic acids), consists in the condensation of an aromatic aldehyde and a salt of an aliphatic acid, which occurs in the presence of acetic anhydride: C 6 H 5 .CHO + CHa.CO.ONa = C 6 H 5 .CH:CH.CO.ONa+ H 2 INTRODUCTION TO ORGANIC CHEMISTRY (Benzalchloride may be used here in place of benzaldehyde.) When slowly distilled, or more readily when heated with lime, cinnamic acid gives styrene, C6H 5 .CH:CH 2 , and carbon dioxide (calcium carbonate). When cinnamic acid is oxidized, the double bond becomes the point of attack; a mild oxidation (KMnO 4 ) yielding phenyl- glyceric acid, C 6 H 6 .CHOH.CHOH.COOH, and a stronger oxida- tion (HNOs) giving benzaldehyde and benzoic acid. As an unsaturated compound it unites with halogens to form dihalogen derivatives, e.g., Ce^.CHCl.CHQ.CO.OH; and by reduction with sodium amalgam it gives hydro cinnamic acid, or phenylpropionic acid, CeH5.CH2.CH2.CO. OH. By the usual reactions for producing unsaturation (p. 45) cinnamic acid may be converted into phenylpropiolic acid, CeHs- C = C.CO.OH, and from this, phenylacetylene, C 6 H 5 .C ='CH, can be prepared (p. 279). Derivatives of the Monobasic Acids Benzoyl Chloride, CeHs.CO.Cl, is formed like other acyl chlo- rides by the action of phosphorus pentachloride on benzoic acid or its sodium salt; but it is usually prepared in quantity by treat- ing benzaldehyde with chlorine (p. 346), a reaction that differs from that of chlorine with aliphatic aldehydes (cf. p. 80). Benzoyl chloride is a liquid of disagreeable, tear-compelling odor that boils at 198. It is insoluble in water but is slowly decom- posed by it with the formation of benzoic and hydrochloric acids (cf. p. 115). It reacts with practically all alcohols and phenols, primary or secondary amines, with the formation of benzoyl com- pounds which are useful in the identification and characteriza- tion of these substances. These reactions are greatly facilitated by the presence of an alkali (Schotten-Baumann reaction) : C 6 H 5 .CO.C1 + C 2 H 5 OH + NaOH = C6H 5 CO.OC 2 H 5 + NaCl + H 2 C 6 H 5 .CO.C1 + C 6 H 5 NH 2 + NaOH = C 6 H 5 .CO.NHC 6 H 5 + NaCl + H 2 AROMATIC ACIDS 359 Benzamide, C 6 H 5 .CO.NH 2 , is readily prepared by bringing together benzoyl chloride and ammonia or ammonium carbonate. It crystallizes from hot water in glistening plates that melt at 128. One hydrogen atom of the amido group is replaceable by metals (cf. p. 140), and the metal may in turn be replaced by alkyl radicals by the action of alkyl halides. Like the aliphatic amides benzamide appears to exist in two forms (cf. p. 141). Benzonitrile, C 6 H 5 .CN, can be formed by the withdrawal of water from benzamide, (P2O 5 ), but is best prepared from anilin by the Sandmeyer reaction (p. 316). It is a liquid with the odor of bitter almonds and boils at 191. It has all the properties of the aliphatic nitriles (p. 153). Hippuric Acid, C 6 H 5 .CO.NH.CH 2 .CO.OH, which occurs in the urine of herbivora, is benzoylglycine, and can be made by shak- ing a mixture of benzoylchloride and aminoacetic acid (glycine) with sodium hydroxide: C 6 H 5 .CO.C1 + NH 2 CH 2 .CO.OH = Benzoyl chloride Glycine C 6 H 5 .CO.NH.CH 2 .CO.OH + HC1 Hippuric acid Benzoic acid was formerly obtained to some extent from the natural hippuric acid, which was discovered in 1776 in the urine of cows and camels. Hippuric and benzoic acids were not clearly distinguished until 1829 (Liebig). / co \ Saccharin, CeH 4 <^ y>NH (i, 2), is o-sulphobenzoic-acid- imide and a derivative of the ortho sulphonic acid of benzoic acid. Since the chief product of the sulphonation of benzoic acid is the meta compound, the starting point for the preparation of sac- charin is toluene. The steps are: C 6 H 5 .CH3-C 6 H4 -^C 6 X SO 3 OH S0 2 C1 S0 2 NH 2 Toluene Toluene sulphonic Toluene sul- Toluene sulphonamide acid phonyl chloride 360 INTRODUCTION TO ORGANIC CHEMISTRY /CO.OH /COv C 6 H 4 < - C 6 H/ >NH X S0 2 NH 2 X SO/ Toluic acid Saccharin In the sulphonation of toluene, both ortho and para sulphonic acids are produced. These are converted into the acid chlorides, and as the para chloride is a solid and the ortho a liquid, they may be largely separated. The ortho compound is then converted into the amide by ammonia and the amide oxidized by potassium permanganate in neutral solution. On adding hydrochloric acid to the solution, saccharin is obtained. It was discovered in 1879 by Fahlberg and Remsen. It is a colorless, crystalline substance, which melts with some decomposition at 224. It is only slightly soluble in water. Its most striking property is its intensely sweet taste, which is said to be more than 500 times that of cane sugar. On this account it is manufactured and used for sweetening purposes, and as a substitute for sugar by sufferers from diabetes. yCO.OH (l) Anthranilic Acid, C 6 H 4 <( , o-aminobenzoic acid, is \NH, (2) of especial interest on account of its relation to indigo and its use in the artificial preparation of this dye. It was first obtained from indigo (anil) by boiling this substance with potassium hydroxide. The three aminobenzoic acids can be made by reduction of the corresponding nitro compounds; but the o-nitrobenzoic acid is a minor product of direct nitration of benzoic acid. Anthranilic acid is prepared for making indigo from naphthalene by the series of reactions shown by the following formulas: o /CO.OH /C 4 H4 -> C 6 H 4 < -> C 6 H 4 < X CO.OH Naphthalene o-Phthalic Phthalic acid anhydride AROMATIC ACIDS 361 /CONH 2 /NH 2 C 6 H 4 < -> C 6 H/ X CO.OH X CO.OH Phthalic o-Aminobenzenoic amide acid The last reaction is accomplished by bleaching powder and is Hofmann's reaction for the formation of amines, (cf. p. 129). Anthranilic acid melts at 145 and decomposes, on distillation, into aniline and carbon dioxide. By reaction with chloracetic acid, and fusion of the product with sodium hydroxide, indoxyl is produced, which in dilute solution is oxidized to indigo by the air (p. 400). Hydroxy Acids Hydroxy or phenol acids can be made by the introduction of hydroxyl groups into acids: i. through nitro derivatives by reduction of the nitro to the amino groups followed by the diazo reaction : /CO.OH /CO.OH C 6 H 5 .CO.OH -> C 6 H 4 < - C 6 H 4 < -> X NH 2 /CO.OH /CO.OH CTT / f* TT / 6-tl 4 \ ~* L^6-tl-4\ X N 2 C1 X OH 2. or through the sulphonic acids by fusion with potassium hydroxide: /CO.OH KOH /CO.OH C 6 H 6 .CO.OH -> C 6 H 4 < > C 6 H< \gQ 3 jj ^OH 3. The carboxyl group can be introduced into phenols by way of the nitro derivatives. The nitro group is reduced to the amino group, the cyanogen group is substituted for this by Sandmeyer's reaction (p. 316), and the resulting nitrile is finally converted into the carboxyl group by hydrolysis : 362 INTRODUCTION TO ORGANIC CHEMISTRY OH C 6 H 4 /OH /OH / v rvti./ - 64 X X NO 2 NH 2 N 2 C1 /OH /O C 6 H 4 < -> C 6 H< X CN X C H CO.OH 4. Homologues of phenol are converted into phenol acids by the oxidation of the side chains. The reaction is particularly successful when the phenols are first changed into their sulphuric acid or phosphoric acid esters. 5. An important method for making hydroxy acids is by Kolbe's synthesis. As originally carried out, an alkali phenolate is heated in a current of carbon dioxide with the result that half distils as phenol, and the rest is converted into the basic salt of the hydroxy acid: 2C 6 H 6 ONa + CO 2 = C 6 H 6 OH + C 6 H 4 < x CO.ONa But if the alkali phenolate is heated with carbon dioxide under pressure, it is completely transformed into the normal salt by intramolecular change, a phenylcarbonate being formed as an intermediate step : /OH C 6 H 5 ONa + CO 2 = C 6 H 5 OCO.ONa = C 6 H 4 < X CO.ONa It is an interesting fact that the ortho compound results when sodium phenolate is used, while potassium phenolate at tempera- tures from 170 to 210 yields the salt of the para hydroxy acid. The formation of the meta compound by this method has not been observed. Properties. The hydroxy acids are colorless, crystalline sub- stances, more soluble in water (influence of hydroxyl groups) than the acids from which they are derived. The hydrogen of the AROMATIC ACIDS 363 hydroxyl, as well as that of the carboxyl, is replaced by an alkali metal when the hydroxy acid is treated with an alkali hydroxide, but these salts are changed to mono-metal salts of the hydroxy acids by carbon dioxide; and by alkali carbonates only the hydro- gen of the carboxyl group is replaced. They are converted into phenols by heating with lime, the general reaction for replac- ing the carboxyl group with hydrogen: C 6 H 4 (OH).CO.OH + CaO = C 6 H 5 OH + CaCO 3 Effect of Position. The relative positions of the carboxyl and the hydroxyl groups have a striking influence on their activity as acids, as shown by the ionization constants (see also p. 408). kxio* Benzoic acid 6.6 o-Hydroxybenzoic acid 100 . m-Hydroxybenzoic acid 8.3 p-Hydroxybenzoic acid 2.8 2, 6-Dihydroxybenzoic acid 5000 . It is seen from these figures that the hydroxyl group in the meta position produces little effect, and in the para position decreases the acidity to less than one-half that of the simple acid. In the ortho position, however, the acidity is very greatly increased, 17 times by a single hydroxyl group, and 833 times when two stand in the ortho position to the carboxyl group. Similar influences are found in the case of other substitutes, and are most marked, as here, when they occupy the ortho position. Thus the constant for o-nitrobenzoic acid is 100 times that of benzoic acid, that for o-brombenzoic acid is 24 times, and that for o-methyl-benzoic acid (o-toluic) 2 times as large. The ortho hydroxy acids differ from the meta and para com- pounds also, in that they alone give the violet coloration with ferric chloride which is characteristic of phenol, and are volatile with steam. Ortho and para hydroxy-acids are much more read- ily converted into phenols by heating alone or with concentrated 364 INTRODUCTION TO ORGANIC CHEMISTRY hydrochloric acid than are the meta compounds, and the greater stability of the latter is indicated by other reactions. HYDROXY-ACIDS Name Formula Melting point Mandelic C 6 H 6 .CH.OH.CO.OH 118 Phenyl-lactic C 6 H 6 .CH 2 .CH.OH.CO.OH 98 Salicylic acid C 6 H 4 <' H > 159 C, Protocatechuic T /CO.OH (i) Galhc C6H <(OH)3(3,4,5) Mandelic acid, CeHe.CH.OH.CO.OH, phenylglycollic acid, is the simplest hydroxy-acid which has hydroxyl in a side chain. It was originally obtained.from bitter almonds (German, Bitter- mandel). The amygdalin contained in the almonds breaks up, as we have seen, into benzaldehyde, hydrocyanic acid and glucose (p. 345). The mandelic acid is the result of the union of the alde- , hyde and acid, forming the cyanhydrin, CeH5.CHCa = CH 2 < >CO + CaCO 8 X CH 2 .CH 2 .CO.(X X CH 2 .CH/ Calcium pimelate Ketocyclomethylene and this is oxidized by nitric acid to adipic acid, CH 2 .CH 2 .CO.OH CH 2 .CH 2 .CO.OH This is a good illustration of the relation of hydroaromatic com- pounds to aliphatic compounds. Irone, the odoriferous principle of violets, is a hydroaromatic ketone with the carbonyl group in a side chain. Its formula and that of the artificial oil of violets, ionone, which is made from geranial (citral) (p. 87), differ only in the position of the double bond in the ring: 1 For the optical activity of inosite, see Stewart's "Stereo-Chemistry." 375 HYDROAROMATIC HYDROCARBONS CH 3 CH 3 y /\ HC CH.CH:CH.CO.CH 3 II I HC CH.CH 3 C Irone CH 3 CH 3 V C /\ H 2 C CH.CH:CH.CO.CH 3 H 2 C C.CH 3 H lonone The hydroaromatic acids resemble the saturated aliphatic acids having an equal number of carbon atoms. Thus, hexahydro- benzoic acid, CeHn.CO.OH, is like heptylic acid, CeHig.CO.OH in its odor and other characteristics. It melts at 29, boils at 235, and is converted into benzoic acid by heating with anhydrous copper sulphate to 290. Quinic acid, C6H 7 (OH) 4 .CO.OH, a tetrahydroxyl acid which is a derivative of cyclohexane, occurs in cinchona bark and in many other plants, and is obtained as a by-product in the manu- facture of quinine. Its relation to the aromatic compounds is shown by the following facts: When melted with potassium hydroxide it gives protocatechuic acid (p. 364); hydrogen iodide reduces it to benzoic acid; on dry distillation, it yields phenol, quinol, benzoic acid and salicylic aldehyde. Quinic acid melts at 1 6 1. 6 and its solutions are levo-rotatory. INTRODUCTION TO ORGANIC CHEMISTRY 376 Hydromellitic acid, C 6 H 6 (CO.OH) 6 , is of interest as being the compound whose discovery led Baeyer to his fruitful investiga- tions of the hydroaromatic compounds. It is formed by the re- duction of an ammoniacal solution of mellitic acid with sodium amalgam. The Terpenes Terpenes are hydrocarbons which occur in many plants, and they are often the chief constituents of the essential oils obtained by distilling flowers, fruits, parts of plants, or exuded balsams and oleo-resins with steam (cf. p. 160). By fractional distillation of the oils a more or less complete separation of the hydrocarbons from other constituents can be effected; but as it is often difficult to separate the individual terpenes in this way, purification is sometimes accomplished by converting the terpenes into com- pounds which can be freed from impurities by crystallization, and from which the terpenes can then be recovered. Pinene, doHie, is much the most important of all the many terpenes from a practical point of view. It is the chief constituent of turpentine oil. Turpentine is an oleo-resin which exudes from many coniferous trees. It consists chiefly of a solution of resin (colophony) in pinene. On distillation with steam, turpentine oil comes over and the resin is left behind. This well-known oil, often called "turpentine," has a characteristic and pungent odor, which is pleasant when the oil is freshly distilled; but on exposure to the air the odor becomes unpleasant, and the oil gradually grows viscid and finally resinous from absorption of oxygen. Like some other substances which oxidize spontaneously (cf. p. 345) the turpentine oil under these conditions acquires strong oxidizing, properties, and its value in paints and varnishes depends largely on its behavior as an oxygen-carrier to the drying oils which are used. Besides its employment in painting, it is used as an excel- lent solvent for fats, resins, and caoutchouc. It also dissolves sulphur, phosphorus and iodine. 377 HYDRO AROMATIC HYDROCARBONS By fractional distillation of turpentine oil, pinene is obtained nearly pure. Pinene from French turpentine oil is levo-rotatory; from American and most other oils, dextro-rotatory. An optically inactive form can also be obtained from an addition product which is formed with nitrosyl chloride. Pinene is an unsaturated hydrocarbon, and is shown by its addition products with chlorine or bromine to have one double linkage. It also absorbs dry hydrogen chloride with the produc- tion of pinene hydrochloride, doHi 7 Cl, which forms a white crystalline mass, melting at 131, and is called "artificial cam- phor" as it resembles camphor in appearance and odor. Pinene burns with a very smoky flame, and its energetic reac- tion with chlorine is shown by the common lecture experiment of bringing a strip of turpentine-soaked paper into this gas. The evidence for the constitution of pinene and the other ter- penes is much too intricate for discussion here. Most of the terpenes can be converted into cymene, or CH(CH 3 ) 2 by withdrawal of two atoms of hydrogen through heating with sulphuric acid or iodine. These terpenes are therefore hydro- aromatic compounds. Other terpenes are apparently open-chain compounds of the olefine series. Isoprene, C 5 H 8 (p. 50), which is obtained as a distillation product from caoutchouc and some of the terpenes, is considered to be a "hemiterpene" of this kind CH 2 with the formula, >C.CH = CH 2 . CH 3 The structure of pinene as shown in the following formula is dicyclic a ring within the aromatic ring. INTRODUCTION TO ORGANIC CHEMISTRY 378 CH 2 - CH - CH 2 CH 3 .C.CH 3 ;H = c- -CH CH 3 Pinene Artificial Rubber. The fact that isoprene can be converted into rubber has been mentioned (p. 50). The transformation, which is one of polymerization or condensation, may be brought about by contact with hydrochloric acid or certain other reagents. A small amount of metallic sodium produces the change in a few hours or a few days, according to the temperature. Methods for obtain- ing isoprene cheaply and in sufficient quantity for the industrial manufacture of artificial rubber have not yet been found. Another possible source for a commercial synthesis of rubber is butadiene, CH 2 : CH.CH:CH 2 , which is condensed by sodium to a product which, though not identical with natural rubber, seems to be superior to it in some respects. Butadiene is prepared from normal butyl alcohol which, in turn, may be obtained from gelatinized starch by the action of a special ferment acetone being formed at the same time. Camphene, CioHie, which is the only known solid terpene, is also an unsaturated compound whose exact constitution is not yet known, though probably of the same type as that of pinene. It is found in two optically active forms in French and American turpentine and in other vegetable oils. It melts at 48-50, boils at 1 60, and is oxidized to camphor by chromic acid. In another group of terpenes the members combine with four atoms of bromine or two molecules of a hydrogen halide, and are therefore represented with two double bonds. Limonene is a representative of this group. Dextro-limonene is found in considerable quantity in orange-peel oil and in caraway oil; the levo form occurs in pine-needle oil, and the 379 HYDRO AROMATIC HYDROCARBONS racemic form is obtained together with isoprene in distilling caoutchouc. Many other oils also contain these hydrocarbons. The formula for limonene is given below with that of terpinene, which is a constituent of cardamon oil. CHa CHa CHa I I I c c c /V /V /V H 2 C CH H 2 C CH H 2 C CH II | | or || H 2 C CH 2 HC CH 2 H 2 C CH CH CCH.C^ OH CH CH 2 CH Terpine Menthone CioHigO, and Menthol, CioH 20 O, are substances con- tained in peppermint oil, menthol being the chief constituent, and crystallizing out of the oil when it is cooled. Menthol can also be made from pulegone, CioHieO, an unsaturated ketone which is the chief constituent of oil of pennyroyal, by reduction with sodium in alcoholic solution. Menthol has a strong pepper- mint odor, and a pleasant cooling taste. It is used as a remedy for neuralgic headache, etc. It melts at 43. Chemically it stands in the same relation to menthone that borneol does to camphor, one being a saturated ketone and the other a secondary alcohol. CH.CH 3 CHXH 3 /\ /\ H 2 C CH 2 H 2 C CH 2 II II H 2 C CO H 2 C CHOH V V CH:(CH 3 ) 2 CH.CH(CH 3 ) 2 Menthone Menthol CHAPTER XXIX NAPHTHALENE AND ANTHRACENE From the higher boiling fractions of coal tar a number of solid hydrocarbons are obtained which have larger molecular weights than benzene and a smaller proportion of hydrogen. Of these naphthalene and anthracene are much the most important. Naphthalene Naphthalene, Ci H 8 , crystallizes from the fractional distillate of coal tar which comes over between 170 and 230 and is known as " carbolic oil" or "middle oil." Naphthalene is present in coal tar in larger amounts (5-10 per cent.) than any other constit- uent, and forms an inexpensive source for the preparation of valuable azo dyes. After being freed by pressure from most of the oils which cling to it, it is purified by treatment with concen- trated sulphuric acid, followed by distillation with steam or by sublimation. Properties. Naphthalene crystallizes in white lustrous plates, melts at 80 and boils at 218. It sublimes very readily, volatiliz- ing slowly at ordinary temperatures, and has a characteristic odor which is well-known from its wide use in the form of "moth- balls" for protecting woolens and furs from moths. It is insoluble in water, but dissolves freely in various organic solvents. It is one of the principal illuminating constituents of coal gas, and occasionally causes stoppages in the gas mains by crystallizing out of the gas in cold weather. Naphthalene is produced when the vapors of many organic 382 3^3 NAPHTHALENE compounds are passed through a red-hot tube (which explains its presence in coal tar) and it is present in the products of the dry distillation of wood. Chlorine, bromine, and nitric acid act on naphthalene with the production of substitution products; and other groups such as the hydroxyl and amino groups can be introduced by methods used in making benzene derivatives. Chlorine and bromine also form addition products with naphthalene. But while naphtha- lene and its derivatives are, in general behavior, like other aro- matic compounds, there are certain differences which appear in a readier activity of the naphthalene derivatives as compared with those of benzene. The hydrogen addition products hydronaphthalenes and their derivatives, on the other hand, are, in several cases, wholly aromatic or benzene-like in their reactions. Structure. Naphthalene is represented by the formula, H H C C /S/N HC C CH I II I HC C CH C C H H The evidence for this formula is as follows: i. From the products of oxidation: By active oxidizing agents, naphthalene is converted into phthalic acid (p. 368) ; this indicates that it contains a ben- zene ring, and that naphthalene is an ortho di-derivative of ben- zene. When nitronaphthalene is oxidized, nitrophthalic acid (i, 2, 3) is formed; but if the nitronaphthalene is reduced to aminonaphthalene and this is oxidized, unsubstituted phthalic acid is the product, the amino group being in the part that is oxidized: INTRODUCTION TO ORGANIC CHEMISTRY 384 iCO.OH XX Naphthalene N0 2 NO 2 o i I . . 1 * 'CO.OH k A J k /'CO.OH Phthalic acid Nitronaphtha- Nitrophthalic acid NH Aminonaphtha- lene CO.OH CO.OH Phthalic acid The same difference in behavior toward oxidation is observed in other nitro and amino derivatives. The nitro compounds are stable, while the amino compounds are readily attacked. From this we may conclude that naphthalene consists of two benzene molecules which are coalesced with the dropping out of four hy- drogen atoms, as shown in the formula. 2. Syntheses of naphthalene can also be made which lead to the same conclusion as to its structure. One of these is the follow- ing. Phenylisocrotonic acid, which can be made by heating benzaldehyde with sodium succinate and acetic anhydride (Per- kin's reaction p. 357) is converted by continued boiling into a-naphthol, from which naphthalene is readily obtained: iCH:CH.CH 2 .CO.OH Phenylisocrotonic acid -HzO OH a-Naphthol Naphthalene Substitution products are obtained in greater numbers than with benzene, and the number of isomers is in accordance with the possibilities which the naphthalene formula indicates. In the above formula where the hydrogen-bearing carbon atoms are NAPHTHALENE numbered, it is seen that the positions i, 4, 5, and 8 are alike, and different from 2,3,6, and 7, all of which, again, bear the same rela- tion to the molecule. A compound of this formula should, there- fore, yield two and only two monosubstitution products, and this is found to be the case with naphthalene. These compounds are distinguished as a-derivatives when replacement is at i, 4, 5, or 8, and /3-derivatives when in any of the other positions. When further replacements of hydrogen are made the isomeric possibilities are: For two or six like substituents, 10 isomers; for three or five, 14 ; and for four, 22. Two unlike atoms or groups may give 14 isomers, and the total possible number of derivatives by direct replacement of hydrogen has been calculated to be 10,766,600. While only a very few of the polysubstitution products have been made, in no case have more derivatives been obtained than is predicted by the theory, and in the case of dichlor substitutions, all ten have been made. The positions of substituents' may be determined by oxidation into benzene derivatives of known posi- tions, as in the case of nitronaphthalene above. Chlorine and bromine act on boiling naphthalene with the for- mation of a-derivatives. /3-halogen derivatives are obtained indirectly from amino or sulphonic derivatives by methods of replacement used for the derivatives of benzene. From one to four chlorine atoms can be introduced by the action of chlorine alone, and in the presence of a chlorine "carrier" (p. 284) the number may be increased to eight, with replacement of all the hydrogen atoms. Concentrated sulphuric acid at a temperature not above 80 gives chiefly a-naphthalene sulphonic acid; at higher tempera- tures (160) the /3-sulphonic acid is the sole product, since the a-acid passes by intramolecular rearrangement into the -acid when heated to the higher temperature with sulphuric acid. By more energetic sulphonation two sulphonic groups are introduced, the chief products being the 2, 7, and the 2^ 6 compounds, both of INTRODUCTION TO ORGANIC CHEMISTRY 386 them di-/3-derivatives. At higher temperatures and on prolonged heating, the proportion of the 2, 6 sulphonic acid is greater. Nitric acid under usual conditions of nitration produces only a-mono- and a-dinitro derivatives. On further nitration trinitro- and tetranitronaphthalenes in many isomeric forms are obtained. A mixture of nitronaphthalenes is used in making certain explo- sives, but their chief importance is the preparation of naphthyl- amines. The formation of other derivatives is accomplished by the meth- ods used for making benzene derivatives. Naphthols, the hydroxyl derivatives of naphthalene, are of importance in the dye-stuff industry, since they combine readily with all diazo compounds to form azo-derivatives. The hydroxyl group of the naphthols is replaced more easily than that of phenol ; they give ethyl-naphthyl ethers, C2H 6 .O.CioH7, when heated with alcohol and hydrochloric acid to 150; and when heated with zinc chloride at 200, naphthol forms naphthyl ether, (CioHy^O, (reactions not given by phenol). The naphthols also differ from phenol by having much higher melting points and being difficultly soluble in water. The naphthols occur in coal tar, but in very small quantities, and are usually made from naphthalene sulphonic acids by melting with alkalies. a-Naphthol, CioH 7 .OH, melts at 94 and boils at 278-28o. P-naphthol melts at 122 and boils at 285-286. Bleaching powder gives a dark violet color with a-naphthol in aqueous solu- tion, and a pale yellow with /3-naphthol. Ferric chloride oxidizes both to dinaphthols, HO.CioH 6 .CioH 6 .OH. Dinitro- a-naphthol (2, 4) is obtained by the action of dilute nitric acid on a-naphthol-disulphonic acid (2, 4), which effects the replacement of the sulphonic acid groups by nitro groups. The sodium salt is known as "Martius' yellow" which is a direct dye for wool and silk. Naphtbylamines, CioH 7 .NH 2 , can be obtained from the nitro- NAPHTHALENE naphthalenes by reduction, but are often prepared from the naph- thols by heating with ammonium chloride and caustic soda or with zinc chloride and ammonia (cf. p. 303). This reaction is used especially for /3-naphthylamine, as the jS-nitronaphthalene is not formed by direct nitration, and, in fact, is itself most read- ily made from /3-naphthylamine by the diazo reaction; while /3-naphthol is easily obtained from naphthalene sulphonic acid. The naphthylamines are well-crystallizing substances which can be distilled without decomposition. Their melting points are, for the a-amine, 50, for the jS-amine, 112. The ct-amine has a most disagreeable odor, while the other is almost odorless. They are of importance as sources (with benzidine, p-diamino-diphenyl) of the Congo dyes which are substantive dyes for cotton. Congo- red is made by treating diazotized benzidine with naphthy- lamine-sulphonic acid, and converting the product into a sodium salt: NH 2 Benzidine-diazonium chloride Naphthyl- amine sul- phonic acid NaS0 3 /SO 3 Na NH NH 2 Congo-red The acid of this salt is blue. Benzopurpurin is made in the same general way, and differs from Congo-red by having a methyl group replaced in each of the benzene radicals. a-Naphthoquinone, CioH 6 O 2 (i, 4) is formed as the result of direct oxidation of naphthalene by chromic acid in glacial acetic acid, and is also a product of the oxidation of many a-derivatives. It melts at 125 and resembles benzoquinone in its yellow color, odor and other properties, and is reduced to i, 4-dihydroxy- naphthalene by sulphurous acid, but the reduction does not occur as readily as that of benzoquinone. INTRODUCTION TO ORGANIC CHEMISTRY 388 /8-Naphthoquinone, Ci H 6 O 2 (i, 2), forms from its ether solu- tion red crystals which are not volatile, and decompose at 115- 120 without melting. By sulphurous acid it is reduced to i, 2-dihydroxynaphthalene. Some derivatives of the naphtho- quinones are dyes. O O o O a-Naphthoquinone /3-Naphthoquinone Anthracene Anthracene Ci 4 Hio, is obtained from "anthracene oil" which is the highest boiling fraction in the distillation of coal tar. Its amount in coal tar is only 0.25 to 0.45 per cent., but it is an im- portant substance as it serves as the basis for making the valuable dye " alizarin" or "turkey red." It forms white crystals which, when quite pure, have a violet fluorescence. It melts at 216 and boils at 351. It dissolves with difficulty in many of the usual organic solvents, and is most easily soluble in benzene and toluene. It was discovered in coal tar in 1832 and first called "paranaph- thalene," and later, anthracene, from its occurrence in anthracite coal tar. In 1868 Graebe and Liebermann found that alizarin, the dye extracted from madder, was converted into anthracene by distillation with zinc dust; and, in the next year, they synthe- sized alizarin from anthracene through anthraquinone. The structure of anthracene is established by several synthetical methods of formation. The first of these to be carried out was by heating benzylchloride with water at 190: 2C6H 5 .CH 2 C1 -> CuHio + 2HC1 + H 2 Benzychloride Anthracene 389 ANTHRACENE This indicates that there are two benzene rings in anthracene connected with two additional carbon atoms, as in Another synthesis which leads to the same conclusion is from benzene and acetylene tetrabromide by the Friedel-Craft's method: CHBr 2 AlBr, 2C 6 H 6 + | > CHBr 2 It is evident that, in the Kekule' formulation, the middle ring in anthracene cannot have the constitution of a true benzene ring. The double bonds in the two outer benzene rings may have differ- ent positions as shown in the above formulas, and the valence requirement in the middle ring can be met by one (or possibly two) cross bonds as is indicated, or as in formula 3. In fact, anthracene is an unsaturated compound, readily uniting with two bromine or two hydrogen atoms with the formation of H HBr H H H 2 H H/N/N/NH Ci 4 Hi Br 2 , S| T and Ci 4 Hi 2 , or H \AA/ H H HBr H The ortho position of the linking carbon atoms is proved by the synthesis of anthracene from o-tolylphenylketone when heated with zinc dust: xCH 3 (i) /CHv C 6 H 4 < C 6 H 4 < | >C 6 H 4 . + H 2 \rn P.TT, f*\ Nrw/ :O.C 6 H 6 (2) The constitution of anthracene indicates that the number of INTRODUCTION TO ORGANIC CHEMISTRY 390 substitution products should be still greater than those of naph- thalene. There should be, for instance, three monosubstitution products, there being three groups of positions, in which the members of each group are relatively the same, but differ from those of the other groups. These groups are, o: i, 4, 5 } 8; 0: 2, 3, 6, 757: 9, 10. The halogens act on anthracene in much the same way as on naphthalene. Concentrated sulphuric acid usually gives at once disulphonic acids. Nitric acid, however, first oxidizes anthracene to anthraquinone, and then converts this into nitro-derivatives when the acid is strong enough, or heated. Anthraquinone, Ci^HgC^, is very important as the source of alizarine. It is a product of the oxidation of anthracene and of many derivatives of anthracene. It is conveniently prepared by the method used for making naphthoquinone the oxidation by chromic acid of the hydrocarbon in glacial acetic acid. It forms yellow crystals which melt at 284 and sublime in yellow needles, and boils at 382. It is not as volatile with steam as other quinones are, lacks their pungent odor, is not reduced by sulphurous acid, and differs from them in some other respects, having rather the character of a diketone than -of a quinone. Such a structure is indicated by its synthesis from phthalic anhydride and phenol when heated with sulphuric acid, or from phthalic anhydride and benzene in the presence of aluminium chloride: f~*f\ /<-U\ AlCh CeH/ >0 + C 6 H 6 - > C 6 H 4 < >C 6 H 4 + H 2 O anhydride Anthraquinone Anthraquinone resists oxidation to an extraordinary degree. From anthraquinone only two mono-substitution products can be obtained, and it is easily seen that this exhausts the possibilities in tfte formula: 39 1 ANTHRACENE Alizarin, C^HeCMOH^, (i, 2) was formerly obtained from its glucoside which occurs in madder-root, but is now almost wholly prepared from anthracene. Anthraquinone is first made and then converted into monosulphonic acid by heating with fuming sulphuric acid containing 50 per cent, of sulphur trioxide. The sodium salt of this sulphonic acid is then heated in a closed vessel with sodium hydroxide and potassium chlorate. In this operation the sulphonic acid group is replaced by hydroxyl, and a second hydroxyl group formed. On acidifying the product of the fusion with hydrochloric acid, alizarin is precipitated: NaOH /CO\ C 6 H 3 .SO 3 H - > C 6 H/ >C 6 H 2 (ONa) 2 Anthraquinone sulphonic Sodium salt of alizarin acid By another synthesis of alizarin from phthalic anhydride and catechol by heating with sulphuric acid, it is shown that the hydroxyl groups are in the ortho position to each other: XXX /OH(i) /CO. /OH(i) C 6 H 4 < >0 + C 6 H 4 < ->C 6 H 4 <( >C 6 H< XXX X OH( 2 ) XXK X OH( 2 ) Phthalic anhydride Catechol Alizarin and by a study of the nitration products the formula is proved to be: O OH OH INTRODUCTION TO ORGANIC CHEMISTRY 392 Alizarin is only slightly soluble in water. From organic sol- vents it forms reddish-yellow crystals which melt at 289-290, and sublime in orange-colored needles. Its alkali salts are soluble, and give colored precipitates with the salts of most other metals. It is an adjective dye and gives fast colors with mordanted wool, silk, and cotton, forming " lakes" of different colors with the oxides of the metals whose salts are employed as mordants. When fer- ric salts are used, the color is violet-black; with chromium, claret; with aluminium or tin, red, etc. The formulas only of some of the other "condensed ring" hydrocarbons which are found in anthracite coal tar are given here. Fluorene was named from the violet fluorescence it shows. H H "CO" "YYT HS/H H Phenanthrene CH 2 -CH 2 HX\X\H H\/\/H H H Acenaphthene H H 2 H H H Fluorene H H CHAPTER XXX HETEROCYCLIC COMPOUNDS In the chapter on the cycloparaffins reference was made to the existence of compounds which contain a ring formation composed of different elements, and some illustrations were given of such compounds. Other heterocyclic compounds have been met with in our study of the aromatic substances chiefly compounds in which the heterogeneous rings are united with the benzene nucleus such as acid anhydrides, imides, etc. In compounds of this kind the ring is usually broken readily by various reactions, and does not show the persistent integrity and property of forming derivatives by replacement which distinguish the isocyclic compounds which we have studied in the aromatic group. There are, however, a number of compounds obtained from natural sources, and others which have been made in the labora- tory, which have these properties, and are proved to contain ring- nuclei of carbon and oxygen, carbon and sulphur, or carbon and nitrogen. The natural compounds of this group, whose structure has been definitely established, are mostly obtained from coal tar, or from the oil which results from the dry distillation of bones, and which was formerly used in medicine under the name of "Dip- pel's oil." A few of these compounds will be briefly described. It will be noticed that in all of them there are either five or six atoms in the ring-nucleus the conditions for greatest stability according to v. Baeyer's strain theory (p. 259). Furan or Furfuran, C^O, boiling at 32, is present in pine- wood tar. A substance which has the composition CBH 4 O 2 and the properties of an aromatic aldehyde, was discovered in 1849 393 INTRODUCTION TO ORGANIC CHEMISTRY 394 in the products of the dry distillation of bran (furfur). This aldehyde, whose formula may therefore be written C^aO.CHO, is readily oxidized to pyromucic acid, C^sO.CO.OH; andfuran was first obtained by the distillation of barium pyromucate. The HC = CHk formula assigned to f uran is I / O This is based on HC = CH/ the synthesis of furan derivatives, and is supported by the resemblance in properties between some of these derivatives and corresponding aromatic compounds. The oxygen atom of furan can be shown to be neither hydroxyl or carboxyl oxygen. The most important derivatives are the two compounds which have been mentioned; HC = CH fur fur aldehyde, HC = C - CHO HC = CH and pyromucic acid, yO HC = C.CO.OH The aldehyde is formed when pentoses (p. 201) are boiled with, dilute sulphuric or hydrochloric acid. It gives an intense red dye when treated with aniline and hydrochloric acid, and hence its formation, as shown by this test, is a convenient means for recognizing pentoses. It resembles benzaldehyde in its reactions thus with alcoholic potash it yields pyromucic acid (salt) and furfuryl alcohol, C^aO.C^OH. As its name indicates, pyro- mucic acid was originally obtained by dry distillation of mucic acid (p. 206). Thiophene, C 4 H 4 S, gives a blue color with isatin (an oxidation product of indigo) and sulphuric acid (indophenine reaction). This reaction was thought to be characteristic of benzene, and the failure of the test in some benzene which had been made from 395 HETEROCYCLIC COMPOUNDS benzoic acid led to the discovery of thiophene in commercial benzene by V. Meyer (1883). Thiophene is present in coal-tar benzene to the amount of about 0.5 per cent. It can be separated from benzene by the fact that its sulphonic acid is formed more readily than that of benzene. By heating with water under pressure thiophene is regenerated from its sulphonic acid. Methyl derivatives of thiophene are found in coal-tar toluene, xylenes, etc. Thiophene is a colorless liquid boiling at 84, and cannot be separated from benzene by distillation. It is somewhat heavier than water and has no characteristic odor. Its aromatic character, as shown by its reactions, is pronounced. Thiophene has been synthesized by heating sodium succinate with phosphorus trisulphide: CH 2 .C).ONa HC = CH PSt \ S CH 2 .CO.ONa HC = CH Sodium succinate Thiophene Its structure as given in the above formula is inferred from this and other syntheses, and is seen to be of the same type as that of furan, with sulphur in place of oxygen. Pyrrol, C^sN, is a colorless oil which has an odor resembling that of chloroform, and which boils at 131. It is found in coal tar and bone oil. Its name is from its property of giving a bright red (irvppos) color to a pine shaving moistened with hydrochloric acid. It can be synthesized by distilling succinimide with zinc dust: CH 2 .CO HC = CH \ NH \ CH 2 .CO HC = CH Succinimide Pyrrol NH This and other syntheses, and its reactions have led to the establishment of the structure shown above, which makes it a INTRODUCTION TO ORGANIC CHEMISTRY 396 secondary amine. It is, however, only a weak base, dissolving slowly in dilute acids in the cold, and it is changed by strong acids to a resin. As a consequence, no sulphonic acids can be obtained, and nitro derivatives only by an indirect method. Pyrrol shows more striking analogies to the phenols than to the aromatic hydrocarbons. The imide (NH) hydrogen, like the phenol hydroxyl hydrogen, can be replaced by potassium forming potassium pyrrol, C^tNK, and the hydrogen atoms of the CH groups are replaced by halogens with great readiness. It also couples directly with diazonium salts giving azo dyes. Ho- mologous pyrrols occur in bone oil, and can be made by passing vapors of pyrrol and alcohols over zinc dust. Pyrrol derivatives are very widely distributed in nature. The pyrrol ring is found to be present in certain alkaloids, and haemoglobin (the red color- ing matter of the blood) and chlorophyll are to be considered as derivatives of methyl-propyl pyrrol. Pyridine, CsHj^N, a liquid of very disagreeable odor, boiling at 115, can be obtained from the "light oil" distillate from coal tar, and also from bone oil. Syntheses of pyridine and its reac- tions indicate that it may be regarded as benzene with one CH group replaced by a nitrogen atom N HC CH II I HC CH \/ CH It is a very stable compound, behaving very much like benzene, but it cannot be nitrated, and gives sulphonic and halogen deriva- tives with greater difficulty than benzene. It is, however, easily reduced by sodium and alcohol, and adds six hydrogen atoms to form piperidine, 397 HETEROCYCLIC COMPOUNDS <2. 2\ >NH CH 2 .-CH/ a liquid of pepper-like odor, boiling at 106, which is also obtained from pepper. Pyridine is a tertiary amine as its formula shows. Its basic properties are stronger than those of pyrrol, and about the same as aniline, its solutions being weakly alkaline, and fairly stable salts being formed. Homologues of pyridine occur with it, and can also be synthe- sized. The side chains of these homologues are oxidized to car- boxyl groups, as in the case of toluene, etc. One of them is called nicotinic acid because it is also a product of the oxidation of the alkaloid nicotine. Pyridine and its homologues, the pyridine bases, are found to occur in the products of distillation of almost all kinds of nitrogenous substances; and among the naturally occurring members of the pyridine group are several important alkaloids. Quinoline, C 9 H 7 N, which occurs in coal tar and bone oil, is a liquid boiling at 239. It has been synthesized by methods which establish its structure as a condensation of benzene with pyridine: CH N HC C CH I II I HC C CH C C H H Its name is from its discovery as a product of the distillation of quinine. Quinoline is a tertiary base which forms crystalline and very soluble salts with one equivalent of acids. It forms derivatives like other aromatic compounds. It has a penetrating odor and a strong antiseptic action. When oxidized by potassium permanganate the benzene ring breaks down with the production of carboxyl groups and the formation of quinolinic acid: INTRODUCTION TO ORGANIC CHEMISTRY 398 N /\ HC C - CO.OH II I HC C - CO.OH \S CH This when heated is decomposed into nicotinic acid and when dis- tilled with lime gives pyridine. Quinoline adds hydrogen atoms easily, which go almost exclusively into the pyridine ring. An isomer of quinoline, called isoquinoline, also occurs in coal tar. It melts at 21 and boils at 237. The nitrogen atom in isoquinoline is not directly united to the benzene nucleus as in quinoline, but occupies what in naphthalene is called the /3-posi- tion. Isoquinoline is more basic than quinoline, and absorbs carbon dioxide from the air. Indigo, CieHioN2O, is a compound containing two heterocyclic groups, as shown in the following formula which is seen to contain two pyrrol rings: H H C H H C /\ I I /\ HC C NX /N C CH HC C C' C C CH y O O C H H The history of the elucidation of the structure of indigo is very interesting. 1 The following is a brief summary. In 1826 aniline was obtained from indigo by dry distillation. In 1841, anthrani- lic acid (p. 360) was found to be a product of its oxidation. Later, it was found that when indigo was oxidized by nitric acid 1 See Sidgwick's "Organic Chemistry of Nitrogen," 399 HETEROCYCLIC COMPOUNDS was produced, whose constitution was afterward established as x co \ C 6 H 4 CeH 4 <\ - > X N0 2 X NH 2 o-Nitrophenylacetic o-Amidophenylacetic acid acid /CHzv o /CO\ 4 < >CO - >C 6 H/ >CO N NH' X NH/ C 6 H Oxindol Isatin In 1870 indigo was made from isatin by treatment with phos- phorus pentachloride, followed by reduction. This was the first true synthesis of indigo. Its structure, however, was not yet established. The heterocyclic hydrogen compound of which isatin is a /CH. derivative is indol, CeH 4 <( /CH, which is obtained from / indigo or oxindol on distillation with zinc dust, and can be synthesized in several ways. It may be regarded as the mother substance of indigo and its derivatives. It is a crystalline solid, melting at 52 and boiling at 245. The presence of the pyrrol ring in indol is evident in its formula. It resembles pyrrol in many respects and gives the pyrrol reaction with a pine shaving. It was shown that isatin could be reduced by successive steps to indol without the production of indigo: P O CH.OH C 6 H 4 < / N >CO-C 6 H NNH/ Isatin Dioxindol Oxindol INTRODUCTION TO ORGANIC CHEMISTRY 400 C 6 H 4 < Indol In these ways the relation of indigo to indol was determined and its structure was finally established by a synthesis by Baeyer; in 1882 of o-dinitro-diphenyl-diacetylene, c = c - c = Cv CeH 4 C 6 H< XXXOH Chloracetic acid Phenylglycine o-carboxylic acid V CH 2 -> C 6 H C = C >C 6 H 4 X CCK X CCK Indoxyl Indigo 401 HETEROCYCLIC COMPOUNDS The commercial success of the process depends largely upon (i) the cheapness of naphthalene, which is produced from coal tar in great excess of the demand, and (2) on the comparatively inexpensive production of fuming sulphuric acid, for oxidation of the naphthalene, by the contact process, and the fact that the sulphur dioxide which results from the oxidation is readily reoxidized by this same process. Another synthesis that runs on simpler lines and gives a good yield of indigo is now worked in England. The starting point here is aniline, which is treated with chloracetic acid with the production of phenylglycine, C 6 H 5 NH.CH 2 .CO.OH. This when heated with sodium amide, or sodium in the presence of ammonia, is dehydrated with the formation of indoxyl which gives indigo on oxidation by a current of air. Natural indigo occurs as indican (probably a glucoside of in- doxyl) in the indigo plant. It is obtained by immersing the leaves in water and stirring to promote atmospheric oxidation. An enzyme present in the leaves breaks up the indican into glucose and indoxyl, and the latter is oxidized to indigo. Indigo is a dark blue substance, insoluble in most ordinary sol- vents, but dissolving in aniline, melted paraffin, etc., and crys- tallizes from these solutions. It forms a dark red vapor when heated, and under diminished pressure can be sublimed without decomposition. In dyeing it is either converted into a soluble disulphonic acid, or it is reduced to the leuco-base, indigo white (probably a di-indoxyl), by glucose in alkaline solution. In the former case it dyes directly; in the latter, the indigo white depos- ited on the fibres is oxidized to indigo on exposure to the air. CHAPTER XXXI ALKALOIDS PROTEINS The alkaloids are organic bases which occur in plants. Most of them have a powerful physiological action and many are ex- tremely poisonous. They were long considered to be substituted ammonias or ammonium bases. But while this is true of some of them, such as muscarine and amanitine, which occur in toad-stools, most of the important alkaloids are now known to be heterocyc- lic compounds which contain at least one nitrogen atom in their nucleus, and may therefore be regarded as derivatives of pyrrol, pyridine, quinoline, or iso-quinoline. Some of them have been synthesized. Most of the alkaloids are crystalline solids, only a few, such as nicotine and coniine, are liquids. They have a bitter taste, are mostly insoluble in water, but dissolve in alcohol, and to some extent in ether. They have an alkaline reaction, dissolve in acids forming salts which are often well-crystallizing compounds. Most of the alkaloids are precipitated from their acid solutions by certain "general alkaloid reagents": tannic, picric, molybdic, phosphomolybdic, and phosphotungstic acids, potassium mercuric iodide, etc. These precipitates are decomposed by alkalies with liberation of the alkaloids. Many of the alkaloids are optically active and almost all of them are levo rotatory. The alkaloids are often identified by color reactions. A few of the important alkaloids are here briefly described. Coniine, CsHvN, occurs in hemlock, 1 and was the first alkaloid 1 The European poison hemlock, not the American hemlock, which is a species of pine. 402 403 ALKALOIDS to be synthesized. Its structural formula shows the pyridine ring, and that it is more directly a derivative of piperidine (p. 396), being a-propylpiperidine, H 2 C H 2 C CH 2 I I H 2 C CH.CH 2 .CH 2 .CH 2 Y H It is one of the few dextro rotatory alkaloids. Conime is a color- less liquid boiling at 167. Nicotine, doH 14 N 2 , is also a liquid alkaloid, obtained from tobacco. It boils at 247. On oxidation with permanganate it yields nicotinic acid (p. 397), and therefore contains the pyridine ring. The pyrrol nucleus is also present, the formula for nicotine being, It is exceedingly poisonous, but when tobacco is burned most of the nicotine is volatilized or destroyed. Nicotine from tobacco is levo rotatory, but both optical forms have been obtained from the synthetical product. The two forms produce somewhat different physiological effects. 4 Atropine, Ci7H 23 NO 3 , like all alkaloids which contain oxygen, is INTRODUCTION TO ORGANIC CHEMISTRY 404 a solid. It melts at 115. It is the principal alkaloid of bella- donna or deadly nightshade, and is the most important alkaloid of the nightshade family. Its use by oculists to dilate the pupil of the eye is well known. The complicated structure of atropine has been determined. Cocaine, Ci7H 2 iNO 4 , from coca-leaves, is much used as a local anesthetic. It is related in structure to atropine. When heated with hydrochloric acid it gives benzoic acid, methyl alcohol, and ecgonine, a carboxylic acid of tropine, a substance which is ob- tained from atropine by hydrolysis. Morphine, CiyHigNOs, is the chief alkaloid of opium, which is the dried juice of the seed capsules of a variety of poppy. Strychnine, C 2 iH22N 2 O2, andbrucine, C2 3 H26N 2 O4, are obtained from the Strychnos nux wmica. Quinine, C2oH 24 N 2 O 2 , is the most important of the twenty-four alkaloids which have been obtained from "Peruvian bark." Quinine melts at 177. Its structure is evidently very complicated and has not been definitely established. It is known to contain the quinoline ring. Dilute solutions of its salts show a fine blue fluorescence. It is usually employed in medicine in the form of its soluble sulphate. Proteins Among the organic substances present in animals and plants, the compounds called proteins (irpureLov, pre-eminent) are of very great importance. In animals by far the larger part of the tissue solids is generally protein, and protein-containing foods are absolutely essential for their nourishment. Proteins, like the fats and carbohydrates, are found only in living matter or as products of living matter. The proteins in living matter are such a mixture of different kinds, and they are in general so unstable, that the extraction of individual, pure pro- teins is usually very difficult. In a few instances proteins that 45 PROTEINS are apparently pure have been separated from animal tissues. Plants, unlike animals, store proteins as a reserve in their seeds, and these proteins are very stable. From seeds and nuts, there- fore, proteins may be obtained with comparative ease by extrac- tion with water, alcohol, or a solution of salt. The composition of the proteins varies considerably. They all contain carbon, hydrogen, nitrogen, and oxygen, usually sulphur, and sometimes also phosphorus and iron. Typical proteins con- sist of carbon, about 52 per cent.; hydrogen, 7 per cent.; nitrogen, 15 per cent.; oxygen, 23 per cent.; sulphur, 0.5 per cent.; phos- phorus, 0.3-5 P er cent - Many proteins are colloids, and advantage is taken of this property in separating them from salts and other crystalloids by diffusion through membranes. Many of them occur naturally in crystalline form in seeds and nuts, and have been crystallized in the laboratory. Their solutions are optically active and most of them are levo-rotatory. They all have a more or less amphoteric character. In aqueous solution they are coagulated by boiling or on the addition of strong alcohol or inorganic acids. Insoluble compounds are formed with solutions of salts of most of the heavy metals, and also with weak acids such as tannic, picric, and phos- photungstic acids. We owe our present knowledge of these exceedingly complex substances largely to the work of Kossel and of Emil Fischer. It has been found that the final products of the hydrolysis of proteins are ammo acids (p. 252), of which glycine or aminoacetic acid is the simplest representative. Intermediate compounds called polypeptides are formed which are condensation products of various amino acids, such as glycylglycine, NH 2 CH 2 CO.NH. CH 2 .CO.OH, from two molecules of glycine. From these facts and from other considerations the conclusion was drawn that the proteins are largely made up of a-amino acids linked through their amino and carboxyl groups, the number and kind of these amino acids being variable in different proteins. INTRODUCTION TO ORGANIC CHEMISTRY 406 This view is confirmed by the synthesis of more than one hundred complex polypeptides that have the properties of natural proteins after their modification by contact with reagents. One of the most complex of these synthesized substances contained eighteen amino acid groups and had a molecular weight of 1213. The classification of the proteins adopted by the American Society of Biological Chemists is as follows. I. Simple Proteins. Albumins, Globulins, Glutelins, Prolamins, Albuminoids, Histones, Protamins. II. Conjugated Proteins. Nucleoproteins, Glycoproteins, Phos- phoproteins, Haemoglobins, Lecithoproteins. III. Derived Proteins. Primary derivatives: Proteans, Meta- proteins, Coagulated Proteins. Secondary derivatives: Pro- teoses, Peptones, Peptides. The simple proteins and the conjugated proteins are all sub- stances that are supposed to exist in the tissues and juices of ani- mals and vegetables. The conjugated proteins consist of one or more molecules of albumin associated with some other substance of a different nature, such as sugar. They do not always contain sulphur, but phosphorus is a constituent of many of them. Sev- eral, such as haemoglobin, the red coloring matter of blood, contain iron. The derived proteins represent the first stages in the process of decomposition that the proteins, simple or conjugate, undergo in contact with almost any reagent. The solubility is affected by the simple operation of diffusion; and contact with acids, alkalies, or metallic salts causes incipient hydrolysis. While the exact steps that lead to the formation of the natural proteins are obscure, it is probable that they are produced by the condensation of decomposition products of the carbohydrates with ammonia. A few examples of the variety that proteins offer may be of interest. White of egg and serum albumin are illustrations of the albumins, which are the best known of the proteins; to the albu- 407 PROTEINS minoids belong: collagen, the chief constituent of connective tis- sue, bone, and cartilage, which yields gelatin or glue by partial hydrolysis; elastin in the elastic tissue of ligaments and walls of arteries; and keratin which contains sulphur up to 5 per cent., and is the principal constituent of epidermis, hair, feathers, and horny tissues. An example of a phosphoprotein is casein, chief nitrogeneous constituent of milk, which is coagulated by rennet. The molecular weights of the proteins are not accurately known, but they are certainly very large. Osborne has calculated the molecular weights in a number of instances from the percentage of sulphur present, on the assumption that there are two or more atoms of sulphur in the molecule. This assumption is based on the fact that cystine, whose molecule is known to contain two atoms of sulphur, is a constituent of many of these proteins. The following is an illustration of the method of calculation. A globin has the percentage composition: C = 54.98, H = 7.20, N = 16.89, O = 20.51, S = 0.42. If there are two atoms of sulphur in the molecule, weighing 64, the weights in atomic weight units of each of the other elements is readily calculated, and the sum is the molecular weight. From these figures an empirical formula may be obtained. In the case of this globin the figures for the molecular weight are 15,274, and the formula is: Similar figures are obtained for other proteins by this and other methods. INTRODUCTION TO ORGANIC CHEMISTRY 408 Specific Rotations of Some Optically Active Substances The angle through which plane polarized light is rotated by solutions of optically active substances depends on the concentration, the length of solu- tion through which the light passes, the wave-length of the light, and the temperature, as well as on the nature of the substance. The Specific Rota- tion is the rotation produced with yellow (sodium) light in passing through one decimeter of a solution that has one gram of substance in each cubic centimeter, at 2oC. In the following formula [a] is the specific rotation, a the observed angle of rotation, I the length of the solution in decimeters, v the volume in cubic centimeters, and w the weight of substance in the solution. D indicates that the measurement is made with sodium light. In the case of liquid substances examined without a solvent, the formul- becomes [a] D -j in which d is the density. Arabinose Xylose Rhamnose Glucose Fructose Invertose Galactose Mannose Sorbose C 6 (CH 3 )H 9 O 6 C 6 Hi 2 6 C 6 H 12 O 6 C 6 H 12 O 6 C 6 H 12 6 C 6 H 12 O 6 + 105 + 19 +9 + 52 -93 -19 +81 + H 42 .0 .0 .0 7 .8 .6 .0 .0 .0 Sucrose Ci2H 22 Ou Lactose Ci 2 H 22 Ou Maltose Ci 2 H 22 On Raffinose CisH^Oie Tartaric acid Saccharin Quinine sulphate Nicotine Camphor (in alcohol) Oil of turpentine MD +66. +52. + 138. +104. +15. +88. -213. -77. +56. +36. 5 5 o 61 7 7 15 o lonization Constants of Some Organic Acids and Bases Monobasic Acids Formic Acetic Glycollic Glyoxylic Chloracetic Dichloracetic Trichloracetic k X HCO.OH CH 3 .CO.OH CH 2 OH.CO.OH CHO.CO.OH CH 2 C1.CO.OH CHC1 2 .CO.OH CCls.CO.OH 21.4 1.85 15-0 50.0 5,000.0 30,000 . o 409 IONIZATION CONSTANTS OF ORGANIC ACIDS AND BASES Propionic Lactic /3-Hydroxypropionic Glyceric a-Chlorpropionic /3-Chlorpropionic Butyric 7-Oxybutyric a-Chlorbutyric /3-Chlorbutyric 7-Chlorbutyric Fumaric Maleic Valeric Benzoic o-Oxybenzoic wi-Oxybenzoic ^-Oxybenzoic Dioxybenzoic Dioxybenzoic Dioxybenzoic Dioxybenzoic. 0-Nitrobenzoic w-Nitrobenzoic 0-ChJorbenzoic w-Chlorbenzoic ^-Chlorbenzoic Cinnamic Sulphanilic Anthranilic Dibasic Acids Carbonic Oxalic Malonic Tartronic Succinic Malic Tartaric 0-Phthalic m-Phthalic CH 8 .CH 2 .CO.OH CH 3 .CHOH.CO.OH CH 2 OH.CH 2 .CO.OH CHaOH.CHOH.CO.OH CH 3 .CHC1.CO.OH CH 8 C1.CH 2 .CO.OH CH 3 .CH 2 .CH 2 .CO.OH CH 2 OH.CH 2 .CH 2 .CO.OH CH3.CH,.CHC1.CO.OH CH 3 .CHC1.CH 2 .CO.OH CH 2 .C1.CH 2 .CH 2 .CO.OH CO.OH.CH:CH.CO.OH CO.OH.CHrCH.CO.OH CH 3 .CH 2 .CH 2 .CH 2 .CO.OH C 6 H 6 .CO.OH C 6 H 4 (CO.OH)(OH) i, 2 C 6 H 4 (CO.OH)(OH) i, 3 C 6 H 4 (CO.OH)(OH) i, 4 C 6 H 3 .(CO.OH)(OH; 2 1,2,3 C 6 H 3 .(CO.OH)(OH) 2 i, 2, 4 C 6 H 3 .(CO.OH)(OH) 2 i, 2, 6 C 6 H 3 .(CO.OH)(OH) 2 i, 3, 4 C 6 H 4 .(CO.OH)NO 2 i, 2 C 6 H 4 .(CO.OH)NO 2 i, 3 C 6 H 4 .(CO.OH)C1 i, 2 C 6 H 4 .(CO.OH)C1 i, 3 C 6 H 4 .(CO.OH)C1 i, 4 C 6 H 6 .CH:CH.CO.OH NH 2 .C 6 H 4 .SO 3 H C 6 H 4 .(CO.OH)NH 2 i, 2 CO(OH) 2 (CO.OH) 2 CH 2 (CO.OH) a CHOH(CO.OH) 2 CO.OH.CH 2 .CH 2 .CO.OH CO.OH.CHOH.CH 2 .CO.OH CO.OH(CHOH) 2 CO.OH C 6 H 4 (CO.OH) 2 i, 2 C 6 H4(CO.OH)i i, 3 1.4 13-8 3-i 23.0 147.0 8-5 i-S 1.9 139.0 8-94 3-o 100. o 1,500.0 1.6 6.6 IOO.O 8.3 2.8 IIO.O 51.0 5,000.0 3-3 650.0 36.0 132.0 15-5 130.0 3.68 62.0 I .O 0.03 3,800.0 163.0 500.0 6.6 40.0 IIO.O I2O.O 29.0 INTRODUCTION TO ORGANIC CHEMISTRY 410 ^-Phthalic Phenylacetic Phenol 0-Nitrophenol m-Nitrophenol Dinitrophenol Dinitrophenol Dinitrophenol Picric acid Bases Methylamine Dimethylamine Trimethylamine Glycine Aniline Benzylamine Diazoniumhydroxide Ammonia Boric acid Phosphoric acid Sulphuric acid C 6 H 4 (CO.OH) 2 i, 4 C 6 H 6 .CH 2 .CO.OH CH 6 OH C 6 H 4 (OH)N0 2 i, 2 C,H 4 (OH)N0 8 i, 3 C 6 H 3 (OH)(N0 2 ) 2 i,2, 4 C.KUOHXNOOu i, 2,6 C 6 H,(OH)(N0 2 ) 2 i, 3, 6 CH 2 (OH)(N0 2 ), CH 3 NH 2 (CH 8 ) 2 NH (CH 3 ) 8 N CHiNH 2 .CO.OH C 6 H 6 NH 2 C 6 H 8 .CH 2 NH a CH 6 N 2 OH 5-3 0.000013 o . 006800 o . 000530 8.0 17.4 0.7 16,000.0 50.0 74.0 7-4 0.000018 0.000046 2.4 123.0 1.8 0.00006 900.0 45,000.0 BOOKS FOR REFERENCE AND COLLATERAL READING Books for Reference and Collateral Reading MEYER UND JACOBSON, Lehrbuch der Organischen Chemie. ROSCOE AND SCHLORLEMMER, Organic Chemistry. COHEN, J. B., Organic Chemistry for Advanced Students. THORPE, T. E., Dictionary of Applied Chemistry. MARTIN, GEOFFREY, Industrial and Manufacturing Chemistry; Organic. SroowiCK, N. V., Organic Chemistry of Nitrogen. STEWART, A. W., Recent Advances in Organic Chemistry. STEWART, A. W., Stereochemistry. KEANE, C. A., Modern Organic Chemistry. (Stereochemistry and Sugars.) THOMSEN, JULIUS, (Translated by Katharine A. Burke) Thermochemistry. CAIN AND THORPE, Synthetic Dyestuffs. FOWLER, G. J., Introduction to Bacteriological and Enzyme Chemistry. CONHEIM, OTTO, Enzymes. PLIMMER, R. H. A., Chemical Constitution of the Proteins. MATHEWS, A. P., Physiological Chemistry. INDEX Where more than one reference is given, the most important is in heavy type. Acenaphthene, 392 Acetals, 79 Acetaldehyde, 77 Acetamide, 137 Acetanilide, 306 Acetates, 96, 100 Acetic acid, 94, 98 electrolysis, 29 glacial, 96 structure, 97 Acetoacetic acid, 174 ethyl esters, 174 Acetone, 89 Acetonitrile, 100, 129, 138, 153 Acetonylacetone, 163 Acetophenone, 348 Acetoxime, 79 Acetyl chloride, 114 Acetylene, 47 ...J^ C $. H ^ series, 42, 45 Acetylformic acid, 173 Acid anhydrides, 117-119 table, 117 bromides, 116 chlorides, 114 table, 117 iodides, 116 Acids, activity, 250, 362 aliphatic, 94, 100, 107 aromatic, 353-358 dibasic, 177-195 Acids, general properties, 100 halogen-substituted, 247-251 hydroxy, 163-173, 182-197, 36i methods of formation, 98, 178, 353 nomenclature, 102 tables, 101, 177, 197, 356 unsaturated, no, 186, 357 Acrolem, 86, 159 Acrose, 85 Acrylic acid, HO aldehyde, 86 Acyl, 114 halides, 114-117 Aesculin, 202 Alanine, 255 Albumins, 406 Alcohol- acids, 163 Alcoholates, 62 Alcohols, 57 aromatic, 327, 339 classification, 65 formulas, 57 isomeric, 65, 68 oxidation, 64, 112, 161 polyhydric, 155, 157 primary, table, 67 reactions, 62 unsaturated, 68 Aldehyde-alcohols, 162 Aldehyde-ketones, 163 Aldehyde-resins, 82 412 INDEX Aldehydes, aliphatic, 76 aromatic, 343~347 condensation, 82, 345 halogen derivatives, 91, 247 polymerization, 81 reactions of, 78, 344 series, 83 table, 87 tests, 86 unsaturated, 86 Aldol, 82, 162 Aldoses, 199 Aldoximes, 79 Alizarin, 388, 391 Alkaloids, 402-404 Alkenes, 44, 47 Alkyl, 22 cyanides, 153 disulphides, 240 halides, 31, 122 reactions of, 33 tables, 33 isocyanates, 1540 isocyanides, 154 isonitriles, 154 sulphoxides, 240 Alkylene oxides, 157 Allantoin, 234 Alloxan, 234 Allyl alcohol, 69 chloride, 55 Amanitine, 402 Amides, 137-142, 359 reactions, 139 structure, 141 table, 142 Amido group, 127 Amidol, 338 Amines, aliphatic, 127-136 reactions, 131 table of, 136 Amines, aromatic, 301 table, 312 Aminoacetic acid, 254, 405 Amino acids, 252-256, 360, 405 alcohols, 251 aldehydes, 251 group, 127 Aminophenols, 338 Aminopropionic acid, 255 Aminoazo compounds, 317 Ammonium carbamate, 229 cyanate, 150, 231 thiocyanate, 153 Amygdalin, 147, 202, 345, 364 Amyl alcohols, 67, 170 table, 68 Amyloid, 222 Anethol, 347 Aniline, 303-306 derivatives, 306-310 homologues, 310 Anisaldehyde, 347 Anisic acid, 365 Anisol, 341 Anthracene, 282, 388 Anthranilic acid, 360 Anthraquinone, 390 Antifebrine, 307 Antipyrine, 307 Arabinose, 201, 221 Argol, 189 Aromatic acids, 353-3700 table, 356 alcohols, 339-341 aldehydes, 343-348 amines, 301-312 table, 312 ethers, 341 halogen compounds, 284-288 table, 286 hydrocarbons, 265, 273, 282 INDEX 414 Aromatic hydrocarbons, table, 276 ketones, 348 nitro compounds, 293-298 rules for substitution, 299 sulphonic acids, 288-292 table, 292 Arsines, 136 Aryl radicals, 272 Asparagine, 255 Aspartic acid, 255 Aspirin, 365 Asymmetric carbon atoms, 168 Atropine, 403 Azobenzene, 322 Azo-compounds, 321, 322 dyes, 325 Azoxybenzene, 322 Azoxy-compounds, 322 B Bakelite, 339 Beer, 61 Beeswax, 125 Beet sugar, 212 Benzal chloride, 288 Benzaldehyde, 344, 345 Benzamide, 359 Benzene, 265-272 derivatives, isomerism of, 268 homologues, 273 structure, 267-271 Benzidine, 323 Benzil, 349 Benzine, 23 Benzoic acid, 355 Benzoin, 349 gum, 355 Benzonitrile, 359 Benzophenone, 348 Benzopurpurin, 387 Benzoquinone, 350 Benzotrichloride, 288 Benzoylchloride, 358 Benzoylglycine, 359 Benzylalcohol, 340 Benzylamines, 311 Benzylchloride, 287 Betame, 255 Biuret, 232 test, 233 Borneol, 380 Brandy, 6 1 Bromacetylene, 55 Bromalin, 133 Bromhydrins, 247 Brucine, 404 Butadiene, 378 Butter fat, i6oa Butyl alcohols, 65 Butyric acids, 108 Cacodyl, 13? Caffeine, 235 Calcium cyanamide, 145 Camphene, 378 Camphor, 379 artificial, 377, 380 Cane-sugar, 211 Carbamic acid, 229 Carbinol, 66 Carbohydrates, 198 Carbolic acid, 328 Carbon, detection, 5 disulphide, 242 estimation, 8 oxysulphide, 242 tetrachloride, 40 Carbonic acid, 227 amides, 229 415 INDEX Carbonic acids, esters, 228 sulphur derivatives, 243 Carbonyl chloramide, 233 chloride, 39, 227 group, 88, 91 Carboxyl group, 98 Carbylamine reaction, 132, 154 Carvacrol, 332 Casein, 407 Catechol, 333, 366, Celluloid, 223 Cellulose, 221 nitrates, 223 triacetate, 223 Cephalin, 135 Chavicol, 333 Chloracetic acids, 248 Chloral, 80, 91, 245, 247 alcoholate, 92 hydrate, 91 Chloralcohols, 245 Chloranil, 352 Chlorethers, 246 Chlorination, 31, 284 Chlorformic acid, 248 Chlorhydrins, 47, 156, 246 Chloroform, 39 Choline, 134 Chromophore groups, 324, 352 Chrysene, 392 Cineol, 381 Cinnamic acid, 357 aldehyde, 346 Cinnamyl alcohol, 340 Citral, 87 Citric acid, 195 Coal tar, distillation, 266 Cocaine, 404 Collodion, 223 Collogen, 407 Congo dyes, 323, 387 Coniine, 402 Creatine, 254 Cresols, 332 Crotonic acids, in aldehyde, 87 Cumene, 278 Cummic aldehyde, 346 Cyanamide, 149 Cyanic acid, 149 Cyanogen, 145 chloride, 149 compounds, 144 Cyanuric acid, 149 chloride, 148 Cyclic compounds, 257 Cyclohexane, 373 Cycloparaffins, 257-261, 373 stereochemistry, 259 table of, 258 Cymene, 278 Dextrin, 219, 220 Dextrose, 202 Diacetylene, 50 Diastase, 219 Diazoamino-compounds, 316 Diazo compounds, 305, 313-320 reactions, 315 structure, 314, 318 Diazonium compounds, 314 Diazotization, 313 Dibasic acids, table, 177 Dibenzylbenzene, 282 Dichloracetone, 93 Digallic acid, 367 Dihydrobenzene, 371 Dihydroxy acetone, 161, 201' Di-olefines, 44, 50 INDEX 416 Diphenyl, 282 amine, 311 carbinol, 340, 349 ether, 341 ethyl ene, 282 methane, 349 Dipropargyl, 50 Disaccharoses, 211 Distillation, fractional, 7, 23 in steam, 8 of coal tar, 266 of wood, 59 Bisulphides, 240 Divinyl ether, 75 Dulcitol, 205 Durene, 278 Dyes, 323-326 Dynamite, 160 E Elaidic acid, no Elementary analysis, 6, 8 Energy, storage in plants, 223 Enzymes, 224 Eosin, 334, 370 Erytttfose, 201 Essential oils, 160 Esters, 35, 63, 119, 123 of carbonic acid, 228 of inorganic acids, 119-122 of organic acids, 123, 125 reactions, 124 table of ethyl, 123 fitard's method, 344 Ethane, 27 Ether, 70 Ethereal salts, 35, 63, 119, 123 Ethers, aliphatic, 70 aromatic, 341 Ethers, mixed, 74 reactions, 72 table, 75 Ethoxides, 63 Ethyl acetate, 123-125 alcohol, 60-62 ether, 70 hydrogen sulphate, 120 malonate, 181 mercaptan, 238 nitrite, 122 propargylether, 75 sulphate, 120 sulphuric acid, 120 Ethylene, 46, 120 alcohol, 155, 157 bromide, 46 glycol, 155, 157 oxide, 157 series, 42, 45 Ethylidene chloride, 41 Eucalyptol, 381 Eugenol, 342, 347 Fats, 108, 160 Patty acids, 107 Fenchone, 380 Fermentation, 60, 224 acetic, 94 alcoholic, 60, 224 butyric, 108 lactic, 165 Fittig's synthesis, 273, 287 Fluoran, 369 Fluorene, 392 Fluorescein, 334, 370 Formaldehyde, 83 polymerization, 85 Formalin, 84 INDEX Formamide, 139 Formates, 106 Formic acid, 102, 178 Formulas, empirical, 9 establishment, 9-12 molecular, 10 structural, 12, 1 8 Friedel and Craft's synthesis, 274, 348, 349, 354. 389 Fructose, 204 inactive, 208 Fruit sugar, 204 Fulminic acid, 151 Fumaric acid, 186 Furan and derivatives, 393 Fusel oil, 66 Galactose, 205 Gallic acid, 366 Gallotannic acid, 367 Gasoline, 23 Gattermann's reaction, 316, 344 Geranial, 87, 374 Geraniol, 87 Gluconic acid, 204 Glucose, 202 Glucosides, 202, 345 Glyceric acid, 172 Glycerol, 158 Glyceryl aldehyde, 201 trinitrate, 159 Glycine, 254, 405 Glycocoll, 254 Glycogen, 220 Glycol, 155 Glycolide, 172 Gly collie acid, 161, 163 aldehyde, 161, 162, 200 Glycols, 155 Glyoxal, 161, 163 Glyoxylic acid, 161, 173 Grape-sugar, 202 Grignard's reagents, 36 Grignard's syntheses, 28, 36, 66, 81, 89, 96, 99, 274, 287, 354 Guaiacol, 333, 342 Guanidine, 233 Guanine, 235 Gums, 221 Gun-cotton, 223 H Halogen carriers, 31, 284 derivatives, aromatic, 284- 288 hydrolysis, 410 of acids, 247 of aldehydes, 91, 247 of ketones, 93, 247 of paraffins, 31 of unsaturated hydrocar- bons, 54 tables, 33, 40 Halogenhydrins, 246 Halogens, detection, 6 estimation, 9 Heats of combustion, 51 of formation, 51 Heterocyclic compounds, 393-401 Hexachlorethane, 40 Hexahydrobenzene, 282, 371 Hexahydrobenzoic acid, 355, 375 Hexahydroxylbenzene, 336 Hexamethylene, 259, 373 tetramine, 84, 133 Hexoses, 201-211 stereochemistry, 210 Hippuric acid, 359 INDEX 418 Hofmann's reaction, 129, 361 Hydracrylic, acid, 171 Hydramines, 251 Hydrazines, 317 Hydrazo-compounds, 322 Hydrazones, 80, 208, 318 Hydro-aromatic compounds, 371 acids, 375 Hydrobenzenes, 371 Hydrocarbons, aromatic, 265-283 carbocyclic, 257-261 halogen derivatives, 31, 54, 284 hydro-aromatic, 371, 383 methane series, 15 saturated, 15 tables, 17, 45, 258 unsaturated, 42, 50 Hydrocinnamic acid, 358 Hydrocyanic acid, 147 Hydrogen, detection, 6 estimation, 8 Hydromellitic acid, 376 Hydroquinone, 335 Hydroxy acids, 163, 361 dehydration, 171 tables, 197, 364 Hydroxyazo compounds, 317 Hydroxylamine, 122 Hydroxymalonic acids, 182 Hydroxypropionic acids, 164 Hydroxyquinol, 335 Indican, 401 Indigo, 398-401 dyeing with, 401 synthesis, 400 Indol, 399 Indoxyl, 361, 400 Inks, 367 Tnosite, 373 Inulin, 220 Invert sugar, 202, 204, 214 Invertase, 224 lodoacetylene, 55 lodeosin, 370 lodoform, 39 lodohydrins, 247 lonization constants, 363, 408 lonone, 87, 374 Irone, 374 Isatin, 398 Isoborneol, 380 Isobutyric acid, 108 Isocyanic acid, 148, 151 Isolinolenic acid, 112 Isomerism, 13, 17, 29, 41, 44, 65, 151, 166, 186, 268 Isonitriles, 154 Isophthalic acid, 368 Isoprene, 50, 377 Isoquinoline, 398 Isosuccinic acid, 185 Isothiocyanates, 153 K Kerosene, 24 Ketocyclohexane, 374 Ketoles, 162 Ketoses, 199 Ketones aliphatic, 88 aromatic, 348 halogen derivatives, 93 identification, 91 mixed, 89 reactions, 90 table, 88 Ketoximes, 80 Kolbe's synthesis, 362, 365 419 INDEX Laboratory operations, 13 Lactic acid, 165, 170, 364 Lactide, 171, 172 Lactones, 172 Lactose, 215 Lecithins, 134 Levulose, 204 Liebermann's reaction, 131 Limonene, 378 Linolenic acid, 112 Linolic acid, 112 Linseed oil, i6oa Liquors, distilled, 61 Lysine, 255 M Maleic acid, 186 Malic acid, 185, 255 Malonic acid, 180 hydro xy, 182 synthesis, 182 Maltose, 215 Mandelic acid, 364 Mannitol, 205 Mannose, 205 Mellitic acid, 370 Menthol, 381 Menthone, 381 Mercaptans, 238 Mercaptides, 238 Mercerized cotton, 222 Mercury thiocyanate, 153 Mesitylene, 278 Mesotartaric acid, 193 Mesoxalic acid, 183 Metaformaldehyde, 85 Metaldehyde, 82 Methane, 25 series, 17 Methoxides, 63 Methyl alcohol, 59 carbinol, 66 chloride, 38 cyanide, 35, 99 cyclohexane, 373 glyoxal, 163 orange, 326 Methylamines, 132 Methylene iodide, 38 Metol, 339 Milk sugar, 215 Molasses, 212 Monosaccharoses, 1 99-2 1 1 synthesis, 206 Morphine, 404 Muscarine, 251, 402 Mustard oils, 153 N Naphthalene, 282, 382 derivatives, 384 Naphthols, 386 Naphthoquinones, 387 Naphthylamines, 386 Neurine, 133 Nicotine, 403 Nicotinic acid, 397, 403 Nitranilines, 308 Nitration, 293 Nitriles, 99, 100, 140, 153, 164, 178, 290 Nitrobenzene, 298 Nitrocelluloses, 223 Nitro-compounds, aliphatic, 142 aromatic, 293-298 structure, 143, 296 table, 297 Nitroform, 143 Nitrogen, detection, 6 estimation, 8 INDEX 42O Nitroglycerin, 159 Nitrolime, 145 Nitroparaffins, 142 Nitrophenols, 337 Nomenclature, 22, 44, 63, 65, 83, 90, 102, 127, 155, 175, 199, 257, 270, 328 Novocaine, 310 O Oils, essential, 160 hardened, 1606 natural, 160 Olefines, 44 Oleic acid, 108, no Olein, i6oa Optically active substances, 67, 108, 165, 173, 185, 190, 192, 201-216, 255, 374, 378, 379, 408 Orcin, 334 Organic acids, esters, 123 Organic compounds, i characteristics, i classification, 13 elements in, 4, 6 identification, 5 sources, 3 Orientation of aromatic com- pounds, 280 Osazones, 208 Oxalic acid, 161, 177 esters and salts, 179 Oxamic acid, 180 Oxamide, 146, 180 Oxidation of alcohols, 64, 161 study, 112 Oxidizing agents, 64 Oximes, 79 Oxindol, 399 Palmitic acid, 108 Palmitin, i6oa Paraffins, 15 formation, 28 halogen derivatives, 31 identification, 30 normal, table, 17 occurrence, 22 polyhalogen derivatives, table, 40 Paraform, 85 Paraldehyde, 81 Parchment paper, 222 Pentamethylene, 259 Pentoses, 201 Perkin's reaction, 357 Petrolatum, 23 Petroleum, 22 ether, 23 Phenacetin, 342 Phenanthrene, 392 Phenol, 327-330 acids, 360 alcohols, 341 esters, 339 homologues, 332 Phenolphthaleln, 369 Phenols, 327-339 derivatives, 336 esters, 339 table, 331 Phenolsulphonic acids, 337 Phenyl, 272, 328 acetic acid, 357 acetylene, 279, 358 carbinol, 340 glycollic acid, 364 hydrazine, 318 hydrazone, 80, 208 421 INDEX Phenyl, hydroxylamine, 321 propionic acid, 358 Phloroglucinol, 335 Phosgene, 228 Phosphines, 136 Phosphorus, detection, 6 estimation, 9 Phthalic acid, 368 anhydride, 369, 390, 391 Phthalide, 370 Phthalyl chloride, 370 Picric acid, 337 Pinacones, 90, 349 Pinene, 376 Piperidine, 396 Piperonal, 342 Piperonylic acid, 366 Polycarboxylic acids, 177, 368 Polypeptides, 405 Polysaccharoses, 211-223 Potassium cyanate, 146, 150 cyanide, 144 ferrocyanide, 144 thiocyanate, 153 Propargyl alcohol, 69 halides, 55 Propiolic acid, 1 1 1 Propionic acid, 107 Propyl alcohols, 65 Proteins, 404-407 Protocatechuic acid, 365 Prussic acid, 147 Ptomains, 134 Ptyalin, 219 Pulegone, 381 Purification of compounds, 7 Purine bases, 235 Purity, tests, 7 Pyrene, 392 Pyridine, 396 Pyrocatechol, 333 Pyrogallic acid, 335 Pyrogallol, 335 Pyroligneous acid, 59, 95 Pyromellitic anhydride, 370 Pyromucic acid, 394 Pyroracemic acid, 173, 190 Pyrotartaric acid, 190 Pyrrol, 395 Pyruvic acid, 173 Q Quaternary ammonium deriva- tives, 128, 135 Quercite, 373 Quinic acid, 335, 350, 375 Quinine, 404 Quinoid group, 324, 352 Quinol, 335 Quinoline, 397 Quinolinic acid, 397 Quinone, 307, 350 Quinones, 349~352 Racemic acid, 191 compounds, 192 resolution, 192 Raffinose, 216 Reducin, 338 Reference books, 411 Reimer-Tiemann reaction, 347 Resorcinol, 334 Rhamnose, 201 Rochelle salt, 189 Rodinal, 338 Rubber, artificial, 50, 378 Sabatier and Senderens' reaction, 47, 1606, 371 Saccharic acid, 204 INDEX 422 Saccharin, 359 Saccharose, 211 structure, 214 Safrol, 342 Salicyl alcohol, 341 aldehyde, 346 Salicylic acid, 365 Saliformin, 133 Salol, 365 Salvarsan, 339 Sandmeyer's reaction, 316, 359, 361 Sarcosine, 254 Schiff's reaction, 86, 91 Schotten-Baumann reaction, 358 Silk, artificial, 222 Silver cyanamide, 149 Soaps, 109 Sodium cyanide, 144 Sorbic acid, 112 Sorbitol, 204, 206 Sorbose, 206 Specific rotations, 408 Spermaceti, 125 Starch, 218 Stearic acid, 108 Stearin, 109, i6oa Stereochemistry, 166, 186, 193, 210, 259 Strain theory, 259 Strychnine, 404 Styrene, 279, 358 Styrolene, 279 Substitution, rules, 299 Succinamide, 184 Succinic acid, 183 anhydride, 184 hydroxy, 185, 189 Succinimide, 184 Sucrose, 211 Sugars, 199 Sulphanilic acid, 307 Sulphonal, 240 Sulphonation, 289 Sulphones, 240 Sulphonic acids, aliphatic, 241 aromatic, 288 chlorides, 290, 291 table, 292 Sulphonium, bases and salts, 239 Sulphoxides, 240 Sulphur, compounds containing, 236 detection, 6 estimation, 9 Tannic acids, tannins, 367 Tartar emetic, 190 Tartaric acids, 189-195 Tartronic acid, 182 Taurine, 133 Tautomerism, 175 Terephthalic acid, 368 Terpenes, 50, 376 Terpinene, 378 Tetraalkyl ammonium hydroxides, 135 Tetrachlormethane, 40 Tetrachlorquinone, 352 Tetrahydrobenzene, 371 Tetrahydrobenzoic acid, 355 Tetraphenylethane, 282 Tetrose, 201 Theine, 235 Theobromine, 235 Thio acids, 240 alcohols, 238 aldehydes, 240 carbonic acid, 243 cyanic acid, 152 423 INDEX Thio ethers, 238 ketones, 240 urea, 153, 244 Thiophene, 266, 394 Thymol, 332 Toluene, 277 Toluic acids, 357 Toluidines, 310 Trichloracetal, 92 Trichloracetone, 93 Trichlormethane, 39 Triiodomethane, 39 Trimethylamine, 38, 132, 213 Trimethylene, 258 Triphenylamine, 311 Triphenylbenzene, 282 Triphenylcarbinol, 340 Triphenylmethane, 282 Trisaccharoses, 216 Turpentine, 376 Twitchell's method, i6ob U Unsaturated compounds, 42, 50, 68, 86, no, 133, 1 86 stereoisomerism, 186 table of hydrocarbons, 45 Urea, 230 derivatives, 233 Urethanes, 233 Uric acid, 234 Urotropin, 133 Valeric acid, 108, 170 Vanillin, 347 Vaseline, 23 Veratric acid, 366 Vinasse, 213 Vinegar, 94 Vinyl alcohol, 69 amine, 133 halides, 55 Viscose, 222 W Waxes, composition, 125 Whiskey, 61 Wines, 61 Wood alcohol, 59 Wurtz reaction, 129 X Xanthic acids, 243 Xanthine, 235 Xylan, 221 Xylenes, 277 Xylidines, 310 Xylose, 201, 221 Zymase, 224 UNIVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped below. Nov 24 Bar7'50CK APK I 1950 FEE 2 1 1955 IU 22Jan'5f/r LD 21-100m-9,'47(A5702sl6)476 REC'D UD JAN REC'D LD MAY 51958 Tb [6/70 .- 574258 UNIVERSITY OF CALIFORNIA LIBRARY .