THE PRACTICAL METHODS OF 
 ORGANIC CHEMISTRY 
 
 
THE MACMILLAN COMPANY 
 
 NEW YORK BOSTON CHICAGO DALLAS 
 ATLANTA SAN FRANCISCO 
 
 MACMILLAN & CO., LIMITED 
 
 LONDON BOMBAY CALCUTTA 
 MELBOURNE 
 
 THE MACMILLAN CO. OF CANADA, LTD, 
 
 TORONTO 
 
THE PRACTICAL METHODS 
 
 OF 
 
 ORGANIC CHEMISTRY 
 
 BY 
 
 LUDWIG GATTERMANN, PH.D. 
 
 PROFESSOR IN THE UNIVERSITY OF FREIBURG 
 
 WITH N UMER O US ILL US TRA TIONS 
 
 TRANSLATED BY 
 
 WILLIAM B. SCHOBER, PH.D. 
 
 PROFESSOR OF CHEMISTRY IN LEHIGH UNIVERSITY 
 AND 
 
 VAHAN S. BABASINIAN, PH.D. 
 
 ASSOCIATE PROFESSOR OF ORGANIC CHEMISTRY IN LEHIGH UNIVERSITY 
 
 A UTHORISED TRANSLA TION 
 THE THIRD AMERICAN FROM THE ELEVENTH GERMAN EDITION 
 
 THE MACMILLAN COMPANY 
 1921 
 
 *i? 
 
 All rights reserved 
 \ 
 
COPYRIGHT, 1896, 1901, 1914, 
 BY THE MACMILLAN COMPANY, 
 
 J. 8. Gushing Co. Berwick & Smith Co. 
 Norwood, Mass., U.S.A. 
 
, 
 
 TRANSLATOR'S PREFACE 
 
 ' THE success of Professor Gattermann's book in the original 
 has warranted its reproduction in English. The translation is 
 intended for those students of chemistry who have not yet 
 become sufficiently familiar with scientific German to be able 
 to read it accurately without constant reference to a dictionary. 
 To such students this translation is offered, in the hope that it 
 will increase their interest in the science without causing a cor- 
 responding decrease in their efforts to acquire a knowledge of 
 German, which is indispensable to every well-trained chemist. 
 
 My grateful acknowledgments are due to my colleague, Dr. 
 H. M. Ullmann, for many valuable suggestions, and to Professor 
 Gattermann for his courtesy in pointing out several inaccuracies 
 in the German edition. 
 
 WILLIAM B. SCHOBER. 
 SOUTH BETHLEHEM, PENNSYLVANIA, 
 April, 1896. 
 
PREFACE 
 
 THE present book has resulted primarily from the private needs 
 of the author. If one is obliged to initiate a large number of 
 students at the same time into organic laboratory work, it is 
 frequently impossible, even with the best intentions, to direct the 
 attention of each individual to the innumerable details of labo- 
 ratory methods. In order that students, even in the absence of 
 the instructor, can gain the assistance necessary for the carrying 
 out of the common operations, a General Part, dealing with 
 crystallisation, distillation, drying, analytical operations, etc., is 
 given before the special directions for Preparations. In the 
 composition of this General Part, it has been considered of 
 more value to describe the most important operations in such 
 a way that the beginner may be able to carry out the directions 
 independently, rather than to give as fully as possible the numer- 
 ous modifications of individual operations. In the Special Part, 
 to each preparation are added general observations, which relate 
 to the character and general significance of the reaction carried 
 out in practice ; and the result follows, that the student during 
 the period given to laboratory work, becomes familiar with the 
 most varied theoretical knowledge, which, acquired under these 
 conditions adheres more firmly, as is well known, than if that 
 knowledge were obtained exclusively from a purely theoretical 
 
 vii 
 
Vili PREFACE 
 
 book. And so the author hopes that his book, along with the 
 excellent " Introductions " of E. Fischer and Levy, may here and 
 there win some friends. 
 
 For the assistance given by his colleagues, in pointing out 
 deficiencies of his work, the author will always be grateful. 
 
 GATTERMANN. 
 
 HEIDELBERG, August, 1894, 
 
PREFACE TO THE SECOND AMERICAN 
 EDITION 
 
 IN the preparation of this new edition advantage has been 
 taken of the opportunity offered to correct a number of errors 
 in the first edition, and to make the text a reproduction of 
 the fourth German edition of Professor Gattermann's book. In 
 many cases the laboratory directions have been improved, a 
 number of new illustrations have been added, and the Special 
 Part now includes methods for the preparation of glycol, di- 
 methylcyclohexenone, s-xylenol, phenylhydroxylamine, nitroso- 
 benzene, p-tolyl aldehyde (Gattermann-Koch synthesis), salicylic 
 aldehyde (Reimer and Tiemann's oxyaldehyde synthesis), cuprous 
 chloride, the decomposition of inactive mandelic acid into its 
 active constituents, and a zinc dust determination. The prepara- 
 tions of acetylene and acetylene tetrabromide have been omitted. 
 
 WILLIAM B. SCHOBER. 
 
 SOUTH BETHLEHEM, PENNSYLVANIA, 
 May, 1901. 
 
PREFACE TO THE THIRD AMERICAN 
 EDITION 
 
 DURING my absence from the University on sick leave, my 
 colleague, Professor Vahan S. Babasinian, has undertaken the 
 entire labor and responsibility, including the translation, edit- 
 ing, and reading the proofs, involved in the preparation of the 
 new edition of this book. To him, therefore, is due all the credit 
 for the satisfactory results presented in the following pages. 
 
 WILLIAM B. SCHOBER. 
 
 THIS new edition is a reproduction of the eleventh German 
 edition of Professor Gattermann's book. A number of errors in 
 the second edition have been corrected, four new illustrations 
 have been added, improved methods for the preparation of ethyl- 
 ene, glycol and carbon monoxide have been outlined, Dennstedt's 
 Method of Analysis and Grignard's Reaction have been fully de- 
 scribed. This edition contains also discussions of the theoretical 
 grounds upon which rest the processes of distillation with steam, 
 salting out, separation by extraction and esterification. 
 
 VAHAN S. BABASINIAN. 
 
 SOUTH BETHLEHEM, PENNSYLVANIA, 
 September, 1913. 
 
CONTENTS 
 
 GENERAL PART 
 
 PAGE 
 
 Crystallisation I 
 
 Sublimation . . . . . . . . . . . .14 
 
 Distillation 16 
 
 Distillation with Steam 37 
 
 Separation of Liquid Mixtures. Separation by Extraction. Salting Out 43 
 
 Decolourising. Removal of Tarry Matter ...... 50 
 
 Drying 52 
 
 Filtration 56 
 
 Heating under Pressure 63 
 
 Melting-point 71 
 
 Drying and Cleaning of Vessels 75 
 
 ORGANIC ANALYTICAL METHODS 
 
 Detection of Carbon, Hydrogen, Nitrogen, Sulphur, and the Halogens . 77 
 
 Quantitative Determination of the Halogens. Carius' Method . . 80 
 
 Quantitative Determination of Sulphur. Carius' Method ... 86 
 
 Quantitative Determination of Nitrogen. Dumas' Method ... 9 
 
 Quantitative Determination of Carbon and Hydrogen. Liebig's Method 101 
 
 Elementary Analysis. Dennstedt's Method . . . . . 113 
 
 SPECIAL PART 
 
 I. ALIPHATIC SERIES 
 
 1. Reaction: The Replacement of an Alcoholic Hydroxyl Group by a 
 
 Halogen I3 1 
 
 2. Reaction: Preparation of an Acid-Chloride from the Acid . . 141 
 
 3. Reaction: Preparation of an Anhydride from the Acid-Chloride and 
 
 the Sodium Salt of the Acid H7 
 
 xiii 
 
xiv CONTENTS 
 
 PAGB 
 
 4. Reaction : Preparation of an Acid-Amide from the Ammonium Salt 
 
 of the Acid 151 
 
 5. Reaction: Preparation of an Acid-Nitrile from an Acid- Amide . 155 
 
 6. Reaction : Preparation of an Acid- Ester from the Acid and Alcohol 157 
 
 7. Reaction: Substitution of Hydrogen by Chlorine . . . .163 
 
 8. Reaction: Oxidation of a Primary Alcohol to an Aldehyde . .167 
 
 9. Reaction : Preparation of a Primary Amine from an Acid-Amide of 
 
 the next Higher Series 175 
 
 10. Reaction : Syntheses of Ketone Acid-Esters or Polyketones with 
 
 Sodium or Sodium Alcoholate . 179 
 
 11. Reaction: Syntheses of the Homologues of Acetic Acid by means 
 
 of Malonic Ester 185 
 
 12. Reaction: Preparation of a Hydrocarbon of the Ethylene Series by 
 
 the Elimination of Water from an Alcohol. Union with Bromine 191 
 
 13. Reaction: Replacement of Halogen Atoms by Alcoholic Hydroxyl 
 
 Groups ........... 196 
 
 TRANSITION FROM THE ALIPHATIC TO THE AROMATIC 
 SERIES 
 
 Dimethylcyclohexenone and s-Xylenol from Ethylidenebisacetacetic Ester 
 
 (Ring Closing in a 1.5 Diketone. Knoevenagel Reaction) . 202 
 
 II. AROMATIC SERIES 
 
 1. Reaction: Nitration of a Hydrocarbon 212 
 
 2. Reaction: Reduction of a Nitro-Compound to an Amine . . 215 
 
 3. Reaction : (a) Reduction of a Nitro-Compound to a Hydroxylamine 
 
 Derivative. () Oxidation of a Hydroxylamine Derivative to a 
 Nitroso-Compound ......... 223 
 
 4. Reaction : Reduction of a Nitro-Compound to an Azoxy-, Azo-, and 
 
 Hydrazo-Compound 226 
 
 5. Reaction : Preparation of a Thiourea and a Mustard Oil from Car- 
 
 bon Disulphide and a Primary Amine 232 
 
 6. Reaction : Sulphonation of an Amine 235 
 
 7. Reaction : Replacement of the Amido- and Diazo-Groups by Hy- 
 
 drogen 237 
 

 CONTENTS xv 
 
 PAGE 
 
 8. Reaction : Replacement of the Diazo-Group by Hydroxyl . . 243 
 
 9. Reaction : Replacement of a Diazo-Group by Iodine . . . ' 244 
 
 10. Reaction : Replacement of a Diazo-Group by Chlorine, Bromine, or 
 
 Cyanogen 248 
 
 11. Reaction: (#) Reduction of a Diazo-Compound to a Hydrazine. 
 
 (^) Replacement of the Hydrazine- Radical by Hydrogen . . 250 
 
 12. Reaction: (0) Preparation of an Azo-Dye from a Diazo-Compound 
 
 and an Amine. ($) Reduction of the Azo-Compound . . 256 
 
 13. Reaction: Preparation of a Diazoamido-Compound . . . 262 
 
 14. Reaction : The Molecular Transformation of a Diazoamido-Com- 
 
 pound into an Amidoazo-Compound . . . . . . 265 
 
 15. Reaction: Oxidation of an Amine to a Quinone .... 266 
 
 16. Reaction : Reduction of a Quinone to a Hydroquinone . .' . 270 
 
 17. Reaction: Bromination of an Aromatic Compound . . . .271 
 
 18. Reaction : Fittig's Synthesis of a Hydrocarbon .... 276 
 
 19. Reaction : Sulphonation of an Aromatic Hydrocarbon (I) . . 280 
 
 20. Reaction : Reduction of a Sulphonchloride to a Sulphinic Acid 
 
 or to a Thiophenol 287 
 
 21. Reaction: Sulphonation of an Aromatic Hydrocarbon (II) . . 290 
 
 22. Reaction : Conversion of a Sulphonic Acid into a Phenol . . 293 
 
 23. Reaction : Nitration of a Phenol 296 
 
 24. Reaction : (#) Chlorination of a Side-Chain of a Hydrocarbon. 
 
 () Conversion of a Dichloride into an Aldehyde . . . 298 
 
 25. Reaction : Simultaneous Oxidation and Reduction of an Aldehyde 
 
 under the Influence of Concentrated Potassium Hydroxide . . 303 
 
 26. Reaction : Condensation of an Aldehyde by Potassium Cyanide to 
 
 a Benzoin 304 
 
 27. Reaction : Oxidation of a Benzoin to a Benzil .... 306 
 
 28. Reaction : Addition of Hydrocyanic Acid to an Aldehyde . . 307 
 
 29. Reaction: Perkin's Synthesis of Cinnamic Acid .... 313 
 
 30. Reaction: Addition of Hydrogen to an Ethylene Derivative . .316 
 
 31. Reaction : Preparation of an Aromatic Acid-Chloride from the Acid 
 
 and Phosphorus Pentachloride 3*7 
 
 32. Reaction : The Schotten-Baumann Reaction for the Recognition of 
 
 Compounds containing the Amido-, Imido-, or Hydroxyl-Group . 318 
 
xvi CONTENTS 
 
 
 
 PAGE 
 
 33. Reaction : (0) Friedel and Crafts' Ketone Synthesis, (b} Prepa- 
 
 ration of an Oxime. (<r) Beckmann's Transformation of an 
 
 Oxime 320 
 
 34. Reaction : Reduction of a Ketone to a Hydrocarbon . . . 329 
 
 35. Reaction: Aldehyde Synthesis. Gattermann-Koch . . .331 
 
 36. Reaction : Saponification of an Acid-Nitrile 335 
 
 37. Reaction : Oxidation of the Side-Chain of an Aromatic Compound 337 
 
 38. Reaction : Synthesis of Oxyaldehydes. Reimer and Tiemann . 340 
 
 39. Reaction : Kolbe's Synthesis of Oxyacids 344 
 
 40. Reaction : Grignard's Reaction, (a) Benzo'ic Acid from lodoben- 
 
 zene. (^) Benzhydrol from lodo- or Brombenzene and Benz- 
 
 aldehyde 348 
 
 41. Reaction: Preparation of a Dye of the Malachite Green Series . 354 
 
 42. Reaction : Condensation of Phthalic Anhydride with a Phenol to 
 
 form a Phthalem 357 
 
 43. Reaction: Condensation of Michler's Ketone with an Amine to a 
 
 Dye of the Fuchsine Series 364 
 
 44. Reaction : Condensation of Phthalic Anhydride with a Phenol to an 
 
 Anthraquinone Derivative 365 
 
 45. Reaction: Alizarin from Sodium /3-Anthraquinonemonosulphonate 367 
 
 46. Reaction : Zinc Dust Distillation 369 
 
 III. PYRIDINE AND QUINOLINE SERIES 
 
 1. Reaction: The Pyridine Synthesis of Hantzsch .... 371 
 
 2. Reaction : Skraup's Quinoline Synthesis 374 
 
 IV. INORGANIC PART 
 
 1. Chlorine 377 
 
 2. Hydrochloric Acid 377 
 
 3. Hydrobromic Acid 379 
 
 4. Hydriodic Acid . 379 
 
 5. Ammonia <, . . . . 382 
 
 6. Nitrous Acid .... 382 
 
 7. Phosphorus Trichloride . 382 
 
 8. Phosphorus Oxychloride ... .... 3^4 
 
CONTENTS xvii 
 
 PAGE 
 
 9. Phosphorus Pentachloride 384 
 
 10. Sulphurous Acid .......... 385 
 
 11. Sodium 385 
 
 12. Aluminium Chloride 386 
 
 13. Lead Peroxide . 388 
 
 14. Cuprous Chloride 389 
 
 15. Determination of the Value of Zinc Dust . . . ... 390 
 
 INDEX 391 
 
 ABBREVIATIONS 395 
 
 TABLE FOR CALCULATIONS IN NITROGEN DETERMINATION . . . 396 
 
THE PRACTICAL METHODS OF ORGANIC 
 CHEMISTRY 
 
 
 GENERAL PART 
 
 THE compounds directly obtained by means of chemical reac- 
 tions are, only in rare cases, pure ; they must therefore be 
 subjected to a process of purification before they can be further 
 utilised. For this purpose the operations most frequently em- 
 ployed are : 
 
 1 . CRYSTALLISATION. 
 
 2. SUBLIMATION. 
 
 3. DISTILLATION. 
 
 CRYSTALLISATION 
 
 Methods of Crystallisation. The crude solid product obtained 
 directly as the result of a reaction is generally amorphous or not 
 well crystallised. In order to obtain the compound in uniform, 
 well-defined crystals, as well as to separate it from impurities like 
 filter-fibres, inorganic substances, by-products, etc., it is dissolved, 
 usually with the aid of heat, in a proper solvent, filtered from the 
 impurities remaining undissolved, and allowed to cool gradually. 
 The dissolved compound then separates out in a crystallised form, 
 while the dissolved impurities are retained by the mother-liquor. 
 (Crystallisation by Cooling?) Many compounds are so easily 
 soluble in all solvents, even at the ordinary temperature, that 
 they do not separate from their solutions on mere cooling. In 
 this case, in order to obtain crystals, a portion of the solvent must 
 be allowed to evaporate. {Crystallisation by Evaporation^} 
 
2 GENERAL PART 
 
 Solvents. As solvents for organic compounds, the following 
 substances are principally used : 
 
 CLASS I. Water, 
 Alcohol, 
 Ether, 
 
 Ligroin (Petroleum Ether), 
 Glacial Acetic Acid, 
 Benzene. 
 
 Also mixtures of these : 
 
 CLASS II. Water + Alcohol, 
 
 Water -f Glacial Acetic Acid, 
 Ether -f Ligroin, 
 Benzene -f Ligroin. 
 
 Less frequently used than these are : hydrochloric acid, carbon 
 disulphide, acetone, chloroform, ethyl acetate, methyl alcohol, 
 amyl alcohol, toluene, xylene, solvent naphtha, etc. 
 
 But rarely used are : pyridine, naphthalene, phenol, nitro- 
 benzene, aniline, and others. 
 
 Choice of the Solvent. The choice of a suitable solvent is 
 often of great influence upon the success of an experiment, in that 
 a solid compound does not assume a completely characteristic 
 appearance until it is uniformly crystallised. In order to find the 
 most appropriate solvent, preliminary experiments are made in 
 the following manner : successive small portions of the finely 
 pulverised substance (a few milligrammes will suffice) are treated 
 in small test-tubes, with small quantities of the solvents of Class I. 
 If solution takes place at the ordinary temperature, or on gentle 
 heating, the solvent in question is, provisionally, left out of con- 
 sideration. The remaining portions are heated to boiling, until, 
 after the addition of more of the solvent if necessary, solution 
 takes place. The tubes are now cooled by contact with cold 
 water, and an observation will show in which tube crystals have 
 separated in the largest quantity. At times crystallisation does 
 not occur on mere cooling; in this case the walls of the vessel 
 
CRYSTALLISATION 3 
 
 are rubbed with a sharp-angled glass rod, or the solution is 
 "seeded," i.e. a small crystal of the crude product is placed in the 
 solution ; by this means, crystallisation is frequently induced. If 
 the individual solvents of Class I. are shown to be unsuitable, 
 experiments are made with the mixtures, Class II. Compounds 
 which are easily soluble in alcohol or glacial acetic acid, and 
 which consequently do not separate out on cooling, are, as a rule, 
 difficultly soluble in water. In order to determine whether a 
 separation of crystals will take place on cooling, the hot solutions 
 in the pure solvents are treated with more or less water, according 
 to the conditions. Substances easily soluble in ether, benzene, 
 toluene, etc., often dissolve in ligrom with difficulty. Hence 
 mixtures of these solvents can be frequently utilised with ad- 
 vantage, in the manner just described. If these experiments have 
 shown several solvents to be suitable, the portions under examina- 
 tion are again heated until solution takes place, and this time 
 are allowed to cool slowly. That solvent from which the best 
 crystals separate in the largest quantity is selected for the crystal- 
 lisation of the entire quantity of the substance. If a substance 
 is easily soluble in all solvents, recourse must be had to crystallisa- 
 tion by evaporation, i.e. by allowing the different solutions to stand 
 some time in watch-glasses. That solvent from which crystals 
 separate out first is the most suitable. Frequently a compound 
 dissolves in a solvent only on heating and yet does not crystallise 
 out again on cooling; compounds of this class are said to be 
 "sluggish " (trage). In this case, the solution may be allowed to 
 stand for some time, if necessary over night, in a cool place. If 
 a compound is very difficultly soluble, solvents with high boiling- 
 points are use'd, as toluene, xylene, nitrobenzene, aniline, phenol, 
 and others. The crystals obtained in these preliminary experi- 
 ments, especially if they are of easily soluble substances, are pre- 
 served, so that if from the main mass of the substance no crystals 
 can be obtained, the solution may be seeded, thus inducing crystalli- 
 sation. The crystallisation of substances which boil without decom- 
 position may often be facilitated by first subjecting them to distillation. 
 Substances that are solids in the crude form, will sometimes 
 
4 GENERAL PART 
 
 separate out as liquids from solvents. This may be due to the 
 presence of small quantities of water. In this case, the solution in 
 ether, ligroi'n, benzene, etc., is heated with fused Glauber's salt ; 
 crystals will often separate out when this is filtered. 
 
 To dissolve the Substance. When water or glacial acetic acid, 
 or a solvent which is not inflammable or not easily inflammable, is 
 employed, the heating may be done in a beaker on a wire gauze 
 over a free flame if the quantity is small ; if large, a flask is always 
 used. In either case care must be taken to prevent the flask from 
 breaking, by stirring up the crystals from the bottom with a glass 
 rod, or by frequently shaking the vessel. This precaution is 
 especially to be observed when, on heating, the substance to be 
 dissolved melts at the bottom of the vessel. Alcohol and benzene 
 may also be heated in like manner directly over a moderately 
 large flame, if the student has already had a sufficient amount of 
 experience in laboratory work and does not use too large quanti- 
 ties. If the liquid becomes ignited, no attempt to extinguish the 
 flame by blowing on it should be made, but the burner is removed 
 and the vessel covered with a watch-glass, a glass plate, or a wet 
 cloth. In working with large quantities of alcohol, benzene, ether, 
 ligroi'n, carbon disulphide, or other substances with low boiling- 
 points, they are heated on a water-bath in a flask provided with a 
 vertical glass tube (air condenser) or a reflux condenser. A sub- 
 stance to be crystallised from a solvent which is not miscible with 
 water must be dried, in case it is moist, before dissolving.. 
 
 An error which even advanced students too often make in 
 crystallising substances consists in this : an excessive quantity of 
 the solvent is poured over the substance at once. When heat is 
 applied, it is true, solution takes place easily, but on cooling noth- 
 ing crystallises out. So much of the solvent has been taken that 
 it holds the substance in solution even at ordinary temperatures. 
 The result is that a portion of the solvent must be evaporated or 
 distilled off, which involves a loss of time and substance, as well 
 as decomposition of the substance. The following rule should, 
 therefore, always be observed : The quantity of solvent taken at 
 first should be insufficient to dissolve the substance completely, even 
 
CRYSTALLISATION 5 
 
 on heating; then more of the solvent is gradually added, until all oj 
 the substance is just dissolved. In this way only is it certain that 
 on cooling an abundant crystallisation will take place. If a mixt- 
 ure of two solvents is used, one of which dissolves the substance 
 easily and the. other with difficulty, e.g. alcohol and water, the 
 substance is first dissolved in the former with the aid of heat; 
 the heating is continued while small amounts of the second are 
 gradually added (if water is used it is better to add it hot) until 
 the first turbidity appearing does not vanish on further heating. 
 In order to remove this cloudiness, a small quantity of the first 
 solvent is added. On the addition of the first portions of the 
 second liquid (water or ligroin) resinous impurities separate out 
 at times ; in this case, these are filtered off before a further addi- 
 tion of the solvent is made. 
 
 At times it happens that the last portions of a compound will 
 dissolve only with difficulty. The beginner often makes the mis- 
 take here of adding more and more of the solvent to dissolve this 
 last residue, which for the most part generally consists of difficultly 
 soluble impurities, like inorganic salts, etc. The result of this is 
 that on cooling nothing crystallises out. In such cases the diffi- 
 cultly soluble portions may be allowed to remain undissolved, and 
 on filtering the solution are retained by the filter. 
 
 Filtration of the Solution. When a substance has been dis- 
 solved, the solution must next be filtered from the insoluble im- 
 purities like by-products, filter-fibres, inorganic compounds, etc. 
 For filtration a funnel with a very short stem is generally used, 
 i.e. an ordinary funnel the stem of which has 
 been cut off close to the conical portion (Fig. i). 
 The funnels used in analytical operations have 
 the disadvantage that when a hot solution of 
 a compound flows through the stem, it be- 
 comes cooled to such an extent that crystals 
 frequently separate out, thus causing an obstruc- 
 tion of the stem. The funnel with a shortened 
 stem or no stem is prepared with a folded filter. In case the 
 solution contains a substance that easily crystallises out, the filtei 
 
6 GENERAL PART 
 
 is made of rapid-filtering paper (Fig. 2). The solution to be 
 filtered is not allowed to cool before filtering, but is poured on 
 the filter immediately after removing it from the 
 flame or water-bath. If inflammable solvents 
 are used, care must be taken that the vapours 
 are not ignited by a neighbouring flame. Under 
 normal conditions, no crystals or only a few 
 should separate out on the filter during filtra- 
 tion. If large quantities of crystals appear in a 
 solution as soon as it is poured on the filter, it is 
 an indication that too small an amount of the solvent has been 
 used. In a case of this kind, the point of the filter is pierced and 
 the crystals are washed into the unfiltered portion of the solution 
 with a fresh quantity of the solvent ; the solution is further diluted 
 with the solvent, heated, and filtered. 
 
 Very difficultly soluble compounds crystallise during the filtra- 
 tion in the space between the filter and funnel, in consequence 
 of the contact of the solution with the cold walls of the funnel. 
 
 This may be prevented when a small quantity of liquid is to be 
 filtered, by warming the funnel previously in an air-bath, or directly 
 over a flame. If the quantity of the liquid is large, hot water or 
 hot air funnels may be used (Figs. 3 and 4), or the funnel may 
 be surrounded by a cone of lead tubing wound around it through 
 which steam is passed (Fig. 5). Before filtering inflammable 
 liquids, the flame with which the hot water or hot air funnel has 
 been heated is extinguished. Substances which easily crystallise 
 out again, may also be conveniently filtered with the aid of suc- 
 tion and a funnel having a large filtering surface (Biichner funnel, 
 see Fig. 38, p. 58). After filtration the solution is poured into the 
 proper crystallisation vessel. In order to prevent the thick- walled 
 filter-flasks from being cracked by solvents of a high boiling-point, 
 they are somewhat warmed before filtering by immersion in warm 
 water. 
 
 Boiling nitrobenzene, aniline, phenol, and similar substances may 
 be filtered in the usual way through ordinary filter-paper. 
 
 Choice of the Crystallisation Vessel. The size and form of the 
 
CRYSTALLISATION 7 
 
 crystallisation vessel is not without influence upon the separation 
 of the crystals. If a compound will crystallise out on simple cool- 
 ing, without the necessity of evaporating a portion of the solvent, 
 a beaker is used for the crystallisation. The shallow dishes known 
 as " crystallising dishes " are not recommended for this purpose, 
 since they cannot be heated over a free flame, and further, the 
 solution easily " creeps " over the edge, involving a loss of the 
 substance. Moreover, the crusts collecting on the edges are very 
 impure, since, in consequence of the complete evaporation of the 
 solvent, they contain all the impurities which should remain dis- 
 
 FIG. 3. FIG. 4. FIG. 5. 
 
 solved in the mother-liquor. The beaker is selected of such a 
 size that the height of the solution placed in it is approximately 
 equal to the diameter of the vessel, which is thus about one-half 
 to two-thirds filled. 
 
 Heating after Filtration. Many compounds crystallise out in 
 the beaker during filtration. The crystals thus obtained are never 
 well formed, in consequence of the rapid separation ; therefore, 
 after the entire solution has been filtered, it is heated again until 
 the crystals have redissolved, and is then allowed to cool as slowly 
 
8 , GENERAL PART 
 
 as possible without being disturbed. In order to protect the solu- 
 tion from dust as well as to prevent it from cooling too rapidly, the 
 vessel is covered first with a piece of filter-paper and then with a 
 watch-glass or glass plate." The paper is used to prevent drops of 
 the solvent formed by the vapours condensing on the cold cover- 
 glass from falling into the solution, by which the crystallisation 
 would be disturbed. The paper need not be used if the vessel is cov- 
 ered with a watch-glass, the convex surface of which is uppermost : 
 the condensed vapours will thus flow down the walls of the beaker. 
 Crystallisation. In order to obtain as good crystals as possible, 
 the solution is allowed to cool slowly without being disturbed. In 
 exceptional cases only is it placed in cold water to hasten the separa- 
 tion of crystals. The vessel must not be touched until the crystalli- 
 sation is ended. If a substance, on slow cooling, separates out in 
 very coarse crystals, it is expedient, in case a sample of the substance 
 for analysis is desired, to accelerate the crystallisation by artificial 
 cooling, so that smaller crystals will separate out. Very coarse 
 crystals are commonly more impure than smaller ones, in that they 
 enclose portions of the mother- liquor. If a deposit of crystals as 
 abundant as possible is desired, the vessel is put in a cool place - 
 in a cellar or ice-chest if practicable. Should a compound crys- 
 tallise sluggishly, the directions given on page 2, under " Choice of 
 the Solvent," may be followed (rubbing the sides of the vessel with 
 a glass rod ; seeding the solution ; allowing to stand over night). 
 At times a compound separates out on cooling, not in crystals, but 
 in a melted condition. This may be caused by the solution being 
 so concentrated that crystallisation already takes place at a tem- 
 perature above the fusing-point. In this case the solution is again 
 heated until the oil which has separated out is dissolved, more of 
 the solvent is then added, the quantity depending upon the condi- 
 tions. In other cases this may be prevented by rubbing the walls 
 of the vessel a short time with a sharp-edged glass rod, as soon as 
 a slight turbidity shows itself, or by seeding the solution with a 
 crystal of the same substance. This difficulty may also be avoided, 
 in many cases, by allowing the solution to cool very slowly ; e.g. the 
 beaker is placed in a larger vessel filled with hot water and allowed 
 to cool in this. 
 
CRYSTALLISATION 9 
 
 At times the separation of crystals takes place suddenly, within a 
 few seconds, throughout the entire solution. Since the crystals thus 
 obtained are generally not well formed, the liquid, after some of the 
 crystals have been removed, is heated until solution again takes place. 
 After it has partially cooled, those crystals which were taken out 
 are now added to it, by which a gradual crystallisation is caused. 
 
 Separation of Crystals from the Mother-Liquor. When crystals 
 have been deposited, they are then to be separated from the liquid 
 (mother-liquor). This is always done with the aid of suction, and 
 never by merely pouring off the liquid. The filter to be used is 
 previously moistened with the same substance which was employed 
 as the solvent. Crusts, formed on the sides and edges of the ves- 
 sel by the complete evaporation of the solvent, are not filtered 
 with the crystals ; they are removed with a spatula before the filter- 
 ing, and are worked up with the mother-liquor. In order to re- 
 move the last traces of the mother-liquor adhering to the crystals, 
 they are washed several times with fresh portions of the solvent ; 
 obviously, if the substance is easily soluble, too large quantities of 
 the solvent must not be used. If a solvent that will not evaporate 
 easily in the air or on the water-bath has been used, e.g. glacial 
 acetic acid, toluene, nitrobenzene, etc., it must be removed from 
 the crystals by a more volatile substance, like alcohol or ether. 
 This is done by first washing with a fresh quantity of the solvent, 
 then with a mixture of the solvent and a small quantity of the more 
 volatile liquid, the proportion of the latter in the washing mixture be- 
 ing gradually increased, until finally the volatile substance is used 
 alone. Glacial acetic acid may, in this way, be displaced by water. 
 
 Drying of Crystals. When crystals have been freed from the 
 mother-liquor they must be dried. This may be effected (i) at 
 the ordinary temperature by the gradual evaporation of the solvent 
 in the air, and (2) at higher temperatures by heating on a water- 
 bath or in an air-bath. In the first case the crystals are spread 
 out in a thin layer upon several thicknesses of filter-paper and 
 covered with a watch-glass, funnel, beaker, or similar vessel. In 
 order that the vapours of the solvent may escape, the covering must 
 be so placed that the air is not shut off completely from the crys- 
 
IO GENERAL PART 
 
 tals ; this is conveniently done by supporting it on several corks. 
 Crystals may also be dried in a desiccator which is partially ex- 
 hausted, if necessary. In drying substances at higher temperatures 
 the crystal form may be lost by the fusion of the substance or by 
 the separation of the water of crystallisation. Since many sub- 
 stances will liquefy far below their melting-point if they contain 
 even small quantities of the solvent, a preliminary experiment with 
 a small portion is always made when the drying is to be effected 
 at higher temperatures. Compounds, not easily soluble in ether, 
 which crystallise from a solvent miscible with ether, can be very 
 quickly dried by being washed several times with it. After a 
 short exposure to the air they are dry. 
 
 Treatment of the Mother-Liquor. The mother-liquor filtered 
 off from crystals still contains more or less of the substance, in 
 proportion to its solubility at the ordinary temperature ; in many 
 cases it is advantageous to extract the last portions remaining in 
 solution. A " second crystallisation " is obtained by distilling or 
 evaporating off a portion of the solvent. The mother-liquor may 
 also be diluted with a second liquid, in which the dissolved sub- 
 stance is difficultly soluble ; e.g. a solution in alcohol or glacial 
 acetic acid may be diluted with water, or a solution in ether or 
 benzene with ligroi'n. 
 
 Crystallisation by Evaporation. If a compound is so easily 
 soluble in all solvents that it will only crystallise out on partial 
 evaporation, then, in order to get good crystals, a solution, not 
 too dilute, is made, by the aid of heat if necessary, and filtered 
 from the impurities remaining undissolved. In this case, as a 
 crystallisation vessel, one of the various forms of shallow dishes 
 the so-called crystallising dishes is used, in which the solution 
 is allowed partially to evaporate. In order to protect the vessel 
 from dust, it is covered with a funnel or watch-glass, in the 
 manner indicated under "Drying of Crystals." In crystallising 
 by this method, it sometimes happens that the solution, owing to 
 capillary action, will " creep " over the edge of the dish. To 
 avoid loss of the substance from this source, the dish is placed on 
 a watch-glass or glass plate. Under these conditions, the vessel 
 
CRYSTALLISATION I X 
 
 is never covered with filter-paper, since, after standing some time, 
 it may absorb the entire quantity of the substance. If, in order 
 to obtain well-formed crystals, the solvent is to be evaporated as 
 slowly as possible the solution is placed in a beaker or test-tube, 
 which is then loosely covered with filter-paper. Evaporation may 
 be hastened by placing the crystallisation vessel in a desiccator, 
 charged, according to the nature of the solvent, with different sub- 
 stances ; for the absorption of water or alcohol, calcium chloride 
 or sulphuric acid is used ; glacial acetic acid is absorbed by soda 
 lime, solid potassium hydroxide, or sodium hydroxide. The evap- 
 oration.of all solvents may be hastened by exhausting the desiccator. 
 
 Since the purifying effect of crystallisation depends upon the 
 fact that the impurities remain dissolved in the mother-liquor, and 
 with this are filtered off, in no case must the solvent be allowed 
 to evaporate completely, but the crystals must be filtered off while 
 still covered with the mother-liquor. Before filtering, crusts depos- 
 ited, generally on the edges of the vessel, are removed with the 
 aid of a small piece of filter-paper or a spatula. Even though 
 the substance is very soluble, the mother-liquor adhering to the 
 crystals is washed away with small quantities of the solvent. If 
 the quantity of crystals is very small, the adhering mother-liquor 
 may be separated, in cases of necessity, by placing them on porous 
 plates and moistening with a spray of the solvent. 
 
 Fractional Crystallisation. Up to this point, it has been 
 assumed that the substance to be crystallised possessed an essen- 
 tially homogeneous nature, and the object of crystallisation was 
 only to change it to a crystallised form. Crystallisation is often 
 employed for another purpose that of separating a mixture of 
 different substances into its individual constituents, a task that 
 is generally far more difficult than the crystallisation of an individ- 
 ual substance. The simplest case is one in which two substances 
 are to be separated. If the solubilities of the two substances are 
 very different, as is generally the case when a mixture of two dif- 
 ferent highly substituted compounds is under examination, it is 
 frequently not difficult to find a solvent which will dissolve a con- 
 siderable portion of the more easily soluble substance, and but a 
 
12 
 
 GENERAL PART 
 
 small portion of the less soluble. If, now, the mixture be treated 
 with such a solvent, in not too large quantities, a solution will be 
 obtained containing all of the easily soluble substance and a small 
 portion of the difficultly soluble substance. 
 This is filtered from the residue remaining 
 undissolved. The mixture has thus been 
 divided into two fractions. By evaporating 
 the solution to a certain point, the more in- 
 soluble compound will crystallise out, unac- 
 companied by any of the other compound ; 
 the crystals are filtered off, and the solution 
 further evaporated. If the crystallisation of 
 the two fractions be repeated a second time, 
 a complete separation will be effected. For 
 separating a mixture of this kind, specially 
 constructed apparatus the so-called ex- 
 traction apparatus may be employed, the 
 use of which possesses the advantage over 
 the method of simple heating, that much 
 smaller quantities of the solvent are required. 
 An apparatus of this kind is represented in 
 Figs. 6 and 7. To a wide glass tube d is 
 fused a narrow tube which acts as a siphon, 
 bent as in Fig. 7. This portion of the 
 apparatus is surrounded by a glass jacket b, 
 narrowed at its lower end. This is con- 
 nected with the flask that is to contain the 
 FIG. 6. FIG. 7. so i vent A cork bearing a reflux condenser 
 
 a ball condenser is convenient is fitted in the opening at the 
 apper end of the jacket. A shell of filter-paper is next prepared 
 in the following manner : Three layers of filter-paper are rolled 
 around a glass tube with half the diameter of the inner tube d. 
 One end of the roll must extend somewhat beyond the edge of the 
 glass tube ; this is turned over and securely fastened with thread. 
 To preserve the form of the roll, thread is loosely wound around its 
 middle and upper portion. The length of the roll is such that it 
 
CRYSTALLISATION 1 3 
 
 extends i cm. above the highest point of the narrow siphon-tube. 
 In the shell is placed the mixture of the easily soluble and diffi- 
 cultly soluble substance to be extracted ; the upper end is closed 
 by a loose plug of absorbent cotton. The flask a, containing the 
 solvent, is now heated on a water-bath or over a free flame, accord- 
 ing to the nature of the solvent. The condensed vapours drop from 
 the condenser into the shell, dissolve the substance, filter through 
 the paper, and fill the space between shell and inner glass tube. 
 As soon as the liquid has reached the highest point of the siphon- 
 tube, the solution siphons off and flows back into the flask a. 
 This operation may be continued as long as necessary. The 
 amount of solvent used should be one and a half or two times 
 the volume of the inner tube up to the highest point of the siphon. 
 The construction of a ball condenser is 
 .represented in Fig. 8. In order to dis- 
 tinguish the tube by which the water en- 
 ters from the outlet-tube, the former is 
 marked with an arrow. Comparatively 
 easy also is the separation of two sub- 
 stances about equally soluble, if the one 
 
 is present in larger quantity than the other. ~~~/J^^\ r^\^~~ fl 
 If a mixture of this kind is dissolved, then, 
 on cooling, the substance which was pres- 
 ent in larger quantity generally crystal- 
 lises out. Occasionally, after standing 
 some time, crystals of the second sub- 
 stance will appear ; under these conditions the crystallisation 
 must be carefully watched, and as soon as crystals differing 
 from those first appearing are observed, the solution is filtered 
 with suction at once, even though it is still warm. 
 
 If two compounds crystallise simultaneously at the outset, as is 
 the case when they possess approximately the same solubility and 
 are present in almost equal quantities, they can be separated me- 
 chanically. If, e.g., one of the compounds crystallises in coarse 
 crystals, and the other in small ones, they may be separated by 
 sifting through a suitable sieve or wire gauze. A compound crys- 
 
14 GENERAL PART 
 
 tallising in leaflets can frequently be separated from one crystal- 
 lising in needles by a sieve. If these methods fail, the separation 
 may be effected by picking out the crystals with small pincers or a 
 quill. In all these mechanical operations, the crystals must be as 
 dry as possible. 
 
 In many cases, when one of the compounds is heavier than the 
 other, it is possible to separate them by causing the lighter crystals 
 to rise to the top of the liquid, by imparting to it a rotatory motion 
 by rapid stirring with a glass rod. The heavier compound collects 
 at the bottom of the vessel, and the liquid with the lighter com- 
 pound floating in it can be poured off. 
 
 Double Compounds with the Solvent. Many substances crys- 
 tallise from certain solvents in the form of double compounds, 
 composed of the substance and the solvent. It is well known that 
 many substances, in crystallising from water, combine with a cer- 
 tain portion of water. Alcohol, acetone, chloroform, benzene, and 
 others also have the power of uniting with other substances to 
 form double compounds. As a familiar example, the combination 
 of triphenylmethane with benzene may be mentioned in this con- 
 nection. If double compounds of this kind are heated, the com- 
 bined solvent is generally vaporised. 
 
 SUBLIMATION 
 
 Much less frequently than crystallisation, sublimation is used to 
 purify a solid compound. The principle involved is this : A 
 substance is converted by heat into the gaseous condition. The 
 vapours do not assume the liquid phase when they are condensed 
 on a cold surface, but deposit in the form of crystals. 
 
 The sublimation of a small quantity of a substance can be con- 
 veniently effected between two watch-glasses of the same size. 
 The substance to be sublimed is placed on the lower one, which is 
 then covered with a round filter perforated several times in its 
 centre and projecting over the edges ; the second watch-glass with 
 its convex side uppermost is placed on it, and the two are held 
 together by a watch-glass clamp. If the lower glass is now heated 
 
SUBLIMATION jcj 
 
 very slowly on a sand-bath with a free flame, the vaporised sub- 
 stance condenses on the cold surface of the upper watch-glass 
 in crystals; the filter-paper prevents the very small, light crys- 
 tals from falling back on the hot surface of the 
 lower glass. To keep the upper glass cool, it is 
 covered with several layers of wet filter-paper 
 or with a small piece of wet cloth. If large 
 quantities of a substance are to be sublimed, 
 the upper watch-glass in the apparatus just de- 
 scribed is replaced by a funnel somewhat smaller 
 than the lower glass (Fig. 9). To prevent the 
 escape of vapours, the stem of the funnel is 
 closed by a plug of cotton or is covered with 
 a small cap of filter-paper. The apparatus for 9 FlG 
 sublimation designed by Briihl is admirably 
 adapted to the purpose for which it is intended (Fig. 10). It 
 consists of a hollow metal plate through which water flows. In 
 the conical opening is placed a crucible containing the substance 
 to be sublimed. The plate is covered with a concave glass dish, 
 the ground edges of which fit the plate tightly. The crucible is 
 heated directly with a small flame, while cold water flows through 
 the plate. The vapours condense in part on the glass cover, but 
 
 more abundantly on the upper cold surface of the plate in crystals. 
 The glass cover is not removed until the apparatus is completely 
 cold. 
 
1 6 GENERAL PART 
 
 Sublimations can also be conducted in crucibles, flasks, beakers, 
 retorts, tubes, etc. The heating may be done in an air- or oil-bath. 
 In order to lead off the vapours rapidly, a current of an indifferent 
 gas is sent through the apparatus. 
 
 Of late years substances of high purity have been obtained by 
 causing them to sublime in vacuo. An apparatus devised for this 
 purpose is described in ti\z Journal fur praktische Chemie, Vol. 78 
 (1908), page 201. 
 
 DISTILLATION 
 
 Kinds and Objects of Distillation. By distillation is meant the 
 conversion by heat of a solid or liquid substance into a vapour and 
 the subsequent condensation of this. When a solid is distilled it 
 does not condense directly in crystals, as is the case in sublima- 
 tion. The distillate is a liquid which may solidify into a crystal- 
 line mass on standing. When distillation is conducted at the 
 atmospheric pressure, it is called ordinary distillation; if in a 
 partial vacuum, vacuum distillation. The object of distillation is 
 either to test the purity of an individual substance by the determi- 
 nation of its boiling-point, or to separate a mixture of substances 
 boiling at different temperatures into its constituents. (Fractional 
 Distillation^ 
 
 Distillation Vessels. The heating of the substance to be dis- 
 tilled is generally effected in a fractionating flask (Figs, n, 12, 13). 
 These flasks differ, not only in size, but in the diameter of the con- 
 densation-tube (side-tube), as well as in the distance of the latter 
 from the bulb. In selecting a fractionating flask the following points 
 are to be observed. For distillation at the atmospheric pressure a 
 flask is selected having a bulb of such a size that when it contains the 
 substance to be distilled it will be about two-thirds filled. There 
 are two objections to distilling small quantities of a substance from 
 a large flask : the vapours are easily overheated, thus giving a 
 boiling-point that is too high ; a loss of the substance follows, in 
 that, after the distillation is finished, a larger volume of vapours 
 which condense on cooling, remains behind in the bulb, than if a 
 smaller flask had been used. In the distillation of low boiling 
 
DISTILLATION 1^ 
 
 compounds, a flask is selected which has its condensation-tube as 
 high as possible above the bulb, so that the entire thread of mer- 
 cury of the thermometer employed is heated by the vapour of the 
 liquid. By using a flask of this kind it is not necessary to cor- 
 rect the observed boiling-point, as is the case when the mercury 
 column is not entirely surrounded by the vapour. The higher a 
 substance boils, the nearer must the side-tube be to the bulb, in 
 
 FIG. it. 
 
 FIG. 13. 
 
 order that the vapours shall have as little opportunity as possible 
 of condensing below the tube and flowing back into the bulb. 
 
 If large quantities of a substance are to be distilled, an ordi- 
 nary flask is used. This can be converted into a fractionating 
 flask with the aid of a cork bearing a T-tube, as illustrated in 
 Fig. 14. 
 
 For the distillation of solid substances which solidify in the 
 condensation-tube, a fractionating flask with a wide side-tube is 
 used. 
 
 A fractional distillation can also be conducted in the fractionating 
 flasks just described ; but the operation can be carried out more 
 c 
 
1 8 GENERAL PART 
 
 rapidly and more completely by the use of apparatus especially 
 adapted to fractionating (Fig. 15). These can be fused directly 
 on the bulb or they can be attached to an ordinary flask by means 
 of a cork (Fig. 14) ; the round, short-necked flasks such as rep- 
 resented in Fig. 1 6, are well adapted to this purpose. Flasks ol 
 
 FIG. 14. 
 
 FIG. 15. 
 
 Fractionating Apparatus. 
 
 WURTZ LlNNEMANN HEMPEL 
 
 this description can be obtained in different sizes but still possess 
 ing the same width of neck ; this enables one to use the same 
 cork with any flask. The value of these different forms of fraction- 
 ating apparatus depends upon the fact that the higher boiling 
 portions carried along with the vapours do not pass immediate!) 
 
DISTILLATION X g 
 
 to the outlet tube, but before entering this they have an oppor- 
 tunity of condensing and flowing back into the flask. In the 
 apparatus of Wurtz (a) the condensation takes place on the large 
 upper surfaces of the bulbs. More complete condensation is ob- 
 tained in Linnemann's apparatus (b), which differs from that of 
 Wurtz in that the narrow tubes between the bulbs contain small 
 platinum-wire sieves. Since the lower 
 boiling portions condense to a liquid 
 and collect in these, the ascending 
 vapours are so far cooled by the pas- 
 sage through them that the accom- 
 panying portions of the higher boiling 
 substances are likewise condensed. 
 The apparatus of Hempcl is filled with 
 glass beads which act like the sieves in 
 the Linnemann apparatus. For the 
 distillation of large quantities of a 
 liquid the Hempel apparatus is par- 
 ticularly well adapted ; in working with 
 it as well as the Linnemann form, the 
 heating must be interrupted from time 
 to time, in order that the liquid col- ' IGt l6 ' 
 
 lecting in the beads or sieves may have an opportunity to flow 
 back to the distillation flask. If the Le Bel-Henninger form is 
 used, this precaution is unnecessary, since in this apparatus 
 special tubes for conducting off the condensed liquid are joined 
 to the sides of the bulb somewhat above the sieves. 
 
 Experiments have shown that a single distillation with one of the 
 forms of apparatus just described, effects a more complete separa- 
 tion than repeated fractionations in an ordinary fractionating flask. 
 
 Supporting the Fractionating Flask. If it is necessary to 
 support the fractionating flask with a clamp, it is placed as far 
 above the outlet tube as possible, never below it ; the glass ex- 
 pands by contact with the hot vapours, and since the expansion 
 is impeded by the clamp, particularly if it is firmly attached, the 
 flask frequently breaks. 
 
20 GENERAL PART 
 
 Supporting the Thermometer. The thermometer is passed 
 through a cork (no rubber) which fits the neck of the flask. The 
 most exact determinations of the boiling-point are obtained if the 
 entire thread of mercury is surrounded by the vapour of the sub- 
 stance. With low boiling compounds this condition is easily 
 obtained by the use of a fractionating flask having its outlet tube 
 at a sufficient distance above the bulb. In this case the ther- 
 mometer is so placed that the degree corresponding to the boil- 
 ing-point of the liquid is opposite the outlet tube, but the bulb 
 of the thermometer must not extend into the bulb of the flask 
 and never into the liquid ; if it does, another flask must be used, 
 the outlet tube of which is still higher above the bulb. If in 
 dealing with high boiling compounds such an arrangement is 
 not possible, the thermometer is thrust so far into the neck of the 
 flask that the thermometer-bulb is somewhat below the outlet 
 tube. In this case, if an exact determination of the boiling-point 
 is desired, the observed reading is corrected in the manner 
 described below. In order to avoid making a correction a special 
 form of thermometer is used, the graduation of the scale begin- 
 ning at 1 00, 200, or at other convenient points. By employing 
 an instrument of this kind the mercury column may be kept in 
 the vapours at any temperature. 
 
 In making distillations, it occasionally happens that the mercury 
 column ascends to that point in the scale which is hidden by the 
 cork supporting the thermometer, thus preventing the temperature 
 from being read. In a case of this kind the thermometer is 
 either raised or lowered, so that the top of the mercury is visible, 
 or if this is not possible, from that portion of the cork which pro- 
 jects above the flask, a section is cut which will enable the scale 
 to be seen. 
 
 Condensation of Vapours. The condensation of vapours is 
 effected in various ways, depending upon the height of the boiling- 
 point. If a compound boils at a relatively low temperature (up to 
 100), the outlet tube of the fractionating flask is connected with 
 a Liebig condenser by a cork (not a rubber stopper) . For very 
 low boiling compounds a long condenser is used, and for those of 
 
DISTILLATION 
 
 21 
 
 high boiling-points a short one. If the boiling-pomi of a com- 
 pound is very low, the flask in which the condensed liquid collects 
 (the receiver) is connected with the condenser by means of a cork 
 and a bent adapter (Fig. 63), and the receiver is cooled by ice 
 or a freezing mixture. If the boiling-point is moderately high, 
 between 100 and 200, the receiver, connected to the condensing 
 tube by a cork, is cooled by running water (Fig. 17). If the 
 substance is to be distilled 
 again, a fractionating flask 
 is employed as a receiver; a 
 tubulated suction-flask may 
 also be used. It is often 
 unnecessary to employ run- 
 ning water for cooling pur- 
 poses if to the outlet tube of 
 the flask a wide glass tube 
 50 cm. long (extension tube) 
 is connected by a cork (Fig. 
 1 8) . With still higher boil- 
 ing substances even this is 
 superfluous, since the con- 
 densation tube of the frac- 
 tionating flask, provided it 
 is not too short, will suffice 
 for the condensation. 
 
 If a small quantity of a substance is to be distilled, and it is 
 desired to avoid the loss of substance necessarily incident to the 
 use of a condenser, the distillation even of low boiling compounds 
 is conducted in a small distillation flask as slowly and carefully 
 as possible, the source of heat being a minute flame (the so-called 
 microburner). 
 
 If large quantities are to be distilled, a condenser is always used, 
 since when other condensation apparatus is employed, the tube 
 finally becomes, so hot that the vapours are not completely con- 
 densed. If the vapours of a substance attack corks, the outlet 
 tube is inserted far enough into the condenser or extension tube 
 
 FIG. 17. 
 
22 
 
 GENERAL PART 
 
 so that the vapours do not come in contact with the cork. Bui 
 generally a cork is not used ; the outlet tube being inserted suffi- 
 ciently far into the condenser. 
 
 Heating. Low boiling substances (those boiling up to about 
 80) are not generally heated over the free flame, but on the water- 
 bath gently or to full boiling. Frequently it is more convenient 
 to immerse the bulb of the fractionating flask as far as the level 
 of the liquid which it contains in a dish or beaker filled with 
 water, which is heated gently or strongly as the case requires. 
 Low boiling substances may also be heated by immersing the bulb 
 
 FIG. 18. 
 
 of the flask from time to time in a vessel filled with warm water. 
 If a substance is not distilled over a free flame, in order to prevent 
 "bumping" a few pieces of platinum wire or foil, or bits of glass, 
 are thrown into the liquid (see below). When a substance to be 
 distilled is heated on the water-bath, it may easily happen that 
 the vapour inside the flask may be overheated by the steam escap- 
 ing between the rings. For this reason, in the determination of 
 exact boiling-points it is better to use a small free flame. The 
 so-called microburner is well adapted to this purpose. High boil- 
 
DISTILLATION 23 
 
 ing substances are always heated over the free flame. In this case 
 the flask may be protected by heating it on a wire gauze ; still by 
 working carefully the gauze need not be used. In heating, the 
 flame is not placed under the flask at once, since the latter is likely 
 to break easily on sudden heating ; it is better to pass the flame 
 back and forth slowly and uniformly over the bottom of the flask 
 until the liquid is brought to incipient ebullition. Substances which 
 have been previously dissolved, after the evaporation of the solvent 
 on the water-bath, often stubbornly refuse to give up the last por- 
 tions of the solvent, particularly when ether has been used. If now 
 a free flame be applied, it frequently happens that in consequence 
 of a retarded boiling during which the solution becomes overheated, 
 a sudden active ebullition and foaming will take place. In order 
 to prevent this the flask is shaken repeatedly during the heating, 
 since if the liquid is kept in motion, overheating cannot easily take 
 place. It may also be prevented frequently by heating the flask 
 on the side. During the actual distillation the heating may be con- 
 tinued by slowly passing the flame over the bottom of the flask as in 
 the preliminary heating, but in this case care must be taken not to 
 apply the flame to the flask at any point above the liquid inside, 
 since an overheating of the vapours would result. In order to 
 protect the hand in case the flask should break, the burner is held 
 obliquely and not directly under the flask ; or during the distilla- 
 tion the burner may be placed under the flask and allowed to re- 
 main stationary. The size of the flame is so regulated that the 
 condensed distillate flows into the receiver regularly in drops. If 
 vapours escape from the receiver, it is an indication that the heat- 
 ing is too strong. Toward the end of the distillation the burner is 
 turned down somewhat. 
 
 To collect the Fractions. If a substance which is not quite 
 pure is being treated, and it is desired to test the purity by a 
 determination of its boiling-point, then on distillation a small por- 
 tion will generally pass over below the true boiling-point (" first 
 runnings "); this is collected separately in a small receiver. Then 
 follows the principal fraction, passing over at the true boiling-point, 
 the temperature remaining constant. If there is only a small 
 
24 GENERAL PART 
 
 quantity of the liquid in the bulb of the flask, it is difficult, in spite 
 of using a small flame, to prevent the vapours from being some- 
 what overheated ; this will cause a rise of the mercury The por- 
 tion passing over a few degrees above the true boiling-point can, 
 in preparation work, be collected with that portion which boils at 
 the correct temperature, without evil results. High boiling portions 
 collected separately are designated as "last runnings." The oper- 
 ation of fractional distillation is conducted in a wholly different 
 manner. The preparation of benzoyl chloride (see page 317) 
 will furnish a practical example of the method of procedure. This 
 compound is obtained by treating benzoic acid with phosphorus 
 pentachloride. The product of the reaction is a mixture of phos- 
 phorus oxychloride (b. p. 110) and benzoyl chloride (b. p. 200). 
 If this mixture is subjected to distillation, the entire quantity of 
 phosphorus oxychloride does not pass over at about 110, and 
 afterwards the benzoyl chloride at 200 ; but the distillation will 
 begin below 110, and a mixture consisting of a large quantity of 
 the lower boiling substance and a small quantity of the higher 
 boiling substance will pass over ; the temperature then rises gradu- 
 ally ; while the quantity of the former steadily decreases, that of 
 the latter increases, until finally, at 200, a mixture consisting essen- 
 tially of the higher boiling substance passes over. A quantitative 
 separation of the constituents of a mixture cannot be effected by 
 the method of fractional distillation. However, in most cases, it 
 is possible to obtain fractions which contain the largest part of 
 the individual constituents, particularly when, as in the example 
 selected, the boiling-points of the constituents lie far apart, by 
 collecting the different fractions and repeating the distillation a 
 number of times. It is almost impossible to give definite rules of 
 general application for fractional distillation ; the number of frac- 
 tions to be collected depends upon the difference of the boiling- 
 points, upon the number of compounds to be separated, upon the 
 relative proportion of the compounds present, and upon other 
 factors. If but two substances are to be separated, as is generally 
 the case in preparation work, the procedure is, very commonly, as 
 follows : as a basis for the fractions to be collected, the interval 
 
DISTILLATION 25 
 
 between the boiling-points is divided into three equal parts ; in the 
 case of the example selected the temperatures would be 1 10, 140, 
 170, 200. The fraction passing over between the temperature 
 at which the distillation first begins, up to 140, is collected (frac- 
 tion I.), then in another vessel the fraction passing over between 
 140-! 70 (fraction II.), and finally in another receiver that pass- 
 ing over between 170 and 200 (fraction III.). The quantities 
 of the three fractions thus obtained are about equal. Fraction I. 
 is now redistilled from a smaller flask, and the portion passing 
 over up to 140 is collected as in the first distillation in the empty 
 receiver I., which in the meantime has been washed and dried. 
 When the temperature reaches 140, the distillation is stopped, 
 and to the residue remaining in the flask is added fraction II., and 
 the distillation continued. The portion passing over up to 140 
 is collected in receiver I., that from 140-: 70 in the empty re- 
 ceiver II. When the temperature reaches 170, the distillation is 
 again interrupted, and to the residue in the flask is added fraction 
 III., and the distillation is again continued : in this way the three 
 fractions are collected. These are again distilled as in the first 
 distillation, but now the lower and higher boiling fractions are much 
 larger than the intermediate one ; further, a larger portion of these 
 end fractions boil nearer the true boiling-points than in the first 
 distillation. If it is now desired to obtain the two substances in 
 question in a still purer condition, the two end fractions are once 
 more distilled separately, and the portion passing over a few de- 
 grees above and below the true boiling-point, for phosphorus oxy- 
 chloride about 105-! 15, for benzoyl chloride, i95-2O5 are 
 collected. 
 
 Vacuum Distillation. Many compounds, not volatile at the 
 atmospheric pressure without decomposition, may be distilled 
 undecomposed in a partial vacuum. The vacuum distillation is 
 used advantageously for the fractionation of small quantities of a 
 substance, since the separation of the individual constituents can 
 be effected more rapidly and more completely than at the atmos- 
 pheric pressure. 
 
 Vacuum Apparatus. The simplest form of a vacuum apparatus 
 
26 
 
 GENERAL PART 
 
 is represented in Fig. 19. Two fractionating flasks a and b are 
 connected by a cork. The neck of a is closed by a tightly fitting 
 cork bearing the glass tube d, reaching to the bottom of the flask, 
 its lower end being drawn out to a fine point, the object of which 
 will be explained below. A thermometer is placed in the tube. 
 
 FIG. 19. 
 
 In place of the flask b, a suction-flask such as finds application 
 in filtering under pressure, may be used (Fig. 20). But this kind 
 of flask is used only in case low boiling substances are to be 
 distilled, since the contact of too hot liquids with the thick walls 
 causes them to crack easily : this is likely to prove very destructive 
 in vacuum distillation. With low boiling substances, in order to 
 get complete condensation of the vapours, the jacket of a Liebig 
 condenser through which water is allowed to flow is fitted over 
 the outlet tube of the fractionating flask. These simple forms 
 of apparatus are used only when it is desired to collect a few 
 fractions, since it is troublesome to be obliged to change the 
 receiver, and thus destroy the vacuum, for each new fraction. 
 If it is desired to collect a larger number of fractions, an 
 
DISTILLATION 2; 
 
 apparatus is employed by means of which the receiver can be 
 changed without destroying the vacuum. 
 
 FIG. 20. 
 
 Briihl's apparatus is very well adapted to this purpose (Figs. 21 
 and 22). By turning the axis b, so arranged that it supports the 
 receivers firmly, each receiver may in turn be brought under the 
 end of the condenser tube c. 
 
 The receiver shown in Fig. 23 is also very convenient for frac- 
 tional distillation in a vacuum. By grasping the cork a and the 
 tube c firmly with the fingers and turning, the different portions 
 of the receiver may be brought under the condensing tube. 
 
 Construction of a Vacuum Apparatus. In vacuum distillations 
 the evolution of bubbles of vapour occurs to a much greater 
 extent than under ordinary conditions. In order to prevent the 
 liquid from foaming up and passing over, a flask of such a size is 
 selected, that when it contains the liquid it must in no case be 
 more than half full ; it is better to have it but one-third full. The 
 individual parts of the apparatus are connected by rubber stoppers. 
 Ordinary corks may also be used with almost equally good results, 
 but only those are selected which are as free as possible from 
 
28 
 
 GENERAL PART 
 
 pores ; they are pressed in a cork-press, and then very carefully 
 bored. If, after the apparatus is put together, the corks are coated 
 
 FIG. 21. 
 
 with a thin layer of collodion, there is no difficulty in obtaining a 
 vacuum. The thermometer and capillary tube may be arranged as 
 
 shown in Fig. 19. It is also 
 a very excellent arrangement 
 to use a two-hole cork, the 
 thermometer passing through 
 one, and the capillary tube 
 through the other, as in Fig. 
 21. The capillary tube is 
 made by drawing out a glass 
 tube of 1-2 mm. diameter ; 
 the narrow hole in the cork 
 through which this passes is 
 made conveniently by a hot 
 knitting-needle. Instead of 
 using a capillary tube to 
 prevent " bumping," other 
 
 FIG. 22. 
 
DISTILLATION 
 
 means may be employed (see below), in which case the ther- 
 mometer is supported in the fractionating flask as in ordinary 
 distillations. When a tube drawn out to 
 a capillary point is used, a short piece of 
 thick-walled rubber tubing, which can be 
 closed by a screw pinch-cock (Fig. 19, e 
 and c), is attached to the upper end. 
 
 The flasks recommended by Claisen 
 (Fig. 24) may be used advantageously in 
 vacuum distillations in place of the com- 
 mon fractionating flasks. A tube drawn 
 out to a capillary point is secured in the 
 limb a by a piece of thick-walled rubber 
 tubing or a cork. The thermometer is 
 inserted in b. When a few large pieces of 
 broken glass are placed in b, these flasks 
 possess the advantage of preventing por- FlG g 
 
 tions of the liquid (even in cases of violent 
 
 boiling) from being carried over into the condenser. The space 
 above the pieces of broken glass may be filled, partially or 
 
 FIG. 25. 
 
 FIG. 24. 
 
 wholly, with glass beads obviously these are only to be used in 
 the distillation of liquids not having a too high boiling-point 
 
30 GENERAL PART 
 
 thus combining the advantages of a Hempel column with vacuum 
 distillation. 
 
 For the distillation of solids a fractionating flask with a wide, 
 bent sabre-shaped condensing tube is used (Fig. 25). In order 
 to determine the efficiency of the vacuum, the lower tube of the 
 Briihl apparatus is connected with a manometer (Fig. 26), by 
 means of a thick-walled rubber tubing which will not collapse 
 upon exhausting the apparatus. The other end 
 of the manometer is connected with suction, by 
 the same kind of rubber tubing. 
 
 Since in consequence of the varying water 
 pressure, it happens, at times, that the water from 
 the suction pump may be forced into the man- 
 ometer or receiver, it is advisable to insert a 
 thick-walled suction flask between the suction 
 pump and manometer. 
 
 In order that the apparatus may be perfectly 
 tight, the corks, ends of the rubber tubing, as well 
 as the ground surfaces of the Briihl receiver, are 
 covered with a thin layer of grease or vaseline. If ordinary corks 
 are used, these, as well as the ends of the tubing, are covered 
 with collodion after the apparatus is set up. Before the distil- 
 lation, the apparatus is tested to determine whether it will give the 
 desired vacuum. For this purpose, the pinch-cock on the capil- 
 lary tube is closed, the suction attached, and after some time the 
 manometer is read : this will indicate whether the desired vacuum 
 has been obtained. In case it is not, the corks are pressed more 
 firmly into the tubes, greased again or covered with more collodion, 
 and the rubber tubing is pushed farther over the ends of the glass. 
 Frequently the suction pump will not work satisfactorily; it is 
 then examined to see if it is stopped up, or a better pump is used. 
 When the apparatus has been exhausted, the air must not be 
 admitted suddenly, by removing a rubber joint, for the sudden 
 rushing in of the air may easily destroy the apparatus. The 
 rubber tube attached to the suction is closed by a screw pinch- 
 cock which has been placed on it beforehand, and in case a 
 
DISTILLATION 3 1 
 
 capillary tube has been used, the pinch-cock on this is gradually 
 opened and the air allowed to enter through it, or after discon- 
 necting the rubber tubing from the suction, the pinch-cock which 
 has just been closed may be opened. The same object may be 
 accomplished most rapidly by closing the tubing leading to the 
 suction with the fingers, detaching it and opening the tube re- 
 peatedly for an instant at a time, until the rushing sound made 
 by the inflowing air ceases. After a test has shown that the 
 apparatus does not leak, the liquid to be distilled is poured in 
 the flask and the distillation begun. 
 
 Heating. In vacuum distillation the flask can be heated 
 directly with a free flame, but the flame must be applied to the 
 side, and not to the bottom of it, as in the ordinary way. Care 
 must be taken to keep the flame constantly moving. It is much 
 more satisfactory and safer to use an oil- or paraffin -bath, or better 
 a metallic air-bath (iron crucible). The latter is covered with 
 a thick asbestos plate containing a round opening in the centre, 
 through which the neck of the fractionating flask may pass ; from 
 the opening to the edge of the plate there is a straight narrow slit. 
 The air-bath must not be too large ; the bottom is covered with 
 a thin layer of asbestos, which will prevent the flask from coming 
 in contact with the metal. The temperature of the oil- or air- 
 bath should, in exact experiments, not be more than 2O-3O 
 higher than the boiling-point indicated by the thermometer. A 
 thermometer is immersed in the bath and the flame so regulated 
 that the difference between the two thermometers is not greater 
 than that mentioned. The heating is not begun until the appara- 
 tus is exhausted. 
 
 To prevent Bumping. In vacuum distillations a troublesome 
 bumping (a sudden, violent ebullition) frequently occurs. To pre- 
 vent this a slow, continuous current of air is drawn through the 
 Hquid, thus keeping it in constant motion. The air current, con- 
 trolled by a pinch-cock, must not be allowed to enter too rapidly, 
 otherwise it will be difficult to maintain a high vacuum. The 
 same effect may be obtained by placing certain substances in the 
 liquid splinters of wood the size of a match, capillary tubes, bits 
 of glass, pieces of porcelain, powdered talc, scraps of platinum 
 wire or foil. Small pieces of pumice-stone bound with platinum 
 
GENERAL PART 
 
 wire also act satisfactorily. For further details concerning vacuum 
 distillation consult " Die Destination unter vermindertem Druck 
 im Laboratorium," R. Anschtitz. 
 
 Lowering of the Boiling-Point. In order that some idea may 
 be obtained as to the approximate lowering of the boiling-point, 
 by diminishing the pressure, the following table is given : 
 
 Substance. 
 
 Boiling-point at 
 12 mm. 
 
 Boiling-point at 
 Ordinary Pressure. 
 
 Difference. 
 
 Acetic acid 
 
 I 9 
 
 118 
 
 99 
 
 Monochloracetic acid . 
 
 8 4 
 
 1 86 
 
 102 
 
 Chlorbenzene 
 
 2 7 
 
 132 
 
 I0 5 
 
 p-Nitrotoluene .... 
 
 1 08 
 
 236 
 
 128 
 
 Acetanilide 
 
 I6 7 
 
 295 
 
 128 
 
 Corrections of the Boiling-Point. If it is not possible in 
 making an exact determination of the boiling-point to have the 
 mercurial column entirely surrounded by the vapour of the liquid, 
 a condition usually obtained by employing a flask, the side-tube 
 of which is at a sufficient distance from the bulb, or a sectional 
 thermometer, or both, then a correction may be applied to the 
 observed boiling-point in one of two ways. The portion of the 
 mercurial column not heated by the vapours that portion above 
 the side-tube is read in degrees (Z). Another thermometer 
 is brought as near as possible to the middle point of this col- 
 umn, the temperature of which is also read (/). If T is the 
 observed boiling temperature, then the following correction is 
 added : L(Tt} . 0.000154. The so-called " corrected " boiling- 
 point may also be obtained as follows : The boiling-point is 
 determined in the usual way ; after the distillation, another sub- 
 stance, the corrected boiling-point of which is known, and which 
 lies near the one in question, is placed in the same flask and dis- 
 tilled under the same conditions. The difference between the 
 corrected and observed boiling-points is applied to the boiling- 
 point of the first substance. 
 
 Distilling oif a Solvent. An operation frequently employed 
 in organic work is distilling off a solvent from the substance dis- 
 
DISTILLATION 33 
 
 solved in it. When the boiling-point of the solvent is sufficiently 
 far away from that of the dissolved substance, a complete separa- 
 tion can be effected by a single distillation. The methods used 
 depend upon the quantity of the solution, that of the dissolved 
 substance and the boiling-point of the solvent. The methods 
 which can be used for distilling off low boiling solvents, like ether, 
 ligroin, carbon disulphide, alcohol, and others, will be described 
 first. If a small quantity of a solvent is to be evaporated, and it 
 is not worth the trouble to recover it by condensation, then, in 
 case the solvent is ether, ligroin, or carbon disulphide, the solution 
 is poured into a small flask, and this is immersed in a larger vessel 
 filled with warm water. The vaporisation is considerably accel- 
 erated by shaking the flask. The operation is more rapidly per- 
 formed by heating the flask on a water-bath. To prevent a 
 sudden foaming, due to retarded ebullition, some small pieces of 
 platinum wire or capillary tubes are placed in the liquid ; the 
 evaporation is also facilitated by frequent shaking. Should the 
 vapours become ignited from the flame of the water-bath, no 
 attempt to blow out the burning vapours should be made; but 
 the burner is extinguished, the flask removed from the bath with 
 a cloth, and the mouth covered with a watch-glass. Carbon disul- 
 phide, on account of its great inflammability, is never vaporised 
 in this way, but always without a flame. 
 
 Large quantities of solvents may also be evaporated by these 
 two methods, but the entire quantity is not treated at once. A 
 portion is placed in a small flask, and when this has been evap- 
 orated, a second portion is added, and so on. The danger of 
 ignition of the- solvent may be avoided by inserting in the flask 
 a glass tube, extending to within a few centimetres of the level 
 of the liquid, supported firmly by a clamp, and attached by rubber 
 tubing to the suction. The tube must at no time touch the 
 liquid. 
 
 For rapid evaporation of small quantities of ether, the following 
 method of procedure is recommended : A few cubic centimetres 
 of the solution are placed in a sufficiently wide test-tube ; this is 
 warmed, with continuous shaking, over a small, luminous flame. 
 
34 
 
 GENERAL PART 
 
 After the first portion is evaporated, the second is added, and 
 so on. Since the vapours of the ether almost regularly become 
 ignited, this event should always be expected, and should occasion 
 no alarm. When it happens, the heating is interrupted for a 
 moment, and the flame is easily extinguished by blowing on it or 
 covering the mouth of the test-tube. If the tube is held as nearly 
 horizontal as possible during the heating, the danger of ignition 
 is lessened. 
 
 If it is desired to distil off a larger quantity of ether, ligrdin, 
 or carbon disulphide, and to recover it by condensation, the re- 
 ceiver is attached to the condenser tube by a cork, and the flask 
 is heated by immersing it in a water-bath containing hot water. 
 To prevent the liquid from being superheated, a silk thread as 
 frayed as possible at the end reaching to the bottom of the flask 
 is suspended from the neck and the flask is shaken frequently 
 during the distillation (Fig. 28). The entire quantity of the liquid 
 is not placed in the flask at once, but only a portion : after the 
 solvent has been distilled off from this, an- 
 other portion is added, and so on. 
 
 By the use of the so-called safety water- 
 bath, i.e. one in which the flame is sur- 
 rounded by a wire gauze as in Davy's Safety 
 Lamp, ether and ligro'in can be distilled by 
 continuous heating with a flame. It is not 
 safe to distil off carbon disulphide even from 
 this apparatus, since, when it becomes suffi- 
 ciently hot, it will ignite spontaneously with- 
 out the intervention of a flame. 
 
 By the use of a coil condenser (Fig. 
 27) the distillation of solvents is greatly 
 facilitated. The free flame, if it be sur- 
 rounded by a cylinder of wire gauze, may 
 be employed in place of a water-bath. 
 A piece of rubber tubing attached to the 
 side tube of the receiver carries the vapours to a hood or below 
 the surface of the table. 
 
 FIG. 27. 
 
DISTILLATION 
 
 35 
 
 The apparatus best adapted to distilling off any desired quan- 
 tity of ether is represented in Fig. 29. A fractionating flask, 
 into the neck of which a dropping-funnel is inserted, is con- 
 nected with an ordinary condenser or an upright coil condenser. 
 During the heating by means of hot water, or in special cases, 
 the water-bath may be heated with a flame, or the flask may be 
 heated directly by a flame protected by a safety gauze, the ethereal 
 solution is allowed to flow gradually from the dropping-funnel into 
 the flask in the bottom of which are a few scraps of platinum, 
 or pieces of unglazed porcelain. 
 
 
 FIG. 28. 
 
 If the flow of the solution is regulated so that the same quantity 
 of liquid is added as that distilled, the operation may be carried 
 on continuously, for hours. The quantity of ether collected in the 
 receiver is prevented from becoming too large, by pouring it into a 
 larger vessel from time to time. To protect the ether from igni- 
 tion, the mouth of the receiver is closed by a loose plug of cotton, 
 or the receiver, united to the condensing tube by a cork, is con- 
 nected with the hood by rubber tubing. Besides its convenient 
 manipulation, this method possesses the further advantage that 
 after the ccmpletion of the distillation the dropping-funnel may 
 be replaced by a thermometer, and the residue can be distilled 
 directly from the fractionating flask. This is an especially eco- 
 
36 GENERAL PART 
 
 nomical procedure when the quantity of the dissolved substance 
 is small. In a case of this kind the size of the flask is selected 
 with reference to the residue that may be expected. In distilling 
 off alcohol, it is necessary to heat the water-bath continuously, 
 and to always use threads. The distillation may be hastened by 
 placing the flask not upon, but in, the water-bath. If a solution 
 of common salt is employed in the bath, the temperature is raised, 
 and the distillation proceeds still more rapidly. 
 
 Cylinders that fit in the water-bath, and are perforated at the 
 bottom and on the sides, may be used with great advantage in 
 place of the simple ring covers. This device permits the heating 
 of the distillation flask with steam, not only at the bottom, but also 
 on the sides. 
 
 If one has had sufficient experience in laboratory work, alcohol 
 
 FIG. 29. 
 
 may be distilled off by heating the flask on a wire gauze or sand- 
 bath over a flame. In this case especial care must be taken not 
 to use too large quantities at one time. Benzene can be distilled 
 off under the same conditions as alcohol. The methods appli- 
 cable to high boiling liquids have been given under "Distilla- 
 tion." (See page 16.) 
 
DISTILLATION WITH STEAM 
 
 37 
 
 In comparatively few cases the difference between the boiling- 
 points of the solvent and the dissolved substance is a slight one ; 
 under these conditions the separation must be effected by a 
 systematic fractional distillation with the aid of fractionating 
 apparatus. 
 
 DISTILLATION WITH STEAM 
 
 A particular kind of distillation, very frequently employed in 
 organic work for the purification or separation of a mixture, is 
 distillation with steam. Many substances, even those distilling far 
 above ioo, or those not volatile without decomposition, possess 
 the property, when heated with water, or when steam is passed 
 over or through them, of volatilising with the steam. This phe- 
 nomenon is explained as follows : Suppose we take a mixture of 
 two liquids that are absolutely insoluble in one another. Each 
 liquid will exert its own vapour pressure as it would if it were 
 alone, and will not in any way be influenced by the other. A 
 practical example of this, to be taken up later, is a mixture of 
 water (B. P. 100) and brombenzene (B. P. 155). When this is 
 gradually heated, the vapour pressure of both substances will in- 
 crease, and boiling will begin when the sum of the vapour pres- 
 sures is equal to the barometric pressure, which we shall assume 
 to be 760 mm. The mixture will boil at 95.25, as will be seen 
 from the following table : 
 
 t 
 
 Vapour pressure 1 of C c H.-,Br 
 
 Vapour pressure of H 2 O 
 
 Total 
 
 95 
 
 120 mm. 
 
 634 mm. 
 
 754 mm. 
 
 95.25 
 
 121 mm. 
 
 639 mm. 
 
 760 mm. 
 
 96 
 
 124 mm. 
 
 657 mm. 
 
 781 mm. 
 
 Thus at this temperature a mixture of water and brombenzene 
 distils over. The proportion of the two substances will be seen 
 from the following considerations : According to Avogadro's Law, 
 
 1 The vapour pressure of brombenzene is calculated by interpolation from the 
 values found by Young at 90 and 100. (Journ. Chem. Soc. 55, p. 486.) 
 
38 GENERAL PART 
 
 under the same conditions of temperature and pressure equal 
 volumes of all ideal gases contain the same number of molecules. 
 If temperature is the same and pressure different, the number of 
 molecules in the same volume will be proportional to the pressure. 
 Let us now consider the mixture consisting of the vapours of water 
 and brombenzene at 95.25. Since at this temperature the former 
 exerts a vapour pressure of 639 mm., and the latter a vapour pres- 
 sure of 121 mm., the molecular quantities must be in the same 
 ratio, i.e. for every 639 molecules of water 121 molecules of brom- 
 benzene will be present. In order to calculate the weights of the 
 substances that distil over, we must multiply the number of mole- 
 cules with the molecular weight of each substance. In our 
 example, for 639 x 18 parts by weight of water, 121 x 157 parts 
 by weight of brombenzene will distil over, which corresponds 
 approximately to 3 parts by weight of water and 5 parts by weight 
 of brombenzene. This proportion remains constant until one of 
 the two has completely distilled over. 
 
 It must be stated that such an ideal condition of distillation 
 with steam is never realised. There are no substances that are 
 absolutely insoluble in one another. Furthermore, there is the 
 disturbing influence of vapour pressure, which is quite small in the 
 example given above. And again, since vapours do not strictly 
 obey Avogadro's Law, the ratio of the two substances in the dis- 
 tillate is somewhat irregular. Finally, since the heating is carried 
 out by steam, and the temperature of the substance is never raised 
 to the exact boiling point, the mean temperature is somewhat 
 different from that given above, and the proportions are therefore 
 altered. 
 
 Apparatus. The apparatus used for distillation with steam 
 is represented in Fig. 30. A round flask inclined at an angle 
 is closed by a two-hole cork; through one hole passes a not 
 too narrow glass tube reaching to the bottom and serving to 
 lead in the steam; the other hole bears a short glass tube 
 the end of which is just below the cork, the other end is con- 
 nected with a long condenser. The distillation flask selected is 
 of such a size that the liquid fills it not more than half full. 
 
DISTILLATION WITH STEAM 39 
 
 In order that the steam may act on an oil at the bottom of 
 the flask, the inlet tube is bent so that it may reach the lowest 
 point of the flask. Steam is generated in a tin vessel about 
 half-filled with water, the neck being closed by a two-hole stop- 
 per ; into one hole is inserted a safety-tube partially filled with 
 mercury ; the lower end of this tube does not touch the water ; 
 through the other hole passes the outlet tube bent at a right 
 angle. 
 
 Method of Procedure. The experiment is begun by heating 
 the steam generator and the flask simultaneously, the former con- 
 veniently by means of a low burner (Fletcher burner). The flask 
 may be heated on a wire gauze over a free flame ; but since at 
 times a very troublesome " bumping " will occur, it is better, if 
 this happens, to heat on a briskly boiling water-bath. As soon 
 as the water in the generator boils and the liquid in the flask has 
 been heated to the proper point, the tubes of the two vessels are 
 connected with rubber tubing. The distillation is then continued 
 until the condensed steam passes over unaccompanied by any of 
 the substance. Should the steam escape from the safety-tube, 
 the generator is being heated too strongly, and the flame should 
 be lowered. To prevent the partial condensation of vapours in 
 the upper cool part of the flask this should be covered with sev- 
 eral layers of thick cloth to lessen the radiation of heat. If the 
 quantity of substance to be distilled is small, so that only a small 
 flask need be used, the preliminary and continued heating of the 
 latter is superfluous : the steam can be passed at once into the 
 cold liquid. If a compound is very easily volatile with steam, 
 the introduction of the latter may be omitted ; in this case it is 
 only necessary to mix the compound with several times its volume 
 of water and distil directly from the flask. If the substance to 
 be distilled is solid, and its vapour forms crystals in the condenser, 
 these may be removed provided the substance melts below 100, 
 by drawing off the water in the condenser for a short time. The 
 substance is melted by the hot steam and flows into the receiver. 
 If after this operation the water is to be turned into the condenser 
 again, it must be done slowly at first, otherwise the cold water 
 
4 o 
 
 GENERAL PART 
 
DISTILLATION WITH STEAM 4! 
 
 coming in contact with the hot condenser may easily crack it. 
 When the melting-point of the substance is above 100, in order 
 to keep the condenser free from crystals, the distillation is inter- 
 rupted for a short time, and the crystals are pushed out of the 
 tube by a long glass rod. 
 
 The end of the operation is indicated, if the substance is diffi- 
 cultly soluble in water, by the fact that the water passing over 
 carries no drops of oil or crystals with it. But when the substance 
 * is soluble, even though the condensed water is apparently pure, it 
 may still contain considerable quantities of the dissolved substance. 
 In this case, to determine when the end of the operation has been 
 
 FIG. 31. 
 
 reached, a small quantity, about 10 c.c., is collected in a test-tube, 
 shaken up with ether, the ether decanted and evaporated. If no 
 residue remains, the distillation is finished. When a substance 
 shows a colour reaction, e.g. aniline with bleaching powder, 
 advantage is taken of this to decide the question. After the 
 distillation is ended the rubber tubing is first removed from the 
 distilling flask, and then, after this has been done, the flame under 
 the generator is extinguished. This point is also carefully ob- 
 served when the distillation is interrupted ; otherwise it may 
 happen that the contents of the flask will be drawn back into 
 the generator. 
 
 Superheated Steam. In dealing with very difficultly volatile 
 compounds, it is frequently necessary to conduct the distillation 
 
42 GENERAL PART 
 
 with the aid of superheated steam. A conically wound copper 
 tube is interposed between the steam generator and the distilling 
 flask (Fig. 31). In order to superheat the steam, a large burner is 
 placed under the spiral in such a position that the flame comes in 
 contact with the interior of the spiral. Since for many purposes 
 it is necessary to use superheated steam at a definite temperature, 
 a small opening is made in the steam exit and a piece of metal 
 tubing affixed to it. A thermometer is inserted into this tubulure 
 and held in position by means of asbestos twine. The distillation 
 is still further facilitated by heating the flask to a high tempera- 
 ture in an oil- or water-bath. Under these conditions the sub- 
 stance to be distilled is not covered with a layer of water. 
 
 The apparatus represented in Fig. 31 A was proposed by 
 V. Haehl and Co. of Strassburg. It is made in different sizes, 
 
 =y 
 
 FIG. 31 A. 
 
 and may be used with great advantage in the laboratory and for 
 work on the large scale. It consists of a hollow filter-plate, sur- 
 rounded with a double layer of thick asbestos board. The latter 
 is provided with a large opening in the lower half for the heat of 
 the flame. A number of smaller openings are found in the upper 
 half, which permit the escape of the hot gases. The superheat- 
 ing of the steam is rendered very efficient by the passage of the 
 hot gases through the numerous canals. 
 
SEPARATION OF LIQUID MIXTURES 43 
 
 SEPARATION OF LIQUID MIXTURES. SEPARATION 
 BY EXTRACTION. SALTING OUT 
 
 Separation of Liquids. If the separation of large quantities ot 
 two non-miscible liquids, one of which is for the most part water 
 or a water solution, is to be effected, it can be done 
 with a separating funnel (Fig. 32). If the liquid 
 desired is of a greater specific gravity than that of 
 water, it is allowed to flow off through the stem by 
 opening the cock. If, however, it floats upon the 
 water, the latter is first allowed to flow off, and the 
 liquid remaining is poured out of the top of the fun- 
 nel. By this manipulation the liquid is prevented 
 from coming in contact with the portion of water 
 remaining in the cock, and adhering to the sides of 
 the stem. For the separation of small quantities of 
 liquids a small separating funnel, the so-called drop- 
 ping funnel, is employed. If the quantity of liquid is 
 so small that even a dropping funnel is too large, a FIG - 3 2 - 
 capillary pipette is used (Figs. 33 and 34). The mixture to be 
 separated is placed in a narrow test-tube, the pipette is immersed 
 in the mixture almost to the surface of contact of the two liquids 
 in case the upper layer is to be removed, the test-tube is brought 
 to the level of the eyes, and the upper layer drawn off. The 
 tubing is then closed by pressure with the teeth or fingers and the 
 pipette removed from the tube. If the lower layer is the one 
 desired, the pipette is immersed to the bottom of the test-tube, 
 and the operation conducted as before. Pipettes of this kind are 
 very easily -made from glass tubing; and if one is accustomed to 
 work with them, are indispensable. 
 
 Separation by Extraction. When a substance is held in sus- 
 pension or dissolved in a liquid, generally water, the removal of 
 the dissolved substance may be effected by agitating the solution 
 with another solvent which will more readily dissolve the substance, 
 but which is not miscible with the first liquid, drawing off this and 
 
44 GENERAL PART 
 
 distilling it. For extraction, ether is generally used ; in special 
 cases carbon disulphide, ligroi'n, chloroform, benzene, amyl alco- 
 hol, etc., may be used. In the discussion following it will be 
 assumed that the extraction is made with ether. 
 
 If the liquid to be separated is insoluble in water and is present 
 in such a small quantity that a direct separation would cause a 
 loss owing to the adhesion of the liquid to the walls of the vessel, 
 or if it is held in suspension by the water in the form of individual 
 
 FIG. 33. FIG. 34. 
 
 drops, ether is added to the mixture ; it is then shaken, allowed 
 to stand, the two layers separated, and the ether evaporated. 
 
 A similar method is followed if the substance is completely 
 soluble in water, or if a portion of it is soluble and the 
 remainder held in suspension. If from an aqueous solution a 
 considerable portion of a solid or liquid separates out, it is not 
 immediately extracted with ether, but if the substance sepa- 
 rating out is a solid, it is first filtered off; if a liquid, the oily 
 layer is separated in a dropping funnel, and then the filtrate is 
 
SEPARATION BY EXTRACTION 45 
 
 extracted with ether. In many cases, e.g. when the layer of oil 
 is very turbid, or the solution strongly acid or alkaline, thus 
 rendering filtration difficult, the entire solution may be treated 
 at once with ether. With substances soluble in water the extrac- 
 tion must be repeated one or more times in proportion to the 
 greater or less solubility of the substance. If it is desirable to avoid 
 using large quantities of ether, after the first extraction it is dis- 
 tilled off and used for the second extraction, and so on. The 
 extraction is repeated until a test portion of the ethereal solution, 
 evaporated on a watch-glass, leaves no residue. If the test portion 
 is evaporated by blowing the breath on it, the beginner will prob- 
 ably often be deceived by the appearance of an abundant quan- 
 tity of crystals of ice, formed by the condensation of the moisture 
 of the breath, due to the cold produced by the evaporation of the 
 ether. Another error into which the beginner often falls when 
 extracting with ether is this : in most chemical processes small 
 quantities of coloured impurities are formed ; on extraction, these 
 impart a colour to the ether. The tendency is to continue the ex- 
 traction until the ether is no longer coloured ; but the proper method 
 of procedure is just the reverse of this. On extracting colourless 
 compounds, the colouring of the ether does not show that it still 
 contains any of the substance dissolved; the above-mentioned test 
 gives the only safe indication of the presence of the substance. 
 
 In an extraction the following points are to be observed : Hot 
 liquids are allowed to stand until they are cold before they are ex- 
 tracted with ether, carbon disulphide, or other low boiling solvents. 
 It frequently happens that, after long standing, two layers of liquids 
 will not separate, in consequence of the formation of a flocculent 
 precipitate floating in the liquids at the surface of contact. This 
 difficulty may be obviated either by stirring the liquids with a glass 
 rod, or by giving the separating funnel a circular motion in a hori- 
 zontal plane, in such a way as not to cause the two layers to be 
 mixed by the shaking. Under certain conditions the neck of the 
 funnel may be closed with a cork bearing a glass tube attached to 
 the suction ; by this means the space over the liquid is exhausted. 
 The bubbles of gas which now rise through the liquid frequently 
 
46 GENERAL PART 
 
 destroy the troublesome emulsion. The same object may also be 
 attained by adding a few drops of alcohol to the ether. If the sepa- 
 ration of the layers is very imperfect, the cause is often due to the 
 fact that an insufficient quantity of ether has been used ; in this case 
 more ether is added. If all of these methods prove ineffectual, then 
 a complete separation may be obtained by first filtering the mix- 
 ture, best with the aid of a Biichner funnel, which will retain the 
 precipitate causing the emulsion, and then allowing it to stand. 
 
 Occasionally when extracting an aqueous solution containing 
 inorganic salts with ether, they will separate out as solids. In 
 this case water is added until the salts are redissolved, or the 
 solution is filtered, with suction. 
 
 If the specific gravity of an ethereal solution is approximately the 
 same as that of the water solution, the separation often takes place 
 only with difficulty. Some common salt is then added, by which 
 the specific gravity of the aqueous solution is increased. 
 
 Under certain conditions both the ethereal and aqueous solu- 
 tions are so coloured that they cannot be distinguished. In this 
 case the separating funnel is held toward the light ; in the even- 
 ing a luminous flame is placed behind it, and the eye is directed 
 to the liquid at a point just above the cock. On opening the 
 cock, the eye will readily detect the layer separating the two 
 liquids, as it approaches the opening. 
 
 Theory of Separation by Extraction. Suppose we take a mix- 
 ture of two immiscible solvents i. and 2., and add to this a sub- 
 stance that has the same molecular weight in both liquids, and is 
 furthermore twice as soluble in i. as in an equal volume of 2. If 
 we use a quantity of the substance that will saturate both solvents, 
 then in a unit volume of i. we shall have twice as much in solution 
 as we have in a unit volume of 2., and the concentrations will be 
 in the ratio of 2 : i. If to both solvents in a vessel we add a 
 quantity of the substance that will only form an unsaturated solu- 
 tion, or if we dissolve the substance in one solvent and shake this 
 with the second solvent, we shall find that, in either case, the sub- 
 stance distributes itself in such a way that the ratio of the concen- 
 trations (the distribution coefficient /) is again 2 : i (Berthelot and 
 
SEPARATION BY EXTRACTION 
 
 47 
 
 Jungfleisch). Suppose we represent the maximum concentrations 
 by ^ and K^ and let k and k. 2 represent the concentrations of 
 the unsaturated solutions. We have the equation : 
 
 k = * = ^ - 
 K% 2 
 
 If, for example, the amount of the dissolved substance is a, and 
 if equal volumes of solvents i. and 2. are taken, after the first ex- 
 traction solvent i. will contain f a, while solvent 2. will only con- 
 tain ^ a. The greater the difference in solubility the more com- 
 plete will the extraction be. When two volumes of i. and one 
 volume of 2. are used for extraction, the amount of a in two vol- 
 umes of i. may be calculated in the following manner : 
 
 Solvent. 
 
 Volumes. 
 
 Dissolved 
 Substance. 
 
 Concentration, i.e. quotient of 
 dissolved substance and volumes 
 of solvents. 
 
 
 
 
 X 
 
 I. 
 
 2 
 
 X 
 
 
 
 
 
 2 
 
 2. 
 
 I 
 
 a x 
 
 (-*) 
 
 The ratio of concentrations must now be equal to the distribution 
 coefficient, i.e. : 
 
 x 
 
 2 2 4 
 
 -, 7 = - , and hence x - a. 
 
 (a-x) i' 5 
 
 The principle of distribution may be generally expressed as 
 bllows : 
 
 Solvent. 
 
 Volumes. 
 
 Dissolved 
 substance. 
 
 Concentration. 
 
 Coefficient of dis- 
 tribution of i. 
 according to 2. 
 
 
 
 
 X 
 
 
 ' 
 
 V l 
 
 X 
 
 
 
 
 
 
 a - x 
 
 * 
 
 
 *, 
 
 
 v, 
 
 
4 8 
 
 GENERAL PART 
 
 , > i 
 
 K, * *At 7 
 
 In practical work we have this question to consider : Is it expedi- 
 ent to carry on the extraction in one operation by a given volume of 
 the solvent, or do this in several operations by the use of small por- 
 tions of the solvent ? The question may be answered as follows : In 
 the example under consideration, a single extraction by an equal 
 volume of i. dissolved f a. If in a second experiment we only 
 use a half volume of i. then x parts of a will go into solution, and 
 x will be smaller than |- a. The portion that remains in solution 
 in 2. will be (a x). We therefore have the following ratio : 
 
 
 
 
 Concentration, i.e. 
 
 Solvent. 
 
 Volumes. 
 
 Dissolved substance. 
 
 quotient of dissolved 
 substance and vol- 
 
 
 
 
 umes of solvents. 
 
 I. 
 
 I 
 2 
 
 X 
 
 X 
 - 2.X 
 I 
 
 
 
 
 2 
 
 2. 
 
 I 
 
 a - x 
 
 a x 
 
 But the ratio of concentrations must be equal to the coefficient 
 of distribution ; consequently : 
 
 2X 2 a 
 
 = - ; or x - 
 
 a x i 2 
 
 One half of a is therefore in solvent i. and the other half remains 
 in solvent 2. If we now shake 2. with the second half of solvent 
 
 i., a portion equal to one half of -, namely -, will be extracted 
 
 by the latter. The total amount extracted by using solvent i. in 
 
 a & -7 
 two portions is - + - = ^ a, whereas the amount extracted when 
 
 2 4 4 
 the solvent is used in one operation is -| a. Thus a given quantity 
 
SEPARATION BY EXTRACTION 49 
 
 of the solvent is much more efficient when it is used in small 
 portions than it is when all of it is used in one operation. The 
 first procedure has the disadvantage of requiring more time than 
 the second. But since in laboratory work time is of greater con- 
 sequence than the price of the solvent, large quantities of the 
 solvent are used in one operation. It is clear from these obser- 
 vations that a quantitative extraction, in the strict sense of the 
 word, is impossible, even by a repetition of the process. Thus 
 
 --!--'+ +-? cannot possibly be equal to a. 
 2 4 8 16 
 
 The above discussions apply to solvents only which are not 
 themselves miscible. This is not strictly true for mixtures of 
 water and ether, since ether is soluble in water, as water is in ether. 
 
 The same formulas may be used to express the solubilities of 
 unit weights, as well as of unit volumes of solvents. In each case 
 the distribution coefficient will naturally have a different value. 
 
 Salting Out. A very valuable method to induce substances 
 dissolved in water to separate out is known as " salting out." 
 Many substances soluble in pure water are insoluble or difficultly 
 soluble in an aqueous solution of certain salts ; if, therefore, sodium 
 chloride, potassium chloride, potash, calcium chloride, ammonium 
 chloride, Glauber's salt, sodium acetate, ammonium sulphate, or 
 other salt is added to the solution, this is dissolved, and the sub- 
 stance previously in solution separates out. By this method many 
 compounds like alcohol, acetone, etc., which are so easily soluble 
 in water that they cannot be removed from it by extraction with 
 ether, can be separated out with ease. The method of procedure 
 is this : One of the above-mentioned salts, usually solid potash, is 
 added to the solution until no more will dissolve. The substance 
 thus forced out of solution collects above the heavier salt-solution 
 and is removed by decantation or suction. 
 
 A combination of extraction and salting out also presents many 
 advantages. If to the solution of a compound in water one of 
 the salts mentioned is added it is best to use finely pulverized 
 sodium chloride before the extraction with ether, this latter is 
 greatly facilitated for several reasons. In the first place, a portion 
 E 
 
50 GENERAL PART 
 
 of the dissolved substance will separate out, due to the " salting 
 out " action ; furthermore, the solubility of the substance in the 
 the new solvent sodium chloride solution will be diminished 
 so that on extracting, a larger portion is dissolved by the ether 
 than on treating the solution directly with it, and finally, ether 
 does not dissolve so readily in a sodium chloride solution as in 
 water, so that the volume of the ethereal solution is larger. The 
 amount of sodium chloride to be added is about 25-30 grammes 
 of the finely pulverised salt to 100 c.c. of the aqueous solution. 
 Unfortunately the method of " salting out " has not been so 
 generally adopted in scientific laboratories as it deserves, while in 
 the laboratories of technical chemists it has long been in daily 
 use. Among the reagents constantly used, a bottle of solid sodium 
 chloride should not be wanting. In many cases, instead of the 
 salt, a concentrated aqueous solution may also be used. Con- 
 cerning the salting out of electrolytes see theoretical considera- 
 tions under " Benzenesulphonic Acid." 
 
 DECOLOURISING. REMOVAL OF TARRY MATTER 
 
 As is well known, animal charcoal possesses the property of 
 being able to remove the colour from certain solutions ; for this 
 reason it is frequently employed in the laboratory to free a colour- 
 less substance from coloured impurities. If it is to be used to 
 remove the colour of a solid substance, the latter is first dissolved 
 in a suitable solvent, then boiled with the animal charcoal and 
 filtered. Before treating a hot solution, it is allowed to cool 
 somewhat, since when animal charcoal comes in contact with 
 liquids heated nearly to the boiling-point, a violent ebullition is 
 frequently caused, and an overflowing of the liquid may easily take 
 place. When a solvent not miscible with water is used, the ani- 
 mal charcoal, which is generally moist, is previously dried on the 
 water-bath. The solvent selected is such that upon cooling the 
 decolourised solution, the substance will crystallise out. In carry- 
 ing out this operation, the general rule that no animal charcoal is 
 added until the substance to be decolourised has completely dis- 
 
DECOLOURISING. REMOVAL OF TARRY MATTER 5 1 
 
 solved, should be followed. Under these conditions only, is it 
 certain that a portion of the substance does not remain undissolved 
 mixed with the charcoal. The quantity of animal charcoal to be 
 added to a solution depends upon the intensity of the colour of 
 the latter. To a solution very slightly coloured, a small quantity 
 is added ; to a deeply coloured solution, a larger quantity. Very 
 finely divided precipitates in water which pass through the filter 
 may also be removed by the use of animal charcoal. When, e.g. 
 tin is precipitated with hydrogen sulphide, the tin sulphide is 
 often so finely divided that it runs through the filter. If the 
 liquid is boiled with animal charcoal, the filtration presents no 
 difficulty. 
 
 The use of animal charcoal, especially when it is in a very finely 
 divided condition, has the disadvantage that at times it passes 
 through the filter and contaminates the filtrate. This may be 
 prevented frequently, by filtering again, or by boiling the filtrate 
 a few minutes before the second filtration. When substances to 
 be analysed have been decolourised with animal charcoal, care 
 must always be taken to prevent the contamination of the sub- 
 stance. In such cases it is again crystallised without the use of 
 animal charcoal. This difficulty may also be prevented or essen- 
 tially lessened, by washing the charcoal with water several times 
 before using ; the portion suspended in the water is decanted, and 
 only the coarser residue which easily settles at the bottom is used. 
 
 Recently the use of animal charcoal in the sugar industry has 
 been replaced in part by a mixture of fine wood meal and floated 
 infusorial earth (kieselguhr) . This mixture ought to be of great 
 advantage in the laboratory, for decolourising purposes, if used in 
 the same way on a small scale. To the mixture is ascribed very 
 superior purifying properties, so that by using much smaller quan- 
 tities the same effect is obtained as with far larger quantities of 
 animal charcoal. In order to prevent an easily oxidisable liquid 
 from decomposing when it is heated in the air this action being 
 generally attended with more or less colouration a gaseous re- 
 ducing or protecting agent is passed through it ; e.g. sulphur dioxide, 
 hydrogen sulphide, or carbon dioxide. Very easilv oxidisable sub- 
 
52 GENERAL PART 
 
 stances are not evaporated in a dish, but in a flask, since in this 
 the liquid is better protected from the action of the air. 
 
 Not only coloured impurities, but those of a tarry character, 
 may also be removed by boiling with animal charcoal as above 
 described. A mixture of wood meal and infusorial earth with 
 which the solution may likewise be boiled is said to be of great 
 value. 
 
 For the absorption of tarry impurities, in so far as they are 
 liquid or oily, unglazed, porous plates (drying plates) may be 
 used with advantage, the substances being firmly pressed out with 
 a spatula in a thin layer. If one pressing out is insufficient, the 
 substance is spread out again upon a fresh, unused portion of 
 the plate. The absorption of an oil may often be facilitated by 
 moistening the substance on the plate with alcohol, ether, or 
 ligroin, which at times will dissolve the impurities without causing 
 a solution of the substance. Oily by-products may also be removed 
 by pressing the substance between a number of layers of filter- 
 paper. For this purpose either a screw-press is used, or the 
 substance is placed in layers of filter- paper between two wooden 
 blocks, the upper one of which bears a heavy object. 
 
 DRYING 
 
 Drying Solid Compounds. Under the chapter on "Crystallisa- 
 tion," page 9, the method of drying moist crystals has already been 
 given. This method is naturally applicable to all solids, even if 
 they are not crystallised, or only imperfectly crystallised, so that it 
 will be unnecessary to repeat the directions already given. But 
 a few methods, not so refined, and generally employed in dealing 
 with crude products will be referred to here. Before a substance 
 is dried by allowing it to lie in the air or in a desiccator, or by 
 heating, the greatest portion of the moisture is removed by press- 
 ure, as follows : The substance lying between a number of layers 
 of filter-paper is placed in a screw press, and pressure applied. 
 The operation is repeated, and the paper renewed, until it is no 
 longer moistened. If a solid is not contaminated by water or other 
 
DRYING 
 
 53 
 
 solvent, but by a liquid by-product, which one desires to obtain, 
 the paper, after it has absorbed this liquid substance, can be ex- 
 tracted with a solvent, like ether. Large masses of a compound 
 not too finely granulated can be tied up in a piece of filter-cloth 
 of fine texture, placed in the screw press, and pressure applied. 
 Smaller quantities of a substance may be pressed out between two 
 wooden blocks, the upper of which bears a heavy object. 
 
 Very often solids may be dried by making use of the power 
 of unglazed porcelain to absorb liquids with avidity. The sub- 
 stance to be dried is pressed out in a thin layer upon a suitable 
 piece of an unglazed porcelain plate, with a spatula, and is allowed 
 to stand for some time, longer or shorter, as may be necessary. 
 If one pressing out is not sufficient, the operation is repeated, 
 using a fresh plate. Oily and tarry impurities may also be removed 
 in this way, as mentioned above. 
 
 Compounds which fuse without decomposition may be dried 
 either upon the water-bath or in an air-bath, or by heating over 
 a free flame until they melt, allowing them to solidify, and then 
 pouring off the water. 
 
 In order to dry a substance at a high temperature in a vacuum, 
 two glass hemispheres, the edges of which are ground and fitted 
 together, are used. The upper vessel is supplied with a tubulure, 
 the opening of which is closed by a cork bearing a glass tube bent 
 at a right angle connected with suction. The sphere may be 
 heated by immersion in a large quantity of hot water or on a 
 boiling water-bath. The upper hemisphere is enveloped in a 
 cloth to prevent the condensation of the vapours. 
 
 Drying Agents for Liquids. Liquids are dried (deprived of 
 water) either by placing in them, or in a solution of them, drying 
 agents. The most frequently employed drying agents are : 
 
 Calcium chloride, 
 
 (a) granulated, 
 
 (*) fused, 
 
 Potassium hydroxide, 
 Sodium hydroxide, 
 
54 GENERAL PART 
 
 Ignited potash, 
 
 Fused sodium sulphate, 
 
 Dehydrated magnesium sulphate. 
 
 Less frequently used are : lime, barium oxide, anhydrous sodium 
 carbonate, anhydrous copper sulphate, phosphorus pentoxide, 
 sodium, and others. 
 
 In the choice of a drying agent care must be taken to select 
 one which will not react with the substance to be dried. For 
 example, calcium chloride unites to form double compounds with 
 alcohols as well as with bases. Consequently, for drying these 
 two classes of compounds, calcium chloride is never used. Caustic 
 potash and caustic soda, as is well known, react with acids and 
 phenols to form salts, upon alcohols to form alcoholates, and upor 
 esters, saponifying them. These drying agents are never used 
 with these substances. Further, acids are never dried with car- 
 bonates, owing to the salt formation taking place. 
 
 Calcium chloride is employed in two forms, granulated and 
 fused. The former acts more energetically, since it possesses a 
 larger acting surface. Still, it has the disadvantage of being more 
 porous than the fused variety and in consequence of this porosity 
 the loss of the substance being dried is greater. For drying small 
 quantities of a substance, or liquids containing very little moisture, 
 it is better, therefore, to use fused calcium chloride. 
 
 On drying bases with caustic potash or caustic soda, it must be 
 borne in mind that these drying agents may be contaminated, at 
 times, with potassium nitrite or sodium nitrite. Since these latter 
 act upon bases, decomposing them, it is necessary to use the pure 
 alkalies, or in place of them potassium carbonate or Glauber's salt. 
 
 Methods of Drying. As already mentioned, liquids may be 
 dried either in the undiluted form or in solution. The first method 
 is followed when the quantity of the liquid is considerable, so that 
 the loss of the substance necessarily incident to the adhesion of 
 the liquid to the drying agent cannot amount to a large percent- 
 age of the whole. Low boiling liquids are always dried directly, 
 without the use of a solvent. If a "solution of a higher boiling 
 
METHODS OF DRYING 55 
 
 compound is to be dried, it is done before the solvent is distilled 
 off. A small quantity of a substance or a viscous substance is 
 designedly treated with a diluting agent, generally ether, and 
 is then dried. 
 
 The drying is accomplished by placing the drying agent in the 
 liquid and allowing the two substances to remain in contact for 
 a longer or shorter time, according to circumstances. So long 
 as a liquid appears turbid, it has not been deprived of its moisture. 
 A liquid about to be dried must never contain drops of water 
 which are visible ; in case it does, it must be treated in a separating 
 funnel or the water drawn off with a capillary pipette : it is then 
 dried. If only a few small drops of water are present, the liquid 
 is first filtered through a small folded filter, or it is poured care- 
 fully into another vessel, and the water drops will remain in the 
 first vessel, adhering to the walls. When a separation of an ethereal 
 from an aqueous solution is to be made, to prevent a portion of 
 the water from being carried along with the ethereal solution, the 
 former is not drawn off through the cock of the vessel, but is 
 poured out of the mouth, as has already been mentioned. 
 
 If a liquid contains very much moisture, and this is the case 
 especially in turbid, milky liquids, it frequently happens that the 
 drying agent will absorb enough water to dissolve itself and thus 
 form an aqueous solution. In this case a fresh quantity of the 
 drying agent is not added at once, but the separation of the two 
 layers is effected by a separating funnel, pipette, or by decanting 
 one of the layers. 
 
 A similar rule obtains for undiluted liquids. The drying of 
 high boiling substances, if they are not volatile at the temperature 
 of the water-bath, may be greatly facilitated by heating them with 
 the drying agent on the water-bath. 
 
 If the boiling point of a liquid is above 200, it may be freed 
 from water, without the aid of a drying agent, by heating for some 
 time on a water-bath under diminished pressure. The water 
 will thus distil over. The apparatus represented in Fig. 20, 
 page 27 is employed for this purpose. The use of a manometer 
 will be unnecessary if this is connected with a good suction pump. 
 
GENERAL PART 
 
 Before distilling a liquid which has been dried, or before dis- 
 tilling off the solvent from such a liquid, it is poured off from the 
 drying agent. To obtain the small portions which adhere to the 
 latter it may be washed with a small quantity of the dried solvent. 
 Low boiling individual liquids (boiling on water-bath) can, under 
 certain conditions, be distilled without a previous separation from 
 the drying agent. If the liquid to be dried is of such a specific 
 gravity that the drying agent will float in it, then, in order to effect 
 the separation, it is poured through a funnel containing a small 
 quantity of glass wool, or asbestos. In some cases, which, how- 
 ever, are rare, a liquid not easily volatile may be dried by expos- 
 ing it in a dish as shallow as possible in a partially exhausted 
 desiccator. 
 
 FILTRATION 
 
 While in analytical operations it is much more desirable to 
 conduct filtrations without employing pressure, the precipitates 
 obtained in organic preparation work are filtered with pressure 
 whenever it is possible. The method presents a number of ad- 
 vantages : the filtration may be made in a much shorter time ; the 
 liquid may be much more completely sepa- 
 rated from the precipitate, in consequence of 
 which the latter will dry more rapidly, etc. 
 
 The student has already learned the meth- 
 ods of filtering without pressure in the opera- 
 tions of analytical chemistry, but he is advised 
 to reread the chapter on Crystallisation (see 
 page i). 
 
 Filtration with Suction. For filtering un- 
 der pressure (suction), a filtering flask a (suc- 
 tion flask) with a side-tube b (Fig. 35) is used. 
 An ordinary flask may be converted into a 
 suction flask by fitting to it a two-hole rubber 
 stopper ; through one hole is passed the stem 
 of a funnel, through the other a glass tube, 
 bent at a right angle, one end of which passes just through the cork, 
 
FILTRATION 5; 
 
 while the other is attached to the suction. For this purpose flasks 
 with thick walls are selected, in order that they may not be crushed 
 by the atmospheric pressure on exhaustion ; if a thin- walled flask 
 is used, it must be exhausted but slightly. 
 
 The funnel used is, in many cases, the ordinary conical glass form, 
 in which is placed the filter. If the funnel is imperfect in construc- 
 tion, and does not possess the correct angle (60), the filter is made 
 narrower or wider, as the case may be, to accommodate it to the 
 angle of the funnel. In order that the point of the filter not sup- 
 ported by the glass walls of the funnel, may not tear on exhaustion, 
 a platinum cone c is previously placed in the funnel. 
 
 If a platinum cone is not at hand, it may be replaced by a coni- 
 cally folded piece of parchment paper or filter-cloth. The filter 
 is moistened with the same liquid which is to be filtered, otherwise 
 it may happen that the filtration is prevented, or, at least, rendered 
 difficult ; e.g. if the filter has been moistened with water, and an 
 alcoholic solution is to be filtered through it, the substance dis- 
 solved in the alcohol may be precipitated in the pores of the filter 
 by the water. If a liquid foams excessively on filtering, as happens 
 at times with alkaline liquids, the rubber tubing is removed sud- 
 denly from time to time from the filter-flask. The pressure of the 
 in-rushing air destroys the bubbles. The foaming may also be pre- 
 vented at times by treating the filtrate with a few drops of alcohol 
 or ether. This is one of the common methods of preventing foam- 
 ing in general. When filtering very small quantities of a liquid, a 
 test-tube is placed in the filter-flask, as is represented in Fig. 36. 
 
 The suction surface may be increased by placing a so-called 
 filter-plate of 'glass or porcelain in the funnel (Fig. 37). If a 
 filter-plate is used, the filter-paper should be of two thicknesses. 
 Upon the plate is first placed a round filter of exactly the same 
 size as the plate, and upon this another round filter, the edge of 
 which projects about 2-3 mm. beyond that of the plate. 
 
 The Blichner funnel is indispensable in working with organic 
 substances. In consequence of its large suction surface, a very 
 rapid filtration is possible. In the filtration of large quantities 
 of substance it should always be used (Fig. 38). 
 
GENERAL PART 
 
 A double filter (described above) may be used in this, but in 
 most cases a single filter is sufficient. Since the Biichner funnels 
 are made of porcelain, and consequently are opaque, they must be 
 carefully cleaned immediately after using. 
 
 FIG. 36. 
 
 FIG. 37 . 
 
 FIG. 38. 
 
 Similar to the Biichner funnel in its construction and action is 
 the so-called " Nutsch " filter. This consists of a shallow dish with 
 a perforated bottom, which is 
 fitted to the cover of a tubu- 
 lated cylinder by means of a 
 rubber ring, the joint being 
 air-tight (Fig. 39). 
 
 If the solution to be filtered 
 acts on the filter-paper, filter- 
 cloth may be used in its place. 
 A fine or coarse meshed cloth 
 is selected, according to the 
 nature of the precipitate ; it is 
 moistened before the filtra- 
 tion. 
 
 If this is also attacked, 
 nitrocellulose cloth may be 
 used ; it is made by treating FlG - 39- 
 
 a cloth woven from plant fibres with a mixture of nitric and sul- 
 phuric acids. Concentrated sulphuric acid may be filtered through 
 
FILTRATION 59 
 
 it. Such cloth and other substances containing nitrocellulose must 
 always be preserved under water, on account of their explosiveness. 
 In cases of this kind the precipitate is retained by using glass 
 wool, or better, long fibrous asbestos, with which the bottom of the 
 funnel, containing in this case a platinum cone, is filled, or it is 
 spread out in thin layers over a filtering plate, or on the surface of 
 a Biichner funnel. Under these conditions, the suction is applied 
 gently at the beginning of the filtration ; as soon as a large quantity 
 of the precipitate has accumulated, the suction is increased. Re- 
 cently acid- and alkali-proof filter disks have also been used in the 
 arts. By the aid of asbestos linings these may be placed in conical 
 or Biichner funnels, and made to render excellent service. Very 
 coarse-grained precipitates can be filtered without the use of a filter 
 by placing in the point of an ordinary glass funnel a sphere of glass (a 
 marble) ; this is surrounded by glass wool, or asbestos, if necessary. 
 Pukall Cells. For the filtration of precipitates, like calcium 
 sulphate, barium sulphate, of strongly acid liquids, etc., PukalPs 
 
 cells (porous cells), made of 
 unglazed clay, are very use- 
 ful. They may be procured 
 in different sizes in the mar- 
 ket, and possess either the 
 form of a cylinder or a mor- 
 tar pestle. The operation is 
 performed as follows : In the 
 
 mouth of the cell is placed a 
 FIG. 40. 
 
 closely fitting stopper bearing 
 
 a glass tube bent twice at right angles, connected with a filter-flask. 
 The tube at each end projects slightly below the stopper (Fig. 40). 
 The cell is now immersed in the liquid to be filtered, contained in 
 a beaker, not too wide, until it almost touches the bottom. When 
 the suction is applied, the liquid filters through the porous walls 
 until the cell is filled, and is then drawn into the flask ; the pre- 
 cipitate remains behind in the vessel, and for the most part is 
 deposited on the exterior walls of the cell. 
 
 Filter-Press. For the filtration of large quantities of substances 
 which filter with difficulty, especially dye-stuffs, barium sulphate, 
 
6o 
 
 GENERAL PART 
 
 calcium sulphate, etc., fil- 
 ter-presses are often used, 
 of which the Hempel form 
 will be described (Fig. 41). 
 The separation of the liquid 
 from the precipitate is ef- 
 fected in the cell c, which 
 consists of two perforated 
 porcelain plates between 
 which is a rubber ring. The 
 first operation in working 
 with the press is the prepara- 
 tion of the cells. Two circu- 
 lar pieces of filter-cloth and 
 two of filter-paper the same 
 size as the plates are cut ; 
 after the cloth (linen or 
 muslin) has been thoroughly 
 moistened with water, the 
 cells are made as follows : 
 At the bottom comes the 
 perforated plate upon which 
 is placed one layer of the 
 filter-paper, and upon this 
 the cloth. After a wide glass 
 tube^-, which extends almost 
 to the opposite side of the 
 cell, has been inserted into 
 the opening of the rubber 
 ring, this is placed upon the 
 cloth, then follows the other 
 piece of cloth, filter-paper, 
 and finally the second plate. 
 The cell is now secured by 
 three clamps, one of which 
 is attached near the glass 
 
 FIG. 41. 
 
SEPARATION OF LIQUID MIXTURES 6i 
 
 tube, and the others equally distant from this. The cell is now 
 ready for the nitration, and is placed between the two corrugated 
 glass plates d. Before it is connected with the vertical tube b, the 
 pinch-cock on this is closed, water is poured into the funnel a, 
 and the cock is now opened until the vertical tube is filled. The 
 cock is again closed and the tube is connected with the cells, the 
 liquid to be filtered poured into the funnel and the cock opened. 
 During the resulting filtration care is taken to keep the funnel 
 partially filled so that the vertical tube is constantly full. If the 
 first portions run through turbid, they are returned to the funnel. 
 In order to wash the precipitate collecting in the cell, the glass 
 tube passing through the rubber ring is partly withdrawn, so that 
 it projects into the cell but a few centimetres. This causes a 
 canal to be formed in the cell from which the wash water can 
 permeate the precipitate in all directions. If the precipitate is 
 large enough to completely fill the interior space of the cell, it 
 forms a solid cake that can be removed without difficulty. But 
 if the precipitate is small, and it is desired to obtain it, the glass 
 tube is withdrawn from the rubber ring, the contents of the cell, 
 
 generally half-fluid, are 
 poured into a beaker, 
 the cell taken apart, and 
 the precipitate adhering 
 to the sides scraped off 
 with a spatula. By fil- 
 tering with suction a 
 complete separation of 
 the liquid and precipi- 
 FIG. 42. tate is effected. If it is 
 
 desired to filter larger quantities of a precipitate than can con- 
 veniently be done in a single cell, two cells connected by a Y-tube 
 may be used. 
 
 Filtering through Muslin. Precipitates which are not too 
 finely divided may be filtered off through a filter-cloth (muslin) 
 stretched over a wooden frame (filter-frame) (Fig. 42). A square 
 piece of muslin or linen, after being thoroughly moistened, is 
 
62 GENERAL PART 
 
 fastened on the four nails of the frame in such a way as to cause 
 a shallow bag in the middle. The frame is placed over a dish oi 
 the proper size and the liquid to be filtered is poured on the 
 cloth and generally filters rapidly through it. If it is desired after 
 washing the precipitate to press it out, the cloth is taken from 
 the four corners, folded together, and squeezed with the hands. 
 The precipitate may be further dried, by tying up the opening 
 of the bag with twine, and then pressing it out carefully under a 
 screw-press. 
 
HEATING UNDER PRESSURE 63 
 
 HEATING UNDER PRESSURE 
 
 Sealed Tubes. Method of Filling. If it is desired to induce 
 a reaction between two substances at a temperature above their 
 boiling-points, they are generally heated in sealed tubes. If a 
 quantitative determination is not to be made, if the substances 
 to be heated do not attack the glass or generate no gases, and if 
 the heating is not to be high, soft glass tubes may be used. But 
 generally, and in quantitative determinations always, difficultly 
 fusible tubes of potash glass are used, since they are not so easily 
 acted upon and do not crack so readily as the former. In filling 
 the tubes the following points are observed. The tube is dried 
 before placing the substance in it. Never put solid or liquid 
 substances directly in the tube, but with the aid of a funnel- tube 
 which should be as wide as possible when the substance is a solid. 
 In proportion to the temperature of the heating a greater or less 
 pressure is developed ; therefore more or less of the substance is 
 placed in the tube, depending on the conditions. The tube is 
 never more than half-filled. Easily volatile substances as well 
 as those giving off vapours, like hydrochloric and hydriodic acids, 
 which render the sealing of the tube difficult, are transferred to 
 the tube just before the sealing is to be done. In withdrawing 
 the funnel-tube care is taken to avoid bringing it in contact 
 with the walls of the tube. 
 
 Sealing. To seal the open end of a tube charged with the 
 substance, it is warmed by holding it at an angle of about 45, 
 with constant turning, in the small luminous flame of a blast- lamp, 
 and then heated strongly in a larger non-luminous flame ; when 
 the glass becomes soft, a previously somewhat warmed glass rod 
 is fused to it (Fig. 43, I). The flame is then applied to the tube 
 at a short distance from the opening, and as soon as the glass has 
 become soft the tube is narrowed by drawing it out suddenly (II). 
 After breaking off or cutting off the end of the capillary tube at 
 z, to allow the air to escape on further heating, it is heated at b, 
 when the tube is softened at this point it is drawn out slightly, 
 
6 4 
 
 GENERAL PART 
 
 the heat is applied just below , it is drawn out again, and so 
 on ; the result is that the form of the end of the tube gradually 
 changes from a cylinder to a sharp-pointed cone. The narrowest 
 part of the latter is then heated with a not too large flame 
 without drawing it further. The soft glass melts together, and 
 there is thus obtained a thick-walled capillary tube which is 
 melted off at the proper place (III). Figure 44 shows the 
 sealed portion of a tube in its natural size. In the formation of 
 
 -a 
 
 ii 
 FIG. 43. 
 
 Ill 
 
 FIG. 44. 
 
 the capillary portion, it is desirable not to turn the tube in the 
 manner previously directed, but to give it a few turns in one direc- 
 tion and then to reverse the motion, otherwise a spiral would be 
 formed owing to the smallness of the glass at that point. After 
 sealing, the heated portion is cooled gradually by holding it in 
 the luminous flame until it is blackened. The sealing of hard 
 glass tubes may be facilitated by placing a brick or tile near the 
 flame in such a position that the heat will be reflected. If ^na 
 
HEATING UNDER PRESSURE 6$ 
 
 is in possession of a cylinder of oxygen, it may be attached to 
 the blast-lamp in place of the blast. At the high temperature 
 of the illuminating gas : oxygen flame, the sealing may be effected 
 with great ease. 
 
 In many cases the operation is rendered difficult by the vapours 
 of the substance attacking the glass, or by the decomposition of 
 the substance with the evolution of troublesome products like 
 carbon, iodine, etc. Under these conditions, the tube is not 
 drawn out first to a narrow tube, as above, but the glass rod 
 fused on is allowed to remain, and this is used to draw out the 
 tube. The sealing is rendered less difficult by allowing the air 
 to have free access to the tube, in order that the evolved vapour 
 may pass out unimpeded. The separation of carbon may be 
 avoided by having an assistant direct a continuous current of air, 
 during the heating, through a narrow tube into the upper part 
 of the tube being sealed ; this will cause the oxidation of the 
 carbon. When dealing with very volatile substances, during the 
 sealing the lower part of the tube is cooled by water, ice, or a 
 freezing mixture. In this case, the services of an assistant will 
 be needed to give to the vessel containing the cooling agent a 
 circular motion corresponding to that of the tube. Under these 
 conditions, it is often advisable to narrow the tube before charging 
 it with the substance, so that it will just admit a funnel-tube as 
 narrow as possible. 
 
 Heating. The heating of sealed tubes (bombs) is conducted 
 in the so-called " bomb-furnace," of which a convenient form is 
 represented in Fig. 45. To be able to carry out the operation of 
 heating at a definite temperature, a cork, covered with asbestos 
 paper, bearing a thermometer, is fitted into the opening at the 
 top of the furnace. The bulb of the thermometer must be about 
 i cm. above the bottom of the iron tube. The sealed tube is not 
 heated directly, but in a thick- walled protecting case of iron 
 closed at one end, in which the glass tube is so placed that the 
 capillary portion is at the open end. In transferring the glass 
 tube to the iron casing the latter is not held vertically, but is 
 slightly inclined from the horizontal, so that the glass tube may 
 
66 
 
 GENERAL PART 
 
 not be broken by suddenly striking the bottom. The iron casft 
 is pushed into the furnace open end first, so that in case of an 
 explosion the fragments of glass are not thrown out of the for- 
 ward end but from the rear of the furnace, directed toward a wall. 
 A "fragment cage" renders the flying pieces of glass harmless. 
 After the tube is in position the front opening is closed by a 
 " drop-slide." The tubes are not heated at once up to the desired 
 temperature, but are warmed gradually. If it is desired to 
 heat a furnace similar to the one represented to a low tempera- 
 ture, the gas tubes are raised and small flames used, rather than 
 a lowering of the gas-tube and the corresponding increase in size 
 
 FIG. 45. 
 
 of flame. The danger of the bursting of the glass tubes may 
 be diminished in many cases, particularly in those in which a 
 very high pressure is developed, by interrupting the heating after 
 a certain length of time, opening the capillary after the tube has 
 completely cooled, and allowing the gases which have been gen- 
 erated to escape. The tube is then resealed and heated again. 
 
 If tubes are to be heated not higher than 100, the convenient 
 so-called " water-bath cannon " is used, in which the case enclos- 
 ing the tube is heated by steam at ordinary pressure ; in this case 
 overheating is impossible. 
 
 Opening the Tubes. Sealed tubes must not be opened until 
 after they are completely cold. The protecting case of iron, con- 
 taining the tube, is removed from the furnace and held in a slightly 
 
HEATING UNDER PRESSURE 6/ 
 
 inclined position, the end of the capillary being higher than the 
 rear end. By means of a slight jerk the capillary end of the glass 
 tube is caused to project from the iron case. The extreme end 
 of the capillary is now held in the flame of a Bunsen burner. In 
 case there is an internal pressure in the tube, the glass on becom- 
 ing soft will be blown out and the gases will escape from the 
 opening thus made, often with such force as to extinguish the 
 flame. If on the softening of the glass the capillary is not blown 
 out, it may be due to the absence of internal pressure or the tube 
 may be stopped up by some of the substance. In the latter case 
 the substance is removed by heating. To show that there is an 
 internal pressure the capillary is held after it has been opened 
 near a small luminous flame ; if the latter is blown out in a long 
 thin flame sidewise, obviously there is pressure. If great pressure 
 exists in a tube to be opened, before blowing the capillary the 
 hand holding the iron casing is protected by a thick glove or a 
 cloth is wrapped around the casing several times at the point 
 where it is held, so that if the tube bursts, in consequence of the 
 sudden diminution of pressure, and the seam of the case should 
 be torn open, the hand is protected from injury. In handling an 
 unopened tube the greatest care possible must be observed. It is 
 never removed from the iron casing to look at it or for any other 
 purpose. On opening, it is held in such a position that neither 
 the operator nor any one else can be injured in case of bursting. 
 
 On heating substances with hydriodic acid and phosphorus, it 
 sometimes happens, that the tube on being opened by a flame, 
 explodes. In this case the explosion is -due to the fact that the 
 phosphine as -well as the hydrogen evolved in the reaction have 
 formed an explosive mixture with the oxygen of the air present 
 in the tube. Under these conditions, the capillary is opened by 
 snipping off the end with pincers or tongs, but in doing so the 
 greatest care must be observed. To remove the end of the cone, 
 it is not necessary to proceed as described below, but the end 
 of the tube is broken directly with a blow of a hammer. 
 
 In order to break off the end of a tube after it has been opened, 
 so that the contents may be emptied out, the procedure is as 
 
68 . GENERAL PART 
 
 follows : At that point of the tube where the cone begins, a well- 
 defined file mark is made, not extending completely around the 
 tube ; this is touched lightly with the hot end of a glass rod, 
 previously heated to fusion in the blast-flame. If the crack caused 
 by this does not extend entirely around the tube, the extreme 
 end of it is again touched with a hot glass rod, by which it is 
 extended, so that the conical end may be lifted off. Instead of a 
 glass rod, a thick iron wire, the end of which has been bent around 
 the iron casing to a semicircle, may be used. If this is heated 
 to redness, the file mark touched with it, and the wire turned, the 
 end of the tube breaks off smoothly. To prevent the fragments 
 of glass from falling into the tube (when a quantitative determina- 
 tion is being made), the method of procedure is this : As before, 
 a deep file mark is made, and on each side of it, at a distance 
 of ^ cm., a strip of moistened filter-paper i cm. wide is wrapped 
 around the tube several times. That portion of the tube between 
 the strips is heated by a small flame, the tube being con- 
 stantly turned, this causes the end to split off smoothly 
 without splintering. If the glass does not crack at once, 
 the heated portion is moistened with a few drops of 
 water, and the breaking off will follow with certainty. 
 
 Volhard Tubes. The tube described by Volhard 
 (Fig. 46) may be used to great advantage when it is 
 desired to heat large quantities of substances in a single 
 tube. It consists of a wide tube to the end of which a 
 narrower one is fused. A tube of this kind, 35 mm. in 
 diameter and 45 cm. in length, contains about \ of a 
 litre, and possesses the further advantage of being easy 
 to seal. If on opening the tube care be taken to cut 
 off as small a portion of the narrow end as possible, 
 it may be used repeatedly. If, finally, the narrowed 
 portion becomes too short, another piece of the same 
 kind of tubing is sealed on. 
 
 Pressure Flasks. Autoclaves. In order to heat substances 
 under pressure at a moderate temperature which on reacting with 
 each other evolve no gaseous products, so that no pressure due 
 
 Jl 
 
HEATING UNDER PRESSURE 
 
 to the reaction is developed, they are sometimes enclosed in 
 
 strong-walled flasks (pressure flasks), wrapped up in a cloth and 
 heated in a water-bath. 
 
 Very well adapted to this purpose are the common 
 soda-water or beer bottles, of the kind represented 
 in Fig. 47. In using them they are not immersed in 
 water already heated, but are slowly heated with the 
 water. The water-bath is closed by a loosely fitting 
 cover, so that in case the bottle bursts, one may not 
 be burned by the hot water. The flasks are not 
 opened until after they are 
 completely cold. 
 
 Large quantities of sub- 
 stances which do not act on metals may 
 
 be heated under pressure in closed ves- 
 sels, generally made of iron, bronze or 
 
 copper (autoclaves). Such vessels are 
 
 not suited for heating acid substances, 
 
 but may be used for neutral or alkaline 
 
 substances. In this laboratory Mannes- 
 
 mann tubes (without seams) are in use, 
 
 one end being welded together, and the 
 
 other is supplied with a screw-thread 
 
 and cap. The open end is cone-shaped. 
 
 The tube is closed by a threaded cap, 
 
 which in section shows a cone. The cap 
 
 is partially filled with lead. After the 
 
 substance has been put in, the cover is 
 
 screwed on as far as possible with the 
 
 hand, the tube is then clamped in a 
 
 vise, and the cap made fast with a 
 
 wrench. The conical end of the tube is 
 
 pressed into the soft lead, thus giving 
 
 an excellent joint. The heating may be 
 
 conducted in an oil-bath, or directly in the bomb-furnace. If the 
 
 heating is to be carried beyond the point at which lead softens, a 
 
 FIG. 48. 
 
70 GENERAL PART 
 
 short metallic condenser about 10 cm. in length may be screwed 
 on the threaded portion of the tube. A slow current of water is 
 passed through the condenser. 
 
 Another form of autoclave is represented in Fig. 48. For the 
 packing a ring of lead or asbestos is used. The tube leading to 
 the interior is designed for a thermometer. The lower portion 
 contains oil in which the thermometer is placed. 
 
MELTING-POINT 
 
 MELTING-POINT 
 
 In organic work the most common method of testing the 
 purity, of characterising and of recognising a solid compound, 
 is the determination of its melting-point. The apparatus most 
 generally used for this purpose is represented in Figs. 49 and 50. 
 A long-necked flask is closed by a cork provided ;vith several 
 canals cut in the sides, through which the heated air and vapours 
 
 may escape, bearing a thermometer. 
 The bulb of the flask is two-thirds 
 rilled with pure concentrated sul- 
 phuric acid, into which is dropped 
 a crystal of .potassium nitrate the 
 size of a pin-head, to prevent it 
 from becoming dark in colour. The 
 substance is placed in a small nar- 
 row tube (melting-point tube), made 
 in the following way : A glass tube 
 4-5 mm. wide is heated at one point 
 while constantly turned, in a small, 
 blast-lamp flame, until it becomes 
 soft, and is then drawn out from 
 Ct both ends to a tube i mm. wide. 
 The narrow tube thus produced is 
 then fused off at its middle point ; 
 the portion lying next to that part 
 of the glass' tube which has not been drawn out is heated as 
 before and is again drawn out, and so on. There is thus pro- 
 duced a tube having the form represented in Fig. 51 a. In 
 order to prepare the melting-point tube from this a file-mark is 
 made at the points indicated, the tube broken off and fused at 
 the narrow end by holding it nearly vertical in a Bunsen flame. 
 Fig. 51 b represents the melting-point tube in its natural size. 
 A supply of several dozen of these is made and preserved in a 
 closed bottle. To transfer to the tube the substance the melt- 
 
 FIG. 49. 
 
 FIG. 50. 
 
72 GENERAL PART 
 
 ing-point of which is to be determined, a small portion of it is 
 pulverised, the end of the tube dipped into it ; by gentle tapping 
 the substance is caused to fall from the upper end to the bot- 
 tom of the tube. In order that it may not form a 
 too loose layer, it is packed by a thin glass rod or 
 platinum wire. The height of the layer should be 
 i mm. and in no case more than 2 mm. To attach 
 the tube different methods may be used. The 
 upper end of the tube may be touched with a drop 
 of sulphuric acid ; this, when brought in contact 
 with the thermometer, will cause it to adhere. It 
 is safer to fasten the tube, just below the mouth, to 
 the thermometer with a thin platinum wire or a 
 rubber ring i mm. wide. The substance is placed 
 at the middle point of the thermometer bulb. 
 The thermometer is now immersed in the sul- 
 phuric acid until the bulb is at about the centre of 
 the liquid ; the flask is heated with a free flame 
 which is given a continuous, uniform motion as in 
 distillation. The burner is inclined at a conven- 
 ient angle, so that, if the flask should break, the 
 hand would not be directly under it. When the 
 melting temperature is reached, it is observed that 
 the previously opaque, unfused substance suddenly 
 becomes transparent and a meniscus is formed on 
 its upper surface. If it is known at about what 
 point the substance will melt, it may be heated 
 rapidly to within 10 of this point, and then slowly 
 with a small flame so that the behaviour of the sub- 
 stance from degree to degree can be easily observed. 
 If the melting-point is not known, it can be readily a * 
 
 ascertained on heating it rapidly to a high tempera- 
 ture. In this case the determination is repeated, heating rapidly 
 until the temperature approaches the melting-point, and then 
 slowly. In many cases when the temperature nears the melting- 
 point this is shown by a softening of the substance before melt- 
 
MELTING-POINT 
 
 73 
 
 ing ; it loosens from the walls of the tube and collects in the 
 middle. If this phenomenon occurs the heating is conducted 
 very slowly from degree to degree. At times proximity to the 
 melting-point may also be recognised by the fact that the par- 
 ticles of the substance which adhered to the upper portion of 
 the tube during the filling, melt before the mass of the sub- 
 stance ; since the hotter and therefore lighter layers of the acid 
 rise to the top, the upper layers of the 
 bath are heated somewhat higher than 
 the lower. 
 
 Instead of the apparatus just de- 
 scribed the one represented in Fig. 52 
 serves very well for the same purpose. 
 The liquid used may be water or sul- 
 phuric acid, depending on the melting- 
 point of the substance to be examined, 
 or in case of a substance with a high 
 melting-point paraffin is placed in a 
 beaker supported on a wire gauze. In 
 order to keep the liquid at a uniform 
 temperature, it is stirred by an up-and- 
 down motion of the glass stirrer a. 
 
 A substance is regarded as pure in 
 most cases, if it melts sharply within 
 one-half or a whole degree, and if after 
 repeated crystallisation the melting-point 
 does not change. In determining the 
 melting-point of a newly discovered sub- 
 stance, one determination is not sufficient even if it is very sharp ; 
 a small portion is recrystallised and the melting-point again deter- 
 mined. Many substances decompose on fusing, if this takes place 
 suddenly at a definite temperature, this may also be regarded as 
 a characteristic of the substance. 
 
 Since many compounds on heating decompose explosively, and 
 since in the last few years it has happened that the explosion of 
 minute quantities of a compound has shattered the melting-point 
 
 FIG. 52. 
 
74 
 
 GENERAL PART 
 
 apparatus, and serious wounds have been caused by the hot 
 sulphuric acid, it is safer before the melting-point of a hitherto 
 unknown substance is determined in the apparatus described 
 above, to take the slight trouble of making a preliminary test by 
 heating a small tube containing the substance directly in a small 
 flame to the melting temperature, and by this means ascertaining 
 if the substance will explode. 
 
 Testing the Thermometer. At this point a few observations 
 concerning the testing and correcting of the thermometer will be 
 added. Since the ordinary thermometers, at least the cheaper 
 varieties, are never exact, they must be corrected before using. 
 If a normal thermometer is at hand, the correction to be applied 
 may be determined by slowly heating the thermometer to be tested 
 by the side of the normal instrument in a bath of sulphuric acid, 
 glycerol, or vaseline, and noticing the reading of both thermometers 
 for every 10. There is thus obtained a table from which the cor- 
 rections may be read directly. For many purposes it is sufficient 
 to determine the deviation at only a few points ; the corrections 
 for the degrees lying between these may be calculated by inter- 
 polation. Thus, e.g., the point to be considered as the true zero 
 point may be determined as follows : A thick-walled test-tube of 
 about 2\ cm. in diameter and 1 2 cm. in length is one-third filled 
 with distilled water. The mouth is closed by a cork bearing a 
 thermometer dipping into the water. Through an opening cut 
 out of the side of the cork is introduced a thick copper wire, the 
 end of which is bent into a circle at a right angle to its length. 
 The test-tube is surrounded by a freezing mixture of ice and salt. 
 The water is frequently agitated with the stirrer ; the temperature 
 at which crystals first begin to form is carefully noted. 
 
 The true 100 point is found by placing distilled water in a not 
 too small fractionating flask and determining the boiling-point of it, 
 the entire column of mercury being in the vapour. In an analo- 
 gous manner, the boiling-point of naphthalene (218 at 760 mm. 
 pressure) and of benzophenone (306 at 760 mm. pressure) may 
 serve for the correction of the higher degrees. Since the boiling- 
 point is influenced by the pressure, the barometer must be read at 
 
DRYING AND CLEANING OF VESSELS 
 
 75 
 
 the same time with the thermometer and a correction, taken from 
 the table given below, applied. 
 
 Pressure. 
 
 Water. 
 
 Naphthalene. 
 
 Benzophenone. 
 
 720 mm. 
 
 98.5 
 
 2I5.7 
 
 303.5 
 
 725 
 
 98.7 
 
 216.0 
 
 303.8 
 
 730 
 
 98.9 
 
 216.3 
 
 304.2 
 
 735 
 
 99 .I 
 
 216.6 
 
 304.5 
 
 740 
 
 99-3 
 
 216.9 
 
 304.8 
 
 745 
 
 99-4 
 
 217.2 
 
 305.2 
 
 750 
 
 99.6 
 
 217.5 
 
 305-5 
 
 755 
 
 99.8 
 
 217.8 
 
 305.8 
 
 760 
 
 IOO.O 
 
 218.1 
 
 306.1 
 
 765 
 
 100.2 
 
 218.4 
 
 306.4 
 
 770 
 
 100-4 
 
 218.7 
 
 306.7 
 
 DRYING AND CLEANING OF VESSELS 
 
 While in analytical operations, since one generally deals with 
 aqueous solutions, the cleaned vessels may be used even if wet, it 
 frequently happens in organic work, in experimenting with liquids 
 not miscible with water, that dry vessels must be employed. In 
 order to dry small pieces of apparatus rapidly, they should be 
 rinsed first with alcohol and then with ether. To remove the last 
 portions of the easily volatile ether, air from a blast is blown 
 through the' vessel for a short time, or the ether vapours are 
 removed by suction. The alcohol and ether used for rinsing can 
 frequently be used again ; it is convenient to keep two separate 
 bottles for the wash alcohol and wash ether, into which the sub- 
 stances, after being used, may be poured. 
 
 For rapid drying of large vessels this method is costly. In this 
 case the procedure is as follows : The wet vessel is first drained 
 as thoroughly as possible, and then heated with constant turning 
 in a large luminous blast-flame, while, by means of a blast of air 
 from bellows or other source, the water vapour is driven out. It 
 may also be removed by careful heating and simultaneous suction. 
 
76 GENERAL PART 
 
 Thick-walled vessels like suction flasks must not be heated over 
 a flame, but are dried by the first method. 
 
 Vessels may be cleaned in part by rinsing them out with water 
 with the use of a feather or flask-cleaner. If the last portions 
 of the solution of a solid, e.g. in alcohol, are to be removed from 
 a flask, it is not washed out at once with water, but first with a 
 small quantity of the solvent, and then afterwards with water. 
 If the vessel contained a liquid not miscible with water, it is first 
 washed with alcohol and then with water. Resinous or tarry 
 impurities adhering firmly to the walls can be removed by crude 
 concentrated sulphuric acid. The action of this latter may be 
 strengthened by adding a little water to it, by which heat is gener- 
 ated ; also by the addition of some crystals of potassium dichro- 
 mate. At times the impurities adhere so firmly that the vessel 
 must be allowed to stand in contact with sulphuric acid for a long 
 time. Crude concentrated nitric acid, or a mixture of this with 
 sulphuric acid, is also used at times for cleaning purposes. Im- 
 purities of an acid character can, under certain conditions, be 
 removed by caustic soda or caustic potash. 
 
 Finally, a method for cleaning the hands may be mentioned if 
 they are discoloured by dyes which cannot be removed by water. 
 If the dye, e.g. fuchsine, contains an amido (NH 2 ) group, the hands 
 are dipped into a dilute, weakly acid solution of sodium nitrite. 
 The dye is diazotised, and may be removed by washing in water. 
 The two methods following are applicable to all dyes ; the hands 
 are immersed into a dilute solution of potassium permanganate 
 to which some sulphuric acid has been added, and are allowed to 
 remain for some time ; the dye is oxidised, and thereby destroyed. 
 After the permanganate has been washed off with water, the hands, 
 especially the nails, are coloured brown by manganese dioxide. 
 This is removed by washing the hands with a little sulphurous acid, 
 or oxalic acid (ammonium oxalate plus hydrochloric or sulphuric 
 acid). The second method is this : A thick paste of bleaching 
 powder and a sodium carbonate solution is rubbed on the hands. 
 This causes the oxidation and destruction of the dye as above. In 
 order to take away the unpleasant odour of the bleaching powder, 
 the hands are scrubbed with a brush, care being taken to remove 
 the particles adhering to the upper and under surface of the nails, 
 and are then washed, as just described, with sulphurous acid, or 
 oxalic acid. 
 
ORGANIC ANALYTICAL METHODS 7; 
 
 ORGANIC ANALYTICAL METHODS 
 
 DETECTION OF CARBON, HYDROGEN, NITROGEN, SULPHUR, AND THE 
 
 HALOGENS 
 
 Tests for Carbon and Hydrogen. If on heating a substance on 
 platinum foil, it burns with a flame (exceptions, e.g. S), or de- 
 composes with charring, it is an organic substance. Carbon and 
 hydrogen may be detected in one operation, by mixing a small 
 portion of the dried substance with several times its volume of 
 ignited fine cupric oxide, placing the mixture in a small test-tube, 
 adding more cupric oxide to the top of the mixture, and heating 
 strongly, the tube being closed by a cork bearing a delivery tube 
 bent twice at right angles. If the gas evolved (carbon dioxide) 
 will cause a clear solution of barium hydroxide to become turbid, 
 the original substance contained carbon ; if it also contained hy- 
 drogen, small drops of water will collect in the upper cold part of 
 the tube. 
 
 Test for Nitrogen. To test an organic substance for nitrogen, 
 it is heated in a small test-tube of difficultly fusible glass, about 
 5 mm. wide and 6 cm. long, with a piece of bright potassium the 
 size of a lentil, which has been pressed between layers of filter- 
 paper, in a Bunsen flame until decomposition, generally accom- 
 panied by slight detonations and dark colouration, takes place. 
 The tube is finally heated to redness ; while still hot it is dipped 
 into a small beaker containing 10 c.c. of water; by this the tube 
 is shattered, and any potassium unacted upon becomes ignited. 
 The aqueous solution containing potassium cyanide, if nitrogen 
 was present in the substance, is filtered from the carbon and glass 
 fragments, the filtrate treated with- a few drops of caustic potash 
 or caustic soda until it shows an alkaline reaction ; to this solution 
 is then added a small quantity of ferrous sulphate solution and 
 ferric chloride solution ; it is boiled 1-2 minutes, and if potassium 
 cyanide was present, potassium ferrocyanide will be formed. After 
 cooling, the alkaline liquid is acidified with hydrochloric acid, the 
 
78 GENERAL PART 
 
 precipitated ferric and ferrous hydroxides will be dissolved, and 
 being acted upon by the potassium ferrocyanide, will form Berlin 
 blue. Accordingly, if nitrogen was present, a blue precipitate is 
 obtained, otherwise only a yellow solution will be formed. If the 
 substance contains only a small proportion of nitrogen, at times no 
 precipitate is obtained at first, but only a bluish-green solution. 
 If this is allowed to stand some time, under certain conditions, 
 ever night, the precipitate will separate out. In testing easily 
 volatile substances for nitrogen, a longer tube is used and the por- 
 tions of substance condensing in the upper cold part of the tube 
 flow back a number of times on the potassium. In place of potas- 
 sium, sodium may also be used in most cases, but the former acts 
 more certainly. In testing for nitrogen, in a substance containing 
 sulphur, a larger quantity of potassium or sodium than that given 
 above is used (for 0.02 grm. of substance, about 0.2 grm. potassium, 
 in order to prevent the formation of an alkali sulphocyanate). 
 Substances which evolve nitrogen at moderate temperatures, e.g. 
 diazo-compounds, cannot be tested in the manner described. In 
 dealing with a substance of this kind it must be determined whether 
 on heating the substance with cupric oxide in a tube filled with car- 
 bon dioxide, a gas is given off which is not absorbed by a solution 
 of caustic potash. (See quantitative determination of nitrogen.) 
 
 In a limited number of substances containing nitrogen, the pres- 
 ence of the latter may be proved by heating the substance with an 
 excess of pulverised soda-lime in a test-tube with a Bunsen flame ; 
 this causes decomposition with evolution of ammonia, which is 
 detected by its odour or by means of a black colour imparted to a 
 piece of filter-paper moistened with a solution of mercurous nitrate. 
 Nitro-compounds, e.g., do not give this reaction. 
 
 Test for Sulphur. The qualitative test for sulphur is made in 
 the same manner as that for nitrogen. The substance is heated 
 in a small tube with sodium. After the mass has cooled it is 
 treated with water, and to one-half of the solution is added a 
 small quantity (a few drops) of a solution of sodium nitroprus- 
 siate, just prepared by shaking a few crystals with water at the 
 ordinary temperature. A violet colouration indicates the presence 
 
ORGANIC ANALYTICAL METHODS 79 
 
 of sulphur. Since the nitroprussiate reaction is very delicate, no 
 conclusion as to the amount of sulphur can be drawn from the 
 test, therefore the second half of the solution is treated with a 
 lead acetate solution and acidified with acetic acid. In propor- 
 tion to the amount of lead sulphide formed, the liquid will assume 
 a dark colour, or a more or less heavy precipitate will appear, in 
 this way indicating the original quantity of sulphur. 
 
 Easily volatile substances cannot usually be tested by this 
 method. They are heated with fuming nitric acid in a bomb- 
 tube to about 200 or 300. After diluting with water the solution 
 is tested with barium chloride for sulphuric acid. (See method for 
 the quantitative determination of sulphur.) 
 
 Test for the Halogens. The presence of chlorine, bromine, 
 .and iodine in organic compounds can only in rare cases be shown 
 by precipitation with silver nitrate. This is explained by the fact 
 that most organic compounds are non-electrolytes ; i.e. that the 
 solutions of the same do not contain free halogen ions, as is the 
 case in solutions of the inorganic salts of the halogen hydracids. 
 
 In order to detect the halogens, the substance to be tested is 
 heated in a not too narrow test-tube with a Bunsen flame with an 
 excess of chemically pure lime, the tube while still hot is dipped 
 into a little water, chemically pure nitric acid is added to acid 
 reaction, the solution is then filtered and treated with silver nitrate. 
 
 In compounds containing no nitrogen, a test for the halogens 
 may be made by the same method given for nitrogen heating 
 with sodium. In this case the solution, filtered from the decom- 
 position products and fragments of glass, is acidified with nitric 
 acid and silver nitrate added. .Substances containing nitrogen 
 cannot be tested in this way for the halogens, since, as shown 
 above, these on fusion with sodium give sodium cyanide, which, 
 like the sodium halides, reacts with silver nitrate. 
 
 The presence of halogens may be recognised very quickly and 
 conveniently by Beilstein's test. A piece of cupric oxide the size 
 of a lentil, or a small rod of the oxide \ cm. long, is wrapped 
 around with a thin platinum wire, the other end of which is fused 
 to a glass handle, and heated in the Bunsen flame until it becomes 
 
8O GENERAL PART 
 
 colourless. If, after cooling, a minute particle of the substance con- 
 taining a halogen is placed on this and then heated in the outer part 
 of the flame, the carbon burns first and a luminous flame is noticed. 
 This soon vanishes, and there appears a green or bluish-green colour 
 due to the vaporisation of the copper halide. From the length of 
 time the colour is visible, conclusions may be drawn concerning the 
 presence of a trace or more of the halogen in the original substance. 
 
 QUANTITATIVE DETERMINATION OF THE HALOGENS 
 CARIUS' METHOD 
 
 The method consists in heating a weighed amount of the sub- 
 stance to be analysed in a sealed glass tube with silver nitrate and 
 fuming nitric acid, by which it is completely decomposed (oxidised), 
 and weighing the quantity of the silver halide thus formed. 
 
 Requisites for the analysis : 
 
 1. A tube of difficultly fusible glass sealed at one end, length 
 
 about 50 cm.; outside diameter, 18-20 mm.; thickness of 
 walls, about 2 mm. (Sealing- tubes, bomb-tubes.) 
 
 2. A funnel-tube about 40 cm. long, for transferring the silver 
 
 nitrate and nitric acid to the glass tube. 
 
 3. A weighing-tube of hard glass (length, 7 cm. ; outside diameter, 
 
 .about 6-8 mm.). 
 
 4. Solid silver nitrate and pure fuming nitric acid. The purity of 
 
 the latter is tested by diluting 2 c.c. of it with 50 c.c. of distilled 
 water, and adding a few drops of a silver nitrate solution. 
 Neither an opalescence nor a precipitate should appear. 
 
 Filling and Sealing the Tube. After the bomb-tube, weighing- 
 tube, and funnel-tube have been cleaned with distilled water, they 
 are dried, not with alcohol and ether, but by heating over a flame. 
 (See page 75, Drying.) The exact weight of the weighing-tube 
 is next determined. Into this, with the help of a spatula, is placed 
 0.15 to 0.2 gramme of the substance to be analysed, finely powdered. 
 The open end of the tube is wiped off with a cloth, and the exact 
 
ORGANIC ANALYTICAL METHODS 8 1 
 
 weight of the tube plus the substance is found. With the aid of 
 the funnel-tube, about 0.5 gramme of finely powdered silver nitrate 
 is transferred to the bomb-tube (a correspondingly larger amount 
 up to i gramme is used for substances containing a high percent- 
 age of halogen) and 2 c.c. of fuming nitric acid. If a number of 
 halogen determinations are to be made, it is advisable to measure 
 off 2 c.c. of water in a narrow test-tube, mark the volume with a 
 file on the outside, and then use this to measure the acid for the 
 different determinations. After removing the funnel-tube, care 
 being taken not to touch the walls of the bomb-tube with it, the 
 weighing-tube is inserted in the bomb held at a slight angle, and 
 is allowed to slide down to the bottom, but the substance must 
 not come in contact with the acid. The tube is now sealed in 
 the manner described on page 63. During the sealing, the sub- 
 stance must be prevented from coming in contact with the acid. 
 Even after the tube is closed, this is not brought about purposely, 
 as by violently shaking the tube. 
 
 If the substance to be analysed is liquid, it is placed in the 
 weighing-tube with a capillary pipette, otherwise the procedure is 
 just as described. In dealing with easily volatile sub- ^^ 
 stances, the weighing- tube is closed by a glass stopper, jjJF 
 made by heating a piece of glass rod in the blast-flame 
 until it softens, and then pressing it on a metal surface 
 until a head is formed (Fig. 53). 
 
 Heating the Tube. After cooling, the tube is trans- 
 ferred to the iron protecting case, and heated in the bomb- 
 furnace, in accordance with the directions on page 65. 
 The temperature and time of heating depend upon the greater or 
 less ease with which the compound is decomposed. In many 
 cases, it is necessary to heat aliphatic compounds, or aromatic 
 compounds that oxidise easily, 2-4 hours at a temperature of 
 150-200, while substances that do not easily oxidise, especially 
 those that contain sulphur, must be heated 8-10 hours, and 
 finally up to 250-300. In this case it is convenient to so 
 plan the analysis that the bombs may be sealed in the even- 
 ing, so that the heating may be begun the first thing the next 
 
82 GENERAL PART 
 
 day. The sealed tube is kept under the hood in the bomb-room, 
 in the iron case, over night, which is clamped with its open end 
 directed vertically upwards. The tube is never allowed to remain 
 at the working table. If the furnace is not loaded, naturally it 
 is most convenient to place the bomb at once in that. Since in 
 many cases the oxidation begins even at the ordinary temperature, 
 pressure is developed in the tube ; therefore, after it has been 
 standing over night, it must not be removed from the iron case 
 to be examined. The heating is done gradually ; at first, with 
 a small flame, the gas-tubes being lowered from the furnace. 
 Gradually these are raised, and the flames increased in size. The 
 following table will show how the heating of a moderately refractory 
 substance should be regulated. 
 
 The heating is begun at 9 o'clock A.M. 
 
 From 9-10 the temperature is raised to about 100, 
 150, 
 
 11-12 200, 
 
 12-3 2 5> 
 
 3-6 300. 
 
 If an especially high pressure is generated by the decomposition 
 of a substance, the danger of the bursting of the tube may be 
 lessened by turning off the gas before leaving the laboratory at 
 noon, and then in the afternoon opening the capillary, sealing and 
 heating again to a higher temperature. The same method is 
 followed in working with a substance so refractory that several 
 days' heating is required ; in this case at the beginning of the 
 second day the pressure is reduced by opening the tube. 
 
 If two bombs are heated in the furnace at the same time, an 
 entry is made in the note-book to show which tube lies to the 
 right and which to the left. If this has been neglected, and the 
 identity of the two tubes is in doubt, the neglect may be corrected 
 by again weighing the two weighing tubes. 
 
 To Open and Empty the Tube. The perfectly cooled tube is 
 opened according to the directions given on page 66. Especial 
 care must be taken before heating the capillary to softening in a 
 
ORGANIC ANALYTICAL METHODS 83 
 
 large flame, to drive back into the tube by gentle heating over a 
 small flame, any of the liquid which may have collected in the 
 capillary. Before the conical end is broken off the tube is exam- 
 ined to see whether it still contains crystals or oily drops of the 
 undecomposed substance. In case it does, the capillary is again 
 sealed and the tube reheated ; but if it does not, the conical end 
 is removed according to the directions given on page 66. The 
 part broken off is first washed free from any liquid or any of the 
 precipitate which may have adhered to it, with distilled water, into 
 a beaker ; the portion in the tube is diluted with distilled water, 
 upon which there is generally obtained a bluish-green solution, 
 coloured by nitrous acid ; this is poured, together with the weigh- 
 ing-tube into a beaker by inverting the tube, care being taken that 
 .the sudden falling of the weighing- tube does not break the bottom 
 of the beaker. In pouring out the ^tube-contents, the attention 
 should be directed to the open end of the tube and not to the 
 liquid in the rear end, otherwise some of the liquid may easily be 
 spilled. After the outer open portion of the tube has been washed 
 with distilled water the tube is revolved and the precipitate in the 
 interior is washed out ; this is repeated as often as may be neces- 
 sary. If a portion of the silver halide adheres firmly to the glass > 
 it may be removed by loosening it with a long glass rod over the 
 end of which has been drawn a piece of rubber tubing (such as is 
 used in the quantitative analysis of inorganic substances) and then 
 washing it out with distilled water. The weighing-tube is removed 
 from the bottom of the beaker with a glass rod or thick platinum 
 wire held against the walls above the liquid, washed thoroughly 
 inside and out' with distilled water, and then raised with the fingers 
 and washed several times again. At times the weighing-tube be- 
 comes yellow to deep brown in colour due to the formation of 
 silver silicate. This is not detrimental to the results of the analysis. 
 To filter off and weigh the Silver Halide. The beaker is now 
 heated on a wire gauze until the silver halide has settled to the 
 bottom and the supernatant liquid is clear. Since the excess of 
 silver nitrate at times packs together with the silver halide to form 
 thick, solid lumps, the precipitate is from time to time crushed 
 
84 GENERAL PAR! 
 
 with a glass rod, the end of which has been flattened out to a broad 
 head. After cooling, the silver halide is collected on a filter, the 
 weight of the ash of which is known, and washed with hot water 
 until, on testing the filtrate with hydrochloric acid, no turbidity 
 follows ; the filter, together with the funnel, is then dried in an 
 air-bath at 100-110, the funnel being covered with a piece of 
 filter-paper. In order to weigh the dry halide, as large an amount 
 as possible is separated from the paper carefully, and transferred 
 to a watch-glass placed on a piece of black glazed paper. The 
 portions which fall on the paper are swept into the watch-glass 
 with a small feather. The filter is rolled up tightly, wrapped with 
 a platinum wire, and ignited in the usual way over a weighed por- 
 celain crucible ; the heating is done only with the outer part of 
 the flame, and not with the inner, reducing part. The folded filter 
 may also be incinerated directly in the crucible, which is first 
 heated over a small flame, and the temperature increased later ; 
 the heating is continued until the filter ash appears uniformly 
 light. In order to convert the silver which has been reduced in 
 the incineration back to the silver halide, the fused residue is 
 moistened, by the aid of a glass rod, with a few drops of nitric 
 acid, if the latter method of incineration has been employed, 
 only after complete cooling of the crucible. It is now evaporated 
 to dryness on the water-bath. It is then treated with a few drops 
 of the corresponding halogen acid, and again evaporated to dry- 
 ness on the water-bath. The principal mass of the silver halide 
 on the watch-glass is transferred to the crucible with the aid of a 
 feather, and heated directly over a small flame until it just begins 
 to fuse : the crucible is then placed in a desiccator, and allowed to 
 cool. If the analysis is intended to be very exact, the principal 
 mass of the silver halide may be moistened before fusion, with a 
 few drops of nitric acid, and then evaporated on the water-bath 
 with the halogen acid. 
 
 The silver halide can also be conveniently weighed, either in an 
 asbestos tube, or in a Gooch crucible. Concerning this compare 
 Jannasch, " Praktischer Leitfaden derGewichtsanalyse," Second Ed., 
 
ORGANIC ANALYTICAL METHODS 85 
 
 pages 10 and 145 ; also Chemical News, 37, 181 ; and Zeitschrifl 
 fur analytische Chemie, 19, 333. 
 
 Even after taking the usual precautions, it sometimes happens 
 that the silver halide is mixed with fragments of glass, which will, 
 of course, cause the percentage of halogen to be too high. If the 
 substance 'under examination is silver chloride, and the presence 
 of glass is noticed in the beaker or on filtering, an error may be 
 avoided, by pouring over the completely washed, moist silver 
 chloride on the filter, slightly warmed dilute ammonium hydroxide 
 several times, then washing the filter with water, and precipitating 
 the pure silver chloride in the filtrate by acidifying with hydro- 
 chloric acid. If the compound under examination is silver bromide 
 or iodide, and glass fragments have been noticed, the analysis is 
 carried out to the end in the usual way. To determine the amount 
 of glass present, the silver halide in the crucible is treated with very 
 dilute pure sulphuric acid, and a small piece of chemically pure 
 zinc is added. In the course of several hours, the silver halide is 
 reduced to spongy, metallic silver. By careful decantation, the 
 liquid is separated from the silver, water is added and decanted ; 
 this is repeated several times. It is then treated with dilute nitric 
 acid, and heated on the water-bath until all the silver is dissolved. 
 After dilution with water, it is filtered through a quantitative filter, 
 the undissolved glass fragments are also well washed on the filter, 
 and the latter incinerated. The weight of the glass is to be sub- 
 tracted from the weight of the halide obtained. It is obvious that 
 the purity of the fused silver chloride may also be tested in this way. 
 
 In conclusion, the atomic weights of the halogens, the molecular 
 weights of the corresponding silver compounds, and the logarithms 
 of the analytical constants are here given : 
 
 Cl 
 = 3546 ; AgCl = 143-34 ; log ^ = 0.39337 - i 
 
 Br = 79.92 ; AgBr = 187.80 ; log = 0.62896 i 
 
 1 = 126.92; Agl = 234.80; log -^-=0.73283 - i 
 
86 GENERAL PART 
 
 Kiister's Modification. The determination of the halogens 
 may be materially facilitated by using 16-20 drops of fuming nitric 
 acid instead of iJ-2 c.c. The tube so charged is heated directly 
 up to 320-340, it is unnecessary to heat it gradually. When 
 an ordinary thermometer is employed to register temperatures 
 above 300, the column of mercury frequently parts. A bomb- 
 thermometer made by C. Desaga, Heidelberg, Germany, at the 
 suggestion of the author, corrects this defect. It contains nitro- 
 gen over the mercury column, and possesses but two degree marks, 
 corresponding to 320 and 340. 
 
 QUANTITATIVE DETERMINATION OF SULPHUR 
 CARIUS' METHOD 
 
 This method, like the preceding one, depends upon the com- 
 plete oxidation of the weighed substance, by heating it with 
 fuming nitric acid in a sealed tube. The sulphuric acid thus 
 formed is weighed as barium sulphate. The charging, sealing, 
 heating, opening, and emptying of the tube are performed in 
 exactly the same way as in the halogen determinations ; but in 
 this case it is evident that the use of silver nitrate is superfluous. 
 Before breaking off the conical end, the tube is examined to see 
 that no undecomposed portions of the substance are present ; if 
 there should be, the capillary is again sealed and the tube re- 
 heated. Before the sulphuric acid is precipitated with barium 
 chloride, the bottom of the beaker must be examined for any 
 fragments of glass which may be present ; if there are any, they 
 are filtered off through a small filter. 
 
 Precipitation of the Barium Sulphate. The liquid from the 
 bomb, diluted with water up to 400 c.c., is heated almost to boiling 
 on a wire gauze and acidified with hydrochloric acid ; a solution 
 of barium chloride heated to boiling in a test-tube is gradually 
 added until a precipitate is no longer formed. This can be easily 
 observed by allowing the precipitate to settle somewhat before 
 adding more of the solution. The liquid is then heated over a 
 
ORGANIC ANALYTICAL METHODS 87 
 
 small flame until the barium sulphate settles at the bottom of the 
 beaker and the supernatant liquid is perfectly clear : at times 
 from one to two hours' heating may be necessary. After cooling, 
 the liquid is filtered, without disturbing the precipitate at the 
 bottom, through a small filter the weight of the ash of which is 
 known ; the precipitate remaining in the beaker is boiled several 
 minutes with 100 c.c. water and filtered through the same filter. 
 The precipitate occasionally at first goes through the paper ; in 
 case it does, another beaker is placed under the funnel so that the 
 entire quantity of liquid need not be refiltered. The precipitate 
 is washed with hot water until a portion of the filtrate tested with 
 dilute sulphuric acid shows no turbidity. Before throwing away 
 the filtrate, barium chloride is added in order to be sure that a 
 sufficient quantity was used in the first instance. If a precipitate 
 is formed, the above process is repeated and the second precipitate 
 collected on the filter containing the first. 
 
 The method just described has the disadvantage that if a 
 smaller quantity of water be used for diluting the contents of the 
 tube than that given above, the barium sulphate may easily carry 
 along with it some barium nitrate, which is only removed with diffi- 
 culty on washing with water. Since, in consequence of this, the 
 percentage of sulphur is too high, it is for many reasons preferable 
 to wash the contents of the bomb into a porcelain dish instead of 
 a beaker, and to evaporate the liquid on the water-bath until the 
 acid vapours vanish, before adding the barium chloride ; by this 
 operation the nitric acid is removed. After evaporating, the res- 
 idue is diluted with water, filtered if necessary, from any glass 
 fragments, and the operation just described above repeated. 
 Under these conditions, too much of an excess of barium chloride 
 is to be avoided. 
 
 Ignition and Weighing of the Barium Sulphate. In order to 
 prepare the barium sulphate for weighing, it is not necessary to 
 dry it before incineration ; if Bunsen's method is followed, it may 
 be incinerated while still moist. With the aid of a small spatula 
 or knife the moist filter is removed from the funnel and folded in 
 the form of a quadrant. Should any barium sulphate adhere to 
 
88 GENERAL PART 
 
 the funnel, it is removed with a small piece of filter-paper, which 
 is incinerated with the main mass. After the filter has been 
 carefully folded toward the centre, it is pressed into the bottom 
 of a weighed platinum crucible, placed on a platinum triangle in 
 such a position that its axis is inclined 20-30 from a vertical 
 position. The cover, also inclined at an angle of 20-30, in the 
 opposite direction, however, is supported before the crucible, so 
 that the upper half of the opening of the latter is uncovered. 
 The burner under the crucible is placed in such a position that 
 the flame, which must not be too large at first, is directly under 
 the angle formed by the crucible and cover. This will allow the 
 ignition of the filter to take place at so low a temperature that 
 reduction of the barium sulphate need not be feared. It some- 
 times happens that on heating the filter, the gases formed take 
 fire at the mouth of the crucible, which, however, does no harm. 
 After some time the burner is placed under the bottom of the 
 crucible, the flame increased, and the heating continued until the 
 residue has become white. The crucible is now placed in an up- 
 right position, heated a short time with the full flame, and then 
 allowed to cool in a desiccator. It is entirely superfluous to treat 
 the barium sulphate with sulphuric acid and then evaporate it off. 
 The barium sulphate may also be weighed in a Gooch crucible. 
 (See page 84.) If the percentage of sulphur found is too high, this 
 may have been caused, under certain conditions, by the fact that 
 in the precipitation too great an excess of barium chloride has 
 been used, and that the barium sulphate has carried along some of 
 it. This source of error may be rectified by treating the ignited 
 barium sulphate with water until the crucible is half full, then add- 
 ing a few drops of concentrated hydrochloric acid, and heating on 
 the water-bath for fifteen minutes. The liquid is filtered from the 
 precipitate through a quantitative filter ; the greatest portion of 
 the precipitate remaining in the crucible is again treated with 
 water and hydrochloric acid, and the contents of the crucible 
 poured on the filter already used ; after washing repeatedly with 
 water, the filter and precipitate are again ignited as before. This 
 process is obviously only employed when the barium sulphate has 
 
ORGANIC ANALYTICAL METHODS 89 
 
 not been evaporated down with sulphuric acid. For the calcula 
 tion of the analysis the atomic and the molecular weights are 
 
 given : 
 
 g 
 S = 32.07 ; BaSO 4 = 233.44 ; log ^ = 0.13792 - i 
 
 Simultaneous Determination of the Halogens and Sulphur. 
 
 If a substance contains both a halogen and sulphur, they may be 
 determined in a single operation by the following method : As in 
 the determination of the halogens, the bomb is charged with silver 
 nitrate and nitric acid, and the silver halide filtered off after the 
 heating, as above described. The filtrate thus obtained contains, 
 besides the excess of silver nitrate, the sulphuric acid formed 
 by oxidation. This latter cannot be precipitated as before with 
 barium chloride, since the silver as silver chloride would also be 
 thrown down. In its place is used a solution of barium nitrate, 
 the purity of which has been tested by adding silver nitrate to it. 
 The precipitation is made hot as above directed, the solution used 
 being as dilute as possible the volume of which must be at 
 least 500 c.c. A large excess of barium nitrate is particularly to 
 be avoided. If the barium nitrate solution contains halogen salts 
 as impurities, it is heated, and silver nitrate added so long as a 
 precipitate is formed, the precipitate filtered off, and the solution, 
 which is now free from halogens, is used for the precipitation. 
 
go GENERAL PART 
 
 QUANTITATIVE DETERMINATION OF NITROGEN 
 DUMAS' METHOD 
 
 In scientific laboratories, the method almost exclusively used 
 for determining nitrogen quantitatively is that of Dumas. The 
 principle involved is that the substance is completely burned by 
 cupric oxide in a tube filled with carbon dioxide, the nitrogen is 
 evolved as such, and its volume measured, while the carbon and 
 hydrogen are completely oxidised to carbon dioxide and water. 
 
 Requisites for the analysis : 
 
 1. A combustion tube of difficultly fusible glass, 80-85 cm - l n S > 
 
 outside diameter, about 15 mm. 
 
 2. A glass funnel- tube with wide stem (at least 10 mm. in 
 
 diameter) . 
 
 3. 400 grammes of coarse and TOO grammes of fine cupric oxide. 
 
 The former is kept in a large flask, the latter in a small 
 one, both of which are closed by a cork covered with tin- 
 foil. 
 
 4. 500 grammes of magnesite, in pieces the size of a pea. The 
 
 fine powder, which cannot be used, is sifted out in a wire 
 sieve. The dark grains which have become discoloured 
 by impurities are thrown out. 
 
 5. A small flask of pure methyl alcohol (50 grammes) for reduc- 
 
 ing the copper spiral. 
 
 6. A copper spiral, 10-12 cm. long. This is made by winding 
 
 an oblong piece of copper wire gauze spirally around a 
 thin glass rod. It is made of such a width that when in 
 position it will touch the walls of the combustion tube ; 
 a space between the walls and spiral is disadvantageous. 
 Also a short copper spiral from 1-2 cm. long. 
 
 7. A solution of 150 grammes of potassium hydroxide in 150 
 
 grammes of water. It is prepared in a porcelain dish, 
 and not in a glass beaker or flask, since these are fre- 
 quently broken by the heat generated by the solution. 
 After cooling, it is preserved in a well-closed bottle. 
 
ORGANIC ANALYTICAL METHODS 9! 
 
 8. A nickel crucible 6 cm. high ; diameter of top 7 cm., for the 
 
 ignition of the coarse cupric oxide. 
 
 9. A moderately large porcelain crucible for the ignition of the 
 
 fine cupric oxide. 
 10. A small mortar with a glazed bottom. 
 
 Besides these, a weighing-tube, a one-hole rubber stopper for 
 closing one end of the combustion tube, a sieve to sift the copper 
 oxide, a small feather, thermometer, absorption apparatus, and a 
 eudiometer. 
 
 Preparations for the Analysis. The analysis is conveniently 
 begun by heating the entire quantity of coarse copper oxide in 
 the nickel crucible over a large flame (Fletcher burner), and 
 the fine copper oxide in the porcelain crucible over a Bunsen 
 flame for a long time, the crucibles being supported on wire tri- 
 angles. The covers are placed on the crucibles loosely, and 
 the copper oxide occasionally stirred with a thick wire. While 
 the copper is being heated, one end of the combustion tube is 
 sealed to a solid head, the narrower end being selected for this 
 purpose, if the tube is not perfectly cylindrical. The sealing is 
 done as follows : The end of the tube is first warmed in a luminous 
 flame, with constant turning ; it is then heated to softening, in the 
 blast-flame, a glass rod fused on it, and the heated portion suddenly 
 drawn out to a narrow tube. The glass rod is now fused off, and 
 the conical part of the tube just produced is heated and drawn 
 out. The cone is then heated in the hottest flame until it falls 
 together ; it is finally allowed to cool gradually over a small 
 luminous flame. When this operation is finished, the open end 
 of the tube is warmed in a luminous flame, and, with constant 
 turning, the sharp edges are rounded by the blast-flame : it is then 
 allowed to cool in the luminous flame again. After complete 
 cooling, the soot is removed, the tube rinsed out several times 
 with water, the water allowed to drain off as completely as possible, 
 and the tube finally dried in one of the two following ways : The 
 tube, with constant turning, is repeatedly passed through the large 
 luminous flame of a blast-lamp, while a current of air is blown 
 
9 2 GENERAL PART 
 
 from a blast into the bottom of it by means of a narrower, longer 
 (10 cm.) tube inserted in the larger tube; this operation is con- 
 tinued until all moisture is removed. Or the combustion tube is 
 clamped in a horizontal position, a narrower tube extending to 
 the sealed end, attached to suction, is inserted, and the combustion 
 tube equally heated with a Bunsen burner throughout its entire 
 length ; the water vapour is drawn off by the suction. To reduce the 
 long copper spiral which is to be used for the reduction of oxides 
 of nitrogen which may be formed, the method of procedure is as 
 follows : Into a test-tube large enough to admit the spiral, i c.c. of 
 methyl alcohol is placed ; the spiral, held by crucible tongs, is then 
 heated to glowing in a large, somewhat roaring blast-flame, and 
 dropped as quickly as possible into the test-tube ; since this be- 
 comes strongly heated at its upper end, it is clamped in a test-tube 
 holder, or wrapped in a cloth or strips of paper. The dark spiral 
 soon assumes a bright metallic lustre, while vapours, having a sharp, 
 pungent odour (oxidation products of methyl alcohol like formic 
 aldehyde and formic acid), which frequently become ignited, are 
 formed ; after a few minutes, the tube may be loosely corked, and 
 the spiral allowed to cool. When this operation is ended, the cop- 
 per oxide will have been sufficiently heated, and the flames may be 
 removed. During the cooling, the substance to be analysed is 
 weighed. A convenient method is this : The weight of the weigh- 
 ing-flask is determined with exactness to centigrammes, this weight 
 is entered in the note-book at a convenient place for future use. 
 The substance to be analysed is now placed in the weighing-tube, 
 and the weight of the tube, plus substance, is determined exactly 
 to the tenth of a milligramme. In the meantime, the copper 
 oxide has cooled sufficiently to be transferred to the appropriate 
 flask. The combustion tube is next filled. 
 
 Filling the Tube. At the edge of the working table is placed 
 a stand ; fastened firmly near the bottom of this is a clamp pro- 
 jecting over the edge of the table supporting the combustion tube 
 in a vertical position, the mouth being at about the level of the 
 table. The tube is now directly filled with the magnesite until 
 the layer has a height of 10-12 cm. (Fig. 54). A small roll of 
 
ORGANIC ANALYTICAL METHODS 
 
 93 
 
 30 cm. coarse oxide 
 
 copper gauze 1-2 cm. long, held with pincers or tongs, is heated 
 for a short time in a Bunsen flame (it need not be reduced) and 
 dropped on the magnesite. The funnel- tube is then placed in 
 the tube, and from the flask coarse copper oxide is poured in until 
 the layer measures 8 cm., and upon this is poured a layer of 2 cm. 
 of the fine oxide. To the operation following the mixing of the 
 
 substance with copper oxide 
 s cm. free and the transference of the 
 
 mixture to the tube especial 
 
 10 cm. reduced copper spiral care mus t be given. In the 
 
 bottom of a small mortar, 
 standing on black, glazed pa- 
 per a ^ cm. layer of the fine, 
 perfectly cooled copper oxide 
 is placed ; to this is added from 
 the weighing- tube the sub- 
 stance to be analysed, of which 
 0.15-0.20 gramme is taken, 
 unless the substance contains 
 a small proportion of nitrogen, 
 when more is taken. Since 
 the weight of the empty tube 
 is known as well as that of 
 the substance contained there- 
 in, one can easily decide, by 
 measuring with the eye, how 
 much of the substance to 
 take. Fine copper oxide is 
 now added until the substance 
 is completely covered, and the 
 two are carefully mixed by 
 stirring with the pestle, without pressure ; during the mixing care 
 must be taken not to stir so rapidly as to cause dust-like particles 
 of the mixture to leave the mortar. With the aid of a clean, 
 clipped feather, such as is used in quantitative operations, or a 
 small brush, the contents of the mortar are transferred through 
 
 10 cm. substance + fine oxide 
 
 2 cm. fine oxide 
 
 8 cm. coarse oxide 
 
 ;m. copper spiral 
 
 12 cm. magnesite 
 
 FIG. 54. 
 
94 GENERAL PART 
 
 the funnel-tube into the combustion tube. The operation must be 
 done cautiously to prevent the light, dusty particles from being 
 blown away. The mortar, as well as the pestle, is now rinsed 
 with a fresh portion of the fine copper oxide, and this is likewise 
 transferred to the tube with the aid of the feather. The layer of 
 substance plus copper oxide should be about 10 cm. long. Then 
 follows a layer of 30 cm. of coarse copper oxide, and finally the 
 reduced copper spiral. 
 
 The length of the tube, as well as that of the single layers, is 
 regulated in accordance with the size of the combustion furnace ; 
 the figures given above refer to a furnace possessing a flame surface 
 of 75 cm. Generally the tubes are 5 cm. longer than the furnace ; 
 the tube contents are of the same length as the flame surface. 
 
 Heating the Tube. After the tube is filled it is held in a hori- 
 zontal position and tapped gently on the table in order that a 
 canal may be formed in the upper portion of the fine copper 
 oxide ; it is then connected with a rubber stopper to the absorp- 
 tion apparatus which has been charged with caustic potash solution, 
 and placed in the combustion furnace, the rear end of which (that 
 under the magnesite) has been raised on a block (Fig. 55). The 
 following points are to be observed : In the lower part of the 
 absorption apparatus there must be a sufficient amount of mercury 
 to extend almost to the side-tube ; if this is not the case, more mer- 
 cury is added : the end of the glass tube passing through the 
 rubber stopper must be flush with the end of the stopper. In 
 order to protect the latter from the heat, there is placed over the 
 portion of the tube projecting beyond the furnace, an asbestos 
 plate having a circular opening in the centre. After opening the 
 pinch-cock of the absorption apparatus, the burners under the last 
 half of the magnesite are lighted ; the flames, being small at first, 
 are increased in size, as soon as the tube becomes warmed, but not 
 sufficiently to cause them to meet above the tube. In order to 
 raise the temperature higher when it becomes necessary, the tube 
 is covered from both sides with the tiles. After about ten minutes 
 a rapid current of carbon dioxide is evolved, the magnesite being 
 decomposed by heat as represented in the following equation : 
 
ORGANIC ANALYTICAL METHODS 
 
96 GENERAL PART 
 
 During this operation the glass stop-cock of the absorption appa- 
 ratus is opened, and the pear-shaped vessel placed as low as pos- 
 sible, so that it contains the principal portion of the caustic potash. 
 After a rapid current of carbon dioxide has been evolved for about 
 fifteen minutes, the burners under the copper spiral are lighted 
 in order to drive out any occluded gas (hydrogen), the pear- 
 shaped vessel is raised high enough to cause the caustic potash 
 to ascend somewhat above the tubulure in the glass cock, the 
 latter is closed, and the pear-shaped vessel again lowered as far 
 as possible. When the air in the tube has ' been completely 
 replaced by carbon dioxide, only a minimum quantity of light 
 foam should collect over the potash in the course of two minutes. 
 If this is not the case, and a large air volume collects, the glass 
 cock is opened, upon which the potash flows in to the lowered 
 pear vessel, and carbon dioxide is caused to pass through the 
 tube for five minutes longer. The pear vessel is then raised as 
 high as at first, the glass cock closed, and the former lowered. An 
 observation will show whether the air has been displaced, which 
 should be the case under normal conditions. If now after two 
 minutes only a trace of foam has collected, the end of the delivery 
 tube is dipped under the water in a dish as shown in Fig. 55, the 
 pear raised to the highest point of the delivery tube, and the glass 
 cock opened in order that the potash may drive out the air in the 
 delivery tube : when this has been done, the cock is closed again 
 and the pear lowered to the bottom. All the flames but one 
 under the magnesite are now extinguished or lowered, and those 
 under the long copper spiral as well as those under four-fifths of 
 the adjacent layer of coarse copper oxide are lighted at the same 
 time ; the flames, small at first, are increased in size, after the tube 
 has become somewhat heated, until the copper oxide is heated 
 to dull redness. Concerning the steps taken in heating the tube, 
 refer to Fig. 54 the numbers on the left indicate the portions of 
 the tube to be heated successively. At .this point care is taken 
 that the flames are not so large as to meet above the tube. As 
 before in heating the magnesite, after the first warming the heated 
 portions of the tube are covered on both sides with the tiles. As 
 soon as the forward layer of coarse copper oxide becomes dark 
 red, the burners under the rear layer of coarse oxide adjacent to 
 
ORGANIC ANALYTICAL METHODS 97 
 
 the magnesite are lighted small flames at first, which are increased 
 after a time, the tube being covered simultaneously with the tiles. 
 Care must be taken that the flames nearest the layer of substance 
 plus fine copper oxide are not too large, in order that the substance 
 may not yet be burned. Upon the operation which now follows 
 the gradual heating of the fine oxide containing the substance 
 virtually depends the success of the analysis. For the proper 
 manipulation of this operation especial care must be taken. It is 
 a rule that the heating had better be somewhat too slow than too 
 rapid. A small flame is now lighted at the point adjacent to the 
 short layer of coarse oxide : an observation of the absorption appa- 
 ratus will show whether after some time any unabsorbed gas collects. 
 If this is the case, no other burners are lighted until the evolution 
 of gas ceases. When the gas no longer collects, another burner 
 on the opposite side of the fine oxide is lighted. In this way the 
 burners are gradually lighted from both sides, toward the middle 
 of the fine oxide, and after, in each case, the cessation of the 
 evolution of the gas, the flames are gradually made larger until 
 finally the tube covered with tiles is heated with full flames ; thus 
 the substance is regularly and quietly burned. The combustion 
 must be so conducted that the bubbles of gas ascend in the absorp- 
 tion apparatus with a slow regularity. If the single bubbles cannot 
 be counted, or if they are so large as to occupy almost the entire 
 cross-section of the absorption tube, the heating is too strong, and 
 the last burners lighted must be extinguished or lowered, the tiles 
 being also laid back at the same time if necessary, until the gener- 
 ation of the gas is lessened. When this is ended, small flames are 
 again lighted under the entire layer of magnesite, and increased in 
 size after some time. As soon as the evolution of carbon dioxide 
 has become active, the flames under the rear half of the magnesite 
 lighted at the beginning of the analysis are extinguished. After a 
 rapid current of carbon dioxide has passed through the tube for 
 ten minutes, all the nitrogen is carried over to the absorption 
 apparatus. This is shown by the complete absorption of the gas 
 bubbles by the potash, as at the beginning of the analysis, except 
 for a minimum foam-like residue. The absorption apparatus is 
 H 
 
9 8 
 
 GENERAL PART 
 
 then closed by the pinch- cock and the rubber stopper bearing tha 
 connecting tube is withdrawn from the combustion tube. The gas 
 is not immediately transferred to the eudiometer, but the pear is 
 raised until the surfaces of the liquid in the pear and that in the 
 tube are at the same level : the apparatus is then allowed to stand 
 for at least half an hour. The flames under the combustion tube 
 are not turned out simultaneously, but first one is extinguished, 
 and then after a short time another, and so on. During the cool- 
 ing of the tube the weighing-flask is weighed again. 
 
 Transferring the Nitrogen. After the nitrogen has stood in 
 contact for at least half an hour with the caustic potash, in order 
 that the last portions of carbon 
 dioxide may be absorbed, the 
 end of the delivery tube is dipped 
 under the surface of the water 
 contained in a wide-mouth cylin- 
 der, as represented in Fig. 56, 
 care being taken that in the 
 lower bent portion of the de- 
 livery tube no air bubbles are 
 present ; if there are, they must 
 be removed with a capillary 
 pipette. The eudiometer is now 
 filled with water, the end closed 
 with the thumb, inverted and 
 dipped below the surface of the 
 
 r IG. 50. 
 
 water, the thumb removed and 
 
 the tube clamped to the cylinder, at an oblique angle, so that the 
 end of the delivery tube may be passed under it. The pear 
 supported by the clamped ring is raised as high as possible above 
 the delivery tube, and the glass cock gradually opened. The 
 nitrogen is thus transferred to the eudiometer, the cock being 
 left open until the delivery tube is completely filled with the 
 caustic potash. The absorption apparatus is then removed, the 
 eudiometer wholly immersed in the water. To obtain the tem- 
 perature, a thermometer, held in the -clamp which supported the 
 
ORGANIC ANALYTICAL METHODS 99 
 
 delivery tube, is immersed in the water as far as possible. After 
 about ten minutes, the nitrogen has come to the same tempera- 
 ture as the water, the eudiometer is then seized with a clamp 
 especially adapted to this purpose, or crucible tongs, never with 
 the hands, and is raised so far out of the water that the level 
 of water inside and outside the tube is the same. The volume of 
 gas thus read off, is under the same pressure as that indicated by 
 a barometer. 
 
 Calculations of the Analysis. If s is the amount of substance 
 in grammes, v the volume of nitrogen read at the temperature /, 
 and b the height of the barometer in millimetres, w the tension 
 of the water vapour in millimetres at /, then the percentage of 
 nitrogen is p : 
 
 _ v (b w) 0.12505 
 
 ~~ 760 (i + 0.00367 /) s' 
 
 The calculation of the analysis is rendered easier by referring to 
 the table in which the weight of one cubic centimetre of moist 
 nitrogen is given in milligrammes at different temperatures and 
 pressures. If this, under the observed conditions, is g, then the 
 percentage of nitrogen is : 
 
 100 XVX 
 
 In this formula, s is the weight of the substance in milligrammes. 
 
 A table is given at the end of the book for these calculations. 
 The values for the height of the barometer not found in the table 
 may be obtained by interpolation. For ordinary work it is 
 unnecessary to read off fractions of degrees on a thermometer, 
 or of millimetres on a barometer, since the slight differences in 
 values found in this manner lie within the limits of experimental 
 error. 
 
 The upper figure in each space in the table is the weight of 
 moist nitrogen in milligrammes, and the lower figure is the mantissa 
 of the logarithm of the weight of nitrogen. 
 
 Length of Time for an Analysis. The following abstract will 
 give an approximate iclea" of ' the length of time that the single 
 
100 GENERAL PART 
 
 operations of a well-conducted cpmbustion ought to occupy. 
 From the beginning of the heating of the magnesite to the ap- 
 pearance of a rapid current of carbon dioxide requires about 
 10 minutes, the first test as to whether air is still present in the 
 tube follows after a further 15 minutes ; length of time for various 
 tests, 5 minutes. From the warming of the forward layer of the 
 copper oxide with the spiral to the heating of the rear layer of 
 oxide to a dark red heat, 15 minutes. The actual combustion 
 of the substance requires 30 minutes. The displacement of the 
 last portions of nitrogen by heating the magnesite requires 10 
 minutes. Total, i hour and 25 minutes. 
 
 These time figures are, of course, only to be considered as 
 approximate, since they depend upon the efficiency of the fur- 
 nace, upon the nature of the substance burned, upon the skill 
 of the experimenter, and upon other factors. 
 
 Subsequent Operations. After the tube has cooled and the 
 copper spiral taken out, all the copper oxide is sifted to separate 
 the coarse from the fine, and may be used again for further 
 analyses as often as desired, provided that it is reheated each 
 time in the nickel crucible to oxidise it. The tube may also be 
 used again if it has not been distorted by high heating. The 
 magnesite is useless for further analyses. 
 
 The caustic potash in the absorption apparatus, which can be 
 used a second time, is poured into a bottle, which is then well 
 closed. The absorption apparatus, including the rubber tubing, is 
 washed out repeatedly with water, so that the latter may not be 
 corroded by the caustic potash. 
 
 General Remarks. The above-described method of Dumas 
 for nitrogen is used in variously modified forms, but the principle 
 is the same in all. It is preferred in many places to generate the 
 carbon dioxide from acid sodium carbonate or manganese car- 
 bonate. A combustion tube open at both ends may be used, if a 
 number of nitrogen determinations are to be made. The tube 
 is charged as represented in Fig. 60 (page 107). The substance 
 is placed in a porcelain or copper boat. In order to replace the 
 air by carbon 'dioxide, t're fear 'end 1 of the'tuBe 'is connected with 
 
ORGANIC ANALYTICAL METHODS IOI 
 
 another tube of difficultly fusible glass (closed at one end), 25-30 
 cm. long and 15-20 ram. wide, which is three-fourths filled (in 
 cross section) with sodium bicarbonate. In order to absorb the 
 water generated from this on heating, a small sulphuric acid wash 
 bottle is interposed between the two tubes. The layer of bicar- 
 bonate is heated with a single Bunsen burner, beginning at the 
 fused end. In order to protect the bicarbonate tube from the 
 direct flame, it is surrounded by a cylinder of coarse iron gauze 
 (Fig. 57). The bicarbonate may be replaced by a Kipp generator. 
 Further, the mixing of the substance with the fine copper oxide 
 may be done in the tube. Instead of the absorption apparatus 
 
 FIG. 57. 
 
 of Schiff, described above, a graduated tube from which the vol- 
 ume of the gas may be read directly may be used, thus obviating 
 the necessity of transferring it to a eudiometer. This modifica- 
 tion carries with it, however, the disadvantage that the tension of 
 caustic potash is not exactly known, and therefore a somewhat 
 arbitrary correction must be applied. But as mentioned these 
 modifications- do not differ essentially. 
 
 QUANTITATIVE DETERMINATION OF CARBON AND HYDROGEN 
 LIEBIG'S METHOD 
 
 The essential part of the method consists in completely burning 
 with copper oxide a weighed amount of the substance, and then 
 weighing the combustion products, carbon dioxide and water. 
 
 The requisites for analysis are : 
 
102 GENERAL PART 
 
 1. A hard glass tube open at both ends; outside diameter 12- 
 
 15 mm. It should be about 10 cm. longer than the furnace. 
 
 2. Four hundred grammes of coarse and 50 grammes of fine 
 
 copper oxide, preserved in bottles closed with tin-foil- 
 covered corks as in the nitrogen determination. But the 
 copper oxide used for the latter purpose and that for the 
 carbon and hydrogen determinations are always kept in 
 separate bottles. 
 
 3. A U-shaped and a straight calcium chloride tube. 
 
 4. A caustic potash apparatus. The Geissler form is the most 
 
 convenient. 
 
 5. A drying apparatus for air or oxygen. 
 
 6. Two one-hole rubber stoppers fitting the ends of the com- 
 
 bustion tube. 
 
 7. A glass tube provided with a cock. 
 
 8. Two copper spirals of 10 and 12-15 cm - length, respectively ; 
 
 two short spirals 1-2 cm. long. 
 
 9. A piece of good rubber tubing 20 cm. long ; six pieces rubber 
 
 tubing 2 cm. long (thick-walled and seamless). 
 
 10. A porcelain and a copper boat. 
 
 11. A screw pinch-cock. 
 
 12. Two asbestos plates for the protection of the rubber stoppers. 
 
 Preparations for the Analysis. The sharp edges of the com- 
 bustion tube are rounded by careful heating in a blast-flame. After 
 cooling the tube is rinsed out with water several times ; this is 
 allowed to drain off, and the tube dried by one of the methods 
 given on pages 91 and 92. 
 
 The coarse copper oxide is not previously heated in the nickel 
 crucible as in the determination of nitrogen, but this is done later 
 in the tube itself. If the nature of the substance to be analysed 
 is such that it is necessary to mix it with fine copper oxide, the 
 latter is ignited for a quarter hour in the porcelain crucible and 
 allowed to cool in a desiccator. 
 
 The U-tube for the absorption of the water (Fig. 61) is filled 
 with granulated, not fused, calcium chloride, which must be freed 
 
ORGANIC ANALYTICAL METHODS 1 03 
 
 from any powder by sifting. In order to prevent the calcium 
 chloride from falling out, both ends of the tube are provided with 
 loose plugs of cotton. The open leg is closed by a rubber stopper 
 or a good cork bearing a glass tube bent at a right angle. The 
 cork stopper is covered with a thin layer of sealing-wax. Calcium 
 chloride tubes, in which the open leg is longer than the other, are 
 very convenient. After the tube is filled the open end may be 
 sealed in a blast-flame. In this case the plug in this end is not 
 cotton, but asbestos or glass-wool. In order that the tube may 
 be suspended from the arm of the balance in weighing, a platinum 
 wire with a loop in the centre is attached to both legs. Calcium 
 chloride often contains basic chlorides, which not only absorb 
 water, but also carbon dioxide, thus causing an error in the results 
 of the analysis ; before the filled tube is used a stream of dry 
 carbon dioxide is passed through it for about two hours, dried air 
 is then drawn through for half an hour to displace the carbon 
 dioxide. The two side tubes of the calcium chloride tube are 
 closed by pieces of rubber tubing 2 cm. long, in which is inserted 
 a glass rod rounded at both ends, i| cm. long. The tube may 
 be used repeatedly until the calcium chloride begins to liquefy. 
 The straight calcium chloride tube is filled in like manner, but it 
 is unnecessary to pass carbon dioxide through this before using. 
 
 The three bulbs of the potash apparatus similar to the one 
 represented in Fig. 58 are three-fourths filled with a solution of 
 caustic potash (2 parts potassium hydroxide, 3 parts water) as 
 follows : the horizontal tube which is to be charged with solid 
 caustic potash is removed, and to the free end of the bulb tube 
 rubber tubing is attached. The inlet tube represented in Fig. 58 
 at the left is now dipped into the caustic potash solution, con- 
 tained in a shallow dish, and this is sucked up with the rubber tub- 
 ing until the three bulbs are three-fourths filled. Care must be 
 taken not to suck too strongly, otherwise some of the caustic potash 
 solution may be drawn into the mouth. This may be prevented by 
 inserting an empty wash bottle between the potash apparatus and 
 the n outh, or the suction-pump may be used, in which case the 
 watei -cock must be opened to a very slight extent. After filling 
 
104 GENERAL PART 
 
 the bulbs that part of the tube immersed in the potash solution 
 is cleaned with pieces of rolled-up filter-paper. The horizontal 
 potash tube, removed before filling the bulbs, is now filled with 
 coarse-grained soda-lime and solid caustic potash in pea-size 
 pieces as follows : In the bulb is placed a plug of glass-wool or 
 asbestos, then follows a layer of the soda-lime, a layer of caustic 
 potash, and finally another plug of glass-wool or asbestos. When 
 this is done, it is closed in the same way as the calcium 
 chloride tube. In handling the Geissler tubes it is always to be 
 remembered that they are very fragile, and in all cases the lever- 
 
 FlG. 58. 
 
 arm formed in lifting them should be as short as possible. When 
 the apparatus is to be closed by rubber tubing, e.g., it is not 
 grasped by the bulbs, but immediately behind the place over 
 which the tubing is to be drawn or pushed. When the potash 
 apparatus has been used twice, it must be refilled. The longer of 
 the two so-called copper oxide spirals need not be reduced before 
 the combustion ; on the contrary, it is oxidised in the combustion 
 tube, as will be pointed out below. In order to be able to remove 
 it from the tube conveniently a loop of copper wire is fastened in 
 the meshes of the gauze near the end, or a not too thin copper 
 wire is passed through the centre of the spiral and bent at one 
 end to a right angle and at the other in the form of a loop. The 
 
ORGANIC ANALYTICAL METHODS 
 
 105 
 
 shorter spiral, which, as in the nitrogen determination, serves to 
 reduce any oxides of nitrogen, is next reduced according to the 
 directions given on page 92. To remove any adhering organic 
 substances like methyl alcohol or its oxidation products the spiral 
 is placed, after cooling, in a glass tube 20 cm. long, one end of 
 which is narrowed ; carbon dioxide is passed through it, and as 
 soon as the air has been displaced, it is heated for a few minutes 
 with a Bunsen flame and then allowed to cool in a current of car- 
 bon dioxide. To remove the mechanically adhering gas the spiral 
 is placed in a vacuum desiccator. If this is not at hand, an ordi- 
 nary desiccator containing a small dish of solid caustic potash or 
 unslaked lime is used. (It may also be heated in an air-bath at 
 loo-no .) 
 
 For drying the oxygen or air an apparatus consisting of two wash 
 cylinders and two U-shaped glass tubes mounted on a wooden 
 stand is employed. The gas passes first 
 through a wash cylinder containing a 
 solution of potassium hydroxide (i : i), 
 then a tube filled with soda-lime, then 
 one filled with granulated calcium chlo- 
 ride, and finally a wash cylinder contain- 
 ing sulphuric acid (Fig. 59). 
 
 The legs of the glass tube containing 
 the stop-cock are fused off and slightly 
 narrowed at the ends, so that on either 
 side of the cock the length is 5 cm. 
 
 Filling the Tube. The simplest case 
 of combustion with which one can deal 
 is that involving the analysis of a sub- 
 stance containing no nitrogen. In a 
 case of this kind, assuming that the furnace has a flame surface 
 of 75 cm., the tube is filled in the following manner : A short 
 copper gauze roll, 1-2 cm. long, of sufficient diameter to fit the 
 tube tightly, and somewhat elastic, is pushed into the tube 5 cm., 
 and then the opposite side of the tube is partially filled with a 
 layer of coarse copper oxide 45 cm. held in position by another 
 
 FIG. 59. 
 
I0 6 GENERAL PART 
 
 small elastic copper spiral at its upper end. Into the tube lying 
 in a horizontal position the copper oxide spiral is pushed so far 
 that its loop is 5 cm. from the mouth of the tube (Fig. 60). 
 
 Igniting the Copper Oxide. The charged tube is placed in the 
 furnace, the end nearest the copper oxide spiral is closed by a 
 rubber stopper bearing the glass stop-cock tube, and the latter is 
 connected with the drying apparatus by means of rubber Jtubing 
 provided with a screw pinch-cock. The other end of the tube 
 is allowed to remain open at first ; while a current cf oxygen is 
 passed through the tube, slow enough to enable one to count the 
 bubbles (the glass stop-cock is opened wide and the current regu- 
 lated with the pinch-cock), the entire length of the tube is heated, 
 at first with flames as small as possible ; these are gradually in- 
 creased until finally, the tiles being in position, the copper oxide 
 begins to appear dark red. The water deposited at the beginning 
 of the heating, in the forward cool end of the tube, is now removed 
 with filter paper wrapped around a glass rod. When no more 
 water collects, the front end of the tube is closed by a ru ;>b^r 
 stopper bearing the straight calcium chloride tube. After atnut 
 20 or 30 minutes' heating the burners under the copper oxide 
 spiral, the adjacent empty space, and those under about 5 cm. of 
 the copper oxide layer lying next, are extinguished, and at the 
 same time the current of oxygen is cut off. 
 
 Weighing the Absorption Apparatus and the Substance. While 
 the rear part of the tube is cooling, the calcium chloride tube, the 
 potash bulbs, and the substance are weighed. Before the absor^ 
 tion apparatus is weighed, it is wiped off with a clean cloth, free 
 from lint, and the rubber tubing and glass rods removed ; after the 
 weighing, these are replaced. The substance, if solid, is weighed 
 in a porcelain boat which has previously been heated strongly, and 
 cooled in a desiccator. The boat is first weighed empty, 0.15 to 
 0.20 gramme of the substance placed in it and weighed again ; it 
 is then placed on a tin-foil-covered cork, in which a suitable groove 
 has been cut, and transferred to a desiccator. 
 
 The Combustion. When the rear end of the tube is cold, the 
 copper oxide spiral is withdrawn with a hooked glass rod or wire, 
 
S cm. free 
 
 Short copper spiral 
 
 45 cm. coarse oxide 
 
 Short copper spiral 
 
 10 cm. free 
 
 15 cm. copper oxide 
 spiral 
 
 5 cm. free 
 
 FIG. 60. 
 
I0 8 GENERAL PART 
 
 the porcelain boat is inserted as far as the coarse copper oxide, 
 care being taken not to upset the boat, and finally the spiral is 
 replaced. The stop-cock tube, with the cork closed, is then put 
 in position. The straight calcium chloride tube is replaced by 
 the weighed U-tube, with its empty bulb, which will condense the 
 greater portion of the water, nearest the furnace. To the U-tube 
 is connected, by a rubber joint, the potash apparatus, and the 
 soda-lime tube of the latter with the straight calcium chloride 
 tube in the same way (Fig. 61). The connecting of the different 
 parts of the apparatus may be facilitated by blowing air from the 
 lungs through each rubber joint before pushing it on the glass 
 tubes. Especial care is taken to have a good joint between 
 the U -calcium chloride tube and the potash bulbs, since at this 
 point very commonly lies the source of error in analyses not con- 
 cordant. A thick-walled seamless rubber tubing is employed ; 
 it is drawn over the two ends of the glass tubes until they touch. 
 In order to provide against any possible leak, two ligatures of thin 
 copper wire or " wax ends " are bound around the joints. A test 
 as to whether the apparatus is perfectly tight is not always con- 
 vincing when the combustion is conducted in an open tube ; since, 
 on the one hand, the heating is 1 not constant, and on the other, 
 in consequence of the friction of the solution in the narrow tubes, 
 a leak, at times, may not be detected. ' The rubber stoppers 
 closing the tube may be protected from the heat by placing on 
 the tube, close to the furnace, an asbestos plate with a circular 
 hole in the centre. After closing the screw pinch-cock, the glass- 
 cock is opened, and a slow current of oxygen (two bubbles per 
 second) is admitted to the tube by carefully opening the pinch - 
 cock. Small flames are now lighted under the copper oxide 
 spiral, which are increased after some time, until, finally, the spiral 
 is brought to a dark red glow. When this is done, the flames 
 under the unheated copper oxide are gradually lighted, care being 
 taken not to allow any flame near the porcelain boat to be too 
 large. Now follows the most difficult operation of the analysis, 
 upon which the success of it virtually depends, viz. the gradual 
 heating of the substance. This is conducted in exactly the same 
 
ORGANIC ANALYTICAL METHODS 1 09 
 
 way as that given under the nitrogen determination. The heating 
 is begun, at first, with a single small flame ; this is gradually in- 
 creased in size, or several others may be lighted, then the tube is 
 covered on one side with the tiles, and after a short time, on the 
 other, and finally the full flames are used. With easily volatile 
 substances, the heating at the beginning is not done with the 
 flame, but by covering that portion of the tube containing the 
 boat with hot tiles, taken from the forward highly heated portion 
 of the furnace. Numerous modifications have been applied to 
 this most difficult part of the analysis, concerning which no satis- 
 factory general directions can be given. A valuable rule is to 
 conduct the heating in such a way that the gas bubbles passing 
 through the potash apparatus follow one another with as slow a 
 regularity as possible. If the passage of bubbles becomes too 
 rapid, the heating is moderated. If, during the combustion, 
 water should condense in the glass-cock, or in the rear, cold 
 portion of the tube, as it always does in the front end, it is 
 removed by holding a hot tile under it, or by heating with a small 
 flame. When the boat has been heated some time with the full 
 flames, the combustion is considered to be ended. In order to 
 drive the last portions of carbon dioxide and water from the tube 
 into the absorption apparatus, a somewhat more rapid current of 
 oxygen is passed through the tube, until a glowing splinter held 
 before the opening of the straight calcium chloride tube is ignited. 
 During this operation, the water, condensed for the most part in 
 the front end of the tube, is also driven over into the calcium 
 chloride tube, as above described. When this has been done, the 
 rubber stopper is withdrawn from the front end of the combustion 
 tube, care being taken to prevent the water in the calcium chloride 
 tube from running out. To remove the oxygen in the absorption 
 apparatus, a slow current of air which need not be dried is drawn 
 through it for 1-2 minutes, with the mouth or suction. The 
 apparatus is taken apart, closed up as above described, allowed 
 to stand in the weighing-room for half an hour, and is then 
 weighed. From the difference in the weights of the absorption 
 apparatus before and after the combustion, the percentage of 
 carbon and hydrogen is found from the following equations 
 
HO GENERAL PART 
 
 Wt. CO 2 X 300 
 
 Percentage of Carbon = , 
 
 Wt. Substance x n 
 
 log --=0.435 73- i 
 
 VyW2 
 
 Wt. H 2 O X 201.6 
 Percentage of Hydrogen = 
 
 Wt. Substance X 18.01 6' 
 
 log -^-=0.04884 -i 
 rl 2 U 
 
 Modifications of the Method. In many cases instead of using 
 oxygen for the ignition of the copper oxide, the same result may 
 be obtained by using a current of air. The combustion may also 
 be conducted in a current of air ; but when the substance is diffi- 
 cult to burn, it is still necessary toward the end of the operation to 
 pass oxygen through the tube for some time. As soon as a glow- 
 ing splinter held at the end of the straight calcium chloride tube 
 is ignited, the combustion is ended. The combustion may also be 
 conducted without passing a current of air or oxygen into the tube 
 at the beginning, in which case the glass stop-cock is closed. 
 Under these conditions, as soon as the substance has been 
 heated for some time with the full flames, toward the end of the 
 operation the glass stop-cock is opened and a current of air 
 or oxygen passed through the tube. Substances which burn with 
 great difficulty can also be mixed with fine copper oxide in a 
 copper boat (see below), and then burned in the same way in 
 oxygen. 
 
 Combustion of Substances containing Nitrogen. Since in the 
 combustion of nitrogenous compounds, the reduced copper spiral 
 serving for the reduction of the oxides of nitrogen must be used, 
 the combustion tube is charged somewhat differently in this case. 
 The first copper roll is inserted in the tube, not 5 cm., but 15 cm., 
 the space in front of it being reserved for the reduced spiral. 
 Consequently the layer of coarse copper oxide is but 35 cm., and 
 not 45 cm., in length. No change is made in the disposition of 
 the copper oxide spiral. The ignition of the copper oxide is 
 conducted exactly as above, except that a current of air is used. 
 
ORGANIC ANALYTICAL METHODS III 
 
 If, however, the ignition should be conducted throughout with 
 oxygen, at the end of the operation this is displaced by air. The 
 further operations are the same as those described above, except 
 that the reduced copper spiral is put in position last just before 
 connecting the combustion tube with the absorption apparatus. 
 In order to prevent the oxidation of the copper, the combustion 
 proper is performed with the glass-cock closed, and oxygen is 
 not admitted to the tube until at the end. As soon as the oxy- 
 gen is admitted, the flames under the reduced copper spiral are 
 extinguished. The gas is passed through until it can be detected 
 at the end of the apparatus as above described. In the 
 combustion of substances which leave a charred, difficultly 
 combustible, nitrogenous residue, it is necessary to burn them 
 by mixing with fine copper oxide. Since the porcelain boats 
 are generally too small to contain a sufficient quantity of this, 
 a boat made of sheet copper, 8 cm. long and of a width suffi- 
 cient to enable it to be just passed into the tube, is used. It 
 is filled as follows : After it has been previously ignited, it is 
 placed upon a sheet of black glazed paper, and half filled with 
 fine copper oxide also previously ignited and afterwards cooled 
 in a desiccator. Upon this is carefully spread the weighed sub- 
 stance from a weighing-tube as in the nitrogen determination, 
 then a layer of fine copper oxide is added until the boat is 
 three-fourths full : the substances are now well mixed by care- 
 ful stirring with a thick platinum wire. If some of the mixture 
 should fall upon the glazed paper, it is returned to the boat with 
 the aid of a feather or brush. The combustion is made with the 
 glass-cock closed. Oxygen is not admitted until at the end of 
 the operation. 
 
 Combustion of Substances containing Sulphur or a Halogen. 
 Sulphur compounds cannot be burned with copper oxide in 
 the manner described, since at a red heat the copper sulphate 
 formed gives off sulphurous acid, which is absorbed by the 
 potash apparatus along with the carbon dioxide, giving a result 
 in which the percentage of carbon is too high. In this case 
 the oxidation is accomplished with granulated lead chromate. 
 
H2 GENERAL PART 
 
 The filling of the tube, open at both ends, is done just as described 
 above : copper oxide spiral, empty space for boat, long layer of 
 lead chromate. The ignition in oxygen, etc., is also the same. 
 But two points are here to be observed : (i) the lead chro- 
 mate is not heated as strongly as the copper oxide, otherwise 
 it fuses in the glass; and (2) the most forward portion of 
 the lead chromate layer, nearest the calcium chloride tube 
 (that above about three burners), is heated very slightly, since 
 lead sulphate is not completely stable at a red heat. The sub- 
 stance is mixed in the copper boat with powdered, ignited lead 
 chromate. 
 
 Halogen compounds can be burned in the usual way with cop- 
 per oxide ; but since the copper halides are partially volatile and 
 give up the halogen on being heated to redness, a silver spiral 
 must be inserted in the tube to retain the halogen. The tube is 
 filled in the same way as for the combustion of a nitrogen com- 
 pound, only in place of the reduced copper spiral, one of silver 
 is used. But it is better to perform the combustion with lead 
 chromate, in which case it will not be necessary to use a silver 
 spiral. Since the lead halides are also somewhat volatile at a red 
 heat, so, as above, the front part of the tube containing the lead 
 chromate is heated but slightly. 
 
 Combustion of Liquids. If the compound to be analysed is a 
 liquid, it can be weighed directly in the porcelain boat, provided 
 it is very difficultly volatile. Moderately volatile substances 
 are weighed in a small glass tube which is loosely closed 
 with a glass stopper (see Fig. 53, page 81). In order to 
 introduce this into the tube, it is placed in the porcelain 
 boat in such a position that the mouth of the tube is 
 directed upwards. A preliminary trial will show whether 
 the boat containing the empty tube will pass into the com- 
 bustion tube. Very easily volatile substances are weighed 
 2 ' in small bulb-tubes which are sealed after weighing (Fig. 
 62). The filling is done as follows : The empty tube is weighed, 
 heated gently, and the open end dipped under the liquid to be 
 analysed. On cooling, the liquid will be drawn up into the bulb. 
 
ORGANIC ANALYTICAL METHODS 113 
 
 If a sufficient quantity is not obtained the first time, the operation 
 is repeated ; before it is sealed care must be taken that the 
 capillary contains none of the liquid ; if it does, it must be 
 removed by heating. It is now sealed, and the tube plus sub- 
 stance weighed. Care must again be taken to prevent any of the 
 liquid from finding its way into the 'capillary, due to sudden 
 movements or other causes. To prepare the tube for the com- 
 bustion, the extreme end is filed and broken off, during which 
 operation the tube is not held by the bulb. It is placed in the 
 boat with its open end elevated 'and directed toward the front 
 end of the furnace. The precaution to ascertain beforehand 
 whether the boat loaded with the tube will pass into the com- 
 bustion tube, should always be taken. If necessary, the capillary 
 is shortened. 
 
 ELEMENTARY ANALYSIS 
 DENNSTEDT'S METHOD 
 
 Dennstedt's method consists in burning the substance with free 
 oxygen x exclusively, in the presence of platinum as contact sub- 
 stance (catalyser). 
 
 In addition to the frame of a combustion furnace, and an oxy- 
 gen gasometer, Dennstedt recommends the use of two flasks 
 provided with tubulures at the bottom and having a capacity of 5 
 litres, the requisites for analysis are : 
 
 1. A hard glass tube open at both ends ; length 86 cm. ; diame- 
 ter 18-20 mm. ; also an inner tube and a small wash bottle. 
 
 2. A drying tower for the oxygen. 
 
 3. A U-shaped calcium chloride tube with two ground stop- 
 cocks and a ground-in stopper (next to the bulb). 
 
 4. A soda-lime tower with two ground stoppers. 
 
 5. A U-shaped soda-lime-calcium chloride tube with two 
 ground stop-cocks ("Testing-tube "). 
 
 1 Not electrolytically prepared. 
 I 
 
114 
 
 GENERAL PART 
 
 6. A wash bottle for palladious chloride (" Palladium bottle ") 
 
 7. A straight calcium chloride tube. 
 
 8. A strip of star-shaped platinum, and a roll of thin platinum 
 foil. 
 
 9. A rod of hard glass for the inner tube, with a loop and plati- 
 num thread or platinum wire. 
 
 10. A porcelain boat (for the substance) divided into three 
 parts, length 8 cm. ; also several ordinary porcelain boats (Absorp- 
 tion boats). 
 
 11. Rubber stoppers and seamless rubber tubing, to be used 
 for the analysis only. 
 
 12. Chemicals: calcium chloride, soda-lime, palladious chlo 
 ride, lead peroxide, minium, sodium carbonate, molecular silver. 
 
 1. The Combustion Furnace consists of two stands supporting 
 three loose iron troughs. The middle one is covered with thin 
 asbestos paper, and serves as a support for the combustion tube, 
 while the other two troughs support the covers, the inner surfaces 
 of which are lined with asbestos. Of these five are needed ; a 
 large cover 25 cm. in length, and four smaller covers each one 
 having a length of 12 cm. Of the latter, one is provided with a 
 
 FIG. 62 A. 
 
 sliding window of mica (10 cm. : 2 cm.), through which the cata- 
 lyser may be observed. The sheet of mica is renewed when it 
 becomes opaque. The iron covers are provided with projections 
 on the upper edges, and may be moved back and forth with crucible 
 tongs. They should not touch the combustion tube. The com- 
 bustion tube is heated with three, or preferably four, burners. The 
 
ORGANIC ANALYTICAL METHODS 115 
 
 two burners shown at the left of Fig. 62 A are used to vaporise 
 the substance. They are Bunsen orTeclue burners to which wing 
 burners may be attached. One burner is sometimes used for the 
 purpose. Then follows a stronger Bunsen or Teclue burner, pro- 
 vided with a wing burner and a regulation device. This is placed 
 under the contact star and supplies the combustion flame. The 
 rear of the tube (the part preceding the absorption apparatus) is 
 heated with a movable flame tube consisting of 20 non-luminous 
 flames. During the combustion a temperature of 300-320 is 
 necessary in this part of the tube. The height of the flames that 
 will produce this temperature is determined in a preliminary ex- 
 periment by inserting a thermometer in the combustion tube. 
 
 2. Drying Tower for the Oxygen. Pure concentrated sulphuric 
 acid is poured into the lower part of the tower (Fig 62 A, left) to a 
 height of 2 cm., so that the end of the conducting tube, which is 
 2 mm. wide, dips into this to a depth of J-i cm. Ligatures 
 (string or wire) are bound around the joints. A small funnel, 
 with its tube bent sidewise, is introduced into the lower narrow 
 part of the tower. The funnel is covered with a little glass-wool 
 or cotton, and the lower half of the cylindrical tower (about 10 
 cm.) is filled with coarse, sifted soda-lime ; the upper half is filled 
 with calcium chloride. Then follows a layer of glass-wool or cot- 
 ton. Concerning the quality of the soda-lime and the calcium 
 chloride, see below (Filling of absorption apparatus). 
 
 3. The Small Wash Bottle. A plug of cotton is placed at the 
 bottom of the wide tube attached to the small wash bottle (Fig. 
 62 B) ; it is then filled with calcium chloride and covered with a 
 layer of cotton (see 4 a). The lower narrow part of the small 
 wash bottle is filled with concentrated sulphuric acid. A capillary 
 tube is used for this purpose. The bottle is held in an inverted 
 position ; the tip of the capillary is now inserted as far into the 
 U-shaped curve as possible, and by proper manipulation the acid 
 is allowed to flow through the inner bulb into the lower narrow 
 end. The limb nearest the calcium chloride tube is dried with 
 blotting-paper. The small wash bottle must be constructed so 
 that there is a space of at least i mm. between the inner bulb and 
 
GENERAL PART 
 
 the outer tube. The connecting parts of the apparatus may be 
 made tight by moistening the two holes of the stopper, as well as 
 its lower surface, with a saturated solution of calcium chloride. 
 In order to regulate the stream of oxygen as perfectly as possible 
 by the aid of the three stop-cocks of the small wash bottle, the 
 perforations of the cocks are filed on both sides with a sharp tri- 
 angular file, as seen in Fig. 620. The calcium chloride is renewed 
 from time to time, and the stoppers are kept closed when the 
 apparatus is not in use. 
 
 4. Absorption Apparatus. (a) Calcium Chloride Tube. It 
 contains two ground stop-cocks, a small ground glass stopper, 
 
 FIG. 62 B. 
 
 FIG. 62 c. 
 
 and the bulb in which a greater part of the water condenses. The 
 previously sifted calcium chloride is poured into a wide test-tube, 
 clamped in a slanting position, and carefully heated with a free 
 flame until no more water deposits in the cooler part of the tube. 
 The heating must be done cautiously, and only for a short time. 
 In filling the U-tube care must be taken that no dust particles or 
 calcium chloride settle in the side-tubes ; to prevent this the side- 
 
ORGANIC ANALYTICAL METHODS II 7 
 
 tubes are plugged with cotton during the filling. The cotton is 
 removed with forceps after filling the tube. A short roll of paper 
 may also serve the same purpose, protecting not only the side-tubes 
 but also the ground part of the U-tube. A roll of cotton is finally 
 introduced into the calcium chloride tube. The ground parts of 
 the tube are then cleaned and slightly oiled. Before the newly 
 filled tube is used, dry carbon dioxide is passed through it (see 
 page 103). The carbon dioxide is then displaced by oxygen. 
 
 (b) Soda-lime Tower. Commercial soda-lime is often too dry 
 and does not therefore readily absorb carbon dioxide. Before 
 filling the absorption apparatus a few grammes are carefully heated 
 in a test-tube over a free flame. Much water should condense in 
 the cooler parts of the tube. If this is not the case, the entire 
 quantity is moistened with the necessary amount of water (spray). 
 The soda-lime must be freed from small particles by sifting, and 
 care must be taken that no small particles settle in the side-tubes. 
 The precautions outlined for calcium chloride are followed here. 
 As soda-lime expands by the absorption of carbon dioxide, in order 
 to avoid the danger of breaking the apparatus care is taken not to 
 use too much. The perforations of the glass stoppers are then 
 filled with dry cotton ; the ground surfaces are very carefully 
 cleaned, and slightly greased. When it is desired to refill a tower 
 that has been used, the stoppers are removed, the apparatus is 
 freed from grease, and dipped for several hours in water that has 
 been slightly acidified with hydrochloric acid. During the com- 
 bustion the tower is always kept in the same position ; in order to 
 prevent mistakes the side-tubes are marked (arrow, or coloured 
 glass-button).- 
 
 (c) Soda-lime-calcium Chloride Tube ("Testing- Tube"). One 
 limb of this tube is filled with soda-lime and the other with calcium 
 chloride. The precautions mentioned in (a] and (<) are observed. 
 The testing-tube is inserted in such a manner that the soda-lime 
 limb is next to the soda-lime tower. 
 
 (d) The Weighing of the Absorption Apparatus. The three 
 absorption tubes are always filled with oxygen before weighing. 
 When used for the first time, dry oxygen is conducted into the 
 
H8 GENERAL PART 
 
 apparatus until all the air has been driven out. (Test : vigorous 
 flaming of a glowing splinter.) One of the two stop-cocks in each 
 apparatus is opened for a moment before weighing, in order to 
 equalise the differences in pressure. In weighing after a combus- 
 tion, the temperature should be as nearly the same as it was before 
 combustion. In most cases it is sufficient to carry out the final 
 weighing when the apparatus has remained in the balance room 
 for one or two hours. It is safer to check the weighing on the 
 following morning. In winter-time the temperature of the balance 
 room should be kept uniform over night. Should a long period 
 elapse between two analyses, the apparatus is again filled with 
 oxygen. 
 
 (e) The Palladious Chloride Wash Bottle (" Palladium Bottle") 
 is half filled with a clear dilute water solution of palladious chloride 
 of a straw-yellow colour. The solution is filtered when it becomes 
 cloudy. The separation of palladium (by the action of carbon 
 monoxide) indicates an incomplete combustion. In addition to 
 this the solution is also of service in showing the rate of flow of 
 the gas stream. 
 
 5. The Combustion Tube and Accessories. All combustions 
 are carried out by the use of a duplex supply of oxygen. For this 
 purpose a T-tube is inserted in the stopper in the rear end of the 
 combustion tube. The vertical limb of the T-tube is provided with 
 a stop-cock, and is connected with the calcium chloride tube of 
 the small wash bottle as shown in Fig. 62 B. Through the hori- 
 zontal part of the T-tube passes the capillary of the inner tube ; 
 these two are connected with a short rubber tubing (ligature). 
 The wider part of the inner tube fills the space inside the com- 
 bustion tube almost completely, and serves as a receiver for the 
 boat containing the substance taken for analysis. In order to 
 prevent the fusion of the inner tube into the combustion tube, a 
 coil of fairly thick platinum wire is placed around the wide, open 
 end of the former. Furthermore, in order to prevent the forma- 
 tion of an explosive mixture by the combustible vapours and the 
 oxygen, a rod of hard glass is introduced into the inner tube. 
 The rod is .of a size that nearly fills the empty space in the inner 
 
ORGANIC ANALYTICAL METHODS 1 19 
 
 tube. It is provided with a loop in the fore-part ; to this is 
 attached a roll of platinum wire which reaches the open end of 
 the inner tube. Or, instead of the platinum roll, a thin platinum 
 wire is wound around the rod. This arrangement will also prevent 
 the rod from fusing. The glass rod is unnecessary in most in- 
 stances. Its place is taken by a roll of thin platinum foil. This is 
 placed at the opening of the inner tube in such a way that one 
 half rests in the inner tube, the other half in the combustion tube ; 
 then follows the contact star. Vapours of high boiling substances 
 will sometimes condense and run into the inner tube. In order 
 to protect the tube, it is covered to within i cm. of the opening 
 and over one-third of the inner surface with a strip of thin asbestos 
 paper. This must be heated with the combustion tube in a stream 
 of oxygen during the drying of the apparatus. (In the simulta- 
 neous estimation of sulphur the asbestos is not used.) Before the 
 analysis, the previously washed and dried combustion tube, the 
 inner tube (including the glass rod), the platinum coil, and the 
 platinum star are heated for a while in a moderate stream of 
 oxygen at 250-300. During the heating the burners are evenly 
 distributed, and the covers are placed in position. The opening 
 at the forward end is finally closed with a straight calcium chloride 
 tube, and the combustion tube is allowed to cool in a stream of 
 oxygen. As the bulky Dennstedt tubes break more readily than 
 those used in Liebig's method, special care is exercised in the 
 heating as well as the cooling of the former, and in exposing them 
 to sudden changes of temperature. It is also necessary, at all 
 times, to prevent the covers from coming in contact with the 
 hot tube. 
 
 6. The Combustion Proper. In combustions by Liebig's method 
 it has not been found possible to prescribe details that will cover 
 all cases. This is still less possible in Dennstedt's method, in 
 which the number of modifications and combinations is much 
 greater. A general outline of the method will be given for sub- 
 stances containing carbon, hydrogen and oxygen, and Dennstedt's 
 own words will be used in 'part. 
 
 While the combustion tube is being heated and cooled in a 
 
120 GENERAL PART 
 
 stream of oxygen, the absorption apparatus is weighed (a stop-cock 
 is opened for an instant) ; the boat having the three divisions is 
 also weighed, first empty, and then with the substance. The 
 supply of oxygen is now cut off, and the inner tube (with small 
 wash bottle, etc.) is withdrawn by removing the stopper at the rear 
 end of the combustion tube. The long rubber connection be- 
 tween the drying tower and the small wash bottle is not removed. 
 The boat containing the substance is introduced into the inner 
 tube, and pushed in, as far as possible. Then follows the glass 
 rod with its platinum wire, or the platinum roll alone, as described 
 above, and the apparatus is securely attached to the combustion 
 tube. The different parts of the absorption apparatus are finally 
 connected by the use of short, thick-walled, seamless rubber joints. 
 The rubber should be drawn over the ends of the glass tubes until 
 they touch. The Hrnb of the U-tube containing soda-lime 
 should be kept next to the soda-lime tower. The drying apparatus 
 is most conveniently connected with the combustion tube in the 
 following manner : A rubber stopper is first placed on the calcium 
 chloride tube (at the bulb end) ; the tube is then connected with 
 the soda-lime tower, which is in turn attached to the testing-tube ; 
 and finally, the end of the combustion tube is securely closed by 
 the rubber bearing the calcium chloride tube. Then follows the 
 palladium bottle. 
 
 Before the combustion proper, a test as to whether the apparatus 
 is perfectly tight is conducted in the following manner : All the 
 stop-cocks, from the stopper of the gasometer to the last stopper 
 of the U-tube (testing- tube) are closed. The stop-cock of the 
 gasometer and the lower stop-cock of the drying tower are now 
 opened, so that a few gas bubbles pass through the sulphuric acid. 
 If the joints are perfectly tight, the bubbling will stop as soon as 
 the pressure between gasometer and drying tower ,is equalised. If 
 the bubbling continues, then there is a leak which must be pre- 
 vented. The upper stop-cock of the drying tower is now opened, 
 and left open until the bubbling stops.- This is continued to 
 the last stop-cock of the testing- tube. During this test, the stop- 
 cock of the small wash bottle containing sulphuric acid is opened 
 
ORGANIC ANALYTICAL METHODS 12 1 
 
 in such a way that not more than two bubbles per second escape. 
 The combustion is commenced when the apparatus is found to be 
 perfectly tight. " For its success it is absolutely necessary to 
 thoroughly mix the vapour of the burning compound when it 
 reaches .the contact substance (platinum) with as much oxygen at 
 every instant as is required for its complete combustion, i.e. there 
 should always be present an excess of oxygen. In the combustion 
 of volatile substances, in order to mix the vapour with the proper 
 quantity of oxygen, the oxygen stream is introduced in two parts ; 
 one part is known as the slow vaporising stream, which sweeps 
 over the burning substance, and carries away its vapour in a 
 regular manner ; the other part is known as the combustion stream, 
 which meets the vaporising stream near the glowing platinum." 
 The former is regulated through the stop-cock of the small wash 
 bottle (Fig. 62 B, upper left hand), the latter through the stop-cock 
 of the calcium chloride tube (Fig. 62 B, upper right hand). The 
 lower stop-cock of the calcium chloride tube permits the passage 
 of both streams. The small wash bottle shows the velocity of the 
 vaporising stream, and the palladium bottle that of the combus- 
 tion stream. Whenever the velocity of these streams is specified, 
 e.g. by the number of bubbles for every 10 seconds, it is under- 
 stood that the bubbles in the small wash bottle are much smaller 
 than those in the palladium bottle. The outer stream is regulated 
 in such a manner that in 10 seconds 10-15 bubbles pass through 
 the palladium bottle. " When the vaporisation of the substance 
 becomes too rapid, the velocity of this stream may be temporarily 
 doubled, or increased even more, without hesitation." The inner 
 stream is so regulated that if the substance is easily volatile, 5-10 
 bubbles pass through the small wash bottle every 10 seconds, and 
 if the substance is not easily volatile 10-30 bubbles pass through 
 the wash bottle every 10 seconds. The velocity of the inner stream 
 should not be altered in the early part of the combustion. A small 
 flame is first lighted under the contact star. This is gradually in- 
 creased, until finally the star appears to glow brightly through the 
 mica window of the small cover. The flame, the small cover, and 
 the end of the inner tube lie in the same vertical plane. The 
 
122 GENERAL PART 
 
 forward empty part of the combustion tube is heated at the sarnt 
 time to about 300 with the burner tube, and a large cover is 
 placed next to the small cover with the mica window. "The 
 burner used to vaporise the substance is turned on almost entirely, 
 and burns with a moderately high flame. It is now placed at the 
 rear and kept so far away from the boats that even very volatile 
 substances are just vaporised without undergoing much change. 
 When the contact substance begins to glow brightly, the vaporis- 
 ing flame is quickly moved forward, about i cm. every 3-4 minutes, 
 depending upon the volatility of the substance, until the latter 
 melts or begins to decompose. With substances that do not 
 vaporise or decompose readily, the flame is brought near the boat. 
 It is then allowed to remain undisturbed. An observation will 
 now show whether the contact substance is glowing, whether there 
 is condensation of water at the forward end of the tube, in short, 
 whether combustion proper has started. If this is the case, every- 
 thing is left unchanged for 15 minutes. If combustion does not 
 progress smoothly at the end of this period, the combustion flame 
 and the cover are moved 1-2 mm. to the rear. This is repeated 
 after a short time, until it is found that, depending upon the nature 
 of the substance, it begins to burn completely, i.e. it first melts, 
 and then chars, etc., even in the first division of the boat. Should 
 the decomposition slow down, the combustion flame and the cover 
 are slowly, millimetre by millimetre, moved backwards, until finally 
 there is complete vaporisation, decomposition, or charring. The 
 combustion flame should never be moved far enough to diminish the 
 glow of the platinum at the open end of the inner tube. The cover, 
 however, may be moved back and kept directly above the boat. 
 The position of the burners need not be changed when the contact 
 mass is seen to glow brightly, since this is only an indication that 
 the combustion is progressing briskly. But if the glowing is very 
 sudden and too active, or, if flames appear at the open end of the 
 inner tube, both burners are pushed backwards in order to prevent 
 rapid decomposition, and the vaporising flame is again brought 
 near the boat in order to secure normal conditions once more. 
 The combustion flame is also moved back gradually to the extreme 
 
ORGANIC ANALYTICAL METHODS 123 
 
 limit. Should this stop the progress of the combustion, the va- 
 porising flame is moved forward, and the cover at the rear of the 
 tube is put in position. When the contents of the boat have either 
 entirely disappeared, or are completely carbonised, the inner 
 stream of oxygen is increased, and the tube heated to redness." 
 The part of the tube adjacent to the absorption apparatus is finally 
 covered with a small cover. 
 
 When the combustion is ended, the flames are first lowered and 
 then turned off entirely, and the apparatus is cooled in a stream 
 of oxygen. The palladium bottle is now removed. The lower 
 stop- cock of the drying tower is first closed, and the absorption ap- 
 paratus is taken apart after turning off the stop-cocks. The small 
 stopper near the bulb of the calcium chloride tube must not be 
 forgotten. Concerning the weighing of the apparatus see direc- 
 tions given above. Under normal conditions, the soda-lime- 
 calcium chloride tube should not increase in weight more than a 
 few milligrammes. An increase in weight amounting to more 
 than 10 mg. indicates that the soda-lime tower is exhausted and 
 needs refilling. In this case its original position should not be 
 reversed by oversight. 
 
 Very often in dealing with substances that are not very volatile, 
 it is more convenient to use two vaporising flames in place of 
 one. Even in this case the combustion flame under the platinum 
 star is first lighted. The flame is not placed under the substance, 
 but is allowed to remain under the contact star. The vaporising 
 flame at the rear is also kept, as before, as far away from the boat 
 as possible ; its position is changed only towards the end of the 
 combustion. In this case the substance is vaporised by the for- 
 ward vaporising flame, which is kept very low at first and placed 
 near the combustion flame, and is slowly brought near the boat 
 with a gradual increase of the flame, the time required for this 
 being the same as that given above for the combustion flame. As 
 soon as the forward flame is brought under the boat, the rear 
 flame is also pushed towards the substance. 
 
 It is to be noted once more that the rate of the combustion 
 depends upon the number and the height of flames, the use of 
 
I2 4 GENERAL PART 
 
 burners without or with wing burners, their distance from the 
 boat, the use of covers, the velocity of the oxygen stream, etc. 
 These are conditions that may be readily controlled. 
 
 Should the palladious chloride become very black during the 
 combustion, the analysis may be considered unsuccessful. Under 
 these conditions either the absorption apparatus is removed, and 
 the tube is heated to glowing in the presence of a stream of 
 oxygen, as described above (the absorption apparatus being re- 
 filled with oxygen for a new analysis), or the combustion is 
 brought to completion as under normal conditions. The weight 
 of the absorption apparatus is, of course, worthless in this case. 
 A combustion is also considered unsuccessful when the substance 
 or its decomposition products sublime, or distil beyond the con- 
 tact star. If this is the case, the absorption apparatus is im- 
 mediately removed, and the tube is heated to glowing in the 
 presence of a stream of oxygen. If necessary, the absorption 
 apparatus is freshly prepared. Finally, weak or strong explosions 
 may occur inside the tube during the combustion. If these do 
 not produce a sublimate, or a distillate, and cause no blackening 
 of the palladious chloride solution, then the analysis, including the 
 final weighing, is brought to a normal end. If analyses give per- 
 sistently inaccurate results, a blank combustion is carried on 
 (without substance) to ascertain the defect in the apparatus. 
 
 The Combustion of Substances containing Nitrogen or Sulphur, 
 or both at the same time, is in principle exactly the same as 
 described above, with the only modification that, in order to 
 absorb the nitric oxide, the sulphurous acid, and sulphuric acid, a 
 mixture of minium and lead peroxide is placed in the combustion 
 tube and heated to 320-350 with the flame-tube. 
 
 The quality of lead peroxide. Lead peroxide especially pre- 
 prepared for the Dennstedt analysis is placed on the market by 
 the firms of Merck and Kahlbaum under the label' of "Lead 
 Peroxide according to Dennstedt." But Dennstedt's investiga- 
 tions show that even these pure preparations almost always contain 
 small quantities of organic substances, such as fibres, dust particles, 
 etc., which must be destroyed before the substance is used. This 
 
ORGANIC ANALYTICAL METHODS 125 
 
 is done by drying a large quantity on a watch crystal in an oven, 
 at a temperature of 120-140, and heating this for at least half an 
 hour, or longer, in a hard glass tube in a stream of oxygen at 
 320-350. For the preparation of minium the required amount 
 of pure lead peroxide is heated in a stream of air at 400-450, 
 or in an open porcelain dish, until the dark-brown colour is 
 changed to a dull red ; it is then allowed to cool in a desiccator. 
 Equal quantities of lead peroxide and minium are intimately 
 mixed and used for the analysis. The quantity used for each 
 analysis is 7-8 grammes (not over 10 grammes) of the mixture, 
 weighed out to within -i- gramme, by the use of ordinary weights. 
 The substance is introduced into the tube in three small boats, 
 the boat in the rear containing the main portion. The boats 
 should be in the tube during the heating of the latter in a stream 
 of oxygen. 
 
 When a substance contains sulphur, the boat in the rear is 
 pushed to within 6-7 cm. of the contact star, but when sulphur is 
 not present, the boat is kept at a distance of 8-10 cm. from the 
 contact star. Under these conditions the heating in a stream of 
 oxygen (320-350) is done very cautiously in the course of at 
 least a half hour, or better still, a whole hour, or more. The 
 course of the combustion is otherwise the same as that described 
 above. A rapid current of oxygen is avoided as much as possible, 
 otherwise complete absorption by lead peroxide will be prevented. 
 
 Should the platinum (star, roll, etc.) come in contact with lead 
 peroxide or minium at any time, the particles of the latter are 
 removed first mechanically, and then by the use of hot dilute 
 hydrochloric acid. 
 
 If a substance explodes on heating, it is mixed in the boat with 
 quartz-powder or quartz-sand (previously treated with hot hydro- 
 chloric acid and heated to glowing), or with lead chromate which 
 has been heated to redness. 
 
 Simultaneous Determination of Sulphur with Carbon and Hydro- 
 gen. In this case the lead peroxide-minium mixture should nat- 
 urally be free from sulphates. In order to test the substance 
 for sulphuric acid 20-25 grammes of the mixture is digested on a 
 
126 GENERAL PART 
 
 water-bath for one hour with a 20 % solution of sodium carbonate, 
 free from sulphuric acid. The mixture is crushed and stirred fre- 
 quently. It is then filtered, washed with 50 c.c. of water, and 
 acidified with hydrochloric acid. The hot solution is now treated 
 with barium chloride. The liquid should remain perfectly clear, 
 even after standing overnight. 
 
 At the end of the combustion, and after the removal of the 
 absorption apparatus, the boats are carefully drawn out by the use 
 of a strong copper wire with a little hook at one end. The sur- 
 face of the substance in the first two boats will be covered with a 
 white layer of lead sulphate. The contents of the boats are trans- 
 ferred into a beaker ; the empty boats are placed into a wide test- 
 tube and heated on a water-bath with a 5 % solution of pure 
 sodium carbonate ; the liquid is added to the main portion of lead 
 peroxide and the boats are once more washed with a dilute solu- 
 tion of sodium carbonate. Traces of sulphuric acid may also 
 adhere to the contact substance, the roll, the combustion tube 
 and the inner tube. These are, therefore, rinsed freely with water. 
 The mouth of the inner tube is also dipped in a few cubic centi- 
 metres of water, but the small wash bottle is not removed. If the 
 salt of a sulphonic acid was analysed the combustion boat is also 
 washed with water, or better still, it is treated, with the boats, 
 with a solution of sodium carbonate. In this case the wider por- 
 tion of the inner tube is also rinsed with water. All the washings 
 containing sulphuric acid are poured into the beaker, which holds 
 the contents of the boats. The mixture should give an alkaline 
 reaction. It is heated over an actively boiling water-bath for at 
 least one hour. It is frequently stirred, and the precipitate is 
 crushed with a glass rod which has been flattened out at one end. 
 
 The sulphuric acid is determined quantitatively as barium sul- 
 phate by one of the following two methods : The entire liquid is 
 separated from the precipitate by filtration. The latter is washed 
 with water. Should the filtrate show turbidity by this treatment, it 
 is once more poured through the same filter. The clear filtrate is 
 then acidified with dilute hydrochloric acid, and is finally precipi- 
 tated at the boiling point with barium chloride by the usual method. 
 
ORGANIC ANALYTICAL METHODS I2/ 
 
 The second method is that proposed by Dennstedt. The con- 
 tents of the beaker (solution and precipitate) are transferred into 
 a measuring cylinder. (The beaker must be rinsed.) The volume 
 is now increased to a convenient round number by the addition 
 of water. Suppose the volume is 100 c.c. Since the specific 
 gravity of the precipitate is about 7 (if 7 grammes of lead peroxide 
 were used), then in 100 c.c. of the mixture we have i c.c. of the 
 precipitate and 99 c.c. of the liquid. To simplify the calculation 
 another cubic centimetre of water is added so as to make the 
 liquid volume just 100 c.c. An aliquot part is then taken, i.e. 
 95 c.c., and filtered through a dry filter as described above. 
 The washings from the precipitate are also saved. After acidify- 
 ing with hydrochloric acid, the sulphuric acid is precipitated as 
 barium sulphate. From the quantity of barium sulphate in 95 c.c. 
 of the liquid the amount in 100 c.c. is calculated; in other words, 
 from the quantity in the partial volume that in the total volume 
 is calculated. 
 
 Determination of Sulphur alone. It is evident that the method 
 described above may also be used for the determination of sul- 
 phur alone, by leaving out the absorption apparatus. It is, how- 
 ever, simpler and more convenient to use anhydrous sodium car- 
 bonate as an absorption medium, in place of lead peroxide. The 
 boats are filled with pure, calcined sodium carbonate (free from 
 sulphuric acid). The substance is gently pressed down with a 
 spatula. The combustion tube containing the boats is heated in 
 a stream of oxygen, the sodium carbonate being heated to about 
 400 with the flame-tube. The absorption apparatus is replaced 
 by a straight calcium chloride tube which is connected with the 
 palladium bottle. At the end of the combustion the cooled boats 
 are drawn out of the tube by means of a bent wire, and their con- 
 tents are transferred into a beaker. The boats are placed in a 
 wide test-tube and treated with hot water. The liquid is added 
 to the dry sodium carbonate. The combustion tube, the platinum 
 star, the inner tube, and the combustion boat are rinsed with water. 
 In short, the process described above is exactly followed. In 
 order to change traces of sulphites in the alkaline solution into 
 
I2 8 GENERAL PART 
 
 sulphates, it is heated and then treated with a few cubic centi- 
 metres of a saturated solution of bromine water. The beaker is 
 now covered with a watch crystal, and the solution is carefully 
 acidified (evolution of carbon dioxide) with moderately strong 
 hydrochloric acid. The solution is heated until the yellow colour, 
 due to excess of bromine, disappears. It is then treated hot with 
 barium chloride. 
 
 This method is so easy and convenient after a few trials, that it 
 seems to be destined to finally replace, the Carius method. The 
 analysis, including the weighing of the barium sulphate, may be 
 usually completed without difficulty in half a day. The method 
 has the further advantage over Carius' method that whereas in the 
 latter oxidation is sometimes incomplete with substances like 
 sulphonic acids or sulphones, the difficulty is not experienced in 
 this method. If a sufficient quantity of the substance is on hand, 
 it is much more advantageous to carry on a separate determina- 
 tion for sulphur by the sodium carbonate method, and ignore the 
 results from lead peroxide in the simultaneous determination of 
 sulphur, carbon and hydrogen. 
 
 If the substance contains a small percentage of sulphur, the 
 addition of barium chloride may not precipitate barium sulphate, 
 even after long heating, due to the solubility of the latter in excess 
 of barium chloride. But the precipitate will form when the solu- 
 tion is allowed to stand overnight. If a larger quantity of sulphur 
 is present, and a precipitate forms as soon as barium chloride is 
 added, the precipitate is filtered in the usual way, after the solu- 
 tion has become clear. The filtrate is then allowed to stand for a 
 day so as to recover any precipitate that may form. The same 
 procedure is also followed in the lead peroxide method. 
 
 Analysis of Substances containing a Halogen. If an organic 
 substance contains a halogen in addition to carbon, hydrogen and 
 oxygen (but no nitrogen or sulphur), a simultaneous determina- 
 tion of carbon, hydrogen and halogen may be carried out by the 
 use of " molecular silver " (Kahlbaum). A long porcelain boat is 
 filled with a few grammes of molecular silver. During the heating 
 of the combustion tube this is also heated by the flame-tube, a 
 
ORGANIC ANALYTICAL METHODS I2Q 
 
 somewhat higher temperature being used than that prescribed for 
 lead peroxide. 
 
 The warm boat is then removed and transferred into a weighing 
 tube (preferably a tube with two short legs near the open end), 
 and is weighed after cooling. During the combustion the boat is 
 kept at a distance of about 6 cm. from the contact star, and is 
 heated to 300-350 with the flame-tube. At the end of the 
 analysis the weight of the silver boat gives directly the amount of 
 halogen in the substance. 
 
 Halogen compounds, and especially compounds very rich in 
 halogen, burn much more slowly than halogen- free substances. 
 On this account they easily distil over the contact star without 
 decomposition, and the typical glow of the platinum, as well as 
 . the blackening of the tube, are not noticed. When this is the 
 case the combustion is carried out very carefully and slowly, and 
 the oxygen is not allowed to stream too rapidly. 
 
 The method described above cannot be used directly if the 
 halogen compound contains nitrogen or sulphur, due to the forma- 
 tion of silver nitrite and silver nitrate or silver sulphate. For the 
 determination of halogen in this case, as well as the determination 
 of sulphur and halogen (by the use of lead peroxide) see Prof. Dr. 
 M. Dennstedt's "Anleitung zur vereinfachten Elementaranalyse " 
 (Hamburg, Otto Meissners Verlag, 2. Aufl., 1906). 
 
 Calculation of the Atomic Formula. In order to calculate the 
 simplest formula of a substance from the figures giving its per- 
 centage composition, the method is as follows : If a subtance 
 contains, e.g. : 
 
 Carbon = 48.98 % 
 Hydrogen = 2.72 % 
 Chlorine = 48.30 % 
 
 the percentage figures are divided by the corresponding atomic 
 weights. There is thus obtained : 
 
 
 48.98 -r- 1 2 =4.o8C 
 2.72 -5- i = 2.72 H 
 8.0-5-- = J - 6 Cl 
 
130 GENERAL PART 
 
 These figures are divided by the smallest in this case 1.36 : 
 
 4.08-^- 1.36 = 3 C 
 2.72 -s- 1.36 = 2 H 
 1.36^- 1.36 = i Cl 
 
 The simplest atomic formula, therefore, is C 3 H 2 C1. If the num- 
 bers obtained in the last division are not integers, they are multi- 
 plied by the smallest integer which will convert the fractions into 
 whole numbers. If, e.g., the following numbers have been found, 
 1.25, 1.75, and 0.5, they are multiplied by 4, the results being 
 5, 7, and 2. 
 
 The simplest formula thus obtained from the analytical data 
 does not always correspond with the true molecular weight. This 
 must be determined by one of the usual methods, unless it may 
 be inferred from the nature of the reaction by which the sub- 
 tance analysed was produced. 
 
 The exact atomic weights of the elements used in analytical 
 calculations are : 
 
 H = 1.008 
 
 C = I2.OO 
 
 N = 14.01 
 S = 32.07 
 Cl= 35-46 
 Br 79.92 
 I = 126.92 
 O = 16.00 
 
 These figures are taken from Kuster's " Logarithmischen Rechen^ 
 tafeln fur Chemiker." 
 
SPECIAL PART 
 
 I. ALIPHATIC SERIES 
 
 i. REACTION: THE REPLACEMENT OF AN ALCOHOLIC HYDROXYI 
 GROUP BY A HALOGEN 
 
 I . EXAMPLE : Ethyl Bromide from Ethyl Alcohol l 
 
 To 200 grammes (noc.c.) of concentrated sulphuric acid con- 
 tained in a round litre-flask, add quickly with constant shaking, 
 without cooling, 90 grammes of alcohol (about 95%). After 
 cooling the mixture to the room temperature, add carefully 75 
 grammes of ice-water, the cooling being continued, and then 100 
 
 grammes of finely pul- 
 verised potassium bro- 
 mide (see Hydrobromic 
 Acid, page 379). The 
 mixture is subjected to 
 distillation, which must 
 not be too slow, the flask 
 being heated on a small 
 sand-bath with a large 
 flame (Fig. 63). Since 
 the boiling-point of ethyl 
 bromide is low (38), a 
 long condenser, with a 
 quite rapid current of water passing through it, is used. An up- 
 right coil condenser (see Fig. 27, page 34) may be employed 
 advantageously. At the beginning of the operation, the receiver 
 is filled with a sufficient amount of water containing a few pieces 
 of ice to allow the end of the adapter to dip under the surface. 
 The reaction is ended as soon as the oily drops which sink to the 
 bottom of the receiver cease passing over. If, during the distilla- 
 tion, the contents of the receiver should be drawn up into the con- 
 ij. 1857,441. 131 
 
 FIG. 63. 
 
132 SPECIAL PART 
 
 denser, this difficulty may be overcome by placing the receiver 
 in such a position that the end of the adapter reaches just below 
 the surface of the water. The same result may be attained by turn- 
 ing the adapter to one side, so that air may enter it. The lower 
 layer of the distillate consisting of ethyl bromide is washed in the 
 receiver several times with water, and finally with a dilute solution 
 of sodium carbonate, during which the flask must not be closed. 
 The lower layer is then run out of a separating funnel, dried with 
 calcium chloride, and finally distilled, the same precautions as to 
 cooling, mentioned above, being observed. In this case a very 
 small flame of a microburner is used, or the burner tube of a 
 Bunsen burner is removed and a luminous flame, a few millimetres 
 high, is lighted at the nozzle. The ethyl bromide distils between 
 35-40, the main portion at 38-39. In consequence of the low 
 boiling-point of ethyl bromide, it is never allowed to stand in open 
 vessels for any length of time ; during the drying over calcium 
 chloride, the flask must be closed by a tight-fitting cork. The 
 finished preparation, particularly at summer temperature, must 
 not be preserved in thin-walled vessels of any kind, but always in 
 thick-walled, so-called specimen bottles. Yield, 70-80 grammes. 
 At the conclusion of this experiment, as well as in all the follow- 
 ing preparations, the amount of actual yield is compared with the 
 percentage required by theory. The following points are there- 
 fore noted : According to the chemical equation, one molecular 
 weight of potassium bromide (119) requires one molecular weight 
 of alcohol (46). In actual work, especially in a large number of 
 organic reactions which do not take place quantitatively, and 
 where economy is to be considered, one of the reacting substances 
 is taken in excess, in accordance with the Law of Mass Action. 
 Since the price of one kg. of potassium bromide is about 4 
 marks, and that of one kg. of alcohol (including duty) is about 
 i. 80 marks, duty-free alcohol 0.90 mark, the price of one 
 molecule of potassium bromide (119 x 4) compared with that of 
 one molecule of alcohol (including duty) (46 X 1.80), or duty- 
 free alcohol (46 x 0.90), is in the ratio of 6 : i, or 12 : i. From 
 the standpoint of economy it is more rational to use an excess 
 
ALIPHATIC SERIES 133 
 
 of the cheaper alcohol and convert the more expensive potassium 
 bromide, as completely as possible, into ethyl bromide. The 
 quantities used in the above experiment are in accordance with 
 these considerations. 100 grammes of potassium bromide require 
 theoretically 39 grammes of alcohol, while the quantity of alcohol 
 used is 86 grammes (90 grammes of 95 %), i.e. more than twice 
 the theoretical amount. In order to calculate the yield theoreti- 
 cally possible, the quantity of potassium bromide must be taken as 
 the basis, since the conversion of the total amount of alcohol into 
 ethyl bromide is impossible. When the alcohol used for the prepa- 
 ration of its corresponding bromide is more expensive than potas- 
 sium bromide, then the substance to be taken in excess is naturally 
 potassium bromide. (Compare the discussion of the Law of Mass 
 Action under Acetic Ester.) 
 
 The ethyl bromide thus obtained is contaminated with a small 
 amount of ether. If it be desired to remove this, the well-cooled 
 crude ethyl bromide, contained in a flask surrounded by a freezing 
 nixture of ice and salt, is treated, before drying with calcium 
 chloride, with concentrated sulphuric acid, added drop by drop 
 and with frequent shaking, until it separates out in a layer under 
 the ethyl bromide. The acid containing the dissolved ether is 
 then run off (in a separating funnel) from the ethyl bromide, which 
 is shaken up several times with ice water, dried with calcium chlo- 
 ride, and redistilled as before. For the preparation of ethyl ben- 
 zene (which see) the ethyl bromide need not be thus purified. 
 
 2. EXAMPLE : Ethyl Iodide from Ethyl Alcohol l 
 
 To a mixture of 5 grammes of red phosphorus and 40 grammes 
 of absolute alcohol, contained in a small flask of about 200 c.c. 
 capacity, 50 grammes of finely pulverised iodine are added gradu- 
 ally in the course of a quarter hour ; the flask is frequently shaken 
 during the addition, and cooled from time to time by immersion 
 in cold water. An air condenser a straight vertical glass tube 
 is the common form is connected with the flask, and the reac- 
 
 1 A. 126, 250. 
 
134 SPECIAL PART 
 
 tion mixture is allowed to stand at least four hours. (In czce the 
 experiment was begun late in the afternoon, it may stand until 
 the next day.) In order to complete the reaction, the mixture is 
 heated for two hours on the water-bath, a reflux condenser being 
 attached to the flask. The ethyl iodide is then distilled off conven- 
 iently by immersing the flask in a rapidly boiling water-bath. The 
 distillation is facilitated by the use of a frayed thread (see page 34). 
 Should the last portions go over with difficulty, the water-bath is 
 removed, the flask is dried and heated for a short time with a 
 luminous flame kept in constant motion. The distillate, coloured 
 brown by iodine, is washed several times with water to free it from 
 alcohol, and then with water to which a few drops of caustic soda 
 have been added, to remove the iodine ; the colourless oil is now 
 separated in a dropping funnel, dried with a small quantity of 
 granular calcium chloride, and distilled. If the calcium chloride 
 should float on the oil, it is poured through a funnel containing 
 some asbestos or glass-wool into the fractionating flask. The boil- 
 ing-point of ethyl iodide is 72. Yield, about 50 grammes. 
 
 The following questions are to be answered at this point : Which 
 one of the reacting substances was taken in excess ? Why ? What 
 percentage of the theoretical yield of ethyl iodide is obtained ? 
 
 Both of these reactions are special cases of a reaction of general 
 application, viz. : the replacement of an alcoholic hydroxyl group with 
 a halogen atom. This may be effected in two ways : (i) by causing 
 the alcohol to react with the halogen hydracid as in the preparation 
 of ethyl bromide, e.g. : 
 
 C 2 H- . |QH + Hj Br = H 2 O + C 2 H 5 . Br 
 (HC1, HI) 
 
 (2) by treating the alcohol with a phosphorus halide, as in the prepara- 
 tion of ethyl iodide, e.g.: 
 
 3 C 2 H 5 . OH + PI 3 = 3 C 2 H 5 . 1 + P(OH) 3 
 (PC1 3 , PBr 3 ) 
 
 i . The first reaction takes place most easily with hydriodic acid ; in 
 many cases saturation with the gaseous acid being sufficient to induce 
 the reaction. Hydrobromic acid reacts with greater difficulty ; it is 
 
ALIPHATIC SERIES 135 
 
 frequently necessary to heat the alcohol saturated with the acid in a 
 sealed tube. The above method for the preparation of ethyl bromide 
 is a simple case of the general reaction. In place of using hydrobromic 
 acid directly, it can in some cases, like the one given, be generated by 
 warming a mixture of potassium bromide and sulphuric acid : 
 
 KBr + H 2 SO 4 = HBr + KHSO 4 . 
 
 Hydrochloric acid reacts with most difficulty, and it is, e.g., in the prepa- 
 ration of methyl chloride and ethyl chloride, necessary to employ a 
 dehydrating agent zinc chloride is the best or with the alcohols of 
 high molecular weights, to heat in a closed vessel under pressure. 
 
 This reaction is not only applicable to the aliphatic, but also to the 
 aromatic alcohols ; e.g. : 
 
 C 6 H 5 . CH 2 . OH + HC1 = C G H 5 . CH 2 C1 + H 2 O 
 
 Benzyl alcohol Benzyl chloride 
 
 But phenol hydroxyl groups cannot be replaced by the action of a 
 halogen hydracid. 
 
 With di-acid and poly-acid alcohols the reaction takes place, at least 
 with hydrochloric and hydrobromic acids ; but, in this case, the number 
 of hydroxyl groups which are replaced by the halogen depends upon 
 the conditions of the experiment, the quantity of the halogen acid, the 
 temperature, etc., e.g. : 
 
 CH 2 .OH CH 2 .Br 
 
 + HBr = \ + H 2 
 
 CH 2 .OH CH 2 .OH 
 
 Ethylene glycol Ethylene bromhydrine 
 
 CH 2 .OH CH 2 .OH 
 
 CH.OH +2HC1 =CHC1 +2H 2 O 
 CH 2 .OH CH 2 C1 
 
 Glycerol Dichlorhydrine 
 
 CH 2 .OH CH 2 .Br 
 
 CH 2 -f2HBr =CH 2 + 2 H 2 O 
 
 CH 2 .OH CH 2 .Br 
 
 Trimethylene glycol Trimethylene bromide 
 
 Hydriodic acid, in consequence of its reducing properties, acts upon the 
 poly-acid alcohols in a different manner. A single hydroxyl group, and 
 that particular one in combination with a carbon atom which is in turn in 
 combination with other carbon atoms, is replaced by iodine, while at times 
 other hydroxyl groups are replaced by the hydrogen of the acid, e.g. : 
 
C 
 
 SPECIAL PART 
 
 CH 2 .OH CH 3 
 
 CH . OH + 5 HI = CHI + 3 H 2 O -f 4 1 
 ;H 2 .OH CH 3 
 
 Glycerol Isopropyl iodide 
 
 CH 2 (OH).CH(OH).CH(OH).CH 2 (OH) + 7 HI 
 
 Erythrite 
 
 = CH 3 .CH 2 .CHI.CH 3 + 4H 2 O + 6I 
 
 -Sec. Butyl iodide 
 
 CH 2 (OH).CH(OH).CH(OH).CH(OH).CH(OH).CH 2 (OH)+ uHI 
 
 Ma unite 
 
 = CH 3 .CHI.CH 2 .CH 2 .CH 2 .CH 3 + 6H 2 + 10! 
 
 -Sec. Hexyl iodide 
 
 With derivatives of alcohols, e.g. alcohol-acids (hydroxy acids) the 
 
 first reaction takes place : 
 
 CHo. OH . CH, . COOH + HI = CHJ . CH 2 . COOH + H 2 O 
 
 j3-Hydroxyproprionic acid -Iodoproprionic acid 
 
 CH 2 (OH). CH(OH). COOH + 2 HC1 = CH 2 C1 . CHC1 . COOH + 2 H 2 O 
 
 Glyceric acid a-/3-Dichlorproprionic acid 
 
 2. The second reaction takes place much more energetically, espe- 
 cially when a phosphorus halide which has been previously made is 
 used. This is not always necessary, at least in introducing bromine 
 and iodine; in many cases it is better to generate the phosphorus halides 
 in the course of the reaction, by adding to the mixture of alcohol and 
 red phosphorus either bromine from a dropping funnel, or as above, 
 finely pulverised iodine. This reaction, as well as the first, is applicable 
 to poly-acid alcohols and substituted alcohols, e.g. : 
 
 (a) CH 2 (OH) . CH S (OH) + 2 PCI. = CH 2 C1 . CH 2 C1 + 2 FOCI, + 2 HC1 
 
 Ethylene glycol Ethylene chloride 
 
 (b) CH 2 (OH) . CHC1 . CH 2 C1 + PC1 5 
 
 Dichlorhydrine 
 
 = CH 2 C1 . CHC1 . CH,C1 + POC1 3 + HC1 
 
 Trichlorhydrine 
 
 This example illustrates the more energetic action of the phosphorus 
 halide as compared with the corresponding hydrogen halide ; it is im- 
 possible to replace the third hydroxyl group of glycerol with chlorine 
 by the use of hydrochloric acid. 
 
 (0 CH, . CH(OH). COOH + PC1 5 = CHo . CHC1 . COOH + POC1., + HC1 
 
 (1) (I) 
 
 a-Hydroxyproprionic acid a-Chlorproprionic acid 
 
 In cases of this kind a complication arises, due to the fact that the 
 phosphorus halide also acts upon the hydroxyl of the carboxyl group, 
 replacing it with the halogen, giving rise to an acid-chloride : 
 
ALIPHATIC SERIES 137 
 
 CH 3 . CHC1 . CO . OH + PC1 3 = CHo . CHC1 . CO . Cl + POC1, + HC1 
 
 The acid may be regenerated by treating the acid-chloride with water: 
 
 CH 3 . CHC1 . CO . Cl + H 3 O = CH 3 . CHC1 . CO . OH + HC1 
 
 The action of phosphorus iodide on poly-acid alcohols is similar to the 
 action of hydriodic acid referred to under Reaction i . 
 
 The more energetic action of the phosphorus halides may also be 
 perceived in the fact that phenol hydroxyl groups can be replaced by a 
 halogen, by the use of the phosphorus compounds, which, as mentioned 
 above, is impossible with the halogen hydracids, e.g. : 
 
 C G H 5 . OH + PC1 5 = C 6 H 5 . Cl -f POC1 3 + HC1 
 
 ' Phenol (Br) (Br) 
 
 3 9 /NO 2 
 
 -f PC1 5 = C 6 H 4 < + POC1 3 + HC! 
 OH \C1 
 
 /OH /Cl 
 
 ,H <f -f PCL = C fi H 9 <f 
 
 C 6 H 2 < + PC1 5 = C 6 H 2 <T + POC1 3 + HC1 
 
 X N O 2 ) 3 ' X N 2)s 
 
 Picric acid Picryl chloride 
 
 But the quantities obtained are much less satisfactory, the reason being 
 that the phosphorus oxychloride attacks the unacted-upon phenol, form- 
 ing phosphoric acid esters, e.g.: 
 
 POC1 3 + 3 C 6 H 5 .OH = PO. (OQH 5 ), + 3 HC1 
 
 In this way a large portion of the phenol is withdrawn from the main 
 reaction. 
 
 The monohalogen alkyls C n H (2n +i)Cl(Br, I) are in most cases colour- 
 less liquids, the exceptions being methyl and ethyl chlorides and methyl 
 bromide, which are gaseous at the ordinary temperature, and the mem- 
 bers of the series having high molecular weights, like cetyl iodide, 
 C 1B H 33 I, which are semi-solid, salve-like substances. The iodides are 
 only colourless when freshly prepared ; on long standing, especially 
 under the influence of light, a slight decomposition, resulting in the 
 separation of iodine, takes place, imparting to them a faint pink colour 
 at first, which becomes brownish red after a long time. This decom- 
 position can be prevented if some finely divided, so-called molecular 
 silver is added to the liquid. A coloured iodide can be made colourless 
 by shaking it with some caustic soda solution. The halogen alkyls 
 mix readily with organic solvents, as alcohol, ether, carbon disulphide, 
 
138 
 
 SPECIAL PART 
 
 benzene, etc., but not with water. The chlorides are lighter, the bro- 
 mides and iodides heavier than water; the latter have the highest 
 specific gravities. This property decreases in all three classes with the 
 decrease in halogen percentage from the lower up to the higher mem- 
 bers of the series ; i.e. the higher molecular weight compounds have a 
 smaller specific gravity than the lower members. The chlorides have 
 the lowest boiling-points ; the corresponding bromides boil about 25, 
 and the iodides 50 higher. 
 
 The ease with which the monohalogen alkyls react with other com- 
 pounds gives them great importance ; they are used primarily as a means 
 of introducing alkyl groups into other molecules, i.e. by replacing an 
 hydrogen atom with an alkyl group. If it is desired, e.g., to replace in 
 an alcohol, mercaptan, phenol, or acid the hydrogen of the (OH)-, 
 (SH)-, or (COOH) -group by an alkyl radical, i.e. to prepare an ether, or 
 ester of these substances, the corresponding sodium compound, or in 
 case of acids, better the silver salt, is treated with the halogen alkyl, e.g. ; 
 
 C 2 H 5 . ONa + IC 2 H 5 = C 2 H 5 . . C 2 H 5 + Nal 
 
 Sodium alcoholate Ethyl ether 
 
 C 2 H 5 . SNa + IC 2 H 5 = C 2 H 5 . S . C 2 H 5 + Nal 
 
 Sodium ethyl mercaptide Ethyl sulphide 
 
 QH 5 . ONa + ICHo = C 6 H 5 . . CH 3 + Nal 
 
 Sodium phenolate Phenyl methyl ether 
 
 = Anisol 
 
 CH 3 . COOAg + IC 2 H 3 = CH 3 . COO . C 2 H 5 + Agl 
 
 Silver acetate Ethyl acetate 
 
 The alkyl groups may be introduced into the ammonia molecule and 
 into organic amine molecules by means of the halogen alkyls ; e.g. : 
 
 NH, + ICHo = NH 2 .CH 3 + HI 
 
 Methyl amine 
 
 Di- and tri-methyl amine are also formed at the same time. 
 C 6 H 5 . NH 2 + 2 CH 3 C1 - C 6 H S . N(CH 3 ) 2 + 2 HC1. 
 
 Aniline Dimethyl aniline 
 
 Hydrogen atoms in combination with carbon may also be replaced by 
 alkyl radicals, by means of the halogen alkyls. Since under these con- 
 ditions another radical is introduced into the molecule, it presents a 
 method of preparing the higher members of a series from the lower. 
 simpler ones. Various examples of this will be taken up later in labor 
 
ALIPHATIC SERIES 139 
 
 atory practice. Here it will be sufficient to refer to several equations 
 showing this kind of reaction. 
 
 CH 3 . CO . CHNa . COOC 2 H 5 + ICH 3 = CH 3 . CO . CH - COOC 2 H 5 + Nal 
 
 Sodium acetacetic ester 
 
 CH 3 
 
 Methylacetacetic ester 
 
 COOC 2 H 6 COOC 2 H 5 
 
 :HNa + IC 2 H 5 = CH - C 2 H 5 + Nal 
 "OOC 2 H 5 COOC 2 H 5 
 
 Sodium malonic ester Ethyl malonic ester 
 
 C 6 H 6 -f C1C 2 H 5 = C 6 H 5 . C 2 H 5 + HC1 
 
 Benzene Ethyl benzene 
 
 (In presence of A1C1 3 ) 
 
 Fittig's Synthesis, to be taken up later, is a case of this kind, by 
 which a halogen atom is replaced by an alkyl group ; e.g. : 
 
 C 6 H 5 Br + BrC 2 H 5 + 2 Na = C 6 H 5 . C 2 H 5 + 2 NaBr 
 
 Brom benzene Ethyl benzene 
 
 Further, the halogen alkyls serve for the preparation of the unsatu- 
 rated hydrocarbons of the ethylene series. 
 
 CH, . CHI . CH, = CH, . CH = CH 9 + HI 
 
 Isopropyfr iodide Propylene 
 
 In many cases the alcohols may also be prepared from the halogen 
 alkyls ; e.g. : 
 
 CH 8 .CHI.CH 3 + HOH = CH 3 .CH(OH).CH 3 + HI 
 
 Isopropyl alcohol 
 
 This reaction is obviously only of importance when the halogen alkyl 
 is not obtained from the corresponding alcohol, as is the case in the 
 example given. As above mentioned, the isopropyl iodide is most 
 simply obtained from glycerol and hydriodic acid, so that by this 
 reaction the glycerol can be converted into the isopropyl alcohol 
 (compare Reaction 13). Halogen alkyls also unite directly with other 
 compounds, like sulphides and tertiary animes : 
 
 9r 
 M 
 
 Ethyl sulphide Triethylsulphine iodide 
 
140 SPECIAL PART 
 
 N(CH 3 ) 3 + CHgCl = N(CH 3 ) 4 C1 
 
 Trimethyl amine Tetramethyl ammonium chloride 
 
 C 5 H R N + ICH 8 - C 5 H,N ICH 3 
 
 Pyridine Methylpyridine iodide 
 
 With these examples the list of the many-sided reactions of the hal- 
 ogen alkyls is not exhausted ; they are also used for the preparation 
 of the metallic alkyls, e.g. zinc alkyls ; for the preparation of the 
 phosphines, and for many other compounds. Through the Grignard 
 reaction, with its many-sided applications, the halogen alkyls have re- 
 cently become extremely important. Finally, attention is called to the 
 characteristic difference between the organic and inorganic halides. 
 While, e.g., potassium chloride, bromide, or iodide in solution act 
 instantly with a silver nitrate solution to form a quantitative precipitate 
 of silver chloride, bromide, or iodide respectively, silver nitrate in a 
 water solution does not act on most organic halides, so that this reagent 
 does not serve in the usual way to show the presence of a halogen. 
 
 EXPERIMENT : Treat a solution of silver nitrate with a few drops 
 of ethyl bromide. Not the least trace of silver bromide is formed. 
 
 It has been customary to explain this by saying that the affinity 
 between the halogen atom and carbon is greater than that between the 
 halogen and the metallic atom. According to our later views the differ- 
 ence between the two classes of compounds is explained thus : The 
 metallic halides belong to the class of so-called electrolytes, i.e. sub- 
 stances which are dissociated in water solution, e.g. the molecule KC1 
 
 is dissociated into its ions, K and Cl. The organic halides are non- 
 
 f 
 
 electrolytes, i.e. the solutions of these contain the undissociated mole- 
 cules. According to this conception, the potassium chloride reacts 
 with silver nitrate, because no further separation of the potassium from 
 the chlorine (other than that effected by solution) is necessary, while in 
 case of the brom alkyls, the brom-carbon union must first be severed. 
 Only halogen ions react, at once, quantitatively with the silver ions of 
 silver nitrate. 
 
 Ethyl iodide is an exception ; when shaken with a solution of silver 
 nitrate, it gives an abundant precipitate of silver iodide. Other iodides, 
 especially tertiary iodides, do not react with a water solution of silver 
 nitrate, as readily as ethyl iodide. Methyl and ethyl iodides react 
 quantitatively when an alcoholic solution of silver nitrate is used. The 
 reaction is employed, according to Zeisel, for the determination of 
 methoxyl groups. Ethyl bromide reacts with alcoholic silver nitrate on 
 heating; ethyl chloride reacts more slowly. 
 
ALIPHATIC SERIES 
 
 141 
 
 2. REACTION: PREPARATION OF AN ACID-CHLORIDE FROM THE 
 
 ACID 
 
 EXAMPLE : Acetyl Chloride from Acetic Acid l 
 
 To 100 grammes of glacial acetic acid contained in a fraction- 
 ating flask connected with a condenser (coil condenser), 80 
 grammes of phosphorus trichloride are added through a dropping 
 funnel, the flask being cooled by water. The bulb is then im- 
 
 FIG. 64. 
 
 mersed in a porcelain dish filled with v/ater at a temperature of 
 40-50, and the heating continued until the active evolution of 
 hydrochloric acid gas slackens, and the liquid which was homo- 
 geneous before heating has separated into two layers. To sepa- 
 rate the acetyl chloride which forms the upper, lighter layer, from 
 the heavier layer of phosphorous acid, the mixture is heated on a 
 
 1 A. 87, 63. 
 
142 
 
 SPECIAL PART 
 
 rapidly boiling water-bath until nothing more passes over. Since 
 acetyl chloride is very easily decomposed by moisture, the distillate 
 must not be collected in an open receiver, but the condenser-tube 
 must be tightly connected with a tubulated flask (suction flask), 
 protected from the air by a calcium chloride tube, as represented 
 in Fig. 64. For complete purification, the distillate is distilled in 
 a similar apparatus, except that the dropping funnel is replaced by 
 a thermometer. The apparatus represented in Fig. 17, page 21, 
 may be used for the redistillation. The portion distilling from 
 50-56 is collected in a separate vessel. Boiling-point of pure 
 acetyl chloride, 51. Yield, 80-90 grammes. 
 
 In order to replace the hydroxyl of a carboxyl group (CO . OH) by 
 chlorine, a reaction, similar to the one employed above for the substi- 
 tution of an alcoholic hydroxyl group by a halogen, may be used. If, 
 e.g., a mixture of an acid and phosphoric anhydride is treated with 
 gaseous hydrochloric acid (heating if necessary), there is formed an 
 acid-chloride, the reaction being analogous to that by which ethyl 
 bromide was prepared. 
 
 X.CO.OH + HC1 = X.CO.C1 + H 2 
 
 This reaction is without practical importance, since the reactions in- 
 volved in the methods described under (2), page 136, take place much 
 more smoothly and easily, and, therefore, are exclusively used. In 
 practice, the acid-chlorides are almost always prepared by the action of 
 phosphorus tri- or penta-chloride on the acid directly, or in many cases, 
 on the sodium or potassium salt. Phosphorus oxychloride is employed 
 in rare cases. The selection of the chloride of phosphorus depends 
 upon(i) the ease with which the acid under examination reacts, and 
 (2) upon the boiling-point of the acid-chloride. If, as in the case of 
 acetic acid and its homologues, the trichloride of phosphorus reacts 
 easily with the formation of the acid-chloride, this is selected in prefer- 
 ence to the more energetic pentachloride. The reaction probably takes 
 place in accordance with the following equation : 
 
 3 CH ;5 . CO . OH + 2 PC1 3 = 3 CH 3 . CO . Cl + P 2 O 3 + 3 HC1 
 
 The quantity of acetic acid used is made the basis for the calculation of 
 the yield required by theory. 
 
 In cases in which the boiling-point of the acid-chloride desired does 
 
ALIPHATIC SERIES 143 
 
 not lie far from that of phosphorus oxychloride (iio),thus rendering 
 a fractional distillation for the separation of the products difficult, the 
 trichloride is always used. If an acid does not react too energetically, 
 as is the case with the higher members of the acetic acid series with 
 the pentachloride, this is used. With the aromatic acids, the latter is 
 used exclusively, since the trichloride and oxychloride react with great 
 difficulty : 
 
 C 7 H 15 . CO . OH + PC1 5 = C 7 H 15 . CO . Cl + POC1 3 + HC1 
 
 Caprylic acid 
 
 C 6 H 5 . CO . OH + PC1 5 = C 6 H 5 . CO . Cl + POC1 3 + HC1 
 
 Bcnzoic acid Benzoyl chloride 
 
 Attention is called to the fact that for one molecule of phosphorus 
 pentachloride, but one molecule of the acid-chloride is obtained. 
 
 The phosphorus oxychloride is used generally only when dealing 
 with the salts of carbonic acids, upon which it acts as indicated by the 
 equation : 
 
 2 CH 3 . CO . ONa + POC1 3 - 2 CH 3 . CO . Cl + NaPO 3 + NaCl 
 
 This reaction may be used with advantage in order to utilise more 
 of chlorine of the phosphorus pentachloride than is the case when the 
 latter acts upon the free acids. If the pentachloride is allowed to act 
 on a sodium salt, as above, there is formed, for an instant, phosphorus 
 oxychloride, and while this no longer acts upon the free acid, it can 
 convert two other molecules of the salt into the chloride : 
 
 3 CH 3 . CO . ONa + PC1 5 = 3 CH 3 . CO . Cl + NaPO 3 + 2 NaCl 
 
 In this way, with the use of one molecule of phosphorus pentachloride, 
 three molecules of the acid-chloride are obtained. 
 
 The lower members of the series of acid-chlorides are colourless 
 liquids ; the higher, colourless crystalline substances. They boil, gen- 
 erally, at ordinary pressure without decomposition, but the higher 
 members are more conveniently distilled in a vacuum. The boiling- 
 points of the acid-chlorides are lower than those of the acids; the 
 replacement of hydroxyl by chlorine usually causes a lowering of the 
 boiling-point. 
 
 CH 3 . CO . Cl Boiling-point 5 1 c 
 CH..CO.OH " 118 
 
 C 6 H 5 .CO.C1 Boiling-point 199 
 C 6 H,.CO.OH " 250 
 
 The acid-chlorides possess pungent odours. They fume in the air, since 
 they unite with the moisture and decompose, thus forming the corre- 
 
144 
 
 SPECIAL PART 
 
 spending acid and hydrochloric acid. They are heavier than water, 
 and do not mix with it, but are easily soluble in indifferent organic 
 solvents like ether, carbon disulphide, benzene. 
 
 To separate the chlorides from the by-products formed by the phos- 
 phorus chloride, one can proceed as in the case of acetyl chloride, by 
 distilling off the volatile chloride from the non-volatile phosphorus acid, 
 either on a water-bath or over a free flame. In order to separate a 
 chloride, in case it distils without decomposition, from the volatile phos- 
 phorus oxychloride formed when phosphorus pentachloride is used, a 
 fractional distillation is made. In other cases, the mixture is heated 
 in a vacuum apparatus on an actively boiling water-bath, upon which 
 the phosphorus oxychloride passes over. The non-volatile residue 
 can be used, in many cases, without further purification; it may be 
 obtained perfectly pure by distilling it in a vacuum. 
 
 Chemical Reactions. The acid-chlorides are decomposed by water 
 with the formation of the corresponding acid and hydrochloric acid. 
 
 CH 3 . CO . Cl + H 2 O = CH, . CO . OH + HC1 
 
 This decomposition takes place often with extreme ease ; the chlorine 
 atom is united to the acid radical much less firmly than it is in the case 
 of an alkyl radical. While it is generally necessary, in order to convert 
 a halogen alkyl into an alcohol, to boil it a long time with water, often 
 with the addition of sodium hydroxide, or potassium hydroxide, a car- 
 bonate or acetate, the analogous transformation of an acid-chloride 
 takes place with far greater ease. With the lower members, e.g. acetyl 
 chloride, the reaction begins almost instantly at the ordinary tempera- 
 ture,, and continues with violent energy ; but it is necessary to heat the 
 higher members to induce the transformation, e.g. benzoyl chloride, 
 which will be prepared later. 
 
 EXPERIMENT : To 5 c.c. of water in a test-tube is gradually 
 added -J- c.c. of acetyl chloride. If the water is very cold, the 
 oily drops, sinking to the bottom, do not mix with it, and may be 
 observed for a short time. On shaking the tube, an energetic 
 reaction sets in with evolution of heat, and the chloride passes 
 into solution, which happens immediately if the water is not 
 cold. 
 
 The acid-chlorides react with alcohols and phenols to form esters ; 
 
ALIPHATIC SERIES 145 
 
 CH 3 . CO . Cl + C 2 H 5 . OH = CH 3 . CO . OC 2 H 5 + HC1 
 
 Ethyl acetate 
 
 CH 3 . CO . Cl + C 6 H 5 . OH = CH 3 . CO . OC 6 H 5 + HC1 
 
 Phenol Phenyl acetate 
 
 EXPERIMENT : To i c.c. of alcohol in a test-tube, cooled with 
 water, add an equal volume of acetyl chloride, drop by drop ; 
 this mixture is then treated with an equal volume of water, the 
 tube being cooled as before ; the liquid is then carefully made 
 weakly alkaline with sodium hydroxide. If the pleasant-smelling 
 ethyl acetate does not separate out on the water solution in a 
 mobile layer, finely pulverised salt is added until no more will 
 dissolve. This will cause the ethyl acetate to separate out. 
 
 The acid-chlorides are also used to determine whether a substance 
 under examination contains an alcoholic or a phenol hydroxyl group or 
 not. If the compound reacts readily with an acid-chloride, it contains 
 either alcoholic or phenol hydroxyl, since compounds containing oxygen 
 in some other form of combination, e.g. as in ethers, do not react with 
 acid-chlorides. 
 
 The addition of anhydrous sodium acetate often materially assists the 
 reaction. 
 
 Finally, the action of the acid-chlorides upon alcohols and phenols 
 is made use of to separate the latter from solution, or in order to detect 
 them. However, benzoyl chloride is most generally used for this pur- 
 pose, concerning the importance of which more will be said later. 
 
 Acid-chlorides act upon the salts of carbonic acids, forming anhy- 
 drides : 
 
 = CH 3 .CO.O.CO.CH 3 
 
 Acetic anhydride 
 
 The next preparation will deal with this reaction. The acid-chlorides 
 react with ammonia as well as with primary and secondary organic 
 bases with great ease : 
 
 
 CH 3 . CO . Cl 4- NH 3 = CH 3 . CO . NH 2 + HC1, 
 
 Acetamide 
 
 CH 3 . CO . Cl 4- C 6 H 5 . NH 2 = C 6 H, . NH . CO . CH 3 + HC1 
 
 Aniline Acetanilide 
 
 EXPERIMENT : To i c.c. of aniline, acetyl chloride is added in 
 drops ; an energetic reaction takes place with a hissing sound, 
 L 
 
I 4 6 SPECIAL PART 
 
 which ceases when about the same volume of the chloride is added. 
 The mixture is cooled with water, and five times its volume of 
 water is added, upon which an abundant precipitate of acetanilide 
 separates out, the quantity of which is increased by rubbing the 
 walls of the test-tube with a glass rod. The precipitate is filtered 
 off, and recrystallised from hot water. Melting-point, 115. 
 
 This reaction is also used to characterise organic bases by converting 
 them into their best crystallised acid derivatives, and in order to detect 
 small quantities, especially of liquid bases, by a melting-point deter- 
 mination. Since the tertiary bases do not react with acid-chlorides, 
 because they no longer contain any ammonia hydrogen, this reaction 
 may be employed to decide whether a given base is, on the one hand, 
 primary or secondary, or, on the other, tertiary. 
 
 The fact that hydrogen in combination with carbon can be replaced 
 by an acid radical by the use of an acid-chloride is of special importance. 
 In this connection, the Friedel-Crafts ketone synthesis is particularly 
 mentioned. This will be taken up later, in practice. The reaction is 
 indicated by the following equation : 
 
 C 6 H 6 + CH 3 . CO . Cl - C 6 H 5 . CO . CH 3 + HCi 
 
 Benzene Acetophenone 
 
 (in presence of A1C1 3 ) 
 
 The acid-chlorides are also of service for the synthesis of tertiary 
 alcohols (Butlerow's Synthesis), as well as for that of ketones. The 
 final reactions will only be indicated here; in regard to the details, 
 reference must be made to larger works. 
 
 yen. /CH S 
 
 NCH, 
 
 Zinc methyl 
 
 CH 3 . CO . C1 + Zn = CH 3 . C-CH + ZnO 
 
 \CH 3 
 
 
 
 \ ^ A1 3 
 
 X OH 
 
 Trimethyl carbinol 
 
 /CH 3 
 
 2 CH 3 . CO . Cl + Zn<" =2 CH 3 . CO . CH 3 + ZnCl 2 
 \CHo 
 
 Acetone 
 
ALIPHATIC SERIES 147 
 
 3. REACTION: PREPARATION OF AN ANHYDRIDE FROM THE ACID- 
 CHLORIDE AND THE SODIUM SALT OF THE ACID 
 
 EXAMPLE : Acetic Anhydride from Acetyl Chloride 
 and Sodium Acetate 1 
 
 For the preparation of acetic anhydride an apparatus similar 
 to that used in the preparation of acetyl chloride is employed, 
 except that the fractionating flask is replaced by a tubulated retort 
 (Fig. 65, page I48). 2 
 
 To 70 grammes of finely pulverised, anhydrous sodium acetate 
 (for the preparation of this, see below) contained in the retort, 
 50 grammes of acetyl chloride are added drop by drop from a 
 separating funnel. As soon as the first half of the chloride is 
 added, the reaction is interrupted for a short time, in order that 
 the pasty mass may be stirred up with a glass rod. The second 
 half is then allowed to run in. If in consequence of a too rapid 
 addition of acetyl chloride some of it should distil over into the 
 receiver undecomposed, this is poured back into the funnel and 
 again allowed to act on the sodium acetate. The separating 
 funnel is then removed, the tubulure closed with a cork, and the 
 anhydride distilled off from the salt residue by means of a luminous 
 flame which is kept in constant motion. The distillate is finally 
 purified by distilling in an apparatus similar to the one used in the 
 rectification of the acetyl chloride (see also Fig. 17) with the 
 addition of 3 grammes of finely pulverised anhydrous sodium 
 acetate, which serves to convert the last portions of acetyl chloride 
 into the anhydride. Boiling-point of acetic anhydride, 138. 
 Yield, about 50 grammes. 
 
 Preparation of Anhydrous Sodium Acetate : Crystallised sodium 
 acetate contains three molecules of water of crystallisation. In 
 order to dehydrate it is placed in a shallow iron or nickel dish and 
 heated over a free flame (120 grammes for this experiment). The 
 salt first melts in the water of crystallisation, on further heating 
 steam is copiously evolved, and the mass solidifies as soon as 
 
 1 A. 87, 149. 
 
 2 An upright coil condenser may be used, in which case an adapter is unnecessary. 
 
148 
 
 SPECIAL PART 
 
 the main portion of the water has been driven off, provided the 
 flame is not too large. In order to remove the last portions of the 
 water, the mass is now heated with a large flame, the burner being 
 constantly moved, until the solidified mass melts for the second time. 
 Care must be taken not to overheat ; in case this should happen, 
 
 FIG. 65. 
 
 the fact will be recognised by the evolution of combustible gases and 
 the charring of the substance. After cooling, the salt is removed 
 from the dish with a knife. If commercial anhydrous sodium 
 acetate is at hand, it is recommended that this also be melted once, 
 since when it is kept for a long time it always takes up water. 
 
 The reaction of acetyl chloride with sodium acetate takes place in 
 accordance with the following equation : 
 
 CH,CO\ 
 
 CH 3 . CO . Cl + CHo . CO . ONa = >O + NaCl 
 
 CH 3 C(X 
 
 This reaction is capable of general application, and the anhydride of 
 the acid may be made by treating its chloride with the corresponding 
 sodium salt. The so called mixed anhydrides, containing two different 
 
ALIPHATIC SERIES 149 
 
 acid radicals, can also be prepared by this reaction, by using the chloride 
 and sodium salt of two different acids : 
 
 CH 3 .CO\ 
 
 CH,.CO.Cl + CH 3 .CH 2 .CO.ONa = >O +NaCl 
 
 CH 3 .CH 2 .CO/ 
 
 Since, as stated, an acid-chloride may be obtained from an alkali salt of 
 the acid and phosphorus oxychloride, it is not necessary for the prepa- 
 ration of an anhydride to first isolate the chloride ; it is better to allow 
 the same to act directly on an excess of the salt, so that from the oxy- 
 chloride and salt an anhydride is directly obtained : 
 
 2 CH 3 . CO . ONa + POC1 3 = 2 CH 3 . CO . Cl + PO 3 Na + NaCl 
 
 CH 3 .CO\ 
 2CH 3 .CO.ONa + 2CH 3 .CO.C1 = 2 >O + 2 NaCl 
 
 (~>T_] CT\/ 
 
 CHg.CO/ ^ 
 
 CH 3 .CO\ 
 
 4 CH 3 . CO . ONa + POC1 3 = 2 >O + PO 3 Na + 3 NaCl 
 
 CH 3 .CO/ 
 
 The lower members of the acid-anhydride series are colourless liquids ; 
 the higher members, crystallisable solids. They possess a sharp odour, 
 are insoluble in water, but soluble in indifferent organic solvents. Their 
 specific gravities are greater than that of water. The boiling-points 
 are higher than those of the corresponding acids : 
 
 Acetic acid. 118, 
 Acetic anhydride, 138. 
 
 The lower members can be distilled without decomposition at ordinary 
 pressure ; but the higher members must be distilled in a vacuum. 
 
 The chemical conduct of anhydrides toward water, alcohols, and 
 phenols, as well as bases, is wholly analogous to that of the chlorides ; 
 but the anhydrides react with more difficulty than the chlorides. Thus 
 with water, the anhydrides yield the corresponding acids : 
 
 CH 3 .CO\ 
 
 >O + H 9 O = 2CH 3 .CO.OH 
 CH 3 .CO/ 
 
 EXPERIMENT : 5 c.c. of water are treated with ^ c.c. of acetic 
 anhydride. The latter sinks to the bottom and does not dissolve 
 even on long shaking. It will be recalled that the corresponding 
 chloride reacts instantly with water very energetically. If the 
 mixture be warmed, solution takes place. 
 
150 SPECIAL PART 
 
 In the presence of alkalies, solution takes place much more readily 
 with the formation of the alkali salts : 
 
 CH 3 .CO 
 CH 3 
 
 .CO\ 
 
 >0 + 2 NaOH = 2CH 3 .CO.ONa + H 2 O 
 .CO/ 
 
 EXPERIMENT : Mix 5 c.c. of water with -| c.c. of acetic anhy- 
 dride, and add a little caustic soda solution. On shaking, without 
 warming, solution takes place. 
 
 Anhydrides of high molecular weight react with water with still 
 greater difficulty, and require a longer heating to convert them into the 
 corresponding acid. 
 
 With alcohols and phenols, the anhydrides form acid-esters on heat- 
 ing, while the acid-chlorides react at the ordinary temperature : 
 
 CHg.COv 
 
 V) + C 2 H 5 .OH = CH 3 .CO.OC 9 H 5 + CH 3 .CO.OH 
 CH 3 .CO/ 
 
 CHo.CCK 
 
 _>0 + C 6 H 5 .OH = CH 3 .CO.OC 6 H 5 + CH 3 .CO.OH 
 
 CH 3 . CO/ Phenyl acetate 
 
 It is to be noted that one of the two acid radicals in the anhydride is 
 not available for the purpose of introducing the acetyl group into other 
 compounds, acetylating, since it passes over into the acid. 
 
 EXPERIMENT : 2 c.c. of alcohol are added to i c.c. of acetic anhy- 
 dride in a test-tube, and heated gently for several minutes. It is 
 then treated with water and carefully made slightly alkaline. The 
 acetic ester can be recognised by its characteristic pleasant odour. 
 If it does not separate from the liquid, it may be treated with 
 common salt, as in the experiment on page 145. 
 
 With ammonia and primary or secondary organic bases, the anhy- 
 drides react like the chlorides : 
 
 CH 3 .COv 
 
 NH 3 + >0 = CH 3 .CO.NH 2 + CH 3 .CO.OH 
 
 CH 8 .CO/ 
 
 CH 8 .COv 
 C 6 H 5 .NH 2 + ^O = C 6 H 5 .NH.CO.CH 3 + CH 3 .CO.OH 
 
 CHo. CO/ 
 
ALIPHATIC SERIES 151 
 
 EXPERIMENT : Add i c.c. of aniline to i c.c. of acetic anhydride, 
 heat to incipient ebullition, and then, after cooling, add twice the 
 volume of water. The crystals of acetanilide separate out easily 
 if the walls of the vessel be rubbed with a glass rod ; these are 
 filtered off, and may be recrystallised from a little hot water. 
 
 The acid-anhydrides can, therefore, be used, like the chlorides, for 
 the recognition, separation, characterisation, and detection of alcohols, 
 phenols, and amines. 
 
 In order to complete the enumeration of the reactions of the acid- 
 anhydrides, it may be mentioned briefly that they yield alcohols, and 
 the intermediate aldehydes when treated with sodium amalgam : 
 
 CH 3 .CO\ 
 
 >0 + H 2 = CH 3 .CHO + CH 3 .CO.OH 
 
 CHg.CO/ Aldehyde 
 
 CH 3 . CHO + H 2 = CH 3 . CH 2 . OH 
 
 It is, therefore, possible to pass from the anhydride of an acid to its 
 aldehyde or alcohol. 
 
 4. REACTION: PREPARATION OF AN ACID-AMIDE FROM THE 
 AMMONIUM SALT OF THE ACID 
 
 EXAMPLE : Acetamide from Ammonium Acetate 1 
 
 To 75 grammes of glacial acetic acid heated to 40-50 in a 
 porcelain dish on a water-bath, finely pulverised ammonium car- 
 bonate is added (100 grammes will be necessary) until a test- 
 portion diluted in a watch-glass with water just shows an alkaline 
 reaction. The viscous mass is warmed on an actively boiling 
 water-bath to 80-90, until a few drops of it diluted with water 
 just show an acid reaction ; it is then poured (without the use of 
 a funnel-tube) directly into two wide bomb-tubes of hard glass, 
 which have been previously warmed in a flame. A single Volhard 
 tube (see page 68) is much more convenient. After the por- 
 tions of substance adhering to the upper end of the tube have 
 been removed by melting down carefully with a flame, the last 
 traces are removed with filter-paper, the tube sealed and heated 
 
 i B. 15, 979. 
 
152 
 
 SPECIAL PART 
 
 for five hours in a bomb-furnace at 2 20-230. * The liquid re- 
 action product is fractionated under the hood in a distilling-flask 
 provided with a condenser. There is first obtained a fraction 
 boiling between 100-130, consisting essentially of acetic acid and 
 water. The temperature then rises rapidly to 180 (an extension 
 tube is substituted for the condenser, see page 22), at which 
 point the acetamide begins to distil. The fraction passing over 
 between 180-230 is collected in a beaker, cooled by ice water 
 at the end of the distillation, and the walls are rubbed with a 
 sharp-edged glass rod ; the crystals separating out are pressed on 
 a drying plate to remove the liquid impurities. By another dis- 
 tillation of the pressed-out crystals, the almost pure acetamide 
 boiling at 223 passes over. Yield, about 40 grammes. The 
 product thus obtained possesses an odour very characteristic of 
 mouse excrement ; this is not the odour of pure acetamide, but 
 of an impurity accompanying it. In order to remove the im- 
 purity, a portion of the distilled amide is again pressed out on a 
 drying plate, and then crystallised from ether. There are thus 
 obtained colourless, odourless crystals, melting at 82. 
 
 The reaction involved in the preparation of an amide from the am- 
 monium salt of the acid is capable of general application. The latter 
 is subjected to dry distillation, or more conveniently, heated in a sealed 
 tube at 220-230 for five hours : 
 
 CH 3 . CO . ONH 4 = CH, . CO . NH 2 + H 2 O 
 
 In order to purify the amide thus obtained, the reaction-mixture may be 
 fractionated, as in the case of acetamide, or if the amide separates out 
 in a solid condition, it may be purified by filtering off the impurities and 
 crystallising. Substituted acid-amides, and especially easily substituted 
 aromatic amides, e.g. acetanilide, can also be readily obtained by this 
 method, by heating a mixture of the acid and amine a long time in an 
 open vessel : 
 
 CH 3 . COOH 3 N . C 6 H 5 = CH 3 . CO . NH . C 6 H 5 + H 2 O 
 
 Aniline acetate Acetanilide 
 
 The ammonium salts of di- and poly-basic acids react in a similar way, 
 
 *&' CO.ONH 4 CO.NH 2 
 
 I =1 +2H 2 
 
 CO.ONH 4 CO.NH 2 
 
 Ammonium oxalate Oxamide 
 
 1 Above this temperature the tube is liable to explode. 
 
ALIPHATIC SERIES 153 
 
 Concerning further methods of preparation, it may be stated thai 
 acid-chlorides or anhydrides when treated with ammonia, primary or 
 secondary bases form acid-amides very easily: 
 
 CH 3 .CO.C1 + NH 3 = CH 3 .CO.NH 2 
 CHg. 
 
 X 
 >0 
 
 + NH 3 = CH 3 .CO.NH 8 + CH 8 .CO. OH 
 
 The acid-amides may be furthermore obtained by two methods oi 
 general application: (i), by treating an ethereal salt with ammonia, 
 and (2), by treating a nitrile with water: 
 
 Acetic acid, Boiling-point, 118 
 Acetamide, 223 
 
 Ethyl acetate 
 
 CH, . CN + H 2 = CH 3 . CO . NH 
 
 Acetonitrile 
 
 The acid-amides are, with the exception of the lowest member, 
 formamide, H . CO . NH 2 (a liquid), colourless, crystallisable compounds, 
 the lower members being very easily soluble in water, e.g., acetamide ; 
 the solubility decreases with the increase of molecular weight, until 
 finally they become insoluble. The boiling-points of the amides are 
 much higher than those of the acids : 
 
 Proprionicacid, Boiling-point, 141 
 Proprionamide, 213 
 
 While the entrance of an alkyl residue into the ammonia molecule 
 does not change the basic character of the compound, as will be dis- 
 cussed more fully under methylamine, the entrance of a negative acid 
 radical enfeebles the basic properties of the ammonia residue, so that 
 the acid-amides possess only a very slight basic character. It is true that 
 a salt corresponding to ammonium chloride CH 3 .CO.NH 2 .HC1 
 can be prepared from acetamide by the action of hydrochloric acid; 
 but this shows a strong acid reaction, is unstable, and decomposes 
 easily into its components. If it is desired to assign to the acid-amides 
 a definite character, they must be regarded as acids rather than bases. 
 One of the amido-hydrogen atoms possesses acid properties in that it 
 may be replaced by metals. The mercury salts of the acid-amides may 
 be prepared with especial ease, by boiling the solution of the amide 
 with mercuric oxide : 
 
 2CH 3 .CO.NH 2 -r HgO = (CH 3 .CO.NH) 2 Hg + H,O 
 
154 SPECIAL PART 
 
 EXPERIMENT: Some acetamide is dissolved in water, treated 
 with a little yellow mercuric oxide, and warmed. The latter goes 
 into solution, and the salt of the formula given above is formed. 
 
 The amido-hydrogen atoms can also be replaced by the negative 
 chlorine and bromine atoms, as well as by the positive metallic atoms. 
 These substitution compounds are obtained by treating the amide with 
 chlorine or bromine, in the presence of an alkali : 
 
 CH 3 . CO . NHC1 CH 3 . CO . NHBr CH 3 . CO . NBr 2 
 
 Acetchloramide Acetbromamide Acetdibromamide 
 
 The monohalogen substituted amides are of especial interest, since, on 
 being warmed with alkalies, they yield primary alkylamines : 
 
 CH 3 . CO . NHBr + H 2 O = CH 3 . NH 2 + HBr + CO 2 
 
 This important reaction will be taken up later, under the preparation 
 of methyl amine from acetamide. 
 
 In the acid-amides, the acid radical is not firmly united with the 
 ammonia residue ; this is shown by the fact that they are saponified, 
 i.e. decomposed into the acid and ammonia, on boiling with water, 
 more rapidly by warming with alkalies : 
 
 CH 3 . CO . NH 2 + H 2 O = CH, . CO . OH + NH 3 
 
 EXPERIMENT : Heat some acetamide in a test-tube with caustic 
 soda solution. A strong ammoniacal odour is given off, while 
 the solution contains sodium acetate. 
 
 If an acid-amide is treated with a dehydrating agent, e.g., phosphorus 
 pentoxide, it is converted into a nitrile : 
 
 CH 3 . CO . NH 2 = CH 3 . CN + H 2 O 
 
 Acetonitrile 
 
 The same result is obtained by treating it with phosphorus penta- 
 chloride ; but in this case the intermediate products, the amide-chlorides 
 or imide-chlorides are formed : 
 
 CH 3 . CO . NH 2 + PC1 5 - CH 3 . CC1 2 . NH 2 + POCL 
 
 Amide-chloride 
 
 The very unstable amide-chloride then passes over, with the loss of one 
 molecule of hydrochloric acid, into the more stable imide-chloride : 
 CH, . CC1 2 . NH 2 = CH 3 . CC1= NH 4- HC1 
 
 Imide-chloride 
 
 And this finally into the nitrile, 
 
 CH 3 .CC1=NH = CH 3 .CN + Hd 
 
ALIPHATIC SERIES 155 
 
 5. REACTION: PREPARATION OP AN ACID-NITRILE FROM AN 
 ACID- AMIDE 
 
 EXAMPLE : Acetonitrile from Acetamide 1 
 
 To 15 grammes of phosphoric anhydride, contained in a small, 
 dry flask, 10 grammes of dry acetamide are added. After the two 
 substances are shaken well together, the flask is connected with a 
 short condenser, and then heated carefully, with a not too large 
 luminous flame kept in constant motion. The reaction proceeds 
 with much foaming. After the mixture has been heated a few 
 minutes, the acetonitrile is then distilled over with a large luminous 
 flame, kept in constant motion, into the receiver (test-tube). The 
 distillate is treated with half its volume of water, and then solid 
 potash is added until it is no longer dissolved by the lower layer 
 of liquid. The upper layer is removed with a capillary pipette 
 and distilled, a small amount of phosphoric anhydride being placed 
 in the fractionating flask for the complete dehydration of the nitrile. 
 Boiling-point, 82. Yield, about 5 grammes. 
 
 If an acid-amide is heated with a dehydrating agent (phosphorus 
 pentoxide, pentasulphide, or pentachloride), it loses water, and passes 
 over into the nitrile, e.g. : 
 
 CH 3 .CO NH 2 = CH 3 .CEEN + H 2 O 
 
 Acetonitrile 
 
 Since, as has just been done, the acid-amide may be made by dehy- 
 drating the ammonium salt of an acid, thus, in a single operation the 
 nitrile may be obtained directly from the ammonium salt, if it is treated 
 with a powerful dehydrating agent, e.g. ammonium acetate heated with 
 phosphoric anhydride : 
 
 CH 3 .COONH 4 = CH 3 .CN + 2H 2 O 
 
 The acid-nitriles may also be obtained by heating alkyl iodides (or 
 bromides, chlorides) with alcoholic potassium cyanide : 
 
 CH,|I + K|CN = CH 3 . CN + KI 
 
 CH 2 Br CH 9 .CN 
 
 | +2KCN=I +2KBr 
 
 CH 2 Br CH 2 .CN 
 
 ____________ Ethylene cyanide 
 
 1 A. 64, 33*- 
 
156 SPECIAL PART 
 
 C 6 H 5 . CH 2 . Cl + KCN = C 6 H 5 . CH 2 . CN + KC1 
 
 Benzyl chloride Benzyl cyanide 
 
 or by the dry distillation of alkyl alkali sulphates with potassium 
 
 cyanide : 
 
 X O|C 2 H 5 CNJK 
 SO,/ ~~~fT~ = C 2 H 5 . CN + K 2 SO 4 
 
 >K 
 
 Ethyl potassium sulphate Proprionitrile 
 
 These two reactions differ from those above in that the introduction of 
 a new atom of carbon is brought about. The nitriles thus appear to be 
 cyanides of the alkyls, and, therefore, may be equally well designated 
 as cyanides, e.g. : 
 
 CH 3 . CN = Acetonitrile = Methyl cyanide 
 CgH^CN = Proprionitrile = Ethyl cyanide 
 etc. etc. etc. 
 
 The lower members of the nitrile series are colourless liquids, the 
 higher members, crystallisable solids ; the solubility in water decreases 
 with the increase in molecular weights. If they are heated with water 
 up to 1 80 under pressure, they take up one molecule of water and are 
 converted into the acid-amides : 
 
 CH 3 .CN + H 2 = CH 3 .CO.NH 2 
 
 On heating with acids or alkalies, they take up two molecules of water, 
 and pass over into the ammonium salt as an intermediate product : 
 
 CH 3 . CN + 2 H 2 O = CH 3 . COONH 4 
 
 which immediately reacts with the alkali or acid, in accordance with 
 the following equations : 
 
 CH 3 .COONH 4 + KOH = CH 3 .COOK + NH 3 + H 2 O 
 CH 3 .COONH 4 + HC1 = CH 3 .COOH + NH 4 C1 
 
 This process is called " saponification." 
 
 If nascent hydrogen (e.g. from zinc and sulphuric acid) be allowed 
 to act on nitriles, primary amines are formed (Mendius 1 reaction) : l 
 
 CH 3 .CN + 2 H 2 = CH 3 .CH 2 .NH 2 
 
 Ethyl amine 
 
 l A. lai, 129. 
 
ALIPHATIC SERIES 157 
 
 Further, but of less importance, general reactions may be indicated 
 by the following equations: 
 
 CH 3 . CN + H 2 S = CH 8 . CS . NH 2 
 
 Thioacetamide 
 
 CH 3 .CO\ 
 CH 3 . CN + CH 3 . CO . OH = >NH = Diacetamide 
 
 CH 3 .CO/ 
 CH 3 .CO\ 
 
 CH 3 . CN + >0 = N(CO . CHo) 3 = Triacetamide 
 
 CH 3 .CO/ 
 
 NH 2 
 
 CH 3 .CN + NH 2 .OH = 
 
 Hydroxylamine Acetamide-oxime 
 
 CH 3 .CN 
 
 Imide-chloride 
 
 6. REACTION: PREPARATION OF AN ACID-ESIER FROM THE ACID 
 AND ALCOHOL 
 
 EXAMPLE : Acetic Ester from Acetic Acid and Ethyl Alcohol 1 
 
 A i-litre flask, containing a mixture of 50 c.c. of alcohol and 50 
 c.c. of concentrated sulphuric acid, is closed by a two-hole cork ; 
 through one hole passes a dropping funnel, through the other a 
 glass delivery tube connected with a long condenser or coil con- 
 denser. The mixture is heated in an oil-bath to 140 (thermome- 
 ter in oil) ; when this temperature is reached, a mixture of 400 c.c. 
 of alcohol and 400 c.c. of glacial acetic acid is gradually added 
 through the funnel, at the same rate at which the ethyl acetate 
 (acetic ester), formed in the reaction, distils over. In order to 
 remove the acetic acid carried over, the distillate is treated in an 
 open vessel with a dilute solution of sodium carbonate until the 
 upper layer will not redden blue litmus paper. The layers are 
 now separated with a dropping funnel ; the upper layer is filtered 
 through a dry folded filter, and shaken up with a solution of 100 
 
 i Bl. 33, 350. 
 
158 SPECIAL PART 
 
 grammes of calcium chloride in 100 grammes of water, in order 
 to remove the alcohol. 1 The two layers are again separated with 
 the funnel, the upper one dried with granular calcium chloride 
 and then distilled on the water-bath (see page 16). Boiling 
 point, 78. Yield, about 80-90 % of the theory. 
 
 The formation of an ester from acid and alcohol is analogous to the 
 formation of a salt from an acid and a metallic hydroxide : 
 
 NO 3 . H + Na . OH = NO 3 . Na + H 2 O 
 CH 3 . COOH + C 2 H 5 OH = CH 3 . COOC,H 5 + H 2 O 
 
 The two reactions take place quantitatively, but not in a similar 
 manner. A strong acid reacts almost quantitatively with an equivalent 
 weight of a strong base, and the product of this neutralisation is a salt. 
 Upon this depend the processes of acidimetry and alkalimetry. But 
 equimolecular quantities of an acid and an alcohol do not yield the 
 theoretical quantity of the ester. A maximum quantity of ester is 
 formed, but this falls short of the quantity required by theory, and it is 
 impossible, even when the reacting substances are kept in contact, to 
 convert the unchanged acid and alcohol into ester beyond a certain 
 limit. If. for example, equimolecular quantities of acetic acid and 
 alcohol are allowed to interact, only two-thirds of these enter into the 
 reaction, the maximum yield of ester being 66.7% of the theory. It is 
 impossible to cause a union between the remaining one-third of acetic 
 acid and alcohol, even when the reaction is continued for a long time. 
 The difference in the quantitative course of the reaction in the forma- 
 tion of an ester is due to the "reversibility of the reaction"; i.e. the 
 reaction products on the right-hand side of the equation (ester and 
 water) will interact in such a manner as to reverse the reaction : 
 
 CH 3 . COOC 2 H 5 + H 2 O = CH 3 . COOH + C 2 H 5 OH 
 In reactions of this order the two sides of the equation are united, not 
 by an equation sign, but, as proposed by van't Hoff, by two arrows 
 pointing in opposite directions : 
 
 CH 3 . COOH + C 2 H 5 OH ^> CH 3 . COOC 2 H 5 + H 2 O 
 The reaction in the neutralisation of a strong acid with a strong 
 base is, on the other hand, unlike esterification, since it is " an irre- 
 versible or a complete reaction " ; the water that is liberated does not 
 react with the salt to reverse the reaction and regenerate the acid and 
 the base. In reality this difference does not exist. All reactions are 
 
 1 Calcium chloride forms a compound with alcohol. (Compare page 54.) 
 
ALIPHATIC SERIES 159 
 
 reversible. But when a reaction product is extremely insoluble, or 
 when it is a gas, or when for other reasons the final products have 
 little tendency to react and bring about the reverse change (and this 
 is the case in the above example of the neutralisation of a strong acid 
 with a strong base), then one of the two opposing reactions is said to 
 be complete " within measurable limits," and it is called an u irreversible 
 reaction in the ordinary sense," although not in the strictest sense. 
 While in irreversible reactions chemical equations enable us to calculate 
 the amount of the products from given quantities of reacting substances, 
 in reversible reactions strictly quantitative stoichiometric methods 
 do not give the desired information. But by the aid of the highly 
 important Law of Mass Action (Guldberg and Waage, 1867), it is pos- 
 sible to determine to what extent a reversible reaction may be complete. 
 As has already been mentioned, when equimolecular quantities of 
 acetic acid and ethyl alcohol are allowed to react for some time, only 
 two-thirds of these substances will be transformed into acetic ester and 
 water. A " state of equilibrium " will finally be established, and the 
 reaction mixture will have the following constant composition : 
 
 | ester -f f water +^ acetic acid + i alcohol 
 
 The same equilibrium is established, if, instead of a mixture of acid 
 and alcohol, a similar mixture of ester and water is taken. In this case 
 the ester will be partially saponified into acetic acid and alcohol, but 
 the reaction will proceed only until of the ester is saponified. An 
 equilibrium will once more be established as above, so that f of ester 
 and water, and of acetic acid and alcohol will be obtained. 
 
 It must not be assumed that in an equilibrium of this kind the mole- 
 cules of the four substances remain unaltered (static equilibrium). On 
 the contrary, while acetic acid and alcohol are forming ester and water, 
 the molecules of ester and water are simultaneously reacting to bring 
 about the reverse change (dynamic equilibrium). In spite of this con- 
 tinuous reaction an equilibrium will exist, i.e. the composition of the 
 system will remain unaltered, when the velocities of the two opposing 
 reactions are the same, i.e. when in unit time an equal number of ester 
 molecules is formed and saponified. 
 
 The formation of ethyl acetate from acetic acid and alcohol may be 
 expressed by the following equation of mass action : 
 
 where C s , C A , C E , C w show the " concentration " of acetic acid, alcohol, 
 ester, and water respectively, and K is a constant. By concentration, 
 
160 SPECIAL PART 
 
 or " active mass " (Guldberg and Waage) is not meant the weight of 
 each substance in the total volume or in unit volume, but the relative 
 number of molecules, i.e. the weight of each substance divided by its 
 molecular weight (the number of gramme-molecules or moles). The 
 equation shows that when the four substances are in equilibrium with 
 one another, the product of the concentrations of acetic acid and alco- 
 hol divided by the product of the concentrations of ester and water 
 will be equal to a constant. How can this constant be calculated ? 
 We simply ascertain by analytical methods the weights of the four 
 substances that are in equilibrium with one another in a concrete ex- 
 ample, calculate the concentrations in accordance with deductions men- 
 tioned above, and introduce these values into the equation given. 
 This may be readily done in our example, since three of the substances 
 (alcohol, ester, and water) are neutral, and the quantity of the fourth, 
 the acetic acid, may be easily ascertained by titration. If we take, e.g., 
 equimolecular quantities of acetic acid and alcohol, namely, 60 grammes 
 of acetic acid and 46 grammes of alcohol (and this will contain an 
 equal number of molecules), we can determine the amount of acid in 
 one c.c. of this mixture, at the first minute, by titration. If we now 
 allow the two substances to react for some time, and titrate one c.c. of 
 the mixture at stated intervals, the titre of the acid will be found to 
 diminish gradually, until finally it remains constant, due to equilibrium. 
 If now we compare the maximum first titre with the final minimum 
 titre, we shall find that the latter is exactly one-third of the former ; 
 i.e. at equilibrium only one-third of the original molecules of acetic 
 acid remain uncombined, the other two-thirds having been changed 
 into the ester. Since one molecule of acid yields one molecule of ester, 
 the number of ester molecules is exactly two-thirds of acetic acid mole- 
 cules used originally for the experiment. Since further, with the 
 formation of every ester molecule a water molecule is also formed, the 
 number of water molecules is also exactly two-thirds of acetic acid 
 molecules taken originally. And finally, since with every molecule of 
 acid one molecule of alcohol reacts to form the ester, two-thirds of the 
 alcohol molecules are used up, and only one-third remain unchanged at 
 equilibrium. We have thus determined the amount of all four sub- 
 stances at equilibrium by a mere titration. Consequently, we have the 
 following values in our equation : 
 
 C a = 1 1 C A = I ; Cjt = | ; C w =. 
 If we carry these values into the above equation, we obtain : 
 
 *-=iii= 
 
 M 4 
 
ALIPHATIC SERIES l6l 
 
 Thus when we have accurately determined the value of A' in a single 
 experiment, we shall be in a position to calculate the quantitative yield 
 of acetic ester at equilibrium for all proportions of acetic acid and 
 alcohol. Suppose we use, e.g., one gramme-molecule of acetic acid with 
 two gramme-molecules of alcohol, and let x be the number of gramme- 
 molecules of ester at equilibrium ; the gramme-molecular quantity of 
 water will also be represented by x. The gramme-molecular quantity 
 of unchanged acetic acid will then be (i x), and that of unchanged 
 alcohol will be (2 x). Making these substitutions in our equation, 
 we obtain : 
 
 (i -x). (2 -x) _ \ 
 x.x 4 
 
 X= 2 2VJ 
 
 Since the quantity of acetic acid used is only one gramme-molecule, 
 x cannot be greater than one, and we are thus concerned only with the 
 negative sign. Thus .ris equal to 2 2>/| = 0.85, i.e. 0.85 gramme- 
 molecules of ester are obtained at equilibrium, i.e. 85% of the acetic 
 acid is transformed into ester. If, therefore, instead of using equi- 
 molecular quantities of acetic acid and alcohol, we double the theoreti- 
 cal quantity of the latter, 85 % of the acetic acid will be transformed into 
 ester instead of 66.7 %. 
 
 The following problems may be solved in this connection : 
 How much ester will be formed when one gramme-molecule of acetic 
 acid is treated with three gramme-molecules of alcohol ? How much 
 ester will be formed when 30 grammes of acetic acid and 50 grammes of 
 alcohol are used ? What proportions of acetic acid and alcohol must 
 be used in order to transform 75 % of the former into ester ? 
 
 As the above example shows, the yield of ester from the same 
 quantity of acetic acid is greater, the larger the amount of alcohol used. 
 This also follows directly from the equation of mass action given above. 
 As we have seen, K must have the constant value of \ for all propor- 
 tions of reacting substances. Thus when C A , the concentration of 
 the alcohol, is increased, the remaining three quantities will also be 
 changed in such a manner that the quotient will have a constant value. 
 This can only happen when the quantities in both denominators in- 
 crease, i.e. when the concentrations of the ester and the water formed 
 at the same time become greater. The equalisation of the quotient, 
 however, takes place not only through the denominator, but also through 
 the numerator ; because when more ester is formed, more acetic acid will 
 also be used up. This is shown by the decrease in the concentration 
 of acetic acid. Thus a large excess of alcohol is taken when it is desired 
 
1 62 SPECIAL PART 
 
 to convert an acid, as completely as possible, into an ester. If, on the 
 other hand, it is desired to convert an alcohol into an ester quantita 
 tively, a large excess of acid is used. 
 
 The practical application of these principles in preparation work has 
 already been pointed out under ethyl bromide. 
 
 In the preparation of ethyl acetate described above, sulphuric acid is 
 also used in addition to acetic acid and alcohol. This reacts in two 
 ways. It is a well-known fact that concentrated sulphuric acid com- 
 bines with water chemically. Consequently, the water liberated during 
 the formation of ester is either completely, or in part, removed, and the 
 reverse reaction from right to left, i.e. the saponification of the freshly 
 formed ester, is either rendered impossible or difficult. Thus the yield 
 of ester is much larger in the presence of sulphuric acid. But sulphuric 
 acid also acts as a catalytic agent in the reaction, i,e. it accelerates the 
 formation of ester, as well as its saponification, and indeed in the same 
 ratio, so that the state of equilibrium is not changed. Other acids may 
 also be employed as catalytic agents in this sense. Thus esters may 
 be formed by simply conducting hydrochloric acid gas into a mixture 
 of acid and alcohol, or by heating the acid with alcoholic hydrochloric 
 acid (containing a small percentage of HC1). (Compare B. 28, 3252.) 
 The speed of the catalytic action is proportional to the strength of the 
 acid used as a catalytic agent. The stronger the dissociation of the 
 acid, i.e. the greater the concentration of hydrogen ions in the reaction 
 mixture, the more rapid the formation of the ester. By this method, 
 and others, is the strength of many acids determined. 
 
 In many cases, where the salts of organic acids are more readily 
 obtained than the free acids, they may be used for the preparation of 
 the esters by heating them directly with alcohol and sulphuric acid. 
 Other methods for the preparation of acid-esters have been referred to, 
 and, in part, carried out practically on the small scale in the foregoing 
 preparations, so that at this point it is only necessary to recall the 
 equations : 
 
 (1) CH., . CO . OAg + IC 2 H 5 = CH 3 . CO . OC 2 H 5 + Agl, 
 
 (2) CH 3 . CO . Cl + C a H 5 . OH = CH 8 . CO . OC 2 H 5 + HC1, 
 
 CTT (~*O\ 
 
 (3) CH 3 ' co / O + C 2 H 5 . OH = CH 3 . CO . OC 2 H 5 + CH 3 . CO .OH. 
 
 (4) Acid-esters may also be readily obtained by treating the alkali 
 salts of acids with alkyl sulphate, 1 at the ordinary temperature : 
 
 R . CO . OMe + (CH 3 ) 2 SO 4 = R . CO . OCH, + CH 3 . SO 4 . Me 
 (Compare B. 37, 3658.) It must be remembered that methyl sulphate 
 is poisonous. 
 
 1 The hydrogen atom in a hydroxyl group in phenols, as well as a hydrogen 
 atom in combination with nitrogen, may readily be exchanged for a methyl group 
 by the use of dimethyl sulphate. See A. 327, 104. 
 
ALIPHATIC SERIES 163 
 
 Concerning the purification of the acid-esters, it may be mentioned, 
 that the crude reaction-product is shaken with a sodium carbonate 
 solution until the ester no longer shows an acid reaction. The 
 alcohol may be removed from esters difficultly soluble in water by 
 repeatedly washing with water ; in case an ester is moderately soluble 
 in water, as ethyl acetate, it is better to use a solution of calcium 
 chloride. 
 
 The lower members of the series of acid-esters are colourless liquids 
 with pleasant, fruit-like odours ; the higher members, as well as those 
 of the aromatic acids, are crystallisable compounds. The boiling-points 
 of esters containing alky! residues of small molecular weights (CH 3 , 
 C 2 H 5 , C 3 H 7 ) are lower than those of the corresponding acids ; the 
 entrance of more complex alkyl residues raises the boiling-points : 
 
 CH 3 . CO . OCH 3 Boiling-point, 57 
 
 CH 3 .CO.OC 2 H 5 78 
 
 CH 3 .CO.OH ' " 118 
 
 CH 3 .CO.OC 6 H 13 169 
 
 Hexyl acetate 
 
 As already mentioned, the esters are saponified by heating with water : 
 
 CH 3 . CO . OC 2 H 5 + H 2 = CH 3 . CO . OH + C 2 H 5 . OH 
 The saponification is effected more readily by heating with alkalies : 
 CH 3 . CO . OC 2 H 5 + KOH = CH 3 . CO . OK + C 2 H 5 . OH 
 
 Other methods of saponification will be fuither discussed when a 
 practical example is taken up. The action of ammonia upon acid- 
 esters, forming acid-amides, has already been referred to under acet- 
 amide : 
 
 CH 3 . CO . OC 2 H S + NH 3 = CH 3 . CO . NH 2 + C 2 H 5 . OH. 
 
 7. REACTION: SUBSTITUTION OP HYDROGEN BY CHLORINE 
 EXAMPLE : Monochloracetic Acid from Acetic Acid and Chlorine l 
 
 A current of dry chlorine is passed into a mixture of 150 
 grammes of glacial acetic acid and 1 2 grammes of red phosphorus, 
 contained in a flask provided with a delivery tube and an inverted 
 
 iR. 23,222; A. 102,1. 
 
1 64 SPECIAL PART 
 
 condenser; the flask is heated on a rapidly boiling water-bath, 
 and must be placed in such a position as to receive as much light 
 as possible. The best result is obtained by performing the reac- 
 tion in the direct sunlight, since the success of the chlorination 
 depends essentially on the action of the sun's rays. The reaction 
 is ended when a small test- portion cooled with ice-water solidifies 
 on rubbing the walls of the vessel (test-tube) with a glass rod. 
 In summer the chlorination may require a single day, while dur- 
 ing the cloudy days of winter, two days may be necessary. For 
 the separation of the monochloracetic acid the reaction-product is 
 fractionated from a distilling flask connected with a long air con- 
 denser. The fraction passing over from 150-200 is collected in 
 a separate beaker ; this is cooled in ice-water and the walls rubbed 
 with a glass rod. The portion solidifying, consisting of pure mono- 
 chloracetic acid is rapidly filtered with suction, the loose crystals 
 being pressed together with a spatula or mortar-pestle. The suc- 
 tion must not be continued too long, because the monochloracetic 
 acid gradually becomes liquid in warm air. The filtrate is again 
 distilled, and the portion passing over between 1 70-200 is col- 
 lected in a separate vessel. This is treated as before (cooling 
 and filtering), and there is obtained a second portion of mono- 
 chloracetic acid ; this is united with the main quantity, which is 
 again distilled. The product thus obtained is perfectly pure. 
 Boiling-point, 186. Yield varying, 80-125 grammes. 
 
 Since monochloracetic acid, especially when warm, attacks the 
 skin with great violence, care must be taken in handling it. 
 
 Chlorine or bromine substitution products of aliphatic carbonic acids 
 can be obtained by the direct action of the halogen on the acids : 
 
 CH 3 .CO.OH + C1 2 = CHUC1.CO.OH + HC1 
 (Br 2 ) (Br) (HBr) 
 
 If the reaction is allowed to continue for a long time, other substitution 
 products can also be obtained. But the action of chlorine or bromine 
 on acids is very sluggish. It may be substantially facilitated by certain 
 conditions. If, e.g., the operation is conducted in direct sunlight, the 
 reaction proceeds much more rapidly than in a dark place. The reac- 
 tion is assisted more effectively by adding a so-called " carrier." Iodine 
 
ALIPHATIC SERIES 165 
 
 may be used as such for the introduction of chlorine or bromine. When 
 added in small quantities to the substance to be substituted, it causes 
 the substitution to take place more rapidly and completely. The con- 
 tinuous action of this carrier depends upon the following facts : In 
 the first phase of the reaction, chlorine iodide is formed : 
 
 (i) Cl + I = IC1 
 
 This acts, then, as a chlorinating agent in the second phase, according 
 to the following reaction : 
 
 (2) CH 3 . CO . OH + IC1 = CH 2 C1 . CO . OH 4- HI 
 The chlorine acts upon the hydriodic acid as follows : 
 (3) HI + C1 3 = IC1 + HC1 
 
 The molecule of chlorine iodide is thus formed anew (equation i) 
 and can chlorinate another molecule of acetic acid, and so on. The 
 action of the iodine in the last case depends upon the fact that the 
 molecule of chlorine iodide (1C1) is more easily decomposed into its 
 atoms than the molecule of chlorine (C1 2 ) . The disadvantage neces- 
 sarily incident to the use of iodine as a carrier is, that the reaction- 
 product is easily contaminated with iodine derivatives, in small 
 quantities, it is true. 
 
 In an entirely different way the chlorination is facilitated by the 
 addition of red phosphorus. In this case, phosphorus pentachloride 
 is first formed from the phosphorus and chlorine ; this, acting on the 
 acetic acid, generates acetyl chloride, and this latter, with an excess 
 of the acid, forms the anhydride. Direct experiments have shown that 
 acid-chlorides, as well as anhydrides, are substituted by chlorine with 
 much greater ease than the corresponding acids ; in this fact the action 
 of red phosphorus finds its explanation. Since a small amount of 
 phosphorus is sufficient for the chlorination of a large amount of acetic 
 acid, the question as to how this is continuously effected remains to be 
 answered. In accordance with the above statements, the following 
 reactions take place : 
 
 (1) P + C1 5 = PC1 5 
 
 (2) CH 3 . CO . OH + PC1 5 = CH 3 . CO . Cl + POC1 3 + HC1 
 
 CH 3 .CO\ 
 
 CH 
 
 (3) CH..CO.C1 + CH^.CO.OH= >O + HC1 
 
 ,.CO/ 
 
1 66 SPECIAL PART 
 
 If the chlorine now acts on the anhydride, monochloracetic anhydride 
 is formed : 
 
 (4) CH 3 .CO\ CH,C1.CO\ 
 
 NV-V , ri - \n -i. wn 
 
 >U + L,1 2 = /\J T rlLxl 
 
 CH 3 .CO/ CH 3 .CO/ 
 
 But this reacts directly with the hydrochloric acid, in accordance with 
 this equation : 
 
 (5) CH 2 C1.0X 
 
 >0 + HC1 = CH 9 C1.CO.OH + CH,.CO. Cl 
 
 CHg.CO/ 
 
 There is thus obtained, besides the molecule of chloracetic acid, the 
 molecule of acetyl chloride, first formed in reaction 2, which is utilised 
 repeatedly by its regeneration in accordance with reactions 3, 4, and 5. 
 
 As a substitute for red phosphorus, sulphur is also recommended 
 for the chlorination of aliphatic acids. This acts in a wholly similar 
 manner, since it first forms sulphur chloride, which, reacting on the 
 acid, like phosphorus chloride, converts it into an acid-chloride. The 
 other phases of the reaction are similar to those given above. 
 
 The bromination of -aliphatic carbonic acids, which is not only 
 of great importance in preparation work, but also as a means for 
 determining constitution, is also conducted with the addition of red 
 phosphorus (Hell-Volhard-Zelinsky Method). 1 
 
 The halogen atoms always enter the a-position to the carboxyl 
 group. Thus, e.g., when proprionic and butyric acids are brominated, 
 they yield : 
 
 CH 3 .CHBr.CO.OH CH 3 .CH 2 .CHBr.CO.OH 
 
 a-Bromproprionic a-Brombutyric acid 
 
 If no a-hydrogen atom is present, e.g., in trimethyl-acetic acid 
 (CH 3 ) 3 .C .CO . OH, bromination will not take place. The ability of 
 
 an acid to form a bromine substitution product can, therefore, be used 
 as a test for the presence of an a-hydrogen atom. Iodine cannot be 
 introduced directly into aliphatic acids like chlorine and bromine. To 
 obtain iodine substitution products, it is necessary to treat the corre- 
 sponding chlorine or bromine compound with potassium iodide : 
 
 CH 2 C1 . CO . OH + KI = CH 2 I . CO . OH + KC1 
 
 The halogen derivatives of the fatty acids are in part liquids, in part 
 1 B. 14, 891 ; 21, 1726; A. 242, 141 ; B. 21. 1904; B. 20, 2026; B. 24, 2216. 
 
ALIPHATIC SERIES l6/ 
 
 solids. In their reactions they resemble the acids, on the one hand, 
 since they form salts, chlorides, anhydrides, esters, etc. ; on the other 
 hand, the halogen alkyls. They are of great value in the preparation 
 of oxy- and amido-acids, of unsaturated acids, for the synthesis of poly- 
 basic acids, etc. Below are given a few equations capable of general 
 application : 
 
 CH 2 C1 . CO . OH + H 2 O = CH 2 (OH). CO . OH + HC1 
 
 Oxyacetic acid = 
 Glycolic acid 
 
 CH 2 C1 . CO . OH + NH 3 = CH 2 . NH 2 . CO . OH + HC1 
 
 Amidoacetic acid = 
 Glycocoll 
 
 CH 2 I CH 2 
 
 CHo + KOH = CH +KI + H 9 O 
 
 COOH CO. OH 
 
 (From glyceric acid + PI 3 ) Acrylic acid 
 
 CH 2 C1.CO.OH + KCN = CH 2 .CN.CO.OH + KC1 
 
 Cyanacetic acid 
 
 CO. OH 
 
 CH, 
 
 2CH 2 Br.CO.OH + Ag 2 = | +2AgBr 
 
 .OH 
 
 Succinic Acid 
 
 8. REACTION: OXIDATION OP A PRIMARY ALCOHOL TO AN 
 ALDEHYDE 
 
 EXAMPLE : Acetaldehyde from Ethyl Alcohol * 
 
 A ij-litre flask containing no grammes of concentrated sul- 
 phuric acid and 200 grammes of water is closed by a two-hole 
 cork ; through one hole passes a dropping funnel, through the 
 other a glass delivery tube connected with a long condenser. To 
 the lower end of the condenser is attached an adapter bent down- 
 wards, the narrower portion of which passes through a cork in 
 
 IA. 14, 133; j. 1853,329. 
 
1 68 SPECIAL PART 
 
 the neck of a thick-walled suction flask of about ^-litre capacity. 
 (See Fig. 65, page 148.) By using an upright coil condenser con- 
 nected directly with the suction flask, an adapter is unnecessary. 
 The suction flask is placed in a water-bath filled with a freezing 
 mixture of ice and salt. The larger flask is heated over a wire 
 gauze until the water just begins to boil ; a solution of 200 grammes 
 of sodium dichromate in 200 grammes of water which has been 
 treated with 100 grammes of alcohol is then added in a small 
 stream through the dropping funnel, the lower end of which is 
 about 3 cm. above the surface of the liquid in the flask. During 
 
 the addition of the mixture, it 
 will be unnecessary to heat the 
 flask, since the heat produced 
 by the reaction is sufficient 
 to cause ebullition. The alde- 
 hyde thus formed distils into 
 the receiver, besides some al- 
 cohol, water, and acetal. If 
 uncondensed vapours of the 
 aldehyde escape from the re- 
 ceiver, the mixture is admitted 
 to the flask more slowly. On 
 
 the other hand, if boiling is not caused by the flowing in of the 
 mixture, the reaction is assisted by heating with a small flame. 
 After all of the mixture has been added, the flask is heated for a 
 short time by a flame, until boiling begins. 
 
 Since the aldehyde cannot be obtained easily from the reaction- 
 products by fractional distillation, it is first converted into alde- 
 hyde-ammonia, which, on proper treatment, readily yields the 
 pure aldehyde. 
 
 The apparatus for this purpose is arranged as follows : A small 
 flask to contain the aldehyde, placed on a wire gauze, is connected 
 with a moderately large reflux condenser. Into the upper end 
 of the condenser is placed a cork bearing a n L -shaped glass tube, 
 which is connected with two wash-bottles, each containing 50 c.c. 
 of dried ether. After the condenser has been filled with water at 
 
ALIPHATIC SERIES 169 
 
 30 (the lower side-tube of the condenser is closed with rubber 
 tubing and a pinch-cock), the crude aldehyde is heated for 5-10 
 minutes to gentle boiling, and the aldehyde that is not condensed 
 passes over, and is absorbed by the ether. Should the ether begin 
 to ascend in the connecting tube, the flame must be somewhat 
 increased immediately. To obtain aldehyde-ammonia, a current 
 of dry ammonia (see page 382) is conducted, with the aid of a 
 wide adapter or funnel (Fig. 66), into the ethereal solution con- 
 tained in a beaker surrounded by a freezing mixture of ice and salt, 
 until the liquid smells strongly of it. After an hour, the aldehyde- 
 ammonia which has separated out is scraped from the sides of the 
 vessel and adapter with a spatula or knife, filtered with suction, 
 washed with a little ether, and then allowed to dry on filter-paper 
 in a desiccator. Yield, about 30 grammes. 
 
 In order to obtain pure aldehyde, 10 grammes of aldehyde- 
 ammonia are dissolved in 10 grammes of water, treated with a 
 cooled mixture of 15 grammes of concentrated sulphuric acid 
 and 20 grammes of water, and heated on the water-bath. Since 
 aldehyde has a low boiling-point (21), the receiver is connected 
 with the condenser by a cork, and well cooled with ice and salt. 
 
 Aldehydes can be obtained by the use of the general reaction, which 
 in many cases serves as a method of preparation, of extracting two 
 hydrogen atoms from a primary alcohol by oxidation. 
 
 /H 
 
 CH 3 .CH 2 .OH + O = CH 3 .C^ + H O 
 
 ^O 
 
 The name of th.e class of compounds is derived from this action : Alde- 
 hyde = Al(cohol)dehyd (rogenatus). As an oxidising agent in the 
 above case, chromic acid is the most suitable in the form of potassium, 
 or sodium dichromate in the presence of sulphuric acid : 
 
 Na 2 Cr 2 O 7 + 4 H 2 SO 4 = O 3 + (SO 4 ) 3 Cr 2 + Na 2 SO 4 + 4 H 2 O 
 
 The rather difficultly soluble potassium dichromate (i part dissolves in 
 10 parts water) was formerly generally used, but at present the more sol- 
 uble and cheaper sodium salt (i part dissolves in 3 parts of water) is em- 
 ployed wherever it is possible. But in the preparation of the simplest 
 aldehyde (formaldehyde) from an alcohol a different oxidising agent is 
 
SPECIAL PART 
 
 used, viz. the oxygen of the air. On passing a mixture of the vapour 
 of methyl alcohol and air over a heated copper spiral, formaldehyde is 
 produced. 
 
 While by the first reaction one proceeds from substances which in 
 comparison with the aldehydes are oxidation products of a lower order, 
 the aldehydes may also be obtained by a second method involving the 
 use of compounds of the same substitution series, viz. the dihalogen 
 derivatives of the hydrocarbons containing the group CHC1 2 or CHBr 2 . 
 If these are boiled with water, or, better, water containing sodium car- 
 bonate, potash, lead oxide, or calcium carbonate, etc., the two halogen 
 atoms are replaced by one oxygen atom : 
 
 CH 8 .CHC1 2 + H 2 O = CH 3 .CHO + 2. HC1 
 
 Ethylidene chloride 
 
 C 6 H 5 .CHC1 2 + H 2 = C 6 H 5 .CHO + 2 HC1 
 
 Ben/ylidene chloride = Benzaldehyde 
 
 Benzalchloride 
 
 This method is used on the large scale for the manufacture of the com- 
 mercially important benzaldehyde. It will be referred to under benzal- 
 dehyde. 
 
 Finally, aldehydes can be prepared from their oxidation products, 
 the carbonic acids, by two methods, one of which has been already 
 mentioned under acetic anhydride. If sodium amalgam is allowed to 
 act on acid-anhydrides, an aldehyde is first formed : 
 
 CH 3 .CO 
 CH 
 
 3 . 
 
 >0 + H 2 = CH 3 .CHO + CHg.CO.OH 
 3 .CO/ 
 
 But this reaction is of little practical value for the preparation of alde- 
 hydes. The second method, which is the real preparation method, 
 consists in the dry distillation of a mixture of the calcium or barium 
 salt of the acid with calcium or barium formate : 
 
 CH 3 .CO.Oca + H. CO. Oca = CH 3 .CHO + CaCO 
 
 (ca = 
 
 The lower members of the aldehyde series are colourless liquids, soluble 
 in water, possessing pungent odours. The intermediate members are 
 also liquids, but insoluble in water ; the higher members are solid, crys- 
 tallisable substances. The boiling-points of the aldehydes are lower 
 than those of the corresponding alcohols. 
 
ALIPHATIC SERIES I /I 
 
 jCHg.CHO Boiling-point, 21 
 
 <CH 3 .CH 2 .OH "78 
 
 fCH 3 .CH 2 .CHO " "50 
 
 lCH 3 .CH 2 .CH 2 .OH .... " 97 
 
 Aldehydes are oxidised to acids by free as well as combined oxygen 
 (compare benzaldehyde) : 
 
 CH 3 .CHO + O = CH 3 .CO.OH 
 
 Upon this action depends the fact that aldehydes cause metals to sepa- 
 rate from certain salts, e.g. silver nitrate : 
 
 CH, . CHO + Ag 2 = CH 3 . CO . OH + Ag,, 1 
 
 EXPERIMENT : Treat a few cubic centimetres of a diluted silver 
 nitrate solution with a few drops of ammonium hydroxide and 5 
 drops of aldehyde. Silver will be deposited in the form of a brill- 
 iant mirror on the walls of the vessel ; the deposition is especially 
 beautiful if the vessel has previously been treated with a solution 
 of caustic soda to remove any fatty matter. The reaction fre- 
 quently takes place at the ordinary temperature, but in many 
 cases only on gentle warming. The reaction is used for the 
 detection of aldehydes. 
 
 Another reaction which can also be employed for the recognition of 
 aldehydes, depends upon the fact that they give a red colour to fuchsine- 
 sulphurous acid. (Caro's reaction.) 
 
 EXPERIMENT : Fuchsine-sulphurous acid is prepared by dissolv- 
 ing fuchsine in water ; a sufficient quantity of the latter is taken 
 to prevent the solution from being too intense in colour. Sulphur 
 dioxide is conducted into this until a complete decolouration takes 
 place. To a few cubic centimetres of this solution add several drops 
 of aldehyde. On shaking, a violet-red colour will be produced. 
 
 Finally aldehydes may also be detected by a method depending upon 
 the fact that when treated with diazobenzene sulphonic acid and sodium 
 amalgam, they give a violet colour. 
 
 EXPERIMENT : To as much diazobenzene sulphonic acid as can 
 be held on the point of a knife, add 5 c.c. of water, a few drops 
 
 1 B. 15, 1635 and 1828. 
 
\J2 SPECIAL PART 
 
 of caustic soda, and then a few drops of aldehyde, and finally a 
 piece of solid sodium amalgam as large as a pea. After some 
 time the red-violet colour appears. 
 
 That aldehydes upon reduction pass over to primary alcohols has 
 been mentioned under acetic anhydride : 
 
 CH 3 . CHO + H 2 = CH 3 . CH 2 . OH 
 
 It is wholly characteristic of the aldehydes that they unite directly 
 (i) with ammonia, (2) sodium hydrogen sulphite, and (3) hydrocyanic 
 acid. The union with ammonia takes place in accordance with the 
 following equation : 
 
 CHo.CHO + NH 3 = CH 3 .CH<^ 
 
 \NH 2 
 
 Aldehyde-ammonia= 
 a-amidoethyl alcohol 
 
 This reaction is not so common as the second and third. Thus, 
 e.g., formic aldehyde and most of the aromatic aldehydes behave 
 differently toward ammonia. Whenever this reaction does take place 
 it can also be used with advantage for the purification of the aldehyde, 
 as in case of acetaldehyde ; by allowing the well -crystallised double 
 compound to separate out, on treating it with dilute sulphuric acid, the 
 free aldehyde is obtained. 
 
 The union with sodium hydrogen sulphite takes place in accordance 
 with the following equation : 
 
 /OH 
 CH 3 .CHO + SO 3 NaH = CH 3 .CH< 
 
 \S0 3 Na 
 
 Sodium-a-oxyethyl sulphonate 
 
 This reaction may also be used for the purification of aldehydes, 
 since when a concentrated solution of the sulphite is employed, the 
 double compound generally separates out in a crystallised condition. 
 The free aldehydes can be obtained from the sulphite compounds by 
 heating with dilute acids or alkali carbonates. (Compare benzalde- 
 hyde.) 
 
 EXPERIMENT : Treat 5 c.c. of a cooled concentrated solution of 
 sodium hydrogen sulphite with i c.c. of aldehyde and shake the 
 mixture. The double compound separates out in a crystallised 
 condition. 
 
ALIPHATIC SERIES 1/3 
 
 As distinguished from the union of aldehyde with ammonia, this re- 
 action is wholly general, and is frequently of great value in dealing with 
 the aldehydes of the aromatic series. It should be noticed in this con- 
 nection, that the ketones, which are closely related to the aldehydes, 
 show similar reactions : 
 
 CH 3 
 
 I /OH . 
 CH 3 .CO.CH 3 + SO 3 NaH = C< 
 
 Acetone I \SOoNa 
 
 The addition of hydrocyanic acid to ketones as well as to aldehyde? 
 is also general : 
 
 /OH 
 CHo.CHO + HCN = CH 3 .CH< 
 
 \CN 
 
 a-oxyproprionitrile 
 
 This reaction is of especial interest, since the addition of a new 
 carbon atom is brought about. Concerning the value of this reaction 
 for the synthesis of a-oxyacids, see Mandelic Nitrile, page 307. 
 
 Aldehydes possess further a marked tendency to combine with them- 
 selves (polymerise). 
 
 EXPERIMENT : Treat i c.c. of aldehyde with one drop of con- 
 centrated sulphuric acid. The aldehyde boils, and polymerisation 
 (condensation) takes place. 
 
 The compound thus obtained is called paraldehyde ; it boils much 
 higher (124) than ordinary aldehyde; the determination of its vapour 
 density shows that one molecule is composed of three molecules of 
 ordinary aldehyde. Paraldehyde does not show the characteristic alde- 
 hyde reactions ; on distillation with dilute sulphuric acid it is converted 
 back into the ordinary variety. For this reason it is believed that no 
 new union of carbon atoms takes place in the molecule, but that three 
 molecules are united by means of the oxygen atoms : 
 
 O - CH CH 3 
 
 CH 3 .CH<^ No 
 
 O - CH CH 3 
 
 If aldehyde is cooled and treated with sulphuric acid, or if at the 
 ordinary temperature gaseous hydrochloric acid, sulphur dioxide, or 
 other compounds are passed into it, a solid polymerisation product, 
 
1/4 SPECIAL PART 
 
 metaldehyde, is formed; this can also be converted back into the ordi- 
 nary variety. 
 
 The aldehydes undergo a wholly different kind of polymerisation 
 under certain conditions, concerning which reference must be made to 
 the chemical literature and treatises. For example, two molecules ot 
 acetaldehyde can unite with the formation of a compound in. which a 
 new carbon union is present. 
 
 CH 3 .CHO + CH 3 .CHO - CH 3 .CH(OH) .CH 2 .CHO 
 
 Aldol 
 
 This compound, as distinguished from paraldehyde and metaldehyde, 
 is a true aldehyde, in that it cannot be converted back to acetalde- 
 hyde. Aldol loses water easily, and is converted into an unsaturated 
 aldehyde : 
 
 CH 3 . CH(OH) . CH 2 . CHO = CH 3 . CH=CH . CHO -f- H 2 O 
 
 Crotonaldehyde 
 
 In connection with these condensations, it may be pointed out that 
 many aldehydes, when heated with alkalies, polymerise to resinous 
 products of high molecular weight (aldehyde resins). 
 
 EXPERIMENT : Treat a few cubic centimetres of caustic potash 
 solution with several drops of aldehyde, and warm. A yellow 
 colouration takes place with the separation of a resinous mass. 
 
 In order, finally, to represent the great activity of the aldehydes, the 
 following equations are given : 
 
 CH 3 . CHO + PC1 5 = CH 3 . CHC1 2 + POC1 3 
 
 Ethyhdene chloride 
 
 CH 3 .CHO + NH 2 .OH =CH 3 .CH=NOH + H 2 O 
 
 Aldoxime 
 
 CH 3 .CHO + NH 2 .NH.C 6 H 5 = CH 3 .CH N.NH.C 6 H 5 -f- H 2 O 
 
 Phenylhydrazine Hydrazone of aldehyde 
 
 OC 2 H 5 
 
 CH 3 . CHO + 2 C 2 H 5 . OH = CH 3 . CH<( -f H 2 O 
 
 X OC 2 H 5 
 
 f Acetal, the ether of aldehyde- "I 
 
 hydrate CH 3 . CH < g which does 
 
 [ not exist in the free condition J 
 
 / C 6 H 5 
 
 CH 3 . CHO + 2 C 6 H 6 = CH 3 . CH/ + H 2 O 
 
 Diphenyl ethane 
 
ALIPHATIC SERIES 175 
 
 9. REACTION : PREPARATION OP A PRIMARY AMINE FROM AN 
 ACID-AMIDE OF THE NEXT HIGHER SERIES 
 
 EXAMPLE : Methyl Amine from Acetamide 1 
 
 To a mixture of 25 grammes of acetamide, which has been 
 previously well pressed out on a porous plate, and 70 grammes 
 (23 c.c.) of bromine contained in a J-litre flask, add a solution of 
 40 grammes of caustic potash in 350 c.c. of water (the flask is well 
 cooled with water), until the brownish red colour formed at first is 
 changed to a bright yellow, for which the greater portion of the 
 potash solution will be required. This reaction : mixture is then, 
 in the course of a few minutes, allowed to flow from a dropping 
 funnel in a continuous stream into a litre flask containing a solution 
 of 80 grammes of caustic potash in 150 c.c. of water heated to 
 70-75. In case the temperature rises higher than 75, the flask 
 must be cooled by immersion for a short time in cold water. The 
 liquid is maintained at this temperature until it becomes colourless, 
 which usually requires a quarter to half hour. The methyl amine 
 is then distilled off with steam, and collected in a receiver contain- 
 ing a mixture of 60 grammes of concentrated hydrochloric acid 
 and 40 grammes of water. In order that the methyl amine may 
 be completely absorbed by the acid, the end of the condenser is 
 connected with an adapter which dips i cm. below the surface of 
 the liquid in the receiver. If a coil condenser is employed, the 
 end of it dips directly into the acid. As soon as the liquid in the 
 condenser no longer shows an alkaline reaction, the distillation is 
 discontinued. The methyl amine hydrochloride is partially evapo- 
 rated in a porcelain dish over a free flame, then to dryness on the 
 water-bath, and is finally heated for a short time in an air-bath at 
 1 00 to dusty dryness. In order to separate the methyl amine 
 salt from the ammonium chloride mixed with it, the finely pul- 
 verised substance is crystallised from absolute alcohol, and the 
 crystals separating out dried in a desiccator. Yield, varying. 
 
 1 B. 15, 762 ; B. 17, 1406 and 1920. 
 
176 SPECIAL PART 
 
 Under the discussion of acid-amides, it has already been mentioned 
 that the hydrogen of the amido group (NH 2 ) can be substituted by 
 bromine. If a 10 % solution of caustic potash is added to a mixture 
 of one molecule of the amide and one molecule of bromine, until the 
 brownish red colour of the latter has vanished, a monobromamide is 
 formed, e.g., in the above case, acetmonobromamide in accordance 
 with this equation : 
 
 CH, . CO . NH 2 + Br 2 + KOH = CH 3 . CO . NHBr + KBr + H 2 O 
 The monobromamide may be isolated in pure condition in the form 
 of colourless, hydrous crystals. If hydrobromic acid is abstracted, 
 no water being present, the position of the carbonyl group (CO) is 
 changed, and an ester of isocyanic acid is formed : 
 
 CH, . CONHBr = CH 3 . N=CO + HBr 
 
 Methyl isocyanate 
 
 If the attempt is made to eliminate hydrobromic acid in the presence 
 of water by the use of caustic potash solution, the above reaction takes 
 place, but the isocyanate is unstable in the presence of alkalies, and 
 decomposes immediately by taking up the water forming carbon dioxide 
 and a primary amine : 
 
 CH 3 . NCO + H 2 O = C0 2 + CH, . NH 2 
 
 Methyl amine 
 
 The two reactions may also be simply expressed as follows : 
 CH 3 . CO . NH 2 + O = CH 3 . NH 2 + CO 2 
 
 Bromine + 
 alkali 
 
 This reaction, discovered by A. W. Hofmann, is, therefore, in its last 
 phase, identical with the historical reaction of Wurtz, which led him, 
 in 1848, to the discovery of the primary amines. 
 
 The Hofmann reaction is capable of general application. By use of 
 it, the primary amine of the next lower series may be obtained from 
 any acid-amide, since the elimination of carbon dioxide takes place. 
 With the higher members of the series, the reaction in part proceeds still 
 further, since the bromine acts upon the primary amine to form a nitrile : 
 C 7 H 15 .CH 2 . NH 2 + Br 4 + 4NaOH = C 7 H 15 . C=N + 4NaBr + 4H 2 O 
 
 Octyl amine Octonitrile 
 
 There is thus obtained from the higher members (compounds having 
 five or more carbon atoms) of the amides, first the primary amine, and 
 secondly, the nitrile of the next lower acid. In the aromatic series, the 
 reaction for the preparation of primary amines, which contain the amido 
 group in the benzene ring, is not of general importance, since these 
 
ALIPHATIC SERIES 177 
 
 may be obtained from the easily accessible nitro-compounds ; and 
 since, on the other hand, if the above reaction is employed, bromine 
 substitution products are easily formed. But in those cases in which 
 the nitro-compound corresponding to the amine is not known, or can 
 be prepared only with difficulty, the reaction is also of importance in 
 the aromatic series. Two cases of this kind may be mentioned in this 
 place. If phenyl acetamide is treated in accordance with Hofmann's 
 reaction, there is formed in the usual way benzyl amine : 
 
 C 6 H, . CH 2 . CO . NH 2 + O = C 6 H 5 . CH 2 . NH 2 + CO 2 
 
 Phenyl acetamide Benzyl amine 
 
 Further, the reaction is of practical value in the preparation of o-amido- 
 benzoic acid, used in the manufacture of artificial indigo. If, as above, 
 bromine and caustic potash are allowed to act on phthalimide (techni- 
 cally bleaching powder is used), there is first formed, by the addition 
 of water, an acid-amide : 
 
 OK CO . NH 9 
 
 /OK / 
 
 o-C 6 H 4 < >NH + H 2 = C 6 H 4 < 
 \CO/ \ 
 
 CO . OH 
 
 which in accordance with the following reactions gives the amido-acid. 
 
 /CO . NH 2 /CO . NHBr 
 
 HBr 
 
 C 6 H + Br 2 = C 6 H 4 < 
 
 \CO . OH \CO . OH 
 
 /CO .NHBr /N=C=z O 
 
 C 6 H 4 < = C 6 H 4 < 
 
 \ 
 
 /NH 
 / 
 
 64 + HBr 
 
 \CO . OH \CO . OH 
 
 + H 2 = C 6 H / + C0 2 
 
 D . OH \CO . OH 
 
 Since the nitro-acid corresponding to the o-amido benzoic acid is dif- 
 ficult to obtain, and phthalimide is easily prepared (naphthalene is 
 changed to phthalic anhydride by oxidation, and when this is treated 
 with ammonia, phthalimide is formed with the separation of water), the 
 Hofmann reaction in this case gives a very convenient method of prep- 
 aration fcr the amido-acid. 
 
 Primary aliphatic amines can also be prepared according to the fol- 
 lowing equations : 
 
 (i) By the action of alcoholic ammonia on halogen alkyls : 
 
 CH 8 I + NH S = CH 3 . NH 2 4- HI 
 
 In this case, secondary and tertiary bases, or the corresponding ammo 
 nium compounds, are also formed. 
 
 N 
 
178 SPECIAL PART 
 
 (2) From alcohols and zinc chloride-ammonia : 
 
 C 2 H 5 .OH + NH 3 = C 2 H 5 .NH 2 + H 2 O 
 
 (3) By the reduction of nitriles (Mendius 1 reaction) : 
 
 CHg.CN + 2H 2 = CH 3 .CH 2 .NH 2 
 
 (4) By the reduction of nitro-compounds : 
 
 CH 3 .NO 2 + 3H 2 = CH 3 .NH 2 + 2H 2 O 
 
 (5) By the reduction of oximes and hydrazones : 
 
 CH 3 .CH=N.OH + 2 H 2 = CH 3 .CH 2 .NH 2 + H 2 O 
 
 Acetaldoxime 
 
 CH 3 . CH=N - NH . C 6 H 5 + 2 H 2 = CH 3 . CH 2 . NH 2 + C 6 H 5 . NH 2 
 
 Ethylidene phenyl hydrazone Aniline 
 
 The lowest members of the amines in the free condition are gaseous 
 compounds soluble in water, possessing odours suggestive of ammonia : 
 they differ from ammonia in being inflammable. 
 
 EXPERIMENT : Treat some solid methyl amine hydrochloride in 
 a small test-tube with a concentrated solution of caustic potash, or 
 caustic soda, and warm gently. A gas, smelling like ammonia, is 
 evolved, which burns with a pale flame. 
 
 The higher members are liquids or insoluble solids. Since they are 
 derivatives of ammonia, they possess basic properties, and, like ammo- 
 nia, unite with acids to form salts, the composition of which is analo- 
 gous to that of the ammonium compounds : 
 
 NH 3 . HC1 >- CH 3 . NH 2 . HC1 
 
 (NH 4 Cl) 2 PtCl 4 ^(CH 3 .NH 2 .HCl) 2 PtCl 4 
 
 NH 4 C1, AuCl 3 ^CH 8 .NH 2 .HC1, AuCl 3 
 
 The hydrochlorides of organic bases are distinguished from ammonium 
 chloride by their solubility in absolute alcohol. Use was made of this 
 property above. 
 
 The numerous reactions of the primary amines* need not be men- 
 tioned here, since, under the aromatic amines, frequent reference will 
 be made to them. At this place, one difference between the aromatic 
 and aliphatic amines will be pointed out. If nitrous acid is allowed to 
 
ALIPHATIC SERIES 179 
 
 act on an aliphatic primary amine, an alcohol is formed with evolution of 
 nitrogen : CRg ^ + NQOH = ^ . O H + N 2 + H 2 O 
 
 while, under these conditions, an aromatic amine is converted into a 
 diazo-compound (see Diazo-compounds). 
 
 10. REACTION: SYNTHESES OF KETONE ACID-ESTERS OR 
 POLYKETONES WITH SODIUM OR SODIUM ALCOHOLATE 
 
 EXAMPLE : Acetacetic Ester from Acetic Ester and Sodium 1 
 
 For .the successful preparation of acetacetic ester, the character 
 of the acetic ester used is of great importance, since, if it is com- 
 pletely free from alcohol, it will be attacked very slowly by sodium, 
 even on heating ; if, on the other hand, it contains too much alco- 
 hol, the sodium acts easily, but the yield of the product is varying 
 and usually small. According to the experiments of the author, 
 the following method of procedure gives a good yield and is one 
 that does not fail. 
 
 Purification of Acetic Ester : The acetic ester prepared accord- 
 ing to Reaction 6, even after it has been freed from acetic acid 
 and alcohol by shaking with sodium carbonate and calcium chloride 
 respectively, dried over calcium chloride, and finally rectified, is 
 not suitable for this preparation, since it reacts too violently with 
 sodium. But if it is allowed to stand, after distilling, for some 
 hours, over night at least, in a well-closed flask, over about \ its 
 volume of granulated calcium chloride, and is then filtered, it may 
 be used for the successful preparation of acetacetic ester. 
 
 If commercial acetic ester is to be used, it must be shaken with 
 a sodium carbonate solution, as described on page 157, treated 
 with calcium chloride solution, etc. ; in short, it is treated as the 
 crude product obtained in the preparation of acetic ester. Ob- 
 viously, it is also necessary to allow it to stand over night in 
 contact with calcium chloride, after the distillation. 
 
 The yield of acetacetic ester may be further increased if the 
 acetic ester, after being filtered from the calcium chloride, is again 
 distilled, care being taken to prevent the absorption of moisture. 
 All parts of the apparatus must be perfectly dried, and the end of 
 
 1 A. 186, 214. 
 
l8o SPECIAL PART 
 
 the condenser tube must be connected to the receiver (suction* 
 flask) by a good cork. 
 
 Preparation of Acetacetic Ester: 25 grammes of sodium from 
 which the outside layers have been removed are cut with the aid 
 of a sodium knife (Fig. 89) into pieces as thin as possible, and 
 placed in a dry litre-flask. After this is connected with a long 
 reflux condenser, inclined at an oblique angle, 250 grammes of 
 dried acetic ester is poured into the top of the condenser, by a 
 funnel which must not be attached to the condenser, but is 
 held in the hand, so that the air may escape. If the acetic ester 
 is added properly, no violent ebullition will occur, but at first a 
 gradual, gentle boiling. After 10 minutes, the flask is placed on 
 a previously heated water-bath, the temperature of which is so 
 regulated that the acetic ester boils but gently; the reaction- 
 mixture is heated until all the sodium is dissolved, which will 
 require from 3-4 hours. To the warm liquid is added a mixture 
 of 80 grammes of glacial acetic acid and 80 grammes of water, 
 until it just shows an acid reaction. If a thick, porridge-like 
 mass should separate out, this is again dissolved by vigorous 
 shaking, or carefully breaking up the small lumps with a glass 
 rod. To the liquid is then added an equal volume of a cold 
 saturated solution of sodium chloride, and the lower aqueous layer 
 is separated from the upper one, consisting of acetic ester and 
 acetacetic ester, by allowing it to run off from a dropping funnel. 
 Should a precipitate settle out on the addition of the salt solution, 
 it is dissolved by adding some water. To separate the acetacetic 
 ester from the main portion of the excess of the acetic ester used, 
 the mixture is distilled from a flask, heated by a free flame over 
 a wire gauze, or, more conveniently, without the wire gauze, with a 
 luminous flame. As soon as the thermometer indicates 95, the 
 heating is discontinued, and the residue is subjected to vacuum- 
 distillation, as described on page 25 . In place of the usual con- 
 denser, the outside jacket of a Liebig condenser is pushed over 
 the long side-tube of the distillation flask, and water is allowed 
 to circulate through it. The heating is done in an air-bath. 
 After small quantities of acetic ester, water, and acetic acid have 
 
ALIPHATIC SERIES l8l 
 
 passed over, the temperature becomes constant, and the main 
 portion of the acetacetic ester distils over within one degree. 
 The following table gives the boiling-points at various pressures, 
 A reference to this will show at what approximate points the col- 
 lection of the preparation should begin : 
 
 Boiling-point 71 at 12.5 mm. pressure. 
 
 " 74 " 14 " " 
 
 " 79 " 1 8 " " 
 
 " 88 " 29 " " 
 
 94 " 45 " 
 
 97 " 59 " 
 
 " 100 " 80 " " 
 
 The yield of acetacetic ester amounts to 55-60 grammes. 
 
 In the preparation of this substance, it must be borne in mind 
 that the experiment must be completed in one day. The opera- 
 tion should be begun in the morning, the acetic ester heated with 
 sodium at midday, and the experiment completed in the afternoon. 
 If the reaction is discontinued at any point, and the unfinished 
 preparation allowed to stand over night, the yield is materially 
 diminished. 
 
 The formation of acetacetic ester from acetic ester, discovered by 
 Geuther in 1863, takes place in accordance with the following equation : 
 
 CH 3 . CO |OC 2 H 5 + H.I CH 2 . CO . OC 2 H 5 
 
 = CH 3 .CO.CH 2 .COOC 2 H 5 + C 2 H 5 .OH 
 
 Acetacetic ester 
 
 But the mechanism of the reaction is much more complicated than 
 here indicated. . According to the views of Claisen, the sodium first 
 acts on the alcohol, which, as above mentioned, must be present in 
 small quantities, forming sodium alcoholate, and this unites with the 
 
 acetic ester as follows : 
 
 X)C 2 H 5 
 
 CH 3 .CO.OC 2 H 3 + C,H..ONa = CHo.C^-OC 2 H 5 
 
 \ONa 
 
 Reaction then takes place between this addition product and a second 
 molecule of acetic ester, with the elimination of two molecules of alcohol, 
 and the formation of the sodium salt of the acetacetic ester : 
 
1 82 SPECIAL PART 
 
 ONa = CH 3 .C=CH.CO.OC 2 H 5 + 2C 2 H 5 .OH 
 
 ONa 
 
 On acidifying with acetic acid, the sodium salt is decomposed with 
 the formation of the free ester, CH 3 .CzzCH .CO.OC 2 H 5 (enolform), 
 
 OH 
 
 which spontaneously changes into the desmotropic form (ketoform). 1 
 
 CH 3 .CO.CH 2 .CO.OC 2 H 5 . 
 
 In the form indicated above, the reaction is not capable of general 
 application ; but a reaction closely related to it, discovered by Claisen 
 and W. Wislicenus, is of general applicability, and is of great value in 
 synthetical operations; for this reason it will be briefly mentioned 
 here. If sodium alcoholate is allowed to act on a mixture of the esters 
 of two monobasic acids, a ketone acid-ester, having a constitution anal- 
 ogous to that of acetacetic ester, is formed by the action of the sodium 
 alcoholate on one of the esters with the elimination of alcohol, e.g. : 
 C 6 H 5 . CO |OC 2 H 5 + H| CH 2 . COOC 2 H 5 
 
 Benzoic ester Acetic ester 
 
 = C 6 H 5 . CO . CH 2 . CO . OC 2 H 5 + C 2 H 5 . OH 
 
 Benzoyl acetic ester 
 
 If one of the compounds is formic ester, esters of aldehyde-acids will 
 be obtained, e.g. : 
 
 H.CO. |OC 2 H 5 + H|CH 2 .CO.OC 2 H 5 = H.CO.CH 2 .CO.OC 2 H 5 
 
 Formic ester Acetic ester Formyl acetic ester 
 
 If one molecule of a dibasic ester is used, a ketone dicarbonic acid 
 ester will be formed, e.g. : 
 
 CO . |OC 2 H 5 H| . CH 2 . CO . OC 2 H 5 CO . CH 2 . CO . OC 2 H 5 
 
 + = I -f C 2 H 5 .OH 
 
 CO.OC 2 H 3 CO.OC 2 H 5 
 
 Oxalic ester Acetic ester Oxalacetic ester 
 
 In place of the acid-ester in the above reaction, which is susceptible 
 of many combinations, a ketone may be used ; a ketone acid-ester is 
 not formed, it is true, but polyketones, or ketone-aldehydes : 
 
 CH 3 . CO |OC 2 H 5 + H| CH 2 . CO . CH 8 
 
 Acetic ester Acetone 
 
 = CH 3 .CO.CH 2 .CO.CH 3 +C 2 H 5 .OH 
 
 _ Acetylacetone 
 
 1 B. 31, 205, and 601. 
 
ALIPHATIC SERIES 183 
 
 C 6 H 5 .CO OC 2 H 5 + H. CH 2 .CO.CH 
 
 Benzole ester - C gH 5 . CO . CH 2 . CO . CH 3 + C 2 H 5 . OH 
 
 Benzoylacetone 
 
 H.CO. JOC 2 H 5 + H.|CH 2 .CO.C 6 H 5 
 
 Formic ester Acetophenone 
 
 = O=CH . CH 2 . CO . C 6 H 5 + C 2 H 5 . OH 
 
 Benzoylaldehyde 
 
 These few examples are sufficient to show the many-sided applica- 
 tions of the above reaction. 
 
 The most remarkable characteristic of acetacetic ester is that a portion 
 of its hydrogen may be substituted by metals. If sodium is allowed to 
 act on it, the sodium salt is formed with the elimination of hydrogen : 
 
 CH 3 .CO.CHH.CO.OC.,H 5 + Na = CH 3 .CO.CHNa.CO.OC 2 H 5 + H 
 
 The same salt is also formed by shaking the ester with a solution of 
 sodium hydroxide. The reason for this phenomenon is to be sought 
 in the acidifying influence of the two neighbouring carbonyl (CO) 
 groups. 
 
 The synthetical importance of acetacetic ester depends on the fact 
 that the most various organic halogen substitution products react with 
 sodium acetacetic ester, the halogen uniting with the sodium, with the 
 condensation of the two remaining residues. Thus a large number of 
 compounds may be built up from their constituents. A few typical 
 examples may elucidate these statements: 
 
 (1) CH 8 .CO.CHNa.COOC 2 H 5 -f-ICH, 
 
 - CH 3 . CO . CH . CO . OC 2 H 5 + Nal 
 
 CH 3 
 
 Methylacetacetic ester 
 
 (2) CH 3 . CO . CHNa . CO . OC 2 H 3 + C 6 H, . CO . Cl 
 
 Benzoyl chloride 
 
 = CH 3 . CO . CH - CO . OC 2 H 5 -f NaCl 
 CO 
 
 Benzoylacetacetic ester 
 
 (3) CH 3 .CO.CHNa.COOC 2 H 5 + Cl.CH 2 .CO.OC 2 H 5 = 
 
 Chloracetic ester 
 
 CH 3 .CO.CH.CO.OC 2 H 5 
 
 CH 2 -f- NaCl. 
 
 COOCo 
 
 Acetsuccinic ester 
 
1 84 SPECIAL PART 
 
 In the compounds thus obtained the second methylene hydrogen 
 atom is also replaceable by sodium, and this salt is likewise capable of 
 entering into similar reactions, by which the number of derivatives is 
 largely increased, e.g. : 
 
 CH 3 .CO.C.Na-CO.OCoH i + IC 2 ri 5 = CH 3 .CO.C CO.OC,H 3 +NaI. 
 CH 3 CH, C 2 H. 
 
 Sodiummethylacetacetic ester Methylethylacetacetic ester 
 
 From all these compounds simpler ones may be obtained on saponi- 
 fication. The acetacetic ester breaks up in one of two ways, depend- 
 ing upon the conditions of the saponification : 
 
 Acetone 
 
 CH 3 .CO.iCH 2 .CO.OC 2 H 5 + 2HOH = 2CH,.CO.OH + C 2 H-.OH. 
 
 : Acetic acid 
 
 The first kind of decomposition is called "ketone decomposition," 
 the second, "acid decomposition. 1 ' Since, as shown above, either one 
 or both of the methylene hydrogen atoms in acetacetic ester can be 
 replaced by different radicals, X or Y, these substances yield either 
 mono- or di- substituted acetones : 
 
 X \ 
 X.CH..CO.CH.J and >CH.CO.CH, 
 
 Y/ 
 as well as mono- and di- substituted acetic acids, 
 
 X \ 
 X.CHn.CO.OH and >CH.CO.OH. 
 
 Y/ 
 
 The variety of the acetacetic ester syntheses is still further increased 
 by the fact that two molecules of the ester, by reaction with aldehydes 
 or alkylene bromides, may be united with one another by the most 
 various bivalent radicals. 
 
 According to recent researches of K. H. Meyer 1 and Knorr 2 espe- 
 cially, the optical behaviour of ordinary acetacetic ester indicates that 
 it consists of a mixture of the ketoform mainly, with a small quantity 
 of the enolform (/3-oxycrotonic ester), these two being in a state of 
 
 i A. 280, 212. 2 B. 44, 1138. 
 
ALIPHATIC SERIES 185 
 
 equilibrium. When the mixture is cooled with solid carbon dioxide 
 and ether to 78, the pure ketoform crystallises out. When the dry- 
 sodium salt of acetacetic ester is decomposed at a low temperature with 
 dry hydrogen chloride, pure enolform is obtained which does not 
 solidify at 78. It readily reacts with ferric chloride and is coloured 
 red. The ketoform does not behave in this manner. It is true that 
 the latter may also give the red colouration on standing for a short or 
 a longer period ; this, however, is due to the enolform produced in the 
 reaction mixture. The two forms are converted one into the other at 
 ordinary temperatures, the final product being the "equilibrium acetic 
 ester ".mentioned above. 
 
 The sodium salt of acetacetic ester is also derived, according to its 
 optical behaviour, from the enolform. The transpositions mentioned 
 above are brought about by the action of methyl iodide. A double 
 compound is first formed, with a subsequent decomposition into sodium 
 halide. 
 
 (a) CH 3 . C = CH . COOC 2 H 5 + ICH 3 = CH 3 . C CH . COOC 2 H 5 
 ONa ONa I CH 3 
 
 (J) CH 3 . C CH . COOCoH, - CH 3 . CO . CH . COOC 2 H 5 + Nal 
 
 /\, I I 
 
 OJNa I] CH 3 CH 3 
 
 11. REACTION: SYNTHESES OF THE HOMOLOGUES OF ACETIC ACID 
 BY MEANS OF MALONIC ESTER 
 
 EXAMPLE : Butyric Acid from Acetic Acid 
 (a) Preparation of Malonic Ester^ 
 
 Dissolve 50 grammes of chloracetic acid in 100 grammes of 
 water; warm gently (about 50), and neutralise with solid, dry, 
 potassium carbonate, for which 30-40 grammes will be required. 
 The solution is then heated gradually, with thorough stirring, while 
 40 grammes of pure, finely pulverised potassium cyanide are added. 
 (Use a sand-bath or asbestos plate, under the hood.) The forma- 
 
 1 A. 204, 121 ; Journ. Amer. Chem. Soc. 18, 1105. 
 
1 86 SPECIAL PART 
 
 tion of cyanacetic acid takes place, with vigorous ebullition. When 
 the reaction is complete, the mixture is evaporated as quickly as 
 possible on the sand-bath until a thermometer placed in the vis- 
 cous brownish salt indicates 135. Since the substance "bumps" 
 and spatters during the evaporation, it is constantly stirred with 
 the thermometer, the hand being protected by a glove or cloth. 
 It is allowed to cool, the stirring being continued during the cool- 
 ing, otherwise the product bakes into a hard, scarcely pulverisable 
 mass. It is then quickly powdered as finely as possible, placed in 
 a ^-litre flask provided with a reflux condenser, and treated with 
 20 c.c. of absolute alcohol. A cooled mixture of 80 c.c. of absolute 
 alcohol and 80 c.c. of concentrated sulphuric acid is then added 
 gradually, with good shaking, through the condenser tube. The 
 pasty mass is now heated, with frequent shaking, two hours in 
 a water-bath (hood) ; it is then well cooled, and treated with 150 
 c.c. of water (shaking). After the undissolved salt has been filtered 
 off with suction, it is washed on the filter several times with ether. 
 The filtrate, consisting of the water solution and the ether wash- 
 ings, is then carefully extracted with a sufficiently large quantity 
 of ether. The ethereal extract is shaken up in a separating funnel 
 with a concentrated solution of sodium carbonate until it no longer 
 shows an acid reaction. ( Owing to the copious evolution of gas the 
 funnel is not closed at first.) It is then dried over fused Glauber's 
 salt, and after the evaporation of the ether, distilled. Boiling- 
 point, 195. Yield, 45-50 grammes. 
 
 The compound may also be advantageously dried, without the 
 use of Glauber's salt, by evaporating off the ether, and heating 
 the residue about a quarter hour in a vacuum on a water-bath. 
 (Compare page 55.) 
 
 (b) The Introduction of an Ethyl Group 
 
 Dissolve 2.3 grammes of sodium in 25 grammes of absolute 
 alcohol in a small flask connected with a reflux condenser ; treat 
 the cooled solution gradually with 16 grammes malonic ester, 
 the transparent crystals of sodium ethylate separating out at first 
 pass over into a voluminous pasty mass of sodium malonic ester, 
 
ALIPHATIC SERIES 1 87 
 
 and then, with shaking, add through the condenser 20 grammes 
 of ethyl iodide in small portions. The mixture is then heated on 
 the water-bath until the liquid no longer shows an alkaline reac- 
 tion, for which one or two hours may be necessary. The alcohol 
 is then distilled off on an actively boiling water-bath, a thread being 
 placed in the flask to facilitate the boiling ; the residue is taken 
 up with water and extracted with ether, the ether evaporated, and 
 the residue distilled. Boiling-point, 206-208. Yield, about 15 
 grammes. 
 
 (c) Saponification of Ethyl Malonic Ester 
 
 For the saponification of the ester, a concentrated solution of 
 caustic potash is prepared ; for every gramme of the ester, a 
 solution of 1.25 grammes potassium hydroxide in i gramme of 
 water is used. The cooled solution is placed in a flask provided 
 with a reflux condenser ; through this the ester is gradually added ; 
 an emulsion is first formed, which soon solidifies to a white solid 
 mass, probably potassium ethylmalonic ester. On heating the mix- 
 ture on a water-bath a sudden energetic boiling-up sets in, especially 
 if the flask be shaken. The heat generated in the reaction causes 
 the alcohol, liberated in the saponification, to boil. After about 
 an hour's heating on the water-bath, the oily layer disappears, 
 showing that the saponification is complete. 
 
 The free ethyl malonic acid may be obtained by following either 
 of the methods given below : 
 
 (i) The solution is diluted with ii times the volume of water 
 previously used to dissolve the caustic potash. To this is added, 
 gradually, with cooling, a quantity of concentrated hydrochloric 
 acid equivalent to the total amount of caustic potash used (the 
 strength of the acid is determined by a hydrometer). The ethyl- 
 malonic acid liberated is taken up with not too little ether, the 
 ethereal solution dried over anhydrous Glauber's salt, the ether 
 evaporated, and the residue heated, with stirring, on a water-bath, 
 in a large watch crystal or dish, until it begins to solidify. After 
 cooling, it is pressed out on a drying plate and crystallised from 
 benzene. Melting-point, 111.5. Yield, about 7 grammes. 
 
1 88 SPECIAL PART 
 
 (2) The solution is diluted with the same volume of water pie- 
 viously used to dissolve the caustic potash. To this is added 
 carefully and with cooling concentrated hydrochloric acid, until an 
 acid reaction may just be detected. The ethyl malonic acid is 
 precipitated out in the form of its difficultly soluble calcium salt, 
 by the addition of a cold solution of calcium chloride, as concen- 
 trated as possible. This is filtered off, well pressed on a porous 
 plate, and the ethyl malonic acid liberated by treating carefully 
 with concentrated hydrochloric acid is obtained pure as in ( i ) . 
 
 (d) Elimination of Carbon Dioxide from Ethyl Malonic Acid 
 
 The ethyl malonic acid is placed in a small fractionating flask 
 provided with a long condensing tube supported in an oil-bath at 
 an oblique angle, so that its outlet tube is inclined upward. The 
 mouth is closed by a cork bearing a thermometer. The acid is 
 heated at 180, until carbon dioxide is no longer evolved, which 
 will require about a half-hour. The residue is distilled from the 
 same flask in the usual way ; the butyric acid passes over between 
 162-163. Yield, about 80-90% of the theory. 
 
 (a) In the first phase of the reaction which gives ethylmalonic ester, 
 the potassium cyanide acts on the chloracetic acid, or on its potassium 
 salt, with the formation of cyanacetic acid : 
 
 CH 2 C1.CO.OH + KCN = CH 2 .CN.CO.OH 
 
 Cyanacetic acid 
 
 As already mentioned in the preparation of acetonitrile, a halogen 
 united with aliphatic residues may generally be replaced by the cyanogen 
 group, on heating with potassium or silver cyanide. If alcohol and 
 sulphuric acid or ethylsulphuric acid are now allowed to act on the 
 cyanacetic acid, three reactions take place. At first there is an esterifi- 
 -ation in accordance with the equation : 
 
 CH 2 . CN . CO . OH + C 2 H 5 . OH = CH 2 . CN . CO . OC 2 H 5 + H 2 O 
 
 Cyanacetic ester 
 
 Under the discussion of acetic ester, it has already been brought 
 forward that, in general, acid esters can be obtained by treating a mix- 
 ture of the alcohol and acid with sulphuric acid. In the second place, 
 
ALIPHATIC SERIES I9 
 
 the sulphuric acid has a saponifying action on the cyanacetic ester, 
 t.e.j the cyanogen group is converted into carboxyl (COOH). 
 
 CO. OH 
 
 CH 2 .CN.CO.OC 2 H 5 + 2 H 2 O = CH 2 + NH 3 . 
 
 CO.OC 2 H 5 
 
 Acid ester of malonic acid 
 
 The carboxy] group thus formed is then acted on in the same way 
 as the carboxyl group of cyanacetic acid above, with the formation of 
 an ester : 
 
 CO. OH CO.OC 2 H 5 
 
 H 2 + C 9 H 6 .OH = CH, + H 2 
 
 I I 
 
 CO.OC 2 H, CO.OC 2 H 5 
 
 Malonicdiethyl ester 
 
 {b) The ester of malonic acid, like acetacetic ester, possesses the 
 property in virtue of which one of the two methylene hydrogen atoms 
 can be replaced by sodium, in consequence of the acid properties im- 
 parted by the two neighbouring carbonyl (CO) groups. When the 
 sodium compound is treated with organic halides, like alkyl halides, 
 halogen derivatives of acid-esters, acid-chlorides, etc., the sodium is 
 replaced by alkyl residues, acid residues, etc., just as in the case of the 
 closely related acetacetic ester. In the above-mentioned examples, the 
 sodium salt of the malonic ester is first formed from sodium alcoholate 
 and the ester : 
 
 CO.OCjjH- CO.OC 2 H 5 
 
 CH H + C 2 H 5 .0 Na = CHNa + C 2 H 5 .OH 
 
 CO.OC 2 H 5 CO.OC 2 H 5 
 
 Ethyl iodide reacts on this as follows : 
 
 CO.OC 2 H 5 CO.OC 2 H 5 
 
 CH|Na + I|C 2 H 3 =CH.C 2 H 5 -f Nal 
 
 I I 
 
 CO.OC 2 H S CO.OC 2 H 5 
 
 Ethylmalonicdiethyl ester 
 
 As in acetacetic ester, the second hydrogen of the malonic ester can 
 also be replaced by sodium ; cpnsequently the malonic ester is capable 
 
IQO SPECIAL PART 
 
 of reacting a second time with organic halides, so that disubstituted 
 malonic esters can also be prepared. 
 
 (c) The compounds thus obtained of the general formulae : 
 
 CO.OC,H 5 CO.OCoH. 
 
 I ! /x 
 
 CH-X and C< 
 I I\Y 
 
 CO.OC 2 H 5 CO.OC 2 H 5 
 
 are distinguished from the corresponding derivatives of acetacetic ester 
 in that on saponification they do not decompose, but yield the free 
 substituted malonic acids. Thus, the ethylmalonicdiethyl ester reacts 
 with caustic potash as follows : 
 
 CO.OC 2 H 5 KOH CO. OK 
 
 CH . C 2 H 5 + = CH . C 2 H 5 + 2 C 2 H 5 . CH 
 
 CO.OC 2 H, KOH CO. OK 
 
 (d) From the substituted malonic acid thus obtained, derivatives 
 of acetic acid may be prepared by heating it to a high temperature. 
 It is a general law that one carbon atom cannot hold two carboxyl 
 groups in combination at high temperatures, since carbon dioxide will 
 be eliminated from one. By this means, a dicarbonic acid is converted 
 into a monocarbonic acid, e.g. : 
 
 |CO.Q|H 
 
 1 CH 3 
 
 CH 2 + CO, 
 
 CO. OH 
 CO. OH 
 
 From the mono- or di- substituted malonic acid a substituted acetic 
 acid is obtained of the formula, 
 
 A, 
 
 CH..X CH< 
 
 or | \Y 
 
 :O.OH co. OH 
 
 Thus from ethylmalonic acid, there is formed ethylacetic acid = 
 butyric acid. If, instead of ethyl iodide, methyl or propyl iodide 
 is used, proprionic acid or valerianic acid respectively is obtained. 
 If two methyl groups are introduced into malonic ester, then, on 
 decomposition, a dimethylacetic or isobutyric acid will be formed. 
 
 As shown above, similar acids may be prepared from the acetacetic 
 ester. Since the decomposition of the acetacetic ester derivatives may 
 take place in two different ways (acid- and ketone-decomposition) ; 
 
ALIPHATIC SERIES igi 
 
 and since these decompositions frequently take place side by side, while 
 the malonic acid derivatives decompose in only one way, so in most 
 cases it is more advantageous to use the malonic ester for the synthesis 
 of the homologous fatty acids. 
 
 12. REACTION: PREPARATION OF A HYDROCARBON OF THE 
 ETHYLENE SERIES BY THE ELIMINATION OF WATER FROM AN 
 ALCOHOL. COMBINATION OF THE HYDROCARBON WITH BROMINE 
 
 EXAMPLE : Ethylene from Ethyl Alcohol. Ethylene Bromide 1 
 
 (a) From Ethyl Alcohol and Sulphuric Acid 
 
 A mixture of 25 grammes of alcohol, 150 grammes of concen- 
 trated sulphuric acid, and 30 grammes of coarse-grained sea-sand 
 (freed from fine particles) is heated, not too strongly, in a litre 
 round flask on a sand-bath or a wire gauze covered with thin 
 asbestos paper. As soon as an active evolution of ethylene takes 
 place, add, through a dropping funnel, a mixture of i part alcohol 
 and 2 parts concentrated sulphuric acid (made by pouring 150 
 grammes of alcohol into 300 grammes of sulphuric acid, with con- 
 stant stirring), slowly, so that a regular stream of gas is evolved. 
 If the mixture in the flask foams badly with a separation of car- 
 bon, it has been too strongly heated, and it is advisable to empty 
 the flask and begin the operation anew with a. smaller flame. In 
 order to free the ethylene from alcohol, ether, and sulphur dioxide, 
 it is passed through a wash-bottle containing sulphuric acid, and a 
 second one, provided with three tubulures, the central one sup- 
 plied with a -safety-tube, containing a dilute solution of caustic 
 soda. It then enters two wash-bottles, each containing 25 c.c. of 
 bromine, covered with a layer of water i cm. high. Since the 
 combination of ethylene with bromine causes the evolution of heat, 
 the bromine bottles are placed in thick-walled vessels filled 
 with cold water. In order to get rid of the bromine vapours 
 which escape from the last bottle, it is connected with the hood 
 or with a flask containing a solution of caustic soda ; to prevent the 
 
 1 A. 168, 64; A. 192, 244. 
 
IQ2 SPECIAL PART 
 
 caustic soda from being drawn back into the bromine bottle, the 
 delivery tube must not dip under the surface of the caustic soda, 
 and the stopper must be provided with canals cut in the sides. 
 As soon as the bromine is decolourised, which requires 4-5 
 hours under normal conditions, the operation is discontinued, 
 care being taken to disconnect all of the vessels immediately; 
 
 t 
 
 FIG. 67. 
 
 otherwise, in consequence of the cooling of the large flask, the 
 contents of the bottles will be drawn back. The ethylene bromide 
 is then washed repeatedly with water in a dropping funnel, and, 
 finally, with caustic soda solution. It is dried over calcium 
 chloride, and, on distillation, is obtained perfectly pure. Boiling- 
 point, 130. Yield, 125-150 grammes. 
 
 The addition of the alcohol-sulphuric acid mixture is often at- 
 tended with difficulty, in that as soon as the cock is opened, the gas 
 passes out through the funnel, thus preventing the entrance of the 
 mixture. This difficulty may be obviated by taking the precaution 
 of always keeping the stem of the funnel filled with the mixture. 
 Before the heating is begun, a portion of the mixture is placed in 
 a porcelain dish, the end of the stem of the funnel immersed 
 in it and filled by suction. The cock is then closed, the funnel 
 placed in the cork of the generating flask, and the heating 
 begun. 
 
ALIPHATIC SERIES 1 93 
 
 (fr) From Ethyl Alcohol and Phosphoric Acid 
 
 Separation of carbon and foaming will be prevented in the 
 preparation of ethylene when syrupy phosphoric acid is used in 
 place of sulphuric acid. A 200 c.c. round flask, with a wide mouth, 
 is provided with a three-hole cork. Through one hole passes a 
 thermometer extending to the bottom of the flask, through the 
 second hole is inserted a dropping funnel ; the stem of the latter 
 is at least 25 cm. long and is drawn to a fine point. The end of 
 the stem is kept only a few millimetres below the stopper. Through 
 the third hole passes a delivery tube, not too narrow, bent at right 
 angles. The tube is attached with rubber to a Wolfe flask, pro- 
 vided with two tubulures flush with the stoppers. The flask is 
 completely surrounded with broken ice. Then follow two wash- 
 bottles surrounded with ice for bromine, and finally a flask con- 
 taining a solution of sodium hydroxide, as in method (a). For 
 the preparation of ethylene 120 grammes of syrupy phosphoric 
 acid, sp, gr. 1.7-1.75, are placed in an open vessel and gradually 
 heated. The acid is stirred with a thermometer. At 160 water 
 begins to be given off. The heating is continued, until at 220 the 
 evolution of vapour is very slight. The acid is somewhat cooled 
 and poured into the flask. It is heated to 210-220 over an 
 asbestos gauze ; at this temperature ordinary alcohol is allowed to 
 run into the flask, drop by drop, from the funnel, the steam of 
 which should have been previously filled with alcohol, as in method 
 (a). A steady current of ethylene is thus evolved. The decolouri- 
 sation of bromine requires 3^-4-9- hours. The crude product is 
 purified as in method (a). 
 
 The hydrocarbons of the ethylene series may be prepared, in general, 
 by abstracting water from the corresponding alcohol, e.g. : 
 
 CH 3 . CH 2 . OH = CH2=CH 2 + H 2 O 
 
 If sulphuric acid or phosphoric acid is used as the dehydrating agent, 
 the reaction does not follow the above equation, but ethylsulphuric acid 
 or ethylphosphoric acid is first formed, and this, on heating, yields sul- 
 phuric acid or phosphoric acid. 
 
SPECIAL PART 
 
 C 2 H 5 . OH + S0 2 = S0 2 + H 2 O 
 
 X)H X>H 
 
 Ethylsulphuric add 
 
 X)C 2 H 5 X)H 
 
 $0 2 = C 2 H 4 + S0 2 . 
 
 NOH NDH 
 
 In many cases the elimination of water takes place so easily that 
 the use of concentrated sulphuric acid is unnecessary, since the diluted 
 acid answers the purpose. With the higher members of the series the 
 reaction is complicated by the fact that the simple alkylenes polymerise 
 under the influence of sulphuric acid. Thus there is formed, besides 
 butylene, C 4 H 8 , hydrocarbons having respectively twice and three times 
 its molecular weight, e.g. : 
 
 C 8 H 16 Dibutylene 
 
 C 12 H 24 Tributylene 
 
 In these cases it is much more convenient to prepare an ester from 
 the alcohol by the action of the chloride of a higher fatty acid, and 
 subjecting this to distillation by which it is decomposed into an hydro- 
 carbon of the ethylene series and the free fatty acid, e.g. : 
 
 C 15 H 31 .CO.OC 16 H 33 - C 14 H. r CO.OH 4- C 16 H 32 
 
 Cetyl palmitate Palmitic acid Hexadecylene 
 
 The first four members of the alkylene series are gases at ordinary 
 temperatures, which burn with strongly luminous, smoky flames. The 
 intermediate members are colourless liquids, not miscible with water, 
 which can be distilled at ordinary pressures without decomposition; 
 the higher members are solids, and can only be distilled without de- 
 composition in a vacuum. Chemically these compounds are charac- 
 terised primarily by the property of uniting with two univalent atoms, 
 or a univalent atom and a univalent radical, upon which the double 
 union is changed to single union. 
 
 They take up, especially in the presence of platinum-black, two 
 atoms of hydrogen, thus passing over to the hydrocarbons of the satu- 
 rated series (paraffins) : 
 
 CH,=CH, + H 9 = CH - CH. 
 
ALIPHATIC SERIES 1 95 
 
 Hydrogen halides may also be added to them ; hydriodic acid with 
 the greatest ease, hydrobromic acid with less, and hydrochloric acid 
 only with difficulty : 
 
 CH^CH, + HI = CH 3 .CH 2 I. 
 
 Ethyl iodide 
 
 The homologues of ethylene also form addition products ; the halo- 
 gen atom seeks that carbon atom which is combined with the smallest 
 number of hydrogen atoms : 
 
 CH 2 =CH . CH 3 + HI = CH 3 . CHI . CH 3 . 
 
 Propylene Isopropyl iodide 
 
 The constituents of water (H and OH) may also be added indirectly 
 to the alkylenes. If concentrated sulphuric acid be allowed to act on 
 one of them, it dissolves, forming a sulphuric acid ester : 
 
 /OH X)C 2 H 5 
 CHgzrCH, + S0 2 - S0 2 , 
 \DH \DH 
 
 If this is boiled with water, the ester is decomposed into alcohol and 
 sulphuric acid : 
 
 / /OC 2 H 5 
 
 SO 2 -fHOH = C 2 H 5 .OH 
 
 X)H X)H 
 
 so that finally H and OH have been added to ethylene : 
 CH^CH, H- H.OH - CH 3 .CH 2 .OH. 
 
 Analogous to the halogen atoms, the hydroxyl (OH) group unites 
 with that carbon atom holding in combination the smallest number of 
 hydrogen atoms. 
 
 The alkylenes take up two atoms of chlorine or bromine with great 
 ease: 
 
 CH 2 =CH 2 + C1 2 = CH 2 C1 - CH 2 C1 
 
 CH 2 =CH 2 + Br 2 = CH 2 Br - CH 2 Br. 
 
 Finally they combine directly with hypochlorous acid to form glycol- 
 chlorhydrines. 
 
 The reactions taking place in the formation of the alkylenes as well 
 as those in the formation of addition products are not only applicable 
 
196 SPECIAL PART 
 
 to the hydrocarbons but also to their substitution products. Thus, 
 e.g., unsaturated acids are commonly obtained from oxyacids by the 
 elimination of water : 
 
 CH 2 .OH.CH 2 .CO.OH = CH 2 =CH.CO.OH + H 2 O 
 
 /3-hydroxypropionic acid Acrylic acid 
 
 C 6 H 5 . CH . OH . CH 2 . CO . OH = C 6 H 5 . CHzzCH . CO . OH + H 2 O 
 
 Phenyllactic acid Cinnamic acid 
 
 All compounds in which the ethylene condition is present show the 
 addition phenomena, in accordance with the following equations : 
 
 CH 2 CH.CH 2 .OH + Br 2 = CH 2 Br - CHBr.CH 2 .OH 
 
 Allyl alcohol Dibromhydrine 
 
 CH 2 =CH . CO . OH + Br 2 = CH 2 Br - CHBr . CO . OH 
 
 Acrylic acid Dibrompropionic acid 
 
 C 6 H 5 .CH=CH.CO.OH + Br 2 = C 6 H 5 .CHBr - CHBr. CO. OH 
 
 Cinnamic acid Dibromhydrocinnamic acid 
 
 C 6 H 5 .CHziCH.CO.OH + HBr = C 6 H 5 .CHBr - CH 2 .CO .OH 
 
 Bromhydrocinnamic acid 
 
 C 6 H 5 . CH=CH 2 + Br 2 = C 6 H 5 .CHBr - CH 2 Br, 
 
 Styrene Styrene dibromide 
 
 C 6 H 5 .CH=CH.CO.OH4 C1.OH=C 6 H 5 .CH.OH.CHC1.CO.OH 
 
 Phenylchlorlactic acid 
 
 CH 2 CH.CO.OH + H 3 = CH 3 .CH 2 .CO.OH. 
 
 Acrylic acid Propionic acid 
 
 13. REACTION: REPLACEMENT OP HALOGEN ATOMS BY ALCOHOLIC 
 HYDROXYL GROUPS 
 
 EXAMPLE : Ethylene Alcohol (Glycol) from Ethylene Bromide 
 (a) Conversion of Ethylene Bromide into Glycoldiacetate 
 
 A mixture of 60 grammes ethylene bromide, 20 grammes glacial 
 acetic acid, and 60 grammes of freshly fused, finely pulverised 
 
ALIPHATIC SERIES 197 
 
 potassium acetate, 1 placed in a i-litre, short-necked, round ft>sk, 
 provided with a reflux condenser, is heated to active boiling for 
 two hours on a sand-bath over a large flame. The reaction prod- 
 uct is then distilled (with a condenser) over a large luminous 
 flame kept in continuous motion. Toward the end of the distilla- 
 tion the flame is gradually made non-luminous. The distillate is 
 then further treated with 60 grammes ethylene bromide and 80 
 grammes potassium acetate, and the mixture, as above, heated to 
 active boiling for two to three hours on a sand-bath. The re- 
 action product is then again distilled over (with a condenser) by 
 a luminous flame. The distillate is fractioned using a 10 cm. 
 long Hempel tube. The fractions are collected as follows : i. up 
 to 140; 2. from 140-175; 3. above 175. Fractions 2 and 3 
 are then again distilled separately. The pure glycoldiacetate 
 goes over between 180-190, the main portion at 186. Yield, 
 about 70 grammes. 
 
 If it is desired to increase the yield, the portion going over 
 under 180 is heated for three hours longer with potassium acetate. 
 The product is then treated as above described. This causes an 
 increase of about 15 grammes. 
 
 (fr) Saponification of Glycoldiacetate* 
 
 Glycoldiacetate is saponified by heating with a solution of hydro- 
 chloric acid in methyl alcohol. For this purpose a mixture of 
 100 grammes ordinary methyl alcohol and a quantity of compact 
 slaked lime (about one-third of the alcoholic volume) is heated 
 for several hours on a water-bath to active boiling, in a flask at- 
 
 1 Potassium acetate (Kalium aceticum pur. Ph. G. III.), differing from sodium 
 acetate (compare page 147), crystallises without water of crystallisation. Never- 
 theless, for this experiment it must be heated to fusion over a free flame in an iron 
 or nickel dish. The melted salt is poured into a shallow, flat iron or copper dish, 
 in a thin layer. While still warm it is pulverised as finely as possible, and must be 
 at once transferred to a bottle which is to be kept tightly closed. For this experi- 
 ment 200 grammes of the salt are fused. 
 
 2 A private method; by courtesy of Prof. Henry (Lowen). 
 
1 98 SPECIAL PART 
 
 tached to a reflux condenser. The dehydrated methyl alcohol is 
 now distilled. It is then subjected to fractional distillation, and 
 the portion distilling at 66-67 * s collected separately. 44 
 grammes of pure methyl alcohol are weighed in a small flask tared 
 with its delivery tube. Gaseous hydrochloric acid is now passed 
 into the alcohol with cooling under water, until a gain of i.i 
 grammes is obtained. Should the increase in weight be more than 
 this, a calculated quantity of pure methyl alcohol is added in order 
 to obtain a 2\ % alcoholic solution of hydrochloric acid, which is 
 the necessary strength. 
 
 In a flask, provided with a reflux condenser, 45.1 grammes of 
 the alcoholic solution of hydrochloric acid, and 50 grammes of 
 glycoldiacetate are heated on an actively boiling water-bath for 
 half an hour. The reaction mixture is then quickly distilled from 
 a water-bath with frequent shaking ; methyl alcohol and methyl 
 acetate will thus distil over, while glycol will remain in the flask 
 with a small quantity of unsaponified ester. These cannot be 
 separated from one another by distillation, as their boiling points 
 are close together. But the thick liquid in the flask is shaken twice 
 with an equal volume of dry ether, whereby glycoldiacetate is taken 
 up, while glycol remains undissolved. The ethereal layer is re- 
 moved, either by decantation, or by the use of a pipette. The gly- 
 col is then poured into a small fractionating flask connected with a 
 long condenser. During the distillation (heat slowly at first) a low- 
 boiling fraction (to 100) is first obtained, when the thermometer 
 rises rapidly to 190. The main portion of glycol distils over at 
 195. Yield about 80-90% of the theory (17-19 grammes). 
 
 This preparation shows a method for replacing a halogen atom by 
 an alcoholic hydroxyl group. In Reaction i the reverse replacement 
 was brought about, the substitution of a hydroxyl group by a halogen. 
 This method is obviously only of importance in those cases in which it 
 is more convenient to obtain the halogen derivative than the alco- 
 hol. Among the monacid alcohols it is of value for preparing 
 isopropyl alcohol, normal secondary butyl, and normal secondary hexyl 
 alcoholso 
 
ALIPHATIC SERIES 1 99 
 
 As stated on page 135, the action of hydriodic acid on polyacid alco- 
 hols does not yield, as might be expected, the poly-iodine derivatives, 
 but mono-iodine derivatives. Thus from glycerol, isopropyl iodide is 
 obtained ; from erythrite, normal secondary butyl iodide ; from man- 
 nite, the normal secondary hexyl iodide. These iodides, as pointed 
 out, may be converted into the corresponding alcohols. The method 
 is of practical value in the preparation of tertiary alcohols from acid- 
 chlorides and zinc alkyls. Butlerow^s synthesis. Compare page 146. 
 In this reaction the tertiary chloride is formed as an intermediate 
 product. The method is of importance for the preparation of di-acid 
 alcohols (glycols), especially for the a-glycols, in which the hydroxyl 
 groups are combined with the two adjacent carbon atoms. The 
 dibromides corresponding to these alcohols are easily obtained by the 
 . addition of bromine to the hydrocarbons of the ethylene series. In 
 this way glycol was first prepared by Wurtz. 1 
 
 Other glycols may be obtained in a similar manner, e.g., if allyl 
 bromide be treated with hydrobromic acid, trimethylene bromide is 
 formed, from which a /?-glycol trimethylene glycol may be obtained 
 by the above reaction. 
 
 If, to unsaturated mono-acid alcohols containing a double union, two 
 bromine atoms be added, dibrom-alcohols are obtained which, by re- 
 placing the bromine with hydroxyl, yield tri-acid alcohols : 
 
 H2=:CH.CH 2 Br + BrH = CH 2 Br.CH 2 .CH 2 Br >- CH 2 (OH) .CH 2 .CH 2 (OH) 
 
 Allyl bromide Trimethylene bromide Trimethylene glycol 
 
 CH 3 CH 3 CH 3 
 
 H CHBr CH(OH) 
 
 + Br 2 = | -^ | 
 H CHBr CH(OH) 
 
 I I I 
 
 CH 2 (OH) CH 2 (OH) CH,(OH) 
 
 From these examples the value of this method for obtaining alcohols is 
 evident. 
 
 Oxyaldehydes, oxyketones, and oxyacids may also be obtained by this 
 reaction, from the corresponding halogen compounds. Finally, it may 
 be employed to replace the halogen, in side-chains of aromatic com- 
 pounds, by hydroxyl. 
 
 The substitution of halogen atoms by hydroxyl groups may be done 
 
 1A. ch. (3), 55, 400. 
 
200 SPECIAL PART 
 
 by two methods: (i) Directly in a single operation. (2) In two re- 
 actions ; (a) by preparing an acid-ester of the desired alcohol, and 
 (b) subjecting this to saponification. If method (i ) be used, the halogen 
 derivative is heated with water at the ordinary pressure, or if necessary, 
 at an increased pressure. The same object is attained more quickly, 
 and in many cases with a better yield, by the addition to the reaction- 
 mixture of certain oxides, hydroxides, or carbonates. Silver oxide, lead 
 hydroxide, barium hydroxide, potassium or sodium carbonate, and others 
 may be used for this purpose. It appears to be true that a tertiary 
 halogen atom reacts more easily than a secondary or primary, and that 
 a secondary, more easily than a primary. By following this method, 
 glycol may be obtained .directly from ethylene bromide, if the latter be 
 heated with water and potassium carbonate : 
 
 CH.Br CH.,(OH) 
 
 4- K 2 CO 3 + H 9 O =| + CO 2 + 2 KBr 
 
 CH 2 Br CH 2 (OH) 
 
 The separation of the glycol from the large excess of water used is 
 troublesome. 
 
 In accordance with method (2) certain salts, as silver, potassium, or 
 sodium acetate are allowed to act on the halogen substitution product. 
 This results in the formation of an ester of the desired alcohol : 
 
 CH 2 Br CH.,.OOC.CH 3 
 
 | +2CH 3 .COOK = | ' +2 KBr 
 
 CH 2 Br CH 2 .OOC.CH, 
 
 Glycoldiacetate 
 
 The ester is then saponified under the proper conditions, upon which 
 the free alcohol is obtained : 
 
 CH 2 .OOC.CH 3 CH 2 (OH) 
 
 + 2HC1= I +2CH 8 .CO.C1. 
 
 CH 2 .OOC.CH 3 CH 2 (OH) 
 
 The acetyl chloride reacts with methyl alcohol forming methyl acetate 
 with the liberation of a fresh quantity of hydrochloric acid. Glycol is a 
 thick, colourless, odourless liquid, boiling at 195; it melts at 11.5 after 
 having been solidified by low temperature. Like all poly-acid alcohols, 
 it has a sweet taste. It is easily soluble in water and in alcohol, but not 
 in ether. Chemically it differs only from the mono-acid alcohols in its 
 ability to form mono- or di- derivatives according to the conditions : 
 
 CH 2 .ONa CH 2 .ONa CH,.OOC.CH 3 CH,.OOC.CH 3 
 
 and | |_ and I 
 
 CH 2 .OH CH a .ONa CH 2 .OH CH 2 .OOC.CH 3 
 
ALIPHATIC SERIES 2OI 
 
 Both hydroxyl groups are replaced by the action of phosphorus penta 
 chloride : 
 
 CH 2 (OH) CH 2 .C1 
 
 | + 2 PC1 5 = | +2 POC1 3 + 2 HC1 
 
 CH. 
 
 But if glycol be heated with hydrochloric acid, only one hydroxyl group 
 is replaced : 
 
 CH,(OH) CH 2 .C1 
 
 | + HC1 = | + H 2 
 
 CH 2 (OH) CH 2 (OH) 
 
 Ethylene chlorhydrine 
 
 From these so-called halogen hydrines, by the action of alkalies the 
 inner anhydrides of the glycols are obtained : 
 
 CH 9 .C1 O 
 
 | = I 
 
 CH 2 .(OH) CH 
 
 Ethylene oxide 
 
202 SPECIAL PART 
 
 TRANSITION FROM THE ALIPHATIC TO THE 
 AROMATIC SERIES 
 
 Dimethylcyclohexenone and s-Xylenol from Ethylidenebisacetacetic 
 Ester. (Ring Closing in a 1.5 Diketone. Knoevenagel Reaction. 1 ) 
 
 1. ETHYLIDENEBISACETACETIC ESTER 
 
 In a thick-walled flask closed by a cork bearing a thermometer 
 reaching almost to the bottom, treat 50 grammes of pure (in vac- 
 uum distilled), cooled acetacetic ester with 8.5 grammes of pure 
 aldehyde distilled just before the experiment. The flask is cooled 
 to 10-15 in a freezing mixture of ice and salt. To the reac- 
 tion-mixture is then added a few drops of diethyl amine from a 
 small medicine " dropper." In most cases no elevation of tem- 
 perature takes place at first. Since it is very difficult to obtain 
 acetacetic ester and aldehyde absolutely free from acids, the first 
 portions of the amine are neutralised by the acids present, and are 
 thus not available for the main reaction. The addition of the 
 amine is continued slowly until at a certain point an elevation of a 
 few degrees in the temperature is observed. Normally this should 
 occur on the addition of the first ten drops. When this takes 
 place, the liquid, clear at first, becomes turbid. From this point, 
 during the gradual addition of a further portion of ten drops of the 
 base, the temperature is slowly allowed to rise to o. The addi- 
 tion of the base in drops is continued, gradually and with frequent 
 shaking, until, collectively, 60 drops = 1.5 grammes have been 
 used. The length of the operation is about an hour. After the 
 reaction-mixture has stood a further quarter hour, it is removed 
 from the freezing mixture and allowed to come to the room tem- 
 perature. If, in consequence of a secondary reaction, the temper- 
 
 i A. 281, 25. 
 
TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 2O3 
 
 ature should go up to 20, the flask is cooled off a short time in 
 ice water. The reaction-product is a viscous, bright yellow liquid 
 in which numerous drops of water are suspended. It is allowed 
 to stand undisturbed until it solidifies to a crystalline mass, which 
 generally requires from two to three days. 
 
 A small specimen is pressed out on a porous plate and recrystal- 
 lised from diluted alcohol. Colourless needles are thus obtained 
 which melt at 79-80. Concerning the constitution of this sub- 
 stance see the remarks on page 207. 
 
 The solidification of the crude product may be hastened by 
 seeding it, after one day's standing, with crystals obtained in a 
 previous preparation. This is best done on the upper portion 
 of the flask, which is only moistened by the liquid. 
 
 2. DIMETHYLCYCLOHEXENONE 
 
 The crude product liquefied by heating in a water-bath is poured 
 into a mixture of 400 grammes of water and 100 grammes of con- 
 centrated sulphuric acid contained in a round litre flask provided 
 with a long reflux condenser. The reaction-mixture is heated to 
 lively boiling on a wire gauze ; a few pieces of unglazed porcelain 
 are placed in the flask to insure a regular ebullition. 
 
 After about seven hours' heating (the experiment should be 
 commenced in the morning of a working-day), the reflux con- 
 denser is replaced by an ordinary condenser, and steam is passed 
 into the mixture until the distillate measures about 100 c.c. The 
 flask is heated by a free flame up to the boiling-point of its con- 
 tents. The distillate is preserved in a well-closed vessel. 
 
 On the second day the mixture is again heated for seven hours 
 (with a reflux condenser, new porcelain scraps in the flask), and 
 then 100 c.c. are again distilled off with steam. This is repeated 
 on the third day, and finally stearn is passed into the mixture until 
 from a test portion of the distillate saturated with solid potash no 
 oil, or only a minute quantity, separates out. The three distillates 
 in which the reaction-product is for the most part dissolved are 
 now united. Solid potash is added until it is no longer dissolved. 
 
 For the success of the salting out, one must use anhydrous potash 
 
204 SPECIAL PART 
 
 as pure as possible. From the potash solution a brownish red oily 
 layer separates out : it consists of dimethylcyclohexenone and 
 alcohol. It is separated from the water solution m a dropping 
 funnel, and the alcohol is distilled off by the aid of a Hempel tube 
 10 cm. long rilled with glass beads. The residue is dried over 
 fused Glauber's salt and distilled from an ordinary fractionating 
 flask. The portion going over between 200-215 ^ s collected 
 separately. Boiling-point of the pure compound, 211. Yield, 
 15-20 grammes. 
 
 3. s-XYLENOL 
 
 A mixture, cooled by ice water, of 10 grammes of the ketone 
 dissolved in 20 grammes of glacial acetic acid (the acid must not 
 be allowed to solidify) is treated gradually with a mixture of 13 
 grammes of bromine and 10 grammes of glacial acetic acid from 
 a dropping funnel. The reaction-mixture is then allowed to stand, 
 under the liood, at least half a day, or better over night, at the 
 room temperature. Hydrobromic acid is evolved copiously. The 
 mixture is heated, with frequent shaking, about an hour on a water- 
 bath to about 50, the temperature is then increased until the 
 water boils, and the heating is continued until there is only a 
 slight evolution of hydrobromic acid. It is heated finally, using 
 an air condenser, on a wire gauze, to incipient ebullition of the 
 acetic acid, until the evolution of hydrobromic acid almost entirely 
 ceases. After cooling, it is poured carefully into a cooled solution 
 of 75 grammes of caustic potash in 150 grammes of water, upon 
 which only a small quantity of an oil should separate out. The 
 by-products insoluble in the alkaline solution are extracted with a 
 sufficient quantity of ether, the alkaline solution is saturated with 
 carbon dioxide, and the s-xylenol liberated is distilled over in the 
 presence of carbon dioxide with steam (use a three-hole cork). 
 The end of the distillation may be readily determined. So long 
 as the xylenol is coming over, a test of the distillate by adding a 
 few drops of bromine will show a precipitate of tribromxylenol. 
 
 If the distillate be allowed to stand in a cool place over night, 
 
TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 2O5 
 
 the larger portion of the xylenol will crystallise out. In order to 
 obtain the portion remaining dissolved, the crystals are filtered off, 
 and the filtrate saturated with solid salt and extracted with ether. 
 Melting-point of s-xylenol, 64. Boiling-point, 220-221. Yield, 
 5-6 grammes. 
 
 A better characterisation of this phenol is obtained by covering 
 a few drops of it in a test-tube with 5 c.c. of water and then adding 
 bromine drop by drop until the reddish brown colour of the latter 
 does not disappear. The excess of bromine is removed by the 
 addition of a solution of sulphur dioxide. The precipitate is 
 recrystallised from alcohol. There are thus obtained colourless 
 needles of tribromxylenol, which melt at 165. 
 
 i. Aldehydes unite, with the elimination of water, with compounds 
 containing the group CH 2 between two negative radicals (acetacetic 
 ester, malonic ester, acetylacetone, and others), in two ways. i. Equal 
 molecules unite in accordance with the following equation : 
 
 CH.R 
 
 Example 
 
 CH 3 CH, 
 
 CO CO 
 
 HC.CH 3 = H 2 O + C = CH .CH 3 
 
 I 
 C 
 
 COOC 2 H, COOC 2 H 5 
 
 Ethylideneacetacetic ester 
 
 2. The reaction may take place between one molecule of the alde- 
 hyde and two molecules of the other compound : 
 
 R X 
 CH - CH - CH 
 
206 SPECIAL PART 
 
 Example, carried out in practice: 
 
 CH 3 CH 3 CH 3 CH 3 
 
 CO CH 3 CO CO CH 3 CO 
 
 CH[Hl + CH|0 + H|CH = H 2 O + CH - CH - CH 
 COOC 2 H 5 COOC 2 K 5 COOC 2 H 5 COOC 2 H 5 
 
 a^tic ester. 
 
 For bringing about the first reaction the following-named substances 
 may be used as condensation agents : hydrochloric acid, acetic anhy- 
 dride, as well as primary and secondary amines (ethyl amine, diethyl 
 amine, piperidine, and others). For the second reaction the bases 
 mentioned may be used. A small quantity of one of these may pro- 
 duce large quantities of the condensation product : this is a case of a 
 so-called continuous reaction. It is probable that the amine reacts 
 first with the aldehyde, water being eliminated : i 
 
 N \ NR // 
 
 (R" = a bivalent radical or two univalent radicals.) 
 
 In the example above : 
 
 N(C 2 H 5 ) 2 
 
 /IN (V^ ons^o 
 
 CH 3 . CH IO + 2H N(C 2 H 5 ) 2 = CH 3 . CH < + H 2 O 
 
 X N(C 2 H 5 ) 2 
 
 The aldehyde derivative thus formed then acts upon the second com 
 pound with the regeneration of the amine : 
 
 X X 
 
 R.CH = NR, + H 2 C = RNH + C=CH.R 
 
 1 B. 31, 738. 
 
TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 2O/ 
 
 H\ CH = 2 HNR, 
 
 R X 
 
 I I 
 
 - CH - CH 
 i 
 Y 
 
 In the above example : 
 
 CH 3 R 
 CO CH 
 
 CH 3 
 CO 
 
 CHH + tfCc5yTN(QH,)j 
 
 f HCH 
 
 COOC 2 H 5 
 
 COO 
 
 CH, 
 
 CH 3 
 
 CO CH 3 CO 
 
 = 2 NH(C 2 H 5 ) 2 -f CH - CH - CH 
 
 C( 
 
 COOC 2 H 5 COOC 2 H 
 
 The amine thus regenerated carries over anew the aldehyde residue to 
 the acetacetic ester, and so on. 
 
 According to Rabe (A. 323, 83 and 332, i), the substance melting at 
 79-80 does not possess the constitution of an ethylidenebisacetacetic 
 ester, but it shows a desmotropic modification, forming a cyclic com- 
 pound as follows : 
 
 C 2 H 5 OOC - CH - CO 
 
 CH..CH CH H 
 
 C 2 H 5 OOC - CH - CO - CH 3 
 
 Ethylidenebisacetacetic ester" (liquid ) 
 
 C 2 H 5 OOC - CH - CO 
 CH 3 .CH CH 2 
 
 C 2 H 5 OOC - CH - C - OH 
 \CH 3 
 
 Dimethylcyclohexanoldicarbonic ester 
 (m. p. 79-80) 
 
 But compare the objections of Knoevenagel (B. 36, 2118). 
 
 2. Of the compounds which can be obtained by reaction (2), of 
 especial interest are those which, like the ethylidenebisacetacetic ester 
 prepared above, contain two carbonyl groups (i.5-diketones) and in 
 addition a methyl group. If such compounds are treated with those 
 
208 
 
 SPECIAL PART 
 
 substances which have the power to eliminate water (alkalies or acids), 
 six-membered carbon rings are formed as follows : 
 
 R.CH 
 X.CH- 
 
 X . CH - CO 
 
 CO -CH, 
 
 In the above example : 
 
 JO 
 CH Q .CH 
 
 CoH.OOC 
 
 >CH- 
 
 X - CH - CO 
 
 R ^ \* 
 
 K. . \^ri V^rl 
 
 X - CH - C - CH 3 
 C 9 H,OOC - CH - CO 
 
 H = H 9 O + 
 -CH 3 
 
 CH, 
 
 C 2 H 5 OOC 
 
 .CH CH 
 
 -\H-/-C 
 
 According to Rabe, ring formation takes place as indicated above, 
 and the change at this stage is as follows : 
 
 C 2 H 5 OOC - CH - CO 
 
 CH 3 . CH CH 
 
 = H 2 + S 
 
 C 2 H,OOC - CH - C - CH 3 
 
 C 2 H 5 OOC - CH - CO 
 
 CH 3 .CH CHjH"' 
 
 C 2 H 5 OOC - CH - C ! OH 
 \CH 3 
 
 Beside this ring closing, a second reaction takes place in the experiment 
 made above. The sulphuric acid saponifies the primarily formed acid- 
 ester, with the elimination of carbonic acid : 
 
 H 
 
 OOC.CH-CO 
 \ 
 
 \ S 
 
 :.CH-C- 
 
 CH = 2 C0 2 + 2 C 2 H 5 OH + CH 
 
 CH, 
 
 CH 2 -CO 
 
 ,-CH CH 
 
 \ // 
 
 CH 2 -C-CH 3 
 
 Dimethylcyclohexenone 
 
 This ring closing with 1.5 diketones is capable of many modifications. 
 By using formaldehyde, acetaldehyde, proprionaldehyde, benzaldehyde, 
 etc., R = H, CH 3 , C 2 H 5 , C 6 H 5 , etc. By using acetaceticester, acetylace- 
 tone, benzoylacetone, etc., X = COOC,H., CH 3 CO, C C H 5 CO, etc. 
 
 The many-sidedness of the reaction is materially increased by starting 
 with the unsymmetrical 1.5 diketone, e.g.: 
 
TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 2OQ 
 
 f" I 
 
 CO R CO 
 CH - CH - CH 
 :OOC 2 H 5 COOC 2 H 5 
 
 The nature of the reaction requires, however, that one of the two car- 
 bonyl groups must be connected with a methyl group, otherwise the 
 elimination of water cannot take place. The compounds so obtained 
 are all derivatives of the mother substance : 
 
 CH 2 - CO 
 CH 
 
 which is called cyclohexenone, and which may be considered as the 
 keto-derivative of tetrahydrobenzene 
 
 CH 2 -CH 2 
 
 <fH 2 CH 
 
 CHo - CH 
 
 This, therefore, is a transition from the aliphatic to the (hydro) aromatic 
 series. 
 
 This primarily obtained compound may by different reactions be 
 converted into other hydroaromatic and aromatic substances. If, e>g-, 
 the dimethylcyclohexenone be reduced, the ketone group is converted 
 into the secondary alcohol group, at the same time the double union is 
 severed, and two hydrogen atoms are added on, so that there is obtained 
 an alcohol derivative of hexahydro-benzene or -xylene. 
 
 OH 
 
 CH 2 - CH 
 CH 3 - CH CH 2 
 
 CH 2 - CH - CH 3 . 
 
 Hexahydroxylenol 
 
 If this compound be oxidised, the secondary alcohol group is changed 
 to a ketone group, and a keto-derivative of a hexahydroxylene is formed : 
 
210 SPECIAL PART 
 
 CH 2 - CO 
 CH 3 - CH CH 2 
 
 CH 2 - CH - CH 3 
 
 If the hexahydrogen addition alcohols be treated with substances hav- 
 ing the power to eliminate water, there is obtained a tetrahydrogen 
 addition product of the hydrocarbon, e.g. : 
 
 CH 2 - CH 
 
 / % 
 
 CH 3 . CH CH = Tetrahydroxylene 
 
 CH 2 -CH.CH 3 
 
 If in compounds like hexahydroxylenol, the hydroxyl be replaced by 
 iodine, and the resulting iodide reduced, there is obtained a hexahy- 
 drogen addition product of the hydrocarbon, e.g. : 
 
 CH 2 - CH 2 
 
 CH 3 . CH CH 2 = Hexahydroxylene 
 
 CH 2 -CH.CH 5 
 
 It is thus evident that the syntheses of a great variety of hydroaromatic 
 compounds are possible. 
 
 3. By these reactions the compounds of the pure aromatic series 
 may be reached. If bromine be allowed to act on the primarily arising 
 ring compound, as has been done practically, the double union is broken 
 up by the addition of two atoms of bromine : 
 
 CO 
 CHBr 
 
 CH 2 
 
 -CO 
 
 CH 2 
 
 CH 3 .CH 
 
 a 
 
 H + Br 2 = CH 3 .CH 
 
 \ 
 
 A 
 
 V 
 
 CH 2 
 
 -C - 
 
 CH, CH 2 
 
 / 
 - CBr - 
 
 CH 
 
 These dibromides are very unstable, and even in the cold give off two 
 molecules of hydrobromic acid : 
 
 CH, - CO CH 2 - CO 
 
 CH -C-CH, 
 
TRANSITION FROM ALIPHATIC TO AROMATIC SERIES 211 
 
 Finally, this unstable keto-form (CH 2 -CO) changes itself into the 
 stable enol-form (CH = C .OH), and the s-xylenol is obtained. 
 
 OH 
 
 CH = C 
 CH.C 
 
 CH-C 
 
 CH 
 
 For further information concerning the transition from aliphatic 
 to aromatic or hydroaromatic compounds, compare Bernthsen, XI Ed., 
 p. 382; Richter, X Ed., Vol. II, pp. 4-6, and 35; Krafft, IV Ed., 
 p. 446; Meyer- Jacobson, II Vol., p. 79. 
 
212 SPECIAL PART 
 
 II. AROMATIC SERIES 
 
 1. REACTION: NITRATION OF A HYDROCARBON 
 
 EXAMPLES: Nitrobenzene and Dinitrobenzene l 
 
 Nitrobenzene 
 
 To 150 grammes of concentrated sulphuric acid contained in a 
 J-litre flask, add gradually, and with frequent shaking, 100 grammes 
 of concentrated nitric acid (sp. gr. 1.4). After cooling the mix- 
 ture to the room temperature, by immersion in water, gradually 
 add 50 grammes of benzene, with frequent shaking. If the tem- 
 perature should rise above 50-60, the operation is interrupted, 
 and the flask immersed in water for a short time. When all of the 
 benzene has been added, a vertical air condenser is attached to 
 the flask ; it is then heated in a water-bath for an hour at 60* 
 (thermometer in the water) ; during the heating the flask is fre- 
 quently shaken. After cooling, the lower layer, consisting of sul- 
 phuric and nitric acids, is separated from the upper layer of 
 nitrobenzene in a separating funnel. The nitrobenzene is then 
 agitated in the funnel several times with water : it must be borne 
 in mind that the nitrobenzene now forms the lower layer. After 
 being washed, it is placed in a dry flask, and warmed on a water- 
 bath with calcium chloride until the liquid, milky at first, becomes 
 clear. 2 It is finally purified by distillation from a fractionating 
 flask provided with a long air condenser. Boiling-point, 206-207. 
 Yield, 60-70 grammes. 
 
 Dinitrobenzene 
 
 To a mixture of 25 grammes of concentrated sulphuric acid and 
 15 grammes of fuming nitric acid, 10 grammes of nitrobenzene are 
 
 1 A. 9, 47 ; 12, 305. Ostwald's Klassiker der exacten Wissenschaften Nr. 98. 
 
 2 The crude product, separated from the acid and treated with water, may also be 
 distilled with steam. The higher nitro derivatives are not volatile with steam. 
 The distillate is now treated as above. 
 
AROMATIC SERIES 213 
 
 gradually added (hood) ; the reaction-mixture is then heated for 
 half an hour on a water- bath, with frequent shaking; after cooling 
 somewhat, it is poured, with stirring, into cold water. The dinitro- 
 benzene which solidifies is filtered off, washed with water, pressed 
 out on a porous plate, and recrystallised from alcohol. Melting- 
 point, 90. Yield, 10-12 grammes. 
 
 The property of yielding nitro-derivatives, when treated with nitric 
 acid, is a characteristic of aromatic compounds. According to the 
 conditions under which the nitration is carried out, one or more nitro- 
 groups can be introduced at the same time. The above reactions take 
 place in accordance with the following equations : 
 
 C 6 H 6 + N0 2 . OH = C 6 H 5 . NO 2 + H 2 O, 
 
 C 6 H 5 . NO 2 + NO 2 . OH = C 6 H 4 . (NO 2 ) 2 + H 2 O. 
 
 If a saturated aliphatic residue is present in an aromatic compound, 
 the nitration under the above conditions always affects the benzene 
 ring, and not the side-chain. Since the benzene carbon atoms are in 
 combination with only one hydrogen atom, the nitro-compounds ob- 
 tained on nitration are tertiary ; they therefore do not have the power 
 to form salts, nitrolic acids, or pseudo-nitroles, like the primary and 
 secondary nitro-compounds. 
 
 Recently the nitro-group has been introduced directly into the side- 
 chain. 1 If, e.g., toluene or ethyl benzene be heated with weak nitric 
 acid (sp. gr. 1.076) in a bomb up to about 100, phenylnitromethane, 
 C 6 H S . CH 2 . NO 2 , or phenylnitroethane, C 6 H 5 . CH . NO 2 . CH 3 is ob- 
 tained. 
 
 Not only can the mother substances, the aromatic hydrocarbons, but 
 all their derivatives, as phenols, amines, aldehydes, acids, etc., undergo 
 similar reactions. But the nitration does not take place in every case 
 with the same. ease. In each case, therefore, the most favourable con- 
 ditions for the experiment must be determined. If a compound is very 
 easily nitrated, the nitration may be effected, according to the condi- 
 tions, by nitric acid diluted with water, or the substance may be dis- 
 solved in a solvent which is not attacked by nitric acid ; glacial acetic 
 acid is frequently used for this purpose, and then treated with nitric 
 acid. The reverse process may also be employed, i.e. the substance is 
 added to a mixture of nitric acid and water, or nitric acid and glacial 
 acetic acid. If a substance is moderately difficult to nitrate, it is added 
 
 1 B. 27. Ref. 194 and 468. 
 
214 SPECIAL PART 
 
 to concentrated or fuming nitric acid. If the nitration is difficult, the 
 elimination of water is facilitated by the addition of concentrated sul- 
 phuric acid to ordinary or fuming nitric acid. In the nitration, tha 
 substance may either be added to the mixture of nitric acid and sulphuric 
 acid, or the nitric acid is added to the substance dissolved in concen- 
 trated sulphuric acid. In working with sulphuric acid solutions, at times 
 either potassium nitrate or sodium nitrate may be used instead of nitric 
 acid. The three nitration methods just described may be still further 
 modified in two ways: (i) the temperature may be varied; (2) the 
 quantity of nitric acid may be varied. The nitration can be effected in 
 a freezing mixture, in ice, or in water, by gentle heating, or finally, at 
 the boiling temperature. Further, the theoretical amount of nitric acid, 
 or an excess, may be used. In order to determine which of these nu- 
 merous modifications will give the best results, preliminary experiments 
 on a small scale must be made. Since the nitro-compounds are gener- 
 ally insoluble in water, or difficultly soluble, they can be separated from 
 the nitrating mixture by diluting it with water, or in many cases better, 
 with a solution of common salt. 
 
 The chemical character of a substance is not changed in kind, but in 
 degree, by the introduction of a nitro-group. Thus, the nitro-derivatives 
 of the hydrocarbons are indifferent compounds like the hydrocarbons. 
 If a nitro-group is introduced into a compound of an acid nature like 
 phenol, it becomes more strongly acid, e.g. the nitro-phenols are more 
 strongly acid than phenol. When a nitro-group is introduced in a basic 
 compound, the resulting substance is less basic ; e.g. nitro-aniline is less 
 basic than aniline. 
 
 The great importance of the nitro-compounds is due to their behav- 
 iour on reduction ; this will be considered under the next preparations. 
 
 Concerning the introduction of the nitro-group, 1 the following laws 
 are of general application. 
 
 The introduction of one nitro-group in the benzene molecule can, 
 obviously, only result in the formation of one mononitrobenzene. If an 
 alkyl radical is present in the benzene molecule, the riitro-groups enter 
 the ortho- and para-, but only to a slight extent the meta-position to the 
 radical. On nitrating toluene, e.g., there are formed almost exclusively : 
 
 CH 3 CH 3 
 
 I I 
 
 NO 2 
 
 and 
 
 NO, 
 
 1 The same laws apply also to the introduction of halogen and sulphonic acid 
 groups. 
 
AROMATIC SERIES 21 5 
 
 The nitro-groups seek the same position when a benzene-hydrogen 
 atom has been substituted by hydroxyl. Thus, e.g., phenol gives on 
 nitration a mixture of o- and p-nitrophenol. On the other hand, if a 
 compound contains an aldehyde-, carboxyl-, or cyanogen-group, on ni- 
 tration the nitro-group goes in the meta-position to this. Benzaldehyde, 
 benzoic acid, and benzonitrile give on nitration respectively : 
 
 CHO CO. OH 
 
 If a compound already contains a nitro-group, a second one will take 
 the meta-position to this. Thus, on nitrating nitrobenzene, m-dinitro- 
 benzene is formed. O-nitrotoluene or o-nitrophenol yield on nitrating : 
 
 NO 2 
 
 respectively. 
 
 From m-nitrobenzoic acid the following dinitrobenzoic acid is formed : 
 
 CO. OH 
 N0 2 . 
 
 The nitro-compounds are in part liquids, in part solids ; in case 
 these latter distil without decomposition, they possess a higher boiling- 
 point than the mother substance. 
 
 2. REACTION.: REDUCTION OP A NITRO-COMPOUND TO AN AMINE 
 
 EXAMPLES: (i) Aniline from Nitrobenzene 1 
 
 (2) Nitroaniline from Dinitrobenzene 
 
 A mixture of 90 grammes of granulated tin 2 and 50 grammes 
 of nitrobenzene is placed in a i^-liter round flask. To this are 
 gradually added 200 grammes of concentrated hydrochloric acid 
 
 1 A. 44, 283. 
 
 2 If granulated tin is not at hand, it may be prepared by melting block-tin in an 
 iron spoon over a blast flame. The molten mass is allowed to fall in drops into a 
 pail of water from a height of 5-1 metre. 
 
2l6 SPECIAL PART 
 
 in the following manner : At first only about one-tenth of the 
 acid is added ; an air condenser, not too narrow, is then attached 
 to the flask and the mixture well shaken. After a short time it 
 becomes warm, and finally an active ebullition takes place. As 
 soon as this happens, the flask is immersed in cold water until the 
 reaction has moderated. The second tenth of the acid is then 
 added, and the above operation repeated. After one half of the 
 acid has been used, the reaction becomes less violent, and the 
 second half may be added in larger portions. In order to effect 
 the reduction of the nitrobenzene completely, the mixture is 
 finally heated one hour on the water-bath. To separate the free 
 aniline, the warm solution is treated with 100 c.c. of water, then a 
 solution of 150 grammes of caustic soda in 200 grammes of water 
 is gradually added. The mixture should finally give a strongly 
 alkaline reaction. If the action of the caustic soda causes the 
 liquid to boil, the flask is cooled by water for a short time, before 
 a further addition of caustic soda. When all of the solution has 
 been added, a long condenser is attached to the flask, and steam 
 is passed into the hot liquid, upon which aniline, as a colourless 
 oil, and water pass over, the aniline collecting under the water. 
 As soon as the distillate no longer appears milky, and becomes 
 clear, the receiver is changed and about 300 c.c. more of the 
 liquid distilled over. The distillates are mixed, treated with 25 
 grammes of finely powdered sodium chloride for every 100 c.c. 
 of the liquid, shaken until all the salt is dissolved, and the aniline 
 extracted with ether. After the ethereal solution has been dried 
 by treating it with a few pieces of solid potassium hydroxide, 
 the ether is evaporated and the aniline subjected to distillation. 
 Boiling-point, 182. Yield, 90-100% of the theory. If the 
 circumstances are such as not to permit the experiment to be 
 completed without interruption, it is so arranged that the neu- 
 tralisation with sodium hydroxide, and the distillation with steam 
 immediately following, may take place within a short time, so that 
 the heat of neutralisation may be utilised. 
 
 To the nitro-compounds of the aromatic series, as well as those of 
 the aliphatic series, belongs the property of being converted into primary 
 amines on energetic reduction. For the reduction of every nitro-group, 
 
AROMATIC SERIES 21 7 
 
 six atoms of hydrogen are necessary, and the following equation is th 
 general expression of the reaction : 
 
 X . NO 2 + 3 H 2 = X . NH 2 + 2 H 2 O. 
 
 For the reduction of nitro-compounds on the small scale in the 
 laboratory, it is most convenient to use, as the reducing agent, granu- 
 lated tin and hydrochloric acid, or stannous chloride and hydrochloric 
 acid : 
 
 (1) 2C 6 H 5 .NO 2 + 3Sn + I2HC1 = 2C 6 H 5 . NH 2 + 3 SnCl 4 + 4H 2 O, 
 
 (2) C 6 H 5 . N0 2 + 3 SnCl 2 + 6 HC1 = C 6 H 5 . NH 2 + 3 SnCl 4 + 2 H 2 O. 
 
 To i molecule of a mononitro-compound, \\ atoms of tin, or 3 mole- 
 cules of stannous chloride, are therefore used. In calculating the amount 
 of the latter necessary for a reaction, it is to be remembered that the salt 
 crystallises with two molecules of water (SnCl 2 + 2 H 2 O). If the re- 
 duction is to be effected by metallic tin, double the above quantity is 
 frequently used, i.e. to i nitro-group, 3 atoms of tin. In this case, the 
 tin is not converted into stannic chloride, but into stannous chloride : 
 
 C 6 H 5 . NO 2 + 3 Sn + 6 HC1 = C 6 H 5 . NH 2 + 3 SnCl 2 + 2 H,O 
 
 Since, in the cases mentioned, hydrochloric acid is always present 
 in excess, and the amines unite with it to form soluble salts, the end 
 of the operation occurs when no more of the insoluble nitro-compound 
 is present, and the reaction-mixture dissolves clear in water. In order 
 to get the free amine from the acid mixture, various methods may be 
 employed. If, as in the above example, the amine is volatile with 
 steam, and insoluble in alkali, then the acid solution is treated with 
 caustic potash, or caustic soda, until the oxide of tin which separates 
 out at first is redissolved in the excess of alkali ; the liberated amine 
 is driven over with steam. Further, volatile or non-volatile amines 
 can be extracted from an alkaline solution by a proper solvent, like 
 ether. But this process is often troublesome, since the alkaline tin 
 solution forms an emulsion with ether, which subsides with great diffi- 
 culty. If the free amine is solid, it may be obtained by filtering off the 
 alkaline liquid. In many cases, where a non-volatile amine is under 
 examination, it is advisable to precipitate the tin before liberating the 
 amine. This is done by diluting the acid solution with much water, 
 heating on the water-bath, and as soon as the liquid has reached the 
 temperature of the bath, hydrogen sulphide is passed into it. The tin 
 is precipitated as stannous or stannic sulphide ; this is separated from 
 
2l8 SPECIAL PART 
 
 the amine hydrochloride by filtering. Since tin, in the presence of a 
 large excess of hydrochloric acid, is precipitated only with difficulty by 
 hydrogen sulphide, it is frequently necessary to drive off the excess 
 of the acid before treating with hydrogen sulphide. This is done by 
 evaporating to dryness on the water-bath. 
 
 After the tin sulphide has been filtered off, a portion of the filtrate 
 is tested with hydrogen -sulphide for tin ; if it should be present, the 
 whole filtrate is evaporated on the water-bath, as completely as possible, 
 to remove the hydrochloric acid, then diluted with water, and hydrogen 
 sulphide is again passed into it. At times, the amine forms with 
 hydrochloric acid, a difficultly soluble salt, or the amine hydrochloride 
 combines with the tin chloride to form a difficultly soluble double salt. 
 In this case, the isolation of the amine may be facilitated by filtering 
 it off, washing with hydrochloric acid, and pressing out on a porous 
 plate, if necessary. If one is dealing with amines, which, like amido- 
 acids, possess an acid character, obviously, these cannot be separated 
 by the use of an alkali, as in the above example. In a case of this 
 kind, the tin is always removed first, the acid solution evaporated to 
 dryness, and the amido-compound is now liberated by the addition 
 of sodium acetate. With amido-phenols, sodium hydrogen carbonate, 
 sodium carbonate, or sodium sulphite may be used to decompose the 
 hydrochloric acid salt. 
 
 In the laboratory, other metals, like iron, zinc, etc., in connection 
 with an acid, are only rarely used in the place of tin or stannous 
 chloride, for the reduction of nitro-compounds. On the large scale, 
 iron, owing to its cheapness, is used in the preparation of bases like 
 aniline, toluidine, a-naphthyl amine, etc., from the corresponding nitro- 
 compounds. By the use of iron and hydrochloric acid, the reduction 
 should theoretically take place in accordance with the following equa- 
 tion: 
 
 C 6 H 5 . NO 2 + 3 Fe + 6 HC1 = 3 FeCl 2 + 2 H 2 O + C 6 H 5 . NH 2 . 
 
 As a matter of fact, on the large scale, much less hydrochloric acid 
 (only L) is used than that required by the above equation. In the 
 presence of ferrous chloride, the nitro-compound is reduced by the iron 
 without the action of hydrochloric acid, according to the equation : 
 
 C 6 H 5 . NO 2 + 2 Fe + 4 H 2 O = C 6 H 5 . NH 2 + 2 Fe(OH) 3 
 
 For the neutralisation of the hydrochloric acid, a small quantity of 
 which is always used on the large scale, slaked lime is employed in 
 preference to the more costly alkalies. 
 
AROMATIC SERIES 2IQ 
 
 The complete reduction of nitro-compounds containing several nitro- 
 groups is conducted in the same way as for mononitro-compounds. 
 If it is desired to reduce but one or two of several nitro-groups, it 
 cannot be done by adding just the calculated amount of the reducing 
 agent ; for cases of this kind, special methods are necessary. For this 
 purpose, hydrogen sulphide in the presence of ammonia or ammonium 
 sulphide is often used for the reduction : 
 
 H 2 S = H 2 -f S 
 
 The compound to be reduced is dissolved in water or alcohol, accord- 
 ing to circumstances, treated with ammonia, heated, and hydrogen 
 sulphide passed into it ; or it is heated in a water or alcohol solution 
 with a previously prepared water or alcohol solution of ammonium 
 sulphide. In this way, e.g., dinitrohydrocarbons may be converted 
 into nitro-amines. A second method, which may be generally used for 
 the reduction, step by step, of compounds containing several nitro-groups, 
 is this : An alcoholic solution of the theoretical amount of stannous 
 chloride saturated with hydrochloric acid is gradually allowed to flow 
 into an alcoholic solution of the substance to be reduced, which is well 
 cooled, and constantly shaken. (B. 19, 2161.) 
 
 EXPERIMENT : l The recrystallised dinitrobenzene is dissolved in 
 alcohol (4 grammes alcohol to i gramme dinitrobenzene), in a 
 flask, the solution is quickly cooled down, upon which a portion 
 of the dinitrobenzene separates out ; it is then treated with 0.8 
 gramme of concentrated ammonia for i gramme dinitrobenzene 
 (the ordinary dilute solution of ammonia employed as a reagent 
 must not be used). After the flask and its contents have been 
 tared, the mixture is saturated with hydrogen sulphide at the 
 ordinary temperature ; the current of hydrogen sulphide is then 
 shut off, and the flask, provided with a reflux condenser, is heated 
 for about half an hour on a water-bath. It is then allowed to cool 
 to the ordinary temperature, and hydrogen sulphide again passed 
 into it to saturation, etc. This operation is repeated until there 
 is an increase of 0.6 gramme in weight for every gramme of dini- 
 trobenzene used. If in consequence of insufficient cooling the 
 required increase in weight does not take place, hydrogen sulphide 
 
 i A. 176 44. 
 
22O SPECIAL PART 
 
 is again passed into the mixture. It is then diluted with water, 
 the precipitate filtered off, washed with water, and extracted 
 several times by warming with dilute hydrochloric acid. From 
 the acid filtrate, the nitro-aniline is set free by neutralising with 
 ammonium hydroxide ; it is recrystallised from water. Melting- 
 point, 114. Yield, 70-80% of the theory. 
 
 /NO 9 /NO 2 
 
 CflH/ > 3 H 2 S=C 6 H 4 <( +2H 2 + 3 S 
 \NO 2 \NH 2 
 
 Special methods are necessary for the reduction of nitro-compounds 
 containing groups capable of being acted upon by hydrogen, e.g., an 
 aldehyde-group, an unsaturated side-chain, etc. In cases of this kind, 
 ferrous hydroxide is frequently used : 
 
 2 Fe(OH) 2 + 2 H 2 O = 2 Fe(OH) 3 + H 
 
 2 
 
 The reduction is effected by adding to the substance to be reduced, 
 in the presence of an alkali (potassium-, sodium-, or barium-hydrox- 
 ide), a weighed quantity of ferrous sulphate. By this reaction, o-nitro- 
 benzaldehyde is reduced to o-amidobenzaldehyde ; o-nitrocinnamic acid 
 to o-amidocinnamic acid. 
 
 As a perfectly neutral reducing agent, which appears to be well 
 adapted for a great variety of reduction reactions, aluminium amalgam 1 
 is recommended. It is made by treating aluminium filings or shavings, 
 which have been slightly acted on by caustic soda, with a solution of 
 mercuric chloride. It reacts with water in accordance with this equation : 
 
 Al + 3 HOH = A1(OH) 3 + 3 H 
 
 Besides the reducing agents mentioned, there is still a large number 
 of others which find only an occasional application in reducing nitro- 
 compounds to amines. They will be referred to under the different 
 preparations. 
 
 The primary mon-amines are in part colourless liquids, e.g., aniline, 
 o-toluidine, xylidine ; or colourless solids like p-toluidine, pseudo- 
 cuminidine, the naphthyl amines, etc. They can be distilled without 
 decomposition, are volatile with steam, and difficultly soluble in water. 
 The di- and poly-amines are for the most part solids, non-volatile with 
 steam, and much more readily soluble in water than the mon-amines 
 
 1 B. 38, 1323. 
 
AROMATIC SERIES 221 
 
 The amines possess a basic character, but the basicity is weaker than 
 that of the aliphatic amines, in consequence of the negative nature 
 of the phenyl group. 
 
 Salts: C 6 H 5 .NH 2 .HC1 . . . . Aniline hydrochloride 
 C 6 H 5 .NH 2 .HNO 3 . . . Aniline nitrate 
 (C 6 H 5 .NH 2 ) 2 .H 2 SO 4 . . Aniline sulphate 
 
 Like ammonia, the amines unite with calcium chloride to form double 
 compounds ; for this reason they must not be dried with this substance 
 (see page 54). 
 
 The primary mon-amines find numerous applications in the labora- 
 tory, as well as on the large scale, in consequence of their great activity. 
 Frequent reference will be made to the subject in the following pages. 
 
 With the aniline prepared above, the following experiments are 
 made: 
 
 (1) Add 3 drops of aniline to 10 c.c. of water in a test-tube, 
 and shake the mixture. The aniline dissolves. At moderate tem- 
 peratures, i part of aniline dissolves in about 30 parts of water. 
 
 (2) Dilute i c.c. of this aniline solution with 10 c.c. of water, 
 and add a small quantity of a filtered water solution of bleach- 
 ing powder. A violet colouration takes place ; by this reaction 
 (Runge's), the most minute quantity of free aniline may be de- 
 tected. If in this experiment the solution should not remain clear, 
 but a dirty violet precipitate separate out, a too concentrated solu- 
 tion has been used ; the aniline water is diluted further, and the 
 experiment repeated. If a salt of aniline is to be tested, it is dis- 
 solved in water, treated with alkali, the free aniline extracted with 
 ether, this latter evaporated, and the residue dissolved in water. 
 Then proceed exactly as just directed. 
 
 This reaction may also be used to detect small quantities of 
 benzene or nitrobenzene. In a test-tube mix 5 drops of concen- 
 trated sulphuric acid with 5 drops of concentrated nitric acid, 
 then add i drop of benzene, shake, and warm gently by passing 
 the tube through a flame several times. Then add 5 c.c. of 
 water, and extract the nitrobenzene with a little ether ; the ether 
 layer is removed with a capillary pipette, and the ether evapo- 
 rated. The residue is treated with i c.c. of concentrated hydro- 
 
222 SPECIAL PART 
 
 chloric acid, and to this is added a piece of zinc the size of a 
 lentil, to effect the reduction. When the zinc is dissolved, the 
 mixture is diluted with water, and made strongly alkaline, until 
 the hydroxide of zinc precipitated at first is redissolved ; the ani- 
 line is then extracted with a little ether. Then proceed as just 
 described. 
 
 If it is desired to determine whether a given compound is 
 nitrobenzene, it is at once reduced with zinc and hydrochloric 
 acid. 
 
 (3) In a small porcelain dish place 5 drops of concentrated 
 sulphuric acid, and with a glass rod add i drop of aniline. The 
 aniline sulphate thus formed solidifies for the most part on the 
 rod ; remove it by rubbing it against the walls of the dish. Then 
 add 4 drops of an aqueous solution of potassium dichromate, and 
 mix the liquid by revolving the dish. After a short time the liquid 
 assumes a beautiful blue colour. If the reaction does not take 
 place, add 2 more drops of the dichromate, or heat a moment 
 over a small flame. 
 
 (4) Isonitrile Reaction : Heat a piece of caustic potash the 
 size of a bean with 5 c.c. of alcohol, pour off the solution from the 
 undissolved residue into another test-tube ; the warm solution is 
 treated with i drop of aniline and 4 drops of chloroform. A re- 
 action takes place immediately, or on gentle warming; this is 
 recognised not only by the separation of potassium chloride, but 
 by a most highly characteristic, disagreeable odour. The odour 
 becomes more pronounced on pouring off the liquid and adding 
 some cold water to the tube. If the vapours of the isonitrile are 
 inhaled through the mouth, a peculiar sweet taste is noticed in 
 the throat. 
 
 The reaction must be carried out under a hood with a good 
 draught. 
 
 While the two colour reactions with bleaching powder and chromic 
 acid are used especially for the recognition of aniline, the isonitrile 
 reaction will show the presence of any primary amine of the aliphatic 
 or aromatic series. The reaction takes place in accordance with the 
 following equation : 
 
 QH 5 . NH 2 + CHC1 3 = C 6 H 5 . NC + 3 HC1 
 
AROMATIC SERIES 223 
 
 For the elimination of hydrochloric acid, caustic potash is added 
 Since all isonitriles or carbylamines possess a characteristic odour, on 
 the one hand the smallest quantity of a primary base may be detected 
 by this reaction, and on the other a base may be shown to be primary. 
 Secondary and tertiary bases do not give the reaction. 
 
 In the isonitriles it is very probable that the carbon atom combined 
 with the nitrogen atom is only bivalent: C 6 H 5 . N=C::::. The iso- 
 nitriles are isomeric with the acid-nitriles, e.g., C 6 H 5 .C=N, benzo- 
 nitrile. While the nitriles on saponification give acids, the isonitriles 
 decompose into a primary amine and formic acid : 
 
 C 6 H 5 . CN + 2 H 2 O = C 6 H 5 . CO . OH + NH 3 
 
 3. REACTION : (a) REDUCTION OF A NITRO-COMPOUND TO A HYDROX- 
 YLAMINE DERIVATIVE, (b) OXIDATION OF A HYDROXYLAMINE 
 DERIVATIVE TO A NITROSO-COMPOUND 
 
 EXAMPLES : (a) Phenylhydroxylamine from Nitrobenzene 
 (b) Nitrosobenzene from Phenylhydroxylamine 
 
 (a) Phenylhydroxylamine : In a thick- walled |-litre battery jar 
 treat a solution of 5 grammes of ammonium chloride in 160 c.c. of 
 water with 10 grammes freshly distilled nitrobenzene. In the 
 course of an hour add, with constant stirring, 15 grammes of zinc 
 dust. The jar containing the liquid is surrounded with water and 
 kept at a temperature of 13 (thermometer in water ; small pieces 
 of ice are used if necessary). In order to secure an intimate mix- 
 ture, the zinc dust is divided into four equal portions, and each 
 portion is added in the course of a quarter of an hour. After the 
 addition of the last portion the* stirring is continued for 10 minutes ; 
 it is then filtered, using suction and a Buchner funnel, from the 
 zinc oxide ; the filtrate (solution I) is poured into a beaker, and 
 the zinc oxide deposit on the funnel is washed with 200 c.c. of 
 water at 45 ; before the water is poured on the residue, the suc- 
 tion is disconnected from the funnel, and is only attached later 
 to draw the liquid through gently, drop by drop. The residue is 
 then pressed together and filtered with strong suction (solution II). 
 
224 
 
 SPECIAL PART 
 
 The two water solutions are separately saturated (with stirring) 
 with finely pulverised salt ; for solution I, about 45 grammes, and 
 for solution II, about 60 grammes of salt will be required. They 
 are cooled in ice for 15 minutes to o. The colourless crystals 
 separating out are filtered off with suction, and, without washing, 
 are pressed out on a porous plate. Yield, almost quantitative. 
 
 A small test-portion of the crude product is recrystallised from 
 benzene. Melting-point, 81. The remainder, without further 
 purification, is worked up into nitrosobenzene. 
 
 The success of the reaction depends essentially upon the quality 
 of the zinc dust used. It is therefore necessary to make a zinc dust 
 determination (see page 390), and then use about 10% more than 
 is required by the theory. Zinc dust of 75% is referred to above. 
 
 Precautions : In the preparation of phenylhydroxylamine, care 
 is taken to prevent it, and particularly a warm solution of it, from 
 coming in contact with the skin, since it causes very painful and 
 annoying inflammation. Even in pressing it out or pulverising it 
 under the hood, care must be taken not to breathe in any of the 
 dust, since it causes extraordinarily violent attacks of sneezing. 
 
 (fr) Nitrosobenzene: To a solution of 30 grammes of con- 
 centrated sulphuric acid in 270 c.c. of water, well cooled by ice 
 water, add 4 grammes of freshly prepared and finely pulverised 
 phenylhydroxylamine ; the solution is then quickly treated with 
 an ice-cold solution of 4.6 grammes of potassium dichromate 
 in 200 c.c. of water ; the pure nitrosobenzene separates out imme- 
 diately in crystals. 
 
 " On account of the splendid phenomena, steam should be 
 passed into the liquid containing the oxidation product ; the total 
 quantity of nitrosobenzene is carried over in 45 minutes. At the 
 beginning of the heating the walls and neck of the flask take on a 
 deep green colour, and soon the nitrosobenzene sublimes in white, 
 lustrous plates in the bent tube entering the condenser; a few 
 moments later beautiful emerald-green oil drops appear which 
 solidify so completely, in the lower part of the condenser, to snow- 
 white crystals, that the distillate presents the appearance of a 
 faintly green liquid containing only a few minute crystals. The 
 
AROMATIC SERIES 22$ 
 
 crystals of nitrosobenzene are pushed out of the condenser with a 
 glass rod, the end being covered with a cotton plug, spread out 
 on a porous plate and washed upon the plate with ligroin (boiling- 
 point 40-70). Melting-point 67.5-68." 
 
 (a) The primary amines discussed in the preceding reaction are the 
 lowest reduction products of nitro-compounds. Recently two classes of 
 compounds have been discovered which appear to be intermediate prod- 
 ucts between the nitro-compounds and amines. In order to distinguish 
 them from the compounds referred to in the next preparation, they may 
 be called " monomolecular intermediate reduction products." 
 
 /H 
 
 C 6 H 5 . N0 2 *- C 6 H, . NO - C 6 H 5 N< -+ C 6 H 5 . NH 2 
 
 X)H 
 
 Nitrobenzene Nitrosobenzene Phenylhydroxylamine Aniline 
 
 Phenylhydroxylamine 1 was obtained simultaneously by Bamberger 
 and Wohl by the reduction of nitrobenzene with zinc dust in a neutral 
 solution : 
 
 /H 
 
 C 6 H 5 NO, + 2 Zn + H 9 O = C G H 5 N< + 2 ZnO 
 
 X OH 
 
 The presence of certain salts, e.g., calcium or ammonium chloride, pro- 
 motes the reaction. Nitro-compounds may also be reduced into 
 hydroxylamine derivatives by the action of ammonium sulphide. 2 
 Phenylhydroxylamine acts like a base towards acids. If it be warmed 
 with mineral acids, it undergoes a noteworthy transformation into 
 paraamidophenol : 
 
 H NH 2 
 
 This behaviour explains the electrolytic reduction of aromatic nitro- 
 compounds. 8 
 
 If a nitro-compound dissolved in concentrated sulphuric acid is 
 subjected to electrolytic reduction, not only is the nitre -group reduced 
 to the amido-group, but a hydroxyl group enters the para position (to the 
 amido-group) if it is vacant. Thus from nitrobenzene p-amidophenol 
 is obtained. In accordance with our present knowledge the reaction is 
 
 1 B. 27, 1347, 1432, 1548; 28, 245, 1218. 3 B. 26, 1844, 2810; 27, 1927; 29, 3040 
 
 2 B. 41, 1936. 
 
226 SPECIAL PART 
 
 no longer considered remarkable. Phenylhydroxylamine is first formed, 
 which immediately undergoes a molecular transformation into the 
 amidophenol. 
 
 Phenylhydroxylamine is a strong reducing agent, which reduces 
 Fehling's solution and an ammoniacal solution of silver nitrate even in 
 the cold. With nitrous acid it forms a nitroso-derivative : 
 
 /H /NO 
 
 C 6 H 5 N< + NOOH = C 6 H 5 N< + H 2 O 
 
 X)H X)H 
 
 With aldehydes it reacts thus : 
 
 / H /\ 
 
 C 6 H 5 . N< + C 6 H 5 . CHO - C 6 H 5 . N< >CH . C 6 H 5 + H 2 O 
 
 X)H XK 
 
 By the oxygen of the air it is oxidised to azoxybenzene ; more energetic 
 oxidising agents convert it into nitrosobenzene. 
 
 (&} Nitrosohydrocarbons may best be obtained by the oxidation of 
 hydroxylamine derivatives : 
 
 / H 
 C 6 H 5 . N< + O = C 6 H 5 . NO + H 2 
 
 X)H 
 
 The nitrosohydrocarbons in the solid state form colourless crystals, 
 but when fused or in solution an emerald-green liquid. They possess a 
 characteristic piercing odour which suggests quinone and the mustard 
 oils ; they are extremely volatile. On reduction they go over into amines. 
 With primary amines they combine to form an azo-compound, e.g., 
 
 C 6 H 5 . NO + H 2 N . C fi H 5 = C 6 H 5 . N = N . C 6 H 5 + H 2 O 
 Combined with hydroxylamine they form isodiazo-compounds, e.g., 
 
 4. REACTION: REDUCTION OF A NITRO-COMPOUND TO AN AZOXY-, 
 AZO-, AND HYDRAZO-COMPOUND 
 
 EXAMPLES : Azoxybenzene, Azobenzene, Hydrazobenzene 
 
 (i) Azoxybenzene: 1 To 200 grammes of methyl alcohol con- 
 tained in a 2-litre flask provided with a wide reflux condenser, 
 20 grammes of sodium in pieces the size of a bean are gradually 
 
 * 8.15,865. 
 
AROMATIC SERIES 22/ 
 
 added ; the flask is not cooled (heat being generated by the re- 
 action). Since methyl alcohol frequently contains much water, 
 the first portions of the sodium must not be added too rapidly. 
 When the metal is dissolved, 30 grammes of nitrobenzene are 
 added, and the mixture heated for 3 hours on an actively boiling 
 water-bath (reflux condenser). Crystals of sodium formate soon 
 begin to separate out ; this often causes a troublesome bumping. 
 The greater portion of the methyl alcohol is then distilled off 
 (the flask being placed in the water-bath; silk thread). The 
 residue is treated with water, and the reaction-mixture poured 
 into a beaker. After long standing, especially in a cool place, 
 the oil at the bottom solidifies to a bright yellow crystalline mass, 
 which is separated from the liquid by decanting the latter ; it is 
 washed several times with water and finally pressed out on a 
 porous plate. If the azoxybenzene does not solidify, the main 
 quantity of the water solution is poured off and the oil treated 
 with small pieces of ice. If solidification does not take place 
 now, it is due to the presence of nitrobenzene ; this is distilled off 
 with steam, and the difficultly volatile residue, after it has cooled, 
 is further cooled with ice. From methyl alcohol (use 3 c.c. 
 of the alcohol for every gramme of the substance) the azoxy- 
 benzene crystallises in bright yellow needles, melting at 36. 
 Yield, 20-22 grammes. 
 
 (2) Azobe nze ne ; l Five grammes of crystallised azoxybenzene, 
 dried completely by heating on a water-bath for an hour, are finely 
 pulverised and intimately mixed in a mortar with 15 grammes of 
 coarse iron filings, which must also be completely dry ; the mixture 
 is distilled from a small retort, not tubulated. It is first warmed 
 with a small luminous flame kept in constant motion ; the size of 
 the flame is increased after some time ; finally the last portions 
 are distilled over with a non-luminous flame. If, on heating, a 
 sudden but harmless explosion should occur, it is due to the fact 
 that the substances were not dry ; the experiment must be re- 
 peated. The reddish distillate is collected in a small beaker, and, 
 after it has solidified, is washed with hydrochloric acid to remove 
 
 1 A. 12, 311 ; 207, 329. 
 
228 SPECIAL PART 
 
 the aniline, then with water, and pressed out on a porous plate, 
 The experiment is repeated a second time with a fresh quantity of 
 azoxybenzene ; by working carefully the same retort can be used 
 again. The two pressed-out crude products are united. Azoben- 
 zene crystallises from ligroi'n, after a partial evaporation of the 
 solvent, in the form of coarse red crystals melting at 68. 
 
 (3) Hydrazobenzene : l Dissolve 5 grammes of azobenzene in 
 50 grammes of alcohol (about 95%) in a flask provided with a 
 reflux condenser, and treat with a solution of 2 grammes of caustic 
 soda in 4 grammes of water. To the boiling solution gradually 
 add zinc dust in small portions (best by occasionally removing 
 the cork) until the orange-coloured solution becomes colourless : 
 about 8 grammes of zinc dust will be necessary. The hot solution 
 is then filtered with suction (Buchner funnel) from the excess of 
 zinc; 20 c.c. of a water solution of sulphur dioxide and 100 c.c. 
 of water are previously placed in the filter-flask. The hydrazo- 
 benzene precipitating out of the alcoholic solution is quickly 
 filtered, washed with water containing sulphur dioxide, and pressed 
 out on a porous plate. . By crystallising from ligroi'n it is obtained 
 pure. Melting-point, 126. Yield, 80-90% of the theory. 
 
 Under the influence of suitable reducing agents, nitre-compounds 
 undergo a partial reduction in such a way that two molecules enter into 
 combination. There are thus obtained first the azoxy-, then the azo-, 
 and finally the hydrazo-compound, which in order to distinguish them 
 from the compounds obtained in Reaction 3 may be called u dimolecular 
 intermediate reduction products." 
 
 C 6 H,.NO C H -\ C.H-NC^.-NH 
 
 - 
 
 2 Mol. i Mol. i Mol. i Mol. A/ r | 
 
 Nitro- >- Azoxy- >- Azo- - *~ Hydrazo- - >- A n ? m. 
 benzene benzene benzene benzene 
 
 In order to reduce a nitro-compound to an azoxy-compound, either 
 sodium amalgam or alcoholic-caustic potash or caustic soda is used. 
 With nitrobenzene, particularly, the reaction takes place most surely 
 by dissolving sodium in methyl alcohol as above. The reducing action 
 of sodium methylate depends upon the fact that it is oxidised to 
 
 i Z. 1868, 437. 
 
AROMATIC SERIES 22Q 
 
 sodium formate, two hydrogen atoms of the methyl group being re 
 placed by one atom of oxygen : 
 
 CH 3 .ONa + O 2 = H 2 O + H.CO.ONa 
 
 In the operation carried out above the reaction is expressed by the 
 equation : 
 
 = 2 C H <7> 
 
 CJI/.N/ 
 
 + 3 H.CO.ONa + 3 H 2 O 
 
 A few words may be said here concerning the relatively weak reducing 
 power of previously prepared alcoholates, in comparison with the 
 extremely energetic action of a mixture of undissolved sodium and 
 alcohol. While the previously prepared alcoholates can generally 
 only abstract oxygen, the mixture just referred to belongs to the class 
 of very strong reducing agents. With the aid of this, it is possible to 
 break up the double or centric union of the benzene ring, and thus 
 prepare hydrogen derivatives of benzene. In this case the alcoholate 
 does not act as a reducing agent as above, but the hydrogen effects the 
 reduction : 
 
 CH 3 .OH + Na = CH 3 .ONa + H 
 
 The azoxy-compounds are yellow- to orange-red cry stall isable sub- 
 stances, which, like the nitro-compounds, are of an indifferent charac- 
 ter; but they are not volatile with steam, and cannot be distilled 
 without undergoing decomposition. On reduction they yield first 
 the azo-compounds, then the hydrazo-compounds, and finally two 
 molecules of a primary amine. By heating with sulphuric acid, azoxy- 
 benzene is converted into its isomer oxyazobenzene : 
 
 C 6 H 5 . N N . C 6 H 5 = C 6 H 5 . N=N . C 6 H 4 . OH 
 O 
 
 If an azoxy-compound is distilled carefully over iron filings, its oxygen 
 atom is removed, and an azo-compound is formed : 
 
 C 6 H 5 .N-N.C 6 H 5 H- Fe - C 6 H 5 .N=N.C 6 H 5 + FeO 
 O 
 
 Azo-compounds may also be obtained directly from nitro-compounds, 
 since they are reduced by sodium amalgam, or, in an alkaline solution, by 
 
230 SPECIAL PART 
 
 zinc dust or stannous chloride (sodium stannous oxide). The lattei 
 reducing agent acts in accordance with this equation : 
 
 X)Na 
 C 6 H 5 .N / 
 
 \ C 6 H 5 .N \ 
 
 N ONa N O 
 
 Na 
 
 Sodium stannate 
 
 Azo-compounds may also be obtained by the oxidation of hydrazo 
 compounds : 
 
 C 6 H 5 . NH . NH . C 6 H 5 + O - C 6 H 5 . N=N . C 6 H 5 + H 2 O 
 
 The azo-hydrocarbons are orange-red to red crystalline substances 
 which can be distilled without decomposition, differing in this respect 
 from the azoxy-compounds. 
 
 EXPERIMENT: A few crystals of azobenzene are heated in a 
 test-tube to boiling, over a free flame. A red vapour is evolved, 
 which again condenses to crystals on cooling. 
 
 The azo-compounds thus differ in their stability from the very easily 
 decomposable diazo-compounds, which also contain the group N = N, 
 but it is in a different combination. 
 
 By the reduction of an azo-compound, a hydrazo-compound is first 
 formed and finally an amine. 
 
 The hydrazo-compounds are formed by the reduction of azo-com- 
 pounds with ammonium sulphide or zinc dust and an alkali. Zinc dust 
 with caustic soda acts as follows : 
 
 CNa 
 _ 
 
 They may also be formed on the direct reduction of nitro-compounds 
 in alcoholic solution by zinc dust and an alkali ; this method is used 
 practically on the large scale. 
 
 The hydrazo-compounds, in contrast with the azoxy-, and especially 
 with the intensely coloured azo-compounds, are colourless. They are 
 derived from hydrazine, NH 2 NH 2 , in which one hydrogen atom of 
 the two amido-groups has been replaced by a hydrocarbon radical. The 
 
AROMATIC SERIES 231 
 
 basic character of hydrazine is so weakened by the presence of the 
 negative hydrocarbon residues, that the hydrazo-compounds no longer 
 possess a basic character. On oxidation hydrazo-compounds pass over 
 to azo-compounds, a reaction which takes place slowly but completely, 
 under the influence of the oxygen of the air. The hydrazo-compounds 
 decompose, on heating, into azo-compounds and primary amines. 
 
 2C 6 H 5 .NH.NH.C 6 H 3 =C 6 H 5 .N N.C 6 H 5 + 2 C 6 H 5 .NH 2 . 
 
 EXPERIMENT : A few crystals of hydrazobenzene are heated in 
 a small test-tube to boiling ; the colourless compound becomes 
 red, azobenzene being formed. In order to show the presence 
 of aniline, after cooling, the substance is shaken with water and 
 the bleaching-powder test applied. 
 
 If the hydrazo-compounds are treated with concentrated acids like 
 hydrochloric or sulphuric acids, they are converted into derivatives 
 of diphenyl : l 
 
 C 6 H 3 . NH . NH . C 6 H 5 = NH 2 . C 6 H 4 . C 6 H 4 . NH 2 
 
 p-Diamidodiphenyl = Benzidine 
 
 The molecular transformation takes place essentially in para position 
 to the imide (NH) groups. 
 
 EXPERIMENT : Hydrazobenzene is covered with concentrated 
 hydrochloric acid, and allowed to stand for about 5 minutes. 
 It is then treated with water, and half the solution is made alkaline 
 with caustic soda : the free benzidine is extracted several times 
 with ether, the ether evaporated, and the substance crystallised 
 from hot water. Leaflets of a silvery lustre are obtained. Melt- 
 ing-point, 122. The other half of the solution is treated with 
 dilute sulphuric acid, upon which the difficultly soluble benzidine 
 sulphate separates out. 
 
 Benzidine differs from hydrazobenzene, in that it is a strong, di-acid 
 primary base. It is prepared technically, since the azo dyes derived 
 from it possess the important property of colouring unmordanted cotton 
 fibre directly ; for most azo dyes the cotton must first be mordanted. 
 The first representative of these dyes made was Congo Red, prepared 
 from the bisdiazo-compound of benzidine and naphthionic acid. In con- 
 sequence, the entire class of these dyes is called the " Congo Dyes." 
 
 1 J- pr- 36, 93 : J- 1863, 424. 
 
232 SPECIAL PART 
 
 /NH 2 
 C 6 H 4 .N = N.C 10 H/ 
 
 In a wholly analogous manner, from o-nitrotoluene and o-nitroanisol 
 are prepared o-tolidine and dianisidine, respectively. 
 
 CH OCH 3 
 
 /NH, 
 
 OCH 
 
 Tolidine Dianisidine 
 
 If, in hydrazo-compounds, the para position to the imido (NH) 
 group is occupied as, e.g., in p-hydrazotoluene, then the benzidine 
 transformation cannot occur. 
 
 In such cases, derivatives of o- and p-amidodiphenyl amine are 
 formed through the so-called "Semidine transformation." 1 
 
 NH NH-/~~\CH 
 CH 
 
 CHo.CO.NH- 
 
 N / \ / 
 
 / \ y \ 
 
 -NH 2 . 
 
 5. REACTION : PREPARATION OF A THIOUREA AND A MUSTARD OIL 
 FROM CARBON DISULPHIDE AND A PRIMARY AMINE 
 
 EXAMPLE : Thiocarbanilide and Phenyl Mustard Oil from Carbon 
 Bisulphide and Aniline 
 
 Thiocarbanilide : A mixture of 40 grammes of aniline, 50 
 grammes of carbon disulphide, 50 grammes of alcohol, and 
 
 1 B. 26, 681, 688, 699: A. 287, 97. 
 
AROMATIC SERIES 233 
 
 10 grammes of finely pulverised potassium hydroxide is gently 
 boiled for 3 hours on a water-bath in a flask provided with a 
 long reflux condenser. The excess of carbon disulphide and 
 alcohol is then distilled off, the residue treated with water, the 
 crystals separating out are filtered off, and washed first with water, 
 then with dilute hydrochloric acid, and finally with water. For 
 the preparation of phenyl mustard oil, the crude product is used 
 directly, after it has been dried on the water-bath. In order to 
 obtain pure thiocarbanilide, 2 grammes of the dried crude product 
 are recrystallised from alcohol. Large, colourless tablets are thus 
 obtained, which melt at 154. Yield, 30-35 grammes. If a 
 mixture of equal parts, by weight, of aniline, carbon disulphide, 
 and alcoho 1 (40 grammes of each) placed in a flask provided 
 with a reflux condenser is heated, with the addition of 0.3 gramme 
 of crystallised sulphur, 1 to gentle boiling on the water-bath for 
 6 hours, a better, almost quantitative yield of thiocarbanilide is 
 obtained, although a longer time is required. After the heating, 
 proceed as above. 
 
 Phenyl Mustard Oil : z In a flask of about 400 c.c. capacity 
 place 30 grammes of the crude thiocarbanilide, and treat with 
 120 grammes of concentrated hydrochloric acid; the mixture is 
 distilled by heating to the boiling-point of the acid, on a sand- 
 bath, with a large flame under a hood. When only about 20 c.c. 
 of the liquid remain in the flask, the distillation is discontinued. 
 The distillate is treated with an equal volume of water, the mustard 
 
 011 separated in a dropping funnel, dried with a little calcium 
 chloride, and distilled. Boiling-point, 222. Yield, almost quan- 
 titative. 
 
 Triphenyl Guanidine : The residue remaining in the flask after 
 the distillation with hydrochloric acid is treated with 100 c.c. of 
 water, and then allowed to stand for several hours, when colourless 
 crystals of triphenylguanidine hydrochloride separate out. These 
 are filtered off, and warmed with some dilute caustic soda solution. 
 The salt is decomposed, and the free base obtained, which on 
 recrystallising from alcohol forms colourless crystals. Melting- 
 point, 143. 
 
 l B. 32, 2245. B. 15, 986. Z. 1869, 589. 
 
234 SPECIAL PART 
 
 Carbon disulphide acts upon primary aromatic amines (NH 2 in the 
 nucleus) to form symmetrical disubstituted thioureas, e.g. 
 
 /NH.C 6 H 5 
 
 CSS + 2 C 6 H 5 . NH 2 = C=S + H 2 S. 
 
 \NH.C 6 H ? 
 
 Diphenyl thiourea = Thiocarbanilide 
 
 By the addition of caustic potash the elimination of hydrogen sul- 
 phide is facilitated, so that the reaction takes place in a shorter time 
 than without the use of the alkali. 
 
 From the thioureas thus obtained the mustard oils may be prepared 
 by heating with acids, as hydrochloric acid, sulphuric acid, phosphoric 
 acid. The reaction takes place in accordance with the following 
 equation : 
 
 = C 6 H 5 .N=C=S + C 6 
 
 H 5 Phenyl mustard oil 
 
 The primary amine formed in addition to the mustard oil combines 
 with the acid. Besides this reaction a second one takes place, viz. : 
 the amine formed acts upon some still undecomposed thiourea, result- 
 ing in the formation of a guanidine derivative : 
 
 /NH.C 6 H 5 /NH.C 6 H 5 
 
 CS + C 6 H 6 .NH 2 = C=N.C 6 H 5 + H 2 S. 
 
 \NH.C 6 H 5 \NH.C 6 H 5 
 
 Triphenyl guanidine 
 
 /NH 2 
 Since guanidine C~ NH is an extremely strong base, which, like 
 
 \NH 
 
 caustic potash and caustic soda, absorbs carbon dioxide from the air, 
 the introduction of the three negative phenyl groups in the above com- 
 pound has not neutralised the basic properties entirely, and it still has 
 the power to form salts. 
 
 The aromatic mustard oils are in part colourless liquids, in part crys- 
 tallisable solids, the lower members are easily volatile with steam, and 
 possess a characteristic odour. In chemical behaviour they are very 
 active. If they are warmed for a long time with an alcohol, they com- 
 bine with the alcohol, addition taking place, and a thiourethane is 
 formed : 
 
 C 6 H 5 . NCS + C 2 H 5 . OH = C 6 H 5 . NH . CS . OC 2 H 5 . 
 
 Phenylthiourethanc 
 
AROMATIC SERIES 235 
 
 In the same way, ammonia and primary bases are added with the 
 formation of a thiourea : 
 
 C 6 H 5 .NCS + NH 3 = CS 
 
 \NH.C 6 H 5 
 
 Phenylthiourea 
 
 /NH.C 6 H 5 
 C 6 H 5 . NCS + C 6 H 5 . NH 2 = CS 
 
 s-Diphenylthiourea 
 
 EXPERIMENT : Treat 2 drops of phenyl mustard oil on a watch- 
 glass with 2 drops of aniline, and warm gently over a small flame. 
 On stirring the reaction-product after cooling, with a glass rod, 
 the thiocarbanilide will solidify in crystals, from which in the 
 above reverse reaction the mustard oil itself was prepared. 
 
 By heating with yellow mercuric oxide, the sulphur is replaced by 
 oxygen, and an isocyanate is formed, which may be easily recognised 
 by its extremely disagreeable odour : 
 
 C 6 H 5 . NCS + HgO = C 6 H 5 . NCO + HgS. 
 
 Phenyl isocyanate 
 
 EXPERIMENT : Heat ^ c.c. of phenyl mustard oil in a test-tube 
 with the same volume of yellow mercuric oxide for some time, 
 until the oil boils. The yellow oxide is changed to the black 
 sulphide, at the same time the extremely disagreeable odour of 
 the phenyl isocyanate arises ; the vapour of the compound attacks 
 the eyes, causing tears. 
 
 6. REACTION: THE SULPHONATION OF AN AMINE 
 EXAMPLE : Sulphanilic Acid from Aniline and Sulphuric Acid 1 
 
 To 100 grammes of pure concentrated sulphuric acid in a dry 
 flask, 30 grammes of freshly distilled aniline are added gradually, 
 with shaking ; the mixture is heated in an oil-bath up to 1 80- 
 190, until, from a test-portion diluted with water and treated 
 
 1 A. 60, 312; ioo, 163; 120, 132, 
 
236 SPECIAL PART 
 
 with caustic soda, no aniline separates out : about 4-5 hours' 
 heating will be necessary. The cooled reaction-mixture is poured, 
 with stirring, into cold water, upon which the sulphanilic acid 
 separates out in crystals. It is filtered off, washed with water, and 
 recrystallised from water, with the addition of animal charcoal, if 
 necessary. Yield, 30-35 grammes. 
 
 When an aromatic compound is treated with sulphuric acid, a por- 
 tion of the benzene-hydrogen is replaced by a sulphonic acid group, 
 the reaction taking place in accordance with the equation below. The 
 aliphatic compounds do not react in a similar manner. Under the 
 preparation of benzene sulphonic acid, the details of the reaction will 
 
 be discussed. 
 
 X)H /NH 2 
 
 C 6 H 5 . NH 2 + S0 2 = C 6 H 4 + H 2 0. 
 
 p-Amidobenzenesulphqnic acid = 
 sulphanilic acid 
 
 In the above example, it happens, as in many cases, that the sulphonic 
 acid group enters in the para-position to the amido-(NH 2 ) group. 
 The amido sulphonic acids are colourless crystallisable compounds 
 melting with decomposition ; they possess acid properties, i.e. in dis- 
 solving in alkalies. The basic character of the amine is so greatly 
 weakened by the introduction of the negative sulphonic acid group that 
 the amido sulphonic acids cannot form salts with acids. They differ 
 
 . yNH 2 N 
 
 in this from the analogous carbonic acids ( e.g., C 6 H 4 < J. which 
 
 \ \co.onJ 
 
 Amidobenzoic acid 
 
 dissolve in both acids and alkalies. 
 
 The amido-sulphonic acids, since they are derivatives of a primary 
 amine, may like them be diazotised by the action of nitrous acid ; upon 
 this fact depends their great technical importance. If the diazo-com- 
 pounds thus obtained are combined with amines or phenols, azo dyes 
 are formed which contain the sulphonic acid group, and in the form of 
 their alkali salts are soluble in water. Sulphanilic acid particularly, 
 and its isomer, metanilic acid, obtained by the reduction of m-nitro- 
 benzenesulphonic acid, as well as the numerous mono- and poly-sul- 
 phonic acids derived from a and (3 naphthyl amines, find extensive 
 technical application in the manufacture of azo dyes. 
 
AROMATIC SERIES 237 
 
 1. REACTION: REPLACEMENT OF THE AMIDO- AND DIAZ-GROUPS 
 BY HYDROGEN 
 
 EXAMPLE : Benzene from Aniline 
 
 Dissolve 5 grammes of aniline in a mixture of 15 grammes of 
 concentrated hydrochloric acid and 30 c.c. of water ; cool with 
 ice, and treat with a solution of 5 grammes of sodium nitrite in 
 15 c.c. of water, until free nitrous acid may be recognised with 
 starch-potassium-iodide paper. The diazobenzenechloride solu- 
 tion thus obtained is allowed to flow carefully into a solution of 
 10 grammes caustic soda in 30 c.c. of water contained in a 400 c.c. 
 flask which is well cooled with ice. Further, dissolve 20 grammes 
 of stannous chloride in 50 c.c. of water, and treat this solution 
 with a concentrated solution of sodium hydroxide (2 parts to 3 of 
 water), until the precipitate at first formed (stannous oxide) is 
 redissolved in the excess of the alkali. Treat the alkaline diazo- 
 benzene solution, well cooled with ice-water, gradually with small 
 portions of the sodium-stannous oxide solution, previously well 
 cooled, waiting after each addition until the lively evolution of 
 nitrogen has ceased before adding more. When all the reducing 
 liquid has been added, the flask is connected with a condenser, 
 and the liquid heated to boiling. The benzene formed passes over 
 first, and is collected in a test-tube. By a careful distillation from 
 a small fractionating flask (without condenser), it is obtained per- 
 fectly pure. Boiling-point, 81. Yield, 3-4 grammes. 
 
 As already mentioned, under the preparation of methyl amine, the 
 behaviour of the aliphatic primary amines toward nitrous acid is very 
 different from that of the aromatic compounds. While the former yield 
 alcohols with the elimination of nitrogen, the latter, in a mineral acid 
 solution, under the influence of nitrous acid, yield diazo-compounds, 
 discovered by Peter Griess, 1 in the form of their mineral acid salts 
 CH 3 . NH 2 + NOOH = CH 8 . OH + N, + H,O 
 
 C 6 H 5 . NH 2 + NOOH + HC1 = C C H, . NzzN . Cl + 2 H 2 O 
 
 Diazobenzene chloride 
 
 it has been held that the mother substance of the diazo-compounds, 
 free diazobenzene possessed the constitution: 
 
 in in 
 C H 5 . N=N - OH 
 
 1 A. 137, 39- 
 
238 SPECIAL PART 
 
 In accordance with which the diazo salts were expressed by : 
 
 C 6 H 5 . NzzN . Cl = Diazobenzene chloride, 
 
 C 6 H 5 . N N . NO 3 = Diazobenzene nitrate, 
 
 C 6 H 5 . N=N . O . SO 2 . OH = Diazobenzene sulphate. 
 
 More recently this view has been abandoned, and the one proposed 
 earlier by Blomstrand taken up. It is, however, not accepted generally. 
 According to this conception the above salts are represented thus : 
 
 65 . ; C 6 H 5 . Nf 
 
 \C1 \N0 3 \O.S0 2 .OH 
 
 In accordance with this view the diazotising process consists in re- 
 placing the three hydrogen atoms combined with a nitrogen atorr 
 having a valence of 5, by a trivalent nitrogen atom : 
 
 C 6 H 5 .N 
 
 + N 
 
 OOH 
 
 Cl 
 
 Aniline hydrochloride 
 
 \C1 
 
 To emphasise the similarity to ammonium compounds, in which the 
 valence of the nitrogen atom is probably 5, the diazo salts are called 
 diazonium salts. The diazo-compounds can also form double salts, e.g.: 
 
 C 6 H 5 .N=N.Cl.AuCl 3 and (C 6 H 5 . Ni=N. Cl) 2 . PtCl 4 
 
 Diazobromides have the power of taking up two atoms of bromine to 
 form perbromides : 
 
 C 6 H 5 . N=N . Br + Br 2 = C 6 H 5 . N 2 . Br 8 
 
 Diazobenzene perbromide 
 
 EXPERIMENT : Dissolve i c.Co of aniline in an excess of hydro- 
 chloric acid, diazotise as above, and add i c.c. of bromine dissolved 
 in a water solution of hydrobromic acid, or in a concentrated 
 solution of potassium bromide. A dark oil separates out, from 
 which the solution is decanted. It is washed several times with 
 water ; on cooling, it solidifies to crystals. 
 
 If ammonia is allowed to act on the perbromide, diazobenzeneimide 
 is obtained : 
 
 /N 
 C 6 H 6 . NBr . NBr 2 + NH 3 = C 6 H 5 . N 1 1 + 3 HBr 
 
 1 
 
 \i 
 
 Diazobenzeneimide 
 
AROMATIC SERIES 239 
 
 EXPERIMENT : The perbromide just obtained is covered with 
 water, and concentrated ammonium hydroxide added to it. A 
 vigorous reaction takes place with the formation of an oil possess- 
 ing a strong odour (diazobenzeneimide). 
 
 Under the influence of alkalies the diazonium compounds yield salts, 
 thus acting like acids. 
 
 C 6 H 5 . N 2 . Cl + 2 NaOH = C 6 H 5 . N 2 . ONa + NaCl + H 2 O 
 
 These can exist in two isomeric modifications. The one primarily 
 obtained is characterised by the fact that in alkaline solution it unites 
 with phenols to form azo dyes ; while the second modification obtained 
 by a longer action of the alkali, at higher temperature if necessary, does 
 not possess this property at all, or only in a slight degree. If they 
 (the latter) be treated with acids, they are converted back into the 
 diazonium salts, and now have the property of combining with phenols 
 in alkaline solutions. 
 
 The view of Hantzsch is that the salts in which the diazonium com- 
 pound behaves as an acid, are not derived from diazonium hydroxide, eg. : 
 
 in 
 
 v /N 
 C 6 H 5 .N/ 
 
 \OH 
 
 but they are derived from a compound having the following constitution : 
 
 in in 
 C 6 H 5 . N = N - OH 
 
 Consequently, for metallic salts, the first formula must be modified. 
 The differences underlying the constitution of the two metallic salts 
 are due to stereoisomerism ? e.g. 
 
 C,H 5 .N C 6 H 5 .N 
 
 NaO . N N . ONa 
 
 Syn-diazo compound Anti-diazo compound 
 
 Unites with phenols Does not unite with phenols 
 
 The principles underlying the space arrangement of the three valences 
 of nitrogen, as illustrated in these examples, will be discussed under 
 Benzophenoxim. Compare Hantzsch : " Die Diazoverbindungen " (Stutt- 
 gart, 1902), also Hantzsch : Stereochemie " (2 Ed.), p- 142. The salts 
 of the diazo-compounds formed with acids are, in most cases, colourless, 
 crystallisable substances, easily soluble in water, insoluble in ether. 
 
240 SPECIAL PART 
 
 In order to prepare them in the solid condition, various methods may 
 be used. Thus, e.g., the very explosive diazobenzene-nitrate may be 
 obtained in colourless needles by conducting gaseous nitrous acid into 
 a well-cooled pasty mass of aniline nitrate and water, and treating the 
 diazo-solution with alcohol and ether. In general, the solid diazo-salts 
 may be prepared by adding to an alcoholic solution of the amine that 
 acid the salt of which is desired, and then treating the well-cooled mix- 
 ture with amyl nitrite : 1 
 
 C 6 H 5 . NH 2 + N0 2 . C,H n + HC1 = C 6 H 5 . N=N . Cl + C 5 H n . OH + H 2 O 
 
 Amyl nitrite Amyl alcohol 
 
 If the solid diazo-compound does not separate out at once, ether is 
 added. On heating, the dry diazo-salts decompose either, as in the 
 case of diazobenzene nitrate, with explosion, or a sudden evolution of 
 gas takes place without detonation. A few diazo-compounds are so 
 stable that they may be recrystallised from water. 
 
 In rare cases only, in working with diazo-compounds, is it necessary 
 to isolate them in a pure condition ; generally, the very easily prepared 
 water solutions are used. These compounds were formerly obtained 
 by passing gaseous nitrous acid into a salt of the amine until it was 
 diazotised. But at present this method is employed only in rare cases ; 
 the free nitrous acid obtained from sodium nitrite is used. In order to 
 diazotise an amine, a solution of it in a dilute acid most frequently 
 hydrochloric acid or sulphuric acid is first prepared. Theoretically, 
 two molecules of a monobasic acid are required to diazotise one mole- 
 cule of a monamine : 
 
 C C H, . NH^ + NaNO 2 + 2 HC1 = C 6 H. . N 2 . Cl + NaCl + 2 H 2 O 
 
 but an excess is always taken, not less than three molecules of hydro- 
 chloric acid or two of sulphuric acid to one molecule of a monamine. 
 In many cases, the hydrochloride or sulphate of the amine is difficultly 
 soluble in water. Under these conditions, it is not necessary to add 
 water until the salt is entirely dissolved, but the solution of the nitrite 
 may be poured into the pasty mass of crystals ; when the undissolved 
 salt is diazotised, it passes into solution. For the diazotisation of one 
 molecule of a monamine, one molecule of sodium nitrite is necessary, 
 theoretically ; but since the commercial salt is never perfectly pure, it 
 is advisable to weigh off from 5-10 % more than the calculated amount, 
 and to determine by the method given below when a sufficient quantity 
 
 i B. 23, 2994. 
 
AROMATIC SERIES 241 
 
 of this has been added. The nitrite is dissolved in water, generally 
 5-10 parts of water to I part of salt. The nitrite solution must be 
 added gradually to the amine solution, and the liquid must not be 
 allowed to become warm. In many cases, the experimenter is often 
 too careful, in that he cools the amine solution with a freezing mixture, 
 and adds the nitrite solution drop by drop from a separating funnel. 
 Frequently it is sufficient to place the solution in a water-bath filled 
 with cold water, or ice is thrown into the water, or the amine solution 
 is cooled by ice. It is very convenient to cool the solution, not from 
 without, but by throwing into it from time to time small pieces of ice. 
 The nitrite solution may be poured directly from a flask. If the addi- 
 tion causes evolution of gas bubbles or vapours of nitrous acid, the 
 temperature of the solution must be lowered and the nitrite added more 
 slowly. In order to be cognisant of the course of the reaction, as well 
 as to be able to determfne when it is completed, starch-potassium-iodide 
 paper, prepared as follows, is used : 
 
 A piece of starch the size of a pea is finely pulverised, and added to 
 200 c.c. of boiling water ; it is boiled a short time, with stirring. After 
 cooling, a solution of a crystal of potassium iodide the size of a lentil, 
 in a little water, is added to it. With this mixture, saturate long strips 
 of filter-paper 3 cm. wide ; the strips are dried by suspending them 
 from a string in a place free from acids. After drying, the strips are 
 cut up and preserved in a closed vessel. 
 
 In order now to diazotise an amine, the cooled solution is first 
 treated with a small portion of the nitrite solution ; it is well stirred, 
 and a drop of it transferred with a clean glass rod to the starch- 
 potassium-iodide paper. If the nitrous acid is already used up in the 
 diazotisation, no dark spots appear, and further portions of the sodium 
 nitrite may be added, the test is again repeated, and so on. But if a 
 dark spot is formed at once, the nitrous acid is still present ; and in 
 this case, before more of the nitrite is added, one waits until the reaction 
 has been completed, and so on. After the addition of three-fourths 
 of the nitrite solution, larger quantities may be added at one time, but 
 toward the end of the reaction small quantities must again be employed. 
 The diazotisation is ended when, after standing some time, the mixture 
 shows the presence of nitrous acid. Since the diazotisation of the last 
 portions of the amine often requires some time, the addition of the 
 nitrite is not discontinued at once, even if after one minute the test 
 for nitrous acid is obtained, but the solution is allowed to stand 
 5-10 minutes, and is then tested again. At times, it happens that the 
 R 
 
242 SPECIAL PART 
 
 weighed-off quantity of sodium nitrite is apparently not sufficient to 
 complete the diazotisation, and that even after the addition of a fresh 
 quantity, the test will not show the presence of nitrous acid. This 
 phenomenon has its cause generally in the fact that the acid (hydro- 
 chloric or sulphuric) has been used up, and consequently the nitrite 
 cannot enter into the reaction. Thus, in case the weighed-off amount 
 of sodium nitrite is not sufficient, some acid is first added to a small 
 portion of the liquid, and this is then tested to determine whether the 
 desired reaction has taken place. Further, often the diazo-solution 
 becomes cloudy toward the end of the reaction, or a precipitate sepa- 
 rates out. This is the diazoamido-compound ; its formation is also 
 caused by the lack of free acid. On the addition of acid and solution 
 of the nitrite, the precipitate disappears. The replacement of the 
 diazo-group by hydrogen in the above reaction takes place in accord- 
 ance with the following equation : 
 
 C C H, . N 2 . OH + H 2 = C 6 H 6 + N 2 + H 2 O * 
 
 In this way it is possible in many cases to replace a primary amido- 
 group by hydrogen. Obviously, such a reaction is superfluous, if, as 
 in the above case, the amine is obtained by the nitration of the hydro- 
 carbon and the reduction of the nitro-compound. But there are cases 
 in which an amine is not obtained in this way, and where it is of 
 importance to prepare the amido-free compound (see below). 
 
 The replacement of a diazo-group by hydrogen may be effected by 
 other reducing agents. If, e.g., a diazo-compound is boiled with 
 alcohol, the latter is converted into aldehyde, thus liberating two 
 hydrogen atoms, by which the diazo-compound is reduced : 
 
 C 6 H 5 .N a .OH + CH 8 .CH a .OH = C 6 H 6 + N a + CH 3 .CHO-f H 2 O 
 
 Aldehyde 
 
 The reaction is effected either by conducting gaseous nitrous acid into 
 the boiling alcohol solution of the amine, or by heating the amine with 
 alcohol saturated with ethyl nitrite ; or the boiling alcohol solution of the 
 amine, acidified with sulphuric acid, may be treated with sodium nitrite. 
 
 At this place, two examples may be mentioned which illustrate the 
 theoretical as well as the practical value of the reaction : by the oxida- 
 tion of a mixture of aniline and p-toluidine, there is formed a complex 
 dye, para-fuchsine, the constitution of which was unknown for a long 
 time. This was first explained by E. and O. Fischer. They heated 
 the diazo-compound of the leuco-base of the dye, paraleucaniline with 
 
 i B. 22, 587. 
 
AROMATIC SERIES 243 
 
 alcohol, which gave the mother substance the hydrocarbon triphenyl 
 methane (A. 194, 270). 
 
 As an example of the preparation value of the reaction, the following 
 case is cited : 
 
 No method is known by which m-nitrotoluene can be prepared on a 
 large scale by the nitration of tuluene ; this results in the formation of 
 the o- and p-compounds mainly. In order to obtain the m-nitrotoluene, 
 the starting-point is p-toluidine. This is nitrated, upon which a nitro- 
 toluidine of the following constitution is obtained : 
 
 CH, 
 
 NH 2 
 
 If the amido-group is replaced by hydrogen, using the method last 
 described, the desired m-nitrotoluene is obtained. 
 
 By boiling a diazo-compound with alcohol the reaction may take place 
 in a different wav ; at times the diazo-group is not replaced by hydrogen, 
 but by the ethoxy (-OC H 5 ) group, thus giving rise to a phenol ether. 
 
 ,. X . N N . SO 4 H + C 2 H 5 . OH = X . OC 2 H 5 + N 2 + H 2 SO 4 
 
 In conclusion, special attention is called to the fact that not only 
 aniline and its homologues can be diazotised, but all the derivatives of 
 these, as the nitro-amines, halogen-substituted amines, ammo-alde- 
 hydes, amino-carbonic acids, etc. 
 
 8. REACTION: REPLACEMENT OF THE DIAZO-GROUP BY 
 HYDROXYL 
 
 EXAMPLE : Phenol from Aniline 
 
 Pour 20 grammes of concentrated sulphuric acid as rapidly as 
 possible, with stirring, into 50 grammes of water ; to the hot 
 solution add 10 grammes of freshly distilled aniline, with stirring, 
 by allowing it to flow down the side of the beaker, then add 
 100 c.c. of water. After the hot liquid has been cooled by im- 
 mersion in cold water, it is treated with a solution of 8.5 grammes 
 of sodium nitrite in 40 c.c. of water, until it shows a blue spot on 
 starch-potassium-iodide paper. The diazobenzene sulphate solu- 
 
244 SPECIAL PART 
 
 tion thus obtained is gently heated (40-50) for half an hour on 
 the water-bath, the phenol is then distilled over with steam, and 
 the distillate, after being saturated with salt, is extracted several 
 times with ether. The ethereal solution is allowed to stand for 
 some time over fused sodium sulphate. The ether is then evapo- 
 . rated, and the residue of phenol is subjected to distillation in a 
 small flask. Boiling-point, 183. Yield, 7-8 grammes. 
 
 The liquid remaining back in the flask after the steam distilla- 
 tion is filtered hot. On cooling, a small quantity of oxydiphenyl 
 crystallises out. 
 
 If a diazo-compound is heated with water, it will pass over to a 
 phenol with the evolution of nitrogen, e.g. : 
 
 For this reaction the diazosulphate is most advantageously used. Under 
 certain circumstances, the diazochloride may also be employed. But 
 the use of the diazonitrate is avoided, since, in this case, the nitric acid 
 liberated, acting upon the phenol, readily forms nitro-compounds. In 
 many cases, it is more convenient not to isolate the diazo-compound, 
 but to add a water solution of the calculated amount of sodium nitrite 
 to a boiling solution of the amine in dilute sulphuric acid. The diazo- 
 tisation of the substance and the immediate decomposition of the diazo- 
 compound take place in one operation. 
 
 The same reactions are also applicable to substituted amines, like 
 amido- carbonic acids, amido-sulphonic acids, halogen substituted 
 amines, etc. 
 
 The oxydiphenyl obtained as a by-product is formed in consequence 
 of the action of some of the undecomposed diazo-compound on phenol : 
 
 C 6 H 5 . N 2 . SO 4 H + H . QH 4 . OH = C 6 H 5 . C 6 H 4 . OH -f H 2 SO 4 + N 2 
 (Compare B. 23, 3705.) 
 
 9. REACTION: REPLACEMENT OF A DIAZO-GROUP BY IODINE 
 EXAMPLE : Phenyl Iodide from .Aniline 
 
 (Phenyliodidechloride, lodoso-benzene, Phenyl iodite, and 
 Diphenyliodonium iodidi) 
 
 A solution of 10 grammes of aniline 1 in a mixture of 50 grammes 
 of concentrated hydrochloric acid and 150 grammes of water 
 
 1 Twenty grammes of aniline should be used if the Grignard reaction is to be 
 carried out later on. 
 
AROMATIC SERIES 345 
 
 cooled with ice-water is gradually treated with a solution of 8.5 
 grammes of sodium nitrite in 40 c.c. of water, until a test will give 
 a blue colour to the starch-potassium-iodide paper. The diazo- 
 solution is then treated in a flask, not too small, with a solution of 
 25 grammes of potassium iodide in 50 c.c. of water, the mixture is 
 allowed to stand several hours, being cooled by water, finally it is 
 gently heated on the water-bath until the evolution of nitrogen 
 ceases. The liquid is made strongly alkaline with caustic soda or 
 caustic potash, and the iodobenzene distilled over with steam ; 
 the steam delivery tube should reach almost to the bottom of the 
 flask. The iodobenzene is separated from the water in a dropping 
 funnel, dried with calcium chloride and redistilled. Boiling- 
 point, 189-190. Yield, about 20 grammes. 
 
 If a diazoiodide is heated, the diazo-group is replaced by iodine, the 
 reaction taking place smoothly in most cases. 
 
 C 6 H 5 .N 2 .I = C 6 H 5 .I + N 2 
 
 The reaction is effected by diazotising the amine in a hydrochloric acid 
 or sulphuric acid solution, and then treating it with potassium iodide. 
 From the diazochloride or diazosulphate there is formed a diazoiodide, 
 the reaction, in many cases, taking place at the ordinary temperature ; 
 in others, on heating, as above. Since the reaction occurs without 
 difficulty, it is used as the method of preparation of many iodides. 
 
 The aromatic iodides (iodine in the nucleus) possess the noteworthy 
 property of combining with two atoms of chlorine, the iodine previously 
 univalent becoming trivalent : 
 
 i in 
 
 C t H d .l4-0, = C 8 H 5 .ICl f 1 
 
 Phenyliodidechloride 
 
 EXPERIMENT : A portion of the phenyl iodide obtained is dis- 
 solved in five times its volume of chloroform, the solution is cooled 
 by ice water, and a current of dry chlorine is passed into it from 
 a very wide delivery tube, until no more is absorbed. The crystals 
 separating out are filtered off, washed with a fresh quantity of 
 chloroform, spread out in a thin layer on a pad of filter-paper, 
 and allowed to dry in the air. 
 
 1 J- P r - 33. J S4- B. 25, 3494 ; 26, 357 ; 25, 2632. Concerning aliphatic iodide- 
 chlorides see A. 369, 119. 
 
246 SPECIAL PART 
 
 If caustic soda is allowed to act on an iodochloride, the two chlorine 
 atoms are replaced by one oxygen atom, and an iodoso-compound is 
 obtained : 
 
 C 6 H 5 . IC1 2 + H 2 O = C 6 H S . lO + 2 HC1 
 
 lodosobenzene 
 
 Besides this reaction another takes place, resulting in the formation of 
 an iodonium base. This formation is probably due to the fact that a 
 small part of the iodosobenzene is oxidised to phenyl iodite, and this 
 condenses with iodosobenzene, iodic acid being eliminated : 
 
 /on 
 
 C 6 H 5 . I<f f I0 2 . C 6 H 5 =C 6 H 5 - I - C 6 H 5 + HI0 3 . 
 
 I< 
 
 Hypoth. lodoso- OH 
 
 benzene hydrate Diphenyliodonium hydroxide 
 
 This base is present in the alkaline solution filtered off from the iodoso- 
 benzene. If the filtrate be treated with sulphur dioxide, this reduces 
 the iodic acid to hydriodic acid, which, combining with the iodonium 
 base, forms an iodide insoluble in cold water : 
 
 HIO ;i + 3 S0 2 = HI + 3 S0 3 
 
 CTT T (~* TT 
 
 6 n 5 ^"6 n 5 "I 
 
 I C 6 H 5 C 6 H 5 + H 2 O 
 
 [OH + H|I J 
 
 i 
 
 EXPERIMENT : The iodochloride is carefully triturated with dilute 
 caustic soda in a mortar (for i gramme of the iodochloride, use a 
 solution of 0.5 gramme sodium hydroxide in 4 grammes of water), 
 and allowed to stand over night. The iodosobenzene is then 
 filtered off, washed with water, and pressed out on a porous plate. 
 
 The alkaline filtrate is treated with a solution of sulphur dioxide 
 until it smells strongly of it. The precipitate formed is filtered 
 off and dissolved in hot water. On cooling, colourless needles of 
 diphenyliodonium iodide are obtained. 
 
 The iodoso-compounds have the power of uniting with acids to form 
 
 /OH 
 salts, in which they act like a di-acid base, e.g., C G H-.I<f 
 
 \OH 
 
 EXPERIMENT : Several grammes of iodosobenzene are dissolved 
 with heat in as small a quantity of glacial acetic acid as possible , 
 
AROMATIC SERIES 247 
 
 the solution is evaporated on the water-bath to dryness, in a watch- 
 glass, or shallow dish. The solid residue is pulverised and re- 
 crystallised from a little benzene. lodosobenzene acetate is thus 
 
 obtained, 
 
 XX)C.CH 3 
 
 C 6 H 5 .I< 
 
 \OOC.CH 3 
 
 in the form of colourless prisms, melting at 157. 
 
 The iodoso-compounds, on treatment with hydriodic acid, are reduced 
 to iodides, with a separation of iodine. 
 
 C 6 H 5 . 10 + 2 HI = C 6 H 5 . 1 + I 2 + H 2 O 
 
 This reaction is used for the quantitative determination of iodoso- 
 oxygen. 
 
 EXPERIMENT : Some potassium iodide is dissolved in water, 
 acidified with dilute sulphuric acid, or acetic acid, and a few 
 grains of iodosobenzene are added. The iodine separates out as 
 a brown precipitate. 
 
 If an iodoso-compound is heated carefully to 100, it passes over to 
 an iodite (Jodoverbindung) : 
 
 2C 6 H 5 .IO = C 6 H 5 .I0 2 + C 6 Hs.I 
 
 Phenyl iodite Phenyl iodide 
 
 The same compound may also be obtained by treating an iodoso- 
 compound with steam. 
 
 EXPERIMENT : lodosobenzene is treated in a flask with enough 
 water to form a thin paste. Into this steam is conducted (appa- 
 ratus for distillation with steam), until no more phenyl iodide 
 passes over with the steam and all the iodosobenzene has been 
 dissolved. If the phenyliodite formed does not dissolve com- 
 pletely, water is added until solution takes place. The solution 
 is then evaporated on the water-bath until a test-portion cooled 
 off yields an abundant crystallisation of phenyl iodite. 
 
 The iodites, like the iodoso-compounds, puff up and suddenly decom- 
 pose on heating. (Try it.) They also abstract iodine from hydriodic 
 acid, and in double the quantity as compared to the similar action of 
 the iodoso-compounds. 
 
248 SPECIAL PART 
 
 CgH, . IO 2 + 4 HI = C 6 H 5 I -f 4 1 + 2 H 2 O 
 
 They do not form salts with acids. 
 
 The iodonium bases l are prepared most conveniently by the action 
 of silver oxide on a mixture of equal molecules of iodoso and iodite 
 
 compounds : 
 
 in 
 C G H 5 . 10 -f C 6 H 5 . 10 a + AgOH - C 6 H 5 . 1 . C 6 H 5 + AgIO 3 
 
 OH 
 
 They are soluble in water, show a strong alkaline reaction like the 
 sulphonium and ammonium compounds, and give with halogen hydracids 
 precipitates of the corresponding salts. If the dried salts be heated, 
 they decompose into two molecules of the hydrocarbon substitution 
 
 product, e.g. : 
 
 in 
 C 6 H 5 .I.C C H 5 = 2C 6 H 5 I 
 
 I 
 
 i 
 
 EXPERIMENT : The diphenyliodonium iodide obtained as a by- 
 product in the preparation of iodosobenzene is heated carefully in 
 a test-tube over a small flame. Suddenly the substance begins to 
 melt in one place; the fusion increases, without the need of 
 further heating, and the whole mass boils up. lodobenzene, easily 
 recognised by its odour, is obtained. 
 
 10. REACTION: REPLACEMENT OF A DIAZO-GROUP BY CHLORINE, 
 BROMINE, OR CYANOGEN 
 
 EXAMPLE : p-Tolyl Nitrile from p-Toluidine 
 
 Dissolve 50 grammes of copper sulphate in 200 grammes of 
 water in a 2-litre flask by heating on the water-bath; then add 
 gradually, with continuous heating, a solution of 55 grammes of 
 potassium cyanide in 100 c.c. of water. Since cyanogen is evolved, 
 the reaction must be conducted under a hood, with a good draught, 
 and the greatest care taken not to breathe the vapours. 
 
 While the cuprous cyanide solution is further gently heated up 
 to about 60-70 on the water-h?tb, the diazotoluenechloride solu- 
 
 1 B. 27, 426, 502, and 1592. 
 
AROMATIC SERIES 249 
 
 tion is prepared in the following way : 20 grammes of p-toluidine 
 are heated with a mixture of 50 grammes of concentrated hydro- 
 chloric acid and 150 c.c. of water until solution takes place; the 
 liquid is then quickly immersed in cold water and vigorously 
 stirred with a glass rod, in order that the toluidine hydrochloride 
 may separate out in as small crystals as possible. A solution of 
 1 6 grammes of sodium nitrite in 80 c.c. of water is then added 
 to the amine hydrochloride, cooled by ice-water, until a perma- 
 nent reaction of nitrous acid upon the starch-potassium-iodide 
 paper, is obtained. The diazotoluene chloride thus formed is 
 poured from a flask into the cuprous cyanide solution, with 
 frequent shaking. After the addition of the diazo-solution, which 
 should require about 10 minutes, the reaction mixture is 1 heated 
 on the water-bath for about a quarter-hour. The tolyl nitrile is 
 then distilled over with the steam. This operation must also be 
 done under a hood with a good draught, since hydrocyanic acid 
 passes over. The nitrile distils as a yellow oil, which after some 
 time solidifies in the receiver. It is separated by decanting the 
 water, pressed upon a porous plate, and purified by distillation. 
 If the oil will not solidify, the entire distillate may be taken up 
 with ether, the ethereal solution shaken with caustic soda solution 
 to remove the cresol, and then, after evaporating the ether, the 
 residue remaining is distilled directly, or, in case it is solid, it is 
 pressed out on a porous plate, as above, and then distilled. Boiling- 
 point, 218. Yield, about 15 grammes. 
 
 The diazo-group cannot be replaced in the same way by iodine as 
 by chlorine, bromine, or cyanogen. If a water solution of a diazo- 
 chloride, -bromide, or -cyanide is heated, a phenol is formed, as is also 
 the case on heating a diazo-sulphate : 
 
 C 6 H 5 . N 2 . Cl + H 2 O = C 6 H 5 . OH + N 2 + HC1 
 
 To Sandmeyer 1 we are indebted for the important discovery that, if 
 the heating be done in the presence of cuprous chloride, bromide, 01 
 cyanide, the reaction taking place is analogous to the one by which 
 phenyl iodide is formed : 
 
 1 B. 17, 1633 and 2650; 18, 1492 and 1496. 
 
2JO SPECIAL PART 
 
 C 6 H,.N,.C1 =C 6 H 5 .C1 +N 2 ] 
 CH .Ni.Br =CH .Br +N 
 CeH 5 . N*. CN = C 6 H 5 . CN + N! J 
 
 The manner in which the cuprous salts act is not known ; in any 
 case they unite first with a diazo-compound to form a double salt, 
 which plays a part in the reaction. 
 
 The reaction in the above preparation of cuprous cyanide takes place 
 in accordance with the following equation : 
 
 CuSO 4 + 2 KCN = CuCN 2 + K 2 SO 4 
 2 CuCN 2 = Cu 2 CN 2 + 2 CN 
 
 In order to replace the diazo-group by chlorine or bromine, the 
 above method is followed exactly. A diazo-solution is first prepared, 
 and gradually added to a heated solution of cuprous chloride or bromide. 
 With easily volatile chlorine or bromine compounds, it is desirable to 
 use a reflux condenser, and to allow the diazo-solution to flow in from a 
 dropping funnel. In some cases it is more advantageous not to use 
 a previously prepared diazo-solution, but to proceed as follows : The 
 amine is dissolved in an acid solution of a copper salt ; this is heated, 
 and to the hot solution, the solution of nitrite is added from a dropping 
 funnel. The diazotisation and replacement of the diazo-group then 
 takes place in one reaction. If the reaction-product is not volatile with 
 steam, it may be obtained from the reaction-mixture by filtering, or 
 extracting with ether. 
 
 The Sandmeyer reaction is capable of general application. Since 
 the yield of the product is generally very good, for many substances it 
 is used as a method of preparation. It should be finally pointed out 
 that by the replacement of the diazo-group by cyanogen a new carbon 
 union takes place. 
 
 11. REACTION: (a] REDUCTION OF A DIAZO-COMPOUND TO A HY- 
 DRA ZINE. (b) REPLACEMENT OF THE HYDRAZINE-RADICAL BY 
 HYDROGEN 
 
 EXAMPLES : (a) Phenyl Hydrazine from Aniline 
 (b) Benzene from Phenyl Hydrazine 
 
 (a) Add 10 grammes of freshly distilled aniline to 100 c.c. of 
 concentrated hydrochloric acid in a beaker, with stirring ; aniline 
 hydrochloride partially separates out in crystals. To the mixture, 
 
AROMATIC SERIES 251 
 
 cooled with ice, add slowly from a dropping funnel, a solution of 
 10 grammes of sodium nitrite in 50 c.c. of water, until a test with 
 starch-potassium-iodide paper shows free nitrous acid. In this 
 case the strong acid solution must not be brought directly upon 
 the test-paper, but a test-portion is diluted with water in a watch- 
 glass and then the test applied. To the diazo-solution add, with 
 stirring, a solution of 60 grammes of stannous chloride in 50 c.c. 
 of concentrated hydrochloric acid cooled with ice ; a thick paste of 
 crystals of phenyl hydrazine hydrochloride separates out. After 
 standing several hours this is filtered off' with suction (Biichner 
 funnel and filter-cloth), the precipitate is pressed firmly together 
 on the filter with a pestle ; it is then transferred to a small flask 
 and treated with an excess of caustic soda solution. Free phenyl 
 hydrazine separates out as an oil, it is taken up with ether, the 
 ethereal solution dried with ignited potash, and the ether evap- 
 orated. For the later experiments the phenyl hydrazine thus 
 obtained can be used directly. If it is desired to purify the sub- 
 stance, the best method is to distil it in a vacuum, or it can be 
 cooled by a freezing-mixture, and the portions remaining liquid 
 are poured off. Yield, about 10 grammes. 
 
 Since the diazotisation in a strong hydrochloric acid solution 
 as well as the filtration of strongly acid liquids is liable to mis- 
 carry, it is better to perform the experiment as follows : Dissolve 
 10 grammes of freshly distilled aniline in a mixture of 30 grammes 
 of concentrated hydrochloric acid and 75 c.c. of water and diazo- 
 tise it with a solution of 8 grammes of sodium nitrite in 30 c.c. 
 of water, the beaker being cooled with ice-water. The diazo- 
 solution is saturated with finely pulverised salt (about 30 grammes) 
 with shaking the solution is poured off from any undissolved salt, 
 and being cooled with ice is treated with a cold solution of 60 
 grammes of stannous chloride in 25 grammes of concentrated 
 hydrochloric acid. After several hours' standing, the phenyl- 
 hydrazine hydrochloride separates out, this is filtered off with 
 suction, washed with a little saturated salt solution, pressed out 
 on a porous plate, and treated as above. 
 
 (b) In a i -litre flask provided with a dropping funnel and con- 
 
252 
 
 SPECIAL PART 
 
 denser (Fig. 68) 150 grammes of water and 50 grammes of cop- 
 per sulphate are heated to boiling, then from the funnel add 
 gradually a solution of 10 grammes of free phenyl hydrazine in 
 a mixture of 8 grammes of glacial acetic acid and 75 grammes of 
 water. The oxidation of the phenyl hydrazine proceeds with an 
 energetic evolution of nitrogen ; the benzene is immediately dis- 
 tilled over with steam and collected in a test-tube. By another 
 careful rectification from a small fractionating flask (without con- 
 
 FlG. 68. 
 
 denser), pure benzene, boiling at 81, is obtained. Yield, about 
 5 grammes. 
 
 Monosubstituted hydrazines of the type of phenyl hydrazine may 
 be obtained according to the method of V. Meyer and Lecco, 1 by 
 reducing the diazo-compounds with stannous chloride and hydrochloric 
 
 acid : 
 
 C 6 H 5 . N 2 . Cl + 2 H a = C 6 H 5 . NH . NH 2 , HC1 
 
 Phenyl hydrazine hydrochloride 
 
 The reaction is always conducted as above : The amine is diazotised 
 in a strong hydrochloric acid solution, and then a solution of stannous 
 chloride in strong hydrochloric acid is added to it. Since the hydro- 
 chlorides of the hydrazines are difficultly soluble in concentrated 
 hydrochloric acid, these separate out directly on the addition of the 
 
 i B. 16, 2976. 
 
AROMATIC SERIES 2$ 3 
 
 stannous chloride, and can easily be obtained pure by filtration, as 
 above. 
 
 The reduction of the diazo-compounds to hydrazines may be ac- 
 complished by the method of Emil Fischer 1 which led to the dis- 
 covery of this class of compounds, and also by another method. If 
 neutral sodium sulphite is allowed to act on a diazo-salt, the acid 
 radical of the diazo-compound is replaced by a residue of sulphurous 
 acid, e.g. : 
 
 C C H 5 . N,. Cl + NaSO, . Na = C 6 H 5 . N 2 . SO 3 Na + NaCl 
 
 Sodium diazobenzenesulphonate 
 
 If this salt is now reduced with sulphurous acid, or with zinc dust 
 and acetic acid, it takes up two atoms of hydrogen and is converted 
 into a hydrazine sulphonate : 
 
 C G H- . N 2 . SO,Na + H 2 = C 6 H 5 . NH . NH . SO 3 Na 
 
 Sodium phenyl hydrazine sulphonate 
 
 If this is heated with hydrochloric acid, the sulphonic acid group is 
 split off, and phenyl hydrazine hydrochloride is formed, which, on 
 evaporation, crystallises out : 
 
 C 6 H 5 .NH.NH.SO 3 Na+HCl + HOH = C 6 H 5 .NH.NH 2 ,HCl + NaHSO 4 . 
 
 According to this method, which is slower, but cheaper than the 
 former, phenyl hydrazine is prepared on the large scale. 
 
 The monosubstituted hydrazines possess a basic character ; in spite 
 of the fact that they contain two ammonia residues, they combine with 
 only one molecule of a monobasic acid, e.g. : 
 
 C 6 H,.NH.NH 2 , HC1. 
 
 Phenyl hydrazine hydrochloride 
 
 Phenyl hydrazine reacts with aldehydes and ketones, the two hydro- 
 gen atoms of the amido-groups unite with the oxygen atom of the 
 CHO- or CO-groups, and are eliminated as water : 2 
 
 C 6 H , . CHO + C 6 H - . NH . NH 2 = C C H , . CH=N . NH . C 6 H 5 + H 2 O 
 
 Benzaldehyde Benzylidenephenyl hydrazone 
 
 C 6 H 5 \ 
 
 C 6 H 5 . CO . C 6 H 5 + C 6 H 5 . NH . NH 2 - V=N . NH . QH 5 + H 2 Q 
 
 C 6 H 5 ' 
 
 Benzophenone 
 
 1 A. 190, 67. 2 B. I 7 , 572. 
 
254 SPECIAL PART 
 
 This reaction can be used for the recognition and detection ol 
 aldehydes and ketones. In order to prepare a hydrazone, formerly a 
 solution of i part of phenyl hydrazine hydrochloride and i| parts of 
 crystallised sodium acetate in 10 parts of water was used as a reagent. 
 If this is added to an aldehyde or ketone, there is formed, in many cases 
 at the ordinary temperature, but in others only on heating, the hydra- 
 zone. Since, at present, perfectly pure free phenyl hydrazine may be 
 purchased in the market, a mixture of equal volumes of phenyl hydra- 
 zine and 50 % acetic acid, diluted with three times its volume of water, 
 is used as the reagent. 
 
 EXPERIMENT : To a mixture of 4 drops of phenyl hydrazine and 
 5 c.c. of water, add 3 drops of glacial acetic acid. To this is 
 added 2 drops of benzaldehyde (from a glass rod), and the mix- 
 ture shaken. At first there appears a milky turbidity, but very 
 soon a flocculent precipitate of benzylidenephenyl hydrazone sepa- 
 rates out. The smallest quantity of benzaldehyde may be recog- 
 nised in this way. 
 
 Phenyl hydrazine is of extreme importance in the chemistry of the 
 sugars for the separation, recognition, and transformation of the dif- 
 ferent varieties of the sugars. Without this reagent, the fundamental 
 explanations of the last few years in this field could scarcely have been 
 made. If one molecule of phenyl hydrazine is allowed to act on one 
 molecule of a sugar, a normal hydrazone is formed, e.g. : 
 
 CH 2 .OH(CH.OH) 4 .CHO + C 6 H 5 .NH.NH 2 
 
 Grapesugar = CH 2< OH(CH . OH) 4 . CH + H 2 O 
 
 N-NH.CgH,, 
 
 But if the phenyl hydrazine is used in excess, it acts as an oxidising 
 agent toward the sugar, extracting water, e.g., in the above case, 
 one of the secondary alcohol (CH.OH) groups adjoining the alde- 
 hyde (CHO) group is oxidised to a ketone group, which again reacts 
 with the hydrazine. The compound thus obtained is called an "Osa- 
 zone." In the above example, there is obtained a compound of this 
 composition : 
 
 CH 2 .OH.(CH.OH) 3 .C CH=N.NH.C 6 H 5 
 
 N 
 NH.C 6 H 5 
 
AROMATIC SERIES 255 
 
 If this compound is heated with hydrochloric acid, it acts in the 
 same way as all hydrazones, and phenyl hydrazine is eliminated ; the 
 original unchanged sugar is not formed again, but an oxidation product 
 of it is obtained, a so-called "Osone." In the example selected, the 
 osone is : 
 
 CH 2 .OH.(CH.OH) 3 .CO.CHO. 
 
 If this compound is treated with a reducing agent, the aldehyde 
 group and not the ketone group is reduced, and the original sugar is 
 not obtained : 
 
 CH 2 .OH(CH.OH) 3 .CO.CH 2 .OH. 
 
 The aldose is converted into a ketose, the grape sugar into fruit 
 sugar. The general importance of the reaction as applied to the sugars 
 may be inferred from these brief statements. 
 
 EXPERIMENT : A cold solution of 2 grammes of phenyl hydrazine 
 hydrochloride and 3 grammes of crystallised sodium acetate in 
 15 c.c. of water is treated with a solution of i gramme of pure 
 grape sugar in 5 c.c. of water, and warmed on the water-bath. 
 After about 10 minutes, the fine, yellow needles of the osazone 
 begin to separate out; the quantity is increased by a longer 
 heating. After heating an hour, the crystals are filtered off, 
 washed with water, and allowed to dry in the air. Melting-point, 
 
 205. 
 
 Phenyl hydrazine undergoes condensation with /?-diketones and 
 /?-ketone-acid-esters with the formation of ring compounds contain- 
 ing nitrogen the so-called pyrazoles and pyrazolones. The phenyl 
 methyl pyrazolone formed from acetacetic ester and phenyl hydrazine 
 is of importance : 
 
 CH,.C 
 
 . CH 2 CO OC 2 H 5 j - CH 3 - C - CH 2 . CO + H 2 O + C 2 H 5 OH 
 
 N- N[HJ.C 6 H 5 N NC C H 5 
 
 rom which, by the action of methyl iodide, the important febrifuge 
 " Antipyrine " dimethyl phenyl pyrazolone is obtained: 
 
 CH 3 .C CH CO 
 CH 3 -N N-C 6 H 5 
 
 Antipyrine 
 
256 SPECIAL PART 
 
 If the primary hydrazines are boiled with copper sulphate, 1 or ferric 
 chloride, 2 the hydrazine radical is replaced by hydrogen, and there is 
 obtained, e.g., from phenyl hydrazine, benzene : 
 
 C 6 H 5 . NH . NH 2 + 2 CuO = C 6 H 6 + N 2 + H 2 O + Cu 2 O, 
 or C 6 H 5 .NH.NH 2 + CuO = C 6 H 6 + N a + H 8 O + Cu. 
 
 The statements made above concerning the replacement of a diazo- 
 group by hydrogen are also applicable to this reaction. If it is desired 
 to prepare an amido-compound from an amido-free compound, and if 
 the direct reduction of the diazo-compound by sodium stannous oxide 
 or alcohol (see page 237) has been shown to be impracticable, then, as 
 above, the hydrochloric acid salt of the corresponding hydrazine is pre- 
 pared, the free hydrazine is liberated, and oxidised with caustic soda. 
 The amido-free substance is not always easily volatile, as in the example 
 cited. In a case of this kind, the oxidation may be effected in an open 
 vessel ; the reaction product is obtained either by filtering or by extract- 
 ing with ether. It may be pointed out here that it is more convenient to 
 separate the hydrazine from the hydrochloric acid salt, and subject this 
 to oxidation. If a hydrochloric acid salt of a hydrazine is oxidised, it 
 may happen that the hydrazine radical will be replaced by chlorine : 
 
 C 6 H 5 .NH .NH 2 , HC1 + O 2 =C 6 H 5 .C1 + N 2 + 2 H 2 O, 
 which may give rise to complications. 
 
 12. REACTION: (a) PREPARATION OP AN AZO DYE FROM A DIAZO- 
 COMPOUND AND AN AMINE. (&) REDUCTION OF THE AZO-COM- 
 POUND 
 
 EXAMPLES : (a) Helianthine from Diazotised Sulphanilic Acid and 
 
 Dimethyl Aniline 
 () Reduction of Helianthine 
 
 (a) Dissolve 10 grammes of sulphanilic acid, dried on the 
 water-bath, in a solution of 3.5 grammes of dehydrated sodium 
 carbonate in 150 c.c. of water, and treat with a solution of 4.2 
 grammes of pure sodium nitrite in 20 c.c. of water. To rhis 
 mixture, after being cooled by water, is added a quantity of 
 hydrochloric acid solution corresponding to 2.5 grammes of an- 
 
 i B. 18, 90. 2 B. 18, 786. 
 
AROMATIC SERIES 
 
 257 
 
 hydrous hydrochloric acid. For this purpose, concentrated hydro- 
 chloric acid is diluted with an equal volume of water, and the 
 specific gravity of the dilute acid is determined by a hydrometer. 
 Consult a table, to find the amount of anhydrous hydrochloric 
 acid corresponding to the reading of the hydrometer. (See 
 Graham-Otto, Vol. II i, p. SiS.) 1 
 
 Before diazotising the sulphanilic acid, a solution of 7 grammes 
 of dimethyl aniline in the theoretical amount of hydrochloric acid 
 is prepared. Aromatic bases cannot be neutralised with hydro- 
 chloric acid in the same way as caustic potash, caustic soda, 
 and ammonium hydroxide, by gradually treating with the acid and 
 testing with blue litmus-paper until the liquid is just acid. In con- 
 sequence of the weak basic character of the amines, their hydro- 
 chlorides still give an acid reaction with blue litmus-paper, there- 
 fore an acid reaction can be obtained even at the beginning of 
 the neutralisation. Red fuchsine-paper possesses the property of 
 becoming decolourised by free hydrochloric acid, which converts 
 the red monoacid fuchsine into a colourless polyacid salt. The 
 hydrochloric acid salts of bases, on the contrary, do not produce 
 this decolourisation. In order to neutralise the dimethyl aniline 
 (7 grammes), it is treated with 25 c.c. of water, and, with stirring, 
 small quantities of concentrated hydrochloric acid are added; 
 after each addition a test is made to show whether or not the 
 fuchsine-paper is decolourised. 
 
 The dimethyl aniline hydrochloride thus obtained is added to 
 the diazo-solution, and the mixture is made distinctly alkaline by 
 the addition of not too much caustic soda solution. The dye 
 separates out directly; the quantity can be increased if 25 
 grammes of finely pulverised sodium chloride are added to the 
 solution. After filtering off and pressing out on a porous plate, 
 the dye is recrystallised from a little water. 
 
 1 If the specific gravity of the hydrochloric acid has been determined, the per- 
 centage of free anhydrous acid may be found without a table, by the following 
 calculation : The decimal number is multiplied by 2, and a decimal point placed 
 after the first two figures thus obtained, e.g., sp. gr. = 1.134; 2X134 = 268. 
 Percentage contents = 26.8. If the sp. gr. is greater than 1.18, a table must be 
 consulted. 
 
 s 
 
258 .SPECIAL PART 
 
 Preparation of Fuchsine- Paper : A crystal of fuchsine, the size 
 of a lentil, is pulverised, dissolved by heating in 100 c.c. of water, 
 and the solution filtered. 
 
 Into this immerse strips of filter-paper 2 cm. wide ; they, are 
 dried either by suspending from a string in an acid-free place, 
 or on the water-bath. The paper must not be an intense red, 
 but only a faint rose colour. If the colour is too intense, the 
 fuchsine solution must be correspondingly diluted with water. 
 
 Instead of the fuchsine-paper, the commercial Congo-paper will 
 serve, the red colour of which is changed to blue by free acid. 
 
 (^) Dissolve 2 grammes of the dye in the least possible amount 
 of water by heating ; while the solution is still hot, treat with a 
 solution of 8 grammes of stannous chloride in 20 grammes of 
 hydrochloric acid until decolourisation takes place. The colour- 
 less solution is then well cooled, upon which, especially if the 
 sides of the vessel are rubbed with a glass rod, sulphanilic acid 
 separates out : it is filtered off through asbestos or glass-wool. 
 The filtrate is diluted with water, and caustic soda solution is 
 added until the oxyhydrate of tin separating out at first is again 
 dissolved. It is then extracted with ether several times, the 
 ethereal solution dried with potash, and the ether evaporated, 
 upon which the p-amidodimethyl aniline remains as an oil : on 
 cooling and rubbing with a glass rod, it solidifies. 
 
 Reactions of p-Amidodimethyl Aniline : 1 The amidodimethyl 
 aniline is treated gradually with small quantities of dilute sul- 
 phuric acid until it is just dissolved. Add a few drops of this 
 solution to a dilute solution of hydrogen sulphide in a beaker 
 which has been treated with -$ of its volume of concentrated 
 hydrochloric acid. To this mixture now add several drops of a 
 dilute solution of ferric chloride. An intensely blue colouration, 
 due to the formation of methylene blue, takes place. 
 
 Diazo-compounds react with amines, as well as phenols, to form the 
 Azo dyes : 2 
 
 1 B. 16, 2235. 2 A. 137, 60 ; B. 3, 233. 
 
AROMATIC SERIES 259 
 
 (1) C 6 H 5 . N 2 . Cl + C 6 H S . N(CH 3 ) 2 
 
 = C fi H 5 . N=N . C 8 H 4 . N(CH 3 ) 2 + HC1 
 
 Dimethylamidoazo benzene 
 
 (2) C 6 H 5 . N 2 . Cl + C 6 H 5 . OH = C 6 H 5 . N=N . C 6 H 4 . OH + HC1 
 
 (In presence of alkali) Oxyazo benzene 
 
 According to Hantzsch the reaction takes place in the following 
 manner : 
 
 C C H 5 C C H 4 .OH C 6 H 5 C 6 H 4 OH C C H 5 
 
 N=N + 
 
 = N:=:N 
 
 Cl H C C H 4 .OH 
 
 An unstable syn-azo compound is formed first, which rapidly changes 
 into the more stable anti-azo compound. 
 
 In accordance with these two typical reactions, the vast number of 
 monoazo dyes are prepared. The great number of possible combina- 
 tions can be inferred from the following considerations : In reaction 
 (i), instead of diazotised aniline, other bases, like o-toluidine, p-tolui- 
 - dine, xylidine, cuminidine, a-naphthyl amine, /?-naphthyl amine, etc., 
 may be used. In addition, the most varied derivatives of these bases, 
 especially their sulphonic acids, like sulphanilic acid, metanilic acid, 
 the large number of a- and /3-naphthyl amines mono- to poly-sulphonic 
 acids, may also be employed. Instead of dimethyl aniline, the diazo- 
 compound can be combined or " coupled " with other tertiary, and in 
 part also with secondary and primary amines, like diphenyl amine, or 
 m-diamines, etc. In the second reaction, the diazo-compounds of the 
 just mentioned bases can be employed as the starting-point, and these 
 can be combined with mon-acid phenols, like cresol, naphthols, or di- 
 acid phenols like resorcinol, or the sulphonic acids of these phenols, 
 especially the numerous sulphonic acids of both naphthols. Since a dye 
 must be soluble in water, and the alkali salts of the sulphonic acids of the 
 dyes are more easily soluble than the mother substance containing no 
 sulphonic acid groups, therefore, in the preparation of the azo dyes, the 
 starting-point is usually a sulphonic acid. A few examples will explain 
 these statements : 
 
 I. A mi do azo Dyes 
 
 /SO.H 
 
 p-C 6 H/ .C (; H 4 .N(CH 3 ) 2 = Helianthine, 
 
 Diazotised sulphanilic acid + dimethyl aniline 
 
 . C 6 H 4 . NH . C C H 5 = Metanilic Yellow, 
 
 Diazot. Metanilic acid + diphenylamine (secondary base) 
 
 /NH. 
 
 C,H r .N=N.C K H. { < = Chrysoidine. 
 
 \NH ? 
 
 Diazot. Aniline + m-phenylenediamine (primary 'base 1 ! 
 
26O SPECIAL PART 
 
 II. Oxyazo Dyes 
 
 /S0 3 H 
 
 p-C 6 H/ . C 10 H 6 . OH = Orange II., 
 
 >NzzN 
 
 Diazot. Sulphanilic acid + -naphthol 
 
 /S0 3 H 
 C 10 H,/ . C 10 H 6 . OH = Fast Red (first red azo dye) ? 
 
 \NzzN 
 
 Diazot. a-Naphthionic acid + |3-naphthol 
 
 /OH 
 
 C 6 H 5 . N=N . C 10 H / = Croceine Orange, 
 
 \SO 3 H 
 
 Diazot. Aniline + croceine acid 
 (/3-Naphthol sulphonic acid) 
 
 /OH 
 
 (CH 3 ) 2 .C 6 H 3 .N=N.C 10 H/ = Xylidine Ponceau. 
 
 \(S0 3 H) 2 
 
 Diazot. Xylidine + |3-naphthol disulphonic acid 
 
 Concerning the constitution of the azo dyes, provided the com- 
 ponents are known, the only question to solve is : which hydrogen 
 atom of the undiazotised component combines with the acid radical of 
 the diazo-compound (the acid thus formed being eliminated). The 
 question may be answered by investigating the reduction products of 
 the azo dyes. By energetic reduction, best in acid solution with stan- 
 nous chloride, the double NuiN union is broken up, thus forming, with 
 the addition of 4 atoms of hydrogen, two molecules of a primary 
 amine, e.g. : 
 
 /S0 3 H /S0 3 H /NH 2 
 
 C 6 H/ .C G H 4 .N(CH 3 ) 2 + 2H 2 = C 6 H/ + C 6 H/ 
 
 \N=N \NH 2 \N(CH 3 ) 2 
 
 From this equation it is evident that by reduction, the amine which 
 was diazotised in 'the above case sulphanilic acid may be obtained 
 again on the one hand, on the other an amido-group is introduced into 
 the second component. If the constitution of this second product can 
 be determined, then the constitution of the azo dyes is also determined. 
 It may be stated as a general rule that, when a diazo-compound com- 
 bines with an amine or phenol, the hydrogen atom in the para position 
 to the amido- or hydroxyl-group is always substituted. In accordance 
 with this, in the above case, p-amidodimethyl aniline ought to be 
 obtained on reduction. If the para position is already occupied, then 
 the o-hydrogen atom unites with the acid radical. 
 
AROMATIC SERIES 26 1 
 
 In some cases, the formation and consequent reduction of an azo 
 dye with the introduction of an amido-group into a phenol or amine is 
 of practical value. 
 
 Azo dyes which contain two " chromophore groups," NzzN, and 
 which are called dis- or tetr-azo dyes, can be prepared ; two methods 
 may be employed : (i) The starting-point is an amido-azo-compound 
 which already contains one azo group; this is diazotised, and then 
 united with an amine or phenol. " Biebrich scarlet" is obtained in 
 this way, by diazotising the disulphonic acid of amidoazobenzene, and 
 combining it with /3-naphthol : 
 
 0H 
 
 Diazot. Amidoazobenzene disulphonic acid + /3-naphthol 
 
 (2) A diamine is the starting-point ; this is diazotised, and the bisdiazo- 
 compound is combined with two molecules of an amine or phenol. 
 To this class belong the important dyes of the Congo group, prepared 
 from the benzidine bases (see page 231), e.g. : 
 
 /NH 2 
 C 6 H 4 -N=N-C ]0 H/ 
 
 Diazot. Benzidine + 2 mol. a-naphthionic acid 
 
 )H 
 
 ^TO.OH = chrysamine . 
 
 6 H 4 .N=N.C 6 H/ 
 * \CO.OH 
 
 Diazot. Benzidine + 2 mol. salicylic acid 
 
 These Congo dyes possess the noteworthy property of colouring 
 vegetable fibres (cotton) directly, whereas, with almost all other azo 
 dyes, the cotton must be mordanted before dyeing. 
 
 In conclusion, the above dye-stuff reaction (which may be used for 
 detecting the smallest amount of hydrogen sulphide) is technically 
 carried out on the large scale, for the manufacture of the important 
 methylene blue. The reaction takes place as follows : From two mole- 
 cules of the diamine there is split off on oxidation with ferric chloride. 
 
262 SPECIAL PART 
 
 one molecule of ammonia, while a derivative of diphenyl amine is 
 formed : 
 
 X N(CH 3 ) 2 /N(CH 3 ) 2 
 
 C 6 H 4 
 
 \N(CH 3 ) 2 
 
 In the presence of hydrogen sulphide and hydrochloric acid, there 
 is formed from this, by the oxidising action of ferric chloride, a deriva- 
 tive of thiodiphenylamine, as follows : 
 
 N(CH 3 ) 
 
 /N(CH S ), 
 
 lH3 > 
 
 TJ / 
 
 Methylene blue 
 
 l_+0- 
 
 13. REACTION: PREPARATION OF A DIAZOAMIDO-COMPOUND 
 
 EXAMPLES: Diazoamidobenzene from Diazobenzenechloride and 
 
 Aniline l 
 
 Dissolve 10 grammes of freshly distilled aniline in a mixture 
 of 100 c.c. of water, and that quantity of concentrated hydro- 
 chloric acid corresponding to 1 2 grammes anhydrous hydrochloric 
 acid (determine the sp. gr. by a hydrometer). The solution is 
 cooled with ice-water, and diazotised with a solution of 8 grammes 
 of sodium nitrite in 50 c.c. of water, in the manner already de- 
 scribed. A solution containing 10 grammes of aniline, 50 grammes 
 of water, and the exact theoretical amount of hydrochloric acid is 
 previously prepared according to the directions given on pages 
 
 i A. 121, 257. 
 
AROMATIC SERIES 263 
 
 256 and 257 ; this is well cooled with ice water, and added to the 
 diazo-solution, with stirring. Further, 50 grammes of crystallised 
 sodium acetate are dissolved in the least possible amount of water, 
 the cooled solution is added, with stirring, to the mixture of the 
 diazo-compound with aniline hydrochloride. After standing half an 
 hour, the diazoamidobenzene separates out, and is filtered off with 
 suction, washed several times with water, well pressed out on a 
 porous plate, and recrystallised from ligroin. Melting-point, 98. 
 Yield, almost theoretical. 
 
 If one molecule of a diazo-compound is allowed to act on one mole- 
 cule of a primary amine, the acid radical of the former unites with the 
 hydrogen atom of the latter, upon which the organic residues combine, 
 as in the formation of the azo dyes. In this case, an amido-hydrogen 
 atom is eliminated, so that a compound containing a chain of three 
 nitrogen atoms is formed ; in the formation of an azo dye, one of the 
 benzene-hydrogen atoms of the amine is eliminated : 
 
 C 6 H 5 . N 2 .C1 + C 6 H 5 . NH 2 = C 6 H 5 . N=N . NH .C 6 H 5 + HC1 
 
 Diazoamidobenzene 
 
 Mixed diazo-compounds may also be prepared by causing the diazo- 
 derivative of an amine to combine with another amine : 
 
 /CH 3 
 C 6 H 5 . N, . Cl + C 6 H/ = C 6 H 5 . N=N . NH . C 6 H 4 . CH 3 + HC1 
 
 \Nri2 
 
 Benzenediazoamidotoluene 
 
 Diazo-compounds combine only with the free amines to form diazo- 
 amido compounds ; the object of the addition of sodium acetate at the 
 end of the reaction (see above) is to set free the base from aniline 
 hydrochloride. 
 
 The diazoamido-compounds are yellow substances which do not dis- 
 solve in acids. They are far more stable than the diazo-compounds, 
 and may be recrystallised without decomposition. Still, if they are 
 heated rapidly they puff up suddenly and decompose. In their reac- 
 tions they behave like a mixture of a diazo-compound and an amine. 
 If, e.g., they are boiled with hydrochloric acid, they decompose with 
 evolution of nitrogen, and form a phenol and an amine : 
 
264 SPECIAL PART 
 
 On heating with cuprous chloride and hydrochloric acid, the Sand- 
 meyer reaction takes place : 
 
 C 6 H 5 . N=N . NH . C 6 H 5 + HC1 = C 6 H- . Cl + C 6 H 5 . NH 2 + N 2 
 By reduction with acetic acid and zinc dust, they form a hydrazine : 
 C 6 H 5 .N=N.NH.C (J H 5 + 2 H 2 = C ( ,H,.NH . NH 2 + C 6 H 5 . NH 2 
 
 But, in addition to the reaction-product of the diazo-radical, there is 
 always formed one molecule of an amine. 
 
 Under the influence of nitrous acid, they decompose, the amine 
 residue being diazotised, into two molecules of a diazo-compound : 
 
 C 6 H 5 . NziN . NH . C,H 5 + HNO 2 + 2 HC1 = 2 C 6 H 5 . N 2 . Cl + 2 H 2 O 
 
 If a diazcamido-compound is warmed with an amine in the presence 
 of some amine hydrochloride, transformation to the isomeric amidoazo- 
 compound takes place : 
 
 C 6 H 5 . N=N . NH . C B H a = C 6 H 5 . N ~N . C 6 H 4 . NH 2 
 
 Amidoazobenzene 
 
 The next preparation deals with this reaction. 
 
 The diazo-compounds also have the power of combining with sec- 
 ondary amines to form diazoamido-compounds, the combinations 
 with an alkaloid base, piperidine C.H U N : 
 
 CH 2 
 
 H 2 C/\CH 5 
 H 2 Cl JCH, 
 
 NJ 
 
 are of especial value for preparations. If they are gradually warmed 
 with hydrofluoric acid, they are decomposed with the evolution of nitro- 
 gen into piperidine and a fluoride : 1 
 
 C 6 H 5 .Nz=N.N.C 5 H 10 + HF1 = C G H-.F1 + C 5 H U N + N 2 
 
 Benzenediazopiperidine Fluorbenzene 
 
 In this way it has been possible to prepare the aromatic fluorides. 
 
 In accordance with the older views it was believed that the aromatic 
 fluorides could not be obtained from the diazo-compounds in the same 
 way in which the analogous chlorides, bromides, and iodides are pre- 
 pared ; recently however they have been obtained by the direct decom- 
 position of the diazo-fluorides. 
 
 243, 239. 
 
AROMATIC SERIES 265 
 
 14. REACTION: THE MOLECULAR TRANSFORMATION OF A DIAZO 
 AMIDO-COMPOUND INTO AN AMIDOAZO-COMPOUND 
 
 EXAMPLE : Amidoazobenzene from Diazoamidobenzene 
 
 To a mixture of 10 grammes of crystallised diazoamidobenzene, 
 finely pulverised, and 5 grammes of pulverised aniline hydro- 
 chloride, contained in a small beaker, add 25 grammes of freshly 
 distilled aniline ; the mixture is then heated, with frequent stirring, 
 one hour, on the water-bath, at 45. It is then transferred to a 
 larger vessel, and treated with water ; dilute acetic acid is added, 
 until all the aniline has passed into solution, and the undissolved 
 precipitate remaining is completely solid. This is filtered off, 
 washed with water, heated in a large dish with a large quantity 
 of water (about a litre), and gradually treated with hydrochloric 
 acid until the greatest portion of the precipitate is dissolved. 
 From the filtered solution, steel-blue crystals of amidoazobenzene 
 hydrochloride separate out, on long standing ; these are filtered 
 off, and washed with dilute hydrochloric acid, not with water. 
 
 If aniline hydrochloride is not at hand, prepare it by adding 
 aniline to concentrated hydrochloric acid, with stirring. After 
 cooling, the pasty mass of crystals separating out is filtered on 
 glass-wool, pressed firmly together on the filter with a pestle, and 
 then spread in thin layers on a porous plate. 
 
 In order to obtain the free amidoazobenzene, the hydrochloride 
 is warmed with dilute ammonia, the free base filtered off, dis- 
 solved in alcohol by heating, and hot water is added until the liquid 
 begins to be turbid. Melting-point, 1 2 7-1 28. Yield, 6-8 grammes. 
 
 If a diazoamido-compound is heated with an amine and some amine 
 hydrochloride, it goes over to an amidoazo-compound. The most 
 probable cause of the reaction is that the amine residue of the diazo- 
 amido-compound unites with a benzene-hydrogen atom of the amine 
 hydrochloride, upon which the diazo-residue unites with the residue 
 of the amine salt to form amidoazobenzene : 
 
 C 6 H 5 . N=N . |NH . QH, + H i . C,.H 4 . NH 2 
 
 ""= C 6 H ,. N N . C 6 H 4 . NH 2 + C 6 H 5 . NH a 
 
 Amidoazobenzene 
 
266 SPECIAL PART 
 
 While the amidoazobenzene does not unite with hydrochloric acid, 
 the new molecule of the amine formed in the reaction does, and thus 
 there is a molecule of the amine hydrochloride present, which again 
 causes the transformation, so that a small amount of the hydrochloride 
 may transform an indefinitely large amount of the diazoamido-compound. 
 
 If amidoazobenzene is reduced, p-phenylene diamine and aniline are 
 obtained. The transformation accordingly results in the formation of 
 a compound in which the amido-groups are in the para position, which 
 always happens when the para position is unoccupied. The amidoazo- 
 compounds possess weakly basic properties ; but if their salts are 
 treated with much water, they partially dissociate. 
 
 The amidoazobenzene hydrochloride came into the market formerly, 
 as a yellow dye, under the name of "Aniline Yellow." At present, it 
 is scarcely used, but there is prepared from it, by heating with sulphuric 
 acid, a mono- or di-sulphonic acid, which in the form of its alkali salts 
 finds application as a dye under the name of " Acid Yellow," or " Fast 
 Yellow." As already mentioned under the dis-azo dyes, from the 
 diazo-compound of this dye, " Biebrich Scarlet" may be made by com- 
 bination with /?-naphthol. Finally, the amidoazobenzene is still used 
 for the preparation of the Induline dyes. 
 
 15. REACTION: OXIDATION OF AN AMINE TO A QUINONE 
 EXAMPLE : Quinone from Aniline l 
 
 To a solution of 25 grammes of aniline in a mixture of 200 
 grammes of concentrated pure sulphuric acid and 600 c.c. of water 
 contained in a thick-walled beaker (a small battery jar), cooled 
 to 5 by being surrounded with ice, add gradually, with constant 
 stirring (use a small motor), from a dropping funnel, a solution of 
 25 grammes of sodium dichromate in 100 c.c. of water (Fig. 69). 
 Should the temperature rise above 10, the addition of the dichro- 
 mate must be discontinued for a short time and a few pieces of ice 
 thrown into the beaker. The reaction-mixture is then allowed to 
 stand over night in a cool place, and the next morning it is again 
 cooled and stirred, while a solution of 50 grammes of sodium di- 
 chromate in 200 c.c. of water is added. After the mixture has been 
 allowed to stand until midday, it is divided into two equal parts, one 
 of which is worked up into quinone as follows : In -a large separating 
 
 * A. 27, 268; 45,354; 215, 125; B. 19, 1467; 20, 2283. 
 
AROMATIC SERIES 
 
 267 
 
 funnel one half is treated with | its volume of ether, and the two 
 layers thus formed are carefully shaken together. If the shaking 
 is too vigorous, the layers will not readily separate. After allowing 
 it to stand for half an hour, the lower layer is run off (see page 
 44, Separation of coloured liquids), the ethereal solution is filtered 
 through a folded filter, and the ether distilled off (water-bath with 
 warm water). The water solution is again extracted with the con- 
 densed ether, and the ether again distilled from the same flask as 
 before. In order to obtain perfectly pure quinone, a rapid current 
 of steam is passed over the crude product it is not treated with 
 
 FIG. 69. 
 
 water ; the pure quinone is carried over with the steam to the 
 condenser and receiver, where it crystallises in the form of golden- 
 yellow needles ; they are filtered off and dried in a desiccator. 
 Melting-point, 116. Yield, 10-12 grammes. 
 
 If sodium dichromate is not at hand, the potassium salt may be 
 used for the oxidation. In this case, 25 grammes of aniline are 
 dissolved in a mixture of 200 grammes of sulphuric acid and 800 
 c.c. of water ; then add, as above, with stirring and good cooling, 
 25 grammes of potassium dichromate, powdered extremely fine. 
 On the next day add 50 grammes of this salt. In other respects, 
 proceed as above. 
 
 For the preparation of hydroquinone from quinone see p. 270. 
 
 Many primary aromatic amines yield quinones on oxidation with 
 chromic acid. But the reaction cannot be expressed in a simple equa- 
 tion ; still, it is always true that the amido-group and the hydrogen 
 
268 SPECIAL PART 
 
 atom in the para position to this are each replaced by an oxygen 
 atom, e.g. : 
 
 C 6 H S .NH 2 ^C 6 H,0 2 
 
 Quinone 
 
 ,CH 3 
 o-C 6 H 4 < - 
 
 \NH 2 O 
 
 Toluidine Tolyl quinone 
 
 The tendency to form quinones is so great that even in cases where the 
 para position to the amido-group is occupied by an alkyl (methyl) radical, 
 the latter is split offand a quinone (poorer in carbon contents) is formed. 
 Indeed, in the simplest cases, like p-toluidine and asym. m-xylidine, the 
 reaction is very incomplete ; however, mesidine, as well as pseudocumidine, 
 give satisfactory yields of quinones belonging to the next lower series : 
 
 NH O 
 
 H,C /-CH 
 
 H 3 C- 
 
 :H S o 
 
 Pseudocumidine p-Xyloquinone 
 
 But if the para position is occupied by an amido-, oxy-, or sulphonic 
 acid-group, this is eliminated and a quinone formed : 
 
 P-C 6 H/ 
 
 NH 
 
 , 
 X 
 
 From these methods of formation it follows that the two quinone- 
 oxygen atoms are in the para position to each other. The quinone 
 reaction can be used in doubtful cases to decide whether a compound 
 
AROMATIC SERIES 
 
 269 
 
 belongs to the para series. The quinones can also be obtained very 
 easily from p-dioxy-compounds as well as from the p-sulphonic acids 
 of mon-acid phenols : 
 
 p-C 6 H/ + O = C 6 H 4 2 + H 2 
 X)H 
 
 /OH 
 
 p-C 6 H/ _^c 6 H 4 2 - 
 
 X SO 3 H 
 
 Two formulae for the quinones have been proposed: 
 
 According to the former the quinones still contain the true benzene 
 ring with either three double or six centric bonds. The two oxygen 
 atoms are only singly united with the benzene-carbon atoms, and are 
 united to each other. According to the second formula, the quinones 
 do not contain the true benzene ring, but they are derived from a 
 dihydrobenzene, 
 
 H H 
 
 H 
 
 and are regarded as the di-ketone derivative of this. According to 
 this conception, the oxygen atoms are connected by two bonds, as in 
 the ketones, with the carbon atoms of the benzene nucleus. The facts 
 in favour of the first formula are these : In many reactions both of the 
 
27O SPECIAL PART 
 
 oxygen atoms are replaced by two univalent atoms or radicals. Thus, 
 e.g., by the action of phosphorus pentachloride on quinone, p-dichlor- 
 benzene is formed, while the second formula would lead one to expect 
 a tetra-chloride. In support of the second formula is the fact that 
 hydroxylamine acts directly on quinones, as on ketones, with the 
 formation of a mono- or di-oxime. 
 
 The p-quinones are coloured compounds, possessing a characteristic 
 odour ; they are easily volatile with steam, but with a slight decomposi- 
 tion. They are somewhat volatile even with the vapour of ether, as 
 one observes in the preparation of quinone. On reduction they take 
 up two hydrogen atoms and pass over to hydroquinones. (See the 
 next preparation) e.g. : 
 
 /OH 
 C 6 H 4 O 2 + H 2 C 6 H 4 \ 
 
 \OH 
 
 Hydroquinone 
 
 Of late years ortho-benzoquinone has also been prepared by the 
 oxidation of pyrocatechin (o-dihydroxy benzene) with silver oxide. 1 
 Under certain conditions a c&lourless* o-quinone is first formed, but 
 being very unstable it passes over into red quinone. For the colourless 
 quinone the so-called Peroxide formula has been proposed, and for the 
 red quinone the Ketone formula : 
 
 UU 
 
 Colourless Red 
 
 The o-quinones are less stable than the p-quinones. They are odour- 
 less, and non-volatile with steam. 
 
 16. REACTION: REDUCTION OF A QUINONE TO A HYDROQUINONE 
 EXAMPLE : Hydroquinone from Quinone 
 
 Conduct sulphur dioxide into the second half of the quinone 
 solution obtained above, until the liquid smells intensely of the 
 gas, then allow it to stand for 1-2 hours. Should the odour of 
 sulphur dioxide vanish, it is passed in again and the mixture 
 allowed to stand for some time as before. It is then extracted 
 with the ether distilled from the quinone in the preceding experi- 
 
 l B. 37, 4744. 2 B. 41, 2580. 
 
AROMATIC SERIES 2/1 
 
 ment, several times ; the ether is evaporated or distilled, and the 
 hydroquinone, well pressed out on a porous plate, is crystallised 
 with the use of animal charcoal from a little water. Melting-point, 
 169. Yield, 8-10 grammes. 
 
 Since the hydroquinone solution may be extracted with ether 
 with much greater ease than the quinone solution, and since the 
 hydroquinone is smoothly oxidised to quinone, the preparation of 
 quinone may be done as follows : The entire quantity of the oxi- 
 dation product is saturated with sulphur dioxide, and as just de- 
 scribed the hydroquinone may be obtained by repeated extraction 
 with ether. In order to convert it into quinone it is dissolved in the 
 least possible amount of water, to which is added 2 parts of con- 
 centrated sulphuric acid to i part of hydroquinone ; the well- 
 cooled liquid is treated with a water solution of sodium dichro- 
 mate until the green crystals of quinhydrone (an intermediate 
 product between quinone and hydroquinone) separating out in 
 the beginning have changed into pure yellow quinone. 
 
 The equation for the formation of hydroquinone from quinone has 
 been given above. All homologous quinones react in the same way. 
 The hydroquinones are di-acid phenols, which dissolve in alkalies and 
 show all the properties of phenols. They are not volatile with steam. 
 
 17. REACTION: BROMINATION OF AN AROMATIC COMPOUND 
 EXAMPLE : Mono- and Di-brombenzene from Bromine and Benzene 
 
 A wide-neck 250 c.c. flask is connected with a vertical tube 
 50 cm. long and i^ cm. wide, the upper end of which is closed by 
 a cork bearing a glass tube, not too narrow, bent twice at right 
 angles. The- other end is connected with a flask containing 
 250 c.c. of water, by a cork having a small canal in the side 
 (Fig. 70). The tube does not touch the liquid, but the end is 
 about i cm. above the surface. After 50 grammes of benzene 1 and 
 i gramme of coarse iron filings (the bromine carrier) have been 
 placed in the flask, it is cooled in a large vessel (battery jar) filled 
 
 1 One hundred grammes of benzene should be used if the Grignard reaction 
 (see p. 348) is to be carried out later on. 
 
272 
 
 SPECIAL PART 
 
 with ice-water ; through the vertical tube there is added 40 c.c. 
 = 120 grammes of bromine: the narrow tube is immediately 
 connected with the vertical tube. After 
 some time an extremely energetic reaction 
 will begin, generally spontaneously, with the 
 evolution of hydrobromic acid, which is 
 completely absorbed by the water. Should 
 the reaction not begin at once, the ice-water 
 is removed for a short time, and if necessary 
 the flask is immersed for a moment in 
 slightly warm water. But as soon as even a 
 weak gas evolution begins, the flask is at 
 once cooled again, since otherwise the re- 
 action easily becomes too violent. Should 
 this happen in spite of the cooling, the cause 
 is found in the fact that the iron filings used 
 were too fine. In other experiments use 
 coarser filings or small iron nails. When 
 the main reaction is over, the ice-water is 
 removed, the flask dried and heated over a 
 small flame until the red bromine vapours are no longer visible 
 above the dark-coloured liquid. The reaction-product is washed 
 several times with water and then distilled with steam. As soon 
 as crystals of dibrombenzene separate out in the condenser, the 
 receiver is changed and the distillation continued until all the 
 dibrombenzene has passed over. The liquid monobrombenzene 
 is separated from the water, dried with calcium chloride, and sub- 
 jected to a fractional distillation ; the portion passing over between 
 140-170 is collected separately. This is again distilled, and the 
 portion going over between 150-160 collected. The boiling-point 
 of the pure monobrombenzene is 155. Yield, 60-70 grammes. The 
 residue boiling above 1 70 remaining in the flask after the two dis- 
 tillations, is poured, while still warm, on a watch-glass, and after 
 cooling is pressed out, together with the separately collected dibrom- 
 benzene, on a porous plate. On crystallising from alcohol, coarse 
 colourless crystals of p-dibrombenzene are obtained, which melt 
 at 89. 
 
 FIG. 70. 
 
AROMATIC SERIES 2/3 
 
 The by-product, hydrobromic acid, is purified as described in 
 the Inorganic Part. (See page 379.) 
 
 A portion of the hydrogen of the aromatic hydrocarbons is very 
 easily replaced by bromine, especially in the presence of a carrier, even 
 at low temperatures ; while in the aliphatic series the direct substitution 
 of bromine is not used as a preparation method for alkyl bromides, 
 the aromatic bromides are readily prepared in this way. According 
 to the amount of bromine used one or more hydrogen atoms may be 
 substituted ; it may happen, e.g., particularly with benzene under the 
 influence of an energetic bromination, that all the hydrogen atoms may 
 be replaced by bromine. A single bromide, even on using only the 
 theoretical amount of bromine, is never formed ; but rather a portion 
 of the hydrocarbon is brominated short of the theoretical action, and 
 another portion is always acted upon farther, with the formation of a 
 higher bromine substitution product. Thus in the example above cited, 
 besides the principal product, monobrombenzene, a small quantity of 
 dibrombenzene is formed : 
 
 C 6 U G + Br 2 = C 6 H 5 Br + HBr 
 C 6 H 6 + 2 Br 2 = C 6 H 4 Br 2 + 2 HBr 
 
 In most cases, however, the principal product may be separated 
 from the by-product without difficulty by distillation or crystallisation. 
 Since the hydrogen atoms substituted by bromine combine with bromine 
 to form hydrobromic acid, therefore, for the introduction of each 
 bromine atom, a molecule (two atoms of bromine) must be used. 
 
 The introduction of bromine can be essentially facilitated by the use 
 of a so-called bromine carrier. As such, the bromides of metalloids, 
 or metals, are used; (i) either in the already prepared condition, or 
 (2) they can be generated from their elements in the reaction. To 
 the first class belong ferric bromide and aluminium bromide. The 
 action of ferric bromide depends on the fact that on being reduced tc 
 ferrous bromide, it yields bromine in statu nascendi: 
 
 FeBr 3 = FeBr 2 + Br. 
 
 Ferric bromide Ferrous bromide 
 
 Since the ferrous bromide unites with bromine again, to form ferric 
 bromide, a small quantity of this has the power to transfer an indefi- 
 nitely large quantity of bromine : 
 
 FeBr 2 + Br = FeBr 3 . 
 
2/4 SPECIAL PART 
 
 Instead of ferric bromide, ferrous bromide or anhydrous ferric chloride 
 may be used. The latter decomposes with hydrobromic acid to ferric 
 bromide and hydrochloric acid : 
 
 FeCl 3 + 3 HBr = FeBr 3 -f 3 HC1. 
 
 The activity of aluminium bromide is explained by the fact that it 
 unites with the hydrocarbon to form a double compound which is more 
 capable of reacting with other substances than the hydrocarbon itself. 
 
 To the second class belong iodine, sulphur, phosphorus, iron, alumin- 
 ium, etc. If these elements are added to the brominating mixture, 
 the corresponding bromides are formed, e.g. : 
 
 While these give up all their bromine, or a portion of it, as is the 
 case with ferric bromide, in the atomic condition, the residue again 
 unites with bromine, and as above, a small quantity of the carrier may 
 transfer large quantities of atomic bromine. 
 
 Bromine can also act on aromatic hydrocarbons to form addition 
 products, since it may be added in one, two, or three molecules, and 
 thus break up the double or centric union. Thus, e.g., the hexabrom- 
 addition product, C 6 H 6 Br 6 , is obtained from the action of bromine on 
 benzene in the sunlight. Since the addition products render difficult 
 the purification of substitution products, especially on distillation (they 
 decompose when distilled), it is often necessary to remove them before 
 the purification, by long boiling with alcoholic caustic potash, or alco- 
 holic caustic soda. Under these conditions, one-half of the bromine 
 atoms added in common with the same number of hydrogen atoms 
 are abstracted as hydrobromic acid ; the residue of the molecule is 
 converted into a substitution derivative, which is not troublesome in 
 the purification : 
 
 C 6 H 6 Br 6 - C 6 H 8 Br 8 + 3 HBr. 
 
 On brominating benzene, the same products will be formed, whether 
 the temperature is high or low, but when its homologues are treated 
 with bromine, the nature of the products depends upon the temperature. 
 As will be pointed out more fully, under the chlorination of toluene, 
 the law holds here, that at low temperatures the halogen enters the 
 ring ; at high temperatures, the side-chain, e.g. : 
 
 1 Compare page 165. 
 
AROMATIC SERIES 
 
 275 
 
 C 6 H 5 . CH 3 + Br 2 = C 6 H 4 <^ + HBr 
 
 Ordinary temperature Bromtoluene 
 
 C 6 H 5 . CH 3 + Br 2 = C 6 H 5 . CH 2 . Br + HBr. 
 
 Boiling temperature Benzylbromide 
 
 The aromatic bromides which contain bromine in the benzene 
 nucleus are either colourless liquids or crystals, which in contrast with 
 the side-chain substituted isomers in part possess an aromatic odour, 
 and their vapours do not attack the eyes and nostrils. The bromine 
 is held very firmly in them, more firmly than in the aliphatic bromides, 
 and cannot be detected by silver nitrate. While the aliphatic bromides, 
 as mentioned under bromethyl, decompose with ammonia, alcoholates, 
 alkalies, etc., to form amines, ethers, alcohols, i 
 
 etc., respectively, these reagents do not act on 
 the aromatic bromides. The bromides contain- f 
 ing. the bromine in the side-chain, behave like 
 their aliphatic analogues. 
 
 By the action of sodium amalgam, the bro- 
 mine may be replaced by hydrogen, e.g. : 
 
 C 6 H B . Br + H 2 = C G H (! 
 
 From the 
 amalgam 
 
 HBr 
 
 The aromatic bromides are of synthetical 
 importance, 1 especially for the building up of 
 homologous hydrocarbons and the preparation 
 of carbonic acids : 
 
 C 6 H 5 . Br + BrC 2 H 5 + Na 2 = C 6 H 5 .C 2 H 5 + 2NaBr 
 C fi H 3 .Br + Na 2 + CO 2 =C 6 H 5 .CO.ONa+NaBr 
 
 The next preparation will take up the first of 
 these reactions in detail. 
 
 The hydrocarbons and most of their deriva- 
 tives, like nitro-, amido-compounds, aldehydes, 
 acids, etc., may be brominated with greater or 
 less ease. At this place, the various modifica- 
 tions by which the bromination may be effected 
 will be mentioned. If a substance is very easily 
 
 brominated. the bromine may be used in a diluted condition. For this 
 purpose, either bromine water or a mixture of bromine with carbon 
 
 1 Compare also the Grignard reaction (p. 348). 
 
2/6 SPECIAL PART 
 
 disulphide or glacial acetic acid may be employed. In many cases a 
 bromination may be very well effected by using gaseous bromine. The 
 method of procedure is as follows : The substance is spread out in thin 
 layers on a watch-glass and placed under a glass bell-jar, under which 
 is also a small dish containing bromine. If it is desired to cause bromine 
 to act gradually, it is allowed to drop from, a separating funnel, in con- 
 cenf-ated form or in solution, on the compound to be brominated. If 
 an extremely slow and very careful bromination is desired, the bromine 
 may be allowed to flow drop by drop from a siphon-shaped capillary 
 tube. If bromination takes places with difficulty, the brominating 
 mixture is heated, either in an open vessel or in a sealed tube. In the 
 first case the condensing apparatus cannot, as usual, be connected to 
 the flask with a cork or rubber stopper, since this is soon attacked and 
 destroyed by the bromine. Instead, the condenser is well wrapped 
 with asbestos twine and then pushed into the conical part of the neck 
 of the flask, the asbestos being pressed in with a knife. A condenser 
 of the kind represented in Fig. 71 can also be used. A long tube <r, 
 sealed at one end, is closed by a two-hole cork, through one of which 
 passes a long glass tube reaching almost to the bottom a ; the other 
 bears a short tube just passing through the cork. Water is caused to 
 flow through a ; it flows out of b. This cooling apparatus is suspended 
 in the heating-flask, which is selected with as long a neck as possible. 
 
 18. REACTION: FITTIG'S SYNTHESIS OP A HYDROCARBON 
 EXAMPLE : Ethyl Benzene from Brombenzene and Bromethyl l 
 
 In a dry, round, i-litre flask, provided with a long reflux con- 
 denser (the flask is supported on a straw ring in an empty water- 
 bath), place 27 grammes of sodium, cut in scales as thin as 
 possible with a sodium knife, and add 100 c.c. of alcohol-free, 
 dry ether prepared as described below. As soon as this has 
 been completely dried by the sodium, which may be recognised 
 by the fact that the upper surface is no longer disturbed by wave- 
 like motions (after several hours' standing), pour through the con- 
 denser a mixture of 60 grammes of brombenzene and 60 grammes 
 of bromethane, and allow to stand until the next day. Should the 
 
 i A. 131,303. 
 
AROMATIC SERIES 2/7 
 
 liquid begin to boil gently, which may easily happen at a summer 
 temperature, cold water is poured into the water-bath. Water is 
 not allowed to run through the condenser over night. During the 
 reaction, the bright sodium will be changed to a blue powder, and 
 an ethereal solution of ethylbenzene is formed. The ether is then 
 distilled off on a water-bath, and the condenser is replaced with 
 an air condenser 40-50 cm. long and i cm. wide, containing a 
 short bend. After the flask has been placed in an oblique posi- 
 tion, the extreme end of its neck is clamped loosely, and the 
 ethylbenzene is distilled from the sodium bromide and sodium 
 by a large, luminous flame, which is kept in constant motion. 
 With the use of a Linnemann apparatus, the crude product is 
 finally subjected to two distillations. The boiling-point of pure 
 ethylbenzene is 135. Yield, about 25 grammes. 
 
 The residue of sodium bromide and sodium remaining in the 
 flask must be handled with extreme caution. Water must not be 
 added to it, nor must it be thrown into the sink or waste-jars, nor 
 allowed to stand a long time ; it is better to throw the flask, which 
 cannot be used again, and its contents into some open place. The 
 sodium residue may be rendered harmless by throwing water on it 
 from a great distance. 
 
 Preparation of Anhydrous, Alcohol-free Ether 
 
 Shake 200 grammes of commercial ether in a separating fun- 
 nel with half its volume of water ; the latter is allowed to run off, 
 and the operation repeated a second time with a fresh quantity 
 of water, by which the alcohol is removed. The ether is dried by 
 standing over calcium chloride, not too little, two hours. It is 
 then filtered through a folded filter, and can now be used for the 
 above reaction. 
 
 Fittig's synthesis of the aromatic hydrocarbons is the analogue of 
 Wurtz 1 synthesis of the aliphatic hydrocarbons, e.g.: 
 
 2 C 2 H 5 I + 2 Na = C 2 H 5 . C 2 H 5 + 2 Nal 
 
 Ethyl iodide Butane 
 
 C 6 H 5 . Br + C 2 H 5 Br + 2 Na = C 6 H 5 . C 2 H a + 2 NaBr. 
 
 Ethylbenzene 
 
278 SPECIAL PART 
 
 The bromides of the homologues of benzene react in a similar way, e.g. \ 
 
 /CH 3 /CH 3 
 
 C 6 H/ + ICH 3 + Na 2 = C 6 H 4 < + NaBr + Nal. 
 
 \Br \CH 3 
 
 Bromtoluene Xylene 
 
 The three isomeric bromtoluenes do not react with the same ease. 
 While the p-bromtoluene gives a good yield of p-xylene, the o : com- 
 pound does not give good results, and the m-compound generally forms 
 no xylene. Two alkyl residues can also, in many cases, be introduced 
 into a hydrocarbon simultaneously, e.g. : 
 
 /Br /CH 3 
 
 p-C 6 H 4 < + 2 ICH 3 + 2 Na 2 = p-C 6 H 4 <; + 2 NaBr + 2 Nal. 
 NBr \CH 3 
 
 The great number of hydrocarbons which may be prepared by Fittig's 
 reaction is apparent from the above examples. The value of the reac- 
 tion is still further increased by the fact that a halogen atom in the 
 side-chain of an aromatic hydrocarbon also reacts in the same way. 
 Though the halogen cannot be replaced by a methyl or ethyl radical, 
 yet the reaction for the introduction of the higher alkyl residues is 
 of great service, e.g. : 
 
 C 6 H 5 . CH 2 C1 + CH 3 . CH 2 . CH 2 Br + Na 2 
 
 Benzyl chloride Propyl bromide 
 
 = C 6 H 5 .CH 2 .CH 2 .CH 2 .CH 3 + Nad + NaBr. 
 
 Butylbenzene 
 
 Also by means of this reaction, two aromatic residues may be made 
 to combine, and thus form the hydrocarbons of the diphenyl series, e.g. : 
 
 2 C 6 H 5 . Br + Na 2 = C 6 H 5 . C 6 H 5 + 2 NaBr. 
 
 Diphenyl 
 
 Finally, the hydrocarbons of the dibenzyl series can also be prepared, 
 e.g. : 
 
 2C 6 H 5 .CH 2 C1 + Na 2 = C 6 H 5 .CH 2 .CH 2 .C 6 H 5 + 2NaCl. 
 
 Dibenzyl 
 
 In conducting operations involving the Fittig reaction, various 
 modifications may be introduced, according to the ease with which the 
 reaction takes place. If the reaction occurs at the ordinary temperature 
 easily, then an indifferent diluent like ether, ligroin, carbon disulphide, 
 
280 SPECIAL PART 
 
 or benzene is employed. These substances are not alike in their activity, 
 since ligro'in and benzene generally prolong the reaction, and on this 
 account find application in a very energetic reaction ; ether does not 
 retard the reaction, but causes it to be more regular. At times, the 
 reaction-mixture will not act, even on long standing. In this case, 
 the reaction can frequently be started by a short heating, or the addi- 
 tion of a few drops of ethyl acetate. Since the use of this compound, 
 at times, causes a very stormy action, it is more advantageous to wait 
 for the reaction to begin spontaneously, even if a long time is necessary. 
 In syntheses which are moderately difficult, the reaction-mixture, treated 
 with a diluent, can be heated on the water-bath or in an oil-bath; 
 while, if the reaction takes place with great difficulty, the mixture, 
 generally without dilution, must be heated in an oil-bath. In the 
 latter case, the reaction may be still further facilitated by heating under 
 pressure of a mercury column. By this means, it is possible to heat 
 the reacting substances in an open vessel above their boiling-points. 
 (Fig. 72.) 
 
 19. REACTION: SULPHONATION OF AN AROMATIC HYDRO- 
 CARBON (I) 
 
 EXAMPLE : (a) Benzenemonosulphonic Acid from Benzene and 
 
 Sulphuric Acid 1 
 
 () Sulphobenzide. Benzenesulphonchloride. Ben- 
 zenesulphonamide 
 
 (a) To 150 grammes of liquid fuming sulphuric acid, containing 
 from 5-8% of anhydride, placed in a 200 c.c. flask provided 
 with an air condenser, gradually add, with good shaking and cool- 
 ing with water, 40 grammes of benzene ; before the addition of a 
 new portion, always wait until the last portion, which at first floats 
 on the surface of the acid, dissolves on shaking. The sulphona- 
 tion requires about 10-15 niinutes. The reaction-mixture is then 
 added, with stirring, drop by drop, from a separating funnel, to 
 three to four times its volume of a cold, saturated solution of 
 sodium chloride contained in a beaker. In order that the solution 
 may not be heated above the room temperature, the beaker is 
 !P. 31, 283 and 631; A. 140, 284; B. 24, 2121. 
 
AROMATIC SERIES 28 1 
 
 placed in a large water-bath filled with ice-water. After some 
 time, but with especial ease when the walls of the vessel are rubbed 
 with a sharp-edged glass rod, the sodium salt of benzenesulphonic 
 acid separates out in the form of leaflets of a fatty lustre ; the 
 quantity is increased, on long standing, to such an extent that the 
 contents of the beaker are converted into a thick pasty mass of 
 crystals. If the separation of crystals does not begin, 10 c.c. of the 
 liquid is shaken in a corked test-tube, and cooled by immersion in 
 water. The solidified content of the tube is then added to the main 
 quantity in the beaker. In summer, at times, it may require a 
 several hours' standing before the separation of crystals is ended. 
 The pasty mass of crystals is then filtered off with suction on a 
 Biichner funnel, firmly pressed together with a pestle, and washed 
 with a little saturated sodium chloride solution. 
 
 To obtain the salt perfectly dry it is transferred to a linen bag 
 and well squeezed under a screw-press. After being pulverised it 
 is heated to dusty dryness in an air-bath at 110. Yield, about 
 TOO grammes. 
 
 If even after long standing an abundant separation of crystals 
 does not take place, the qause is probably due to the large per- 
 centage of anhydride in the fuming sulphuric acid. Under these 
 conditions it is diluted with concentrated acid, and the experiment 
 repeated. If on the other hand the acid is too weak, the benzene 
 will not dissolve in it. In this case, during the sulphonation the 
 mixture is not cooled, and the reaction is allowed to take place at 
 40-50. 
 
 In order to obtain pure sodium benzenesulphonate, 5 grammes 
 of the crude product is crystallised from absolute alcohol, upon 
 which it is noticed that the sodium chloride mixed with it is insol- 
 uble in alcohol. 
 
 (b} In order to obtain the by-product, sulphobenzide, 30 
 grammes of the pulverised salt is wanned with 50 c.c. of ether, 
 filtered with suction while hot, and washed with ether. After 
 evaporating the ether, a small amount of a crystalline residue is 
 obtained ; this is recrystallised in a test-tube from ligroi'n. Melt- 
 ing-point, 129. 
 
282 SPECIAL PART 
 
 To prepare benzenesulphonchloride from sodium benzenesul 
 phonate, the extracted salt and unextracted salt are treated in a 
 dry flask (under the hood) with finely powdered phosphorus pen- 
 tachloride (for 3 parts dry sodium benzenesulphonate, use 4 parts 
 phosphorus pentachloride). Mix by thorough shaking. The 
 mixture is warmed to ^ hour on an actively boiling water-bath. 
 The cold reaction-product is then poured gradually into ice-water 
 in a flask (use ten times the weight of the sodium salt) ; it is shaken 
 up from time to time, and, after standing for two to three hours, 
 the sulphonchloride is taken up with ether and the generally turbid 
 ethereal solution filtered ; the ether is then evaporated off. Yield, 
 40-50 grammes. 
 
 In a porcelain dish 10 grammes of finely powdered ammonium 
 carbonate are treated with about i c.c. of benzenesulphonchloride, 
 and rubbed together intimately ; the mixture is heated, with good 
 stirring, over a small flame, until the odour of the sulphonchloride 
 has vanished. After cooling, it is treated with water, filtered with 
 suction, washed several times with water, and the benzenesulphon- 
 amide crystallised from alcohol to which hot water is added until 
 turbidity begins. Melting-point, 156. 
 
 Under the sulphonation of aniline it was mentioned that the aromatic 
 compounds differ from the aliphatic compounds in that they can be 
 sulphonated by the action of sulphuric acid ; i.e. the benzene-hydrogen 
 atoms are replaced by the sulphonic acid group, SO 3 H. Thus the above 
 reaction takes place in accordance with the following equation : 
 
 C 6 H 6 +. S0 2 / ( - C 6 H 5 . S0 3 H + H 2 
 \OH 
 
 Since, in the sulphonation, an excess of sulphuric acid is always used, 
 after the reaction is complete it is necessary to separate the sulphonic 
 acid from the excess of sulphuric acid. Many sulphonic acids, espe- 
 cially those of the hydrocarbons, are very easily soluble in water, so 
 that the pure acid cannot be separated out on mere dilution with water, 
 as is the case with sulphanilic acid. There are three methods in com- 
 mon use for the isolation of sulphonic acids soluble in water. The 
 sulphonic acids obtained most easily are those difficultly soluble in cold 
 sulphuric acid. In this case it is only necessary to cool the sulphon- 
 
AROMATIC SERIES 283 
 
 ating mixture, and filter off the sulphonic acid separating out, with 
 suction over asbestos or glass-wool. A second method consists in 
 allowing the sulphuric acid solution to flow into a saturated solution 
 of common salt ; in many cases the difficultly soluble (in sodium chlo- 
 ride solution) sodium salt of the sulphonic acid separates out. Fre- 
 quently it is more advantageous to use sodium acetate, potassium 
 chloride, ammonium chloride, or other salts, instead of sodium chloride. 
 Almost all soluble sulphonic acids, in the form of their alkali salts, can 
 be separated by these two methods in the shortest time. In dealing 
 with a new substance, preliminary experiments with small quantities 
 of the substance are made to determine which salt is best adapted for 
 the separation. The Theory of Salting out is discussed at the end of 
 this chapter. The third method, which is the one generally appli- 
 cable, depends upon the property of sulphonic acids, of forming soluble 
 salts of calcium, barium, and lead in contradistinction to sulphuric acid. 
 If the sulphuric acid solution, diluted with water, is neutralised with the 
 carbonate of one of these metals and then filtered, the filtrate contains 
 only the corresponding salt of the sulphonic acid, while the sulphuric 
 acid in the form of calcium, barium, or lead sulphate remains on the 
 filter. If the alkali salts of the sulphonic acids are desired, the water 
 solution of one of the above salts is treated with the alkali carbonate 
 until a precipitate is no longer formed. The precipitate is filtered off, 
 and the pure alkali salt of the sulphonic acid is obtained in solution, 
 which, on evaporation to dryness, yields the salt in the solid condition. 
 
 In order to obtain the free sulphonic acid, the lead salt is prepared 
 and then decomposed with sulphuretted hydrogen. 
 
 The sulphonic acids of the hydrocarbons are generally colourless, 
 crystallisable compounds, very easily soluble in water, insoluble in ether, 
 behaving like strong acids. By heating with hydrochloric acid, under 
 pressure if necessary, or by the action of steam, the sulphonic acid group 
 may be split off, e.g. : 
 
 C 6 H 5 . S0 3 H + H 2 = C 6 H 6 + H 2 S0 4 
 
 This reaction is of importance in many cases for the separation of 
 hydrocarbon mixtures. If under certain conditions one hydrocarbon 
 is sulphonated, and another is not, the latter can be separated from the 
 former by removing the sulphuric acid solution of the sulphonic acid 
 of the first, and from this the original hydrocarbon may be regenerated 
 by one of the methods mentioned. 
 
 Of particular importance is the behaviour of sulphonic acids when 
 
284 SPECIAL PART 
 
 fused with caustic potash or caustic soda, by which the sulphonic acid 
 group is eliminated and a phenol formed : 
 
 C 6 H 3 . SO 3 K + KOH = C 6 H 5 . OH + K 2 SO 3 
 
 With benzenesulphonic acid this important reaction does not take 
 place smoothly; for this reason the directions for carrying it out prac- 
 tically will be given later in another place (see /3-naphthol). Poly- 
 acid phenols may also be obtained from poly-basic sulphonic acids. 
 The formation of m-dioxybenzene or resorcinol from benzenedisul- 
 phonic acid is of practical value : 
 
 ,OH 
 
 C 6 H 4 (SO,K) 2 + 2 KOH = C e H / + 2 K 2 SO 3 
 
 X)H 
 
 If an alkali salt of a sulphonic acid mixed with potassium cyanide or 
 potassium ferrocyanide is subjected to dry distillation, the sulphonic 
 acid group is replaced by cyanogen and an acid-nitrile is obtained, e.g. : 
 
 C 6 H 5 . SO 3 K + KCN = C 6 H 5 .CN + K 2 SO 3 
 
 Benzonitrile 
 
 The sulphonic acids behave toward phosphorus pentachloride like the 
 carbonic acids, with the formation of acid-chlorides : 
 
 C 6 H 5 . SO 8 Na + PC1 5 = C 6 H 5 . S0 2 .C1 + NaCl + POC1 3 
 
 Benzenesulphonchloride 
 
 The sulphonchlorides are not decomposed, or only slightly decom 
 posed by cold water. In order to separate them from the phos- 
 phorus oxychloride, the mixture is generally poured into cold water; 
 after long standing the oxychloride is converted into phosphoric acid, 
 and the acid-chloride insoluble in water is obtained by decanting 
 the water or extracting with ether ; or in case it is solid, by filtering. 
 The sulphonchlorides are generally distinguished by a very characteristic 
 odour. They can be distilled in a vacuum only, without decomposition. 
 Treated with ammonia they form sulphonamides, which crystallise well 
 and are used for the characterisation of the sulphonic acids : 
 
 C 6 H 5 . SO 2 . Cl + NH 3 = QH S , SO 2 . NH 2 + HC1 
 
 Benzenesulphonamide 
 
 In the sulphonamides, in consequence of the strongly negative 
 character of the X . SO 2 -group, the hydrogen of the amido-group is 
 
AROMATIC SERIES 285 
 
 so easily replaced by metals, that they dissolve in water solutions or 
 the alkalies to form salts of the amide. (Try it.) If a sulphon- 
 chloride is allowed to stand a long time with an aliphatic alcohol, a 
 sulphonic acid ester is formed, e.g. : 
 
 C 6 H 5 . SO 2 . Cl -f C 2 H 5 . OH = C 6 H, . SO 2 . OC 2 H 5 + HC1 
 
 Benzenesulphonic ester 
 
 If this is now .warmed with an alcohol, an aliphatic ether is formed, 
 with the generation of the sulphonic acid, e.g. : 
 
 C 6 H 5 . S0 2 . OC,H 5 + C 2 H 5 ,OH = C H 5 . SO 3 H + C 2 H 5 . O . C 2 H 5 
 
 The formation of ether in this case is analogous to the formation of 
 ethyl ether on heating ethyl sulphuric acid with alcohol : 
 
 SO 2 + C 2 H, . OH = H,SO 4 + C 2 H 5 . . C 2 H 
 
 Since this reaction is continuous, and since the benzene sulphonic acid 
 formed in the reaction is a weaker acid than sulphuric acid, and conse- 
 quently does not carbonise the alcohol like sulphuric acid, the operation 
 may be continued for a long time uninterruptedly. For these reasons 
 recently attempts have been made to employ the aromatic sulphonic 
 acids for the technical preparation of ether. If the sulphonation is 
 effected as above with fuming sulphuric acid, in many cases, besides 
 the sulphonic acid a small quantity of sulphone is formed, e.g. : 
 
 2C 6 H 6 +S0 3 = S0 2 + H 2 
 X C C H 5 
 
 Diphenylsulphone 
 = Sulphobenzide 
 
 For sulphonating purposes, either ordinary concentrated sulphuric acid 
 or the so-called monohydrate or fuming sulphuric acid of various grades 
 is used, according to the conditions. The reaction is conducted with 
 cooling, at the room temperature, or with heating. 
 
 To facilitate the elimination of water, phosphorus pentoxide or 
 potassium sulphate may be added to the sulphonating mixture. 
 
 In some cases it is of advantage to use chlorsulphuric acid instead 
 
286 SPECIAL PART 
 
 of sulphuric acid; the reaction takes place in accordance with the fol. 
 lowing equation : 
 
 C 6 H 6 + Cl . S0 3 H = C 6 H 5 . S0 3 H + HC1 
 
 Theory of Salting out. The process of salting out depends 
 upon the following conditions : According to the theory of electro- 
 lytic dissociation, the water solution of an electrolyte like sodium 
 benzenesulphonate, contains the ions of C 6 H 5 SO 3 ' and Na* , and 
 the electrically neutral, undissociated molecules of C 6 H 5 .SO 3 Na. 
 Now it must not be assumed that in such a solution, at any given 
 time, ions and molecules remain in this condition ; it is more likely 
 that as the ions of C 6 H 5 .SO 3 ' and Na* come into contact with 
 each other under favourable conditions, they recombine forming 
 new molecules, while at the same time undissociated molecules 
 dissociate. We therefore have a dynamic equilibrium of a reversi- 
 ble reaction (similar to that mentioned under ethyl acetate), which 
 may be expressed by the following equation : 
 
 C 6 H 5 . S(V + Na' ^ C 6 H 5 . SO 3 Na 
 
 If we indicate the concentrations of the ions and molecules by 
 Cc e Hg . so 3 , CNH and Cc 6 H 5 . so 3 Na, the mass action equation for this 
 equilibrium will be : 
 
 . so a X C Na _ 
 
 Cc 6 H 5 . S0 3 Na 
 Or, (II) Cc 6 H 5 . S0 3 X C Na = K X Cc 6 H 5 . SO 3 Na 
 
 where K is the dissociation constant. Suppose we add solid com- 
 mon salt to such a solution and take care that no solid salt sepa- 
 rates out ; then since common salt is a strong electrolyte, it will 
 largely dissociate into ions in the solution, and the concentration 
 of Na-ions will be increased. But since the constant K has the 
 same value for all proportions, the increase of CNa will decrease 
 Cc 6 H 5 . so 3 and will consequently increase Cc 6 H 5 . so 3 Na- In this 
 way only can K have a constant value. Hence, the addition 
 of common salt will cause a decrease in the number of C 6 H 5 . SO 3 - 
 ions, and an increase in the number of undissociated molecules. 
 This is known as " diminution in dissociation by the addition of 
 an electrolyte containing one ion in common." If we now con- 
 tinue to add more common salt, the concentration of C<jH 5 . SO 3 - 
 ions will constantly diminish, while that of the undissociated 
 molecules will constantly increase, and a point will finally be 
 reached when the solution will become saturated with undis- 
 sociated molecules ; i.e. a maximum number of molecules will be 
 held in solution. If more common salt is now added, the newly 
 formed undissociated molecules will separate out in the solid form. 
 
AROMATIC SERIES 287 
 
 At this stage Cc R H 5 .so. s Na becomes a constant, and the product 
 of the concentration of ions is called the "solubility product." 
 When the solid begins to separate out, the amount of the soluble 
 undissociated portion becomes independent of the presence of the 
 electrolyte having a common ion, although the concentration of 
 the ions is variable, and is determined by the solubility product 
 Thus, to mention an extreme example, in one case Cc^H^sOg 
 may be large and CN S small, while in another case CNa may be 
 large and Cc fi H 5 .so 3 small. Thus it becomes impossible, even 
 by the addition of a large quantity of an electrolyte having a com- 
 mon ion, to salt out the undissociated molecules that are in solu- 
 tion. This may be termed the solution-tension of the undissociated 
 molecules, and corresponds with Dalton's law of the vapour-tension 
 of a substance, which is independent of external pressure. The 
 vapour-tension of liquid water whether it be confined in a vacuous 
 space, or kept at a definite pressure in physical equilibrium with 
 other gases, will always be the same at any given temperature. 
 
 In the practical example described above, the conditions are 
 somewhat complicated. Neglecting the excess of sulphuric acid 
 used, we have a water solution of benzenesulphonic acid, treated 
 with common salt. But according to the ionic dissociation theory, 
 such a solution will contain ions of C 6 H 5 . SO 3 ', Cl', Na" and 
 H' in addition to undissociated molecules of C 6 H 5 . SO 3 Na, NaCl, 
 C 6 H 5 . SO 3 H and HC1. 
 
 But the main fact to be taken into consideration is the equi- 
 librium existing between C 6 H 5 . SO 3 ', Na' and C 6 H 5 . SO 3 Na, which 
 is not influenced by the presence of other substances. When the 
 solubility limit for this equilibrium is exceeded by increasing 
 the number of Na-ions, by the addition of common salt, then 
 the undissociated sodium benzenesulphonate will separate out 
 in the solid state. 
 
 It is hardly necessary to state that with certain solubility pro- 
 portions, not only solid salt, but also its solution, can be used for 
 salting out. 
 
 20. REACTION: REDUCTION OF A SULPHON CHLORIDE TO A 
 SULPHINIC ACID OR TO A THIOPHENOL 
 
 EXAMPLES: (a) Benzenesulphinic Acid. 1 (ft) Thiophenol 2 
 
 (a) Heat 40 grammes of water to boiling in a 300 c.c. flask 
 provided with a short reflux condenser and a dropping funnel ; 
 add 10 grammes of zinc dust, and without further heating by the 
 flame, gradually allow to flow in from the funnel, with thorough 
 
 i 6.9,1585. 2 A. 119, 142 
 
288 SPECIAL PART 
 
 shaking, 10 grammes of benzenesulphonchloride in small portions. 
 After each addition wait until the vigorous reaction accompanied 
 by a hissing sound has moderated. The mixture is then heated 
 a few minutes over a small flame, filtered after cooling from the 
 precipitate of zinc dust and the zinc salt of benzenesulphinic acid, 
 and the precipitate washed several times with water. The insig- 
 nificant-looking gray precipitate is the reaction-product, and not 
 the filtrate, which can be thrown away. The precipitate is then 
 heated for about ten minutes, not quite to boiling, with a solution 
 of 10 grammes of dehydrated sodium carbonate in 50 c.c. of water, 
 and then filtered with suction. The precipitate remaining on the 
 filter is worthless, while the filtrate contains the sodium benzene- 
 sulphinate in solution. This is evaporated to about one-half its 
 original volume, and, after cooling, acidified with dilute sulphuric 
 acid, upon which the free benzenesulphinic acid separates out in 
 colourless crystals ; the separation is facilitated by rubbing the 
 sides of the vessel with a glass rod. After filtering, the substance 
 is recrystallised from a little water. Melting-point, 83-84. 
 
 Should the free acid not separate on acidifying the sodium salt, 
 it is extracted several times with ether; this is evaporated, and 
 the residue, in case it does not solidify of itself, is rubbed with a 
 glass rod and then recrystallised. 
 
 (b) In order to convert the residue of benzenesulphonchloride 
 obtained in Reaction 19 into thiophenol, it is heated on a water- 
 bath with granulated tin and concentrated hydrochloric acid, in a 
 large flask provided with a long reflux condenser and dropping 
 funnel ; the sulphonchloride is allowed to flow in gradually from 
 the dropping funnel. (To i part of the chloride use 2\ parts of 
 tin and 5 parts of concentrated acid.) The heating is continued 
 until most of the tin is dissolved. The thiophenol formed is dis- 
 tilled over with steam, extracted with ether, dried over anhydrous 
 Glauber's salt, and, after the evaporation of the ether, rectified. 
 Boiling-point, 173. 
 
 In the preparation of thiophenol, care is taken that there are 
 no flames in the neighbourhood of the flask in which the reaction 
 is conducted, otherwise there may be an explosion of the mixture 
 
AROMATIC SERIES 289 
 
 of oxygen and hydrogen. Since the thiophenol possesses an 
 extremely unpleasant odour, and the vapours attack the eyes, 
 causing tears, the experiment must not be carried out in the 
 laboratory, but in a side room (hydrogen sulphide room), or in 
 the open air, in the basement, or at least under a hood with a 
 good draught. Further, care must be taken not to allow the 
 substance to come in contact with the skin, since it produces a 
 violent burning. 
 
 If zinc dust is allowed to act on a sulphonchloride, the zinc salt of 
 the sulphinic acid is formed : 
 
 C 6 H 5 .S0 2 .C1 C 6 H 5 .S0 2 \ 
 
 >Zn + ZnCL 
 C 6 H 5 . SO 2 . Cl + ZnZn = C 6 H 5 . SO 2 / 
 
 Zinc benzenesulphinate 
 
 The zinc salts thus formed are insoluble in water, and can be easily 
 obtained by filtering off. In order to prepare the free sulphinic acid 
 from a zinc salt, it is first converted into the easily soluble sodium salt 
 by boiling with a sodium carbonate solution ; the solution of the sodium 
 salt is concentrated, and the free acid is precipitated with dilute sulphuric 
 acid. The sulphinic acids differ from the sulphonic acids in that they 
 are difficultly soluble in cold water, and can, therefore, be recry stall ised 
 from water. They are also soluble in ether, in which sulphonic acids 
 do not dissolve. On fusing with potassium hydroxide, the sulphinic 
 acids pass over to the hydrocarbons : 
 
 C 6 H 5 . S0 2 K + KOH = K 2 S0 3 + C 6 H 6 
 
 If they are reduced, a thiophenol is finally obtained, as above: 
 C 6 H 5 . SO 2 H + 4 H = C 6 H 5 . SH + 2 H 2 O 
 
 The thiophenols may also be prepared by the direct reduction of the 
 sulphonchlorides : 
 
 C 6 H 5 . S0 2 C1 + 6 H = C 6 H 5 . SH + 2 H 2 + HC1 
 
 The thiophenols are liquids of unpleasant odours ; the higher mem- 
 bers of the series are solids. Like the mercaptans of the aliphatic 
 series, they form difficultly soluble salts with lead and mercury, 
 u 
 
290 SPECIAL PART 
 
 EXPERIMENT : Dissolve mercuric chloride or lead acetate in a 
 test-tube with alcohol by heating ; then cool, and filter. If the 
 alcoholic solution is treated with a few drops of thiophenol, a 
 precipitate of the difficultly soluble salt is obtained. The lead 
 salt is yellow, and possesses the composition represented by the 
 formula : 
 
 (C 6 H 5 .S) 2 Pb 
 
 In the air, and on treatment with oxidising agents like nitric acid, 
 chromic acid, iodine, etc., the thiophenols are oxidised to disulphides : 
 
 2 C 6 H 5 . SH + O = C 6 H 5 . S S . C 6 H. + H 2 O 
 
 EXPERIMENT : A few drops of phenyl mercaptan are dissolved in 
 alcohol, treated with some ammonia, and evaporated to dryness on 
 the water-bath in a watch-glass. (Under the hood.) Colourless 
 needles of the disulphide remain. Melting-point, 61. 
 
 By reduction the disulphides are easily converted back to the thio- 
 phenols : 
 
 C 6 H 5 . S S . C 6 H 5 + 2 H = 2 C 6 H 5 . SH 
 
 Like the phenols the thiophenols have the power of forming ethers, 
 
 C 6 H S .SCH, =Thioanisol, 
 C 6 H 5 . S . C 6 H 5 = Phenylsulphide. 
 
 21. REACTION: SULPHONATION OP AN AROMATIC HYDRO- 
 CARBON (II) 
 
 EXAMPLE : p-Naphthalenesulphonic Acid 
 
 A mixture of 50 grammes of finely pulverised naphthalene and 
 60 grammes of pure concentrated sulphuric acid is heated in an 
 open flask in an oil-bath for 4 hours to 170-180. After cool- 
 ing, the solution is carefully poured, with stirring, into i litre of 
 water, and the naphthalene not attacked is filtered off; in case 
 the filtration takes place very slowly, only the turbid liquid is 
 poured off from the coarse pieces of naphthalene ; the mixture is 
 
AROMATIC SERIES 2QI 
 
 neutralised at the boiling temperature in a large dish with a paste 
 of lime, not too thin, prepared by triturating about 70 grammes 
 of dry slaked lime with water. The mixture is filtered as hot 
 as possible through a filter-cloth, which has been previously 
 thoroughly moistened (see page 61) and the precipitate washed 
 with hot water. The filter-cloth is then folded together and 
 thoroughly squeezed out in another dish ; the expressed, generally, 
 turbid liquid, after filtering, is united with the main quantity. 
 The solution is then evaporated in a dish over a free flame until 
 a test-portion will solidify to a crystalline paste on rubbing with a 
 glass rod. After the solution has been allowed to stand over night 
 the calcium /3-naphthalenesulphonate is filtered off with suction, 
 washed once with a little water, pressed firmly together with a 
 pestle, and spread out on a porous plate. In order to obtain the 
 sodium salt, it is dissolved in hot water, and the solution gradually 
 treated with a concentrated solution of 50 grammes of crystallised 
 sodium carbonate until a test-portion filtered off no longer gives 
 a precipitate with sodium carbonate. After cooling, the precipi- 
 tate of calcium carbonate is filtered off with suction, washed with 
 water, and the filtrate evaporated over a free flame until crystals 
 begin to separate from the hot solution. After standing several 
 hours at the ordinary temperature, the crystals are filtered off, and 
 the mother-liquor further concentrated ; after long standing, the 
 second crystallisation is filtered off, and the mixture of the two 
 lots of crystals dried on the water-bath. Yield, 60-70 grammes. 
 
 Naphthalene is sulphonated on heating with sulphuric acid, in ac- 
 cordance with the following equation : 
 
 There is formed not as in the case of benzene, in which the six 
 hydrogen atoms are equivalent, a single sulphonic acid, but a mixture 
 of two isomeric sulphonic acids : 
 
 SO 3 H 
 
 jo0 3 H. 
 
 o-Naphthalenesulphonic acid /3-Naphthalenesulphonic acid 
 
SPECIAL PART 
 
 According to the temperature at which the sulphonation takes place, 
 more of one than of the other acid is formed ; at lower temperatures an 
 excess of the a-acid is obtained, at higher an excess of the /2-acid. If 
 the mixture is heated to 100, a mixture of 4 parts of the a-acid and 
 i part of the y3-acid is formed, while at 170 a mixture of 3 parts of 
 the /3-acid and I part of the a-acid is obtained. In order to separate 
 the sulphonic acids from the excess of sulphuric acid, advantage is 
 taken of the fact that sulphonic acids differ from sulphuric acid in that 
 they form soluble salts of calcium, barium, and lead, as mentioned 
 under benzenesulphonic acid. For the separation of the sulphonic acid 
 from sulphuric acid, the calcium salt is prepared by neutralising the 
 acid mixture with chalk or lime, since it is cheaper than lead carbonate 
 or barium carbonate. This method is followed technically on the large 
 scale as well as in laboratory preparations. Since the calcium salts of 
 the two isomeric sulphonic acids possess a very different solubility in 
 water, at 10 i part of the a-salt dissolves in 16.5 parts of water, and 
 i part of the /3-salt dissolves in 76 parts of water, the /3-salt, which is 
 more difficultly soluble, and consequently crystallises out first, can be 
 separated by fractional crystallisation from the a-salt which remains in 
 solution. For the conversion into naphthol the calcium salt cannot be 
 used directly ; it must first be changed into the sodium salt by treatment 
 with sodium carbonate : 
 
 (C 10 H 7 . S0 3 ) 2 Ca + Na 2 C0 3 = 2 C 10 H r . SO 3 Na + CaCO 3 . 
 
 In order to remove the last portions of the a-salt, it is advisable not 
 to evaporate the solution of sodium salt directly to dryness, but to 
 allow the more difficultly soluble /3-salt to crystallise out, upon which 
 the a-salt remains dissolved in the mother-liquor. 
 
 The reactions of the naphthalenesulphonic acids are similar to those 
 given above under benzenesulphonic acid. It is still to be mentioned 
 that the a-acid is converted into the /3-acid by heating with concen- 
 trated sulphuric acid to almost 200 ; a reaction which is explained by 
 the fact that the sulphonic acid decomposes in the small amount of water 
 always present, 'into naphthalene and sulphuric acid, and that the 
 former is then sulphonated to the /3-acid at the higher temperature 
 (200) . The sulphonation of naphthalene to the a- and /3-acids is 
 carried out on the large scale in technical operations, since when fused 
 with sodium hydroxide these acids yield naphthols of great importance 
 for the manufacture of dyes. The next preparation deals with this 
 reaction. 
 
AROMATIC SERIES 
 
 22. REACTION: CONVERSION OP A SULPHONIC ACID INTO A 
 
 PHENOL 
 
 EXAMPLE : p-Naphthol from Sodium-p-Naphthalene Sulphonate and 
 Sodium Hydroxide 1 
 
 In order to convert sodiums-naphthalene sulphonate into 
 /3-naphthol the proportions of the necessary reagents used are : 
 
 10 parts sodium-/?-naphthalene sulphonate ; 
 30 parts sodium hydroxide, as pure as possible ; 
 i part water. 
 
 The sodium hydroxide is broken in pieces about a centimetre in 
 length, or the size of a bean, treated with the water, and heated 
 in a nickel crucible (a crucible n cm. high and 8 cm. in diameter 
 is a convenient size), with stirring, to 280 (Fig. 73). The stirring 
 is done with a thermometer, the lower end of which is protected 
 by a case of copper or nickel, about 16 cm. long and 8 mm. wide. 
 This is supported by a cork, containing a narrow canal at the 
 side, fitting the case. In order to be able to determine the tem- 
 perature as exactly as possible, a layer of oil i cm. high is placed 
 in the case, in which the bulb of the thermometer is immersed. 
 If the stirring is done with the case, the upper portion is covered 
 with several layers of asbestos board, secured with wire, or a cork 
 is pushed over the case (Fig. 73). Since, on fusion of the sodium 
 hydroxide, a troublesome spattering takes place, the hand is 
 protected by a glove, and the eyes by glasses. As soon as the 
 temperature reaches 280, the heating is continued with a some- 
 what smaller flame, and the sodium naphthalene sulphonate is 
 gradually added, with stirring. After each new addition, the tem- 
 perature falls somewhat ; no more of the salt is added, until the 
 temperature again reaches 280. After all the salt is added, the 
 flame is made somewhat larger, upon which the fusion becomes 
 viscid with evolution of steam and frothing, until finally, at about 
 310, the real reaction takes place. After the temperature is held 
 
 1 E. Fischer, Prep, of Organic Compounds, 7 Ed. page 55. Z. 1867, 299. 
 
294 SPECIAL PART 
 
 at 310-320 for about 5 minutes, the fusion becomes liquid, 
 and the reaction is complete. The melted mass is then poured 
 in a thin layer on a strong copper plate the edges of which 
 have been turned up. The portions of 
 dark sodium naphtholate may be easily 
 distinguished from the brighter caustic 
 soda. After cooling, the solid mass is 
 broken up and dissolved in water. The 
 naphthol is precipitated at the boiling 
 temperature with concentrated hydro- 
 chloric acid (under the hood), and after 
 cooling is extracted with ether. The 
 ethereal solution is dried over anhydrous 
 Glauber's salt, and then the ether is 
 evaporated in an apparatus similar to 
 the one described on page 35 ; a frac- 
 tionating flask with a very wide condens- 
 ing tube is used. After the removal of 
 the ether, the naphthol remaining back is 
 distilled over without the use of a con- 
 denser. Melting-point, 123. Boiling-point, 286. Yield, half 
 the weight of the sulphonate used. 
 
 As above indicated, in a sodium hydroxide, or potassium hydroxide 
 fusion of a sulphonic acid, besides the phenol, the alkali sulphite is 
 formed, e.g. : 
 
 C 10 H 7 . S0 3 Na -f 2 NaOH = C 10 H 7 . ONa + Na 2 SO 3 + H 2 O 
 
 Sodium naphtholate 
 
 The free phenol is, therefore, not directly obtained on fusion, but 
 the alkali salt of it, from which, after the solution of the fusion in water, 
 the phenol is liberated on acidifying with hydrochloric acid. 
 
 The reaction just effected is in practice carried out on the largest 
 scale in iron kettles to which stirring apparatus is attached. /?-naph- 
 thol as well as its numerous mono- and poly-sulphonic acid derivatives 
 obtained by treatment with sulphuric acid find extensive application for 
 
AROMATIC SERIES 2Q5 
 
 the manufacture of azo dyes. Further, from the y8-naphthol, /3-naph- 
 thylamine is prepared by the action of ammonia under pressure : 
 
 C 10 H 7 .OH + NH, = C 10 H 7 .NH 2 + H 2 O, 
 
 which also finds technical use for the manufacture of azo dyes, as such 
 and in the form of its sulphonic acids. a-Naphthol is also prepared in 
 the same way by fusion of a-sodiumnaphthalene sulphonate with sodium 
 hydroxide, although not in so large quantities as the /2-naphthol. 
 
 The phenols, in consequence of the negative character of the aromatic 
 hydrocarbon residue, are weak acids which dissolve in water solutions 
 of the alkalies to form salts. Still the acid nature is so weak that the 
 salts can be decomposed by carbon dioxide ; use is frequently made of 
 this property for the purification and separation of phenols. 
 
 EXPERIMENT: A mixture of /8-naphthol and benzo'ic acid is 
 dissolved in a diluted caustic soda solution, and carbon dioxide 
 passed into it for a long time. /?-Naphthol only separates out ; 
 this is filtered off. The filtrate is acidified with concentrated 
 hydrochloric acid upon which the benzo'ic acid is precipitated. 
 
 The naphthols differ from the phenols of the benzene series, in that 
 their hydroxyl groups are more capable of reaction than those of the 
 phenols, cresols, etc. While, for example, the ether of phenol cannot 
 be prepared from the phenol and corresponding alcohol by abstracting 
 water : 
 
 (C 6 H-.OH + CH 3 .OH = C 6 H 5 .O.CH 3 + H 2 O), 
 
 Does not take place 
 
 but can only be obtained by the action of halogen alkyls, or salts of 
 alkyl sulphuric acid on phenol salts : 
 
 C 6 H 8 . ONa + ICH 3 = C 8 H B . O . CH, + Nal. 
 
 By heating the naphthols with an aliphatic alcohol and sulphuric acid 
 the ethers are easily prepared : 
 
 C 10 H 7 .OH + CH 3 .OH = C 10 H 7 .O.CH 3 4 H 2 O. 
 
 NaphthylmethyJ ether 
 
296 SPECIAL PART 
 
 23. REACTION: NITRATION OP A PHENOL 
 EXAMPLE : o- and p-Nitrophenol 
 
 Dissolve 80 grammes of sodium nitrate in 200 grammes of 
 water by heating; after cooling, the solution is treated, with 
 stirring, with 100 grammes of concentrated sulphuric acid. To 
 the mixture cooled to 25 contained in a beaker, add drop by 
 drop, from a separating funnel, with frequent stirring, a mixture 
 of 50 grammes of crystallised phenol and 5 grammes of alcohol, 
 melted by warming. During this addition the temperature is kept 
 between 25-30 by immersing the beaker in water. Should the 
 phenol solidify in the separating funnel, it is again melted by a 
 short warming in a large flame. After the reaction-mixture has 
 been allowed to stand for two hours with frequent stirring, it is 
 treated with double its volume of water ; the reaction-product 
 collects as a dark oil at the bottom of the vessel. The principal 
 portion of the water solution is then decanted from the oil, this is 
 washed again with water, and after the addition of % litre of water, 
 is distilled with steam until no more o-nitrophenol passes over. 
 Concerning the removal of the o-nitrophenol solidifying in the 
 condenser, see page 39 (temporary removal of the condenser- 
 water). 
 
 After cooling, the distillate is filtered, the o-nitrophenol washed 
 with water, pressed out on a porous plate, and dried in a desic- 
 cator. Since it is obtained completely pure, it is unnecessary to 
 subject it to any further process of purification. In order to 
 obtain the non-volatile p-nitrophenol remaining in the flask, the 
 mixture is cooled by immersion in cold water, the water solution 
 is filtered from the undissolved portions, and the filtrate boiled for 
 a quarter-hour with 20 grammes of animal charcoal, the water 
 evaporating being replaced by a fresh quantity. The charcoal is 
 then filtered off and the filtrate allowed to stand in a cool place 
 over night, upon which the p-nitrophenol separates out in long, 
 almost colourless needles. The oil still present in the distillation 
 flask is boiled with a mixture of i part by volume of concentrated 
 
AROMATIC SERIES 297 
 
 hydrochloric acid and 2 parts by volume of water, with the addi- 
 tion of animal charcoal, filtered after partial cooling and the ni- 
 trate allowed to stand over night. There is thus obtained a 
 second crystallisation. If the crystals which have separated out 
 are still contaminated by the oil, they are recrystallised from 
 dilute hydrochloric acid with the use of animal charcoal. 
 
 Melting-point of o-Nitrophenol, 45 ; 
 Melting-point of p-Nitrophenol, 1 14. 
 
 Yield, 30 grammes and 5-10 grammes respectively. 
 
 The mon-acid phenols of the benzene series are, in contrast to the 
 corresponding hydrocarbons, very easily nitrated. In the nitration of 
 benzene, in order to facilitate the elimination of the water, concen- 
 trated sulphuric acid must be added ; whereas the action of concen- 
 trated nitric acid alone upon phenol is so energetic, that in this case 
 it must be diluted with water. Upon nitrating phenol, the o- and 
 p-nitrophenols are formed simultaneously, the former of which is vola- 
 tile with steam : 
 
 /N0 2 
 C 6 H 5 . OH -f NO . OH = C 6 H 4 < + H 2 O. 
 
 NDH 
 
 o- and p-Nitrophenol 
 
 On nitrating the homologues of phenol, the nitro-groups always enter 
 the o- and p-positions to the hydroxyl group. In order to prepare 
 m-nitrophenol, it is necessary to start from m-nitroaniline ; this is diaz- 
 otised and its diazo-solution boiled with water. 
 
 The nitrophenols behave in all respects like the phenols. But by 
 the entrance of the negative nitro-group, the negative character of the 
 phenol is so strengthened that the nitrophenols not only dissolve in 
 alkalies, but also in the alkali carbonates. 
 
 EXPERIMENT: Dissolve some o-nitrophenol in a solution of 
 sodium carbonate by warming ; the scarlet red sodium salt is 
 formed. 
 
 In consequence of this action, the nitrophenols cannot be precipi- 
 tated from their alkaline solutions by carbon dioxide. 
 
 In addition, the nitrophenols show the characteristics of the nitro- 
 compounds in general, since they, for example, pass over to amido- 
 phenols on energetic reduction, etc. 
 
298 
 
 SPECIAL PART 
 
 24. REACTION: (a) CHLORINATION OF A SIDE-CHAIN OF A HYDRO- 
 CARBON, (b) CONVERSION OF A DICHLORIDE INTO AN ALDEHYDE 
 
 EXAMPLES : (a) Benzalchloride from Toluene 
 
 (b) Benzaldehyde from Benzalchloride 
 
 (a) A joo c.c. round flask with a wide neck (Fig. 74) con- 
 taining 50 grammes of toluene is placed in a well-lighted posi- 
 tion, best in the sunlight. The toluene is heated to boiling 
 and a current of dry chlorine conducted into it until its weight 
 
 FIG. 74 . 
 
 is increased by 40 grammes. In order to be able to judge 
 of the course of the reaction, the flask, with the toluene, is 
 weighed before the experiment. By interrupting the passage of 
 the chlorine from time to time, cooling and weighing the flask, 
 the increase in weight will indicate how far the chlorinating action 
 
AROMATIC SERIES 299 
 
 has proceeded. The length of the operation varies greatly. In 
 summer the reaction is complete in a few hours ; during the 
 cloudy days of winter a half or a whole day may be necessary. 
 The reaction may be materially assisted by adding 4 grammes of 
 phosphorus pentachloride to the toluene. 
 
 (^) In order to convert the benzalchloride into benzaldehyde, 
 the crude product thus obtained is treated in a round flask pro- 
 vided with an effective reflux condenser, with 500 c.c. of water 
 and 150 grammes of precipitated calcium carbonate (or floated 
 chalk or finely pulverised marble) and the mixture heated four 
 hours in a hemispherical oil-bath to 130 (thermometer in the 
 oil). Without further heating, steam is passed through the hot 
 contents of the flask until no more oil distils over. For this pur- 
 pose the apparatus necessary (cork with a glass tube) has been 
 prepared before the heating in the oil-bath. 
 
 Before the crude benzaldehyde is subjected to purification, the 
 liquid remaining in the distilling flask is filtered while hot through 
 a folded filter, and the filtrate acidified with much concentrated 
 hydrochloric acid. On cooling, the benzoi'c acid obtained as a 
 by-product in the preparation of benzaldehyde separates out in 
 lustrous leaves. It is filtered off and recrystallised from hot water, 
 during which it must not be heated too long, since it is volatile 
 with steam. Melting-point, 121. 
 
 The oil passing over with the steam is treated, together with all 
 of the liquid, with a concentrated solution of sodium hydrogen 
 sulphite, until after long shaking the greater part of the oil has 
 passed into solution. Should crystals of the double compound of 
 benzaldehyde and sodium hydrogen sulphite separate out, water is 
 added until they are dissolved. The water solution is then filtered 
 through a folded filter from the oil remaining undissolved, and 
 the filtrate treated with anhydrous sodium carbonate until it shows 
 a strong alkaline reaction. This alkaline liquid is now subjected 
 to distillation with steam, when perfectly pure benzaldehyde passes 
 over ; it is taken up with ether, and, after the evaporation of the 
 ether, is distilled. Boiling-point, 179. 
 
 Under the preparation of brombenzene it has already been men- 
 tioned that by the action of chlorine or bromine on aromatic hydro- 
 carbons containing aliphatic side-chains, different products are formed, 
 
3OO SPECIAL PART 
 
 depending on the temperature at which the action takes place. If, e.g^ 
 chlorine acts at lower temperatures on toluene, chlortoluene is formed, 
 the chlorine entering the benzene ring : 
 
 /CH 3 
 C 6 H 5 .CH 3 + C1 2 = C 6 H 4 <^ +HC1. 
 
 At ordinary temperatures Chlortoluene 
 
 If, on the other hand, chlorine is conducted into boiling toluene, the 
 chlorine atom enters the side-chain : 
 
 C 6 H 6 .CH 3 + C1 2 = C 6 H 5 .CH 2 C1 + HC1. 
 
 At boiling temperature Benzylchloride 
 
 If chlorine is conducted into toluene at the boiling temperature for 
 a long time, a second, and finally a third, hydrogen atom of the methyl 
 group is substituted : 
 
 C 6 H 5 .CH 2 C1 + C1 2 = C 6 H 5 .CHC1 2 -f HC1 
 
 Boiling Benzalchloride 
 
 C 6 H 5 . CHC1 2 + C1 2 = C 6 H 5 . CC1 3 + HC1. 
 
 Benzotrichloride 
 
 The formation of benzotrichloride is the final result of the action 
 of chlorine under these conditions, since the benzotrichloride is not 
 changed even by passing in the chlorine for a longer time. 
 
 The replacement of hydrogen by chlorine directly presents the diffi- 
 culty, unlike the liquid bromine, that weighed quantities cannot be 
 used, and the exact point to which the introduction of chlorine should 
 be continued in order to get a certain definite compound must be 
 determined. This is accomplished if, from time to time, the increase 
 in weight of the substance being chlorinated is determined. Since 
 the conversion of one molecule of toluene to benzylchloride requires 
 an increase of weight equal to the atomic weight of chlorine minus the 
 atomic weight of hydrogen (Cl H = 34.5), therefore in the prepara- 
 tion cf benzylchloride, 100 parts by weight of toluene must take up 
 an additional weight of chlorine = 37.5 parts by weight, and corre- 
 spondingly in the preparation of benzalchloride or benzotrichloride, 
 the increase in parts by weight must be respectively 2 x 37.5 = 75 
 and 3 x 37.5 = 112.5. 
 
 In most organic chlorinating reactions, besides the main reaction, a 
 side reaction also takes place which, in the above example, results in 
 the conversion of a portion of the toluene to benzalchloride and 
 
AROMATIC SERIES 301 
 
 benzotrichloride, while another portion is only chlorinated to benzyl 
 chloride. Accordingly the reaction-product obtained above consists 
 essentially of benzalchloride mixed with a small quantity of benzyl 
 chloride and benzotrichloride. 
 
 The halogen derivatives of the aromatic hydrocarbons containing 
 the halogen in the side-chain are in part liquids, in part colourless crys 
 tallisable solids, which are distinguished from their isomers containing 
 the halogen in the benzene ring, in that their vapours violently attack 
 the mucous membrane of the eyes and nose. Care is taken therefore 
 in the above preparation not to expose the face to the vapours, and 
 further to prevent the chlorination products from coming in contact 
 with the hands. 
 
 Concerning their chemical properties, these two isomeric series differ 
 in that the compounds containing the halogen in the side-chain are far 
 more active than those in which the halogen occurs in the benzene 
 ring, as is apparent from the following equations : 
 
 C 6 H 5 . CH 2 C1 + NH 3 = C 6 H 5 . CH 2 . NH 2 + HC1 
 
 Benzylamine 
 
 C 6 H 5 . CH 2 C1 + CH 3 . COONa - CH 3 . CO . OCH 2 . C 6 H 5 + NaCl 
 
 Benzylacetate 
 
 C 6 H 5 .CH 2 C1 + KCN = C 6 H,,.CH 2 .CN + KC1 
 
 Benzyl cyanide 
 
 The chlorides obtained by substituting a side-chain are of importance 
 for making certain preparations, the aromatic alcohols, aldehydes, 
 and acids. On boiling with water, they decompose, in accordance with 
 the following equations : 
 
 (1) C 6 H 5 . CH 2 C1 + H 2 = C 6 H 5 .CH 2 .OH + HC1 
 
 Benzyl alcohol 
 
 (2) C 6 H 5 . CHC1 2 + H 2 O = C 6 H 5 . CHO + 2 HC1 
 
 Benzaldehyde 
 
 (3) C (; H . . CC1 3 + 2 H 2 = C 6 H 5 . CO . OH + 3 HC1 
 
 Benzo'ic acid 
 
 If the halogen atom is in the ring, none of these transformations will take 
 place. But since, in cases i and 2, the hydrochloric acid formed in the re- 
 action acts in the opposite way and may regenerate the original chloride, it 
 must be neutralised. This is usually accomplished by the addition of a 
 carbonate, upon which the acid acts with the liberation of carbon dioxide, 
 
302 SPECIAL PART 
 
 In practice, the cheap calcium carbonate (marble dust) is used, and the 
 above method for the preparation of benzaldehyde is, as far as possible, 
 an imitation of the technical process used for obtaining the substance. 
 From benzylchloride, benzaldehyde may also be prepared directly by 
 boiling it with water in the presence of lead nitrate or copper nitrate. 
 From the benzylchloride, benzyl alcohol is first formed, which is oxi- 
 dised by the nitrate to benzaldehyde. 
 
 As above mentioned, the chlorination product obtained consists 
 essentially of benzalchloride, mixed with small amounts of benzyl- 
 chloride and benzotrichloride. If the mixture is boiled with water, 
 with the addition of calcium carbonate, a mixture consisting mainly of 
 benzaldehyde, besides benzylchloride and benzole acid the latter 
 being converted into the calcium salt by the carbonate is obtained. 
 If the reaction-mixture is distilled with steam, benzaldehyde, benzyl 
 alcohol, and a small amount of chlorides which have not taken part 
 in the reaction, pass over with the steam, while the calcium benzoate 
 remains in the distillation flask. By acidifying the residue, the free 
 benzole acid may be obtained as above. A large proportion of the 
 so-called "benzoic acid from toluene" is obtained in this way as a 
 by-product in the technical preparation of benzaldehyde. In order to 
 separate the benzaldehyde from benzyl alcohol, the chlorides, and other 
 impurities, advantage is taken of the general property of aldehydes of 
 uniting with acid sodium sulphite to form soluble double compounds. 
 If the distillate is shaken with a solution of sodium hydrogen sulphite, 
 the aldehyde dissolves, while the impurities remain undissolved. These 
 are filtered off, and the sulphite compound of the aldehyde decomposed 
 with sodium carbonate ; on a second distillation with steam, the pure 
 aldehyde passes over. 
 
 The aromatic aldehydes are in part liquids, in part solids, possessing 
 a pleasant aromatic odour. 
 
 They show the characteristic aldehyde reactions, yielding primary 
 alcohols on reduction and carbonic acids on oxidation, 
 
 EXPERIMENT: A few drops of benzaldehyde are allowed to 
 stand in a watch-glass in the air. After a long time, crystals of 
 benzo'ic acid appear. 
 
 C 6 H 5 .CHO + O = C 6 H 5 .CO.OH. 
 
 That they unite with acid sulphites to form crystalline compounds has 
 been mentioned : 
 
AROMATIC SERIES 303 
 
 /OH 
 C 6 H 5 .CHO 4- HS0 3 Na = C 6 H 5 .CH 
 
 \SO 3 Na 
 
 EXPERIMENT : To \ c.c. of benzaldehyde add a concentrated 
 solution of sodium hydrogen sulphite, and shake. The mixture 
 solidifies after a short time to a crystalline mass. 
 
 Further, the aldehydes react, as mentioned under acetaldehyde, with 
 hydroxylamine and phenyl hydrazine, to form oximes and hydrazones. 
 With hydrazine they yield, according to the experiment conditions, the 
 not very stable hydrazines or the more stable and characteristic azines : 
 
 C 6 H 5 . CH |O+H 2 | N - NH 2 = H 2 O + C 6 H 5 . CH=N . NH 2 
 
 Benzalhydrazine 
 
 C 6 H 5 . CH |O + H 2 | N C 6 H 5 . CH=N 
 
 . = 2 H 2 O + | 
 
 C fi H,.CH|O + H,|N C 6 H 5 .CH=N 
 
 Benzalazine 
 
 Aldehydes also condense readily with primary aromatic bases with the 
 elimination of water : 
 
 C 6 H 5 . CHO + C 6 H 5 . NH 2 = C 6 H 5 . CH=N . C 6 H 5 + H 2 O 
 
 Benzylideneaniline 
 
 EXPERIMENT : In a test-tube make a mixture of i c.c. of benzal- 
 dehyde and i c.c. of pure aniline, and warm gently. On cooling, 
 drops of water separate out, and the mixture solidifies, crystals of 
 benzylideneaniline being formed. 
 
 An additional number of characteristic aldehyde reactions will be 
 taken up later in practice. Benzaldehyde is prepared technically on 
 the large scale. Its most important application is for the manufacture 
 of the dyes of the Malachite Green series, and of cinnamic acid (see 
 these preparations). 
 
 25. REACTION: SIMULTANEOUS OXIDATION AND REDUCTION OF 
 AN ALDEHYDE UNDER THE INFLUENCE OF CONCENTRATED 
 POTASSIUM HYDROXIDE 
 
 EXAMPLE : Benzoic Acid and Benzyl Alcohol from Benzaldehyde 1 
 
 Treat 20 grammes of benzaldehyde in a stoppered cylinder or a 
 thick-walled vessel with a cold solution of 18 grammes of potas- 
 sium hydroxide in 1 2 grammes of water, and shake until a perma- 
 nent emulsion is formed ; the mixture is then allowed to stand 
 over night. The vessel is closed by a cork, and not a glass 
 stopper, since at times a glass stopper becomes so firmly fastened 
 that it can be removed only with great difficulty. To the crys- 
 
 1 B. 14, 2394. 
 
304 SPECIAL' PART 
 
 talline paste (potassium benzoate) separating out, water is added 
 until a clear solution is obtained from which the benzyl alcohol is 
 extracted by repeatedly shaking with ether. After the evapora- 
 tion of the ether the residue is subjected to distillation ; benzyl 
 alcohol passes over at 206. Yield, about 8 grammes. The ben- 
 zoi'c acid is precipitated from the alkaline solution on acidifying 
 with hydrochloric acid. 
 
 While many aliphatic aldehydes (see acetaldehyde) are converted 
 by alkalies into more complex compounds, with higher molecular 
 weights, the so-called aldehyde resins, the aromatic aldehydes under 
 similar conditions react smoothly ; two molecules are decomposed by 
 one molecule of potassium hydroxide, one aldehyde molecule being 
 oxidised to the corresponding acid, and the other being reduced to a 
 primary alcohol : 
 
 2C,,H 5 .CHO + KOH =C (; H,.CO.OK + C C H,. CH 2 . OH. 
 
 Since the aldehydes are in part easily obtained, the different primary 
 alcohols may be prepared advantageously by this reaction. 
 
 The primary aromatic alcohols behave in all respects like the corre- 
 sponding aliphatic alcohols in forming ethers and esters, e.g. : 
 
 C,H,.CH 2 \ C fi H..CH 2 \ 
 
 2 \0 2 CH.CO.OCR,.CH 
 
 Benzyl ether Benzylmethyl ether Aceticbenzyl ester 
 
 On oxidation they are converted first into aldehydes and finally into 
 acids : 
 
 C 6 H..CH 2 .OH + O - C H 5 .CHO + H 2 O, 
 2 = C fi H 5 . COOH + H 2 O. 
 
 26. REACTION: CONDENSATION OF AN ALDEHYDE BY POTASSIUM 
 CYANIDE TO A BENZOIN 
 
 EXAMPLE : Benzoin from Benzaldehyde l 
 
 Mix 10 grammes of benzaldehyde with 20 grammes of alcohol 
 and treat the mixture with a solution of 2 grammes of potassium 
 cyanide and 5 c.c. of water. Boil on the water- bath for one hour 
 (reflux condenser). The hot solution is poured into a beaker 
 and allowed to cool slowly the crystals separating out are filtered 
 
 i A. 198, 150. 
 
AROMATIC SERIES 305 
 
 off, washed with alcohol, and dried on the water-bath. For con- 
 version into benzil (see next preparation), they need not be re- 
 crystallised. In order to obtain perfectly pure benzoin, a small 
 portion of the crude product is recrystallised from a little alcohol 
 in a test-tube. Melting-point, 134. Yield, about 90% of the 
 theory. 
 
 If an aromatic aldehyde of the type of benzaldehyde is warmed in 
 alcohol solution with a small quantity of potassium cyanide, substances 
 are obtained which possess the same composition, but with double the 
 molecular weight of the aldehyde : 
 
 C 6 H 5 .CO.CH-C 6 H 5 
 2C 6 H 5 .CHO= | 
 
 OH 
 
 Benzoi'n 
 
 This is unlike aldol formation, since here condensation takes place 
 between the two aldehyde groups (p. 174). 
 
 In the same way from anisic aldehyde and cuminol, there are obtained 
 aniso'in and cuminoin, respectively : 
 
 yOCH 3 = CH 3 O . C 6 H 4 . CO . CH . C 6 H 4 . OCH 3 
 \CHO OH 
 
 Idehyde Aniso'in 
 
 C 3 H r = C 3 H 7 . C 6 H 4 . CO . CH C 6 H 4 . C 3 H 7 . 
 
 2 P -C 6 H/ 
 
 \CHO OH 
 
 Cuminol Cuminoin 
 
 With potassium cyanide furfurol yields furoi'n : 
 
 C 4 H 3 O . CO . CH . C 4 H 3 O 
 2 C 4 H 3 . CHO = 
 
 Furfurol OH 
 
 Furo'in 
 
 Benzoin and its analogues are derivatives of the hydrocarbon di- 
 benzyl, C, ; H 3 . CH 2 . CH 2 .C 6 H 5 , and in fact benzoin on reduction with 
 hydriodic acid is converted into this hydrocarbon. 
 
 The benzoins act, on the one hand, like ketones if the carbonyl 
 group (CO) takes part in the reaction, and, on the other hand, like 
 secondary alcohols if the group CH . OH (the secondary alcohol group) 
 reacts. Thus they have the power to form oximes and hydrazones 
 with hydroxylamine and phenyl hydrazine respectively. If benzoin is 
 reduced with sodium amalgam, the ketone group is converted into the 
 secondary alcohol group. 
 
 * 
 
306 SPECIAL PART 
 
 C 6 H 5 . CO . CH . C 6 H 5 C 6 H 5 . CH CH . C 6 H 5 
 
 f H 2 = 
 OH OH OH 
 
 Hydrobenzo'in 
 
 If the reduction is effected by zinc and hydrochloric acid or glacial 
 acetic acid, the carbonyl group is not attacked, but the alcohol group 
 is reduced and desoxybenzo'in is obtained : 
 
 C 6 H 5 .CO CH . C 6 H 5 _ C 6 H 5 .CO.CH 2 .C 6 H 5 + H 2 O, 
 
 OH Desoxybenzo'in 
 
 a compound of especial interest, because in it, as in acetacetic ester, one 
 of the two hydrogen atoms of the methylene group (CH 2 ), in conse- 
 quence of the acidifying influence of the adjoining negative carbonyl 
 and phenyl groups, may be replaced by sodium ; with the sodium com- 
 pound the same kind of syntheses may be effected as with acetacetic 
 ester : 
 
 C 6 H 5 . CO . CH . C 6 H 5 C 6 H 5 . CO . CH-C 6 H 5 
 
 | +IC 2 H 5 = +NaI. 
 
 Na C 2 H 5 
 
 Sodium desoxybenzo'in Ethyl desoxybenzoin 
 
 Benzoin, further, acts as an alcohol, the hydroxyl group being capa- 
 ble of reacting with alkyl- and acid-radicals to form ethers and esters. 
 If oxidizing agents act on benzoin, the alcohol group is oxidized to a 
 ketone group, as is the case with all secondary alcohols : 
 
 C 6 H 5 .CO.CH.C 6 H 5 +0 
 
 | = C d H 5 . CO . CO . C 6 H 5 + H 2 O. 
 
 Dibenzoyl = Benzil 
 
 The next preparation will deal with this reaction. 
 
 27. REACTION: OXIDATION OF A BENZOIN TO A BENZIL 
 EXAMPLE : Benzil from Benzoin 
 
 The crude benzoin obtained in the preceding preparation is 
 finely pulverised after drying, and heated in an open flask, with 
 frequent shaking, with twice its weight of pure concentrated nitric 
 acid, for \\-2 hours on a rapidly boiling water-bath. When the 
 oxidation is ended, the reaction -mixture is poured into cold water ; 
 
AROMATIC SERIES 307 
 
 after the mass solidifies the nitric acid is poured off; it is 
 then washed several times with water, pressed out on a porous 
 plate, and crystallised from alcohol. After filtering off the 
 crystals separating out, they are dried in the air on several layers 
 of filter-paper. Melting-point, 95. Yield, about 90% of the 
 theory. 
 
 The equation representing the oxidation of benzoin to benzil has 
 been given under the preceding preparation. The analogues of ben- 
 zoin also give, on oxidation, compounds of the benzil series. Thus 
 from anisoin and cuminom, anisil and cuminil respectively are 
 obtained : 
 
 CH 3 . C 6 H 4 . CO .CO . C 6 H 4 .OCH 3 ; C 3 H 7 . C 6 H 4 . CO . CO . C 6 H 4 . C 3 H 7 . 
 
 Anisil Cuminil 
 
 Benzil acts like a ketone in that it forms oximes with hydroxylamine. 
 The oximes are of exceptional interest, since our knowledge of the 
 stereochemistry of nitrogen proceeds from them. Benzil forms two 
 monoximes and three dioximes. The constitution of these compounds 
 will be discussed later, under the preparation of benzophenone-oxime. 
 
 On fusion with potassium hydroxide or by long heating with a water 
 solution of potassium hydroxide, benzil undergoes a remarkable change, 
 in that by taking up water it passes over to the so-called benzilic acid : 
 
 C 6 H 5 . CO . CO . C 6 H 5 + H 2 - *Sc . CO . OH. 
 
 C 6 H/ | 
 
 OH 
 
 Diphenylglycolic acid = 
 Benzilic acid 
 
 Anisil and cuminil also yield, in a similar way, anisilic and cuminilic 
 acids. 
 
 28. REACTION: THE ADDITION OP HYDROCYANIC ACID TO AN 
 ALDEHYDE 
 
 EXAMPLE: Mandelic Acid from Benzaldehyde l 
 (a) Mandelic Nitrile 
 
 In a flask containing 13 grammes of finely pulverised 100% 
 potassium cyanide, or an equivalent amount of the purest salt 
 
 1 B. 14, 235 
 
308 SPECIAL PART 
 
 available, pour 20 grammes of freshly distilled benzaldehyde, and 
 add to this from a separating funnel, the flask being cooled with 
 ice, a quantity of the most concentrated hydrochloric acid, corre- 
 sponding to 7 grammes of anhydrous hydrochloric acid (about 20 
 grammes concentrated acid), drop by drop, carefully, under a 
 hood, with frequent shaking. The reaction-mixture is then 
 allowed to stand, with frequent shaking, for one hour, then 
 poured into about 5 volumes of water, the -oil washed with water 
 several times, and finally separated in a dropping funnel. Owing 
 to the ease with which the nitriles decompose, a further purifica- 
 tion is not possible. Yield, almost quantitative. 
 
 Much better results are obtained by preparing mandelic nitrile 1 
 thus : Pour 50 c.c. of a concentrated solution of sodium bisulphite 
 over 15 grammes of benzaldehyde in a beaker; stir the mixture 
 
 / H 
 
 with a glass rod until the addition product C 6 H 5 .C OH 
 
 \SO 3 Na 
 
 solidifies to a pasty mass. It is then filtered with suction, pressed 
 firmly together, and washed once with a little water. The double 
 compound is stirred up with water to a thick paste, and treated 
 with a cold solution of 12 grammes potassium cyanide in 25 
 grammes of water. After a short time, very easily on stirring, the 
 crystals go into solution, and the nitrile appears as an oil, which is 
 separated from the solution in a dropping funnel. 
 
 (b) Saponification of the Nitrile 
 
 The nitrile is mixed with four times its volume of concentrated 
 hydrochloric acid in a porcelain dish, and evaporated on the 
 water-bath until crystals begin to separate out on the upper surface 
 of the liquid. 
 
 The reaction-mixture is then allowed to stand over night in a 
 cool place; the crystals separating out, are triturated with a little 
 water, filtered off with suction, and then washed with not too 
 much water. A further quantity of the acid may be obtained by 
 
 i Ch. Z. 1896, 90. 
 
AROMATIC SERIES 309 
 
 extracting the filtrate with ether ; after evaporating off the ether, 
 the residue is heated in a watch-crystal some time on a water- 
 bath. The crude mandelic acid is pressed out on a porous plate, 
 and is obtained pure by recrystallising it from benzene. Melting- 
 point, 1 1 8. Yield, about 10-15 grammes. 
 
 (c) Separation of the Inactive Mandelic Acid into its Active 
 Components 1 
 
 A mixture of 20 grammes of crystallised cinchonine, 10 grammes 
 of crystallised mandelic acid, and 500 c.c. of water is heated 
 with quite frequent shaking in an open flask for an hour on an 
 actively boiling water-bath. After cooling, the portions undis- 
 solved are filtered off, and are not washed. To this clear solution 
 (a) add a few crystals of d-cinchonine mandelate (see below), and 
 allow it to stand, according to the conditions, one or more days in 
 a cool place (6-8; in summer in a refrigerator, in winter in a 
 cellar if necessary). In order to purify the crude d-cinchonine 
 mandelate separating out, it is filtered off (filtrate A), pressed out 
 on a porous plate, and recrystallised from water, using for each 
 gramme of the dried salt 25 c.c. of water (heating as above 
 described for an hour, with quite frequent shaking, in an open 
 flask upon a water-bath). On filtering the cold solution the un- 
 dissolved portions remaining are not washed. If the solution be 
 seeded with a few crystals of d-cinchonine mandelate and allowed 
 to stand under the same conditions referred to above, a purer salt 
 will crystallise out. To obtain the free dextro-mandelic acid the 
 purified salt is dissolved in not too much water, and then treated 
 with a slight excess of ammonia, which precipitates the chincho- 
 nine ; this is filtered off, and, after recrystallisation from diluted 
 alcohol, may be used for other experiments. The filtrate, which 
 contains dextro-ammonium mandelate, is acidified with hydro- 
 chloric acid and extracted with ether. If the residue obtained on 
 evaporating the ether be heated in a watch-glass some time on a 
 water-bath, then, on cooling, crystals of dextro-mandelic acid 
 
 1 B. 16, 1773 ; 32, 2385. 
 
310 SPECIAL PART 
 
 separate out ; they are pressed out on a porous plate and recrys* 
 tallised from benzene. Melting-point, 133-134. 
 
 The pure laevo-mandelic cannot be obtained readily from small 
 quantities of mandelic acid ; but a preparation showing to a slight 
 extent laevo-rotatory power may be obtained in the following way : 
 The filtrate A is worked up for the free acid exactly as in the 
 method described for pure dextro-cinchonine mandelate ; since a 
 portion of the d-modification has been removed from the solution, 
 it should be laevo-rotatory. 
 
 From the three preparations thus obtained, viz. inactive mandelic 
 acid, the pure d-acid, and the impure 1-acid, water solutions of the 
 proper concentration are prepared, and their properties investi- 
 gated by a polariscope (consult text-books on Physics). 
 
 If one is not in possession of d-cinchonine mandelate for the 
 first experiment, a proper seeding material is prepared as follows : 
 To a few cubic centimetres of solution (a) obtained above is added, 
 drop by drop, a saturated solution of salt until a slight precipita- 
 tion takes place. The solution is now heated until the precipitate 
 redissolves, and is allowed to stand until crystals separate out, 
 which may require several days. The crystals thus obtained are 
 those of cinchonine hydrochloride upon which small quantities of 
 d-cinchonine mandelate have been deposited ; the latter are in 
 sufficient quantity, however, to cause a further separating out of 
 the d-salt. 
 
 Hydrocyanic acid unites with aromatic as well as aliphatic aldehydes 
 and ketones with the formation of a-oxyacid nitriles : 
 
 /OH 
 CH 3 . CHO + HCN = CH 3 . CH< 
 
 \CN 
 
 Aldehydecyanhydrine 
 a-lactic nitrile 
 
 OH 
 C 2 H 3 . CO . C 2 H 5 + HCN = 
 
 - 9 11 r 
 
 Diethylketone Diethylglycolic nitrile 
 
 /OH 
 
 C 6 H 5 . CHO 4- HCN = C G H 5 . CH/ 
 
 NDN 
 
 Benzaldehyde Mandelic nitrile 
 
AROMATIC SERIES 311 
 
 C 6 H. 5V /OH 
 
 HCN = 
 
 : N 
 
 Acetophenone Acetophenonecyanhydrine 
 
 This reaction also takes place with more complex compounds con- 
 taining the carbonyl group : 
 
 CH. 3 . CO . CH 2 . CO . OC 2 H 3 + HCN = CH 3 . C CH 2 . CO . OC 2 H 5 
 
 Acetacetic ester / >^ 
 
 OH CN 
 CH 3 . CO . CO . OH + HCN = CH 3 . C CO . OH 
 
 Pyroracemic acid /\^ 
 
 OH CN 
 
 a-Cyan-a-lactic acid 
 
 QH 5 .CO.CH,.OH + HCN = C 6 H 5 .C CH 2 .OH 
 
 Benzoylcarbinol //\^ 
 
 OH CN 
 
 The reaction may be effected by digestion with already prepared 
 hydrocyanic acid at ordinary or higher temperatures, but in most cases 
 it is more advantageous to employ nascent hydrocyanic acid as above. 
 
 If the second method be followed, treating the aldehyde with 
 sodium bisulphite, the reaction takes place in accordance with the 
 following equation : 
 
 OH /OH 
 
 C 6 H 3 .CH =C 6 H 5 .CH +KNaSO 3 
 
 If the oxynitriles are subjected to saponification, for example, by 
 boiling with hydrochloric acid, the free oxyacid is obtained, e.g. : 
 
 /OH /OH 
 
 C 6 H-.CH< + 2 H.,0 + HC1 = C H 5 .CH< + NH 4 C1 
 
 >CN \CO.OH 
 
 Mandelic nitrile Mandelic acid 
 
 Since the cyanhydrine reaction takes place smoothly in most cases, 
 it is frequently used for the preparation of a-oxyacids. 
 
 Thus in the sugar group the cyanhydrine reaction is of extreme im- 
 portance, not only for its value in determining constitution, but also for 
 the syntheses of sugars or sugar-like substances containing long chains 
 of carbon atoms. 
 
 In reference to the latter, one example may be mentioned. If hydro- 
 
312 SPECIAL PART 
 
 cyanic acid is united with grape sugar, which is an aldehyde, there is 
 first obtained an oxynitrile, which on saponification yields an oxyacid. 
 If this, or rather the inner anhydride (lactone) into which it easily 
 passes, is reduced, the carboxyl group is reduced to an aldehyde group, 
 and there is thus obtained a sugar containing one more secondary 
 alcohol (CHOH) group than the original grape sugar: 
 
 CN CO.OH 
 
 CHO | CHO 
 
 | CH.OH CH.OH | 
 
 (CH.OH) 4 +HCN= | saponified-*- | reduced -*-(CH.OH) 5 
 
 (CH.OH), (CH.OH) 4 
 
 CH 2 .OH | | CH 2 .UH 
 
 CH 2 .OH CH 2 .OH 
 
 Aldohexose Aldoheptos* 
 
 With the substance thus obtained a similar reaction may be carried 
 out, and so on. 
 
 Mandelic acid belongs to the class of substances containing an 
 asymmetric carbon atom, i.e., one which is in combination with four 
 different substituents : ^ ^ 
 
 * C <OH 5 
 \CO.OH 
 
 Like all compounds of this class, it exists in two different space 
 modifications, which bear the same relation to each other as does an 
 object and its image, and owing to their power of revolving the plane 
 of polarisation, are called dextro- and laevo-mandelic acids. The acid 
 obtained in the above synthesis is optically inactive ; since, in the 
 synthesis of compounds with an asymmetric carbon atom from inactive 
 substances, an equal number of molecules of the dextro- and laevo- 
 varieties are always obtained, which, in the above case, unite to form 
 the inactive, so-called, para-mandelic acid. But, by different methods, 
 the active acids can be obtained from the inactive modifications. If, 
 e.g., the cinchonine salt of para-mandelic acid is allowed to crystallise, 
 the more difficultly soluble salt of the dextro-acid separates out first, 
 and then, later, the laevo-salt crystallises. 
 
 With the aid of certain micro-organisms, the inactive compounds 
 may be decomposed into their active constituents. If, e.g., the well- 
 known Penicillium glaucum is allowed to grow in a solution of ammo- 
 nium para-mandelate. it destroys the laevo-modification ; while another 
 organism, Saccharomyces ellipso'ideus, consumes the dextro-modification, 
 and leaves the other. 
 
AROMATIC SERIES 313 
 
 29. REACTION: PERKIN'S SYNTHESIS OP CINNAMIC ACIDi 
 EXAMPLE : Cinnamic Acid from Benzaldehyde and Acetic Acid 
 
 A mixture of 20 grammes of benzaldehyde, 30 grammes of 
 acetic anhydride, both freshly distilled, and 10 grammes of anhy- 
 drous pulverised sodium acetate (for the preparation, see page 
 147), is heated in a flask provided with a wide vertical air-con- 
 denser about 60 cm. long, for 8 hours, in an oil-bath at 180. 
 If the experiment cannot be completed in one day, a calcium 
 chloride tube is placed in the upper end of the condenser over 
 night. After the reaction is complete, the hot reaction-product 
 is poured into a large flask ; add water, and then distil with steam, 
 until no more benzaldehyde passes over. The quantity of water 
 used here is large enough so that all of the cinnamic acid dissolves 
 except a small portion of an oily impurity. The solution is then 
 boiled a short time, with some animal charcoal, and filtered ; on 
 cooling, the cinnamic acid separates out in lustrous leaves. Should 
 it not possess the correct melting-point, it is recrystallised from hot 
 water. Melting-point, 133. Yield, about 15 grammes. 
 
 The reaction involved in the Perkin synthesis takes place in accord- 
 ance with this equation : 
 
 C 6 H 5 .CHO + CH 3 .CO.ONa = C 6 H 5 .CH=CH.CO.ONa+H 2 O. 
 
 Sodium cinnamate 
 
 The reaction, however, does not take place, as appears from the 
 equation, by the direct union of the aldehyde-oxygen atom with the 
 hydrogen atoms of the methyl group and a combination of the resulting 
 residues, but it proceeds in two phases. 
 
 In the first, the sodium acetate unites with the aldehyde, forming 
 sodium phenyl lactate : 
 
 C 6 H 5 .CH.CH 2 .CO.ONa 
 (i) C 6 H 5 .CHO + CHo.CO.ONa = 
 
 OH 
 
 Sodium phenyl lactate 
 
 1 J- l8 77. 789 ; B. io, 68 ; 16, 14365 A. 227, 48. 
 
314 SPECIAL PART 
 
 In the second phase, this salt, under the influence of acetic anhydride, 
 loses water, upon which the sodium cinnamate is formed : 
 
 (2) C 6 H 5 .CH.CH 9 .CO.ONa 
 
 = C 6 H 5 . CH=CH . CO . ONa + H 2 O. 
 OH 
 
 That sodium acetate, and not the. acetic anhydride, condenses with 
 the benzaldehyde, is proved by the following facts : If, instead of sodium 
 acetate, sodium proprionate is used, and this is heated with benzalde- 
 hyde and acetic anhydride, cinnamic acid is not obtained, but methyl 
 cinnamic acid : 
 
 QH,. CH CH CO . ONa 
 
 (1) C 6 H s .CHO + CH 3 .CH 9 .CO.ONa= | I 
 
 OH CH 
 
 (2) C 6 H 5 .CH CH.CO.ONa C G H 5 . CH=C CO . ONa + H 2 O. 
 
 OH 
 
 CH, CHc 
 
 Sodium methyl cinnamate 
 
 It follows from this that the sodium salt used always takes part in 
 the reaction. In the experiment it is of course necessary that the 
 fusion is not carried out at so high a temperature as in the above 
 'example, but only at the heat of the water-bath ; at higher tempera- 
 tures the sodium salt of proprionic acid and acetic anhydride decom- 
 pose into sodium acetate and proprionic anhydride, so that cinnamic 
 acid is obtained, and therefore, apparently, the anhydride reacts with 
 the aldehyde. 
 
 The Perkin reaction is capable of numerous modifications, since in 
 place of benzaldehyde, its homologues, its nitro- and oxy-derivatives, 
 etc., may be used. On the other hand, the homologues of sodium 
 acetate may be used as has been pointed out. The condensation 
 in these cases always takes place at the carbon atom adjoining the 
 carboxyl group. Halogen substituted aliphatic acids will also react; 
 thus from benzaldehyde and chloracetic acid, chlorcinnamic acid is 
 obtained : 
 
 C fi H 5 .CHO + CH 2 .Cl.CO.OH = C 6 H 5 . CH=CC1 . CO . OH -f H 2 O. 
 
 In place of the aliphatic homologues of acetic acid the aromatic sub 
 stituted acetic acids can also be used, e.g. : 
 
 Q.H- . CH=C CO . OH + H 2 O. 
 C 6 H 5 .CHO + C fi H 5 .CH 2 .CO.OH = | 
 
 C C H 5 
 
 Phenyl acetic acid Phenyl cinnamic acid 
 
AROMATIC SERIES 315 
 
 These examples are sufficient to show the wide application of the Per- 
 kin reaction. 
 
 A very similar reaction takes place on heating sodium acetate with 
 the cheaper benzalchloride, instead of benzaldehyde : 
 
 C 6 H 5 . CHC1 3 + CH 3 . CO . ONa = C 6 H 5 . CH=CH . CO . ONa + 2HC1. 
 
 Cinnainic acid, its homologues and analogues, behave on the one 
 hand like acids, since they form salts, esters, chlorides, amides, etc. 
 Further, they show the properties of the ethylene series in that they 
 take up by addition the most various kinds of atoms and groups. By 
 the action of nascent hydrogen two atoms of hydrogen are added to 
 the molecule of cinnamic acid with a change from double to single 
 union : 
 
 C 6 H 5 . CHizCH . CO . OH + H 2 = C 6 H 5 . CH 2 . CH 2 . CO . OH. 
 
 Hydrocinnamic acid 
 
 It also combines with chlorine and bromine : 
 
 C 6 H 5 . CH=CH . CO . OH + C1 2 = C 6 H 5 . CHC1 . CHC1 . CO . OH 
 
 Dichlorhydrocinnamic acid 
 
 C 6 H, . CH=CH . CO . OH -f Br 2 = C 6 H, . CHBr . CHBr . CO . OH. 
 
 Dibromhydrocinnamic acid 
 
 Further, it unites with hydrochloric, hydrobromic, and hydriodic 
 acids, e.g. : 
 
 C fi H 5 . CH=CH . CO . OH + HBr = C 6 H- . CHBr . CH 2 . CO . OH. 
 
 /3-bromhydrocinnamic acid 
 
 The halogen atom in these cases always unites with the carbon atom 
 not adjoining the carboxyl group. 
 
 Hypochlorous acid also unites with cinnamic acid with the forma- 
 tion of phenylchlorlactic acid : 
 
 C 6 H 5 . CH CHC1 . CO . OH. 
 C (5 H, . CH- CH . CO . OH + C1OH = | 
 
 OH 
 
 The o-nitrocinnamic acid from which indigo is synthetically prepared 
 is of technical importance. If cinnamic acid, or better, an ester of it, 
 is nitrated, a mixture of the o- and p-nitroderivatives is obtained 
 which can be separated into its constituents. If bromine is allowed to 
 act on the o-nitrocinnamic acid, there is obtained : 
 
 /N0 2 
 o-C 6 H 4 < 
 
 \CHBr CHBr, CO. OH 
 
3l6 SPECIAL PART 
 
 If this acid is boiled with alcoholic potash, two molecules of hydro, 
 bromic acid are split off as in the preparation of acetylene from ethyl- 
 ene bromide, and o-nitrophenylpropriolic acid is formed, which, with 
 alkaline reducing agents, yields indigo, and is used in indigo printing.' 
 
 .NO 2 
 o-CgH 4 ^ 
 
 \C=C.CO.OH. 
 
 Cinnamic acid is known in two stereoisomeric forms : 
 
 C 6 H 5 .C.H C 6 H 5 .CH 
 
 H.L 
 
 CO. OH HO.OC.CH 
 
 (Cinnamic acid) (Allocinnamic acid) 
 
 Trans-form Cis-form 
 
 30. REACTION: ADDITION OF HYDROGEN TO AN ETHYLENE 
 DERIVATIVE 
 
 EXAMPLE: Hydrocinnamic Acid from Cinnamic Acid 
 
 In a glass-stoppered cylinder, or a thick-walled preparation glass, 
 treat 10 grammes of cinnamic acid with 75 c.c. of water; add a 
 very dilute solution of caustic soda until the acid passes into solu- 
 tion and the liquid is just alkaline. If a precipitate of sodium 
 cinnamate separates out at this point, too much caustic soda has 
 been used. It is then treated gradually with about 200 grammes 
 of 2 % sodium amalgam, and heated gently, as soon as this has 
 become liquid, on the water-bath for a short time. The liquid is 
 then decanted from the mercury and acidified with hydrochloric 
 acid, upon which the hydrocinnamic acid separates out as an oil ; 
 when cooled with ice-water and rubbed with a glass rod, it solidifies 
 to a crystalline mass. After pressing it out on a porous plate, the 
 acid is recrystallised from water. Since it possesses a low melting- 
 point, it may separate out as an oil on cooling, in which case pro- 
 ceed according to the directions given on page 8. Melting-point, 
 47. Yield, 8-9 grammes. 
 
 The equation for the reaction has been given under cinnamic acid. 
 The same reaction also takes place on heating with hydriodic acid and 
 red phosphorus. 
 
AROMATIC SERIES 
 
 31. REACTION: PREPARATION OF AN AROMATIC ACID-CHLORIDE 
 FROM THE ACID AND PHOSPHORUS PENTACHLORIDE 
 
 EXAMPLE : Benzoyl Chloride from Benzoic Acid 1 
 
 Treat 50 grammes of benzoic acid in a dry J-litre flask, with 90 
 grammes of finely pulverised phosphorus pentachloride under the 
 hood ; the two are shaken well together, upon which, after a short 
 time, reaction takes place with energetic evolution of hydrochloric 
 acid, and the mass becomes liquid. In order to prevent the 
 vessel, which has become strongly heated by the reaction, from 
 cracking, it is not placed on the cold stone floor of the hood, but 
 on a wooden block or straw ring. After standing a short time, 
 it is gently heated on a water-bath, and the completely liquid 
 mixture is twice fractionated (under the hood) with the use 
 of an air condenser, observing the directions given on pages 
 24 and 25. Boiling-point of benzoyl chloride, 200. Yield, 
 90 % of the theory. 
 
 The formation of benzoyl chloride takes place in accordance with 
 the following reaction : 
 
 C 6 H, . CO . OH + PCI., = C C H 5 . CO . Cl + POC1 3 + HC1 
 
 It has been mentioned under acetyl chloride that, for the preparation 
 of the aromatic acid-chlorides, phosphorus pentachloride is generally 
 used. Benzoyl chloride differs from acetyl chloride in that it is more 
 difficultly decomposed by water. 
 
 EXPERIMENT : Treat c.c. of benzoyl chloride with 5 c.c. of 
 water and shake. While acetyl chloride, under these conditions, 
 decomposes violently, the benzoyl chloride is scarcely changed. 
 It is then warmed somewhat. It must be subjected to a longer 
 heating before all the oil has been decomposed. 
 
 In other respects, benzoyl chloride is a wholly normal acid-chloride, 
 and what was said under acetyl chloride is applicable to this chloride ; 
 only it is 'possible to prepare aromatic amides by a different method 
 from that used for the preparation of acetamide. 
 
 1 A. 3, 262. Ostwald's Klassiker der exakten Wissenschaften, Nr. 22. (Investi- 
 gations concerning the Radical of Benzoic Acid, by Wohler and Liebig.) 
 
3l8 SPECIAL PART 
 
 EXPERIMENT : In a porcelain dish, 10 grammes of finely pulver- 
 ised ammonium carbonate are treated with 5 grammes of benzoyl 
 chloride ; they are intimately mixed with a glass rod and heated 
 on the water-bath until the odour of the acid-chloride has van- 
 ished. The mixture is then diluted with water, filtered with suction, 
 washed with water, and crystallised from water. Melting-point of 
 benzamide, 128. 
 
 C 6 H 5 . CO . Cl + NH 3 = C 6 H 5 . CO . NH 2 + HC1 
 
 32. REACTION: THE SCHOTTEN-BAUMANN REACTION FOR THE 
 RECOGNITION OF COMPOUNDS CONTAINING THE AMIDO-, IMIDO-, 
 OR HYDROXYL-GROUP 
 
 EXAMPLE : Benzoicphenyl Ester from Phenol and Benzoylchloride 1 
 
 Dissolve a small quantity of crystallised phenol (about ^ gramme) 
 in 5 c.c. of water in a test-tube and add \ c.c. of benzoyl chloride ; 
 make the solution alkaline with a solution of caustic soda and, with 
 shaking, heat gently a short time over a free flame. If the reac- 
 tion-mixture is cooled by water and then shaken and the sides of 
 the tube rubbed with a glass rod, the oil separating out solidifies 
 to colourless crystals, which are filtered off with suction, washed 
 with water, pressed out on a porous plate, and recrystallised in a 
 small test-tube from a little alcohol. Melting-point, 68-69. 
 
 As already mentioned under acetyl chloride, acid-chlorides react with 
 alcohols, phenols, primary and secondary amines, the chlorine atom 
 uniting with the hydrogen of the hydroxyl-, amido-, or imido-group, 
 with the elimination of hydrochloric acid, while the residues combine 
 to form an ester or a substituted amide. The value of the Schotten- 
 Baumann reaction depends on the fact that this reaction is so essen- 
 tially facilitated by the presence of sodium hydroxide or potassium 
 hydroxide, that even in the presence of water the decomposition takes 
 place. 
 
 5 .CO.Cl + NaOH=C 6 H 5 .O.OC.C 6 H 5 +NaCl + H 2 O 
 
 l B. 19, 3218 ; 21, 2744; 23, 2962; 17, 2545. 
 
AROMATIC SERIES 319 
 
 The reaction is of great importance, especially for the recognition and 
 characterisation of soluble compounds containing the groups mentioned 
 above. It is obvious that if it is desired to test even small quantities 
 of those compounds, the most difficultly soluble acid derivatives of 
 them must be prepared. The benzoyl derivatives are particularly well 
 adapted to this purpose. A few examples may render this statement 
 clearer : If a water solution of a poly-acid aliphatic alcohol, e.g., 
 glycerol, or of the various sugars, from which the dissolved substance 
 will only separate with difficulty, is treated with benzoyl chloride and 
 alkali, a benzoate is formed, which is generally insoluble in water, and 
 which can be recognised by its melting-point. For the recognition of 
 primary and secondary amines the method of procedure is the same. 
 Thus, e.g-, it is not difficult to convert aniline (one drop dissolved in 
 water) by the above method to benzanilide, which can be recognised 
 by its melting-point, 163. (Try the experiment.) 
 
 The soluble amido-phenols, di- and poly-amines are also converted 
 into difficultly soluble benzoyl derivatives : 
 
 /NH 2 /NH.CO.C e H 5 
 
 C t; H 4 < + 2 C 6 H, . CO . Cl = C 6 H 4 < + 2 HC1 
 
 \OH \O.OC.C 6 H 3 
 
 /NH, /NH.CO.QH, 
 
 C fJ H 4 < " + 2 C fl H , . CO . Cl = C 6 H 4 < +2 HC1. 
 
 \NH 2 \NH.CO.C 6 H 5 
 
 In place of benzoyl chloride, other chlorides, e.g., phenylacetyl chloride, 
 or benzenesulphon chloride, can be used, which act in a similar way. 
 Acetyl derivatives may also be prepared in the presence of alkalies in 
 water solution, only in this case acetic anhydride and not the easily 
 decomposed acetyl chloride is used. At times the reaction takes place 
 better by using- potassium hydroxide, or pyridine, in place of sodium 
 hydroxide. 
 
320 SPECIAL PART 
 
 33. REACTION: (a) PRIEDEL AND CRAFTS' KETONE SYNTHESIS 1 
 (*) PREPARATION OF AN OXIME 
 (e) BECKMANN'S TRANSFORMATION OF AN OXIME 
 
 EXAMPLE : Benzophenone from Benzoylchloride, Benzene and 
 Aluminium Chloride 
 
 (a) To a mixture of 30 grammes of benzene, 30 grammes of 
 benzoyl chloride, and 100 c.c. (= 130 grammes) cf carbon disul- 
 phide in a dry flask, add, in the course of about 10 minutes, with 
 frequent shaking, 30 grammes of freshly prepared and finely pulver- 
 ised aluminium chloride, which is weighed in a dry test-tube closed 
 by a cork. The flask is then connected with a long reflux con- 
 denser, and heated on a gently boiling water-bath (a water-bath 
 heated to 50 is better) until only small amounts of hydrochloric 
 acid are evolved : this will require about 2-3 hours. The 
 carbon disulphide is then distilled off, and the residue, while 
 still warm, is carefully poured into a large flask containing 
 300 c.c. of water and small pieces of ice. The residue adher- 
 ing to the walls of the first flask is treated with water, and 
 the water added to the main quantity. After the reaction-mixture 
 has been treated with 10 c.c. of concentrated hydrochloric acid, 
 steam is passed into it for about a quarter-hour. The residue 
 remaining in the flask is, after cooling, extracted with ether, the 
 ethereal solution washed several times with water, filtered, and 
 shaken up with dilute caustic soda solution. After drying with 
 calcium chloride, the ether is evaporated, and the residue distilled 
 from a fractionating flask, the side-tube of which is as near as pos- 
 sible to the bulb. Boiling-point, 297. Melting-point, 48. Yield, 
 about 30 grammes. 
 
 (<) A solution of 2 grammes of benzophenone in 15 c.c. of al- 
 cohol is, with cooling, treated with a cold solution of 1.5 grammes 
 of hydroxylamine hydrochloride in 5 c.c. of water, and 3.5 
 grammes of caustic potash in 6 grammes of water ; the mixture 
 is heated two hours on the water-bath, with a reflux condenser. 
 Then add 50 c.c. of water, and filter off, if necessary, any un* 
 
 1 A. ch. [6] i, 518. 
 
AROMATIC SERIES 32! 
 
 changed ketone which balls together very easily on shaking; 
 acidify the filtrate slightly with dilute sulphuric acid, and recrys- 
 tallise the free oxime from alcohol. Melting-point, 140. 
 
 (c) A weighed amount of the oxime is dissolved in some 
 anhydrous, alcohol-free ether, at the ordinary temperature, and 
 gradually treated with i^- times its weight of finely pulverised 
 phosphorus pentachloride. The ether is then distilled off, the 
 residue, with cooling, is treated with water, and the precipitate 
 separating but is recrystallised from alcohol. Melting-point, 163. 
 
 (a) If an aromatic or an aliphatic acid-chloride is allowed to act on 
 an aromatic hydrocarbon in the presence of an anhydrous aluminium 
 chloride, one of the benzene-hydrogen atoms will be replaced by an 
 acid radical, a ketone being formed : 
 
 C 6 H 6 + C 6 H 5 . CO . Cl - C 6 H 3 . CO . C 6 H 5 + Hd 
 
 Diphenyl ketone 
 =Benzophenone 
 
 C 6 H 6 + CH 3 . CO . Cl = C 6 H, . CO . CH 3 + HC1. 
 
 Phenylmethyl ketone 
 =Acetophenone 
 
 The reaction may be varied if (i) in place of benzene a homologue is 
 
 used: 
 
 /CH 3 
 
 C 6 H 5 .CH 3 + C 6 H 5 .CO.C1 = p-C 6 H/ + HC1. 
 
 \CO.C 6 H 5 
 
 Toluene Phenyltolyl ketone 
 
 [n cases of this kind, the acid-radical always enters the para position 
 to the alkyl radical. If this is already occupied, it then goes to the 
 ortho position. (2) In place of hydrocarbons, phenol-ethers, which 
 react with extreme ease, can be used : 
 
 /OCH 3 
 
 C 6 H 3 . OCH 3 + C 6 H 5 . CO . Cl = C 6 H/ + HC1. 
 
 \CO.C 6 H 5 
 
 Anisol Anisylphenyl ketone 
 
 Concerning the entrance of the acid-radical, the statements made above 
 are also true for this case. (3) In place of ben-zoyl chloride or acetyl 
 chloride, their homologues can be used : 
 
 /CH 3 
 C 6 H 6 + C 6 H 4 < = C 6 H 6 .CO.C 6 H 4 .CH 3 + HC1 
 
 Toluyl chloride 
 
322 SPECIAL PART 
 
 C,H 6 + CH 3 . CH 2 . CO . Cl = C 6 H 5 . CO . CH 2 . CH 3 + HC1 
 C 6 H 6 + C 6 H 5 . CH 2 . CO . Cl = C 6 H 5 . CO . CH 2 . C 6 H 5 + HC1. 
 
 ;' benzyl ketom 
 soxybenzo'in 
 
 Phenylacetyl chloride Phenylbenzyl ketone = 
 
 des 
 
 In this way, starting from o- or m-toluic acid, the o- or m-tolyl- 
 phenyl ketone can be prepared ; it cannot be obtained by the action of 
 benzoyl chloride on toluene. (4) Substituted acid-chlorides like 
 brombenzoyl chloride, nitrobenzoyl chloride, etc., can be used, and 
 thus halogen or nitroketones are obtained: 
 
 C G H 6 + C 6 H / = C 6 H 5 . CO . C 6 H 4 . Br + HC1 
 
 CO . Cl Brombenzophenone 
 
 Brombenzoyl chloride 
 
 /N0 2 
 C 6 H 6 + C 6 H / = C 6 H 5 . CO . C 6 H 4 . NO 2 + HC1. 
 
 CO . Cl Nitrobenzophenone 
 
 jphenor 
 Nitrobenzoyl chloride 
 
 (5) Finally, the chlorides of dibasic acids react with the formation of 
 diketones or ketonic acids : 
 
 CH 9 CO . Cl CH 9 . CO . C 6 H 5 
 
 | +2C 6 H 6 =| +2HC1 
 
 CH 2 -CO.C1 CH 2 .CO.C 6 H 5 
 
 Succinic chloride 
 
 /CO.C1 /CO.C 6 H 5 
 
 m- and p-C 6 H 4 < + 2 C G H 6 = C 6 H 4 < + 2 HC1 
 
 XTO.Cl \CO.C 6 H 5 
 
 Iso- and tere-phthalyl chloride 
 
 CO + 2 C 6 H 6 = C 6 H 5 . CO . C 6 H 5 + 2 HC1. 
 
 >Q 
 
 Phosgene Benzophenone 
 
 In these reactions if but one chlorine atom should react, the chlorides 
 of the three following acids would be obtained : 
 
 CH 2 .CO.C 6 H 5 /CO.QH 5 
 
 CM/ , C 6 H 5 .CO.OH. 
 
 CH 2 .CO.OH \CO.OH "Benzotcacid 
 
 Benzoylproprionic acid Benzoylbenzoic acid 
 
AROMATIC SERIES 323 
 
 From the chloride of phthalic acid phthalophenone is formed, im- 
 portant on account of its relation to the fluorescei'h dyes : 
 
 CCL 
 
 + 2 C 6 H 6 = C 6 H 4 < >0 + 2 HC1. 
 XX) / 
 
 Phthalophenone 
 
 Michler's ketone, tetramethyldiamidobenzophenone is of technical 
 importance ; it is obtained from dimethyl aniline and phosgene, and is 
 used in the preparation of dyes of the fuchsine series (see Crystal 
 Violet) : 
 
 x?ift.N(cii fl 
 
 2 C 6 H 5 . N(CH 3 ) 2 + COC1 2 = CO +2 HC1. 
 
 \C 6 H 4 .N(CH 3 ) 2 
 
 The Friedel-Crafts reaction can also be used for the preparation of 
 ,the homologous aromatic hydrocarbons, since in place of the acid- 
 chloride, halogen alkyls may be caused to act on the hydrocarbons : 1 
 
 C 6 H 6 + C 2 H 5 Br = C 6 H 5 .C 2 H 5 + HBr 
 
 /CH 3 
 
 C 6 H 5 . CH 3 + CH 3 C1 = C 6 H 4 < + HC1. 
 
 \CH 3 
 
 Toluene Xylene 
 
 But in this connection the reaction is in many cases, and indeed in 
 the simplest case, not of equal importance with its application for the 
 ketone syntheses, for three reasons : First, the product of the reaction 
 is a hydrocarbon which can again react; thus it is often difficult to 
 limit the reaction to the desired point. For example, in the action of 
 methyl chloride on toluene, not only is one hydrogen atom substituted, 
 with the formation of dimethyl benzene, but varying quantities of tri-, 
 tetra-, penta-, and hexa-methyl benzene are also formed. A second 
 disadvantage is this: In the different series a mixture of isomers is 
 obtained; in the above case, e.g., not only one of the three dimethyl 
 benzenes, but a mixture of the o-, m-, and p-varieties is formed, which 
 cannot be separated like the homologues by fractional distillation. 
 The reaction is still further complicated in that the aluminium chloride 
 partially splits off the alkyl groups : 
 
 C 6 H 5 . CH 3 + HC1 = C 6 H 6 + CH 3 C1. 
 i B. 14, 2627. 
 
324 
 
 SPECIAL PART 
 
 Since the lower homologues thus formed again react synthetically with 
 the halogen alkyls, and the halogen alkyls on elimination also take part 
 in the reaction, mixtures often difficult to separate are formed. In 
 some favourable cases the reaction is of use in the preparation of the 
 homologues of benzene. The reaction is also applicable to aromatic 
 chlorides which contain the halogen in the side-chain : 
 
 C 6 H 5 .CH,.C1 + C 6 H 6 - C 6 H 5 .CH 2 .C 6 H 5 + HC1 
 
 Benzyl chloride Diphenyl methane 
 
 NO 2 .C 6 H 4 .CH 2 .C1 + C 6 H 6 = NO 2 .C 6 H 4 .CH 2 .C 6 H, + HC1. 
 
 Nitrodiphenyl methane 
 
 As the chlorides of dibasic acids yield diketones, the alkylene chlorides 
 or bromides, as well as tri- and tetra-halogen substituted hydrocarbons, 
 can react with several hydrocarbon molecules, e.g. : 
 
 2CH+ CHBr CHBr = CH.CH. CH.CH + 2 HBr 
 
 Dibenzyl = 
 s-Diphenyl ethane 
 
 65 
 
 3 C 6 H 6 + CHC1 3 = CH . (C 6 H 5 ) 3 + 3 HC1 
 
 Chloroform Triphenyl methane 
 
 5 - 
 
 4C 6 H 6 -|-CHBr 2 CHBr 2 = CH CH +4 HBr. 
 
 C 6 H 5 C 6 H 5 
 
 Acetylene tetrabromide 
 
 s-Tetraphenyl ethane 
 
 In the latter reaction, anthracene is also formed, according to the 
 equation : 
 
 4 HBn 
 
 Anthracene 
 
 For the synthesis of aromatic acids the Friedel-Crafts reaction is also 
 of value, although the acids themselves are not directly obtained, but 
 derivatives of them, which upon saponification yield the free acid, e.g. : 
 
 C 6 H 6 + Cl . CO . NH 2 - C 6 H 5 . CO . NH 2 + HC1, 
 
 Urea chloride Benzamide 
 
AROMATIC SERIES 325 
 
 C 6 H 6 + C 6 H 5 . NCO = C 6 H 5 . CO . NH . C 6 H 5 
 
 Phenyl cyanate Benzanilide 
 
 C 6 H 6 + C 6 H 5 .NCS = C 6 H 5 .CS.NH.C 6 H 3 . 
 
 Phenyl mustard oil Thiobenzanilide 
 
 The last two reactions are to be considered as cases of the normal 
 Friedel-Crafts reaction, since the cyanate and mustard oil unite in the 
 first phase with hydrochloric acid, forming an acid-chloride, which then 
 reacts with the hydrocarbon with elimination of hydrochloric acid, e.g. : 
 
 /NH.C 6 H 5 
 C 6 H 5 .NCO 
 
 Phenyl carbarn ine chloride 
 
 If one considers that in the modifications, in place of the hydro- 
 carbons, ethers, mono- and poly-acid phenols, naphthalene, thiophene, 
 diphenyl, naphthol-ethers, halogen substitution products of hydro- 
 carbons, and many other compounds can be used, the great value 
 of the Friedel-Crafts reaction will be readily understood. 
 
 Concerning the role which aluminium chloride plays in the reaction, 
 it is still not perfectly clear ; certain it is that hydrocarbons as well as 
 phenol-ethers unite with it to form double compounds which are of 
 assistance in causing the reaction to take place. 
 
 (b) By the action of hydroxylamine on aldehydes and ketones, 
 oximes 1 (aldoximes, ketoximes) are formed in accordance with the 
 following typical reactions : 
 
 C 6 H 5 . CHO + NH 2 . OH = C 6 H 5 . CH=N . OH + H 2 O 
 
 Benzaldoxime 
 
 C 6 H 5 .C.C 6 H 5 
 C 6 H 5 . CO . C 6 H 5 + NH 2 . OH = N + H 2 O. 
 
 OH 
 
 Benzophenone oxime 
 
 Oximes may be obtained by three methods: (i) The alcoholic 
 solution of the aldehyde or ketone may be treated, generally, with a 
 concentrated water solution of hydroxylamine hydrochloride and the 
 mixture allowed to stand at the ordinary temperature, or it may be 
 heated in a flask provided with a reflux condenser, or in a bomb-tube. 
 An addition of a few drops of concentrated hydrochloric acid often 
 
 18.15,1324. 
 
326 SPECIAL PART 
 
 expedites the reaction. (2) The formation of oximes may be brought 
 about by the use of free hydroxylamine obtained by treating its hydro- 
 chloride with the theoretical amount of a solution of sodium carbonate 
 (3) Oximes may in many cases be very easily obtained, if, as above* 
 for one carbonyl group three molecules of hydroxylamine hydro- 
 chloride and nine molecules of potassium hydroxide are used ; in the 
 presence of a large excess of hydroxylamine in a strongly alkaline 
 solution, generally a very smooth decomposition takes place. Since 
 the oximes possess a weak acid character, under these conditions the 
 alkali salt of the oxime is first obtained, e.g. : 
 
 C 6 H 5 .C.C 6 H 6 
 
 1 
 
 K 
 
 from which the free oxime is liberated by treating it with an acid. 
 
 Of especial significance for the stereo-chemistry of nitrogen are the 
 oximes of aldehydes as well as those of the unsymmetrical ketones. 
 By the action of hydroxylamine on benzaldehyde, e.g., there is formed 
 not only a single oxime, but a mixture of two stereo-isomers. This is 
 also true when oximes are formed from many unsymmetrical ketones. 
 The existence of these isomers is explained by the assumption that 
 the three valencies of nitrogen do not lie in a plane, but that they 
 extend into space, proceeding from a point like the three edges of a 
 regular triangular pyramid. 1 Since, e.g., in the formation of benzald- 
 oxime, the hydroxyl-group of the hydroxylamine is vicinal to either 
 the phenyl-group or hydrogen atom, the two following stereo-isomers 
 are possible : 
 
 C 6 H 5 .C.H C 6 H 5 .C.H 
 
 and 
 HO N N OH 
 
 OH vicinal to C 6 H 5 OH vicinal to H 
 
 The stereoisomeric forms of an unsymmetrical ketone are, according to 
 this conception, to be expressed by the following formulae, e.g. : 
 
 BrC,H 4 . C . C 6 H 5 BrC 6 H 4 . C . C 6 H 5 
 
 and 
 HO N N OH 
 
 OH vicinal to C 6 H 4 Br OH vicinal to C 6 H, 
 
 1 B. 23, ii, 1243. 
 
AROMATIC SERIES 32? 
 
 With symmetrical ketones it is obviously immaterial upon which of 
 the two similar sides the hydroxyl-group finds itself, so that here only 
 one oxime is possible. 
 
 In this place the two mono-oximes and three dioximes of benzil may 
 be referred to again. These compounds gave the impetus to the 
 investigations 1 of this class of compounds. They are explained by 
 the following space-formulae : 
 
 C (! H 5 . C . CO . C 6 H 5 C 6 H 5 . C . CO . C 6 H 5 
 
 II and || 
 
 HO N N OH 
 
 C 6 H 5 . C . C . C 6 H 5 C 6 H 5 . C C . C 6 H 5 C 6 H 5 . C C . C 6 H 5 
 
 II II ,11 II II II 
 
 HO N N OH HO N HO N N OH HO N 
 
 Not all aldehydes and unsymmetrical ketones yield two oximes. In 
 many cases one form is so unstable (labile) that only the other 
 (stabile) modification exists. 
 
 (<:) If phosphorus pentachloride is allowed to act on an oxime, it 
 is transformed into an anilide, 2 e.g. : 
 
 C 6 H 5 .C.C B H 5 
 
 = C 6 H 5 .NH.CO.C 6 H 5 
 
 Benzanilide 
 
 OH 
 
 Benzophenone oxime 
 
 This so-called Beckmann transformation has been of great significance 
 for the explanation of the constitution of the isomeric oximes. If, eg., 
 phosphorus pentachloride is allowed to act on both of the above 
 formulated stereoisomeric oximes of the brombenzophenone, the same 
 compounds are not obtained from both, but two different ones, which, 
 as follows from their saponification products, correspond on the one 
 hand to the benzoyl derivative of bromaniline, and, on the other, to 
 the brombenzoyl derivative of aniline : 
 
 C G H 5 . CO . NH . C (; H 4 . Br and BrC 6 H 4 . CO . NH . C 6 H 5 
 
 The transformation takes place, probably, in the following way: If 
 phosphorus pentachloride is allowed to act on an oxime, the hydroxyl- 
 group is replaced by chlorine : 
 
 i B. 16, 503; 21, 784, 1304, 3510; 22, 537, 564, 1985, 1996. 
 a B. 19, 988 ; 20, 1507 and 2580; A. 252, i. 
 
328 SPECIAL PART 
 
 C 6 H 5 .C.C 6 H 5 C 6 H 5 .C.C 6 H 5 
 
 N +PC1 5 = N +HC1 + POC1 3 
 
 OH Cl 
 
 But a compound of this kind, in which chlorine is united with nitrogen, 
 is unstable, and it is immediately transformed into a more stable imido- 
 chloride, the chlorine atom being replaced by a phenyl-group : 
 
 C 6 H 5 .C.C 6 H 5 C 6 H 5 .C.C1 
 
 i! II 
 
 N >- N 
 
 Cl C C H 5 
 
 Imidochloride of Benzanilide 
 (Compare p. 154) 
 
 If this is now treated with water, benzanilide is formed, in accord- 
 ance with the following equation : 
 
 C 6 H 5 . C . Cl = N . C 6 H 5 + H,O = C 6 H 5 . CO . NH . C 6 H 5 + HC1 
 
 If the oxime of brombenzophenone, formulated above, is subjected 
 to a similar reaction, the unstable chlorides are first obtained: 
 
 Br . C 6 H 4 . C , C C H 5 Br . C 6 H 4 . C . C 6 H 5 
 
 II and || 
 
 Cl N N Cl 
 
 Cl vicinal to C 6 H 4 Br Cl vicinal to C 6 H 6 
 
 If the most probable assumption is now made, that the chlorine 
 atom gives up its position to the vicinal hydrocarbon radical, there are 
 formed : 
 
 C1.C.C,H 5 Br.C,H 4 .C.Cl 
 
 I! and || 
 
 Br.C 6 H 4 .N N.C 6 H 5 
 
 from which, by treatment with water, there are obtained : 
 
 Br . C 6 H 4 . NH . CO . C 6 H 5 and Br . C 6 H 4 . CO . NH . C 6 H 5 
 
 Benzoyl bromanilide Brombenzoyl anilide 
 
 Upon saponification, these yield : 
 Br.C G H 4 .NH 2 + C 6 H 5 .CO.OH and Br. C 6 H 4 . CO . OH + C 6 H 5 NH 2 
 
 Bromanilme Benzo'ic acid Brombenzoic acid Aniline 
 
AROMATIC SERIES 32Q 
 
 That hydrocarbon radical which in the oxime was vicinal to the 
 hydroxyl-group, is, therefore, on saponification of the polymerised 
 product, obtained in the form of a primary amine. In this way, the 
 constitution of the stereoisomeric oximes of the unsymmetrical ketones 
 is determined. 
 
 Whatever may be the space configuration of the stereoisomeric al- 
 doximes, the derivatives containing an acid radical (acetyl derivative) 
 of the one form easily yield an acid-nitrile on being treated with soda, 
 while the second form does not. The hypothesis proposed, which 
 seems very probable, suggests 'that in the first case the acid radical (or 
 in the corresponding oxime) the hydroxyl-group is vicinal to the alde- 
 hyde hydrogen atom, while in the second case it is vicinal to the hydro- 
 carbon residue : 
 
 C 6 H 5 .C. 
 
 N. 
 
 H 
 OH 
 
 Owin to the nearness of the CH r .C.H. Yields no 
 
 oxygen and hydroxyl, it loses nitrile. 
 
 water easily, and yields a ni- 
 
 Syn-Oxime . ., r w r = fj Anti-Oxime 
 
 34. REACTION: REDUCTION OF A KETONE TO A HYDROCARBON 
 EXAMPLE : Diphenyl Methane from Benzophenone l 
 
 A mixture of 10 grammes of benzophenone, 12 grammes of 
 hydriodic acid (boiling-point, 127), and 2 grammes of red phos- 
 phorus is heated in a sealed tubV' for 6 hours at 160. The 
 reaction-mixture is then treated with ether, poured into a small 
 separating funnel, and shaken up with water several times. The 
 ethereal solution is filtered through a small folded filter, and dried, 
 the ether evaporated, and the residue distilled. Boiling-point, 
 263. On cooling, the diphenyl methane solidifies to crystals 
 which melt at -2 7. Yield, almost quantitative. 
 
 Hydriodic acid, especially at high temperatures, is an extremely 
 energetic reducing agent, which can be used to effect reduction when, 
 as in the above case, another reducing agent, e.g., a metal and acid, 
 could not be employed. The reducing action depends on the following 
 decomposition : 
 
 1 B. 7, 1624. 2 Before opening the tube, see page 67. 
 
330 SPECIAL PART 
 
 The above reaction takes place in accordance with the following 
 equation : 
 
 C 6 H 5 . CO . C C H 5 + 4 HI = C 6 H 5 . CH 2 .C 6 H 5 + H 2 O + 2 I 2 
 
 Diphenyl methane 
 
 With the aid of hydriodic acid, not only ketones but also aldehydes 
 and acids may be reduced to the hydrocarbon from which they are 
 derived, e.g. : 
 
 C,.H 5 . CHO + 4 HI = C,H 5 . CH, + H 2 O + 4 I 
 
 Toluene 
 
 C 6 H 5 . CO . OH + 6 HI = C C H 5 . CH 3 + 2 H 2 O + 3 I 2 
 
 Benzoic acid Toluene 
 
 C 17 H 35 . CO . OH + 6 HI = C 18 H 38 + 2 H 2 O + 3 I 2 
 
 Stearic acid Octodecane 
 
 Alcohols, iodides, etc., can also be reduced to their final reduction 
 products, the hydrocarbons, e.g. : 
 
 C 2 H 5 I + HI = C 2 H 6 + I 2 
 
 Ethyl iodide Ethane 
 
 CH 2 .OH CH 3 
 
 CH.OH +6.HI =CH 2 + 3H 2 + 3l f 
 
 CH 2 .OH CH 3 
 
 Glycerol Propane 
 
 By heating with hydriodic acid, the unsaturated compounds take up 
 hydrogen, e.g. : 
 
 C 6 H 6 + 6HI =C 6 H 12 + 3 I 2 
 
 Hexahydrobenzene 
 
 The effect of hydriodic acid is increased by the addition of red 
 phosphorus. Under these conditions, during the course of the re- 
 action, the liberated iodine unites with the phosphorus to form phos- 
 phorus tri-iodide : 
 
 3 I + P = PI 3 
 
 which with the water present again decomposes to form hydriodic acid : 
 PI 3 + 3 H,0 = 3 HI + P(OH) 3 
 
 Phosphorous acid 
 
 A definite amount of hydriodic acid can thus, provided a sufficient 
 quantity of phosphorus is present, act as a continuous reducing agent. 
 
AROMATIC SERIES 
 
 331 
 
 35. REACTION: ALDEHYDE SYNTHESIS GATTERMANN-KOCH 
 EXAMPLE : p-Tolylaldehyde from Toluene and Carbon Monoxide 1 
 
 To 30 grammes of freshly distilled toluene (boiling-point 110) 
 contained in a wide-necked vessel (an " extract of beef" jar is con- 
 venient) cooled with water, add, not too quickly, 45 grammes of 
 pulverised, freshly prepared aluminium chloride and 5 grammes 
 pure cuprous chloride (see page 389). The vessel is closed by a 
 three-hole cork ; in the middle hole is inserted a glass tube which 
 carries a stirrer (paddle wheel of glass) ; the other holes are used 
 for the inlet and outlet tubes (Fig. 75). 
 After the apparatus has been fastened firm- 
 ly in a clamp it is immersed into 
 a casserole filled with water at 
 20. A current, not too rapid, of 
 carbon monoxide and hydro- 
 chloric acid gas is led in through 
 the prong-shaped tube while the stirrer is 
 set in motion (a small motor is convenient). 
 The carbon monoxide, contained in a gas- 
 ometer of about 10 litres, is passed first 
 through a solution of caustic potash 2 ( i : i) 
 and then through a wash-bottle containing 
 concentrated sulphuric acid. The hydro- 
 chloric acid is generated in a Kipp ap- 
 paratus from fused ammonium chloride and 
 concentrated sulphuric acid. It is passed 
 
 FIG. 75. 
 
 through a wash-bottle containing concentrated sulphuric acid. 
 The gas currents are so regulated that the volume of the carbon 
 monoxide is about twice as large as that of the hydrochloric acid. 
 The escaping gas is led directly to the hood opening. In the 
 course of an hour when about 1-2 litres of carbon monoxide have 
 been passed into the mixture, the temperature rises to 25-30 ; 
 the remainder of the gas is passed in during four to five hours. 
 
 1 B. 30, 1622; 31, 1149. A. 347, 347. 
 
 2 If carbon monoxide is prepared from formic acid, the caustic potash wash- 
 bottle is unnecessary. 
 
332 
 
 SPECIAL PART 
 
 If the reaction- mixture should become so viscous before the lapse 
 of this time that the stirrer revolves only with difficulty, the re- 
 action may be stopped. The viscid product is then poured into 
 a large flask containing crushed ice ; the aldehyde formed and 
 any unattacked toluene is distilled over with steam. The distil- 
 late oil and water is then shaken up with a sodium bisulphite 
 solution for a long time. The toluene, remaining undissolved, is 
 separated in a dropping funnel. If the aldehyde-bisulphite com- 
 pound should crystallise out, water is added until it dissolves. The 
 filtered water solution is then treated with anhydrous soda until it 
 shows a decided alkaline reaction ; the aldehyde is then again 
 distilled over with steam. It is extracted from the distillate with 
 ether. Upon evaporating the ether, from 20-22 grammes of per- 
 fectly pure tolylaldehyde remains. Boiling-point, 204. 
 
 Preparation of Carbon Monoxide 
 
 i. From Oxalic Acid. 
 
 In a round litre flask heat 100 grammes of crystallised oxalic 
 acid with 600 grammes of concentrated sulphuric acid. 1 The gases 
 evolved are passed into two 
 large wash-cylinders (Fig. 74) 
 filled with a solution of caus- 
 tic potash (i part caustic 
 potash to 2 parts of water), 
 and then into a gasometer 
 (Fig. 76). At first the sul- 
 phuric acid is heated some- 
 what strongly. As soon as 
 the oxalic acid has dissolved 
 and a regular current of gas 
 comes off, the flame is 
 lowered. Before filling the 
 gasometer the gas is tested 
 by collecting a test-tube 
 full over water and apply- 
 ing a match. So long as 
 air remains in the apparatus, 
 a slight explosion will occur. 
 But as soon as pure gas is 
 evolved, it burns quietly in the tube. It is then admitted into the 
 gasometer. When the evolution of gas ceases, the apparatus is taken 
 
 1 The outlet tube through which the gaseous mixture passes before coming in 
 contact with the caustic potash solution should be as wide as practicable, in order 
 that it may not be clogged by the sublimed oxalic acid. 
 
AROMATIC SERIES 333 
 
 apart. Since carbon monoxide is poisonous, the experiment is carried 
 out under the hood, and care is taken not to breathe the gas. 
 
 2. From Formic Acid. 
 
 Carbon monoxide is more readily liberated from formic acid. 
 The latter may now be obtained at a low cost. In a half-litre 
 flask, provided with a dropping funnel, a thermometer and an out- 
 let tube, place 100 c.c. (no grammes) of 98-100% formic acid. 
 To this add, gradually, concentrated sulphuric acid. Upon the 
 addition of about 50 c.c. of acid the temperature will rise to 60- 
 70. The acid is now added more slowly, drop by drop, in order 
 to keep the temperature at 50-60. If necessary, the mixture is 
 gently heated on a water-bath for a short time. When the air has 
 been completely replaced, the gas, consisting of pure carbon 
 monoxide, is admitted into the gasometer. 
 
 If it is desired to avoid the use of a gasometer, a regular and 
 continuous current of carbon monoxide may be generated as 
 follows : A litre flask, provided with a safety-tube, containing 
 200 grammes of oxalic acid and 200 grammes of sulphuric acid 
 (cone.), is heated in an oil-bath to 120 ; the temperature is 
 gradually increased according to the conditions. If the gas be 
 passed first into two caustic potash cylinders, and then into two 
 sulphuric acid (cone.) cylinders, it may be used directly for the 
 synthesis. Or, the carbon monoxide obtained from formic acid 
 may be used directly, after it has been dried by passing through 
 a wash-bottle containing concentrated sulphuric acid. But the 
 yield of aldehyde is not as good as when a gasometer is used. 
 
 A direct synthesis of the aromatic aldehydes by means of the Friedel- 
 Crafts reaction could not be brought about until recently, because of 
 the instability of formyl chloride, which, if formed, decomposes imme- 
 diately into carbon monoxide and hydrochloric acid : 
 H . CO . Cl = CO + HC1 
 
 If it were stable, it should form aldehydes, in accordance with this 
 equation : x | H + a j . Co . H = X . COH + HC1 
 
 But now it is known that a mixture of carbon monoxide and hydro- 
 chloric acid in the presence of cuprous chloride, which combines with 
 the former, behaves like formyl chloride. 
 
 The Gattermann-Koch synthesis may be expressed by the following 
 equation : CH 
 
 C 6 H/ =C 6 H 4 / <H + 
 
 NH + CII.CO.H \COH 
 
 From other hydrocarbons like o- and m-xylene, mesitylene, ethylben- 
 zene, diphenyl, etc., in an analogous way, aldehydes may be obtained. 
 As has been shown in the ketone syntheses, the acid radical goes into 
 the para position to the alky] residue, so also in the aldehyde syntheses 
 
334 SPECIAL PART 
 
 the aldehyde group always enters the para position to the alkyl residue 
 Thus from toluene there is obtained : 
 
 :OH 
 
 From o-xylene 
 
 From m-xylene 
 
 Y 
 
 COH 
 
 Since the Friedel-Crafts reaction, when applied to phenol ethers, yields 
 the corresponding aldehydes far more easily than the same reaction 
 applied to the hydrocarbons, it is remarkable that the Gattermann-Koch 
 method cannot be used with phenol ethers. If it be desired to obtain 
 aldehydes from them, hydrocyanic acid is used in place of carbon mon- 
 oxide ; in these cases the presence of cuprous chloride is unnecessary. 
 The action takes place, due to the union of hydrocyanic and hydro- 
 chloric acids to form the chloride of imidoformic acid : 
 
 == 
 \C1 
 
 which, under the influence of aluminium chloride, reacts with the phenol 
 ether, liberating hydrochloric acid : 
 
 OCH 
 
 - C 6 H 4 / + HC1 
 
 + ClLCH NH \CH=;NH 
 
AROMATIC SERIES 335 
 
 There is thus obtained first the aldehyde-imide which, through the 
 action of acids, passes over into the aldehyde with great ease : 
 
 /OCH 3 /OCH 3 
 
 C 6 H 4 < _ - NH 3 + C 6 H/ 
 
 HjO \CHO 
 
 In this way it is possible to introduce the aldehyde group into phenol 
 ethers as well as into the phenols. The latter always enters the para 
 position to the oxalyl or hydroxyl groups. The carbon monoxide is 
 obtained in accordance with the following equations : 
 
 COOH 
 
 (1) | =CO + CO 2 + H.O 
 COOH 
 
 The mixture of gases is separated by passing it through a solution of 
 caustic soda or caustic potash ; the carbon dioxide is absorbed, and the 
 carbon monoxide emerges in a pure condition. 
 
 (2) H . COOH = CO -f H 2 O 
 
 36. REACTION: SAPONIFICATION OF AN ACID-NITRILE 
 EXAMPLE : Toluic Acid from Tolyl Nitrile l 
 
 The p-tolyl nitrile obtained in Reaction 10 is heated with 
 slightly diluted sulphuric acid on the sand-bath in a round flask 
 with reflux condenser until crystals of toluic acid appear in the 
 condenser. For each gramme of the nitrile a mixture of 6 
 grammes of concentrated sulphuric acid with 2 grammes of water 
 is used. After cooling it is diluted with water, the acid separating 
 out is filtered off and washed several times with water. A small 
 portion is dissolved in a little alcohol, and hot water added until 
 the solution just becomes turbid ; it is then boiled jome time 
 with animal charcoal. On cooling, the pure acid is obtained. 
 Melting-point, 177. Yield, 80-90% of the theory. 
 
 By saponification in a narrow sense is understood the splitting up 
 of an acid-ester into an alcohol and acid. It is, however, used in a 
 wider sense to indicate the conversion of acid-derivatives, like nitriles, 
 amides, substituted amides, e.g., anilides, into acids of the same name. 
 Saponification may be conducted either in an alkaline or an acid solu- 
 tion. Thus, for instance, acetamide reacts on heating with a solution 
 
 1 A. 258, 10. 
 
SPECIAL PART 
 
 of caustic potash or caustic soda with the formation of the alkali salt 
 of acetic acid and the evolution of ammonia. Nitriles and esters may 
 frequently be saponified by water solutions of the alkalies. Further, 
 alcoholic caustic potash or caustic soda can be used for a similar pur- 
 pose. Finally, saponification may be effected by heating with a sodium 
 carbonate solution under pressure ; this method is especially well 
 adapted for difficultly saponifiable amides or anilides. 
 
 In order to effect saponification in acid solution, the substance to be 
 saponified is heated with either hydrochloric acid or sulphuric acid in 
 varying degrees of dilution, e.g. : 
 
 /CH 3 /CH 3 
 
 C 6 H/ + 2 H 2 = C e H/ + NH 3 
 
 \CN \CO.OH 
 
 p-Tolyl nitrile p-Toluic acid 
 
 Acid amides may be easily saponified by dissolving in concentrated 
 sulphuric acid, cooling, adding sodium nitrite, and then gradually 
 heating, 1 e.g. : 
 
 C 6 H <5 . CO . N H 2 + NOOH = C 6 H 5 . COOH + N 2 + H 2 O 
 
 In order to saponify a nitrile by this method it is first converted by 
 heating with 85 % sulphuric acid into the amide, and this is treated as 
 directed above. 
 
 Frequently it is better to allow the nitrite to act directly on the warm 
 dilute sulphuric acid solution of the amide. 
 
 The decomposition of the ethers of phenols is also designated as 
 
 saponification. Such decomposition cannot be effected by the methods 
 
 hitherto given. Hydriodic acid is used which, when heated with 
 
 phenol-ethers, decomposes them into the phenol and the alkyl iodide : 
 
 C 6 H 5 .OCH 3 + HI = C C H 5 .OH + CH 3 I 
 
 Anisol 
 
 Anhydrous aluminium chloride may be used here with great advantage ; 
 upon heating, it acts on the phenol-ether in the manner indicated by 
 the following equation: 
 
 3 C 6 H 5 . OCH 3 + A1C1 3 = (C 6 H, . O) 3 A1 + 3 CH 3 C1 
 
 Aluminium salt 
 of phenol 
 
 If a phenol salt is treated with an acid, the free phenol will separate 
 out. This method presents the advantage that it may be applied to 
 substances containing, in addition to the phenol-ether radical, a redu- 
 cible carbonyl group, which, if treated with hydriodic acid, would be 
 changed. 
 
 1 B. 26, Ref. 773; 28, Ref. 917; 32, 1118. 
 
AROMATIC SERIES 337 
 
 37. REACTION: OXIDATION OF THE SIDE-CHAIN OP AN 
 AROMATIC COMPOUND 
 
 EXAMPLE : Terephthalic Acid from p-Toluic Acid 
 
 Dissolve 5 grammes of the crude toluic acid obtained in Reac- 
 tion 36 in a solution of 3 grammes of sodium hydroxide in 250 c.c. 
 of water ; heat in a porcelain dish on the water-bath, and gradually 
 treat with a solution of 12 grammes of finely powdered potassium 
 permanganate in 250 c.c. of water until, after long boiling, the red 
 colour of the permanganate no longer vanishes. Alcohol is then 
 added until the liquid is colourless, and, after cooling, the manga- 
 nese dioxide separating out is filtered off; this is washed with hot 
 water, and the filtrate, heated to boiling, is acidified with concen- 
 trated hydrochloric acid. After cooling, the terephthalic acid is 
 filtered off, washed with water, and dried on the water-bath. Yield, 
 90 % of the theory. Terephthalic acid is insoluble in water. On 
 heating, it sublimes' without melting. 
 
 It is a common property of aliphatic side-chains, united with the 
 benzene nucleus, to pass over to carboxyl groups on oxidation. A 
 methyl group requires 3 atoms of oxygen for oxidation : 
 
 C 6 H 5 .CH 3 + 30 = C 6 H 5 .CO.OH + H 2 O 
 
 Toluene Benzo'ic acid 
 
 If several side-chains are present in a compound, either all or a portion 
 of them may be converted into carboxyl groups : 
 
 /CH 
 C 6 H/ 
 
 \CO. 
 
 CH 
 
 OH 
 .OH 
 .OH 
 
 3 
 
 CTT / r^tj 
 6* 1 3\r~'-'* 1 3 
 
 \CO.OH 
 / 
 
 /CH 3 
 C 6 H^CH 3 gives 
 
 \CH 3 \ 
 
 ^.OH 
 
 C 6 H.-CO . OH 
 \CO . OH 
 
338 SPECIAL PART 
 
 If a side-chain contains s.everal carbon atoms, in many cases only 
 the methyl group at the end of the chain can be oxidised, e.g. : 
 
 X . CH 2 . CH 3 + 3 O = X . CH 2 . CO . OH + H 2 O 
 
 But by an energetic oxidation all the carbon atoms, with the excep- 
 tion of the last, are split off, e.g. : 
 
 C 6 H 5 . CH 2 . CH 3 + 3 O 2 = C 6 H 5 . CO . OH + CO. + 2 H 2 O 
 
 Ethyl benzene 
 
 The basicity of the acid derived from the oxidation of a hydrocarbon 
 accordingly gives an indication concerning the number of side-chains 
 of the hydrocarbon. Derivatives of hydrocarbons are also capable of 
 similar reaction, e.g. : 
 
 'CO. OH 
 
 + H 2 O 
 
 Chlortoluene Chlorbenzoic acid 
 
 /CH, /CO. OH 
 
 C 6 H/ +30 = C 6 H 4 < + H 2 
 
 \NO 2 \NO 2 
 
 Nitrotoluene Nitrobenzoi'c acid 
 
 CH 3 . CO . C 6 H 5 + 30 = C 6 H 5 . CO . COOH 4- H 2 O 
 
 Acetophenone Phenyl glyoxylic acid 
 
 The reaction carried out above takes place in accordance with this 
 equation : 
 
 /CH 3 /CO. OH 
 
 C 6 H 4 < +30- C 6 H/ + H 2 
 
 NCO.OH \CO.OH 
 
 Amines and phenols cannot be directly oxidised in most cases, but 
 an indirect method must be employed, by which the former are con- 
 verted into an acid derivative, and the latter into an ester. If, e.g., it is 
 desired to convert p-toluidine into p-amidobenzoic acid, the base is first 
 acetylated, and the acetatoluide is then oxidised : 
 
 /CH 3 /CO . OH 
 
 C 6 H 4 <; +3O = C 6 H 4 < + H 2 O 
 
 \NH . CO . CH 3 \NH . CO . CH 3 
 
 The acid thus obtained is then saponified, and the desired amida 
 ben zoic acid is formed : 
 
 /CO. OH /NH 
 
 C 6 H 4 < +H 2 O = C 6 H 4 < + CH 3 .CO.OH 
 
 \NH.CO.CH, \CO.OH 
 
AROMATIC SERIES 339 
 
 If it is desired, on the other hand, to oxidise a phenol, e.g., cresol, 
 
 C 6 H 4 <^ , the sulphuric acid- or phosphoric acid-ester of it is first 
 
 \OH 
 
 prepared and oxidised ; the reaction-product is then saponified. As 
 oxidising agent, dilute nitric acid (i vol. cone, nitric acid to 3 vol. 
 water 1 ), chromic acid or potassium permanganate is used. The mildest 
 effect is obtained with the nitric acid, which is therefore used when all 
 the side-chains are not to be oxidised, but only a portion of them, e.g.: 
 
 /CH 3 /CHo 
 
 CH/ >- C C H/ 
 
 \CH 3 \CO.OH 
 
 Nitric acid is also used in other cases, where, as frequently happens 
 with ortho derivatives, other oxidising agents totally destroy the sub- 
 stance. 
 
 Chromic acid, in the form of its anhydride generally, dissolved in 
 glacial acetic acid, or as a water solution of potassium dichromate or 
 sodium dichromate acidified with dilute sulphuric acid, can also be 
 used as an oxidising agent, not only in the case in hand, but also for 
 the oxidation of alcohols, ketones, etc. In oxidation reactions, two 
 molecules of chromic anhydride (CrO 3 ) give three atoms of oxygen : 
 
 2 CrO 3 = C 2 O 3 + 30 
 
 For the oxidation of aromatic hydrocarbons, 2 experience has shown 
 that a good oxidising mixture is 40 parts of potassium dichromate, 
 55 parts of concentrated sulphuric acid, diluted with twice its volume 
 of water. 
 
 With potassium permanganate 3 oxidation can be effected either in 
 alkaline or in acid solution. In the first case, manganese dioxide is 
 deposited : 
 
 2 KMnO 4 + H,O = 3 O + 2 MnO 2 + 2 KOH 
 
 Two molecules of potassium permanganate yield, therefore, in alkaline 
 solution, three atoms of oxygen. 
 
 In acid solution (sulphuric acid), no manganese dioxide separates 
 out, since it is dissolved by the sulphuric acid, with evolution of 
 oxygen, to form manganous sulphate : 
 
 2 KMnO 4 + 3 H 2 SO 4 = 50 + K 2 SO 4 + 2 MnSO 4 + 3 H 2 O 
 
 Two molecules of the permanganate in acid solution, therefore, yield 
 5 atoms of available oxygen. 
 
 In oxidising with potassium permanganate, a 2-5 % solution is gen- 
 erally used. An excess of the permanganate can be removed by the 
 addition of alcohol or sulphurous acid. The alcohol is oxidised into 
 aldehyde or acetic acid, and the sulphurous acid into sulphuric acid. 
 
 i A. 137, 302. 2 A. 133, 41. s B. 7( I057 . 
 
340 SPECIAL PART 
 
 38. REACTION : SYNTHESIS OF OXY ALDEHYDES. REIMER AND 
 
 TIEMANNi 
 
 EXAMPLE : Salicylic Aldehyde from Phenol and Chloroform 
 
 In a round litre flask dissolve 80 grammes of caustic soda 
 in 80 c.c. of water by heating. Add 25 grammes of phenol ; 
 cool the solution without shaking to 60-65 by immersion in cold 
 water. By means of a two-hole cork attach to the flask an effective 
 reflux condenser, arid insert a thermometer the bulb of which dips 
 into the liquid. Add 60 grammes of chloroform gradually, as fol- 
 lows : At first add one-third through the condenser ; on gentle 
 shaking the liquid becomes a fuchsine-red in colour. After a 
 short time the colour changes to orange, and the temperature 
 rises. When it reaches 70 the entire flask is immersed in cold 
 wa f er until the thermometer indicates 65. In this way during 
 the entire reaction the temperature is always kept between 65 
 and 70. Should it fall below 60, the mixture is warmed by im- 
 mersing it a short time in hot water until the mercury rises to 65. 
 After 10-15 minutes the second third of the chloroform is added, 
 observing the precautions just given. Finally, after about 20 
 minutes, the remainder of the chloroform is added. Since toward 
 the end the reaction takes place very quietly, the flask is frequently 
 immersed in hot water in order to maintain the temperature 
 between the prescribed limits. The synthesis requires in all from 
 i^ to 2 hours. Frequent shaking of the mixture, especially during 
 the last phase, increases the yield materially. When the reaction 
 is complete the chloroform is distilled off with steam. The orange* 
 coloured alkaline liquid is allowed to cool somewhat, and is acidi- 
 fied carefully with dilute sulphuric acid, upon which it becomes 
 almost colourless ; finally, steam is passed into it until drops of oil 
 no longer go over. 
 
 The distillate is then extracted with ether, the ethereal solution 
 separated from the water, and the ether evaporated. The residue, 
 consisting of unchanged phenol and salicylic aldehyde, is treated 
 
 1 B. 9, 423, 824 ; 10, 1562 ; 15, 2685, etc. 
 
AROMATIC SERIES 341 
 
 with twice its volume of a concentrated solution of commercial 
 sodium bisulphite. Upon stirring well for a long time with-a glass 
 rod, a solid paste of the double compound of the aldehyde and 
 bisulphite should separate out. After standing from ^-i hour the 
 crystals are filtered with suction, pressed firmly together, and 
 washed several times with alcohol to remove completely the ad- 
 hering phenol, and finally with ether. The pearly, lustrous leaflets 
 are then well pressed out on a porous plate and the aldehyde set 
 free by a gentle warming with dilute sulphuric acid on the water- 
 bath. On cooling, the mixture is extracted with ether, the ethereal 
 solution dried over anhydrous Glauber's salt, the ether is evapo- 
 rated, and the residue of the pure aldehyde is distilled. Boiling- 
 point, 196. Yield, 10-12 grammes. 
 
 The small amount of the p-oxybenzaldehyde formed with the 
 salicylic aldehyde is not volatile with steam, and remains back in 
 the flask after the distillation with steam. In order to obtain it, 
 the residue remaining in the flask after cooling is filtered through 
 a folded filter, and the clear filtrate saturated with solid salt, upon 
 which the p-oxybenzaldehyde separates out at once or on stand- 
 ing. If this be filtered off, and the filtrate extracted with ether, 
 a further quantity is obtained, which, together with the first, is 
 purified by recrystallisation from water with the addition of a 
 solution of sulphur dioxide. Melting-point, 116. Yield, 2-3 
 grammes. 
 
 The synthesis takes place in accordance with this equation : 
 
 /ONa 
 
 C,H 5 ONa + CHCL + 3 NaOH = C,H 4 < + 3 NaCl + 2 H O 
 
 X CHO 
 
 Probably the reaction takes place in the two phases : 
 
342 SPECIAL PART 
 
 By this method the aldehyde group may be introduced into mono- 
 and poly-acid phenols; it enters the ortho and para positions to a 
 hydroxyl group : 
 
 Phenol gives o- and p-oxybenzaldehyde, 
 
 CH CH 3 
 
 o-Cresol _ I and 
 
 CH, CH 
 
 OHG/N 
 
 m-Cresol *- \___ and 
 
 :HO 
 
 CH 3 
 
 p-Cresol ^ [ I onl y- 
 
 OH 
 OH 
 
 Pyrocatechin >- ( J O1 = Protocatechuic aldehyde. 
 
 CHO 
 OH OH 
 
 ^^Isoadialdehyde | | 
 
 CHO CHO 
 
 OH 
 
 Hydroquinone > \ \ Gentisin aldehyde. 
 
 OH 
 
 The reaction also takes place with the ethers of poly-acid phenolu 
 Thus guaiacol gives : 
 
 OH OH 
 
 OHC/NOCH, and O 3 Vanillin. 
 
 V 
 
AROMATIC SERIES 343 
 
 From resorcinmonomethyl ether there are formed two monoaldehydes 
 and two dialdehydes. The reaction is also applicable to oxyaldehydes 
 as well as oxycarbonic acids. Thus from salicylic aldehyde there is 
 formed a mixture of two oxyisophthalic aldehydes : 
 
 OH 
 /OH /\ 
 
 CgHgy CHO p-oxybenzaldehyde gives : f 
 
 X:HO \s 
 
 CHO 
 
 That resorcin, in addition to a monoaldehyde, yields a dialdehyde, 
 has already been mentioned. From the three oxybenzoic acids are 
 formed two oxyaldehyde acids, 
 
 /OH 
 
 This synthesis is capable of very wide application. But it has some 
 defects. Thus the yield of aldehyde obtained in accordance with the 
 original directions leaves much to be desired. The yield is very much 
 decreased by the fact that a portion of the phenol does not enter into 
 the reaction, and another portion reacts with the chloroform to produce 
 an ester of ortho formic acid : 
 
 3 C (; H 5 ONa + CHC1 3 = 3 Nad + CH(OC 6 H 5 ) 3 
 
 A portion of the aldehyde first formed is lost by condensation with 
 some unattacked phenol, forming a derivative of triphenylmethane : 
 
 C 6 H 4 .OH 
 C /C 8 H 4 .OH 
 %C 6 H 4 .OH 
 
 X H 
 
 Further, a portion of the oxyaldehydes is converted into resins by 
 the alkali. 
 
 And again, many phenols react as keto-compounds, and give rise to 
 varying quantities of by-products, e.g. : 
 
 H 3 C\ y|H4-Cl|CHCl 2 H 3 C\ /CHC1 2 
 
 I) + HC1 
 
 Y 
 
 p-cresol Dichlormethyl 
 
 [Ketodihydrotoluene] Ketodihydrotoluene 
 
344 
 
 SPECIAL PART 
 
 In some cases, the chief product of the reaction consists of chlorinated 
 ketones of this order. (B. 35, 4209 ; A. 352, 288.) 
 
 In addition, the separation of the mixture of the mono- and dialde- 
 hydes is often attended with serious difficulty. 
 
 As already mentioned on page 334, the aldehyde group may be in- 
 troduced into phenols by the use of condensation agents like aluminium 
 chloride, zinc chloride, hydrocyanic and hydrochloric acids. These re- 
 actions possess many advantages over those discussed above. They 
 take place more smoothly, yield only the p-oxyaldehydes, and introduce 
 only one aldehyde group ; further, only small amounts of resins are 
 formed, and finally they may be applied to phenols like pyrogallol, 
 phloroglucin, the two naphthols, poly-acid phenols of naphthalene, etc. 
 With these substances the other reaction is useless. (See B. 31, 1765 ; 
 32, 278, etc. ; A. 357,313-) 
 
 39. REACTION: KOLBE'S SYNTHESIS OF OXYACIDS 
 
 EXAMPLE : Salicylic Acid from Sodium Phenolate and 
 Carbon Dioxide 1 
 
 Dissolve 12^- grammes of chemically pure sodium hydroxide in 
 20 c.c. of water in a porcelain dish, or better a nickel dish, and 
 
 with stirring, treat gradually 
 with 30 grammes of crystal- 
 lised phenol. The greatest 
 portion of the water is then 
 evaporated by heating over 
 a free flame, the mass being 
 continually stirred. As 
 soon as a crystalline film 
 forms on the surface of the 
 liquid, the heating is con- 
 tinued with a luminous 
 flame, which is not placed 
 directly under the dish, but 
 is kept in constant motion. 
 In order to fasten the dish, 
 a pair of crucible tongs is 
 FlG> 77> clamped in a vertical posi- 
 
 tion, and the dish supported between its jaws. There is first ob- 
 tained a caked, bright-coloured mass, which is crushed from time 
 to time with a mortar-pestle. As soon as the particles no longer 
 
 ij.pr. [2] 10,89; 27,39: 3I.397- 
 
AROMATIC SERIES 345 
 
 bake together, the mass is pulverised quickly in a dry mortar, the 
 dry mass is then heated with thorough stirring in a nickel dish to 
 dusty dryness. It is then placed in a tubulated retort of 200 c.c. 
 capacity. The retort is then immersed as far as possible in an oil- 
 bath (Fig. 77). This is heated to 110, and at this temperature 
 a current of dry carbon dioxide is passed over the sodium pheno- 
 late (the end of the delivery tube is i cm. above the upper surface 
 of the sodium phenolate) ; this is passed into the retort for an 
 hour. The temperature is then gradually raised (20 per hour) 
 during the course of four hours, while a not too rapid current is 
 passed in, to 190. The mixture is finally heated 1-2 hours at 
 200. During the operation the mass is stirred several times with 
 a glass rod. After cooling, the phenol in the neck of the retort is 
 melted by the application of a flame to the outside, the dusty, fine 
 powder is poured into a large beaker, the retort is washed out 
 several times with water, and the salicylic acid precipitated with 
 much concentrated hydrochloric acid. After the reaction-mixture 
 has been cooled with ice-water a long time, and the sides of the 
 vessel rubbed with a glass rod, the crude salicylic acid is filtered 
 off, washed with a little water, and pressed out on a porous plate. 
 
 The purification of the crude salicylic acid is accomplished 
 best with superheated steam. For this purpose the acid, in a dry 
 condition, is placed in a short-necked flask, and heated in an oil- 
 bath to 170, a not too rapid current of steam at a temperature 
 of 170-180 (see page 41) is passed over it. The connection 
 between the flask and steam generator must not be made until 
 the oil-bath and the steam have the same temperature. Since the 
 acid distilling over very soon stops up a condenser tube of the 
 usual width, one should use for this experiment a tube of 2.5 cm. 
 width (width of mantel 5 cm., length of same 75 cm.). The 
 connecting tube between the flask and condenser must be 2 cm. 
 wide, and as short as possible. If the acid removed from the 
 condenser be dissolved in the watery distillate in the receiver by 
 heating, long colourless needles separate out on cooling. Melting- 
 point, 156. Yield, 5-10 grammes. 
 
 The preparation of salicylic acid does not always take place 
 
34-6 SPECIAL PART 
 
 successfully the first time. The success of the experiment depends 
 particularly on the conditon of the sodium phenolate, which must 
 be perfectly dry} If it " cakes " on heating the retort, there is 
 great probability that the experiment will be unsuccessful. 
 
 The operation should be so arranged that the sodium phenolate 
 is prepared toward evening, so that it may be allowed to stand in 
 a sulphuric acid desiccator over night. The drying in the current 
 of carbon dioxide is begun immediately next morning. 
 
 The synthesis is named after its discoverer, Kolbe. It takes place 
 in three phases. In the first, the carbon dioxide is added to the 
 sodium phenolate, which forms sodium phenyl carbonate : 
 
 (I .) C 6 H, . ONa + C0 2 = C H 5 . . CO_ 9 Na 
 
 In the above experiment this reaction is completed during the heat- 
 ing up to 110 for one hour. In the second phase, the sodium phenyl 
 carbonate is transformed into the so-called neutral sodium salicylate : 
 
 /OH 
 (II.) C < ,H..O.CO.,Na = C ( .H 4 < 
 
 x CO,Na 
 
 while in the last phase a molecule of this salt reacts with a molecule of 
 unchanged sodium phenolate in the following way : 
 
 /OH /ONa 
 
 (III.) C 6 H/ + C 6 H a .ONa = C c H/ +C 6 H 5 .OH 
 
 X CO . ONa X CO . ONa 
 
 These two latter reactions take place during the gradual heating up 
 to 200. Only one-half of the phenol, therefore, is converted into 
 salicylic acid, the second half being obtained unchanged. 
 
 A modification of the Kolbe synthesis which permits the immediate 
 conversion of all the phenol into salicylic acid is known as Schmitfs 
 synthesis. According to this method, as in the other, the sodium 
 phenyl carbonate is first prepared ; this is then further heated in an 
 
 1 The experiment is more certain of success if the sodium phenolate is heated 
 a half hour in a current of dry hydrogen at 140 (retort in the oil-bath) before the 
 introduction of the carbon dioxide; the mass must be cooled to 110 before the 
 latter is led in. 
 
AROMATIC SERIES 347 
 
 autoclave under pressure to 140, upon which it is completely trans- 
 formed into sodium salicylate according to Equation II. Instead of 
 preparing the sodium phenyl carbonate with gaseous carbon dioxide, 
 the sodium phenolate may be mixed directly with liquid or solid carbon 
 dioxide in the autoclave. 
 
 The Kolbe synthesis is capable of very common application, since 
 from each mon-acid phenol, a carbonic acid may be obtained in the 
 same way as that used above. The carboxyl group under these condi- 
 tions primarily seeks the ortho position to the hydroxyl group. The 
 derivatives of phenols, e.g. the three chlorphenols, yield chlorinated 
 salicylic acids. With acid-ethers of poly-acid phenols which still con- 
 
 tain a free hydroxyl group, as, e.g., guaiacol, C 6 H 4 , this reaction 
 
 X)H 
 likewise takes place. From the two naphthols C 10 H 7 .OH the oxy- 
 
 X)H 
 
 naphthoic acids C ]n H r <f , can be obtained. . 
 
 XTO.OH 
 
 If in the Kolbe reaction instead of sodium phenolate, potassium 
 phenolate is used, the para-oxybenzoiic acid is obtained, and not the 
 ortho-acid. The potassium phenolate, like the sodium phenolate, first 
 absorbs carbon dioxide, and the potassium phenyl carbonate thus 
 formed, heated in carbon dioxide up to 1 50, also yields salicylic acid ; 
 but if the temperature is increased, an increasingly larger quantity of 
 the para-acid is obtained, until finally at 220 the potassium para- 
 oxybenzoate is the only product. 
 
 The addition of carbon dioxide is effected with greater ease in poly- 
 acid phenols. With these compounds the reaction begins if the phenol 
 is boiled in a water-solution of ammonium carbonate or potassium 
 hydrogen carbonate, e.g. : 
 
 /OH /OH 
 
 C 6 H/ 4 HO . CO . OK - C 6 H 3 ^-OH + H 2 O 
 X>H \CO.OK 
 
 Salicylic acid is prepared technically on the large scale. Since it 
 is an excellent antiseptic, it finds extensive application in . preventing 
 fermentation, for the preservation of meat, for the disinfection of 
 wounds. It may easily be recognised, since its water solution gives 
 a violet colour with ferric chloride ; in this action it differs from the 
 para- and meta-modifications. It is volatile with steam ; for this rea- 
 son it must not be boiled too long in an open vessel when it is to be 
 recrystallised. All ortho-oxycarbonic acids show this property; the 
 
348 SPECIAL PART 
 
 meta- and para-isomers are not volatile with steam. If salicylic acid 
 is heated strongly, it decomposes into carbon dioxide and phenol : 
 
 /CO . OH 
 
 C 6 H 4 < = C 6 H 5 .OH + C0 2 . 
 
 \OH 
 
 The para-oxycarbonic acids show the same property while the meta- 
 acids are stable. 
 
 40. REACTION: GRIGNARD'S REACTION 
 
 (a) Benzoic Acid from lodobenzene. (b) Benzhydrol from lodo- 
 or Brombenzene and Benzaldehyde 
 
 (a) 2.4 grammes of magnesium shavings (or thin magnesium 
 ribbon, about 2 mm. in width, rubbed with fine emery-cloth, 
 cleaned with filter paper, and cut in pieces 1-2 cm. long) are 
 placed in a flask provided with a reflux condenser, and treated 
 with a mixture of 20.4 grammes of thoroughly dried iodobenzene, 
 40 c.c. of absolute ether l and a granule of iodine. The flask is 
 dipped in hot water, or heated in a water-bath at the boiling 
 point of the ether. In \^ hour a white, flocculent precipitate 
 will begin to form, and the heat of the reaction will cause the 
 ether to boil actively when the water-bath is removed. If, now, 
 the bottom of the flask is wrapped up in dry cloth, so as to utilise 
 the heat of the reaction, the greater part of the magnesium will go 
 into solution in the course of two hours. At the end of this period 
 
 1 For experiments (a) and (b) absolute ether is prepared as follows : 250 c.c. of 
 commercial ether are shaken several times with 100 c.c. of water, and allowed to 
 remain over granular calcium chloride over night. The ether is separated from 
 the calcium chloride and treated with thin, bright scales of sodium. The vessel is 
 stoppered with a cork to which is attached a calcium chloride tube, open at both 
 ends. As soon as the evolution of gas ceases, the ether is distilled off from the 
 sodium in the same vessel. It is collected in a suction flask attached to the lower 
 end of the condenser with a cork, and having a calcium chloride tube connected to 
 its side tube to prevent moisture from entering the receiver. For the success of the 
 experiments the use of thoroughly dry materials and vessels is absolutely necessary. 
 Should the progress of the experiment (the dissolving of magnesium) require more 
 time than is prescribed above, then the reagents were not dry enough. The experi- 
 ment is repeated. The ether must again be kept in contact with sodium over night, 
 and must be freshly distilled from the sodium just before it is to be used' 
 
AROMATIC SERIES 349 
 
 the boiling of the ether will either slacken or entirely cease. It is 
 once more heated for half an hour on a water-bath, then cooled by 
 surrounding the flask with ice water. The condenser is removed, 
 and in the course of 2-3 hours a slow current of carbon dioxide 
 (dried by passing through two wash-bottles containing concentrated 
 sulphuric acid) is run into the ethereal solution of phenyl magne- 
 sium iodide, which may still contain a small quantity of undis- 
 solved magnesium. The flask is kept cold during this operation. 
 The reaction mixture consists of two layers, a light upper layer of 
 ether, and a heavy, viscous layer of the reaction product. When 
 too rapid a current of carbon dioxide is passed, a single layer of 
 viscous mass will be obtained. This will not impair the success of 
 the experiment if the mixture was cooled thoroughly. It is now 
 treated with finely broken ice, and with a cooled mixture of 15 c.c. 
 of concentrated hydrochloric acid and an equal volume of water. 
 The benzoic acid is extracted with commercial ether. The ether 
 is evaporated, and the residue is gently warmed with caustic 
 soda or caustic potash. After filtering the undissolved portion, 1 
 the alkaline solution is treated with hydrochloric acid. The pre- 
 cipitated benzoic acid is filtered. More acid is obtained by 
 extracting the mother liquor with ether. Yield of the crude 
 product 10-12 grammes. It crystallises from water in colourless 
 lustrous leaves. M.P. 121. 
 
 (&) 2.4 grammes of magnesium, 20.4 grammes of* iodobenzene 
 and 40 c.c. of absolute ether are converted into phenyl mag- 
 nesium iodide as in (a). The product is cooled and carefully 
 added, drop by drop, and with constant shaking, to a mixture of 
 10.6 grammes of freshly distilled benzaldehyde, and 30 c.c. of 
 absolute ether. During this treatment the mixture is kept cold 
 with ice water. A violent reaction takes place, with the formation 
 of a yellow, and finally a white, precipitate. The reaction mixture 
 is treated with ice as in (a), and then gradually with a cooled 
 mixture of 15 c.c. concentrated hydrochloric acid in an equal 
 volume of water. It is extracted with commercial ether. In 
 order to remove benzaldehyde, e ethereal layer is shaken 
 
 i B. 40, 1584. 
 
350 SPECIAL PART 
 
 thoroughly with a dilute water solution of sodium bisulphite. 
 Upon evaporating the ether an oily reaction product is obtained, 
 which solidifies completely when it is cooled and rubbed with a 
 glass rod. It is pressed on a porous plate and crystallised from 
 ligroin. Yield of the crude product 10-14 grammes. Benzhydrol 
 forms colourless needles which melt at 68. 
 
 With brombenzene and magnesium the experiment is carried 
 out in the following manner : 2.4 grammes of magnesium are 
 covered, in the presence of a granule of iodine, with a mixture 
 of 15.7 grammes of brombenzene that must be perfectly dry and 
 must possess a constant boiling point, and 50 c.c. of absolute 
 ether. If the materials used were pure and perfectly dry, the 
 reaction will commence in a short time when the mixture is 
 heated on a water-bath as in (a), i.e. the ether will continue to 
 boil when the water- bath is removed. Almost all the magnesium 
 goes into solution after ^-1 hour, and the boiling of the ether 
 ceases. It is now heated moderately on the water-bath for a 
 quarter of an hour. The treatment with benzaldehyde is exactly 
 the same as with phenyl magnesium iodide. 
 
 We are indebted to Grignard for the important observation that mono- 
 brom or monoiodo derivatives of different hydrocarbons (i molecular 
 weight) unite with magnesium (i atomic weight) in the presence of 
 absolute ether, e.g. : 
 
 CH 3 I + Mg = 
 
 Methyl magnesium iodide 
 
 C 2 H,,Br + Mg = Mg< 
 
 x Br 
 
 Ethyl magnesium bromide 
 
 With long carbon chains in the aliphatic series, saturated hydro- 
 carbons are also formed, and the longer the chain the more readily 
 will this reaction take place. With molecules containing six or more 
 carbon atoms, the main reaction consists in the removal of halogen, and 
 the formation of the hydrocarbon : 
 
 2 C 6 H 13 .Br + Mg = MgBr 2 + C U H M . 
 
AROMATIC SERIES 351 
 
 In an analogous way are formed C 6 H 5 . Mg . Br and C 6 H . . Mg . I = 
 phenyl magnesium bromide and iodide ; C 6 H 5 . CH 2 . Mg. I = benzyl 
 magnesium iodide ; C 6 H U . Mg . I hexahydrophenyl magnesium io- 
 dide (from iodocyclohexamethylene), etc. Since these compounds are 
 formed only in the presence of ether as solvent, it is probable that the 
 ether not only serves as a solvent, but also plays an essential part in 
 the reaction. As a matter of fact a compound C 2 H 5 . Mg . I + (C 2 H 5 ) 2 O 
 has been isolated which may be regarded as an oxonium derivative : 
 
 CJA *\L 
 
 C a H,/ N 
 
 The alkyl magnesium haloids or their ether derivatives are soluble 
 in ether. . On account of their unusual reactivity they may be used gen- 
 erally for the synthetic preparation of a large number of compounds. 
 Thus hydrocarbons may be obtained when organo-magnesium com- 
 pounds are treated with water or other substances containing the 
 hydroxyl group, e.g. : 
 
 A 
 
 Hydrocarbons are likewise obtained synthetically by the action of alkyl 
 sulphates, e.g. : 
 
 /Br 
 C 6 H 5 . Mg . Br + S0 4 (CH 3 ) 2 = QH 5 . CH 3 + Mg<f 
 
 X O.S0 3 CH 3 
 
 [n the synthesis of alcohols (mentioned below) hydrocarbons of the 
 ethylene series are formed, either as by-products, or as main products. 
 
 They unite with aldehydes to form double compounds, which are 
 decomposed with water, yielding secondary alcohols , eg. : 
 
 / H 
 C 6 H 5 .Mg.I = C e H 4 .cA).Mg.I, 
 
 CH 
 
 . 
 
 C 6 H 5 . CO . |Mg.I + HO| H = Mg< + C 
 
 
 Basic mag- OH 
 
 nesiuin iodide Diphenyl carbinol 
 or benzhydrol 
 
 This reaction was carried out above in (b). 
 
 When the simplest aldehyde (formaldehyde) is used in the form of 
 its polymer ? trioxymethylene, primary alcohols are formed. 
 
 In an analogous manner, tertiary alcohols are formed when ketones 
 are used, e.g. : 
 
352 SPECIAL PART 
 
 / rv **'*J 
 
 Acetophenone 
 
 H 3 N OH VCH, 
 
 X OH 
 
 Phenyl -dimethyl 
 carbinol 
 
 The esters of mono- and poly-basic carbonic acids also react readily 
 with alkyl magnesium haloids with the formation of alcohols. In this 
 case, two molecules of the magnesium compound react with one molecule 
 of the ester. Thus from the esters of formic acid secondary alcohols are 
 formed, e.g.: 
 
 'H /O.Mg.Br 
 
 + C 2 H 5 .Mg.Br = C< 
 
 CTT VY" "PT 
 
 2 H 5 \ ( -2 hl 5 
 
 Ethyl formate OC 2 H 5 
 
 /H 
 
 . Mg . Br 
 
 / 
 
 a , /Br /O 
 
 )C a H,+ Br.Mg^1 C H 5 = Mg< + C< 
 
 ^~^ " ' ^nr 1 w xV' 
 
 OCi** \ c 
 
 O.Mg.Br 
 2 H 5 
 
 /Br /C 2 H 5 
 
 .Mg.Br+HOH = Mg< + C< 
 X OH VH 
 
 H 5 X OH 
 
 fj Diethyl carbinol 
 
 In an analogous manner the esters of all the other monobasic acids 
 form tertiary alcohols. Thus ethyl acetate forms with ethyl magnesium 
 bromide : 
 
 = Methyl diethyl carbinol. 
 
 The reaction amounts essentially to the replacement of the carbonyl 
 oxygen atom of the corresponding free acid by two univalent hydrocarbon 
 residues. In this way, the esters of dibasic acids yield diacid alcohols j 
 Thus from oxalic ester is formed : 
 
AROMATIC SERIES. 353 
 
 H 3 
 
 Tetramethyl glycol, or Pinacone. 
 
 In place of acid esters the corresponding chlorides or anhydrides 
 may also be used. 
 
 As has already been mentioned, in the synthesis of alcohols, unsatu- 
 rated hydrocarbons are also formed in addition to alcohols, either as 
 by-products, or as main products. These are formed by the removal 
 of water from alcohols, e.g. : 
 
 = H 2 + |1 
 H 3 CH 2 
 
 H 
 
 When organo-magnesium compounds are allowed to react with excess 
 of formic ester, aldehydes are formed, and not secondary alcohols, e.g. : 
 
 A 
 C 6 H 3 . Mg . I + H . CO . OC 2 H 5 = C 6 H 5 . CHO + Mg<^ 
 
 OC 2 H 5 
 
 The same reaction will take place when, instead of formic ester, ortho- 
 formic ester, disubstituted formamide, and other derivatives of formic 
 acid are used. 
 
 Nitriles unite with alkyl magnesium haloids to form compounds 
 which yield ketones when they are decomposed with water : 
 
 /C 6 H 5 
 C 6 H 5 C=N + CH 3 . Mg . I = C=N . Mg . I. 
 
 Benzonitrile ^CH 3 
 
 /C,H. /C 6 H 5 
 
 C=N.Mg.I + HOH = I.Mg.OH + C=NH, 
 
 \CH 3 \CH 3 
 
 C=NH + H 2 O = NH 3 + C 6 H 5 . CO . CH 3 . 
 
 \CH Acetophenone 
 
 When alkyl magnesium haloids are treated with dry carbon dioxide, 
 carbonic acids are formed, e.g. : 
 
 CHg.Mg.H- C0 2 = CH 3 .COOMgI, 
 CH 3 .COOMgI + HOH = I.Mg.OH + CH 3 .COOH, 
 or, according to the experiment under (a) : 
 
354 SPECIAL PART 
 
 C 6 H 5 . Mg . 1 + C0 2 = C 6 H 5 . COOMgl, 
 C 6 H 5 . COOMgl + HOH = I . Mg . OH + C 6 H 5 . COOH. 
 
 Thus from the bromide or iodide of a hydrocarbon the monocarbonic 
 acid 1 of the next higher series is formed. 
 
 These simple examples are sufficient to show the great importance 
 of the Grignard reaction. Further details may be obtained from Jul. 
 Schmidt's work on "Die organischen Magnesium-verbindungen und 
 ihre Anwendung zu Synthesen I u. II " (Stuttgart, Enke ; 1905 u. 1908). 
 
 41. REACTION: PREPARATION OF A DYE OF THE MALACHITE 
 GREEN SERIES 
 
 EXAMPLE : Malachite Green from Benzaldehyde and Dimethyl- 
 aniline 2 
 
 (a) Preparation of the Leuco-Base. A mixture of 50 grammes 
 of dimethylaniline and 20 grammes of benzaldehyde (both freshly 
 distilled) is heated in a porcelain dish, with frequent stirring, on 
 the water-bath, for 4 hours, with 20 grammes of zinc chloride, 
 which has been previously fused in a porcelain dish, and pulver- 
 ised, after cooling. (See p. 358.) This viscous mass, which can- 
 not be poured directly out of the dish, is melted by covering it 
 with hot water, and heating it at the same time on the water-bath ; 
 while hot, it is transferred to a ^-litre flask. Steam is conducted 
 into it, until no drops of it pass over. There is thus obtained the 
 non-volatile leuco-base of the dye, in the form of a viscous mass, 
 which adheres firmly to the walls of the distilling flask. After the 
 liquid is cold, the water is poured off, the base adhering to the 
 sides of the flask is washed with water several times, and then dis- 
 solved in the flask with alcohol, on the water-bath. After filtering, 
 the solution is allowed to stand over night in a cool place, upon 
 which the base separates out in colourless crystals ; these are fil- 
 tered off, washed with alcohol, and dried in the air on several 
 layers of filter-paper. By concentrating the mother-liquor, a 
 second crystallisation may be obtained. Should the base not 
 crystallise, but separate out in an oily condition, which frequently 
 
 1 Concerning the other course of the reaction see B. 40, 1584. 
 
 2 A. 206, 83 ; 217, 250. 
 
AROMATIC SERIES 355 
 
 happens after a short standing of the filtered solution, this is due 
 to the fact that an insufficient amount of alcohol has been used. 
 In this case, more alcohol is added, and the mixture heated until 
 the oil is dissolved. 
 
 (b) Oxidation of the Leuco-base. Dissolve i o parts, by weight, 
 of the completely dry leuco-base by heating in a quantity of 
 dilute hydrochloric acid corresponding to 2.7 parts, by weight, 
 of anhydrous hydrochloric acid. For the purpose, dilute pure 
 concentrated hydrochloric acid with double its volume of water, 
 determine the specific gravity of the diluted acid, and refer to a 
 table to find out how much anhydrous acid the solution contains, 
 and from this calculate how much of the solution must be taken 
 in order to get the required amount of the anhydrous acid 
 (2.7 grammes). The colourless solution of the leuco-base is 
 then diluted in a large flask with 800 parts, by weight, of water, 
 and treated with 10 parts of 40 % acetic acid (sp. gr. 1.0523), 
 prepared by gradually diluting glacial acetic acid with water ; the 
 mixture is well cooled by throwing in pieces of ice ; then, with 
 frequent stirring, gradually add (during 5 min.) a quantity of 
 freshly prepared lead peroxide paste 1 corresponding to 7.5 grammes 
 of pure lead peroxide. The peroxide is weighed off in a beaker, 
 and treated with a quantity of water sufficient to form a very thin 
 paste. The residue remaining in the beaker after the first empty- 
 ing is washed out with water. After the addition of the peroxide, 
 the reaction-mixture is allowed to stand five minutes, with frequent 
 shaking; then add a solution of 10 parts of Glauber's salt and 
 50 parts of water ; the solution is then filtered off through a folded 
 filter from the precipitated lead sulphate and chloride. The filtrate 
 is treated with a filtered solution of 8 parts of zinc chloride dis- 
 solved in as small a quantity of water as possible ; then a saturated 
 sodium chloride solution is added, until all the dye is precipitated. 
 This is easily recognised by bringing a drop of the solution, with 
 a glass rod on a piece of filter-paper ; a bluish green precipitate 
 surrounded by a circle of a still fainter bright green colour will be 
 formed. The precipitated dye is filtered off with suction, washed 
 with a little saturated sodium chloride solution, and pressed out 
 
 1 See page 388. 
 
356 
 
 SPECIAL PART 
 
 on a porous plate. In order to purify it further, it may be dis- 
 solved again in water ; and from the filtered solution, after cooling, 
 it is again thrown out by sodium chloride. 
 
 The reaction just carried out, discovered by Otto Fischer in 1877, is 
 also used in the large scale for the preparation of Malachite Green, or 
 Bitter Almond Green. In the formation of the leuco-base, the follow- 
 ing reaction takes place : 
 
 X C 6 
 
 C 6 H 5 .CH 
 
 C (; H 4 .N(CH 3 ) 2 = / C 6 H 4 .N(CH 3 ) 2 
 C 6 H 4 .N(CH 3 ) 2 
 
 H 
 
 Tetramethyldiamidotriphenylmethane 
 = Leuco-base of Malachite Green 
 
 The substance thus obtained is not a dye, but the reduction product 
 of the real dye, which, on oxidation, passes over to the dye. Formerly, 
 the dye formation was believed to take place in accordance with the 
 following equation : 
 
 / 
 
 / 
 < 
 
 C 6 H 4 .N(CH 3 ) 2 
 <C 6 H 4 .N(CH 3 ) 2 |.H|C1 
 
 H 
 
 +H 2 0. 
 
 The union, effected by the oxidation between the pentavaient nitrogen 
 atom of the dimethyl aniline residue and the common methane-carbon 
 atom, was considered to be the condition which determined the nature 
 of the dye. At present, the view that the latter is determined by the 
 presence of the quinone-like secondary benzene residue is generally 
 accepted, and the formula of the dye-salt is written thus : 
 
AROMATIC SERIES 357 
 
 Further, it may be pointed out in this place that, in the formation ot 
 the leuco base, the hydrogen atom in the para position to the dimethyl- 
 amido groups N(CH 3 ) 2 unites with the aldehyde oxygen atom to form 
 water. The salt of the formula given above is difficult to separate 
 from its solution. But if zinc chloride is added, a double salt of the 
 same colour is formed : 
 
 3(C, 3 H, 5 N 2 C1) + 2 ZnCl 2 + H 2 O 
 
 which may be separated from its water solution by common salt. 
 
 Malachite Green may also be made by a second method, which was 
 discovered by Dobner: it consists in heating benzotrichloride with 
 dimethyl aniline in the presence of zinc chloride: 
 
 C 6 H 4 .N(CH 3 ) 2 / C 6 H 4 .N(CH 3 ) 2 
 .C 6 H 4 .N(CH 3 ) 2 \XH 4 .N(CH 3 ) 2 
 X C1 
 
 Since the chlorine atom remaining over migrates toward a nitrogen 
 atom, the dyestufF salt is directly formed by the transformation. Still, 
 since the preparation of pure benzotrichloride on the large scale is diffi- 
 cult, this method, which was formerly used, has been abandoned, and 
 the dye is now prepared exclusively by Fischer's method. 
 
 Malachite Green is a representative of a whole series of dyes, the 
 Malachite Green Series. If, instead of dimethyl aniline, diethyl aniline 
 is used, an analogous substance, which bears the name of Brilliant 
 Green, is formed. In place of benzaldehyde, substituted benzalde- 
 hydes, etc., can be used. The dyes of the Bitter Almond Series colour 
 only the animal fibres, silk and wool, directly. Vegetable fibre (cot- 
 ton) is not coloured unless it has been previously mordanted. 
 
 42. REACTION: CONDENSATION OF PHTHALIC ANHYDRIDE WITH 
 A PHENOL TO FORM A PHTHALEIN 
 
 EXAMPLE: (a) Fluorescein. 1 (b} Bromination of Fluorescein 
 with the Formation of Eosin 
 
 (a) In a mortar grind up and intimately mix 15 grammes of 
 phthalic anhydride with 22 grammes of resorcinol, and heat in an 
 
 1 A. 183, 1. 
 
358 
 
 SPECIAL PART 
 
 oil-bath to 180 (Fig. 78). As a vessel for heating the mixture 
 an "extract of beef" jar, glazed inside, is well adapted to the 
 purpose ; it can be obtained readily at a small cost, and may be 
 used several times for the same fusion. It is suspended by its 
 projecting edge from a triangle into the oil-bath. To the fused 
 
 mass add, with stirring (glass rod), 
 in the course of 10 minutes, 7 
 grammes of pulverised zinc chlo- 
 ride. This is prepared in the 
 following way : 10 grammes of the 
 commercial salt, which always con- 
 tains water, is carefully heated to 
 fusion over a free flame in a por- 
 celain dish. After the mass has 
 been kept in a fused condition for 
 a few minutes, it is allowed to cool, 
 and the solidified subsiance is re- 
 moved from the dish with a knife 
 and pulverised. After adding 7 
 grammes of the anhydrous salt 
 thus obtained, the temperature is 
 increased to 210, and the heating 
 continued until the liquid, which 
 gradually thickens, becomes solid, 
 for which about 1-2 hours is required. The cold friable melt 
 is removed from the crucible with a sharp instrument (it is best 
 to use a chisel), finely pulverised, and boiled 10 minutes in a 
 porcelain dish with 200 c.c. of water and 10 c.c. of concentrated 
 hydrochloric acid. This causes the solution of the substance 
 which did not enter into the reaction ; the addition of hydro- 
 chloric acid is necessary to dissolve the zinc oxide and basic 
 zinc chloride. The fluorescem is filtered from the solution, 
 washed with water until the filtrate no longer gives an acid 
 reaction ; it is then dried on the water-bath. Yield, almost 
 quantitative. 
 
 () Over 15 grammes of fluorescein in a flask, pour 60 grammes 
 
 FIG. 78. 
 
AROMATIC SERIES 
 
 359 
 
 of alcohol (about 95 %), add, with frequent shaking, 33 grammes 
 of bromine, drop by drop, from a separating funnel. This should 
 require about a quarter-hour. In place of a separating funnel, it 
 is advisable, as in all cases of bromination, to use a burette, by which 
 the troublesome weighing of bromine is obviated. Since the spe- 
 cific gravity of bromine at moderate temperatures is very nearly 3, 
 it is only necessary to divide the required weight by 3, in order to 
 find the number of cubic centimetres corresponding to the weight. 
 Of the numerous kinds of burettes, the one best adapted to this 
 
 FIG. 79. 
 
 FIG. 80. 
 
 purpose is the Winckler form ; since it possesses no cock, it can 
 be inserted into the body of a flask with a not too narrow neck, 
 and by this manipulation the disagreeable bromine vapours may 
 be avoided (Fig. 79). In the above case, n c.c. of bromine 
 are necessary. On the addition of bromine, it is observed that the 
 quantity of fluorescein insoluble in alcohol steadily decreases, and 
 that when about one -half of the bromine has been added, a clear, 
 dark, reddish-brown solution is formed. This is due to the fact 
 that the dibromide is first formed, which is easily soluble in 
 
360 SPECIAL PART 
 
 alcohol. On the further addition of bromine, the tetra-bromide 
 is formed, which, since it is difficultly soluble in alcohol, separates 
 out in the form of brick-red leaflets. After all the bromine has 
 been added, the reaction-mixture is allowed to stand for 2 hours, 
 the precipitate is filtered off, washed several times with alcohol, 
 and dried on the water-bath. The product thus obtained is a 
 compound of i molecule of eosin and i molecule of alcohol. In 
 order to obtain pure eosin from it, the substance is heated a half- 
 hour in an air-bath at 110 : during the heating, its colour becomes 
 brighter. Since eosin is insoluble in water, the soluble potassium-, 
 sodium-, or ammonium-salt is prepared on the large scale for dyeing. 
 Ammonium Eosin. Over a flat-bottom crystallising dish, \ 
 filled with a concentrated ammonia solution, place a filter, of paper 
 as strong as possible. Upon this is spread the eosin acid, in a 
 layer about \ cm. thick, and the whole is covered with a funnel 
 (Fig. 80). The bright-red crystals of the free eosin acid very 
 soon assume a darker colour, and, after about three hours, it is com- 
 pletely converted into the ammonium salt, which forms dark-red 
 crystals with a greenish lustre. The end of the reaction is easily 
 recognized, by testing a small portion with water. If it dissolves, 
 the conversion is complete. 
 
 On the large scale, this reaction is carried out in wooden chests 
 containing a number of frames covered with coarse linen, arranged 
 like drawers. After the eosin is spread out on the linen in thin layers, 
 dry ammonia evolved from ammonium chloride and lime is passed into 
 the chest, until a test-portion of the substance will completely dissolve. 
 
 Sodium Eosin. Grind 6 grammes of eosin with i gramme of 
 dehydrated sodium carbonate, and in a not too small beaker 
 moisten it with a little alcohol; after the addition of 5 c.c. of 
 water, heat on the water-bath until the evolution of carbon dioxide 
 ceases. To the water solution of sodium eosin thus obtained, add 
 20 grammes of alcohol, heat to boiling, and filter the hot solution. 
 On cooling, the soluble sodium salt sepafates out in the form of 
 splendid, brownish- red needles of a metallic lustre. As is the 
 case with many dyes, the crystallisation requires a long time ; one 
 day, at least, is necessary. 
 
AROMATIC SERIES 361 
 
 Phthalic anhydride and phenols can react with each other in two 
 different ways, (i) An equal number of molecules of each can con 
 dense, the oxygen atom of the anhydride, which unites the carbonyl 
 groups, can combine with two ring-hydrogen atoms of the phenol to 
 form one molecule of water ; this action results in the formation of an 
 anthraquinone derivative : 
 
 /CO /CO\ 
 
 QH/ >|0 + Hj . C C H 3 . OH = C 6 H/ >C 6 H 3 . OH + H..O 
 
 N:o \co/ 
 
 Phenol Oxyanthraquinone 
 
 Or (2) one molecule of the anhydride can react with two molecules of 
 the phenol in such a way that one of the two carbonyl-oxygen atoms 
 of the former combines with one ring-hydrogen of the two phenol 
 molecules to form a so-called phthalem: 
 
 HO OH 
 
 H|.C 6 H 4 .OH | | 
 
 , |0 + H . C 6 H 4 . OH C 6 H 4 C 6 H 4 
 
 < >0 
 
 x:D 
 
 = V 
 
 C 6 H 4 < 
 
 Phenolphthale!n= 
 dioxyph thalophenone 
 
 For the knowledge concerning this class of compounds, to which be- 
 long numerous important dyestuffs, we are indebted to the investiga- 
 tions of A. Baeyer (1871). Phthalophenone is considered to be the 
 mother-substance of the group : 
 
 which, as already stated, is obtained from phthalyl chloride and benzene 
 in the presence of aluminium chloride. If one conceives that the 
 mother-substance can take up one molecule of water, a hypothetical 
 mono-carbonic acid of triphenyl carbinol would result : 
 
 4 .CO.OH, 
 
 6 
 X)H 
 
3^2 SPECIAL PART 
 
 the formula of which shows very clearly the connection between the 
 phthalei'ns and the triphenyl methane derivatives. 
 
 If, as expressed by the above equation, phthalic anhydride is allowed 
 to act on phenol, phenolphthaleiin is obtained, a substance of acid 
 properties, colourless in the free condition ; its salts are red. It is 
 used as an indicator in volumetric analysis. 
 
 By the action of phthalic anhydride on resorcinol, the formation of 
 a tetraoxyphthalophenone would naturally be expected ; but fluorescein, 
 containing the constituents of one molecule of water less than this, is 
 obtained, an inner anhydride formation taking place between the two 
 hydroxyl groups : 
 
 >H HO OH 
 
 IOHI 
 
 UH -\/ - - 
 
 + 2H 2 0. 
 
 C 6 H 4 <^>0 
 
 Fluorescein 
 
 Fluorescein is technically prepared on the large scale by the method 
 given above. While phenolphthalein, in spite of the intense colour 
 of its salts, is not a dye, in that it does not colour fibres, fluorescein is 
 a true dye which colours animal fibres a fast yellow. But it is not 
 manufactured as a dye, since it has been replaced by other dyes that 
 give as beautiful colours and are cheaper. A number of its halogen- 
 and nitro-substitution products have valuable colouring properties, and 
 are prepared from it. The simplest dye of this kind is eosin or tetra- 
 brom-fluorescein, discovered in 1874 by Caro. The four bromine 
 atoms are equally divided between the two resorcinol residues : 
 
 HO ~ OH 
 
 I 
 C 6 HBr/\C 6 HBr 2 
 
 C 6 H, 
 
 which follows from the fact that eosin in fusion with potassium hydrox- 
 ide yields di-bromresorcinol besides phthalic acid. Instead of phthalic 
 anhydride, the di- and tetra-chlor-substitution products are fused with 
 
AROMATIC SERIES 
 
 363 
 
 resorcinol on the large scale ; and so there is obtained in the phthalic 
 acid residue, the di- and tetra-chlorfluoresce'ins from which halogen sub- 
 stitution products, nitro-derivatives, ethers, etc., are prepared on the 
 large scale (Phloxine, Rose Bengal). 
 
 Besides fluorescein there is practically only one other phthalein 
 prepared technically, Galleiin. This is done by heating phthalic anhy- 
 dride with the ^-trioxybenzene pyrogallol. In this case the same 
 anhydride formation takes place as in the preparation of fluorescein : 
 
 CO 
 
 >0 /OH 
 
 C 6 H Q ^OH = Galleiin. 
 X) 
 
 From gallein, a derivative of anthracene, coerulein, a new dye, is ob- 
 tained by heating with sulphuric acid. Since 1887 the phthaleins have 
 been on the market under the name of rhodamines, which are prepared 
 in a manner similar to that of fluorescein, except that instead of 
 resorcinol, m-amidophenol, or amidophenols substituted by alkyls in 
 the amido-group, are used : 
 
 /NH 2 
 CM ' 
 
 H N 
 
 NH 
 
 NH. ; 
 
 C 6 H 4 
 
 Simplest Rhodamine 
 
 The rhodamine on the market is the tetra-ethyl derivative of this 
 mother-substance . 
 
364 SPECIAL PART 
 
 43. REACTION: CONDENSATION OF MICHLER'S KETONE WITH AN 
 AMINE TO A DYE OP THE FUCHSINE SERIES 
 
 EXAMPLE: Crystal Violet from Michler's Ketone and Dimethyl 
 
 Aniline 
 
 A mixture of 25 grammes of dimethyl aniline, 10 grammes of 
 Michler's ketone (this is on the market), and 10 grammes of 
 phosphorus oxychloride, is heated in an open, dry flask, 5 hours, 
 on an actively boiling water-bath. The blue-coloured mass is 
 then poured into water, made alkaline with a solution of caustic 
 soda, and treated with steam until no drops of the unattacked 
 dimethyl aniline pass over. After cooling, the solidified colour- 
 base remaining in the distillation flask is filtered from the alkaline 
 solution, washed with water, and boiled with a mixture of i litre 
 of water and 5 grammes of concentrated hydrochloric acid. The 
 blue solution is filtered while hot from the colour-base, which 
 remains undissolved ; the latter is boiled again with a fresh quan- 
 tity of dilute hydrochloric acid ; this operation is repeated until 
 the substance has been almost entirely dissolved. After cooling, 
 the solution of the dye is treated with finely pulverised salt 
 (stirring) until the dye is precipitated. It is then filtered with 
 suction, pressed out on a porous plate, and crystallised from a 
 little water. On cooling, the Crystal Violet separates out in 
 coarse crystals of a greenish colour j these are filtered off and 
 dried in the air on filter-paper. 
 
 If Michler's ketone is heated with an amine in the presence of a 
 condensation agent (phosphorus oxychloride, POC1 3 ), addition takes 
 place, in accordance with the following equation : 
 
 C 6 H 4 .N(CH 3 ) 2 C 6 H 4 .N(CH 3 ), 
 
 CO + H.C 6 H 4 .N(CH 3 ) 2 =C<^'N(CH 3 ) 2 
 
 \L fi H 4 .N(LH 3 ) 2 
 .N(CH 3 ) S 
 
 Michler's ketone Hexamethylpararosaniline = 
 
 Colour-base of Crystal Violet 
 
AROMATIC SERIES 
 
 365 
 
 If this is dissolved in hydrochloric acid, one molecule of this is added, 
 and, as in the formation of Malachite Green, the elimination of a mole* 
 cule of water immediately takes place and the dye is formed : 
 
 N(CH 3 ) a 
 N(CH 8 ), 
 
 P 4 .N(CHa), 
 
 S H 4 .N(CH 3 ) 2 
 .H 4 .N(CH 3 ) 2 C1 
 
 or 
 
 Crystal Violet 
 
 It is a derivative of parafuchsine : 
 
 6 H 4 .NH 2 
 H 4 .NH 2 
 H 4 . NH 2 CJ 
 
 or 
 
 C 6 H 4 .NH 2 
 
 . Cl 
 
 indeed, it may be considered as a hexamethyl parafuchsine. It is pre- 
 pared technically in the same way, and forms the principal constituent 
 of the Methyl Violet obtained by the oxidation of dimethyl aniline. 
 
 Dyes can also be prepared in the same way by the combination of 
 other amines with Michler's ketone, of which it is only possible to 
 mention here Victoria Blue and Night Blue. 
 
 44. REACTION: CONDENSATION OP PHTHALIC ANHYDRIDE WITH 
 A PHENOL TO AN ANTHRAQUINONE DERIVATIVE 
 
 EXAMPLE : Quinizarin from Phthalic Anhydride and 
 Hydroquinone l 
 
 A mixture of 5 grammes of pure hydroquinone and 20 grammes 
 of phthalic anhydride is heated in an open flask with a mixture 
 of 100 grammes of pure concentrated sulphuric acid and 10 
 
 l B. 6, 506; 8, 152; A. 212. lo. 
 
366 SPECIAL PART 
 
 grammes of water for 3 hours in an oil-bath to 170-180, and 
 finally for i hour at 190-200. The directions as to time and tem- 
 perature must be followed as exactly as possible. The hot solution 
 is poured, with stirring, into about 400 c.c. of water in a porcelain 
 dish, heated to boiling, and filtered hot with the aid of a Biichner 
 funnel. The residue remaining on the filter is again boiled out 
 with water and filtered while hot. In order to separate the quini- 
 zarin from carbonaceous decomposition products, the precipitate 
 is boiled with 200 c.c. of glacial acetic acid, filtered hot with 
 suction, the filtrate poured into a beaker, and, while hot, treated 
 with its own volume of hot water. The residue remaining on the 
 filter is again boiled up with 100 c.c. glacial acetic acid, and, after 
 filtering, treated as above. On cooling of the diluted acetic acid 
 solution, the crude quinizarin separating out is filtered off, washed 
 with water several times, dried first on the water-bath, and finally 
 in an air-bath at 120. Since it is difficult to obtain it pure by 
 crystallisation, after drying it is distilled from a small retort of 
 difficultly fusible glass, and is driven over as rapidly as possible 
 with a large flame. A beaker is used as a receiver. It is more 
 convenient to use a porcelain mortar, and a porcelain dish as a 
 cover. After the distillate in the receiver and that in the neck of 
 the retort (this is broken) has been finely pulverized, it is crystal- 
 lized from glacial acetic acid, from which, on cooling, the quinizarin 
 separates out in the form of large, orange-yellow leaves ; these are 
 filtered off and washed with glacial acetic acid, which is steadily 
 diluted with water, until finally only pure water is used. Better 
 crystals (dark-red compact needles) may be obtained by dissolving 
 the distilled quinizarin in toluene, heated on a water-bath. The 
 filtered crystals are washed first with toluene and then with alcohol. 
 
 Under the preparation of fluoresce'in, it has already been mentioned 
 that phthalic anhydride condenses with phenols in certain proportions, 
 to form derivatives of anthraquinone. The reaction just effected takes 
 place in accordance with the following equation : 
 
 /co\ /co\ 
 
 [ 4\ >|0 + H 2 .|C fi H 2 .(OH) 2 = C r> H 4 < >C 6 H 2 (OH) 2 
 \C(X \CO/ 
 
 Quinizarin 
 
AROMATIC SERIES 367 
 
 In an analogous way, mono-acid- as well as poly-acid phenols, condense 
 with phthalic anhydride. It is of theoretical importance that from 
 pyrocatechol (o-dioxybenzene), besides a second isomer, alizarin is 
 obtained, showing that the two hydroxyl groups in alizarin are in the 
 ortho position to each other. Of practical significance is the above 
 reaction for the preparation of anthragallol, which is obtained on the 
 large scale by heating pyrogallol with phthalic anhydride : 
 
 H 2 |.C 6 H.(OH) 3 = C 6 H 4 <^ ^C 6 H.(OH) 3 + H,0. 
 
 Pyrogallol Trioxyanthraquinone = 
 
 Anthragallol 
 
 It may be mentioned briefly that by the condensation of benzole 
 acid with oxybenzoi'c acids, similar compounds are also obtained : 
 
 Anthragallol 
 
 Quinizarin dissolves, like oxyanthraquinones, in alkalies with a 
 violet colouration. (Try it.) 
 
 45. REACTION: ALIZARIN FROM SODIUM p-ANTHRAQUINONE- 
 MONOSULPHONATEi 
 
 In an autoclave or an iron pipe with a cap which can be 
 screwed on (see page 69), heat a mixture of 10 parts commercial 
 sodium anthraquinonemonosulphonate, 30 parts of sodium hy- 
 droxide, 1.8 parts of finely pulverised potassium chlorate, with 40 
 parts of water, for 20 hours to 170. After cooling, the melt is 
 boiled out with water several times, and acidified at the boiling- 
 point of the solution in a large dish with concentrated hydro- 
 chloric acid. The alizarin separating out is then filtered off 
 according to the quantity, either with suction or with the aid of 
 a filter-press, washed with water, pressed out on a porous plate, 
 and dried in an air-bath at 120. In order to obtain it com- 
 pletely pure, it is distilled rapidly from a small retort, and is 
 
 1 A. Spl. 7, 300 ; B. 3, 359 ; 9, 281, 
 
368 SPECIAL PART 
 
 crystallised from glacial acetic acid, or in large quantities from 
 nitrobenzene. 
 
 The sodium hydroxide fusion of the sodium anthraquinonemono- 
 sulphonate is an abnormal reaction to the extent that besides the re- 
 placement of the sulphonic acid group by hydroxyl, a hydrogen atom 
 is also oxidised to a hydroxyl group : 
 
 + 3 NaOH + O 
 
 ,Na 
 
 )Na 
 
 The tendency to the formation of alizarin is so great that even with- 
 out the addition of an oxidising agent (potassium chlorate or nitrate), 
 it is formed with the evolution of hydrogen. Formerly the oxygen of 
 the air was used as the oxidising agent, the reaction being effected 
 in air. 
 
 In order to prepare alizarin on the large scale, anthracene is the 
 starting-point ; this is obtained from the highest-boiling fractions of 
 coal tar (anthracene oil). It is oxidised by chromic acid to anthra- 
 quinone (see below), and this on heating with sulphuric acid is con- 
 verted into the monosulphonic acid. The separation of this latter 
 compound is greatly facilitated by the fact that it forms a sodium salt 
 difficultly soluble in water, which, on account of its silvery appearance, 
 is called " Silver salt." If the sulphonation mixture is diluted with 
 water and neutralised with sodium carbonate, the sodium anthraquinone- 
 monosulphonate is precipitated directly, which thus obviates the neces- 
 sity of removing the excess of sulphuric acid beforehand. On the large 
 scale the alizarin fusion is conducted exactly as on the small scale, 
 except that autoclaves, with stirring attachments, are used. The con- 
 stitutional formula of alizarin is : 
 
 OH 
 CO 
 
 The salts are intensely coloured. The red aluminium salt, the 
 violet ferric salt, and the garnet-brown chromic salt are especially im- 
 
AROMATIC SERIES 369 
 
 portant in dyeing With alizarin and all its related compounds the 
 dyeing is effected by mordanting the fibre with a salt of one of the 
 three oxides just mentioned; the thus prepared fibre is heated with 
 a thin dilute water-paste of the free insoluble dye, whereby salts are 
 formed on the fibre (Lakes). 
 
 From two disulphonic acids of anthraquinone, two trioxyanthra- 
 quinones, flavo- and anthra-purpurin, are prepared in a manner analo- 
 gous to that by which alizarin is obtained from the monosulphonic 
 acid. 
 
 From alizarin there can be prepared, further, by nitration, the a- or 
 /3-nitro-alizarin, and from this, by reduction, the corresponding amido- 
 alizarin. From /?-nitro- and amido-aiizarin, by heating with glycerol 
 and sulphuric acid, the important Alizarin Blue is obtained. Further, 
 by the action of fuming sulphuric acid on alizarin there is obtained a 
 tetraoxyanthraquinone (Bordeaux), etc. 
 
 46. REACTION: ZINC DUST DISTILLATION 
 EXAMPLE: Anthracene from Alizarin or Quinizarin 
 
 To a paste prepared by rubbing up 100 grammes of zinc dust 
 with 30 c.c. of water, add pieces of porous pumice stone of a size 
 that will conveniently pass into a combustion tube, and stir them 
 around so that they become covered with the zinc dust paste. 
 They are removed from the paste with pincers, heated in a porce- 
 lain dish over a free flame (in constant motion) until the water is 
 evaporated. A combustion tube of hard glass 60-70 cm. long 
 is drawn out at one end to a narrow tube, the narrowed end is 
 closed by a loose plug of asbestos, and a layer of zinc dust 5 cm. 
 long is placed next to the plug ; then follows a mixture of |-i 
 gramme of alizarin or quinizarin with 10 grammes of zinc dust, 
 and finally, a layer of pumice-zinc dust 30 cm. long. After a 
 canal has been formed over the zinc dust, by placing the tube in 
 a horizontal position and tapping it, the tube is transferred to a 
 combustion furnace inclined at an oblique angle, and dry hydrogen 
 is passed through the tube without heating. In order to test 
 whether the air has been completely expelled from the tube, the 
 
 2 B 
 
3/0 SPECIAL PART 
 
 open end is closed by a cork bearing a small glass tube to which 
 is attached a piece of rubber tubing ; the gas being evolved is 
 conducted into a soap solution, and the bubbles formed are 
 ignited, during which the greatest care must be taken to keep 
 the flame from coming in contact with the gas issuing from the 
 rubber tubing, otherwise a serious explosion may result. If an 
 explosion accompanied by a report takes place when the bubbles 
 are ignited, the air has not been completely removed, but if they 
 burn quietly, then only pure hydrogen is present. 1 When this is 
 the case, the current of gas is diminished so that only two bubbles 
 per second pass through the wash-bottle; the pumice-zinc dust 
 is then heated with small flames, these are increased in size 
 gradually, and finally, the tiles being placed in position, it is 
 heated as strongly as possible ; then the rear layer of 5 cm. of 
 zinc dust is similarly heated, and as soon as this glows, as in the 
 nitrogen determination, the mixture of the substance and zinc 
 dust is gradually heated. The anthracene formed condenses to 
 crystals in the forward cool part of the tube. After the reaction 
 is complete, while the tube is allowed to cool, a moderately rapid 
 current of hydrogen is passed through it ; the forward part of the 
 tube containing the anthracene is broken off and the substance 
 removed with a small spatula; it is purifed by sublimation in a 
 suitable apparatus (see pages 14 and 15). Melting-point, 213. 
 The sublimed anthracene is dissolved by heating in a test- 
 tube with a little glacial acetic acid ; it is treated with about 
 double its weight of chromic anhydride, and heated a short time 
 to boiling. The solution is then diluted with several times its 
 volume of water, the anthraquinone separating out is filtered off, 
 washed with some dilute sulphuric acid, then with water, and is 
 finally crystallised in a test-tube from a little glacial acetic acid. 
 Long colourless needles of anthraquinone, which melt at 277, are 
 thus obtained. 
 
 1 As described under Carbon Monoxide, the test may also be made by filling 
 a test-tube with the gas over water, and applying a match to the mouth of the 
 tube. 
 
PYRIDINE SERIES 3/1 
 
 Zinc dust is, especially at high temperatures, an excellent reducing 
 agent (Baeyer, A. 140, 205), which can be used for the reduction of 
 almost all aromatic oxygen compounds derived from hydrocarbons, e.g. : 
 
 C 6 H, . OH + Zn = C 6 H 6 + ZnO 
 
 Phenol Benzene 
 
 C 10 H r . OH + Zn = C 10 H 8 + ZnO 
 
 Naphthol Naphthalene 
 
 Also ketone-oxygen, as. the above example shows, can be replaced 
 by hydrogen. The reaction given under Alizarin possesses an historical 
 interest, since, by means of it, Gra'be and Liebermann, in 1868, dis- 
 covered that alizarin, which had been previously obtained from madder 
 root, was a derivative of anthracene, and could be prepared synthetically 
 from it. (B. i, 43.) 
 
 III. PYRIDINE AND QUINOLINE SERIES 
 
 1. REACTION: THE PYRIDINE SYNTHESIS OF HANTZSCHi 
 
 EXAMPLE : Collidine = Trimethylpyridine 
 
 Dihydrocollidinedicarbonic Acid Ester. A mixture of 25 
 grammes of acetacetic ester and 8 grammes of aldehyde-ammonia 
 is heated in a small beaker on a wire-gauze, about three minutes, to 
 loo-iio , the mixture being stirred with the thermometer. The 
 warm reaction-mixture is then treated with double its volume 
 of dilute hydrochloric acid, and stirred vigorously without further 
 heating until' the liquid mass solidifies. It is then thoroughly tritu- 
 rated in a mortar, filtered, washed with water, and dried, either 
 by pressing out, or by warming on the water-bath. For the further 
 working up of the collidinedicarbonic acid ester, the crude product 
 can be directly used. In order to obtain the dihydroester in a 
 crystallised condition, 2 grammes of the crude product are dissolved 
 in a small quantity of alcohol in a test-tube, by heat, and allowed 
 
 i A. 215, i. 
 
372 
 
 SPECIAL PART 
 
 FIG. 81. 
 
 to cool slowly. Colourless tablets with a bluish fluorescence are 
 thus obtained. Melting-point, 131. 
 
 Collidinedicarbonic Acid Ester. The crude dihydroester is 
 treated in a small flask with an equal weight of alcohol ; complete 
 
 solution does not take place. 
 Into the mixture cooled by 
 water pass nitrous fumes (Fig. 
 81), until the dihydroester goes 
 into solution, and a test-portion 
 dissolves to a clear solution in 
 dilute hydrochloric acid. The 
 alcohol is then evaporated by 
 heating on the water-bath, the 
 thick residue is treated with a 
 sodium carbonate solution to 
 alkaline reaction ; the oil sepa- 
 rating out is taken up with ether. 
 After the ethereal solution has 
 
 been dried by a small piece of potassium hvdroxide, or potash, 
 the ether is evaporated, and the residue subjected to distillation ; 
 on account of the high boiling-point of the ester, a fractionating 
 flask is selected, having the condensation tube as near as possible 
 to the bulb. The fraction passing over between 290-310 can be 
 used for the following experiment : 
 
 Potassium Collidine Dicarbonate. The saponification of the 
 ester is effected by boiling with alcoholic potash, prepared in the 
 following manner : Finely pulverised potassium hydroxide (2 parts 
 to i part of ester) is moderately heated in a flask on a wire-gauze 
 with 3 times its weight of absolute alcohol, until the greater portion 
 has passed into solution. The alcoholic solution is then poured 
 off from the portion remaining undissolved, treated with the ester 
 to be saponified, and heated 4-5 hours on a rapidly boiling water- 
 bath (with reflux condenser) ; the potassium salt separates out in 
 crusts. The alcoholic liquid is then poured off from the salt, 
 and the latter washed on the filter with alcohol and finally with 
 ether. 
 
PYRIDINE SERIES 373 
 
 Collidine. The dried potassium salt is intimately mixed in a 
 mortar with double its weight of slaked lime, and placed in one 
 end of a hard glass tube (about 2 cm. wide and 55 cm. long). 
 In order to prevent the mixture from being carried over into the 
 receiver on heating, a small, loose plug of asbestos is placed in the 
 tube in front of it. After a canal has been made by tapping, 
 the tube is connected with an adapter bent downwards, by means 
 of a cork or asbestos paper ; it is then transferred to a combustion 
 furnace, the rear end of which is somewhat elevated and warmed 
 throughout its entire length with small flames, beginning at the 
 closed end. The flames are steadily increased in size until, with 
 the tiles in position, the tube is heated as strongly as possible. 
 The collidine passing over is taken up with ether, dried with 
 potassium hydroxide, and, after the evaporation of the ether, is 
 subjected to distillation. Boiling-point, 172. 
 
 On heating acetacetic ester with aldehyde-ammonia, the following 
 reaction takes place (see A. 215, 8) : 
 
 CH S 
 
 OCH 
 
 C 2 H 5 O.OC.C C.CO.OQHs 
 
 QHgO.OC.CHjj CHg.CO.OQHs = 
 
 CH 3 C C CH 3 
 
 CH 3 .CO CO.CH 3 \XT/ 
 
 HNH 2 N 
 
 H + 3 H 2 0. 
 
 Dihydrocollidinedicarbonicethyl ester 
 
 The reaction may be modified by using other aldehydes instead of acet- 
 aldehyde ; thus there is obtained from benzaldehyde, acetacetic ester, 
 and ammonia, the dihydrophenyllutidinedicarbonic ester: 
 
 C* TJ CgHs 
 
 ^e^lg I 
 
 OCH / H \ 
 
 C 2 H 5 O . OC CH 2 CH 2 CO . OC 2 H 6 = QHsO . OC C C CO . OC 2 H 
 
 CH 8 CO CO CH 3 H 8 C C C CH 3 
 
 NH 2 H XTVTTI/ 
 
374 SPECIAL PART 
 
 With proprionic aldehyde, butyraldehyde, valeraldehyde, oenanthol, 
 myristic aldehyde, nitrobenzaldehyde, phenylacetaldehyde, furfurol, 
 .md others, the reaction can be carried out. All the compound* 
 obtained contain the methyl groups of the two acetacetic ester mole- 
 cules, but the third side-chain is different, depending upon the nature 
 of the aldehyde employed. 
 
 By passing nitrous fumes into an alcoholic solution of the dihydro- 
 ester, two hydrogen atoms, and those particular hydrogen atoms in 
 combination with carbon and nitrogen in the methenyl- and imido- 
 groups, respectively, will be oxidised off, and there is formed a deriva- 
 tive of pyridine, containing no ring hydrogen. While the dihydro- 
 esters possess no basic properties, the pyridine derivative dissolves in 
 acid. Therefore, by treating the solution with hydrochloric acid, it 
 can be determined whether any unchanged dihydroester (insoluble in 
 acid) is present. 
 
 Concerning the saponification of the ester, refer to what was said 
 under Reaction 36. 
 
 The splitting off of carbon dioxide fiom a carbonic acid, or a salt 
 of a carbonic acid, is generally designated as a " pyro-reaction." For 
 this kind of action a calcium salt is most frequently used ; this is mixed 
 with slaked lime and subjected to distillation, e.g. : 
 
 QH,.|COOca + caO|H = C 6 H 6 + CaCO 3 . 
 
 Calcium benzoate 
 
 (ca-i Ca) 
 
 In poly-basic acids, all the carboxyl groups can be replaced by hydro- 
 gen. In this way an acid may be transformed into the hydrocarbon 
 from which it was derived. In the above case, the potassium salt may 
 be used instead of the calcium salt. 
 
 2. REACTION: SKRAUP'S QUINOLINE SYNTHESIS 
 EXAMPLE : Quinoline 
 
 In a flask of about ii litres capacity containing a mixture of 
 24 grammes of nitrobenzene, 38 grammes of aniline, and 120 
 grammes of glycerol, add, with stirring, 100 grammes of concen- 
 trated sulphuric acid. The flask is then connected with a long, 
 wide reflux condenser, and heated on the sand-bath. As soon 
 
QUINOLINE SERIES 375 
 
 as the reaction begins, which is recognised by the sudden evolu- 
 tion of bubbles of vapour ascending through the liquid, the flame 
 is removed, and the energetic reaction is allowed to complete 
 itself without further heating from without. When the reaction- 
 mixture has become quiet, it is again heated for three hours on 
 the sand-bath, diluted with water, and from the acid liquid the 
 unchanged nitrobenzene is removed with steam. As soon as no 
 drops of oil pass over, the distillation with steam is discontinued. 
 The liquid remaining in the distillation flask is allowed to cool 
 somewhat, and then made alkaline with concentrated caustic soda 
 solution, upon which the liberated quinoline, mixed with the 
 unchanged aniline, is distilled over with steam. Since these sub- 
 stances cannot be separated by fractional distillation, their separa- 
 tion must be effected by a chemical method. For this purpose 
 the distillate (oil and water solution) is treated with dilute sulphuric 
 acid until all oil is dissolved and an excess of the acid is present ; 
 to the cold solution a solution of sodium nitrite is added until a 
 drop of the liquid will cause a blue spot on potassium iodide-starch 
 paper ; if the blue colour does not appear, add more sulphuric 
 acid to the mixture. The aniline (primary amine) is converted 
 into diazobenzenesulphate, while the tertiary quinoline remains 
 unchanged. The mixture is heated for some time on the water- 
 bath, by which, as in Reaction 8, the diazo-sulphate is converted 
 into phenol. The liquid is again made alkaline, upon which the 
 phenol goes into solution, while the quinoline is liberated. The 
 mixture is now distilled with steam, and the quinoline is obtained 
 in a pure condition : it is taken up with ether, the ether evaporated, 
 and the residue distilled. Boiling-point, 237. Yield, 40-45 
 grammes. '(See Wiener Monatshefte 2, 141.) 
 
 Quinoline is formed in the above reaction according to the following 
 equation : 
 
 H C.H 9 .OrI TT TT 
 
 HH \CH.OH H/\/\H 
 
 + 0= +4H 2 
 
 CH 2 .CH + HA H 
 
 H N 
 
 Quinoline 
 
376 
 
 SPECIAL PART 
 
 The oxygen necessary for the reaction is taken from the nitrobenzene, 
 which is hereby reduced in a manner that is not wholly clear. It is 
 possible that the reaction may take place in this way : first, acrolein is 
 formed from glycerol, under the influence of sulphuric acid : 
 
 CH 2 .OH CH 2 
 CH.OH =CH 
 OH CHO 
 
 CH 9 . 
 
 2H 2 O, 
 
 Like all aldehydes, this condenses with aniline to form acrolein 
 aniline. 
 
 C 6 H 5 . NH 2 + CHO . CH=CH 2 = C 6 H 5 . NzzCH CH=CH 2 + H 2 O . 
 
 While this, under the influence of the oxidising action of the nitro- 
 compound, loses two atoms of hydrogen, and thus quinoline is formed : 
 
 Quinoline 
 
 The Skraup reaction is capable of a very many-sided application. 
 If, instead of aniline, its homologues are used, methyl-, dimethyl-aniline, 
 etc., the corresponding quinoline is obtained. Also halogen-, nitro-, 
 etc., substituted amines, yield halogen-, nitro-, etc., substituted quino- 
 lines. Amidocarbonic acids, amidosulphonic acids, amidophenols, yield 
 carbonic acid-, sulphonic acid- or oxy-derivatives of quinoline. The 
 reaction is also applicable to the corresponding amido-compounds of 
 the naphthalene series. By starting from the diamines, two new pyri- 
 dine rings, connected with the benzene ring, are formed ; in this way 
 the so-called phenanthrolines, etc., are obtained. 
 
 Of technical and historical interest is the discovery which was made 
 by Prudhomme in the year 1877, that /8-nitroalizarin, on heating with 
 glycerol and sulphuric acid, yields a blue dye, Alizarin Blue. This 
 gave the impetus to Skraup's synthesis. To Grabe's investigations we 
 are indebted for the knowledge of the process by which, as above, a 
 quinoline synthesis is effected in the following way : 
 
HYDROCHLORIC ACID 
 
 377 
 
 OH 
 
 Nitroalizarin 
 
 OH 
 
 Residue of the glycerol added 
 Alizarin Blue 
 
 IV. INORGANIC PART 
 1. CHLORINE 
 
 A flask is one-third filled with manganese dioxide (pyrolusite) 
 in pieces the size of filberts ; to this is added a quantity of con- 
 centrated hydrochloric acid which is just sufficient to cover it. 
 On heating the mixture on a wire gauze with a free flame, a regular 
 current of chlorine is generated ; this is passed through two wash- 
 bottles containing water and concentrated sulphuric acid respect- 
 ively ; the water retains any hydrochloric acid which is carried 
 along with the gas, and the sulphuric acid dries it. (See Figs. 74 
 and 87.) A piece of thin asbestos-paper is placed on the wire 
 gauze, as is always done on heating large flasks, by which the 
 danger of breaking is essentially diminished. A very regular 
 current of chlorine can also be obtained from finely pulverised 
 potassium dichromate and crude concentrated hydrochloric acid 
 by heating the mixture on the water-bath. To i litre of hydro- 
 chloric acid, use 180-200 grammes of pulverised potassium 
 dichromate. 
 
 Concerning the preparation of chlorine from potassium per- 
 manganate and hydrochloric acid see B. 35, 43. 
 
 2. HYDROCHLORIC ACID 
 
 Gaseous hydrochloric acid, which is frequently needed for the 
 preparation of acid-esters, is generated most conveniently in a 
 
378 
 
 SPECIAL PART 
 
 Kipp apparatus charged with fused ammonium chloride in pieces 
 as large as possible, and concentrated sulphuric acid. The opera- 
 tion is conducted in the same way as that for the generation of 
 carbon dioxide or hydrogen from a Kipp apparatus. 
 
 If the apparatus is not available, the acid can be generated very 
 conveniently in the following manner : 
 
 In concentrated hydrochloric acid contained in a suction flask 
 allow to flow from a separating funnel concentrated sulphuric acid, 
 drop by drop (Fig. 82). The hydrochloric acid evolved is dried 
 by passing it through concentrated sulphuric acid contained in a 
 
 FIG. 82. 
 
 FIG. 83. 
 
 safety wash-bottle (Fig. 83) ; this latter is always used, since 
 otherwise, with an irregular gas current, the liquid to be saturated 
 may be easily drawn back into the wash-bottle and then into the 
 generating mixture. In place of a Woulff-flask with three tubu- 
 lures, a single-neck wash-bottle may be converted into a safety- 
 bottle as follows (see Fig. 84) : Into a two-hole cork place a 
 straight tube as wide as possible ; through this insert a narrow 
 delivery tube, bent at a right angle, which reaches almost to the 
 bottom of the bottle. 
 
 The liquid to be saturated cannot flow back into the wash- 
 bottle with this arrangement, since in case there should be a 
 tendency to do so, air would enter the suction-flask through the 
 space between the delivery tube and the wider tube, thus relieving 
 
HYDROBROMIC ACID 
 
 379 
 
 the pressure. If a wash-bottle having a side-tube is available, it 
 can also be converted into a safety-tube (see Fig. 85). 
 
 FIG. 84. 
 
 FIG. 85. 
 
 Hydrochloric acid gas may also be obtained by warming 10 
 parts of sodium chloride with a cold mixture of 3 parts of water 
 and 1 8 parts of concentrated sulphuric acid. 
 
 3. HYDROBROMIC ACID (see Brombenzene) 
 
 The hydrobromic acid obtained as a by-product in the bromina- 
 tion reactions is purified by distilling it from a fractionating flask. 
 Water first passes over until finally the temperature remains con- 
 stant at 126, when a 48 % acid goes over ; this is collected. 
 
 In order to prepare potassium bromide for use in the prepara- 
 tion of ethyl bromide, the acid is diluted with some water and 
 then treated with dry potash until there is no further evolution of 
 carbon dioxide and the liquid shows a neutral reaction. To 
 i part of hydrobromic acid 0.5 part potassium carbonate is used. 
 The water solution of the potassium bromide is evaporated to dry- 
 ness on a water-bath. The product thus obtained may be used 
 directly for the preparation of ethyl bromide. 
 
 4. HYDRIODIC ACID 
 
 To 44 grammes of iodine (not pulverised) contained in a small 
 round flask of about 100 c.c. capacity (Fig. 86), gradually add 4 
 grammes of yellow phosphorus divided into about 8 pieces under 
 
380 SPECIAL PART 
 
 water ; these are dried just before transferring them to the flask, by 
 pressing between layers of blotting-paper. The first piece of phos- 
 phorus added unites with the iodine with an active evolution of 
 heat and light. When the first action is ended, after shaking the 
 contents of the flask, which soon become liquid, the second piece 
 is added. The reaction still proceeds with evident energy, al- 
 though it is less intense than when the first piece was added. 
 Care is taken to place the phosphorus as nearly as possible in the 
 middle of the flask, and not to allow it to fall on the walls, since 
 otherwise the flask may be easily broken. When all of the phos- 
 phorus is added, a fused, dark mass of phosphorus triiodide is 
 obtained which becomes solid on cooling. The hydriodic acid pre- 
 pared from this by warming with 
 water, must be passed over red 
 phosphorus in order to free it 
 from iodine which is carried 
 along with it. Proceed as fol- 
 lows : 5 grammes of red phos- 
 phorus are rubbed u~? f o a paste 
 with 2 c.c. of a water solution 
 of hydriodic acid, or in case this 
 is not available, with as little 
 water as possible (i c.c. at the 
 most). In this is placed glass 
 beads, or bits of broken glass, 
 
 which on stirring around in the mixture become covered with the 
 paste. They are then transferred to a U-tube. Wide connecting- 
 tubes are used between the generating flask and the U-tube. In order 
 to prepare a water solution of hydriodic acid, the gas issuing from the 
 U-tube is passed into 45 c.c. of water (see Fig. 86). The glass tube 
 is not immersed in the water, but its end must be i cm. above the 
 surface ; otherwise, in consequence of the great affinity of water for 
 hydriodic acid, under certain conditions the water may be drawn back. 
 The hydriodic acid is now obtained by treating the completely 
 cooled phosphorus triiodide with 6 grammes of water and warm- 
 ing with a very small luminous flame. The contents of the flask 
 steadily become clearer, while in the other flask the heavy layer 
 
HYDRIODIC ACID 381 
 
 of hydriodic acid sinks to the bottom. The heating is continued 
 until only a clear, colourless liquid remains in the generating flask. 
 
 In order to obtain a concentrated solution of hydriodic acid, 
 the liquid in the receiver is distilled. At first a few cubic centi- 
 metres of water pass over at 100, then the temperature rises in 
 a short time to 125; the concentrated acid passing over up to 
 130 is collected separately. This boils for the most part at 127. 
 
 This experiment teaches much concerning the chemistry of 
 phosphorus and iodine. First, it shows that iodine and phos- 
 phorus unite directly with a vigorous reaction, to form phosphorus 
 
 trii'odide : 
 
 P + 3 I=PI 3 . 
 
 The iodide then decomposes with water, to form hydriodic acid, 
 which is evolved, while the phosphorous acid (H 3 PO 3 ) remains in 
 the flask : 
 
 P|i 8 + 3H|.OH = 3 HI + PH 3 3 . 
 
 The gaseous hydriodic acid is an intensely fuming substance, 
 which may be easily shown by removing the cork from the 
 receiver containing the aqueous acid, for a moment. Hydriodic 
 acid is absorbed by water with great avidity. The acid, boiling 
 constantly at 127, contains approximately 50% of anhydrous 
 hydriodic acid. 
 
 In this experiment it is observed that the connecting tubes of 
 the apparatus, especially those between the generating flask and 
 the U-tube become coated with crystals of a diamond-like bril- 
 liancy. These are crystals of phosphonium iodide, PH 4 I, which is 
 formed by the decomposition of phosphorous acid. 
 
 It is a common property of all the lower oxidation products 
 of phosphorus, to pass over to the highest oxidation product 
 phosphoric acid, with the evolution of phosphine on heating. 
 With phosphorous acid, the reaction takes place as follows : 
 
 The phosphine thus formed unites, since it possesses weak basic 
 properties, with hydriodic acid, to form phosphonium iodide : 
 
382 SPECIAL TART 
 
 Since this may easily clog the connecting tubes, the tubes 
 selected are as wide as possible. On cleaning the tubes with 
 water, this reacts with the phosphonium iodide with the evolution 
 of phosphine, a gas with a garlic-like odour, and which in this 
 case is not spontaneously inflammable. The phosphonium iodide 
 decomposes with water into its components, in accordance with 
 this equation : 
 
 PH 4 I = PH., + HI. 
 
 This reaction, as is well known, is employed for preparing pure 
 phosphine which is not spontaneously inflammable. 
 
 5. AMMONIA 
 
 Gaseous ammonia is prepared most conveniently by heating 
 the most concentrated ammonia solution in a flask over a wire 
 gauze with a small flame. In order to dry the gas, it is passed 
 through a drying tower filled with soda-lime. (See Fig. 66.) 
 
 6. NITROUS ACID 
 
 For the preparation of gaseous nitrous acid, arsenious acid, 
 broken into pieces the size of a pea, is treated with nitric acid, 
 sp. gr. 1.3, and heated gently on a wire gauze with a free flame 
 (under the hood). In order to condense the nitric acid carried 
 along with the gases, an empty wash-bottle, cooled by cold water, 
 is employed. (See Fig. 81.) 
 
 7. PHOSPHORUS TRICHLORIDE 
 
 Under water, in a porcelain mortar, cut 40 grammes of yellow 
 phosphorus, with a knife or chisel, into pieces which will con- 
 veniently p^iss into the tubulure of a 300 c.c. retort. After the air 
 in the retort has been displaced by dry carbon dioxide (Fig. 87), 
 each single piece of phosphorus is taken from the water by pincers, 
 and dried quickly by pressing it between several layers of filter- 
 paper, and immediately placed in the retort, care being taken to 
 prevent it from becoming ignited by friction in the opening of 
 the tubulure. As soon as all the phosphorus has been transferred 
 
PHOSPHORUS TRICHLORIDE 
 
 383 
 
 to the retort, the tubulure is connected with a delivery tube which 
 must move easily in the cork, and a moderately rapid current of 
 
 dry chlorine passed over the phosphorus ; phosphorus, chloride is 
 thus formed with evolution of heat and light. If crystals of phos- 
 phorus pentachloride should collect in the neck of the retort, the 
 
SPECIAL PART 
 
 delivery tube is pushed somewhat farther into the retort. If, on 
 the other hand, phosphorus distils to the upper part of the retort, 
 the tube is somewhat raised. The phosphorus trichloride con 
 densing in the receiver is distilled from a dry fractionating flask. 
 Boiling-point, 74. Yield, 125-140 grammes. 
 
 8. PHOSPHORUS OXYCHLORIDEi 
 
 To 100 grammes of phosphorus trichloride, contained in a large 
 tubulated retort connected with a condenser, add gradually, in 
 small portions of about 2-3 grammes, 
 32 grammes of finely pulverised potas- 
 sium chlorate. After each addition, 
 wait until the liquid bubbles up, before 
 adding a new quantity. If, on the 
 addition of the first portion, no reac- 
 tion takes place, it is started by a gentle 
 warming. During the addition, no 
 liquid should distil into the receiver, 
 but if this does happen, it is poured 
 back into the retort. After all of the 
 chlorate has been added, the phos- 
 phorus oxychloride formed is distilled, 
 by heating the retort in an oil-bath, 
 to 130, or with a luminous flame. A 
 suction-flask is used as a receiver; 
 this is firmly connected with the end 
 of the condenser, by means of a cork. 
 The distillate is rectified from a frac- 
 tionating flask provided with a thermometer. Boiling-point, 110. 
 Yield, loo-no grammes. 
 
 9. PHOSPHORUS PENTACHLORIDE 
 
 Through the upper delivery tube of an apparatus similar to that 
 represented in Fig. 88, a stream of dry chlorine is admitted, which 
 
 FIG. 88. 
 
 1 J. pr. 
 
 , [2] Vol. 23,382, 
 
SULPHUROUS ACID 385 
 
 passes out of the lower, right-angled tube. From time to time, 
 several cubic centimetres of phosphorus trichloride are allowed to 
 flow into the bottle from a separating funnel, upon which the 
 trichloride unites with the chlorine to form the solid pentachloride. 
 Since this operation can be repeated, as soon as it is evident that 
 the union is completed, any desired quantity of phosphorus penta- 
 chloride can be prepared. Should the delivery tube become 
 stopped up, it is cleared by the glass rod with which the apparatus 
 is provided. As the quantity of the pentachloride formed in- 
 creases, the tube is correspondingly raised. Yield, quantitative. 
 
 10. SULPHUROUS ACID 
 
 Gaseous sulphurous acid is generated in an apparatus similar to 
 the one represented in Fig. 82, by adding to a concentrated water 
 solution of sodium hydrogen sulphite a cold mixture of equal parts, 
 by volume, of water and concentrated sulphuric acid, drop by drop. 
 The generating flask i? shaken frequently, to keep the contents 
 from separating into layers. 
 
 11. SODIUM 
 
 (a) To cut Sodium. In order to divide sodium into small 
 portions, it can be cut into scales with a knife, or pressed out into 
 a wire with a sodium-press. To cut it into scales, an apparatus 
 similar to that represented in Fig. 89 is convenient. After both 
 
 sides of the knife and the front part 
 of the table have been coated with 
 a thin layer of vaseline, a long stick 
 of the metal to be cut, the end of 
 which is wrapped in filter-paper, in 
 order that it may be handled, is 
 >\ placed on the table so that it projects 
 somewhat over the front end ; it is 
 FlG - 89 ' then cut with a short stroke of the 
 
 knife. On the front part of the lower platform is placed a small 
 dish filled with ether or ligroi'n, into which the scales fall. When 
 2 c 
 
386 SPECIAL PART 
 
 using the knife, two points are to be especially observed. The 
 eye is never placed in front of the knife, but always behind it, so 
 that the fingers holding the sodium can always be seen. Only in 
 this way can a wound be prevented. Further, the cross-section 
 of the piece of sodium must not be too large, otherwise the metal 
 adheres to the knife. Quadratic scales, the edge of which must 
 not, at most, be more than 5-6 mm. long, are cut. With a little 
 practice, large quantities of the metal can be cut in very thin 
 scales in a short time. 
 
 The sodium residues are not thrown into water nor into waste- 
 jars, but are dropped into alcohol contained in a beaker or flask. 
 
 (b) Sodium Amalgam. Sodium scales, about the size of a 
 20-cent piece, are pressed to the bottom of mercury contained in 
 a porcelain mortar, in rather rapid succession, by means of a short, 
 moderately thick glass rod, drawn out to a point and bent at a 
 short right angle. The scales are speared on the glass rod (under 
 the hood ; eyes protected by spectacles ; hands, with gloves) . 
 
 The mercury may also be warmed in a porcelain casserole on 
 the water-bath (60-70), and, without further heating, small 
 pieces of sodium, the size of a half bean, are thrust to the bottom 
 of the vessel with the aid of a glass rod. 
 
 12. ALUMINIUM CHLORIDE 
 
 A wide tube, diameter 1^2 cm., of hard glass drawn out to 
 a narrow tube, is at one end connected by means of a cork 
 with a wide-neck so-called "salt bottle" (Fig. 90). The cork 
 with which this is closed is supplied with a second, smaller hole, 
 bearing a delivery tube of at least 9 mm. diameter, extending 
 to the centre of the receiver. The tube is half filled (half of 
 its cross-section) with aluminium shavings, which have been 
 previously freed from oil by boiling with alcohol and then dried 
 in an air-bath at 120; an asbestos plug is placed at each end 
 of the layer. A rapid current of hydrochloric acid gas, most 
 conveniently obtained from a Kipp apparatus charged with fused 
 ammonium chloride and concentrated sulphuric acid, is passed 
 
ALUMINIUM CHLORIDE 387 
 
 through the apparatus. Care must be taken that the drying flask 
 containing sulphuric acid is not too small, since the acid foams 
 easily. As soon as the air is driven out of the apparatus, this 
 has been accomplished when the gas. evolved is completely 
 absorbed by water (a piece of rubber tubing is attached to the 
 tube, and the gas tested from time to time by immersing the end 
 of the tubing in water in a beaker), the tube is heated in a com- 
 bustion furnace throughout its entire length, at first with small 
 flames, which are gradually increased (Fig. 90). When the flames 
 have reached a certain size, white vapours of aluminium chloride, 
 condensing in the receiver, are noticed. The reaction is ended 
 as soon as the aluminium, except for a small, dark-coloured resi- 
 
 ITTTmTTl 
 
 FIG. 90. 
 
 due, disappears. For the success of the preparation, the following 
 points are particularly observed : ( i ) All parts of the apparatus 
 must be perfectly dry. (2) The air must be removed as com- 
 pletely as possible, since, otherwise, an explosion of oxygen and 
 hydrogen may take place. (3) The portion of the tube extend- 
 ing beyond the furnace must be as short as possible, to prevent 
 the aluminium chloride from condensing in it, which results in a 
 stopping up of the apparatus. In order that the cork may not 
 burn, it is protected by an asbestos plate, provided with a circular 
 hole in the centre. (4) The aluminium must not be heated to 
 melting. If this should happen at any particular point, the flames 
 must be immediately lowered. (5) The hydrochloric acid cur- 
 rent must be extremely rapid. One should not be able to count 
 single bubbles of the gas, but they should follow one another 
 
388 SPECIAL PART 
 
 uninterruptedly. The evolution of a small quantity of a smoky 
 vapour from the outlet-tube will always occur, but the greatest 
 part of the aluminium chloride is condensed even if the hydro- 
 chloric acid rushes through the wash-bottles. Should the first 
 experiment be unsuccessful, in consequence of a stoppage of the 
 tube, the method for correcting this will readily suggest itself. 
 
 Recently it has been shown that it is better to use for the re- 
 ceiver an iron tube 25 cm. long and 4 cm. wide (inner diameter). 
 To one end of this is welded a narrower tube, 2 cm. long; by 
 filing it on the inside the end is given a somewhat conical shape ; 
 it. is selected of such a diameter that the glass tube can fae fastened 
 in it with a few turns of asbestos paper. The end not narrowed 
 is closed by a cork bearing a glass tube as wide as possible lead- 
 ing to the hood. A receiver of this kind is advantageous because 
 the glass tube can be heated strongly to its extreme end, and thus 
 a stopping up of the apparatus may be entirely prevented. If the 
 iron tube should become too hot, a wet towel is placed on it and 
 moistened from time to time. 
 
 The aluminium chloride condensing in the receiver is preserved 
 in well-closed bottles, or best, in a desiccator. 
 
 13. LEAD PEROXIDE 
 
 In a large porcelain dish dissolve, with heat, 50 grammes of 
 lead acetate in 250 c.c. of water, and treat with a solution of 
 bleaching-powder, prepared by shaking TOO grammes of bleaching- 
 powder with T^- litres of water and filtering, heat not quite to 
 boiling, until the precipitate, bright at first, becomes deep dark 
 brown. A small test-portion is then filtered hot, and the filtrate 
 treated with the bleaching-powder solution and heated to boiling ; 
 if a dark brown precipitate is formed, more of the bleaching- 
 powder solution is added to the main quantity, and it is heated 
 until a test gives no precipitate with the bleaching-powder solution. 
 The main quantity of the liquid is separated from the heavy pre- 
 cipitate by decantation ; the latter is washed several times with 
 water (decantation), and then filtered with suction; the precipi- 
 
LEAD PEROXIDE 389 
 
 tate is washed repeatedly with water. The lead peroxide is not 
 dried, but is preserved in a closed vessel in the form of a thick 
 paste. 
 
 Value Determination, In order to determine the value of the 
 paste, a weighed portion is heated with hydrochloric acid, the 
 chlorine evolved is passed into a solution of potassium iodide, 
 
 N 
 
 and the liberated iodine is titrated with a solution of sodium 
 
 10 
 
 thiosulphate (refer to a text-book on Volumetric Analysis) . The 
 determination, carried out as follows, is sufficiently accurate for 
 preparation work : On an analytical balance weigh off exactly 6.2 
 grammes of pure, crystallised sodium thiosulphate ; this is dis- 
 solved in enough cold water to make the volume of the solution 
 just 250 c.c. In a small flask weigh off 0.5-1 gramme of the 
 peroxide paste ; treat this (with cooling) with a mixture of equal 
 volumes of concentrated hydrochloric acid and water ; the flask 
 is immediately connected with a delivery tube, and this is inserted 
 in an inverted retort, the neck of which has been expanded to a 
 bulb, and which contains a solution of four grammes of potassium 
 iodide in water. When heat is applied to the flask, chlorine is 
 generated, which liberates iodine from the potassium iodide. 
 After the end of the heating, care is taken that the potassium 
 iodide solution is not drawn back into the flask. The contents 
 of the retort are then poured into a beaker and treated with the 
 thiosulphate solution from a burette until the yellow colour of 
 the iodine just disappears. Since a molecule of the peroxide 
 liberates two atoms of iodine, a cubic centimetre of the thiosul- 
 phate solution corresponds to = .012 gramme pure lead 
 peroxide. 
 
 14. CUPROUS CHLORIDE 
 
 Heat a solution of 50 grammes of copper sulphate and 24 
 grammes of salt to 60-70. Into this conduct a current of sulphur 
 dioxide until the precipitate of cuprous chloride no longer increases. 
 The precipitate is filtered with suction and washed, first with sul- 
 
3QO SPECIAL PART 
 
 phurous acid and then with glacial acetic acid until it runs through 
 colourless. The moist preparation is then heated in a shallow 
 porcelain dish or a large watch crystal on the water- bath until the 
 odour of acetic acid cannot be detected. It is preserved in a well- 
 closed flask. 
 
 15. DETERMINATION OF THE VALUE OF ZINC DUST 
 
 From a weighing-tube pour into a 100 c.c. round flask o.i 
 gramme zinc dust (exact weighing) and add a few cubic centi- 
 metres of water. The flask is closed by a good three- hole cork. 
 In the middle one is inserted a small dropping funnel ; the side 
 holes carry the inlet and outlet tubes (Fig. 91). The stem of 
 the funnel is previously filled with water by open- 
 ing the cock, immersing the end in water and 
 applying suction. The inlet tube is connected with 
 a Kipp carbon dioxide generator, and the outlet 
 tube with a nitrometer charged with a solution of 
 caustic potash. Carbon dioxide is passed into the 
 apparatus until all the gas escaping from the outlet 
 tube is absorbed by the potash. The current of 
 carbon dioxide is then lessened and from the drop- 
 ping funnel a mixture of 10 c.c. of concentrated 
 FIG. 91. hydrochloric acid and 10 c.c. water containing a 
 few drops of platinic chloride, is allowed to flow in on the zinc 
 dust ; the flask is finally heated. From the volume of hydrogen 
 obtained the percentage of zinc in the zinc dust may be calcu- 
 lated. The individual operations of this analysis are conducted 
 as described under " Determination of Nitrogen." 
 
INDEX 
 
 Abbreviations, 395. 
 Acetacetic ester, 179. 
 Acetaldehyde, 167. 
 Acetamide, 151. 
 Acetanilide, 145. 
 Acetic anhydride, 147. 
 Acetic ester, 157. 
 Acetonitrile, 155. 
 Acetyl chloride, 141. 
 Active mandelic acid, 309. 
 Aldehyde, 167. 
 Aldehyde-ammonia, 169. 
 Alizarin, 367. 
 Aluminium chloride, 386. 
 Amidoazobenzene, 265. 
 Amidodimethyl aniline, 258. 
 Ammonia, 382. 
 Ammonium eosin, 360. 
 Aniline, 215. 
 Animal charcoal, 50. 
 Anthracene, 369. 
 Anthraquinone, 370. 
 Antipyrine, 255. 
 Autoclaves, 68. 
 Azines, 303. 
 Azobenzene,. 226. 
 Azo dyes, 256. 
 Azoxybenzene, 226. 
 
 Beckmann's Reaction, 320. 
 Benzal chloride, 298. 
 Benzaldehyde, 298. 
 Benzamide, 318. 
 Benzene from aniline 237. 
 Benzene from phenylhydrazine, 250. 
 Benzenesulphinic acid, 287. 
 Benzenesulphon amide, 280. 
 
 Benzenesulphon chloride, 280. 
 
 Benzenesulphonic acid, 280. 
 
 Benzhydrol, 348. 
 
 Benzidine, 231. 
 
 Benzil, 306. 
 
 Ben zoic acid, 299, 303, 348. 
 
 Benzoi'cphenylester, 318. 
 
 Benzoin, 304. 
 
 Benzophenone, 320. 
 
 Benzophenone oxime, 320. 
 
 Benzotrichloride, 300. 
 
 Benzoyl chloride, 317. 
 
 Benzyl alcohol, 303. 
 
 Benzyl chloride, 300. 
 
 Bitter almond green, 356. 
 
 Boiling-point, corrections of, 32. 
 
 Bomb-furnace, 66. 
 
 Bomb-tubes, 63. 
 
 Brombenzene, 271. 
 
 Bromethane, 131. 
 
 Bromine carrier, 273. 
 
 Bromine, determination of, 80, 128. 
 
 Briihl's apparatus, 15, 27. 
 
 Biichner funnel, 58. 
 
 " Bumping," 31. 
 
 Butlerow's Synthesis, 146. 
 
 Butyric acid, 185. 
 
 Carbon, determination of, 101. 
 Carbon monoxide, 332. 
 Chloracetic acid, 163. 
 Chlorine, 377. 
 
 Chlorine, determination of, 80, 128. 
 Cinnamic acid, 313. 
 Cleaning the hands, 76. 
 Cleaning vessels, 75. 
 Collidine, 371. 
 391 
 
392 
 
 INDEX 
 
 Collidinedicarbonic ester, 372. 
 Congo-paper, 258. 
 Crystallisation, i. 
 Crystal violet, 364. 
 Cuprous chloride, 389. 
 
 Decolourising, 50. 
 Diazoamidobenzene, 262. 
 Diazobenzeneimide, 239. 
 Diazobenzeneperbromide, 238. 
 Diazo-compounds, 237. 
 Diazonium compounds, 238. 
 Diazotisation, 237. 
 Dibrombenzene, 271. 
 Dihydrocollidinedicarbonic ester, 371. 
 Dimethylcyclohexenone, 203. 
 Dinitrobenzene, 212. 
 Diphenyliodonium iodide, 244. 
 Diphenylmethane, 329. 
 Diphenylthiourea, 234. 
 Disazo dyes, 261. 
 Distillation, 16. 
 Distillation with steam, 37. 
 Distribution coefficient, 46. 
 Drying, 52. 
 Drying agents, 53. 
 Drying, of vessels, 75. 
 
 Elementary Analysis, Dennstedt's 
 
 Method, 113. 
 Eosin, 357. 
 Ether, pure, 277, 348. 
 Ethyl acetate, 157. 
 Ethyl benzene, 276. 
 Ethyl bromide, 131. 
 Ethylidene bisacetacetic ester, 202. 
 Ethylene, 191. 
 Ethylene alcohol, 196. 
 Ethylene bromide, 191. 
 Ethyl iodide, 133. 
 Ethyl malonic acid, 187. 
 Ethyl malonic ester, 185. 
 Extraction with ether, 44. 
 
 Filter press, 59. 
 Filtration, 56. 
 Fittig's Synthesis, 276. 
 
 Fluorescei'n, 357. 
 Fractional crystallisation, n. 
 .Fractional distillation, 23. 
 Friedel-Crafts' Reaction, 320. 
 Fuchsine-paper, 258. 
 
 Gattermann-Koch Reaction, 331. 
 Glycol, 196. 
 Glycoldiacetate, 196. 
 Grignard's Reaction, 348. 
 Guanidine, 234. 
 
 Halogens, determinations of, 80, 128. 
 Heating under pressure, 63. 
 Helianthine, 256. 
 Hofmann Reaction, 176. 
 Hydrazobenzene, 226. 
 Hydrazones, 254. 
 Hydriodic acid, 379. 
 Hydrobromic acid, 379. 
 Hydrochloric acid, 377. 
 Hydrocinnamic acid, 316. 
 Hydrogen, determination of, 101, 113. 
 Hydroquinone, 270. 
 
 Inactive mandelic acid, 307. 
 Iodine chloride, 165. 
 Iodine, determination of, 80, 128. 
 lodobenzene, 244. 
 lodoethane, 133. 
 lodosobenzene, 244. 
 Isodiazo compounds, 239. 
 Isonitrile reaction, 222. 
 
 Knoevenagel's ring closing, 202. 
 Kolbe's Reaction, 344. 
 
 Law of Mass Action, 159. 
 Lead peroxide, 388. 
 
 Malachite green, 354. 
 
 Malonic ester, 185. 
 
 Mandelic acid, 307. 
 
 Mandelic nitrile, 307. 
 
 Melting-point, determination of, 71. 
 
 Methyl amine, 175. 
 
 Methylene blue, 262. 
 
INDEX 
 
 393 
 
 Michler's ketone, 364. 
 Monobrombenzene, 271. 
 Monochloracetic acid, 163. 
 
 Naphthalenesulphonic acid (/3) ( 290. 
 
 Naphthol (18), 293. 
 
 Nitroaniline, 215. 
 
 Nitrobenzene, 212. 
 
 Nitrogen, determination of, 90, 124. 
 
 Nitrophenol (o and p) , 296. 
 
 Nitroso benzene, 223. 
 
 Nitrous acid, 382. 
 
 Opening bomb tubes, 66. 
 Osazones, 254. 
 Oxybenzaldehyde (p), 341. 
 
 Perkin's Reaction, 313. 
 Phenol from aniline, 243. 
 Phenyldisulphide, 290. 
 Phenylhydrazine, 250. 
 Phenylhydroxylamine, 223. 
 Phenyliodide, 244. 
 Phenyliodide chloride, 244. 
 Phenyliodite, 244. 
 Phenyl magnesium bromide, 350. 
 Phenyl magnesium iodide, 348. 
 Phenyl mercaptan, 289. 
 Phenyl mustard oil, 233. 
 Phosphorus oxychloride, 384. 
 Phosphorus pentachloride, 384. 
 Phosphorus trichloride, 382. 
 Pipette, capillary, 43. 
 Potassium acetate, 197. 
 Potassium collidine dicarbonate, 372. 
 Potassium-iodide-starch-paper, 241. 
 Pressure flasks, 68. 
 Pukall cells, 59. 
 Pyro-reaction, 374; 
 
 Qualitative tests for carbon, hydrogen, 
 
 nitrogen, sulphur, chlorine, bromine, 
 
 iodine, 77. 
 Quantitative determination of carbon 
 
 and hydrogen, 101, 113. 
 Quantitative determination of halogens, 
 
 80, 128. 
 
 Quantitative determination of nitrogen, 
 
 90, 124. 
 Quantitative determination of sulphur, 
 
 86, 125, 127. 
 Quinizarin, 365. 
 Quinoline, 374. 
 Quinone, 266. 
 
 Reduction of an azo dye, 256. 
 Runge's Reaction, 221. 
 
 Safety wash-bottle, 378. 
 
 Salicylic acid, 344. 
 
 Salicylic aldehyde, 340. 
 
 ' Salting out,' 49. 
 
 Sandmeyer's Reaction, 249. 
 
 Saponification of ethyl malonic ester, 
 
 187. 
 
 Schotten-Baumann Reaction, 318. 
 Sealing of bomb-tubes, 63. 
 Separation by extraction, theory of, 46. 
 Separation of liquids, 43. 
 Sodium, 385. 
 
 Sodium acetate, anhydrous, 147. 
 Sodium amalgam, 386. 
 Sodium eosin, 360. 
 Sodium knife, 385. 
 Solubility product, 287. 
 Solvents, 2. 
 Steam distillation, 37. 
 Sublimation, 14. 
 Sulphanilic acid, 235. 
 Sulphobenzide, 280. 
 Sulphur, determination of, 86, 125, 127. 
 Sulphurous acid, 385. 
 Superheated steam, 41. 
 
 Tarry matter, removal of, 50. 
 Terephthalic acid, 337. 
 Testing thermometers, 74. 
 Tests for carbon, 77. 
 Tests for halogen, 79. . 
 Tests for hydrogen, 77. 
 Tests for nitrogen, 77. 
 Tests for sulphur, 78. 
 Thermometer, tests of, 74. 
 Thiocarbanilide, 232. 
 
394 
 
 INDEX 
 
 Thiophenol, 287. 
 Toluic acid, 335. 
 Tolyl aldehyde, 331. 
 Tolyl nitrile, 248. 
 Trimethylpyridine, 371. 
 Triphenylguanidine, 233. 
 
 Vacuum distillation, 25. 
 Volhard Tubes, 68. 
 
 Xylenol (s), 204. 
 
 Zinc dust determination, 390. 
 Zinc dust distillation, 369. 
 
ABBREVIATIONS 
 
 A. = Liebig's Annalen der Chemie. 
 
 A. ch. = Annales de chimie et de physique. 
 
 B. = Berliner Berichte. 
 
 Bl. = Bulletin de la societe chimique de Paris. 
 
 Ch-Z. = Chemiker Zeitung. 
 
 J. = Jahresbericht liber die Fortschritte der Chemie. 
 
 J. pr. = Journal fur praktische Chemie. 
 
 P. = Poggendorff' s Annalen. 
 
 R. = Journal der russischen chemischen Gesellschaft 
 
 Z. = Zeitschrift fur Chemie. 
 
 395 
 
396 
 
 TABLE FOR NITROGEN DETERMINATION 
 
 00 w co<<tOOONrO"3-OOrt 
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 to to ^" O ^OO CO O 1 ^ f*O M Ci CS 
 
 M O t" 1 OO IH SO IH ^f >H CO M M 
 
 O to to to O O to O\ O oo 
 
 cso) MCOM^QcoOco 
 
 M ^ H t^* M tO M CO *H M 
 
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 tO M O'ttOOO MCOO<N 
 
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TABLE FOR NITROGEN DETERMINATION 
 
 397 
 
 O MO 
 
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 M J? 
 
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 OO OcoOM O 
 
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398 
 
 TABLE FOR NITROGEN DETERMINATION 
 
 VO M M O O M 
 
 ONOO ON ON oo M 
 
 M 00 
 00 <N 
 M CS 
 
 M-st-ONO M CO 10 Tj- O 
 
 t^ rt vO >0 NO NO tONO tOO 
 
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 M O M Tf" M CS 
 
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 M t^ M to 
 
 O NO 10 M O J^ 
 
 ON ^ 00 VO OO t^ 
 
 M IO M CO M M 
 
 Tf ON ON O ^ t~ ONOO 
 NOO IOCS IOCS ^t-CS ^-CS 
 
 M ^ M . .5" M . 2 M Q M oo 
 
 t-- O\ *N co *>* O\ 
 
 OO O) OO ^- t^ to 
 
 M T^ M CS MO 
 
 M S" O O 
 
 MQNOCS MOONOOMM 
 
 NOONIOO too -*o 
 
 to cs O OO 
 
 CO M CO O 
 
 M IO M CO 
 
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 M ON M t^. M IO 
 
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TABLE FOR NITROGEN DETERMINATION 
 
 399 
 
 
 OOVOCNCNVOOO MCO^O 
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400 
 
 TABLE FOR NITROGEN DETERMINATION 
 
 o oso 
 
 CO Os HI 
 
 CO HI CO CO CM IO 
 CM CO CM M 
 
 Os O Os Os 
 
 CM CO CM HI CM O\ HI 
 
 uJ ON .! Os ' ON * Os " OO .J OO .J OO .J OO ' OO " ^ " 
 
 O O O O O O II O O O 
 
 CO OO ON CO CO 00 HI CM 
 
 O HI so M 00 O Os O 
 
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 M VQ M 
 
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 O 00 O Ol 
 
 CM CO CM to 
 
 CM 00 CM O 
 
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 CM -rj- CM CM CM 
 
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 HI OO MO 
 
 CM CO f^O M Tj- 
 
 M ^ O to O O 
 
 CM CO CM M CM ON 
 
 a- 
 
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 H M $ M^ H <g M 
 
 O O O ON to r^ 
 
 O M O CM ON CO 
 
 CM M CM ON M t^ 
 
 M ^ M ^" M ^" 
 
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 M IO M CO 
 
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 CO "^1" OO O 
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 -^Q vr 
 
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 CM IO IO Os CM 
 
 
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 ^8 
 
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 oo * t^ * t^ 
 
 M >< M rt M ,-. M 
 
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TABLE FOR NITROGEN DETERMINATION 
 
 4OI 
 
 O ON vo PO ON CM ! 
 
 00 ON t^ ON O 00! 
 
 MM M ON M t^. 
 
 MCOO CM ON O t^ O 
 
 r-~ voO vo co "t M T(- 
 
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 OO vo 
 O vo 
 
 O oo 
 
 
 
 00 
 
 Printed in the United States of Americc