Edmund O'Neill 
 
A LABORATORY MANUAL 
 
 OF 
 
 ORGANIC CHEMISTRY 
 

A LABORATORY MANUAL 
 
 OF 
 
 ORGANIC CHEMISTRY 
 
 A COMPENDIUM OF LABORATORY METHODS 
 
 FOR THE 
 
 USE OF CHEMISTS, PHYSICIANS, 
 AND PHARMACISTS 
 
 BY 
 
 DR. LASSAR-COHN 
 
 M 
 
 PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF KONIGSBERG 
 
 TRANSLATED, WITH THE AUTHOR'S SANCTION, FROM THE 
 SECOND GERMAN EDITION BY 
 
 ALEXANDER SMITH, B.Sc., PH.D. 
 
 ASSISTANT-PROFESSOR OF GENERAL CHEMISTRY IN THE UNIVERSITY OF CHICAGO 
 
 & o n ft o n 
 
 MACMILLAN AND CO. 
 
 AND NEW YORK 
 1895 
 
 The Right of Translation and Reproduction is Reserved 
 
RICHARD CLAY AND SONS, LIMITED, 
 LONDON AND BUNGAY. - 
 
 IN MEMOR1AM 
 
 
TRANSLATOR'S PREFACE 
 
 THE book which is herewith presented in English translation 
 has met with such success in the original language that a second 
 edition was called for in less than three years from the date of 
 its first publication. It covers a field not previously occupied, 
 and the fact that the first edition has appeared in a French 
 dress leads to the hope that a welcome may likewise be 
 extended to an English version. The translation has been 
 made from the second edition (1893). 
 
 The work does not take the place of any of the text-books 
 of organic chemistry, but bears towards them the relation of 
 an almost indispensable complement. Most text-books deal 
 mainly with the description of substances and of chemical 
 reactions. The present volume is a compendium of the 
 methods actually used in the laboratory in the prosecution of 
 organic work. 
 
 To render the book more easily available for rapid reference, 
 a few modifications have been introduced by the translator 
 with the approval of the author. The classification according 
 to subject of the contents of each chapter, and the division 
 into numbered sections with conspicuous headings, have in- 
 volved no alterations beyond occasional slight rearrangements 
 
 889784 
 
vi TRANSLATOR'S PREFACE 
 
 in the order of the paragraphs and should greatly facilitate 
 the finding of any particular method. In connection with this, 
 a detailed table of contents has been supplied in place of a 
 bare list of the titles of the chapters. This seemed an 
 especially desirable change inasmuch as the index, although it 
 has been made as complete as possible, could not, in the very 
 nature of the case, enable the reader to make the fullest use of 
 the book. He would be more likely to take up the volume 
 in order to get suggestions along a certain line, than information 
 on a specific point. 
 
 A number of matters of subordinate interest, and methods 
 differing but slightly from others previously described, have 
 been printed in smaller type in order to relieve the main text 
 of details which might otherwise overcrowd and confuse it. 
 
 Beyond these, very few changes from the original have been 
 made, and since they have all been carried out in consultation 
 with the author, and sometimes at his suggestion, it has not 
 been thought necessary to designate them particularly in the 
 text. With the exception of some half dozen, they have been 
 insignificant. 
 
 In a few places, references to papers published within 
 the last two years have been added. New reactions and 
 new substances are discovered in large numbers every year, 
 but new methods of work are devised in much less rapid 
 succession, so that a book of the nature of the present is less 
 in danger of becoming out of date than an ordinary text-book. 
 More extensive changes, with the view of correcting this 
 tendency of most chemical works, were therefore unnecessary. 
 
 The references to the original literature are a valuable 
 feature of the book. These have all been verified, as far as 
 the sources were accessible, and a number of errors have been 
 corrected. While it can hardly be hoped that perfection has 
 
TRANSLATOR'S PREFACE vii 
 
 been attained, every care has been taken in securing substantial 
 accuracy in this particular. 
 
 To render easier the use of the abstracts published in the 
 Berichte der deutschen chemischen Gesellschaft or the Journal of 
 the Chemical Society by those who have not access to other 
 journals, a concise table, showing the year of publication of 
 each volume of the periodicals mentioned, has been inserted 
 as an appendix. The paper will usually be found in the 
 volume of abstracts for the year of its publication, or at all 
 events in that for the following year. 
 
 In conclusion the translator desires to extend his sincerest 
 thanks to Mr. J. B. Garner for his kind and valuable assistance 
 in revising the proof sheets, and to several friends to whom he 
 owes useful suggestions. 
 
 THE TRANSLATOR, 
 
 UNIVERSITY OF CHICAGO, 
 April, 1895. 
 
AUTHOR'S PREFACE TO THE FIRST 
 GERMAN EDITION 
 
 IN consequence of the comparative ease with which the 
 operations of inorganic chemistry can be carried out, we 
 commonly find all the necessary general instructions, as well 
 as the details of particular operations, given with sufficient 
 fulness even in the smaller books on the subject. The text- 
 books on organic chemistry, however, usually treat the practical 
 side of the science in a very perfunctory manner. The reader 
 may even get the impression that there are no difficulties in 
 the way of realising the actions expressed in the most com- 
 plicated equations, and that the yields calculable from the 
 equations will invariably be attained in practice. 
 
 Theoretically nothing can be simpler than the preparation 
 of an ester. It is formed from an acid and an alcohol, and 
 water is eliminated in the process. But the student soon finds 
 that the largest attainable yield of ester can only be reached in 
 the laboratory when certain definite conditions are rigidly 
 observed. 
 
 It is conceded that the discovery of methods which will give 
 quantitative yields is as much expected of the worker in organic 
 
x AUTHOR'S PREFACE TO FIRST GERMAN EDITION 
 
 as in inorganic chemistry. Indeed the very satisfactory processes 
 used in the technical preparation of organic bodies show that 
 this ideal can frequently be reached . It is true also that in many 
 interactions several chemical changes take place simultaneously, 
 and here we may take the sum total of the products as repre- 
 senting the yield. This will be the case, for example, where, in 
 dealing with substances having a constitution represented by 
 atoms or groups of atoms arranged in a closed chain, a number 
 of isomeric derivatives may be produced by the action of one 
 reagent. But how often it happens that only two or three per 
 cent, of the material used is transformed into what we regard 
 as the chief product, and we remain entirely in ignorance of 
 the fate of the bulk of the interacting substances. 
 
 The fundamental rule of submitting various substances to 
 chemical change in molecular proportions by weight, in order 
 to limit the opportunities for subsidiary actions, is not always 
 adhered to in practice. Indeed there must be exceptions to 
 this, as to every rule, particularly if the expression is restricted 
 to cases in which one molecular proportion of a body is 
 brought in contact with not more than four such proportions 
 of another. The difference which a wider interpretation of 
 the rule may make in the ultimate yield is strikingly illustrated 
 by the following example. 
 
 It had been shown by Hofmann (Her. 4, 667) that by the 
 action of excess of alcoholic ammonia on ethylene chloride at 
 100-120, only about 5 percent, of ethylene diamine hydro- 
 chloride was formed. The product contained large amounts 
 of bases of more complicated constitution. 
 
 Kraut (Ann. 212, 251) re-examined the matter and found 
 that, in accordance with Hofmann's results, 2.5-3 molecular 
 proportions of ammonia to one of ethylene chloride gave a 
 small quantity of the ethylene diamine salt and nearly 73 per 
 
AUTHOR'S PREFACE TO FIRST GERMAN EDITION xi 
 
 cent, of ammonium chloride. He offered the following 
 equations in explanation of the action : 
 
 C 2 H 4 C1 2 + 2NH 3 = C 2 H 4 (NH 3 C1) 2 . 
 
 C 4 H 8 (NH 2 C1) 2 +2NH 4 C1. 
 
 The formation of the product sought involved the production 
 of no ammonium chloride, while that of the hydrochlorides of 
 diethylene diamine and triethylene diamine led to the formation 
 of 54-04 and 72-05 per cent, respectively of this by-product. 
 It was evident therefore that the ethylene diamine first pro- 
 duced had been for the most part altered by further chemical 
 changes. 
 
 In addition to this, Kraut observed that the product of the 
 action of ethylene chloride on three molecular proportions of 
 alcoholic ammonia, after it had cooled, contained free ethy- 
 lene bases whose formation was accounted for by the equa- 
 tion : 
 
 C 2 H 4 C1 2 + 4NH 3 = C 2 H 4 (NH 2 ) 2 + 2 NH 4 C1. 
 
 The ammonium chloride survived the action only in virtue 
 of the fact that it crystallised out of the alcoholic solution. In 
 the absence of alcohol, water being used in its stead, when the 
 liquid was evaporated the hydrochloric acid united with the 
 less volatile ethylene bases and the ammonia was driven off. 
 In the first stages of the interaction, therefore, free ammonia 
 and free ethylene diamine were both present. The action of 
 fresh ethylene chloride on these produced ethylene diamine 
 and diethylene diamine, and the greater the amount of 
 ammonia present, the greater would be the extent to which the 
 former would be produced in proportion to the latter. 
 
 Kraut therefore heated ethylene chloride (i mol.) and 33 
 per cent, aqueous ammonia (18 mol.) in a sealed tube for five 
 
xii AUTHOR'S PREFACE TO FIRST GERMAN EDITION 
 
 hours at 115-1 20, and obtained 95 per cent, of the theoretically 
 possible yield of ethylene diamine. 
 
 Of recent years several works have appeared in which all the 
 methods for the preparation of certain classes of bodies are 
 collected. But even these confine themselves almost entirely 
 to the statement of the equations representing the chemical 
 actions. By using the numerous references to the literature 
 which they contain, it is easy for the reader who has access to 
 an adequate library to ascertain the exact course which was 
 followed in any particular case. In the present volume, on 
 the other hand, an effort has been made to bring together the 
 methods which may be employed for carrying out all the 
 common operations, such as sublimation, reduction, and the 
 preparation of nitro-bodies and of sulphonic acids, without 
 reference to the particular substances employed. Care has 
 been taken also to show by means of examples how various 
 investigators have overcome the difficulties of any particular 
 case. It was not possible of course to give all the methods 
 that have ever been used. The attempt has been made, how- 
 ever, to give a sufficient selection, and the material has been 
 drawn from all accessible foreign, as well as German, sources. 
 
 The possible variations in methods of work are as in- 
 exhaustible as the science of chemistry itself. Every day 
 brings its novelty and an exhaustive treatment of such a 
 subject is impossible. But those who have not had, or do 
 not have, time to read extensively in chemical literature will 
 find here collected all that is essential in the large volume of 
 experience in the practice of organic chemistry which is 
 scattered and hidden in the great stores of published matter. 
 Thus one who, for example, attempts all reductions by means 
 of tin and hydrochloric acid and similar agents may find in 
 the following pages methods which will suit his purpose 
 
AUTHOR'S PREFACE TO FIRST GERMAN EDITION xiii 
 
 better ; or be led to their discovery by the study of cases 
 similar to that with which he is dealing, which may be cited 
 in the text. Its object will have been attained if the book 
 encourages work in the field of organic chemistry and lightens 
 the labour of the workers. 
 
 THE AUTHOR. 
 
 KONIGSBERG, 
 
 May, 1890. 
 
CONTENTS 
 
 PART I GENERAL METHODS 
 
 CHAPTER I. BATHS. i. General remarks. 2. High temperatures. 
 3. Dry baths and air baths Pp. I to 2 
 
 CHAPTER II. CRYSTALLISATION. i. Solvents. 2. Filtration and 
 precipitation. 3. Recrystallisation. 4. The transformation of sub- 
 stances into closely allied derivatives. 5. Crystallographic examination. 
 6. Dialysis Pp". 3 to 18 
 
 CHAPTER III. DECOLOURISING OF LIQUIDS. i. Charcoal. 2. 
 Extraction of bitter principles. 3. Sulphurous acid. 4. Precipitation. 
 
 Pp. 19 tO 21 
 
 CHAPTER IV. DISTILLATION. i. Ordinary distillation. 2. Ther- 
 mometers and their use. 3. Fractional distillation. 4. The con- 
 denser. 5. Distillation in a current of steam. 6. Dry distillation. 
 7. Distillation in vacua. 8. Leading vapours through red-hot tubes. 
 9. Distillation under pressure. 10. Determination of the boiling-point 
 of small quantities of liquids Pp. 22 to 43 
 
 CHAPTER V. DRYING SOLIDS AND LIQUIDS. i. Drying in desiccators. 
 2. Drying liquids. 3. Drying alcohol and ether .... Pp. 44 to 5 1 
 
 CHAPTER VI. EXTRACTION. i. Extraction with ether. 2. Ex- 
 traction with amyl alcohol. 3. Solubility. 4. Continuous extraction. 
 5. Extraction of solids. 6. Solvents and diluting media . . Pp. 52 to 60 
 
 CHAPTER VII. FILTRATION. Filtration through paper, asbestos, and 
 cloth. Clarification of filtrates Pp. 61 to 62 
 
xvi CONTENTS 
 
 CHAPTER VIII. DETERMINATION OF MELTING-POINTS. i. Com- 
 parison of methods. 2. Heating in a capillary tube. 3. Effect of 
 impurities. 4. Peculiarities in some classes of bodies . . . Pp. 63 to 65 
 
 CHAPTER IX. DETERMINATION OF MOLECULAR WEIGHTS. i. By 
 measuring the vapour density ; ( i ) Method where the mercury expelled 
 by the vapour is weighed (Victor Meyer) ; (2) Hofmann's method ; (3) Me- 
 thod by expulsion of Wood's alloy ; (4) Method by expulsion of air (Victor 
 Meyer) ; (5) Demuth and Meyer's method. 2. Raoult's freezing-point 
 method. 3. Beckmann's boiling-point method Pp. 66 to 88 
 
 CHAPTER X. SEALED TUBES. i. Reactions in closed vessels. 2. 
 The gases in sealed tubes. 3. Experiments on a small scale. 4. The 
 oven and accessories Pp. 89 to 96 
 
 CHAPTER XI. SUBLIMATION. Methods of sublimation under atmo- 
 spheric pressure and in vacua Pp. 97 to 100 
 
 PART II SPECIAL METHODS 
 
 CHAPTER XII. CONDENSATION. i. General remarks. 2. Con- 
 densing agents. 3. Acetic acid. 4. Acetic anhydride. 5. Aluminium 
 chloride. 6. Ammonia. 7. Antimony trichloride. 8. Barium hy- 
 droxide. 9. Benzotrichloride. 10. Boron trifluoride. n. Calcium 
 chloride. 12. Calcium hydroxide. 13. Copper. 14. Hydrochloric 
 acid. 15. Hydrocyanic acid. 16. Magnesium chloride. 17. Oxalic 
 acid. 1 8. Perchloroformic ether. 19. Phosgene. 20. Phosphorus 
 oxychloride. 21. Phosphorus pentoxide. 22. Phosphorus trichloride. 
 23. Potassium bisulphate. 24. Potassium cyanide. 25. Potassium 
 hydroxide. 26. Silicic ether. 27. Silver. 28. Sodium. 29. So- 
 dium acetate. 30. Sodium ethylate. 31. Sodium hydroxide. 32. 
 Sulphur. 33. Sulphuric acid. 34. Tin tetrachloride. 35. Zinc. 
 36. Zinc chloride. 37. Zinc dust. 38. Zinc oxide. 39. Effects of 
 heat alone Pp. 101 to 136 
 
 CHAPTER XIII. PREPARATION OF DIAZO-BODIES. i. General re- 
 marks. 2. Preparation of nitrous acid. 3. Use of nitrous acid. 
 4. Use of sodium nitrite. 5. Other ways of obtaining diazo-bodies. 
 6. Fatty diazo-bodies Pp. 137 to 143 
 
 CHAPTER XIV. PREPARATION OF ESTERS. i. Action of hydro- 
 chloric acid on the free acid and an alcohol. 2, Preparation of esters from 
 
CONTENTS xvii 
 
 anhydrides and alcohols. 3. Action of sulphuric acid on the free acid and 
 an alcohol. 4. Action of sulphuric acid on an organic salt and an 
 alcohol. 5. Preparation of esters of inorganic acids in presence of sul- 
 phuric acid. 6. Use of bisulphate and pyrosulphate of potassium. 
 7. Use of phosphorus oxychloride in preparing phenyl esters. 8. Action 
 of salts of ethyl sulphate on organic salts. 9. Action of alkyl halides on 
 organic salts. 10. Action of acid chlorides on alcohols. n. Prepara- 
 tion of ethers by the action of alcoholic caustic potash on chloro-derivatives. 
 12. Preparation of salol Pp. 14410 154 
 
 CHAPTER XV. FUSION WITH CAUSTIC ALKALIS. i. Description 
 of the apparatus and method. 2. Oxidation accompanies the fusion. 
 3. Promotion and restraint of the oxidising influence. 4. Differences 
 between the action of sodium and potassium hydroxides. 5. Differences 
 In result under different conditions. 6. Fusion of calcium and other salts 
 with alkalis. 7. Reduction of nitro-phenols. 8. Analogy of this 
 reaction to putrefaction Pp. 155 to 160 
 
 CHAPTER XVI. PREPARATION OF HALOGEN COMPOUNDS. SEC- 
 TION I. BROMO-DERIVATIVES. I. Bromine. 2. Bromine carriers. 
 3. Hydrobromic acid. 4. Phosphorus pentabromide. 5. Metallic bro- 
 mides, SECTION II. CHLORO-DERIVATIVES. i. Preparation of 
 chlorine. 2. Use of free chlorine. 3. Nascent chlorine. 4. Addition 
 of chlorine or hydrochloric acid to unsaturated compounds. 5. Action of 
 hydrochloric acid on alcohols. 6. Halogen compounds from diazo -bodies 
 and hydrazine derivatives. 7. Replacement of bromine and iodine by 
 chlorine. 8. Chlorine carriers. 9. Phosphorus pentachloride. 10. 
 Acetyl chloride. n. Antimony pentachloride. 12. Bleaching powder. 
 13. Cuprous chloride. Sandmeyer's and Gattermann's reactions. 14. 
 Mercuric chloride. 15. Phosphorus oxychloride. 16. Phosphorus 
 trichloride. 17. The chlorides of sulphur. 18. Sulphuryl chloride. 
 19. Chlorsulphonic acid. 20. Thionyl chloride. SECTION III. 
 IODO-DERIVATIVES. i. Free iodine. 2. Iodine with solvents. 3. 
 Iodine carriers phosphorus. 4. Iodine carriers ferrous iodide. 5. 
 Application of sulphuric acid. 6. Use of a solution of iodine in potassium 
 hydroxide. 7. Addition of iodine. 8. Action of hydriodic acid. 9. 
 Addition of hydriodic acid to unsaturated bodies. 10. Addition of iodine 
 chloride. 11. Phosphonium iodide and iodide of nitrogen. 12. Action 
 of boron tri-iodide and of iodides of calcium, sodium, and potassium on 
 chloro-derivatives. 13. Dissimilarity in properties of ethyl chloride, 
 bromide, and iodide. SECTION IV. FLUORO-DERIVATIVES. i. In- 
 teraction of silver fluoride with iodo- and chloro-derivatives. 2. Action 
 of hydrofluoric acid on diazo-bodies. 3. Chromium hexafluoride. 
 
 Pp. 161 to 223 
 b 
 
xviii CONTENTS 
 
 CHAPTER XVII. PREPARATION OF NITRO-DERIVATIVES. i. General 
 remarks. 2. Method of using nitric acid. 3. Preparation of nitro- 
 derivatives of bases. 4. Nitro- derivatives of easily oxidisable substances. 
 5. Other special cases. 6. Influence of time and temperature. 7. 
 Use of nitric acid containing 100 per cent, of HNO 3 . 8. Action of dilute 
 nitric acid. 9. Action of nitric acid on fatty bodies. 10. Use of ether 
 as a solvent. n. Use of acetic acid as a solvent. 12. Use of a mix- 
 ture of nitric and sulphuric acids. 13. Use of sodium and potassium 
 nitrates. 14. Separation of nitro-compounds from acid solutions in which 
 they are formed. 15. Less common methods of preparing nitro-compounds. 
 1 6. Nitro-compounds of the fatty series Pp. 224 to 242 
 
 CHAPTER XVIII. OXIDATION. I. Oxidising agents. 2. General 
 remarks. 3. Air. 4. Arsenic acid. 5. Azobenzene. 6. Barium 
 peroxide. 7. Bleaching powder. 8. Bromine. 9. Chloranil. 10. 
 Chloric acid. 11. Chloride of iodine. 12. Chlorine. 13. Chromic 
 acid. 14. Chromyl chloride. 15. Copper solution alkaline. 16. 
 Cupric acetate. 17. Cupric oxide and hydroxide. 18. Cupric sul- 
 phate. 19. Ferric chloride. 20. Ferric hydroxide. 21. Hydrogen 
 peroxide. 22. Hydroxylamine. 23. Internal oxidation. 24. Lead 
 monoxide. 25. Lead peroxide. 26. Manganese dioxide. 27. Mer- 
 curic acetate. 28. Mercuric chloride. 29. Mercuric nitrate. 30. 
 Mercuric oxide. 31. Nitrobenzene. 32. Nitric acid. 33. Nitrous 
 acid. 34. Oxygen. 35. Ozone. 36. Platinum tetrachloride. 37. 
 Potassium bichromate. 38. Potassium chlorate. 39. Potassium ferri- 
 cyanide. 40. Potassium hydroxide. 41. Potassium iodate. 42. Po- 
 tassium manganate. 43. Potassium permanganate. 44. Soda lime. 
 45. Sodium bichromate. 46. Sodium nitrite. 47. Sodium peroxide. 
 48. Silver acetate. 49. Silver nitrate. 50. Silver oxide. 51. Sul- 
 phuric acid. 52. Tin tetrachloride. 53. Zinc permanganate. 
 
 Pp. 243 to 286 
 
 CHAPTER XIX. REDUCTION. i. Reducing agents. 2. Aluminium. 
 3. Ammonia. 4. Ammonium sulphide. 5. Chromous chloride. 6. 
 Ferrous chloride or sulphate. 7. Ferrous potassium oxalate. 8. 
 Formaldehyde. 9. Grape sugar. 10. Hydriodic acid. 11. Hy- 
 drogen sulphide. 12. Hydroxylamine. 13. Iron. 14. Magnesium. 
 15. Palladium -hydrogen. 16. Phenylhydrazine. 17. Phosphorous acid. 
 1 8. Phosphorous iodide. 19. Phosphorus. 20. Potassium arsenite. 
 21. Potassium hydrosulphide. 22. Alcoholic potassium hydroxide. 
 23. Sodium. 24. Sodium amalgam. 25. Sulphurous acid. 26. Tin. 
 27. Tin bichloride. 28. Zinc. 29. Zinc dust .... Pp. 287 to 328 
 
CONTENTS xix 
 
 CHAPTER XX. PREPARATION OF SALTS. SECTION i. GENERAL 
 REMARKS. i. Salts of acids. 2. Salts of bases. 3. Precipitation 
 of salts soluble in water. 4. Water of crystallisation. 5. Determina- 
 tion of the solubility of salts. 6. Precipitation by alcohol and ether. 7. 
 Double salts of bases. 8. Obtaining acids from their salts. 9. Obtaining 
 bases from their salts 10. Preparation of salts by double decomposition. 
 SECTION II. PREPARATION AND ANALYSIS OF SALTS. 11. Salts of 
 organic acids containing metals. 12. Salts of organic bases with organic 
 acids. 13. Ignition of explosive salts. 14. Determination of the ash 
 in organic matter Pp. 329 to 349 
 
 CHAPTER XXI. SAPONIFICATION. i. Saponifying agents. 2. 
 Aqueous caustic potash or soda. 3. Alcoholic caustic potash. 4. So- 
 dium ethylate. 5. Baryta water. 6. Lime water. 7. Oxides of lead 
 and silver. 8. Acids. 9. Aluminium chloride. 10. Non-saponifiable 
 esters Pp. 350 to 357 
 
 CHAPTER XXII. PREPARATION OF SULPHONIC ACIDS. i. Re- 
 agents used. 2. Concentrated sulphuric acid. 3. Isolation of the pro- 
 ducts. 4. Sulphuric acid containing 100 per cent, of H 2 SO 4 . 5. 
 Fuming sulphuric acid. 6. Use of phosphorus pentoxide or potassium 
 sulphate with sulphuric acid. 7. Sulphuryl oxychloride. 8. Potassium and 
 sodium bisulphates and pyrosulphates. 9. Fatty sulphonic acids. 10. 
 Use of alkaline sulphites. 11. Use of carbyl sulphate. 12. Transfor- 
 mation of acid sulphates and alkyl sulphates of bases . . .Pp. 358 to 371 
 
 CHAPTER XXIII. REMARKS ON ORGANIC ANALYSIS. i. The com- 
 bustion method. 2. Other methods for the determination of carbon and 
 hydrogen. 3. Qualitative determination of nitrogen. 4. Quantitative 
 determination of nitrogen by combustion. 5. Kjeldahl's method. 6. 
 Determination of chlorine, bromine, and iodine. 7. Estimation of sul- 
 phur Pp. 372 to 390 
 
 TABLE SHOWING DATES OF REFERENCES Pp. 391 to 392 
 
 INDEX Pp. 393 to 403 
 
ABBREVIATIONS 
 
 A. Path. Pharm. = Archiv fur experimentelle Pathologic und Pharma- 
 
 kologie. 
 
 Am. Ch. J. = American Chemical Journal. 
 Ann. = Liebig's Annalen der Chemie und Pharmacie 
 Ann. Ch. Ph. = Annales de Chimie et de Physique. 
 Ar. Pharm. = Archiv der Pharmacie. 
 Ber. = Berichte der deutschen chemischen gesellschaft. 
 Bull. Ch. = Bulletin de la Societe Chimique de Paris. 
 
 C. R. = Comptes rendus de 1' Academic des Sciences (Paris). 
 Centralblatt - Chemisches Centralblatt. 
 
 Ch. N. = Chemical News. 
 Ch. Z. = Chemiker-Zeitung. 
 
 D. P. J. = Dingler's Polytechnisches Journal. 
 Ger. Pat. = German Patent. 
 
 Jahresb. = Jahresbericht iiber die Fortschritte der Chemie. 
 
 J. Ch. Soc. = Journal of the Chemical Society (London). 
 
 J. pr. Ch. = Journal fiir praktische Chemie. 
 
 M. f. Ch. = Monatshefte fur Chemie. 
 
 P. Ar. = Pfliiger's Archiv fiir die ges. Physiologic. 
 
 Z. analyt. Ch. = Zeitschrift fiir analytische Chemie. 
 
 Z. angew. Ch. = Zeitschrift fiir angewandte Chemie. 
 
 Z. Bio. = Zeitschrift fiir Biologic. 
 
 Z. Ch. = Zeitschrift fiir Chemie. 
 
 Z. physik. Ch. = Zeitschrift fiir physikalische Chemie. 
 
 Z. physiolog. Ch. = Zeitschrift fiir physiologische Chemie. 
 
PART I 
 
 GENERAL METHODS 
 
 CHAPTER I 
 
 BATHS 
 
 1. General Remarks. Batfe-ajrrt ijsed in order to heat vessels 
 more uniformly than is possible with" the naked 1 flame. Among 
 the kinds employed are water^alj, saltpetre, a^d;d~tlori<4e of calcium 
 baths. The last named sjbsta'rce attacks copper" Ver^Vigourously 
 on prolonged exposure to the boiling sol^jon of the salt. A 
 saturated solution of common salt boils at^e^(Gerlach, Z. analyt. 
 Ch. 26, 427), a saturated sodium nitrate solution at 120, and a 
 saturated chloride of calcium solution at 180 (Legrand, Ann. 
 17, 34). 
 
 2. High Temperatures. By the use of oil, paraffin, or sulphuric 
 acid high temperatures may be attained. Metal baths are however 
 preferable to any of these, as the disagreeable odours of the two 
 first and the pungent odour of the last substance are entirely avoided, 
 and the use of a hood is rendered unnecessary. These baths are 
 made of easily melted alloys. For high temperatures lead contained 
 in a cast-iron vessel may be employed. Smith and Davies (J. Ch. 
 Soc. 37, 416) recommend that, in using such a bath, the part of the 
 flask which dips into the lead should be covered with lampblack, 
 from a smoky flame, as this prevents the lead adhering to the 
 glass and makes the vessel less liable to crack. 
 
 IE B 
 
2 BATHS [CH. i 
 
 3. Dry Baths and Air Baths. Dry baths are shallow iron 
 basins containing a little sand ; the quantity of the latter should 
 be small on account of its low conductivity for heat. Sometimes 
 graphite and iron filings are used in place of sand. Such baths 
 are applicable where materials are to be boiled for days in connec- 
 tion with a reflux condenser. Even where the liquid is alcohol or 
 ether, their use is advisable, since all attention to keeping a constant 
 level, as in a water bath, is avoided. 
 
 Air baths are extremely useful for all purposes, especially in the 
 form which Lothar Meyer (Ber. 22, 879) has recently given to 
 them. It is unnecessary to describe them, as they cannot be con- 
 structed in the laboratory, and should be bought ready made. 
 
 Where it is necessary to evaporate ether and other easily inflam- 
 mable substances, the tripod stand should be surrounded with fine- 
 meshed wire gauze. This application of the Davy safety lamp 
 effectually prevents ignition of the vapour. 
 
CHAPTER II 
 
 CRYSTALLISATION 
 
 1. Solvents, The crystallisation of organic substances is effected 
 by dissolving them in suitable solvents. A hot saturated solution 
 of the substance is prepared, which, on cooling, deposits the dis- 
 solved material in crystalline form. Immersion in a freezing 
 mixture, such as equal parts of snow and salt, producing a tem- 
 perature of 17 C., or of snow and chloride of calcium, producing 
 - 48 C., is sometimes necessary. Many solvents remain perfectly 
 liquid at these temperatures. Carbon disulphide, for example, freezes 
 at 116 C., 95 per cent, alcohol at 130 C., and pure ether 
 probably demands a still lower temperature (Ber. 10, 831). Crystal- 
 lisation may likewise be brought about by permitting the solvent to 
 evaporate. With the exception of sublimation, other methods of 
 obtaining crystals are seldom used in organic chemistry. 
 
 The following substances, or suitable mixtures of two or more 
 of them, are used as solvents ; but their application in any par- 
 ticular case is regulated by the requirement that they must have 
 no chemical action on the substance to be dissolved : 
 
 Acetic acid. 
 
 Acetic ether. 
 
 Acetone. 
 
 Alcohol and its homologues. 
 
 Ammonia water. 
 
 Benzene and its homologues, 
 
 Toluene, Xylene, 1 and 
 
 Cumene. 2 
 
 Carbon disulphide. 
 Chloroform. 
 
 Ber. 25, 185^. 
 
 Ether. 
 Hydrochloric acid. 
 
 Naphthalene. 
 Nitric acid. 
 Nitrobenzene. 
 Petroleum ether. 
 Phenol. 
 Pyridine. 
 Sulphuric acid. 
 Water. 
 
 2 Ber. 17, 2,812. 
 B 2 
 
4 CRYSTALLISATION [CH. n 
 
 The following are occasionally employed : Aniline (for indigo 
 and naphthylamine, Ber. 3, 289) ; Azobenzene (Ber. 23, 184) ; 
 Canada balsam, or rosin, for the study of crystallisation under the 
 microscope (Ber. 23, 1,747) ; Kerosene (Ber. 24, R. 652) ; Cresol ; 
 Dimethylamine (Ber. 25, 2,008) ; Glycerol (Ger. Pat. 46,252) ; 
 Hydrofluoric acid (Ber. 12, 581) ; Isobuty lalcohol (Ber. 20, 3,275) ; 
 Olive oil (much used as a harmless solvent for substances to be 
 given to animals by subcutaneous injection) ; Paraffin (Ber. 25, 
 R. 488) ; Petroleum (Ber. 24, 2,597) ; Phosphorus oxychloride 
 (Ber. 18, R. 22) ; Sodium hydroxide solution (Ber. 24, 2,714) ; 
 Spermaceti (Ber. 4, 334) ; Turpentine. 
 
 In reference to the various solvents a few remarks may be made. 
 
 When glacial or common Acetic acid has been used for re- 
 crystallisation, it is advisable, if possible, to free the substance from 
 traces of the solvent by passing a stream of air over it in a Liebig's 
 drying tube at 100, or to let it stand in vacuo over soda-lime 
 (Ann. 228, 303). It is usually sufficient, however, to let the acetic 
 acid evaporate in an ordinary desiccator charged with potassium 
 hydroxide (Ber. 14, 1,867). Acetic acid of crystallisation was found 
 by LatschinofF (Ber. 20, 1,046) in the case of choleinic acid, 
 C 25 H 42 O 4 -f C 2 H 4 O 2 . Crystals of haemin are likewise said to retain 
 some acetic acid (A. Path. Pharm. 20, 328). 
 
 Acetone is being found more and more useful as a solvent every 
 day. Cholic acid crystallises from it with one molecule of acetone 
 of crystallisation. 
 
 That Alcohol can enter into combination as alcohol of crystallisa- 
 tion was first noticed by Graham, and, although the observation 
 attracted not only notice but contradiction, it has since been 
 confirmed (Ann. 65, 120). Hesse seems to have found in con- 
 chairamine (Ann. 225, 247), C2 2 H2 6 N 2 O 4 -f-H 2 O+C 2 H 6 O, an alkaloid 
 occurring with quinine, the only example of a substance crystallis- 
 ing with both water and alcohol. In the barium salt of choleinic 
 acid, Mylius (Ber. 20, 1,970) met with the unusual case of a sub- 
 stance which will not dissolve either in water or absolute alcohol, 
 but is easily soluble in dilute alcohol. 
 
 A partial transformation of organic acids into esters is sometimes 
 effected by mere boiling with alcohol. This action cannot be 
 considered as a method of preparing esters, but it is occasionally 
 encountered in recrystallising acids from alcohol. In the case of 
 cholic acid, for example, a very large proportion seems to disappear 
 in the alcoholic mother-liquors, considerable quantities of which 
 
ij SOLVENTS 5 
 
 result from the crystallisation. The author (Ber. 25, 807, and Z. 
 physiolog. Ch. 16, 497) has shown that it is converted into the 
 more soluble ethyl ester. Where acids with such properties are 
 met, acetone, benzene, etc., are used in order to avoid the difficulty. 
 Certain substances are equally soluble in hot and cold, or even 
 cold dilute alcohol, although insoluble in water. They can often 
 be obtained in a crystalline form by evaporating the alcoholic 
 solution, after the addition of much water, on the water bath until 
 a slight turbidity appears. The crystals separate on cooling. 
 Frequently the alcohol must be of a definite strength. Kiliani 
 (Ber. 24, 339) found, for example, that digitonin crystallised 
 perfectly from 85 per cent, alcohol, while the yield from stronger 
 spirit was amorphous, and from weaker spirit was smaller in 
 quantity and mostly amorphous. 
 
 According to Herzfeld (Ber. 12, 2,120), it seems to be necessary to 
 exercise special care in the case of maltose. The crystallisation is best 
 carried out by dissolving it in hot 80 or 85 per cent, alcohol, letting the 
 solution stand for some time in the cold in a closed vessel, and then 
 allowing the alcohol to evaporate. This process may be explained by 
 supposing that maltose turns into a deliquescent hydrate on heating, and 
 only returns to the state of anhydride on long standing. 
 
 The acid sodium salts of many organic acids can only be crystallised by 
 dissolving them in absolute alcohol and adding ether, the precipitate pro- 
 duced becoming crystalline in the course of a few days. It is in this way, 
 for example, that, as Plattner first showed, the so-called crystallised 
 bile can be obtained. It is a mixture of sodium taurocholate and 
 glycocholate. 
 
 It occasionally happens that acidified is preferable to neutral alcohol. A 
 few drops of acetic or some other acid are used. Caffein sulphate was 
 held to be a very difficult substance to prepare until Biedermann (Ar. 
 Pharm. 1883, 181) found that this salt could be obtained in crystals with 
 extraordinary ease by dissolving the alkaloid in about ten times its weight 
 of hot alcohol, which had been strongly acidified with sulphuric acid, and 
 allowing the solution to stand for some time in a cool place. 
 
 Many substances which tend to separate out in amorphous form 
 may be obtained in a crystalline condition by the use of a mixture 
 of water, alcohol, and ether, a method which is less used than 
 it deserves. Parthiel (Ber. 24, 636) prepared cystine hydrobromide 
 from the concentrated aqueous solution of the base by neutralising 
 
6 CRYSTALLISATION [CH. n 
 
 with 25 per cent, hydrobromic acid, and obtained it from the 
 solution by adding absolute alcohol and covering with a layer of 
 ether. According to Bayer (Z. physiolog. Ch. 3, 303), if water is 
 added to an alcoholic solution of cholic acid till it is permanently 
 turbid, and ether is then poured on the surface, the acid comes 
 out in clumps of crystals. 
 
 Amyl alcohol (cf. Chap. VI., 2) is an excellent solvent for 
 substances which can hardly otherwise be obtained in crystalline 
 form. For example, Niementowsky (J. pr. Ch. 148, 22) used it to 
 dissolve ;;z-methyl-0-uramidobenzoyl, which is difficultly soluble in 
 all solvents, and needles came out on cooling the solution. 
 
 Haemine hydrochloride, made from red blood-corpuscles, crystal- 
 lises, according to Nencki (A. Path. Pharm. 20, 328), with one 
 molecule of alcohol of crystallisation, C 32 H 31 ClN 4 FeO+C 5 H 12 O. 
 
 Benzene can enter into combination as benzene of crystallisation 
 and may be held very tenaciously. Thrular (Ber. 20, 669) found 
 that thio-/-tolylurea did not completely lose its three molecules of 
 benzene even after heating for four hours at 100-1 10. Liebermann 
 and Limpach (Ber. 25, 325) recrystallised tropine from benzene, 
 and endeavoured, by heating to 70, to determine the amount of 
 the latter present in the crystals. As, however, the weight refused 
 to become constant, owing to volatilisation of the tropine itself, 
 they convinced themselves of the absence of benzene of crystallisa- 
 tion by determining the nitrogen in a freshly prepared specimen. 
 Kishner (Ber. 24, R. 559) states that triphenylbenzene unites with 
 benzene in such a way that if it is warmed with a solution con- 
 taining the latter, and allowed to crystallise, it takes the benzene 
 down with it. He uses this as a method for separating benzene 
 from other substances. 
 
 As Liebermann and Seyewitz (Ber. 24, 788) have shown, com- 
 mercial benzene (boiling point 80-82) contains from o - 2 to 0*3 per 
 cent, of carbon disulphide, which in certain cases leads to undesirable 
 secondary reactions. It is best removed by shaking with con- 
 centrated alcoholic potassium hydroxide, which converts the impurity 
 into potassium xanthate, and redistilling. 
 
 Chloroform is found combined in crystals. The triazine of ben- 
 zene (Ber. 20, 325), C 27 H 18 N 6 , crystallises with one molecule of 
 chloroform, colchicine (M. f. Ch. 7,57i) with two, leukon-ditoluy- 
 lene-chinoxalin (Ber. 19, 776) with one, which is completely 
 expelled only at 140, and Schmidt found it so firmly held in 
 berberine-chloroform, C 20 H 17 NO 4 CHC1 3 (Ar. Pharm. 1887, 147), 
 
i] SOLVENTS 7 
 
 that he doubts the presence of a mere addition product containing 
 the components unchanged. 
 
 Chloroform usually contains a little alcohol, and may be freed from it by 
 washing with water. Contrary to ordinary experience, Oudemans (Ann. 
 166, 74) found that cinchonine was more soluble in a mixture of alcohol 
 and chloroform than in either of the constituents. 
 
 Ether appears in exceptional cases as ether of crystallisation. 
 Fischer and Zeigler (Ber. 13, 673), for example, obtained crystals of 
 pseudo-leukaniline containing ether. It is advisable to dry ethereal 
 solutions with chloride of calcium before setting them aside to 
 crystallise, as otherwise the crystals will be damp from the water 
 left by the moist ether on evaporation. 
 
 Commercial ether has usually an acid reaction (Ber. 24, 1,491). 
 It may be purified by shaking with sodium hydroxide and subse- 
 quently with water. If it is tested after standing for a long time, it 
 will be found to contain traces of acid once more. 
 
 Many substances do not crystallise out of water unless their solution is 
 covered with a layer of ether. In order to obtain crystalline glycocholic 
 acid from ox-gall the gall of oxen from the neighbourhood of Tubingen 
 is used, as that from other districts contains too little the gall is placed in 
 a narrow cylinder, covered with ether, and I cc. of concentrated hydrochloric 
 acid is added for each 20 cc. of ether. The crystals appear after the whole 
 has stood for several days. 
 
 Warm hydrochloric acid is often very useful, as many resinous 
 matters are insoluble in it. For instance, in recrystallising crude 
 para-nitrophenol from it the resin remains undissolved, and the 
 same is true of meta-bromonitrophenol (Ber. 25, 552). 
 
 lj Nitrobenzene was used by Gabriel (Ber. 19, 837) for recrystallising 
 
 jiitroacetylene-diphthalide, which comes out of it in thick needles. Grabe 
 
 ^^Vnd' Philips (Ber. 24, 2,298) used nitrobenzene, or a mixture with acetic 
 
 . acid, for recrystallising some of the series of dyes which are obtained by 
 
 ^''successive additions of hydroxyl groups to alizarin when it is heated with 
 
 /w^ulphuric acid (see Chap. XVIII. " Oxidation"). 
 
 Naphthalene was used by Witt for recrystallising naphthazine, as it 
 
 cannot otherwise be obtained in crystals. It was dissolved in the boiling 
 
 "*** hydrocarbon, and the solid cake was afterwards extracted with hot alcohol 
 
 until only the azine in crystalline form remained. It is stated in a patent- 
 
8 CRYSTALLISATION [CH. n 
 
 specification (Ger. Pat. 59,190) that nitro-alizarin blue, which is difficultly 
 soluble in ordinary solvents, may be recrystallised from naphthalene. 
 
 For Petroleum ether it is best to use the fraction of the com- 
 mercial product which distils over between 60 and 70 on the 
 water bath (Ber. 23, 142). Wislicenus (Ann. 272, 19) names the 
 part which comes over, after repeated rectification, between 33 
 and 39 petroleum-pentane, and the part between 60 and 69 
 petroleum-hexane. 
 
 N6tlingandSchwarz(Ber. 24, 1,606) dissolved crude triquinylmethane in 
 the smallest possible quantity of benzene, and added petroleum ether, of 
 boiling point under 100, to the solution. They used petroleum ether 
 which had been purified by treatment with sulphuric acid and distillation 
 because the commercial product gave nothing but tar. As soon as the 
 precipitate produced by the ether was no longer resinous they filtered, and, 
 after adding a little more of the ether, allowed the solution to crystallise 
 over paraffin and sulphuric acid. 
 
 Phenol, which is an excellent solvent although it has been too 
 little used for purposes of crystallisation, was employed by Witt 
 (Ber. 19, 2,791) in the following way in order to obtain crystalline 
 eurhodol, a substance which is left untouched by all known solvents. 
 He dissolved the . hydrochloride of the base in phenol, and, after 
 cooling to 1 00, added boiling alcohol with which a little aniline 
 had been mixed. The aniline neutralised the hydrochloric acid 
 and eurhodol began to separate out in needles. 
 
 The phenol which remains adhering to the crystals may be re- 
 moved by washing with alcohol. It is met with also as phenol of 
 crystallisation, as for instance with urea (Ar. Pharm. 1886, 625) 
 and cholic acid (Ber. 20, 3,278). 
 
 Pyridine seems to be a specially useful solvent for the recrystal- 
 lisation of substances of the class of chlorinated benzidine and 
 tolidine derivatives, which are scarcely soluble in other solvents 
 (Bottinger, Dissert. Jena, 1891). 
 
 Concentrated sulphuric acid may be used where all other sol- 
 vents fail. Baeyer obtained bichloro-hydurilic acid in crystalline 
 form with its help by dissolving the substance in the concentrated 
 sulphuric acid and adding water cautiously. Many sulpho-acids, 
 like Lonnies' y-sulphoisophthalic acid (Ber. 13, 704), which come 
 out of water in the form of resin, are easily recrystallised from 
 dilute sulphuric acid. 
 
2] FILTRATION AND PRECIPITATION 9 
 
 Where water is used for the recrystallisation of substances on 
 which the oxygen of the air may act, as for example amines which 
 are coloured by its action, some hydrogen sulphide or sulphurous 
 acid may be added. 
 
 Water of crystallisation is found in the most various proportions. 
 For example, some carbohydrates contain one sixtjpf a molecule, 
 phenyldihydro-3-naphthotriazin (Ber. 24, 1,003), two thirds of a mole- 
 cule, and so forth. Such water is sometimes held wfth extraordinary 
 tenacity ; in the case of the barium salt of an acridone sulphonic 
 acid the one and a half molecules can be driven off only at 220 
 (Ber. 25, 1,981). 
 
 The case of citric acid is very extraordinary in this respect (Ber. 25, 
 1,159). According to Witter, if its solution is evaporated till the tempera- 
 ture reaches 130, the acid crystallises out on cooling free from water, 
 and the product may be recrystailised from cold water without change. If 
 however a crystal of ordinary citric acid, containing water of crystallisa- 
 tion, be inserted into the solution, crystals containing water come out. 
 This unusual property is not destroyed by conversion into the lead salt, as 
 is shown by the properties of the acid when it is once more set free. 
 
 In connection with the foregoing it may be worth mentioning 
 that a cold saturated solution of borax is sometimes useful as a 
 solvent, especially for colouring matters which are insoluble in 
 water. For example, after the tannin has been extracted from 
 sandalwood by means of water, a solution of borax extracts the 
 santalin, and the latter may then be precipitated from solution with 
 sulphuric acid. Investigations in this direction are due to Palm 
 (Z. analyt. Ch. 22, 324)- 
 
 2. Filtration and Precipitation. In filtering hot saturated 
 solutions a hot water funnel must be used, as otherwise crystals are 
 apt to form and stop up the funnel. If the quantity of the solution 
 is small the funnel can be warmed directly in a flame before the 
 filter-paper is placed in it. Where suitable filter-paper is used, this 
 is almost always sufficient to prevent crystallisation either in the 
 stem of the funnel or in the funnel itself. 
 
 It is not always best to wait for the complete cooling of the crystallising 
 solution. Crystallised veratrine can be obtained easily and in good yield, 
 according to Schmidt and Bosetti (Ar. Pharm. 1883, 84), only by 
 dissolving the commercial alkaloid, after it has been purified with ether, in 
 a large beaker in absolute alcohol, heating to 60-70, and adding water 
 
io CRYSTALLISATION [CH. n 
 
 till permanent turbidity appears. This is cleared up with a little more 
 alcohol and the whole allowed to evaporate at 60-70. The veratrine 
 crystallises out plentifully in a nearly pure condition. The moment the 
 solution begins to become turbid by the separation of the resinous modifica- 
 tion, the liquid is poured off the crystals. The operation may be repeated 
 several times with the liquid, and a total of about 33 per cent, of the base 
 obtained pure. 
 
 Precipitation "by the addition of a salt to water solutions is a 
 method frequently applied. It is used with solutions of both solids 
 and liquids, and its action depends on the fact that the addition of 
 the salt produces a liquid in which the substance can no longer 
 remain dissolved. Common salt, Glauber's salt, and potassium car- 
 bonate are thus used. For example, the addition of potash to water 
 containing alcohol causes the latter to separate out in a layer on 
 the surface. 
 
 Separations which are of great importance in the chemistry of albuminous 
 substances may also be carried out in this way. Ammonium sulphate is 
 used for separating albumens from peptones (albumen derivatives which 
 have been altered by digestion and are no longer coagulated by boiling 
 water). The former are insoluble in solutions containing ammonium 
 sulphate, and so are precipitated by the addition of a solution of that salt 
 (Z. Bio. 22, 4 2 3)- Such separations play a decisive part in this department 
 of chemistry, and many regard them as quantitative, although no one has 
 yet obtained unassailable proof that they are so (see below). On the other 
 hand the method is naturally admirable where the substance can only be 
 obtained pure with great difficulty in any other way, and subsequent 
 recrystallisation proves that this has given a pure product. Baeyer (Ber. 12, 
 1,317), for example, dissolved amido-indigo in dilute hydrochloric acid, 
 neutralised with soda and reprecipitated with sodium acetate. In a similar 
 manner he purified ethyl amido-phthalate (Ber. 10, 1,079). 
 
 Precipitation from alcoholic solutions by means of water has 
 already been referred to. It is frequently found that a substance 
 which is very soluble in alcohol and not soluble in water, can be 
 induced to crystallise by adding water to the alcoholic solution till 
 a faint turbidity appears. The method is however much more 
 frequently applied to ethereal solutions, in which case, as many 
 bodies are insoluble in petroleum ether while soluble in ether, the 
 former is added till slight turbidity is noticed. Phenol solutions 
 may be similarly diluted with alcohol (Ber. 27, 2,403). 
 
 Crystals are freed from the mother-liquor by washing. Where a 
 large quantity of material is to be treated, it is put into a funnel and 
 
3 ] RECRYSTALLISAf ION i 1 
 
 a water pump is used. If the liquid is strongly alkaline or strongly 
 acid it is preferable to use a glass bead, with or without paper, in- 
 stead of a platinum cone. 
 
 . If there are very few crystals, and especially if the accompanying 
 liquid is thick, they are spread on unglazed porcelain to dry. 
 Bisque plates, which are damaged and useless for making china, 
 are very suitable. In their absence any kind of tile which will 
 absorb the mother-liquor may be used. The crystals may also be 
 pressed between filter-paper, although the results are less satisfactory 
 in this case. If the mother-liquor is of value it may be recovered 
 from the porcelain or paper by extraction, ^j^^}^^^^^-^^^ - 
 
 3. Recrystallisation. To obtain chemically pure substances is 
 the object of recrystallisation. If this is not accomplished the first 
 time, the operation is repeated till the material is pure, and all the 
 impurities are collected in the mother-liquors. The assumption is 
 that mixtures of crystals may be separated by their different solu- 
 bilities in different media ; that, in fact, with a suitable amount of 
 the solvent more of the one substance than of the other will remain 
 in the mother-liquor. As a matter of fact, substances which cannot 
 be separated by fractional crystallisation have been found almost 
 exclusively among thiophene derivatives. Cohn (Z. 17, 306) has 
 lately made the interesting observation that if molecular quantities 
 of ^-nitrobenzoic acid and ^-acetylamidobenzoic acid are dissolved 
 in hot water, they crystallise out together on cooling and cannot be 
 separated again by crystallisation alone. Mixed crystals in the 
 ordinary sense are frequently mentioned in chemical literature. 
 Herrmann (B. 19, 2,235) found, for example, that succino-succinic 
 ether and quinone dihydro-carboxylic ether, although the former is 
 asymmetric and the latter rhombic, formed mixed crystals. 
 
 Inoculation (Z. physiolog. Ch. 10, 151), with a crystal from an- 
 other lot of the same substance, is a frequent means of causing oils 
 to crystallise, but this is not always available. Stadel has found 
 however that a crystal of the same substance is not always abso- 
 lutely necessary ; that a fragment of a substance of similar con- 
 stitution is sometimes effective in starting crystallisation. Thus 
 he took ;;z-kresol, which is said not to solidify at - 80, and rendered 
 it crystalline by adding a minute crystal of phenol. Ott (B. 24, 
 2,603) states that the dibromide of propylidene-acetic acid refuses 
 to crystallise, but may be induced to do so by infecting it with 
 a crystal of the dibroiruda of ethylidene-propionic acid. 
 
12 CRYSTALLISATION [CH. n 
 
 Fractional recrystallisation is the name given to the operation 
 when it has to be repeated frequently and guided in a particular 
 direction so as to lead to a chemically pure product. An example 
 will best illustrate how, mutatis mutandis^ one should proceed in 
 such a case. 
 
 Schwalb (Ann. 235, no) saponified bees-wax with sodium 
 hydroxide and extracted the dry soap with petroleum ether. The 
 non-acid products of the saponification were submitted to fractional 
 crystallisation in such a way that the higher-melting fractions were 
 always recrystallised from fresh petroleum, while for the lower- 
 melting part the mother-liquor of the next higher-melting fraction 
 was used. In this manner the low-melting substance accumulated 
 in the mother-liquors, while high-melting material appeared in first 
 quantities of crystals. This systematic method was pursued until 
 the melting point of the crystals no longer differed appreciably 
 from that of the substance obtained by the evaporation of their 
 mother-liquor. As soon as this point was reached this portion of 
 crystals was set aside for further treatment, and the recrystallisation 
 of the still impure middle fractions was continued. In this way 
 three principal portions were obtained, and these were then 
 separately submitted to the same process. Besides many other 
 products, a substance which on analysis seemed to be a hydrocarbon 
 was obtained. But before the melting points of the crystals and 
 the deposit from the mother-liquor agreed, it was necessary to 
 recrystallise this product alone thirteen times more. 
 
 The only way by which Zinoffsky (Dissert. Dorpat, 1885) was able to 
 determine that oxy haemoglobin from horse's blood, purified by recrystal- 
 lisation, was really a pure substance, was by ascertaining that the per- 
 centages of iron in the crystals and in the residue from evaporation of the 
 mother-liquor were identical. 
 
 It is hardly possible to obtain the oxyhaemoglobin from the blood of 
 some animals in a pure condition. To this class belongs that of swine 
 Hiiffner (Z. physiolog. Ch. 7> 67) made the extraordinary discovery that if 
 defibrinated blood from this species was treated with one third of its volume 
 of a i per cent, alcoholic solution of quinoline and then placed in a freezing 
 mixture, it changed in a few days into a mass of red crystals. Otto has 
 followed up this observation in other directions. 
 
 When substances are met with which refuse absolutely to crystallise, it is 
 necessary to start from pure materials in making them, and to use what- 
 ever means are available for purification. Such methods were used by 
 Herth (M. f. Ch. 1, 89 ; see also Ber. 25, 930 in the synthesis of biguanid. 
 
4 ] FORMATION OF DERIVATIVES 13 
 
 From what has been said, it is evident that workers in the field 
 of organic chemistry have to use a great amount of patience and 
 ingenuity in obtaining new preparations in crystalline form. It 
 must be admitted that chemists are able to work confidently with 
 organic substances only when these are volatile without decomposi- 
 tion, or can be obtained either immediately, or after change into a 
 closely related derivative (see below), in crystalline form. Careful 
 fractional precipitation (see also A. Path. Pharm. 20, 351) may be 
 mentioned as a third method. It is on account of this poverty 
 of methods that the chemistry of organised products (albuminous 
 matters, etc.) is still in its infancy. No general methods whatever 
 are known by which such bodies can be obtained in a pure state, or 
 can be proved to be chemically simple substances when they have 
 been obtained. 
 
 Berzelius (Lehrbuch der Chemie, Vol. 4, Pt. I, p. 671) makes the 
 same complaint, and it cannot be said that since his time any 
 important or widely applicable improvement has been introduced. 
 He says in this connection : " One of the most difficult tasks of 
 organic chemistry is to gain a knowledge of the nature of the change 
 when a substance in solution in water passes gradually into several 
 substances having the same property, without the use of any 
 reagent or the appearance of gaseous or solid products. In such 
 cases it is only by chance that the chemist finds means to separate 
 the new bodies from each other and from the original material." 
 
 The study of recent literature forces from us the question, why so 
 many students of the science, leaving of course the workers in 
 colour-chemistry and in the synthesis of alkaloids out of account, 
 regard themselves as in duty bound to study the products of the 
 distillation of coal, the relics of a long extinct organic world, and 
 their derivatives, instead of turning their attention to the living forms 
 which surround them. To invent new methods and to follow their 
 application in this region would surely not be less interesting than 
 the piling up of many-membered rings. As an example of what 
 might be done Schmiedeberg's (A. Path. Pharm. 28, 355) recent 
 magnificent work on cartilage may be mentioned. Even from a 
 purely analytical point of view there is much to be accomplished in 
 this department of chemistry. 
 
 4. The Transformation of Substances into Closely Allied 
 Derivatives. This subject has been mentioned already, and must 
 now be treated more fully. The conversion of non-crystalline com- 
 
H CRYSTALLISATION [CH. I 
 
 pounds into such as are crystalline or volatile without decomposition 
 being of the greatest interest, methods of pretty general applica- 
 bility have been worked out for these purposes. 
 
 Basic liquids are converted into their salts, or into platinum, gold, 
 or mercury (Ann. 247, 5) double salts, which can then be purified ; 
 acid liquids yield derivatives in similar ways. 
 
 The ease with which the hydrogen of a hydroxyl group can be 
 replaced by radicals, is often used to obtain crystalline derivatives 
 which will afford definite information about the constitution of the 
 original substance. Acids are even converted into esters. Crude 
 bilianic acid (Ber. 20. 1,982) can only be purified by conversion 
 into the di-ethyl ester, an easily crystallisable substance, from which 
 the acid itself can finally be got in solid form. Most frequently the 
 suggested interaction is carried out with substances containing 
 alcoholic hydroxyl groups, and with amines. If the carboxyl group 
 is also present, it is usually desirable to convert that into an ester, 
 say the ethyl ester. 
 
 The hydrogen atoms of the hydroxyl, or the amine or amido 
 groups are replaced by the radicals Acetyl, Benzoyl, Benzo-sul- 
 phonyl, or FormyL 
 
 The best method of Acetylising is that given by Liebermann 
 (Ber. 11, 1,619). The substance is heated for a considerable length 
 of time with acetic anhydride and dry (fused) sodium acetate in a 
 vessel attached to an inverted condenser. Even very unstable 
 substances can be converted into derivatives which resist exposure to 
 the air. Thus Liebermann (Ber. 24, 4,130) succeeded in obtaining 
 the acetyl derivative of indigo-white in crystals which were stable 
 in the air, by conducting the reduction of the indigo and the acetyl- 
 ising at the same time. He mixed one part of the substance to be 
 reduced with two parts of sodium acetate and three parts of zinc 
 dust, and boiled the whole with from ten to fifteen parts of acetic 
 anhydride. Nietzki (B. 16, 468) used a similar method in prepar- 
 ing diacetyl-safranine hydrochloride. As the free base is difficult to 
 obtain, he mixed the hydrochloride with sodium acetate and boiled 
 it with excess of acetic anhydride. 
 
 If reduction is carried out after acetylising, very unstable substances may 
 be obtained in spite of the presence of the acetyl radical. The reduction 
 product which Baeyer (Ber. 12, i>3O9, obtained from acetyl-isatin with acetic 
 acid and zinc dust is reconverted into acetyl-isatin by the action of the air. 
 
 By heating pyrogallol-benzem (5 gr.) with acetic anhydride ( 1 2 gr.), 
 
4] FORMATION OF DERIVATIVES 15 
 
 and fused sodium acetate (10 gr.) in a paraffin bath at 120 for two 
 hours, using an inverted condenser, and then treating with water 
 and recrystallising from alcohol, Dobner and Forster (Ann. 257, 63) 
 obtained a tetra-acetyl compound of the formula, C3 8 H 20 O U (C 2 H3O) 4 . 
 In suitable substances many more acetyl groups may be intro- 
 duced by the help of condensing agents (see Chap. XII.) which act 
 more strongly than sodium acetate. 
 
 It should be said that acetyl chloride and acetic anhydride are 
 able to produce acetylisation even when used by themselves. The 
 number of the acetyl groups which enter the compound is of course 
 dependent on the method employed. Erwig and Konigs (Ber. 22, 
 1,457) report that if quinic acid is boiled with seven parts of acetic 
 anhydride, triacetyl-quinid is the chief product. If the latter, or 
 even quinic acid itself, is heated with acetic anhydride to 240 in a 
 sealed tube, an isomeric triacetyl-quinid is formed. By Lieber- 
 mann's method the first mentioned isomer is formed. If a grain of 
 fused zinc chloride is added to the acetic anhydride, then tetra-acetyl- 
 quinid is formed in almost quantitative amount. Finally, according 
 to Hesse (Ann. 200, 233), if quinic acid and the anhydride are 
 heated in a sealed tube at 170 for ten hours, a mixture of the 
 tri- and tetra-acetyl derivatives is obtained. 
 
 JBischoff (Ber. 24, 2,007) found that acetyl-malanile was formed when 
 malanile was dissolved in benzene and boiled with an equi-molecular propor- 
 tion of acetyl chloride ; Kiliani (Ber. 24, 342) states that digitogenin gives 
 a monoacetyl derivative when treated by Liebermann's method. He found 
 that sulphuric acid could take the place of the sodium acetate yielding the 
 same substance, while zinc chloride gave amorphous products. 
 
 The number of acetyl groups which has entered the molecule is 
 sometimes hard to determine, as mono-, di-, and tri-substitution pro- 
 ducts have a very similar percentage composition if the molecule 
 is large. It is usually preferable to saponify the acetylised sub- 
 stance, and estimate the acetic acid. This is frequently done by 
 adding phosphoric acid, distilling, and titrating the distillate. This 
 reagent is preferred to sulphuric acid, as the latter may give rise to 
 sulphurous acid. 
 
 The radical of formic acid may be introduced in a similar way to that of 
 acetic acid. Fischer and Hepp (Ber. 23, 842) made diformyl-diamido- 
 phenazine by boiling the base with concentrated formic acid and dry 
 sodium formate. 
 
CRYSTALLISATION [CH. n 
 
 The radical benzoyl vj&s, first used by Schotten (Ber. 17, 2,545), 
 in order to obtain a crystalline derivative of piperidine. He pre- 
 pared benzoyl-piperidine by the use of benzoyl chloride with 
 sufficient sodium hydroxide to neutralise the hydrochloric acid 
 formed. 
 
 Baumann (Ber. 19, 3,219) worked out the method systematically, 
 and the following example shows how it may be applied. Grape 
 sugar (5 gr.) is dissolved in water (15 cc.) and a 10 per cent, solution 
 of sodium hydroxide (2iocc.) and the necessary benzoyl chloride 
 (30 cc.) are added. After the whole has been shaken until the odour 
 of benzoyl chloride has disappeared, 13 grains of an ester, chiefly 
 the tetra-benzoyl derivative of grape sugar, is found to have been 
 formed. 
 
 Pechmann (Ber. 25, 1,045) dissolved aceto-acetic ether (20 gr.) in water 
 (30cc.) and a 15 per cent, solution of sodium hydroxide (35 cc.), and shook 
 the mixture up seven times with as many quantities of benzoyl chloride 
 (logr.)and caustic soda (3occ.), continuing the shaking each time until 
 the odour of the benzoyl chloride had disappeared. The mixture was kept 
 cool with water so that the temperature did not exceed 25 at any time 
 during the hour or so which the experiment occupied. The product 
 consisted of equal parts of benzoyl- and dibenzoyl-acetoacetic ether. 
 
 In the case of glycerol, Diez (Z. physiolog. Ch. H, 472) states that 
 where the solution contains less than 2 per cent. , the yield of benzoate by 
 this method is so good that it can be used for quantitative estimation. 
 
 For the complete conversion of carbohydrates into the benzoic ester 
 Panormow (Ber. 24, R- 97 1) states that stronger caustic soda than 
 Baumann used is necessary. By using 6 parts of benzoyl chloride and 48 
 parts of 18-20 per cent, caustic soda for every part of the carbohydrate or 
 alcohol he obtained pentabenzoyldextrose, dibenzoylglycogen, and hexa- 
 benzoylmannite. 
 
 Victor Meyer (Ber. 24, 4,251) has drawn attention to the fact that 
 ordinary benzoyl chloride often contains chloro-benzoyl chloride, which may 
 lead to the formation of chloro-derivatives. He mentions also elsewhere 
 (Ber. 25, 209) that it sometimes contains benzaldehyde, which has a 
 disturbing influence owing to the ease with which it acts chemically. 
 
 Benzoic anhydride was used by Keller (Ber. 24, 2,502) for the 
 purpose of introducing benzoyl groups into phenyl-0-phenylene- 
 guanidine. He heated the latter for an hour and a half to 130- 
 140 with five times its weight of the anhydride. After extraction 
 with soda solution, a product remained which was found to be the 
 dibenzoyl derivative, C 13 H 9 N 3 (C 7 H 5 O) 2 . 
 
5,6] DIALYSIS 17 
 
 Benzosulphonyl chloride, C 6 H 5 SO 2 C1, was first applied by H ins- 
 berg (Ber. 23, 2,962). Schotten and Schlomann (Ber. 24, 3,689) 
 prepared benzosulphonylpiperidine, C 5 H 10 N.SO 2 C 6 H 5 , by the action 
 of benzosulphonyl chloride on piperidine in presence of an alkali 
 in aqueous solution. The yield of this product, which distils un- 
 changed, was 90 per cent, of the theoretical. 
 
 Picric acid, di- and trinitrochlorobenzene, and other substances 
 frequently give excellently crystallising compounds with hydrocar- 
 bons having a ring structure. Naphthalene yields a picric acid com- 
 pound melting at 149 (Jahresb. 1857, 456), a dinitrochloroben- 
 zene derivative melting at 78 (Ber. 11, 603), and a trinitrochloro- 
 benzene derivative melting at 96 (Ber. 8, 378). 
 
 5. Crystallographic Examination, The crystallographic char- 
 acteristics frequently afford means of identifying substances 1 inde- 
 pendent of analysis. Indeed since substances with the same 
 empirical formula give the same numbers on combustion, the 
 crystallographic investigation affords the best means of distinguish- 
 ing isomeric and other bodies related in this way. Crystals 
 selected for examination should not be large merely for conveni- 
 ence in attaching to the goniometer. Good reflecting surfaces and 
 sharp angles are absolutely necessary, and are more usually found 
 in small crystals. 
 
 6. Dialysis. This process was discovered by Graham (J. Ch. 
 Soc. 3, 6 and 257), and may be used for separating crystalline sub- 
 stances from non-crystalline ones like resins and albumens. The 
 method has received but little attention however. Where it is 
 desired to separate such a mixture, the substance is placed in a 
 
 tube, the bottom of which is made of a 
 
 piece of parchment or bladder held firmly 
 
 in position with twine. This tube, the dia- 
 
 lyser, is then suspended in a larger outer 
 
 vessel containing a suitable liquid. The 
 
 crystalline substance will be found to have 
 
 passed almost entirely into the outer liquid 
 
 after the lapse of a short time, especially if the FIG. i. 
 
 amount of the latter liquid is large. To 
 
 facilitate the diffusion the membrane should have a large area and 
 
 1 A condensed but very excellent account of the methods which may be 
 used will be found in Dr. O. Lehmann's " Die Krystallanalyse," 82 pp., 
 Leipzig, 1891 (Tr.). 
 
i8 CRYSTALLISATION [CH. n 
 
 the heavier liquid should be placed in the dialyser. The dialyser 
 should hang in the outer liquid, usually water, so that the membrane 
 is not pressed inwards. 
 
 Neumeister's method of obtaining pseudo-peptone (Z. Bio. 27, 
 372) may serve as an example of the use of dialysis. The white 
 of several hens' eggs was slightly acidulated with acetic acid and 
 boiled until coagulation was complete. The filtrate was saturated 
 with ammonium sulphate, and the precipitate which this treatment 
 produced was placed on a filter and washed with saturated 
 ammonium sulphate solution. The precipitate was found to be 
 almost completely soluble in water, and by dialysis the ammonium 
 sulphate was entirely removed in the course of a few days, without 
 an appreciable amount of the substance sought being lost by dif- 
 fusion. The solution was evaporated on the water bath and gradu- 
 ally deposited a glassy material. From the mother-liquor a jelly 
 was precipitated by alcohol which showed properties with the usual 
 reagents similar to the glassy deposit. On account of its relation 
 to peptone it received the name pseudo-peptone. 
 
 Instead of water various organic liquids may be used. Graham 
 obtained for example solutions of silicic acid in alcohol, ether, and 
 carbon disulphide. Schneider (Ber. 25, 1,166) even made an 
 alcoholic solution of colloidal silver. 
 
 Warming and frequent gentle shaking promote the dialysis of 
 water solutions. Since the process becomes slower as the propor- 
 tion of the diffusible material becomes less, it is advisable, after 
 some time, partially to evaporate the contents of the dialyser, and 
 then submit them afresh to the operation. 
 
CHAPTER III 
 
 /" 
 
 DECOLOURISING LIQUIDS 
 
 1. Charcoal. The decolourising power of charcoal was first 
 recognised last century by Lowitz. For laboratory use pure blood 
 charcoal is best. According to Skraup (M. f. Ch. 1, 185), charcoal 
 containing iron is to be avoided. 
 
 The decolourisation is produced by boiling the liquid with animal 
 charcoal, and the operation has sometimes to be continued for 
 hours (Ann. 240, 169). It must be noted that the charcoal 
 frequently takes up a considerable proportion of the substance 
 which is being purified. According to Liebermann (Sitzungs- 
 berichte d. Wiener Akad. 1877, 2, 331), potassium urate is held by 
 it very tenaciously, and the same is true of aromatic acids ; and 
 salts of fatty acids are decomposed so that the free acid is found 
 in the filtrate. It has a similar effect on salts of alkaloids, such as 
 acetate of morphine and citrate of caffeine. Such decompositions 
 occur however only in water, and not in absolute alcohol solutions. 
 
 Experience teaches that finely divided charcoal, especially from 
 blood, passes through the filter in small quantity, and in this con- 
 nection an observation of Liebig's on allantoin may be mentioned 
 (cf. Biog. notice, Ber. 23, 8i9<f). On this account substances which 
 have come directly from solutions decolourised by charcoal should 
 never be analysed without recrystallisation and filtration. By 
 boiling the charcoal afterwards with alcohol, or other solvent, the 
 most of the material which remained adhering to it may be 
 recovered. 
 
 Heintz (Ar. Pharm. 1876, 390) states that when charcoal has no 
 effect, terra alba is frequently of use. 
 
 C 2 
 
20 DECOLOURISING LIQUIDS [CH. in 
 
 2. Extraction of Bitter Principles with Charcoal. Many 
 
 substances are so strongly held by charcoal that they can even be extracted 
 by its means. Hopff was the first to discover that wood and animal 
 charcoal have the power of extracting bitter principles from infusions of 
 plants, if not in the cold at all events on boiling. According to Kromayer, 1 
 bone charcoal is the most active form of the substances for this purpose, and 
 is best applied in the granular state, as this is the only one which permits of 
 easy and rapid washing. The use of powdered charcoal leads to many 
 difficulties. For the removal of any ammoniacal compounds which may be 
 contained in it, it must be subjected first to prolonged boiling with water, 
 and then be freshly ignited before use. 
 
 Thorns (Ar. Pharm. 1886, 4-86) extracted in this way '29 grams of a 
 principle from 300 grams of calamus root. Geuther boiled 
 the infusion of this root with animal charcoal until the taste showed that 
 everything of a bitter nature had been taken out of the solution. He 
 then dried the charcoal and extracted the bitter material from it by boiling 
 with absolute alcohol. 
 
 3. Sulphurous Acid, Besides charcoal, sulphurous acid is used 
 for decolourising. Knorr (Ber. 17, 549) employed this agent for 
 removing the colouring matter from i-phenyl-2-3-dimethyl-5- 
 pyrazolon (antipyrine). A few drops of a solution of potassium 
 permanganate have a powerful effect in the same direction with 
 many fluids. 
 
 4. Precipitation. When a sufficient amount of lead acetate is 
 used almost all colouring matters are precipitated. In general a solu- 
 tion of the neutral or basic acetate of lead is added to the neutral or 
 alkaline aqueous or alcoholic solution of the substance until the 
 filtrate is colourless. For use with alcoholic solutions, basic lead 
 acetate is dissolved in five or six times its weight of alcoholic 
 ammonia. When the filtrate has become as colourless as is attain- 
 able by this means, the lead is precipitated with hydrogen sulphide 
 or sulphuric acid. It frequently happens that the precipitate of 
 lead sulphide carries down any remaining colouring matter (Ber. 
 24, 4,216). 
 
 It must not be forgotten that basic lead acetate precipitates, 
 besides colouring matters, many other indifferent substances. All 
 glucosides, for example, come under this head. According to 
 Schmiedeberg (Z. physiolog. Ch. 3, 114), gum and bassorin are 
 usually thrown down by neutral acetate of lead and always by the 
 1 "Die Bitterstoffe," Erlangen, 1861, p. 18. 
 
4] PRECIPITATION 21 
 
 basic salt. The soluble carbohydrates are neither precipitated 
 by the one nor by the other ; the addition of ammonia is required 
 to cause the deposit of their lead compounds. These relations may 
 be somewhat disturbed however by the presence of other substances 
 along with the sugar. Briicke (Ar. Pharm. 1880, 447) has shown 
 that, although lead acetate gives no precipitate in pure glucose 
 solution, it may cause a slight partial precipitation from artificial or 
 pathological urines containing sugar. 
 
 This is of course of importance in the determination of sugar in urine, 
 which has to be carried out so frequently by means of the polariscope. 
 The specimen has usually to be decolourised after it has been boiled to 
 remove the (laevo-rotatory) albumen. The acetate is added in known 
 quantity so that the dilution it causes may be considered in calculation. 
 There seems to be no good reason why the use of the acetate should not be 
 replaced by shaking with a small quantity of animal charcoal. In this case 
 there would be no dilution to introduce a complication. It is said, however, 
 that even charcoal can retain a little sugar. 
 
 In place of the addition of ammonia referred to above, other bases may 
 be used. Fischer (Ber. 24, 4,220), for example, precipitated the lead 
 compound of ribose by adding to the solution an excess of the basic acetate 
 and then enough baryta water to throw clown all the lead. By decom- 
 posing the thoroughly washed precipitate with sulphuric acid and evaporat- 
 ing the filtrate from the lead sulphate, he obtained ribose almost free 
 from ash. 
 
 It is obvious that the treatment of solutions with acetate of lead 
 for the purpose of decolourisation is at the same time applicable to 
 obtaining the substance carried down, and is in this respect to be 
 preferred to the use of charcoal. Indeed many colouring matters 
 can only be prepared by precipitation in this way, and subsequent 
 separation from the lead. Lead acetate, however, is not the only 
 reagent used for extracting substances by this method. Haemato- 
 porphyrine, for example, may be completely precipitated from 
 urine with the acetate, but Salkowski (Z. physiolog. Ch. 15, 286) 
 recommends, as preferable, mixing the urine with equal parts of 
 baryta water and a ten per cent, solution of barium chloride. The 
 advantage in this case is that the substance sought may be extracted 
 in a pure condition from the precipitate by alcohol acidified with 
 hydrochloric acid. 
 
CHAPTER IV 
 
 DISTILLATION 
 
 1. Ordinary Distillation. The object of distillation is the 
 separation of volatile from non-volatile bodies, while fractional 
 distillation is used for obtaining pure chemical substances by 
 carrying out the process systematically under definitely arranged 
 conditions. 1 
 
 The liquids to be distilled are heated in glass or metal retorts, 
 or flasks, and Liebig's condensers are usually employed in the 
 
 FIG. 
 
 laboratory for condensing tne products which pass over during the 
 operation. 
 
 To prevent prolonged contact of the vapours with corks or 
 
 1 The special precautions which the preparation of pure distilled water 
 demands are described in Stas' " Untersuchungen ueber die chemische 
 Proportionen, etc." Trans, by Aronstein, Leipzig, 1867, P- no. Cf. Ber 
 24, 1,492. 
 

 i] ORDINARY DISTILLATION 23 
 
 rubber connections, adapters are used for joining retorts to 
 condensers. 
 
 In the case of flasks, a tube sealed into the side of the neck 
 passes through a cork, and so conducts the vapour into the con- 
 denser. This tube should take an upward direction for a very 
 short distance, before descending for convenient adjustment to the 
 condenser. If the connection between the flask and condenser is 
 established by means of a suitably bent tube passing through the 
 cork of the former, the end of the tube inside the flask should be 
 ground to a point (Fig. 3), so that the drops collecting in the tube 
 may not be carried over, and a hole should 
 be filed just above the end to permit the 
 unobstructed passage of the vapour. 
 
 In order that the connecting parts of re- 
 torts or flasks may easily enter the condenser, 
 the inner tube of the latter should be rather 
 wide. On the other hand, the narrower this 
 tube is the more perfect the condensation. 
 To meet this difficulty, several methods have 
 been devised. A narrow tube may have a FlG - 3- 
 
 wider part fused on at the top, long enough 
 
 to permit of union with retorts and flasks in the ordinary way. 
 Or a piece of somewhat narrower tubing sealed at both ends 
 may be placed inside the inner tube. To prevent its slipping out 
 the latter may be narrowed at a suitable point, while small knobs 
 will prevent the former from resting on the inner tube for its whole 
 length. Ether may be distilled without loss through a short con- 
 denser provided with this arrangement, when without it most of the 
 vapour would pass through uncondensed. 
 
 Noyes has suggested the use of still another arrangement. He 
 inserts a narrow glass tube, twice as long as the condenser and 
 bent sharply back upon itself in the middle, into the inner tube. 
 The free ends of the tube are bent at an angle of 45. The same 
 stream of water circulates first through this interior tube and then 
 through the jacket of the condenser. This not only diminishes the 
 section of the inner tube but greatly increases the condensing 
 surface. 
 
 In almost all distillations it is necessary to know the temperature 
 of the vapour above the liquid, and all statements of boiling-points 
 refer to this, unless it is expressly mentioned that the temperature 
 has been determined in some other way. The thermometer is 
 
DISTILLATION 
 
 [CH. iv 
 
 therefore fixed in position so that the bulb is a few centimetres 
 above the boiling liquid. 
 
 Many liquids have a tendency to " bump " violently while boiling. 
 Producing a slow evolution of gas in them is the best means of 
 rendering the boiling steady. If the materials being used will 
 suffer it without harm, a little sodium amalgam is added to acid 
 
 solutions (A. Path. Pharm. 7, 57), 
 and to alkaline ones a little zinc. 
 If these cannot be employed, 
 platinum clippings, pieces of porce- 
 lain, capillary tubes, glass beads, or 
 talc may be used. Kelbe (Ber. 13, 
 1,401) recommends a piece of 
 pumice stone weighted with plati- 
 num wire as an infallible remedy. 
 
 FIG. 4. 
 
 FIG. 5. 
 
 The most certain method seems to be that suggested by BischofT 
 and Hjelt (Ber. 21, 2,094). The flask, which should be a round 
 bottomed one, is placed in a Babo's funnel. A cylindrical box of 
 sheet asbestos is inverted over the flask so that the neck projects 
 from a hole in the bottom, and the box is in contact with the sides 
 all round (Fig. 5). 
 
 Kunz prevents the frothing 1 over of liquids during distillation 
 
 1 It is worth noticing that large quantities of froth, from whatever cause 
 arising, may be at once dissipated in cold liquids by pouring a little ether 
 on the surface. 
 
2] THERMOMETERS AND THEIR USE 25 
 
 in quite a different manner by adding some paraffin. The paraffin 
 forms a ring one or two centimetres wide at the surface of the 
 liquid and in contact with the sides of the flask. The liquid is 
 said to boil in the centre with perfect regularity. When a liquid 
 deposits solid matter while boiling, this may be prevented from 
 adhering to the bottom of the flask, and so causing irregular 
 boiling, by the passage of a rapid stream of gas through the liquid. 
 Frequently also liquids which " bump " violently when heated with 
 the naked flame, may be distilled quietly when a suitable bath is 
 used. 
 
 2. Thermometers and their Use, In the determination of 
 boiling-points it is desirable, whenever possible, to have the stem 
 of the thermometer up to the top of the mercury column immersed 
 in the vapour, and for this purpose the flask must have the side 
 tube inserted in the neck at a sufficient height. This cannot 
 always be done, however, and consequently, to allow for the part 
 of the column projectingabove the vapour, a correction has to 
 be applied. ^kjCj^^ 
 
 According to Kopp (Ann. 94, 263), the correction is applied in 
 the following manner : The temperature is read off on the ther- 
 mometer projecting from the apparatus. Another thermometer 
 is held by means of a clamp, so that its bulb is close to the stem 
 of the first and on a level with the middle of the projecting part 
 of its mercury column. A horizontal screen protects the air round 
 the thermometers from being heated by the -flame. The corrected 
 temperature is equal to T -j- N(T t) x 0*000154, where T is the 
 apparent boiling temperature, t the reading on the second ther- 
 mometer, and N is the length of the projecting mercury column 
 from the middle of the cork up to T. 
 
 The boiling-point depends also on the pressure of the atmosphere. 
 Landolt (Ann. Suppl. 6, 175) states that, for pressures not far from 
 the normal, it is depressed "043 for each decrease of i mm. in the 
 pressure. It is usual at present to give the pressure at which the 
 boiling-point was determined, instead of following the really pre- 
 ferable plan of correcting the observed boiling-point and giving it 
 with reference to normal pressure. 
 
 Stadel and Hahn (Ann. 195, 218) have devised an apparatus 
 which permits distillations and boiling-point determinations to be 
 carried out under any desired pressure. The apparatus need not, 
 however, be described, as these operations are seldom conducted 
 
26 DISTILLATION [CH. iv 
 
 under abnormal conditions except in the single case of distillation 
 in almost complete vacuum, which will be considered later. Some 
 attacks (Ber. 13, 839) to which the apparatus has been subjected 
 have been successfully repelled by the authors. Improvements 
 have been suggested by Schumann (Pogg. Ann. 212, 44). 
 
 In connection with the choice of a thermometer some points are 
 worthy of notice. Zincke (Ann. 161, 95) suggested that it should 
 be so constructed that the mercury column was only a short 
 distance above the bulb when it stood at 100. In this way the 
 stem might be made shorter than in the common form and the 
 instrument much handier. Grabe (Ann. 238, 320) then suggested 
 that thermometers should be made so that the whole, or practically 
 the whole, of the mercury could be immersed in the vapour. 
 
 By the use of such instruments it is possible to obtain corrected 
 boiling- or melting-points with any thermometer after its readings 
 have been compared with those of four short standard thermometers. 
 The latter are constructed so that the first only goes up to 100, 
 the second begins at 100, the third at 216-218 (b.-p. of naphthalene), 
 and the fourth at 304-306 (b.-p. of benzophenone). The com- 
 parison must be carried out under as nearly as possible similar 
 conditions. 
 
 Anschiitz l states that for still greater accuracy the whole scale 
 may be divided among seven thermometers whose degrees are 
 divided into fifths. The smaller number of degrees on each thermo- 
 meter still permits the whole column to be immersed in the vapour. 
 
 Thermometers, filled under pressure with nitrogen, reading as 
 high as 460 (Ann. 259, 106, and 264, 124), are manufactured by 
 Geissler, while Schweitzer (Ann. 264, 194) speaks of one made 
 by Gerhardt whose scale almost reached 500. In the case of the 
 last, however, comparison with an air thermometer showed that 
 a correction of 29 was necessary above 400. For higher tem- 
 peratures Meyer and Goldschmidt (Ber. 15, 141) suggest a form 
 of air thermometer which is well suited for chemical work. 
 
 The new electric thermometers are now most convenient for 
 measuring high temperatures. They are especially applicable in 
 the case of explosives, as the scale on which the temperature is 
 read off may be placed at any distance. 
 
 Breakage of the stem is very apt to occur in inserting thermo- 
 meters into corks and rubber stoppers or in withdrawing them 
 
 1 " Destination unter vermindertem Druck," Bonn, 1887, p. 16. 
 
31 
 
 FRACTIONAL DISTILLATION 
 
 27 
 
 FIG. 6. 
 
 again. To avoid this the following arrangement may be used : A 
 short piece of tubing, ab (Fig. 6), just wide enough for the passage 
 of the thermometer is fitted into the cork. 
 On the outer end of this is slipped a piece of 
 rubber tubing, c, which holds the thermo- 
 meter firmly when it is in position. In this 
 way the thermometer can be easily inserted 
 after the apparatus has been put together, 
 and removed when the distillation is over. 
 If the apparatus is a complicated one and 
 leaks slightly in one or two places, a gentle 
 stream of air can be drawn through the 
 whole by a pump, and so any escape of 
 vapours may be prevented. 
 
 3, Fractional Distillation, In the frac- 
 tional distillation of a mixture the distillate 
 is collected in separate portions, each of 
 which has come over within narrow limits 
 of temperature. By repeating the process 
 several times one or more products are 
 
 finally obtained during whose distillation the mercury column has 
 hardly moved perceptibly. The results are then, except in a very 
 few exceptional cases, pure chemical substances. 
 
 This operation is greatly assisted by the use of certain pieces of 
 apparatus which closely resemble in principle the towers used by 
 manufacturing establishments. Sometimes the separation can be 
 effected in no other way (Ber. 22, 607). 
 
 Under the direction of Victor Meyer, Kreis (Ann. 224, 268) sub- 
 mitted the various forms of the apparatus to a test of their efficiency, 
 and obtained the following results : 
 
 (i) For substances which boil in the neighbourhood of 100 the 
 Linnemann tube (Ann. 160, 195), containing little wire gauze trays 
 of platinum, and the Hempel, tube (Z. analyt. Ch. 20, 502) are 
 found to be the most effective. The Le Bel-Henninger apparatus 
 (Ber. 7, 1,084), which only differs from Linnemann's in having side 
 tubes to let the liquid flow easily back into the flask, is declared to be 
 too complicated and not in the least better than the plain apparatus. 
 It is said to be no disadvantage that the boiling has to .be frequently 
 interrupted on account of the platinum gauze cups becoming filled 
 with the liquid. The frequent stoppage of the distillation gives the 
 
28 
 
 DISTILLATION 
 
 LlNNEMANN. 
 
 
 HEM PEL. 
 
 WURTZ. 
 
 LE BEL-HENNINGER 
 
 [CH. IV 
 
 \J 
 
 FLASK WITH BULBED NECK. 
 FIG 7. 
 
31 
 
 FRACTIONAL DISTILLATION 
 
 29 
 
 lower boiling constituent time to volatilise, and so facilitates the 
 separation. Hempel's apparatus consists of a glass tube filled with 
 beads, and may perhaps be preferred to Linnemann's apparatus, 
 because it consists entirely of glass and is very easily made. 
 
 By the use of these devices as good a separation may be attained 
 with one distillation as with twelve distillations from an ordinary flask. 
 
 (2) By the use of Wurtz's bulb tube (Ann. 93, 108), as good a 
 result is obtained with six distillations as with twelve from an 
 ordinary flask without its intervention. The efficiency of Wurtz's 
 apparatus is not increased if four bulbs instead of two are used, nor 
 when the tube is made of the full width of the bulbs all the way up. 
 
 (3) Even for substances boiling at a high temperature the result 
 is appreciably better when a bulb tube is added than when a long- 
 necked flask is substituted for one of the ordinary pattern. 
 
 When the quantity of the substance is small, or when the vapour 
 has a tendency to attack cork or rubber, Hantzsch (Ann. 249, 57) 
 recommends the use of a flask with a long and wide neck, which 
 can be filled with beads. To prevent the latter falling into the 
 flask a piece of platinum or nickel wire 
 gauze is placed at the base of the 
 neck. Frequent references in the 
 literature show that in general flasks 
 having somewhat lengthened bulbed 
 necks are to be preferred to ordinary 
 flasks with bulb tubes attached above. 
 
 Winssinger (Ber. 16, 2,642) suggests 
 an excellent way of separating the 
 constituents of the vapour during 
 fractionation (Fig. 8). Through the 
 neck of the flask he passes a tube, 
 closed at the bottom, in which a very 
 slow stream of water or mercury cir- 
 culates, whose speed is controlled by 
 a stopcock. Water is used for sub- 
 stances boiling below 100, mercury 
 when the boiling point is higher. The 
 smallest alteration in the speed of the 
 stream produces instantly a rise or 
 
 fall in the column of mercury in the thermometer. By proper 
 regulation a definite temperature, suitable for the separation of the 
 vapours, may be maintained with great exactness. Claudon (Bull. 
 
 FIG. 
 
DISTILLATION 
 
 [CH. IV 
 
 FIG. 9. 
 
 Ch. 42, 613) states that the efficiency of the apparatus is greatly in- 
 creased by surrounding the inner tube with wire gauze and sheltering 
 
 the whole apparatus from draughts. 
 When distillation in a stream 
 of hydrogen, carbon dioxide, or 
 other gas is to be carried out, 
 Hoffmann (Ber. 6, 293) recom- 
 mends the use of a flask like that 
 in the figure (Fig. 9). 
 
 4. The Condenser, If it is de- 
 sired to heat a liquid which is all 
 or partly volatile, the flask or re- 
 tort containing the liquid is at- 
 tached to a condenser in such a 
 way that the condensed material 
 must always flow back into the 
 flask. If a higher pressure than 
 that of the atmosphere is required 
 during the boiling, the upper end 
 
 of the condenser is connected with a glass tube which is bent 
 downwards and dips into a vessel of mercury. If the question is 
 to ascertain whether gases issue from the condenser during the 
 process, a Liebig's bulb apparatus, filled with a suitable solution, 
 is attached to the open end. On the other hand it is often requisite 
 to permit water, formed by the chemical action, to escape in spite 
 of the condenser. Ephraim (Ber. 24, 1,027) attained this by using 
 a simple tube surrounded by a coil of lead tubing through which 
 steam was passed. Gabriel (Ber. 18, 3,4?o) even bent the upper 
 end of the tube over and followed the course of the reaction by 
 measuring the amount of the water which came off. In a precisely 
 similar manner Bischoff (Ber. 21, 2,093) secured the removal of an 
 easily volatile alcohol produced by the saponification of an ester of 
 high boiling point. 
 
 If a solid condenses in the tube and threatens to stop it up, a 
 suitable volatile solvent is poured in. For example, Gottschalk 
 (Ber. 20, 3,287) found that in oxidising pentamethylbenzene with 
 nitric acid, the hydrocarbon volatilised, and had to be washed back 
 into the flask with benzene. 
 
 If a gas is generated during the boiling, or a stream of gas is led through 
 the contents of the flask, it will be found that, in spite of the most thorough 
 
4] 
 
 THE CONDENSER 
 
 cooling, an amount of the vapour corresponding to the vapour tension of 
 the liquid will be carried off with the gas. The greater part of this may be 
 caught by leading the gas, after it leaves the condenser, through a vessel of 
 water. If, for example, in order to make carbon tetrachloride, chlorine is 
 led through chloroform in sunlight and the gas escaping from the condenser 
 is passed into water, a heavy liquid, consisting of a mixture of chloroform 
 and carbon tetrachloride, will soon collect at the bottom of the vessel. 
 Where the liquid does not attack metals, the Liebig's condenser, which is 
 
 FIG. 10. 
 
 somewhat unhandy on account of its length, may be conveniently replaced 
 by Soxhlet's bulb condenser. 
 
 Volhardt (Ann. 253, 207) recommends that when retorts have to be 
 heated rather strongly for long periods in connection with inverted con- 
 densers, they should be made of potash glass, and that, reviving an old 
 custom, the part within reach of the flame should be covered with a thin 
 layer of clay and sand. He was able to keep such protected retorts in use 
 for weeks, while naked glass, especially soda glass, seldom stood more than 
 one operation. 
 
 I 
 
32 DISTILLATION [CH. iv 
 
 Otto l suggests that lean clay should be ground up to a fine paste with 
 water containing a little soda, and this mixture should be painted on with 
 a brush. When the first coat is dry a second is added, and this treatment 
 is usually sufficient even if the layer is not thicker than a visiting card. If 
 the whole retort is painted over, two bare places are left opposite to each 
 other for observing changes going on in the interior. Winkler (Ber. 24, 
 1,971) stirs up three parts of finely powdered firebrick and one part of 
 common clay with ordinary water glass solution, and applies this paste to 
 the surface of the glass. The coating is repeated two or three times and 
 each layer is dried on the sand bath. 
 
 5. Distillation in a Current of Steam. A current of steam is 
 frequently used for volatilising substances which cannot be distilled 
 alone or can only be distilled with decomposition. This treatment 
 is often the best way of separating one body from the other com- 
 ponents of a mixture. 
 
 The operation consists in passing a stream of water vapour through 
 the liquid while the latter is itself heated on a water or sand bath. 
 The steam is best made in a metallic boiler. In the absence of 
 such a vessel, a flask holding two or three litres may be substituted. 
 It is filled half full of water and a few drops of sulphuric acid and 
 several pieces of zinc are added. The slow evolution of hydrogen 
 prevents irregular boiling, and so a steady stream of vapour may 
 be maintained for hours in succession. 
 
 When substances which are easily coloured by oxidation, like aromatic 
 amido-compounds, are to be driven over with steam, it may be necessary to 
 work in a current of carbon dioxide, or following Bechhold's suggestion 
 (Ber. 22, 2 ?378), to saturate the water in the boiler with hydrogen sulphide 
 before starting the experiment. Schultz (Ber. 20, 2,721) states that 
 colourless products may be secured by adding animal charcoal to the liquid 
 to be distilled. 
 
 If the substance passes over very slowly with a current of ordin- 
 ary steam, or even fails to pass over at all, the desired result may 
 often be attained by using superheated steam. The superheating 
 is produced by leading the steam through a coil of copper tubing 
 (Fig. n), containing about ten turns, and heated by a quadruple 
 Bunsen burner. The tube should have a bore of about 5 mm., the 
 thickness of the wall should be 1*5 mm., and the internal diameter 
 of the spiral about 3 cm. The extremity next to the flask may 
 conveniently be brazed into a wider tube in which a cork can be 
 
 1 Graham-Otto, " Lehrbuch d. Chemie" [4], pp. 127, 385. 
 
51 
 
 DISTILLATION IN A CURRENT OF STEAM 
 
 33 
 
 inserted. The connections must be made with corks, as rubber 
 stoppers will not stand such temperatures for many minutes. If 
 corks also fail, soapstone, or some similar material, may be used. 
 
 Attention need be paid to the extent of the superheating in the case of 
 very sensitive substances only. Salkowski (Z. physiolog. Ch. 9, 493) 
 says that in driving over skatole carboxylic acid, when obtained as a pro- 
 duct of decay, in this way, a large part is resinised if the steam is heated 
 too much. 
 
 The glass tube conducting the steam into the distilling liquid is bent 
 
 FIG. ii. 
 
 slightly at the point and is usually made of hard glass. Both kinds of glass 
 become brittle after repeated use, but hard glass is less liable to crack acci- 
 dentally. It is unnecessary in this case to heat the liquid, as the steam 
 keeps it up to its natural boiling-point. This may be raised, however, by 
 judicious addition of some indifferent salt. 
 
 Rasinski (J. pr. Ch. 137, 39) made experiments on fractional 
 distillation with steam, but the results with petroleum hydrocarbons 
 were unfavourable. After Naumann had proved that liquids which 
 do not mix with water must be carried over by steam at tempera- 
 tures below the boiling-point of water, Lazarus (Ber. 18, 57?) took 
 
 D 
 
34 
 
 DISTILLATION 
 
 [CH. IV 
 
 the matter up again. He distilled the mixtures in a stream of 
 steam of moderate speed, and caught the distillate in two or three 
 portions. From a mixture of 25 cc. toluene and 25 cc. nitrobenzene 
 he obtained 
 
 
 
 
 Content. 
 
 Fraction. 
 
 Temp. 
 
 Vol. 
 
 
 
 
 
 Toluene. 
 
 Nitrobenzene 
 
 I 
 
 90-95 
 
 21 CC. 
 
 19 cc. 
 
 
 2 
 
 95-98 
 
 6cc. 
 
 3'5 cc. 
 
 - 
 
 3 
 
 98* 
 
 23 cc. 
 
 
 23 cc. 
 
 He thus recovered 22*5 cc. of toluene and 23 cc. of nitrobenzene. 
 Benzene and toluene could not be separated sharply by this 
 method, so that it seems to apply only to cases where the boiling- 
 points are sufficiently far apart. 
 
 The vapours of alcohol, ether, and perhaps other substances, may 
 likewise be used for separating mixtures. Bunzel (Ber. 22, 1,053) 
 found that distillation with alcohol vapour was the best method for 
 obtaining pure a-pipecoline, while Askenasy and Victor Meyer 
 (Ber. 25, 1,702) obtained perfectly pure nitropropylene by distilling 
 in a stream of ether vapour. Acetonylacetone and acetylacetone 
 are likewise examples of substances volatile with ether. In pre- 
 paring such substances, where repeated extraction with ether is 
 necessary, the same ether will naturally be used over and over 
 again ; that which has been obtained by distillation from the result 
 of one extraction being applied to extracting the next lot, in order 
 that the loss of material may be reduced to a minimum. 
 
 6. Dry Distillation, The dry distillation of organic substances 
 always results in considerable loss by decomposition. It was not 
 until 1830 that anything further was known than that, water, tarry 
 oils, and solid residues were formed. It was discovered then that 
 organic substances are broken up into simpler bodies like water, 
 carbon dioxide, carbon monoxide, solid, liquid and gaseous hydro- 
 carbons, and carbon. On the other hand Saussure (Gmelin [4], 4, 
 552) showed that leading alcohol or ether vapour through red-hot 
 tubes produced naphthalene. 
 
6] DRY DISTILLATION 35 
 
 In 1832, Liebig and Dumas found that water, carbon dioxide, 
 and acetone were formed by distilling acetates, and Persoz (Ann. 
 33, 181) discovered the formation of carbon dioxide and methane 
 by decomposing the same salts under other conditions. After 
 Mitscherlich (Ann. 9, 43) had determined, in 1833, that the dry 
 distillation of benzoates yields equal volumes of benzene and carbon 
 dioxide, both measured as gases, the operation became a common 
 one in all laboratories. 
 
 The experiment is usually carried out by distilling the substance 
 in limited quantities from small retorts or bulb tubes, or simply 
 from hard glass tubes heated in a combustion furnace. To prevent 
 the material caking together, it is mixed with sand, fragments of 
 pumice, or other similar substance. Jacobsen's suggestion (Ber. 
 12, 429), to add iron filings to the calcium salt or whatever is dis- 
 tilled, is a very valuable one. This overcomes the disadvantages 
 arising from the low conducting power for heat and tendency to 
 cake together which characterise the lime salts. A steady distillation 
 can be accomplished at a relatively low temperature, and the glass 
 vessels can be used repeatedly, as they are much less apt to crack. 
 
 Dry distillations are usually very wasteful of time, as good yields 
 can only be obtained by heating a small amount at once ; a larger 
 amount must be strongly overheated, in order that the temperature 
 may be high enough in the heart of the mass. The tall shape of 
 the body of the ordinary retort contributes somewhat to this 
 inconvenience. 
 
 This difficulty has been met in two ways. The first suggestion was 
 that of ter Meer (Ber. 9, 844), who used a 
 shallow iron vessel, on which a flat iron top, 
 with a tube to conduct away the vapour, 
 could be clamped. _ The substance was 
 spread in a thin layer on the floor of the 
 retort. 
 
 The advantage of this apparatus may 
 be seen from the fact that Lieben and FIG 12. 
 
 Rossi (Ann. 158, 147) obtained 250 
 
 grams of the crude aldehyde by distilling a mixture of calcium buty- 
 rate and formate in a hundred portions of 10 grams each from 
 small glass retorts. With ter Meer's apparatus twenty lots of 50 
 grams each yielded 270 grams of the same aldehyde. A better 
 result even than this seems to be obtainable when carbon dioxide 
 gas is led through the apparatus and the vapours are swept out 
 
 C 2 
 
36 DISTILLATION [CH. iv 
 
 as soon as they arise, especially if at the same time a constant 
 source of heat, such as a bath of sulphur vapour, is used. Sidney 
 Young (J. Ch. Soc. 59, 623) describes an apparatus made on this 
 plan by means of which he obtained very nearly the theoretical 
 yield of dibenzylketone from the calcium salt of phenylacetic 
 acid. When no such apparatus is available the yield, with use 
 of small glass retorts, may be much improved by covering them 
 with an adjustable mantle of sheet iron (Mager, Dissert. Leipzig, 
 1890) to aid in distributing the heat. 
 
 The calcium salt is usually thoroughly dried before distillation, 
 although this is more a matter of tradition than a result of any 
 special reasoning. The admixture of dry chalk is said to improve 
 the yield. 
 
 It is worth mentioning that the same acid will not always give 
 the same products when heated with different bases. Meyer and 
 Hoffmeyer (Ber. 25, 2,121) obtained xanthone by distilling hydro- 
 fluoranic acid with lime ; but on applying baryta or soda lime they 
 obtained an entirely different derivative. 
 
 In many cases the sodium or potassium salt is to be preferred to 
 the salts of the alkaline earths for some particular purpose. Gros- 
 iean (Ber. 25, 478) mixed two parts of the dry barium salt of 
 undecylenic acid with one part of powdered sodium ethylate, and 
 heated the mixture in a hard glass retort under a diminished 
 pressure of 50 mm. He obtained more than fifty per cent, of the 
 theoretical yield of decylene. 
 
 By distilling the sodium salt of <?-quinol5ne sulphonic acid with 
 five times its weight of potassium cyanide under diminished pressure, 
 Lellmann and Reusch (Ber. 22, 1,391) obtained 0-cyanoquinoline. 
 
 Dry silver salts are frequently distilled, and Kachler (M. f. Ch. 
 12, 339) even tried to give a general equation for the results of 
 distilling silver salts of fatty acids. 
 
 Pechmann (Ann. 264, 305) found that the silver salt of cumalic 
 acid was not obtainable, and used instead the mercurous salt, which 
 he distilled in a stream of hydrogen, in portions of 20 grams at a 
 time, from tubulated retorts. 
 
 7. Distillation in a Vacuum. The introduction of distillation 
 in vacua was a great advance in the art of distilling, and is now 
 easily carried out. Its convenience lies in the fact that many 
 substances may be distilled under diminished pressure, which would 
 decompose if treated in the ordinary way. 
 
7] DISTILLATION IN A VACUUM 37. 
 
 It is somewhat extraordinary that common distilling flasks and 
 retorts, provided that they are not unusually thin, may be used with 
 safety, even when the air is pumped out so as to leave only a few 
 millimetres pressure in the interior. The only limitation is that it 
 is not advisable to use vessels larger than half a litre, as with larger 
 flasks breakage is very common (Ber. 24, 937). The ordinary 
 glass apparatus may therefore be employed in all cases, provided 
 that baths are used for heating instead of the naked flame. As a 
 precaution against accidents, it is advisable to use a plate of glass 
 or to cover the flask with an asbestos cloth for the protection of the 
 experimenter. 
 
 The only disadvantage to which this operation is exposed, is that 
 the liquid is apt to boil irregularly, causing portions to be thrown 
 up into the condenser. Anschtitz, in his paper on this subject, 1 
 points out that Dittmar was the first to show, in a paper published 
 in 1869, how this may be overcome in almost every case. His 
 suggestion was to permit a small but regular stream of dry gas to 
 be drawn through the boiling liquid during the distillation. Flasks 
 may now be bought (Ber. 24, 597) which have suitable capillary 
 tubes fused in. When these are not obtainable an ordinary dis- 
 tilling flask with side tube is provided with a rubber stopper with 
 two holes. The thermometer passes through one of these, and 
 through the other a tube is inserted which is drawn out into a 
 capillary at the lower end, and reaches almost to the bottom of the 
 flask (Fig. 13). At the upper end a rubber tube and screw clamp 
 are attached. By means of the latter a little air may be admitted, 
 and so regulated that a constant stream of minute bubbles rises 
 through the liquid. When air is unsuitable, carbon dioxide or 
 hydrogen can be used instead. Rubber stoppers are usually 
 employed in fitting up the apparatus in preference to corks, as it is 
 more easily kept air-tight when they are used. Briihl (Ber. 24, 
 3,375), however, recommends the use of corks dipped in strong 
 collodion solution, as they are in every way as good for the purpose 
 as rubber stoppers. 
 
 According to Hell and Jordanoff (Ber. 24, 937), it is advisable 
 to fix the tube bearing the capillary with a special clamp, as the 
 heat of the distillation is apt to soften the rubber stopper and 
 permit the tube to be sucked in and its capillary broken. This 
 
 1 " Destination unter vermindertem Druck im Laboratorium," Bonn, 
 1887. 
 
DISTILLATION 
 
 [CH. IV 
 
 precaution may prevent the untimely interruption of a half-com- 
 pleted distillation. 
 
 In regard to thermometers the remarks made under the head 
 of ordinary distillation apply equally here. 
 
 It is in most cases unnecessary to use a condenser, although the 
 receiver may be cooled with ice, and possibly a simple tube inserted 
 between the flask and receiver. 
 
 It sometimes happens that the pressure of the water changes, 
 or that from some other cause the water runs back into the 
 apparatus. To avoid this a WoulfPs bottle may be connected 
 
 FIG. 13. 
 
 between the pump and the apparatus. Better still is the ar- 
 rangement (Fig. 13) used in the Konigsberg laboratory, as it 
 absolutely prevents the possibility of any water passing back. 1 A 
 tube connects the pump with a bottle of mercury. Through the 
 other hole in the stopper of this bottle passes a tube, at least a 
 metre in length, reaching to the bottom of the mercury. The 
 apparatus to be exhausted is connected with the second tube. If 
 the pump ceases entirely, the mercury will rise about 760 mm. in 
 this tube ; but, as its length is over a metre, nothing can reach the 
 interior of the apparatus, and the distillation cannot suffer. 
 
 1 This apparatus is manufactured by Max Stuhl, Philippstrasse, 22, 
 Berlin, N.W. The glass tubes are all sealed together in one piece, thus 
 doing away with rubber connections, and the arrangement is mounted on a 
 narrow board. 
 
7] DISTILLATION IN A VACUUM 39 
 
 The pressure in the apparatus is read off by means of a mano- 
 meter. To avoid breakage of this, if the mercury should be allowed 
 to rise too rapidly and strike the top with violence, it is well to 
 narrow the bore of the tube at a point a little below the top, so that 
 the mercury may have to traverse an almost capillary opening before 
 it can completely fill the tube. A similar precaution may be recom- 
 mended in the case of the vertical tube. The narrow part should 
 be placed just above the surface of the mercury in the bottle. In 
 the figure a is an opening for admitting air after the distillation is at 
 an end. 
 
 It is most usual to employ the lowest pressure which the pump 
 can produce, yet there seems to be a difference of opinion as to 
 what reduction of pressure is most serviceable. 
 
 Krafft (Ber. 15, 1,692) states that a pressure of 100 mm. of mer- 
 cury is the best to use, because, while it is sufficient to protect most 
 substances from decomposition, variations in the pressure produce 
 less effect on the readings of the thermometer than when very low 
 pressures are used. Irregular boiling also requires no special at- 
 tention, as it rarely appears except at much lower pressures. In 
 order to keep the pressure within 0*5 mm. of that desired, he inserts 
 between the apparatus and the pump a large bottle, which acts as a 
 kind of vacuum reservoir. This bottle may be connected with the 
 air, or with a gas holder filled with hydrogen or carbon dioxide, by 
 a tube closed by a stopcock. After a little practice a stream of gas 
 can be admitted sufficient to keep the mercury in the manometer 
 at any desired level. According to Kahlbaum, 1 on the other hand, 
 the full advantages of distillation in partial vacuum are obtained 
 only when 25 mm. pressure or less is used. 
 
 This method of distilling was at first very inconvenient where 
 fractionation was necessary, as the apparatus had to be taken apart 
 every time the receiver was changed. Of all the forms of apparatus 
 which have been invented to simplify the operation, that of Claisen 
 is perhaps the one that best combines absence of complication with 
 efficiency. The more elaborate apparatus of Lothar Meyer (Ber. 
 20, 1,834) has also its special advantages. 
 
 In Claisen's apparatus (Fig. 14) the condenser is connected 
 with the wide tube a. The tube b leads to the manometer and 
 pump, either directly or with intervention of the large bottle 
 and mercury valve for preventing back flow of water already 
 
 1 " Siedetemperatur und Druck," Leipzig, 1885, p. 72, 
 
4 o 
 
 DISTILLATION 
 
 [CH. IV 
 
 described. By means of the three-way stopcock c air may be 
 admitted, either into the whole apparatus, or only into the test tube 
 or flask attached at d, which acts as receiver. In this way the 
 receiver, which fits tightly on to a rubber stopper, may be changed 
 as often as may be necessary without causing the level of the 
 manometer to vary appreciably. 
 
 If the distillate solidifies quickly an additional inconvenience is 
 added to the others attending this mode of fractionating. The sub- 
 stance will in this case usually collect above the stopcock in Clai- 
 sen's apparatus. If the part a is made wide enough to hold all the 
 distillate, this need not interrupt the distillation until the whole has 
 
 FIG. 14. 
 
 passed over. The contents can then be melted out by the cautious 
 application of heat after the apparatus has been taken apart. 
 
 Where the moisture passing back into the apparatus from the 
 pump has a disturbing influence, a tube containing phosphorus 
 pentoxide may be inserted between them. 
 
 8. Leading Vapours through a Red-hot Tube, This method 
 
 is frequently used for preparing aromatic hydrocarbons where 
 milder means do not suffice. If one heating only is desired, the 
 vapours are led through an iron, or if necessary a glass, tube placed 
 
8] LEADING VAPOURS THROUGH A RED-HOT TUBE 41 
 
 in a combustion furnace. Kramer and Spilker (Ber. 23, 84) sug- 
 gest the use of a double tube (Fig. 15). The lower branch is placed 
 in the furnace, the upper heats the vapours preliminary to their 
 
 entering the lower. For example, although cumarone passes 
 through unchanged at a dull red heat, a mixture of cumarone and 
 naphthalene loses water and forms chrysene. 
 
 I o+c ia H 8 = | 
 
 C.H/ C H 
 
 It is suggested by Liiddens (Ber. 8, 870) that carbon dioxide may 
 be led through the tube along with the vapours so as to prevent 
 their lingering too long in the passage. By this means he obtains 
 diphenyl from benzene without any great deposition of carbon. At 
 other times it is desirable to expose the vapour repeatedly to the 
 influence of a high temperature if a single exposure is not sufficient. 
 In this case an apparatus may be employed which was originally 
 used by Michaelis (Ann. 181, 283) for making phosphenyl deriva- 
 tives. It was adopted later by La Coste and Sorger (Ann. 230, 5), 
 
 FIG. 16. 
 
 who were thus enabled to expose benzene vapour to a bright red heat 
 for weeks in succession. 
 
 The benzene or other substance is placed in the flask A (Fig. 16). 
 The adapters c and F and the connecting tubes are made of lead. 
 
DISTILLATION 
 
 [CH. IV 
 
 The iron tube D is placed in an inclined combustion furnace. After 
 the vapour has been heated it passes through a part of the tube, 
 which is cooled by a spray of water from the tube E. Whatever is 
 still condensible is cooled by a condenser attached at e. The cool- 
 ing by the water from E prevents the melting of the adapter F at 
 its junction with the iron tube. The condensed material 
 flows back to the flask A through the long lead tube. 
 Another tube, passing to the bottom of both, connects 
 the flask A with the safety flask B. The top of the 
 condenser is provided with a descending tube for the 
 purpose of causing any escaping gases to bubble 
 through a vessel of water. The openings , a, a, and 
 the coupling G are provided for convenience in cleaning 
 the apparatus. 
 
 9. Distillation under Pressure. No apparatus 
 specially designed for this purpose is in use in the 
 laboratory. Engler made petroleum hydrocarbons on 
 a large scale by distilling fats in an apparatus invented 
 by Krey (Ger. Pat. 37,728) for technical use. In some 
 parallel experiments in the laboratory (Ber. 21, 1,818), 
 he employed sealed tubes containing each about thirty 
 grams of the substance. They were bent at an obtuse 
 angle and placed in a digester in such a way that the 
 empty limbs of the tubes hung downwards outside. 
 After having been heated for four hours at 350 the 
 FIG. 17. tubes were removed, the gases allowed to escape, and 
 the capillaries resealed. This operation was repeated 
 until the appearance of a sufficiently mobile liquid product indicated 
 that the action was complete. The results were the same as when 
 Krey's apparatus was used. 
 
 10. Boiling-Points. When the boiling-point of a liquid, on 
 account of the small quantity available for examination, cannot be 
 ascertained by distillation, this important constant may be deter- 
 mined by the use of a single drop even of the substance by the 
 method suggested by Siwoloboff (Ber. 19, 795). 
 
 The liquid is placed in a glass tube which has been drawn out 
 and sealed at the bottom. A capillary tube, sealed up at A, is 
 introduced, and the whole is attached to a thermometer and treated 
 as in the determination of, a. melting-point (Chap. VIII.). Before 
 
io] BOILING-POINTS 43 
 
 the liquid reaches the boiling-point single air bubbles proceed from 
 the small volume of air in the capillary below A ; these become 
 gradually more numerous till an uninterrupted thread of small bells 
 of vapour is established. At this moment the thermometer shows 
 the exact boiling-point of the liquid. The operation should be 
 repeated several times and the mean of the observations taken. 
 The capillary prevents violent boiling, and must be renewed for 
 each experiment. 
 
 Main (Ch. News, 35, 59), Hasselet (Z. analyt. Ch. 18, 251), and 
 Schleiermacher (Ber. 24, 944), suggest other forms of apparatus 
 for this determination. 
 
CHAPTER V 
 
 DRYING SOLIDS AND LIQUIDS 
 
 1. Drying in Desiccators. Solids may be dried by heating to 
 a sufficiently high temperature in a Lothar Meyer's air bath (Ber. 
 22, 879) ; when they will not stand this treatment they are placed in 
 desiccators. The latter are used also for keeping substances which 
 have been dried in the heat, to avoid their attracting moisture again. 
 
 As sunlight produces more decomposition than is ordinarily 
 supposed, it is well to have a dark glass bell jar at hand for such 
 cases (Ber. 21, 2,529). 
 
 A variety of drying agents, such as concentrated sulphuric acid, 
 calcium chloride, quicklime, barium oxide, and potassium and 
 sodium hydroxides, are used to charge the desiccator. If the sub- 
 stance has a tendency to lose carbon dioxide or ammonia, it will 
 be dried in an atmosphere of one or other of these gases ; in the 
 latter case moist sal-ammoniac may conveniently be scattered on 
 the pieces of potassium hydroxide. 
 
 The relative drying power of various substances has been ex- 
 amined by Miiller-Erzbach (Ber. 14, 1,096). He finds that phos- 
 phoric anhydride, concentrated sulphuric acid, and dry potassium 
 hydroxide are almost equal in power ; sodium hydroxide and 
 calcium chloride containing but little water are likewise nearly 
 equivalent in drying capacity. Moist caustic soda, however, is 
 entirely deprived of its water by caustic potash, while the difference 
 in the vapour tension of water over phosphoric anhydride and 
 almost anhydrous calcium chloride is only a fraction of a millimetre 
 of mercury ; sulphuric acid works more rapidly than calcium chloride 
 (Ar. Pharm. 1884, 107). 
 
 Hempel (Ber. 23, 3,566) drew attention to the fundamental defect 
 
!] DRYING IN DESICCATORS 45 
 
 in ordinary non-evacuated desiccators, which consists in the fact 
 that the drying agent is placed at the bottom. Since moist air is 
 lighter than dry air only a slow interchange can take place between 
 the strata of gas in the vessel. He found that in fact a quantity 
 of water which took nine days to evaporate in the ordinary form of 
 desiccator, was absorbed by the drying agent in three, when the 
 only difference between the experiments was that the drying agent 
 was placed above instead of below. He has lately described a 
 convenient form of the apparatus (Z. f. angew. Ch. 1891, 201) in 
 which he has given effect to this principle. 
 
 All drying is much accelerated by using desiccators provided with 
 a tubulus through which the air is withdrawn after the substance 
 has been placed in position. A suitable grease for rendering the 
 adjustment of the ground glass surfaces air-tight may be made by 
 melting together three parts of tallow and one part of white wax. 
 
 According to Pfliiger (P. Ar. 38, 311), a good water pump will 
 reduce the pressure in a desiccator to 11 mm. of mercury at 
 16-20. If concentrated sulphuric acid is then admitted, the pres- 
 sure sinks quickly to less than I mm., showing that practically i 
 all the air has been removed. 
 
 Instead of concentrating small quantities of solutions by heat, A 
 they may conveniently be allowed to evaporate in a desiccator, a / 
 process which is much assisted by placing the apparatus in a warm 
 place, or by evacuating. Desiccators have even been designed in 
 which liquids may be boiled and so evaporated in vacua. Anschiitz 
 (Ann. 228, 305) and Briihl (Ber. 24, 2,458) have described 
 arrangements for this purpose. The author has found the following 
 easily constructed apparatus very convenient (Fig. 18). 
 
 The strong ground-glass plate on which the bell jar rests is 
 bored in the centre and provided with a rubber stopper through 
 which a lead pipe passes. A porcelain dish stands on a tripod 
 above the hole, and its interior surface is covered as completely as 
 possible with coils of the lead pipe ; wire can be used to hold these 
 in position. By this means a current of hot water or steam may 
 be led through the pipe and a kind of steam bath produced. For 
 the better distribution of the heat the coils of pipe may be covered 
 with powdered copper, such as is obtained by the reduction of the 
 cxide. Small dishes of sulphuric acid can be placed under the 
 tripod, and the plate is elevated on two pieces of wood to give the 
 space necessary below for the exit of the lead pipe. 
 
 The air is withdrawn by a tube passing through the neck of the 
 
4 6 
 
 DRYING SOLIDS AND LIQUIDS 
 
 [CH. v 
 
 bell jar. A second tube provided with a stopcock entering with this, 
 is bent twice at right angles and dips into a beaker. When the 
 stopcock in this tube is opened the liquid is forced in by the pres- 
 sure of the air, and the basin can therefore be replenished during 
 the evaporation without interrupting the pump. Walter (J. pr. 
 Ch. 32, 425), to whom we owe the suggestion of the second tube, 
 
 FIG. 18. 
 
 has also designed an apparatus for evaporation in vacua, but it is 
 less simple than that described. 
 
 It might be more advantageous to connect the pump with the 
 lower part of the bell jar by passing the tube leading from it 
 through the rubber stopper in the plate. 
 
 If it is desired to evaporate carbon disulphide, ether, chloroform, 
 or benzene, the desiccator is charged with crude paraffin of low 
 melting-point in place of the usual drying agents. Liebermann 
 (Ber. 12, 1,294) states that the evaporation goes on very quickly 
 most rapidly in the case of the first-named solvent, and least so 
 in the case of the last. The paraffin becomes liquid during the 
 process, but does not thereby lose its absorbing power. The 
 solvents may be recovered in a pure condition by distilling the 
 paraffin solution. 
 
 Many substances are extremely hard to dry. Schmiedeberg 
 (A. Path. Pharm. 28, 364) found, for example, that acid chon- 
 droitine sulphate and chondroitine itself were decomposed by 
 remaining in a desiccator at 100 either in vacuo or at the normal 
 pressure. On the other hand, it was hardly possible to reach a 
 
2] DRYING LIQUIDS 47 
 
 condition of constant weight by mere remaining over sulphuric 
 acid at the ordinary temperature. Usually the loss of weight - 
 ceases after long standing over sulphuric acid in vacuo,but with' 
 some substances an exposure for several months is necessary. 
 
 2. Drying Liquids. Liquids are dried by putting into them 
 such substances as barium oxide, calcium bromide, chloride, iodide, 
 or nitrate, quicklime, anhydrous cupric sulphate, potassium bi- 
 sulphate, carbonate, or hydroxide, anhydrous potassium ferrocyanide, 
 phosphorus pentoxide, silicon tetrachloride, sodium, sodium hy- 
 droxide (Ber. 25, 145), fused sodium sulphate (Ann. 256, 29), con- 
 centrated sulphuric acid, or zinc chloride (Ber. 24, 1,019). If the 
 liquid has a high boiling-point the water maybe removed, according 
 to Briihl, by passing carbon dioxide through it on the water bath. 
 
 Naturally such drying agents only will be used in any particular 
 case as will have no chemical action on the liquid. 
 
 The commonest drying agent is chloride of calcium, which is 
 fused before use to destroy its porosity. It forms compounds, 
 however, with many substances. It cannot be employed, for 
 example, for drying alcohol in the laboratory, as it forms an 
 alcoholate which can only be decomposed by distillation from 
 copper retorts. Propyl alcohol (Ber. 23, 181) forms a compound 
 of the formula CaCl 2 + 3C 3 H 8 O. Warm benzyl alcohol dissolves 
 so much of it that the solution solidifies to a crystalline mass on 
 cooling (Ber. 14, 2,395), and Lieben (M. f. Ch. 1, 919) states that 
 the fatty acids likewise form crystalline compounds. Many esters 
 like acetic ether and gluconic ether unite with calcium chloride. The 
 compound with the latter has the formula C 6 H U O 7 . C 2 H 5 -f CaCl 2 . 
 
 An occasional disadvantage is that it does not always remove the last 
 traces of moisture completely. Where this is important, as in determining 
 exact boiling-points, sodium may be used for hydrocarbons and phosphorus 
 pentoxide or sulphuric acid for other substances. 
 
 Calcium nitrate is used almost exclusively for drying unstable nitro- 
 clerivatives and for nitrous anhydride, 1 while calcium iodide is employed for 
 hydriodic acid gas (C. R. 112, 717). 
 
 1 If necessity arises for removing chlorine from a mixture of gases, they 
 may be led over warm metallic antimony. Where carbon disulphide has to 
 be eliminated the mixture should be led through a tube filled with rubber 
 (Than, Ann. Suppl. 5, 236). 
 
4$ DRYING SOLIDS AND LIQUIDS [CH. V 
 
 On one occasion Ladenburg (Ben 3 35) used silicon tetrachloride to 
 free acetic ether from the last traces of alcohol and water. Frieclel and 
 Crafts (Ann. Ch. Ph. [4], 9, 5) state that heating ordinary alcohol at IOO 
 with silicic ether converts it into absolute alcohol. Hartmann (Ber. 24, 
 1,019) used zinc chloride for drying petroleum. 
 
 Wertheim (Ann. 127 79) used glacial phosphoric acid for drying 
 liquids. 
 
 It is often better to dry an ethereal solution than to attempt to dry the 
 substance after distilling off the ether. Liebermann (Ber. 22, 676), for 
 example, dissolved hygrine in absolute ether, and added potassium hy- 
 droxide in order to get the base free from water and at the same time to 
 avoid access of carbon dioxide from the air. 
 
 3. Drying Alcohol and Ether. The chemist is often under 
 the necessity of making absolute alcohol and absolute ether. In 
 the former case the following are the special methods employed : 
 
 (1) The alcohol is allowed to remain in a flask for two days 
 (Z. Ch. 1865, 260), with a large quantity of quicklime (Soubeiran, 
 Ann. 30, 356), and is then distilled off. The quicklime does not 
 
 . show much appearance of disintegration, but the alcohol, if the 
 \Vr\lx W- ^ rst an( * ^ ast P ort i ns which pass over are rejected, 1 is found to be 
 * absolute. It is not rendered red by potassium permanganate, but 
 acquires only a faint brown tinge by contact with this salt. 
 
 (2) The flask containing ordinary alcohol and quicklime, which 
 should be present in such quantity that some pieces project above 
 the surface of the liquid, is connected with a reflux condenser and 
 boiled on the water bath for an hour. The condenser is then 
 reversed and the alcohol distilled off. In this case the lime falls 
 to powder. The flask must not contain too much alcohol, as the 
 heat developed by the formation of the hydrate may cause the 
 alcohol to boil so violently as to be partly thrown out through 
 the condenser. 
 
 If the alcohol contains more than five per cent, of water, this 
 treatment must be repeated one or more times (Ann. 160, 247). 
 If it contains a large proportion of water, the alcohol is only half 
 
 1 The rejection of the first fraction is necessary, because Soubeiran (Ann. 
 30, 360) has shown that, even in the case of almost absolute alcohol, a 
 product containing a larger proportion of water comes over first. On the 
 other hand, Mendelejeff (Z. Ch. 1865, 210) has shown that, on account of 
 the rising temperature, the last portions are apt to contain moisture ex- 
 tracted from the hydroxide by means of the absolute alcohol. 
 
3] DRYING ALCOHOL AND ETHER 49 
 
 filled with quicklime, as otherwise the flask may be broken by the 
 violence of the hydration process. 
 
 Barium oxide (Jahresb. 1862, 392) is exceedingly well adapted for the 
 preparation of absolute alcohol. The removal of the last trace of water 
 may be recognised by the liquid assuming a yellow colour. The oxide is 
 made by the decomposition of the nitrate by a gradually increasing heat. 
 
 If a little barium oxide is added to the quicklime, as it is usually employed, 
 the appearance of the yellow colour indicates the completion of the drying. 
 
 Vincent and Delachanel (C. R. 90, 1.360) found that barium oxide could 
 not be used for drying all alcohols since allyl alcohol gave a compound 
 with it having the composition 2C 3 H 6 O.BaO. Hiibner and Lellmann 
 mixed such alcohols with three or four times their bulk of chloroform, and 
 dried the solution with chloride of calcium. 
 
 Sodium and sodium amalgam are not adapted to removing water from 
 alcohol because, according to Mendelejeff (Z. Ch. 1865, 260), when they 
 are used, traces of sodium and mercury are found in the distillate. 
 
 Raimundus Lullus attempted drying with potassium carbonate, but it is 
 too weak to extract water from alcohols. Tornoe (Ber. 24? 2,671) found 
 that allyl alcohol still contained relatively large quantities of water after 
 the ignited carbonate had removed all that it was capable of extracting. 
 
 (3) It will usually be found that, after the absolute alcohol has 
 been distilled off, the glass flask containing a large mass of lime 
 will be broken in the attempt to clean it. This disadvantage may 
 be avoided by a process used by the author. Its working depends 
 on the fact, ascertained by Squibbs (Z. analyt. Ch. 1887, 94), that 
 the laboratory method does not yield such pure alcohol as that 
 employed in making it technically by filtration over quicklime in 
 the cold. Such alcohol has a lower specific gravity than that 
 obtained in any other way. 
 
 A cylindrical vessel between two and three times as tall as it 
 is wide, holding twenty litres and provided with a stopcock at the 
 bottom, is used. It is fitted internally with a perforated lining, 
 having two handles at the top to facilitate its removal when 
 necessary. In the centre, and attached to the inner cylinder, is 
 a tube almost as tall as the vessel. The apparatus is filled with 
 lumps of quicklime, and as much alcohol is added as it will hold. 
 After remaining from ten to fourteen days the alcohol may be 
 drawn off by the stopcock as absolute. The same lime may be 
 used for three or four lots of alcohol, if fresh lumps are thrown 
 in to make up for the subsidence. When the stopcock becomes 
 
 E 
 
DRYING SOLIDS AND LIQUIDS 
 
 [CH. V 
 
 plugged by fine particles of the hydroxide, it may be cleaned out 
 by a wire passed down the central tube. The apparatus can be 
 suspended from the wall of the laboratory, and should always be 
 kept filled with lime and alcohol. 
 
 The solubility of lime in alcohol is very small. Smith (Ar. 
 Pharm. 1876, 356) found that 50 cc. of alcohol which had been 
 in contact with lime for some time left, after filtration and evapora- 
 tion, less than '005 grams of residue. So that alcohol made as 
 above requires only filtration to render it suffi- 
 ciently pure for most purposes. When distilled 
 it contains over 99*9 per cent, of pure alcohol. 
 
 In this connection it may be remarked that, even 
 when free from water, alcohol dried in these ways 
 cannot be quite pure since alcoholic caustic potash 
 prepared with it gradually becomes brown. According 
 to Waller (Ch. Z. 1890, 23), the very purest alcohol 
 does not possess this property. To get rid of these 
 last traces of impurity, absolute alcohol is shaken 
 with powdered potassium permanganate till it has ac- 
 quired a distinct colour. It is then allowed to remain 
 for some hours until the permanganate has decom- 
 posed and the brown oxide of manganese has separated 
 out. Finally a little precipitated chalk is added, and 
 the liquid is distilled with a Hempel tube in such a 
 way that only 50 cc. pass over in twenty minutes. 
 Ten cubic centimetres of the distillate are taken from 
 time to time, boiled with a few drops of strong caustic 
 potash, and set aside for twenty minutes. When a 
 sample is obtained which shows no trace of yellow 
 
 colour by this test the distillation is continued and the alcohol preserved for 
 
 use. The last portion must be rejected however. 
 
 Alcohol prepared in this way is perfectly neutral, and is suitable for 
 
 making solutions of caustic alkalis or of silver nitrate. The solutions after 
 
 boiling, or indefinitely prolonged standing, remain as colourless as distilled 
 
 water. 
 
 FIG. 19. 
 
 Absolute ether is obtained from the commercial article by washing 
 it with water, if necessary, to remove alcohol, then drying over 
 chloride of calcium or phosphorus pentoxide, and finally boiling 
 for some time with sodium in a flask attached to a reflux condenser. 
 According to Squibbs (Ch, N. 51, 66 and 76), chloride of calcium 
 
3] DRYING ALCOHOL AND ETHER 51 
 
 is alone capable of drying ether completely if they are left in 
 contact for several weeks. 
 
 The presence of water may be detected by the cloud which is 
 formed on mixing impure ether with carbon disulphide. Alcohol 
 is proved to be present if the ether becomes coloured on shaking 
 with aniline violet. Pure ether remains colourless. 
 
 E 2 
 
CHAPTER VI 
 
 EXTRACTION 
 
 1. Extraction with Ether. By extraction we mean the removal 
 of a substance from a liquid in which it is dissolved or suspended, 
 by dissolving it in another liquid which is not miscible with the first. 
 
 The liquids are usually shaken together in a separating funnel, 
 and the resulting layers are then separated. Instead of such 
 funnels, Schiff (Ann. 261, 255) recommends the use of cylinders 
 400 mm. in length, and with diameters of 60 and 30 mm. They are 
 provided with stopcocks and may be used for many other purposes 
 in the laboratory, while their shape enables one to estimate the 
 relative amounts of liquid and extracting medium being used. 
 
 Laboratory turbines are now in use for facilitating the agitation. 
 
 The liquids ordinarily used for extracting are : amyl alcohol, 
 benzene, carbon disulphide, chloroform, ether, and petroleum ether ; 
 while acetic ether, phenol, and toluene are occasionally employed. 
 
 The number of times that the extraction must be repeated depends 
 on the relative solubility of the substance in the liquid, usually 
 largely water, in which it is contained, and in the extracting medium. 
 Herb (Ann. 258, 46), for example, found it necessary to extract an 
 acidified solution of tetrahydroterephthalic acid no less than thirty 
 times with ether. In general it is advisable to evaporate a portion 
 of the last extract in order to see whether it has removed anything 
 from the liquid. Where the extraction is difficult, it is sometimes 
 possible to concentrate the liquid by evaporation before beginning 
 the operation. 
 
 It should not be forgotten that 10 parts of water dissolve i part 
 of ether, while 492 parts are necessary to dissolve i part of carbon 
 disulphide. Those numbers apply, however, to pure water only, 
 
i] EXTRACTION WITH ETHER 53 
 
 and so, as the liquids to be extracted are most frequently solutions 
 containing salts, the actual solubility will vary from case to case in 
 practice. 
 
 When the liquid to be extracted is of a thick nature, or contains solid 
 matter which might plug the stopcock of the separating funnel, the shaking 
 is done in a strong bottle, and the liquids are not poured into the funnel till 
 all suspended matter has settled. If an emulsion is formed on shaking, so 
 that no clear separation into layers can be obtained, a small portion may be 
 examined in a test tube to see whether the addition of more water or more 
 ether will not bring about separation. Where this fails the addition of a 
 small amount of alcohol is frequently useful. Indeed, ether containing 
 alcohol (Z. physiolog. Ch. 7, 162) is often preferable to pure ether. 
 
 To assist the separation into layers, where acetic ether is used, Schroder 
 (Z. physiolog. Ch. 3, 325) recommends the addition of common salt to the 
 water solution, while others advise the use of calcium chloride. 
 
 On the other hand, ether may be used for separating some emulsions. 
 Kramer and Spilker (Ber. 24, 2,788) found that in washing synthesised 
 lubricating oils emulsions were formed similar to those which are familiar in 
 the case of natural oils of the same kind, and long standing had no effect in 
 the way of separating them, although the addition of ether produced the 
 desired result in a short time. 
 
 Liquids are known which cannot be extracted with ether directly at all. 
 For example, the physiological chemist frequently desires to remove 
 substances soluble in ether from the urine of animals which have been 
 fed with drugs of various kinds. But it is seldom possible to extract the 
 urine directly, as a more or less jelly-like mass is apt to be formed. In 
 such a case, the urine is evaporated to dryness and the residue extracted 
 with about one-and-a-half volumes of boiling alcohol for one volume of the 
 original urine. On cooling, the alcoholic solution deposits much tarry 
 matter, urea, etc. After 24 hours the liquid is poured off, evaporated, 
 diluted with water, and either directly, or after the addition of alkali or 
 acid, extracted with ether, acetic ether, or amyl alcohol. 
 
 Although this process is almost universally applicable, quite other methods 
 for the examination of urines are sometimes preferred. Schmiedeberg and 
 His (Ann. Path. Pharm. 22, 255), for example, discovered one of the most 
 extraordinary syntheses observed in the animal body the conversion of 
 
 /OH 
 
 pyridine, C 5 H 5 N, into methylpyridylammonium hydroxide, C 5 H 5 N<( n rr 
 
 \v_,rl 3 
 
 in the following manner. The urine was purified by the addition of lead 
 acetate and ammonia followed by nitration, and the lead was removed from 
 the filtrate with sulphuric acid. After this treatment a crystalline precipitate 
 of a double salt of the base was obtained by adding a solution of potassium 
 and mercuric iodides. 
 
54 EXTRACTION [CH. vi 
 
 When solutions containing an acid, such as hydrochloric or acetic 
 acid, have to be extracted, and the ethereal extract has an acid re- 
 action in consequence of this, potassium hydroxide, or better still 
 sodium, potassium, or calcium carbonate (Ber. 25, 3,651) is added. 
 If the extract contains organic acids in addition, the hydrochloric 
 (Ber. 24, 2,583) or acetic acid (Ber. 25, 950) may be removed by 
 shaking with water. Subsequent treatment with sodium carbonate 
 solution gives the sodium salt of the organic acid free from sodium 
 chloride or acetate. It is much better, however, to use tartaric acid 
 or some other acid which will not be extracted by the ether for 
 acidifying the solution in the first place. 
 
 Where the ethereal or other extract cannot be submitted to distil- 
 lation for fear of decomposition, as happens in the case of alkaloids, 
 a strong current of air is drawn through the liquid, or it is allowed 
 to evaporate in vacua over sulphuric acid and paraffin (A. Path. 
 Pharm. 26, 242). 
 
 Where the substance extracted by the ether is volatile in ether 
 vapour, as is the case with Bamberger's dekahydroquinoline (Ber. 
 23, 1,144), the vapour is caused to pass up through a Hempel's tube 
 filled with glass beads (cf. Chap. IV., 3) before entering the 
 condenser. 
 
 Ether was found by Salkowski (Z. physiolog. Ch. 9, 493) to take 
 up traces of the sodium salts of volatile organic acids. 
 
 2. Extraction with Amyl Alcohol. Amyl alcohol would be of 
 wide application as an extracting agent if it could be easily obtained 
 in a pure condition. The commercial article contains impurities 
 which yield tarry matters under the influence of either acid or 
 alkaline solutions, and the purification of the substances extracted 
 is rendered more difficult on this account. Udransky (Z. physiolog. 
 Ch. 13, 248) has shown by an extended investigation that this un- 
 fortunate property is chiefly due to the presence of furfurol which 
 cannot be eliminated except by converting the alcohol into potas- 
 sium amyl sulphate, and purifying this by repeated recrystallisation. 
 The salt is decomposed by heating for five hours on the water bath 
 with ten per cent, sulphuric acid, and the amyl alcohol is separated. 
 Traces of acid are removed with calcium carbonate, and the product 
 is distilled with steam. 
 
 Amyl alcohol is much used for the isolation of alkaloids, 
 especially where small quantities, such as those found in cases of 
 poisoning, have to be extracted and identified. Uslar and Erdmann 
 
3, 4] CONTINUOUS EXTRACTION 55 
 
 (Ann. 120, 121 ) were the first to show that vegetable bases are 
 mostly very soluble in it, especially when it is warm. Since it boils 
 at 132 hot water solutions may be extracted with it. They showed 
 also that even large amounts of water containing a trace of alkali 
 were unable to remove any of the alkaloids from solution in the 
 alcohol. On the other hand, the hydrochlorides of the alkaloids 
 were quite insoluble in the alcohol, and consequently shaking with 
 water containing hydrochloric acid removed the bases completely. 
 
 When the substance cannot be recovered by shaking with water 
 containing alkalis or acids, the alcohol is distilled off with the help 
 of an oil or metal bath. This operation is best conducted in vacno 
 
 (Ber. 24, 513). 
 
 Phenol was used by Bernthsen (Ann. 251, 5) for extracting 
 methylene red from the mother-liquor of methylene blue. By 
 adding alcohol and ether to the phenol solution a mass of crystals 
 was precipitated which could be purified by recrystallising from 
 alcohol. 
 
 3. Solubility. A substance shows often very different degrees 
 of solubility in different extracting agents. For example, I part of 
 hippuric acid dissolves in 200-270 parts of ether saturated with 
 water at 20-25, while it will dissolve in 16-22 parts of acetic ether 
 under the same conditions. Bunge and Schmiedeberg (A. Path. 
 Pharm. 6, 237) found that this acid could be separated almost 
 quantitatively from benzoic acid by shaking the solution of both 
 acids in water with petroleum ether. The benzoic acid was com- 
 pletely removed while the other remained untouched. It has been 
 shown that solanine (Z. analyt. Ch. 21, 620) can be extracted from 
 alkaline solution by amyl alcohol, while ether, benzene, chloroform, 
 acetic ether, and petroleum ether have no such power. 
 
 4, Continuous Extraction. This process is used in order to 
 economise ether where the substance is not very soluble in it, or 
 where a large amount of liquid is to be extracted. Neumann (Ber. 
 18, 3,064), and still more recently Hagemann (Ber. 26, i,975), have 
 suggested forms of apparatus for the purpose. We shall describe 
 one of Neumann's (Fig. 20). 
 
 The ether is boiled in the flask B, and the vapour passes through 
 the tube c into the liquid in the cylinder D. The extract accumu- 
 lates on the surface of the liquid, while the condenser E serves to 
 retain any uncondensed vapour. As soon as the ethereal layer has 
 
EXTRACTION 
 
 [CH. VI 
 
 risen above the highest point of the tube /j it is syphoned over into 
 the flask B. The separating funnel g serves for the admission of 
 
 the solution, while the stopcock 
 h is used for its removal when 
 exhausted. 
 
 It is well known that corks can 
 be rendered perfectly vapour-tight 
 only with great difficulty. When 
 boiling ether or benzene are in 
 question, Neumann (Ber. 18, 3,064) 
 suggests the use of chromgelatine, 
 as, after exposure to light, it be- 
 comes insoluble in the liquids 
 ordinarily used. The parts of the 
 apparatus which are to be made 
 impervious by vapours, are simply 
 coated with this substance by 
 means of a small brush, and ex- 
 posed to the light for two days. 
 The chromgelatine is made by 
 dissolving 4 parts of gelatine in 
 52 parts of boiling water, filtering, 
 and adding i part of ammonium 
 bichromate. 
 
 When small quantities of liquid 
 have to be extracted, the much 
 simpler Schwartz apparatus may 
 be used. 
 
 The ether is boiled in the flask 
 A, and its vapour passes through 
 the tube B into an adapter of the 
 form shown, and finally reaches 
 FIG. 20. the condenser D. The condensed 
 
 ether flows from the adapter c 
 
 through the tube E to the bottom of the flask F, and, rising through 
 the liquid to be extracted, accumulates on the surface until it flows 
 over into the flask A by the bent side tube, thus completing the 
 circuit. 
 
 5. Extraction of Solids. For the extraction of solids, most of 
 the liquids already mentioned may be used. Many forms of appara- 
 
51 
 
 EXTRACTION OF SOLIDS 
 
 57 
 
 tus have been designed for the purpose. That of Farnsteiner 
 (Fig. 22) is very useful, and its construction maybe understood from 
 the figure. 
 
 Its special advantage lies in the fact that the cooling arrange- 
 ment is in the same tube with the substance under extraction, and 
 
 FIG. 21. 
 
 FIG. 
 
 the number of joints is reduced to a minimum. The extraction 
 tube is 32 cm. long, with a bore of 3 cm. 
 
 Reinsch's apparatus (Ch. Z. 1889, 94) for extraction with cold 
 ether is one of the best, and large quantities of material can be ex- 
 tracted at one operation. The ether traverses the tube B (Fig. 23) 
 in the form of vapour, and after condensation runs into the vessel C. 
 which fits loosely into the tu,be D, and after passing through the 
 
58 EXTRACTION. [CH. vi 
 
 mass to be extracted flows back into the flask A. A trap prevents 
 the backward passage of vapour. 
 
 It may be mentioned here that ether sometimes explodes when 
 distilled by itself, and that this has been ascribed to its containing 
 an abnormally large amount of hydrogen peroxide or of ethyl 
 peroxide (Proc. Chem. Soc. 1891, 15). Such explosions are also 
 known to occur during the evaporation of ethereal solutions, at about 
 60, on the water bath. Schar (Ar. Pharm. 1887, 623) has investi- 
 gated the matter very fully. No test is known whereby it can be 
 
 FIG. 23. 
 
 ascertained beforehand whether a specimen of ether is likely to 
 explode or not. 
 
 6. Solvents and Diluents. The use of proper media as solvents, 
 for the purpose of bringing substances in contact with each other 
 in such a way as to facilitate chemical action, may be discussed 
 here since the liquids used are for the most part the same as those 
 used in extracting and recrystallising. 
 
 The boiling-point of the solvent should be considered. If an 
 
6] SOLVENTS AND DILUENTS 59 
 
 action takes place most easily at, say, 80, it is advisable to use 
 benzene in place of ether. Many expected actions fail to take place 
 from improper choice of diluting media. 
 
 For example, Hofmann and Geiger, Martius, and Nietzky, were all 
 unsuccessful in their attempts to prepare amidoazoparatoluene from parato- 
 luidine in alcoholic solution. Nolting and Witt (Ber. 17, 78) obtained the 
 desired amidoazo-derivative with ease by carrying out the transformation of 
 the diazoamidoparatoluene in paratoluidine solution. 
 
 Zetter (Ber. H, 169) states that phenanthrene gives different bromo- 
 derivatives according as the action takes place in ether or in carbon disul- 
 phide solution. Pinner (Ann. 179, 68) made bromine substitution products 
 from aldehyde by using acetic ether as the solvent. He found that with 
 carbon disulphide and carbon tetrachloride no definite derivatives could be 
 isolated. 
 
 In making allyl cyanide from allyl iodide and potassium cyanide Rinne 
 found (Ber. 6, 389) that when ethyl alcohol was used for dilution a 
 compound of allyl cyanide with the solvent was formed, having the formula 
 C 3 H 5 CN + C 2 H 6 O, which boiled without decomposition at 173- 174. 
 When he used allyl alcohol he got a substance having the composition 
 represented by the formula C 3 H 5 CN + 3C 3 H 6 O. 
 
 In addition to the liquids used in extracting, many others are 
 employed for diluting. Glacial acetic acid, for example, is used very 
 commonly indeed. Xylene is less often employed. BischofF (Ber. 
 24, 1,046) added 120 cc. of xylene to 90 grams of methylmalonic 
 ether, and then warmed the mixture with 11*5 grams of sodium, 
 thus obtaining the sodium salt. Briihl (Ber. 24, 3,378) had re- 
 course to the same medium after he had found that the action of 
 sodium on borneol was incomplete in ether or toluene solution. 
 The same investigator (Ber. 25, 1,873) diluted /3-methylamido- 
 crotonanilide with benzoic ether, when attempting to insert a 
 benzoyl group by shaking with caustic soda and benzoyl chloride. 
 
 In endeavouring to condense chloral with derivatives of aniline, 
 when chloral hydrate was applied, almost no result was obtained, 
 but when chloral diluted with phenol was used the yield was 
 almost quantitative. For example (Ger. Pat. 61,551), 14 parts 
 of chloral were mixed with 9 parts of phenol, and 12 parts of 
 dimethylaniline were allowed to flow into the mixture. After 
 twenty-four hours a large amount of dimethyl-/-amidophenyloxy- 
 trichlorethane crystallised out (Ger. Pat. 49,844). Glycerol, 
 dimethylaniline, and naphthylamine were used in the same way. 
 
60 EXTRACTION . [CH. vi 
 
 The dilution of liquids and solids with Sand, Talc, Salt (Ber. 
 25, 3,031), c., is no longer in favour. 
 
 In this connection, a discovery of Heusler's (Ann. 260, 228) is 
 worth mentioning. After having tried the use of sand during the 
 decomposition of diazoamido-compounds to prevent explosion, he 
 found that liquid paraffin was much more convenient. When 
 diazoamidobenzene, or any of its homologues, is mixed with eight 
 or ten times its weight of this substance, the diazo-body dissolves 
 on warming, and a quiet evolution of nitrogen takes place as the 
 heating continues. 
 
 It is frequently the case that solutions of inorganic substances are 
 added to alcoholic solutions of organic bodies for the purpose of 
 bringing about chemical action. As the use of solutions of the 
 former in water generally gives poor results, it is advisable to select, 
 where possible, salts which are soluble in alcohol. For bromide 
 and iodide of potassium, the corresponding salts of sodium are pre- 
 ferably used, as they dissolve easily in alcohol. Tscherniac (Ber. 16, 
 348) suggests the use of sulphocyanate of barium in place of the 
 potassium compound. Cupric chloride, lead chloride, and lead 
 acetate, are all soluble in alcohol. Gabriel (Ber. 24, 1,112) puri- 
 fied ethylmercaptophthalimide by mixing its solution in hot alcohol 
 with a similar solution of acetate of lead, to which a few drops of 
 acetic acid had been added to remove the milkiness. The insolu- 
 ble lead compound of the mercaptan was precipitated. No com- 
 pound which fulfils the required condition is known which can take 
 the place of potassium cyanide ; possibly, the little known cyanide 
 of calcium is such a substance. Cyanide of potassium is freely 
 soluble, however, in 60 per cent, alcohol as well as in a mixture of 
 2 parts of alcohol and I part of concentrated hydrocyanic acid. 
 But alcohol precipitates it from concentrated solutions in water. In 
 all cases the so-called 100 per cent, potassium cyanide should be 
 used, as the commercial article contains cyanate, whose presence 
 gives rise to undesirable by-products. 
 
CHAPTER VII 
 
 FILTRATION 
 
 FILTRATION is carried out in the same way as in inorganic 
 chemistry. Ordinary filter paper is generally employed, but 
 asbestos and other substances are frequently used. 
 
 The material for asbestos filters is prepared, according to Casa- 
 major's receipt- (Ar. Pharm. 1883, 377), as follows : The asbestos 
 is rubbed through a sieve with coarse meshes, and the material 
 which has passed through is washed with a stream of water in a 
 sieve with finer meshes to remove the smallest particles. It is then 
 boiled with strong hydrochloric acid, thoroughly washed in a funnel 
 containing a perforated platinum cone, and ignited in a porcelain 
 crucible. 
 
 In organic work, however, many precipitates occur in such large 
 quantities and of such a nature that they cannot be separated by 
 decantation or with the help of the filter pump. 
 
 In such cases square pieces of cheese-cloth with a wide hem on 
 all four sides are frequently used. Four strong pieces of string pass 
 through the hems and hang free at the four corners. A frame is 
 made of four pieces of wood somewhat longer than the sides of the 
 cloth and united into a square in such a way that the ends project 
 cross-fashion at the corners. The cloth is moistened before use to 
 contract the meshes and prevent the precipitate running through, 
 and bound by means of the strings to the frame so that it hangs 
 down loosely in the middle. A vessel under the centre of the cloth, 
 as it is distended by the weight of the precipitate, serves to catch 
 the filtrate. The first portion to run through is usually milky, and 
 is returned to the cloth. The filtration may be accelerated by stir- 
 ring the precipitate. 
 
62 FILTRATION [CH. vn 
 
 The cloths will not last long if not carefully washed after use. 
 
 When the liquid cannot be made clear by filtration, lead acetate 
 or subacetate, or if the liquid is neutral or alkaline, barium chloride 
 and sodium carbonate (Z. physiolog. Ch. 9, 493) may be added 
 previously to assist in carrying down the precipitate. 
 
 Simple filtration has no effect in the case of putrefying liquids, as 
 the bacteria pass through the pores of the paper and render the 
 filtrate turbid. A clear filtrate may be obtained, according to a 
 suggestion of Jolles (Z. analyt. Ch. 29, 406), by shaking the liquid 
 violently with tripoli. 
 
 By this means it is possible to clarify urine, which is cloudy from the 
 presence of bacteria, and recognise the presence of traces of albumin in the 
 filtrate by a very slight precipitate which appears on boiling, and does not 
 redissolve on the addition of a drop of acetic acid. The tripoli takes up a 
 small amount of albumin, however, just as charcoal retains a little grape 
 sugar. It is hardly necessary to say that Chamberland's " bougies," Berkefeld 
 filters, and similar devices employed in hygienic laboratories, yield filtrates 
 free from bacteria, but they are not ordinarily used in chemical laboratories. 
 
 Filter-presses of size suitable for laboratory use are now obtainable. The 
 method of working the press depends however on its construction. 
 
 In concluding this chapter it may be worth mentioning that, except 
 where the use of distilled water is necessary, a very weak solution of a salt is 
 often preferable for washing a precipitate, because where the former is used 
 the solid is apt to be carried, to a small extent, through the filter. For 
 example, Baeyer (Ann. 245, 139) found that, in an oxidation by means 
 of potassium permanganate in alkaline solution, the precipitated manganese 
 dioxide was carried through the cloth filter by water in washing. On sub- 
 stituting water containing a little soda for distilled water this trouble was 
 avoided. It is well known that clay will settle rapidly in river water 
 while distilled water containing the same substance will remain cloudy for 
 days. The principle is doubtless the same in both cases. 
 
CHAPTER VIII 
 
 DETERMINATION OF MELTING-POINTS 
 
 1. Comparison of Methods. We owe the first thorough investi- 
 gation and comparison of the various methods of determining the 
 melting-point to Landolt (Z. physik. Ch. 4, 357). The methods 
 he examined were : 
 
 Melting and resolidification of large quantities, with the thermo- 
 meter immersed in the substance. 
 
 Heating the substance in capillary tubes, and tubes of the form 
 suggested by Piccard (Ber. 8, 687), in liquid or air baths. 
 
 Lowe's method (Z. analyt. Ch. 11, 211), by covering a platinum wire 
 with the substance and warming it in a bath of mercury till the 
 melting of the non-conducting film permits an electric current to 
 pass. Christomanos (Ber. 23, 1,093) nas described a plan similar 
 to this. 
 
 Landolt found that the first was the only thoroughly reliable 
 method, and always led to constant results. About 20 gr. of the 
 substance must be employed, however. When large quantities are 
 used, the temperature of resolidification is easier to observe than 
 that of melting. 
 
 To illustrate by means of a particular case, that of anthracene may be 
 described. 1 8 grams of powdered anthracene were placed in a test tube of 
 30 mm. diameter and 175 mm. long, and this tube was surrounded by a 
 larger one of about 40 mm. diameter. The whole was let down into a 
 glass cylinder open at both ends, beneath which a lamp with annular flame 
 was placed. The inner tube was closed with a cork through which the 
 thermometer and a wire for stirring passed. The stirrer was operated by 
 the hand as soon as melting began. Melting began at 196 and was com- 
 plete at 197. Resolidification began at 196*2, but remained incomplete 
 at a low temperature. 
 
64 DETERMINATION OF MELTING-POINTS [CH. vin 
 
 Melting-point determinations in capillary tubes of various forms 
 show inaccuracy of different degrees for different substances. 
 Sometimes the observed temperatures agree with the correct 
 figures, but usually they are too high, especially when narrow tubes 
 are used. 
 
 The results by the electrical method are also irregular and are 
 frequently too high. 
 
 2, Heating in a Capillary Tube. This method is the one 
 usually employed in the laboratory, because very little of the sub- 
 stance is used for the determination in this way. 
 
 Reissert (Ber. 23 2,241), who has studied the degree of accuracy attain- 
 able, states that the point when melting begins is the real melting-point, 
 for the interior of the tube is always cooler than its walls, and the particles 
 in contact with the latter melt nearest to the correct temperature. It is 
 therefore often advisable, after charging the tube, to shake out the contents 
 and notice when the particles which remain adhering to the sides melt. 
 
 A thin-walled capillary is chosen, charged with some of the sub- 
 stance and attached to the thermometer by means of a rubber ring 
 or platinum wire, so that the substance is close to the bulb. 
 
 The thermometer is suspended in a test tube, which is then filled 
 for 2 cm. of its height with concentrated sulphuric acid, or may be 
 left empty to serve as an air bath. The test tube is itself immersed 
 in a flask containing sulphuric acid. The flask is gradually warmed, 
 and as soon as the substance in the tube melts the temperature is 
 read. 
 
 The double bath, which was first suggested for this purpose by 
 Grabe (Ann. 238, 320), insures uniform heating of the acid or air 
 contained in the inner tube. When the thermometer is placed 
 directly in sulphuric acid in a flask or beaker, even if the acid is 
 stirred or shaken, the heating is not uniform and the result is 
 inaccurate. 
 
 If glycerol is used in place of sulphuric acid there is less chance 
 that the rubber ring will colour the fluid brown even at high tem- 
 peratures. It is better, however, to fasten the capillary by means 
 of a suitably bent loop of platinum wire. 
 
 Many chemists use glycerol in all cases instead of sulphuric 
 acid. For substances which melt below 100 C. water is frequently 
 employed. In the particular case of fats a capillary, open at both 
 ends, is dipped into the melted specimen, and, after solidification is 
 
3, 4l PECULIARITIES IN SOME BODIES 65 
 
 complete, is attached to a thermometer in the usual way. Both 
 are then placed in a vessel of water, and the temperature at which 
 the melted fat and the water rise in the capillary is taken. 
 
 3. Influence of Impurities. It is found that impurities almost 
 always depress the melting-point a relatively large amount. The 
 opposite hardly ever occurs, although Wallach (Ber. 25, 919) 
 mentions that impure specimens of camphor derivatives melt 
 higher than the same substances in the pure state. 
 
 4. Peculiarities in some Classes of Bodies, Some classes of 
 bodies show peculiarities in the matter of melting-point. Isomers, 
 for example, which have almost identical melting-points, be- 
 come widely separated in this respect when converted into acetyl 
 derivatives. Hydrazones (Ber. 23, 1,583) must be rapidly heated 
 to get constant observations. 
 
 The addition product of hydrochloric acid and turpentine, C 10 H 16 
 HC1, loses the acid so easily that to find its melting-point (Riban, 
 Bull. Ch. 24, 14) it had to be sealed up in a capillary filled with 
 hydrochloric acid gas. Chloranil sublimes completely below the 
 melting temperature, but Grabe (Ann. 263, 19), by sealing it up 
 completely in a capillary tube, 'ascertained that it melted at 290. 
 
CHAPTER IX 
 
 DETERMINATION OF MOLECULAR WEIGHTS 
 
 THREE methods are at present in use for determining the 
 molecular weights of organic bodies. 
 
 1. By measuring the vapour density. 
 
 2. By Raoult's method of measuring the lowering of the freezing- 
 point of a solution. 
 
 3. By Beckmann's method of measuring the elevation of the 
 boiling-point of a solution. 
 
 1. By Measuring the Vapour Density. The application of 
 
 measurement of the vapour density depends on the following con- 
 siderations. According to Boyle's and Charles's laws, all gases 
 behave equally in their relations to temperature and pressure. 
 This is explicable only on the hypothesis that equal volumes of all 
 gases contain equal numbers of molecules. Consequently the 
 molecular weight is found by comparing the specific weight of 
 the gas with that of hydrogen, which is selected as having the 
 smallest specific weight. Since, however, to the specific weight of 
 hydrogen is assigned the value one, while its molecular weight is 
 two, the molecule of hydrogen consisting of two atoms, the mole- 
 cular weights of other gases are obtained by multiplying their 
 specific weights by two. 
 
 The molecular weights of such substances as are permanent 
 gases at ordinary temperatures can be determined by direct weigh- 
 ing of a known volume. As, however, we have no balances capable 
 of weighing directly the vapours of slbStances which require an 
 elevation of temperature to bring them into this form, various 
 methods of determining the vapour density have been devised 
 
i] BY MEASURING THE VAPOUR DENSITY 67 
 
 where measurements are made, from which the desired information 
 can be obtained by calculation. 
 
 The plans suggested for carrying out the determination have been 
 numerous. Those recommended by Victor Meyer (Ber. 15, 2,777), to 
 whom we owe the most convenient methods, and whose opinion will 
 be regarded by all as decisive on this subject, are here described. 
 
 (1) Where the substance boils not higher than 260, and can 
 bear heating about 30 over its boiling-point, the method by ex- 
 pulsion of mercury devised by Victor Meyer is in every way suit- 
 able, whether we consider the accuracy of the results, the small 
 amount of mercury required (about 35 cc.), or the simplicity of the 
 operation. Of course the substance must be without action on 
 mercury. For heating, water, xylene, aniline, ethyl and amyl 
 benzoates and diphenylamine are used. 
 
 (2) Substances which cannot be vaporised without decom- 
 position under atmospheric pressure, or which will not bear heat- 
 ing above their boiling-points, may be examined by Hofmann's 
 method, provided they boil below 310 and do not attack mercury. 
 
 (3) For difficultly volatile substances, which boil between 260 
 and 420, and do not act on metals, Victor Meyer's method, depend- 
 ing on the expulsion of Wood's alloy, may be employed. 
 
 (4) To determine the vapour density where the substance boils 
 at a higher temperature than this, or where it attacks mercury, 
 Victor Meyer's air expulsion method must be used. 
 
 (5) Demuth and Victor Meyer (Ber. 23, 311) have described 
 yet another method which may be used where substances can only 
 be volatilised under diminished pressure. Other suggestions ap- 
 plicable to such cases have been made by Eykman (Ber. 22, 2,754), 
 and by Schall (Ber. 25, 1,491). 
 
 (i) Description of method where the quantity of mercury expelled 
 by the vaporised substance is measured (Ber. 10, 2,068). The 
 liquid whose vapour is to heat the substance, and of which only 
 50-60 cc. are necessary, is contained in a thin-walled glass vessel, 
 whose bulb has about 80 cc. capacity, and whose neck is 750 mm. 
 long by 42 mm. diameter. The frequent heating and cooling of 
 the bulb are apt to make it brittle, and it has a tendency to break 
 after repeated use. To avoid this Victor Meyer (Ber. 19, 1,862), 
 suggests the use of a cast-iron crucible whose margin is so made 
 that a glass cylinder rests in a groove, which is filled with mercury 
 to render the joint air-tight. Such a mantle will hardly ever break, 
 and, if it does, can easily be replaced. 
 
 F 2 
 
68 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 The construction of the thin glass vessel A, which contains the 
 substance under examination, may be understood from the figure 
 (Fig. 24). It holds about 35 cc., and the narrow limb has a 
 diameter of 6 mm. It is kept in a vertical position by a wire, and 
 
 --A 
 
 FIG. 24 
 
 hangs from a hook on a long and somewhat stouter wire, which is 
 supported by a stand. When the determination is carried out, a 
 known quantity of the substance is placed in the vessel and the 
 whole weighed correctly to ^ gram. In order to introduce the 
 substance conveniently, it is weighed out, if a liquid, in a small 
 
i BY MEASURING THE VAPOUR DENSITY 69 
 
 Hofmann tube. Following a suggestion of BriihFs (Ber. 9, 1,371), 
 Victor Meyer employed always the same size of tube and partially 
 filled it with mercury when a smaller quantity of the substance was 
 to be used. When the substance is solid, a small open tube 
 answers the purpose better. The glass vessel A is next completely 
 rilled up with mercury, and, after the capillary has been sealed, is 
 weighed once more and lowered into the outer tube by the wire. 
 
 The liquid is now heated to boiling. When the jacket contains 
 water, some of it will escape uncondensed, but in the case of aniline 
 and other substances of high boiling-point the vapour will only rise 
 a short distance above the vessel containing the substance. After 
 mercury is no longer expelled, the vessel is drawn out again, and, 
 when cold, is weighed. The height of the barometer and the 
 original temperature of the mercury, which will be that of the air, 
 being known, it remains to measure the pressure which the mer- 
 cury column in the narrow limb of the vessel exercised. The 
 capillary is opened, and by inclining the vessel the mercury is 
 brought up to the top of the narrow limb, and a mark is made 
 showing the level of the mercury in the wide limb. The difference 
 in height between this point and the top of the narrow limb at the 
 temperature of the air is measured, and is added to the reading of 
 the barometer to find the total pressure. It is necessary finally to 
 determine the volume of the Hofmann tube by measuring the 
 weight of mercury which it will hold. The vessel A may be used 
 repeatedly if the capillary is preserved. 
 
 The result is calculated by means of the formula : 
 
 S(i +0-00366T) X 7988000 
 d = - 
 
 '(P+p-s)[(a+q)|i+o-oooo303(T-t)^-r|T+o-oooi8(T-t)|](i+o'oooi8t) 
 
 where S = Weight of substance taken, 
 
 T = Temperature of vapour-mantle, 
 t = Temperature of the air, 
 P = Barometric pressure reduced to o C., 
 p = Height of mercury column in the vessel, 
 s = Tension of mercury vapour at temperature T, 
 a = Weight of mercury first taken, 
 q = Weight of mercury which the little tube will hold, 
 r = Weight of mercury remaining in the vessel after the 
 heating. 
 
 0*0000303 is the coefficient of expansion of glass, and 0*00018 that 
 
70 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 of mercury. (For temperatures above 240 C. the value 0*00019 must 
 be used.) 
 
 The temperature of the vapour-mantle does not require to be 
 determined, as the boiling-points of the liquids used are known. 
 Meyer states that for amyl benzoate the temperature is 253 C., and 
 for diphenylamine 290 C. The difference between these values and 
 the values of the boiling-points usually given is due to the fact that 
 here these substances are mixed with mercury while boiling. 
 
 (2) Description of Hofmanrfs Method (Ber. 1, 198, and 9, 1,304). 
 A tube about I metre in length is sealed at one end, filled with 
 mercury, and inverted in a trough. The mercury descends in the 
 tube, leaving a vacuum about 25 cm. long, and the height of the 
 mercury column above the level of the free surface is measured, 
 giving the barometric reading. It is essential that the tube and the 
 mercury should be perfectly clean 1 and dry. One of Hofmann's 
 small stoppered glass vessels is next filled with a known quantity 
 of the substance, and is put into the tube, which is then enclosed 
 in the mantle. The vapour of the boiling liquid enters at the 
 bottom (Fig. 25), and whatever part condenses flows back into the 
 flask. A part will also escape as vapour at the top. As the sub- 
 stance becomes volatilised the level of the mercury is depressed. 
 When the column has become stationary, a cathetometer is set at 
 the level corresponding to the height of the column, and when the 
 mantle and tube are cold the former is removed and a strip of 
 paper is pasted on the tube at the level indicated by the catheto- 
 meter. In this way the volume which the vapour occupied during 
 the experiment is registered. To ascertain what this volume was, 
 the tube is afterwards filled with mercury up to the mark, and this 
 quantity weighed to within o'5 grams. The volume in cubic centi- 
 metres is obtained by dividing this by the specific gravity of 
 mercury. 
 
 In addition to the barometric height at the beginning of the 
 experiment, it is necessary to measure the height of the mercury 
 when the column had descended to the point at which it became 
 stationary. 
 
 The measured volume which the vapour occupied is reduced to 
 o and 760 mm. pressure. This correction is included in the follow- 
 ing formula. The density is given in terms of hydrogen as unity. 
 
 1 Mercury is best purified by distillation in vacua in the glass apparatus 
 devised by Weinhold, which requires little attention and yields about I kilo- 
 gram per hour. 
 
i] BY MEASURING THE VAPOUR DENSITY 71 
 
 oJfiLo 
 
 FIG. 25. 
 
72 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 ~ Vxo-ooi2934XB 
 
 B = - _ / b> b " 
 
 ~ i +O-CQOI 8/~ Vi+o-oooi8/" X i+o-oooi8/ + 
 
 where Devalue of the density sought, 
 V = volume of the vapour at /, 
 /= temperature of the air, 
 / = temperature of the vapour-mantle, 
 /'= temperature of the mercury column not heated by the 
 
 vapour, 
 
 p = weight of substance taken, 
 b = height of the barometer reduced to o, 
 b'= height of the column below the vapour-mantle, 
 b" = height of the column within the heated vapour at the 
 
 temperature /, 
 s= vapour tension of mercury vapour at /. 
 
 Vapott? Tension of Mercury Vapour in Millimetres (Regnaulf). 
 
 Temp. 
 
 Tension, j Temp. 
 
 Tension, j Temp. 
 
 Tension. 
 
 100 . 
 
 . . 075 
 
 180. 
 
 . . iroo 
 
 260 . 
 
 9673 
 
 120 
 
 1*53 
 
 200 . 
 
 . . 19-90 280 . 
 
 I55'I7 
 
 I40 
 
 .3-06 
 
 220. 
 
 3470 
 
 300. 
 
 . . 242-15 
 
 160 
 
 . . 5-00 
 
 240 . 
 
 . . 58-82 
 
 320. 
 
 .36873 
 
 (3) Description of method where the quantity of Woods alloy 
 expelled by the vaporised substance is measured : for use in the case 
 of substances which are volatilised without decomposition at 
 444"2 (boiling-point of sulphur), and do not act on Wood's alloy 
 (Ber. 9, 1,220). 
 
 The substance is weighed out in a small vessel like that in 
 Fig. 26, which shows the natural size. The vessel is selected 
 according to the expected molecular weight, where this is small a 
 smaller vessel being taken, so that the volume of vapour produced 
 may always be smaller than the volume of the bulb. The vessel is 
 slightly bent to enable it to pass easily into the bulb. 
 
 To fill the small vessel, which has been previously weighed, it is 
 bound to a platinum wire, and is pressed beneath the surface of a 
 quantity of the melted substance contained in a narrow test tube. 
 Any air bubbles which may remain in it are removed by shaking, 
 or warming, or by touching them with a fine capillary tube. The 
 vessel is then drawn out, and when the substance has solidified is 
 
1] 
 
 BY MEASURING THE VAPOUR DENSITY 
 
 73 
 
 released from the wire, wiped with a silk cloth, and weighed again. 
 If there is too little of the substance for this method of filling, it 
 may be melted in the vessel itself. A stoppered tube is used for 
 liquids. For solids no stopper is required, as they adhere firmly to 
 the vessel and there is no danger of any being lost. The bulb 
 apparatus is very carefully cleaned before the substance is 
 introduced. 
 
 After the small vessel containing the substance has been intro- 
 duced, the apparatus is weighed correctly to o'i gram. It is then 
 
 ..*, / 
 
 FIG. 26. 
 
 held by a clamp attached to the limb A, while the Wood's alloy is 
 poured in. The alloy is brought to a temperature of about 100 
 before being used. During the filling the apparatus must be so 
 inclined that the vessel containing the substance passes up into the 
 bulb and not into the other limb. 
 
 The alloy, if it has not previously been used, must be boiled 
 several times, first with benzene and then with alcohol, and is finally 
 heated on the water bath with constant stirring till dry. If it has 
 been used for similar determinations before, it is simply extracted 
 
74 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 with alcohol and dried. It is best kept in a porcelain evaporating 
 dish, in which it is allowed to solidify, and preserved in a desiccator 
 to exclude moisture. When required for use it is melted on the 
 water bath, and heated by a small flame to I5o-i8o, to expel every 
 trace of moisture, and after it has cooled once more to about 100 
 is ready for use. Meyer suggests the wearing of a leathern glove 
 when handling the dish containing the melted alloy. 
 
 After the apparatus is filled with the alloy some bubbles of air 
 may remain attached to the sides. By judicious shaking and tap- 
 ping they are brought to the top and escape through the capillary 
 B. Small traces of air remaining do not appreciably influence the 
 determination. When the apparatus is finally filled the capillary is 
 sealed. In order that the apparatus may be just filled with alloy 
 at 100, it is now suspended in a beaker of boiling water by a wire 
 similar to that described later, but lacking the thinner wires for 
 binding it securely. A few drops of the metal will be expelled. 
 After a few minutes the apparatus is removed from the beaker, and 
 any water or protruding globule of metal is removed from the open 
 limb by means of a piece of filter paper. It is dried carefully, 
 weighed again correctly to o'l gram, and bound by means of thin 
 piano wire to a stout iron wire in the way shown in the figures. All 
 of these operations are as easy to carry out as if the apparatus were 
 filled with mercury. Before the second weighing the metal 
 solidifies. It must not be allowed to cool 
 completely, as it cracks the apparatus. This 
 does not happen, however, till it has stood 
 for about forty-five minutes. 
 
 The heating in sulphur vapour takes place 
 in a cast-iron crucible holding about 400 cc., 
 and containing 120-130 grams of sulphur. 
 The apparatus is hung in the middle of 
 the crucible, which is covered by a per- 
 forated lid, and heated by means of a 
 quadruple Bunsen burner. When the sul- 
 phur boils the vapour issues beneath the lid, 
 and burns in a large flame half a foot high. 
 The experiment must therefore be carried 
 out in a hood provided with good venti- 
 lation. 
 
 After about twenty-five minutes the flame is extinguished, the lid 
 removed, and the apparatus drawn out. The level of the metal in 
 
 FIG. 27. 
 
i] BY MEASURING THE VAPOUR DENSITY 75 
 
 the bulb is marked immediately by touching the glass with a little 
 sealing-wax adhering to the end of a glass rod. A permanent mark 
 remains which enables the observer, after the cooling and weighing 
 are accomplished, to measure the height of the column of alloy to 
 whose pressure the vapour of the substance was subjected. As the 
 specific gravity of the alloy at 444'2 is to that of mercury in the 
 ratio 2 : 3, the number of millimetres found is multiplied by two 
 thirds, and the result added to the barometric pressure. Before 
 weighing, the apparatus is carefully wiped with filter paper. 
 The density of the vapour is obtained from the formula : 
 
 8X14146000 
 
 D is the density, that of air being unity ; S is the weight of the 
 substance taken ; b is the weight of alloy taken, and a that of the 
 quantity expelled ; P is the barometric pressure, and p the height 
 of the column of alloy ; 0*036 represents the proportion of the alloy 
 lost through expansion. 
 
 As the metal is not attacked by sulphur, the portion extruded is 
 recovered by pouring off the sulphur before it solidifies, and the 
 bulb is broken to recover the alloy contained in it. The weighing 
 tube is cleaned with boiling nitric acid. 
 
 The Wood's alloy which Meyer used (Ber. 9, 1,217) consisted of 
 | bismuth (15 parts), lead (8 parts), tin (4 parts), and cadmium (3 
 C parts). It melts below 70, and can be as easily manipulated as 
 | mercury ; it is not attacked by most organic bodies in a state of 
 
 I vapour, and it can be very easily purified from substances which 
 become mixed with it in course of use. 
 (4) Description of method where the air expelled by the vaporised 
 substance is measured (Victor Meyer). 
 
 The apparatus (Fig. 28) consists of an inner tube like that in the 
 figure, of about 100 cc. capacity, closed at the top by a rubber 
 stopper, which is always pushed in to the same extent. This 
 stopper has been replaced by a stop-cock in later forms of the 
 apparatus. An outer tube contains the heated vapour-mantle, and 
 when a high temperature is required a metal bath can be substi- 
 tuted. A side tube a permits the escape of air driven forth by ex- 
 pansion. When the temperature has become constant and no more 
 air bubbles appear, a graduated glass tube filled with water is in- 
 verted over the end of the side tube, and the tube being opened 
 at d, the portion of the substance weighed out is dropped in, and 
 
76 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 the tube rapidly closed. The temperature being high enough, the 
 substance is volatilised, and a quantity of air corresponding to the 
 volume of the vapour is expelled into the graduated tube, where it 
 
 can be measured. In order that 
 the little vessel containing the 
 substance may not break the 
 tube, the bottom of the latter is 
 covered with sand or asbestos. 
 When the vaporisation is rapid 
 and the quantity of the sub- 
 stance is so small that only the 
 Lower part of the apparatus is 
 filled with its vapour, the error 
 owing to diffusion of the vapour 
 will be negligible. 
 
 The following points about 
 the apparatus deserve descrip- 
 tion. The side tube a is made 
 as small as possible. It is I mm. 
 in diameter and 140 mm. long. 
 The quantity of substance taken 
 must be such that its vapour will 
 fill less than a half of the bulb b. 
 This bulb is 200 mm. long, and 
 holds about 100 cc. It is at- 
 tached to a tube 600 mm. long, 
 and 4-6 mm. internal diameter. 
 The side tube a is connected 
 with the tube at a height of 
 500 mm. For temperatures up 
 to the boiling-point of diphenyl- 
 amine (310), a glass outer vessel 
 is used with a bulb of 80 cc. 
 capacity and a neck 520 mm. 
 long and 40 mm. in diameter. 
 The mantle is therefore the 
 same as that used for the first 
 method. The vapours employed 
 
 are water, xylene, aniline, ethyl benzoate, amyl benzoate,and diphenyl- 
 amine. Ladenburg (Ber. 21, 762) used anisol on one occasion, 
 These bodies do not require to be pure, as mixtures boiling under 
 
1] 
 
 BY MEASURING THE VAPOUR DENSITY 
 
 77 
 
 such conditions yield constant temperatures, and the exact tempera- 
 ture used does not enter into the calculation. 
 
 For temperatures above 310, iron tubes (Ber. 17, 1,335) made from 
 pieces of gas pipe welded up at the end, and containing anthracene (b.-p. 
 335), anthraquinone (b.-p. 368), and sulphur (b.-p. 444), are kept in 
 readiness. For still higher temperatures (518), an iron tube charged with 
 phosphorus pentasulphide l is employed. As this substance will not stand 
 long exposure to the air, it is prepared freshly each time it is needed by 
 melting together two parts of red phosphorus with five parts of sulphur. 
 For still higher temperatures a bath of molten lead can be used (Ber. ll t 
 2,255), hut this is seldom necessary in organic work. 
 
 In making a determination, the inner tube, whose volume does 
 not require to be known, is introduced into the mantle. As 
 was mentioned above, the bottom of the inner bulb should be 
 covered with a layer of asbestos, sand, or mercury, to break the fall 
 of the vessel containing the substance. The end of the side tube 
 opens beneath the surface of the water in a small 
 trough. As soon as the temperature has become 
 constant, the substance is dropped in and the 
 graduated tube is placed over the end of the side 
 tube at the same instant to catch the expelled air. 
 
 If the apparatus is provided with the arrange- 
 ment suggested by Mahlmann (Z. physik. Ch. 1, 
 157), which is shown in Fig. 28, the vessel con- 
 taining the substance is allowed to drop into the 
 tube from the small chamber at the top by simply 
 turning a stop-cock provided with a large passage 
 way. Even if the tube has to be closed by an 
 ordinary rubber stopper, however, the withdrawal 
 of the latter to introduce the substance may be 
 avoided by using the arrangement in Fig. 29 
 (Noyes). A glass tube closed at one end passes 
 through the stopper, and in it is placed the tube 
 containing the weighed portion of the substance. 
 The latter is supported by a bent wire in such a 
 way that it can be released at the proper moment 
 and allowed to drop into the bulb. 
 
 After about fifteen seconds the substance begins to volatilise, and 
 when no more bubbles issue from the tube the stopper is removed, 
 
 1 The first application of phosphorus pentasulphide for this purpose was 
 made by Hittorf (Pogg. Ann. 126, 193)- 
 
78 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 and the graduated cylinder is placed in a deeper vessel, so that the 
 water reaches the same level without and within. After a little 
 time the volume is read off and the temperature of the water and 
 height of the barometer are noted. 
 
 n - c (i+o'Q03665*)X 587780 
 (B-- ze/)V 
 
 where S = the weight of substance used, 
 
 B = the height of the barometer reduced to o, 
 w = the vapour tension of water vapour at the temperature /, 
 V = the measured volume of air, 
 /= temperature of the water or of the air. 
 
 In many cases solids can be used in the form of little cylinders instead of 
 being enclosed in small vessels of glass. When the substance is fusible, 
 such cylinders are very easily made (Ber. 23, 3 J 3)- The substance is melted 
 in a dish and drawn up into a short tube about 2. mm. in diameter. When 
 it is cold and once more solid, it will adhere only partially to the tube. 
 After gentle heating in a small flame it may be pushed out of the tube by a 
 wire without its shape being destroyed. Victor Meyer recommends the 
 employment of substances in this form very strongly, as the weighing out 
 and introduction into the apparatus are greatly simplified by their use. 
 More than O'l gram should not be employed so that the vapour may 
 always occupy less than 50 cc. 
 
 When the substance is acted on by oxygen, the apparatus is filled with 
 dry nitrogen before the experiment by leading a stream of the gas through 
 a tube which passes to the bottom of the apparatus. Better still, a form of 
 the apparatus shown in the figure may be used where a tube for the admis- 
 sion of the nitrogen is fused into the bottom of the bulb (Ber. 21, 688). 
 
 Meyer made the nitrogen by Gibbs and Bottger's process 1 by boiling a 
 solution of one part potassium bichromate, one part ammonium nitrate, and 
 one part commercial sodium nitrite in three parts of water. He found it 
 advisable to pass the gas over red-hot copper to remove all traces of 
 oxygen. 
 
 (5) Description of method for determination of the vapour density 
 of a substance at a temperature below its boiling-point (Demuth and 
 Meyer, Ber. 23, 311). 
 
 The method of Hofmann already described attains the same end 
 as the present method, and, on account of the accurate results which 
 it yields, will always be a favourite when the properties of the 
 substance permit its use. 
 
 1 Jahresb. d. phys. Vereins zu Frankfurt a. M. 1876-77, 24. 
 
i] BY MEASURING THE VAPOUR DENSITY 79 
 
 Since Victor Meyer's method by expulsion of air was invented, 
 chemists have striven to increase the simplicity and convenience of 
 the operation, yet the methods introduced never quite equalled 
 Hofmann's in these respects. The first hints of this fifth method 
 are to be found in the report of the sixty-second meeting of the 
 " Gesellschaft deutscher Naturforscher " (corresponding- to the 
 " British Association"), at Heidelberg, in 1889. The idea rests on 
 the fact that in the ordinary determinations by air expulsion, a 
 certain amount of mixing of the vapour with the air above it always 
 takes place, and therefore a reduction of the pressure of the vapour 
 considered by itself. If the vapour diffuses sufficiently rapidly, this 
 reduction may be equivalent in effect to the action of an air pump, 
 or to the mercury column in the Hofmann method. When the 
 vessel is filled with air, indeed, this effect does not come into play 
 appreciably, but with an atmosphere of hydrogen, the more rapid 
 diffusing power of this gas leads to a remarkable lowering of the 
 temperature necessary for volatilising the substance. 
 
 When used for this method the bulb has a capacity of about 100 
 cc. and a diameter of 3 cm. The bottom is rather strong and 
 somewhat flat in form so as to facilitate the spreading out of the 
 substance and its evaporation. The stem is not more than 4-5 mm. 
 wide, The amount of the substance must be taken so that the 
 amount of expelled gas may be between 9 cc. and 1 1 cc. 
 
 The introduction of the substance in suitable form may present 
 some difficulties. If it can be cast in small cylinders it will melt 
 and spread itself on the floor of the bulb without further trouble. 
 In the case of liquids some kind of vessel is essential. A small, very 
 thin tube made of Wood's alloy, as it melts on reaching the hot 
 bulb, is very serviceable. The necessary lightness may be attained 
 by filing the outside of the vessel down. In any case it should be 
 dropped repeatedly into the tube before the experiment so as to be 
 sure that the bulb is strong enough to withstand the impact. If it 
 chance that the substance whose examination is in hand acts chemi- 
 cally on the alloy, or if the temperature is below its melting-point, 
 then recourse must be had to a wide, loosely stoppered glass tube. 
 
 It must be mentioned that asbestos or sand cannot be used for 
 protecting the bottom of the bulb, as they soak up the melted sub- 
 stance and prevent its volatilisation. Demuth and Meyer used small 
 spirals of platinum wire in a few cases, but with sufficiently thin 
 vessels protection is seldom necessary. Where it is admissible a 
 thin layer of mercury is sometimes useful. 
 
8o DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 When this method is used, the same values for the vapour density 
 are obtained, at temperatures considerably below the boiling-point 
 of the substance, as were formerly obtained by heating several 
 degrees above it. For example, xylene gave the value 373 40 
 below its boiling-point, and naphthalene 4'65 35 below its boiling- 
 point, where the calculated values were 3'68 and 4*44 respectively. 
 These values are calculated for air and not hydrogen as unity. 
 
 In calculating, the same formula as before is employed. 
 
 Schall (Ber. 25, 1,491) and Eykman (Ber. 22, 2,754) have like- 
 wise suggested methods for determining the vapour density under 
 diminished pressure, which can be used instead of Hofmann's or 
 Demuth and Meyer's. 
 
 2. Raoult's Method. The measurement of the lowering of the 
 freezing-point of a solvent has only come into use during the past 
 few years as a means of determining the molecular weight. But 
 the fact that the vapour density method can only be applied when 
 the substance can be volatilised without decomposition, while the 
 new method is applicable to almost all substances of which suitable 
 solutions can be prepared, has led to its rapid introduction in every 
 laboratory. 
 
 It was found by De Coppet and Raoult (Ann. Ch. Ph. [5], 28, 
 J 33 5 [6], 2, 115), that when a known amount of a substance was 
 dissolved in a measured quantity of a solvent (such as benzene 
 or glacial acetic acid), the lowering of the freezing-point of the 
 latter produced by the presence of the former was a function of the 
 molecular weight of the dissolved substance. 
 
 Various forms of apparatus have been devised for carrying out 
 the determination. The principal ones were those of Auwers (Ber. 
 .21, 701), Hollemann (Ber. 21, 860), Hentschel (Z. physik. Ch. 
 2, 306), Beckmann (Z. physik. Ch. 2, 638), Eykman (Z. physik. Ch. 
 2, 964; 3, 113 and 203; 4, 497), and von Klobukow (Z. physik. 
 Ch. 4, 10). 
 
 Beckmanrts apparatus is widely used and is very convenient. 
 Its construction is shown in Fig. 30. 
 
 The tube A holds the solution to be frozen, and has a capacity of 
 about 25 cc. up to the side tube. A delicate thermometer graduated 
 to hundredths of a degree passes through the rubber stopper of this 
 tube, as does also a stout platinum wire for stirring. This tube is 
 placed in a somewhat wider tube B so as to be surrounded by an 
 air jacket. The whole is' suspended in a wide battery jar C, which 
 
RAOULT'S METHOD 
 
 81 
 
 contains cold water. or a freezing mixture, the temperature of which 
 is selected so as to be from 2 to 5 below the freezing-point of the 
 solvent. A cover and stirrer are 
 provided for this outer jar. 
 
 The inner tube, containing a 
 few clippings of platinum foil, is 
 weighed charged with about 15 
 grams of the solvent, and weighed 
 again. The apparatus is then put 
 together, and the freezing-point de- 
 termined. 
 
 In practice the temperature has 
 always to be carried below the 
 actual freezing temperature, before 
 the formation of crystals begins. 
 The platinum is added, and con- 
 stant stirring is kept up in order 
 that this over-cooling may be as 
 small as possible. The crystals 
 should always appear in the liquid. 
 If the over-cooling has been ex- 
 cessive, a thick crust may be formed 
 on the side of the tube and, on 
 account of the concentration of the 
 rest of the solution, too low a 
 temperature will be read off. 
 When crystallisation begins the 
 temperature rises to the real 
 freezing-point, and when the mer- 
 cury column has come to rest 
 the reading is made. The frozen 
 material should then be remelted, 
 and the operation repeated as a 
 check on the first result. This 
 precaution should be observed all 
 through the determination. 
 
 The thermometer demands spe- 
 cial description. If it were of the 
 
 common construction, it would require to be extremely long and 
 unhandy so as to be applicable with different solvents, such as 
 water, benzene, and acetic acid, and still be divided into hundredths 
 
 G 
 
 FIG. 30. 
 
82 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 of a degree. The only alternative would be to employ a different 
 thermometer for each solvent. For the present use, however, it 
 does not require to show actual temperatures but only differences 
 of temperature. The scale is therefore constructed to show only six 
 degrees. The capillary is provided with a small reservoir for mer- 
 cury at the top, and the instrument is filled in such a way that at o 
 the mercury almost reaches the top of the scale. If it is to be used 
 in the neighbourhood of a higher temperature say 16 the instru- 
 ment is warmed to 18 or so, and the mercury which has flowed 
 into the reservoir is separated from the column by cautious tapping 
 with the finger. Slight cooling will now bring the end of the 
 column back on to the scale, and temperatures between 11 and 17 
 may be read off. A similar adjustment can be made for any desired 
 temperature. 
 
 A known quantity of the substance, which is contained in a 
 weighing tube, or in the case of a liquid, in a pyknometer, is intro- 
 duced through the side tube ; the amount to be taken is regulated by 
 the depression which it will produce. A depression of less than 0*2 
 is of no service, as the experimental errors will render the result 
 unreliable. With a depression of from i to 2 the error will not 
 be more than one or two per cent. It is desirable also to make 
 several observations at different concentrations ; a suitable series 
 may be obtained by adding the substance in three or four portions, 
 weighing the tube and determining the freezing-point after each 
 addition, in such a way that depressions ranging from 0*2 to 2 are 
 obtained. Dissociation will sometimes be brought to light in 
 this way. 
 
 The molecular weight is calculated from the formula : 
 
 where M is the molecular weight, c the constant for the liquid, 
 / the percentage of the substance contained in the solvent, and / 
 the depression of the freezing-point in degrees Centigrade. 
 
 The following table gives the values of the constant for the sol- 
 vents most commonly used : 
 
 Benzene 49 
 
 Glacial acetic acid . . 39 
 
 Nitrobenzene 71 
 
 Phenol 74 
 
 Water 18-9 
 
 Formic acid 27*7 
 
 Diphenylamine ..... 88 
 
 Naphthalene 69 
 
 Naphthylamine .... 78 
 
 Palmitic acid 44 
 
 ^-Toluidine 51 
 
 Thymol 92 
 
3] BECKMANN'S METHOD 83 
 
 A solvent must be chosen which will have no chemical action on 
 the substance under examination. 
 
 The values obtained are never quite accurate, because the mole- 
 cular depressions are not quite constant for any solvent ; but taken 
 with the results of analysis they always make it abundantly clear 
 what formula must be selected. For example, Baumann and 
 Fromm (Ber. 24, 3,595) proved by its help that the polymer of thio- 
 furfurol possessed a molecular weight eighteen or twenty times as 
 great as the empirical formula indicated. 
 
 Eykman's apparatus (Z. physik. Ch. 2, 964) is much simpler 
 than Beckmann's, but it gives less accurate results ; it has the 
 advantage, however, of working equally easily with solvents of high 
 melting-points, such as phenol, thymol, naphthalene, and diphenyl- 
 amine ; with Beckmann's apparatus a beaker of warm water must 
 be substituted for the jar in such cases. 
 
 Fabinyi (Z. physik. Ch. 3, 38) uses the depression in the melt- 
 ing-point of a well-known substance, such as naphthalene, which is 
 produced by the addition of a known proportion of the substance 
 under investigation, for calculating the molecular weight of the 
 latter. A minute amount of the substance suffices for the deter- 
 mination. 
 
 3. Beckmann's Method by Measuring the Elevation of the 
 Boiling-Point of a Solvent. Using an idea suggested by Raoult's 
 work, Beckmann has worked out a method by which the elevation 
 in the boiling-point of a liquid, produced by dissolving any substance 
 in it, can be used for the determination of the molecular weight of 
 the substance. He has devised an apparatus (Z. physik. Ch. 8, 
 223), 1 which renders the measurement of the rise both simple and 
 exact, as well as comparatively rapid. When the solvent has been 
 boiling so long that the mercury column is steady, the temperature 
 is read off, the substance is added, and another reading is made. 
 The addition usually takes place in six or eight portions, and the 
 thermometer is observed after each addition ; the molecular weight 
 is deduced from the data almost as easily as in the case of the 
 freezing-point method. 
 
 Construction and charging of the apparatus? The solution is 
 
 1 Cf. ibid. 4, 543, and 6 437- 
 
 2 This apparatus, as well as that used for freezing-point determinations, or 
 any separate parts of either, can be obtained from F. O. R. Gotze, Leipzig. 
 
 G 2 
 
84 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 boiled in the tube A, which is of the same shape as that used for 
 freezing-point determinations, and has a small piece of platinum 
 wire fused into the bottom to render the boiling steady. It is two 
 
 and a half centimetres in 
 diameter, and is filled for 
 three and a half to four 
 centimetres of its height 
 with garnets or glass 
 beads. The thermometer, 
 which is of the construc- 
 tion described in the last 
 section, passes through 
 a cork in the tube, and 
 has its bulb partially em- 
 bedded in the garnets. 
 This tube is surrounded 
 by the vapour jacket B, 
 whose construction can 
 be best understood from 
 the figure. The jacket is 
 separated- from the tube 
 by a sheath of asbestos 
 paper, , at the bottom, 
 and a little common as- 
 bestos at the top ; it is 
 charged with about 20 cc. 
 of the solvent and some 
 chips of porous earthen- 
 ware, to promote regular 
 boiling. The vessels are 
 provided with the con- 
 densing tubes K t and K 2 
 for liquids boiling above 
 60 ; for low-boiling li- 
 quids, such as carbon 
 
 disulphide and ether, short light Liebig's condensers take their 
 place. Loosely filled chloride of calcium tubes may be attached 
 to these, when the contents of the vessels are hygroscopic. 
 
 Heating. The heat is distributed by means of an asbestos box 
 C, of peculiar construction, which rests on a tripod stand. Two 
 
 nvn 
 
 1 Vi A 
 
 FIG. 31. 
 
3 ] BECKMANN'S METHOD 85 
 
 small Bunsen flames 1 are arranged corner-wise, so that their heat 
 impinges on an annular opening in the asbestos sheet covered with 
 wire gauze ; this is arched over by a ring of asbestos d, which 
 directs the heated air against the jacket. The rings, h x and h 2 , are 
 likewise made of asbestos board, and protect the central tube from 
 the direct heat of the flames. Of the solvents mentioned below, 
 water, on account of its high specific and latent heats, is the only 
 one which requires to be heated directly by a third flame ; in all 
 other cases the heat from the vapour jacket suffices to keep the 
 solvent in ebullition. 
 
 The rate of boiling can be judged very easily by the heating of the 
 condenser tube and by the number of drops per minute which return 
 to the liquid ; the heating should be arranged so that one drop falls 
 every five to fifteen seconds, according to the volatility of the solvent. 
 
 Boiling-point of the solvent. As in the case of the freezing-point 
 method, it is not necessary to know the actual temperature of the 
 boiling-point. What is wanted is an exact datum from which to 
 measure the rise ; the thermometer, divided into hundredths of a 
 degree described above, is therefore used here also. 
 
 As small variations occur in the readings of a thermometer when 
 it is cooled and heated alternately, it is advisable to take the 
 reading always after a rise in the mercury column ; as an addi- 
 tional precaution the stem should be tapped with the finger before 
 reading. 
 
 When the present form of the apparatus is used, the thermometer 
 shows a constant temperature much more quickly than was the 
 case with the older form ; the constancy is recognised by the fact 
 that two readings taken five minutes apart do not differ by more 
 than one or two thousandths of a degree ; this does not occur till 
 after the liquid has been boiling from thirty to sixty minutes. 
 
 Care should be taken that the chloride of calcium tube does not 
 prevent rapid equalisation of pressure through being partially 
 plugged up, on account of having absorbed much moisture, or for 
 any other cause. 
 
 Introduction of the substance. The substance is introduced 
 through the side tube, the condenser being removed and the boiling 
 momentarily interrupted for the purpose. 
 
 For the introduction of liquids, pyknometers, similar to those used 
 
 1 For information about this method and particularly the regulation of 
 the heating, see Sakuri, J. Ch. Soc. 61> 995 
 
86 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 in the freezing-point method, are employed. They are provided with 
 a long capillary (Fig. 32), so that when ether or carbon disulphide 
 is used, they may reach down to the tube containing the solvent 
 through the condenser tube, without the removal of the condenser 
 itself being necessary. They may be graduated into cubic centi- 
 metres to facilitate the estimation of the amount introduced. They 
 are filled by suction, the end of the capillary being dipped into the 
 liquid, and a chloride of calcium tube being placed at the other end 
 to prevent access of moisture. 
 
 Solid bodies are best introduced in the form of compressed tablets, 
 made by pressing the dry powder in a small machine made for the 
 
 FIG. 32. 
 
 purpose, or they may be made into little cylinders by V. Meyer's 
 method (p. 78), when they melt without decomposition. 
 
 Both solids and liquids can be introduced in the little tube shown 
 in Fig. 33. It is provided with a valve which opens as soon as the 
 tube touches the garnets. The introduction of vessels of any de- 
 scription, however, should be avoided as much as possible. 
 
 Reading of the elevation in the boiling-point. The introduction and 
 solution of the substance causes a depression of the temperature, 
 but it soon rises again, and becomes constant at a point higher than 
 the original reading. If the ascent of the column lasts more than 
 a minute or two, this must be caused by delay in the solution of 
 the substance. The height of the column is constant when the 
 reading does not vary more than a few thousandths of a degree in 
 from three to four minutes. 
 
3] BECKMANN'S METHOD 87 
 
 It is advisable to make the determination at different concentra- 
 tions, just as in the case of the freezing-point method. Immediately 
 after the first reading a second quantity of the substance is added, 
 then a third, and even a fourth quantity, o'l gr. or so with an 
 elevation of o'i maybe used to start with, and the amount gradually 
 increased as far as may be convenient. 
 
 If more of the substance is added than can be dissolved a slow 
 depression of the mercury column frequently follows the elevation. 
 The solution is at first supersaturated, and then some of the sub- 
 stance is redeposited. In such cases the undissolved part will be 
 found afterwards underneath the beads at the bottom of the tube. 
 The thermometer gives complete information of all that goes on 
 inside the apparatus during the experiment, and although the con- 
 tents are visible during the entire progress of the experiment direct 
 observation is not of much service. 
 
 The barometer-reading. With the latest perfected form of the 
 apparatus, the time occupied by a determination is so short that no 
 appreciable change in the level of the barometer can take place 
 during its progress. When a long series of determinations is made, 
 however, it will be advisable to check the barometric reading by a 
 second observation. 
 
 Completion of the experiment. When the last thermometer- 
 reading has been made, the heating is interrupted and the 
 apparatus allowed to cool. The progress may be hastened 
 finally by dipping the inner tube in cold water. The condenser 
 is then removed and the tube weighed, as at first, to deter- 
 mine the exact concentration for use in calculation. With careful 
 work the loss of solvent by evaporation need not exceed a few 
 decigrams. 
 
 The fraction of the solvent which is removed from the solution 
 by evaporation and condensation in the condenser is greater in the 
 present form of the apparatus than in the older, as the total amount 
 used is less than before. To allow for this Beckmann finds that 
 from 0*15 to 0*2 gr. in case of easily condensed liquids, and about 
 '35 g r - m the case of water must be deducted from the amount of 
 the solvent taken. 
 
 The substance used can be recovered completely by allowing the 
 solvent to evaporate. To obtain the part adhering to the beads, the 
 latter must be placed in an extraction apparatus, and exhausted with 
 a small quantity of the solvent. 
 
88 DETERMINATION OF MOLECULAR WEIGHTS [CH. ix 
 
 The formula M = 100 c ~-f- gives the result directly from 
 the data. 
 
 M = the molecular weight, 
 
 <:=the molecular elevation of the boiling-point for 100 gr. of the 
 
 solvent, 
 
 ^-=the weight of the substance, 
 G = the weight of the solvent, 
 
 / =the boiling-point of the solvent, 
 ^ = the boiling-point of the solution. 
 
 Solvent. 
 
 Boiling-point. 
 
 c. 
 
 Acetic acid (glacial) . . 
 
 118-1 
 
 25*3 
 
 Acetone 
 
 56-3 
 
 167 
 
 Aniline 
 
 183-0 
 
 32-2 
 
 Benzene 
 
 80-3 
 
 267 
 
 Carbon disulphide ... 
 
 46^2 
 
 237 
 
 Chloroform 
 
 6l'2 
 
 36-6 
 
 Ethyl alcohol 
 
 78-3 
 
 11-5 
 
 Ethyl ether 
 
 35'o 
 
 21*1 
 
 Methyl alcohol .... 
 
 66-0 
 
 9'2 
 
 Phenol 
 
 1 8 vo 
 
 1O'A 
 
 Water 
 
 vj <-. 
 
 lOO'O 
 
 J^q 
 C'2 
 
 
 
 j ~ 
 
 It may be remarked, in concluding this chapter, that other simple 
 methods of determining the molecular weight are known. That 
 devised by Will and Bredig(Ber. 22, 1,084 and 25, 1,491) is worthy 
 of mention. 1 They determine the loss of weight which a solution 
 of the substance under investigation undergoes when a stream of 
 air is drawn through it, all necessary precautions being observed. 
 In order that the air may become thoroughly saturated with the 
 vapour of the solvent, the solution is placed in a sort of Liebig's 
 apparatus provided with nine bulbs instead of the usual three. 
 The numbers obtained show about the same degree of accuracy as 
 those given by Eykman's apparatus. 2 
 
 1 They give a complete bibliography of the subject in their first paper. 
 
 2 A new method of determining molecular weights by measuring the 
 "diminution of solubility" of a substance containing a foreign body has 
 been described by Kuster, Ber. 27 328. 
 
 
CHAPTER X 
 
 SEALED TUBES 
 
 1. Reactions in Closed Vessels, When it is desired to bring 
 
 about an interaction between two substances at a temperature 
 higher than the boiling-point of one of them, it is necessary in 
 almost all cases 1 to heat them together in a closed vessel. No 
 description is required of the autoclaves which are used on a large 
 scale and the pressure bottles in use in laboratories for this purpose. 
 The details depend on their construction. 
 
 As an example of the use of the latter may be mentioned the synthesis of 
 rosinduline by Kehrmann and Messinger (Ber. 24, 5^7). Oxynaphtho- 
 quinoneimide (5 gr. ) was heated with the amount of amidodiphenylamine 
 corresponding to one molecule, acetic acid (5 cc. ), and alcohol (300 cc.), in 
 a pressure bottle in boiling water for 48 hours. 
 
 I O +H 9 N 
 1 OH HN 
 
 C 6 H 5 
 
 Sealed tubes are generally preferred in the laboratory for purposes 
 of this kind. 
 
 Sealed tubes can stand a very high pressure without bursting 
 if they are properly handled. Potash glass is preferable to soda 
 glass, but is not absolutely essential. Indeed, the former is not 
 unattacked by water at a high temperature. Hoppe-Seyler 
 (Z. physiolog. Ch. 13, 73) mentions that he charged a tube 30 cm. 
 1 See however Chap. IV. 4. 
 
SEALED TUBES 
 
 [CH. x 
 
 long of the best potash glass with water, and heated it for six 
 hours at 180-200. He found that the interior became covered 
 with a whitish film, and that the water had taken up a small, but 
 perfectly measurable amount of alkali. 1 
 
 When solid bodies are in question they are placed in a tube 
 closed at one end, and the other end 
 is then drawn off and sealed. 
 
 In the case of liquids the open end 
 is slightly drawn out and the sub- 
 stances are poured in through a thistle - 
 tube with a long narrow stem. It 
 depends entirely on the degree of 
 pressure which is expected what pro- 
 portion of the whole length of the 
 tube may be filled. In withdrawing 
 the thistle-tube, care must be taken 
 not to touch the part to be fused with 
 the fluid, as this might make the 
 proper sealing an impossibility. 
 
 The operation of sealing is con- 
 ducted in such a way that the end is 
 drawn out into a capillary point, while 
 the tube wall is not allowed to become 
 too thin. 
 
 The opening of the tube, after the 
 interaction is complete, must always 
 be conducted with care. The tube 
 must first be completely cold. If 
 volatile substances like methyl chloride 
 may have been formed, the tube should 
 be cooled in ice before opening. If 
 the gases which have been formed are 
 not to be examined, the whole tube, 
 with the exception of the extreme 
 point, is wrapped in a towel ; it is 
 then fixed in a clamp and a flame applied to the point. As soon 
 as the glass softens the gases force their way out. If the pressure 
 has not been excessive, none of the other contents of the tube will 
 be carried out with them. 
 
 1 See also Ber. 25, 2,494. 
 
 \J 
 
 FIG. 34. 
 
2] 
 
 THE GASES IN SEALED TUBES 
 
 9' 
 
 Excessive pressure may be avoided by not adding the whole 
 of the gas-producing substance at once. If, for example, bromine 
 is used and hydrobromic acid is liberated, only one third of the 
 necessary amount may be added at first. Then when the action 
 is complete the tube may be opened, the second third put in, and 
 the tube resealed. The remainder may be added later in like 
 manner. If, on the other hand, the pressure is due to the high 
 temperature employed, it may be advisable to heat at first to 200 
 only, to cool the tube and let out the gas, and, 
 after resealing, to complete the heating. 1 
 
 Stadel (Ann. 195, 190) recommends, as espe- 
 cially applicable in the case of pressure due to 
 hydrobromic acid, filing the tube near the point 
 under water. The tube empties itself without 
 any loss of material through the small opening. 
 
 When the product is solid it maybe extracted 
 without damage to the tube by filling this with 
 a suitable solvent and inverting it in a wide 
 beaker containing some of the same liquid. As 
 the layer of liquid at the top dissolves the sub- 
 stance it becomes heavier, and, sinking down- 
 wards, is replaced by a less nearly saturated 
 portion of the solvent. In a short time the 
 whole is dissolved automatically. 
 
 Only one instance seems to be found in 
 chemical literature where the tube was opened 
 while still hot. Einhorn (Ber. 16, 2,208) says 
 that he warmed 10 grams nitrocinnamic acid 
 with 100 grams of glacial acetic acid saturated 
 with hydrobromic acid at o, and that the tube was agitated and 
 the heating continued till solution was complete. As soon as this 
 occurred the tube was opened to prevent the excess of hydro- 
 bromic acid destroying the addition product. 
 
 2. The Gases in Sealed Tubes. If the gases are to be investigated 
 they are collected in a gasholder of suitable dimensions, and are 
 then conducted through an absorption apparatus, of which the 
 separate parts contain ammoniacal silver solution, dilute hydro- 
 
 1 If a high pressure is wanted and a high temperature must not be 
 used, an indifferent substance of low boiling-point such as ether, acetone, 
 or chloroform may be added. 
 
 FIG. 35. 
 
92 SEALED TUBES [CH. x 
 
 chloric acid, solution of ferrous sulphate, bromine under water, 
 and solution of potassium or barium hydroxide. In the am- 
 moniacal silver solution such substances as acetylene and allylene 
 produce precipitates which, after drying (the drying must be carried 
 out in vacuo], are very explosive. To analyse them a weighed 
 portion is decomposed in a porcelain crucible with hydrochloric 
 acid. 
 
 The dilute hydrochloric acid catches ammonia and volatile bases. 
 The bromine is dissolved with cold dilute caustic potash, and any 
 oil which remains undissolved must be an addition product of 
 bromine with an unsaturated body. The baryta water, which can 
 be replaced by an ammoniacal solution of barium chloride, takes 
 up the carbon dioxide. The ferrous sulphate takes up nitric oxide. 
 What passes out unabsorbed can only be investigated fully by a 
 quantitative analysis. Yet it is usually possible to ascertain from the 
 equation what the product is and to identify it by qualitative tests. 
 
 Carius (Ann. 169, 319) has devised the following method for catching 
 the gases when the pressure is high. A graduated glass tube is filled with 
 water, inverted, and a rubber tube pushed up inside it half way to the top. 
 The lower end of the rubber tube is attached firmly to a wide, but rather 
 short, bent tube, with whose second upturned limb another short rubber 
 tube is connected. The end of the sealed tube is pushed firmly into this, 
 so that the capillary reaches into the bent tube itself, and the joint is under 
 the water in the trough. When the point of the capillary is cautiously 
 broken a part of the gaseous and almost all the fluid contents are expelled 
 into the apparatus. 
 
 'X-a Salkowski (Z. physiolog. Ch. 4, 464) has given complete instructions 
 for the removal of ammonia from tubes for the purpose of quantitative 
 
 ^ Estimation. This is necessary in cases like the urea determination by 
 Bunsen's method. 
 
 If it is desired to generate chlorine or ammonia in a sealed tube 
 the following methods may be used : 
 
 For chlorine, hydrochloric acid is added after the tube has re- 
 ceived its charge of material. Then a plug of glass wool is inserted, 
 and on the top of that some dry potassium chlorate, potassium 
 bichromate, or manganese dioxide is placed (Ann. 255, 370). After 
 the tube has been sealed and laid in the oven the development of 
 chlorine begins. 
 
 For generating ammonia, ammonio-zinc chloride and bromide 
 mixed with chloride and bromide of ammonium are used. Am- 
 
2] THE GASES IN SEALED TUBES 93 
 
 monio-calcium chloride may also be employed. For example, 
 when a-w-xylenol (one part) is mixed with ammonio-zinc bromide 
 and ammonium bromide (one part), and heated at 340 for forty 
 hours, a 25 per cent, yield of xylidine is obtained (Ber. 20, 1,039). 
 Seyewitz (C. R. 109, 816), by heating resorcinol C 6 H 4 (OH) 2 with 
 ammonio-calcium chloride for three hours at 300 in a sealed 
 tube converted 60 per cent, of it into metaphenylendiamine. 
 
 Ammonio-zinc chloride is made, according to Merz and Miiller 
 (Ber. 19, 2,902), by leading dry ammonia into melted zinc 
 chloride in a retort. The gas is absorbed with evolution A 
 of heat, and when the salt is saturated it is allowed to 
 cool in a stream of the gas. Made in this way it is a 
 solid transparent substance which is not deliquescent and 
 has the composition ZnCl^NHg. The addition of am- 
 monium chloride is to prevent the formation of zinc 
 oxychloride through the partial decomposition of the 
 chloride, as the presence of this substance would tend to 
 defeat the action. Ammonio-zinc bromide is made in the 
 same way, and has the composition ZnBr 23 2NH 3 . It is 
 hygroscopic, however. 
 
 To determine the pressure in a sealed tube, Reychler's 
 method (Ber. 20, 2,461) may be used. A thin glass 
 tube about 40 cm. long is silvered on the inside for 4 
 or 5 cm. from one end, bent in the middle, and filled to 
 a certain height with mercury. The silvered end is then 
 sealed hermetically, and the mercury in the open limb 
 covered with a protecting layer of a hydrocarbon. After FI G- 36- 
 the length, Z, of the enclosed air (A B), the temperature, /, 
 and the barometric pressure, P, have been taken, the tube is let 
 down into the wider tube containing the substance, and the latter is 
 sealed up. The pressure developed in the tube compresses the air 
 in A B, and the mercury column dissolves the silver up to C. After 
 the operation the manometer is withdrawn and the distance A c, 
 (Z/), gives the volume of the air at the maximum pressure attained. 
 P is the pressure in millimetres of mercury in the tube at /, the 
 temperature of the bath, k' is the vapour tension of mercury 
 expressed in millimetres of mercury, and a is the coefficient of ex- 
 pansion of the gas ( = 0-00367). The following formula gives the 
 value of P f : 
 
 ._ 
 
 ~ ' H 
 
94 SEALED TUBES [CH. x 
 
 This method is only approximate, as the length L is sometimes 
 difficult to measure exactly. The silvering must be carefully 
 carried out and the apparatus kept in an inclined, or, better still, 
 vertical position. The result may be checked by experiments 
 carried out in autoclaves, when the gauge attached to the apparatus 
 gives the pressure directly. 
 
 3. Experiments on a Small Scale. Such experiments can be 
 made by Drechsel's very excellent method (J. pr. Ch. 135, 422). 
 
 The tubes generally used for sealing require considerable 
 quantities of material, and much is lost by explosions. By employ- 
 ing ordinary glass tubes 3 or 4 mm. in internal diameter with walls 
 I mm. thick, however, preliminary experiments with a few milli- 
 grams of the substance can be made. The tube is sealed at one 
 end, charged with the materials, and drawn out at the other end to 
 a very long thin capillary. The tube after being drawn out should 
 not be more than from 5 to 6 cm. long, while the capillary should be 
 from 10 to 15 cm. in length. The tube is fixed in a long wide test 
 tube, and maintained in position by a notched cork, which is split 
 along its length to hold the capillary, so that the lower end is about 
 i cm. from the bottom of the outer tube. A liquid of suitable boil- 
 ing-point is added, so that the tube is covered for half its length by 
 it. The flame which heats the apparatus is regulated so that the 
 vapour plays upon the whole of the tube and part of the capillary, 
 and yet does not reach the cork. The whole is placed in a hood 
 and the window is shut. Explosions seldom occur even with 
 sulphur vapour, and when they do no serious damage can be done. 
 When a general idea of the progress of, and the conditions 
 necessary for, the reaction has been obtained in this way, it is 
 much easier to make proper arrangements for repeating it on a 
 larger scale. 
 
 4. The Oven and Accessories. Iron tubes enclose the sealed 
 glass tubes during the heating. A brass wire like that in Fig. 34 
 is bound round the tube so as to be used in drawing it forth without 
 fear of breakage. 
 
 The furnace must have the following qualities according to Babo 
 (Ber. 13, 1,219). 
 
 It must permit of the heating of several tubes of the usual dimen- 
 sions to a temperature near the boiling-point of mercury, each tube 
 being heated as uniformly as possible. 
 
4] THE OVEN AND ACCESSORIES 95 
 
 The measurement of the temperature must be provided for, and 
 the apparatus should be so arranged that a certain maximum 
 cannot be surpassed. 
 
 It should be so arranged that if one tube bursts the others may 
 not explode from the shock, and all danger to the experimenter 
 must be avoided. 
 
 The expenditure of gas should be as small as possible, and irregularities 
 in its flow should be prevented by proper regulators. Such regulators, it 
 may be mentioned, are also useful in heating air baths and for similar pur- 
 poses. Victor Meyer (Ber. 17, 478) recommends Giroud's rheometer, 
 which is made of metal, while Beckmann (Z. physik. Ch. 4, 546) prefers 
 the Elster membrane-regulator. 
 
 The furnace should be placed in a hood so that if an explosion takes place 
 the vapours may be carried off. 
 
 Explosions cannot be avoided entirely, and usually the only 
 precautions taken are to secure that they shall do no damage. 
 Yet some efforts have been made to prevent them. 
 
 Hittorf, in heating phosphorus and lead together so as to get 
 crystals of the former, embedded the tube in magnesia in an iron 
 tube closed at both ends by screw caps and heated directly in a 
 fire. Bunsen, in his method for determining nitrogen, placed about 
 0*3 gram of the substance with 5 grams of cupric oxide in a dry 
 tube filled with hydrogen. The tube was put into a mould contain- 
 ing plaster of Paris, and when this was dry the whole was kept at 
 a dull red heat for an hour. 
 
 Wohler (1857, Ann. 103, 117) heated tubes to 150 in a steam 
 boiler in which a pressure of about five atmospheres was main- 
 tained. As his tubes were charged with solutions in water, the 
 pressure outside and inside the tubes was nearly the same, and no 
 explosions were possible. 
 
 Ullmann (Ber. 27, 379) finds that at high temperatures water 
 disintegrates the glass of the tube. He encloses the glass tubes 
 in tubes of steel closed by tightly fitting caps and containing a 
 volatile liquid. The pressure of the latter on the outside of the 
 sealed tube balances the internal pressure and reduces the risk 
 of bursting to a minimum. Furnaces and tubes constructed on 
 this plan are made by Muencke of Berlin. 
 
 On account of the inconvenience and risk of explosion and 
 consequent loss of material attaching to work with sealed tubes 
 their use is avoided whenever it is possible. The effort to find 
 
96 SEALED TUBES [CH. x 
 
 other ways of carrying out chemical actions has frequently been 
 successful. It was supposed, for instance, that splitting off the 
 sulpho-group from aromatic compounds where this could be 
 accomplished at all was only to be attained by heating with 
 hydrochloric acid in sealed tubes. Yet it has been shown by 
 Turner (Ber. 25, 968) that a good yield of #-nitraniline can be 
 bbtained by boiling 0-nitraniline sulphonic acid with three times 
 
 Jits weightr-'of 68 per cent, sulphuric acid for half an hour after 
 
 . ^solution is complete. 
 
 1 
 
CHAPTER XI 
 
 SUBLIMATION 
 
 " THE sublimation of organic bodies is an operation which must 
 often be used for their purification. In such cases the amount 
 of material at hand is limited, and the losses entailed by re- 
 crystallisation, decolorisation, and similar operations are so con- 
 siderable that it seems very desirable to reduce these losses to 
 a minimum in order that the thorough examination of such bodies 
 may be facilitated. The apparatus used in sublimation, however, 
 does not usually fulfil this condition, and its many defects are 
 familiar to the chemist." Thus wrote Gorup-Besanez (Ann. 93, 265) 
 in the year 1855 on sublimation as practised in the laboratory ; 
 and while the question has been solved as far as manufacturing- 
 chemistry goes, the want of a generally applicable apparatus for 
 use on a small scale is still felt. So far the advantage seems to 
 lie with those designed to work with diminished pressure. 
 
 We owe to Kolbe the suggestion of an apparatus for the purpose, 
 consisting of two watch-glasses ground to fit together closely and 
 held in position by a brass clip. A piece of filter paper cut to the 
 size of the glasses is placed between them. Gorup-Besanez re- 
 commends heating on an air bath, and controlling the temperature 
 in accordance with the readings of a thermometer (Fig. 37). The 
 vapour of the substance is filtered, so to speak, by the paper, and 
 I condenses on the highly-arched upper watch-glass, usually in 
 i beautifully crystalline form. To cool the upper glass a small piece 
 of netting is placed on it, and ether is dropped cautiously from 
 above. 
 
 The paper septum prevents the falling back of the sublimate 
 amongst the residue. 
 
 H 
 
SUBLIMATION 
 
 [CH. XI 
 
 Larger quantities of material are sublimed from a retort, and we 
 owe to Liebig (Ann. 101, 49) t^ie idea of passing a stream of gas 
 through it to facilitate vthe operation and remove the sublimate 
 from the danger of decomposition by long exposure to a high 
 temperature. The use of an indifferent gas in this way was found 
 in fact to effect a great improvement in the yield. By the use 
 of a stream of carbonic acid he got, for 
 example, more than 80 per cent, of the 
 theoretical yield of pyrogallic acid from 
 gallic acid. 
 
 Baeyer (Ann. 202, 164) used a dif- 
 ferent method for very difficultly volatile 
 substances. The bottom of a small 
 wide beaker was covered with the sub- 
 stance. A glass tripod stand with short 
 legs was placed in the beaker, and on 
 this rested a disc of filter paper touch- 
 ing the sides all round. Another disc 
 of filter paper, covered' .-,by a funnel, 
 rested on the top of the beaker. Through 
 the stem of the funnel, and through 
 the filters, passed a glass tube which 
 reached almost to the bottom of the 
 vessel. The beaker was heated strongly 
 on a sand bath, and during the heat- 
 ing a rapid current of carbonic acid 
 was led through the tube. At the close 
 of the operation the substance was 
 found between the filter papers and on 
 the inside of the funnel. 
 . Schiitzenberger places not more than 
 i gram of the dry substance in a wide 
 porcelain crucible about 5 or 6 cm. high. 
 This is covered with a filter paper, 
 
 the lid is placed over the whole, and the apparatus heated on 
 a sand bath. Fischer (Ber. 22, 357) recommends the same 
 method. 
 
 Another way consists in spreading the substance on the floor 
 of an Erlenmeyer flask and immersing this, along with a ther- 
 mometer, about i cm. deep in a sulphuric acid bath. When the 
 sublimate ceases to increase in quantity, the flask is removed from 
 
 FIG. 37. 
 
CH. XI] 
 
 SUBLIMATION 
 
 99 
 
 the bath, and, if necessary, the bottom can be cracked off to separate 
 the sublimate from the residue. 
 
 Tollens (Ber. 15, 1,830) sublimed trimethylene oxide I gram at 
 a time by placing it in a sealed tube, and packing this in the steel 
 tube of a Carius furnace with asbestos, so that the part containing 
 the substance was in the furnace and the empty half projected. 
 He then raised the temperature to 180-185. 
 
 Briihl and Landolt have contrived arrangements in which cooling 
 by water plays a part. 
 
 FIG. 38. 
 
 BriihPs apparatus (Ber. 22, 238), which is specially suitable for 
 easily fusible sublimates, consists of a tripod stand surmounted by 
 a low disc shaped tin box. A conical opening in the centre holds 
 a crucible, and two attachments for leading water through the box 
 are provided at opposite sides. This cooling arrangement is 
 covered by a glass basin with ground edge. The crucible should 
 be long in form and made of a good conductor such as copper or 
 platinum. The original form of the apparatus may be improved 
 by covering the tin box with a plate of glass, perforated in the 
 middle, which precludes contact of the sublimate with the metal 
 of the cooler. If the basin is rather high, almost all the sublimate 
 will be deposited on the cooled glass plate. 
 
 The apparatus can be used for fractional sublimation also. 
 
 Landolt's (Ber. 18, 57) arrangement for sublimation consists of 
 a tube of thin platinum foil about 150 mm. long and 18 mm. wide. 
 It is closed at the bottom, and two glass tubes traverse the stopper 
 at the top. Water enters by the longer of the two, which reaches 
 
 H 2 
 
too SUBLIMATION [CH. xi 
 
 almost to the bottom, and finds an exit by the other. The appa- 
 ratus is let down into a wide-necked flask in which the substance 
 is heated, and the substance deposits itself on the cold surface, ,and 
 so can be easily withdrawn and scraped off. 
 
 When difficultly volatile substances are heated in a platinum or 
 porcelain crucible, a screen of tin plate or asbestos board must be 
 provided to protect the projecting part of the tube, as otherwise 
 a considerable amount of water may condense upon it. 
 
 Success has not attended efforts to replace the platinum tube by 
 a glass test tube. 
 
 Very recently Hertkorn (Ch. Z. 1892, 795) has described still 
 another form of laboratory sublimation apparatus. 
 
 Sublimation in vacua was probably first used by Sommaruga 
 (Ann. 195, 305). After vain attempts to purify indigo by sublima- 
 tion without decomposition, he finally placed it in flasks of about 
 80 cc. capacity, and reduced the pressure of air in them to 30-40 
 mm. By direct heating he could then obtain any desired quantity 
 of the sublimate in a short time. 
 
 Volhard (Ann. 261, 380) placed crude pyromucic acid between two 
 plugs of asbestos in a glass tube which was then heated in an air 
 bath. The one end of the tube was connected through a receiver 
 with the pump ; at the other was a tube provided with a screw clip 
 through which dry air could enter. With a pressure of 50-60 mm. 
 the acid sublimed in long white needles at 130-140. 
 
 In a similar manner Bourgeois sublimed urea in vacuo, by the 
 use of a mercury bath heated to 120-130. Thiourea when treated 
 in the same way was converted into ammonium sulphocyanate. The 
 employment of a mercury bath does not seem desirable, however, 
 on account of the poisonous nature of the fumes arising from it. 
 
PART II 
 
 SPECIAL METHODS 
 
 CHAPTER XII 
 
 CONDENSATION 
 
 1. General Remarks. By condensation we mean the formation 
 of a substance from two others with loss of water, alcohol, hydro- 
 chloric acid, ammonia, or a halogen horn both components. 
 
 The union may take place without the addition of any condensing 
 agent, as in the case of the action o* hyc^ovy laming, and \phenyl- 
 hydrazine on aldehydes and ketones: " ' Senhofei kritf 'Bilinher (Z. 
 physiolog. Ch. 2, 22) found, for example, that polyatomic phenols 
 (e.g. resorcinol), interact directly with ammonium carbonate 
 dissolved in water and produce carboxylic acids. 
 
 C 6 H 4 (OH) 2 +NH 4 HCO 3 =C 6 H 3 (OH) 2 .COONH 4 +H 2 O. 
 
 In most cases however the tendency to condensation is strength- 
 ened by the addition of suitable agents. 
 
 We include under this heading also the phenomenon of internal 
 condensation in which a body loses water, and forms a new sub- 
 stance. Thus diacetosuccinic acid is transformed into carbopyro- 
 tritaric acid in presence of phosphoric acid (Ber. 17, 2,863). 
 
 When substances condense with themselves without loss of water, 
 the process is called polymerisation, 
 
102 CONDENSATION [CH. xn 
 
 By means of condensation chemists have been able to prepare 
 far more new bodies and entire classes of bodies than by any other 
 process. With its help also the transformation of substances 
 constituted with open chains into those with closed chains has been 
 vastly simplified. As an example of the latter, Hantzsch's synthesis 
 of pyridine derivatives (Ann. 215, 74) may be mentioned. Thus 
 he obtained hydrocollidine dicarboxylic ether by the union of two 
 molecules of acetoacetic ether with one molecule of aldehyde 
 ammonia, and loss of three molecules of water. 
 
 COOC 2 H 5 -HCH CH 2 -COOC 2 H 5 . COOC 2 H 5 -HC C-COOC 2 H 5 . 
 CH 3 -HCOH CO-CH 3 CH 3 -HC C-CH 3 
 
 \H 3 Y 
 
 + 3H 2 0. 
 
 _ \^ b Another example similar to this is afforded by Beyer and Claisen's 
 
 ^ (Ber. 20, 2,186) preparation of diphenylpyrazol carboxylic ether 
 
 by the action of phenylhydrazine on benzoylpyruvic ether : 
 
 ^CHa-CO-CsH, . - HC-C-C 6 H 5 
 
 i\' ; ; ,; ;;' ; II II 
 
 COOC 2 H 5 -CO r NH 2 '^COOC 2 H 5 -C N +2H 2 O 
 
 ^-A\S" ^?:,4tfT;'^:?; ;./' V 
 
 
 C 6 H B 
 
 In most cases condensations can be carried out in open vessels, 
 and the use of sealed tubes is seldom necessary. An instance 
 where this is necessary is reported by Behrend (Ann. 233, 2). 
 He found that phenylurea and acetoacetic ether in alcoholic 
 solution did not combine even in presence of hydrochloric acid. 
 Even heating to the boiling-point of acetoacetic ether did not bring 
 about the desired result. But the interaction was easily induced 
 by heating phenylurea ^10 gr.), acetoacetic ether (20 gr.), and ether 
 (locc.)for six hours at 140-150. The yield was equal to 90 per 
 cent, of the theoretical. 
 
 C 7 H 8 N 2 + C 6 H 10 8 = C 13 H 1G N 2 3 + H 2 O. 
 It is hardly necessary to point out that the formation of esters, 
 
2] 
 
 CONDENSING AGENTS 
 
 and ethers is only a special case of condensation, 
 separate chapter for the sake of convenience. 
 
 103 
 It is treated in a 
 
 2. Condensing Agents. The following are the chief agents used 
 for bringing about condensation. 1 They are arranged alphabetically, 
 and will be discussed in detail in the order given. 
 
 Acetic acid. 
 Acetic anhydride. 
 Aluminium chloride. 
 Ammonia. 
 
 Antimony trichloride. 
 Barium hydroxide. 
 Benzotrichloride. 
 Boron trifluoride. 
 Calcium chloride. 
 Calcium hydroxide. 
 Copper. 
 
 Hydrochloric acid. 
 Hydrocyanic acid. 
 Magnesium chloride. 
 Oxalic acid. 
 Perchloroformic ether. 
 Phosgene. 
 Phosphorus oxychloride. 
 
 Phosphorus pentoxide. 
 
 Phosphorus trichloride. 
 
 Potassium bisulphate. 
 
 Potassium cyanide. 
 
 Potassium hydroxide. 
 
 Silicic ether. 
 
 Silver. 
 
 Sodium. 
 
 Sodium acetate. 
 
 Sodium ethylate. 
 
 Sodium hydroxide. 
 
 Sulphur. 
 
 Sulphuric acid. 
 
 Tin tetrachloride. 
 
 Zinc. 
 
 Zinc chloride. 
 
 Zinc dust. 
 
 Zinc oxide. 
 
 It must be emphasised that one condensing agent cannot, as a 
 rule, take the place of another ; indeed, in cases where equivalence 
 might d priori be assumed, it is often found that quite divergent 
 results are obtained, especially in respect to yields. Thus Baeyer 
 (Ber. 6, 223) found aldehydes and hydrocarbons are not always 
 satisfactorily condensed by sulphuric acid or a mixture of that with 
 glacial acetic acid. Griepentrog(Ber. 19, 1,876), on the other hand, 
 found that zinc chloride almost invariably gave good results. 
 In this connection also the behaviour of oxalic acid ( 17) may 
 be cited. 
 
 1 The extraordinary effect of sunlight in causing condensation has been 
 investigated by Klinger. Klinger and Standke (Ber. 24, I 340) found that 
 sunlight could with extreme ease induce the formation of substances which 
 could only be obtained in its absence by very powerful or very subtle 
 chemical means. 
 
104 CONDENSATION [CH. xn 
 
 3. Acetic Acid. Acetic acid can be used for promoting the con- 
 densation of aldehydes and alcohols to acetals. 
 
 6 OH = CH 3 . CH(O. C 2 H 6 ) 2 + H 2 O. 
 
 Thus Geuther (Ann. 126, 65) prepared acetal by allowing alcohol 
 (6 vols.), aldehyde (2 vols.), and glacial acetic acid (i vol.) to stand 
 in a sealed tube for eight days and then heating the mixture at 100 
 for twelve hours. 
 
 4. Acetic Anhydride, The use of this substance is almost con- 
 fined to Perkin's synthesis. Baum heated aniline hydrochloride (12 
 parts) with acetic anhydride (18 parts) for twelve hours at 180-200. 
 The action took place according to the equation 
 
 2 C 6 H 5 NH 2 . HC1 + (CH 3 CO) 2 = C 16 H 14 N 2 . HC1 + 3H 2 O 
 
 without previous formation of acetanilide. A part of the acetic 
 anhydride acted as a condensing agent. 
 
 The discovery of Perkin's synthesis (J. Ch. Soc. 31. 391) led to the 
 opening of a wide field for the use of acetic anhydride. 
 
 Perkin prepared cinnamic acid by heating benzaldehyde (2 parts), 
 sodium acetate (i part), and acetic anhydride (3 parts). Tiemann 
 and Herzfeld (Ber. 10, 68) used the proportions, benzaldehyde 
 (3 parts), pulverised acetate (3 parts), and acetic anhydride (10 parts), 
 and boiled the mixture in a flask, provided with a condensing tube, 
 for eight hours. When the mass is extracted with water an oil 
 remains which is dissolved in ether. Any unused benzaldehyde is 
 removed by shaking with sodium bisulphite, and then the cinnamic 
 acid is extracted with a solution of sodium carbonate. On 
 acidifying the solution with hydrochloric acid the organic acid is 
 precipitated. 
 
 Fittig has shown (Ber. 14, 1,826) that combination first occurs 
 between the aldehyde and the sodium salt, and then the acetic 
 anhydride removes the water. 
 
 C 6 H 5 COH + CH 3 . COONa = C 6 H 5 . CH(OH) . CH 2 . COONa = 
 C 6 H 6 . CH : CH . COONa + H 2 O. 
 
 Cumarin (J. Ch. Soc. 31, 389) is formed by boiling salicylic alde- 
 hyde with acetic anhydride and sodium acetate. By using different 
 aldehydes different acids are obtained, and homologues are formed by 
 using homologues of sodium acetate in place of the simple acetate. 
 
 The yields obtained by the use of Perkin's synthesis lie usually 
 
5] ALUMINIUM CHLORIDE 105 
 
 between 40 and 50 per cent., but often sink below this level when 
 there is opportunity for secondary reactions. 
 
 It may be worth mentioning that Plochl and Wolfrum (Ber. 18, 1,183) 
 heated hippuric acid (i mol.) and salicylic aldehyde (i mol.) with three 
 times their weight of acetic anhydride and half their weight of sodium 
 acetate on the water bath. The condensation took place exclusively 
 between the first two substances, and not a trace of cumarin was found. 
 
 Edeleanoand Budistheano (Bull. Ch. [3], 3, 191) have combined Perkin's 
 synthesis with an old observation of Bertagnini's. The latter obtained 
 cinnamic acid by the action of benzaldehyde on acetyl chloride (Ann. 100, 
 126) 
 
 C 6 H 5 . COH + CH 3 . CO . C1 = C 6 H 5 . CH : CH . COOH + HC1. 
 
 Now the former observers found that by boiling benzaldehyde (i mol.), 
 acetyl chloride (i mol.), and sodium acetate (3 mol.), for twenty-four hours 
 an almost quantitative yield of cinnamic acid was obtainable. If this is 
 literally true, the very favourable result may be due to the acetic anhy- 
 dride, formed from the two last ingredients, acting, so to speak, in statu 
 nas&ndi. 
 
 5. Aluminium Chloride. We owe the use of aluminium 
 chloride for synthetical purposes to the work of Friedel and Crafts 
 (Bull. Ch. 29, 2). As Baeyer has remarked, this method has been so 
 fruitful and so varied in its results that an account of them reminds 
 one of a fairy tale. If we include with this the zinc chloride method 
 we have here certainly far the most prolific of all the modern 
 synthetical methods. It has brought to our knowledge whole 
 classes of bodies of the most diverse kinds. 
 
 The theory of the action is even now not perfectly settled, as is 
 shown by some recent work of Gustavson (J. Ch. Soc. 60, 182). 
 
 The chloride freshly prepared from aluminium and chlorine 
 usually gives better results than the frequently impure commercial 
 article (cf. however Biltz, Ber. 26, 1,960). It melts at 194 (Ber. 
 24, 2,577). Stockhausen and Gattermann (Ber. 25, 3,521) give the 
 following directions for preparing it. A wide combustion tube of 
 infusible glass, drawn out at one end to a narrower tube, is connected 
 with a wide-mouthed bottle by a doubly perforated cork. A suffi- 
 ciently wide tube passes through the other hole and conducts escaping 
 fumes to the draught. The combustion tube is filled with aluminium 
 turnings, placed in a furnace, and dry hydrochloric acid gas is led 
 through it. When all the air has been driven out of the apparatus 
 
io6 CONDENSATION [CH. xn 
 
 and there is no danger of an explosive mixture being formed, the 
 metal is heated to a temperature such that it will not melt into 
 drops. The chloride then distils into the bottle, whose cork must 
 be protected with asbestos paper to prevent its being burned during 
 the process. The yield is four parts of chloride from each part of 
 the metal taken. 
 
 According to Anschiitz (Ann. 235, 154), actions involving the 
 use of aluminium chloride are best carried out in a rather large 
 round-bottomed flask attached by a tubulated adapter to an inverted 
 condenser (Fig. 10). The chloride can be introduced through the 
 tubulus, which can serve also for the introduction of a thermometer 
 showing the temperature of the liquid during the operation. The 
 action can be promoted by warming in a water bath if necessary, 
 and when hydrochloric acid ceases to be evolved, the product is 
 poured into water and extracted with benzene, ether, or other 
 suitable medium. 
 
 The yields are frequently unsatisfactory, and vary very greatly 
 when different classes of substances are compared. Thus better 
 yields are obtained with homologues of benzene than with benzene 
 itself, while with aromatic halogen derivatives the opposite is true 
 (Schopff, Ber. 24, 3,766). 
 
 Possibly the occurrence of bad yields may be ascribed to the fact 
 that the action of the chloride on undiluted substances is too 
 violent and leads to the formation of resins. To test this, Claus 
 and Wollner (Ber. 18, 1,856) placed 100 grams of the chloride in a 
 flask provided with a condenser, and covered it completely with 
 carbon disulphide. Then they added a mixture of ^-xylene (100 gr.) 
 and acetyl chloride (75 gr.) in small portions at the ordinary tem- 
 perature. The operation was interrupted at the end of an hour 
 and a half, although hydrochloric acid was still being evolved, 
 because resinous matter was seen to be forming. The mass was 
 poured into water and the mixture extracted with ether, ^-xylyl- 
 methylketone (60 gr.) was obtained from the extract. 
 
 With the same object in view, Elbs (J. pr. Ch. 141, 181) mixed 
 hydrocarbons with acid chlorides in molecular proportions, and 
 added enough carbon disulphide to produce a clear solution. 
 
 All vessels used for syntheses by this method must first be well 
 dried. Then an amount of carbon disulphide equal in volume to 
 the mixture of substances to be combined is placed in the flask 
 and about the same quantity of aluminium chloride is added. The 
 mixture is then ooured through the adapter in portions, an interval 
 
51 ALUMINIUM CHLORIDE 107 
 
 elapsing between each addition to permit the violence of the action 
 to abate. When the whole has been added, the mass is warmed in 
 the water bath until the evolution of hydrochloric acid has ceased. 
 When the mixture has cooled a little water is added and the whole 
 is agitated. This process is repeated as long as any fresh action is 
 visible, and finally the product is distilled in a current of steam. 
 Ketones of high molecular weight remain in the residue as heavy 
 oils, with a solution of aluminium chloride floating on the top. 
 The ketones are washed with very dilute hydrochloric acid, to free 
 them from alumina, and purified by distillation. The yield of the 
 pure products reaches 50-80 per cent, of the theoretical. 
 
 Elbs ascribes the usefulness of the carbon disulphide to three 
 causes. In the first place it dilutes the substances and ensures 
 quicker action. Secondly, it keeps the temperature during the 
 operation at 50, a height which seems to be generally favourable. 
 And, finally, it moderates the violent action of the water on the 
 product and prevents the formation of resin. This last property he 
 holds to be especially valuable. 
 
 The quantity of aluminium chloride can frequently be diminished 
 to one half the weight of the acid chloride used without interfering 
 with the yield. The time necessary for the completion of the 
 action varies from a half to two days. 
 
 The following actions differ somewhat from those cited. Gattermann 
 (Ann. 244, 50) acted with carbamic chloride, NH 3 . CO.C1, on benzene in 
 presence of powdered aluminium chloride, using carbon disulphide for 
 dilution, and obtained a quantitative yield of benzamide. Gottschalk (Ber. 
 22, I ?2I9) dissolved pentamethylbenzene (20 gr. ) in carbon disulphide 
 (60 gr. ), and added first carbamic chloride (20 gr. ) and then, gradually, 
 aluminium chloride (24 gr. ). The mixture was warmed for a short time 
 in the water bath, and 80 per cent, of the theoretical amount of the amide 
 of pentamethylbenzoic acid was formed. 
 
 Elbs (J. pr. Ch. 149, 147) finds that for some purposes the 
 boiling-point of carbon disulphide is too low, and recommends for 
 such cases the use of petroleum ether. Thus, for the formation of 
 phenylbenzoyl-<?-benzoic acid from diphenyl and phthalic anhydride 
 
 CO\ ~* -FT /- TT TT CO . CH . CHr 
 
 the most favourable temperature is 90-100, so that petroleum ether 
 of this boiling-point is the best diluent to use. 
 
io8 CONDENSATION [CH. xn 
 
 The method usually works well with benzene and its homologues, 
 but is less satisfactory with more complicated aromatic hydro- 
 carbons, and sometimes fails entirely. Substances with halogen 
 atoms attached to the ring act poorly, while nitro-bodies hardly act 
 at all. The method cannot be employed with compounds con- 
 taining hydroxyl, since the chloride interacts directly with this. 
 
 Gaseous substances are amenable to its influence. Thus, by 
 conducting sulphur dioxide (Jahresb. 1878, 739) into benzene 
 containing the chloride, addition takes place, and benzene sul- 
 phinic acid, C 6 H 5 SO 2 H, is formed. By using oxygen in place of 
 sulphur dioxide (Ann. Ch. Ph. [6], 14, 433), phenol is obtained. 
 
 Galle (Ber. 16, 1,744) found that for introducing ethyl groups 
 into benzene it was preferable to employ the liquid ethyl bromide 
 rather than the gaseous chloride. The mixture was heated in a 
 tube at 100. Tetraethylbenzene was the chief product after nine 
 hours' heating, while after fifteen hours the greater part of the 
 benzene had been converted into hexaethylbenzene. 
 
 Acid radicals can be introduced in the same way as alkyl radicals. 
 Doebner and Wolff (Ber. 12, 661) even prepared dibenzoyl 
 quinol (C 6 H 5 .CO) 2 C 6 H 2 (OH) 2 by heating quinol dibenzoate 
 (i mol.) with benzoyl chloride (2 mol.) in a flask at 190-200, 
 and gradually adding aluminium chloride. The quinol had to be 
 used in the form of an ester to avoid the direct action of the 
 condensing agent on the hydroxyl. After the operation had gone 
 on for forty-eight hours, fresh addition of the chloride produced no 
 new evolution of hydrochloric acid. The ester was finally sa- 
 ponified with alcoholic caustic potash, and the product precipitated 
 with carbon dioxide. 
 
 Jacobsen (Ber. 22, 1,220) mixed phosgene (50 gr.) cooled to 10, 
 and pentamethylbenzene (70 gr.), added gradually aluminium 
 chloride (5-10 gr.), and allowed the whole to remain at a tempera- 
 ture not exceeding o for two weeks. The liquid was then exposed 
 to moist air in shallow basins for a short time, and finally warmed 
 with water and caustic soda. The latter converted the chloride 
 into the sodium salt of the acid. A small amount of unused penta- 
 methylbenzene was removed and a good yield of pentamethyl- 
 benzoic acid obtained by precipitation with hydrochloric acid. 
 
 C fl (CH a ) 6 COCl + HCL 
 
 Phenyl cyanate unites with hydrocarbons in presence of alu- 
 minium chloride, forming an acid anilide, from which, by hydro- 
 
5] ALUMINIUM CHLORIDE 109 
 
 lysing, the corresponding aromatic acid is obtainable (J. pr. Ch. 
 149, 301). 
 
 C 6 H 6 + CON . C 6 H 5 =C 6 H 5 . CO . NH . C 6 H 5 . 
 
 This action is exceptional in the sense that no hydrochloric acid 
 is evolved. 
 
 The acetyl group can be united to the benzene ring by this 
 agency. Thus Schweitzer (Ber. 24, 550) diluted bromobenzene 
 and acetyl chloride with carbon disulphide and by the usual process 
 obtained acetylbromobenzene, C 6 H 4 Br.CO.CH 3 , after three hours' 
 heating. 
 
 Even inorganic chlorides can be induced to unite with organic 
 radicals. For example, Michaelis and Schenk (Ann. 260, 2) mixed 
 phosphorus trichloride (100 gr.) with dimethylaniline (70 gr.) and 
 added fresh aluminium chloride (20 gr.) in small portions at once. 
 The mixture was cooled during the process. Dimethylamidophenyl- 
 phosphine dichloride was formed according to the equation 
 
 PC1 3 + C 6 H 5 N(CH 3 ) 2 = PC1 2 . C 6 H 4 N(CH 3 ) 2 + HC1. 
 
 In making acetovanillone, Otto (Ber. 24, 2,869) departed somewhat 
 from the ordinary course. He cooled a solution of pure guaiacol (60 parts) 
 in glacial acetic acid (120 parts), and added gradually a finely pulverised 
 mixture of aluminium and zinc chlorides. He finally heated the mixture at 
 140-150, keeping the temperature constant between these limits. Even 
 thus, however, the yield was unsatisfactory. 
 
 Those examples give some idea of the wide applicability of this 
 synthetical method. It must be said, however, that the action 
 sometimes takes the opposite course. Thus along with actions 
 like 
 
 C 6 H 6 +CH 8 C1 = C 6 H 6 . CH 3 +HC1, 
 
 those of the opposite nature 
 
 C 6 H 5 . CH 3 . +HC1 = C 6 H 6 +CH 3 C1 
 
 likewise occur. This was shown by Jacobsen (Ber. 18, 339), who 
 heated hexamethylbenzene with one tenth of its weight of aluminium 
 chloride in a stream of dry hydrochloric acid gas, at a temperature 
 near to its melting-point. He obtained pentamethylbenzene, 
 durene, and even benzene. More remarkable still was the observa- 
 tion of Anschiitz and Immendorff (Ber. 18, 657), that (e.g.) toluene 
 
I io CONDENSATION [CH. xn 
 
 gave both benzene and *#-xylene and /-xylene under the same 
 circumstances (cf. Chap. XXI. 9). 1 
 
 6. Ammonia, Like other alkaline solutions, ammonia shows 
 condensing properties. It may be remarked here, however, that 
 sodium hydroxide seems to be the most energetic member of the 
 group, and is therefore the most frequently used alkali. 
 
 The following case of the use of ammonia is reported by Japp 
 and Streatfield (Ber. 16, 276). When phenanthrenequinone, aceto- 
 acetic ether, and concentrated ammonia are heated at 100 for a 
 short time under pressure, phenanthroxylene-acetoacetic ether 
 
 p u p . p/CO CH 3 
 I 8 " 4 | - C \COOC 2 H 5 
 
 QH 4 -CO 
 
 is formed. As the authors remark, this seems to be the first occa- 
 sion on which the somewhat unusual dehydrating influence of 
 aqueous ammonia has been noticed. 
 
 The same influence seems to be specially helpful in assisting the 
 addition of hydrocyanic acid to aldehyde and ketone groups. Thus 
 Kiliani (Ber. 21, 916, and 22, 370) found that the addition product 
 with arabinose took eight days for its formation under ordinary cir- 
 cumstances, while the addition of four drops of ammonia for every 
 100 grains of arabinose diminished the time to from twelve to 
 twenty-four hours. The same observation was made in the case of 
 galactose carboxylic acid. In preparing the cyanhydrine he added 
 water (6 cc.) to finely pulverised galactose (30 gr.), and then the 
 calculated amount of 50 per cent, hydrocyanic acid with one drop 
 of ammonia. The mixture became gradually solid and was filtered 
 after twelve hours. The crystals consisted of the amide of galactose 
 carboxylic acid, and the quantity was equal to 40 50 per cent, of 
 the sugar taken. 
 
 7. Antimony Trichloride. Smith (Ber. 9, 467) states that 
 antimony trichloride can be used for increasing the yields of hydro- 
 carbons obtained by condensation. Thus, when naphthalene is 
 conducted through red-hot tubes, a very small amount of isodi- 
 
 1 Kondakoff (J. pr. Ch. 156 4^7) has recently classified the cases in 
 which aluminium chloride and zinc chloride respectively give the best 
 results. He finds that the former is in general most advantageously used 
 With aromatic bodies, and the latter with fatty derivatives. 
 
8-12] CALCIUM HYDROXIDE ill 
 
 naphthyl, C 10 H 7 . C 10 H 7 , is formed. But when the vapour o* antimony 
 chloride is passed through at the same time, hydrochloric acid is 
 formed, and a large yield of the condensation product is obtained. 
 
 6C 10 H 8 + 2SbCl 3 = Sb 2 + 6HCl + 3C 10 H 7 . C 10 H r . 
 
 Tin tetrachloride seems to be even more efficient in such cases, 
 as it is transformed into the dichloride, but chloro-derivatives 
 appear always to be formed at the same time. A large amount 
 of diphenyl can be obtained from benzene by its means. 
 
 8. Barium Hydroxide. Bottinger (Ann. 172, 241) found that 
 pyruvic acid could be condensed by means of barium hydroxide. 
 He mixed pyruvic acid (5 parts) with the crystallised hydroxide (3 
 parts) and enough water to produce a mixture boiling at 140 (Ann. 
 208, 126). The products were methylsuccinic acid and pyrotri- 
 tartaric acid. 
 
 9. Benzotrichloride. Wittenberg (J. pr Ch. 134, 67) found that 
 resocyanin, C 21 H 18 O 6 (J. pr. Ch. 132, 126), could be obtained from 
 resorcinol and acetoacetic ether in presence of benzotrichloride. 
 Still he found that concentrated sulphuric acid gave a better yield. 
 
 10. Boron Trifluoride. This substance, which is prepared by 
 the action of sulphuric acid on a mixture of fused and pulverised 
 boric acid with calcium fluoride, has special powers of bringing 
 about internal condensation (Landolph, Ber, 12, 1,579)- Thus it 
 transforms camphor into cymene. It is capable, however, of form- 
 ing compounds directly with aldehydes, ketones, and probably 
 amines. 
 
 11. Calcium Chloride. This agent is not employed alone, but 
 is frequently used with zinc chloride (cf. 36). 
 
 12. Calcium Hydroxide. Low obtained formose, C 6 H ]2 O 6 , by 
 polymerisation of formaldehyde, CH 2 O, by shaking a 3'5~4 per 
 cent, solution of the aldehyde with excess of lime-water for half an 
 hour and then filtering. In the course of six days the liquid 
 acquired an intense power of reducing Fehling's solution. The 
 solution was neutralised with oxalic acid, and the calcium formate 
 precipitated with alcohol. The filtrate was then evaporated to a 
 syrup, and the sugar precipitated as a plastic mass by addition of 
 alcohol and ether. 
 
ii2 CONDENSATION [CH. xir 
 
 13. Copper. This metal brings about condensation by removing 
 sulphur and so permitting the union of the organic groups attached 
 to it. It is used in a finely-divided state : probably that prepared 
 by Gattermann's method (Chap. XVI., sec. II., 13), will be 
 found very suitable for the purpose when dried in a stream of 
 hydrogen or illuminating gas. 
 
 Its use may be exemplified by reference to an application made 
 by Ris (Ber. 19, 2,243). He thoroughly mixed thio-/3-dinaphthyl- 
 amine (i part) with copper (2 parts), which was freshly ignited in 
 a stream of hydrogen just before use, and heated the mixture in a 
 retort in a stream of carbon dioxide ; soon the metal became black 
 and a yield of fifty per cent, of -dinaphthylcarbazole distilled over. 
 
 CioH 6 \ ^ jj /CioH 6 + CuS. 
 
 The attempt to unite two different hydrocarbon groups by this 
 agency seems not to have been made as yet. 
 
 14. Hydrochloric Acid. Hydrochloric acid, which is the agent 
 most generally used in the preparation of esters, was probably first 
 employed successfully for the removal of water in other directions by 
 Chiozza in 1856. He conducted the gas into a mixture of aldehyde 
 and benzaldehyde to saturation, noticed the cloudiness due to the 
 separation of water, and isolated cinnamic aldehyde from the product. 
 
 C 6 H 5 . COH-f-CHg . COH = C 6 H 5 . CH : CH . COH + H 2 O. 
 
 This method is still in use in the same form. The amount of water 
 produced is sometimes measured by placing the mixture in a burette 
 and allowing the water to collect on the surface. 
 
 Claisen (Ann. 218, 172) obtained ethylidene acetoacetic ether by 
 saturating a mixture of aldehyde (i part) and acetoacetic ether, 
 placed in a freezing mixture, with hydrochloric acid. The material 
 increased in weight forty-three per cent. At the end of twenty-four 
 hours he poured the liquid into water ; the oil which separated 
 was washed with water and carbonate of soda, and finally dried 
 with calcium chloride. On distilling the result he found that much 
 hydrochloric acid came off through the decomposition of an addition 
 product, and then the condensation product, boiling at 210, passed 
 over. The yield was equal to seventy or eighty per cent, of the 
 theoretical. 
 
 CH 3 . COH + CH 3 . CO . CH 2 . COOC 2 H 5 = 
 
 + H 2 0. 
 
i 4 ] HYDROCHLORIC ACID 113 
 
 Beyer's synthesis of homologues of quinoline (Ber. 20, 1,767) 
 likewise depends on the condensation of primary aromatic amines 
 with unsaturated ketones, or with mixtures of ketones and aldehydes, 
 by means of hydrochloric acid. He obtained a-y-dimethylquinoline 
 (J. pr. Ch. 141, 401) by the following process. 
 
 He took paraldehyde and acetone in the proportions required by 
 the equation 
 
 CH 3 . COH + CH 3 . CO . CH 3 =CH 3 . CH : CH . CO . CH 3 +H 2 O, 
 
 using a small excess of acetone, saturated the cooled mixture with 
 dry hydrochloric acid, and allowed the mixture to remain for one 
 or two days. He then poured it slowly into a solution of aniline 
 in twice its weight of concentrated hydrochloric acid. A little less 
 than the amount of aniline required by the equation was taken and the 
 whole was warmed for several hours in the water bath. A good yield 
 of the base was obtained from the proportions paraldehyde ( 1 20 gr.), 
 acetone (200 gr.), aniline (200 gr.), and concentrated hydrochloric 
 acid (400 gr.). The principal part of the action is represented by 
 the equation 
 
 In isolating the product the liquid is first distilled in a current 
 of steam to remove volatile substances. On then adding excess of 
 caustic soda the basic constituents can be driven off. The bases 
 are dissolved in alcohol, and the picrate of dimethylquinoline is 
 precipitated by adding an alcoholic solution of picric acid. The 
 crystals are washed with alcohol and decomposed with caustic soda, 
 when the free base can be driven over with steam and thus obtained 
 in a pure condition. 
 
 In the same way Doebner and Miller (Ber. 16, 2,465) found that quinal- 
 dine could be prepared in a few hours by warming a mixture of paraldehyde 
 (i parts), aniline (i part), and crude hydrochloric acid (2 parts), on the 
 water bath. 
 
 CH CH 
 HQ/\/\CH 
 
 C 6 H 7 N + 2C 2 H 4 0= | J | +2H 2 + 2H 
 
 HC\/VC.CH 3 
 CH N 
 
 The nascent hydrogen acts upon a part of the quinaldine. 
 
 One of the methods of preparing the soporific, sulphonal, depends on the 
 condensation of acetone with mercaptan to mercaptol by means of hydro- 
 chloric acid, when oxidation of the product gives sulphonal. 
 
 I 
 
ii4 CONDENSATION [CH. xn 
 
 When solid substances are to be condensed, they are dissolved 
 in alcohol, provided this solvent will not affect the action, or, still 
 better, in glacial acetic acid ; the actual use of gaseous hydrochloric 
 acid is not always essential, the addition of a few drops of the 
 aqueous acid sometimes suffices. 
 
 Claisen (Ann. 237, 271) supplies an example of this. He dis- 
 solved /3-naphthol (7 parts) and paraldehyd (3 parts) in glacial 
 acetic acid (15 parts), added fuming hydrochloric acid (i part), 
 and warmed the whole in the water bath. Ethylidene-glycoldi- 
 naphthylacetal appeared as an oil which soon crystallised. 
 
 2C 10 H 7 .OH + CH 3 .COH = CH 3 .CH(C 10 H 7 0) 2 + H 2 0. 
 
 Similarly Caro (Ber. 25, 946) found that hexoxydiphenylmethane 
 dicarboxylic acid was extremely easily formed by boiling gallic 
 acid (2 mol.) and formaldehyde (i mol.) with fifteen times as much 
 dilute hydrochloric acid (i : 5) on the water bath till the substance 
 had completely separated as a white powder. 
 
 2C 6 H 2 (OH) 3 COOH + CHoO = CH 2 (C 6 H(OH) 3 COOH) 2 + H 2 O. 
 
 Condensations similar to these occur also in the pyrrole series. 
 Baeyer (Ber. 19, 2,184) states that when pyrrole (i part) is dissolved 
 in pure acetone (10 parts;, and one drop of hydrochloric acid is 
 added, the liquid becomes coloured and soon begins to boil ; if it 
 is cooled rapidly crystals of a substance having the composition 
 C 14 H ]6 N 2 appear. 
 
 2 C 3 H 6 + 2C 4 H 6 N = C 14 H 16 N 2 + 2H 2 O + 2H. 
 
 According to Dianin (J. Ch. Soc. 64, i. 214), fatty ketones condense 
 with phenol to form diatomic phenols. The most favourable temperature 
 for the action is 40-60. The larger the amount of hydrochloric acid, and 
 the smaller the molecular weight of the ketone, the more quickly is the 
 condensation accomplished. Beyond a certain limit, however, excess of the 
 acid acts disadvantageously. In preparing dimethyl-/-diphenolmethane he 
 mixed acetone (220 gr.), phenol (1,600 gr.), glacial acetic acid (1,800 cc.), 
 and fuming hydrochloric acid of sp. gr. 1*19 (600 cc.), and allowed the 
 liquid to remain at a temperature of 40-60. At the end of twenty-four 
 hours he cooled the mixture, separated the crystals, and set it aside again at 
 the same temperature. In this case he found that heating in a sealed tube 
 at 80-90 completed the action in two days. 
 
 The following example illustrates the use of alcohol for diluting. 
 Tetramethyldiamidobenzhydrol (5 parts) is dissolved in hydrochloric acid of 
 
15-17] OXALIC ACID 115 
 
 sp. gr. 1*18 (3 '5 parts), and alcohol (20 parts) and dibenzaniline (5 parts) 
 are added. The mixture is heated in the water bath until the hydrol has 
 disappeared, and is then diluted with water and filtered. The leuco base is 
 finally precipitated by the addition of water. 
 
 Hydrochloric acid is also efficient in promoting internal con- 
 densation. Thus Engler and Berthold (Ber. 7, 1,123) find that 
 acetophenone absorbs dry hydrochloric acid rapidly. After the 
 saturated substance has remained for several days in a warm place 
 crystals of triphenylbenzene appear ; by repeating the process 
 sixty per cent, of the acetophenone can be finally converted into 
 the new body 
 
 3 C 6 H 5 . CO . CH 3 = C 24 H 18 
 
 Wurtz (C. R. 74, i, 361) obtained aldol by the action of hydrochloric acid 
 on aldehyde. 1 He failed however to condense formaldehyde by this 
 method (Bull. Ch. 31, 434)- The polymerisation of the substance to 
 formose, C 6 H 12 O 6 (Ber. 23, 2,126), which is interesting on- account of the 
 relation of the latter to the carbohydrates, was achieved by Low (J. pr. Ch. 
 141, 327) by the use of calcium hydroxide (cf. 12). 
 
 15. Hydrocyanic Acid, Lorenz (Ber. 14, 791) states that 
 piperonal and alcoholic ammonia condense differently in presence 
 of hydrocyanic acid and in its absence ; in the former case the 
 action is represented by the equation 
 
 3 C 8 H 6 3 + 2NH 3 =C 24 H 18 N 2 6 + 3 H 2 0, 
 
 and the product melts at 213. In the latter case the substance 
 produced has the same empirical formula, but melts at 172, and 
 differs from its isomer in other respects as well ; it may be that 
 the difference between the substances is stereo-chemical. It is not 
 known whether hydrocyanic acid has any special influence on the 
 course of other condensations or not. 
 
 16. Magnesium Chloride. By the action of phenol on isobutyl 
 alcohol in presence of magnesium chloride, Mazzara (J. Ch. Soc. 
 42, 838) obtained isobutylphenol 
 
 C 6 H 6 OH + C 4 H 9 OH = C 4 H 9 . C 6 H 4 OH + H 2 O. 
 
 17. Oxalic Acid. Anhydrous oxalic acid was used by Girard 
 and De Laire (Jahresb. 1867, 963) for preparing diphenylamine- 
 
 1 His work was suggested by the theoretical speculations of Baeyer's 
 paper on "The Role of Condensation in Plant Life" (Ber. 3, 68). 
 
 I 2 
 
ii6 CONDENSATION [CH. xn 
 
 blue from diphenylamine. In this particular case, however, the 
 acid is itself decomposed. Anschiitz (Ber. 17, 1,078) used dry oxalic 
 acid in making tetramethyldiamidotriphenylmethane. He added 
 pulverised anhydrous oxalic acid (7*5 gr.) to a solution of benzalde- 
 hyde (5 gr.) in dimethylaniline (11*5 gr.), and heated the mixture, 
 with constant stirring, for two hours at 1 10. The yield was almost 
 quantitative 
 
 /CH 3 
 C 6 H 4 N\CH 3 
 
 2C 6 H 6 N/5S 8 +C fl H 6 . COH = C 6 H 6 . CH/ +H 2' 
 
 \ CHs X 
 
 After the publication of this, Fischer (Ber. 17, 1,893) stated that it had 
 been well known to manufacturers ever since the discovery of malachite- 
 green, which is formed by the oxidation of the above derivative, that the 
 condensation of diethylaniline with benzaldehyde is much less satisfactory 
 than that of dimethylaniline when zinc chloride is used as the condensing 
 agent. Indeed it is almost impossible to obtain the diethyl derivative in a 
 crystalline condition when zinc chloride is used in its preparation. So that 
 both for the preparation of the leuco base of malachite-green and the corre- 
 sponding ethyl derivative, other condensing agents had long been in use. 
 One of these was oxalic acid, which Anschiitz first employed in the 
 laboratory. 
 
 The presence of other groups in place of hydrogen in the benzene ring 
 does not interfere with the efficiency of this agent. Thus when a mixture 
 of 0-nitrobenzaldehyde (i part), diethylaniline (3-4 parts), and oxalic acid 
 (i\ parts), is heated in the water bath, an excellent yield of 0-nitrophenyl- 
 tetraethyl-/-amidodiphenylmethane is obtained. 
 
 When resorcinol (7 gr. ), phthalic anhydride (5 gr. ), and oxalic acid (3 "5 gr. ), 
 are heated for ten hours, fluoresceine (2*3 gr.) is formed (Ber. 17, i>o79). 
 
 Kaeswurm (Ber. 19, 744) showed that /-chlorobenzaldehyde and/-nitro- 
 benzaldehyde condensed as easily as the 0-nitro-derivative with diethyl- 
 aniline to form similar products. 
 
 18. Perchloroformic Ether. Hentschel (Ber. 18, 1,177) has 
 a full investigation of the condensing powers of perchloro- 
 formic ether. The preparation of the ether itself is described by 
 him as follows. A flask containing liquid phosgene is placed in a 
 freezing mixture and connected with a reflux condenser. Methyl 
 alcohol is then added slowly. Each drop of the alcohol dissolves 
 with a hissing sound, and torrents of methyl chloride are evolved. 
 As soon as the addition of alcohol calls forth no further action the 
 ester is poured into water, washed, and dried with calcium chloride. 
 
19-21] PHOSPHORUS PENTOXIDE n? 
 
 This methyl ester of chloroformic acid boils at 69-71. When it is 
 submitted to the action of chlorine in sunlight (J. pr. Ch. 144, 100), 
 perchloroformic ether is obtained. 
 
 This substance has a very considerable condensing power. Thus 
 when it is added to a mixture of dimethylaniline and benzaldehyde 
 a few minutes' warming on the water bath converts the whole into 
 the leuco base of malachite-green. 
 
 The use of this substance on a large scale is frequent, but in such 
 cases it is generally mixed with aluminium chloride. 
 
 19. Phosgene. This substance seems to be used in manufactur- 
 ing (Ger. Pat. 62,539) as a condensing agent. 
 
 20. Phosphorus Oxychloride. Nencki (M. f. Ch. 9, 1,148) 
 prepared the leuco base of malachite-green by warming benzalde- 
 hyde (40 gr.) and dimethylaniline (100 gr.) with 93 per cent, alcohol 
 (40 grs.) in a flask of two litres capacity attached to a reflux con- 
 denser. Through a small separating funnel he allowed phosphorus 
 oxychloride (65 gr.) to flow slowly into the warm liquid. When the 
 whole had been added the heating was continued for half an hour, 
 and then the liquid was dissolved in water, and the solution filtered. 
 On adding the proper amount of caustic soda the leuco base was 
 precipitated as an easily crystallisable oil, and in almost quantitative 
 amount. 
 
 For use on a large scale the following method is prescribed. Benzanilide 
 (20 parts) and dimethylaniline (40 parts) are mixed with phosphorus 
 oxychloride (20 parts), and the whole gently warmed on the water bath 
 and constantly stirred. As soon as a marked rise in the temperature sets 
 in, due to development of heat by the action, the vessel is removed from 
 the water bath, and the progress of the action regulated by cooling, so that 
 the temperature does not exceed 120. When the action becomes less 
 energetic the heating on the water bath is renewed for one or two hours. 
 The syrupy mass which remains contains the condensation product. 
 
 According to Friedlander's " Farbenfabrikation " (p. 47), dichlorobenzyl- 
 anilide is first formed, and this interacts with the tertiary amine, producing 
 a substitution derivative of phenylimidobenzophenone 
 
 C 6 H 5 CC1 2 . NHC 6 H 5 + C 6 H 5 N(CH 3 ) 2 - N(CH3) C : NC 6 H 5 + 2 HC1. 
 This agent can also be used for internal condensation (Ber. 20 2 >863). 
 
 21. Phosphorus Pentoxide. This substance is an excellent 
 condensing agent, as might be expected from its powerful attraction 
 
li8 CONDENSATION [CH. xn 
 
 for water. Thus a mixture of benzoic acid and benzene (Kollarits 
 and Merz, Ber. 6, 537), with phosphorus pentoxide gives diphenyl- 
 ketone 
 
 C 6 H 6 COOH + C 6 H 6 = C 6 H 5 . CO . C 6 H 6 + H 2 O. 
 
 Michael and Adair (Ber. 11, 116), find that sulphonic acids act 
 similarly. For example, when ^-toluenesulphonic acid and benzene 
 are heated with the pentoxide in a sealed tube at 150-170, a cer- 
 tain amount of phenyltoluylsulphone is produced 
 
 C 6 H 4 (CH 3 ) . S0 2 OH + C 6 H 6 = C 6 H 4 (CH 3 ) . SO 2 . C 6 H 5 + H 2 O. 
 
 According to Hemilian (Ber. 7, 1,204), when the pentoxide is 
 covered with a solution of benzhydrol in pure benzene in a sealed 
 tube and heated for four hours, 50 per cent, of the possible quantity 
 of triphenylmethane can be obtained by washing away the phos- 
 phoric acid with water and distilling 
 
 (C 6 H 6 ) 2 CH . OH + C 6 H 6 = (C 6 H 5 ) 3 CH + H 2 0. 
 
 By using fluorenyl alcohol (Ber. 11, 202), he prepared diphenyl- 
 enephenylmethane 
 
 ^6^4^ C 6 H 4 K 
 
 | >CH.OH + C G H 6 = | >CH.C 6 H 5 +H 2 0. 
 C 6 H/ C 6 H/ 
 
 The pentoxide can also be used in intramolecular condensation 
 as in the formation of nitriles from amides 
 
 R. CO.NH 2 = R. CN + H 2 O. 
 
 Knorr (Ber. 17 2,863) obtained dimethylfurfurane dicarboxylic 
 ether (carbopyrotritartaric ether) by the action of a concentrated 
 solution of phosphoric acid on diacetosuccinic ether. 
 
 22. Phosphorus Trichloride, The use of phosphorus tri- 
 chloride in the intramolecular extraction of water was first noticed 
 by Frankland and Duppa (Ann. 136, 16). An early example of its 
 application in this way is given by Semljanitzin and Saytzeff (Ann. 
 197, 73). They placed the trichloride (2 mol.) in a retort and 
 added gradually /3-oxyisovaleric ether (3 mol.) and heated the mix- 
 ture in the water bath until the evolution of hydrochloric acid 
 ceased. On adding water, dimethylacrylic ether separated as an 
 oily layer 
 (CH 3 ) 2 : C(OH). CH 2 . COOH = (CH 3 ) 2 : C : CH . COOH + H 2 O. 
 
 This agent is used also on a manufacturing scale. For example, 
 finely pulverised dry tetramethyldiamidobenzophenone (10 parts) 
 
23, 24] POTASSIUM CYANIDE 119 
 
 is dissolved in hot dimethylaniline (20 parts), and, when the solution 
 is cold, the trichloride (6 parts) is added. The interaction begins 
 at once, and the mixture becomes blue in colour and mobile. After 
 a short time crystallisation begins, accompanied by much evolution 
 of heat. The temperature is controlled by cooling, and the mass 
 soon becomes entirely solid. After remaining for a few hours the 
 product is dissolved in warm water, and, after the addition of a 
 slight excess of caustic soda, the excess of dimethylaniline is driven 
 off with steam. 
 
 23. Potassium Bisulphate, Wallach and Wusten (Ber. 16, 
 149) made a special study of the applicability of this substance as 
 a condensing agent, and they found it of considerable value. Thus 
 when benzaldehyde (2 parts), dimethylaniline (5 parts), and potas- 
 sium bisulphate (6 parts) are heated in a flask, immersed in a 
 paraffin bath, to 120- 150 for four to six hours, the leuco base of 
 malachite-green is formed, and can easily be extracted from the pro- 
 duct in a pure form. Nitrobenzaldehyde acts as easily as benz- 
 aldehyde itself. 
 
 Experimenting in another direction, they obtained the mono- 
 methyl ether of resorcinol by heating resorcinol (i mol.), methyl 
 alcohol (i mol.), and bisulphate (i mol.), for ten hours at 180. 
 
 On a large scale it can be used with advantage for the condensation 
 of aldehydes with secondary and tertiary amines and phenols, and of 
 alcohols with phenols. For example, benzaldehyde (21 parts), naphthol 
 (58 parts), and potassium bisulphate (54 parts), are heated for some hours 
 at 150. The mass is dissolved in alkali and the excess of benzaldehyde 
 expelled with steam, and the condensation product is finally precipitated by 
 addition of an acid. In this, as in many other cases, sodium and ammonium 
 bisulphates may be used in place of the potassium salt. 
 
 It may be well here to mention also the use of the bisulphate in distilling 
 glyceric acid and tartaric acid (Erlenmeyer, Ber. 14, 321) to obtain pyruvic 
 acfd. The latter yields 50-60 per cent, of the theoretically possible amount. 
 
 24. Potassium Cyanide. It has been shown by A. Smith (J. 
 Ch. Soc. 57, 643; Ber. 26, 60) that benzoin and other ketols con- 
 dense with acetophenone when boiled with this ketone in dilute 
 alcoholic solution in presence of a small quantity of potassium 
 cyanide. Benzoin yields desylacetophenone. 
 
 C 6 H 5 . CH(OH) + CH 3 . CO . C 6 H 5 = C 6 H 5 . CH . CH 2 . CO . C 6 H r> 
 i I +H 2 6. 
 
 C 6 H 5 . CO C 6 H 5 . CO 
 
izo CONDENSATION [CH. xn 
 
 Knoevenagel (Ber. 25, 294) finds that the nitrile of mandelic 
 acid and benzyl cyanide condense in presence of dilute potassium 
 cyanide solution to form the nitrile of diphenylsuccinic acid 
 
 C 6 H 6 .CH(OH) CH 2 .C 6 H 5 C 6 H 6 . CH - CH . C 6 H 5 
 
 I + I II +H 2 0. 
 
 CN CN CN CN 
 
 25. Potassium Hydroxide. Heintz (Ann. 169, 117) was pro- 
 bably the first to examine carefully the condensing power of caustic 
 potash. He found that pure acetone was not influenced by it, but 
 that impure acetone gave " polyacetone." 
 
 Japp and Streatfield (Ber. 16, 276) found that this hydroxide 
 was a much more convenient agent than ammonia for preparing 
 phenanthroxyleneacetoacetic ether. They mixed pulverised 
 phenanthrenequinone (100 gr.) with acetoacetic ether (90 gr.), 
 added 16 per cent, caustic potash solution (150 cc.), and warmed 
 the mixture gently. The temperature rose markedly, and the 
 colour of the solution changed as the action progressed. The yield 
 was very good. 
 
 Fossek (M. f. Ch. 4, 664) prepared di-isopropylglycol from 
 isobutyric aldehyde by the action of alcoholic caustic potash. 
 
 As in the case of ammonia, very small amounts of caustic potash 
 seem to suffice to induce condensation. 
 
 For example, Vogtheer (Ber. 25, 635) found that on mixing 
 equi-molecular proportions of amidodimethylaniline and benzil in 
 alcoholic solution no action took place. But as soon as a few drops 
 of caustic potash were added an almost quantitative yield of red 
 crystals was deposited. The substance had the formula C 22 H 20 N 2 O, 
 and was formed by loss of one molecule of water. 
 
 26. Silicic Ether. Ladenburg (Ann. 217, 78) experimented 
 with silicic ether as a condensing agent to convert the tropic acid 
 salt of tropine into atropine. 
 
 27. Silver. In the finely divided state silver has the power of 
 removing halogen atoms from organic compounds and so permit- 
 ting the union of the residues. 
 
 28. Sodium. In many condensations sodium is preferable even 
 to that marvellously useful substance sodium ethylate. 
 
 Wurtz (Ann. 96, 365) was the first to employ sodium for con- 
 
28] SODIUM 121 
 
 densation by preparing di-isobutyl by the action of the metal on 
 isobutyl iodide 
 
 2(CH 3 ) 2 : CH . CH 2 I + 2Na = (CH 3 ) 2 : CH . CH 2 . CH 2 . CH : (CH 3 ) 2 
 
 + 2NaI. 
 
 Potassium acts too violently, and cannot therefore take the place of 
 sodium. This reaction acquired more prominence when Fittig 
 (Ann. 149, 342) found that different radicals could be linked 
 together by its means. For example, he built up homologues of 
 benzene 
 
 The usual course of the method is to dilute the iodides with dry 
 ether, benzene, or toluene, and add about one and a half times the 
 calculated amount of the metal in thin clean slices. The vessel is 
 connected with a condenser, and is also cooled during the addition 
 of the sodium. As warming often causes the action to proceed 
 with extreme violence, it is better to allow it to go on slowly in the 
 cold. The yields reach 50-75 per cent, of the theoretical. 
 
 Sodium amalgam was used by Wurtz (Ann. Suppl. 7, 125), 
 particularly in the preparation of carboxylic acids. For example, 
 he heated bromobenzene (90 gr.) with chlorocarbonic ether (60 gr.) 
 and one per cent, sodium amalgam (3*5 kilos.) for several days in a 
 brine bath at 110, using a reflux condenser. At the expiration of 
 this time he poured the mercury away from the solid mass of salt, 
 extracted the latter with ether, and obtained benzoic ether by 
 fractional distillation of the extract 
 
 C 6 H 5 Br + C1COOC 2 H 5 + 2Na = C 6 H 5 . COOC 2 H 6 -f NaBr + NaCl. 
 
 Oxymethylenecamphor (Ann. 281, 331) is prepared by Bishop, 
 Claisen, and Sinclair as follows : Sodium (i mol.) in form of wire 
 is placed in a large flask containing dry ether. Camphor (i mol.) 
 dissolved in ether, and finally amyl formate in slight excess are 
 added in small portions at a time. The materials are carefully 
 cooled during the entire operation. After the mixture has remained 
 for a considerable time, ice-cold water is added, the ethereal layer is 
 removed, and the substance precipitated from its alkaline solution 
 by means of acetic acid. The substance, at first oily, soon becomes 
 crystalline 
 
 C 8 H 14 < | +HCOOC 5 H 11 = C 8 H 14 < | + C 6 H n OH. 
 
122 CONDENSATION [CH. xn 
 
 29. Sodium Acetate. This substance is used as a condensing 
 agent in the anhydrous form, and is prepared for the purpose by 
 fusing the ordinary crystalline sodium acetate. For example, 
 Grabe and Guye (Ann. 233, 241) heated a mixture of phthalide 
 ( 10 parts) and phthalic anhydride (17-20 parts) with the acetate 
 (5 parts) for ten hours at 260-265. On extracting the resulting 
 mass with water and a small quantity of alcohol, a fifty-five per 
 cent, yield of crystalline diphthalyl remained 
 
 + H 2 0. 
 
 Ruhemann (Ber. 24, 3>965) fused paratoluylacetic acid (i part) with 
 phthalic anhydride (i parts) and sodium acetate ( T V part) in a small flask. 
 The progress of the action could be traced by the rate of evolution of carbon 
 dioxide and steam. The product was /-xylidenephthalide, and the yield 
 was 75 per cent, of the theoretical 
 
 C 8 H 4 3 + C 9 H 10 2 = C 16 H 12 2 + C0 2 + H 2 C. 
 
 Gabriel (Ber. 17, 1,389) made some experiments on the condensation of 
 phthalic anhydride with acetoacetic ether in presence of sodium acetate, and 
 found that very complicated derivatives were formed. 
 
 A thorough examination of the subject by Liebens (M. f. Ch. 1, 
 8 1 8), has shown that even solutions of sodium acetate in water 
 have some condensing power. 
 
 30. Sodium Ethylate. The use of this remarkable condensing 
 agent is due to Claisen (Ber. 20, 655). 
 
 When solid sodium ethylate is used it should be freshly prepared, 
 ground in a warm iron mortar, and rapidly passed through a fine 
 sieve ; it cannot be preserved, except in hermetically sealed glass 
 flasks, as it absorbs not only moisture, but also oxygen. Hemmel- 
 mayr (M. f. Ch. 12, 115) has shown that it is converted into sodium 
 acetate. 
 
 When more than a very small quantity of sodium ethylate, free 
 from alcohol, is required, it cannot easily be prepared in glass 
 vessels, as they are liable to crack. Claisen uses a copper cylinder, 
 the head of which is fastened on with clamps, and heats it in an 
 oil bath at 200. The sodium is dissolved in portions in absolute 
 alcohol in a large flask attached to a reflux condenser, and the 
 saturated solution is poured through a tube in the lid into the 
 cylinder. The alcohol distils off through another tube connected 
 
30] SODIUM ETHYLATE 123 
 
 with a condenser, and can be used again with fresh absolute alcohol 
 for dissolving more sodium. A slow stream of dry hydrogen passes 
 constantly through the apparatus, entering by the first tube, and 
 serves to prevent access of air and to sweep out the last traces of 
 alcohol vapour ; by this process several kilograms of the substance 
 can be prepared in a day. 
 
 Small quantities can be made by a method suggested by Briihl 
 and Biltz (Ber. 24, 649). The methyl or ethyl alcohol is dissolved 
 in benzene or xylene, and the theoretical amount of sodium is 
 added. The mixture has to be heated in a flask attached to a 
 condenser for a considerable time, because the alcoholate is in- 
 soluble in the hydrocarbon and tends to protect the metal from 
 further action ; shaking the vessel helps to break the crusts of 
 alcoholate. Finally, the product remains as a white gelatinous 
 substance suspended in the diluent. 
 
 Many condensations have been carried out by Claisen with this 
 agent. For example, dibenzoylmethane (Ber. 20, 655) was formed 
 from benzoic ether and acetophenone, and the action is a general 
 one for esters and ketdhes 
 
 C 6 H 5 . COOC 2 H 5 + CH 3 . CO . C 6 H 5 = C 6 H 5 . CO . CH 2 . CO . C 6 H 5 
 
 + C 2 H 5 OH. 
 
 He mixed the pulverised sodium ethylate with molecular quantities 
 of the other ingredients, and found that the liquid mixture soon 
 became warm and solidified to a mass consisting chiefly of the 
 sodium salt of dibenzoylmethane ; the product is dissolved in 
 water and the diketone precipitated by means of a stream of carbon 
 dioxide ; the amount of the substance obtained is equal to fifty per 
 c^nt. of the acetophenone used. 
 
 By the help of the same condensing agent he also prepared 
 nitroso-ketones from mixtures of ketones with nitrous ether ; in such 
 cases the ethylate did not require to be free from alcohol. Thus 
 sodium was dissolved in twenty times its weight of alcohol, the 
 solution was cooled, and acetophenone and amyl nitrite added. 
 After the liquid had remained at a low temperature for twelve to 
 twenty-four hours the reddish-brown sodium salt of the nitroso-ketone 
 crystallised out 
 
 C H 5 . CO . CH 3 + C 2 H 5 ONa + C 5 H U O . NO = 
 C 8 H 5 .CO.CH:N.ONa+C 2 H 6 OH + C 6 H u OH. 
 
 On adding an acid the nitroso-ketone was obtained in the free 
 state. 
 
124 CONDENSATION [CH. xn 
 
 Benzoylacetone (Ber. 20, 2,178), C 6 H 5 .CO.CH 2 .CO.CH 3 , is prepared by 
 covering dry sodium ethylate (i mol.) with excess of acetic ether (2 mol.), 
 cooling the mixture in ice and adding acetophone ( I mol. ). The mass first 
 becomes fluid and then solid again, owing to the separation of the sodium 
 salt of benzoylacetone. The yield is equal to 80-90 per cent, of the aceto- 
 phenone taken. The higher homologues are formed by taking the corre- 
 sponding esters. 
 
 Benzoylpyruvic acid is prepared by dissolving sodium (9*2 gr.) in alcohol 
 (150 gr.), cooling the solution in ice, adding acetophenone (48 gr.) and 
 oxalic ether (58*4 gr.) and shaking the mixture. After the liquid has 
 remained for twelve hours a large amount of the sodium salt is deposited. 
 The yield is 78 per cent, of the theoretical 
 
 C 6 H 5 . CO . CH 3 + C 2 H 5 O . CO . CO . OC 2 H 5 = 
 C 6 H 5 . CO . CH 2 . CO . CO . OC 2 H 5 + C 2 H 5 OH. 
 
 Benzoylaldehyde, C 6 H 5 .CO.CH 2 .COH, whose preparation in other ways 
 had been attempted in vain, was made by Claisen by dissolving sodium 
 (i atom) in twenty times its weight of alcohol, cooling in ice, and adding 
 acetophenone (i mol.) and formic ether (i mol.). The sodium salt 
 separated in the course of two or three days, and the yield was good. 
 
 The method has been found to be applicable on a large scale, and is used 
 for the preparation of diketones and of esters of keto-acids. 
 
 An application made by V. Meyer (Ann. 250, I2 4) ma y be mentioned. 
 He treated benzylcyanide and benzaldehyde with sodium ethylate. The 
 mixture became warm and gave a solid mass of benzylidenebenzylcyanide, 
 the nitrile of a-phenylcinnamic acid 
 
 CgHs C 6 H 5 
 
 C 6 H 5 .COH+ | = | 
 
 CH 2 .CN C 6 H 5 .CH:C.CN 
 
 31. Sodium Hydroxide. The condensing power of very dilute 
 caustic soda was first noticed by Schmidt (Ber. 14, 1,459), and has 
 been carefully investigated by Claisen (Ber. 14, 2,468). Many 
 interactions proceed in presence of caustic soda with extreme 
 ease ; as, for example, the union of furfurol and acetone to form 
 furfurylideneacetone 
 
 C 4 H 3 . COH + CH 3 . CO . CH 3 = C 4 H 3 . CH : CH . CO . CH 3 + H 2 O. 
 
 According to Geigy and Konigs (Ber. 18, 2,406), quantitative 
 yields can be obtained by choosing the proper strength of the 
 alkaline solution ; in some cases boiling must be resorted to. 
 
 Fischer (Ber. 20, 3,386) oxidised glycerol with bromine and 
 carbonate of soda, obtaining a solution which contained glyceric 
 aldehyde, and also the isomeric dioxyacetone. By adding this 
 
31] SODIUM HYDROXIDE 125 
 
 solution to a liquid containing one per cent, of caustic soda, and 
 allowing the mixture to remain for four or five days at o, he 
 obtained a sugar, 1 a-acrose. 
 
 CH 2 (OH) . CH(OH) . COH + CH 2 (OH) . CO . CH 2 (OH) = 
 CH 2 (OH) . CH(OH) . CH(OH) . CH(OH) . CO . CH 2 (OH). 
 
 Einhorn and Diehl (Ber. 18 2,320) allowed 10 per cent, caustic soda to 
 drop into a mixture of cinnamic aldehyde (10 parts) and acetone (6 parts). 
 At first the alkaline reaction disappeared and the liquid became" warm. It 
 was cooled with water, and the addition of the alkali continued until the 
 alkaline reaction became permanent. After the lapse of twelve hours the 
 mixture was poured into water. The oil which separated soon solidified. 
 It was composed of two substances which could be separated by repeated 
 recrystallisation from absolute alcohol. There were formed cinnamylvinyl 
 methyl ketone and dicinnamylvinyl ketone. 
 
 Einhorn and Gehrenbeck (Ann. 253, 353) dissolved /-nitrobenzaldehyde 
 (5 g r -) i n boiling absolute alcohol (80 gr.), added water (15 cc.), and 
 allowed the solution to cool until it began to show turbidity. They then 
 added acetone (iogr.), and finally 2 percent, caustic soda drop by drop 
 until the alkaline reaction remained for five minutes. In this way they 
 obtained compounds corresponding to those described above. 
 
 Friedlander (Ber. 15, 2,574) prepared quinoline by adding a few 
 drops of caustic soda to a solution of 0-amidobenzaldehyde and 
 acetic aldehyde in dilute water solution, and then setting the base 
 free by addition of excess of alkali. He found that this method 
 was of almost perfectly general applicability for obtaining quinoline 
 derivatives having various groups attached to the pyridine nucleus 
 (Ber. 16, 1,833)- 
 
 H 
 
 H H C 
 
 H/XCOH CH 2 B H/\/\C . B 
 
 I II +1 = I II I +2HoO. 
 
 H\/NH 2 CO. A H\/V/C'A 
 H H N 
 
 For example, acetoacetic ether 
 
 CH 2 .COOC 2 H 5 
 
 CO . CH 3 
 
 can take the place of the aldehyde, and when it is used crystals of 
 
 1 The syntheses of sugars are treated fully in the author's " Moderne 
 Chemie, z wolf Vort rage vor Aerzten gehalten." Hamburg, 1891. 
 
126 CONDENSATION [CH. xn 
 
 a-methylquinoline /3-carboxylic ether are almost immediately de- 
 posited. 
 
 Victor Meyer (Ber. 17, 1,078), having found that sodium ethylate 
 gave a very bad yield, condensed methyl iodide and benzyl cyanide 
 by means of solid caustic soda. He used freshly-fused and pul- 
 verised sodium hydroxide (i mol.), added molecular proportions of 
 the other ingredients, and warmed the mixture. The interaction 
 took place with violence, and was completed by gently heating in 
 the water bath. The product contained methylbenzyl cyanide 
 along with some unchanged benzyl cyanide. 
 
 32. Sulphur. This substance has the power of removing 
 hydrogen and so inducing condensation. Thus Ziegler (Ber. 21, 
 780) prepared tetraphenylethylene by heating diphenylmethane 
 (20 gr.) with sulphur (8 gr.) in an oil bath at 240-250 
 
 The union of dissimilar radicals by this means does not seem to 
 have been investigated. 
 
 33. Sulphuric Acid. The condensing power of sulphuric acid 
 depends on its very strong attraction for water. Thus Baeyer 
 (Ber. 5, 1,098) mixed benzene (2 mol.) with chloral (i mol.) and 
 added an equal volume of concentrated sulphuric acid. On shaking 
 the mass became warm, and external cooling was used to keep the 
 temperature down. The upper blue-coloured layer was poured off 
 and shaken with fresh acid until it turned into a crystalline mass. 
 This was washed with water and purified by recrystallisation. The 
 yield of trichlorodiphenylethane was quantitative 
 
 CC1 3 . COH + 2C 6 H 6 = CC1 3 . CH/ 6 ^ 5 + H 2 O. 
 
 Similarly benzaldehyde (i mol.) was mixed with thymol (2 mol.) and 
 slightly diluted (4:1) sulphuric acid (10 cc.). The acid was added drop by 
 drop, with an interval after the addition of the first half to allow the 
 mixture to cool. On shaking, the mass crystallised and dithymolphenyl- 
 methane was formed. The yield was about 85 per cent, of the theoretical 
 
 C 6 H 5 . COH + 2C 10 H 14 = C 6 H 5 . CH(C 10 H 13 O) 2 + H 2 O. 
 
 Bottinger (Ber. 14, l>595) prepared diphenylpropionic acid by allowing 
 pyruvic acid to flow into ten times its volume of concentrated sulphuric 
 acid cooled to - 10. On adding benzene and shaking, the latter froze in 
 contact with the cold acid. The flask was then removed from the freezing 
 
331 SULPHURIC ACID 127 
 
 mixture and the shaking continued. The temperature gradually rose, and 
 the action was complete before the thermometer registered + 10. Above 
 this temperature decomposition takes place. 
 
 A modification of this plan was introduced by Jager (Ber. 7, 
 1,197). He dissolved thymol (2 mol.) in chloral (i mol.) and added 
 four or five times its bulk of sulphuric acid diluted with one third of 
 its volume of glacial acetic acid. The trichlorodithymolethane was 
 gradually deposited as a soft mass which became granular on 
 addition of water 
 
 CC1 . COH + 2C 10 H 13 OH = 
 
 This use of sulphuric acid and acetic acid together seems to be 
 advantageous in many cases. Thus Konigs (Ber. 24, 180) mixed 
 dihydronaphthalene (40 gr.) and phenol (28 gr.), cooled the mixture, 
 added pure sulphuric acid (40 cc.) and glacial acetic acid (40 cc.), 
 and shook the whole at intervals during twenty-four hours. Under 
 these circumstances the product became acetylised, and this part 
 of the action had to be undone by boiling the product with alcoholic 
 caustic potash. Tetrahydronaphthylphenol, C 10 H n .C c H 4 .OH, is 
 formed by addition, the yield being seventy per cent., but its purifi- 
 cation is far from simple. 
 
 Sulphuric acid is likewise applicable in cases of internal con- 
 densation. Thus Miller and Rohde (Ber. 25, 2,095) obtained 
 phenylhydrindone from a-phenylhydrocinnamic acid 
 
 C 6 H 
 
 \HHCK 
 
 They added the dry pulverised acid (10 gr.) to concentrated sul- 
 phuric acid (80 gr.) at a temperature of 140. The mixture was 
 shaken till solution was complete, an operation which occupied only 
 a few seconds, and then the brown effervescing mass was poured at 
 once upon three times its weight of ice. The resulting milky liquid 
 deposited gradually a flocculent crystalline precipitate of phenyl- 
 hydrindone. 
 
 For such internal condensations phosphoric acid (Ann. 234, 241) 
 or fuming sulphuric acid is frequently added. 
 
 A combination of condensation and oxidation is used in the pre- 
 paration of aurin tricarboxylic acid (Ber. 25, 939). This substance 
 
128 CONDENSATION [CH. xn 
 
 is formed by the action of salicylic acid (3 mol.) on methyl alcohol 
 (i mol.), for which formaldehyde or methylal can be substituted, in 
 presence of sulphuric acid and sodium nitrite 
 
 /C 6 H 3 (OH).COOH 
 3C 6 H 4 (OH). COOH + CH 3 OH + 30 = C C 6 H 3 (OH) . COOH + 
 
 \C 6 H 3 . COOH 4H 2 O. 
 
 There may be a difference of opinion as to whether Skraup's 
 synthesis of quinoline can be regarded as a case of oxidation com- 
 bined with condensation or not, but the method demands a place 
 here on account of its importance. 
 
 In 1877 Prudhomme (Ber. 11, 522) stated that nitroalizarin gave 
 a blue colouring matter when heated with glycerol and sulphuric 
 acid. Following this up Brunk devised a method of preparing the 
 substance on a large scale by the action of glycerol and sulphuric 
 acid on alizarin and nitroalizarin at a high temperature. A little 
 later Grabe (Ber. 11, 1,646) expressed the opinion that the glycerol 
 not only acted as a reducing agent, but also took part in a remark- 
 able synthesis expressed by the equation 
 
 C 14 H 7 4 (N0 2 ) + C 3 H 8 3 = C ir H 9 N0 4 + sH 2 O + 2O, 
 
 producing a substance, C 17 H 9 NO 4 , which was closely related to 
 quinoline. Finally this led Skraup (M. f. Ch. 2, 141) to investigate 
 the action of sulphuric acid on glycerol and nitrobenzene. He 
 added also aniline in order to supply the oxygen set free by the 
 action with a substance which it could easily oxidise. Quinoline 
 was formed in accordance with the equation 
 
 C 6 H 5 NH 2 + C 6 H 5 N0 2 +2C 3 H 8 3 =2C 9 H 7 N + 7H 2 + 0. 
 
 In practice nitrobenzene (144 parts), aniline (216 parts), glycerol 
 of sp. gr. i '24 (600 parts), and sulphuric acid (600 parts), are mixed 
 together (Am. Pat. 241,738) in a flask connected with a reflux con- 
 denser and heated, at first gently and later more strongly, for 
 several hours. The mixture is then diluted with water, and the 
 unchanged nitrobenzene driven over with steam. On now adding 
 caustic soda the quinoline is set free and can likewise be driven 
 over. The yield is about seventy per cent, of the theoretical. 
 
 A great variety of quinoline derivatives can be prepared by this 
 method, by using, instead of aniline and nitrobenzene, their homo- 
 logues and isologues. Whether these can be replaced by sub- 
 stances resembling them in chemical properties while differing from 
 
34] TIN TETRACHLORIDE 129 
 
 them in chemical nature (iaidioms, Ber. 25, 2,394) does not seem to 
 have been investigated. 
 
 In connection with this subject mention must be made of the 
 interesting cases in which concentrated sulphuric acid brings about 
 the addition of water. The acid has the power, for example, of 
 transforming nitriles into amides. Thus Tiemann and Stephan 
 (Ber. 15, 2,035) rnixed a-anilidopropionitrile with sulphuric acid 
 guarding at the same time against any considerable rise in temper- 
 ature in the mass. After the mixture had remained at rest for a 
 sufficient time, addition of water precipitated none of the unchanged 
 nitrile, and on adding ammonia to the diluted solution the amide 
 was thrown down 
 CH 3 .CH(NHC G H 5 ).CN + H 2 = CH 3 .CH(NHC 6 H 5 ).CO.NH 2 
 
 Baeyer (Ber. 15, 2,705) dissolved phenylpropiolic ether in 
 sulphuric acid, allowed the solution to remain for some time, and 
 then poured it on to ice. By purifying the oil which separated 
 benzoylacetic ether was obtained 
 
 C 6 H 5 . CiC. COOC 2 H 5 + H 2 O = C 6 H 6 . CO. CH 2 . COOC 2 H 6 . 
 
 He found that phenylacetylene, amidophenylacetylene, and^-nitro- 
 phenylpropiolic acid had the same property. 
 
 Flawitzki and Krylow (Centralblatt, 1878, 262) found that methyl- 
 isopropylketone, (CH 3 ) 2 : CH.CO. CH 3 , was formed when isopro- 
 pylacetylene, (CH 3 ) 2 : CH.C ! CH, was shaken with sulphuric acid 
 srj. gr. 1-64. 
 
 The student may be reminded in conclusion of the use of a few 
 drops of sulphuric acid in converting polymerised aldehydes into 
 the simple forms. Thus Weidenbusch (Ann. 66, 157) converted 
 paraldehyde into aldehyde, and Fossek (M. f. Ch. 4, 662) tri-isobu- 
 tyric aldehyde into isobutyric aldehyde by this means. 
 
 34. Tin Tetrachloride, Baeyer (Ann. 202, 68) found in this 
 substance the most efficient condensing agent for preparing phtha- 
 leins. He heated phthalic anhydride with phenol and stannic 
 chloride for five hours at 120. The resulting reddish-brown mass 
 was warmed with water on the water bath and the residue dis- 
 solved in sodium carbonate. The solution was filtered from the 
 precipitate, which contained the tin. The phthalein was deposited 
 in an almost pure condition on the addition of hydrochloric acid to 
 the filtrate. 
 
 Graebe (Ann. 247, 286) heated diphenyleneketone carboxylic 
 
13 CONDENSATION [CH. xn 
 
 acid (15 gr.) with phenol (20 gr.) and stannic chloride (25 gr.), obtain- 
 ing an excellent yield (20-22 gr.) of the condensation product. 
 
 Fabinyi (Ber. 11, 283) added the chloride drop by drop to a cold 
 mixture of phenol and paraldehyde until, even after the lapse of 
 half an hour, the fumes of stannic chloride were still perceptible. 
 After washing the product with water and distilling it in vacua, 
 he obtained diphenolethane 
 
 CH 3 . COH + 2C 6 H 6 OH = CH 3 . CH(C 6 H 4 OH) 2 + H 2 O. 
 
 Steiner (Ber. 11, 286) recommends the dilution of the chloride 
 with chloroform. 
 
 Michael (Ber. 16, 2,298) heated phenol (50 gr.) and salicylic 
 acid (50 gr.) with stannic chloride (40 gr.) for fourteen hours at 
 115-120, raising the temperature finally to 125. The phenol was 
 removed with steam, and the residue boiled with great excess of 
 sodium carbonate. Carbon dioxide precipitated salicylphenol, 
 
 <C T-T OT-T 
 C H OH' from the filtrate - The Y ield was much better than 
 
 when zinc chloride was used. 
 
 35. Zinc. This substance was first used as a condensing agent 
 by Frankland and Duppa (Ann. 133, 80). They began by causing 
 zinc ethyl to act upon oxalic acid, but found later that the same end 
 was attained by the action of zinc on ethyl iodide and oxalic ether. 
 Thus they mixed methyl iodide (2 mol.) with methyl oxalate 
 (i mol.) and excess of amalgamated granulated zinc, and heated 
 the whole in a flask attached to a condenser, the top of which was 
 connected with a tube dipping into mercury. Methyl dimethyl- 
 oxyacetate was produced as the result of continuous heating for 
 twenty-four hours, at first at 70 and later at 100. Later investi- 
 gations showed that it was preferable (Ann. 135, 25) to allow the 
 mixture to stand for four days without heating. 
 
 This method is susceptible of general application. For example, 
 Saytseff (Ann. 175, 363) mixed formic ether (i mol.) with an excess 
 of ethyl iodide (4 mol.), and added some zinc-sodium and so much 
 dry finely granulated zinc that it was not completely covered by the 
 liquid. After heating the whole, with a reflux condenser -attached, 
 and decomposing the product with water, he obtained secondary 
 
 amyl alcohol 
 
 /OH 
 
 + 2Zn = H . C C 2 H 5 + C 2 H 6 OH 
 \C 2 H 6 
 
 + ZnI 2 + ZnO 
 
36] ZINC CHLORIDE 131 
 
 In these cases, therefore, the carbon yl oxygen was replaced by two 
 alkyl groups. 
 
 Hofmann (Ann. 201, 85) has shown that allyl iodide can be used 
 in the same way as the saturated alkyl iodides. 
 
 The amalgamated zinc mentioned above was used also by 
 Daimler (Ann. 249, 174). He prepared it by dipping the granu- 
 lated metal into a dilute solution of mercuric chloride, and washing 
 and drying it. 
 
 In preparing naphthyl ketones from naphthalene and benzoyl 
 chloride, Kegel (Ann. 247, 1,807) mixed the ingredients, using one 
 and a half molecular proportions of the naphthalene, and, to avoid 
 over violent action, merely dipped a small strip of zinc into the 
 heated liquid. Two ketones were formed. 
 
 Zincke (Ann. 159, 373) boiled benzyl chloride (100 gr.) and 
 toluene (72 gr.) with zinc, and obtained 32 grams of distillate and 
 90 grams of residue. The interaction took place in accordance 
 with the equation 
 
 C 6 H 5 .CH 2 C1 + C 6 H 5 .CH 3 = C 6 H 5 .CH 2 .C 6 H 4 .CH 3 + HC1 
 
 36. Zinc Chloride. The use of this substance was first dis- 
 covered by O. Fischer (Ann. 206, 86), who drew attention to the 
 fact that it had a surprisingly great condensing power, even ap- 
 proaching aluminium chloride itself in this respect. He used the 
 chloride in the form of a fine powder, and pointed out that, to give 
 good results, it should be pure. In particular, it should be free 
 from the basic carbonate which the commercial chloride often con- 
 tains. In making fused zinc chloride, copper basins are said to be 
 the best vessels to use. Merz and Muller (Ber. 19, 2,902) state 
 that it can be obtained by passing excess of hydrochloric acid gas 
 into the common chloride which has been fused in a retort. 
 Usually no great amount of the gas is required. The excess is 
 expelled with dry hydrogen. 
 
 The following preparation illustrates Fischer's method. Dry 
 chloride of zinc is added, a little at a time, to a mixture of phthalic 
 anhydride (i mol.) and dimethylaniline (2 mol.) until an amount of 
 it equal to that of the base has been used. The action begins at 
 1 00, and the mixture is warmed and stirred on the water bath for 
 several hours. To complete the action it is heated for four hours 
 in an oil bath at 120-150. The mixture becomes gradually semi- 
 solid, and on cooling forms a hard, brittle lump. This is dissolved 
 in dilute hydrochloric or sulphuric acid, and the solution is placed 
 
 K 2 
 
132 CONDENSATION [CH. xn 
 
 in a large flask along with excess of concentrated caustic soda. 
 The unused dimethylaniline is driven off with steam, and the 
 phthalein solidifies on cooling in the residue. The yield is about 
 50 per cent, of the theoretical 
 
 Fischer and Korner (Ber. 17, 99) heated orthoformic ether (i part) with 
 dimethylaniline (3-4 parts) on the water bath for several hours, and added 
 the chloride (2 parts) gradually. The hexamethylparaleucaniline which 
 was formed was isolated from the resulting blue mass by driving off the 
 excess of dimethylaniline with steam, dissolving the residue in hydrochloric 
 acid and pouring the solution into cooled ammonia. The base was 
 deposited in crystalline form and almost theoretical amount 
 
 When substances prepared by this method are soluble in water 
 they are extracted with ether. 
 
 Zinc chloride has also the power of condensing acid chlorides 
 with anhydrides. Thus Doebner (Ber. 14, 648) heated benzoic 
 anhydride with benzoyl chloride in a flask provided with a con- 
 densing tube. The action was started and maintained by adding 
 small amounts of zinc chloride from time to time. At the end of 
 eight hours fresh additions of the chloride produced no further 
 evolution of hydrochloric acid. The product was benzoylbenzoic 
 acid, C 6 H 5 .CO.C 6 H 4 .COOH. 
 
 Liebmann (Ber. 14, 1,842) dissolved phenol (100 gr.) in isobutyl 
 alcohol (80 gr.), and heated it with zinc chloride (240 gr.) in a flask 
 attached to a condenser. One molecule of water was eliminated, 
 and as soon as the evolution of white vapours began, an indication 
 that decomposition was taking place, he allowed the mass to cool, 
 and dissolved it in water acidulated with hydrochloric acid. On 
 distilling the supernatant oil he obtained isobutylphenol (105 gr.) 
 C 4 H 9 .C 6 H 4 .OH. 
 
 Hantzsch (Ber. 13, 1,347) states that when naphthylamine (3 
 parts) is heated in a sealed tube with an equal amount of methyl 
 alcohol and zinc chloride (4 parts) at 180-200, ammonia is evolved 
 and an almost quantitative yield of a-methoxynaphthalene obtained. 
 
 This power which zinc chloride has of effecting syntheses with 
 elimination of ammonia was used by E. Fischer (Ann. 236, 116) 
 for the synthesis of indole derivatives. He found that phenyl- 
 hydrazones of aldehydes and ketones were easily converted into 
 
36] ZINC CHLORIDE 133 
 
 indoles by loss of ammonia. Thus, when acetone phenylhydrazone 
 is heated to 170-180 with four or five times its weight of zinc 
 chloride, the action begins almost immediately, and when it is over 
 a molten dark-coloured mass remains. This is treated with water 
 and the a-methylindole driven over with steam. It appears as an 
 almost colourless oil which soon solidifies in the receiver. The 
 yield is more than sixty per cent, of the theoretical 
 
 P H NH N r/ 3 P 
 
 ^ 6 n 5 rsiri.rs, . L,V jj U 6 
 
 Chloride of zinc can also be used for the synthesis of pyrrole 
 derivatives (Ber. 20, 851), but the yields attained so far have been 
 rather poor. 
 
 It has already been pointed out (Chap. II. 4), that zinc 
 chloride assists greatly the introduction of acetyl groups by means 
 of acetic anhydride. When glycerol is mixed with four times its 
 weight of acetic anhydride and a little piece of the chloride is 
 added, the action is explosively violent (Ber. 12, 2,059). Erwig 
 and Konigs (Ber. 22, 1,465) obtained the pentacetyl derivative of 
 grape sugar by dissolving a little zinc chloride in 20 cc. of acetic 
 anhydride and adding 5 grams of dextrose to the boiling-hot solu- 
 tion. The yield was sixty per cent. When the action took place 
 at 100 and the solution was boiled for a short time, after remaining 
 on the water bath for half an hour, octacetyldiglucose was formed. 
 
 Zinc chloride has some condensing power in solution, although in 
 most cases the yields are better when the substances are fused 
 together without a solvent. Thus Bourquin (Ber. 17, 502) dis- 
 solved zinc chloride (3 parts) in warm glacial acetic acid (2 parts), 
 added salicylic aldehyde (i part), and heated the whole for a short 
 time at 145. The condensation product was separated by pouring 
 the solution into water 
 
 2C 7 H 6 2 =C 14 H 10 3 +H 2 0. 
 
 If the acetic acid is removed by distillation, instead of by pour- 
 ing into water, it is found to have acquired condensing powers 
 which it does not ordinarily possess. 
 
 Friedlander and Weinberg (Ber. 15, 2,103) warmed amido- 
 cinnamic ether in a saturated alcoholic solution of zinc chloride at 
 80-90. On rendering the solution alkaline they found that ethoxy- 
 quinoline was driven over by steam. 
 
 The investigations of Varennes (Bull. Ch. 40, 266) illustrate 
 well the statement made above, that condensing agents are not 
 
i 3 4 CONDENSATION [CH. xn 
 
 interchangeable. He found, for example, that no mesitylene was 
 formed from acetone by the action of zinc chloride. But when 
 acetone (180 gr.) and sulphuric acid (300 gr.) were warmed for an 
 hour, and steam finally driven through the mixture, 40 grams of 
 impure mesitylene were carried over. 
 
 A combination of condensation and oxidation was used by 
 Bindschedler (Ber. 16, 865). He took an aqueous solution of 
 dimethyl-/-phenylenediamine (i mol.) and dimethylaniline (i mol.) 
 containing a little zinc chloride, and treated it, at 30, with as much 
 potassium bichromate as would release two atomic proportions of 
 oxygen. In a few minutes glittering copper-coloured crystals of 
 pure " dimethylphenylene green " were deposited 
 
 + 20 = C 16 H 19 N 3 + 2H 2 0. 
 
 The temperature used in zinc chloride condensations may have 
 an important influence on the result. Where nitro-derivatives are 
 used it is especially necessary to keep the temperature as low as 
 possible. Thus Fischer and Schmidt (Ber. 17, 1,889) found that 
 in condensing 0-nitrobenzaldehyde (i part) with dimethylaniline 
 (3-4 parts), the mixture had to be warmed on the water bath, the 
 zinc chloride (i part) added very slowly, and the greatest care 
 taken to keep the temperature from exceeding 100. When 
 sufficient care was not taken the mass became resinised through 
 the oxidising influence of the nitro-group. On the other hand with 
 careful treatment an almost quantitative yield was attained. 
 
 The different effects of different temperatures may be further 
 illustrated by reference to some experiments described by Boessnek 
 (Ber. 19, 367). When chloral hydrate (20 parts), diethylaniline 
 (50 parts), and zinc chloride (10 parts) are allowed to interact at 
 100 the mixture becomes green in colour and stiff in consistency at 
 the end of five hours. If the mass is now dissolved in dilute 
 sulphuric acid a substance having the constitution 
 
 [(C 2 H 5 ) 2 N . C 6 H 4 ] 3 i C . CH : [C 6 H 4 . N(C 2 H 6 ) 2 ] 2 
 
 is precipitated. When, instead of heating the substances, zinc 
 chloride (10 gr.) is mixed with the chloral hydrate (20 gr.) and 
 diethylaniline (60 gr.) in the cold and the mixture is allowed to 
 remain at 40 for two days, and the mass is dissolved in dilute 
 hydrochloric acid, the addition of ammonia precipitates nothing 
 but zinc hydroxide. This can be dissolved in excess of ammonia. 
 
37, 38] ZINC OXIDE 135 
 
 and extraction of the solution with ether then removes a substance 
 having the constitution CC1 3 .CH(OH).C 6 H 4 .N(C 2 H 5 ) 2 . 
 
 Doebner (Ber. 12, 813) heated in a sealed tube acetone (i mol.), 
 dimethylaniline (2 mol.), and zinc chloride (i mol.) for several 
 hours at 150. Tetramethyldiamidodiphenyldimethylmethane was 
 formed 
 
 CH 3X CH 3X / C H 4 .N(CH 3 ) 2 
 
 >CO + 2C 6 H 5 . N(CH 3 ) 2 = >C< +H 2 
 
 CH/ CH/ \C 6 H 4 .N(CH 3 ) 2 
 
 Calm (Ber. 16, 2,786) found that excellent results could be 
 obtained by using a mixture of zinc chloride and calcium chloride. 
 The yields were sometimes as high as 90 per cent, of the theoretical. 
 Thus he prepared diphenyl-/-phenylenediamine by heating 
 quinol (i mol.) and aniline (4 mol.) with calcium chloride (3-4 
 mol.) and zinc chloride ( mol.) at 200-210 in a sealed tube. As 
 good yields as his can now be obtained in open vessels by other 
 methods. 
 
 37. Zinc Dust. Zincke (Ann. 159, 374) condensed benzyl 
 chloride and benzene to diphenylmethane, C 6 H 5 .CH 2 .C 6 H5, by 
 means of zinc dust. Similarly Symons and Zincke (Ann. 171, 123) 
 synthesised diphenylacetic acid from phenylbromacetic acid (20 gr.) 
 and benzene (40 gr.). Larger amounts cannot be used at one time 
 as the interaction is very violent. The substances are mixed and 
 warmed on the water bath, and zinc dust is added in small 
 portions as long as hydrogen is evolved from the action of hydro- 
 bromic acid on the metal. The action is completed by continuing 
 the heating for several hours 
 
 C 6 H 5 . CHBr. COOH + C 6 H 6 =(C 6 H 6 ) 2 CH . COOH + HBr. 
 
 Paat (Ber. 17, 911) dissolved benzophenone (i mol.) and acetyl 
 chloride (4 mol.) in dry ether and added zinc dust. The solvent 
 boiled spontaneously, and 3-benzpinacolin was formed in quantitative 
 amount. When only one molecular proportion of acetyl chloride 
 was used an equally good yield of a-benzpinacolin was obtained. 
 
 38. Zinc Oxide. Doebner and Stackmann (Ber. 9, 1,919) 
 acted with benzotrichloride on phenol in presence of zinc oxide and 
 obtained benzoylphenol 
 
 2C 6 H 5 . CCl 3 + 2C 6 H 6 QH + 3 ZnO = 2C 6 H 5 . CO . C 6 H 4 OH + 3 ZnCl 2 
 
 + H 2 O. 
 
136 CONDENSATION [CH. xn 
 
 39. Effect of Heat Alone, We have already seen (Chap. IV. 
 8) that when organic bodies are conducted through red-hot 
 tubes all kinds of chemical changes take place. Many of these 
 are of the nature of condensations. Hydrocarbons are particularly 
 liable to lose hydrogen and condense to form larger molecules. 
 Thus benzene and ethylene (Z. Ch. 1866, 709) form styrene 
 
 C 6 H 6 + C 2 H 4 = C 6 H 5 . CH : CH 2 + H 2 
 
CHAPTER XIII 
 
 PREPARATION OF DIAZO-BODIES 
 
 1. Introductory. As is well known, Griess was the first to 
 prepare diazo-bodies by the action of nitrous acid on salts of 
 amido-compounds. 1 As they are very powerfully reactive they are 
 frequently prepared, but are less frequently isolated from the solu- 
 tions in which they are made. The chief reason why they are at 
 once worked up into other compounds is that many of them are 
 highly explosive in the dry condition. For example, diazobenzene 
 nitrate explodes more violently than fulminate of mercury (Ber- 
 thelot, Bull. Ch. 37, 385) on being slightly warmed. 
 
 Diazo-bodies are now seldom prepared by the direct action of 
 free nitrous acid. The usual course is to apply this in the nascent 
 condition by adding sodium or potassium nitrite to an acid solution 
 of the base. In exceptional cases amyl nitrite is employed, and 
 more rarely still silver nitrite or oxidation processes. 
 
 2. Preparation of Nitrous Acid. The gas is best prepared 
 by warming arsenious oxide with 50 per cent, nitric acid in the 
 water bath. When starch is used in place of arsenious oxide the 
 stream of gas is very rapid, and only lasts a short time. An 
 alternative method is to prepare the gas by the action of dilute 
 sulphuric acid on sodium nitrite. 
 
 The exact composition of the gases obtained by such means is 
 uncertain, and doubtless a gas of constant composition is pro- 
 curable only by working always under the same conditions. Thus 
 
 1 In regard to the direct use of the solutions of amido-compounds 
 obtained by reduction from the corresponding nitro-derivatives, see the 
 chapter on " Reduction" (XIX.) under the use of tin in acid solution. 
 
138 DIAZO-BODIES [CH. xm 
 
 Silberstein (J. pr. Ch. 135, 101) found that when nitrous acid, from 
 arsenious oxide and nitric acid, was conducted into tribromaniline, 
 which was partly dissolved and partly suspended in cold water, in 
 a rapid stream, the chief product was tribromodiazobenzene nitrate. 
 When the gas arising from arsenious oxide and nitric acid, without 
 warming, was conducted in a slow stream into the same mixture, 
 hexabromodiazoamidobenzene was formed, and much tribromaniline 
 remained unattacked even after prolonged exposure to the action 
 of the gas. 
 
 3. Use of Nitrous Acid. The earliest notice of the interesting 
 action of nitrous acid on amido-derivatives is due to Piria (Ann. 
 68, 349). By its action on asparagine in nitric acid solution he 
 obtained malic acid, with intermediate formation of aspartic acid 
 
 COOH . CH . NH 2 COOH- CH OH 
 
 | + HN0 2 = | +N 2 + H 2 0. 
 COOH . CH 2 COOH . CH 2 
 
 Strecker (Ann. 88, 54) and others used the same reaction for 
 the production of oxy-compounds. 
 
 Ganahl (Ann. 99, 240) was the first, however, according to 
 Chiozza, to obtain a body containing more nitrogen than the 
 parent substance by the action of nitrous acid on naphthylamine. 
 Griess (Ann. 113, 207) then obtained, by the action of nitrous acid 
 on a solution of ;;z-dinitro-0-amidophenol in nitric acid, a substance 
 which he named diazodinitrophenol on account of the fact that it 
 retained the properties of a phenol and had half of its nitrogen 
 bound in a peculiar manner. He soon found (Ann. 120, 126) 
 that the same action takes place in nitric acid solutions containing 
 alcohol or ether in place of water, that a low temperature is the 
 essential condition for diazotisation, and that the action takes a 
 different course when the amido-body is employed in the free 
 state from that which it follows when the base is combined with 
 an acid. 
 
 For example, when nitrous acid acts on amidobenzoic acid in 
 cold alcoholic solution diazoamidobenzoic acid is produced. But 
 if the amidobenzoic acid is dissolved in water or alcohol with nitric 
 acid, the nitrate of diazobenzoic acid is formed, and, if the solution 
 is concentrated, separates as a precipitate. 
 
 In preparing diazobenzene nitrate he (Ann. 137> 4 1 ) covered aniline 
 
3 ] USE OF NITROUS ACID 139 
 
 nitrate with a quantity of water insufficient to dissolve it, and, keeping the 
 temperature below 30, passed nitrous acid into the mixture 
 
 C 6 H 5 . NJHsi ;HiNO 3 
 
 -fjOjNiOH] '=C 6 H 5 .N :N.N0 3 + 2H 2 0. 
 
 As soon as a sample showed no separation of aniline on addition of 
 caustic potash the reaction was complete, and the solution was filtered and 
 diluted with three times its volume of alcohol. On the further addition of a 
 little ether, the new body came out almost completely in crystalline form. 
 
 As early as 1867 (Jahresb. 1866 461, and J. pr. Ch. 101, 90, he made 
 the first of the tetrazo-compounds which are now of such importance in the 
 preparation of substantive d^yes. He obtained it by treating a solution of 
 benzidine nitrate in water with nitrous acid. On filtering the solution to 
 remove a brown impurity and adding alcohol and ether, tetrazodiphenyl 
 nitrate crystallised out 
 
 C 6 H 4 . NH., . HNO 3 C 6 H 4 . N : N . NO 3 
 
 + 2HNO^= | + 4H 2 O. 
 
 C 6 H 4 . NH 2 . HNO 3 C 6 H 4 . N : N . NO 3 
 
 Before distilling the mother liquors on the water bath to recover the 
 ether, the liquids must be shaken with water to remove any crystals which 
 may be present in them. Neglect of this precaution may lead to dangerous 
 explosions. 
 
 Heinzelmann (Ann. 188, J 74) prepared diazobenzenedisulphonic acid 
 by leading nitrous acid into an alcoholic solution of crystallised aniline- 
 disulphonic acid and precipitating with ether. The product appeared as an 
 oil which solidified on standing over sulphuric acid. 
 
 Many diazo-derivatives are insoluble in absolute alcohol. Thus Ascher 
 (Ann. 161, 8) suspended toluidinesulphonic acid in this solvent, treated it 
 with nitrous acid, and obtained at once diazotoluenesulphonic acid in 
 crystalline form. According to Mohr, however (Ann. 221, 220), alcohol 
 frequently hinders diazotisation. He found, for example, that ^-diazobenzyl- 
 sulphonic acid was not formed on leading nitrous acid into an alcoholic 
 solution of the amido-acid, but that it was formed by covering the acid with 
 water, introducing the nitrous acid, and then precipitating with alcohol. 
 
 Many diazo-compounds cannot be removed from solution in 
 water by mixing with alcohol and ether. In such cases they can 
 often be obtained by the addition of mineral acids, sometimes 
 appearing in the form of free diazo-bodies, sometimes in the form 
 of salts. 
 
 Thus Kollrepp states (Ann. 234, 29) that when chloroamido- 
 phenolsulphonic acid was suspended in water, and nitrous acid 
 
140 DIAZO-BODIES [CH. xni 
 
 conducted into the mixture, a clear solution was soon produced, 
 from which alcohol and ether did not precipitate anything. On 
 now leading gaseous hydrochloric acid into the liquid, crystals 
 appeared, which turned out to be chlorodiazophenolsulphonic acid. 
 They were recrystallised from dilute hydrochloric acid. 
 
 Schmitt (Ber. 1, 67) diazotised amidophenol hydrochloride by 
 covering it with alcohol saturated with nitrous acid and cooling 
 the mixture with ice. Ether was finally added in large quantity, 
 and the solution became nearly solid from the separation of 
 crystalline diazophenol chloride. 
 
 4. Use of Sodium Nitrite. The method of diazotisation by the 
 use of nitrous acid in gaseous form presents many inconveniences, 
 and its use is probably confined to the laboratory. Even there 
 the addition of a solution of sodium nitrite to an acidified solution 
 of the amide is the more usual method (cf. Meyer and Ambiihl, 
 Ber. 8, 1,074). The commercial sodium nitrite contains ninety- 
 eight per cent, of NaNO 2 , and the nitrous acid set free from it acts 
 quantitatively in statu nascendi. By this means the operation of 
 diazotisation has been greatly simplified. 
 
 Friedlander (Fortschritte d. Farbenfabrikation, I. 542) makes 
 the following clear and precise statement in regard to the process 
 and the behaviour of various bodies when submitted to it : When 
 the molecular proportion of sodium nitrite dissolved in water is 
 added to acid solutions of aromatic amines, whose salts are soluble 
 in water, such as aniline and xylidine, they are diazotised almost 
 instantaneously. When the salts are difficultly soluble, as with 
 benzidine sulphate, the action may be prolonged through several 
 hours ; and the same is true of amidosulphonic acids, such as 
 sulphanilic acid and naphthionic acid, which are usually but slightly 
 soluble. To secure a sufficiently fine state of division, substances 
 of the latter kind are always precipitated from an alkaline solution 
 with acids, and then submitted directly to the action of the mole- 
 cular proportion of sodium nitrite with previous addition of a 
 corresponding proportion of hydrochloric acid. After the mixture 
 has remained in the cold for several hours the interaction is 
 quantitative as with the former class of bodies. 
 
 The following examples illustrate the use of sodium nitrite. 
 Fischer and Kuzel (Ann. 221, 272) dissolved amidocinnamic acid 
 (10 parts) in a warm mixture of two molecular proportions of 
 hydrochloric acid of sp. gr. 1*19 .(9 parts) with water (70 parts). 
 
4] USE OF SODIUM NITRITE 141 
 
 When the solution cooled crystals separated out in large quantities, 
 and the calculated amount of sodium nitrite was run in, the whole 
 being well cooled and shaken during the process. Usually the 
 crystalline matter passed completely into solution under this treat- 
 ment, and a little later the chloride of the diazo-compound appeared 
 as a yellow crystalline powder. 
 
 Erdmann (Ann. 247, 3 2 9) used a modification of this process in 
 diazotising naphthionic acid. The sodium salt of naphthionic acid (180 
 gr. ) was dissolved in warm water (800 cc. ) and the solution allowed to cool 
 In a large basin 1-2 litres of water were mixed with 13 per cent, hydro- 
 chloric acid (650 cc.), or with concentrated sulphuric acid (120 gr.), and 
 the whole was cooled by throwing into it pieces of carefully cleansed ice. 
 Two burettes were suspended over this basin, one filled with 5 per cent, 
 sodium nitrite solution, the other, having a very small exit for the liquid, 
 with the prepared solution of the salt of naphthionic acid. First a few 
 cubic centimetres of the sodium nitrite were allowed to flow into the basin, 
 and then a very small continuous stream of the solution of the organic salt 
 was started. The contents of the basin were violently stirred with a glass 
 rod to prevent the aggregation into lumps of the naphthionic acid which 
 was at first precipitated by the mineral acid. Meanwhile the addition of 
 sodium nitrite was continued at such a speed that the liquid always smelt 
 slightly of nitrous acid, and a piece of filter paper containing starch and 
 potassium iodide was rendered blue by a drop of the mixture. About 760 
 cc. of the sodium nitrite solution was required. 
 
 When the naphthionic acid has all been introduced and the mass has 
 remained at rest for half an hour it must still show the reaction with 
 potassium iodide, as otherwise more sodium nitrite is needed. The yellow 
 cliazoamido- compound, after settling, is collected on cheese-cloth, washed 
 with water, pressed to remove the most of the latter, and dried on clay 
 plates in vactto over sulphuric acid. It is better, if the substance is not 
 required in a dry condition, to wash it by decantation, place it in a tall 
 cylinder, and make up the mass to a volume of i '8 litres. This paste con- 
 tains 10 per cent, of the diazo-compound which may be preserved for use 
 in this state. 
 
 Gabriel (Ber. 15, 2,295) boiled amidocinnamic acid with 20 per cent, 
 hydrochloric acid (7*5 gr. ) and water (27^5 cc. ) till the whole went into 
 solution, allowed the liquid to cool, and added to the lukewarm semi- 
 crystalline mass a solution of sodium nitrite (2*5 gr.) in water (50 cc.) in 
 small portions at a time. The mixture became entirely fluid and was 
 rapidly filtered from a small amount of undissolved yellow matter. On 
 adding about twice its volume of concentrated nitric acid yellowish-brown 
 crystals of 0-diazocinnamic acid (5 gr. ) began to collect at the bottom. 
 
142 DIAZO-BODIES [CH. xin 
 
 5. Other Ways of Obtaining Diazo-Bodies. The presence of 
 mineral acids may be avoided by acidifying with oxalic acid instead 
 of hydrochloric or sulphuric acids. 
 
 Inorganic substances can be avoided entirely by using amyl 
 nitrite as a source of nitrous acid. Thus Victor Meyer and Ambiihl 
 (Ann. 251, 56) dissolved aniline (2 mol.) in several times its volume 
 of ether, added amyl nitrite (i mol.), and allowed the mixture to 
 evaporate in open vessels over sulphuric acid. Beautiful golden- 
 yellow transparent crystals of diazoamidobenzene, quite free from 
 resinous matter, were formed, which had only to be pressed in 
 filter paper to remove adhering amyl alcohol. The interaction is 
 represented by the equation 
 
 According to Pabst and Girard (Ger. Pat. 6,034), sulphanilic acid 
 heated with lead chamber crystals yields the corresponding diazo- 
 derivative. 
 
 Mohlau (Ger. Pat. 25,146) found that diazobenzene chloride was 
 formed by the action of zinc dust (7 parts) on a cold solution of 
 aniline nitrate (15*5 parts) in water (500 parts), when hydrochloric 
 acid of sp. gr. ri6 (34 parts) was added gradually 
 
 C 6 H 5 .NH 2 .HNO 3 + Zn + 3HCl = C 6 H 6 .N : N . Cl + ZnCl 2 + 3H 2 O. 
 
 The reaction is stated to be capable of general application. 
 
 The oxidation of hydrazines yields diazo-compounds. Thus 
 Fischer (Ann. 199, 302) prepared diazoethane potassium sulphite 
 by adding excess of mercuric oxide to a concentrated solution of 
 ethylhydrazine potassium sulphite, and filtering at once. By 
 addition of alcohol and then ether he obtained the body in 
 crystalline form 
 
 C 2 H 6 .NH.NH.SO 3 K + O = C 2 H 5 .N:N.SO 3 K + H 2 0. 
 
 6. Fatty Diazo-Bodies, While nitrous acid transforms primary 
 aromatic amines in acid solution into diazo-bodies, and in the 
 absence of acid into diazoamido-derivatives, the fatty amines are in 
 general hydroxylated without any intermediate diazo-compounds 
 being produced. 
 
 Curtius (J. pr. Ch. 146, 401) has found however that the esters 
 of fatty amido-acids can be diazotised as easily as the members of 
 
6] FATTY DIAZO-BODIES 143 
 
 the aromatic series, and one of the results of this work has been the 
 
 N\ 
 isolation of hydrazoic acid II NH. 
 
 N/ 
 
 Thus diazoacetic ether is prepared by taking amidoacetic ether 
 hydrochloride (50 gr.), which has been freed from excess of hydro- 
 chloric acid by heating in the water bath, placing it in a separating 
 funnel of one litre capacity with just enough water to dissolve it, an 
 operation which at once lowers the temperature of the mixture to 
 o^, and adding a concentrated solution of sodium nitrite (25 gr.). 
 When pure materials have been used no diazoacetic ether is formed 
 at this stage. But as soon as dilute sulphuric acid is added drop 
 by drop, a gradual rise in temperature is observed, and the liquid 
 becomes turbid. Oily yellowish drops begin to collect on the 
 surface, and soon a layer of oil would form. It is better however 
 to extract the liquid at once with ether before this takes place. The 
 ethereal layer is removed, and more sulphuric acid added, and this 
 process is continued as long as any milkiness is produced by the 
 addition of fresh acid. The diazoacetic ether is then separated 
 from the ether, care being taken to avoid bringing its explosive 
 properties into play. 
 
CHAPTER XIV 
 
 PREPARATION OF ESTERS 
 
 BY esters we mean ethereal salts of acids. They may be regarded 
 as alcohols in which the hydrogen of the hydroxyl group has been 
 replaced by acid radicals, or as acids in which the hydrogen of the 
 carboxyl has been replaced by alcohol radicals. 
 
 1. Action of Hydrochloric Acid on the Free Acid and an 
 
 Alcohol. Esters are frequently made by conducting dry hydro- 
 chloric acid into a solution, if necessary a warm solution, of an 
 acid in an alcohol. Thus in the case of formic acid and methyl 
 alcohol the powerful attraction of the hydrochloric acid for water 
 produces the ester in accordance with the equation 
 
 HCOOH + CH 3 OH = HCOOCH 3 + H 2 O. 
 
 From dibasic acids, acid esters can be prepared in this manner. 
 
 As nearly all esters are insoluble in water, they are separated by 
 pouring the mixture, which has been saturated with hydrochloric 
 acid and allowed to remain at rest for some time, into a consider- 
 able volume of water. The ester appears as an oily layer. If the 
 ester is somewhat soluble, the liquid must be extracted with ether. 
 The addition of potassium carbonate to the water assists the 
 extraction, as the esters are much less soluble in a strongly alkaline 
 solution. 
 
 The oily layer is in most cases fractionally distilled, as the esters, 
 excepting when they have large and complicated formulae, can 
 usually be distilled unchanged under the ordinary pressure of the 
 air. 
 
 Exceptions to this rule are very uncommon. A decomposition like that 
 of isopropyl benzoate into benzoic acid and propylene (Linnemann, Ann. 
 
i] ACTION OF HYDROCHLORIC ACID 145 
 
 161, 15) is so rare that, in this case, it serves as a test for isopropyl alcohol. 
 Equally unusual is the quantitative decomposition of laevo-rotatory methyl 
 malate into methyl fumarate and water (Anschiitz and Bennert, Ann. 
 
 254, 164). 
 
 When the acid is a solid it is never completely converted into 
 ester by this process, so that the oil, precipitated on addition to 
 water, has to be washed with an akaline solution to remove un- 
 changed acid. If the latter is left mixed with the ester it separates 
 during the distillation as a solid, and its presence is apt to lead to 
 the cracking of the flask. 
 
 Anschiitz and Pictet (Ber. 13, 1,175) have drawn attention to the 
 fact that many esters are partially saponified by contact with water. 
 Thus it is impossible to obtain the esters of tartaric and racemic 
 acids in neutral condition by this method. The pure esters are 
 obtained by direct fractionation of the mixture, saturated with 
 hydrochloric acid, in vacua. Recourse may also be had to some 
 other reaction, such as that involving the use of the silver salts. 
 
 The formation of the esters here depends on the abstraction of 
 water by the hydrochloric acid. The water produced by the 
 action itself necessarily accumulates and so interferes with the final 
 completeness of the chemical change. It stands to reason there- 
 fore that, as Anschiitz and Pictet (Ber. 13, 1,176) have shown, the 
 more perfectly this is removed the more nearly will the yield of 
 ester approach the theoretical. 
 
 Their procedure was as follows : The powdered tartaric acid was 
 covered with an equal weight of methyl, ethyl, or propyl alcohol, 
 and, after the cooled mixture had been completely saturated with 
 hydrochloric acid gas, was allowed to remain at rest for at least 
 twenty-four hours. The liquid was then decanted from a small 
 quantity of undissolved acid, a stream of dry air was drawn through 
 it, and then the alcohol and aqueous hydrochloric acid were re- 
 moved by heating on the water bath under considerably diminished 
 pressure. In accordance with the above principle a fresh quantity 
 of alcohol was next added to the residue, and the whole once more 
 saturated with hydrochloric acid. Finally the mixture was fraction- 
 ally distilled under diminished pressure. The yield was 70 per 
 cent, of that theoretically possible. 
 
 In rebuttal of the statement that this general method was not applicable 
 to the case of oxyglutaric acid (Ber. 24 3 2 5)> they showed that the ester 
 
 L 
 
U6 PREPARATION OF ESTERS [CH. xiv 
 
 could easily be obtained as a liquid boiling at 150 under a pressure of 
 II mm. (Ber. 25 1926). 
 
 It is true that some acids, which are soluble with difficulty in alcohol, are 
 less easy to convert into esters by this method. Terephthalic acid (Ann. 
 245, 140) is a case in point. When this difficulty arises it is better to use 
 the acid chloride to start from (cf. 10). 
 
 2. Preparation of Esters from Anhydrides and Alcohols. 
 
 By boiling anhydrides of acids with alcohols we obtain the esters 
 of the acids. Thus acetic anhydride and methyl alcohol give 
 methyl acetate 
 
 (CH 3 . CO) 2 O + CH 3 OH = CH 3 . CO . OCH 3 + CH 3 . COOH. 
 
 Under the same circumstances the anhydrides of dibasic acids, 
 such as succinic acid, give the corresponding acid esters (Heintz, 
 Pogg. Ann. 108, 82 ; cf. Crum Brown and Walker, Ann. 261, 117). 
 
 3. Action of Sulphuric Acid on the Free Acid and an 
 Alcohol. This method is less often used than that of distilling a 
 mixture of a salt with an alcohol and sulphuric acid. Yet Markowni- 
 koff(Ber. 6, 1,17?) has shown that, just as in the case of Boullay's 
 method of preparing ether, here a relatively small amount of 
 sulphuric acid is capable of transforming a large quantity of a 
 mixture of an acid and an alcohol into the corresponding ester. 
 He heated the sulphuric acid in a retort to 130, and allowed a 
 mixture of molecular proportions of alcohol (93 per cent.) and 
 acetic acid to flow slowly into it. By using sulphuric acid (10 gr.), 
 acetic acid of sp. gr. 1*065 (5 g r -)> an ^ alcohol (38 gr.), he obtained 
 acetic ether (70 gr.) in four hours. The sulphuric acid could be 
 used over again, and the same sample gave eventually 232 grams 
 of crude acetic ether. 
 
 This method can also be used for preparing the esters of dibasic 
 acids, but their high boiling-points prevent the process being con- 
 tinuous. The yields, however, are very good, for succinic acid (20 gr.), 
 alcohol (8 gr.), and sulphuric acid (i gr.), after being boiled together 
 for two hours with a reflux condenser, produced 25 grams of succinic 
 ether, the theoretically possible quantity being 28 grams. The 
 ester is separated as before by pouring the product into water. 
 
 Bottinger (Ber. 14, 317) evaded the hydrolytic effect of the water 
 as follows : He mixed equal volumes of pyruvic acid and alcohol, 
 cautiously added half a volume of concentrated sulphuric acid, and 
 
4] ACTION OF SULPHURIC ACID 147 
 
 after the mixture had become cold, poured it into a layer of ether 
 floating on water. The pyruvic ether, which is so easily hydrolysed 
 that on standing for a short time in contact with water it is com- 
 pletely decomposed, was separated from the ether by spontaneous 
 evaporation of the latter. 
 
 The same observer (Ber. 13, 2,345) found that, when a-oxyuvitic acid was 
 dissolved in methyl alcohol and concentrated sulphuric acid was added drop 
 by drop the acid was partially precipitated. When the mixture was heated 
 to 50, however, the mass became fluid again, and the ester was formed 
 in the normal manner. Hougouneng (Bull. Ch. 45? 328) obtained results 
 diverging from Markownikoff s in so far that he found actions of this nature 
 were often completed in a very short time. Thus by boiling molecular 
 proportions of monochloroacetic acid and amyl alcohol with a small 
 amount of sulphuric acid for a few minutes and then pouring the product 
 into water, he obtained the ester of the acid very expeditiously. 
 
 Occasionally an acid is itself prepared in solution in concentrated 
 sulphuric acid. In such cases the solution can be poured directly 
 into alcohol without first isolating the acid. Thus when citric acid 
 is dried at 150, and heated on the water bath with two parts of con- 
 centrated sulphuric acid, carbon monoxide is given off, and acetone 
 dicarboxylic acid (Ger. Pat. 32,245) remains behind. This loss of 
 carbon monoxide is a common property of many o-oxy-acids (Ann. 
 264, 262). To prepare the ester the mass is poured directly into 
 thoroughly cooled absolute alcohol, and the mixture is allowed 
 to remain for twelve hours. The liquid is finally diluted with a 
 solution of common salt and extracted with ether ten times. 
 
 4. Action of Sulphuric Acid on an Organic Salt and an 
 Alcohol. Although the above method is very successful, salts of 
 organic acids are more frequently used than the acids themselves. 
 As a matter of course the salt is invariably used when it is more 
 easily obtained than the free acid. The yields by this method are 
 very good. 
 
 The method may be illustrated by citing the preparation of 
 propyl butyrate. Pierre and Puchot (Ann. 163, 272) mixed dry 
 potassium butyrate (378 gr.) in small pieces with propyl alcohol, 
 and added to it, with constant stirring, concentrated sulphuric acid 
 (295 gr.) in small portions at a time. When rather more than three 
 quarters of the acid had been added the mixture began to boil, 
 and at the same time separated into two layers, an upper ethereal 
 one, and a lower one containing potassium sulphate. When the 
 
 L 2 
 
I 4 S PREPARATION OF ESTERS (CH. xiv 
 
 sulphuric acid had all been used the mixture was allowed to cool, 
 and water was added. 382 grams of the ester, about 98 per cent, 
 of the theoretical amount, were obtained. 
 
 If the liquid fails to boil of its own accord, as in making butyl valerianate 
 (Ann. 163, 285), it is heated to a temperature near the boiling-point for 
 forty minutes. The yield here is 97 per cent, of the theoretical. 
 
 In making ethyl malonate, Conrad used the calcium salt of the acid. He 
 first boiled sodium chloracetate with potassium cyanide. By adding the 
 requisite amount of caustic soda and further boiling, sodium malonate was 
 produced. He then neutralised with hydrochloric acid, and precipitated the 
 calcium salt of the organic acid. Finally the salt was dried at 150, mixed 
 with four times the calculated amount of absolute alcohol and a quantity of 
 concentrated sulphuric acid equivalent to the calcium, and heated in a 
 water bath for twenty-four hours. After filtering, to remove the calcium 
 sulphate and distilling off the alcohol at 100, the ester was separated by ad- 
 dition of water. The yield was from 40 to 50 per cent, of the theoretical. 
 
 This method of preparing ethyl malonate has been superseded by that of 
 Claisen and Crismer (Ann. 218, JS 1 )- By mixing the cyanacetate of 
 potassium, got by the action of potassium cyanide on potassium chloracetate, 
 with alcohol, and conducting hydrochloric acid gas into the mixture, the 
 saponification of the nitrile is combined with the transformation into the 
 ester (cf. Backunts and Otto, Ber. 9, i>59o), and a much better yield of the 
 ester is obtained in a very simple manner. 
 
 5. Preparation of Esters of Inorganic Acids in Presence of 
 Sulphuric Acid. Processes similar to the above are used also for 
 the preparation of esters of inorganic acids. Thus, according to 
 Witt (Ber. 19, 915), the simplest way of preparing ethyl, isobutyl, 
 and amyl nitrites is by mixing sodium nitrite with a slight excess of 
 the alcohol and adding dilute hydrochloric acid to the cold mixture. 
 Ethyl nitrite comes off in gaseous form and can be washed, dried, 
 and condensed by cooling. The higher homologues appear as oily 
 layers, which can be separated and rectified. In all cases the yield 
 of nitrite is nearly quantitative. 
 
 6. Use of Bisulphate and Pyrosulphate of Potassium. For 
 
 certain purposes acid salts of sulphuric acid can take the place of 
 the acid itself. Thus phenol (9 parts), methyl alcohol (3 parts), and 
 potassium bisulphate (14 parts) heated in a sealed tube for a few 
 hours at 1 50, give anisol, the methyl ether of phenol. 
 
 Sulphates of phenol radicals may be obtained by the action 
 of potassium pyrosulphate. Baumann (Ber. 11, 1,907) used the 
 
7 ] USE OF PHOSPHORUS OXYCHLORIDE 149 
 
 following method for obtaining them. Phenol (100 parts), potas- 
 sium hydroxide (60 parts), and water (80 parts) were mixed in a 
 large flask. As soon as the mixture had cooled to 60-70, finely 
 powdered potassium pyrosulphate was gradually added. The 
 mixture was kept at 60-70, a temperature which must not be ex- 
 ceeded, for eight to ten hours, and frequently shaken. At the end 
 of that time the interaction was complete, and the contents of the 
 flask were extracted with boiling 95 per cent, alcohol, and the ex- 
 tract filtered while warm. On cooling, the solution deposited crys- 
 tals of phenyl potassium sulphate. Although this salt is not very 
 stable the yield was equal to 25-30 per cent, of the phenol taken 
 K 2 S 2 O r + C 6 H 6 OK = K 2 SO 4 + C 6 H 6 O.SO 2 .OK. 
 
 The sulphates of oxy-acids can be prepared in the same way. 
 Thus salicylic acid (10 parts) is mixed with caustic potash (8 parts) 
 and water (25 parts), and powdered potassium pyrosulphate (17 
 parts) is gradually added to the warm mixture, which is continually 
 agitated during the process. After remaining at rest for some hours 
 the mass is extracted with twice its volume of boiling 90 per cent, 
 alcohol. On filtering the extract and adding an equal volume of 
 ether, a thick liquid containing the salt separates out. This liquid 
 is dissolved in a small amount of water, neutralised with acetic acid, 
 and alcohol is then added until a permanent turbidity is produced. 
 After a short time crystals of the potassium salt of the sulphuric 
 ether of salicylic acid appear. The quality of the potassium pyro- 
 sulphate seems to have an important influence on the success of the 
 action. 
 
 7. TTse of Phosphorus Oxychloride in Preparing Phenyl 
 Esters. Nencki (J. pr. Ch. 133, 282) made the important ob- 
 servation that the energetic action of phosphorus oxychloride on 
 water could be used with advantage in the preparation of phenyl 
 esters. According to Seifert (J. pr. Ch. 139, 467), almost quanti- 
 tative yields and pure products can be obtained by using a sufficient, 
 but not too great, excess of the oxychloride, and working slowly at 
 a low temperature. A mixture of equal parts of formic acid and 
 phenol were warmed to 80, and treated gradually with phosphorus 
 oxychloride ( mol. 1 ). The fluid product was poured into a cold 
 dilute solution of carbonate of soda, when the evolution of hydro- 
 chloric acid had ceased, and the oil which separated was rectified 
 in vacua. 
 
 1 Probably a half molecular proportion would be better. [Author. ] 
 
150 PREPARATION OF ESTERS [CH. xiv 
 
 Using Seifert's method a yield of 92*5 per cent, of salol (phenyl 
 salicylate) can be obtained 
 
 5 OH + POC1 3 =2C 6 H 4 (OH)COOC 6 H 5 
 
 HC1. 
 
 The free metaphosphoric acid produced by the action gives an 
 opportunity for the formation of phenyl esters of phosphoric acid, and 
 when a metal is present which can convert this into a salt, the yield 
 is much improved. By using the sodium or other salts, both of the 
 phenol and the acid, the yield is increased and the equation takes 
 the form 
 
 ONa + POCl 3 =2C 6 H 4 (OH)COOC 6 H 5 
 
 The operation is carried out by melting the sodium salts with 
 phosphorus oxychloride or pentachloride. The temperature is not 
 stated in the original papers. Seifert used 135 for the preparation 
 of salol. 
 
 8. Action of Salts of Ethyl Sulphate on Organic Salts. The 
 salt of ethyl sulphate is dissolved in water or alcohol, and a solution 
 of the organic salt is added. The mixture is heated in hermetically 
 sealed vessels, if necessary, and finally distilled or extracted with 
 ether. The following equation represents an action of this type 
 
 Salts of phenols act in a similar manner. Thus Weselsky and 
 Benedikt (M. f. Ch. 1, 91) prepared the ethyl ether of resorcinol by 
 boiling on the water bath, in a flask connected with an upright 
 condenser, a mixture of resorcinol (200 gr.), caustic potash (400 gr.), 
 and potassium ethyl sulphate (800 gr.), with enough alcohol to make 
 the whole into a thin paste. 
 
 Hlasiwetz and Habermann (Ann. 177, 340) obtained the mono- 
 methyl ether of quinol by heating quinol (10 gr.), potassium 
 methyl sulphate (15 gr.), and caustic potash (6 gr.), for six hours 
 in a sealed tube at 170. An attempt made by Habermann 
 (M. f. Ch. 5, 228), however, to obtain the diethyl ether of alizarine, 
 using the calculated molecular proportions of the reagents, gave 
 only a small yield of the product. 
 
 In this case, as in others, the silver salts probably give better 
 Results than those of potassium. Brasch and Freyss(Ber. 24, 1,961) 
 
9] ACTION OF ALKYL HALIDES ON ORGANIC SALTS 151 
 
 report, for example, that the silver salt of nitrocresol reacts 
 smoothly with methyl iodide at the ordinary temperature, while the 
 potassium salt fails to act even in the boiling mixture. Even in the 
 case of the latter, interaction can be brought about by heating in a 
 sealed tube for four hours at 100. 
 
 Briihl (Ber. 24, 3,376) prepared menthyl ethyl ether, C 10 H 19 OC 2 H 3) 
 by dissolving menthol (50 gr.) in dry toluene (30 gr.), adding sodium 
 (8 gr.), and heating with a reflux condenser in an oil bath. At the 
 end of fifteen hours the unattacked sodium was removed, excess of 
 ethyl iodide was added to the solution, and the mixture was heated 
 in the oil bath until it ceased to show an alkaline reaction. The 
 sodium iodide was removed with water, the liquid dried again, the 
 toluene and ethyl iodide distilled off, and the residue fractionated in 
 
 9. Action of Alkyl Halides on Organic Salts, As a rule the 
 salts are covered with ether or alcohol, and the halide, usually diluted 
 with ether, is added. Bromides frequently give better results than 
 iodides. Silver salts are more often used than any others, although 
 occasionally other salts are preferable. The mixtures are heated 
 with an inverted condenser, or in a sealed tube. 
 
 The difference between the actions of salts of different metals is 
 exemplified by experiments of Strecker and Fischer. The former 
 (Ann. 118, 172) heated argento-xanthine with methyl iodide, and 
 obtained a methylxanthine, which was not identical with theo- 
 bromine. The latter (Ber. 15, 454), on the other hand, used the 
 crystalline lead compound in place of the amorphous silver one, and 
 found that theobromine was produced under these conditions. The 
 salt was dried at 130, and heated at 100 in a sealed tube for twelve 
 hours with i J parts by weight of methyl iodide. The interaction 
 was almost quantitative, and the contents of the tube formed a 
 nearly dry mass, coloured strongly yellow by the lead iodide pro- 
 duced by the action. The product was extracted with water and a 
 small amount of dissolved lead precipitated from the filtrate with 
 hydrogen sulphide. On adding excess of ammonia and evaporating, 
 the theobromine separated out. 
 
 Seidel (Ber. 25, 431) states that the silver salt of fulminuric acid is hardly 
 affected by ethyl iodide when the mixture is boiled with a reflux condenser. 
 He finds, however, that on heating these substances for a few minutes in a 
 sealed tube at 80-90, the change into the ester, C 3 HoN 3 Oo(OC 2 H 5 ) is 
 quantitative (cf. Nef. Ann. 280, 334)- 
 
152 PREPARATION OF ESTERS [CH. xiv 
 
 Potassium salts are frequently employed. They are not prepared directly, 
 but are formed by neutralising the acid with the calculated amount of 
 potassium hydroxide or carbonate. The further treatment is the same as in 
 the case of silver salts. 
 
 After a number of vain attempts Ladenburg (Ber. 25 2,771) found the 
 following was the only way of preparing the ester of nipecotinic acid. Equi- 
 molecular quantities of the hydrochloride of the acid and sodium carbonate 
 were evaporated in water solution, and the residue was dried at 130. The 
 resulting brown hygroscopic mass was pulverised in a warm mortar, and 
 heated in a sealed tube at 100 for 5 to 6 hours with a molecular proportion of 
 methyl iodide. The product was extracted with absolute alcohol, and the 
 alcohol was driven off by dilution with water and evaporation. The liquid 
 was then shaken with freshly precipitated chloride of silver. On adding 
 mercuric chloride to the filtrate an insoluble double salt was formed, which 
 was finally decomposed with hydrogen sulphide. The filtrate gave on 
 evaporation crystals of the hydrochloride of the methyl ester of nipecotinic 
 acid, having the formula C 5 H 9 O 2 CH 3 NH.HC1. 
 
 It is seldom observed that actions of the present nature follow an 
 abnormal course. In this connection Hjelt (Ber. 25, 525) states that when 
 the potassium salt of benzyl alcohol 0-carboxylic acid is warmed in alcoholic 
 solution with ethyl iodide, phthalid is formed on account of the instability of 
 the ester. 
 
 COOK 1 + C^ 1 - C 6 H 4\CO 2 / + KI + C 2H 5 OH. 
 
 Sodium salts can also be used, and are often preferred for manufacturing 
 purposes on account of their cheapness. Thus the ethyl ester of rosaniline 
 sulphonic acid may be prepared by heating the sodium salt ( 10 kilos. ), water 
 (50!.), alcohol of sp. gr. 0^830 (50!.), and caustic soda of sp. gr. 1*38 
 (75 g r -)> with ethyl iodide (1*3 kilos.) in a vessel attached to a condenser 
 till the liquid has changed its colour from yellowish-brown to violet-red. 
 At this point fresh portions of the same amounts of caustic soda and 
 ethyl iodide are added, and this process repeated each time as soon as 
 the change in colour has taken place. The total amount of caustic soda 
 used is 4 '5 kilos., and of ethyl iodide 7 '8 kilos. 
 
 It may be well to give also the method of recovering the iodine, as the 
 necessity for doing this frequently arises in the laboratory. When the 
 action is completed, the product is neutralised with hydrochloric acid, the 
 alcohol is distilled off, and excess of sulphurous acid is added to the cold 
 residue. After remaining for twelve hours the liquid becomes almost colour- 
 less, and the iodine can be precipitated as cuprous iodide. 
 
 10. Action of Acid Chlorides on Alcohols. Just as alkyl 
 halides interact with salts giving esters, so, inversely, the same 
 
ii] PREPARATION OF ETHERS, ETC. 153 
 
 products are obtained by the action of acid chlorides on potassium 
 or sodium alcoholates. The alcoholate is diluted with alcohol and 
 the acid chloride is added. This general method is seldom de- 
 parted from, although Emery (Ber. 22, 3,185) prepared methyl 
 succinate by the action of succinyl chloride in ethereal solution on 
 dry sodium ethylate. 
 
 Acid chlorides are so energetic in their action, however, that 
 esters may be obtained by simply pouring them into alcohols, 
 hydrochloric acid being given off. This process is so satisfactory 
 that acids might advantageously be converted into esters, by way of 
 the chlorides, more frequently than is actually the case. It has 
 already been shown that terephthalic acid cannot conveniently be 
 made into the ester with the help of hydrochloric acid. Baeyer 
 (Ann. 245, 140) obtained a good yield of the methyl ester, however, 
 by warming the powdered acid with the calculated amount of phos- 
 phorus pentachloride in the water bath till it was completely dis- 
 solved, and then pouring the product into excess of methyl alcohol. 
 The methyl ester was insoluble in the alcohol and soon separated 
 itself from the latter. Rupe (Ann. 256, 7) prepared the methyl 
 ester of dichloromuconic acid in the same way. Here too the most 
 of the ester deposited itself directly, and the rest was precipitated 
 by adding water. 
 
 Benzoyl chloride has an unusual capacity for forming esters (Baum, Z. 
 physiolog. Ch. 9, 465). Even in aqueous solutions of alcohols, provided 
 they are first rendered alkaline, the esters are formed at once and are easily 
 separated, as they are usually quite insoluble in water. 
 
 The carbohydrates likewise give benzoates in the presence of water. 
 Thus Baumann (Ber. 19, 3,219) dissolved grape sugar (5 gr. ) in water 
 (15 cc.), added 10 per cent, caustic soda (210 cc.), and shook the mixture 
 with benzoyl chloride (30 cc. ) until the odour of the latter was no longer 
 perceptible. The total product was 13 grams, and consisted chiefly of the 
 tetrabenzoate. 
 
 The sulphonic chlorides act in the same way as ordinary acid chlorides, 
 only less energetically. Schiaparelli (Jahresb. 1881, 539) suggests the 
 addition of zinc dust or zinc chloride to assist their action. 
 
 11. Preparation of Ethers by the Action of Alcoholic 
 Caustic Potash on Chloro-Derivatives. Alkyloxy-derivatives can 
 frequently be made by the action of alcoholic caustic potash on 
 chloro-derivatives. For example, Willgerodt (Ber. 12, 762) has 
 investigated the action of solutions of caustic potash in various 
 
154 PREPARATION OF ESTERS [CH. xiv 
 
 alcohols on a-dinitrochlorobenzene, and obtained ethyl, allyl, phenyl, 
 and other ethers. Thus he dissolved a-dinitrochlorobenzene in 
 methyl alcohol, added slowly a solution of caustic potash in methyl 
 alcohol, and agitated the mixture continuously. The .interaction 
 proceeded smoothly, and by distilling off the alcohol and recrystal- 
 lising from alcohol he obtained the pure methyl ether. In another 
 experiment he dissolved the same chloro-derivative in glycerol, in 
 which it was only soluble with difficulty, added the solution of 
 caustic potash in the same solvent, and so prepared the mono-a- 
 dinitrophenyl ether C 6 H 3 (NO 2 ) 2 .O.C 3 H 6 (OH)2. In all cases an 
 excess of alkali is to be avoided, as it is apt to produce saponifi- 
 cation. 
 
 12. Preparation of Salol. An exceptional case is that of sali- 
 cylic acid, which turns quantitatively into salol when heated alone 
 at 160 240. Provision must be made for the removal of the water 
 formed, and access of air is prevented as far as possible. The 
 behaviour of other oxy-acids whose constitution would favour such 
 a transformation seems not to have been investigated. 
 
 It may be mentioned, in concluding this chapter, that some esters 
 decompose into resinous material on short exposure to the air. 
 The methyl ester of A 1 ' 5 dihydroterephthalic acid (Ann. 258 18) is 
 a case in point. 
 
CHAPTER XV 
 
 FUSION WITH CAUSTIC ALKALIS 
 
 1. Description of the Apparatus and Method. The fusion of 
 
 organic bodies, such as sulphonic acids, resins, etc., with caustic 
 alkalis, is a method in frequent use for obtaining well-defined 
 decomposition products. For example, Hlasiwetz and Habermann 
 (Ann. 175, 62) found that gentisin was decomposed by its means in 
 accordance with the equation 
 
 Gentisin Phloroglucin Gentisic acid. 
 
 Gentisic acid was later identified as quinol carboxylic acid. 
 
 Fusion with potassium hydroxide does not require so high a 
 temperature as that with sodium hydroxide, but the actions of the 
 two are not always identical. The temperature at which the opera- 
 tion is conducted also frequently affects the result. 
 
 The method has been almost invariably to melt the substances in 
 a silver basin over the naked flame. A better plan is suggested by 
 Liebermann (Ber. 21, 2,528). He employs nickel basins, and heats 
 them on a copper bath shaped like Victor Meyer's drying baths 
 (Fig. 39). The bath can be charged with naphthalene, anthracene, 
 anthraquinone, or other substance of high boiling-point. When 
 carried out under these conditions the fusion requires neither stirring 
 nor other attention. Anthraquinonesulphonic acid can be fused 
 with caustic potash at the temperature of boiling naphthalene. For 
 anthracenesulphonic acid this temperature is too low, and anthra- 
 cene vapour must be used. Boiling anthraquinone need only be 
 employed in extreme cases. 
 
I 5 6 
 
 FUSION WITH CAUSTIC ALKALIS 
 
 [CH. XV 
 
 FIG. 39. 
 
 When the substance is soluble in water it is dissolved in as little 
 of the solvent as possible. Then the caustic potash and sometimes 
 
 a little more water are added. As 
 much as fifteen times their weight of 
 alkali is used with some substances. 
 
 The following apparatus (Fig. 40) 
 has been found by the author to be 
 serviceable in most cases. A rather 
 large test tube (3-3 cm. X 30 cm.) 
 passes through a hole in a flat cork 
 which rests on the rim of a larger 
 tube of Jena glass (4^5 cm. X 35 cm.), 
 which serves as a mantle. Substances 
 of known boiling-point are placed in 
 the outer tube so as to fix the tem- 
 perature at which the melting takes 
 place. Even at 250 the inner tube 
 is not attacked by the fused alkali. 
 The convenience of the apparatus lies in 
 the fact that 100 grams of the mixture 
 can be operated on at one time, 
 
 the progress of the action can be easily observed, the gases 
 which are evolved can be readily collected, and the apparatus is 
 more easily handled than a basin. Silver or nickel basins need 
 therefore only be resorted to when large quantities 
 of material have to be worked up at one opera- 
 tion. 
 
 Heumann's synthetic preparation of indigo 
 (Ber. 23, 3,434) affords a good example of a fusion. 
 Amidophenylacetic acid (i part) was melted with 
 potassium hydroxide (3 parts) and water (i part). 
 The mass became yellow about 180-200, and later 
 the colour became fiery reddish-yellow, and the 
 heating was continued until the colour ceased to 
 deepen. The substance was then allowed to cool, 
 and was dissolved in water (200 parts), and air was 
 drawn through the solution until all the indigo- 
 white was converted into indigo. FIG. 40, 
 
 It is frequently possible, although not always so convenient in the 
 laboratory, to carry out actions of this class with dilute alkalis in sealed 
 
2, 3 ] PROMOTION, ETC., OF OXIDISING INFLUENCE 157 
 
 tubes. For example, dimethyl-a-naphthylaminesulphonic acid (one part), 
 when melted with caustic soda (two parts), and water (one part), for half an 
 hour at 280 290, yields dimethyl-a-amidonaphthol. But the action is 
 just as successful if more dilute alkali is used and the operation is conducted 
 in a hermetically sealed tube. Similarly Roemer and Schwarzer (Ber. 15, 
 1,401) prepared isoanthraflavic acid by heating -anthraqiiinonedisulphonate 
 of sodium with a solution of caustic potash, and found that under these 
 conditions of temperature and concentration less isopurpurin was formed 
 than under any other circumstances. 
 
 2. Oxidation accompanies the Fusion, When the tempera- 
 ture is high enough one effect of fusing is always to produce 
 oxidation with evolution of hydrogen gas. Many years ago 
 Varrentrapp (Ann. 35, 196) found that on fusing oleic acid, 
 palmitic acid and acetic acid were formed according to the 
 equation 
 
 Earth and Schreder (Ber. 12, 418) state that when phenol is 
 melted with six times its weight of sodium hydroxide the sodium 
 phenolate melts and floats on the surface as an oily layer. Gradually, 
 however, a slight frothing due to the evolution of hydrogen 
 becomes visible. This increases, and the fluid becomes brown till 
 finally it turns into a homogeneous spongy mass. When this 
 stage has lasted some time, and the froth has begun to subside, 
 the flame is removed. The substance, when cold, is thrown into 
 dilute sulphuric acid and the solid matter separated by filtration. 
 On extracting the filtrate with ether a quantity of trioxybenzene is 
 obtained (20 per cent, of the phenol used), which consists chiefly of 
 phloroglucinol. The effect is therefore here to oxidise the phenol. 
 The fused mass is almost invariably worked up in the manner 
 described. 
 
 Tiemann and Reimer (Ber. 10, 1,568) transformed aldehydosalicylic 
 acid almost quantitatively into phenol dicarboxylic acid by gentle fusion 
 with caustic potash. They used from ten to fifteen times as much of the 
 alkali as of the acid and a little water in addition. The fusion lasted only 
 6-8 minutes. On dissolving the fused mass in water and adding hydro 
 chloric acid most of the product was precipitated, and the rest was separated 
 by extraction with ether. 
 
 3. Promotion and Restraint of Oxidising Influence. The 
 
 hydrogen which is evolved naturally has a tendency to undo part 
 
158 FUSION WITH CAUSTIC ALKALIS [CH. xv 
 
 of the oxidising effect ^of the fusion with alkalis. Thus, in pre- 
 paring dioxyanthraquinone from anthraquinonesulphonic acid and 
 sodium hydroxide, the nascent hydrogen produced by the action 
 
 C 14 H 7 O 2 SO 3 H+2NaOH = C H H 6 O 2 (OH) 2 + Na 2 SO 3 + 2H 
 
 partially reduces some of the dioxyanthraquinone, or even recon- 
 verts it into anthraquinone. Koch's discovery was therefore an 
 important one when he found that this reversal of the action could 
 be avoided by introducing oxidising agents into the fusing mass. 
 He found that potassium chlorate was the best substance, and that 
 the yield of alizarin became almost quantitative when it was 
 employed 
 
 a 24 
 + 6H 2 0. 
 
 In the manufacturing process a little water is added, the fused 
 mixture is kept at 160-170, and is constantly stirred. The opera- 
 tion occupies from two and a half to three days. 
 
 If this action is compared with the last example, the oxidation of 
 aldehydosalicylic acid, it will be observed that bodies with com- 
 plex aromatic rings are more readily attacked than simple benzene 
 derivatives. 
 
 When the substances taking part in the action are not appreciably 
 attacked by the nascent hydrogen, good yields may be obtained without 
 the addition of oxidising agents, provided the other conditions are favour- 
 able. Thus Degener (J. pr. Ch. 128, 300) found that when benzene- 
 sulphonate of potassium was heated at 252 with six molecular proportions 
 of potassium hydroxide, the yield of phenol was 96 per cent, of the 
 theoretically possible amount 
 
 When it is desired to restrain the oxidising effect of the 
 operation, iron filings are frequently added to the fusing mass. 
 
 4. Differences between the Action of Sodium and Potassium 
 
 Hydroxides A striking illustration of the difference between 
 potassium and sodium in their effects on organic actions may be 
 found in Kolbe's synthesis of salicylic acid. Sodium phenolate 
 gives salicylic acid, while potassium phenolate yields ^-oxybenzoic 
 acid. 
 
 Earth and Schreder (Ber. 12, 422) found that by continuous 
 heating of benzenetrisulphonic acid with caustic potash, first one 
 
5-7] REDUCTION OF NITROPHENOLS 159 
 
 sulphonic acid group, then a second was replaced by hydroxyl, but 
 that efforts to replace the third by further raising the temperature 
 led only to the almost complete combustion of the whole substance. 
 Fused caustic soda, on the other hand, acts with ease and gives 
 25-30 per cent, of phloroglucinol (trioxybenzene). 
 
 5. Differences in Result under Different Conditions, Accord- 
 
 ing to Giirke and Rudolph, when naphthalene trisulphonate of 
 sodium is heated with half its weight of caustic soda and an equal 
 amount of water for several hours at 170-180 in an oil bath, a 
 mixture of naphtholdisulphonic acids is obtained. The operation 
 must be conducted in closed vessels to avoid loss of water and con- 
 sequent drying of the mixture. If naphthalenetetrasulphonate of 
 sodium (10 parts) is dissolved in as little water as possible, mixed 
 with caustic soda (6 parts), and heated in closed vessels at 180, 
 the sodium salt of naphtholtrisulphonic acid is formed. But if the 
 temperature is raised to 250 this substance is transformed into the 
 corresponding salt of dioxynaphthalenedisulphonic acid. 
 
 Fischli. (Ber. 12, 621) found that when bromoterephthalic acid 
 was fused for some time with sodium hydroxide, sodium phenolate 
 was produced 
 
 But when he modified the action by adding the acid to the molten 
 alkali and letting the mass cool at once, a large amount of oxytere- 
 phthalic acid was formed. 
 
 6, Fusion of Calcium and other Salts with Alkalis. Calcium 
 
 salts may be used in fusions instead of those of potassium and 
 sodium. For example, Weber (Ber. 14, 2,206) dissolved a-naphtha- 
 lenedisulphonate of calcium in a little water in a rather large flask, 
 added two and a half times as much caustic soda, and stirred the 
 mass while heating it up to 290-300. By conducting hydrogen 
 into the flask the air was displaced, the substance remained white, 
 and pure dioxynaphthalene was formed. 
 
 Lead salts have occasionally been fused with caustic potash. 
 
 7. Reduction of Nitrophenols. It has been established as a 
 general action by Weselsky and Benedikt (Ber. 11, 398) that 
 mononitrophenols give azophenols on fusion with caustic potash. 
 For example, 0-nitrophenol is thrown into 4-6 times its weight 
 of potassium hydroxide fused with a little water. The mixture 
 
160 FUSION WITH CAUSTIC ALKALIS [CH. xv 
 
 is at first coloured red by the nitrophenolate of potassium. The 
 heating is stopped as soon as the mass has acquired a dark-green 
 colour and a metallic lustre and begins to give off ammonia. The 
 fused substance becomes dark-red again almost immediately, and 
 is then dissolved in water. Sulphuric acid precipitates a solid, 
 which is washed, dried, and extracted with ether. The latter 
 deposits on evaporation pure azophenol. The yield is not mentioned. 
 
 8. Analogy of this Reaction to Putrefaction. It may be 
 
 worth while to draw attention to the fact that the unusual oxidation 
 accompanied by evolution of hydrogen, which is brought about 
 by fusion with alkalis, is quite analogous to the decomposition 
 which organic substances, like albumen, undergo during putre- 
 faction (Nencki, J. pr. Ch. 125, 123, and Hoppe-Seyler, P. Ar. 
 12, i). Albumens in process of putrefaction give tyrosine, and 
 Liebig (Ann. 57, 127) obtained the same substance on fusing casein 
 with caustic potash. 
 
 Similarly, in a simpler case, calcium formate decomposes accord- 
 ing to the equation 
 
 As is the case in fusions, the hydrogen acts as a reducing agent 
 when it has opportunity. Thus calcium acetate decomposes 
 according to the equation 
 
 When putrefaction takes place in the air, the hydrogen set free 
 by the chemical change combines with oxygen from the air. The 
 atomic oxygen set free by this means from the molecules of the 
 free gas then gives occasion to very complicated oxidations. 
 
 Hydrogen from solution in palladium also combines with oxygen, 
 and for the same reason is able to produce oxidation of organic 
 bodies (Z. physiolog. Ch. 2, 22). Indeed, the oxygen obtained 
 under such conditions is the most active form of the element that 
 we know. Baumann (Z. physiolog. Ch. 5, 244) has shown that 
 it can convert carbon monoxide into carbon dioxide at the ordinary 
 temperature, an effect which even ozone is incapable of producing. 
 
CHAPTER XVI 
 
 PREPARATION OF HALOGEN COMPOUNDS 
 
 SECTION I. BROMO-DERIVATIVES 
 
 IN most cases bromination is effected by the use of bromine 
 itself, sometimes in presence of substances which assist its action. 
 
 Other agents, such as hydrobromic acid, bromides of copper, phos- 
 phorus and calcium, and potassium hypobromite, are also employed. 
 
 1, Bromine. Commercial bromine is almost never pure. Ac- 
 cording to Reimann (Ber. 8, 792), it may contain as much as 
 10 per cent, of impurities, of which bromoform is one of the most 
 common (Ann. 95, 211). 
 
 Gessner (Ber. 9, 1,507) recommends repeated shaking with dis- 
 tilled water and subsequent distillation over concentrated sulphuric 
 acid for the removal of chlorine. The first part of the distillate 
 is rejected. Hydrobromic acid is removed by distilling over pre- 
 cipitated manganese dioxide or mercuric oxide (Ber. 13, 1,338). 
 Drying is managed by shaking with concentrated sulphuric acid 
 or adding phosphorus pentoxide. If greater purity is required 
 chemically pure bromine may easily be made by Stas' method 1 
 in pounds at a time. 
 
 Bromine is a much less active agent when dry than when moist. 
 This is easily explained by a consideration of Thomsen's deter- 
 minations (Ber. 5, 770) of the heat given out by its union with 
 hydrogen in each condition. For the former it is 8*4 cal., and 
 for the latter 28*3 cal. Zincke and Kegel (Ber. 23, 235) state, for 
 example, that pure bromine will not act on hexachlorotriketone, 
 
 1 Stas' " Nouvelles recherches sur les lois des proportions chimiques, 
 etc." Brussels, 1865. 
 
 M 
 
162 BROMO-DERIVATIVES [CH. xvi 
 
 even when they are heated together at 100 for a considerable 
 time. But when some water 1 is present carbon dioxide is evolved 
 immediately, and hexachlorodibromoacetylacetone is formed ac- 
 cording to the equation 
 
 C 6 C1 6 O 3 + 2Br 2 + H 2 O = C 5 Cl 6 Br 2 O 2 + CO 2 + 2H Br. 
 
 Bromine is sometimes used without dilution. In such cases it 
 is mixed with the substance, and the excess is removed by evapora- 
 tion on the water bath. For example, Jacobsen (Ber. 14, 2,351) 
 dissolved w-toluic acid in excess of bromine, and after twelve hours 
 allowed the latter to evaporate. He brought the residue into 
 solution by means of calcium carbonate, and by precipitation with 
 hydrochloric acid obtained two monobromo-;;z-toluic acids. 
 
 Furil is not attacked by chlorine or bromine in chloroform solution, but 
 by dissolving one part of furil in forty parts of previously cooled bromine, 
 Fischer (Ber. 13 1,338) obtained an addition product having the compo- 
 sition C 10 H 6 Br 8 O 4 . 
 
 Paal (Ber. 17, 2,760) obtained bromophenylmethylfurfurane tetra- 
 bromide, C u H 9 Br 5 O, by dissolving phenylmethylfurfurane in excess of 
 bromine (which was kept so cold that a part of it was frozen during the 
 operation), allowing the bromine and hydrobromic acid to evaporate in the 
 air, and recrystallising the residue. 
 
 Hermetically sealed tubes have frequently to be used, as bromine 
 boils at 58. It is often diluted in such cases (see below). Bischoff 
 (Ber. 24, 2,016) heated ethylsuccinic anhydride (36 gr.) with bromine 
 (46 gr.) and chloroform (40 gr.) in tubes at 130-140 for five 
 hours. At the end of this time the colour of the bromine had 
 disappeared. The mixture was placed in vacuo to remove hydro- 
 bromic acid, and the chloroform was evaporated on the water bath 
 Bromoethylsuccinic anhydride remained. 
 
 Its power of combining is so great that it can often be added to sub- 
 stances which are heated to a high temperature and with which it combines 
 rapidly in the act of being volatilised. This may be illustrated by the case 
 of GreifFs dibromoanthranilic acid (Ber. 13, 288). He allowed bromine 
 
 1 The frequent necessity for the presence of water may be further illus- 
 trated by Nef s statement (Ann. 266 7)? that sodium has no action on 
 phthalic, succinic, and other acids in absolute ethereal solution. Briihl 
 (Ber. 25 367) finds the same to be true of many alcohols like menthol 
 and borneol. 
 
~i 
 
 SEC. i, i] BROMINE 163 
 
 to flow slowly into o-nitrotoluene at 170. Ilydrobromic acid was rapidly 
 evolved and so much heat produced that no further heating from the outside 
 was necessary for the quantity (200 gr. ) of the substance used. After two 
 atomic proportions of bromine had been added, the operation was inter- 
 rupted, and the mass, which became crystalline on cooling, was treated 
 with sodium carbonate. From the solution acids precipitated the dibromo- 
 anthranilic acid which had been produced by molecular rearrangement. 
 To further illustrate this way of applying bromine, the actions on benzyl- 
 cyanide and ethylsuccinic acid may be mentioned. In the former ' case 
 Reimer heated the substance to 170. A violent reaction ensued as the 
 bromine was slowly added, and stilbene dicyanide was formed according to 
 the equation 
 
 CeH 3 -C-CN 
 
 || 
 C 6 H 5 -C-CN 
 
 In the second case Bischofif (Ber. 24, 2,015) melted 15 grams ethylsuccinic 
 acid in a small flask, and as the temperature was gradually raised to 200, 
 he added 16 grams bromine through a funnel with a capillary stem. 
 
 > fSS^ l/\ 
 
 Application in the form of vapour renders the action of bromine WU} W< 
 much less violent. The substance is brought in contact with the 
 bromine under a bell jar. This method was used as early as 1836 
 by Peligot (J. pr. Ch. 8, 258) for preparing bromobenzoic acid, 
 as he found that the direct action on silver benzoate was too . J^ 
 energetic. The substances stood side by side for twenty-four 
 hours, and at the end of that time the bromobenzoic acid could 
 be extracted by alcohol, while silver bromide remained behind. 
 On the other hand, Kekule (Ann. 117, 122) attempted to make 
 bromosuccinic acid in this way and failed. Silver bromide was 
 formed indeed, but, on extracting the mass with water, nothing 
 but unchanged succinic acid was obtainable. 
 
 Sometimes this method is varied by placing the substance in 
 a tube and carrying the vapour of bromine over it by means of a 
 stream of carbon dioxide. The bromine is placed in a small flask 
 behind the tube, and the vaporisation can be accelerated by gentle 
 warming. If the bromine is made by heating potassium bromide, 
 potassium bichromate, and sulphuric acid, an application may be 
 found in this way for the bromide which is formed as a by-product 
 in so many actions. 
 
 Niementowski (Ber. 25, 868) applied this method as follows : 
 200 grams of 0-acettoluide were dissolved in 1,300 grams of glacial 
 acetic acid, and a stream of air laden with bromine was led through 
 
pI\OMO-DERIVATIVS |CH. xvi 
 
 \^<^\ ^ Y N >^ 
 
 the solution until it had solidified to a mass of white crystals. 
 After the mother-liquor had been removed by filtration and pressure 
 the product was recrystallised once from alcohol, and gave 150 
 grams of chemically pure 7/z-bromo-0-acettoluide. The mother- 
 liquor contained considerable quantities of ?;z-bromo->-toluidine in 
 consequence of the saponifying effect of the hydrobromic acid. 
 
 Actions like the present are usually assisted by sunlight, although 
 in some cases exceptions to this rule must be recognised. For 
 example, 0-nitrocinnamic acid can be brominated, just like cinnamic 
 acid itself, by adding it to liquid bromine or exposing it to bromine 
 vapour. Yet Friedlander (Ber. 13, 2,257) found that sunlight 
 prevented the absorption of the vapour, for when the acid was 
 exposed to the action of bromine in this form in bright sunlight, 
 practically no increase in weight was observable. Special interest 
 attaches to an observation of Wislicenus (Ann. 272, 98) in this 
 connection. He found that, when light is carefully excluded, 
 angelic acid yields dibromoangelic acid, while the admission of 
 light leads to the formation of the isomeric dibromotiglic acid. A 
 thorough investigation of the influence of light on the progress 
 of the action of halogens on aromatic compounds has been made 
 v v by Schramm (M. f. Ch. 8, 101). 
 
 The bromination of the side chains of aromatic hydrocarbons 
 x follows the rule given for their chlorination. Toluene itself is 
 ~SAAAX/~^. in this respect perfectly regular ; but, according to Schramm 
 (Ber. 17, 2,922), its derivatives do not all show the same regularity. 
 ^y th e action of bromine on melted /-bromotoluene in molecular 
 proportions he obtained ^-bromobenzyl bromide in almost quanti- 
 tative amount. 
 
 Bromine drives out iodine from many compounds and takes its 
 place. For example, ethylene chloriodide is converted into ethylene 
 chlorobromide. 
 
 Meyer and Miiller (Ber. 15, 1,904) found this method convenient 
 for making isopropyl bromide since secondary propyl iodide is 
 easily made, and bromine acts on it with great violence, replacing 
 the iodine. The best result was attained by using one and a half 
 times the theoretical amount of bromine. Henry (Ann. Ch. Ph. 
 30, 266) made dibromomethane according to the equation 
 
 and removed the BrI with potassium hydroxide. 
 
 The addition of bromine to unsaturated bodies does not seem to 
 
SEC. i, i] BROMINE 165 
 
 be always achieved with ease. At least Bennet (Ber. 12, 656) could 
 get no addition product with dichloroacrylic acid. It was obtained 
 by Andrews (Ber. 14, 1,679) by heating the acid to 100 with bro- 
 mine (i mol.). The almost colourless product of the reaction was 
 the expected dichlorodibromopropionic acid. Henry, on the other 
 hand (J. pr. Ch. 117, 231), has made dipropargyl octobromide, C 6 H 6 
 Br g , easily by addition of bromine to dipropargyl CH = C CH 2 
 CH 2 - CEECH. A case of a somewhat different kind is the forma- 
 tion of trimethylene bromide, where, according to Freund (M. f. 
 Ch. 2, 642), the addition of bromine to trimethylene is a slow 
 process. 
 
 When nascent bromine is required, sodium bromide and bromate 
 are added to the solution of the substance and the amount of 
 sulphuric acid required by the equation 
 
 is run in (Ger. Pat. 26,642). 
 
 Heinichen (Ann. 253, 269) found that in making dibromo- 
 sulphanilic acid, either from sulphanilic acid itself or from its 
 barium salt, it was necessary to use nascent bromine in order to 
 avoid the formation of tribromoaniline. The yield was almost 
 equally excellent, whether he used a freshly prepared dilute solution 
 of bromine in sodium hydroxide and allowed it to flow slowly into 
 a solution of sulphanilic acid containing the requisite amount of 
 hydrochloric acid, or mixed the sulphanilic acid with hydrobromic 
 acid and added the calculated quantity of potassium bromate. He 
 dissolved, for example, sulphanilic acid (17*3 gr.) in half a litre of 
 water, added 43 per cent, hydrobromic acid (37*6 gr.), and with 
 continual agitation allowed a solution of potassium bromate (in 
 gr.) in water (250 cc.) to flow in slowly. The experiment lasted 
 thirty minutes, and the yield was 90 per cent, of the theoretical. 
 When bromine and sodium hydroxide were used the yield even 
 reached 95 per cent. 
 
 To restrain the too violent action of bromine a solvent such as 
 ether, chloroform, glacial acetic acid, hydrochloric acid, carbon 
 disulphide, or water, or a mixture of some of these, is employed. 
 Less commonly alcohol, potassium bromide solution, hydrobromic 
 acid, acetic ether, and other substances are used. It is not always 
 a matter of indifference what solvent is taken, as the examples 
 given below show. 
 
 On the other hand the substance to be acted upon is often dis- 
 
 % V 
 
1 66 BROMO-DERIVATIVES [CH. xvi 
 
 solved in, or diluted with, a suitable medium. An excess of bromine 
 is removed by heating, addition of sulphurous acid, or shaking with 
 mercury. 
 
 It is generally found to be advantageous to use silver salts or 
 esters instead of free acids for bromination. 
 
 The usual course is to drop the diluted bromine into the solution 
 of the substance, or vice versa. 
 
 For example, bromanil is best made, according to Grabe and 
 Weltner (Ann. 263, 32), by dissolving powdered paraphenylene 
 diamine (logr.)in glacial acetic acid (40 cc.), warming slightly if 
 necessary to bring about solution, and letting this solution, when 
 cold, flow into a small flask surrounded by water and containing 
 the bromine (40 cc.). The flow must be quite slow in order that as 
 little bromine as possible may be driven off in the form of vapour. 
 The resulting mass, which soon becomes solid, is stirred from time 
 to time, allowed to stand over night, and is then warmed on the 
 water bath till the evolution of hydrobromic acid and of unused 
 bromine has ceased. The product is next mixed with water, and, 
 after being warmed for a short time, is separated by filtration 
 and thoroughly washed. After the oxidation with nitric acid 
 (see Chap. XVII.) a yield of 30-32 grams of bromanil is 
 obtained. 
 
 In brominating anhydro-pyrogallopropionic acid, Bottinger (Ber. 
 16, 2,411) used as solvent a mixture of glacial acetic acid ana 
 chloroform. Acids containing three and five atoms of bromine were 
 formed. 
 
 According to Schunk and Romer (Ber. 10, 1,823) bromine has no 
 action on flavopurpurin even when boiled with it in carbon disulv 
 phide solution. But when the substance is dissolved in boiling 
 glacial acetic acid and bromine is added, the solution deposits on 
 cooling needles of tribromoflavopurpurin. 
 
 Michael (Am. Ch. J. 5, 203) showed that by dissolving one mole- 
 cular proportion each of bromine and acetic acid in some carbon 
 disulphide, and, with use of a reflux condenser, boiling till no more 
 hydrobromic acid was given off, a yield of bromoacetic acid equal 
 to 90 per cent, of the theoretical could be attained. Here, as in all 
 cases of bromination, a small excess of bromine (about 5 per cent.) 
 must be taken to make up for the part which is carried off along 
 with the hydrobromic acid. 
 
 This method cannot be applied to homologues of acetic acid, but 
 Michael (J. pr. Ch 143, 92) found that it was effectual with 
 
SEC. i, i] BROMINE 167 
 
 chlorides of such acids. 1 He heated the chloride, dissolved in a 
 considerable amount of carbon disulphide, with rather more than 
 the amount of bromine necessary to form the bromo-compound, 
 until hydrobromic acid was no longer evolved. In this case the 
 materials must be perfectly dry. When the brominated chloride is 
 poured into water the bromo-acid, when into alcohol the bromo- 
 ester, is obtained. For example, from 200 grams butyryl chloride 
 Michael made nearly the theoretically possible amount of bromo- 
 butyric ether in ten hours' time. 
 
 As was discovered by Wolff (Ann. 264, 233), hydrochloric acid 
 is a useful solvent in brominating. 
 
 For example, a solution of three parts of levulinic acid in twelve 
 parts of concentrated hydrochloric acid is cooled a few degrees 
 below o, and to it is added drop by drop four parts of bromine in 
 such a way that by continual shaking the latter is dissolved imme- 
 diately. After the mixture has been kept at a low temperature until 
 the red colour of the bromine has vanished, it is poured into much 
 cold water. The whole is then filtered to remove any dibromole- 
 vulinic acid which may have separated out, and extracted with 
 ether to obtain the monobromolevulinic acid. To purify the latter 
 it is recrystallised from boiling carbon disulphide. When ether or 
 chloroform is used as solvent instead of hydrochloric acid, the 
 bromination goes too far, and almost nothing but the dibromo- 
 derivative results. 
 
 In connection with this work, Gans succeeded in forming the previously 
 unknown monobromopyruvic acid. He dissolved one part of pyruvic acid 
 (b.-p. 165-170) in four parts of concentrated hydrochloric acid, and added 
 the necessary bromine, keeping the temperature meanwhile between 12 
 and 15. This process is also the best for making the dibromo-derivative. 
 To achieve this the requisite amount of bromine is taken and the tempera- 
 ture kept between 30 and 35. 
 
 Many substances are brominated by merely dissolving or siispending them 
 in water and adding bromine. 
 
 To illustrate this, the case of the three chlorobenzoic acids may be men- 
 tioned. Claus (Ber. 5, 656) has shown that while the acids themselves 
 are very variously affected by bromine, their bromo-derivatives are easily 
 formed by adding bromine to warm solutions of their silver salts. Thus 
 o-chlorobenzoic acid is scarcely attacked by bromine, even on prolonged 
 heating in a sealed tube, while a warm solution of the silver salt in water 
 
 1 In this connection see Volhard's method depending on the presence of 
 phosphorus to be described later. 
 
1 68 BROMO-DERIVATIVES [CH, xvi 
 
 on addition of bromine gives o-chlorobromobenzoic acid in crystalline form 
 on cooling. 
 
 The great difference which is sometimes found in the action of bromine 
 when different solvents are ^^sed may be further illustrated by reference to a 
 case examined by Baeyer and Bloem (Ber. 17 996). They found that 
 o-acetamidoacetophenone was brominated in the benzene ring in presence 
 of water or acetic acid. But in chloroform or sulphuric acid (cf. M. f. 
 Ch. 10, 813) solution, or when bromine vapour was used, it acquired 
 bromine both in the side chain and the ring, and w-bromo-0-acetamido- 
 dibromoacetophenone was formed 
 
 T H Br/ C0 " CHBr 2 
 v_/fjn JJAV TVTTT f~*r\ /^ILT 
 
 Alcohol can only be used as a solvent when bromine acts on the substance 
 more rapidly than on the alcohol. Wallach (Ann. 227, 280), in making 
 tetrabromides of the terpenes, diluted I volume of the terpene with 4 
 volumes each of alcohol and ether, and added gradually 07 volumes of 
 bromine. The tetrabromide being insoluble in alcohol was at once separated 
 from the easily soluble oily by-products which were always formed at the 
 same time. 
 
 Spitzer(M. f. Ch. 10 no) made monobromopentamethylphloroglucinol 
 by dissolving pentamethylphloroglucinol (2*5 gr. ) in absolute methyl alcohol 
 (23 gr.), and adding bromine (2*3 gr.) slowly to the cooled solution. 
 
 Kronfeld (Ber. 17 716) found in a solution of bromine in potassium 
 bromide the best agent for brominating amidonaphthoquinoneimide hydro- 
 chloride. 
 
 Bromine water, which, according to Slessor (New Edin. Phil. Jour. 7, 
 287), contains at 5, 3*6 per cent., and at 30, 3*1 per cent, of bromine, is 
 sometimes used for brominating. For instance, Fischer (Ann. 239, 189) 
 heated finely powdered dibromopyvureide with it in the proportion of i 
 part to 20, and obtained on cooling tribromopyvurine. The yield was 
 equal to 120 per cent, of the original substance. 
 
 Many substances can be brominated quantitatively with dilute bromine 
 water, and when the bromo-derivative is insoluble it comes out completely. 
 Landolt (Z. physiol. Ch. 6 J 84) determined the exact conditions, for 
 example, under which phenol _ could be precipitated from solution in water 
 as tribromophenol, and based thereon a method of quantitative estimation. 
 Cresol is not precipitated quantitatively in the same way. 
 
 Acetic ether was used as a solvent by Pinner (Ann. 209, 48). In trying 
 to make bromo-derivatives of aldehyde he found that when the paraldehyde 
 was dissolved in carbon disulphide or carbon tetrachloride no analysable 
 products could be isolated, but by the use of twice its weight of acetic ether 
 he obtained dibromo- and tribromo-aldehyde. 
 
 To make ethylene chlorobromide, James (Ber. 16 79) dissolved bromine 
 
SEC. i, i] BROMINE 169 
 
 (200 gr. ) in a mixture of equal parts of hydrochloric acid and water (i kg.)? 
 and saturated the whole with chlorine gas at o. Ethylene was passed into 
 this solution, and the oil which separated out was purified by distillation. 
 He obtained 140 grams of ethylene chlorobromide. 
 
 An indirect mode of obtaining bromo-derivatives is that, first 
 recognised as pretty general in its scope by Kelbe (Ann. 210, 48), 
 whereby aromatic sulphonic acids are converted into brominated 
 hydrocarbons. By the action of bromine at the temperature of the 
 water bath on 39' 5 grams of a-cymenesulphonate of sodium, he 
 made 28*5 grams bromocymene where 31 '3 grams were theoretically 
 obtainable 
 
 C ]0 H 13 SO 3 H + Br 2 + H 2 O - C 10 H 13 Br + HBr + H 2 SO 4 . 
 
 This action goes the more easily, the stronger the action of 
 bromine on the corresponding hydrocarbon itself is ; so that its 
 use is specially to be recommended where the latter action would 
 be excessive in violence. The corresponding application of chlorine 
 gives a less satisfactory result (Ber. 16, 617). 
 
 Two other indirect methods are worthy of mention. Pfeiffer 
 (Ber. 20, 1,345) found that collidine gave no substitution products 
 with bromine, but that such compounds could be obtained from the 
 potassium salt of collidine carboxylic acid. He dissolved the latter 
 in three times its weight of water, and boiled it in a flask attached 
 to a reflux condenser with twice its weight of bromine. A violent 
 action ensued, and after a few minutes' further boiling, the excess of 
 bromine was removed with sodium hydroxide. The oil which had 
 separated out soon solidified to a mass of crystals, which gave on 
 recrystallisation pure dibromocollidine 
 
 CH 3 
 Br/\Br 
 
 CH 3 \/CH 3 . 
 
 N 
 
 Lutidine dicarboxylic acid acts in a precisely similar manner. 
 In the case of other acids of the group, such as a-/3-pyridine 
 dicarboxylic acid, the reaction goes less smoothly. 
 
 Many other substances do not yield bromo-compounds directly, 
 although simple derivatives give them readily enough. To this 
 class belong, for example, the fatty nitro-bodies. Thus bromine 
 
1 70 BROMO-DERIVATIVES [CH. xvi 
 
 does not attack nitromethane at all (Ann. 180, 128), while it acts 
 easily on sodium nitromethane, forming bromonitromethane 
 
 CH 2 NaNO 2 + Br 2 = CH 2 BrNO 2 + NaBr. 
 
 The hydrobromic acid, which is given off in almost all the 
 methods of bromination described, is sometimes injurious. When 
 this is the case, it is frequently removed by passing a stream of 
 air or carbon dioxide during the operation. The object is best 
 attained, however, by adding potassium bromate, mercuric oxide, 
 or lead oxide, a method similar, therefore, to that used in the 
 case of iodine. The efficiency of the method has been tested by 
 Krafft (Ber. 8, 1,044). He took potassium bromate, bromine, and 
 benzene in the proportions required by the equation 
 
 and added sufficient sulphuric acid, diluted with twice its weight of 
 water, to combine with the potassium. The reaction was complete 
 after two hours, and the yield amounted to 70-80 per cent, of the 
 theoretical. 
 
 When spontaneously inflammable bromoacetylene is evolved, 
 the method given under chloracetylene is employed. 
 
 2, Bromine Carriers. These agents are similar to the more 
 familiar chlorine carriers, and are very commonly used. Such 
 substances are iodine, metallic iron, ferric bromide, ferric chloride, 
 aluminium bromide (Ber. 25, 797^), phosphorus, together with a 
 few substances which have been used by their discoverers only. 
 The most complete investigation of the subject has been made by 
 Scheufelen (Ann. 231, 52). 
 
 Iodine is added as such to the bromine, and considerably in- 
 creases its activity. For example, Kolbe found that bromine did 
 not act on carbon disulphide to produce a bromide even when the 
 vapours of the two substances were passed through red-hot tubes. 
 But Bollas and Groves (Ber. 3, 508) heated carbon disulphide 
 (2 parts) with bromine (14 parts) and iodine (3 parts) in an her- 
 metically sealed tube for forty-eight hours at 1 50, and on adding 
 sodium hydroxide to the contents and distilling, obtained carbon- 
 tetrabromide. 
 
 By the action of bromine on nitrobenzene, Kekule (Ann. 137, i? 2 ) 
 obtained pentabromobenzene as the final product, but by using 
 bromine (free from chlorine) to which a little iodine had been 
 
SEC. i, 2] BROMINE CARRIERS 171 
 
 added, and heating for 150 hours at 350-400, Gessner (Ber. 9, 
 l i$7) obtained hexabromobenzene (see below). 
 
 Scheufelen (Ann. 231, 164) obtained bromonitrobenzene, quite 
 free from chlorine, by placing nitrobenzene (10 gr.), ferric chloride 
 (2 gr.), and bromine (4*3 cc.), all carefully dried, in a tube and 
 heating for twelve hours at 100. On further heating, monobromo- 
 nitrobenzene (14 gr.), ferric chloride (4 gr.), and bromine (ii'2 gr.), 
 for the same length of time at 75-80, he obtained dibromonitro- 
 benzene. 
 
 As is well known, bromine only acts on benzene after weeks of 
 contact ; but the same observer, by taking bromine (300 gr.), 
 adding a few grams of ferric chloride to it, and allowing it to 
 flow drop by drop into benzene (17 gr.), obtained no grams of 
 hexabromobenzene, while the theoretical yield would have been 
 1 19 grams. 
 
 In connection with Scheufelen's work, Schiff (M. f. Ch. 10, 39) 
 made dibromobenzene, and obtained the ortho-compound in par- 
 ticular, as follows : Paranitrobromobenzene (20 gr.) was heated in 
 a sealed tube with the theoretically necessary quantity of bromine, 
 together with enough excess of bromine to convert all the ferric 
 chloride into bromide. The heating continued for fifty hours at 
 85-90. The viscid contents of the tube were washed with water to 
 remove iron salts, and by recrystallisation from alcohol a 90 per 
 cent, yield of dibromonitrobenzene was attained. The nitro-group 
 was replaced by hydrogen by first reducing with tin and hydro- 
 chloric acid, and then acting with ethyl nitrite, and ^-dibromo- 
 benzene was the final product. 
 
 At Scheufelen's suggestion, Kerrow (Ber. 24, 2,939) endeavoured to fix 
 the limits of the action of chlorine and bromine carriers, and one of his 
 results was the discovery that while the presence of one nitro-group greatly 
 assists the introduction of halogens in place of hydrogen, more than one 
 prevents it altogether. In such cases the nitro-groups themselves are more 
 easily replaced by halogens than the neighbouring hydrogen atoms. But 
 with the removal of the nitro-groups the influence of the halogen carriers 
 reasserts itself, and the introduction of more halogen atoms progresses 
 rapidly. 
 
 Ferric bromide (or the more easily prepared ferrous salt) has sometimes 
 to be used in place of the chloride, because while up to 100 the chlorine of 
 the carrier combines with the hydrogen to form hydrochloric acid, at higher 
 temperatures such as 180 a part of the chlorine is likely to enter into the 
 organic compound. 
 
172 BROMO-DERIVATIVES [CH. xvi 
 
 By using iron wire, Meyer and Miiller (Ber. 24, 4,249) avoided 
 the difficulty sometimes caused by the chlorine of the chloride. 
 They heated molecular proportions of ethyl bromide and bromine 
 for an hour in a sealed tube with this agent, and found that, save 
 for a small portion which remained unchanged, the substance had 
 been converted completely into ethylene bromide. 
 
 Aluminium bromide is an excellent bromine carrier, transforming 
 CC1 4 , C 2 C1 4 , and C 2 C1 C , according to Gustavson (Ber. 14, 1,709), 
 into the corresponding bromine derivatives. 
 
 Bliimlein (Ber. 17, 2,486) threw aluminium (i gr.) in small por- 
 tions into carefully cooled bromine (150 gr.), an operation which 
 was attended by a considerable evolution of light and heat, and, 
 after the liquid had been cooled to o again, added a-naphthol. The 
 excess of bromine was then driven off, and the resulting mass ex- 
 tracted with cumene. Pentabromonaphthol, C 10 H 2 Br 5 OH, remained 
 undissolved. 
 
 In a similar manner Ris (Ber. 20, 2,621) added finely powdered 
 /3-dinaphthylamine to more than eight times the actually necessary 
 amount of bromine, prepared as above by the addition of a little 
 aluminium. A doughy substance was formed which, after being 
 ground up with water, left as residue octobromo-/3-dinaphthylamine, 
 C 20 H 7 Br 8 N. 
 
 The use si. phosphorus as a halogen carrier was discovered by 
 Corenwinder (Ann. Ch. Ph. 30, 248), who made hydriodic acid by 
 the action of water on phosphorus iodide. The application of red 
 phosphorus instead of the yellow variety was first suggested by 
 Personne (C. R. 52, 468). The method is quite generally applied 
 for the preparation of hydrocarbon bromides from alcohols. 
 
 The action takes place according to the equation 
 
 For example, in making ethyl bromide, red phosphorus is placed in 
 a retort connected with a reflux condenser, and the proper amount 
 of alcohol of at least 90 per cent, strength is poured over it. The 
 calculated amount of bromine is added slowly. During this operation 
 the retort must be cooled on account of the heat developed by the 
 violence of the action. The ethyl bromide is finally separated by 
 fractional distillation (cf. Ethyl iodide). 
 
 The ease with which acids could be brominated in prgse-qce of 
 phosphorus was first pointed out by Hell (Ber. 14, 891), and later 
 (Ann. 242, 144) showed what splendid results could be 
 
SEC. i, 2] BROMINE CARRIERS 173 
 
 attained by this almost forgotten method when used under proper 
 conditions. 
 
 The prime condition necessary for the successful use of this way 
 of brominating acids is that all the materials must be perfectly dry. 
 As the red phosphorus usually contains some phosphoric acid, it 
 must be washed with water until the washings cease to show an 
 acid reaction, and once more dried. 
 
 The case of succinyl bromide will serve as a general example. 
 The succinic acid and phosphorus are ground together in a mortar, 
 and during the addition of the bromine the retort in which the 
 mixture is placed is kept in motion to aid in mixing the ingredients. 
 It is necessary to take a small excess of phosphorus and rather 
 more bromine than the theory demands, as from 51015 per cent, 
 of the latter may be carried over mechanically by the hydrobromic 
 acid. He describes in detail, as follows, the method of preparing 
 the bromide of bromosuccinic acid. The action is expressed by the 
 equation 
 
 CH 2 - COOH CHBr - COBr 
 
 3 | +2P+i6Br = 3 | +2HPO 3 + 7HBr. 
 
 CH 2 -COOH CH 2 -COBr 
 
 The reaction is best carried out in a tubulated retort, to whose 
 neck a tube about 1 1 mm. in internal diameter, and 70 cm. in length 
 is fused. This tube is inserted in a condenser jacket supplied with 
 cold water. The upper projecting end of the tube is connected 
 with absorption bottles to catch the hydrobromic acid. The con- 
 necting tube just passes through the cork of the first bottle and no 
 more. Two bottles are used. They contain each a little water, and 
 a tube reaching to the bottom of each connects them. This 
 arrangement enables the liquid to pass from the one to the other, 
 and yet excludes the possibility of its mounting back into the 
 retort. Any escaping gases are carried by another tube into an 
 open flask containing water, beneath the surface of which, however, 
 the tube does not dip. Even when the evolution of hydrobromic 
 acid and bromine is rapid, they are completely absorbed. The 
 movements in the two bottles give an indication of the rate at 
 which the gases are coming off. An apparatus resembling this has 
 been described by Stadel (Ber. 19, 1,950- 
 
 Rubber connections must be avoided as far as possible, as bromine 
 destroys them rapidly. 
 
 Flashes of flame and violent bursts of hydrobromic acid 
 accompany the fall of each drop of bromine at first so that the 
 
174 BROMO-DERIVATIVES [CH. xvi 
 
 stream must be very slow. When the drops cease to produce 
 instant effect, the mixture is allowed to cool a little and the 
 remainder of the bromine is added. The retort is then heated on 
 the water bath till the bromine disappears. More than 200 grams of 
 the acid cannot well be worked up at once. The action under 
 these conditions, which should not be departed from if it can be 
 avoided, lasts from 3 to 5 hours. 
 
 When succinic anhydride is used the action is much quieter 
 (cf. Sec. II. 9). 
 
 To prepare bromosuccinic acid from the bromide, half a litre of 
 water is taken for every 100 grams of succinic acid originally used. 
 The water is heated to boiling, and, after the burner has been 
 removed, the bromide is run in from a funnel provided with a stop- 
 cock. The operation must be performed in a hood on account of 
 the fumes given off. After all the bromide has been added, the 
 liquid is filtered and the bromosuccinic acid is extracted with ether. 
 The yield is 80-90 per cent, of the theoretical. To prepare the corre- 
 sponding esters, the bromides are run into alcohol instead of water. 
 
 By this process the a-bromo-derivatives of the fatty acids may be pre- 
 pared. The ingredients are taken so as to correspond with the equation 
 
 3CH 3 . COOH + P + 8Br = 3CH 2 Br . COBr+HPO 3 + 2HBr. 
 
 Here the fluid fatty acid covers the amorphous phosphorus and the action 
 is much less violent ; still the necessary precautions must never be neglected. 
 To obtain the bromo-acids themselves a larger amount of water is taken 
 than for succinic acid, and the bromides are dropped into it while it boils. 
 The bromo-derivative is then fractionated invacuo. The yield is excellent. 
 The great advantage of the method as compared with the earlier ones, 
 which nearly all required the use of sealed tubes, is that open vessels can 
 be employed and yet the yields are very good. 
 
 According to Auwers and Bernhardy (Ber. 24, 2,215), the 
 general rule may be stated that in the aliphatic series as many 
 bromine atoms are introduced as there are carboxyl groups in 
 the molecule, provided that there is at least one a-hydrogen atom 
 to be replaced. 
 
 When it is necessary for any reason to work with sealed tubes, 
 the use of phosphorus is still advantageous. Thus Bujard and 
 Hell (Ber. 22, 68) found that while lepargylic acid heated for 8 
 hours at 100 with a molecular proportion of bromine was not acted 
 upon at all, the addition of only ^ per cent, of red phosphorus 
 brought about the change completely in three hours. 
 
SEC. i, 3] HYDROBROMIC ACID 175 
 
 Although a full statement of the case would lead us too much 
 into detail, it ought to be mentioned that Krafft and Beddies 
 (Ber. 25, 488) found that heating fatty acids of large molecular 
 weight directly with bromine in sealed tubes led to the formation 
 of very curious and unexpected substitution products. 
 
 A variation in Volhard's process introduced by Alexander 
 (Ann. 258, 76) may be exemplified by mention of the case of 
 phenylsuccinic acid. He placed the acid (10 gr.) in a retort with 
 reflux arrangement, and poured over it phosphorus tribromide (i I gr.). 
 No action took place, but when bromine (16 gr.) was dropped in 
 slowly from a funnel the acid dissolved, hydrobromic acid gas 
 was evolved with violence, and the bromide was produced. The 
 product of the interaction was worked up in the way already 
 described. 
 
 The author (Ann. 251, 346) has found that Volhard's bromo- 
 bromides are easily converted into dibromo-derivates by heating 
 in a sealed tube to 100 with bromine. 
 
 3. Hydrobromic Acid. Hydrobromic acid can be made in two 
 ways. In Recoura's method (C. R. 110, 784), the long known 
 action of hydrogen sulphide on water and bromine is used. The 
 gas is led into a tall vessel through a quantity of bromine, which 
 is covered with a layer of water, or better still hydrobromic acid 
 solution. After the water has become completely saturated, a 
 regular evolution of hydrobromic acid begins. The gas is washed 
 by passing through a solution of hydrobromic acid or potassium 
 bromide to which some red phosphorus has been added. Accord- 
 ing to Fileti and Crosa (Gazz. Chim. 21, 64), the gas is washed 
 better by passage through a tower containing a mixture of asbestos 
 and red phosphorus moistened with hydrobromic acid. By one of 
 these means it is freed from bromine. It is not found to be con- 
 taminated with hydrogen sulphide, even when a rapid stream of 
 this gas is used. 
 
 The other method we owe to Feit and Kubierschky (Ber. 25, 
 411^). Potassium bromide (100 gr.) is dissolved in sulphuric acid 
 of sp. gr. i '4 1 (150 cc.), and the solution is distilled until the 
 thermometer registers 200?. The well-nigh theoretical yield of 
 hydrobromic acid is almost free from bromine, but contains a 
 trace of sulphuric acid. Fractional distillation yields a portion 
 boiling constantly at 126. Its sp. gr. is 1*49, corresponding to 
 48 per cent, hydrobromic acid. From 150 grams of the bromide 
 
1 76 BROMO-DERIVATIVES [en. xvi 
 
 about 200 grams of this acid are obtained. The gas is made from 
 it by adding dry calcium bromide and warming. 
 
 When alcohols are saturated with hydrobromic acid and the 
 solution is heated in sealed tubes at ioo c , alkyl bromides are 
 formed. If the acid is required in a perfectly dry condition, it is 
 led first over phosphorus pentoxide. Usually, however, a bromine 
 carrier, like phosphorus, is used in such cases. 
 
 As an example of this method may be mentioned Veley's 
 (Ch. News, 47, 39) preparation of monobromhydrin. He saturated 
 glycerol with dry hydrobromic acid, washed with caustic potash 
 and distilled under diminished pressure. 
 
 The extraordinary solubility of hydrobromic acid in glacial 
 acetic acid, amounting to 68 per cent, at ordinary temperatures 
 (Ber. 11, i, 221), renders such a solution very valuable in the 
 preparation of addition products, and it is much used for this 
 purpose. According to the directions of Anschiitz and Kinnkutt, 
 who prepared monobromohydrocinnamic acid from cinnamic acid, 
 the substance may be placed with the solution in a sealed tube 
 and heated if necessary in a water bath for a short time. 
 
 The temperature may, however, have some influence on the way 
 in which the addition takes place. For instance, Kraut and 
 Merling (Ann. 264, 320) found that at 100 hydrobromic acid, used 
 in the form of fuming hydrobromic acid, added itself to atropic 
 acid so as to produce /3-bromohydratropic acid, while, according to 
 Fittig (Ann. 195, 147), a-bromohydratropic acid is formed at o c . 
 
 Similarly the process is influenced by other conditions. Thus 
 dry hydrobromic acid and dry allyl bromide, CH 2 : CH.CH 2 Br, 
 give chiefly trimethylene bromide, CH 2 Br.CH 2 .CH 2 Br, while 
 in presence of a solvent or with moist acid the production of 
 propylene bromide, CH 3 .CHBr.CH 2 Br, is favoured. The latter 
 statement has been called in question by Bogomolez (Ber. 1], 
 1,257) however. 
 
 Bromo-derivatives are also obtained by the action of hydrobromic 
 acid on diazo-bodies (Ann. 137, 49), only in the case of this halogen 
 acid the action is not so satisfactory as with hydriodic acid. The 
 best way is to add strong hydrobromic acid and bromine water 
 to the salt of the diazo-body. By this means a perbromide is 
 produced, which, on boiling with alcohol, yields the bromo-deriva- 
 tive. The course of the action is represented by the equations 
 
 C 6 H 5 . N 2 . N0 3 +HBr + Br 2 = C 6 H 5 N 2 Br. Br 2 +HNO, 
 C 6 H 5 N 2 BrBr 2 +C 2 H 5 OH-C 6 H 6 Br+N 
 
SEC. i, 4] PHOSPHORUS PENTABROMIDE 177 
 
 According to Richter (Ber. 8, 1,428), this process frequently 
 gives very poor results. Yet in his hands tribromoaniline gave a 
 quantitative yield of tetrabromobenzene. He poured glacial 
 acetic acid over the former, and led into it nitrous acid until the 
 whole was dissolved. On adding concentrated hydrobromic acid 3 
 large quantities of crystalline diazotribromobenzene bromide, 
 C H 2 Br 5 N 2 Br, separated out. After boiling with an additional 
 amount of acetic acid till nitrogen ceased to be evolved, tribromo- 
 benzene crystallised out. Jackson and Bancroft (Am. Ch J. 12, 289) 
 state that when prepared in this manner it often contains some 
 pentabromobenzene. 
 
 4. Phosphorus Pentabromide. This substance cannot be used 
 for making acid bromides, one respect in which it differs markedly 
 from the pentachloride. Yet it can be used for making bromo- 
 derivatives. Wurtz, for example, obtained ethylidene bromide 
 (C. R. 47, 418) with this reagent, and Gabriel (Ber. 24, 3,100) 
 speaks of effecting a bromination by its help. 
 
 Claus and Pollitz (J. pr. Ch. 149, 41) succeeded in making 
 a-bromoquinoline from carbostyril by mixing one part of the latter 
 with three parts of freshly prepared pentabromide, and heating the 
 mixture for three to four hours at 120-130. A constant stream of 
 dry carbon dioxide was led through the apparatus, and the tem- 
 perature was not allowed to exceed these limits, as otherwise there 
 was a tendency to form more highly brominated products. The 
 a-bromoquinoline was isolated by distillation in a current of steam. 
 As the polybromo-derivatives come over last, the stream is inter- 
 rupted before the drops of oil in the condenser begin to solidify. 
 
 Claisen states (Ber. 14, 2,474) that phosphorus pentabromide 
 has hardly any action on benzoic acid. The reaction takes place 
 much more freely when phosphorus tribromide is used. Benzoic 
 acid (3 mol.) is melted and powdered and mixed with the tribromide 
 (2 mol.) and the whole heated in connection with a condenser. 
 As the acid dissolves, an easily controllable reaction sets in during 
 which streams of hydrobromic acid are evolved. After warming 
 for forty-five minutes, the residue is distilled in vacua and the 
 distillate rectified at the ordinary pressure. The action follows the 
 equation 
 
 3C 6 H 5 . COOH + PBr 3 = 3C G H 5 . COBr + H 3 PO 3 , 
 
 and 500 grams of the acid yields 400 grams of the bromide. 
 
 N 
 
1 78 BROMO-DERIVATIVES [CH. xvi 
 
 Phosphorus chlorobromide, PCl 3 Br 2 , is often used in place of the penta- 
 bromide. Ladenburg and Friedel first showed that it had the same action 
 on organic compounds containing oxygen as the latter. It is prepared by 
 the action of bromine on excess of the trichloride at ordinary temperatures. 
 The ingredients were placed by Michaelis (Ber. 5, 9) m sealed tubes, the 
 tubes being half filled with the materials. The reaction was complete in a 
 few days, and the excess of the trichloride could be poured off the crystals 
 of the chlorobromide. These were yellowish red in colour, and decomposed 
 on heating to 35. 
 
 By the help of this agent Paterno and Pisati (Ann. 221, J 37) converted 
 aldehyde into ethylidene bromide, CH 3 CHBr 2 , and Michael (Ber. 14, 
 2,105) ma de butylidene bromide from butyl aldehyde. 
 
 5. Metallic Bromides. Calcium bromide was used by Lellmann 
 and Schwaderer (Ber. 22, 1,327) for brominating piperidine. They 
 mixed calcium hydroxide (300 gr.), suspended in water, with bromine 
 (130 gr.) in a retort, and dropped a solution of piperidine in water 
 into it, while a current of steam passed through the mixture. An 
 oil, consisting of bromopiperidine, C 5 H 10 NBr, passed over. 
 
 Some time before this Preibisch (J. pr. Ch. 116, 316) had failed 
 to observe any interaction between calcium bromide and nitro- 
 methane. Stenhouse, too (Ann. 91, 309), had made bromopicrin 
 (tribromonitromethane) by the action of the same agent on picric 
 acid. Bolas and Groves gave later (J. Ch. Soc. 23, 153) the best 
 proportions. Lime (4 parts) was slaked with water (50 parts), and 
 to the cold mixture bromine (6 parts) and then picric acid (i part) 
 were added. On distilling, the bromopicrin passes over with the 
 first quarter of the distillate. It is dried with calcium chloride and 
 purified by fractional distillation. The yield is about 95 per cent, 
 of that theoretically derivable from their equation. 
 
 For the Sandmeyer reaction (see Sec. II.) cuprous bromide 
 solution is prepared as follows. Crystalline cupric sulphate 
 (125 gr.) and potassium bromide (360 gr.) are dissolved in water 
 (800 gr.), concentrated sulphuric acid (no gr.) and copper (200 gr.) 
 are added, and the whole is boiled, using a reflux condenser, till the 
 colour has nearly vanished. Aniline, after being prepared for the 
 operation, is converted by this agent into bromobenzene. 
 
 According to Gattermann (Ber. 23, 1,218), finely divided copper 
 may be employed as a carrier instead of the cuprous bromide. 
 This action is described in detail under chlorination. 
 
 Cupric bromide, on account of its solubility in alcohol, is much 
 used for converting organic iodides into bromides. For example, 
 
SEC. ii, i] PREPARATION OF CHLORINE 179 
 
 by mixing its solution with ethyl iodide a change represented by 
 the equation 
 
 2CuBr 2 + 2C 2 H 5 I = 2C 2 H 6 Br 4- Cu 2 I 2 + Br 2 
 
 takes place, and the insoluble cuprous iodide is precipitated. In 
 this case the bromine set free by the action might prove a disturb- 
 ing element. Berthelot (Ann. 100, 124) suggests the addition of 
 finely divided copper to prevent interference with the course of the 
 action from this source. 
 
 Potassium and silver bromides produce similar actions, but the 
 yields are usually poor. 
 
 Worthy of mention is the discovery of Ciamician and Silber 
 (Ber. 17, i,745) that a 5 P er cent, solution of potassium hypo- 
 bromite acts on pyrrol producing chiefly dibromomaleimide. 
 
 SECTION II. CHLORO-DERIVATIVES. 
 
 The chlorination of organic compounds is brought about chiefly 
 by the action of chlorine gas, phosphorus pentachloride, and hydro- 
 chloric acid. The following are less commonly employed : acetyl 
 chloride, antimony trichloride, bleaching powder (hypochlorous 
 acid), cuprous chloride, mercuric chloride, phosphorus oxychloride, 
 phosphorus trichloride, sulphur monochloride and tetrachloride, 
 sulphuryl chloride, chlorsulphonic acid, thionyl chloride. 
 
 1. Preparation of Chlorine, Chlorine gas is prepared by cover- 
 ing a mixture of common salt (5 parts) and manganese dioxide (5 
 parts) with a cold mixture of concentrated sulphuric acid (12 parts) 
 and water (6 parts), and then warming gently. These proportions 
 give a regular stream of almost dry chlorine. Recently Klason 
 (Ber. 23, 330), has recommended the use of an earthenware 
 apparatus charged with manganese dioxide and hydrochloric acid. 
 
 The use of bleaching powder as a source of chlorine in the 
 laboratory was apparently first seriously suggested by Kammerer 
 (Ber. 9, 1,548). The method became more popular after Winkler 
 (Ber. 20, 184) had devised a method of using it in an ordinary 
 Kipp's apparatus, by moulding the powder into cubical pieces with 
 the help of plaster of Paris. According to Klason (Ber. 23, 330), 
 the powder itself can be employed. Still the method has not 
 preserved its popularity, as when the apparatus is used continuously 
 many inconveniences arise. 
 
 Now that the " Badische Anilin und Sodafabrik" has introduced 
 
 N 2 
 
i8o CHLORO-DERIVATIVES [CH. xvi 
 
 liquid chlorine (Ann. 259, 100) as an article of commerce, the 
 larger laboratories will doubtless use it in this form. 
 
 As chlorine attacks corks and rubber stoppers, these should be 
 coated with vaseline. Rubber stoppers which have been thoroughly 
 rubbed with this substance are not only protected but even retain 
 their softness for a considerable time. 1 
 
 2. The Use of Free Chlorine, To bring about the action of 
 
 chlorine on liquids, it may be led directly into them. To modify the 
 violence of the action the liquid may be diluted with water, chloro- 
 form, acetic acid, or other suitable solvent. If this is undesirable 
 then the chlorine itself may be diluted (Ann. 246, 98), by forcing 
 a stream of air or carbon dioxide through the generating apparatus, 
 or by drawing such a stream through the apparatus with an aspirator. 
 
 The amount of chlorine which has been taken up is ascertained by 
 weighing from time to time, and in this way, if the substance can 
 take up several atoms of chlorine, the operation can be stopped 
 when a sufficient amount has been introduced. 
 
 If an exact amount of chlorine is to be used, it is produced from 
 weighed quantities of potassium permanganate or chlorate and 
 hydrochloric acid, and a stream of carbon dioxide is finally con- 
 ducted through the apparatus. 
 
 In the case of aromatic bodies the temperature has an important 
 influence on the part of the molecule which the chlorine will attack. 
 For example, Varnholt (J. pr. Ch. 144, 22) finds that when phenol 
 is treated with chlorine at a temperature just above that at which it 
 would solidify, as much as 43 per cent, of 0-chlorophenol is formed ; 
 while at the ordinary temperature a much smaller amount of this in 
 proportion to the quantity of the para-compound is produced. For 
 aromatic hydrocarbons, Beilstein and Geitner's rule (Ann. 139, 332) 
 holds. It is : that in the cold, in presence of chlorine carriers, the chlor- 
 ine enters the phenyl group, while at the boiling-point of the substance 
 the side chain is attacked. The latter action seems to take place 
 with especial ease where the side chain is an aldehyde group, the 
 
 1 In connection with this property of indiarubber, it may be mentioned 
 that rubber stoppers absorb considerable quantities of hydrocarbons (Bunge, 
 Ber. 23, 113^')- I n this connection also, attention may be drawn to 
 Levoir's statement that the adhesion of rubber tubing to brass gas connec- 
 tions, when they have remained in contact for a considerable time, is due to 
 the formation of crystallised sulphide of copper. It may be prevented by 
 rubbing the tubing with soap. Grease should not be used. 
 
SEC. ii, 2] THE USE OF FREE CHLORINE 181 
 
 acid chloride being formed. Benzoyl chloride was first made in 
 this way. Liebig and Wohler (Ann. 3, 262) obtained it by passing 
 chlorine into boiling benzaldehyde as long as hydrochloric acid 
 was evolved, and rectifying the product. It seems to be made 
 commercially in this way still. 
 
 Chlorine is always more active in sunlight than in diffused light. 
 Thus chloroform can be converted into tetrachloride of carbon 
 under those circumstances only. 
 
 When solids have to be chlorinated they are dissolved in water, 
 acetic acid, chloroform, carbon tetrachloride, nitrobenzene, or ether, 
 and these solutions are treated like liquids. 
 
 That a substance is saturated with the gas is recognised by its 
 becoming green on account of the presence of free chlorine. The 
 excess can be removed by adding some sulphurous acid, by warm- 
 ing, or by leading a rapid stream of air through the liquid. In the 
 last case the completeness of its removal is tested by the action en 
 potassium iodide and starch (Ber. 22, 2,525). 
 
 Agitation with mercury will also remove it, but in this case it 
 must be noticed that when a liquid which has been so treated is 
 shaken with ether, some chloride of mercury passes into the ether 
 with the substance. 
 
 In the case of dissolved substances, the temperature and the 
 solvent used have naturally an important influence on the product 
 quite apart from considerations of isomerism. For example, the 
 chlorination of j^-acettoluide is very unsatisfactory at o and in 
 acetic acid solution, and the yield is even poorer with other solvents. 
 By splitting off the acetyl group, ;;z-chloro-/-toluidine is finally 
 formed (Ann. 168, 196). But Erdmann (Ber. 24, 2,767) obtained 
 this product quite easily by dissolving /-acettoluide (100 gr.) in hot 
 glacial acetic acid (100 cc.), and passing chlorine through the 
 solution. The gas was rapidly absorbed, and the liquid remained 
 at the boiling-point without the application of external heat. From 
 i kilogram of commercial ^-acettoluide, 400 grams of ?;z-chloro- 
 toluidme, boiling within seven degrees, were obtained. Further Lell- 
 mann remarks (Ber. 24, 4, in) on this method that, in conse- 
 quence of the high temperature, the product is less pure than need 
 be, and that the yield can be raised from 38 per cent, to 42 per 
 cent, by passing chlorine diluted with two volumes of carbon 
 dioxide into a cold solution of ^-acettoluide (50 gr.) in glacial 
 acetic acid (400 gr.). 
 
 Sulphuric acid is used as a solvent in exceptional cases. Thus to 
 
182 CHLORO-DERIVATIVES [CH. xvi 
 
 make tetrachlorophthalic acid, phthalic anhydride is warmed to 60 
 with sulphuric acid containing 50-60 per cent, of sulphuric anhy- 
 dride (Ger. Pat. 50,177), a little iodine is added, and chlorine is 
 passed in while the temperature is gradually raised to 180-200. 
 The tetrabromo- and tetraiodo-derivatives can be made in the same 
 way. 
 
 Hafner (Ber. 22, 2,525) tried in vain to chlorinate aniline and 
 toluidine in the presence of large amounts of sulphuric acid of 
 various strengths. But Claus and Philipson (J. pr. Ch. 151, 59) 
 succeeded in making dichloronaphthylamine by suspending - 
 naphthylamine sulphate in fifty times its weight of 80 per cent, 
 sulphuric acid, cooling the mixture with ice, and leading into it 
 chlorine gas in the proportion of two molecules of the latter to one 
 of the substance. The chlorinated product was deposited when 
 the mixture was poured into water. It was washed with ammonia 
 to remove the acid, and recrystallised from alcohol or distilled in a 
 current of steam. 
 
 Substances which can be melted without decomposition are fused, 
 and chlorine is passed into the liquid mass. Thus /-nitrotoluene is 
 melted in an oil bath, and the temperature gradually raised from 
 130 to 160, while the calculated amount of chlorine is being led in. 
 The resulting product is washed successively with water, dilute 
 soda solution, and again with water, and is finally recrystallised 
 from alcohol, yielding pure /-nitrobenzylidene chloride. Yet it 
 should be mentioned that Zimmermann and Miiller failed to obtain 
 it in this way, and prepared it otherwise by the action of phosphorus 
 pentachloride on p-nitrobenzaldehyde. 
 
 To secure the exposure of a large surface to the action of chlorine a 
 device like that used by Cloez (Bull. Ch. 39, 636) may be employed. He 
 dissolved citric acid in one and a half times its weight of water, and allowed 
 this solution to drop on pieces of pumice in a vertical cylinder, while a 
 stream of chlorine passed upwards to meet it. The product of the action 
 was pentachloroacetone. 
 
 To render the action of chlorine as vigorous as possible, the substances 
 on which it is to act may be brought in contact with it in the vaporous 
 condition by boiling them in a flask attached to a reflux condenser and 
 conducting the chlorine through a tube opening just above the surface of the 
 liquid. Sometimes the vapour is mixed with chlorine and led through a 
 red-hot tube containing animal charcoal, which has been previously ignited 
 in an atmosphere of chlorine (Bull. Ch. 27, H3)- In this way phosgene 
 gas is made from carbon monoxide and is caught in benzene, in which it 
 dissolves very readily. 
 
SEC. ii, 2] THE USE OF FREE CHLORINE 183 
 
 Whenever monochloroacetylene, which is spontaneously inflammable, is 
 formed during chlorination, a rapid stream of an indifferent gas must be 
 conducted through the vessels lest admixture of air should lead to explosions 
 which might destroy the apparatus. 
 
 Chlorine Water. Perhaps the small solubility of chlorine in 
 water has caused this reagent to be used less than it deserves to 
 be. Witt (Ber. 8, 143) states that, as might be expected, it acts 
 much less energetically in this form than when used as a gas. It 
 was used on this account by Korner in preparing dichloro-^-nitr- 
 aniline. The nitraniline, which was converted into tar by chlorine 
 gas, was dissolved in a large excess of hydrochloric acid, the 
 mixture was cooled strongly, and chlorine water was added until 
 the solution smelt strongly of chlorine. The product appeared in 
 the form of a lemon-yellow precipitate. No tar was produced as 
 long as the solution was kept cool. 
 
 Although, according to Gay Lussac, 1 the maximum absorption of 
 chlorine by water takes place at 8, when it takes up three volumes, 
 yet by leading a rapid stream of the gas into water at o crystals of 
 the composition, Cl + 5H 2 O, are obtained, and this hydrate ought to 
 be useful for work at low temperatures, especially where an excess 
 of chlorine must be present throughout the operation. 
 
 This method was used by Stenhouse and Groves (Ann. 203, 
 291), as it was found to be the only one by which tetrachloro- 
 betorcinol, C 8 H 6 C1 4 O 9 , could be obtained. They conducted a stream 
 of chlorine through a mixture of ice and water, and then added a 
 cooled solution of betorcinol in such quantity that the chlorine 
 hydrate remained in slight excess. After 12-20 hours colourless 
 crystals of the tetrachloro-derivative had separated out. Ditte (C. 
 R. 95, 1,283) employed the same method. 
 
 Grimaux (Ber. 5, 222) used a solution of chlorine in chloroform, which 
 takes up 28 per cent, at o, and 25 per cent, at 10. By sealing up in a 
 tube with benzene and with naphthalene he prepared benzene hexachloride 
 and napthalene tetrachloride, C 10 H 8 Cl4, respectively. 
 
 Dilute aqua regia can also be used, but it leads often to the introduction 
 of nitrogen as well as chlorine, and substances of complicated constitution 
 may result. 
 
 When a calculated amount of chlorine is to be used in a sealed 
 tube, Beilstein (Ann. 179, 287) suggests the following method. 
 
 1 Wurtz, " Diet, de Chimie," 1, 858. 
 
184 CHLORO-DERIVATIVES [CH. xvi 
 
 First fuming hydrochloric acid (25 cc.) is placed in the tube, a plug 
 of glass wool is placed above it, and then the substance is added, 
 and finally the calculated amount of potassium bichromate is put 
 in. After the tube has been sealed the chlorine is evolved on 
 heating. 
 
 3. Nascent Chlorine. The application of nascent chlorine is a 
 method which has long been in use. Thus Kolbe (Ann. 45, 44) 
 stated, in 1843, that thiophosgene, CSC1 2 , was best made by placing 
 carbon disulphide, manganese dioxide, and hydrochloric acid in a 
 closed vessel, and, with frequent agitation, allowing them to remain 
 in contact for a considerable length of time. The method is now 
 no longer used for making this particular substance however (Ann. 
 167, 195). 
 
 Claus (Ber. 19, 1,142) prepared dichloro-a-naphthochloroquinone, 
 C 10 H 4 C1 4 O 2 , by heating dichloro-a-naphthoquinone (10 gr.) with 
 manganese dioxide (10 gr.) and pure hydrochloric acid, sp. gr. i'2 
 (40 cc.), in sealed tubes for ten hours at 230. 
 
 At present the usual method is to dissolve or suspend the sub- 
 stance in hydrochloric acid and add bichromate, or chlorate of 
 potassium, or bleaching powder (q.v.}. In this way Hofmann 
 (Ann. 52, 58) made chloranil from phenol. He advises that such 
 operations should be carried out in basins, as the violence of the 
 actions sometimes brings about explosions. 
 
 Fischer (Ber. H, 735) modified the process in making chloro- derivatives 
 of naphthalene as follows. Using an idea of Depouilly's (Bull. Ch. 1865, 
 4, 10), he mixed the naphthalene in a mortar with the amount of potassium 
 chlorate necessary to chlorinate it to the desired extent, an operation 
 demanding caution. The powder was then moistened with sufficient water 
 to enable him to mould it into pellets, which he dropped one at a time into 
 concentrated hydrochloric acid. Very little chlorine escaped, and by using 
 one and a half times the amount of chlorate necessary to give four atoms of 
 chlorine to each molecule of naphthalene he obtained naphthalene tetra- 
 chloride as the principal product. 
 
 4. Addition of Chlorine or Hydrochloric Acid to Unsatu- 
 rated Compounds. This method is of very wide application, and is 
 often the only one by which the desired result can be attained. In 
 gaseous form the substances unite readily, and it was in this way 
 that Deimann and Trostwyk, in 1795, prepared the so-called "oil 
 of Dutch chemists," ethylene chloride, by the union of ethylene 
 
SEC. ii, 5] HYDROCHLORIC ACID ON ALCOHOLS 185 
 
 and chlorine. The usual method is to dissolve the unsaturated 
 body in water, acetic acid, ether, or other solvent, and add a solution 
 of chlorine or hydrochloric acid in the same medium. 
 
 The presence of sufficient chlorine may be tested by the fact 
 that the mixture should have no, or at least hardly any, power to 
 decolourise dilute bromine water. 
 
 An example of the use of the addition method is supplied by the 
 /3-derivatives of the fatty acids. The union of chlorine with the 
 carbon atom not already combined with carboxyl can be achieved 
 by adding hydrochloric acid to the unsaturated compound. Thus 
 /3-chloropropionic acid is made by the addition of hydrochloric acid 
 to acrylic acid (Ann. 163, 96). 
 
 CH 2 : CH . COOH + HC1 = CH 2 C1 . CH 2 . COOH. 
 
 Chlorine derivatives of terpenes are likewise made by the addi- 
 tion of hydrochloric acid. Thus Deville (Ann. 71, 348), in 1843, 
 found that terpene unites with that acid to form the compound 
 C 10 H 18 C1 2 , and Wallach (Ann. 236, 9) has recently stated that 
 limonene in acetic acid solution unites with the same acid to form 
 the body, C 10 H 16 . 2HC1, which is deposited at once, and the same is 
 true of hydrobromic and hydriodic acids. 
 
 5. Action of Hydrochloric Acid on Alcohols. The general 
 action corresponds to the equation, CH 3 OH -j- HCl=CH 3 Cl-j-H 2 O, 
 and chloro-derivatives of the hydrocarbons are formed. 
 
 The hydrochloric acid may be prepared (Hofmann, Ber. 1, 272) 
 by filling a flask to the extent of one third with commercial hydro- 
 chloric acid, and allowing concentrated sulphuric acid (sp.gr. i'843) 
 to flow in from a funnel provided with a stop-cock. After some 
 preliminary irregularity, during which the possible passage of the 
 substance to be acted upon back into the flask must be guarded 
 against, the evolution of the gas becomes very regular and con- 
 tinues till the sulphuric acid has attained a density of 1*566 and 
 only 0*32 per cent, of hydrochloric acid remains behind. Another 
 method is to place large pieces of ammonium chloride in a flask and 
 drop concentrated sulphuric acid upon them from a funnel. Biltz 
 (Z. physik. Ch. 2, 965) contends that Kipp's apparatus gives better 
 results, but the use of salammoniac and sulphuric acid in this way 
 is dangerous because when the apparatus is shaken the hydro- 
 chloric acid gas dissolved by the acid is apt to be suddenly evolved, 
 and, by the pressure thus created, to project the acid through the 
 upper opening in the apparatus with considerable violence. 
 
1 86 CHLORO-DERIVATIVES [CH. xvi 
 
 The use of hydrochloric acid may be illustrated by Geuther's 
 method of preparing ethyl chloride (Z. Ch. 1871, 147). Hydro- 
 chloric acid is passed into alcohol, and the solution is then heated 
 slowly on the water bath, while the gaseous ethyl chloride is washed 
 in water at 20 and dried with chloride of calcium. The best yield 
 is obtained from alcohol diluted with two volumes of water and 
 nearly saturated with the gas. 
 
 The addition of water to alcohols is rendered necessary by the 
 fact that they are unable by themselves to dissolve sufficient hydro- 
 chloric acid. Thus Malbot (Bull. Ch. [3], 1, 604) found that al- 
 though in saturating amyl alcohol with hydrochloric acid the 
 volume increased from I litre to 17 litres, this amount did not 
 suffice for its conversion into amyl chloride. Half as much again, 
 by volume, of concentrated hydrochloric acid had to be added. By 
 heating this mixture at 120-130 pure amyl chloride, boiling at 97, 
 and free from the alcohol was obtained. If the temperature is 
 allowed to reach 150, by-products are formed. 
 
 To Groves (Ann. 174, 372) we owe the use of zinc chloride (cf. 
 Chap. XII. 36) in this reaction. He uses I part of fused zinc 
 chloride to 1*5-2 parts of the alcohol, and boils the mixture with a 
 reflux arrangement while hydrochloric acid is being led into it. 
 At first the gas is absorbed, but soon a stream of (e.g.} ethyl 
 chloride issues from the condenser at a speed corresponding to that 
 at which the acid is supplied. Kriiger (J. pr. Ch. 122, 195) like- 
 wise recommends the method, while Schorlemmer (Ber. 7, 1,792) 
 states that the only objection to it is that, when primary alcohols of 
 high molecular weight are treated, the zinc chloride causes water to 
 be split off, leaving unsaturated hydrocarbons of the ethylene series, 
 which, with hydrochloric acid, yield secondary chlorides. 
 
 The hydroxyl groups of bodies belonging to other classes may 
 also be replaced by chlorine in this way. Thus glycollic acid gives 
 monochloroacetic acid, and Werigo and Melikoff (Ber. 12, 178) 
 obtained a chlorolactic acid and dichloropropionic acid by heat- 
 ing glyceric acid, CH 2 OH . CHOH . COOH, for some time in a 
 sealed tube with hydrochloric acid saturated at o. 
 
 6. Halogen Compounds from Diazo-Bodies and Hydrazine 
 Derivatives. The action of haloid acids on the sulphates of 
 diazo-bodies whereby halogen derivatives are formed is a very 
 important one. 
 
 The sulphates are easily prepared from the nitrates by dissolving 
 
SEC. II, 7] REPLACING BROMINE AND IODINE 187 
 
 in a mixture of equal parts of sulphuric acid and water and adding 
 first alcohol and then ether to the solution. The sulphate soon 
 comes out in crystalline form. 
 
 The reaction in the case of the sulphate of diazobenzoic acid, for 
 example, takes place in accordance with the equation 
 
 OH , Hri r H /COOH, M ,TT on 
 
 : N SO 4 H + = C6H 4\C1 + N 2 + H 2 SO 4 . 
 
 Griess (Ber. 18, 960) recommends the use of 3-5 parts of haloid 
 acid for each part of the diazo-body. The reaction is completed by 
 boiling and the product crystallises out. In the above case it con- 
 sists of nearly pure chlorobenzoic acid. 
 
 The researches of Baeyer and of Zincke have shown that primary 
 aromatic hydrazines are easily converted into the corresponding 
 hydrocarbons by oxidation. And when the hydrochloric acid salts 
 are employed almost theoretical yields of the chloro-derivatives of 
 the same hydrocarbons are obtained. 
 
 The operation, according to Gattermann and Holzle (Ber. 25, 
 1,075) i g carried out as follows : A solution of cupric sulphate 
 (loogr.) in water (100 cc.) is heated to boiling in a flask of 1*5 
 litres capacity, provided with dropping funnel and a reflux condenser. 
 A hot solution of phenylhydrazine (10 gr.) in concentrated hydro- 
 chloric acid (25 cc.) and water (100 cc.) is run in. Nitrogen is 
 evolved with violence, metallic copper is deposited, and an oil 
 passes over with steam which, on rectification, yields chlorobenzene, 
 boiling at 132. The amount represents 86*4 per cent, of the 
 theoretical yield. 
 
 Wallach and Kolliker (Ber. 17, 396) state that when pure amidoazo- 
 benzene hydrochloride (10 parts) is boiled, with reflux arrangement, with 
 hydrochloric acid of sp. gr. 1*12 (100 parts) the compound is decomposed in 
 a few hours, and a current of steam carries over trichloroquinol. The yield 
 is poor however. 
 
 Losanitsch (Ber. 18, 39) describes a method of replacing amido-groups in 
 aromatic bodies by halogens, without an intermediate diazo-stage, by acting 
 with a mixture of the halogen acid and nitric acid. The results do not 
 seem however to commend the method strongly. 
 
 7. Replacement of Bromine and Iodine by Chlorine. By 
 
 shaking bromo- and iodo-derivatives with silver chloride they 
 exchange halogens, and bromide or iodide of silver is formed. Thus, 
 according to Conrad and Eckhardt (Ber. 22, 74), y-hydroxyquinal- 
 
1 88 CHLORO-DERIVATIVES [CH. xvi 
 
 dine methiodide yields the corresponding chloride in crystalline 
 form by digesting a warm solution of the former in water with the 
 necessary amount of freshly precipitated silver chloride and evapor- 
 ating the filtered liquid. 
 
 Gaseous chlorine has likewise the power of driving out other 
 halogens. Thus tetrachlorothiophene was made by Weitz (Ber. 17, 
 795) passing a rapid stream of chlorine through dibromothiophene 
 till the bromine was removed. During this operation the vessel 
 was cooled with ice. Then the resulting substance was boiled for 
 some time with alcoholic potash to decompose addition products. 
 Finally pure C 4 C1 4 S was obtained by fractionation. 
 
 When organic acids are in question it is best to use the silver 
 salts and to suspend them in ether (J. pr. Ch. 140, m), or chloro- 
 form, in order to obtain the chloro-acids. With the dry salts com- 
 plicated products result, as might be expected. Thus Krutwig 
 (Ber. 15, 1,340) states that silver acetate yields chloroacetyl chloride, 
 and according to Nef (Ber. 25, 842) the dry silver salt of chloranilic 
 acid gives tetrachlorotetraketohexamethylene. 
 
 Frequently chlorine, and the same remark applies to bromine 
 (cf. p. 169), acts only on salts of compounds and not on the com- 
 pounds themselves. Thus chloronitromethane, CH 2 NO 2 C1, can be 
 obtained only by the action of chlorine on sodio- or potassio-nitro- 
 methane (Ber. 8, 608). 
 
 8. Chlorine Carriers. While chlorine can only act by substitu- 
 tion on saturated fatty substances, in the aromatic series the action 
 takes the form of an addition, on account of the presence of the 
 double bonds. Thus benzene gives benzene hexachloride. The 
 difference can be recognised by the fact that during substitution 
 hydrochloric acid is necessarily evolved, while in the case of 
 addition no such evolution is observable. 
 
 Miiller (Z. Ch. 1862, 100) found, however, that when he tried to 
 make iodo-derivatives in the aromatic series by the use of iodine 
 chloride a violent action took place, and nothing but chloro-deriva- 
 tives were obtained. This led him to make the same experiment 
 with benzene, and he found that* as a matter of fact, when a little 
 iodine was added and chlorine was passed into the liquid, a regular 
 evolution of hydrochloric acid gas occurred. This action takes 
 place in consequence of the formation of iodine chloride, which leads 
 to the formation of hydriodic acid according to the equation 
 
 C 6 H 6 +IC1 = C 6 H 6 C1 + HI. 
 
SEC. ii, 8] CHLORINE CARRIERS 189 
 
 The chlorine acts on this further, reproducing iodine chloride 
 HI + C1 = HC1 + ICL 
 
 The only disadvantage attending the use of iodine as a chlorine 
 carrier is the fact that small quantities of iodo-derivatives are 
 formed. 
 
 Even earlier than this the chlorinating power of antimony 
 trichloride had been noticed by Wohler, and Hofmann (Ann. 115, 
 266) had made carbon tetrachloride by adding it to chloroform and 
 passing in chlorine. It seems not to have been applied to aromatic 
 compounds at that time. 
 
 Molybdenum pentacJiloride was found by Lothar Meyer (Ber. 8, 
 1,400), when he tried to recrystallise it from benzene, to attack the 
 latter with evolution of hydrochloric acid. He suggested therefore 
 that it might be used instead of iodine as a chlorine carrier. 
 
 Aronheim's experiments confirmed this supposition. Benzene, 
 containing about one per cent, of molybdenum pentachloride, was 
 found to absorb chlorine with such avidity that hardly a trace of it 
 could be discovered mixed with the hydrochloric acid gas which 
 poured off in torrents. Carbon disulphide (Ber. 9, 1,788) is likewise 
 powerfully attacked by chlorine in presence of this agent. 
 
 The difficulty in preparing the molybdenum pentachloride (Ann. 
 169, 344) led to a search for other metallic chlorides which should 
 have the same effect. Page's researches (Ann. 225, 199) showed 
 that molybdenum trichloride, ferric chloride, aluminium trichloride, 
 thallous chloride (T1C1) and thallic chloride (T1C1 3 ), were also 
 serviceable as chlorine carriers. 
 
 Ferric chloride and the chlorides of thallium are specially valuable. 
 In their presence the chlorination advances rapidly and with regu- 
 larity. The advantage lies on the whole with the latter, as they are 
 easy to separate from the products of the action, while ferric chloride 
 produces by-products which often leave appreciable residues. 
 
 For example, to nitrobenzene (75 gr.), which is not attacked by 
 chlorine, dry ferric chloride (9'$6 gr.) was added, and a slow stream 
 of chlorine was passed into the mixture at 100. The weight in- 
 creased by 82*57 gr., and tetrachloronitrobenzene was found to be 
 the chief product. At a higher temperature, hexachlorobenzene was 
 formed. It was washed with water and recrystallised from carbon 
 disulphide. 
 
 In general only two per cent, of ferric chloride requires to be 
 added. 
 
190 CHLORO-DERIVATIVES [CH. xvi 
 
 Antimony trichloride was used by Beilstein and Kurbatow (Ann. 
 182, 102) as follows : For example, nitrobenzene (20 gr.) was 
 warmed with the trichloride (40 gr.), and a rapid stream of chlorine 
 was passed through the mixture. When the flask and material had 
 gained 68 grams in weight, the contents were washed successively 
 with hydrochloric acid, water, caustic soda, and water again. The 
 result was distilled, and the fraction boiling between 230 and 245 
 was cooled strongly. Crystals of w-chloronitrobenzene were de- 
 posited. 
 
 The following process is used on a large scale (Ger. Pat. 32, 564) : 
 Phthalic anhydride (5 parts) and antimony pentachloride (30 parts) 
 are heated for several hours at 200. The heating is then continued 
 for eight to twelve hours, during which a current of chlorine gas is 
 conducted into the fused mass. By this means almost the whole of 
 the anhydride is converted into the tetrachloro-derivative. The 
 antimony pentachloride, which may contain some of the trichloride, 
 is first distilled off and preserved for use in other similar operations. 
 Then, on further heating, the tetrachlorophthalic anhydride comes 
 over. 
 
 The metals in the form of powder may be used instead of their 
 chlorides, the transformation into the latter being effected by the 
 chlorine itself. 
 
 Willgerodt (J. pr. Ch. 143, 391) finds that the halogen carrying 
 power of the elements is a function of their atomic weights. 
 
 Willgerodt and Salzman (J. pr. Ch. 147, 465) chlorinated/-bromo- 
 toluene in presence of metallic iroji. Soon after the action starts, 
 a considerable elevation of temperature takes place, under whose 
 influence the substance melts. A little later artificial cooling has 
 to be resorted to. As soon as the proper increase in weight shows that 
 the operation is completed, the product, which is brown in colour 
 from the presence of iron compounds, is shaken with caustic soda 
 and with water. On fractionating the dried and now colourless 
 liquid, the greater part passes over between 210 and 220. It is 
 a mixture of the two theoretically possible monochloro-^-bromo- 
 toluenes. 
 
 Petricou (Bull. Ch. [3], 3, 189) added granulated tin (90 gr.) to 
 benzene (400 cc.), and passed a current of chlorine through the 
 liquid while it was boiling with reflux arrangement. In thirty-six 
 hours, dichlorobenzene was formed, and in eighty-six hours, tetra- 
 chlorobenzene. In this case, however, the ease with which the 
 chloride of the metal could be removed from the product would 
 
SEC. ii, 9] PHOSPHORUS PENTACHLORIDE 191 
 
 scarcely compensate for the excessive amount of time consumed by 
 the process. 
 
 9. Phosphorus Pentachloride. This is an agent in very general 
 use for replacing hydroxyl groups by chlorine. It was used by 
 Dumas and Peligot (1836) for the production of cetyl chloride from 
 cetyl alcohol, and ten years later Cahours (C. R. 22, 846, and 25, 
 724) examined thoroughly both the substance itself and its action 
 on cinnamic acid, benzaldehyde, and other bodies. It is used par- 
 ticularly for the conversion of acids into acid chlorides. In the 
 case of succinic acid, for example, the following action takes place : 
 
 CH 2 -COOH CH 2 -CO.C1 
 
 | +2PC1 5 = | +2POCU + 2HC1. 
 
 CH 2 -COOH CH 2 -CO.C1 
 
 If acid anhydrides are used, only half as much of the pentachloride 
 is necessary 
 
 CH 2 -CO V CH 2 -CO.C1 
 
 | >0 + PC1 6 = | +POC1 3 , 
 
 CH 2 -CCK CH 2 -CO.C1 
 
 Instead of the acids, the salts of the alkali metals maybe taken, 
 a method which is valuable where the free acids can only be 
 obtained perfectly dry with difficulty 
 
 C G H 5 . COONa + PCl 6 = C 6 H 5 . CO . Cl + POCl 3 + NaCl. 
 
 The operation is always carried out in practice by adding phos- 
 phorus pentachloride gradually to the dry acid. If the action is 
 very violent, the vessel may be cooled during the action, and the 
 acid and chloride may be cooled before mixing. The vessels used are 
 flasks or retorts in connection with reflux condensers. The fol- 
 lowing will serve as illustrations. 
 
 The action on hydroxyazo-compounds was found by Paganini 
 (Ber. 24, 365) to be characteristic. By heating equi-molecular quan- 
 tities of ^-tolueneazophenol and pentachloride of phosphorus on the 
 water bath for two hours, an orange-red mass was obtained, which 
 was freed from excess of the chloride by treatment with water. 
 Alcohol extracted from the product ^-tolueneazochlorobenzene, 
 CH 3 . C 6 H 4 . N 2 . C G H 4 C1, and the residue, recrystallised from acetone, 
 yielded /-tolueneazophenyl phosphate, (CH 3 C 6 H 4 N 2 C 6 H 4 O) 3 PO. 
 
 By way of dilution to restrain the action of the pentachloride, it 
 may be mixed with five times its weight of phosphorus oxychloride. 
 
192 CHLORO-DERIVATIVES [CH. xvi 
 
 Benzene, chloroform, or petroleum ether may be used for the same 
 purpose. For example, Baeyer (Ber. 12, 456) heated isatin (5 gr.) 
 with phosphorus pentachloride (7 gr.) in dry benzene (8 - 10 gr.) in 
 a flask, connected with a reflux condenser. When the violence of 
 the action had abated, the mass solidified to a cake of brown 
 crystals of isatin chloride, C 8 H 4 C1NO. The yield was 4 grams in 
 place of the theoretical 5*5 grams. 
 
 Geigy and Konigs (Ber. 18, 2,402) dissolved 0-nitrobenzyl alcohol 
 just as in making the chlorides of cinchona alkaloids, in dry chloro- 
 form (10 parts), cooled the solution, added the calculated amount of 
 pentachloride, and afterwards decomposed the resulting oxychloride 
 with water. On separating the chloroform layer and distilling off 
 the solvent, <?-nitrobenzyl chloride remained. 
 
 A modification of this method is recorded by Berkenheim (Ber. 
 25, 686), who covered an amount of the pentachloride, slightly in 
 excess of that necessary, with petroleum ether, and added menthol 
 (100 gr.) in small portions to the carefully cooled mixture. He 
 waited after each addition until the evolution of hydrochloric acid 
 gas had ceased. The petroleum ether was removed and the pro- 
 duct distilled, when 15 gr. of a fraction boiling at 167-169 and 
 70 gr. of another boiling at 209-210 were obtained. The former 
 was menthene, C 10 H 18 , and the second, menthyl chloride, C 10 H 19 C1. 
 The first had arisen as the result of the abstraction of water from 
 the menthol, C 10 H 19 OH. 
 
 Wallach (Ann. 263, H8) dissolved fenchyl alcohol (45 gr. ) in petroleum 
 ether of low boiling-point (80 gr.), and added slowly to the solution 
 phosphorus pentachloride (60 gr. ). A violent action took place, at the 
 conclusion of which the liquid was poured off from a small quantity of 
 unchanged pentachloride, and the petroleum ether and oxychloride were 
 distilled off in vacua by heating on the water bath. The fenchyl chloride, 
 being liquid, could not be purified by recrystallisation, and was therefore 
 driven over with steam to free it completely from phosphorus compounds. 
 Perfect purity was finally attained by fractionation in vacua. 
 
 Pechmann (Ann. 264 282) moistened crude cumalinic acid (14 gr.) with 
 phosphorus oxychloride in a fractionating flask connected hermetically 
 with a receiver, and added phosphorus pentachloride (22 gr. ) in small 
 portions, assisting the action meanwhile by heating on a water bath. When 
 the change was complete the oxychloride was distilled off on an oil bath, 
 and the residue distilled under a pressure of 80 mm. It all passed over at 
 about 1 80. He did not succeed however in freeing the chloride entirely 
 from phosphorus. 
 
SEC. ii, 9] PHOSPHORUS PENTACHLORIDE 193 
 
 The separation of the products of actions like the above, chiefly 
 acid chloride and phosphorus oxychloride, is sometimes attended 
 with difficulty. 
 
 If excess of pentachloride has been used a little phosphorus is 
 added so as to form the trichloride, which is a liquid boiling at 74 
 and is easily distilled off. 
 
 When the acid chloride is volatile without decomposition, it may 
 be separated from the oxychloride by fractional distillation either 
 under atmospheric pressure, or if necessary under diminished 
 pressure. 
 
 It is stated by Krafft and Burger (Ber. 17, i,3?8) that the higher 
 homologues of acetic acid, when mixed with pentachloride in 
 molecular proportions, warmed on the water bath, and finally 
 heated to 1 50 under 1 5 mm. pressure to remove the oxychloride, 
 give as residue the exact theoretical amounts of the chlorides, 
 C n H 2n -iOCl. They prepared thus chemically pure lauryl chloride, 
 C 12 H 23 OC1., myristyl chloride, C 14 H 2 7OC1., and other members 
 of the series. 
 
 Grabe and Bungener (Ber. 12, 1,079) found that in preparing the 
 chloride of phenylacetic acid, although the action seemed to proceed 
 normally, a yield of only 10 per cent, was obtained on distilling. When 
 they repeated the operation by heating equimolecular parts of the sub- 
 stances, instead of distilling the product they heated it to 100-120, and 
 passed through it a stream of dry carbonic acid until nothing further passed 
 over. The almost colourless residue in the retort consisted of the chloride 
 in relatively large quantity and almost pure. 
 
 A residue obtained in this way is apt to contain some acid anhydride 
 formed according to the equation 
 
 C 2 H 4 (COOH) 2 + PC1 5 = C 2 H O + 2HC1 + POC1 
 
 It may be dissolved out with a little absolute ether. 
 
 The separation may be effected in quite another way by adding dry 
 petroleum ether to the mixture, as long as the cloudiness increases, and 
 shaking. The petroleum ether mixes easily with the oxychloride (Ber. 8, 
 301), while the acid chloride settles to the bottom when the mixture is left 
 at rest. 
 
 Sulphonic Acids are converted into their respective chlorides by 
 means of phosphorus pentachloride, in accordance with the 
 equation 
 
 C 6 H 5 . SO 3 H + PC1 5 = C G H 5 . SO 2 C1 + POC1 3 + HC1. 
 
194 CHLORO-DERIVATIVES [CH. xvi 
 
 The chlorination is carried out just as in the case of carboxyl 
 acids, only here exceptional actions occasionally occur. Thus 
 Claus and Knyrim (Ber. 18, 2926) failed to obtain the chloride of 
 a-naphthol-/3-sulphonic acid by using the pentachloride with the 
 sodium salt of the acid in equimolecular proportions. Part of the acid 
 always remained unchanged and part was converted into dichloro- 
 naphthol. Similar irregularity is shown by /3-naphthol-0-sulphonic 
 acid (Ber. 18, 3,157). On the other hand, Zielstorff (Dissert. 
 Greifswald, 1890) prepared the chloride of diphenyldisulphonic 
 acid by drying its potassium salt at 180, and warming it with two 
 molecules of pentachloride. After washing the product with water 
 until it was neutral, it was purified by recrystallisation from 
 chloroform. 
 
 Such chlorides can also be recrystallised from ether, benzene, acetic acid, 
 carbon disulphide (Ber. 24 654*-), and other solvents. Thus Jakel (Ber. 
 19, 189) obtained thiophenedisulphonic chloride, C 4 SH 2 (SO 2 C1) 2 , from 
 ether in needles. 
 
 The sulphonic chlorides are distinguished from the ordinary acid chlorides 
 by the fact that they are often very stable towards water, and prolonged 
 boiling with this, or even with dilute alkalis, may be necessary to convert 
 them into the corresponding acids. 
 
 Barbaglia and Kekule (Ber. 5, 876) state that sulphonic chlorides are 
 decomposed by phosphorus pentachloride at 200, in accordance with the 
 equation 
 
 C 6 H 5 . SO 2 C1 + PC1 5 = C 6 H 5 C1 + SOC1 2 + POC1 3 . 
 
 The formation of these products has been explained by Michaelis (Ber. 5, 
 929) in a different manner. 
 
 Using this action, Konigs and Geigy (Ber. 17, 1,832) obtained some, till 
 then unknown, chlorinated derivatives. Thus they heated the barium salt 
 of pyridinesulphonic acid with pentachloride to 200, poured the product 
 into ice-cold water, and, after the chlorine compounds of phosphorus had 
 been decomposed, distilled the product in a current of steam. From the 
 distillate a dichloropyridine and a trichloropyridine were isolated. 
 
 Erdmann (Ber. 20, S^S) used the same process with naphthylamine- 
 sulphonic acid. 
 
 In aldehydes and ketones, phosphorus pentachloride replaces 
 the carbonyl oxygen by C1 2 , thus : 
 
 CH 3 . CHO + PC1 5 -CH 3 . CHC1 2 + POC1 3 . 
 
 It acts energetically on acid cyanides. Thus Claisen (Ber. 12, 
 626) states that with benzoyl cyanide it gives a yellow liquid, which, 
 
SEC. ii, 10] ACETYL CHLORIDE 195 
 
 on being poured onto ice, leaves a heavy oil. When this is washed 
 with caustic potash to remove any remaining cyanide and rectified, 
 it consists of pure phenyldichloroacetonitrile 
 
 C G H 5 .CO.CN + PC1 5 = C 6 H 5 .CC1 2 . 
 
 With the ester of phenylglyoxylic acid it forms phenyldichloro- 
 acetic ether which can be purified by fractionation 
 
 C C H 5 . CO . COOC 2 H, + PC1 5 = C 6 H 5 . CC1 2 COOC 2 H 5 + POC1 3 . 
 
 Wallach (Ber. 8, 301) announced the fact that when an acid 
 amide contains more than one carbonyl group, the oxygen attached 
 to the same carbon atom with the amido-group is first attacked. 
 Thus the ethyl ester of oxamic acid gives dichloroamidoacetic 
 ether 
 
 COOC 2 H 5 COOC 2 H 5 
 
 | +PC1 5 = | +POC1 3 . 
 
 CO.NH 2 CC1 2 .NH 2 
 
 From 50 grams of oxamic ether, 50 grams of the chloro-product 
 were finally obtained by precipitation with petroleum ether. 
 
 This reaction was of some importance in connection with the 
 synthesis of indigo. When the attempt was made to reduce isatin, 
 
 C 6 H 4 <^ j^ , (pseudoisatin), only the carbonyl group next 
 
 to the benzene ring is attacked. But Baeyer (Ber. 11, 1,296), by 
 first treating it with phosphorus pentachloride and then reducing, 
 succeeded in removing the oxygen from the other carbon atom 
 also. The lactime chloride was probably formed as an intermediate 
 
 product, C 6 
 
 Homologues of benzene can be chlorinated by means of the 
 pentachloride. According to Colson and Gautier (C. R. 102, 
 690), the substances are placed in sealed tubes and heated at 200. 
 They prepared hexachloroxylene, C 6 H 4 (CC1 3 ) 2 , for example, in this 
 manner. The chlorine does not appear in the ring until the 
 hydrogen atoms of the side chains have been fully replaced. 
 
 10, Acetyl Chloride. In view of the fact that acetyl chloride is 
 frequently employed for introducing an acetyl group, it may be 
 worth mentioning that its use seems sometimes to lead to chlorina- 
 tion. At all events Becker (Ber. 20, 2,007) states that, on heating 
 acetyl chloride and azobenzene in a sealed tube at 160 for four 
 
 O 2 
 
I 9 6 CHLORO-DERIVATIVES [CH. xvi 
 
 hours, he obtained chiefly /-chloroacetanilid and /-dichloroazo- 
 benzene. 
 
 Bredt (Ann. 256, 334) found that when levulinic acid was mixed 
 with acetyl chloride (2 mol.) a violent action ensued which had to 
 be restrained by external cooling. After the excess of acetyl 
 chloride and the acetic acid had been removed by distillation in 
 vacua, the residue was found to consist of levulinic chloride, which 
 passed over at 80 under a pressure of 1 5 mm. 
 
 11, Antimony Pentachloride. This substance, which has 
 already been noticed as a chlorine carrier, is used also for direct 
 chlorination. Thus Beilstein (Ann. 179, 284) heated ^-chloro- 
 benzoic acid (i part) with antimony pentachloride (7*5 parts) at 
 200 for several hours. Dichlorobenzoic acid was obtained from 
 the product by first removing the antimony with concentrated 
 hydrochloric acid, then dissolving the residue in ammonia, evaporat- 
 ing to dryness, and finally re-acidifying. 
 
 Merz and Weith (Ber. 16, 2,870) used the pentachloride for 
 perchlorination ; that is to say, for the addition of chlorine until all 
 the double bonds of the substance had been converted into single 
 ones. The material under investigation was usually treated with a 
 large excess of the antimony compound in a sealed tube at 350, 
 and the heating continued till no further production of hydrochloric 
 acid could be noticed. If the action of the chloride was too violent 
 at first, a preliminary treatment with chlorine gas preceded the 
 enclosure in the tube. Phenanthrenequinone gave perchloro- 
 diphenyl, C 12 C1 10 , dibenzyl gave perchlorobenzene and perchloro- 
 ethane, and /3-naphthonitrile gave perchlorobenzene. 
 
 Following the same line of work, Hartmann (Ber. 24, i>O25) has shown 
 that many substances of the fatty series, such as hydrocarbons, palmitic acid, 
 and wax, on being treated with antimony pentachloride at 300-450 in 
 presence of a little iodine, are converted into perchloromethane and perchloro- 
 benzene. These substances may, in fact, be regarded as the ultimate com- 
 bustion products, so to speak, of aliphatic derivatives in respect to chlorine. 
 
 Henry states (C. R. 97, i>49i) that antimony pentachloride can likewise 
 be used for exchanging bromine for chlorine. Thus by heating chloro- 
 ethylene bromide, CH 2 Br - CHClBr, with it, bromoethylidene chloride is 
 produced, and in like manner (Ann. Ch. Ph. 30 271) dibromomethane gives 
 dichloromethane. 
 
 12. Bleaching Powder and Hypochlorous Acid. Bleaching 
 
 powder is used both alone and in presence of acids as a chlorinat- 
 ing agent. For example, Beilstein (Ann. 179, 286) found that when 
 
SEC. ii, 12] BLEACHING POWDER 19? 
 
 0-chlorobenzoic acid was gently boiled with bleaching powder solu- 
 tion, dichlorobenzoic acid was easily formed, although it was difficult 
 to avoid the simultaneous formation of the trichloro-derivative. 
 
 Witt gives the following method of preparing chlorine derivatives 
 of aniline : Acetanilide (5 parts) is dissolved in a warm mixture of 
 glacial acetic acid (10 parts) and alcohol (10 parts) ; the mixture is 
 diluted with water (100 parts), and, the solution having been 
 brought to 50, a bleaching powder solution (100 parts), containing 
 10 per cent, of calcium hypochlorite, is added slowly during con- 
 tinuous agitation. A snow-white precipitate, consisting of minute 
 needles of monochloroacetanilide soon appears. It is purified by 
 recrystallising from warm acetic acid or alcohol (cf. Bender, Ber. 
 19, 2,272). 
 
 By altering the conditions slightly a different result is obtained. 
 The acetanilide (5 parts) is dissolved in a boiling mixture of acetic 
 acid (20 parts) and water (100 parts), and, the flame having been 
 removed, bleaching powder solution of the above concentration 
 (400 parts) is slowly added. The first 100 parts produce a pre- 
 cipitate which, after 200 parts have been added, is transformed into 
 the much more compactly crystalline dichloroacetanilide. If the 
 solution is once more warmed, in case its temperature has fallen 
 below 60-70, and the remainder of the bleaching powder added a 
 little at a time and with constant agitation, a heavy oil sinks to 
 the bottom of the vessel. It consists of an addition product of 
 hypochlorous acid and dichloroacetanilide. If the oil is taken up 
 with ether and the extract dried with calcium chloride, it deposits on 
 standing beautiful crystals of the dichloroacetanilide as the result 
 of gradual decomposition. This substance may be obtained more 
 readily by interrupting the addition of bleaching powder as soon as 
 the mass has become yellow and acquired a pulpy consistency. 
 
 Tscherniak (Ber. 9, 146) added ethylamine hydrochloride (25 gr.) to 
 bleaching powder (250 gr.) which had been mixed with water so as to form 
 a paste in a large flask, and distilled the mixture as long as drops of oil 
 passed -over. The distillate was then treated once more in the same manner 
 with an equal amount of bleaching powder and redistilled. The second 
 distillate was treated successively with sulphuric acid, caustic soda, and 
 water, and was finally dried and fractionated. A good yield of a di- 
 chloroethylamine was obtained, to which he ascribed the constitution 
 CH 3 .CH 2 . NC1 2 (?). 
 
 Chandelon (Ber. 16, 1,749) states that alkaline hypochlorites act 
 on phenols in dilute (3 per cent.) solutions at the ordinary tem- 
 
198 CHLORO-DERIVATIVES [CH. xvi 
 
 perature, and that by using the calculated amounts of the material 
 the operation may be carried as far as the production of trichloro- 
 derivatives. Thus when a mixture containing phenol and sodium 
 hypochlorite (made from bleaching powder and soda) is neutralised 
 with hydrochloric acid, 0-chlorophenol separates out as an oil. 
 The yield is considerable. 
 
 It is thus evident that bleaching powder is a valuable chlorinating 
 agent, although it is usually hard to predict what its exact action 
 will be in any given case. Liebig (Ann. 1, 199) observed that it 
 converted alcohol and acetone into chloroform. Then Belohoubek 
 (Ann. 165, 350) showed that while this statement was true for 
 ethyl alcohol, it did not hold for methyl alcohol. Finally Goldberg 
 (J. pr. Ch. 132, 114) made an exhaustive examination of the action 
 of bleaching powder on various alcohols, and proved that chlorine 
 never entered the carbinol group ; that, in fact, this part of the mole- 
 cule was always oxidised to formic acid or carbonic acid. Accord- 
 ing to Goldberg the following equation best represents the amount 
 of chloroform obtained when working on a manufacturing scale, 
 the actual result being uniformly less favourable however : 
 
 Chlorination can be accomplished with bleaching powder m 
 presence of nascent hydrochloric acid, but the employment of 
 potassium chlorate is usually to be preferred. 
 
 The action of hypochlorous acid on organic bodies can be best 
 studied in connection with that of bleaching powder. 
 
 Now that its power in breaking ring structures (cf. e.g. Ber. 25, 
 1,493) h as come to be recognised, it must be regarded as a valuable 
 reagent for such purposes. 
 
 It may be well first to describe the best ways of preparing hypochlorous 
 acid. Reformatzky (J. pr. Ch. 148, 396) gives the following method : The 
 chlorine is evolved from a mixture of hydrochloric acid and potassium 
 bichromate contained in a flask of \\ litres capacity. The gas, after being 
 washed by passing through water contained in a three-necked bottle, is led 
 nto a flask of about 500 cc. capacity, containing mercuric oxide covered with 
 five times its volume of water. This flask stands in water cooled with ice, 
 and is provided with a doubly bored stopper. The tube leading the chlorine 
 passes through one hole and reaches almost to the bottom of the flask, 
 while from the other projects a second tube which conducts any escaping 
 gases into the chimney of the hood. Towards the conclusion of the action, 
 which is marked by the disappearance of the oxide of mercury, the flask is 
 
SEC. ii, 13] SANDMEYER'S REACTION 199 
 
 agitated periodically. The solution of hypochlorous acid and mercuric 
 chloride in water which remains is now distilled to separate the former from 
 the latter, and the receiver is connected with the chimney of the hood as 
 before. Large quantities of hypochlorous acid are easily prepared in this way. 
 As a part of the acid is decomposed, yielding free chlorine during the dis- 
 tillation, and this may have a disturbing effect in some actions, producing, 
 for example, by-products where addition to unsaturated bodies is in 
 question, it is advisable to remove it by passing a stream of carbon dioxide 
 through the solution until all odour of chlorine is removed. 
 
 Another method is the well-known one of adding a sufficient amount of 
 boric acid to a bleaching powder solution. This gives a preparation, how- 
 ever, containing a large quantity of foreign material. 
 
 The use of hypochlorous acid may be illustrated by an experi- 
 ment of Reformatzky's (J. pr. Ch. 148, 400). He placed allyldi- 
 methylcarbinol (20 gr.) in a large flask with some ice-cold water, 
 and added a solution of hypochlorous acid, free from chlorine, in 
 small portions until the odour of the acid became permanent. The 
 slight excess was then destroyed by means of sodium thiosulphate. 
 On extracting the filtrate with ether and evaporating, 23 grams of 
 the monochlorhydrin of glycerol remained, while a yield of 30 
 grams was theoretically possible. 
 
 Schlebusch (Ann. 141, 323) mixed equivalent quantities of 
 sodium valerate and hypochlorous acid in water solution. After 
 standing for several days in the dark, the solution deposited mono- 
 chlorovaleric acid along with unchanged valeric acid 
 
 C 5 H 10 O 2 + HC1O = C 5 H 9 C1O 2 + H 2 O. 
 
 Carius (Ann. 140, 317) found that hypochlorous acid was capable 
 of adding itself to all unsaturated organic bodies, one molecule of 
 HC1O being taken up for every H 2 that was lacking to complete 
 saturation. 
 
 Schiitzenberger (C. R. 52 135) ' 1S responsible for the discovery that, 
 when anhydrous hypochlorous acid acts on acetic anhydride at a low 
 temperature, a liquid of the same composition as monochloroacetic acid, 
 but differing widely from it in properties, is formed. He named it chlorine 
 acetate. 
 
 13, Cuprous Chloride, Sandmeyer's and Gattermann's 
 
 Reactions. The use of cuprous chloride for the replacement of 
 the amido-group in aromatic compounds by chlorine was intro- 
 duced by Sandmeyer (Ber. 17, 1,633). He discovered that large 
 
200 CHLORO-DERIVATIVES [CH. xvi 
 
 quantities of chlorobenzene were formed by the action of cupro- 
 acetylene on diazobenzene chloride, and attributed this to the 
 influence of cuprous chloride formed during the action. Further 
 experiments showed that this view was correct. 
 
 The preparation of chlorobenzene, according to his method, is as 
 follows : Aniline (30 gr.) is dissolved in hydrochloric acid of sp. 
 gr. 1*17 (67 gr.) diluted with water (200 cc.). To the cooled 
 solution sodium nitrite (23 gr.) dissolved in water (60 cc.) is 
 gradually added. This mixture is now allowed to flow, drop by 
 drop, through a funnel provided with a stop-cock, to a 10 per cent, 
 solution of cuprous chloride in hydrochloric acid which has been 
 previously heated almost to boiling. Each drop of the diazo- 
 benzene solution produces a yellow precipitate, which however 
 immediately disappears with evolution of nitrogen and deposition 
 of an oil. Subsequent distillation in a current of steam yields about 
 26 grams of chlorobenzene. 
 
 According to Feitler (Z. physik. Ch. 4, 68), the cuprous chloride 
 solution for Sandmeyer's reaction is best prepared thus : Crystal- 
 line sulphate of copper (250 parts), sodium chloride (120 parts), 
 and water (500 parts) are heated to boiling, and concentrated 
 hydrochloric acid (1,000 parts) and copper turnings (130 parts) are 
 added. The mixture is. heated in a loosely-stoppered flask till it 
 loses its colour. The solution is now decanted, leaving undissolved 
 copper and some sediment behind, into a tared bottle previously 
 filled with carbon dioxide. The weight is now made up to 2,036 
 parts by the addition of concentrated hydrochloric acid, and a 
 solution containing about 10 per cent, of cuprous chloride is the 
 result. This solution can be preserved for a long time unchanged 
 in a carefully-stoppered bottle when the air has been displaced by 
 carbon dioxide. 
 
 Gattermann found somewhat later (Ber. 23, 1,218), in attempting 
 to prepare diphenyl by condensation from diazobenzene chloride 
 (2 mol.) by the action of various metals, that copper in a finely- 
 divided condition produced a specially violent action even at o, 
 but instead of diphenyl, chlorobenzene was the chief product. And, 
 continuing the investigation, he found that the amido-group in 
 aniline and its homologues could be replaced in like manner by 
 Br and CN, and even by the nitro-group and the radical of 
 sulphocyanic acid. 
 
 This method reminds one at once of the Sandmeyer reaction, 
 but possesses certain advantages over the latter. Thus, since it 
 
SEC. ii, 13] SANDMEYER'S REACTION 201 
 
 uses cold solutions, the heating of large quantities of liquids is 
 avoided. The yields are also frequently better, and while Sand- 
 meyer's method demands the preparation of the cuprous salt of 
 the acid whose radical is to be introduced, Gattermann's reaction 
 dispenses with this preliminary. 
 
 The finely-divided copper used in decomposing the diazo-bodies 
 is prepared by the action of zinc dust on cupric sulphate. A cold 
 saturated solution of the latter is placed in a porcelain dish, and 
 the zinc dust is shaken into it through a fine sieve while the liquid 
 is thoroughly stirred, these precautions being taken to prevent the 
 formation of lumps. The addition ceases when the liquid retains 
 only a trace of blue colour. By this time the temperature will 
 have risen to about 80. The copper, in the state of fine powder, 
 settles to the bottom of the vessel in a dark, red-coloured layer. 
 It is washed as well as possible with water, and then, to remove 
 traces of zinc, is covered with water and stirred up, while dilute 
 hydrochloric acid is added as long as effervescence is observable. 
 The liquid is again decanted and the precipitate washed on a 
 filter till the washings are neutral. As it is easily oxidised, even 
 in a nearly dry condition, it is best preserved in the form of a 
 paste in closely-stoppered bottles. 
 
 As an example of the use of Gattermann's method, the prepara- 
 tion of chlorobenzene may be given. Aniline (31 gr. = ^ mol.) 
 is dissolved in 40 per cent, hydrochloric acid (300 gr.) and water 
 (i5occ.). Solution will not be complete; but without regard to 
 this the mixture is cooled by throwing in pieces of ice, and 
 diazotised by adding not too slowly a concentrated solution of 
 sodium nitrite (23 gr.). The moist copper paste (40 gr.) is next 
 added, and the evolution of nitrogen begins immediately. The 
 action lasts about half an hour, and its completion is marked by 
 the fact that the copper, at first carried to the surface by the 
 liberated gas, finally settles to the bottom with the chlorobenzene. 
 The greater part of the water is poured off and the chlorobenzene 
 driven over in a current of steam. The yield is about the same 
 as that obtained by the other process. The use of smaller quantities 
 of hydrochloric acid or copper affects it unfavourably. 
 
 The yield of 0-chlorotoluene from 0-toluidine is 66*3 per cent, 
 against 31-5 per cent, by Sandmeyer's method. The yields of 
 /3-chloronaphthalene from /3-naphthylamine and /-chloronitro- 
 benzene from ^-nitraniline are 30 per cent, and 70 per cent, of 
 the theoretical respectively. 
 
202 CHLORO-DERIVATIVES [CH. xvi 
 
 Angeli (Ber. 24 952^) used solutions of sulphate of copper, to which he 
 added the necessary amounts of the halogen acids and of sodium hypophos- 
 phite instead of employing metallic copper or Sandmeyer's solutions. He 
 found that the preparation of chlorine, bromine, iodine, and nitro-derivatives 
 from aniline was very satisfactory when conducted in this manner. 
 
 14. Mercuric Chloride, When a solution of mercuric chloride 
 in water or ether is heated with ethyl iodide in a sealed tube at 
 100, ethyl chloride is formed (Schlagdenhauffen, Jahresb. 1856, 
 576). According to Oppenheim (Ann. 141, 207), this action holds 
 generally for alkyl iodides. 
 
 15. Phosphorus Oxychloride. This reagent, which occurs as 
 a by-product in preparing acid chlorides with phosphorus penta- 
 chloride, and can be prepared (Odling, " Manual of Chemistry/' 
 1, 287) by direct union of phosphorus trichloride at its boiling- 
 point with oxygen, may be used for the preparation of chloro- 
 derivatives from alcohols 
 
 Although it has no action on free acids, Chiozza (C. R. 36, 655) 
 has found that it does react with their sodium salts. Geuther 
 (Ann. 123, 114) finds that sodium metaphosphate is formed as 
 a result of the action 
 
 2CH 
 
 The operation is carried out by adding the oxychloride to the 
 finely-powdered sodium salt in a flask connected with a return 
 condenser. After the chemical action has begun, the mixture is 
 heated for a short time in a water bath. 
 
 Quite recently Gabriel (Ber. 19, 1,655) nas use ^ the oxychloride 
 for removing the oxygen from homo-0-phthalimide, which contains 
 the arrangement of carbon and nitrogen atoms peculiar to iso- 
 quinoline. By heating the imide (8 gr.) in a sealed tube with 
 phosphorus oxychloride (24 gr.) for three hours at 150-170, it was 
 converted into dichloroisoquinoline 
 
 /CH 2 -CO /CH=CC1 
 
 C 6 H/ | ->C 6 H/ | 
 
 \CO-NH \CC1=N 
 
 which separated out in crystalline form when the contents of the 
 tube were poured into five times their volume of alcohol (Ber. 
 19, 2,355). 
 
SEC. ii, 1 6, 17] THE CHLORIDES OF SULPHUR 203 
 
 Ruhemann (Ber. 24, 3,975) heated iso-/-xylalphthalimidine with twice its 
 weight of phosphorus oxychloride for half an hour in the water bath. On 
 adding alcohol the excess of oxychloride was decomposed, and a crystalline 
 substance began to appear, which increased in quantity on the addition of 
 water. The resulting product was a-chloro--/-tolylisoquinoline 
 
 CH = C . C 7 H 7 /CH = C . C 7 H 7 
 
 / 
 
 C 6 H 4 < | -> C 6 H 
 
 \CO-NH 
 
 \CC1 
 
 16. Phosphorus Trichloride. This reagent is used like the 
 last for the conversion of alcohols into chloro-derivatives. It like- 
 wise converts acid into acid chlorides 
 
 a reaction first noticed by Bechamp (C. R. 42, 224). Its action 
 is less violent than that of the pentachloride ; but the non-volatile 
 phosphorus acid, arising as a by-product in place of the volatile 
 oxychloride, is sometimes hard to separate from acid chlorides 
 which cannot be distilled without more or less decomposition. On 
 the other hand, three molecules of acid chloride are obtained with 
 one of the trichloride, while the pentachloride yields but one. 
 
 17. The Chlorides of Sulphur. Heintz, and later Carius, 
 (Ann. 122, 73) recommended the use of the monoMoride, S 2 C1 2 , for 
 the preparation of dichlorhydrin from glycerol, and it is still used 
 for the purpose, although it has, until lately, received no other such 
 application. According to Claus (Ann. 168, 43), the action which 
 takes place is represented by the equation 
 
 The operation is carried out as follows : About 800 grams of 
 glycerol, boiling at 195 (?) Rossing (Ber. 19, 64) recommends 
 anhydrous glycerol boiling at 176-177 for the purpose are 
 placed in a two-litre flask, which is connected with a condenser. 
 While this is heated in a brine bath and continuously agitated, 2 
 kilograms of chloride of sulphur are added. After the heating has 
 continued for 7-8 hours the action is complete, and the condenser 
 is removed so as to allow sulphurous acid and hydrochloric acid to 
 be driven off during a final hour's heating. On cooling, the mass 
 becomes pasty. Two or three times its volume of ether is added, 
 the mixture is filtered, and the filtrate distilled. After repeated 
 rectification, pure dichlorhydrin, boiling at 179, is obtained. 
 
204 CHLORO-DERIVATIVES [CH. xvi 
 
 Morley (Ber. 13, 222) states that the yield is more than 50 per 
 cent, of the theoretical. 
 
 With glycol, chloride of sulphur gives ethylene chlorhydrin, but 
 the product cannot be freed from impurities containing sulphur. 
 The action may be represented thus : 
 
 CH 2 .OH CH 2 .C1 
 
 2 | + 2S 2 C1 2 =2 j + 2HCl + SOo+3S. 
 
 CH 2 .OH CH 2 .OH 
 
 Sulphur tetrachloride acts on acetic acid according to the 
 equation 
 
 SC1 4 +2CH 3 COOH = 2CH 3 COC1+SO 2 +2HC1. 
 
 Anger and Behal (Bull. Ch. [3], 2, 144) describe the operation 
 as follows : Glacial acetic acid and sulphur, or chloride of sulphur, 
 in the proportion of two molecules of the former to one of the latter, 
 are placed in a flask surrounded by a freezing mixture, and chlorine 
 gas is led in till it is no longer absorbed. The mass, after having 
 reached the ordinary temperature, is heated and distilled with the 
 aid of a good condenser. The distillate is caught in a receiver 
 surrounded by ice, as otherwise the streams of sulphur dioxide and 
 hydrochloric acid may carry off much of the acetyl chloride. The 
 part passing over below 60 is rectified, shaken with mercury or 
 finely-divided copper, to remove an impurity containing sulphur, 
 and finally redistilled. From 600 grams of the acid about 500 
 grams of the chloride are obtained. 
 
 When the mixture of acetic acid and sulphur is boiled during the 
 absorption of the chlorine, the chief product is monochloroacetic 
 acid, and but little acetyl chloride is formed. As the investigators 
 obtained i kilogram of monochloroacetic acid from 800 grams of 
 acetic acid in a single day, this is probably the best way of preparing 
 the former substance. 
 
 18, Sulphuryl chloride. 1 This substance has been frequently 
 
 1 It may be of interest here to describe the best way of preparing sul- 
 phuryl chloride, as it depends on a peculiar contact effect of an organic 
 body. According to Schulze (J. pr. Ch. 132, 168), when camphor is 
 treated with sulphur dioxide it becomes moist on the surface and finally 
 melts to a clear liquid (this was observed earlier by Bineau, Ann. Ch. Ph. 
 [3] 24, 326), which continues to absorb sulphur dioxide up to O'88 of the 
 weight of the original camphor at 725 mm. pressure. This liquid is now 
 cooled with ice and saturated with chlorine. When the camphor, by a 
 
SEC. ii, 19] CHLORSULPHONIC ACID 205 
 
 used for preparing chlorinated compounds. Thus Wenghoffer (J. 
 pr. Ch. 124, 449) took a measured quantity of the chloride, and 
 allowed the equivalent amount of aniline, diluted with six times its 
 weight of ether, to drop into it. The resulting mixture became 
 solid, and after somewhat laborious purification by recrystallisation, 
 trichloroaniline was isolated 
 
 C 6 H 5 NH 2 + 3S0 2 C1 2 =C G H 2 C1 3 NH 2 +3S0 2 +3HC1. 
 
 The yield was only 1 5 per cent, of the theoretical. 
 
 Reinhold (J. pr. Ch. 125, 322) dissolved resorcinol in three times 
 its weight of ether, and allowed sulphuryl chloride to flow, drop by 
 drop, into the mixture. By fractional distillation, an amount or 
 monochlororesorcinol equal to the resorcinol taken was obtained 
 
 C 6 H 4 (OH) 2 + SO 2 C1 2 = C 6 H 3 C1(OH) 2 + SO 2 + HC1. 
 
 By adding sulphuryl chloride to acetoacetic ether, Allihn (Ber. 
 11, 569) obtained a liquid consisting almost entirely of monochloro- 
 acetoacetic ether boiling between 193 and 195 
 
 CH 3 . CO . CH 9 . COOC 2 H 6 + SO 2 C1 2 = CH 3 . CO . CHC1 . COOC 2 H 6 
 
 + SO 2 + HC1. 
 
 Similarly Roubleff (Ann. 259, 254) added sulphuryl chloride (i mol.) 
 slowly to well-cooled methylacetoacetic ether. The action began when 
 one third of the quantity had been added, and the evolution of hydrochloric 
 acid and sulphur dioxide continued till the mixing was completed. The 
 mixture was warmed on the water bath for a short time, diluted with ether, 
 and washed with water until neutral. The ethereal solution was dried with 
 calcium chloride, and, after fractionation, yielded pure chloromethylaceto- 
 acetic ether. 
 
 19. Chlorsulphonic Acid, HC1S0 3 . This and the succeeding 
 substances are used to a very limited extent only. 
 
 Chlorsulphonic acid is not suited for the preparation of simple 
 acid chlorides, but it has been used by Heumann and Kochlin, 
 
 continuation of this alternating treatment, has taken up twice its weight of 
 sulphuryl chloride, both gases can be led in together. If the column of 
 liquid be tall enough, and care be taken that the tubes leading the gases 
 distribute them through the liquid, very rapid streams of gas will be 
 perfectly absorbed. The sulphuryl chloride is distilled off at as low a 
 temperature as possible (it boils at 77), to avoid the carrying over of more 
 than a trace of camphor. The presence of this is shown by the white 
 flakes which remain suspended when the substance is shaken with water. 
 
206 IODO-DERIVATIVES [CH. xvi 
 
 (Ber. 15, 1,166) for the conversion of aromatic sulphonic acids into 
 sulphonic chlorides. Thus they mixed /-toluenesulphonate of 
 sodium (97 gr. = i mol.) with chlorsulphonic acid (58'25 gr. = i mol.), 
 and poured the mixture into water. Toluenesulphonic chloride 
 (S^'S gr.) was deposited. 
 
 20. Thionyl Chloride, SOC1 2 Thionyl chloride was tested by 
 the same authors (Ber. 16, 1,627), with regard to its action on 
 several organic acids. Butyric acid (10 gr.) reacted at once, giving 
 butyryl chloride (6 gr.). Benzoic acid (10 gr.) boiled with thionyl 
 chloride, with use of a return condenser, gave benzoyl chloride 
 (10 gr.). The yields obtainable seem to be good. 
 
 Cyanuric chloride acts on sodium salts of acids when heated with them 
 for several hours in sealed tubes at 100, producing acid chlorides. The 
 yield from sodium acetate, according to Senier (Ber. 19, 310) is only 22 per 
 cent, of the theoretical, while sodium benzoate gives 88 per cent. The 
 equation 
 
 represents the course of the interaction. 
 
 SECTION III. IODO-DERIVATIVES. 
 
 Although iodine is frequently used alone in the solid form for the 
 preparation of iodo-derivatives, it is most frequently employed in 
 the presence of oxidising agents or of phosphorus. 
 
 As solvents alcohol, ether, chloroform, carbon disulphide, potas- 
 sium iodide solution, hydriodic acid, benzene, toluene, and other 
 substances are used. 
 
 Among the less commonly used agents for the production of 
 iodo-derivatives are iodine chloride, phosphonium iodide, and 
 iodide of nitrogen. 
 
 The chlorine or omine in substances containing these elements 
 can often be replaced by iodine by the action of potassium, sodium, 
 or silver iodides. 
 
 Iodo-derivatives are likewise obtained by the action of hydriodic 
 acid on several classes of bodies, and by addition of that substance 
 and of iodine and iodine chloride to unsaturated bodies. 
 
 1. Free Iodine. Fischer (Ann. 211, 233) found that tolane was 
 not attacked by iodine in solution in chloroform or carbon disul- 
 
SEC. in, i] FREE IODINE 207 
 
 phide, but that when they were heated alone to the melting-point 
 of iodine, a violent action took place and the mixture became 
 crystalline on cooling. Cold chloroform removed unchanged tolane 
 and iodine, and the residue after recrystallisation proved to be tolane 
 di-iodide, C 14 H 10 I 2 . The addition of ferrous iodide or mercuric 
 oxide would doubtless be advantageous in cases like this (cf. 4). 
 
 Birnbaum and Reinherz (Ber. 15, 457) obtained iodobenzoic acid 
 and di-iodosalicylic acid by the action of iodine on the dry silver 
 salts of benzoic and salicylic acids. The yield was poor however. 
 Birnbaum had previously observed (Ann. 152, 116) that no 
 iodoacetic acid could be obtained from silver acetate by this 
 method. 
 
 In spite of its general resemblance to chlorine and bromine, 
 iodine never produces substitution products by acting on dissolved 
 organic bodies. Kekule was the first (Ann. 131, 122) to discuss 
 this peculiarity fully. The cause is to be found in the fact that the 
 hydriodic acid arising from the action immediately decomposes the 
 derivative, or even prevents its formation. Kekule' proved that 
 when iodoacetic acid is mixed with concentrated hydriodic acid in 
 the cold, iodine is deposited and acetic acid is formed 
 
 CH 2 I.COOH + HI = CH 3 .COOH+ 2 I. 
 
 On the other hand this very fact explains why bases can be 
 converted into iodo-derivatives with ease, for they unite at once 
 with the hydriodic acid as soon as it is set free. Thus aniline gives 
 directly iodoaniline hydriodide 
 
 C 6 H 5 NH 2 + 2 I = C 6 H 4 INH 2 .HI. 
 
 Kekule suggested later (Ann. 137, 162) the use of iodic acidto 
 destroy the influence of the hydriodic acid by oxidising its hydrogen, 
 when non-basic bodies were in question. Thus by heating benzene 
 (20 gr.), iodine (15 gr.), and iodic acid (10 gr.) at 200-240 in a 
 sealed tube, he obtained iodobenzene 
 
 A modification of this method is to dissolve iodine and iodic acid 
 in a very dilute caustic potash, and add the solution to the acid 
 reacting substance e.g. phenol, into which the iodine is to be intro- 
 duced, and then mix with the necessary amount of hydrochloric 
 acid. Derivatives containing more iodine can be obtained by 
 using the proper molecular amounts of iodine and iodic acid. 
 
208 IODO-DERIVATIVES [CH. xvi 
 
 Kehrmann and Tiesler (J. pr. Ch. 148, 487) prepared iodo-chloro- 
 dioxyquinone, 
 
 O 
 Cl /\ OH 
 
 HO \/ I 
 O 
 
 by dropping potassium iodide and iodate, mixed in the proper 
 proportions, into a strongly acid solution of chlorodioxyquinone. 
 The free iodine formed at first disappears almost immediately, and 
 after a short interval a crystalline powder, consisting of an almost 
 quantitative yield of the desired substance, is precipitated. 
 
 Hlasiwetz and Weselsky (Centralblatt, 1870, 63) recommend 
 the use of an easily reducible oxide of a metal whose iodide is 
 insoluble, in place of iodic acid. They state that mercuric oxide, 
 prepared in the wet way, is best suited to this purpose. Thus 
 iodine and mercuric oxide are thrown in small quantities at a time, 
 with continual agitation, into an alcoholic solution of phenol, so 
 much mercuric oxide being always taken that the brown colour of 
 the solution disappears. The reaction proceeds rapidly, and the 
 natural warming of the solution is moderated by external cooling. 
 When the ingredients are used in the proportions required by the 
 equation 
 
 some di-iodide is formed at the same time. The di-iodide is almost the 
 sole product when the proportions used correspond to the equation 
 
 Tohl (Ber. 25, 1,522) mixed iodine (25 gr.), petroleum ether 
 (250 cc.), durene (20 gr.), and mercuric oxide (n gr.), and, after 
 allowing them to remain together for three weeks, washed the 
 solution with sodium hydroxide. On distilling off the petroleum 
 ether and fractionating the residue, he obtained iododurene (cf. 4). 
 
 Stenhouse dissolved orcinol in ether (6 parts), added iodine 
 (2 parts), shook the mixture till all the iodine had dissolved, and 
 then added finely powdered litharge. A violent action took place, 
 and iodo orcinol, C r H 7 IO 2 was formed. 
 
 Clermont and Chautard (C. R. 100, 745) state that when acetone 
 (200 gr.), iodine (icogr.), and iodic acid (40 gr.), are allowed to stand 
 for eight days, and the mixture is then heated, with reflux condenser, 
 
SEC. in, 2] IODINE WITH SOLVENTS 209 
 
 for two to three hours, addition of water precipitates iodoacetone, 
 C 3 H 6 IO. This is a very unstable substance. They found also(C. R. 
 102, 119) that, using the same method with aldehyde, if the 
 mixture remained until the iodine had completely disappeared, iodo- 
 aldehyde was formed according to the equation 
 
 2. Iodine with Solvents. In connection with the discussion of 
 the use of solvents for iodine, it may be pointed out that, as many 
 liquids dissolve iodine, the substance to be acted upon will 
 frequently have this property, and so the addition of a special 
 solvent will be unnecessary. 
 
 Curtius (Ber. 18, 1,285) dissolved iodine and diazoacetamide in 
 alcohol and obtained di-iodoacetamide. 
 
 CHN 2 . CONH 2 + 2l = CHI 2 . CONH 2 + N 2 
 
 Schall (Ber. 16, 1,897) suspended perfectly dry phenol-sodium 
 (20 gr.) in carbon disulphide (300 cc.) and added iodine (45 gr.) 
 gradually. A large quantity of iodophenol was formed at once, 
 although its separation from other products presented considerable 
 difficulties. 
 
 Baeyer (Ber. 18, 2,274) added a solution of iodine \n potassium 
 iodide to the undried copper compound of propargylic ether as long 
 as the colour of the iodine continued to disappear rapidly after each 
 addition. The resulting precipitate, after being pressed free from 
 water and moistened with a few drops of alcohol, was extracted 
 twenty times with ether. The extract deposited on evaporating 
 iodopropargylic ether, I-C = C - COOC 2 H 6 . 
 
 According to Fischer (Ber. 10, i>335)> the interaction of phenylhydra- 
 zine and iodine produces chiefly hydriodic acid, diazobenzene imide, and 
 aniline 
 
 Meyer (J. pr. Ch. 144, US) finds, however, that this only holds in the 
 presence of excess of phenylhydrazine. If iodine (2 mol. ) and phenyl- 
 hydrazine (i mol. ) are taken, iodobenzene is produced and nitrogen gas 
 escapes. 
 
 C 6 H 5 NH . N 
 
 Meyer dissolved iodine (18*5 gr. ) in potassium iodide solution, and added 
 slowly to this a solution of phenylhydrazine (4 gr.) in much water. The 
 action was completed by warming for a short time in the water bath. A 
 
 P 
 
210 IODO-DERIVATIVES [CH. xvi 
 
 dark-coloured oil was deposited, which, on being dried and distilled, was 
 found to consist mainly of iodobenzene. The yield was 6*5 grams in place 
 of 7 '4 grams. The reaction became quantitative when a very dilute solution 
 of iodine ( T V normal) was used. 
 
 When excess of iodine has been added, the unused part can be 
 removed by steam, potassium iodide solution, or mercury, when it is 
 unadvisable to employ an alkali for the purpose. Partheil (Ber. 24, 
 636) decolourised a solution containing iodine with carbon disul- 
 phide, and expelled the excess of the latter with carbon dioxide. 
 
 3. Iodine Carriers Phosphorus. This substance is principally 
 used in preparing iodides of hydrocarbon radicals from alcohols. 
 
 3CH 3 CH 2 OH + P + 3! = 3 CH 3 CH 2 I + H 3 PO 3 . 
 
 The method was discovered by Serullas (Ann. Ch. Ph. 25, 223). 
 Hofmann (Ann. 115, 273) describes the use of yellow phosphoms 
 in this connection as follows : The phosphorus is placed in a retort 
 whose neck is connected with a condenser. One quarter of the 
 alcohol to be used is poured on to the phosphorus through a 
 funnel, provided with a stop-cock, and passing through a cork in 
 the tubulus of the retort. The apparatus is placed on a water bath, 
 and, the iodine having been dissolved in the remainder of the 
 alcohol, the solution is allowed to flow in slowly through the funnel. 
 The interaction begins immediately, and almost as fast as the liquid 
 enters through the funnel a mixture of alcohol and ethyl iodide 
 distills over into the receiver. As iodine is not very soluble in 
 alcohol, a good deal which the alcohol at disposition has not been 
 able to dissolve will always remain over. It is very soluble in 
 ethyl iodide, however, so the first part of the distillate is used to 
 dissolve the residue, and this is allowed to flow into the apparatus 
 once more, when the remaining iodine is almost immediately con- 
 verted into ethyl iodide. The distillate is washed with water, dried 
 and rectified. With proper proportions such as iodine (1,000 gr.), 
 methyl alcohol (500 gr.), and phosphorus (60 gr.), a yield equal to 
 94-95 per cent, of the theoretical may be attained. 
 
 Ethyl iodide, which was first made by Gay-Lussac in 1835, 
 requires iodine (1,000 gr.), alcohol (700 gr.), and phosphorus (50 gr.) 
 The yield is 96-98 per cent., on account of the smaller volatility of 
 the ethyl iodide. 
 
 Beilstein (Ann. 126, 250) gives the method of using red phos- 
 phorus as follows : In a retort connected with a return condenser 
 
SEC. in, 4] IODINE CARRIERS FERROUS IODIDE 211 
 
 are placed red phosphorus (10 parts) and alcohol, sp. gr. 0x83 
 (50 parts). Iodine (100 parts) is then thrown in in small portions at 
 a time, and after the mixture has remained for twenty-four hours 
 the ethyl iodide is distilled off. The distillate is treated with a 
 trace of caustic soda to precipitate any dissolved ethyl iodide, and at 
 the same time to decolourise the product. A second distillation gives 
 the pure substance in almost theoretical quantity. The red colour, 
 which ethyl iodide always acquires on standing, may be hindered 
 from appearing by placing a clean piece of copper wire in the bottle. 
 Walker (J. Ch. Soc. 61, 717) recommends a method which does 
 away with the tediousness of the gradual addition of iodine. The 
 iodine is placed, 100 grams at a time, in an apparatus similar to 
 those used in fat extraction, placed between the flask, containing the 
 phosphorus and alcohol, and the condenser. The flask is charged 
 with equal parts of red and yellow phosphorus. The yield is 
 570 grams of ethyl iodide from 500 grams of iodine. 
 
 V. Meyer (Ber. 19, 3 S 295) gives the following method of making &- 
 iodopropionic acid. Glycerol is oxidised in the usual manner with nitric 
 acid (cf. Chap. XVIII.), and the liquid is evaporated and the nitric acid 
 expelled on the water bath. The sirup which results is diluted to a sp. 
 gr. i "26, and is poured 30 cc. at a time on iodide of phosphorus, which has 
 meanwhile been prepared by mixing iodine (50 gr.)and yellow phosphorus 
 (6 '5 gr.) in a flask. If the action does not begin of itself, it is started by 
 gentle heating. After the violence of the action has abated the mixture is 
 allowed to cool, and in doing so forms a mass of almost colourless plates of 
 iodopropionic acid. The substance may be made perfectly pure by 
 recrystallisation from water, but is sufficiently pure for most purposes after 
 simple pressing and drying. 
 
 In the case of solid alcohols, the substance is melted with the red 
 phosphorus and the iodine added to the fused mass. Thus Hell 
 and Hagele (Ber. 22, 503) heated myricyl alcohol with ordinary 
 phosphorus in an oil bath to 130-140, and added iodine in small 
 portions until violet vapours began to be continuously emitted. 
 The heating was carried on as long as gases were evolved, and 
 finally the cold reddish-brown mass was extracted with boiling 
 water. The residue, consisting of myricyl iodide, was recrystallised 
 from alcohol and petroleum ether. 
 
 4. Iodine Carriers Ferrous Iodide. Besides phosphorus, 
 ferrous iodide is used as an iodine carrier, while aluminium iodide 
 and ferric chloride are less useful in this respect. 
 
 P 2 
 
212 IODO-DERIVATIVES [CH. xvi 
 
 Here also the method of melting solid alcohols with iodine and 
 the iodine carrier is useful. Thus when phenylpropiolic acid 
 (20 gr.) was allowed to remain in contact with iodine in carbon 
 disulphide solution, only i'5 grams of the di-iodide were formed. 
 But by mixing the acid with the molecular proportion of iodine, 
 adding a little ferrous iodide, and keeping the whole for an hour at 
 140-145, Liebermann and Sachse (Ber. 24, 4,113) obtained di-iodo- 
 phenylpropiolic acid very readily. The corresponding compound 
 of behenolic acid is formed even at 100. 
 
 lododurene, whose somewhat complicated preparation in the wet 
 way has already been explained, can be made with the utmost 
 ease by melting durene and iodine and gradually adding mercuric 
 oxide until the halogen has disappeared (Ber. 25, 1,523). 
 
 Anhydrous ferrous iodide has likewise been used in producing 
 iodides in the wet way. Thus Liebermann and Sachse (Ber. 24, 
 4,113) dissolved phenylpropiolic acid and iodine in cold carbon 
 disulphide, and added one-tenth as much ferrous iodide as of the 
 acid. After twenty-four hours 3*5 grams of the iodide had been 
 formed, and in ten days the action was practically complete. 
 
 Lothar Meyer (Ann. 231, 195) showed that, in presence of ferric 
 chloride, the action of iodine on benzene probably takes place 
 according to the equation 
 
 The course of the action is therefore rather complicated, and appears 
 also to be somewhat uncertain. Gustavson (Ber. 9, 1,607) has 
 shown that aluminium iodide is of little use for the present purpose. 
 
 5. Application of Sulphuric Acid, According to Neumann 
 (Ann. 241, 37), sulphuric acid is, in a sense, an iodine carrier, since 
 by its aid many monoiodo-compounds can be converted into di-iodo- 
 compounds. Thus when iodobenzene (50 gr.) was added to con- 
 centrated sulphuric acid (50 gr.), and the mixture warmed and 
 frequently agitated for two hours at 170, cooling caused a separa- 
 tion of crystals which, after washing with water and purification, 
 were found to be ^-di-iodobenzene (20 gr.). The equation 
 
 2 C 6 H,:I + H 2 S0 4 = C 6 H 4 I 2 + C 6 H 6 S0 3 H + H 2 O 
 
 explains its formation. lodotoluene and iodophenol gave corre- 
 sponding di-iodo-derivatives. 
 
 Hammerich (Ber. 23, 1,635) covered iodo-;-xylene with three 
 
SEC. in, 6, 7] ADDITION OF IODINE 213 
 
 times its weight of concentrated sulphuric acid, and allowed them 
 to remain in contact, with frequent shaking, for six weeks. The 
 upper layer, consisting of sulphuric acid, was then poured off, 
 and the lower layer was washed with water, decolourised with 
 sodium thiosulphate, and distilled in vacua, when di-iodoxylene was 
 obtained. 
 
 6. Use of a Solution of Iodine in Potassium Hydroxide. 
 
 Messinger and Vortmann's method (Ber. 22, 2,312) is based on 
 this, and gives excellent yields of iodophenols. An alkaline solu- 
 tion of the phenol is heated to 50-60, and an excess of iodine 
 (8 atoms iodine to i mol. phenol dissolved in 4 mol. potassium 
 hydroxide) is added. A dark-red precipitate is produced, which is 
 almost entirely soluble in caustic potash. Precipitation with acids 
 gives tri-iodophenol, C 6 H 3 I 3 O. Thymol gives, with the same treat- 
 ment, the di-iodo-derivative C 10 H 12 I 2 O. 
 
 It is noteworthy that a slight modification of this process leads 
 not only to the replacement of the hydrogen atoms in the nucleus, 
 but also of that in the hydroxyl group. Thus iodothymol iodide 
 (Ger. Pat. 49,739) is obtained by allowing a solution of iodine in 
 potassium iodide or a solution of iodine in caustic potash, to which 
 an agent for setting the iodine at liberty, such as chlorine or 
 bleaching-powder, had been added, to flow into an alkaline solution 
 of phenol at 10-30. The iodide of iodosalicylic acid (Ger. Pat. 
 52,833) and similar compounds can be made in the same way. 
 
 7. Addition of Iodine, All alkaloids take up iodine and iodine 
 chloride (cf. 10) directly, when solutions of the salts of the 
 alkaloids are mixed with the proper amount of iodine dissolved in 
 potassium iodide. Thus Jorgensen (J. pr. Ch. 109, 433) obtained 
 tarkonine heptiodide, C 12 H 12 NO 3 If. The tetra-alkylammonium 
 derivatives possess the same property as is shown by the existence 
 of Marquart's tetra-ethylammonium tri-iodide (J. pr. Ch. 110, 433). 
 Einhorn (Ber. 20, 1,221) precipitated anhydroecgonine almost 
 quantitatively as periodide 1 by means of a solution of iodine in 
 hydriodic acid. 
 
 1 It is worthy of mention that alkaloids likewise form addition products 
 with hydrogen polysulphide. For example, Schmidt (Ar. Pharm. 25, 
 149) found that when yellow ammonium sulphide was added to a warm 
 alcoholic solution of berberine hydrochloride or sulphate, brown crystals 
 
2i 4 IODO-DERIVATIVES [CH. xvi 
 
 Metallo-deri f uatives of acid amides seem to possess the same 
 property, according to Tafel and Enoch (Ber. 23, 1,552). They 
 prepared acetamidomercuric iodide, (CH 3 CONH) 2 HgI 2 , and other 
 similar compounds. 
 
 Finally, iodo-derivatives are obtained by the addition of iodine to 
 unsaturated bodies. Only two atoms, however, can be added to a 
 triple linkage. Thus, when acetylene is led into a solution of iodine 
 in absolute alcohol, ethylene di-iodide is formed 
 
 CHiCH + I 2 = CHI :CHI. 
 
 Even if propargylic acid (Ber. 24, 4,120), CH \ C . COOH, is 
 heated in chloroform with two molecules of iodine for six hours at 
 100, nothing more than di-iodoacrylic acid is obtained. 
 
 8. Action of Hydriodic Acid. Griess first showed that hy- 
 driodic acid acts on diazo-bodies producing iodo-derivatives. 
 C 6 H 5 N :N.NO 3 + HI = C 6 H 5 I + N 2 +HNO 3 . 
 
 Thus Gabriel and Herzberg (Ber. 16, 2,037) diluted hydriodic 
 acid with an equal volume of water, and warmed the nitrate of 
 0-diazocinnamic acid with four times its weight of the diluted acid 
 until the evolution of nitrogen ceased. On adding more water, 
 filtering and washing with a little sodium thiosulphate to remove 
 free iodine, and finally recrystallising, pure iodocinnamic acid, 
 IC 6 H 4 .C 2 H 2 .COOH, was obtained. 
 
 This reaction sometimes goes with unexpected smoothness, as 
 in a case where Hahle (J. pr. Ch. 151, 72), following the directions 
 of Schmitt (Ber. 1, 68), treated nitrodiazophenol chloride with 
 hydriodic acid. The action was too violent at ordinary tempera- 
 tures, so he added the diazo-compound gradually to a suitable 
 amount of ice-cold hydriodic acid. After the last traces of nitrogen 
 had been driven off by warming, iodonitrophenol was precipitated 
 quantitatively by adding water. 
 
 Sandmeyer's and Gattermann's methods (cf. Chap. XVI, Sections 
 I and II) can of course be used for preparing iodo-derivatives. 
 The latter prepares iodo-benzene by taking aniline (31 gr.), con- 
 centrated sulphuric acid (200 gr.), water (200 cc.), sodium nitrite 
 (23 gr.), potassium iodide (126 gr.), and finely divided copper (40 gr.). 
 The yield, 48 grams of iodobenzene, corresponds to 70 per cent, of 
 the theoretical. 
 
 of a berberine polysulphide, (C 20 H 17 NO 4 )2H 2 S 6 , came out. Strychnine 
 gives under the same conditions, (C 21 H 22 N 2 O 2 ) 2 H 2 S 6 . 
 
SEC. in, 8] ACTION OF HYDRIODIC ACID 215 
 
 Higher alcohols as well as secondary and tertiary alcohols give 
 iodo-derivatives directly on being treated with hydriodic acid. 
 Thus Freund and Schonfeld (Ber. 24, 3,354) warmed octylic 
 alcohol on the water bath, the action being too weak in the cold, 
 and conducted into it hydriodic acid. This was rapidly absorbed, 
 and the current of gas was continued until a yellow layer of the 
 acid began to accumulate on the bottom of the vessel, and the 
 liquid smelt very strongly of the same substance. As the iodide 
 decomposes on distilling, it was simply decolourised by shaking 
 with sodium bisulphite. A yield of 180 grams of CH 3 .CHI.C 6 H 13 
 was obtained from 100 grains of the alcohol. 
 
 Tertiary butyl alcohol (CH 3 ) 3 COH gives tertiary butyl iodide, 
 according to Butlerow (Ann 144, 5), when saturated with hydriodic 
 acid gas, or shaken with a concentrated solution of the acid. The 
 product is decolourised by shaking with caustic potash or potassium 
 bisulphite and distilled. Erlenmeyer (Ann. 126, 305) states that 
 when glycerol is boiled with excess of hydriodic acid, isopropyl 
 iodide is formed. It should be noticed that when polyhydric 
 alcohols are treated in this manner, secondary iodides are always 
 formed. Thus erythrol gives secondary butyl iodide. 
 
 lodo-alcohols cannot be prepared in this way, as the hydriodic 
 acid attacks all the hydroxyl groups at once. Iodo-derivatives of 
 the hydrocarbons are always obtained instead. 
 
 In connection with this method one more example, Munsche's (Dissert. 
 Jena, 1890) preparation of hexyl iodide, may be described. He makes 
 part of the hydriodic acid during the process out of iodine, phosphorus, 
 and water, an operation which is facilitated by the presence of iodine pro- 
 duced by the action itself. 
 
 C 6 H 8 (OH) 6 + 1 1 HI = C 6 H 13 I + lol + 6H 2 O. 
 
 Iodine (200 gr. ) and hydriodic acid sp. gr. 17 (100 gr.) are placed in a 
 tubulated retort, and red phosphorus (90 gr.) is added. At first the part of 
 the phosphorus necessary just to decolourise the solution is taken, and then, 
 while the vessel is gently warmed on a sand bath, the rest of the phosphorus 
 is added in small portions alternately with portions of mannitol (120 gr.). 
 After two thirds of the latter has been used, the rest of the phosphorus 
 and mannitol, together with the portion of hexyl iodide mixed with hydri- 
 odic acid which has meanwhile distilled over, are introduced into the retort. 
 The resulting iodide is first distilled in a current of steam, and then by itself, 
 The yield is said to be good, 
 
216 IODO-DERIVATIVES [CH. xvi 
 
 Leser (Ber. 17, 1,826) prepared o-xylilene iodide, C 8 H 8 I 2 , by boiling 
 phthalyl alcohol with fuming hydriodic acid and a little red phosphorus. 
 The iodide was extracted from the solution, after dilution with water, by 
 means of ether. 
 
 Iodine ivas introduced in place of chlorine by means of 
 hydriodic acid by Friedlander and Weinberg (Ber. 18, 1,531). 
 On heating a-chloroquinoline at 240 with acetic acid and 
 hydriodic acid, quinoline itself was formed, but by altering the 
 conditions of the action the intermediate a-iodoquinoline was 
 obtained. For this purpose chloroquinoline was heated with 
 hydriodic acid (b.-p. 127) and a little amorphous phosphorus at 
 140-150 for three hours. On cooling, the contents of the tube 
 deposited crystals of a-iodoquinoline hydriodide. 
 
 Finally, it should be mentioned that diazo-bodies containing 
 chlorine, bromine, or iodine give mixed halogen derivatives. Thus 
 Silberstein (J. pr. Ch. 135, 119) found that on adding concen- 
 trated hydriodic acid to an aqueous solution of tribromodiazobenzene 
 nitrate, nitrogen was rapidly evolved, and tribromoiodobenzene 
 deposited. 
 
 9, Addition of Hydriodic Acid to Unsaturated Bodies.- 
 
 Hydriodic acid unites with unsaturated substances much more 
 easily than hydrochloric or hydrobromic acids, and forms iodo- 
 derivatives. 
 
 Thus Markownikoff (Z. Ch. 1870, 423) prepared iodopropyl 
 
 /\ 
 
 alcohol, C 3 H 7 IO, as follows : Propylene oxide, CH 3 CH CH 2 , 
 was diluted with a little more than an equal amount of water, 
 and hydriodic acid was conducted through a tube just to the 
 surface of the liquid. As soon as the solution acquired a strongly 
 acid reaction it was diluted with more water. The iodopropyl 
 alcohol, which was thrown down, was then purified by fractionation 
 in vacuo. 
 
 A common method is to dissolve the unsaturated substance 
 in acetic acid and add a solution of hydriodic acid in the same 
 solvent, then, after heating if necessary, to pour the mixture into 
 water, when the product separates out. 
 
 Lippmann (C. R. 53, 968) obtained iodo-alcohols directly from 
 unsaturated hydrocarbons by addition of hypoiodous acid, or its 
 elements, at the moment of its formation. Thus by dissolving 
 
SEC. in, 10] ADDITION OF IODINE CHLORIDE 217 
 
 iodine and amylene in chloroform in presence of freshly pre- 
 cipitated mercuric oxide, he obtained from the solution a heavy 
 yellow oil which turned out to be a mixture of different iodo- 
 alcohols. 
 
 Melikoff obtained iodolactate of potassium by the action of 
 fuming hydriodic acid on the dry potassium salt of glycidic 
 acid. 
 
 10. Addition of Iodine Chloride. The chloride (and bromide) 
 of iodine give mixed halogen derivatives by addition. Dittmar 
 (Ber. 18, 1,612) mentions particularly its power of combining with 
 alkaloids. He states that the number of molecules of the halogen 
 compound taken up corresponds with the number of pyridine rings 
 in the compound. He prepared his iodine chloride solution by 
 mixing potassium iodide, sodium nitrite, and hydrochloric acid, 
 or by conducting chlorine into water containing suspended 
 iodine. 
 
 Iodine chloride was first used for producing iodo-derivatives by 
 Brown (Phil. Mag. [4] 8, 201), and later by Stenhouse (J. Ch. 
 Soc. 17, 327 ; Ann. 134, 219). The latter found however that, 
 while iodine was often introduced, the chlorine frequently acted as 
 if it had been alone present and free iodine separated out. 
 
 Michael and Norton (Ber. 9, 1,752) have revived its claims 
 to be considered a good reagent for producing iodo-compounds. 
 They prepared it by passing a stream of dry chlorine over iodine, 
 until the weight of the latter had increased by a little less than the 
 calculated amount. Acetanilide (Ber. 11, 108) was dissolved by 
 them in much glacial acetic acid, and iodine chloride was added. 
 A good deal of iodoacetanilide separated out at once, and the rest 
 was precipitated on addition of water. The yield was 89-90 per 
 cent of /-iodoacetanilide. They likewise prepared di-iodoaniline 
 by dissolving aniline in several times its volume of acetic acid, 
 and leading into it gaseous iodine chloride (2 mol.). With a 
 solution of aniline in hydrochloric acid and the necessary amount 
 of iodine chloride (3 mol.) they obtained tri-iodoaniline (yield 15 
 per cent.). 
 
 Volker (Ann. 192, 90) dissolved solid iodine trichloride (96 gr.) 
 in a litre of water, added acetone (48 gr.), warmed the whole to 
 66, when cloudiness appeared, and finally cooled again to the 
 ordinary temperature. An oil was deposited from which di-iodo- 
 acetone was separated. From 5,225 grams of iodine trichloride 
 
218 IODO-DERIVATIVES [CH. xvi 
 
 and 2,600 grams of acetone he obtained, after elaborate purification, 
 1,020 grams of the crude product. An examination of the by- 
 products led him to give the following equation for the action : 
 
 Green (C. R. 90, 40) caused iodine chloride to act on benzene 
 containing some aluminium chloride, and obtained iodobenzene 
 along with products containing more iodine. 
 
 11. Phosphonium Iodide and Iodide of Nitrogen. Girard 
 
 (C. R. 101, 478) states that phosphonium iodide and ethylene oxide 
 give ethylene iodide and phosphine. 
 
 Willgerodt (J. pr. Ch. 147, 290) found that phenols could be 
 easily converted into iodo-derivatives by means of the iodides of 
 nitrogen, and he devised a method by which the separate prepara- 
 tion of these bodies could be avoided : 
 
 =C 6 H 2 I 3 OH + NH 3 . 
 
 Thus for preparing iodo-thymol he dissolved thymol (5 gr.) in 
 ammonia (6 cc.) and alcohol (2 cc.), and added gradually powdered 
 iodine (8*5 gr.). On addition of water the product was precipitated 
 (yield 45 per cent.). A di-iodo-derivative could not be obtained by 
 this method. But with 0-cresol di-iodocresol was the chief pro- 
 duct. Rise in temperature must be prevented, as otherwise tarry 
 matters are formed. Experiments with polyatomic phenols were 
 unsuccessful. 
 
 12. Action of Boron Tri-iodide and Iodides of Calcium, 
 Sodium, and Potassium on Chloro-Derivatives. Perkin and 
 
 Duppa (Ann. 112, 125) were the first to show that such compounds 
 as these could be used for the purpose of replacing chlorine by 
 iodine. 
 
 Boron tri-iodide has the property of converting chloroform into 
 iodoform when the substances remain in contact for several days 
 (Moissan, C. R. 113, 19). 
 
 It likewise changes carbon tetrachloride into carbon tetriodide, a 
 substance which can hardly be obtained in any other way. 
 
 Lothar Meyer (Ann. 225, 166-170) investigated thoroughly the 
 
SEC. in, 12] ACTION OF IODIDES 219 
 
 exchange of chlorine, bromine, and iodine between organic and 
 inorganic bodies, and gave a list of all previously recorded cases. 
 Later Spindler (Ann. 231, 258) found that while dried calcium 
 iodide had no action, the common form of the salt, containing a little 
 less than four molecules of water of crystallisation, could transform 
 all liquid chloro- and bromo-derivatives into corresponding iodo- 
 derivatives. Unfortunately the slowness of the action and the 
 frequent poorness of the yield diminish the value of the method. 
 
 In using this process, the substance (carefully dried) is placed in 
 a dry sealed tube with calcium iodide and exposed to a temperature 
 of 70-75 for 120 hours. For example, chloroform (i'35 gr.) and 
 calcium iodide (5 gr.) gave 17*4 per cent, of iodoform ; carbon 
 tetrachloride (2*3 gr.) gave 14*4 per cent, of carbon tetriodide. But 
 if sufficient time is allowed the action in the latter case becomes 
 almost quantitative. Ethylene chloride gave 86 per cent, of 
 ethylene iodide. 
 
 Sodium iodide is preferred to the potassium salt for actions like 
 the present because it is easily soluble in strong alcohol. Liebig 
 and Wohler (Ann. 3, 266) obtained benzoyl iodide by distilling 
 benzoyl chloride with potassium iodide, a process which is still the 
 only one for making acid iodides. 
 
 According to Perkin (Ber. 18, 221), when trimethylene bromide, 
 dissolved in alcohol, is treated with excess of potassium iodide, 
 (sodium iodide would probably work better), it is transformed 
 almost quantitatively into the iodide. 
 
 CH 2 Br.CH 2 .CH 2 Br + 2KI = CH 2 I.CH 2 .CH 2 
 
 It is therefore very probable that many iodo-derivatives, which can 
 only be made with difficulty or not at all directly, can be obtained 
 thus indirectly with ease. For example, Henry (Ber. 17, 1,132) 
 found that the best way to make propargyl iodide, CH C . CH 2 I, 
 was by the action of sodium iodide on C 3 H 3 Br in alcoholic solution. 
 The same observer found (Ber. 24, 74 c) that actions of this kind 
 are most effective in methyl alcohol as solvent. He states that 
 under these circumstances methyl chloride can be converted almost 
 quantitatively into the iodide by warming the mixture gently in a 
 pressure bottle. 
 
 Glaus (Ann. 168, 24) obtained j-di-iodhydrin by heating, in a brine 
 bath, dichlorhydrin with slight excess of potassium iodide and 
 enough water to dissolve them. 
 
 Demuth and Meyer (Ann, 256, 28) made the till then vainly 
 
220 IODO-DERIVATIVES [CH. xvi 
 
 sought iodoethyl alcohol by forming a thin paste of ethylene 
 chlorhydrin, C 2 H 4 C1OH (25 gr.), and finely powdered potassium 
 iodide and heating them, with frequent agitation, on the water bath 
 for twenty-four hours. The product was then filtered and the 
 residue washed with ether. The filtrate was decolourised with 
 sodium thiosulphate, and the ethereal layer having been separated 
 was dried with dehydrated sodium sulphate. On distilling off the 
 ether a faintly reddish oil, the iodhydrin, C 2 H 4 IOH (25 gr.), 
 remained. 
 
 13. Dissimilarity in Properties of Ethyl Chloride, Bromide, 
 and Iodide. In connection with the subject of this chapter it may 
 be well to mention that ethyl chloride, bromide, and iodide, which 
 are closely allied and frequently used substances, do not by any 
 means always act similarly towards other bodies. This is true in 
 spite of the fact that the two last are often regarded as inter- 
 changeable. 
 
 An illustration of this difference is seen in the fact that an 
 alcoholic solution of ethyl chloride has no action on silver nitrate 
 even when boiled with it, while ethyl bromide under the same 
 circumstances gives rise to ethyl nitrate and silver bromide. 
 
 Again, Fischer (Ber. 9, 885) found that when molecular propor- 
 tions of phenylhydrazine and ethyl iodide were mixed heat began 
 to be developed in a short time, and, if large quantities were used, 
 the action became so violent that the whole of the material was 
 decomposed with explosive evolution of gas. By substituting ethyl 
 bromide, however, the action could be conducted by heating in 
 connection with a return condenser on the water bath, and at the 
 end of a few hours the interaction was complete and the solution 
 solidified to a mass of crystals. 
 
 The difference is likewise shown in cases like the introduction of 
 the propyl radical into benzyl cyanide. V. Meyer (Ann. 250, 153) 
 found that propyl iodide acted very easily, while propyl bromide had 
 no effect at all. 
 
 Henry (C. R. 96, 1,149) investigated fully the relative activity of 
 the haloids in mixed halogen compounds, and in this connection 
 James' (J. pr. Ch. 128, 351) synthesis of taurine from ethylene 
 chlorobromide may also be recalled. 
 
 It may not be out of place here to remind the reader that potas- 
 sium and sodium do not always behave alike towards organic bodies, 
 
SEC. iv, i] USE OF SILVER FLUORIDE 221 
 
 How very different their action towards the same substance may 
 be is shown by an observation made by Merz and Weith (Ber. 6, 
 1,518). They found that sodium could be kept unchanged for years 
 in dry bromine, and could even be heated with it to 200 without 
 much action taking place. Potassium, on the other hand, even 
 when placed in bromine which had been perfectly dried with 
 sodium, produced immediate ignition and explosion. 
 
 SECTION IV. FLUORO-DERIVATIVES. 
 
 Reinsch (J. pr. Ch. 19, 314) was the first systematically to 
 attempt to make organic compounds containing fluorine. As early 
 as 1 840 he tried to obtain ethyl fluoride by leading hydrofluoric 
 acid gas into absolute alcohol, but without success. Stadeler 
 (Ann. 87, 137) showed that the solution of hydrofluoric acid in water 
 was completely indifferent towards many organic bodies, and 
 suggested the use of gutta-percha bottles for holding it. 
 
 Reinsch draws attention to the corrosive action on the skin of 
 organic liquids containing hydrofluoric acid, having found that such 
 liquids, especially if they get under the nails, produce protracted 
 and almost unendurable pain, which can only be mitigated by dip- 
 ping the members affected in ice water. Another writer recom- 
 mends bathing with caustic soda. 
 
 The gaseous methyl and ethyl fluorides were made by Fremy 
 (C. R. 38, 393) by distilling the potassium alkyl sulphate with acid 
 potassium fluoride. 
 
 CH 
 
 The action is probably more complicated, however, than this equa- 
 tion indicates, since Seubert (Ber. 18, 2,646), when making ethyl 
 fluoride by this method, found that caustic alkali removed about 
 25 per cent, of carbon dioxide from the resulting gas. 
 
 Borodine (Repert. de Chim. 1862, 336) obtained benzoyl fluoride 
 as a liquid boiling at 161 by distilling benzoyl chloride with acid 
 potassium fluoride from a platinum retort. It had but little corro- 
 sive effect on glass. 
 
 1. Interaction of Silver Fluoride with lodo- and Chloro- 
 Derivatives. It is strange that silver fluoride was not used until 
 recently for the preparation of fluoro-derivatives, seeing that, as 
 might be expected, it yields them very readily. 
 
222 FLUORO-DERIVATIVES [CH. xvi 
 
 Thus Moissan (C. R. 107, 260 and 1,155) obtained ethyl fluoride 
 by allowing a stream of ethyl iodide to flow slowly into silver 
 fluoride. He freed the gas from -the ethyl iodide, which was carried 
 off mechanically, by passing it first through a tube cooled to 20 
 and then over a fresh quantity of silver fluoride. 
 
 Meslans (C. R. 110, 717) placed chloroform (i part), iodoform 
 (2 parts), and silver fluoride ( i part) in a flask cooled with ice. As 
 it was allowed to become warmer, a gas was evolved consisting 
 chiefly of fluoroform. This was purified by passage first through 
 a tube cooled to -23, then once more over warmed silver 
 fluoride, and then over caoutchouc to remove chloroform vapour. 
 After passing finally through cuprous chloride, to remove carbonic 
 oxide, the gas was pure. 
 
 Chabri^ (C. R. 110, 1,202) prepared gaseous methylene fluoride 
 CH 2 F 2 in a similar way from methylene chloride. 
 
 2. Action of Hydrofluoric Acid on Diazo-Bodies. This 
 method has frequently been used for the production of fluoro- 
 derivatives. Thus, on boiling diazobenzenesulphonic acid with 
 the ordinary solution of hydrofluoric acid in water, Lenz (Her. 12, 
 581) obtained fluobenzenesulphonic acid, C 6 H 4 FSO 3 H. 
 
 Ekbom and Mauzelius (Ber. 22, 1,846) dissolved naphthylamine 
 in warm, strong hydrofluoric acid, and added excess of potassium 
 nitrite dissolved in a small amount of water. Nitrogen was evolved, 
 and a considerable amount of fluonaphthalene formed. 
 
 Schmitt and Gehren (J. pr. Ch. 109, 395) added diazoamido- 
 benzoic acid in portions of 10-15 grams at a time to 200 cc. of 
 fuming hydrofluoric acid contained in a large platinum basin. 
 Fluobenzoic acid was formed, along with amidobenzoic acid hydro- 
 fluoride, according to the equation 
 
 In a similar manner Mauzelius (Ber. 22, 1,844) obtained fluo- 
 naphthalenesulphonic acid by adding a-diazonaphthalenesulphonic 
 acid to 50 per cent, hydrofluoric acid. 
 
 As the result of some investigations on this subject, Paterno and 
 Oliver! stated that fluorine derivatives of hydrocarbons could not 
 be obtained by the decomposition of salts of diazo-bodies with 
 hydrofluoric acid. But Wallach (Ann. 235, 258) has found a 
 means of preparing them easily and in large quantities from 
 diazoamido-compounds. Thus by mixing solutions in water of 
 
SEC. iv, 3] CHROMIUM HEXAFLUORIDE 223 
 
 diazobenzene chloride and piperidine a quantitative yield of benzene 
 diazopiperidide results. By mixing a quantity of this substance 
 ( 10 gr.), after drying it in the air, with concentrated hydrofluoric 
 acid (20-30 cc.), a violent reaction sets in, and fluobenzene is formed 
 according to the equation 
 
 CHN : N . NC 5 H 1 + 2HF = C 6 H 5 F + N 2 + NHC 5 H 10 . HF. 
 
 On account of the volatility of the fluobenzene a worm condenser 
 surrounded by a freezing mixture should be used, and the receiver 
 should be closed with a doubly bored cork and provided with a 
 tube bent so as to dip into a vessel of mercury. More than the 
 above quantities must not be used. 
 
 Ekbom and Mauzelius (Ber. 22, 1,846) have recently prepared 
 fluonaphthalene, C 10 H 7 F, by dissolving a- or /3-naphthylamine in 
 strong hydrofluoric acid in a platinum basin and adding the 
 necessary amount of potassium nitrite dissolved in a little water. 
 A good deal of tarry material is formed with the fluonaphthalene, 
 and the latter is separated by neutralising the acid with soda, 
 adding caustic soda to hold naphthols, and distilling in a current 
 of steam. 
 
 3, Chromium Hexafluoride, Jackson and Hartshorn (Ber. 
 18, 1,993) prepared difluobenzoic acid by the action of chromium 
 hexafluoride on dry benzoic acid. A black crust was formed, from 
 which the product was extracted with soda. The hexafluoride, 
 which is reduced to CrF 3 by the action, they prepared by distilling 
 fuming sulphuric acid (180 gr.), potassium dichromate (60 gr.), and 
 fluor spar (100 gr.). 
 
CHAPTER XVII 
 
 PREPARATION OF NITRO-DERIVATIVES 
 
 1. General Remarks. The agents used in preparing nitro- 
 derivatives are nitric acid, fuming nitric acid, mixtures of sulphuric 
 acid with nitric acid, alkaline nitrates and nitrate of urea/ a mixture 
 of nitric and acetic acids, silver nitrite, and potassium nitrite. A 
 few less common methods will be mentioned in the sequel. 
 
 Substances of the aromatic series can usually be converted into 
 nitro-derivatives by the action of nitric acid. In the case of fatty 
 bodies this is not possible, because the acid tends rather to oxidise 
 the substances submitted to its influence. 
 
 In regard to aromatic substances it may be said that, in general, 
 as low a temperature must be employed as possible, as the acid 
 has a greater tendency to oxidise the higher the temperature is. 
 Side chains are particularly apt to be oxidised to carboxyl groups. 
 The more numerous the side chains are, however, the easier is it 
 to prepare nitro-derivatives. Sulphonated compounds are specially 
 easily acted upon. It has not hitherto been found possible to 
 introduce more than four nitro-groups into one ring. 
 
 Nitro-groups have the effect of rendering neighbouring halogen 
 atoms much more replaceable. Thus ortho- and parachloronitro- 
 benzene give nitraniline when they are heated with alcoholic 
 ammonia. The meta-compound does not react. The presence 
 of two or three nitro-groups is still more favourable to the action. 
 
 The following table, abbreviated from that of Ure, gives the 
 content of HNO 3 in nitric acids of different densities 1 : 
 
 1 The use of this table in preparing acid of any required strength may be 
 illustrated as follows : If the problem is to convert acid of sp. gr. I '476, 
 
2] 
 
 METHOD OF USING NITRIC ACID 
 
 225 
 
 Table 
 
 of Specific Gravity 
 
 of Nitric Acid at 
 
 16-5. 
 
 Sp. Gr. 
 
 HNO 3 . 
 
 Sp. Gr. 
 
 HNO 3 . Sp. Gr. 
 
 HN0 3 . 
 
 I "500 . . 
 
 93"o 
 
 I-383 
 
 62-3 
 
 1-196 . 
 
 . . 31-6 
 
 1-498 . . 
 
 . 92*0 
 
 1-368 . . 
 
 . 59-6 
 
 1-183 
 
 297 
 
 1-494 . , 
 
 . 90-2 
 
 1-358. . 
 
 57-6 
 
 1-171 . 
 
 27'9 
 
 1-488 . . 
 
 .88-3 
 
 1-348 . . 
 
 55'9 
 
 1-159 . 
 
 . . 26-0 
 
 1-482 . . 
 
 . 86-4 
 
 I-338 
 
 53'9 
 
 1*146 . 
 
 . . 24-1 
 
 1-476 . . 
 
 . 84-6 
 
 1-322 . . 
 
 . 51-1 
 
 I-I34 
 
 . . 22-3 
 
 1-470 . '. 
 
 .827 
 
 1-311 . . 
 
 49'2 
 
 1-123 
 
 . . 20-4 
 
 1-464 . 
 
 . 80-9 
 
 1-300 . . 
 
 . 47-1 
 
 rni . 
 
 . . 18-5 
 
 i '453 
 
 . 78-0 
 
 1-289 
 
 45'5 
 
 099 . 
 
 . . 167 
 
 1-446 . . 
 
 . 76-2 
 
 1-276. . 
 
 43-7 
 
 088 . 
 
 . . 14-8 
 
 i '439 
 
 74"4 
 
 1-258 . 
 
 40-9 
 
 -076 . 
 
 I3' 1 
 
 i"43 J 
 
 . 72*6 1*246 . . 
 
 39-1 
 
 059 . 
 
 . . I0'2 
 
 1-423 . . 
 
 . 70-7 
 
 1-234 . . 
 
 . 37-2 
 
 048 . 
 
 . . 8-4 
 
 1-415 
 
 . 68-8 
 
 I '22 1 . . 
 
 35'3 
 
 "037 
 
 . . 6-5 
 
 1-406 . . 
 
 .66-9 
 
 1-208 . . 
 
 33'5 
 
 027 . 
 
 4'7 
 
 i "394 - 
 
 . 64-1 
 
 
 
 
 
 To obtain nitric acid free from nitrous acid, 6 grams of urea are 
 added to each litre of the nitric acid (sp. gr. 1*40). The acid is 
 then heated to boiling, and a rapid current of air is driven through 
 it for a few seconds. The action of the urea was explained by 
 Millon (Ann. Ch. Ph. [3], 6, 37). 
 
 ^\NH2 + N 23 = : 2 + 2N 2 + 2H 2 0. 
 
 In preparing nitro-derivatives of aromatic acids, salts of the 
 acids may be used to start from. 
 
 2, Method of using Nitric Acid. Ordinary or fuming nitric 
 acid is simply poured on to the substance, if it is a liquid. If it 
 
 containing therefore 84-6 per cent. HNO 3 , to acid of sp. gr. I '208, con- 
 taining 33-5 per cent, of HNO 3 , we divide the former percentage by the 
 latter and obtain the quotient 2 '52. This tells us that 100 parts of the 
 concentrated acid and 152 parts of water will give us 252 parts of acid of 
 the required strength. 
 
 If, on the other hand, the question is to prepare 500 grams of acid of sp. 
 gr. I '208 from acid of sp. gr. I "476, we calculate as follows : 
 
 . 
 
 This tells us that 198 grams of the concentrated acid with 302 cc. of water 
 will give the required amount of dilute acid. 
 
 Q 
 
226 PREPARATION OF NITRO-DERIVATIVES [CH. xvn 
 
 is solid, it is either pulverised or dissolved in a little water, alcohol, 
 ether, or acetic acid. If the action proceeds with difficulty only, 
 the substance may be added to the nitric acid, and the latter may 
 be warmed if necessary. In some cases the pure acid of the 
 composition HNO 3 is used. 
 
 3. Preparation of Nitro-Derivatives of Bases. The above 
 method holds for almost all aromatic substances excepting amines. 
 The amine group interacts with the acid before the nitro-body can 
 be formed, and so nitro-amines are not produced. 
 
 This undesirable secondary action does not take place in presence 
 of a large excess of sulphuric acid, and it can also be avoided by 
 replacing one or both of the hydrogen atoms of the NH 2 by organic 
 radicals. Nitric acid, in presence of sulphuric acid, forms chiefly 
 meta-compounds while acetyl and benzoyl derivatives give chiefly 
 ortho- and para-compounds. 
 
 N biting and Collin (Ber. 17, 561) have stated that in presence 
 of sulphuric acid meta-compounds are formed exclusively. But 
 later investigations have shown that, although the meta-compound 
 is always the chief product, it is not invariably the only one. 
 
 Hiibner (Ber. 10, 1,706) dissolved sulphate of aniline in a large 
 quantity of cold concentrated sulphuric acid, and added drop by 
 drop the calculated amount of nitric acid largely diluted with 
 sulphuric acid. Water was then added, the mixture being kept 
 cool during the process, and the acid was neutralised with car- 
 bonate of soda. The precipitated nitranilines were separated by 
 driving the ortho- and meta-compounds over with steam, while the 
 para-compound remained behind, not being volatile with water 
 vapour. 
 
 When nitric acid acts on /-toluidine in presence of ten parts of 
 concentrated sulphuric acid, two nitrotoluidines, melting at 114 and 
 78 respectively are formed. If fifteen or twenty or more parts of 
 sulphuric acid are taken, the nitro-compound melting at 78 is 
 formed alone. To prepare this substance (Ber. 17, 263) /-toluidine 
 (100 gr.) is dissolved in sulphuric acid sp. gr. 1*842 (2,000 gr.) in a 
 strong vessel. The solution is cooled by means of ice and salt to a 
 temperature below o, and a mixture of nitric acid sp. gr. I '48 (75 gr.) 
 and sulphuric acid sp. gr. 1*84 (300 gr.) is allowed to flow into the. 
 well-stirred solution. The temperature must not be allowed to 
 exceed o by more than a few degrees. The lower the temperature, 
 the purer the product will be. When all the acid has been added 
 
3] PREPARATION OF NITRO-DERIVATIVES OF BASES 227 
 
 the mixture is allowed to stand for a short time and is then poured 
 slowly into 5-6 litres of water which is cooled with ice, so that the 
 temperature may never exceed 25. After being filtered from im- 
 purities, this solution is diluted to 15-20 litres and neutralised 
 with solid carbonate of soda, care being taken as before to keep 
 the temperature as low as possible. If caustic soda is used, the 
 temperature rises too high. The precipitate is collected on cheese 
 cloth and pressed dry. The product is finally recrystallised from 
 alcohol. In this way from 100 grams of toluidine at least a like 
 amount of ;;z-nitrotoluidine, melting at 78, may be obtained. 
 
 Following a suggestion given later by Nolting and Stoecklin 
 (Ber. 24, 566), it is advisable to add a little urea to the solutions of 
 the bases in sulphuric acid, to decompose any nitrous acid which 
 may be formed. The yields are thereby improved, and the products 
 are purer. 
 
 Groll (Ber. 19, 198) dissolved dimethylaniline (200 gr.) in sulphuric 
 acid of sp. gr. 1*84 (4,000 gr.) and cooled the solution in a freezing 
 mixture. If less acid is taken, much of the material will become 
 resinised and thus be lost. A cold mixture of nitric acid of sp. gr. 
 r 37 ( ! 93 g r -) an d sulphuric acid of sp. gr. r84 (600 gr.) is then 
 added drop by drop in such a way that the temperature does not 
 exceed +5. After the whole has remained at rest for five hours, it 
 is poured into ten litres of ice-water. ^>-Nitrodimethylaniline is pre- 
 cipitated, and the quantity increases when soda is added, until the 
 colour of the liquid suddenly changes to red. At this point the 
 precipitate is filtered off. More soda is added to the filtrate, and a 
 red substance is precipitated along with sodium sulphate. About 
 160-170 grams of the former, which is w-nitrodimethylaniline, 
 can be extracted from the precipitate with alcohol. 
 
 Amido-acids can be converted into nitro-derivatives (Ber. 22, 
 292) by this method. 
 
 Nolting and Collin (Ber. 17, 262) prepared /-nitraniline by dissolving 
 acetanilide ( I kg. ) in sulphuric acid of sp. gr. i '84 (4 kg. ) and allowing 
 nitric acid of sp. gr. 1*478 (590 gr.) diluted with sulphuric acid (1,200 gr.) 
 to flow in slowly. During the whole operation the vessel stood in a 
 freezing mixture of ice and salt. On account of the difficulty in dissolving 
 the acetanilide in sulphuric acid, it was first dissolved in a small amount of 
 warm glacial acetic acid, and this solution, when cold, was mixed with the 
 sulphuric acid. When this mixture was poured into water, 95 per cent, of 
 the possible amount of nitracetanilide was precipitated, /-nitraniline was 
 
 Q 2 
 
228, PREPARATION OF NITRO-DERIVATIVES [CH. xvir 
 
 obtained from it eventually by hydrolysis. A little o-nitraniline remains in 
 the mother-liquors. 
 
 Hiibner (Ann. 208, 2 9 2 ) obtained larger quantities of the latter by the 
 action of nitric acid on benzanilide (cf. p. 226). He added pulverised 
 benzanilide (10 gr.) gradually to nitric acid of sp. gr, 1*45 (100 gr. ) at 14, 
 and immediately poured the mixture into 12-14 times its bulk of cold 
 water. A mixture of o-nitrobenzanilide and /-nitrobenzanilide was pre- 
 cipitated with hardly any of the meta-compound, and by boiling with 
 caustic soda these were decomposed into sodium benzoate and the corre- 
 sponding nitranilines. The latter were separated by distillation in a current 
 of steam. 
 
 Mertens (Ber. 10 995) prepared dinitrodimethylaniline by dissolving 
 dimethylaniline (10 parts) in nitric acid (no parts) and water (no parts), 
 and allowing the mixture to stand for six hours. 
 
 4. Nitro-Derivatives of Easily Oxidisable Substances. Sub- 
 stances which, like quinol, are easily oxidised, cannot be treated 
 directly with nitric acid. Nietzki (Ann. 215 142) first converted 
 it into diacetylquinol, and then dissolved the acetyl derivative in 
 5-6 times as much nitric acid of sp. gr. 1*5. The acid was cooled 
 so as to keep the temperature Mow 10. After allowing the 
 solution to remain in the freezing mixture for several hours, it 
 was poured into ice-water and the dmitrodiacetylhydroquinone 
 precipitated. The acetyl groups were removed by the action of 
 cold caustic potash. 
 
 Similarly gallic acid (trioxybenzoic acid) would be oxidised by 
 nitric acid to oxalic acid, but the triethyl ether can be easily con- 
 verted into nitropyrogallol triethyl ether, carbon dioxide being lost 
 in the process (Schiffer, Ber. 25, 722). 
 
 If care is taken, nitroaldehydes can be prepared from aldehydes 
 without any acid being formed. Thus when nitric acid acts at a 
 low temperature and for a short time on w-oxybenzaldehyde, 1 nitro- 
 w-oxybenzaldehyde is formed. 
 
 Erdmann dissolved^-chlorobenzaldehyde in six parts of sulphuric 
 acid and treated it, at a temperature not exceeding 25, with 78 per 
 cent, nitric acid. The yield of ^-chloro-w-nitrobenzaldehyde was 
 quantitative. In this substance the chlorine atom is very easily re- 
 placed. In a later communication he recommends heating the 
 mixture for a quarter of an hour at 80-90 before pouring it into 
 water. 
 
 1 Ber. 22 2,348. Cf. Ber. 9, 1463, and 13, 310. 
 
5] OTHER SPECIAL CASES 229 
 
 When the substances are very sensitive still lower temperatures than 
 these must be used. Thus comparatively few nitropyrrol derivatives are 
 known because they are unable to withstand the action of the nitric acid. 
 Ciamician and Silber (Ber. 18, 1,456) found that pyrrylmethylketone was 
 entirely decomposed by nitric acid at the ordinary temperature, but by 
 taking only 5 grams at a time and dissolving it in fuming nitric acid cooled 
 to - 1 8, and then pouring the solution into ice- water, they obtained nitro- 
 pyrrylmethylketone. Three other nitro-derivatives were formed at the same 
 time. 
 
 5. Other Special Cases. In preparing nitrophenanthrene 
 Schmidt (Ber. 12, 1,154) proceeded as follows : He tried first 
 nitricacidofsp.gr. 1*5 at 10 and acid of sp. gr. 1*35 at the 
 ordinary temperature, but in both cases obtained much resinous 
 matter and very little of the desired product. Finally, he mixed 
 phenanthrene (i part) with coarse sand (3^ parts), which had 
 previously been washed with nitric acid, and stirred the mixture 
 thoroughly with nitric acid of sp. gr. i'35 (8 parts). The object of 
 the addition of sand was to enable the acid to reach every part of 
 the phenanthrene and prevent its collecting in a tough sticky mass. 
 The whole was left to itself for three or four days at 10. On 
 washing away the acid and extracting the residue with 90 per cent, 
 alcohol, about 49 per cent, of the phenanthrene was recovered as 
 mononitrophenanthrene. 
 
 In trying to prepare trinitronaphthol, Martius (Z. Ch. 1868, 82) 
 found that dinitronaphthol could be dissolved in cold nitric acid 
 without decomposition, but that on boiling the solution the substance 
 was broken down into phthalic acid and oxalic acid. So that 
 naphthopicric acid could not be obtained in this way. Later, 
 Eckstrand (Ber. 11, 162) succeeded in preparing it (cf. 12) by 
 adding dinitronaphthol to four times its weight of a mixture of equal 
 parts of fuming and ordinary nitric acid, and, with frequent stirring, 
 warming the solution for several hours in a water bath at 4-5 c > 
 care being taken that the temperature did not exceed these limits. 
 Although the whole of the substance had not even finally gone into 
 solution, the mixture was poured into water. The precipitate con- 
 sisted of a mixture of the unchanged substance with trinitronaphthol. 
 These were separated by recrystallisation. The yield was 20 per 
 cent, of the theoretical. 
 
 Mono- and dinitrothiophene were obtained by Meyer and Stadler 
 (Ber. 17, 2,648), by passing the thiophene in a current of air through 
 red fuming nitric acid. 
 
230 PREPARATION OF NITRO-DERIVATIVES [CH. xvn 
 
 6. Influence of Time and Temperature. To illustrate the 
 influence of these factors on the result of the action of nitric acid, 
 some experiments of Wehr's (Dissert. Freiburg, 1891) may be 
 mentioned. He found that /-tolylacetic acid (2 gr.) was not 
 attacked after standing for twelve hours with fuming nitric acid 
 (10 gr.). When the mixture was evaporated on the water bath, 
 mono- and dinitro-derivatives were formed. When the same 
 quantity was dissolved in glacial acetic acid (10 gr.) and warmed 
 with nitric acid of sp. gr. r$2 (10 gr.) on the water bath 
 w-;;z-dinitro-/-tolylacetic acid was obtained. Taking the same 
 quantities of the substance and of fuming nitric acid, and allowing 
 them to remain together for three weeks at the ordinary temperature, 
 he found as chief product mononitrotolylacetic acid. Under the 
 same conditions the same amount of the substance with fuming 
 nitric acid (5 gr.) and concentrated sulphuric acid (10 gr.) gave 
 dinitrotolylacetic acid. Finally, to avoid all possibility of oxidation, 
 fuming nitric acid (5 gr.) was mixed with pure sulphuric acid, H 2 SO 4 
 (10 gr.), and cooled to 10. The tolylacetic acid (3 gr.) was added 
 cautiously so that the temperature remained below -}-io. Under 
 these circumstances, ;;z-;/z-dinitro-/-tolylacetic acid was formed. 
 
 Bauer (Ber. 24, 2,835) found that when a solution of butyltoluene 
 in glacial acetic acid was slowly mixed with fuming nitric acid, 
 an oil was formed which could be driven over with steam and con- 
 sisted of mononitrobutyltoluene. But when the hydrocarbon itself 
 was allowed to drop into strongly cooled fuming nitric acid, and the 
 mixture was set aside at the ordinary temperature, the mono-, 
 di-, and trinitro-derivatives were produced. Trinitrobutyltoluene, 
 artificial musk, is obtained by allowing the hydrocarbon to flow 
 slowly into five times its weight of a cold mixture of nitric acid of 
 sp. gr. i '5 (i part) and fuming sulphuric acid containing 15 per 
 cent, of anhydride (2 parts), and warming the whole on the water 
 bath for 8-9 hours. On pouring the product into water the sub- 
 stance which is precipitated is not yet fully converted into the 
 trinitro-compound. To achieve this the material must be collected, 
 dried, and passed through the same process a second time. 
 
 Nietzki and Rosel (Ber. 23, 3,216) obtained tetramidotoluene. 
 They started from ;;z-toluylenediamine. This they mixed with 20 
 per cent, of nitrate of urea and added to nitric acid distilled over 
 sulphuric acid, keeping the temperature between 5 and 10. This 
 gave dinitrodiamidotoluene along with a little of the mononitro- 
 derivative. The former gave the required substance on reduction. 
 
;, 8] ACTION OF DILUTE NITRIC ACID 231 
 
 7. Use of Nitric Acid containing 100 per cent. HN0 3 . 
 
 Nietzki and Hagenbach's work (Ber. 20,333) shows that pure HNO 3 
 is required for preparing many nitro-compounds. Thus they found 
 that the action of nitric and sulphuric acids and of fuming nitric acid 
 of sp. gr. i '52 simply converted diacetyl-;-phenylenediamine into 
 the mononitro-derivative. Dinitrodiacetylphenylenediamine required 
 the use of nitric acid containing 100 per cent, of HNO 3 for its forma- 
 tion. This acid is best prepared by distilling fuming nitric acid 
 with twice its weight of sulphuric aci'd. Its sp. gr. at 15 is 1*533. 
 
 According to L. Meyer (Ber. 22, 23), however, the only way to 
 obtain nitric acid perfectly free from water, is to add nitric anhy- 
 dride in excess to the acid got by distillation over sulphuric acid, 
 determine the excess of the anhydride by titration, and add the 
 amount of more dilute acid shown by the analysis to be required. 
 
 Meyer (J. pr. Ch. 114, 342) prepared the anhydride by distilling 
 almost anhydrous nitric acid over phosphorus pentoxide. Very 
 little heat is giving out on mixing the ingredients. 
 
 The action of nitric anhydride itself is much more violent than 
 that of the strongest nitric acid, but the products are the same in 
 both cases. 
 
 8. Action of Dilute Nitric Acid, The investigations of 
 Norton and Allen (Ber. 18, 1,995) show that the general impres- 
 sion, that dilute nitric acid usually acts as an oxidising agent 
 towards organic bodies, is incorrect. As early as 1859 Fritzsche 
 (Ann. 110, 151) had shown that when phenol (2 parts) is dissolved 
 in warm water (100 parts) and fuming nitric acid (3 parts) is 
 added, a large amount of nitrophenol is obtained. But this 
 remained an isolated statement. Norton and Allen used nitric acid 
 of sp. gr. i '029, which contained therefore only about 4 per cent, of 
 the acid. On boiling i gram of methylacetanilide in 100 cc. of 
 this for two hours, dinitromethylaniline was deposited when the 
 solution cooled. Even when acid of only half the above strength 
 was taken the same compound was formed with somewhat greater 
 difficulty. Dinitroethylacetanilide was prepared in the same way. 
 Phenylacetanilide gave trinitrodiphenylamine. To obtain the same 
 substance from phenylbenzanilide the boiling had to be continued 
 for several days. Even then a good deal of unchanged substance 
 was recovered. It is probable that the more easily the acid radical 
 is removable from the anilide, the easier it is to form the nitro- 
 compound. 
 
 Lellmann and Donner (Ber. 23, 169) tested the action of nitric 
 
232 PREPARATION OF NIT RO-DERIVATIVES [CH. xVii 
 
 acid on phenacyltoluidine. They found that a 22 per cent, acid 
 gave the mononitro-compound 
 
 CH 3 . C C H 3 (N0 2 ) . NH . CH 2 . CO . C 6 H 5 , [CH 3 : NO 2 : NH . = 
 
 i : 3 ' 4], 
 
 while a 65 per cent, acid introduced two nitro-groups. 
 
 9. Action of Nitric Acid on Fatty Bodies, The resem- 
 blance of fatty tertiary alcohols to the phenols might render the 
 formation of nitro-derivatives of this class of substances not unex- 
 pected. In both classes the group COH is connected with carbon 
 only. In order that oxidation may take place the molecule must 
 be broken up, a circumstance which would therefore favour the 
 other possibility. Taking these things into consideration Haitinger 
 (Ann. 193, 368), at the instigation of Lieben, examined the action 
 
 /-'TT \ /f~"TJ 
 
 of nitric acid on tertiary butyl alcohol, /-rr 3 yC\ <-\ri*- By run- 
 
 \^ rl 3 / \^ -M- 
 
 ning the alcohol gradually into the cooled nitric acid, the method 
 which experience showed to be the best, he obtained nitrobutylene 
 as an oil, which was dried with anhydrous calcium nitrate. The 
 yield was 8-10 per cent, of the alcohol used. In another paper 
 (M. f. Ch. 2, 286), he describes the preparation of the same sub- 
 stance by leading isobutylene gas in a slow stream into an absorption 
 tower. Nitric acid is allowed to trickle through the latter at such 
 a rate that the liquid flowing out at the foot is green in colour. 
 Hardly any nitroethylene can be made by this method. 
 
 10. Use of Ether as a Solvent, This solvent was used by 
 Benedikt (M. f. Ch. 3, 386). He dissolved pyrocatechin (10 gr.) in 
 ether (500 cc.) and added fuming nitric acid (4 cc.). After the 
 substances had remained in contact for twenty-four hours, mono- 
 nitropyrocatechin was found in the ether. When eugenol was 
 treated in the same way the yield of nitroeugenol was almost 
 quantitative. The product was extracted by adding alcoholic 
 caustic potash to the reddish-brown liquid until all the nitric acid 
 was precipitated as potassium nitrate. This was removed by filtra- 
 tion, and the addition of caustic potash was continued as long as 
 the red precipitate of nitroeugenol-potassium increased in quantity. 
 The salt was finally dissolved in water and decomposed with 
 sulphuric acid. 
 
n, 12] MIXTURE OF NITRIC AND SULPHURIC ACIDS 233 
 
 11. Use of Acetic Acid as a Solvent, The use of acetic acid 
 has already been mentioned. It seems to be very valuable in many 
 cases, because in its presence the calculated amount only of nitric 
 acid need be taken. Thus Cosak (Ber. 13, 1,088) dissolved 
 /-acettoluide (10 gr.) in glacial acetic acid (45 gr.) and added the 
 calculated amount of nitric acid of sp. gr. 1*47 (37 gr.). In such a 
 case the formation of a dinitro-derivative is almost an impossibility, 
 since the nitric acid is not present in excess, and besides its action 
 is weakened by the acetic acid. 
 
 Stadel and Kolb (Ann. 259, 210) mixed w-cresol (140 gr.) with 
 glacial acetic acid (140 gr.), cooled the mixture to - 5, and allowed a 
 slow stream of a solution of nitric acid of sp. gr. 1*5 (200 gr.) in 
 acetic acid (400 gr.) cooled to 15 to flow into it. During the hour 
 and a half that this operation lasted the temperature never rose 
 above 1. The reddish-brown liquid was then poured into a 
 kilogram of ice, and water (i| kg.) was added. After the lapse of 
 twelve hours, the crystals were collected on a filter, and the filtrate 
 was extracted with ether. The crystals left on evaporation of the 
 latter were distilled with steam. 39+12 grams of volatile, and 
 47 + 18 grams of non-volatile, nitro-;;/-cresol were obtained. 
 
 12, Use of Mixture of Nitric and Sulphuric Acids, This 
 
 mixture is used even more frequently than that with acetic acid. 
 The constituents of the acid used by Schonbein (Pogg. Ann. 70, 320), 
 in 1846, for preparing gun cotton were concentrated sulphuric acid 
 of sp. gr. r846 and nitric acid of sp. gr. 1*385- 1*440. According to 
 Friedlander, 1 it has entirely taken the place of the expensive fuming 
 nitric acid in manufacturing operations, on account of the incon- 
 veniences attending the employment of the latter and the fact that 
 the powerful attraction of sulphuric acid for water permits the use 
 of little more than the theoretical amount of nitric acid, and none is 
 wasted. 
 
 The mixture is used in the same way as nitric acid itself. The 
 nitro-compounds of benzene, toluene, and xylene are prepared in 
 the cold, while in the case of naphthalene a temperature of 40-50 
 is required. Dinitrobenzene is formed when the mixture acts on 
 nitrobenzene in the heat. 
 
 According to Armstrong and Rossiter (Proc. Ch. Soc. 1891, 
 87-89 ; Ber. 24, 72 1"), the sulphuric acid, besides keeping up 
 
 1 Fortschrilte der Teerfarbenfabrikation, 3 
 
234 PREPARATION OF NITRO-DERIVATIVES [CH. xvn 
 
 the concentration of the nitric acid, has also an influence in direct- 
 ing the course of the action. 
 
 In laboratories the proportions of the acids used frequently vary 
 from those used in chemical works. Thus Schultz (Ann. 174, 221) 
 placed diphenyl (3 gr.) in a flask, and covered it with nitric acid of 
 sp. gr. i '4 5 (6 gr.) and sulphuric acid (i gr.). The action was 
 completed by boiling the mixture, which, on cooling, deposited a 
 mass of crystals, consisting of dinitrodiphenyl entirely free from ts 
 isomers. The crystals were collected on a filter, washed with 
 water, and boiled several times with alcohol. 
 
 Bladin (Ber. 25, 742) boiled phenyltriazole carboxylic acid (10 
 gr.) with fuming nitric acid (100 gr.) and sulphuric acid (50 gr.) for 
 eight or ten minutes. On pouring the liquid into ice-water, nitro- 
 phenyltriazole carboxylic acid (ii'5 gr.) was obtained 
 
 NO 2 .C G H 4 .N-N 
 COOH.C CH 
 
 V 
 
 N 
 
 The addition of fuming sulphuric acid in preparing artificial musk 
 has already been mentioned ( 6). 
 
 Here, as usual, temperature has an important influence on the 
 course of the action and on the yield. 
 
 In preparing nitro- derivatives of azoxybenzene, Klinger and 
 Zuurdeeg (Ann. 255, 319) found that when the substance (20 gr.) 
 was covered with nitric acid of sp. gr. 1*50 (200 gr.) and sulphuric 
 acid of sp. gr. i'8o (100 gr.) and the mixture was immediately 
 poured into water, the product was extremely resinous. But when 
 the ingredients were cooled during the operation, the trinitroazoxy- 
 benzene separated out free from resinous matter in the course of 
 twenty-four hours. From 60 grams of azoxybenzene, with the tem- 
 perature at -20, they got 55 grams of the crude product. With 
 the temperature at - 10, they got only 35 grams ; while working 
 at + 10, nothing separated from the mixture at all. 
 
 Trinitronaphthol (cf. 5) was prepared by Diehl and Merz 
 (Ber. 11, 1,661), as follows : They mixed finely pulverized dinitro- 
 naphthol with excess of sulphuric acid, cooled the mixture, and 
 added a solution of fuming nitric acid in sulphuric acid. After the 
 liquid had remained at rest for some time it was poured into ice- 
 water. The most of the precipitate was trinitronaphthol. They 
 tried to improve the yield by varying the proportions of the acids. 
 
13] USE OF SODIUM AND POTASSIUM NITRATES 235 
 
 Finally, they found that dinitronaphthol (loogr.) with nitric acid 
 (25 cc.) and sulphuric acid (1,500 gr.), after standing for ten days, 
 gave 83*9 per cent, of the theoretical yield of the product. The 
 mass stood for that length of time in cold water, and was stirred 
 periodically, a point which seemed to be of material importance. 
 
 The use of nitric acid or of the mixture may make a great 
 difference in the relative amounts of the various isomers obtained. 
 Thus, according to Nolting (Ber. 18, 2,672), toluene gives with 
 nitric acid alone chiefly/-nitrotoluene (66 per cent.), while with the 
 mixed acids it gives chiefly the ortho-compound (60-66 per cent.). 
 Probably the temperature and strength of the acids likewise make 
 a difference in the proportions of the isomers formed. These facts 
 are of great importance from a technical point of view. Baeyer's 
 synthesis of indigo, for example, cannot be employed on economical 
 grounds, because in preparing the orthonitrocinnamic ether so 
 much of the comparatively valueless para-compound is formed at 
 the same time (Caro, Ber. 25, 987^). 
 
 13. Use of Sodium and Potassium Nitrates. Many substances 
 
 which yield nitro-compounds with difficulty can be successfully 
 treated by adding first sulphuric acid and then saltpetre or vice versa. 
 This method used to be a favourite one. For example, Gerland 
 (Ann. 91, 187) prepared nitrobenzoic acid by mixing benzoic acid 
 with twice its weight of saltpetre and adding an equal quantity of 
 concentrated sulphuric acid. The yield is stated to be good. The 
 method seems recently to have recovered its popularity. 
 
 The preparation of ^-nitro-w-chlorobenzaldehyde by Erdmann 
 has already been mentioned. Eichengriin and Einhorn (Ann. 262, 
 136) obtained the orthonitro-compound by cooling a solution of 
 sodium nitrate (11 gr.) in sulphuric acid (200 gr.) and adding drop 
 by drop w-chlorobenzaldehyde (15 gr.) from a pipette with a 
 capillary opening, and continuously stirring the solution during 
 the addition. It is best to keep the temperature below cr. When 
 the mixture is poured into ice, some hours after the completion of 
 the action, the compound is deposited in crystalline form. 
 
 Timber (Ber. 23, 795) dissolved pure benzidine sulphate (28*2 gr. 
 = T V mol.) in sulphuric acid (300 gr. ), warming the mixture slightly to 
 facilitate the solution, and then cooling it to 10-20. This temperature is 
 not low enough to cause a re-deposit of the sulphate. He then added 
 gradually potassium nitrate (2O'2 gr. = $ mol.), stirred the mixture for 
 several hours, and then poured it into three times its weight of water. A 
 
236 PREPARATION OF NITRO-DERIVATIVES [CH. xvn 
 
 small amount of a yellow precipitate is removed by filtration, and the m- 
 dinitrobenzidine is precipitated from the filtrate with soda. 
 
 When oxyazobenzenesulphonic acid is dissolved in concentratedsulphuric 
 acid of sp. gr. I '842 at 10-20, potassium nitrate is added to the well- 
 stirred solution, the stirring being continued for two hours, and the mixture 
 is finally poured into water, a quantitative yield of nitroxyazobenzenesul- 
 phonic acid is obtained. 
 
 Seitz (Ber. 22, 257) prepared a dinitro-compound of /3-naphthoquinaldine 
 by mixing the dry nitric acid salt of the base with concentrated sulphuric 
 acid. 
 
 When the substance is acted on by nitric acid with difficulty, it may be 
 dissolved in sulphuric acid and the solution heated to 100 before the cal- 
 culated amount of potassium nitrate is added. 
 
 14, Separation of Nitre-Compounds from Acid Solutions in 
 which they are formed, A few general remarks on this subject 
 may not be out of place here. Cases have already been mentioned 
 in which the compounds crystallise out directly. In others, we 
 have seen, the product separates when the solution is poured into 
 water. When neither of these methods is successful, the nitro- 
 compounds can be extracted from the solution in water by means 
 of ether. To avoid this labour, or in cases where the extraction 
 cannot be carried out, the nitric acid can be cautiously evaporated 
 on the water bath, alcohol being added from time to time to prevent 
 the acid becoming too concentrated, or else the acid may be 
 neutralised with sodium carbonate before the evaporation begins, 
 and the dry residue may then be extracted with alcohol, ether, or 
 other suitable medium. 
 
 When Suida and Plohn (M. f. Ch. 1, 182) prepared nitroethyl- 
 phenol by addition of fuming nitric acid to ethylphenol and dilution 
 with water, most of the product was at once precipitated. The 
 portion which remained dissolved was obtained by neutralising 
 with ammonia and precipitating with lead acetate. The insoluble 
 salt was very explosive and was decomposed by addition of acid to 
 the moist compound. 
 
 15, Less Common Methods of Preparing Nitro-Compounds. 
 
 A very generally applicable method is to dissolve the substance 
 in glacial acetic acid and conduct into the solution the gases given 
 off on heating lead nitrate. 
 
 The oxidation of nitroso-bodics also gives nitro-compounds. Thus 
 Schraube (Ber. 8, 620) treated nitrosodimethylaniline with alkaline 
 
1 5 ] LESS COMMON METHODS 237 
 
 solutions of potassium ferricyanide and of potassium permanganate. 
 He prepared nitrodimethylaniline in both those ways, and extracted 
 it from the solution with ether. As the product can only be extracted 
 with difficulty by ether, Wurster (Ber. 12, 529), who repeated the 
 experiments with permanganate, recommended the evaporation of 
 the mass to dryness and extraction of the residue with benzene 
 
 (CH 3 ) 2 N . C 6 H 4 . NO + O = (CH 3 ) a N . C C H 4 . NO 2 . 
 
 Sodittm nitrite in acid solution has likewise the power of produc- 
 ing nitro-derivatives. For example, Niementowsky (Ber. 20, 
 1,890) dissolved tetramethyldiamidotoluene in glacial acetic acid, 
 and added a solution of sodium nitrite as long as any fresh turbidity 
 appeared. When the precipitate had been recrystallised from 
 petroleum ether it was found to be, not the expected nitrosamine, 
 but mononitrotetramethyldiamidotoluene 
 
 QH 2 (CH 3 )[N(CH 3 ) 2 ] 2 (N0 2 ); [CH 3 : N(CH 3 ) 2 : NO 2 = i : 3 and 4 : ?]. 
 
 Deninger (J. pr. Ch. 148, 298) likewise succeeded in preparing 
 nitro-compounds from amines and phenols by means of nascent 
 nitrous acid. Of course, the amines are converted through the 
 diazo-stage into phenols by this process. 
 
 The yields, which are often very good, depend on the conditions 
 of experiment. In the case of aniline (iogr.), the substance is 
 dissolved in concentrated sulphuric acid (20 cc.) and water (80 cc.), 
 and the solution is cooled to 15. Commercial sodium nitrite 
 (300 gr.) dissolved in water (100 cc.) is then added. During the 
 addition of the first third of the nitrite the solution is cooled, the 
 remainder is then poured in rapidly without cooling. The mixture 
 is then placed in a large vessel on a water bath and boiling dilute 
 sulphuric acid (i :i) is added as rapidly as the violent action will 
 permit. When the interaction is over, the ortho-compound can be 
 driven over with steam. The para-compound is isolated from the 
 residue by recrystallisation from water or hydrochloric acid. The 
 yield is 47 grams ortho- and 3*3 grams paranitrophenol. 
 
 When substances are employed in which the para-position is 
 occupied, the yield is almost quantitative. Thus 50 grains of 
 toluidine give 70 grams of dinitrodicresol. 
 
 When salicylic acid (i mol.) is suspended in water and sodium 
 nitrite (2 mol.) is added, the acid goes gradually into solution. On 
 mixing this solution with sulphuric acid until the temperature has 
 reached 60, heating the mixture on the water bath till nitrous 
 fumes cease to be evolved, and then allowing the mass to cool, a 
 
238 PREPARATION OF NITRO-DERIVATIVES [CH. xvn 
 
 deposit of salicylic acid and asymmetrical nitrosalicylic acid is 
 formed. The yield of the latter is 80 per cent. By working in 
 glacial acetic acid solution the yield is improved ; 10 grams of 
 salicylic acid give 1 1 grams of the nitro-acid. 
 
 In a later communication Deninger (J. pr. Ch. 150, 550) states 
 that, while nitric acid gives rise almost exclusively to the asym- 
 metrical nitrosalicylic acid melting at 228, and yields but little of 
 the isomer melting at 144, his process permits of the preparation 
 of either of these substances, the yield being in each case better 
 than by any previously known method. His method likewise gives a 
 90 per cent, yield of nitro-/-oxybenzoic acid [COOH : NO 2 : OH = 
 1:3:4]. To obtain asymmetrical w-nitrosalicylic acid [COOH : OH : 
 NO 2 =i : 2 : 5], salicylic acid (100 gr.) and sodium nitrite (130 gr.) 
 are mixed with water (150 cc.), and sulphuric acid of sp. gr. 1*52 
 (1,200 cc.) is slowly added. The temperature of the acid must not 
 exceed 1 5. After a lapse of four hours the mixture is warmed to 
 50, and allowed to stand until nitrous fumes cease to be evolved. 
 Finally, the mass is warmed on the water bath. The crystals 
 which separate on cooling are collected on a filter, washed, and 
 recrystallised twice from water. The yield is 85 grams. 
 
 The ;;z-nitrosalicylic acid [COOH : OH : NO 2 = 1 12 : 3] is obtained 
 by mixing salicylic acid (loogr.), sodium nitrite (170 gr.), and water 
 (150 cc.), and adding rapidly warm (6o c ) sulphuric acid of sp. gr. 
 1*52 (i 1.). As the action is very violent, a large vessel, which 
 stands from the beginning on the water bath, must be taken. If 
 the mass does not become red by this treatment an extra 100 cc. of 
 sulphuric acid must be added. The material which separates on 
 cooling is removed by filtration and boiled for some time with 
 animal charcoal. The nitrophenol which is always formed is 
 removed by this process. A second crystallisation from water 
 gives 70-80 grams of the required isomer, melting at 144. 
 
 Goldschmidt (M. f. Ch. 2, 250) attempted to obtain isomers 
 of already known nitropyrenes by superposing an ethereal solution 
 of the pure hydrocarbon on a moderately concentrated solution of 
 potassium nitrite in water, and adding sulphuric acid slowly through 
 a dropping funnel. An already known dinitropyrene along with a 
 small amount of a mononitro-compound were the only products 
 however. 
 
 In the course of his researches on diazo-bodies, Griess showed 
 that they give dinitrophenols on being warmed with nitric acid. 
 This explains the fact that when amines are heated with nitric acid 
 
15] LESS COMMON METHODS 239 
 
 they give dinitrophenols. This action was first noticed by Ballo 
 (Z. Ch. 1870, 51), who obtained dinitronaphthol by mixing naphthyl- 
 amine and nitric acid, and allowing them to become warm spon- 
 taneously. He explained this at the time by giving the extraor- 
 dinary equation 
 
 The yield by this method is so good in this particular case that 
 it is said to be still in use for technical purposes. 
 
 Nolting and Wild (Ber. 18, 1338) tried successfully to pre- 
 pare mononitrophenols by the action of one molecular proportion 
 of nitric acid on diazo-bodies. Thus they converted aniline into 
 nitrophenol. Aniline (93 gr.) was dissolved in concentrated sul- 
 phuric acid (150 to 200 gr.) and water (2 1.), and the solution having 
 been cooled with ice, sodium nitrite (69 gr.) was added. After the 
 lapse of a short time nitric acid of sp. gr. i'335 (119 gr. = 63 gr. 
 HNO 3 ) was added, and the whole was heated in a flask attached to 
 a reflux condenser until the evolution of nitrogen had ceased. The 
 ^-nitrophenol was then distilled off with steam, and the ^-nitro- 
 phenol which remained behind was purified by recrystallisation from 
 water.. An excellent yield, consisting of almost equal quantities of 
 the isomers, was obtained. The action is represented by the 
 equation 
 
 Paratoluidine, 0-toluidine and naphthylamine gave good, moder- 
 ately good, and rather poor yields respectively. 
 
 Fittica (J. pr. Ch. 125, 189) obtained a fourth nitrobenzoic acid by 
 dissolving benzoic acid (i mol.), in absolute ether, adding ethyl 
 nitrate (i mol.), and allowing this mixture to flow drop by drop into 
 concentrated sulphuric acid. Quantities of nitrobenzoic ether and 
 other products were formed. He prepared also in the same way a 
 nitrobenzaldehyde corresponding to this acid. 
 
 Sandmeyer's method (Ber. 20, 1,494) enables us to replace 
 aromatic amine groups by nitro-groups. Aniline (9 gr.), water 
 (50 cc.), and nitric acid of sp. gr. 1*4 (20 gr.) are mixed, and to the 
 cooled solution sodium nitrite (15 gr.) dissolved in water (50 cc.) is 
 added. This mixture is poured slowly into a flask containing the 
 solution of cuprous salt, and the mass is allowed to remain for an 
 hour during the evolution of the nitrogen. Nitrobenzene (5 gr.) was 
 finally isolated by distillation. 
 
240 PREPARATION OF NITRO-DERIVATIVES [CH. xvn 
 
 The solution of cuprous salt for such purposes is prepared as 
 follows : Crystallised cupric sulphate (50 grams) (2 mol.) and ordi- 
 nary grape sugar (15 grams) are dissolved in 100 cc. of warm water, 
 and to the boiling liquid a cold solution of 20 grams of caustic soda 
 in 60 cc. of water is added. The mixture is shaken until all the 
 copper has been reduced to the cuprous state, and then the mass 
 is rapidly cooled. The excess of caustic soda is finally neutralised 
 by the addition of an equivalent amount, or slight excess, of acetic 
 acid. 
 
 It may be mentioned in closing this paragraph that Ihrfeld (Ber. 
 22, 692^) found that benzenesulphonamidoacetic acid, C 6 H 5 . SO 2 . 
 NH . CH 2 . COOH, with fuming nitric acid gave a nitroso-derivative, 
 C 6 H 5 . SO 2 . N(NO) . CH 2 . COOH, instead of a nitro-compound. 
 
 16. Nitre-Compounds of the Fatty Series. As we have already 
 stated, nitro-compounds of the fatty series can be obtained by the 
 use of silver nitrite only, although Kolbe (J. pr. Ch. 113, 427) has 
 shown that its place can sometimes be taken by potassium nitrite. 
 The method was discovered by V. Meyer (Ann. 171, 18), and the 
 few compounds of this class known before his work began are 
 mentioned in the first page of his paper. 
 
 To prepare the silver nitrite, he recommends mixing lukewarm 
 concentrated solutions of silver nitrate (2,400 gr.) and potassium 
 nitrite (1,500 gr.), and allowing the mixture to cool. The precipitate 
 of silver nitrite is then collected on a filter and rapidly washed. 
 
 In making nitroethane he places the silver nitrite (2,090 gr.) in a 
 large round-bottomed flask, closed by a cork provided with two 
 holes. A long wide condenser passes vertically through one of the 
 openings. A funnel to hold the ethyl iodide, provided with a stop- 
 cock, passes through the other. In this work silver and iodine can- 
 not be replaced by cheaper materials. A trial with lead nitrite was 
 unsuccessful, and ethyl bromide, chloracetic acid, and ethylene 
 bromide were found to be without action on silver nitrite even at 
 the boiling temperature. 
 
 The ethyl iodide (1,700 gr.) is then allowed to flow into the flask. 
 During this process the flask is not disturbed, as it is important that 
 the silver nitrite should be gradually penetrated by the iodide. The 
 iodide is admitted at such a rate that the liquid boils vigorously, 
 but not too violently. The mass is finally wanned for some time 
 on the water bath. When this method is pursued, the annoying 
 aggregation of the silver nitrite into lumps is avoided, and admix- 
 
16] NITRO-COMPOUNDS OF THE FATTY SERIES 241 
 
 ture with sand to prevent this is rendered unnecessary. The presence 
 of sand interferes greatly with the recovery of the silver, causing 
 frothing over of the mass when the iodide is fused with soda. The 
 nitroethane is isolated by fractional distillation. The yield is about 
 50 per cent., and it appears that approximately equal amounts of 
 nitroethane and ethyl nitrite are found. 
 
 The reaction failed in the cases of allyl iodide, methylene iodide, 
 and similar substances. Oils containing nitrogen were formed 
 which could not be purified. Twenty years later Meyer found that 
 these oils gave pure sodium salts of nitrohydrocarbons on addition 
 of sodium ethylate. He continued the experimental investigation in 
 association with Askenasy (Ber. 25, 1,701). They dissolved allyl 
 iodide in two or three times its bulk of ether, and then treated it 
 with silver nitrite. The almost colourless solution of the product 
 was filtered from the precipitate, and the latter was extracted with 
 ether. After standing for six hours the solution deposited some 
 more silver iodide. It was filtered again, and twice its volume of 
 absolute alcohol and then sodium ethylate were added. The pre- 
 cipitate was dried on clay plates, and the nitropropylene was set 
 free by dissolving it in water, adding the calculated amount of 
 dilute sulphuric acid and extracting with ether. 1 
 
 The preparation of dinitro-compounds could only be achieved 
 indirectly. Thus Meyer and Locher (Ber. 7, 1,617) prepared propyl 
 pseudonitrole by the action of nitrous acid on secondary nitropropane, 
 and by oxidising the former with chromic acid obtained dinitro- 
 propane. 
 
 CHg CHg C/Hg 
 
 I H <L_NO I NO, 
 
 I NO, | NO, ' | NO.; 
 
 CHg CHjj CHg 
 
 Forcrana (C. R. 88, 974) obtained nitroacetic ether by the action 
 of silver nitrite on bromacetic ether, but could not purify it on 
 account of the tendency of the liquid to decompose. 
 
 At the suggestion of Kolbe, Preibisch (J. pr. Ch. 116, 316) experi- 
 mented on the action of potassium nitrite (3 parts) on chloracetate 
 of potassium (i part). The concentration of the solutions seems to 
 have no influence on the yield, but to avoid violent foaming it is 
 
 1 In regard to the constitution of fatty nitro-compounds cf. Nef. Ann. 
 
 280 263. 
 
242 PREPARATION OF NITRO-DERIVATIVES [CH. xvn 
 
 best to use dilute solutions. When 100 grams of chloracetic acid 
 are used, the yield of nitromethane is one-half of the theoretical, 
 with larger amounts only one-third. The nitroacetic acid is very 
 unstable, and changes immediately into nitromethane with loss of 
 carbon dioxide 
 
 Cl . CH 2 . COOK + KNO.-KCl + NOa . CH 2 . COOK, 
 NO 2 . CH 2 . COOK + H 2 6 = CH 3 N0 2 +KHC0 3 . 
 
 Bewad (Ber. 24, 973) succeeded in preparing tertiary nitrohydro- 
 carbons of the fatty series by a very complicated process. Villiers 
 (C. R. 94, 1,122) made tetranitroethylene bromide by the action of 
 fuming nitric acid on an equal volume of ethylene bromide, but the 
 isolation of the product presented great difficulties. Losanitsch 
 (Ber. 15, 472, and 16, 2,731), by the action of concentrated nitric 
 acid on tribromoaniline, obtained a product by the disruption of the 
 aromatic ring, which turned out to be dibromodinitromethane. 
 
CHAPTER XVIII 
 
 OXIDATION 
 
 1, Oxidising Agents. The following substances are used as 
 oxidising agents. They will be discussed in alphabetical order. 
 
 Air. 
 
 Arsenic acid. 
 
 Azobenzene. 
 
 Barium peroxide. 
 
 Bleaching powder. 
 
 Bromine. 
 
 Chloranil. 
 
 Chloric acid. 
 
 Chloride of iodine. 
 
 Chlorine. 
 
 Chromic acid. 
 
 Chromyl chloride. 
 
 Copper solution alkaline. 
 
 Cupric acetate. 
 
 Cupric oxide and hydroxide. 
 
 Cupric sulphate. 
 
 Ferric chloride. 
 
 Ferric hydroxide. 
 
 Hydrogen peroxide. 
 
 Hydroxylamine. 
 
 Internal oxidation. 
 
 Lead monoxide. 
 
 Lead peroxide. 
 
 Manganese dioxide. 
 
 Mercuric acetate. 
 
 Mercuric chloride. 
 
 Mercuric nitrate. 
 
 Mercuric oxide. 
 
 Nitrobenzene. 
 
 Nitric acid. 
 
 Nitrous acid. 
 
 Oxygen. 
 
 Ozone. 
 
 Platinum tetrachloride. 
 
 Potassium bichromate. 
 
 Potassium chlorate. 
 
 Potassium ferricyanide. 
 
 Potassium hydroxide. 
 
 Potassium iodate. 
 
 Potassium manganate. 
 
 Potassium permanganate. 
 
 Soda-lime. 
 
 Sodium bichromate. 
 
 Sodium nitrite. 
 
 Sodium peroxide. 
 
 Silver acetate. 
 
 Silver nitrate. 
 
 Silver oxide. 
 
 Sulphuric acid. 
 
 Tin tetrachloride. 
 
 Zinc permanganate. 
 
 R 2 
 
244 OXIDATION [CH. xvm 
 
 2. General Remarks. The very large number of substances 
 which has been used for the oxidation of organic bodies illustrates 
 the diversity of effects to be produced, and makes it easy to under- 
 stand that the products may vary considerably with change in the 
 agents employed. Lieben (Ber. 8, 1,020) was probably the first to 
 examine this question. At his suggestion Reichardt investigated 
 the action of different agents on soluble starch. He found that 
 potassium permanganate in neutral, alkaline and acid solutions, as 
 also chromic acid, act upon it energetically, but all alike give 
 rise to dirty brown, unpleasant products. Experiments with chlorine 
 and alkaline copper solution gave no better results. On the other 
 hand, by warming the solution of starch with bromine, and after- 
 wards treating the product with silver oxide, gluconic acid was 
 obtained. Nitric acid in the heat gave carbon dioxide and oxalic 
 acid. Fuming nitric acid gave a mononitro-derivative of starch. 
 
 With manganese dioxide and sulphuric acid, aniline gives am- 
 monia and very little quinone. Chromic acid mixture gives a 
 quantitative yield of the latter. Potassium permanganate in alka- 
 line solution gives azobenzene, ammonia, and oxalic acid. In acid 
 solution it gives aniline-black, which, with more energetic oxidation, 
 is converted into quinone. In neutral solution, nitrobenzene and 
 azobenzene are the chief products. Boiling bleaching powder solu- 
 tion likewise gives nitrobenzene. Hydrogen peroxide in presence 
 of weak acids gives ammonia and dianilidobenzoquinoneanilide. 
 In presence of strong acids it seems to give an induline derivative. 
 
 Schmiedeberg and Harnack (A. Path. Pharm. 6, 101) state that 
 efforts to oxidise choline with permanganate and with chromic acid 
 led to negative results. But when concentrated nitric acid was 
 used, muscarine was easily obtained. 
 
 It has long been known that w-xylene, C 6 H 4 (CH 3 ) 2 , is not attacked 
 by dilute nitric acid, but that chromic acid mixture converts it into 
 isophthalic acid, C 6 H 4 (COOH) 2 . Paraxylene, however, is oxidised 
 by the former to/-toluic acid, C 6 H 4 (CH 3 )COOH, and by the latter 
 to terephthalic acid, C r) H 4 (COOH) 2 . And finally methyl groups, 
 which stand in the ortho-position towards halogen atoms, are only 
 attacked very slowly and with extreme difficulty by acid oxidising 
 agents (Ber. 24, 3,778). 
 
 The following general statements may be useful. When the 
 oxidation product is easily decomposed by further oxidation, it is 
 often possible to cover the solution with a carefully chosen extract- 
 ing agent, so that after each addition of the oxidising substance 
 
31 AIR *45 
 
 the whole may be shaken and the product removed from the 
 sphere of action of the latter. In such cases, also, the use of ice 
 to keep the temperature as low as possible may have a favourable 
 effect. 
 
 When the oxidised substance is volatile with steam, a current 
 of water vapour may be conducted through the mass during the 
 oxidation. 
 
 In many cases, where the preparation of a particular product by 
 oxidation from another substance is found to be specially hard, it 
 may be better to use some judiciously chosen derivative of the 
 substance which by proper treatment will yield the same product 
 (cf. 8, p. 248). 
 
 3. Air. The investigations of Bandrowsky (M. f. Ch. 10, 124) 
 show that not only can easily oxidisable bodies be oxidised by 
 exposure to the air in open vessels, but that the yields obtained 
 in this way may often be quantitative. By this method he oxidised 
 the hydrochlorides of paraphenylenediamine and para-amidophenol 
 in dilute solution. In the case of the first the action was repre- 
 sented by the equation 
 
 C 6 H 4 (N H 2 ) 2 + O = H 2 + C C H G N 2 , 
 
 and the yield almost reached the theoretically possible. The action 
 was considerably hastened by passing oxygen through the solution 
 or by using hydrogen peroxide. 
 
 Glaser (Ann. 154, 1 50) shook the copper salt of phenylacetylene 
 with air, in presence of alcoholic ammonia, and obtained cupric 
 oxide and diphenyldiacetylene. This extraordinary substance has 
 since been prepared by the action of potassium ferricyanide on 
 cupro-phenylacetylene (cf. 39). 
 
 Oxidation by means of air has attained increased importance 
 since Hofmann (Ann. 145, 358) discovered that by its means 
 alcohols can be oxidised to aldehydes in presence of platinum. He 
 prepared by this means the till then unknown formaldehyde, a 
 substance which even now is obtainable in large quantities by this 
 method alone. 
 
 On conducting the vapour of methyl alcohol in a current of air 
 over a heated platinum spiral, he found that aldehyde was formed 
 and could be collected by passing the products through a con- 
 denser. The apparatus was improved by Tollens (Ber. 16, 917). 
 
 To Low (J. pr. Ch. 141, 323) we qwe the discovery that a super- 
 
246 OXIDATION [CH. xvm 
 
 ficially oxidised spiral of copper is more effective than platinum. 
 In place of a solution containing at most 3^ per cent, of the alde- 
 hyde, he obtained solutions containing 15-20 per cent. Low found 
 that by this method also ethers, esters, hydrocarbons, and even 
 bases could be oxidised to aldehydes. Thus ethyl ether and acetic 
 ether give acetic aldehyde, toluene gives benzaldehyde, and ethyla- 
 mine gives acetic aldehyde and nitric oxide. 
 
 Only a few months after this, Tollens (Ber. 19, 2,133) showed 
 that by retaining the platinum and conducting the air through 
 warm methyl alcohol, in an apparatus which he designed, a solu- 
 tion containing 30-40 per cent, of formaldehyde could be prepared 
 by the litre with great ease. 
 
 4, Arsenic Acid, This substance is seldom used, on account 
 of its poisonous properties, especially as the same results can be 
 achieved by other means. The old method of preparing fuchsine 
 supplies an example of its application. A mixture of aniline and 
 toluidine (Friedlander, Farbenfabrikation, p. 31) is mixed with one 
 and a half parts of a syrupy solution of arsenic acid of sp. gr. 2 - o6, 
 and the mixture, containing the white arseniates, is heated gradually 
 to 180-190. 
 
 5, Azobenzene. Parafuchsine is prepared by heating anhydro- 
 formaldehydeaniline with five times its weight of aniline, and ten 
 times its weight of aniline hydrochloride, using azobenzene as the 
 oxidising agent, for three hours at 170-200. After the excess of 
 aniline has been driven off with steam, the residue is treated with 
 dilute acid, and parafuchsine precipitated from the solution by the 
 addition of salt. 
 
 6, Barium Peroxide. This substance was employed by Lipp- 
 mann (M. f. Ch. 5, 561) for the preparation of organic peroxides. 
 Dry hydrated barium peroxide was gradually added to benzoyl 
 chloride, and the mixture was left at rest for two hours. The mass 
 was then treated with water to dissolve the barium chloride. Then 
 the benzoic acid was removed by treatment with dilute sodium 
 carbonate. Finally, the residue was extracted three times with 
 much boiling ether until the substance which remained burned 
 quietly on being heated on platinum foil. In this way he obtained 
 from 53 to 60 per cent, of the theoretical amount of benzoyl per- 
 oxide, 
 
7, 8] BROMINE 247 
 
 7. Bleaching Powder. The action of bleaching powder as an 
 oxidising agent corresponds closely with that of bromine in alkaline 
 solution. It resembles this agent also* in the fact that chloro- 
 derivatives are apt to be formed (cf. 12). According to a 
 patent specification (Ger. Pat. 21,162), orthonitrocinnamic acid may 
 be prepared by warming orthonitrobenzalacetone (20 parts) with a 
 3 per cent, solution of sodium hypochlorite (800 parts), prepared 
 from bleaching powder and soda, until the presence of hypochlorous 
 acid in the solution cannot be demonstrated. The yield is quanti- 
 tative 
 
 C c H 4\CH 2 : CH . CO . CH, + 3NaOCl - C H 4 ^ CH * : CH COONa 
 
 As soon as the action represented by the equation is complete, the 
 chloroform is separated from the liquid, and the nitrocinnamic acid 
 is precipitated with sulphuric acid and purified by recrystallisation. 
 Meyer and Bellmann (J. pr. Ch. 141, 29) examined the action of 
 bleaching powder on isatoic acid in absence of water by suspending 
 it in chloroform. They obtained an isomeric isatoic acid along 
 with much resinous matter. 
 
 8. Bromine. This agent is used both in water and in alkaline 
 solution, and frequently substances can be made by its means 
 which cannot be prepared otherwise. Its value for obtaining cry- 
 stalline oxidation products from sugar was first demonstrated by 
 Hlasiwetz (Ann. 119, 281). He heated milk sugar (i mol.) with 
 bromine (4 mol.) and water at IOO Q , removed the bromine with 
 silver or lead oxide, filtered and precipitated the dissolved metal 
 with hydrogen sulphide, and finally isolated the acid in the form of 
 a crystalline ammonium salt. Later (Ann. 122, 109), he prepared 
 the acid itself in crystalline form, found that the composition 
 corresponded to the formula C 6 H tu O 7 and named it " isodiglycol- 
 ethylenic acid." Grieshammer (Ar. Pharm. 1879, 193) obtained 
 an acid isomeric with this by the action of bromine on cane sugar. 
 
 Blomstrancl (Ann. 123, 250), in 1862, working about the same 
 time as Hlasiwetz, examined the oxidising action of bromine on 
 substances to which a ring structure is now ascribed. His views as 
 to the action of the bromine in giving rise to certain acids are of 
 historical interest. 
 
 To Fischer, however, belongs the credit of fully recognising the 
 
248 OXIDATION [CH. xvm 
 
 importance of this oxidising agent in explaining the relations 
 between, and in the synthesis of the members of the carbohydrate 
 group. He also worked out the best methods of employing the 
 agent. Thus in association with Meyer (Ber. 22, 362) he prepared 
 lactobionic acid by dissolving milk sugar (i part) in water (7 parts) 
 and adding bromine (i part) at the ordinary temperature. By 
 shaking frequently, the whole was brought into solution in the 
 course of 24-48 hours. At the end of two more days the solution 
 was warmed slightly, most of the free bromine was expelled by 
 means of a current of air, and the remainder was reduced to hydro- 
 bromic acid by means of a current of hydrogen sulphide. The 
 greater part of this was removed by boiling with albumen, and the 
 last traces were precipitated with silver oxide. After finally treat- 
 ing the solution with hydrogen sulphide once more, a filtrate was 
 obtained containing lactobionic acid C^H^Ojo. 
 
 Glycerose, the synthetic carbohydrate, he (Ber. 23, 2,125 5 20, 
 3,385) prepared as follows: Glycerol (10 gr.) and soda (35 gr.) 
 were dissolved in warm water (60 cc.), and bromine (15 gr.) was 
 added when the solution had returned to the temperature of the 
 room. On shaking the mixture the bromine dissolved and carbon- 
 dioxide was evolved. The action was complete at the end of half an 
 hour, and the solution was found to contain a large amount of 
 glycerose, C 3 H 6 O 3 , a substance which reduced Fehling's solution 
 
 C 3 H 8 O 3 + O = C 3 H 6 O 3 + H 2 O. 
 
 Its isolation from the solution as glycerosazone, by the action of 
 phenylhydrazine, presented great difficulties. He found, however, 
 that treating lead glycerate with bromine could take the place of 
 the other method of oxidation (Ber. 21, 2,634), and gave an ex- 
 cellent yield of glycerose 
 
 The metal had therefore taken the place of the hydrogen atoms 
 to be removed by oxidation, and the tendency of the metal to unite 
 with the halogen rendered the preparation of the product much 
 easier. He made the lead salt by boiling lead hydroxide, dried at 
 1 00, with 85 per cent, glycerol, precipitating with alcohol and 
 purifying the product. 
 
 Kiliani and Kleemann (Ber. 17, 1,298) added bromine (2 parts) 
 to a cold solution of grape sugar (i part) in water (5 parts), and 
 agitated the mixture at; intervals during 36 hours. By the end 
 
8] BROMINE 249 
 
 of that time all the bromine had dissolved. They then warmed 
 and shook the liquid over the naked gas flame until the odour of 
 bromine had disappeared. After the solution had cooled, it was 
 restored to its original volume by dilution. The amount of bromine 
 was then determined by analysing a measured portion of the liquid, 
 and by calculation the quantity of lead carbonate was found which 
 would suffice to neutralise the whole of the hydrobromic acid. The 
 carbonate was added a little at a time to the cold liquid, which was 
 subsequently concentrated to half its volume in an evaporating 
 dish over the naked flame. The filtrate was diluted with water, 
 enough silver oxide added to remove any remaining bromine, and 
 the lead and silver in solution were precipitated with hydrogen 
 sulphide. The filtrate, which contained the free gluconic acid, was 
 finally boiled with calcium carbonate, filtered, and evaporated. The 
 concentrated solution deposited gluconate of calcium, (C H 11 O 7 ) 2 Ca, 
 the amount formed being 70 grams from 100 grams of grape sugar. 
 
 Reformatzky (J. pr. Ch. 149, 7 1 ) prepared the anhydride cu a pentatomic 
 alcohol from diallylcarbinol, C 7 H n O(OH) 3 , and found that this substance 
 could not be oxidised any further by the use of bromine. Continuing a 
 research of Gabriel's (Ber. 22, 1,142), Rosenthal (Ber. 22, 2,987) dissolved 
 propylene-4/-thiocarbamide (3 '5 gr. ) in water (200 cc. ), neutralised the base 
 with hydrobromic acid, and added bromine water (500 cc. ). The precipitate 
 produced by these reagents was redissolved by heating on the water bath, 
 and a clear solution coloured by the excess of bromine was formed. On 
 evaporation this solution left a syrup as residue, which was dissolved in a 
 little water. This solution deposited crystals of /3-methyltaurocarbamic 
 acid (2-4 gr.). 
 
 CH 3 .CH-S v CH. 3 .CH.S0 3 H 
 
 | >C:NH + H 2 + 3 0- | 
 
 CH 2 - Nil/ CH 2 . NH . CO . NH 2 
 
 The possibility of obtaining products containing bromine is illustrated by 
 the fate of an attempt of Prager's (Ber. 22, 2,993) to oxidise ^-propylene- 
 ^-thiocarbamide by this method. 
 
 Behrend and Roosen (Ann. 251, 242) covered isobarbituric acid (4gr.) 
 with water (30 cc. ) and added bromine until a permanent red colour was 
 established, the mixture being well stirred during the process. A quantita- 
 tive yield of isodialuric acid is obtained partly by spontaneous crystalli- 
 sation, partly after evaporation over sulphuric acid. 
 
 A patented process (Ger. Pat. 21,162), for the preparation of 
 cinnamic acid, shows that the action of bromine in alkaline solution 
 
250 OXIDATION [CH. xvm 
 
 can also give almost quantitative results. Benzylideneacetone (15 
 parts) is warmed gently on the water bath with a solution of 
 bromine (48 parts) in 4 per cent, caustic soda (650 parts). When 
 the presence of hypobromous acid is no longer perceptible, the 
 interaction is complete (cf. 7). 
 
 C 6 H 5 .CH :CH . CO. CH 3 + 3NaOBr = C 6 H 5 . CH : CH . COONa 
 
 + CHBr s +2NaOH. 
 
 Fischer and Hess (Ber. 17, 563) oxidised methylindole to methyl- 
 pseudoisatoic acid by means of sodium hypobromite. A halogen 
 derivative of methylindole is first formed, which, on treatment with 
 alcoholic potash, gives the potassium salt of methylpseudoisatoic 
 acid. 
 
 9. Chloranil. This substance, which is now frequently used 
 for oxidising, is best prepared by Grabe's method (Ann. 263, 19). 
 Paraphenylenediamine, when treated with potassium chlorate and 
 hydrochloric acid, gives a yellow product which no longer contains 
 nitrogen, and consists of a mixture of tetra- and dichloroquinone 
 in the proportion of 3:1. This mixture is used directly as an 
 oxidising agent instead of isolating the pure tetrachloroquinone 
 (chloranil). 
 
 It is usually employed in solution in alcohol (Ber. 20, 515), 
 glacial acetic acid (Ber. 19, 760), or ether (Ber. 24, 1,707), or in 
 alcoholic solution acidified with acetic acid. An example of its 
 use is Levi's conversion of the leuco base of thiophene green, 
 tetramethyldiamidodiphenylthienylmethane, into thiophene green 
 by means of an alcoholic solution of chloranil. When the con- 
 densation product of benzaldehyde with dimethylaniline, freed from 
 zinc chloride, is warmed with from a half to one part of chloranil 
 at 50-60, malachite green is formed. Dilute caustic soda is used 
 to remove the chloranil, or chlorinated quinols produced from it, 
 from the mass containing the colouring matter. 
 
 The difficulty in finding just the proper oxidising agent for the 
 treatment of leuco bases has been mentioned prominently by von 
 Miller and Plochl (Ber. 24, 1,707). 
 
 10. Chloric Acid, This substance is not often used as an 
 oxidising agent, as it too frequently burns up completely the 
 substance submitted to its influence. This was the case in Prager's 
 experiments (Ber. 22, 2,993) on /z-phenylpropylene-^-thiocarbamide, 
 
n-i3l CHROMIC ACID 251 
 
 The commercial article always contains barium, as the safe pre- 
 paration of the acid requires the presence of barium salts. 
 
 Feit and Kubierschky (Ch. Z. 1891, 352) found that bromic acid 
 was still more powerful, but might be used in special cases. 
 
 11. Chloride of Iodine. This substance was used by Poirrier 
 and Chappat (Fr. Pat. 71,970) for the oxidation of methylaniline. 
 The reagent is used diluted with five or six times its weight of 
 water, or a mixture is employed which will produce it in this 
 state (?). The proportions prescribed are : methylaniline (100 parts), 
 iodine (20 parts), and potassium chlorate (20 parts), or methyl- 
 aniline (i part), mercuric iodide (3 parts), and potassium chlorate 
 (i part). 
 
 12. Chlorine. This agent was used by Hlasiwetz and Haber- 
 mann (Ann. 155, 123) in preparing gluconic acid from grape sugar. 
 They conducted a current of chlorine through a dilute solution 
 containing 100 grams of grape sugar for several days. After 
 removing the excess of the gas by means of air, the chlorine was 
 precipitated with silver oxide, and, on adding carbonates of barium, 
 cadmium, zinc, or calcium, they obtained the corresponding salt 
 of gluconic acid, C 6 H 12 O 7 . 
 
 Zincke and Kiister oxidised hexachloro-cyclopentane oxycar- 
 boxylic acid 
 
 CCl-CCl 
 
 /OH 
 
 CCl-CCl/ 
 
 by dissolving it in cold water, passing chlorine into the solution, and 
 gradually wanning this on the water bath while the addition of 
 chlorine continued. A milky turbidity soon appeared, and after 
 the heating had continued a little longer the vessel was removed 
 from the water bath. When the liquid had cooled, a crystalline 
 mass was deposited, which was recrystallised from petroleum. 
 This was the ketone corresponding to the acid, and the yield was 
 quantitative. 
 
 13. Chromic Acid. This oxidising agent is very widely used, 
 and is employed either in the form of free acid, or of a mixture 
 of a salt with sulphuric acid (cf. 37 and 45). 
 
 The solution of chromic acid in water gives a precipitate of 
 chromic oxide, a circumstance, which renders its use in this way 
 
252 OXIDATION [CH. xvm 
 
 inconvenient. Indeed, the formation of the oxide may interfere 
 with the operation where the production of organic acids is in 
 question, since the latter may combine with it to some extent. 
 The chromic acid is therefore almost always used in solution in 
 acetic acid, or else the solution in water is acidified by the addition 
 of sulphuric or hydrochloric acids. 
 
 In using glacial acetic acid, Kolbe (J. pr. Ch. 138, 469) suggests 
 that to regulate the speed of the action it is best to place the 
 chromic acid in a funnel, dissolve it by gradual addition of acetic 
 acid, and let the solution flow into the flask, and thus reach the 
 substance to be oxidised. 
 
 Grabe (Ann. 201, 356) suggests that the substance be dissolved 
 in acetic acid in a small flask having a constriction in its neck. 
 The chromic acid is placed above a platinum cone, which rests in 
 this constriction, and is gradually dissolved by the condensed acid 
 and washed into the flask. 
 
 Seitz (Ber. 23, 2,257 and 2,259) dissolved chromic acid (27 gr.) 
 in concentrated sulphuric acid (38 gr.) and water (75 cc.), and added 
 the mixture to a solution of a-/3-dimethylquinoline (15 gr.) in 20 
 per cent, sulphuric acid. On heating the mixture on the water 
 bath the chromate, which is at first precipitated, seems to be 
 rapidly attacked by the oxidising agent. After two days' heating 
 the solution becomes green, but still contains a large amount of 
 unchanged substance. After adding excess of ammonia this un- 
 changed material can be driven off with steam. The filtrate from 
 the chromium hydroxide is evaporated to dryness, the ammonia 
 being by this process expelled from combination with the organic 
 acid. The methylquinoline carboxylic acid is extracted from the 
 residue with alcohol. 
 
 Meyer (Ber. 23, 2 >259) dissolved orthotoluquinaldine (10 gr.) in dilute 
 sulphuric acid, and added a mixture of chromic acid (30 gr. ), concentrated 
 sulphuric acid (40 gr.), and water (100 cc. ). The oxidation was complete 
 after the heating on the water bath had been continued for four or five days. 
 He diluted the solution and precipitated the chromium with ammonia, 
 filtered, and then precipitated the sulphuric acid with the calculated amount 
 of barium hydroxide, and filtered again. Finally, the filtrate was evaporated, 
 and the oxidation product extracted from the residue with alcohol. 
 
 A very valuable modification of the process, suggested by Ham- 
 marsten (Ber. 14, 71), consists in dissolving the substance in acetic 
 acid in a flask, and running a 10 per cent, solution of chromic aqid 
 
i 3 ] CHROMIC ACID 253 
 
 in the same solvent into the flask from a burette in portions of 
 10 cc. at a time. A thermometer is used to note the temperature 
 of the mixture, a convenient height being 45-50. When further 
 additions of chromic acid produce no rise in temperature, and the 
 green colour of the solution has become tinged with brown, the 
 process is complete. On pouring the liquid into water the new 
 substance is generally precipitated at once. 
 
 Dorsch (J. pr. Ch. 141, 45) dissolved the substance in acetic 
 acid in a flask, and cooled the solution in a freezing mixture until 
 the acid began to freeze on the sides of the vessel. He then added 
 the chromic acid and shook the whole vigorously. The flask was 
 replaced in the freezing mixture, and the temperature was allowed, 
 during twelve hours, gradually to rise to that of the room. Then 
 the warming was continued to 50, and finally to 80. After this 
 the oxidation product was precipitated by pouring the solution into 
 cold dilute sulphuric acid, 
 
 Rohde (Ber. 22 267) states that when a-3-diraethylquinoline, dissolved in 
 dilute sulphuric acid, is oxidised with chromic acid sufficient to oxidise one 
 methyl group only, it is easy to separate an acid which is insoluble in 
 water and has the composition of methylquinoline carboxylic acid, 
 C 9 H 5 N(CH 3 )COOH. 
 
 The use of molecular quantities of the substances seems to be generally 
 desirable in oxidations with chromic acid. Thus Holm (Ber. 16, 1,081) 
 states that when dibromofluorene in acetic acid solution is treated with the 
 calculated amount of the oxidising agent a dibromofluorene ketone, melting 
 at 142 '5, is obtained, while with a slight excess of the agent another modi- 
 fication of the ketone, melting at 197, is formed. 
 
 Then, too, it does not seem always to be a matter of indifference whether 
 acetic acid or dilute sulphuric acid is used as the solvent. Fischer and Van 
 Loo (Ber. 19, 2,474) found that when /3-diquinolyline is boiled in acetic acid 
 solution and the calculated amount of chromic acid is very gradually added, 
 the boiling being continued for 15-20 hours for 5 grams of substance, the 
 solution deposits, on dilution with much water, metaquinoline carboxylic 
 acid. But when they dissolved -diquinolyline in dilute sulphuric acid, 
 containing equal parts of acid and water, and added a dilute solution or 
 chromic acid drop by drop, an oxidation went on in the cold which could be 
 hastened by finally warming the mixture. When this solution was cooled 
 again it deposited crystals of pyridylquinoline carboxylic acid. As the same 
 agent was used in both cases, the difference in result must have depended 
 on the different solvents employed. In the cases of natural alkaloids, for 
 whose oxidation chromic acid has recently been so popular, this influence 
 of the solvent should probably be taken into account. 
 
254 OXIDATION [CH. xvm 
 
 14, Chromyl Chloride, We owe the first use of chromyl chloride 
 as an oxidising agent for organic bodies to Etard (Ann. Ch. Ph. 
 1881, 218). His investigations show that it has the extraordinary 
 property of converting the methyl groups of aromatic hydrocarbons 
 into aldehyde groups, and that the action holds equally for sub- 
 stituted hydrocarbons. Some exceptions to this rule are mentioned 
 below. Thus nitrotoluene is oxidised to nitrobenzaldehyde. By 
 this process the synthesis of aldehydes from hydrocarbons directly 
 is rendered possible. As an intermediate product in this reaction 
 a substance having the formula x . 2CrO 2 Cl 2 is always formed, 
 where x represents an aromatic hydrocarbon. The substance 
 loses 2HC1 very easily, giving xi}\ . 2CrO 2 Cl, and finally water 
 decomposes this, forming the aldehyde. 
 
 In many cases the aromatic ring also is itself attacked and a 
 quinone is produced. 
 
 Etard prepared the chromyl chloride by the action of fuming 
 sulphuric acid, salt and potassium bichromate. In making two 
 kilograms of the substance he took a flask of 4-5 litres capacity, 
 and charged it with the materials in the proportions represented by 
 the equation 
 
 K 2 Cr,,O 7 + 4NaCl + 3H 2 S 2 O 7 = 2CrO 2 Cl 2 + K 2 SO 4 + 2Na,SO 4 
 
 + 3 H 2 S0 4 . 
 
 Chlorine is given off during the whole interaction. The distillation 
 is stopped when the contents of the flask begin to foam. The 
 yield is 70 per cent, of the theoretical. A secondary reaction 
 expressed by the equation 
 
 6CrO 2 CL 2 + 3H 2 S 2 O 7 - 2Cr 2 (SO 4 ) 3 -1- 2CrO 3 + 6C1 2 + 3H 2 O 
 
 accounts for the loss of part of the product and the formation of 
 chlorine. 
 
 Moissan (Bull. Ch. 43, 7) states that when hydrochloric acid gas 
 acts upon chromic acid in a tube it is absorbed, and dark-red 
 fumes of chromyl chloride (b.-p. 107) are given off, and can be 
 condensed in a receiver. 
 
 The extremely violent action of undiluted chromyl chloride is 
 illustrated by an unfortunate experiment made by Walter (Ann 
 Ch. Ph. 66, 387). On attempting to examine its action upon 
 alcohol he found that the mixture caught fire and exploded, and 
 the experimenter nearly lost his eyesight as a result of the accident. 
 A little later Carstanjen (J. pr. Ch. 110, 51) attempted to use it 
 
i 4 ] CHROMYL CHLORIDE 255 
 
 with acetic acid as diluent, but with no better success. The proper 
 choice of a diluent seemed to be of the utmost importance, and 
 Etard found that carbon disulphide was the most suitable one for 
 most purposes. For example, a 10 per cent, solution of chromyl 
 chloride in carbon disulphide is poured into an equally dilute 
 solution of toluene in the same solvent. If necessary, external 
 cooling is applied to prevent the solution boiling. It is preferable 
 to keep adding the former solution as long as it is decolourised, 
 as this gives a better result than using the theoretical quantity. 
 When the precipitate, which is formed during the addition, is 
 decomposed with water, benzaldehyde is formed. Etard states 
 that nitrobenzene is oxidised to nitroquinone by this process. But 
 Henderson and Campbell were unable to repeat the experiment, 
 and suggested that Etard's substance must have contained nitro- 
 toluene and that his product was^-nitrobenzoic acid. 
 
 As a further illustration of the use of chromyl chloride, Borne- 
 mann's (Ber. 17, 1,464) very exact description of the method of pre- 
 paring ;;z-toluylaldehyde may be given. It shows incidentally that 
 Etard's process does not exclude all possibility of explosion. 
 
 He took a little more than one molecular proportion ofmetaxylene 
 (35 parts) and two molecular proportions of chromyl chloride (loo 
 parts), and diluted them with carbon disulphide in the proportion 
 15 : 100. He then added the latter solution, 10-15 grams at a time, 
 to the former. After a time, a brown crystalline precipitate began 
 to collect on the bottom of the vessel. At the same time the tem- 
 perature rose and cooling had to be resorted to. If care was not 
 taken to wait, after each addition, until the red colour had given 
 place to a chocolate-brown shade, and the rise of temperature had 
 subsided, disagreeable explosions occurred. The whole operation 
 lasted about seven hours. At the end of twelve hours more, the 
 precipitate had completely subsided, and the supernatant liquid was 
 colourless. The precipitate was collected in a funnel plugged with 
 glass wool, and washed with carbon disulphide. The substance 
 was then placed in a closed dry flask on the water bath, and the 
 carbon disulphide vapour was removed by connecting the interior 
 with a pump. After this treatment had lasted forty-five minutes, a 
 perfectly dry, very hygroscopic substance remained behind. It was 
 not advisable to continue the heating beyond this point, as a 
 violent emission of gas was apt to occur which burst the flask. 
 The solid was then thrown into cold water in small quantities at a 
 time, when it decomposed into ;;/-toluylaldehyde, chromic acid, and 
 
256 OXIDATION [CH. xvni 
 
 chromic chloride. As the chromic acid oxidised the aldehyde, if 
 they remained in contact, it had to be removed by leading sulphur 
 dioxide into the mixture, and then immediately driving the aldehyde 
 over with steam. Or the aldehyde could be secured by rapidly 
 extracting the mixture with ether. For further purification the 
 aldehyde was converted into its compound with sodium bisulphite. 
 To effect this, the ethereal solution was violently shaken with a 
 concentrated solution of sodium bisulphite. Bornemann found 
 that unless all these precautions were observed satisfactory results 
 could not be obtained. 
 
 Richter (Ber. 19 1,061) prepared /-nitrobenzaldehyde by the same 
 process. He was unsuccessful however in an attempt to prepare dinitro- 
 benzaldehyde from dinitrotoluene. Etard himself states that for the 
 oxidation of acids like benzole acid and acetic acid this agent is not 
 serviceable. 
 
 Using the process of Etard, v. Miller and Rohde (Ber. 23, 1,074) found 
 that pcopylbenzene gave benzylmethylketone in place of its isomer hydro- 
 cinnamic aldehyde, not a trace of the latter being formed. From isopropyl- 
 benzene (Ber. 24, l ,35&) they obtained hydratropic aldehyde and aceto- 
 phenone, which they separated by means of sodium bisulphite. 
 
 15. Copper Solution Alkaline, This agent is used as an 
 oxidiser chiefly for grape sugar, but it has also been used for 
 synthetic purposes with many other substances. 1 Thus Bosler 
 (Ber. 14, 327) found in it the best oxidising agent for the conversion 
 of anisoin into anisil. Anisoin (i part) is dissolved in hot 70 per 
 cent, alcohol (5 parts), and the alkaline copper solution is added 
 until a permanent blue tint remains. The solution is then filtered 
 from cuprous oxide, and the anisil precipitated with water. The 
 yield is quantitative. 
 
 Breuer and Zincke (Ber. 13, 639) dissolved acetyl carbinol (i 
 mol.) in 20 parts of water, and added caustic soda (6 mol.) A 
 
 1 Alkaline copper solutions play an important part in the chemistry of the 
 carbohydrates because cane sugar, starch, etc. , can all be converted into 
 grape sugar by boiling with dilute acids (Kirchoff, 1811). In 1819, Bracon- 
 not showed that cellulose was inverted by the same treatment. Fehling's 
 solution, in which tartaric acid is used to retain the cupric oxide in solution, 
 has the disadvantage of not keeping well. When mannite is used 
 (Schmiedeberg, A. Path. Pharm. 28 363) a solution is obtained which 
 serves equally well for the quantitative determination of sugar, and can be 
 kept unchanged for years. 
 
i6-i8] CUPRIC SULPHATE 257 
 
 solution of cupric sulphate (2 mol.) was then allowed to run in, and 
 the whole was warmed on the water bath. The following equations 
 represent the actions : 
 
 CH 3 . CO . CH 2 OH = CH 3 . COH + HCOH 
 
 Aldehyde. Formaldehyde. 
 
 CH 3 . COH + HCOH + O = CH 3 . CHOH . COOH 
 
 Lactic acid. 
 
 After trying other oxidising agents, E. Fischer (Ann. 211, 229) 
 found in the alkaline copper solution a suitable agent for converting 
 benzfuroin into benzfuril. He dissolved benzfuroin (2 parts) 
 in warm alcohol (35 parts), and added a weak alkaline 
 copper solution (70 parts) and enough water to cause the 
 two liquids to mix. The temperature was kept at 50, and the 
 oxidation was quickly completed. As soon as a filtered sample of 
 the liquid ceased to reduce Fehling's solution in the heat, the 
 whole was diluted, filtered, and extracted with ether. The oxidis- 
 ing agent was prepared by dissolving crystallised cupric sulphate (6 
 parts) with the requisite amounts of tartaric acid and caustic soda. 
 
 16. Cupric Acetate. Baeyer (Ber. 24, 2,693) oxidised a 
 very unstable hydrazo-compound in absence of water by dissolving 
 one gram of it in 15 cc. of warm absolute alcohol, and adding to 
 the boiling liquid a hot saturated solution of 0*7 grams of neutral 
 cupric acetate containing a drop or two of acetic acid. When the 
 liquid, which became red from separation of cuprous oxide, was 
 filtered into ice, yellow needles of the oxidation product soon 
 separated. 
 
 17. Cupric Oxide and Hydroxide. When leucaniline hydro- 
 chloride is mixed with cupric oxide and heated to 120-160, it is 
 converted into fuchsine (Ger. Pat. 19,484). This seems to be the 
 only application of this agent to the synthesis of organic bodies. 
 
 For the oxidation of various carbohydrates, Habermann and 
 K6nig(M. f. Ch. 5, 208) frequently boiled them for several hours in 
 alkaline or neutral solution with cupric hydroxide. Treated in this 
 way, galactose gave carbon dioxide, formic acid, glycollic acid, lactic 
 acid, and other undetermined acids. 
 
 18. Cupric Sulphate. By dry oxidation with anhydrous 
 cupric sulphate, Briihl (Ber. 24, 3,374) converted menthol easily 
 into cymene. When the substances had been heated for several 
 hours at 250-280 and the tube was opened, streams of sulphur 
 
 S 
 
258 OXIDATION [CH. xvm 
 
 dioxide issued, and cupric oxide saturated with an oil remained 
 behind. If a small amount only of cupric sulphate is used, the 
 reduction may be carried so far as to give hydrogen sulphide and 
 cupric sulphide. The oil was found to be nearly all volatile with 
 steam, and turned out to be cymene 
 
 C 10 H 20 + 2 = C 10 H 14 + 3 H 2 0. 
 
 When chromic acid was tried as an oxidising agent, menthone 
 was formed, while permanganate gave oxymenthylic acid with 
 pimelic and other fatty acids. 
 
 He obtained the same substance (Ber. 25, 143) by heating 
 menthene with cupric sulphate at 250. 
 
 C 10 H 18 + 2 =C 10 H 14 + 2H 2 0. 
 
 The following example will illustrate the use of cupric sulphate 
 on a large scale (Friedlander, Farbenfabrikation, 33). Pure di- 
 methylaniline is mixed with a large amount of dry salt or chalk 
 (Ger. Pat. 32,829), for the purpose of keeping it in a state of fine 
 division. It is then heated for 8-10 hours at 50-60, with 50 per 
 cent, of pulverised cupric sulphate and 20 per cent of liquid phenol 
 (containing cresol). The phenol probably acts as an oxygen 
 carrier by being converted into quinone derivatives. Methyl violet 
 is prepared from the product. 
 
 19. Ferric Chloride. This substance is usually applied in 
 solution in water, and, if necessary, at the boiling temperature. The 
 action takes place according to the equation 
 
 2FeCl 3 + H 2 O = 2FeCl 2 +2HCl + O. 
 
 It will be noticed that hydrochloric acid is set free by the action. 
 The following admirable method was used by Baeyer (Ber. 15, 775) 
 to avoid the inconvenience arising from this cause. He found that 
 ethyl indoxanthinate was best prepared by the oxidation of ethyl 
 indoxylate by means of ferric chloride. Yet the operation was one 
 of the most delicate in the whole investigation of the indigo group, 
 for the hydrochloric acid decomposed the ethyl indoxanthinate, and 
 in addition to this there was danger of the action stopping halfway 
 at an intermediate product. The ethyl indoxylate (i part) was 
 dissolved in acetone (4 parts), and ferric hydroxide freshly precipi- 
 tated from crystallised ferric chloride (2 parts) was added. In 
 another vessel, crystallised ferric chloride (4 parts) was dissolved in 
 acetone (4 parts). Both solutions were warmed to 60 and mixed, 
 
20, 21] HYDROGEN PEROXIDE 259 
 
 and a dark-green solution was obtained. This was diluted with a 
 large amount of water, also at 60, and the mixture, which became 
 yellow, was filtered from the ferric hydroxide and extracted with 
 ether. 
 
 Fischer and Busch (Ber. 24, 1,871) prepared the corresponding 
 azonium base from a hydroquinoxaline very easily by dissolving the 
 latter in boiling alcohol and adding aqueous ferric chloride. 
 
 Solutions of ferric chloride in glacial acetic acid have also been 
 used. Dianin found this an excellent method for oxidising naphthols 
 to dinaphthols. With a similar object in view, Witt (Ber. 21, 728) 
 dissolved /-tolylnaphthylamine (10 gr.) and solid ferric chloride 
 (10 gr.) each in acetic acid (40 cc.), mixed the solutions, and boiled 
 for some time. He obtained the corresponding substance of the 
 dinaphthyl series. The yield was only 4 grams, but chromic acid 
 did not give even a trace of the dinaphthyl base either in hot or 
 cold solution 
 
 2C 10 H 7 OH + 2FeCl 3 = C 20 H 12 (OH) 2 + 2HC1 + 2FeCl 2 . 
 
 20, Ferric Hydroxide. This substance is recommended for 
 the oxidation of leuco bases (Ger. Pat. 19,484). Thus, when an 
 intimate mixture of leucaniline with excess of ferric hydroxide is 
 heated at 120-160 in open or closed vessels, a metallic-looking, 
 green-coloured fused mass is produced. This is boiled with water 
 to extract the dye, which is precipitated by adding salt. 
 
 21. Hydrogen Peroxide. This is a very valuable agent, and 
 many oxidations can be conducted quantitatively by its means. 
 
 Radziszewski (Ber. 18, 355) has shown that it converts nitriles 
 into amides with evolution of oxygen 
 
 The reaction goes with special ease in alkaline solution and at 
 40. Thus, when benzonitrile and caustic potash are added to 
 peroxide of hydrogen, and the mixture is shaken, a quantitative yield 
 of benzamide is obtained. Even cyanogen is converted, by 3 per 
 cent, hydrogen peroxide and a drop of caustic potash, quantitatively 
 into oxamide. 
 
 Hektor (Ber. 22, 1,177) oxidised phenylthiourea by its means as 
 follows : The substance (5 gr.) was dissolved in fifty per cent. 
 alcohol with a few drops of hydrochloric acid, and three per cent. 
 hydrogen peroxide (40-50 gr.) was added in small portions at a 
 
 S 2 
 
260 OXIDATION [CH. xvm 
 
 time. The liquid became turbid from separation of sulphur. This 
 was removed by filtration, and the warm liquid, when neutralised 
 with alkali, gave a quantitative precipitate of dianilidooiazothiol 
 
 C 6 H 6 NH . C . S JH HSijC .NHC 6 H 5 
 
 II """+ I ! II +2H 2 O 2 = 
 
 NlH"" 1 HN 
 
 S 
 
 C 6 H 5 NH.C C.NHC C H 6 
 
 II II 
 
 N- N 
 
 Bernthsen (Ber. 20, 937) succeeded in oxidising juglone to oxyphthalic 
 acid by means of alkaline hydrogen peroxide, although the action did not 
 go as smoothly as either of the above examples. 
 
 The action of hydrogen peroxide is frequently used in attempts to deter- 
 mine the constitution of alkaloids. Wolffenstein (Ber. 25, 2,777) an d 
 Merling (Ber. 25, 3> I2 4) have used it in this way. The latter transformed 
 bases of the pyridine series into oxy-bases. Thus when o-methyltropidine 
 (i part) is frequently shaken with ordinary hydrogen peroxide (15 parts) for 
 several days at the temperature of the room the conversion into the oxy-base 
 is quickly completed. 
 
 The observation of Leeds (Ber. 14, 977) that benzene is partially con- 
 verted into phenol by boiling for sixty hours with I '2 per cent, hydrogen 
 peroxide is of considerable theoretical interest. The direct conversion of 
 benzene into phenol was first attained by Schultzen and Naunyn (P. Ar. 12, 
 294) by feeding dogs with benzene. 
 
 22. Hydroxylamine. The oxidising influence of this substance 
 has frequently been noticed. Thus Meyer (J. pr. Ch. 137, 497) 
 states that when oxanthranol is heated with the hydrochloride and 
 a few drops of hydrochloric acid for 2-3 hours at 160-170, ammo- 
 nium chloride and anthraquinone are formed, and a part of the 
 latter is converted into an oxime. Similarly croconic acid (Ber. 19, 
 305) is converted by it into the pentoxime of leuconic acid. Even 
 under these conditions, however, its action frequently takes a quite 
 different direction (Ber. 20, 614), so that the substance can hardly 
 be regarded as an oxidising agent. 
 
 23. Internal Oxidation. An example of this is the oxidation of 
 nitrolactic acid to oxalic acid and hydrocyanic acid, observed by 
 Henry (Ber. 12, 1,837). He gives the rather peculiar equations : 
 
 CH 3 . CH(N0 3 ) . COOH = C(OH) 3 . COOH + HCN = 
 
 COOH , COOH + HCN + H O. 
 
24, 2 5 1 LEAD PEROXIDE 261 
 
 He explains by this reaction the occurrence of hydrocyanic acid, 
 which is characteristic of all oxidations with nitric acid. In 
 Gmelin- Kraut's " Handbuch der organischen Chemie" (4th ed., p. 
 303), a number of statements have been collected showing that this 
 fact has been known since the beginning of the century. 
 
 24. Lead Monoxide. This oxidising agent is used either by 
 mixing it with the substance and distilling from a retort, or by con- 
 ducting the vapour over the heated oxide. Thus Wittenberg and 
 Meyer (Ber. 16, 502) led the vapour of benzil over lead oxide and 
 obtained benzophenone 
 
 C 6 H 5 -CO C 6 H 6X 
 
 | +PbO= >CO + C0 2 + Pb. 
 
 C 6 H 5 -CO C 6 H/ 
 
 By the same process Behr and van Dorp (Ber. 6, 753) prepared 
 acenaphthylene from acenaphthene 
 
 Ci H 1( / 
 
 /CH 2 ,CH 
 
 + PbO = C 10 H ie / I! + H 2 + Pb. 
 
 e 
 CH 2 > CH 
 
 25. Lead Peroxide. The oxidising power of this substance is 
 generally utilised by adding it to a solution of the material to be 
 oxidised either in the cold or in the heat. 
 
 According to Fehrmann (Ber. 15, 1,882), the oxide is best 
 obtained by mixing a warm (6o c ) concentrated solution of lead 
 chloride with a solution of bleaching powder. The latter is added 
 until a filtered sample gives no further brown colour on addition of 
 a drop of the same reagent. The precipitate is filtered and washed, 
 access of air being avoided during the process. When dry it 
 forms an almost black powder, but it keeps better in the moist 
 condition. 
 
 It is one of the most valuable agents for oxidising leuco bodies. 
 For example (Ger. Pat. 50,782), a leucosulphonic acid (100 parts) is 
 dissolved in water (400 parts) and 35 per cent, caustic soda (31 
 parts). In another vessel lead peroxide, containing 34 per cent, of 
 PbO 2 (120 parts), is stirred up with water (1,500 parts). The first 
 solution is cooled to 20 and added to the second, and then 
 immediately afterwards a cold (20) solution of sulphuric acid of 
 sp. gr. 1*842 (45 parts) in water (300 parts) is mixed with the other 
 two. The whole is stirred for a short time and then neutralised by 
 the addition of a solution of soda (30 parts) in water (200 parts). 
 
262 OXIDATION [CH. xvm 
 
 The lead precipitate is filtered off and the dye thrown down by 
 addition of common salt in the solid form. 
 
 Glaser and Morawsky (M. f. Ch. 10, 578) noted the extra- 
 ordinary fact that, when lead peroxide acts upon dilute alkaline 
 solutions of alcohol, glycol, cane sugar, and other similar substances, 
 hydrogen gas and formic acid are produced. In the case of glycol 
 the equation is : 
 
 C 2 H 6 2 +20 = 2C0 2 H 2 +H 2 . 
 
 26. Manganese Dioxide. This substance is sometimes used in 
 the form of pyrolusite, but more frequently as precipitated hydrated 
 or anhydrous manganese dioxide. 
 
 E. and O. Fischer (Ber. 12, 796) oxidised the leuco base of 
 malachite-green by treating a cold solution of the base in dilute 
 sulphuric acid with finely divided pyrolusite. 
 
 Schmidt and Wilhelm (Ar. Pharm. 1888, 347) added gradually 
 finely pulverised pyrolusite (7*5 gr.) to a boiling solution of hydrastine 
 (5 gr.) in water (75 gr.) and sulphuric acid (5 cc.). They boiled the 
 mixture as long as any gas was evolved, and then filtered. When 
 it cooled the whole mass became filled with crystals of opianic 
 acid, and hydrastinine was found in the mother-liquor. 
 
 Donath (Ch. Z. 1888, 1,191) found that when the vapour of 
 alcohol was conducted over pyrolusite heated to 150-360 it was 
 mostly converted into acetone. 
 
 Carius (Ann. 148, 51) obtained some rather extraordinary 
 results by using this oxidising agent. He mixed a cold solution of 
 pure sulphuric acid (600 gr.) in water (120 gr.) with benzene (100 gr.) 
 and finely pulverised pyrolusite (100 gr.), and shook them till an 
 emulsion was formed. The flask was immersed in water from time 
 to time to keep the temperature below 20. After the mixture had 
 remained for several days it was examined and found to contain 
 formic acid, benzoic acid, and phthalic acid. A satisfactory 
 explanation of their formation has not yet been given. 
 
 Dobereiner (Ann. 3, 144) first made the observation that on 
 boiling a solution of tartaric acid with pyrolusite and sulphuric acid 
 carbon dioxide and formic acid are produced. Liebig prepared formic 
 acid by treating starch (100 gr.) with pyrolusite (370 gr.), sulphuric 
 acid (300 gr.), and water (300 cc.). He obtained 33-5 grams. 
 
 Formic acid is now much more readily prepared by Berthelot's 
 process from oxalic acid (Ann. 98, 139). It seems, however, that 
 formic ether is still manufactured by the following process (Dingl. 
 
27-30] MERCURIC OXIDE 263 
 
 Polyt. Jour. 187, 402) : Starch (4*5 kg.), and pyrolusite, containing 
 at least 85 per cent, of MnO 2 (14-5 kg.), are placed in a vessel, and 
 upon them is poured a cold mixture of sulphuric acid (14 kg.), water 
 (2*5 kg.) and 80 per cent, alcohol (7*5 kg.). After the action has 
 been started, further external heating is unnecessary. At first 
 alcohol comes over, then commercial formic ether. The free acid 
 in the latter is neutralised with calcium hydroxide. When, finally, 
 heat is applied, a liquid containing much formic acid passes over. 
 
 Precipitated manganese dioxide, or its hydrate, is chiefly employed 
 for oxidation in acid solutions such as those of bases in sulphuric acid 
 or acetic acid. Pyrolusite or hausmannite is frequently added as well. 
 
 Nietzki (Ber. 24, 3,367) dissolved molecular proportions of nitro- 
 soresorcinol (10 parts) and resorcinol(i5 parts) in cold alcohol, and 
 suspended manganese dioxide (i mol.) in the solution. He then 
 cooled the mixture and added sulphuric acid (2 mol.) diluted with 
 an equal volume of water. After a short time the liquid became 
 cherry-red. By precipitating the filtered solution with water 
 resazurin was thrown down 
 
 C 6 H 6 2 + C 6 H 5 N0 3 = C 12 H ir N0 4 + H 2 O + 2H. 
 
 27. Mercuric Acetate, Tafel (Ber. 25, 1,619) states that this 
 is a suitable oxidising agent for converting derivatives of piperidine 
 and tetrahydroquinoline into the corresponding derivatives of 
 pyridine and quinoline. Thus quinoline itself is easily made from 
 tetrahydroquinoline by heating with a solution of mercuric acetate 
 at 1 50. Metallic mercury is formed at the same time (cf. 48). 
 
 28. Mercuric Chloride. This substance is specially recom- 
 mended by Goldberg (Ber. 24, 3,553) for the preparation of fuch- 
 sine. He heats a mixture of paratoluidine (i mol.) and aniline 
 (2 mol.) with the theoretical amount of mercuric chloride for an 
 hour and a half at 180-200. Fuchsine prepared in this way is 
 mixed with almost none of the coal-like amorphous substances 
 which are always formed when arsenic acid or other oxidising 
 agents are used. 
 
 29. Mercuric Nitrate. Gerber and Keller (Jahresb. 1860, 
 720) used mercuric nitrate as an oxidising agent in the preparation 
 of fuchsine. 
 
 30. Mercuric Oxide. Both the red and the yellow varieties of 
 mercuric oxide are frequently used as oxidising agents. 
 
264 OXIDATION [CH. xvm 
 
 E. Fischer (Ber. 11, 2,209) added yellow mercuric oxide gradually 
 to a cold solution of diethylhydrazine in water until the oxide was 
 no longer reduced. The solution became turbid from separation of 
 an oil which was taken up mechanically by the mercury compounds. 
 These were separated by filtration and the oil was extracted from 
 them with alcohol. It was found to be tetraethyltetrazone, (C 2 H 6 ) 2 
 N . N : N. N . (C 2 H 5 ) 2 . The action is therefore quite different from 
 that of Fehling's solution, which converts diethylhydrazine almost 
 entirely into diethylamine and nitrogen 
 
 2 (C 2 H 6 ) 2 N . NH 2 + = 2(C 2 H 6 ) 2 NH + H 2 + N 2 . 
 
 Heffter (Ber. 22, 1,049) boiled a 10 per cent, solution of glucose 
 with yellow mercuric oxide until no further reduction took place. 
 The warm solution was filtered from the mercury and mercurous 
 oxide, and on cooling gave an excellent yield of the crystalline 
 mercurous salt of gluconic acid. 
 
 Bornstein and Herzfeld (Ber. 18, 3,354) found that a solution of 
 levulose in water could be boiled with red mercuric oxide without 
 being attacked, but that the addition of a drop of barium hydroxide 
 brought about instant oxidation. The red colour of the oxide 
 changes at once into the black of mercurous oxide. In carrying 
 out the process it is advisable to add alternately mercuric oxide and 
 barium hydroxide. The levulose is largely converted into trioxy- 
 butyric acid and glycolic acid. Herzfeld (Ann. 245, 27) tried this 
 method with glucose and obtained chiefly gluconic acid. 
 
 Curtius (Ber. 22, 2,162) obtained the calculated amount of mono- 
 ketazobenzil by shaking a solution of monohydrazobenzil in benzene 
 with mercuric oxide 
 
 HN V N\ 
 
 | >C-C 6 H 6 ||>C-C 6 H 6 
 
 HN/ | +HgO = N/ | +H 2 + Hg. 
 
 CO-C 6 H 5 CO-C 6 H 6 
 
 Fischer and Hepp (Ann. 256, 252) obtained complicated oxida- 
 tion products by boiling tetranilidonaphthalene in benzene solution 
 with mercuric oxide. 
 
 31. Nitrobenzene. The oxidising power of this substance is 
 chiefly known from its use by Coupier in the preparation of fuchsine. 
 The method consists in heating a mixture of aniline, toluidine, nitro- 
 benzene, and nitrotoluene with some hydrochloric acid and a little 
 zinc chloride at 180-190. The yield of fuchsine, about 38 per cent., 
 is not very different from that obtained by the older method, by use 
 
32] NITRIC ACID 265 
 
 of arsenic acid, but the present method has the advantage of 
 avoiding the use of this very poisonous substance. 
 
 It has seldom been used for oxidation in the laboratory. Lell- 
 mann and Geller (Ber. 21, 1,921) heated piperidine (5 gr.) with 
 nitrobenzene (22 gr.) for four hours in a sealed tube at 250-260. 
 They obtained some pyridine, but the yield was unsatisfactory. 
 
 32- Nitric Acid. Oxidation with nitric acid is generally carried 
 out in the traditional manner by boiling the substance, often for 
 several days, with the more or less diluted acid, a large excess of the 
 latter being always taken. As Krafft remarks (Ber. 21, 2,735), this 
 leads frequently to the formation of secondary products by the 
 continued action of the acid. Indeed the amount of these is often 
 greater than that of the substance sought. Krafft found that it was 
 frequently better to pour the substance to be oxidised into a 
 quantity of cold nitric acid whose temperature is kept between 
 o and 10. With one part of the substance, from one to three parts 
 of the acid of sp. gr. 1*5 are taken. When the first phase of the 
 action seems to be complete, the mixture is slowly heated to 50. 
 The course of the action can often be followed by observing the 
 appearance of the mass. Thus the effervescence may cease or 
 coloured intermediate products may disappear. In all cases caution 
 must be used, but when successful this method occupies at most 
 only a few hours, and the quantity of secondary products is reduced 
 to a minimum. Of course this process is entirely inapplicable to 
 aromatic substances, as they are converted into nitro-derivatives by 
 such treatment. 
 
 This method will naturally be used where a convenient reaction 
 showing the presence of the unchanged substance is available. 
 
 For example, Schmiedeberg and Meyer (Z. physiolog. Ch. 3, 444) 
 oxidised camphoglycuronic acid by warming it in a flask connected 
 with a condenser with dilute nitric acid. As the original substance 
 reduces Fehling's solution, they were able, by testing with this 
 reagent, to ascertain when it was all decomposed. They then 
 neutralised most of the nitric acid and distilled the product, 
 adding water from time to time, in order to separate any volatile 
 acids which might have been formed. They neutralised the 
 distillate with lime, extracted a little campherol which had passed 
 over with ether, and reduced the nitric acid to ammonia by adding 
 caustic potash and zinc dust. Finally, they obtained formic acid 
 by filtering the liquid, acidifying with sulphuric acid, and again 
 
266 OXIDATION [CH. xvm 
 
 distilling. They identified it by means of the lead salt. It is a 
 difficult matter to demonstrate the formation of formic acid in 
 oxidations with nitric acid, because, as Ballos (Ber. 17, 9) has shown, 
 it is converted by this agent in the heat into carbon dioxide, water, 
 and even to a large extent oxalic acid. 
 
 Siegfried (Ber. 24, 421) used lead hydroxide for eliminating the 
 nitric acid after the oxidation was completed. The hydroxide when 
 precipitated in the cold and carefully washed is best preserved 
 under water. It dissolves in the latter to some extent in the colloid 
 form. A large excess of it, when added to an acid mixture, preci- 
 pitates the acid as basic nitrate. So that even without boiling 
 the solution which is basic from the presence of the dissolved 
 hydroxide, a proceeding which might lead to decomposition, the 
 acid can be completely eliminated. The dissolved lead is removed 
 from the filtrate with hydrogen sulphide. 
 
 Substances which are hard to oxidise may be treated with nitric 
 acid in sealed tubes. Thus sulphoxides are easily converted into 
 sulphones by heating with fuming nitric acid for a considerable 
 time at 100 
 
 (C 2 H 5 ) 2 SO + = (C 2 H 5 ) 2 S0 2 . 
 
 When it is desired to use nitric acid for the oxidation of aromatic 
 bodies with fatty side chains, it is best to boil with dilute nitric acid 
 to avoid the formation of nitro-derivatives. In many such cases, 
 however, a nitrate can be substituted for the nitric acid, and all 
 danger of the formation of nitro-derivatives avoided. The prepara- 
 tion of benzaldehyde (Lauth and Grimaux, Ann. Ch. Pharm. 143, 
 1 86) from benzyl chloride and an aqueous solution of lead or copper 
 nitrate is an example of this. 
 
 Debus (Ann. 106, 80) suggested the method of placing a layer of 
 nitric acid above or below the substance in order to moderate the 
 action of the nitric acid. Thus he diluted glycerol (i part) with a 
 little more than an equal bulk of water, placed it in a cylinder, and 
 passed down to the bottom, through a long funnel, nitric acid of 
 sp. gr. 1*5 ( i part). The two layers gradually mixed and became 
 blue in colour. He stated that five or six days were required to 
 complete the action, but found later that exposure to sunlight not 
 only improved the yield, but also reduced the time to twelve hours. 
 The product is glyceric acid 
 
 CH 2 OH . CHOH . CH 2 OH + 20 = CH 2 OH . CHOH.COOH + H 2 O. 
 
33] NITROUS ACID 267 
 
 When the substances are mixed together, oxalic acid is the chief 
 product, and very little glyceric acid is found. The brilliant work 
 of Fischer and Tafel (Ber. 20, 1,089), which has led to the synthesis 
 of sugar, has shown that aldehydes or ketones are formed as inter- 
 mediate products. These had remained unnoticed, not to say 
 unisolated, for want of suitable methods. On addition of phenyl- 
 hydrazine they are precipitated as osazones. 
 
 Very remarkable are the results obtained by V. Meyer and 
 Wachter (Ber. 25, 2,632), by dissolving orthoiodobenzoic acid in 
 fuming nitric acid, boiling for a few minutes to complete the action, 
 and finally pouring the solution, when cold, into water. An acid is 
 
 thrown down which they name iodosobenzoic acid, 
 
 lodosobenzene and iodoxybenzene, C 6 H 5 IO 2 have since been ob- 
 tained by Willgerodt (Ber. 26, 358). 
 
 The substances formed by the action of nitric acid frequently 
 either separate spontaneously or are thrown down on addition of 
 water. Sometimes they are extracted by some suitable solvent 
 from the diluted solution. As the products of the action of nitric 
 acids are usually acids, it is often sought to precipitate them in the 
 form of insoluble salts, and so separate them from the nitric acid 
 whose salts are all soluble. When no insoluble salt can be found, a 
 separation by crystallisation may be attempted. 
 
 Apart from ways already mentioned of getting rid of the nitric 
 acid, it can often be removed by evaporation, water being added 
 from time to time to prevent the acid which remains becoming too 
 concentrated (cf. Chap. XVII. 14). 
 
 33. Nitrous Acid. Nitrous acid, which is best prepared by 
 heating arsenious oxide with 50 per cent, nitric acid (cf. Chap. XIII. 
 2), is a much more convenient oxidising agent than is usually 
 supposed. This unpopularity may have arisen from the fact, 
 ascertained by Lenssen (J. pr. Ch. 82, 307) in comparing various 
 oxidising agents in regard to their applicability to titration, that it 
 is not in our power to determine its reduction to the stage of NO, 
 N 2 O, or N 2 at will. This seems to depend on conditions such as the 
 temperature and the duration of the action. 
 
 It is a very mild oxidising agent. For example, Benedikt and 
 Hiibel (M. f. Ch. 2, 323) found that dinitrosoresorcinol was at once 
 converted into trinitroresorcinol by dilute nitric acid, while potassium 
 permanganate and potassium ferricyanide decomposed it com- 
 
268 OXIDATION [CH. xvm 
 
 pletely. But when it was suspended in ten parts of ether, and 
 nitrous acid was led into the mixture until the substance dissolved, 
 and the nitric acid which was formed was removed by washing with 
 water, the desired product, dinitroresorcinol, was easily obtained. 
 
 Hydrocollidine dicarboxylic ether is entirely decomposed by 
 nitric acid, while potassium permanganate gives at once lutidine 
 tricarboxylic acid. Collidine dicarboxylic acid can only be obtained 
 by the use of nitrous acid. Hantzsch (Ann. 215, 21) mixed the 
 ether with an equal amount of alcohol, cooled the mixture, and led 
 nitrous acid into it until a sample of the liquid formed a clear 
 solution in dilute hydrochloric acid. Much heat is given out, and 
 the portion of the substance not at first dissolved, goes later into 
 solution in the alcohol. When the alcohol is evaporated and 
 sodium carbonate in excess is added, the collidine dicarboxylic 
 ether is thrown down as an oil which, after being dried, shows a 
 constant boiling-point. The yield is quantitative. 
 
 According to Wallach (Ber. 5, 256), a large amount of nitrous 
 acid dissolves in chloral and the liquid becomes green. When this 
 stage has been reached it is sealed up in a tube, and heated for an 
 hour in the water bath. On account of the great pressure produced 
 only a little of the substance can be enclosed in each tube. When 
 the tube is opened the contents solidify to a mass of trichloracetic 
 acid, if the amount of nitrous acid has been sufficient. The acid 
 is purified by pressure between sheets of filter paper. It is possible 
 that other aldehydes, free from halogen, may be equally easily 
 oxidisable by this reagent, and that it may therefore take the place 
 of the silver oxide or oxygen which has hitherto been in use. 
 
 34, Oxygen. Oxygen may be prepared in Kipp's apparatus as 
 follows (Baumann, Z. ang. Ch. 1890, 79) : The middle bulb of the 
 apparatus is filled with pure pyrolusite in pieces of the size of a pea. 
 To prevent the substance falling into the lower bulb, a rubber ring 
 covered with long-fibred asbestos is placed over the annular 
 opening connecting the two. The fluid is prepared by pouring 
 gradually 150 cc. of sulphuric acid into a litre of ordinary peroxide 
 of hydrogen, which is cooled during the process. According to 
 Blau (M. f. Ch. 13, 280) oxygen entirely free from nitrogen may be 
 obtained by the action of hydrogen peroxide on potassium 
 bichromate. 
 
 Oxygen is usually applied in oxidation by conducting the gas 
 through the liquid to be treated. For example, Miiller (Ber. 22, 
 
34] OXYGEN 269 
 
 857) dissolved triamidobenzene hydrochloride (10 gr.) and sodium 
 acetate (18 gr.) in water (200 cc.), warmed the solution, and led 
 oxygen through it for two or three hours. Probably triamidophen- 
 azine was formed in accordance with the equation 
 
 Michaelis and Lampe (Ber. 24, 3,739) state that when phenyl- 
 pyrazolidine is placed on a watch glass it loses two atoms of 
 hydrogen and forms phenylpyrazoline. 
 
 The activity of oxygen is much increased by adding platinum 
 black to the liquid. Thus Grimaux (Bull. Ch. 45, 481) obtained by 
 this process from glycerol a liquid which reduced Fehling's 
 solution, so that, in view of Fischer and Tafel's work, he must have 
 had a solution of glyceric aldehyde. Oxidations similar to this were 
 made by Demole and Diirr (Ber. 11, 315 and 1,302). 
 
 Loew (Ber. 23, 289) states .that the catalytically most powerful 
 platinum black is prepared as follows : Platinum tetrachloride 
 (50 gr.) is dissolved in water (50-60 cc.) and a 40-45 per cent. 
 solution of formaldehyde (70 cc.) is added. This mixture is 
 thoroughly cooled, while caustic soda (50 gr.) dissolved in an equal 
 weight of water is added. The greater part of the metal is at once 
 precipitated. The mixture is filtered at the end of twelve hours, 
 and a yellow liquid passes through the filter, which deposits a little 
 more platinum on being boiled. When the greater part of the 
 sodium chloride and formate has been washed out, a black liquid 
 runs through produced by the solution of a part of the very fine 
 powder. The washing is therefore interrupted at this stage until a 
 process of oxidation which begins on the filter is completed. The 
 moist black substance begins to absorb oxygen from the air, and for 
 several hours a rustle, caused by the breaking of small gas bubbles 
 . all over the precipitate, may be heard. The black substance turns 
 into a porous mass during this process, and is finally washed free 
 .from sodium chloride, whose presence greatly interferes with the 
 activity of the platinum, as Dobereiner had already shown. The 
 powder is finally dried over sulphuric acid. 
 
 Platinised asbestos, which is also useful for oxidation, was pre- 
 pared by Weidel (M. f. Ch. 8, 121) by intimately mixing asbestos 
 (loogr.) with platinum black (80 gr.). Tischtschenko (Ber. 20, 704^) 
 states, however, that it should not contain so much platinum, and 
 should not be black but gray. Lunge (Sodaindustrie, 1, 601) says 
 that the platinised asbestos used in the preparation of sulphur 
 
270 OXIDATION [CH. xvm 
 
 trioxide from sulphur dioxide and oxygen in manufactories contains 
 only eight per cent, of platinum. Platinised quartz, recommended 
 by Zulkowski and Lepez (M. f. Ch. 5, 538), may be better than 
 platinised asbestos. 
 
 Oxygen carriers, similar to the chlorine carriers, are known. The 
 most active substance of this nature has been shown by Loew 
 (J. pr. Ch. 126, 300) to be a solution of cupric oxide in ammonia. 
 Nitrogen compounds particularly, when mixed with this substance 
 and shaken with air, seem to undergo profound changes. 
 
 He neutralised uric acid (i gr.) with the theoretical amount of 
 caustic potash, placed it in a flask with the copper solution (100 cc.), 
 and allowed it to remain in a warm place for several days. During 
 this time it was frequently shaken, and the air was periodically 
 renewed. The liquid was then evaporated and nearly neutralised 
 with sulphuric acid. An acid reaction must be carefully avoided 
 on account of the nitrite which is formed. The mass was dried on 
 the water bath and extracted with alcohol. Urea and a large 
 amount of oxalic acid went into solution. Amidoacetic acid and 
 amidosuccinic acid are similarly attacked under such circumstances, 
 producing oxalic acid and carbon dioxide. 
 
 L. Meyer (Ber. 20, 3,058) investigated a number of salts in 
 regard to their power as oxygen carriers, and found that manganous 
 sulphate was the most active of those examined. 
 
 35. Ozone. The action of ozone upon organic bodies has been 
 known for years (Ann. 125, 207). Great care has to be exercised 
 in its use, as substances of quite extraordinary explosive power are 
 frequently formed. Houzeau and Renard (C. R. 76, 572) obtained 
 such a body by its action on benzene, and named it ozobenzene. 
 Nencki and Giacosa (Z. physiolog. Ch. 4, 340) were able to prepare 
 very small quantities of phenol from benzene in the same way. 
 Berthelot (C. R. 92, 895) speaks of an excessively explosive liquid 
 which he obtained by its action on absolute ether. 
 
 In opposition to these statements, Leeds (Ber. 14, 975) asserts 
 that, when ozone acts upon benzene, carbon dioxide, oxalic acid, 
 formic acid, and acetic acid along with a black amorphous substance 
 are formed. He found no ozobenzene. He also studied the action 
 of nascent oxygen prepared by covering phosphorus with water and 
 exposing it to the air. In absence of benzene, ozone was produced. 
 But when benzene was added the ozone reaction could not be 
 obtained. Under these circumstances, when the mixture was 
 
36, 37] POTASSIUM BICHROMATE 271 
 
 exposed to sunlight phenol and oxalic acid were formed. In 
 diffused light oxalic acid was formed but not phenol. The most 
 active form of oxygen has already been mentioned (cf. Chap. XV. 
 8). 
 
 36. Platinum Tetrachloride. This salt is seldom used for 
 oxidation on account of its expensiveness. Platinum black and 
 platinised asbestos, as we have already seen (cf. 34), assist very 
 energetically the action of free oxygen and air. 1 
 
 Schmidt and Wilhelm (Ar. Pharm. 1888, 350) dissolved hydra- 
 stine five grams at a time in dilute hydrochloric acid, added excess 
 of platinum tetrachloride, and boiled the solution for six hours in a 
 flask connected with an inverted condenser. The liquid gradually 
 acquired a dark-red colour. On being filtered from the deposited 
 platinum and cooled, white needles of opianic acid and crystals of 
 a platinum double salt, which could be easily separated with ether, 
 appeared. A further batch of crystals was obtained on evaporation. 
 The double salt was hydrastinine-platinous chloride, (C U H U NO 2 
 HCl) 2 PtCl 2 . 
 
 Dullo (J. pr. Ch. 78, 370) states that platinum dissolves very 
 rapidly in aqua regia without leaving any residue when the opera- 
 tion is conducted under pressure. A flask is used which is con- 
 nected with a bent glass tube, whose longer limb dips about a metre 
 beneath the surface of a cylinder of water. The vapours from the 
 acid can easily overcome this pressure, and the solution of the 
 metal occupies very little time. 
 
 37. Potassium Bichromate. Until this salt was largely re- 
 placed by sodium bichromate, the reagent known as chromic acid 
 mixture, in which the chromic acid was set free from potassium 
 bichromate by means of dilute sulphuric acid, was one of the most 
 generally used oxidising agents. Usually forty parts of bichromate 
 and fifty-five of sulphuric acid, the latter diluted with twice its 
 volume of water, are taken. This mixture is added to that contain- 
 ing the substance to be oxidised either at once or in a fine stream. 
 The reaction is frequently incomplete in the cold and has to be 
 assisted by boiling the mass. The first careful investigation of the 
 
 1 These substances seem also to have the power of increasing the activity 
 of other elements. For example, Debus states (Ann. 128, 200) that 
 methylamine is formed when hydrocyanic acid and hydrogen are led over 
 platinum black, 
 
272 OXIDATION [CH. xvm 
 
 applicability of bichromate in solution for the purpose of oxidation 
 was made by Penny (J. pr. Ch. 55, 210), who sought a liquid which 
 could be used in titrating. 
 
 Pfeiffer (Ber. 5, 699) oxidised isobutyl alcohol (100 gr.) by mix- 
 ing it with water (750 cc.) and a solution of chromic acid (95 gr.) in 
 a retort. Lipp (Ann. 205, 2) used the corresponding amount of 
 potassium bichromate dissolved in five times its weight of water in 
 place of the latter, and added the amount of sulphuric acid necessary 
 to set the chromic acid free. He warmed the alcohol and water to 
 70-80, and allowed the oxidising mixture to drop into it from a 
 funnel provided with a stop-cock. The author found that it was 
 advantageous to lead carbon dioxide through the solution during 
 the process, so as to facilitate the distillation of the aldehyde and 
 prevent its being oxidised further. The aldehyde was extracted 
 from the distillate by shaking with sodium bisulphite and was 
 finally isolated by redistilling the bisulphite compound with a 
 sufficient amount of a solution of sodium carbonate. 
 
 An excess of sulphuric acid beyond the theoretical amount usually 
 accelerates the process of oxidation. Beilstein (Ann. 133, 4) re- 
 commends the use of four times their weight of bichromate for 
 aromatic hydrocarbons. Popow (Ann. 161, 291) uses bichromate 
 (3 parts), sulphuric acid (i part), and water (10 parts) for oxidising 
 ketones. 
 
 The conversion of alcohols into ketones or aldehydes can be 
 carried out extremely well (Ber. 26, 822) by Beckmann's method 
 (Ann. 250, 325). By its use he was able to convert menthol, which 
 is hard to oxidise, into laevo-menthone. A solution of bichromate 
 (60 gr. = i mol.) and concentrated sulphuric acid (50 gr. = 2*5 mol.) 
 in water (300 cc.) is cooled to 30, at which temperature the salt 
 begins to crystallise, and the menthol (45 gr.) is added. The latter 
 becomes black superficially from the formation of a chromium com- 
 pound. Diligent shaking soon brings the oxidation to completion. 
 The liquid acquires a dark-brown tint and becomes gradually 
 warmer. The menthol becomes first soft and then turns into small 
 crystals of a chromium compound. When the temperature reaches 
 53 the black chromium compound suddenly breaks up into a 
 brown substance, which soon melts and decomposes into menthone. 
 If the temperature does not reach the necessary height, external 
 heat must be applied. If larger quantities are taken the mass must 
 be correspondingly cooled. 
 
 Departing somewhat from the rule in the above examples, it is 
 
37] POTASSIUM BICHROMATE 273 
 
 frequently necessary to use rather concentrated sulphuric acid. 
 Thus Grabe and Schultess (Ann. 263, 10) found that to oxidise 
 thioxanthone with potassium bichromate and sulphuric acid the 
 latter had to contain at least 50 per cent, of H 2 SO 4 . The same 
 result was attained easily by using chromic acid in acetic acid 
 solution. The product in either case was benzophenonesulphone 
 
 Other acids can be substituted for sulphuric acid. Thus Heinze- 
 mann (Ger. Pat. 4,570) oxidises anthracene to anthraquinone by 
 means of bichromate and hydrochloric acid. 
 
 Formerly potassium bichromate and nitric acid were used. For 
 example, Grabe and Liebermann (Ann. Suppl. 7, 288) oxidised 
 tetrabromoanthracene (i part) with potassium chromate (2 parts) 
 and colourless nitric acid of sp. gr. 1*4 (5-6 parts) in a large flask, 
 At first the action was violent and bromine was set free. When this 
 ceased the mixture was diluted with water and the yellow mass of 
 dibromoanthraquinone, which was precipitated, was recrystallised 
 from benzene. This oxidation is much more successful with chromic 
 acid and acetic acid. 
 
 A mixture of potassium bichromate and acetic acid sometimes 
 gives quantitative results. For example, Anselm (Ber. 25, 653) 
 obtained the theoretical amount of naphthalic acid from acenaph- 
 thene by this process. He heated acenaphthene (100 gr.) and 
 finely pulverised bichromate (600 gr.) with glacial acetic acid 
 (1,200 cc.) for five hours on the water bath at 80, and then boiled 
 the mixture, using an inverted condenser, for twenty-five hours 
 more. The product was poured into water, and sufficient sulphuric 
 acid was added to dissolve a chromium compound whose presence 
 otherwise interfered with filtration. The precipitated substance 
 which still remained was collected on a filter and dissolved in 
 boiling dilute caustic soda. This solution was decolourised by 
 boiling with animal charcoal, and the substance was reprecipitated. 
 In place of 140 grams, the theoretical amount, 125 grams of the 
 acid were obtained (cf. 45). 
 
 The oxidising power of these mixtures is calculated on the 
 principle that the CrO 3 is converted into Cr 2 O 3 
 
 K 2 Cr 2 O 7 + 4H 2 SO 4 = K,5SO 4 -f Cr 2 (SO 4 ) 3 + 4H 2 O + 3O. 
 
 The opinion was once expressed by Fittig (Z. Ch. 1871, 179) that 
 
 T 
 
274 OXIDATION [CH. xvm 
 
 ortho-compounds when oxidised were completely decomposed, and 
 failed therefore to yield products similar to those obtained from meta- 
 and para-derivatives. Exceptions to this rule have been observed 
 during succeeding years, so that the law seems not to be so general 
 as he had supposed (Am. Ch. J. 1, 36). 
 
 38, Potassium Chlorate. This substance has frequently been 
 used as an oxidising agent (M. f. Ch. 4, 134), and usually in pre- 
 sence of hydrochloric acid. But it must also be remembered that 
 the mixture can give rise to chloro-derivatives. 
 
 For example, Prager (Ber. 22, 2,994) dissolved ^-phenylpropylene- 
 vj'-thiourea (5 g r - = I mol.) in a mixture of equal parts of water and 
 crude hydrochloric acid (50 cc.), warmed the mixture slightly, and 
 added potassium chlorate (i mol.). After the liquid had remained 
 at rest for a considerable time, the product was deposited partly in 
 the form of white needles and partly as a brown resin. The latter 
 gave a quantity of the white crystals on being treated with alcohol. 
 
 Andreasch (Ber. 13, 1,423) covers sulphhydrantoin (5 gr.) with 
 hydrochloric acid of sp. gr. ro8 (50 cc.), and adds potassium 
 chlorate (4*2 gr.) in five portions. When the action becomes too 
 violent and chlorine is evolved, the mixture must be cooled. If 
 these instructions are observed the body dissolves without any 
 noticeable escape of gas, and the colourless liquid soon becomes 
 turbid from the deposition of a crystalline powder. The sulphhy- 
 drantoin is oxidised to carbamidesulphonacetic acid 
 
 C 3 H 4 N 2 SO + H 2 O + 30 = C 3 H 6 N 2 SO 6 . 
 
 The yield of potassium salt averages 70 per cent, of the sulphhy- 
 drantoin used, but when the above conditions are not carefully 
 observed the yield is zero, as the reaction takes a different 
 direction. 
 
 39. Potassium Ferricyanide. This oxidising agent is used in 
 alkaline solution. It is converted into potassium ferrocyanide 
 according to the equation 
 
 The colour changes during the process from the dark red of the 
 former substance to the light yellow of the latter. 
 
 Potassium and sodium hydroxides are the alkalis generally 
 employed, but when these would attack either the substance taken 
 or the product, sodium carbonate may be used. 
 
40, 41] POTASSIUM IODATE 275 
 
 Baeyer (Ber. 15, 57) employed this oxidising agent for obtaining 
 diphenyldiacetylene from phenylacetylene. He added the copper 
 salt of phenylacetylene (i mol.) to a solution of ferricyanide (i mol.) 
 containing caustic potash ( i mol.), and allowed the mixture to remain 
 for twenty-four hours. The precipitate was dried and extracted 
 with alcohol 
 
 2C 6 H 5 . C i CH + = C 6 H 6 . C i C . C i C . C 6 H 5 + H 2 O. 
 
 In some cases a large excess of the oxidising agent is used. For 
 example, Noyes (Ber. 16, 53) dissolved potassium ferricyanide (50 
 gr.) and caustic potash (23 gr.) in warm water (200 cc.), added 
 nitrotoluene (2 gr.) and boiled with reflux condenser for two to three 
 hours. Ortho- and paranitrobenzoic acid were formed. Toluene 
 itself is only oxidised by this agent with difficulty. It is worth 
 noticing that with equal quantities of the oxidising mixture twenty- 
 five times more /-nitrotoluene than toluene could be oxidised (Ber. 
 16, 2,296). 
 
 Konig (Dissert. Leipzig, 1891) shook a base (2 gr.) with ether 
 (45 cc.), a solution of ferricyanide (7*5 gr.), and caustic potash (13*5 
 gr.) in water (60 cc.) in a separating funnel. When the ethereal 
 solution was placed in a flask and the ether removed with a current 
 of air, the oxidation product remained behind in crystalline form. 
 
 40. Potassium Hydroxide. The oxidising action of fused 
 potassium hydroxide has been discussed already (cf. Chap. XV.). It 
 may be added here that by its means some syntheses can be 
 effected which are beyond the power of most other oxidising 
 agents (Ber. 21, 728). Thus it can oxidise phenol, and other similar 
 substances containing a carbon ring, to bodies containing two 
 carbon rings. Thus phenol itself gives diphenol 
 
 2 C 6 H 5 OH + = C 12 H 10 2 + H 2 0. 
 
 41, Potassium lodate. This salt has been used as an oxidising 
 agent in solutions containing sulphuric acid. 
 
 Warneke (Ar. Pharm. 1888, 281) dissolved wrightine (logr.) in five 
 percent, sulphuric acid (roogr.), added a solution of potassium iodate 
 (5 gr.) in water (150 cc.) and set the mixture aside in a dark place 
 for twenty-four hours. The iodine which separated was extracted 
 with chloroform, and ammonia was cautiously added to the colour- 
 less liquid. The oxywrightine came out in crystalline form, and 
 the quantity obtained was approximately equal to that of the 
 
 T 2 
 
276 OXIDATION [CH. xvm 
 
 original alkaloid. The preparation of this product by means of 
 other oxidising agents had been attempted in vain. 
 
 42. Potassium Manganate. Baeyer found that this salt was 
 much less active than the permanganate, and could be used for the 
 oxidation of such substances as were over-oxidised by the latter. 
 A solution of the subtance is best made by adding a sufficient 
 amount of alcohol to an alkaline solution of permanganate. 
 
 Fahlberg and List (Ber. 21, 243) stated that 0-sulphaminebenzoic 
 acid was most easily prepared by oxidising 0-toluenesulphamide with 
 an alkaline solution of potassium manganate. They prepared the 
 oxidising agent by fusing caustic potash (2 parts) with manganese 
 dioxide (i part) and dissolving the mass in water. The content of 
 manganate is readily ascertainable by titration with oxalic acid. 
 It is advisable to use excess of the manganate solution. The 
 oxidation is accomplished in a few seconds on the water bath, 
 and the excess of manganate is decomposed with alcohol. The 
 solution is filtered from the deposited manganese dioxide, nearly 
 neutralised with acid, concentrated on the water bath, and extracted 
 with ether. By using this process the above observers obtained 
 yields almost equivalent to those theoretically possible. 
 
 43. Potassium Permanganate. In contrast to the manganate, 
 which is seldom employed, the present salt is more frequently used 
 than any other oxidising agent. Its popularity may be explained 
 by the fact that it can be used in neutral, alkaline, or acid solution, 
 and that the termination of the operation is indicated by the dis- 
 appearance of its very marked colour. Baeyer (Ann. 245, 146) 
 founded his method of distinguishing between unsaturated acids 
 and saturated acids containing open or closed chains and carboxylic 
 acids of benzene and similar bodies on the precision with which 
 alkaline permanganate acts upon whole classes of organic sub- 
 stances in a perfectly analogous manner. 
 
 When used in neutral solution the decomposition is in accordance 
 with the equation 
 
 If the caustic potash formed by the action has a disturbing influ- 
 ence, carbon dioxide may be conducted through the liquid while 
 the permanganate solution flows in slowly in a thin stream (see 
 below). The oxidation is often conducted very slowly, and the 
 
43l POTASSIUM PERMANGANATE 277 
 
 addition of permanganate is stopped when it ceases to be de- 
 colourised after standing for a considerable time, say twenty-four 
 hours. The solution usually employed contains about 40 grains of 
 the crystallised salt in a litre. 
 
 The process of oxidation in alkaline solution is exactly similar to 
 that in neutral solution. In both cases the theoretical oxidising 
 power is calculated on the assumption that hydrated manganese 
 dioxide is precipitated. 
 
 In working with an add solution, it must be remembered that 
 the metal is dissolved and forms a manganous salt, so that the 
 equation is 
 
 In this case the acid and permanganate are added alternately in 
 small quantities, so that the whole of the acid is not present at one 
 time. 
 
 Aromatic sulphides are converted into sulphones by the action 
 of the calculated amount of dry pulverised permanganate in acetic 
 acid solution. An unusual method pursued by Semmler (Ber. 24, 
 3,819) was to pulverise the permanganate, pour melted myristicine 
 over it, repulverise the mixture when it solidified, and throw it into 
 boiling water. When the water cooled myristicinic aldehyde, a sub- 
 stance which could be obtained by no other method, was deposited. 
 On adding phosphoric acid to the mother-liquor, myristicinic acid 
 was precipitated. 
 
 The activity of the permanganate naturally varies with the 
 conditions under which it is applied. For example, Fahlberg and 
 List (Ber. 21, 243) found that when 0-toluenesulphamide was 
 oxidised by it in neutral solution, benzoylsulphinide was formed, 
 but as the amount of free alkali increased with addition of the per- 
 manganate, more and more 0-sulphaminebenzoic acid was produced. 
 The latter was formed exclusively when a strongly alkaline solution 
 was used. But when hydrochloric acid was present or carbon 
 dioxide was conducted through the liquid during the operation, the 
 action was very rapid, and more than twice as much permanganate 
 was used as would suffice to oxidise the methyl group. The 
 solution was found on examination to contain 0-sulphobenzoate and 
 nitrate of potassium. Using Schlosing's method they were able to 
 show that the whole of the nitrogen of the toluenesulphamide had 
 been oxidised to nitric acid. 
 
 Weith (Ber. 7, 1,058) dissolved pure orthotoluic acid in caustic 
 
278 OXIDATION [CH. xvm 
 
 soda, and added to the solution rather more permanganate than the 
 equation- 
 
 4 \COOK 
 
 requires. After heating the mixture for ten hours on the water 
 bath the oxidation was complete. The faintly green solution was 
 decolourised with alcohol and filtered, and the phthalic acid was 
 precipitated with hydrochloric acid. 
 
 Luff (Ber. 22, 297) dissolved nitroxycinnamic acid, m.-p. 218 
 (2 gr.), in soda, warmed the solution on the water bath, and added 
 the solution of permanganate (5 gr.) slowly. After heating the 
 solution for a long time, it was acidified, the manganese dioxide 
 was dissolved fcy adding sodium sulphite, and the clear solution was 
 extracted with ether. Nitroxybenzoic acid was obtained. 
 
 Baeyer (Ann. 245, 139) oxidised the diacetate of /-xylylene 
 alcohol, C 6 H 4 (CH 2 . C 2 H 3 O2)2, by warming it in a large basin on the 
 water bath along with water (1,000 cc.) and caustic soda of sp. gr. 
 1*22 (500 gr.). A 10 per cent, solution of permanganate (4*5 1.) was 
 gradually added. Finally, a further quantity of permanganate was 
 added, if necessary, until the solution became permanently violet, 
 and retained this colour even after three hours' heating. After the 
 excess of permanganate had been decomposed the liquid was 
 filtered through cloth to remove the dioxide. The latter, being 
 very finely divided, had to be washed with water containing soda 
 to prevent any of the precipitate running through. By adding 
 acid very slowly to the warm solution, terephthalic acid was thrown 
 down in needles. The yield was 125 per cent, of the /-xylene 
 originally used. 
 
 Reactions of this kind can be carried out quantitatively in very 
 dilute solution. On this fact, for example, Fox and Wanklyn (Z. 
 analyt. Ch. 25, 587) base a method for the quantitative estimation 
 of glycerol, in which an alkaline solution containing at most '25 per 
 cent, of this alcohol is employed. 
 
 The following was a very guarded method of oxidising used by Laves 
 (Ber. 23, I >4i 5)- He dissolved phenyl trithioformate(5-io gr.) in benzene, 
 and added gradually to the solution, which was shaken continuously, per- 
 manganate solution and enough sulphuric acid to preserve a constant acid 
 reaction. After the operation had occupied about two hours, the action was 
 brought to an end by heating on the water bath, and the excess of per- 
 manganate was destroyed with sulphuric acid. The aqueous layer was found 
 
44] SODA LIME 279 
 
 to contain a considerable amount of benzenesulphonic acid. From the 
 dried manganese dioxide a disulphonsulphide was extracted by alcohol. 
 When the process was modified (Ber. 25, 347) by dissolving the ester in 
 very little benzene and adding a cold mixture of equal parts of 5 per cent, 
 permanganate and 2 per cent, sulphuric acid until it was no longer de- 
 colourised, the mixture being shaken constantly during the gradual addition 
 of the liquid, it was found that, on dissolving the manganese dioxide 
 with sulphurous acid, the evaporated benzene solution gave twice as much 
 as before of that oxidation product which was insoluble in water. 
 
 It is often observed that the action of the permanganate is very violent. 
 For example, Cottau (Ber. 18, 376^) found that the action on an aqueous 
 solution of chloral hydrate took place in two stages. In the first phase, 
 the chloral was completely decomposed, and chlorine, oxygen, and carbon 
 dioxide were evolved, and manganese dioxide and potassium manganate were 
 formed. In the second phase, the last product converted the chloral into 
 chloroform, and carbon dioxide and oxygen, without chlorine, were given off. 
 
 As has already been mentioned, the small excess of permanganate, which 
 remains after an oxidisation is complete, is decomposed with alcohol or 
 sulphurous acid. Sodium formate may also be used for the purpose. 
 
 44. Soda Lime. After Dumas and Stas (Ann. 35, 133) had 
 come to the conclusion, on purely theoretical grounds, that when 
 alcohol was converted into acetic acid in presence of alkalis, the 
 acid must owe its formation to the oxygen of the water, they found 
 that soda lime, which they were the first to prepare, was a very 
 suitable alkali for the purpose. They prepared it by raising to a 
 red heat a mixture of equal parts of potassium hydroxide and pul- 
 verised caustic lime. This mixture became very hard on cooling, 
 and could then be reduced to powder. 
 
 When this mixture is brought in contact with alcohol, addition 
 takes place at once. The excess of the liquid can be expelled on 
 the water bath, and a solid mass containing lime, caustic potash, 
 and alcohol remains. When this solid is heated in a tube without 
 access of air, hydrogen gas is evolved very copiously, and strong 
 acids set acetic acid free from the residue, 
 
 CH 3 . CH 2 OH + KOH = CH 3 . COOK + 2 H 2 . 
 
 Brodie (Ann. 71, 149) used this process for converting ceryl 
 alcohol into cerotic acid and melissic alcohol into melissic acid. 
 
 Hell (Ann. 223, 269) then devised a quantitative method, de- 
 pending on this reaction, for determining the molecular weight and 
 atomicity of the higher fatty alcohols. The quantity of hydrogen 
 evolved evidently depends on the molecular weight of the alcohol 
 
28o OXIDATION [CH. xvm 
 
 in such a way that the larger the molecular weight is, the less 
 hydrogen will be evolved. Since alcohols and aldehydes con- 
 taining the same amount of carbon in the molecule produce the 
 same acids when fused with caustic potash, while the former will 
 evolve twice as much hydrogen in the process as the latter, the 
 fusion provides a convenient means of deciding to which class an 
 unknown substance belongs. The value of this method depends on 
 the fact that the ordinary ways fail to give precise information 
 when bodies of high molecular weight are in question. 
 
 Still later Liebermann (Ber. 20, 962) found in examining coc- 
 cerylic alcohol by this process that the oxidation took a very ir- 
 regular course. He obtained a well characterised acid, however, 
 by using a solution of chromic acid in acetic acid. 
 
 45. Sodium Bichromate, This salt has the great advantage 
 over potassium bichromate that it is much more soluble m water, 
 and it can therefore be used in solution without great dilution being 
 necessary. The potassium salt requires ten times its weight of 
 water at 20, while the sodium salt requires only from two to three 
 times its weight of the same solvent. The amount of chromic acid 
 in the commercial salt varies, however, and consequently, except 
 where a change of colour gives information as to the progress of 
 the action, the quantity which will be necessary has to be deter- 
 mined by previous analysis. 
 
 Kissling (Ch. Z. 1891, 374) recommends the titration of the salt 
 with a solution of ferrous ammonium sulphate, using potassium 
 ferricyanide as indicator. A drop of the solution is brought in 
 contact with a drop of the indicator from time to time. The con- 
 tent of sodium bichromate varies from 88 to 92 per cent., but may 
 be as low as 84 per cent. 
 
 In most cases the mixture used in oxidation has a concentration 
 similar to that given for potassium bichromate. It is often found 
 that a large amount of sulphuric acid cannot be added on account 
 of its action on the substance to be oxidised. It is therefore usual 
 to add only sufficient acid to decompose the bichromate. 
 
 Nietzki (Ber. 19, 1,468) gives the following method of oxidising 
 aniline to quinone, to take the place of his earlier process in which 
 potassium bichromate (Ann. 215, 127) was used. 
 
 A mixture of aniline (i part), water (25 parts), and sulphuric acid 
 (8 parts) is well cooled, and a concentrated solution of sodium 
 bichromate is allowed to flow in. The liquid soon becomes dark- 
 
45] SODIUM BICHROMATE 281 
 
 green, and, towards the end of the action, black. When more 
 bichromate is added, the most of the precipitate disappears, and a 
 brown turbid liquid remains, in which quinone and quinol are 
 suspended. The latter can be oxidised, by further additions of 
 bichromate, to quinone. 
 
 To obtain quinol, sulphurous acid is led through the mass 
 until the whole has been reduced, and the filtered liquid is ex- 
 tracted with ether. The direct extraction of the quinone is almost 
 impossible, on account of the formation of an emulsion. The 
 quinol is dissolved in the minimum amount of water, and 
 twice its weight of sulphuric acid is added. The mixture is then 
 cooled, and a solution of sodium bichromate is added until the 
 quinhydrone, which is at first formed, is all converted into pure 
 yellow quinone. It is removed by filtration and the part dissolved 
 is extracted with ether. The yield of quinone from quinol is equal 
 to that theoretically possible. 
 
 When the temperature of the mixture was kept at 5-10, Nietzki 
 obtained yields up to 85 per cent, of crude quinol. Later 
 Schniter (Ber. 20, 2,283) succeeded in increasing the yield by a 
 slight change in the conditions. He added the oxidising agent, 
 which in this case was potassium bichromate, in two portions, 
 allowing a period of from twelve to twenty-four hours to elapse 
 between the addition of the first third and the last two-thirds of 
 the salt. From 20 grams of aniline he obtained 19 grams of quinone, 
 or 86 per cent, of the theoretically possible amount. Thus quinone, 
 which, before Nietzki discovered the method of preparing it from 
 aniline, was quoted at a price almost equal to that of gold itself 
 (Ber. 10, 1,934), has now become one of the substances which are 
 easily prepared in large quantities. 
 
 According to Hesse (Ann. 200, 240), quinone is best crystallised 
 from petroleum ether. Sarauw (Ann. 209, 99) states that the hot 
 saturated solution in petroleum ether, after being filtered, should 
 not be allowed to become completely cold, as the substance last 
 deposited is somewhat impure. The warm mother-liquor should 
 be poured off as soon as a slight cooling has led to the deposit a 
 large proportion of the crystalline quinone. 
 
 Under potassium bichromate, a method of converting acenaphthene quan- 
 titatively into naphthalic acid was described. Even here the sodium salt 
 may be used with advantage, as the oxidation is more expeditious and the 
 product can be obtained directly in a purer condition. The yields are only 
 slightly smaller 25 grams of the hydrocarbon give 28-29 grams of the 
 
282 OXIDATION [CH. xvm 
 
 anhydride of the acid. Gr'abe and Gfeller (Ber. 25, 653) state however 
 that the oxidation must be conducted at first with caution, as the action is 
 liable to become too intense. The acenaphthene (25 gr.) is dissolved in 
 warm glacial acetic acid (300 cc.). When the solution has cooled to 80 
 coarsely powdered sodium bichromate (170-175 gr.) is added, at first very 
 cautiously, care being taken that the temperature does not exceed 85. 
 When the action becomes less violent the bichromate is added more rapidly, 
 and finally the whole is warmed on the water bath. The whole operation, 
 with the quantities given, occupies an hour. The mixture is finally heated, 
 with inverted condenser, in an oil bath for two hours, and then poured into 
 warm water. The granular precipitate is collected on a filter with the help 
 of a filter pump. On warming with 5 per cent, caustic soda (400 cc. ) the 
 product dissolves, and any of the unchanged substance which may remain 
 behind is oxidised by a repetition of the same process. 
 
 It is usually stated that phthalic acid is prepared by oxidising tetrachloro- 
 naphthalene with nitric acid. Liiddens (Ch. Z. 1891, 585) mentions that 
 it is now prepared technically by the oxidation of naphthalene or naphtha- 
 lenesulphonic acid with sodium bichromate and sulphuric acid. 
 
 46. Sodium Nitrite. Sodium nitrite is not very frequently 
 used as an oxidising agent, but, as Nolting has found, it can occa- 
 sionally be used very effectively. Nietzki and Steinmann (Ber. 
 20, 1,278) employed it in preparing purpurogallin from pyrogallol, 
 and obtained a better yield in this way than by any other process. 
 The solution of pyrogallol was acidified with acetic acid, and 
 sodium nitrite solution was added as long as nitrogen was evolved. 
 The precipitated substance was recrystallised after boiling with 
 animal charcoal. 
 
 Some years before this, Bernthsen (Ber. 16, 1,817) investigated 
 its action on methylhydrophenylacridine. On adding sodium 
 nitrite and hydrochloric acid to an alcoholic solution of the sub- 
 stance, he found that the colour changed at once and methyl - 
 phenylacridinium hydroxide was isolated by evaporating the 
 alcohol, dissolving the residue in water, and precipitating with 
 caustic alkali. The fact that the methyl group remained intact 
 is unprecedented in the history of oxidation. 
 
 V. Pechmann states (Ber. 26, 1,045) tnat hydrazones are most 
 easily oxidised to tetrazones by amyl nitrite (cf. 30). 
 
 47. Sodium Peroxide. This substance, which has recently 
 become an article of commerce, has not as yet found very wide 
 application as an oxidising agent in organic chemistry (cf., how- 
 ever, Ber. 26, 3,083). 
 
4 S- 5 o] SILVER OXIDE 283 
 
 48. Silver Acetate. Tafel (Ber. 25, 1,621) found in this salt a 
 very useful agent for converting piperidine and hydroquinoline deri- 
 vatives into the corresponding pyridine and quinoline compounds. 
 Piperidine (2*5 gr.) was dissolved in 10 per cent, acetic acid (25 cc.), 
 and the solution was heated for four hours in a hard glass tube with 
 silver acetate (30 gr.) at 180. When the tube was opened, carbon 
 dioxide escaped, and the silver acetate was found to have been 
 replaced by a gray spongy mass of silver, while the liquid had 
 become brown. The liquid was filtered, the silver was washed 
 with water, and the filtrate was mixed with much solid caustic 
 potash and distilled. The pyridine which passed over still con- 
 tained a little piperidine. By a similar process he prepared 
 conyrine from coniine. 
 
 49. Silver Nitrate. This salt was used by Bladin (Ber. 25, 
 185) for oxidising ethylidenedicyanphenylhydrazine by dissolving 
 the latter in alcohol and adding a solution of silver nitrate at the 
 ordinary temperature. When the liquid was filtered from precipi- 
 tated silver, phenylmethylcyantriazol was thrown down by water. 
 
 50. Silver Oxide. Effective oxidation with silver oxide seems 
 only to be possible in alkaline solution. For example, Kiliani 
 (Ber. 16, 2,415) found that it had very little action on a dilute 
 solution of glycerol, even when the mixture was heated for several 
 days at 60. On the other hand, large quantities of glycollic acid 
 were obtained in alkaline solution. He added the silver oxide, 
 obtained from silver nitrate (60 gr.), to a solution of 85 per cent, 
 glycerol (10 gr.) in water (200 cc.), with which calcium hydroxide 
 (6 gr.) had been mixed, and warmed the whole slowly to 60 on the 
 water bath. All the oxide was reduced at the end of four hours. 
 Carbon dioxide was conducted through the solution, and the precipi- 
 tated chalk filtered off. On evaporating the filtrate, glycollate of 
 calcium (4*6 gr.) crystallised out. The yield was relatively very good. 
 
 As is well known, ammoniacal silver solutions are the best re- 
 agents for recognising aldehydes or converting them into the 
 corresponding acids. The silver is precipitated as metal. Tollens 
 (Ber. 15, 1,830) states that such a solution is best prepared by 
 mixing a solution of silver nitrate (i part) in water (10 parts) and 
 of caustic soda (i part) in water (10 parts), and adding ammonia 
 drop by drop until the silver oxide has dissolved. The solution is 
 preserved in a stoppered bottle, and kept in a dark place. The 
 
284 OXIDATION [CH. xvm 
 
 ingredients should never be mixed in chance proportions, and care 
 should be taken never to let this solution evaporate, as the fulminate 
 of silver which is deposited may lead to dangerous explosions. 
 
 Eichengriin and Einhorn (Ber. 23, 2,886) found that the follow- 
 ing was the only way in which dihydrobenzoic acid could be ob- 
 tained from the aldehyde. Stronger oxidising agents always gave 
 benzoic acid. Freshly precipitated silver oxide (25 gr.) was dis- 
 solved in the quantity of very dilute ammonia which just sufficed 
 for the purpose, a few drops of caustic soda were added, and the 
 solution was warmed on the water bath to 60-70. The dihydro- 
 benzaldehyde (5 gr.), dissolved in a little alcohol, was allowed to 
 flow in drop by drop. The liquid became dark during the process 
 from the separation of metallic silver. The mixture was warmed 
 and shaken for a short time until a thick mirror of silver had 
 deposited itself on the side of the flask. It was then acidified with 
 hydrochloric acid, and the hydrobenzoic acid was removed from 
 the filtrate by extraction with ether. 
 
 51, Sulphuric Acid, Both concentrated and fuming sulphuric 
 acids are very useful oxidising agents for substances which are 
 attacked with difficulty, especially as high temperatures can be used 
 without the assistance of sealed tubes. 
 
 As early as 1861 Erlenmeyer and Lisenko (Jahresb. 1861, 590) 
 prepared ethyl disulphide from mercaptan by this method 
 
 Konigs (Ber. 12, 2,342) finally achieved the long sought conver- 
 sion of piperidine into pyridine by heating piperidine (10 gr.) with 
 excess of sulphuric acid for seven hours at 300. During the 
 operation a gentle stream of sulphur dioxide was given off, and the 
 liquid became brown, although no carbon was deposited. 
 
 Michler and Pattinson (Ber. 14, 2,162) heated dimethylaniline 
 with three or four times its weight of sulphuric acid for six hours at 
 180-210. A continuous stream of sulphur dioxide was evolved, 
 and tetramethylbenzidine was formed 
 
 C 6 H 4 .N(CH 3 ) 2 
 
 2C H 6 .N(CH,) 2 +H 2 S0 4 = | +S0 2 + 2H 2 0. 
 
 C C H 4 .N(CH 3 ) 2 
 
 An observation was made by Schmidt (J. pr. Ch. 151, 238), the 
 importance of which seems to have been realised so far only by 
 
52, 531 ZINC PERMANGANATE 285 
 
 technical chemists. He found that when anthracene derivatives, 
 including even anthraquinone, were treated at a low temperature 
 with large excess of sulphuric acid containing 70-85 per cent, of 
 anhydride, oxidation products alone were obtained, and no sulphonic 
 acids were formed. 
 
 For example, he heated one part of dry alizarin (dioxyanthra- 
 quinone) with ten or more parts of sulphuric acid containing 70-80 
 per cent, of SO 3 at 25-30 for a period of from one to four days, 
 and then poured the product into ice. An orange-yellow precipi- 
 tate, insoluble in water, was formed, whose properties agreed with 
 those of the neutral sulphate of a new colouring matter. It could be 
 crystallised under certain conditions. It was soluble in caustic 
 alkalis. When the alkaline solution was acidified a deep brownish- 
 yellow clear liquid resulted, which on boiling deposited a copious 
 precipitate of the final product, alizarin-bordeaux. The yield was 
 almost equal to the theoretical. 
 
 The investigations of Gattermann have shown that this substance 
 is a tetroxyanthraquinone, and contains no sulphonic acid group. 
 It contains therefore two atoms of oxygen more than the original 
 substance 
 
 O OH OH O OH 
 
 /\/\/\OH /\/\/\OH 
 
 ! I ! I - ' 
 
 O OH 
 
 When this substance is acted on by sulphuric acid (J. pr. Ch. 
 151, 250 ; cf. also Ber. 24, 3,067), at 200, or anthraquinone itself 
 is treated with sulphuric anhydride at 30, dark -green crystals of 
 hexoxyanthraquinone are obtained. It is evident therefore that 
 under these conditions sulphuric acid always acts as an oxidising 
 agent towards bodies of this class. 
 
 52. Tin Tetrachloride. This substance was used by Poirrier 
 and Chappat (Fr. Pat. 71,970) for the oxidation of methylaniline. 
 They added one part of the former to six parts of a concentrated 
 solution of the latter, and heated the mixture until it became viscous. 
 They precipitated the tin with alkali, and separated the dye by ad- 
 dition of salt. 
 
 53. Zinc Permanganate. Guareschi (Ann. 222, 305) sus- 
 pended thioaldehyde (150 gr.) in portions of 25-50 grams in water 
 
286 OXIDATION [CH. xvm 
 
 (400 cc.), and added zinc permanganate (450 gr.) in water (6 1.). 
 The action was complicated, and the results differed from those 
 obtained by the use of potassium permanganate. 
 
 In a few cases oxidation can be combined with condensation 
 (cf. Chap. XII. 36). 
 
 Heusler (Ber. 25, 1,668) sought to separate the constituents of 
 the tar, obtained by distilling brown coal, by fractional oxidation. 
 
CHAPTER XIX 
 
 REDUCTION 
 
 1. Reducing Agents, The following substances have been used 
 as reducing agents l : 
 
 Aluminium. 
 Ammonia. 
 
 Phenylhydrazine. 
 Phosphorous acid. 
 
 Ammonium sulphide. Phosphorous iodide. 
 Chromous chloride. i Phosphorus. 
 
 Ferrous chloride. Potassium arsenite. 
 
 Ferrous sulphate. Potassium hydrosulphide. 
 
 Ferrous potassium oxalate. Potassium hydroxide, alcoholic. 
 
 Formaldehyde. Potassium xanthate. 
 
 Grape sugar. Sodium. 
 
 Hydriodic acid. Sodium amalgam. 
 
 Hydrogen sulphide. Sulphurous acid. 
 
 Hydroxylamine. 
 Iron. 
 
 Magnesium. 
 Palladium-hydrogen. 
 
 Tin. 
 
 Tin bichloride. 
 
 Zinc. 
 
 Zinc dust. 
 
 1 The use of nascent hydrogen produced by electrolysis (Ger. Pat. 
 21,131) for the reduction of organic compounds seems to have met with no 
 success in the laboratory. For example, Haussermann (Ch. Z. 1893, I2 9) 
 states that when nitrobenzene is treated in this way in presence of alcoholic 
 caustic soda hydrazobenzene and benzidine sulphate (yield, together, 60 per 
 cent. ) are formed. In presence of dilute sulphuric acid and alcohol ben- 
 zidine sulphate and azoxybenzene are obtained. Even at a temperature of 
 60 (Ch. Z. 1893, 209), only traces of aniline are produced. On the other 
 hand, by using a cathode of zinc in place of platinum, aniline becomes the 
 chief product. 
 
288 REDUCTION [CH. xix 
 
 Here, as with oxidation, a better result is sometimes obtainable 
 by substitution of some other chemical change for direct reduc- 
 tion. 
 
 As may be seen from some of the examples given below it is 
 sometimes necessary to protect the product of reduction from the 
 oxidising influence of the air. In such cases an atmosphere of 
 carbon dioxide is used, or hydrogen sulphide is conducted through 
 the liquid, or a solution of sodium hyposulphite or of sodium thio- 
 sulphate is added to the mixture. The hyposulphite solution is 
 obtained by adding zinc dust to sodium hydrogen sulphite. In 
 many cases also a layer of ether on the surface of the liquid will be 
 effective. 
 
 2. Aluminium. This metal was used by Curtius and Jay (J. 
 pr. Ch. 147, 27) instead of zinc, but it did not appear to have any 
 advantages over the commoner metal. 
 
 3. Ammonia, Ammonia has a reducing effect on many nitro- 
 derivatives. For example, Laubenheimer (Ber. 9, 1,826) found 
 that after a solution of dinitrochlorobenzene, saturated with am- 
 monia, had remained at rest for four days a change had taken 
 place which was represented by the equation 
 
 Six years earlier, however, Clemm (J. pr. Ch. 109, 170) had shown 
 that, when the substance was heated with strong ammonia at 120, 
 the reaction took quite a different course. 
 
 4. Ammonium Sulphide, When several nitro-groups are 
 present they may be reduced one after the other by means of 
 ammonium sulphide. Orthonitraniline (Ber. 25, 987), however, 
 may be boiled for hours with ammonium sulphide without the 
 neighbouring nitro-group being attacked. This was formerly sup- 
 posed to be the only method by which such results could be 
 obtained, but now other reducing agents are known which act in 
 the same way. 
 
 Very often alcoholic solutions of ammonium sulphide are used. 
 They act less energetically than aqueous solutions. For example, 
 Schultze (Ann. 251, 158) states that w-nitrobenzamide is reduced 
 by the latter but not by the former. 
 
 Aside from this, however there are other circumstances which 
 
4 J AMMONIUM SULPHIDE 289 
 
 give the alcoholic solution an advantage. For example, Morgan 
 (Ch. N. 36, 269) prepared carbostyril by reducing 0-nitrocinnamic 
 acid with aqueous ammonium sulphide. Later, Friedlander and 
 Ostermaier (Ber. 14, 1,916) found that the method was only of 
 practical value when alcohol took the place of water. In Morgan's 
 experiment large quantities of resinous matters were formed so 
 that the yield of carbostyril was diminished and its purification 
 hindered. By using the ester of the acid and treating it with 
 alcoholic ammonium sulphide the authors avoided the formation 
 of resin entirely. Along with the carbostyril, however, another 
 substance, oxycarbostyril, was always formed in greater or less 
 amount. Hardly a trace of it was obtained by Morgan's method. 
 The authors endeavoured in vain, by altering the concentration 
 and quantity of the reducing agent and the duration of the action, 
 to determine exactly what conditions favoured its formation. 
 
 The preparation of these two substances is as follows : The 
 0-nitrocinnamic ether is heated in portions of thirty or forty grams 
 for several hours with concentrated alcoholic ammonium sulphide 
 in strong soda-water bottles placed in a water bath. When the 
 reduction is complete and the liquid becomes cold, a part of the 
 oxycarbostyril separates as an ammonium salt in shining plates, 
 and can be collected on a filter. The alcoholic filtrate, which has 
 acquired a brown colour from the separation of sulphur, is then 
 evaporated to dryness, and the residue is extracted with dilute 
 caustic soda. Pure carbostyril is thrown down by passing carbon 
 dioxide through the alkaline solution, and on subsequently adding 
 sulphuric acid the oxycarbostyril is precipitated. 
 
 Ammonium sulphide also lends itself to the reduction of -one of 
 three nitro-groups. Tiemann (Ber. 3, 218) found that trinitro- 
 toluene could be reduced to dinitrotoluidine by this means. 
 Beilstein (Ber. 13, 243) found the yield to be so poor that he 
 communicated an improvement on Tiemann's method. He dis- 
 solved trinitrotoluene (i part) in alcohol (2 parts), and added 
 gradually the theoretical amount of hydrogen sulphide (3 mol.) 
 in the form of ^ concentrated aqueous solution of ammonium 
 sulphide. After each addition of the latter the precipitate was well 
 stirred. The mixture was allowed to rest for a short time, and 
 was finally mixed with water. The precipitate was filtered, washed, 
 and boiled repeatedly with dilute hydrochloric acid as long as 
 ammonia caused any precipitation in the extract. The dinitro- 
 toluidine was purified by recrystallisation. 
 
 V 
 
290 REDUCTION [CH. xix 
 
 Bader (Ber. 24, 19654) obtained an almost quantitative yield of dinitrani- 
 line from trinitrobenzene. He dissolved trinitrobenzene ( 1 5 gr. ) in absolute 
 alcohol (450 cc.) by boiling in a large flask attached to a condenser till a 
 clear solution resulted. He then allowed a strong solution of ammonium 
 sulphide (90 cc. ) to flow drop by drop from a funnel into the boiling liquid. 
 Even after the addition of a few drops of the sulphide the liquid became 
 brown. The boiling was continued for an hour or an hour and a half, and 
 the solution was then poured into two or three litres of ice-cold water, the 
 latter being well stirred during the addition. The dinitraniline separated at 
 once in the form of a yellow flocculent precipitate. 
 
 Alcoholic ammonium sulphide is sometimes enclosed in a sealed tube 
 with the substance to be reduced. This method was employed by Schopff 
 for the reduction of w-nitro-/-anilidobenzoic acid. 
 
 Beilstein and Kurbatow (Ber. H, 2,056) attempted to reduce one of the 
 nitro-groups in chlorodinitro benzene with alcoholic ammonium sulphide. 
 They obtained, however, a substance containing sulphur, through the action 
 of the chlorine atom, instead of chloronitraniline. Further experiment 
 showed them that ammonium sulphide acted as a reducing agent only on 
 substances like symmetrical nitrodichlorobenzene in which the nitro-group 
 had no chloro-group or other nitro-groups as neighbours. In all other 
 cases, the chloro- or nitro-group is exchanged for sulphur or a group con- 
 taining sulphur. 
 
 5. ChromoilS Chloride, A solution of chromous chloride in 
 glacial acetic acid was used by Gimbel (Ber. 20, 975) for the 
 reduction of nitrosoanthrone. 
 
 6. Ferrous Chloride or Sulphate. These salts are often used 
 where free hydrogen cannot be employed ; as, for example, where 
 the latter might add itself to the substance to be reduced. 
 
 Ferrous chloride can be used in the solid form or in aqueous or 
 alcoholic solution (Centralblatt, 1849, 807). 
 
 O. Fischer (Ger. Pat. 16,750) has even found it possible to 
 obtain reduction and oxidation simultaneously in presence of ferrous 
 chloride. Paranitrodiamidotriphenylmethane gives on reduction 
 paraleucaniline, which can be oxidised in turn to rosaniline. In- 
 stead of conducting the operation in two stages, he converts the 
 substance directly into rosaniline as follows : The paranitrodi- 
 amidotriphenylmethane (i part) is heated with solid ferrous chloride 
 (2 parts) at 160-180 and stirred until a homogeneous fused mass 
 of a bronze colour is obtained. The product is extracted with 
 dilute hydrochloric acid, and the dissolved fuchsine is afterwards 
 
6] FERROUS CHLORIDE OR SULPHATE 291 
 
 separated from the solution. In this case the ferrous chloride 
 reduces the nitro-group, and simultaneously the methane group is 
 oxidised. The formation of rosaniline is expressed by the equation 
 
 N0 2 . C 6 H 4 
 
 The same reaction can also be carried out with homologues of 
 nitrodiamidotriphenylmethane as well as with a mixture of aniline 
 and toluidine. 
 
 Ferrous sulphate is much more frequently employed than ferrous 
 chloride, on account of the fact that its solid form permits of more 
 convenient quantitative use. In applying it for the purpose of 
 reduction, an aqueous solution is added to an alkaline liquid, and 
 the ferrous hydroxide which is precipitated effects the reduction. 
 It is specially useful in the case of unstable substances. The alkalis 
 used are ammonia, baryta water, and caustic soda. 
 
 Baeyer and Bloem (Ber. 15, 2,147) dissolved 0-nitrophenylpro- 
 piolic acid in excess of ammonia, and added gradually a saturated 
 solution of ferrous sulphate (10 parts). During the operation the 
 alkalinity of the liquid was maintained by addition of ammonia. 
 The reduction proceeded quickly, and its termination was recognised 
 by the fact that the brownish-black precipitate became reddish- 
 brown in colour. 
 
 Sometimes the ferrous sulphate is added to a boiling alkaline 
 solution. 
 
 Gnehm (Ber. 17, 754) suspended nitrodichlorobenzaldehyde (10 
 gr.) in a solution of ferrous sulphate (100 gr.) in water (i 1.), and 
 added excess of ammonia to the liquid. The amido-compound 
 which was formed was driven over with steam. This substance 
 was little soluble in water, but had the unusual property of dis- 
 solving in a solution of sodium bisulphite, from which it could be 
 reprecipitated by acids or alkalis. 
 
 The use of baryta water originated with Wohler (Pogg. Ann. 
 13, 448), who reduced picric acid (trinitrophenol), to picramic acid 
 (dinitroamidophenol), in its presence. 
 
 Claisen and Thompson (Ber. 12, 1,946) used the same alkali in 
 reducing nitro-acids as follows : The nitro-acid was dissolved with 
 the calculated amount of barium hydroxide ; the necessary quantity 
 of ferrous sulphate was then added to the warm solution, and 
 finally sufficient baryta water was added to precipitate the whole 
 of the iron. The mixture was warmed on the water bath until the 
 
 U 2 
 
292 REDUCTION [CH. xix 
 
 ferrous oxide had acquired the reddish-brown colour of ferric hy- 
 droxide. The barium sulphate and ferric oxide were then removed 
 by filtration, the barium in solution was precipitated with carbon 
 dioxide, and the solution, which contained the barium salt of the 
 amido-acid, was concentrated by evaporation. From the warm 
 solution the acid, which in this case was ;;z-amidophenylglyoxylic 
 acid (?;z-isatoic acid), was precipitated by adding hydrochloric acid. 
 An excess of the latter had to be carefully avoided, as it formed 
 a soluble hydrochloride with the amido-acid. The authors found 
 that it was best to add a small portion only of the hydrochloric 
 acid at one time, allow the liquid to cool, and remove by filtration 
 the crystalline precipitate, which formed very slowly. This opera- 
 tion was repeated until at length no more crystals could be 
 obtained. The employment of acetic acid, which is generally used 
 for precipitating amido-acids, was here inapplicable because it does 
 not decompose the salts of ;-isatoic acid. 
 
 In separating amido-acids from their hydrochlorides the method 
 of Dobner and v. Miller (Ber. 17, 939) may be used. The hydro- 
 chloride is dissolved in water, and the calculated amount of sodium 
 acetate or carbonate is added. If the acid is insoluble, it is at once 
 precipitated, or at all events crystallises out on standing. If it is 
 soluble, the solution is evaporated on the water bath, and the acid 
 or its sodium salt is extracted from the residue with alcohol. 
 
 Attempts to use ferrous sulphate in acid solution as, for example, 
 with concentrated sulphuric acid have been unsuccessful. 
 
 7. Ferrous Potassium Oxalate. Eder (M. f. Ch. 1, 137) states 
 that ferrous potassium oxalate is a much more efficient reducing 
 agent than any other organic or inorganic salt of iron. He finds 
 that its action is similar to that of ferrous hydroxide in alkaline 
 solution, ammoniacal cuprous chloride, or an alkaline solution of 
 pyrogallic acid. The reducing power manifests itself, not only in 
 faintly alkaline and neutral solutions, but also in those which are 
 slightly acid. The addition of too much acid, however, causes 
 deposit of yellow ferrous oxalate. 
 
 8. Formaldehyde. This substance is used in the reduction of 
 azo-dyes formed from nitramines (Ger. Pat. 62,352). 
 
 9. Grape Sugar. Grape sugar and milk sugar are used for 
 reducing purposes in 10 per cent, solution in water. This is added 
 
10] HYDRIODIC ACID 293 
 
 to an alkaline solution of the substance and the mixture is boiled. 
 This process is frequently used in the reduction of substances which 
 form dyes. 
 
 10. Hydriodic Acid, The very powerful reducing action of 
 hydriodic acid on organic bodies was discovered by Berthelot 
 (Bull. Ch. [2] 7, 53, and J. pr. Ch. 104, 103). 
 
 Mendelejeff (Principles of Chem. I., p. 500) gives the strength 
 and specific gravity of hydriodic acid as follows : 
 
 Sp. Gr. Content of HI. Sp. Gr. Content of HI. 
 
 i '07 5 I0 /o r 399 40% 
 
 1-164 20% 1-567 50% 
 
 1-267 30% 1769 6o/ 
 
 The strongest acid preparable by distillation boils at 127, con- 
 tains 57'57 per cent, of hydriodic acid, and has a specific gravity of 
 1-67. 
 
 The ease with which it decomposes irito hydrogen and iodine 
 accounts for its reducing power. It is used in aqueous solution 
 with or without phosphorus, and in acetic acid solution. 
 
 Berthelot, who applied it in absence of phosphorus, states that it 
 reduces every organic substance to the hydrocarbon containing the 
 same amount of carbon and the maximum amount of hydrogen in 
 the molecule. According to him it can be applied to all com- 
 pounds from fatty alcohols and acids to aromatic compounds and 
 from the nearly saturated ethylene derivatives to those in which all 
 the hydrogen has been replaced by chlorine. By its means 
 hydrogen can be added to amides and even to cyanogen (cf. how- 
 ever 23, p. 307). 
 
 His method consisted in heating the substance with a great 
 excess of strong hydriodic acid (sp. gr. 2) for ten hours at 275. 
 He estimated that a pressure of a hundred atmospheres was 
 reached under these circumstances. For aromatic bodies he 
 sometimes used as much as one hundred times their weight of the 
 acid. 
 
 In this way he reduced ethyl iodide and ethyl alcohol to ethane, 
 glycerol to propane, and thought he had reduced benzene to the 
 normal hydrocarbon, C 6 H 14 . 1 Methylamine gave methane and 
 ammonia ; aniline, benzene and ammonia, and so forth. 
 
 Baeyer (Ber. 19, 1,806) prepared hexahydroterephthalic acid by 
 heating tetrahydroterephthalic acid for six hours at 240 with 
 1 These experiments were carried out in 1867-68. 
 
294 REDUCTION [CH. xix 
 
 hydriodic acid of 127 boiling-point. The contents of the tube were 
 decolourised with sulphurous acid, and the precipitated acid was 
 dissolved in soda, reprecipitated, and recrystallised from hot water. 
 A very extraordinary and entirely unexpected action of hydriodic 
 acid was discovered by Eckbom (Ber. 24, 337). He found that, 
 when w-nitrobenzenesulphonic chloride was dissolved in acetic 
 acid, hydriodic acid of sp. gr. 1*5 was added, and the mixture was 
 warmed on the water bath for a short time, the sulpho-group was 
 completely reduced, while the nitro-group remained unattacked. 
 The product was ;//-dinitrodiphenyldisulphine. 
 
 2C 6 H 4 (NO 2 ) . SO,C1 + ioHI = C 6 H 4 (NO 2 ) . S . S . C C H 4 (NO 9 ) 
 
 + ioI+4H 2 O. 
 
 Kolbe (Ann. 118, 122) had found as early as 1861 that benzene 
 derivatives, when treated with sodium amalgam, have the power of 
 taking up hydrogen. After him other observers noticed the same 
 fact, but it was always found that not more than six hydrogen 
 atoms could be added, and the compounds formed had a marked 
 tendency to turn into benzene derivatives again. Those hydro- 
 genated compounds remained difficult to prepare until Baeyer 
 (Ber. 25, 1,037) showed how they could be made synthetically of 
 almost any desired type out of substances with simple carbon chains 
 
 ( 24). 
 
 Kolbe's communication induced Baeyer (Ann. 155, 267) to test 
 Berthelot's results, soon after their publication, under conditions 
 which he expected would be still more favourable to reduction. In 
 Berthelot's process iodine was set free and could not at all assist 
 the reduction by its presence, and furthermore water was present 
 and must have somewhat hindered the action even when the most 
 concentrated acid was used. Both of these substances could be 
 eliminated however by using phosphonium iodide. Any iodine, 
 which was set free by the decomposition of hydriodic acid, would 
 react with the phosphine, as Hofmann had shown, to form iodide of 
 phosphorus, and phosphonium iodide would be reproduced. When 
 the hydriodic acid of this new phosphonium iodide had been in 
 turn decomposed, the same action would again take place until all 
 was converted into iodide of phosphorus and phosphonium iodide, 
 in accordance with the equation 
 
 Although the action followed the expected course, the reducing 
 
io] HYDRIODIC ACID 295 
 
 power of this combination was found to be much less than that of 
 hydriodic acid itself. Still Baeyer found the reagent valuable as 
 it reduced hydrocarbons to exactly the same extent as sodium 
 amalgam reduced acids. 
 
 In heating hydrocarbons with phosphonium iodide thick-walled rather 
 narrow tubes must be chosen, as the pressure is sometimes considerable. 
 The weighed quantity of hydriodic acid is first placed in the tube, the 
 hydrocarbon is poured upon it, and finally the air is displaced by carbon 
 dioxide before the tube is sealed up. If the latter precaution is not ob- 
 served, an explosion may occur from the combustion of the phosphine when 
 heat is applied. When the reduction is complete long red needles are 
 observed in the tube, which probably have the composition PI. This de- 
 composition sometimes takes place without any reduction occurring. The 
 action then follows the equation 
 
 and a very powerful pressure is manifest when the tube is opened. 
 
 The object which Baeyer sought to attain, the removal of the 
 iodine, can be accomplished by adding phosphorus. The idea 
 originated with Lautemann (Ann. 125, 9), and with its adoption the 
 method became quite generally applicable, since now the formation 
 of unwelcome by-products containing iodine was reduced to a 
 minimum. 
 
 The free phosphorus unites at once with the iodine to form 
 phosphorus iodide, which in turn reacts with water to form hydriodic 
 acid and phosphorus acid 
 
 Still, in the heat, some by-products arise (C. R. 91, 883), and their 
 formation interferes slightly with the course of this theoretically 
 beautiful reaction. Thus when phosphorus and hydriodic acid are 
 heated at 160, phosphonium iodide is produced. 
 
 Yellow and red phosphorus are both used. With the former, 
 reductions can be carried out by simply boiling the substance with 
 strong hydriodic acid in a vessel attached to an inverted condenser. 
 The escaping gaseous acid is caught in water. Even red phos- 
 phorus may be used in this way. For example, Liebermann and 
 Topf(Ber9, 1,201) obtained dihydroanthracene by boiling hydriodic 
 acid (80 gr.) and yellow phosphorus (6 gr.) with anthraquinone 
 (20 gr.) for an hour. Later, however (Ber. 20, 1,854), they found 
 that red phosphorus produced the same result. 
 
 Baeyer (Ber. 5, 1,095) connected a flask of one litre capacity 
 
296 REDUCTION [CH. xix 
 
 with a wide condenser placed vertically. The upper end of the 
 condenser tube was fitted with a I- tube, through one limb of which 
 pieces of phosphorus could be introduced, while the other served 
 for the escape of hydriodic acid. In the flask hydriodic acid, boil- 
 ing at 127 (200 gr.), and iodoform (50 gr.) were placed. The 
 mixture was heated to boiling, and small pieces of phosphorus were 
 thrown in until the liquid ceased to become brown even on pro- 
 longed boiling. Then further portions of iodoform (100 gr.) and 
 the necessary amounts of phosphorus were added alternately with 
 the same precautions. The iodoform, CHI 3 , was reduced to methy- 
 lene iodide, CH a I 2 , which was separated by distillation. 
 
 Fischer (Ber. 24, 1,844) heated trioxyglutaric acid (i part) with 
 concentrated hydriodic acid (10 parts) and red phosphorus (^ part) 
 for four hours, in a flask attached to a reflux condenser, diluted the 
 product with water, and removed the hydriodic acid with silver 
 oxide. The warm, colourless filtrate was then freed from silver 
 with hydrochloric acid, and evaporated to a syrupy consistency. 
 This residue solidified to a mass of glutaric acid on cooling. From 
 mannose carboxylic acid (Ber. 22, 372) he obtained heptylic acid by 
 boiling its barium salt (35 gr.) with hydriodic acid, boiling at 127 
 (250 gr.), and red phosphorus (10 gr.) for five hours. The dark 
 solution was diluted with water, and the oil which separated was 
 extracted with ether. The extract was shaken with mercury to 
 remove free iodine, and evaporated. The oil which remained 
 (27 gr.) contained much iodine in combination. To decompose 
 the iodine compounds, dilute sulphuric acid was added, and zinc 
 dust was thrown in in small portions. After the mixture had re- 
 mained at the ordinary temperature for twelve hours, it was distilled 
 m a current of steam. Heptylic acid passed over, and was purified 
 by conversion into the barium salt. 
 
 Energetic reduction is attained with this method, as with Berthe- 
 lot's, by heating in sealed tubes. The amount of hydriodic acid 
 used does not require to be great. Grabe (Ann. 163, 352) states 
 that it suffices to take such a quantity that the water contained in 
 it is enough to convert the separated iodine and the phosphorus into 
 hydriodic acid and phosphorous acid. In preparing carbazoline, 
 
 C" H 
 c i2H 15 N, he took carbazol, j 4 \NH(6 gr.), phosphorus (2 gr.), and 
 
 CgH/ 
 
 hydriodic acid (7-8 gr.). He recommends the use of hard glass 
 tubes for such purposes. 
 
ii] HYDROGEN SULPHIDE 297 
 
 Some recent work of Lucas (Ber. 21, 2,510) has shown however that the 
 maximum reduction of aromatic hydrocarbons can only be reached by using 
 a large excess of the reducing agent and a sufficiently high temperature. 
 Thus he heated anthracene (1*5 gr.) in a sealed tube with red phosphorus 
 ( i '5 gr. ) and hydriodic acid of sp. gr. 1 7 (8 gr. ) for twelve hours at 250, and 
 obtained in this way the hydrocarbon, C 14 H 2 4. Grabe reached only C 14 H 16 . 
 
 Chrysene was supposed to be irreducible with hydriodic acid and phos- 
 phorus, because too little of the latter had been used. But Liebermann 
 and Spiegel (Ber. 22, !35> an d 23, M43) obtained perhydrochrysene by 
 heating chrysene (i part) with red phosphorus (i part) and hydriodic acid 
 of sp. gr. 1 7 (5 parts) for sixteen hours at 250-260. 
 
 Krafft (Ber. 15, 1,687) has found that the higher fatty acids, from 
 nonylic acid upwards, can be reduced by this method to normal hydro- 
 carbons. He charged strong tubes of hard glass with the fatty acid (2-4 
 gr.), hydriodic acid of sp. gr. 17 (3-4 gr.), and red phosphorus ('3- '4 
 gr.) and heated them at first to 210-240. These quantities being insuffi- 
 cient for completing the reduction, the exposure to the above heat was 
 limited to a short time lest the iodine seJt free should decompose the pro- 
 duct. This heating was repeated two or three times, and between each 
 heating the tube was opened and a little phosphorus was added. At the 
 third opening or so, an equal amount of water was added from a burette 
 along with the phosphorus, so as to supply a sufficient quantity of this 
 liquid to decompose the phosphorous iodide formed, and thus regenerate the 
 hydriodic acid. At the termination of the operation the hydrocarbon was 
 usually found floating upon the rest of the contents of the tube, and could 
 be separated from them mechanically. In the contrary case, water was 
 added to effect the separation. The products could also be extracted with 
 ether or other solvents. 
 
 Glaus (J. pr. Ch. 153, 3o) reduced mixed fatty and aromatic ketones to 
 hydrocarbons by stirring one molecular proportion of the ketone with one 
 third of its weight of water and an equal weight of red phosphorus, and 
 then adding iodine (4-5 mol.) to the warm mixture. After the whole had 
 been heated for eight days in an open flask with the naked flame, a few 
 drops of water being added if necessary, the brown oily product was dis- 
 tilled with a current of steam. The distillate was extracted with ether. 
 The extract was dried and deprived of free iodine with sodium, and finally 
 the ether was evaporated and the residue distilled over sodium. In this 
 way hydrocarbons of constant boiling-point were obtained, and the yields 
 were from 20 to 25 per cent, (minimum 15 per cent.) of the ketone used. 
 Metamethyl-/-ethyltoluene, for example, was prepared in this way from m- 
 xylylmethylketone. 
 
 11. Hydrogen Sulphide. Organic bodies are reduced by hydro- 
 gen sulphide, but it acts with difficulty in neutral or acid solution. In 
 
298 REDUCTION [CH. xix 
 
 the latter case reduction may be possible if the reagent is applied 
 in the nascent condition, as, for example, by adding zinc, barium, or 
 calcium sulphide to an acid solution of the reducible substance. 
 
 Merz and Weith state also that the action is assisted by the pre- 
 sence of finely divided copper. 
 
 Bernthsen mentions (Ann. 251, 23) that methylene red, which is 
 easily reducible with zinc and hydrochloric acid and by stannous 
 chloride and hydrochloric acid, is also reduced by hydrogen sul- 
 phide 
 
 C 8 H 9 N 2 S 2 C1 + 2H 2 S = C 8 H 12 N 2 S . HCl + sS. 
 
 Although seldom thus employed, it is an almost indispensable 
 reducing agent in alkaline solution. Its action depends on the fact 
 that its hydrogen unites with oxygen to form water, and the sulphur 
 is deposited or dissolves in excess of the alkaline sulphide. When 
 an ammoniacal solution is used, the excess of the reducing agent 
 can finally be removed by prolonged boiling with water. 
 
 The operation usually consists in adding ammonia to the liquid 
 to be reduced and saturating it with hydrogen sulphide. If neces- 
 sary, the addition of ammonia can be repeated, and more hydrogen 
 sulphide led into the mixture. 
 
 Zinin (Ann. 44, 283) first reduced a nitro-group to an amido- 
 group by this method, by acting with ammonium sulphide on nitro- 
 benzene. This was the first occasion on which a base containing 
 nitrogen had been prepared synthetically from a substance free 
 from nitrogen (benzene), and attracted much attention at the time, 
 as it marked a step in the direction of the artificial preparation of 
 alkaloids. 
 
 12. Hydroxylamine. Free hydroxylamine has the power of 
 reducing quinones to quinols. Still, on the whole, its reduc- 
 ing power towards organic bodies is very small. For example, 
 Boniger (Ber. 21, 1,762) made many experiments with it, all of 
 which failed. This is the more extraordinary, as the powerful 
 reducing action, which it shows in alkaline solution, has led to its 
 very wide application in photography. Silver is instantly preci- 
 pitated from its solutions in metallic form, and when no other noble 
 metal is present, this is probably the most convenient way of quickly 
 preparing pure silver. 
 
 13. Iron. Metallic iron is often used as a reducing agent, as 
 well as the salts which have been mentioned already. 
 
299 
 
 Schmidt and Schultz (Ann. 207, 329) distilled azoxybenzene 
 (60 gr.) with three times its weight of iron filings, and not a trace of 
 the unchanged substance passed over. The chief product was 
 azobenzene(72'5 percent.) with aniline and a small amount of car- 
 bonised material. 
 
 Iron is seldom employed in this way, however, as zinc dust is 
 more effective, but in presence of acids it is very frequently used. 
 
 For example, iron and hydrochloric acid is an excellent reducing 
 agent. In this case the extraordinary fact is sometimes observed 
 that much less hydrochloric acid is required than the simplest 
 equation representing the action seems to require. Thus for nitro- 
 benzene, the amount required is represented by the equation 
 
 This peculiarity is explicable as follows : The aniline which is 
 formed decomposes the ferrous or ferric chloride in presence of 
 water giving ferrous or ferric hydroxide and aniline hydrochloride, 
 and the latter is in turn decomposed by the excess of free iron into 
 ferrous chloride, aniline, and hydrogen. The last reduces a further 
 portion of the nitrobenzene, while the ferrous chloride goes through 
 the same transformation once more. The following equations 
 represent these changes 
 
 2C 6 H 5 NH 2 . HCl + Fe = FeCl 2 + H 2 + 2C H 6 NH 2 . 
 
 In the laboratory, iron filings and acetic acid are generally used, 
 and in fact this is the original form in which the method was sug- 
 gested by Bochamp (Ann. 92, 401). When the solution is boiled 
 after the reduction is complete, the acetate of iron is decomposed, 
 and finally little or no iron remains in solution. This property 
 gives the method an advantage over others in which a complicated 
 process is necessary for the final removal of the metal. 
 
 In working on a small scale, also, very little acetic acid need be 
 used. This renders the method applicable to substances in whose 
 case, for example, there would be danger of saponification by excess 
 of hydrochloric acid. 
 
 Thus with ^-nitracetanilide, tin and hydrochloric acid cannot be 
 used as the hydrochloric acid splits off the acetyl group. This 
 attempt having failed in the hands of Hobrecker (Ber. 5, 920), 
 Nietzki (Ber. 17, 343) employed iron and acetic acid. Amido- 
 acetanilide was easily formed, and was extracted from the product 
 
300 REDUCTION [CH. xix 
 
 with hot water. It is best to add soda to faint alkaline reaction, 
 and then, all the iron having been precipitated as carbonate, to boil 
 with water. 
 
 Lachowitz (Ber. 17, 1,162) finds also that iron and acetic acid is 
 the best reducing agent for the successive removal of chlorine 
 atoms from chloroketones. His investigations show that no action 
 takes place in the cold. The temperature must first be raised to 
 a definite point before the evolution of hydrogen begins, and the 
 action is more energetic the higher the temperature. The activity 
 of other reducing agents, such as zinc and hydrochloric acid in 
 alcoholic solution, although apparently less is really greater since 
 they remove several chlorine atoms immediately even in the cold. 
 
 In particular the examination of dichlorophenanthrone showed 
 that one chlorine atom was replaced at a temperature not exceed- 
 ing 1 00. Under these conditions the monochloro-product is ob- 
 tained pure and free from results of further reduction. Only when 
 the action has continued for a long time is a part of the mono- 
 chlorophenanthrone reduced to phenanthrone. This more extensive 
 reduction occurs completely when the temperature is raised from 
 1 00 to 110. 
 
 The removal of one of the atoms of chlorine from dichlorobenzil 
 was achieved in the same way. 
 
 In the applications of iron for the purpose of reduction which 
 have been thus far described, the action is due to the hydrogen gas 
 which is set free. If the observer wishes to ascertain whether all 
 the hydrogen produced is being used for reduction, the apparatus is 
 filled with carbon dioxide and a stream Of the gas is kept up during 
 the action. If the whole of the escaping gas is absorbed by caustic 
 potash, the absence of free hydrogen is proved. 
 
 The use of nascent hydrogen in neutral solutions will be described 
 under zinc. 
 
 14. Magnesium, This metal, which is obtainable in the forms 
 of powder and ribbon, has been little used hitherto for the reduction 
 of organic bodies. Baeyer (Ber. 2, 99) experimented on its action 
 upon acid chlorides. He dissolved the latter, for the purpose, in 
 glacial acetic acid, or suspended them in it. Phthalyl chloride gave 
 phthalic aldehyde. 
 
 15, Palladium-hydrogen. Saytzeff's work (J. pr. Ch. 114, 
 128) has shown the great reducing power of palladium charged 
 
16-18] PHOSPHOROUS IODIDE 301 
 
 with hydrogen. For example, he converted nitrobenzene into 
 aniline by its agency. The method is very inconvenient however. 
 
 16. Phenylhydrazine. The reducing power of this substance 
 was first recognised by Baeyer. Haller (Ber. 18, 92) reduced 
 pseudocumidine to pseudocumene by its agency. Zincke (Ber. 
 
 18, 787) converted quinone into quinol. Merz and Ris (Ber. 
 
 19, i,754) noticed, in connection with attempts to make o-nitrani- 
 line (cf. Ber. 25, 985), which was then difficult to prepare, more 
 easily accessible, that both the ortho- and para-compounds reacted 
 energetically with phenylhydrazine. Following up this observation, 
 Barr found (Ber. 20, 1,498) that when nitrophenol was warmed 
 with twice the calculated quantity of phenylhydrazine (2 mol.) 
 diluted with xylene, gas was rapidly evolved, and, on cooling, the 
 mixture deposited crystals of amidophenol. The nitro-group had 
 therefore been reduced to the amido-group. 
 
 Seidel (Ber. 23, 186) found that the ordinary reducing agents 
 had hardly any reducing action on the dye, C 18 H 12 N 2 O 2 . But when 
 it was heated to 120 with a solution of phenylhydrazine in xylene, 
 an energetic liberation of nitrogen took place, and soon a substance 
 crystallising in colourless plates was deposited. The phenylhy- 
 drazine was broken up quantitatively into benzene, nitrogen, and 
 hydrogen, and the last added itself to the dye forming the leuco 
 base, C 18 H 14 N 2 O 2 . Neither aniline nor ammonia was formed. 
 
 Phenylhydrazine may be applicable in many other cases, as its 
 power of giving hydrogen at rather high temperatures permits its 
 use in open vessels. 
 
 17. Phosphorous Acid. This reagent seems to possess no 
 special advantages as a reducing agent, and it has seldom been 
 used in this capacity. 
 
 18. Phosphorous Iodide. Phosphorous iodide may be used in- 
 stead of the mixture of red phosphorus and iodine or hydriodic 
 acid mentioned above. If its employment is desired, it may be 
 prepared according to Annaheim's directions (Ann. 172, 51). He 
 dissolved the iodine (60 gr.) in a little carbon disulphide, and added 
 phosphorus (8 gr.) in small pieces at a time. Then he evaporated 
 the solvent rapidly on the water bath, and removed the last traces 
 by warming in a current of dry air. 
 
 A substance to be reduced, such as dry diamidomethoxysulpho- 
 
302 REDUCTION [CH. xix 
 
 benzide (4 gr.), was placed on the iodide, and they were covered 
 with boiling water (30-50 cc.). An energetic emission of gas began 
 at once, and streams of hydriodic acid were evolved. The mass 
 became fluid, and the action seemed to be complete at the end of a 
 few minutes. In this particular case, however, the original sub- 
 stance was recovered unchanged. 
 
 19. Phosphorus. Purpurin (trioxyanthraquinone) is converted 
 into purpuroxanthin (metadioxyanthraquinone) (Ann. Ch. Ph. [5], 
 18, 224) by the action of phosphorus and caustic soda. 
 
 20. Potassium Arsenite. A solution of arsenious acid in 
 potassium hydroxide was used by Williams (Ann. 102, 127) for 
 the conversion of nitrobenzene into aniline. He digested the nitro- 
 benzene with the solution for some time, and then isolated the 
 aniline by distillation. 
 
 21. Potassium HydrosulpMde. Potassium or sodium hydro- 
 sulphide may be used exactly like ammonium sulphide. They have 
 the disadvantage that they cannot be removed by evaporation. 
 
 22. Alcoholic Potassium Hydroxide. Alcoholic caustic potash 
 
 or soda 1 is used almost exclusively for the reduction of nitro-bodies 
 to azoxy-derivatives. They act consequently like sodium amalgam, 
 the nitro-group being reduced through its oxygen oxidising the 
 alcohol. For example, nitrobenzene (i part) is dissolved in strong 
 alcohol (5-6 parts) and first warmed and finally boiled with solid 
 caustic soda (i part). The alcohol is distilled off until the residue 
 separates into two layers. The upper brown layer is washed with 
 water until it solidifies to a crystalline mass. Pure azoxybenzene is 
 obtained from this by recrystallisation. The method was devised 
 by Zinin (cf. p. 304), and the yield may reach 40 per cent, of the 
 nitrobenzene used. 
 
 Buchka and Schachtbeck (Ber. 22, 835) employed methyl 
 alcohol. In preparing w-azoxytoluene, w-nitrotoluene (10 gr.) was 
 heated in a flask attached to a condenser with caustic soda (10 gr.) 
 dissolved in methyl alcohol (90 gr.) for about six hours on the 
 water bath. The alcohol was distilled off, and the unchanged nitro- 
 toluene was driven over with steam. The oil which remained was 
 
 1 Very strong solutions of caustic potash in methyl or ethyl alcohol are 
 best prepared by mixing a very concentrated aqueous solution with the 
 alcohols. 
 
23] SODIUM 303 
 
 extracted with ether, and when this was allowed to evaporate a 
 crystalline residue remained. 
 
 23. Sodium. Both sodium and sodium amalgam are in very 
 frequent use on account of their great reducing power and the ease 
 with which they can be applied. 
 
 The sodium is usually employed in the form of thin discs, al- 
 though this way of using it has some disadvantages, especially 
 when the surface tends to become covered with an insoluble layer 
 which hinders the action of the parts concealed. 
 
 Hofmann (Ber. 7, 534) introduced the use of a press which sup- 
 plies it in the form of wire. Briihl (Ber. 24, 3,384) makes the 
 remark that the metal for producing thin sodium or potassium wire 
 should be purified by fusion under toluene. The wire he used had 
 a diameter of '2 mm. If the metal is not purified in this way the 
 press may easily become stopped up, and in the case of potassium 
 dangerous explosions take place. The metal which has been once 
 fused under toluene so that it flows to a clean liquid metallic mass 
 is sufficiently pure for all purposes. It should be preserved under 
 light petroleum rather than heavy petroleum or toluene. In the 
 former the metals, especially sodium, can be kept almost indefinitely, 
 and may be used directly without being scraped. 
 
 The metals may be obtained in a finely divided state, without 
 the intervention of any machine, as follows : The sodium is covered 
 with petroleum, and heated to about 120. The flask is corked, well 
 shaken, and, the cork having been removed, is then set aside till 
 cold, in a place where it will not be disturbed. The metal, in 
 cooling, retains its fine granular form. If the temperature exceeds 
 120 the metal cakes together again on cooling. Levy and 
 Andreocci (Ber. 21, 1,464), state that when melted paraffin is used 
 in place of petroleum, the metal obtained is still more finely 
 divided. In this case after the shaking the paraffin is poured off", 
 and the remainder washed out with petroleum ether at 50. They 
 state that the metal is best kept under the same liquid, so that it 
 can be rapidly dried before use. 
 
 When considerable quantities of sodium have been used, the 
 addition of water to remove any excess of the metal which may 
 remain is attended with the danger of violent explosion. It is 
 preferable, when the amount of sodium remaining must be small, to 
 add powdered ice. In the contrary case, the flask should be broken, 
 if it cannot be emptied otherwise. 
 
304 REDUCTION [CH. xix 
 
 The sodium is allowed to act both on aqueous, alcoholic, and 
 ethereal solutions. To hasten its action the sodium hydroxide 
 which is formed is partially neutralised with acids from time to 
 time, care being taken that the liquid does not actually become 
 acid. 
 
 Sometimes the presence of caustic soda is harmful, and yet the 
 liquid may not be rendered acid with a strong acid even tem- 
 porarily. In such cases an amount of sodium bicarbonate sufficient 
 to neutralise the caustic soda may be added at the beginning. 
 
 Klinger (Ber. 15, 866) has found that a solution of sodium in 
 methyl alcohol, as distinct from ethyl alcohol, is very suitable for 
 the reduction of nitro-bodies to azo-bodies. 1 He used sodium 
 (10 parts) dissolved in methyl alcohol (250 parts), added pure 
 nitrobenzene (30 parts), and boiled the mixture on the water bath 
 for five or six hours in a flask attached to a condenser. The liquid 
 became reddish-brown in colour and remained clear. When the 
 methyl alcohol was distilled off the colour became lighter, crystals 
 of sodium formate separated, and finally a light yellow mass 
 saturated with oil remained behind. On treating this with water, 
 he found that light yellow liquid azoxybenzene, which soon solidified, 
 was deposited. The yield was copious. The action was repre- 
 sented by the equation 
 
 4 C 6 H 5 N0 2 + 3NaOCH 3 = 2 (C C H 5 N) 2 + 3 NaHCO 2 
 
 When p- and <?-nitrotoluene were used, no azoxytoluene was 
 obtained. 
 
 The reducing action of sodium on solutions in ethyl alcohol is 
 best bi ought into play by adding the metal to the boiling solution. 
 This method was probably first used by Baeyer (Ber. 12, 459) in 
 the reduction of dichloroindole. Using the same method Wischne- 
 gradsky (Ber. 13, 2,401) prepared hexahydroethylpyridine from 
 ethylpyridine. 
 
 Ladenburg (Ann. 247, 51 and 80), who adopted the method on 
 account of its usefulness, states that it is a point of importance to 
 use as small an excess as possible of absolute alcohol, and to keep 
 the temperature at the boiling-point of the solution. 
 
 In converting pyridine into piperidine, he dissolved the pyridine 
 (20 gr.) in absolute alcohol (150 gr.) in a flask attached to a con- 
 
 1 Cf. Witt's use of an alkaline solution of stannous hydroxide for the 
 same purpose (p. 320). 
 
23] SODIUM 305 
 
 denser, and warmed the solution on the water bath. He then 
 added, not too slowly, the required amount of sodium (75 gr.), which 
 had previously been cut into small pieces and preserved in dry 
 ether. When the action became slow or sodium ethylate separated 
 he added more alcohol, and in general hastened the reduction as 
 much as possible. 
 
 When all the sodium was dissolved he allowed the solution to 
 cool, added an equal bulk of water, and distilled the mixture 
 cautiously on the water bath. The piperidine passed over almost 
 entirely with the alcohol. After neutralising with hydrochloric acid 
 the distillate was evaporated to dryness. The yield was practically 
 quantitative. 
 
 In reducing a-lutidylalkine (Ber. 24, 1,674), C 6 H 4 (CH 2 . CH 2 . CH 2 
 OH)N (13 gr.), the base was dissolved in hot absolute alcohol 
 (130 gr.), and the solution was poured on to sodium (50 gr.) which 
 was contained in a large, flask attached to a condenser and was 
 warmed on the water bath. As soon as the action became slower 
 more hot absolute alcohol was added. By adding water, extracting 
 with ether, and evaporating the extract, he obtained a base contain- 
 ing six additional atoms of hydrogen, C 5 H 9 (CH 2 . CH 2 . CH 2 OH)NH, 
 and having the composition of conhydrine. 
 
 He dissolved trimethylene cyanide in eight times its weight of 
 absolute alcohol, added gradually 4 parts of sodium, taking care to 
 exclude moisture, and so obtained pentamethylenediamine 
 
 rH /CH 2 CN rH /CH 2 . CH 2 NH 2 
 CH 2\CH 2 CN + 4H 2 - -H 2 ^ CH2>CH2NH2 
 
 Pentamethylenediamine, whose preparation by Ladenburg's method 
 is extremely easy, had previously (Ber. 16, 1,151) been obtained in 
 traces only by the use of other reducing agents. 
 
 It may be mentioned that the first reduction of cyanides to 
 amides by means of nascent hydrogen was accomplished by 
 Mendius (Ann. 121, 129). He prepared methylamine from hydro- 
 cyanic acid, using zinc and hydrochloric acid 
 
 When amyl alcohol is used instead of ethyl alcohol with sodium 
 (cf. Baeyer, Ber. 12, 459) the combination has a much greater 
 reducing power and capacity for adding hydrogen atoms to un- 
 saturated substances. 
 
 When used in this way the metal sinks to the bottom of the 
 vessel and may easily crack it. Tafel (Ber. 20, 250) suggests the 
 
 x 
 
306 REDUCTION [CH. xix 
 
 addition of coarse sand, or some similar substance, to prevent 
 contact of the metal with the bottom of the flask and so avoid this 
 danger. 
 
 This method has been worked out and applied particularly to the 
 naphthalene derivatives by Bamberger (Ber. 20, 2,916). The 
 necessary amount of sodium is placed in a flask, and the boiling 
 solution of the substance in amyl alcohol is allowed to flow on to it 
 The sodium is cut in thin pieces, and a flask with a long neck is 
 selected and is provided with an efficient condenser. The tempera- 
 ture is kept up to the boiling-point of the alcohol till all the sodium 
 has disappeared. 
 
 Bamberger noticed at the time of his first experiments that the 
 hydrogenated bases are also formed, but in much smaller quantity, 
 when the sodium is gradually added to the alcoholic solution. 
 When ethyl alcohol was used the yield sank to a minimum, and by 
 far the greater part of the naphthylamine, for example, escaped 
 reduction (see below). 
 
 Further details of the method are as follows : For 1 5 grams of 
 sodium about 1 50 grams of amyl alcohol are used, and the solution 
 occupies about half an hour. From one and a half to two times as 
 much sodium is taken as the theory requires. When the operation 
 is over the solution is poured into water, and the upper layer is 
 separated and dried with potash. Then the amyl alcohol is distilled 
 off, a vertical tube full of beads being interposed, and the residue is 
 crystallised or fractionated. The yields vary from 40 to 80 per 
 cent, of the theoretical, and in a few cases nearly reach 100 per 
 cent. (Ber. 20, 3,075)- 
 
 He has stated in a later paper (Ber. 22, 944) that the same result 
 may be attained by adding the sodium, in portions of 5 grams, to 
 the boiling solution ; that, in fact, this method is preferable to the 
 other since the hydrogen is evolved more gradually and so acts 
 more effectively. It is only when the hydro-base cannot be ex- 
 posed to a temperature of 130 for any length of time without 
 danger of decomposition that the more rapid method is to be 
 preferred. In either case, care must be taken towards the end of 
 the operation, when the sodium begins to dissolve slowly, to add 
 boiling amyl alcohol to assist the operation. 
 
 In the reduction of 1*5 napthalenediamine (m.-p. 189) he dis- 
 solved the base (14 gr.) in boiling amyl alcohol (200 gr.), and added 
 sodium (18-20 gr,) cut in small pieces in portions of five grams at 
 a time. The liquid, which was at first dark-red in colour, became 
 
23] SODIUM 307 
 
 light brown. The hydrochloride of the 1*5 tetrahydronaphthalene- 
 diamine which was formed, being very soluble in water but almost 
 insoluble in amyl alcohol, could be extracted quantitatively by 
 repeated shaking with very dilute hydrochloric acid 
 
 H NH 2 .H 
 HV/H 
 
 This method has great advantages over the use of hydriodic acid. 
 The operations are carried out in open vessels, and large quantities 
 of the substance can be treated at one time. The results are 
 usually, although not invariably, the same with both agents. For 
 example, the present method brings about the introduction of four 
 atoms of hydrogen into phenanthrene very easily. This result can 
 only be reached otherwise by heating the hydrocarbon with hydri- 
 odic acid and phosphorus at 220-240 for six or eight hours. In 
 some cases even, reductions can be effected which are beyond the 
 power of hydriodic acid. Thus retene resists the action of 
 the latter at 100, while sodium and amyl alcohol introduce 
 four hydrogen atoms. And diphenyl, which had previously 
 been unreducible, and remained intact after heating at 280 with 
 phosphorus and hydriodic acid, was easily converted, to the extent^ 
 of more than 70 per cent., into a liquid tetrahydro-derivative by the 
 present reducing agent. 
 
 Anthracene, on the other hand, takes up only two atoms of hydro- 
 gen, while hydriodic acid and phosphorus produce complete 
 hydrogenation. Hydrocarbons containing only one ring are not 
 reducible by sodium and amyl alcohol. The process does not 
 therefore give the most complete hydrogenation, although this 
 might be attained by substituting a product of higher boiling-point, 
 such as secondary octyl alcohol (Ber. 25, 3,345), which boils at 180. 
 Still, even this failed in the case of aniline (Ber. 22, 1,311), and 
 Briihl (Ber. 25, 1,792) could not reduce camphoric anhydride in 
 solution in boiling naphthalene, using sodium and borneol, an 
 alcohol boiling at 212, for the purpose. 
 
 In ethereal solutions the sodium is applied by dissolving the 
 substance in five or six times its volume of undried ether and 
 adding the metal to the solution. Or the substance may be dis- 
 solved in so much ether, benzene, or other solvent that sodium 
 
 X 2 
 
308 REDUCTION [CH. xix 
 
 will sink in the solution, and this solution may then be floated upon 
 water. 
 
 - For example, Bogdanowska (Ber. 25, 1,272) obtained the corre- 
 sponding secondary alcohol from dibenzyl ketone by dissolving 
 the ketone in ether, pouring this upon a solution of sodium bi- 
 carbonate, and throwing in the sodium in small pieces while the 
 flask was kept cold in a stream of water. The operation occupied 
 six or seven days. For each part, by weight, of the ketone at least 
 as much sodium must be taken, and the presence of sufficient 
 sodium bicarbonate to prevent the formation of free caustic soda 
 must be assured. When these conditions are fulfilled the yield 
 reaches 80 per cent, of that theoretically possible 
 
 (C 6 H 5 . CH 2 ) 2 CO + 2H = (C 6 H 5 . CH 2 ) 2 CHOH. 
 
 24. Sodium Amalgam, The method of using sodium amalgam 
 is similar to that described for sodium, but its action is less energetic 
 than that of the latter. 
 
 The amalgam is prepared by gradually adding sodium to mercury 
 in a porcelain mortar. The operation must be conducted under 
 a hood on account of the poisonous mercury vapour which is given 
 off. It usually is made to contain 2.\ per cent, of sodium (Taeel, 
 Ber. 22, 1,870), as the product is then solid and can be pulverised 
 An a mortar and passed through a sieve. Prepared in this way, it 
 should contain no pieces larger than a pea. 
 
 All the experimenters who may be regarded as authorities on 
 the use of sodium amalgam concur in finding that the success with 
 which it may be employed in delicate reactions depends largely 
 on its quality (Ber. 25, 1,255). Aschan (Ber. 24, 1,865) uses care- 
 fully purified mercury, and brings it in contact with the sodium 
 in a vessel of such a nature that no foreign metal can gain access 
 to it. To avoid the presence of carbon in the amalgam, the sodium 
 should be carefully cleansed from oil. This author suggests that 
 impurities in the mercury may produce electrical currents which 
 bring about the liberation of molecular, and therefore inactive, 
 hydrogen. To Aschan is also due the discovery of the mode of 
 using the amalgam in presence of carbon dioxide, a method which 
 seems to bring out its reducing power most fully. For example, 
 when sodium benzoate is boiled in aqueous solution with sodium 
 amalgam some hydrogen is added indeed ; but the action becomes 
 slower and slower as the sodium hydroxide accumulates in the 
 
24] SODIUM AMALGAM 309 
 
 solution. If the attempt is made to neutralise this from time to 
 time by adding mineral acids, the amalgam dissolves more rapidly, 
 but the hydrogen does not add itself to the benzene ring. But 
 when the alkali is continually removed by carbon dioxide, the 
 addition goes on rapidly to completion. The details of his method 
 are as follows : 
 
 The benzoic acid (50 gr.) is dissolved in a 10 per cent, solution 
 of soda (250 cc.) in a strong flask provided with a vertical tube 
 to condense the vapour. The flask is placed in a large water bath, 
 and the sodium amalgam (25- kg.) is added three to four hundred 
 grams at a time. A gentle stream of carbon dioxide is conducted 
 into the solution during the operation. Under these circumstances 
 very little hydrogen escapes as gas. It is necessary occasionally 
 to remove the mercury which accumulates at the bottom of the 
 flask and to add a little water when the sodium bicarbonate begins 
 to crystallise. The reduction occupies from twenty to twenty-five 
 hours, and its termination is marked by the fact that when acid 
 is added to a small sample of the liquid an acid is precipitated 
 which remains fluid in the cold, even after standing for hours. It 
 differs in this respect from benzoic acid, and is in fact tetrahydro- 
 benzoic acid (Ber. 24, 2,619). It may be remarked in passing 
 that hexahydrobenzoic acid may be prepared from this by add- 
 ing hydrobromic acid to the remaining double bond, and then 
 replacing the bromine with hydrogen by reduction with sodium 
 amalgam. 
 
 This method of reduction has since been used by Baeyer (Ber. 
 25, 1,038) for preparing quinite, the simplest sugar of the inosite 
 group. Maquenne has shown that inosite possesses a closed chain, 
 and is a hexamethylene derivative of the composition C C H 12 O C . 
 
 By the action of sodium or sodium ethylate on succinic ether 
 succinosuccinic ether is formed. The acid prepared from this 
 substance gives easily diketohexamethylene by loss of two molecules 
 of carbon dioxide 
 
 CH, - CO - CH . COOC 2 H 5 CH 9 - CO - CH 9 
 
 I I - I I 
 
 COOC 2 H 5 . CH - CO - CH 2 CH 2 - CO - CH 2 
 
 Baeyer added hydrogen to this substance by dissolving the ketone 
 (5 gr.) in sodium bicarbonate, throwing in sodium amalgam (260 gr.), 
 and conducting a rapid stream of carbon dioxide through the 
 
3 io REDUCTION [CH. xix 
 
 mixture for seven hours. The amalgam was added rather gradually 
 at first. The product, quinite or dioxyhexamethylene 
 
 CH 2 -CH(OH)-CH 2 
 CH 2 -CH(OH)-CH, 
 
 was similar in appearance and properties to the sugars of the 
 inosite group. 
 
 Formerly the method of conducting hydrochloric acid into sodium 
 amalgam used to be employed. Thus Lippmann (Z. Ch. 1865, 
 700) covered the liquid amalgam with benzoyl chloride, and passed 
 hydrochloric acid into the mixture. The product was benzyl 
 alcohol 
 
 The partial neutralisation of the sodium hydroxide with an acid 
 increases the reducing power and speed of action of sodium amalgam 
 just as it does that of sodium. The way in which the effectiveness 
 of the amalgam varies with the conditions is shown by the number 
 of hydrophthalic acids which Baeyer obtained by its use (Ann. 
 251, 290). The reduction of lactones in acid solution by Emil 
 Fischer (Ber. 23, 932), in connection with the synthesis of grape 
 sugar, has demonstrated in the clearest way the value of destroying 
 the effect of the free alkali by using some acid, not necessarily 
 carbon dioxide. 
 
 The lactone, or syrup containing the lactone, is dissolved in ten 
 parts of water in a bottle. The liquid is slightly acidified with 
 sulphuric acid, placed in a freezing mixture until ice begins to 
 form, and then a small amount of i\ per cent, sodium amalgam 
 is added. When the whole is violently shaken the amalgam is 
 quickly exhausted without evolution of hydrogen gas. This process 
 is repeated, with occasional cooling and frequent addition of sul- 
 phuric acid to preserve the acid reaction of the liquid, until finally 
 towards the end of the operation hydrogen is given off. It is best 
 to determine the quantity of amalgam which is required by titrating 
 a small sample of the liquid, say '2 cc., with Fehling's solution 
 from time to time. When the reduction of Fehling's solution 
 reaches a maximum the action is complete. Pure lactones require 
 ten to fifteen times their weight of amalgam of the above strength. 
 
 Weidel (M. f. Ch. 11, 510) reduced nicotinic acid (40 gr.) in 
 alkaline solution by dissolving it in 25 per cent, caustic potash. 
 To the boiling solution he added gradually 4 per cent, sodium 
 
25] SULPHUROUS ACID 311 
 
 amalgam until the evolution of ammonia ceased. The operation 
 occupied from three to four hours. 
 
 The amalgam is used also in alcoholic, ethereal, and acetic acid 
 solutions. For example, Glaus (Ann. 137, 92) dissolved benzalde- 
 hyde in five or six times its weight of moist ether, and added 
 excess of semi-solid amalgam. An energetic action took place, 
 so that cooling was necessary to keep the ether from boiling. 
 The products were freer from coloured by-products the lower the 
 temperature was kept. 
 
 Tafel (Ber. 22, 1,855) has devised a very convenient way of 
 preparing amines by the reduction of hydrazones. Phenylhydrazine 
 reacts quantitatively with aldehydes and ketones, and the products 
 give two amines on reduction. For example, acetone phenyl- 
 hydrazone gives isopropylamine and aniline 
 
 . NH 2 +NH 2 . C G H 5 . 
 
 The operation is carried out as follows : The hydrazones are 
 dissolved or suspended in from ten to twenty times their weight 
 of alcohol, and to this solution, which is continually cooled and 
 shaken, portions of acetic acid (25 cc.) and 2^ per cent, amalgam 
 (250 gr.) are added from time to time. The temperature must 
 be kept constant within two or three degrees, and care must be 
 taken that excess of acetic acid is always present. About twice 
 the amount of amalgam which is theoretically necessary must be 
 used. About two hours will be required for working up 3,500 grains 
 of the amalgam. Towards the end of the action sodium acetate 
 is deposited. The liquid is finally rendered alkaline with caustic 
 soda and distilled. Bases of high boiling-point are separated from 
 aniline by Tafel by carefully neutralising the aqueous distillate 
 with sulphuric or hydrochloric acid and concentrating on the water 
 bath. Extraction with ether then removes the aniline. 1 
 
 25. Sulphurous Acid. Sulphurous acid exercises a reducing 
 action towards very few substances, and is chiefly used for the 
 conversion of quinones into quinols. The gas is conducted 
 through an aqueous solution of the quinone. In the case of quinone 
 itself the liquid first becomes brown, owing to the formation of 
 quinhydrone, and then loses its colour again when this is converted 
 into quinol (cf. Chap. XVIII. 45). 
 
 1 Cf. Miller's method, 29. 
 
312 REDUCTION [CH. xix 
 
 Neumann (Ber. 20, 1,584) states that sulphur dioxide can be 
 generated in a Kipp's apparatus by charging it with common 
 concentrated sulphuric acid and a mixture of calcium sulphite 
 (3 parts) and gypsum (i part) made up into little cubes. Half a 
 kilogram of this material will give a continuous stream of the gas 
 for thirty hours. 
 
 Glaus and Berkefeld (J. pr. Ch. 151, 585) found that the reduction 
 of 4 . 5 dichloroorthoxylo 3 . 6 quinone presented extraordinary difficulties. 
 Even when an ethereal solution was shaken with stannous chloride and 
 hydrochloric acid no reduction took place. The substance had to be 
 heated at 100 with concentrated aqueous sulphurous acid in a sealed 
 tube. 
 
 Sodium hyposulphite, NaHSO 2 , which might be expected to be a 
 valuable reducing agent, does not seem to have received any application in 
 this direction. Experiments of the author's, in one particular case, where 
 a favourable result might have been anticipated, showed that no reduction 
 had been effected. 
 
 26, Tin. This metal can be used either in acid or alkaline 
 solution. 
 
 The metal is applied either granulated or in the form of foil 
 (Ber. 23, 1,626). Treadwell (Ber. 25, 2,381) states that tin is best 
 granulated by melting at as low a temperature as possible, and 
 pouring through a sieve made of sheet iron containing a few holes, 
 which is held just above the surface of a vessel of cold water. The 
 metal obtained in this way consists of solid pear-shaped uniform 
 grains half the size of a pea. The acid employed is usually hydro- 
 chloric, occasionally hydrobromic, because, after the tin has been 
 taken out with hydrogen sulphide, these acids can be removed by 
 evaporation on the water bath. Under these conditions therefore 
 the substances used for reduction can easily be separated from the 
 products. The process originated with Beilstein (Ann. 130, 243). 
 
 Reductions by this method sometimes occupy much time, 
 especially when conducted in the cold. Lossen (Ann. Suppl. 6, 
 221), for example, allowed nitric ether to remain in contact with 
 the mixture for fourteen days in order to obtain the maximum yield 
 of hydroxylamine. On the other hand the action may be so violent 
 that the substance to be reduced must be added in small portions, 
 or drop by drop, to the reducing mixture, which is often maintained 
 at the boiling temperature during the action (Ber. 12, 2,039). 
 Strong hydrochloric acid is generally employed. 
 
TIN 3,3 
 
 Even when the acid liquid is very greatly diluted, the precipita- 
 tion of the tin by hydrogen sulphide may be incomplete. Since 
 the sulphide formed in the cold is with difficulty retained by a 
 filter, it is advisable, whenever possible, to pass the hydrogen 
 sulphide into the liquid in the heat. To drive off the free hydro- 
 chloric acid the liquid must be evaporated. The naked flame can 
 be used at first for this purpose. When hydrogen sulphide is 
 passed through the liquid for the second time a further precipitation 
 of sulphide takes place. The filtrate, after further evaporation, 
 must be tested for tin again, and this process repeated until all the 
 metal is finally thrown down. 
 
 During the concentration the hydrochloride of the base, being 
 usually insoluble in strong hydrochloric acid, begins to crystallise 
 out. This fact may even be taken advantage of for the purpose of 
 isolating the base without first precipitating the tin. This metnod 
 is exemplified in Seidel's process (Ber. 25, 423 and 976) for making 
 amidonaphthol hydrochloride. One kilogram of the potassium salt 
 of benzeneazonaphtholsulphonic acid 
 
 r /N : N . C 10 H G . OK, 
 
 which is sold as a dye under the name of " Orange I.," is mixed 
 with five litres of water and brought into solution by passing steam 
 through the mixture. The boiling liquid is poured into five litres 
 of warm concentrated hydrochloric acid of sp. gr. rig containing 
 the calculated amount of stannous chloride. Almost the whole of 
 the amidonaphthol hydrochloride is at once precipitated, and is 
 found to be free from tin and from sulphanilic acid. The latter 
 forms a soluble salt with the hydrochloric acid. As soon as the 
 liquid has cooled to 40-50 it is filtered, and the crystals are washed 
 with dilute hydrochloric acid. The yield is 360 grams. 
 
 A somewhat different method of isolating the product of the 
 reduction was used by Hiibner (Ann. 208, 304). Benzorthom- 
 tranilide (10 gr. = i mol.) was mixed with the necessary amount of 
 finely granular tin (3 atoms), and the mixture was made into a thin 
 paste with strong crude hydrochloric acid. This was gently 
 warmed in a flask until the anilide had gone completely into solution. 
 Since under these circumstances stannous chloride and hydrochloric 
 acid give off some hydrogen, a part of the tin remains undissolved. 
 The solution is poured off and evaporated to dryness, and the 
 residue is stirred up with a little saturated ammonia water, and 
 
3H REDUCTION [CH. X ix 
 
 warmed with yellow ammonium sulphide to dissolve the sulphide 
 of tin. At first only a little ammonium sulphide is added, and the 
 amount is gradually increased until the solid residue does not 
 seem to decrease in quantity. This substance, the product of the 
 reduction, is then collected on a filter, and thoroughly washed with 
 water. It is needless to add that this process can only be used 
 with bases which are insoluble in water. 
 
 Insoluble bases can also be isolated by rendering the solution 
 alkaline with caustic soda, which precipitates the base. The latter 
 can be purified by recrystallisation (Ber. 15, 1,920, and 20, 1,878). 
 In this case the prior removal of the tin and hydrochloric acid is 
 unnecessary, as the hydroxide, which is at first precipitated, redis- 
 solves in excess of caustic soda, and the acid is of course neutralised. 
 When the base is volatile with steam it is best to use this method 
 for removing it from the alkaline mixture. 
 
 Many solutions containing reduced substances have the disagree- 
 able property of becoming dark in colour during evaporation, after 
 the last traces of tin have been removed with hydrogen sulphide. 
 
 This is usually attributable to oxidation by air, and may be 
 prevented by conducting the evaporation in a flask provided with a 
 Bunsen valve. Or a suitable reducing agent may be introduced by 
 passing hydrogen sulphide through the solution, or adding sulphur- 
 ous acid or sodium hyposulphite to it. Even a drop of a stannous 
 chloride solution may be used (Ber. 20, 1,148). 
 
 If the base is likely to suffer decomposition by being evaporated 
 with hydrochloric acid after the removal of the tin, it may be set 
 free by adding sodium carbonate,- and removed by filtering or 
 extraction (Ber. 25, 860). 
 
 Another method consists in neutralising the acid by shaking 
 with lead hydroxide (cf. Chap. XVIII. 32) or moist silver oxide 
 after the tin has been removed. If any of the metal passes into 
 solution it can be precipitated with hydrogen sulphide from the 
 filtrate. It may be remarked here that silver chloride is soluble in 
 very strong hydrochloric acid. 
 
 Hlasiwetz and Habermann (Ann. 169, 155) 'have found that 
 cuprous oxide may be used for the removal of the greater part of 
 the hydrochloric acid in such solutions. They warmed the acid 
 solution to 50 in a flask, and added a paste of cuprous oxide, shak- 
 ing after each addition, until the red colour of the foam showed 
 that an excess of the oxide was present. The liquid standing over 
 the precipitate was seen to be blue owing to the presence of copper, 
 
26] TIN 315 
 
 and was consequently by no means free from chlorine. The liquid 
 was filtered, and the copper precipitated with hydrogen sulphide. 
 The filtrate was then concentrated, and the remainder of the hydro- 
 chloric acid was removed with silver oxide. 
 
 The cuprous oxide may be most conveniently prepared by 
 Mitscherlich's method (J. pr. Ch. 19^ 450). Caustic soda is added 
 to a solution containing equal parts of cupric sulphate and grape 
 sugar until the cupric hydroxide at first precipitated is redissolved. 
 When this solution is warmed, the cuprous oxide is thrown down 
 as a powder, which is free from hydroxide, and is not changed by 
 exposure to the air. 
 
 If the hydrochloride is stable while the base itself is unstable the 
 method applied by Pukall (Ber. 20, i, 148) to 0-amidodiethylresorcinol 
 may be used. This base was extremely unstable when moist. He 
 therefore saturated the solution of the pure hydrochloride with 
 hydrogen sulphide, and precipitated the base with lime water or 
 sodium carbonate. The crystalline scales which appeared were 
 washed with water containing the same gas, and dried in a place 
 free from draughts. Even this last process was better carried out 
 in an indifferent atmosphere. 
 
 It has long been known that when nitro-bodies are treated with 
 zinc or tin and hydrochloric acid, chloroamido-compounds are 
 sometimes formed. Their formation can be entirely excluded by 
 reducing with tin and acetic acid. For example, Fittig (Ber. 8, 15) 
 states that when he used the former way he obtained chloro- 
 bromaniline along with bromaniline from /-bromonitrobenzene. 
 Kock (Ber. 20, 1,569) reduced nitrobenzene (70 gr.) with zinc and 
 hydrochloric acid, and found that aniline (29 gr.) and pure /-chlor- 
 aniline (i7'5 gr.) were formed. 
 
 V. Miller and Rohde (Ber. 23, 1,891) reduced /-nitrohydro- 
 cinnamic acid (25 gr.) by treating it with tin (45 gr.) and hydro- 
 bromic acid of sp. gr. 1*49 (165 gr.) at a low temperature. 
 
 Tin and hydrochloric acid are also used for reduction in alcoholic 
 solution. For example, Friedlander and Weinberg (Ber. 15, 1,422) 
 added these substances to a hot alcoholic solution of 0-nitrocinnamic 
 ether until, when the violence of the action had somewhat abated, 
 no turbidity was produced by adding water. The tin was removed 
 with hydrogen sulphide, and the amido-ester precipitated in yellow 
 needles by addition of sodium acetate (Chap. II. 2). When ten 
 or twenty grams of the substance were used the action took place 
 quantitatively. 
 
316 REDUCTION [CH. xix 
 
 The use of ethereal solutions also has been introduced by Fried- 
 lander and Mahly (Ber. 16, 852). They found the problem of re- 
 ducing dinitrocinnamic ether presented great difficulties on account 
 of the instability of that compound. Alkaline reducing agents are 
 necessarily unsuitable. And on the other hand, when acids are 
 present, a part of the nitrogen is lost in the form of ammonia, and 
 easily soluble oxy-acids are formed. To diminish the violence of 
 the action therefore the ester was dissolved in small portions, each 
 in ten or twenty grams of ether, concentrated hydrochloric acid and 
 granulated tin were added, and the mixtures were allowed to remain 
 in the cold for twelve hours. When the action was over the yellow 
 solutions were diluted with water, and the ether and tin were re- 
 moved. Then the acid was neutralised with soda and the liquids 
 concentrated. Finally, they were evaporated to dryness with hydro- 
 chloric acid, and the diamidohydrocinnamic acid was extracted from 
 the residue with alcohol. 
 
 As a general rule, when substances are reduced with tin and 
 hydrochloric acid each nitro-group is replaced by an amido-group, 
 but this seems only to hold so long as not more than one nitro- 
 group is attached to the same carbon atom. 
 
 For example, Victor Meyer and Locher (Ber. 8, 215) have found 
 that when dinitropropane is treated with tin and hydrochloric acid, 
 acetone and hydroxylamine are formed instead of the expected 
 product 
 
 Ethyl nitrolic acid gives hydroxylamine and acetic acid under the 
 same conditions 
 
 CH 3 CH 3 
 
 | /N.OH + 4H + H 9 O= | /O +2NH 3 O. 
 C\NO 2 C\OH. 
 
 With sodium amalgam the products are quite different. 
 
 Kachler (Ann. 191, 164) reduced dinitroheptylic acid with tin 
 and hydrochloric acid, obtaining methylisopropylketone, ammonia, 
 hydroxylamine, and carbon dioxide 
 
 Hoffmann and Meyer (Ber. 24, 3,528) state that very extra- 
 ordinary intermediate products, which are extremely hard to 
 isolate, may be formed in these reductions. Thus nitromethane 
 
27] TIN BICHLORIDE 317 
 
 gives methylhydroxylamine, which subsequently passes over into 
 methylamine 
 
 CH 3 .N0 3 -> CH 3 .N< H -> CH 3 .NH 2 . 
 
 27. Tin Bichloride. Many reductions can be carried out more 
 easily with an acid solution of stannous chloride than with tin and 
 hydrochloric acid. This was first observed by Spiegelberg (Ber. 
 Hj 35)- He added the nitro-compound which was to be reduced 
 to a clear solution of stannous chloride, containing about 1 50 grams 
 of tin per litre dissolved in excess of acid. The action usually 
 began without the aid of external heating when the ingredients 
 were mixed, and, if large quantities were worked up at one time, 
 often became so violent as to lead to boiling and frothing over of 
 the mixture. 
 
 The facility with which this action took place led Limpricht to 
 make experiments in regard to its suitability as a method for the 
 quantitative estimation of the NO 2 groups in organic compounds. 
 The action is represented by the equation 
 
 It was found that as a matter of fact an accurate estimate of the 
 proportion of NO 2 contained in the compound could be made by 
 titrating the excess of stannous chloride which remained after the 
 reduction. When the nitro-body is volatile, the operation is carried 
 out in a sealed tube at the temperature of the water bath. 
 
 Experience has shown that a proportion of 40 grams of bichloride 
 to loo cubic centimetres of acid of sp. gr. ri7 gives the best re- 
 ducing liquid for most purposes, although in special cases varia- 
 tions from this may be advisable. 
 
 A process for reducing perchloromercaptan, CC1 3 SC1, to thio- 
 phosgene, CSC1 2 , which is described in a patent applied for by 
 Kern, will illustrate the use of this method. The patent was not 
 granted for some unknown reason. Crystallised stannous chloride 
 (27 parts) is dissolved in hydrochloric acid (10 parts) and water 
 (7 parts), and perchloromercaptan (20 parts) are added. The mixture 
 is digested for twelve hours at 30-35, the air being excluded, and 
 the whole being vigorously stirred during the process. Finally, 
 the thiophosgene is separated mechanically or distilled off. 
 
 Any one who has tried Rathke's method (Ann. 167, 204) for re- 
 ducing perchloromercaptan to thiophosgene with finely divided 
 
3 i8 REDUCTION [CH. xix 
 
 silver will recognise the advance which has been made in the art of 
 reduction during the last eighteen years. In Rathke's time the 
 other known methods were even less effective in this particular 
 case. 
 
 It is often desirable to add some metallic tin to the acid solution 
 of stannous chloride. 
 
 Stannous chloride is one of the few reducing agents with whose help any- 
 thing can be made of the reduction of bases containing nitrobenzyl groups. 
 For example Lellmann and Mayer (Ber. 25, 3,584) made many vain at- 
 tempts to prepare o-diamidoclibenzylaniline. Finally, they succeeded by 
 placing finely pulverised dinitrodibenzylaniline, C 6 H 5 N(CH 2 . C 6 H 4 . NO 2 );> 
 (3 g r -)> an d stannous chloride (15 gr.) in a small flask, and adding glacial 
 acetic acid and an equal volume of concentrated hydrochloric acid (5 o g r -)- 
 The mixture was cooled during the whole process and repeatedly shaken. 
 The cooling prevents the action becoming too rapid, and the operation occu- 
 pies several hours. It is complete when no small yellow particles of the nitro- 
 compound are visible mingled with the tin double salt which forms. The 
 base is isolated by treating the double salt with excess of ammonium sul- 
 phide, and crystallising the residue from benzene (cf. p. 314). 
 
 The following process was used by Brunner and Witt (Ber. 20, i>O25). 
 Orthodinitrodiamidodiphenyl was mixed with the requisite amount of the 
 bichloride, hydrochloric acid was added, and the mixture was warmed on 
 the water bath until no precipitate was produced on adding water to a 
 sample. Tin was then added, and the warming was continued until the 
 stannic chloride which had been formed was itself reduced. The liquid 
 was then greatly diluted and freed from tin with hydrogen sulphide. The 
 product was the hydrochloride of tetramidodiphenyl. 
 
 Many observers recommend the preparation of the stannous chloride 
 just before use on account of the questionable quality of the commercial 
 article. The solution is made by dissolving 200 grams of tin in a litre of 
 concentrated hydrochloric acid, and adding a few cubic centimetres of con- 
 centrated sulphuric acid. Grandmougin and Michel (Ber. 25, 981) 
 suggest that it is well not to add all the acid at once. They add first one 
 third of the quantity to the tin, and further portions when the slower rate at 
 which the metal begins to be dissolved seems to demand it. The final 
 addition of a few drops of platinum tetrachloride or cupric chloride is 
 advised. 
 
 Stannous chloride is soluble also in alcohol, and can consequently 
 be dissolved in alcoholic hydrochloric acid. Victor Meyer (Ann. 
 264, 131) states that the alcoholic solution of the salt is often an 
 excellent reducing agent. It acts smoothly, and frequently succeeds 
 
27] TIN BICHLORIDE 319 
 
 where other reducing agents fail entirely or give the products in 
 such a condition that they cannot be isolated. 
 
 Willgerodt (Ber. 25, 608) used this method in reducing ;#-dinitro- 
 benzene to j-;//-dinitrazoxybenzene 
 
 N0 2 .C 6 H 4 .N-N.C 6 H 4 .N0 2 . 
 O 
 
 Claus (]. pr. Ch. 151, 565) found it necessary to boil dinitrodi- 
 bromocymene for twelve hours with the alcoholic solution to com- 
 plete its reduction. Schulhofer and Meyer (Ann. 264, 131) found 
 in nitroindazol carboxylic acid a substance whose nitro-group was 
 proof against every reducing agent even including the present. By 
 long warming on the water bath it seemed only to take up hydrogen 
 by addition. 
 
 With the solution of stannous chloride, as with ammonium 
 sulphide, it is in one's power to reduce by successive steps the 
 nitro-groups of a substance containing more than one. Thus 
 Lauterbach (Ber. 14, 2,029) mentions that in reducing dinitronaph- 
 tholsulphonic acid with the solution of bichloride in hydrochloric 
 acid a nitroamido-acid is formed intermediately, although he made 
 no attempt to isolate it. Nietzki (Ber. 16, 2,094), treating the 
 potassium salt of nitranilic acid in aqueous solution, obtained a 
 substance to which he assigned the constitution of a nitroamido- 
 tetroxybenzene, C (OH) 4 NH 2 NO 2 . A method for the step-by- 
 step replacement of nitro- by amido-groups in aromatic bodies, 
 which is of quite general applicability, in which the use of the 
 alcoholic solution is essential, has been devised by Anschiitz (Ber. 
 19, 2,161) 
 
 For example, he prepares nitraniline easily by dissolving m- 
 dinitrobenzene in alcohol, and allowing the calculated amount of 
 stannous chloride dissolved in alcohol saturated with hydrochloric 
 acid to flow in drop by drop while the mixture is kept cool and 
 constantly shaken. By the same process he obtains 0-amido-/- 
 nitrotoluene from 0-^-dinitrotoluene. The 0-nitro-^-amidotoluene 
 which is the sole product when alcoholic ammonium sulphide is 
 used in the cold, could not be traced in the product formed by 
 stannous chloride. The interesting fact is brought out by this that 
 the nitro-group selected by stannous chloride for reduction is the 
 very one which is spared by ammonium sulphide. 
 
320 REDUCTION [CH. xix 
 
 Claus (Ber. 20, 1,379) discovered this property of the alcoholic solution 
 almost simultaneously with AnschUtz. He dissolved, for example, dinitro- 
 chlorobenzene in absolute alcohol, added concentrated hydrochloric acid, 
 and allowed this mixture to flow gradually into the amount of stannous 
 chloride necessary for the reduction of one nitro-group. 
 
 A mixture of one part of glacial acetic acid and one part of concentrated 
 stannous chloride solution is also used for reduction. 
 
 It may be well here to recall the fact that in the decomposition of com- 
 plex bodies like the protein substances (Ann. 169, 151), with hydrochloric 
 or other non-oxidising acids, the addition of stannous chloride supplies 
 the best means of preventing the formation of coloured secondary products. 
 In fact, all decompositions of this kind seem to proceed more smoothly and 
 sharply in its presence. 
 
 If some other metal being present in the solution would have less disturb- 
 ing effect than tin, or if it is desired to recover the tin on account of its 
 value, clippings of zinc may be added to the liquid. This causes the pre- 
 cipitation of the metal in a very finely divided condition, which renders it 
 particularly valuable for later use in other reductions (Ann. 247, 291). 
 
 On account of the tendency of stannous chloride to pass over into stannic 
 chloride, and consequently to act as a reducing agent, it is impossible to 
 convert the amides into diazo-bodies directly in the solutions in which they 
 occur. On the other hand, zinc chloride interferes in no way with the 
 accomplishment of this additional step. So that when the latter metal is 
 used there is no need of removing it from solution before working up the 
 product further. 
 
 The alkaline solution of tin is also in frequent use as a reducing 
 agent. Bottger and Petersen (J. pr. Ch. 112, 327) were the first 
 to recommend the use of this substance. They prepared the 
 solution by adding -finely pulverised stannous chloride to rather 
 strong caustic soda or caustic potash until a precipitate of stannous 
 hydroxide began to form. The mixture was thoroughly stirred 
 during the process, and finally filtered to obtain a clear solution. 
 To reduce dinitroanthraquinone they boiled it with this solution for 
 a considerable time. 
 
 This method has acquired great importance since Witt (Ber. 18, 
 2,912) founded on it a process for the preparation of azo-bodies. 
 In Griess' methods we have very convenient ways of preparing 
 quantitatively azo-compounds containing hydroxyl- and amido- 
 groups. But for making other azo-compounds we have almost 
 entirely to rely on the reduction of the corresponding nitro-bodies. 
 Zinin's method, in which alcoholic alkalis are used, is only successful 
 in isolated cases. Klinger's method, by reduction with sodium, can 
 
2 7 ] TIN BICHLORIDE 321 
 
 only be applied to such nitro-compounds as are soluble in alcohol. 
 Sodium amalgam would be more applicable if the difficulty of 
 recognising when the action is completed were not so great. Zinc 
 dust is used with caustic potash and with a solution of -calcium 
 chloride, but difficulties are met with in the separation of the azo- 
 body from the pasty product of the action. This can only be 
 accomplished by repeated extraction with alcohol. The method of 
 Weselsky, which consists in fusing nitrophenols with potassium 
 hydroxide, is only applicable to a limited number of substances. 
 
 In view of the limitations of these methods therefore, Witt intro- 
 duced the solution of stannous hydroxide (Prometheus, 2, 640) as 
 being a more suitable reducing agent. The calculated amount of 
 stannous chloride is dissolved in water and added to excess of cold 
 caustic potash. The clear solution is then allowed to act upon the 
 nitro-body at the temperature of the water bath. If the body is 
 liquid or easily melted it suffices to shake it with the prepared 
 solution. If the substance is soluble in alcohol the solution in this 
 solvent may be added to the alkaline solution. In this case the 
 reduction is energetic and is soon complete. Finally when nitro- 
 sulphonic acids are in question an aqueous solution of a salt may 
 be added to the reducing agent. 
 
 In the last case, that of nitrosulphonic acids, it is far preferable 
 to use the potassium salts rather than the sodium salts, and to work 
 with a solution of stannous hydroxide in caustic potash, as the 
 potassium salts of the azosulphonic acids formed are usually less 
 soluble and crystallise better than the sodium salts. 
 
 As a general rule the azo-body crystallises out without further 
 trouble when the solution cools. When this does not occur the tin 
 is precipitated with carbon dioxide, and the solution is concentrated 
 until crystallisation begins. In some cases it may be necessary, 
 however, to separate the azo-body from potassium carbonate with 
 dilute alcohol. 
 
 Friedlander (Ber. 22, 587) finds that the reduction of diazo- 
 bodies to hydrocarbons is best accomplished by the alkaline 
 solution of stannous hydroxide. The method of Griess by boiling 
 with alcohol often fails, as in the case of ^-diazoxylene. Fischer's 
 conversion into the hydrazine and oxidation of the latter with ferric 
 chloride (Ber. 23, 2,672) usually gives better yields, but is too 
 laborious. 
 
 Friedlander's method, which performs the reduction in the 
 absence of alcohol, avoids these difficulties. He takes advantage 
 
 Y 
 
322 REDUCTION [CH. xix 
 
 of the fact that most diazo-derivatives are soluble without decompo- 
 sition in excess of cold caustic soda. This alkaline solution is 
 usually as stable as the acid solution. But when an alkaline 
 reducing agent is added a vigorous evolution of nitrogen begins 
 even in the cold, and the nitrogen is replaced by hydrogen. 
 
 The application of this method to aniline will serve as an ex- 
 ample. The aniline is first converted into diazobenzene chloride, 
 and the faintly acid solution, which should not be too dilute (i : 10, 
 or i : 20), is poured into cold caustic soda containing pieces of ice. 
 When a solution of stannous chloride in caustic soda is added to 
 the clear alkaline solution, nitrogen gas is given off rapidly even at 
 the ordinary temperature, and when the action is at an end a 
 layer of benzene is found floating on the surface. Similarly a- 
 naphthylamine gives naphthalene and sulphanilic acid, benzene- 
 sulphonic acid. This method is specially useful where the product 
 of the reduction is insoluble in caustic soda, as is the case with 
 hydrocarbons. 
 
 28. Zinc. This metal is not so frequently used as tin. Like 
 the latter it can be used in alkaline or acid solution, and can even 
 be employed in neutral liquids in addition. 
 
 Hydrogen is given off when zinc and iron are brought in contact 
 with ammonium and amine salts in water even at the ordinary 
 temperature, and better still at or above 40. Lorin (Ann. 139, 
 374) found that when zinc and iron acted on an aqueous solution 
 of ammonium sulphate at the temperature of the room, acetone, 
 which had been added to the solution, was reduced to isopropyl 
 alcohol. 
 
 Leykauf states (J. pr. Ch. 19, 124) that when sheet zinc is intro- 
 duced into a solution of sulphate of copper in three times its weight 
 of water a considerable amount of hydrogen is evolved. 
 
 Liebermann and Scholz (Ber. 25, 950) succeeded in replacing 
 the bromine atom in the addition product of phenylpropiolic acid 
 and hydrobromic acid by hydrogen, without at the same time 
 saturating the remaining double bond with the same element. 
 They accomplished this by boiling the bromocinnamic acid with 
 twice its weight of zinc filings not zinc dust and ten times its 
 weight of absolute alcohol for three or four hours in a flask pro- 
 vided with a condenser. 
 
 Usually, however, the metal is used as a reducing agent in 
 alkaline solutions. In order to give as large a surface as possible 
 
28] ZINC 323 
 
 it is melted in the flame of a blast lamp and allowed to fall in 
 single drops on clay plates. The zinc foil so obtained can after- 
 wards be cut in pieces if necessary. When the action is over the 
 zinc can be precipitated with carbon dioxide. Both aqueous and 
 alcoholic caustic potash are used as solvents. Zagoumenny 
 (Ann. 184, 175) finds that the latter works particularly well in the 
 reduction of aromatic ketones to alcohols. Thus benzophenone 
 gives diphenylcarbinol when treated by this method, while with 
 zinc and acetic acid it gives benzpinacone. 
 
 Zinc is also used in acid solution, generally alcoholic. Years 
 ago Girard (Ann. 100, 306) converted carbon disulphide into 
 trimethylene sulphide, (CH 2 S) 3 , by this method. The process now 
 generally used is to place zinc in the solution to be reduced and 
 add hydrochloric or acetic acid from time to time. For example, 
 Bischoff (Ann. 251, 305) dissolved 0-nitrobenzoylmalonic ether 
 (5 gr.) in absolute alcohol (50 gr.), added pure zinc clippings (14*7 
 gr.) to the cold solution, surrounded the whole with ice, and passed 
 a stream of dry hydrochloric acid gas through the mixture. 
 
 The use of acetic acid has the advantage over that of mineral 
 acids that the metal can afterwards be precipitated with a current 
 of hydrogen sulphide. 
 
 Perkin (Ber. 16, 1,031) used a copper-zinc couple and acetic acid 
 for reductions. Gladstone and Tribe (J. Ch. Soc. 45, 154) applied 
 the same method to the preparation of methane from methyl iodide, 
 and obtained 99 per cent, of the calculated quantity. They poured 
 a two per cent, solution of cupric sulphate over granulated zinc, 
 leaving the substances in contact till the liquid became decolour- 
 ised, and repeated the process with the same zinc three or four 
 times. The zinc being plated with copper was well washed and 
 moistened with alcohol. It was then placed in a 600 cc. flask 
 provided with a vertical tube 36 cm. long and 3 cm. in diameter to 
 act as a condenser. The condensing tube, which was partially 
 drawn out at the bottom, was connected with the flask by a 
 stopper with two openings. The stem of a separating funnel 
 containing alcohol and methyl iodide and provided with a stop- 
 cock passed through the second opening. Another similar stopper 
 closed the upper end of the tube, and was provided with holes for 
 another separating funnel containing alcohol to moisten the zinc- 
 copper and a tube to conduct off the gas. Forty-five grams of 
 methyl iodide gave seven litres of methane in less than an hour and a 
 half. Somewhat later Weigth recommended that the escaping gas 
 
 Y 2 
 
324 REDUCTION [CH. xix 
 
 should be further purified by being led through a series of tubes 
 containing the same zinc-copper couple moistened with alcohol. 
 
 29. Zinc Dust. In this form the metal has extremely powerful 
 reducing qualities. It even decomposes chalk quantitatively when 
 a mixture of the substances is heated in a combustion tube (Ber. 
 19, 1,141) 
 
 Zn + CaCO 3 = ZnO + CaO + CO. 
 
 It is obtained during the manufacture of zinc, and collects in the 
 iron receivers into which the metal is distilled from tubes or retorts. 
 The first part of the distillate consists of zinc dust, which is a mix- 
 ture containing 10 to 20 per cent, of zinc oxide, and often some 
 cadmium. 
 
 We owe to Baeyer the introduction of this valuable reducing 
 agent. It is particularly applicable to the reduction of aromatic 
 substances, and gives the corresponding hydrocarbons as the result 
 of its action. By its use Grabe and Liebermann (Ber. 1, 49) re- 
 duced alizarin to anthracene. This led them to achieve the artificial 
 preparation of alizarin from the hydrocarbon anthracene, which 
 occurs in large quantities in coal tar. 
 
 In distilling with zinc dust, a large excess of the metal is always 
 used. The operation is best carried out by heating the mixture in 
 hard glass tubes in a combustion furnace, while a stream of hydrogen 
 or carbon dioxide is conducted through the apparatus. If the action 
 is too energetic, dry sand may be mixed with the substance. 
 
 Its value may be illustrated by mention of its use in converting 
 nitrogen compounds of substances with a simple carbon chain into 
 compounds containing rings. Thus Bernthsen (Ber. 13, 1,047) dis- 
 tilled the imide of succinic acid with zinc dust, and obtained pyrrol 
 
 CH 9 -CO X CH = CH X 
 
 | >NH -> | >NH. 
 
 CH 2 -CO/ CH = CH/ 
 
 Following this up, Leblanc (Ber. 21, 2,299) distilled homophthal- 
 imide, which differs from the above imide in having a C 6 H 4 in 
 place of the CH 2 group, with the same reagent, and succeeded in 
 synthesising isoquinoline 
 
 CH.-COx /CH = CH 
 
 | >NH -> C 6 H 4 
 
 C 6 H 4 -CO/ 
 
2 9 ] ZINC DUST 325 
 
 When simply boiled 'with water, zinc dust exhibits great reducing 
 power. Miller (Ber. 13, 269) therefore recommends its use in this 
 way in cases where it acts as effectively without acids as in their 
 presence, since under those circumstances it forms no zinc salts 
 whose presence might interfere with the isolation of the products of 
 the reduction. He uses this method particularly for the decomposi- 
 tion of azo-dyes. These bodies split at the double linkage between 
 the nitrogen atoms, and take up hydrogen, forming amido-com- 
 pounds. For example, chrysoidine, C 6 H 5 . N : N . C 6 H 3 (NH 2 ) 2 , breaks 
 up into aniline and triamidobenzene. 1 
 
 Usually, however, acids are added, and as a general rule aqueous 
 or alcoholic hydrochloric acid is employed. Reductions by this 
 method ordinarily take a good deal of time. For example, Schlieper 
 (Ann. 239, 237) boiled an alcoholic solution of a-naphthindole, 
 adding zinc dust and hydrochloric acid from time to time, until 
 a splinter of pine was no longer coloured bluish violet when 
 dipped in the liquid. The change into u-hydronaphthindole was 
 easy to trace, but the conversion of 5 grams occupied 12-15 
 hours. 
 
 Krafft's work (Ber. 16, 1,715) exhibits fully the value of using 
 zinc dust for reductions in presence of acetic acid. The advantages 
 of this easily prepared reducing mixture are that it generally re- 
 tains the organic substance in solution, it is not rapidly used up 
 even when heated for a considerable period, and the chief product 
 of the action can usually be separated from it without much loss of 
 material or time. When the glacial acid is used the metal is but 
 slowly attacked even in the heat, unless very easily reducible sub- 
 stances are present, and the zinc salt collects in compact crusts, so 
 that the action of the acid is not interfered with up to the very 
 end of the operation. Thus the soluble product can finally be 
 obtained almost instantly by pouring off the acetic acid solution 
 and adding water to it. If insoluble in the latter, the new body is 
 at once precipitated. When glass vessels are used, very energetic 
 digestion is out of the question, and under these circumstances a 
 part of the metal will be protected by the deposition of the zinc 
 acetate upon it. This difficulty can be avoided, however, by adding 
 the dust at intervals of two or three days. In this way a sufficient 
 amount of active surface can be maintained without the use of an 
 excessive quantity of the metal altogether. This method was used 
 
 1 Cf. Tafel's method, end of 25. 
 
326 REDUCTION [CH. xix 
 
 by Krafft for the reduction of aldehydes to alcohols. The latter 
 were isolated in the form of esters of acetic acid. 
 
 The difficulties which Tiemann encountered (Ber. 19, 354) in attempt- 
 ing to obtain a well-characterised alcohol glucoside from glucoferulic 
 aldehyde by the action of sodium amalgam and water, led him to investigate 
 the use of zinc dust and glacial acetic acid in reducing aldehydes to alcohols. 
 For example, he boiled benzaldehyde with this reducing mixture for twelve 
 hours in a flask connected with a reflux condenser. The supernatant liquid 
 was then poured off the excess of zinc dust and the precipitate of zinc 
 acetate into a vessel of water. The product was then neutralised with 
 soda or chalk and extracted with ether. The substance formed was found 
 to be benzyl acetate so that the alcohol had at once passed over into the 
 ester 
 
 C 6 H 6 . COH + CH 3 COOH + 2H = CH 3 . COOCH 2 C 6 H 5 + H 2 O. 
 
 In the case of oxybenzaldehyde (Ber. 24, S* 1 ? )? however, the same 
 process led to the formation of complicated products. 
 
 Dilute acetic acid is also very useful, especially when the substance to be 
 reduced is insoluble in glacial acetic acid. For example, Fischer and Tafel 
 (Ber. 22, 99) found that a-acrosone was completely reduced when heated 
 on the water bath for an hour in dilute aqueous solution with zinc dust and 
 acetic acid. They filtered the resulting liquid, precipitated the zinc with 
 hydrogen sulphide, and evaporated the filtrate in vacua on the water bath. 
 When the residue was taken up with absolute alcohol, the solution filtered 
 and ether added to the filtrate, a-acrose was thrown down. This substance, 
 the first sugar to be prepared synthetically, ferments with yeast like ordinary 
 sugar, but is optically inactive. 
 
 Fischer and Hepp (Ber. 21, 680) treated anilidonaphthoquinoneanil 
 (15 gr.) with zinc dust (70 gr.) and a mixture of glacial acetic acid (200 gr.) 
 and sulphuric acid (50 gr.) diluted with water (5occ.). The products were 
 aniline and naphthalene. 
 
 V. Pechmann found (Ber. 25, 3,188) that when formazyl hydride was 
 boiled with acetic anhydride and zinc dust, hydrogen was added and an 
 acetyl derivative was formed. 
 
 Zinc dust is used in alkaline solutions also as a reducing agent. 
 The substance may be boiled with aqueous or alcoholic ammonia 
 and zinc dust in a flask connected with a condenser. The alcoholic 
 ammonia is made from sixty per cent, alcohol. 
 
 For example, Wohman (Ann. 259, 283) dissolved a diazo- 
 compound in ten or twenty per cent, ammonia, and added zinc dust 
 in small portions. The solution became slightly warm during the 
 process. As soon as no more heat was developed, the mixture was 
 
29] ZINC DUST 327 
 
 filtered with the help of a pump, and the hydrazine derivative was 
 extracted from the filtrate with ether. 
 
 Elbs (J. pr. Ch. 149, 15) found the following to be the only suit- 
 able method for reducing w-dimethylanthraquinone. The substance, 
 in quantities of five grams, was finely pulverised and mixed inti- 
 mately with zinc dust (30 gr.). Concentrated aqueous ammonia 
 (200 cc.) and a solution of basic carbonate of copper in ammonia 
 (5 cc.) were then poured on to it. When this mixture was shaken 
 up it became warm. The whole was boiled for six hours, and 
 during this operation portions of a few cubic centimetres of the 
 same solution of carbonate of copper were added at short intervals. 
 When the whole had cooled it was filtered, the filtrate was evapo- 
 rated to dryness, and the residue was extracted with alcohol. The 
 quantity of the hydrocarbon which was so obtained was about 20- 
 25 per cent, of the original substance. 
 
 When the boiling is prolonged, fresh ammonia must be added 
 from time to time. 
 
 The result is not always perfectly satisfactory. Thus Lautebach 
 (Ber. 14, 2,030) dissolved dinitronaphtholsulphonic acid in a litre 
 and a half of water, added zinc dust, and, after a short interval, 
 ammonia. He obtained a blood-red solution, which deposited 
 crystals, having the composition C 20 H 18 N 3 O 12 S 2 instead of the 
 expected reduction product. 
 
 Caustic soda and caustic potash are frequently used instead of 
 ammonia. 
 
 Messinger (Ber. 18, 1,636) used this method in reducing mono- 
 and di-iodothioxene to thioxene. At first he caused sodium to act 
 on the alcoholic solution, but this process was found to have many 
 disadvantages. For example, not more than twenty grams of the 
 substance could be treated at one time, the action was besides very 
 slow, and the mixture had to be shaken continuously. Then, too, a 
 good deal of the thioxene was carried off by the great amount of 
 hydrogen evolved during the continuance of the process, and even 
 at the end the reduction was incomplete, and a rather tedious sepa- 
 ration of the thioxene from the iodo-derivatives was necessary. 
 
 All of these disappeared when zinc dust and alcoholic caustic soda 
 were used. The caustic soda (100 gr.) was dissolved in alcohol 
 (400 gr.), and the iodothioxenes (100 gr.) were added to the cold 
 solution. Then zinc dust (150 gr.) was put into the mixture, and 
 the whole was warmed on the water bath in a flask attached to a 
 condenser for an hour. At the end of this time the reduction was 
 
328 REDUCTION [CH. xix 
 
 complete, and the thioxene and alcohol were driven over in a current 
 of steam. 
 
 Barsilowsky (Ann. 207, US) found that w-azotoluene, CH 3 . C 6 H 4 . N : 
 N . C 6 H 4 . CH 3 , could easily be made from w-nitrotoluene by gently warm- 
 ing the latter with zinc dust and alcoholic potash and then extracting with 
 ether. 
 
 Ladenburg (Ann. 217, u) recommends the use of a small amount of 
 iron filings with the zinc dust. Probably the addition of a little of the 
 ammoniacal copper solution, which gives rise to the formation of the copper- 
 zinc couple, is equally effective. 
 
 He found that chlorotropic acid could not be reduced by sodium amal- 
 gam. He therefore dissolved the acid gradually in ten times its weight of 
 concentrated caustic potash, and added zinc dust and some iron filings to 
 the solution. The reducing agent was allowed to act for two days at the 
 ordinary temperature, and small quantities of the metals were added from 
 time to time so that a slow evolution of hydrogen gas was perceptible 
 during the whole operation. Finally, the mixture was diluted with water 
 and filtered. The filtrate was acidified with hydrochloric acid, and the zinc 
 precipitated with carbonate of soda. The final filtrate was acidified again, 
 and the tropic acid was extracted with ether. 
 
 Bamberger and Berle (Ber. 24, 3,208) attempted in vain to reduce 
 carvacrol by dissolving it in fused potassium hydroxide at 180-220 and 
 adding zinc dust. 
 
 We owe to Dechend (Ger. Pat. 43,230) the method of reducing nitro- 
 bodies by means of zinc dust, with or without iron filings, and an aqueous 
 solution of a salt. 
 
 For example, he heated nitrobenzene (100 gr. ) to 130, and added to it 
 an aqueous solution of calcium chloride boiling at 103 (loogr. ), and zinc 
 dust (100 gr.) The action began as soon as the materials were mixed. 
 The products of the reduction were extracted from the zinc oxide with 
 alcohol, benze'ne, and other solvents. Such substances as azoxybenzene 
 and azoxynaphthalene were prepared by this method. Solutions of 
 sodium chloride, potassium carbonate, potassium acetate, and other salts 
 could be used in place of calcium chloride. 
 
CHAPTER XX 
 
 PREPARATION OF SALTS 
 
 SECTION I. GENERAL REMARKS 
 
 THE preparation of salts from acids and bases can be effected in 
 so many ways that nothing like a complete account of the possible 
 methods can be given here. Some of these are so well known that 
 they require no description. They will be used as a matter of 
 course whenever they are applicable. 
 
 1. Salts of Acids. All acids which are insoluble in water can 
 be dissolved by addition of caustic soda, caustic potash, or am- 
 monia. Substitution products of the last are seldom employed, 
 although Kleeberg (Ann. 263, 285) used phenylhydrazine on one 
 occasion. It must be noted however that many salts are insoluble 
 in strongly alkaline solutions. 
 
 Where the acid is soluble in water it can be converted by alkalis 
 into the corresponding salts, and an excess of lime or baryta can 
 be precipitated by means of carbon dioxide. If the quantity of the 
 acid is known, the proper proportion of the alkali can be added 
 at first. If the quantity of the acid is unknown and the acid can 
 displace carbon dioxide, then the solution may be shaken with an 
 insoluble carbonate till neutrality is reached. Barium and calcium 
 carbonates are most frequently used for the purpose, although the 
 carbonates of lead, silver, and other metals may be employed. If 
 the acid dissolves oxides, lead oxide, moist silver oxide, and similar 
 substances are applicable. Potassium and sodium carbonates are 
 less used for this purpose, as it is difficult to determine the point 
 when the acid is neutralised without the aid of standard solutions 
 and titration. 
 
330 PREPARATION OF SALTS [CH. xx 
 
 The behaviour of solutions towards litmus and other indicators 
 does not always give reliable information. Thus Ost (J. pr. Ch. 
 127, 183) found that even the acid salts of pyromeconic acid of the 
 formula, C 6 H 3 O 2 . OM+C 6 H 3 O 2 . OH, showed an alkaline reaction, 
 and Pinner and Wolffenstein (Ber. 24, 64) stated that an oxynico- 
 tine prepared by them had the properties of a base while exhibiting 
 a feebly acid reaction. 
 
 Many organic acids resemble carbonic acid in giving no salts 
 with weak bases. In one such case Altmann (Dissert. Neisse, 
 1874) evaded the difficulty by preparing the potassium salt of 
 saccharic acid, mixing it with the calculated amount of aniline 
 hydrochloride, and distilling the mixture, his object being to study 
 the decomposition products of the saccharate of aniline. 
 
 2. Salts of Bases. Bases soluble in water, alcohol, ether, and 
 other solvents can be converted into neutral or acid salts by the 
 addition of the proper acids. Thus Bernthsen (Ber. 16, 2,235) 
 prepared the neutral sulphate of amidodimethylaniline by mixing a 
 known quantity, dissolved in ether, with an ethereal solution of the 
 calculated amount of concentrated sulphuric acid. Under these 
 circumstances the neutral salt was precipitated at once. Excess of 
 sulphuric acid gave rise to the poorly crystallising acid salt. 
 
 Sulphuric acid is preferable to hydrochloric acid in such cases, as sulphates 
 usually crystallise well while the hydrochlorides have a tendency to acquire 
 a brown colour. Carbonic acid has no action on the majority of bases. The 
 carbonate of tetrahydroquinoline, discovered by Bamberger (Ber. 22, 354)' 
 for example, is exceptional. 
 
 Lellmann (Ann. 263, 286) describes a method of determining the affinity 
 coefficients of many organic bases, and another method has been worked 
 out by Fuchs (M. f. Ch. 9 1,132). 
 
 3, Precipitation of Salts Soluble in Water. Salts which are 
 soluble in water are frequently precipitated by means of alcohol or 
 some other liquid in which they are not soluble. Hydrochlorides 
 are often obtained by leading hydrochloric acid into a solution of 
 the base in absolute ether or benzene (Ann. 256, 290). In other 
 cases the hydrochloride is insoluble in strong hydrochloric acid, 
 and can therefore be thrown down from solution in water by leading 
 in a stream of hydrochloric acid gas until precipitation is complete. 
 Sometimes this method is modified by adding strong hydrochloric 
 
4 ] WATER OF CRYSTALLISATION 331 
 
 acid to the solution and evaporating on the water bath until, with 
 increasing concentration, the salt gradually separates out. 
 
 Oxalatcs and picrates of organic bases are very often prepared 
 because they are usually difficultly soluble and have excellent 
 power of crystallisation. For example, the alcoholic solution of 
 the base is neutralised with a similar solution of oxalic acid, and the 
 oxalate is precipitated by adding ether. 
 
 The use of these salts may be illustrated by reference to the case 
 of a base obtained by condensation from w-phenylene diamine and 
 cenanthol by Miller and Gerdeissen (Ber. 24, 1,732). The platinum 
 double salt was non-crystalline, and purification was finally attained 
 by preparing the picrate. The oily base was dissolved in alcohol, 
 and a strong alcoholic solution of picric acid was added. After the 
 mixture had remained at rest for a considerable time a mass of 
 crystals permeated with oil separated out. By washing with cold 
 acetic acid and recrystallising from the same solvent the salt was 
 finally obtained as a crystalline powder. The base itself, dihexyldi- 
 amylphenanthroline, could then be freed from combination, and 
 obtained from alcohol in snow-white crystals. 
 
 As a rule, salts are more soluble in hot than in cold water. The 
 most remarkable exception to this rule is probably zinc xylidatc 
 (Jacobsen, Ber. 10, 859). At o 100 parts of water dissolve nearly 
 36 parts, while at 100 they dissolve only 075 parts, and at 130 
 almost exactly 0*5 parts of the salt. A similar phenomenon has been 
 noticed in the case of liquids. Kekule and Zincke (Ann. 162, 145) 
 found that 100 parts of water at 13 dissolved 12 parts of paralde- 
 hyde. On warming the solution it became cloudy at 30, and at 
 100 about half of the substance had separated out. 
 
 4. Water of Crystallisation. The amount of water of crystal- 
 lisation is determined usually by warming a weighed portion of the 
 salt in a drying oven or in vacuo until the water is driven off. The 
 substance may also be exposed in vacuo at the ordinary temperature. 
 
 The water of crystallisation in salts is frequently determined by 
 the elementary analysis, especially when, during the ordinary 
 method of heating, decomposition sets in before constancy in 
 weight has been obtained. 
 
 The loss of water of crystallisation is in many substances accom- 
 panied by a change of colour. Thus the steel-blue needles of 
 /-azotoluenenaphthylamine sulphate, on being warmed to 105 (Ber. 
 12, 229), lose three molecules of water and become green. 
 
332 PREPARATION OF SALTS [CH. xx 
 
 Jacobsen (Ber. 15, 1,854) determined the proportion of water of 
 crystallisation in acids by titration with normal caustic soda. 
 Bases might be treated in the corresponding manner. 
 
 5. Determination of the Solubility of Salts. The determina- 
 tion of the solubility of salts is very valuable (Limpricht, Ber. 8, 
 350) for deciding as to the identity or non-identity of similar, and 
 particularly of isomeric, substances. The importance of this pro- 
 perty is especially great in the case of salts whose melting- or 
 boiling-points cannot be observed, whose crystalline form is not 
 sufficiently well developed to permit of exact study, or whose water 
 of crystallisation is variable in amount. 
 
 V. Meyer's method (Ber. 8, 999) for determining the solubility 
 of a substance is as follows : The material under examination is 
 dissolved in hot water in a test tube holding 50-60 cc. The tube 
 is placed in a large beaker of cold water, and the contents are 
 stirred vigorously with a sharp-edged glass rod until they have 
 attained the temperature of the water. After the whole has re- 
 mained at rest for two hours the water is stirred and its temperature 
 taken. The contents of the tube are then once more stirred 
 violently, and a quantity sufficient for the determination is poured 
 through a folded filter into a tared crucible provided with a lid. 
 The solution is weighed, and the amount of dissolved substance 
 determined either by evaporating the solvent and weighing the 
 residue, or in any other suitable manner. 
 
 To determine the solubility of a substance in hot solvents, the 
 boiling saturated solution is filtered into a tared flask through an 
 ashless filter paper placed in a warm funnel. After the flask has 
 remained closely stoppered for three to four hours the stopper 
 is removed momentarily to equalise the pressure, and the flask with 
 its contents is weighed. The solution is then evaporated in a water 
 bath, and the residue finally dried in a drying oven. A third 
 weighing gives the amount of solid material which the solution 
 contained. 
 
 When it is desirable to measure the solubility at a definite temper- 
 ature, a quantity of the substance is taken and covered with the 
 solvent previously heated to the desired temperature, an amount of 
 the latter being chosen which is insufficient to dissolve all the sub- 
 stance. The flask is then placed in a bath, and shaken periodically 
 during several hours, the temperature meanwhile being maintained at 
 the proper point. The subsequent treatment is the same as before. 
 
6, ;] DOUBLE SALTS OF BASES 333 
 
 6. Precipitation by Alcohol and Ether, As has been men- 
 tioned, many salts which are soluble in water are insoluble in 
 alcohol, so that they can be precipitated by addition of the latter to 
 a water solution. The inverse of this however is very unusual. It 
 was noticed by Hemilian (Ber. 16, 2,364) in the case of barium 
 salt of methyltriphenylmethane carboxylic acid. This salt is almost 
 insoluble in water, but is rather soluble in 70 per cent, alcohol, and 
 can be obtained in crystalline form from such a solution. Strecker 
 (Ann. 67, 4) observed that barium cholate was more soluble in 
 alcohol than in water. 
 
 Salts which are soluble in alcohol can usually be precipitated by 
 ether or petroleum ether. It is very unusual to find organic salts, 
 especially those containing heavy metals, dissolving in the latter 
 substances, although as early as the thirties Gusserow (Ann. 35, 
 197) noticed that lead oleate was easily soluble in ether. The 
 property of dissolving in ether seems to be characteristic of many 
 of the salts of the oleic acid series. Thus Krafft and Beddies 
 (Ber. 25, 483) found that the barium salts of bromostearylenic acid 
 and several of its homologues were soluble in this medium. Such 
 salts are on this account valuable for effecting separations. 
 
 7. Double Salts of Bases. Many organic bases, including 
 alkaloids (M. f. Ch. 9, 511), form compounds with salts of heavy 
 metals which are practically insoluble in water. Many years ago 
 Hofmann (Ann. 47, 56) recorded that "cyanol," now known as 
 aniline, gave a green precipitate with solutions of cupric sulphate 
 consisting of a compound, (C G H-NH 2 ) 2 . CuSO 4 . Later Schiff 
 (Ann. Suppl. 3, 348) prepared a double salt of ethylideneaniline 
 and mercuric chloride. It may be also mentioned that quinoline 
 forms with cobaltous chloride a compound of the composition, 
 CoCl 2 . 2C 9 H 7 N (Ber. 23, 434)- 
 
 The relative insolubility of these compounds in water often sug- 
 gests the best method for the isolation of the base concerned. Thus 
 Kossel (Z. physiolog. Ch. 5, 155) separated hypo-xanthine from a 
 solution obtained by boiling nuclein for forty hours, by adding 
 ammonia and silver nitrate, when a compound of hypoxanthine 
 with this salt was precipitated. 
 
 Such compounds are usually insoluble in water, but they can 
 generally be recrystallised from alcohol to which a little acid has 
 been added. The last-mentioned compound of hypoxanthine is 
 best purified by crystallisation from hot nitric acid (sp. gr. ri). 
 
334 PREPARATION OF SALTS [CH. xx 
 
 Lachowicz (M. f. Ch. 10, 884) states that of all salts nitrate of 
 silver has the greatest power of uniting with bases. He ascribes this 
 power in general to the " residual energy " of the acid. 
 
 Phospho-molybdic acid in acid solution precipitates all alkaloids 
 and organic basis containing nitrogen (Sonnenschein, Ann. 104, 
 45). The reagent is prepared by precipitating ammonium molyb- 
 date with sodium phosphate, dissolving the well-washed precipitate 
 in warm soda solution, evaporating the solution to dryness, and 
 igniting the residue until the ammonia is completely expelled. If 
 the molybdic acid should be partially reduced by this treatment, the 
 mass is moistened with nitric acid and ignited again. The dry 
 residue is then warmed with water, nitric acid is added to strong 
 acid reaction, and more water added so as to produce 10 parts of 
 solution from i part of the solid residue. The resulting solution is 
 golden yellow, and when ammonium bases, alkaloids, or salts of 
 these are added to portions of it precipitates are formed at once 
 When these are exposed to the prolonged action of the hydrates or 
 carbonates of the alkaline earth metals, the bases are set free, and 
 salts of the metals with phospho-molybdic acid are formed. 
 Barium carbonate is the most convenient substance to use for this 
 purpose. 
 
 Phospho-tungstic acid may \xz used in a precisely similar manner. 
 
 As an example of the use of this method Pellacani's (A. Path. 
 Pharm. 16, 442) preparation of nigelline may be described. The 
 powdered seeds of the fennel flower (nigella) were extracted with 
 50 per cent, alcohol, and the liquid was precipitated with basic lead 
 acetate. The precipitate, consisting of lead salts of vegetable acids, 
 was removed by filtration, the excess of lead precipitated by means 
 of hydrogen sulphide, and the solution concentrated at a gentle 
 heat. Extraction with ether next removed a fluorescent substance 
 along with traces of ethereal oils. After complete elimination of 
 the extracting agent, sulphuric acid was added to acid reaction, and 
 then phospho-tungstic acid. The resulting copious precipitate was 
 collected on a filter, washed, and decomposed by mixing with water 
 and barium hydroxide. The free alkaloid dissolved in the water. 
 The excess of barium was removed with carbon dioxide, and the 
 solution concentrated. Hydrobromic acid was finally added to the 
 syrupy residue, and crude nigelline bromide crystallised out in the 
 course of forty-eight hours. 
 
 Schulzeand Steiger (Z. physiolog.Ch.H, 44) obtained arginine from lupine 
 seeds, which had been allowed to germinate in the dark for two weeks, in 
 
;] DOUBLE SALTS OF BASES 335 
 
 the following manner : The dried and finely powdered cotyledons were 
 first extracted with water. The extract was strained through a cloth and 
 precipitated with tannic acid, and then, without previous filtration, with 
 lead acetate. The lead was moved from the filtrate with sulphuric acid, 
 and, after renewed filtration, a solution of phospho-tungstic acid was added. 
 A large quantity of a bulky precipitate, which settled very slowly, was 
 formed, and was removed by filtration and washed with slightly acidified 
 water, being somewhat soluble in pure water. It was next pressed between 
 sheets of filter paper to remove as much of the mother-liquor as possible, 
 and thoroughly ground in a mortar with calcium hydroxide and water, with 
 addition of a little barium hydroxide. The filtrate was then freed from 
 calcium and barium by a current of carbon dioxide, neutralised with 
 nitric acid, and evaporated almost to a syrup. On standing some time 
 the solution deposited a large amount of nitrate of arginine in crystalline 
 form. 
 
 Hofmeister (Z. physiolog. Ch. 2, 31 i) decomposed a phospho-molybdate 
 precipitate with lead carbonate, and removed the metal which went into 
 solution from the filtrate with hydrogen sulphide. 
 
 Fischer (Ann. 190, 184) has found that many, if not all, bases 
 can be precipitated as difficultly soluble substances in the form of 
 sails of hydroferrocyanic acid. Thus dimethylaniline and diethyl- 
 aniline may be precipitated from very dilute acid solutions by 
 potassium ferrocyanide, aniline itself from concentrated solutions 
 only. These salts, when suspended in water, are instantly decom- 
 posed by alkalis and the bases set free. 
 
 This method is very convenient for separating bases from 
 resinous material and for obtaining the last portions of bases which 
 are but slightly soluble in water (Ber. 16, 714). It can even be 
 used for the quantitative precipitation and separation of alkaloids. 
 Thus strychnine can be determined in presence of brucine as acid 
 ferrocyanide of strychnine. Beckurts (Ann. Pharm. 1890, 347) has 
 investigated a large number of such compounds. 
 
 Wurster and Roser (Ber. 12, 1,827) found that the salts of hydro- 
 ferricyanic acid examined by them were more soluble than those 
 of hydroferrocyanic acid. The former are sometimes acid salts and 
 sometimes neutral, the latter are always acid salts. The determina- 
 tion of the water of crystallisation has to be conducted with caution, 
 as many of the substances decompose more or less even at 100. 
 
 It is also worth notice that alkaloids can usually be precipitated 
 as periodides, and as double salts 'with cadmium iodide^ bismuth 
 
336 PREPARATION OF SALTS [en. xx 
 
 iodide, and other similar compounds. And their salts not merely 
 the bases themselves have frequently the property of forming 
 with other salts more or less insoluble double salts. 
 
 Double compounds with the salts of the noble metals, such as 
 gold chloride, platinum chloride, and mercuric chloride, have long 
 been known. The first double salt with zinc chloride was prepared 
 by Pettenkofer (Ann. 52, 97), and since then almost all metallic- 
 chlorides have been used for preparing such substances. Where it 
 is necessary and is found to be possible they may be purified by 
 recrystallisation. Details will be given below, under the respective 
 metals. Sometimes the same pair of substances yields double salts 
 of different composition according to the proportions of the ingredi- 
 ents used. 
 
 8, Obtaining Acids from their Salts. In releasing acids from 
 a state of combination, a mineral acid is added to the solution of 
 the salt, when the organic acid either falls out as a precipitate or 
 can be extracted from solution by a suitable agent. If the latter 
 method fails, the solution is evaporated to dryness, and the residue 
 extracted with alcohol or other solvent. If an excess of mineral 
 acid is to be avoided, tropaoline is added to the water solution. 
 The smallest trace of free mineral acid changes the colour, while 
 organic acids have no effect. 1 
 
 If the acids are liquids and soluble in water, and can be distilled 
 unchanged, they may be obtained free from water by decomposing 
 their salts with dry hydrogen sulphide or hydrochloric acid. With 
 the help of the former, dry formic acid can be prepared from dry 
 lead formate. By the action of the latter Wallach (Ber. 9, 1,213) 
 made dichloroacetic acid from the dry potassium salt. The salt 
 was placed in a long combustion tube, which rested in a furnace 
 standing in an inclined position. One end of the tube was con- 
 nected with a generator of hydrochloric acid, and the other with a 
 condenser. The gas was at first absorbed rapidly. As soon as it 
 began to issue from the condenser the tube was cautiously warmed, 
 and the acid distilled off in a slow stream of hydrochloric acid. The 
 yield was almost quantitative. 
 
 9. Obtaining Bases from their Salts. Bases are usually set 
 free from salts by means of alkalis or alkaline carbonates. Thus 
 
 i Cf. Chap. XXII. 3. 
 
TO] PREPARING SALTS BY DOUBLE DECOMPOSITION 337 
 
 pseudo-ephedrine (Ber. 22, 1,823) is made by adding potassium 
 carbonate to a solution of the hydrochloride and extracting with 
 ether. It appears in crystalline form as the ether evaporates. 
 Dragendorff (A. Path. Pharm. 7, 57) separated delphinine from the 
 acid solution, in which it was finally isolated from the vegetable 
 extract, by adding powdered sodium bicarbonate to distinct alkaline 
 reaction and subsequent extraction with ether. Neutral alkali 
 carbonates and caustic alkalis could not be used on account of the 
 instability of the alkaloid. Buchka (Ber. 24, 253) obtained cytisine by 
 decomposing the tannate found in the vegetable extract with litharge. 
 
 Many bases can be set free with sodium acetate. Thus Bischler 
 (Ber. 22, 2,802) added an excess of this salt to a warm solution of 
 0-nitrophenylhydrazine in water, and the base was deposited quanti- 
 tatively in crystalline form. 
 
 Many solid bases take the form of an oil when set free in water 
 solutions of their salts, and effectually resist every effort to change 
 them to the solid form. In such cases, if the base can be distilled 
 unchanged, it is mixed in the form of the salt with sodium carbonate 
 and distilled in a retort. Under these circumstances the base 
 passes over free from water, and solidifies in the receiver. This 
 process is necessary in the case of m- and /-phenylene diamine, for 
 example (Ber. 7, 1,531). 
 
 10, Preparation of Salts by Double Decomposition. When 
 
 it is desired to prepare insoluble salts of acids by double decom- 
 position it is best to use salts like barium and magnesium acetates, 
 as the precipitates are less likely to be at all soluble in the dilute 
 acetic acid produced by the action than they would be in the nitric 
 or hydrochloric acid set free from salts like silver nitrate. Or all 
 presence of free acids may be avoided by adding the reagents 
 to solutions of the sodium, potassium, or ammonium salts of the 
 organic acids. 
 
 When a mixture of acids or of bases is present in a solution a 
 separation may be effected by fractional addition of the reagents. 
 Thus, if we have a mixture of sodium salts of different acids, the 
 addition of an insufficient amount of a mineral acid will set the 
 weakest acid free first. 
 
 The reader may here be reminded of the use of dextrotartaric 
 acid and laevotartaric acid for separating synthesised bases into the 
 optically active components. This method was used by Ladenburg 
 (Ann. 247, 86) in his study of synthetic coniine. Fischer's work 
 
 z 
 
338 PREPARATION AND ANALYSIS OF SALTS [CH. xx 
 
 (Ber. 23, 2,611), in which he obtained optically active acids with 
 several asymmetric carbon atoms, or altered the rotatory power 
 of such acids, by the help of quinoline, strychnine, and similar 
 alkaloids should also be mentioned. 
 
 SECTION II. PREPARATION AND ANALYSIS OF SALTS. 
 
 11. Salts of Organic Acids containing Metals. Neutral 
 ammonium salts are obtained by dissolving the acid in excess of 
 ammonia and allowing the solution to evaporate either in the air 
 or in the desiccator over sulphuric acid. 
 
 Antimony salts and antimonyl compounds are seldom prepared 
 if we except tartar emetic. Causse (C. R. 114, 1,073) describes 
 an antimonyl compound with catechol with the formula 
 
 C 6 H 4 O 2 : SbOH. 
 
 In barium salts the metal is determined as BaSO 4 . 
 
 When the barium salt is soluble in water, it is usually prepared 
 by dissolving the acid in excess of baryta water and removing the 
 excess of barium with carbon dioxide. Insoluble salts are obtained 
 by double decomposition. 
 
 It is unusual to obtain acid salts, although Konig (Ber. 22, 787) 
 made one, having the composition (C 10 H 5 . OH . COOH . SO 3 ) 2 Ba, 
 by precipitating a warm solution of oxynaphthosulphonic acid with 
 
 barium chloride. The neutral salt, C 10 H 5 (OH)/^NBa, he 
 
 \ ^^3 / 
 
 formed by treating the acid with barium carbonate. Acid barium 
 salts of complicated composition, such as that from glycuronic 
 acid (Z. physiolog. Ch. 3, 442), occur but seldom. 
 
 For the conversion of potassium salts into soluble barium salts 
 Berthelot (C. R. 109, 227) recommends the precipitation of the 
 potassium with hydrofluosilicic acid, addition of barium carbonate 
 to the filtrate, and renewed filtration. Instead of this the theoretical 
 amount of a normal solution of sulphuric acid can be added, and 
 the potassium sulphate precipitated by adding ten times its volume 
 of absolute alcohol to the mixture. The filtrate can then be treated 
 with barium carbonate either directly or after the alcohol has been 
 removed by distillation, 
 
 Cadmium salts usually crystallise well. They were used by 
 E. Fischer (Ber. 24, 4,217) in the purification of ribonic acid. 
 The determination of the cadmium by precipitating solutions of 
 
ii] SALTS OF ORGANIC ACIDS CONTAINING METALS 339 
 
 its salts with alkaline carbonates, and ignition of the precipitates 
 gives very variable results. On account of the volatilisation of 
 some of the metal from the part of the precipitate remaining on 
 the filter paper, the proportion of cadmium found is too low. 
 According to Earth and Hlasiwetz (Ann. 122, 104), better results 
 are obtained by covering the salts with fuming nitric acid and 
 evaporating on the water bath. This operation is repeated till 
 the organic part of the substance is completely destroyed, and the 
 dry residue is carefully heated, and the resulting oxide strongly 
 ignited. 
 
 In calcium salts the metal is determined as CaSO 4 . 
 
 These salts, like those of barium, are frequently made by dis- 
 solving the acid in lime water and precipitating the excess of lime 
 with carbonic acid. As the latter retains some of the carbonate 
 in solution as bicarbonate, the solution must be thoroughly boiled 
 before filtration to convert thi-s into the insoluble neutral carbonate. 
 Where boiling is inadvisable the plan used by Schulze and Steiger 
 (Z. physiolog. Ch. 11, 47) maybe followed, and the solution exposed 
 to the air for twenty-four hours in an open dish in order to permit 
 as complete a change into the insoluble carbonate as possible. 
 
 According to Destrem (Ann. Ch. Ph. [5], 27, 7), the calcium salts of the 
 primary alcohols may be prepared by heating the latter in a dry condition 
 with calcium oxide at 120-130. These salts, like the corresponding barium 
 salts, which are prepared by the same method, are unstable in contact with 
 water. 
 
 According to Niederhausern (Ber. 15, 1,120), the calcium salts of the 
 phenols are formed by acting on finely powdered slaked lime with a slight 
 excess of the phenol dissolved in ether. The mixture is frequently shaken 
 during twenty-four hours, the ether is distilled off, and the pasty material 
 which remains is evaporated to complete dryness while being constantly 
 stirred. The granular substance which remains is almost completely soluble 
 in water. 
 
 Acids can be obtained from their calcium salts by E. Fischer's 
 method (Ber. 24, 1,842). The powdered salt is thrown into a 
 dilute solution of oxalic acid containing little more than the cal- 
 culated amount of acid, and the small excess is afterwards removed 
 by adding calcium carbonate. 
 
 In cobalt salts the metal is determined as such, the oxides being 
 reduced to metallic cobalt by ignition in a stream of hydrogen. 
 
 Z 2 
 
340 PREPARATION AND ANALYSIS OF SALTS [CH. xx 
 
 In copper salts the metal is determined as Cu 2 S, obtained by 
 ignition with sulphur in a stream of hydrogen. 1 
 
 Liebermann and Kiihling (Ber. 24, 410) used the solubility of 
 the copper salt of hygrinic acid in chloroform as a means of 
 purification by dissolving it in chloroform, precipitating with ether, 
 and repeating the process several times. 
 
 Copper salts likewise give double compounds with organic bases. 
 Thus Forster (Ber. 25, 3,421) prepared a compound of copper 
 acetate with pyridine, Cu(C 2 H 3 O 2 ) 2 , 4C 6 H 5 N, by grinding finely 
 powdered copper acetate with excess of pyridine. 
 
 Organic compounds of copper occur which are somewhat volatile, 
 and cannot therefore be ignited either in the air or in a stream 
 of oxygen without loss of copper. Such substances may be treated 
 by Walker's method (Ber. 22, 3,246), by first warming them gently 
 in a Rose's crucible in a stream of hydrogen sulphide until the 
 organic body is volatilised, and then finishing the analysis in a 
 stream of hydrogen. 
 
 In the case of gold, double salts are almost the only ones prepared. 
 They are constituted according to the formula, B. HC1, AuCl 3 , in 
 which one molecule of the hydrochloride of the base is united 
 with one molecule of auric chloride. The percentage of gold is 
 ascertained by ignition of the salt. 
 
 When a determination of the chlorine is also required, Scheibler 
 (Ber. 2, 295) dissolves a weighed quantity of the gold salt in water, 
 or suspends it in water if it is insoluble, and introduces some 
 magnesium ribbon. The gold is deposited in the metallic state, 
 and hydrogen is evolved. The operation is carried out in the 
 cold, or, in the case of less soluble substances, in the water bath. 
 It is sometimes advisable to acidify the liquid. The precipitated 
 metal is washed by decantation and collected by filtration. The 
 filtrate is set aside for the determination of the chlorine, and the 
 metal is washed again with water containing some hydrochloric 
 acid to remove all traces of magnesium or magnesium hydroxide. 
 The same treatment holds also for platinum double salts. 
 
 Water of crystallisation is seldom found in gold double salts. 
 Nicholson (Ann. 62, 71) described the double chloride of gold 
 and caffein as free from water ; but Biedermann (Ar. Pharm. 
 1883, 182) found that when the equivalent amount of auric 
 
 1 The value of this old-established method has recently been contested by 
 Uhl(Ber. 23 2,153). 
 
ii] SALTS OF ORGANIC ACIDS CONTAINING METALS 341 
 
 chloride was added to a warm solution of caffein in dilute hydro- 
 chloric acid, the solution deposited on cooling almost all the 
 double salt in the form of small plates, having the composition 
 C 8 H 10 N 4 O 2 .HC1, AuCl 3 +2H 2 O. Schmidt (Ar. Pharm. 1883, 
 664) has shown that synthesised caffein exhibits almost the same 
 behaviour. 
 
 In lead salts, the lead is determined as PbSO 4 by repeated 
 evaporation with sulphuric acid. 
 
 Lewkowitsch (Ber. 24, 653^) states that in preparing glyceric 
 acid by the decomposition of its lead salt with hydrogen sulphide 
 a certain amount of the lead always remains in solution. In this 
 case it can be obtained quite pure by decomposing the calcium 
 salt with oxalic acid. 
 
 In the case of magnesium^ the salts are ignited and the residue 
 weighed as MgO. 
 
 Kiliani (Ber. 24, 343) confirmed the formula assigned to digito- 
 genic acid by determining the magnesium in the crystalline salt. 
 He moistened the acid with alcohol, and then added strong caustic 
 potash until only a trace of the acid remained undissolved. To 
 the filtered liquid he added so much water that the addition of 
 a solution of magnesium nitrate (i : 10) only produced a faint 
 opalescence. Excess of this reagent having been added, and the 
 mixture having been left at rest for twenty-four hours, the magnesium 
 salt of digitogenic acid crystallised out in a white mass, which was 
 washed with cold water. 
 
 Gaze (Ar. Pharm. 1891, 490) obtained the magnesium salt of 
 propionic acid in crystalline form by dissolving the salt in alcohol 
 and adding acetic ether to the solution. 
 
 Manganese salts are analysed by ignition and subsequent heating 
 of the residue with ammonium nitrate. The metal remains behind 
 as Mn 3 O 4 . 
 
 Mercury salts are not very frequently made. The metal is deter- 
 mined as sulphide. 
 
 Heuser and Stohr (J. pr. Ch. 150, 437) describe a double salt of aa- 
 dimethyldipipcridyl, having the formula C 12 H 12 N 2 . 2HCl-f 6HgCl 2 . 
 The usefulness of double salts of this nature for the separation of 
 isomers among the pyridine bases was recognised by Ladenburg. 
 Pure pyridine itself (Ann. 274, 4) is obtained by dissolving com- 
 mercial pyridine (20 gr.), which boils between 1 14 and 1 18, in 10 per 
 cent, hydrochloric acid (100 gr.), and adding a solution of mercuric 
 chloride (135 gr.) in I litre of hot water. On cooling, the solution 
 
342 PREPARATION AND ANALYSIS OF SALTS [CH. xx 
 
 deposits a double salt, which can be purified by recrystallising from 
 boiling water, and melts at 178. By distillation with caustic soda 
 the base is set free again, and may be dried with solid caustic 
 potash. It is finally distilled, and all passes over at 114. 
 
 Nickel salts leave behind NiO on ignition. 
 
 Platinum double salts are probably more frequently prepared than 
 any others. They are usually obtained by the addition of a solution 
 of platinum tetrachloride to a solution of the hydrochloride of the 
 base in water or alcohol. They generally appear as crystalline pre- 
 cipitates, or at least change into such in a short time. Thus Nietzki 
 (Ber 16, 467) mentions that when platinum tetrachloride is added 
 to a solution of phenosafranine hydrochloride a red cheese-like pre- 
 cipitate is formed, which almost immediately turns into beautiful 
 golden plates. In composition the salts correspond to the double 
 chloride of platinum and ammonia, PtCl 4 +2NH 3 . HC1, the ammonia 
 being replaced by the base in question. Double salts containing 
 water of crystallisation are very uncommon. In this connection it 
 may be mentioned that Baeyer (Ber. 12, 1,322) found that the double 
 salt of quinoline had the composition (C 9 H 7 N . HC1) 2 PtCl 4 + H 2 O, 
 and he also states that the platinum salt of synthetic picoline 
 crystallises sometimes with and sometimes without water of crystal- 
 lisation in a purely arbitrary fashion. 
 
 According to Zincke (Ber. 25, 1,497), the double salt of platinum with 
 isoquinoline crystallises with two molecules of water,(C 9 H 7 N . HCl) 2 PtCl 4 + 
 2H 2 O. Andreocci (Ber. 24, 9550 finds that when the chloroplatinate of 
 i -phenyl-3-methylpyrazol crystallises from hydrochloric acid containing 
 excess of platinum tetrachloride it unites with three molecules of water. 
 When i-phenyl-3-methylpyrodiazolon is dissolved with platinum tetra- 
 chloride in fuming hydrochloric acid a double salt containing four molecules 
 of water is obtained. Like many other similar double salts it cannot be re- 
 crystallised from water. On adding a very strong solution of platinum tetra- 
 chloride to phenylammeline, made into a paste with concentrated hydro- 
 chloric acid, and heating, Smolka and Friedrich (M. f. Ch. llj 7) found that 
 the whole went into solution. But the crystals deposited on cooling were 
 decomposed by water,. so the substance was purified by adding alcohol to the 
 warm solution, and afterwards washing the crystals with the same substance. 
 
 When it is desired to recover the base from the double salt, or to 
 use the preparation of the latter as a means of purification, it is 
 usual to suspend the salt in water and decompose it with hydrogen 
 sulphide. The precipitated sulphide of platinum is very difficult 
 
ii] SALTS OF ORGANIC ACIDS CONTAINING METALS 343 
 
 to filter, and unstable bases, like choline, are decomposed by such 
 treatment. According to Schmiedeberg and Harnack (A. Path. 
 Pharm. 6, 14), the hydrochloride of choline can be best obtained 
 from the platinum double salt by evaporating a solution of the 
 latter to dryness with an equivalent amount of potassium chloride, 
 and extracting the residue with alcohol. Gram (A. Path. Pharm. 20, 
 119) recommends the decomposition of this salt with potassium 
 chloride in the cold. The alcohol removes the hydrochloride of the 
 base, and leaves the potassium chloroplatinate undissolved. 
 
 Bases which are volatile without decomposition can be isolated 
 by distilling the double salts with sodium carbonate. 
 
 A few platinum double salts, varying from the type given above, 
 are known. Thus Hofmann (Ber. 20, 2,253) by treating the ami- 
 dine of 0-amidophenylmercaptan with hydrochloric acid and 
 adding platinum tetrachloride to the resulting hydrochloride, with- 
 out bringing it first into solution, obtained a salt crystallising in 
 needles, which, after being washed with hydrochloric acid and 
 dried, had the composition C 8 H 7 N 3 S . 2HC1, PtCl 4 . The gold 
 double salt had the normal composition, however, C 8 H 7 N 3 S . HC1, 
 AuCl 3 . 
 
 The platinum is determined by ignition. " But in all cases where 
 the composition of a base is determined solely by that of the 
 platinum double salt an estimation of the chlorine must also be 
 made. Wallach (Ber. 14, 753) recommends the following method: 
 The platinum salt is weighed out in a platinum dish, covered with 
 a fresh concentrated solution of from one half to one gram of 
 sodium in absolute alcohol, and evaporated on the water bath until 
 a crystalline scale begins to be formed on the surface. The basin 
 is then placed on a triangle, and the alcohol set on fire. The 
 alcohol and alcoholate will now burn quietly without spurting or 
 frothing provided fresh alcoholate was used to start with. The 
 platinum salt is completely decomposed, yielding metallic platinum, 
 while the chlorine all combines with the sodium. When the flame 
 has gone out the vessel is heated for a short time longer over the 
 naked flame. When it has cooled once more, the contents, consist- 
 ing of sodium carbonate and chloride, platinum, and carbon, are 
 washed into a beaker, acidified with nitric acid, and filtered. The 
 chlorine can be determined in the filtrate. The platinum and 
 carbon on the filter are restored to the platinum basin, and the 
 platinum determined by ignition. The numbers for chlorine are 
 very accurate. Those for platinum are often less satisfactory, but 
 
344 PREPARATION AND ANALYSIS OF SALTS [CH. xx 
 
 amply suffice for the recognition of the proportion of platinum to 
 chlorine in the salt. 
 
 According to Mylius and Forster (Ber. 24, 2,439), the loss of 
 metal in platinum determinations may be due to the formation of 
 volatile carbonyl-platinous chloride, COPtCl 2 . In the heating of 
 platinum double salts there is certainly opportunity for carbon 
 monoxide and chlorine to interact with the chloride. 
 
 The recovery of the platinum from double salts is such a frequent task that 
 the method devised by Duviliers (Ann. Ch. Ph. [5], 10, 872) for the 
 purpose may be described. The double salt (100 gr.) is thrown in portions 
 into a boiling solution of sodium formate (50 gr.) and 25 per cent, caustic 
 soda (5occ.) in a litre of water. The reduction begins immediately, and 
 after one hour's boiling the solution is filtered, and the platinum washed 
 with warm water containing hydrochloric acid. 
 
 Potassitim salts are usually obtained from the acids by treat- 
 ment with caustic potash or potassium carbonate. From salts 
 containing heavy metals they are made by double decomposition. 
 If such salts are insoluble in water, they are covered with a solution 
 of potassium carbonate, and the mixture is evaporated on the water 
 bath, when the interaction takes place quantitatively. 
 
 To separate potassium chloride from an organic salt of potassium 
 by extraction of the latter with alcohol, it is necessary to take 
 almost absolute alcohol (Barth and Schmidt, Ber. 12, 1,262), as 
 otherwise much of the inorganic salt may go into solution also. 
 When the organic salt is not sufficiently soluble in absolute alcohol, 
 it is advisable to treat the aqueous solution first with silver sulphate 
 to convert the potassium chloride into sulphate. The latter is 
 practically insoluble even in 70 per cent, alcohol. 
 
 The potassium is always determined as K 2 SO 4 , by ignition with 
 sulphuric acid. 
 
 Konig (Ber. 22, 788) describes an acid potassium salt. 
 
 Silver salts are prepared by the general methods. In many 
 cases it is desirable to apply the nitrate of silver in alcoholic solu- 
 tion ; it dissolves in four parts of boiling alcohol (Gmelin, Handbuch, 
 3, 624). Silver salts are almost always neutral and free from water, 
 so that they are useful for determining the valency of acids and for 
 similar purposes. 
 
 According to Konigs and Korner (Ber. 16, 2,153), carbon dioxide 
 is frequently most easily removed by distilling the silver salts. 
 This method is specially advantageous in treating acids which con- 
 
n] SALTS OF ORGANIC ACIDS CONTAINING METALS 345 
 
 tain a strongly acid hydroxyl group, besides the carboxyl, like the 
 aromatic oxy-acids. For such purposes it is preferable to the dis- 
 tillation with bases of the free acids or their calcium salts. The 
 above observers found that on distilling oxycinchoninic acid with 
 bases much charring took place ; while on heating the silver salt 
 (5 gr.) in a combustion tube in a stream of carbon dioxide, it yielded 
 two grams of oxyquinoline and the charring was very slight. 
 
 Although in the case of inorganic acids, neither acid nor basic 
 silver salts are known (Mendelejeff, Principles of Chemistry, Vol. 
 2, p. 396), a few acid salts of organic acids are met with. Thus 
 Thate (J. pr. Ch. 137, 157) prepared both the neutral silver salt, 
 C 1(i H 12 N 2 O 7 Ag 2 , and the acid salt,C 10 H 13 N 2 O 7 Ag,ofazoxy-0-phenoxy- 
 acetic acid. Schmidt (Ar. Pharm. 1886, 521) prepared both the 
 neutral and acid salts of jervic acid with the formulae, C 7 H 2 Ag 2 O 6 
 and C 7 H 3 AgO +H 2 O, respectively. According to Jeanrenaud 
 (Ber. 22, 1,281), a silver salt of tetrahydrodioxyterephthalic acid 
 with the unusual constitution, C H 2 (OAg) 2 (COOAg) 2 H 4 +2H 2 O, can 
 be prepared. Claus and Kohlstock (Ber. 18, 1,849) prepared 
 amarine-silver, C 21 H 17 N 2 Ag, and found along with it large crystals 
 of diamarine silver nitrate, (C 21 H 18 N 2 ) 2 AgNO 3 +H 2 O, when they 
 allowed a solution of amarine and silver nitrate in dilute alcohol 
 to remain for several weeks. Dimethylpyron carboxylic acid (Feist, 
 Ann. 257, 290) gives a salt of the composition, C 8 H 7 AgO 4 +AgNO 3 , 
 and diphenylpyron dicarboxylic acid (Feist, Ber 23, 3,733) g ives 
 likewise a salt containing nitrate of silver having the composition 
 (C 18 H n Ag0 4 ) 2 +AgN0 3 . 
 
 Schmiedeberg and Meyer (Z. physiolog. Ch. 3, 433) found that 
 the silver salt of camphoglycuronic acid is represented by the 
 formula, C 10 H 23 AgO 8 -f3H 2 O, and Eckhardt (Ber. 22, 276) prepared 
 a silver salt of metaquinaldineacrylic acid having a composition 
 represented by the formula, C 13 H ]0 NO 2 Ag+4H 2 O. 
 
 When organic salts of silver are ignited the metal remaining 
 behind often contains carbon. 
 
 In sodium salts the metal is always estimated as Na 2 SO 4 . 
 
 The fact that most organic sodium salts are soluble in alcohol, 
 while sodium carbonate, as well as many other substances, inorganic 
 and organic (albumens, &c.), are insoluble in it, suggests a method 
 of obtaining sodium salts of organic acids which is of very wide 
 application. The material under examination is treated with cold 
 or warm caustic soda, and carbon dioxide is led into the filtrate to 
 convert the sodium into carbonate. The solution is then evapor- 
 
346 PREPARATION AND ANALYSIS OF SALTS [CH. xx 
 
 ated as far as possible in the water bath, and the residue extracted 
 with 80 to 90 per cent, alcohol, when the organic sodium salt is 
 obtained in almost complete purity. 
 
 Briihl (Ber. 24, 3,390) prepared the sodium salt of camphor 
 carboxylic acid by suspending the acid in water, and adding caustic 
 soda until the solution showed a faintly alkaline reaction. After 
 passing carbon dioxide through the solution he allowed it to eva- 
 porate in vaciiO) and dissolved the residue in alcohol. On evaporat- 
 ing this alcoholic solution in like manner over sulphuric acid he 
 obtained a crystalline powder, which was easily soluble in water, 
 methyl alcohol,. and chloroform. When the water solution was 
 allowed to evaporate in the air, good crystals of the sodium salt 
 were obtained. 
 
 Some sodium salts, like that of acetylendicarbodiazoacetic acid 
 (Buchner, Ber. 22, 845), are nearly insoluble in cold water. Konig 
 (Ber. 22, 787) prepared the sodium salt, C 10 H 5 (OH)(COOH) 
 (SO 3 Na), by adding a saturated solution of common salt in large 
 excess to a warm solution of oxynaphthosulphonic acid, filtering off 
 the precipitate, and recrystallising it from warm water. 
 
 In strontium salts the metal is determined as SrSO 4 . 
 
 Tin double salts, especially in the form of double salts with 
 stannous chloride, are of common occurrence. They appear in 
 crystalline form from mixtures in which tin and hydrochloric acid 
 have been used for the purpose of reducing". 
 
 Hofmann (Ber. 18, 115) recommends the use of tin tetrachloride 
 in the investigation of volatile bases. Thus he separated coneine 
 from y-coniceine by evaporating a mixture of their hydrochlorides 
 until crystallisation set in, and adding stannic chloride to the con- 
 centrated solution. The use of excess of the inorganic salt was 
 carefully avoided. The liquid soon became semi-solid from the 
 presence of crystals of the double salt with y-coniceine hydro- 
 chloride, while the corresponding compound with coneine, which 
 does not crystallise, remained in the mother-liquor and appeared as 
 a gummy mass on evaporation of the solvent. Pure y-coniceine 
 was isolated by further treatment. For the analysis, the salt, 
 2(C 18 H 15 N . HC1) . SnCl 4 , was dissolved in water, and the tin pre- 
 cipitated with hydrogen sulphide. The sulphide was then ignited 
 in the air, and weighed as stannic oxide. 
 
 In zinc salts the metal is weighed as ZnO. 
 
 The zinc salts seem to be specially suited for assisting in the 
 preparation of pure acids. Thus Hell and Rempel (Ber. 18, 817) 
 
12] SALTS OF ORGANIC BASES WITH ORGANIC ACIDS 347 
 
 made pure oxysuberic acid by neutralising an aqueous solution of 
 the acid, as it is obtained in syrupy form, with ammonia, and pre- 
 cipitating with a concentrated solution of zinc sulphate. The zinc 
 salt was collected on a filter, and decomposed in a porcelain dish 
 with moderately strong sulphuric acid. The oxysuberic acid was 
 insoluble in the solution of zinc sulphate, and was collected as a 
 crystalline powder by filtration and recrystallised from ether. The 
 same method was used by Bujard and Hell (Ber. 22, 70) for the 
 purification of oxylepargylic acid. 
 
 The zinc salts of isomeric acids frequently show characteristic 
 differences. Thus, that 'from lactic acid from fermentation crystal- 
 lises with 3H 2 O, that from sarcolactic acid with 2H 2 O, and that 
 from ethylenelactic acid with 4H 2 O. The solubilities of these salts 
 in water and in alcohol are likewise quite different. 
 
 Mekilow (Jahresb. 1885, 1,350) even separated /3- from y -chloroxy- 
 butyric acid by means of the different solubility of their zinc salts in 
 water. 
 
 Double salts containing zinc are also sometimes useful, as in the 
 case of ethylenelactic acid, which Heintz purified by this means. The 
 salts of this acid are hard to crystallise on account of their great 
 solubility in water. But when Heintz (Ann. 157, 294) divided a 
 quantity of the impure acid into two portions, saturated one with 
 quicklime and the other with zinc oxide and mixed them, part of 
 the double salt was precipitated at once, and the rest came out of 
 the mother-liquor on evaporation. From this salt, after recrystallisa- 
 tion, he removed the zinc with hydrogen sulphide, and the lime with 
 an equivalent quantity of oxalic acid, and so obtained the acid in a 
 pure condition. This appeared to be the only possible way of 
 obtaining the pure acid from such a source. 
 
 For the preparation of bases in the form of sulphates from double 
 salts with zinc chloride, a method used in manufactories (Ger. 
 Pat. 46,438) may often be found useful in the laboratory. The zinc 
 double salt with diamidocarbazol hydrochloride, for example, is 
 mixed with sodium sulphate, and the sulphate of diamidocarbazol, 
 which is but slightly soluble, crystallises out. 
 
 12. Salts of Organic Bases with Organic Acids. Organic 
 salts of organic bases are frequently prepared, as they often serve to 
 characterise the acid or assist in its purification. Thus allocinnamic 
 acid forms a salt with aniline (Ber. 25, 950, which is insoluble in 
 benzene, while the closely related hydrocinnamic acid is not precipi- 
 
348 PREPARATION AND ANALYSIS OF SALTS [CH. xx 
 
 tated in benzene solution by aniline. E. Fischer (Ber. 24, 3,624) 
 found that talonic acid could be best purified by conversion into a 
 salt with brucine. This salt was obtained by boiling a dilute solu- 
 tion of the acid in water, with a slight excess of brucine, for fifteen 
 minutes, evaporating to a syrup, and allowing the residue to crys- 
 tallise. The remaining water was removed by stirring with 
 absolute alcohol and filtering. The salt was finally purified by 
 recrystallisation from methyl alcohol. 
 
 13. Ignition of Explosive Salts. The analysis of explosive 
 salts may be conveniently discussed in closing this chapter. The 
 violence of the action may be modified by mixing with sand, or 
 recourse may be had to the conversion of the compounds into non- 
 explosive ones by evaporating them with strong mineral acids, 
 bromine water, or other reagents before the ignition. Thus Fischer 
 (Ann. 199, 303) decomposed potassium diazoethanesulphonate by 
 evaporation on the water bath with dilute sulphuric acid, and could 
 then ignite the residue without danger of explosion. 
 
 14. Determination of the Ash in Organic Matter. The esti- 
 mation of the amount of ash in organic substances containing salts 
 is rendered difficult by the fact that by mere ignition in an open 
 basin all the carbon is not removed. Small pieces of the latter are 
 surrounded by the melting alkali salts, and are protected from in- 
 cineration. Efforts to burn the charred matter by using ammonium 
 nitrate (Gorup Besanez), oxygen, or by fusion with soda and potas- 
 sium nitrate (Stahel) have the disadvantages that either loss by 
 spurting is to be feared, or inconveniently large amounts of material 
 are accumulated when the quantity of ash is itself large. Combus- 
 tion with potassium nitrate alone does not give exact figures, for 
 alkaline chlorides are somewhat volatile at the high temperature of 
 ignition. And besides, even prolonged ignition up to six hours, as 
 recommended by Graanboom (Dissert. Amsterdam, 1881), does not 
 give a perfectly white ash. 
 
 Bemmelen (Z. physiolog. Ch. 7, 505) recommends the following 
 method for escaping all these difficulties. The dry substance is 
 first spread in small portions at a time in a thin layer in a platinum 
 basin, and slowly charred with the heat of a small flame. As soon 
 as the dry distillation has ceased, the carbonised mass is carefully 
 broken up, stirred, and heated anew. It is possible in this way to 
 carbonise the whole without any loss on account of swelling or 
 
i 4 ] THE ASH IN ORGANIC MATTER 349 
 
 frothing. If several platinum basins are available, 50 grams can be 
 worked up in this way in from one to two days. The whole mass 
 of incinerated matter is finally thrown, in small portions at a 
 time, into one or two platinum basins, or still better, into a Deville's 
 platinum tray, and heated in a muffle such as Wiesnegg's. The 
 material is kept at a dark-red heat, so as to avoid volatilisation of 
 chlorides of potassium and sodium, and with a good draught the 
 carbon is soon all consumed. If a portion should remain unburnt, 
 the contents of the basin are washed into a beaker. The particles 
 of carbon remaining undissolved by the water are collected on 
 a filter and burnt in the muffle. Under such circumstances, being 
 free from alkaline chlorides and phosphates, they easily burn to 
 a white ash. By adding the residue from the evaporation of the 
 water extract, the total ash is ascertained 
 
CHAPTER XXI 
 
 SAPONIFICATION 
 
 1. Saponifying Agents. By saponification is meant the decom- 
 position of an ester into its components, the acid and the alcohol, 
 water being taken up in the process 
 
 CH 3 COOC 2 H 6 + H 2 = CH 3 COOH + C 2 H 6 OH. 
 
 The water can be taken up directly under certain circumstances, 
 as in Wilson and Gwynne's process for saponifying fats on a large 
 scale. The fats are heated to 300, and decomposed into fatty 
 acids and glycerol by means of a current of steam heated to 315- 
 
 Einhorn and Rassow (Ber. 25, i,397) obtained dihydroxyan- 
 hydroecgonine from the methyl ester by boiling it with water for 
 twenty-four hours. The haloid compounds of alcohol radicals, 
 which may be regarded as esters of hydrochloric acid, are decom- 
 posed on heating with water in accordance with this conception. 
 Thus Niederist (Ann. 196, 350) heated methyl iodide (26-2 gr.) 
 with water (400 cc.) for eight hours in a closed vessel in the water 
 bath. He found that the action took place almost quantitatively 
 in the direction of producing methyl alcohol and hydriodic acid 
 
 = CH 3 OH + HI. 
 
 In the case of allyl iodide the substances required only to be boiled 
 in a flask attached to a condenser. 1 
 
 1 It may be worth mentioning here that Buchanan (Ber. 4, 34) and 
 Thomsen (Ann. 200, ?6) both showed that when monochloracetic acid 
 was boiled with water for several days, it was converted into glycollic acid 
 and hydrochloric acid. Holzer (Ber. 16, 2,955) found later that this 
 
2] AQUEOUS CAUSTIC POTASH OR SODA 351 
 
 In the laboratory saponifications, almost without exception, are 
 conducted with the help of alkalis, sodium ethylate, lead or silver 
 oxide, or acids. Quite recently aluminium chloride has been added 
 to the list, and often renders the accomplishment of the object at 
 the ordinary temperature possible. 
 
 2. Aqueous Caustic Potash or Soda. These alkalis are much 
 more frequently used than the hydroxides of the alkaline earths. 
 Although the effects in both cases are nearly always identical, the 
 former are preferred, because they can be applied in more con- 
 centrated solution. 
 
 The irregular way in which solutions of the alkalis boil is very 
 inconvenient. When small quantities of very concentrated solu- 
 tions are used for example, one part of water to two parts of caustic 
 potash, it is preferable to seal the substances up in a tube and heat 
 at about 100. 
 
 BischofF (Ber. 24, 2,015) dissolved potassium hydroxide (500 gr.) 
 in water (200 cc.) in a basin, and added ethylacetosuccinic ether 
 (400 gr.) in small portions at a time. The temperature was kept 
 between 120 and 126. The alcohol which was split off evaporated, 
 and when the last portion had been added, about fifteen minutes 
 after the first, the saponification was complete. The mass was 
 diluted with water, and the solution rendered faintly acid with 
 dilute nitric acid, and added to a solution containing lead nitrate 
 (830 gr.). The precipitate was collected on a filter, and, while still 
 moist, was decomposed with the calculated amount of sulphuric 
 acid. The filtrate from the lead sulphate, when evaporated, 
 deposited the ethylsuccinic acid. The yield was 50 per cent. 
 
 Baeyer (Ber. 14, 1,743) found that indoxylic ether was best 
 saponified by mixing with fused caustic soda at 180. When the 
 resulting yellow salt was treated with acids, indoxylic acid was 
 thrown down as an almost colourless and hardly soluble precipitate. 
 
 Very complex acids can sometimes be freed from combination in 
 
 action proceeded much more smoothly when pulverised marble (probably 
 precipitated chalk would be still better) was added. Haussermann and 
 Beck (Ber. 25, 2,445) a ^ so converted 0-nitrobenzyl chloride into 0-nitro- 
 benzyl alcohol (b.-p. 74) by boiling with a dilute solution of potassium 
 carbonate. From these facts it would seem that we might expect that the 
 saponification of esters by water would be assisted by the presence of 
 chalk, or that esters, which are easily split by caustic alkalis, might prefer- 
 ably be treated with this reagent. 
 
352 SAPONIFICATION [CH. xxi 
 
 esters without decomposition only by using alkali of definite con- 
 centration. For example, Guthzeit (Ann. 214, 72) could obtain 
 nothing but ethane tricarboxylic acid by saponifying ethane tetra- 
 carboxylic ether. Buchner, however (Ber. 25, 1,158), boiled the 
 ester (i gr.) with caustic soda of sp. gr. i'2 (4-5 cc.) for an hour and 
 a half, neutralised, evaporated, and acidified the liquid, and finally 
 extracted it with ether. He obtained, by evaporation of the extract, 
 crystals of ethane tetracarboxylic acid. 
 
 As an example of saponification in the cold, it may be mentioned 
 that Knorr treated diacetosuccinic ether (4 parts) with 25 per cent, 
 caustic soda (5 parts) by allowing the mixture to remain for eight 
 days. The decomposition into acid and alcohol was complete. 
 
 In the case of acids as complex as this, the strength of the caustic soda 
 solution may have a considerable influence on the final result, even when 
 the action takes place in the cold. Thus Knorr (Ber. 22, 169) allowed the 
 same ester to remain in the cold for several days with a slight excess of 
 3 per cent, caustic soda, and found that it broke up into alcohol, carbon 
 dioxide, and acetonylacetone, under these circumstances 
 
 C 12 H 18 6 + 2H 2 = 2C 2 H 6 + 2C0 2 + C 6 H 10 2 . 
 
 Paal prepared phenacylacetylacetic acid from the ester by letting the 
 latter remain with 2 per cent, caustic potash for a few hours, and then 
 filtering the solution into dilute sulphuric acid. 
 
 It will not always be convenient to isolate complex acids made from 
 esters obtained by condensation of acetoacetic ether or malonic ether by 
 simply precipitating the acid or extracting it from the acid solution with 
 ether. For example, Conrad (Ann. 204, 132) finds that the free acids from 
 alkylmalonic ethers are best isolated by neutralising the alkaline mixture 
 with acetic or hydrochloric acid, and precipitating the calcium salt of the 
 organic acid by adding calcium chloride to the solution. This salt is usually 
 crystalline, and can be best decomposed by adding the calculated amount of 
 oxalic acid. The mixture is boiled for some time, and filtered from the 
 insoluble calcium oxalate. The filtrate is evaporated to dryness, and the 
 residue treated with ether to separate the acid from any oxalic acid which 
 may still be present. The acid then remains as a white crystalline mass, 
 and is purified by recrystallisation. 
 
 3. Alcoholic Caustic Potash. When, as is often the case, the 
 saponification is conducted by boiling with alcoholic caustic potash, 
 the excess of the alkali can be precipitated for the most part by 
 means of carbonic acid. 
 
4l SODIUM ETHYLATE 353 
 
 Paal and Hoffmann (Ber. 23, i,497), in trying to saponify iso- 
 amylmalonic ether, C fi H u . CH(COOC 2 H 6 ) 2 , found that this could 
 not be completely effected by alcoholic caustic potash, although 
 boiling for several hours with an aqueous solution successfully 
 accomplished the object. This is a very exceptional observation. 
 
 The author has found, after much experimentation, that the following is 
 the best method of saponifying animal fat : The fat (i,25ogr.) is melted 
 on the water-bath and poured into 96 per cent, alcohol ( I -5 1. ) which has 
 previously been heated in a six litre flask. Caustic potash (400 gr.) is 
 allowed to dissolve spontaneously in a little water, and this solution is 
 immediately, while still hot, added in portions to the alcoholic solution of 
 fat. The action is very violent, and as soon as the last portion of caustic 
 potash has been added, and the whole has been shaken, the saponification 
 is complete. This is seen from the fact that the product is completely 
 soluble in water. No external heating is necessary during the operation. 
 
 4. Sodium Ethylate, Kossel and Obermiiller (Z. physiolog. 
 Ch. 14, 599) have found that, even in the cold, sodium ethylate is a 
 capital saponifying agent, especially for fats. The process is de- 
 scribed in a patent specification (Ber. 24, 419^) as follows : The 
 fat, cotton oil, spermaceti, Chinese wax or other similar substance 
 is dissolved in benzene, petroleum ether, or ether, and sodium 
 ethylate is added. Instead of this, alcohol and sodium can be 
 used. After a few minutes an easily filtered precipitate is deposited 
 which is chiefly composed of the soaps. When metallic sodium is 
 used, its surface quickly becomes covered with this product and the 
 mixture must be vigorously shaken so as to permit the action to 
 continue. By this method, only 40-50 grams of sodium are re- 
 quired for a kilogram of cotton oil that is, not much more than the 
 calculated amount, and the operation occupies twenty-four hours. 
 The same quantity of oil would have to be heated for twenty hours 
 with excess of alcoholic caustic potash to attain the same result. 
 The filtrate from the soap will, in this case, contain cholesterin and 
 isocholesterin. 
 
 The same observers (Z. physiolog. Ch. 15, 422) saponified 
 phenyl salicylate (salol) by this method and obtained ethyl salicylate 
 and phenol, and the former had to be finally decomposed with 
 aqueous caustic soda. When sodium amyl alcoholate was used, 
 the product was amyl salicylate. The method is therefore 
 applicable only to fats. 
 
 According to Obermiiller's view the glycerol ester and sodium 
 
 A A 
 
354 SAPONIFICATION [CH. xxi 
 
 ethylate change first into the sodium salt of glycerol and the ethyl 
 ester of the fatty acid. The former then reacts with the traces of 
 water contained in the alcohol giving glycerol and sodium hy- 
 droxide. Finally this last easily decomposes the ethyl ester. 
 
 5. Baryta Water. Esters may be saponified by prolonged 
 boiling with baryta water in a flask connected with a condenser, or, 
 if the temperature is not high enough, by heating the mixture in a 
 sealed tube. The acid, which is found as barium salt at the con- 
 clusion of the action, is set free by a stronger acid and filtered off 
 or extracted with ether as the case may be. If the barium salt 
 itself is wanted, the excess of barium hydroxide can be precipitated 
 with carbon dioxide and the filtrate evaporated until crystallisation 
 begins. If, on the other hand, it is the alcohol whose isolation is 
 desired, a case which seldom occurs, it may be distilled off or 
 driven over with steam. Its separation from the distillate can be 
 effected by adding a large amount of potassium carbonate or, if the 
 nature of the alcohol permits, extracting with ether. 
 
 Baeyer (Ber. 14, 1,743) saponified the ester of ethylindoxylic 
 acid by boiling with alcoholic barium hydroxide, and found that the 
 free acid was deposited in white flakes when the liquid was 
 acidified. 
 
 6. Lime Water. The action of lime water is similar to that of 
 baryta water. The inferior solubility of calcium hydroxide renders 
 it less useful than the other. 
 
 7. Oxides of Lead and Silver. As is well known, fats are de- 
 composed when boiled with lead oxide and water. They decompose 
 into the lead salt of the fatty acid and glycerol. The lead salts so 
 obtained are known as lead soaps. 
 
 Hantzsch (Ber. 19, 32) treated methyl nicotinate methchloride 
 with silver oxide, and obtained the free acid, 
 
 r /COOCH 3N /C1 c /COOH N /OH . 
 
 5 \H 4 \CH 3 ' C ->\H 4 \CH 3 
 
 so that here, not only was the chlorine removed, but the oxide 
 saponified the ester as well. 
 
 8. Acids. Not only do alkalis saponify esters, but acids like 
 sulphuric and hydrochloric also split them into their components. 
 
8] ACIDS 355 
 
 This is the more curious as these are the very agents used in form- 
 ing esters out of acids and alcohols. The first observation in this 
 connection was made by Lautemann (Ann. 125, 13). He found 
 that when hydriodic acid was led into methyl salicylate, salicylic 
 acid was deposited and methyl iodide formed. 
 
 C 6 H 4 (OH).COOCH 3 4-HI = C C H 4 (OH).COOH + CH 3 I. 
 
 Then Gal (C. R. 59, 1,049) stated that when esters were treated 
 with hydrobromic acid they uniformly broke up into the acid and 
 alkyl bromide. For example, methyl formate gave formic acid and 
 methyl bromide. 
 
 Auwers and Meyer (Ber. 23, 298) found that a mixture of the 
 isomers, tetramethylsuccinic ether and trimethylglutaric ether, could 
 not be separated by fractional distillation. He heated them with 
 an equal volume of hydrobromic acid of sp. gr. 17 for ten hours at 
 100 in a sealed tube. The saponification was only partial, but, 
 for the purpose of separation, was more advantageous than that 
 with alcoholic potash. 
 
 Sapper (Ann. 211, 179) has found that hydrochloric acid is the 
 least suitable of the three for this work, which agrees with the fact 
 that it is the most valuable for preparing esters. Hydrofluoric 
 acid is still less effective. 
 
 The most convenient form in which this method can be applied 
 is to saturate glacial acetic acid at o with hydrobromic acid and 
 allow the ester to remain in contact with this solution for some 
 time. 
 
 Baeyer (Ber. 23, 1,625) states that the best way of saponi- 
 fying acetyl-/-amidotriphenylcarbinol, in order to remove the 
 acetyl group, is to dissolve the substance in glacial acetic acid and 
 add the solution slowly to warm dilute sulphuric acid. The mixture 
 is boiled till solution is complete, and finally the base is precipitated 
 with ammonia. 
 
 Paal and Bodewig (Ber. 25, 2,963) found that the benzoyl group also 
 was best split off by the aid of sulphuric acid. They prepared orthonitro- 
 benzyl alcohol by acting with sodium benzoate (1^-2 parts) on nitrobenzyl 
 chloride (i part) and decomposing the nitrobenzyl benzoate so obtained by 
 boiling for three or four hours with 50 per cent, sulphuric acid. 
 
 Bischoff and Mintz (Ber. 23, 650) saponified ethylbutenyl tricarboxylic 
 ether with sulphuric acid. Two parts of the ester were mixed with one 
 part ot water and one of concentrated sulphuric acid, and heated at 150-170 
 
 A A 2 
 
356 SAPONIFICATION [CH. xxr 
 
 in a round-bottomed flask connected with an inverted condenser until a 
 drop of the mixture wa completely soluble in alkali. The operation did 
 not take much time, but secondary reactions always accompanied the 
 saponification. 
 
 Stein (Ger. Pat. 61,329) states that when fat and oils are heated in a 
 closed vessel with a 3 per cent, solution of sulphuric acid or of a bisulphate 
 at 170-180, a pressure of eighteen atmospheres is developed, and in the 
 course of nine hours the substances are completely decomposed into fatty 
 acids and glycerol. 
 
 9. Aluminium Chloride. It has been shown by Hartmann and 
 Gattermann (Ber. 25, 3,531) that ethers of phenol and its derivatives, 
 as well as esters, are very easily saponified by aluminium chloride. 
 Besides the superior ease with which the operation can be carried 
 out, this method presents the advantage over the use of hydriodic 
 acid that it can be employed with substances like ethers of nitro- 
 phenols and ketonic derivatives of phenol which would be reduced 
 by the other reagent. 
 
 When the saponification is too energetic, carbon disulphide is 
 used as a diluent. For example, orthonitroanisol (10 gr.) is dissolved 
 in twice its volume of carbon disulphide and aluminium chloride 
 (10 gr.) is added. The mixture begins to boil at once, as a result 
 of the heat given out by the action. After the boiling has continued 
 for half an hour, the flask being connected with a condenser from 
 the first, the liquid separates into two layers. The upper one con 
 sists of carbon disulphide, and the lower of the aluminium salt 
 of nitrophenol. After the former has evaporated, the residue is 
 mixed with water and acidified with hydrochloric acid, and the free 
 nitrophenol is driven over with steam. The yield is 90 per cent, 
 of the theoretical. 
 
 A1C1 3= ( C H 4 <( 02 ) A1 + 3 CH 3 C1. 
 
 10. Nonsaponifiable Esters. To decompose the esters of 
 tertiary alcohols it is sufficient to heat them at their boiling-points 
 in a sealed tube for a considerable time. They break up into the 
 acid and an unsaturated hydrocarbon. Quite at the other extreme 
 however, we have esters which cannot be saponified at all. For 
 example, Friedlander and Mahly (Ber. 16, 850) found that dinitro- 
 cinnamic ether, C 6 H 4 (NO 2 ) . CH : C(NO 2 ) . COOC 2 H 5 , was not 
 saponifiable either by alkalis or acids. The former decomposed 
 
10] NONSAPONIFIABLE ESTERS 357 
 
 it and gave a brown-coloured product ; by the latter it was entirely 
 split up into^-nitrobenzaldehyde and hydrjxylamine. 
 
 It was first shown by Liebig (Ann. 9, 130) that ammonia cannot 
 take the place of the other alkalis in saponifying. Amides are 
 formed by its action on esters. Thus acetic ether gives acetamide 
 and alcohol. 
 
 CH 3 . COOC ? H 6 +NH 3 =CH 3 . CONH 2 +C a H 6 OH. 
 
CHAPTER XXII 
 
 PREPARATION OF SULPHONIC ACIDS. 
 
 1. Reagents Used. Sulphonic acids are prepared by replacing 
 hydrogen atoms by the group SO 3 H. The reagents used for the 
 purpose are the following : 
 
 Concentrated sulphuric acid. 
 
 Acid of composition H 2 SO 4 . 
 
 Fuming sulphuric acid. 
 
 Sulphuric acid with phosphorus pentoxide or potassium bi- 
 
 sulphate. 
 
 Sulphuryl oxychloride SO 3 HC1. 
 Potassium or sodium bisulphate. 
 
 Potassium or sodium pyrosulphate. ^ -S>^.V^>. ^^-S^ 
 Alkaline sulphites and bisulphites. 
 Carbylsulphate. o -^ vl v^ l^^-v^ -v~ 
 Bisulphates and alkylsulphates of bases. 
 
 2. Concentrated Sulphuric Acid. Even in the cold sulphuric 
 
 acid interacts with many substances, producing sulphonic acids. 
 For example, it had been generally accepted on the authority of 
 Laurent that phenol and sulphuric acid gave a phenyl ester, but 
 Kekule (Z. Ch. 1867, 199) showed conclusively that when equal 
 parts of phenol and sulphuric acid were allowed to remain for 
 several days in contact with each other, two phenolmonosulphonic 
 acids were formed. This was a brilliant confirmation of the theory 
 'of the constitution of the aromatic bodies which he had published 
 just before. 
 
 Most usually, however the action is assisted by heating. Thus 
 Michel and Adair (Ber. 10, 585) found that benzenesulphonic acid 
 
2] CONCENTRATED SULPHURIC ACID 359 
 
 was best prepared by gently boiling a mixture of equal volumes of 
 benzene and sulphuric acid for twenty or thirty hours in a flask 
 attached to a condenser. Four-fifths of the benzene went into 
 solution during the process. 
 
 The temperature at which the operation is carried out has an 
 important influence on the position which the sulphonic acid group 
 will occupy in the aromatic ring. For example, when naphthalene 
 (4 parts) is moderately heated with concentrated sulphuric acid 
 (3 parts) in such a way that a part of the hydrocarbon remains un- 
 changed, the product is a-naphthalenesulphonic acid. But when 
 equal parts of the materials are heated at 200, /3-naphthalenesul- 
 phonic acid is formed. 
 
 Sempotowsky (Ber. 22, 2,663) states that ethylbenzene is soluble 
 with difficulty in concentrated sulphuric acid, but that it dissolves 
 easily in the warm acid or in fuming sulphuric acid, giving two 
 sulphonic acids. The following method, however, gives the p- 
 sulphonic acid alone, and thus avoids the necessity of separating the 
 isomers. The ethylbenzene is heated to the boiling point, and an 
 equal volume of concentrated sulphuric acid is allowed to flow slowly 
 into it, the mixture being vigorously shaken during the process. 
 When the light yellow solution is cold, the sulphonic acid is mostly 
 precipitated by adding ice-cold water to it. The remainder can be 
 secured by using barium carbonate. 
 
 When quinoline is treated in the ordinary way only o- and m- 
 quinolinesulphonic acids are formed. To obtain the ^-compound 
 the quinoline (10 parts) must be heated to 275-280 with concen- 
 trated sulphuric acid (70 parts) in a sealed tube for twenty-four 
 hours. The operation does not proceed further than the formation 
 of the monosulphonic acids in the absence of sulphuric anhydride. 
 
 Nietzki (Ber. 15, 305) stirred pulverised /3-naphthol (i part) with 
 concentrated sulphuric acid (1^-2 parts) and warmed the mixture 
 slightly, obtaining a crystalline mass of naphthyl sulphate C 10 H 7 O 
 SO 3 H. On the other hand, Schaeffer (Ann. 152, 293) heated 
 the same materials on the water bath and found that under 
 these circumstances naphtholsulphonic acid C 10 H G (OH)SO 3 H was 
 formed. 
 
 In treating acids it is sometimes advantageous to use the potass- 
 ium salt as the starting point. And similarly in the case of bases 
 it is often helpful to the action to use a salt instead of the free base 
 
 (cf- 5)- 
 
 The termination of the operation is usually recognisable by the 
 
360 PREPARATION OF SULPHONIC ACIDS [CH. xxn 
 
 fact that a drop of the product is completely soluble in dilute 
 alkali. 
 
 3. Isolation of the Products. The strongly acid liquids ob- 
 tained as above are worked up somewhat as follows : 
 
 The solution is mixed with half its weight of ice, and by this 
 treatment many sulphonic acids crystallise out at once (Ber. 15, 
 1,854) ; or the liquid is poured on to three times its weight of ice 
 or into water containing a considerable amount of ice. The result- 
 ing dilute solution is neutralised with calcium or barium carbonate 
 and filtered to remove the precipitated sulphate. The most active 
 form of lime-water is made by placing quicklime in hot water. The 
 calcium salts of sulphonic acids are usually soluble and crystallise 
 when the solution is evaporated. If an insoluble barium salt of a 
 sulphonic acid is mixed with the barium sulphate, the precipitate 
 is washed and treated with dilute sulphuric acid. The sulphonic 
 acid can then be extracted with ether or converted into a salt as 
 may be most convenient. 
 
 If the acid liquid is neutralised with lead hydroxide or carbonate 
 the lead salt of the sulphonic acid remains in solution. When the 
 lead sulphate has been removed by filtration, the dissolved metal 
 can be separated by means of hydrogen sulphide and an aqueous 
 solution of the free sulphonic acid obtained. 
 
 Sometimes the acid solution is neutralised with soda and evapor- 
 ated to dryness. The sodium salt of the sulphonic acid can 
 usually be extracted from the residue with alcohol. Or salt is 
 added to the neutralised solution to throw down the sodium salt. 
 Thus Witt (Ger. Pat. 49,857) added common salt to the solution of 
 the acid sodium salt of amido-)3-naphtholdisulphonic acid 
 
 NH 2 \ /S0 3 H , 
 
 and obtained the substance at once in crystalline form. 
 
 This process, with which we have long been familiar in technical work, 
 has recently been recommended for use in the laboratory by Gattermann 
 (Ber. 24, 2,121). He gently warmed benzene, for example, with slightly 
 fuming sulphuric acid, converting it into the monosulphonic acid, and 
 poured the mixture into twice its volume of cold water. Pulverised salt 
 was added and shaken with this liquid until no more was dissolved. When 
 this point was reached the solution was cooled. The benzenesulphonate of 
 sodium crystallised out in a short time, and the crystals were filtered off and 
 
4] SULPHURIC ACID 361 
 
 washed with a solution of salt. The yield was almost quantitative. If the 
 removal of all the salt is desired, the substance can be recrystallised from 
 absolute alcohol. He prepared in a similar manner the sodium salts of 
 mesitylenesulphonic acid, w-sulphobenzoic acid, phenoldisulphonic acid, 
 and many other compounds of this class. 
 
 After operations like this, the amount of sulphuric acid which remains 
 unused can be determined by titration, an azo-dye being used as indicator 
 (Ann. 219, 210), and the addition of barium carbonate or other neutralising 
 agent can then be regulated so that, after filtration, the free sulphonic acid 
 remains in solution. 
 
 Lunge (" Sodaindustrie " 1, 40) states that, for ascertaining the presence of 
 sulphuric or any other strong acids, dyes of this class, such as amidoazoben- 
 zene (aniline yellow) and tropaoline, form the best indicators. They are not 
 affected by salts of metals, but are sensitive to the presence of the least trace 
 of a strong acid, and are quite indifferent to such substances as carbon 
 dioxide, hydrogen sulphide, and acetic acid (cf. Chap. XX., 8). 
 
 4. Sulphuric Acid containing 100 per cent, of H 2 S0 4 . 
 
 Acid of this strength is often very effective in preparing sulphonic 
 acids. It is best made, according to Lunge, by mixing ordinary 
 sulphuric acid with the fuming acid, so that the strength is brought 
 up to 98 per cent., and then cooling it till some crystals of pure 
 H 2 SO 4 are deposited. These crystals can then be used for obtain- 
 ing a large quantity of the same acid by throwing them into a vessel 
 of concentrated acid cooled to o. The mass is stirred and cooled 
 still further until the formation of crystals ceases. After these 
 crystals have been filtered from the mother liquor they melt at the 
 temperature of the room to form the desired hydrate, H 2 SO 4 . 
 
 Benzidineinonosulphonic acid (Ber. 22, 2,459), for example, can 
 be obtained by this method only. This substance has acquired 
 great importance from the fact that azo-dyes, which dye unmor- 
 danted cotton and resist washing, so-called " substantive " dyes, 
 are derived from it. When fuming sulphuric acid or mixtures which 
 often take its place are used, at least four different benzidinesul- 
 phonic acids are formed simultaneously. To prepare the mono- 
 sulphonic acid, benzidine or, better still, its sulphate (i part), is 
 mixed with the prepared acid (2 parts) and heated for an hour and 
 a half at 170. The mass is then poured into water, and the sul- 
 phonic acid which separates is filtered off (cf. 12). 
 
 Vignon (Ger. Pat. 32,291) obtained a-naphtholdisulphonic acid 
 by heating a-naphthol with the same acid for eight or ten hours at 
 100-110. 
 
362 PREPARATION OF SULPHONIC ACIDS [CH. xxn 
 
 5. Fuming Sulphuric Acid. The advantage of using fuming 
 sulphuric acid lies in the fact that all secondary reactions brought 
 about by the presence of water are necessarily excluded. Bender 
 (Ber. 22, 994) has actually found that some sulphonic acids of 
 a-naphthol even lose sulphonic acid groups, when the temperature 
 rises, under the influence of the excess of sulphuric acid associated 
 with the water originally contained in the acid and that formed by 
 the progress of the action. 
 
 Naturally fuming sulphuric acid acts much more vigorously than 
 the ordinary acid, on account of the anhydride which it contains. 
 
 For example, Giirke and Rudolph (Ger. Pat. 38,281) find that 
 naphthalenetrisulphonic acid may be obtained by adding naphtha- 
 lene (i part) to fuming sulphuric acid containing 24 per cent, of 
 SO 3 (8 parts), and heating the mixture for several hours at 180. Or 
 the same result is attained by cautiously adding naphthalene (i part) 
 to fuming sulphuric acid containing 40 per cent, of SO 3 (6 parts), 
 care being taken that the temperature does not exceed 80, and then 
 heating the mixture on the water bath until all signs of the anhy- 
 dride disappear. 
 
 In order to modify the action of the fuming acid and restrict the 
 number of sulphonic acid groups introduced to the desired num- 
 ber, it may be advisable sometimes to dissolve the substance in 
 pure H 2 SO 4 and then add enough fuming sulphuric acid to bring 
 the content of anhydride up to that just necessary to form the 
 product wanted. 
 
 Here, as in former cases, it will often be desirable to use the 
 substance in the form of a salt instead of employing the free acid or 
 base, if it belongs to these classes. For example, Witt (Ber. 19, 
 578) finds that the action of the acid on free a-naphthylamine is 
 somewhat violent, and the product dark in colour from the 
 presence of black impurities. On the other hand, the interaction 
 progresses very smoothly when the hydrochloride of the base is 
 used. The salt is thoroughly dried and added, in small portions at 
 a time, to the fuming acid, containing 20 to 25 per cent, of anhy- 
 dride. The vessel is kept in ice or snow during the process. The 
 operation is interrupted before a quantity of the salt sufficient to 
 exhaust the calculated amount of free anhydride has been added, 
 and the resulting mixture is poured into broken ice. The a-naphthyl 
 aminesulphonic acid separates as a slimy clotted mass, and is 
 purified by conversion into the calcium salt. 
 
 In case of necessity, heating in a sealed tube may be resorted to. 
 
6] USE OF PHOSPHORUS PENTOXIDE 363 
 
 La Coste and Valeur (Ber. 19, 996) obtained quinolinedisulphonic 
 acid in this way by heating quinolinesulphonic acid with twice its 
 weight of fuming sulphuric acid at 250. Lonnies (Ber. 13, 704) 
 prepared y-sulphoisophthalic acid [SO 3 H : COOH : COOH = i:3 : 5] 
 by heating isophthalic acid with strong fuming sulphuric acid at 200. 
 
 Heine (Ber. 13, 493) obtained the same substance by submitting 
 isophthalic acid, in 10 gram portions, to the action of sulphuric 
 anhydride, heating the mixture gently until it was changed into a 
 dark homogeneous liquid. He attempted to crystallise the sub- { 
 stance from water, but obtained nothing but a syrup. Lonnies 
 found that it separated from dilute sulphuric acid in long needles < 
 or prisms, a property which belongs to many sulphonic acids. 
 
 Earth (Ann. 148, 33) found that w-sulphobenzoic acid could be 
 made by placing dry benzoic acid in a flask and conducting the 
 vapour of pure sulphuric anhydride into it. The vapour was easily 
 obtained by heating the strongest fuming sulphuric acid. During 
 the process the operation was assisted by the large amount of heat 
 developed by the chemical action. 
 
 Fischli (Ber. 12, 616) conducted the vapour of sulphuric anhy- 
 dride over pulverised toluic acid and found that it was rapidly 
 absorbed, forming a thick paste. By pouring this into water 
 sulpho-/-toluic acid CH 3 . C H 3 (SO 3 H)COOH was obtained. 
 
 Sand seems to be the only substance used for diluting the 
 materials in actions of the present class. Thus Heymann (Ber. 24, 
 1,477), m making indigodisulphonic acid, mixed phenylglycocoll 
 ( i part) with ten or twenty times its weight of sand, with the object 
 of preventing local excessive heating of any part of the substance 
 during the addition to the sulphuric acid. The mixture was then 
 thrown into warm (20-25) fuming sulphuric acid containing 80 per 
 cent, of anhydride (20 parts) in such a way that the temperature 
 never rose above 30. When the interaction was over the product 
 was diluted with sulphuric acid of sp. gr. i'7i, ice was added, and 
 the indigo carmine, the sodium salt of indigodisulphonic acid, 
 thrown down with common salt. 
 
 6. Use of Phosphorus Pentoxide or Potassium Sulphate 
 
 with Sulphuric Acid. When fuming sulphuric acid was not suffi- 
 ciently powerful, Barth and Senhofer (Ann. 159, 217) found that it 
 could be reinforced by the presence of anhydrous phosphoric acid. 
 They prepared disulphobenzoic acid [COOH : SO ;5 H : SO 3 H = 
 i : 3 : 5] by warming benzoic acid (10 gr.) with oil of vitriol (20 gr.), 
 
364 PREPARATION OF SULPHONIC ACIDS [CH. xxn 
 
 and, when the mixture had cooled, adding glacial phosphoric acid 
 (15 gr.) and very strong fuming sulphuric acid (15 gr.), and heating 
 the mixture in a sealed tube at 250. 
 
 Earth and Herzig (M. f. Ch. 1, 808) dissolved mesitylene (i part) 
 in fuming sulphuric acid (10 parts), and heated the solution for from 
 two to three days at 30-40. At uniform intervals of about ten 
 hours three or four parts of phosphoric anhydride were added. 
 This leisurely procedure was justified by the fact that when the 
 operation was hurried the product was partially or even completely 
 carbonised. 
 
 Weidel and Cobenzel (M. f. Ch. 1, 845) satisfied themselves that, 
 even above 200, fuming sulphuric acid was without action on 
 cinchoninic acid. But they succeeded in obtaining a yield of 70 
 per cent, of a monosulphonic acid by heating dry cinchoninic acid 
 (10 gr.) with phosphoric anhydride (20 gr.) and oil of vitriol (20 gr.) 
 at 170-180 in a sealed tube for six hours. 
 
 The use of a sealed tube may often be avoided when pure H 2 SO 4 
 and metaphosphoric acid are used. A mixture of two parts of the 
 former with one of the latter has the same effect as fuming sulphuric 
 acid containing 20 or 25 per cent, of anhydride, yet it emits only 
 traces of the vapour of the anhydride when heated at 280-300. For 
 example, a rosanilinesulphonic acid is obtained when rosaniline 
 sulphate or chloride (2 parts) is added to a solution of anhydrous 
 metaphosphoric acid (3 parts) in pure H 2 SO 4 (7 parts) and the 
 mixture is heated on the water bath, or better at 120-130, until the 
 product is completely soluble in alkalis. 
 
 As has been mentioned already, it is often advisable to use salts 
 instead of free acids. When the potassium or sodium salts are 
 taken, the acid sulphates of the alkali metals, which are formed at 
 once, may be as effective in furthering the action of the sulphuric 
 acid as phosphoric acid has been shown to be. 
 
 Benzenetrisulphonic acid (Ann. 174, 244) was formerly a sub- 
 stance very hard to prepare. It had to be made by heating benzene 
 with fuming sulphuric acid and phosphoric acid in a sealed tube. 
 It may now be obtained by Jackson and Wing's method (Am. Ch. 
 J. 9, 325) in an open vessel. Benzene-;;z-disulphonate of potassium 
 (15 gr.) is mixed with concentrated sulphuric acid (18 gr.) in a 
 porcelain basin and carefully heated over the naked flame so as not 
 to allow the edges of the liquid to char. After a few minutes the 
 mass becomes pasty and the evolution of vapour becomes less. The 
 yield reaches 44 per cent, of the theoretical 
 
7 ] SULPHURYL OXYCHLORIDE 365 
 
 The hydrocarbon itself may also be used as the starting point. 
 In the first place equal volumes of benzene and sulphuric acid are 
 boiled until the former has dissolved. Thereupon an equal volume 
 of concentrated sulphuric acid is added along with an amount of 
 potassium sulphate equal to 70 per cent, of the original benzene 
 used. The mixture is then placed in a retort, without tubulus, and 
 one third of the total sulphuric acid is distilled off and the residue 
 is treated as above. 
 
 7. Sulphuryl Oxychloride. One of the difficulties attending 
 the preparation of sulphonic acids is that ordinary sulphuric acid 
 is often too weak, while the fuming acid is, on the one hand, 
 also inadequate, or else, on the other hand, too strong. In such 
 cases sulphuryl oxychloride SO 3 HC1 is often found to be an efficient 
 substitute. When desirable it can be diluted with chloroform. 
 
 Beckurts and Otto (Ber. 11, 2,058) state that it may be prepared 
 by placing fuming sulphuric acid containing 40 per cent, of anhy- 
 dride in a retort connected with a well-cooled receiver. The acid 
 is melted, and hydrochloric acid gas is led into it as long as it 
 is absorbed. The product is then distilled off, and, after a second 
 distillation, boils at 149-151. The yield is nearly quantitative. 
 Friedlander (Farbenfabrikation, p. in) obtains it, diluted of course 
 with concentrated sulphuric acid, by adding common salt to fuming 
 sulphuric acid. 
 
 Limpricht (Ber. 18, 2,172), who made a careful investigation of 
 the matter, found that reactions with sulphuryl chloride went very 
 smoothly with little or no formation of by-products. This reagent, 
 he found, was decidedly to be preferred for making disulphonic 
 acids on account of the time which is lost in their purification 
 when sulphuric acid is used. 
 
 The apparatus used by him consisted of a tubulated retort 
 connected by an air-tight joint with a tubulated receiver. The 
 tubulus in the latter was provided with a tube to conduct off the 
 hydrochloric acid gas. That in the retort was either closed with 
 a stopper after the materials had been introduced or with a cork 
 through which a separating funnel passed to serve for the gradual 
 admission of the sulphuryl chloride. The retort was heated to the 
 proper temperature in an oil bath. 
 
 As a rule the same products are obtained with sulphuryl chloride 
 as with sulphuric acid. Thus from ordinary alcohol we get, in both 
 cases, ethylsulphuric acid. 
 
366 PREPARATION OF SULPHONIC ACIDS [CH xxn 
 
 C 2 H 5 O. SO 3 H + H 9 O, 
 C 2 H 5 OH + C1S0 3 H = C 2 H 6 O . SO 3 H + HC1. 
 
 From acid amides, however, we get not acids, but acid chlorides, 
 and from amines sulphaminic acids. These exceptions hold both 
 in the fatty and aromatic series. Thus Traube (Ber. 23, 1,654) 
 prepared salts of phenylsulphaminic acid by dissolving aniline 
 (3 mol.) in several times its volume of chloroform, cooling the 
 solution, and adding gradually sulphuryl oxychloride (i mol.). A 
 mixture of aniline salts of the sulphaminic acid and hydrochloric 
 acid was at once precipitated. 
 
 S0 3 HC1 + 3C 6 H 5 NH 2 = C C H 5 NH . SO 3 H . C C H 5 NH 2 + C 6 H 5 NH 9 . 
 
 HC1. 
 
 Nitrobenzene (50 gr.) was treated with the calculated amount of 
 the chloride for four hours, the temperature being allowed gradually 
 to rise during this time until it finally reached 150. Metanitro- 
 benzenesulphonic acid was almost the sole product, just as when 
 sulphuric acid was used. 
 
 Toluidinesulphonic acid was prepared in the same way. To 
 avoid charring, the temperature was not permitted to exceed 160. 
 
 Claessen (Ber. 14, 307) succeeded in obtaining toluenetrisulphonic acid by 
 mixing toluenedisulphonate of potassium (i mol.) with sulphuryl oxy- 
 chloride (3 mol.) and heating them in a flask at 240 until a sample removed 
 from the vessel dissolved completely in water. The mass did not become 
 deeper coloured than pale yellow, and comparative little vapour was 
 given off. 
 
 Hodgkinson and Matthews (Ber. 16, 1,103) state that when dibromo- 
 fluorene is dissolved in chloroform, and the calculated amount of sulphuryl 
 oxychloride is added, dibromofluorenesulphonic acid is produced. 
 
 Reinhard (J. pr. Ch. 125, 332) mentions a somewhat complicated 
 reaction which took place when finely pulverised dichlororesorcinol (10 gr.) 
 was added to sulphuryl oxychloride (40 gr. ), and which was represented by 
 the equation : 
 
 The substance C 12 H 6 C1 4 S 2 O 9 was either the anhydride of a dichloro- 
 resorcinolsulphonic acid, or a sulphonicacid containing two dichlororesorcinol 
 molecules. The irregular course of the action was probably due to the 
 presence of the free hydroxyl groups. It would have been advisable to 
 convert the substance into the acetyl derivative before proceeding to make 
 the sulphonic acid. 
 
8, 9] FATTY SULPHONIC ACIDS 367 
 
 8. Potassium and Sodium Bisulphates and Pyrosulphates, 
 
 Bischoff (Ber. 23, 1,912) mixed aniline and naphthylamine with 
 potassium bisulphate, and heated the mixtures at 200-240. The 
 expected sulphonic acids were formed, but the yields were very 
 poor. 
 
 Kendall (Am. Pat. 421,049) finds, however, that when rosaniline 
 is mixed with potassium or sodium bisulphate and heated for a 
 sufficient length of time, the desired sulphonic acid can be obtained. 
 
 Girard (Bull. Ch. 25, 333) states that sulphonic acids may be 
 readily prepared by heating- the substance with sodium pyrosulphate 
 (free sulphuric acid may be present also) at 200-250. 
 
 No suitable method was known for converting phenylhyclrazine into salts 
 of phenylhydrazinesulphonic acid until Fischer (Ann. 190 97) used 
 potassium pyrosulphate for the purpose. The pyrosulphate is made by 
 heating the bisulphate. When the finely-pulverised pyrosulphate ( i mol. ) 
 is mixed with the base (2 mol. ) and heated to 80, the mass completely 
 solidifies in a short time and is then found to contain potassium sulphate, 
 phenylhydrazine sulphate, and potassium phenylhydrazinesulphonate. The 
 latter is secured by dissolving the substances in warm water and removing 
 the greater part of the sulphuric acid with barium carbonate. The greater 
 part of the free base separates as an oil. The warm liquid is filtered and, 
 concentrated caustic potash having been added, the salt of the sulphonic 
 acid crystallises out. It is not yec certain (Ann. 199 301) whether the 
 action is represented by the following equation or not : 
 
 4C 6 H 5 N 2 H 3 + 2K 2 S 2 7 = 2C 6 H 5 . N 2 H 2 . SO 8 K + K 2 SO 4 
 
 + (C C H 5 .N 2 H 4 ) 2 S0 4 . 
 
 The yield of ethylhydrazinesulphonate of potassium reached 80 per cent, 
 of that theoretically possible. 
 
 9. Fatty Sulphonic Acids. All the methods so far described 
 have been applicable to the preparation of aromatic sulphonic acids 
 only. Those of the fatty series are obtained almost exclusively by 
 double decomposition. 
 
 As early as 1841 Fehling (Ann. 38, 286) succeeded in making 
 sulphosuccinic acid by leading sulphuric anhydride over succinic 
 acid at a temperature not exceeding 50, and allowing the product 
 to remain for twenty-four hours. Hemilian (Ber. 6, 196) prepared 
 sulphobutyric acid by the action of sulphuryl oxychloride on butyric 
 acid. The oxidation of mercaptans supplies another way of making 
 sulphonic acids. But a method of preparing them easily in large 
 
368 PREPARATION OF SULPHONIC ACIDS [CH. xxn 
 
 quantities was first found by Strecker (Ann. 148, 91), and consisted 
 in the action of alkylhalides on sulphites of the alkalis. Mayer 
 (Ber. 23, 909) has since shown that salts of ethylsulphuric acid 
 can take the place of the former. Hemilian (Ann. 168, 146) has 
 shown that ammonium sulphite is the most suitable salt, since its 
 use permits of the isolation of the usually very soluble sulphonic 
 acids without much loss. For example, ethyl iodide (20 gr.) is 
 boiled for six hours with crystallised ammonium sulphite (20 gr.) 
 dissolved in water (40 cc.) in a flask attached to a condenser. 
 When the iodide has all gone into solution, the liquid is diluted 
 with water, and is boiled with lead oxide until all the ammonia 
 has been driven off. The lead iodide is removed by filtration, and 
 the lead salt of ethylsulphonic acid contained in the filtrate is 
 decomposed with hydrogen sulphide. The solution is then treated 
 with barium carbonate, and on evaporation gives 22 grams of the 
 barium salt of ethylsulphonic acid (theory = 24 gr.). 
 
 10. Use of Alkali Sulphites. It is an extraordinary fact that 
 ammonium sulphite reacts with nitro-bodies forming sulphonic 
 acids. This was discovered by Piria (Ann. 78, 31) as early as 
 1850. Smit (Ber. 8, 1,443) heated nitrobenzene (60 gr.), ammonium 
 sulphite (170 gr.), and absolute alcohol (i 1.) on the water bath for 
 about thirty hours. To preserve the alkalinity of the mixture he 
 added ammonium carbonate. This was gradually volatilised and 
 collected in the condenser, sometimes stopping it up. When the 
 action was over, he filtered from the ammonium sulphate, which 
 had been deposited. When the filtrate cooled, beautiful crystals 
 of the ammonium salt of sulphanilic acid NH 2 . C 6 H 4 . SO 3 NH 4 
 appeared. He prepared the ammonium sulphite in the first place 
 by leading moist sulphur dioxide and excess of ammonia into 
 absolute alcohol (Muspratt). 
 
 Mayer placed crystallised sodium sulphite (2 parts) in pressure 
 bottles and dissolved it as far as possible in an equal weight of 
 water. Sodium ethyl sulphate (i part) was then added. After 
 four hours' heating at 100-120 the contents were emptied into a 
 basin and the sodium sulphate allowed to crystallise. The filtrate 
 was then evaporated to dryness and the residue extracted with 
 96 per cent, alcohol. This removed the sodium salt of ethylsulphonic 
 acid. 
 
 3 = C 2 H5 . SO 3 Na + Na 2 SO 4 . 
 
ID] USE OF ALKALI SULPHITES 369 
 
 Laubenheimer (Ber. 15, 597) found that when dinitrochloro- 
 benzene was boiled for several days with excess of sodium sulphite 
 dissolved in water, a nitrochlorobenzenesulphonic acid and sodium 
 nitrite were formed [Cl : SO 3 Na : NO 2 = I : 3 : 4]. 
 
 Erdmann (Ger. Pat. 61,843) states that, in consequence of the fact 
 that a chlorine atom standing in the ortho-position to a nitro-group 
 is easily replaced by other radicals, w-nitrobenzaldehyde-/-sulphonic 
 acid can be readily prepared on a large scale from /-chloro-;;z- 
 nitrobenzaldehyde by boiling it with excess of sodium sulphite in 
 aqueous solution. 
 
 Schmitt and Glutz (Ber. 2, 51) were the first to prepare sulphonic 
 acids by the action of alkali sulphites on cliazo-bodies. Somewhat 
 later Strecker (Ber. 4, 784) dissolved diazobenzene nitrate in a 
 solution of potassium bisulphite. On evaporating the solution a 
 salt remained, which Fischer's work (Ann. 190, 73) has since shown 
 to have been the potassium salt of a sulphonic acid derived from 
 phenylhydrazine 
 
 /S0 3 H 
 
 When, however, diazobenzene nitrate is added to a cold neutral 
 or faintly alkaline solution of potassium sulphite, the yellowish-red 
 solution solidifies either spontaneously, or on addition of caustic 
 potash, to a mass of crystals of the potassium salt of diazobcnzene- 
 sulphonic acid, C H 5 . N 2 . SO 3 K (Ann. 190, 73). 
 
 The interesting point about the former reaction is that, as Fischer 
 recognised, we have in the product a member of a class of 
 phenylhydrazine derivatives which can be obtained by transforma- 
 tion from diazo-compounds. 
 
 Unsaturated bodies have the power of adding themselves to 
 potassium sulphite directly, and so forming saturated sulphonic 
 acids. Thus Messel (Ann. 157, 15) dissolved potassium carbonate 
 (100 gr.) in water (400 cc.), and treated the solution with sulphur 
 dioxide. He boiled maleic acid (23 gr.) with this solution of neutral 
 potassium sulphite (100 cc.) in a retort attached to a reflux con- 
 denser for several hours. When the solution cooled, crystals of 
 sulphosuccinate of potassium were deposited 
 
 CH.COOH CH 2 .COOH 
 
 | +H 2 S0 3 = | XSQH 
 
 CH.COOH CH<gg H 
 
 B B 
 
370 PREPARATION OF SULPHONIC ACIDS [CH. xxn 
 
 Pinner states (Ber 16, 1,727) that when mesityl oxide remains 
 long in contact with a concentrated solution of sodium bisulphite it 
 dissolves, forming the salt of isopropylacetonesulphonic acid 
 
 (CH 3 ) 2 C : CH . CO . CH 3 + NaHSO 3 = (CH 3 ) 2 C(NaSO 3 ) . CH 2 . CO. 
 
 CH 3 . 
 
 Similarly phorone forms C 9 H 16 O(NaHSO 3 ) 2 + 2^H 2 O under the 
 same circumstances. 
 
 Spiegel (Ber. 18, 1,481) found that many azo-dyes had the power 
 of uniting with bisulphites and forming sulphonic acids. He heateu 
 azobenzene with alcohol and a considerable excess of ammonium 
 bisulphite in a pressure bottle in the water bath. At first the whole 
 went into solution, and then turned into a solid mass of crystals 
 consisting of the ammonium salt of a monosulphonic acid of 
 benzidine, NH 2 . C C H 4 . C 6 H 4 NH . SO 3 H . The action therefore in 
 this case went beyond mere addition, and was accompanied by a 
 molecular change analogous to that characteristic of hydrazo- 
 benzene. 
 
 Bertagnini (Ann. 85, 271) was the first to state the now familiar 
 fact that acid sulphites add themselves to aldehydes forming 
 sulphonic acids 
 
 CH 3 . COH + NaHSO 3 = CH 3 . CH(OH)SO 3 Na. 
 
 Ludwig (M. f. Ch. 9, 661) obtained a sulphonic acid of the 
 composition C 6 H 12 O . SO 3 H by saturating a solution of methyl- 
 ethylacrolein (i part) in water (3 parts) with sulphur dioxide, and 
 heating the solution in a tube at 80. He found that sodium 
 bisulphite unites with special ease with unsaturated aldehydes to 
 form sulphonic acids. 
 
 11. Use of Carbyl Sulphate. Both this substance and its 
 
 chlorhydrin have been suggested for use in preparing sulphonic 
 acids. It seems that sulphonic acids of rosaniline dyes, in 
 particular, may be obtained by heating the materials at 100 until 
 the product is completely soluble in alkalis. The carbyl sulphate, 
 C 2 H 4 S 2 O 6 , is made by the union of ethylene with sulphuric 
 \V ^ QX, anhydride. 
 
 The chlorhydrin was prepared by Purgold (Z. Ch. 1868, 669) by 
 leading ethyl chloride over sulphuric anhydride at o. The latter 
 gradually liquefies. The product is heated to 100, and poured drop 
 by drop into ice-cold water. A heavy oil separates, which is dried 
 
Q V4<- I\>Go, 
 
 12] ACID SULPHATES AND ALKYL SULPHATES 371 
 
 with anhydrous cupric sulphate (Ber. 6, 502). The yield is 600 
 grams from 2,000 grams of the anhydride. By fractionation in 
 
 /SO Cl 
 vacua the pure C 2 H 4 <T gQ 2 ^ boiling at 80-82 is obtained. 
 
 12. Transformation of Acid Sulphates and Alkyl Sulphates 
 of Bases. The sulphonic acids of many bases may be formed by 
 heating their acid sulphates. Thus Griess and Duisberg (Ber. 22, 
 2,458) state that benzidinemonosulphonic acid is best prepared by 
 making benzidine sulphate into a thin paste with water, adding 
 sulphuric acid (i^ mol.) also diluted with water, thoroughly mixing, 
 and then evaporating to.dryness. The acid sulphate so obtained 
 is then pulverised and heated for twenty-four hours in an air bath 
 at 170. The shrunken black mass is again pulverised and 
 extracted with dilute alkali, and the benzidinemonosulphonic acid 
 is precipitated from the filtrate with acetic acid. 
 
 The acid sulphate of rosaniline is likewise easily converted into 
 the sulphonic acid. Rosaniline (30 parts), sulphuric acid of sp. gr. 
 1,714 (20 parts), and water (100-200 parts) are thoroughly mixed 
 with sand (400 parts), evaporated todryness, and heated at 130-140. 
 This product, when pulverised and heated at 180-200 for five or 
 six hours in a stream of carbon dioxide, and extracted with boiling 
 water, gives the mono- and clisulphanic acids. " 
 
 The sulphonic acids of amides can also be obtained by heating 
 their alkyl sulphuric acid salts at 200 (Ber. 3, 970). The salt may 
 be prepared by diluting a hot solution of the alcohol in sulphuric 
 acid with water and neutralising with calcium hydroxide, concen- 
 trating the filtrate and adding a solution of the oxalate of the base. 
 After filtering again the solution is evaporated to dryness, and the 
 residue heated to the requisite temperature in a small flask. At 
 first some frothing takes place and alcohol is given off. When the 
 mass is cold it is dissolved in hot water, decolourised with animal 
 charcoal, and evaporated until the sulphonic acid begins to crystal- 
 lise (Ber. 7, 1,349)- 
 
 Bernthsen (Ann. 251, 49) obtained amidodimethylaniline thio- 
 sulphonic acid by using aluminium thiosulphate in accordance with 
 equation 
 
 /N . (CH 3 ),C1 /N(CH 3 ) 2 
 
 C G H 4 < | +HS . S0 3 H = C 6 H 3 -NH 2 4- HC1. 
 
 \N . H \S . S0 3 H 
 
 B B 2 
 
CHAPTER XXIII 
 
 REMARKS ON ORGANIC ANALYSIS 
 
 1. The Combustion Method. The general process followed in 
 carrying out a combustion may be assumed to be familiar to the 
 reader and will not therefore be described. Lavoisier was the first 
 (in 1781) to attempt to determine the composition of organic bodies 
 by burning them with oxygen. Whether it is preferable to conduct 
 the operation in a bayonet tube or an open tube, and to use oxygen 
 from the beginning or only towards the end of the combustion are 
 still open questions. It is certain at least that both lead to the 
 same result, though the second may be a little quicker, and in the 
 long run neither seems to have any advantage over the other which 
 gives any prospect that either will be superseded by the other. 
 
 In the same way the use of cupric oxide for substances containing 
 no non-metals, and of lead chromate for such as contain them, has 
 not given place to the employment of platinum (Ber. 9, 1,377), 
 manganese dioxide (Ber. 21, 3,173), or other compounds which may 
 have been suggested from time to time ; nor has the platinum 
 tube displaced the glass tube for ordinary purposes. We owe the 
 employment of cupric oxide to Gay-Lussac, who first used it in 1815. 
 This substance is markedly hygroscopic, so that it should be warm 
 when placed in the tube. Lead chromate possesses the same 
 property (J. pr. Ch. 81, 184) to about the same extent. According 
 to Ritthausen (J. pr. Ch. 133, 141) it also retains some carbon 
 when ignited in the air, and this can only be removed by burning 
 in a stream of oxygen. Liebig (Anleitg. z. Anal. org. Korper, 32) 
 recommends the use of a mixture of lead and potassium 
 chromates. 
 
 It is a common experience to find that substances containing 
 
i] THE COMBUSTION METHOD 373 
 
 much halogen give too high values for carbon (M. f. Ch. 1881, in). 
 To secure the more complete removal of the halogens, therefore, a 
 coil of silver is placed in the end of the tube. In the combustion 
 of iodosobenzoic acid (Ber. 25, 2,632) it was even found necessary 
 to insert several such coils, for, in their absence, some free iodine 
 passed over, even when a very long layer of lead chromate was 
 used. When the coils have become covered with halogen com- 
 pounds of silver through frequent use, they may be purified by 
 ignition in a stream of hydrogen. Coils of copper are much less 
 effective because, when they become too hot, the halogen compound 
 of copper is volatilised and is carried over into the chloride of 
 calcium tube. 
 
 Substances which yield carbon monoxide easily must be burnt 
 with a very long layer of oxide of copper, as otherwise the results 
 may be 3 per cent, too low (Ann. 242, 27 ; and Ber. 25, 408). 
 
 Anschutz and Kekule (Ann. 228, 303) state that substances 
 intended for combustion should be dried in a Liebig's drying tube. 
 This is placed in an air bath, kept at a suitable temperature, and 
 the drying is carried out either in vacua or in a stream of air or of 
 some indifferent gas. When substances treated in this way give off 
 hydrochloric acid or ammonia, the gases are caught in solutions 
 of known strength and estimated by titration or gravimetrically. 
 
 As Liebig himself remarks (Ann. 95, 259), even substances con- 
 taining no hydrogen always yield a little water on combustion, 
 and it has not yet been found possible to exclude this source of error. 
 Berzelius was the first (in 1815) to introduce the chloride of calcium 
 tube for weighing the water formed in the analysis. 
 
 Lieben has drawn attention to the fact that if long rubber tubes 
 are employed to connect the apparatus for drying the air, and 
 oxygen with the combustion tube, the effect is often almost the 
 same as if the carefully dried gas had been bubbled through water 
 again. He used, therefore, tubes of glass or lead. In this connec- 
 tion the recent work of Berthelot (C. R. 110, 684) on the removal 
 of traces of moisture from gases may be consulted. 
 
 When pulverised compounds have to be mixed with cupric oxide 
 or lead chromate, Thorner recommends that the mixing be effected 
 in a tube made for the purpose. This tube is 12 to 15 cm. long, 
 10 to n mm. in diameter, closed at one end and considerably 
 drawn out at the other, so that it can be conveniently introduced 
 into the combustion tube. The substance is weighed out in a glass 
 tube whose end can be introduced into the mixing tube. The latter 
 
vl \ .r 
 ^MJit 
 
 374 REMARKS ON ORGANIC ANALYSIS [CH. xxm 
 
 is charged with a layer several centimetres high of cupric oxide or 
 lead chromate, which has been freshly ignited and cooled over 
 sulphuric acid. The substance is thrown in above this, tWe tube is 
 closed with a cork, and then thoroughly shaken. A little of the 
 oxide or chromate is placed in the combustion tube, the contents of 
 the tube are emptied in above this, and finally all traces of the sub- 
 stance are cleared out of the tube by repeated shaking with small 
 quantities of the oxide or chromate. 
 
 The necessity of placing a coil of copper at the end of the com- 
 bustion tube to decompose any nitric oxide which may be formed 
 has lately been re-examined by Klingemann (Ber. 22, 3,064). He 
 estimated the amount of nitric oxide formed in the combustion of 
 an azine, C 28 H 1G N 2 , and found that it reached 8*40 per cent, of the 
 quantity of the original substance. 
 
 Copper coils are preferable to those of silver for this purpose. In 
 this connection Zincke and Kegel remark (Ber. 23, 246) that in 
 the combustion of dichloromalonamide the coil of silver did not 
 suffice to decompose all the oxides of nitrogen, and that in conse- 
 quence the percentage of carbon obtained was too high. 
 
 Schulze and Steiger (Z. physiolog. Ch. 11, 49) found that in 
 analysing arginine nitrate, C H 14 N 4 O 2 . HNO 3 + |H 2 O, in spite of the 
 presence of a copper coil, the carbon was always too high and the 
 nitrogen too low. In order to ascertain whether any nitric oxide 
 was escaping from the combustion tube, he replaced the potash 
 bulbs by a similar apparatus filled with ferrous sulphate. No 
 change of colour was observable in the solution, however. On the 
 other hand, the water which condensed in the bulb of the chloride 
 of calcium tube showed a strong acid reaction, which might have 
 been due to the presence of a small amount of nitric acid. 
 
 Schwarz (Ber. 13, 559) states that copper coils which have been 
 reduced in a stream of hydrogen should be gently warmed until a 
 outer oxidised layer has been formed. They lose a small 
 amount of hydrogen in the process. It is doubtless better, however, 
 to reduce them in carbon monoxide. The gas can be prepared by 
 action of sulphuric acid on oxalic acid, and the presence of the 
 carbon dioxide in the gas does not interfere with the reduction. 
 
 When salts containing an inorganic base are burned, the latter 
 may retain carbon and carbon dioxide. To avoid this potassium 
 bichromate is placed in the boat. This substance assists in the 
 combustion of the carbon, and drives the carbon dioxide out of its 
 combination with the alkali. 
 
2] DETERMINATION OF CARBON AND HYDROGEN 375 
 
 Schwarz and Pastrovich (Ber. 13, 1,641) mixed an excess of finely 
 divided chromic oxide with the substance. They prepared it by 
 precipitating mercurous nitrate with pure neutral potassium chro- 
 mate, and, after filtering and washing, ignited the chromate of 
 mercury in a porcelain crucible. 
 
 If the substance has a tendency to leave a deposit of carbon 
 which cannot be burned even in a stream of oxygen, the substance, 
 after being placed in the boat, should be covered with three or four 
 times its weight of previously ignited platinum black. 
 
 When explosive substances have to be analysed, they must be 
 mixed with sufficient cupric oxide to counteract this tendency. 
 
 2. Other Methods for Determination of Carbon and Hydro- 
 gen. No improvement has taken place in the results of the com- 
 bustion method since 1830, and the enormous amount of time which 
 even experienced workers must devote to such almost mechanical 
 operations is a great disadvantage of the process. It would certainly 
 be a great boon to chemists if some method, like that of KjeldahPs 
 for nitrogen, could be devised, by which the estimation of carbon 
 and hydrogen could be conducted in the wet way in an apparatus 
 which would not demand constant attention. 
 
 It may perhaps be hoped that the investigations of physical 
 chemists may put some weapon in our hands which will be as 
 valuable for the present purpose as the replacement of the compli- 
 cated methods of determining molecular weights by the freezing- 
 and boiling-point methods has been for another branch of the 
 work of the organic chemist. Possibly in the future some way may 
 be devised say by the use of compressed oxygen which will 
 greatly simplify the estimations of carbon and hydrogen, or at least 
 that of the former. 
 
 Many years ago Brunner (Pogg. Ann. 95, 379) described a 
 method of using sulphuric acid and potassium bichromate for 
 determining the carbon as carbon dioxide in the wet way. 
 Messinger (Ber. 21, 2,910) has recently developed this process 
 more fully, and with further improvement it promises to supply a 
 way of making carbon determinations of every kind. It is given 
 here as an example of wet-way processes. 1 
 
 1 Messinger has more recently (Ber. 23> 2,756) described an improved 
 form of his apparatus, in which, however, the simplicity which was charac- 
 teristic of the earlier one has been sacrificed to a certain extent. He 
 
376 
 
 REMARKS ON ORGANIC ANALYSIS [CH. xxm 
 
 The organic body is placed in an apparatus devised by Classen 
 (Quant. Anal. [3], 239), and heated with sulphuric acid and chromic 
 acid. The carbon dioxide which is formed is swept by a stream 
 of air into a set of potash bulbs. In order that a very small flask 
 may be used, the funnel is fused into the tube which introduces 
 the air. 
 
 The evolution of carbon dioxide is often rapid, and it is therefore 
 necessary to connect the potash bulbs with a weighed tube con- 
 taining soda-lime. Liquids are enclosed in small glass 
 bulbs just as in ordinary combustions. 
 
 To carry out the analysis, chromic acid (5 to 6 gr.) 
 or pulverised potassium bichromate, and a small tube 
 containing the substance ('15 to '35 gr.), are placed in 
 the flask. In connecting the flask with the condenser, 
 care must be taken that the substance does not come 
 in contact with the chromic acid. When potassium 
 bichromate is taken, no attention need be paid to this 
 point. A slow stream of air, purified by passing through 
 caustic soda and a tube containing soda-lime is led 
 into the apparatus to expel any carbon dioxide which 
 may be present. While this operation is going on 
 the potash bulbs and soda-lime tube can be weighed. 
 These are then connected with the drying tube filled 
 FIG. 41. with glass beads. A chloride of calcium tube must 
 be attached to the soda-lime tube so as to prevent 
 the entrance of moist air. When everything is in readiness the 
 stream of air is momentarily interrupted, and sulphuric acid (30 cc.) 
 is allowed to enter by the funnel tube. Care must be taken to keep 
 the condenser cool from this stage onwards. 
 
 When liquids are analysed, the bulb must be broken with the 
 help of the funnel tube. 
 
 The flask is now warmed with a very small flame, which hardly 
 touches the asbestos, placed beneath. 
 
 After the lapse of a few minutes a slow evolution of carbon dioxide 
 can be noticed at the surface of the mixture. The flame must be 
 instantly removed, and not replaced until the production of gas has 
 almost ceased. The heating can then be continued to the end of 
 
 mentions that when the form, described in the text is used, some substances 
 give values for the carbon which are constantly o'8-i per cent, too small. 
 It must therefore be noticed particularly that the method is not applicable 
 to all substances. 
 
2] DETERMINATION OF CARBON AND HYDROGEN 377 
 
 the operation. The oxidation requires very little attention. The 
 decomposition of the substance occupies two hours. At the end 
 of that time air is driven through the apparatus to remove the 
 oxygen. 
 
 If substances which sublime are left out of account, the method 
 will be found frequently to give good results. But care must be 
 taken not to overheat the mixture at first, as otherwise a very 
 violent action takes place, foglike fumes are generated, and the 
 result obtained is too high. 
 
 When the substance contains a halogen, a small Drechsel's wash 
 bottle (100 cc.) must be filled with a concentrated solution of 
 potassium iodide, connected with a small U-tube containing glass 
 wool, and inserted behind the condenser. One half of the glass 
 wool must be moistened with a solution of silver nitrate, and the 
 other half, that next to the drying tube, with concentrated sulphuric 
 acid. 
 
 Sulphur, phosphorus, and arsenic are oxidised to sulphuric, phos- 
 phoric, and arsenic acids respectively. The halogens are given off 
 in the free state. 
 
 Cross and Bevan (J. Ch. Soc. 53, 889) collected the carbon 
 dioxide obtained by this method over mercury, instead of weighing 
 it. Their experience showed that carbon monoxide was always 
 formed to some extent, although the proportion was greater at the 
 beginning of the operation than towards the end. Oxygen is not 
 given off unless the temperature exceeds 100. The analyses which 
 they publish show that good results may be obtained if a correction 
 is applied for the carbon dioxide absorbed by the sulphuric acid. 
 To do this there must be added to the percentage of carbon a 
 number obtained by multiplying this value by the constant "016. 
 For example 1 
 
 >< -016 = 44-25%. 
 
 1 Without paying any attention to the work that has already been done 
 in this field, Okada has recently discovered and made known a method of 
 analysing substances of interest to students of hygiene and physiology such 
 as flesh, milk, uric acid, salicylic acid, &c. He treats them, much as in 
 Kjeldahl's process, with slightly fuming sulphuric acid with addition of 
 substances like mercury. The carbon is converted quantitatively into 
 carbon dioxide (!), and this gas is not weighed in potash bulbs, but caught 
 in baryta water and titrated ! The sulphur dioxide, which is formed 
 simultaneously, seems to have the valuable property of being completely 
 removed from the mixture of gases when the latter is passed through a 
 
378 REMARKS ON ORGANIC ANALYSIS [CH. xxm 
 
 3. Qualitative Determination of Nitrogen. The presence 
 of nitrogen can be ascertained by heating the substance with soda- 
 lime in a small tube, and observing whether ammonia is given off 
 or not. 
 
 The method employed by Lassaigne (Ann. 48, 367), however, is 
 much more delicate. The substance is raised to a red heat with 
 potassium or sodium in a small tube. The residue is treated with 
 water, care being taken to avoid harm from flying pieces of the 
 metal, and to the filtrate are added ferrous sulphate, ferric chloride, 
 and, finally, hydrochloric acid. If a blue precipitate is formed, the 
 presence of nitrogen is proved. The cause of the precipitate is, of 
 course, that the nitrogen and sodium in presence of carbon unite to 
 form sodium cyanide. This, with the salts of iron in the alkaline 
 liquid, is converted into sodium ferrocyanide, and the latter gives 
 Berlin blue with the excess of iron when the solution is acidified. 
 Naturally, ammonia and salts of nitric acid must be absent. 
 
 Jacobsen (Ber. 12, 2,317) was the first to call attention to the 
 fact that the method occasionally fails, especially when the organic 
 body contains sulphur along with nitrogen. For example, in the 
 presence of amides of sulphonic acids, thiourea, c., sodium sulpho- 
 cyanide is formed. In a few such cases, when the substance is 
 ignited, a carbonised mass remains behind, which contains much of 
 the nitrogen and very little of the sulphur, and the test may succeed 
 with this. But by a slight modification he devised a process, 
 depending on the partial reduction of the sulphocyanide to cyanide, 
 by means of iron, which is in all cases reliable. 
 
 A grain of the substance is mixed with four or five times its 
 volume of finely divided iron, and this mixture is fused with 
 potassium or sodium exactly as above. The cold mass is treated 
 with water for a few minutes and filtered. The filtrate is acidified 
 with a few drops of hydrochloric acid, and dilute ferric chloride is 
 added. The iron must be previously tested with sugar, or some 
 other substance which contains no nitrogen, and should give no 
 blue or green coloration. 
 
 Grabe (Ber. 17, 1,178) states that the ordinary test for nitrogen 
 
 layer of saturated permanganate solution several centimetres high. The 
 presence of carbon monoxide and other trifling details were not observed. 
 Finally the author surmises that his method may be used for the determin- 
 ation of the oxygen in organic bodies. Further information will be found 
 in the Archiv. f. Hygiene, 14, 4> 3^4~373- 
 
4] DETERMINATION OF NITROGEN 379 
 
 will succeed, even in presence of sulphur, if only a large amount of 
 potassium is used. The excess then exercises the functions of the 
 iron in Jacobsen's method. On the other hand, the presence of 
 nitrogen in diazo-bodies can hardly ever be shown by this method, 
 because the nitrogen escapes before the action of the alkali metal 
 begins. 
 
 4. Quantitative Determination of Nitrogen by Combustion. 
 
 Nitrogen is now usually estimated quantitatively by Dumas' or 
 Kjeldahl's methods. 
 
 It may be assumed that the reader is acquainted with the general 
 procedure in Dumas' method. The various forms of apparatus 
 suggested for the collection of the nitrogen have been discussed 
 by Ilinski (Ber. 17, 1,347). The simplest is probably that of a 
 graduated tube provided with a stopcock. It is filled with caustic 
 potash up to the latter by suction. When all the air has been 
 driven out of the apparatus, suction is again applied, and the com- 
 bustion of the substance is begun. The caustic potash is prepared 
 by dissolving potassium hydroxide (i part) in water (2 parts). 
 Caustic soda cannot be used. To avoid the passage of any of the 
 liquid into the mouth, a bulb-shaped enlargement should be blown 
 on the tube above the stopcock. 
 
 The carbon dioxide can be generated by heating powdered magne- 
 site. Ilinski recommends manganese carbonate, as it is very slightly 
 hygroscopic, gives a uniform stream of the gas, and by turning 
 brown enables one to follow the progress of the decomposition. 
 
 Substances which are hard to burn may be mixed with a little 
 mercuric oxide in addition to cupric oxide. Of course, care must 
 be taken to regulate the amount, so that the oxygen will be com- 
 pletely absorbed by the copper coil. 
 
 When substances containing nitrogen are decomposed by warm 
 carbon dioxide, or are volatilised by it to any appreciable extent, the 
 gas must not be evolved as described. In this case a Kipp's appa- 
 ratus is used, and a rather rapid stream is conducted through the 
 tube for a limited time. The rear end of the combustion tube 
 should be drawn out to a capillary. 
 
 For example, Fischer (Ann. 190, 124) mixed phenylhydrazine- 
 carbazolate with pulverised cupric oxide in a small tube, filled the 
 latter up with cupric oxide, and introduced it into the combustion 
 tube. When all the air had been expelled by a rapid stream of 
 cold carbon dioxide, the capillary was sealed off, the tube connected 
 
380 REMARKS ON ORGANIC ANALYSIS [CH. xxm 
 
 with the other end of the combustion tube dipping meanwhile 
 under mercury. By cautious tapping, the narrow tube containing 
 the substance was then emptied into the wider combustion tube, 
 and the burning was begun in the ordinary way. 
 
 Gehrenbeck (Ber. 22, 1,694) has recently proposed a way of 
 determining nitrogen and hydrogen simultaneously by a modi- 
 fication of Dumas' method. This process is highly praised by 
 Kehrmann and Messinger (Ber. 24, 2,172). 
 
 O'Sullivan states (J. Soc. Chem. Ind. 1892, 327) that, when 
 Dumas' method is used, from 4 to n per cent, of the nitrogen 
 escapes from the tube in the form of nitric oxide. 
 
 5. Kjeldahl's Method. The principle of this method (Z. analyt. 
 Ch. 1883, 366) consists in heating the substance with a large 
 quantity of concentrated sulphuric acid at a temperature near to 
 the boiling-point of the latter, and finally distilling off the ammonia 
 and estimating its quantity by titration. Various substances are 
 added during the process to assist the oxidation. There is as 
 yet no unanimity on the subject of what compounds are most 
 effective in this respect. Potassium permanganate was first 
 used, and has been succeeded by cupric sulphate and mercury (cf. 
 P. Ar. 46, 581). More recently Gunning (Z. analyt. Ch. 1889, 
 189) has suggested potassium sulphate. This salt and mercuric 
 oxide are both very convenient to use and very effective, so their 
 application is here described. 
 
 Gunning uses a mixture made by melting together potassitim 
 sulphate (i part) and sulphuric acid (2 parts). The product is semi- 
 solid at ordinary temperatures, but can be easily poured out of 
 warmed vessels. In special cases very large quantities of the 
 substance to be investigated can be analysed. Thus 100 grams of 
 flesh may safely be used if a sufficiently large flask is selected. For 
 ordinary purposes-, however, from a half to one gram of the material 
 is placed in a round-bottomed flask with a short wide neck. 
 To this is added 20 to 30 cc. of the mixture described above, and the 
 whole is heated with a Bunsen burner. When the substance is a 
 liquid it is first evaporated nearly to dryness. A little acid can be 
 added to it if necessary during this process. 
 
 At first a good deal of frothing is observable, while water with 
 some acid, and later stronger acid, pass off. This loss of acid and 
 concentration of the acid in the flask must not be allowed to go too 
 far. The process is easily regulated, however, for when a funnel, 
 
5J KJELDAHL'S METHOD 381 
 
 which fits the mouth of the flask closely, is inserted and is covered 
 with a watch glass, the acid vapours are almost completely con- 
 densed and flow back into the vessel. 
 
 Arnold and Wedemeyer (P. Ar. 52, 590) state that when a mix- 
 ture of sulphuric acid (3 parts) and potassium sulphate (i part) is 
 used no considerable frothing occurs. 
 
 As soon as the frothing decreases the apparatus can be left to 
 itself. If the flame is so regulated that the evaporated acid con- 
 denses and flows down the walls of the flask, carrying carbonised 
 material adhering thereto along with it, the maximum speed 
 attainable by the method will be reached. The product is colour- 
 less unless metallic oxides are present which can confer some colour 
 on it. When cold it is dissolved in water. 
 
 The time required for the decomposition of the substance is not 
 always the same. Often half an hour suffices, sometimes less ; 
 more than one and a half or two hours is never necessary. The 
 analyses published with the description of the method show that 
 excellent results are obtainable. 
 
 Mercuric oxide is used by the author (cf. Wilfarth, Centralblatt, 
 1885, 113) as follows: A flask is selected whose bulb has a 
 capacity of 600 cc. and neck a length of 15 cm. In it is placed a 
 quantity of the substance containing about '03 grams of nitrogen. 
 To this is added sulphuric acid containing 15 per cent, of anhydride 
 (7-8 cc.) and some mercuric oxide ("4 gr.). The acid is not drawn 
 up into a pipette but measured in a glass vessel. When first heated 
 on the sand bath the mixture froths considerably, but this ceases 
 entirely after a short time. The heating continues until the liquid 
 becomes colourless. On account of the escape of the sulphur 
 dioxide, formed by the reduction of the sulphuric anhydride, the 
 operation must be conducted under a hood. 
 
 The treatment of liquids is precisely similar to that of solids. 
 When urine (10 cc.), for example, is placed in the flask and sulphuric 
 acid and mercuric oxide are added, a considerable rise in temperature 
 takes place. So much dilute acid escapes during the boiling that 
 that which remains is, with the help of the mercuric oxide, fully 
 equal to the task of decomposing the organic matter and convert- 
 ing its nitrogen into ammonia. 
 
 The clear liquid which is finally obtained by the treatment with 
 sulphuric acid and mercuric oxide is diluted with water. 1 To the 
 
 1 The liquid obtained in Gunning's process is treated in the same way in 
 every respect, except that relatively more caustic soda is used. 
 
382 
 
 REMARKS ON ORGANIC ANALYSIS 
 
 [CH. XXIII 
 
 solution 25 per cent, caustic soda (80 cc.) is added. This must be 
 done cautiously so that the very warm liquid remains faintly acid. 
 After the mixture has been cooled in a stream of water the 
 remainder of the alkali is added, as there is then little danger of 
 any of the ammonia escaping. In any case the work must be done 
 rapidly. 
 
 The ammonia is then distilled over by boiling vigorously for 
 half an hour. To prevent bumping in the alkaline liquid one or 
 
 two grams of zinc dust are 
 added. The expulsion of the 
 whole of the ammonia can be 
 attained without the residue 
 becoming too concentrated if 
 the apparatus shown in Fig. 42 
 is used to connect the flask 
 with the condenser. This has 
 also the effect of obviating the 
 possibility of any of the liquid 
 being projected directly into 
 the condenser. The length of 
 this adapter is 25 cm., the dia- 
 meter at the wider part 3*2 cm. 
 The stem A passes through the 
 stopper of the flask, while B is 
 connected with the condenser. 
 The opening in the side of the 
 
 tube near A is a specially valuable feature, as without it the drops of 
 liquid which condense in the apparatus are continually thrown 
 upwards through the whole length of the adapter by the current of 
 vapour. Pieces of granulated zinc cannot here take the place of 
 the zinc dust (P. Ar. 52, 591). They are equally effective in making 
 the ebullition steady, but in this form the zinc does not set ammonia 
 free from a sort of amido-compound which it forms with mercury 
 as the zinc dust does. 
 
 When many nitrogen determinations have to be carried out, a 
 flat jacket of sheet tin is used, through which six condensing tubes 
 can pass simultaneously. 
 
 Since the reagents which are used, such as sulphuric acid and 
 caustic soda, are never quite free from nitrogen, this correction 
 is determined once for all and is subtracted from the results 
 obtained. With this in view a supply of the reagents sufficient 
 
 FIG. 42. 
 
5] KJELDAHL'S METHOD 383 
 
 for a large number of analyses is prepared, and a determination 
 is made with some substance like sugar. This gives the amount 
 of the nitrogen which may be looked for from this source. 
 
 The ammonia is collected in a receiver. For this purpose a 
 flask or Peligot's tube is used. This is charged with water to 
 which a slight excess of decinormal sulphuric acid (say 25-50 cc.) 
 has been added. Each centimetre corresponds to '0014 grams of 
 nitrogen. The excess is titrated back with decinormal caustic soda. 
 
 As indicator Mays' litmus solution (Z. analyt. Ch. 25, 402) is 
 employed. Ordinary litmus in the granular form (100 gr.) is 
 heated with water (700 cc.) to boiling, and the liquid is decanted. 
 The residue is further boiled with a fresh supply of water (300 cc.). 
 The extracts are united, set aside for one or two days, then acidified 
 with hydrochloric acid, and finally dialysed until the acid cannot 
 be detected in the water any longer. If the water is frequently 
 changed, this may occupy eight days. The solution is preserved 
 in a flask closed with a plug of cotton. As the solution remains 
 at rest for months at a time it continually deposits solid matter, 
 from which it must be freed by filtration ; but in spite of this it 
 retains for years the greatest sensitiveness both towards acids and 
 alkalis. 
 
 Dafert (Z. analyt. Ch. 1888, 224), who has most thoroughly 
 examined the range of applicability of the Kjeldahl method, has 
 come to the conclusion that substances containing nitrogen may 
 be divided into two classes with respect to it. These are : 
 
 (1) Substances which may be submitted to analysis without 
 preparatory treatment, and 
 
 (2) Substances which require such preparatory treatment. 
 
 To the first group belong amides and ammonium bases, pyridines 
 and quinolines, alkaloids, bitter principles, and albumens and 
 related bodies. Most likely indole derivatives belong to this class. 
 
 To the second belong, with isolated exceptions, all nitro-, nitroso-, 
 azo-, diazo-, hydrazo-, and amidoazo-compounds, derivatives of nitric 
 and nitrous acids, hydrazines, and probably also cyanogen com- 
 pounds. 
 
 He gives the following as the most effective treatment which 
 he could devise for nitro-bodies : If the substance is soluble in 
 alcohol (10 cc.), it is dissolved in this medium (if not, in concen- 
 trated sulphuric acid). Zinc dust and sulphuric acid are added, and 
 the mixture is heated until the alcohol has all been expelled. 
 
384 REMARKS ON ORGANIC ANALYSIS [CH. xxm 
 
 When this stage is reached ten cubic centimetres of an acid 
 mixture recommended by Kreusler is added and the analysis is 
 carried on as already described. Kreusler's solution is made by 
 mixing rectified concentrated sulphuric acid (i 1.) with phosphoric 
 anhydride (200 gr.) and a little mercury. Dafert found that the 
 nitroso-bodies and an azoxy-compound examined by him, when 
 treated HI the same or a similar manner, gave equally satisfactory 
 results. 
 
 Chenel (Bull. Ch. [3], 7, 324) states that nitro-derivatives should 
 be reduced with iodine and phosphorus. By reducing nitronaph- 
 thalene to naphthylamine, for example, in this way, he found the 
 method gave accurate results. 
 
 The description of the application of Kjeldahl's method to the 
 determination of nitric acid (Z. analyt. Ch. 1887, 92) lies beyond 
 the limits of the present work. 
 
 Experiments made by L. L'Hote (C. R. 1889, 817), with a 
 view to comparing the Will-Varrentrapp, Dumas, and Kjeldahl 
 methods as regards their reliability, showed that differences between 
 the results occurred only when the sulphuric acid used for the last 
 failed to become colourless after the heating had continued for a 
 day and a half. The difference was attributed to the volatilisation 
 of a small amount of ammonium sulphate during the prolonged 
 heating. 
 
 Nothing on earth is perfect, and even this attractive method 
 seems to share the general fallibility of earthly things. For example, 
 Griinhagen (Ann. 256, 289 and 293) found it unserviceable in the 
 
 case of methylenedi-/-toluidine, CH /^ ' 6 [ 4 ' 3 , and other 
 
 bases closely related to it. Yet one might have expected, a priori^ 
 that the conversion of its nitrogen into ammonia would have been 
 easy. Grunhagen used Dumas' method first, but found the per- 
 centage of nitrogen invariably too low. The cause of this might 
 have been found in the retention of some of the nitrogen along 
 with the unburnt carbon. At all events it was found during the 
 combustion of the substance in a stream of oxygen that the last 
 particles of graphite-like carbon were very hard to burn. Yet 
 Kjeldahl's method gave the nitrogen 3 per cent, too low. In the 
 case of this substance the Will-Varrentrapp method (Ann. 39, 257), 
 consisting in the combustion of the substance with soda-lime, was 
 the only one which gave a result in agreement with the calculated 
 figures. 
 
6] CHLORINE, BROMINE, AND IODINE 385 
 
 Thiele (Ann. 270, 56) states that when derivatives of amido- 
 guanidine are analysed by the Kjeldahl method they only give up 
 part of their nitrogen. Amidotetrazotic acid in particular gave 
 only about one fifth of the calculated amount. 
 
 6. Determination of Chlorine, Bromine, and Iodine. The 
 
 presence of these elements is ascertained by igniting the substance 
 to be tested with quicklime, and examining the solution for calcium 
 chloride, bromide, or iodide in the ordinary way. Substances like 
 chlorobenzene and chlorotoluene, however, are not easily decom- 
 posed by lime. 
 
 The method devised by Beilstein (Ber. 5, 620) is more delicate 
 and requires less of the substance. He heats the substance with 
 pure cupric oxide placed in a loop of platinum wire, first in the 
 inner and then in the outer layer of a Bunsen burner flame. The 
 production of a green tinge indicates the presence of halogens, 
 and the persistence of the colour gives some indication of the 
 amount. The test is successful even with very volatile substances 
 like methyl iodide and chloroform. 
 
 The quantitative estimation of the halogens is attained by igniting 
 the substance in an open tube with quicklime, or by heating it 
 in a sealed tube with nitric acid. Others of the many proposed 
 methods are seldom used. 
 
 In using the former process a rather narrow, hard glass tube, 
 40 centimetres long and closed at one end, is taken. It is charged 
 with first a little quicklime, then a mixture of this with the sub- 
 stance, and finally more lime. The lime must be free from chlorine. 
 When the ignition, which must begin at the open end, is completed, 
 and the tube has cooled, the contents are dissolved in dilute nitric 
 acid and the halogen estimated in the usual manner. 
 
 As substances containing iodine may give rise to iodic acid or 
 free iodine, some sulphur dioxide is added before the silver nitrate 
 in such cases. 
 
 The use of nitric acid in a sealed tube was introduced by Carius 
 (Ann. 136, 129). The tube, which should be of potash glass, may 
 be half a metre long, and will then serve for from four to six 
 determinations. It should possess an internal diameter of 13 mm., 
 and the walls should be 1*5-2 mm. thick. The nitric acid must 
 have a sp. gr. as near to 1*5 as possible, corresponding to about 
 90 per cent, of HNO 3 . When a liquid or other substance on 
 which nitric acid acts violently is being analysed, it should be 
 
 C C 
 
386 REMARKS ON ORGANIC ANALYSIS [CH. xxm 
 
 weighed out in a small tube about 10 cm. long, and introduced 
 into the large tube enclosed in this manner. From '2 to "3 grams 
 of the substance and 3-4 grams of nitric acid are taken. For 
 fatty bodies a temperature of 1 50-200 suffices ; for those of the 
 aromatic series a temperature of 250-260 must be maintained for 
 an hour and a half. A slight excess of solid silver nitrate is added 
 so that it may unite at once with the halogen. 
 
 If the substance is a liquid and has, for any reason whatever, 
 to be weighed in a small glass bulb, this must finally be weighed 
 along with the silver salt. The bulb should in this case be made 
 of hard glass, as if it is made of soda glass (Tollens, Ann. 159, 95) 
 it will lose so much alkali during the heating with nitric acid that 
 a considerable error will be introduced into the result. 
 
 Silver iodide retains silver nitrate with great persistency, and 
 must therefore be boiled repeatedly with water before being placed 
 on the filter. 
 
 If the organic body contains more than one of the halogens, 
 their separation must be effected by the usual methods of inorganic 
 analysis. 
 
 Recently a modification by Schiff (Ann. 195, 293) of Piria's 
 method, in which an open vessel is employed, has come into 
 use. 
 
 The substance containing chlorine or bromine, which should not 
 be very volatile, is weighed into a platinum crucible as large as 
 a .thimble, and the rest of the vessel is filled up with a mixture 
 of dry sodium carbonate (i part) and quicklime (4-5 parts). This 
 small vessel is then placed in an inverted position at the bottom 
 of a larger crucible. The annular space between them is then 
 filled with the same mixture. By heating the arrangement with 
 a pointed blowpipe flame it is rendered certain that a part of the 
 mass will become red-hot before decomposition begins to take 
 place. The total quantity of material used in one analysis amounts 
 to about 14 grams. The mass is easily dissolved out of the large 
 crucible. 
 
 When the substance contains iodine, sodium carbonate must 
 be used alone, because, in the presence of lime, calcium iodate 
 would be formed. The production of this salt would add greatly 
 to the difficulty of carrying out the analysis. 
 
 7. Estimation of Sulphur. The best quantitative tests for 
 sulphur are probably those of Vohl (Z. analyt. Ch. 1863, 442) and 
 
7] ESTIMATION OF SULPHUR 387 
 
 Horbaczewski (Z. physiolog. Ch. 6, 331). The former heats the 
 substance with sodium, dissolves the product in water, and tests 
 for the presence of sulphide in the filtrate with sodium nitroprusside. 
 When sulphur is present a bluish-violet coloration is observed. 
 The latter proved the absence of sulphur in elastin by dissolving 
 two grams of that substance in boiling concentrated caustic potash, 
 and saturating the cold solution with chlorine. The product is 
 then acidified with hydrochloric acid, and boiled until chlorine is 
 no longer evolved. If after barium chloride has been added and 
 the solution has remained for two days no trace of a precipitate 
 is visible, the absence of sulphur is demonstrated. 
 
 Neither of these methods gives any information as to the state 
 of combination of the sulphur. To test this Vohl (Ber. 9, 876) 
 uses a special solution. He heats water with twice its volume of 
 pure glycerol to the boiling-point, and adds freshly prepared calcium 
 hydroxide in small quantities till the liquid is saturated with it. 
 He then adds excess of fresh lead hydroxide or of litharge and 
 boils gently for a few minutes. The solution when cold is de- 
 canted from undissolved substance, and kept in a bottle so that 
 'access of carbon dioxide is avoided. 
 
 When substances containing sulphur, such as hair, taurine, etc., 
 are warmed with this liquid, lead sulphide is formed, and the 
 mixture darkens. But no interaction takes place with bodies which 
 contain sulphur united to oxygen. 
 
 The quantitative determination of sulphur is carried out by 
 Carius 3 method (Ann. 116, i) with nitric acid exactly as 
 described for halogens. With aromatic sulphonic acids however 
 the heating must be carried to 300. In cases like this, the danger 
 that the tube will burst is avoided by first heating to 200 only, 
 allowing the tube to cool, and letting the accumulated gas escape. 
 After re-sealing, the heating can be continued up to the higher 
 temperature, The sulphuric acid formed is weighed as barium 
 sulphate. 
 
 Holand (Ch. Z. 1893, 991) has made a comparison of all the 
 methods which have been suggested. He recommends the use of 
 moderately concentrated nitric acid, and states that with substances 
 which are easily oxidisable and do not contain too much carbon, 
 this method gives by far the most reliable results. It fails however 
 when the substance contains much carbon or is hard to oxidise. 
 No matter how gradually and regularly the temperature is raised, 
 it seems to be impossible to make it- high enough for the purpose 
 
CH 2 - 
 of /z-methylmercapto-r-thiazoline, j_ \C . S . CH 3 , which con- 
 
 388 REMARKS ON ORGANIC ANALYSIS [CH. xxm 
 
 without explosion. Raising it degree by degree, does not seem to 
 do away with this evil, nor does frequent opening to relieve the 
 pressure seem to make any difference. It is evident that a rapid 
 decomposition, accompanied by generation of carbon dioxide, occurs 
 at some stage in the process and bursts the tube. 
 
 Gabriel (Ber. 22, 1,154) had to modify this method in the analysis 
 
 \, 
 CH 2 -N 
 
 tained 48' 12 per cent, of sulphur. It was first heated for three hours 
 at 200 with fuming nitric acid. The liquid was then concentrated, 
 neutralised with potassium carbonate, evaporated to dryness, and 
 finally fused with soda and potassium chlorate. When the fusion 
 was omitted, only half of the sulphur was converted into sulphuric 
 acid, and the remainder formed methanesulphonic acid, a very 
 stable substance. A process of the same nature had already been 
 described by Arendt, 1 and recommended for use in the estimation 
 of sulphur in plant ashes. 
 
 When the substance under examination is not volatile, it can be 
 fused with potassium chlorate, or potassium nitrate and carbonate 
 directly. The sulphur is converted into sulphate, which can then 
 be precipitated in the usual way. 
 
 Messinger (Ber. 21, 2,914) describes another method which gives 
 good results with most, though not with all, comparatively involatile 
 compounds. A weighed quantity of the substance is placed with 
 potassium permanganate (i|-2 gr.) and pure potassium hydroxide 
 (^ gr.) in a flask of 500 cc. capacity connected with a reflux 
 condenser. Some water (25-30 cc.) is then poured in through 
 the condenser tube, and the mixture is heated for two or three 
 hours. The liquid when cold should have a faint red tint. 
 Hydrochloric acid is then added in small portions, and the liquid 
 warmed when the first evolution of gas has ceased after each 
 addition. This treatment is continued until the liquid becomes 
 clear. The contents of the flask are finally washed out into a 
 beaker, and the sulphuric acid precipitated with barium chloride. 
 In order that the barium sulphate may be easily collected on 
 a filter, both the chloride and the liquid must be boiling when 
 mixed. 2 
 
 1 "Wachstum der Haferpflanze. " Leipzig, 1857, p. 28. 
 8 Cf. Lunge, " Sodaindustrie," Braunschweig, 1879, I. 93. 
 
7] ESTIMATION OF SULPHUR 389 
 
 The combined sulphur can be oxidised in many cases by dis- 
 solving the substance in glacial acetic acid, and adding potassium 
 permanganate in small quantities until the operation is complete. 
 
 A detailed comparison of many methods of estimating sulphur 
 has been published by Hammarsten (Z. physiolog. Ch. 9, 273), and 
 his paper should be consulted in the original. 
 
DATES OF REFERENCES 
 
 To find the year in which any volume of the chief journals men- 
 tioned in the text appeared 
 
 Am. Ch. J. Add the number of the volume to 1878. 
 
 Ann. For volumes 1-164, divide the number of the volume by 4 
 and add the quotient 1 to 1831. 
 
 165-170 1873 
 
 I7I-I74 1874 
 
 i75~!79 1875 
 
 180-184 1876 
 
 185-190 1877 
 
 191-194 1878 
 
 195-199 
 200-205 
 
 206-210 1881 
 
 211-215 1882 
 
 216-222 1883 
 
 223-226 1884 
 
 227-232 1885 
 
 233-236 1886 
 
 237-242 1887 
 
 243-248 1888 
 
 249-255 1889 
 
 256-260 1890 
 
 261-266 1891 
 
 267-271 1892 
 
 272-277 1893 
 
 278-283 1894 
 
 Ann. Ch. Ph. For series 3, vols. 1-69, divide the number of the 
 volume by 3 and add the quotient to 1840. For series 4, vols. 
 1-30, divide by 3 and add to 1863. For series 5, vols. 1-30, 
 divide by 3 and add to 1873. For series 6, vols. 1-30, divide 
 by 3 and add to 1883. 
 
 Ber. Add the number of the volume to 1867. 
 
 Bull. Ch. For series 2, vols. 1-50, divide by 2 and add to 1863. 
 For series 3, divide by 2 and add to 1888. 
 
 1 N.B. If the quotient contains a fraction the next higher whole number 
 must be taken in all cases where no statement to the contrary is made. 
 
392 DATES OF REFERENCES 
 
 C. R. Vol. i, 1835. For following volumes, divide by 2, and, 
 neglecting fractions, add to 1835. 
 
 C. N. Divide the number of the volume by 2 and add to 1859. 
 
 J. Ch. Soc. For vols. 1-28, add to 1848. For vols. 29-66, divide 
 by 2 and add to 1861. 
 
 J. pr. Ch. For vols. 1-108, divide by 3 and add to 1833. For 
 vols. 109-158, divide by 2 and add to 1815. 
 
 M. f. Ch. Add the number of the volume to 1879. 
 
 Z. physik. Ch. Vol. i (1887). Vol. 2 (1888). For vols. 3-12 
 divide by 2 and add to 1887. Vols. 13-15 (1894). 
 
 Z. physiolog. Ch. Vol. i (1878). Vols. 2, 3 (1879). For vols. 4-18, 
 add the number of the volume to 1876. 
 
INDEX 
 
INDEX 
 
 Acenaphthene, 261, 273, 281 
 
 Acetal, 104 
 
 Acetanilide, 197, 217 
 
 Acetic acid, condensation by, 104 
 
 acid of crystallisation, 4 
 Acetic anhydride, 104, 133 
 Acetic ether, 146 
 Acetone of crystallisation, 3 
 0-Acettoluide, 163 
 /-Acettoluide, 181, 233 
 Acetyl carbinol, 256 
 Acetyl chloride, 204 
 
 derivatives, 14, 133, 355 
 
 derivatives, analysis of, 15 
 Acids, bromination of, 172 
 
 isolation of, 336 
 
 preparation of, 248, 252, 262, 
 277 
 
 sapomfication by, 354 
 Air, oxidation by, 245, 314 
 Alcohol, absolute, 48 
 
 of crystallisation, 4 
 
 solubility of inorganic salts in, 
 
 60, 178, 318 
 
 Alcohols, bromo-compounds from, 
 176 
 
 chloro-compounds from, 185, 
 203 
 
 iodo-compounds from, 215 
 
 molecular weight and atomicity 
 
 of, 279 
 
 Aldehyde, 209 
 
 Aldehydes, preparation of, 255, 272 
 Alizarin, 285 
 
 Alkaloids, 213, 260, 275, 334, 335, 
 
 338 . 
 Aluminium chloride, 105 
 
 chloride, condensation by, 105 
 
 chloride, saponification by, 
 356 
 
 iodide, 212 
 Amines, 311 
 
 Ammonia, condensation by, no 
 Ammonium sulphide, 288 
 Amyl alcohol of crystallisation, 6 
 
 alcohol, use as solvent in re- 
 ductions, 305 
 
 nitrite, use in making diazo- 
 
 bodies, 142 
 Analysis of explosive salts, 348 
 
 of salts, 338 
 
 organic, 372 
 
 Aniline, 200, 205, 226, 246, 280 
 Anisol, 148 
 Antimony pentachloride, 196 
 
 trichloride as chlorine carrier, 
 189, 190 
 
 trichloride, condensation by, 1 10 
 Arsenic acid, 246 
 Ash, estimation of, 348 
 
 Barium hydroxide, condensation by, 
 
 in 
 hydroxide, saponification by, 
 
 354 
 
 peroxide, 246 
 
 Bases, affinity coefficients of, 330 
 isolation of, 336, 342 
 
396 
 
 INDEX 
 
 Baths, i, 2 
 
 BAUMANN'S method for benzoyl 
 derivatives, 16, 153 
 
 BECKMANN'S apparatus for " freez- 
 ing point " method, 80 
 "boiling point" method, 83 
 
 Benzene, 171, 190 
 
 of crystallisation, 6 
 sulphonic acids, 363, 364 
 
 Benzfuroin, 257 
 
 Benzidine sulphonic acid, 361 
 
 Benzil, 261 
 
 Benz-0-nitranilide, 313 
 
 Benzoic acid, reduction of, 309 
 
 Benzotrichloride, condensation by, 
 in 
 
 Benzoyl bromide, 177 
 chloride, 191 
 derivatives, 16, 153 
 group, removal of, 355 
 iodide, 219 
 
 Benzoylacetone, 124 
 
 Benzoylpyruvic acid, 124 
 
 Benzyl cyanide, 163 
 
 Benzylideneacetone, 250 
 
 Bleaching powder, 247 
 
 Boiling points, correction of, 25 
 points, determination of, 42 
 prevention of irregular, 24 
 
 Boron trifluoride, condensation by, 
 in 
 
 Bromine, 161 
 
 action on sulphonic acids, 169 
 as oxidising agent, 247 
 carriers, 170 
 estimation of, 385 
 nascent, 165 
 
 Bromo-derivatives, aromatic, 164 
 agents used in making, 161 
 diluents used in making, 165 
 indirect preparation of, 169 
 influence of carboxyl groups in 
 
 making, 169, 174 
 influence of nitro-groups in 
 
 making, 171 
 made by addition of bromine, 
 
 164 
 
 made from diazo-bodies, 176 
 made from iodo-derivatives, 164 
 made from sulphonic acids, 169 
 made with bromine, 162 
 made with bromine vapour, 163 
 
 Bromo-derivatives, made with hy- 
 
 drobromic acid, 176 
 made with metallic bromides, 
 
 178 
 made with phosphorus chloro- 
 
 bromide, 178 
 made with phosphorus penta- 
 
 bromide, 177 
 made with phosphorus tribro- 
 
 mide, 177 
 Bromopicrin, 178 
 /-Bromotoluene, 190 
 " Bumping," prevention of, 24 
 
 Calcium chloride, condensation by, 
 
 m> 135 
 
 hydroxide, condensation by, 1 1 1 
 Camphogluconic acid, 265 
 Carbon, determination of, by com- 
 bustion, 372 
 determination of, by wet way, 
 
 .375 . 
 
 disulphide, 170 
 monoxide, loss of, 147 
 Carbostyril, 289 
 CARIUS' method, 385, 387 
 Chloranil, oxidation by, 250 
 Chloric acid, 250 
 Chlorine, 179 
 carriers, 188 
 determination of, 385 
 oxidation by, 251 
 Chlorobenzene, 200, 201 
 Chloro-derivatives, 179 
 aromatic, 180 
 influence of carboxyl groups in 
 
 making, 185 
 made by action of hydrochloric 
 
 acid on alcohols, 186 
 made by addition of chlorine 
 
 or hydrochloric acid, 184 
 made by Gattermann's reaction, 
 
 200 
 
 made by replacement of bro- 
 mine and iodine, 187 
 made by Sandmeyer's reaction, 
 
 199 
 made from diazo-bodies and 
 
 hydrazines, 186 
 
 made with acetyl chloride, 195 
 made with antimony penta- 
 chloride, 196 
 
INDEX 
 
 397 
 
 Chloro-derivatives, made with chlo- 
 rides of sulphur, 203 
 made with chlorine carriers,! 88 
 made with chlorosulphonicacid, 
 
 205 
 
 made with cyanuric chloride, 206 
 make with free chlorine, 180 
 made with hypochlorites, 196 
 made with mercuric chloride, 202 
 made with nascent chlorine, 1 84 
 made with phosphorus oxy- 
 
 chloride, 202 
 made with phosphorus penta- 
 
 chloride, 191 
 
 made with phosphorus tri- 
 chloride, 203 
 made with sulphuryl chloride, 
 
 204 
 
 made with thionyl chloride, 206 
 Chloroform of crystallisation, 6 
 Chlorsulphonic acid, 205 
 Chromic acid, 251 
 Chromyl chloride, 254 
 Cinnamic acid, 104, 250 
 Citric acid, 182 
 Combustion analysis, 372 
 Condensation, 101 
 
 combined with oxidation, 127, 
 
 134 
 
 intramolecular, 115, 118, 127 
 Condensers, 22, 24, 30 
 Condensing agents, 103 
 Copper, condensation by, 112 
 
 finely divided, 201 
 Correction of boiling point readings, 
 
 25 
 
 Coumann, 104 
 Crystallisation, 3 
 
 acetic acid of, 4 
 
 acetone of, 3 
 
 alcohol of, 4 
 
 amyl alcohol of, 6 
 
 benzene of, 6 
 
 ether of, 7 
 
 in mixed crystals, 1 1 
 
 phenol of, 8 
 
 water of, 9, 331, 340, 342, 345 
 Crystallographic examination, 17 
 Cuprous chloride, 199 
 
 oxide, 314 
 Cyanhydrins, no 
 Cyanuric chloride, 206 
 
 Decolorising, 19, 20, 21 
 Dehydrogenation, 263, 265, 269, 
 
 283, 284, 293 
 Desiccators, 44 
 Desylacetophenone, 119 
 Diacetosuccinic acid, 352 
 Dialysis, 17 
 Diazoacetic ether, 143 
 Diazobenzene chloride, 142, 322 
 Diazo-bodies, 137 
 
 action of hydrobromic acid on, 
 176 
 
 conversion into chloro-deriva- 
 tives, 1 86 
 
 made by oxidising hydrazines, 
 142 
 
 made with amyl nitrite, 142 
 
 made with nitrous acid, 138 
 
 made with sodium nitrite, 140 
 
 of the fatty series, 142 
 0-Diazocinnamic acid, 141 
 Dibenzoylhydroquinone, 108 
 Dibenzoylmethane, 123 
 Dichlorhydrin, 203, 219 
 Di-isobutyl, 121 
 Diluents, 59, 106 
 
 Dimethylaniline, 227, 236, 258, 284 
 Dimethylquinoline, 252, 253 
 Dinaphthyl, no 
 Dinitropropane, 241 
 
 reduction of, 316 
 Dioxyanthraquinone, 158 
 Diphenyl, 235 
 Diphenylacetic acid, 135 
 Diphenyldiacetylene, 245, 275 
 Diphthalyl, 122 
 Distillation, 22 
 
 dry, 34 
 
 fractional, 27 
 
 in a current of steam, 32 
 
 in vacuo, 36 
 
 under pressure, 42 
 Drying agents, 44, 47, 49 
 
 alcohol, 48 
 
 ether, 50 
 
 liquids, 47 
 
 solids, 44 
 
 DUMAS' method for estimating 
 nitrogen, 379 
 
 Electrolysis, 287 
 Esters, 144 
 
398 
 
 INDEX 
 
 Esters, hydrolysed by water, 145, 146 
 made by action of acid chlorides 
 
 on alcohols, 152 
 made by action of alcoholic 
 
 caustic potash on chloro- 
 
 derivatives, 153 
 made by action of alkyl halides 
 
 on organic salts, 151 
 made by action of anhydrides 
 
 on alcohols, 146 
 made by action of organic 
 
 salts on alcohols, 147 
 made by action of salts of ethyl 
 
 sulphate on organic salts, 1 50 
 non-saponifiable, 356 
 of inorganic acids, 148 
 spontaneous decomposition of, 
 
 154 
 use of hydrochloric acid in 
 
 making, 144 
 use of phosphorus oxychloride 
 
 in making, 149 
 
 use of potassium bisulphate or 
 
 pyrosulphate in making, 148 
 
 use of sulphuric acid in making, 
 
 146 
 
 ETARD'S reaction, 254 
 Ether, absolute, 50 
 explosions, 58 
 of crystallisation, 7 
 Ethereal salts, see Esters 
 Ethyl chloride, 186 
 
 chloride, bromide, and iodide, 
 difference in properties of, 
 220 
 
 iodide, 210 
 nitrate, 239 
 
 Ethylene iodhydrin, 219 
 Ethylideneacetoacetic ether, 112 
 Ethylsuccinic anhydride, 162 
 Extraction, agents used in, 52 
 by precipitation, 21 
 continuous, 55 
 of bitter principles, 20 
 of liquids, 5 2 
 of solids, 56 
 with amyl alcohol, 54 
 
 FEHLING'S solution, 256 
 
 Ferric chloride as halogen carrier, 
 
 171, 189 
 chloride, oxidation by, 258 
 
 Ferrous chloride or sulphate, re- 
 duction by, 290 
 Filtration, 9, 61 
 FISCHER, E., synthesis of sugars, 
 
 124, 248 
 
 FITTIG'S synthesis, 121 
 Fluoro-derivatives, 221 
 
 made by use of chromium 
 
 hexafluoride, 223 
 made by use of hydrofluoric 
 
 acid, 222 
 made by use of silver fluoride, 
 
 221 
 FOBINYI'S method for determining 
 
 molecular weights, 83 
 Formaldehyde, in, 245 
 Formic acid, formation in oxida- 
 tion, 265 
 
 Formyl derivatives, 15 
 Fractional crystallisation, 12 
 distillation, 27, 33 
 oxidation, 286 
 precipitation, 337 
 Freezing mixtures, 3 
 Fuchsine, 246, 257, 263, 264 
 Fusion with caustic alkalis, 155 
 
 with caustic alkalis, analogy to 
 
 putrefaction, 160 
 with caustic alkalis, calcium 
 
 and other salts, 158 
 with caustic alkalis, effect of 
 
 differing conditions, 158 
 with caustic alkalis, oxidation 
 
 by, 157, 275 
 
 with caustic alkalis, reduction 
 
 of nitrophenols, 159 
 with caustic alkalis, restraint 
 
 and promotion of oxidation, 
 
 157 
 
 GATTERMANN'S reaction, 178, 200, 
 
 214 
 
 Glycerol, 203, 248, 266, 278, 283 
 Gold double salts, 342 
 
 HANTZSCH'S synthesis, 102 
 Heat, condensation by, 40, 136 
 HEMPEL'S tube, 27, 28 
 Hermetically sealed tubes, 89 
 HOFMANN'S method of measuring 
 
 vapour density, 70 
 Homo-0-phthalimide, 202 
 
INDEX 
 
 399 
 
 Hydrastine, 262, 271 
 Hydrazines, conversion into chloro- 
 derivatives, 187 
 
 oxidation of, 257, 264, 283 
 Hydrazones, oxidation of, 282 
 
 reduction of, 311 
 Hydriodic acid, 214, 293 
 Hydrobromic acid, 175 
 
 acid, action on alcohols, 176 
 
 acid, action on diazo-bodies, 
 176 
 
 acid, addition products, 176 
 Hydrochloric acid, 185 
 
 acid, condensation by, 112 
 
 acid, use in making esters, 144 
 Hydrocyanic acid, addition of, no 
 
 acid, condensation by, 115 
 
 acid, formation in oxidation, 260 
 Hydroferricyanic acid, 335 
 Hydroferrocyanic acid, 335 
 Hydrogen peroxide, 259 
 
 sulphide, 298 
 Hydrolysis, 350 
 Hydroxylamine, 101, 3 12 
 
 oxidation by, 260 
 
 reduction by, 298 
 Hypochlorous acid, 198 
 
 Indole derivatives, Fischer 's syn- 
 thesis of, 132 
 Intramolecular condensation, 115, 
 
 118, 127 
 oxidation, 260 
 lodic acid, 207 
 Iodine, 206 
 
 as bromine carrier, 170 
 carriers, aluminium iodide, 212 
 carriers, ferric chloride, 212 
 carriers, ferrous iodide, 21 1 
 carriers, phosphorus, 210 
 chloride, 188, 217, 251 
 determination of, 385 
 recovery of, 152 
 lodoacetone, 208 
 lodo-derivatives, 206 
 
 made by action of iodine on 
 
 diazo-bodies, 209 
 made by addition of iodine, 213 
 made by addition of iodine 
 
 chloride, 217 
 
 made by replacement of 
 bromine, 219 
 
 lodo-derivatives, made by replace- 
 ment of chlorine, 218 
 made with hydriodic acid, 214 
 made with iodic acid, 207 
 made with iodine, 206 
 made with iodine carriers, 210 
 made with mercuric oxide, 
 
 208 
 made with phosphonium iodide 
 
 and iodide of nitrogen, 218 
 made with solution of iodine in 
 
 potassium hydroxide, 213 
 made with sulphuric acid, 212 
 locloform, 218, 219 
 lodosobenzoic acid, 267 
 Iron as chlorine carrier, 190 
 reduction by, 158, 298 
 
 Ketols, oxidation of, 256 
 KIPP'S apparatus for chlorine, 179 
 apparatus for oxygen, 268 
 apparatus for sulphur dioxide, 
 
 312 
 
 KJELDAHL'S method, 380 
 KUSTER'S method for determining 
 molecular weights, 88 
 
 Lead peroxide, 261 
 
 LE BEL-HENNINGER tube, 27, 28 
 
 Levulinic acid, 167, 196 
 
 LlNNEMANN tube, 27, 28 
 
 Magnesium chloride, 115 
 Malachite green, 116, 117, 119 
 Malonic ether, 148 
 Manganese dioxide, 262 
 Melting points, 63 
 Menthol, oxidation of, 257, 272 
 Mercuric chloride, 2O2 
 Methylaniline, 251 
 Methylbenzyl cyanide, 126 
 MEYER, V., methods of measuring 
 
 vapour densities, 67, 72, 75, 78 
 Molecular weights, determination 
 
 of, by Beckmann's method, 
 
 83 
 weights, determination of, by 
 
 Fobinyt's method, 83 
 weights, determination of, by 
 
 Krister's method, 88 
 weights, determination of, by 
 
 Raoult's method, 80 
 
400 
 
 INDEX 
 
 Molecular weights, determination of, 
 
 by vapour density methods, 66 
 Molybdenum pentach-loride, 189 
 
 Naphthalenediamine, 306 
 Naphthionic acid, 141 
 Naphthol sulphonic acid, 359 
 Nitranilines, 226, 227, 237, 239, 
 
 288, 319 
 Nitration, by dilute nitric acid, 231 
 
 by less common methods, 236 
 
 by nitric acid, 225 
 
 by nitric and sulphuric acids, 23 3 
 
 by pure HNO 3 , 231 
 
 by sodium and potassium 
 nitrates, 235 
 
 isolation of products, 236 
 
 of fatty bodies, 232, 240 
 
 solvents used in, 232 
 Nitric acid, action of dilute, 231 
 
 acid, action on fatty bodies, 232 
 
 acid, as oxidising agent, 265 
 Nitroaldehydes, 228, 235 
 Nitrobenzene, 170, 190, 233, 302, 
 
 328, 366, 368 
 Nitro-bodies, 224 
 
 non-reducible, 319 
 
 reduction of, see Reduction 
 
 see Nitration 
 Nitrobutylene, 232 
 Nitro-?;z-cresol, 233 
 /-Nitrodimethylaniline, 227, 236 
 Nitroethane, 240 
 
 Nitrogen, determination of, qualita- 
 tive, 378 
 
 determination of, quantitative, 
 379, 380 
 
 iodide, 218 
 
 Nitrohydroquinone, 228 
 Nitrolic acids, reduction of, 316 
 Nitromethane, 241 
 Nitrophenanthrene, 229 
 Nitrophenols, 7, 159, 182, 231, 238 
 Nitropropylene, 241 
 Nitropyrocatechin, 232 
 Nitrosalicylic acid, 237 
 Nitroso-derivatives, 236, 240 
 Nitrotoluene, oxidation of, 275 
 Nitrotoluidine, 226 
 Nitrous acid, 137 
 
 acid, oxidation by, 267 
 
 ethers, 148 
 
 Optically active bases, 337 
 Oxalic acid, condensation by, 115 
 Oxidation of acids, 247, 249, 251, 
 
 265, 270, 276, 278 
 of alcohols, 245, 249, 257,259, 
 
 262, 263, 266, 269, 272, 278, 
 
 279, 282, 283 
 of amines, 245, 246, 250, 251, 
 
 257, 259, 262, 263, 264, 269, 
 
 271, 275, 280, 284, 285 
 of carbohydrates, 247, 251, 
 
 257, 262, 264 
 of haloid derivatives, 246, 267, 
 
 268, 273, 279 
 of hydrazo-bodies, 257, 264, 
 
 282, 283 
 of hydrocarbons, 244, 245, 252, 
 
 254, 258, 260, 261, 262, 263, 
 
 265, 266, 269, 273, 275, 277, 
 282, 283, 284 
 
 of ketols, 256 
 
 of ketones, 247, 250, 261 
 
 of sulphur compounds, 257, 
 
 266, 273, 274, 276, 277, 278, 
 284, 285 
 
 with fused caustic alkalis, 157 
 with palladium hydrogen, 160 
 
 Oxidising agents, 243 
 
 Oxygen carriers, 270 
 
 most active form of, 160 
 made in Kipfs apparatus, 268 
 oxidation by, 268 
 
 Oxymethylenecamphor, 1 2 1 
 
 Ozone, oxidation by, 270 
 
 Pentamethylbenzoic acid, 108 
 Perchloroformic ether, 116 
 PERKIN'S synthesis, 104 
 Peroxides, organic, 246 
 Phenol, 114, 218, 260 
 
 of crystallisation, 8 
 Phenols, ethers of, 150 
 /-Phenylenediamine, 166 
 Phenyl esters, preparation of, 1 49 
 Phenylhydrazine, 101, 102 
 
 reduction by, 301 
 Phenylsuccinic acid, 175 
 Phloroglucinol, 157 
 Phosgene, 117 
 Phospho-molybdic acid, 334 
 Phosphonium iodide, 218 
 Phosphorus, 294, 302 
 
INDEX 
 
 401 
 
 Phosphorus, as bromine carrier, 172 
 
 oxychloride, 202 
 
 oxychloride, condensation by, 
 117 
 
 oxychloride, use in making 
 esters, 149 
 
 pentachloride, 191 
 
 pentoxide, 363 
 
 pentoxide, condensation by, 117 
 
 trichloride, 203 
 
 trichloride, condensation by, 
 
 118 
 
 Phospho-tungstic acid, 334 
 Phthalic anhydride, 190 
 Picric acid, compounds with, 17, 331 
 
 acid, reduction of, 291 
 Pinacolines, 135 
 Platinised asbestos, 269 
 Platinum black, 269, 27 1 
 
 double salts, 342 
 Polymerisation, in, 115, 129 
 Potassium bichromate, 271 
 
 bisulphate, condensation by, 1 19 
 
 bisulphate, use in making es- 
 ters, 148 
 
 chlorate, 274 
 
 cyanide, 119 
 
 ferricyanide, 274 
 
 hydroxide, alcoholic, reduction 
 by, 302 
 
 hydroxide, condensation by, 
 1 20 
 
 hydroxide, fusion with, 155 
 
 iodate, 275 
 
 nitrite, 238 
 
 permanganate, 276 
 
 pyrosulphate, 148 
 
 sulphate, 363 
 Precipitation, 10 
 Propyl butyrate, 147 
 Pseudonitroles, 241 
 Putrefaction, 160 
 Pyruvic acid, 167 
 
 Quinite, 309 
 
 Quinol, 108, 150, 155, 228, 250, 
 
 281, 298, 301, 311 
 Quinoline, synthesis of, 113, 125, 
 
 128 
 Quinone, 280, 298, 311 
 
 RAOULT'S method, 80 
 
 Recrystallisation, n 
 
 Red-hot tube, leading vapours 
 
 through a, 40, 136 
 Reducing agents, 287 
 Reduction by stages in aromatic 
 
 series, 288, 300, 319 
 of acids, 297, 309 
 of alcohols, 293, 296, 302, 324 
 of aldehydes, 311, 326 
 of bases, 305, 306, 310, 315 
 of diazo-bodies, 326 
 of diazo-bodies to hydrocarbons, 
 
 321 
 of haloid derivatives, 293, 300, 
 
 310, 322 
 
 of hydrazones, 311 
 of hydrocarbons, 297, 301, 304, 
 
 307, 325 
 
 of ketones, 297, 308, 323 
 of lactones, 310 
 of nitriles, 305 
 of mtro-bodies, fatty, 316 
 of nitro-bodies to amines, 288, 
 
 290, 298, 299, 301,302,313, 
 
 315, 3i6,3i7,3i8,3i9, 323 
 of nitro-bodies to azo-bodies, 
 
 302, 304, 320, 328 
 of nitro-bodies to azoxy-bodies, 
 
 302, 304, 319, 328 
 of nitrophenols with caustic 
 
 potash, 159 
 of quinones, 281, 295, 307, 
 
 309, 311,326,327 
 simultaneous with oxidation, 
 
 290 
 
 Resazurin, 263 
 Resorcinol, 116, 205, 263 
 Rubber connections, 173, 180 
 
 Salol, 150, 154, 353 
 
 Salts, double, 333, 336, 340, 342, 
 
 347 
 
 of bases, 330 
 of organic acids, 329, 338 
 of organic acids with organic 
 
 bases, 347 
 
 organic, of antimony, 338 
 organic, of barium, 338 
 organic, of cadmium, 338 
 organic, of calcium, 339 
 organic, of cobalt, 339 
 organic, of copper, 340 
 
 D D 
 
4-O2 
 
 INDEX 
 
 Salts, organic, of gold, 340 
 organic, of lead, 341 
 organic, of magnesium, 341 
 organic, of manganese, 341 
 organic, of mercury, 341 
 organic, of nickel, 342 
 organic, of platinum, 342 
 organic, of potassium, 344 
 organic, of silver, 344 
 organic, of sodium, 345 
 organic, of strontium, 346 
 organic, of tin, 346 
 organic, of zinc, 346 
 precipitation of, 330 
 preparation of, 329, 333 
 preparation of, by double de- 
 composition, 337 
 
 SANDMEYER'S reaction, 178, 199, 
 214, 239 
 
 Saponification, 350 
 
 Sealed tubes, apparatus for heating, 
 
 94 
 tubes, experiments on a small 
 
 scale in, 94 
 tubes, explosion of, 95 
 tubes, gases in, 91 
 tubes, pressure in, 93 
 tubes, reactions in, 89, 92 
 tubes, use of chlorine in, 183 
 Silicic ether, 120 
 Silver, 120 
 
 salts, oxidation by, 283 
 SKRAUP'S synthesis of quinoline, 
 
 128 
 
 Soda lime, 279 
 Sodium acetate, 122 
 
 amalgam, condensation by, 121 
 amalgam, reduction by, 308 
 and potassium hydroxides, dif- 
 fering effects of infusion, 158 
 bichromate, 280 
 condensation by, 120 
 ethylate, condensation by, 122 
 ethylate, saponification by, 353 
 hydroxide, condensation by, 
 
 124 
 
 hydroxide, fusion with, 155 
 nitrite, oxidation by, 282 
 nitrite, use in making diazo- 
 
 bodies, 140 
 
 nitrite, use in making nitro- 
 bodies, 237 
 
 Sodium peroxide, 282 
 reduction by, 303 
 reduction by, in amyl alcohol 
 
 solution, 305 
 
 Solubility, determination of, 332 
 of inorganic salts in alcohol, 
 
 60, 178, 318 
 relative, in various extracting 
 
 agents, 55 
 Solvents, 3, 58 
 Stannic chloride, 129 
 Stannous chloride, 317 
 
 hydroxide, alkaline solution of, 
 
 320 
 
 Steam, distillation in a current of, 32 
 Sublimation, apparatus for, 97 
 
 in vacuo, 99 
 Succinic acid, 173, 191 
 
 ether, 146 
 
 Succinimide, reduction of, 324 
 Sugars, 21, 124, 133, 153, 251, 264 
 Sulphanilic acid, 165 
 Sulphites, alkali, 368 
 Sulphonic acids, 358 
 acids, fatty, 367 
 acids, made by transformation 
 
 of sulphates of bases, 371 
 acids, made with alkali sul- 
 phites, 368 
 
 acids, made with carbyl sul- 
 phate, 370 
 acids, made with cone, sulphuric 
 
 acid, 358 
 
 acids, made with fuming sul- 
 phuric acid, 362 
 acids, made with 100 per cent. 
 
 H 2 S0 4 , 361 
 acids, made with phosphorus 
 
 pentoxide, 363 
 
 acids, made with potassium and 
 sodium bisulphates and pyro- 
 sulphates, 367 
 
 acids, made with potassium sul- 
 phate, 363 
 acids, made with sulphuryl oxy- 
 
 chloride, 365 
 Sulphur, 126 
 
 chlorides of, 203 
 determination of, 386 
 dioxide, 311 
 
 Sulphuric acid, causes addition of 
 water, 129 
 
INDEX 
 
 403 
 
 Sulphuric acid, condensation by, 
 
 126 
 
 acid, fuming, 362 
 acid, oxidation by, 284 
 acid, use in making esters, 
 
 147 
 
 ethers, 149 
 
 Sulphurous acid, 20, 284, 311 
 Sulphuryl chloride, 204 
 Sunlight, effects of, 103, 164, 181 
 Superheated steam for distillation, 
 32 
 
 Tartaric ether, 145 
 Tetraphenylethylene, 126 
 Tetrazo-compounds, 139, 264 
 Thallium, chlorides of, 189 
 Thermometers, 25 
 Thionyl chloride, 206 
 Thymol, 126, 127, 218 
 Tin, 312 
 
 tetrachloride, 129 
 0-Toluic acid, 277 
 w-Toluyl aldehyde from w-xylene, 
 
 255 
 
 Trimethylene iodide, 219 
 Trinitronaphthol, 229 
 Trinitrotoluene, 289 
 
 Vapour density, determination of, 
 
 by Demuth and Meyer's 
 
 method, 78 
 density, determination of, by 
 
 expulsion of air, 75 
 density, determination of, by 
 
 expulsion of mercury, 67 
 density, determination of, by 
 
 expulsion of Wood's alloy, 72 
 density, determination of, by 
 
 ffofmantfs method, 70 
 Veratrine, 9 
 
 Water, addition of, 129, 259 
 
 influence of, on chemical ac- 
 tion, 161 
 of crystallisation, 9, 331, 340, 
 
 342, 345 
 
 WOOD'S alloy, 75 
 WURTZ, bulb tube, 28, 29 
 
 Zinc, condensation by, 130 
 
 reduction by, 322 
 Zinc chloride, 131 
 
 dust, condensation by, 135 
 
 dust, reduction by, 324 
 
 oxide, 135 
 
 permanganate, 285 
 
 THE END 
 
 RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY. 
 
op 
 
 DAY AND TO *.00 ON THE 2JO HE F U " TH 
 OVERDUE. HE SEVENTH DAY 
 

 
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