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CATALYTIC HYDROGENATION 
 AND REDUCTION 
 
Zext-books of Chemical Research and 
 Engineering. 
 
 Edited by W. P. DREARER, F.I.C. 
 
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TEXT-BOOKS OF CHEMICAL RESEARCH AND ENGINEERING 
 
 CATALYTIC 
 HYDROGENATION 
 AND REDUCTION 
 
 BY 
 
 EDWARD B. MAXTED, PH.D., B.Sc., F.C.S, 
 ^ 
 
 With 12 Illustrations 
 
 PHILADELPHIA 
 
 P. BLAKISTON'S SON & CO. 
 
 1012 WALNUT STREET 
 1919 
 
\^ 
 
 Printed in Great Britain 
 
PREFACE 
 
 THE present volume has been written with the 
 object of presenting in an easily accessible form the 
 numerous examples of catalytic hydrogenation which 
 have from time to time been published. 
 
 Special attention has been given to experimental 
 methods and, in addition to the simple hydrogenation 
 of unsaturated linkages, such as the conversion of 
 ethylene to ethane or of benzene to cyclohexane, 
 various catalytic reductions of a less simple nature, 
 usually involving the splitting off of water or of a 
 halogen acid, have been included. A chapter has 
 also been devoted to dehydrogenation. 
 
 E. B. M. 
 
 WALSALL. 
 
CONTENTS 
 
 PACE: 
 PREFACE ... v 
 
 CHAPTER I 
 
 Historical introduction- Division of catalysts into 
 groups- Temperature and activity- Catalyst poisons 
 
 CHAPTER II 
 THE PREPARATION OF CATALYSTS ..... 615 
 
 Nickel group. Temperature of reduction Preparation 
 of briquettes- Use of nickel oxide Cobalt, copper 
 and iron Platinum group- Colloidal catalysts- 
 Protective colloids Inoculation method of prepar- 
 ing colloidal metals. 
 
 CHAPTER III 
 THE METHODS OF CATALYTIC HYDROGENATION . . 16-27 
 
 Vapour method- Treatment of gases- Hydrogenation 
 by bubbling, shaking and stirring Types of shaking 
 apparatus- Work under pressure. 
 
 CHAPTER IV 
 THE HYDROGENATION OF UNSATURATED CHAINS . . 28-41 
 
 Unsaturated hydrocarbons- Alcohols and ethers- Alde- 
 hydes and ketones* Acids and esters Halogen 
 compounds- Acetylenic linkages. 
 
viii CONTENTS 
 
 CHAPTER V 
 THE HYDROGENATION OF UNSATURATED RINGS . 
 
 Benzene hydrocarbons- Condensed rings- Aromatic 
 acids and esters Various aromatic derivatives 
 Terpenes' Heterocyclic rings- Hydrogenation of 
 alkaloids. 
 
 CHAPTER VI 
 MISCELLANEOUS REDUCTIONS 61-72 
 
 Oxides of carbon Ketones- Simultaneous hydrogena- 
 tion and dehydration Reduction of C:N group- 
 Reduction of isonitriles- Azo-group- Oxides of 
 nitrogen- Nitro-compounds Removal of halogens 
 Reduction of metallic oxides. 
 
 CHAPTER VII 
 DEHYDROGENATION 73-Si 
 
 Dehydrogenation of alcohols' Amines- Reduced benz- 
 ene derivatives Hydroquinone- Hydrazobenzene 
 Dihydronaphthalene Mechanism of dehydrogena- 
 tion Wieland's views on mechanism of oxidation. 
 
 CHAPTER VIII 
 
 THE TECHNICAL HYDROGENATION OF UNSATURATED 
 
 OILS 82-101 
 
 Acids of the natural oils- Reduction of nickel catalyst 
 Manufacture of hydrogen* Oil hardening plant- 
 Details of typical operation- Iodine value- Re- 
 fractive index- Detection of nickel. 
 
CATALYTIC HYDROGENATION 
 
 CHAPTER I 
 
 WHILE it has long been known that hydrogen 
 in statu nascendi possesses a very much more active 
 character than the comparatively inert free gas, 
 any systematic investigation of the results obtain- 
 able by activating free hydrogen by the presence 
 of catalysts belongs almost entirely to the last 
 two decades. The subject received its impetus by 
 the discovery of the hydrogen-activating properties 
 of nickel by Sabatier and Sender ens in 1899, and 
 by the commercial application of the reaction to 
 the hydrogenation of unsaturated glycerides. True 
 it is that M. P. de Wilde in I.874 1 found that acetylene 
 is hydrogenated to ethane in presence of platinum 
 black, that M. Saytzeff and Kolbe 2 as long ago as 
 1871 had succeeded in reducing benzoyl chloride, 
 nitrobenzene, and nitromethane by leading the 
 vapours of these bodies, mixed with hydrogen, over 
 palladium black, and that Cooke 3 in 1888 had 
 carried out various reductions in presence of platinum 
 but, save for these isolated results, catalytic hydro- 
 genation had received little attention up to the time 
 of Sabatier 's work. 
 
 Free hydrogen in presence of a catalyst is often 
 
 1 M. P. de Wilde, Ber. 1874, 7, 353. 
 
 2 Saytzeff and Kolbe, /. prakt. Chem. (N.F.), 1871, 4, 418 ; 
 1872, 6, 128. 
 
 8 Cooke, Chem. News, 1888, 58.. 103. 
 
2 CATALYTIC , HYDROGENATION 
 
 more active than that in a nascent condition ; thus 
 while oleic acid is scarcely affected by nascent 
 hydrogen, it is easily and quantitatively reduced 
 to stearic acid by free hydrogen in the presence of 
 a catalyst. 
 
 Catalytic hydrogenation has rendered easy the 
 preparation of many aromatic derivatives and even 
 of bodies of an extremely complicated nature, such 
 as reduced alkaloids. The introduction of saturating 
 hydrogen is by no means limited to the saturation of 
 ethylenic, benzenoid, or triple bonds between carbon 
 atoms, but finds application also inter alia in the 
 hydrogenation of linkages between carbon and 
 nitrogen, carbon and oxygen, nitrogen and nitrogen, 
 and nitrogen and oxygen. 
 
 It is, further, possible to effect catalytically many 
 reduction reactions which do not consist merely in 
 the introduction of hydrogen, such as the reduction 
 of the carbonyl group CO to CH ? , of the group 
 CH'OH to CH 3 , and of metallic oxides to metal. 
 
 The metallic catalysts, on the surface of which 
 the hydrogen exists in an active condition, may 
 conveniently be divided into two classes. To the 
 first class belong the metals of the iron group iron 
 nickel, and cobalt, together with copper. These, 
 metals begin, in general, to exert a marked acti- 
 vating influence on hydrogen only at an elevated 
 temperature. The minimum temperature at which 
 activity begins to be developed is different for each 
 metal, and there exists, in general, a definite optimum 
 temperature for each catalyst, in the determination 
 of which the reaction to be carried out also plays 
 an important part, and above which temperature 
 the activity of the catalyst, instead of becoming 
 increased by increasing temperature, begins to 
 decrease. Thus, while metallic nickel "begins to 
 effect the addition of hydrogen to the ethylenic 
 linkage in an unsaturated glyceride at tempera- 
 tures not far above 100 C., activation to a satis- 
 
CATALYTIC HYDROGENATION 3 
 
 factory degree does not take place till nearer 150 C., 
 and the optimum temperature, at any rate as far as 
 velocity is concerned, is considerably higher than 
 this. 
 
 The minimum temperature at which the metals 
 of the first class begin to exert activity is, in general, 
 higher for cobalt than for nickel, for copper than for 
 cobalt, and for iron than for copper. Thus, from this 
 point of view, the series may be written : nickel, 
 cobalt, copper, iron, in ascending order of minimum 
 activating temperature. The order of activity of 
 these metals at any given temperature, at any rate 
 for moderate temperatures, varies from metal to 
 metal in the same direction, nickel being more 
 active than cobalt, cobalt than copper, and copper 
 than iron. 
 
 In determining temperatures, it is to be noted 
 that we are only able to ascertain the mean tempera- 
 ture of the space surrounding the seat of reaction. 
 It is probably fair to assume that the actual seat of 
 reaction is in a very different thermal condition 
 from the main bulk of the substance which is being 
 hydrogenated. 
 
 It is, further, interesting to note that silver, 
 which is so nearly related chemically to copper, has 
 been found by Paal and Gerum to be slightly active 
 for the reduction of nitrobenzene to aniline at 80 C. 
 The use of finely divided silver and gold at 200- 
 250 C. for the catalytic reduction of nitrobenzene 
 to aniline has been protected by the Badische 
 Anilin- & Soda-Fabrik. 1 
 
 To the second class of catalysts belong the metals 
 of the platinum and palladium groups, consisting of 
 ruthenium, rhodium, palladium, osmium, iridium, 
 and platinum. Of these, platinum and palladium 
 have been more extensively used than the other 
 metals of the family. All members of this group 
 of metals are active at the ordinary temperature, 
 1 Badische Anilin- & Soda-Fabrik, German patent, 263396. 
 
 I 2 
 
4 CATALYTIC HYDROGENATION 
 
 osmium being by far the least active. Directions 
 for the preparation of the various metals for cata- 
 lytic purposes will be found in the second chapter 
 of this book. 
 
 It is to be noted that, instead of introducing the 
 metals in the metallic form into the substance to 
 be hydrogenated, an oxide or salt of the metal may 
 often conveniently, and sometimes even advan- 
 tageously, be substituted, provided that under the 
 conditions of the reaction a sufficient amount of 
 reduction of the oxide or salt by the hydrogen takes 
 place. Thus instead of platinum black, platinum 
 chloride may be introduced, or instead of metallic 
 nickel, nickel oxide or a suitable salt such as the 
 formate. 
 
 For the success of the reaction, it is in general 
 necessary that catalyst poisons such as sulphur 
 compounds, arsenic and phosphorus and their 
 compounds, carbon monoxide and lead and its 
 compounds should be absent. In certain cases, 
 however, such as in the hydrogenation of unsaturated 
 glycerides by nickel, the catalyst itself may contain 
 a considerable amount of sulphur as sulphate or 
 even as sulphide without any very bad effect being 
 observed, while in other reactions, such as the 
 hydrogenation of benzene to cyclohexane, the 
 smallest trace of sulphur in the form of thiophene 
 is sufficient to stop the reaction. 
 
 Besides chemical poisoning from impurities, in 
 the substance to be hydrogenated, in the catalyst, 
 or in the hydrogen, a second form of poisoning of 
 a more mechanical nature is sometimes found in 
 reactions in liquid media, where colloidal or other 
 impurities may settle on the surface of the catalyst 
 and thus clog its action. This clogging of the 
 catalytically active surface is also observed in gas 
 reactions. 
 
 We have at present very little experimental 
 evidence as to the part played by the catalyst in 
 
CATALYTIC HYDROGENATION 5 
 
 the activation process or as to the actual course 
 of the reaction itself. Sabatier supposes that the 
 reaction depends on the intermediate formation of 
 an unstable metallic hydride, but a good case can 
 also be made out for action of a more physical 
 nature. A theory as to the activity of the metallic 
 oxides themselves, as well as the metals, has lately 
 been advanced, but it should be emphasised that, 
 while there are many examples of activity in cata- 
 lysts consisting of oxide-free metals, no activity of 
 oxides has been observed under conditions where 
 reduction of the oxide by hydrogen to a consider- 
 able extent has not already taken place or is not 
 possible. 
 
CHAPTER II 
 
 THE PREPARATION OF CATALYSTS 
 A. The Nickel Group (Ni, Fe, Co, and Cu) 
 
 THIS group contains the catalysts originally used 
 by Sabatier and Senderens. For the preparation of 
 these metals in an active form, attention must be 
 paid, not only to the purity of all materials used, 
 but also to the highest temperature to which the 
 metallic oxide or salt is subjected both immediately 
 before the production of the actual catalyst and 
 during the course of the catalytic reaction itself. 
 The purity of the materials is rather to be reckoned 
 from the point of view of the absence of catalyst 
 poisons than from the ordinary chemical viewpoint 
 of purity. Thus while the presence of extremely 
 small quantities of arsenic or its compounds inter- 
 feres seriously with the activity of the catalyst, the 
 presence of a non-poisonous foreign substance may 
 not only have no harmful effect but may even exert 
 a beneficial influence on the activity. The subject 
 of promoters the opposite of catalyst poisons 
 becomes an important one where, for commercial 
 or other reasons, it is desired to carry out the 
 reaction as rapidly as possible. 
 
 For the production of a nickel catalyst, a nickel 
 salt which has been manufactured from nickel 
 produced by the Mond carbonyl process should be 
 employed. In many cases it is almost immaterial 
 
THE PREPARATION OF CATALYSTS 7 
 
 which salt of this pure nickel is taken, even the 
 sulphate, although it contains a catalyst poison, 
 giving almost as good a catalyst, for instance for 
 the hardening of oils, as the poison-free, but more 
 expensive, nitrate. 
 
 The exact method of preparing the catalyst 
 depends largely on how it is to be employed when 
 made. Thus for the hydrogenation of benzene or 
 oleic acid by the vapour method, it is preferable 
 to support the nickel in such a way that it presents 
 a large active surface without stopping the passage 
 of gas through the reaction chamber. For purposes 
 of this sort asbestos rope or pumice may be tho- 
 roughly cleaned by treatment with dilute nitric 
 acid, followed by ignition. The asbestos or pumice 
 is soaked in nickel nitrate melted in its water of 
 crystallisation, or in a strong solution of the salt, 
 and heated to the lowest temperature necessary for 
 the conversion of the nitrate to oxide. The oxide, 
 thus supported, is introduced into the actual tube 
 or vessel in which hydrogenation is to be carried 
 out and reduced there by means of pure hydrogen, 
 preferably immediately before it is required. 
 
 The nature of the catalyst will vary largely with 
 the temperature at which it is reduced. In general, 
 after a certain minimum has been passed, the lower 
 the temperature of reduction the higher will be the 
 activity, though the keeping down of the reduction 
 temperature below that at which it is proposed to 
 carry out the catalytic reaction means only that 
 the time required for the catalyst preparation is 
 lengthened without ultimate gain in activity. 
 
 Reduction at a comparatively high temperature, 
 while detracting from the activity of the catalyst, 
 is in general conducive to the development of a 
 higher power of resistance to the action of catalyst 
 poisons. Nickel oxide, if prepared without over- 
 heating, is reduced slowly by hydrogen at about 
 200 C., and Sabatier and Senderens recommend 
 
8 CATALYTIC HYDROGENATION 
 
 that the reduction should be carried out at a tempera- 
 ture slightly below 300 C. From 300-350 C. is, 
 however, perhaps the most suitable temperature 
 for general work by the vapour method. 
 
 Instead of heating the supported nickel nitrate 
 and transforming it thus to oxide, the nitrate may 
 be treated with a solution of sodium or potassium 
 hydroxide or carbonate, followed by a thorough 
 washing with distilled water, while in place of 
 employing asbestos or pumice coated with nickel as 
 the catalyst, an excellent result may be obtained 
 by employing porous briquettes containing nickel 
 or nickel oxide. 
 
 The following example illustrates a method of 
 making briquettes for purposes such as the reduc- 
 tion of benzene to hexahydrobenzene. Nickel 
 nitrate is dissolved in distilled water and to the 
 solution magnesium nitrate is added in sufficient 
 quantity to give with soda a weight of magnesium 
 oxide equal to the nickel in the nickel nitrate. The 
 mixed nitrates are precipitated with sodium hydr- 
 oxide or carbonate, and the precipitate, after 
 being washed with distilled water, is spread with a 
 nickel or porcelain spatula, as a layer of about a 
 quarter of an inch thick, on a clean, square sheet of 
 nickel. The moist mass is conveniently divided 
 into squares of suitable size by means of a needle 
 mounted in a wooden holder, when it may be dried 
 by the cautious and gentle application of a Buns en 
 flame to the supporting nickel plate. 
 
 The above remarks apply more especially to 
 hydrogenation by the vapour method. For the 
 hydrogenation of liquid or dissolved substances it 
 is usual to employ the nickel catalyst in the form 
 of a suspension and to remove the nickel particles 
 after the operation by filtering. 
 
 The nickel catalyst for suspension in the liquid 
 may be prepared by reducing pure nickel oxide or 
 carbonate by means of pure hydrogen at 300-320 C., 
 
THE PREPARATION OF CATALYSTS 9 
 
 or even at a slightly higher temperature. The oxide 
 or carbonate should be precipitated from nickel 
 sulphate, or preferably nitrate, by pure sodium 
 carbonate or hydroxide, or it may be prepared by 
 gently heating the nitrate to the lowest temperature 
 required for its conversion to oxide. 
 
 For laboratory purposes, the reduction of the 
 oxide to metal is conveniently carried out in a dis- 
 tilling flask heated on a sand-bath. The oxide 
 should not fill more than a quarter of the flask at 
 the most, and this must be frequently shaken in 
 order to expose fresh surfaces of oxide or carbonate 
 to the action of the hydrogen. From two to three 
 hours' reduction at 320-350 C. should be amply 
 sufficient to obtain an active catalyst when working 
 with a 300 c.c. distilling flask one-quarter full of 
 nickel oxide, provided that a fairly rapid current of 
 hydrogen be used. With less oxide, reduction 
 would probably have proceeded to a satisfactory 
 degree in less time. It is to be noted that complete 
 reduction to metal never takes place under ordinary 
 conditions of working at these comparatively low 
 temperatures, and, further, that unnecessarily pro- 
 longed reduction reduces the activity of the catalyst. 
 
 For certain reactions it is possible and sometimes 
 preferable to effect the reduction in the liquid itself. 
 This is particularly the case where non-volatile 
 liquids boiling at above 280 C. are to be hydro- 
 genated by the bubbling method, and where there 
 is no danger of the body decomposing at the tem- 
 perature employed. Reduction of the oxide or salt 
 in liquid media may be carried out at considerably 
 lower temperatures than 300 C. ; for instance, 
 Bedford and Williams recommend 255 C. as a 
 suitable reduction temperature for nickel oxide in 
 the presence of an unsaturated glyceride. 
 
 If the nickel oxide is reduced dry, it is preferable 
 that this should be done immediately before use, 
 the reduced nickel being allowed to cool completely 
 
io CATALYTIC HYDROGENATION 
 
 in the current of hydrogen before the liquid to be 
 treated is run in. In order to increase the surface 
 of the nickel, the oxide, from which the catalyst is 
 prepared, may, if desired, be supported on an inert 
 substance such as kieselguhr or carbon. To do this, 
 the nitrate or sulphate solution, from which the 
 oxide is made, is mixed with kieselguhr in the 
 proportion of from two to ten parts of kieselguhr 
 to one of metallic nickel and the precipitation of the 
 oxide or carbonate carried out with constant stirring. 
 
 The other members of this group of catalysts are 
 of far less importance than nickel from the point of 
 view of the extent to which they are used. Copper 
 is chiefly used for hydrogenation reactions in which a 
 milder action is required than would be obtained with 
 nickel. Sabatier and Senderens 1 recommend a 
 reduction temperature for copper of slightly under 
 200 C. Iron and cobalt are even less used than 
 copper. Iron is prepared by reduction of its oxide 
 or carbonate at 400-500 C., cobalt at a slightly 
 lower temperature than this. The remarks made 
 under nickel with respect to the manufacture of 
 the catalyst also apply to iron, cobalt, and copper. 
 Cobalt is usually less active than nickel and more 
 active than copper. Iron is only at its best slightly 
 active and is for many reactions inactive, the initial 
 temperature at which iron becomes active being far 
 higher than for the other metals. 
 
 In certain cases, where the substance to be hydro- 
 genated is extremely sensitive to the presence of 
 small quantities of poisons, an impure catalyst may 
 be rendered efficient by alternate reduction with 
 pure hydrogen and oxidation with pure oxygen 
 provided that the final reduction be carried out at 
 a comparatively low temperature, or instead of being 
 reduced directly the purified oxide may be dissolved 
 in pure nitric acid and worked up as usual. 
 
 1 Sabatier and Senderens, Compt. rend., 1900, 130, 1761 ; 
 1901, 133, 321. 
 
THE PREPARATION OF CATALYSTS n 
 
 The above methods of preparation all treat of the 
 reduction of an oxide at moderate temperatures 
 by hydrogen. Certain inorganic or organic nickel 
 or other metal salts, such as lactate, formate, or 
 carbonate, may be substituted for the oxide with 
 the production of catalysts possessing a high activity. 
 The production of nickel by the decomposition of 
 the carbonyl has also been proposed. 
 
 The Platinum Group. 
 
 While the metals of the nickel group are usually 
 used for hydrogenation reactions at high tempera- 
 tures between gases and for the industrial hydro- 
 genation of such liquids as the natural fats and their 
 acids, the catalysts of the platinum group have 
 principally been employed for the hydrogenation of 
 substances in the liquid or dissolved condition, at 
 the ordinary temperature or at temperatures not 
 very far removed from this. If the reaction is to 
 be carried out in a liquid, the state of division of the 
 catalyst is of the utmost importance as a factor for 
 determining the velocity of the reaction, and for 
 this reason the introduction of colloidal catalysts by 
 Paal and others has rendered possible the carrying 
 out of many hydrogenation reactions which would 
 have been unattainable with less finely divided 
 catalysts owing to the slowness with which they 
 proceed and the ease with which they are stopped by 
 poisons. 
 
 Salts of the platinum metals are very easily 
 reduced to the metallic state by such reducing agents 
 as free or nascent hydrogen in the cold, formaldehyde, 
 hydrazine, etc., but in general the metal is produced 
 in a flocculent condition possessing the disadvantage 
 of a comparatively small catalytic surface. 
 
 A non-colloidal platinum catalyst may be pre- 
 
12 CATALYTIC HYDROGENATION 
 
 pared according to Low's 1 method by dissolving 
 5 grams of platinic chloride in 5-6 c.c. of water and 
 mixing in 7 c.c. of a 40-50 per cent, solution of 
 formaldehyde. Ten grams of a 50 per cent, sodium 
 hydroxide solution are added and the mixture is 
 allowed to stand for twelve hours. The platinum 
 may be washed on a Buechner funnel until the wash- 
 water runs through black, or the alkaline liquid may 
 be warmed for a quarter of an hour to 50 C. and 
 washed by dec^ntation till the washings no longer 
 give a reaction with silver nitrate. 2 
 
 For some purposes, a sufficiently active catalyst 
 is obtained by suspending or dissolving the platinum 
 chloride in the substance to be reduced, or in any 
 suitable solvent, and passing free hydrogen at about 
 100 C. or even less, sodium carbonate being added 
 in quantity sufficient to neutralise the hydrochloric 
 acid liberated. Thus with an unsaturated glyceride, 
 such as refined olive oil, rapid hydrogenation is 
 obtained by this simple method of treatment even 
 when using only o-i per cent, of platinum, or an 
 even smaller quantity of palladium. 3 
 
 Colloidal metals of the platinum group were 
 prepared in very dilute solution by Bredig 4 by his 
 disintegration method ; by Lottermoser, 5 by reduc- 
 tion of a solution of platinic chloride by means of 
 formaldehyde in presence of alkali ; by Gutbier, 6 
 by reduction with hydrazine hydrate ; by Henrich, 7 
 using pyrocatechin, and by Garbowski 8 with tannin, 
 gallic acid, and other organic reducing agents. 
 These dilute solutions of the colloid metals are of 
 little use for catalytic hydrogenation, by reason of 
 
 1 Low, Ber., 1890, 3, 289. 
 
 2 Willstatter, Ber., 1912, 45, 1472. 
 
 3 Paal, U.S. patent 1023753 (1912). 
 Bredig, Anorg. Fermente, Leipzig, 1901. 
 Lottermoser, Uber anorg. kolloide, Stuttgart, 1901. 
 Gutbier, Zeit anorg. Chem., 1902, 32, 352. 
 Henrich, Ber., 1903, 36, 609. 
 
 Garbowski, ibid., 1903, 36, 1215. 
 
THE PREPARATION OF CATALYSTS 13 
 
 the ease with which they are coagulated by electro- 
 lytes. 
 
 The necessary stability is easily obtained by the 
 use of a so-called protective colloid. C. Paal and 
 C. Amberger 1 use for this purpose sodium protalbate 
 or lysalbate, two products of the degradation of 
 egg-albumin by means of aqueous alkalies, hydrazine 
 being stated to form the most suitable reducing 
 agent for the preparation of colloidal platinum or 
 palladium. Hydroxylamine and formaldehyde were 
 found to be unsuitable. For iridium, nascent 
 hydrogen from sodium amalgam was used. 
 
 The following directions are given by Paal and 
 Amberger 2 for the preparation of colloidal platinum. 
 One gram of sodium lysalbate is dissolved in 30 c.c. 
 of water, together with rather more sodium hydroxide 
 than is necessary for reaction with the chlorine of 
 the chloroplatinic acid taken. Two grams of 
 chloroplatinic acid are now dissolved in a little 
 water and added to the alkaline liquid, the clear 
 dark brown solution being then reduced by means of 
 a slight excess of hydrazine hydrate. The colloidal 
 platinum thus produced is purified by dialysis, and 
 may be obtained, by evaporating first on the water- 
 bath and then to dryness in a vacuum, in the form 
 of black plates, easily soluble in water to a black, 
 opaque liquid. The product contains sodium lysal- 
 bate in addition to platinum. Colloidal palladium 
 is obtained in a similar manner and sodium protalbate 
 may be substituted for the lysalbate. In a later 
 paper, 3 the above authors use gaseous hydrogen as 
 the reducing agent. 
 
 Colloidal palladium prepared according to Paal 
 and Amberger 's method is not suitable for the 
 hydrogenation of bodies in acid media, since in the 
 presence of acids an adsorption compound of 
 
 1 Paal and Ambei^er, Ber., 1904, 35, 124 et seq. 
 
 2 Paal and Amberger, ibid., 1902, 35, 2195. 
 
 3 Paal and Amberger, Hid., 1905, 38, 1398. 
 
4 CATALYTIC HVDROGENAtlON 
 
 protalbic acid and palladium is precipitated. In 
 order to avoid the coagulating of the catalyst, 
 it is necessary to prepare the colloidal palladium in 
 the presence of a protective colloid stable in the 
 presence of acids. For this purpose, C. Kelber 
 and R. Schwarz 1 recommend the colloid produced 
 by the action of an organic acid on gluten. Colloidal 
 palladium prepared according to the following 
 directions is not coagulated by dilute mineral acids. 
 Take 16 grams of a protective colloid solution, 
 obtained by treating gluten with acetic acid and 
 containing about 50 per cent, of the treated gluten. 
 To this add 4 grams of palladium chloride dissolved 
 in a little water. A little ammonia is added to the 
 dark brown solution, followed by hydrazine hydrate, 
 drop by drop. The liquid froths and gives off gas, 
 becoming a deep brownish-black. As soon as the 
 reduction is complete, the colloidal palladium 
 preparation should be dialysed till the outside 
 water gives no chloride reaction, after which it is 
 cautiously evaporated down, finally in a vacuum. 
 The product consists of black, lustrous scales, easily 
 soluble in water and in glacial acetic acid. 
 
 In certain cases, direct reduction in presence 
 of a protective colloid is sufficient for the prepara- 
 tion of a colloid catalyst, which may, where re- 
 quired, be purified by dialysing in the usual way. 
 Thus Skita 2 finds that by reducing platinum chloride 
 in presence of gum arabic and an unsaturated 
 ketone a colloidal metal is produced. The colloid 
 thus obtained may, where desired, be purified in the 
 usual way by dialysis. 
 
 Perhaps the simplest method of preparing colloidal 
 platinum or palladium catalysts, provided that a 
 small sample of the colloidal metal is available, is 
 by Skita's inoculation method. Equal parts of 
 platinum or palladium chloride and gum arabic are 
 
 1 Kelber and Schwarz, Ber. 1912, 45, 1946. 
 
 2 Skita, ibid., 1909, 42, 1027- 
 
THE PREPARATION OF CATALYSTS 15 
 
 dissolved in a small quantity of water. A trace of 
 colloidal platinum, prepared either as described by 
 Skita and Meyer 1 or by any other suitable method, 
 is added and the whole reduced by hydrogen, when 
 the bulk of the reduced metal separates in a colloidal 
 state. This is not the case if no colloidal metal is 
 added. Colloidal solutions made as described are 
 stable in the presence of glacial acetic acid and may 
 be used for the hydrogenation of organic substances 
 soluble in this but insoluble in water. 
 
 1 Skita and Meyer, Ber., 1912, 45, 
 
CHAPTER III 
 
 THE METHODS OF CATALYTIC HYDROGENATION 
 
 THE methods employed for catalytic hydrogenation 
 will be governed by the state of aggregation of the 
 body to be treated, and by the temperature at 
 which the proposed reduction can be most satis- 
 factorily effected. The methods of treatment may 
 therefore be divided into two classes, the first of 
 which deals with the hydrogenation of gases, in- 
 cluding the vapours of volatile substances, while 
 the second relates to the hydrogenation of liquids. 
 
 Vapour Treatment. 
 
 The original hydrogenation work of Sabatier 
 and Senderens was carried out by passing the vapour 
 of various unsaturated organic bodies together with 
 hydrogen over a catalytically active metal contained 
 in a heated tube. A large excess of hydrogen is 
 usually desirable, and complete saturation in one 
 passage is seldom attained. 
 
 For cases where a very exact regulation of the 
 relative proportions of hydrogen and unsaturated 
 body is not necessary, the apparatus shown in Fig. i 
 may be employed. 
 
 This consists of a distilling flask, A , containing the 
 unsaturated substance and heated by a Bunsen 
 flame, or, where the body is Jiable to boil with 
 decomposition, by means of a water- or oil-bath. 
 A current of pure hydrogen, obtained for convenience 
 
 16 
 
THE METHODS OF HYDROGENATION 17 
 
 from a cylinder, is passed into the distillation flask, 
 and carries with it into the reaction tube, B, a 
 
 quantity of vapour depending on the temperature 
 in A, and on the velocity of the current of hydrogen. 
 
i8 
 
 CATALYTIC HYDROGENATION 
 
 It is usually sufficient to regulate roughly this 
 gas current by observing its rate of passage through 
 A, but if it is desired to maintain this at a strictly 
 
 FIG. 2. 
 
 constant value, a flow meter, which is conveniently 
 of the simple form illustrated on a larger scale in 
 Fig. 2, may be interposed between the cylinder 
 and the distilling flask. 
 
THE METHODS OF HYDROGENATION 19 
 
 This meter consists of a tube with a capillary 
 constriction as shown in the figure, through which 
 tube the hydrogen current is passed, the velocity 
 _of passage being measured by the difference in 
 pressure between the two extremities of the capillary 
 portion, as indicated by the movement of the liquid 
 in the U-tube. The scale is calibrated once for 
 all in litres per hour by actual trial with hydrogen 
 currents of known velocity, measured by collecting 
 in a gasholder the hydrogen which leaves the meter 
 in a given time for a certain difference of pressure. 
 
 In any case the mixture of hydrogen and un- 
 saturated vapour passes into the reaction chamber, 
 
 B, which consists of a glass or, better, silica- 
 tube mounted in an air-bath and heated in a com- 
 bustion furnace to the temperature required. It 
 is usual to support the catalyst in B by precipitation 
 on to pumice or purified asbestos, but the catalyst 
 may also be employed in the briquette form already 
 described. In making up briquettes it is, of course, 
 essential that the porous binding material, with 
 which the catalytic body is mixed, should be inert 
 towards the compound to be hydrogenated at the 
 temperature employed for treatment. After passage 
 over the heated catalyst, the mixture of vapour 
 and hydrogen passes into the condensing apparatus, 
 
 C, in which a separation of gas from condensed 
 liquid is effected. The apparatus described has 
 shown itself particularly adapted for the hydrogena- 
 tion of benzene and other aromatic hydrocarbons. 
 
 Should the hydrogenated product be solid at the 
 ordinary temperature, a wide straight tube, inclined 
 downwards and cooled either by a water-jacket or 
 by air, should be substituted for the condenser 
 shown, the product being run out of this receiver, 
 when necessary, by warming. 
 
 If a more exact control of the rate of passage of 
 the unsaturated body is desired, a bent burette 
 may be substituted for the distilling flask as shown 
 
 2 2 
 
20 CATALYTIC HYDROGENATION 
 
 in Fig. 7 (see Chapter V), which illustrates Sabatier 
 and Senderens's original apparatus. 
 
 For the hydrogenation of permanent gases, such 
 as ethylene and propylene, it is usually sufficient to 
 mix these in a gasholder with the required volume 
 of hydrogen and to pass the mixture over a heated 
 tube containing catalyst, the product being collected 
 in a second gasholder. In some cases, for instance 
 with acetylene, the reaction is so vigorous that 
 caution must be observed with regard to heating the 
 catalyst employed, and the air-bath may be replaced 
 by immersion of the reaction tube in a water- or 
 oil-bath, the temperature of which is capable of 
 being more accurately controlled, this bath being 
 preferably provided with an automatic temperature 
 regulator of any standard type. 
 
 Hydrogenation of Liquids. 
 
 The methods of procedure usually adopted on 
 a laboratory scale for the hydrogenation of liquids 
 may be subdivideed into three types, according to 
 whether the necessary intimate contact between the 
 liquid, gaseous and solid (i.e., the catalyst) phases of 
 the system undergoing treatment is induced by 
 simple bubbling, by shaking, or by stirring respec- 
 tively. 
 
 Hydrogenation by Bubbling. The bubbling 
 method, first described by Normann in T-903, 1 
 constitutes a simple and effective method of hydro- 
 genating a non-volatile liquid. The liquid, con- 
 taining a suitable catalyst in suspension, is con- 
 tained in a conical beaker or, better, in a distilling 
 flask a rapid stream of pure hydrogen, which 
 serves the double purpose of agitation and hydro- 
 genation proper, being led through. The distilling 
 flask may be tilted in order to prevent expulsion 
 of the liquid by "the rapid current of gas, and the 
 
 1 Normann, English patent 1515, 1903. 
 
THE METHODS OF HYDROGENATION 21 
 
 hydrogen inlet tube slightly bent, as in a distillation 
 in steam. For a full discussion of the necessity 
 for a rapid stream of hydrogen and of other necessary 
 experimental conditions, more particularly from the 
 point of view of the hydrogenation of oils by the 
 bubbling method, the evidence given in the Patents 
 case, Crosfield v. Techno-Chemical Laboratories, 
 Ltd., 1 may be consulted. The excess of hydrogen is 
 usually large enough to preclude the determination 
 of the degree of hydrogenation of the unsaturated 
 body by a direct measurement of the hydrogen 
 absorbed, but it is usually possible to estimate this 
 indirectly, for instance by an iodine value determi- 
 nation. 
 
 A description of the standard methods employed 
 for this is included in a later chapter. 
 
 Hydrogenation by Shaking, etc.-f- According to this 
 method, with which are associated the names, 
 inter alia, of Paal, Willstatter and Skita, the liquid 
 to be treated is contained in a glass vessel of suitable 
 size, mounted in a shaking apparatus and connected 
 with a known volume of hydrogen, the absorption 
 of which can be read off from time to time as the 
 reaction proceeds. The method may be used for 
 the reduction of liquids proper or of solids dissolved 
 in a suitable solvent such as water, alcohol, glacial 
 acetic acid, acetone, ether, or chloroform. 
 
 The apparatus employed will depend on the 
 weight of substance taken, and on the temperature 
 and pressure at which the reduction is to be carried 
 out. In its simplest form and for work at atmos- 
 pheric temperature and pressure it may consist of 
 a shaking vessel, mounted in a shaker of any standard 
 design, such as may readily be bought from stock 
 or if desired constructed in the laboratory. This 
 shaking vessel, A, is connected (see Fig. 3) to a 
 gasholder of hydrogen, B, by means of a metal 
 
 1 Patents Journal, 30, Supplement, June 18, 1913, Reports of 
 Cases No. 12. 
 
22 CATALYTIC HYDROGENATION 
 
 spiral or thick-walled rubber tubing. If desired, 
 access of moisture from the gasholder may be 
 prevented in the usual way by the interposition of 
 a drying tube containing freshly fused calcium 
 chloride shown at C. For the preliminary displace- 
 ment of air by hydrogen a side tap, D, is provided, 
 connected when required to a vacuum, the hydro- 
 genation vessel and drying tube being alternately 
 evacuated (E being closed) and filled with hydrogen 
 
 FIG. 3. 
 
 from the holder several times before starting an 
 experiment. 
 
 The progress of absorption can be followed approxi- 
 mately by noting the diminution in volume of the 
 hydrogen contained in B. Should the velocity of 
 hydrogenation fall off unduly owing to the accumu- 
 lation of gaseous impurities in the shaking vessel, 
 the contents ol this may be pumped out from time 
 to time through D, fresh hydrogen being admitted 
 through E. It is to be noted, however, that the 
 velocity of absorption necessarily falls off as the 
 saturation proceeds owing to the disappearance of 
 
THE METHODS OF HYDROGENATION 23 
 
 unsaturated molecules. Fokin 1 has shown that the 
 course of the saturation with hydrogen of a double 
 bond at constant temperature and pressure follows, 
 as would be expected, the ordinary monomolecular 
 formula : 
 
 in which a instead of being 
 expressed in terms of un- 
 saturated substance may con- 
 veniently be taken as the 
 total volume of hydrogen 
 absorbable by the weight of 
 unsaturated body taken for 
 treatment, x being the 
 volume of hydrogen actually 
 absorbed after time /. 
 
 For successful hydrogena- 
 tion the necessity for hydro- 
 gen of the highest purity 
 cannot be too strongly empha- 
 sised. A suitable gas may be 
 prepared by electrolysis and 
 subsequent elimination of the 
 small percentage of oxygen 
 usually present in such a gas 
 (by passage over heated nickel 
 or palladium) or, more con- 
 veniently, hydrogen of suit- 
 able purity may readily be 
 bought in a compressed state 
 in cylinders. 
 
 If the hydrogenation is to be carried out at an 
 elevated temperature the reaction vessel is shaken 
 in a bath maintained at the temperature required 
 by means of an automatic thermo-regulator. It 
 has also been proposed to heat the shaking vessel 
 1 Fokin, /. Russ. Phys. Chem. Soc., 1908, 40, 276. 
 
 FJG. 4. 
 
24 CATALYTIC HYDROGENATION 
 
 internally by means of a small electric lamp as 
 shown in Fig. 4, a thermometer being inserted 
 through the second neck. 
 
 Further, instead of employing a regular shaker 
 it is also possible to obtain satisfactory results 
 with a distilling flask provided with an efficient 
 rotating stirrer, the apparatus being sealed off from 
 
 FIG. 5. 
 
 the air by means of liquid seals in the usual manner 
 and attached to a supply of hydrogen. In this case, 
 the air is of course displaced by means of a hydrogen 
 current instead of by evacuation. An apparatus 
 of this type has been employed by Reid 1 for the 
 treatment of gases such as ethylene, the catalyst 
 being suspended in paraffin or other inert liquid 
 medium. 
 
 1 Reid, /. Amer. Chem. Soc., 1915, 37, 2112. 
 
THE METHODS OF HYDROGENATION 25 
 
 The above types of apparatus admit of only a 
 very approximate measurement of the volume of 
 hydrogen absorbed, and for cases where it is necessary 
 to follow more exactly the course of absorption 
 the apparatus shown in Fig. 5 may be employed. 
 
 This consists of a gas burette, A, containing hydro- 
 gen and connected by way of the calcium chloride 
 drying tube, C, to the shaking vessel, D. B is a 
 hydrogen supply burette by means of which a 
 known volume of hydrogen can be added to the 
 system A C D as required. 
 
 To use the apparatus, the substance to be hydro- 
 genated is mixed with catalyst and run into D, 
 the connecting rubber or flexible copper tube being 
 for this purpose removed and afterwards re- 
 connected. A and B are filled with boiled water to 
 the top of the taps G and H. The three-way tap, 
 E, is then connected by means of its two branches 
 to a vacuum and to a hydrogen supply respectively, 
 and, G and H being closed, the system A C D is 
 alternately evacuated and filled with hydrogen by 
 operating the three-way tap, E. 
 
 After several evacuations and subsequent fillings, 
 G is opened and hydrogen allowed to flow into it 
 from the supply at E. As soon as A is filled down to 
 the lower mark (250 c.c. is a convenient volume), 
 E is closed and the hydrogen supply removed, 
 D being, of course, not shaken up to this point. 
 The filling being now complete, the hydrogen in the 
 measuring burette, A, is adjusted to atmospheric 
 pressure and its volume noted, this burette being 
 placed in communication with the shaking vessel, 
 and this latter being adjusted in its heating bath, 
 if one is used. Shaking is now begun and the course 
 of the absorption followed by noting the diminution 
 of the volume of hydrogen in A, adjusted to atmos- 
 pheric pressure by means of the water reservoir 
 attached to it. 
 
 As soon as the gas in A is nearly absorbed, a 
 
26 
 
 CATALYTIC HYDROGENATION 
 
 hydrogen supply is connected to F, and, by operating 
 the three-way cock, H, a convenient "amount is 
 allowed to pass into B, the volume added being 
 read off after adjusting levels. This known volume 
 is now added to the system A CD by turning H 
 and raising the reservoir attached to B, that attached 
 to A being temporarily lowered. Hydrogen is 
 added to the system in this way from B from time 
 to time as required by the absorption, the hydrogen 
 
 FIG. 6. 
 
 supply remaining connected to F during the whole 
 of the experiment. 
 
 For work at an increased pressure, an apparatus 
 designed by Skita and Meyer 1 and illustrated in 
 Fig. 6, is to be recommended. 
 
 This consists of a closed copper vessel provided 
 with a sight glass and a manometer, and connected 
 to the shaking vessel by means of a flexible spiral 
 copper tube. The hydrogen contained in the 
 apparatus is maintained at an elevated pressure by 
 
 ajnd Meyer, Ber., 1912, 45, 3370- 
 
THE METHODS OF HYDROGENATION 27 
 
 means of the head of water existing in the laboratory 
 mains, and may be regulated as desired by inter- 
 posing in the path of the water a mercury column of 
 suitable height, arranged to act as a valve in that it 
 releases the water in excess of that necessary for 
 the maintenance of the pressure desired. The 
 greater part of Skita's work with this apparatus 
 was carried out at an excess pressure of about one 
 atmosphere. 
 
 For work at higher pressure still, it is of course 
 possible to connect a hydrogen cylinder provided 
 with a reducing valve directly to a shaking vessel, 
 which may, if the pressure is extremely high, be of 
 copper instead of glass. Ipatiew has reduced many 
 compounds at pressures up to 150 atmospheres 
 in a stationary reaction vessel provided with a 
 carefully-packed stirrer, but such high pressures 
 are seldom required in practice. 
 
 The pressure employed plays, however, an impor- 
 tant part, not only in directing the speed of the 
 reaction, but even in deciding the nature of the 
 product. This is particularly the case where easily 
 reducible chains or rings are attached to nuclei 
 which are less susceptible to reduction. 
 
 Many reactions, on the other hand, not only 
 require no excess pressure for their successful 
 realisation, but will even proceed in such a way that, 
 if the hydrogen supply is cut off, a vacuum is pro- 
 duced by absorption of the gas present in the 
 shaking vessel. 
 
CHAPTER IV 
 
 THE HYDROGENATION OF UNSATURATED CHAINS 
 
 THE preceding chapters of this book have dealt 
 with the general methods of catalytic hydrogenation 
 and with the preparation of suitable catalysts. 
 Attention will now be paid to some of the results 
 which have been obtained by the introduction of 
 hydrogen into unsaturated molecules, this particular 
 chapter being devoted to the saturation by hydrogen 
 of ethylenic and acetylenic bonds between carbon 
 atoms. 
 
 Unsaturated Hydrocarbons. 
 
 The simplest ethylenic hydrocarbon is ethylene 
 itself. The hydrogenation of ethylene to ethane 
 was described by Sabatier and Sender ens 1 in 1897. 
 Ethylene together with an excess of hydrogen was 
 led at 35-40 C. over nickel, freshly reduced from 
 the oxide at 300 C. A considerable rise in tempera- 
 ture takes place and ethane results. 
 
 A similar synthesis of ethane from ethylene and 
 hydrogen, using other metals as catalysts, is des- 
 cribed by Sabatier and Senderens in a later paper. 2 
 On passing the ethylene-hydrogen mixture over 
 freshly reduced cobalt, a slight reaction was obtained 
 even in the cold. This, however, soon stopped 
 
 1 Sabatier and Senderens, Compt. rend., 1897, 124, 616. 
 
 2 Sabatier and Senderens, ibid., 1900, 130, 1761. 
 
 28 
 
UNSATURATED CHAINS 29 
 
 owing to the deposition of a layer of carbon on the 
 catalyst. At 100-150 C., in presence of nickel, 
 the reduction takes place more readily, and this 
 appears to be the most suitable temperature region 
 for the reaction. At temperatures above 300 C. 
 condensation and secondary products begin to be 
 formed. 
 
 Finely divided copper does not begin to induce 
 the reaction until 180 C. Between this and 300 C. 
 the product consists of ethane, accompanied by 
 only traces of methane and higher hydrocarbons. 
 Iron, even when reduced below 400 C., is far less 
 active than cobalt or copper. The reaction starts 
 at 1 80 C., but soon stops on account of carbon 
 deposition. Platinum black 1 was found to be 
 active even at the ordinary temperature, but to 
 lose this activity quickly owing to deposition of 
 carbon. The most satisfactory reaction temperature 
 is 180 C. 
 
 Propylene, and the higher ethylenic hydrocarbons 
 generally, may easily be hydrogenated in a similar 
 manner by leading the hydrocarbon in the gaseous 
 state mixed with excess of hydrogen over finely 
 divided nickel at 160 C. 2 At temperatures above 
 200 C. the hydrocarbon chain is ruptured, and the 
 formation of simpler methane hydrocarbons and 
 complex condensation products in small quantities 
 is observed. In the case of hydrocarbons boiling 
 at temperatures considerably above the atmos- 
 pheric temperature, the hydrogenation may often 
 be more conveniently carried out by the bubbling or 
 shaking methods already described, using either 
 colloidal platinum or palladium, or finely divided 
 nickel at a higher temperature, as catalyst. 
 The unsaturated body may also be dissolved in 
 alcohol, ether, or glacial acetic acid, and saturated in 
 the dissolved condition. 
 
 1 Sabatier and Senderens, Compt. rend., 1900, 131, 40. 
 
 2 Sabatier and Senderens, ibid., 1902, 134, 1137. 
 
30 CATALYTIC HYDROGENATION 
 
 The reduction of ethylene and other unsaturated 
 aliphatic hydrocarbons may also be carried out at 
 the ordinary temperature in presence of colloidal 
 palladium or platinum. Thus Paal and Hartmann 1 
 found that on shaking an aqueous solution of 
 colloidal palladium, in presence of a protective 
 colloid, with a mixture of equal volumes of hydrogen 
 and ethylene contained in a gas burette, hydrogena- 
 tion to ethane took place rapidly, accompanied 
 by a contraction of the gas mixture to one-half its 
 initial volume. 
 
 The hydrogenation of unsaturated side chains 
 attached to aromatic nuclei, with or without the 
 saturation of the aromatic nucleus itself, has also 
 been effected. Thus, Sabatier and Senderens 2 found 
 that by leading styrolene together with hydrogen 
 over heated copper, ethyl benzene resulted, the 
 ethylene portion only being reduced. 
 
 On substituting nickel for copper the benzene 
 nucleus in addition to the side chain was attacked, 
 with production of ethyl hexahydrobenzene : 
 
 CH CH 
 
 HCUCH HCCH 
 
 CH CH 
 
 CH CH 2 
 
 HC^\C-CH:CH 2 -f 4 H 2 Rf,/\CH- 
 HCl "CH s H 2 d 'CH 
 
 CH CH 2 
 
 The reduction of hydrocarbons containing more 
 than one ethylenic linkage has been studied by 
 Kelber and Schwarz, 3 who find that aromatic 
 
 1 Paal and Hartmann, Bar., 1909, 42, 2239. 
 
 2 Sabatier and Senderens, Compt. rend., 1901, 132, 1254. 
 
 3 Kelber and Schwarz, Ber., 1912, 45, 1946. 
 
UNSATURATED CHAINS 31 
 
 derivatives of butadiene are easily converted into 
 compounds possessing a saturated aliphatic portion 
 by hydrogen in presence of colloidal palladium pro- 
 tected from coagulation by " degraded " gluten. 
 
 Unsaturated Alcohols and Ethers. 
 
 The non-catalytic reduction of unsaturated alco- 
 hols by nascent hydrogen is often an operation of 
 extreme difficulty, even the lower members of the 
 series, such as allyl alcohol, being scarcely attacked. 
 By means of hydrogen in presence of a catalyst, 
 the ethylenic alcohols may without exception be 
 easily reduced to the corresponding saturated com- 
 pounds, and even, if desired, to the hydrocarbons 
 themselves. 
 
 The most suitable catalysts are colloidal platinum 
 or palladium, the operation being carried out in a 
 shaker and stopped when the desired volume of 
 hydrogen has been absorbed. 
 
 From allyl alcohol, normal propyl alcohol is 
 obtained : 
 
 CH 2 :CH-CH 2 -OH +H 2 =CH 3 -CH 2 -CH 2 -OH. 
 
 Similarly, crotonyl alcohol yields normal butyl 
 alcohol. 
 
 Bouveault and Blanc 1 studied the reduction of 
 some higher unsaturated alcohols in presence of 
 non-colloidal platinum black. The saturation of 
 these higher alcohols seems to be accompanied by 
 the reduction of the hydroxyl group, saturated 
 hydrocarbons being obtained in addition to the 
 corresponding saturated alcohol. From oleic alcohol 
 Bouveault and Blanc prepared octadecyl alcohol, 
 C 18 H 37 'OH, and from erucyl alcohol docosyl alcohol, 
 
 1 Bouveault and Blanc, Bull., 1904 (3), 31, 1210. 
 
32 CATALYTIC HYDROGENATION 
 CH 3 (CH 2 ) 7 -CH:CH(CH 2 ) 8 -OH +H 2 = 
 
 Oleic alcohol. 
 
 CH 3 (CH 2 ) 17 -OH 
 
 Octadecyl alcohol. 
 
 CH 3 (CH 2 ) 7 -CH:CH(CH 2 ) 12 -OH+H 2 = 
 
 Erucyl alcohol. 
 
 CH 3 (CH 2 ) 21 -OH, 
 
 Docosyl alcohol. 
 
 The hydrogenation of some higher secondary 
 ethylenic alcohols was undertaken by R. Douris 1 
 at 195-200 C. in presence of nickel. He found that, 
 at this high temperature, very little, if any, of the 
 corresponding saturated alcohol was obtained, the 
 reaction proceeding as far as the corresponding 
 saturated hydrocarbon. 
 
 The alcohols studied included propenyl isoamyl 
 carbinol, 
 
 CH 3 -CH:CH-CH(OH)-CH 2 -CH 2 -CH(CH 3 ) 2 , 
 and vinyl isobutyl carbinol, 
 
 CH a :CH-CH(OH)-CH a -CH(CH,) a . 
 
 Douris found that the reaction product always 
 contained a saturated ketone, formed by intramole- 
 cular change thus : 
 
 R-CH:CH-CH(OH)-R=R-CH 2 -CH 2 -CO-R. 
 
 Ipatiew, 2 working with nickel at 95 C. (3 grams of 
 nickel in 30 grams of anethol) under a hydrogen 
 pressure of 50 atmospheres, succeeded in hydro- 
 genating anethol to the dihydro-compound in four 
 hours : 
 
 C-CH:CH-CH 3 C-CH 2 -CH 2 -CH 3 
 
 HC/VH HC/VH 
 
 Hd'CH M2 : HCli^CH 
 
 C-OCH 3 C-OCH 3 
 
 1 R. Douris, Compt. rend., 1913, 157, 55. 
 
 2 Ipatiew, Ber., 1913, 46, 3589. 
 
UNSATURATED CHAINS 33 
 
 By continuing the hydrogenation at 200 C. for 
 twenty hours, hexahydropropyl benzene was formed, 
 a methoxy-group being split off. 
 
 Similarly, eugenol, CH 8 O-C H 3 (OH)-CH 2 -CH:CH 2 , 
 was reduced to dihydroeugenol in presence of nickel 
 at 95 C. On raising the temperature to 195 C. 
 and continuing the reduction for seven hours longer, 
 a mixture of hexahydroanethol and octahydro- 
 eugenol was obtained. Isoeugenol, on being re- 
 duced with nickel for two hours at 95 C., yielded 
 the normal dihydro-compound identical with that 
 obtained from eugenol. 
 /O 
 
 Safrol, CH/ >C 6 H 3 -CH 2 -CH:CH 2 , was similarly 
 
 X CX 
 
 reduced to the dihydro-compound by the introduc- 
 tion of two hydrogen atoms into its side chain in 
 presence of nickel at 95 C., working for two hours in 
 a pressure apparatus. 
 
 On raising the temperature to 180 C. and con- 
 tinuing the reduction, oxygen was split off and an 
 isomer of hexahydroanethol produced. Isosafrol, 
 
 /\ 
 
 CH 2 < >C 6 H 3 -CH:CH-CH,, yielded, as would be 
 
 ' MK 
 
 expected, a dihydro-product indentical with that 
 obtained from safrol. 
 
 The hydrogenation of geraniol has been studied 
 by Willstatter 1 and by Enklaar, 2 using platinum or 
 palladium as a catalyst. 
 
 Aldehydes and Ketones. 
 
 The hydrogenation in presence of colloidal palla- 
 dium of acrolein, the simplest olefinic aldehyde, has 
 been investigated by Skita. 3 In addition to the 
 normal hydrogenation product, propionic aldehyde, 
 
 1 Willstatter, Ber., 1908, 41, 1478. 
 
 2 Enklaar, ibid., 1908, 41, 2084. 
 
 3 Skita, ibid., 1912, 45, 3312. 
 
34 CATALYTIC HYDROGENATION 
 
 some allyl alcohol, resulting from the reduction of the 
 aldehydic group, was obtained. 
 
 CH 2 :CH-CHO +H 2 =CH 3 -CH 2 -CHO 
 CH 2 :CH-CHO +H 2 =CH 2 :CH-CH 2 -OH 
 Various unsaturated ketones and aldehydes have 
 been reduced by Ipatiew with hydrogen under high 
 pressure, methyl ethyl acrolein, for instance, being 
 converted into methyl isobutyl ketone, while mesityl 
 oxide gave a mixture of methyl isobutyl ketone and 
 carbinol : 
 
 CH 8 -CO-CH:C(CH 3 ) 2 -f-H 8 == 
 
 Mesityl oxide. 
 
 CH 8 -CO;CH 2 -CH(CH a ) 2 
 
 Methyl isobutyl ketone. 
 
 CH 3 -COCH 2 -CH (CH 3 ) 2 +H 2 - 
 
 CH 3 -CH-OH-CH a -CH(CH 8 ) 2 
 
 Methyl isobutyl carbinol. 
 
 Skita 1 has since obtained a similar result with 
 methyl ethyl acrolein at the ordinary pressure in 
 presence of palladium. 
 
 The hydrogenation of aldehydes and ketones 
 containing several ethylenic linkages has been 
 described by Borsche, 2 who states that, in general, 
 when working according to Paal's method, highly 
 unsaturated ketones containing one double linkage 
 on each side of the CO group are easily converted 
 with a good yield into the corresponding saturated 
 body. If, however, either side of the CO group 
 contains more than one double linkage, the yield 
 of the normal reduction product is diminished very 
 considerably by the formation of resinous bodies. 
 
 Thus dibenzal acetone, 
 
 C 6 H 5 -CH:CH-CO-CH:CH-C 6 H 5 , 
 
 is capable of easy and quantitative reduction. With 
 cinnamal acetophenone, 
 
 C 6 H 5 -CO-CH:CH-CH:CH-C 6 H 5 , 
 
 1 Skita, Ber., 1915, 48, 1486. 2 Borsche, 1912, ibid., 45, 46. 
 
UNSATURATED CHAINS 35 
 
 and still more so with benzal cinnamal acetone, 
 C 6 H 5 -CH:CH-CO-CH:CH-CH:CH-C 6 H 5 , 
 
 side reactions occur. 
 
 Skita, 1 using colloidal palladium in alcoholic 
 solution, with gum arabic as a protective colloid, 
 reduced phorone by the addition of 6 atoms of 
 hydrogen to di-isobutyl carbinol while isophorone 
 was converted into dihydroisophorone. 
 
 Ipatiew 2 succeeded in preparing the saturated 
 alcohol decanol by the reduction of citral. Skita 3 
 had previously only been able to hydrogenate citral 
 to a mixture of citronellal and citronellol, one double 
 bond being left unsaturated : 
 
 CH 3 
 (CH 3 ) 2 -C:CH'CH 2 -CH 2 -C:CH-CHO +H 2 = 
 
 Citral. 
 
 CH 3 CH 3 
 
 CH 2 :C-CH 2 -CH 2 -CH a -C-CH 2 -C HO 
 
 Citronellal. 
 
 CH 3 
 (CH,) 2 -C:CH-CH 2 -CH a -C:CH-CHO +3H 2 = 
 
 Citral. 
 
 CH 3 
 (CH 3 ) 2 -CH(CH 2 ) 3 -C'CH 2 -CH 2 -OH 
 
 Decanol. 
 
 Acids and Esters. 
 
 While the lower unsaturated fatty acids such as 
 acrylic acid are attacked more or less readily by 
 nascent hydrogen, the higher members of the 
 series, on the other hand, are not affected. It is 
 
 1 Skita, 1909, Ber., 42, 1630. 2 Ipatiew, 1912, ibid., 45, 3218, 
 3 Skita, loc. cit. 
 
 32 
 
36 CATALYTIC HYDROGENATION 
 
 for this reason that the commercial manufacture 
 of stearic acid from oleic acid only became possible 
 after Saba tier's work on the activation of free 
 gaseous hydrogen by nickel and other metals. 
 The so-called hardening of technical fats and oils 
 will receive special attention in a later chapter, 
 and it is therefore proposed to deal here only with the 
 laboratory side of the question. 
 
 The unsaturated fatty acids are as a class ex- 
 tremely easily hydrogenated by any of the methods 
 already described. This applies also to the un- 
 saturated dibasic acids and to unsaturated acid 
 chains attached to an aromatic nucleus. Thus, 
 employing colloidal metals of the platinum group 
 as catalyst Paal and Gerum 1 reduced fumaric, maleic 
 and cinnamic acids to the corresponding saturated 
 compounds. 
 
 Paal's method of hydrogenation of the sodium 
 salts in aqueous solution has been extended by 
 Boeseken, van der Weide and Mom 2 to acids such as 
 crotonic, cinnamic, sorbic, and undecylenic. These 
 investigators found further that an accumulation 
 of carboxyl groups round the unsaturated linkage 
 impeded hydrogenation. 
 
 Oleic acid in ethereal solution was reduced to 
 stearic acid by Fokin 3 with platinum metal catalysts, 
 a 90 per cent, yield of stearic acid being reported. 
 R. Willstatter 4 effected a more rapid reduction of 
 oleic acid, using platinum black prepared according 
 to Low's method. 5 
 
 The use of hydrosols of the platinum metals 
 was introduced by Paal and Roth, 6 who hydro- 
 
 1 Paal and Gerum, Ber., 1908, 41, 2273. 
 
 2 Boeseken, van der Weide, and Mom, Rec. trav. chim. Pays-Bas, 
 1916, 35, 260. 
 
 3 Fokin, Chem. Centralblatt, 1906 (ii), 758 ; 1907, (i), 324, (ii), 
 1324. 
 
 4 Willstatter, Bey., 1908, 41, 1475. 
 
 5 Low, ibid., 1890, 23, 289. 
 
 6 Paal and Roth, ibid., 1908, 41, 2282. 
 
UNSATURATED CHAINS 37 
 
 genated in this way both the alkali salts of the fatty 
 acids and the natural fats. Castor oil was re- 
 duced by these investigators in alcoholic solution ; 
 olive and fish oils in the form of an emulsion with 
 water, containing a little gum arabic as a protective 
 colloid. In a later paper 1 a similar hydrogenation 
 of croton, sesame, cotton and linseed oils, also butter 
 fat and lard, is described. 
 
 It is not, however, necessary to dissolve the 
 unsaturated fatty acid or glyceride in any way. 
 A satisfactory method of carrying out the hydro- 
 genation on a laboratory scale is to mix intimately 
 with the oil or other substance sufficient finely 
 powdered platinum or palladium oxide or palladium 
 chloride to give on reduction o-i gram of platinum 
 or palladium for every 100 grams of the oil. The 
 oil and catalyst are either treated in a shaker in 
 the usual way or hydrogenated by simple passage of 
 a rapid current of hydrogen, this operation being 
 with advantage carried out at a temperature of 
 100 C. or even higher. 
 
 If it is desired to use nickel as a catalyst, this 
 may be reduced from oxide and added to the oil 
 in the proportion of about i per cent., the hydro- 
 genation being carried out at about 200 C. or 
 lower if desired. The nickel oxide may also be 
 added as such to the oil and the hydrogenation 
 carried out by passing a rapid current of hydrogen 
 through the mixture heated to 250-260 C. in an 
 oil-bath according to Bedford and Williams's 
 method. For fatty acids which are easily volatile 
 in a current of hydrogen, Sabatier's vapour method 
 of treatment may well be used. 
 
 Borsche 2 has obtained various new or difficultly 
 prepared acids containing several double bonds. 
 S-Phenyl valeric acid was prepared from cinnamenyl 
 
 1 Paal and Roth, Per., 1909, 42, 1541. 
 
 2 Borsche, ibid., 1912, 45, 620. 
 
38 CATALYTIC HYDROGENATION 
 
 acrylic acid, C 6 H 5 -CH:CH-CH:CH-COOH ; phenyl 
 w-propyl malonic acid, 
 
 C 6 H 5 -CH 2 -CH 2 -CH 2 -CH(COOH) 2 , 
 from cinnamal malonic acid, 
 
 C 6 H 5 -CH:CH-CH:C(COOH) 8 . 
 
 On heating this saturated acid, carbon dioxide was 
 given off and phenyl valeric acid produced. 
 
 Similarly, w-phenyl w-propyl cyanacetic acid 
 was obtained from cinnamal cyanacetic acid, 
 C 6 H 5 -CH:CH-CH:C(CN)-COOH, aS-diphenyl valeric 
 acid from cinnamal phenyl acetic acid, and 
 aS-diphenyl valeric -nitrile from cinnamal benzyl 
 cyanide, C 6 H 5 -CH:CH-CH:C(C 6 H 5 )-CN. 
 
 The hydrogenation of various highly unsaturated 
 bodies, including cinnamal malonic acid, has also 
 been studied by Paal. 
 
 Reduction of Unsaturated Halogen Compounds. 
 
 Attempts to obtain the corresponding saturated 
 halogen bodies have not been successful with 
 certain aromatic derivatives of ethylene, the hydro- 
 genation of which was investigated by Borsche and 
 Heimbiirger. 1 o>-Bromostyrolene, for instance, was 
 found to pass by hydrogenation and elimination of 
 hydrobromic acid into ethyl benzene, while methyl- 
 ene dioxy-w-chlorostyrolene gave the methylene 
 ether of ethyl pyrocatechin : 
 
 ,CH:CHBr+2H 2 ' x f CH 2 -CH 3 -f HBr 
 
 a-Bromostyrolene. Ethyl benzene. 
 
 The Saturation of Acetylenic Bonds. 
 
 Acetylene and its homologues, as a class, combine 
 with free or nascent hydrogen even more readily 
 than the olefines. 
 
 1 Borsche and Heimbiirger, Ber,, 1915, 48, 452. 
 
UNSATURATED CHAINS 39 
 
 The hydrogenation of acetylene itself to ethane 
 in presence of platinum black was described in 
 1874 by de Wilde. 1 Sabatier and Senderens, 2 work- 
 ing later on the same subject, found that copper, 
 cobalt, iron, and, above all, nickel could be 
 substituted for' the platinum black, but that 
 the energy of the reaction, combined with the 
 endothermic nature of acetylene, led to the for- 
 mation of polymeric products and to the libera- 
 tion of free carbon. These phenomena also resulted 
 by leading acetylene alone over various finely 
 divided metals, hydrogen being absent. 8 The hydro- 
 genation begins with platinum black at the ordinary 
 temperature, with nickel at about 100 C., while 
 copper, iron, and cobalt require temperatures lying 
 between 130 C. and 200 C. 
 
 A more satisfactory reaction, accompanied by 
 a quantitative yield and absence of by-products, 
 may be obtained by shaking a mixture of hydrogen 
 and acetylene with an aqueous suspension of colloidal 
 platinum or palladium. 
 
 A further and interesting example of the com- 
 parative activity of nickel and copper is furnished 
 by the hydrogenation of amyl acetylene. 4 By 
 passage, mixed with excess of hydrogen, over 
 copper at 180 C., normal amyl ethylene was pro- 
 duced, 
 
 CH 3 -(CH 2 ) 4 -CiCH+H 2 = CH 3 -(CH 2 ) 4 -CH:CH 2 , 
 
 while nickel was found to give the saturated paraffin 
 heptane, 
 
 CH 3 -(CH 2 ) 4 -CiCH+2H 2 = CH 3 -(CH 2 ) 5 -CH 3 . 
 A somewhat similar differentiation was obtained 
 
 1 De Wilde, Ber., 1874, 7, 353. 
 
 2 Sabatier and Senderens, Compt. rend., 1899, 128, 1173; 
 1900, 130, 1559, 1628 ; 1900, 131, 40. 
 
 3 Sabatier and Senderens, ibid., 1897, 124, 616 ; 1900, 130, 
 250 ; 1900, 131, 187, 267. 
 
 4 Sabatier and Senderens, ibid., 1902, 135, 87. 
 
40 CATALYTIC HYDRO GEN ATI ON 
 
 with phenyl acetylene, this being reduced in presence 
 of copper at i8oC. to ethyl benzene, or, in presence 
 of nickel, to ethyl cyclohexane, the benzene ring 
 being in this case also attacked : 
 
 CH CH 
 
 H2 
 
 CH CH 
 
 CH CH 2 
 
 Nc-CiCH H a C/\CH-CH 2 -CH 
 
 HC !)CH f5H2 H 2 d CH 
 
 CH CH 2 
 
 Paal and Hohenegger l find that the hydrogenation 
 of acetylene in presence of colloidal palladium is 
 complicated by adsorption of acetylene by the 
 palladium, so that the hydrogen, which was added 
 only in volume calculated to produce ethylene, was 
 really in effective excels, ethane resulting. It was 
 found, however, that by using colloidal palladium 
 which had already been treated with acetylene 
 and had thus lost its power of adsorbing the gas, 
 a reaction product consisting almost entirely of 
 ethylene is produced. With colloidal platinum 
 (Paal and Schwarz 2 ) adsorption of acetylene is less 
 pronounced but hydrogenation proceeds more slowly 
 and less completely than with palladium. 
 
 The hydrogenation in stages of aromatic substi- 
 tution products of acetylene has been studied by 
 Kelber and Schwarz. 3 Two grams of phenyl- 
 acetylene, dissolved in 5 c.c. of glacial acetic acid 
 together with o-i c.c. of colloidal palladium in 10 c.c. 
 of glacial acteic acid, were reduced after several 
 
 1 Paal and Hohenegger, Ber., 1915, 48, 275. 
 
 2 Paal and Schwarz, ibid., 1915, 48, 1202. 
 
 8 Kelber and Schwarz, ibid., 1912, 45, 1946. 
 
UNSATURATED CHAINS 41 
 
 hours' hydrogenation in a shaker at the ordinary 
 temperature first to styrolene, then to ethyl benzene, 
 the yield being almost quantitative : 
 
 C 6 H 5 -CiCH+H 2 C 6 H 5 -CH:CH 2 
 
 Phenyl acetylene. Styrolene. 
 
 C 6 H 5 -CH:CH 2 +H 2 = C 6 H 5 -CH 2 -CH 3 
 
 Ethyl benzene. 
 
 Similarly, tolane was found to pass into iso-stilbene 
 and finally into di-benzyl, 
 
 C 6 H 5 -C-C-C 6 H 6 -> C 6 H 5 -CH:CH-C 6 H 6 -* 
 
 while from diphenyl diacetylene a mixture of about 
 25 per cent, of cis-cis-aS-diphenyl-ay-butadiene 
 and 75 per cent., of cis-trans-aS-diphenyl-ay- 
 butadiene and finally a quantitative yield of 
 aS-diphenylbutane was obtained : 
 
 C 6 H 5 -C;C-C;C-C 6 H 5 C 6 H 5 -CH:CH-CH:CH-C 6 H 5 
 
 Diphenyldiacetylene. Diphenylbutadiene. 
 
 C 6 H 5 '(CH 2 ) 4 -C 6 H 5 
 
 Diphenylbutane. 
 
 The ease of reduction of the acetylenic union 
 renders possible the use of non-colloidal catalysts, 
 even for reactions carried out in a shaker at the 
 ordinary temperature. 
 
 Finally, Lespieau and Vavon l reduced di-allylene 
 dicarboxylic acid containing two acetylenic bonds 
 to suberic acid in presence of platinum black : 
 
 CHo-C:C-COOH CH,-CH,-CH,-COOH 
 
 ;H 2 -C:OCOOH CH 2 -CH 2 -CH 2 -COOH 
 
 Diallylene dicarboxylic Suberic acid, 
 
 acid. 
 
 1 Lespieau and Vavon, Compt. rend., 1909, 148, 1331. 
 
CHAPTER V 
 
 THE HYDROGENATION OF UNSATURATED RINGS 
 
 IT is particularly in connection with the reduction 
 of benzene and other cyclic bodies that catalytic 
 hydrogenation has opened a way for the easy prepara- 
 tion of saturated bodies which were otherwise 
 difficult to obtain. Thus hexahydrobenzene, which 
 had hitherto only been obtained directly in small 
 yield by the action of hydriodic acid on benzene 
 at high temperatures, or indirectly by means of a 
 series of complicated reactions from ^-ketohexa- 
 methylene, as demonstrated by the classical work 
 of A. von Baeyer, was prepared by Sabatier and 
 Senderens with the greatest ease by leading the 
 vapours of benzene mixed with hydrogen over a 
 nickel catalyst. 
 
 The hydrogenation of an unsaturated ring is in 
 general an endothermic process and takes place 
 with less readiness than the saturation of an ethylenic 
 or acetylenic linkage, the reaction being in the case 
 of the last two classes of bodies accompanied by 
 a considerable evolution of heat. Thus the tech- 
 nical " hardening " of oils, an operation which is 
 carried out under conditions for preventing loss of 
 heat during reaction, may be accompanied by a rise 
 in temperature of as much as 50 C. or even more 
 (see Chapter VIII). This difference has already 
 been the subject of comment in connection with the 
 saturation of styrolene, under the influence of nickel 
 and of the less energetic catalyst copper. 
 
UNSATURATED RINGS 
 
 43 
 
 It may further be noted that Ipatiew, in studying 
 the effect of hydrogen under pressure on substances 
 containing both an ethylenic bond and an un- 
 saturated benzene ring, using copper as a catalyst, 
 found that whereas the ethylenic bond was hydro- 
 genated at 270-300 C., the benzene nucleus remained 
 unattacked. When nickel was substituted for copper 
 it was found that an addition of hydrogen to the 
 ethylenic linkage took place at 95 C., while for the 
 hydrogenation of the benzene ring a temperature 
 of 185-190 C. was necessary. 
 
 Hydrogenation of the Benzene Ring. 
 
 As has already been mentioned, the direct hydro- 
 genation of benzene in presence of a nickel catalyst 
 was first carried out by Sabatier and Senderens. 1 
 
 "J= TO Co*c 
 
 FIG. 7. 
 
 Benzene, mixed with excess of hydrogen, is passed 
 over a layer of freshly reduced nickel contained in 
 a glass, or, better, silica tube. The reaction takes 
 place with appreciable velocity at 180 C., and 
 
 1 Sabatier and Senderens, Compt. rend., 1901, 132, 210, 566, 
 1254- 
 
44 CATALYTIC HYDROGENATION 
 
 appears to proceed most satisfactorily at about 
 250 C. Above 300 C. reversal (dehydrogenation) 
 sets in, hexahydrobenzene being reconverted to 
 benzene. 
 
 The reaction may well be carried out in the 
 apparatus already described for hydrogenation by 
 the " vapour " method (see Fig. i). Sabatier and 
 Senderens's original apparatus is illustrated in Fig. 7. 
 
 The nickel catalyst employed remains active for 
 a considerable time, whereas Sabatier and Senderens 
 state that cobalt and platinum black lose their 
 activity after a few minutes' use, while iron, copper, 
 and platinum sponge were found by them to be 
 inactive. 
 
 The reduction of benzene to hexahydrobenzene 
 in a shaker at the ordinary temperature has been 
 studied by Willstatter and Hatt. 1 Using as a 
 catalyst non-colloidal platinum, prepared by Low's 
 method, these investigators found that while com- 
 mercially " pure " benzene (containing traces of 
 thiophene) absorbed no hydrogen, pure benzene 
 was quantitatively reduced to the hexahydro- 
 compound. 
 
 Under the conditions employed, i gram of benzene 
 absorbed in the presence of 0-6 gram of platinum 
 the theoretical volume of hydrogen for hexahydro- 
 benzene in seven hours. 
 
 By working in glacial acetic acid solution, the 
 reduction took place more quickly and less platinum 
 could be used. Thus 3-7 grams of benzene dissolved 
 in 5 c.c. of glacial acetic acid and containing 0-4 
 gram of platinum were hydrogenated completely 
 after shaking for six hours. The addition of even 
 a trace of thiophene to pure benzene was found to 
 stop the reaction completely. Henrichsen and 
 Kaempf 2 report, however, that caoutchouc is non- 
 poisonous for the reaction. 
 
 1 Willstatter and Hatt, Ber., 1912, 45, 1471. 
 
 2 Henrichsen and Kaempf, ibid., 1912, 45, 2106. 
 
UNSATURATED RINGS 45 
 
 Ipatiew l investigated the reduction of benzene by 
 hydrogen under high pressure in presence of nickel 
 oxide. Working with 2-5 grams of benzene and 
 2 grams of nickel oxide, reduction to hexahydro- 
 benzene was obtained in i|- hours at 250 C., the 
 hydrogen pressure being 150-200 atmospheres. 
 Iron was found to be inactive for the reaction. 
 
 Toluene, xylene, cymene, and other homologues 
 of benzene are reduced with equal or even with 
 greater ease than benzene itself, both by the vapour 
 method and by treatment with hydrogen in a shaker. 
 Sabatier and Senderens state, however, that the 
 presence of long side-chains is liable to lead to 
 decomposition and to side reactions. Willstatter 
 and Hatt found that the cheapest form of toluene 
 absorbed hydrogen even more rapidly than pure 
 benzene. For instance, 1-8 grams of toluene dis- 
 solved in 3 grams of glacial acetic acid, after treat- 
 ment in a shaker in presence of 0-5 gram of platinum, 
 absorbed in 3^ hours the theoretical volume of 
 hydrogen for conversion into hexahydrotoluene, the 
 temperature being 20 C. and the pressure 725 mm. 
 
 Similar results were obtained with xylene and 
 with durene. Six grams of xylene with 0-9 gram 
 of platinum absorbed in one day at 20 C. a volume 
 of hydrogen equivalent to complete conversion 
 into hexahydroxylene. Pure durene was found to 
 be soluble with difficulty in glacial acetic acid and 
 was treated as a suspension in this medium. Two 
 grams of durene suspended in 12 grams of glacial 
 acetic acid were quantitatively hydrogenated in six 
 hours at 20 C. 
 
 The hydrogenation of benzene and toluene in 
 glacial acetic acid in presence of colloidal platinum, 
 and of gum arabic as a protective colloid, has been 
 described by Skita and Meyer, 2 normal reduction 
 products being obtained. 
 
 1 Ipatiew, Ber., 1907, 40, 1281. 
 
 2 Skita and Meyer, ibid., 1912, 45, 3579. 
 
46 CATALYTIC HYDROGENATION 
 
 Of other hydrocarbons derived from benzene, 
 diphenyl has been the subject of several investiga- 
 tions. Eijkman, 1 who first studied the reduction 
 of this compound by the vapour method in presence 
 of nickel, obtained only the semi-hydrogenated 
 C G H n -C 6 H 5 . Sabatier and Murat 2 found that if 
 the vapours of diphenyl are led over nickel at 180 C. 
 together with a large excess of hydrogen, phenyl- 
 cyclohexane is formed, as above, without an appre- 
 ciable quantity of dicyclohexyl. If, however, the 
 reaction product be further hydrogenated in the 
 presence of nickel at 160 C., dicyclohexyl is pro- 
 duced. 
 
 The varied reduction of styrolene in presence of 
 nickel and of copper has already been discussed. 
 
 The hydrogenation of the tetra-ring body cyclo- 
 butene in presence of nickel was found by Will- 
 statter and Bruce 3 to proceed normally at 100 C. 
 with formation of cyclobutane. At 200 C., however, 
 reduction proceeded to butane, the ring being 
 ruptured. 
 
 CH 9 CH CH 2 CH 2 
 
 CH 2 CH CH 2 CH 2 
 
 Cyclobutene. Cyclobutane. 
 
 C- -. "' 
 
 Hydrogenation of Naphthalene. 
 
 The direct hydrogenation of naphthalene by 
 distillation over nickel at 200 C. was first described 
 by Sabatier and Senderens. 4 
 
 Willstatter and Hatt 5 state that purest com- 
 mercial naphthalene cannot be hydrogenated in a 
 
 1 Eijkman, Chem. Weekblad., 1903, 1, 7. 
 
 2 Sabatier and Murat, Compt. rend., 1912, 154, 1390- 
 
 3 Willstatter and Bruce, Ber., 1907, 40, 3979- 
 
 4 Sabatier and Senderens, Compt. rend., 1901, 132, 1254. 
 
 5 Willstatter and Hatt, Ber., 1912, 45, 1471. 
 
UNSATURATED RINGS 47 
 
 shaker, even when dissolved in glacial acetic acid, 
 on account of its sulphur content. It may be 
 obtained sufficiently pure for reaction by about 
 twelve recrystallisations from acetone, alcohol, or 
 glacial acetic acid. For the preparation of naphtha- 
 lene in a still purer condition, the above authors 
 recommend the following indirect method. 
 
 Pure a-naphthylamine is converted into the 
 hydrazine derivative, the hydrochloride of which is 
 recrystallised and the base distilled off in a vacuum. 
 By oxidation with copper sulphate the hydrocarbon 
 is obtained pure enough readity to absorb hydrogen 
 in presence of platinum, the decahydro-derivative 
 being produced. 
 
 Willstatter and Hatt found that the reaction 
 was three times as rapid in glacial acetic acid as in 
 ethereal solution. 0-9 Gram of naphthalene in 6 
 grams of ether with 0-5 gram of platinum was 
 completely reduced after 15 hours' shaking, while 
 6 grams of naphthalene in 65 grams of glacial acetic 
 acid with 2*5 grams of platinum required five 
 hours only. 
 
 Naphthalene is also readily hydrogenated in 
 presence of colloidal platinum or palladium. 
 
 The hydrogenation of naphthalene to the deca- 
 hydro-body has also been carried out by Leroux. 1 
 
 Anthracene and other poly-ring hydrocarbons 
 may be reduced under conditions similar to those 
 described for naphthalene. Anthracene was reduced 
 to tetrahydroanthracene by Godchot 2 in presence 
 of nickel at 250 C. On effecting the reduction at 
 200 C., octahydroanthracene was formed. 
 
 The hydrogenation of phenanthrene has been 
 studied by Breteau. 3 In the presence of nickel at 
 1 60 C., using the vapour method, phenanthrene was 
 converted into a mixture of tetrahydro- and octa- 
 
 1 Leroux, Compt. rend., 1904, 139, 672. 
 
 2 Godchot, ibid., 1904, 139, 604. 
 
 3 Breteau, ibid., 1910, 151, 1368. 
 
48 CATALYTIC HYDROGENATION 
 
 hydro-phenanthrene. On dissolving phenanthrene 
 in hexahydrobenzene and hydrogenating in this 
 solvent in presence of platinum, the pure tetrahydro- 
 compound was obtained. 
 
 J. Schmidt and E. Fischer l find that phenanthrene 
 may be quantitatively reduced to 9 : lo-dihydro- 
 phenanthrene by dissolving in ether and refluxing 
 in the presence of platinum black, hydrogen being 
 passed through the liquid. 
 
 irl Jti jH.2 Hg 
 
 /=\ /~\ 
 
 s~\_s~\ > ^~\_^~\ 
 \=/ \=/ \=/ \=/ 
 
 Phenanthrene. 9 : lo-Dihydrophenanthrene. 
 
 Reduction of Rings containing a Higher Number 
 oj Carbon Atoms. 
 
 Willstatter 2 and his pupils have paid considerable 
 attention to the hydrogenation of cyclo-octene to 
 cyclo-octane. Nickel is stated to be unsuitable even 
 at low temperatures owing to side reactions. By 
 using platinum black, pure cyclo-octane was ob- 
 tained. Similarly, dimethylgranatanine was reduced 
 to dimethylaminocyclo-octane. 
 
 The reduction of other ring bodies in presence 
 of nickel oxide at a high pressure has been studied 
 by Ipatiew. 3 Fluorene after treatment with hydro- 
 gen at 1 20 atmospheres at a temperature of 29OC. 
 passed into decahydrofluorene, acenaphthene suc- 
 cessively into the tetrahydro- and decahydro-deriva- 
 tives, while retene gave decahydroretene. 
 
 1 J. Schmidt and E. Fischer, Ber., 1908, 41, 4225. 
 
 2 Willstatter and Waser, ibid., 1910, 43, 1176; Willstatter and 
 Veraguth, ibid., 1907, 40, 957 ; Willstatter and Kametaka, ibid., 
 1908, 41, 1480. 
 
 3 Ipatiew, ibid., 1909, 42, 2092. 
 
UNSATURATED RINGS 49 
 
 Reduction of Phenols. 
 
 Phenol vapour, passed, together with hydrogen, 
 over nickel at 200-300 C. is reduced to cyclohexanol, 
 which by loss of hydrogen passes into cyclohexanone. 1 
 
 OH 
 
 C CH-OH 
 
 HC^\CH HjC/NcHa 
 
 Tjp PTT i 3-*^2 TJ P PTT 
 
 1^,^ LJUxl 1 2 LA ;^r 2 
 
 CH CH 2 
 
 Cyclohexanol. 
 
 CH-OH CO 
 
 H 2 C/\CH 2 H 2 C/\CH 2 
 
 HP PTT UP PTJ ~T" -H-2 
 
 2^\ /^ Jrl 2 rt 2^\ /^ xjtrl 2 
 
 CH 2 CH 2 
 
 Cyclohexanone. 
 
 Pure cyclohexanol is obtained by reduction of 
 phenol with hydrogen in presence of nickel at 140- 
 150 C. On treating cyclohexanol with copper at 
 300 C. in absence of hydrogen, pure cyclohexanone 
 is formed. 
 
 Skita and Ritter 2 found that by distilling mixtures 
 of phenol and hydrogen over nickel considerable 
 decomposition took place, cyclohexanone, hexa- 
 hydrobenzene, and tetrahydrobenzene being formed 
 according to conditions. From m-cresol, hexa- 
 hydrotoluol and methylcyclohexanone were obtained. 
 
 Cyclohexanone was found to pass into cyclohexane 
 and by dehydrogenation into phenol. It appears, 
 .therefore, that the direct hydrogenation of phenol 
 by the vapour method is extremely liable to be accom- 
 panied by side reactions an effect which is in 
 
 1 Sabatier and Senderens, Compt. rend., 1903, 137, 1025. 
 
 2 Skita and Ritter, Ber., 1912, 45, 668. 
 
50 CATALYTIC HYDROGENATION 
 
 general not obtained in a shaker, especially at the 
 ordinary temperature. The direct hydrogenation of 
 polyphenols to hexahydro-compounds by the vapour 
 method at 130 C. has also been studied by Sabatier 
 and Mailhe. 1 
 
 Acids and Esters. 
 
 Benzoic acid was found by Skita and Meyer 2 to 
 absorb 6 atoms of hydrogen when treated in a shaker 
 in presence of colloidal platinum or palladium, 
 hexahydrobenzoic acid being produced. 
 
 The hydrogenation of benzoic esters by distilla- 
 tion over nickel is described by Sabatier and Murat. 3 
 On leading methyl benzoate together with hydrogen 
 over nickel at 210-225 C. some reduction was 
 obtained, but the fixation of hydrogen was soon 
 stopped by deposition of a thin film of benzoate 
 over the surface of the nickel. However, on carry- 
 ing out the reaction at 180 C. and employing a large 
 excess of hydrogen, the hexahydro-reduction product 
 resulted and the hydrogenation proceeded smoothly. 
 In a similar manner, Sabatier and Murat succeeded 
 in preparing hexahydro-compounds from ethyl and 
 isoamyl benzoates. 
 
 Zelinski and Glinka 4 hydrogenated tetrahydro- 
 terephthalic ester, a mixture of the normal hexa- 
 hydroterephthalic ester and a hydroxy-compound 
 being obtained. 
 
 Various Aromatic Derivatives. 
 
 Aniline, led with hydrogen over nickel at 190 C. 
 is converted into a mixture of cyclohexylamine, 
 
 1 Sabatier and Mailhe, Compt. rend., 1908, 146, 1193. 
 
 2 Skita and Meyer, Ber., 1912, 45, 3579- 
 
 3 Sabatier and Murat, Compt. rend., 1912, 154, 922. 
 
 4 Zelinski and Glinka, Ber., 1911, 44, 2305. 
 
UNSATURATED RINGS 51 
 
 dicyclohexylamine, and cyclohexylaniline, 1 analogous 
 results being obtained with diphenylamine. 
 
 C-NH 9 CH'NH, 
 
 -\/ H 2 C X/ 
 
 CH CH 
 
 Aniline. Cyclohexylamine. 
 
 CH NH C 
 
 H 2 C/\CH 2 HC 
 
 HC* I /"*TT TT/"* 
 
 2^\ /^-^-2 dv 
 
 CH 2 CH 
 
 Cyclohexylaniline. 
 
 CH NH- 
 
 H,C/ X ,CH 2 H 2 Cr X CH 5 
 
 Hirtj TJ rl 
 2 \ 
 
 \/ 
 
 CH 2 
 
 Dicyclohexylamine. 
 
 Methyl and ethyl aniline behave similarly. 2 
 
 An interesting variation in the hydrogenation of 
 benzaldehyde has been recorded by Skita. 3 
 
 Using platinum as a catalyst, this passed in alco- 
 holic solution to benzyl alcohol, in acetic acid 
 solution at ordinary pressure to toluene, and, at 
 a pressure of three atmospheres, to hexahydrotoluene. 
 
 CH CH 
 
 HO NCR HcL JCH 
 
 CH CH 
 
 Benzaldehyde. Benzyl alcohol. 
 
 1 Sabatier and Senderens, Compt. rend., 1904, 138, 457. 
 
 2 Sabatier and Senderens, ibid., 1904, 138, 1257. 
 
 3 Skita, Ber., 1915, 48, 1486. 
 
 42 
 
52 CATALYTIC HYDROGEN ATION 
 CH CH 
 
 2 
 HCL JCH H 8 C' 'CH 2 
 
 CH CH 2 
 
 Toluene, Hexahydrotoluene. 
 
 Sabatier and Mailhe 1 on attempting to hydrogenate 
 chlorobenzene by the vapour method in presence 
 of nickel obtained only decomposition products. 
 The same authors 2 found that aromatic quinones 
 and diketones under similar conditions underwent 
 reduction of their carbonyl groups without appreci- 
 able hydrogenation of the benzene ring. 
 
 Reduction of Terpenes . 
 
 We may well consider at this point the hydro- 
 genation of various terpenic compounds. Skita 3 
 studied the action of hydrogen, at the ordinary 
 temperature in the presence of palladium, on the 
 ionones. 9-6 Grams of a-ionone, o-oi gram of 
 palladium chloride and o-oi gram of gum arabic 
 were dissolved in a mixture of 100 c.c. of alcohol and 
 50 c.c. of water. The ionone was converted after 
 shaking for forty-five minutes, at an increased pres- 
 sure of one atmosphere, to dihydro-ionone, and after 
 seventy-five minutes to the tetrahydro-compound. 
 /3-Ionone behaved similarly. 
 
 CH 3 CH, 
 
 C 
 
 H 2 C' JC-CH 3 HS : 
 
 CH 
 
 Ionone. 
 
 1 Sabatier and Mailhe, Compt. rend., 1904, 138, 245. 
 
 2 Sabatier and Mailhe, ibid., 1907, 145, 1126; 1908, 146, 
 
 3 Skita, Ber., 1912, 45, 3312. 
 
UNSATURATED RINGS 53 
 
 CH 3 CH 3 
 
 c 
 
 HC/NCH-CH-CH-CO-CH, 
 
 H 2 C 
 
 CH 
 
 Dihydro-ionone. 
 
 CH 3 CH 3 
 
 \/ 
 
 C 
 
 HA ^C-CH, 
 
 CH 
 
 CH 3 CH 3 
 
 \/ 
 
 C 
 
 H 2 C/NCH'CH 2 -CH 2 -CO-CH 3 
 
 CH 2 
 
 Tetrahydro-ionone. 
 
 It will be noticed that in each case it is the extra- 
 cyclic double bond which first of all becomes satu- 
 rated. The odour of ionone disappeared with the 
 saturation of the first double bond. It may be 
 mentioned that Skita succeeded in preparing, by a 
 condensation method, a dihydro-ionone satu- 
 rated in the ring but containing an ethylenic 
 linkage. This body possessed a smell reminiscent 
 of ionone. 
 
 All the ionone reductions given above are 
 characterised by the fact that the CO group is left 
 untouched, a- and /3-Iononesgive isomeric dihydro- 
 compounds but identical tetrahydro-derivatives. 
 
54 
 
 CATALYTIC HYDROGENATION 
 
 Pseudoionone (which, although not a ring body may 
 conveniently be grouped with the ionones) is 
 similarly hydrogenated to tetrahydro-pseudo- 
 ionone. 
 
 Of other terpenes, camphor has been hydrogenated 
 in presence of non-colloidal platinum to dihydro- 
 camphene, and pinene, in presence of colloidal 
 platinum, to pinane. 1 
 
 CH 2 CH CH 2 
 
 CH 3 -C-CH 3 
 
 CH^ rz:C- -CH 
 
 CH 3 
 
 Pinene. 
 
 CH 
 
 CH. 
 
 Boeseken and Bilheimer 2 have studied the rate 
 of reduction of pinene in various solvents. In 
 formic acid and in alcohol hydrogenation proceeded 
 very slowly, and the activity of the catalyst was 
 observed to decrease. In ether the activity dimin- 
 ished in a similar manner, but no catalytic poisoning 
 was noted. In ethyl acetate reduction took place 
 regularly at first, then stopped, the activity of the 
 catalyst being, however, not permanently impaired, 
 a similar effect being observed in acetic acid. 
 These hydrogenations were carried out at the 
 ordinary temperature in a shaker. 
 
 By distilling pulegone together with hydrogen 
 over a nickel catalyst at an elevated temperature, 
 Skita and Ritter 3 obtained menthane. 
 
 1 Skita and Meyer, Ber., 1912, 45, 3579- 
 
 2 Boeseken and Bilheimer, Rec. trav. chim. Pays-Bas, 1916, 
 35, 288. 
 
 3 Skita and Ritter, Ber., 1912, 45, 668. 
 
UNSATURATED RINGS 55 
 
 CH 3 CH 3 
 
 CH CH 
 
 HC CH TT HC, CH TT 
 
 C CH 
 
 I AH 
 
 CH 3 CH 3 CH 3 CH 3 
 
 Pulegone. Menthane. 
 
 Menthane has also been obtained by Smirnoff 1 in 
 a similar manner from />-tolylisopropyl alcohol : 
 
 CH 3 CH 3 
 
 C CH 
 
 HCf >,CH , ,TT H 2 Cf X ,CH 
 
 I PTT ~r 4^2 UP 
 
 ' v \ /\JJLJL. STLn\s 
 
 \X 2 \/ 
 
 C CH 
 
 C-OH 
 
 CH 3 CH 3 CH 3 CH 3 
 
 Tolyl isopropyl alcohol. 
 
 Working with hydrogen under a pressure of 
 approximately 100 atmospheres in presence of a 
 nickel catalyst, Ipatiew and Balatschinsky 2 observed 
 that the formation of menthol and menthane from 
 pulegone (by reduction of the CO group) only took 
 place above 250 C. At lower temperatures, 
 
 1 Smirnoff, /. Russ. Chem. Phys. Soc., 1909, 41, 1374. 
 3 Ipatiew and Balatschinsky, Ber., 1911, 44, 3461. 
 
56 CATALYTIC HYDROGENATION 
 
 hydrogen was added normally to the double bond, 
 menthone being formed : 
 
 CH?i CH 3 
 
 CH CH 
 
 i 
 
 H, 
 
 TrV Iro" ^ H>I ro 
 
 -LlaV^v ,\j\J JLloV-/\ /\^\J 
 
 C CH 
 
 i i, 
 
 /\ /\ 
 
 CH 3 CH 3 CH 3 CH 3 
 
 Pulegone. Menthone. 
 
 CH 3 
 
 in 
 
 HgC/ Y-H 2 
 H 2 Cl JCH-OH 
 
 CH 
 CH 
 
 CH 3 CH 3 
 
 Menthol. 
 
 Analogous results were obtained with carvone and 
 with thymol. 
 
 The hydrogenation of the thujenes and of sabinene 
 has been effected by Tschugaeff and Fomin, 1 thujane 
 'being obtained in each case. 
 
 1 Tschugaeff and Fomin, Compt. rend,, 1910, 151, 1058. 
 
UNSATURATED RINGS 57 
 
 CH 3 CH 3 CH 2 
 
 ii 
 
 c 
 
 v^j.j.g 
 
 CH 
 
 HC/^.CH 
 
 H 2 C^JCH 2 H a C^JlCH Had^JCH 
 . C C C 
 
 CH CH C 
 
 n 
 
 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 
 
 o-Thujene. /3-Thujene. Sabinene, 
 
 CH. 
 
 CH 
 H. HC/NCH, 
 
 C 
 
 in 
 
 CH 3 CH 3 
 
 Thujane. 
 
 Hydrogenation of Heterocyclic Rings 
 
 Sabatier and Mailhe 1 attempted to hydrogenate 
 pyridine by the vapour method, but were able to 
 obtain only a splitting of the pyridine ring without 
 direct hydrogenation of the unsaturated linkages 
 contained therein. Pyridine is, however, easily 
 reduced to piperidine by treatment with hydrogen 
 at the ordinary temperature in acetic acid solution 
 in the presence of colloidal platinum, 2 while quinoline 
 was found to pass successively into the tetra- and 
 
 1 Sabatier and Mailhe, Compt. rend., 1907, 144, 784. 
 
 2 Skita and Meyer, Ber., 1912, 45, 3579. 
 
58 CATALYTIC HYDROGENATION 
 
 decahydro reduction products, the pyridine nucleus 
 being attacked before the benzene ring. 
 
 Skita and Brunner 1 have effected the reduction 
 of pyridine to piperidine in dilute hydrochloric acid 
 solution. Hydrogenation was also effected with 
 a-picoline, of ay-lutidine and of 2:4: 5-collidine, 
 and good results were obtained in acetic acid solu- 
 tion at 25-45 C. with an excess pressure of three 
 atmospheres in presence of platinum. 
 
 7-Phenyl quinoline carboxylic acid was reduced 
 to tetrahydro-phenyl quinoline carboxylic acid at 
 two atmospheres pressure at 50-60 C., while the 
 decahydro-compound was obtained with hydrogen 
 at a pressure of ten atmospheres, employing a larger 
 quantity of catalyst. 
 
 The reduction of quinoline has also been carried 
 out by Ipatiew 2 in presence of nickel in the course 
 of his work on hydrogenation at high temperatures 
 and pressures. Twenty grams of quinoline together 
 with 2 grams of nickel oxide were treated with 
 hydrogen for twenty hours at 240 C. at a pressure 
 of 100 atmospheres, complete transformation into 
 decahydro-quinoline being obtained : 
 
 CH CH CH 2 CH 
 
 HC 
 
 CH/ X CH 2 
 
 CHv JCH, 
 
 CH N CH 2 NH 
 
 Ouinoline. 
 
 Isoquinoline, on the other hand, has up to the 
 present only been hydrogenated to the tetrahydro- 
 derivative. It would seem, therefore, in this case 
 at any rate, that the heterocyclic ring is more easily 
 
 1 Skita and Brunner, Ber., 1916, 49, 1597. 
 a Ipatiew, ibid., 1908, 41, 991. 
 
UNSATURATED RINGS 59 
 
 reduced catalytically than the benzene nucleus, 
 this being the case also with nascent hydrogen. 
 
 CH CH CH CH 
 
 HC 
 
 JN HC. XvxNH 
 
 CH CH CH CH 2 
 
 Isoquinoline. Tetrahydro-isoquinoline. 
 
 The hydrogenation of pyrrol to pyrrolidine by 
 the vapour method in presence of nickel has been 
 carried out by Padoa. 1 In the case of indol, how- 
 ever, decomposition took place 2 with formation of 
 toluidine. Decomposition is also found to attend 
 the hydrogenation of acridine by Sabatier's method, 
 the principal product of the reaction being afi- di- 
 methyl quinoline. 
 
 Of other heterocyclic rings, the hydrogenation 
 of furfurane derivatives has also been studied, 
 reduction proceeding normally. 
 
 Hydrogenation of Alkaloids and other Bodies possessing 
 a Complicated Structure. 
 
 Catalytic hydrogenation has made easy the 
 production of many derivatives of alkaloids, such 
 derivatives often possessing valuable modifications 
 of the properties of the parent substance. Thus, 
 taking a few typical examples, quinine and cinchonine 
 are easily hydrogenated to dihydroquinine and 
 dihydrocinchonine in presence of palladium. 3 Cin- 
 chonidine, 4 tropine and dimethyl piperine 5 behave 
 
 1 Padoa, Alt. Lincei, 1906, 15, i, 219. 
 
 2 Padoa, ibid., 1906, 15, I, 699. 
 
 3 Skita and Franck, Ber., 1911, 44, 2862. 
 
 4 Skita and Franck, ibid., 1912, 45, 3312. 
 
 5 Skita and Franck, ibid., 1910, 43, 1176. 
 
60 CATALYTIC HYDROGENATION 
 
 similarly, while pipeline 1 takes up four atoms of 
 hydrogen, with saturation of its aliphatic chain, 
 the benzene nucleus being left unattacked. 
 
 CH 
 
 CH 2 CH 2 
 CH:CH-CH:CH-CON/ 
 
 CH7CH, 
 
 Piperine. 
 
 = CH, 
 
 \0 
 
 CH CH, 
 
 CON/ \CH 2 
 CH^CH, 
 
 Tetrahydropiperine. 
 
 Morphine, on being treated with hydrogen in 
 presence of palladium, is found to pass into dihydro- 
 morphine. Strychnine 2 is hydrogenated to a dihydro- 
 strychnine, which is not identical with the dihydro- 
 derivative obtained by non-catalytic reduction of 
 the base and, unlike this, is capable of being further 
 hydrogenated to tetrahydrostrychnine. Morphine, 
 brucine, and codeine also yield dihydro-products. 
 
 Of non-alkaloidal substances possessing a compli- 
 cated structure, santonine has been hydrogenated to 
 tetrahydrosantonine. Similarly, phytol and chol- 
 esterine have been reduced by Willstatter and 
 Mayer 3 to dihydrophytol and dihydrocholesterine 
 respectively, using a platinum catalyst in ethereal 
 solution. 
 
 1 Borsche, Ber., 1912, 45, 2943. Skita and Meyer, ibid., 
 1912, 45, 3579- 
 
 2 Skita and Frank, loc. cit. 
 
 3 Willstatter and Mayer, Ber,, 1908, 41, 1475, 2199. 
 
CHAPTER VI 
 MISCELLANEOUS REDUCTIONS 
 
 WE have up to the present considered principally 
 cases of simple introduction of hydrogen into un- 
 saturated linkages. There are, however, reactions 
 in which something more than this occurs, and to 
 these, together with the direct hydrogenation of 
 various linkages other than those already treated, 
 it is proposed to devote the present chapter. 
 
 Perhaps the simplest example of a reduction 
 differing essentially in character from a simple 
 saturation with hydrogen is to be found in the pro- 
 duction of methane from carbon monoxide or 
 carbon dioxide. 
 
 Sabatier and Sender ens, 1 in 1902, found that, on 
 passing a mixture of carbon monoxide and hydrogen 
 over nickel, formation of methane began at 200 C. 
 and took place easily and smoothly at 250 C. 
 Similar results were obtained with mixtures of 
 carbon dioxide and hydrogen, a suitable reaction 
 temperature being in this case 300 C. Cobalt was 
 found to be less active and to require a higher 
 reaction temperature than nickel. 
 
 CO +3H 2 - CH 4 + H 2 
 C0 2 +4H 2 = CH 4 + 2H 2 
 
 A copper catalyst was found to be incapable of 
 inducing the complete reduction of carbon dioxide 
 to methane, carbon monoxide only being obtained. 
 CO 2 +H 2 = H 2 O+CO. 
 
 1 Sabatier and Senderens, Compt. rend., 1902, 134, 514, 689. 
 
 61 
 
62 CATALYTIC HYDROGENATION 
 
 Vignon, 1 who studied the reduction of carbon 
 monoxide, to methane at a later date, recommends 
 nickel as the most suitable catalyst and 600 C. as 
 the optimum temperature. 
 
 Examples of the reduction of the carbonyl group 
 of organic compounds to CH-OH or to CH 2 have 
 already been given in the preceding chapters, 
 usually in connection with the simultaneous satura- 
 tion of an ethylenic, acetylenic, or benzenoid 
 linkage. Some cases of reduction of a carbonyl 
 group, unaccompanied by such saturation, will be 
 considered here. 
 
 The action of hydrogen on acetone in presence 
 of platinum has been investigated by Vavon. 2 
 In ethereal solution, reduction to propane was 
 obtained, but the reaction was found soon to come 
 to a standstill, probably by reason of the presence 
 of poisons in the acetone used. 
 
 CH 3 -COCH 3 +2H 2 == H 2 O+CH 3 -CH 2 -CH 3 . 
 
 If, however, the acetone is diluted with an equal 
 volume of water and hydrogenated in this condition 
 in presence of platinum, a slow and complete reduc- 
 tion to isopropyl alcohol was observed. 
 
 CH 3 -COCH 3 +H 2 == CH 3 -CH-OH-CH 3 . 
 
 Similarly, secondary butyl alcohol was obtained 
 from diluted methyl ethyl ketone. Acetophenone 
 in ether, alcohol, ethyl acetate, or acetic acid solu- 
 tion is converted to the corresponding hydrocarbon, 
 while, on carrying out the reduction in dilute 
 alcoholic solution, formation of almost pure phenyl- 
 ethyl-carbinol takes place. It will be noticed that, 
 in general, organic solvents lead to a complete 
 reduction to hydrocarbon, while an aqueous solu- 
 tion of the body to be reduced is only converted to 
 alcohol. 
 
 1 Vignon, Compt. rend., 1913, 157, 131. 
 
 2 Vavon, ibid., 1912, 155, 286. 
 
MISCELLANEOUS REDUCTIONS 63 
 
 The catalytic reduction of a CO group to CH 2 
 has been used by Borsche 1 for the preparation of 
 o>o>'-diaryl aliphatic hydrocarbons. The first stage 
 in the synthesis consists in a condensation of the 
 following type : 
 
 CH 2 -COC1 CH 2 -CO-C 6 H 6 
 
 | +2C 6 H 6 = | +2HC1, 
 
 CH 2 -COC1 CH 2 -CO-C 6 H 6 
 
 the resulting product being dissolved in methyl 
 alcohol and hydrogenated at the ordinary tempera- 
 ture in presence of colloidal palladium. 
 
 C 6 H 5 -CO-CH 2 -CH 2 -CO-C 6 H 6 + 4 H 2 = . 
 
 grx5 -p 2Jx 2 O 
 
 By reducing the ketone, 
 
 C 6 H 5 -CH 2 -CH 2 -CO-CH 2 -CH 2 -C 6 H 5 , 
 
 in presence of not very active nickel at 180 C., 
 Sabatier and Murat 2 obtained oxw'-diphenyl pentane, 
 C 6 H 5 -CH 2 'CH 2 -CH 2 -CH 2 -CH 2 -C 6 H 5 , while similar 
 treatment in presence of very active nickel at 
 165 C. gave the corresponding dicyclohexyl pen- 
 tane, the benzene nucleus being, in this case, also 
 attacked. 
 
 Various aliphatic diketones, on the other hand, 
 were found by Sabatier and Mailhe 3 to be hydro- 
 genated by distillation over nickel to corresponding 
 alcoholic bodies. 
 
 The reduction of a carbonyl group to CH 2 in 
 presence of nickel can also be effected when the 
 carbon atom is a member of a ring. Thus Skit a 3 
 hydrogenated, by distillation with hydrogen over 
 
 1 Borsche, Ber., 1911, 44, 3185. 
 
 2 Sabatier and Murat, Compt. rend., 1913, 156, 1951. 
 
 3 Sabatier and Mailhe, ibid., 1907, 144,, 1086. 
 
 4 Skita, Ber., 1909, 42, 1627. 
 
64 CATALYTIC HYDROGENATION 
 
 nickel, the esters of the cyclohexanone carboxylic 
 acids to esters of the naphthenic acids : 
 
 C-H-2 C.H.2 
 
 H 2 C/\CH'COO-C 2 H 5 ^ H.C/ \CH-COO-C 8 H B 
 OCl JCH-CH a ^HXl JCH-CH, 
 
 CH 9 CH 
 
 An exceedingly interesting method for the con- 
 version of the CO group into CH 2 has been described 
 by Ipatiew 1 for certain ketones of the terpene class. 
 It consists in the combined action of a hydrogenating 
 and of a dehydrating catalyst, the ketone being first 
 reduced to a secondary alcohol under the influence 
 of the hydrogenating catalyst present. The second- 
 ary alcohol, in presence of the dehydrating catalyst, 
 passes by loss of water into an unsaturated hydro- 
 carbon which, in its turn, takes up hydrogen to 
 form a saturated hydrocarbon. 
 
 The series of reactions is found to take place at 
 a much lower temperature when carried out simul- 
 taneously than when brought about by the separate 
 action of the hydrogenation and dehydration cata- 
 lysts. Thus, while the hydrogenation of camphor 
 to borneol by means of nickel in Ipatiew'' s high 
 pressure apparatus required a temperature of from 
 320 C. to 350 C., and the dehydration of borneol 
 to camphene 350 C. to 360 C., the camphene being 
 easily hydrogenated to camphane in presence of 
 nickel at 240 C., the transformation of camphor to 
 isocamphane in presence of a catalyst consisting of 
 a mixture of nickel oxide and aluminium oxide takes 
 place at 200 C., or even less. 
 
 Ipatiew found it impossible, even at 400 C., to 
 obtain camphane from camphor by direct hydro- 
 genation in presence of nickel oxide. 
 
 Another instance of the difference in the activity 
 
 1 Ipatiew, Ber. 1912, 45, 3205. 
 
MISCELLANEOUS REDUCTIONS 
 
 of nickel and copper may be observed by substi- 
 tuting copper for nickel in the above combined 
 hydrogenation and dehydration catalyst. In this 
 case the reaction stops at camphene, which, in the 
 presence of copper, is not further reduced. Further, 
 instead of starting with camphor, borneol or iso- 
 borneol may be taken. From either of these iso- 
 camphane can be obtained by the action of the 
 combined catalyst in a pressure apparatus at 215 C. 
 
 H CH, 
 
 CH 3 
 
 Camphor. 
 
 OH, 
 
 Borneol. 
 
 H 9 C- 
 
 -CH- 
 
 -CH 
 
 CH 3 -OCH 3 
 
 H 2 C C- 
 
 -CH 
 
 i 
 
 H CH, 
 
 CH 
 
 Camphane. 
 
 Similar results have been obtained for the hydro- 
 genation of fenchone to fenchane in presence of 
 nickel and alumina. 
 
 The reduction of the oxymethylene group, accor- 
 ding to Paal's or Skita's method, has been studied 
 by Kotz and Schaeffer. 1 From oxymethylene 
 acetoacetic ester, methyl acetoacetic ester was 
 obtained. Other oxymethylene compounds were 
 found to be capable of being reduced similarly. 
 
 1 Kotz and Schaeffer, Ber., 1912, 45, 1952. 
 
66 CATALYTIC HYDROGENATION 
 
 Hydrogenation of the C:N Group 
 
 Sabatier and Senderens 1 succeeded in preparing 
 various aliphatic amines by the catalytic reduction 
 of nitriles by the vapour method over nickel at 
 180-200 C., a reduction which is also easily effected 
 by nascent hydrogen. The primary amine formed, 
 however, w^as found to pass, by loss of ammonia, 
 to some degree into a secondary or tertiary amine : 
 
 CH 3 -C:N+2H 2 = CH 3 -CH 2 -NH 2 
 
 CH 5 -CH 2 y 
 2CH 3 -CH 2 -NH 2 - >NH+NH 3 
 
 CH 3 -CH/ 
 
 3 CH 3 -CH 2 -NH 2 = (CH 3 -CH 2 ) 3 N+2NH 3 
 Aromatic nitriles, on being reduced in a similar 
 way, gave as the principal reaction product a mixture 
 of amines, hydrocarbons, and ammonia. 
 
 The reduction of the C:N group may also be 
 carried out at the ordinary temperature in presence 
 of colloidal platinum or palladium. Paal and 
 Gerum 2 reduced in this way benzonitrile in alcoholic 
 solution to a mixture of benzylamine, dibenzyl- 
 amine, and ammonia, together with a little benzalde- 
 hyde. 
 
 Mandelic nitrile the cyanhydrin of benzaldehyde 
 was converted by a similar hydrogenation to 
 mono- and di-benzylamine, ammonia, and benzyl 
 alcohol, decomposition taking place, while benzal- 
 doxime was found to give the same reduction pro- 
 ducts as those obtained from benzonitrile. Simi- 
 larly, acetonitrile is reduced in presence of colloidal 
 palladium to ethylamine : 3 
 
 C 6 H 5 -CN+2lJ 2 = C 6 H 5 -CH 2 -NH 2 
 
 Benzonitrile. Benzylamine. 
 
 C 6 H 5 -CH:NOH+2H 2 = C 6 H 5 -CH 2 -NH 2 -f H 2 O. 
 
 Benzaldoxime. 
 
 1 Sabatier and Senderens, Com.pt. rend., 1905, 140, 482. 
 
 2 Paal and Gerum, Ber., 1909, 42, 1553. 
 
 3 Skita, Ber., 1909, 42, 1636. 
 
MISCELLANEOUS REDUCTIONS 67 
 
 Reduction of Isonitriles. 
 
 Isonitriles, on being subjected to catalytic hydro- 
 genation, give, in accordance with their constitu- 
 tion, a reaction product differing essentially from 
 that obtained from the corresponding nitrile. 
 Sabatier and Mailhe, 1 who studied the reduction of 
 aliphatic carbylamines by distillation with hydrogen 
 over nickel, obtained, in general, a reaction of the 
 following type : 
 
 CH 3 -N:C+2H 2 == CH 3 -NH-CH 3 . 
 
 It was found that a copper catalyst could be 
 substituted for the nickel, but was less active. 2 
 The course of the reduction should be compared with 
 that of the true nitriles described above. 
 
 Reduction of Isocyanic Esters. 
 
 Ethyl isocyanate, on being distilled with hydrogen 
 over nickel at 250-290 C., was converted princi- 
 pally into secondary methyl-ethyl-amine. 3 
 
 O:C:N-C 2 H 5 +3H 2 = CH 3 *NH-C 2 H 5 +H 2 O 
 
 Reduction of the -N:N- Group. 
 
 Skita 4 dissolved 9 grams of azobenzene in 250 c.c. 
 of alcohol and added 35 c.c. of colloidal palladium 
 solution, containing 0-03 gram of palladium and 
 0*05 gram of gum arabic. On hydrogenating in a 
 shaker with hydrogen under an increased pressure 
 of one atmosphere, the theoretical volume of 
 hydrogen for production of hydrazobenzene was 
 absorbed in five minutes, while, on continuing the 
 
 1 Sabatier and Mailhe, Compt. rend., 1907, 144, 955. 
 
 2 Sabatier and Mailhe, Bull., 1907, 1, 612. 
 
 3 Sabatier and Mailhe, Compt. rend., 1907, 144, 824. 
 
 4 Skita, Ber., 1912, 45, 3312. 
 
 52 
 
68 CATALYTIC HYDROGENATION 
 
 treatment for 4^ hours, the hydrazobenzene was 
 completely reduced to aniline : 
 
 C 6 H 5 -N:N-C 6 H 5 +H 2 = C 6 H 5 -NH-NH.C 6 H 5 
 C 6 H 5 -NH-NH-C 6 H 5 +H 2 - 2C 6 H 5 -NH 2 . 
 
 It will be noticed that the reduction to hydrazo- 
 benzene takes place far more rapidly than the 
 conversion of this to aniline. 
 
 Reduction of Oxides of Nitrogen. 
 
 Oxides of nitrogen are easily reduced to ammonia 
 by treatment with hydrogen in presence of a suitable 
 catalyst. Sabatier and Sender ens 1 recommend 
 nickel, but state that copper may also be used. A 
 somewhat similar reaction has been noticed by the 
 author in the course of the reduction by hydrogen 
 of a mixture of pure iron and sodium nitrate at 
 an elevated temperature. The reduction of nitrites 
 to ammonia in presence of palladium is mentioned 
 by Bredig. 2 
 
 It is interesting in connection with reactions of 
 the above type to note that the easy reduction of 
 hydroxylamine to ammonia by hydrogen in presence 
 of platinum was observed by Victor Meyer 3 as 
 long ago as 1891. 
 
 Reduction of Nitro-compounds. 
 
 The catalytic reduction of nitrobenzene and 
 nitromethane to aniline and methylamine by leading 
 the vapours of these bodies together with hydrogen 
 over palladium was, as already mentioned, noticed 
 by Saytzeff in 1871. 4 
 
 1 Sabatier and Senderens, Compt. rend., 1902, 135, 278. 
 
 2 Bredig, Anorg. Fermente,, Leipzig, 1904, p. 46. 
 ' Victor Meyer, A., 1891, 264, 126. 
 
 4 Kolbe and Saytzeff, /. prakt. Chem., 1871, 4, 418. 
 
MISCELLANEOUS REDUCTIONS 69 
 
 Sabatier and Senderens 1 recommend finely divided 
 copper at 300-400 C. as the most suitable catalyst 
 for the conversion of nitrobenzene to aniline, and 
 state that if too little hydrogen be employed, azo- 
 benzene is formed. 
 
 C 6 H 5 -N0 2 +3H 2 = C 6 H 5 -NH 2 +2H 2 
 2C 6 H 5 -N0 2 + 4 H 2 = C 6 H 5 -N:N-C 6 H 5 + 4 H 2 0. 
 
 Nickel was found to be too energetic and to tend to 
 split off ammonia with the formation of benzene or, 
 at temperatures above 300 C., even of methane. 
 Cobalt and iron behave similarly to nickel. Finely 
 divided platinum at 230-300 C. induces a normal 
 reduction to aniline, but if insufficient hydrogen for 
 complete reduction be present, hydrazobenzene is 
 formed. 
 
 2C 6 H 5 -N0 2 +5H 2 = C 6 H 5 -NH-NH-C 6 H 5 +4H 2 0. 
 
 The reaction was extended in a later paper 2 to other 
 nitro-compounds, including a- and /3-nitronaphthal- 
 enes. Copper was again found to be more suitable 
 than nickel, the action of which was too violent, and 
 gave rise to ammonia and tetrahydronaphthalene. 
 
 Paal and Gerum 3 examined the reduction of 
 nitrobenzene to aniline in presence of colloidal metal- 
 lic catalysts at temperatures varying from 60-85 C- 
 and in alcoholic solution. Colloidal palladium, 
 prepared according to Paal and Amberger's method 
 by the reduction with hydrazine hydrate of a 
 palladium chloride solution containing sodium pro- 
 talbinate as a protective colloid, was found to be 
 an excellent catalyst for the reaction in question. 
 Colloidal copper and gold were found to be inactive, 
 colloidal silver and osmium slightly active. The 
 reduction of nitrobenzene to aniline and of o-nitro- 
 
 1 Sabatier and Senderens, Compt. rend. 1901, 133, 321. See 
 also Senderens, German patent 139457 (1901). 
 
 2 Sabatier and Senderens, ibid., 1902, 135, 225. 
 8 Paal and Gerum, Ber., 1907, 40, 2209. 
 
70 CATALYTIC HYDROGENATION 
 
 acetophenone to o-aminoacetophenone has also 
 been studied by Skita and Meyer. 1 
 
 An interesting variation in the course of the 
 catalytic reduction of nitro-compounds is described 
 by Brochet. 2 Nitrobenzene in alkaline solution is 
 found to pass through azoxybenzene, azobenzene, 
 and, finally, hydrazobenzene before becoming con- 
 verted to aniline. A similar reduction by nascent 
 hydrogen in alkaline solution had, of course, long 
 been known. 
 
 2C 6 H 5 -N0 2 + 3 H 2 == C 6 H 5 -N N-C 6 H 5 +3H 2 
 
 Nitrobenzene. \ / 
 
 o 
 
 Azoxybenzene. 
 
 C 6 H 5 -N-N-C 6 H 5 +H 2 = = C 6 H 5 -N:N-C 6 H 5 +H 2 
 
 \/ Azobenzene. 
 
 o 
 
 C 6 H 5 -N:N-C 6 H 5 +H 2 == C 6 H 5 -NH-NH-C 6 H 6 
 
 Hydrazobenzene. 
 
 C 6 H 5 -NH-NH-C 6 H 5 +H 2 == 2C 6 H 5 -NH a 
 
 Aniline. 
 
 Paal and Hartmann 3 take advantage of the ease 
 of reduction of nitro-groups in devising a method for 
 the volumetric estimation of hydrogen in gas 
 mixtures. These authors point out the advantages 
 accruing from the employment of a liquid absorbing 
 medium instead of the solid palladinised asbestos 
 usually employed, in that dead space may be 
 eliminated by using a Hempel absorption pipette 
 either of the usual type or of the slightly modified 
 form described in Paal and Hartmann's paper. 
 
 1 Skita and Meyer, Ber., 1912, 45, 3579- 
 
 2 Brochet, first addition, dated Oct. 8, 1912, to French patent 
 458033. 
 
 3 Paal and Hartmann, Ber., 1910, 43, 243. 
 
MISCELLANEOUS REDUCTIONS 71 
 
 An effective absorbing liquid is prepared by dis- 
 solving 5 grams of sodium picrate and 2-5 grams of 
 colloidal palladium in 200 c.c. of water. During an 
 analysis, the pipette is shaken from time to time. 
 Absorption should be complete after about ten 
 minutes. 
 
 Removal of Halogens by Hydrogen. 
 
 C. Kelber 1 has proposed to utilise the catalytic 
 removal of halogens from organic compounds by 
 hydrogen in presence of nickel or palladium as an 
 analytical method for the quantitative estimation of 
 halogens. The catalysts recommended are either 
 palladinised calcium carbonate or nickel reduced 
 from carbonate at 310-320 C. For a determination, 
 three grams of the catalyst are placed in a reaction 
 vessel attached to a shaker and shaken with water 
 or dilute alcohol in presence of hydrogen until no 
 more of the gas is absorbed. The substance to be 
 analysed is now added and shaking continued until 
 hydrogen absorption ceases, when the catalyst is 
 filtered off and the halogen in the filtrate determined 
 gravimetrically or by titration. 
 
 Catalytic Reduction of Metallic Oxides. 
 
 The direct reduction to metal of nickel and copper 
 oxides is a remarkable example of the activation of 
 hydrogen by means of catalysts. Paal, 2 working 
 in this direction, has found that freshly precipi- 
 tated, or colloidal, copper or nickel hydroxide can 
 be reduced to colloidal metals by treatment with 
 hydrogen at the ordinary temperature in presence 
 of colloidal palladium. 
 
 1 Kelber, Ber., 1917, 50, 305. 
 
 2 Paal, ibid., 1914, 47, 2202. 
 
72 CATALYTIC HYDROGENATION 
 
 Paal and Biittner 1 have investigated further the 
 reduction of ammonium molybdate in presence of 
 colloidal palladium. At the ordinary temperature 
 reduction took place slowly and stopped at the 
 tetrahydroxide. On raising the temperature to 
 60 C. reduction recommenced, black molybdenum 
 trihydroxide being precipitated. 
 
 1 Paal and Buttner, Ber., 1915, 48, 220. 
 
CHAPTER VII 
 
 DEHYDROGENATION 
 
 THE simple dehydrogenation of straight carbon- 
 hydrogen chains has up to the present not been 
 realised. Ipatiew showed, however, that alcohol 
 could be dehydrogenated to aldehyde in presence of 
 finely divided copper, 
 
 CH 3 -CH 2 -OH = CH 3 -CHO+H 2 . 
 
 Sabatier and Senderens 1 recommend leading alcohol 
 over a copper catalyst at a temperature between 
 200 C. and 230 C. No formation of water or 
 ethylene was noted under these conditions. Nickel 
 and platinum appear not to be as suitable as copper 
 for the promotion of the dehydrogenation and tend 
 to lead to side reactions. 
 
 In a later paper, Sabatier and Senderens 2 describe 
 the application of the reaction to other alcohols of 
 the methane series. It is found, in general, that 
 the lower the molecular weight of the alcohol, the 
 easier is the dehydrogenation. 
 
 Unsaturated alcohols behave similarly, but are, as 
 would be expected, liable to be hydrogenated simul- 
 taneously to saturated bodies. Ally! alcohol, 3 for 
 instance, on being led over finely divided copper at 
 180-300 C., is dehydrogenated to acrolein, which 
 
 1 Sabatier and Senderens, Compt. rend., 1903, 136, 738. 
 
 2 Sabatier and Senderens, ibid., 1903, 921. 
 
 3 Sabatier and Senderens, ibid., 1903, 983. 
 
 73 
 
74 CATALYTIC HYDROGENATION 
 
 in turn combines to a certain degree with the 
 hydrogen liberated, propyl aldehyde being formed : 
 
 CH 2 :CH-CH 2 -OH - CH 2 :CH-CHO + H 2 
 CH 2 :CH-CHO+H 2 == CH 3 -CH 2 -CHO. 
 
 Similarly, benzyl alcohol, led over copper at 300 C., 
 is dehydrogenated to benzaldehyde, 
 
 C 6 H 5 -CH 2 -OH - C 6 H 5 -CHO+H 2 . 
 
 The dehydrogenation of alcohols in presence of 
 copper affords an interesting test as to their nature. 
 Primary alcohols decompose-, as already described, 
 according to the general equation 
 
 R-CH 2 -OH : R-CHO+H 2 . 
 
 Secondary alcohols, on the other hand, pass by loss 
 of hydrogen into ketones, while with tertiary alcohols 
 unsaturated hydrocarbons are formed by dehydra- 
 tion instead of dehydrogenation : 
 
 >CH-OH = )CO+H 2 
 
 CH/ CH/ 
 
 CH 3 \ CH 3 \ 
 
 CH/C-OH = >C:CH 2 +H 2 O. 
 
 CH/ CR/ 
 
 Sabatier and Gaudion 1 find that dehydrogenation 
 of amines to nitriles may be effected either in 
 presence of nickel at 300-350 C. or of copper at 
 300-400 C., according to the general equation 
 
 R-CH 2 -NH 2 - R-CN + 2H 2 
 
 The hydrogen is not, however, obtained to any 
 degree as such, since it enters into side reactions 
 with the original amine, with formation of ammonia. 
 In the case of benzylamine, a yield of benzonitrile 
 approximating to 30 per cent, was isolated, the 
 
 1 Sabatier and Gaudion, Compt. rend., 1917, 165, 224. 
 
DEHYDROGENATION 75 
 
 principal by-products being ammonia and toluene. 
 Similarly, isoamylamine was converted into iso-. 
 valeronitrile. 
 
 (CH 8 ) a -CH-CH 2 -CH 2 -NH a = 
 
 Isoamylamine. 
 
 (CH 3 ) 2 -CH-CH 2 -CN +2H 2 
 
 Isovaleronitrile. 
 
 The dehydrogenation of methyl alcohol to form- 
 aldehyde in presence of copper has been proposed by 
 Mannich and Geilmann 1 as a method of detecting 
 this body. The liquid under examination is passed 
 over coppered pumice at 280-300, the formaldehyde 
 being recognised by the violet coloration which it 
 produces with morphine and concentrated sulphuric 
 acid. 
 
 Dehydrogenation of Reduced Benzene Derivatives. 
 
 The dehydrogenation of cyclohexane to benzene 
 in presence of nickel was observed by Sabatier and 
 Senderens 2 in 1901. Sabatier and Mailhe, 3 who 
 subjected the reaction to a thorough study, recom- 
 mend distilling cyclohexane over the nickel catalyst 
 at 270-280 C. It is found, however, that consider- 
 able quantities of by-products, notably methane, are 
 formed : 
 
 CH 2 CH 
 
 CH/^CH. CHf^\CH 
 
 CH 2 ' X ^JCH, CH> I'CH ' 3H 2 
 
 CH 2 CH 
 
 A more satisfactory reaction with absence of by- 
 products is obtained by substituting palladium for 
 nickel. 4 With this catalyst dehydrogenation begins 
 at 170 C., is rapid at 200 C., and reaches its maxi- 
 
 1 Mannich and Geilmann, Arch. Pharm., 1916, 254, 50. 
 
 2 Sabatier and Senderens, Compt. rend., 1901, 132, 566. 
 
 3 Sabatier and Mailhe, ibid., 1903, 137, 240. 
 
 4 Zelinsky, Ber., 1911, 44, 3121. 
 
76 CATALYTIC HYDROGEN ATION 
 
 mum velocity at 300 C. Hexahydrotoluene behaves 
 similarly. In a typical experiment, 22-3 grams of 
 hexahydrobenzene were led over 16-6 grams of 
 palladium black contained in a tube 38 cm. long 
 and 14 mm. internal diameter. The complete 
 distillation was carried out in twelve minutes at 
 300 C., 15-97 litres of hydrogen (83-5 per cent, of 
 the theoretical volume) being produced. No tetra- 
 or di-hydrobenzene was observed in the product. 
 Platinum was found to be less active than palladium, 
 while copper was inactive even at 300 C. The 
 reaction is confined to hexa-rings, hexane or penta- 
 rings, for instance, remaining unchanged after 
 similar treatment. 
 
 A simultaneous dehydrogenation and hydrogena- 
 tion has been observed in the case of tetrahydro- 
 naphthalene, the reaction product consisting of a 
 mixture of naphthalene itself and of hydrogenated 
 naphthalenes formed by the action of the hydrogen 
 liberated by the dehydrogenation. 
 
 Passing from the dehydrogenation of cyclic 
 hydrocarbons to that of their derivatives, the 
 dehydrogenation of dihydroterephthalic acid may 
 be mentioned. Knoevenagel 1 found, in 1903, that 
 dehydrogenation of this body took place in presence 
 of palladium, and obtained similar results with 
 benzhydrol and benzoin. 
 
 The whole subject of dehydrogenation is one which 
 has, up to the present, only been studied for isolated 
 cases. Systematic investigation of the phenomenon 
 would without doubt lead to the discovery of many 
 more reactions in which bodies are capable of passing 
 in presence of a suitable catalyst into a less hydro- 
 genated substance and free hydrogen. 
 
 Several interesting examples of dehydrogenation 
 at the ordinary temperature have been studied by 
 H. Wieland, 2 who bases his experiments on the 
 
 1 Knoevenagel, Ber., 1903, 36, 2816. 
 
 2 H. Wieland, ibid., 1911, 45, 484. 
 
DEHYDROGENATION 77 
 
 view that, at any rate in many cases, hydrogenation 
 of an unsaturated compound with an equivalent 
 quantity of hydrogen would not proceed to comple- 
 tion, but would stop at a certain equilibrium, which 
 could be displaced towards complete hydrogenation 
 by a high concentration of hydrogen, this being the 
 procedure usually adopted in actual hydrogenation 
 practice. 
 
 If, however, such an equilibrium really exists, 
 then it should be attainable also by starting with 
 the hydrogenated substance. 
 
 In the investigation of ' the dehydrogenation of 
 various bodies at the ordinary temperature, Wieland 
 made use of specially prepared oxygen-free palladium 
 in order to avoid the possibility of catalytic oxidation 
 being mistaken for dehydrogenation. An aqueous 
 solution of hydroquinone was found to be partially 
 dehydrogenated to quinone by shaking with palla- 
 dium black. The amount of quinone formed can 
 be increased by raising the concentration of the 
 hydrogen absorber in this case the palladium. 
 The metal here, besides acting as a catalyst, has 
 also a non-catalytic, purely absorbent, function. 
 
 OH O 
 
 HC CH HC^CH 
 
 C-OH C 
 
 Hydroquinone. 
 
 O 
 
 Quinone. 
 
 The dehydrogenation of hydrazobenzene and of 
 dihydronaphthalene takes place much more com- 
 pletely than that of hydroquinone. The colourless 
 solution of hydrazobenzene, on being shaken with 
 palladium, immediately becomes yellow, and after 
 
78 CATALYTIC HYDROGENATION 
 
 a few hours no trace of the original substance 
 remains. The solution now contains azobenzene, 
 aniline, and hydrogen absorbed by the palladium. 
 This reaction is therefore another example of simul- 
 taneous dehydrogenation and hydrogenation, and is 
 similar to those already mentioned. 
 
 C 6 H 5 -NH-NH-C 6 H 5 = C 6 H 5 -N:N-C 6 H 5 +H 2 . 
 
 The hydrogen liberated then acts on unchanged 
 hydrazobenzene according to the equation 
 
 C 6 H 5 -NH-NH-C 6 H 5 +H 2 == 2C 6 H 5 -NH 2 . 
 
 The dehydrogenation of dihydronaphthalene takes 
 place in a similar way. Either alone or in benzene 
 solution, it is converted into naphthalene and 
 hydrogen, this latter acting on unchanged dihydro- 
 naphthalene to form tetrahydronaphthalene, which 
 is found in the solution together with the naphtha- 
 lene : 
 
 C 10 H 8 +H 2 
 
 = C 10 H 12 . 
 
 Dihydroanthracene can also be dehydrogenated 
 to anthracene, but the velocity of the reaction is 
 much lower. 
 
 Wieland attempted in a similar way to dehydro- 
 genate two bodies of the ethane type, acenaphthene 
 and bidiphenylene ethane. 
 
 H 2 C- CH 2 
 C C 
 
 HC 
 
 C 
 
 :CH c 6 H/ 
 
 X C 6 H 4 
 >CH-CH< | 
 
 \/ 
 
 CH CH Bidiphenylene ethane. 
 
 Acenaphthene. 
 
DEHYDROGENATION 79 
 
 Only a trace of dehydrogenation was obtained under 
 his conditions. 
 
 In a consideration of the mechanism of the 
 dehydrogenation process, Wieland puts forward 
 evidence for the intermediate formation of a 
 compound between palladium and the satu- 
 rated substance, this addition compound breaking 
 up into palladium, hydrogen, and unsaturated body. 
 He finds, on examining the dehydrogenation of 
 alcohols to aldehydes by palladium black, that on 
 adding palladium to alcohol a considerable evolution 
 of heat takes place and a palladium is obtained from 
 which the alcohol cannot be removed by a vacuum. 
 On shaking the alcohol with the palladium for some 
 time, aldehyde may be recognised in the solution. 
 Ethyl alcohol undergoes dehydrogenation more 
 rapidly than methyl alcohol, and higher alcohols 
 still more so. 
 
 Wieland has put forward arguments for regarding 
 certain oxidation reactions as being in reality cases 
 of the dehydrogenation of the hydrate of the body 
 in question. He has shown, for instance, that 
 carbon monoxide, in presence of palladium and 
 water, may be oxidised to carbon dioxide in complete 
 absence of air or oxygen, 1 and suggests that the 
 reaction takes place, not according to the ordinarily 
 accepted formula, 2CO + O 2 == 2CO 2 , but according 
 to the dehydrogenation equation, 
 
 C0+H 2 == C0 2 +H 2 . 
 
 The hydrogen given off* is absorbed by the palladium, 
 or it may be removed by burning in air, as was done 
 in Baumann and Traube's work on the same subject. 
 The above equation says little about the course of 
 the reaction. Wieland, however, was able to show 
 that, as the first product of the action of water on 
 carbon monoxide in presence of palladium, formic 
 
 1 Wieland, Ber., 1912, 45, 679. 
 
8o CATALYTIC HYDROGENATION 
 
 acid was formed, which decomposes in presence of 
 the finely divided palladium into hydrogen and carbon 
 monoxide, the hydrogen being absorbed by the 
 palladium. 
 
 The course of the catalytic formation of carbon 
 dioxide from carbon monoxide may therefore be 
 represented thus : 
 
 Hv 
 
 CO+H 2 O = >C:O 
 OH/ 
 
 H \ 
 
 C:0 = C0+H. 
 
 Wieland has further been able to recognise formic 
 acid as the first product of the burning of carbon 
 monoxide at high temperatures without a catalyst, 
 by allowing a carbon monoxide flame to play on ice, 
 and there seems no reason why the formation of 
 carbon dioxide from carbon monoxide at all tempera- 
 tures with or without a catalyst should not proceed 
 by way of the same equation. 
 
 At a higher temperature, the reaction between 
 carbon monoxide and water can be reversed, water 
 and carbon monoxide being formed from carbon 
 dioxide and palladium-hydrogen. Wieland regards 
 the hydrogen peroxide found by Traube in the 
 carbon monoxide as being produced by the burning 
 of the hydrogen and oxygen. 
 
 In the same way, the oxidation of sulphur dioxide 
 to sulphur trioxide is a reaction which does not pro- 
 ceed in absence of water, but can actually take 
 place in the absence of oxygen, a phenomenon which 
 may be explained by the dehydrogenation of 
 sulphurous acid. 1 Wieland found that on leading 
 moist oxygen-free sulphur dioxide over oxygen- 
 free palladium black a considerable quantity of 
 
 1 Wieland, Ber., 1912, 45, 685. 
 
DEHYDROGENATION 
 
 Si 
 
 sulphuric acid was produced according to the 
 equation 
 
 (i) S0 2 +H 2 - H 2 S0 3 
 
 (2) O 2 S< 
 
 - SO.+HL. 
 
 Accordingly, the course of the reaction in the 
 sulphuric acid contact process is not one of real 
 oxidation, but a dehydrogenation in which the 
 hydrogen split off by the platinum is taken up by 
 the oxygen, while the water present in the system 
 acts as a second catalyst, in a similar manner 
 to the nitrous acid in the lead-chamber process. 
 Wieland's results throw quite a new light on the 
 necessity for, and role of, water in oxidation reactions 
 generally. 
 
CHAPTER VIII 
 
 THE TECHNICAL HYDROGENATION OF 
 UNSATURATED OILS 
 
 THE operation of " oil hardening," now carried 
 out on an extensive scale for the manufacture of 
 solid fats for use in the soap, edible fat, and candle 
 industries, consists in the saturation with hydrogen 
 of the glycerides of various unsaturated fatty acids, 
 most of which contain a straight chain of eighteen 
 carbon atoms and are thus convertible to stearic 
 acid. 
 
 The following table summarises the most impor- 
 tant acids of this class : 
 
 Con- 
 tained 
 Acid. Formula. in 
 
 Oleic CH 3 (CH 2 ) 7 -CH:CH-(CH 2 ) 7 -COOH Almost 
 
 acid pure in 
 
 olive 
 oil. 
 
 Linolic CH 3 (CH 2 ) 4 .CH:CH-CH 2 .CH:CH(CH 2 ) 7 -COOH Poppy 
 acid oil, etc. 
 
 Linolenic C 17 H 29 'COOH Linseed 
 
 acid oil. 
 
 Clupano- C 17 H 27 -COOH Fish 
 
 donic oils, 
 
 acid 
 
 Ricino- CH 8 -(CH 2 ) 5 -CH-OH-CH 2 -CH:CH(CH 2 ) 7 -COOH Castor 
 leic acid oil. 
 
 The structure of the natural oils is complicated, 
 
 not only by the variety of the acids present, but also 
 
 82 
 
UNSATURATED OILS 83 
 
 by reason of the tribasic character of glycerine, 
 whereby the existence of various mixed glycerides 
 becomes possible and, further, by the possibility 
 of stereo- (cis-trans)isomerism. 
 
 The oils usually taken for hardening purposes 
 are, inter alia, whale and other fish oils, cotton-seed 
 oil, linseed oil, arachis oil, olive oil, rape oil, sesame 
 oil, and castor oil. 
 
 In most cases the crude oil is found to contain 
 various catalytically injurious impurities which 
 must be removed before subjecting the material to 
 hydrogenation. The exact method of refining will 
 depend on the nature of the oil, but in general 
 it may be stated that the object of the refining 
 process should be to remove before everything free 
 fatty acids, albuminous impurities, and traces of 
 suspended water. For a detailed description of the 
 methods, reference should be made to a work on oil 
 refining, it being remembered that while almost 
 any oil which is pure enough for edible purposes will 
 harden satisfactorily, it is often unnecessary to 
 refine to this degree. 
 
 The manufacture of the nickel catalyst on a 
 large scale consists of a suitable modification of the 
 methods described in Chapter II. In many works 
 the nickel is employed on a porous support such as 
 kieselguhr or pumice, it being either precipitated as 
 hydroxide or carbonate on this supporting material, 
 or the porous support may be immersed in a concen- 
 trated aqueous solution of nickel nitrate or in the 
 salt melted in its water of crystallisation, the nitrate 
 being in this case subsequently converted to oxide by 
 ignition in the usual way. In any case, the dry 
 carbonate or oxide thus obtained is reduced to nickel 
 before use by means of a current of hydrogen, or 
 the oxide may, if desired, be introduced in an 
 unreduced condition into the oil and reduced there 
 in conjunction with the hardening of the oil, in 
 which case, however, the hydrogenation reaction is 
 
 62 
 
84 CATALYTIC HYDROGENATION 
 
 necessarily carried out at a temperature higher than 
 the reduction temperature of nickel oxide, for 
 instance at 260 C., while hardening in presence of 
 metallic nickel proceeds satisfactorily even at 
 160 C. 
 
 The activity of the catalyst and its power of 
 resistance to the action of poisons may be modified 
 to a very great degree by variations in the method 
 of its preparation and reduction, as well as in the 
 procedure adopted in the actual hydrogenation 
 operation itself ; further, the optimum catalyst 
 for a particular sort of oil is, by reason of the im- 
 purities contained in the oil, not necessarily that 
 which possesses the highest activity for the satura- 
 tion of, for instance, pure oleic acid. 
 
 For the reduction of the nickel oxide in a dry 
 condition various forms of plant have been described. 
 The reducing gas employed is usually pure hydrogen, 
 which is led over the oxide at a temperature of 
 3 -35 C. The material after reduction should 
 not, on account of the easily oxidisable and even 
 pyrophoric nature of nickel reduced at low tempera- 
 tures, be allowed, even when cold, to come into 
 contact with air before immersion in oil. The 
 reduction to metal is never complete, at any rate 
 at temperatures suitable for the preparation of 
 active nickel catalyst, and is facilitated by not 
 exposing the oxide before reduction to a higher 
 temperature than is necessary. Thus Sabatier and 
 Espil state that nickel oxide prepared from nitrate 
 by ignition at 550 C. was reduced to the extent of 
 93 per cent, by three hours' treatment with hydrogen 
 at 240 C., while oxide prepared by ignition of 
 nitrate at 800 C. was only reduced about 33 per 
 cent, by a similar treatment. 
 
 A simple and efficient plant for the reduction of 
 catalyst on a large scale is illustrated in Fig. 8. 1 
 
 A horizontal cylindrical reduction vessel, along 
 
 1 Ellis, " Hydrogenation of Oils/' p. 192. 
 
UNSATURATED OILS 85 
 
 which the nickel is conveyed as required by means of 
 special conveyors, may also be employed. 
 
 For the manufacture of catalyst for large installa- 
 tions several reduction units, of whatever type of 
 continuously working reducer is adopted, may be 
 connected together in series in such a way that that 
 unit containing fresh oxide receives hydrogen which 
 has already passed through the rest of the system, 
 
 HYDROGEN 
 
 FIG. 
 
 while fresh hydrogen enters at the unit containing 
 nearly reduced nickel, or the nickel oxide itself 
 may be moved through a sufficiently long heated 
 system in counter-current to hydrogen, a continuous 
 supply of reduced catalyst being in this way obtained. 
 In designing a reduction apparatus suitable for 
 continuous running it is, however, to be remembered 
 that considerable quantities of reaction water are 
 given off, accompanied by fine dust from the o ide, 
 and that for this reason, unless straight exit tubes 
 of sufficient diameter are provided, there is a 
 
86 CATALYTIC HYDROGENATION 
 
 risk of these becoming choked by the mud thus 
 formed. 
 
 If the nickel oxide is reduced in a dry condition 
 the subsequent hardening operation may be carried 
 out at 140-180 C. Should, however, the oxide 
 be introduced as such into the oil it will be necessary, 
 as already mentioned, in order to effect reduction, 
 to heat this to 250 C. at least, an operation which 
 with certain oils is undesirable in that it may, 
 especially with oils containing highly unsaturated 
 acids, lead to polymerisation and to the formation 
 of undesirable decomposition products. 
 
 In addition to carefully prepared oil and catalyst, 
 the use of hydrogen of as high a purity as possible 
 and above all free from catalyst poisons is a factor 
 of supreme importance in determining the speed and 
 success of the hydrogenation reaction. For this 
 reason, electrolytic hydrogen is, for purposes where 
 the comparatively high cost of this is not prohibitive, 
 a very suitable gas for catalytic reduction generally. 
 
 In view, however, of the high cost of electrolytic 
 hydrogen, the production of pure hydrogen from 
 water gas has in the last few years received con- 
 siderable attention. 
 
 The most important methods of manufacturing 
 hydrogen in this way are : 
 
 (1) By the interaction of water gas and steam in 
 
 presence of a catalyst. 
 
 (2) By the alternate reduction of iron oxide by 
 
 water gas and oxidation of the iron with 
 steam. 
 
 (3) By the low temperature separation of hydrogen 
 
 from water gas. 
 
 For the manufacture of hydrogen by the first 
 method, advantage is taken of the reaction between 
 carbon monoxide and steam at elevated tempera- 
 tures, whereby the carbon monoxide is oxidised to 
 dioxide at the expense of the steam, with liberation 
 
UNSATURATED OILS 87 
 
 of an equivalent volume of hydrogen, according to 
 the equation 
 
 CO+H 2 O - CO a +H 8 , 
 
 the carbon dioxide being subsequently absorbed by 
 compressing on to water or by other means. In 
 order to displace the equilibrium as far as possible 
 in the required direction it is essential first to 
 carry out the reaction at as low a temperature as 
 possible, in presence of an active catalyst, and 
 secondly, as will be seen from the nature of the 
 equation, to employ a large excess of steam. The 
 equilibrium between carbon monoxide and steam 
 has been studied by Hahn 1 (although for tempera- 
 tures somewhat higher than those employed for the 
 manufacture of hydrogen), but it is found difficult 
 in practice to obtain by this method hydrogen free 
 from carbon monoxide without subsequent purifica- 
 tion with calcium carbide or with alkalies at an 
 elevated temperature and pressure. 
 
 The reaction is carried out in practice by leading 
 the mixture of water gas and steam through retorts 
 containing a catalyst and maintained at 500-600 C., 
 either by external heating or, according to a varia- 
 tion introduced by the Badische Anilin- & Soda- 
 Fabrik 2 by injecting air or oxygen into the retorts 
 together with the steam and water gas. 
 
 As a catalyst, iron is usually employed. Nickel 
 and cobalt 3 have also been proposed, but have been 
 found to be less efficient. The iron employed may 
 be activated by the addition of promoters such as 
 copper, 4 the alkalies, 5 preferably fixed to the iron 
 as " ferrites " by previous ignition at a high tem- 
 perature and subsequent lixiviation, or according 
 
 1 Hahn, Zeit. physikal. Chem., 1903, 42, 705; 44, 51; 1904, 
 48, 735- 
 
 2 Badische Anilin- & Soda-Fabrik, English patent, 27117/12. 
 
 3 Mond and Langer, English patent, 12608/88. 
 
 4 Buchanan and Maxted, English patent, 6477/14. 
 
 5 Buchanan and Maxted, English patent, 6476/14. 
 
88 CATALYTIC HYDROGENATION 
 
 to the Griesheim process 1 a contact mass containing 
 lime, with or without iron, may be employed. 
 In this case, the base has an absorbent function in 
 addition to a catalytic one, part of the carbon dioxide 
 produced being fixed as calcium carbonate, 
 
 CO+H 2 O+CaO :, CaCO 8 +H 2 . 
 
 The second method used for the manufacture of 
 hydrogen consists in the alternate and separate 
 treatment of iron oxide with an industrial reducing 
 gas such as water gas and steam respectively. The 
 process is by no means a recent one, and for details 
 of earlier proposals reference may be made to the 
 patent specifications, inter alia, of Hart, 2 Lewes, 3 and 
 Lane. 4 In its modern form the plant is made in two 
 types, consisting either of externally heated and 
 usually vertical retorts or of internally heated 
 producers, the heat in this case being applied 
 by injection of air during the reducing phase. The 
 material with which the retorts are filled may 
 consist of natural iron ore, of compact iron, or of 
 artificially prepared briquettes. Further, the yield 
 for a given size of furnace may be increased by the 
 incorporation or addition of promoters such as the 
 oxides of lead, copper, chromium, or manganese. 5 
 
 Hydrogen produced from water gas by the 
 intermittent process contains as a rule, in addition 
 to impurities capable of being removed by purifiers, 
 from i to 3 per cent, of carbon monoxide. This 
 impurity is not, as in hydrogen manufactured by 
 the continuous process, a direct residue from the 
 water gas used for reduction, but is formed by the 
 action of steam on carbon deposited on the iron 
 contact mass during the reducing phase by decom- 
 
 1 Griesheim Elektron, English patent, 2523/09. 
 
 2 Hart, English patent, 7741/89. 
 
 3 Lewes, English patent, 20752/90 and 4134/9. 
 
 4 Lane, English patent, 10356/03. 
 
 5 Jaubert, English patent, 22126/10 ; Messerschmitt, French 
 patent, 461480 (1913) ; Saubermann, English patent, 401/11. 
 
UNSATURATED OILS 89 
 
 position of carbon monoxide contained in the 
 water gas used for such reduction. 
 
 Carbon monoxide, especially at temperatures 
 below 200 C., exerts an injurious effect on the 
 hardening of oils, 1 and in order to obtain a maximum 
 speed of reaction, at any rate under the usual 
 industrial conditions, it is therefore necessary to 
 employ hydrogen free from this impurity. 
 
 This absence of carbon monoxide may be obtained 
 by modifying the ordinary intermittent process in 
 such a way that no carbon is deposited during the 
 reducing phase. The deposition takes place by 
 reason of the fact that carbon monoxide at high 
 temperatures, especially in the presence of a catalyst 
 such as iron, is unstable, passing into a mixture of 
 carbon dioxide, carbon, and unchanged monoxide 
 according to the equation, 
 
 2CO=CO 2 4-C. 
 
 The carbon thus produced persists into the steaming 
 phase, where, by the action of steam, carbon monoxide 
 is generated simultaneously with the production of 
 hydrogen by the interaction of the steam with the 
 reduced iron. Such deposition of carbon may be 
 prevented by employing for the reduction a special 
 reducing gas containing a sufficient proportion of 
 carbon dioxide to monoxide to approximate to 
 or exceed the carbon dioxide-carbon monoxide 
 equilibrium ratio for the temperature and conditions 
 used for reduction, 2 such reducing gas being em- 
 ployed without the introduction into the retorts of 
 air or steam during the reducing phase, or, if desired, 
 air 3 or steam 4 may be introduced into the retorts 
 during the reduction phase in addition to ordinary 
 water gas. 
 
 1 Caro, Seifensieder Zeitung, 1913, 852. 
 
 2 Maxted and Ridsdale, English patent, 12896/15. 
 
 3 Messcrschmitt, English patent, 17691/13. 
 
 4 Dellwik Fleischer Wassergas Ges., English patent, 21479/08. 
 
go CATALYTIC HYDROGENATION 
 
 Working with the first of these methods, the 
 author has obtained a gas containing not the slightest 
 trace of carbon monoxide and possessing the follow- 
 ing composition : 
 
 Hydrogen 99.94 
 
 Carbon monoxide . . . . . . nil. 
 
 Carbon dioxide 
 
 Nitrogen . . . . . . . . 0-06 
 
 100-00 
 
 For the attainment of this high degree of freedom 
 from traces of air or its components, it is necessary 
 to employ heated feed- water for the boiler generating 
 steam for the hydrogen plant, and to instal surface 
 condensers in preference to open water scrubbers. 
 
 The freedom of hydrogen from traces of carbon 
 monoxide may also be effected by purifying the 
 impure gas by compression on to alkalies with 
 formation of formates, 1 or by treatment with heated 
 calcium carbide according to Frank's method. 
 Using an 80 per cent, soda solution for the purifica- 
 tion, a pressure of 50 atmospheres at 260 C. is 
 employed, so that while the method is extremely 
 suitable for the synthesis of ammonia, it is in 
 general preferable for catalytic hydrogenation to 
 prepare the hydrogen directly in a pure condition 
 without having recourse to a subsequent rather 
 difficult purification process. 
 
 Passing to the third general method of hydrogen 
 manufacture, namely, the low temperature separa- 
 tion of the constituents of water gas (hydrogen and 
 carbon monoxide), it will be seen that the maximum 
 purity of the hydrogen obtainable will under normal 
 conditions be determined by the partial pressure 
 of carbon monoxide at the lowest temperature 
 employed in the separation. 
 
 1 Badische Anilin- & Soda-Fabrik, English patent, 1759/12. 
 
UNSATURATED OILS 91 
 
 The vapour pressure of carbon monoxide at various 
 temperatures is given in the following table i 1 
 
 Temperature. Vapour pressure of CO. 
 183 C. i722mm. 
 
 i 88 1065 
 
 193 616 
 
 198 329 
 
 203 158 
 
 205 114 
 
 207 Solidification point. 
 
 Since it is desirable in low temperature separa- 
 tions to avoid the deposition of solid bodies, which 
 by obstruction, especially in tubular exchangers, 
 may seriously endanger the smoothness and con- 
 tinuity of running, it will be seen that the low 
 temperature method, even if carried out at tempera- 
 tures approaching the solidifying point of carbon 
 monoxide, will not give by itself hydrogen of suffi- 
 cient purity for catalytic use. The purity may be 
 increased by working at an elevated pressure, 
 but it is found necessary to separate the last traces 
 of carbon monoxide by treatment with calcium 
 carbide according to Frank's method, or by com- 
 pression on to heated alkalies or alkaline earths with 
 formation of formates as already described. 
 
 For details of the plant utilised in the commercial 
 manufacture of hydrogen by this method, reference 
 is made to the original patent specifications of 
 Linde and others. 2 
 
 For the carrying out of the fat-hardening reaction 
 itself, various forms of plant have been devised, 
 the effect desired being to obtain as intimate a 
 contact as possible between the gaseous, liquid, 
 and solid phases of the system, represented by 
 hydrogen, oil, and nickel respectively. 
 
 1 Baly and Donnan, Trans. Ghent. Soc. 1902, 81, 919. 
 
 2 Linde, English patents, 7205, 1911 ; 9260, 1911. Frank, 
 English patent, 26928, 1906, Societ L'Air Liquide, English 
 patents, 7147, 1913 ; 13160, 1914. 
 
CATALYTIC HYDROGENATION 
 
 The degree of contact obtained by the simple 
 bubbling of hydrogen through a vessel containing 
 heated oil and nickel is insufficient for the satisfactory 
 carrying out of the hydrogenation in practice, 
 where a high reaction velocity and consequent 
 large output for a plant of given size are essential 
 for economic success. 
 
 A well-known design of plant in which this contact 
 is increased by spray action is that evolved by 
 
 K IL 
 
 fHK 
 
 HYDROGEN 
 
 FIG. 9. 
 
 Wilbuschewitsch. 1 It consists of a series of auto- 
 claves connected together in such a way (see Fig. 9) 
 that hydrogen and oil containing finely divided nickel 
 are passed in counter-current to one another through 
 each unit of the system by means of sprays as shown. 
 The oil is introduced at the top of the first autoclave, 
 A, and, collecting in the conical reservoir, D, at 
 the bottom, is partly projected into the hydrogen 
 
 1 Wilbuschewitsch, English patent, 30014/10. 
 
UNSATURATED OILS 
 
 93 
 
 atmosphere by means of the gas entering the vessel 
 at E and partly conveyed to the spray, F, at the 
 top of the next vessel by means of the pump, G, 
 the oil subsequently passing in a similar manner 
 from B to C. The hydrogen, entering the vessel A 
 by way of the jet, E, passes through the system by 
 means of K, L, M, and N. The pressure employed 
 is about nine atmospheres, a suitable initial tem- 
 perature being 150-160 C. 
 
 FIG. 10. 
 
 Testrup 1 projects the mixture of oil and catalyst 
 by means of hydrogen pressure from vessel to 
 vessel of a series of autoclaves somewhat similar 
 to that employed by Wilbuschewitsch, the pressure 
 being allowed to decrease from vessel to vessel in 
 order to obtain the spraying effect desired (see 
 Fig. 10). 
 
 1 Testrup, English patent, 7726/10. 
 
94 
 
 CATALYTIC HYDROGENATION 
 
 A plant which is capable of bringing about 
 intimate contact between oil and hydrogen without 
 the use of several vessels is illustrated in Fig. n. 1 
 The oil alone is circulated by means of the rotary 
 pump, A, and, entering the vessel by the jet B, 
 causes by injector action in C the mixing effect 
 
 necessary for the short- 
 ening of the time of 
 reaction. 
 
 Calvert 2 mixes the oil 
 and gas by means of a ro- 
 tary stirrer driven by an 
 electric motor contained 
 in an extension of the 
 autoclave and under a 
 hydrogen pressure equal 
 to that at which the 
 reaction is carried out. 
 
 The author 3 has em- 
 ployed a plant in which 
 an intimate mixing of 
 practically the whole of 
 the oil under treatment 
 with hydrogen is ob- 
 tained by projecting the 
 oil and hydrogen in 
 counter-current to one 
 another through a 
 column provided with a 
 series of fixed propeller- 
 like baffles, by the action 
 FIG. ii. of which the moving oil- 
 
 gas mixture is alternately 
 
 rotated clockwise and anti-clockwise respectively, 
 the circulation being carried out at such a speed 
 that the vessel becomes filled with a foam of hydro- 
 
 1 Ellis, U.S. patent, 1059720. 
 
 2 Calvert, English patent, 18350/13. 
 
 3 Maxted and Ridsdale, English patent, 109993/1917. 
 
UNSATURATED OILS 95 
 
 gen and oil. The plant used is illustrated in 
 Fig. 12. 
 
 The saturation of an oil with hydrogen is a 
 strongly exothermic reaction, and is accordingly 
 accompanied by a considerable rise of temperature, 
 which in a typical operation in a well insulated 
 vessel* may be as much as from 160-200 C., in the 
 course of a hardening operation lasting from two to 
 three hours ; indeed this spontaneous rise of tem- 
 perature during treatment affords an extremely 
 useful indication that saturation has begun and is 
 taking place with a satisfactory velocity. The 
 velocity of absorption of hydrogen necessarily 
 falls off as the reaction proceeds, and for this reason 
 it is advisable in installations provided with several 
 hydrogenation vessels to begin the hardening of 
 successive charges at different times in order to 
 ensure a uniform consumption of hydrogen. It 
 has already been stated that the hydrogenation 
 reaction follows the ordinary monomolecular 
 formula. 
 
 The time required for the hardening operation 
 is determined by the nature and purity of the oil, 
 by the temperature and presssure, and by the 
 amount of catalyst employed. 
 
 The following particulars relate to a typical 
 hardening operation with an experimental unit of 
 the type illustrated in Fig. 12. 
 
 The charge consisted of three-quarters of a 
 ton of crude rape oil which was pumped from the 
 storage tanks into the hardening vessel and heated 
 to 140 C. by means of high pressure superheated 
 steam passed through the heating jacket surrounding 
 the vessel. 
 
 As soon as this requisite initial temperature 
 had been obtained the usual proportion of nickel 
 catalyst was added, this catalyst having been 
 prepared by the dry reduction of nickel oxide at 
 350 C., and subsequent mixing, for convenience 
 
9 6 
 
 CATALYTIC HYDROGENATION 
 
 in handling, with a small quantity of the oil for the 
 treatment of which it was to be used. 
 
 COLUMN 
 
 CONTAI N I NC 
 
 BAFFLES AS 
 
 DESCRIBED 
 
 GAS 
 
 CIRCULATING 
 PUMP 
 
 OIL CIRCULATING 
 PUMP 
 
 FIG. 12. 
 
 Pure hydrogen prepared from water gas by a 
 modified intermittent process as already described 
 
UNSATURATED OILS 97 
 
 and at a pressure of 60 Ib. to the square inch was 
 now introduced into the vessel, this having been 
 previously evacuated to eliminate air. The circu- 
 lating pumps were put into action and the reaction 
 allowed to proceed, fresh hydrogen to replace 
 that absorbed by the oil and to maintain the pressure 
 at 60 Ib. being continuously admitted by means of 
 an automatically constructed valve. 
 
 In two hours 1,800 cubic feet of hydrogen had 
 been absorbed, corresponding with a reduction of 
 iodine value from 99 to 27, and samples of the oil 
 (which were drawn off from time to time during the 
 operation) were found to solidify to a hard, brittle 
 fat. The temperature of the charge had, by reason 
 of its heat of reaction, risen from 140 C. to 185 C. 
 in the course of the two hours' run. 
 
 The hydrogenated charge was pumped into a 
 filtering tank and filtered while still hot by means 
 of a steam heated filter-press of the usual type, 
 the filtered fat being run into barrels and allowed 
 to solidify. 
 
 The heating of the charge of oil to the requisite 
 initial temperature for hardening without over- 
 heating and without the formation of decomposition 
 products presents certain difficulties in practice 
 where large volumes of oil have to be treated. 
 It is effected in some systems by means of flue 
 gases, while in others superheated steam is used, 
 the latter method being preferable. 
 
 This steam is preferably employed at a pressure 
 above the vapour pressure of water at the minimum 
 temperature required for starting hydrogenation, 
 so that a certain amount of condensation takes place 
 in the heating jacket, the water resulting from this 
 being removed by suitable traps. By adopting this 
 procedure the large amount of latent heat evolved 
 during the condensation of the steam is effectively 
 utilised for heating the oil to. reaction temperature 
 and the time required for the preliminary heating 
 
 7 
 
98 CATALYTIC HYDROGENATION 
 
 becomes very much shorter than is the case when 
 low pressure dry superheated steam is used. 
 
 The following table contains the minimum boiler 
 pressure required for the rapid heating of the 
 charge in this way to various initial temperatures. 
 In practice this pressure must be very considerably 
 above the minimum value indicated. 
 
 Initial temperature, Minimum boiler pressure, 
 
 C. Ib. per square in. 
 
 130 25 
 
 14 39 
 
 150 56 
 
 1 60 76 
 
 170 101 
 
 The degree of hardness of the oil after treatment 
 may be estimated roughly by allowing a few drops 
 to solidify on a cold surface or more exactly by 
 determining the " titer," i.e., the melting point, 
 under standard conditions, of the fatty acids liberated 
 from the hardened oil by saponification. A more 
 satisfactory determination of the degree of un- 
 saturation is, however, obtained by measuring the 
 iodine value or, as a quick approximation, the 
 refractive index, these tests being the methods of 
 control most commonly employed in practice. 
 
 The iodine value of an unsaturated oil or fatty 
 acid may be defined as the number of grams of 
 iodine which are taken up under standard conditions 
 of working by 100 grams of the oil or acid in question. 
 Saturation by iodine takes place much in the same 
 way as by hydrogen. Thus oteic acid on being 
 brought together with iodine under suitable condi- 
 tions undergoes conversion into the saturated di-iodo- 
 derivative according to the equation : 
 
 CH 3 -(CH 2 ) 7 -CH:CH-(CH a ) 7 -COOH+I a = 
 
 CH 3 (CH 2 ) 7 -CHI-CHI-(CH 2 ) 7 -COOH. 
 
 Two methods of determination, namely, those 
 of Hubl and Wijs, are in common use. For estima- 
 
UNSATURATED OILS 99 
 
 tions carried out according to Hubl's method, an 
 iodine solution 1 made by dissolving 25 grams of 
 iodine in 500 c.c. of pure 95 per cent, alcohol is 
 employed in conjunction with a mercuric chloride 
 solution consisting of 30 grams of HgCl 2 in 500 c.c. 
 of alcohol, equal volumes of these stock solutions 
 being mixed not more than twenty-four hours before 
 use. In order to carry out a determination, from 
 0-2 to i-o gram of the fat, depending on the degree 
 of saturation, is accurately weighed out and placed 
 in a stoppered bottle of about 800 c.c. capacity. 
 About 20 c.c. of chloroform are added to dissolve 
 the fat, followed by 25-30 c.c. of the mixed iodine 
 and mercuric chloride solution. The well-stoppered 
 bottle is now placed in a dark place and allowed to 
 stand for six to twelve hours in order to complete 
 the reaction. The excess of iodine remaining un- 
 combined is determined, after adding 20 c.c. of a 
 10 per cent, potassium iodide solution and 400 c.c. 
 of water, by titration with a standard thiosulphate 
 solution. During the titration, the bottle is well 
 shaken from time to time, and as soon as the con- 
 tents have become a pale yellow, starch is added as 
 an indicator, the end-point being marked by the 
 vanishing of the dark colour due to iodide of starch. 
 
 According to Wijs's method the iodine and mer- 
 curic chloride solutions are replaced by a solution 
 of iodine and iodine trichloride in glacial acetic 
 acid. 
 
 7-9 Grams of iodine trichloride and 8-7 grams of 
 iodine 2 are dissolved separately in glacial acetic 
 acid on a water-bath, access of moisture being 
 avoided. The two solutions are poured into a 
 i -litre flask and made up to the mark with glacial 
 acetic acid. The determination is carried out much 
 the same as by Hubl's method, but has the important 
 
 1 Lewkowitsch, " Technology of Oils, Fats, and Waxes," 
 p 311 et seq. 
 
 2 Lewkowitsch, loc. cit. 
 
ioo CATALYTIC HYDROGENATION 
 
 advantage that the protracted standing is un- 
 necessary in that the reaction is usually complete in 
 from two to three hours. 
 
 The degree of saturation of an oil may also be 
 determined by measuring its index of refraction, 
 this method being particularly valuable for following 
 the course of the hardening reaction while this is 
 proceeding and forming in this way a check on the 
 hydrogen absorption read off from the meters 
 attached to the plant. C. Ellis 1 gives the following 
 typical figures for cotton oil, hydrogenated for 
 ten hours, samples being withdrawn at the end of 
 every hour. 
 
 Time of hydrogenation Melting point, Index of refraction 
 in hours. C. at 55 C. 
 
 1-4588 
 
 1 28-2 1-4577 
 
 2 31-3 I-4568 
 
 3 34-3 1-4557 
 
 4 37'9 1-4549 
 
 5 40-8 1-4540 
 
 6 43-8 I-4527 
 
 7 45-6 I-45I8 
 8 
 
 47-3 
 10 55-9 1-4496 
 
 The principal uses of hardened oils are in the 
 manufacture of soaps, of candles, of edible fats such 
 as artificial lard, also of margarine, chocolate, etc. 
 For edible purposes, complete elimination of nickel 
 by filtration is essential. Bower 2 states that neutral 
 oils do not take up even traces of nickel in a form 
 not capable of being removed by filtering, such 
 solution of nickel only taking place in cases where 
 the oil contains considerable quantities of free 
 fatty acids. 
 
 Small quantities of nickel contained in hardened 
 fats are easily detected colorimetrically by dimethyl- 
 glyoxime (Tchugaeff s reagent) the method giving 
 
 1 C. Ellis, " Hydrogenation of Oils," p. 124. 
 
 2 Bower, Zeitsch. Nahr. und Genussm., 1912, 104. 
 
UNSATUR^TED 
 
 also an approximate idea of the quantity of nickel 
 present. The method of carrying out the reaction 
 has been improved and standardised by Fortini x 
 and by Kerr, 2 the determination being made by 
 ashing 10-20 grams of the hardened fat, dissolving 
 in hydrochloric acid, evaporating the solution to 
 dryness, and igniting the residue to free it from 
 traces of organic matter and excess of HCL This 
 residue is transferred to a tall 50 c.c. cylinder and 
 moistened with a few c.c. of distilled water, 50 c.c. of 
 standard dimethylglyoxime solution being added. 
 A red coloration (or precipitate, if the nickel content 
 is high) results either at once or on standing, the 
 tint being compared with that produced under 
 the same conditions with a nickel solution of known 
 strength. The standard solution of dimethyl- 
 glyoxime is made up by dissolving 5 grams of this 
 body in 50 c.c. of absolute alcohol and making up to 
 100 c.c. with strong aqueous ammonia, the solution 
 being kept in a well-stoppered bottle. For edible 
 purposes, the fat should not contain more than 
 0-05 milligram of nickel per kilo. 
 
 1 Fortini, Chem. Zeit., 1912, 36, 1461. 
 
 2 Kerr, /. Ind. and Eng. Chem., 1914, 207. 
 
;::;.--V:.AME; INDEX 
 
 Amberger, 13 
 
 Badische Anilin-& Soda-Fabrik, 
 
 3. 87, 90 
 
 Balatschinsky, 55 
 Baly, 91 
 Bilheimer, 54 
 Blanc, 31 
 Boeseken, 36, 54 
 Borsche, 34, 37, 38, 60, 63 
 Bouveault, 31 
 Bower, 100 
 Bredig, 12, 68 
 Breteau, 47 
 Brochet, 70 
 Bruce, 46 
 Brunner, 58 
 Buchanan, 87 
 Biittner, 72 
 
 Calvert, 94 
 Caro, 89 
 Cooke, i 
 
 Dellwik Fleischer Wassergas 
 
 Gesellschaft, 89 
 Donnan, 91 
 Douris, 32 
 
 Ellis, 84, 94, 100 
 Enklaar, 33 
 Eijkman, 46 
 
 Fischer, 48 
 Fokin, 23, 36 
 Ejomin, 56 
 Fortini, 101 
 Franck, 59, 60 
 Frank, 91 
 
 Garbowski, 12 
 Gaudion, 74 
 Geilmann, 75 
 Gerum, 36, 66, 69 
 Glinka, 50 
 Godchot, 47 
 Griesheim Elektron, 88 
 Gutbier, 12 
 
 Hahn, 87 
 Hatt, 44, 46 
 
 CATALYTIC HYDROGENATION IO2 
 
 Hart, 88 
 
 Hartmann, 30, 70 
 Heimbiirger, 38 
 Henrich, 12 
 Henrichsen, 44 
 Hohenegger, 40 
 
 Ipatiew, 32, 35, 45, 48, 55, 58, 64 
 Jaubert, 88 
 
 Kametaka, 48 
 Kaempf, 44 
 Kelber, 14, 30, 40, 71 
 Kerr, 101 
 Knoevenagel, 76 
 Kolbe, i, 68 
 Kotz, 65 
 
 Lane, 88 
 Langer, 87 
 Leroux, 47 
 Lespieau, 41 
 Lewes, 88 
 Lewkowitsch, 99 
 Linde, 91 
 Lottermoser, 12 
 Low, 12, 36 
 
 Maihle, 50, 52, 57, 63, 67, 75 
 Mannich, 75 
 Maxted, 87, 89, 94 
 Messerschmitt, 88, 89 
 Meyer, 15, 26, 45, 50, 54, 57, 
 
 60, 68 
 Mom, 36 
 Mond, 87 
 Murat, 46, 50, 63 
 
 Normann, 20 
 
 Paal, 12, 13, 30, 36, 37, 40, 66, 
 
 69, 7> ?i. 7 2 
 Padoa, 59 
 Patents Journal, 21 
 
 Reid, 24 
 Ridsdale, 89, 94 
 Ritter, 49, 54 
 Roth, 36, 37 
 
SUBJECT INDEX 
 
 103 
 
 Sabatier, 10, 28, 29, 30, 39, 43, 
 46, 49, 50, 51, 52, 57, 61, 63, 
 66, 67, 68, 69, 73, 74, 75 
 
 Saubermann, 88 
 
 Saytzeff, 68 
 
 Schaeffer, 65 
 
 Schmidt, 48 
 
 Schwarz, 14, 30, 40 
 
 Senderens, 10, 28, 29, 30, 39, 
 43, 46, 49, 51, 61, 66, 68, 73, 
 
 Skita, 14, 15, 26, 33, 34, 35, 
 
 45, 49, 50, 51. 52, 54, 57. 5. 
 
 59, 60, 63, 66, 67, 70 
 Smirnoff, 55 
 Societe L'Air Liquide, 91 
 
 Testrup, 93 
 Tschugaeff, 56 
 
 Vavon, 41, 62 
 Veraguth, 48 
 Vignon, 62 
 
 Waser, 48 
 Weide, 36 
 Wieland, 76, 79, 80 
 Wilbuschewitsch, 92 
 Wilde, i, 39 
 
 Willstatter. 12, 33, 36, 44, 46, 
 48 
 
 Zelinski, 50, 75 
 
 SUBJECT INDEX 
 
 Acetone, 62 
 
 Acetylenic linkages, Hydro- 
 
 genation of, 38 
 Acids, Fatty, Hydrogenation 
 
 of, 35 
 
 Acridine, 59 
 Acrolein, 33 
 Alcohols, Dehydrogenation of, 
 
 Alkaloids, Hydrogenation of, 59 
 Allyl alcohol, 31 
 Anethol, 32 
 Aniline, 50 
 Anthracene, 47 
 Azobenzene, 67 
 
 Benzal cinnamal acetone, 35 
 
 Benzaldehyde, 51 
 
 Benzene, Hydrogenation of, 
 
 43 
 
 Benzoic acid, 50 
 Bromostyrolene, Reduction of, 
 
 38 
 
 Camphor, 64 
 
 Carbon monoxide, 61 
 
 Carbon monoxide, Mechanism 
 of oxidation of, 79 
 
 Carbon monoxide, Vapour pres- 
 sure of, 91 
 
 Cholesterine, 60 
 
 Cinnamal acetophenone, 34 
 Cinnamal malonic acid, 38 
 Cinnamenyl acrylic acid, 38 
 Citral, 35 
 Cobalt catalyst, Preparation of, 
 
 10 
 
 Collidine, 58 
 Copper, Activity of, compared 
 
 with nickel, 30, 39 
 Copper catalyst, Preparation 
 
 of, 10 
 
 Crotonyl alcohol, 31 
 Cyclobutene, 46 
 Cyclohexane, Dehydrogenation 
 
 of, 75 
 
 Cyclo-octene, 48 
 Cymene, 45 
 
 Dibenzal acetone, 34 
 Diphenyl, 46 
 Durene, 45 
 
 Erucyl alcohol, 31 
 Ethylene, 28 
 Eugenol, 33 
 
 Fluorene, 48 
 
 Gases, Hydrogenation of, 20 
 Gluten as a protective colloid, 
 14 
 
104 
 
 SUBJECT INDEX 
 
 Gold, Catalytic activity of, 3 
 Gum arable as a protective 
 colloid, 14 
 
 Halogen compounds, Reduc- 
 
 tion of, 38 
 Halogens, Removal of, by 
 
 hydrogen, 71 
 Hydrazobenzene, Dehydrogen- 
 
 ation of, 77 
 Hydrogen, Catalytic estima- 
 
 tion of, 70 
 Hydrogen, Commercial manu- 
 
 facture of, 86 
 Hydroquinone, Dehydrogena- 
 
 tion of, 77 
 
 Index of refraction of oils, 100 
 
 Indol, 59 
 
 Inoculation method for col- 
 
 loidal catalysts, 14 
 Iodine value, 98 
 lonone, 52 
 Iron catalyst, Preparation of, 
 
 10 
 
 Isocyanic esters, 67 
 Isonitriles, Reduction of, 67 
 Isophorone, 35 
 Isoquinoline, 58 
 
 Liquids, Hydrogenation of, 20 
 Lutidine, 58 
 
 Mesityl oxide, 34 
 
 Metallic oxides, Reduction of, 
 
 Naphthalene, 46 
 Naphthalene derivatives, De- 
 
 ny drogenation of, 76 
 Nickel, Detection of, 100 
 Nickel catalyst, Commercial 
 
 reduction of, 84 
 Nickel catalyst, Preparation 
 
 of, 6 
 
 Nitriles, Reduction of, 66 
 Nitrobenzene, 69 
 
 Oil hardening, Particulars of 
 
 typical operation, 95 
 Oil hardening plant, 92 
 
 Oleic acid, 36 
 Oleic alcohol, 31 
 Oxides of nitrogen, Reduction 
 of, 68 
 
 Palladium catalyst, Prepara- 
 tion of colloidal, 13 
 
 Phenanthrene, 47 
 
 Phenol, 49 
 
 Phenyl acetylene, 40 
 
 Phorone, 35 
 
 Picoline, 58 
 
 Pinene, 54 
 
 Piperine, 60 
 
 Platinum catalyst, Preparation 
 of non-colloidal, n 
 
 Platinum, Preparation of col- 
 loidal, 13 
 
 Pressure, Hydrogenation under, 
 26 
 
 Propenyl isoamyl carbinol, 32 
 
 Propylene, 29 
 
 Protective colloids, 13 
 
 Pulegone, 54, 55 
 
 Pyridine, 57 
 
 Pyrrol, 59 
 
 Quinoline, 58 
 Retene, 48 
 
 Sabinene, 56 
 
 Safrol, 33 
 
 Santonine, 60 
 
 Shaking method, Hydrogena- 
 tion by, 21 
 
 Silver, Catalytic activity of, 3 
 
 Styrolene, 30 
 
 Sulphur dioxide, Mechanism of 
 oxidation of, 80 
 
 Terpenes, 54 
 
 Thujene, 56 
 
 Tolane, 41 
 
 Toluene, 45 
 
 Tolyl isopropyl alcohol, 55 
 
 Vapour treatment for hydro- 
 
 genation, 16 
 
 Velocity meter for gas flow, 18 
 Vinyl isobutyl carbinol, 32 
 
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