The Uses of Raney Nickel

The Uses of Raney Nickel E U GENE LIEBER

AND

F R E D L . MORRITZ

Department of Chemistry. Illinois Institute of Technology. Chicago. Illinois Page I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 I1. Preparation and Properties . . . . . . . . . . . . . . . . . . . . . . 418 1 . Preparation of Raney Nickel Catalysts . . . . . . . . . . . . . . 418 2 . Properties of Raney Nickel Catalysts . . . . . . . . . . . . . . . . 419 420 3 . Other Raney Catalysts . . . . . . . . . . . . . . . . . . . . 4. The Effect of Additives . . . . . . . . . . . . . . . . . . . . . . 420 a . Platinic Chloride . . . . . . . . . . . . . . . . . . . . . . . . 421 b . Alkali . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422 5 . Selectivity of Raney Nickel Catalyst . . . . . . . . . . . . . . . . 424 6. Reductions with Nickel-Aluminum Alloy and Aqueous Alkali . . . . . 426 I11. Special Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 429 429 1. Oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . a . Raney Nickel as a n Oxidation-Reduction Catalyst . . . . . . . . . 429 b . The Cannizzaro Reaction . . . . . . . . . . . . . . . . . . . . 432 c . Dehydrogenation . . . . . . . . . . . . . . . . . . . . . . . 433 2. Amines by Reductive Alkylation . . . . . . . . . . . . . . . . . 434 3 . Rearrangements . . . . . . . . . . . . . . . . . . . . . . . . . 438 4 . Dehalogenation . . . . . . . . . . . . . . . . . . . . . . . . 440 5 . Desulfuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 6. Hydrogenations without the Use of Added Hydrogen . . . . . . . . . 447 7. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . 449 a . Ozonide Decomposition . . . . . . . . . . . . . . . . . . . . . 449 b . Raney Nickel in an Acid Medium . . . . . . . . . . . . . . . . 449 c . Catalysis of Hydrazine Decomposition . . . . . . . . . . . . . . 450 d . Reduction of a Hydroperoxide . . . . . . . . . . . . . . . . . . 450 e . Decarboxylation . . . . . . . . . . . . . . . . . . . . . . . . 450 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451

I . INTRODUCTION I n 1925 Murray Raney (la) was granted a patent covering a new method of preparation of a nickel catalyst . A pulverized nickel-silicon alloy was reacted with aqueous sodium hydroxide to produce a pyrophoric. brownish nickel residue with superior catalytic properties. Upon investigation of other alloys of nickel and alkali-soluble metals. it was found that the aluminum alloy could be made with ease ( l b ) and was easily pulverized . The catalyst which is prepared by the action of aqueous sodium hydroxide on this nickel-aluminum alloy is known as 417

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EUGENE LIEBER AND FRED L. MORRITZ

Raney nickel. Similar methods have been patented by workers in Germany (2), England (3), and the U.S.S.R. (4). Raney nickel is very probably the most commonly used nickel catalyst. It is also the most versatile of catalysts. In one or other of its several modifications it has been used for hydrogenations over a wide range of pressures varying from high t o subatmospheric, for desulfuration, for dehalogenation, and for very many other reactions. This chapter will not concern itself with the topic of hydrogenation of specific functions. Such topics as the hydrogenation of the double bond, the carbonyl group, and the cyanide group have been well covered in recent reviews (5,6,7). It is the authors' intention to demonstrate the versatility of Raney nickel by citing the many uses t o which i t can be put over and above the simple addition of hydrogen t o an unsaturated function. No attempt is made, however, to ignore this best-known reaction of Raney nickel. Examples and references are cited where they most aptly fit into the context. 11. PREPARATION AND PROPERTIES 1. Preparation of Raney Nickel Catalysts

The process used for the preparation of Raney nickel was originally described in a patent issued to Murray Raney in 1927. The catalyst is prepared from Raney alloy which is commercially available and which consists of approximately equal weights of nickel and aluminum. Schroter ( 5 ) lists several ways in which the alloy may be treated after pulverization. That method in which the alloy is decomposed by the action of caustic alkali gives rise t o Raney catalyst. Several methods of processing the alloy to give the catalyst have been described in the literature. I n the original process recommended by Raney (la) and developed by Covert and Adkins (8), there was involved a prolonged period of digestion of the alloy at 115'. Mozingo (9) later improved the process, shortening and lowering the temperature of the digestion [period. At the suggestion of Adkins, the catalyst of Covert is known as W-1 and that of Mozingo is known as W-2, a similar designation being applied t o the improved preparations described by Adkins and his co-workers (10,ll). The W-6 Raney nickel catalyst of Adkins and Billica (11) has been claimed to be the most active form of Raney nickel known. The leaching and the digestion processes are accomplished a t about 50°, and the washing is done by a continuous flow method under pressure of hydrogen. W-7 catalyst is alkaline in nature and has given good results in the hydrogenations of ketones, phenols, and nitriles for which alkali in the reaction mixture is beneficial (12,13).

THE USES OF RANEY NICKEL

419

Smith et al. (14) have claimed that different temperatures of solution of the inactive portion of the alloy, different temperatures and lengths of digestion, and different methods of washing have little effect on the catalytic activity as measured by the rate of hydrogenation of d-limonene. I n their procedure the alcohol was evaporated under vacuum from the catalyst after which the terpene was added. With the probable large loss of hydrogen under these conditions, it is doubtful that these authors were investigating actual Raney nickel of the W-6 type. Adkins and Krsek (15)) in comparing the various types of Raney nickel catalyst, found their activities to vary considerably in the hydrogenation of @-naphthol. Pattison and Degering (16) have prepared a catalyst of the Raney type from a nickel-magnesium alloy. These authors used acetic acid to dissolve the inactive portion of the alloy. The catalyst was found to be as active as the W-4 Raney nickel of Pavlic and Adkins (10) and twice as active as the W-2 catalyst of Mozingo (9). Paul (17) has described nickel catalysts of the Raney type which were prepared from alloys of nickel, aluminum and cobalt, or chromium, or molybdenum. The alloy contained 52% aluminum to 48% of the other twp metals. Bernstein and Dorfman (18) have prepared a modified catalyst by allowing the reaction mixture to stand at room temperature overnight after the addition of the alloy. Bougault, Cattelain, and Chabrier (19) and Mozingo (20) have prepared similarly modified catalysts. Delepine and Horeau (21) and Reichstein and Gatzi (22) received good results using small amounts of Raney nickel catalyst prepared in amounts just sufficient for use. The procedures consumed very little time because of the small quantities concerned. The advantage of always working with freshly prepared catalyst is obvious. 2. Properties of Raney Nickel Catalysts

The composition of the catalyst will, of course, vary with the method of preparation. Aubrey (23) indicates the following composition for his catalyst: A1 1-3 %, Fe 1%, Cu 0.1 %, Co 0.05%, Mn 0.04 %. The aluminum content is a function of the duration of the treatment with the alkali. Paul ( 6 ) has used catalysts which titrated to 17% aluminum. Heublen (24) has used catalysts even richer in aluminum. Adkins and Billica (11) reported their W-6 catalyst to contain 11% aluminum, the remainder being nickel. Ipatieff and Pines (25), however, found 21% alumina, 1.36% aluminum, 0.5% sodium aluminate, and about 77% nickel in W-6 catalyst.

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EUGENE LIEBER AND FRED L. MORRITZ

There has been some conflict in the literature concerning the deterioration of the activity of Raney nickel as the preparation increases in age. Aubry (23) reports that, when the surface of Raney nickel is exposed t o water, it is oxidized t o the hydroxide. Mozingo (9) cautions against the preparation of more than a six-month supply because the catalyst deteriorates on standing, whereas Paul (6) assumes that the catalyst is easily preserved. I t has been claimed (5b) that the catalyst can be stored in a sealed container without much loss in activity. Adkins and Billica (11) maintain that the high activity of their W-6 modification is due t o the large amount of adsorbed hydrogen and that on standing the catalyst reverts to ordinary Raney nickel. Many writers have found relatively old catalyst to be quite active. Recently, Fanta (26)’ used year-old Raney nickel for the conversion of 5-nitro-2-phenyl pyrimidine to 2,2’-diphenyl-5,5’-azoxypyrimidine. Pattison and Degering (27) have shown that oxygen is responsible for the major part of the loss in activity. Smith et al. (14) studied the influence of aging and were able to obtain a correspondence of the surface area, which lessened with age, and the catalytic activity. Dupont and Piganiol (28) have applied x-ray analysis to the study of Raney nickel. The crystal dimensions lie between 40 and 80 A . , a magnitude ten times smaller than that of the reduced nickel of Sabatier and Senderens, the dimensions of which lie between 400 and 1090 A. The spectral lines of Raney nickel are also more diffuse than those of reduced nickel. Raney nickel catalyst contains hydrogen, most of which is probably bound by van der Waals forces. A good part of the hydrogen can be removed by heating. After prolonged heating of the catalyst at a temperature of 95”, some hydrogen is still held by the catalyst. Unlike ordinary nickel, Raney nickel can form an amalgam. This property can be attributed to the hydrogen which acts as a third component. 3. Other Raney Catalysts

Other Raney catalysts have been prepared. Raney cobalt has been described by several authors (28,29). The active cobalt has been claimed t o be especially suitable for the reduction of nitriles. The preparation of an active copper has been described by Faucounau (30). Paul and Hilly (31) have described the preparation of Raney iron. It is claimed that Raney iron reduces acetylenic bonds to ethylenic bonds with no further hydrogenation occurring.

4. The E$ed of Additives There are two general methods for the activation of Raney nickel catalysts. Many examples can be found in the literature of the addition

THE USES OP RANEY NICKEL

421

of a base to activate the catalyst, or of the addition of a noble metal. More recently, combinations of the two have been used. a. Platinic Chloride. I n 1936, Lieber and Smith ( 3 2 ) found th a t the addition of small amounts of platinic chloride to Raney nickel catalyst just prior t o the start of reduction produced a marked enhancing effect on the activity of the catalyst for a variety of functional groups. DelBpine and Horeau (21) independently proposed a similar use of platinic chloride whereby, prior to the reduction, the catalyst was shaken in a solution of platinic chloride for a relatively long period. The platinized catalyst was used in an alkaline medium. More recently, Jayme and Sartre (33) have described a catalyst activated in a manner similar t o th a t of Deldphe. This catalyst was used with good results for the hydrogenation of oxidized xylan. Both types of preparation have been described as having a high degree of activity. The two methods of activation by platinic chloride have been compared (34), and it is claimed that the method of Delepine is superior. Workers in G.B.L. Smith’s laboratory, however, have failed to confirm this fact. It is to be noted that the difference in opinion probably lies in the fact th at the two groups studied different types of compounds and that the French school, unlike the American, used alkali in conjunction with their platinized Raney nickel. Further studies dealt with the reduction of nitro and carbonyl compounds (35,36). Voris and Spoerri (37) used platinized Raney nickel to effect the reduction of 2,4,6-trinitro-m-xylene. Platinic chloride, high temperature, and high pressure were used because of the difficulty of reducing the third nitro group. Using the platinized Raney nickel catalyst of DelBpine, Decombe (38) succeeded in hydrogenating triphenyiacetonitriIe, the end product being 2,2,2-triphenyIethyIamine. More recently, Samuelson, Garik, and Smith (39) have used their platinized catalyst in conjunction with alkali to effect the hydrogenation of nitro compounds. Since the earlier investigations there have been marked improvements in the methods of preparation of the catalyst (11). Accordingly, the activating effect of platinic chloride on the improved catalysts, in particular that designated as W-6, was investigated (40,41). Adkins and Billica had noted that the addition of a small amount of triethylamine had a beneficial effect in the hydrogenation of carbonyl compounds. The time required for the hydrogenation of aldehydes and ketones was approximately cut in half. Lieber and his co-workers investigated the hydrogenation of a variety of compounds using platinic chloride and triethylamine separately and together. In the ketones the use of platinic chloride alone resulted in complete poisoning, whereas the use of

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EUGENE LIEBER AND FRED L. MORRITZ

triethylamine reduced the time for complete hydrogenation. A mixture of triethylamine and platinic chloride also lessened the reaction time. A variety of aldehydes, aliphatic and aromatic, were reduced in the presence of the amine alone and in the presence of the mixture. I n general, the time for reduction in the presence of the mixture was less than in the presence of triethylamine alone. An exception was cinnamaldehyde, in which molecule the conjugated double bonds may be a complicating factor. The mixture proved also to have a beneficial effect in the hydrogenation of nitroethane, p-nitrotoluene, and phenylacetonitrile. The use of preformed triethylamine chloroplatinate was also studied, and, though the data are sparse, it seems that the preformed basic chloroplatinate is the more effective promoter for nitro compounds, whgreas the best results are obtained for benzaldehyde by using an excess of the amine over the platinic chloride. It has been reported (42) that ammonium chloroplatinate used in conjunction with alkali showed a favorable effect in the reduction of the fatty acids in butter. Campbell and O’Connor (43) have used platinic chloride alone and in conjunction with alkali for the reduction of substituted acetylenes. When the platinic chloride and the alkali were used together, the reduction occurred more rapidly in the case of amyl acetylene, but there was no significant change in the reduction velocity of dibutylacetylene. Although the action of most additives on a catalytic surface is somewhat obscure, it seems safe to assume that the action of platinic chloride is a promoter action through the formation of metallic platinum under these reductive conditions. The platinum is plated out on the nickel surface. Promoter action has been observed when platinic chloride in amount sufficient to provide only 0.4 mg. of platinum is mixed with as much as 3 g. of Raney nickel catalyst (41). b. Alkali. The additive used probably most frequently for the activation of Raney nickel catalyst is sodium hydroxide. Delepine (21), noting that pinonic acid could be hydrogenated only if alkali were added in excess of the amount needed for neutralization, extended the investigation t o the reduction of many carbonyl compounds. When small amounts of alkali are added to the reduction mixture, there is a severalfold increase in the rate of hydrogenation. This activation is even more apparent when the catalyst has been platinized. Smith and Lieber (36) reported that, although the use of alkali activated Raney nickel for the hydrogenation of carbonyl groups, it had a deterring effect on the reduction of aromatic nitro compounds. I n particular, alkali retarded the reduction of nitrobenzene and the three isomeric sodium nitrobenzoates, whereas it increased the velocity of reduction of the methyl and ethyl esters of nitrobenzoic acid.

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T H E USES O F R A N E Y NICKEL

To check the .general applicability of activation by alkali, Paty (44) extended the investigation t o several functional groups. The addition of small amounts of sodium hydroxide considerably reduced the time for reduction of 2-methyl-2-butene, phenylacetonitrile, and anethole. Larger amounts of alkali, in the case of phenylacetonitrile and in the case of anethole, increased the time for complete hydrogenation. P a ty considers that the activating effect is due t o the action of sodium hydroxide on the residual aluminum or nickel-aluminum alloy in the catalyst. Ungnade and McLaren (45) studied the effect of alkali on the catalytic reduction of phenols, using Raney nickel catalyst. The ease of reduction was not affected by substitution in the ring unless two ethyl or n-propyl groups occupied the ortho positions. I n the latter case, with no alkali, no cyclohexanols were formed. 2,6-Di-n-propylphenol was recovered unchanged, but 2,6-diethyl-4-me t hylphenol underwent hydrogenolysis and reduction of the ring to give l-methyl-3,5-diethylcyclohexane. When the hydrogenations were carried out in the presence of a small amount of sodium hydroxide, the corresponding cyclohexanols were formed. With other phenols, the addition of alkalies led t o a slight promotion effect, inasmuch as a lower initial temperature was required for reduction. It was also found (46) that the hydrogenation of alkyl phenols is promoted by small amounts of their sodium salts. Chabrier and Sekera (47) found th at in the presence of alkali the sodium salt of the semicarbazone of a-keto-y-phenyl butyric acid was hydrogenated four times as rapidly as in the presence of Raney nickel alone. Similarly, the semicarbazone of P-benzoylpropionic acid was hydrogenated slowly in neutral solution and four times as rapidly in 0.1 N alkali. CsHaCH(=NNHCONH,)CH2CH2COOH---* CeHsCHCH2CHtCONHCONHNH I

I

Newman, Underwood, and Reno11 (48) studied the reduction of 1,2-epoxydecane. Over Raney nickel the product was 1-decanol. I n the presence of alkali, however, the main product was 2-decanol. Chemical reduction also leads to 2-decanol. It is interesting t o note that, when styrene oxide is reduced over Raney nickel, the primary alcohol is received as the main product whether or not alkali is present. Heilmann (49) reported the use of sodium hydroxide in conjunction with platinum and Raney nickel for the reduction of the double bond in a,@-unsaturatedketones. Burnette (50) used sodium hydroxide in the hydrogenation of silvan over Raney nickel. Delepine (51) has shown that many hydrogenations over Raney nickel, for which high temperatures and pressures have been used, can be run under ordinary conditions, particularly if sodium carbonate is added.

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E U G E N E LIEBER A N D FRED L. MORRITZ

Smith (52,53) has investigated the affect of various additives on the rate constants for the hydrogenation of terpenes. The most effective additive tried was palmitic acid. Soaps, amines, sulfated alcohols, quaternary ammonium salts, and amides also increased the rate. 6. Selectivity of Raney Nickel Catalyst

One of the most important and intriguing tasks before the catalytic chemist today is the selective hydrogenation of one functional group in the presence of a second, also reducible, functional group. The role of Raney nickel in this respect is a bit obscured because of the many methods of preparation. Although the activity of the older forms of the catalyst toward the carbonyl function was not great, it is evident that the newer types of Raney nickel, the W-6 and W-7 catalysts of Adkins and Billica (1l),can smoothly reduce aldehydes and ketones to the respective alcohols. I n the following examples it is not claimed that no other catalyst will better perform the task but, rather, it is sought merely t o point out some of the uses t o which this catalyst has been put. The effect of temperature upon selectivity has been shown in a striking manner by Zafiriadis (54,55) in the hydrogenation of cinnamylidenemethylhexyl ketone with Raney nickel. At 40" the ethylenic bonds were reduced; a t 130" the carbonyl function was reduced to the alcohol; and at 260" the phenyl ring was reduced. AcOEt, 5 % catalyst

C~H~CH=CH-CH=CH-COC~€II~ ------+ CsH s(CHz)&OCeH 13

AcOEt, 5 % catalyst

40°, 100 atrn., 3 hr.

CeHs(CHz)rCOCeHla

CaHs(CH2)4CHOHCsH13

130". 100 atm.. 3 hr. AcOEt, 10% catalyst + CsHs(CHz)rCHOHCeH13 260°, 100 atrn.. 12 hr.

CeH1 I (CH2)dCHOHCeHtr

Cornubert and Phelisse (56), using Raney alloy as catalyst, studied the selective hydrogenation of a,ðylenic ketones. The reduction of benzalacetone gave w-phenyl-Bpentanol when the reaction was run in absolute alcohol. When, however, the reaction was run in a solution of ethanol containing chloroform in a concentration of 2 g./l., or HC1 in a concentration of 1.1 g./l., benzyl acetone was obtained. Similar results were noted with dibenzalacetone. Difurfurylideneacetone adds seven molecules of hydrogen in absolute ethanol or in ethanol containing 0.6 g./l. of chloroform. In ethanol containing 10 to 500 g./l. of chloroform, only two molecules of hydrogen are taken up. With higher concentrations of chloroform, the catalyst is inactive. Blout and Silverman (57) have reported a good example of selective reduction with Raney nickel. It was found th a t Raney nickel effectively catalyzes the hydrogenation of aromatic nitro compounds in

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THE USES O F RANEY NICKEL

preference t o aliphatic double,bonds conjugated to the benzenoid ring. The hydrogenations of the isomeric nitrocinnamic acids and esters were studied. Since these compounds are not readily soluble in organic solvents, i t was found necessary to use an alcoholic suspension. When the suspension was shaken with Raney nickel under a pressure of 2-3 atm. and a t 20-30°, rapid reduction took place, the rate remaining steady until three equivalents of hydrogen were taken up, after which the rate fell to 0.3-0.01 of its former value. The esters were hydrogenated more rapidly than the acids. The data in Table I illustrate the case. TABLE I The Selective Hydrogenation of Nitrocinnamic Acids and Eslers" Acceptor p-Nitrocinnamic acid Methyl-p-nitrocinnamate m-Nitrocinnamic acid Methyl-m-nitrocinnamate a-Methyl-p-nitrocinnamic acid o-Nitrocinnamic acid Methyl-0-nitrocinnamate

Product p-Aminocinnamic acid Methyl-p-aminocinnamate nz-Aminocinnamic acid Methyl-m-aminocinnamate a-Methyl-p-aminocinnamic acid o-Aminocinnamic acid Methyl-o-aminocinnamate

Hours

Yield, %

6 3 12 4.5 6

73 76 76

5 1.5

37 74

81

a4

OAbstracted from Blout and Silverman, J . Amer. Chem. SOC.,66, 1442 (1944), with the perniission of the authors and copyright owner, the American Chemical Society.

The o-nitro compounds show a much smaller decrease in reduction rate when the nitro group has been hydrogenolyzed, and it was necessary to stop the reduction immediately after absorption of the calculated amount of hydrogen. On further reduction hydrocarbostyril was formed in 80% yield (if R = H, the yield is 90%).

Hilditch and Pathak (58) studying the catalytic reduction of methyl eleostearate, found that the reaction a t 110" and a t 170" was extremely selective in the presence of Raney nickel. No methyl stearate was formed until 90% of the linoleate had been transformed into octadecenoates. Ehrhart (59) used Raney nickel to hydrogenate compounds of the type RCH(CN)NHCOR'. The nitrile was reduced t o the amine, but the amide was untouched.

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EUGENE LIEBER AND FRED L. MORRITZ

6. Reductions with Nickel-Aluminum Alloy and Aqueous Alkali

A rather unique variation in the application of Raney nickel to the reduction of organic compounds is the use of nickel-aluminum alloy in the presence of aqueous alkali. The procedure has the advantage of ease of application. The reduction is effected as part of the procedure for the preparation of the Raney nickel hydrogenation catalyst itself. The technique has been developed largely through the efforts of Papa, Schwenk, and co-workers (60). The reduction is probably due to the activation, by the freshly formed nickel catalyst, of the hydrogen liberated by the action of the alkali on the aluminum component of the alloy. Similar reductions have been observed when aluminum was used along with previously prepared Raney nickel catalyst. In these cases, if the nickel catalyst is omitted and only aluminum is used, either no hydrogenation occurs or amorphous products are obtained from which no pure substances can be isolated. GENERAL PROCEDURE

(60a)

Ten grams of the compound is dissolved in 300 ml. of 10% sodium hydroxide and heated to 90" after which 30 g. of Raney's nickel-aluminum alloy is added in small portions with stirring. The reaction mixture is stirred for an additional hour, the temperature being maintained a t 90". The original volume is maintained by the addition of water. A few drops of octyl alcohol are added occasionally to prevent any excessive foaming. Although this treatment is usually sufficient to complete the reduction, further heating of the reaction mixture with the addition of 5 g. of alloy and 50 ml. of 10% sodium hydroxide generally results in increased yields, especially with alkali-insoluble compounds. The hot solution is filtered and the residue washed thoroughly with water in such a manner that it is always covered with liquid. If the nickel residue is allowed to become dry, it will ignite. The filtrate is cooled and made acid to Congo red paper with concentrated HC1. It is desirable to effect the acidification by adding the alkaline solution to the acid with stirring. The reduction product is isolated by filtration or by extraction of the acidified solution. For the alkali-insoluble compounds, the reductions are carried out in a 1-1. flask equipped with an adaptor and a reflux condenser. During the addition of the alloy the reaction mixture is shaken frequently. In some cases toluene may be added to retain the compound in a uniform surface layer. Alcohol may also be used in sufficient amount to keep the compound in solution. The reduction product may be isolated either by steam distillation or extraction of the alkaline solution. One of the first reports (60b) on this method described the reduction of

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THE USES OF RANEY NICKEL

estrone t o a mixture of a- and P-estradiol. Further investigation of many carbonyl compounds showed that the method gives results comparable t o those obtainable by the Clemmensen reduction (61). The use of the alloy with aqueous alkali is not specific. The carbonyl compounds are converted either to the corresponding carbinol or to the hydrocarbon, the extent of reaction depending only upon the structure of the compound. Carbonyl compounds of the general formula I yield the hydrocarbon, whereas carbonyl compounds of the general formula I1 yield the carbinol. CsH6COR

R = H, alkyl or aryl

I

CE.H~(CH,),COR’

R‘

=

H or alkyl

I1

I n order t o obtain reduction of the carbonyl group to the hydrocarbon, it is necessary that the carbonyl group of I be directly attached t o a n aromatic nucleus, thus forming a conjugated system. When the carbonyl group, even a s part of a conjugated system, is not directly attached to an aromatic carbon atom, the reduction of the carbonyl group proceeds only as far as the alcohol. I n Table I1 are listed the carbonyl compounds which Papa and his co-workers have reduced by this method. It will be noted that, whereas TABLE I1 Reduction of Carbonyl Compounds by Nickel-Aluminum Alloya Compound Benzaldehyde Salicylaldehyde p-Hydroxybenzaldehyde Cinnamic aldehyde Acetophenone m-Nitroacetophenone p-Hydroxyacetophenone p-Hydroxypropiophenone p-Hydroxybenzophenone 2-Methylcyclohexanone Dibenzyl ketone Salicylacetone pHydroxybenzalacetophenone Desoxybenzoin Benzoin Anisil (toluene as solvent) Anisil (EtOH and toluene as solvent)

Reduction product Toluene o-Cresol p-Cresol Hydrocinnamyl alcohol Ethylbenzene m-Aminoethylbenzene p-Ethylphenol p-Hydroxy propylbenzene p-Hydrox ydiphenylmethane 2-Methylcyclohexanol Dibenzyl carbinol 4-(o-Hydroxyphenyl)-butanol-Z p-Hydroxydiphenylpropane Dibenzyl Dibenzyl Anisoin Hydroanisoin

Abstracted from Papa, Schwenk, and Whitman, J . Ore. Chem., 7, 587 (1042). 10 g. of carbonyl compound.

* Based on the reduction of

Yield, 60 75 80 50 70 76 72 78 90 80 70 85

50 70 50 80 80

%b

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EUGENE LIEBER AND FRED L. MORRITZ

benzaldehyde gives toluene and acetophenone gives ethylbenzene, cinnamic aldehyde and salicylacetone are reduced to hydrocinnamyl alcohol and 4-(o-hydroxyphenyl)butano1-2, respectively. I n addition to the carbonyl group, other functional groups, such as the nitro group which is reduced to the amine, are reduced as usual with no interference with the reduction of the carbonyl function. Table I1 also illustrates an interesting effect resulting from change of solvent in the reduction of an alkali-insoluble compound. Anisil, which is not reduced without solvent, gave anision as the only reduction product in the presence of toluene, while hydroanision was obtained by using toluene and ethanol as solvent. The use of nickel-aluminum alloy in aqueous alkali for the reduction of organic compounds has been observed (6Oc) to briny about the displacement by hydrogen of methoxy, halogen, and sulfonic acid groups from several types of benzenoid compounds. Table I11 summarizes the TABLE I11 Displacement of Halogen and Sulfonic Groups by Nickel-Aluminum Alloy i n Ayueous Alkali" Compound

Reduction product

Halogen Compounds Bromobenzene Benzene m-Chlorobeneoic acid Benzoic acid p-Chloronitrobeneene Aniline Toluene p-Chlorobenzaldehyde 5-Chloro-2-hydroxybenealdehy de o-Cresol Ethylbenzene p-Bromoacetophenone @-(p-Chlorobenzoy1)propionicacid 7-Phenylbutyric acid Sulfonic Acids Benzenesulfonic acid Benzene o-Sulfobenzoic acid Benzoic acid rn-Sulfobenzoic acid Benzoic acid Naphthalene-@-sulfonic acid Naphthalene 2-Naphthol-6-sulfonic acid @-Naphthol 2-Naphthol-3,6-disulfonicacid @-Naphthol 0

Yield, %

100 100 65 60 75 67 70 10 40 50 40 30 30

Sohwenk, Papa, Whitman, and Ginsberg, J . Ore. Chem., 9. 1 (1944).

results of observations on the displacement of halogen and sulfonic acid groups. I n general the displacement of sulfonic acid groups has been limited t o the a-naphthalenesulfonic acids, only a few instances of a similar displacement being observed for the beta compounds (62). By means of nickel-aluminum alloy in aqueous alkali, sulfonic groups are displaced from a- and 0-naphthalenesulfonic acids as well a s from the benzenesulfonic acids. The low yields in some cases are probably due t o

THE USES O F RANEY NICKEL

429

a poisoning of the nickel catalyst by the sulfite or sulfide formed during the reaction. The displacement of an alkoxy group by hydrogen using nickelaluminum alloy in aqueous alkali depends upon the nature and position of the other substituents in the benzenoid ring (60c). When subjected t o this reduction procedure, p-anisidine and o-, m-, and p-cresyl methyl ether were recovered unchanged. When the ortho-para-directing methyl or amino groups in these compounds are replaced by the meta-directing carboxyl group, quantitative displacement of the methoxy group takes place in o- and p-methoxybenzoic acid. The meta acid, however, is recovered unchanged, and in no case has a meta-substituted methoxy group been observed to be displaced. Similar displacement of the methoxy group takes place in compounds having other meta-directing groups such as -NOz, -CHO, and -COCHs. In addition t o the displacement reaction, the meta-orienting groups in these compounds are subject t o reduction to the ortho-para-orienting amino or alkyl groups. I n a compound containing such a reducible substituent, elimination of the methoxy group occurs only before the reduction has converted the meta-directing into an ortho-para-directing group. For example, in the reduction of p-nitroanisole, a 20% yield of aniline and a 70% yield of p-anisidine were obtained. The aniline must result from a n initial displacement of the methoxy group followed by reduction of the nitrobenzene thus formed, whereas the p-anisidine arises from the initial reduction of the nitro group.

111. SPECIAL REACTIONS 1. Oxidation

a. Raney Nickel as a n Oxidation-Reduction Catalyst. If Raney nickel is added t o a slightly alkaline solution of sodium hypophosphite, immediate frothing occurs with liberation of hydrogen. Bougault, Cattelain, and Chabrier (19) demonstrated th at the sodium hypophosphite was oxidized t o sodium phosphite. This is a remarkable reaction in th a t a reduction catalyst is used to effect an oxidation. It was observed th a t NaH2POz

+ H ~ 0 - tNaH2P03 + H2

0.5 g. of Raney nickel was capable of transforming 35 g. of sodium hypophosphite t o sodium phosphite. It is probable th a t the oxidation is

430

EUGENE LIEDER AND FRED L. MORRITZ

effected by a dehydrogenation of the hydration product, the last step being the one catalyzed. I n a second example, Bougault et al. showed

/

H

HO

O=P-H

\

\ /

+HzO+ ONa

H

/H -+O=P-OH

P-H

HO

/ \

\

ONa

+Hz

ONa

that sodium stannite is oxidized t o sodium stannate under the same conditions. Sn/OH

+ 2H20

+

Sn(OH),

+ Ha

\OH

By conducting the oxidation in the presence of a hydrogen acceptor, the first oxidation-reduction reaction to be catalyzed by Raney nickel was effected. Sodium phenylisocrotonate was readily converted to sodium phenylbutyrate. Ashida (63) observed that glucose in a saturated solution in cyclohexanol was reduced to d-sorbitol by heating a t 130-135" NaHzPOz

+ CsH&H=CHCH2COZNa + HzO

---f

NaHZP03

+ C6H6(CH2)&02Na

in the presence of Raney nickel. I n the absence of the catalyst no reduction was observed. Ashida, however, failed to determine whether the hydrogen for the reduction came from the nucleus or from hydrcjxyl groups of the cyclohexanol. A report (64) of the work of H. Ruschig has described the catalytic conversion of pregnenolone (I) to progesterone (11) in the presence of a special Raney nickel catalyst, with cyclohexanone as a hydrogen acceptor. Kleiderer and Kornfeld ( 6 5 ) , in an interesting investigation, determined the generality of this oxidation and studied the

I

I1

possibility of using it in the reverse sense, i.e., as a reductive method in the presence of a hydrogen donor. Preliminary attempts to oxidize cholesterol to cholestenone with cyclohexanone as hydrogen acceptor showed that the special aerated Raney nickel as prepared by Ruschig was considerably less effective than the usual Raney nickel kept under toluene. Because of its favorable oxidation potential (66), cyclohexanone is an

43 1

THE USES O F RANEY NICKEL

excellent hydrogen acceptor to use in these types of Raney nickel catalyzed oxidations. The method merely involves the refluxing of a mixture of the compound t o be oxidized, the hydrogen acceptor and the catalyst in toluene. Table IV shows the variety of secondary alcohols which may be TABLE I V Catalytic Oxidation of Secondary Alcohols with Raney Nickel in Presence of Cyclohexanone as Hydrogen Acceptoro Compound oxidized

g./g. compound

Catalyst,

Time of reflux, hr .

Product

Yield, % '

Cholesterol Benzoin Benzhydrol Dihydrocholesterol Fluorenol Epieoprostanol

2.0 2.0 2.0 2.5 2.5 1.5

24 24 22 24 24 24

Cholestenone Bend Benzophenone Cholestenone Fluorenone Coprostanone

80 35 30 80 76 50

a

Kleiderer and Kornfeld, J . Org. Chem.. lS, 455 (1948).

converted t o ketones by this procedure. The oxidation of cholesterol, i t may be noted, involves a simultaneous shift of the A 5double bond t o the A4 position in conjugation with the carbonyl group. This shift occurs likewise in the Oppenauer oxidation of cholesterol (67). When, next, the redox reaction was studied as a preparative reduction method, i t was found that a wide variety of compounds could be reduced in the presence of any of several hydrogen donors. Table V summarizes some typical results which can be accomplished by this type of reduction. I n general, the types of conversion obtained are similar t o those brought TABLE V Catalytic Reductions with Raney Xickel in the Presence of Various Types of Hydrogen Donors" Compound reduced

Hydrogen donor

Product

Yield, % ~

Diphenylacetylene Laurone 3-Acet ylquinoline

Ethanol Isopropanol Isopropanol

Cholestanone Benzoin Benzophenone Desoxyanisoin Stilbene Ethyl o-benzylbenzoate

Cyclohexanol Cyclohexanol Diethy lcarbinol Cyclohexanol Diethylcarbinol Isopropanol

a

Dibenzyl Diundecylcarbinol

77 80

quinoline Dihydrocholesterol Dibenzyl Diphenylmethane p,p'-Dimethoxydibenzyl Dibenzyl o-Benzylbeneoic acid

62 50

3-Ethyl-5,6,7,8-tetrahydro-

Abstracted from Kleiderer and Kornfeld, J . Org. Chem., 19,455 (1948).

53 75 80 60 86

432

EUGENE LIEBER AND FRED L. MORRITZ

about by high-pressure reduction (7) or by the action of alkali on nickelaluminum alloy (68). Carboriyl groups, activated ethylenic bonds, and acetylenic bonds in varied environments are smoothly reduced. Hydrogenolysis of the carbon-oxygen bond occurs when it is alpha to a n aromatic ring. Related reductions have been carried out by Bougault (19) and by Mozingo (69) with Raney nickel, the latter using ethanol as solvent. These workers believed that the hydrogen for the reduction was supplied by the catalyst and have not mentioned the possibility that the hydroxylic solvent employed might act as hydrogen donor. Support for this latter view was obtained (66) in the isolation of acetone from hydrogenation experiments in which isopropanol was used as a hydrogen donor. Under similar conditions Wolfrom (70) has isolated acetaldehyde when using ethanol as solvent. It is probable that both the hydrogen donor and the hydrogen held by the catalyst play a part in these reductions, especially when only small amounts of catalyst are used. Kleiderer and Kornfeld (65), however, found that, in the presence of excess Raney nickel, stilbene may be reduced in 80% yield to dibenzyl when dioxane is the solvent. It is evident, therefore, that reduction may be effected entirely by means of the hydrogen adsorbed on the catalyst and that the role of the hydrogen donor solvents is an accessory one. b. The Cannizzaro Reaction. Raney nickel has been known to catalyze the Cannizzaro reaction of aldehydes. As is well known, this reaction, in the ordinary sense, is catalyzed by strong bases and proceeds when the carbon alpha to the carbonyl group has no hydrogen bound to it. In the Raney nickel induced reaction, however, the presEnce of a n a-hydrogen seems to have no effect. Butyraldehyde, undergoes an aldol condensation in the presence of alkali alone, but in the presence of both Raney nickel and alkali disproportionation takes place a t ordinary temperatures (71). Formaldehyde is entirely disproportionated in 70 minutes in the presence of the Raney nickel catalyst, whereas in its absence it is only 50% transformed in 30 hours. The data below are due to Del6pine (71). Formaldehyde, g. 3

3 3 6 12

Solveni, 2% NaOI1, ml. 100 100 100 200 400

Catalyst, Raney nickel None 4.5 4.5 4.5 4.5

Time, min. 1800

70 30 180 65

Transformed, % 50 100 97 94.5 52.5

Benzaldehyde, glucose, galactose, and arabinose also undergo the reaction. The reaction has been formulated as follows:

THE USES O F RANEY NICKEL (1) (2)

(3)

+

433

RCHO NaOH + RCH(0Na)OH followed by dehydrogenation RCH(0Na)OH -+ RCOONa HZ RCH(0Na)OH H 2 + RCH9OH NaOH

+

+ +

Reaction (3) is assumed to be fast, since there is no observed release of hydrogen. The Cannizzaro reaction can be avoided if an easily reducible substance is added to the reaction mixture. Thus Delepine reacted Raney nickel with a mixture of galactose and the sodium salt of either cinnamic or crotonic acid in the presence of alkali. This reaction has also been noted by Tomkuijak (72), who, when hydrogenating D-xylose in water RCH(0Na)OH

+ R'CH=CHC02Na

-+ RC02Na

+ R'CH&H2C02Na

with 30% Raney nickel, found that d-xylonic acid was produced. The results of Delepine were confirmed by Ashida and Bebiko (73). I n the presence of Raney nickel, the Cannizzaro reaction was observed with formaldehyde, butyraldehyde, D-glucose, benzaldehyde, and furfural in 2% NaOH solution. In the absence of Raney nickel formaldehyde, D-glucose and furfural did not react in 2% NaOH solution. Evidence has also been presented (74) that the Cannizzaro reaction can occur in the absence of alkali if sufficient Raney nickel is present. c. Dehydrogenation. There does not exist a large literature concerning the activity of Raney nickel as a dehydrogenation agent. Palfray and Sabetay (75) and Paul (76,77) have made a study of the dehydrogenation of alcohols using Raney nickel as a catalyst. It was found that dehydrogenation could be accomplished with Raney nickel at lower temperatures than with reduced nickel. By distillation from a suspension of Raney nickel in alcohol, Paul was able to dehydrogenate sec-butyl alcohol at go", receiving a 90% yield of butanone. Hexanol-3, dehydrogenated a t 130°, gave an 80% yield of hexanone-3. Octanol-2 and octanol-3 a t 176" gave 95% yields of the respective octanones. Isopropyl alcohol at 80" gave a 30% yield of acetone. Secondary alcohols are easier to dehydrogenate than primary alcohols. I n the primary alcohols, hydrocarbons are formed along with carbon monoxide, condensation products, and products of crotonization. When dodecanol was heated a t 200" with hydrogen under 220 lb. pressure in the presence of Raney nickel, an almost theoretical yield of undecane was obtained (78). The fact that the same result is obtained when the hydrogen is replaced by nitrogen is evidence for this not being purely a hydrogenolysis. Since a small amount of lauryl aldehyde could be obtained at ordinary pressures, it is inferred that it is the first formed product and later dissociates into undecane and carbon monoxide. The carbon monoxide reacts with hydrogen to form methane and water.

434

EUGENE LIEBER AND FRED L. MORRITZ

Tishchenko (79)) using a modified form of Raney nickel, obtained a 95.7%yield of camphor from the dehydrogenation of borneol. Rutovskii, (80) received a 93.5% yield of camphor with Raney alloy. Reeves and Adkins (81)) studying the dehydrogenation of primary alcohols, removed the hydrogen with ethylene. It was found that, though Raney nickel could be used for a catalyst for the reaction, the yields were low and, in general, the Raney nickel was inferior t o a catalyst composed of copper, zinc, nickel, and barium chromite. Moretti (82,83) has studied the catalytic dehydrogenation of fatty acids over a Raney nickel catalyst. The fatty acid, in a nitrogen atmosphere, was spread in a thin layer over the catalyst and was heated without agitation. Part of the fatty acid was dehydrogenated t o form an unsaturated acid; part reacted with the nickel t o form a salt. It is postulated that the hydrogen liberated by these two reactions reduces the acid to the aldehyde and to the alcohol. Although the aldehyde was not found to be present in determinable quantity, a yield of 5 t o 6% of the alcohol as the stearic ester was found. The aldehyde and the alcohol are degraded to carbon monoxide and a hydrocarbon. Thus, though the fatty acids can be dehydrogenated by means of Raney nickel, the yields are poor because of the complex ensuing reactions. Harlay (84) has used Raney nickel to dehydrogenate dihydropapaverine to papaverine in 50% yield. He found Raney nickel t o be more satisfactory for this purpose than the nickel of Sabatier and Senderens, but not as effective as a palladium catalyst. Mosettig and Duvall (85) used Raney nickel to transform the tetrahydrophenanthrone-1and -4 into the respective phenanthrols a t the boiling point of benzene, but also found this catalyst less advantageous than palladium.

2: Amines by Reductive Allcytation By the action of ammonia, primary or secondary amines, carbonyl groups can be converted, in the presence of hydrogen and a suitable catalyst, to primary, secondary, or tertiary amines. This reaction has proved to be a useful tool in the field of synthetic organic chemistry. The conversion can be formulated as follows:

THE USES OF RANEY NICKEL

(1) (2) (3) (4)

+

435

RR’CO RNHz + RR’CZNR’’ RR’C=NR” H, + RR’CHNHR” or R”R’”NH RR’CO R”R’”NH + RR’C(0H)NR”R”’ RR’C(0H)NR’’R”’ H P-+ RR’CHNR’””‘

+

+ +

The conditions can be adjusted so as to give primary amines in the case of ammonia or secondary amines in the case of a primary amine. Whether the aldimine, as in (l),is formed or the hydroxy compound, as in (3), is of little consequence, since either species can be hydrogenated to the desired product and since, in this procedure, there is no necessity of isolating and purifying intermediates. Experimentally (86), the carbonyl compound and the amine together with a condensing agent are condensed and hydrogenated in one step. Robinson and Snyder (86) used acetophenone and ammonia over W-2 Raney nickel a t 150” and 3500-5000 lb. pressiire t o produce a-phenethylamine in 44 to 52% yield. By this general

+ Hz + C~HF,CH(NH~)CH,+ HzO

C6H5COCHa f NHa

method, first observed by Mignonac (87) in 1921, it is not necessary to prepare and t o isolate imines, hydroamides, or Schiff bases; they are formed during the reaction as intermediates. The catalysts usually encountered in this reaction are platinum oxide and Raney nickel. Cope and Hancock synthesized several alkylaminoethanols, using both catalysts (88). Although they prepared the compounds with Adams’ catalyst, they found Raney nickel to be also suitable a t elevated temperatures and pressures. An 86% yield of 2-sec-butylaminoethanol was obtained from methyl ethyl ketone and CH3COCH2CH3

+ HzNCHzCHzOH + HP Raney nickel

150°,

t

CsH5CH(CHa)NHCHzCH20H

+ HzO

1000-2000 p.s.i.

ethanolamine. Emerson and Walters (89) found that, for the reductive alkylation of aniline, Raney nickel and sodium acetate as condensing agent gave the best results. A 58% yield of N-ethylaniline was received when 58 g. of W-1 Raney nickel and 1 g. of sodium acetate were used. With 0.2 g. of platinum oxide and 1 g. of sodium acetate, a 41 % yield was obtained. With Raney nickel the following results were obtained: Aniline Ethyl n-Propyl n-€3 u ty 1 n-Amy1 n-Heptyl Benzyl

Yield 58 52 47 62 65 50

436

EUGENE LIEBER AND FRED L. MORRITZ

Emerson (90,91,92) has extended the reaction to include aromatic nitro compounds and azo compounds as starting materials. When a n alcoholic solution of an aromatic nitro compound and an aldehyde are reduced with hydrogen over W-1 Raney nickel in the presence of sodium acetate, the corresponding secondary amine is formed in good yield. Azo compounds treated with hydrogen and Raney nickel in the presence of an aldehyde and sodium acetate give secondary amines. When activating groups such as hydroxyl or diethylamino are ortho or para to the azo group, tertiary amines are produced. Table V I summarizes the significant results of these investigations. It seems probable that with azo compounds the reaction is a reduction to the hydrazo compound, condensation of the latter with the aldehyde, followed by reduction and further alkylation to the secondary or tertiary amine. Schwoegler and Adkins (93) reacted alcohols with primary and secondary amines over Raney nickel to form secondary and tertiary amines, respectively. Since tertiary alcohols do not undergo the reaction, it is assumed that the catalyst dehydrogenates the alcohol to a carbonyl compound which reacts with an amine to give a product th a t can be readily hydrogenated to a more complex amine. Piperidine was reacted with ethyl, n-butyl, and n-dodecyl alcohols to give 82,70, and 69% yields, respectively, of the corresponding alkylpiperidines. RzCHOH

R”H2

---f

RZCO --+

R&(OH)NHR’

Ha

+

RZCHNHR’

R = H, alkyl

Couturier (94) obtained a rather good yield of dl-ephedrine by reacting a diketone, phenylpropanedione, with methylamine in the presence of Raney nickel. Schwoegler and Adkins (93), on reducing acetonylacetone in ammonia, received a 28% yield of 2,5-dimethylpyrrolidine and a 59 % yield of 2,5-dimethylpyrrole. From acetylacetone a quantitative yield of acetamide was obtained. Winans (95) has studied the hydrogenation of aldehydes in the presence of Raney nickel in alcoholic ammonia solution. Aldehydes with no hydrogen on the a-carbons were used, and the amounts of ammonia were varied. When a 1 : 1 ratio of equivalents of ammonia to aldehyde was used, the main product was the primary amine. With a 1:2 ratio, a high yield of the secondary amine was obtained. I n the former case o-chlorobenzaldehyde gave an 85% yield of the primary amine and a 7.G% yield of the secondary amine. In the latter case there was obtained a 3.6% yield of the primary and an 84.6% yield of the secondary amine. Henze and Humphreys (96) have used the reaction for the preparation of several mixed secondary amines in yields varying from 26 to 56%.

TABLE VI Reductive Alkylations Using Nitro Compounds and Azo Compounds"

N Compound

Nitrobenzeneb

Aldehyde Formaldehyde Acetaldehyde n-Butyraldehyde n-Valeraldehy de n-Heptaldeh y de Benzaldehyde n-Butyraldehyde n-But yraldehyde n-Valeraldehyde n-Butyraldehyde n-Heptaldehyde n-But yraldeh y de

Product N-methvlaniline N-eth ylaniline N-n-butylaniline N-n-amylaniline N-n-heptylaniline N-benz ylaniline N-n-buty 1-p-anisidine N-n-butyl-a-naphthylamine N-n-am y 1-a-naphthylamine N-n-butyl-p-toluidine N-n-heptyl-p-toluidine N, N ,di-n-butylaniline

~ - N = N - - P ~ ' ( C HJ~

n-Butyraldehyde

a N H C 4 H p

73

(n-CdH9)r N O N ( C H 2 )P

76

N-n-bu tylaniline

71

Nitrobenzene

p-Nitroanisole 1-Nitronaphthalene p-Nitrotoluene

= - N = N - ~

n-Butyraldehyde

n-Butyraldehy de

'

Yield, % 50 57-63 94-96 84 40 34 31

60 43 85 35 63

41

N, H-Di-n-butyl-p-aminophenol .Emeraon, J . Am. Chem. Soc., 62, 69 (1940); 63, 749, 751 (1941). Trimethylamine hydrochloride was used as condensing agent.

~

46

438

E U G E N E LIEBER AND FRED L. MORRITZ

Metayer (97) has alkylated, over Raney nickel, such nitrogen compounds as indole and N-formyl-1-phenethylamine. For a Raney nickel catalyzed acylation of an amine, see Blout and Silverman (57), who obtained hydrocarbostyril when the hydrogenation of o-nitrocinnamic esters was continued after three equivalents of hydrogen had been taken up. 3. Rearrangements

It was noted by Delepine and Horeau (98) that in the hydrogenation acid over Raney nickel a migration of of 2,6-epoxy-3-heptene-3-carboxylic the double bond occurs. The acid 2,6-dimethyl-5,6-dihydro-3-carboxypyran was received in 21 % yield a t ordinary temperatures. I n 1 hour a t 100' a 60 % isomerization was observed.

The migration of the double bonds of asymmetric octahydrophenanthrene when in contact at 130" with Raney nickel was reported by Durland and Adkins (99). A 15% yield of the symmetric octahydrophenanthrene was obttLined after 5 hours, and a 28% yield was obtained after contact for 19 hours.

f - l

O-D-C%

When dipropenylglycol is distilled under reduced pressure from a suspension of Raney nickel, the diketone, dibutyryl, is obtained in 30% yield and the acyloin, propenylbutyrylcarbinol, is obtained in 15% yield (100). CHsCH=CHCII (OH) CH (OH)CH=CHCHa 4 CsIIrCOCOC3H7

+ CHaCH=CH-CH(OH)COCjHT

Divinylglycol reacts with greater difficulty to give a 20% yield of dipropionyl. The reaction can be formulated as a 1,3 shift of a hydride ion followed by ketonixation of the resulting enol. H

H

n y -CH=CH-C-

u

0

-D

-CHz-CH=C-

I

+

-CH&H2CO-

In the catalytic hydrogenation of aldoximes with Raney nickel Paul (101) observed a small amount of rearrangement of the aldoxime to the acid amide. Raney nickel induces the rearrangement which takes place

439

THE USES OF RANEY NICKEL

even under cold conditions. The reaction is complete with a yield of 75 to 100% after a few hours in refluxing alcohol. Some of the results obtained are summarized below. The role played by the catalyst has not been clearly established. When Raney nickel is introduced to the oxime Oxime Acetaldoxime Heptaldoxime Benxaldoxime Furfuraldoxime

Arnide Acetamide Oenanthamide Benzamide Fiiramide

Yield, % 60-86 90 75 80-96

or to the oxime solution, a deep red color due to solution of the metal is noted. After separation of the undissolved Raney nickel, it is found that the dissolved metal (i.e., the complex) is capable of carrying the reaction to completion. Bryson and Dwyer (102) have provided evidence for Paul's suggestion that the aldoxime-nickel complex is an intermediate in the reaction. By means of this reaction Caldwell and Jones (103) obtained citronellamide in 50% yield when 20 g. of citronellaldoxime and 3 g. of Raney nickel were heated a t 100-105" for 2 hours, and, after dilution with ether, the catalyst was removed by filtration through activated alumina. The oxime of tetrahydrocitral, when heated for 2 hours a t 110-120' with Raney nickel, gave a 70% yield of the amide of 2,6-dimethyloctanoic acid. Among the products resulting from the catalytic hydrogenation of dinitroneopentane with Raney nickel, Rockett and Whitmore (104) found a 67% yield of the expected diaminoneopentane and a 5% yield of the diamide of dimethylmalonic acid. It is thought that a small amount of oxime, which is an intermediate in the hydrogenation, rearranges t o the diamide. There is a possibility that the hydrogenation of a nitro compound or an oxime t o the corresponding amine proceeds by way of the CHs

CHzNOz

C'

/ \

CH1

Ha

CH2

\c/

-+ CHzNOz

CHz

/ \

CH=NOH CH=NOH CH3

-+

CONHg

\C/ CH3/

'CONHg

+

CH3

CHzNHz

\C/

CH,

/ \

CHzNH2

intermediate amide. The difficulty, however, of reducing amides t o amines would indicate that this is not the most important reaction. Although Raney nickel will induce the rearrangement of an aldoxime to the amide, it will not effect the reaction with a ketoxime. This type of rearrangement has been effected with reduced copper with which

440

E UGE NE LIEBER AND F RE D L. MORRITZ

both aldoximes and ketoximes can be used. The yields, however, are small. When heated with Raney nickel at 200', substituted formamides rearrange with the elimination of ammonia to form a carbonyl compound (105). This is t,he reverse of the Leuckart-Wallach reaction. The reaction is postulated to take the following course: Raney nickel, 200'

RR'CHNHCHO

;-RR'CO ---+

HCONIIz, 180'

HCONHCHRR'

---f

CHzNHCRR' -+ OCRR' 0 ''

I I

I1 = I1 or C-

Substituted formamides react below 185' by scission of the formyl groups t o give amines. Above 1 8 5 O , carbonyls are formed. When the carbon bearing the nitrogen is monosubstituted, aldehydes are received. Raney nickel. Hz 185O, 750 p.8.i.

--

CsHIsCH(CH3)NHCHO ------+

C

H

,

~

~ ( cCH ~NHCHO )H

3GO p.8.i.

CS+H~~CH(CH~)NII~

O C O C H , among other products

C H 3 0 0 C H & H ( C H 3 ) N H C H 0 185'

C H 3 O ~ C I l ~ C O C H ~

600 p.8.i.

-

When the carbon is disubstituted, ketones are received. trisubstituted, only the amine is formed.

If the carbon is

4. Dehalogenation Reduction is a well-known method for the dehalogenation of organic compounds. The application of reductive methods for the quantitative determination of halogens is based on the conversion of the halogens into salts of the halogen acids and their subsequent determination by standard methods. Molecular hydrogen, derived for example, from zinc and acid, is not generally applicable for this conversion, since only a limited number of organic compounds quantitatively undergo the halogen displacement when treated in this manner. The use of catalytically activated hydrogen as an analytical tool for the dehalogenation of organic compounds was discovered by Husch and Stowe (106)) who used a palladium-ralcium carhonate catalyst. Later, Kelber (107) reported a similar procedure, using a reduced nickel catalyst. Whitmore and Revukas (108) observed that, in the reductive splitting of substituted azo compounds with hydrogen in the presence of Raney

THE USES OF RANEY NICKEL

44 1

nickel at 1 to 3 atm. of pressure, halogen was quantitatively displaced if alkali was present in sufficient amount to combine with the halogen acid formed. I n the absence of alkali the hydrogen acted only upon the azo bond to produce the normal fission. Paty (109) reported the use of Raney nickel in the debromination of several aromatic compounds of the type

where R is an aliphatic group. The reaction seemed to be facilitated if potassium hydroxide was added in amount slightly in excess to that required t o neutralize the hydrogen bromide formed. I n each case the halogen was replaced by hydrogen without the aliphatic functions being reduced. When R = -CHzOH, the percentage yield was 55%; R = -CHzOCzHs, 88%; R = -COOH, 88%; R = -CHzCOOH, 87%; R = -CHzCONHz, 95%. Halogens in the ally1 position seem to be readily replaceable by hydrogen. Anglade (110) treated bis-2,4-(chloromethyl)anisole with Raney nickel and hydrogen in alcohol a t ordinary temperatures. A 25% yield of 2,4-dimethylanisole was obtained, with ethyl ether formed as a by-product by interaction with the solvent. Aromatic halogens, however, seem t o possess a much greater degree of stability. Winans (111) was able t o reduce aromatic halogen compounds over Raney nickel catalyst without displacement of the halogen by being careful t o maintain the temperature below 150". An exception is such a compound as 2,4-dinitrochlorobenzene,which gives a 91 % yield of m-phenylenediamine a t 40". Shriner (112), in describing a procedure for the dehalogenation of 2-chlorolepidine to produce lepidine, noted that the reduction did not run smoothly a t room temperatures. At higher temperatures, with palladium on charcoal as catalyst, the theoretical amount of hydrogen was absorbed in 1.5 to 2 hours with a yield of 81 to 87 %. Raney nickel in alcohol can be used a t room temperatures, but 15 hours is required for the hydrogenolysis. Grigorovskii (I 13a), investigating the dehalogenation of chloroacridines over Raney nickel, found that halogen atoms in position other than 9 were unaffected. Chloroacridine (10 g.) and Raney nickel paste (10 g.) in 250 ml. of methanol were boiled with stirring for 4 hours. Upon treatment of the reaction mixture, a 66% yield of 9,9'-biacridine was isolated. When 3,9-dichloroacridine was treated in a similar manner, 3,3'-dichloro-

442

EUGENE LIEBER AND FRED L. MORRITZ

9,9'-biacridine was obtained in 70% yield. This Wurtz type of condensation was also found to occur in the dehalogenation of benzyl chloride (113b) over large amounts of Raney nickel. When bensyl chloride (10 g.) was heated with Raney nickel (20 g.) in boiling methanol for 4 hours, dibenzyl (0.6 g.) and toluene (2.6 g.) were obtained. With less catalyst more dibenzyl was formed, and with more catalyst more toluene was formed. Alkali, without an external supply of hydrogen, inhibited the dehalogenation. In the cold, in the presence of alkali and with hydrogen supplied, the tendency toward condensation disappeared almost completely. Little is known of the effect of nuclear substituents on the dehalogenation of aromatic halogen compounds. Schwab (114) debrominated several 4-bromoanthraquinones by means of hydrogen over Raney nickel. A p-hydroxyl group causes a much more rapid removal of bromine than a p-methoxy group. Methoxy groups in the 6 or 8 positions had very little inhibitory effect. The application of the displacement of halogen by nickel-aluminum alloy in aqueous alkali to the quantitative determination of halogens in organic compounds (115) is of considerable interest. Many of the above methods, when adapted for analysis, require the use of hydrogen gas, a prepared catalyst, and a hydrogenation apparatus of the conventional type. These requirements are obviated by the use of nickelaluminum alloy in aqueous alkali, and the method is advantageously used for the quantitative determination of halogen in many aliphatic, aromatic, alicyclic, and heterocyclic compounds. GENERAL PROCEDURE

Approximately 0.3 g. of sample, accurately weighed, is added to 100 ml. of 5% aqueous sodium hydroxide contained in a beaker. Three grams of the nickel-aluminum alloy is added in three or four portions over a period of 10 minutes. When the reaction has subsided, the mixture is heated on a steam bath for 1 hour and then filtered, the residue being carefully washed. An aliquot portion of the filtrate may now be analyzed for halogens by any standard procedure. Ethanol may be used to facilitate the reduction of alkali insoluble compounds,

443

THE U S E S OF RANEY NICKEL

Table VII summarizes some of the results that have been obtained by this method. The fact that only the usual laboratory apparatus is required to carry out the analyses gives the procedure a definite advantage over other reduction methods for the determination. The results obtainable compare favorably in both accuracy and precision with those of other methods. Its ease of manipulation over such methods as the Carius nitric acid sealed-tube procedure and the peroxide bomb procedure is obvious. TABLE V I I Quantitative Determination of Halogen by Means of Nickel-Aluminum Alloy in Aqueous Alkalia ~

Halogen Compound

Theory, 9% Found, %

3,5-Diiodo-4-hydroxyphenylaceticacid ~-(3,5-Diiodo-4-hydroxyphenyl)-~-phenylpropionic acid 8-Bromopropionic acid

62.84 51.40 52.21

Bromobenzene

50.85

2-Bromopyridine m-Chlorobenzoic acid

50.61 22.67

p-Nitrochlorobenzene

22.52

2-Chloropyridine

31.25

62.15 51.61 52.33 52.06 51.01 50.87 50.76 23.04 23.06 22.57 22.68 31.02

,. Reprinted from Ind. Eng. Chem. Anal. Ed.. 16, 576 (Sept. 1943), hy permission of the copyright owner. the American Chemical Society.

Raney alloy has also been used (116) for the dehalogenation of 4-chloro-5-methylquinaldine and 4-chloro-7-methylquinaldine t o form the 2,5- and 2,7-dimethylquinaldines. Zinc, in alkaline solution, in the presence of Raney nickel has been used to dehalogenate organic compounds (117). The halogen is then determined by a Volhard determination. GENERAL PROCEDURE

For compounds containing chlorine or bromine, a weighed sample is dissolved in 10 ml. of methanol; 10 ml. of 20% sodium hydroxide, 2 g. of zinc, and 0.5 g. of Raney nickel are added, and the mixture is heated with reflux for 1 hour over a water bath. It is then cooled and decanted. After acidification with nitric acid, 20 ml. of standard silver nitrate solution and 5 ml. of a ferric alum solution are added, and the solution is titrated with standard potassium thiocyanate. The procedure is modi-

444

EUGENE LIEBER AND FRED L. MORRITZ

fied for iodine-containing compounds by filtration of the silver iodide prior t o the titration. Although this method was unsatisfactory for DDT, excellent results were obtained with a wide variety of halogenated derivatives including acyclic, phenolic, aromatic, and steroid types. 5. Desulfuration

Sulfur can be effectively removed from a compound, organic or inorganic, by contact with Raney nickel. The action has been described by Aubry (118) as being noncatalytic in nature. One atom of sulfur is removed from sodium thiosulfate in the cold, yielding sodium sulfite from which the sulfur can be completely removed a t 100". Although sulfur can be completely removed from stannous sulfide, it can be only partially removed from antimony sulfide. Following are some of the inorganic compounds from which sulfur removal by use of Raney nickel has been observed (119). NazS

+ 2Hz0 + Ni(Hn)

+ 2NaOH + ( n / 2 + l ) H z + 2NaOH + Ha0 + NazS03+ (n/2)Hz + NazSOs + (3n/2 - 3)Hz + 3ILO

NiS NiS Ni(Hn) 3 NiS Ni(H,) -+ 3NiS Ni(H,) 3 NiS 3Ni(H,) 3 NiS 3Ni(H,) 3 NiS Ni(H,) 3 NiS

+ Ni(H,)

Na2S03 Na2S203 NazS40e NatSaO, Ass3

+ + + + SbzSa+ SnS +

3

+ Na2SOa+ ( n / 2 - 1 ) I L + NiAsS + (n/2)Hz + 2NiSbS + (n/2)Hz + Sn(OH)2 + (n/2 + 1)H2

Raney nickel acts to remove sulfur from organic compounds even in the cold (119,120). The use of Raney nickel for the removal of thiophene from benzene and methylthiophene from toluene has also been reported. Mozingo (20) has shown with a wide variety of compounds that Raney nickel catalyst in the presence of a solvent and with only its adsorbed hydrogen can cleave either reduced or oxidized sulfur from the remainder of the molecule a t a moderate temperature. Two courses for the reaction can be postulated: RSR'

+ Ni(H)-

+ RR + R'R' RH + R'H

,-+(A) RR'

+(B)

Similar postulates can be written for the reactions of disulfides, sulfoxides, and sulfones. Only reaction B was observed by Mozingo, who used sufficient catalyst to contain a large excess of adsorbed hydrogen. It is of interest to note the ease with which a carbon-sulfur bond in an aromatic sulfide is cleaved. Simple refluxing of the compound in a n ethanol suspension of Raney nickel is sufficient t o effect hydrogenolysis,

445

THE USES O F RANEY NICKEL

the conditions being so mild that the ring does not react with the hydrogen. Diphenyl sulfide yields benzene in 68% yield, and di-p-tolydisulfide yields toluene in 87 % yield. A similar case of cleavage is observed in oxidized sulfur compounds. The cleavage of oxidized sulfur compounds has also been reported by Shah et al. (121), who converted J-acid to 6-amino-1-naphthol, and by Kenner and Murray (122), who converted alkyl esters of p-toluenesulf onic acid t o the corresponding alcohols. A new method for the transformation of a carboxyl group t o a methyl group has been developed (123,124). I n an intermediate step of this method, a thiol ester is cleaved with Raney nickel t o the alcohol. The method may be outlined as follows: -CO2H

Raney

----t

-COSCHa y+

nickel

-CH&H

+ -CH,I

Raney

---+ nickel

-CHa

Note that the method also involves the use of Raney nickel for dehalogenation. The method is also applicable t o the reduction of a single carboxyl group of a polycarboxylic acid. Wolfrom and Karabinos (125) CHaSH

HOzC(CHZ)iaCOzH 4 CH~OCO(CHZ),~COZH -+ CHaOCO(CH2)14COCl--

Py ridine

Raney

CH30CO(CHz) irCOSCH3 7- CH,OCO(CHJ 14CH20H nickel

developed a similar procedure a t about the same time t o receive the aldehyde. Spero, McIntosh, and Levin (126) using W-1 Raney nickel catalyst, in like manner converted a thiol ester to the alcohol, receiving also traces of aldehyde. With W-4 catalyst (127,128) the thiol ester (I) was rapidly OCHO CH-CH2COSEt

c6c'":I,?

4

Cholane alcohol

+ Cholttnic aldehyde

HCO I

I1

111

and quantitatively reduced and desulfurized to the alcohol (11). When a catalyst deactivated in boiling acetone (126-128) was used, the aldehyde (111)was obtained in good yield. Miescher and Heer (129) have received aldehydes from the reaction in water and alcohols from the reaction in absolute alcohol.

446

EUGENE LIEBER AND FRED L. MORRITZ

A novel method of converting a carbonyl t o a methylene group has been reported by Wolfrom and Karabinos (70). The carbonyl group is converted to the mercaptal or mercaptol which is hydrogenolyzed over Raney nickel to give the methylene group. This method has found applications in the fielda, among others, of steroids (130-132) and streptomyces antibiotics (133).

Mozingo postulated two courses by which Raney nickel might react with an organic sulfur compound to split out sulfur, Reaction A (p. 444) was not observed by Mozingo, but shortly afterwards Campaigne (134) showed such a Wurtz type of reaction to occur. The thiocarbonyl group in thioacetophenone was found to react with W-2 Raney nickel to form a carbon-carbon double bond. Bergmann (135), seeking to form 9-methylphenanthrene, treated phenanthrene-9-thioaldehyde with Raney

CH3

nickel. The sole product was that of coupling. Hauptmann et al. (136,137), using a Raney nickel catalyst which had been freed of hydrogen

HS

\

\

\

CH=CH

/ /

by heating under a vacuum at 200°, found that all mercaptals of benzaldehyde gave stilbene in varying yields. Benzaldehyde diethylmercaptal gave a 70% yield of stilbene, and the dibenzylmercaptal gave dibenzyl. When the diphenyl mercaptal was used, some diphenyl sulfide was formed in addition to stilbene. Diphenyl sulfide was formed from formaldehyde diphenyl mercaptal in 71 % yield. Di-p-tolysulfide and di-9-naphthylsulfide are similarly made. The formation of thioethers under these conditions was observed only when the sulfur was directly bound to an aromatic ring. When benzaldehyde dibenzylmercaptal was used, only stilbene and sym-diphenylethane could be isolated. In one of the early papers (119) describing work in the field there was reported the hydrogenolytic cleavage of simple sulfides, disulfides, and mercaptans. Snyder and Cannon et al. (138,139), studying the desul-

447

THE USES OF RANEY NICKEL

furation of disulfides, found evidence of carbon-to-carbon cleavage in the fact that, when RSCHzCHzSR is reacted with Raney nickel, not only ethane but also methane is formed. Karrer (140) synthesized methyltocols using cleavage of a sulfide in the final step. King and Campbell

CHs

CHI

(141) used W-1 catalyst for the thiohydrogenolysis of a thiourea derivative of a steroid, and Rosenkranz et al. (142) used W-2 catalyst for the hydrogenolysis of 3-thioenol ethers of A4-3-ketosteroids. Mozingo, Folkers, and co-workers (143) used the desulfuration reaction in the determination of the structures of biotin and its derivatives. 0

0

/I

/I

HN%H

H h ’ h

I 1 1 1 ’ /I-‘CH214C02H

c-c’ ‘s ,,,pH

lH

-+

,,/

c-c

A H 3

,,,pH

bHz[CHz]4COzH

Blicke and Sheets (144), using Raney nickel in sodium carbonate solution, were able to eliminate the sulfur from a thianaphthene.

Modest and Szmuszkovicz (145) applied the same reaction to make naphthalene and phenanthrene derivatives, and Papa, Schwenk, and Ginsberg (60e) used the reaction to cleavage thiophene derivatives utilizing, however, Raney alloy and aqueous alkali in the reaction mixture. Thiohydrogenolysis with Raney nickel has been used as a tool in the elucidation of structures of organic compounds. The technique has been used in establishing the configuration of streptose (146), the pyranose structure of ethyl-1-thio-a-d-mannoside (147) and the structure of tetraacetylpolygalitol (148). 6. Hydrogenations without the Use of Added Hydrogen

In one of the earlier communications (8) dealing with a preparation of Raney nickel catalyst, it was shown that this catalyst when mixed with

448

E U G E N E LIEDER AND FR E D L. MORRITZ

nitrobenzene or p-nitrophenol in an open beaker deoxygenates the compounds with 38 to 50% yields of azo- and azoxybenzene. Although the mechanism of the reaction is obscure, it is probably safe to assume that the hydrogen held by the catalyst surface plays some part in the reaction. Bougault et al. (19) ch im that 1 g. of Raney nickel catalyst holds the equivalent of 140 ml. of hydrogen. With Raney nickel catalyst and its large amount of loosely held hydrogen, a large number of organic compounds can be hydrogenated without adding hydrogen from a n external source. Orchin (149) has described a novel method for the preparation of small quantities of tetrahydroanthracene from 9,lO-dihydroanthracene or from anthracene. PROCEDURE

To about 0.54 g. of 9,lO-dihydroanthracene in 25 ml. of ethanol, 8 g. of Raney nickel catalyst was added. After refluxing for 2% hours in an atmosphere of nitrogen, the mixture was filtered and the filtrate was concentrated. On cooling, about 0.33 g. of 1,2,3,4-tetrahydroanthracene was obtained. The mother liquor, when treated with 0.3 g. of s-trinitrobenzene, yielded about 0.25 g. of the 1,2,3,4-tetrahydroanthracene-trinitrobenzene complex. The total yield was 81% of the theoretical. When about 0.34 g. of anthracene in 50 ml. of ethanol was treated with 10 g. of Raney nickel, a 71 % yield of the same product was obtained. Mozingo et al. (143) has hydrogenated several organic compounds, using only the hydrogen contained on the catalyst. The following is a typical procedure. PROCEDURE

Five grams of cyclopentanone, about 25 g. of Raney nickel catalyst, 100 ml. of ethanol, and 35 ml. of water were refluxed for 2 hours. The nickel was removed by filtration, and the product extracted with benzene. The benzene and the alcohol were carefully distilled through a fractionating column, the residue being taken as the reduction product. From half the residue and 7.0 g. of 3,5-dinitrobenzoyl chloride in pyridine, 5.1 g. of cyclopentyl-3,5-dinitrobenzoatewas obtained. The yield was 61 % of the theoretical. The process is not applicable to simple aromatic compounds such as benzene and toluene. Table VIII summarizes the results. I n the authors’ laboratory, approximately 3 g. of W-6 Raney nickel catalyst was mixed with 5 ml. of cyclohexene in a test tube. A vigorous reaction took place a t once. Mass spectrographic analysis showed a 43 % conversion to cyclohexane (156).

449

THE USES OF RANEY NICKEL

TABLE VIII Hydrogenations without Added Hydrogen' Hydrogen acceptor Toluene Cyclopentanone Hydrazobenzene Azoxybenaene Ethyl acetoacetate Benzalacetone Benzaldehyde Acetone Eugenol Cholesterol

Product No reaction Cyclopentanolb N-ethylnnilinec N-eth ylaniline" Ethyl-p-hydroxybutyrate 4-Phenyl-2-butanol Toluene Isopropanol Dihy droeugenol" Incomplete reduction

Yield, % 61 43 36 96d 73 78 78 75

Abstracted from Moringo, Spencer, and Folkers, J. Am. Chem. SOC.,66, 1859 (1944). Isolated as the 3,5-dinitrobenzoate and as the p-nitrobenroate. C Isolated as the hydrochloride. d Ten grams of acceptor was used with 50 g. of catalyst. I n the case of eugenol a n d of rholesterol 2 g. of acceptor was used with 25 g. of catalyst. I n the other cases 5 g. of acceptor was used along with 25 g. of catalyst. * Isolated as the p-nitrohensoate. 0

b

7. Miscellaneous

a. Ozonide Decomposition. Cook and Whitmore (150) have found that Raney nickel reacts with ozonides t o give aldehydes or ketones and nickel oxide. The reaction is vigorous at 35". The yields obtained are comparable t o those obtained by the less convenient method of Fischer. I n the actual procedure, 75 g. of the nonenes prepared by the dehydration of methylethylneopentylcarbinol was ozonized. The ozonide, dissolved in 200 ml. of pentane, was slowly added t o 48 g. of Raney nickel in 100 ml. of pentane. Upon being stirred overnight with the catalyst, the mixture showed no test for the ozonide. The yields of aldehydes and ketones were about 75 %. Boord and his co-workers (151) used this reaction as a proof of the identity of a reaction product believed to be vinylcyclopropane. The

aCH=CH~ carbonyl compound was obtained in 8%' yield. It is assumed th a t the remainder of the carbonyl compound was hydrogenated or decarbonylated by contact with the hot catalyst. b. R a n e y Nickel in a n Acid M e d i u m . Adkins (7) has claimed that "acids may not be used with base metal catalysts," Noble metals have

450

EUGENE LIEBER AND FRED L. MORRITZ

almost exclusively been used when an acid medium is desired. Wenner (152), however, has reported the use of Raney nickel for catalytic hydrogenations in solutions with pH as low as 3. For the hydrogenation of Schiff bases of type I to the corresponding alcohols of type 11, Raney RzNCHzC[CH31zCHO

R2NCHzC[CHa]zCHzOH

I

I1

nickel was not only found to be an efficient catalyst but it proved superior to the noble metal catalysts. When noble metal catalysts were used for the hydrogenation of the hydrochlorides of amines of type I, only poor yields of the alcohols resulted. In all cases some hydrogenolysis of the amine portion took place. With Raney nickel, however, the hydrogenations proceeded smoothly and high yields of the alcohols were obtained. The pH of the hydrochlorides in aqueous solution varies from about 3.5 to 4.5. The results are important in the sense that they show that Raney nickel catalyst, contrary to generally accepted opinion, can be used efficiently for hydrogenations in distinctly acid solutions. Strongly acid solution containing a large amount of free mineral acid cannot, of course, be used. c. Catalysis of Hydrazine Decomposition. It has been postulated that hydrazine in the presence of platinum black decomposes according to the following equation: 2NzH4-t 2NHa

+ Nz + HZ

I t was found, however, by Irrera (153) that the volume of gas obtained from the decomposition of hydrazine in the presence of Raney nickel is always greater than that indicated by the equation above. An increase in the amount of catalyst increases the quantity of gas obtained, which approaches the volume required by the following equation : 3NzHd 4 2NHs

+ 2N2 + 3Hz

d. Reduction of a Hydroperoxide. A recent patent (154) describes the application of Raney nickel for the catalytic reduction of hydroperoxidcs to give alcohols of the type R2ArCOH. The hydroperoxide of cumene is converted to dimethylphenylcarbinol. Platinum and cobalt are also described as catalyzing the reaction. e. Decarboxylation. Raney nickel has been shown to catalyze the decarboxylation of 2-furanacrylic acid in quinoline (155). When 0.1 of the catalyst is used, only trace amounts of vinylfuran are obtained, but when 3% of the catalyst is used, the yield is 41%. Several types of catalyst were examined in this study, but Raney nickel appeared to give the best yield.

T H E USES O F RANEY NICKEL

451

REFERENCES 1. Raney, Murray, (a) U. S. Patent 1,563,787 (Dec. 1, 1925); (b) U. S. Patent

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38.

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452

EUGENE LIEBER A N D FRED L. MORRITZ

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69. 70. 71. 72. 73.

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(1942); 9, 175 (1944).

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