Raney nickel benzylic alcohols

P-Phenylethylamine is conveniently prepared by the hydrogenation under pressure of benzyl cyanide with Raney nickel catalyst (see Section VI,5) in the presence of either a saturated solution of dry ammonia in anhydrous methyl alcohol or of liquid ammonia the latter are added to suppress the formation of the secondary amine, di- P phenylethylamine ... 

T-4)-J or Raney nickel and hydrogen.8 Alcohols of the benzylic type have also been reduced directly with hydrogen under pressure in the presence of various catalysts,9 and benzoic acids have been reduced to toluenes with rhenium-type catalysts and hydrogen at high temperatures and pressures.10... 

In contrast to phenolic hydroxyl, benzylic hydroxyl is replaced by hydrogen very easily. In catalytic hydrogenation of aromatic aldehydes, ketones, acids and esters it is sometimes difficult to prevent the easy hydrogenolysis of the benzylic alcohols which result from the reduction of the above functions. A catalyst suitable for preventing hydrogenolysis of benzylic hydroxyl is platinized charcoal [28], Other catalysts, especially palladium on charcoal [619], palladium hydride [619], nickel [43], Raney nickel [619] and copper chromite [620], promote hydrogenolysis. In the case of chiral alcohols such as 2-phenyl-2-butanol hydrogenolysis took place with inversion over platinum and palladium, and with retention over Raney nickel (optical purities 59-66%) [619]. 

Nickel, Raney nickel and copper chromite are other catalysts suitable for hydrogenation of aldehydes to alcohols with little if any further hydrogenolysis. Benzaldehyde was hydrogenated to benzyl alcohol over nickel [43], Raney nickel [45] and copper chromite [50] in excellent yields. In the last-... 

Reduction of derivatives of ally lie alcohols. Nickel boride can effect reduction of allylic alcohols to alkenes, but yields are generally improved by reduction of the acetates, benzoates, or trifluoroacetates.1 Reduction of allylic benzyl ethers to alkenes is effected in higher yield with Raney nickel. Methyl ethers are not reduced by either reagent. The trimethylsilyl ethers of allylic alcohols are reduced to alkenes by nickel boride in diglyme.2... 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

It was hoped that the resulting benzylic carbinols 59 could be stereose-lectively reduced by catalytic hydrogenation to the required protected kainoid derivatives 60 (Scheme 24). The reduction of benzylic alcohols varies in stereospecificity depending on the catalyst employed.53 Hydrogenation over Raney nickel generally proceeds via retention of configuration, whereas hydrogenation over palladium on charcoal leads to inversion at the benzylic carbon. 

The overhydrogenation of aromatic aldehydes beyond benzylic alcohols is rarely important with copper-chromium oxide and Raney nickel unless the reaction conditions are too vigorous. Thus, over copper-chromium oxide o- and p-methoxybenzaldehydes were hydrogenated to the corresponding methoxybenzyl alcohols in high yields in methanol at 110-125°C and 22-24 MPa H2 (eq. 5.18).42 At 185°C, however, / -methoxybenzyl alcohol was hydrogenolyzed to give p-cre-sol methyl ether (eq. 5.18). 

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