Studies of Raney Nickel-Catalysed Asymmetric Hydrogenation Reactions

The hydrogenation of the prochiral beta-keto ester, methyl acetoacetate, to the beta-hydroxy ester, methyl 3-hydroxy butyrate, has been studied in some detail, using Raney nickel catalysts which have previously been treated with an optically active stereoisomer of tartaric acid. Various physical methods for the separation of the two enantiomers of the chiral reaction product have been investigated and the results are reported, together with a brief summary of recent developments in this field. Variations in the reaction conditions and the methods of catalyst preparation and modification have been found to exert a considerable influence on the conversion and enantioselectivity obtained during reactions. As a consequence of carrying out extensive series of investigations, the conditions which result in maximum conversion and optimum enantiomeric excess have been identified. The catalyst with maximum enantio-differentiating ability is prepared by modifying Raney nickel with sodium bromide and optically pure tartaric acid at pH 3.2, with the temperatures of modification and Raney alloy alkaline digestion fixed at 10