Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XXIV. The Effect of Unsaturated Compounds on the Asymmetric Activity of the Catalyst

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Dehydroacetic acid and methyl <I>cis</I>-3-acetoxycrotonate were picked out as trace impurities of the substrate, methyl acetoacetate. The effects of dehydroacetic acid, methyl <I>cis</I>-3-acetoxycrotonate, and diketene, which is the starting material for the preparation of methyl acetoacetate, on the asymmetric activities of catalysts modified with L-amino acids were examined in the hydrogenation of methyl acetoacetate. The above three compounds, when added to the hydrogenation system, raised the asymmetric activity of the catalyst. Also, simple unsaturated compounds, such as acetone and diethyl maleate, has a similar effect on the catalyst. The effects of the above unsaturated compounds on the asymmetric activities of the catalysts modified with L-amino acids were discussed, and it was suggested that the unsaturated compounds adsorb on the catalyst surface and might scavenge the asymmetrically uncontrolled active hydrogen absorbed on the catalyst surface.
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