Asymmetric Hydrogenation of C=O Double Bond with Modified Raney Nickel. XX. The Effect of Additives on the Asymmetric Activity

Abstract

Abstract The effects of various additives in methyl acetoacetate were tested in the asymmetric hydrogenation reaction. Among them, water has a particular effect on the asymmetric activities of the catalysts; in the presence of a certain amount of water, the catalysts modified with l-Glu, l-Val, and l-Ala hydrogenated methyl acetoacetate to methyl ls(+)3-hydroxybutyrate, while, without the addition of water, the catalysts promoted the hydrogenation to yield methyl ds(−)3-hydroxybutyrate. The catalyst modified with l-Ala at pH 6.0 and the catalyst modified with l-Glu at pH 5.0 and 100°C were especially sensitive to water, and both catalysts showed (+) asymmetric activity when a trace of water was also present. Even in the hydrogenation without the addition of water, the recovered catalysts modified with l-Glu, l-Val, and l-Ala from the hydrogenation in the presence of water gave results similar to those in the hydrogenation in the presence of water. The effect of water as an additive was discussed, and it was concluded that the water affects the asymmetric site of the catalyst rather than the keto-enol equilibrium of the substrate.