1966 Volume 39 Issue 10 Pages 2223-2226
Asymmetric hydrogenation catalysts were prepared by modifying Raney nickel with aqueous solutions of D-tartaric acid, monomethyl D-tartrate, L-erythro- and D-threo-2, 3-dihydroxybutyric acid, L-malic acid, (+)-erythro- and (−)-threo-3-methylmalic acid, L-citramalic acid and L-methyl-succinic acid. Their asymmetric activities in the hydrogenation of methyl toacetate to methyl 3-hydroxybutyrate were compared with each other in order to study the effect of the chemical structure of the modifying reagent on the activity. Monomethyl D-tartrate, L-erythro- and D-threo-2, 3-dihydroxybutyric acid are less effective in asymmetric activity than D-tartaric acid. On modification with these three reagents, optimum asymmetric activities were obtained under acidic conditions. With D-tartaric acid, however, while high asymmetric activities were obtained at pH 5–9, there was a considerable decrease in activity at lower pH values. This suggests that the β-carboxyl group of tartaric acid plays an important role in the modification. (−)-threo-3-Methylmalic acid is more effective in asymmetric activity than L-malic acid, while (+)-erythro-3-methylmalic acid and L-citramalic acid are less effective. It has been suggested that these differences are related to hindrances due to the methyl groups on the α- or β-asymmetric centers, and also related to the correlations of the configurations of the asymmetric centers of 3-methylmalic acids. L-Methyl-succinic acid has little asymmetric effect on Raney nickel.
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