THE ENANTIOSELECTIVE HYDROGENATION OF METHYL ACETOACETATE OVER SUPPORTED NICKEL-CATALYSTS .1. THE MODIFICATION PROCEDURE

Enantioselective Ni/SiO2 catalysts have been prepared by modification with (R)-(+)-tartaric acid (TA) and used in the asymmetric hydrogenation of methyl acetoacetate (MAA) to (R)-(-)-methyl-3-hydroxybutyrate (MHB). The effects on the overall asymmetric activity of systematically varying modification conditions, namely time, temperature, TA concentration, and pH, are discussed. The amounts of TA adsorbed have been correlated with conversion and selectivity and an optimum surface coverage of 0.2 was identified. The nature of the interaction of TA with the surface nickel metal is considered and data on the corrosive leaching and the changes in metal dispersion are presented. The consequences of adding NaBr as a subcomponent of the modification solution are examined and the results are discussed in terms of surface coverage and nonselective site poisoning. The results obtained reveal the interrelated effects of each modification variable on surface TA coverage and ultimately on enantiomeric selectivity. © 1992.