Preparation of tartaric acid modified Raney nickel catalysts: study of modification procedure

Chiral modification of Raney nickel using (2R,3R)-tartaric acid was studied . The prepared catalyst was used in enantioselective hydrogenation of methy lacetoacetate (MAA) to methyl-(3R)-hydroxybutyrate. The influence of the mo st important modification parameters, such as pH, temperature, time, concen tration of the modifier and the presence of a co-modifier, on the optical y ield of MAA hydrogenation was systematically investigated. From the data ob tained: a considerable influence of modifying conditions on the resulting e nantioselectivity of the catalyst was evident. The optical yield increased with an increasing of the modifying temperature and time. Dependencies of t he optical yield on the tartaric acid concentration and on the modifying pH passed through a maximum. Therefore, there exists an optimal value of modi fying pH, at which a minimal catalyst amount is leached to the modifying so lution. Furthermore, significant adsorption of tartaric acid and subsequent complex formation of nickel and tartaric acid occurs on the catalyst surfa ce. It was found that the presence of sodium bromide in the modifying solut ion resulted in a lower degree of the nickel leaching, and a decrease of th e residual aluminum content in the catalyst increased the optical yield of the reaction. (C) 2001 Elsevier Science B.V. All rights reserved.