ENANTIOSELECTIVE CATALYSIS - INFLUENCE OF CONVERSION AND BULK DIFFUSION LIMITATIONS ON SELECTIVITY IN THE HYDROGENATION OF ETHYL PYRUVATE

Several unexpected observations were made in studying the hydrogenatio n of ethyl pyruvate over dihydrocinchonidine-modified Pt. A marked tre nd of increasing optical yield with increasing conversion was observed over a wide range of reaction temperatures, ultimately reaching a pla teau between 54-58% enantiomeric excess at high conversion. In additio n, reactions carried out under bulk hydrogen diffusion limitations exh ibited a strong suppression in optical yield. These results reveal the dynamic nature of the catalyst surface as the reaction progresses and demonstrate the need to develop a complete kinetic picture of the rea ction. (C) 1995 Academic Press, Inc.