SONOCHEMICAL ENANTIOSELECTIVE HYDROGENATION OF ETHYL PYRUVATE OVER PLATINUM CATALYSTS

Chiral sonochemical hydrogenation of an aliphatic alpha-ketoester, eth yl pyruvate to ethyl lactate was carried out over various platinum cat alysts in different solvents under atmospheric hydrogen pressure. The reaction rates and the enantiomeric excesses were determined over Pt/C , Pt/SiO2 and Pt/K-10 catalysts both under conventional and sonochemic al conditions. The effect of ultrasounds on the catalytic activity and enantioselectivity was tested applying sonochemical pretreatment befo re the reaction. The ultrasonic irradiation was found to be highly adv antageous in these hydrogenations. After insonation of the catalysts, the enantioselectivity was highly improved over Pt/SiO2 and Pt/K-10 ca talysts. In addition, the reactions took place in quantitative yield a nd with complete chemoselectivity and the hydrogenation rates increase d with one order of magnitude despite the very mild (atmospheric hydro gen pressure, room temperature) experimental conditions. (C) 1997 Else vier Science B.V.