Heterogeneous asymmetric reactions -: Part 40.: New data on repeated use of Pt-alumina catalyst during enantioselective hydrogenation of ethyl pyruvate

The repeated use of Pt-alumina (E4759) catalyst modified by dihydrocinchonidine (DHCD) was studied in the enantioselective hydrogenation of ethyl pyruvate under mild experimental conditions not studied before (hydrogen pressure: 1 bar, temperature: 253-298 K, DHCD concentration: 0.001-0.1 mmol/1) in toluene and AcOH. The effects of different reuse methods, DHCD concentration and temperature on the conversion and enantiomeric excess were studied. In toluene depending on the reaction conditions an "increase in ee on reuse" of 10-20% was observed. This effect was not found in AcOH medium. In our opinion, the phenomenon is an intrinsic feature of the Pt-alumina-cinchona catalyst system, in which the restructuring of the catalyst Pt surface may play an important role. (C) 2004 Elsevier B.V. All rights reserved.