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Continuous stable enantioselective hydrogenation of alkyl pyruvate esters using pre-modified cinchonidine platinum catalysts Robert L. Jenkins, Paul McMorn, and Graham J. Hutchings* Department of Chemistry, Cardiff University, P. O. Box 912Cardiff, CF10 3TB UK Received 15 July 2004; accepted 5 December 2004 Pre-modification of a 5 wt% Pt/c-Al2O3 catalyst with cinchonidine (0.1 g g)1 catalyst) leads to a catalyst that give stable enantioselection when using a trickle-bed flow reactor at ambient temperature and pressure. With dichloromethane as solvent sustained enantiomeric excess of >70% for the hydrogenation of ethyl pyruvate to (R)-ethyl lactate is observed and this is maintained with very low cinchonidine/catalyst ratios. With dichloromethane the conversion decreases with time an effect we consider to be due to the formation of small amounts of polymer on the catalyst surface. When ethanol is used as solvent the yield of (R)-ethyl lactate is stable throughout the test period, although the enantiomeric excess was much lower at ca. 35%. KEY WORDS: enantioselective hydrogenation; ethyl pyruvate hydrogenation; butadione hydrogenation; Pt/c-Al2O3 catalysts. |
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