Continuous stable enantioselective hydrogenation of alkyl pyruvate esters using pre-modified cinchonidine platinum catalysts

Pre-modification of a 5 wt% Pt/γ-Al 2 O 3 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%.