Enantioselective hydrogenation of alpha-keto esters over cinchona-Pt/Al2O3 catalyst. Kinetic evidence for the substrate-modifier interaction in the liquid phase.

The hydrogenation of ethyl pyruvate was studied over cinchonidine-Pt/Al-2/O-3 catalyst. Contrary to earlier results it has been found that the initial enantiomeric excess extrapolated to zero conversion is close to zero. Based on kinetic analysis the results are considered as indirect evidence for the substrate-modifier interaction taking place in the liquid phase. The above interaction leads to the formation of a weak substrate-modifier complex. The formation of the complex in the liquid phase is the key step to control both the rate acceleration and the induction of enantio-differentiation in the hydrogenation of alpha-keto esters in the presence of cinchona-Pt/A1(2)O(3) catalysts. The character of interactions in the substrate-modifier complex is discussed. By using molecular modelling the possible form of the complex is also given.