LIQUID-PHASE ASYMMETRIC HYDROGENATION ON PT-CONTAINING ZEOLITE-Y CATALYSTS

5 wt.-% Pt/MNaY catalysts (M=rare earths, Ca, Mg and H with ion exchan ge degrees of alpha approximate to 0.65) combined with (-)cinchonidine as the chiral auxiliary were used successfully for the enantioselecti ve hydrogenation of ethyl pyruvate to R(+)ethyl lactate which resulted in enantiomeric excesses of about 73% (with cyclohexane as the solven t) and 85% (with acetic acid as the solvent). The acidity of the zeoli te carrier and the dispersion of the active Pt component do not influe nce the enantioselectivity of the reaction within the range investigat ed, but both distinctly control the catalytic activity, which increase s with decreasing dispersion and rising acidity. The activities of the catalysts were obtained from kinetic data of the hydrogenation relate d to the specific surfaces of the active Pt components. The specific P t surfaces and the dispersion data were derived from volumetric CO che misorption measurements. 30 to 50 vol.-% of ethyl pyruvate are regarde d as the optimal range for the initial concentration concerning both e nantioselectivity and reaction rate. Furthermore, initial hydrogen pre ssure of at least 3 MPa is necessary in order to achieve good enantios electivities and catalytic activities. The temperature range of 293 to 303 K was found to be optimal. With respect to the dependence of the initial reaction rate on temperature, a change in reaction kinetics wa s observed between 323 and 333 K.