Catalyst selection and solvent effects in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione

1-Phenyl-1,2-propanedione was hydrogenated at 5 bar and 25 °C over Pt/Al₂O₃ catalysts in the presence of cinchonidine. The effect of four different solvents, ethyl acetate, toluene, ethanol and dichloromethane in the enantioselective hydrogenation of the dione was tested. The highest enantiomeric excess of (R)-1-hydroxy-1-phenyl-2-propanone, 65 %, was obtained in dichloromethane. Also toluene and ethyl acetate gave relatively high enantiomeric excesses. In ethanol, which highly interacts with Pt surface, the enantiomeric excess was only 12 %. Two different alumina supports and Pt-precursors were investigated using ethyl acetate as solvent. The highest enantiomeric excesses of (R)-1-hydroxy-1-phenyl-2-propanone were obtained with α-Al₂O₃ supported Pt catalyst prepared from hydrogen hexachloroplatinate(IV)hydrate precursor. The highest Pt loadings in the catalyst preferred enantiodifferentiation. Higher enantiomeric excesses were obtained by increasing the mean metal particle size of Pt.