Pyruvic acid hydrogenation, modified metal catalyst

Heterogeneous catalytic hydrogenation of the methyl esters of a-keto acids over modified metal catalysts other than nickel have been studied using a cinchonidine-modified platinum catalyst. " Methyl pyruvate and methyl benzoylformate were hydrogenated to form methyl (R)-lactate and (R)-mandelate with high ee (81-84%). 

Chiral molecules on the surface of the metal colloid can induce enantioselective control. Following this concept a new type of enantioselective platinum sol catalyst stabilized by the alkaloid dihydrocinchonidine was designed [120, 121]. Chirally modified Pt catalyst precursors have been prepared in different particle sizes by the reduction of platinum tetrachloride with formic acid in the presence of different amounts of the chiral alkaloid. Optical yields up to 80% ee were obtained in the hydrogenation of ethyl pyruvate. This type of catalyst was demonstrated to be structure insensitive since turnover frequencies (ca. 1 s ) and enantiomeric excess are independent of the particle size. 

The development of aqueous phase hydrogenation reactions catalysed by water soluble transition metal sulfonated phosphine complexes began with the pioneering work of Joo and Beck in the Ru/tppms-catalysed hydrogenation of pyruvic acid to lactic acid in 1974 which coincides with the first application of water soluble RhH(CO)(tppts)3 catalysts in the biphasic propene hydroformylation. The success of Ru/tppms contrasted with the lack of activity observed using transition metal complexes modified with water soluble ligands such as the system 57 [Table 4, n=l] in hydrogenation reactions in aqueous media. ... 

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