OXIDATION OF PROPYLENE-GLYCOL AND LACTIC-ACID TO PYRUVIC-ACID IN AQUEOUS PHASE CATALYZED BY LEAD-MODIFIED PALLADIUM-ON-CARBON AND RELATED SYSTEMS

Oxidation of propylene glycol and related compounds to pyruvic acid was carried out in aqueous phase at 90-degrees-C with a controlled pH of 8 in the presence of Pd/C modified by Pb, Bi and/or Te as additives. Oxidation of propylene glycol was observed on Pd/C at both the primary and secondary hydroxyl groups to yield lactic acid, hydroxyacetone and pyruvic acid with low selectivities. Pd/C, which alone was inactive in the oxidation of lactic acid, bound Pb on the metallic Pd with a strong interaction. The resultant Pb/Pd/C revealed activity for the selective conversion of lactic acid into pyruvic acid. A trace amount of the additive Pb, as low as the atomic ratio Pb/Pd = 0.05, was enough to afford pyruvic acid, and the initial rate of the oxidation showed a maximum at Pb/Pd = 0.3. Similar catalysts gave results as follows: Pb/Pt/C, highly active, but less selective; Te/Pd/C, highly selective to pyruvic acid with mild activity; Bi/Pd/C, moderate in both activity and selectivity. Commercially available Pb/Pd/CaCO3 (Lindlar catalyst) and Pb/Pd/Al2O3 were also active, giving 60% yield of pyruvic acid.