Liquid-phase oxidation of propylene glycol using heavy-metal-free Pd/C under pressurized oxygen

The liquid-phase oxidation of propylene glycol using Pd/C undoped with any heavy metal such as tellurium in the presence of aqueous NaOH under pressurized oxygen resulted in a significant production of lactic acid and a minimal amount of hydroxyl acetone, although, under these conditions, sodium lactate as sodium analogue of lactic acid has been known to easily convert to sodium pyruvate. The advantageous effect of doping Pd/C with a heavy metal, which has been reported for various catalytic reactions in an aqueous phase, was not observed in the present oxidation. Previous papers have reported that oxidation using heavy-metal-free Pd/C and Pd/C doped with a heavy metal at atmospheric pressure and a pH 8 produced pyruvic acid via the formation of hydroxyl acetone and lactic acid, respectively, and that Pd/C doped with a heavy metal rather than Pd/C was suitable for the formation of pyruvic acid from propylene glycol. However the results of the present study show that the use of pressurized oxygen conditions as used in the present study can result in the exclusion of doping with a heavy metal in the preparation of the catalyst, which is amenable to green chemistry.