CATALYTIC-OXIDATION OF GLYOXAL TO GLYOXYLIC-ACID ON PLATINUM METALS

Aqueous solutions of glyoxylic acid (CHOCOOH) have been prepared by catalytic oxidation of aqueous glyoxal (CHOCHO) solution with air slightly above room temperature. The catalysts are carbon-supported platinum metals. Provided the pH is regulated near neutrality, the yield of glyoxylic acid (GLY) can be as high as 70% at 85.5% glyoxal conversion. GLY is subsequently oxidized quantitatively into oxalic acid. The oxidation mechanism probably involves an end-on adsorption of the glyoxal dihydrate molecule on the metal surface followed by dehydrogenation. The initial rate of GLY formation increases in the series 0 = Ru < Rh < Pd < Ir < Pt, similar to the series of the redox potentials of these elements. Ruthenium is totally inactive because it is probably covered with hydroxyl groups that catalyze side reactions such as dismutation (Cannizzaro reaction) and direct oxidation of glyoxal into formic acid (C-C bond rupture). © 1992.