Gold on carbon as a new catalyst for selective liquid phase oxidation of diols

Catalytic oxidation of vicinal diols to alpha-hydroxy carboxylates with dioxygen in alkaline solution has been performed by using gold based catalysts. The optimization of the catalytic system has highlighted the influence of the support and preparation method on both activity and selectivity. Under mild conditions (T = 343-363 K, pO(2) = 300 kPa (absolute)) high selectivities (90-100%) toward monooxygenation in the cases of ethane-1,2-diol and propane-1,2-diol were achieved at high diol conversions (80-94%). The racemization of optically active propane-1,2-diol during its oxidation as well as isotopic H-D exchange experiments allowed us to deduce new features in the mechanism of diol oxidation and concerning the dependence of selectivity on reaction conditions. The recycling of gold on carbon catalyst revealed its good resistance toward deactivation, greater than palladium or platinum on carbon catalysts which were respectively affected by metal leaching and a considerable loss of selectivity. (C) 1998 Academic Press.