Selectivity control in the oxidation of phenylethane-1,2-diol with gold catalyst

The selective oxidation of phenilethane-1,2-diol to mandelic acid was performed in aqueous solution at different pH values in the presence of gold catalyst using dioxygen as the oxidant under mild conditions (343/363 K, pO2/300 kPa). The reaction mechanism highlights that the phenyl group activates the benzylic position thus decreasing the selectivity toward the primary alcoholic function precedently observed using aliphatic substrates. Optimisation of the reaction condition based on the knowledge of base-catalysed side reactions allowed the production of sodium mandelate with selectivity up to 83% at 100% conversion.