Kinetics and mechanism of rhodium(III) catalysed oxidation of polyhydric alcohols by acidified potassium bromate

The kinetics of the Rh^III catalysed oxidation of ethylene glycol and glycerol by an acidified solution of KBrO₃ in the presence of Hg(OAc)₂ as a scavenger, have been studied in the 30–45 °C range. The rate is first order in bromate and in Rh^III but zero order with respect to the substrate and to HClO₄. The influence of Hg(OAc)₂, ionic strength and Cl^– on the rate was found to be insignificant. A transient complex, formed between Rh^III and bromate ion in a slow and rate determining step, reacts with the polyhydric alcohol to give the product in a series of fast steps, which lead to regeneration of the catalyst. Activation parameters have been calculated and a suitable mechanism is proposed.