Oxidation of Vicinal Diols by Cerium(IV) in Aqueous Acidic Media Catalyzed by Rhodium(III)

Potential of rhodium(III) chloride in catalyzing, in aqueous sulfuric acid medium, the oxidation of vicinal diols, and the kinetics of reaction of cerium(IV) with propane-1,2-diol and butane-2,3-diol catalyzed by rhodium(III) chloride was investigated. Data show that the reactions follow first order kinetics with respect to low cerium(IV) for lower concentrations, but a further increase in the oxidant concentration retards the reaction velocity. The reaction rate shows direct proportionality with respect to low concentrations of diol, which tends to become zero order at higher concentrations of the organic substrate. The Rate is first order in catalyst. Increase in the concentrations of hydrogen and cerium(III) ions show retarding effects while increase in chloride ion concentration and in turn ionic strength of the medium has a positive effect on the rate. Stoichiometry and spectral studies confirmed the formation of one molecule each of formaldehyde and acetaldehyde and two molecules of acetaldehyde as the products of oxidation in case of propane-1,2- diol and butane-2,3-diol respectively. Thermodynamic parameters like enthalpy of activation, free energy of activation and entropy values were calculated and it was found that the formation of activated complex in the case of butane-2,3-diol was easy compared to that in the case of propane-1,2-diol.