Iridium(III) catalyzed oxidation of toluene and ethyl benzene by cerium(IV) in aqueous acidic medium

Iridium(III) chloride catalyzed oxidation of toluene and ethyl benzene by cerium(IV) sulphate in aqueous sulphuric acid medium was studied. Change in the concentration of oxidant shows a specific effect that the rate increases in the beginning at low concentrations, it reaches to a maximum and further increase in oxidant concentration decreases the rate. Oxidation was highly selective as it oxidizes toluene to benzaldehyde and ethyl benzene acetophenone. It is proposed that the complex formed between cerium(IV) and the organic substrate in first equilibrium step gives another complex in the presence of iridium(III) which ultimately gives rise to products of oxidation. Order of the reaction follows first order kinetics at low concentrations tending to become zero order at higher concentrations of organic substrate in both the cases. Rate of the reaction follows direct proportionality with respect to catalyst concentrations, while the rate decreases sharply with increasing hydrogen ion and cerium(III) concentrations. Change in ionic strength of the medium and the effects of changing concentrations of acetic acid, Cl− ions, and HSO4− ions on the rate were studied. Energy of activation, free energy of activation and entropy parameters were also calculated.

Graphical abstractRate of the reaction in oxidant is first order in the beginning, reaches to a maximum and then starts decreasing. Oxidation is selective to benzaldehyde in toluene and to acetophenone in ethyl benzene.Figure optionsDownload full-size imageDownload as PowerPoint slide