Oxidation of cyclic alcohols by cerium(IV) in acidic medium in the presence of iridium(III) chloride

Kinetic data suggest reduction of CeIV into CeIII and elimination of Cl− and H+ ions before the rate-determining step in iridium(III) chloride catalyzed oxidation of cyclohexanol and cyclooctanol by cerium(IV) sulphate in aqueous sulphuric acid medium. IrCl3 was found to be equal or even a better catalyst compared to ruthenium for oxidations involving ceric ions. Effects of change of concentrations of CeIV, cycloalcohols, IrIII, H+, Cl− and CeIII on the reaction rate were determined. The order of the reaction changes from one to zero on increasing the concentration of the oxidant. Rate of the reaction was found to follow direct proportionality with respect to catalyst concentrations. Change in the order of reaction from first to zero was observed on increasing the concentration of organic substrate. External addition of H+, Cl− and CeIII ions retards the reaction velocity. Spectrophotometric evidence was provided that it is the cerium and not catalyst, which forms complex with substrate. Parameters such as energy of activation, free energy of activation and entropy data were collected at five different temperatures, which suggest that cyclooctanol is more easily oxidizable compared to cyclohexanol.

IrIII catalyzed oxidation of cyclic alcohols by CeIV in acidic medium gives dicarboxylic acids. CeIII, Cl− and H+ ions are eliminated before the slow step. Spectral evidence proves that substrate forms complex with cerium and not with catalyst. Catalytic efficiency of iridium(III), surpasses the efficiency of RuIII, RuVIII and OsVIII. Cyclooctanol oxidizes easily compared to cyclohexanol.Figure optionsDownload as PowerPoint slide