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

• Published in: Journal of molecular catalysis. A, Chemical Chemical, 2008-03, Vol.282 (1), p.136-143
• Main Authors: Tandon, Praveen K., Singh, Alok K., Sahgal, Sumita, Kumar, Santosh
• Format: Article
• Language: English
• Subjects: Catalysis; Cerium(IV) and Catalysis; Chemistry; Cyclic alcohols; Exact sciences and technology; General and physical chemistry; Iridium(III); Oxidation; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2007.12.001

Ir III catalyzed oxidation of cyclic alcohols by Ce IV in acidic medium gives dicarboxylic acids. Ce III, 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 Ru III, Ru VIII and Os VIII. Cyclooctanol oxidizes easily compared to cyclohexanol. ▪ Kinetic data suggest reduction of Ce IV into Ce III 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. IrCl 3 was found to be equal or even a better catalyst compared to ruthenium for oxidations involving ceric ions. Effects of change of concentrations of Ce IV, cycloalcohols, Ir III, H +, Cl − and Ce III 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 Ce III 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.