Thermodynamics of Ru(III)-edta catalyzed oxidation of saturated organic compounds by molecular oxygen

Abstract

The thermodynamics of Ru(III)-EDTA catalyzed oxidation of cyclohexane to cyclohexanol and of cyclohexanol to cyclohexanone by molecular oxygen in acidic medium has been investigated in the temperature range 288-318 K, μ=0.1 M KNO₃ in a 1:1 water:1,4-dioxane mixture (v/v). The dependence of the rate of oxidation on factors such as temperature (288-318 K), catalyst, substrates, molecular oxygen concentrations and pH was studied. The order of the reaction with respect to the concentrations of substrate and catalyst is unity. The dependence in molecular oxygen was found to be one-half and zero for the oxidations of cyclohexane and cyclohexanol, respectively. No dependence on [H⁺] was observed for oxidation of cyclohexane. The rate of oxidation of cyclohexanol is inversely proportional to the hydrogen ion concentration. The thermodynamic parameters corresponding to equilibrium constants and activation parameters corresponding to rate constants were computed. The mechanisms proposed on the basis of the kinetic data are discussed in terms of thermodynamic stability and reactivity. The activation energy for the oxidation of cyclohexane is 7.3 kcal mol⁻¹ higher than that of cyclohexanol. Thermodynamic factors are more favourable for the oxidation of cyclohexanol, which proceeds by a rate higher than that of cyclohexane.