Mild Oxidation of Cyclohexane Catalyzed by Cobalt(II) Acetate and Initiated by H2O2 in the Acetic Acid Medium

Abstract

The homogeneous catalytic oxidation of cyclohexane by molecular oxygen and hydrogen peroxide in a solution of acetic acid (HOAc) in the presence of cobalt(II) acetate Co(OAc)2 is studied. The high yields of cyclohexanol, cyclohexanone, and cyclohexyl hydroperoxide (0.10–0.15 mol/l) and the high rate of the process (w = 10–5–10–4 mol l–1 s–1) are explained by (1) mild conditions of oxidation in the medium of the HOAc solvent and (2) efficient initiation of the process due to the fast kinetics-controlled dissociation of H2O2 into radicals in the studied reaction medium under the action of cobalt cations. Quantitative relationships are found for the cyclohexane oxidation rate, the yield of target products, and the ratio of reactants participating in the process. The effect of hydrogen hydroperoxide additives on the concentrations of reduced and oxidized forms of the catalyst is studied by spectrophotometry in model mixtures. Quantum chemistry is employed to calculate the probabilities of some key elementary reactions. Calculated data agree well with the experiment.