Effect of Quinones on the Cobalt(II) Acetate–Catalyzed Mild Oxidation of Cyclohexane with Hydrogen Peroxide in Acetic Acid

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The effects of free-radical reaction inhibitors (InH), hydroquinone (HQ) and quinone (Q), on the oxidation of cyclohexane catalyzed by cobalt(II) acetate Co(OAc)2 · 4H2O and on the decomposition of hydrogen peroxide in acetic acid (HOAc) at 303 K were studied. It was found that an increase in the concentration of HQ in the starting reaction mixture containing cyclohexane, the catalyst, and H2O2 dissolved in HOAc resulted in an exponential decrease in the yields of the target products of oxidation: cyclohexanol, cyclohexanone, and cyclohexyl hydroperoxide. In the presence of Q, the dependence of the yield of the target products on the initial inhibitor concentration exhibited a maximum at (1.8–2.5) × 10–2 M Q. At (2.2–2.4) × 10–2 M Q concentrations, the yield of the target products was 55–60% of that in an uninhibited process. Based on kinetic, spectrometric, and quantum-chemical data, the effect found was explained by the fact that under the experimental conditions highly active hydroxyl derivatives of radicals rather than a hydroxy quinolide hydroperoxide (the homolysis of which can produce species with a free valence, which are capable of initiating free-radical reactions) were largely formed from Q.