Autoxidation of Cyclohexane in the Presence of Fatty Acids and Decomposition of Cyclohexyl Hydroperoxide

Abstract

In order to elucidate the catalytic action of fatty acids on the autoxidation of cyclohexane, the autoxidation of cyclohexane and the decomposition of cyclohexyl hydroperoxide (CHP), which was regarded as an intermediate of the autoxidation, were studied in the presence of various fatty acids such as acetic [1], propionic [2], caproic [3], monochloroacetic [4], and dichloroacetic [5] acids.
It was found that the addition of the fatty acids caused the considerable effects on the cornposition of the expected products(cyclohexanol+cyclohexanone), as well as an acceleration of the rates of both the oxidation of cyclohexane and the decomposition of CHP as described below.
The decomposition rate of CHP was first-order and zero-order with respect to the concentrations of CHP and acid, respectively.
The decomposition rate constants of CHP at 130°C in n-dodecane containing 3.8 mol% fatty acid at the initial CHP concentration of 0.02 mol/l were 5.98×10^-3 for [1], 8.61 × 10^-3 for [2], 7.51×10^-3 for [3], 35.4×10^-3 for [4] and 38.4 × 10^-3 min^-1 for [5]. Furthermore, the activation energy for the decomposition in the presence of acetic acid at 130∼170°C was 17.9 kcal per mole. The main products of the decomposition were the acid esters of cyclohexanol and cyclohexanone, and the yields of the products after saponification of the decomposition products were 82.3, 79.9, 80.3, 68.9 and 59.1 mol% for [1], [2], [3], [4] and [5], respectively. The order of these values were approximately in the inverse order of the acidic strengths which were related to the above decomposition rate constants. A similar tendency in the yields was observed in the autoxidation of cyclohexane.
From the above results, it was presumed on the autoxidation of cyclohexane in the presence of fatty acid that the decomposition of CHP by the ionic mechanism to the formation of the desired products takes place predominantly.