Kinetics and mechanism of cyclohexane oxidation with molecular oxygen in the presence of propionic aldehyde

The kinetics and mechanism of the liquid-phase oxidation of cyclohexane wit h molecular oxygen in the presence of the additives of propionic aldehyde a re studied at 303.0, 322.5, and 341.5 K by measuring the rates of oxygen an d propionic aldehyde consumption and the yields of the main reaction produc ts (cyclohexanol (COL), cyclohexanone (CON), cyclohexyl hydroperoxide, and propionic acid and peracid). A kinetic scheme is proposed and rate constant s of elementary reactions are estimated based on the analysis of their rate s and the yields of the main cyclohexane products. The key reactions of the main steps (including chain initiation, propagation, and termination) are determined. An increase in the rate of cyclohexane oxidation and the yield of the target products (cyclohexanol, cyclohexanone, and cyclohexyl hydrope roxide) in the presence of propionic aldehyde suggests that highly active a cylperoxy radicals participate in chain propagation. The [CON]/[COL] ratio indicates that these products are mainly formed in chain propagation. The s trong effect of the Baeyer-Villiger rearrangement on both the rate of oxyge n consumption and the yield of the target products at the initial stages of the process and at high propionic aldehyde concentrations is explained.