Kinetics and Mechanism of the Liquid-Phase Oxidation of n-Carboxylic Acids

Short reaction chains participate in the oxidation of C-3-C-6, C-8, C-10, and C-12 n-carboxylic acids. The quadratic-law recombination of peroxy radicals occurs both without and with chain termination. The ratio of the rate constants of these reactions increases to k'/k(t) = 4.5 on passing from propanoic acid to pentanoic acid, and then it decreases almost to zero for dodecanoic acid. The anomalous variation of the k'/k(t) ratio is explained by the fact that the radicals resulting from carboxylic acid oxidation at the CH bonds nearest to the functional group make different contributions to the recombination process, depending on the carbon chain length. The cross recombination of secondary hydrocarbon peroxy radicals with the HO2 center dot radicals resulting from the oxidation of carboxylic acids at the beta-C-H bonds proceeds without chain termination.