Kinetics and mechanisms of the reactions of organic cation radicals and dications. Part V. Kinetics of thermodynamically unfavourable electron transfer reactions between cation radicals and aromatic compounds

The kinetics of the electron transfer reactions between the cation radicals derived from thianthren, dibenzo-p-dioxin, and 9, 10-diphenylanthracene with anisole and anthracene in acetonitrile and dichloromethane were investigated. The reactions were found to be complex under the conditions employed being either first or second order in cation radical depending upon the radical ion concentration. The pseudo-second-order reactions were inhibited by the presence of unoxidized substrate. In all cases, the reactions were found to be first order in the compound undergoing oxidation. The disproportionation mechanism was ruled out for the second-order segment of all the reactions, except for that between diphenylanthracene cation radical and anisole, on the grounds that the disproportionation equilibrium constants are much too small to account for the reaction rates observed.