THE SELECTIVE OXIDATION OF TOLUENES TO BENZALDEHYDES BY CERIUM(III), HYDROGEN-PEROXIDE AND BROMIDE ION

4-t-Butyltoluene can be oxidised in acetic acid to 4-t-butylbenzaldehy de by hydrogen peroxide in a process catalyzed by cerium(III) and brom ide ions. The conversion proceeds via benzylic bromination, hydrolysis of the bromide to alcohol and the rapid oxidation of the alcohol to t he aldehyde by bromine. The reaction is ineffective in the absence of bromide but is also inhibited by significant quantities of the ion, ap parently because the hydrolysis step is reversible. The role of the ce rium has not been clearly established, Cerium(IV) is formed in the sys tem but the first step appears not to involve electron transfer from t he aromatic ring. Nor can simple radical bromination explain the rate of formation of benzylic bromide.