Kinetics and mechanism of the oxidation of diols by pyridinium hydrobromide perbromide

摘要

Kinetics of oxidation of five vicinal, four non-vicinal diols, and one of their monoethers by pyridinium hydrobromide perbromide (PHPB) have been studied. The vicinal diols yield products arising out of the glycol bond fission while the other diols yield hydroxycafbonyl compounds. The reaction is first order with respect to PHPB. Michaelis-Menten type kinetics are observed wih respect to the diol. There is no effect of added pyridinium bromide on the reaction. The oxidation of [1,1,2,2-~2H_4] ethanediol shows the absence of a primary kinetic isotope effect. The values of solvent isotope effect, k(H_2O)/k(D_2O), at 313 K, for the oxidation of ethanediol, propane-l,3-diol and 3-methoxybutan-l-ol are 4.71, 2.17 and 2.23 respectively. A mechanism involving glycol-bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidised by a hydride-transfer mechanism as they are monohydric alcohols.