Kinetics and mechanism of oxidation of some vicinal and non-vicinal diols by quinolinium bromochromate

1219-1223Kinetics of oxidation of four vicinal, four non-vicinal diols and two of their monoethers by quinolinium bromochromate (QBC) have been studied in dimethyl sulphoxide (DMSO). The main product of oxidation is the corresponding hydroxycarbonyl compound. The reaction is first order each in QBC and the diols. The reaction is catalysed by hydrogen ions. The hydrogen ion dependence is taking the form : kobs = a + b[H+]. The oxidation of [1,1 ,2,2-2H4] ethanediol exhibits a substantial primary kinetic isotope effect (kH/kD = 5.83 at 298 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft's and Swain's multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed