Kinetics and mechanism of oxidation of secondary alcohols by benzyltriethylammonium chlorochromate

Abstract

Oxidation of several aliphatic secondary alcohols by benzyltriethylammonium chlorochromate in dimethylsulfoxide leads to the formation of corresponding ketones. The reaction is first order each in benzyltriethylammonium chlorochromate and the alcohols. The reaction is catalysed by hydrogen ions. Hydrogen-ion dependence has the form: <i>k</i>_obs = <i>a+b </i>[H⁺]. The oxidation of benzhydrol-α-d exhibits a substantial primary kinetic isotope effect (<i>k</i>_H/<i>k</i>_D = 6.12 at 288 K). Oxidation of 2-propanol has been studied in nineteen different organic solvents. The solvent effect has been analysed using Taft's and Swain's multiparametric equations. The reaction has been subjected to both polar and steric effects of the substituents. A mechanism involving transfer of hydride ion from alcohol to the oxidant via a chromate ester is also proposed.