Studies on the Kinetics of Tetraethylammonium Bromochromate Oxidation of Some Meta- and Para-Substituted Benzyl Alcohols in Non-Aqueous Media

Tetraethylammonium bromochromate (TEABC) oxidation of 18 meta- and para-substituted benzyl alcohols (BnOH) in dimethylsulphoxide (DMSO) leads to the formation of corresponding aldehydes. The reaction is first order each in TEABC and the alcohols. The reaction is catalyzed by hydrogen ions. The hydrogen ion dependence has the form: k(obs) = a +b[H+]. The oxidation of alpha alpha'-dideuterio benzyl alcohol exhibited a substantial primary kinetic isotope effect (k(H)/k(D) = 5.71 at 303 K). Oxidation of benzyl alcohol was studied in 17 different organic solvents. The solvent effect has been analyzed using Kamlet's and Swain's multi parametric equation. A correlation of data with Kamlet-Taft solvatochromic parameters (alpha, beta, pi*) suggests that the specific solute-solvent interactions play a major role in governing the reactivity. A mechanism involving a hydride ion transfer via chromate ester is proposed.