A Study for Mechanism and Oxidation Reaction of Substituted Benzyl Alcohols using Cr(VI)-Heterocyclic Complex(Cr(VI)-2-methylpyrazine)

Abstract Cr(VI)-heterocyclic complex[Cr(VI)-2-methylpyrazine] was synthesized by the reaction between of heterocyclic compound(2-methylpyrazine) and chromium trioxide, and characterized by IR and ICP analysis. The oxidation of benzyl alcohol using Cr(VI)-2-methylpyrazine in various solvents showed that the reactivity increased with the increase of the dielectric constant(e), in the order : cyclohexene＜chloroform＜acetone＜N,N-dimethylformamide(DMF). In the presence of DMF solvent with acidic catalyst such as hydrochloric acid(HCl solution), Cr(VI)-2-methylpyrazine oxidized benzyl alcohol(H) and its derivatives(p- CH3, m-Br, m-NO2). Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(ρ) was Cr(VI)-2-methylpyrazine= -0.65(308K). The observed experimental data have been ratiolized. The hydride ion transfer causes the prior formation of a chromate ester in the rate-determining step. Key Words : Chromate ester, Hydride ion transfer, Hammett reaction constant(ρ), Rate-determining, Step.substitutedbenzyl alcohol.