Kinetic study on the oxidation reaction of substituted benzyl alcohols by Cr(VI)-heterocyclic complex (2,2′-bipyridinium dichromate)

초록

Cr(VI)-heterocyclic complex (2,2′-bipyridinium dichromate) was synthesized by the reaction between of 2,2′-bipyridine and chromium trioxide in H<inf>2</inf>O, and characterized by IR and ICP. The oxidation of benzyl alcohol using 2,2′-bipyridinium dichromate in various solvents showed that the reactivity increased with the increase of the dielectric constant, in the order: cyclohexene < chloroform < acetone < N,N-dimethylformamide. In the presence of DMF solvent with acidic catalyst such as H<inf>2</inf>SO<inf>4</inf> solution, 2,2′-bipyridinium dichromate oxidized the benzyl alcohol and its derivatives (p-OCH<inf>3</inf>, m-CH<inf>3</inf>, H, m-OCH<inf>3</inf>, m-Cl, m-NO<inf>2</inf>). Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant was -0.66 (303 K). The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

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