Direct and indirect electrochemical reduction of organic halides in aprotic media

Abstract

Cyclic voltammetric reduction of 17 different organic halides including alkyl, allyl, and benzyl chlorides, bromides, and iodides in aprotic media (DMF, DMSO, and acetonitrile, AN), containing 0.1 M Bu₄NClO₄, have been reported at glassy carbon (gc) and graphite as working electrodes. A single two-electron irreversible and diffusion-limited reduction of the carbon-halogen bond is observed, the reduction potentials ranging from −1.20 to −2.70 V (versus silver wire quasireference electrode) depending on the halide, the solvent, and the electrode. Indirect reduction of these 17 halides, however, is effected at much lower potentials (−0.79 to −0.92 V versus SCE) depending on the experimental conditions by in situ electrogenerated superoxide ion (O ^⋅−₂ ) by CPE. The products have been characterized by TLC, GC, CV, or chemical estimation. The diorganic peroxide and the organic hydroperoxide were the major products. In case of tertiary alkyl halides, however, alkenes predominated, due to basic nature of O ^⋅−₂ in these reactions. These studies indicate sufficient strength of O ^⋅−₂ as a nucleophile or base depending on the experimental conditions.