Electrochemically induced decomposition of benzopinacol.

Chemical bond cleavage by electron transfer to an organic molecule is a typical electro-initiated reaction; however, there are few examples of carbon—carbon bond cleavage. In this study, using cyclic voltammetry, chronoamperometry, controlled-potential electrolysis with chromatographic characterization of products, and ab initio quantum chemical calculations, it was shown that the electrochemical reduction of benzopinacol (1,1,2,2-tetra-phenyl-1,2-ethanediol) in aprotic solvents (DMF, MeCN, THF) in the presence of Bu4NClO4 as a supporting electrolyte is accompanied by cleavage of the central C–C bond, which follows the electron transfer. This initiates a chain reaction giving equimolar amounts of benzophenone and benzhydrol (diphenylmethanol). The decomposition is inhibited in the presence of medium-strength proton donors (phenol, benzoic and acetic acids, etc.) in the solution. A similar effect is attained by the addition of divalent metal salts, in particular Mg(ClO4)2. According to the results of quantum chemical calculations, the effective C–C bond cleavage in the benzopinacol radical anion to give a radical and an anion is due to a very low energy barrier (1.7 kcal mol−1) and is very thermodynamically favorable (ΔG°298 = −16.6 kcal mol−1). [ABSTRACT FROM AUTHOR]