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 Bu 4 NClO 4 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(ClO 4 ) 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 (Δ G ° 298 = −16.6 kcal mol −1 ).