Electron Transfer Catalyzed Reactions. Electrochemical Induction of the Hydrogen Atom Transfer Oxidation of Alcohols and Other Substrates by Aromatic Halides

Article abstract of DOI:10.1021/ja00239a035

The reduction of aryl halides in the presence of primary or secondary alcohols in liquid ammonia or in pure alcohol leads to the formation of the corresponding carbonyl compounds along an elctrocatalytic process consuming a vanishingly small amount of electricity.The aryl radical generated upon electrochemical reductive cleavage of the aryl halide first abstracts a H atom from the alcohol leading to an hydroxyalkyl radical which deprotonates into the ketyl anion radical, which is itself oxidized into the carbonyl compound.Side reactions are the reduction of the aryl radical and of the hydroxyalkyl radical.A detailed study of the feasibility and the mechanism of the reacton has been carried out by cyclic voltammetry and preparative scale electrolysis.The results underscore the fact that besides its acid-base properties, the H-atom donation ability of the solvent can play an important role in the course of electrochemical reactions.The electron stoichiometry, varying between 0 and 2, and the product distribution are functions of the redox and acid-base properties of the radical resulting from H-atom abstraction and of the redox and cleavage characteristic of the aryl halide anion radical.The reaction allows the oxidation of a large variety of substrates under electrochemically reducing conditions, those which lead to the formation of the aryl radical from the starting aryl halide.