ELECTRON TRANSFER INDUCED REACTIONS. ELECTROCHEMICALLY STIMULATED AROMATIC NUCLEOPHILIC SUBSTITUTION IN ORGANIC SOLVENTS.

Article abstract of DOI:10.1021/ja00367a028

The main difference between organic solvents and solvents such as liquid ammonia as far as electrochemically induced aromatic nucleophilic substitution is concerned regards the role of H-atom abstraction from the solvent. This reaction and electron transfer at the electrode and in the solution are major side reactions competing with nucleophilic attack on the aryl radical. The resulting four-cornered competition is analyzed in the context of cyclic voltammetry and preparative scale electrolysis. In most cases, the experimental conditions can be adjusted so that the competition only involves nucleophilic attack, heterogeneous electron transfer, and H-atom abstraction. This allows a quantitative evaluation of the role of the latter reaction. Experimentally, a detailed investigation of the substitution of 9-haloanthracenes by cyanide and thiophenoxide ions has been made. Other systems for which preparative scale results were previously gathered are analyzed in the same context. A general mechanistic picture of the S//R//N1 reaction can be drawn which is applicable to the case of electrochemical inducement but also to the other modes of stimulation.