Electrochemical reduction of di-, tri-, and tetrahalobenzenes at carbon cathodes in dimethylformamide Evidence for a halogen dance during the electrolysis of 1,2,4,5-tetrabromobenzene

Abstract

Abstract Cyclic voltammetry and controlled-potential electrolysis have been employed to examine the electrochemical reduction of a series of di-, tri-, and tetrahalobenzenes at carbon cathodes in dimethylformamide containing tetramethylammonium perchlorate. Cyclic voltammograms for the reduction of 1,2,4,5-tetrabromo-, 1,2,3,4-tetrachloro-, and 1,2,4,5-tetrachlorobenzene exhibit four irreversible waves, those for 1,2,4-tribromo-, 1,3,5-tribromo-, 1,2,3-trichloro-, 1,2,4-trichloro-, ad 1,3,5-trichlorobenzene show three irreversible waves, and those for 1,3-dibromo-, 1,4-dibromo-, 1,2-dichloro-, 1,3-dichloro-, and 1,4-dichlorobenzene reveal two irreversible waves. Products derived from the electrolytic reduction of 1,2,4,5-tetrabromobenzene are 1,2,4-tribromo-, 1,3-dibromo-, and 1,4-dibromobenzene, along with 1,3,5-tribromobenzene, and the appearance of the last compound indicates that an electrolytically induced halogen dance takes place. For all of the other polyhalobenzenes investigated, except 1,2-dibromobenzene, the distributions of electrolysis products are consistent with expectations based on their voltammetric behavior.