Electrochemical reduction of decabromodiphenyl ether at carbon and silver cathodes in dimethylformamide and dimethyl sulfoxide

An investigation of the electrochemical reduction of the flame-retardant, decabromodiphenyl ether (DBDE), at carbon and silver cathodes has been undertaken with the aid of cyclic voltammetry and controlled-potential (bulk) electrolysis in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), each solvent containing 0.10 M tetra-n-butylammonium tetrafluoroborate (TBABF4). Cyclic voltammograms for reduction of DBDE at a glassy carbon electrode exhibit five irreversible and comparably sized cathodic peaks that are associated with a sequence of debromination processes, whereas cyclic voltammograms acquired with a silver cathode show fewer discrete stages of irreversible reduction and are accentuated by one very prominent peak. Bulk electrolyses of DBDE at either a reticulated vitreous carbon or a silver cathode in DMF lead to approximately 20–25% conversion of DBDE to a mixture of diphenyl ether, dibenzofuran, benzene, and phenol, and the remaining products are congeners of dibromodiphenyl ether. When DMSO is employed as solvent for bulk electrolyses, diphenyl ether is formed in approximately 20% yield, and a mixture of congeners ranging from decabromo- to monobromodiphenyl ether is found. Bulk electrolyses of DBDE in DMF–TBABF4 at carbon held at a potential near the cathodic limit indicate that complete debromination can be achieved.