Catalytic reduction of 1,2,5,6,9,10-hexabromocyclododecane by nickel(I) salen electrogenerated at vitreous carbon cathodes in dimethylformamide

摘要

Catalytic reduction of 1,2,5,6,9,10-hexabromocyclododecane (HBCD) by nickel(I) salen electrogenerated at a carbon cathode has been investigated by means of cyclic voltammetry and controlled-potential (bulk) electrolysis in dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF_4). Cyclic voltammograms for reduction of nickel(II) salen in the presence of HBCD exhibit the characteristics of a catalytic process: (a) at low concentrations of HBCD, a tiny cathodic prepeak is observed that merges with the peak associated with reduction of nickel(II) salen and (b) as the substrate concentration increases, the cathodic peak current rises and the anodic peak current falls for the nickel(II) salen-nickel(I) salen redox couple. Bulk electrolyses at a reticulated vitreous carbon cathode of solutions containing 1.0 mM nickel(II) salen and less than 20.0 mM HBCD result in conversion of the starting material to 1,5,9-cyclododecatriene (CDT, 88-95%), along with small amounts of cyclododeca-1,5-dien-9-yne (CDY, 3-4%), in a six electron process. Incomplete catalytic reduction occurs for concentrations of HBCD at or above 20.0 mM; CDT is produced in only 35% yield, and traces of unreduced starting material remain. In addition, at this higher concentration of HBCD, other products (pentabromocyclododecene, tetrabromocyclododecene, tribromocyclododecadiene, dibromocyclododecadiene, and bromocyclodo-decatriene) have been detected, but not quantitated.