Dechlorination of beta-methylallyl chloride by electrogenerated [Co(I)(bipyridine)3]+: an electrochemical study in the presence of cationic surfactants

We have investigated the electrocatalytic dehalogenation of beta-methylallyl chloride (beta-mAC), widely used in the polymer industry, using Co(I)(bpy)3]+ (where bpy=2,2'-bipyridine) electrochemically generated in situ from Co(II)(bpy)3]2+ at a glassy carbon electrode in the presence of three different cationic surfactants in aqueous solution. Cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TDTAB), and cetylbenzyldimethylammonium chloride (CBDAC) were employed in the present investigation. The Co(II)(bpy)3]2+-cationic surfactant systems show excellent electrocatalytic activity toward dehalogenation of beta-mAC. The dependence of the catalytic current, the corresponding potential, and the current function on the potential scan rate has been analyzed to assess the nature of the catalytic reaction. The second-order rate constant, kchem, for the reaction between the beta-mAC substrate and the electrogenerated-micelle stabilized-Co(I) complex has been calculated by a cyclic voltammetry technique. The reduction products after 3 h of bulk electrolysis have been identified by GC/MS to be one nonchloro compound (2-methyl-1,5-hexadiene (IV)) and two chloro compounds (1-chloro-2,5-dimethyl-2,5-hexadiene (V) and spiro1.2]cylopropyl-6-chloro-5-methyl-hex-4-ene (VI)). Based on the electrochemical results and the mass spectral data, a reaction scheme involving all the reduction products has been proposed. Finally, a good correlation between the catalytic efficiency and the structural features of the surfactant molecules is demonstrated. The present study emphasizes the need for further optimization work to achieve maximum yield of nonchloro compound (IV) to employ the present Co(II)(bpy)3]2+-cationic surfactant systems with a high catalytic efficiency as promising for possible applications.