Comparative Study of Monomeric and Polymeric Redox Mediatores in Indirect Electrochemical Reductiont

Monomeric and polymeric 1-alkylpyridinium compounds as redox mediators in the indirect electrochemical reduction of dihalo compounds were studied comparatively in aprotic solvents. A 4-ethoxycarbonyl-1-methylpyridinium cation was found to give two reversible cyclic voltammetric waves which may demonstrate the formation of corresponding neutral radical in acetonitrile and the anion at aat more negative potential. It was confirm ed by both cyclic voltammetry and preparative electrolysis that meso-1, 2-dibromo-1, 2-diphenylethane [3] and 1, 1-dibromo-2, 2-diphenylcyclopropane [4] could be reduced indirectly with electrogenerated and respectively. A platinum electrode which was chemically modified with 4-oxycarbonyl-1-methylpyridinium groups did not give any clear redox waves. At the next stage, a polymeric mediator having a molecular structure equivalent to monomeric one was examined in a similar way. Poly(4-vinyloxy-1-methylpyridinium cation) seemed to undergo reductive decomposition in DMF, while a coated pla tinum electrode mediated the reduction of [3] at the first wave potential in acelonitrile. The current at the second wave was so small that the coated-electrode could not be used for the the preparative electrolysis of [4]. As a conclusion, it was indicated that indirect electrochemical reactions were greatly affected by the status of mediators used.