Enhanced Rates of Organic Dehalogenations in a Microemulsion Using Adsorbed Metal Phthalocyanines on Electrodes

Copper and nickel phthalocyanines and their tetrasulfonates adsorbed onto carbon electrodes were used for electrochemical catalytic reduction of 1,2-dibromobutane (DBB), trans-1,2-dibromocyclohexane (DBCH), and trichloroacetic acid (TCA) in a bicontinuous microemulsion made from didodecyldimethylammonium bromide (DDAB), dodecane, and water and in homogeneous acetonitrile/water. Square wave voltammetry was used to obtain apparent pseudo-first-order rate constants (k‘) for the rate-determining step (rds) involving reaction of organohalides with catalysts reduced by two electrons. Reductions of DBCH and DBB gave larger k‘ values in the microemulsion than in homogeneous solvent. For reduction of TCA, larger k‘ values were found in the homogeneous solvent. Results suggest that DBCH and DBB give higher reaction rates in the microemulsion because of preconcentration of the relatively nonpolar organohalides into a surfactant film on the MPCTS-coated electrode. TCA may be partly rejected from the film, decreasing its reaction rate. Thus, when using electrodes with adsorbed catalysts in microemulsions, reactant concentration in an adsorbed film on the electrode appears to be an important rate-controlling factor.