NW 31) and by the Fonds der Chemischen Ind. is gratefully acknowledged. J.S.F. is thankful for a Humboldt fellowship. We are indebted to F. Mallendorf for his assistance in electrochemical measurements.Supplementary Material Available: Tables giving the experimental details of the synthesis reactions, the elemental analyses of the new compounds, and the NMR and IR data of the new compounds (4 pages). Ordering information is given on any current masthead page.

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Alkyl vicinal dibromides were reduced at glassy carbon electrodes In Isooctane/water emulsions stabilized by Aero-sokOT (AOT) and tetraethylammonium perchlorate (TEAP) by using an electrocatalytic cycle Involving vitamin B12. Catalysis lowers the overpotential by about 0.8 V compared to direct reduction In a homogeneous medium. The heterogeneous rate constant (0.0056 cm s-1) for the key Co(II)/Co(I) reduction step of the catalyst was about 3-fold smaller than In pH 2.3 aqueous acetonitrile. Apparent rate constants on the order of 104 L mol"1 s"1 for the rate-limiting chemical reactions of 1,2-dibromoethane and 1,2-dibromobutane with Co(I) were considerably smaller than In aqueous acetonitrile because of the partitioning of substrate Into the hydrocarbon phase. Despite these kinetic limitations, square-wave voltammetry could be used with the catalytic cycle to estimate total ethylene dlhalldes In unleaded and leaded gasoline In AOT/ TEAP emulsions prepared with gasoline.

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