Alkyl vicinal dibromides are reduced by cob(I)alamin generated at a glassy carbon cathode in weakly acidic aqueous acetonitrile in a two-electron electrocatalytic cycle with a lowering in overpotential of 0.84 V compared to direct reduction. Unlike reactions of primary alkyl halides with cob(I)alamin that yield stable alkylcobalamins, 1,2-dibromobutane and 1,2-dibromoethane are reduced completely to alkenes at potentials somewhat positive of the E°' of Co(II)/Co(I). Spectroelectrochemistry showed

Kinetic control of the two-electron electrocatalytic dehalogenation of monohalobiphenyls to biphenyl was elucidated by analyzing voltammetric data with expanded-grid digital simulation/nonlinear regression. The method involves comparing goodness of fit of limiting and mixed kinetic simulation models to the data and is applicable to second-order conditions. The rate-determining step in the dehalogenations was confirmed as electron transfer between the electrochemically generated phenanthridine anion radical and 4-chloro-(4-CB) and 4-bromobiphenyl (4-BB), rather than decomposition of the halobiphenyl anion radical. Rate constants for this step of (1.42 ± 0.12) X 103 M-1 s-1 for 4-CB and (5.1 ± 1.8) X 104 M-1 s-1 for 4-BB showed considerably improved precision (and accuracy in the latter case) over rate constants obtained under pseudo-first-order conditions, where the catalytic current had to be extracted from large currents for direct reduction of excess substrate. The simulation/regression method is general for two-electron homogeneous electrocatalytic reactions following similar mechanisms. Synthetic data were used to show that, for systems under mixed kinetic control, rate constants for both homogeneous electron transfer and decomposition of the haloaromatic anion radical can be estimated simultaneously.

The use of Excel for peak deconvolution by nonlinear regression analysis is discussed. Excel is easily employed in an experiment that introduced students to the use of nonlinear regression analysis for the deconvolution of overlapped gas chromatographic peaks (J. Chem. Educ. 1994, 71, 483-486). Excel gave similar results to those reported previously that used the Fortran program KINFIT for nonlinear regression analysis.

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