ELECTROCHEMISTRY OF THE CARBON-HALOGEN BOND - 9-FLUORENYL AND BENZHYDRYL HALIDES IN DIMETHYLFORMAMIDE AT PLATINUM AND VITREOUS CARBON ELECTRODES

Electrochemical reductive dehalogenations of 9-fluorenyl and benzhydryl bromides and chlorides at platinum and vitreous carbon electrodes in dimethylformamide initially require two electrons/molecule and afford the corresponding carbanions as short-lived intermediates. The electrogenerated carbanions may be protonated by diethyl malonate to give their corresponding hydrocarbons or, in the absence of added proton donor, react with their starting halides by either proton transfer or displacement of halide ion. Reaction by the first of the latter two pathways leads to the corresponding olefin via an electroactive monohaloethane, whereas reaction involving the displacement of halide ion gives an electroinactive nonhalogenated ethane; the pathway which is followed appears to be determined by the ease with which halide ion is displaced. Reaction by either channel is rapid : the rate constants obtained for the displacement of bromide ion from 9-bromofluorene and benzhydryl bromide are 1 X 105 and 8 X 104 M-1 s-1, respectively, while the rate constant for proton transfer from 9-chlorofluorene to 9-fluorenyl anion is 8 X 103 M-1 s-1. All starting halides give multiple reduction waves on platinum because of either adsorption of halide ion or electrocatalysis from electrode products and adventitious impurities. No specific surface effects are observed with vitreous carbon electrodes. © 1979, American Chemical Society. All rights reserved.