Electrochemical reduction of substituted benzophenones and fluorenones in media of low proton availability mechanism of the reductive cleavage of bromo and chloro benzophenones

摘要: Abstract The reduction of a wide series p- and m-substituted benzophenones 2-substituted fluorenones is studied in dimethylformamide. With the exception p-Cl, m-Br p-Br benzophenones, first process consists simply formation stable anion radical. It thus possible to correlate, this series, characteristic potentials having definite thermodynamical meaning with Hammett constants. behaviour halo-derivatives benzophenone cited different as indicated by plot. A reductive cleavage carbon-halogen bond observed leading unsubstituted benzophenone. subsequent evolution species initially formed not same conditions preparative-scale electrolysis, where two electrons are exchanged, polarographic voltammetric only one electron exchanged. In last case, experimental observations rationalized assuming reaction sequence composed an expulsion halide ion from radical generated followed abstraction hydrogen atom solvent. Other mechanisms discussed. Assuming mechanism, it shown, using linear sweep voltammetry for kinetic analysis, that dehalogenation step presumably rate determining one. Considering second process, i.e. formed, shown exchange solution interferes e.c.e. type mechanism. influence on polarization patterns