Influence of Br- Concentration on (Br)+-Mediated Indirect Electrooxidation of Alcohols to the Corresponding Carbonyl Compounds

Article abstract of DOI:10.1246/bcsj.60.3137

Current efficiency for the (Br)⁺ (positive bromine species)-mediated indirect electrooxidation of alcohols to the corresponding carbonyl compounds decreased with increase in Br^- concentration in dichloromethane and aqueous acidic solutions, while no concentration dependence was observed in an aqueous neutral solution.These facts suggested a general practical guideline for the indirect electrooxidation, i.e. low Br^- concentration is favorable in an electrolytic solution of low nucleophilicity.It was also found that the kind of (Br)⁺ species formed anodically in the absence of the alcohols in dichloromethane celarly depended on charge(Q) passed as follows:Br3^- at Q-1 (1F = 96480 C), Brn^- (n>3) at 2/3-1, and Br2 at Q = 1F mol^-1.Among these species, Br3^- and Br2 seemed to be the weakest and strongest oxidizing agents, respectively.Lower efficiency for the direct electrooxidation in higher Br^- concentration was rationalized as due to more predominant formation of Br3^- and/or Brn^- with smaller n values.