Evidence for the involvement of CrII and free radicals as intermediates in the reduction of HCrO4- by saccharides, alcohols and hydroxyacids

Intermediacy of free radicals and CrII in the reaction of HCrO4- with a variety of neutral and acid saccharides, hydroxyacids and alyphatic alcohols was demonstrated by the observation of free radical induced polymerization of acrylonitrile and acrylamide, and detection of CrO22+ when working in O2-saturated solutions and low [HCrO4-]. The results are interpreted in terms of a mechanism combining the CrVI → CrIV → CrII and CrVI → CrIV → CrIII pathways.

The reduction of HCrO4- by d-glucuronic acid and d-galactose in O2-saturated solution yield 50% of CrO22+, at pH 1. At this pH, the CrVI → CrIV reduction is rate limiting and competitive one- and two-electron reductions of CrIV take place at the same rate.Figure optionsDownload as PowerPoint slide