Electroreduction mechanism of some sugars on mercury

The electroreduction mechanism on mercury of the aldoses glucose and galactose, the ketoses fructose and tagatose, and the disaccharides lactose and lactulose was investigated in neutral and weakly alkaline solutions. Measurements at different temperatures ranging from 0 to 45 degrees C indicate that the chemical reaction of the hemiacetal ring opening, which controls the polarographic limiting current, proceeds mainly in the adsorbed state below room temperature and in the nonadsorbed state above room temperature. Along the rising portion of the polarographic wave the electrode process is under the mixed control of the chemical reaction of ring opening and of a subsequent electrochemical step involving the uptake of the first transferring electron, with no protonation step in between.