Kinetics and mechanism of the oxidation of reducing sugars by osmium tetroxide in alkaline medium

A general mechanism for oxidizing reducing sugars (pentoses, hexoses and disaccharides) by OsO₄ in alkaline medium is proposed. The reactions exhibit pseudounimolecular kinetics with respect to OsO₄, are first order with respect to lower sugar] and OH⁻], but tend towards zeroth order with respect to both higher sugar] and OH⁻]. These results suggest the formation of an activated complex between the enediol andd osmium tetroxide, which slowly disproportionates to give osmium(VI) species and the intermediate products. The reaction products were identified. When an aldehydo sugar is treated with alkali, structural changes occur and an equilibrium is set up, mainly involving a keto sugar product and the starting aldehydo sugar consumed. This process is reversible. These changes are mainly due to the well-known Lobry-de-Bruyn-Alberda Van Ekenstein transformations. This revised version was published online in June 2006 with corrections to the Cover Date.