KINETICS AND MECHANISM OF THE OXIDATION OF REDUCING SUGARS BY OSMIUM-TETROXIDE IN ALKALINE-MEDIUM

A general mechanism for oxidizing reducing sugars (pentoses, hexoses a nd disaccharides) by OsO4 in alkaline medium is proposed. The reaction s exhibit pseudo-unimolecular kinetics with respect to OsO4, are first order with respect to lower [sugar] and [OH-], but tend towards zerot h order with respect to both higher [sugar] and [OH-]. These results s uggest the formation of an activated complex between the enediol and o smium tetroxide, which slowly disproportionates to give osmium(VI) spe cies and the intermediate products. The reaction products were identif ied. When an aldehydo sugar is treated with alkali, structural changes occur and an equilibrium is set up, mainly involving a keto sugar pro duct and the starting aldehydo sugar consumed. This process is reversi ble. These changes are mainly due to the well-known Lobry-de-Bruyn-Alb erda Van Ekenstein transformations.