Mechanisms of Oxidative Degradation of Carbohydrates During Oxygen Delignktcation. I. Reaction of Methyl β-D-Glucopyranoside with Photochemically Generated Hydroxyl Radicals

Abstract

Hydroxyl radical is considered to be the major species causing degradation of carbohydrates during oxygen delignification. In this study, reactions involving a carbohydrate model compound and either photochemically generated hydroxyl radical or superoxide from potassium superoxide were carried out to investigate the cleavage of glycosidic linkages. Experiments show that hydroxyl radicals are responsible for the degradation of glycosidic linkages in methyl β-D-glucopyranoside by a substitution reaction displacing D-glucose. Once the glycosidic linkage is broken, reducing carbohydrates undergo a series of reactions forming aldonic acids and lower order aldoses. Control experiments established that no reaction occurs in the absence of UV light under otherwise identical conditions.