INVESTIGATION ON THE HYDROGEN ABSTRACTION FROM METHYL GLUCOSIDE BY ACTIVE OXYGEN SPECIES UNDER OXYGEN DELIGNIFICATION CONDITIONS. PART 5: COMPREHENSIVE RESULTS ON EXPERIMENTS USING DEUTERIUM-LABELED METHYL GLUCOSIDES

摘要

A pair of carbohydrate model compounds, methyl beta-D-glucopyranoside (MGP) and a deuterated MGP labeled at each C-H bond, was reacted with active oxygen species (AOS) generated from reactions between O-2 and a co-existing phenolic compound, 2,4,6-trimethylphenol (TMPh) or 4-hydroxy-3-methoxybenzyl alcohol (vanillyl alcohol, Valc), under O-2 delignification conditions. The pair were also reacted with O radical anion generated in the alkaline H2O2 treatment with the addition of FeCl3. Clear kinetic isotope effects were observed only in the reactions of two pairs using the deuterated MGPs labeled at the anomeric and C-2 positions in this system. These results suggest that at least a specific AOS is generated only in this system and that a major AOS in the O(2)(-)Valc system is highly reactive O radical anion It is also suggested that the AOS specifically generated only in this system is a peroxyl radical derived by the combination reaction between the TMPh phenoxyl radical and O-2.