Investigation on the Hydrogen Abstraction from Methyl Glucoside by Active Oxygen Species under Oxygen Delignification Conditions. Part 2: Study on the C-2 Position

Abstract

It was investigated whether active oxygen species (AOS) generated in situ by reacting a phenolic compound, 2,4,6-trimethylphenol, with O₂ abstract the C-2 hydrogen from a carbohydrate model compound, methyl β-d-glucopyranoside (MGPβ), under conditions simulating oxygen delignification (0.5 mol/l NaOH, 0.36 mmol/l FeCl₃, 1.1 MPa O₂, 95°C). MGPβ was degraded less than methyl β-d-mannopyranoside (MMPβ) when they were reacted together with AOS. It was suggested that the configurational difference at their C-2 positions results in their different reactivity toward AOS. When MGPβ and methyl β-d-(2-²H)glucopyranoside (MGPβ-2D) were reacted together with AOS, MGPβ was degraded slightly but more than MGPβ-2D, which clearly indicates that the C-2 hydrogen of MGPβ is abstracted by AOS. MGPβ and MGPβ-2D were also subjected together to alkaline H₂O₂ treatment (0.5 mol/l NaOH, 0.36 mmol/l FeCl₃, 58.8 mmol/l H₂O₂, 95°C) in which oxyl anion radical (O^-•) is likely the only AOS to degrade these compounds. At least some AOS other than O^-• abstract the C-2 hydrogen from MGPβ in the aforementioned oxygen-alkali treatments.

Keywords:

• Active oxygen species
• bleaching
• carbohydrate
• hydrogen peroxide
• hydroxyl radical
• kinetic isotope effect
• lignin

Acknowledgments

The authors gratefully acknowledge financial support from the Japan Society for the Promotion of Science (Grant-in-Aid for Young Scientists (A), No. 20688007).