Reaction Selectivity of Active Oxygen Species in Oxygen-Alkali Bleaching

Abstract

A non-phenolic lignin model compound, 3, 4-dimethoxybenzyl alcohol (veratryl alcohol, VA), and a carbohydrate model compound, methyl β-D-glucopyranoside (MGP), were subjected together to the reaction with active oxygen species which were generated by an oxygen-alkali oxidation of a phenolic compound, 2, 4, 6-trimethylphenol (TMPh), at different temperature or different pH. The reaction selectivity of active oxygen species between VA and MGP (ΔA/ΔMGP) under these conditions were examined. The rates of VA and MGP degradation were similar at 70 °C while the degradation of MGP was much faster than that of VA at 95 °C. This result indicates that active oxygen species produced at 70°C and at 95 °C are different. The degradation of MGP was greater and the reaction selectivity between VA and MGP was lower (undesirable for the carbohydrate protection) when the initial reaction pH was increased. These results clearly demonstrate that the reactivity of active oxygen species produced during oxygen bleaching is significantly dependent on reaction conditions, the reaction temperature and the pH of the solution.