Reaction selectivity of active oxygen species in oxygen-alkali bleaching

A non-phenolic lignin model compound, 3,4-dimethoxybenzyl alcohol (veratryl alcohol, VA), and a carbohydrate model compound, methyl beta-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 (Delta VA/Delta MGP) under these conditions were examined. The rates of VA and MGP degradation were similar at 70 degrees C while the degradation of MGP was much faster than that of VA at 95 degrees C. This result indicates that active oxygen species produced at 70 degrees C and at 95 degrees 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.