Non-Chlorine Bleaching of Kraft Pulp. V. Participation of Radical Species in Ozonation of Methyl 4-O-Ethyl-β-D-Glucopyranoside

Abstract

Methyl 4-O-ethyl-β-D-glucopyranoside was treated with ozone both in anhydrous CH 2 Cl 2 and in aqueous solutions, to investigate the participation of radical species in the degradation of the polysaccharide during ozone bleaching. The reactivity of C in the model compound during ozonation was compared with that during oxidation with Fenton's reagent. It was found that ozone itself brings about glycosidic bond cleavage with a high degree of selectivity. The degradation of the model compound during ozonation in distilled water is due in part to radical species, and in part to ozone itself. The contribution of radical species to the degradation in distilled water is estimated to be about 40-70 %. Initial high pH and Fe 2+ ions enhanced the degradation of the model compound, and the contribution of radical species increased. However, the degradation of the model compound with radical species generated by Fe 2+ ions can be inhibited by adjusting to pH 2 without the removal of Fe 2+ ions. Vanillyl alcohol also enhanced the degradation of the model compound during ozonation. Radical reactions initiated by vanillyl alcohol participate in the degradation of the model compound even at pH 2. although the additional degradation of the model compound was inhibited by the low pH. Inhibition of the degradation of carbohydrates by radical species is one of the keys to prevent the viscosity drop in ozone bleaching of pulp.