Mechanistic studies of the oxidation of a non‐phenolic lignin model compound by the laccase/1‐hydroxybenzotriazole redox system

The use of a laccase‐mediator system is one of the promising possibilities for an environmentally benign pulp‐bleaching process. Thus a better understanding of the mechanism for the oxidation of lignin by a laccasemediator system would facilitate the commercialization of such a system for pulp bleaching. By using 1‐hydroxybenzotriazole (1‐HBT) as a mediator, it was found to be partly regenerated during the oxidation of a lignin dimer, 1‐(3, 4‐dimethoxyphenyl)‐2‐(2‐methoxyphenoxy)propan‐1, 3‐diol (I). A free radical of 1‐HBT, generated by laccase, was probably responsible for the oxidation of I. The free radical of 1‐HBT was, however, transformed to benzotriazole, which could not mediate the oxidation of I. The hypothesis that 1‐HBT acted as an activator or a co‐substrate for laccase was not confirmed. Active oxygen species such as hydroxyl free radical (HO•) and superoxide (O2•‐) were also found not to be involved in the oxidation of I.