The Interplay between Oxygen-Derived Radical Species in the Delignification during Oxygen and Hydrogen Peroxide Bleaching

Superoxide and hydroxyl radicals are important intermediates in oxygen and hydrogen peroxide bleaching. They play essential roles in the degradation of wood constituents during these processes both by reacting directly with the substrate and by participating in the generation of each other. Thus, superoxide adds to substrate radicals, bringing about cleavage of carbon-carbon bonds (fragmentation), and dismutates, affording hydrogen peroxide and subsequently - by reductive cleavage of the latter - hydroxyl radicals. Hydroxyl radicals, on the other hand, attack substrate molecules which results not only in direct degradation, but also in generation of substrate radicals, required for the formation and the reactions of superoxide.