The role of oxygen in the photodegradation of lignin in solution

The role of oxygen in the photo-oxidation of lignin was ascertained by identification of the different steps in which it participates. From studies using flash photolysis and continuous illumination techniques with the addition of various quenchers, filters and quinones it was found that oxygen does not participate in the initial processes. No evidence was found to indicate that singlet oxygen is generated in these stages via carbonyl triplets. However, reactions of singlet oxygen are involved in the chain propagation steps, and are sensitized by excited quinonoid species. Ground state triplet oxygen participates in dark reactions of formation of intermediate hydroperoxides. A scheme for the photo-oxidation of lignin in solution is presented.