Flash photolysis of lignin: Part 1. Deaerated solutions of dioxane-lignin

Abstract

Low molecular weight dioxane-lignin has been submitted to flash photolysis in deaerated solutions. The transient spectra show absorption maxima that can be identified with ketyl and phenoxy radicals, confirming that the initial mechanism is the abstraction of a phenolic hydrogen by a triplet excited carbonyl. The second-order decay rates, ca $\text{10}{}^9\text{M}{}^{\mathrm{-1}}\text{s}{}^{\mathrm{-1}}$, are also consistent with the nature of those radicals. Flash photolysis of model compounds vanillin and p-hydroxybenzaldehyde showed similar behaviour. The photolysis of a model compound (Ether I) with no carbonyl or phenol groups confirmed the occurrence of β-scission as the photolytic pathway.