Photochemical studies on a phenolic phenylcoumarone lignin model molecule in relation to the photodegradation of lignocellulosic materials. Part 1. Structure of the photoproducts

The contribution of phenols, absorbing above 300 nm, to the photodegradation of lignin was approached by studying a phenolic phenylcoumarone lignin model molecule PCO. The compound was irradiated in solution and adsorbed on filter paper. The isolation and analysis of the photoproducts formed during the irradiation indicate the presence of a catechol structure (involving demethylation of the starting material) and two dimeric stilbene compounds: a ketone and a conjugated quinone methide giving high colouration to the irradiated solution. Those compounds have been detected as well in the solid state. The structure elucidation of the photoproducts was mainly based on mass spectrometry and 2D NMR experiments at 500 MHz. The major role played by the phenol group was supported by studying the O-methylated analogue PCOMe.