Change in the concentration of free radicals on the photolysis of lignin

Abstract

It has been shown that under the action of UV light on solid preparations of lignin the generation of electron paramagnetic centers (EPCs) takes place, their concentration rising with a fall in the wavelength of the exciting light. In a dark stage there is a slow “death” of EPCs with time. The reactivities of individual model compounds of lignin in radical reactions in solutions were followed with the aid of a stable nitrogen radical used as a spin label. The results show that the efficiency of quenching differs considerably for individual chromophores and decreases in the sequence benzoquinone, vanillin, quinone methide, Bjorkman lignin, and soda lignin. The change in the concentration of EPCs of the stable radical with time is described by a first-order equation.