STUDY OF FREE-RADICAL CENTERS IN LIGNIN W ITH 2-MM BAND ESR SPECTROSCOPY

The nature of paramagnetic centers in pristine lignin and lignin, trea ted with molecular chlorine, aqueous solutions of acids and alkalis, a nd gamma and UV-irradiated, was studied with 2-mm band ESR spectroscop y. Most of the observed singlet ESR lines are accounted for by radical s with conjugated bonds. High reactivity of double bonds of polyconjug ated systems was found in the processes studied. It was shown that alk aline treatment of phenol groups of lignin results in formation of pol ymer o-semiquinone radicals.