Origin of free radicals produced from the syringyl end groups in lignins

Enzyme Lignin was prepared from reed; it was acid-hydrolyzed and reduced wi th NaBH4. Spin concentrations of radicals produced by oxidation of the lign ins with K-3[Fe(CN)(6)] or H2O2 were determined from electron spin resonanc e spectra. The radicals were observed by the oxidation of sinapyl alcohol. It was found that the two radicals observed by the oxidation of dioxane lig nins were deprotonated 2,6-dimethoxy-p-benzosemiquinone and 6-hydroxy-2-met hoxy-p-benzosemiquinone, and that they were produced from syringyl end grou ps. The production rate of radicals from syringyl end groups possessing an alpha-carbonyl group was greater than that possessing an alpha-hydroxyl gro up. It was suggested that stilbene-type syringyl end groups were produced f rom phenylcoumaran moieties in lignins by acidolysis. The radicals produced from guaiacyl end groups were not observed by the oxidation process.