FREE-RADICALS PRODUCED BY THE OXIDATION OF DIOXANE LIGNINS

Dioxane lignins were isolated from four species of woody and eleven sp ecies of herbaceous plants, and spin concentrations of radicals produc ed by the oxidation of each lignin were determined using electron spin resonance (ESR) spectroscopy. Hardwood lignin and lignins from herbac eous plants showed ESR signals due to 2,6-dimethoxy-p-benzosemiquinone radical anions and 5-hydroxy-2-methoxy-p-benzosemiquinone radical ani ons by their oxidation, and softwood lignins showed quite weak signals of only 5-hydroxy-2-methoxy-p-benzosemiquinone radicals. The differen ces in the spin concentrations of these radicals between softwood and hardwood lignins are explained as being due to the differences in inte rmonomeric linkages between syringyl and guaiacyl units.