STRUCTURE AND DEPOLYMERIZATION OF ACID-CONDENSED LIGNIN

The condensed structures of sulfuric acid lignin, a typical highly-condcnsed lignin, were analyzed quantitatively. The nucleus exchange technique was used for depolymerizing sulfuric acid lignin. The yield of nucleus exchange products (guaiacol and catechol) was much higher in sulfuric acid lignin than in any other lignin derivatives. The condensation of lignin during sulfuric acid treatment of wood was mainly the diphenylmethane types, and more than 70% of phenyl nuclei in sulfuric acid lignin were associated with diphcnylmcthane type structures. The depolymerization of sulfuric acid lignin by nucleus exchange method proceeded below 100°C and the resulting lignin formed highly phenolic fragments with molecular weight (w) of 500 which were easily dissolved in various solvents. A combination of the condensation and the nucleus exchange was proposed as a new technique for simplifying the lignin molecule. © 1990, Walter de Gruyter. All rights reserved.