BEHAVIOR OF LIGNIN DURING ALKALINE SULFITE QUINONE COOKING .3. DELIGNIFICATION MECHANISM-BASED ON BETA-ETHER CLEAVAGE AND SULFONATION OF LIGNIN MODELS

To clarify the role of sulfite on alkaline-quinone pulping, the degree of beta-ether cleavage of free phenolic lignin models by sulfite is c ompared with that by 1,4,4a,9a-tetrahydro-anthraquinone (THAQ) or hydr osulfide, and sulfonation is also discussed. The models were treated i n homogeneous systems at 170-degrees-C with dilute solutions of soda, strongly alkaline sulfite, and kraft pulping liquors. The degree of be ta-ether cleavage by sulfite was smaller than that of THAQ and hydrosu lfide. The compositions of sulfonated products in the presence of THAQ were quite different from those in the absence of THAQ. The main sulf onated product from guaiacylglycerol-beta-guaiacyl ether in the presen ce of THAQ corresponded to the one from coniferyl alcohol. The main ro le of sulfite in delignification during alkaline sulfite-quinone pulpi ng should be to decrease the condensation reactions of lignin by sulfo nation. Sulfite should not play an important role in it in cleaving th e beta-ether bonds of lignin.