KINETIC ANALYSIS OF THE 0-O-4 BOND CLEAVAGE OF LIGNIN DURING ALKALINE COOKING PROCESS

摘要

The reactivity of lignin during alkaline delignification was quantitatively investigated focusing on the effect of the structural difference between syringyl and guaiacyl aromatic nuclei and between erythro and threo isomers in the side chain of p-O-Atype lignin substructure on the /3-0-4 bond cleavage rate. The presence of a syringyl nucleus strongly influenced the reaction rate. The effect of syringyl nucleus on the enhancement of the reaction rate appeared to be greater when the syringyl nucleusconsists of the cleaving ether bond than being present as a member of the carbon framework. The effect of the presence of y-hydroxymethyl groups on the rate of the fi-O-4 bond cleavage during this process was also examined by comparing C6-C3 and C6-C2 type model compounds. In most case the disappearance rate of C6-C2 type model compounds was in between those of erythro and threo isomers of the corresponding C6-C3 type model compounds when their aromatic nuclei are the same. This result seems to be reasonably explained when the steric repulsions of the three staggered conformations are taken into consideration.