STUDIES ON LIGNIN AND RELATED COMPOUNDS: XXI. INSOLUBLE METHANOL LIGNIN

Abstract

When spruce wood meal is extracted with anhydrous methyl alcoholic hydrogen chloride, about 30% of the lignin can be removed in soluble form. The insoluble lignin in the residual wood can be isolated as a fully methylated derivative by a prior complete methylation with dimethyl sulphate followed by hydrolysis with methyl alcoholic hydrogen chloride. The fully methylated insoluble methanol lignin is insoluble in organic solvents.Demethylation experiments followed by subsequent treatment with methylating and acetylating agents, alone or combined, have established a very close relation between the insoluble and the soluble form. The formation of the insoluble form from the native lignin is accompanied by loss of one hydroxyl group as indicated in the two formulas: soluble methanol lignin, C42H32O6(OCH3)6(OH)4, and insoluble methanol lignin (fully methylated), C42H32O6OCH3)9. The new evidence obtained indicates that of the five methoxyl groups present in the original native lignin, at least three are phenolic or enolic in character.