STUDIES ON LIGNIN AND RELATED COMPOUNDS: XXVII. METHYLATION AND STRUCTURE OF METHANOL LIGNIN (SPRUCE)

Abstract

The composition of spruce methanol lignin prepared by the action of anhydrous methanol-hydrogen chloride on spruce meal was found to vary with the temperature and time of extraction. The reaction mixture contains two products, having methoxyl contents of 21.6 and 24%, respectively. Higher temperatures and longer time of heating favor formation of the latter. Long continued extraction of the crude methanol lignin with ether removed the second product (OCH3, 24%). This showed that this was a true "ether-soluble" fraction, but it was not found possible to isolate the pure methanol lignin (OCH3, 21.6%) by this process. The two substances can be separated either by solvent extraction or, as now shown, by use of 8–10% sodium hydroxide. Methylation of methanol lignin with dimethyl sulphate and alkali gives rise to the formation of new hydroxyl groups, the extent of the changes increasing markedly with rise in temperature of methylation and with increase in concentration of alkali used.A methanol lignin (OCH3, 22.3%) on repeated methylation yields a methylated lignin containing 37.2% methoxyl. Degradation during methylation is restricted by the use of acetone as solvent and only a slight excess of alkali (5–10%) at 20 °C. The results indicate the necessity for caution in the interpretation of data based on methylation experiments involving the use of alkali, and point to the presence of heterocyclic oxygen rings, non-furane in type, as part of the lignin structure. When refluxed for 48 hr. with 65 % aqueous methyl alcohol containing 9% sulphuric acid, ether-insoluble methanol lignin (OCH3, 22.3%) yielded a product with methoxyl content 21.3% which decreased to 20.9% when the product was treated for a further 52 hr.