ON THE ACID-CATALYZED ALKYLATION OF LIGNINS

Acid-catalysed alkylation (temperature, 20-35-degrees-C; catalyst, p-toluenesulfonic acid) of spruce lignin and model compounds has been studied. Alkylation of veratrylglycerol-beta-guaiacyl ether in a mixture of equimolar amounts of metanol, ethanol and 2,2,2-trifluoroethanol resulted in a preferential formation of methyl benzyl ether; the yield of ethyl ether was slightly lower while only trace amounts of the trifluoroethyl ether was formed. When 2,2,2-trifluoroethanol was used as reaction medium, condensation reactions occured. Methylation of spruce lignin resulted in a liberation of ca. 0.05 phenolic groups/phenylpropane unit. Methylation experiments with spruce lignin and a model compound provided evidence for the occurrence of glyceraldehyde-2-aryl ethers in the lignin. The possibility that such structures are liberated during the acid treatment is discussed.