Reactions of the β-Aryl Ether Lignin Model 1-(4-Hydroxy-3-Methoxyphenyl)-2-(2-Methoxyphenoxy)-1-Propanol on Heating in Aqueous Solution

Abstract

Summary The reactions of the β-aryl ether lignin model 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol on heating in aqueous solution have been studied. Guaiacol, isoeugenol, vanillin, 1-(4-hydroxy-3-methoxyphenyl)-1-ethanol, 1,2-bis(4-hydroxy-3-methoxyphenyl)-1-propanol, 2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-3-methyl-2,3-dihydrobenzo[b]furan, dehydrodiisoeugenol and trans-1,2-dihydrodehydroguaiaretic acid were detected in the reaction mixtures. The formation of the products can be envisioned to proceed via homolysis of an intermediate quinone methide. When 2,6-dimethoxyphenol was present in the reaction mixtures large amounts of 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(4-hydroxy-3-methoxyphenyl)-1-propanol were formed and the yields of guaiacol and isoeugenol were comparatively high. The reaction product pattern can be explained by the occurrence of radical-exchange reactions. The presence of wood meal in the reaction mixtures resulted in an increase in the yield of isoeugenol and a lowering of the yield of dehydrodiisoeugenol. The changes in yields in this case can also be explained by radical-exchange reactions. The significance of homolytic cleavage of β-aryl ether linkages in connection with the technical processing of wood is discussed.