EFFECT OF SOLVENT ON THE BETA-O-4 BOND CLEAVAGE OF A LIGNIN MODEL COMPOUND BY TERT-BUTOXIDE UNDER MILD CONDITIONS

The beta-O-4 bond cleavage of a non-phenolic β-O-4 type dimeric lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)-ethanol (III), was examined in systems using potassium tert-butoxide as a base (0.5 mol/l) and tert-butanol (tBuOH), dimethylsulfoxide, 1,4-dioxane, or tetrahydrofuran as a solvent. The β-O-4 bond of compound III was cleaved in any system at 30°C, and 2-methoxyphenol (II) was liberated. The amount of compound II liberated was close to the quantitative yield on the basis of the amount of compound III that disappeared, except for the treatment in the t-BuOH system. The reaction rate was dependent on what solvent was used. Half-life periods for these systems were roughly about 6.0, 3.0, 0.7, and 0.2h, respectively. It seemed that the rates were very high when the polarity of the solvents was low. Two reaction products generated from the aromatic ring with two methoxyl groups of compound III, 4-acetyl-1,2-dimethoxybenzene and 3,4-dimethoxybenzoic acid, were detected in all the systems. A peculiar reaction product, 1,2-dimethoxybenzene, was detected in a fairly large quantity, only when the latter two solvents with low polarities were applied.