Analysis of a delignification system using tert-butoxide as a base

The β-O-4 bond cleavage of dimeric non-phenolic lignin model compounds, 2-(2-methoxyphenoxy)-1-(3, 4-dimethoxyphenyl) ethanol (3) and 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl) propane-1,3-diol (4), was examined in potassium tert-butoxide/tert-butanol (KO'Bu/'BuOH) and potassium tert-butoxide/dimethyl-sulfoxide (KO'BuDMSO) systems. β-O-4 bonds of (3) and (4) cleaved in both systems under conditions, 0.5 mol/1 KO'Bu at 30 °C, which are much milder than those in general alkaline based pulping processes. The yields of an identified reaction product, 4-acetyl-1, 2-dimethoxybenzene (acetoveratrone, (5) ), in both systems were different from each other. This result suggests that the mechanism of the β-O-4 bond cleavage is dependent on the solvents. The disappearance of (4) was faster than (3), suggesting the participation of the γ -position of (4) in the β-O-4 bond cleavage. The degree of delignification was also examined in these systems using beech wood meal and chip. When the wood meal was applied, delignification was sufficiently attained in the KO'Bu/ DMSO system under conditions, 0.5 mol/1 KO'Bu at 110 °C), while the KO'BU/'BuOH system did not work well. Neither system attained delignification, when the wood chip was cooked. A mild soda cooking as a post-treatment and a soaking in DMSO at room temperature for 2 weeks as a pre-treatment did not improve delignification. These results suggest that the insufficient delignification is probably attributed to the difficulty in the penetration of KO'Bu into the chip.