Studies on quantitative relationships between reactivity and stereo structure of lignin

通过对臭氧氧化法的改进，以β-O-4型木质素模型化合物愈创木基甘油-β-愈创木基醚为原料，合成季酮酸（丙酸和苏糖酸）的产率达到70%。根据两种特窗酸的产率计算出的β-O-4红/苏比值的测定也令人满意。通过对臭氧化法的改进，建立了木质素立体结构的定量方法。首先，将臭氧化法应用于β-O-4结构的对映体分析。结果表明，β-O-4结构以外消旋形式存在。苏型β-O-4的总对映体过量小于5%，表明β-O-4是光学不活泼的。本文还研究了β-O-4的苏/苏比与脱木素反应活性的关系。随着碱脱木素的进行，木素中特窗酸的产率和反苏比均显著降低。季酮酸的减少证实了碱对残余木质素中β-O-4结构的裂解作用。β-O-4的立体优先断裂和木质素原有结构特征对反应的“阻碍”是导致β-O-4立体优先断裂的主要原因。另一方面，当用Na 2SO 4脱木素时，脱木素与残余木素中β-O-4的顺式/苏式比例以及季酮酸的产率无关，表明Na 2SO 4脱木素不依赖于侧链结构。木质素在高锰酸盐氧化过程中，虽然β-O-4键的立体结构不影响木质素的氧化反应，但木质素在高锰酸盐氧化过程中出现了赤霉素优先降解现象，说明臭氧氧化法有助于分析木质素的立体结构与反应活性之间的关系。

By the improvement of ozonation method, the yield of tetronic acids (erythronic and threonic acids) from β-O-4 type lignin model compond, guaiacylglycerol-β-guaiacyl ether, reached 70 %. Determination of β-O-4 rythro/threo ratio calculated based on the yields of two tetronic acids was also quite satisfactory. By this improvement, ozonation method was established as a quantitative method for the stereo structure of lignin.First, this method was applied to the enantiomer analysis of β-O-4 structure. The results confirmed that erythro type of β-O-4 structure is present as racemic forms. There was some difficulty to evaluate the threo type but the total enantiomer excess of side-chain β carbon is, if present, less than 5 %, indicating that β-O-4 type is optically inactive.Relationships between the erythro/threo ratio of β-O-4 and reactivity during delignification reactions was also investigated. With the progress of alkali-delignification, both the yield of tetronic acids and erythro/threo ratio in the residual lignin decreased significantly. The decrease in tetronic acids confirmed that β-O-4 structure in the residual lignin is well cleaved by alkali. The decrease in erythro/threo ratio was attributed to stereo preferential β-O-4 cleavage and to the original structural feature of lignin "hindered" from the reaction. On the other hand, when delignified by sodium chlorite, delignification was not related to the erythro/threo ratio of β-O-4 in residual lignin nor to the yield of tetronic acids, indicating that chlorite delignification is not dependent on the side-chain structure. Although the oxidation of lignin by chlorite was not affected by the stereo structure of β-O-4 linkage, the occurrence of erythro-preferential degradation was found during the permanganate oxidation of milled wood lignin (MWL).As summarized above, the ozonation method contributed to the analysis of relationships between stereo structure and reactivity of lignin.