Studies on quantitative relationships between reactivity and stereo structure of lignin

通过对臭氧化方法的改进，以β-O-4型木质素模型化合物愈创木酰甘油-β-愈创木酰醚为原料，制得糖醛酸（红醛酸和苏醛酸）的收率达到70%。根据两种钛酸的产率计算出的β-O-4红氧/三氧比的测定结果也令人满意。通过这一改进，建立了臭氧化法作为木质素立体结构定量分析的方法。首先，将该方法应用于β-O-4结构的对映体分析。结果证实红细胞型β-O-4结构以外消旋形式存在。对三型的评价有一定的困难，但侧链β碳的总对映体过量如果存在，则小于5%，表明β- o -4型具有旋光性。还研究了脱木质素反应中β-O-4的红/三比与反应活性的关系。随着碱-脱木质素过程的进行，木质素残馀液中糖醛酸的产率和赤素/三氧比均显著降低。电子酸的减少证实了残木质素中的β-O-4结构被碱很好地切割。赤素/三氧比的降低归因于β-O-4的立体优先裂解和木质素的原始结构特征“阻碍”了反应。另一方面，当用亚氯酸钠脱木质素时，脱木质素与残余木质素中β-O-4的红/三氧比无关，也与电子酸的产率无关，说明亚氯酸钠脱木质素不依赖于侧链结构。虽然绿草酸对木质素的氧化不受β-O-4键立体结构的影响，但在高锰酸盐氧化磨木木质素（MWL）过程中发现了红优先降解的发生。综上所述，臭氧化方法有助于分析木质素的立体结构与反应性之间的关系。

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.