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Mechanism and Control of Cleavage of the beta-O-4 Bonds in Lignin

木质素中β-O-4键断裂的机理和控制

基本信息

批准号：
63560172
负责人：
SAKAI Kokki
金额：
$ 1.41万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

项目摘要

The beta -omicron-4 bonds in lignin and its model compounds were reductively cleaved to give eugenol and/or isoeugenol during the alcohol-bisulfite pulping at 160 ﾟC . The mechanism and the control method of this reductive cleavage has been studied using some dimeric compounds.1. Mechanism. (1) This cleavage seems to proceed via a quinone method intermediate because non-phenolic, alpha -carbonyl and alpha -methylene models did not produce high yield of isoeugenol. Sulfonation or alkylation at alpha position of the side chain of the quinone method more or less retarded the cleavage reaction under alcohol bisulfite pulping conditions. (2) Cleavage of the beta -syringyl ether was much faster than that of the guaiacyl ether. This strongly suggests that the quinone method formation is not the rate determining step of the cleavage reaction. (3) A reaction mechanism involving single electron transfer from bisulfite anion or from bisulfite radical to the quinone method seems to explain this cleavage reaction well. The possibility of homolytic cleavage is also discussed.2. Control. (1) The cleavage was extensive in aqueous solutions of some primary and secondary alcohols and in aqueous dimethylformamide but much less extensive in many other solvents including aqueous ethers, tertiary alcohols, ketones, carboxylic acids, amines, a phenol, and a sulfoxide. (2) Concerning solvent concentration, the cleavage proceeded most rapidly in 50 % ethanol. Thus, the cleavage can be controlled to some extents by changing solvents and their concentration. However it is necessary to inhibit sulfonation which is competitive with the cleavage. We should study to solve this problem in the future.

在160℃的醇-亚硫酸氢盐制浆过程中，木质素及其模型化合物中的β-omicron-4键被还原断裂，生成丁香酚和/或异丁香酚。利用一些二聚体化合物研究了这种还原裂解的机理和控制方法。 1．机制。 (1) 这种裂解似乎是通过醌法中间体进行的，因为非酚、α-羰基和α-亚甲基模型不能产生高产率的异丁香酚。醌法侧链α位的磺化或烷基化或多或少地延迟了醇亚硫酸氢盐制浆条件下的裂解反应。 (2) β-紫丁香基醚的裂解比愈创木基醚的裂解快得多。这强烈表明醌法形成不是裂解反应的速率决定步骤。 (3)涉及从亚硫酸氢盐阴离子或从亚硫酸氢盐自由基到醌方法的单电子转移的反应机制似乎很好地解释了这种裂解反应。还讨论了均裂的可能性。 2．控制。 (1) 在某些伯醇和仲醇的水溶液以及二甲基甲酰胺水溶液中，裂解很广泛，但在许多其他溶剂中，包括醚、叔醇、酮、羧酸、胺、苯酚和亚砜的水溶液，裂解程度要小得多。 (2) 关于溶剂浓度，在 50% 乙醇中裂解进行得最快。因此，可以通过改变溶剂及其浓度在一定程度上控制裂解。然而，有必要抑制与裂解竞争的磺化作用。今后我们应该研究解决这个问题。