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

木质素及其模型化合物中的β - ommicon -4键在160℃下还原裂解得到丁香酚和/或异丁香酚。用一些二聚体化合物研究了这种还原解理的机理和控制方法。机制。(1)这种裂解似乎是通过醌类中间体进行的，因为非酚类、-羰基和-亚甲基模型不能产生高产量的异丁香酚。在亚硫酸醇制浆条件下，醌法侧链α位置的磺化或烷基化或多或少地延缓了裂解反应。(2) -丁香基醚的裂解速度比愈创酰基醚快得多。这有力地表明醌方法的形成并不是裂解反应速率的决定步骤。(3)单电子从亚硫酸根阴离子或亚硫酸根向醌转移的反应机制似乎可以很好地解释这一裂解反应。讨论了均溶解理的可能性。控制。(1)在一些伯醇和仲醇和二甲基甲酰胺的水溶液中，解理作用广泛，但在许多其他溶剂中，包括水醚、叔醇、酮、羧酸、胺、苯酚和亚砜，解理作用要小得多。(2)就溶剂浓度而言，50%乙醇的解理速度最快。因此，可以通过改变溶剂及其浓度在一定程度上控制解理。但有必要抑制与解理相竞争的磺化反应。我们将来应该研究解决这个问题。

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.