1-丁基-3-甲基咪唑甲基磺酸盐水溶液中酚型木质素单体溶解的二维相关红外光谱分析

Insights into the Dissolution of Lignin Model Phenolic Monomer in 1‑Butyl‑3‑methylimidazolium Methanesulfonate Aqueous Solutions Using Two‑Dimensional Correlation Infrared Spectroscopy

当离子液体(IL)水溶液—1-丁基-3-甲基咪唑甲基磺酸盐([C_(4)C_(1)im]CH_(3)SO_(3))的摩尔分数x_(IL)=0.20时,酚型木质素单体模型化合物2,6-二甲氧基苯酚(2,6-DMP)的溶解度最高。这一现象与木质素溶解规律相似。利用二维相关红外光谱(2D-IR)研究2,6-DMP在[C_(4)C_(1)im]CH_(3)SO_(3)水溶液中溶解过程,以帮助深入理解木质素在IL水溶液中溶解机制。以x_(IL)变量的2D-IR分析结果表明,x_(IL)=0.02~0.20条件下IL加入破坏水的弱氢键结构,IL阴阳离子以水合离子对形式存在,疏水性2,6-DMP与[C_(4)C_(1)im]+和CH_(3)SO_(3)−同时发生相互作用,促进2,6-DMP溶解;x_(IL)=0.20~1.0条件下,IL形成致密离子簇结构,不利于2,6-DMP与IL阴阳离子相互作用。以2,6-DMP摩尔分数(x_(DMP))为变量的分析结果表明,加入2,6-DMP对IL结构影响小,而对水的微观结构影响大。对于具有离子对结构的IL水溶液(x_(IL)=0.10),水优先与CH_(3)SO_(3)−作用;对于具有离子簇结构的IL水溶液(x_(IL)=0.60),水优先形成自缔合小水簇结构。IL水溶液微观结构影响IL-水与2,6-DMP之间相互作用和2,6-DMP溶解特性,同时2,6-DMP溶解也导致IL水溶液的微观结构变化。

In the ionic liquid(IL)-1-butyl-3-methimidazole methylsulfonate([C_(4)C_(1)im]CH_(3)SO_(3))aqueous solutions,the solubility of the model lignin phenolic monomer 2,6-dimethoxyphenol(2,6-DMP)is the highest at IL molar fraction(x_(IL))of 0.2.This phenomenon is similar to dissolution of lignin.Thus,dissolution of 2,6-DMP in[C_(4)C_(1)im]CH_(3)SO_(3) aqueous solution is studied using two-dimensional correlated infrared spectroscopy(2D-IR)in order to help us deeply understand the dissolution mechanisms of lignin in IL aqueous solutions.In the case of x_(IL)=0.02~0.2,adding ILs could destroy the weak hydrogen bonding structure of water,and the anion and cation ions of ILs are in the form of hydrated ionic pairs;relative hydrophobic 2,6-DMP dissolution is greatly enhanced by the interactions between 2,6-DMP and[C_(4)C_(1)im]+,CH_(3)SO_(3)−.In the case of x_(IL)=0.2~1.0,ILs form dense ionic clusters structure which is unfavourable for the interactions between 2,6-DMP and the anion,cation ions of ILs.The 2D-IR analyses with 2,6-DMP molar fraction(x_(DMP))as disturbance show that adding 2,6-DMP slightly influences the ILs structure,but greatly affects the microstructure of water.For the IL aqueous solutions with ionic pairs structure(x_(IL)=0.1),water molecules preferentially interactes with CH_(3)SO_(3)−;for the IL solutions with ionic clusters(x_(IL)=0.6),water forms the self-associated small clusters.The microstructure of IL aqueous solutions affects the interactions of IL-water-2,6-DMP and solubility,and at the same time 2,6-DMP dissolution influences the variation tendency of the solution microstructure.