2,6-二甲氧基苯酚在1-丁基-3-甲基咪唑四氟硼酸盐水溶液中溶解行为的红外光谱分析

利用衰减全反射红外光谱(ATR-IR)和二维相关红外技术研究2, 6-二甲氧基苯酚(2, 6-DMP)在1-丁基-3-甲基咪唑四氟硼酸盐(C₄mim]BF₄)水溶液(离子液体摩尔分数x_IL=1.0～0.02)中的溶解行为。随着水量增大, 2, 6-DMP溶解度先增大而后急剧减小, 对应的x_IL阈值为0.1。2, 6-DMP与C₄mim]BF₄之间存在强相互作用, 2, 6-DMP上的甲氧基是重要作用位点之一;当少量的水加入C₄mim]BF₄(x_IL=0.1～1.0), 致密的离子簇结构被解离, 2, 6-DMP容易与C₄mim]BF₄作用, 溶解度增大;随着大量水加入(0.02IL<0.1), 离子簇完全解离为大分子水簇包围的离子对, 憎水的2, 6-DMP与C₄mim]BF₄作用困难, 溶解度减小。这种由于水量改变引起的C₄mim]BF₄水溶液微观结构变化影响2, 6-DMP溶解行为。

Understanding dissolution behavior of 2, 6-dimethoxyphenol in 1-butyl-3-methylimidazolium tetrafluoroborate aqueous solutions by infrared spectroscopy

Dissolution behavior of 2, 6-dimethoxyphenol (2, 6-DMP) in 1-butyl-3-methylimidazolium tetrafluoroborate (C₄mim]BF₄) aqueous solutions (ionic liquid mole fraction x_IL=1.0-0.02) was investigated by attenuated total reflectance infrared (ATR-IR) spectroscopy and two-dimensional correlation IR spectroscopy. The results indicated that 2,6-DMP solubility increases and then dramatically decreases with increasing amount of water added into C₄mim]BF₄. The corresponding threshold of x_IL is 0.1. There is a strong interaction between 2, 6-DMP and C₄mim]BF₄, and the methoxyl group of 2, 6-DMP is one of main active sites. In the case of adding small amount of water into C₄mim]BF₄ (x_IL=0.1-1.0), compact ionic clusters of C₄mim]BF₄ could be dissociated. 2, 6-DMP is easy to interact with C₄mim]BF₄, which results in the increase of its solubility. In the case of adding a large amount of water into C₄mim]BF₄ (x_IL=0.02-0.1), the ionic clusters are completely dissociated into ionic pairs surrounded by large molecular water clusters. The interactions between hydrophobic 2, 6-DMP and C₄mim]BF₄ become difficult, and the 2, 6-DMP solubility decreases. This transformation of microstructure with water addition influences the 2, 6-DMP dissolution.