Dissolution behavior of 2

6-dimethoxyphenol (2

6-DMP) in 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]BF4) aqueous solutions (ionic liquid mole fraction xIL=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 xIL 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 (xIL=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 (xIL=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.