Studies On The Solution Structure And Properties Of The Anionic PH-responsive Ionic Liquids

In recent years, ionic liquids (ILs) have been the subject of intense studies in academic and industry.Owing to their low vapor pressure, negligible volatility and high thermal stability, ionic liquids have beenused as environmentally benign solvents to replace the conventional organic solvents, and found wideapplications in chemical synthesis, extraction and separation science, catalysis and material preparation. Asa part of the project supported by the National Natural Science Foundation of China (No.20873036), themain content of the present work is as follows:1. The effect of the solution pH on the physicochemical properties and microstructures of the systemsconsisted of anionic pH-response additive, ionic liquid and water has been studied by dynamic lightscattering, Uv-vis, viscosity, transmission electron microscopy and1HNMR at298K. It is shown that theviscosity, Uv-vis absorbance of aqueous ILs solution in the presence of the anionic pH-response additivesand the size of the ILs aggregates are also obviously affected by the solution pH. The results are ascribedthat the interactions between anion of the additive and cation of the ILs are changed by solution pH,therefore resulting in the change of the microstructure of ILs aggregates.2. A series of anionic pH-responsive ionic liquids composed with the [Cnmim]+(n=2,4,6,8,10,12,14) cation and anions including [C6H4COOKCOO]-,[C6H3OHCOOSO3Na]-,[C-6H4COOSO3Na],[C6H4OHCOO]-and [CH3C6H3OHCOO]-were synthesized through two-step method. It was found that themethod was simple. The purity of the as-prepared ILs can satisfy the need of the thermodynamic andspectrum investigation about the ILs. The most of ILs have low melting point. The effect of the length ofcation and structure of the anion on the melting point of the ILs is very important.3. The effect of the solution pH on the physicochemical properties and microstructures of aqueous anionic pH-responsive ionic liquids solution were investigated by dynamic light scattering, Uv-vis andviscosity methods at298.15k. The results show that compared with alkylimidazolium bromide ionicliquids, the critical aggregation concentration of the anionic pH-responsive ionic liquids in water is lessthan an order of magnitude. The viscosity, Uv-vis absorbance of aqueous ILs solution and the size of theILs aggregates are also obviously affected by the solution pH. The reason is that the interactions betweenanion and cation of the ILs are changed by solution pH, therefore resulting in the change of themicrostructure of ILs aggregates.