Synthesis and investigation of physicochemical properties of dicationic ionic liquids

A series of dicationic ionic liquids (ILs) including [C4(MIM)2] [PF6] 2, [C5(MIM)2] [PF6] 2, [C6(MIM)2] [PF6] 2and [C4(PYR)][PF6]2 were synthesized. Their thermal stability and melting points were analyzed. It was found that dicationic ILs presented important implications in the design of homogeneous and heterogeneous system with water. A homogeneous system of dicationic ILs with water could be formed at a relatively high temperature and then a heterogeneous system was formed when the solution was cooled to a low temperature. The recovered ILs by altering the temperature were obtained in high yields of [C46]2(0.98 g), [C5(MIM)2][PF6]2 (0.97 g), [C6(MIM)2][PF6]2 (0.98 g) and [C4(PYR)2][PF6]2 (0.94 g). In the other hand, [C4(MIM)2][PF6]2 and [C5(MIM)2][PF6]2 exhibited good solubility in acetonitrile and acetone. A homogeneous system could be achieved with imidazolium-based ILs with a relatively low amount of water and acetonitrile at room temperature. All of the properties of dicationic ILs have a strong correlation with the nature of dications, the linkage chain and the symmetry of dications. Dicationic ILs may provide new opportunity for some specific applications in order to enable the effective separation and isolation of products.