Dicationic Imizadolium-Based Tetrafluoroborate Ionic Liquids: Synthesis and Hydrothermal Stability Study

Six novel dicationic imizadolium-based tetrafluoroborate ionic liquids were synthesized, with four of which contained hydroxyl groups. Their chemical structures were identified by FTIR and H-1 NMR, and their onset decomposition temperatures (T-onset) were measured by thermogravimetric analysis (TGA). For investigating the hydrothermal stability, all DILs were mixed with water and heated for 1, 5, and 9 hours to 240 degrees C in an airtight kettle.The results show that DILs with hydroxyls have a higher T-onset but they exhibit evident changes in chemical structures after heating with water for 9 hours. The conflicts between T-onset and long-term stability tests is ascribed to the reason that water forms new hydrogen bonds with hydroxyls and therefore weakens the intramolecular interaction between the cation and anion.