Switchable Ionic liquids (SILs) based on glycerol and acid gases

Abstract

New types of switchable ionic liquids (SILs), containing 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), glycerol and an acid gas (CO₂, SO₂), were synthesized and characterized in this study. [DBU][Carbonate] or [sulfonate] were easily synthesized from a non-ionic mixture of molecular organic polyol and amidine base upon bubbling of an acid gas (CO₂, SO₂). Moreover, they were switched back to the original molecular solvents by flushing out the acid gas (CO₂, SO₂) by heating and/or bubbling an inert gas such as N₂ through it. The structures of the SILs were confirmed by NMR and FTIR. The change from low polarity (molecular solvent) to high polarity (Switchable Ionic Liquid, SIL) was also indicated by the changes in properties, such as viscosity and miscibility with different organic solvents. The decomposition temperatures of the SILs were determined by means of Thermo Gravimetric Analysis (TGA) and gave values in the range of 50 °C and 120 °C for DBU-glycerol-CO₂ (SIL1) and DBU-glycerol-SO₂ (SIL2), respectively. Due to the reasonable decomposition temperatures, these novel SILs can be employed in multiple applications.