Long-term thermal stability of five imidazolium ionic liquids

Thermal stability is an essential property to select the most suitable compounds for applications as high-temperature lubricants, thermal fluids and solvents for high-temperature organic reactions. Thermal stability of five imidazolium ionic liquids (ILs) was determined using a thermogravimetrical analyzer (TG). The ILs were 1-butyl-2,3-dimethylimidazolium tris(pentafluoroethyl) trifluorophosphate, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide, 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium ethylsulfate and 1,3-dimethylimidazolium dimethylphosphate. Onset temperatures were determined from dynamic experiments for the five ILs at scanning rate of 10 degrees C . min(-1) under air atmosphere. Additionally, dynamic scans were carried out with nitrogen gas for two 1-butyl-2,3-dimethylimidazolium ILs, finding that onset temperatures are 14 degrees C higher than those obtained with air gas flow. The three 1-butyl-2,3-dimethylimidazolium ILs present the highest onset temperatures under air atmosphere. For these last ILs, isothermal scans at lower temperatures than the onset temperature, were performed in air gas flow, finding that the most stable is 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate. Finally, for these ILs, lifetimes were also determined for several temperatures. (c) 2013 Elsevier Ltd. All rights reserved.