Synthesis and properties of room-temperature choline carboxylate zwitterionic ionic liquids as potential electrolytes
Choline carboxylate zwitterions were prepared by two different synthetic routes through esterification of choline salts with a range of anhydrides. Their conjugation with lithium bis(trifluoromethylsulfonyl) imide resulted in the formation of stable room-temperature ionic liquids. In view of their use as potential electrolytes the physicochemical characterization of these attractive ionic liquids was performed. These compounds presented a glass transition temperature between -43 and -34 °C, good thermal stability up to 2248C, densities above 1.44 gcm-3 at 25°C, and viscosities between 3.56 and 12.27 Pa s at 258C. In terms of conductivity the most promising ionic liquid showed an excellent conductivity between 8.66 105 Scm-1 at 258C and 1.8010-3 Scm-1 at 908C. These zwitterionic ionic liquids maintained a liquid state, and no dissociation was observed even after six months of storage at room temperature.