Exploring the Effect of Structural Modification on the Physical Properties of Various Ionic Liquids

A few classes of ionic liquids were synthesized and investigated for their physical properties as a function of structural variation. Bis(oxalato)borate (BOB) and bis(trifluoromethylsulfonyl)imide (NTf2) ionic liquids (ILs) containing pyridinium, 4dimethylaminopyridinium (DMAP) and pyrrolidinium cations bearing alkyl, benzyl, hydroxyalkyl and alkoxy substituents, were prepared from the corresponding halide salts. The physical properties of the DMAP based ionic liquids including viscosity, conductivity and thermal profiles were compared to those of their unsubstituted pyridinium analogues. The properties of the BOB and NTf2 salts bearing similar cations were also compared. It was found that the DMAP salts were easier to synthesize and purify and have higher thermal decomposition points compared to their pyridinium and pyrrolidinium analogues. The BOB salts were found to be higher melting and more viscous than the NTf2 salts. The synthesis and physical properties of the various ILs are discussed.