Physicochemical Characterization of Sulfonate-Based Phosphonium Ionic Liquids

A new series of phosphonium-based room-temperature ionic liquids containing various sulfonate-based anions was prepared and physicochemically characterized. Although the tetra- n -butylphosphonium salts having alkanesulfonate anions showed relatively high melting points forming the crystalline solids, the phosphonium salts together with amino- and hydroxy-substituted alkanesulfonate anions were viscous liquids at room temperature. Such phosphonium ionic liquids exhibited the relatively high density, the high viscosity and the low conductivity when compared to the conventional phosphonium-based ionic liquids. The phosphonium salts showed higher thermal stability than the corresponding ammonium salts.