Preparation and characterization of new phosphonyl-substituted imidazolium ionic liquids

A new series of diethoxyphosphinyl-substituted imidazolium 'room-temperature ionic liquids' (RTILs) were synthesized and characterized. The new compounds 1-12 (Table 1) were shown to have similar densities, but higher viscosities, than common ionic liquids. The new materials remain liquid over a broad temperature range, possess extremely low vapor pressures, display relatively high thermal stabilities (up to 325°), and decompose in a two-step process. Analysis of the solid/liquid phase transition showed that all of the new RTILs possess low glass-transition temperatures (T_g) associated with an intense change in molar heat capacity (ΔC _pm).