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 (Tg) associated with an intense change in molar heat capacity (ΔCpm).