A non-isocyanate approach to preparing carbamate- and thiocarbamate-containing ionic liquids

Abstract

The versatility of 1,1′-carbonyldiimidazole (CDI) as a reagent in a non-isocyanate synthesis of carbamate- and thiocarbamate-containing ionic liquids (ILs) is described herein. Through the initial reaction with various linear alcohols or thiols, followed by addition of 3-aminopropylimidazole, CDI was sequentially transformed into a series of imidazoles bearing a carbamate or thiocarbamate functional group. The imidazoles were further quaternized with various lengths of alkyl groups (C2–C12) and anion exchanges were performed, producing a small library of 20 room-temperature ILs. Fundamental temperature-dependent properties such as density, viscosity, and conductivity were determined for each material. All of the ILs were found to exhibit glass transition temperatures (T_g) below room temperature and conductivities of up to 10⁻³ S cm⁻¹ at 30 °C. Changes in the counteranion ([Br], [OMs], [OTf], [NTf₂], [NFBSI]) produced the greatest breadth of physicochemical properties.