Properties of New Asymmetrically Quaternized Dicationic Ammonium Based Room-Temperature Ionic Liquids with Ether Functionality

Eleven asymmetrically quaternized dicationic ammonium-based room-temperature ionic liquids (DRTILs) with bis­(trifluoromethanesulfonyl)­imide (TFSI) were synthesized and characterized, along with 11 analogous dibromide precursors. Two-step synthesis was used to diquaternize tetramethyl-1,3-propanediamine and 2-(dimethylamino)-ethyl ether amines with a variety of alkyl and ether functionalized side chain groups (R₁ ≠ R₂). Each salt contain 1 to 3 ether groups located either in a linkage or in a side chain moieties. Structural and thermoanalytical properties, water content, and viscosity have been characterized using, for example, NMR, mass spectrometry (MS), X-ray diffraction, and thermal analysis (TG/DTA, DSC). DRTILs have extensive fluid ranges [(∼330 to 370) °C], which are the consequence of low glass transition [(−60 to −40) °C] and high thermal degradation temperatures of the salts [(279 to 325) °C; heating rate 1.25 °C·min^–1]. Thermal stabilities of DRTILs were examined as a function of a heating rate [(1.25, 2.5, 5, 10, and 20) °C·min^–1], and degradation onset temperature overshoots of about (45 to 55) °C were observed between the slowest and the fastest heating rates. Thereby it is suggested that ILs should preferably be analyzed by TG using heating rates of ≤ 5 °C·min^–1 in order to reduce the possibility of an erroneous interpretation of the thermal stability. The ether group count and its location affected the viscosities significantly, which varied between (1150 and 6670) mPa·s at RT and lowered significantly when heated at 60 °C, being typically ≤ 200 mPa·s. The ether-functionalized DILs are potentially applicable in various IL applications, such as lubricants, heat transfer fluids, high temperature synthesis solvents, or as stationary phase in applications such as gas chromatography, MS, and capillary electrophoresis.