Temperature-Driven Mixing-Demixing Behavior of Binary Mixtures of the Ionic Liquid Choline Bis(trifluoromethylsulfonyl)imide and Water

Abstract

The ionic liquid (2-hydroxyethylammonium)trimethylammonium) bis(trifluoromethylsulfonyl)imide (choline bistriflimide) was obtained as a supercooled liquid at room temperature (melting point=30 degrees C). Crystals of choline bistriflimide suitable for structure determination were grown from the melt in situ on the X-ray diffractometer. The choline cation adopts a folded conformation, whereas the bistriflimide anion exhibits a transoid conformation. The choline cation and the bistriflimide anion are held together by hydrogen bonds between the hydroxyl proton and a sulfonyl oxygen atom. This hydrogen bonding is of importance for the temperature-dependent solubility properties of the ionic liquid. Choline bistriflimide is not miscible with water at room temperature, but forms one phase with water at temperatures above 72 degrees C (equals upper critical solution temperature). 1H NMR studies show that the hydrogen bonds between the choline cation and the bistriflimide anion are substantially weakened above this temperature. The thermophysical properties of water-choline bistriflimide binary mixtures were furthermore studied by a photopyroelectric technique and by adiabatic scanning calorimetry (ASC). By photothermal analysis, besides highly accurate values for the thermal conductivity and effusivity of choline bistriflimide at 30 degrees C, the detailed temperature dependence of both the thermal conductivity and effusivity of the upper and lower part of a critical water-choline bistriflimide mixture in the neighborhood of the mixing-demixing phase transition could be determined with high resolution and accuracy. Together with high resolution ASC data for the heat capacity, experimental values were obtained for the critical exponents alpha and beta, and for the critical amplitude ratio G+/G-. These three values were found to be consistent with theoretical expectations for a three dimensional Ising-type of critical behavior of binary liquid mixtures.

Mutual solubilities between water and non-aromatic sulfonium-, ammonium- and phosphonium-hydrophobic ionic liquids

“…28 The V m of each IL at 298.15 K was determined based on the experimental density data taken from the literature. [37][38][39] As shown in Fig. 4, the sulfonium-based ILs fall close to the correlation previously presented for a wide range of [NTf 2 ]-based ILs.…”

Large Stokes Shift Ionic‐Liquid Dye

“…Although significant "hydrophobic" F···F interaction ("fluorine segregation") is commonly encountered for bis(trifluoromethylsulfonyl) imide structures,s uch short distances have not been observed so far. [27] They are supported by the layered structure (see Figure 2) and the stacking clearly compensates for the anionic repulsive forces.T he situation is similar to that in ILs in which H-bonds can overcome the repulsion between like-charged ions. [28][29][30][31][32][33] TheX -ray structural features are strongly supported by B3LYP/6-311G** and B3LYP-D3/6-311G** calculations on dimers and tetramers of ion-pairs.…”

“…Thed istances between the hydroxy oxygen and the sulfonyl oxygen are d(O2···O8) = 2.80 and d(O5···O1) = 2.743 .B oth values lie in the expected range for these kinds of hydrogen bonds. [27] That the H-bond distances slightly vary is caused by the stacking of the Nmethyl-6-hydoxyquinolinium cations with as mall twist by 5.648 8 towards each other.T he vertical distance between the cations is 7 .T he bis(trifluoromethylsulfonyl) imide anions form ag roove-like cavity,w herein the fluorine atoms are in close proximity with am inimum distance of about 2.843 . Although significant "hydrophobic" F···F interaction ("fluorine segregation") is commonly encountered for bis(trifluoromethylsulfonyl) imide structures,s uch short distances have not been observed so far.…”

Thermomorphic Behavior of the Ionic Liquids [C4mim][FeCl4] and [C12mim][FeCl4]

“…This is striking, as most previous examples show a two-phase region at intermediate IL contents and a one-phase region at both ends of the composition diagram. [11,15,16] In contrast, the current system only shows one phase at low IL weight fractions and two phases at high IL weight fractions, Figure 3 ]. This is further confirmed by elemental analysis, which matches with the original IL.…”

“…ILs include commercially available compounds such as [C 4 4 ] and [C 4 mim][NTf 2 ] (C 4 mim = 1-butyl-3-methylimidazolium), [10,13,14] ILs carrying additional functionalities such as the IL betaine bis(trifluoromethylsulfonylsulfonyl)imide [Hbet]-[Tf 2 N], [15,16] and a few others. [17][18][19][20] Conversely, so far, only a few ILs show a lower critical solution temperature (LCST).…”