Effect of Water on the Local Structure and Phase Behavior of Imidazolium-Based Protic Ionic Liquids

Abstract

We report on the effect of water on local structure and phase behavior of two protic ionic liquids, C2HImTFSI and C2HImTfO. Raman and infrared spectroscopy are employed to investigate the local coordination state. We find that water interacts weakly with TFSI(-) while more specifically with TfO(-) through the -SO3 group. Additionally, we observe that upon addition of water the -NH stretching frequency does not change in C2HImTFSI, while it red-shifts in C2HImTfO, indicative of different hydrogen bonding configurations. Supported by the appearance of some additional features in the 800-1000 cm(-1) frequency range where ring out-of-plane bending (γ) modes are found, we hypothesize that in C2HImTFSI water interacts only with the cation coordinating to the ring C(2)H and the N(3)H sites, while it interacts with both cation and anion in C2HImTfO forming hydrogen bonds that involve the cationic N-H site as well as the anionic -SO3 group. These different local structures also reflect in the phase behavior investigated by DSC, which reveals a more homogeneous solution when water is added to C2HImTfO, as compared to H2O/C2HImTFSI mixtures. Finally we report that the addition of water also significantly affects both Tm and Tg.

Two‐dimensional Raman spectroscopy study of ionogel phase formation in long‐chain ionic liquid/water systems

“…The wavenumber correlation was found in experimental data where the assignment was made to the vibrational mode νC(2)‐H of the Raman band at around 3080 cm −1 and to the vibrational mode νC(4,5)‐H of the Raman band at around 3150 cm −1 (Table ). LC phase formation and the strength of the cation–anion interaction through hydrogen bonding were investigated monitoring the wavenumber of Raman spectra bands assigned to the [C 10 mim] + cation C–H stretching vibrational modes of imidazolium ring at the carbon positions 2, 4, and 5 . According to the literature, the hydrogen bond involving aromatic C–H on the imidazolium ring classified as red shift H bond .…”

“…LC phase formation and the strength of the cation-anion interaction through hydrogen bonding were investigated monitoring the wavenumber of Raman spectra bands assigned to the [C 10 mim] + cation C-H stretching vibrational modes of imidazolium ring at the carbon positions 2, 4, and 5. [29] According to the literature, the hydrogen bond involving aromatic C-H on the imidazolium ring classified as red shift H bond. [30,31] In Fig.…”

A Raman spectroscopic approach to investigate the production of biodiesel from soybean oil using 1-alkyl-3-methylimidazolium ionic liquids with intermediate chain length

“…SI-4. A blue-shift of these vibrations is typically associated with the anion experiencing a stronger interaction [42], which may a priori be to the cation or the enzyme's surface. In any case, the observed shift is rather small (below 1 cm À1 ) indicating that the change in interaction strength is marginal.…”

“…Thus, our conclusion is that for both C 2 HImTfO and C 10 C 1 ImTFSI the ionic liquid-enzyme interaction is weak and such that the structure of the enzyme is not significantly altered. This is interesting since the protic ionic liquid C 2 HImTfO has a propensity to form hydrogen bonds, for instance with water, through both the cation and the anion [42]. Nonetheless, infrared difference spectra in the range of O-H stretching show that water hydrating the enzyme and water coordinated to C 2 HImTfO maintain their nature even in the C 2 HImTfO-impregnated enzyme.…”

A computational study of ion speciation in mixtures of protic ionic liquids with various molecular solvents: Insight into the solvent polarity and anion basicity

“…Recent studies have shown that the presence of water or other organic solvents in ILs can have great effect on the physical and chemical properties of the ILs, such as viscosity, electrical conductivity, polarity, reactivity, and solvation properties. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Therefore, nowadays, as a simple strategy to expand the applications of those Coulomb fluids, the mixtures of ILs with other solvents have drawn growing attention in many industrial processes, such as synthesis, catalysis, industrial cleaning, solvent extraction, and separation. Then, in these applications, to find the suitable cosolvent partner of ILs, it is crucial to understand not only the properties of pure ILs, but also those of ILs-cosolvent mixtures.…”