Bernd Rathke

The general phase behavior of mixtures of 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide ionic liquids with n-alkyl alcohols.

The liquid-liquid equilibrium (LLE) phase behavior of mixtures of 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide (C(2)mimNTf(2)) with the n-alkyl alcohols (C(n)OH; 3≤n≤8) is described. By applying the cloud-point method, the LLEs were determined over a temperature range of 275-423 K at ambient pressure. Partial miscibility with upper critical solution temperatures (UCST) was observed. The UCST increase with increasing chain length of the alcohols. The phase diagrams were analyzed numerically by presuming Ising criticality. Concepts for the description of the asymmetry of the phase diagram by presuming the validity of the rectilinear diameter rule or a nonlinear diameter requested by the theory of complete scaling were applied. The results (UCST, critical composition, width and diameter of the phase diagrams) are compared with similar systems and discussed in terms of the corresponding state behavior; they map on a single curve. From at least 45 individual phase diagrams, general aspects of the behavior of this ionic liquid-alcohol mixture type were extracted. A simple empirical relationship was formulated to allow the description of the UCST with an accuracy of about 10 K when taking the ratio of the molar volumes of the alcohol and the 1-alkyl-3-methylimidazolium cation of the ionic liquid into account.

Molecular Structure and Interactions in the Ionic Liquid 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate

Quantum chemical theory (DFT and MP2) and vibrational spectroscopy (ATR-IR and Raman) were employed to investigate the electronic structure and molecular interactions in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Various possible conformers of a cation-anion pair based on their molecular interactions were simulated in the gas phase. All the different theoretical (MP2, B3LYP, and the dispersion-corrected wB97XD) methods assume the same ion-pair conformation for the lowest energy state. Basis set superimpose error (BSSE) correction was also introduced by using the counterpoise method. Strong C-H···O interactions between the most acidic hydrogen atom of the cation imidazole ring (C2H) and the oxygen atom of the anion were predicted where the anion is located at the top of (C2H). In this case, methyl and alkyl groups also interact with the anion in the form of a C-H···O hydrogen bond. Interestingly, the dispersion-corrected methodology neglects the C4/C5-H···O and C-H···F interaction in the ion-pair calculations. The theoretical results were compared with the experimental observations from Raman scattering and ATR-IR absorption spectroscopy, and the predictions of the molecular interactions in the vibrational spectra were discussed. The wavenumber shifts of the characteristic vibrations relative to the free cation and anion are explained by estimating the geometric parameters as well as the difference in the natural bond orbital (NBO) charge density.

Vapor Liquid Equilibria of Binary Mixtures of 1-Butyl-3-methylimidazolium Triflate (C4mimTfO) and Molecular Solvents: n-Alkyl Alcohols and Water

Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (C4mimTfO) with either water or short chained n-alkyl alcohols (methanol, ethanol, propan-1-ol, and butan-1-ol) are described in this study. Two different microebulliometers and a classical VLE apparatus were compared and the VLEs were determined in the composition range 0.4 ≤ x(solvent) ≤ 1 at three different pressure levels ( p = 500 mbar, 700 mbar, and 1000 mbar). The experimental data were modeled using the soft-SAFT equation of state, which was able to accurately describe the nonideal behavior of these mixtures. The combined experimental-modeling results obtained contribute to establish the structure-property relationship between the C4mimTfO and n-alkyl alcohol molecules and to infer about its influence on the phase behavior of these solvents.