Probing molecular interactions underlying imidazolium and pyridinium based ionic liquids

Determination of physicochemical properties of ionic liquids by gas chromatography

Over the years room temperature ionic liquids have gained attention as solvents with favorable environmental and technical features. Both chromatographic and conventional methods afford suitable tools for the study of their physicochemical properties. Use of gas chromatography compared to conventional methods for the measurement of physicochemical properties of ionic liquids have several advantages; very low sample concentrations, high accuracy, faster measurements, use of wider temperature range and the possibility to determine physicochemical properties of impure samples. Also, general purpose gas chromatography instruments are widely available in most laboratories thus alleviating the need to purchase more specific instruments for less common physiochemical measurements. Some of the main types of physicochemical properties of ionic liquids accessible using gas chromatography include gas-liquid partition constants, infinite dilution activity coefficients, partial molar quantities, solubility parameters, system constants of the solvation parameter model, thermal stability, transport properties, and catalytic and other surface properties.

Ion Pair Structures and Hydrogen Bonding in RnNH4-n Alkylammonium Ionic Liquids with Hydrogen Sulfate and Mesylate Anions by DFT Computations

Density function theory calculations are employed to study the interaction of amines bearing different numbers of alkyl substituents of different sizes on the nitrogen atom with sulfuric and methanesulfonic acids. The proton affinities of the studied amines are calculated, and it is shown that the higher the value is, the more probable is its protonation. The most stable structures of the ion pairs resulting from the acid-base interaction are obtained and characterized. The geometric parameters of the ion pairs and the characteristics derived from the NBO and QTAIM analysis show that there are hydrogen bonding interactions between the cation and the anion. The hydrogen bonding character of the ion pairs and the strength of the interaction between the ions strongly depend on the nature of the cation itself. The interaction between the ions in the ion pairs weakens with the increase in the cation size. The trend of change in the structural parameters of the H-bonds and energetic characteristics in the cation series for the studied ion pairs is not dependent on the nature of the anion.