The Sulfur Dioxide−1-Butyl-3-Methylimidazolium Bromide Interaction:  Drastic Changes in Structural and Physical Properties

Abstract

The contact between minor amounts of SO2 and crystalline 1-butyl-3-methyl-imidazolium bromide (BMIBr) causes the almost immediate melting of the ionic liquid (mp 45 degrees C) as well as a dramatic decrease in its viscosity in comparison to the pure molten phase. The same behavior was observed for other halide ionic liquids of higher melting points (70, 135, and 220 degrees C). The Raman spectrum of BMIBr-SO2 clearly indicates a specific charge transfer interaction involving SO2 and the halide. The measurements of ionic conductivity and diffusion coefficients obtained for the neat BMIBr (molten phase) and for the BMIBr-SO2 strongly suggest a higher degree of ionic association in the presence of SO2. Molecular dynamic simulations indicate that although the cation-anion distance is preserved in the short range, there is a variation in the interionic distances in the second shell, leading to a less organized structure in the long range. The modulation of the structural and physical properties of ionic liquids by SO2 and the convenient choice of the ions for gas absorption are suggested.

Detailed analysis of the charge transfer complex N,N‐dimethylaniline–SO2 by Raman spectroscopy and density functional theory calculations

“…[21] Vertical absorption electronic spectra were computed at the B3LYP/6-311++G(3df,3pd) optimized geometries employing TDDFT protocol implemented in Gaussian03 package, following similar procedure successfully employed previously. [22] Bond length (Å) 3 1.3873 1.3857 C 3 -C 4 1.3896 1.3911 C 4 -C 5 1.3896 1.3867 C 5 -C 6 1.3873 1.3909 C 6 -C 1 1.4088 1.3984 C 1 -N 9 1.3882 1.4237 N 9 -C 7 1.4503 1.4593 N 9 -C 8 1.4503 1.4669 N 9 -S 10 2.6009 S 10 -O 11 1.4461 a S 10 -O 12 1.4483 a a S-O bond distance calculated for free SO 2 = 1.4367. Figure 1 shows schematically the DMA molecule and the calculated optimized geometry for the complex DMA-SO 2 with the respective atom numbering.…”

SO2-Induced Variations in the Viscosity of Ionic Liquids Investigated by in Situ Fourier Transform Infrared Spectroscopy and Simulation Calculations

“…In 2007, Santos et al 32 firstly reported an interesting phenomenon that the imidazolium salt [Bmim]Br experienced significant variations on the structures and physical properties such as density, viscosity and conductivity upon contact with gaseous SO 2 . It was worth mentioning that the density of [Bmim]Br increased slightly and the viscosity decreased dramatically in the presence of SO 2 , which provides the possibility by using SO 2 gas to modulate the physical properties of ILs.…”

Electrode–Electrolyte Interfacial Processes in Ionic Liquids and Sensor Applications

“…For example, multiple sterically hindered allylic functional groups could be incorporated to minimize IL-electrode interactions and maximize compressibility of the solvation layers [22][23][24]. It was reported that the adsorption and dissolution of gas molecules in the IL-electrified metal interface can lead to the change of the doublelayer structure and thickness and the change of IL viscosity and the dielectric constant (i.e., less organized arrangement of ILs) [25,26]. The molecular structure of ILs such as alkyl chain length influences the relative permittivity [27].…”