SANS, ATR-IR, and 1D- and 2D-NMR studies of mixing states of imidazolium-based ionic liquid and aryl solvents

Abstract

The mixing states of imidazolium-based ionic liquid, 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (C₁₂mim⁺TFSA⁻), and two aryl solvents toluene and α,α,α-trifluorotoluene (TFT) have been clarified on both meso- and microscopic scales using small-angle neutron scattering (SANS) and ATR-IR techniques. To elucidate the interactions between C₁₂mim⁺TFSA⁻ and aryl solvent molecules from the change in the electron densities of C₁₂mim⁺ and TFSA⁻, 1D-NMR measurements for ¹H and ¹³C atoms have been conducted on C₁₂mim⁺TFSA⁻–aryl solvent solutions as a function of the aryl solvent mole fraction. In addition, the interactions between the dodecyl chain of C₁₂mim⁺ and aryl solvent molecules have been observed using 2D-NMR techniques of ¹H{¹H} ROESY and ¹⁹F{¹H} HOESY. These results have been compared with those of benzene solutions previously investigated. The SANS measurements have shown that toluene is heterogeneously mixed with C₁₂mim⁺TFSA⁻ as well as benzene. However, the heterogeneity of the toluene solutions is slightly lower than that of the benzene solutions. In contrast, TFT is homogeneously mixed with the ionic liquid at least on the present SANS scale. The substituent effects of the three aryl solvent molecules of benzene, toluene, and TFT on the mixing states of the solutions have been discussed in terms of the cation–π interaction between the imidazolium and phenyl rings and the interaction between the dodecyl group and aryl solvent molecules.