Practical Determination of the Solubility Parameters of 1-Alkyl-3-methylimidazolium Bromide ([CnC1im]Br, n = 5, 6, 7, 8) Ionic Liquids by Inverse Gas Chromatography and the Hansen Solubility Parameter

Abstract

The physicochemical properties of four 1-alkyl-3-methylimidazolium bromide ([C_nC₁im]Br, n = 5, 6, 7, 8) ionic liquids (ILs) were investigated in this work by using inverse gas chromatography (IGC) from 303.15 K to 343.15 K. Twenty-eight organic solvents were used to obtain the physicochemical properties between each IL and solvent via the IGC method, including the specific retention volume and the Flory⁻Huggins interaction parameter. The Hildebrand solubility parameters of the four [C_nC₁im]Br ILs were determined by linear extrapolation to be δ 2 ( [ C 5 C 1 im ] Br ) = 25.78 (J·cm^-3)^0.5, δ 2 ( [ C 6 C 1 im ] Br ) = 25.38 (J·cm^-3)^0.5, δ 2 ( [ C 7 C 1 im ] Br ) =24.78 (J·cm^-3)^0.5 and δ 2 ( [ C 8 C 1 im ] Br ) = 24.23 (J·cm^-3)^0.5 at room temperature (298.15 K). At the same time, the Hansen solubility parameters of the four [C_nC₁im]Br ILs were simulated by using the Hansen Solubility Parameter in Practice (HSPiP) at room temperature (298.15 K). The results were as follows: δ t ( [ C 5 C 1 im ] Br ) = 25.86 (J·cm^-3)^0.5, δ t ( [ C 6 C 1 im ] Br ) = 25.39 (J·cm^-3)^0.5, δ t ( [ C 7 C 1 im ] Br ) = 24.81 (J·cm^-3)^0.5 and δ t ( [ C 8 C 1 im ] Br ) = 24.33 (J·cm^-3)^0.5. These values were slightly higher than those obtained by the IGC method, but they only exhibited small errors, covering a range of 0.01 to 0.1 (J·cm^-3)^0.5. In addition, the miscibility between the IL and the probe was evaluated by IGC, and it exhibited a basic agreement with the HSPiP. This study confirms that the combination of the two methods can accurately calculate solubility parameters and select solvents.