Excess enthalpies of [C_nMIM][NTf₂] n = (2 or 10) + ethanol or + N-methyl-2-pyrrolidone binary mixtures at 298.15 K and 0.1 MPa

Abstract

Mixtures containing 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C_nMIM][NTf₂] n = {2, 10}, + ethanol or + N-methyl-2-pyrrolidone have been investigated to determine excess molar enthalpies, H^E, and excess partial molar enthalpies of components, $H_{1}^{{\text{E}}}$ and $H_{2}^{{\text{E}}}$, over the entire mole fraction, x₁, range, at 298.15 K and 0.10 MPa. Ionic liquids, ILs, were pre-treated by heating and by using activated molecular sieves. Both mixtures in ethanol are endothermic and the $H_{{\text{i}}}^{{\text{E}}}$ of the components are always positive while those in NMP are exothermic and the corresponding values of $H_{{\text{i}}}^{{\text{E}}}$ are negative, in the whole x₁ range. The deviations from ideality are quite significant, being the H^E values at equimolar composition, $H_{{{\text{eq}}}}^{{\text{E}}} \pm u$; (+ 1800 ± 40 and + 2110 ± 10) J mol⁻¹ for ethanol-containing mixtures and (− 1410 ± 10 and − 1980 ± 20) J mol⁻¹ for NMP-containing mixtures ($u$ is the standard uncertainty). The values of the excess partial molar enthalpies at infinite dilution of the components, $H_{\rm i}^{{{\text{E,}}\infty }}$, show regular trends. The $H_{1}^{{{\text{E,}}\infty }}$ are always greater than the $H_{2}^{{{\text{E,}}\infty }}$; their ratio is about 1.8 for mixtures in EtOH and 2.5 for NMP-containing mixtures. The greatest thermal effects are found when the molecular compound acts as a solvent in the dissolution of one mole of IL, under extreme dilution condition.