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

Olla G.;Meloni D.;Salis A.;Ennas G.;Piras A.;Porcedda S.

2022-01-01

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Abstract

Mixtures containing 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [CnMIM][NTf2] n = {2, 10}, + ethanol or + N-methyl-2-pyrrolidone have been investigated to determine excess molar enthalpies, HE, and excess partial molar enthalpies of components, H1E and H2E, 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 HiE of the components are always positive while those in NMP are exothermic and the corresponding values of HiE are negative, in the whole x1 range. The deviations from ideality are quite significant, being the HE values at equimolar composition, HeqE±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, HiE,∞, show regular trends. The H1E,∞ are always greater than the H2E,∞; 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.