Measuring and predicting ΔvapH298 values of ionic liquids

Abstract

We report the enthalpies of vaporisation (measured using temperature programmed desorption by mass spectrometry) of twelve ionic liquids (ILs), covering four imidazolium, [C(m)C(n)Im]+, five pyrrolidinium, [C(n)C(m)Pyrr]+, two pyridinium, [C(n)Py]+, and a dication, [C3(C1Im)2]2+ based IL. These cations were paired with a range of anions: [BF4]-, [FeCl4]-, [N(CN)2]-, [PF3(C2F5)3]- ([FAP]-), [(CF3SO2)2N]- ([Tf2N]-) and [SCN]-. Using these results, plus those for a further eight imidazolium based ILs published earlier (which include the anions [CF3SO3]- ([TfO]-), [PF6]- and [EtSO4]-), we show that the enthalpies of vaporisation can be decomposed into three components. The first component is the Coulombic interaction between the ions, DeltaU(Cou,R), which is a function of the IL molar volume, V(m), and a parameter R(r) which quantifies the relative change in anion-cation distance on evaporation from the liquid phase to the ion pair in the gas phase. The second and third components are the van der Waals contributions from the anion, DeltaH(vdw,A), and the cation, DeltaH(vdw,C). We derive a universal value for R(r), and individual values of DeltaH(vdw,A) and DeltaH(vdw,C) for each of the anions and cations considered in this study. Given the molar volume, it is possible to estimate the enthalpies of vaporisation of ILs composed of any combination of the ions considered here; values for fourteen ILs which have not yet been studied experimentally are given.

Vapor pressures of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with long alkyl chains

“…[5][6][7][8][9] Despite the importance of the vapor pressures of the ionic liquids and the related thermodynamic properties of vaporization (enthalpies, entropies, and Gibbs energies of vaporization), most of the works performed until know were focused in estimate/determine the enthalpies of vaporization. 7,[10][11][12][13][14][15][16][17][18][19][20][21] The nature of the gas phase of ionic liquids is still in debate; however, the theory that the vaporization of ionic liquids occurs as a direct liquid to gas transfer of the intact ionic pair has been supported by several studies using photoionization, 22 line of sight mass spectrometry, 11,12,23 Fourier transform ion cyclotron resonance, 24,25 field ionization method, 26 tunable vacuum ultraviolet photoionization, 15 and more recently by molecular dynamics simulations. 27,28 Recently, we reported the thermodynamic study concerning the vaporization of the [C N-1 C 1 im][NTf 2 ] (N = 3-9, 11, and 13) ionic liquid series, where important trends for the enthalpies and entropies of vaporization were found, which are related to a change in the molecular structure of the liquid phase around [C 6 C 1 im][NTf 2 ].…”

Analysis of evaporation and thermal decomposition of ionic liquids by thermogravimetrical analysis at ambient pressure and high vacuum

“…for an industrial application of ILs. For a different criterion with regard to the limit of mass loss and decomposition time, the general eqn (22) should be taken, for example, by researchers who only want to measure a certain property of an IL in a certain experimental time of, say, only an hour, but have to be sure that the properties do not change considerably during the measurement.…”

Temperature Effects on the Kinetics of Ferrocene and Cobaltocenium in Methyltriphenylphosphonium Bromide Based Deep Eutectic Solvents

“…For example, the diffusion coefficient of Fc is a function of concentration, nonlinear peak current versus Fc concentration relationships 24 as well as nonlinear correlations between the enthalpy of vaporization and molar surface energy z E-mail: mohammedharun77@yahoo.com of the [C n C 1 Im][BF 4 ] ILs. 25,26 With the exception of some electrochemical studies in organic solvents at different temperatures, [27][28][29] the investigation has been performed at room temperature. In the case of ILs, the voltammetry of both Fc and Cc was evaluated over a range of temperatures 21 and the kinetics of the Fc/Fc + electrochemical system was investigated in the temperature range of 298-373 K. 30 Despite such progress, no fundamental study on the effect of temperature on Fc/Fc + oxidation and Cc + /Cc reduction processes in DESs is available.…”