Aprotic Ionic Liquids: A Framework for Predicting Vaporization Thermodynamics

Abstract

Ionic liquids (ILs) are recognized as an environmentally friendly alternative to replacing volatile molecular solvents. Knowledge of vaporization thermodynamics is crucial for practical applications. The vaporization thermodynamics of five ionic liquids containing a pyridinium cation and the [NTf2] anion were studied using a quartz crystal microbalance. Vapor pressure-temperature dependences were used to derive the enthalpies of vaporization of these ionic liquids. Vaporization enthalpies of the pyridinium-based ionic liquids available in the literature were collected and uniformly adjusted to the reference temperature T = 298.15 K. The consistent sets of evaluated vaporization enthalpies were used to develop the “centerpiece”-based group-additivity method for predicting enthalpies of vaporization of ionic compounds. The general transferability of the contributions to the enthalpy of vaporization from the molecular liquids to the ionic liquids was established. A small, but not negligible correction term was supposed to reconcile the estimated results with the experiment. The corrected “centerpiece” approach was recommended to predict the vaporization enthalpies of ILs.

Thermal Decomposition, Low Temperature Phase Transitions and Vapor Pressure of Less Common Ionic Liquids Based on the Bis(trifuoromethanesulfonyl)imide Anion

“…For the presently investigated ionic liquids, it varies from 136 ± 18 kJ/mol for m-C 6 H 4 (CH 2 ImMe)][NTf 2 ] 2 to 147 ± 12 and 147 ± 13 kJ/mol for [DABCO10][NTf 2 ] and [p-C 6 H 4 (CH 2 ImBu)][NTf 2 ] 2 , respectively, and finally to 180 ± 17 kJ/mol for [C 6 Py][NTf 2 ]. These values are consistent with those previously reported for the other ionic liquids [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

“…Bulow et al reported a comparison of the vapor pressure of ILs containing the same 1-ethyl-3-methyl-imidazolium cation and a series of anions, such as PF 6 , B(CN) 4 , (C 2 H 5 O) 2 PO 2 , NTf 2 , SCN, CF 3 CO 2 , CF 3 SO 3 , BF 4 , C(CN) 3 , (C 2 F 5 ) 3 PF 3 , 4-CH 3 -Ph-SO 3 [ 32 ]. Finally, in the last couple of years some models were also proposed to derive the vapor pressure and vaporization enthalpy values from the knowledge of the structure of ILs [ 33 , 34 , 35 ].…”

Dissecting Noncovalent Interactions in Carboxyl‐Functionalized Ionic Liquids Exhibiting Double and Single Hydrogens Bonds Between Ions of Like Charge

“…The contributions for (CH 3 )=6.33 kJ mol −1 and (COOH)=44.0 kJ mol −1 are well‐established for the molecular liquids [69,70] . The principle transferability of the (R) contributions from molecular liquids to ionic liquids was explored and validated in our recent work [65,66] . Thus, the numerical value for the vaporization enthalpy of [HOOC‐CH 2 ‐py][NTf 2 ] was calculated as follows: (298.15 K)=(131.7−6.33+44.0) kJ mol −1 =169.4 kJ mol −1 (Figure 9).…”

“…The experimental determination of enthalpy of vaporization is a challenging task, so the experimental values must be validated with every theoretical method. A general approach to estimating enthalpies of vaporization based on a so‐called “centerpiece” molecule is under development in our recent work [65,66] . This approach is related to the conventional group additivity (GA), where the property of a molecule of interest is collected from a set of possibly small groups with well‐defined contributions [67] .…”

“…A general approach to estimating enthalpies of vaporization based on a so-called "centerpiece" molecule is under development in our recent work. [65,66] This approach is related to the conventional group additivity (GA), where the property of a molecule of interest is collected from a set of possibly small groups with well-defined contributions. [67] In contrast, the idea of the "centerpiece" approach is to select a potentially large "core" molecule that can mimic the structure of the molecule of interest, but the selected "core" molecule is supposed to possess well-established thermodynamic properties.…”