Vaporization and Formation Enthalpies of 1-Alkyl-3-methylimidazolium Tricyanomethanides

Abstract

Thermochemical studies of the ionic liquids 1-ethyl-3-methylimidazolium tricyanomethanide [C(2)MIM][C(CN)(3)] and 1-butyl-3-methylimidazolium tricyanomethanide [C(4)MIM][C(CN)(3)] have been performed in this work. Vaporization enthalpies have been obtained using a recently developed quartz crystal microbalance (QCM) technique. The molar enthalpies of formation of these ionic liquids in the liquid state were measured by means of combustion calorimetry. A combination of the results obtained from QCM and combustion calorimetry lead to values of gaseous molar enthalpies of formation of [C(n)MIM][C(CN)(3)]. First-principles calculations of the enthalpies of formation in the gaseous phase for the ionic liquids [C(n)MIM][C(CN)(3)] have been performed using the CBS-QB3 and G3MP2 theory and have been compared with the experimental data. Furthermore, experimental results of enthalpies of formation of imidazolium-based ionic liquids with the cation [C(n)MIM] (where n = 2 and 4) and anions [N(CN)(2)], [NO(3)], and [C(CN)(3)] available in the literature have been collected and checked for consistency using a group additivity procedure. It has been found that the enthalpies of formation of these ionic liquids roughly obey group additivity rules.

Dispersion and Hydrogen Bonding Rule: Why the Vaporization Enthalpies of Aprotic Ionic Liquids Are Significantly Larger than those of Protic Ionic liquids

“…[8,9] All types of interaction have their special features:t hey can be strong and long-range,m oderate and directional, or weak from short-to long-range.I nm olecular liquids such as alcohols the vaporization enthalpies are mainly stipulated by the hydrogen bonding network combined with increasing dispersion interactions due to increasing alkyl chain lengths. [13][14][15][16][17][18][19][20][21][22][23] Most results indicate that ionic liquids evaporate as neutral ion pairs or ion pair aggregates.The experimental vaporization enthalpies of AILs range from 122 to 163 kJ mol À1 ,t hus substantial interaction energy must be overcome to get the ionic pair in the vapor.In contrast, vaporization enthalpies of PILs are practically absent in the literature,e xcept for methylimidazolium nitrate [14] and ethylammonium nitrate. [10][11][12] In ionic liquids the situation is more complicated.…”

Surface tension and 0.1MPa density for members of homologous series of ionic liquids composed of imidazolium-, pyridinium-, and pyrrolidinium-based cations and of cyano-groups containing anions

“…That is why the data cannot be reasonably described within a single common group contribution model for parachor Eq. (12). The data allow to create a common A c c e p t e d M a n u s c r i p t model separately for imidazolium-, pyridinium-and pyrrolidinium-based tricyanomethanides and the other for the surface tension of imidazolium based thiocyanates and dicyanamides.…”

“…Tables 1 and 2 give an overview of the data sources [1], [11]- [25] available in the literature on 0.1 MPa density and surface tension of the four tricyanomethanides of interest. Among the properties of the four ionic liquids, the density of [C 2 MIM][TCM] [1], [11]- [17] and of [C 4 MIM][TCM] [12], [15], [16], [18], [19] and [25] have been most studied. For [C 4 MPYR][TCM], 18 data points in temperature range from (298 to 363) K have been published by Domańska et al [20]- [22].…”

The Relation between Vaporization Enthalpies and Viscosities: Eyring's Theory Applied to Selected Ionic Liquids

“…Whereas the measurement of transport properties is well established, the determinationo fv aporization enthalpies of these extremelyl ow volatile compounds is still ac hallenge. [8][9][10][11][12][13][14] At low temperatures ILs show no measurable vapor pressures, at higher temperatures where the vapor pressure becomes detectable many ILs begin to decompose. However,e ighty years ago Eyring suggested at heory which related viscosities and vaporization enthalpies to each other.T he model is based on Eyring's theory of absolute reaction rates.R ecent attempts to apply Eyring'st heory to ionic liquids failed.…”

“…For that reason ILs turned from al ab curiosity into materialso ft remendous academic and industrial interest. [8][9][10][11][12][13][14] At low temperatures ILs show no measurable vapor pressures, at higher temperatures where the vapor pressure becomes detectable many ILs begin to decompose. Mosti nterestingly,I Ls play ap otentialr ole in energy devices, as in battery technology,s upercapacitors, and dye sensitized solar cells.…”