Excess molar enthalpies of ternary mixtures containing 1-ethyl-3-methylimidazolium tetrafluoroborate and organic solvents
Introduction
Ionic liquids have generated burgeoning interest in industry and academia over the past decade [1], [2]. The knowledge of thermo physical properties of mixtures (excess molar volumes, VE, excess isentropic compressibilities, , excess molar enthalpies, HE and excess Gibb's free energy, GE, etc.) is important for the interpretation of nature of intermolecular interactions and in the development of solution models/theories; they are also useful in design and optimization of industrial processes. The extraction of aromatic from aliphatic hydrocarbons may have ionic liquids or their mixtures with organic solvents better replacements for volatile organic liquids. The thermodynamic properties of mixtures containing ionic liquids, 2-methylaniline, pyridine or isomeric picolines may be very suitable for extraction, electrochemistry, organic synthesis, etc. Several investigations on imidazolium based ionic liquids for capacitors [3], [4], [5], solar cells [6], fuel cells [7] and batteries [8] have been carried out and the tetrafluoroborate anion is also widely used due to its competitive properties and low cost. As a part of our systematic investigations on thermodynamic properties of binary ionic liquid mixtures [9], [10], we have reported VE, HE and of 1-ethyl-3-methylimidazolium tetrafluoroborate [emim][BF4] (i) + pyridine or α- or β- or γ-picoline or aniline or N-methyl aniline or 2-methylaniline (j) binary mixtures. In the present study, we extend our study to ternary mixtures and report excess molar enthalpies, data of ternary [emim][BF4] (i) + 2-methylaniline (j) + pyridine or α- or β- or γ-picoline (k) mixtures at 298.15 K. It would be of interest to see how the topology of constituent molecules of the mixtures (Graph theory) describes the experimental data.
Section snippets
Experimental
1-Ethyl-3-methylimidazolium tetrafluoroborate [emim][BF4] (Fluka, 0.98 GC) was used without further purification. The water content in ionic liquid was regularly checked using Karl Fischer titration [11] and found to be less than 336 ppm. 2-Methylaniline (2MA) (Fluka, 0.99 GC), pyridine (Py) (Fluka, 0.99 GC), α-picoline (Fluka, 0.98 GC), β-picoline (Fluka, 0.99 GC) and γ-picoline (Fluka, 0.99 GC) were purified by standard methods [12]. The densities and speeds of sound values for the purified
Results
The Redlich–Kister equation [22] was fitted to the measured excess molar enthalpies, data of ternary 1-ethyl-3-methyl imidazolium tetrafluoroborate (i) + 2-methylaniline (j) + pyridine or α- or β- or γ-picoline (k) mixtures at 298.15 K (recorded in Table 2).where are adjustable parameters of various binaries (i + j), (j + k), (i + k) and were taken from the literature [9], [10], [19].
Discussion
Excess molar enthalpies, data of the investigated ternary ionic liquid mixtures are not available in the literature. The values for [emim][BF4] (i) + 2MA (j) + Py or α- or β- or γ-picolines (k) are negative over entire mole fraction range. The sign and magnitude of values are due to cumulative effect of contributions due to rupture of associated molecular entities and formation of binary or ternary unlike contact among the constituent of mixtures. The data for the studied
Conclusion
The paper reports excess molar enthalpies data, for [emim][BF4] (i) + 2MA (j) + Py or α- or β- or γ-picoline (k) mixtures at 298.15 K and atmospheric pressure. Graph theory has been utilized to obtain values of the investigated mixtures. Results indicate that the values determined by Graph theory compare well with experimental data. The agreement between measured values and the values determined from Graph theory suggest that while [emim][BF4] exist as monomer; 2MA or Py or
Acknowledgements
Subhash Solanki is grateful to CSIR, New Delhi, India for the award of JRF. The authors are also grateful to the Head of Chemistry Department and authorities of M.D. University, Rohtak, for providing research facilities.
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