Elsevier

Thermochimica Acta

Volume 569, 10 October 2013, Pages 36-41
Thermochimica Acta

Excess molar enthalpies of ternary mixtures containing 1-ethyl-3-methylimidazolium tetrafluoroborate and organic solvents

https://doi.org/10.1016/j.tca.2013.07.006Get rights and content

Highlights

  • The HijkE data of 1-ethyl-3-methylimidazolium tetrafluoroborate mixtures have been measured.

  • The Redlich–Kister equation was fitted to HijkE data to evaluate ternary adjustable parameters.

  • The observed data have been analyzed in terms of Graph theory.

  • The HijkE values calculated by Graph theory compare well with experimental HijkE values.

Abstract

Excess molar enthalpies, HijkE of 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + 2-methylaniline (j) + pyridine or α- or β- or γ-picoline (k) ternary mixtures have been measured over an entire mole fraction at 298.15 K using micro differential scanning calorimeter [Model-μ DSC 7 Evo]. The Redlich–Kister equation parameters have been fitted to measured data. The HijkE values for the studied mixtures are negative over entire composition range. The topology of the constituents of the mixtures has been utilized to (Graph theory) predict HijkE values of the investigated mixtures. It has been observed that HijkE values determined by Graph theory compare well with their corresponding experimental values.

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, κSE, 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 κSE 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, HijkE 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 HijkE 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, HijkE 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).HijkE=xixjn=02Hij(n)(xixj)n+xjxkn=02Hjk(n)(xjxk)n+xkxin=02Hik(n)(xkxi)n+xixjxkn=02Hijk(n)(xjxk)nxinwhere Hij(n) 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, HijkE data of the investigated ternary ionic liquid mixtures are not available in the literature. The HijkE 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 HijkE 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 HijkE data for the studied

Conclusion

The paper reports excess molar enthalpies data, HijkE 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 HijkE values of the investigated mixtures. Results indicate that the HijkE values determined by Graph theory compare well with experimental data. The agreement between measured HijkE 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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