Elsevier

Fluid Phase Equilibria

Volume 261, Issues 1–2, 1 December 2007, Pages 444-448
Fluid Phase Equilibria

Determination of partial molar excess enthalpies at infinite dilution for the systems four alcohols + [bmim]PF6 at different temperatures by isothermal titration calorimeter

https://doi.org/10.1016/j.fluid.2007.06.007Get rights and content

Abstract

Molar excess enthalpies of ethanol, 1-propanol, 2-propanol and 1-butanol + 1-butyl-3-methyl-imidazolium hexafluorophosphate, [bmim]PF6 at highly diluted region of organic solvents were determined using isothermal titration calorimeter (ITC) at 288.15, 298.15, 308.15 and 318.15 K. The experimental data were fitted with a Redlich–Kister equation. The partial molar excess enthalpies at infinite dilution, hiE, were calculated using the parameters of the Redlich–Kister equation.

Introduction

In recent years, ionic liquids have got tremendously interest in many kinds of fields because of the attractive features of nonvolatile, excellent dissolvent properties, high conductivity, wide electrochemical window and good stability. As a kind of “green chemicals”, they have been widely used in organic synthesis as solvents [1] or catalysts [2], in chromatography as stationary or mobile phases or running electrolytes [3], in batteries as supporting electrolyte [4] and in electrochemical reactions [5].

Thermodynamic properties of mixtures containing ionic liquids have been investigated from experimental [6], [7], [8] and theoretical [9], [10], [11] to better understand and explain molecular interaction between molecules, as well as to test and develop new models and theories that were able to describe the thermodynamic behaviour of ionic liquids. Under the direction of these models and theories, the appropriate ionic liquids could be designed for organic reactions and other requirements.

An important thermodynamic property was the partial molar excess enthalpy at infinite dilution, hiE,. The dependence of activity coefficients at infinite dilution on temperature could be expressed bylnγi(T)TP,xi=hiE,(T)RT2Pfeffer et al. [12] has used an isothermal flow calorimeter to determine the partial molar excess enthalpy at infinite dilution. In this paper, the molar excess enthalpies of binary mixtures containing 1-butyl-3-methyl-imidazolium hexafluorophosphate, [bmim]PF6 at highly diluted region of organic solvents were determined using isothermal titration calorimeter (ITC) at 288.15, 298.15, 308.15 and 318.15 K. The Redlich–Kister equation was used to correlate the experimental data. The partial molar excess enthalpies at infinite dilution, hiE, were calculated using the parameters of Redlich–Kister equation.

Section snippets

Chemicals

Ethanol, 1-propanol, 2-propanol and 1-butanol, 1-heptane were analytical reagents. All these solvents were dried with Molecular Sieves (3 Å), filtrated through Millipore filter (0.45 μm) and then degassed by vacuums before the measurement. The purities of these compounds were determined by gas chromatography and were found to be between 99.5 and 99.9 mass%. Deionized water was distilled by using a quartz sub-boiling purifier.

The ionic liquid [bmim]PF6 investigated in this paper was synthesized

Calculation

To correlate the experimental data of the molar excess enthalpies, the empirical Redlich–Kister equation (2) [15] was used:hE(x)(J/mol)=x(1x)i=0nAi(2x1)iFor the binary system the partial excess molar enthalpies at infinite dilution, hiE, could be derived from Redlich–Kister equation as follows:h1E,(J/mol)=i=0n(1)iAiwhere the subscript i is referred to the titrant, the unit of the coefficient Ai is J/mol.

The molar excess enthalpy was obtained from the following equation:hE=Qρ1v/1000M1+m2

Results and discussion

In order to confirm the reliability of the isothermal titration calorimeter, the molar excess enthalpies at high dilution region for the systems of ethanol + water and ethanol + 1-heptane were determined and are listed in Table 1 at T = 298.15 K. The Redlich–Kister equation was used to correlate the experimental data. The values of the Redlich–Kister parameters together with the root mean square deviations (RMSD) are also listed in Table 2. The RMSD is defined asRMSD=1nin(hcal(i)Ehexp(i)E)2where hcal

References (16)

  • T. Fráter et al.

    Inorg. Chim. Acta

    (2006)
  • G. Inoue et al.

    Fluid Phase Equilib.

    (2007)
  • A. Diedrichs et al.

    Fluid Phase Equilib.

    (2006)
  • J.J. Jodry et al.

    Tetrahedron Lett.

    (2004)
  • S.U. Lee et al.

    Chem. Phys. Lett.

    (2005)
  • T. Pfeffer et al.

    Fluid Phase Equilib.

    (1995)
  • S. Fujita et al.

    Int. J. Mol. Sci.

    (2006)
  • X.H. Xiao et al.

    Anal. Chim. Acta

    (2004)
There are more references available in the full text version of this article.

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