ARTICLE pubs.acs.org/jced
Ultrasonic and Volumetric Properties of 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate Ionic Liquid with 2-Propanol or Tetrahydrofuran at Several Temperatures Ernesto Vercher, A. Vicent Orchilles, Francisco J. Llopis, Vicenta Gonzalez-Alfaro, and Antoni Martínez-Andreu* Departamento de Ingeniería Química, Escuela Tecnica Superior de Ingeniería, Universitat de Valencia, 46100 Burjassot, Valencia, Spain ABSTRACT: Densities and speeds of sound of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate mixtures with 2-propanol and tetrahydrofuran (THF), as well as of the pure components, have been measured over the whole range of compositions at T = (278.15 to 328.15) K and P = (101 ( 2) kPa. From these experimental data, the excess molar volume, excess speed of sound, and excess isentropic compressibility have been calculated and fitted to an extended version of the RedlichKister equation, which takes into account the dependence on composition and temperature simultaneously. The PrigogineFloryPatterson theory has also been used to explain the behavior of these systems.
’ INTRODUCTION Ionic liquids (ILs) are salts made up of an organic greatly asymmetric substituted cation such as imidazolium, pyridinium, pyrrolidinium, tetraalkylphosphonium, quaternary ammonium, and so forth and an anion such as halide, hexafluorophosphate, tetrafluoroborate, trifluoromethanesulfonate, acetate, alkylsulfate, and so forth, being its main feature to have a very low melting point, mainly below 100 °C. These cations, substituents, and anions can be virtually varied at will to change their chemical and physical properties.1 Because of their structure and ionic interactions,1 ILs exhibit unique properties: they are liquid in a wide range of temperatures, have no effective vapor pressure, are outstandingly good solvents for a wide range of inorganic, organic, and polymeric materials, and have a high thermal stability.2 They are often used as a “green” solvent replacing volatile organic solvents, extraction media for separation processes,3 and entrainers for extractive distillation.4 Applications as catalysts for organic and organometallic synthesis,5,6 lubricants, thermofluids, plasticizers, and electrically conductive liquids in electrochemistry have also been reported.2 During the past few years, investigations on thermophysical and thermodynamic properties of pure ILs and their mixtures with molecular solvents have shown great augmentation. However, it is necessary to have a sufficiently large data bank available not only for process and product design but also for the development of property correlations. Specifically, experimental data of density and speed of sound of binary mixtures are important not only to design and control chemical processes but from the theoretical point of view to predict the properties and characteristics of ILs.7 In the present work, we report the volumetric and acoustical properties of binary mixtures of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][triflate]) with two polar solvents, a protic one, 2-propanol, and an aprotic, tetrahydrofuran (THF), over the whole range of compositions, at temperatures from (278.15 to 328.15) K and a pressure of 0.1 MPa. Both binary mixtures have total miscibility in the operation range. The values of the excess molar volume, excess isentropic compressibility, r 2011 American Chemical Society
and excess speed of sound were then calculated from the measured density and speed of sound data and fitted to polynomial equations. Despite the importance of triflate-based ILs in industrial applications, physical properties of few binary mixtures of [emim][triflate] with solvents have been reported, and those are as follows: water,810 methanol,9 ethanol,9,11 1-propanol,9 nitromethane,12 acetone,13 methyl acetate,13 and ethyl acetate.13 To our knowledge, no experimental density and speed of sound measurements have been reported in the literature for the binary mixtures studied in this work.
’ EXPERIMENTAL SECTION Materials. The IL used was 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (CAS Registry No. 145022-44-2). Because of its hygroscopic character, it was desiccated at 0.2 Pa overnight prior to use. The water content of the IL, determined by Karl Fischer titration, was lower than 0.0005, expressed as mass fraction. 2-Propanol (CAS Registry No. 67-63-0) and THF (CAS Registry No. 109-99-9) were purchased from Merck. Both solvents were degassed ultrasonically and dried over molecular sieves of type 3 Å supplied by Grace, the purities of them being ascertained by gas chromatography (GC). The chemical specifications of the materials used are reported in Table 1. As shown in Table 2, densities and speeds of sound of all the chemicals gave a good agreement with the corresponding literature values at 298.15 K.8,9,11,1326 Apparatus and Procedure. Samples of (5 to 8) g were prepared by filling glass vials with the liquids and weighing them on a Mettler AE200 analytical balance, which measured with a precision of 0.0001 g. Vials were closed with screw caps to ensure Special Issue: Kenneth N. Marsh Festschrift Received: June 21, 2011 Accepted: August 5, 2011 Published: August 23, 2011 4633
dx.doi.org/10.1021/je200609g | J. Chem. Eng. Data 2011, 56, 4633–4642
Journal of Chemical & Engineering Data
ARTICLE
Table 1. Specifications of Chemical Samples chemical name
source
2-propanol
Merck
b
THF
Merck
[emim][triflate]c
Solvent Innovation
a
purification method
0.998
ultrasonic degassing, molecular sieve drying
0.998
ultrasonic degassing, molecular sieve drying
>0.98
b
final water mass fraction
mass fraction purity
vacuum desiccation
analysis method GCa GC KFd
