Physico-chemical properties of binary and ternary mixtures of ethyl acetate + ethanol + 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide at 298.15 K and atmospheric pressure

Article abstract of DOI:10.1007/s10953-010-9507-z

Densities, viscosities and refractive indices have been measured at 298.15 K and atmospheric pressure for binary and ternary mixtures of ethanol, ethyl acetate and 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) imide [C₄mim][NTF₂]. From these experimental properties, the corresponding excess properties have been calculated and adequately fitted with the Redlich-Kister polynomial equation. The adjustable parameters and standard deviations between experimental and calculated values are reported. Interest of this mixture is due to the possibility of using [C₄mim][NTF ₂] as an entrainer in the extractive distillation of ethanol + ethyl acetate. These results are compared with previously determined experimental data for mixtures of ethyl acetate and/or ethanol with the ionic liquid 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, [C ₈mim][NTF₂].

Full text of DOI:10.1007/s10953-010-9507-z

J Solution Chem (2010) 39: 371–383
DOI 10.1007/s10953-010-9507-z
Physico-chemical Properties of Binary and Ternary
Mixtures of Ethyl Acetate + Ethanol +
1
-Butyl-3-methyl-imidazolium
bis(trifluoromethylsulfonyl)imide at 298.15 K and
Atmospheric Pressure
AA nl f ao nS s oi nt oa E. Andreatta · Alberto Arce · Eva Rodil ·
Received: 7 September 2009 / Accepted: 2 October 2009 / Published online: 6 March 2010
©
Springer Science+Business Media, LLC 2010
Abstract Densities, viscosities and refractive indices have been measured at 298.15 K and
atmospheric pressure for binary and ternary mixtures of ethanol, ethyl acetate and 1-butyl-3-
methyl-imidazolium bis(trifluoromethylsulfonyl) imide [C4mim][NTF2]. From these exper-
imental properties, the corresponding excess properties have been calculated and adequately
fitted with the Redlich-Kister polynomial equation. The adjustable parameters and standard
deviations between experimental and calculated values are reported. Interest of this mixture
is due to the possibility of using [C4mim][NTF2] as an entrainer in the extractive distil-
lation of ethanol + ethyl acetate. These results are compared with previously determined
experimental data for mixtures of ethyl acetate and/or ethanol with the ionic liquid 1-octyl-
3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, [C8mim][NTF2].
Keywords Density · Refractive index · Dynamic viscosity · Ionic liquid
1
Introduction
Room temperature ionic liquids (ILs) are emerging as replacements for traditionally used
volatile organic solvents. They are composed of organic cations and organic or inorganic
anions. They are called “designer solvents” because desired properties can be obtained by
combination of their ions [1]. To design processes involving ionic liquids as solvents, it
A.E. Andreatta · A. Arce (ꢀ) · E. Rodil · A. Soto
Chemical Engineering Department, University of Santiago de Compostela,
15782 Santiago de Compostela, Spain
e-mail: alberto.arce@usc.es
Present address:
A.E. Andreatta
PLAPIQUI, Universidad Nacional del Sur – CONICET, Camino La Carrindanga Km 7, Casilla 717,
8000 Bahía Blanca, Argentina

372
J Solution Chem (2010) 39: 371–383
is necessary to know the physico-chemical properties of the pure salts and their related
mixtures.
In recent years, ionic liquids of the 1-alkyl-3-methylimidazolium bis(trifluoromethyl-
sulfonyl) imide, [Cnmim][NTF2] series have become popular due to their combined rela-
tively low viscosity [2, 3] and high thermal stability [4]. Experimental measurements of
their physico-chemical properties are scarce and clearly needed.
In this context, physico-chemical properties such as densities, refractive indices and dy-
namic viscosities have been measured at 298.15 K and atmospheric pressure for ternary
mixtures of ethyl acetate + ethanol + 1-butyl-3-methyl-imidazolium bis(trifluoromethyl-
sulfonyl)imide [C4mim][NTF2], and for their corresponding binary mixtures containing
[C4mim][NTF2]. Interest in this mixture is based on the possibility of using [C4mim][NTF2]
IL as an entrainer for the extractive distillation of ethanol + ethyl acetate [6]. No avail-
able information was found in the literature about the volumetric and viscosity prop-
erties of these binary and ternary mixtures. A comparison was made of the physico-
chemical and excess properties of mixtures of ethyl acetate and/or ethanol with the IL
studied in this work and the corresponding system with 1-octyl-3-methyl-imidazolium
bis(trifluoromethylsulfonyl)imide [C8mim][NTF2] [5], in order to analyze the effect of the
alkyl chain.
2
Experimental Section
2.1 Chemicals
The chemicals purchased for the experiments were ethyl acetate (99.8%, Sigma-Aldrich)
and ethanol (99.9%, Merck). Gas chromatographic (GC) analysis did not detect any ap-
preciable peaks due to impurities. No further purification of these products was car-
ried out. The ionic liquid 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide,
[C4mim][NTF2], was synthesized in our laboratory by reaction of 1-methylimidazole
(Aldrich, > 99% by GC) with an excess of 1-bromobutane (Merck, > 98%) to produce the
[C4mim][Br]. This bromide salt was mixed with the lithium bis(trifluoromethanesulfonyl)-
imide salt, Li[NTF2] (Solvionic, >99%), in deionized water to obtain [C4min][NTF2] by an
ion metathesis reaction. After washing, the purification of [C4min][NTF2] was completed
by heating it under high vacuum for 48 h (1 mbar, 353.15 K). More details about the ex-
perimental procedure can be found in earlier publications [7]. The water mass fraction was
determined by means of a Karl Fischer titration carried out in a Metrohm 737 KF, which
−
6
yielded the mass fraction ω = 46.3 × 10 . No bromide was detected by means of capillary
1
13
electrophoresis. The ionic liquid was analyzed by H NMR and C NMR spectroscopy to
confirm the absence of any major impurities.
Table 1 gives a comparison between experimental and literature [8–12] data of the den-
sity, refractive index and dynamic viscosity, in addition to reporting the water content of the
pure components.
2.2 Experimental Setup and Procedure
Weighings were carried out in a Mettler Toledo AT 261 balance with an uncertainty of
−
4
±
1 × 10 g, and the uncertainties of the compositions of the prepared mixtures were esti-
mated to be ± 0.0002 mole fractions. Densities were measured in an Anton Paar DMA 5000
densimeter. This instrument automatically corrects for the influence of viscosity on density

J Solution Chem (2010) 39: 371–383
373

374
J Solution Chem (2010) 39: 371–383
over the whole viscosity range. The viscosity correction for this type of densimeter has been
adequately checked [13]. The uncertainties in the temperature and density measurements
−
5
−3
are ± 0.01 K and ± 3 × 10 g·cm , respectively. Refractive indices were measured with
an ATAGO RX-5000 refractometer with a Hero Therm thermostat to maintain the tempera-
−
5
ture within ± 0.02 K. The uncertainties in the refractive index measurements are ± 4×10
.
The kinematic viscosities were determined with micro Ubbelohde viscometers. Two mi-
cro Ubbelohde viscometers (capillaries I and II) were used in the experiments according to
the different viscosity values of the mixtures. The capillaries were calibrated and certified
by the manufacturer, and were verified by us by measuring the viscosity of different pure
liquids. Flow-time measurements were performed with the Lauda Processor Viscosity Sys-
tem PVS1 with a resolution of 0.01 s. The temperature of the viscometer was kept constant
within ± 0.005 K using a Lauda clear view thermostat D 20 KP with a through-flow cooler
DLK 10. Viscosity measurements were repeated at least three times for each sample, and
were found to be repeatable to within ± 0.03 s for times less than 100 s and ± 0.5 s for higher
times. The kinematic viscosity of a solution, υ, is given by
υ = K(t − y)
(1)
where υ is the kinematic viscosity, t is the flow time, K is the capillary constant reported by
the manufacturer, and y is the kinetic energy correction that is used if necessary. Dynamic
viscosities were calculated from the kinematic viscosities and densities. The uncertainty for
the dynamic viscosity determinations is estimated to be ± 0.5%.
3
Experimental Results and Discussion
Densities, ρ, refractive indices, nD, dynamic viscosities, η, excess molar volumes, V E
and molar refraction changes of mixing, ꢀR, at 298.15 K and atmospheric pressure
are reported in Table 2 for the binary systems ethyl acetate + [C4min][NTF2] and
ethanol + [C4min][NTF2], and in Table 3 for the ternary system ethyl acetate + ethanol +
[
C4min][NTF2]. The physico-chemical properties of the ethyl acetate + ethanol binary sys-
tem have been published previously [5].
E
The excess molar volumes V , and the viscosity ꢀη and molar refraction ꢀR changes
of mixing were calculated from the experimental values using the following expressions:
ꢀ
E
V
= VM −
xiVi
xiRi
(2)
(3)
(4)
i
ꢀ
ꢀ
η = η −
xiηi
i
ꢀ
ꢀ
R = RM −
i
where VM is the molar volume of the mixture, RM is the molar refraction of the mixture
obtained from the Lorentz–Lorenz equation:
ꢁ
ꢂ
2
n − 1
D
RM =
VM
(5)
2
n + 2
D
and xi, Vi, ηi , and Ri are the mole fraction, the molar volume, the viscosity, and the molar
E
refraction, respectively, for component i. Uncertainties in the values of V and ꢀR were

J Solution Chem (2010) 39: 371–383
375
E
Table 2 Densities ρ, refractive indices nD, dynamic viscosities η, excess molar volume V , molar refraction
changes of mixing ꢀR, and viscosity changes of mixing ꢀη at 298.15 K for binary systems
ρ/(g·cm 3
−
)
nD
η/(mPa·s)
V
E
/(cm ·mol
3
−1
)
ꢀR/(cm ·mol
3
−1
)
ꢀη/(mPa·s)
x
x Ethyl acetate + (1 − x) [C mim][NTF ]
4
2
0
0
0
0
0
0
0
0
0
0
0
.0522 1.42735
1.42614 44.4
1.42546 40.0
1.42377 30.6
1.42274 26.5
1.42116 21.1
1.41775 13.67
1.41591 10.91
−0.132
−0.217
−0.430
−0.538
−0.674
−0.915
−0.978
−1.139
−1.212
−1.167
−0.871
0.008
−3.63
−6.02
−11.0
−12.6
−14.6
−15.9
−15.9
−14.3
−11.8
−8.50
−4.68
.0920 1.41978
.1818 1.40111
.2303 1.38988
.2982 1.37254
.4204 1.33575
.4752 1.31612
.5937 1.26566
.6953 1.21004
.7954 1.13855
.8933 1.04377
0.011
0.013
0.013
0.018
0.019
0.026
0.031
0.029
0.022
0.020
1.41114
1.40569
1.39835
1.38804
6.54
3.93
2.21
1.105
x Ethanol + (1 − x) [C mim][NTF ]
4
2
0.0793 1.42561
0.1174 1.41977
0.1393 1.41618
0.2058 1.40462
0.2578 1.39448
0.3450 1.37484
0.3840 1.36489
0.4122 1.35716
0.5622 1.30478
0.6880 1.23928
0.7967 1.15332
0.8984 1.02390
1.42581 42.6
1.42521 38.5
1.42486 36.8
1.42366 31.4
1.42265 27.3
1.42066 21.6
1.41969 19.4
1.41891 17.91
1.41362 11.15
−0.022
0.004
0.006
0.011
0.009
0.013
0.015
0.017
0.016
0.014
0.020
0.019
0.010
−4.20
−6.38
−6.93
−9.11
−10.6
−12.0
−12.3
−12.3
−11.6
−9.43
−6.78
−3.63
−0.028
−0.023
−0.049
−0.067
−0.097
−0.127
−0.152
−0.230
−0.291
−0.343
−0.335
1.40712
1.39852
1.38526
7.11
4.36
2.46
3
−1
estimated to be less than 0.005 cm ·mol . The uncertainty in the ꢀη values was estimated
to be less than 0.1 mPa·s.
Figure 1 shows the excess molar volumes and viscosity changes from mixing for the
ethanol + [C4min][NTF2] and ethyl acetate + [C4min][NTF2] binary systems. As it can be
seen, the excess molar volumes for the ethanol + [C4min][NTF2] binary system are neg-
3
−1
ative over the whole composition range with a minimum value of −0.38 cm ·mol . The
ethyl acetate + [C4min][NTF2] binary system also shows negative values over the whole
3
−1
range, with a minimum value around −1.2 cm ·mol . No comparable data were found
in the surveyed literature for these binary systems. The viscosity changes from mixing of
these binary liquids are negative with large values, due to the differences between the vis-
cosity of the compounds of around −12.5 mPa·s for ethanol + [C4min][NTF2] and around
−
16 mPa·s for ethyl acetate + [C4min][NTF2] systems.
If we compare these results with previously obtained data [5] for binary mixtures of
ethanol or ethyl acetate with a different imidazolium ionic liquid having a longer alkyl chain
length and the same anion, [C8min][NTF2], then we can observe that increasing the alkyl

3
76
J Solution Chem (2010) 39: 371–383
E
Table 3 Densities ρ, refractive indices nD, dynamic viscosities η, excess molar volumes V , molar refrac-
tion changes of mixing ꢀR, and viscosity changes of mixing ꢀη at 298.15 K for the ternary ethyl acetate (1)
+
ethanol (2) + [C mim][NTF ] (3) mixtures
4
2
ρ/(g·cm 3
−
)
nD
η/(mPa·s)
V
E
/(cm ·mol
3
−1
)
ꢀR/(cm ·mol
3
−1
)
ꢀη/(mPa·s)
x
1
x
2
0.8229 0.1591 0.91487
0.7708 0.2059 0.92100
0.6745 0.2924 0.93274
0.5842 0.3736 0.94410
0.4786 0.4684 0.95759
0.3908 0.5473 0.96915
0.2861 0.6413 0.98322
0.1894 0.7282 0.99650
0.1579 0.7565 1.00093
0.1037 0.8052 1.00869
0.0584 0.8459 1.01531
0.8998 0.0800 0.92341
0.7923 0.1658 0.95365
0.6933 0.2448 0.98058
0.5989 0.3201 1.00565
0.5020 0.3974 1.03076
0.3986 0.4799 1.05680
0.2957 0.5621 1.08203
0.2115 0.6293 1.10241
0.1551 0.6743 1.11582
0.1181 0.7038 1.12442
0.0632 0.7476 1.13728
0.8644 0.0953 0.95418
0.7989 0.1414 0.98104
0.6967 0.2132 1.02031
0.6021 0.2797 1.05423
0.4946 0.3553 1.09040
0.3973 0.4237 1.12109
0.2658 0.5162 1.15940
0.1954 0.5657 1.17895
0.1495 0.5980 1.19121
0.0992 0.6333 1.20462
0.0564 0.6634 1.21551
0.9051 0.0571 0.95250
0.8020 0.1191 1.00798
0.6956 0.1830 1.05877
0.6152 0.2314 1.09329
0.5057 0.2972 1.13624
0.3878 0.3681 1.17747
0.2880 0.4281 1.20914
0.1963 0.4832 1.23588
1.37267 0.523
1.37350 0.557
1.37505 0.658
1.37648 0.736
1.37821 0.869
1.37947 1.023
1.38111 1.252
1.38245 1.533
1.38289 1.636
1.38368 1.848
1.38431 2.09
1.37366 0.526
1.37747 0.681
1.38069 0.829
1.38357 1.006
1.38629 1.235
1.38911 1.585
1.39164 2.03
1.39369 2.49
1.39494 2.84
1.39573 3.11
1.39692 3.67
1.37746 0.656
1.38067 0.789
1.38523 1.026
1.38902 1.324
1.39273 1.727
1.39589 2.32
1.39955 3.24
1.40142 3.92
1.40254 4.39
1.40379 5.10
1.40487 5.74
1.37724 0.658
1.38384 0.890
1.38954 1.289
1.39325 1.684
1.39767 2.33
1.40168 3.28
1.40464 4.46
1.40716 5.71
−0.139
−0.166
−0.226
−0.281
−0.318
−0.344
−0.354
−0.347
−0.344
−0.340
−0.338
−0.203
−0.366
−0.456
−0.512
−0.540
−0.534
−0.496
−0.467
−0.440
−0.409
−0.379
−0.383
−0.510
−0.626
−0.671
−0.685
−0.660
−0.544
−0.490
−0.441
−0.417
−0.371
−0.411
−0.644
−0.766
−0.785
−0.781
−0.695
−0.600
−0.487
0.010
0.014
0.018
0.018
0.024
0.019
0.022
0.017
0.016
0.013
0.009
0.008
0.014
0.020
0.024
0.024
0.029
0.029
0.028
0.024
0.023
0.018
0.011
0.013
0.021
0.030
0.025
0.028
0.028
0.026
0.024
0.018
0.021
0.005
0.016
0.024
0.031
0.033
0.032
0.026
0.027
−0.908
−1.17
−1.61
−2.05
−2.52
−2.86
−3.23
−3.49
−3.57
−3.66
−3.68
−0.967
−1.96
−2.86
−3.69
−4.49
−5.25
−5.89
−6.33
−6.59
−6.71
−6.73
−1.85
−2.73
−4.06
−5.22
−6.46
−7.36
−8.46
−8.87
−9.11
−9.16
−9.19
−1.71
−3.58
−5.35
−6.60
−8.19
−9.65
−10.5
−11.1

J Solution Chem (2010) 39: 371–383
377
Table 3 (Continued)
ρ/(g·cm 3
−
)
nD
η/(mPa·s)
V
E
/(cm ·mol
3
−1
)
ꢀR/(cm ·mol
3
−1
)
ꢀη/(mPa·s)
x
1
x
2
0.1550 0.5080 1.24741
0.1007 0.5407 1.26179
0.0452 0.5740 1.27602
0.8911 0.0549 0.97594
0.8023 0.0997 1.03210
0.7070 0.1477 1.08484
0.6042 0.1995 1.13394
0.5100 0.2470 1.17366
0.3928 0.3062 1.21653
0.2940 0.3560 1.24889
0.1983 0.4042 1.27698
0.1490 0.4291 1.29041
0.0982 0.4547 1.30379
0.0511 0.4784 1.31560
0.8887 0.0450 0.99331
0.7818 0.0882 1.06887
0.6908 0.1250 1.12240
0.6032 0.1604 1.16644
0.5106 0.1978 1.20697
0.3940 0.2449 1.25121
0.2933 0.2857 1.28394
0.1993 0.3236 1.31091
0.1470 0.3448 1.32471
0.0940 0.3662 1.33771
0.0516 0.3833 1.34781
0.9014 0.0299 0.99689
0.7971 0.0615 1.08085
0.6947 0.0925 1.14643
0.6116 0.1177 1.19054
0.5201 0.1455 1.23230
0.3920 0.1843 1.28078
0.2974 0.2130 1.31101
0.1969 0.2434 1.33919
0.1391 0.2609 1.35387
0.0996 0.2729 1.36310
0.0538 0.2868 1.37337
0.8938 0.0216 1.01732
0.8009 0.0405 1.09794
0.6895 0.0632 1.17271
0.6181 0.0777 1.21184
0.5164 0.0984 1.25861
0.3937 0.1234 1.30458
0.3101 0.1404 1.33112
1.40828 6.45
1.40964 7.42
1.41103 8.70
1.38007 0.714
1.38669 1.050
1.39240 1.521
1.39750 2.19
1.40148 3.05
1.40559 4.40
1.40868 5.97
1.41143 7.96
1.41250 9.07
1.41382 10.36
1.41483 11.87
1.38220 0.803
1.39076 1.308
1.39648 1.976
1.40099 2.80
1.40493 3.97
1.40914 5.82
1.41219 8.02
1.41472 10.53
1.41595 12.41
1.41715 14.33
1.41803 16.14
1.38256 0.806
1.39207 1.440
1.39898 2.35
1.40338 3.32
1.40750 4.81
1.41215 7.60
1.41499 10.46
1.41759 14.03
1.41892 16.65
1.41973 18.50
1.42067 21.0
−0.449
−0.370
−0.303
−0.522
−0.731
−0.870
−0.886
−0.863
−0.716
−0.616
−0.483
−0.408
−0.354
−0.299
−0.628
−0.890
−0.975
−0.951
−0.886
−0.807
−0.663
−0.505
−0.413
−0.297
−0.236
−0.653
−0.950
−1.037
−1.009
−0.959
−0.790
−0.632
−0.468
−0.385
−0.289
−0.195
−0.753
−1.029
−1.098
−1.091
−0.992
−0.812
−0.693
0.027
0.030
0.034
0.011
0.027
0.023
0.027
0.026
0.030
0.028
0.037
0.022
0.025
0.013
0.014
0.022
0.027
0.035
0.033
0.021
0.018
0.021
0.016
0.021
0.013
0.011
0.021
0.025
0.026
0.025
0.028
0.030
0.026
0.019
0.019
0.019
0.020
0.020
0.029
0.031
0.032
0.028
0.020
−11.2
−11.4
−11.2
−2.46
−4.36
−6.30
−8.23
−9.74
−11.4
−12.3
−12.7
−12.8
−12.9
−12.5
−2.99
−5.71
−7.79
−9.61
−11.2
−12.9
−13.8
−14.1
−13.8
−13.5
−12.9
−3.09
−6.13
−8.83
−10.8
−12.5
−14.2
−14.7
−14.7
−14.1
−13.6
−12.7
−3.71
−6.77
−10.0
−11.7
−13.7
−15.2
−15.1
1.38506 0.982
1.39395 1.644
1.40177 2.89
1.40572 4.09
1.41025 6.16
1.41456 9.59
1.41701 13.03

378
J Solution Chem (2010) 39: 371–383
Table 3 (Continued)
ρ/(g·cm 3
−
)
nD
η/(mPa·s)
V
E
/(cm ·mol
3
−1
)
ꢀR/(cm ·mol
3
−1
)
ꢀη/(mPa·s)
x
1
x
2
0.1949 0.1639 1.36246
0.1475 0.1735 1.37385
0.0957 0.1841 1.38555
0.0430 0.1948 1.39676
0.9023 0.0086 1.02310
0.8040 0.0173 1.11632
0.7051 0.0260 1.18725
0.6029 0.0350 1.24412
0.5210 0.0422 1.28137
0.3936 0.0534 1.32830
0.2942 0.0622 1.35831
0.2189 0.0688 1.37811
0.1444 0.0754 1.39536
0.1168 0.0778 1.40132
0.0753 0.0815 1.40977
1.41985 18.29
1.42088 21.3
1.42201 24.4
1.42298 28.1
1.38572 0.967
1.39611 1.818
1.40335 3.29
1.40891 5.36
1.41256 7.65
1.41692 12.87
1.41973 17.63
1.42149 22.5
1.42310 28.1
1.42362 30.1
1.42438 34.1
−0.487
−0.383
−0.278
−0.184
−0.789
−1.079
−1.161
−1.098
−1.011
−0.789
−0.610
−0.485
−0.313
−0.255
−0.148
0.010
0.009
0.015
0.005
0.019
0.035
0.031
0.029
0.034
0.030
0.030
0.016
0.021
0.017
0.018
−14.5
−13.4
−12.3
−10.8
−3.94
−7.60
−10.7
−13.3
−14.8
−15.4
−15.2
−13.8
−11.6
−10.8
−8.77
chain length decreases the density of the pure ionic liquid and their mixtures while the
dynamic viscosity increases.
For excess properties, the same qualitative behavior has been found for both ILs. The
binary system ethyl acetate + [C4min][NTF2] has slightly more negative excess molar vol-
umes than the ethyl acetate + [C8min][NTF2] system. The same type of behavior occurs for
mixtures with ethanol, raising in this case the S-shape found for ethanol + [C8min][NTF2]
mixtures (Fig. 1). Comparing the viscosity changes from mixing, both binary systems with
[C4min][NTF2] have considerably less negative values for this property than those for mix-
tures with [C8min][NTF2]. The same type of behavior was observed in previous studies
carried out by other authors [14, 15] concerning the effect of the alkyl chain of the IL on the
physico-chemistry properties of their mixtures.
For the ethyl acetate + ethanol + [C4min][NTF2] ternary system, Figs. 2, 3 and 4 show
the density, refractive index and dynamic viscosity isolines, respectively; whereas Figs. 5
and 6 show the isolines for excess molar volume and viscosity changes of mixing, respec-
tively. The ethyl acetate + ethanol + [C4mim][NTF2] ternary system exhibits relatively
large and negative excess molar volumes over the entire range of homogeneous mixtures.
3
−1
They reach a minimum value of around −1.2 cm ·mol , which corresponds to that of
the binary ethyl acetate + [C4mim][NTF2] system. The viscosity changes from mixing are
negative with a minimum value around −16 mPa·s corresponding to the ethyl acetate +
[
C4mim][NTF2] binary system. Regarding molar refraction changes from mixing for the
studied systems, it is difficult to draw a real conclusion due to their small values. The quali-
tative behavior is exactly the same as was found for ternary mixtures with [C8mim][NTF2].
4
Correlation of Physico-chemical Properties
E
Calculated values of the excess molar volumes V , and viscosity ꢀη and molar refraction
R changes from mixing, were correlated with the composition data using the Redlich-
ꢀ

J Solution Chem (2010) 39: 371–383
379
Fig. 1 Experimental excess molar volume and dynamic viscosity changes from mixing for: F, ethanol (1)
[C mim][NTF ] (2); Q, ethanol (1) + [C mim][NTF ] (2); E, ethyl acetate (1) + [C mim][NTF ] (2);
+
4
2
8
2
4
2
P, ethyl acetate (1) + [C mim][NTF ] (2) binary mixtures at 298.15 K and atmospheric pressure. The lines
8
2
correspond to the Redlich-Kister correlations
Kister polynomial [16]. For binary mixtures the equation is
ꢀ
k
Qij = xixj
Ak(xi − xj )
(6)
k
E
where Qij represents V , ꢀη or ꢀR; xi is the mole fraction of component i; Ak is the poly-
nomial coefficient; and k is the number of the polynomial coefficient. For ternary systems
the corresponding equation is
ꢃ
ꢄ
A + B(x1 − x2) + C(x2 − x3) + D(x1 − x3)+
Q123 = Q12 + Q23 + Q13 + x1x2x3
2
2
2
E(x1 − x2) + F(x2 − x3) + G(x1 − x3) + ···
(7)
E
where Q123 represents V , ꢀη or ꢀR for the ternary system and Qij is the corresponding
Redlich-Kister polynomial for the same property fitted to the binary systems data.

380
J Solution Chem (2010) 39: 371–383
−
3
)
Fig. 2 Density ρ (g·cm
isolines for ethyl acetate (1) +
ethanol (2) +
[
C mim][NTF ] (3) mixtures at
4 2
298.15 K and atmospheric
pressure
Fig. 3 Refractive index nD
isolines for ethyl acetate (1) +
ethanol (2) +
[
C mim][NTF ] (3) mixtures at
4 2
298.15 K and atmospheric
pressure
Tables 4 and 5 show the Redlich-Kister coefficients for the binary and ternary systems
and the standard deviations obtained in the correlations, respectively. The coefficients were
obtained by fitting the coefficients of Eqs. 6 and 7 by least-squares regression. Fisher’s F-
test was used to define the appropriate polynomial degree.
5
Conclusions
In the present work, new experimental densities, refractive indices, and dynamic viscosities
were determined for ethyl acetate + ethanol + [C4mim][NTF2] ternary mixtures and for

J Solution Chem (2010) 39: 371–383
381
Fig. 4 Dynamic viscosity
η (mPa·s) isolines for ethyl
acetate (1) + ethanol (2) +
[
C mim][NTF ] (3) mixtures at
4 2
298.15 K and atmospheric
pressure
Fig. 5 Excess molar volume
3
−1
(
cm ·mol ) isolines for ethyl
acetate (1) + ethanol (2) +
[
C mim][NTF ] (3) mixtures at
4 2
298.15 K and atmospheric
pressure
the corresponding binary mixtures containing [C4mim][NTF2] at 298.15 K and atmospheric
E
pressure. The excess molar volumes V , and viscosity ꢀη and molar refraction ꢀR changes
of mixing, were calculated for the binary and ternary systems.
These properties were compared with previously obtained data for an imidazolium ionic
liquid with a longer alkyl chain length and the same anion ([C8mim][NTF2]). Increasing
the alkyl chain length causes the density of the ionic liquid and their mixtures to decrease,
and the excess molar volumes become slightly less negative. For the dynamic viscosity, in-
creasing the alkyl chain length of the imidazolium ionic liquid causes the dynamic viscosity
to increase dramatically, which is reflected in the higher negative values of the viscosity
changes of mixing.

382
J Solution Chem (2010) 39: 371–383
Fig. 6 Viscosity change of
mixing ꢀη (mPa·s) isolines for
ethyl acetate (1) + ethanol (2) +
[
C mim][NTF ] (3) mixtures at
4 2
298.15 K and atmospheric
pressure
Table 4 Coefficients and standard deviations σ obtained using the Redlich-Kister polynomial, Eq. 6, to
E
correlate V , ꢀη and ꢀR for binary systems
Property
A
0
A
1
A
2
A
3
σ
{
x Ethyl acetate + (1 − x) [C mim][NTF ]}
4
2
E
3
−1
)
V
/(cm ·mol
−4.0707
0.1111
−2.8547
0.0565
16.520
−2.9027
−1.9981
0.007
0.003
0.12
3
−1
ꢀR/(cm ·mol
)
–
–
–
–
ꢀη/(mPa·s)
−62.457
{
−0.7022
0.0768
x Ethanol + (1 − x) [C mim][NTF ]}
4
2
E
3
−1
−1
V
/(cm ·mol
)
−1.0542
0.0312
12.739
−1.6765
−1.5478
0.013
0.002
0.10
3
ꢀ
R/(cm ·mol
η/(mPa·s)
)
–
–
–
–
ꢀ
−48.875
Table 5 Coefficients and standard deviations σ obtained using the Redlich-Kister polynomial, Eq. 7, to
E
correlate V , ꢀη and ꢀR for the ethyl acetate (1) + ethanol (2) + [C mim][NTF ] (3) ternary system
4
2
Property
A
B
C
D
E
F
G
σ
E
3
−1
)
V
/(cm ·mol
−5.7541
0.6573 −8.7791 −10.697
6.2955 −8.6410 −17.728 0.026
3
−1
ꢀR/(cm ·mol
)
0.0340 −0.1096
0.0152
5.8764
0.1956
1.2938
–
–
–
–
–
–
0.005
0.08
ꢀη/(mPa·s)
12.258
11.908
The Redlich-Kister equation was successfully applied to the correlation of excess prop-
erties of the studied binary and ternary systems.
Acknowledgements The authors are grateful to the Universidad de Santiago de Compostela, Ministerio
de Educación y Ciencia (Spain) (Project CTQ2006-07687/PPQ), CONICET, Universidad Nacional del Sur
(Argentine), and the European Union (project ALFA II-0400-FA) for financial support.

J Solution Chem (2010) 39: 371–383
383
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