Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Phase Behavior of Imidazolium-Based Ionic Liquid + PhosphoniumBased Ionic Liquid Mixtures with a Common Anion: Effects of the Alkyl-Chain Length of Cation Takuya Shimomura* and Masakazu Sugiyama Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido 050-8585, Japan S Supporting Information *
ABSTRACT: The phase behavior of imidazolium-based ionic liquid (IL) + phosphonium-based IL binary mixtures with a common anion has been investigated in the temperature range 253−453 K. Bis(trifluoromethanesulfonyl)amide ([NTf2]−) and tetrafluoroborate ([BF4]−) were selected as common anions. The imidazolium-based IL + phosphonium-based IL mixtures with a common anion showed an upper critical solution temperature (UCST). The phase separation temperatures of the mixtures decreased with increasing alkyl-chain length of the imidazolium cation. In contrast, the phase separation temperatures of the mixtures increased as the alkyl-chain length of the phosphonium cation increased. The phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with [BF4]− as a common anion were remarkably higher than those with [NTf2]−.
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with increasing quadrupole moment of fluorinated benzene derivative.6,7 Recently, IL + IL mixtures have been proposed as a method to adjust the properties of ILs. Therefore, many researchers have reported on the properties of IL + IL mixtures, such as excess molar volume,8−11 surface tension,12 and viscosity.8,10,13 In addition, some IL + IL mixtures have been used in liquid− liquid extraction,14,15 chemical reaction,16 and CO2 separation.8 Several studies have been reported on the phase separation of IL + IL mixtures. Arce et al. have found that [C2mim][NTf2] is immiscible with trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)amide ([P66614][NTf2]), although the [C2mim][NTf2] + [P66614][NTf2] mixture includes [NTf2]− as a common anion.17,18 The same tendency was observed for N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([C3mpyr][NTf2]) + [P66614][NTf2],19 1-ethyl-3-methylimidazolium acetate ([C2mim][ O A c ] ) + [ P 6 6 6 1 4 ] [ O A c ] , 2 0 a n d c h o l i n i um bi s (trifluoromethylsulfonyl)amide ([Chol][NTf 2 ]) + [P66614][NTf2].21 In contrast to [C2mim][NTf2], 1-butyl-3methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim][NTf2]) is totally miscible with [P66614][NTf2].17,18 This suggests that the phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with a common anion decrease with increasing alkyl-chain length of the imidazolium cation. Omar et al. have predicted the phase behavior of more than 200 IL + IL mixtures using the
INTRODUCTION In order to develop applications of ionic liquids (ILs) as new solvents in many fields, such as organic synthesis, catalysis, and separation, a number of investigations have been reported on the phase behavior of IL + molecular liquid (ML) mixtures. For example, Crosthwaite et al. studied the phase behavior of imidazolium-based IL + alcohol mixtures.1,2 Imidazolium-based IL + alcohol mixtures exhibit upper critical solution temperatures (UCSTs). The phase separation temperatures of imidazolium-based IL + alcohol mixtures decrease with increasing alkyl-chain length of the imidazolium cation. Moreover, they have reported that the choice of anion remarkably affects the phase behavior of imidazolium-based IL + alcohol mixtures; the phase separation temperatures of the mixtures decrease in the order of dicyanamide ([(CN)2N]−) > trifluoromethanesulfonate ([CF3SO3]−) > bis(trifluoromethanesulfonyl)amide ([NTf2]−) > tetrafluoroborate ([BF4]−) > hexafluorophosphate ([PF6]−). Shao et al. have precisely investigated the phase behavior of imidazolium-based IL + alcohol mixtures.3 The phase separation temperatures of the mixtures decrease with increasing alkyl-chain length of alcohol. For other mixtures, Shiflett et al. have reported that the phase separation temperatures of imidazolium-based IL mixtures of benzene derivatives with alkyl substituent increase with increasing alkyl-chain length of benzene derivatives, i.e., propylbenzene > ethylbenzene > toluene > benzene.4,5 The phase behavior of imidazolium-based IL + fluorinated benzene mixtures has also been reported. The miscibility of fluorinated benzene derivatives with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]) increases © XXXX American Chemical Society
Received: September 9, 2017 Accepted: December 26, 2017
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DOI: 10.1021/acs.jced.7b00808 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 1. Name, Abbreviation, and Purity of ILs Used in the Present Investigation IL name
CAS no.
abbreviation
source
purity (mol %)
analysis method
1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)amide 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide 1-methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)amide tributyldodecylphosphonium bis(trifluoromethanesulfonyl)amide tributyltetradecylphosphonium bis(trifluoromethanesulfonyl)amide tributylhexadecylphosphonium bis(trifluoromethanesulfonyl)amide trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)amide 1-ethyl-3-methylimidazolium tetrafluoroborate 1-methyl-3-propylimidazolium tetrafluoroborate tributyldodecylphosphoniumtetrafluoroborate tributylhexadecylphosphonium tetrafluoroborate
174899-81-1 174899-82-2 216299-72-8 1002754-39-3 855788-71-5 1002754-40-6 460092-03-9 143314-16-3 244193-48-4 638989-30-7 638989-29-4
[C1mim][NTf2] [C2mim][NTf2] [C3mim][NTf2] [P44412][NTf2] [P44414][NTf2] [P44416][NTf2] [P66614][NTf2] [C2mim][BF4] [C3mim][BF4] [P44412][BF4] [P44416][BF4]
synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized synthesized
>99 >99 >99 >98 >98 >98 >98 >98 >98 >98 >98
NMR NMR NMR NMR NMR NMR NMR NMR NMR NMR NMR
COSMO-RS method.22 It was found that combinations of two ILs with remarkable differences in their constituent ions give rise to phase separation of IL + IL mixtures. In contrast to ML + ML and IL + ML mixtures, the separated IL + IL mixtures can generate the liquid−liquid interface composed only of ions. One can possibly expect that chemical reactions at the liquid− liquid interface composed only of ions are different from those at the liquid−liquid interface composed only of molecules. To promote application of IL + IL mixtures in many fields, such as liquid−liquid interface reactions, it is very important to investigate the phase behavior of IL + IL mixtures. However, a small number of papers on the phase behavior of IL + IL mixtures are available compared to the much larger number for ML + ML and IL + ML mixtures. Therefore, the effects of the structures of cation and anion on the phase behavior of IL + IL mixtures are still unclear. In the present investigation, the phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with a common anion were measured. We chose three imidazolium cations {1,3-dimethylimidazolium ([C1mim]+), [C2mim]+, 1-propyl-3-methylimidazolium ([C3mim]+)} and four phosphonium cations {tributyldodecylphosphonium ([P44412]+), tributyltetradecylphosphonium ([P44414]+), tributylhexadecylphosphonium ([P44416]+), [P66614]+} because the effects of the alkyl-chain length of the imidazolium and phosphonium cations on the phase behavior of the imidazolium-based IL + phosphonium-based IL mixtures with a common anion are still unclear. Moreover, [NTf2]− and [BF4]− were chosen as common anions to clarify the effect of a common anion on the phase behavior of the mixtures.
residues were no longer detected by AgNO3. All of the ILs used in the present investigation were dried under a vacuum at 333 K for at least 72 h. The purities of ILs synthesized were estimated by 1H NMR (JEOL, JNM-ECA500) spectra of each IL. The 1H NMR spectra of ILs are summarized in the Supporting Information. The name, abbreviation, and purity of ILs used in the present investigation are summarized in Table 1. The structures of cations and anions are illustrated in Figure 1.
Figure 1. Structures of cations and anions used in the present investigation.
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Sample Preparation. Imidazolium-based IL + phosphonium-based IL mixtures with sizes of about 5 g at given mole fractions of imidazolium-based IL (x1) were prepared in a glass vial under a dry nitrogen atmosphere. The x1 of imidazoliumbased IL + phosphonium-based IL mixtures prepared is summarized in Tables 2 and 3, respectively. The uncertainty of the mole fraction x1 is u(x1) = 2.0 × 10−4. Measurement of Phase Separation Temperature. The prepared imidazolium-based IL + phosphonium-based IL mixture in a glass vial was immersed in a water or oil bath at given temperatures. The sample temperature was kept within ±0.2 K with a Pt-100 thermometer (accuracy = ±0.1 K). The phase separation temperatures were determined visually in a water (253−353 K) or oil (353−453 K) bath. By visual determinations, the expanded uncertainty (k = 2) of the phase separation temperatures is U(T) = 1.0 K.
EXPERIMENTAL SECTION Materials. [C1mim][NTf2], [C2mim][NTf2], and [C3mim][NTf2] were synthesized with the conventional method previously reported.23 [C2mim][BF4] and [C3mim][BF4] were synthesized and purified using an anion metathesis method reported by K. Takao et al.24 The phosphonium-based ILs ([P44412][NTf2], [P44414][NTf2], [P44416][NTf2], [P66614][NTf2], [P44412][BF4], and [P44416][BF4]) were synthesized using a metathetic reaction between phosphonium halides {[P44412]Br (Tokyo Chemical Industry, 98%), [P44414]Cl (Kanto Chemical, 95%), [P44416]Br (Tokyo Chemical Industry, 98%), [P66614]Cl (Kanto Chemical, 95%)} and lithium bis(trifluoromethanesulfonyl)amide (Li[NTf2], Kanto Chemical, 99%) or sodium tetrafluoroborate (Na[BF4], Kanto Chemical, 98%). The synthesized ILs, except for [C2mim][BF4] and [C3mim][BF4], were washed with water until halide B
DOI: 10.1021/acs.jced.7b00808 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 2. Phase Separation Temperatures of Imidazolium-Based IL + Phosphonium-Based IL Mixtures with [NTf2]− at Various Imidazolium-Based IL x1 and Pressure p = 0.1 MPaa x1
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[C1mim][NTf2] + [P44412][NTf2] 0.5006 0.5498 0.5998 0.6501 0.7004 0.7500 0.7997 0.8501 0.9005 0.9191 0.9301 0.9401 0.9501 [C1mim][NTf2] + [P44414][NTf2] 0.4002 0.4494 0.4998 0.5499 0.6004 0.6510 0.6999 0.7500 0.8001 0.8499 0.9001 0.9199 0.9402 0.9602 0.9700 0.9800 [C1mim][NTf2] + [P44416][NTf2] 0.3500 0.3764 0.3993 0.4253 0.4505 0.4996 0.5496 0.5999 0.6518 0.7006 0.7507 0.7998 0.8505 0.9012 0.9200 0.9402 0.9602 0.9800 0.9850 0.9900 0.9925
x1
T (K)
[C1mim][NTf2] 0.2005 0.2259 0.2505 0.2755 0.2999 0.3999 0.4999 0.6000 0.6247 0.9370 0.9500 0.9900 0.9925 0.9950 [C2mim][NTf2] 0.6003 0.6500 0.7007 0.7510 0.8002 0.8503 0.9002 0.9501 0.9701 [C2mim][NTf2] 0.2999 0.4001 0.4990 0.5992 0.7047 0.8046 0.9000 0.9200 0.9503 0.9712 [C3mim][NTf2] 0.4495 0.4998 0.5498 0.5934 0.6501 0.7002 0.7497 0.8001 0.8500 0.9007 0.9250 0.9500 0.9700
271.1 280.5 286.8 291.6 293.8 295.6 295.7 296.0 292.1 289.8 286.3 282.6 277.2 282.4 298.4 310.7 319.5 326.7 331.7 334.8 337.3 337.5 337.8 335.3 332.3 326.7 313.5 303.9 288.6 298.2 310.0 319.4 326.4 333.6 346.0 356.3 365.9 371.5 376.3 377.7 379.5 379.6 379.8 374.7 369.8 360.3 329.4 317.3 300.4 288.3
T (K) + [P66614][NTf2] 284.5 304.5 322.0 336.2 352.5 395.5 423.3 443.4 447.5 440.2 430.7 346.2 331.2 309.5 + [P44416][NTf2] 294.1 300.7 305.1 307.8 309.5 310.8 311.2 304.8 293.1 + [P66614][NTf2] 284.6 335.3 362.2 379.8 389.5 392.3 387.7 383.6 370.3 344.3 + [P66614][NTf2] 270.8 285.1 301.8 309.0 316.2 320.3 322.1 323.4 323.0 318.8 313.4 299.8 277.0
Standard uncertainties are u(x1) = 2.0 × 10−4, u(p) = 0.005 MPa. Expanded uncertainty for the phase separation temperatures U(T) = 1.0 K (0.95 level of confidence). a
RESULTS AND DISCUSSION The phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with [NTf2]− or [BF4]− as a common anion are summarized in Tables 2 and 3, and plotted as a function of imidazolium-based IL mole fraction x1 in
Figures 2 and 3. All of the mixtures that cause phase separation show an upper critical solution temperature (UCST). In Figure 2b, the phase separation temperatures of the [C2mim][NTf2] + [P66614][NTf2] mixture are compared with the literature data determined by the NMR method.17 The present data below x1 C
DOI: 10.1021/acs.jced.7b00808 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 3. Phase Separation Temperatures of ImidazoliumBased IL + Phosphonium-Based IL Mixtures with [BF4]− at Various Imidazolium-Based IL x1 and Pressure p = 0.1 MPaa x1
T (K) [C2mim][BF4] + [P44412][BF4]
0.2018 0.2998 0.4000 0.9752 0.9850 0.9900
338.7 400.4 443.8 430.6 398.9 370.1 [C2mim][BF4] + [P44416][BF4]
0.1490 0.2000 0.2498 0.9950
344.0 391.7 442.1 429.6 [C3mim][BF4] + [P44412][BF4]
0.3963 0.5000 0.6000 0.7022 0.7924 0.9022 0.9705 0.9895
335.9 366.6 385.1 392.9 395.8 391.9 346.0 287.5 [C3mim][BF4] + [P44416][BF4]
0.2988 0.4003 0.9900
361.3 415.5 394.1
Standard uncertainties are u(x1) = 2.0 × 10−4, u(p) = 0.005 MPa. Expanded uncertainty for the phase separation temperatures U(T) = 1.0 K (0.95 level of confidence). a
≈ 0.8 are in good agreement with the literature data, whereas those above x1 ≈ 0.8 are not. Probably, the accuracy of the NMR method is lower than that of the visual determination method. This is because the integral intensity of the 1H peaks of the phosphonium cation is significantly lower than that of the imidazolium cation at higher x1. As a result, the phase separation temperatures of the [C2mim][NTf2] + [P66614][NTf2] mixture in the literature data above x1 ≈ 0.8 have been underestimated compared with those of the present data. As shown in Figure 2a, [C1mim][NTf2] is immiscible with four phosphonium-based ILs with [NTf 2 ] − . However, [C2mim][NTf2] is totally miscible with [P44412][NTf2] and [P44414][NTf2] in the temperature range examined. Moreover, [C3mim][NTf2] is only immiscible with [P66614][NTf2]. These results show that the phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with [NTf2]− decrease with increasing alkyl-chain length of the imidazolium cation. The same tendency is observed for the imidazolium-based IL + phosphonium-based IL mixtures with [BF4]−, as shown in Figure 3. This tendency is consistent with the previous investigation;17 Arce et al. have reported that [C2 mim][NTf2] is immiscible with [P66614][NTf2] but [C4mim][NTf2] is totally miscible with [P66614][NTf2]. Probably, the hydrophobicity of the imidazolium-based ILs is lower than that of the phosphonium-based ILs. As the alkylchain length of the imidazolium cation increases, the hydrophobicity of the imidazolium-based ILs increases. This leads to the increase in the miscibility of the imidazolium-based ILs with the phosphonium-based ILs, resulting in the decrease in the
Figure 2. Phase diagrams for imidazolium-based IL + phosphoniumbased IL mixtures with [NTf2]−: (a) [C1mim][NTf2] + [P44412][NTf2] (red circles), [C1mim][NTf2] + [P44414][NTf2] (red triangles), [C1mim][NTf2] + [P44416][NTf2] (red squares), [C1mim][NTf2] + [P66614][NTf2] (red diamonds); (b) [C2mim][NTf2] + [P44416][NTf2] (blue squares), [C2mim][NTf2] + [P66614][NTf2] (blue diamonds, this work), [C2mim][NTf2] + [P66614][NTf2] (black diamonds, ref 17); (c) [C3mim][NTf2] + [P66614][NTf2] (green diamonds). The solid lines are regressed by eq 1.
phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with increasing alkyl-chain length of the imidazolium cation. In contrast, the phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with a common anion rise as the alkyl-chain length of the phosphonium cation increases, as shown in Tables 2 and 3 and Figures 2 and 3. The hydrophobicity of the phosphonium cation increases with increasing alkyl-chain length of the phosphonium cation. Therefore, the miscibility of the phosphonium-based ILs with the imidazolium-based ILs decreases with increasing alkyl-chain D
DOI: 10.1021/acs.jced.7b00808 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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T = Tc −
|x1 − xc|3 B3 ± 3A |x1 − xc|2 ± 3CB|x1 − xc|
(1)
where A, B, and C show the linear coefficient of the diameter, the width of the phase diagram, and the coefficient of the nonlinear contribution of the diameter, respectively. xc represents critical imidazolium-based IL mole fractions. Equation 1 is derived as approximations to the scaling equations for systems with Ising-critical behavior.3,25−27 The plots are given in Figures 2 and 3 as the solid lines. A, B, C, Tc, and xc with the standard errors and the average relative deviations of the fits (ARDs) are summarized in Table 4. The data for the [C1mim][NTf2] + [P66614][NTf2] and [C2mim][BF4] + [P44412][BF4] mixtures are approximate values because the phase separation temperatures of these mixtures above 453 K could not be determined; therefore, these data are marked by a star. To elucidate the dependence of the alkyl-chain length of the cations on the Tc values for the imidazolium-based IL + phosphonium-based IL mixtures, the Tc values for the mixtures with [NTf2]− are depicted against the number of alkyl carbons of the phosphonium and imidazolium cations in Figures 4 and
Figure 3. Phase diagrams for imidazolium-based IL + phosphoniumbased IL mixtures with [BF4]−: (a) [C2mim][BF4] + [P44412][BF4] (open blue circles), [C2mim][BF4] + [P44416][BF4] (open blue squares); (b) [C3mim][BF4] + [P44412][BF4] (open green circles), [C3mim][BF4] + [P44416][BF4] (open green squares). The solid lines are regressed by eq 1.
length of the phosphonium cation. This results in the rise in the phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with increasing alkyl-chain length of the phosphonium cation. To obtain the critical temperature (UCST) Tc for the imidazolium-based IL + phosphonium-based IL mixtures, the phase separation temperatures of the mixtures, except those of the [C2mim][BF4] + [P44416][BF4] and [C3mim][BF4] + [P44416][BF4] mixtures, were fitted by eq 1
Figure 4. Critical temperature, Tc, for imidazolium-based IL + phosphonium-based IL mixtures with [NTf2]− against the number of alkyl carbons of the phosphonium cation: [C1mim][NTf2] + phosphonium-based IL (red symbols), [C2mim][NTf2] + phosphonium-based IL (blue symbols), [C3mim][NTf2] + phosphonium-based IL (green symbol). The solid line indicates the result of fit by a linear equation.
Table 4. Coefficients, Critical Temperature (UCST) Tc, and Critical Imidazolium-Based IL Mole Fractions xc of the Fits for eq 1 for Imidazolium-Based IL + Phosphonium-Based IL Mixtures with a Common Anion mixture [C1mim][NTf2] + [P44412][NTf2] [C1mim][NTf2] + [P44414][NTf2] [C1mim][NTf2] + [P44416][NTf2] [C1mim][NTf2] + [P66614][NTf2]b [C2mim][NTf2] + [P44416][NTf2] [C2mim][NTf2] + [P66614][NTf2] [C3mim][NTf2] + [P66614][NTf2] [C2mim][BF4] + [P44412][BF4]b [C3mim][BF4] + [P44412][BF4] a
A (K−1) −0.00080 −0.00044 −0.00002 −0.00066 0.00091 −0.00086 −0.00034 −0.00074 −0.00023
Average relative deviation (ARD), ARD =
± ± ± ± ± ± ± ± ±
0.00055 0.00019 0.00016 0.00010 0.00153 0.00022 0.00035 0.00051 0.00023
B (K−1/3) 0.08040 0.07810 0.07306 0.07760 0.06983 0.07829 0.07098 0.07960 0.07459
± ± ± ± ± ± ± ± ±
0.00131 0.00086 0.00104 0.00103 0.00355 0.00146 0.00146 0.00564 0.00122
|(exp. value) − (calc. value)| 100 Σ , (no. of data) (exp. value)
C (K−2/3) 0.01174 0.01078 0.00930 0.01141 0.01032 0.01215 0.00855 0.01169 0.00916
± ± ± ± ± ± ± ± ±
0.00176 0.00076 0.00072 0.00059 0.00468 0.00118 0.00143 0.00290 0.00096
Tc (K) 295.7 337.4 379.4 452.9 310.5 390.7 322.9 494.0 395.5
± ± ± ± ± ± ± ± ±
0.2 0.3 0.5 1.0 0.4 0.7 0.5 8.7 0.4
ARDa of fit (%)
xc 0.806 0.814 0.825 0.811 0.861 0.811 0.809 0.800 0.804
± ± ± ± ± ± ± ± ±
0.002 0.002 0.002 0.002 0.005 0.004 0.003 0.005 0.001
0.072 0.137 0.225 0.285 0.115 0.202 0.174 0.138 0.078
where exp. value denotes experimental and calc. value denotes
b
calculated. Approximate values because the phase separation temperatures above 453 K could not be determined. E
DOI: 10.1021/acs.jced.7b00808 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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5, respectively. Figure 4 clearly shows that the Tc values increase with increasing alkyl-chain length of the phosphonium
Figure 6. Phase diagram for [C2mim][NTf2] + [P44416][NTf2] (solid blue squares) and [C2mim][BF4] + [P44416][BF4] (open blue squares) mixtures. The solid line is regressed by eq 1. Figure 5. Critical temperature, Tc, for imidazolium-based IL + phosphonium-based IL mixtures with [NTf2]− against the number of alkyl carbons of the imidazolium cation: imidazolium-based IL + [P44412][NTf2] (circle symbol), imidazolium-based IL + [P44414][NTf2] (triangle symbol), imidazolium-based IL + [P44416][NTf2] (square symbols), imidazolium-based IL + [P66614][NTf2] (diamond symbols). The solid line indicates the result of fit by a linear equation.
temperatures of the mixtures have been measured in the temperature range 253−453 K. All of the imidazolium-based IL + phosphonium-based IL mixtures with a common anion that cause phase separation showed an upper critical solution temperature (UCST). The phase separation temperatures of the mixtures decreased with increasing alkyl-chain length of the imidazolium cation. In contrast, as the alkyl-chain length of the phosphonium cation increased, the phase separation temperatures of the mixtures increased. The Tc values for the mixtures with [NTf2]− linearly increased with increasing alkyl-chain length of the phosphonium cation and decreased with increasing the alkyl-chain length of the imidazolium cation. This shows that the Tc values are linearly dependent on the alkyl-chain length of the imidazolium and phosphonium cations. The phase separation temperatures of the imidazolium-based IL + phosphonium-based IL mixtures with [BF4]− as a common anion were remarkably higher than those with [NTf2]−. In conclusion, the phase behavior of the imidazoliumbased IL + phosphonium-based IL mixtures with a common anion can be controlled by the change in the structure of the imidazolium and phosphonium cations and common anions.
cation. Interestingly, the Tc values for the [C1mim][NTf2] + phosphonium-based IL mixtures linearly increase. In fact, the Tc values for these mixtures can be well reproduced by a linear equation (the plot is given in Figure 4 as the solid line) with the correlation coefficient r2 = 0.999. On the other hand, Figure 5 shows that the Tc values decrease with increasing number of alkyl carbons of the imidazolium cation. The Tc values for the imidazolium-based IL + [P66614][NTf2] mixtures are also well reproduced by a linear equation with the correlation coefficient r2 = 0.999, showing that the Tc values linearly decrease with increasing alkyl-chain length of the imidazolium cation. These results show that the Tc values for the imidazolium-based IL + phosphonium-based IL mixtures with a common anion are proportional to the alkyl-chain length of the phosphonium cation and inversely proportional to the alkyl-chain length of the imidazolium cation. Figure 6 illustrates the phase diagram for the [C2mim][NTf2] + [P44416][NTf2] and [C2mim][BF4] + [P44416][BF4] mixtures to clarify the effect of a common anion on the phase behavior of the imidazolium-based IL + phosphonium-based IL mixtures with a common anion. The phase separation temperatures of the [C2mim][BF4] + [P44416][BF4] mixture are drastically higher than those of the [C2mim][NTf2] + [P44416][NTf2] mixture. This suggests that the imidazoliumbased IL + phosphonium-based IL mixtures with [BF4]− more easily cause phase separation than those with [NTf2]−. The same tendency is observed for other mixtures. For example, the [C3mim][BF4] + [P44412][BF4] mixture causes phase separation, whereas the [C3mim][NTf2] + [P44412][NTf2] mixture does not in the temperature range examined.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00808. The 1H NMR spectra of [C1mim][NTf2] (Figure S1), [C3mim][NTf2] (Figure S2), [P44412][NTf2] (Figure S3), [P44416][NTf2] (Figure S4), [P66614][NTf2] (Figure S5), and [C2mim][BF4] (Figure S6) (PDF)
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AUTHOR INFORMATION
Corresponding Author
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*E-mail:
[email protected].
CONCLUSION In order to elucidate the effect of the alkyl-chain length of the imidazolium and phosphonium cations on the phase behavior of the imidazolium-based ionic liquid (IL) + phosphoniumbased IL mixtures with a common anion, the phase separation
ORCID
Takuya Shimomura: 0000-0001-8544-9197 Notes
The authors declare no competing financial interest. F
DOI: 10.1021/acs.jced.7b00808 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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(20) Castro, M. C.; Arce, A.; Soto, A.; Rodríguez, H. Liquid-liquid equilibria of mutually immiscible ionic liquids with a common anion of basic character. J. Chem. Thermodyn. 2016, 102, 12−21. (21) Neves, C. M. S. S.; Silva, A. M. S.; Fernandes, A. M.; Coutinho, J. A. P.; Freire, M. G. Towards an understanding of the mechanisms behind the formation of liquid-liquid systems formed by two ionic liquids. J. Phys. Chem. Lett. 2017, 8, 3015−3019. (22) Omar, S.; Lemus, J.; Ruiz, E.; Ferro, V. R.; Ortega, J.; Palomar, J. Ionic Liquid Mixtures−An Analysis of Their Mutual Miscibility. J. Phys. Chem. B 2014, 118, 2442−2450. (23) Nockemann, P.; Binnemans, K.; Driesen, K. Purification of imidazolium ionic liquids for spectroscopic applications. Chem. Phys. Lett. 2005, 415, 131−136. (24) Takao, K.; Takao, S. Efficient and Versatile Anion Metathesis Reaction for Ionic Liquid Preparation by Using Conjugate Acid and Ortho Ester. Bull. Chem. Soc. Jpn. 2014, 87, 974−981. (25) Kim, Y. C.; Fisher, M. E.; Orkoulas, G. Asymmetric fluid Criticality I. Scaling with Pressure Mixing. Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top. 2003, 67, 061506. (26) Wang, J.; Cenderina, C. A.; Anisimov, M. A.; Sengers, J. V. Principle of Isomorphism and Complete Scaling for Binary-Fluid Criticality. Phys. Rev. E 2008, 77, 031127. (27) Schröer, W.; Vale, V. R. Liquid−liquid phase separation in solutions of ionic liquids: phase diagrams, corresponding state analysis and comparison with simulations of the primitive model. J. Phys.: Condens. Matter 2009, 21, 424119.
REFERENCES
(1) Crosthwaite, J. M.; Aki, S. N. V. K.; Maginn, E. J.; Brennecke, J. F. Liquid Phase Behavior of Imidazolium-Based Ionic Liquids with Alcohols. J. Phys. Chem. B 2004, 108, 5113−5119. (2) Crosthwaite, J. M.; Aki, S. N. V. K.; Maginn, E. J.; Brennecke, J. F. Liquid phase behavior of imidazolium-based ionic liquids with alcohols: effect of hydrogen bonding and non-polar interactions. Fluid Phase Equilib. 2005, 228−229, 303−309. (3) Shao, X.; Schröer, W.; Rathke, B. Liquid−Liquid Phase Behavior of Solutions of 1,3-Dimethylimidazolium- and 1-Methyl-3-propylimidazolium Bis((trifluoromethyl)sulphonyl)amide (C1,3mimNTf2) in nAlkyl Alcohols. J. Chem. Eng. Data 2014, 59, 225−233. (4) Yokozeki, A.; Shiflett, M. B. Binary and Ternary Phase Diagrams of Benzene, Hexafluorobenzene, and Ionic Liquid [emim][Tf2N] Using Equations of State. Ind. Eng. Chem. Res. 2008, 47, 8389−8395. (5) Shiflett, M. B.; Niehaus, A. M. S. Liquid-Liquid Equilibria in Binary Mixtures Containing Substituted Benzenes with Ionic Liquid 1Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide. J. Chem. Eng. Data 2010, 55, 346−353. (6) Blesic, M.; Lopes, J. N. C.; Padua, A. A. H.; Shimizu, K.; Gomes, M. F. C.; Rebelo, L. P. N. Phase Equilibria in Ionic Liquid-Aromatic Compound Mixtures, Including Benzene Fluorination Effects. J. Phys. Chem. B 2009, 113, 7631−7636. (7) Shimizu, K.; Gomes, M. F. C.; Padua, A. A. H.; Rebelo, L. P. N.; Lopes, J. N. C. On the Role of the Dipole and Quadrupole Moments of Aromatic Compounds in the Solvation by Ionic Liquids. J. Phys. Chem. B 2009, 113, 9894−9900. (8) Kanakubo, M.; Makino, T.; Umecky, T. CO2 solubility in and physical properties for ionic liquid mixtures of 1-butyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. J. Mol. Liq. 2016, 217, 112−119. (9) Canongia Lopes, J. N.; Cordeiro, T. C.; Esperancüa, J. M. S. S.; Guedes, H. J. R.; Huq, S.; Rebelo, L. P. N.; Seddon, K. R. Deviations from Ideality in Mixtures of Two Ionic Liquids Containing a Common Ion. J. Phys. Chem. B 2005, 109, 3519−3525. (10) Annat, G.; Forsyth, M.; MacFarlane, D. R. Ionic Liquid Mixtures−Variations in Physical Properties and Their Origins in Molecular Structure. J. Phys. Chem. B 2012, 116, 8251−8258. (11) Navia, P.; Troncoso, J.; Romaní, L. Excess Magnitudes for Ionic Liquid Binary Mixtures with a Common Ion. J. Chem. Eng. Data 2007, 52, 1369−1374. (12) Oliveira, M. B.; Domínguez-Pérez, M.; Cabeza, O.; Lopes-daSilva, J. A.; Freire, M. G.; Coutinho, J. A. P. Surface tensions of binary mixtures of ionic liquids with bis(trifluoromethylsulfonyl)imide as the common anion. J. Chem. Thermodyn. 2013, 64, 22−27. (13) Navia, P.; Troncoso, J.; Romaní, L. Viscosities for Ionic Liquid Binary Mixtures with a Common Ion. J. Solution Chem. 2008, 37, 677− 688. (14) Garcia, S.; Larriba, M.; Garcia, J.; Torrecilla, J. S.; Rodriguez, F. Liquid-Liquid Extraction of Toluene from n-Heptane using Binary Mixtures of N-Butylpyridinium Tetrafluoroborate and N-Butylpyridinium Bis(Trifluoromethylsulfonyl)Imide Ionic Liquids. Chem. Eng. J. 2012, 180, 210−215. (15) Potdar, S.; Anantharaj, R.; Banerjee, T. Aromatic Extraction using Mixed Ionic Liquids: Experiments and COSMO-RS Predictions. J. Chem. Eng. Data 2012, 57, 1026−1035. (16) Weber, C. C.; Masters, A. F.; Maschmeyer, T. Controlling Hydrolysis Reaction Rates with Binary Ionic Liquid Mixtures by Tuning Hydrogen-Bonding Interactions. J. Phys. Chem. B 2012, 116, 1858−1864. (17) Arce, A.; Earle, M. J.; Katdare, S. P.; Rodriguez, H.; Seddon, K. R. Phase equilibria of mixtures of mutually immiscible ionic liquids. Fluid Phase Equilib. 2007, 261, 427−433. (18) Arce, A.; Earle, M. J.; Katdare, S. P.; Rodriguez, H.; Seddon, K. R. Mutually immiscible ionic liquid. Chem. Commun. 2006, 2548− 2550. (19) Annat, G.; Forsyth, M.; MacFarlane, D. R. Ionic Liquid Mixtures − Variations in Physical Properties and Their Origins in Molecular Structure. J. Phys. Chem. B 2012, 116, 8251−8258. G
DOI: 10.1021/acs.jced.7b00808 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
