Comparing Composition- and Temperature-Dependent Excess Molar

Article pubs.acs.org/jced

Comparing Composition- and Temperature-Dependent Excess Molar Volumes of Binary Systems Involving Ionic Liquids Elise A. Cade, David R. Saeva, and Markus M. Hoffmann* The College at Brockport, State University of New York, 350 New Campus Drive, Brockport, New York 14420, United States S Supporting Information *

ABSTRACT: A total of 167 data sets of composition- and temperature-dependent excess molar volumes, VE, which are derived from density measurements, for ionic liquid−molecular solvent binary systems are inspected concerning their temperature dependence at fixed compositions. It is found that the VE temperature dependence is generally linear regardless of the sign and shape of the VE composition dependence. Plotting the slopes and intercepts of the linear VE temperature dependence as a function of composition allows for convenient comparisons of existing data sets. In doing so, VE data sets are critically examined with respect to data quality as well as obtaining insight into structure−property relationships. This study also includes new density measurements for the binary systems 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide−chloroform and 1-butyl-3-methylimidazolium methylsulfonate−water, measured in the respective temperature ranges of (288.15 and 318.15) K and (298.15 and 358.15) K.

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INTRODUCTION

EXPERIMENTAL SECTION The two new density data sets were obtained at ambient pressure with an Anton Paar DMA 4100 vibrating tube density meter to a precision of 0.0001 g·cm−3. The instrument controls the temperature with a Peltier system within 0.02 K and applies internally a viscosity compensation. The first and last density measurements of a temperature series were done at the same temperatures to ensure sample integrity during the temperature cycle. These densities agreed within 0.0001 g·cm−3, i.e., within the precision of the instrument. The CHCl3 (CAS Registry No. 67-66-3), 99.8 % purity, was obtained from Acros and contained < 0.8 % by volume ethanol as a stabilizer that was not removed. The deionized water used was purified by a Barnstead UV purification system. Both ILs were obtained from Iolitec to 99 % purity. [C6mim][NTf2] (CAS Registry No. 382150-50-7, batch no.: J0019.1.2. Inc.) was of clear and colorless appearance. Its water content was determined by Karl Fischer titration to be smaller than a mass fraction of 1.5·10−4. The [C4mim][MeSO3] (CAS Registry No. 342789-81-5, batch no. G00203.1.2) was at ambient conditions solid, consisting of slightly off-white crystals. The ILs and the CHCl3 were stored and solutions were prepared in an inert atmosphere glovebox using an analytical balance. Overall, the precision of the solution compositions is estimated to be ± 0.001 mole fraction units. To check that handling of the prepared sample for density measurements did not alter their composition, the solution compositions were

Ionic liquids (ILs) are generally defined as salts that are liquid below 100 °C.1 The interest in ILs has been very high as evidenced for example by nearly 7000 “hits” for the year 2013 when searching the concept “ionic liquids” in the SciFinder database. In many of these investigations the IL is in contact with a second or more components. For example, ILs are used as a medium for chemical synthesis,2 extraction,3 and supported liquid membranes.4 Therefore, there is a need not only for physical property data of neat ILs but also for binary systems with ILs. One of the most investigated physical property of binary systems with ILs is density. However, even here the number of studied systems is limited, in particular with regard to density studies covering a wide range of composition and temperature for binary systems where the IL is very soluble if not completely miscible with the second component. Since it is practically impossible to study every conceivable binary IL− molecular solvent system, it seems valuable to critically evaluate existing data sets. Since we have been studying such binary IL− molecular solvent systems to better understand their structural organization and dynamics,5−7 an additional motivation of this study was to hopefully discern any structure property trends while meta-analyzing and comparing existing data sets. We also include new density and excess molar volume data for the binary systems 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C6mim][NTf2])−trichloromethane (chloroform, CHCl3), and 1-butyl-3-methylimidazolium methanesulfonate ([C4mim][MeSO3])−water (H2O), which we previously investigated but, respectively, only for low IL concentrations or only at one temperature.5,8 © XXXX American Chemical Society

Received: January 16, 2014 Accepted: April 25, 2014

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dx.doi.org/10.1021/je500053c | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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combined temperature ranges of both experimental data sets. Finally, a universal fit to a composition- and temperaturedependent VE data set can be obtained by incorporating the linear VE(T) dependence into eq 3 to obtain eq 4,

confirmed after completion of density measurements by means of integrating resonances in the 1H NMR spectrum of the recovered samples.

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RESULTS AND DISCUSSION New Density Measurements and Data Analysis. The excess molar volume, VE, of a binary, in this case, IL−molecular solvent, system is defined as the difference between the real and the ideal molar volume of the mixture, where the ideal molar volume is the sum of the mole fraction weighted molar volumes of the neat IL, VIL, and molecular solvent, Vsolv, as shown in eq 1 ⎡ x M + xsolvMsolv ⎤ ⎡ x ILMIL x M ⎤ + solv solv ⎥ V E = ⎢ IL IL ⎥−⎢ ⎣ ⎦ ⎣⎢ ρIL ρ ρsolv ⎥⎦

n

VE =

where am,i and ab,i are the polynomial fit coefficients of slope and intercept, respectively, and T is the temperature. Fitting VE data with eq 4 is not entirely a new idea. Iglesias et al. used such an equation to fit the ρ(x,T) data themselves.42 The Domańska ́ group and the Martinez-Andreu group made the coefficients of the Redlich−Kister equation a function of temperature to obtain a universal fit of their VE data.29,43−45 Nevertheless, to the best of our knowledge, eq 4 has not been used to universally fit VE data of binary liquid systems, at least not for such systems containing ILs. Therefore, we tested the utility of eq 4 for a large number of existing data sets, which therefore, as a byproduct, also leads to a critical evaluation of their quality. We will illustrate the outlined data analysis with our two new unpublished data density sets, which are listed in Tables 1 and 2.

(1)

n i=0

(2)

Table 1. Densities in g·cm−3 at Ambient Pressure for the [C6mim][NTf2]−CHCl3 Binary Systema

where ai are the fit coefficients. Specifically, the overwhelming majority of the literature included in this report10−40 employs eq 2 or a closely related form thereof.41−46 However, inspecting the original work by Redlich and Kister, they use eq 2 for the purpose of eliminating inconsistent experimental results for log(γ1/γ2) data from vapor pressure measurements and for classifying binary systems based on which ai coefficients in eq 2 are zero. Such critical inspection of experimental data as outlined by Redlich and Kister is commonly not done in the case of VE data, and eq 2 is simply used as a fit equation. Therefore, using the simpler nth-order polynomial expression of eq 3 is in principle equally valid for fitting experimental compositiondependent VE data, as long as the number of needed fitting parameters is the same (or less) as we have previously observed.7

T/K

n

VE =

∑ aixILi i

(4)

i=1

In eq 1, x is the mole fraction, M the molar mass, and ρ is the density. It has become standard practice to fit compositiondependent VE data (as well as other thermodynamic excess quantities) with an nth-order polynomial expression as shown in eq 2 first proposed by Redlich and Kister,9 V E = x ILxsolv ∑ ai(x IL − xsolv )i

∑ (am,ixILi )T + ab ,ixILi

(3)

Typically, a carefully temperature-controlled vibrating tube density meter is used to obtain highly accurate and precise densities of liquid samples. In practice, the vibrating tube density meter is loaded with the binary solution and the density determined at several temperatures; i.e., ρ(T) data are measured for fixed xIL. Several authors have shown that such ρ(T) data at fixed compositions is nearly linear16,39 but should be fitted with a second-order polynomial since a statistical analysis showed a significant improvement of the fit, and a second-order polynomial would also avoid the thermal expansion coefficient becoming a constant.16 However, since VE are the difference of real and ideal molar volumes, these nonlinearities of the densities and thus molar volumes subtract themselves out, and as we will show, the temperature dependence of VE is generally linear. Because of the linearity of the VE(T) at fixed solution compositions, it would seem advisible to inspect the temperature dependence of VE data first to assess their quality rather than their composition dependence. Furthermore, by plotting the composition dependent slopes and intercepts of VE(T), it is possible to compare independently measured data sets of the same binary system even if their temperature ranges differ, assuming that nonlinearity of VE(T) is indeed negligible for the

xIL

288.15

298.15

308.15

318.15

1.000 1.000 0.906 0.805 0.707 0.651 0.580 0.492 0.418 0.266 0.186 0.090 0.000 0.000

1.3813b 1.3814 1.3850 1.3890 1.3944 1.3981 1.4022 1.4088 1.4181 1.4366 1.4496 1.4704 1.4908 1.4975c

1.3723b 1.3720 1.3754 1.3793 1.3845 1.3880 1.3919 1.3982 1.4070 1.4242 1.4361 1.4546 1.4719 1.4783c

1.3633b 1.3627 1.3659 1.3697 1.3747 1.3780 1.3817 1.3877 1.3959 1.4118 1.4226 1.4387 1.4528 1.4591c

1.3542b 1.3535 1.3566 1.3602 1.3649 1.3681 1.3716 1.3772 1.3849 1.3994 1.4090 1.4226 1.4335 1.4398c

a

The CHCl3 contained 0.8 % by volume ethanol as stabilizer. Standard uncertainties of densities and temperature are respectively 0.0001 g·cm−3 and 0.02 K. The standard uncertainty in xIL is 0.001. b From an equation recommended by Chirico et al.49 cFrom the interpolation of density data for pure CHCl3 by Clará et al.48

Tables 1 and 2 also contain density values from the literature for neat [C6mim][NTf2], CHCl3, and water.47−49 The accuracy of the new density data is confirmed with excellent agreement for pure water, and good agreement for pure [C6mim][NTf2] where the literature values was obtained by an equation recommended by the authors who carefully assessed the available density data in the literature.49 The densities for CHCl3 are slightly lower than the values interpolated from the results of a recent publication by Clará,48 reflecting the presence of the < 0.8 % ethanol. We note that the density values listed in Table 1 might be more helpful in practice because the alcohol stabilizer prevents the formation of phosgene and HCl, and CHCl3 would therefore be always used with a present stabilizer (most commonly ethanol) in practical applications. B



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Table 2. Densities in g·cm−3 at Ambient Pressure for the [C4mim][MeSO3]−H2O Binary Systema T/K xIL 0.000 0.000 0.025 0.050 0.075 0.100 0.148 0.199 0.251 0.298 0.346 0.441 1.000

298.15 b

0.9971 0.9971 1.0381 1.0684 1.0893 1.1045 1.1239 1.1371 1.1457 1.1513 1.1549 1.1606 1.1720c

313.15 b

0.9922 0.9922 1.0312 1.0597 1.0797 1.0935 1.1136 1.1268 1.1355 1.1412 1.1448 1.1506 1.1625c

323.15 b

0.9880 0.9881 1.0259 1.0536 1.0731 1.0876 1.1066 1.1199 1.1286 1.1344 1.1381 1.1440 1.1562c

333.15 b

0.9832 0.9832 1.0201 1.0471 1.0662 1.0805 1.0995 1.1129 1.1217 1.1276 1.1314 1.1373 1.1499c

343.15 b

0.9778 0.9778 1.0139 1.0403 1.0592 1.0733 1.0923 1.1057 1.1147 1.1207 1.1246 1.1307 1.1436c

358.15 0.9686b 0.9683 1.0039 1.0297 1.0482 1.0623 1.0812 1.0949 1.1041 1.1103 1.1144 1.1207 1.1343c

a Standard uncertainties of densities and temperature are respectively 0.0001 g·cm−3 and 0.02 K. The standard uncertainty in xIL is 0.001. bFrom ref 47. cEstimated from the group contribution method reported by Blesic et al.50

subtracted out, and the resulting VE values match up well with the VE values from CHCl3 solutions, as can be seen in Figure 1. For Figure 2, we included VE values for 358.15 K from our previous study.8 The densities of the neat components are needed to evaluate VE from solution densities, but [C4mim][MeSO3] is a solid at ambient conditions, as it melts at about 383 K. Fortunately, Blesic et al. have reported relationships from a group contribution method,50 which we used for estimating the densities of neat [C4mim][MeSO3] that are included in Table 2. VE data for the [C4mim][MeSO3]−H2O binary system for xIL greater than about 0.5 are not present in Table 1 and Figure 2 because these binary mixtures were solid at room temperature prohibiting solution density measurements. Next, we inspected the temperature dependence of the VE values at fixed compositions, shown in Figure 3 for the new

Figure 1. Excess molar volume, VE, at ambient pressure for the [C6mim][NTf2]−CHCl3 binary system as a function of IL mole fraction, xIL at ▽, 288.15 K; □, 298.15 K; ○, 308.15 K; and △, 318.15 K. Values from Scharf et al.5 were included for xIL ≤ 0.1. The solid lines are from eq 4 with parameters from Table 7 for data set S1.

Figure 2. Excess molar volume, VE, at ambient pressure for the [C4mim][MeSO3]−H2O binary system as a function of IL mole fraction, xIL at ▽, 313.15 K; ○, 323.15 K; □, 333.15 K; △, 343.15 K; and ◇, 358.15 K, taken from Stark et al.8 The solid lines are from eq 4 with parameters from Table 8 for data set S2.

Figure 3. Temperature dependence of VE at ambient pressure for the [C6mim][NTf2]−CHCl3 binary system for (a) xIL = ○, 0.906; +, 0.805; ×, 0.707; ▽, 0.651; ☆, 0.511, and ◇, 0.418; and for (b) xIL = △, 0.266 and ⬡, 0.186. The lines are linear least-squares fits.

The VE data evaluated with eq 1 from the entries in Tables 1 and 2 are plotted in Figure 1 for the [C6mim][NTf2]−CHCl3 binary system and in Figure 2 for the [C4mim][MeSO3]−H2O binary system. For Figure 1 we included data at low concentrations (xIL ≤ 0.1) we previously obtained for [C6mim][NTf2] solutions in deuterated chloroform, CDCl3.5 Even though the [C6mim][NTf2] solutions are slightly more dense in CDCl3 than in CHCl3, these differences are essentially

data for the [C6mim][NTf2]−CHCl3 binary system and in Figure 4 for the [C4mim][MeSO3]−H2O binary system. For clarity, we split Figures 3 and 4 into two graphs for xIL below and above the composition of the VE minimum observed in C



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name of the ILs. To organize the wealth of data sets, we distinguished between binary systems showing a temperature dependence of VE that is decreasing, increasing, and is displaying a crossover in temperature dependence. Table 7 lists fitting parameters to the VE data according to eq 4 for the data sets displaying a decreasing VE temperature dependence. Also included in Table 7 are the R2 values for fitting the slopes (R2m) and the intercepts (R2m) and the overall standard deviation of the fit, σ, as evaluated by eq 5 N

σ=

∑i (ViE − ViE,calc)2 N−1

(5)

where the term in the parentheses is the difference between the measured and the calculated VE for the ith of N measurements. Furthermore, we also include in Table 7 the steepest slope value, am,max and its corresponding mole fraction xIL,max, which in most but not all cases corresponds with the xIL value where VE displays an extremum when plotted against xIL. Likewise, these pieces of information are displayed in Table 8 for the data sets displaying an increasing VE temperature dependence. Only four data sets display a crossover in temperature dependence; i.e., they display an increasing VE temperature dependence for a range of xIL values but a decreasing VE temperature dependence for the remaining xIL values. Similar pieces of information as in Tables 7 and 8 are listed in Table 9 for these four data sets except that here am,min and am,max correspond to the xIL values with largest decreasing slope and largest increasing slope. We also wanted to inspect if eq 4 could similarly be applied to data sets of limited composition range where the composition is expressed in IL molalities. For this purpose we inspected several data sets from Sadeghi et al.51 and summarized in Table 10 the fitting results in a similar fashion as in Tables 7 and 8. Consequently, for each data set in the Supporting Information section we list a table with the VE values, the slopes, intercepts, R2 value, and standard deviation, σ, of the temperature dependence for each composition, and a figure showing the VE data points and the fit lines according to eq 4 using the fit parameters listed in Tables 7 to 10. The binary system entries in Tables 7 to 10 are organized first by the molecular solvent in consecutive order as listed in Table 3, next by the anion as listed in Table 4, and finally by the cation as listed in Table 5. Having analyzed and summarized the 167 VE data sets, we wish to discuss them in the next subsections with respect to two major lines of thought, namely (a) reliability of the data sets and (b) any insights such as, for example, structure−property trends, that one might be able to discern from comparing the data sets. Reliability of Data Sets. Before beginning any error discussion of specific VE data sets, it is important to remember that the uncertainty of VE measurements tend to be rather large as pointed out by Vercher et al.45 Specifically, it is a worthwhile exercise to evaluate the overall measurement standard uncertainty of our new VE data sets S1 and S2 by applying to eq 1 error propagation as generally stated in eq 6

E

Figure 4. Temperature dependence of V at ambient pressure for the [C4mim][MeSO3]−H2O binary system for (a) xIL = ○, 0.025; +, 0.050; ×, 0.075; ▽, 0.100; □, 0.148; ☆, 0.199; and ◇, 0.251; and for (b) xIL = △, 0.298; ⬡, 0.346, and , 0.44. The lines are linear leastsquares fits.

Figures 1 and 2. As is evident in Figures 3 and 4, these temperature dependences are linear. The slopes and intercepts of the linear least-squares lines in Figures 3 and 4 are plotted in Figure 5 and were fitted to fourth order polynomials that were then used for eq 4 to produce the solid fit lines in Figures 1 and 2.

Figure 5. (a) Slopes and (b) intercepts of least linear square fits to VE data from Figure 3 for the [C6mim][NTf2]−CHCl3 binary system (□), and from Figure 4 for the [C4mim][MeSO3]−H2O binary system (○) and for same binary system for data set S3 (×). The solid lines are fourth-order polynomial fits with coefficients listed in Tables 7 and 8 for data sets S1 and S2.

We tested eq 4 for fitting a total of 165 other compositionand temperature-dependent VE data sets for IL−molecular solvent binary systems that cover a wide, if not the entire, range of xIL values. These data sets with literature sources are summarized in the Supporting Information section, listed as data sets S1 to S167, including the two new data sets from this study (data sets S1 and S2). These data sets encompass 38 different molecular solvents and 57 different ILs. In Tables 3 to 5 we respectively show the molecular structures of the molecular solvents, the IL anions, and IL cations. Table 6 lists the full

σR =

⎛ ∂R

⎞2 σ Xi⎟ ⎝ ∂Xi ⎠

∑⎜ i

(6)

where X is one of i measured properties needed to evaluate some resulting quantity R, in this case VE. Typically, the molar masses of the ILs are very large and thus also much larger than that of the molecular solvent. Consequently, the largest D



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Table 3. Structural Identification of Molecular Solvents

E



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Table 3. continued

than the contributions to σ from the mole fractions, and σ amounts to about (0.01 to 0.03) cm3·mol−1, depending on the composition. If the density measurement standard uncertainty is increased to 0.001 g·cm−3, its contribution to σ and consequently σ itself increases 10-fold. Therefore, for binary systems that are near ideal, which is the case for many of the 167 VE data sets listed in the Supporting Information section, the standard uncertainty of VE may become as large as the

contributions to σ in eq 6 come from the density measurements of the pure IL and for the binary system, especially for large xIL because these two contributions are heavily weighted by the large molar mass of the IL. Specifically, assuming standard uncertainties of 0.001 for the mole fractions (contributions from the standard uncertainty of the molar masses are negligibly small), the contributions to σ from the density measurements with a standard uncertainty of 0.0001 g·cm−3 are at least two times larger F



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Table 4. Structural Identification of Molecular IL Anions

VE values themselves, especially for compositions approaching the neat components. With this general comment in mind, from inspecting the 167 VE data sets, it appears to be generally confirmed that the VE temperature dependence is linear regardless if VE values are greater or smaller than zero or if temperature dependence of VE is increasing or decreasing. Values for R2 and σ for the least linear square fits (see Supporting Information section)

tend to be respectively low and high only for xIL approaching the end points 0 or 1, which is understandable since VE is approaching zero here. Otherwise, low R2 and high σ values for the linear VE(T) dependence at fixed compositions are indicative of present outliers or indicative of a data set of overall lower quality. Indeed, there are some data sets of questionable reliability. Data set S3 for [C4mim][MeSO3]−H2O binary system, included also in Figure 5, shows inconsistent temperature G



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Even though some data sets display high R2 and low σ values for the least linear square fits of the VE temperature dependence in the Supporting Information section, their compositiondependent slopes and intercepts actually display large scatter and thus result in rather low R2 values in Tables 7 to 9 for their polynomial fits. However, many of these data sets nevertheless display reasonably low σ values for the universal fit according to eq 4. This seemingly contradictory behavior can be explained by the observation that these data sets tend to consist of only few temperatures and contain more data points near xIL = 0 or xIL = 1 where VE values are very small. Two extreme examples for this behavior are data sets S95 and S96 where the σ values in Table 7 for their universal fits are below 0.040 cm3·mol−1 even though the R2 values for slope and intercept are below 0.5 for data set S95 and below 0.8 for data set S96. In fact, the scatter for the composition-dependent slopes and intercepts were so large for data set S95 that we needed to keep the order of the fit polynomials to a stiffer third order. Several VE data sets are reported for the same IL−molecular solvent binary system. In Figures 6 to 11 the plotted slopes and intercepts of the linear temperature dependence as a function of xIL allow for convenient comparison between data sets even if they cover different temperature ranges. The solid (or dashed) lines in Figures 6 to 11 are the polynomial fits for the data set that possesses the smallest σ in Tables 7 and 8. In Figure 6, data sets S73 and S155 as well as data sets S103, S148 and S158 for the binary systems of [C2mim][TfO] with, respectively, ethanol and water are in excellent agreement. Also for the [C2mim][EtSO4]−H2O binary system in Figure 7, agreement is very good between the data sets S32, S101, and S149, while data set S113 slightly differs from these three data sets. The shape of the graphs in Figure 7 for data sets S33 and S71 for the [C2mim][EtSO4]−ethanol binary system are very similar but do not quantitatively agree. To discern which one is the more accurate data set would require new independent measurements. However, the more precise data set is S71 in part due to covering five different temperatures as opposed to three different temperatures for data set S33. A similar situation is observed in Figure 8 for the [C4mim][MeSO4]−H2O binary system where data sets S83 and S102 are in slight quantitative disagreement. Although data set S83 has a lower value for σ in Table 8, data set S102 might be more reliable because it covers a larger number of different temperatures over a slightly wider range of temperatures. From the four different data sets for the [C4mim][MeSO4]−ethanol binary system in Figure 8, data set S123 is in excellent agreement with data set S72, the most precise of the four data sets. Data sets S83 and S94 also agree with data sets S72 and S123 but display more scatter in the graphs of Figure 8. Very good agreement is again observed between data sets S69 and S121 in Figure 9 for the [C4mim][BF4]−ethanol binary system. Here we did not include data set S43 because it displays slope and intercept values that are larger by nearly a factor of 10 and thus grossly disagree with the values obtained from data sets S69 and S121. For the corresponding [C4mim][BF4]−H2O binary system in Figure 9 agreement is only excellent between data sets S35, S61, and S75 for xIL < 0.3. It should be noted that data set S35 is from a careful study of not only the temperature but also the pressure dependence of VE, and it is actually composed of two independently obtained data sets measured in two different laboratories. There are also four data sets available for the [C1mim][MeSO4]−H2O binary system shown in Figure 10. While data

Table 5. Structural Identification of IL Cations

trends. The authors report density measurements carried out with a vibrating tube density meter for IL rich compositions52 where we have observed the physical state to be solid.8 Inconsistent temperature trends are also observed in data sets S60 and S110 and to a minor degree in S76. Data set S44 is of comparably very poor quality, and data set S68 shows entirely unreasonable VE data, which we therefore did not even attempt to fit. Data set S41 shows an unphysical progression of the VE data for 0.5 < xIL < 0.8. For data sets S4, S22, S23, S35, and S132 the VE temperature dependence is observed to be very small at high xIL which then also results in low R2 and high σ values for the linear least-square fits to these compositions. H



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Table 6. Identification of ILs abbreviation [C4mim]Cl [C6mim]Cl [C8mim]Cl [C6mim]Br [C2mim][SCN] [C4mim][SCN] [C4mpip][SCN] [C4-4-mpy][SCN] [C4mpyr][SCN] [C4mim][NO3] [Pyr][NO3] [C4mim][N(CN)2] [C6mim][N(CN)2] [C4mpyr][N(CN)2] [C4mim][C(CN)3] [C2mim][BF4] [C4mim][BF4] [C6mim][BF4] [C8mim][BF4] [C3dmim][BF4] [C4py][BF4] [C8py][BF4] [C4mim][PF6] [C6mim][PF6] [C8mim][PF6] [HOC2NH3][HCO2] [C2mim][AcO] [C4NH3][AcO] [(HOC2)2NH2][AcO] [C2mim][TFA]

name

abbreviation

name

1-butyl-3-methylimidazolium chloride 1-hexyl-3-methylimidazolium chloride 1-octyl-3-methylimidazolium chloride 1-hexyl-3-methylimidazolium bromide 1-ethyl-3-methylimidazolium thiocyanate 1-butyl-3-methylimidazolium thiocyanate 1-butyl-1-methylpiperidinium thiocyanate 1-butyl-4-methylpyridinium thiocyanate 1-butyl-1-methylpyrrolidinium thiocyanate 1-butyl-3-methylimidazolium nitrate pyrrolidinium nitrate 1-butyl-3-methylimidazolium dicyanamide 1-hexyl-3-methylimidazolium dicyanamide 1-butyl-1-methylpyrrolidinium dicyanamide 1-butyl-3-methylimidazolium tricyanomethide 1-ethyl-3-methylimidazolium tetrafluoroborate 1-butyl-3-methylimidazolium tetrafluoroborate 1-hexyl-3-methylimidazolium tetrafluoroborate 1-methyl-3-octylimidazolium tetrafluoroborate 1-propyl-2,3-dimethylimidazolium tetrafluoroborate 1-butylpyridinium tetrafluoroborate 1-octylpyridinium tetrafluoroborate 1-butyl-3-methylimidazolium hexafluorophosphate 1-hexyl-3-methylimidazolium hexafluorophosphate 1-octyl-3-methylimidazolium hexafluorophosphate 2-hydroxyethylammonium formate 1-ethyl-3-methylimidazolium acetate n-butylammonium acetate bis(2-hydroxyethyl)ammonium acetate 1-ethyl-3-methylimidazolium trifluoroacetate

[NEP][C2CO2] [Pyr][C7CO2] [C4mim][Gly] [C4mim][Asp] [C4mim][Glu] [C2mim][C(OC2)2OSO3]

N-ethyl piperazinium propionate pyrrolidinium octanoate 1-butyl-3-methylimidazolium glycine acid 1-butyl-3-methylimidazolium aspartate 1-butyl-3-methylimidazolium glutamic acid 1-ethyl-3-methylimidazolium diethylene glycol monomethyl ethersulfate 1-butyl-3-methylimidazolium diethylene glycol monomethyl ethersulfate 1-octyl-3-methylimidazolium diethylene glycol monomethyl ethersulfate 1-butyl-3-methylimidazolium perchlorate 1-ethyl-3-methylimidazolium methylsulfonate 1-butyl-3-methylimidazolium methylsulfonate 1-ethyl-3-methylimidazolium trifluoromethanesulfonate 1-butyl-3-methylimidazolium trifluoromethanesulfonate 1-butyl-3-ethylimidazolium trifluoromethanesulfonate 1-butyl-3-methylpyridinium trifluoromethanesulfonate 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate diethyl ammonium hydrogen sulfate 1,3-dimethylimidazolium methyl sulfate 1-butyl-3-methylimidazolium methyl sulfate 1-methylpyridinium methyl sulfate 1,3-dimethylimidazolium ethyl sulfate 1-methyl-3-ethylimidazolium ethyl sulfate 1-ethylpyridinium ethyl sulfate 1,2-diethylpyridinium ethyl sulfate 1-hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl)amide 1,2-dimethyl-3-hexylimidazolium bis (trifluoromethylsulfonyl)amide 1-ethyl-3-methylimidazolium bis (perfluoroethylsulfonyl)amide

[C4mim][C(OC2)2OSO3] [C8mim][C(OC2)2OSO3] [C4mim][ClO4] [C2mim][MeSO3] [C4mim][MeSO3] [C2mim][TfO] [C4mim][TfO] [C4eim][TfO] [C4-3-mpy][TfO] [C4mpyr][TfO] [Et2NH2][HSO4] [C1mim][MeSO4] [C4mim][MeSO4] [C1py][MeSO4] [C1mim][EtSO4] [C2mim][EtSO4] [C2py][EtSO4] [C2-2-epy][EtSO4] [C6mim][NTf2] [C6dmim][NTf2] [C2mim][BETA]

where disagreements with the fit is large near the end points of xIL = 0 or 1 such as S30, S32, S36, S37, and S115; and for data sets with VE values of rather large magnitude (i.e., the relative standard deviation is actually quite good) such as S34, S58, S117, and to a somewhat lesser extent S125−S127. Therefore, for the purpose of fitting temperature- and compositiondependent VE data sets, it is fair to say that eq 4 is equally capable to fulfill this purpose as the use of Redlich−Kister type polynomials. Insights. It is remarkable that the linearity of the VE temperature dependence seems to hold true for any of the analyzed binary systems. The linear VE temperature dependence implies that for each binary system there is a specific temperature where VE crosses from being greater than zero to smaller than zero or vice versa, depending on the sign of the temperature dependence. Indeed, there are a number of binary systems where such change is observed within the studied temperature range: S51−S54, S61, S79, S81, S89, S134, S135, S137, S138, S140, S141, S148, S153, S157−S159, and possibly S30, S32, S102−S104, S132, S133, S139, and S149. For this reason we differentiated the data sets sets only by inspecting if the temperature dependence is decreasing or increasing (or both) but not if VE is greater or smaller than zero (or both).

sets S104 and S140 are in excellent agreement, data sets S158 and to a somewhat lesser extent S128 mostly follow data sets S104 and S140. For the [C4mim][TfO] −ethanol binary system in Figure 10 we have again two data sets, S82 and S93, which display the same shape but do not agree quantitatively. Both data sets consist of three different temperatures, but data set S82 covers a wider range of temperatures and displays nearly perfect linearity for the VE temperature dependence for each of the measured compositions. Three different binary systems are included in Figure 11. Each of these three binary systems is represented by two data sets: S40 and S109 for [C4mim][BF4]−methanol, S120 and S139 for [C4mim][N(CN)2]−H2O, and S134 and S157 for [C4mim][TfO]−H2O. Each of the data set pairs is in very good agreement with each other, not withstanding 1−2 somewhat outlying data points for data set S109. Overall, eq 4 results in good universal fits to each of the VE data sets achieving values for σ for the universal fits to the data set typically considerably less than 0.050 cm3·mol−1 as can be seen in Tables 7 to 10. Larger values for σ are only observed for data sets that appear to be of poorer quality such as S61 (which was obtained actually not from experimental work but from MD simulations)53 S97, S98, S109, and S111; data sets I


61

this work and ref5 S1 MeOH

J

H2O

S151 MeOH

11

303.15−353.15 −0.0444 0.0850 −0.0431 0.0024 0.895 19.31 −44.88 34.67 −9.07 0.950 0.043 0.433 −1.7

MeOH

[(HOC2)2NH2][AcO]

H2 O

S77

62

MeOH

308.15−328.15 −0.1925 0.4237 −0.2617 0.0309 0.915 60.68 −143.46 102.98 −20.32 0.881 0.022 0.553 −9.3

[Pyr][C7CO2]

MeOH

S142

13

298.15−328.15 0.1384 −0.3324 0.2864 −0.0920 0.945 −26.70 64.68 −56.77 18.68 0.926 0.058 0.265 −9.8

[C8mim]Cl

MeOH

S125 MeOH

29

298.15−328.15 0.1344 −0.3332 0.2901 −0.0910 0.964 −25.61 62.54 −53.08 16.08 0.950 0.071 0.250 −9.3

[C4mim][SCN]

MeOH

S109

58

MeOH

298.15−318.15 0.0410 −0.1280 0.1430 −0.0550 0.931 1.20 6.70 −16.43 8.53 0.898 0.071 0.360 −9.6

[C4mim][BF4]

MeOH

S40

61

MeOH

27

MeOH

24

EtOH

[C4mim][BF4]

EtOH

[C4mim][NO3]

283.15−318.15 0.1448 −0.3586 0.3079

T range/K am,4 am,3 am,2

298.15−328.15 1.4351 −3.4024 2.7398

33 S7

32 S20

IL

298.15−313.15 0.0390 −0.1142 0.1350 −0.0597 0.998 4.66 −7.20 −1.28 3.83 0.999 0.048 0.356 −8.7

293.15−313.15 0.0821 −0.2100 0.1920 −0.0641 0.982 −9.17 24.49 −23.20 7.85 0.977 0.057 0.270 −7.0

EtOH 293.15−323.15 0.0964 −0.2307 0.1965

EtOH [C4mim][BF4]

10 S36

293.15−318.15 0.0881 −0.2038 0.1650

[C6mim][BF4]

EtOH

298.15−313.15 0.1384 −0.3235 0.2694 −0.0842 0.900 −27.52 61.76 −49.44 15.21 0.830 0.080 0.260 −8.7

293.15−318.15 0.0847 −0.2061 0.1790

63 S44

298.15−318.15 −0.7571 0.9722 −0.0330 −0.1805 0.809 163.47 −172.70 −45.01 53.82 0.736 0.941 0.322 −70.1

[C4mim][BF4]

62 S78

308.15−328.15 −0.1197 0.2390 −0.0963 −0.0213 0.721 45.48 −88.39 42.51 −0.11 0.525 0.032 0.489 −12.3

283.15−323.15 0.1579 −0.2891 0.1695

[C8mim][BF4]

10 S37 EtOH

EtOH 303.15−323.15 0.1840 −0.4380 0.3630

[C4py][BF4]

298.15−313.15 0.1572 −0.3485 0.2882 −0.0963 0.930 −32.87 68.80 −55.71 19.63 0.917 0.069 0.304 −11.1

EtOH

−0.0024 0.0143

293.15−303.15

[C4mim][PF6]

10 S38

298.15−313.15 0.1210 −0.2458 0.1862 −0.0612 0.943 −27.65 51.36 −35.10 11.36 0.913 0.037 0.260 −7.1

293.15−303.15 0.1454 −0.3078 0.2409

[C6mim][PF6]

45 S156 EtOH

12 S145 EtOH 293.15−303.15 0.1665 −0.3342 0.2180

S86

42

13 S143 EtOH

298.15−328.15 0.1455 −0.3525 0.3066 −0.0991 0.955 −32.82 78.78 −68.51 22.44 0.956 0.063 0.265 −10.6

288.15−323.15 0.1094 −0.2167 0.1660

EtOH 293.15−313.15 0.0437 −0.1170 0.1130

[C4NH3][AcO]

29 S126

298.15−348.15 0.1269 −0.3218 0.2972 −0.1019 0.986 −25.97 66.15 −61.01 20.76 0.984 0.059 0.280 −11.5

[C4mim][SCN]

EtOH

288.15−323.15 0.1512 −0.3200 0.2482 −0.0803 0.973 −33.53 67.27 −47.91 14.44 0.929 0.022 0.319 −9.2

[HOC2NH3][HCO2]

298.15−328.15 0.1634 −0.3798 0.3101 −0.0935 0.970 −36.66 82.63 −64.75 18.75 0.968 0.074 0.247 −9.3

[C8mim][PF6]

278.15−338.15 0.0980 −0.2405 0.2071 −0.0643 0.975 −17.92 44.33 −38.35 11.88 0.972 0.040 0.243 −6.5

MeOH [HOC2NH3][HCO2]

[C8mim]Cl

EtOH

298.15−318.15 0.1051 −0.2482 0.1997 −0.0564 0.879 −15.31 36.72 −29.56 8.13 0.747 0.071 0.221 −5.1

[C4mim][PF6]

S115 MeOH

293.15−323.15 0.1360 −0.3490 0.3010 −0.0883 0.991 −32.40 81.90 −68.40 18.90 0.980 0.068 0.217 −8.3

[C4py][BF4]

S11 MeOH

293.15−323.15 0.1070 −0.2558 0.2105 −0.0613 0.979 −19.65 46.98 −38.33 10.92 0.936 0.040 0.229 −5.8

[C4mim][BF4]

[C4NH3][AcO] [NEP][C2CO2] [Pyr][C7CO2] [C4mim][ASP] [C2mim][C(OC2)2OSO3] [C4mim][C(OC2)2OSO3] [C8mim][C(OC2)2OSO3] [C2mim][TfO] [C2mim][EtSO4]

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref data set 1

IL

S41 MeOH

293.15−323.15 0.0603 −0.2289 0.2552 −0.0880 0.754 −14.81 56.85 −62.63 20.96 0.717 0.093 0.248 −9.4

288.15−318.15 0.0701 −0.1856 0.1971 −0.0812 0.992 −19.741 45.739 −42.210 16.074 0.975 0.022 0.345 −11.2

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref

data set 1

C3H6Cl2

[C4mim][BF4]

CHCl3

[C6mim][NTf2]

1

IL

Table 7. Fit Parameters to eq 4 for VE in cm3·mol−1 for Binary Systems of Molecular Solvent (1) and IL (IL) with Decreasing Temperature Dependence

Journal of Chemical & Engineering Data Article


64 S43 EtOH

35 S89 EtOH

36 S121 EtOH

−0.0619 0.976 −24.29 56.80 −46.35 13.75 0.963 0.025 0.257 −6.4

EtOH

65 S69 EtOH

−0.0573 0.963 −21.48 50.53 −41.52 12.39 0.929 0.021 0.261 −6.0

EtOH −0.0492 0.984 −20.06 45.00 −35.13 10.17 0.970 0.016 0.244 −4.8

EtOH

[C6mim][BF4]

65 S70 EtOH

[C4mim][BF4]

EtOH

39 S97

−0.0382 0.985 −12.91 29.23 −23.02 6.63 0.720 0.091 0.792 −5.4

EtOH −0.1089 0.993 −50.20 118.00 −95.20 27.30 0.989 0.022 0.241 −10.7

[C4py][BF4]

27 S12 EtOH

[C8mim][BF4]

K

298.15−328.15 0.0429 −0.1451 0.1754 −0.0737 0.981 −3.76 21.38

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3

298.15−328.15 0.1097 −0.2679 0.2398 −0.0814 0.965 −24.27 59.63

C3OH

[C8mim]Cl

EtOH

[C2py][EtSO4]

IL

EtOH

41 S95 EtOH

−4.29 5.22 −0.41 0.228 0.039 0.557 −3.6

−0.0137 0.421

[C4mim][PF6]

EtOH

41 S131 EtOH

−0.0780 0.885 −37.39 75.33 −56.09 18.00 0.851 0.018 0.311 −8.9

[C6mim][PF6]

EtOH

41 S96 EtOH

−0.0502 0.780 −41.74 79.98 −47.97 9.71 0.766 0.033 0.182 −3.7

[C8mim][PF6]

EtOH

42 S87 EtOH

−0.0596 0.972 −25.97 49.50 −34.60 11.34 0.983 0.016 0.597 −8.6

EtOH

[HOC2NH3][HCO2]

EtOH

32 S21 EtOH

−0.0406 0.994 −4.41 12.93 −13.44 4.92 0.976 0.029 0.288 −4.8

[C4NH3][AcO]

C3OH

45 S155 C3OH

65 S74 C3OH

66 S82

0.1512 −0.3697 0.3316 −0.1129 0.988 −39.92 95.60 −81.66 25.91 0.979 0.029 0.285 −12.8

C3OH

41 S93 C3OH

11.36 −23.66 12.46 0.952 0.040 0.367 −10.5

−0.0536 0.1174 −0.0645 0.972

293.15−303.15

67 S84 C3OH

0.1164 −0.2948 0.2685 −0.0895 0.962 −28.82 72.58 −64.25 20.38 0.946 0.043 0.269 −9.9

298.15−328.15

41 S94 C3OH

0.1295 −0.3243 0.2840 −0.0893 0.945 −31.93 79.22 −67.61 20.39 0.908 0.036 0.250 −9.1

293.15−303.15

36 S123 2-propanol

0.0997 −0.2456 0.2187 −0.0726 0.984 −23.09 56.47 −49.09 15.68 0.983 0.034 0.273 −8.0

293.15−323.15

65 S72 C4OH

0.0958 −0.2374 0.2132 −0.0717 0.983 −21.86 54.31 −48.14 15.72 0.974 0.026 0.277 −8.0

293.15−318.15

37 S33 C4OH

0.1854 −0.4217 0.3428 −0.1061 0.935 −50.73 112.26 −87.78 26.11 0.908 0.041 0.262 −11.0

298.15−328.15

65 S71 C4OH

293.15− 318.15 0.1198 −0.2886 0.2504 −0.0813 0.979 −26.97 65.01 −55.80 17.69 0.976 0.034 0.268 −8.7

298.15−348.15 0.0805 −0.2144 0.2191 −0.0849 0.986 −19.36 51.03

283.15−318.15 0.0873 −0.2009 0.1752 −0.0617 0.998 −24.35 53.88

293.15−313.15 −0.0047 −0.0050 0.0252 −0.0156 0.984 7.18 −13.26

298.15−313.15 −0.0264 0.0573 −0.0209 −0.0101 0.968 10.80 −27.40

278.15−338.15 0.0532 −0.1369 0.1345 −0.0507 0.989 −11.52 30.04

298.15−328.15 0.0429 −0.1274 0.1433 −0.0587 0.978 −8.44 28.24

298.15−328.15 0.0942 −0.2149 0.1832 −0.0623 0.973 −24.20 54.64

298.15−328.15 0.1893 −0.4370 0.3728 −0.1251 0.986 −52.87 121.50

293.15−313.15 −0.0271 0.4647 −0.0161 −0.0033 0.941 12.05 −24.16

298.15−313.15 −0.0439 0.0980 −0.0597 0.0055 0.967 16.50 −38.40

283.15−318.15 0.1266 −0.2773 0.2135 −0.0629 0.989 −39.42 82.92

[C4mim][SCN] [C4mim][NO3] [C4NH3][AcO] [NEP][C2CO2] [C2mim][TfO] [C2mim][EtSO4] [C2py][EtSO4] [C2mim][EtSO4] [C4NH3][AcO] [NEP][C2CO2] [C4mim][NO3]

65 S73

0.0645 −0.1672 0.1554 −0.0524 0.957 −12.33 32.72 −31.20 10.78 0.938 0.034 0.270 −5.8

62 S80

0.0761 −0.1920 0.1770 −0.0607 0.987 −14.60 37.40 −35.10 12.20 0.988 0.035 0.277 −6.9

33 S8

0.1008 −0.2415 0.2079 −0.0670 0.973 −22.91 54.02 −45.53 14.38 0.967 0.036 0.267 −7.2

0.6963 −1.3998 0.8917 −0.1914 0.705 −224.76 465.44 −305.73 66.02 0.695 0.036 0.849 −14.6

−0.0007 −0.0172 0.0508 −0.0330 0.999 8.91 −17.50 7.71 0.85 0.989 0.016 0.413 −6.2

am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref data set 1

298.15−313.15 308.15−328.15 293.15−318.15 278.15−338.15 293.15−318.15 298.15−328.15

T range/K

IL

EtOH [C4mim][BF4]

[C2mim][NEP][C2CO2] [Pyr][C7CO2] [C2mim][TfO] [C2mim][TfO] [C4mim][TfO] [C1mim][MeSO4] [C1mim][MeSO4] [C4mim][MeSO4] [C4mim][MeSO4] [C4mim][MeSO4] [C4mim][MeSO4] [C2mim][EtSO4] [EtSO4]

−0.7695 0.933 −411.63 976.26 −785.96 220.46 0.934 0.201 0.218 −69.5

−0.0943 0.990 −35.26 88.44 −74.61 21.53 0.969 0.034 0.242 −9.4

am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref data set 1

EtOH

[C4mim][BF4]

EtOH

[C4mim][NO3]

1

IL

Table 7. continued



L

30 S110

BzAld

[C4mim][PF6]

298.15−313.15

0.0001 0.0135 −0.0143 0.843

−6.42 10.50 −3.92 0.726 0.055 0.530

68 S105

BzOH

[C4mim][PF6]

298.15−313.15

−0.0052 0.0150 −0.0098 0.978

−4.79 8.00 −3.23 0.933 0.027 0.420

1

IL

C3OH

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope

30 S112

C3OH

298.15−313.15 0.3335 −0.4650 0.1560 −0.0262 0.907 −98.15 131.43 −33.39 0.79 0.901 0.026 0.779

32 S22

C3OH

278.15−318.15 0.3468 −0.8729 0.7956 −0.2686 0.986 −37.88 90.91 −74.20 21.06 0.921 0.18 0.276

[C2mim][TfO]

33 S9 DEGMME

20.00 −3.36 0.894 0.015 0.525 −4.8

acetone 298.15−313.15 0.1213 −0.3529 0.3592 −0.1277 0.966 −23.31 72.83 −78.35 28.91 0.954 0.044 0.276

[C2mim][BETA]

30 S106

298.15−318.15 0.0654 −0.1511 0.1275 −0.0417 0.996 −4.67 9.97 −8.47 3.17 0.996 0.032 0.282 −4.6

[C8mim][BF4]

6.29 −0.19 0.847 0.014 0.369 −2.7

acetone

298.15−318.15 0.1382 −0.3700 0.4006 −0.1688 1.000 −22.27 58.35 −63.01 26.93 1.000 0.025 0.353 −23.8

[C4mim][PF6]

35 S90 EGDME

−43.43 13.92 0.993 0.022 0.318 −7.5

[C4mim][BF4]

BzAld

298.15−318.15 0.0389 −0.1106 0.1135 −0.0421 0.959 −4.78 1.54 1.19 2.29 0.922 0.266 0.295 −5.1

298.15−318.15 0.0398 −0.1197 0.1179 −0.0385 0.798 0.33 7.35 −12.47 5.20 0.390 0.113 0.244 −4.0

[C4mim][PF6]

29 S127 EGMME

−50.68 18.95 0.986 0.056 0.320 −10.9

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref data set

13 S144 EGMME

−54.81 19.40 0.971 0.050 0.284 −9.2

[C8mim][BF4]

40 S24

−32.58 14.85 0.956 0.039 0.318 −9.8

C3OH

C3OH

C3OH

C3OH

2-propanol

C4OH

C4OH

C4OH

293.15−303.15 0.6049 −1.2815 0.9141 −0.2406 0.881 −162.05 336.35 −228.62 55.28 0.781 0.058 0.217

[C8mim][PF6]

butanone

59 S55

298.15−318.15 0.0153 −0.0423 0.0583 −0.0312 0.989 9.26 −23.89 16.89 −2.25 0.957 0.048 0.422 −5.5

[C4mim][PF6]

45 S154 DEGMME

−30.27 11.71 0.991 0.030 0.312 −6.4

278.15−318.15 0.2155 −0.5737 0.5724 −0.2138 0.998 −25.41 67.28 −63.95 22.02 0.994 0.077 0.306

[C2mim][TfO]

methyl acetate

30 S111

TEGMME

30 S107

278.15−318.15

11.15 −23.15 12.06 0.993 0.222 0.373

14.56 −2.41 0.714 0.009 0.431 −1.6

59 S56

293.15−323.15 0.0821 −0.2453 0.2751 −0.1118 0.993 −15.38 46.76 −52.36 20.95 0.993 0.057 0.321

[C4mim][PF6]

293.2−333.2 0.4418 −0.8015 0.5228 −0.1355 0.993 −1.29 228.80 −143.80 35.44 0.988 0.019 0.233

33 S10 TEGDME

27.70 −57.70 0.941 0.006 0.561 −2.8

59 S57

283.15−353.15 0.0905 −0.2568 0.3002 −0.1337 0.998 −11.58 35.91 −48.09 23.74 0.996 0.088 0.363

[C4mim][PF6]

methyl methacrylate

298.15−318.15 0.0245 −0.0803 0.1469 −0.0909 0.990 4.04 −13.14 3.37 5.72 0.963 0.044 0.439 −17.5

[C6dmim][NTf2]

DMC

298.15−318.15 0.0588 −0.1407 0.1346 −0.0524 0.968 −7.75 12.06 −6.75 2.40 0.726 0.040 0.347 −7.0

[C4mim][PF6]

32 S23 TEGMME

[C4mim][BF4]

DMC

298.15−318.15 0.0435 −0.1087 0.1040 −0.0387 1.000 −5.62 11.95 −9.23 2.90 0.9956 0.016 0.317 −4.8

ethyl acetate

−0.1336 0.3013 −0.1689 0.991

12 S147

−102.10 33.47 0.984 0.041 0.294 −14.3

[C8mim][BF4]

40 S25

−45.17 14.71 0.960 0.041 0.304 −7.3

[C2mim][TfO]

298.15−318.15 0.4367 −0.7162 0.3903 −0.1092 0.924 −156.88 256.33 −118.76 19.30 0.872 0.347 0.741 −26.3

[C4mim][PF6]

12 S146 DEGDME

−34.19 14.36 0.971 0.022 0.326 −7.8

298.15−318.15 0.1498 −0.3822 0.3535 −0.1205 0.949 −35.58 88.07 −77.79 25.15 0.927 0.085 0.277

[C4mim][PF6]

CH3CN

59 S58

298.15−318.15 0.1026 −0.2473 0.2564 −0.1109 0.989 −7.30 10.11 −8.37 5.46 0.969 0.107 0.386 −16.6

[C4mim][PF6]

35 S91 TetEGDME

−58.22 14.73 0.974 0.026 0.252 −6.2

[C4mim][SCN] [C4mim][NO3] [C4NH3][AcO] [NEP][C2CO2] [C2mim][TfO] [C2mim][EtSO4] [C2py][EtSO4] [C2mim][EtSO4] [C4NH3][AcO] [NEP][C2CO2] [C4mim][NO3]

IL

ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref data set 1

C3OH

[C8mim]Cl

EtOH

[C2py][EtSO4]

1

IL

Table 7. continued



[C4mim][PF6]

−3.8

18 S6

[C4mim][PF6]

−1.9

18 S5

IL

M

293.15−323.15 0.0964 −0.2372 0.2076 −0.0667 0.983 −22.30 54.01 −46.25 14.52 0.984 0.033 0.261 −7.0

36 S124

298.15−318.15 0.2381 −0.5559 0.4556 −0.1377 0.977 −54.38 124.54 −98.46 28.29 0.965 0.064 0.247 −13.7

58 S108 DMSO


298.15−328.15 −0.0141 0.0307 −0.0156 −0.0009 0.933 4.94 −11.12 7.28 −1.14 0.765 0.005 0.527 −1.4

28 S28

298.15−328.15 0.0649 −0.1590 0.1455 −0.0508 0.941 −14.26 34.06 −28.46 8.50 0.773 0.014 0.293 −5.9

28 S29

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref data set

[Et2NH2][HSO4]

[C4mim]Cl

DMSO

CH3NO2

[C4mim][MeSO4]

CH3CN

[C4mim][BF4]

21 S17

−23.0

1

IL

BzAld

43 S116

−29.9

293.15−323.15 0.0348 −0.0875 0.0743 −0.0215 0.953 −8.09 20.30 −16.45 4.23 0.949 0.014 0.220 −2.0

[C4mim][BF4]

36 S122

acetone

MEA

69 S130

−14.6

11 S152

303.15−353.15 0.1939 −0.3791 0.2535 −0.0687 0.937 −82.33 142.30 −81.41 21.59 0.981 0.037 0.445 −6.2

17 S92 N-methyl-2pyrrolidinone

−20.9

[C8mim][PF6]

butanone

19 S30

298.15−313.15 0.7644 −1.3044 0.6726 −0.1350 0.925 −233.51 392.53 −193.49 35.28 0.919 0.062 0.798 −32.3

[C4mim][BF4]

[C2mim][BETA]

acetone

[(HOC2)2NH2][AcO]

[C2mim][TfO]

CH3NO2

[C4mim][BF4]

IL

1000am,max/ cm3·mol−1 ref data set

BzAld

BzOH

1

Table 7. continued

19 S31

298.15−313.15 0.0096 −0.0175 0.0491 −0.4104 0.999 6.13 −14.91 3.14 5.62 0.995 0.015 0.505 −5.2

[C4mim][PF6]

43 S117 N-methyl-2pyrrolidinone

−26.4

[C2mim][TfO]

methyl acetate

22 S27

−43.45 45.45 −0.24 0.798 0.042 0.766 −26.2

0.1169 −0.0948 −0.0279 0.808

298.15−313.15

[C4mim][BF4]

aniline

43 S118

−28.0

[C2mim][TfO]

ethyl acetate

60 S13

293.15−308.15 0.3570 −0.7300 0.5110 −0.1390 1.000 −103.45 205.09 −132.52 30.89 0.999 0.008 0.239 −12.7

[C2mim][BF4]

pyridine

61 S42

−14.8

[C4mim][BF4]

DMC

60 S14

293.15−308.15 0.4660 −0.9610 0.6920 −0.1970 0.999 −153.18 315.92 −213.48 50.75 0.998 0.027 0.258 −19.3

[C2mim][BF4]

a-picoline

70 S160

−12.0

[C6dmim][NTf2]

DMC

60 S15

293.15−308.15 0.3070 −0.5180 0.3120 −0.1000 0.990 −99.08 169.65 −92.17 21.57 0.998 0.015 0.718 −21.5

[C2mim][BF4]

b-picoline

20 S34

−19.7

[C4mim][PF6]

methyl methacrylate

CH3CN

60 S16

293.15−308.15 −0.0007 0.0882 −0.0644 −0.0231 0.999 0.90 −16.25 15.06 0.30 0.994 0.050 0.630 −18.2

[C2mim][BF4]

g-picoline

24 S114

−13.5

[C4mim][PF6]



N

H2O

H2O

H2O

S35 H2O

23

278.15−333.15 −0.1001 0.2652 −0.2411 0.0756 0.936 31.42 −81.37 70.64 −20.55 0.897 0.022 0.241 7.6

S26 H2O

34

298.15−343.15 −0.0578 0.0943 −0.0619 0.0256 0.987 15.93 −24.93 14.08 −5.12 0.978 0.027 0.671 6.1

[C3dmim][BF4]

H2O

H2O

38

[C8py][BF4]

H2O

S100 H2 O

38

H2O

72 S76

56

H2 O

298.15−323.15 −0.0083 0.1578 −0.0115 0.0040 0.966 3.78 −7.11 5.14 −1.82 0.974 0.012 0.637 0.6

[C2mim][AcO]

71 S52

15 S139

S150 H2O

H2 O

73 S120

S4

278.15−338.15 −0.0683

H2 O

S3

52

H2O

298.15−313.15 0.3467 −0.6978 0.4345 −0.0834 0.937 −133.78 272.72 −170.57 31.62 0.951 0.080

[C4mim][MeSO3]

15 S141 H2O

288.15−308.15 −0.1470 0.3564 −0.2998 0.0900 0.977 43.66 −106.50 89.88 −26.94 0.979 0.009 0.237 8.8

[C4mpyr][N (CN)2]

293.15−318.15 −0.0513

[C1mim][MeSO4] [C4mim][MeSO4]

this work and ref 8 S2 H2 O

298.15−3583.15 −0.4042 0.6343 −0.3489 0.0748 0.997 59.76 −141.68 99.74 −25.67 0.997 0.014 0.189 5.4

[C4mim][MeSO3]

15 S137 H2 O

288.15−308.15 298.15−328.15 −0.1028 −0.0506

[C4-3mpy][TfO]

H2 O

313.15−353.15 −0.0585 0.1438 −0.1163 0.0310 0.989 17.00 −43.78 38.64 −11.86 0.988 0.033 0.199 2.6 7

H2 O [C6mim][N (CN)2]

278.15−358.15 288.15−308.15 −0.1358 0.0188 0.3362 −0.0428 −0.2917 0.0240 0.0910 0.989 0.987 40.37 −2.51 −99.89 7.07 86.32 −4.53 −26.72 0.974 0.986 0.027 0.009 0.248 9.2

[C4mim][N (CN)2]

[C2mim][MeSO3]

H2 O

288.15−308.15 −0.1249 0.3081 −0.2655 0.0820 0.977 37.45 −92.12 78.61 −23.85 0.974 0.007 0.245 8.2

278.15−348.15 −0.1499 0.3607 −0.2938 0.0830 0.978 48.66 −120.70 102.20 −30.12 0.985 0.029 0.218 7.5 16

H2 O [C4mim][N (CN)2]

[C2mim][TFA]

H2O

298.15−333.15 0.1376 −0.2793 0.1277 0.0143 0.754 −124.14 267.98 −172.54 28.38 0.875 0.375 0.507 12.7

[Pyr][NO3]

298.15−348.15 −0.1186 0.2895 −0.2482 0.0771 0.969 32.87 −80.76 70.29 −22.31 0.997 0.048 0.249 7.8

S50 H2O

283.15−343.15 −0.0665 0.0930 −0.0460 0.0194 0.985 25.95 −39.28 18.71 −5.36 0.977 0.091 0.709 6.8

71 S54

298.15−348.15 −0.0492 0.1482 −0.1591 0.0601 0.984 10.88 −36.20 42.82 −17.51 0.998 0.023 0.294 7.3

283.15−343.15 −0.0846 0.1120 −0.0463 0.0191 0.995 23.00 −29.34 9.47 −3.16 0.992 0.012 0.728 8.3

[C4py][BF4]

S99 H2O

71 S53

298.15−348.15 −0.0518 0.1524 −0.1578 0.0572 0.999 12.07 −38.46 43.29 −16.89 0.998 0.018 0.281 6.7

H2O

H2O [C4-4mpy][SCN]

[C2mim][TfO] [C2mim][TfO] [C2mim][TfO] [C4mim][TfO] [C4mim][TfO] [C4mim][TfO] [C4mim][TfO] [C4eim][TfO] [C4mpyr][TfO] [C4mpyr][TfO]

S61 H2 O

H2O

71 S51

298.15−348.15 −1.0073 0.2489 −0.2153 0.0669 0.977 28.13 −70.06 61.54 −19.56 0.974 0.017 0.247 6.8

[C4mim][BF4]

57 S67

289.15−353.15 −0.0496 0.1403 −0.1527 0.0607 0.916 15.66 −44.22 48.03 −19.06 0.907 0.069 0.316 7.9 53

H2O

[C2mim][SCN] [C4mim][SCN] [C4mpyr][SCN] [C4mpip][SCN]

H2O

298.15−323.15 −0.0158 0.0318 −0.0224 0.0064 0.998 6.56 −12.86 8.91 −2.60 0.998 0.003 0.271 0.6

[C4mim][BF4]

25 S88

293.15−333.15 −0.1246 0.2619 −0.1830 0.0452 0.731 32.26 −70.70 52.10 −13.51 0.747 0.012 0.195 3.6

[C6mim]Br

H2 O

T range/K 293.15−318.15 278.15−338.15 278.15−348.15 278.15−338.15 293.15−318.15 288.15−308.15 303.15−343.15 278.15−338.15 288.15−308.15 −0.0925 −0.1035 −0.1081 −0.1011 −0.1019 −0.1103 −0.1902 −0.0997 −0.8554 am,4

IL

S119 H2O

data set 1

S75 H2O

74

73

2.42 −0.09 −2.64 0.970 0.033 0.450 1.7

−0.0144 0.0082 0.0073 0.971

303.15−353.15 −0.0190 0.0889 −0.1364 0.0668 0.946 2.20 −19.12 34.50 −17.63 0.928 0.038 0.356 10.2

278.15−258.15

[C4mim][BF4]

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref

IL

H2O

14 S133

14 S132

H2O

[C8mim]Cl

298.15−343.15 −0.9460 0.2371 −0.2036 0.0610 0.973 19.97 −53.89 52.15 −18.21 0.982 0.017 0.233 5.9

[C6mim]Cl

298.15−343.15 −0.1474 0.3480 −0.2685 0.0678 0.978 41.28 −99.32 80.14 −22.10 0.982 0.037 0.187 5.4

IL


[C4mim][C (CN)3]

H2O

1

H2O

Table 8. Fit Parameters to eq 4 for VE in cm3·mol−1 for Binary Systems of Molecular Solvent (1) and IL (IL) with Increasing Temperature Dependence



H2O

H2 O

O

H2O

H2O

pyrrole

[C2mim][AcO]

298.15−323.15 −0.0176 0.0362

T range/K am,4 am,3

298.15−323.15 −0.0178 0.0366

46 S113

pyrrole

15 S138

67 S83

H2O

298.15−323.15 −0.0191 0.0394

[C2mim][SCN]

H2 O

H2O

298.15−323.15 −0.0185 0.0386

[C2mim][AcO]

H2 O

H2 O

H2O

16 S149 indoline

278.15−348.15 −0.1145 0.2786 −0.2310 0.0668 0.991 34.24 −85.03 73.21 −22.41 0.994 0.033 0.225 6.2

298.15−323.15 −0.0178 0.0366

298.15−323.15 −0.0174 0.0357

[C2mim][AcO]

15 S136 indoline

quinoline 298.15−323.15 −0.0172 0.0352

[C2mim][SCN]

21 S18

[C2mim][AcO] 298.15−323.15 −0.0178 0.0367

H2O

288.15−323.15 −0.0760 0.1484 −0.0987 0.0263 0.923 24.99 −51.06 34.26 −8.21 0.879 0.023 0.760 2.8

[C2mim][SCN] 298.15−323.15 −0.0204 0.0425

DMEA

298.15−323.15 −0.0189 0.0394

[C2mim][AcO]

75 S60 thiophene

288.15−323.15 −0.1003 0.1884 −0.1110 0.0229 0.839 34.07 −70.97 53.50 −16.60 0.956 0.070 0.818 2.7

[C4mim][PF6]

26 S102

0.300 6.6

0.1418 −0.1446 0.0540 0.986 14.34 −40.08 42.83 −17.11 0.985 0.025

[C4mim][PF6]

MEA

75 S59 thiophene

66 S81

0.241 3.5

0.1291 −0.1138 0.0352 0.955 10.93 −30.04 29.04 −9.87 0.931 0.046

308.15−328.15 −0.2172 0.7331 −0.8264 0.3109 0.992 50.22 −190.92 234.34 −93.73 0.992 0.027 0.311 36.9 62 S79 quinoline

−0.0663 0.0333 0.0345 0.859 16.11 −0.29 −16.25 0.891 0.031 0.616 18.4

−0.0042 −0.0784 0.0825 0.999 −1.09 30.96 −29.84 0.999 0.015 0.506 21.1 21 S19

298.15−313.15

CH3CN

H2 O

[C1mim][MeSO4] [C4mim][MeSO4]

[Pyr][C7CO2]

15 S135

0.265 9.0

[C4mim][Glu]

BzOH

H2 O [C4-3mpy][TfO] 0.2677 −0.2481 0.0828 0.986 34.13 −87.61 79.52 −25.93 0.984 0.015

298.15−313.15

[C4mim][Gly]

288.15−308.15 −0.1326 0.3430 −0.2993 0.0884 0.968 41.58 −108.50 96.36 −29.35 0.976 0.049 0.224 8.3

BzOH

44 S157

0.284 8.5

0.1959 −0.2005 0.0728 0.978 20.25 −59.62 61.64 −22.26 0.976 0.024

H2O

15 S134

0.273 9.4

0.2398 −0.2383 0.0835 0.983 28.22 −77.93 75.95 −26.09 0.981 0.017

[C2-2epy][EtSO4]

44 S159

0.277 9.2

0.2562 −0.2382 0.0816 0.994 31.27 −81.08 75.30 −25.43 0.992 0.018

[C2mim][EtSO4]

31 S128

0.210 7.6

0.4189 −0.3142 0.0855 0.992 53.77 −118.93 89.03 −23.87 0.986 0.019

[C2mim][SCN]

293.15−318.15 −0.1208 0.2903 −0.2382 0.0686 0.985 37.12 −90.66 76.69 −23.11 0.992 0.089 0.218 6.4

[C2mim][EtSO4]

15 S140 H2 O

0.260 8.6

0.2781 −0.2489 0.0809 0.976 36.48 −90.63 79.31 −25.08 0.972 0.026

26 S101 pyridine

[C2mim][EtSO4]

26 S104 H2O

0.270 8.3

0.2547 −0.2288 0.0759 0.991 33.40 −82.50 72.55 −23.36 0.988 0.019

298.15−328.15 −0.2024 0.4647 −0.3535 0.0910 0.911 60.54 −140.88 109.80 −29.40 0.926 0.094 0.196 7.5 37 S32 pyridine

[C2mim][EtSO4]

44 S158 H2O

0.284 8.3

0.2540 −0.2294 0.0763 0.989 34.15 −83.95 73.50 −23.74 0.988 0.008

278.2−338.2 −0.0982 0.2371 −0.1940 0.0540 0.876 34.92 −85.69 72.49 −21.40 0.933 0.038 0.212 4.8

[C2mim][SCN]

288.15−308.15 −0.8305 0.1970 −0.1627 0.0484 0.964 22.09 −53.40 45.34 −13.96 0.977 0.027 0.238 4.7

298.15−328.15 −0.1452 0.3340 −0.2602 0.0712 0.977 44.62 −103.22 82.44 −23.77 0.984 0.014 0.214 6.3

IL

[C1py][MeSO4]

H2 O

16 S148

0.251 7.2

0.2640 −0.2269 0.0709 0.988 33.25 −82.10 70.33 −21.46 0.985 0.011


[C4mim][MeSO4]

26 S103

45 S153

0.2545 −0.2216 0.0705 0.985 31.79 −78.68 68.21 −21.24 0.982 0.014

ref data set 1

0.2337 −0.2095 0.0682 0.983 29.21 −73.75 65.23 −20.63 0.978 0.011

0.254 7.3

IL

H2 O

[C2mim][TfO] [C2mim][TfO] [C2mim][TfO] [C4mim][TfO] [C4mim][TfO] [C4mim][TfO] [C4mim][TfO] [C4eim][TfO] [C4mpyr][TfO] [C4mpyr][TfO]

H2O

xIL,maxslope 0.261 1000am,max/ 7.3 cm3·mol−1

am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/ 3 ·molcm −1

IL

1

Table 8. continued



56 S45

57 S65

56 S48

57 S64

56 S47

57 S66

56 S49

Inspecting the graphs of slopes and intercepts in Figures 5 to 11 there are several remarkable features. There is a certain symmetry between the graphs of slopes and graphs of intercepts such that their shapes are nearly mirror images. This is not entirely surprising because the VE values are centered around the value zero and thus a positive slope results in a negative intercept and vice versa. Likewise, a steeper slope results in an intercept further away from zero. We inspected if the ratio of slope and intercept would amount to a constant value across all compositions, but such simple relationship was generally not indicated. Figures 5 to 11 only concern binary systems with either water or ethanol and in one case methanol as the molecular solvent, since no other binary system has been measured more than once. The similarity between the graphs in Figures 5 to 11 with respect to their shapes for the ethanol binary systems as well as for the water binary systems is striking. This similarity in shape for binary systems with same molecular solvent seems to suggest that the structural details of the IL play a much less important role than for the molecular solvent. Despite the large number of available data sets, there are actually only few suitable binary systems for which data are available to further investigate this matter. In Figure 12 we compare IL−water binary systems for ILs with [C4mim]+ as the cation and varying anions. To guide the eye, one of the IL−water binary systems is shown as a solid (polynomial fit) line. All six data sets display similar shapes for their graphs in Figure 12 that only differ quantitatively slightly from one another. This observation is interesting from a standpoint that the IL anion has been observed to more strongly influence properties of ILs such as the activity coefficients of solutes at infinite dilution, γ∞, than the choice of cation.54 However, these anions may simply be rather similar in nature resulting in similar ion hydration behavior. In a review concerning which ILs are kosmotropic or chaotropic, i.e., have the ability to increase or to break the water structure, [BF4]− and [SCN]− are listed as chaotropic.55 The other anions involved in Figure 12 are not listed in this review but are likely to be chaotropic as well given that their hydrogen bond basicities are also greater than that of Cl−,54 which is borderline kosmotropic/chaotropic.55 In fact, inspecting the other anions present in IL−water binary systems in Table 8, they are almost all chaotropic except for two data sets S50 and S150 with the ILs [C2mim][AcO]− and [C2mim][TFA]−, which brings us to Figure 13 where we compare IL−water binary systems with [C2mim]+ cation and varying anions. In Figure 13, the binary IL−water systems with [TFO]−, [TFA]−, and [EtSO4]− display graphs that in shape and even quantitatively are very similar to the graphs in Figure 12 for [C4mim]+ ILs. The graphs for the [C2mim][MeSO3]−H2O binary systems in Figure 13 also display a similar shape as the IL−water systems with [TFO]−, [TFA]−, and [EtSO4]−, but are in magnitude smaller. As for the graphs in Figure 13 for the two binary water systems with [C2mim][AcO] and [C2mim][SCN], these both appear to be unreasonably different from the other data sets shown in Figure 13, and we caution here that the corresponding data sets S50 and S67 may be questionable. Specifically, both data sets were obtained from two studies by Anantharaj and Banerjee where they obtained densities for binary IL−molecular solvent systems using in each study the same IL but varying molecular solvents.56,57 For each binary system, the obtained VE data were extremely small in magnitude and thus resulted in very small slope and intercept values for

−0.0262 0.0074 0.996 6.22 −12.18 8.36 −2.39 0.997 0.011 0.253 0.7

56 S46 57 S63

57 S62

−0.0288 0.0083 0.999 7.56 −15.53 11.27 −3.30 0.999 0.003 0.257 0.8 −0.0309 0.0087 0.988 8.78 −17.99 12.87 −3.66 0.991 0.003 0.249 0.8 −0.0266 0.0076 0.995 7.28 −14.77 10.54 −3.05 0.997 0.002 0.259 0.7 −0.0253 0.0073 0.998 7.77 −15.71 11.18 −3.24 0.998 0.002 0.265 0.7 −0.0257 0.0074 0.998 7.47 −15.19 10.88 −3.16 0.998 0.002 0.259 0.7 −0.0263 0.0075 0.997 7.53 −15.14 10.69 −3.08 0.998 0.003 0.259 0.7 −0.0281 0.0081 0.996 6.73 −13.43 9.42 −2.72 0.998 0.027 0.257 0.8

Article

am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL,maxslope 1000am,max/ cm3·mol−1 ref data set

−0.0259 0.0073 0.996 6.60 −12.82 8.68 −2.47 0.997 0.004 0.257 0.7

−0.0283 0.0080 0.998 7.10 −14.05 9.74 −2.79 0.999 0.003 0.252 0.8

thiophene thiophene

[C2mim][SCN] [C2mim][AcO]

quinoline quinoline


indoline indoline


pyridine pyridine

[C2mim][SCN]

pyrrole

[C2mim][AcO]

pyrrole

[C2mim][SCN]

1

IL

Table 8. continued

[C2mim][AcO]


P



Article

Table 9. Fit Parameters to eq 4 for VE in cm3·mL−1 for Binary Systems of Molecular Solvent (1) and IL (IL) where VE Exhibits a Crossover Point in Temperature Dependence 1

H2O

H2O

MeOH

EtOH

IL

[C2mim][C(OC2)2OSO3]

[HOC2NH3][HCO2]

[C2mim][BETA]

[C4mim][ClO4]

T range/K am,4 am,3 am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 xIL, min 1000am,min/cm3·mol−1 xIL,max 1000am,max/cm3·mol−1 ref data set

298.15−313.15 −0.0755 0.2260 −0.2134 0.0626 0.970 26.41 −78.53 74.57 −22.35 0.974 0.014 0.794a −1.7 0.210a 1.6 10 S39

288.15−323.15 0.0481 −0.0537 −0.0063 0.0107 0.869 −10.01 6.26 10.46 −6.36 0.897 0.016 0.836a −3.3 0.256a 1.6 42 S85

298.15−313.15 0.6951 −0.1827 0.1486 −0.0354 0.928 −19.61 50.69 −40.94 9.82 0.905 0.014 0.1649b −2.6 0.692b 2.1 69 S129

283.15−343.15 −0.3416 0.4154 −0.0091 −0.0691 0.659 93.79 −120.13 16.98 10.55 0.570 0.271 0.298b −13.1 0.821b 11.8 39 S98

a E

V values of data set are all less than zero. bVE values of data set are both greater and less than zero, and the mole fractions coincide with the minimum and maximum of VE.

Table 10. Fit Parameters to eq 4 but Using Molality Instead of Mole Fraction for VE in cm3·mL−1 from Sadeghi and Ebrahimi51 for Binary Systems of Molecular Solvent (1) and [C6mim]Cl, 288.15 K to 313.15 K 1

H2O

MeOH

EtOH

C3OH

2-propanol

C4OH

CH3CN

am,2 am,1 R2m ab,4 ab,3 ab,2 ab,1 R2b σ/cm3·mol−1 data set

0.00036 0.00199 1.000

0.00258 −0.01067 0.999

0.00381 −0.01502 1.000

0.00337 −0.01606 1.000

−0.49 0.93 0.996 0.006 S162

0.00395 −0.01421 1.000 −3.03 4.67 −2.84 0.90 0.998 0.015 S164

0.00497 −0.01848 1.000

−0.12 −0.73 1.000 0.001 S161

0.00208 −0.01152 0.999 −0.18 0.73 −1.25 1.03 0.994 0.031 S163

1.15 −2.05 1.74 1.000 0.013 S165

0.02 −0.56 0.31 0.975 0.007 S166

0.65 −1.40 1.93 1.000 0.019 S167

temperature weakens the hydrogen bonded water structure this reorganization is facilitated leading to the observed increasing VE temperature dependence. We should also point out that the interactions between IL and solvent must be favorable in the first place for the binary IL−water systems discussed here because these are completely miscible, at least for the investigated temperature ranges. Even though alcohols are also hydrogen-bonded, it is evident from Figures 6 to 11 that the reorganization of the molecular solvent around the IL ions is either a negligible contribution or leads to a volume decrease. It is interesting that application of the Prigorine−Flory−Patterson (PFP) theory resulted in a reasonably good reproduction of VE data for methanol binary systems with [C4mim][BF4] and [C4mim][BF6]58 even though the PFP theory does not specifically account for hydrogen bonding and strong electrostatic interactions as pointed out by Kumar et al.30 Application of the PFP theory allows the evaluation of three contributions to VE: an interactional contribution, a free volume contribution, and an internal pressure contribution. For methanol binary systems with [C4mim][BF4] and [C4mim][BF6] the largest contribution to VE was found to be the internal pressure contribution,58 which is interestingly

their temperature dependence as can be seen in Figure 13. Compared to the many other studied binary IL−molecular solvent systems summarized in the Supporting Information and Tables 7 to 10, their VE values are the smallest from all studies. It seems particularly questionable that binary systems with water as the molecular solvent would result in such low VE values and not differentiate more from the other molecular solvents that were composed of aromatic compounds such as thiophene or aniline. Disregarding then data sets S50 and S67, one might therefore be inclined to conclude that only IL−water binary systems with chaotropic IL anions display a positive VE temperature dependence, if it were not for the [C2mim][TFA]−H2O binary system (data set S150), where the [TFA]− anion is kosmotropic. Interestingly, the only two IL−water binary systems displaying a negative VE temperature dependence are with the ILs [(HOC2)2NH2][AcO] and [Pyr][C7CO2] where [AcO]− and possibly also [C7CO2]− are kosmotropic (data sets S155 and S77 in Table 7). In any case, it appears that the largest contribution to VE of IL−water binary systems stems from a reorganization of the water structure around the IL ions, which apparently requires in most instances an increase of volume because as an increase in Q



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Figure 8. (a) Slopes and (b) intercepts of least linear square fits to VE temperature dependencies for the [C4mim][MeSO4]−EtOH binary system for data sets □, S72; ○, S84; ×, S94, and ▽, S123 and the [C4mim][MeSO4]−H2O binary system for data sets, △, S83, and ◇, S102. The solid lines are polynomial fits to data sets S72 and S83 with coefficients listed in Tables 7 and 8.

Figure 6. (a) Slopes and (b) intercepts of least linear square fits to VE temperature dependencies for the [C2mim][TfO]−EtOH binary system for data sets ×, S73 and □, S155 and the [C2mim][TfO]− H2O binary system for data sets ○, S103; △, S148, and ◇, S153. The solid lines are polynomial fits to data sets S148 and S155 with coefficients listed in Tables 7 and 8.

Figure 7. (a) Slopes and (b) intercepts of least linear square fits to VE temperature dependencies for the [C2mim][EtSO4]−EtOH binary system for data sets □, S33 and ×, S71 and the [C2mim][EtSO4]− H2O binary system for data sets ○, S32; △, S101; ▽, S113, and ◇, S149. The solid lines are polynomial fits to data sets S71 and S149 with coefficients listed in Tables 7 and 8.

Figure 9. (a) Slopes and (b) intercepts of least linear square fits to VE temperature dependencies for the [C4mim][BF4]−EtOH binary system for data sets ×, S69, and □, S121 and the [C4mim][BF4]− H2O binary system for data sets △, S35; ◇, S61, and ▽, S75. The solid lines are polynomial fits to data sets S35 and S69 with coefficients listed in Tables 7 and 8.

the contribution most closely related to structure-breaking effects of the molecular solvent.43 Because the internal pressure contribution was also found to be negative this might indeed indicate that the reorganization of the alcohols around the IL ions leads to a volume reduction. Indeed, there is not a single IL−primary alcohol system that displays an increasing VE temperature dependence. The PFP theory was applied several times for VE evaluations of binary IL−molecular solvent systems19,30,43,58,59 and reproduced reasonably well the VE data

as long as their shape was not too complex such as, for example, the [C4mim][BF4]−N-methyl-2-pyrrolidinone binary system.19 The PFP theory did also not perform well for binary IL systems with ethylene glycol based molecular solvents.30,59 The interested reader is referred to these works and references therein to learn more about the PFP theory. We also should mention at this point that the Sharma group used graph theory, i.e., a topological approach for quantifying specific R



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Figure 12. Comparison of (a) slopes and (b) intercepts of VE temperature dependences of several IL−water binary systems with the same [C4mim]+ cation but different anions: [SCN]− (□, data set S51), [N(CN)2]− (×, data set S139), [BF4]− (△, data set S35), [MeSO4]− (◇, data set S83), [MeSO3]− (▽, data set S2), and [TFO]− (solid lines from polynomial fits with coefficients listed in Table 8 for data set S158). Figure 10. (a) Slopes and (b) intercepts of least linear square fits to VE temperature dependencies for the [C1mim][MeSO4]−EtOH binary system for data sets □, S93 and ×, S82 and the [C4mim][TfO]−H2O binary system for data sets, △, S104; ○, S128; ◇, S140, and ▽, S158. The solid lines are polynomial fits to data sets S82 and S158 with coefficients listed in Tables 7 and 8.

Figure 13. Comparison of (a) slopes and (b) intercepts of VE temperature dependences of several IL−water binary systems with the same [C2mim]+ cation but different anions: [SCN]− (○, data set S67), [AcO]− (×, data set S50), [MeSO3]− (◇, data set S4), [TFO]− (△, data set S148), [TFA]− (□, data set S150), and [EtSO4]− (solid lines from polynomial fits with coefficients listed in Table 8 for data set S149).

the graphs in Figure 14 are again very similar, but the magnitudes vary more than was observed for the IL−water binary systems in Figures 12 and 13. Perhaps here too the reorganization of the ethanol is the largest VE contribution but not as large in magnitude as is the case for water as the molecular solvent and contributing a negative VE contribution as opposed to a positive VE contribution. Therefore, other VE contributions as accounted for by the PFP theory are modulating the VE more so for IL binary systems with ethanol than for IL binary systems with water. Furthermore, it is noteworthy that for data sets S89−S91 for [C4mim][NO3] with ethanol, 1-propanol, and 1-butanol, the magnitude of the negative temperature dependence is systematically decreasing resulting also in smaller negative VE values as the authors reporting these data sets noted.35 Figure 15 compares binary IL−ethanol systems with a homologous series of [Cnmim][BF4] ILs showing graphs for [C4mim][BF4]−ethanol as solid lines to again aid the eye (data set S69). While the shapes of the graphs for the [C6mim][BF4]−ethanol binary system (data set S70) resemble that for [C4mim][BF4]−ethanol and are only slightly decreased in

Figure 11. (a) Slopes and (b) intercepts of least linear square fits to VE temperature dependencies for the [C4mim][BF4]−MeOH binary system for data sets □, S40 and ×, S109; the [C4mim][N(CN)2]− H2O binary system for data sets ○, S120 and △, S139; and the [C4mpyr][TfO]−H2O binary system for data sets +, S134 and ◇, S157. The solid lines are polynomial fits to data sets S40 and S139, and the dashed lines are polynomial fits to data set S157, with all fit coefficients listed in Tables 7 and 8

intermolecular interactions, to rather successfully reproduce VE data of [C2mim][BF4] binary systems with pyridine and several isomeric picolines (data sets S13−S16).60 Figure 14 inspects the effect of different IL anions on the slope and intercept of the VE temperature dependence for ethanol binary systems with [C4mim]+ based ILs. The shapes of S



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[Pyr][NO3]−H2O; S26, [C3dmim][BF4]−H2O; S99, [C4py][BF4]−H2O; S100, [C8py][BF4]−H2O; S18, [C4mim][Glu]− BzOH; S19, [C4mim][Gly]−BzOH; S59, [C4mim][PF6]− MEA; S60, [C4mim][PF6]−DMEA. More than half of these binary systems involve molecular solvents that are of similar size as the IL ions. Interestingly, a fair number of the data sets of the binary systems with steepest slope at xIL > 0.5 also display very large slope values. In this regard, when inspecting Tables 7 to 9, the largest positive values for 1000am,max/cm3·mol−1 are found for data sets S18, [C4mim][Glu]−BzOH (18.4); S19, [C4mim][Gly]−BzOH (21.1); and S79, [Pyr][C7CO2]−CH3CN (36.9). Very large negative values for 1000am,max/cm3·mol−1 are found for data sets with molecular solvents that bear a carbonyl functional group: S34, [C4mim][BF4]−methyl acetate (−19.7); S92, [C8mim][PF6]−butanone (−20.9); S17, [C4mim][BF4]− BzAld (−23.0); S117, [C 2 mim][TFO]−methyl acetate (−26.4); S118, [C2mim][TFO]−ethyl acetate (−28.0); S116, [C2mim][TFO]−acetone (−29.9); and S30, [C4mim][BF4]− N-methyl-2-pyrrolidinone (−32.3). Data sets with nitrogen bearing aromatic solvents: S16, [C2mim][BF4]−g-picoline (−18.2); S14, [C 2 mim][BF4 ]−a-picoline (−19.3); S15, [C2mim][BF4]−b-picoline (−21.5); S27, [C4mim][BF4]− aniline (−26.2); and data sets with dimethylated ethylene glycols as molecular solvents: S112, [C4mim][PF6]−EGDME (−23.8); S111 [C4mim][PF6]−DEGDME (−26.3), are also showing large negative VE temperature dependences. Some of these binary systems are also among those that display the largest negative VE values, which are topped by data sets S118, [C2mim][TFO]−ethyl acetate and S116, [C2mim][TFO]− acetone, both having VE values up to about −7.3 cm3·mol−1. The carbonyl functional group present in the above-listed molecular solvents is likely to hydrogen bond with the most acidic H(2) proton of the imidazolium ring of the IL. One may speculate that this hydrogen bond is rather temperaturedependent and the change in volume from breaking the hydrogen bond at higher temperature is very large, which thus would explain the observed large magnitudes of the slope values. We also note that many of the above stated binary systems with a strong VE-temperature dependence concern aromatic molecular solvents. As briefly noted in a recent review,54 aromatic compounds have been observed to form inclusion compounds with imidazolium based ILs, and the breaking of these specific IL−aromatic solvent structures at higher temperatures may also involve large changes in molar volumes.

Figure 14. Comparison of (a) slopes and (b) intercepts of VE temperature dependences of several IL−EtOH binary systems with the same [C4mim]+ cation but different anions: [SCN]− (△, data set S126), [NO3]− (×, data set S89), [TFO]− (○, data set S74), and [MeSO4]− (solid lines from polynomial fits with coefficients listed in Table 7 for data set S72).

Figure 15. Comparison of (a) slopes and (b) intercepts of VE temperature dependences of several IL−EtOH binary systems with the same [BF4]− anion and imidazolium based cation with an increasing alkyl side chain: [C8mim]+ (○, data set S97), [C6mim]+ (□, data set S70), and [C4mim]+ (solid lines from polynomial fits with coefficients listed in Table 7 for data set S69).

magnitude, the data set S97 for the [C8mim][BF4]−ethanol system displays extrema near xIL = 0.7, and the VE plots themselves shown in the Supporting Information section seem to be of lower quality and are not too well reproduced by fitting with eq 4 as pointed out earlier. Given that the large majority of binary IL−molecular solvent systems display their extrema for the VE temperature dependences for xIL values < 0.5, mostly 0.2 < xIL < 0.3 (Tables 7 to 9), the validity of data set S97 may have to be first confirmed by others repeating independently these VE measurements. Several other general observations can be made about the VE data sets summarized in Tables 7 to 9. Besides the somewhat questionable data sets S97, S95, and S50, it is worthwhile to specifically list the relatively few data sets where xIL > 0.5 for the steepest VE temperature dependence: S77, [Pyr][C7CO2]−H2O; S87, [HOC2NH3][HCO2]−EtOH; S80, [Pyr][C7CO2]−EtOH; S9, [NEP][C2CO2]−C3OH; S10, [NEP][C2CO2]−C4OH; S111, [C4mim][PF6]−DEGDME; S6, [C4mim][PF6]−BzAld; S17, [C4mim][BF4]−BzAld; S30, [C4mim][BF4]−N-methyl-2-pyrrolidinone; S31, [C4mim][PF 6 ]−N-methyl-2-pyrrolidinone; S27, [C 4 mim][BF 4 ]− aniline; S15, [C4mim][BF4]−b-picoline; S16, [C4mim][BF4]− c-picoline; S28, [Et2NH2][HSO4]−DMSO; S76,

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CONCLUSION Overall, we have shown that excess molar volumes for a total of 167 inspected binary IL−molecular solvent systems are generally linear with temperature. Plots of slopes and intercepts of the linear VE temperature dependence as a function composition offer a convenient way to adequately fit the entire VE data set and to compare VE data sets even when they were measured over different temperature ranges. A comparison of VE data sets in this way revealed several questionable data sets reported in the literature. The plots of slopes and intercepts were found to be rather insensitive to the nature of the IL cation or anion for binary IL systems with the protic solvents water and primary alcohols. It appears that for these systems the main contributing factor to VE stems from the reorganization of the molecular solvent, which in nearly all cases for water gives rise to a positive VE temperature dependence but for the alcohols always a negative VE temperature dependence. It is remarkable that T



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(11) Taib, M. M.; Murugesan, T. Densities and Excess Molar Volumes of Binary Mixtures of Bis(2-Hydroxyethyl)ammonium Acetate + Water and Monoethanolamine + Bis(2-Hydroxyethyl)ammonium Acetate at Temperatures from (303.15 to 353.15) K. J. Chem. Eng. Data 2010, 55, 5910−5913. (12) González, E. J.; González, B.; Calvar, N.; Domínguez, Á . Physical Properties of Binary Mixtures of the Ionic Liquid 1-Ethyl-3Methylimidazolium Ethyl Sulfate with Several Alcohols at T = (298.15, 313.15, and 328.15) K and Atmospheric Pressure. J. Chem. Eng. Data 2007, 52, 1641−1648. (13) González, E. J.; Alonso, L.; Domínguez, Á . Physical Properties of Binary Mixtures of the Ionic Liquid 1-Methyl-3-Octylimidazolium Chloride with Methanol, Ethanol, and 1-Propanol at T = (298.15, 313.15, and 328.15) K and at P) 0.1 MPa. J. Chem. Eng. Data 2006, 51, 1446−1452. (14) Gómez, E.; González, B.; Domínguez, Á .; Tojo, E.; Tojo, J. Dynamic Viscosities of a Series of 1-Alkyl-3-Methylimidazolium Chloride Ionic Liquids and Their Binary Mixtures with Water at Several Temperatures. J. Chem. Eng. Data 2006, 51, 696−701. (15) González, E. J.; Domínguez, Á .; Macedo, E. A. Physical and Excess Properties of Eight Binary Mixtures Containing Water and Ionic Liquids. J. Chem. Eng. Data 2012, 57, 2165−2176. (16) Rodríguez, H.; Brennecke, J. F. Temperature and Composition Dependence of the Density and Viscosity of Binary Mixtures of Water + Ionic Liquid. J. Chem. Eng. Data 2006, 51, 2145−2155. (17) Pereiro, A. B.; Rodríguez, A. Measurement and Correlation of (liquid + liquid) Equilibrium of the Azeotrope (cyclohexane+2Butanone) with Different Ionic Liquids at T = 298.15 K. J. Chem. Thermodyn. 2008, 40, 1282−1289. (18) Zhong, Y.; Wang, H.; Diao, K. Densities and Excess Volumes of Binary Mixtures of the Ionic Liquid 1-Butyl-3-Methylimidazolium Hexafluorophosphate with Aromatic Compound at T = (298.15 to 313.15)K. J. Chem. Thermodyn. 2007, 39, 291−296. (19) Qi, F.; Wang, H. Application of Prigogine-Flory-Patterson Theory to Excess Molar Volume of Mixtures of 1-Butyl-3Methylimidazolium Ionic Liquids with N-Methyl-2-Pyrrolidinone. J. Chem. Thermodyn. 2009, 41, 265−272. (20) Fan, W.; Zhou, Q.; Sun, J.; Zhang, S. Density, Excess Molar Volume, and Viscosity for the Methyl Methacrylate + 1-Butyl-3Methylimidazolium Hexafluorophosphate Ionic Liquid Binary System at Atmospheric Pressure. J. Chem. Eng. Data 2009, 54, 2307−2311. (21) Gao, H.; Qi, F.; Wang, H. Densities and Volumetric Properties of Binary Mixtures of the Ionic Liquid 1-Butyl-3-Methylimidazolium Tetrafluoroborate with Benzaldehyde at T = (298.15 to 313.15) K. J. Chem. Thermodyn. 2009, 41, 888−892. (22) Li, Y.; Ye, H.; Zeng, P.; Qi, F. Volumetric Properties of Binary Mixtures of the Ionic Liquid 1-Butyl-3-Methylimidazolium Tetrafluoroborate with Aniline. J. Solution Chem. 2010, 39, 219−230. (23) Rebelo, L. P. N.; Najdanovic-Visak, V.; Visak, Z. P.; Nunes da Ponte, M.; Szydlowski, J.; Cerdeirina, C. A.; Troncoso, J.; Romani, L.; Esperanca, J. M. S. S.; Guedes, H. J. R.; de Sousa, H. C. A Detailed Thermodynamic Analysis of [C4mim][BF4] + Water as a Case Study to Model Ionic Liquid Aqueous Solutions. Green Chem. 2004, 6, 369− 381. (24) Zafarani-Moattar, M. T.; Shekaari, H. Volumetric and Speed of Sound of Ionic Liquid, 1-Butyl-3-Methylimidazolium Hexafluorophosphate with Acetonitrile and Methanol at T = (298.15 to 318.15) K. J. Chem. Eng. Data 2005, 50, 1694−1699. (25) Li, J.-G.; Hu, Y.-F.; Sun, S.-F.; Liu, Y.-S.; Liu, Z.-C. Densities and Dynamic Viscosities of the Binary System (water + 1-Hexyl-3Methylimidazolium Bromide) at Different Temperatures. J. Chem. Thermodyn. 2010, 42, 904−908. (26) García-Miaja, G.; Troncoso, J.; Romaní, L. Excess Enthalpy, Density, and Heat Capacity for Binary Systems of AlkylimidazoliumBased Ionic Liquids + Water. J. Chem. Thermodyn. 2009, 41, 161−166. (27) García-Mardones, M.; Pérez-Gregorio, V.; Guerrero, H.; Bandrés, I.; Lafuente, C. Thermodynamic Study of Binary Mixtures Containing 1-Butylpyridinium Tetrafluoroborate and Methanol, or Ethanol. J. Chem. Thermodyn. 2010, 42, 1500−1505.

this difference in the temperature dependence is even observed for the four data sets listed in Table 9 displaying a crossover in temperature dependence, where for the two data sets S39 and S85 for binary systems with water the VE temperature dependence is positive at water-rich compositions, while for S98 and S128 for binary systems with alcohols the temperature dependence is positive for IL-rich compositions. While we focused here on VE data sets of IL−molecular solvent binary systems, the described approach of inspecting and fitting the data sets should apply for VE data sets of other binary liquid− liquid systems as well as for fitting other excess properties as long as the data sets were measured at same compositions for varying temperatures.

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ASSOCIATED CONTENT

S Supporting Information *

Analyzed data sets including the VE data from Figures 1 and 2, tabulated and plotted. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: mhoff[email protected]. Phone: 585-395-5598. Fax: 585-395-5805. Funding

This report is based upon work supported by the National Science Foundation under RUI-Grant No. 0842960. Notes

The authors declare no competing financial interest.

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