Densities and Viscosities of Binary Mixtures of 2-Ethyl-1,1,3,3

Article pubs.acs.org/jced

Densities and Viscosities of Binary Mixtures of 2‑Ethyl-1,1,3,3tetramethylguanidinium Ionic Liquids with Ethanol and 1‑Propanol Xiaoxing Lu,† Di Wu,† Dengfeng Ye,† Youping Wang,‡ Yongsheng Guo,*,† and Wenjun Fang*,† †

Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China Education College, Beijing Normal University Zhuhai, Zhuhai 519085, P. R. China

‡

S Supporting Information *

ABSTRACT: Two guanidinium-based ionic liquids (ILs), 2-ethyl-1,1,3,3tetramethylguanidinium bis(trifluoromethylsulfonyl)imide ([TMGEt][NTf2]) and ethyl sulfate ([TMGEt][C2OSO3]) were synthesized and characterized. Experimental densities and viscosities for the binary mixtures of the ILs with ethanol and 1-propanol from (293.15 to 323.15) K were measured over the whole composition range and at the atmospheric pressure of 0.1 MPa. The excess molar volumes (VmE) and the viscosity deviations (Δη) for the binary systems were calculated and fitted with the Redlich−Kister equation. It is found that the density of [TMGEt][NTf2] is much higher than that of [TMGEt][C2OSO3] at the same temperature, while the viscosity of the former with the value of 74.61 mPa·s is only 1/9 of that of the latter at 293.15 K. This indicates that the difference of the anions has a significant influence on the density and viscosity of the ILs with the same guanidinium cation. The addition of ethanol or 1-propanol leads to negative values of VmE and Δη, which result from the efficient packing of the constituents in the binary mixtures and the weakening of anion−cation interactions of the ILs. The partial molar volumes, excess partial molar volumes, Gibbs energy, and excess Gibbs energy of activation for viscous flow of the binary mixtures also have been calculated. It is hoped that the results provide useful information for the fundamental physicochemical properties of the guanidinium-based ILs and their further applications.

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INTRODUCTION Organic salts with melting points lower than 373.15 K are generally considered as ionic liquids (ILs).1−3 ILs have so many attractive features, such as low melting point, low volatility, nonflammability, and high thermal and chemical stabilities, that they have been studied extensively since the end of the 20th century. Nowadays, a large amount of scientific works have been carried out with ILs as alternative solvents for dissolution of various substances (acidic gases,4−8 cellulose,9−11 metals, and metallic compounds,12−14 etc.) and extraction of different target compounds (hydrocarbons,15−19 organic sulfurs,20−24 and proteins,25,26 etc.) from liquids. The ILs are also treated as specific reaction media in some cases.27−30 As the cations and anions are both switchable, new species of ILs are continuously synthesized in the laboratory for various purposes. By far, the most favored cation and anion are the imidazolium cation and the bis(trifluoromethylsulfonyl)imide ([NTf2]−) anion. In most cases, the ILs containing these ionic moieties are low-viscous, low-melting, and stable to heat and moisture, and they are often inert in terms of chemical changes. However, the disadvantage of the higher viscosity of the pure IL compared with traditional solvents is considerable. Thus, a combination of the IL with other low-viscous and low-toxic liquid components such as ethanol can be considered as an alternative to the pure IL. This approach may also alleviate the cost problem for expensive ILs such as the [NTf2]-based ones. © XXXX American Chemical Society

On the other hand, the introduction of the ethyl sulfate anion ([C2OSO3]−) to the ILs, considered from an environmental point of view, leads to a generation of novel ILs which are lowcost and halogen-free.31 These ILs containing [C2OSO3]− can be promising candidates to replace the expensive ILs when keeping good performance at the same time.19,32 In our previous work, guanidinium-based ILs including 2-ethyl-1,1,3,3-tetramethylguanidinium bis(trifluoromethylsulfonyl)imide ([TMGEt][NTf2]) and ethyl sulfate ([TMGEt][C2OSO3]) have been applied to absorb SO2 at different temperatures, which demonstrated satisfactory performance.33 Considering that the knowledge of fundamental physicochemical properties is important to determine the optimal conditions and it is better to be understood for further applications of ILs, in this work, the densities and viscosities for [TMGEt][NTf2] and [TMGEt][C2OSO3] and their binary mixtures with ethanol and 1-propanol have been measured at different temperatures. The calculated excess molar volumes (VmE) and the viscosity deviations (Δη) provide information about the properties of the ILs and their alcohol solutions. Received: March 19, 2015 Accepted: August 4, 2015

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DOI: 10.1021/acs.jced.5b00259 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Chemical Specifications chemical name

water mass fraction

purification method

analytical method

< 0.0001

none none none none none none heating at 353 K under vacuum for 48 h freeze-drying

NMR,c KFd

< 0.0002

freeze-drying

NMR,c KFd

source

purity

ethanol 1-propanol ethyl acetate dichloromethane iodoethane 1,1,3,3-tetramethylguanidine bis(trifluoromethylsulfonyl) imide lithium

Aladdin Aladdin Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich Aldrich Aldrich

< 0.002 < 0.0005 < 0.00005 < 0.00001 < 0.001 < 0.005

2-ethyl-1,1,3,3-tetramethylguanidinium bis(trifluoromethylsulfonyl)imide 2-ethyl-1,1,3,3-tetramethylguanidinium ethyl sulfate

synthesized

0.998a 0.999a 0.998a 0.998a 0.990a 0.990a 0.9995 trace metals basisa 0.948b

synthesized

0.980b

a

b

c1

d

13

In mass fraction. In mole fraction. H and C nuclear magnetic resonance. Karl Fischer titration.

Scheme 1. Synthetic Approaches of the 2-Ethyl-1,1,3,3-tetramethylguanidinium ILs

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EXPERIMENTAL SECTION Materials. Ethanol (mass fraction > 0.998, CAS Registry No. 64-17-5) and 1-propanol (> 0.999, CAS Registry No. 71-23-8) were purchased from Aladdin. Iodoethane (> 0.990, CAS Registry No. 75-03-6), dichloromethane (> 0.998, CAS Registry No. 75-09-2) and ethyl acetate (> 0.998, CAS Registry No. 141-78-6) were purchased from Sigma-Aldrich. 1,1,3,3Tetramethylguanidine (> 0.990, CAS Registry No. 80-70-6) and bis(trifluoromethylsulfonyl)imide lithium (Li[NTf2], 0.9995 trace metals basis, CAS Registry No. 90076-65-6) were purchased from Aldrich. Li[NTf2] was heated at about 353 K under vacuum (< 10 Pa) for at least 48 h to remove water thoroughly. The other agents were used without further purification. Detailed information on the reagents can be found in Table 1. Water was produced by a Millipore Q3 system. Syntheses and Characterizations of ILs. The synthetic approaches of the guanidinium-based ILs studied in this work are briefly shown in Scheme 1. Iodoethane (0.10 mol) and ethyl acetate (50 mL) were loaded into a 250 mL round-bottom flask immersed in an ice−water bath. 1,1,3,3-Tetramethylguanidine (0.10 mol) in ethyl acetate (50 mL) was added dropwise into the flask. The mixture was magnetically stirred at 360 rpm for 24 h, and was subsequently filtered. The solid was recrystallized with the mixed solvent of methanol and ethyl acetate. A colorless crystalline compound, 2-ethyl-1,1,3,3-tetramethylguanidinium iodide ([TMGEt]I), was obtained. Thereafter, [TMGEt]I was dissolved in dichloromethane, and mixed with an aqueous solution of an equivalent mole of Li[NTf2]. The mixture was magnetically stirred for 6 h under ambient conditions. The lower organic layer was washed with water until no iodide ion in the water was observed through

Table 2. Density (ρ) and Viscosity (η) Data of Ethanol, 1-Propanol, and ILs at T = 298.15 K and p = 0.1 MPaa ρ/g·cm−3 substance

η/mPa·s

exptl.

lit.

exptl.

lit.

ethanol

0.78525

1.071

1-propanol

0.79949

[TMGEt][NTf2] [TMGEt][C2OSO3]

1.41003 1.16724

0.78550b 0.78517c 0.78506d 0.7855e 0.78522f 0.79956b 0.79952c 0.79974d 0.7996e 0.79940f N.A. N.A.

1.091b 1.09c 1.078d 1.0569e 1.085f 1.941b 1.94c 1.9448d 1.973g 1.951f N.A. N.A.

1.948

58.86 441.5

Uncertainties are u(T) = 0.01 K, u(p) = 200 Pa, u(ρ) = 3·10−5 g·cm−3 and u(η) = 0.005·η for the experimental data. N.A. = not available. b From ref 34. cFrom ref 35. dFrom ref 36. eFrom ref 37. fFrom ref 38. g From ref 39. a

a titration with AgNO3 aqueous solution. After evaporation of the volatile component, the freeze-drying (Peking Sihuan Scientific Instrument, LGJ-10C, PR China) method was applied. Finally, [TMGEt][NTf2] was obtained and stored in a dry nitrogen atmosphere. The synthesis of [TMGEt][C2OSO3] was more facile than that of [TMGEt][NTf2]. 1,1,3,3-Tetramethylguanidine (0.10 mol) and diethyl sulfate (0.10 mol) reacted in an ice-water bath for 24 h with ethyl acetate as the solvent. The crude product was washed with ethyl acetate for at least 3 times. After evaporation of the B



Article

Figure 1. Experimental density (ρ) for binary systems of (a) [TMGEt][NTf2] (1) + ethanol (2), (b) [TMGEt][NTf2] (1) + 1-propanol (2), (c) [TMGEt][C2OSO3] (1) + ethanol (2), and (d) [TMGEt][C2OSO3] (1) + 1-propanol (2) at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K.

Figure 2. Experimental viscosity (η) for binary systems of (a) [TMGEt][NTf2] (1) + ethanol (2), (b) [TMGEt][NTf2] (1) + 1-propanol (2), (c) [TMGEt][C2OSO3] (1) + ethanol (2), and (d) [TMGEt][C2OSO3] (1) + 1-propanol (2) at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K. C



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Table 3. Experimental Density (ρ) for Binary Systems of IL (1) + Alcohol (2) at T = (293.15 to 323.15) K and p = 0.1 MPaa ρ/g·cm−3

a

x1

T/K = 293.15

T/K = 298.15

0.0000 0.1006 0.2004 0.3001 0.4005 0.5018 0.6011 0.6999 0.8020 0.8920 1.0000

0.78962 1.02301 1.14825 1.22591 1.27870 1.31697 1.34548 1.36771 1.38671 1.40066 1.41489

0.78525 1.01829 1.14337 1.22107 1.27382 1.31210 1.34060 1.36279 1.38182 1.39579 1.41003

0.0000 0.1024 0.2019 0.2973 0.4011 0.4988 0.5962 0.6997 0.7931 0.9014 1.0000

0.80349 0.99739 1.11471 1.19209 1.25275 1.29536 1.32836 1.35659 1.37781 1.39872 1.41489

0.79949 0.99296 1.11007 1.18740 1.24797 1.29053 1.32353 1.35173 1.37297 1.39386 1.41003

0.0000 0.0998 0.2003 0.3006 0.4016 0.4980 0.5996 0.6976 0.7969 0.9008 1.0000

0.78962 0.91021 0.98430 1.03378 1.06961 1.09576 1.11754 1.13451 1.14858 1.16083 1.17076

0.78525 0.90620 0.98034 1.03000 1.06596 1.09212 1.11391 1.13091 1.14502 1.15730 1.16724

0.0000 0.0997 0.2003 0.3066 0.3996 0.5016 0.5989 0.6984 0.7999 0.8981 1.0000

0.80349 0.89860 0.96492 1.01648 1.05152 1.08240 1.10632 1.12659 1.14402 1.15838 1.17076

0.79949 0.89470 0.96116 1.01278 1.04786 1.07878 1.10273 1.12301 1.14047 1.15486 1.16724

T/K = 303.15

T/K = 308.15

[TMGEt][NTf2] (1) + Ethanol (2) 0.78089 0.77652 1.01356 1.00882 1.13851 1.13365 1.21629 1.21151 1.26894 1.26409 1.30724 1.30236 1.33571 1.33083 1.35794 1.35307 1.37695 1.37211 1.39094 1.38612 1.40519 1.40038 [TMGEt][NTf2] (1) + 1-Propanol (2) 0.79546 0.79139 0.98850 0.98403 1.10548 1.10081 1.18267 1.17793 1.24316 1.23835 1.28570 1.28088 1.31870 1.31387 1.34689 1.34209 1.36814 1.36332 1.38902 1.38421 1.40519 1.40038 [TMGEt][C2OSO3] (1) + Ethanol (2) 0.78089 0.77652 0.90218 0.89818 0.97655 0.97266 1.02622 1.02245 1.06227 1.05860 1.08847 1.08484 1.11031 1.10673 1.12733 1.12377 1.14146 1.13792 1.15379 1.15029 1.16376 1.16028 [TMGEt][C2OSO3] (1) + 1-Propanol (2) 0.79546 0.79139 0.89090 0.88703 0.95741 0.95365 1.00910 1.00542 1.04426 1.04062 1.07517 1.07158 1.09915 1.09558 1.11944 1.11589 1.13693 1.13341 1.15136 1.14785 1.16376 1.16028

T/K = 313.15

T/K = 318.15

T/K = 323.15

0.77212 1.00407 1.12885 1.20671 1.25925 1.29745 1.32597 1.34822 1.36728 1.38131 1.39559

0.76771 0.99926 1.12403 1.20181 1.25443 1.29257 1.32111 1.34340 1.36245 1.37652 1.39080

0.76326 0.99444 1.11921 1.19701 1.24962 1.28774 1.31628 1.33859 1.35763 1.37174 1.38603

0.78729 0.97955 1.09613 1.17318 1.23359 1.27607 1.30906 1.33729 1.35851 1.37942 1.39559

0.78314 0.97503 1.09146 1.16842 1.22878 1.27127 1.30424 1.33249 1.35372 1.37463 1.39080

0.77893 0.97048 1.08671 1.16366 1.22397 1.26646 1.29940 1.32770 1.34894 1.36987 1.38603

0.77212 0.89415 0.96870 1.01866 1.05491 1.08122 1.10316 1.12023 1.13439 1.14678 1.15680

0.76771 0.89012 0.96481 1.01486 1.05124 1.07762 1.09962 1.11666 1.13088 1.14326 1.15333

0.76326 0.88607 0.96091 1.01105 1.04755 1.07402 1.09611 1.11314 1.12739 1.13976 1.14987

0.78729 0.88316 0.94988 1.00173 1.03698 1.06800 1.09203 1.11237 1.12990 1.14435 1.15680

0.78314 0.87926 0.94611 0.99804 1.03337 1.06443 1.08850 1.10886 1.12640 1.14087 1.15333

0.77893 0.87535 0.94233 0.99435 1.02973 1.06087 1.08497 1.10536 1.12293 1.13740 1.14987

Uncertainties are u(T) = 0.01 K, u(p) = 200 Pa, u(x) = 0.0001, and u(ρ) = 3·10−5 g·cm−3.

6.06 (1H, CNH+). δC: 12.79 and 14.92 (N+−C−CH3), 39.58 to 40.45 (N−CH3), 43.65 (N+−CH2−C), 115.98 to 123.64 (−CF3), 161.49 (N+C). [TMGEt][C2OSO3]. δH: 1.21 to 1.32 (3H, N+−C−CH3), 1.27 to 1.32 (3H, O−C−CH3), 2.99 to 3.07 (12H, N−CH3), 3.24 to 3.31 (2H, N+−CH2−C), 4.06 to 4.10 (2H, O−CH2−C), 7.54 and 7.91 (1H, CNH+). δC: 13.02 and 15.20 (N+−C−CH3), 15.13 (O−C−CH 3 ), 39.76 to 40.37 (N−CH 3 ), 43.55 (N+−CH2−C), 63.13 (O−CH2−C), 161.57 (N+C).

volatile components, the freeze-drying method was followed. The liquid product, [TMGEt][C2OSO3], was obtained and stored in a dry nitrogen atmosphere. Characterizations of the synthesized ILs by 1H and 13C NMR spectra were performed on a Bruker DMX 500 MHz NMR spectrometer with CDCl3 as solvent and tetramethylsilane as internal standard. The chemical shifts (δ) are summarized as follows: [TMGEt][NTf2]. δH: 1.18 to 1.28 (3H, N+−C−CH3), 2.94 to 3.00 (12H, N−CH3), 3.20 to 3.27 (2H, N+−CH2−C), 5.94 and D



Article

Table 4. Experimental Viscosity (η) for Binary Systems of IL (1) + Alcohol (2) at T = (293.15 to 323.15) K and p = 0.1 MPaa η/mPa·s

a

x1

T/K = 293.15

T/K = 298.15

0.0000 0.1006 0.2004 0.3001 0.4005 0.5018 0.6011 0.6999 0.8020 0.8920 1.0000

1.177 2.873 5.270 8.210 13.14 19.52 27.48 36.42 47.47 59.17 74.61

1.071 2.557 4.596 7.081 11.13 16.32 22.71 29.85 38.34 47.22 58.86

0.0000 0.1024 0.2019 0.2973 0.4011 0.4988 0.5962 0.6997 0.7931 0.9014 1.0000

2.164 4.462 7.270 10.87 16.10 21.63 28.19 36.71 45.87 58.37 74.61

1.948 3.868 6.213 9.224 13.49 18.01 23.23 29.87 37.15 46.91 58.86

0.0000 0.0998 0.2003 0.3006 0.4016 0.498 0.5996 0.6976 0.7969 0.9008 1.0000

1.177 2.824 5.826 11.42 22.83 40.88 73.39 127.4 213.6 385.6 673.4

1.071 2.546 5.136 9.821 19.07 33.16 57.20 95.44 154.0 264.4 441.5

0.0000 0.0997 0.2003 0.3066 0.3996 0.5016 0.5989 0.6984 0.7999 0.8981 1.0000

2.164 4.426 8.127 16.78 27.09 48.51 82.64 134.4 243.1 405.5 673.4

1.948 3.900 7.044 13.97 22.36 38.84 63.88 100.3 174.3 278.2 441.5

T/K = 303.15

T/K = 308.15

[TMGEt][NTf2] (1) + Ethanol (2) 0.978 0.895 2.289 2.058 4.049 3.587 6.157 5.391 9.534 8.252 13.80 11.95 19.10 16.25 24.85 20.96 31.52 26.35 38.37 31.73 47.27 38.71 [TMGEt][NTf2] (1) + 1-Propanol (2) 1.707 1.525 3.380 2.972 5.362 4.667 7.898 6.831 11.48 9.85 15.21 12.98 19.43 16.47 24.76 20.85 30.48 25.37 38.17 31.53 47.27 38.71 [TMGEt][C2OSO3] (1) + Ethanol (2) 0.978 0.895 2.307 2.096 4.559 4.072 8.524 7.459 16.15 13.81 27.11 22.56 45.41 36.71 73.08 57.39 114.2 86.55 187.9 134.9 302.5 214.6 [TMGEt][C2OSO3] (1) + 1-Propanol (2) 1.707 1.525 3.455 3.077 6.152 5.412 12.30 10.72 18.74 15.88 31.58 26.07 50.40 40.53 76.66 59.78 128.5 97.50 197.5 145.3 302.5 214.6

T/K = 313.15

T/K = 318.15

T/K = 323.15

0.822 1.861 3.213 4.757 7.206 10.32 13.99 17.94 22.30 26.65 32.2

0.756 1.689 2.884 4.227 6.344 8.977 12.15 15.52 19.11 22.55 27.09

0.698 1.515 2.606 3.780 5.627 7.837 10.65 13.58 16.54 19.32 23.14

1.366 2.630 4.093 5.966 8.525 11.21 14.12 17.73 21.42 26.43 32.20

1.228 2.340 3.684 5.248 7.433 9.743 12.24 15.26 18.28 22.43 27.09

1.107 2.094 3.283 4.640 6.437 8.553 10.70 13.27 15.77 19.26 23.14

0.822 1.910 3.656 6.577 11.92 19.04 30.14 45.97 67.31 103.7 157.2

0.756 1.746 3.298 5.839 10.38 16.26 25.65 37.27 53.38 79.60 118.3

0.698 1.601 2.990 5.215 9.094 14.01 21.20 30.75 43.06 62.70 91.22

1.366 2.751 4.790 9.145 13.59 21.82 33.1 47.59 75.47 110.0 157.2

1.228 2.471 4.266 7.690 11.73 18.48 27.42 38.53 59.70 84.19 118.3

1.107 2.228 3.819 6.777 10.20 15.79 23.01 31.66 47.99 66.48 91.22

Uncertainties are u(T) = 0.01 K, u(p) = 200 Pa, u(x) = 0.0001, and u(η) = 0.005·η.

Density and Viscosity Measurements. The samples of an IL with ethanol or 1-propanol were prepared in 20 mL glass vials by mass utilizing an analytical balance (Mettler Toledo, AL204, Switzerland) with a precision of 0.0001 g. The uncertainty of mole fraction (x) is calculated to be less than 0.00007 and is determined as u(x) = 0.0001. Density (ρ) measurements were carried out on a density meter (Anton Paar, DMA 5000M, Austria) at temperatures (T) from

The water content in the prepared ILs was measured by a Karl Fischer titration on a coulometer (Mettler Toledo, C20, Switzerland). It was found to be lower than 100 ppm for [TMGEt][NTf2] and 200 ppm for [TMGEt][C2OSO3] in mass fraction. The purities of the ILs are 98.0 mol % for [TMGEt][C2OSO3] and 94.8 mol % for [TMGEt][NTf2] according to 1H NMR peak integrals. Detailed information about the IL purities is presented in the Supporting Information. E



Article

Figure 3. Excess molar volumes (VmE) for binary systems of (a) [TMGEt][NTf2] (1) + ethanol (2), (b) [TMGEt][NTf2] (1) + 1-propanol (2), (c) [TMGEt][C2OSO3] (1) + ethanol (2), and (d) [TMGEt][C2OSO3] (1) + 1-propanol (2) at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K. The dashed lines represent the fitting results by the Redlich−Kister equation.

Figure 4. Viscosity deviations (Δη) for binary systems of (a) [TMGEt][NTf2] (1) + ethanol (2), (b) [TMGEt][NTf2] (1) + 1-propanol (2), (c) [TMGEt][C2OSO3] (1) + ethanol (2), and (d) [TMGEt][C2OSO3] (1) + 1-propanol (2) at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K. The dashed lines represent the fitting results by the Redlich−Kister equation.

(293.15 to 323.15) K and at an atmospheric pressure (p) of p = 0.1 MPa. The apparatus was calibrated with ultrapure water

and dry air before the measurements. The uncertainties are u(T) = 0.01 K and u(p) = 200 Pa. The uncertainty of density was F



Article

Table 5. Values of Parameters (Ai) and Standard Deviations (σ) of the Redlich−Kister Equation for Excess Molar Volumes (VmE) at T = (293.15 to 323.15) K and p = 0.1 MPa T/K

A0

A1

293.15 298.15 303.15 308.15 313.15 318.15 323.15

−1.814 −1.870 −1.927 −1.972 −2.015 −2.066 −2.142

2.954 3.051 3.146 3.286 3.420 3.514 3.674

293.15 298.15 303.15 308.15 313.15 318.15 323.15

−1.652 −1.677 −1.695 −1.712 −1.739 −1.769 −1.797

2.233 2.280 2.311 2.323 2.361 2.388 2.440

293.15 298.15 303.15 308.15 313.15 318.15 323.15

−1.365 −1.480 −1.581 −1.695 −1.823 −1.956 −2.101

1.198 1.304 1.412 1.489 1.533 1.582 1.587

293.15 298.15 303.15 308.15 313.15 318.15 323.15

−0.733 −0.823 −0.922 −1.029 −1.151 −1.294 −1.443

−0.211 −0.135 −0.033 0.043 0.086 0.151 0.203

A2

A3

[TMGEt][NTf2] + Ethanol −0.977 −0.490 −0.989 −0.520 −1.023 −0.560 −1.075 −0.696 −1.161 −0.764 −1.213 −0.829 −1.238 −0.973 [TMGEt][NTf2] + 1-Propanol 1.016 −1.609 0.992 −1.647 0.934 −1.627 0.889 −1.583 0.866 −1.581 0.804 −1.551 0.729 −1.600 [TMGEt][C2OSO3] + Ethanol −1.901 1.477 −1.971 1.489 −2.084 1.609 −2.171 1.733 −2.233 1.923 −2.283 2.152 −2.359 2.461 [TMGEt][C2OSO3] + 1-Propanol 0.084 0.915 0.047 0.867 0.128 0.906 0.091 0.978 0.062 1.115 0.063 1.217 −0.002 1.367

calculated to be less than 3·10−5 g·cm−3, and it is determined as u(ρ) = 3·10−5 g·cm−3 in this work. Viscosity (η) was measured by an automated microviscometer (Anton Paar, AMVn, Austria) under the same conditions with those of density measurements. The efflux time (t) of the iron ball in each sample in the quartz tube was recorded to calculate the viscosity values according to the equations given by the manufacture. A built-in Peltier thermostat with an uncertainty of u(T) = 0.01 K was used to control the temperature. The uncertainties are u(T) = 0.01 K, u(p) = 200 Pa, and u(η) = 0.005·η.

σ/cm−3·mol−1

A4

0.007 0.009 0.009 0.011 0.012 0.010 0.011 0.011 0.010 0.009 0.009 0.010 0.010 0.012 0.002 0.004 0.004 0.006 0.008 0.010 0.012 −2.480 −2.506 −2.809 −2.859 −2.950 −3.099 −3.211

0.001 0.002 0.001 0.001 0.001 0.001 0.002

that of the latter. The intramolecular hydrogen-bonding interactions in [TMGEt][C2OSO3] through N−H···O are stronger than those in [TMGEt][NTf2],33 which contribute to the higher viscosity of [TMGEt][C2OSO3]. The excess molar volume (VmE) for the mixtures was calculated using the following equation: VmE =

⎛x M x1M1 + x 2M 2 xM ⎞ − ⎜⎜ 1 1 + 2 2 ⎟⎟ ρ ρ2 ⎠ ⎝ ρ1

(1)

where x1 and x2 are the mole fractions, M1 and M2 are the mole masses, and ρ1 and ρ2 are the mole fractions of IL and alcohol, respectively. The uncertainty of excess molar volume is calculated to be u(VmE) = 0.012 cm3·mol−1. The viscosity deviation (Δη) was calculated according to the following equation:

■

RESULTS AND DISCUSSION Densities and viscosities of ethanol, 1-propanol, and the synthesized ILs at 298.15 K and 0.1 MPa measured in this work and the available literature data34−39 are summarized in Table 2. Densities and viscosities of the IL + alcohol mixtures were measured over the whole composition range at the temperatures from T = (293.15 to 323.15) K, and the results are graphically shown in Figures 1 and 2 with the detailed data listed in Tables 3 and 4, respectively. Both density and viscosity increase with an increase in the IL concentration or decrease in the temperature for the binary systems. At the same temperature, the density of [TMGEt][NTf2] is remarkably higher than that of [TMGEt][C2OSO3], while the viscosity of the former is much lower than

Δη = η − (x1η1 + x 2η2)

(2)

where η1 and η2 are the viscosities of IL and alcohol, respectively. It should be mentioned that the viscosity deviations for binary systems with different ILs have different magnitudes. Thus, the uncertainty of viscosity deviation is determined to be u(Δη) = 0.070·Δη for [NTf2]-based IL + alcohol systems and 0.021·Δη for [C2OSO3]-based IL + alcohol systems. The calculated results of VmE and Δη are presented in Figures 3 and 4, and the detailed data are listed in Tables S1 and S2, respectively. G



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The values of VmE and Δη are related to the mole fraction of IL (x1) by fitting with the Redlich−Kister equation:40 Y = x1(1 − x1) ∑ [Ai (2x1 − 1)i ]

interactions for the IL are significantly weakened compared to those in the pure IL. The small molecules of ethanol or 1-propanol are able to insert into the space formed during the departure of anion and cation. Thus, the total volume of the mixture is compressed, leading to a more efficient packing of the constituents, and consequently giving rise to the negative values of VmE. In addition, the Δη values in the investigated systems are negative as well, which mainly results from the significant weakening of the anion−cation interactions in the ILs with the addition of alcohol. At a fixed concentration of an IL, the values of VmE for the ethanol solutions are smaller than those of the IL + 1-propanol mixtures. It can be inferred that weaker interactions of species and less structural changes through the mixing of IL and 1-propanol are generated. The ion−dipole and the ion−ion interactions with the increase of the alkyl chain of alcohol are weakened, due to the decrease of solvent permittivity and polarity.34,41 In the system of [TMGEt][C2OSO3] + 1-propanol, the change of VmE with composition is different from those in the other systems, mainly due to the weak interactions between IL and 1-propanol, according to the VmE values which are smaller than 0.4 % of the total volumes. The change of temperature from 293.15 K to 323.15 K almost doubles the value of VmE for the mixture with the composition of x1 from 0.2 to 0.6, revealing that the temperature influences the interactions among constituents and the properties of the mixtures significantly. The partial molar volumes (V̅ m,i) and the excess partial molar volumes (V̅ Em,i) in the binary mixtures can be obtained according to the following equations:42−44

(3)

where Y represents Vm or Δη; Aj are adjustable parameters which can be obtained by the method of least-squares. The standard deviation, σ, is calculated by the following equation: E

1/2 ⎡ 2⎤ ∑ − ( Y Y ) exp cal i ⎥ σ=⎢ ⎢ ⎥ n−m ⎣ ⎦

(4)

where n is the number of data points; m is the number of parameters Ai in eq 3. The obtained values for Ai along with σ for VmE and Δη are summarized in Tables 5 and 6, respectively. Table 6. Values of Parameters (Ai) and Standard Deviations (σ) of the Redlich−Kister Equation for Viscosity Deviations (Δη) at T = (293.15 to 323.15) K and p = 0.1 MPa T/K 293.15 298.15 303.15 308.15 313.15 318.15 323.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

A0

A1

A2

A3

[TMGEt][NTf2] + Ethanol −3.99 −7.278 3.341 −5.426 −54.82 −2.235 2.652 −6.753 −41.29 0.955 2.639 −6.814 −31.65 2.619 1.950 −6.409 −24.82 3.573 1.991 −6.037 −19.62 4.466 1.669 −6.764 −15.90 4.659 1.545 −6.374 [TMGEt][NTf2] + 1-Propanol −66.26 −16.83 −16.16 −14.89 −49.20 −12.07 −10.73 −6.418 −36.86 −8.128 −7.828 −3.782 −28.28 −5.242 −6.463 −3.453 −22.11 −3.514 −5.403 −2.732 −17.67 −1.877 −4.188 −3.909 −14.20 −0.993 −3.246 −2.997 [TMGEt][C2OSO3] + Ethanol −1178 −848.8 −644.7 −386.9 −748.0 −504.9 −358.5 −211.9 −495.3 −312.5 −211.8 −127.6 −337.1 −191.5 −145.3 −116.9 −238.1 −129.1 −84.93 −57.79 −171.1 −83.44 −60.83 −50.32 −126.7 −57.86 −42.11 −35.49 [TMGEt][C2OSO3] + 1-Propanol −1163 −847.8 −463.6 −100.2 −736.5 −504.5 −236.8 −18.00 −485.6 −314.2 −128.4 9.570 −331.0 −203.1 −66.65 28.47 −232.6 −134.7 −34.70 32.19 −167.3 −88.29 −21.79 18.42 −123.3 −61.32 −11.80 17.94

σ/mPa·s 0.242 0.168 0.135 0.134 0.116 0.081 0.060

Vm, ̅ i=

0.302 0.186 0.154 0.129 0.113 0.098 0.060

⎛ ∂V E ⎞ Mi + VmE + (1 − xi)⎜ m ⎟ ρi ⎝ ∂xi ⎠T , p

E Vm, ̅ i = Vm, ̅ i−

Mi ρi

(5)

(6)

V̅ Em,i

The values of V̅ m,i and at different temperatures are listed in Table S3, and the values of V̅ Em,i are plotted in Figure 5. It can be observed that V̅ Em,1 and V̅ Em,2 are generally negative. The dramatically decreasing V̅ Em,1 for mixtures at low concentrations of IL indicates that strong interactions between the IL and alcohols are formed. In the [TMGEt][C2OSO3] (1) + 1-propanol (2) system, the V̅ Em,i values for mixtures at x1 from 0.2 to 0.6 are close to 0, complying with the small excess molar volumes, and also indicating that the interactions in the solutions are weak. It can be further speculated that these semidiluted 1-propanol solutions are closer to ideal mixtures compared to the other mixtures. The Gibbs energy (ΔG*) and the excess Gibbs energy of activation for viscous flow (ΔG*E) were calculated on the basis of the following equations:36,42,45,46

1.503 0.832 0.499 0.695 0.311 0.204 0.157 2.041 1.583 1.226 1.015 0.820 0.668 0.549

ΔG* = RT ln

E

As shown in Figure 3, the Vm values for the investigated systems are negative. They are smaller than 1 % of the total volumes of each sample, indicating that the mixtures are nearly ideal. It is also observed that the VmE values at the diluted region with x1 lower than 0.5 are much smaller than those at the concentrated region, since the IL is disassociated more significantly in a diluted alcohol solution. Upon the mixing of IL and alcohol, the anion−molecule and cation−molecule interactions are generated in the solution, and the anion−cation

ηV hNA

(7)

⎛ ⎛ η V ⎞⎞ ⎜⎜ΔG*E = RT ⎜⎜ln ηV − x1 ln 1 1 ⎟⎟⎟⎟ η2V2 ⎠⎠ ⎝ η2V2 ⎝

(8)

where V, V1, and V2 are volumes of the mixture, IL, and alcohol; h, NA, and R represent Planck constant, Avogadro number, and gas constant, respectively. The values of ΔG* and ΔG*E at different temperatures are listed in the Supporting Information, Table S4. H



Article

Figure 5. Excess partial molar volumes (V̅ Em,i) for IL (1) (filled marks) + alcohol (2) (open marks) systems of (a) [TMGEt][NTf2] + ethanol, (b) [TMGEt][NTf2] + 1-propanol, (c) [TMGEt][C2OSO3] + ethanol, and (d) [TMGEt][C2OSO3] + 1-propanol at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K.

Figure 6. Excess Gibbs energy of activation (ΔG*E) for binary systems of (a) [TMGEt][NTf2] (1) + ethanol (2), (b) [TMGEt][NTf2] (1) + 1-propanol (2), (c) [TMGEt][C2OSO3] (1) + ethanol (2), and (d) [TMGEt][C2OSO3] (1) + 1-propanol (2) at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K. I



Article

The values of ΔG*E at different temperatures are plotted in Figure 6. They are positive over the entire composition range for all studied systems. The values of ΔG*E are larger in the ethanol solutions than in the corresponding 1-propanol solutions, revealing that the generated hydrogen bonding interactions between IL and ethanol are relatively stronger.42,47

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CONCLUSION Densities and viscosities for the binary mixtures of ILs, 2-ethyl1,1,3,3-tetramethylguanidinium bis(trifluoromethylsulfonyl)imide ([TMGEt][NTf2 ]) and ethyl sulfate ([TMGEt][C2OSO3]), with ethanol and 1-propanol have been measured over the whole concentration range at T = (293.15 to 323.15) K and p = 0.1 MPa. The densities and viscosities both decrease with increasing temperature and decreasing IL concentration. The [NTf2]-based IL has a higher density and a lower viscosity in contrast with the [C2OSO3]-based IL, resulting from the difference of the anion species. The calculated negative values of the excess molar volume (VmE) and viscosity deviation (Δη) indicate that the weakening of anion−cation interactions is more significant than the enhancements of anion−molecule and cation−molecule interactions by the close packing of ionic moieties with alcohol molecules. The Redlich−Kister equation is used to fit the excess molar volumes and viscosity deviations. The experimental results may provide useful information about the ILs and their liquid mixtures for further investigations.

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ASSOCIATED CONTENT

S Supporting Information *

1

H and 13C NMR spectra of ILs, purity estimation for ILs, data of excess molar volumes, viscosity deviations, partial molar volumes, excess partial molar volumes, the Gibbs energies of activation, and the excess Gibbs energies of activation. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b00259. (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*Tel/Fax: +86-571-88981416. E-mail: [email protected] (W.F.). *E-mail: [email protected](Y.G.). Funding

The authors are grateful for the financial supports from the National Natural Science Foundation of China (Nos. 21473157, J1210042). Notes

The authors declare no competing financial interest.

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Densities and Viscosities of Binary Mixtures of 2-Ethyl-1,1,3,3

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