Density and Viscosity for Binary Mixtures of the Ionic Liquid 2,2-Diethyl

Article pubs.acs.org/jced

Density and Viscosity for Binary Mixtures of the Ionic Liquid 2,2Diethyl-1,1,3,3-Tetramethylguanidinium Ethyl Sulfate with Water, Methanol, or Ethanol Lifeng Zhang, Xiaoxing Lu, Dengfeng Ye, Yongsheng Guo, and Wenjun Fang* Department of Chemistry, Zhejiang University, Hangzhou 310027, People’s Republic of China S Supporting Information *

ABSTRACT: The ionic liquid (IL), 2,2-diethyl-1,1,3,3tetramethylguanidinium ethyl sulfate ([(C2)22(C1)2(C1)23gu][C2OSO3]), was synthesized and characterized. The density and viscosity data were determined for the binary mixtures of [(C2)22(C1)2(C1)23gu][C2OSO3] with water, methanol, or ethanol over the whole concentration range at different temperatures T = 293.15−323.15 K and atmospheric pressure p = 0.1 MPa. The excess molar volume, VEm, and viscosity deviation, Δη, for the binary mixtures are calculated and fitted with the Redlich−Kister type polynomial equation. The values of VEm for [(C2)22(C1)2(C1)23gu][C2OSO3] + water system are observed to be negative, and those for [(C2)22(C1)2(C1)23gu][C2OSO3] + methanol/ethanol system change from negative to positive against the mole fraction (x1) of the IL, which exhibit the minimum values around x1 = 0.2 and the maximum values near x1 = 0.8. The Δη values for all of the three binary systems are negative, and the minimum values occur near x1 = 0.6. The temperature dependence of viscosity for pure [(C2)22(C1)2(C1)23gu][C2OSO3] and its binary mixtures can be well correlated with the Vogel−Fucher−Tammann equation. These fundamental physicochemical properties of the binary mixtures make for a better comprehension of the guanidiniumbased ILs and the potential applications.

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INTRODUCTION In the past decades, the investigations on ionic liquids (ILs) are booming because of their unique physicochemical properties, such as low melting points, wide liquid range, low vapor pressure, high thermal stability, nonflammability, biodegradable, recyclable, and economically feasible.1−6 ILs can be regarded as a series of molten salts composed entirely of ions, and the structures of ILs are strongly variable through a suitable modification of cations and/or anions.7−10 The room-temperature ILs (RTILs) are one class of promising materials that can be used not only as green solvents in the processes of synthesis and extraction but also as electrolytes, catalysts, or additives employed in numerous important application areas.11,12 As typical examples, a series of phosphoric-based ILs are employed as green solvents for the separation of ethanol from hexane.13 The guanidinium-based IL containing allylic functional groups exhibits high densities and low surface tensions as well as nontoxic behavior.14 A kind of powerful catalyst, Fe3O4@SiO2IL-FeTPPS, can catalyze the degradation of 2,4,6-tribromophenol (TrBP), which plays a prominent role in renovating homogeneous catalytic efficiency.15 In practical processes, the determination of physicochemical properties of ILs and the corresponding mixtures, such as density and viscosity, are of great importance for the operation and equipment designs. The viscosity of pure ILs is often much higher than that of traditional organic solvents, which may limit © XXXX American Chemical Society

the industrial applications. Therefore, an appropriate organic solvent is added in the ILs to regulate the viscosity. The fundamental data of the ILs with solvents may provide a better understanding of the interactions between the IL and solvent. For example, from the measurements on the gas−liquid equilibrium at 313.15 K and at the pressure range of (9−12) MPa for ternary systems of CO2 + IL + alcohol, it was found that the viscosity of ILs decreased sharply with the addition of organic solvents, and the mixture of IL and organic solvent could act as a new solvent for capturing CO2.16 The IL, Nethylpiperazinium propionate, with methanol or ethanol added exhibited efficient extraction capability to remove the aromatics from the hydrocarbon fuels.17 In this work, the IL, 2,2-diethyl-1,1,3,3-tetramethylguanidinium ethyl sulfate ([(C2)22(C1)2(C1)23gu][C2OSO3]), is synthesized. The densities and viscosities for three binary systems of the IL with polar molecular solvents (water, methanol, and ethanol) are measured at temperatures from T = 293.15−323.15 K and the atmospheric pressure p = 0.1 MPa over the whole ranges of mole fraction. Calculations and correlations on the excess molar volume and the viscosity deviation are carried out to provide a preferable knowledge for Received: April 26, 2015 Accepted: January 27, 2016

A

DOI: 10.1021/acs.jced.5b00365 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Information of Chemicals in This Work chemical name

CAS No.

source

1,1,3,3-tetramethylguanidine methanol ethanol diethyl sulfate ethyl acetate

80-70-6 67-56-1 64-17-5 64-67-5 141-78-6

Aladdin Aladdin Aladdin Sigma-Aldrich Sinopharm Chemical Reagent Co., Ltd. Sinopharm Chemical Reagent Co., Ltd. synthesized

dichloromethane 2,2-diethyl-1,1,3,3tetramethylguanidinium ethyl sulfate a

75-09-2 NA

final purity (mass fraction)

water (mass fraction)

>0.990 >0.999 >0.998 >0.990 >0.995

0.995, CAS Registry No. 141-78-6) and dichloromethane (mass fraction >0.995, CAS Registry No. 75-09-2) were purchased by Sinopharm Chemical Reagent Co., Ltd., China. These reagents were employed without further purification. Ultrapure water was produced by a Millipore Q3 system. The detailed information on the chemicals is listed in Table 1. The density and viscosity of the used solvents are determined at T = 293.15−323.15 K and compared with the literature data in Table 2. Synthesis and Characterization of Ionic Liquid. [(C2)22(C1)2(C1)23gu][C2OSO3] was synthesized according to the procedures shown in Scheme 1. A solution of 1,1,3,3tetramethylguanidine (TMG, 0.1 mol) in dichloromethane (15 mL) was dropwise added into a 250 mL round-bottomed flask containing a mixture of diethyl sulfate (0.2 mol) in dichloromethane (30 mL) with NaOH (0.1 mol) in an ice−water bath and stirred to obtain a dispersed solution. The mixture was magnetically stirred over 48 h and then filtered. After rotary evaporation, the solvent was removed under vacuum. The crude product was then washed with ethyl acetate and dissolved in ethanol. The mixture was filtered and ethanol was removed by evaporation. The obtained liquid was further purified by freeze-drying (Peking Sihuan Scientific Instrument, LGJ-10, China) to remove the impurities as much as possible. The purity of the IL was estimated to be higher than 0.990 in mass fraction. The Na+ concentration was determined by an ion selective electrode (Shanghai REX Instrument Factory, PXSJ216F, China), and the total mass fraction of sodium salts was estimated to be less than 0.002. The water content in [(C2)22(C1)2(C1)23gu][C2OSO3] was checked to be less than 0.05% of mass fraction through a Karl Fischer titration (Mettler Toledo, C20, Switzerland). Elemental analysis (Carlo Erba 1110, Italy) of the prepared ILs was carried out and the contents were determined in mass fraction of the following: C, 44.3 (44.3); H, 9.2 (9.3); N, 14.1 (14.1); S, 10.7 (10.7); O, 21.7 (21.6).

ρ/g·cm−3 compound water

methanol

ethanol

η/mPa·s

T/K

exptl

lit

exptl

lit

293.15 298.15

0.99821 0.99706

0.991 0.884

303.15

0.99567

308.15 313.15

0.99406 0.99222

0.99219 0.89430 0.8931 0.80130 0.79731 0.72619 0.65630

318.15 323.15

0.99012 0.98796

293.15

0.79133

298.15

0.78662

0.9982119 0.9970519 0.9970420 0.9956519 0.995721 0.9940319 0.9922219 0.9922322 0.9902120 0.9880319 0.9880420 0.7913223 0.7910824 0.786725

303.15

0.78189

0.52

308.15 313.15

0.77714 0.77237

318.15 323.15

0.76756 0.76272

0.7818624 0.7819925 0.777226 0.7723224 0.7722126 0.767523 0.762725

293.15 298.15 303.15

0.78957 0.78528 0.78096

1.177 1.071 0.978

308.15

0.77661

0.7896427 0.7852527 0.7806827 0.780828 0.776527

313.15

0.77223

0.822

318.15

0.76786

0.7721327 0.772228 0.767629

323.15

0.7633

0.763228 0.763629

0.698

0.796 0.723 0.662 0.608 0.566 0.587 0.552

0.491 0.465 0.442 0.421

0.895

0.756

0.59921 0.55421 0.54730 0.58531 0.55331 0.54632 0.5131 0.50133 0.47331 0.44631 0.45634 0.42631 0.40631 0.434 1.17421 1.07821 0.98721 0.9527 0.8727 0.86528 0.79327 0.81421 0.7328 0.7221 0.67328

a Standard uncertainties u are u(T) = 0.01 K, u(p) = 1000 Pa, u(ρ) = 0.001 g·cm−3, and relative expanded uncertainty is ur(η) = 0.04·η.

The as-synthesized ILs characterized by 1H and 13C NMR were operated on a Bruker AVANCE III 500 MHz NMR spectrometer with d6-CDCl3 as the solvent and tetramethylsilane as the internal standard. The 1H and 13C NMR spectra of B



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Scheme 1. Synthetic Approach of 2,2-Diethyl-1,1,3,3-tetramethylguanidinium Ethyl Sulfate ([(C2)22(C1)2(C1)23gu][C2OSO3])

Table 3. Experimental Density (ρ) for Binary Systems of IL + Solvent (Water, Methanol, or Ethanol) at T = 293.15−323.15 K and p = 0.1 MPaa ρ/g·cm−3 x1

a

293.15 K

298.15 K

0.0000 0.0999 0.2003 0.3005 0.4004 0.4989 0.6001 0.7000 0.8010 0.8982 1.0000

0.99821 1.09677 1.11922 1.12795 1.13241 1.13526 1.13723 1.13867 1.13974 1.14063 1.14134

0.99706 1.09281 1.11526 1.12409 1.12868 1.13159 1.1336 1.13507 1.13615 1.13704 1.13777

0.0000 0.1000 0.1991 0.2980 0.3949 0.4982 0.5999 0.6953 0.7999 0.9002 1.0000

0.79133 0.94533 1.01346 1.05136 1.07565 1.09362 1.10683 1.11665 1.12561 1.13362 1.14134

0.78662 0.94121 1.00955 1.04758 1.07193 1.08998 1.10318 1.11310 1.12201 1.13004 1.13777

0.0000 0.1001 0.2003 0.2998 0.4023 0.4998 0.6016 0.6979 0.8024 0.8974 1.0000

0.78957 0.91041 0.97912 1.02296 1.05480 1.07722 1.09542 1.10923 1.12144 1.13127 1.14134

0.78528 0.90644 0.97528 1.01921 1.05112 1.07360 1.09182 1.10564 1.11785 1.12770 1.13777

303.15 K

308.15 K

313.15 K

[(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Water (2) 0.99567 0.99406 0.99222 1.08885 1.08488 1.08089 1.11129 1.10732 1.10334 1.12023 1.11637 1.11250 1.12495 1.12122 1.11747 1.12792 1.12425 1.12056 1.12997 1.12634 1.12273 1.13147 1.12787 1.12428 1.13257 1.12899 1.12542 1.13346 1.12988 1.12632 1.13421 1.13065 1.12711 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Methanol (2) 0.78189 0.77714 0.77237 0.93709 0.93297 0.92886 1.00565 1.00175 0.99786 1.04381 1.04004 1.03627 1.06822 1.06452 1.06084 1.08636 1.08272 1.07910 1.09955 1.09593 1.09234 1.10947 1.10587 1.10230 1.11843 1.11486 1.11131 1.12647 1.12290 1.11936 1.13421 1.13065 1.12711 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Ethanol (2) 0.78096 0.77661 0.77223 0.90248 0.89851 0.89453 0.97144 0.96760 0.96378 1.01545 1.01169 1.00793 1.04744 1.04376 1.04009 1.06998 1.06636 1.06275 1.08823 1.08464 1.08107 1.10205 1.09846 1.09488 1.11427 1.11069 1.10713 1.12414 1.12058 1.11704 1.13421 1.13065 1.12711

318.15 K

323.15 K

0.99012 1.07691 1.09935 1.10861 1.11372 1.11687 1.11911 1.12069 1.12185 1.12277 1.12357

0.98796 1.07292 1.09535 1.10473 1.10997 1.11319 1.1155 1.11711 1.11829 1.11922 1.12003

0.76756 0.92475 0.99397 1.03251 1.05716 1.07547 1.08874 1.09873 1.10777 1.11583 1.12357

0.76272 0.92064 0.99008 1.02875 1.05350 1.07184 1.08514 1.09516 1.10423 1.11230 1.12003

0.76786 0.89052 0.95996 1.00416 1.03642 1.05914 1.07750 1.09131 1.10357 1.11350 1.12357

0.7633 0.88649 0.95614 1.00037 1.03275 1.05553 1.07393 1.08774 1.10001 1.10997 1.12003

Standard uncertainties are u(T) = 0.01 K, u(p) = 1000 Pa, u(x1) = 0.0001, and u(ρ) = 0.001 g·cm−3. x1 is the mole fraction of IL.

[(C2)22(C1)2(C1)23gu][C2OSO3] are given in Figure S1 with the found chemical shifts (δH): 1.21 to 1.28 (9H, N+−(C− CH3)2 and O−C−CH3), 3.01 and 3.07 (12H, N−CH3), 3.27− 3.30 (4H, N+−CH2−C), 4.04−4.08 (2H, O−CH2−C). δC: 13.02 (N+−C−CH3), 15.28 (O−C−CH3), 40.33−40.42 (N− CH3), 43.53 (N+−CH2−C), 62.87 (O−CH2−C), 161.49 (N+C). The 1H spectra of the used materials and solvents, dichloromethane, diethyl sulfate, ethyl acetate, TMG, methanol, and ethanol are also shown in Figures S2−S7.

Thermal transition behaviors of the IL were investigated by differential scanning calorimetry (DSC, Q2000, TA Instruments) with the scanning rate of 5 K·min−1 at the range from 183.15 to 363.15 K and by thermal gravimetric analysis (TGA, Q50, TA Instruments) with the heating rate of 5 K·min−1 from 293.15 to 773.15 K. The DSC and TGA curves of the IL are shown in Figure S8. As shown in Figure S8a, glass-transition (Tg) temperature is Tg = 202 K, while no melting point is found for the IL from 190 to 360 K.35 In Figure S8b, the onset (Tonset) C



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Figure 1. Excess molar volumes (VEm) for binary systems of [(C2)22(C1)2(C1)23gu][C2OSO3] + (a) water, (b) methanol, and (c) ethanol at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K. x1 is the mole fraction of IL. Solid lines represent the fitting results with the Redlich−Kister equation (eq 6).

7.620, 7.630, and 7.760 are densities of the metal balls. Equation 1 is applied to the sample with viscosities lower than 15 mPa·s, eq 2 is suitable for those with viscosities from 15 to 200 mPa·s, while eq 3 is suitable for the samples with viscosities from 200 to 2000 mPa·s, respectively. The standard uncertainty of the temperatures controlled by a built-in Peltier thermostat is 0.01 K, and the relative expanded uncertainty of viscosity is calculated from eqs 1 to 3 and is ur(η) = 0.04η.

and maximum (Tmax) temperatures of thermal decomposition of the IL are Tonset = 432 K and Tmax = 632 K, respectively. It indicates that the IL has satisfactory thermal stability. The weight loss of 10.0% at about 520 K probably represents the decomposition of ethyl sulfate anion.35,36 Apparatus and Procedure for Density and Viscosity Measurements. The binary mixtures were prepared by mass using an analytical balance (Mettler Toledo, AL204, Switzerland) with a precision of 1 × 10−4 g in a 20 mL special glass vial sealed with a polytetrafluoroethylene cap. The standard uncertainty of mole fraction (x) is calculated to be less than 0.00007, and it is determined as u(x1) = 0.0001. The density meter (DMA 5000M, Anton Paar, Austria) was employed to measure the densities (ρ) of the binary mixtures at T = 293.15−323.15 K. It was calibrated with ultrapure water and dry air. The standard uncertainty of the temperatures is 0.01 K, and the standard uncertainty of the density is u(ρ) = 0.001 g·cm−3. An AMVn viscometer (Anton Paar, Austria) was employed to measure the viscosities (η) of the binary mixtures under the same conditions, which were identified by gauging the efflux time of the little metal ball in the samples. The viscosity values are calculated according to the following equations η = 0.01059(7.620 − ρ)t

(1)

η = 0.15342(7.630 − ρ)t

(2)

η = 1.40961(7.760 − ρ)t

(3)

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RESULTS AND DISCUSSION Volumetric Properties. The densities of binary mixtures of [(C2)22(C1)2(C1)23gu][C2OSO3] + solvent (water, methanol, or ethanol) over the whole composition at temperatures from 293.15 to 323.15 K with each interval of 5 K at atmospheric pressure were measured. The experimental density values are listed in Table 3. The coefficient of volume expansion for [(C2)22(C1)2(C1)23gu][C2OSO3], α, can be calculated with the following equation α=

⎛ ∂ ln ρ ⎞ 1 ⎛⎜ ∂V ⎞⎟ ⎟ =−⎜ ⎝ ∂T ⎠P V ⎝ ∂T ⎠P

(4)

where V and ρ are the molar volume and density of [(C2)22(C1)2(C1)23gu][C2OSO3], respectively. From the density values, the value of α = [(6.2834 × 10−4) ± (5.8414 × 10−7)] K−1 is obtained for IL and its mixtures, and it is similar to those of other common ILs.37 The excess molar volume, VEm, for the binary system can be calculated by the following equation

where η denotes the dynamic viscosity, ρ represents the density of the sample, and t is the efflux time of the metal ball. The values of 0.01059, 0.15342, and 1.40961 are the calibration constants according to different viscosity ranges, and those of

VmE = D

x1M1 + x 2M 2 xM xM − 1 1 − 2 2 ρm ρ1 ρ2

(5)



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where ρm is the density of the mixture; ρ1 and ρ2 are the densities of two components in the mixture, respectively; and M1, M2 and x1, x2 are the mole masses and the mole fractions of the pure IL and polar solvent, respectively. The values of VEm for the three binary systems at seven different temperatures are listed in detail in Table S1 in the Supporting Information. The calculated VEm values are fitted to the Redlich−Kister type polynomial equation38

Table 4. Values of Parameters (Ai) and Standard Deviations (σ) of the Redlich−Kister Equation for Excess Molar Volumes (VEm) and Viscosity Deviations (Δη) at T = 293.15− 323.15 K and p = 0.1 MPa T/K

293.15 298.15 303.15 308.15 313.15 318.15 323.15

i

(6)

i=0

VEm,

where Y denotes the excess molar volumes, and x1 is the mole fraction of IL. Ai is the parameter of the Redlich−Kister polynomial equation and k is the degree of the polynomial expansion. The fitting results of VEm are visually shown in Figure 1. The values of parameters Ai are obtained by fitting eq 6 to the experimental values through a least-squares algorithm, and the values are presented in Table 4 together with the standard deviations (σ) ⎡ ∑ (Y − Y )2 ⎤1/2 exp cal ⎥ σ=⎢ ⎢⎣ ⎥⎦ (n − k )

A1

A2

A3

.

VEm

k

Y = x1x 2 ∑ Ai (x1 − x 2)

A0

293.15 298.15 303.15 308.15 313.15 318.15 323.15

(7)

293.15 298.15 303.15 308.15 313.15 318.15 323.15 T/K

where Yexp and Ycal denote the experimental and calculated values, respectively; n is the number of experimental datum points, and k is the number of the parameters (Ai) in the Redlich−Kister equation. It is observed that the VEm values change from negative to positive one for the [(C2)22(C1)2(C1)23gu][C2OSO3] + methanol or ethanol system, which show the minimum around x1 = 0.2 and the maximum values near x1 = 0.8. In diluted solutions, each ion of IL is surrounded only by solvent molecules and not affected by the molecular interaction. With the increase of IL mole fraction, the molecular interaction between two components becomes stronger. The negative excess molar volumes may be attributed to the strong interactions between − OH group of solvent and IL molecules. When the IL concentration keeps rising, the contribution of the steric effects become stronger than the molecular interaction, resulting in the positive VEm value. When the two binary systems containing methanol and ethanol are compared, the absolute value of VEm of the ethanol-contained system is smaller than that of methanol-contained system at the same mole fraction, which is caused by the steric effect of the −CH2CH3 group in the ethanol molecules. For the [(C2)22(C1)2(C1)23gu][C2OSO3] + water system, the contribution of the molecular interaction are much stronger than the steric effects, which leads to the negative excess molar volume. Viscometric Properties. Viscosities (η) for the [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + solvent (2) (water, methanol, or ethanol) binary systems are listed in Table 5. The viscosity of the binary systems at a given composition decreases obviously with the rise of temperature. In the dilute regions of the IL, the change of viscosity is not significant because the distance between two ions is distant and the interactions are relatively weak. However, in concentrated solutions the collective ions leads to the enhanced interactions among ions including H-bonding interactions between two components in the binary mixtures, thus the viscosity increases exponentially. In three binary systems, the system of IL with water shows the largest viscosity values due to the presence of

[(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Water (2) −1.556 1.495 −1.683 1.187 0.005 −1.438 1.338 −1.401 0.972 0.004 −1.321 1.190 −1.142 0.765 0.003 −1.211 1.046 −0.896 0.576 0.004 −1.094 0.893 −0.675 0.432 0.005 −0.982 0.745 −0.487 0.295 0.006 −0.875 0.585 −0.296 0.173 0.007 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Methanol (2) 0.249 4.332 −1.395 3.191 0.017 0.149 4.388 −1.497 3.385 0.018 0.050 4.510 −1.599 3.467 0.019 −0.057 4.608 −1.722 3.601 0.020 −0.170 4.695 −1.858 3.758 0.022 −0.287 4.800 −2.037 3.882 0.023 −0.412 4.917 −2.221 4.002 0.025 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Ethanol (2) −0.135 2.353 −0.352 3.085 0.007 −0.249 2.412 −0.415 3.214 0.035 −0.365 2.467 −0.497 3.377 0.009 −0.488 2.530 −0.589 3.547 0.011 −0.616 2.599 −0.695 3.725 0.013 −0.747 2.662 −0.788 3.894 0.015 −0.907 2.746 −0.952 4.129 0.018 A0 A1 A2 A3 σ/cm3·mol−1 Δη

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

[(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Water (2) −110.8 −56.14 11.67 54.35 −73.68 −40.11 3.961 27.60 −49.94 −29.13 −1.176 12.19 −34.18 −21.71 −4.756 3.491 −23.66 −17.66 −6.321 2.155 −16.49 −15.22 −6.215 4.976 −11.72 −12.90 −3.298 9.678 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Methanol (2) −250.5 −32.54 75.51 44.27 −169.4 −3.808 47.63 7.987 −119.5 4.603 37.00 10.70 −84.50 11.28 28.14 6.659 −61.02 14.25 19.72 1.734 −43.89 17.24 14.04 −3.454 −31.61 17.57 11.46 −2.744 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Ethanol (2) −271.2 −62.79 94.85 88.00 −185.3 −30.35 71.45 60.25 −131.5 −15.39 50.05 39.76 −93.76 −4.395 37.48 26.97 −68.40 1.527 28.35 18.75 −49.92 4.773 20.29 12.30 −36.59 7.632 16.70 8.695

0.122 0.089 0.087 0.100 0.086 0.084 0.287 0.173 0.364 0.135 0.120 0.114 0.133 0.107 0.281 0.179 0.145 0.106 0.075 0.063 0.045

hydrogen bond networks in H2O that can generate strong Hbonding interactions with the IL. The temperature dependence of viscosity for the binary systems is correlated with the Vogel−Fulcher−Tammann (VFT) equation39−41 E



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Table 5. Experimental Viscosity, η, for Binary Systems of Ionic Liquid + Solvent (Water, Methanol, or Ethanol) at T = 293.15− 323.15 K and p = 0.1 MPaa η/mPa·s x1

293.15 K

0.0000 0.0999 0.2003 0.3005 0.4004 0.4989 0.6001 0.7000 0.8010 0.8982 1.0000

0.991 12.38 25.31 39.06 53.18 68.18 85.88 107.0 132.6 160.6 190.9

0.0000 0.1000 0.1991 0.2980 0.3949 0.4982 0.5999 0.6953 0.7999 0.9002 1.0000

0.587 1.785 4.501 9.381 18.38 32.98 53.59 80.20 115.6 153.4 190.9

0.0000 0.1001 0.2003 0.2998 0.4023 0.4998 0.6016 0.6979 0.8024 0.8974 1.0000

1.177 2.916 5.857 11.49 20.43 32.82 54.53 82.56 121.0 160.5 190.9

298.15 K

303.15 K

308.15 K

[(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Water (2) 0.884 0.796 0.723 10.01 8.224 6.765 19.81 15.93 12.88 29.97 23.79 19.09 40.42 31.86 25.43 51.48 40.31 32.02 64.33 49.98 39.28 79.13 60.70 47.26 97.08 73.90 57.08 116.9 88.11 67.41 139.0 104.9 80.44 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Methanol (2) 0.552 0.520 0.491 1.634 1.504 1.389 4.072 3.661 3.307 8.200 7.163 6.417 15.58 13.38 11.63 27.24 22.82 19.37 42.80 34.85 28.79 62.36 49.55 40.16 87.46 67.85 53.89 112.3 86.71 67.59 139.0 104.9 80.44 [(C2)22(C1)2(C1)23gu][C2OSO3] (1) + Ethanol (2) 1.071 0.978 0.895 2.620 2.373 2.155 5.197 4.640 4.166 9.941 8.688 7.649 17.20 14.71 12.71 27.12 22.61 19.18 43.51 35.19 29.07 64.03 50.61 40.85 91.64 70.75 55.99 119.1 90.75 70.53 139.0 104.9 80.44

313.15 K

318.15 K

323.15 K

0.662 5.628 10.63 15.72 20.82 26.05 31.62 37.70 45.18 53.08 63.24

0.608 4.660 8.802 13.04 17.16 21.39 25.68 30.35 36.20 42.47 50.27

0.566 3.828 7.374 10.99 14.30 17.61 21.15 24.97 29.66 34.73 40.55

0.465 1.287 3.000 5.724 10.18 16.65 24.17 33.08 43.49 53.73 63.24

0.442 1.195 2.734 4.994 8.991 14.45 20.55 27.69 35.64 43.24 50.27

0.421 1.113 2.500 4.580 7.999 12.64 17.68 23.46 29.74 35.49 40.55

0.822 1.964 3.765 6.793 11.08 16.48 24.39 33.63 45.19 56.15 63.24

0.756 1.797 3.419 6.036 9.760 14.28 20.68 27.81 36.81 45.06 50.27

0.698 1.649 3.118 5.430 8.634 12.47 17.74 23.62 30.60 36.93 40.55

a

Standard uncertainties are u(T) = 0.01 K, u(p) = 1000 Pa, and u(x1) = 0.0001, and relative expanded uncertainty is ur(η) = 0.04η. x1 is the mole fraction of IL.

η = AT 0.5 exp

B T − T0

Overall, the curves of viscosity deviation for the three systems at different temperatures are similar. All of the viscosity deviations show negative values, and the minimum value for each binary system can be observed around the mole fraction of IL x1 = 0.5. The absolute values of Δη decrease with the increase of temperature, and the values of the water-contained system are much lower than those of alcohol-contained systems at the same concentration and temperature. This indicates that the interaction effects on the viscosity for the water-contained system are stronger and the steric effects are much smaller than those for alcohol-contained systems. The absolute values of Δη of the ethanol-contained system is larger than those of the methanol-contained system, which is caused by the weaker interaction effect and the more disorder steric effect from ethyl group in ethanol.

(8)

where A, B, and T0 are the adjustable parameters. The correlated results are shown in Figure 2, and these parameters are presented in Table S2 in the Supporting Information. The viscosity deviation (Δη) is calculated by using the following equation Δη = η − (x1η1 + x 2η2)

(9)

where ηi (i = 1, 2) are the viscosities of the IL and the molecular solvent, respectively. The data of Δη are presented in Figure 3 and are listed in Tables S3 in the Supporting Information. The values of Δη are correlated with Redlich−Kister type polynomial equation, and the standard deviations (σ) are calculated from eq 7. The correlation coefficients and standard deviations are also listed in Table 4.

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CONCLUSIONS The densities and viscosities for the binary mixtures of the IL, 2,2-diethyl-1,1,3,3-tetramethylguanidinium ethyl sulfate F



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Figure 2. Temperature dependence of viscosity (η) for binary systems of [(C2)22(C1)2(C1)23gu][C2OSO3] + (a) water, (b) methanol, or (c) ethanol at different concentrations. Curves from bottom to top correspond to the increase of IL mole fraction from x1 = 0.0 to 1.0. Solid lines represent the fitting results with the VFT equation (eq 8).

Figure 3. Viscosity deviations (Δη) for binary systems of [(C2)22(C1)2(C1)23gu][C2OSO3] + (a) water, (b) methanol, or (c) ethanol at different temperatures: ■, 293.15 K; ●, 298.15 K; ▲, 303.15 K; ▼, 308.15 K; ⧫, 313.15 K; ◀, 318.15 K; ▶, 323.15 K. x1 is the mole fraction of IL. Solid lines represent the fitting results with the Redlich−Kister equation (eq 6).

([(C2)22(C1)2(C1)23gu][C2OSO3]) with water, methanol, or ethanol have been measured over the whole concentration range at T = 293.15−323.15 K and atmospheric pressure p =

0.1 MPa. Both of the density and viscosity increase with the increased IL concentration or decreased temperature. The calculated values of the excess molar volume, VEm, and viscosity G



Article

deviation, Δη, indicate strong interactions between the two components in the binary mixtures. Redlich−Kister equation is successfully used to fit the values of VEm and Δη. The temperature dependence of viscosity for pure [(C2)22(C1)2(C1)23gu][C2OSO3] and its binary mixtures can be well correlated with the VFT equation. The measured and calculated properties reflect the nonideality of the binary mixtures and contribute to comprehension on the guanidiniumbased IL and its practical applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b00365. 1 H and 13C NMR spectra of IL, 1H NMR spectra of starting materials and solvents, the DSC and TGA curves of the IL, deviations of calculated and measured data of density and viscosity, data of excess molar volumes and viscosity deviations, and correlated values of the parameters, A, B, and T0, for viscosity with the VFT equation. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel/Fax: +86-571-88981416. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support from the National Natural Science Foundation of China (Nos. 21273201 and J1210042).

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Density and Viscosity for Binary Mixtures of the Ionic Liquid 2,2-Diethyl

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