Solubilities of 1, 1′-[1, 2-Ethanediylbis (oxy-1, 2-ethanediyl)] bis-[3

Aug 6, 2014 - The thermal stability of [C6O2(mim)2][PF6]2 was studied with differential scanning calorimetry and thermogravimetric analyses. With the ...
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Solubilities of 1,1′-[1,2-Ethanediylbis(oxy-1,2-ethanediyl)]bis-[3methyl‑1H‑imidazolium-1-yl] Dihexafluorophosphate in Water, Methanol, Ethanol, Dimethylformamide, Dimethyl Sulfoxide, and (Acetone + Water) Binary Solvent Mixtures Jia-rong Guo,† Ling-Hua Zhuang,‡ Guo-Wei Wang,*,§ Yan Wang,§ and Jie Sun§ †

College of Biological and Pharmaceutical Engineering, ‡College of Science, and §College of Food Science and Light Industry, Nanjing Tech University, Nanjing, Jiangsu 211816, People’s Republic of China ABSTRACT: The chemical structure of a new gemini dicationic imidazolium ionic liquid, 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis-[3-methyl-1H-imidazolium-1-yl] dihexafluorophosphate ([C6O2(mim)2][PF6]2), was established by 1HNMR. The thermal stability of [C6O2(mim)2][PF6]2 was studied with differential scanning calorimetry and thermogravimetric analyses. With the use of the analytical stirred-flask method at atmospheric pressure, the solubilities of [C6O2(mim)2][PF6]2 in water, methanol, ethanol, dimethylformamide, dimethyl sulfoxide, and (acetone + water) binary solvent mixtures were measured from (283.00 to 323.00) K. The experimental data was correlated with the modified Apelblat equation.

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INTRODUCTION Room temperature ionic liquids (ILs) have been the object of increasing attention in recent years because of their unique properties such as high thermal stability, nonvolatility, nonflammability, high ionic conductivity, wide electrochemical window and miscibility with organic compounds. Room temperature ILs have been widely applied to electrochemistry, catalysis, separation science, green chemistry, and material science.1,2 Compared to conventional room temperature ionic liquids (ILs), gemini dicationic ILs have been shown to possess superior physical properties in terms of thermal stability and volatility.3,4 Consequently, gemini dicationic ILs have been used as solvents in high-temperature reactions, novel hightemperature lubricants, and ultrastable separation phases where ordinary ILs fail.5−7 1,1′-[1,2-Ethanediylbis(oxy-1,2-ethanediyl)]bis-[3-methyl-1H-imidazolium-1-yl] dihexafluorophosphate ([C6O2(mim)2][PF6]2) is a kind of dicationic IL which can be proposed as a solvent in high-temperature reactions and be used as a high-performance lubricant. A wide variety of dicationic ILs were published while our work was in progress.8−10 To design any process involving ILs on an industrial scale, it is necessary not only to know a range of physical properties including viscosity, density, melting point temperature, electrochemical window, heat capacity, and interfacial tension, but also to study other thermodynamic properties including phase © 2014 American Chemical Society

equilibria such as solid−liquid equilibria (SLE). An understanding of SLE is very important for the design of separation processes. There is an urgent need to develop better solvents for large scale chemical separation. The solubilities of room temperature ILs in different solvents have been investigated extensively.11−13 To our knowledge, relevant researches about the solubilities of dicationic ILs in binary solvent mixture were still rare.14−19 In this study, 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis[3-methyl-1H-imidazolium-1-yl] dihexafluorophosphate ([C6O2(mim)2][PF6]2) was synthesized and confirmed with 1 HNMR. The molecular structure of [C6O2(mim)2][PF6]2 was illustrated in Figure 1. The thermal stability of [C6O2(mim)2][PF6]2 was conducted with differential scanning calorimetry

Figure 1. Molecular structure of [C6O2(mim)2][PF6]2. Received: May 19, 2014 Accepted: July 30, 2014 Published: August 6, 2014 2827

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distillation under reduced pressure. The resulting product was washed with ether and then dried in vacuo for 24 h. Synthesis of 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis[3-methyl-1H-imidazolium-1-yl] dihexafluorophosphate ([C6O2(mim)2][PF6]2) (yield 0.953 in mass fraction): To a solution of [C6O2(mim)2][Br]2 (0.01 mol) in distilled water (50 mL), another solution of potassium hexafluorophosphate (0.02 mol) in distilled water (50 mL), and then potassium hexafluorophosphate aqueous solution was added dropwise over 30 min. The mixture was stirred for 8 h at room temperature. The product was washed with water (5 × 30 mL) and dried in vacuo at 298 K for 12 h. Finally, the [C6O2(mim)2][PF6]2 was obtained as a white solid. Purity of 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis-[3methyl-1H-imidazolium-1-yl] dihexafluorophosphate ([C6O2(mim)2][PF6]2): The packed column (C18, 250 mm × 4.6 mm, 5 μm) was filled with octadecyl silane bonded silica gel (5 μm). The mobile phase was acetonitrile, detection wavelength was 220 nm, and velocity was 1.0 mL/min. Apparatus and Procedure. The solubilities of [C6O2(mim)2][PF6]2 in water, methanol, ethanol, DMF, DMSO, and (acetone + water) binary solvent mixtures were measured by the analytical stirred-flask method at atmospheric pressure.20−23 The solubility apparatus consisted of a jacketed glass vessel (120 mL, Heng Tai Experiment Institute Industry, China) maintained at a desired temperature by water circulated from a water bath with a low-temperature thermostat bath (type DC-1006, Shanghai Heng Ping Instruments Co., Ltd., China). The vessel temperature could be maintained within ± 0.02 K of the required temperature. A mercury-in-glass thermometer (type WNG-01, Changzhou Rui Ming Instrument and Meter Plant, China) was inserted into the inner chambers of the vessel for the measurement of the temperature. The thermometer had an accuracy of ± 0.05 K. Both the thermostat and thermometer ensured that the temperature we need for the solubility measurement had an accuracy of ± 0.02 K. Before the solubility measurement, high-purity nitrogen (0.9999 by mass, 10 mL·min−1) was fed into the solvent for 2 h to remove the dissolved water and oxygen. A total of 8 mL of solvent and excess of [C6O2(mim)2][PF6]2 was added into a 10 mL glass tube with stopper. The dissolution of the solute was carried out in a jacketed glass vessel with designed constant temperature which was maintained by circulating water through the outer jacket from a low-temperature thermostatic bath. To ensure the solution reaching equilibrium, the solution was constantly stirred for 8 h by a magnetic stirrer (type DF-101S, Gongyi Yu Hua Instruments Co., Ltd., China), and when the equilibrium was attained, the stirrer was turned off to let the solution settle at least 6 h to ensure the suspended solid phase precipitated thoroughly. Then 1 mL of the supernatant was taken by pipet (type P1000N, Shanghai Aiyan Biological Technology co., Ltd., China) and quickly transferred to a weighed 5 mL beaker. The breaker filled with solution was weighed again. Finally, the beaker was put into a dryer at 298.00 K and weighed on a regular basis until constant weight. The drying time depended on the volatility of the solvent. The masses of the samples and solvents were obtained using an analytical balance (type BS 124S, Beijing Sartorius Instruments System Co., Ltd., China). The balance had a range of measurement up to 120 g, with an accuracy of ± 0.0001 g. Solubility experiments were conducted at least three times to check the reproducibility, and the mean values were considered as the

(DSC) and thermogravimetric analyses (TG). The solubilities of [C6O2(mim)2][PF6]2 in water, methanol, ethanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and (acetone + water) binary solvent mixtures were measured from (283.00 to 323.00) K using the analytical stirred-flask method at atmospheric pressure,20−23 which could provide reference for large-scale production. Then the solubilities data were correlated with the modified Apelblat equation. To our knowledge, this is the first time the solubilities of [C6O2(mim)2][PF6]2 in water, methanol, ethanol, DMF, DMSO, and (acetone + water) binary solvent mixtures have been reported.

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EXPERIMENTAL SECTION Materials. Analytical reagent (AR) grade methanol (mass fraction > 0.997), ethanol (mass fraction > 0.995), DMF (mass fraction > 0.997), DMSO (mass fraction > 0.995), acetone (mass fraction > 0.997) (from Sinopharm. Chemical Reagent Co. Ltd., China) were used directly without further purification. The water used in the experiments was double distilled. The other organic and inorganic compounds from Shanghai Aladdin Industrial Corporation were used without further purification. High-grade [C6O2(mim)2][PF6]2 was synthesized from our laboratory. The purity of [C6O2(mim)2][PF6]2 was determined by high performance liquid chromatography (type Waters 600E, Waters Co.) to be greater than 0.99 in mass fraction, and the [C6O2(mim)2][PF6]2 was stored under nitrogen. 1HNMR spectra was recorded on the AVANCE AV-300 or AVANCE AV-500 (Bruker Co. Ltd., Germany) operating at 400 MHz or 500 MHz, and chemical shifts were given in ppm units relative to tetramethylsilane (TMS). The splitting patterns are designated as follows: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. Differential scanning calorimetry (DSC) and thermogravimetry analyses (TG) were performed on Netzsch STA 449F3 thermogravimetric analyzer (Netzsch Geratebam GmbH, Germany) over a temperature range of (40−500) °C at a heating rate of 10 °C/min in nitrogen atmosphere. Analysis for water content in [C6O2(mim)2][PF6]2 using the Karl Fischer technique (method TitroLine KF) showed that the mass fraction was less than 0.00005. The melting point temperature (Tm) of [C6O2(mim)2][PF6]2 was (363 to 365) K measured by a digital melting point apparatus (type RY-51, Shanghai Precision & Scientific Instrument Co. Ltd., China). Synthesis and Purity of Gemini Dicationic Ionic Liquids: 24 The experimental steps are as follows. Synthesis of 1-bromo-2-[2-[2-bromo-ethoxy]-ethoxy-ethane (C6H12O2Br2, yield 0.768 in mass fraction): To a stirred mixture of triethylene glycol (C6H14O4) (0.25 mol) and pyridine (1.01 mol) at 273 K, phosphorus tribromide (0.20 mol, distilled) was added slowly over 1 h. The mixture was kept on reflux at 353 K for another 4 h and then cooled to room temperature.The mixture was poured into a NaHCO3 saturated aqueous solution (50 mL). The lower organic layer was washed with water (3 × 40 mL), and then it was dried with MgSO4(3.00 g). Finally, the target compound C6H12O2Br2 was obtained as a yellow liquid. Synthesis of 1,1′-[1,2-ethanediylbis(oxy-1,2-ethanediyl)]bis[3-methyl-1H-imidazolium-1-yl] dibromide ([C6O2(mim)2][Br]2) (yield 0.917 in mass fraction): N-methylimidazole (0.08 mol) and C6H12O2Br2 (0.035 mol) were added to dry toluene (20 mL) in a round-bottomed flask. The mixture was heated under reflux under N2 for 24 h. The flask was cooled to room temperature, and then toluene was removed through 2828

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measured results. The mole fraction solubility (x1) of [C6O2(mim)2][PF6]2 in pure solvents was defined as x1 =

mA /MA mA /MA + mB /MB

(1)

where mA and mB represent the mass of [C6O2(mim)2][PF6]2 and solvent (B = water, methanol, ethanol, DMF, DMSO) respectively; while MA and MB represent molecular weights, respectively. And the mole fraction solubility (x1 ) of [C6O2(mim)2][PF6]2 in binary solvent mixtures was defined as x1 =

mA /MA mA /MA + mB /MB + mC /MC

(2)

where mA, mB, and mC represent the mass of [C6O2(mim)2][PF6]2, water, and acetone, respectively; while MA, MB, and MC represent molecular weights, respectively. In this work, the estimated relative standard uncertainty of solubility in mole fraction was less than 0.02.

Figure 3. DSC and TGA of [C6O2(mim)2][PF6]2.

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directly attached to the positively charged imidazolium nitrogen (shown in Figure 1 as D) was observed as a triplet at δ 4.29. The signal for imidazolium protons (E, −NCHCHN−) were observed at δ 7.64 as a singlet. Because of the symmetrical structure and decoupling effect of adjacent nitrogen atoms, the split patterns of protons E was singlet. The signal for the −NCHN− imidazolium proton (shown in Figure 1 as F) appeared at δ 8.99 as a singlet. The signal appearing at δ 3.33 indicated that there was little water in the solvent (DMSO-d6). Thermal Stability of [C6O2(mim)2][PF6]2. Figure 3 showed the DSC and TGA results of [C6O2(mim)2][PF6]2. From the DSC curve, we found that [C6O2(mim)2][PF6]2 started to absorb heat at 90.5 °C, there was an endothermic peak at 95.0 °C and the endothermic process stopped at 99.5 °C. When the temperature was raised to 340 °C, exothermic peak appeared which meant the product started to disintegrate. The TGA curve showed that the sample was stable when the temperature was below 220 °C (the weight loss was below 0.826%). The TGA curve continuously declined with the rise of temperature. An apparent weight loss appeared when temperature was above 250 °C (the weight loss was 3.23%) and the weight loss was about 68.4% at 430 °C. When the temperature was above 430 °C, the weight loss became not so obvious, and tended to be stable. We could draw the conclusion that [C6O2(mim)2][PF6]2 had good heat resistance, and its melting point was near 95 °C (using a digital melting point apparatus (type RY-51), the melting point temperature (Tm) of [C6O2(mim)2][PF6]2 was (363 to 365) K). Solubility of [C6O2(mim)2][PF6]2 in Different Pure Solvents and (Acetone + Water) Binary Solvent Mixtures. The measured mole fraction solubilities (x) of [C6O2(mim)2][PF6]2 in different pure solvents and (acetone + water) binary solvent mixtures at different temperatures (T) are listed in Table 1 and Table 3, respectively. In the (acetone + water) binary solvent mixtures, the mass fraction of water (w) in the solvents was 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90. The mass fraction of water (w) had an accuracy of ≤ 0.0001.The relationship between temperature and the mole fraction solubility was described by the modified Apelblat equation.25 The modified Apelblat equation was shown as follows: B ln x = A + + C ln(T ) (3) T where x was the mole fraction solubility of [C6O2(mim)2][PF6]2, A, B, and C were empirical constants, and T was the

RESULTS AND DISCUSSION Characterization of [C6O2(mim)2][PF6]2. 1HNMR (500 MHz, DMSO-d6) of [C6O2(mim)2][PF6]2 is shown in Figure 1

Figure 2. 1HNMR of [C6O2(mim)2][PF6]2.

and Figure 2. The location of hydrogen in [C6O2(mim)2][PF6]2 is shown in Figure 1 as A, B, C, D, E, F: 3.50 ppm (s, 4H, 2 × CH2), 3.70 ppm (t, 4H, 2 × CH2), 3.80 ppm (s, 6H, 2 × CH3), 4.29 ppm (t, 4H, 2 × CH2), 7.64 ppm (s, 4H, 4 × NCHCHN-), 8.99 ppm (s, 2H, 2 × NCHN-). As shown in Figure 1, [C6O2(mim)2][PF6]2 is a symmetrical structure. Therefore, the H integrals (number of proton) at different chemical shifts need to be doubled. Because of the structural symmetry and magnetic equivalence, the signal for methylene protons between two oxygens (−O−CH2−CH2− O−, shown in Figure 1 as A) were observed as a singlet at δ 3.50. The chemical shifts for methylene protons between the cationic imidazolium moiety and oxygen (shown in Figure 1 as B) were observed as a triplet at δ 3.70. The signal for the methyl group attached to the imidazolium ring (imidazolium N−CH3, shown in Figure 1 as C) was observed as a singlet at δ 3.80 representing six protons. The signal for the protons 2829

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Table 1. Mole Fraction Solubilities (x) of [C6O2(mim)2][PF6]2 in Water, Methanol, Ethanol, Dimethyl Formamide, and Dimethyl Sulfoxide at the Temperature Range from (283.00 to 323.00) K under Atmospheric Pressurea T/K

102xcib

102xi

102ε

283.00 288.00 293.00 298.00 303.00

0.0150 0.0197 0.0257 0.0334 0.0430

0.0151 0.0196 0.0255 0.0335 0.0427

0.6623 0.5102 0.7843 0.2985 0.7026

283.00 288.00 293.00 298.00 303.00

0.0198 0.0231 0.0285 0.0369 0.0502

0.0195 0.0233 0.0284 0.0367 0.0504

1.5385 0.8584 0.3521 0.5450 0.3968

283.00 288.00 293.00 298.00 303.00

0.0033 0.0040 0.0047 0.0057 0.0072

0.0034 0.0041 0.0048 0.0058 0.0073

283.00 288.00 293.00 298.00 303.00

9.7991 10.1490 10.5110 10.8854 11.2724

9.7989 10.145 10.514 10.8851 11.2728

293.00 298.00 303.00 308.00

10.6366 11.9263 13.0678 14.0125

10.6345 11.9269 13.0668 14.0119

T/K

102xci

102xi

102ε

308.00 313.00 318.00 323.00

0.0551 0.0702 0.0889 0.1120

0.0550 0.0706 0.0886 0.1124

0.1818 0.5666 0.3386 0.3559

308.00 313.00 318.00 323.00

0.0713 0.1055 0.1622 0.2587

0.0712 0.1059 0.1625 0.2586

0.1404 0.3777 0.1846 0.0387

0.0092 0.0118 0.0154 0.0202

0.0093 0.0116 0.0153 0.0201

1.0753 1.7241 0.6536 0.4975

11.6723 12.0852 12.5115 12.9513

11.6719 12.0858 12.5119 12.9518

0.0034 0.0050 0.0032 0.0039

14.7240 15.1800 15.3728

14.7190 15.1910 15.3734

0.0340 0.0724 0.0039

Water

Methanol

Ethanol 2.9412 308.00 2.4390 313.00 2.0833 318.00 1.7241 323.00 1.3699 Dimethylformamide 0.0020 308.00 0.0394 313.00 0.0285 318.00 0.0028 323.00 0.0035 Dimethyl Sulfoxide 0.0197 313.00 0.0050 318.00 0.0077 323.00 0.0043

The standard uncertainty for the temperatures ur(T) is ± 0.02 K; the relative standard uncertainty in solubility ur(Xi) is 0.02. bNotation: solubility calculated from eq3, Xci; experimental solubility value, Xi; relative deviations, ε.

a

Table 2. Apelblat Parameters (A, B, and C) along with rmsd for the [C6O2(mim)2][PF6]2 in Water, Methanol, Ethanol, Dimethyl Formamide and Dimethyl Sulfoxidea solvent

Ab

B

C

104(rmsd)

water methanol ethanol dimethylformamide dimethyl sulfoxide

−48.69 −1345.29 −560.75 −26.52 469.91

−2069.02 55225.17 21317.06 553.00 −22555.51

8.36 202.22 84.16 3.94 −69.57

0.03 0.03 0.01 0.18 0.44

where xci was the solubility calculated from eq 3, and xi was the experimental solubility value. From Table 1, Table 3, and Figure 4, We found that the solubility of [C6O2(mim)2][PF6]2 in water, ethanol, methanol, DMF, and DMSO increased with the increase of temperature. The highest solubility of [C6O2(mim)2][PF6]2 in pure solvents was obtained in DMSO. The solubility of [C6O2(mim)2][PF6]2 in different pure solvents at constant temperature was in the following order: DMSO > DMF> ethanol > water > methanol. The solubilities of [C6O2(mim)2][PF6]2 not only depended on the nature of the Gemini ionic liquid, but also the influence of solvent polarity. [C6O2(mim)2][PF6]2 was a kind of hydrophobic ionic liquids, so it showed poor solubility in water. Also in the above systems, DMSO and DMF had strong polarity compared to ethanol and methanol. Also we found that the calculated solubilities in different pure solvents showed good agreement with the experimental data, which indicated that these data could be used to correlate solvent selection and model research in the process of crystallization of [C6O2(mim)2][PF6]2. From Tables 2, 4, and Figure 5, we found that the solubility of [C6O2(mim)2][PF6]2 increased with the increase of the amount of acetone in the mixed solvent at constant temperature. The solubility of [C6O2(mim)2][PF6]2 in the mixed solvent was lower and slowly increased at temperatures between (283.00 to 303.00) K but it quickly increased at high temperatures between (303.00 to 323.00) K. Also we found that the calculated solubility of ([C6O2(mim)2][PF6]2) was in good

a

Notation: root-mean-square deviations, rmsd. bApelblat coefficients were determined by multivariate least-squares method.

absolute temperature. The values of A, B, and C in the systems together with the root-mean-square deviations (rmsd) are listed in Table 2 and Table 4, respectively. The rmsd was defined as ⎡ N (x − x )2 ⎤1/2 i ⎥ rmsd = ⎢∑ ci ⎢⎣ i = 1 ⎥⎦ N

(4)

where N was the number of experimental points, xci was the solubility calculated by eq 3, and xi was the experimental solubility value. The relative deviations ε was defined as ε% =

|xci − xi| 100 xi

(5) 2830

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Table 3. Mole Fraction Solubilities (x) of [C6O2(mim)2][PF6]2 in (w) Water + (1 − w) Acetone at the Temperature Range from (283.00 to 323.00) K under Atmospheric Pressure, w is the Mass Fractiona T/K

102xcib

102xi

102ε

T/K

102xci

102xi

102ε

283.00 288.00 293.00 298.00 303.00

7.0038 7.6446 8.3455 9.1115 9.9483

7.0042 7.6442 8.3457 9.1111 9.9478

0.0057 0.0052 0.0024 0.0044 0.0050

308.00 313.00 318.00 323.00

10.8618 11.8587 12.9459 14.1309

10.8622 11.8581 12.9451 14.1313

0.0037 0.0051 0.0062 0.0028

283.00 288.00 293.00 298.00 303.00

5.2181 5.8496 6.5589 7.3552 8.2486

5.2185 5.8508 6.5593 7.3558 8.2487

0.0077 0.0205 0.0061 0.0082 0.0012

308.00 313.00 318.00 323.00

9.2505 10.3733 11.6311 13.0391

9.2520 10.3731 11.6308 13.0387

0.0162 0.0019 0.0026 0.0031

283.00 288.00 293.00 298.00 303.00

3.2617 3.8343 4.5087 5.3027 6.2370

3.2619 3.8347 4.50898 5.3028 6.23371

0.0061 0.0104 0.0062 0.0019 0.0528

308.00 313.00 318.00 323.00

7.3359 8.6275 10.1449 11.9264

7.3358 8.6278 10.1446 11.9269

0.0014 0.0035 0.0030 0.0042

283.00 288.00 293.00 298.00 303.00

2.0353 2.4810 3.0253 3.6900 4.5011

2.0345 2.478 3.014 3.678 4.5067

0.0393 0.1211 0.3749 0.3263 0.1243

308.00 313.00 318.00 323.00

5.4904 6.6964 8.1657 9.9543

5.4989 6.6969 8.1645 9.9541

0.1546 0.0075 0.0147 0.0020

283.00 288.00 293.00 298.00 303.00

0.9577 1.2343 1.5917 2.0531 2.6486

0.9571 1.2564 1.5911 2.0534 2.6482

0.0627 1.7590 0.0377 0.0146 0.0151

308.00 313.00 318.00 323.00

3.4167 4.4069 5.6827 7.3250

3.4161 4.4016 5.6823 7.327

0.0176 0.1204 0.0070 0.0273

283.00 288.00 293.00 298.00 303.00 w = 0.7 283.00 288.00 293.00 298.00 303.00 w = 0.8 283.00 288.00 293.00 298.00 303.00 w = 0.9 283.00 288.00 293.00 298.00 303.00

0.5455 0.6867 0.8649 1.0895 1.3726

0.5447 0.6881 0.8655 1.0880 1.3745

0.1469 0.2035 0.0693 0.1379 0.1382

308.00 313.00 318.00 323.00

1.7293 2.1784 2.7434 3.4539

1.7278 2.1689 2.7399 3.4489

0.0868 0.4380 0.1277 0.1450

0.1349 0.1803 0.2412 0.3228 0.4319

0.1345 0.1809 0.2408 0.3213 0.4325

0.2974 0.3317 0.1661 0.4669 0.1387

308.00 313.00 318.00 323.00

0.5780 0.7734 1.0345 1.3831

0.5760 0.7721 1.0329 1.3825

0.3472 0.1684 0.1549 0.0434

0.0639 0.0830 0.1077 0.1398 0.1816

0.0633 0.08351 0.1079 0.1392 0.182

0.9479 0.6107 0.1854 0.4310 0.2198

308.00 313.00 318.00 323.00

0.2358 0.3061 0.3974 0.5156

0.2351 0.3058 0.3979 0.515

0.2977 0.0981 0.1257 0.1165

0.0222 0.0304 0.0409 0.0542 0.0707

0.0224 0.0301 0.0405 0.0548 0.0701

0.8929 0.9967 0.9877 1.0949 0.8559

308.00 313.00 318.00 323.00

0.0909 0.1153 0.1444 0.1786

0.0911 0.114 0.146 0.175

0.2195 1.1404 1.0959 2.0571

w = 0.1

w = 0.2

w = 0.3

w = 0.4

w = 0.5

w = 0.6

a The standard uncertainty for the temperatures ur(T) is ± 0.02 K, the relative standard uncertainty in solubility ur(Xi) is 0.02. bNotation: the solubility calculated from eq 3, xci; experimental solubility value, xi; relative deviations, ε.

agreement with the experimental data, which suggested that the experimental solubility data and the correlation equations in

this work could be used as fundamental data and models in the purification process of [C6O2(mim)2][PF6]2. 2831

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Table 4. Apelblat Parameters (A, B, and C) along with rmsd for the [C6O2(mim)2][PF6]2 + Acetone + Water System at Various Contents of Water (w) in the Mixed Solventa w

Ab

B

C

104(rmsd)

0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90

−68.35 −88.60 −124.73 −152.39 −194.98 −177.87 −224.38 −202.63 151.95

1607.49 2094.50 2967.81 3632.41 4655.86 4223.78 5327.78 4776.70 −11224.71

10.63 13.86 19.63 24.03 30.80 27.94 35.24 31.60 −21.38

0.05 0.08 0.12 0.69 0.81 0.42 0.12 0.06 0.15

Article

CONCLUSIONS In this work, [C6O2(mim)2][PF6]2 was synthesized and confirmed with 1HNMR. The thermal stability of [C6O2(mim)2][PF6]2 was conducted with differential scanning calorimetry (DSC) and thermogravimetry analyses (TG). The solubilities of [C6O2(mim)2][PF6]2 in water, methanol, ethanol, DMF, DMSO, and (acetone + water) binary solvent mixtures were measured from (283.00 to 323.00) K. From the tables and figures, we can draw the following conclusions: (1) As a kind of dicationic IL, [C6O2(mim)2][PF6]2 had a thermal decomposition temperature of about 340 °C, with a higher heat resistance than ordinary ILs. It could be used as good high-temperature solvent in reactions. (2) The structure of material and the polarity of solvent affected the solubility in different solvents. DMSO and DMF presented a relatively good ability of dissolving

a

Notation: mass fraction, w; root-mean-square deviations, rmsd. Apelblat coefficients were determined by multivariate least-squares method.

b

Figure 4. Correlation of experimental mole fraction solubilities (xi) of [C6O2(mim)2][PF6]2 in water, methanol, ethanol, DMF, DMSO: ○, water; ▽, methanol; △, ethanol; □, DMF; ☆, DMSO (solid lines represent the Apelblat solubilities).

Figure 5. Correlation of experimental mole fraction solubilities (xi) of [C6O2(mim)2][PF6]2 in (w) water + (1 − w) acetone, where w is the mass fraction: ●, w = 0.1; △, w = 0.2; ◆, w = 0.3; □, w = 0.4; ○, w = 0.5; ☆, w = 0.6; ▲, w = 0.7; ▽, w = 0.8; ▼, w = 0.9 (solid lines represent the Apelblat solubilities). 2832

dx.doi.org/10.1021/je5004466 | J. Chem. Eng. Data 2014, 59, 2827−2833

Journal of Chemical & Engineering Data

Article

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[C6O2(mim)2][PF6]2 than water, ethanol, and methanol. Also the solubility of [C6O2(mim)2][PF6]2 increased with an increase of temperature. (3) The solubility of [C6O2(mim)2][PF6]2 in (acetone + water) binary solvent mixtures increased with the increase of temperature and decreased with increasing water content at constant temperature. Water could be used as effective antisolvent in the crystallization process. (4) The experimental data fit well with the Apelblat equation and the parameters could be used for optimizing the purification process of [C6O2(mim)2][PF6]2 in industry.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86-25-58139426. E-mail: [email protected]. Funding

This work was supported by Natural Science Foundation of Jiangsu Province (No. BK2011799, No. BK20140939) and the specialized research fund for the Doctoral Program of Higher Education of China (No. 20113221120006). The authors also gratefully appreciate the support from Jiangsu Students Innovation and Entrepreneurship Training Program (No. 2012JSSPITP3054 and No. 201413905004Y). Notes

The authors declare no competing financial interest.

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