and 1-Butyl-3-ethylimidazolium-Based Ionic Liquids - ACS Publications

Article pubs.acs.org/jced

Liquid−Liquid Equilibria in Aqueous 1‑Alkyl-3-methylimidazoliumand 1‑Butyl-3-ethylimidazolium-Based Ionic Liquids Aleksandra Dimitrijević,† Tatjana Trtić-Petrović,† Milan Vraneš,‡ Snežana Papović,‡ Aleksandar Tot,‡ Sanja Dožić,‡ and Slobodan Gadžurić*,‡ †

Laboratory of Physics, Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia Faculty of Sciences, University of Novi Sad, Department of Chemistry, Biochemistry and Environmental Protection, Trg Dositeja Obradovića 3, 21000 Novi Sad, Serbia

‡

S Supporting Information *

ABSTRACT: In this work, novel phase diagrams for aqueous solutions of 1-alkyl-3-methylimidazolium- and 1-butyl-3-ethylimidazolium-based ILs combined with phosphate-based salts, namely, K3PO4 or K2HPO4, are reported and discussed. To correlate the binodal data, the Merchuk equation is applied. The tie lines and tie-line lengths are also presented. The anion influence on the ability to form aqueous biphasic system (ABS) is investigated for the IL with the same1-butyl-3-methylimidazolium cation, [bmim]+, and various anions, for example, salicylate, [SAL]−; trifluoromethanesulfonate, [TFS]−; dicyanamide, [DCA]−; and chloride, [Cl]−. The order of studied anions to form ABS is [TFS]− > [SAL]− > [DCA]− > [Cl]−. The effect of alkyl chain length on imidazolium ion on liquid− liquid equilibrium is discussed in terms of increasing ionic liquid hydrophobicity and poorer affinity for water. It is shown that 1-hexyl-3-methylimidazolium chloride ionic liquid has a better ability to form ABS comparing to ionic liquid with butyl chain and the same anion. Newly synthesized ionic-liquidcontaining ethyl group 1-butyl-3-ethylimidazolium bromide was also investigated, showing the influence of both ethyl group and bromide anion on the ability of ABS formation.

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INTRODUCTION Ionic liquids (ILs) are the salts with melting point lower than 373.15 K showing low toxicity, biodegradability, a negligible vapor pressure, high conductivity and thermal stability.1 Such unique properties make them alternative solvents for toxic volatile organic compounds. Due to their tunable physical and chemical properties, they are called designed solvents and can be applied in many industrial and technological processes, as well in analytical separation techniques.2−8 Recently, the newest generation of ILs with targeted biological properties containing biologically active components extends the sphere of their use in pharmacy, medicine, and agriculture as potential drugs.9−17 Liquid−liquid extraction based on ionic liquids and waterstructuring salts as aqueous biphasic systems have been reported for the first time in 2003.18 These systems have been successfully used to separate drugs,19−22 proteins,23 dyes,24 and pesticides.25 Liquid−liquid equilibrium (LLE) data at different temperatures and compositions are essential for the optimization of extraction process using ABS. For this purpose, water-soluble hydrophilic ionic liquids can be used as extracting solvent, as they induce formation of aqueous biphasic systems with suitable kosmotropic agents forming a new type of partitioning systems.18,26,27 Such ABS with the right proportions of ionic liquid and kosmotropic salt can be used as an © 2015 American Chemical Society

alternative extraction medium to conventional systems of either liquid−liquid or liquid−solid type. Contrary to previous reports that hydrophilic ionic liquids are structure breakers or “chaotropes”,28−31 kosmotropic properties of many imidazolium-based ILs containing different anions such as halide, dicyanamide or salicylate were reported.32−34 It was described that these ILs strongly interacts with water molecules and increase the structuring of water. Thus, having the structure making properties, the recently synthesized ILs 1-butyl-3-methylimidazolium salicylate, [bmim][SAL], and 1-butyl-3-ethylimidazolium bromide, [beim][Br], were investigated as a potential media for LLE in the presence of the commonly used phosphate inorganic salts. The binodal curves of the ternary phase diagrams and the tie lines (TL) of the synthesized ILs were constructed and compared to commercially available ILs: 1-butyl-3-methylimidazolium dicyanamide, [bmim][DCA], 1-butyl-3-methylimidazolium trifluoromethanesulfonate, [bmim][TFS], 1-butyl-3methylimidazolium chloride, [bmim][Cl], and 1-hexyl-3methylimidazolium chloride, [hmim][Cl]. Received: August 17, 2015 Accepted: December 4, 2015 Published: December 15, 2015 549

DOI: 10.1021/acs.jced.5b00697 J. Chem. Eng. Data 2016, 61, 549−555

Journal of Chemical & Engineering Data

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Article

EXPERIMENTAL SECTION Materials. The ionic liquids [bmim][DCA], [bmim][TFS], [bmim][Cl] and [hmim][Cl] were supplied by Iolitec GmbH (Denylingen, Germany). Other two ionic liquids [bmim][SAL] and [beim][Br] were synthesized by the following procedures. Ionic liquid [bmim][SAL] was synthesized starting from the equimolar amounts of 1-butyl-3-methylimidazolium chloride and sodium salicylate. The reagents were dissolved in the acetone and the mixture was stirred in a round-bottom flask under reflux for 12 h. The resulting white precipitate (sodium chloride) was removed and the clear pale yellow liquid is obtained. Then, the IL was heated for 30 min at 343.15 K under vacuum in order to remove the acetone. After achieving a constant mass, obtained product was additionally dried under the vacuum for the next 72 h. Water content in the IL was found to be 240 ppm by the Karl Fischer titration and chloride content 1.5 ppm using ion chromatography. The second ionic liquid, [beim][Br], was prepared using 1ethylimidazole and 1-bromobutane as starting reagents. The reagents were dissolved in the acetone and the mixture was stirred in a round-bottom flask under reflux for 72 h. The product was purified by liquid−liquid extraction using ethyl acetate. In order to remove ethyl acetate from the sample, the ionic liquid was heated for 45 min at 343.15 K under vacuum. After achieving a constant mass, the ionic liquid was additionally dried under the vacuum for the next 72 h. The water content was found to be 252 ppm by the Karl Fischer titration. Structures of the ILs were confirmed by IR and NMR spectroscopy (Figure S1 and S2 in Supporting Information). The provenance and purity of the applied ILs are given in Table 1.

salt, was repeated until enough data points have been acquired for constructing of the binodal curve. The dropwise additions were carried out under vigorously shaken using a vortex agitator (Reax Top, Heidolph, Germany) at 2500 rpm. All experiments were performed at 296 ± 1 K and under atmospheric pressure (0.1 MPa). The compositions of ternary system were determined by measuring the mass of all added components using an analytical balance (CP224S, Sartorius) within an uncertainty of 1 × 10−4 g. The experimental obtained binodal curves of the ternary phase diagrams were fitted by least-squares regression to an empirical relationship developed by Merchuk37 Y = A exp(BX 0.5 − CX3)

where Y and X represent the IL and salt mass fractions, respectively, and A, B, and C, are constants obtained by leastsquares regression. The tie lines which connect two nodes on the binodal curve were determined by a gravimetric method originally proposed by Merchuk.37 The required components of salt and IL solutions were added in a 2 cm3 vial and intensively mixed for 2 min, after that allowed to equilibrate by the phase separation for 24 h, although time needed to reach equilibrium was shorter (30 min).36 Then, top and bottom phases were separated and weighted. Each TL was determined by application of lever arm rule36 using the relationship between the mass of IL-rich phase and the overall system composition.38 For the calculation of the tie-line lengths (TLL), the following equation was applied:39 TLL =

[bmim] [DCA] [bmim] [TFS] [bmim] [Cl] [hmim] [Cl] [bmim] [SAL] [beim] [Br] a

provenance Iolitec GmbH Iolitec GmbH Iolitec GmbH Iolitec GmbH Synthesis Synthesis

(YIL − YS)2 + (XIL − XS)2

(2)

where subscripts IL and S designate the IL-rich phase and the salt-rich phase. The following system of four equations with four unknown values was solved by applying MathCad 15.0 program providing the concentrations of IL and salt in the ILrich phase and the salt-rich phases, YIL, YS, XIL, and XS necessary for determination of TLLs:39

Table 1. Provenance and Purity of the Studied Samples ionic liquid

(1)

product number

final mass fraction

IL-0010HP IL-0013HP IL-0014HP IL-0054HP

> 0.98w

a

none

> 0.99w

a

none

0.5 3 YIL = A exp[BXIL − CXIL ]

(3)

> 0.99wa

none

YS = A exp[BXS0.5 − CXS3]

(4)

a

none

> 0.98w

> 0.96wb > 0.99wb

purification method

evaporation and drying under vacuo extraction and drying under vacuo

Stated by supplier. bConfirmed by NMR spectroscopy.

YIL =

YM 1−α − YS α α

(5)

XIL =

XM 1−α − YS α α

(6)

where M denotes the mixture and α is measured mass ratio of the top phase and the mixture. Coefficients A, B, and C were taken from the fitting parameters of binodal curve. On the basis of obtained values, TLL was calculated applying eq 2.

The inorganic salts, K2HPO4 and K3PO4 were analytical grade reagents purchased from Sigma-Aldrich. All solutions were prepared with Milli-Q water (Millipore Corporation, Bedford, MA, U.S.A.). Phase Diagrams and Tie Lines. The cloud point method was applied for construction of the binodal curves of the ternary phase diagrams.24,31,35,36 Aqueous solutions of either K3PO4 or K2HPO4 and aqueous solution of selected hydrophilic ILs were prepared gravimetrically. A known amount of aqueous solution of IL was taken into a test tube. Drop-wise addition of inorganic salt solution to IL solution was carried out until the mixture became turbid or cloudy, then followed by addition of minimum amount of water to achieve a clear onephase system. This process, sequential addition of water and

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RESULTS AND DISCUSSION Phase Diagrams of the Aqueous Biphasic Systems. The formation of ABS strongly depends on the IL chemical structure. In this study, phase diagrams of the synthesized ILs [bmim][SAL] and [beim][Br] are compared to phase diagrams of commercially available ILs ([bmim][DCA], [bmim][TFS], [bmim][Cl], and [hmim][Cl]). The phase diagrams of the aqueous biphasic systems based on the synthesized ILs combined with inorganic salts (K3PO4 and K2HPO4) are shown in Figure 1. The phase diagrams are shown in molality units, moles of solute (IL or salt) per kilogram of solvent (salt + 550



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Table 2. Weight Fraction Composition for Binodal Data for the {IL (Y) + Salt (X) + Water} ABS at 296 K and at p = 0.1 MPa

Figure 1. Ternary phase diagrams of the studied {IL + salt + H2O} system at T = 296 K and atmospheric pressure (p = 0.1 MPa): purple ●, [bmim][SAL]/K2HPO4; purple ○, [bmim][SAL]/K3PO4; blue ◇, [beim][Br]/K3PO4; blue ◆, [beim][Br]/K2HPO4.

water or IL + water), which allow comparison of diagrams obtained for different ILs. The experimental binodal data for the ternary mixtures of [bmim][SAL] and [beim][Br] are reported in Table 2. The phase diagrams shows: the minimum mass fraction composition to separate the monophasic (left side of curve) and the biphasic system (right side of curve); the concentration of the phase components in the IL-rich phase and salt-rich phase and their volume ratio. The smaller the monophasic region, the lower is the amount of IL or salt necessary to form ABS. The experimental data were fitted by empirical relationship of Merchuk (eq 1) and the regression parameters for this equation were estimated by a least-squares regression. The coefficients A, B, and C of eq 1, corresponding standard deviations and correlations coefficients are provided in Table 3. On the basis of the standard deviations and the regression parameters for all investigated ABS, one can be concluded that eq 1 is satisfactorily used to fit the binodal curves. The ability of the salts to induce the formation of ionic liquid-based ABS38 follows the Hofmeister series. The closer the binodal curve is to the axes, the stronger the salt’s ability to promote the ABS system. Various studies showed that saltingout effect of each salt correlates with the molar entropy of hydratation of the ions and that ion−dipole interaction and formation of ion−water complexes is driving force for ABS promotion.38 When considering three potassium phosphate salts (K3PO4, K2HPO4, and KH2PO4) as salting-out agents, it is found that the charge of anion plays significant role in 2− formation of ABS and that follows the order: PO3− 4 > HPO4 > − H2PO4 . This effect is clearly seen from Figure 1; the ability of formation the ABS is higher with K3PO4 comparing to K2HPO4. The ability of forming ABS depends on the anion capability to bound hydrogen ion.28,40 For comparison with [bmim][SAL]’s ability to form ABS, ILs with the same cation ([bmim]+) and various anions ([TFS]−, [DCA]−, and [Cl]−) were chosen (Figure 2). The experimental binodal data for the ternary mixtures of [bmim][TFS], [bmim][DCA], and [bmim][Cl] are given in Table S1 (Supporting Information). A comparison of obtained

[bmim][SAL]/ K3PO4

[bmim][SAL]/ K2HPO4

[beim][Br]/ K3PO4

[beim][Br]/ K2HPO4

100·Y

100·X

100·Y

100·X

100·Y

100·X

100·Y

100·X

56.79 43.16 38.97 31.12 26.47 22.41 20.52 18.41 17.10 15.82 14.45 14.05 13.70 12.67 11.79 10.85 10.42 9.97 9.45 9.03 8.60 8.13 7.90 7.59 7.30 6.90 6.47 5.98 5.37

1.71 4.05 4.88 6.93 7.97 9.31 9.79 10.59 10.79 11.26 12.14 12.21 12.35 12.73 12.95 13.33 13.46 13.65 13.82 14.08 14.24 14.49 14.60 14.70 14.86 15.11 15.32 15.59 16.08

59.26 46.56 44.89 43.20 41.42 39.64 37.28 35.39 33.98 31.71 30.50 29.37 26.69 25.85 24.70 23.31 22.36 21.58 20.80 19.54 18.63 17.16 15.69 13.86 12.85 11.97 10.90 9.85 8.97 7.94 6.76

0.56 2.24 2.64 2.83 3.40 3.77 4.48 5.00 5.53 6.15 6.54 6.92 7.95 8.21 8.61 9.49 9.55 9.82 10.13 10.65 11.01 11.60 12.21 12.97 13.44 13.84 14.36 14.94 15.38 16.15 16.92

52.02 47.06 40.28 37.15 33.77 30.96 28.29 25.77 23.65 22.09 20.54 18.99 18.03 17.07 16.21 15.34 14.65 14.07 12.96 12.31 11.70 11.28 10.78 10.30 9.88

2.05 3.74 4.78 5.94 6.83 7.57 9.34 10.68 11.75 12.28 13.14 14.29 14.85 15.48 16.04 16.49 17.00 17.36 18.21 18.70 19.21 19.44 19.81 20.24 20.58

51.74 47.87 43.07 36.77 32.91 28.89 25.64 24.29 22.03 21.35 19.33 17.75 16.07 14.91 13.73 12.86 11.74 11.35 10.65 10.17 9.60 9.07

2.45 3.85 3.92 6.55 7.38 9.54 11.42 12.60 13.76 14.33 15.79 16.81 18.27 19.04 20.10 20.65 21.69 22.06 22.72 23.15 23.67 24.20

Standard uncertainties are u(w) = 0.01; u(T) = 1 K. Relative standard uncertainty: ur (p) = 1.5%.

experimental data for commercially available ionic liquids studied in this work with existing literature values is presented in the same figure. [bmim][TFS] was purchased from the same supplier (Iolitec GmbH) in both cases. Excellent agreement was observed in the IL-rich region, but in the salt-rich region, discrepancies are much higher. [bmim][DCN] was purchased from Iolitec GmbH in both cases. Good agreement (≤1%) was observed between our experimental data and those presented in the paper of Mourao et al.41 In the article of Zafarani et al.42 [bmim][Cl] was supplied by Merck, whereas other points were obtained using [bmim][Cl] purchased from Iolitec GmbH. The fitting parameters of the binodal curves shown in Figure 2 are given in Table 3. The lower affinity of IL anion to bound hydrogen ion−the higher will be affinity of IL to promote formation of ABS. It can be seen from Figure 2 that an ability of studied anions to form ABS is the following: [TFS]− > [SAL]− > [DCA]− > [Cl]−. These results agreed with polarity of the IL determined using the solvatochromic probe [Fe(phen)2(CN)2]ClO4.28 The known values of hydrogen bound acidity (α) and basicity (β) of the [bmim][TFS], [bmim][DCA], and [bmim][Cl] are α = 0.50, 0.44, and 0.32 and β = 0.57, 0.64, and 0.95, respectively. 551



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Table 3. Fitting Parameters of the Experimental Data of the Ternary Phase Diagrams, in Figure 2 Obtained by Equation 1 ILs + salt + H2O [bmim][TFS]/K2HPO4 [bmim][SAL]/K2HPO4 [bmim][SAL]/K3PO4 [bmim][DCA]/K2HPO4 [bmim][DCA]/K3PO4 [beim][Br]/K3PO4 [beim][Br]/K2HPO4 [bmim][Cl]/K2HPO4 [hmim][Cl]/K2HPO4

A±σ 172.7 ± 8.26 76.27 ± 0.41 94.56 ± 1.23 80.33 ± 1.24 84.71 ± 1.37 89.21 ± 2.37 91.01 ± 2.76 65.41 ± 0.23 87.76 ± 0.78

B±σ −0.804 −0.331 −0.385 −0.387 −0.404 −0.358 −0.356 −0.296 −0.345

± ± ± ± ± ± ± ± ±

0.023 0.003 0.007 0.009 0.008 0.012 0.013 0.001 0.005

C±σ (−6.920 (2.315 (3.241 (1.672 (1.784 (6.647 (3.797 (2.931 (2.355

± ± ± ± ± ± ± ± ±

1.435) 0.037) 0.064) 0.116) 0.068) 0.553) 0.439) 0.003) 0.315)

R2 × × × × × × × × ×

−5

10 10−4 10−4 10−4 10−4 10−5 10−5 10−5 10−5

0.9864 0.9996 0.9996 0.9979 0.9988 0.9964 0.9957 0.9999 0.9989

Figure 3. Ternary phase diagrams of the studied {IL + salt + H2O} system at T = 296 K and atmospheric pressure (p = 0.1 MPa): blue ◇, [beim][Br]/K3PO4; blue ◆, [beim][Br]/K2HPO4; purple ◀, [hmim][Cl]/K2HPO4; purple ◁, [hmim][Cl]/K2HPO4;43 green ▶, [bmim][Cl]/K2HPO4.

Figure 2. Ternary phase diagrams of the studied {IL + salt + H2O} system at T = 296 K and atmospheric pressure (p = 0.1 MPa): red ■, [bmim][TFS]/K2HPO4; red □, [bmim][TFS]/K2HPO4;41 purple ●, [bmim][SAL]/K2HPO4; aqua ▲, [bmim][DCA]/K2HPO4; aqua △, [bmim][DCA]/K2HPO4;41 gold ▶, [bmim][Cl]/K2HPO4; gray × , [bmim][Cl]/K2HPO4;36 gold *, [bmim][Cl]/K2HPO4;41 gold +, [bmim][Cl]/K2HPO4.42

and our results probably derive from either content of water in IL or other impurities. Tie-Line Lengths. The phase diagram, comprised binodal curve, and tie lines provide information about the concentration of phase-forming components required to form two phases, the concentration of phase components in top and bottom phases, and the ratio of phase volume. Coordinates for all potential systems will lie on a tie line, which connects two nodes on the binodal and represents the final concentration of phase components in top and bottom phases.36 Moving along the tie line, coordinates denote systems with differing total compositions and volume ratios, but with the same final concentration of phase components in top and bottom phases. The tie-line lengths and the slope of TLs data (S) for the investigated ABS were calculated based on experimental data of binodal curves and eqs 2−6) (Table 4). Figure 4 shows the binodal curve and TLs for the synthesized ILs [bmim][SAL] and [beim]Br. These data could be used for determination of the relative distributions of the IL and inorganic salt into ILrich and salt-rich aqueous phases in equilibrium and for prediction of extraction conditions. The results shown in Figures 1 and 4 demonstrate the finetune extraction ability of newly synthesized [bmim][SAL], for example, in the region of high concentration of K3PO4, very low quantity of IL can be applyed to form ABS which can be used during the sample preparation for preconcentration and analyte separation. Additionally, [bmim][SAL] have similar behavior in

Unfortunately, these quantities for [bmim][SAL] are not available in the literature, but it might be concluded that acidity α for [bmim][SAL] lies in the range from 0.44 to 0.50, and β value between 0.57 and 0.64. The effect of alkyl chain length in imidazolium ion (Figure 3 and Table S2 in the Supporting Information file) shows that longer alkyl chain will provide better ability of formation of ABS due to increase the hydrophobicity of ILs and poorer affinity for water. Namely, longer alkyl chain pronounced hydrophobic solvation, which leads to better structuring of water molecules around an alkyl group (cage-like structure) and a decrease in entropy of the system. Addition of inorganic salt sharply undermines such structure increasing the entropy. Thus, [hmim][Cl] shows better ability to form ABS corresponding ionic liquid with butyl chain [bmim][Cl]. Newly studied [beim][Br] shows influence of both ethyl group and bromide anion and forms ABS better than [bmim][Cl] and [hmim][Cl]. Literature data for [hmim][Cl] is compared with those obtained in this work in Figure 3. In the article of Deive et al.43 [hmim][Cl] was synthesized according to the procedure described in the literature elsewhere.44 In our experiments, we used [hmim][Cl] purchased from Iolitec GmbH without any pretreatment. We suppose that the difference existing data 552



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Table 4. Experimental Data of the Weight Fraction Compositions of IL in the IL-Rich Phase, YIL, and in the Salt-Rich Phase, YS, the Salt in the IL-Rich Phase, XIL, and in the Salt-Rich Phase, XS, the Initial Mixture of IL, YM, and Salt, XM, for TLLs of ABS {IL + salt + H2O} and Slope, S, of TL at 296 K and at p = 0.1 MPa IL/salt

100·YIL

100·YS

100·YM

100·XM

100·XIL

100·XS

TLL

S

[bmim][TFS]/K2HPO4 [bmim][DCA]/K2HPO4 [bmim][DCA]/K3PO4 [bmim][SAL]/K2HPO4

49.96 43.94 56.84 49.81 44.52 32.88 56.73 49.81 43.07 33.81 43.05 36.43 42.26

2.38 2.41 0.97 1.71 2.61 5.84 1.75 2.73 4.08 6.97 4.08 6.46 4.49

25.00 25.10 25.00 27.20 22.10 18.20 25.00 25.00 22.00 28.00 25.10 30.00 25.00

12.10 9.80 12.11 11.40 12.00 12.00 12.50 11.10 11.00 10.00 13.80 10.54 15.70

8.42 7.72 3.90 1.11 2.69 6.39 1.11 2.12 3.32 12.76 7.43 10.51 7.57

18.56 16.60 19.38 22.53 20.11 16.95 20.55 18.91 17.48 18.31 23.18 22.89 26.44

44.58 38.90 56.05 52.96 45.34 28.73 58.71 50.36 41.95 23.91 40.42 30.69 41.05

−2.569 −2.552 −2.876 −2.335 −2.385 −2.375 −2.957 −2.710 −2.907 −1.855 −1.905 −1.578 −1.503

[bmim][SAL]/K3PO4

[beim][Br]/K3PO4 [beim][Br]/K2HPO4

Standard uncertainty: u(X, Y) = 0.01; u(T) = 1 K. Relative standard uncertainty: ur(p) = 1.5%.

Figure 4. Binodal curves and TLs of (a) [bmim][SAL]/K2HPO4, (b) [bmim][SAL]/K3PO4, (c) [beim][Br]/K2HPO4, and (d) [beim][Br]/ K3PO4. X and Y denote the weight fraction composition of salt and IL, respectively.

investigated for the IL with same cation ([bmim]+) and

forming ABS as [bmim][TFS], but in the area of high concentration of salt, IL-rich phase has higher density comparing to salt-rich phase and in that case the removal of low quantity of IL is more difficult.

different anions. It was found that the ability of studied anions to form ABS is [TFS]− > [SAL]− > [DCA]− > [Cl]−. The

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effect of alkyl chain length on imidazolium ion on liquid−liquid

CONCLUSIONS In this work we report novel ternary phase diagrams, TLs and TLLs for ABS composed 1-alkyl-3-methylimidazolium and 1butyl-3-ethylimidazolium-based ILs with various anions combined with phosphate-based salts (K3PO4 or K2HPO4). The phase diagrams of the two synthesized ILs ([bmim][SAL] and [beim][Br]) are compared to phase diagrams of commercially available ILs ([bmim][DCA], [bmim][TFS], [bmim][Cl], and [hmim][Cl]). The anion influence on ability to form ABS was

equilibrium was discussed in terms of increasing ionic liquid hydrophobicity and poorer affinity for water. It is found that IL with longer hexyl group on the imidazolium ring shows better ability to form ABS as the corresponding ionic liquid with butyl chain. Newly studied [beim][Br] with the ethyl group in the position N3 of the imidazolium cation forms ABS better than [bmim][Cl] and [hmim][Cl]. 553



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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.5b00697. 1 H NMR and 13C NMR spectra of two synthesized ionic liquids: [beim]Br and [beim][SAL] together with peak integrals (Figures S1 and S2); weight fraction composition for binodal data for {IL (Y) + salt (X) + water} ABS at 296 K, where IL is [bmim][TFS] or [bmim][DCA] (Table S1); and [bmim][Cl] or [hmim][Cl] (Table S2). (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +381 21 485 2744. Fax: +381 21 454 065. E-mail: [email protected]. Funding

This work was financially supported by the Ministry of Education, Science and Technological Development of Serbia under project contracts ON172012 and III 45006. The authors would like to acknowledge the contribution of the COST Action CM1206-Exchange on Ionic Liquids. Notes

The authors declare no competing financial interest.

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REFERENCES

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