LiquidâLiquid Equilibria in Ternary Systems of Hexafluoroisopropanol

Article pubs.acs.org/jced

Liquid−Liquid Equilibria in Ternary Systems of Hexafluoroisopropanol + Perfluorocarbon + Water or Methanol at 298.15 K Martin Strejc,† Karel Ř ehák,*,† Petr Beier,‡ and Pavel Morávek† †

Department of Physical Chemistry, Institute of Chemical Technology, Prague, 166 28 Prague 6, Czech Republic Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague, Czech Republic

‡

ABSTRACT: Liquid−liquid equilibrium data for ternary systems hexafluoroisopropanol + perfluorocarbon (namely perfluoro(n-hexane) or perfluoro(methylcyclohexane)) + water or methanol were determined at 298.15 K. Water, methanol, and other polar solvents exhibit very low miscibility with perfluorocarbons. In contrast, hexafluoroisopropanol is fully miscible with water, methanol, and perfluorocarbons. Consequently, the determined ternary liquid− liquid equilibrium diagrams possess only one heterogeneous binary subsystem. They are of the type 1. Due to specific properties of perfluorocarbons, a special procedure for determination of the liquid−liquid equilibrium in the studied systems was developed. The ternary liquid−liquid equilibrium diagrams were found to be almost identical for perfluoro(n-hexane) and perfluoro(methylcyclohexane) showing that the structure of perfluorocarbon component has minimal influence on the miscibility behavior.

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INTRODUCTION Perfluorocarbons (PFCs) are derivatives of hydrocarbons in which all hydrogens are substituted by fluorine atoms. The resulting compounds containing only C−C and C−F bonds possess unique characteristics such as high thermal and chemical stability, extremely nonpolar character, low polarizability, high vapor pressure, and very low intermolecular attractive forces. PFCs are also nontoxic, nonflammable, and nonozone depleting materials; however, they do have a very long atmospheric lifetimes predicted to be over 2000 years.1,2 There is a large miscibility gap between perfluorocarbons and common organic solvents (including highly hydrophobic solvents) meaning that perfluorocarbons are at the same time hydrophobic and oleophobic. The miscibility of PFCs with organic solvents is strongly temperature-dependent. While heterogeneous liquid−liquid systems are formed with most organic solvents at ambient temperature, under elevated temperature some organic solvents form homogeneous mixtures. This behavior has been used in fluorous biphase separation techniques.2 For example, fluorous-immobilized catalysts have been designed by attaching highly fluorinated fragments that display affinity for fluorous media and are soluble in PFCs. The catalysts modified this way have the advantage to function under homogeneous conditions in the mixture of PFC and organic solvent under higher than critical miscibility temperature. After the reaction is finished, the mixture is cooled, resulting in a heterogeneous liquid−liquid system with products partitioning in organic phase and catalyst in the fluorous phase.3−6 Fluorous catalysis can be also done without PFCs by using fluorous-tagged catalysts with © 2014 American Chemical Society

thermomorphic properties. These catalysts completely phase separate from organic solvents at low temperatures.7,8 More recently, fluorous tagging has been extensively used in chemical biology for separation, derivatization, or identification applications.9−11 In addition to these techniques, PFCs have been utilized as intravascular oxygen delivery agents due to high gas solubilities, ophthalmologic aids, contrast agents for diagnostic ultrasound or magnetic resonance imaging, and inert fluids for lab-on-a-chip experiments.12 In fluorous-organic liquid−liquid separation techniques the crucial quantitative parameter to determine efficiency of separation of a solute is the partition coefficient. Partitioning coefficients of a number of solutes in standard (toluene + perfluoro(methylcyclohexane) at 293.15 K) and other systems have been determined.2,13 There are also methods to predict partitioning coefficients.14,15 Solvent tuning is a very efficient way to influence partitioning.16,17 Generally, organic compounds have no or very low miscibility in fluorous solvents, while partitioning of fluorous-tagged solutes strongly depends on the structure of the solute (including length, flexibility, and branching of the perfluoro-groups) and on the solvent system. An important characteristic in applications of PFCs in fluorous separations is the mutual binary solubility data and critical miscibility temperatures; however, not many systems have been investigated in detail,18 and often only raw test data or Received: May 23, 2014 Accepted: September 9, 2014 Published: September 19, 2014 3510

dx.doi.org/10.1021/je500455u | J. Chem. Eng. Data 2014, 59, 3510−3516

Journal of Chemical & Engineering Data

Article

Table 1. Characterization of Chemicals Used for Measurement ρ/(g·cm−3) at 298.15 K compound

a

abbreviation

supplier

purity

a

this work

perfluoro(n-hexane)

PFH

Sigma-Aldrich

99 %

1.6844

perfluoro(methylcyclohexane)

PFMCH

F2 Chemicals

99 %

1.7866

1,1,1,3,3,3-hexafluoro-2-propanol methanolb

HFIP CH3OH

Sigma-Aldrich Merck

> 99 % 99.9 %

1.60484 0.78658

literature 1.6761 1.6798 1.6717 1.7879 1.788 1.1870 1.60423 0.78647

ref ref ref ref ref ref ref ref

25 26 27 28 29 30 31 32

Declared by the manufacturer. bSeccoSolv, dried, max. 0.003 % H2O.

Table 2. Experimental Liquid Densitya ρ for Perfluoro(nhexane) and Perfluoro-(methylcyclohexane) at Various Temperaturesa T and Pressure p = 0.1 MPa

observations are available. An unexpected miscibility of small organic ethers with PFCs was recently described.19 PFCs and water can be considered as opposite ends of polarity or miscibility scale. Indeed, the mutual miscibilities are very low.20 The only known commercial solvent which displays full miscibility with both water and PFCs is 1,1,1,3,3,3hexafluoroisopropanol (HFIP). This paper reports the results of measurements of liquid−liquid equilibria in ternary systems of HFIP + PFCs + water or methanol at 298.15 K. Two PFCs have been selectedperfluoro(n-hexane) (PFH) and perfluoro(methylcyclohexane) (PFMCH)the former being an example of saturated linear hydrocarbon derivative, and the latter a cyclic derivative, which is used in a standard system for the determination of partition coefficients. Water is important for emulsion formulations for oxygen delivery or contrast agents, and methanol is sometimes used as organic solvent in fluorous extractions because of favorable partitioning of fluorous-tagged solutes into PFCs in the methanol−PFC mixtures.2 No experimental data on liquid−liquid equilibrium (LLE) in ternary systems hexafluoroisopropanol + perfluorocarbons (PHF or PFMH) + water or methanol have been found in literature, and the determination of that data is the subject of this work. Only some data on LLE in binary systems of PFC + water have been published. Markina et al.21 or Kabalnov et al. 20,22 used colloid chemical methods and indirectly determined a very low solubility of PFH or PFMCH in water. Freire et al.23,24 measured the solubilities of water in PFH or PFMCH by a direct analytical method utilizing a KF coulometer.

ρ/(g·cm−3)

a

T/K

perfluoro(n-hexane)

perfluoro(methylcyclohexane)

278.15 283.15 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 338.15 343.15

1.7425 1.7283 1.7138 1.6992 1.6844 1.6694 1.6541 1.6386 1.6229 1.6064 1.5905

1.8410 1.8276 1.8140 1.8004 1.7866 1.7727 1.7587 1.7445 1.7303 1.7158 1.7012 1.6864 1.6715 1.6563

Standard uncertainties are u(T) = 0.005 K and u(ρ) = 0.0001 g·cm−3.

solvents and the high volatility of PFH and PFMCH has to be considered during all sample manipulations. Our determination of the LLE in the ternary systems consisted of four major steps. At first, binodal curve data were obtained by a titration method. Second, the binodal curve was mathematically expressed as a function of composition. Third, two-phase ternary systems were prepared, and necessary experimental data were collected. Finally, tie-lines were evaluated utilizing the obtained experimental data and the mathematical representation of binodal curves. Determination of Binodal Curve Data. The experimental determination of binodal curves in the ternary systems was carried out by the titration method. Its principle, which is described in ref 33, consists of stepwise additions of one pure component to a defined homogeneous binary mixture of the other two components and visual observation of the cloud (i.e., the second liquid phase) appearance. This method was realized in a narrow neck vial (volume 10 mL) equipped with a magnetic stirrer bar. Known amounts of two miscible components (e.g., water + HFIP) were weighted out into the vial which was then immersed into a water bath with temperature (298.15 ± 0.05) K controlled by a Lauda E300 thermostat. The vial was closed by a stopper pierced by a narrow syringe needle connected to a 5 mL syringe. The syringe was loaded by the third component (e.g., PHF). This component was added stepwise (in form of small drops) with the help of a fine screw pushing the syringe piston. The

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EXPERIMENTAL SECTION Chemicals. Characterizations of chemicals used for measurement are given in Table 1. Water was distilled and subsequently treated by a Milli-Q Water Purification System (Millipore, USA). Densities of the used compounds were measured by an Anton Paar density meter DMA 5000. The instrument was calibrated by chemically pure degassed water and decane (density standard with certificate of calibration issued by H&D Fitzgerald Ltd.). The liquid density data for perfluoro(n-hexane) and perfluoro(methylcyclohexane) were determined at several temperatures since these data were utilized in this work for some solubility measurements (see below). The experimental data on density are given in Table 2. Apparatus and Procedure. Due to specific properties of PFCs and their rather high price, a special procedure for the determination of the liquid−liquid equilibrium in the studied systems had to be developed. The usage of common analytical methods is limited since PFCs are insoluble almost in all 3511



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Figure 1. (a) Schematic description of a binodal curve construction and (b) a tie-line evaluation.

which was estimated by the error propagation law, was found to be less than 10 %. Mathematical Representation of Binodal Curve. Establishing a mathematical representation of binodal curves in ternary systems was the next necessary step for the tie-line data evaluation. It was found that straightforward regression with a single mathematical function often failed for several reasons. First, for the regression, data pertaining to binary system (1) + (3) were used as well. Mutual solubilities in that systems are however extremely low (except CF solubilities in methanol), and fitted curves often tend to go outside the composition limits given by intervals wi ∈ ⟨0,1⟩. Second, molar masses of used fluorous compounds differ significantly with that of water or methanol. Due to this, ternary data in diagrams expressed in molar fractions (diagram x1−x2−x3) are significantly shifted in comparison to the same diagrams expressed in weight fractions (diagram w1−w2−w3). To keep a realistic description of the LLE data in both w1−w2−w3 and x1−x2−x3 diagrams, the following mathematical representation of the binodal curve was used. Experimental data obtained by the titration method were regressed with the asymptotic function

addition of the component was stopped just when turbidity appeared. During the titration, the mixture in the vial was agitated by a magnetic stirrer. The amount of added component was determined by differential weighing of the syringe with the needle. The usage of the narrow neck vial was crucial because it minimized the evaporated amount of the components (especially PHF). The uncertainty of the obtained binodal curve data could be estimated by means of the error propagation law. The highest uncertainty was in case of mass of the added component. The standard deviation was estimated from the weight of its one single drop. The estimated combined expanded uncertainty (with coverage factor k = 2) of the obtained data is ± 0.0012 in weight fraction. The described technique was applicable only for certain solubility levels. It cannot be used for the measurement of mutual solubility in binary systems water + PFH or water + PFMCH and for the measurement of solubility of PFH or PFMCH in methanol. These data however were important for the construction of mathematical representation of binodal curves in the ternary systems. Mutual solubilities of components in the binary systems water + PFH and water + PFMCH are extremely low. These data were taken from literature.22−24 No solubility data for the binary systems methanol + PFH or methanol + PFMCH were found. While solubilities of the both PFCs in methanol were measurable by the described titration technique, the opposite case, i.e., solubility of methanol in PFH or PFMCH, were not. To obtain these data, a measuring procedure based on precise density determination was used. This method was suggested because densities of methanol and PFCs differ significantly (in about 0.9 g·cm−3). At first, densities of pure methanol and PFCs were obtained. Second, the density of the PFC phase saturated with methanol at 298.15 K was measured. The saturated PFC phase was prepared by long time (at least 78 h) stirring of heterogeneous mixture of methanol + PFC. The solubility of methanol (its molar fraction) was then evaluated using the Amagat’s law and a correction applied by means of the excess volume (VE). This correction was estimated by the PC-SAFT equation of state.34 The PC-SAFT parameters for methanol were taken from ref 35 and that for PFH and PFMCH were fitted to the measured liquid densities (see Table 2) and vapor-pressure data from literature.30,36−38 Value of binary interaction parameter k12 = 0.10 was found by trial and error calculations. As a criterion for its choice, the agreement between calculated and experimental (determined by the titration method) values of solubility of PFC in methanol was used. The relative uncertainty of the weight fraction solubility,

w1 = A + B /(w3 + C)

for

w3 < w3M

(1)

combined with a straight line described by w1 = Dw3 + E

for

w3 < w3M

(2)

where A, B, and C are adjustable parameters, and D and E are parameters that can be evaluated from additional constraints. The straight line is tangent of the curve given by eq 1 at the point M, and it includes the experimental point N. The situation is schematically described in Figure 1a. The point N represents experimentally determined solubility (weight fraction) of water or methanol in FC. The line segment NM stands for the part of binodal line pertaining to composition region in which data measurement could not be realized by the titration method. Moreover, in this region, any other experimental technique is probably not able to produce data with sufficient precision that could be used for better representation of the binodal curve. Within the regression procedure parameters A, B, C, D, and E together with coordinates of the point M were evaluated; therefore, the binodal curve was finally described by the combination of eqs 1 and 2. Determination of Tie-Lines. Measurement of tie-lines in ternary systems usually requires direct analytical determinations of contents of two components in two liquid phases. This 3512



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Table 3. Binodal Curve Data for Ternary Systems in Weight Fractiona wi at Temperature T = 298.15 Ka and Pressure p = 0.1 MPa w1

w2

w3

Water (1) + HFIP (2) + PFH (3) 1.65·10−5 0 note b 0.0013 0.195 0.804 0.0031 0.232 0.765 0.016 0.391 0.593 0.038 0.594 0.369 0.045 0.695 0.261 0.086 0.747 0.167 0.122 0.776 0.101 0.286 0.681 0.034 0.426 0.563 0.011 0.467 0.524 0.0098 0.674 0.325 0.0011 0.756 0.243 0.0006 note b 0 9.8·10−8 Methanol (1) + HFIP (2) + PFH (3) 0.00102 0.000 0.999 0.016 0.055 0.929 0.045 0.196 0.758 0.072 0.296 0.632 0.083 0.340 0.577 0.092 0.379 0.529 0.122 0.452 0.426 0.140 0.478 0.382 0.250 0.526 0.223 0.293 0.520 0.186 0.376 0.481 0.142 0.442 0.443 0.115 0.547 0.366 0.086 0.580 0.348 0.073 0.616 0.319 0.066 0.730 0.223 0.047 0.788 0.172 0.039 0.981 0.000 0.019 0.982 0.000 0.018

w1

w2

w3

Water (1) + HFIP (2) + PFMCH (3) 1.54·10−5 0 note b 0.021 0.317 0.662 0.029 0.440 0.532 0.043 0.513 0.444 0.059 0.629 0.313 0.088 0.734 0.179 0.131 0.764 0.105 0.204 0.745 0.050 0.283 0.680 0.037 0.371 0.604 0.025 0.458 0.523 0.019 0.498 0.486 0.015 note b 0 2.35·10−7

ref 23

ref 24

ref 20

note d note c

0.00100 0.020 0.044 0.072 0.111 0.137 0.145 0.184 0.237 0.325 0.389 0.434 0.491 0.622 0.723 0.970 0.976

Methanol (1) + HFIP (2) + PFMCH (3) 0.0000 0.9990 0.072 0.908 0.171 0.785 0.271 0.657 0.382 0.507 0.429 0.435 0.435 0.420 0.476 0.340 0.486 0.276 0.473 0.201 0.449 0.163 0.421 0.144 0.387 0.122 0.294 0.085 0.215 0.062 0.000 0.030 0.000 0.024

note c

note c

note c

a

The expanded uncertainties with the coverage factor k = 2 are U(wi) = 0.0012 and U(T) = 0.2 K. bComplement to 100 %. cEvaluated from density measurement. dValue recommended in data compilation.41

method was difficult to realize in the studied systems because solubility of the FC-rich phase was very low in common solvents. For example, Karl Fischer titration could not be used because of limited miscibility with KF electrolyte. The measurement of tie-lines was performed in the following way. All three components were precisely weighted out into a small glass vial (volume 5 mL) which was then firmly closed. The vapor space in the vial containing heterogeneous mixture was less than 0.5 mL. The mixture in the vial was then agitated for at least 15 h by an Ika MS2 minishaker in an air thermostat which maintained a temperature of (298.15 ± 0.1) K. Afterward a sample taken from the water- or methanol-rich phase was analyzed by means of GC for content of HPIF. For this purpose, a method utilizing 2-propanol as the internal standard and methanol as solvent was used. Conditions of the GC analysis were as follows. Column: Agilent Technologies HP-1, 25 m × 0.32 mm × 0.52 μm, carrier gas: helium at 1.1 mL/min, temperature program: 323 K for 5 min, sample injection: pulsed split 20:1 at 423 K, detector: FID at 523 K. Due to high volatility of the used PFCs, all sample manipulations were done with negligible vapor space. The

actions such as withdrawing samples, their weighting, additions of the internal standard, and dilutions with methanol were carried out in gas-tight 10 mL syringes. The result of GC analyses, which were repeated at least six times, was weight fraction (w2) of HFIP in the water- or methanol-rich phase. The mean value for expanded uncertainty (with coverage factor k = 2) of that results was estimated as ± 0.008. The obtained value of w2 in combination with mathematical description of the binodal line eq 1 yielded one end of a tie-line (point K). Its other end (point L) was then determined utilizing the known global composition of heterogeneous mixture (point G) and straight line eq 2 describing the corresponding part of binodal curve. The tie-line evaluation is schematically described in Figure 1b.

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RESULTS AND DISCUSSION The binodal curve data and determined tie-lines are given in Tables 3 and 4, respectively. Uncertainties of the tie-line compositions presented in Table 4 represent expanded values with coverage factor k = 2. They were estimated on the basis of standard deviation of GC peaks area ratios for repeated 3513



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Table 4. LLE Data for Ternary Systems in Weight Fractiona wi at Temperatureb T = 298.15 K and Pressure p = 0.1 MPa PFC-rich phase

aqueous or methanol-rich phase

w1

w2

(1.16 (2.14 (2.64 (3.31 (4.04

± ± ± ± ±

0.92)·10−3 1.8)·10−3 2.1)·10−3 2.6)·10−3 3.3)·10−3

(2.58 (4.80 (5.92 (7.44 (9.10

± ± ± ± ±

(1.70 (2.15 (3.96 (4.61 (5.77 (6.75

± ± ± ± ± ±

1.00)·10−3 1.32)·10−3 2.38)·10−3 2.73)·10−3 3.57)·10−3 3.97)·10−3

(2.63 (3.34 (6.16 (7.17 (8.98 (1.05

± ± ± ± ± ±

(1.04 (2.88 (1.15 (2.10

± ± ± ±

0.31)·10−3 0.83)·10−3 0.36)·10−2 0.62)·10−2

(1.11 (8.70 (4.91 (9.30

± ± ± ±

(1.48 (2.52 (4.30 (7.04 (1.07 (2.41

± ± ± ± ± ±

0.46)·10−3 0.76)·10−3 1.28)·10−3 2.10)·10−3 0.33)·10−2 0.75)·10−2

(2.16 (6.84 (1.49 (2.72 (4.38 (1.04

± ± ± ± ± ±

w1

w2

Water (1) + HFIP (2) + PFH (3) 0.53)·10−2 (8.49 ± 0.05)·10−1 −2 0.9)·10 (6.77 ± 0.05)·10−1 −2 1.0)·10 (5.58 ± 0.05)·10−1 0.9)·10−2 (4.55 ± 0.06)·10−1 0.9)·10−2 (2.93 ± 0.04)·10−1 Water (1) + HFIP (2) + PFMCH (3) 0.53)·10−2 (7.88 ± 0.04)·10−1 0.60)·10−2 (7.13 ± 0.05)·10−1 0.99)·10−2 (5.11 ± 0.04)·10−1 −2 0.86)·10 (3.47 ± 0.03)·10−1 −2 0.91)·10 (2.15 ± 0.02)·10−1 0.09)·10−1 (1.27 ± 0.02)·10−1 Methanol (1) + HFIP (2) + PFH (3) 0.67)·10−4 (8.02 ± 0.04)·10−1 −3 3.46)·10 (6.73 ± 0.04)·10−1 0.75)·10−2 (4.65 ± 0.03)·10−1 −2 0.75)·10 (1.10 ± 0.01)·10−1 Methanol (1) + HFIP (2) + PFMCH (3) 1.30)·10−3 (9.19 ± 0.05)·10−1 2.82)·10−3 (8.32 ± 0.04)·10−1 −2 0.23)·10 (7.02 ± 0.03)·10−1 −2 0.34)·10 (5.26 ± 0.03)·10−1 0.40)·10−2 (4.11 ± 0.02)·10−1 0.08)·10−1 (2.20 ± 0.01)·10−1

(1.48 (3.17 (4.31 (5.29 (6.75

± ± ± ± ±

0.05)·10−1 0.08)·10−1 0.09)·10−1 0.06)·10−1 0.10)·10−1

(2.08 (2.81 (4.75 (6.25 (7.30 (7.69

± ± ± ± ± ±

0.07)·10−1 0.07)·10−1 0.09)·10−1 0.09)·10−1 0.11)·10−1 0.12)·10−1

(1.61 (2.71 (4.29 (4.30

± ± ± ±

0.04)·10−1 0.05)·10−1 0.11)·10−1 0.13)·10−1

(4.93 (1.24 (2.32 (3.64 (4.34 (4.79

± ± ± ± ± ±

0.20)·10−2 0.04)·10−1 0.08)·10−1 0.10)·10−1 0.11)·10−1 0.10)·10−1

a

The listed uncertainties represent the expanded uncertainties U(wi) with the coverage factor k = 2. bThe expanded uncertainties U(T) = 0.2 K with the coverage factor k = 2.

measurements of the same sample, standard deviation of calibration factors, and global compositions of ternary systems. The binodal equation data measured by the titration technique were smoothed utilizing the eqs 1 and 2. Their parameters are given in Table 5. Table 5. Parameters of Equations 1 and 2 A −0.005319 0.0008963 −0.069073 −0.105904

B

C

D

E

Water (1) + HFIP (2) + PFH (3) 0.01376 0.01375 −0.04238 0.0424 Water (1) + HFIP (2) + PFMCH (3) 0.01506 0.01508 −0.06020 0.0602 Methanol (1) + HFIP (2) + PFH (3) 0.09506 0.07177 −0.17648 0.1773 Methanol (1) + HFIP (2) + PFMCH (3) 0.12833 0.09320 −0.18189 0.1827

w3M 0.5561 0.4851 0.6622 0.7468

The obtained liquid−liquid equilibrium diagrams for the systems studied are shown in Figures 2 to 5. As it can be seen, the miscibility gaps in ternary systems are quite large especially in the systems containing water. For instance, to homogenize heterogeneous mixture water + PFH or PFMCH by means of hexafluoroisopropanol, the system must contain usually as much as 80 % (by weight) of hexafluoroisopropanol. Experimental liquid−liquid equilibrium data can be tested by means of the Othmer−Tobias plot.39 Even though this plot is not sensitive enough for an assessment of data consistency, it can be used to identify tie-lines with high random errors. Plotting log[(1 − w3,3)/w3,3] vs log[(1 − w1,1)/w1,1], where wi,j is the weight fraction of the component i in the j-rich phase, can

Figure 2. Liquid−liquid equilibrium data (weight fraction) for the ternary system water (1) + hexafluoroisopropanol (2) + perfluoro(nhexane) (3) at 298.15 K; ■, experimental binodal curve data; ○---○, experimental tie-lines; --, smoothed binodal curve.

be useful to check whether experimental LLE data have a regular (nor necessarily linear) course or not.40 The obtained courses are described in Figure 6. As it can be seen, the data for three ternary systems follow linear trends without any obviously deviated experimental points. The data for the system methanol (1) + hexafluoroisopropanol (2) + perfluoro3514



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Figure 3. Liquid−liquid equilibrium data (weight fraction) for the ternary system water (1) + hexafluoroisopropanol (2) + perfluoro(methylcyclohexane) (3) at 298.15 K; ■, experimental binodal curve data; ○---○, experimental tie-lines; --, smoothed binodal curve.

Figure 5. Liquid−liquid equilibrium data (weight fraction) for the ternary system methanol (1) + hexafluoroisopropanol (2) + perfluoro(methylcyclohexane) (3) at 298.15 K; ■, experimental binodal curve data; ○---○, experimental tie-lines; --, smoothed binodal curve.

Figure 6. Othmer−Tobias plots. ○, water (1) + HFIP (2) + PFH (3); ●, water (1) + HFIP (2) + PFMCH (3); □, methanol (1) + HFIP (2) + PFH (3); ■, methanol (1) + HFIP (2) + PFMCH (3).

display very low mutual miscibilities. Consequently the corresponding ternary liquid−liquid equilibrium diagrams are all of the type 1.42 In these systems, HFIP displays ambivalent character (polar and hydrophobic). It shows affinity for PFC’s due to the presence of trifluoromethyl groups and acts as Hbond donor in polar interactions with water and methanol. The ternary liquid−liquid equilibrium diagrams were found to be almost identical for PFH and PFMCH showing that the structure of perfluorocarbon component has minimal influence on the miscibility behavior despite the globular shape of PFMCH and rod-like shape of PFH (inflexible carbon chain due to repulsive vicinal fluorine interactions).

Figure 4. Liquid−liquid equilibrium data (weight fraction) for the ternary system methanol (1) + hexafluoroisopropanol (2) + perfluoro(n-hexane) (3) at 298.15 K; ■, experimental binodal curve data; ○---○, experimental tie-lines; --, smoothed binodal curve.

(n-hexane) (3) follow a nonlinear but smooth course. The significant curvature of this course is probably caused by the position of the last tile-line which is located quite near to the critical point.

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CONCLUSION In conclusion, liquid−liquid equilibrium data for ternary systems of hexafluoroisopropanol (HFIP) + perfluorocarbon (namely perfluoro(n-hexane) (PFH) or perfluoro(methylcyclohexane) (PFMCH)) + water or methanol were determined at 298.15 K. The binary systems of HFIP + water or methanol and HFIP + PFC’s are fully miscible. In contrast the binary systems of water or methanol + PFH or PFMCH

AUTHOR INFORMATION

Corresponding Author

*Tel: +420 220 444 039. E-mail: [email protected]. Funding

This work was supported by the Academy of Sciences of the Czech Republic (Research Plan RVO: 61388963). M.S. also acknowledges financial support from specific university research (MSMT no. 20/2014). 3515



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Notes

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The authors declare no competing financial interest.

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