Effect of Some Imidazolium-Based Ionic Liquids ... - ACS Publications

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX-XXX

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Effect of Some Imidazolium-Based Ionic Liquids with Different Anions on the Thermodynamic Properties of Acetaminophen in Aqueous Media at T = 293.15 to 308.15 K Hemayat Shekaari,* Mohammed Taghi Zafarani-Moattar, and Fariba Ghaffari Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran S Supporting Information *

ABSTRACT: In this work, the effect of two imidazolium-based ionic liquids with different anions, 1-butyl-3-methylimidazolium bromide, [BMIm]Br, and 1-butyl-3methylimidazolium chloride, [BMIM]Cl, on thermodynamic properties of acetaminophen was investigated. For this purpose, measurement of density ρ speed of sound u and specific electrical conductivity κ for acetaminophen in aqueous solutions of ionic liquid was made at T = 293.15 to 308.15 K and at atmospheric pressure. The standard partial molar volumes V0ϕ, partial molar isentropic compressibility K0ϕ, hydration number nH, and Hepler’s constants (∂2V0ϕ/∂T2)P have been calculated from the density and speed of sound data. The limiting molar conductivities Λ0 and ion association constants KA for the ionic liquids in aqueous solutions of acetaminophen have been estimated using the low concentration chemical model (lcCM). The results confirm presence of a strong attractive interaction between acetaminophen molecules and the ionic liquids which that becomes stronger with increase in anion size.

1. INTRODUCTION Ionic liquids (ILs) are notable chemical compounds, which find applications in many areas of modern science.1 Studies have shown that ionic liquids are very efficient in chemical synthesis and catalysis,2−4 electrochemistry,5,6 biomass conversion,7−10 liquid crystal development,11 biotransformation,12 biotechnology,13 and many other fields. These compounds have unique properties, such as very small vapor pressure, a wide liquid range, high thermal stability, excellent solvent power for organic, inorganic, and polymeric compounds.14−16 The focus of many IL studies now evolves in the direction of life sciences, medicine, and pharmaceutical industry.17,18 The efficiency of a drug depends strongly on its bioavailability, permeability and solubility. Therefore, higher doses are required for reaching a therapeutic effect.19,20 There are numerous approaches for improving drug solubility. One of these methods is turning a drug into a salt form.21 Ionic liquids are liquid salts, therefore turning a drug into an ionic liquid form is an obvious method to improve its bioavailability and increase its solubility.22 The development and design of new processes including drugs and ILs, require measurements of their thermodynamic properties.23 These properties are of great importance to perceive physiological effect, interactions between solute and solvent, and the structure-making/breaking ability of such systems. Shekaari and co-workers22,24,25 have reported densities, viscosities, refractive indices, and electrical conductances of aqueous solutions of glycine and L-alanine with a ionic liquid containing 1-butyl-3-methylimidazolium salicylate [BMIM][SAL] and 1-butyl-3-methylimidazolium ibuprofenate ([BMIM][Ibu]), as an active pharmaceutical ingredient ionic liquid (API-IL). These results have shown that the structure © XXXX American Chemical Society

making ability is more effective in L-alanine. The computed parameters, such as the transfer partial molar volume ΔtV0ϕ and the transfer partial molar isentropic compressibility ΔtK0ϕ, indicate dominance of ion−polar and polar−polar interactions between [BMIM][Ibu] and (glycine, L-alanine). Also, In our previous works, thermodynamic properties of acetaminophen (ACP) in aqueous solutions of 1-butyl-3-methylimidazolium bromide [BMIm]Br and 1-butyl-3-methylimidazolium chloride [BMIM]Cl at different temperatures have been investigated.26,27 Acetaminophen or paracetamol is a drug solute with IUPAC name N-acetyl-p-aminophenol. This drug in treatment of some minor diseases related to pediatric patients is necessarily recommended.28 ACP is widely used for its analgesic and antipyretic properties in all age groups.29 One of the problems about acetaminophen is its low solubility in water. For approach to some information about acetaminophen solubility in this work, two imidazolium-based ionic liquids (1butyl-3-methylimidazolium bromide [BMIM]Br, 1-butyl-3methylimidazolium chloride [BMIM]Cl) were synthesized, then the thermodynamic properties including volumetric, compressibility and electrical conductivity for ternary (acetaminophen + water + [BMIM]Br/[BMIM]Cl) solutions were determined. These results were used to interpret the solute− solute and the solute−solvent interactions between acetaminophen and the ILs in the aqueous media. Received: May 22, 2017 Accepted: October 23, 2017

A

DOI: 10.1021/acs.jced.7b00464 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Sample Provenance of the Chemicals and Purity chemical name acetaminophen 1-butyl-3-methyle-imidazolium bromide 1-butyl-3-methyle-imidazolium chloride N-methylimidazole 1-bromobutane 1-chlorobutane ethyl acetate

CAS No.

616-47-7 109-65-9 109-69-3 141-78-6

source

initial mass fraction purity

Temad Synthesis

>0.99 not measured

Synthesis

not measured

purification method none extraction and distillation extraction and distillation none none none none

Merk Merk Merk Merk

2. EXPERIMENTAL SECTION 2.1. Chemicals. The chemicals specifications, such as names, CAS numbers, sources, and purities in mass fraction, are listed in Table 1. Double distilled water with conductivity less than 1 μS·cm−1 was used to prepare the solutions. 2.2. Synthesis of the Ionic Liquids. [BMIM]Br and [BMIM]Cl were prepared and purified by using the method described in the literature.30,31 The obtained ionic liquids had no major impurity, which was verified by 1H NMR spectrum. Water content estimated in the ionic liquids by Karl Fischer method was less than 0.2% and has been taken into account and the apparent molality corrections have been applied. The ionic liquids were analyzed by 1H NMR (Bruker Av-400) and FT-IR (Bruker, Tensor 27) to confirm the lack of any major impurities. The 1H NMR spectra of the synthesized ionic liquids are shown in Figures S1 and S2. 2.3. Apparatus and Procedure. The solutions were prepared in mass basis by an analytical balance (Shimadzu, 321−34553, Shimadzu Co., Japan) having a standard uncertainty of 1 × 10−4 g. Measurements of densities ρ and speeds of sound u were made by a vibrating tube densitometer (DSA5000, Anton Paar) at low frequency (approximately 3 MHz). Before each series of measurements, the densitometer with doubly distilled deionized and degassed water and dry air at atmospheric pressure was calibrated. The temperature was kept constant within ±1.0 × 10−3 K with Peltier device built in densitometer. The standard uncertainty of density and speed of sound measurements were found to be within 0.15 kg·m−3 and 0.5 m·s−1, respectively. Specific electrical conductivities were measured with a conductivity meter (Metrohm model 712, Switzerland) at a frequency of 300 Hz. The specific electrical conductivities κ of studied systems are given in Table S1. The measurement of KCl solution with concentration of 0.01 mol·kg−1 was used to calibrate of conductometer. About 80 mL of solution consist of doubly distilled deionized and degassed water and acetaminophen was filled in the cell, and then the cell is closed and the conductivity electrode was placed in it. The pure ionic liquid was added to the cell containing solvent and the measurement was performed. Water was circulated around the cell with double wall from a thermostat regulated bath (Julabo ED Germany), which was used to keep the temperature with a precision of 0.02 K.

final purity >0.99 >0.98 >0.98

analysis method Karl Fischer titration and1H NMR, IR Karl Fischer titration and1H NMR, IR

water content less than 0.2% less than 0.2%

>0.99 >0.99 >0.99 >0.99

were measured at different temperatures T = 293.15 to 308.15 K are given in Table 2. The densities of the investigated solutions {acetaminophen + water + ionic liquids} decrease at higher temperatures, also the densities of solutions increase with increasing ionic liquid concentration. The apparent molar volumes Vϕ of acetaminophen in the investigated solutions were determined using density data through the following equation: Vϕ =

1000(ρ − ρ0 ) M − d mρ ·ρ0

(1)

where M is the molar mass of acetaminophen, m is the molality of acetaminophen in aqueous [BMIm]Br and [BMIM]Cl solutions, ρ and ρ0 are the densities of the solutions containing (acetaminophen + [BMIm]Br/ [BMIM]Cl + water) and ([BMIm]Br/[BMIM]Cl + water) solutions, respectively. The calculated Vϕ values for this drug as a function of its molality m at the experimental temperatures are given in Table 2. Figures 1 and 2 represent the apparent molar volume Vϕ values of acetaminophen versus its molality m in aqueous [BMIM]Br and [BMIm]Cl solutions, respectively. The results show that the Vϕ values increase with increasing concentration of ionic liquids at all experimental temperatures. It also increases with changing of anion type in order: [BMIm]Br>[BMIm]Cl. There is an acceptable linear correlation between values of Vϕ and acetaminophen molality m. Therefore, the Masson’s equation32 can be used to calculate the values of apparent molar volumes at infinite dilution (standard partial molar volume) V ϕ0 according to the following equation: Vϕ = V ϕ0 + Svm

(2)

where Sv is the experimental slope which indicates interactions between acetaminophen molecules (solute−solute interactions). The values of V ϕ0 show interactions between acetaminophen and ionic liquid (solute−solvent interactions) and these parameters are independent of solute−solute interactions at infinite dilution. The values of V0ϕ and Sv along with their standard errors and standard deviations are listed in Table 3. It can be seen that the Sv values are negative for all the studied solutions and all experimental temperatures and become more negative with increasing the ionic liquid concentration. The negative values of Sv indicates that the interactions between molecules of acetaminophen in ternary solutions are weak. The low values of Sv suggest that solute− solute interactions become weak and the solute−solvent interactions become stronger. As can be seen from Table 3, the V0ϕ values are positive and increase with increasing ionic liquid concentration. It seems that the ionic liquid with anion Br− has stronger interaction with the drug than the other ionic

3. RESULTS AND DISCUSSION 3.1. Volumetric and Compressibility Properties. The values of experimental density ρ for acetaminophen in various molality (0.1, 0.2, 0.3, and 0.4) mol·kg−1 of [BMIm]Br and [BMIM]Cl as a function of solute (acetaminophen) molality m B



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Table 2. Experimental Densities (ρ) and Apparent Molar Volumes (Vφ) of Acetaminophen in Aqueous Solutions of [BMIm]Br and [BMIm]Cl as a Function of Acetaminophen Molality (m) at T= 293.15, 298.15, 303.15 and 308.15 K and p = 101.3 kPaa T/K m (mol·kg−1)b

293.15 ρ(g·cm3)

mIL = 0.1009 0.0000 0.0299 0.0329 0.0357 0.0395 0.0430 0.0474 0.0495 0.0531 0.0559 mIL = 0.2003 0.0000 0.0300 0.0326 0.0358 0.0395 0.0433 0.0477 0.0497 0.0531 0.0548 mIL = 0.2985 0.0000 0.0310 0.0326 0.0354 0.0392 0.0434 0.0473 0.0504 0.0531 0.0563 mIL = 0.4006 0.0000 0.0302 0.0326 0.0362 0.0395 0.0433 0.0477 0.0503 0.0531 0.0562

mol·kg−1 1.003269 1.004082 1.004165 1.004243 1.004350 1.004450 1.004578 1.004641 1.004743 1.004828 mol·kg−1 1.008106 1.008907 1.008977 1.009067 1.009171 1.009277 1.009402 1.009463 1.009561 1.009613 mol·kg−1 1.012676 1.013485 1.013529 1.013605 1.013710 1.013824 1.013932 1.014018 1.014095 1.014188 mol·kg−1 1.017539 1.018306 1.018370 1.018466 1.018553 1.018656 1.018775 1.018846 1.018922 1.019010

mIL = 0.1010 mol·kg−1 0.0000 0.999535 0.0304 1.000372 0.0329 1.000443 0.0358 1.000527 0.0395 1.000631 0.0433 1.000741 0.0474 1.000860 0.0495 1.000922 0.0531 1.001027 0.0555 1.001099

298.15

Vϕ(cm3·mol−1)

ρ(g·cm3)

123.53 123.43 123.32 123.21 123.09 122.97 122.83 122.73 122.63

1.002026 1.002828 1.002913 1.002994 1.003101 1.003200 1.003329 1.003395 1.003499 1.003587

123.63 123.56 123.41 123.30 123.21 123.10 122.91 122.82 122.73

303.15

Vϕ(cm3·mol−1) [BMIm]Br

308.15

ρ(g·cm3)

Vϕ(cm3·mol−1)

ρ(g·cm3)

Vϕ(cm3·mol−1)

123.98 123.85 123.67 123.56 123.47 123.30 123.13 123.02 122.84

1.000581 1.001376 1.001461 1.001541 1.001649 1.001750 1.001880 1.001940 1.002046 1.002134

124.42 124.27 124.09 123.93 123.77 123.57 123.51 123.34 123.15

0.998918 0.999691 0.999773 0.999849 0.999950 1.000046 1.000169 1.000231 1.000331 1.000417

125.29 125.16 125.04 124.98 124.87 124.73 124.58 124.47 124.27

1.006832 1.007616 1.007688 1.007776 1.007879 1.007984 1.008107 1.008164 1.008261 1.008314

124.28 124.10 123.97 123.85 123.75 123.64 123.51 123.41 123.29

1.005315 1.006091 1.006161 1.006247 1.006349 1.006452 1.006574 1.006629 1.006725 1.006776

124.79 124.65 124.54 124.40 124.31 124.18 124.08 123.96 123.87

1.003616 1.004374 1.004443 1.004526 1.004625 1.004728 1.004846 1.004901 1.004994 1.005044

125.49 125.37 125.29 125.17 125.03 124.93 124.81 124.71 124.62

123.81 123.72 123.61 123.47 123.37 123.28 123.18 123.07 122.94

1.011327 1.012119 1.012161 1.012233 1.012335 1.012448 1.012555 1.012639 1.012715 1.012805

124.39 124.34 124.30 124.18 124.05 123.93 123.84 123.72 123.61

1.009769 1.010553 1.010597 1.010671 1.010772 1.010883 1.010989 1.011073 1.011148 1.011237

124.95 124.82 124.70 124.58 124.47 124.35 124.24 124.13 124.02

1.007999 1.008764 1.008806 1.008878 1.008977 1.009086 1.009189 1.009273 1.009346 1.009434

125.61 125.51 125.40 125.29 125.17 125.07 124.93 124.83 124.71

123.90 123.81 123.73 123.63 123.50 123.41 123.32 123.23 123.10

1.016134 1.016884 1.016947 1.017042 1.017127 1.017227 1.017343 1.017414 1.017489 1.017574

1.014503 1.015246 1.015308 1.015402 1.015487 1.015586 1.015702 1.015771 1.015846 1.015930

125.04 124.95 124.83 124.72 124.61 124.50 124.41 124.29 124.19

1.012704 1.013427 1.013487 1.013578 1.013661 1.013757 1.013870 1.013938 1.014010 1.014092

125.77 125.70 125.61 125.49 125.40 125.29 125.19 125.10 124.99

123.61 123.55 123.44 123.34 123.23 123.14 123.05 122.95 122.89

0.998308 0.999135 0.999207 0.999290 0.999394 0.999504 0.999623 0.999687 0.999792 0.999866

0.996883 0.997697 0.997768 0.997851 0.997955 0.998063 0.998181 0.998243 0.998347 0.998420

124.60 124.45 124.37 124.19 124.07 123.95 123.84 123.71 123.61

0.995222 0.996018 0.996087 0.996167 0.996268 0.996374 0.996488 0.996549 0.996650 0.996722

125.33 125.22 125.12 124.99 124.86 124.77 124.65 124.54 124.43

124.56 124.46 124.35 124.26 124.16 124.07 123.96 123.86 123.75 [BMIm]Cl

124.03 123.91 123.81 123.69 123.56 123.45 123.31 123.20 123.09

C



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Table 2. continued T/K m (mol·kg−1)b

293.15

298.15

303.15

308.15

−1

mIL = 0.1997 mol·kg 0.0000 1.000819 0.0301 1.001643 0.0326 1.001713 0.0356 1.001800 0.0395 1.001911 0.0429 1.002009 0.0477 1.002148 0.0499 1.002210 0.0531 1.002305 0.0555 1.002377 mIL = 0.3007 mol·kg−1 0.0000 1.002099 0.0300 1.002912 0.0326 1.002985 0.0354 1.003064 0.0392 1.003171 0.0430 1.003279 0.0473 1.003403 0.0500 1.003481 0.0531 1.003571 0.0555 1.003642 mIL = 0.4004 mol·kg−1 0.0000 1.003371 0.0298 1.004172 0.0326 1.004248 0.0359 1.004338 0.0390 1.004426 0.0430 1.004539 0.0475 1.004667 0.0497 1.004730 0.0532 1.004827 0.0557 1.004899

123.63 123.52 123.42 123.30 123.20 123.09 123.01 122.91 122.81

0.999565 1.000374 1.000443 1.000528 1.000637 1.000734 1.000870 1.000933 1.001025 1.001097

124.25 124.14 124.04 123.92 123.82 123.71 123.60 123.52 123.40

0.998065 0.998861 0.998928 0.999013 0.999120 0.999215 0.999349 0.999410 0.999501 0.999571

124.83 124.75 124.61 124.50 124.41 124.30 124.21 124.12 124.02

0.996342 0.997125 0.997191 0.997273 0.997378 0.997473 0.997605 0.997665 0.997755 0.997824

125.44 125.35 125.27 125.16 125.02 124.91 124.82 124.73 124.62

123.76 123.69 123.57 123.48 123.37 123.25 123.15 123.06 122.97

1.000788 1.001588 1.001660 1.001737 1.001843 1.001949 1.002070 1.002147 1.002236 1.002307

124.32 124.24 124.15 124.04 123.93 123.84 123.74 123.63 123.53

0.999244 1.000029 1.000100 1.000176 1.000280 1.000384 1.000503 1.000578 1.000665 1.000734

124.98 124.88 124.78 124.68 124.58 124.48 124.39 124.30 124.20

0.997484 0.998256 0.998326 0.998401 0.998503 0.998605 0.998723 0.998797 0.998883 0.998951

125.59 125.49 125.38 125.29 125.19 125.08 124.98 124.89 124.79

123.89 123.84 123.76 123.66 123.52 123.41 123.31 123.30 123.20

1.001999 1.002788 1.002864 1.002954 1.003041 1.003151 1.003277 1.003339 1.003439 1.003511

124.43 124.34 124.23 124.12 124.02 123.92 123.83 123.73 123.62

1.000397 1.001172 1.001248 1.001336 1.001421 1.001529 1.001653 1.001715 1.001813 1.001883

125.05 124.93 124.83 124.74 124.65 124.54 124.43 124.34 124.25

0.998586 0.999349 0.999423 0.999510 0.999594 0.999701 0.999823 0.999883 0.999980 1.000049

125.64 125.54 125.43 125.33 125.22 125.12 125.03 124.93 124.84

Standard uncertainties: u(p) = 0.01 MPa; u(T) = 0.01 K; u(m) = 2.10−4 mol·kg−1; u(ρ) = 0.15 kg·m−3. bm is molality of acetaminophen where solvent is (water + IL). cmIL is molality of ionic liquid where solvent is water.

a

Figure 1. Apparent molar volumes Vϕ of acetaminophen versus its molality m in aqueous [BMIm]Br solutions with different molalities of [BMIm]Br: ▲, 0.1009; △, 0.2003; ■, 0.2985; ◊, 0.4006 at T = 293.15 K.

Figure 2. Apparent molar volumes Vϕ of acetaminophen versus its molality m in aqueous [BMIm]Cl solutions for different molalities of [BMIm]Cl: △, 0.1010; ▲, 0.1997; ■, 0.3007; ◊, 0.4004 at T = 293.15 K.

liquid. The computed V0ϕ values of acetaminophen in the investigated solutions show the following order: [BMIm]Br > [BMIm]Cl. The V0ϕ values for these compounds in water agree well with our previous work26,27 at all investigated temperatures.

The transfer volumes (ΔtV0ϕ) of acetaminophen at infinite dilution from water to aqueous [BMIm]Br/ [BMIm]Cl solutions have been calculated as D



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Table 3. Standard Partial Molar Volumes V0ϕ, Transfer Volumes, ΔtrV0ϕ, Experimental Slopes Sv, Standard Deviations σ(Vϕ), and Solvation Number, nH, of Acetaminophen in Aqueous [BMIm]Br and [BMIm]Cl Solutions at T = 293.15, 298.15, 303.15, 308.15 K mIL (mol·kg−1)

T/K

V0ϕ (cm3·mol−1)

Sv (cm3·mol−2·kg)

ΔtrV0ϕ (cm3·mol−1)

σ(Vϕ)

nH

[BMIm]Br 0.1009 293.15 298.15 303.15 308.15

124.60 125.22 125.79 126.44

± ± ± ±

0.04 0.07 0.05 0.08

−34.56 −41.87 −46.74 −37.09

± ± ± ±

1.82 1.65 1.01 1.90

0.31 0.28 0.20 0.18

0.022 0.040 0.025 0.044

2.57 2.10 1.74 1.43

293.15 298.15 303.15 308.15

124.70 125.31 125.80 126.49

± ± ± ±

0.05 0.04 0.04 0.04

−35.21 −36.24 −34.74 −33.66

± ± ± ±

1.88 1.89 1.91 1.79

0.41 0.37 0.21 0.23

0.037 0.038 0.024 0.025

2.56 2.07 1.74 1.41

293.15 298.15 303.15 308.15

124.77 125.35 125.95 126.58

± ± ± ±

0.03 0.04 0.03 0.03

−32.10 −30.46 −34.19 −33.21

± ± ± ±

1.88 1.87 1.94 1.94

0.48 0.41 0.36 0.32

0.026 0.021 0.029 0.022

2.50 2.06 1.70 1.39

293.15 298.15 303.15 308.15

124.80 125.43 125.99 126.61

± ± ± ±

0.02 0.03 0.06 0.00

−29.83 ± −29.57 ± −31.85 ± −28.85 ± [BMIm]Cl

1.91 1.86 1.59 1.60

0.51 0.49 0.39 0.35

0.017 0.020 0.014 0.014

2.49 2.04 1.69 1.38

293.15 298.15 303.15 308.15

124.48 125.11 125.71 126.37

± ± ± ±

0.02 0.04 0.04 0.04

−28.80 −36.04 −37.80 −34.49

± ± ± ±

1.45 1.65 1.91 1.90

0.19 0.17 0.12 0.11

0.010 0.020 0.021 0.017

2.60 2.13 1.76 1.45

293.15 298.15 303.15 308.15

124.53 125.18 125.74 126.38

± ± ± ±

0.05 0.04 0.04 0.04

−30.59 −31.66 −30.67 −31.27

± ± ± ±

1.88 1.89 1.91 1.79

0.24 0.24 0.15 0.12

0.017 0.021 0.019 0.014

2.59 2.11 1.76 1.44

293.15 298.15 303.15 308.15

124.67 125.22 125.83 126.47

± ± ± ±

0.03 0.04 0.03 0.03

−30.45 −29.88 −29.02 −29.77

± ± ± ±

1.88 1.87 1.94 1.98

0.38 0.28 0.24 0.21

0.012 0.018 0.014 0.015

2.54 2.10 1.73 1.42

293.15 298.15 303.15 308.15

124.72 125.31 125.91 126.51

± ± ± ±

0.02 0.03 0.06 0.09

−27.40 −29.87 −29.65 −29.77

± ± ± ±

1.91 1.89 1.73 1.96

0.43 0.37 0.32 0.25

0.023 0.016 0.020 0.014

2.52 2.07 1.71 1.41

0.2003

0.2985

0.4006

0.1010

0.1997

0.3007

0.4004

Δt V ϕ0 = V ϕ0(in aqueous ionic liquids) − V ϕ0(in water)

the guideline, (1) and (2) types of interactions would lead to a positive values of ΔtV0ϕ and the other types of interactions have negative ΔtV0ϕ values. In this case, the ΔtV0ϕ values show that the polar−ionic group interactions (1) and the polar−polar group interactions (2) between the polar groups of acetaminophen molecules and polar groups and the ions of ionic liquids are dominant. In addition, their increasing values at high ionic liquid concentrations indicate strengthening of these kinds of the interactions in the studied range of concentration. Shahidi and co-workers35 model also shows that the positive ΔtV0ϕ values may be due to decrease in the contraction volume. The transfer volumes ΔtV0ϕ of solution may also be indicated by the McMillan Mayer theory36 of solutions, which separate the transfer volumes to different parts because of pairs, triples or

(3)

The calculated values of the transfer volume ΔtV0ϕ at infinite dilution are also given in Table 3. The values of V0ϕ for binary system of acetaminophen in water were given in our previous work.27 It shows that the values of ΔtV0ϕ are positive. These values increase with increasing ionic liquid molality. Also, the values of ΔtV0ϕ in the investigated solutions show the following order: [BMIm]Br > [BMIm]Cl. According to the cosphere overlap model of ternary mixtures,33,34 some kinds of interactions between the solute and cosolute molecules (in this work, ILs are cosolute) in water are possible: (1) the polar−ionic group interactions, (2) polar−polar group interactions, (3) polar−nonpolar group interactions, and (4) nonpolar−nonpolar group interactions. Taking this model as E



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⎛ ∂V 0 ⎞ ϕ ⎟⎟ = B + 2CT Eϕo = ⎜⎜ ⎝ ∂T ⎠

Table 4. Pair and Triplet Interaction Coefficients VAI, VAII Obtained from Eq 4 for Acetaminophen in Aqueous [BMIm]Br and [BMIm]Cl Solutions at T = 293.15, 298.15, 303.15, and 308.15 K T/ K 293.15 298.15 303.15 308.15 293.15 298.15 303.15 308.15

VAI [BMIm]Br 1.18 1.03 0.67 0.61 [BMIm]Cl 0.84 0.76 0.46 0.43

The Eoϕ obtain from two contribution Eoϕ(Elec) and Eoϕ(Str), where Eoϕ(Elec) is the standard apparent molar expansibility because of electrostriction changes (contribution of hydration layer around the solutes), whereas, Eϕo (Str) denotes the standard apparent molar expansibility which in responsible for the changes in structure of solvent. The structural component at low temperature is Eoϕ(Str) > Eoϕ(Elec), whereas Eoϕ(Elec) > Eoϕ(Str) at the higher temperature. The calculated values of Eoϕ for acetaminophen in the investigated solutions are given in Table 5. The values of Eϕo give us important information about solute−solvent interactions.38 The Eoϕ values are positive for the studied solute, these results indicates that a number of solvent molecules on heating perhaps released from the layers of solvation. The positive expansibility is a particular property of aqueous hydrophobic hydration solutions. This causes solution volume increase a little more quickly than pure water and so EoP, ϕ would be positive.39 These observations again supply the presence of competitive hydrophilic and hydrophobic interactions. The sign of second derivatives of the standard partial molar volume with respect to the temperature (∂2V0ϕ/∂T2)P is a better parameter in characterizing the structure making and breaking ability of solute in solution, which is called Hepler’s constant.38 The general thermodynamic expression were indicated by Hepler according to following equation:

VAII −1.51 −1.40 −0.66 −0.68 −0.51 −0.53 −0.11 −0.20

more interactions between the solute molecules, represented by equation as follow: Δtr V ϕ0 = 2VAI. mI + 3VAII. mI2 + ...

(4)

where A stands for the acetaminophen and I stands for the ILs. VAI and VAII are the paired and triplet volumetric interaction parameters, respectively. These parameters were obtained by fitting the above equation to the ΔtrV0ϕ data which are shown in Table 4. The VAI and VAII values for all investigated solutions are positive and negative, respectively. The magnitude of both interaction coefficients decreases with the increase in temperature. Furthermore, the magnitude of VAI is greater than VAII, which suggest that the interactions between acetaminophen and the ILs are mainly pairwise. The temperature dependence of standard partial molar volumes is positive for acetaminophen in the studied solutions and can be expressed by the equation V ϕ0 = A + BT + CT 2

(6)

⎛ ∂ 2V 0 ⎞ ⎛ ∂C 0 ⎞ φ ⎜ P ⎟ = −T ⎜⎜ 2 ⎟⎟ = −2CT T ∂ ⎝ ∂P ⎠ p ⎠ ⎝

(7)

C0P

where is the partial molar heat capacity. If the sign of (∂2V0ϕ/∂T2)P is negative, the solute is a structure breaker, otherwise, it is structure maker.38 The values of (∂2V0ϕ/ ∂T2)P for acetaminophen in the aqueous ionic liquid have small and negative values and decrease with increasing of the ionic liquids concentration for all of the ionic liquids. Thus, this drug is considered as structure breaker, but with addition of IL this behavior decreases. This means that the ionic liquid has the strong interactions with acetaminophen rather than with water. The hydration number nH which is the number of water molecules hydrated to acetaminophen is related to change in

(5)

where A, B, and C are empirical parameters and T is the absolute temperature. The values of A, B, and C could be obtained by least-squares fits of the Vϕ0 values at the experimental temperatures. The partial molar isobaric expansion EoP, ϕ could be estimated by the following relation37

Table 5. Partial Molar Isobaric Expansions E0p,ϕ and Hepler’s Constants (∂2V0ϕ/∂T2)P for Acetaminophen in Aqueous [BMIm] Br and [BMIm]Cl Solutions at T = 293.15, 298.15, 303.15, and 308.15 K T/K mIL (mol·kg−1)

293.15

298.15

303.15

308.15

(∂2V0ϕ/∂T2)P (cm3·mol−1·K−2)

[BMIm]Br E0p,ϕ (cm3·mol−1·K−1) 0.1009 0.2003 0.2985 0.4006

0.1364 0.1321 0.1351 0.1350

0.1265 0.1221 0.1252 0.1251

0.1167 0.1121 0.1153 0.1152 [BMIm]Cl

0.1069 0.1021 0.1054 0.1053

−0.0020 −0.0021 −0.0021 −0.0021

E0p,ϕ (cm3·mol−1·K−1) 0.1010 0.1997 0.3007 0.4004

0.1400 0.1375 0.1351 0.1340

0.1303 0.1277 0.1252 0.1241

0.1206 0.1179 0.1153 0.1142

0.1109 0.1080 0.1054 0.1043

−0.0019 −0.0021 −0.0021 −0.0021

F


mIL = 0.1009 0.0000 0.0299 0.0329 0.0357 0.0395 0.0430 0.0474 0.0495 0.0531 0.0559 mIL = 0.2003 0.0000 0.0300 0.0326 0.0358 0.0395 0.0433 0.0477 0.0497 0.0531 0.0548 mIL = 0.2985 0.0000 0.0310 0.0326 0.0354 0.0392 0.0434 0.0473 0.0504 0.0531 0.0563 mIL = 0.4006 0.0000 0.0302 0.0326 0.0362

m (mol·kg−1)b

mol·kg−1 1493.46 1495.14 1495.26 1495.37 1495.52 1495.63 1495.77 1495.81 1495.91 1495.98 mol·kg−1 1503.61 1505.04 1505.13 1505.23 1505.34 1505.46 1505.58 1505.61 1505.71 1505.73 mol·kg−1 1512.88 1514.27 1514.32 1514.40 1514.53 1514.61 1514.73 1514.84 1514.91 1515.00 mol·kg−1 1522.64 1523.93 1523.98 1524.08

u (m·s−1)

1.03 1.12 1.22 1.32 1.39 1.50 1.54 1.60 1.64

1.63 1.71 1.78 1.83 1.90 1.98 2.00 2.05 2.08

1.95 1.97 2.05 2.12 2.20 2.26 2.29 2.31 2.34

2.01 2.06 2.12

1515.79 1517.18 1517.24 1517.33 1517.45 1517.55 1517.66 1517.70 1517.78 1517.81 1524.53 1525.81 1525.86 1525.92 1526.01 1526.10 1526.18 1526.25 1526.31 1526.38 1533.06 1534.29 1534.35 1534.45

1.51 1.56 1.62 1.70 1.75 1.83 1.87 1.90 1.95

1.71 1.74 1.80 1.84 1.95 1.99 1.99 2.02 2.04

1.86 1.94 2.01

[BMIm]Br

Kϕ·1014 (m3·mol−1·Pa−1)

298.15 K

1506.49 1508.15 1508.26 1508.34 1508.46 1508.58 1508.69 1508.74 1508.84 1508.91

u (m·s−1)

0.96 1.04 1.10 1.17 1.26 1.36 1.43 1.50 1.55

Kϕ·1014 (m3·mol−1·Pa−1)

293.15 K

T/K

G

1541.99 1543.06 1543.11 1543.20

1534.07 1535.24 1535.28 1535.34 1535.44 1535.53 1535.60 1535.66 1535.71 1535.78

1526.19 1527.49 1527.55 1527.64 1527.74 1527.86 1527.94 1527.99 1528.05 1528.08

1517.88 1519.35 1519.44 1519.53 1519.62 1519.71 1519.81 1519.87 1519.96 1520.05

u (m·s−1)

2.30 2.35 2.39

2.17 2.19 2.24 2.28 2.34 2.41 2.44 2.46 2.48

1.81 1.89 1.95 2.01 2.04 2.13 2.15 2.21 2.23

1.42 1.51 1.56 1.67 1.74 1.84 1.86 1.90 1.91

Kϕ·1014 (m3·mol−1·Pa−1)

303.15 K

1549.37 1550.40 1550.46 1550.52

1542.36 1543.48 1543.52 1543.58 1543.66 1543.75 1543.84 1543.89 1543.95 1544.00

1535.21 1536.44 1536.52 1536.62 1536.73 1536.84 1536.94 1536.99 1537.07 1537.11

1527.71 1529.07 1529.17 1529.24 1529.35 1529.41 1529.54 1529.58 1529.70 1529.76

u (m·s−1)

2.41 2.44 2.52

2.28 2.30 2.35 2.41 2.46 2.50 2.53 2.55 2.58

1.99 2.02 2.06 2.10 2.13 2.20 2.21 2.25 2.26

1.69 1.75 1.82 1.89 1.99 2.03 2.07 2.07 2.10

Kϕ·1014 (m3·mol−1·Pa−1)

308.15 K

Table 6. Experimental Speed of Sound u and Apparent Molar Isentropic Compressibility Kφ Data for Acetaminophen in Aqueous [BMIm]Br and [BMIm]Cl Solutions at T = 293.15, 298.15, 303.15, and 308.15 K and p = 101.3 kPaa

Journal of Chemical & Engineering Data Article


1524.15 1524.25 1524.35 1524.41 1524.46 1524.51

0.0395 0.0433 0.0477 0.0503 0.0531 0.0562

mIL = 0.1010 mol·kg−1 0.0000 1496.72 0.0304 1498.50 0.0329 1498.63 0.0358 1498.78 0.0395 1498.95 0.0433 1499.06 0.0474 1499.21 0.0495 1499.29 0.0531 1499.39 0.0555 1499.48 mIL = 0.1997 mol·kg−1 0.0000 1510.41 0.0301 1511.95 0.0326 1512.04 0.0356 1512.15 0.0395 1512.28 0.0429 1512.39 0.0477 1512.54 0.0499 1512.59 0.0531 1512.69 0.0555 1512.76 mIL = 0.3007 mol·kg−1 0.0000 1523.59 0.0300 1525.10 0.0326 1525.20 0.0354 1525.30 0.0392 1525.43 0.0430 1525.54 0.0473 1525.69 0.0500 1525.76 0.0531 1525.85 0.0555 1525.91

u (m·s−1)

m (mol·kg−1)b

Table 6. continued

H

1.28 1.33 1.39 1.47 1.53 1.59 1.62 1.66 1.70

1.39 1.47 1.53 1.59 1.66 1.74 1.78 1.81 1.85

1522.65 1524.20 1524.29 1524.40 1524.53 1524.64 1524.80 1524.86 1524.96 1525.02 1534.72 1536.21 1536.29 1536.38 1536.51 1536.62 1536.74 1536.81 1536.90 1536.95

1.25 1.30 1.36 1.44 1.50 1.58 1.62 1.66 1.68

1.32 1.37 1.41 1.48 1.56 1.61 1.65 1.69 1.73

0.90 0.95 0.98 1.06 1.14 1.23 1.26 1.33 1.38

2.19 2.24 2.29 2.33 2.37 2.40 [BMIm]Cl

Kϕ·1014 (m3·mol−1·Pa−1)

298.15 K

1509.78 1511.53 1511.65 1511.77 1511.91 1512.04 1512.19 1512.26 1512.37 1512.44

1534.52 1534.61 1534.72 1534.76 1534.81 1534.87

u (m·s−1)

0.79 0.80 0.83 0.88 1.02 1.10 1.13 1.22 1.25

2.09 2.13 2.20 2.23 2.27 2.31

Kϕ·1014 (m3·mol−1·Pa−1)

293.15 K

T/K

1544.34 1545.70 1545.78 1545.85 1545.96 1546.06 1546.16 1546.22 1546.29 1546.34

1532.96 1534.50 1534.59 1534.70 1534.83 1534.93 1535.09 1535.14 1535.23 1535.30

1521.14 1522.73 1522.82 1522.93 1523.06 1523.17 1523.29 1523.34 1523.43 1523.52

1543.26 1543.33 1543.41 1543.44 1543.48 1543.53

u (m·s−1)

1.67 1.73 1.80 1.86 1.93 2.00 2.04 2.08 2.11

1.33 1.39 1.44 1.52 1.59 1.65 1.69 1.74 1.76

1.23 1.29 1.34 1.40 1.49 1.57 1.62 1.68 1.69

2.45 2.51 2.56 2.60 2.63 2.66

Kϕ·1014 (m3·mol−1·Pa−1)

303.15 K

1552.66 1553.95 1554.04 1554.12 1554.22 1554.31 1554.41 1554.48 1554.55 1554.59

1541.95 1543.32 1543.42 1543.52 1543.66 1543.76 1543.90 1543.96 1544.04 1544.11

1530.82 1532.25 1532.35 1532.46 1532.58 1532.71 1532.84 1532.90 1533.00 1533.07

1550.59 1550.65 1550.71 1550.75 1550.79 1550.84

u (m·s−1)

1.83 1.86 1.91 1.98 2.05 2.11 2.13 2.17 2.20

1.68 1.69 1.74 1.78 1.83 1.89 1.91 1.96 1.97

1.58 1.60 1.64 1.69 1.73 1.78 1.81 1.85 1.87

2.56 2.62 2.69 2.72 2.74 2.77

Kϕ·1014 (m3·mol−1·Pa−1)

308.15 K

Journal of Chemical & Engineering Data Article


1.47 1.54 1.59 1.66 1.72 1.79 1.82 1.85 1.88 1546.46 1547.91 1548.00 1548.11 1548.20 1548.32 1548.45 1548.50 1548.61 1548.67 mIL = 0.4004 mol·kg 0.0000 1536.09 0.0298 1537.55 0.0326 1537.66 0.0359 1537.77 0.0390 1537.87 0.0430 1537.99 0.0475 1538.14 0.0497 1538.19 0.0532 1538.29 0.0557 1538.35

−1

volume due to electrostriction. Despite the fact that there are numerous structural studies and attempts at molecular modeling for considering the interactions between water and acetaminophen, it is not easy to accurately determine the number of water molecules that hydrate solute molecules. In this paper, the values of hydration number are calculated using equation as follows:40

Standard uncertainties: u(p) = 0.01 MPa; u(T) = 0.01 K; u(m) = 2.10−4 mol·kg−1; u(u) = 0.5 m·s−1. bm is molality of acetaminophen where solvent is (water + IL). cmIL is molality of ionic liquid where solvent is water.

1562.62 1563.89 1563.98 1564.08 1564.17 1564.27 1564.38 1564.43 1564.52 1564.57 1.74 1.80 1.85 1.90 1.95 2.00 2.02 2.08 2.10 1555.34 1556.66 1556.74 1556.84 1556.93 1557.04 1557.17 1557.22 1557.29 1557.35

Kϕ·1014 (m3·mol−1·Pa−1)

1.42 1.46 1.52 1.58 1.64 1.69 1.73 1.78 1.81

298.15 K

u (m·s−1) Kϕ·1014 (m3·mol−1·Pa−1) m (mol·kg−1)b

u (m·s−1)

293.15 K

T/K

Table 6. continued

Article

nH =

V ϕ0(elect.) V E0 − V B0

(8)

where V0ϕ(elect.) is the electrostriction partial molar volume because of the hydration of acetaminophen and can be computed from the V0ϕ values and intrinsic partial molar volume of acetaminophen by V ϕ0(elect.) = V ϕ0 − V ϕ0(int.)

V ϕ0(int.) =

⎛ 0.7 ⎞ 0 ⎜ ⎟ . V (cryst.) ⎝ 0.634 ⎠ ϕ

(9)

(10)

in which V0ϕ(cryst.) = (M/ρcryst.) is the crystal molar volume of acetaminophen and M is its molar mass, the packing density of molecules in organic crystals is 0.7, and the packing density for random packed spheres is 0.634.24 The crystal density (ρcryst) of acetaminophen is 1.263 g.cm−3. The suggested values of (V0E − V0B) are −2.6, − 3.3, and −4.0 cm3·mol−1, respectively at 288.15, 298.15, and 308.15 K.30 Because there are no the values of (V0E − V0B) for temperatures 293.15 and 303.15 K in reference 41, we obtained them by fitting to a linear equation. The symbols of VE0 and VB0 are the molar volume of electrostricted water and the molar volume of bulk water, respectively. The hydration number values for acetaminophen by using eq 8 and the values of (V0E − V0B) and V0ϕ(elect.) were obtained at different temperatures. It can be noted from Table 3 that the values of hydration number decrease at higher temperatures. Also, this parameter has the smallest values for the ionic liquid with anion Br− and the highest values for the ionic liquid with anion Cl− ; in order: [BMIm]Cl > [BMIm]Br. This observation indicates that the interaction between acetaminophen molecules and ionic liquid increases with temperatures. This interaction for ionic liquid with anion Br− is stronger than ionic liquid with anion Cl−. The apparent molar isentropic compressibility Kϕ values of acetaminophen in aqueous ILs ([BMIm]Br and [BMIm]Cl) solutions at different temperatures were calculated from the following equation: ⎛ Mκ ⎞ ⎡ κs,0ρ − κsρ0 ⎤ ⎥ Kϕ = ⎜ s ⎟ − ⎢ ⎝ ρ ⎠ ⎣⎢ mρ ·ρ0 ⎥⎦

(11)

The κs,0 and κs are the isentropic compressibility of pure solvent and solution, respectively, which are calculated by

κs =

1 u 2ρ

(12)

where u is the speed of sound and ρ is the density of the solutions. The calculated values of Kϕ for acetaminophen in (0.1, 0.2, 0.3, and 0.4) mol·kg−1 of aqueous ionic liquids solutions at the experimental temperatures are given in Table 6. It is observed that Kϕ values are positive at all experimental temperatures, also these values increase with increasing temperature and concentration of ionic liquids. It has been reported that the values of Kϕ in aqueous solutions are (1)

a

1.86 1.89 1.94 1.98 2.04 2.10 2.13 2.16 2.19

Kϕ·1014 (m3·mol−1·Pa−1) Kϕ·1014 (m3·mol−1·Pa−1) u (m·s−1)

303.15 K

u (m·s−1)

308.15 K


I



Article

Table 7. Values of Experimental Slope SK, Partial Molar Isentropic Compressibility K0ϕ, Transfer Partial Molar Isotropic Compressibility ΔtrK0ϕ, and Standard Deviations σ(Kϕ) for Acetaminophen in Aqueous [BMIm]Br and [BMIm]Cl Solutions at T = 293.15, 298.15, 303.15, and 308.15 K mIL (mol·kg−1)

T/K

K0ϕ·1015 (m3·mol−1·Pa−1)

SK.1013 (kg m3·mol−2·Pa−1)

ΔtrK0ϕ (m3·mol−1·Pa−1)

σ(Kϕ)

3.09 2.02 1.73 0.73

0.076 0.024 0.029 0.030

[BMIm]Br 0.1009 293.15 298.15 303.15 308.15

2.88 ± 0.03 4.58 ± 0.03 7.87 ± 0.04 12.40 ± 0.03

2.27 2.36 1.93 1.63

± ± ± ±

293.15 298.15 303.15 308.15

9.99 ± 0.03 11.46 ± 0.04 13.61 ± 0.03 16.59 ± 0.02

9.99 ± 0.03 11.46 ± 0.04 13.61 ± 0.03 16.59 ± 0.02

10.20 8.90 7.47 4.92

0.010 0.016 0.013 0.006

293.15 298.15 303.15 308.15

13.27 14.46 17.77 19.33

± ± ± ±

0.03 0.04 0.03 0.04

1.33 1.62 1.31 1.18

± ± ± ±

0.4 0.5 0.4 0.4

13.48 11.90 11.63 7.66

0.025 0.023 0.012 0.006

293.15 298.15 303.15 308.15

14.10 15.82 18.96 19.97

± ± ± ±

0.03 0.03 0.04 0.02

1.64 1.48 1.39 1.41

± ± ± ±

0.3 0.4 0.4 0.3

14.31 13.26 12.82 8.30

0.020 0.013 0.009 0.014

0.3 0.4 0.4 0.3

0.2003

0.2985

0.4006

[BMIm]Cl 0.1010 293.15 298.15 303.15 308.15

1.45 ± 0.03 3.15 ± 0.03 6.71 ± 0.04 12.15 ± 0.03

1.99 1.91 1.88 1.19

± ± ± ±

0.5 0.5 0.4 0.4

1.66 0.59 0.57 0.48

0.011 0.006 0.007 0.011

293.15 298.15 303.15 308.15

7.40 ± 0.03 8.02 ± 0.04 8.36 ± 0.03 13.12 ± 0.03

1.74 1.64 1.70 0.13

± ± ± ±

0.4 0.5 0.5 0.4

7.61 5.46 2.22 1.45

0.010 0.009 0.004 0.003

293.15 298.15 303.15 308.15

8.48 ± 0.03 9.05 ± 0.04 11.80 ± 0.03 13.81 ± 0.03

1.61 1.73 1.71 1.50

± ± ± ±

0.4 0.4 0.5 0.4

8.69 6.49 5.66 2.14

0.011 0.015 0.014 0.011

293.15 298.15 303.15 308.15

9.66 ± 0.03 10.23 ± 0.04 13.50 ± 0.02 14.73 ± 0.03

1.54 1.58 1.37 1.30

± ± ± ±

0.4 0.5 0.4 0.4

9.87 7.67 7.36 3.06

0.009 0.017 0.010 0.008

0.1997

0.3007

0.4004

Kϕ = Kϕ0 + SK ·m

positive for hydrophobic solutes; (2) negative and large for ionic compounds; and (3) negative, small, and intermediate, for uncharged hydrophilic solutes.42−44 In the present investigation, it can be understood from the positive Kϕ values the IL molecules around the acetaminophen molecules are more compressible than the bulk43 which indicates strong interactions between acetaminophen molecules and the IL molecules. Also, the Kϕ values increase with changing the anion type from Cl− to Br− and the values of Kϕ for acetaminophen in the investigated solutions show the following order: [BMIm]Br>[BMIm]Cl. The partial molar isentropic compressibility K0ϕ is often estimated from the extrapolation of the apparent molar compressibility Kϕ to an infinite dilution using the following linear equation:

(13)

SK is an experimental slope which shows interactions between acetaminophen molecules. The values of K0ϕ and SK with their standard error and standard deviations estimated by leastsquares fits are listed in Table 7. The Kϕ0 values of acetaminophen in 0.2 mol·kg−1 aqueous ILs solutions at different temperatures are graphically represented in Figure 3. The positive values of K0ϕ for acetaminophen at different temperatures are allocated to the strong attractive interactions between acetaminophen and IL molecules,45 which may be due to release of water molecules from the second solvation layer of the solute in water as well as in aqueous ionic liquid solutions. Therefore, there is a strong attractive interaction between J



Article

and R is a distance parameter. The quantities required for the calculations of the parameters E, J1, and J2 were taken from ref 47. In these equations, c is molar concentration of ionic liquid. The other parameters have the usual meanings. The values of KA, Λ0, and R are given in Table 9. The values of limiting molar conductivity Λ0, decrease with the concentration of acetaminophen. These results indicate that the interactions of the ions of ionic liquids and acetaminophen with increasing acetaminophen concentration become stronger, also the viscosity of the solutions increases therefore the mobility of ions decrease.48 The values of ion association KA in ILs solutions increase with increasing temperature. These values also increase with decreasing in anion size. The obtained results from this work show a stronger ion-solvation at low temperature. At higher temperatures, the mobility of free ions and the Λ0 values for the investigated ionic liquids are increased. The Gibbs free energy 0 of ion pair formation ΔGIL (T) was calculated by using following equation:

Figure 3. Variation of partial molar isentropic compressibility K0φ of acetaminophen in aqueous [BMIm]Br and [BMIm]Cl solutions with different temperatures and at 0.2 mol·kg−1 of ILs: (△), [BMIm]Br; (○), [BMIm]Cl.

0 ΔG IL (T ) = −RT ln KA(T )

acetaminophen molecules and ionic liquid which becomes stronger with increasing in anion size. The transfer partial molar isotropic compressibility ΔtK0ϕ values of acetaminophen from water to aqueous solutions of ILs was computed using the following equation Δt Kϕ0

=

Kϕ0(in aqueous ionic liquids)

−

The temperature dependence of polynomial,

(21)

The enthalpy and entropy of ion association were obtained as follows

The values of ΔtK0ϕ are reported in Table 7 which have positive values at all concentration range of ionic liquids. The values of K0ϕ for acetaminophen in water were taken from our previous work.26 According to cosphere overlap model, the positive values of ΔtK0ϕ show the presence of the polar−polar group and the polar−ionic group interactions. 3.2. Conductometric Results. The molar conductivity Λ values of [BMIm]Br and [BMIm]Cl in aqueous acetaminophen solutions are reported in Table 8. The specific electrical conductivities κ of studied systems are given in Table S1. Clearly, increase in both acetaminophen and ionic liquids concentrations result in molar conductivities decrease. According to Figure 4, with increasing the anion size, the molar conductivity increases. Surface electrical charge density decreases with increasing the anion size, therefore the mobility of an anion is increased.46 The molar conductivity Λ values for studied systems were analyzed with low concentration Chemical Model (lcCM)47 using the following set of equations:

⎛ ∂ΔG 0 (T ) ⎞ 0 IL ⎟ = A1 + 2A 2 (298.15 − T ) (T ) = − ⎜ ΔSIL T ∂ ⎠P ⎝ (22) 0 0 0 ΔHIL (T ) = ΔG IL (T ) + T ΔSIL (T )

= A 0 + 298.15A1 + (298.152 − T 2)A 2

(15)

k2 =

q=

(16)

kq 1 + kR

(17)

16000NAz 2e 2αc ε0εkBT

(18)

ln γ± = −

z 2e 2 8πε0εkBT

(23)

The calculated thermodynamic functions are also listed in Table 9. The values of the coefficients A0, A1 and A2 at different molality of acetaminophen are given in Table 10. The values of ln KA for ILs in aqueous acetaminophen solutions at 0.06 mol· kg−1 and at different temperatures are graphically represented in Figure 5. The values of ΔG0A are negative and becomes more negative with increasing temperature. These results suggest that association process at high temperatures is spontaneity and feasibility. The values of ΔS0A are positive for majority of cases over the whole temperature range. Because of the release of solvent molecules from hydration layers as association takes place, the number of degrees of freedom increases and the positive values of ΔS0A may be attributed to this phenomenon. In other words, when ion pairs are formed, the solvation of the individual ions becomes weak. The dehydration of ions causes the positive contribution of entropy which dominates over the negative contribution from the formation of ion pairs. It should be noted that the entropy term TΔS0A is sufficiently positive to exceed the positive contribution of the enthalpy ΔH0A. It is observed that the ΔH0A values for ionic liquids in aqueous acetaminophen solutions are positive at all experimental temperatures. These values suggest that the process of ion pair formation is endothermic.

Λ = α[Λ 0 − S(cα)1/2 + Ecα ln(cα) + J1cα + J2 (cα)3/2 ] 1−α α 2cγ±2

was shown with a

0 ΔG IL (T ) = A 0 + A1(298.15 − T ) + A 2(298.15 − T )2

Kϕ0(in water) (14)

KA =

(20)

ΔG0IL(T)

(19)

4. CONCLUSIONS In the present work, volumetric, compressibility and electrical conductivity measurements have been used to study of the

where Λ0 is the molar conductivity at infinite dilution, (1 − α) is the fraction of oppositely charged ions acting as ion pairs, γ± is the corresponding mean activity coefficient of the free ions, K



Article

Table 8. Molar Conductivities Λ of [BMIm]Br and [BMIm]Cl in Aqueous Acetaminophen Solutions as a Function of Ionic Liquid Molality (mIL) at Different Temperatures and p = 101.3 kPaa T/K 293.15 −1

10 ·mIL (mol·kg ) 3

298.15 −1

Λ (S·cm ·mol ) 2

−1


303.15 −1

Λ (S·cm ·mol ) 2

−1


308.15

Λ (S·cm ·mol )

10 ·mIL (mol·kg )

Λ (S·cm2·mol−1)

2

−1

−1

3

[BMIm]Br mA = 0.0304 mol·kg−1 0.302 105.494 0.627 102.853 0.899 101.605 1.225 99.819 1.571 98.364 1.907 97.124 2.233 95.987 2.599 94.630 2.933 93.806 3.327 92.577 3.665 91.844 4.009 91.170 4.330 90.410 4.622 89.869 4.961 89.151 mA = 0.0601 mol·kg−1 0.273 99.069 0.562 97.642 0.901 96.446 1.204 95.510 1.540 94.484 1.884 93.511 2.223 92.627 2.549 91.753 2.914 91.020 3.296 90.042 3.640 89.304 3.928 88.648 4.279 87.873 4.640 87.275 5.025 86.467

0.267 0.502 0.799 1.064 1.296 1.542 1.854 2.110 2.363 2.661 3.001 3.333 3.607 3.965 4.235

108.405 106.476 104.267 102.603 100.898 99.612 98.033 96.594 95.515 94.294 92.961 91.716 90.845 89.701 88.828

0.300 0.637 0.964 1.262 1.600 1.945 2.245 2.594 2.941 3.261 3.593 3.954 4.275 4.629

112.564 108.756 105.692 103.362 100.842 98.333 96.544 94.576 92.612 91.223 89.603 88.066 86.997 85.707

0.147 0.523 0.830 1.082 1.426 1.705 2.004 2.308 2.539 2.836 3.125 3.391 3.676 4.029

139.249 132.940 128.361 125.207 120.833 118.039 115.278 112.918 110.497 108.475 106.585 104.305 102.536 100.636

0.311 0.640 0.901 1.261 1.648 1.975 2.328 2.612 2.907 3.215 3.550 3.837 4.171 4.410 4.698

102.406 99.871 98.619 96.867 95.553 94.399 93.556 92.774 91.889 90.997 90.190 89.538 88.694 88.229 87.567

0.276 0.640 0.888 1.259 1.542 1.819 2.061 2.314 2.623 2.967 3.241 3.554 3.789 4.043 4.340

108.414 104.367 102.515 99.888 97.989 96.683 95.737 94.047 92.945 91.299 89.999 88.948 88.273 87.303 86.366

0.313 0.661 0.915 1.047 1.679 2.297 2.595 2.926 3.250 3.544 3.920 4.265 4.923 5.211 5.550

115.697 110.447 107.362 105.766 100.432 95.419 93.141 91.230 88.650 87.377 85.609 83.820 80.552 79.501 78.236

[BMIm]Cl mA = 0.0306 mol·kg−1 0.281 89.260 0.467 88.846 0.658 88.078 0.894 87.173 1.078 86.649 1.254 86.034 1.447 85.441 1.646 84.831 1.861 84.424 2.084 83.747 2.306 83.164 2.470 82.680 2.612 82.305 2.777 81.760 2.957 81.193 mA = 0.0602 mol·kg−1 0.249 83.715 0.415 82.399 0.632 80.702 0.805 79.218 1.052 77.848 1.300 76.567

0.141 0.231 0.373 0.491 0.616 0.708 0.938 1.062 1.202 1.363 1.492 1.596 1.718 1.935

99.555 98.949 97.927 97.001 95.991 95.439 93.586 92.671 91.638 90.228 89.031 87.993 87.153 85.130

0.187 0.325 0.510 0.736 0.959 1.121 1.296 1.487 1.665 1.878 2.113 2.282 2.489 2.629 2.822

103.643 102.272 101.513 100.355 99.229 98.488 97.311 96.134 94.785 93.875 92.629 91.546 90.371 89.622 88.665

0.223 0.415 0.568 0.808 1.008 1.403 1.635 1.797 2.030 2.242 2.493 2.748 2.958 3.217

113.761 112.030 111.014 108.983 107.440 104.563 102.962 102.095 100.553 99.172 97.524 95.865 94.658 92.951

0.253 0.456 0.677 0.881 1.080 1.288

92.236 90.771 89.691 88.402 87.606 86.392

0.145 0.466 0.668 0.948 1.239 1.464

97.646 95.873 94.920 93.823 93.074 91.931

0.234 0.456 0.676 0.928 1.243 1.479

105.447 104.007 102.833 101.771 99.655 98.744

L



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Table 8. continued T/K 293.15 −1

298.15 10 ·mIL (mol·kg )

Λ (S·cm ·mol )

10 ·mIL (mol·kg )

Λ (S·cm ·mol )

10 ·mIL (mol·kg )

Λ (S·cm2·mol−1)

1.542 1.761 2.017 2.280 2.554 2.881 3.121 3.360 3.632

75.166 73.578 72.231 71.133 69.965 68.404 67.380 66.420 65.172

1.534 1.812 2.014 2.220 2.520 2.773 2.990 3.139 3.474

85.313 84.609 83.475 82.864 81.583 80.525 79.728 79.232 77.873

1.714 1.933 2.135 2.402 2.658 2.903 3.186 3.560 3.799

90.798 89.901 88.887 88.191 87.404 86.279 85.128 84.093 83.089

1.743 2.023 2.276 2.581 2.861 3.101 3.357 3.642 3.908

96.909 95.617 94.779 93.040 91.732 90.842 90.010 89.055 88.442

a

−1

3

2

−1

−1

308.15

Λ (S·cm ·mol ) 2

−1

303.15


3

−1

2

−1

3

Standard uncertainties u are u(Λ) = 0.08 S·cm2·mol−1, u(T) = 0.01 K, u(m) = 2.10−4 mol·kg−1, and u(P) = 0.01 MPa.

Table 10. The Values of Coefficients A0, A1, A2 Obtained from Eq 21 for [BMIm]Br and [BMIm]Cl in Aqueous Acetaminophen Solutions at T = 293.15, 298.15, 303.15 and 308.15 K mA (mol·kg−1)

10−3A0 [BMIm]Br −8.22 −8.75 [BMIm]Cl −8.698 −9.543

0.0304 0.0601 0.0306 0.0602

A1

A2

383.11 77.00

18.12 −9.41

170.9 115.0

−3.02 −0.51

interactions between a drug, acetaminophen, and two imidazolium based ionic liquids in aqueous medium. The standard partial molar volume V0ϕ, the partial molar isentropic compressibility K0ϕ, and hydration number nH of acetaminophen in the aqueous ionic liquids, ([BMIm]Br/([BMIm]Cl), solutions were calculated from experimental density and

Figure 4. Molar conductivities Λ of the ionic liquids versus molarity of ionic liquids in 0.03 mol·kg−1 of aqueous acetaminophen solutions: (○), [BMIm]Cl; (▲), [BMIm]Br at T = 298.15 K.

Table 9. Association Constants (KA), Limiting Molar Conductivities (Λ0), the Distance of Closest Approach of Ions (R), and Thermodynamic Functions (ΔG0, ΔS0, and ΔH0) of [BMIm]Br and [BMIm]Cl in Aqueous Acetaminophen Solutions at Different Temperatures T/K

KA (dm3·mol−1)

1/T × 104

ln KA

Λ0 (S·cm2·mol−1)

1010R (m)

ΔG0 (kJ mol−1)

ΔS0 (J mol−1.K−1)

ΔH0 (kJ mol−1)

[BMIm]Br mA = 0.0304 mol·kg−1 293.2 18.28 ± 0.37 298.2 25.72 ± 0.50 303.2 49.79 ± 0.63 308.2 53.36 ± 0.59 mA = 0.0601 mol·kg−1 293.2 36.60 ± 0.66 298.2 47.79 ± 0.46 303.2 50.28 ± 0.61 308.2 55.44 ± 0.57 mA = 0.0306 mol·kg−1 293.2 26.63 ± 0.81 298.2 30.32 ± 0.80 303.2 50.19 ± 0.79 308.2 63.36 ± 0.59 mA = 0.0602 mol·kg−1 293.2 39.60 ± 0.66 298.2 47.79 ± 0.46 303.2 54.71 ± 0.61 308.2 66.62 ± 0.57

34.11 33.53 32.98 32.45

2.906 3.247 3.908 3.977

107.53 111.14 116.48 142.38

± ± ± ±

0.33 0.33 0.35 0.35

42.23 43.03 43.76 47.54

−7.08 −8.06 −9.85 −10.19

564.1 383.1 202.1 21.1

159.46 106.16 51.42 −3.68

34.11 33.53 32.98 32.45

3.600 3.867 3.918 4.015

100.27 104.09 110.88 120.77

± ± ± ±

0.42 0.33 0.33 0.33 [BMIm]Cl

2.06 36.86 40.51 47.83

−8.77 −9.59 −9.88 −10.29

−17 77 171 265

−13.75 14.72 41.96 71.37

34.11 33.53 32.98 32.45

3.282 3.412 3.916 4.149

90.87 ± 0.33 102.17 ± 0.34 106.25 ± 0.31 117.39 ± 0.35

2.98 50.86 35.52 44.94

−7.999 −8.457 −9.869 −10.63

140.74 170.94 201.14 231.34

33.25 42.50 51.09 60.65

34.11 33.53 32.98 32.45

3.679 3.867 4.002 4.199

86.83 ± 0.42 94.46 ± 0.33 99.20 ± 0.33 108.09 ± 0.33

6.84 34.16 3.91 4.44

−8.966 −9.585 −10.09 −10.76

109.93 115.03 120.13 125.23

23.25 24.70 26.32 27.82

M



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speed of sound data. It was found that the calculated quantities increase with increasing ionic liquid concentration in all systems. This observation exhibits that the interactions between acetaminophen and ionic liquids were strengthened with increasing ionic liquid concentration. Also, this observation indicates that the ionic liquid with anion of Br− has stronger interactions than the ionic liquid with anion of Cl−. The derived transfer properties, ΔtV0φ and ΔtK0ϕ, indicated the dominance of polar−polar and polar−ion interactions between acetaminophen and ions of the ionic liquid. The calculated Hepler’s constant shows that acetaminophen is a structure breaker and this behavior will be weakened with increasing ionic liquid concentration. The conductometric results represent that the molar conductivity Λ decreases with increasing of both ionic liquids and acetaminophen concentrations. These values also increase with increasing anion size. The values of the limiting molar conductivity Λ0 of [BMIm]Br and [BMIm]Cl in aqueous solutions of acetaminophen increase by increasing acetaminophen concentration. These results confirm the fact that there is a strong attractive interaction between acetaminophen molecules and the ionic liquids, and becomes stronger with increase in anion size.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00464. Specific electrical conductivities, 1H NMR spectra of the ionic liquids (PDF)

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REFERENCES

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Figure 5. Logarithm of ion association constant lnKA(T) versus different 1/T at 0.06 mol·kg−1 of acetaminophen: (△), [BMIm]Br; (■), [BMIm]Cl.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +98 4133393094; Fax: +98 41 33340191; E-mail: [email protected]. ORCID

Hemayat Shekaari: 0000-0002-5134-6330 Funding

The authors wish to thank financial support from the graduate council of the University of Tabriz. Notes

The authors declare no competing financial interest. N



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