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Densities, Speeds of Sound, and Excess and Partial Excess Properties of Room Temperature Ionic Liquids of Type [Cnpy][X] or [Cn4mpy][X] (Where n = 6 or 8, [X] = Cl− or Br−) + Water Binary Mixtures at T = (308.15 and 318.15) K Nandhibatla V Sastry* and Indravijaysinh R Ravalji Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India S Supporting Information *

ABSTRACT: Densities and speeds of sound were measured for six binary mixtures of water + room temperature ionic liquids (RTILs) of type [Cnpy][X] or [Cn4mpy][X] (where n = 6 or 8, [X] = Cl− or Br−) at T = (308.15 and 318.15) K at atmospheric pressure. The molar excess volumes (VmE) excess speeds of sound (υE), and excess isentropic compressibilities (κsE) were calculated from the experimental data. Addition of a small amount of RTIL drastically increased the densities of water initially. The VmE values for water + chloride-based RTILs were more negative across the composition compared to the mixtures with bromide-based RTILs; the negative magnitudes, however, decreased as the alkyl chain length and temperature increased. Speeds of sound of the mixtures could be adequately predicted by the collision factor theory and Nomoto equation. The υE values were positive, while κsE values were negative across the composition. The negative VmE and κsE values in general suggest the predominance of strong heterointeractions, which become enhanced with the increase in hydrocarbon chain length. Analysis of partial excess molar volumes or isentropic compressibilities and their standard transfer functions revealed that, compared to those of the Cl− anion, the Br− anion has the weakest water···RTIL interactions.

1. INTRODUCTION Knowledge of the physical properties or, more precisely, thermophysical properties of room temperature ionic liquids (RTILs) or ionic liquids (ILs) either in their pure state or for their mixtures with polar or nonpolar components is highly essential for the design of new ionic liquids with maximized key desired attributes and properties. Despite this requirement, experimental data on many properties of pure RTILs or their mixtures with a second polar or nonpolar component are scarce in the literature and, even if the data exists, it is often inconsistent among the studies reported by various research groups. Therefore, a growing interest is felt both from experimental and theoretical points of view to either measure or theoretically predict physical properties such as density, viscosity, surface tension, specific heat capacity, thermal conductivity, etc. from simple structural information using group contribution methods or directly from computer simulation.1,2 A considerable amount of experimental data has been reported for densities as a function of temperature for a range of imidazolium, pyridinium, ammonium, phosphonium, and pyrrolidinium-based RTILs.3,4 Densities are found to be dependent strongly on the anion type and also on the alkyl chain length of the ring cation. Group contribution methods were also developed and employed for calculating density of ILs in pure as well as mixed states.5,6 © XXXX American Chemical Society

RTIL + water mixtures are capable of acting as functional fluids especially for biological applications7 and can be obtained to exist as a homogeneous solution phase or a liquid/liquid biphase. Pure RTILs have almost no ability to dissolve protein without denaturation;8,9 however, RTILs that contain a small amount of water are found to be far superior at dissolving and preserving proteins. Besides protein solubility and stability applications, such mixtures are also used as an electrolytes for biofuel cells10−12 that involve electrochemically active enzymes as catalysts. The magnitude of thermophysical and thermodynamic properties of RTIL + water mixtures, however, highly depends on the extent of net interactions and also on the structural features of RTILs. The microscopic structure of RTILs is not very simple and is far from being well-understood. Molecular simulation studies13−15 as well as experimental studies16 established that the alkyl imidazolium-based RTILs exhibit medium range ordering, and hence, the microphase separation between the polar and/or nonpolar domains remains intact even after they are mixed with a second component. For example, the miscibility of RTILs with water (or other solvents) Received: June 6, 2016 Accepted: October 4, 2016

A

DOI: 10.1021/acs.jced.6b00460 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

volumes (VmE), excess speeds of sound (υE), excess isentropic compressibilities (κSE), and partial molar excess volumes and compressibilities for RTIL and water are calculated. The compositional variations of VmE, υE, and κSE functions with mole fractions of water are fitted to a Redlich−Kister-type polynomial equation. The partial molar volumes and compressibilities of RTIL and water at infinite dilution and their transfer functions are also calculated and explained. The effects of nature and size of anions Cl− or Br− for a given RTIL, carbon chain length for a given anion, and also the presence of a methyl group on the pyridine ring on the overall magnitude of VmE and κSE values are reviewed and discussed.

is reported to be highly dependent on the nature of the anions. 1-Butyl-3-methyl imidzaloium, [C4mim+]-based ILs in combination with hydrophilic anions like [Cl−], [Br−], [CF3SO3−], or [BF4−] are miscible with water, but those combined with [C(CN)3−], [CH3(C2H4O)2SO4−], [PF6−], or [N(SO2CF3)2−] phase separate at room temperature. The miscibility or immiscibility in such systems can be explained in terms of net balance of interactions among ion−ion, water−water, and water−ion pairs. Cabeza et al.17 reviewed the studies consisting of measurements of physical properties (densities, dynamic viscosities, refractive indexes, electrical conductivities, and surface tensions) and corresponding excess or deviation functions for RTIL + water mixtures. It is reported that densities of [Cnmim][Cl], where n = 4, 6, or 8, initially increased when water is added and then decreased at high mole fractions of water.18−24 Similar trends were also noted in sulfate-based RTIL + water mixtures.25−27 The size of the respective cation or anion has great influence on density.25,26,28,29 The excess molar volumes (VmE) of some RTIL + water mixtures consisting of alkyl 1-methylimidazolium,30−41 1-butyl-3-methylpyridinum,41 methylpyrrolidinium, or 1-methylpiperidinium42,43 cations and one of anions Cl−, Br−, BF4−, MSO 4 − , ESO 4 − , CF 3 COO − , CF 3 SO 4 − , CF 3 SO 3 − , bis(trifluoromethylsulfonyl)imide, NTf2 − , HSO4−, N(CN)2−, or OSO4− are also reported. Depending upon the nature of a given anion and whether the anion is nonfluorinated or fluorinated, both the structure making and/or structure breaking effects are assumed to be predominant and contribute to the magnitude and sign of the VmE values. In contrast to the large experimental data of VmE for alkyl imidazolium-based RTIL + water mixtures, there are only a few reports in the literature on pyridinium-based RTIL + water mixtures. Some of the reported studies are densities and surface tensions for the binary system of [C4py][NO3] + water at 298.15 K,44 densities and excess molar volumes for ([C4mpy][BF4] + water) mixtures,45 or ([C4py ][BF4] + water) or ([C8py][BF4] + water) mixtures.46 Pyridinium-based cations have various unique and useful applications such as bioactivity as in medicinal drugs and in agricultural products such as herbicides, insecticides, fungicides, and plant growth regulators. The pyridine ring has five substitution sites on 2−6 positions, considering N at one position. The pyridine ring is stable, cyclic, aromatic, and contains 6π electrons and one π-deficient site. The ring nitrogen is more electronegative than the ring carbons, and hence, the two-, four-, and six-membered carbons are electropositive. The pyridine ring acts both as electron pair donor and a proton acceptor and is readily biodegradable47,48 compared to 1-alkyl-3-methylimidazolium bromides, which are resistant to biodegradation.47,49,50 In view of the scarcely available literature data on thermophysical and thermodynamic properties for pyridinium or methylpyridinium cation-based ILs + water mixtures, and also keeping the above-described potential advantages in mind, the present study reports the new data on experimentally measured densities and speeds of sound for six binary mixtures, namely 1-hexylpyridinium chloride, [C6py][Cl], 1-octylpyridinium chloride, [C8py][Cl], 1-hexylpyridinium bromide, [C6py][Br], 1-octylpyridinium bromide, [C8py][Br], 1-octyl-4-methylpyridinium chloride, [C84mpy][Cl], 1-hexyl-4-methylpyridinium bromide, and [C64mpy][Br] + water binary mixtures across the composition at T = (308.15 and 318.15) K. The applicability of semiempirical equations or theories for predicting the speeds of sound for these mixtures was tested. The excess molar

2. EXPERIMENTAL SECTION Chemicals and Room Temperature Ionic Liquids. The origin, purification method, purity, and method of purity determination of the chemicals used for the synthesis of RTILs are listed in Table 1. The details of purification methods along Table 1. Source, Initial Mole Fraction Purity, Purification Method, Final Mole Fraction Purity, and Analysis Method for the Chemical Samples Used in the Present Work purification method

final mole fraction purity

analysis method

chemical name

source

initial mole fraction purity

pyridine 4methylpyridine 1-chlorohexane 1-bromohexane

ARa Aldrich

0.995 0.990

distillation distillation

0.998 0.997

GCb GCb

Aldrich Aldrich

0.990 0.990

distillation distillation

0.998 0.998

GCb GCb

a

Analytical reagent. bGas chromatography.

with the detailed synthetic procedure are as follows: pyridine was dried over potassium hydroxide and fractionally distilled at 388.15 K. 4-Methylpyridine was dried over potassium hydroxide and freshly distilled. The fraction as collected at 418.15 K was used. 1-Chlorohexane, 1-bromohexane, 1chlorooctane, and 1-bromooctane were dried over fused calcium chloride and were freshly distilled before use. 1-Hexylpyridinium chloride [C6py][Cl] was synthesized by a direct reaction between 40.0 g (0.505 mol) of pyridine and 60.996 g (0.505 mol) of 1-chlorohexane in a round-bottom flask equipped with reflux condenser and magnetic stirrer. The contents were refluxed at 393.15 K for 12 h. The resulting light yellow viscous liquid product was cooled to room temperature, and 100 cm3 of analytical reagent grade ethyl acetate was added under thorough mixing. The excess amount of ethyl acetate was decanted, and the procedure was repeated four times using a fresh fraction of ethyl acetate. After a final wash, the traces of ethyl acetate (if present) were removed by evaporation under vacuum for 12 h. 1-Hexylpyridinium chloride (98.658 g) was obtained with a worked out yield of 98% (w/v). The proton NMR chemical shifts and their assignments for the sample are 1 H NMR (400 MHz, δ): 0.777 (3H, t, N-CH2-CH2-(CH2)3CH3), 1.224 (6H, m, N-CH2-CH2-(CH2)3-CH3), 1.967 (2H, m, N-CH2-CH2-(CH2)3-CH3), 4.593 (2H, t, N-CH2-CH2-(CH2)3CH3), 8.056 (2H, t, CHpyr‑m), 8.522 (H, t, CHpyr‑p), 8.838 (2H, d, CHpyr‑o). 1-Octylpyridinium chloride [C8py][Cl] was synthesized by a similar procedure as described above for [C6py][Cl] with 30.0 g (0.379 mol) of pyridine and 56.385 g (0.379 mol) of 1chlorooctane. 1-Octylpyridinium chloride (84.658 g) was B



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Table 2. Comparison of Experimental and Literature Densities (ρ) and Speeds of Sound (υ) of Water and Pure RTILs at T = (308.15 and 318.15) Ka ρ (g·cm−3) T = 308.15 K [C6py][Cl] [C8py][Cl] [C6py][Br] [C8py][Br] [C64mpy][Br] [C84mpy][Cl] water

a

exptl 1.146648 1.128779 1.235719 1.168145 1.214465 1.107792 0.994028

υ (m·s−1) T = 318.15 K

lit.

0.99402963 0.99403265 0.99403366

exptl 1.142773 1.123059 1.229228 1.161808 1.207881 1.102007 0.990203

T = 308.15 K lit.

0.99020863 0.99021065

exptl 1570.7 1482.6 1592.5 1507.1 1589.8 1445.5 1519.6

lit.

1520.1264 1519.0065 1519.8566

T = 318.15 K exptl 1549.2 1448.6 1557.2 1478.3 1558.7 1411.7 1536.4

lit.

1536.7264 1535.1065 1536.4566

Standard uncertainties u:, u(T) = 0.01 K; u(p) = 5 kPa; u(ρ) = 1.8 × 10−6 g·cm−3; and u(υ) = 0.8 m×s−1.

1-Hexyl-4-methylpyridinium bromide [C64mpy][Br] was synthesized by the same procedure as described for 1hexylpyridinium bromide. 4-Methylpyridine (30.0 g, 0.322 mol) and 1-bromohexane (53.152 g, 0.322 mol) were reacted to get a final product of 74.775 g of 1-hexyl-4-methylpyridinium chloride as a yellowish viscous liquid with a yield of 96% (w/v). The proton NMR chemical shifts and their assignments for the sample are 1H NMR (400 MHz, δ): 0.790 (3H, t, N-CH2-CH2(CH2)3-CH3), 1.270 (6H, m, N-CH2-CH2-(CH2)3-CH3), 1.987 (2H, m, N-CH2-CH2-(CH2)3-CH3), 2.657 (3H, s, Cpyr‑p-CH3), 4.562 (2H, t, N-CH2-CH2-(CH2)3-CH3), 7.913 (2H, d, CHpyr‑m), 8.707 (2H, d, CHpyr‑o). The purity of RTILs was ascertained by determining the chloride or bromide by the Mohr method. Typically, 10 cm3 aliquot solutions containing 0.12−0.16 g of chloride or bromide anion were diluted to 100 cm3 by distilled water. The solution was titrated with 0.1 mol·dm−3 of silver nitrate by addition of 1 cm3 of 5% (w/v) potassium chromate solution as an indicator. The end point is detected by the appearance of the red silver chromate. Solutions during the titration were maintained at close to neutral pH. As the silver nitrate reacts with chloride or bromide anion on a 1:1 mol basis, the number of moles of AgNO3 used is equal to number of moles of anions titrated. The purity of the samples was found to be ≥98% on a mole basis. The water was distilled four times from all pyrex glass and degassed by boiling before the preparation of solutions. The mass of the samples accurate to ±0.01 mg was registered on a single pan analytical balance (Dhona 100 DS, India). The binary mixtures of RTILs in desired mole fractions were prepared by dissolving their known amount in water under gentle swirling on a magnetic stirrer. The mole fractions of the mixtures are accurate up to ±0.0001. The density and speed of sound of the pure RTIL and water and the binary mixtures were measured using a high precision digital vibrating tube density and sound velocity meter (DSA 5000 M, Anton Paar GmbH, Austria). The pure liquids or solutions were filled manually by syringe. The period of oscillation of the U-tube was measured by optical pickups. Two integrated Pt 100 thermometers together with Peltier elements provide an extremely precise thermostatting of the sample. The repeatability of temperatures is ±0.001 K; however, the accuracy in temperature during measurements is not greater than ±0.01 K. The viscosity-related errors were automatically corrected over the full viscosity range by measuring the damping effect of the viscous sample followed by a mathematical correction of the density value. The apparatus

obtained with a worked out yield of 98% (w/v). The proton NMR chemical shifts and their assignments for the sample are 1 H NMR (400 MHz, δ): 0.660 (3H, t, N-CH2-CH2-(CH2)5CH3), 1.147 (10H, m, N-CH2-CH2-(CH2)5-CH3), 1.961 (2H, m, N-CH2-CH2-(CH2)5-CH3), 4.616 (2H, t, N-CH2-CH2(CH2)5-CH3), 8.071 (2H, t, CHpyr‑m), 8.553 (H, t, CHpyr‑p), 8.828 (2H, d, CHpyr‑o) 1-Hexylpyridinium bromide [C6py][Br] was also synthesized by a direct reaction between 30.0 g (0.379 mol) of pyridine and 62.605 g (0.379 mol) of 1-bromohexane in the above-described reactor setup. The contents were refluxed at 393.15 K for 12 h. The resulting yellowish viscous liquid product was cooled to room temperature, and the excess of the bromoalkane was removed by the same procedure as described earlier. 1Hexylpyridinium bromide (89.827 g) was obtained with a worked out yield of 97% (w/v). The proton NMR chemical shifts and their assignments for the sample are 1H NMR (400 MHz, δ): 0.807 (3H, t, N-CH2-CH2-(CH2)3-CH3), 1.282 (6H, m, N-CH2-CH2-(CH2)3-CH3), 2.027 (2H, m, N-CH2-CH2(CH2)3-CH3), 4.653 (2H, t, N-CH2-CH2-(CH2)3-CH3), 8.122 (2H, t, CHpyr‑m), 8.590 (H, t, CHpyr‑p), 8.922 (2H, d, CHpyr‑o). 1-Octylpyridinium bromide [C8py][Br] was synthesized by the same procedure as described for [C6py][Br] with 30.0 g (0.379 mol) of pyridine and 56.346 g (0.379 mol) of 1bromooctane. The contents were refluxed at 393.15 K for 12 h. 1-Octylpyridinium bromide (84.619 g) was obtained with a worked out yield of 98% (w/v). The proton NMR chemical shifts and their assignments for the sample are 1H NMR (400 MHz, δ): 0.730 (3H, t, N-CH2-CH2-(CH2)5-CH3), 1.219 (10H, m, N-CH2-CH2-(CH2)5-CH3), 2.037 (2H, m, N-CH2-CH2(CH2)5-CH3), 4.700 (2H, t, N-CH2-CH2-(CH2)5-CH3), 8.178 (2H, t, CHpyr‑m), 8.647 (H, t, CHpyr‑p), 9.046 (2H, d, CHpyr‑o). 1-Octyl-4-methylpyridinium chloride [C84mpy][Cl] was synthesized by a direct reaction between 30.0 g (0.322 mol) of 4-methylpyridine and 56.385 g (0.322 mol) of 1chlorooctane in a round-bottom flask reactor. The contents were refluxed at 393.15 K for 12 h. The resulting yellowish viscous liquid product was obtained, and the same was washed four times and dried. 1-Octyl-4-methylpyridinium chloride (84.658 g) was obtained with a worked out yield of 97% (w/v). The proton NMR chemical shifts and their assignments for the sample are 1H NMR (400 MHz, δ): 0.685 (3H, t, N-CH2-CH2(CH2)3-CH3), 1.152 (10H, m, N-CH2-CH2-(CH2)5-CH3), 1.976 (2H, m, N-CH2-CH2-(CH2)5-CH3), 2.664 (3H, s, CH3CHpyr‑p), 4.661 (2H, t, N-CH2-CH2-(CH2)5-CH3), 7.954 (2H, d, CHpyr‑m), 8.766 (H, d, CHpyr‑o). C



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Table 3. Densities (ρ) and Speeds of Sound (υ) for Water + RTIL Binary Mixtures at T = (308.15 and 318.15) K ρ (g·cm−3) x1

T = 308.15 K

0.0598 0.1085 0.2068 0.2492 0.3024 0.4166 0.4568 0.5065 0.6137 0.6533 0.709 0.7521 0.7936 0.8561 0.8966 0.9528

1.146465 1.146263 1.145596 1.145159 1.144441 1.142045 1.140821 1.138925 1.132917 1.129748 1.124026 1.118198 1.110938 1.095340 1.080314 1.046951

0.0625 0.1156 0.2085 0.2545 0.3060 0.4127 0.4534 0.4995 0.6103 0.6508 0.6962 0.7542 0.8086 0.8512 0.9009 0.9485

1.128683 1.128572 1.128287 1.128081 1.127759 1.126708 1.126087 1.125189 1.121679 1.119680 1.116701 1.111295 1.103646 1.094750 1.078753 1.052468

0.0609 0.1184 0.2091 0.2544 0.3097 0.414 0.4533 0.5028 0.5928 0.6486 0.7138 0.7554 0.7995 0.8534 0.9011 0.9511

1.234998 1.234108 1.232191 1.230929 1.229049 1.224198 1.221812 1.218257 1.209729 1.202637 1.191787 1.182789 1.170693 1.150453 1.124031 1.079199

0.0524 0.1125

1.167921 1.167754

T = 318.15 K

υ (m·s−1) T = 308.15 K

water (1) + [C6py][Cl] 1.142370 1.142037 1.141226 1.140761 1.140033 1.137606 1.136358 1.134427 1.128249 1.124986 1.119084 1.113124 1.105729 1.090016 1.074987 1.042004 water (1) + [C8py][Cl] 1.122768 1.122558 1.122177 1.121955 1.121630 1.120544 1.119904 1.118951 1.115243 1.113119 1.110013 1.104408 1.096627 1.087699 1.071931 1.046379 water (1) + [C6py][Br] 1.228393 1.227431 1.225435 1.224149 1.222251 1.217393 1.215009 1.211458 1.202970 1.195909 1.185103 1.176186 1.164193 1.144158 1.118078 1.073953 water (1) + [C8py][Br] 1.161501 1.161258

(2) 1569.2 1567.4 1564.8 1563.9 1562.9 1560.3 1559.6 1557.6 1553.2 1550.8 1547.4 1542.8 1539.5 1534.0 1529.9 1524.5 (2) 1483.2 1484.1 1485.3 1486.2 1488.0 1491.7 1493.7 1495.0 1499.8 1501.8 1504.9 1507.1 1509.4 1511.3 1513.2 1515.5 (2) 1589.8 1587.3 1583.4 1580.7 1578.7 1574.6 1572.9 1571.8 1570.1 1565.9 1561.6 1557.1 1551.1 1543.3 1535.9 1528.1 (2) 1507.5 1508.2

ρ (g·cm−3)

T = 318.15 K

x1

1548.7 1548.1 1547.2 1546.6 1546.0 1544.8 1544.1 1543.4 1542.0 1541.4 1540.6 1540.0 1539.4 1538.6 1538.2 1537.2

0.2085 0.2612 0.3065 0.4098 0.4611 0.5075 0.6091 0.6541 0.7031 0.7485 0.8065 0.8545 0.9065 0.9503 0.0524 0.1125 0.2085 0.2612 0.3065 0.4098 0.4611 0.5075 0.6091 0.6541 0.7031 0.7485 0.8065 0.8545 0.9065 0.9503

1452.1 1453.2 1456.7 1458.4 1461.8 1464.8 1466.1 1469.4 1473.8 1477.2 1481.8 1487.1 1493.7 1497.9 1505.5 1515.2

0.0612 0.1098 0.2054 0.2476 0.3088 0.4187 0.4521 0.5065 0.6021 0.6532 0.7042 0.7565 0.8029 0.8577 0.9035 0.9511

1556.2 1555.1 1553.2 1552.2 1551.4 1550.0 1549.3 1548.7 1547.5 1547.1 1546.5 1545.7 1545.0 1543.3 1541.3 1539.1

T = 308.15 K

T = 318.15 K

a

υ (m·s−1) T = 308.15 K

water (1) + [C8py][Br] (2) 1.167441 1.160865 1509.1 1.167108 1.160512 1509.6 1.166665 1.160042 1510.1 1.164793 1.158107 1511.2 1.163239 1.156520 1511.8 1.161354 1.154588 1512.2 1.155071 1.148196 1513.8 1.151025 1.144096 1514.5 1.145399 1.138431 1515.1 1.138701 1.131687 1516.0 1.127146 1.120149 1516.8 1.113645 1.106770 1517.5 1.091898 1.085365 1518.2 1.062048 1.056239 1518.8 water (1) + [C64mpy][Br] (2) 1.214115 1.207389 1586.8 1.213445 1.206615 1583.6 1.211694 1.204800 1579.1 1.210335 1.203431 1575.7 1.208903 1.202014 1573.2 1.204557 1.197716 1568.4 1.201709 1.194913 1565.3 1.198654 1.191880 1563.0 1.189793 1.183068 1557.2 1.184571 1.177868 1553.3 1.177579 1.170891 1547.7 1.169438 1.162782 1542.9 1.155557 1.148975 1537.6 1.139329 1.132884 1533.7 1.112818 1.106738 1529.4 1.076220 1.070752 1524.9 water (1) + [C84mpy][Cl] (2) 1.107620 1.101693 1448.6 1.107564 1.101551 1452.0 1.107515 1.101393 1457.5 1.107464 1.101310 1459.9 1.107297 1.101101 1463.2 1.106441 1.100183 1468.7 1.105967 1.099685 1472.2 1.104889 1.098568 1475.1 1.101754 1.095317 1483.4 1.099162 1.092655 1487.9 1.095661 1.089069 1492.5 1.090744 1.084091 1497.2 1.084748 1.078064 1501.7 1.074574 1.067966 1505.2 1.061607 1.055249 1510.4 1.039582 1.033917 1514.3

T = 318.15 K 1483.4 1485.0 1486.3 1489.1 1490.4 1492.0 1494.8 1497.2 1502.2 1506.7 1512.5 1518.0 1523.5 1529.3 1557.9 1557.0 1555.2 1554.2 1553.2 1551.7 1550.7 1549.8 1547.7 1546.0 1544.7 1543.5 1542.0 1540.5 1539.1 1537.8 1417.4 1421.5 1430.4 1435.3 1439.9 1451.7 1454.6 1461.8 1475.0 1482.3 1490.3 1498.6 1506.7 1513.6 1521.1 1528.4

a

Standard uncertainties u: u(x1) = 0.0001; u(T) = 0.01 K; u(p) = 5 kPa; u(ρ) = 1.8 × 10−6 g·cm−3; and u(υ) = 0.8 m·s−1.

1479.5 1481.4

was calibrated by measuring the density and speeds of sound of ultrapure water (supplied by Anton Paar) and dry air according to the instrument operating instructions. The precision in density measurements was estimated by taking the absolute

mean deviations in the measured densities of four times distilled water in three different sessions. The mean deviations were found to be 1.5 × 10−6 g·cm−3. The accuracy in densities was determined by comparing our measured densities for D



Article

distilled water at different temperatures with the literature data (Table 2). This comparison gave a mean absolute deviation (for our experimental values over literature data) of 1.8 × 10−6 g· cm−3. Hence, the precision and accuracy of the densities reported in the present work are 1.5 × 10−6 and 1.8 × 10−6 g· cm−3, respectively. The precision and accuracy of measured speed of sound were found by similar procedure as mentioned above and are calculated to be ±0.3 and ±0.8 m·s−1, respectively.

Vm E (cm 3·mol−1) = ((x1M1 + x 2M 2)/ρ12 ) − (x1M1/ρ1) − (x 2M 2 /ρ2 )

(1)

where x, M, and ρ are the mole fraction, molar mass, and density of the pure components, respectively. The subscripts 1, 2, and 12 represent water, RTIL, and the binary mixture, respectively. The data for VmE of binary mixtures are listed in Table 4. The composition dependence of VmE values were fitted to Redlich−Kister equation of type

3. RESULTS AND DISCUSSION Densities and Excess Molar Volume (VmE). The experimental data for the density (ρ) and speeds of sound (υ) for pure RTILs and water are listed in Table 2. To our knowledge, there are no reports in the literature on ρ and υ of RTILs studied in this work. RTILs based on [Cnpy][Br] have densities higher than those of [Cnpy][Cl], and densities of RTILs with a given anion increased as the number of methylene units of the alkyl chain increased. These trends are similar to those reported for pyrrolidinium, piperidinium,43,51 pyridinium,52−54 and imidazolium cations.55 The experimental ρ and υ for the water + [C6py][Cl], [C8py][Cl], [C6py][Br], [C8py][Br], [C64mpy][Br], or [C84mpy][Cl]; binary mixtures at T = (308.15 and 318.15) K; and atmospheric pressure are given in Table 3. The changes in the densities of binary mixtures with mole fraction of water at (308.15 and 318.15) K are depicted in Figure 1 and Figure S1 of the Supporting

2

Q E = x1(1 − x1) ∑ ai(1 − 2x1)i i=0

(2)

where QE = VmE (cm3·mol−1), υE (m·s−1), or κSE (TPa−1) and ai is a coefficient. The coefficients of the Redlich−Kister equation were determined by a multiple regression analysis based on the least-squares method. The summary of the coefficients along with the standard deviations between experimental and fitted values of each of these functions is given in Table 5. For the six binary systems studied in the work, the maximum uncertainty in VmE was 0.001 cm3·mol−1. The compositional variations in the form of VmE vs xwater curves for the water + RTIL mixtures at T = (308.15 and 318.15) K are also depicted in Figure 2 and Figure S2, respectively. The volumetric behavior of the four water + [C6py][Cl], [C8py][Cl], [C6py][Br], or [C8py][Br] mixtures in general is similar. VmE values for mixtures with Cl− containing RTILs are negative across the composition. The effect of chain length could be observed only beyond water mole fractions ≥0.28. VmE values for mixtures with C8 chainbased RTILs are more negative than their counterpart C6 chainbased RTIL systems. The introduction of Br− into RTILs also resulted in negative VmE but with decreased magnitude in most of the composition range and in fact became slightly positive in the water-rich region. The (VmE) x1=0.5 are −0.586, −0.271, −0.734, and −0.661 for water + [C6py][Cl], [C6py][Br], [C8py][Cl], or [C8py][Br] at 308.15 K. The increase in temperature resulted in either less negative or more positive VmE values. To our knowledge, there are no literature reports on VmE data of these mixtures, and therefore, we could not make a direct comparison of our data with others. More negative VmE values for water + [C8py][Cl] or [C8py][Br] compared to the mixtures with C6 chain-based RTILs are not entirely unexpected because the increase in the chain length of the alkyl branch of RTILs always decreases the densities. The trends in VmE curves for water + [C6 or C8mim][Cl] or [C6 or C8mim][Br] mixtures were also found to be similar, namely, all negative or negative−positive.32 The less negative (VmE) x1=0.5 for water + Br−-based RTIL mixtures (as compared to water + Cl−-based RTIL mixtures) indicates that the specific attractive interactions are less between water and [Cnpy][Br] becuase Br− ions have a shorter hydration radius and prefer to be ion-paired with the cation over interacting strongly with the water molecules through hydrogen bonding. Therefore, one would expect that the addition of water disrupts the RTIL−RTIL interactions to a lesser extent in these mixtures. To understand the effect of the headgroup of cations on the net interactions in these mixtures, our experimental VmE values for water + [C6py][Cl], [C8py][Cl], or [C84mpy][Cl] at T = 308.15 K are plotted as a function of water mole fraction with the literature data for water + [C6mim][Cl] or [C8mim][Cl]30,32 in Figure 3. It is noticed that the VmE values for water + [Cnpy][Cl] mixtures are more negative than those of water +

Figure 1. Variation of density (ρ) for water + (1) RTIL or (2) binary mixtures at T = 308.15 K: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○)[C8py][Br], (▲) [C84mpy][Cl], and (△) [C64mpy][Br]. The symbols are experimental values, and solid lines represent fitted values derived from the Redlich−Kister correlation (eq 2) of the excess molar volumes of the corresponding mixtures.

Information. The increase in water content (up to xwater ≈ 0.75−0.80) produced a slight decrease in density, and the same was drastically and linearly decreased in water-rich regions. Therefore, the density of aqueous solutions of pyridiniumbased RTILs can be fine-tuned just by adding the right proportion of water. The VmE for the water + RTILs was calculated using the relation E



Article

Table 4. Excess Molar Volume (VmE), Excess Speed of Sound (υE), and Excess Isentropic Compressibilities (κSE) for Water + RTIL Binary Mixtures at T = (308.15 and 318.15) Ka VmE (cm3·mol−1) x1 0.0598 0.1085 0.2068 0.2492 0.3024 0.4166 0.4568 0.5065 0.6137 0.6533 0.7090 0.7521 0.7936 0.8561 0.8966 0.9528 1) + [C8py][Cl] (2) 0.0625 0.1156 0.2085 0.2545 0.3060 0.4127 0.4534 0.4995 0.6103 0.6508 0.6962 0.7542 0.8086 0.8512 0.9009 0.9485 1) + [C6py][Br] (2) 0.0609 0.1184 0.2091 0.2544 0.3097 0.4140 0.4533 0.5028 0.5928 0.6486 0.7138 0.7554 0.7995 0.8534 0.9011 0.9511 1) + [C8py][Br] (2) 0.0524 0.1125 0.2085 0.2612 0.3065 0.4098

T = 308.15 K

υE (m·s−1)

T = 318.15 K

T = 308.15 K water (1) + [C6py][Cl] (2) 6.8 10.3 14.9 16.6 18.9 25.9 29.2 33.5 43.4 46.6 49.8 50.8 50.0 44.2 36.8 20.4

κSE (TPa−1) T = 318.15 K

T = 308.15 K

T = 318.15 K

8.2 12.3 17.0 18.5 20.5 27.1 30.4 35.0 45.7 49.3 53.2 54.5 53.9 48.1 40.2 22.5

−3.7 −5.7 −8.2 −9.1 −10.4 −14.2 −16.0 −18.4 −23.8 −25.6 −27.3 −27.9 −27.4 −24.3 −20.2 −11.2

−4.5 −6.8 −9.3 −10.1 −11.2 −14.9 −16.7 −19.2 −25.1 −27.0 −29.1 −29.9 −29.6 −26.4 −22.1 −12.3

−0.118 −0.209 −0.369 −0.426 −0.486 −0.569 −0.582 −0.585 −0.548 −0.519 −0.466 −0.415 −0.358 −0.261 −0.192 −0.090

−0.087 −0.162 −0.310 −0.367 −0.430 −0.519 −0.533 −0.537 −0.497 −0.466 −0.409 −0.357 −0.300 −0.209 −0.147 −0.064

−0.119 −0.217 −0.380 −0.455 −0.531 −0.663 −0.700 −0.733 −0.761 −0.751 −0.723 −0.662 −0.576 −0.486 −0.355 −0.201

−0.085 −0.168 −0.320 −0.395 −0.473 −0.606 −0.643 −0.673 −0.691 −0.675 −0.643 −0.577 −0.492 −0.407 −0.291 −0.161

12.0 19.1 28.8 33.8 40.1 57.3 65.3 74.9 98.2 105.2 111.0 113.7 109.1 99.1 78.6 47.9

16.8 25.2 34.2 38.3 44.0 62.2 71.6 83.6 115.0 125.4 134.8 140.8 137.5 126.5 101.6 62.6

−6.5 −10.3 −15.6 −18.2 −21.7 −31.0 −35.3 −40.5 −53.0 −56.8 −60.0 −61.4 −58.9 −53.5 −42.4 −25.9

−9.1 −13.6 −18.5 −20.7 −23.8 −33.6 −38.7 −45.2 −62.1 −67.7 −72.8 −76.1 −74.3 −68.3 −54.9 −33.8

−0.107 −0.190 −0.285 −0.314 −0.333 −0.321 −0.302 −0.269 −0.187 −0.129 −0.062 −0.022 0.014 0.044 0.053 0.041

−0.088 −0.16 −0.244 −0.27 −0.287 −0.274 −0.255 −0.222 −0.142 −0.085 −0.019 0.018 0.051 0.076 0.078 0.055

5.1 9.0 14.1 16.5 19.6 26.1 28.7 31.9 37.4 39.8 41.1 40.7 38.7 33.8 26.5 15.2

5.9 9.7 14.1 16.1 18.8 25.4 28.4 32.5 39.9 43.9 46.9 47.3 45.9 40.8 32.5 19.0

−2.8 −5.0 −7.8 −9.1 −10.8 −14.4 −15.8 −17.6 −20.6 −22.0 −22.7 −22.4 −21.3 −18.6 −14.6 −8.4

−3.3 −5.3 −7.7 −8.9 −10.4 −14.0 −15.7 −17.9 −22.0 −24.2 −25.8 −26.1 −25.3 −22.5 −17.9 −10.5

−0.099 −0.234 −0.450 −0.549 −0.617 −0.693

−0.082 −0.203 −0.407 −0.504 −0.569 −0.639

7.8 14.0 21.7 26.2 30.8 44.2

10.3 17.9 25.7 29.7 33.8 46.7

−4.2 −7.6 −11.8 −14.3 −16.8 −24.0

−5.6 −9.7 −13.9 −16.2 −18.4 −25.4

F



Article

Table 4. continued VmE (cm3·mol−1) x1 1) + [C8py][Br] (2) 0.4611 0.5075 0.6091 0.6541 0.7031 0.7485 0.8065 0.8545 0.9065 0.9503 + [C64mpy][Br] (2) 0.0524 0.1125 0.2085 0.2612 0.3065 0.4098 0.4611 0.5075 0.6091 0.6541 0.7031 0.7485 0.8065 0.8545 0.9065 0.9503 + [C84mpy][Cl] (2) 0.0612 0.1098 0.2054 0.2476 0.3088 0.4187 0.4521 0.5065 0.6021 0.6532 0.7042 0.7565 0.8029 0.8577 0.9035 0.9511 a

υE (m·s−1)

κSE (TPa−1)

T = 308.15 K

T = 318.15 K

T = 308.15 K

T = 318.15 K

T = 308.15 K

T = 318.15 K

−0.686 −0.654 −0.508 −0.418 −0.310 −0.208 −0.086 −0.004 0.049 0.054

−0.629 −0.593 −0.439 −0.346 −0.237 −0.134 −0.016 0.058 0.097 0.083

52.3 60.3 77.4 83.7 88.6 90.2 86.9 77.9 60.0 36.9

55.0 63.4 82.3 89.6 95.4 97.9 95.1 85.9 66.6 41.2

−28.5 −32.8 −42.1 −45.5 −48.1 −49.0 −47.2 −42.3 −32.6 −20.1

−29.9 −34.5 −44.7 −48.7 −51.9 −53.2 −51.7 −46.7 −36.2 −22.4

−0.114 −0.210 −0.294 −0.310 −0.309 −0.266 −0.228 −0.189 −0.093 −0.051 −0.009 0.024 0.054 0.065 0.062 0.042

−0.089 −0.168 −0.243 −0.258 −0.259 −0.221 −0.187 −0.149 −0.054 −0.012 0.031 0.064 0.093 0.101 0.090 0.060

4.0 7.7 12.4 14.8 16.8 21.6 24.1 26.2 30.2 31.3 31.8 31.3 29.1 25.4 19.1 11.5

3.8 7.6 12.9 15.8 18.3 24.1 27.0 29.5 34.0 35.2 35.6 34.9 32.2 28.0 20.9 12.6

−2.2 −4.3 −6.9 −8.2 −9.4 −12.0 −13.3 −14.5 −16.7 −17.3 −17.6 −17.4 −16.1 −14.1 −10.6 −6.4

−2.1 −4.2 −7.2 −8.8 −10.1 −13.4 −15.0 −16.4 −18.8 −19.5 −19.7 −19.3 −17.8 −15.5 −11.6 −7.0

−0.082 −0.164 −0.338 −0.411 −0.505 −0.616 −0.632 −0.638 −0.591 −0.538 −0.469 −0.385 −0.303 −0.205 −0.126 −0.055

−0.054 −0.121 −0.280 −0.350 −0.441 −0.550 −0.565 −0.570 −0.518 −0.463 −0.392 −0.309 −0.230 −0.141 −0.075 −0.025

8.8 13.5 20.1 22.8 27.1 37.5 41.3 48.1 60.4 65.9 69.8 71.0 68.9 60.9 48.5 28.9

11.1 16.1 21.1 22.9 26.3 37.2 41.9 50.8 68.3 77.2 84.2 88.0 87.0 78.6 63.6 38.4

−4.8 −7.4 −11.0 −12.4 −14.8 −20.5 −22.6 −26.3 −33.0 −36.0 −38.1 −38.8 −37.6 −33.2 −26.5 −15.8

−6.1 −8.8 −11.5 −12.5 −14.4 −20.3 −22.9 −27.8 −37.3 −42.2 −46.0 −48.1 −47.5 −42.9 −34.7 −21.0

Standard uncertainties u: u(x1) = 0.0001; u(VmE) = 0.001 cm−3·mol−1; u(κSE) = 0.03 TPa−1; and u(υE) = 0.1 m·s−1.

poor accuracy in the experimental densities of the mixtures reported by Li et al.31 The pure state of RTIL molecules56−59 is often characterized by supramolecular organization due to a combination of strong Coulombic interactions between the cation and anion or hydrogen bonding between the cationic ring protons and the anion. Therefore, when RTILs are mixed with water, mainly two types of interactions are expected. The first type contributes to the positive VmE values which arise mainly from the disruption of hydrogen bonding in pure water and/or RTIL. Such types of interactions at water-rich mole fractions and at elevated temperatures for water + [C6mim][Cl],

[Cnmim][Cl] mixtures under comparable conditions. Interestingly, the small positive hump seen at high water mole fractions for water + [Cnmim][Cl] mixtures disappeared in water + [Cnpy][Cl] mixtures. Among the two pyridinium-based cations of pyridinium and 4-methylpyridinium, VmE values of water + [C84mpy][Cl] mixtures are less negative than those of water + [C8py][Cl] mixtures. Water + [C6py][Br] or [C8py][Br] systems were characterized by less negative values (with an exception at low water mole fractions (xwater ≤ 0.25−0.30)). The VmE curve for water + [C6mim][Br]31 is an exception and deviates from the usual trend. This may be attributed to the G



Article

[C2mim][OTf] at T = (308.15 to 348.15) K;26,57 for water + [C4mim][CF3SO3] at T = (293.15 to 318.15) K;37 at high RTIL mole fractions and at T = (298.15 to 343.15) K for water + 1-ethyl-1-methylpyrrolidinium ethylsulfate mixtures;42 and for water + [C4 mim][N(CN)2 ] or [C6 mim][N(CN)2 ] mixtures at T = 298.15 K41 is widely reported. Similarly, water + [Cnmim][BF4] mixtures are always characterized by positive VmE values across the composition and at T = (298.15 to 338.15) K.33,35 The second type of interactions contribute to the contraction in volume and hence result in negative VmE. These intermolecular or heterointeractions are highly dependent on the nature of the anion. To understand the role of counteranions on the overall interactions in RTIL and water mixtures, the VmE values for the mixtures of water with RTILs based on C6 or C8 chain-based pyridinium, 4-methylpyridinium cations and Cl− or Br− anions (our data), or BF4− (literature data46) at T = (308.15 and 318.15) K are shown in Figure 4. It is striking to note that replacing Cl− with Br− or BF4− systematically increased the VmE values (from less negative to all positive) across the composition. Br− and BF4− ions are in general less hydrophilic in nature and hence are closely held to the outer shell around the cations and do not favor the RTIL··· water heterointeractions and hence facilitate large volume expansion. Therefore, it is reasonable to state that the water + RTIL mixtures studied in the present work are dominated by structure making interactions across most of the water mole fraction range, and while structure breaking interactions would prevail at water-rich regions for Br−-based RTIL + water systems. Speed of Sound and Related Properties. Speed of Sound. The graphical variations of experimental speeds of sound (υexp) along with the values calculated from the Redlich− Kister fits of κSE values of the binary mixtures using coefficients from Table 6 as a function of water mole fraction are shown in Figure 5 and Figure S3. The υexp values for C6 chain-based pure RTILs or their mixtures with water are larger than the same for C8 chain-based RTILs or their binary mixtures with water. The increase in the water content resulted in a smooth decrease in υexp for the mixtures containing C6 chain-based RTILs on one hand, and the same increase in the mixtures containing C8 chain-based RTILs on the other. The decreasing or increasing trends became sharp at water mole fraction ≥0.65−0.70. Wu et al.60 also observed that alkyl chain length affects the speed of sound of pure RTILs, depending on the type and nature of the cation and/or the anion. Calculation of Speeds of Sound. The group contribution methods for predicting the speeds of sound in binary systems of water + RTILs still must be evolved and developed. However, theoretical or semiempirical formulations based on the intermolecular free length theory (FLT), the collision factor theory (CFT), and the Junjie (UJ) and Nomoto (UN) equations are widely used to calculate speeds of sound in binary systems of nonelectrolyte mixtures. Therefore, we in the present work attempt to extend these formulations for calculating the speeds of sound in water + RTIL mixtures. The pertinent relations are summarized in Figure S1. The values of speeds of sound calculated are listed in Table S1. CFT and Nomoto equations fairly correlate the speeds of sound (with σ% of 0.17−2.38%), while σ% varied from 5 to 24.68% for correlations between experimental and calculated υ values using UJ and FLT. The large σ% for FLT calculations is expected, as this formulation is applicable for nonassociating

Table 5. Coefficients (ai) of Equation 2 with Standard Deviation s(σ) for the Mathematical Representation of Excess Functions for Water + RTIL Binary Mixtures at T = (308.15 and 318.15) K VmE (cm3·mol−1) T= 308.15 K a0 a1 a2 σ

−2.342 −0.050 0.365 0.001

a0 a1 a2 σ

−2.934 1.174 −0.159 0.001

a0 a1 a2 σ

−1.083 −1.522 0.719 0.001

a0 a1 a2 σ

−2.643 −1.734 2.742 0.001

a0 a1 a2 σ

−0.781 −1.776 0.093 0.001

a0 a1 a2 σ

−2.556 −0.102 1.575 0.001

T= 318.15 K

υE (m·s−1) T= 308.15 K

T= 318.15 K

water (1) + [C6py][Cl] (2) −2.149 131.8 137.3 −0.047 −182.2 −192.0 0.833 192.1 229.4 0.001 0.1 0.1 water (1) + [C8py][Cl] (2) −2.694 300.2 335.1 1.045 −429.1 −548.4 0.425 366.6 564.1 0.001 0.1 0.1 water (1) + [C6py][Br] (2) −0.898 127.0 128.9 −1.505 −130.9 −167.6 0.883 100.8 158.3 0.001 0.1 0.1 water (1) + [C8py][Br] (2) −2.401 235.9 247.9 −1.885 −346.8 −368.7 3.041 287.8 360.8 0.001 0.1 0.1 water (1) + [C64mpy][Br] (2) −0.621 103.4 116.5 −1.709 −90.7 −105.1 0.441 73.1 68.1 0.001 0.1 0.1 water (1) + [C84mpy][Cl] (2) −2.282 189.2 198.6 −0.182 −256.9 −345.4 1.948 245.9 387.4 0.001 0.1 0.1

κSE (TPa−1) T= 308.15 K

T= 318.15 K

−72.2 99.8 −105.9 0.03

−75.3 105.2 −125.7 0.03

−162.1 231.7 −198.3 0.03

−180.9 296.3 −305.0 0.03

−70.1 71.8 −55.3 0.03

−71.1 92.4 −86.9 0.01

−128.3 188.3 −156.2 0.03

−134.8 200.5 −195.6 0.03

−57.3 50.0 −40.7 0.03

−64.6 58.1 −37.6 0.03

−103.5 140.3 −133.7 0.03

−108.5 188.7 −211.1 0.03

Figure 2. Excess molar volume for water + (1) RTIL or (2) binary mixtures at T = 308.15 K: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (△) [C64mpy][Br], and (▲) [C84mpy][Cl]. The symbols are experimental points, and the solid lines correspond to the correlations by the Redlich−Kister correlation (eq 2).

[C8mim][Cl],30,32 or [C2mim][MSO4] at T = (298.15 to 338.15) K;39 across the water mole fractions for water + H



Article

Figure 3. Comparison of VmE values of (a) water (1) + (■) [C6py][Cl], (●) [C8py][Cl], (▲) [C84mpy][Cl], (⊞) [C6mim][Cl] (ref 32), (⊕) [C8mim][Cl] (ref 32), (crossed triangle) [C6mim][Cl] (ref 30), or (*) [C8mim][Cl] (ref 30) at 308.15 K; and (b) water (1) + (□) [C6py][Br], (○) [C8py][Br], (△) [C64mpy][Br], (⬒) [C6mim][Br] (ref 32), (◓) [C8mim][Br] (ref 32), or (triangle with top half black) [C6mim][Br] (ref 46) at 308.15 K.

Figure 4. Comparison of VmE values of water (1) + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (▲) [C84mpy][Cl], (△) [C64mpy][Br], and (ⓧ) [C8py][BF4] (ref 46) at 308.15 K; and (b) water (1) + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (▲) [C84mpy][Cl], (△) [C64mpy][Br], and (ⓧ) [C8py][BF4] (ref 46) at 318.15 K.

Table 6. Molar Volume (VT, cm3·mol−1), Molar Volume at Absolute Zero (Vo, cm3·mol−1), Available Volume (Va, cm3·mol−1), Free Length (Lf) (A0), Surface Area per Mole Collision Factor (S), Molecular Radius (rj) (A0), Molar Heat Capacity (Cp, J·K−1· mol−1), and Isobaric Thermal Expansion Coefficient (k, K−1) of Pure Components at T = (308.15 and 318.15) K T = 308.15 K

a

VT

V0

Va

water [C6py][Cl] [C8py][Cl] [C6py][Br] [C8py][Br] [C64mpy][Br] [C84mpy][Cl]

18.12351 174.18004 201.79098 197.59723 233.04334 212.60517 218.27590

14.92761 149.95159 175.38461 171.87402 204.33007 185.90834 191.44542

3.19590 24.22845 26.40637 25.72321 28.71327 26.69683 26.83048

water [C6py][Cl] [C8py][Cl] [C6py][Br] [C8py][Br] [C64mpy][Br] [C84mpy][Cl]

18.19352 174.77107 202.81875 198.64066 234.31446 213.76405 219.42174

14.85119 149.50616 175.24959 171.77848 204.33861 185.88922 191.41475

3.34233 25.26491 27.56916 26.86218 29.98439 27.87483 28.00699

S

B

rj

CPa

α

0.2582 24.7550 0.4204 115.253 0.4128 127.941 0.4076 126.228 0.4054 141.657 0.4014 133.009 0.3956 135.637 T = 318.15 K

3.8165 3.9329 3.7117 3.9862 3.7723 3.9794 3.6186

4.5101 43.4811 50.3785 49.3375 58.1879 53.0864 54.4944

1.2138 2.5835 2.7134 2.6946 2.8469 2.7612 2.7854

75.3 327.8 376.6 384.8 449.8 412.8 405.4

0.452 0.464 0.503 0.527 0.543 0.529 0.529

0.2709 0.4393 0.4312 0.4258 0.4232 0.4192 0.4130

3.8589 3.8786 3.6266 3.8981 3.7005 3.9841 3.5344

4.5272 43.6307 50.6324 49.5962 58.5031 53.3735 54.7772

1.2154 2.5854 2.7180 2.6993 2.8521 2.7662 2.7902

75.3 333.3 383.5 391.0 457.1 419.5 412.9

0.533 0.473 0.508 0.520 0.545 0.523 0.523

Lf

Y

24.6709 115.024 127.875 126.181 141.660 132.999 135.623

Values for RTILs are calculated from a predictive model based on mass connectivity index.67

I



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Figure 6. Excess speed of sound (υE) for water (1) + RTIL (2) binary mixtures at T = 308.15 K: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (▲) [C84mpy][Cl], and (△) [C64mpy][Br]. The symbols are experimental points, and the solid lines correspond to the correlations by the Redlich−Kister eq 2.

Figure 5. Variation of speed of sound (υ) for water (1) + RTIL (2) binary mixtures at T = 308.15 K: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (▲) [C84mpy][Cl], and (△) [C64mpy][Br]. The symbols are experimental values, and solid lines represent the fitted values derived from the excess isentropic compressibility (κSE) of corresponding mixtures.

binary systems, while water + RTIL binary mixtures display strong nonideal deviations. Excess Speeds of Sound. The definition and calculation of the excess properties based on speeds of sound and isentropic compressibility κs (κs = 1/υ2ρ) always pose a problem because the definition of ideal state for these properties is not straightforward. We calculated the excess speeds of sound using the relation proposed by Douheret et al.:61 υe = υ12 − υ id

(3)

υ id = (ρ id κS id)−1/2 = (VT idM m)1/2

(4)

where Mm is the molar mass of liquid mixtures (x1M1 + x2M2), VTid is the molar volume of the mixture in the ideal state [(x1M1 + x2M2)/ρ12], and similarly, κSid is the isentropic compressibility of the mixture in the ideal state (ϕ1κSid1 + ϕ2κSid2). The υE values for the six binary mixtures at T = (308.15 and 318.15) K are listed in Table 4. The compositional variation of υE for the binary mixtures was fitted to eq 2, and the values of the coefficients along with standard deviation are also given in Table 5. The variations of υE values are plotted as a function of water mole fraction, and the same are shown in Figure 6 and Figure S4. It can be seen that υE values are positive and skewed toward water-rich mole fraction in an asymmetric parabolic shape. The (υE)x1=0.5 followed the order: C6 < C8, irrespective of the Cl− or Br− anion, Br− < Cl−, irrespective of the C6 or C8 chain and the Cl− counterion, C8py > C84mpy and for Br− counterion, and C6py > C64mpy. Isentropic Compressibilities and Excess Isentropic Compressibilities. The variation of isentropic compressibility (κS.12) for the six binary mixtures of water + RTIL at T = (308.15 and 318.15) K is shown as a function of water mole fraction in Figure 7 and Figure S5. At both the temperatures, the κS.12 values for water + C8-based RTILs initially decreased with xwater, reached a broad minima (at xwater > 0.8), and increased with a further increase in the mole fraction of water; while for water + C6-based RTILs, the same increased smoothly with the increase in the mole fraction (until xwater ≥ 0.8) and increased steeply thereafter. Therefore, it can be stated that κS.12 for such RTIL aqueous mixtures is very sensitive to the

Figure 7. Variation of isentropic compressibility (κS) for water (1) + RTIL (2) binary mixtures at T = 308.15 K: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○)[C8py][Br], (△)[C64mpy][Br], and (▲) [C84mpy][Cl]. The lines are guides to the eye.

proportion of water and therefore this property can easily be modulated simply by the addition of water. To understand the type and nature of the interactions between water and RTIL in the mixed state, the excess isentropic compressibilities κSE were calculated from the relation κs E (T Pa −1) = κS − κS id

(5)

where 2

κsid

= (∑ ϕi)[κsi + TVi(αi2)/Cpi] i=1 2

2

2

− T (∑ x iVi )(∑ ϕiαi)2 /∑ x iCpi i=1

i=1

i=1

(6)

where ϕi is the ideal state volume fraction, i.e. ϕi = (xi Vi)/∑ (xi Vi), Cp.i is molar heat capacity of the respective pure components, αi is the isobaric thermal expansion coefficient and κT = (κs + (αi2 T/ρi Cpi)) The αi values of pure components were calculated from the accurate densities measured in the temperature range of 293.15−323.15 K. The J



Article

the same value for water + [C6py][Cl]. The trend was similar in the κSE minima for water + [C8py][Br] and [C6py][Br]. The higher the alkyl chain length of the RTIL, the better the interstitial space (hence better accommodation of water into RTIL structures) and the better the heterointeractions. Partial Excess Molar Quantities. Partial molar volumes also provide a basis for understanding the bulk interactions among the two component mixture systems. Partial molar volumes at infinite dilutions (Viα) are of particular interest to examine the solute−solvent interactions, as solute−solute interactions are assumed to be eliminated at infinite dilution, at which the partial molar and apparent molar volume becomes equal. The partial molar quantities of the components of a mixture vary with the composition because the environment of the molecule in the mixture changes with the composition. Therefore, it is the change in the molecular environment (and the consequent alteration of interactions between molecules) that results in the change of thermodynamic properties of a mixture as its composition is altered. To our knowledge, data on partial excess molar volumes and compressibilities for binary mixtures of water + RTIL mixtures are very scarce in the literature. Our own laboratory recently studied the variation of partial excess molar volumes of water or RTIL in a series of binary mixtures consisting of water + [C4mim][I], [C6mim][I], [C6mim][Cl], [C6mim][Br], [C8mim][Cl], or [C8mim][Br] and [C8mim][I] across the composition at T = (298.15 and 308.15) K.32 The profiles depicting the variation of V̅ 1E and V̅ 2E with the mole fraction of water or corresponding RTIL are shown in Figures 9 and 10 and Figures S7 and S8 at T = (308.15 and

summary of various thermophysical parameters of RTILs and water are listed in Table 6. The compositional variation of κSE was fitted through eq 2. The constants, ai (as determined by a multiple regression analysis based on least-squares method) along with σ values are also listed in Table 5. The maximum uncertainty in the κSE values was 0.03 TPa−1, indicating that the κSE data can best be fitted by using a second-order Redlich−Kister polynomial. The experimental and fitted κSE values for the six binary mixtures of water + RTIL are plotted as a function of water mole fraction at T = (308.15 and 318.15) K in Figure 8 and Figure S6. It can be

Figure 8. Excess isentropic compressibilities (κSE) for water (1) + RTIL (2) binary mixtures at T = 308.15 K: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (△) [C64mpy][Br], and (▲) [C84mpy][Cl]. The symbols are experimental points, and the solid lines correspond to the correlations by the Redlich− Kister eq 2.

noticed that κSE values are negative across the composition, and κSE vs xwater curves are highly asymmetric (with the parabolic shape) with a minima skewed toward water-rich mole fractions. The increase in temperature increased the negative values. As far as we know, there exists no literature data on κSE values for the binary mixtures of the type studied in the present work. However, κSE values for water + [C4eim][CF3SO3] or [C4mim][CF3SO3] and [C4mpyrr][CF3SO3] at T = (278.15 to 338.15) K;62 water + RTILs (1-butyl-3-methylimidazolium dicyanamide or 1-hexyl-3-methylimidazolium dicyanamide, 1butyl-1-methylpyrrolidinium dicyanamide, 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, or 1-methylpyridinium methylsufate and 1,2-diethylpyridinium ethylsulfate) at T = 298.15 K;41 and water + 1-ethyl-3-methylimidazolium triflate system at T = (278.15 to 338.15) K40 were also reported to be negative across the composition. The negative κSE values for the binary systems of water + RTILs based on alkylpyridinium or methylpyridinium cations and Cl− or Br− anions are attributed to the strong water···RTIL interactions. The negative minima indicate a maximum of such a structure having interactions at the corresponding compositions. High water concentrations lead to the dissociation of cation and anion of RTILs and weaken the water···RTIL interactions and hence binary mixtures in water-rich mole fractions are characterized by a sharp decrease in the negative κSE values. The effect of alkyl chain length is very striking. The negative minima in κSE values increased almost by 2.75× for water + [C8py][Cl] compared to

Figure 9. Partial molar excess volume of water (V̅ 1E) plotted against the mole fraction (x1) of water in water + RTIL binary mixtures at T = 308.15 K for the binary mixtures: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (△) [C64mpy][Br], and (▲) [C84mpy][Cl]. Lines are guides to the eye.

318.15) K, respectively. One can notice clear differences in the V̅ 1E values, especially in the water deficient mole fractions for the binary systems of water + [C6py][Br], [C8py][Br], or [C64mpy][Br] on one hand and for the mixtures of water with RTILs consisting of Cl− as counteranion on the other. For the first category of mixtures, V̅ 1E values initially were slightly positive and decreased with an increase in water mole fraction at both the temperatures up to zero and then become negative and remained negative with a minima around xwater = 0.32− K



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Figure 11. Partial excess isentropic compressibilities (κES̅ ·1) of water plotted against the mole fraction (x1) of water in water + RTIL binary mixtures at T = 308.15 K for the binary mixtures: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (△) [C64mpy][Br], and (▲) [C84mpy][Cl]. The lines are guides to the eye.

Figure 10. Partial molar excess volume of RTIL (V̅ 2E) plotted against the mole fraction (x2) of RTILs in water + RTIL binary mixtures at T = 308.15 K for the binary mixtures: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (△) [C64mpy][Br], and (▲) [C84mpy][Cl. The lines are guides to the eye.

0.35. In contrast, the second category of mixtures are always characterized by initial large and negative V̅ 1E values, and the negative magnitude decreased with the increase in the mole fraction of water before reaching a near zero value at water-rich compositions. The increase in temperature resulted in less negative or more positive V̅ 1E values at the corresponding compositions. On the basis of the trends in V̅ 1E vs xwater curves, we can mark three regions depending upon the xwater:xwater = 0−0.2 or 0.2−0.6 and xwater > 0.6. The positive V̅ 1E values in water + Br− ion-based RTILs in the first region indicate that these mixtures are dominated by the loss of water···water association compared to the predominance of water···RTIL interactions in water + Cl− anion-based RTIL mixtures (that are characterized by large and negative V̅ 1E values). In the water-rich region, addition of small amount of RTIL may lead to the breakup of hydrogen bonded water associates and also cause the dissociation of cations and anions of the RTIL. These two effects contribute positively to V̅ 1E values and therefore the noted decrease of negative V̅ 1E or near zero values of V̅ 1E can be accounted for. The profiles of V̅ 2E vs xRTIL are also typical. Irrespective of the nature of the halide ion or carbon chain length (C6 or C8) or pyridinium or methylpyridinium cations, V̅ 2E values are large and negative with a negative minima for water + Br−-based RTIL mixtures appearing in the water mole fraction of about 0.2. The increase in water content decreased the negative V̅ 2E values, which crossed over to positive values especially for water + Br− containing RTILs at RTIL-rich compositions. Such positive humps were marginal only for the water + Cl− ionbased RTIL systems. Therefore, it can be rationalized that RTIL···water interactions in general are dominant in these mixtures except at RTIL-rich compositions. In the later compositions, the presence of small amount of water would lead to the dissociation of cations and anions of RTILs and contribute positively to V̅ 2E values. The κS̅ ·1E or κS̅ ·2E vs xwater or xRTIL values are plotted in Figures 11 and 12 and Figures S9 and S10 at T = (308.15 and 318.15) K. The κS̅ ·1E and κS̅ ·2E values are negative across the compositions for the six binary mixtures and become less negative up to xwater ≈ 0.3 (or xRTIL ≈ 0.70), beyond which they

Figure 12. Partial excess isentropic compressibilities (κES̅ ·2) of RTILs plotted against the mole fraction (x2) of RTILs in water + RTIL binary mixtures at T = 308.15 K for the binary mixtures: water + (■) [C6py][Cl], (●) [C8py][Cl], (□) [C6py][Br], (○) [C8py][Br], (△) [C64mpy][Br], and (▲) [C84mpy][Cl]. The lines are guides to the eye.

converge into near zero values. The negative κS̅ ·1E or κS̅ ·2E values in general indicate that the compressibility of mixtures either in the water-rich region or RTIL deficient regions is smaller than that in their pure ideal state. Water···RTIL heterointeractions dominate in the composition regions rich in either water or RTIL. These results are consistent with the conclusions drawn from VmE or κSE vs xwater curves, as explained above. The values V̅ 1∞, V̅ 2∞, κS̅ ·1∞, and κS̅ ·2∞ for water and RTIL components of binary mixtures are listed in Table 7. An insight into the role of Cl− or Br− anions on the overall volumetric or compressibility properties of pure components in the mixed state was obtained by defining and calculating standard transfer functions using the relation: Ys m → n = Ys∝ (n) − Ys∝ (m)

Ys∝(n)

(7)

∝(m)

where and Ys are the partial molar volumes and compressibilities at infinite dilutions of water or RTIL in the L



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Table 7. Partial Molar Volumes at Infinite Dilution (V̅ 1∞ and V̅ 2∞) and Partial Isentropic Compressibilities at Infinite Dilution (κ̅S·1∞ and κ̅S·2∞) for Water + RTIL Binary Mixtures at T = (308.15 and 318.15) Ka ∞

T (K) 308.15 318.15 308.15 318.15 308.15 318.15 308.15 318.15 308.15 318.15 308.15 318.15

V̅ 1∞ (cm3·mol−1)

V̅ 2∞ (cm3·mol−1)

κS̅ ·1 (TPa−1)

water (1) + [C6py][Cl] (2) 172.253 −278.0 173.502 −306.3 water (1) + [C8py][Cl] (2) 13.856 197.524 −592.2 14.879 199.505 −782.3 water (1) + [C6py][Br] (2) 19.281 198.755 −197.2 19.351 200.131 −250.4 water (1) + [C8py][Br] (2) 19.956 234.876 −472.9 20.718 236.839 −530.9 water (1) + [C64mpy][Br] (2) 19.211 213.693 −148.1 19.722 215.293 −160.3 water (1) + [C84mpy][Cl] (2) 17.244 217.397 −377.5 18.041 219.270 −508.4 16.196 16.924

isentropic compressibility of water. The VmE values of mixtures become more negative with the elongation of the alkyl chain. The effect of the counteranion is striking, and the replacement of the bromide ion with chloride decreased the negative VmE values of the mixtures. Excess speeds of sound of mixtures are positive irrespective of C6 or C8 chains or Cl− or Br− as anions, while excess isentropic compressibilities were all negative across the composition and skewed toward water-rich mole fractions. These typical changes suggest the dominance of structuremaking interactions between short alkyl chain pyridinium-based RTILs and water. The deep minima in κsE values close to xwater values of ≈0.80 indicate the dominance of heterointeractions, which may become diluted with further addition of RTILs. A close examination of the variations in the magnitude of partial excess molar volumes of water at RTIL-rich composition reveals that water···RTIL heterointeractions are predominant in Cl−-based RTIL mixtures, while loss of water···water hydrogen bonds significantly may contribute to the thermophysical behavior of water + Br−-based RTIL mixtures. The addition of water initially cause the dissociation of ions of RTILs, resulting in positive partial excess molar volumes. The standard transfer volumes and isentropic compressibility for water or RTIL in general became positive when bromide ions were replaced with chloride ions, suggesting that bromide ions promote the dissociation of water associates and also disrupt the supramolecular structures of RTILs.

∞

κS̅ ·2 (TPa−1) −277.9 −306.2 −592.0 −782.1 −197.1 −250.2 −472.7 −530.8 −147.9 −160.1 −377.4 −508.2

Standard uncertainties u are u(T) = 0.01 K; u(V̅ i∞) = 0.001 cm−3· mol−1; and u(κS̅ ·i∞) = 0.03 TPa−1.

a

■

binary mixtures, and n and m denote RTILs, as shown in the right and left-hand parts of the arrow marks. The changes in these quantities between respective RTILs are listed in Table 8.

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00460. Relations for calculating speeds of sounds, partial molar volumes of water or RTIL and their excess functions, experimental and calculated speeds of sound (υ12), variation of density (ρ), excess molar volume (VmE), variation of speed of sound (υ), excess speed of sound (υE), variation of isentropic compressibility (κS), excess isentropic compressibilities (κSE), partial molar excess volume of water (V̅ 1E), partial molar excess volume of RTIL (V̅ 2E) as a function of the mole fraction (x1) of water and the mole fraction (x2) of RTILs in binary mixtures, partial excess isentropic compressibilities (κES̅ ·1) of water, partial excess isentropic compressibilities (κES̅ ·2) of RTILs versus the mole fraction (x1) of water and the mole fraction (x2) of RTILs in binary mixtures (PDF)

Table 8. Standard Transfer Volumes (V̅ 1∞tr and V̅ 2∞tr) and Standard Transfer Isentropic Compressibilities (κ̅1∞tr and κ̅2∞tr) in Water + RTIL Binary Mixtures at T = (308.15 and 318.15) K T (K)

V̅ 1∞tr (cm3·mol−1)

308.15 318.15

3.085 2.427

308.15 318.15

V̅ 2∞tr (cm3·mol−1)

[C6py][Cl] → [C6py][Br] 26.502 26.629 [C8py][Cl] → [C8py][Br] 6.100 37.352 5.839 37.334

κ1̅ ∞tr (TPa−1)

κ2̅ ∞tr (TPa−1)

80.5 55.9

80.8 55.9

119.3 251.4

119.4 251.4

ASSOCIATED CONTENT

It can be noted that V̅ 1∞tr or V̅ 2∞tr are positive after replacing the Cl− anion with Br− in C6 or C8 chain-based RTILs. A similar trend was observed for κS̅ ·1∞tr and κS̅ ·2∞tr at both temperatures. Br− ions, being larger in size and polarizability, bind strongly with the cation and prevent not only RTIL··· water heterointeractions but also make water···water interactions weaker. The larger Br− anion also disrupts the supramolecular organization among the RTIL molecules. These two effects contribute to the calculated positive transfer volumes.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

I.R.R. thanks University Grants Commission (UGC), New Delhi for a Junior Research Fellowship (JRF) under the Meritorious Scheme.

■

CONCLUSIONS The binary mixtures of water + RTILs of type [Cnpy][X] or [Cn4mpy][X] (where n = 6 or 8, [X] = Cl− or Br−) at T = (308.15 and 318.15) K exhibit strong nonideality in the form of negative molar excess volumes, positive excess speeds of sound, and negative excess isentropic compressibilities. Addition of a small amount of RTIL increases the density and decreases the

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank the Head of the Department of Chemistry for providing laboratory facilities. M



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Article

Imidazolium Based Ionic Liquids at 298.15 K. J. Chem. Thermodyn. 2008, 40 (4), 695−701. (23) Dong, L.; Zheng, D. X.; Wei, Z.; Wu, X. H. Synthesis of 1,3Dimethylimidazolium Chloride and Volumetric Property Investigations of Its Aqueous Solution. Int. J. Thermophys. 2009, 30 (5), 1480− 1490. (24) Calvar, N.; Gómez, E.; González, B.; Domínguez, A. Experimental Determination, Correlation, and Prediction of Physical Properties of the Ternary Mixtures Ethanol + Water with 1-Octyl-3methylimidazolium Chloride and 1-Ethyl-3-methylimidazolium Ethylsulfate. J. Chem. Eng. Data 2007, 52 (6), 2529−2535. (25) Yang, J. Z.; Lu, X. M.; Gui, J. S.; Xu, W. G.; Li, H. W. Volumetric Properties of Room Temperature Ionic Liquid 2 the Concentrated Aqueous Solutions of {1-Methyl-3-Ethylimidazolium Ethyl Sulfate + Water} in a Temperature Range of 278.2 to 338.2 K. J. Chem. Thermodyn. 2005, 37 (11), 1250−1255. (26) García-Miaja, G.; Troncoso, J.; Romaní, L. Excess Enthalpy, Density and Heat Capacity For Binary Systems of AlkylimidazoliumBased Ionic Liquids + Water. J. Chem. Thermodyn. 2009, 41 (2), 161− 166. (27) Domanska, U.; Pobudkowska, A.; Wisniewska, A. Solubility and Excess Molar Properties of 1,3-Dimethylimidazolium Methylsulfate, or 1-Butyl-3-Methylimidazolium Methylsulfate, or 1-Butyl-3-Methylimidazolium Octylsulfate Ionic Liquids with n-Alkanes and Alcohols: Analysis in Terms of the PFP and FBT Models. J. Solution Chem. 2006, 35 (3), 311−334. (28) Carvalho, P. J.; Regueira, T.; Santos, L. M. N. B. F.; Fernandez, J.; Coutinho, J. A. P. Effect of Water on the Viscosities and Densities of 1-Butyl-3-methylimidazolium Dicyanamide and 1-Butyl-3-methylimidazolium Tricyanomethane at Atmospheric Pressure. J. Chem. Eng. Data 2010, 55 (2), 645−652. (29) Stoppa, A.; Hunger, J.; Buchner, R. Conductivities of Binary Mixtures of Ionic Liquids With Polar Solvents. J. Chem. Eng. Data 2009, 54, 472−479. (30) Gomez, E.; Gonzalez, B.; Domınguez, A.; Tojo, E.; Tojo, J. Dynamic Viscosities of a Series of 1-Alkyl-3-methylimidazolium Chloride Ionic Liquids and Their Binary Mixtures with Water at Several Temperatures. J. Chem. Eng. Data 2006, 51, 696−701. (31) Li, J. G.; Hu, Y. F.; Sun, S. F.; Liu, Y. S.; Liu, Z. C. Densities and Dynamic Viscosities of The Binary System (Water + 1-Hexyl-3Methylimidazolium Bromide) at Different Temperatures. J. Chem. Thermodyn. 2010, 42, 904−908. (32) Sastry, N. V.; Vaghela, N. M.; Macwan, P. M. Densities, Excess Molar and Partial Molar Volumes for Water + 1-Butyl- or, 1-Hexyl- or, 1-Octyl-3-Methylimidazolium Halide Room Temperature Ionic Liquids at T= (298.15 And 308.15) K. J. Mol. Liq. 2013, 180, 12−18. (33) Zhang, S.; Li, X.; Chen, H.; Wang, J.; Zhang, J.; Zhang, M. Determination of Physical Properties for the Binary System of 1-Ethyl3-methylimidazolium Tetrafluoroborate + H2O. J. Chem. Eng. Data 2004, 49, 760−764. (34) Zhou, Q.; Wang, L. S.; Chen, H. P. Densities and Viscosities of 1-Butyl-3-methylimidazolium Tetrafluoroborate + H2O Binary Mixtures from (303.15 to 353.15) K. J. Chem. Eng. Data 2006, 51, 905− 908. (35) Taib, M. M.; Murugesan, T. Density, Refractive Index, and Excess Properties of 1-Butyl-3-methylimidazolium Tetrafluoroborate with Water and Monoethanolamine. J. Chem. Eng. Data 2012, 57, 120−126. (36) Gomez, E.; Gonzalez, B.; Calvar, N.; Tojo, E.; Dominguez, A. Physical Properties of Pure 1-Ethyl-3-methylimidazolium Ethylsulfate and Its Binary Mixtures with Ethanol and Water at Several Temperatures. J. Chem. Eng. Data 2006, 51, 2096−2102. (37) García-Miaja, G.; Troncoso, J.; Romaní, L. Excess Enthalpy, Density, and Heat Capacity for Binary Systems of AlkylimidazoliumBased Ionic Liquids + Water. J. Chem. Thermodyn. 2009, 41, 161−166. (38) Wang, S.; Jacquemin, J.; Husson, P.; Hardacre, C.; Gomes, M. F. C. Liquid−Liquid Miscibility and Volumetric Properties of Aqueous Solutions of Ionic Liquids as a Function of Temperature. J. Chem. Thermodyn. 2009, 41, 1206−1214.

REFERENCES

(1) Rooney, D.; Jacquemin, J.; Gardas, R. Thermophysical Properties of Ionic Liquids. Top. Curr. Chem. 2009, 290, 185−212. (2) Aparicio, S.; Atilhan, M.; Karadas, F. Thermophysical Properties of Pure Ionic Liquids: Review of Present Situation. Ind. Eng. Chem. Res. 2010, 49, 9580−9595. (3) Jacquemin, J.; Ge, R.; Nancarrow, P.; Rooney, D. W.; Costa Gomes, M. F.; Padua, A. A. H.; Hardacre, C. Prediction of Ionic Liquid Properties. I. Volumetric Properties as a Function of Temperature at 0.1 MPa. J. Chem. Eng. Data 2008, 53, 716−726. (4) Jacquemin, J.; Husson, P.; Padua, A. A. H.; Majer, V. Density and Viscosity of Several Pure and Water-Saturated Ionic Liquids. Green Chem. 2006, 8, 172−180. (5) Ye, C.; Shreeve, J. M. Rapid and Accurate Estimation of Densities of Room-Temperature Ionic Liquids and Salts. J. Phys. Chem. A 2007, 111, 1456−1461. (6) Huang, Y.; Zhang, X.; Zhao, Y.; Zeng, S.; Dong, H.; Zhang, S. New Models for Predicting Thermophysical Properties of Ionic Liquid Mixtures. Phys. Chem. Chem. Phys. 2015, 17, 26918−26929. (7) Kohno, Y.; Ohno, H. Ionic Liquid/Water Mixtures: From Hostility to Conciliation. Chem. Commun. 2012, 48, 7119−7130. (8) Turner, M. B.; Spear, S. K.; Huddleston, J. G.; Holbrey, J. D.; Rogers, R. D. Ionic Liquid Salt-Induced Inactivation and Unfolding of Cellulose From Trichoderma Reesei. Green Chem. 2003, 5, 443−447. (9) Sate, D.; Janssen, M. H. A.; Stephens, G.; Sheldon, R. A.; Seddon, K. R.; Lu, J. R. Enzyme Aggregation in Ionic Liquids Studied by Dynamic Light Scattering and Small Angle Neutron Scattering. Green Chem. 2007, 9, 859−867. (10) Fujita, K.; Nakamura, N.; Igarashi, K.; Samejima, M.; Ohno, H. Biocatalytic Oxidation of Cellobiose in an Hydrated Ionic Liquid. Green Chem. 2009, 11, 351−354. (11) Fujita, K.; Nakamura, N.; Murata, K.; Igarashi, K.; Samejima, M.; Ohno, H. Electrochemical Analysis of Electrode-Immobilized Dehydrogenases in Hydrated Choline Dihydrogen Phosphate-Type Ionic Liquid. Electrochim. Acta 2011, 56, 7224−7227. (12) Fujita, K.; Murata, K.; Masuda, M.; Nakamura, N.; Ohno, H. Ionic Liquids Designed For Advanced Applications in Bioelectrochemistry. RSC Adv. 2012, 2, 4018−4030. (13) Canongia Lopes, J. N. A.; Padua, A. A. H. Nanostructural Organization in Ionic Liquids. J. Phys. Chem. B 2006, 110, 3330−3335. (14) Urahata, S. M.; Ribeiro, M. C. Structure of Ionic Liquids of 1Alkyl-3-Methylimidazolium Cations: A Systematic Computer Simulation Study. J. Chem. Phys. 2004, 120, 1855−1863. (15) Wang, Y.; Voth, G. A. Unique Spatial Heterogeneity in Ionic Liquids. J. Am. Chem. Soc. 2005, 127, 12192−12193. (16) Santos, L. M. N. B. F.; Canongia Lopes, J. N.; Coutinho, J. A. P.; Esperanca, J. M. S. S.; Gomes, L. R.; Marrucho, I. M.; Rebelo, L. P. N. Ionic Liquids: First Direct Determination of their Cohesive Energy. J. Am. Chem. Soc. 2007, 129, 284−285. (17) Cabeza, O.; García-Garabal, S.; Segade, L.; Domínguez-Perez, M.; Rilo, E.; Varela, L. M. Ionic Liquids: Theory, Properties, New Approaches; Kokorin, A., Ed.; In Tech, 2011. (18) Ge, M. L.; Ren, X. G.; Song, Y. J.; Wang, L. S. Densities and Viscosities of 1-Propyl-2,3-dimethylimidazolium Tetrafluoroborate + H2O at T = (298.15 to 343.15) K. J. Chem. Eng. Data 2009, 54 (4), 1400−1402. (19) Yang, J. Z.; Li, J. B.; Tong, J.; Hong, M. Application of PitzerSimonson Theory and Pitzer-Simonson-Clegg Theory to Aqueous Ionic Liquid PMIBF4. Acta Chim Sinica 2007, 65, 655−659. (20) Gaillon, L.; Sirieix-Plenet, J.; Letellier, P. Volumetric Study of Binary Solvent Mixtures Constituted by Amphiphilic Ionic Liquids at Room Temperature (1-Alkyl-3-Methylimidazolium Bromide) and Water. J. Solution Chem. 2004, 33 (11), 1333−1347. (21) Zafarani-Moattar, M. T.; Shekaari, H. Apparent Molar Volume and Isentropic Compressibility of Ionic Liquid 1-Butyl-3-Methylimidazolium Bromide In Water, Methanol, and Ethanol at T = (298.15 To 318.15) K. J. Chem. Thermodyn. 2005, 37 (10), 1029−1035. (22) Gardas, R. L.; Dagade, D. H.; Terdale, S. S.; Coutinho, J. A. P.; Patil, K. J. Acoustic and Volumetric Properties of Aqueous Solutions of N



Article

(39) Bhattacharjee, A.; Varanda, C.; Freire, M. G.; Matted, S.; Santos, L. M. N. B. F.; Marrucho, I. M.; Coutinho, J. A. P. Density and Viscosity Data for Binary Mixtures of 1-Alkyl-3-methylimidazolium Alkylsulfates + Water. J. Chem. Eng. Data 2012, 57, 3473−3482. (40) Vercher, E.; Orchilles, V.; Miguel, P. J.; Martınez-Andreu, A. Volumetric and Ultrasonic Studies of 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate Ionic Liquid with Methanol, Ethanol, 1Propanol and Water at Several Temperatures. J. Chem. Eng. Data 2007, 52, 1468−1482. (41) Gonzalez, E. J.; Dominguez, A.; Macedo, E. A. Physical and Excess Properties of Eight Binary Mixtures Containing Water and Ionic Liquids. J. Chem. Eng. Data 2012, 57, 2165−2176. (42) Królikowska, M.; Lipiński, P.; Maik, D. Density, Viscosity and Phase Equilibria Study of {Ethylsulfate-Based Ionic Liquid+ Water} Binary Systems as a Function of Temperature and Composition. Thermochim. Acta 2014, 582, 1−9. (43) Gardas, R. L.; Costa, H. F.; Freire, M. G.; Carvalho, P. J.; Marrucho, I. M.; Fonseca, I. M. A.; Ferreira, A. G. M.; Coutinho, J. A. P. Densities and Derived Thermodynamic Properties of Imidazolium-, Pyridinium-, Pyrrolidinium-, and Piperidinium-Based Ionic Liquids. J. Chem. Eng. Data 2008, 53, 805−811. (44) Wang, J. Y.; Zhang, X. J.; Hu, Y. Q.; Qi, G. D.; Liang, L. Y. Properties of N-Butylpyridinium Nitrate Ionic Liquid and its Binary Mixtures With Water. J. Chem. Thermodyn. 2012, 45, 43−47. (45) García-Miaja, G.; Troncoso, J.; Romaní, L. Density and Heat Capacity as a Function of Temperature for Binary Mixtures of 1-Butyl3-Methylpyridinium Tetrafluoroborate + Water, + Ethanol, And + Nitromethane. J. Chem. Eng. Data 2007, 52, 2261−2265. (46) Mokhtarani, B.; Sharifi, A.; Mortaheb, H. R.; Mirzaei, M.; Mafi, M.; Sadeghian, F. Density and Viscosity of Pyridinium-Based Ionic Liquids and their Binary Mixtures with Water at Several Temperatures. J. Chem. Thermodyn. 2009, 41, 323−329. (47) Docherty, K. M.; Dixon, J. K.; Kulpa, C. F., Jr. Biodegradability of Imidazolium and Pyridinium Ionic Liquids by an Activated Sludge Microbial Community. Biodegradation 2007, 18, 481−493. (48) Harjani, J. R.; Singer, R. D.; Garcia, M. T.; Scammells, P. J. Biodegradable Pyridinium Ionic Liquids: Design, Synthesis and Evaluation. Green Chem. 2009, 11, 83−90. (49) Gathergood, N.; Scammells, P. J. Design and Preparation of Room-Temperature Ionic Liquids Containing Biodegradable Side Chains. Aust. J. Chem. 2002, 55 (9), 557−560. (50) Gathergood, N.; Garcia, M. T.; Scammells, P. J. Biodegradable Ionic Liquids: Part I. Concept, Preliminary Targets and Evaluation. Green Chem. 2004, 6, 166−175. (51) Sanchez, L. G.; Espel, J. R.; Onink, F.; Meindersma, G. W.; Haan, A. B. D. Density, Viscosity, and Surface Tension of Synthesis Grade Imidazolium, Pyridinium, and Pyrrolidinium Based Room Temperature Ionic Liquids. J. Chem. Eng. Data 2009, 54, 2803−2812. (52) Yunus, N. M.; Mutalib, M. I. A.; Man, Z.; Bustam, M. A.; Murugesan, T. Thermophysical Properties of 1-Alkylpyridinum Bis(trifluoromethylsulfonyl)imide Ionic Liquids. J. Chem. Thermodyn. 2010, 42, 491−495. (53) Guerrero, H.; Martín, S.; Gregorio, V. P.; Lafuente, C.; Bandres, I. Volumetric Characterization of Pyridinium-Based Ionic Liquids. Fluid Phase Equilib. 2012, 317, 102−109. (54) Bittner, B.; Wrobel, R. J.; Milchert, E. Physical Properties of Pyridinium Ionic Liquids. J. Chem. Thermodyn. 2012, 55, 159−165. (55) Gardas, R. L.; Freire, M. G.; Carvalho, P. J.; Marrucho, I. M.; Fonseca, I. M. A.; Ferreira, A. G. M.; Coutinho, J. A. P. PpT Measurements of Imidazolium-Based Ionic Liquids. J. Chem. Eng. Data 2007, 52, 1881−1888. (56) Moreno, M.; Castiglione, F.; Mele, A.; Pasqui, C.; Raos, G. Interaction of Water with the Model Ionic Liquid [bmim][BF4]: Molecular Dynamics Simulations and Comparison with NMR Data. J. Phys. Chem. B 2008, 112, 7826−7836. (57) Liu, W.; Zhao, T.; Zhang, Y.; Wang, H.; Yu, M. The Physical Properties of Aqueous Solutions of the Ionic Liquid [BMIM][BF4]. J. Solution Chem. 2006, 35, 1337−1346.

(58) Cammarata, L.; Kazarian, S. C.; Salter, P. A.; Welton, T. Molecular States of Water in Room Temperature Ionic Liquids. Phys. Chem. Chem. Phys. 2001, 3, 5192−5200. (59) Singh, T.; Kumar, A. Cation−Anion−Water Interactions in Aqueous Mixtures of Imidazolium Based Ionic Liquids. Vib. Spectrosc. 2011, 55, 119−125. (60) Wu, K. J.; Chen, Q. L.; He, C. H. Speed of Sound of Ionic Liquids: Database, Estimation, and its Application for Thermal Conductivity Prediction. AIChE J. 2014, 60 (3), 1120−1131. (61) Douheret, G.; Davis, M. I.; Reis, J. C. R.; Blandamer, M. Isentropic CompressibilitiesExperimental Origin and the Quest for their Rigorous Estimation in Thermodynamically Ideal Liquid Mixtures. ChemPhysChem 2001, 2, 148−161. (62) Vercher, E.; Miguel, P. J.; Llopis, F. J.; Orchillés, A. V.; MartínezAndreu, A. Volumetric and Acoustic Properties of Aqueous Solutions of Trifluoromethanesulfonate-Based Ionic Liquids at Several Temperatures. J. Chem. Eng. Data 2012, 57, 1953−1963. (63) Spieweck, F.; Bettin, H. Review: Solid and liquid density determination. Tech. Mess. 1992, 59, 285−292. (64) Landolt-Bornstein: Neue Serie, Band 5, Molekularakustik Temperaturskala von 1990. PTB-mitt. 1990, 100, 195−196. (65) George, J.; Sastry, N. V. Densities, Viscosities, Speeds of Sound, and Relative Permittivities for Water + Cyclic Amides (2Pyrrolidinone, 1-Methyl-2-pyrrolidinone, and 1-Vinyl-2-pyrrolidinone) at Different Temperatures. J. Chem. Eng. Data 2004, 49 (2), 235−242. (66) Cibulka, I. Partial Molar Isentropic Compressions of Selected Cyclic Ethers at Infinite Dilution in Water at Temperatures T = (278 to 318) K and Atmospheric Pressure. J. Chem. Eng. Data 2013, 58, 1249−1254. (67) Valderrama, J. O.; Martinez, G.; Rojas, R. E. Predictive Model for the Heat Capacity of Ionic Liquids Using the Mass Connectivity Index. Thermochim. Acta 2011, 513, 83−87.

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