Physical Properties of Ionic Liquids Consisting of 1-Butyl-3

Article pubs.acs.org/jced

Physical Properties of Ionic Liquids Consisting of 1‑Butyl-3propanenitrile- and 1‑Decyl-3-propanenitrile Imidazolium-Based Cations: Temperature Dependence and Influence of the Anion Abobakr Khidir Ziyada*,†,§ and Cecilia Devi Wilfred‡ †

Chemical Engineering Department, ‡Fundamental and Applied Sciences Department, Universiti Teknologi Petronas, Tronoh-31750, Perak, Malaysia ABSTRACT: The effect of cationic and anionic chain lengths and temperature dependence of physical properties for a new series of 1-butyl3-propanenitrile and 1-decyl-3-propanenitrile imidazolium-based ionic liquids were studied in a broad range of temperature (293.15 to 353.15) K at atmospheric pressure. The present ILs show lower densities, higher viscosities, and comparable values of refractive index compared to those of analogous nitrile-functionalized ILs with different anions. The thermal expansion coefficient, compressibility coefficient, and molar refraction were calculated from the experimental values of density and refractive index. These ILs show a weak temperature dependency of the thermal expansion coefficient.

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functionalized ILs.8,9 The scope involved a detailed study on the effect of alkyl chains of cation and anion and temperature (in the range between 293.15 K and 353.15 K) on the physical properties of a series of 1-butyl-3-propanenitrile imidazolium [CNC 2 Bim] and 1-decyl-3-propanenitrile imidazolium [CNC2Dim]-based RTILs incorporating different sulfonatebased anions such as dioctysulfosuccinate (DOSS), dodecylsulfate (DDS), benzenesulfonate (BS), sulfobenzoic acid (SBA), and trifluoromethanesulfonate (TFMS).

INTRODUCTION Room temperature ionic liquids (RTILs) are liquid organic salts, which are generally composed of bulky asymmetric organic cations (pyridinium, imidazolium, phosphonium, ammonium) and inorganic or organic anions (Cl−, BF4−, PF6−, CF3SO3−, NTf2−) with different molecular sizes and are liquid at room temperature.1 RTILs can be tailored for specific application by careful selection of the ions or by incorporating new functionalities such as hydroxyl, carboxylic, amine, and fluorous groups.2,3 Further development of RTILs and their applications often require syntheses of new ionic liquids with suitable properties. The advantage of imidazolium-based functionalized ILs over most of the other functionalized ILs is that their properties can be tuned and controlled to a greater extent resulting in an increasing number of applications.4 The class of imidazolium-based nitrile functionalized ILs have special properties and potential applications in many areas such as catalytic reactions, lithium battery, dye-sensitized solar cells extraction, and dissolution.5,6 The synthesis of imidazolium-based nitrile functionalized ILs is generally facile and has a good yield, it starts from alkylimidazoles with nitrile functionalized alkyl halide using the quaternization method.5,6 Alkylmidazoles with short alkyl chains are often commercially available which results in the synthesis of only the imidazoliumbased nitrile functionalized ILs with short alkyl chains. The effect of the variation in alkyl chain in a large matrix of ILs, on its thermophysical properties such as density, viscosity, and refractive index are imperative toward commercial applications. Imidazolium-based nitrile functionalized ILs with long alkyl chain length attached to the N-3 of the imidazolium ring have been synthesized recently by our group.7 We further added long alkyl chain sulfonate-based anions on these nitrile © 2014 American Chemical Society

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EXPERIMENTAL SECTION

Synthesis of RTILs. The synthesis of the presently studied ionic liquids involves three steps: (i) incorporation of the nitrile group with imidazole, (ii) the formation of the desired cation, and finally (iii) the anion exchange to form the final desired product. Nitrile functionalized IL was synthesized by a direct quaternization reaction of the imidazole-bearing nitrile group with 1-bromobutane or 1-bromoocatne as reported recently.7 Then, a metathesis reaction was carried out using DOSS, DDS, BS, TFMS and SBA anions to synthesize [CNC2Bim]DOSS, [CNC 2 Bim]DDS, [CNC 2 Bim]BS, [CNC 2 Bim]TFMS, [CNC2Dim]DOSS, [CNC2Dim]DDS, and [CNC2Bim]SBA. 1 H and 13C NMR spectra, Fourier transform infrared (FTIR) and elemental analysis were used to confirm the structures of the synthesized RTILs, and the characterizations have been reported recently by our group.7,8 Received: September 20, 2013 Accepted: February 23, 2014 Published: March 6, 2014 1232

dx.doi.org/10.1021/je400849a | J. Chem. Eng. Data 2014, 59, 1232−1239

Journal of Chemical & Engineering Data

Article

Table 1. Molecular Weight (Mw), Mass Fraction of Water (wH2O) and Mass Fraction of Bromide T/K −1

Mw/(g·mol ) wH2O (106w) wBr (106w)

[CNC2 Bim]DOSS

[CNC2 Bim]DDS

[CNC2 Bim]BS

[CNC2 Bim]TFMS

[CNC2 Dim]SBA

[CNC2 Dim]DOSS

[CNC2 Dim]DDS

600.83 198

444.65 170

336.43 182

327.32 179

464.60 212

684.99 184

528.83 235

78

66

73

103

Characterization. The water content measurements of the present RTILs were conducted using the coulometric Karl Fischer titrator, DL 39 (Mettler Toledo) with CombiCoulomat fritless Karl Fischer reagent (Merck). The measurement for each IL was made in triplicate, and the average values are reported. Ion chromatography (Metrohm model 761 Compact IC) with (150·4.0) mm analytical column (Metrosep A Supp 5−150) and (5.0·4.0) mm guard column (Metrosep A Supp 4/ 5) was used to determine the bromide content. The samples were diluted in acetonitrile, and the results were analyzed using Metrodata IC Net 2.3 software. Density and Viscosity Measurements. Values of density and viscosity of the present RTILs were measured using a Stabinger viscometer (Anton-Paar model SVM3000) at atmospheric pressure and over the temperature range (293.15 to 353.15) K. The temperature was controlled to within ± 0.01 °C. The reproducibility of the density and viscosity measurements are ± 5·10−4 g·cm−3 and 0.35 %, respectively. The instrument was calibrated using standard calibration fluid provided by the supplier followed by ionic liquids with known density and viscosity. Refractive Index Measurements. The refractive index values of the present RTILs were determined using ATAGO programmable digital refractometer (RX-5000 alpha) with a measuring accuracy of ± 4·10−5 in a temperature range (298.15 to 333.15) at atmospheric pressure. The temperature of the apparatus was controlled to within ± 0.05 °C. Pure organic solvents with known refractive indices were used to calibrate and check the instrument before each series of measurements. Dried samples kept in desiccators were directly placed into the measuring cell. Reproducibility of the results was confirmed by performing three experiments for each IL in the whole temperature range studied in the present work.

74

83

62

Figure 1. Plot of density values (ρ) of [C2CNBim]X and [C2CNDim]X as a function of temperature. ■, [C2CNBim]DOSS; ×, [C2CNBim]DDS; ◇, [C2CNBim]BS; ●, [C2CNBim]TFMS; ⊗, [C2CNDim]SBA: △, [C2CNDim]DOSS; ○, [C2CNDim]DDS.

showed that the increase of the anion molecular weight does not directly correspond to the rise in the density values for the present ILs and a similar behavior for other imidazolium-based ILs was observed by Sańchez21 and Gardas11 for imidazolium cations, where the increase of the liquid density does not directly correspond to a rise in the molecular weight of the anion. Compared with the density of the [CNC2Bim]Br and [CNC2Dim]Br ILs (2.25 and 1.90 g·cm−3), the present RTILs incorporating DOSS, DDS, SBA, and BS anions show lower density values while the TFMS anion shows higher values of density. Moreover, the densities of the investigated RTILs are lower compared with the other nitrile-functionalized ILs reported by Zhao et al.,5 the densities of [C2CN Mim]BF4, [C3CN Mim]BF4, and [C4CN Mim]Cl, are 2.15, 1.87, and 1.61 g·cm−3, respectively. The effect of each anion on the density values was studied taking into account that the present RTILs are incorporating the same cations and all the anions are based on the SO3 group; the differences in density are due to the contributions of the anions and alkyl chains of cations. The lower densities of DOSS and DDS anions might be due to the presence of long alkyl chains compared to the other anions which prohibits the formation of tight molecular assemblies leading to a lower density as reported by Benjamin, H. et al.12 In general, the addition of −CH2− groups to the alkyl chain of cation decreases the density, while the larger hydrophilic anions and decreases of the alkyl chain length of the anion increase the density of the IL. This may be due to strong molecular attraction and strong hydrogen bonding which increases molecular agglomeration.13 The densities of the present ILs are lower compared to those of the pyrrolidinium-based nitrile functionalized ILs, for 1cyanoalkyl-1-methylpyrrolidinium bistriflimide ([C1CnCNPyr][NTf2], n = 1, 2, 3, 5) ILs the densities are in the range from

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RESULTS AND DISCUSSION The water content and bromide content values (as mass fraction) of the synthesized ILs are presented in Table 1 and are comparable to other nitrile functionalized ILs.10 The effects of impurities (especially water and halide) on the physical properties of ILs are well-known. The presence of water and halide may have a large influence on density, viscosity, refractive index, and thermal stability. The estimated purity values for the present synthesized ionic liquids, namely, [CNC2Bim]DOSS, [CNC 2 Bim]DDS, [CNC 2 Bim]BS, [CNC 2 Bim]TFMS, [CNC2Dim]SBA, [CNC2Dim]DOSS, and [CNC2Dim]DDS, are 98.2 %, 97.5 %, 97.4 %, 97.0 %, 96.8 %, 96.9 %, and 97.0 %, respectively. The experimental density values for the studied RTILs are shown in Figure 1 and presented in Table 2 . [CN C2Bim] TFMS has the highest value and [CNC2Dim]DOSS has the lowest value of density among the studied RTILs. The density values for the [C2CNCnim]-based RTILs decreased in the following order: [CNC 2 Bim]TFMS, [CNC 2 Bim]BS, [CNC 2 Dim]SBA, [CNC 2 Bim]DDS, [CNC 2 Bim]DOSS, [CNC2Dim]DDS, and [CNC2Dim]DOSS. These results 1233



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Table 2. Experimental Density Values, ρ, for [C2CNCnim]X as a Function of Temperature at Pressure p = 0.1 MPaa ρ/(g·cm−3)

a

T/K

[CNC2 Bim]DOSS

[CNC2 Bim]DDS

[CNC2 Bim]BS

[CNC2 Bim]TFMS

[CNC2 Dim]SBA

[CNC2 Dim]DOSS

[CNC2 Dim]DDS

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15

1.1146 1.1105 1.1071 1.1037 1.0992 1.0963 1.0931 1.0886 1.0842 1.0804 1.0761 1.0726 1.0689

1.1289 1.1232 1.1198 1.1161 1.1122 1.1089 1.1050 1.1019 1.0977 1.0936 1.0897 1.0863 1.0822

1.2403 1.2368 1.2334 1.2302 1.2263 1.2237 1.2203 1.2171 1.2135 1.2101 1.2071 1.2044 1.2013

1.3363 1.3324 1.3286 1.3250 1.3213 1.3177 1.3141 1.3105 1.3086 1.3032 1.2996 1.2959 1.2922

1.1366 1.1335 1.1299 1.1263 1.1232 1.1198 1.1162 1.1127 1.1095 1.1059 1.1026 1.0993 1.0958

1.0392 1.0358 1.0327 1.0297 1.0271 1.0246 1.0223 1.0201 1.0179 1.0158 1.0136 1.0114 1.009

1.0530 1.0504 1.0469 1.0433 1.0418 1.0386 1.0361 1.0343 1.0325 1.0299 1.0273 1.0258 1.0239

Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, and u(ρ) = 5·10−4 g·cm−3.

Table 3. Experimental Viscosity Values, η, For [C2CNCnim]X as a Function of Temperature at Pressure P = 0.1 MPaa η/(mPa·s)

a

T/K

[CNC2 Bim]DOSS

[CNC2 Bim]DDS

[CNC2 Bim]BS

[CNC2 Bim]TFMS

[CNC2 Dim]SBA

[CNC2 Dim]DOSS

[CNC2 Dim]DDS

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15

19758 12006 7458 4462 2843 1829 1203 786 497 333 238 154 102

13007 7875 4746 2938 1740 1144 768 485 338 235 162 114 76

4612 2752 1806 1203 792 505 321 214 152 109 78 54 38

1097 719 489 336 227 161 119 85 61 46 35 25 19

17650 11449 7159 4606 3028 1977 1431 944 623 431 294 198

13807 8495 5339 3536 2355 1548 1178 811 537 389

16145 10417 6231 3951 2583 1757 1252 904 588 418 296

Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, and the relative standard uncertainty for viscosity ur(η) = 3.5·10−3 mPa·s.

Figure 2. Plot of viscosity values (η) of [C2CNBim]X and [C2CNDim]X as a function of temperature: ■, [C2CNBim]DOSS; ×, [C2CNBim]DDS; ◇, [C2CNBim]BS; ●, [C2CNBim]TFMS; ⊗, [C2CNDim]SBA: △, [C2CNDim]DOSS; ○, [C2CNDim]DDS.

Figure 3. Arrhenius plot of viscosity values of [C2CNBim]X and [C2CNDim]X as a function of 1/T: ■, [C2CNBim]DOSS; ×, [C2CNBim]DDS; ◇, [C2CNBim]BS; ●, [C2CNBim]TFMS; ⊗, [C2CNDim]SBA: △, [C2CNDim]DOSS; ○, [C2CNDim]DDS.

1.157 g·cm−3 to 1.435 g·cm−3.14 The lower densities when compared to the other nitrile-functionalized ILs are due to the presence of large anions and long alkyl chain of the cations

(butyl and decyl). Figure 1 in the Supporting Information shows that density decreases linearly with increasing temperature as is expected. As general for the ILs, the linear 1234



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Table 4. Arrhenius Parameters Obtained From Plotting of ln η against 1/T and Standard Deviations (SD) Calculated Using Equation 9 ILs

η∞/(mPa·s−1·10−3)

Eη/(J.mol−1·103)

SD

[C2CNBim]DOSS [C2CNBim]DDS [C2CNBim]BS [C2CNBim]TFMS [C2CNDim]SBA [C2CNDim]DOSS [C2CN Dim]DDS

0.114 0.128 0.189 0.705 0.281 0.365 0.335

32.63 31.84 29.82 25.07 30.84 30.83 30.73

0.0116 0.0137 0.0130 0.0083 0.0275 0.0155 0.0166

performance is common as a result of a large temperature difference between their working temperature range and their critical temperatures.16 The viscosity values of [CNC2Bim]TFMS, [CNC2Bim]BS, [CNC 2 Bim]DDS, [CNC 2 Dim]SBA, [CNC 2 Bim]DOSS, [CNC2Dim]DDS, and [CNC2Dim]DOSS ILs at atmospheric pressure and over the temperature range from 293.15 K to 353.15 K are presented in Table 3. The [CNC2Dim]DOSS IL showed highest viscosity while [CNC2Bim]TFMS showed lowest viscosity and in general the viscosity increases with increasing molecular weight or alkyl chain17 as shown in Figure 2. The RTILs investigated show higher viscosities compared with other nitrile functionalized ILs; for [C3CN Mim]BF4 and [C4CN MIm]Cl the viscosities are 352 and 5222 mPa·s, respectively.5,6 These RTILs show lower viscosity compared with the same RTILs incorporating a bromide anion; for [C2CNBim]Br the viscosity at 308.15 K is 19103 mPa·s, while for [C2CNDim]Br it is 16702 mPa·s at 313.15 K.7 The high viscosity of the RTILs incorporating the DOSS and DDS anions may be due to the large volume of the anions which results in low ion mobility.18 The viscosity values of the investigated RTILs show that higher anion size results in higher viscosity, which is in agreement with the literature.15 As shown in Figure 2, the viscosity values decrease as temperature increases. The viscosities of the present ILs are higher compared to the other nitrile-functionalized ILs (for [C1CnCNPyr][NTf2] (n = 1, 2, 3, 5), where the viscosities are in the range from 345 cP to 540 cP as reported by Nockeman, P. and co-workers.14 The high viscosity of the present ILs can also be explained by the increased electrostatic interactions between the cation and anion. The imidazolium cations and sulfonate anions are joined together by a hydrogen bonding network19 which resulted in increased viscosity. Low anion weight and low basicity (for less

Figure 4. Plot of refractive index values (nD) of [C2CNBim]X and [C2CNDim]X as a function of temperature: ■, [C2CNBim]DOSS; ×, [C2CNBim]DDS; ◇, [C2CNBim]BS; ●, [C2CNBim]TFMS; ⊗, [C2CNDim]SBA: △, [C2CNDim]DOSS; ○, [C2CNDim]DDS.

basic anion, the van der Waals forces dominates over the Hbonding due to better charge delocalization and this will reduce the viscosity of the IL) are necessary to obtain ILs with low viscosity.20 The influence of temperature on viscosity for the studied ILs is shown in Figure 2. As can be observed, a rise in temperature caused a significant reduction in the viscosities of the synthesized ILs. An increase in temperature diminishes the strength of interactions between the cation and anion and should result in a lower viscosity.20 Variation of the viscosity with temperature provides information on the structure of the ILs.21 The plots of the temperature dependence of viscosity for all the studied ILs over the temperature range 293.15 K to 353.15 K were fitted with the logarithmic form of the Arrhenius eq 1. ln η = ln η∞ + Eη /RT

(1)

where η is the viscosity, η∞ is the viscosity at infinite temperature, Eη is the activation energy for viscous flow, R is the universal gas constant, and T is temperature in Kelvin. The activation energies for viscous flow (Eη) and the viscosities at infinite temperature (η∞) were calculated from the slopes and intercepts (respectively) of the Arrhenius plots (Figure 3). Table 4 shows the Arrhenius parameters obtained from the Arrhenius plots together with the standard deviations (SD). The standard deviations were calculated using the eq 9.

Table 5. Experimental Refractive Indices Values, nD, for [C2CNCnim]X as a Function of Temperature at Pressure p = 0.1 MPaa nD

a

T/K

[CNC2 Bim]DOSS

[CNC2 Bim]DDS

[CNC2 Bim]BS

[CNC2 Bim]TFMS

[CNC2 Dim]SBA

[CNC2 Dim]DOSS

[CNC2 Dim]DDS

298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

1.48048 1.47926 1.47792 1.47653 1.47504 1.47361 1.47216 1.47070

1.48791 1.48619 1.48443 1.48232 1.48009 1.47842 1.47695 1.47487

1.53378 1.53237 1.53113 1.52975 1.52824 1.52684 1.52544 1.52403

1.53523 1.53357 1.53216 1.53072 1.52925 1.52795 1.52652 1.52515

1.51306 1.51163 1.50998 1.50871 1.50706 1.50582 1.50450 1.50322

1.47610 1.47476 1.47345 1.47203 1.47055 1.46909 1.46761 1.46601

1.47447 1.47296 1.47142 1.46972 1.46813 1.46678 1.46532 1.46391

Standard uncertainties u are u(T) = 0.05 K, u(p) = 0.01 MPa, and u(nD) = 5·10−4. 1235



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Table 6. Thermal Expansion Coefficients (αP) for [CNC2Cnim]X as a Function of Temperature αP·104/(K−1) T/K

[CNC2 Bim]DOSS

[CNC2 Bim]DDS

[CNC2 Bim]BS

[CNC2 Bim]TFMS

[CNC2 Dim]SBA

[CNC2 Dim]DOSS

[CNC2 Dim]DDS

293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15

6.91 6.83 6.86 6.88 6.90 6.93 6.95 6.98 7.00 7.02 7.05 7.07 7.10

6.56 6.59 6.61 6.63 6.65 6.67 6.70 6.72 6.74 6.76 6.79 6.81 6.83

5.24 5.25 5.27 5.28 5.29 5.31 5.32 5.34 5.35 5.37 5.38 5.39 5.41

5.47 5.48 5.50 5.51 5.53 5.54 5.56 5.57 5.59 5.61 5.62 5.64 5.65

5.98 6.00 6.01 6.03 6.05 6.07 6.09 6.11 6.13 6.14 6.16 6.18 6.20

4.72 4.74 4.75 4.76 4.77 4.78 4.79 4.80 4.82 4.83 4.84 4.85 4.86

4.56 4.57 4.58 4.59 4.60 4.61 4.62 4.63 4.65 4.66 4.67 4.68 4.69

Table 7. Calculated Densities (ρ) for [C2CNBim]X and [C2CNDim]X as a Function of Pressure at Temperatures (298.15, 323.15, and 343.15) K ρ/(g·cm−3) P/ MPa

[CNC2 Bim] DOSS

[CNC2 Bim] DDS

[CNC2 Bim] BS

0.1 0.5 1.0 1.5 2.0

1.112461 1.115106 1.118429 1.121773 1.125136

1.125183 1.127858 1.131220 1.134602 1.138004

1.238984 1.241929 1.245631 1.249355 1.253101

0.1 0.5 1.0 1.5 2.0

1.084193 1.086745 1.089952 1.093178 1.096423

1.095996 1.098576 1.101818 1.105079 1.108359

1.210356 1.213205 1.216785 1.220387 1.22401

0.1 0.5 1.0 1.5 2.0

1.046615 1.049031 1.052066 1.055119 1.05819

1.059843 1.062289 1.065362 1.068454 1.071563

1.174026 1.176736 1.18014 1.183565 1.187009

[CNC2 Bim] TFMS T/K = 298.15 1.334753 1.337926 1.341914 1.345925 1.349961 T/K = 323.15 1.303392 1.30646 1.310315 1.314193 1.318095 T/K = 343.15 1.263991 1.266909 1.270575 1.274261 1.27797

[CNC2 Dim] SBA

[CNC2 Dim] DOSS

[CNC2 Dim] DDS

1.135501 1.138201 1.141593 1.145006 1.148440

1.037629 1.040096 1.043196 1.046315 1.049452

1.052255 1.054756 1.057900 1.061063 1.064244

1.107105 1.109711 1.112985 1.116279 1.119593

1.01397 1.016356 1.019356 1.022373 1.025408

1.027657 1.030076 1.033116 1.036174 1.03925

1.072389 1.074864 1.077974 1.081102 1.084249

0.985828 0.988103 0.990962 0.993838 0.99673

0.999152 1.001458 1.004356 1.007271 1.010202

ρ = A 0 + A1T

The experimental refractive index values for the investigated RTILs are presented in Table 5. Among the studied anions, TFMS shows the highest refractive index value while DOSS shows the lowest value. The refractive index value of the SBA anion is in good agreement with that reported 7 for [C2CNOim]Br, 1.51473, while DOSS and DDS anions show lower values. Generally the refractive indices for the investigated RTILs are in the range from 1.45965 to 1.52174 and these values are comparable to other nitrile functionalized ILs (1.4188 to 1.5454).5,7 The refractive index values decrease linearly with increasing temperature as shown in Figure 4. The refractive indices of these nitrile-functionalized ILs with sulfonate anions are much higher compared to [C1CnCNPyr][Tf2N] ILs where the reported refractive indices are in the range from 1.4305 to 1.4365.14 The refractive index values are found to increase after the incorporation of nitrile group which may be due to the high electron mobility around the nitrile group.6 The density values as a function of temperature were used to calculate the coefficients of thermal expansion using the following equations:22

(2)

αP /(K−1) = −(1/ρ)(∂ρ /∂T )P = −(A1/(A 0 + A1T )) (3) −1

where αP is coefficient of thermal expansion in K , T is the absolute temperature, ρ is the density, and A0 and A1 are the fitting parameters of eq 2. The coefficients of thermal expansion of the present ILs are presented in Table 6. The coefficients of thermal expansion of this series of ILs do not appreciably change with temperature in the range between 293.15 K to 353.15 K studied in the present work. The present ILs show weak temperature dependency for the coefficients of thermal expansion, α = (4.37·10−4 to 9.32·10−4) K−1, which are noticeably smaller than those for molecular organic liquids and adequately agree with those reported for imidazolium-, pyridinium-, phosphonium-, and ammonium-based ILs.23,24 The extended version of Ye and Shreeve’s group contribution method for estimation of ILs densities proposed by Gardas, et al.11 was used to predict densities of the synthesized ILs for a wide range of temperatures and pressures. The densities at temperatures (298.15, 313.15, and 343.15) K and pressures 1236



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Table 9. Fitting Parameters of Density and Standard Deviations (SD) Calculated Using Equation 9 fitting parameters ILs

A0

A1

SD·103

[C2CNBim]DOSS [C2CNBim]DDS [C2CNBim]BS [C2CNBim]TFMS [C2CNDim]SBA [C2CNDim]DOSS [C2CNDim]DDS

1.34035 1.34427 1.43117 1.54902 1.33667 1.18076 1.19314

−0.00077 −0.00074 −0.00065 −0.00073 −0.00068 −0.00049 −0.00048

1.33 1.92 0.84 1.24 0.69 0.91 0.67

Table 10. Fitting Parameters of Viscosity (η) and Standard Deviations (SD) Calculated Using Equation 9 fitting parameters

Figure 5. Calculated densities (ρ) for [C2CNBim]X and [C2CNDim]X as a function of pressure at , 298.15 K; ---, 323.15 K; ···, 343.15 K: ■, [C2CNBim]DOSS; ×, [C2CNBim]DDS; ◇, [C2CNBim]BS; ●, [C2CNBim]TFMS; ⊗, [C2CNDim]SBA: △, [C2CNDim]DOSS; ○, [C2CNDim]DDS.

A2

A3

SD·102


−9.07856 −8.96188 −8.57303 −7.25725 −8.17715 −7.91466 −8.00083

3924.28611 3829.48067 3586.11564 3015.04098 3708.77574 3707.93791 3696.42768

1.16 1.37 1.30 0.83 2.75 1.55 1.66

Table 11. Fitting Parameters of Refractive Indices (nD) and Standard Deviations (SD) Calculated using Equation 8

(0.1, 0.5, 1.0, 1.5, and 2.0) MPa were estimated using the following equation: ρ = M /(NAV (a + bT + cP))

ILs

fitting parameters

(4)

where ρ is density (g·cm−3), M is molar mass (g·mol−1), NA is Avogadro’s number, V is molecular volume (Å3), T is temperature (K), and P is pressure (MPa). The constants a, b, and c were proposed by Gardas, et al.11 (a = 0.8005, b = 6.652·10−4 K−1, c = −5.919·10−4 MPa−1). The predicted densities for the present ILs at temperatures (298.15, 313.15, and 343.15) K and pressures (0.1, 0.5, 1.0, 1.5, and 2.0) MPa are presented in Table 7. The effect of pressure on the densities

ILs

A4

A5

SD·103


1.564681 1.599974 1.617089 1.620201 1.597176 1.562092 1.565009

−0.000282 −0.000376 −0.000279 −0.000286 −0.000283 −0.000288 −0.000304

0.10 0.22 0.10 0.14 0.20 0.10 0.11

Table 8. Values of Calculated Molar Volumes (VM) and Molar Refractions (RM) for [CNC2Bim]X and [CNC2Dim]X as a Function of Temperature T K 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15

VM

RM −1

cm ·mol 3

VM −1

cm ·mol 3

RM −1

cm ·mol 3

VM −1

cm ·mol 3

RM −1

cm ·mol 3

VM −1

cm ·mol 3

[CNC2Bim]DOSS

[CNC2Bim]DDS

[CNC2Bim]BS

541.04 153.83 542.71 153.97 544.38 154.07 546.61 154.32 548.05 154.31 549.66 154.36 551.93 154.60 554.17 154.81 [CNC2Dim]SBA 409.88 123.21 411.19 123.31 412.50 123.37 413.64 123.45 414.90 123.48 416.23 123.63 417.54 123.74 418.75 123.83

395.88 114.04 397.08 114.04 398.40 114.07 399.79 114.04 400.98 113.93 402.40 113.99 403.53 114.01 405.07 114.02 [CNC2Dim]DOSS 661.31 186.56 663.30 186.67 665.23 186.77 666.92 186.76 668.54 186.71 670.05 186.63 671.49 186.53 672.94 186.38

272.02 84.53 272.77 84.57 273.48 84.63 274.35 84.71 274.93 84.69 275.69 84.74 276.42 84.77 277.24 84.83 [CNC2Dim]DDS 495.79 139.45 497.24 139.48 498.88 139.55 499.91 139.41 502.00 139.58 503.39 139.62 504.98 139.68 506.33 139.69

1237

cm ·mol 3

RM −1

cm ·mol−1 3

[CNC2Bim]TFMS 245.66 246.36 247.03 247.73 248.40 249.08 249.77 250.13

76.51 76.53 76.57 76.61 76.64 76.69 76.73 76.67



Article

pressure. The molar refraction increases with the increase of the anion volume and alkyl chain length of the cation.

of the studied ILs is shown in Figure 5. The results show that the density values increase almost linearly with increasing pressure. The linear correlation between pressure and density can be used to estimate the compressibility coefficient (kT) for the studied ILs. The refractive index can afford useful information about the behavior of the molecules in the solution and the forces between these molecules using its relation with the electronic polarizability of the molecule (this relation can be expressed in terms of molar polarizability or molar refraction) which is known as the Lorenz−Lorentz equation:16 RM =

NAαe/3ε0Vm((nD2

−

1)/(nD2

■

Corresponding Author

*E-mail: [email protected]; [email protected]. Present Address §

Applied Chemistry & Chemical Technology Department, University of Gezira, Wad Medani-Sudan. Funding

The authors would like to thank Petronas Ionic Liquid Centre at Universiti Teknologi Petronas for the facilties provided in this work and Petronas and University of Gezira sponsorship for Abobakr K. Ziyada.

+ 2))

= (M /ρ)((nD2 − 1)/(nD2 + 2))

(5)

where, RM is the molar refraction in cm3·mol−1, NA is the Avogadro’s number in mol−1, αe is mean molecular polarizability (electronic polarizability), ε0 is the permittivity of free space, Vm is the molar volume in cm3·mol−1 and nD is refractive index. The values of molar refractions for all the studied ionic liquids were calculated and are listed in Table 8 along with their molar values at different temperatures. These results showed that the increase of the anion molecular weight and alkyl chain length of the cation directly corresponds to the rise in the molar refraction values for the present ILs. The molar refractions are often considered as a measure of the hard-core molecular volumes,16 consequently it may be used to estimate the molar free volume (unoccupied part of the molar volume of a substance (where f M is the free volume defined as f M = (VM − RM))25) of the present RTILs. The temperature dependence of density (ρ), viscosity (η), and refractive index (nD) for the present RTILs can be represented by the following empirical equations:7,22 ρ = A 0 + A1T

(6)

log η = A 2 + (A3 /T )

(7)

nD = A4 + A5T

(8)

Notes

The authors declare no competing financial interest.

■

Ndat

∑ (Zexp − Zcal)2 /ndat i

REFERENCES

(1) Lopes, J. N. C.; Cordeiro, T. C.; Esperancüa, J. M. S. S.; Guedes, H. J. R.; Huq, S.; Rebelo, L. P. N.; Seddon, K. R. Deviations from Ideality in Mixtures of Two Ionic Liquids Containing a Common Ion. J. Phys. Chem. B 2005, 109, 3519−3525. (2) Schrekker, H. S.; Stracke, M. P.; Schrekker, C. M. L.; Dupont, J. Ether-Functionalized Imidazolium Hexafluorophosphate Ionic Liquids for Improved Water Miscibilities. Ind. Eng. Chem. Res. 2007, 46, 7389− 7392. (3) Nockemann, P.; Thijs, B.; Parac-Vogt, T. N.; Van Hecke, K.; Van Meervelt, L.; Tinant, B.; Hartenbach, I.; Schleid, T.; Ngan, V. T.; Nguyen, M. T. Carboxyl-Functionalized Task-Specific Ionic Liquids for Solubilizing Metal Oxides. Inorg. Chem. 2008, 47, 9987−9999. (4) Mazille, F.; Fei, Z.; Kuang, D.; Zhao, D.; Zakeeruddin, S. M.; Grätzel, M.; Dyson, P. J. Influence of Ionic Liquids Bearing Functional Groups in Dye-Sensitized Solar Cells. Inorg. Chem. 2006, 45, 1585− 1590. (5) Zhao, D.; Fei, Z.; Scopelliti, R.; Dyson, P. J. Synthesis and Characterization of Ionic Liquids Incorporating the Nitrile Functionality. Inorg. Chem. 2004, 43, 2197−2205. (6) Zhang, Q.; Li, Z.; Zhang, J.; Zhang, S.; Zhu, L.; Yang, J.; Zhang, X.; Deng, Y. Physicochemical Properties of Nitrile-Functionalized Ionic Liquids. J. Phys. Chem. B 2007, 111, 2864−2872. (7) Ziyada, A. K.; Wilfred, C. D.; Bustam, M. A.; Man, Z.; Murugesan, T. Thermophysical Properties of 1-Propyronitrile-3alkylimidazolium Bromide Ionic Liquids at Temperatures from (293.15 to 353.15) K. J. Chem. Eng. Data 2010, 55, 3886−3890. (8) Ziyada, A. K.; Bustama, M. A.; Wilfred, C. D.; Murugesan, T. Densities, Viscosities and Refractive Indices of 1-Hexyl-3-propanenitrile Imidazolium Ionic Liquids Incorporated with Sulfonate-Based Anions. J. Chem. Eng. Data 2011, 56, 2343−2348. (9) Ziyada, A. K.; Bustam, M. A.; Murugesan, T.; Wilfred, C. D. Effect of Sulfonate-Based Anions on the Physicochemical Properties of 1-Alkyl-3-propanenitrile Imidazolium Ionic Liquids. New J. Chem. 2011, 35, 1111−1116. (10) Zhao, D.; Fei, Z.; Ohlin, C. A.; Laurenczy, G.; Dyson, P. J. DualFunctionalised Ionic Liquids: Synthesis and Characterisation of Imidazolium Salts with a Nitrile-Functionalised Anion. Chem. Commun. 2004, 2500−2501. (11) 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. (12) Hasse, B.; Lehmann, J.; Assenbaum, D.; Wasserscheid, P.; Leipertz, A.; Fro ba, A. P. Viscosity, Interfacial Tension, Density, and Refractive Index of Ionic Liquids [EMIM][MeSO3], [EMIM][MeOHPO2], [EMIM][OcSO4], and [BBIM][NTf2] in Dependence

where T is the absolute temperature; A0, A1, A2, A3, A4, and A5 are fitting parameters. The fitting parameters are estimated using the method of least-squares and are presented in Tables 9, 10, and 11 together with the standard deviations (SD). The standard deviations were calculated by applying the following expression:7 SD =

AUTHOR INFORMATION

(9)

where, ndat is the number of experimental points, Zexp and Zcal are the experimental and calculated values, respectively.

■

CONCLUSIONS In the present work we have synthesized and characterized seven RTILs containing [CNC2Bim] and [CNC2Dim] cations incorporating five different anions (DOSS, DDS, SBA, BS, TFMS). Their thermophysical properties such as densities, viscosities, and refractive indices were measured in atmospheric pressure at different temperatures. The density decreases with the increase of the anion volume while the viscosities show the opposite trend. The studied ionic liquids show weak temperature dependency for the coefficient of thermal expansion and the density values increase almost linearly with increasing 1238



Article

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1239


Physical Properties of Ionic Liquids Consisting of 1-Butyl-3

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