Article pubs.acs.org/jced
Surface Properties of Aqueous Solutions of Amino Acid Ionic Liquids: [C3mim][Gly] and [C4mim][Gly] Jing Tong,* Mei Hong, Yan Chen, Hui Wang, and Jia-Zhen Yang Key Laboratory of Green Synthesis and Preparative Chemistry of Advanced Materials, Liaoning University, Shenyang 110036, China S Supporting Information *
ABSTRACT: Glycine ionic liquids [C3mim][Gly] (1-propyl-3-methylimidazolium glycine) and [C4mim][Gly] (1-butyl-3-methylimidazolium glycine) have been prepared by the neutralization method and characterized by 1H NMR spectroscopy and DSC trace. The values of density and surface tension of aqueous [C3mim][Gly] and [C4mim][Gly] with various molality were determined in the temperature range of (288.15 to 328.15 ± 0.05) K, and the experimental values of parachor for these solutions were calculated. Using the empirical equation of parachor, the surface tension of these aqueous solutions was estimated, and the estimated values are in good agreement with experimental values within error.
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INTRODUCTION
EXPERIMENTAL SECTION Chemicals. Deionized water was distilled in a quartz still, and its conductance was (0.8 to 1.2)·10−4 S·m−1. NMethylimidazole AR grade reagent was obtained from ACROS and vacuum distilled prior to use. Glycine, 1bromopropane, and 1-bromobutane were all AR grade and were purchased from Shenyang Reagent Co. Ltd. Glycine was recrystallized twice from water and was dried under reduced pressure. 1-Bromopropane and 1-bromobutane were distilled before use. Ethyl acetate and acetonitrile were all AR grade from Shanghai Reagent Co. Ltd. and, after distillation, stored in tightly sealed glass bottles. Anion-exchange resin (type 717) was purchased from Shanghai Chemical Reagent Co. Ltd. and activated by the regular method before use. Preparation of AAILs. [C3mim][Gly] and [C4mim][Gly] were prepared by a neutralization method according to Fukumoto et al.2 First, [C3mim]Br and [C4mim]Br were synthesized according to the literature.16,17 Then, aqueous 1propyl-3-methylimidazolium hydroxide ([C3mim][OH]) and 1-butyl-3-methylimidazolium hydroxide ([C4mim][OH]) were prepared from [C3mim]Br and [C4mim]Br by use of an activated anion-exchange resin in a 100 cm column, then dripping the aqueous [C3mim][OH] and [C4mim][OH] into the aqueous silver nitrate, respectively, until white deposition appeared. However, [C3mim][OH] and [C4mim][OH] are not particularly stable, and they should be used immediately after preparation. These hydroxide-containing aqueous solutions were added dropwise to a slight excess of glycine in aqueous solution. The mixture was stirred with cooling for 12 h. Then, water was evaporated under reduced pressure at 40−50 °C.
Since the amino acid ionic liquids (AAILs) are synthesized from natural amino acids,1,2 AAILs have attracted considerable attention from the industry and the academic community as greener ionic liquids.1−7 At present, the amino acid ionic liquid researches focus on syntheses and applications, very few experimental researches are about the nature of aqueous solution of AAILs, particularly about the surface tension in literature.8−11 The surface tension is important in the study of physics and chemistry at free surfaces.12 It affects the transfer rates of vapor absorption where a vapor−liquid interface exists. Such data are important in many fields of science and engineering to apply the ILs in different chemical processes, reactor engineering, and biochemistry. The surface tension is also interesting to elucidate fundamental aspects of the ILs at theoretical level. Therefore, in this article, we report the following: (1) two amino acid ionic liquids, [C3mim][Gly] (1propyl-3-methylimi-dazolium glycine) and [C4mim][Gly] (1butyl-3-methylimidazolium glycine), were prepared by the neutralization method; (2) the values of density and surface tension, for aqueous [C3mim][Gly] and aqueous [C4mim][Gly] with various molalities, were measured at (288.15 to 328.15 ± 0.05) K and the experimental values of parachor for these solutions were calculated. With the absence of such data in literature, it is the first report that the experimental values for the density and surface tension of aqueous solutions of [C3mim][Gly] and [C4mim][Gly]. (3) The dependence of the surface tension on molality and the parachor on temperature for the aqueous AAILs were discussed; (4) in terms of the values of the parachor,13−15 the surface tension for the aqueous AAILs were estimated. © 2012 American Chemical Society
Received: February 27, 2012 Accepted: June 20, 2012 Published: July 23, 2012 2265
dx.doi.org/10.1021/je300161h | J. Chem. Eng. Data 2012, 57, 2265−2270
Journal of Chemical & Engineering Data
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Table 1. Values of Density, ρ (g·cm−3), for Aqueous [C3mim][Gly] and Aqueous [C4mim][Gly] with Various Molalities at (288.15 to 328.15) Ka m mol·kg−1
a
T/K 288.15
293.15
298.15
0.0102 0.0166 0.0282 0.0443 0.1117 0.1846 0.2272 0.2865 0.3367 0.3947 0.4497 0.5043
1.00019 1.00040 1.00062 1.00090 1.00248 1.00422 1.00512 1.00655 1.00783 1.00926 1.01062 1.01196
0.99918 0.99939 0.99955 0.99991 1.00140 1.00297 1.00407 1.00546 1.00672 1.00812 1.00942 1.01074
0.99763 0.99792 0.99811 0.99843 0.99984 1.00164 1.00278 1.00415 1.00539 1.00673 1.00802 1.00931
0.0270 0.0379 0.0451 0.0603 0.1158 0.1787 0.2110 0.2807 0.3239 0.3946 0.4475 0.4997
1.00026 1.00062 1.00079 1.00116 1.00249 1.00399 1.00487 1.00644 1.00757 1.00917 1.01054 1.01209
0.99927 0.99964 0.99982 1.00017 1.00139 1.00289 1.00366 1.00543 1.00656 1.00805 1.00951 1.01075
0.99788 0.99817 0.99824 0.99875 1.00017 1.00172 1.00239 1.00415 1.00512 1.00668 1.00794 1.00909
303.15
308.15
[C3mim][Gly] 0.99624 0.99441 0.99644 0.99459 0.99671 0.99479 0.99692 0.99515 0.99852 0.99655 1.00020 0.99836 1.00118 0.99936 1.00261 1.00086 1.00383 1.00206 1.00515 1.00337 1.00658 1.00479 1.00767 1.00584 [C4mim][Gly] 0.99619 0.99433 0.99674 0.9949 0.99681 0.99497 0.99717 0.99533 0.99848 0.99665 0.99996 0.99816 1.00072 0.99893 1.00236 1.00059 1.00338 1.00162 1.00504 1.00331 1.00629 1.00457 1.00771 1.00602
313.15
318.15
323.15
328.15
0.99234 0.99251 0.99272 0.99305 0.99465 0.99637 0.99746 0.99875 0.99989 1.00139 1.00256 1.00384
0.99009 0.99017 0.99042 0.99069 0.99233 0.99408 0.99527 0.99661 0.99792 0.99923 1.00046 1.00167
0.98791 0.98817 0.98834 0.98862 0.99020 0.99199 0.99303 0.99437 0.99553 0.99691 0.99815 0.99944
0.98628 0.98632 0.98654 0.98679 0.98837 0.99011 0.99112 0.99255 0.99369 0.99489 0.99625 0.99733
0.99245 0.99281 0.99288 0.99324 0.99454 0.99592 0.99678 0.99841 0.99943 1.00109 1.00233 1.00376
0.99033 0.9905 0.99056 0.99093 0.99225 0.99385 0.99452 0.99619 0.99722 0.99891 1.00027 1.00161
0.98819 0.98865 0.98862 0.98888 0.9902 0.99169 0.99246 0.99411 0.99514 0.99681 0.99807 0.99951
0.98627 0.98663 0.9867 0.98706 0.98838 0.98987 0.99084 0.99229 0.99332 0.995 0.99625 0.99769
The uncertainty of each experimental value is ± 0.00001; the uncertainty of the molalities is ± 0.0001.
tension of water was measured at (283.15 to 328.15) K and was in good agreement with the literature18 within the experimental error of ± 0.1 mJ·m−2. Then, the values of surface tension of the samples were measured by the same method in the same temperature range.
The mixed solvent of acetonitrile/methanol (volumetric ratio = 9/1) was added to this reaction mixture, and it was stirred vigorously. The mixture was then filtered to remove excess glycine. The filtrate was evaporated to remove solvents. The products of [C3mim][Gly] and [C4mim][Gly] were dried in vacuo for 2 days at 80 °C. The structures of the resulting amino acid ionic liquids were confirmed by 1H NMR spectroscopy, the differential scanning calorimetric (DSC) measurements, and the thermogravimetric analysis. The water content (w2 is water mass fraction, w2 = (8.00 ± 0.01)·10−3 and (8.10 ± 0.01)·10−3 mass fraction in [C3mim][Gly] and [C4mim][Gly], respectively, was determined by use of a Karl Fischer moisture titrator (ZSD-2 type); the results revealed that the purity of [C3mim][Gly] and [C4mim][Gly] was estimated as > 0.99 mass fraction. Measurement of the Density and Surface Tension of the Aqueous Solutions of AAILs. Each sample was immediately used after it was mixed well by shaking. All solutions to be measured were prepared freshly and performed on an electronic balance (ESJ200-4) accurate to 0.1 mg with calibration of air buoyancy. The uncertainty of the molalities of all solutions is within ± 1.0·10−4 mol·kg−1. By using an Anton Paar DMA 4500 oscillating U-tube densitometer, the density of the samples with molalities from 0.01 mol·kg−1 to 0.5 mol·kg−1 were measured at temperatures from (288.15 to 328.15) K. The temperature in the cell was regulated to ± 0.01 K with a solid state thermostat. The apparatus was calibrated once a day with dry air and double-distilled degassed fresh water. By use of the tensiometer of the forced bubble method (DPAW-type produced by Sang Li Electronic Co.), the surface
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RESULTS AND DISCUSSION Experimental Values of Density and Surface Tension. The experimental values of density and surface tension for the samples of aqueous [C3mim][Gly] and aqueous [C4mim][Gly] with various molalities at (288.15 to 328.15) K are listed in Tables 1 and 2, respectively. Each value in the tables is the average of triple measurements. (Figures S1 and S2 in the Supporting Information are the plots of density and surface tension vs the molality of aqueous [C3mim][Gly] and [C4mim][Gly] at each given temperature, respectively.) From these figures, it can be seen that a series of good straight lines are obtained, and all linear correlation coefficients are larger than 0.99. The empirical equation was obtained by fitting the experimental data. Its linear correlation coefficient and the standard deviation are listed in Tables 1 and 2, respectively. Dependence of Surface Tension on Molarity of the Aqueous AAILs. In a large concentration range, the following empirical equation19 was applied to the relationship between surface tension and molarity: γ = γ0 − kc
(1)
where k = −(∂γ/∂c)T is an empirical constant, γ0 is the surface tension of water, and c is molarity, the conversion relationship 2266
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Table 2. Values of Surface Tension, γ (mJ·m−2), for Aqueous [C3mim][Gly] and Aqueous [C4mim][Gly] with Various Molalities at (288.15 to 328.15) K m mol·kg−1
T/K 288.15
293.15
298.15
0a 0.0166 0.0278 0.0443 0.0555 0.1111 0.1676 0.2227 0.2789 0.3349 0.3916 0.4476 0.5039
73.49 73.2 73.1 72.9 72.6 72.0 71.4 70.8 69.9 69.4 68.3 67.6 67.0
72.75 72.4 72.3 72 71.7 71.2 70.6 69.9 69.1 68.4 67.4 66.7 66.1
71.97 71.6 71.4 71.2 71.0 70.4 69.6 69.1 68.3 67.5 66.6 65.9 65.5
0.0105 0.0195 0.0287 0.0583 0.1114 0.1676 0.2217 0.2794 0.3360 0.3926 0.4494 0.5075
73.1 73.0 72.8 72.5 72.0 71.4 70.8 69.9 69.4 68.2 67.6 67.0
72.3 72.2 71.9 71.7 71.2 70.6 69.8 69.1 68.3 67.4 66.7 66.1
71.7 71.6 71.4 71.0 70.4 69.6 69.1 68.3 67.5 66.4 65.8 65.5
303.15
308.15
[C3mim][Gly] 71.20 70.38 70.9 70.1 70.7 69.9 70.5 69.7 70.4 69.6 69.7 68.9 68.7 68.0 68.2 67.4 67.6 66.9 66.8 66.3 65.9 65.4 65.2 64.9 64.8 64.4 [C4mim][Gly] 71.0 70.2 70.9 70.0 70.7 69.8 70.4 69.6 69.7 68.9 68.8 68.1 68.1 67.4 67.3 66.7 66.5 66.1 65.8 65.4 65.2 64.8 64.8 64.1
313.15
318.15
323.15
328.15
69.60 69.1 69.0 68.8 68.7 68.0 67.1 66.5 66.0 65.5 64.5 64.0 63.6
68.74 68.3 68.2 68 67.9 67.0 66.4 65.6 65.4 64.7 63.7 63.1 62.8
67.94 67.5 67.4 67.2 67.0 66.3 65.7 64.9 64.5 63.9 63.0 62.3 62.1
67.05 66.4 66.3 66.2 66.1 65.4 64.3 63.5 63.0 62.5 61.7 61.2 60.8
69.3 69.1 68.9 68.7 68.0 67.2 66.6 66.1 65.5 64.5 64.0 63.5
68.5 68.3 68.1 67.9 67.2 66.4 65.9 65.3 64.7 63.8 63.2 62.7
67.7 67.5 67.3 67.0 66.3 65.5 64.9 64.3 63.6 63.0 62.2 61.5
66.7 66.5 66.3 66.0 65.2 64.5 63.9 63.1 62.6 61.7 61.3 60.8
Surface tension of pure water was taken from ref 18. The uncertainty of each experimental value is ± 0.2; the uncertainty of the molalities is ± 0.0001.
a
between molality and molarity: c = mρ/(1 + 0.001mM2), where ρ is the density of the aqueous AAILs, and M2 is the mass of the solute. The calculated values of molarity are listed in Table A1 of the Supporting Information. The definition of surface pressure, π, is π = γ0 − γ = kc
(2)
k = (∂π /∂c)T
(3)
when k > 0, there is positive adsorption on the surface of solution; when k < 0, there is negative adsorption. As an example, Figure 1 is a plot of surface pressure vs molarity for aqueous [C3mim][Gly] at 303.15 K. The remaining plots for aqueous [C3mim][Gly] at other temperatures and aqueous [C4mim][Gly] are completely similar to Figure 1 and were placed in the Supporting Information (see Figure S3). From Figure 1, it can be seen that k > 0, this means that the AAILs have a certain surface activity. Estimating Surface Tension of the Aqueous AAILs Using Parachor. The parachor, P, is a relatively old concept and is available as a link between the structure, density, and surface tensions of liquids and was defined using the following equation:13,14 P = (Mγ 1/4)/ρ = Vγ 1/4
Figure 1. Plot of surface pressure vs molarity for aqueous [C3mim][Gly] at 303.15 K; π = 0.0482 + 14.0 c; s = 0.11; r2 = 0.998.
aqueous AAILs can be calculated. As an example, the data of Pm(exptl) at (288.15 and 323.15) K are only listed in Table 3, and parachor data at the remaining temperatures are listed in Table A2 in section D of the Supporting Information. Figure 2 is the plot of the experimental parachor of the aqueous AAILs vs temperature, the intercept, the slope, the linear correlation coefficient, and the standard deviation are listed in Table 3. In general, the parachor of organic compounds do not change with temperature.13,14 However, the parachor of the aqueous AAILs is not temperature-independent but decreas slowly with
(4)
where γ is surface tension, M is molar mass, ρ is density of a substance, and V is molar volume. According to the definition (eq 1), the experimental parachor values, Pm(exptl) of the 2267
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Table 3. Intercept, the Slope, the Linear Correlation Coefficient, and the Standard Deviation of the Plot of the Experimental Parachor of the Aqueous AAILs vs Temperature m
[C3mim][Gly]
[C4mim][Gly]
mol·kg−1
a
b
r2
102·s
a
b
r2
102·s
0.0167 0.0278 0.0444 0.0556 0.1112 0.1670 0.2229 0.2789 0.3351 0.3913 0.4477 0.5041
56.5 56.5 56.6 56.7 57.0 57.4 57.7 58.0 58.3 58.6 58.9 59.2
−0.0127 −0.0127 −0.0127 −0.0127 −0.0127 −0.0127 −0.0127 −0.0127 −0.0128 −0.0128 −0.0128 −0.0128
0.99 0.99 0.98 0.98 0.98 0.98 0.97 0.97 0.96 0.95 0.94 0.93
2.22 2.25 2.30 2.34 2.55 2.81 3.11 3.45 3.82 4.22 4.65 5.10
56.2 56.3 56.4 56.5 56.9 57.3 57.7 58.1 58.5 58.9 59.3 59.6
−0.0117 −0.0117 −0.0118 −0.0118 −0.0120 −0.0121 −0.0123 −0.0125 −0.0126 −0.0128 −0.0130 −0.0131
0.99 0.99 0.99 0.99 0.98 0.98 0.98 0.97 0.96 0.95 0.94 0.93
1.9 1.9 1.9 2.0 2.2 2.5 2.8 3.2 3.6 4.1 4.6 5.1
the temperature changes, the molar volume of ionic liquid solution and the changes in surface tension can not compensate for each other, thus this led to the parachor of a slow decline with the rise of the temperature. In 2008, Balasubrahmanyam15 pointed out that the following equation was used to estimate the parachor of solution: Pm = xPsolute + (1 − x)Psolvent
(5)
Pm is the parachor of solution, Psolute and Psolvent are the parachors of solute and solvent, and x is the mole fraction of solute and can be calculated with x = mMA/(1000 + mMA), where MA is the molar mass of solvent in grams. When calculating the experimental values of parachor for the aqueous AAILs with eq 4, M should be replaced with the average molar mass Mm: M m = xMsolute + (1 − x)Msolvent
(6)
where Msolute and Msolvent are the molar mass of the solute and the solvent, respectively. The values of Pm calculated by eq 5 are also listed in Table 4. From Table 4, it can be seen that the difference, ΔP = Pm(exptl) − Pm, between Pm(exptl) and Pm, means the measure of the solute−solvent interaction and can be expressed in the following empirical equation: ΔP = Pm(exptl) − Pm = A pI
(7)
where Ap is an empirical parameter, and I is ionic strength. The values of ΔP were calculated and are listed in Table 4. The values of Ap = −1.65 for aqueous [C3mim][Gly] and Ap = −1.62 were obtained. The following empirical equation, eq 8, may be used to estimate the values of parachor, Pm(calcd), for the AAILs, and the estimated values are also listed in Table 4.
Figure 2. Plot of the experimental parachor vs temperature at given molality for the aqueous (a) [C3mim][Gly] and (b) [C4mim][Gly]. ■, m = 0.0167 mol·kg−1; ●, m = 0.0278 mol·kg−1; ▲, m = 0.0444 mol·kg−1; ▼, m = 0.0556 mol·kg−1; ◆, m = 0.1112 mol·kg−1; ◀, m = 0.1670 mol·kg−1; ▶, m = 0.2229 mol·kg−1; ×, m = 0.2789 mol·kg−1; ★, m = 0.3351 mol·kg−1; ∗, m = 0.3913 mol·kg−1; −, m = 0.4477 mol·kg−1; +, m = 0.5041 mol·kg−1.
Pm(calcd) = xPsolute + (1 − x)Psolvent + A pI
(8)
Figure 3 is a comparative plot of calculated parachor values, Pm(calcd), as a function of corresponding experimental values, Pm(exptl), for the aqueous AAILs. From Figure 3, it can be seen that Pm(calcd) and Pm(exptl) are highly correlated (correlation coefficient squared, r2 = 0.998; standard deviation, s = 0.04) and extremely similar (gradient = 1.01; intercept = 0.284). According to eq 4, the surface tension of the aqueous AAILs can be estimated by the values of Pm(calcd). Figure 4 is a comparative plot of estimated values of surface tension, γ(est), as a function of corresponding experimental values, γ(exptl), for the aqueous [C3mim][Gly] and [C4mim][Gly] at 303.15 K.
increasing temperature (see Table 4 and Figure 2). Interaction between molecules can be used to explain this phenomenon. As the intermolecular interaction of uncharged compounds is mainly van der Waals’ forces, trends of molar volume and surface tension with temperature are each other opposite, which led to compensation, so that parachor is almost independent of temperature. However, for the electrolyte solution in addition to van der Waals’ forces, there are Coulomb−dipole forces in solute−solvent interactions. When 2268
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Table 4. Values of the Experimental Parachor, Pm(exptl), Parachor, Pm, Calculated by eq 5, ΔPm, and Pm(calcd) for the Aqueous [C3mim][Gly] and [C4mim][Gly] at (288.15 and 323.15) K m mol·kg−1
288.15 K 103·x
Pm(exptl)
323.15 K ΔPm
Pm
0.0167 0.0278 0.0444 0.0556 0.1112 0.1670 0.2229 0.2789 0.3351 0.3913 0.4477 0.5041
0.3 0.5 0.8 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
52.8 52.9 53.0 53.1 53.4 53.7 54.0 54.4 54.7 55.0 55.3 55.6
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.2 0.1 0.1 0.1 0.1 0.2 0.1 0.2 0.1 0.2 0.1
52.9 53.0 53.1 53.2 53.6 54.0 54.4 54.8 55.2 55.6 56.0 56.4
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.2 0.2 0.1 0.2 0.2
−0.1 −0.1 −0.1 −0.1 −0.2 −0.3 −0.4 −0.4 −0.5 −0.6 −0.7 −0.8
0.0167 0.0278 0.0444 0.0556 0.1112 0.1670 0.2229 0.2789 0.3351 0.3913 0.4477 0.5041
0.3 0.5 0.8 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
52.8 52.9 53.0 53.1 53.5 53.8 54.2 54.6 54.9 55.2 55.6 55.9
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.1 0.1 0.2 0.1 0.2 0.1 0.2 0.2 0.1 0.2 0.2
52.9 53.0 53.1 53.2 53.7 54.1 54.5 55.0 55.4 55.9 56.3 56.7
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.2 0.2 0.2 0.2
−0.1 −0.1 −0.1 −0.1 −0.2 −0.3 −0.4 −0.4 −0.5 −0.6 −0.7 −0.8
Pm(calcd) [C3mim][Gly] 52.9 ± 0.1 52.9 ± 0.1 53.0 ± 0.2 53.1 ± 0.1 53.4 ± 0.2 53.7 ± 0.1 54.0 ± 0.1 54.3 ± 0.2 54.7 ± 0.1 55.0 ± 0.1 55.3 ± 0.2 55.6 ± 0.2 [C4mim][Gly] 52.8 ± 0.1 52.9 ± 0.1 53.0 ± 0.1 53.1 ± 0.2 53.5 ± 0.1 53.8 ± 0.1 54.2 ± 0.2 54.6 ± 0.1 54.9 ± 0.2 55.2 ± 0.2 55.6 ± 0.1 55.9 ± 0.2
Figure 3. Plot of the estimated parachor for aqueous [C3mim][Gly] and [C4mim][Gly] vs their experimental values: ■, [C3mim][Gly]; ▲, [C4mim][Gly]; Pm(exptl) = 1.01 Pm(calcd) − 0.284; s = 0.04; r2 = 0.998.
Pm(exptl)
Pm
ΔPm
Pm(calcd)
52.4 52.5 52.6 52.6 53.0 53.3 53.6 53.9 54.2 54.5 54.8 55.1
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.1 0.2 0.1 0.2 0.1 0.2 0.2 0.2 0.2 0.2 0.2
52.5 52.5 52.7 52.7 53.2 53.6 54.0 54.4 54.8 55.2 55.6 56.0
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.1 0.2 0.2 0.2
−0.1 −0.1 −0.1 −0.1 −0.2 −0.3 −0.4 −0.4 −0.5 −0.6 −0.7 −0.9
52.4 52.5 52.6 52.7 53.0 53.3 53.6 53.9 54.2 54.5 54.9 55.2
± ± ± ± ± ± ± ± ± ± ± ±
0.2 0.1 0.2 0.1 0.1 0.2 0.1 0.1 0.1 0.1 0.2 0.1
52.4 52.5 52.6 52.7 53.1 53.4 53.8 54.1 54.4 54.8 55.1 55.4
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.1 0.2 0.2 0.2 0.2
52.5 52.6 52.7 52.8 53.2 53.7 54.1 54.6 55.0 55.4 55.9 56.3
± ± ± ± ± ± ± ± ± ± ± ±
0.2 0.2 0.1 0.1 0.1 0.1 0.2 0.2 0.1 0.2 0.2 0.2
0.0 −0.1 −0.1 −0.1 −0.2 −0.3 −0.4 −0.5 −0.6 −0.7 −0.8 −0.9
52.4 52.5 52.6 52.7 53.0 53.4 53.7 54.1 54.4 54.8 55.1 55.5
± ± ± ± ± ± ± ± ± ± ± ±
0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.1 0.2 0.2 0.1 0.2
Figure 4. Plot of the estimated surface tension for aqueous [C3mim][Gly] and [C4mim][Gly] in terms of parachor vs their experimental values at 303.15 K: ■, [C3mim][Gly]; ▲, [C4mim][Gly]; γ(est) = 0.999γ(exptl) + 0.103; s = 0.11; r2 = 0.998.
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CONCLUSIONS The values of density and surface tension, for aqueous [C3mim][Gly] and aqueous [C4mim][Gly] with various molalities, were measured at (288.15 to 328.15) K, and the experimental values of parachor for these solutions were calculated. The dependence of the surface tension on molality showed that the AAILs have a certain surface activity. When the temperature changes, the molar volume of ionic liquid solution and the changes in surface tension cannot compensate for each
The remaining plots for aqueous [C3mim][Gly] at other temperatures and aqueous [C4mim][Gly] are completely similar to Figure 4 and were placed in the Supporting Information (see Figure S4). From Figure 4, it can be seen that estimated surface tension and the experimental values are highly correlated (correlation coefficient squared, r2 = 0.998; standard deviation, s = 0.11) and extremely similar (gradient = 0.991; intercept = 0.558). 2269
dx.doi.org/10.1021/je300161h | J. Chem. Eng. Data 2012, 57, 2265−2270
Journal of Chemical & Engineering Data
Article
(15) Balasubrahmanyam, S. N. Einstein, ‘parachor’ and molecular volume: Some history and a suggestion. Curr. Sci. 2008, 94 (12), 1650−1658. (16) Wilkes, J. S.; Levisky, J. A.; Wilson, R. A.; Hussey, C. L. Dialkylimidazolium chloroaluminate melts, a new class of room temperature ionic liquids for electrochemistry spectroscopy and systhesis. Inorg. Chem. 1982, 21, 1263−1268. (17) Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H. D.; Broker, G. A.; Rogers, R. D. Characterization and comparison of hydrophilic and hydrophobic room temperature ionic liquids incorporating the imidazolium cation. Green Chem. 2001, 3, 156−164. (18) Lide, D. R. Handbook of Chemistry and Physics, 82nd ed.; CRC Press: Boca Raton, 2002. (19) Adamson, A. W. Physical Chemistry of Surfaces, 3rd ed.; JohnWiley: New York, 1976; translated by Gu, T. R.; Science Press: Beijing, China, 1986.
other, thus this led to the parachor of a slow decline with the rise of the temperature.
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ASSOCIATED CONTENT
S Supporting Information *
Plots of density vs m, surface tension vs m, surface pressure vs molarity, and estimated surface tension vs experimental values; tables of calculated molarity values and experimental parachor values. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +86 24 86870976. Fax: +86 24 86870976. E-mail:
[email protected]. Funding
This project was supported by NSFC (20903053), Education Bureau of Liaoning Province (LS2010069), People’s Republic of China, and Liaoning University research funding. Notes
The authors declare no competing financial interest.
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