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Thermodynamic and spectroscopic study of molecular interactions in the binary liquid mixtures of N-methyl-2-pyrrolidone and some substituted benzenes at different temperatures
Journal of Molecular Liquids 174 (2012) 100–111
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Thermodynamic and spectroscopic study of molecular interactions in the binary liquid mixtures of N-methyl-2-pyrrolidone and some substituted benzenes at different temperatures D. Bala Karuna Kumar a, K. Rayapa Reddy a, G. Srinivasa Rao b, G.V. Rama Rao c, C. Rambabu a,⁎ a b c
Department of Chemistry, Acharya Nagarjuna University, Dr. M.R.A.R. campus, Nuzvid, Andhra Pradesh, 521201, India Department of Physics, Andhra Loyola College, Vijayawada, Andhra Pradesh, 520 008, India Department of Physics, DAR College, Nuzvid, Andhra Pradesh, 521201, India
a r t i c l e
i n f o
Article history: Received 11 January 2012 Received in revised form 9 July 2012 Accepted 13 July 2012 Available online 26 July 2012 Keywords: Density Viscosity Excess molar volume Spectroscopy Binary mixture
a b s t r a c t The densities and viscosities for pure liquids N-methyl-2-pyrrolidone (NMP), aniline (AB), bromobenzene (BB), chlorobenzene (CB) and their binary mixtures containing NMP as a common component have been measured at 303.15, 308.15, 313.15 and 318.15 K as a function of composition of NMP. From these results, excess molar volumes, excess Gibb's free energy of activation of viscous flow and deviations in viscosity are computed. Excess properties are fitted to a Redlich–Kister type equation and the corresponding standard deviations are calculated. The experimental data of viscosity is used to test the applicability of empirical relations of Grunberg–Nissan, Katti–Chaudhri, Heric–Brewer and Hind et al. for the systems studied. The excess molar volumes are found to be negative whereas the deviations in viscosity and excess Gibb's free energy of activation of viscous flow values are found to be positive for all the mixtures, over the entire composition range. Partial molar volumes and apparent molar volumes at infinite dilution have been calculated. The variation of these properties with composition of NMP and temperature is discussed in terms of molecular interactions between component molecules. The strength of interaction of AB, BB, CB with NMP is found to obey the order AB > CB > BB. The IR, spectral studies of these binary mixtures also suggest specific interaction between the unlike molecules of the components and supported thermodynamic findings. © 2012 Elsevier B.V. All rights reserved.
1. Introduction In chemical process industries, materials are normally handled in fluid form and as a consequence, the physical, chemical and transport properties of liquids assume importance. When two or more solvent molecules are associated with one another to form a liquid mixture, it brings about a marked effect on the properties of the resulting system and differences in the intermolecular interactions of the solvents. So the properties of the liquid mixtures can be altered continuously within a reasonable range by varying the composition of the mixture till an optimum value of the desired parameter is attained. Pure liquids lack such flexibility. The data on some of the properties associated with liquids and liquid mixtures, like viscosity, density, excess molar volume etc., find extensive application in chemical engineering design, process simulation, solution theory and molecular dynamics. These properties are important from practical and theoretical point of view to understand liquid theory and provide information about molecular interactions [1–4].
⁎ Corresponding author. Tel.: +91 8656 233091; fax: +91 8656 235200. E-mail address: [email protected] (C. Rambabu). 0167-7322/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.molliq.2012.07.019
Liquid solvents play an important role in many chemical reactions and the choice of a proper solvent for a process primarily depends on the availability of physical properties [5]. Among such solvents N-methyl-2-pyrrolidone (NMP) is an important solvent as it is water-miscible, hygroscopic, colorless, and strongly polar liquid. NMP has the potential for use in, solvent extraction process as strong solubilizing agent [6], purification and crystallization of drugs [7]. It is also used in the manufacture of various compounds, including pigments, cosmetics, insecticides, herbicides, and fungicides. Its non-hazardous and ecological properties account for the reality that it is increasingly being used as an alternative for chlorinated hydrocarbons [3]. It is known that amides like NMP interact with substituted benzenes (aromatic hydrocarbons) by dipole–dipole interactions, and form some charge-transfer complexes [8,9]. Due to the strong hydrogen bonding acceptor ability of the oxygen, NMP can interact with hydrogen bond donors [3,10]. Substituted benzenes like chlorobenzene (CB), bromobenzene (BB) and aniline (hydrogen bond donor) find versatile applications in the industry; for instance chlorobenzene is used as a degreaser in the metal industry and thinning, dissolving agent in chemical industry. Both CB and BB readily undergo substitution reactions and can be used to synthesize various derivatives. Aniline (AB) is predominantly used in the manufacture of
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111 Table 1 Comparison of experimental values of density, ρ, and viscosity, η, of pure liquids with the corresponding literature values at 303.15 K. 10−3 × ρ/kg m−3
η/mPa s
Exptl
Lit.
Exptl
Lit.
N-methyl-2-pyrrolidone Chlorobenzene Bromobenzene
1.0238 1.0952 1.4815
1.555 0.721 0.985
1.5544 [21] 0.7210 [24] 0.9844 [24]
Aniline
1.0132
1.02376 [20] 1.0957 [22] 1.4814 [19] 1.4830 [26] 1.0133 [29] 1.0128 [28]
3.037
3.036 [27]
Liquid
Table 3 Coefficients Aj−1 of the Redlich–Kister equation, Eq. (2) and the corresponding stanE dard deviations (σ) of excess molar volumes (Vm /10−6 m3 mol−1) for the three binary mixtures of NMP at different temperatures. A3
A4
σ
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 −2.1268 0.3821 0.3026 308.15 −2.2961 0.3524 0.5879 313.15 −2.3960 0.3526 0.3834 318.15 −2.3800 0.1059 0.2239
−0.2691 0.2080 0.2658 0.2496
−0.6576 −0.9502 −0.9570 0.0554
0.011 0.010 0.011 0.003
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 −1.8124 0.1629 0.0056 308.15 −1.9163 0.1833 0.3091 313.15 −1.9959 0.0877 −0.0929 318.15 −2.1766 0.0572 −0.6205
−0.0454 0.0529 0.2200 0.3282
−0.4220 −0.8635 −0.7257 −0.3122
0.002 0.006 0.006 0.003
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 −3.3019 −0.1677 −0.0366 308.15 −3.5583 0.1463 0.1265 313.15 −3.6831 0.3216 0.3521 318.15 −3.8262 0.1510 −0.4538
0.6234 0.1175 −0.7338 −0.6300
−0.1552 −0.7196 −1.5922 −0.9690
0.016 0.010 0.010 0.007
T/K
synthetic dyes, drugs and as an accelerator in vulcanization of rubber [11]. In this context it will be quite interesting to investigate the properties of binary liquid mixtures of NMP with CB, BB and AB. Detailed literature survey shows that work has been carried out by different researchers on excess molar volumes of binary mixtures containing NMP + aromatic hydrocarbons [12,13], + hydrocarbons [14,15], + chloroethanes and chloroethenes [16], + an ether [17], + ketone [18], + branched alcohol [3] etc. However, no effort appears to have been made to investigate the physico-chemical properties, for the binary mixtures of NMP with chlorobenzene, bromobenzene and aniline. The present work is focused on the study of volumetric and viscometric properties, by measuring the densities and viscosities of the binary mixtures of NMP with chlorobenzene, bromobenzene and aniline over the complete composition range at temperatures of 303.15,
101
A0
A1
A2
308.15, 313.15 and 318.15 K and atmospheric pressure. It is also aimed to study the molecular interactions between NMP and substituted benzenes under investigation, with special reference to dipole–dipole and hydrogen bonding interactions with the help of IR spectral data of these mixtures at 303.15 K. Further, the experimental data of viscosity is used to test the applicability of empirical relations of Grunberg–Nissan, Katti– Chaudhri, Heric–Brewer and Hind et al. for the systems studied.
Table 2 Density, ρ, and viscosity, η, values for the binary mixtures of NMP at different temperatures. x1
ρ/kg m−3 303.15 K
η/mPa s 308.15 K
313.15 K
318.15 K
303.15 K
308.15 K
313.15 K
318.15 K
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 0.0000 1095.2 1087.2 0.1055 1090.1 1082.4 0.2097 1084.5 1077.3 0.3127 1078.3 1071.8 0.4144 1072.0 1066.0 0.5149 1065.2 1059.7 0.6142 1057.7 1052.6 0.7124 1050.1 1045.3 0.8094 1041.9 1037.6 0.9052 1033.1 1029.1 1.0000 1023.8 1019.9
1082.2 1077.6 1072.4 1067.1 1061.3 1055.0 1048.0 1040.7 1033.1 1024.5 1015.1
1072.7 1068.9 1064.3 1059.5 1054.4 1048.5 1042.0 1035.0 1027.6 1019.6 1010.3
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 0.0000 1481.5 1474.9 0.1084 1438.2 1431.9 0.2149 1394.0 1388.1 0.3193 1349.2 1343.6 0.4219 1304.0 1298.7 0.5226 1258.3 1253.4 0.6215 1212.1 1207.4 0.7186 1165.6 1161.1 0.8141 1118.7 1114.5 0.9078 1071.5 1067.5 1.0000 1023.8 1019.9
1467.5 1425.1 1381.7 1337.4 1292.6 1247.5 1201.8 1155.8 1109.5 1062.7 1015.1
1460.5 1418.7 1375.6 1331.7 1287.1 1242.1 1196.6 1150.9 1104.7 1058.0 1010.3
0.985 1.068 1.146 1.220 1.284 1.344 1.396 1.441 1.484 1.522 1.555
0.955 1.026 1.092 1.152 1.205 1.252 1.294 1.331 1.362 1.391 1.411
0.879 0.944 1.005 1.061 1.113 1.160 1.199 1.236 1.268 1.295 1.320
0.793 0.849 0.906 0.958 1.007 1.051 1.089 1.125 1.156 1.184 1.211
N-methyl-2-pyrrolidone(1) + aniline(2) 0.0000 1013.2 0.0954 1017.3 0.1918 1020.7 0.2892 1023.9 0.3876 1026.0 0.4870 1027.5 0.5875 1028.5 0.6890 1028.2 0.7915 1027.5 0.8952 1026.3 1.0000 1023.8
1005.0 1010.0 1013.5 1016.0 1018.4 1019.9 1020.7 1020.6 1019.8 1018.0 1015.1
1000.4 1005.8 1009.4 1012.0 1014.2 1015.5 1016.2 1016.1 1015.4 1013.5 1010.3
3.037 2.998 2.941 2.840 2.721 2.570 2.384 2.187 1.983 1.776 1.555
2.639 2.579 2.515 2.445 2.360 2.238 2.076 1.915 1.758 1.591 1.411
2.304 2.256 2.213 2.150 2.076 1.987 1.857 1.725 1.603 1.463 1.320
2.048 1.999 1.960 1.904 1.844 1.769 1.659 1.550 1.437 1.319 1.211
1008.9 1013.4 1017.0 1020.0 1022.2 1024.0 1025.0 1024.9 1024.1 1022.7 1019.9
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to ± 0.01 s, and the arithmetic mean is taken for the calculation of the viscosity. Because the flow times are greater than 200 s and the capillary diameter is 0.55 mm, which is much less than the tube length of 100 mm, both kinetic energy and tube end corrections are negligible. The viscometer is calibrated with triple distilled water and dry cyclohexane. The estimated uncertainty in the viscosity measurements is found to be less than 1%. The densities, ρ, of pure liquids and their mixtures are determined using a 10 −5 m 3 double-arm pycnometer as described by Nikam et al. [29]. The pycnometer is calibrated using conductivity water with 995.61 kg m −3 as its density at 303.15 K. A traveling microscope that could be read to 0.01 mm is used for recording the position of the liquid levels in the two arms of the air bubble free pycnometer. The density values from triplicate replication at each temperature are reproducible within 2 × 10 −1 kg m −3 and the uncertainty in the measurement of density is found to be 2 parts in 10 4 parts. Temperature control for the measurement of viscosity and density is achieved by using a microprocessor assisted circulating water bath (supplied by Mac, New Delhi) regulated to ± 0.01 K, using a proportional temperature controller. IR measurements for all the three binary mixtures of NMP over the entire composition range are recorded using Bruker FT-IR spectrophotometer (Germany), alpha-T with universal module, with zinc optics operated by opus software, in the frequency range of 4000 to 350 cm −1. The uncertainty in the measurement of wave number is within ± 0.1 cm −1. 3. Results and discussion
Fig. 1. Dependence of excess molar volume on mole fraction of NMP(x1) for the systems NMP + CB (a), NMP + BB (b), NMP + AB (c) at 303.15 K (♦), 308.15 K (■), 313.15 K (▲), 318.15 K (Δ) symbols indicate the experimental values and the solid curves indicate the Redlich–Kister values.
2. Experimental section The commercially available pure solvents are used in the present investigation. NMP (Merck > 99%) is distilled at low pressure and stored over freshly activated 3 Å molecular sieves. Chlorobenzene (>99%), bromobenzene (>99%) and aniline (>99%) procured from S.D. fine chemicals (India) are purified by using fractionating column [19] and the middle fractions are used for the experimental study. The purity of the chemicals was assessed by comparing their measured densities (ρ) and viscosities (η), which were in good agreement with literature [20–28] values as can be seen in Table 1. The mixtures are prepared gravimetrically using an electronic balance (Shimadzu AY120) with an uncertainty of ±1 × 10 −7 kg and stored in air-tight glass bottles. The uncertainty in mole fraction is estimated to be 1 × 10 −4. It is ensured that the components are adequately mixed before being transferred in to the apparatus. The required properties are measured within one day of the mixture preparation. The viscosity, η, of the pure liquids and liquid mixtures is determined using an Ubbelohde suspended-level viscometer. The viscometer is suspended in a thermostated water bath in which the temperature is maintained constant to ±0.01 K. Three sets of readings for the flow times are taken by using a Racer stop watch that can register time
The experimental values of density, viscosity for all the three binary mixtures at temperatures of 303.15, 308.15, 313.15 and 318.15 K are presented in Table 2. It is evident from Table 2 that all the three binary systems exhibit non-linear increase or decrease in ρ and η values with composition of NMP suggesting the presence of intermolecular interactions between the component molecules of the mixtures [26,30]. However, the nature and strength of interaction are well reflected in the E excess parameters like excess molar volume (Vm ), excess partial molar volume (V Em;1 ), excess Gibb's free energy of activation (ΔG⁎E) of viscous flow and deviation in viscosity (Δη) etc., as these parameters are found to be more sensitive toward intermolecular interactions in the liquid mixtures [31–33]. 3.1. Volumetric studies E The excess molar volumes Vm are calculated using the measured densities of pure liquids and their mixtures using the equation:
E
V m ¼ ½ðx1 M 1 þ x2 M2 Þ=ρ−x1 M 1 =ρ1 −x2 M 2 =ρ2
ð1Þ
in which x1, x2, M1, M2, ρ1 and ρ2 represent the mole fractions, molar masses and densities of pure components, respectively, and ρ is the density of the liquid mixture. E The excess molar volumes Vm for each binary mixture are fitted to the Redlich–Kister type polynomial equation [34]: E
j−1
Y cal ¼ x1 x2 ∑Aj−1 ðx2 −x1 Þ
ð2Þ
where Aj − 1 are adjustable parameters. The values of coefficient Aj − 1 are evaluated by the method of least squares with all points weighed equally and the standard deviations are calculated using 1=2 2 E E σ Y E ¼ Σ Y expt −Y cal =ðm−nÞ
ð3Þ
where ‘m’ is the number of experimental data points and ‘n’ is the number of coefficients considered (n = 5 in the present study). The
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103
Table 4 E Excess molar volumes (Vm ) and partial molar volumes (V m;i ) for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. x1
106 × V m;1 /m3 mol−1
E 106 × Vm /m3 mol−1
303.15 K
308.15 K
313.15 K
106 × V m;2 /m3 mol−1
318.15 K
303.15 K
308.15 K
313.15 K
318.15 K
303.15 K
308.15 K
313.15 K
318.15 K
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 0.0000 0.000 0.000 0.000 0.1055 −0.191 −0.181 −0.200 0.2097 −0.335 −0.334 −0.343 0.3127 −0.423 −0.449 −0.476 0.4144 −0.502 −0.536 −0.562 0.5149 −0.534 −0.576 −0.601 0.6142 −0.500 −0.542 −0.574 0.7124 −0.458 −0.489 −0.518 0.8094 −0.359 −0.399 −0.435 0.9052 −0.204 −0.233 −0.256 1.0000 0.000 0.000 0.000
0.000 −0.234 −0.390 −0.526 −0.634 −0.666 −0.641 −0.569 −0.459 −0.292 0.000
94.231 95.053 95.481 95.828 96.154 96.425 96.606 96.699 96.745 96.790 96.826
93.977 95.336 95.828 96.133 96.447 96.752 96.982 97.105 97.150 97.174 97.196
94.067 95.664 96.253 96.583 96.891 97.185 97.409 97.536 97.592 97.627 97.655
95.663 96.197 96.629 96.994 97.313 97.589 97.816 97.984 98.083 98.119 98.119
102.776 102.736 102.657 102.534 102.347 102.113 101.881 101.700 101.552 101.264 100.407
103.532 103.469 103.381 103.273 103.092 102.826 102.531 102.292 102.155 102.004 101.434
104.010 103.935 103.830 103.714 103.537 103.281 102.992 102.745 102.572 102.349 101.659
104.931 104.902 104.821 104.692 104.510 104.270 103.975 103.646 103.335 103.133 103.186
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 0.0000 0.000 0.000 0.000 0.1089 −0.180 −0.182 −0.208 0.2158 −0.301 −0.313 −0.350 0.3205 −0.383 −0.396 −0.430 0.4232 −0.437 −0.452 −0.475 0.5239 −0.454 −0.480 −0.499 0.6227 −0.432 −0.453 −0.475 0.7197 −0.383 −0.399 −0.424 0.8149 −0.296 −0.315 −0.345 0.9083 −0.176 −0.190 −0.215 1.0000 0.000 0.000 0.000
0.000 −0.239 −0.389 −0.484 −0.529 −0.544 −0.519 −0.477 −0.388 −0.247 0.000
94.480 95.330 95.743 96.022 96.258 96.453 96.596 96.687 96.747 96.797 96.826
94.489 95.682 96.089 96.331 96.578 96.812 96.982 97.075 97.121 97.163 97.196
94.533 96.018 96.554 96.811 97.023 97.220 97.379 97.485 97.557 97.618 97.655
94.624 96.217 96.924 97.259 97.462 97.624 97.768 97.895 98.001 98.083 98.119
105.987 105.944 105.867 105.765 105.626 105.452 105.263 105.078 104.879 104.559 103.876
106.461 106.404 106.330 106.241 106.095 105.885 105.658 105.473 105.322 105.047 104.227
106.998 106.926 106.828 106.735 106.610 106.433 106.222 106.006 105.769 105.377 104.491
107.511 107.430 107.300 107.180 107.061 106.916 106.723 106.464 106.110 105.597 104.787
N-methyl-2-pyrrolidone(1) + aniline(2) 0.0000 0.000 0.000 0.0954 −0.276 −0.311 0.1918 −0.489 −0.541 0.2892 −0.686 −0.717 0.3876 −0.783 −0.820 0.4870 −0.826 −0.888 0.5875 −0.824 −0.882 0.6890 −0.703 −0.775 0.7915 −0.543 −0.601 0.8952 −0.334 −0.369 1.0000 0.000 0.000
0.000 −0.410 −0.654 −0.806 −0.922 −0.955 −0.932 −0.843 −0.677 −0.403 0.000
92.877 94.116 94.801 95.235 95.584 95.916 96.234 96.508 96.703 96.803 96.826
92.781 94.217 94.958 95.455 95.891 96.294 96.633 96.876 97.034 97.140 97.196
93.144 94.639 95.305 95.792 96.291 96.761 97.107 97.299 97.406 97.537 97.655
93.349 94.844 95.677 96.264 96.753 97.155 97.452 97.653 97.816 97.996 98.119
91.917 91.861 91.749 91.613 91.434 91.175 90.804 90.320 89.767 89.238 88.879
92.308 92.244 92.123 91.967 91.743 91.429 91.037 90.609 90.163 89.577 88.420
92.667 92.603 92.495 92.340 92.083 91.718 91.319 90.987 90.680 89.919 87.332
93.093 93.026 92.889 92.704 92.454 92.142 91.800 91.446 90.973 89.958 87.365
0.000 −0.368 −0.599 −0.738 −0.869 −0.918 −0.903 −0.803 −0.637 −0.373 0.000
fitting coefficients (Aj − 1) of the Redlich–Kister polynomial along with the standard deviations are presented in Table 3. The variation in excess molar volumes with mole fraction of NMP is shown in Fig. 1. The excess molar volume is negative over the entire E range of composition studied. The magnitude and the sign of Vm can be qualitatively examined by considering the physical, structural and chemical contributions [23]. The physical contribution consists of dispersion forces or weak dipole–dipole interactions that lead to E positive contribution toward Vm . The structural contribution involves
Fig. 2. Excess partial molar volumes, V Em;1 , of NMP (solid lines), in AB (○), CB(Δ), BB (◊), and excess partial molar volumes, V Em;2 , of AB (○), CB (Δ), BB (◊) in NMP (dotted lines) at 303.15 K against the mole fraction (x).
the geometrical effect allowing the fitting of molecules of two different sizes into each others' structure resulting in negative contribution E to Vm . Chemical contribution includes specific interactions such as the formation of hydrogen bonds, formation of charge transfer complexes and other complex forming interactions including strong dipole–dipole interactions between component molecules result in E negative Vm values. The experimental results in the present investigation suggest that the factors which are responsible for contraction in volume are dominant in the mixtures of NMP with AB, BB, and CB over the entire composition range. This indicates that the associated structure of the polar component (NMP) due to dipolar association has been broken by the added AB or BB or CB molecules. The negative E Vm indicates the contributions made by the strong dipole–dipole interactions between the unlike molecules of the components. The graphical representation of Fig. 1 and results in Table 4 reveal that excess molar volumes at 303.15 K for the binary mixtures of NMP with E AB (Vm =−0.826 cm3 mol−1 at x=0.4870) are higher when compared E to the mixtures of NMP+CB (Vm =−0.534 cm3 mol−1 at x=0.5149) or E NMP+BB (Vm =−0.454 cm3 mol−1 at x=0.5226). This may be due to i) the possibility of specific interactions between NMP and AB, besides dipole–dipole interactions, due to hydrogen bond formation [35] between the CO group of NMP (which acts as hydrogen bond acceptor) and N\H of AB which is a hydrogen bond donor (evidenced by IR spectral studies) and ii) higher electro negative difference between the C and N of sp 2C\NH2 bond in aniline. The replacement of Chloro-group by a Bromo-group, resulted in less negative values E of Vm in NMP + BB mixture. The decreased electro negativity and
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Table 5 Partial molar volume at infinite dilution for N-methyl-2-pyrrolidone (V1∞/10−6 m3 mol−1) and substituted benzene (V2∞/10−6 m3 mol−1) in the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. Eq. (12) V1∞
Eq. (11) V2∞
Eq. (12) V2∞
Eq. (10) V1E,∞
Eq. (12) V1E,∞
Eq. (11) V2E,∞
Eq. (12) V2E,∞
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 96.826 102.776 94.806 308.15 97.196 103.532 95.170 313.15 97.655 104.010 95.503 318.15 98.119 104.931 95.668
94.930 95.387 95.769 95.944
100.491 100.990 101.262 101.890
100.401 100.802 101.057 101.714
−2.020 −2.026 −2.152 −2.451
−2.285 −2.542 −2.748 −3.041
−1.896 −1.809 −1.887 −2.176
−2.375 −2.730 −2.953 −3.218
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 96.826 105.987 95.017 308.15 97.196 106.461 95.340 313.15 97.655 106.998 95.598 318.15 98.119 107.511 95.806
95.017 95.340 95.598 95.806
104.021 104.360 104.713 104.930
103.979 104.297 104.671 104.896
−1.809 −1.856 −2.057 −2.313
−1.966 −2.101 −2.285 −2.581
−1.719 −1.731 −1.908 −2.130
−2.008 −2.165 −2.327 −2.615
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 96.826 91.917 93.593 308.15 97.196 92.308 93.668 313.15 97.655 92.667 93.746 318.15 98.119 93.093 93.847
93.593 93.668 93.746 93.847
88.512 88.572 89.631 89.012
88.447 88.517 88.911 89.185
−3.233 −3.528 −3.909 −4.272
−3.405 −3.736 −3.036 −4.081
−3.164 −3.421 −3.878 −4.259
−3.470 −3.791 −3.756 −3.908
T/K
V10
Eq. (10) V1∞
V20
the increased molecular size [36] (molecular radius of chlorobenzene is 2.16 Å, while it is 2.19 Å for bromobenzene at 298.15 K) are E responsible for the observed trend in Vm in case of NMP + CB and NMP + BB mixtures. In addition to this, the strength of interactions may become stronger in NMP + AB mixture, due to the interstitial accommodation of molecules of aniline (Vm = 91.917 cm3 mol−1 at 303.15 K) into the voids of the aggregated NMP molecules [37], whose molar volume is less than that of NMP molecules (Vm = 96.826 cm3 mol−1 at 303.15 K). E The algebraic Vm values of NMP with AB, BB, CB follow the order: AB > CB>BB. Analogously a similar trend has been observed for another polar solvent, N,N-dimethylformamide with substituted benzenes under same experimental conditions by Ramadevi et al. [38]. The uncertainty in excess molar volume is found to be ±1 × 10−3 cm3 mol−1. E For each system the Vm values over the entire range of composition are decreasing with increasing temperature (Fig. 1) from 303.15 to 318.15 K. This may be due to the increase in kinetic energy of molecules with temperature rise, which decreases the existing interactions between NMP and substituted benzene leading to increase E in absolute Vm values. Further, the results of excess molar volume can be substantiated by studying partial molar volumes. The partial molar volumes of components 1 (NMP) and 2 (substituted benzene), respectively in the binary liquid mixtures from their molar volumes are calculated using the following relations [39]:
∂V Em E 0 V m;1 ¼ V m þ V 1 þ ð1−x1 Þ ∂x1
∂V Em E 0 V m;2 ¼ V m þ V 2 −x1 ∂x1
! ð4Þ T;P
! ð5Þ T;P
where V10 and V20 are the molar volumes of the pure NMP and substituted E benzene respectively. The derivatives (∂Vm /∂x1)T,P of Eq. (4) and Eq. (5) are obtained by differentiating Eq. (2) with respect tox1. This leads to the partial molar volumes as expressed by the following relationships:
0 2 V m;1 ¼ V 1 þ x2
n X i¼0
i
2
Ai ð1−2x2 Þ −2x2 ð1−x2 Þ
n X i¼1
i−1
iAi ð1−2x2 Þ
ð6Þ
0 2 V m;2 ¼ V 2 þ ð1−x2 Þ 2
þ 2x2 ð1−x2 Þ
n X i¼0 n X
i
Ai ð1−2x2 Þ
i−1
iAi ð1−2x2 Þ
:
ð7Þ
i¼1
The values of partial molar volumes are used to calculate the excess partial molar volumes using the equations E V m;1 ¼ V m;1 −V 1
ð8Þ
E V m;2 ¼ V m;2 −V 2 :
ð9Þ
The values of partial molar volumes V m;1 and V m;2 along with excess molar volumes are furnished in Table 4. From Table 4 it is clear that the values of V m;1 and V m;2 for both the components in the mixture are smaller than their respective molar volumes in the pure state, i.e., a contraction in volume takes place on mixing NMP with substituted benzenes under study. These results also support the observed negative E values of Vm in all the binary systems at all the four temperatures investigated. Fig. 2 shows the calculated results for excess partial molar volumes ( V Em;i ) of substituted benzenes, AB or BB or CB ( V Em;2 ) in their binary mixtures with NMP (V Em;1 ) at 303.15 K. Examination of Fig. 2 indicates that contraction in partial molar volume takes place either NMP is mixed with the three substituted benzenes (solid line) or vice versa (dotted line) confirming the strong interactions between the unlike E molecules which support the conclusions drawn from Vm values. The E V m;i values at other higher temperatures follow the same trends but show different values, and hence the data is not graphically displayed to minimize the number of figures. The uncertainty in partial molar volumes is found to be ~ 1 × 10 − 3 cm 3 mol − 1. The partial properties at infinite dilution are of interest because, at that limit, the condition of vanishing solute–solute interactions prevails and they provide information regarding solute–solvent interactions, independent of composition effect. To get useful indications in E regard to the accuracy of fitting of the Vm data, we have calculated the partial molar volume at infinite dilution through apparent molar volumes. The apparent molar volume of NMP in substituted benzene, Vϕ1, and the apparent molar volume of substituted benzene in NMP, Vϕ2, can be expressed [40] as: 0 E V ϕ1 ¼ V 1 þ V m =x1
ð10Þ
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111
105
Table 6 Experimental and calculated values of viscosity (η/mPa s) for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. x1
η Expt.
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
η Expt.
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.271 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.781 0.876 0.964 1.046 1.121 1.191 1.254 1.312 1.364 1.411
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.662 0.732 0.803 0.873 0.941 1.006 1.066 1.121 1.170 1.211
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.690 0.779 0.860 0.933 0.998 1.055 1.104 1.147 1.182 1.211
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.271 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.781 0.876 0.964 1.046 1.121 1.191 1.254 1.312 1.364 1.411
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.662 0.732 0.803 0.873 0.941 1.006 1.066 1.121 1.170 1.211
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.690 0.779 0.860 0.933 0.998 1.055 1.104 1.147 1.182 1.211
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.271 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.781 0.876 0.964 1.046 1.121 1.191 1.254 1.312 1.364 1.411
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
308.15 K 0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.476 1.524 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.843 0.955 1.059 1.153 1.240 1.318 1.388 1.451 1.507 1.555
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.723 0.805 0.886 0.965 1.041 1.112 1.177 1.234 1.282 1.320
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.710 0.778 0.845 0.913 0.980 1.048 1.116 1.184 1.252 1.320
313.15 K
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411 318.15 K 0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
308.15 K 0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.476 1.524 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.843 0.955 1.059 1.153 1.240 1.318 1.388 1.451 1.507 1.555
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.723 0.805 0.886 0.965 1.041 1.112 1.177 1.234 1.282 1.320
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.710 0.778 0.845 0.913 0.980 1.048 1.116 1.184 1.252 1.320
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.476 1.524 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.843 0.955 1.059 1.153 1.240 1.318 1.388 1.451 1.507 1.555
313.15 K
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411 318.15 K 0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
308.15 K 0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411
(continued on next page)
106
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Table 6 (continued) η Expt.
x1
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.710 0.778 0.845 0.913 0.980 1.048 1.116 1.184 1.252 1.320
η Expt.
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.662 0.732 0.803 0.873 0.941 1.006 1.066 1.121 1.170 1.211
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.690 0.779 0.860 0.933 0.998 1.055 1.104 1.147 1.182 1.211
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 313.15 303.15 K K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
308.15 K 318.15
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.723 0.805 0.886 0.965 1.041 1.112 1.177 1.234 1.282 1.320
0 E V ϕ2 ¼ V 2 þ V m =x2 :
ð11Þ
Graphical extrapolation of Vϕ1 to x1 = 0 leads to the desired value of V1∞ and extrapolation of Vϕ2 to x2 = 0 gives V2∞. Partial molar volumes at infinite dilution can also be calculated from the excess molar volumes using a method based on extrapolation of the “reduced volume” [41]. Linear extrapolation of the reduced E volume represented by Vm /x1x2 to x1 = 0 leads to the desired V1∞ and a E similar extrapolation of Vm /x1x2 to x2 = 0 leads to V2∞. The expression for reduced volume can be obtained by rearranging Eq. (10) and division by x2 E 0 V m =x1 x2 ¼ V ϕ1 −V 1 =x2 :
0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
3.2. Viscosity studies The dynamic viscosities of the liquid mixtures have been calculated using empirical relations given by Grunberg–Nissan, Katti–Chaudari, Heric–Brewer and Hind et al. Grunberg and Nissan [43] proposed the following equation for the measurement of viscosity of liquid mixtures: ln η ¼ x1 ln η1 þ x2 ln η2 þ x1 x2 G12
ð13Þ
ð12Þ
The partial molar volumes at infinite dilution calculated by the two methods are presented in Table 5 along with V1E,∞ and V2E,∞ values. From the table, it is clear that the V1E,∞ values calculated by the two approaches at all the temperatures under study have the same sign and their differences are small. The agreement between these sets indicates that on mixing, contraction in volume occurs for the binary liquid mixtures of NMP with substituted benzenes under investigation. Similar trends are reported by H. Wang et al. [42] for the binary mixture of NMP with an ionic liquid 1-methyl-3-methylimidazolium hexafluoro phosphate.
Table 7 Interaction parameters calculated from Eqs. (13)–(16) and the corresponding standard deviations for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. Δ12
σ
H12
σ
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 0.608 0.0127 0.589 0.0130 308.15 0.514 0.0085 0.493 0.0089 313.15 0.447 0.0069 0.425 0.0073 318.15 0.380 0.0057 0.356 0.0060
0.616 0.522 0.455 0.388
0.0126 0.0085 0.0069 0.0057
1.317 1.176 1.075 0.959
0.0028 0.0041 0.0427 0.0382
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 0.287 0.0050 0.273 0.0052 308.15 0.274 0.0034 0.259 0.0036 313.15 0.255 0.0028 0.239 0.0031 318.15 0.232 0.0024 0.213 0.0028
0.393 0.379 0.361 0.338
0.0036 0.0022 0.0017 0.0016
1.387 1.302 1.196 1.074
0.0013 0.0009 0.0011 0.0019
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 0.626 0.0047 0.592 0.0047 308.15 0.522 0.0131 0.485 0.0131 313.15 0.452 0.0089 0.414 0.0093 318.15 0.380 0.0108 0.339 0.0114
0.628 0.524 0.454 0.381
0.0047 0.0131 0.0089 0.0108
2.784 2.365 2.090 1.833
0.0265 0.0184 0.0141 0.0144
T/K
G12
σ
Wvis/RT
σ
Fig. 3. Dependence of Deviation in viscosity on mole fraction of NMP(x1) for the systems NMP + CB (a), NMP + BB (b), NMP + AB (c) at 303.15 K (♦), 308.15 K (■), 313.15 K (▲), 318.15 K (Δ) symbols indicate the experimental values and the solid curves indicate the Redlich–Kister values.
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111
107
The experimental values of viscosity for all the three binary mixtures have been used to calculate the viscosity deviation (Δη) which is represented by the equation Δη ¼ ηmix − x1 η1 þ x2 η2
ð17Þ
where η1 and η2 are the viscosities and x1,x2 are the mole fractions of pure liquids 1 and 2 respectively. The variation in deviation of viscosity with mole fraction of NMP is shown in Fig. 3. The value and magnitude of Δη depends on molecular shape of the components in addition to intermolecular forces. In general, for systems where dispersion forces and dipolar interactions are operating Δη values are found to be negative whereas charge transfer and hydrogen bonding interaction lead to positive Δη values [47,48]. In the present study, the values of deviations in viscosity Δη are all positive (Fig. 3) in the entire range of composition with a maximum at a mole fraction range of 0.48–0.53 indicating specific interaction between unlike molecules. Our finding is in good agreement with the view proposed by Fort and Moore [49] that liquids of dissimilar molecular size mix up with decrease in volume, yielding negative E Vm value and positive Δη values. The uncertainty in the deviation of viscosity is found to be less than 0.5%. The absolute value of deviations in viscosity decreases in all the systems as temperature is raised. An increase in temperature decreases the self association of pure components and hetero association between unlike molecules, due to the increase of thermal energy. This leads to less positive values of Δη with increasing temperature as observed in the present study. Similar temperature dependence of Δη has been reported by Chakma et al. [50] for aqueous solutions of NMP. The values of Δη for the binary mixtures of NMP with AB, BB, and CB follow the order: AB > CB > BB.
Fig. 4. Variation of Deviations in excess Gibb's free energy of activation of viscous flow with mole fraction of NMP(x1) for the systems NMP + CB (a), NMP + BB (b), NMP + AB (c) at 303.15 K (♦), 308.15 K (■), 313.15 K (▲), 318.15 K (Δ) symbols indicate the experimental values and the solid curves indicate the Redlich–Kister values.
where G12 is an interaction parameter, which is a function of viscosity of component liquids 1 and 2 and temperature. Katti and Chaudhri's [44] equation for the dynamic viscosity of the liquid mixture is lnðηV Þ ¼ x1 ln η1 V 1 þ x2 ln η2 V 2 þ x1 x2 W vis =RT
ð14Þ
where Wvis is an interaction term. Heric and Brewer [45] derived the following equation to calculate the viscosity of the binary liquid mixtures: ln η ¼ x1 ln η1 þ x2 ln η2 þ x1 ln M1 þ x2 ln M2 − lnðx1 M 1 þ x2 M2 Þ þ x1 x2 Δ12 ð15Þ where Δ12 is the interaction term and other symbols have their usual meaning. The expression to determine the viscosity of the binary liquid mixtures proposed by Hind et al. [46] is given by 2
2
η ¼ x1 η1 þ x2 η2 þ 2x1 x2 H 12
ð16Þ
where H12 is an interaction term. The experimental and theoretical values of viscosity of the liquid mixtures calculated using Eqs. (13)–(16) are presented in Table 6. The evaluated interaction parameters G12, Wvis, Δ12 and H12 along with the standard deviations, σ, are presented in Table 7. All the empirical relations gave a reasonable fit, but the viscosity values calculated using Grunberg–Nissan relation are in good agreement with the experimental values.
3.3. Gibb's free energy studies Excess Gibb's free energy of activation (ΔG⁎E) of viscous flow is obtained by E
ΔG
¼ RT lnðηV Þ− x1 ln η1 V 1 þ x2 ln η2 V 2
ð18Þ
where ‘R’ is the universal gas constant, ‘V’ is the molar volume of the mixture and ‘T’ is the absolute temperature and x1 and x2 are mole fractions. The variation in excess Gibb's free energy of activation of viscous flow with mole fraction of NMP is shown in Fig. 4. It is observed that ΔG⁎E is positive (Fig. 4) in all the three systems under investigation. The positive values of ΔG⁎E suggest the presence of specific and strong interactions [30] (like complex formation, strong dipole–dipole interactions, hydrogen bonding etc.) between the components of the mixtures. In the pure state molecules of CB, BB is associated through dipole–dipole interactions [24] and aniline exists in associated form through hydrogen bonding between like molecules [26]. Observed positive values of ΔG⁎E indicate that the mixing of NMP with CB or BB or AB will induce the breaking up of self associates and leads to the formation of charge transfer complexes as NMP is good donor and substituted benzenes act as good acceptors [10]. The ΔG⁎E values for all the binary systems under study are found to decrease with rise in temperature from 303.15 to 318.15 K indicating the weakening of intermolecular interactions at elevated temperatures. The negative values of excess molar volume and positive values of deviation in viscosity support the observed variation in excess Gibb's free energy of activation of viscous flow. The values of deviation in viscosity, Δη, and Gibb's free energy of activation of viscous flow, ΔG⁎E, for each binary mixture are fitted to the Redlich–Kister polynomial (Eq. (2)) and the corresponding coefficients determined by the method of least squares, together with the standard deviations are represented in Table 8.
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Table 8 Coefficients Aj −1 of the Redlich–Kister equation Eq. (2) together with the standard deviations of excess parameters for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. T/K
A0
A1
A2
A3
0.3678 0.2914 0.2193 0.1538
−0.0208 −0.0362 −0.0365 −0.0848
−0.0801 −0.2028 −0.1921 −0.2315
−0.0210 −0.0296 −0.0011 0.0925
N-methyl-2-pyrrolidone(1) + bromobenzene(2) Δη/mPa s 303.15 308.15 313.15 318.15
0.246 0.237 0.204 0.160
0.027 0.002 −0.018 −0.017
−0.076 −0.014 −0.081 −0.047
−0.062 −0.037 0.014 −0.006
N-methyl-2-pyrrolidone(1) + aniline(2) Δη/mPa s 303.15 308.15 313.15 318.15
1.0088 0.7796 0.6411 0.5121
−0.4071 −0.7976 −0.7031 −0.6487
−0.2706 −0.4652 −0.3704 −0.1353
0.4683 0.3659 0.2997 0.1789
σ
A4
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) Δη/mPa s 303.15 308.15 313.15 318.15
0.0690 0.1774 0.1466 0.1670
0.072 0.040 0.078 −0.003
0.4757 0.8246 0.7137 0.4635
0.002 0.001 0.001 0.001
0.001 0.001 0.001 0.001
0.005 0.006 0.008 0.006
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) ΔG⁎E/J mol−1 303.15 308.15 313.15 318.15
1457.41 1308.30 1172.79 1044.82
427.94 321.68 266.88 67.96
37.89 −356.59 −412.60 −606.69
−23.44 −126.66 −87.75 164.40
77.27 360.06 320.52 406.72
3.100 3.173 2.080 3.128
N-methyl-2-pyrrolidone(1) + bromobenzene(2) ΔG⁎E/J mol−1 303.15 308.15 313.15 318.15
714.13 653.97 641.13 598.97
193.24 136.89 83.07 76.14
−81.64 62.16 −112.46 −115.70
−96.67 −88.40 43.60 −22.83
73.40 −36.01 88.61 −43.48
1.963 1.414 1.823 1.804
1518.55 1341.73 1184.17 1039.01
29.59 90.54 127.66 35.96
−368.42 −901.86 −942.97 −946.96
−243.48 −537.96 −470.42 −129.29
540.01 1060.98 1038.31 637.51
4.628 7.253 10.965 8.832
N-methyl-2-pyrrolidone(1) + aniline(2) ΔG⁎E/J mol−1 303.15 308.15 313.15 318.15
3.4. Spectral studies The IR spectrum, which gives significant information about the functional groups, can be substantially influenced by the surrounding condensed medium. Hence IR studies have been used to investigate solution structure and provide physical information about
intermolecular interaction [44]. In order to study the strength of molecular association at specific concentrations; infrared spectra have been recorded for the pure NMP (Fig. 5) and equimolar mixtures of NMP and X (X = CB or BB or AB) at room temperature (303.15 K). From the recorded infrared spectra it is evident that in pure NMP, stretching band ( band is a typical amide I band in case of
Fig. 5. Neat FT‐IR spectrum of pure NMP.
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111 Table 9 Experimental FT-IR frequencies for the binary mixture NMP + AB at 303.15 K. x
νCO (cm−1)
νNHsys (cm−1)
νNHasym (cm−1)
0.0954 0.1918 0.2892 0.3876 0.4870 0.5875 0.6890 0.7915 0.8952
1674.5 1671.6 1663.3 1661.8 1659.9 1668.7 1679.6 1681.0 1684.1
3348.2 3345.3 3343.1 3342.0 3341.2 3344.7 3349.1 3350.2 3347.7
3430.4 3426.1 3425.2 3423.0 3420.4 3424.3 3429.6 3434.5 3436.0
cyclic tertiary amides) appears at 1684 cm − 1 (Fig. 4). The values of stretching frequency for the equimolar mixtures of NMP + X are observed to be red shifted in the order AB (1659.9 cm − 1); CB (1664.4 cm − 1); BB (1666.4 cm − 1) which supports the conclusions from the thermodynamic parameters as discussed above. In order to analyze the observed stronger interactions in the NMP+ AB mixture than the remaining two systems, the study is focused on the presence of inter molecular hydrogen bonding (NH\O) in the NMP and AB mixture. IR spectrum of pure aniline has exhibited two sharp less intense bands at 3430.0 and 3354.7 cm − 1 respectively due to NH asymmetric and symmetric stretching vibrations. Sharpness in the bands can be attributed to weaker tendency to from hydrogen bond [51]. Addition of NMP to AB results in the red shift of NH bands in AB and stretching band of NMP as explained above. The results indicate that the interactions are taking place through \NH2 group of AB and group of NMP. The wave number at maximum absorbance of the \NH2 and the stretching frequencies for the NMP+ AB mixture over the whole composition range are listed in Table 9. It is seen from Fig. 6 that in the NMP–AB system the bands appear at 3341.2 cm−1 and 3420.4 cm−1 for 0.4870 mole fraction; with further increase or decrease in concentration, the \NH bands shift
109
Table 10 Comparison of experimental and theoretical FT-IR values for the 1:1 complex of NMP + AB. Band
NHasym NHsys
ν/cm−1 Expt.
3420.4 3341.2
ν/cm−1 Theoretical AM1
RM1
PM3
MNDO
3488 3444
3438 3364
3530 3510
3584 3551
toward higher frequency which indicates the weakening of molecular association [52] through inter molecular hydrogen bonding. Thus, the study of IR spectra shows that the strength of complex formation becomes maximum at 0.4870 mole fraction for the NMP+ AB system at 303.15 K. Similar results of hydrogen bonding, between NMP and butanediol are reported by S. K. Mehta et al. [35]. The minimum energy structures of aniline, NMP and the equimolar complex of aniline and NMP for vibrational frequencies are theoretically obtained from Semi-empirical Hamiltonian quantum mechanical calculations [53] such as Austin Model 1 (AM1), Recife Model (RM1), Parameterized Model number 3 (PM3) and Modified Neglect of Differential Overlap (MNDO) converged geometry optimization method using Spartan '08 Modeling software. All these models under study showed a shift in the symmetric and asymmetric stretching frequencies of NH band of aniline in the IR spectra predicted for aniline and 1:1 complex of NMP+ AB using Spartan'08, suggesting the presence of hydrogen bonding interaction [54] between NMP and aniline molecules. However, the comparison of experimental and theoretical FT-IR values shown in Table 10 indicates that the IR values determined theoretically using RM1 are in good agreement with the experimental values. The optimized geometrical structure for the formation of hydrogen bonding in the NMP+ AB system along with the corresponding IR spectrum predicted using RM1 model, obtained from Hamiltonian quantum mechanical calculations using Spartan Modeling software, is shown in Fig. 7.
Fig. 6. Observed \NH stretching bands in IR spectrum of the NMP + AB mixture at three different mole fractions of NMP(x1).
110
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111
References
Fig. 7. (a) The optimized geometrical structure and (b) theoretical IR spectrum using model RM1 for the 1:1 complex of the NMP + AB system obtained from Hamiltonian quantum mechanical calculations.
4. Conclusions New experimental values of liquid densities and viscosities for the binary mixtures of N-methyl-2-pyrrolidone (NMP) with aniline, chlorobenzene and bromobenzene, have been reported at 303.15, 308.15, 313.15 and 318.15 K and at atmospheric pressure over the entire comE position range of NMP. The computed values of Vm are found to be negative, where as Δη and ΔG⁎E values are positive for all the three binary mixtures over the entire range of composition at all the temperatures under investigation. The partial molar volumes at infinite dilution are calculated. The observed viscometric and volumetric studies suggest that strong interactions are present in all the systems investigated. Strength of interaction is maximum in NMP+ AB when compared to NMP + BB or CB. The Grunberg and Nissan empirical relation gives good agreement between experimental and theoretical viscosity values for all the systems studied. IR spectral results also suggest a specific interaction between the NMP and substituted benzenes under study. The NMP + AB system has hydrogen bonding interactions operated besides dipole–dipole and charge transfer interactions. The interaction of NMP with AB, BB, CB follows the order AB> CB > BB.
Acknowledgments One of the authors, Bala Karuna Kumar, D wishes to thank University Grants Commission of India for awarding teacher fellowship under FDP scheme. He also expresses his gratefulness to Rev. Fr. Dr. Francis Xavier S.J., Principal, Andhra Loyola College, Vijayawada for granting study leave.
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Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Thermodynamic and spectroscopic study of molecular interactions in the binary liquid mixtures of N-methyl-2-pyrrolidone and some substituted benzenes at different temperatures D. Bala Karuna Kumar a, K. Rayapa Reddy a, G. Srinivasa Rao b, G.V. Rama Rao c, C. Rambabu a,⁎ a b c
Department of Chemistry, Acharya Nagarjuna University, Dr. M.R.A.R. campus, Nuzvid, Andhra Pradesh, 521201, India Department of Physics, Andhra Loyola College, Vijayawada, Andhra Pradesh, 520 008, India Department of Physics, DAR College, Nuzvid, Andhra Pradesh, 521201, India
a r t i c l e
i n f o
Article history: Received 11 January 2012 Received in revised form 9 July 2012 Accepted 13 July 2012 Available online 26 July 2012 Keywords: Density Viscosity Excess molar volume Spectroscopy Binary mixture
a b s t r a c t The densities and viscosities for pure liquids N-methyl-2-pyrrolidone (NMP), aniline (AB), bromobenzene (BB), chlorobenzene (CB) and their binary mixtures containing NMP as a common component have been measured at 303.15, 308.15, 313.15 and 318.15 K as a function of composition of NMP. From these results, excess molar volumes, excess Gibb's free energy of activation of viscous flow and deviations in viscosity are computed. Excess properties are fitted to a Redlich–Kister type equation and the corresponding standard deviations are calculated. The experimental data of viscosity is used to test the applicability of empirical relations of Grunberg–Nissan, Katti–Chaudhri, Heric–Brewer and Hind et al. for the systems studied. The excess molar volumes are found to be negative whereas the deviations in viscosity and excess Gibb's free energy of activation of viscous flow values are found to be positive for all the mixtures, over the entire composition range. Partial molar volumes and apparent molar volumes at infinite dilution have been calculated. The variation of these properties with composition of NMP and temperature is discussed in terms of molecular interactions between component molecules. The strength of interaction of AB, BB, CB with NMP is found to obey the order AB > CB > BB. The IR, spectral studies of these binary mixtures also suggest specific interaction between the unlike molecules of the components and supported thermodynamic findings. © 2012 Elsevier B.V. All rights reserved.
1. Introduction In chemical process industries, materials are normally handled in fluid form and as a consequence, the physical, chemical and transport properties of liquids assume importance. When two or more solvent molecules are associated with one another to form a liquid mixture, it brings about a marked effect on the properties of the resulting system and differences in the intermolecular interactions of the solvents. So the properties of the liquid mixtures can be altered continuously within a reasonable range by varying the composition of the mixture till an optimum value of the desired parameter is attained. Pure liquids lack such flexibility. The data on some of the properties associated with liquids and liquid mixtures, like viscosity, density, excess molar volume etc., find extensive application in chemical engineering design, process simulation, solution theory and molecular dynamics. These properties are important from practical and theoretical point of view to understand liquid theory and provide information about molecular interactions [1–4].
⁎ Corresponding author. Tel.: +91 8656 233091; fax: +91 8656 235200. E-mail address: [email protected] (C. Rambabu). 0167-7322/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.molliq.2012.07.019
Liquid solvents play an important role in many chemical reactions and the choice of a proper solvent for a process primarily depends on the availability of physical properties [5]. Among such solvents N-methyl-2-pyrrolidone (NMP) is an important solvent as it is water-miscible, hygroscopic, colorless, and strongly polar liquid. NMP has the potential for use in, solvent extraction process as strong solubilizing agent [6], purification and crystallization of drugs [7]. It is also used in the manufacture of various compounds, including pigments, cosmetics, insecticides, herbicides, and fungicides. Its non-hazardous and ecological properties account for the reality that it is increasingly being used as an alternative for chlorinated hydrocarbons [3]. It is known that amides like NMP interact with substituted benzenes (aromatic hydrocarbons) by dipole–dipole interactions, and form some charge-transfer complexes [8,9]. Due to the strong hydrogen bonding acceptor ability of the oxygen, NMP can interact with hydrogen bond donors [3,10]. Substituted benzenes like chlorobenzene (CB), bromobenzene (BB) and aniline (hydrogen bond donor) find versatile applications in the industry; for instance chlorobenzene is used as a degreaser in the metal industry and thinning, dissolving agent in chemical industry. Both CB and BB readily undergo substitution reactions and can be used to synthesize various derivatives. Aniline (AB) is predominantly used in the manufacture of
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111 Table 1 Comparison of experimental values of density, ρ, and viscosity, η, of pure liquids with the corresponding literature values at 303.15 K. 10−3 × ρ/kg m−3
η/mPa s
Exptl
Lit.
Exptl
Lit.
N-methyl-2-pyrrolidone Chlorobenzene Bromobenzene
1.0238 1.0952 1.4815
1.555 0.721 0.985
1.5544 [21] 0.7210 [24] 0.9844 [24]
Aniline
1.0132
1.02376 [20] 1.0957 [22] 1.4814 [19] 1.4830 [26] 1.0133 [29] 1.0128 [28]
3.037
3.036 [27]
Liquid
Table 3 Coefficients Aj−1 of the Redlich–Kister equation, Eq. (2) and the corresponding stanE dard deviations (σ) of excess molar volumes (Vm /10−6 m3 mol−1) for the three binary mixtures of NMP at different temperatures. A3
A4
σ
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 −2.1268 0.3821 0.3026 308.15 −2.2961 0.3524 0.5879 313.15 −2.3960 0.3526 0.3834 318.15 −2.3800 0.1059 0.2239
−0.2691 0.2080 0.2658 0.2496
−0.6576 −0.9502 −0.9570 0.0554
0.011 0.010 0.011 0.003
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 −1.8124 0.1629 0.0056 308.15 −1.9163 0.1833 0.3091 313.15 −1.9959 0.0877 −0.0929 318.15 −2.1766 0.0572 −0.6205
−0.0454 0.0529 0.2200 0.3282
−0.4220 −0.8635 −0.7257 −0.3122
0.002 0.006 0.006 0.003
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 −3.3019 −0.1677 −0.0366 308.15 −3.5583 0.1463 0.1265 313.15 −3.6831 0.3216 0.3521 318.15 −3.8262 0.1510 −0.4538
0.6234 0.1175 −0.7338 −0.6300
−0.1552 −0.7196 −1.5922 −0.9690
0.016 0.010 0.010 0.007
T/K
synthetic dyes, drugs and as an accelerator in vulcanization of rubber [11]. In this context it will be quite interesting to investigate the properties of binary liquid mixtures of NMP with CB, BB and AB. Detailed literature survey shows that work has been carried out by different researchers on excess molar volumes of binary mixtures containing NMP + aromatic hydrocarbons [12,13], + hydrocarbons [14,15], + chloroethanes and chloroethenes [16], + an ether [17], + ketone [18], + branched alcohol [3] etc. However, no effort appears to have been made to investigate the physico-chemical properties, for the binary mixtures of NMP with chlorobenzene, bromobenzene and aniline. The present work is focused on the study of volumetric and viscometric properties, by measuring the densities and viscosities of the binary mixtures of NMP with chlorobenzene, bromobenzene and aniline over the complete composition range at temperatures of 303.15,
101
A0
A1
A2
308.15, 313.15 and 318.15 K and atmospheric pressure. It is also aimed to study the molecular interactions between NMP and substituted benzenes under investigation, with special reference to dipole–dipole and hydrogen bonding interactions with the help of IR spectral data of these mixtures at 303.15 K. Further, the experimental data of viscosity is used to test the applicability of empirical relations of Grunberg–Nissan, Katti– Chaudhri, Heric–Brewer and Hind et al. for the systems studied.
Table 2 Density, ρ, and viscosity, η, values for the binary mixtures of NMP at different temperatures. x1
ρ/kg m−3 303.15 K
η/mPa s 308.15 K
313.15 K
318.15 K
303.15 K
308.15 K
313.15 K
318.15 K
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 0.0000 1095.2 1087.2 0.1055 1090.1 1082.4 0.2097 1084.5 1077.3 0.3127 1078.3 1071.8 0.4144 1072.0 1066.0 0.5149 1065.2 1059.7 0.6142 1057.7 1052.6 0.7124 1050.1 1045.3 0.8094 1041.9 1037.6 0.9052 1033.1 1029.1 1.0000 1023.8 1019.9
1082.2 1077.6 1072.4 1067.1 1061.3 1055.0 1048.0 1040.7 1033.1 1024.5 1015.1
1072.7 1068.9 1064.3 1059.5 1054.4 1048.5 1042.0 1035.0 1027.6 1019.6 1010.3
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 0.0000 1481.5 1474.9 0.1084 1438.2 1431.9 0.2149 1394.0 1388.1 0.3193 1349.2 1343.6 0.4219 1304.0 1298.7 0.5226 1258.3 1253.4 0.6215 1212.1 1207.4 0.7186 1165.6 1161.1 0.8141 1118.7 1114.5 0.9078 1071.5 1067.5 1.0000 1023.8 1019.9
1467.5 1425.1 1381.7 1337.4 1292.6 1247.5 1201.8 1155.8 1109.5 1062.7 1015.1
1460.5 1418.7 1375.6 1331.7 1287.1 1242.1 1196.6 1150.9 1104.7 1058.0 1010.3
0.985 1.068 1.146 1.220 1.284 1.344 1.396 1.441 1.484 1.522 1.555
0.955 1.026 1.092 1.152 1.205 1.252 1.294 1.331 1.362 1.391 1.411
0.879 0.944 1.005 1.061 1.113 1.160 1.199 1.236 1.268 1.295 1.320
0.793 0.849 0.906 0.958 1.007 1.051 1.089 1.125 1.156 1.184 1.211
N-methyl-2-pyrrolidone(1) + aniline(2) 0.0000 1013.2 0.0954 1017.3 0.1918 1020.7 0.2892 1023.9 0.3876 1026.0 0.4870 1027.5 0.5875 1028.5 0.6890 1028.2 0.7915 1027.5 0.8952 1026.3 1.0000 1023.8
1005.0 1010.0 1013.5 1016.0 1018.4 1019.9 1020.7 1020.6 1019.8 1018.0 1015.1
1000.4 1005.8 1009.4 1012.0 1014.2 1015.5 1016.2 1016.1 1015.4 1013.5 1010.3
3.037 2.998 2.941 2.840 2.721 2.570 2.384 2.187 1.983 1.776 1.555
2.639 2.579 2.515 2.445 2.360 2.238 2.076 1.915 1.758 1.591 1.411
2.304 2.256 2.213 2.150 2.076 1.987 1.857 1.725 1.603 1.463 1.320
2.048 1.999 1.960 1.904 1.844 1.769 1.659 1.550 1.437 1.319 1.211
1008.9 1013.4 1017.0 1020.0 1022.2 1024.0 1025.0 1024.9 1024.1 1022.7 1019.9
102
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111
to ± 0.01 s, and the arithmetic mean is taken for the calculation of the viscosity. Because the flow times are greater than 200 s and the capillary diameter is 0.55 mm, which is much less than the tube length of 100 mm, both kinetic energy and tube end corrections are negligible. The viscometer is calibrated with triple distilled water and dry cyclohexane. The estimated uncertainty in the viscosity measurements is found to be less than 1%. The densities, ρ, of pure liquids and their mixtures are determined using a 10 −5 m 3 double-arm pycnometer as described by Nikam et al. [29]. The pycnometer is calibrated using conductivity water with 995.61 kg m −3 as its density at 303.15 K. A traveling microscope that could be read to 0.01 mm is used for recording the position of the liquid levels in the two arms of the air bubble free pycnometer. The density values from triplicate replication at each temperature are reproducible within 2 × 10 −1 kg m −3 and the uncertainty in the measurement of density is found to be 2 parts in 10 4 parts. Temperature control for the measurement of viscosity and density is achieved by using a microprocessor assisted circulating water bath (supplied by Mac, New Delhi) regulated to ± 0.01 K, using a proportional temperature controller. IR measurements for all the three binary mixtures of NMP over the entire composition range are recorded using Bruker FT-IR spectrophotometer (Germany), alpha-T with universal module, with zinc optics operated by opus software, in the frequency range of 4000 to 350 cm −1. The uncertainty in the measurement of wave number is within ± 0.1 cm −1. 3. Results and discussion
Fig. 1. Dependence of excess molar volume on mole fraction of NMP(x1) for the systems NMP + CB (a), NMP + BB (b), NMP + AB (c) at 303.15 K (♦), 308.15 K (■), 313.15 K (▲), 318.15 K (Δ) symbols indicate the experimental values and the solid curves indicate the Redlich–Kister values.
2. Experimental section The commercially available pure solvents are used in the present investigation. NMP (Merck > 99%) is distilled at low pressure and stored over freshly activated 3 Å molecular sieves. Chlorobenzene (>99%), bromobenzene (>99%) and aniline (>99%) procured from S.D. fine chemicals (India) are purified by using fractionating column [19] and the middle fractions are used for the experimental study. The purity of the chemicals was assessed by comparing their measured densities (ρ) and viscosities (η), which were in good agreement with literature [20–28] values as can be seen in Table 1. The mixtures are prepared gravimetrically using an electronic balance (Shimadzu AY120) with an uncertainty of ±1 × 10 −7 kg and stored in air-tight glass bottles. The uncertainty in mole fraction is estimated to be 1 × 10 −4. It is ensured that the components are adequately mixed before being transferred in to the apparatus. The required properties are measured within one day of the mixture preparation. The viscosity, η, of the pure liquids and liquid mixtures is determined using an Ubbelohde suspended-level viscometer. The viscometer is suspended in a thermostated water bath in which the temperature is maintained constant to ±0.01 K. Three sets of readings for the flow times are taken by using a Racer stop watch that can register time
The experimental values of density, viscosity for all the three binary mixtures at temperatures of 303.15, 308.15, 313.15 and 318.15 K are presented in Table 2. It is evident from Table 2 that all the three binary systems exhibit non-linear increase or decrease in ρ and η values with composition of NMP suggesting the presence of intermolecular interactions between the component molecules of the mixtures [26,30]. However, the nature and strength of interaction are well reflected in the E excess parameters like excess molar volume (Vm ), excess partial molar volume (V Em;1 ), excess Gibb's free energy of activation (ΔG⁎E) of viscous flow and deviation in viscosity (Δη) etc., as these parameters are found to be more sensitive toward intermolecular interactions in the liquid mixtures [31–33]. 3.1. Volumetric studies E The excess molar volumes Vm are calculated using the measured densities of pure liquids and their mixtures using the equation:
E
V m ¼ ½ðx1 M 1 þ x2 M2 Þ=ρ−x1 M 1 =ρ1 −x2 M 2 =ρ2
ð1Þ
in which x1, x2, M1, M2, ρ1 and ρ2 represent the mole fractions, molar masses and densities of pure components, respectively, and ρ is the density of the liquid mixture. E The excess molar volumes Vm for each binary mixture are fitted to the Redlich–Kister type polynomial equation [34]: E
j−1
Y cal ¼ x1 x2 ∑Aj−1 ðx2 −x1 Þ
ð2Þ
where Aj − 1 are adjustable parameters. The values of coefficient Aj − 1 are evaluated by the method of least squares with all points weighed equally and the standard deviations are calculated using 1=2 2 E E σ Y E ¼ Σ Y expt −Y cal =ðm−nÞ
ð3Þ
where ‘m’ is the number of experimental data points and ‘n’ is the number of coefficients considered (n = 5 in the present study). The
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111
103
Table 4 E Excess molar volumes (Vm ) and partial molar volumes (V m;i ) for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. x1
106 × V m;1 /m3 mol−1
E 106 × Vm /m3 mol−1
303.15 K
308.15 K
313.15 K
106 × V m;2 /m3 mol−1
318.15 K
303.15 K
308.15 K
313.15 K
318.15 K
303.15 K
308.15 K
313.15 K
318.15 K
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 0.0000 0.000 0.000 0.000 0.1055 −0.191 −0.181 −0.200 0.2097 −0.335 −0.334 −0.343 0.3127 −0.423 −0.449 −0.476 0.4144 −0.502 −0.536 −0.562 0.5149 −0.534 −0.576 −0.601 0.6142 −0.500 −0.542 −0.574 0.7124 −0.458 −0.489 −0.518 0.8094 −0.359 −0.399 −0.435 0.9052 −0.204 −0.233 −0.256 1.0000 0.000 0.000 0.000
0.000 −0.234 −0.390 −0.526 −0.634 −0.666 −0.641 −0.569 −0.459 −0.292 0.000
94.231 95.053 95.481 95.828 96.154 96.425 96.606 96.699 96.745 96.790 96.826
93.977 95.336 95.828 96.133 96.447 96.752 96.982 97.105 97.150 97.174 97.196
94.067 95.664 96.253 96.583 96.891 97.185 97.409 97.536 97.592 97.627 97.655
95.663 96.197 96.629 96.994 97.313 97.589 97.816 97.984 98.083 98.119 98.119
102.776 102.736 102.657 102.534 102.347 102.113 101.881 101.700 101.552 101.264 100.407
103.532 103.469 103.381 103.273 103.092 102.826 102.531 102.292 102.155 102.004 101.434
104.010 103.935 103.830 103.714 103.537 103.281 102.992 102.745 102.572 102.349 101.659
104.931 104.902 104.821 104.692 104.510 104.270 103.975 103.646 103.335 103.133 103.186
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 0.0000 0.000 0.000 0.000 0.1089 −0.180 −0.182 −0.208 0.2158 −0.301 −0.313 −0.350 0.3205 −0.383 −0.396 −0.430 0.4232 −0.437 −0.452 −0.475 0.5239 −0.454 −0.480 −0.499 0.6227 −0.432 −0.453 −0.475 0.7197 −0.383 −0.399 −0.424 0.8149 −0.296 −0.315 −0.345 0.9083 −0.176 −0.190 −0.215 1.0000 0.000 0.000 0.000
0.000 −0.239 −0.389 −0.484 −0.529 −0.544 −0.519 −0.477 −0.388 −0.247 0.000
94.480 95.330 95.743 96.022 96.258 96.453 96.596 96.687 96.747 96.797 96.826
94.489 95.682 96.089 96.331 96.578 96.812 96.982 97.075 97.121 97.163 97.196
94.533 96.018 96.554 96.811 97.023 97.220 97.379 97.485 97.557 97.618 97.655
94.624 96.217 96.924 97.259 97.462 97.624 97.768 97.895 98.001 98.083 98.119
105.987 105.944 105.867 105.765 105.626 105.452 105.263 105.078 104.879 104.559 103.876
106.461 106.404 106.330 106.241 106.095 105.885 105.658 105.473 105.322 105.047 104.227
106.998 106.926 106.828 106.735 106.610 106.433 106.222 106.006 105.769 105.377 104.491
107.511 107.430 107.300 107.180 107.061 106.916 106.723 106.464 106.110 105.597 104.787
N-methyl-2-pyrrolidone(1) + aniline(2) 0.0000 0.000 0.000 0.0954 −0.276 −0.311 0.1918 −0.489 −0.541 0.2892 −0.686 −0.717 0.3876 −0.783 −0.820 0.4870 −0.826 −0.888 0.5875 −0.824 −0.882 0.6890 −0.703 −0.775 0.7915 −0.543 −0.601 0.8952 −0.334 −0.369 1.0000 0.000 0.000
0.000 −0.410 −0.654 −0.806 −0.922 −0.955 −0.932 −0.843 −0.677 −0.403 0.000
92.877 94.116 94.801 95.235 95.584 95.916 96.234 96.508 96.703 96.803 96.826
92.781 94.217 94.958 95.455 95.891 96.294 96.633 96.876 97.034 97.140 97.196
93.144 94.639 95.305 95.792 96.291 96.761 97.107 97.299 97.406 97.537 97.655
93.349 94.844 95.677 96.264 96.753 97.155 97.452 97.653 97.816 97.996 98.119
91.917 91.861 91.749 91.613 91.434 91.175 90.804 90.320 89.767 89.238 88.879
92.308 92.244 92.123 91.967 91.743 91.429 91.037 90.609 90.163 89.577 88.420
92.667 92.603 92.495 92.340 92.083 91.718 91.319 90.987 90.680 89.919 87.332
93.093 93.026 92.889 92.704 92.454 92.142 91.800 91.446 90.973 89.958 87.365
0.000 −0.368 −0.599 −0.738 −0.869 −0.918 −0.903 −0.803 −0.637 −0.373 0.000
fitting coefficients (Aj − 1) of the Redlich–Kister polynomial along with the standard deviations are presented in Table 3. The variation in excess molar volumes with mole fraction of NMP is shown in Fig. 1. The excess molar volume is negative over the entire E range of composition studied. The magnitude and the sign of Vm can be qualitatively examined by considering the physical, structural and chemical contributions [23]. The physical contribution consists of dispersion forces or weak dipole–dipole interactions that lead to E positive contribution toward Vm . The structural contribution involves
Fig. 2. Excess partial molar volumes, V Em;1 , of NMP (solid lines), in AB (○), CB(Δ), BB (◊), and excess partial molar volumes, V Em;2 , of AB (○), CB (Δ), BB (◊) in NMP (dotted lines) at 303.15 K against the mole fraction (x).
the geometrical effect allowing the fitting of molecules of two different sizes into each others' structure resulting in negative contribution E to Vm . Chemical contribution includes specific interactions such as the formation of hydrogen bonds, formation of charge transfer complexes and other complex forming interactions including strong dipole–dipole interactions between component molecules result in E negative Vm values. The experimental results in the present investigation suggest that the factors which are responsible for contraction in volume are dominant in the mixtures of NMP with AB, BB, and CB over the entire composition range. This indicates that the associated structure of the polar component (NMP) due to dipolar association has been broken by the added AB or BB or CB molecules. The negative E Vm indicates the contributions made by the strong dipole–dipole interactions between the unlike molecules of the components. The graphical representation of Fig. 1 and results in Table 4 reveal that excess molar volumes at 303.15 K for the binary mixtures of NMP with E AB (Vm =−0.826 cm3 mol−1 at x=0.4870) are higher when compared E to the mixtures of NMP+CB (Vm =−0.534 cm3 mol−1 at x=0.5149) or E NMP+BB (Vm =−0.454 cm3 mol−1 at x=0.5226). This may be due to i) the possibility of specific interactions between NMP and AB, besides dipole–dipole interactions, due to hydrogen bond formation [35] between the CO group of NMP (which acts as hydrogen bond acceptor) and N\H of AB which is a hydrogen bond donor (evidenced by IR spectral studies) and ii) higher electro negative difference between the C and N of sp 2C\NH2 bond in aniline. The replacement of Chloro-group by a Bromo-group, resulted in less negative values E of Vm in NMP + BB mixture. The decreased electro negativity and
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Table 5 Partial molar volume at infinite dilution for N-methyl-2-pyrrolidone (V1∞/10−6 m3 mol−1) and substituted benzene (V2∞/10−6 m3 mol−1) in the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. Eq. (12) V1∞
Eq. (11) V2∞
Eq. (12) V2∞
Eq. (10) V1E,∞
Eq. (12) V1E,∞
Eq. (11) V2E,∞
Eq. (12) V2E,∞
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 96.826 102.776 94.806 308.15 97.196 103.532 95.170 313.15 97.655 104.010 95.503 318.15 98.119 104.931 95.668
94.930 95.387 95.769 95.944
100.491 100.990 101.262 101.890
100.401 100.802 101.057 101.714
−2.020 −2.026 −2.152 −2.451
−2.285 −2.542 −2.748 −3.041
−1.896 −1.809 −1.887 −2.176
−2.375 −2.730 −2.953 −3.218
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 96.826 105.987 95.017 308.15 97.196 106.461 95.340 313.15 97.655 106.998 95.598 318.15 98.119 107.511 95.806
95.017 95.340 95.598 95.806
104.021 104.360 104.713 104.930
103.979 104.297 104.671 104.896
−1.809 −1.856 −2.057 −2.313
−1.966 −2.101 −2.285 −2.581
−1.719 −1.731 −1.908 −2.130
−2.008 −2.165 −2.327 −2.615
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 96.826 91.917 93.593 308.15 97.196 92.308 93.668 313.15 97.655 92.667 93.746 318.15 98.119 93.093 93.847
93.593 93.668 93.746 93.847
88.512 88.572 89.631 89.012
88.447 88.517 88.911 89.185
−3.233 −3.528 −3.909 −4.272
−3.405 −3.736 −3.036 −4.081
−3.164 −3.421 −3.878 −4.259
−3.470 −3.791 −3.756 −3.908
T/K
V10
Eq. (10) V1∞
V20
the increased molecular size [36] (molecular radius of chlorobenzene is 2.16 Å, while it is 2.19 Å for bromobenzene at 298.15 K) are E responsible for the observed trend in Vm in case of NMP + CB and NMP + BB mixtures. In addition to this, the strength of interactions may become stronger in NMP + AB mixture, due to the interstitial accommodation of molecules of aniline (Vm = 91.917 cm3 mol−1 at 303.15 K) into the voids of the aggregated NMP molecules [37], whose molar volume is less than that of NMP molecules (Vm = 96.826 cm3 mol−1 at 303.15 K). E The algebraic Vm values of NMP with AB, BB, CB follow the order: AB > CB>BB. Analogously a similar trend has been observed for another polar solvent, N,N-dimethylformamide with substituted benzenes under same experimental conditions by Ramadevi et al. [38]. The uncertainty in excess molar volume is found to be ±1 × 10−3 cm3 mol−1. E For each system the Vm values over the entire range of composition are decreasing with increasing temperature (Fig. 1) from 303.15 to 318.15 K. This may be due to the increase in kinetic energy of molecules with temperature rise, which decreases the existing interactions between NMP and substituted benzene leading to increase E in absolute Vm values. Further, the results of excess molar volume can be substantiated by studying partial molar volumes. The partial molar volumes of components 1 (NMP) and 2 (substituted benzene), respectively in the binary liquid mixtures from their molar volumes are calculated using the following relations [39]:
∂V Em E 0 V m;1 ¼ V m þ V 1 þ ð1−x1 Þ ∂x1
∂V Em E 0 V m;2 ¼ V m þ V 2 −x1 ∂x1
! ð4Þ T;P
! ð5Þ T;P
where V10 and V20 are the molar volumes of the pure NMP and substituted E benzene respectively. The derivatives (∂Vm /∂x1)T,P of Eq. (4) and Eq. (5) are obtained by differentiating Eq. (2) with respect tox1. This leads to the partial molar volumes as expressed by the following relationships:
0 2 V m;1 ¼ V 1 þ x2
n X i¼0
i
2
Ai ð1−2x2 Þ −2x2 ð1−x2 Þ
n X i¼1
i−1
iAi ð1−2x2 Þ
ð6Þ
0 2 V m;2 ¼ V 2 þ ð1−x2 Þ 2
þ 2x2 ð1−x2 Þ
n X i¼0 n X
i
Ai ð1−2x2 Þ
i−1
iAi ð1−2x2 Þ
:
ð7Þ
i¼1
The values of partial molar volumes are used to calculate the excess partial molar volumes using the equations E V m;1 ¼ V m;1 −V 1
ð8Þ
E V m;2 ¼ V m;2 −V 2 :
ð9Þ
The values of partial molar volumes V m;1 and V m;2 along with excess molar volumes are furnished in Table 4. From Table 4 it is clear that the values of V m;1 and V m;2 for both the components in the mixture are smaller than their respective molar volumes in the pure state, i.e., a contraction in volume takes place on mixing NMP with substituted benzenes under study. These results also support the observed negative E values of Vm in all the binary systems at all the four temperatures investigated. Fig. 2 shows the calculated results for excess partial molar volumes ( V Em;i ) of substituted benzenes, AB or BB or CB ( V Em;2 ) in their binary mixtures with NMP (V Em;1 ) at 303.15 K. Examination of Fig. 2 indicates that contraction in partial molar volume takes place either NMP is mixed with the three substituted benzenes (solid line) or vice versa (dotted line) confirming the strong interactions between the unlike E molecules which support the conclusions drawn from Vm values. The E V m;i values at other higher temperatures follow the same trends but show different values, and hence the data is not graphically displayed to minimize the number of figures. The uncertainty in partial molar volumes is found to be ~ 1 × 10 − 3 cm 3 mol − 1. The partial properties at infinite dilution are of interest because, at that limit, the condition of vanishing solute–solute interactions prevails and they provide information regarding solute–solvent interactions, independent of composition effect. To get useful indications in E regard to the accuracy of fitting of the Vm data, we have calculated the partial molar volume at infinite dilution through apparent molar volumes. The apparent molar volume of NMP in substituted benzene, Vϕ1, and the apparent molar volume of substituted benzene in NMP, Vϕ2, can be expressed [40] as: 0 E V ϕ1 ¼ V 1 þ V m =x1
ð10Þ
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105
Table 6 Experimental and calculated values of viscosity (η/mPa s) for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. x1
η Expt.
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
η Expt.
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.271 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.781 0.876 0.964 1.046 1.121 1.191 1.254 1.312 1.364 1.411
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.662 0.732 0.803 0.873 0.941 1.006 1.066 1.121 1.170 1.211
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.690 0.779 0.860 0.933 0.998 1.055 1.104 1.147 1.182 1.211
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.271 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.781 0.876 0.964 1.046 1.121 1.191 1.254 1.312 1.364 1.411
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.662 0.732 0.803 0.873 0.941 1.006 1.066 1.121 1.170 1.211
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.690 0.779 0.860 0.933 0.998 1.055 1.104 1.147 1.182 1.211
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.271 1.329 1.376 1.411
0.679 0.770 0.862 0.953 1.041 1.125 1.202 1.270 1.329 1.376 1.411
0.679 0.781 0.876 0.964 1.046 1.121 1.191 1.254 1.312 1.364 1.411
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
308.15 K 0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.476 1.524 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.843 0.955 1.059 1.153 1.240 1.318 1.388 1.451 1.507 1.555
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.723 0.805 0.886 0.965 1.041 1.112 1.177 1.234 1.282 1.320
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.710 0.778 0.845 0.913 0.980 1.048 1.116 1.184 1.252 1.320
313.15 K
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411 318.15 K 0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
308.15 K 0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.476 1.524 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.843 0.955 1.059 1.153 1.240 1.318 1.388 1.451 1.507 1.555
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.723 0.805 0.886 0.965 1.041 1.112 1.177 1.234 1.282 1.320
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.710 0.778 0.845 0.913 0.980 1.048 1.116 1.184 1.252 1.320
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.476 1.524 1.555
0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.721 0.843 0.955 1.059 1.153 1.240 1.318 1.388 1.451 1.507 1.555
313.15 K
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411 318.15 K 0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
0.721 0.839 0.950 1.057 1.153 1.242 1.322 1.390 1.455 1.508 1.555
308.15 K 0.721 0.828 0.937 1.045 1.149 1.247 1.335 1.412 1.475 1.523 1.555
0.679 0.774 0.871 0.962 1.049 1.129 1.196 1.257 1.313 1.366 1.411
(continued on next page)
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Table 6 (continued) η Expt.
x1
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.710 0.778 0.845 0.913 0.980 1.048 1.116 1.184 1.252 1.320
η Expt.
η Eq. (13)
η Eq. (14)
η Eq. (15)
η Eq. (16)
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.662 0.732 0.803 0.873 0.941 1.006 1.066 1.121 1.170 1.211
0.592 0.662 0.733 0.804 0.873 0.941 1.005 1.066 1.120 1.169 1.211
0.592 0.690 0.779 0.860 0.933 0.998 1.055 1.104 1.147 1.182 1.211
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 313.15 303.15 K K 0.0000 0.1055 0.2097 0.3127 0.4144 0.5149 0.6142 0.7124 0.8094 0.9052 1.0000
308.15 K 318.15
0.643 0.726 0.811 0.894 0.973 1.047 1.111 1.167 1.220 1.272 1.320
0.643 0.724 0.805 0.886 0.966 1.041 1.112 1.176 1.233 1.281 1.320
0.643 0.723 0.805 0.886 0.965 1.041 1.112 1.177 1.234 1.282 1.320
0 E V ϕ2 ¼ V 2 þ V m =x2 :
ð11Þ
Graphical extrapolation of Vϕ1 to x1 = 0 leads to the desired value of V1∞ and extrapolation of Vϕ2 to x2 = 0 gives V2∞. Partial molar volumes at infinite dilution can also be calculated from the excess molar volumes using a method based on extrapolation of the “reduced volume” [41]. Linear extrapolation of the reduced E volume represented by Vm /x1x2 to x1 = 0 leads to the desired V1∞ and a E similar extrapolation of Vm /x1x2 to x2 = 0 leads to V2∞. The expression for reduced volume can be obtained by rearranging Eq. (10) and division by x2 E 0 V m =x1 x2 ¼ V ϕ1 −V 1 =x2 :
0.592 0.662 0.735 0.807 0.881 0.950 1.010 1.063 1.111 1.160 1.211
3.2. Viscosity studies The dynamic viscosities of the liquid mixtures have been calculated using empirical relations given by Grunberg–Nissan, Katti–Chaudari, Heric–Brewer and Hind et al. Grunberg and Nissan [43] proposed the following equation for the measurement of viscosity of liquid mixtures: ln η ¼ x1 ln η1 þ x2 ln η2 þ x1 x2 G12
ð13Þ
ð12Þ
The partial molar volumes at infinite dilution calculated by the two methods are presented in Table 5 along with V1E,∞ and V2E,∞ values. From the table, it is clear that the V1E,∞ values calculated by the two approaches at all the temperatures under study have the same sign and their differences are small. The agreement between these sets indicates that on mixing, contraction in volume occurs for the binary liquid mixtures of NMP with substituted benzenes under investigation. Similar trends are reported by H. Wang et al. [42] for the binary mixture of NMP with an ionic liquid 1-methyl-3-methylimidazolium hexafluoro phosphate.
Table 7 Interaction parameters calculated from Eqs. (13)–(16) and the corresponding standard deviations for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. Δ12
σ
H12
σ
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) 303.15 0.608 0.0127 0.589 0.0130 308.15 0.514 0.0085 0.493 0.0089 313.15 0.447 0.0069 0.425 0.0073 318.15 0.380 0.0057 0.356 0.0060
0.616 0.522 0.455 0.388
0.0126 0.0085 0.0069 0.0057
1.317 1.176 1.075 0.959
0.0028 0.0041 0.0427 0.0382
N-methyl-2-pyrrolidone(1) + bromobenzene(2) 303.15 0.287 0.0050 0.273 0.0052 308.15 0.274 0.0034 0.259 0.0036 313.15 0.255 0.0028 0.239 0.0031 318.15 0.232 0.0024 0.213 0.0028
0.393 0.379 0.361 0.338
0.0036 0.0022 0.0017 0.0016
1.387 1.302 1.196 1.074
0.0013 0.0009 0.0011 0.0019
N-methyl-2-pyrrolidone(1) + aniline(2) 303.15 0.626 0.0047 0.592 0.0047 308.15 0.522 0.0131 0.485 0.0131 313.15 0.452 0.0089 0.414 0.0093 318.15 0.380 0.0108 0.339 0.0114
0.628 0.524 0.454 0.381
0.0047 0.0131 0.0089 0.0108
2.784 2.365 2.090 1.833
0.0265 0.0184 0.0141 0.0144
T/K
G12
σ
Wvis/RT
σ
Fig. 3. Dependence of Deviation in viscosity on mole fraction of NMP(x1) for the systems NMP + CB (a), NMP + BB (b), NMP + AB (c) at 303.15 K (♦), 308.15 K (■), 313.15 K (▲), 318.15 K (Δ) symbols indicate the experimental values and the solid curves indicate the Redlich–Kister values.
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107
The experimental values of viscosity for all the three binary mixtures have been used to calculate the viscosity deviation (Δη) which is represented by the equation Δη ¼ ηmix − x1 η1 þ x2 η2
ð17Þ
where η1 and η2 are the viscosities and x1,x2 are the mole fractions of pure liquids 1 and 2 respectively. The variation in deviation of viscosity with mole fraction of NMP is shown in Fig. 3. The value and magnitude of Δη depends on molecular shape of the components in addition to intermolecular forces. In general, for systems where dispersion forces and dipolar interactions are operating Δη values are found to be negative whereas charge transfer and hydrogen bonding interaction lead to positive Δη values [47,48]. In the present study, the values of deviations in viscosity Δη are all positive (Fig. 3) in the entire range of composition with a maximum at a mole fraction range of 0.48–0.53 indicating specific interaction between unlike molecules. Our finding is in good agreement with the view proposed by Fort and Moore [49] that liquids of dissimilar molecular size mix up with decrease in volume, yielding negative E Vm value and positive Δη values. The uncertainty in the deviation of viscosity is found to be less than 0.5%. The absolute value of deviations in viscosity decreases in all the systems as temperature is raised. An increase in temperature decreases the self association of pure components and hetero association between unlike molecules, due to the increase of thermal energy. This leads to less positive values of Δη with increasing temperature as observed in the present study. Similar temperature dependence of Δη has been reported by Chakma et al. [50] for aqueous solutions of NMP. The values of Δη for the binary mixtures of NMP with AB, BB, and CB follow the order: AB > CB > BB.
Fig. 4. Variation of Deviations in excess Gibb's free energy of activation of viscous flow with mole fraction of NMP(x1) for the systems NMP + CB (a), NMP + BB (b), NMP + AB (c) at 303.15 K (♦), 308.15 K (■), 313.15 K (▲), 318.15 K (Δ) symbols indicate the experimental values and the solid curves indicate the Redlich–Kister values.
where G12 is an interaction parameter, which is a function of viscosity of component liquids 1 and 2 and temperature. Katti and Chaudhri's [44] equation for the dynamic viscosity of the liquid mixture is lnðηV Þ ¼ x1 ln η1 V 1 þ x2 ln η2 V 2 þ x1 x2 W vis =RT
ð14Þ
where Wvis is an interaction term. Heric and Brewer [45] derived the following equation to calculate the viscosity of the binary liquid mixtures: ln η ¼ x1 ln η1 þ x2 ln η2 þ x1 ln M1 þ x2 ln M2 − lnðx1 M 1 þ x2 M2 Þ þ x1 x2 Δ12 ð15Þ where Δ12 is the interaction term and other symbols have their usual meaning. The expression to determine the viscosity of the binary liquid mixtures proposed by Hind et al. [46] is given by 2
2
η ¼ x1 η1 þ x2 η2 þ 2x1 x2 H 12
ð16Þ
where H12 is an interaction term. The experimental and theoretical values of viscosity of the liquid mixtures calculated using Eqs. (13)–(16) are presented in Table 6. The evaluated interaction parameters G12, Wvis, Δ12 and H12 along with the standard deviations, σ, are presented in Table 7. All the empirical relations gave a reasonable fit, but the viscosity values calculated using Grunberg–Nissan relation are in good agreement with the experimental values.
3.3. Gibb's free energy studies Excess Gibb's free energy of activation (ΔG⁎E) of viscous flow is obtained by E
ΔG
¼ RT lnðηV Þ− x1 ln η1 V 1 þ x2 ln η2 V 2
ð18Þ
where ‘R’ is the universal gas constant, ‘V’ is the molar volume of the mixture and ‘T’ is the absolute temperature and x1 and x2 are mole fractions. The variation in excess Gibb's free energy of activation of viscous flow with mole fraction of NMP is shown in Fig. 4. It is observed that ΔG⁎E is positive (Fig. 4) in all the three systems under investigation. The positive values of ΔG⁎E suggest the presence of specific and strong interactions [30] (like complex formation, strong dipole–dipole interactions, hydrogen bonding etc.) between the components of the mixtures. In the pure state molecules of CB, BB is associated through dipole–dipole interactions [24] and aniline exists in associated form through hydrogen bonding between like molecules [26]. Observed positive values of ΔG⁎E indicate that the mixing of NMP with CB or BB or AB will induce the breaking up of self associates and leads to the formation of charge transfer complexes as NMP is good donor and substituted benzenes act as good acceptors [10]. The ΔG⁎E values for all the binary systems under study are found to decrease with rise in temperature from 303.15 to 318.15 K indicating the weakening of intermolecular interactions at elevated temperatures. The negative values of excess molar volume and positive values of deviation in viscosity support the observed variation in excess Gibb's free energy of activation of viscous flow. The values of deviation in viscosity, Δη, and Gibb's free energy of activation of viscous flow, ΔG⁎E, for each binary mixture are fitted to the Redlich–Kister polynomial (Eq. (2)) and the corresponding coefficients determined by the method of least squares, together with the standard deviations are represented in Table 8.
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Table 8 Coefficients Aj −1 of the Redlich–Kister equation Eq. (2) together with the standard deviations of excess parameters for the binary mixtures of NMP and substituted benzenes (AB or BB or CB) at temperatures of 303.15, 308.15, 313.15 and 318.15 K. T/K
A0
A1
A2
A3
0.3678 0.2914 0.2193 0.1538
−0.0208 −0.0362 −0.0365 −0.0848
−0.0801 −0.2028 −0.1921 −0.2315
−0.0210 −0.0296 −0.0011 0.0925
N-methyl-2-pyrrolidone(1) + bromobenzene(2) Δη/mPa s 303.15 308.15 313.15 318.15
0.246 0.237 0.204 0.160
0.027 0.002 −0.018 −0.017
−0.076 −0.014 −0.081 −0.047
−0.062 −0.037 0.014 −0.006
N-methyl-2-pyrrolidone(1) + aniline(2) Δη/mPa s 303.15 308.15 313.15 318.15
1.0088 0.7796 0.6411 0.5121
−0.4071 −0.7976 −0.7031 −0.6487
−0.2706 −0.4652 −0.3704 −0.1353
0.4683 0.3659 0.2997 0.1789
σ
A4
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) Δη/mPa s 303.15 308.15 313.15 318.15
0.0690 0.1774 0.1466 0.1670
0.072 0.040 0.078 −0.003
0.4757 0.8246 0.7137 0.4635
0.002 0.001 0.001 0.001
0.001 0.001 0.001 0.001
0.005 0.006 0.008 0.006
N-methyl-2-pyrrolidone(1) + chlorobenzene(2) ΔG⁎E/J mol−1 303.15 308.15 313.15 318.15
1457.41 1308.30 1172.79 1044.82
427.94 321.68 266.88 67.96
37.89 −356.59 −412.60 −606.69
−23.44 −126.66 −87.75 164.40
77.27 360.06 320.52 406.72
3.100 3.173 2.080 3.128
N-methyl-2-pyrrolidone(1) + bromobenzene(2) ΔG⁎E/J mol−1 303.15 308.15 313.15 318.15
714.13 653.97 641.13 598.97
193.24 136.89 83.07 76.14
−81.64 62.16 −112.46 −115.70
−96.67 −88.40 43.60 −22.83
73.40 −36.01 88.61 −43.48
1.963 1.414 1.823 1.804
1518.55 1341.73 1184.17 1039.01
29.59 90.54 127.66 35.96
−368.42 −901.86 −942.97 −946.96
−243.48 −537.96 −470.42 −129.29
540.01 1060.98 1038.31 637.51
4.628 7.253 10.965 8.832
N-methyl-2-pyrrolidone(1) + aniline(2) ΔG⁎E/J mol−1 303.15 308.15 313.15 318.15
3.4. Spectral studies The IR spectrum, which gives significant information about the functional groups, can be substantially influenced by the surrounding condensed medium. Hence IR studies have been used to investigate solution structure and provide physical information about
intermolecular interaction [44]. In order to study the strength of molecular association at specific concentrations; infrared spectra have been recorded for the pure NMP (Fig. 5) and equimolar mixtures of NMP and X (X = CB or BB or AB) at room temperature (303.15 K). From the recorded infrared spectra it is evident that in pure NMP, stretching band ( band is a typical amide I band in case of
Fig. 5. Neat FT‐IR spectrum of pure NMP.
D.B. Karuna Kumar et al. / Journal of Molecular Liquids 174 (2012) 100–111 Table 9 Experimental FT-IR frequencies for the binary mixture NMP + AB at 303.15 K. x
νCO (cm−1)
νNHsys (cm−1)
νNHasym (cm−1)
0.0954 0.1918 0.2892 0.3876 0.4870 0.5875 0.6890 0.7915 0.8952
1674.5 1671.6 1663.3 1661.8 1659.9 1668.7 1679.6 1681.0 1684.1
3348.2 3345.3 3343.1 3342.0 3341.2 3344.7 3349.1 3350.2 3347.7
3430.4 3426.1 3425.2 3423.0 3420.4 3424.3 3429.6 3434.5 3436.0
cyclic tertiary amides) appears at 1684 cm − 1 (Fig. 4). The values of stretching frequency for the equimolar mixtures of NMP + X are observed to be red shifted in the order AB (1659.9 cm − 1); CB (1664.4 cm − 1); BB (1666.4 cm − 1) which supports the conclusions from the thermodynamic parameters as discussed above. In order to analyze the observed stronger interactions in the NMP+ AB mixture than the remaining two systems, the study is focused on the presence of inter molecular hydrogen bonding (NH\O) in the NMP and AB mixture. IR spectrum of pure aniline has exhibited two sharp less intense bands at 3430.0 and 3354.7 cm − 1 respectively due to NH asymmetric and symmetric stretching vibrations. Sharpness in the bands can be attributed to weaker tendency to from hydrogen bond [51]. Addition of NMP to AB results in the red shift of NH bands in AB and stretching band of NMP as explained above. The results indicate that the interactions are taking place through \NH2 group of AB and group of NMP. The wave number at maximum absorbance of the \NH2 and the stretching frequencies for the NMP+ AB mixture over the whole composition range are listed in Table 9. It is seen from Fig. 6 that in the NMP–AB system the bands appear at 3341.2 cm−1 and 3420.4 cm−1 for 0.4870 mole fraction; with further increase or decrease in concentration, the \NH bands shift
109
Table 10 Comparison of experimental and theoretical FT-IR values for the 1:1 complex of NMP + AB. Band
NHasym NHsys
ν/cm−1 Expt.
3420.4 3341.2
ν/cm−1 Theoretical AM1
RM1
PM3
MNDO
3488 3444
3438 3364
3530 3510
3584 3551
toward higher frequency which indicates the weakening of molecular association [52] through inter molecular hydrogen bonding. Thus, the study of IR spectra shows that the strength of complex formation becomes maximum at 0.4870 mole fraction for the NMP+ AB system at 303.15 K. Similar results of hydrogen bonding, between NMP and butanediol are reported by S. K. Mehta et al. [35]. The minimum energy structures of aniline, NMP and the equimolar complex of aniline and NMP for vibrational frequencies are theoretically obtained from Semi-empirical Hamiltonian quantum mechanical calculations [53] such as Austin Model 1 (AM1), Recife Model (RM1), Parameterized Model number 3 (PM3) and Modified Neglect of Differential Overlap (MNDO) converged geometry optimization method using Spartan '08 Modeling software. All these models under study showed a shift in the symmetric and asymmetric stretching frequencies of NH band of aniline in the IR spectra predicted for aniline and 1:1 complex of NMP+ AB using Spartan'08, suggesting the presence of hydrogen bonding interaction [54] between NMP and aniline molecules. However, the comparison of experimental and theoretical FT-IR values shown in Table 10 indicates that the IR values determined theoretically using RM1 are in good agreement with the experimental values. The optimized geometrical structure for the formation of hydrogen bonding in the NMP+ AB system along with the corresponding IR spectrum predicted using RM1 model, obtained from Hamiltonian quantum mechanical calculations using Spartan Modeling software, is shown in Fig. 7.
Fig. 6. Observed \NH stretching bands in IR spectrum of the NMP + AB mixture at three different mole fractions of NMP(x1).
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References
Fig. 7. (a) The optimized geometrical structure and (b) theoretical IR spectrum using model RM1 for the 1:1 complex of the NMP + AB system obtained from Hamiltonian quantum mechanical calculations.
4. Conclusions New experimental values of liquid densities and viscosities for the binary mixtures of N-methyl-2-pyrrolidone (NMP) with aniline, chlorobenzene and bromobenzene, have been reported at 303.15, 308.15, 313.15 and 318.15 K and at atmospheric pressure over the entire comE position range of NMP. The computed values of Vm are found to be negative, where as Δη and ΔG⁎E values are positive for all the three binary mixtures over the entire range of composition at all the temperatures under investigation. The partial molar volumes at infinite dilution are calculated. The observed viscometric and volumetric studies suggest that strong interactions are present in all the systems investigated. Strength of interaction is maximum in NMP+ AB when compared to NMP + BB or CB. The Grunberg and Nissan empirical relation gives good agreement between experimental and theoretical viscosity values for all the systems studied. IR spectral results also suggest a specific interaction between the NMP and substituted benzenes under study. The NMP + AB system has hydrogen bonding interactions operated besides dipole–dipole and charge transfer interactions. The interaction of NMP with AB, BB, CB follows the order AB> CB > BB.
Acknowledgments One of the authors, Bala Karuna Kumar, D wishes to thank University Grants Commission of India for awarding teacher fellowship under FDP scheme. He also expresses his gratefulness to Rev. Fr. Dr. Francis Xavier S.J., Principal, Andhra Loyola College, Vijayawada for granting study leave.
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