Indian Journal of Pure & Applied Physics Vol. 44, August 2006, pp. 587-591 Acoustic studies of binary mixtures of N-methylacetamide with some chloroethanes and chloroethenes at 308.15 K B Sathyanarayana, T Savitha Jyostna & N Satyanarayana * Department of Chemistry, Kakatiya University, Warangal 506 009 Received 9 January 2006; revised 24 April 2006; accepted 12 June 2006 The densities and speeds of sound of mixtures of 1,2 dichloroethane, 1,1,2 trichloroethane, 1,1,2,2 tetrachloroethane, trichloroethene and tetrachloroethene with N-methylacetamide, over the entire range of composition, have been measured at a temperature of 308.15 K. The deviations in speed Δu, isentropic compressibility Δκ S, intermolecular free-length ΔL F and relative association R A have been computed using speed and density values. The Δu values are negative whereas Δκ S and ΔL F values are positive for all the systems, which indicate the non-specific interactions between unlike molecules. The results are discussed in the light of intermolecular interactions occurring in the solutions. The computed results of Δκ S, have been fitted to a Redlich-Kister type polynomial equation. Keywords: Ultrasonics, Binary mixtures, Chloroethanes, Chloroethenes, N-methylacetamide IPC Code: B01J19/10 1 Introduction In recent years, the measurements of ultrasonic velocity have been adequately employed in understanding the nature of molecular interactions in pure liquid mixtures. Ultrasonic propagation parameters result valuable information regarding the behaviour of binary liquid systems, because intramolecular and intermolecular association, dipolar interactions, complex formation and related structural changes affect the compressibility of the system which inturn produces corresponding variations in the ultrasonic velocity. Mixtures containing N-methylacetamide with ethylene glycol, tri ethylene glycol, poly (ethylene glycol)-200 and poly (ethylene glycol)-300 have been studied by Naidu et al 1. for investigating excess volumes and excess viscosities at 308.15 K while Rao et al 2. have studied the ultrasonic studies for binary mixtures of N-methylacetamide with glycols at 308.15 K. Victor and Hazra 3 have reported excess molar volumes, viscosity deviations and isentropic compressibility changes for binary mixtures of N- methylacetamide with 2-methoxyethanol and water at 308.15, 313.15 and 318.15 K. Tangeda and Nallani 4,5 have investigated excess molar volumes, viscosity deviations and isentropic compressibilities for N- methylacetamide-aromatic ketone systems at 308.15 K. In the present study, N-methylacetamide is chosen as a solvent because of its solvent properties, have been the subject of considerable interest due to the versatility of this compound as a solvent and its close relationship to peptides and proteins. N- methylacetamide is a self-associated liquid with a high dielectric constant 1 (ε=169) and dipole moment 6 (μ =4.27). The chloroethanes and chloroethenes; on the other hand have relatively low values of dielectric constants 6 (ε=2-11) and dipole moments 6 (μ=0-1.83). Yet they are familiar solvents in the industrial applications. Keeping the industrial applications of the compounds, the study of binary solvent mixture of N-methylacetamide with chloroethanes and chloroethenes has been taken up. In the present paper, the experimental densities and speeds of sound at 308.15 K for the binary systems of N-methylacetamide with 1,2 dichloroethane, 1,1,2 trichloroethane, 1,1,2,2 tetrachloroethane, trichloroethene and tetrachloroethene have been reported. From the experimental data, deviations in various acoustical properties such as isentropic compressibility Δκ S, intermolecular free-length ΔL F, ultrasonic speed of sound Δu and relative association R A have been computed. 2 Experimental Details All the solvents N-methylacetamide 7 (Merck- Schuchrdt Germany GR), 1,2 dichloroethane 8 (99% Merck GR grade), 1,1,2,2 tetrachloroethane 8 (Acros
588 INDIAN J PURE & APPL PHYS, VOL 44, AUGUST 2006 Organics, USA 98.5%), tetrachloroethene 9 (99% Merck, India), trichloroethene 6 (99% Merck, India) and 1,1,2 trichloroethane 6 (98% Acros Organics, USA) have been purified by the standard methods. The purity of the chemicals was checked by comparing densities and velocities of the pure liquids with literature (Table 1). Binary mixtures were prepared by mixing appropriate volumes of the liquid components in the specially designed glass bottles with air tight teflon coated caps and the mass measurements were performed on a Dhona 100 DS (India) single pan analytical balance, with a precision of ± 0.01 mg. The Table 1 Comparison of experimental densities ρ and speeds of sound u of pure liquids with literature values at 303.15 K Component ρ (g cm -3 ) U (m s -1 ) Expt Lit Expt Lit N-methylacetamide 0.94591 * 0.94604 *6 1362.0* 1354 28 * 3 0.9462 * 3 1360 04 * 4 1,2 dichloroethane 1.24636 # 1.24637 #6 1176.2 1174 0 24 1173 3 25 1,1,2 trichloroethane 1.43216 # 1.43213 #6 1177.8 1,1,2,2 tetrachlroethane 1.57863 1.57860 6 1132.8 1135 0 24 1133 1 25 trichloroethene 1.45146 1.45140 6 1010.8 1012 0 24 1013 6 25 tetrachloroethene 1.60645 1.60640 6 1027.9 1030 0 24 1028 0 25 # values at 298 15 K * values at 308 15 K required properties were measured on the very day immediately after preparing each composition. The uncertainty in the mole fraction is ± 0.0001. The densities of the pure liquids and their mixtures were determined by using 10 cm 3 double walled Pycnometer with the help of traveling microscope 10. The Pycnometer with a capillary bore of about 1mm was calibrated using conductivity water (conductivity less than 1 10-6 ohm -1 cm -1 ) with 0.9970 and 0.9940 g cm -3 as its density at 298.15 and 308.15 K, respectively 6. Each experimental density value is an average of three measurements. The uncertainty in density values is ±0.0001 g cm -3. The speed of sound was measured with an uncertainty of ± 0.3% using a single crystal variable path ultrasonic interferometer (Mittal Enterprises, New Delhi) operating at 2 MHz which is calibrated with water and benzene 11. The temperature stability was maintained within ± 0.01 K by circulating thermostated water around the cell with a circulating pump and detailed experimental procedure is given in our previous paper 12. The results compiled in Table 2 present the average of three independent measurements for each composition of the mixture and pure compound. 3 Results and Discussion Isentropic compressibility κ S, intermolecular freelength L F and relative association R A have been calculated by the standard equations 12,13. The deviation Fig. 1 Variation of Δκ S of the binary liquid mixtures of N-methylacetamide (NMA) (1) with 1,2 dichloroethane (DCE) (2); 1,1,2 trichloroethane (TrCE) (2); 1,1,2,2 tetrachloroethane (TeCE) (2); trichloroethene (TrCEe) (2) and tetrachloroethene (TeCEe) (2) at 308.15 K
SATHYANARAYANA et al. : ACOUSTIC STUDIES OF BINARY MIXTURES 589 Table 2 Values of density ρ, speed of sound u, deviations in speed of sound Δu, isentropic compressibility Δκ S, intermolecular free-length ΔL F and relative association R A of binary mixtures at 308.15 K Mole fraction x 1 Ρ (g cm -3 ) U (m s -1 ) Δκ S (10-11 M 2 N -1 ) ΔL F 10-11 m N-methylacetamide (1) + 1,2 Dichloroethane (2) 0 0000 1.2308 1164.8 0.0000 0.0000 1.0000 0 063 1.21376 1173.6 0.1158 0.0505 0.9837 0 134 1.19468 1183.6 0.2540 0.1107 0.9655 0 2632 1.15908 1200.0 0.7913 0.3426 0.9324 0 3875 1.12425 1220.3 0.9692 0.4206 0.8994 0 4442 1.10822 1230.0 1.0453 0.4540 0.8842 0 5064 1.09046 1241.2 1.1078 0.4816 0.8674 0 6863 1.03845 1279.0 0.9696 0.4236 0.8178 0 807 1.00311 1309.0 0.6316 0.2774 0.7839 0 931 0.96653 1343.6 0.1225 0.0546 0.7488 1 0000 0.94591 1362.0 0.0000 0.0000 0.7295 N-methylacetamide (1) + 1,1,2 Tetva-chloro-ethane (2) 0 0000 1.41606 1138.3 0.0000 0.0000 1.0000 0 0706 1.39036 1139.8 0.7010 0.3136 0.9814 0 2356 1.32416 1158.5 1.2323 0.5489 0.9296 0 3484 1.27597 1176.5 1.3280 0.5902 0.8912 0 452 1.22987 1195.4 1.3720 0.6085 0.8545 0 5461 1.18631 1215.6 1.3033 0.5773 0.8196 0 643 1.13909 1240.9 1.0500 0.4650 0.7816 0 7345 1.09274 1267.4 0.8010 0.3547 0.7445 0 8235 1.04579 1294.9 0.6549 0.2895 0.7075 0 9497 0.9753 1341.5 0.3152 0.1390 0.6520 1 0000 0.94951 1362.0 0.0000 0.0000 0.6316 N-methylacetamide (1) + 1,1,2,2 Trichloroethene (2) 0 0000 1.57243 1134.8 0.0000 0.0000 1.0000 0 0621 1.54552 1138.6 0.0528 0.0322 0.9818 0 2627 1.45051 1156.2 0.1896 0.1119 0.9167 0 3728 1.39303 1169.6 0.2568 0.1467 0.8770 0 4796 1.3316 1186.7 0.2948 0.1648 0.8343 0 5797 1.26893 1206.5 0.3455 0.1857 0.7907 0 6722 1.20651 1229.2 0.3593 0.1878 0.7471 0 7594 1.14374 1256.0 0.2636 0.1396 0.7032 0 8413 1.08068 1285.9 0.1787 0.0953 0.6592 0 9679 0.97476 1344.0 0.0487 0.0251 0.5859 1 0000 0.94591 1362.0 0.0000 0.0000 0.5661 N-methylacetamide (1) + Trichloroethene (2) 0 0000 1.4385 994.0 0.0000 0.0000 1.0000 0 0514 1.41785 1005.6 0.0745 0.0432 0.9818 0 2353 1.3404 1047.4 0.7920 0.3701 0.9157 0 3404 1.29326 1074.0 1.2278 0.5634 0.8761 0 4437 1.24459 1104.5 1.4363 0.6610 0.8353 0 5419 1.19644 1137.0 1.5389 0.7105 0.7953 0 6357 1.14853 1173.1 1.4085 0.6583 0.7555 0 7288 1.09944 1213.2 1.1812 0.5591 0.7152 0 8196 1.04989 1256.4 0.9379 0.4461 0.6750 0 9692 0.96443 1339.4 0.3960 0.1820 0.6070 1 0000 0.94591 1362.0 0.0000 0.0000 0.5920 N-methylacetamide (1) + Tetrachloroethene (2) 0 0000 1.59924 1014.0 0.0000 0.0000 1.0000 0 0571 1.57351 1017.8 0.7522 0.3204 0.9827 0 2569 1.46394 1047.5 2.4220 1.0316 0.9055 0 3691 1.39654 1071.4 2.9767 1.2695 0.8574 0 4749 1.33081 1100.5 3.0463 1.3034 0.8098 0 5719 1.26832 1131.7 2.9341 1.2600 0.7646 0 6637 1.20623 1165.7 2.7332 1.1780 0.7200 0 7039 1.17802 1183.2 2.5137 1.0859 0.6997 0 8385 1.07816 1253.4 1.4313 0.6243 0.6282 0 9666 0.97459 1332.0 0.7148 0.3131 0.5564 1 0000 0.94591 1362.0 0.0000 0.0000 0.5361 R A
590 INDIAN J PURE & APPL PHYS, VOL 44, AUGUST 2006 in properties of the binary liquid mixtures have been evaluated using the general equation: Δy = y mix (x 1 y 1 +x 2 y 2 ) (1) where y indicates the property such as isentropic compressibility κ S, intermolecular free-length L F and ultrasonic speed u, x 1 and x 2 are the mole fractions of the components 1 and 2, respectively. Δy, y 1, y 2 and y mix are the deviation in property, properties of the components 1 and 2 and observed property, respectively. Experimentally determined and computed acoustic properties are given in Table 2. Graphical representation of Δκ S as function of N- methylacetamide (x 1 ) is given in Figure 1. The dependence of Δκ S on mole fraction of N- methylacetamide is fitted to a Redlich-Kister type equation 14 : Δκ S = x 1 (1-x 1 ) Σ a j (1-2x 1 ) j (2) where a 0, a 1,a 2. are the polynomial coefficients. The values of the coefficients determined by the method of least-squares are given in Table 3 along with the standard deviation σ(δκ S ). The standard deviations are calculated by using usual equation 15. The data presented in Table 2 show that the deviations in isentropic compressibility are positive in mixtures of N-methylacetamide with chloroethanes and chloroethenes over the entire range of composition (Fig. 1). All are showing maxima at the mole fraction around x 1 =0.5, indicating the maximum interactions are at that mole fraction range in every system. From Table 2, it is also observed that deviations in speeds of sound values are negative whereas Δκ S values are positive, such trend of negative deviation in u and positive deviation in Δκ S is quite obvious 16-18. N-methylacetamide is a self-associated liquid having high percentage of ionic character 19, and chloroethanes and chloroethenes are electron accepting molecules 20. Hence, the values of Δκ S may be explained in terms of two opposing effects: (i) Expansion of volume due to mutual loss of dipolar association, difference in size and shape of N- methylacetamide and chloro substituted ethanes and ethenes; (ii) contraction of volume due to dipoleinduced dipole, dipole-dipole interactions and complex formation between unlike molecules. The values of Δκ S depend on the relative strength of the two opposing effects. The former factor increases the intermolecular path lengths, as described by Jacobson 21. This in turn causes negative deviation in speed of sound and positive deviation in compressibility. On the other hand, the latter factor decreases the intermolecular path lengths leading to a positive deviation in speed of sound and negative deviation in compressibility. The observed negative values of Δu and positive values of Δκ S for these mixtures indicate that the former factor dominate over the latter factor between unlike molecules. From Table 2, the positive values of ΔL F, substantiate the above argument undoubtedly and undeniably. This conclusion is further fortified by the decreasing values of relative association 22,23 R A (Table 2). All the trends of the above properties conclude that the mixtures are more compressible than their corresponding ideal mixtures. Generally, the deviation properties are considered to be the reflecting agents of the magnitude of polarity at the site of interactions in the molecule. The positive Δκ S values of chloroethanes decreases in the following order: 1,1,2 trichloroethane > 1,2 dichloriethane > 1,1,2,2 tetrachloroethane. Δκ S values for the systems of N-methylacetamide with chloroethenes is explained by taking three factors into consideration: i.e. (i) double bond character of chloroethenes, (ii) shielding of ethylenic double bond by chlorine atoms and (iii) partial saturation of the electron accepting nature of chlorine Table 3 Estimated coefficients a j from Eq. (7 ) and standard deviations σ from Eq. (8) at T=308.15 K Coefficients System Function a 0 a 1 a 2 a 3 a 4 a 5 σ (Δκ S ) N-methylacetamide (1) + 1,2 dichloroethane (2) Δκ S (10-11 m 2 N -1 ) 4.35-0.14-0.57 5.31-3.70-6.91 0.3229 N-methylacetamide (1) + 1,1,2 trichloroethane (2) Δκ S (10-11 m 2 N -1 ) 5.34-2.25-1.58-0.63 7.70 0.1284 N-methylacetamide (1) + 1,1,2,2 tetrachloroethane (2) Δκ S (10-11 m 2 N -1 ) 1.28 1.21-0.08-3.77-0.11 3.35 0.0774 N-methylacetamide (1) + trichloroethene (2) Δκ S (10-11 m 2 N -1 ) 6.14 1.23-5.37-2.04 7.27 9.25 0.1356 N-methylacetamide (1) + tetrachloroethene (2) Δκ S (10-11 m 2 N -1 ) 12.55 2.14-5.40-25.9 12.65 33.46 0.7238
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