1 Indian Journal of Pure & Applied Physics Vol. 44, August 2006, pp Acoustic studies of binary mixtures of N-methylacetamide with some chloroethanes and chloroethenes at K B Sathyanarayana, T Savitha Jyostna & N Satyanarayana * Department of Chemistry, Kakatiya University, Warangal 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 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 K while Rao et al 2. have studied the ultrasonic studies for binary mixtures of N-methylacetamide with glycols at 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 , and K. Tangeda and Nallani 4,5 have investigated excess molar volumes, viscosity deviations and isentropic compressibilities for N- methylacetamide-aromatic ketone systems at 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 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
2 588 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 K Component ρ (g cm -3 ) U (m s -1 ) Expt Lit Expt Lit N-methylacetamide * * * * * * 4 1,2 dichloroethane # # ,1,2 trichloroethane # # ,1,2,2 tetrachlroethane trichloroethene tetrachloroethene # values at K * values at K required properties were measured on the very day immediately after preparing each composition. The uncertainty in the mole fraction is ± 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 ohm -1 cm -1 ) with and g cm -3 as its density at and K, respectively 6. Each experimental density value is an average of three measurements. The uncertainty in density values is ± 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 K
3 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 K Mole fraction x 1 Ρ (g cm -3 ) U (m s -1 ) Δκ S (10-11 M 2 N -1 ) ΔL F m N-methylacetamide (1) + 1,2 Dichloroethane (2) N-methylacetamide (1) + 1,1,2 Tetva-chloro-ethane (2) N-methylacetamide (1) + 1,1,2,2 Trichloroethene (2) N-methylacetamide (1) + Trichloroethene (2) N-methylacetamide (1) + Tetrachloroethene (2) R A
4 590 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 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= 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 ) N-methylacetamide (1) + 1,1,2 trichloroethane (2) Δκ S (10-11 m 2 N -1 ) N-methylacetamide (1) + 1,1,2,2 tetrachloroethane (2) Δκ S (10-11 m 2 N -1 ) N-methylacetamide (1) + trichloroethene (2) Δκ S (10-11 m 2 N -1 ) N-methylacetamide (1) + tetrachloroethene (2) Δκ S (10-11 m 2 N -1 )
5 SATHYANARAYANA et al. : ACOUSTIC STUDIES OF BINARY MIXTURES 591 atoms by п-electrons of the ethylenic double bond. The positive Δκ S values of chloroethenes are in the following order: tetrachloroethene > trichloroethene. An interesting observation is that Δκ S values of mixtures containing tetrachloroethene is more positive than that of mixtures containing 1,1,2,2 tetrachloroethtane, and Δκ S values of mixtures containing trichloroethene are more positive than that of mixtures containing 1,1,2 trichloroethane. This observation gives evidence to the conclusion that the п- bonded tetrachloroethene is shielded by four chlorine atoms and also the electron accepting ability of these chlorine atoms is partially saturated by the п-electrons. Similar trend was observed in case of 1,1,2,2 tetrachloroethane and tetrachloroethene by Reddy et al 20. with a compound of carbonyl functionality. Acknowledgement One of the authors (SB) would like to thank the University Grants Commission, New Delhi, for the award of Junior Research Fellowship. The authors are also thankful to Prof T J Rao, Kakatiya University, Warangal, for his helpful discussion in preparing this manuscript. References 1 Vijaya Kumar Naidu B, Chowdoji Rao K & Subha M C S, J Chem Eng Data, 48 (2003) Sadasiva Rao A, Vijaya Kumar Naidu B & Chowdoji Rao K, J Acous Soc Ind, 28 (2000) Pitchai J V & Dilip K H, J Chem Eng Data, 47 (2002) Tangeda S J & Nallani S N, J Chem Eng Data, 50 (2005) Tangeda S J & Nallani S N, J Chem Thermodynamics, 38 (2005) Riddick J A & Bonger W B, Organic Solvents: Physical Properties and method of purification IV edn, (Willey Inter science, New York), Jan Zielkiewicz, J Chem Thermodynamics, Online 8 Dayananda Reddy K, Iloukhani H & Rao M V P, Fluid Phase Equilibria,17 (1984) Busa Goud, Venkatesu P & Prabhakara Rao M V, J Chem Eng Data, 40 (1995) Subha M C S & Brahmaji Rao S, J Chem Eng Data, 33 (1988) Udaya S T, Mahadevappa Y K, Mrityunjaya I A & Aminabhavi T M, J Chem Eng Data, 45 (2000) Savitha Jyostna T & Satyanarayana N, Indian J Pure & Appl Phys, 43 (2005) Arul G & Palaniappan L, Indian J Pure & Appl Phys, 43 (2005) Redlich O & Kister A T, Ind Eng Chem, 40 (1948) Syal V K, Chauhan S & Kumari Uma, Indian J Pure & Appl Phys, 43 (2005) Aminabhavi T M & Gopalakrishna B, J Chem Eng Data, 40 (1995) Aminabhavi T M & Banerjee K, J Chem Eng Data, 43 (1998) Oswal S L & Prajapathi K D, J Chem Eng Data, 43 (1998) L Pauling The nature of chemical bond, 2 nd Ed (Cornell Univ Press, Ithaca, New York), Reddy D V B, Ramanjaneyulu K & Krishnaiah A, Indian J Tech, 27 (1989) Jacobson B, Acta Chim Scand, 6 (1952) Baluja S & Oza S, Fluid Phase Equilibria, 200 (2002) Agarwal P B & Narwade M L, Indian J Chem, 42A (2003) Gnana Kumari P, Radhamma M, Sekhar G C & Rao M V P, J Chem Eng Data, 47 (2002) Chandra Shekahar G, Venkatesu P & Prabhakara Rao M V, J Chem Eng Data, 46 (2001) 377.