Ultrasonic studies on molecular interactions in binary mixtures of acetonitrile with carbonyl molecules

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1 J. Pure Appl. Ultrason. 27 (2005) pp Ultrasonic studies on molecular interactions in binary mixtures of acetonitrile with carbonyl molecules S. ANURADHA, S. PREMA 1 and K. RAJAGOPAL 2 Department of Physics, Manonmaniam Sundaranar University, Tirunelveli 1 Department of Physics, Rose Mary College for Women, Tirunelveli 2 Department of Physics, Govt. College of Engg., Tirunelveli , Tamil Nadu Densities and ultrasonic velocities have been measured at 299K for the binary mixtures of acetonitrile (ACN) with acetone/ ethyl methyl ketone/ Methyl isobutyl ketone and acetophenone over entire composition range. From these, isentropic compressibility (K S ), intermolecular free length (L f ) and their deviations namely excess isentropic compressibility ( ) and excess inter molecular freelength ( ) have been calculated and interpreted in terms of inter molecular interactions. Further theoretical values of ultrasonic velocity in the four binary liquid mixtures are calculated using two different theoretical models. The relative merits of these theories and relations have been discussed. INTRODUCTION The ultrasonic studies are extensively used to estimate the thermodynamic properties and predict the intermolecular interactions of binary mixtures. The sound velocity is one of those physical properties that helps in understanding the nature of liquid state. Using the measured values of sound velocity (u) and density (ρ), the thermodynamic parameters such as isentropic compressibility (K S ) and intermolecular freelength (L f ) can be computed. The intermolecular free length (L f ) is an important physical property of liquid mixtures which mainly affects the sound velocity. The intermolecular free length decreases with decreases of temperature and hence the close packing of molecules which in effect decreases the sound velocity 1,2. The isentropic compressibility (K S ) decreases with increase of velocity that gives insight into the structure making and structure breaking of components in binary mixtures 3. The excess thermodynamic parameters such as excess isentropic compressibility ( ) and excess intermolecular free length ( ) are very useful to understand the intermolecular interactions in binary mixtures. When negative excess functions are observed 4-6, complex formation is suspected more often. This suggests the occurrence of discrete groups of molecules arranged into specific geometric structures. These structural arrangements are influenced not only by the shape of the molecules but also by their mutual interactions. The positive values in excess properties correspond mainly to the existence of dispersion forces 4. These derived parameters offer a convenient method for the study of thermodynamic properties of liquid mixtures not easily obtained by other means. The present investigation aims at understanding the molecular interactions based on thermodynamical parameters K S & L f and their excess functions J. Pure Appl. Ultrason. Vol. 27 No. 2 & 3 (2005) 49

2 & in the binary mixtures of acetonitrile + acetone/ethyl methyl ketone/ methyl isobutyl ketone and acetophenone at 299K. Acetone, ethyl methyl ketone, methyl isobutyl ketone and acetophenone belong to the carbonyl series having functional group of C = O, while acetonitrile belong to nitrile series having functional group C º N. Carbonyl group is a part of several biologically important molecules such as proteins, lipids and hormones. Acetonitrile molecules are highly polar with their diploes arranged in antiparallel pairs and this strongly ordered structure is stabilized by dipole - dipole interactions. In view of the applications of these solvents and their mixtures in chemistry and modern technology 7, 8 four binary mixtures have been studied and reported in this paper under two categories namely aliphatic nitrile + aliphatic ketones and aliphatic nitrile + aromatic ketones. While ACN + acetone/ ethyl methyl ketone/ Methyl isobutyl ketone mixtures have been studied under aliphatic nitrile + aliphatic ketone categories, the mixture ACN + Acetophenone was studied under aliphatic nitrile + aromatic ketone category. Velocities have also been evaluated theoretically with the help of Nomoto relation 9 and VanDeal ideal mixing law 10. The suitability of these theories and equations were checked by comparing theoretical values of ultrasonic speeds with the values obtained experimentally. EXPREMENTAL PROCEDURE All the liquids used in the preparation of the binary mixtures are of analar grade and were purified as described in literature 11. Before use, all liquids were kept on 4A molecular sieves for several days to reduce the water content. The liquids were distilled prior to use and only middle fractions were used. The purity of the liquids were ascertained from the constancy of their boiling temperatures during distillation and also by comparing their densities, ultrasonic velocities at 299K which agreed reasonably well with the corresponding literature values. The calculated volumes of the liquids were added to get mixtures of different volume ratios. The mixtures were kept in special airtight bottles. Ultrasonic velocities were measured with a single crystal ultrasonic interferometer at a frequency of 2 MHz and these were accurate to ± 0.05%. Densities of the pure liquids and binary mixtures were measured using S.G. bottle of 5ml volume. These values were found to be accurate upto ± 0.1 kg/m 3. The temperature of the test liquids and binary mixtures was maintained at 299K to an accuracy of ± 0.05 K in an electronically controlled thermostatic water bath. RESULTS AND DISCUSSION From the observed values of ρ and u, isentropic compressibility K s, inter molecular free length L f, deviation in isentropic compressibility and excess intermolecular free length were calculated from the following equations 12. K s = 1/ ρ u 2 (1) L f = K/uρ ½ (2) = K S 12 - φ 1 K s1 - φ 2 K s2 = L f 12 - φ 1 Lφ 1 - φ 2 L f2 (3) (4) Where, u, ρ and K are ultrasonic velocity, density and Jacobson's temperature dependent constant. φ 1, K s 1, L f1, and φ 2, K s2 and L f2 are volume fraction, isentropic compressibility and intermolecular free length of components 1 and 2 respectively. K s and L 12 f are isentropic 12 compressibility and intermolecular free length of binary mixture. Table 1 lists u, ρ, K s, L f, and values for all the four binary mixtures at 299K. The variation of ultrasonic velocity in a solution depends upon the increase or decrease of intermolecular free length after mixing the components. On the basis of a model for propagation proposed by Eyring and Kincaid 13 ultrasonic velocity should decrease if the intermolecular free length increases as a result of mixing of components. This is in fact was observed in three binary mixtures belonging to aliphatic nitrile - aliphatic ketone category. However in ACN + acetophenone mixture a decreasing trend in Lf values and hence the corresponding increasing trend in 'u' values are observed with increase in molar concentration. Figs. 1 and 2 show representative plots of variation of and with molar concentration of 50 J. Pure Appl. Ultrason. Vol. 27 No. 2 & 3 (2005)

3 Table 1. Values of Ultrasonic velocity (u), density (ρ), adiabatic compressibility (K s ), intermolecular free length (L f ) of binary mixtures as a function of molar concentration of component 'B' at 299 K. Mole fraction of Expt (u) ρ x 10-3 K s L f component B m/s kg/m 3 m 2 N -1 m Acetonitrile -Ethyl Methyl Ketone Acetonitrile - Acetone Acetonitrile - Methyl Iso Butyl Ketone Acetonitrile Acetophenone J. Pure Appl. Ultrason. Vol. 27 No. 2 & 3 (2005) 51

4 Excess Adiabatc compressibiity S K m 2 N -1 Mole fraction of component B Excess adiabatic compressibility of Acetronitrile - Ethyl Methyl Ketone Acetronitrile - Acetophenone Acetronitrile - Aceton Acetronitrile - Methyl Iso butyl Ketone Fig. 1. Variation of excess adiabatic compressibility of four binary mixtures with the mole fraction of component B component B at 299K. Treszczanowicz and Benson 14 have suggested that & are the resultant of several opposing factors such as strong molecular interactions through charge transfer, dipole induced dipole and dipole-dipole interactions 15, interstitial accommodation and orientational ordering 16 lead to a more compact structure making & negative while break up between the participating molecules tend to make & positive. The magnitude of the various contributions depend mainly on the relative molecular size of the components. Negative and in the present investigation for ACN + acetophenone are an indication of strong interactions in the liquid mixtures as well as interstitial accommodation of acetonitrile molecules into aggregates of acetophenones. The strong dipole-dipole interactions existing in ACN + Acetophenone mixture have been supported through electro optic Kerr effect studies and dipole moment measurements 17. It is of interest to add that negative excess values are reported in literature for binary mixtures having acetophenone as one of the constituents 18. Excess Free Length, m 2 N -1 Mole fraction of component B Excess free length of Acetronitrile - Ethyl Methyl Ketone Acetronitrile - Acetophenone Acetronitrile - Aceton Acetronitrile - Methyl Iso butyl Ketone Fig. 2. Variation of excess free length of four binary mixtures with the mole fraction of component B For the other three binary mixtures of ACN + acetone/ ethyl methyl ketone and methyl isobutyl ketone only positive trend in & are observed with increase in molar concentration. This behaviour may be qualitatively examined as follows. Mixing of aliphatic ketone with ACN will induce the breaking up of the associated structure of ACN releasing several dipoles which inturn can induce a dipole moment in the neighbouring aliphatic ketone molecules resulting in dipoleinduced-dipole interaction between ACN molecules and aliphatic ketone molecules. The former effect (breaking up of associated structure of ACN) leads to an expansion in volume hence an increase in and whereas the later effect (dipole-induced dipole interaction) is responsible for contraction in volume hence a decrease in and values. The observed positive and values in the three binary mixtures of ACN + acetone/ ethyl methyl ketone/ methyl isobutyl ketone suggest that effect due to breaking up of ACN - ACN associates dominates over that of ACN-aliphatic Ketone interactions. Several other 52 J. Pure Appl. Ultrason. Vol. 27 No. 2 & 3 (2005)

5 Table 2. Theoretical values of ultrasonic velocity calculated from Nomoto's, Vandeal & Vangeal relations along with the experimental ultrasonic velocity and percentage of error for Acetonitrile - Ethyl Methyl Ketone, Acetonitrile - Acetone, Acetonitrile- Methyl Iso Butyl Ketone, Acetonitrile - Acetophenone binary mixtures at 299 K Mole fraction of u (m/s.) Percentage of Error component B Expt Nomoto Vandeal & Nomoto Vandeal & Vangeal m/s Vangeal Acetonitrile - Ethyl Methyl Ketone Acetonitrile - Acetone Acetonitrile - Methyl Iso Butyl Ketone Acetonitrile - Acetophenone J. Pure Appl. Ultrason. Vol. 27 No. 2 & 3 (2005) 53

6 binary mixtures are reported in literature having positive and values 18. The theoretical values of ultrasonic speeds in the mixtures ACN + acetone / ethyl methyl ketone/ methyl isobutyl ketone and acetophenone were computed using the following empirical equations : Nomoto's equation u (NOM) = [(x 1 R 1 + x 2 R 2 ) /(x 1 V 1 + x 2 V 2 )] 3 (5) VanDeal and Vangeel equation u (VD)=[(x 1 /m 1 u 1 2 +x 2 /m 2 u 2 2 )(x 1 m 1 +x 2 m 2 )] -½ (6) The details of derivation and terms used are found in literature 9, 10. The theoretical values of ultrasonic speeds obtained by using the relations (5) and (6) along with the experimental speeds and average percentage errors in the calculated values are summarised in Table 2 for comparison with the experimental values. It can be seen from table II that the theoretical values of ultrasonic velocity computed by two theories given above show deviations from experimental values. The limitations and approximations incorporated in these theories are responsible for it. It is assumed that all the molecules are spherical in shape, which is not true every time. In Nomoto theory, it is supposed that the volume does not change on mixing. Therefore, no interaction between the components of liquid mixtures has been taken into account. Similarly, the assumption for the formation of ideal mixing relation due to VanDeal & Vangeel is that, the ratio of specific heats of the components is equal to the ratio of specific heats of ideal mixtures and the volumes are also equal. Again, no molecular interaction is taken into account. But on mixing two liquids, the interaction between the molecules of liquids takes place because of presence of various types of forces such as dispersion forces, charge transfer, hydrogen bonding, dipole-dipole and dipole-induced dipole interactions. Thus the observed deviation of theoretical values of velocity from the experimental values shows that the molecular interaction is taking place between the solute molecules in the liquid mixtures. It is observed from Table 2 that for binary mixtures of ACN + ethyl methyl ketone/ methyl isobutyl ketone and acetophenone the minimum percentage of derivation is exhibited by Nomoto relation and followed by VanDeal's relation. This is in good agreement with the conclusions drawn by others 20. For ACN + acetone mixture VanDeal's relation seems to provide the best result followed by Nomoto relation. REFERENCES 1. Ali. A., and Nain. A.K. Indian J. Pure Appl. Phys., 35 (1997) Jayakumar. S., Karunanidhi, N, and Kannappan. V. Indian J. Pure & Appl. Phys., 34 (1996) Rajendran. V. Indian J. Pure Appl. Phys. 34 (1996) Fort. R.J., Moore. W.R. Trans. Faraday. Soc (GB) 61 (1975) Sheshadri.K. and Reddy. K.C., Acustica (Germany) 29 (1973) Kaulgud. M.V. and Patil. K.J. Indian J. Pure Appl. Phys. 13 (1975) Kovelenko. L.S., Ivanova. E.F. and Kransnoperova. A.P. Russ. J. Phys. Chem. 64 (1960) Nikam. P.S., Shirsat. L. Nano Hasan. M. J. Indian. Chem. Soc. 77(2000) Nomoto J. Phys. Soc. Japan, 13 (1958) VanDeal. W and Vangeel. E., Proc. of the first International Conference on Calorimetry and thermodynamics, Warsaw (1969) Weissberger. A. Techniques of Oragnic Chemistry. Vol VII. Organic Solvents edn. (Inter Science, N.Y.) 2nd Edn. (1955). 12. Nikam. P.S., Jadhave. M.C. and Mehdi Hasan. Indian J. Pure Appl. Phys. 33 (1995) Eyring. H & Kincaid. J.F., J. Chem. Phys., 6 (1938) Treszczanowicz. A.J. and Benson. G.C., J. Chem. Thermodyn. 10 (1978) Rai. R.D., Shukla. R.K., Shukla. A.K. and Pandey. J.D. J. Chem Thermodyn. 21 (1989) Kiyohara. O and Benson. G.C. J. Chem. Thermodyn. 11 (1979) Rajagopal. K. Ph.D. Thesis, IIT, Chennai-36, Yanadi Reddy. N., Subramanyam Naidu. P and Ravindra Prasad. K., Indian J. Pure Appl. Phys. 32 (1994) Bahadur Abisha. S., Subha. M.C.S and Rao. K.C., J. Pure Appl. Ultrason. 23 (2001) Ali. A., Anil Kumar Nain., Narendra Kumar and Mohamed Ibrahim., J.Pure.Appl.Ultrason. 24(2002) J. Pure Appl. Ultrason. Vol. 27 No. 2 & 3 (2005)