versión impresa ISSN 0327-0793
Lat. Am. appl. res. vol.40 no.3 Bahía Blanca jul. 2010
Acoustical properties of Schiff base solutions in dmf
S. Baluja†, K.P. Vaishnani, R. Gajera and N. Kachhadia
Department of Chemistry, Saurashtra University, Rajkot-360005, (Gujarat), India.
Abstract - Density, ultrasonic velocity and viscosity of Schiff bases have been studied in dimethyl formamide at 308.15 K. From the experimental data, various acoustical parameters such as specific Impedance (Z), isentropic compressibility (?s), Rao's molar sound function (Rm), Van der Waals constant (b), relaxation strength (r), intermolecular free length (Lf), internal pressure (p), solvation number (Sn) etc. have been evaluated, which helps in understanding the molecular interactions occurring in these solutions.
Keywords - Schiff Bases. Ultrasonic Study. Acoustical Parameters. DMF.
Ultrasonic technique is one of the most useful technique, which is widely used in medical, engineering and process industries, biology, geography, etc. (Ratobylskaya and Simonoya, 1981; Mason, 1990; Fukui and Nakama, 1992; Murthy et al., 1993; Teslenko and Teslenko, 1996; Thain et al., 2005, Ramesh et al., 2007).
Further, it provides a wealth of information about molecular interactions, nature and strength of interactions. In recent years, much effort has been made to study ultrasonic properties of liquid mixtures (Antosiewicz et al., 1982; Paul et al., 1989; Chennarayappa et al., 1991; Nath, 1996; Tamura et al., 1998; Ali et al., 2001; Nayakulu et al., 2004; Ali et al, 2006; Radhamma et al., 2008). However, scanty work has been done for solutions of organic compounds. In the last few years, our investigation groups have carried out some studies on acoustical properties of organic compounds in various solvents (Baluja and Parsania, 1995; Baluja and Parsania, 1997; Baluja and Oza, 2003; Baluja et al., 2004; Baluja et al., 2007; Baluja et al., 2008)
In continuation of these investigations, the present paper reports acoustical properties of Schiff bases in DMF over entire concentration range at 308.15K. The results are interpreted in terms of molecular interaction occurring in the solution.
The DMF used in the present work were of AR grade and were purified according to the standard procedure (Riddick et al., 1986). The compounds were recrystalized before use. The structure of all these compounds are given in Fig. 1.
Figure 1: Structure of Schiff Bases
The computation of ultrasonic and thermodynamic properties requires the measurements of ultrasonic velocity, viscosity and density.
The densities (r) of pure solvents and their solutions were measured by using a single capillary pycnometer, made of borosil glass having a bulb capacity of 10 ml. The ultrasonic velocity (U) of pure solvents and their solutions were measured by using single crystal variable path ultrasonic interferometer operating at 2 MHz. The accuracy of density and velocity are ± 0.0001 g/cm3 and ± 0.1% cm/sec respectively. The viscosity (h) of pure solvents and solutions were measured by an Ubbelohde viscometer with an accuracy of 0.05%. All the measurements were carried out at 308.15 K. The uncertainty of temperature is ± 0.1 K and that of concentration is 0.0001 moles /dm3.
The experimental data of ultrasonic velocity, density and viscosity are given in Table 1.
Table 1: The density (ρ), ultrasonic velocity (U) and viscosity (η) of Schiff bases in DMF at 308.15K.
From the experimental data of density, viscosity and ultrasound velocity of pure solvent and solutions, various acoustical parameters were calculated using following standard equations reported earlier (Baluja and Parsania, 1995):
IV. RESULTS AND DISCUSSION
The density (ρ), viscosity (η) and sound velocity (U) of pure solvents and different Schiff bases solutions in dimethylformamide (DMF) are reported in Table 1 at 308.15 K. Some of the above calculated parameters are also given in Table 2.
Table 2: Variation of acoustical parameters with concentration of Schiff bases in DMF at 308.15 K.
It is observed from Table 1 that in DMF, ultrasonic velocity (U) increases with concentration for KPV-1, KPV-3, KPV- 5 and KPV- 6 and decreases for KPV-2, KPV-4, KPV-7 and KPV-8. The variation of ultrasonic velocity with concentration for Schiff bases solutions in DMF is shown in Fig. 2, which is reverse of intermolecular free path length (Lf), which is found to decrease with concentration as shown in Fig. 3.
Figure 2: Variation of ultrasonic velocity (U) with concentration of Schiff bases in DMF.
Figure 3: Variation of Inter molecular free path length (Lf) against concentration for Schiff bases in DMF.
It is obvious from Fig. 3 that, Lf decreases for KPV-1, KPV-3, KPV-5 and KPV-6. While in case of KPV-2, KPV-4, KPV-7 and KPV-8, Lf increases, which suggest predominance of solute-solute interactions. The increase in U and decrease in Lf indicates close association between solute and solvent molecules whereas reverse of these suggest solute-solute interactions.
The predominance of a particular interaction in a particular solution can also be decided by isentropic compressibility, which is shown in Fig. 4 for all the bases in DMF. It is observed that in DMF solution, isentropic compressibility decreases with increase in concentration for KPV-1, KPV-3, KPV-5 and KPV-6.
Figure 4: Variation of isentropic compressibility (κs) against concentration for Schiff bases in DMF
It is observed from Table 2 that, relaxation strength (r) also decreases with increase in concentration for
where R = KPV-1, KPV-3, KPV-5 and KPV-6 where as it increases for KPV-2, KPV-4 KPV-7 and KPV-8. However, acoustic impedance (Z) shows reverse nature, which proves the existence of solute-solvent (Nambinarayanan et al., 1993) interactions in KPV-1, KPV-3, KPV-5 and KPV-6. The increase in isentropic compressibility (κs) and relaxation strength (r) in other Schiff bases, KPV-2, KPV-4, KPV-7, KPV-8 suggests the predominance of solute-solute interactions.
The linear variation of Rao's molar function (Rm), molar compressibility (W) and Vander Waal's constant (b) with concentration (correlation coefficient γ = 0.9982-0.9999) in Table 2, suggests the absence of complex formation in these solutions.
The internal pressure (π) is the resultant of the forces of attraction and repulsion between the molecules in a liquid. It is observed from the Table 2 that except for KPV-1 and KPV-2, π values are first increasing and then decreasing. For KPV-3, KPV-6, KPV-7 and KPV-8, it increased continuously. For KPV-4, it decreases continuously whereas for KPV-5, π values first decreased and then increased. Thus, it is observed that in these systems, both solute-solute and solute-solvent interactions exist, although some acoustical parameters suggest predominance of one type of interaction. This is again confirmed by solvation number (Sn).
The solvation number (Sn) is a measure of structure forming or structure breaking tendency of solute in a solution. The increase in Sn values indicates the structure-forming tendency of solute where as decrease in Sn indicates structure breaking tendency of solute. Figure 5 shows the variation of Sn with concentration. It is observed that except KPV-6, other Schiff bases show structure-forming tendency. The Sn decreases with concentration for KPV-6, suggesting thereby structure-breaking tendency of this Schiff base.
Figure 5: Variation of Solvation number (Sn) against concentration for Schiff bases in DMF at 308.15 K.
Overall, both solute-solute and solute-solvent interactions exist in these solutions of Schiff bases in DMF.
Authors are thankful to Head of Chemistry Department for providing facilities.
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Received: November 11, 2008
Accepted: August 28, 2009
Recommended by Subject Editor: Ricardo Gómez