Acoustical Studies of some Chalcones in DMF and DMSO Solutions

This work reports densities, speeds of sound, and isentropic compressibility of the solutions of some synthesized chalcones in N,N-dimethylformamide and dimethyl sulphoxide solutions of various concentrations at 308.15 K with a view to understand molecular interactions in these solutions


INTRODUCTION
Literature survey shows that because of its non destructive nature, ultrasonic waves have been used in various industries for various processes like dyeing 1 , cleaning 2 , design 3 , bleaching 4 , food processing 5 , organic synthesis 6,7 etc. Further, it is also used in medical fields [8][9][10] .
The ultrasonic measurements have also been used to study molecular interactions in various pure liquids 11 , liquid mixtures 12,13 and solutions of organic and inorganic compounds [14][15][16] , polymers 17 , amino acids 18 , drugs 19 etc. The thermodynamic parameters calculated through ultrasonic velocity measurements can give idea about intermolecular attraction between molecules (solute-solute or solute-solvent) 28 .
In our laboratory, the ultrasonic and physicochemical studies of some organic compounds like Schiff bases 20 , triazoles 21 , dihydropyrimidines 22 etc. have been studied in different solvents. In continuation of our previous work, in the present paper, ultrasonic studies of some chalcones base have been studied in N, N dimethylformamide and dimethylsulphoxide solutions of various concentrations at 303.15 K with a view to understand molecular interactions in these solutions.

EXPERIMENTAL
The solvents N, N-dimethylformamide and dimethylsulphoxide were of analytical grade and were distilled by the reported procedure 23 . The purities of these solvents values were checked by a gas-liquid chromatography and were found to be 99.5% and 99.6% for N, N dimethylformamide and dimethyl sulphoxide respectively. The solvents were degassed and dried over molecular sieves (Union Carbide, type 0.4 nm). The chalcones (ANC-1 to ANC-9) were synthesized in our laboratory and were recrystalized before use. The physical constants of all the synthesized chalcones are given in Table 1. The general structure of chalcone is given in Figure 1.
The densities, viscosities and ultrasonic velocities of pure solvents and solutions of chalcones of different concentrations were measured at 303.15 K by using pyknometer, an Ubbelohde suspended level viscometer and single frequency ultrasonic interferometer (Mittal Enterprises, Model No F81) operating at 2 MHz, with the uncertainties of 0.0001 g/cm 3 , + 0.06 % and 0.01% respectively. The temperature was maintained by an electronically controlled thermostatic water bath (NOVA NV-8550 E). The uncertainty of temperature was ±0.1 o C.
All the solutions were prepared by using a Mettler Toledo AB204-S balance with a precision of (1 x 10 -4 ) g. Table 2 shows the experimental data of density (ρ), viscosity (η) and sound velocity (U) of pure solvents and solutions of chalcones in DMF and DMSO solutions at 303.15 K. From these experimental data, various acoustical parameters like specific acoustical impedance (Z), isentropic compressibility (κ s ), inter molecular free length (L f ), Rao's molar sound function (R m ), Vander Waals constant (b), relaxation strength (r), internal pressure (π ), apparent molar compressibility ( k ) etc., were evaluated using the equations reported earlier 20 .

RESULTS AND DISCUSSION
Some of the calculated acoustical parameters are given in Tables 3 and 4 for all the compounds in DMF and DMSO solutions respectively. Figure 2 shows the variation of ultrasound velocity (U) with concentration in DMF and DMSO respectively. It is observed that in both the solvents, ultrasonic velocity (U) increases non linearly with concentration for all the compounds. Whereas Figure 3 shows that intermolecular free length (L f ) decreases with concentration. Thus, ultrasonic velocity is reverse of intermolecular free length (L f ). The decrease of intermolecular free length means the distance between solute (compound) and solvent molecules decreases i.e., strong interaction between solvents and compound molecules exists in these solvents which causes ultrasonic velocity to increase. This is further supported by isentropic compressibility (κ s ) and relaxation strength (r). The isentropic compressibility (κ s ) of the solutions in both the solvents is also found to decrease with increase of concentration, as shown in Figure 4. Due to solute-solvent interactions in the system, compressibility of the solution decreases with the increase in concentration. This is further confirmed by decrease of relaxation strength (r) and increase in specific impedance (Z) values (as reported in Tables 3 and 4). The Rao's molar sound function (R m ) and Vander Waal's constant (b) are also observed to increase linearly (correlation coefficient 0.9985-0.9998) with concentration for all the compounds in both the solvents. The linear increase of these parameters shows absence of complex formation in these systems.
The internal pressure is the result of forces of attraction and repulsion between molecules in a solution. As Tables 3 and 4 shows that internal pressure (π) decreases in both the solvents. This indicates that solute-solute interactions also exist in these solutions.
The predominance of solute-solvent interactions is further confirmed by evaluating some other parameters. The isentropic compressibility of all the solutions was also fitted to the following Bachem's relation 24 : Thus, it is concluded that for the synthesized chalcones, although both solute-solute and solute-solvent interactions exist in these solutions, solute-solvent interactions dominate in both DMF and DMSO solutions.