Densities, viscosities, speed of sound and some acoustical parameter studies of substituted pyrazoline compounds at different temperatures

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1 Indian Journal of Pure & Applied Physics Vol. 53, January 015, pp Densities, viscosities, speed of sound and some acoustical parameter studies of substituted pyrazoline compounds at different temperatures A B Naik Physical Chemistry Laboratory, Department of Chemical Technology, S G B Amravati University, Amravati (MS), India anilnaik@sgbau.ac.in Received 1 April 013; revised 4 August 014; accepted 7 October 014 Density, viscosity and ultrasonic velocity of pure dioxane and ligands, 3-(-hydroxy-5-methyl phenyl)-5-phenyl- pyrazoline [HMPPIZOLINE] and 3-(-hydroxy-5-methylphenyl)-1,5-di-phenyl- pyrazoline [HMPPPIZOLINE] in different mole fraction of dioxane-water mixture have been investigated at different temperatures (98.15, and ) K. Acoustical parameters such as adiabatic compressibility (β), intermolecular free length (L f ), acoustical impedance (Z), apparent molar compressibility (Φ β ), apparent molar volume (Φ V ), relaxation time (Γ), absorption coefficient, free volume, Gibb s free energy and relative association (R A ) have also been determined from the experimental data of density, viscosity and ultrasonic velocity. An excellent correlation between a given parameters is observed at all temperatures and the result suggests the presence of molecular interactions. The effect of temperature variations on the strength of molecular interaction has also been studied and the data have been quantitatively explained in terms of solute-solvent interaction. Keywords: Density, Ultrasonic velocity, Viscosity, Acoustical parameter, Molecular interaction, Pyrazoline 1 Introduction Heterocyclic compounds provide a great synthetic and structural versatility due to their having a number of potential substitution positions. Furthermore, hetero atoms offer the possibility of several modes of coordination 1. Pyrazolines are well known and important nitrogen-containing five-member heterocyclic compounds and various methods have been worked out for their synthesis. Several pyrazoline derivatives have been found to possess considerable biological activities, which stimulated research activity in this field. Their prominent effects are e.g., antimicrobial, antidiabetic, analgesic and antitumor 3. Thus, study of their molecular interactions in solution will be helpful to understand the biological applications. Measurements of physico-chemical properties such as viscosity, density, ultrasonic velocity and refractive indices of pure components and their mixtures are being increasingly used as tools for investigations of the properties of pure components and the nature of intermolecular interactions between the components of liquid mixtures 4,5. Ultrasonic studies have found wide applications owing to their ability to characterize the physico-chemical behaviour of solutions. The measurement of ultrasonic velocity can provide useful information regarding the degree of deviation from ideality, internal structure, complex formation and molecular interaction in liquids because of their accuracy 6. 1, 4-Dioxane (Dx) has been widely used as a solvent, stabilizer for chlorinated solvent such as methyl tert-butyl ether and dichloromethane, greasing agents, components of paint, varnish removers, biosciences, pharmaceuticals, chemical technologies and dispersion agents in the textile industry. The Dx is a hetero cyclic diethyl ether with each of its two oxygen atoms forming an ether functional group. The molecular structure of Dx may be related to ethanediol and methoxy ethanol, but is an almost apolar, aprotic and protophilic solvent 7. It has very low dipole moment and there is no H-bond pair formation between two Dx molecules in pure liquid state, which is mainly due to the fact that in Dx molecule oxygen molecule offers H-bond acceptor sites, but it cannot self-associate due to lack of H-bond donor positions 8. It may be formed during the polymerization of ethylene oxide to produce the polyethylene moiety of the surfactant molecules. This compound can stay long in water owing to well miscibility and cannot happen and decompose in natural Gulwade et al 1. reported the study of acoustical study of substituted azoles in N,N-dimethylformamide at different temperatures and data have been quantitatively explained in term of

2 8 INDIAN J PURE & APPL PHYS, VOL 53, JANUARY 015 solute-solute and solute-solvent interactions. Most of the researchers have studied the acoustic parameters only at single temperature and therefore, clear understanding of the solution structure of Dx-water system is lacking. The present work deals with some aspects of substituted pyrazoline and their thermo-dynamical parameters in mixed aqueous solvent media. The measurements on viscosities, densities and ultrasonic velocity with acoustical properties have been studied in different mole fraction of Dx-water mixtures at (98.15, and ) K. Experimental Details The ligands, 3-(-hydroxy-5-methylphenyl)-5- phenyl- -pyrazoline [HMPPIZOLINE] and 3-(- hydroxy-5-methylphenyl)-1,5-diphenyl- -pyrazoline [HMPPPIZOLINE] were synthesized in the laboratory by known literature method 13. Purity of these compounds exceeds 99.5% and it was verified by the TLC method and confirmed with IR spectra. Stock solutions of ligands were prepared by dissolving an accurate amount in Dx-water solvent 14. Dx used in the present study was AnalR grade and purified according to literature method 15. The water used was doubly distilled and its specific conductivity was found to be 0.74 S at K. The purity of the pure components was assessed by comparing the experimental values of density, viscosity and speed of H 3 C R = H, Ph Fig. 1 OH N N R Ph sound with literature values at K (Table 1), the agreement was satisfactory. The liquid mixtures were prepared by mixing appropriate volumes of the liquid components in standard flasks with airtight caps and the mass measurements were performed by high precision digital balance (Adair Dutt ADGR-00 balance of accuracy ± 0.01 mg). The sound velocity of pure components and their mixtures was measured by ultrasonic interferometer (Mittal enterprises, model F-81s at variable frequency) at MHz with frequency tolerance ± 0.03%. It consists of high frequency generator and a measuring cell. The viscosities and densities were measured by Ostwald s viscometer (accuracy ± N.m -.s) and specific gravity bottle (accuracy ± 0.03 kg.m 3 ), respectively. The temperature of water bath was controlled within 0.1 K using a thermostat. The accuracy of instrument was examined with pure distilled water and Dx, values are agreed closely with literature values (Table 1). The various acoustical parameters were calculated using Microsoft Excel programme and plotted using Origin software. 3 Theory Numerous methods have been reported in the literature for computing ultrasonic velocity. The interferometer is considered as more reliable and precise. The expression used to determine ultrasonic velocity is: u =νλ (1) where u is ultrasonic velocity and is wavelength The compressibility and ultrasonic velocities have been closely studied by a large number of researchers The adiabatic compressibility (β) was calculated from Newton-Laplace equation. It is extensively applicable in physico-chemical behaviour of liquid mixtures such as molecular association, dissociation and formation: 1 β = () u ρ where ρ = density Table 1 Comparison of experimental values of density (), viscosity () and speed of sound (u) of pure liquids along with their literature values at K Liquids T (K) (kg.m 3 ) u (m.s 1 ) 10 3 N.m.s Exp. Lit. Exp. Lit. Exp. Lit. 1,4 Dx Dist. Water

3 NAIK: DENSITIES, VISCOSITIES, SPEED OF SOUND OF PYRAZOLINE COMPOUNDS 9 The intermolecular free length between molecules in the liquid state is an essential and characteristic feature. Intermolecular forces are important to determine the properties of liquids of attractive and repulsive forces 19. The intermolecular free length (L f ) is calculated by using the standard expression: L f = K β (3) where K is a temperature dependent constant known as Jacobson constant. The acoustic impedance (Z) of a wave can be mathematically defined as the product of the wave velocity in the medium and its density. As the waves encounter the interface between the liquid and solid, they sense a change in acoustic impedance and obtained by: Z = u ρ (4) The relative association (R A ) was calculated by the following equation: R 1/3 ρ u0 A = ρ 0 u (5) Where ρ 0, ρ, u 0 and u are the density and ultrasonic velocity of solvent and solution, respectively. The apparent molar compressibility (Φ β ) is calculated by the equation: 1000 β0m Φ β = ( ρ0β ρβ0) + mρρ0 ρ0 (6) where β 0 and β = adiabatic compressibility of solvent and solution, respectively, m is the molal concentration of solute and M is the molar mass of the solute. Φ β is a function of molality as obtained by Gucker 0 from the Debye-Huckel theory 1. The apparent molar volume (Φ V ) is obtained from the relation: 1000 M Φ V = ( ρ0 ρ) + mρρ0 ρ0 (7) The apparent molar volume was found to vary with molality according to Masson s empirical equation. Viscosity (η) is one of the important properties of liquid. It relies on its molecular size, shape and intermolecular attraction. The viscosity measurement like other transport properties of electrolyte provides useful information about the solute-solute and solutesolvent interaction. There are certain acoustical parameters which rely on viscosity 3. Thus, by combining ultrasonic velocity, density and viscosity of the solution, the parameters viscosity relaxation time (Γ) and absorption coefficient have been calculated. The resistance offered by the viscous force in the flow of a sound wave appears as classical absorption associated with relaxation time 4. 4η Γ = 3 ρ.u (8) The absorption coefficient 5 has its origin in viscosity of the medium after neglecting thermal losses. Abs 8π η coeff = 3ρ u (9) The free volume (V f ) is measured by using the relation: V f M eff u = K. η 3/ (10) where M eff is the effective molecular weight and K is temperature independent constant. To study the liquid mixtures, the variation of internal pressure may give some reliable information regarding the nature and strength of forces existing between molecules. In fact, the internal pressure is broader concept and is a measure of the totality of forces of the dispersion, ionic and dipolar that contribute to be overall cohesion of the liquid system. The internal pressure (π i ) is calculated by: 1/ /3 K. η ρ π i = brt 7/6 u M eff (11) where b stands for cubic packing which is assumed to be for liquids and K is dimensionless constant, T the absolute temperature and R is gas constant.

4 30 INDIAN J PURE & APPL PHYS, VOL 53, JANUARY 015 Gibb s free energy ( G) is calculated from the relation:.. G KT log K T Γ = (1) where K is Boltzmann constant, is Planck constant and is relaxation time. 4 Results and Discussion The calibration of the ultrasonic interferometer, Ostwald viscometer and specific gravity bottle was done by measuring the ultrasonic velocity, viscosities and densities with accuracy ± 0.03 of Dx and distilled water at K. The measured values reported in Table 1 are found to be in good concordance with literature values. The values of densities, viscosities and ultrasonic velocities at three experimental temperature (98.15, and ) K are presented in Table. The values are correlated with temperature and concentration of Dx. The trends of, and u are listed in Table It is observed that the values decrease with increase in temperature in mole fraction of Dx-water in all systems. Density is a measure of solvent-solvent and ionsolvent interaction, increases in density with concentration indicates an increase in solvent-solvent and solute-solvent interaction and this may be due to shrinkage in volume owing to the presence of solute (HMPPPIZOLINE and HMPPIZOLINE) molecules. This can be attributed to the structure making ability of the solute in the presence of solvent. The measurements showed that the rate of change of sound velocity with temperature decreases from 3.8 to.6 meter per second per degree 37. As the temperature is increased, available thermal energy facilitates the breaking of the bonds between the associated molecules. Moreover, increase of thermal energy weakens the molecular forces which tends to decrease ultrasonic velocity 38. The linear increase of, and u with concentration of Dx confirmed an increase of cohesive forces because of strong molecular interactions while decrease of three parameters with temperature supported a decrease of cohesive forces. The structural changes influence the viscosity to a certain extent as compared to density and compressibility. It is observed in Table that the viscosity increases with concentration and decreases with temperature, the increasing trend indicates the existence of molecular interaction. The viscosity value HMPPPIZOLINE solution greater than HMPPIZOLINE solution may be due to the presence of phenyl ring an electron rich group and high molar mass. In order to study the effect of HMPPPIZOLINE and HMPPIZOLINE with mole fraction and temperature on molecular interaction in solution the adiabatic compressibility, free length, acoustic impedance, relaxation time, relative association and absorption coefficients were determined and presented in Tables 3 and 4, respectively. The adiabatic compressibility, free length and acoustic impedance show an opposite trend to that of velocity. According to a model proposed by Erying and Kinkaid 39, ultrasonic velocity decreases (Fig. ) with increase in free length and vice versa. This is also in Table Experimental density, ultrasonic velocity and viscosity of HMPPIZOLINE and HMPPPIZOLINE of Dx-water mixture at different temperatures in T (K) (kg.m 3 ) u (m.s 1 ) 10 3 N.m.s (kg.m 3 ) u (m.s 1 ) 10 3 N.m.s

5 NAIK: DENSITIES, VISCOSITIES, SPEED OF SOUND OF PYRAZOLINE COMPOUNDS 31 Table 3 Experimental adiabatic compressibility (), linear free length (L f ) and acoustic impedance (Z) of HMPPIZOLINE and HMPPPIZOLINE of Dx-water at different temperatures m.n 1 L f m Z 10 6 N. m m.n 1 L f 10 =10 m Z 10 6 N. m Table 4 Experimental relaxation time (), relative association (R A ) and absorption coefficient of HMPPIZOLINE and HMPPPIZOLINE of Dx-water at different temperatures P.s. R A 10 7 m 3.mol 1 Absorption coeff X P.s. R A 10 7 m 3.mol 1 Absorption coeff accordance with the expected molecular interaction between the solute-solvent, increases in compressibility. The increase of adiabatic compressibility (Fig. 3) and linear free length with temperature for all system suggest breaking of hetero and homo association of molecules at higher temperature 40. The calculated values of ultrasonic velocity and adiabatic compressibility are found to be in good concordance with reported work 41,4. The acoustic impedance is the parameter related to the elastic properties of medium. Therefore, it is important to examine it in relation to concentration and temperature. It shows from Table 3, the variation of acoustic impedance values increases with increase in mole fraction with temperature. The nonlinear behaviour further suggests the possibility of molecular interaction between solute and solvent through hydrogen bonding. It is inferred from Table 4 that relaxation time increases with increase mole fraction and the same decreases with rise in temperature. This may be due to structural relaxation process 3 and in such situation it is suggested that molecules gets rearranged due to cooperative process 43. The values of relative association are presented in Table 4. It shows an increasing trend with increasing concentration 44. A close examination of relative association values are close to each other which indicates the system under investigation is

6 3 INDIAN J PURE & APPL PHYS, VOL 53, JANUARY 015 Fig. Ultrasonic velocity versus mol fraction of HMPPIZOLINE and HMPPPIZOLINE Dx-water Fig. 4 Apparent molar compressibility versus mol fraction of HMPPIZOLINE and HMPPPIZOLINE Dx-water Fig. 3 Adiabatic compressibility versus mol fraction of HMPPIZOLINE and HMPPPIZOLINE Dx-water essentially ideal in nature. The absorption coefficient generally, increases with increase in concentration (Table 4) and this trend suggests the extents of complexity increase with increase in concentration 45. Figure 4 shows the apparent molar compressibility increases with increase in concentration and temperature. The larger values of Φ β in solutions are attributed to the strong attractive interactions due to the hydrogen bond formation; solute and water molecules induce the dehydration of ions and therefore, increase Φ β. The apparent molar volume increases with increase in concentration and decreases with temperature (Fig. 5). Fig. 5 Apparent molar volume versus mol fraction of HMPPIZOLINE and HMPPPIZOLINE Dx-water The larger values of Φ V in solutions are attributed the strong attractive interactions due to the hydrogen bond formation; solute and water molecules induce the dehydration of ions 46 and therefore increase Φ V (Table 5). From Table 6, free volume shows increase with increase in concentration and temperature. This may be compactness due to association at higher concentration 47 of Dx. The extent of free volume offers the knowledge of type of interaction. In the present case, an increasing trend of free volume with decreasing trend of π i is found with increasing mole

7 NAIK: DENSITIES, VISCOSITIES, SPEED OF SOUND OF PYRAZOLINE COMPOUNDS 33 Table 5 Experimental apparent molar compressibility (Φ β ) and apparent molar volume (Φ V ) of HMPPIZOLINE and HMPPPIZOLINE of Dx-water at different temperatures Φ β m 5.N 1 Φ V T/K Φ β m 5. N 1 Φ V T/K Table 6 Experimental free volume (V f ), internal pressure (π i ) and Gibb s free energy ( G) of HMPPIZOLINE and HMPPPIZOLINE of Dx-water at different temperatures V f 10 3 m 3.mol 1 π i 10 3 atm G V f 10 3 m 3.mol 1 π i 10 3 atm G fraction 48 of Dx. It is observed from Table 6 that the values of G increase with increase in concentration. Moreover, the Gibb s free energy increases with rise in temperature indicating that the need for longer time for cooperative process or the rearrangement of molecules in the mixture Conclusions Densities, viscosities and ultrasonic velocities mixtures of substituted pyrazoline in Dx-water have been experimentally determined over entire mole fraction range at (98.15, and ) K. The values of density and viscosity decrease with increasing temperature. This may be due to decrease in an inner molecular forces and increasing thermal energy. Moreover, increase of thermal energy weakens the molecular forces which tend to decrease ultrasonic velocity. Free length shows molecular interaction between surfaces of molecular interaction between surfaces of molecules so molecular free energy increases. As the temperature increases the acoustical impedance increases in solution which further support the possibility of molecular interaction between solute and solvent. The nonlinear variation of the related parameters such as adiabatic compressibility, apparent molar volume and apparent molar compressibility were elaborated to understand the molecular interactions that lead to the process of

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Molecular Interactions in Substituted Pyrimidines Acetonitrile Solutions at K 1

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2014, Vol. 88, No. 1, pp. 37 41. Pleiades Publishing, Ltd., 2014. PHYSICAL CHEMISTRY OF SOLUTIONS Molecular Interactions in Substituted Pyrimidines