Density , viscosity , ultrasonic velocity and excess thermodynamic parameters of ternary liquid mixtures of morpholine + 1 , 4-dioxane + toluene or nitrobenzene at 308 . 15 K

Densities, viscosities and ultrasonic velocities were measured for the two ternary liquid mixtures containing morpholine (1) + 1,4-dioxane (2) + nitrobenzene (3) or + toluene (3) at 308.15 K over the entire range of mole fractions. Thermodynamic parameters, such as excess volume (VE), deviations in adiabatic compressibility (ΔKS), free length (ΔLF), isothermal compressibility (ΔβT), free volume (ΔVF) and viscosity (Δη) were calculated and applied to the Redlich−Kister polynomial equation to determine the appropriate coefficients. The deviations of the ternary liquid mixtures from their ideal behaviour were determined from the measured and calculated thermodynamic properties. In addition, an insight into the molecular structure and possible interactions for the investigated mixtures was attempted.


INTRODUCTION
Currently, many engineering fields require information regarding thermodynamic and transport properties of liquid mixtures.The study of transport fluid phenomena requires knowledge of density and viscosity of the system. 1,2Other than density and viscosity, 3 an ultrasonic study provides enormous information regarding molecular interactions and the structural behaviour of the molecules in a mixture.
The effectiveness of operations in chemical and engineering processes can be tuned from the investigation of physical properties of the employed liquids MOLECULAR INTERACTIONS IN TERNARY MIXTURES 1133 tures were measured using the relative density method.Relative density bottle of 10 mL capacity was cleaned successively with chromic acid, distilled water and acetone and then dried and used for the density measurements. 10An electronic balance was used to measure the density. 11The accuracy of the measurement of density by relative density method depends on the accuracy of measurement of weight.Density values were accurate to ±0.0002 g cm -3 .TABLE I. Densities (ρ), viscosities (ɳ) and ultrasonic velocities (U) of pure morpholine, nitrobenzene, 1,4-dioxane and toluene; T = 308.15  Viscosities were measured using an Ostwald viscometer.The viscometer was thoroughly cleaned with chromic acid.It comprises a U-tube the left hand limb of which is essentially a pipette with two defining marks.An electronic digital stopwatch with readability of ±0.01 s was used to measure the flow time of a liquid between the marks.The ultrasonic velocity values were obtained using an ultrasonic interferometer (Pico, Chennai, India) with a frequency of 2 MHz that was calibrated using water and nitrobenzene.The overall accuracy in the measurement was ±0.2 %.All the measurements were realized using a digital thermostat with display accuracy ±0.01 K.The details of the methods and techniques of the measurements have been described earlier. 12,13SULTS AND DISCUSSION 1,4-Dioxane could be classified as a non-polar solvent, but the distribution of electric charge gives a large quadurpole moment to 1,4-dioxane. 14,15The presence of a substituent in the aromatic hydrocarbon should modulate its electron-acceptor ability. 16,17The cyclic ethers morpholine and 1,4-dioxane (p-dioxane) are hexa cyclic compounds with similar shapes.Morpholine is a nonaromatic cyclic ether containing a secondary amine (-NH) group, which can serve as a site for possible hydrogen bonding.1,4-Dioxane is a diether and an excellent aprotic solvent with an electron donating ability toward the aromatic ring and has a zero dipole moment. 18Cyclic ethers have a very small polarity, similar to those of linear ethers that do not have a self-associating nature.Hence no self-interaction or association is possible in 1,4-dioxane.
Nitrobenzene is an aromatic hydrocarbon containing an NO 2 as a functional group.The electron withdrawing -NO 2 group draws π-electrons from the aromatic electron cloud of benzene generating a δ + charge in it.Hence, the mode of self-interaction in nitrobenzene is a potential anionic π stacking interaction possible through the nucleophilic oxygen atom of the -NO 2 group with the generated δ + charge of the aromatic π-electron cloud of benzene moiety.Toluene is a methyl carrying benzene ring in which the methyl releases an electron to the benzene moiety.Two different ternary liquid solutions were prepared by mixing morpholine (1) + 1,4-dioxane (2) + nitrobenzene (3) as well as morpholine (1) + 1,4-dioxane (2) + toluene (3) by varying their mole fractions.Experimental densities, viscosity, ultrasonic velocities of the pure components of the liquid mixture were compared with literature values and are reported in Table I.Also their excess thermodynamic parameters were calculated and tabulated at a temperature of 308.15K to understand the possible interactions between them.
The excess volume values for the ternary mixtures were calculated using the relation: where X 1 , X 2 and X 3 , M 1 , M 2 and M 3 and ρ 1 , ρ 2 and ρ 3 are the mole fractions, molar masses and densities of pure components 1, 2 and 3, respectively.The adiabatic compressibility (K S ) was calculated from the Laplace equation: 26 S 2 where ρ and U are the density and ultrasonic velocity of the liquid mixtures, respectively.From the above equation, the excess adiabatic compressibility (ΔK S ) was calculated by: where K S1 , K S2 and K S3 are adiabatic compressibility of the pure liquids and φ 1 , φ 2 and φ 3 are, respectively, the volume fractions of pure liquids calculated by the relation: The viscosity was calculated using the relation: where A and B are constants characteristics of the viscometer that are calculated using the standard liquids water and nitrobenzene, t is the flow time, ρ is the density.Excess viscosity values were calculated using the following relation: where η 1 and η 2 are the viscosity values of pure components1 and 2, respectively.
The free length was calculated using the relation: where K is the Jacobson constant, 27,28 which is a temperature dependent constant but independent of the nature of the liquid.
The isothermal compressibility was calculated using the relation: To calculate the free volume, Suriyanarayana 29 proposed the relation: where K is a temperature independent constant that is equal to 4.28×10 9 for all the liquids and M eff is the effective molecular weight of the mixture, calculated using the relation: where X 1 , X 2 , X 3 and M 1 , M 2, M 3 are the mole fractions and molar masses of the pure components 1, 2 and 3, respectively.The excess values of the other parameters were calculated using the relation: where X i and A i are the mole fraction and parameters of the i th component.
All the calculated excess parameters were fitted to a Redlich-Kister 30 type polynomial equation by the least squares method to derive the adjustable parameters a, b and c.
For binary mixtures: For ternary mixtures: Using the theoretical values, all excess parameters were calculated and the standard deviation values were calculated using the relation: 1136 UMASIVAKAMI, VAIDEESWARAN and VENIS ( ) where n is the number of measurements and m is the number of adjustable parameters.
The calculated thermodynamic parameters and excess acoustical parameters for the ternary liquid mixtures of morpholine, 1,4-dioxane with nitrobenzene or toluene are represented in Tables II-VII.Available on line at www.shd.org.rs/JSCS/The sign of the V E values depends on either expansion or contraction that occurs during the mixing of two liquids.The V E values are negative for most mole fraction values except for a few at 308.15 K for the ternary mixture containing morpholine + 1,4-dioxane + nitrobenzene.This may be due to the strong molecular interactions between the constituent of liquid mixtures. 31The other ternary liquid mixture morpholine + 1,4-dioxane + toluene show positive values for many mole fractions.This may be due to the possibility of weak interactions between the components in the liquid mixtures.
The values of ΔK S are directly proportional to different size and shape of the components and inversely proportional to the velocity.In addition, ΔK S varies due to change in the free volume. 32,33The negative ΔK S values for the ternary mixture containing nitrobenzene may be due to the intermolecular interactions between unlike molecules, which may make the system slightly flexible and slightly compressible.The observed positive values of ΔK S may be due to the weak interaction between the unlike molecules that results in rigidity and less compressibility of the system.The η values also serve as a tool to study the nature of intermolecular interactions.The observation of high magnitude of positive values 34,35 advocates the possibility for specific strong interactions in the nitrobenzene ternary mixtures.
The occurrence of lower magnitude η values for the toluene ternary mixtures suggests the chance for weak and non-specific interactions.The influence of interactions in ternary systems and their deviations from ideal behaviour was studied through excess thermodynamic properties, such as ΔL F , Δβ Τ, ΔV F and Δln η.
The analysis and comparison of the excess thermodynamic properties of both ternary systems show more negative deviations were observed for those associated with nitrobenzene than those associated with toluene.Hence, it could be assumed that both the ternary liquid mixture exhibit intermolecular interactions.Furthermore, it indicates the chance for the occurrence of strong intermolecular interactions in ternary mixtures containing nitrobenzene is greater in comparison to those associated with toluene.The presence of a -NO 2 group in nitrobenzene deactivates the electron cloud in the benzene ring, while the -CH 3 group in toluene tends to activate the electron cloud.The examination of the nat-ure of the functional group attached to the benzene ring aids in analysing the geometrical effects in influencing the possible interactions and also to correlate the observed variations in trends of thermodynamic properties.From the above measured and experimental data, the interactions present between the considered ternary mixtures can be presumed as: morpholine + 1,4-dioxane + nitrobenzene > morpholine + 1,4-dioxane + toluene.

CONCLUSIONS
The densities, ultrasonic velocities, viscosities and other excess thermodynamic properties, such as excess volume, adiabatic compressibility, deviation in viscosity, free length, isothermal compressibility, free volume for the two ternary mixtures of morpholine + 1,4-dioxane + nitrobenzene and morpholine + 1,4-dioxane + toluene were measured at atmospheric pressures and at a temperature of 308.15 K.The relevant values for the pure components of the mixtures are also provided for reference.The corresponding thermodynamic excess parameters were calculated with the formulas reported earlier and fitted to a Redlich-Kister type polynomial equation to determine the variable coefficients.The behaviour of the liquid mixtures and the deviation from ideality has been discussed based on experimental and calculated values.The V E values suggest the existence of intermolecular interactions between the component molecules in the liquid mixtures.The intermolecular interactions may make the morpholine + 1,4-dioxane + nitrobenzene mixtures slightly flexible and a little compressible indicated as suggested by its ΔK S values.In contrast, the ΔK S values of morpholine + 1,4-dioxane + toluene mixtures suggest the possibility for the occurrence of stiffness and a less compressible nature.Both the ternary mixtures exhibit intermolecular interactions between like molecules.The self-interaction may dominate in ternary mixture containing nitrobenzene, and it may become less significant for the ternary mixture associated with toluene.According to the measured and calculated properties, it could be assumed that strong molecular interactions are more possible in morpholine + 1,4-dioxane + nitrobenzene than in morpholine + 1,4-dioxane + toluene.The possibility for activation by the methyl group in toluene and the chance for deactivation by the nitro group in nitrobenzene of the benzene moiety help to rationalize the geometrical effects on the measured and calculated properties.