Molecular Interactions of Aniline in Ternary Liquid Systems
Sound velocity, density and viscosity values have been measured at 303 K in the ternary system of aniline+ethanol+toluene. From these data, acoustical parameters such as adiabatic compressibility, free length, free volume and internal pressure have been estimated using the standard relations. The results are interpreted in terms of molecular interaction between the components of the mixtures. Observed excess values in all the mixtures indicate dipolar and weak dispersive type interactions exist in the system.
Received: January 16, 2012;
Accepted: February 29, 2012;
Published: July 11, 2012
The molecular interactions existing between the components of liquids and their
mixtures reflect the structural arrangement and their functional aspects. The
review of literature has shown that such analyses have been made for hundreds
of binary, ternary, quaternary organic and inorganic mixtures, electrolytic
solutions, bio-liquids (Velusamy and Palaniappan, 2011),
petroleum products etc., using ultrasonic characterizations. For assessing the
nature of molecular interactions and investigating the physic-chemical behavior
or such mixtures, ultrasonic studies have been mostly used in modern trend.
The presence of solute-solute and solute-solvent interactions of tetra alkyl
ammonium borates in 1, 2-dimethoxy ethane have been evaluated by Muhuri
et al. (1996) using the sound velocity measurements and by evaluation
of apparent molar volume and apparent molar compressibilities. The existence
of solute-solvent interaction between the components of the copper sulphate
(CuSO4.5H2O) and nickel sulphate (NiSO4.7H2O)
in water was studied by Jayakumar et al. (2001).
The dipole-dipole interaction between the components of the mixtures containing
poly ethers and ethyl acetate at temperature 298.15 K was attempted by Pal
et al. (2000) using the ultrasonic study.
Nayakulu et al. (2006) have carried out ultrasonic
and sonochemical reaction studies in the mixtures of ortho-cresol with
ethyl acetate and isoamyl acetate. They found that the reaction rate decreases
due to the passage of sonic wave through the medium. Venkatesu
et al. (2006) evaluated the ultrasonic sound velocity and densities
for the ternary mixtures of N, N-dimethylformamide (DMF) and cyclohexanone with
ethanol, 1-butanol, 1-pentanol and 1-hexanol at 303.15 K and they predicted
the possible molecular interaction between the unlike molecules.
Thermodynamic and transport properties of liquid mixtures have been extensively
used to study the departure of a real liquid mixture from ideality (Awasthi
and Shukla, 2003; Pandey and Kumar, 1994; Nikam
et al., 1996). A departure from linearity in the velocity versus
composition behaviour in liquid mixtures is taken as an indication of the existence
of interaction between the different species (Fort and Moore,
1965). The present study deals with the measurement of ultrasonic velocity,
density and viscosity and computation of related parameters and their excess
values at 303 K in the ternary mixture of aniline+ethanol+toluene.
MATERIALS AND METHODS
Experimental details: The mixtures of various concentrations in mole
fraction were prepared by taking purified AR grade samples at 303 K and the
mixtures were analyzed for their purity as done by Farooq
et al. (2008). The ultrasonic velocities in liquid mixtures have
been measured using an ultrasonic interferometer (Mittal type) working at 2
MHz frequency with an accuracy of ±0.1 m sec-1. The density
and viscosity are measured using a pycnometer and an Ostwalds viscometer
respectively with an accuracy of 3 parts in 105 for density and 0.001
nsec m-2 for viscosity.
Using the measured data, the acoustical parameters such as adiabatic compressibility
(β), free length (Lf), free volume (Vf) and internal
pressure (πi) and their excess parameters have been calculated
using the following standard expressions (Ali and Nain, 2002;
where, KT is the temperature dependent constant having a value 201.1209x10-8 in MKS system, k is a constant equal to 4.28x109 in MKS system, independent of temperature for all liquids, Meff = ∑ ximi where, x is the mole fraction and m is the molecular weight of ith component and AE stands for excess property of any given parameter, Aexp is the experimental value and Aid is the ideal value.
RESULTS AND DISCUSSION
Measured values of density, viscosity and velocity at 303 K for the ternary
system of aniline+ethanol+toluene are given in Table 1. All
the measured parameters increase with increasing mole fraction of aniline (Eliel,
1985). Such non-linear variation indicates the presence of intermolecular
interactions between the components (Srivastava et al.,
2010; Sako et al., 2010; Narendra
et al., 2011).
|| Values of density (ρ), viscosity (η) and ultrasonic
velocity (U) of the system: aniline+ethanol+toluene at 303 K
||Values of adiabatic compressibility (β), free length
(Lf), free volume (Vf) and internal pressure (πi)
of the system: aniline+ethanol+toluene at 303 K
Among the three components, aniline and ethanol are expected to involve in
strong interaction due to their polar nature (Dean, 1987).
Even though toluene is unsaturated, it behaves like a saturated compound ordinarily.
Moreover, the presence of toluene molecules as electron donor will give higher
stability to the carbocation of ethanol and hence they cannot provide any strong
interaction. As aniline is having a relatively higher dielectric constant (6.8012)
than toluene (2.362) and as both are electron donors, the interaction between
the molecules of aniline with toluene is found to be stronger (Deshpande
and Bhatgadde, 1968; Palaniappan, 2001, 2012).
The calculated values of β, Lf, Vf and πi
for the present system are given in Table 2. As expected,
β and Lf are continuously decreasing with increasing mole fraction
of aniline (Palaniappan et al., 2003). The inspection
of these trends reveals a unanimous higher β (and Lf) that reveals
that the present system can provide some compactness and the observed trend
of Lf confirms this view. Thus, the existence of strong interactions
due to dipolar type is evident.
Considering Vf and πi values, they are behaving
mutually opposite to each other. Decreasing Vf and increasing πi
values with increasing mole fraction of aniline is noticed, as observed in other
liquid systems by Palaniappan (2002). Further, the gradual
increase in πi indicates that the adhesive forces between the
components are much more enhanced than the cohesive forces within the component.
All these observations are fully supporting the existence of dipolar type interaction,
especially at higher mole fractions of aniline.
To confirm the existence of interactions in the system, it is customary to
calculate the excess values of the parameters considered in the work. These
values represent the deviation of the ideal value from that of the observed
value of the respective parameter.
|| Mole fraction of toluene vs. excess adiabatic compressibility
at 303 K
|| Mole fraction of toluene vs. excess intermolecular free length
at 303 K
|| Mole fraction of toluene vs. excess intermolecular free volume
at 303 K
The ideal values were calculated using the additivity rule which is applicable
only for linear variations. Thus any non-zero value in the excess parameter
is a measure of non-linearity and is the confirmation for the existence of interaction
in the system (Thirumaran and Thenmozhi, 2010).
In the present work, the respective excess parameters have been calculated
and are illustrated in Fig. 1-4. All these
values for ternary mixture are negative. The negative βE and
negative βE shows a continuous increase in magnitude with a
dip at 0.3 mf of aniline and confirms that the strong interactions are enhanced
as aniline mole fraction is increased. The trend of VfE
exhibit a dip at 0.3 whereas for πfE at 0.6 mole
fraction of aniline further, the variations noticed on either side of this dip
are more haphazard (Sundharam and Palaniappan, 2005;
|| Mole fraction of toluene vs. excess internal pressure at
These observations support that all the added aniline are in the cluster formation
with the toluene+ethanol binary complexes at this mole fraction.
Followings conclusions were obtained from the above discussions:
||Presence of specific strong dipolar type interactions is noticed
||Weak dispersive interaction in small magnitude exists at lower mole fractions
||Aniline, at 0.3 mole fraction, serves the best combinational ratio for
this system, as all the component molecules get completely engaged in the
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