198 CHAPTER – 5 Study of volumetric and viscometric properties on non aqueous – non electrolyte liquid mixtures SECTION - A Binary liquid mixtures of propanoic acid with N,N-dimethyl aniline/N,N-diethyl aniline SECTION - B Propanoic acid with equimolar mixture of (N,N-dimethyl formamide and methanol/ethanol/1-propanol)
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198
CHAPTER – 5
Study of volumetric and viscometric properties on non aqueous – non electrolyte liquid mixtures
SECTION - A Binary liquid mixtures of propanoic acid with N,N-dimethyl aniline/N,N-diethyl aniline
SECTION - B Propanoic acid with equimolar mixture of (N,N-dimethyl formamide and methanol/ethanol/1-propanol)
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Introduction
The volumetric and viscometric study of non aqueous – non electrolyte liquid
mixtures enables the determination of some useful thermodynamic and other properties that
are highly sensitive to molecular interactions [1−4]. Knowledge of the temperature
dependence of excess properties of liquid mixtures provides valuable information on the
nature of inter molecular interactions existing among the component molecules [5–7]. The
volumetric and viscometric study of molecular interactions in some non aqueous – non
electrolyte liquid mixtures is presented in this chapter. These molecular interactions are studied
at three different temperatures (303.15, 313.15 and 323.15 K). This chapter is divided into two
sections namely, Section-A and Section-B.
Binary mixtures of Propanoic acid with N,N-dimethyl aniline and N,N-diethyl aniline
are presented in section-A. Thermodynamic properties of liquid acid-base mixtures were
studied by Rattan et al [8], Horacio N. Solimo et al [9] and Begona Garcia et al [10] with
propanoic acid as one component in binary mixtures. Katz et al [11] and Rama Murthy et al
[12-14] studied the volumetric and viscometric properties in binary liquid mixtures of aniline
and substituted anilines such as N-methyl aniline, N,N-dimethyl aniline, N-ethyl aniline,
N,N-diethyl aniline as one component and toluene or n-butanol or m-cresol or o- cresol as
other component. Ghasemi et al [15] reported the densities and viscosities for the binary and
ternary mixtures of 1,4-dioxane+1-hexanol+N,N-dimethylaniline.
Recently, Manukonda et al [16] studied the volumetric, speed of sound data and
viscosity at (303.15 and 308.15) K for the binary mixtures of N,N–diethyl aniline + aliphatic
ketones (C3-C5), + 4-methyl-2-pentanone. Gowrisankar et al [17] reported the volumetric,
speed of sound data and viscosity at (303.15 and 308.15) K for the binary mixtures of N,N-
EmV 2, ), partial molar volumes at infinite dilution (
1,mV ,
2,mV ) and
excess partial molar volumes at infinite dilution ( ,1,
EmV , ,
2,EmV ). The variations of these
properties with composition as well as with temperature are discussed in terms of molecular
interactions existing among the molecules of these mixtures. Deviation/excess properties are
fitted to Redlich-Kister type polynomial equation. The experimental viscosity data of all
binary/equimolar liquid mixtures are correlated with the viscosity models such as Grunberg
and Nissan, Hind et al., Katti and Chaudhrai, and Heric and Brewer.
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Section A
Binary liquid mixtures of propanoic acid with
N,N-dimethyl aniline/N,N-diethyl aniline
5.A.1 Importance and properties of the chemicals
Propanoic acid (PA) is a naturally occurring carboxylic acid with chemical formula
CH3CH2COOH. It is a clear liquid with a pungent odor and it is used as food preservative
(calcium and sodium propionate). It is miscible with water. The melting and boiling points
are -210C and 1410C respectively. Propanoic acid inhibits the growth of mold and some
bacteria at the levels between 0.1 and 1% by weight. Hence, it is consumed as a preservative
for both animal feed and food for human consumption. It is also useful as an intermediate in
the production of other chemicals, especially polymers, plastics, cosmetics.
N,N-dimethyl aniline (DMA) is an organic chemical compound, a substituted
derivative of aniline with chemical formula C6H5N(CH3)2. It consists of a tertiary amine,
featuring dimethyl amino group attached to a phenyl group. This oily liquid is colourless
when pure, but commercial samples are often yellow. The melting and boiling points are 20C
and 1940C respectively. DMA is a key precursor to commercially important triaryl methane
dyes such as malachite green and crystal violet. It serves as a promoter in the curing of
polyester and vinyl ester resins.
N,N-diethyl aniline (DEA) is a chemical compound with the molecular formula
(C2H5)2NC6H5 . The melting and boiling points are -380C and 2160C respectively. It is used
as an intermediate in the manufacture of dyes, pharmaceuticals and other chemicals, and also
as a reaction catalyst. In organic synthesis, the complex diethyl aniline borane (DEANB) is
used as a reducing agent. Diethyl aniline may be genotoxic because it has been found to
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increase the rate of sister chromatid exchange. These, aromatic anilines, N,N-dimethyl
aniline, N,N-diethyl aniline are used as intermediates to manufacture dyes, vanillin, and as a
stabilizer for calorimetric peroxidase determination.
5.A.2 Experimental
High purity and Analytical Reagent (AR) grade compounds of propanoic acid, N,N-
dimethyl aniline and N,N-diethyl aniline obtained from LOBA chemicals, India are used in
the present study. All the chemicals are further purified by standard methods [21,22],
distillation, fractional distillation under reduced pressure and only middle fractions were
collected. Finally, after purification method the purity of the propanoic acid, N,N-dimethyl
aniline and N,N-diethyl aniline is found to be w = 0.997, w = 0.993 and w = 0.993
respectively. Before use, the chemicals were stored over 0.4 nm molecular sieves
approximately for 72 hr to remove water content and degassed.
Binary mixtures of propanoic acid with N,N-dimethyl aniline and N,N-diethyl aniline
(PA+DMA and PA+DEA) are prepared by mass in air tight bottles over the entire
composition range of propanoic acid (i.e 0 to 100% of PA). The mass measurements are
performed on a METTLER TOLEDO (Switzerland make) ABB5- S/FACT digital balance
with an accuracy ±0.01mg. The uncertainty in the mole fraction is 10-4. Densities of pure
liquids and their mixtures have been determined by using a 5 cm3 two stem double-walled
Parker & Parker type pyknometer [23].This pyknometer is calibrated with triply distilled
water.
An Ostwald viscometer has been used to determine the viscosity of the liquid
mixture, which is calibrated as described by Subramanyam Naidu and Ravindra Prasad [24]
using triply distilled water. The viscometer was also calibrated using benzene, CCl4 liquids
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etc at working temperatures. The length of one of the capillary tube of viscometers used in
the present study is 8 cm and its diameter is 0.56 mm. The reproducibility in the measured
parameters density and viscosity are 3 in 105 parts and ± 0.2% respectively.
The experiment is performed at three different temperatures 303.15, 313.15 and
323.15 K. The densities and viscosities measured at 303.15 K and 313.15 K for the pure
liquids used in this investigation are compiled in Table 5.A.1 together with the literature data
[8,11,13] available. These results are in good agreement with the reported data.
5.A.3 Results and discussion
The experimental values of densities (ρ) and viscosities (η) are reported in Tables
5.A.2 and 5.A.3 for DMA+PA and DEA+PA binary mixtures respectively. It has been
observed that the density varies almost linearly with the concentration of propanoic acid as
well as with temperature but the viscosity changes non-linearly showing maxima in all the
systems studied at all temperatures investigated. This type of behaviour could be attributed
to complex formation.
The experimental values of density and viscosity are used to calculate the
deviation/excess properties such as deviation in viscosity, Δη, excess molar volume, EVm and
excess Gibbs free energy of activation of viscous flow, ΔG*E. The deviation/excess
properties are illustrated in Table 5.A.4. The variation of deviation in viscosity with mole
fraction of propanoic acid as shown in Figures 5.A.1 and 5.A.2. Generally, negative values
of Δη indicate the presence of dispersion forces or mutual loss of specific interactions in like
molecules operating in the systems arising due to weak intermolecular interactions and
positive values of deviation in viscosity indicate strong specific interactions [25,26]. The
sign and magnitude of Δη depend on the combined effect of factors such as molecular size,
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shape, and intermolecular forces. In general ethyl groups are more +I effect than methyl
groups. In DEA the ethyl groups are more electron releasing than methyl groups of DMA on
nitrogen atom. So, the nitrogen in DEA possesses more electron density than in DMA,
therefore DEA is more favoured to accept the proton of the PA. Hence it is an appropriate
reason to support the observed more positive Δη values in propanoic acid + N,N-diethyl
aniline system.
Table 5.A.1 Comparison of densities (ρ) and viscosities (η) of pure liquids with literature data at 303.15 and 313.15 K Component temp. T/K ρ/kg·m-3 η/10-3N·s·m-2
present work literature present work literature Propanoic acid 303.15 982.1 982.0 [8] 0.950 0.9498[8]
Table 5.A.2 Experimental values of densities (ρ) and viscosities (η) with mole fraction of propanoic acid, x for N,N-dimethyl aniline + Propanoic acid binary system at 303.15, 313.15 and 323.15 K x T = 303.15 K T = 313.15 K T = 323.15 K
Table 5.A.3 Experimental values of densities (ρ) and viscosities (η) with mole fraction of propanoic acid, x for N,N-diethyl aniline + Propanoic acid binary system at 303.15, 313.15 and 323.15 K x T = 303.15 K T = 313.15 K T = 323.15 K
Table 5.A.4 Calculated values of deviation in viscosities, Δη, excess molar volumes, EmV
and excess Gibbs free energy, ΔG*E with mole fraction of propanoic acid, x for all binary system at 303.15, 313.15 and 323.15 K N,N-dimethyl aniline+propanoic acid N,N-diethyl aniline+propanoic acid
The variations of excess molar volume, EmV with mole fraction of propanoic acid at
all temperatures for the binary systems are shown in Figures 5.A.3 and 5.A.4. The deviation
of a physical and chemical property of the liquid mixture from the ideal behaviour is a
measure of the interaction between molecules of the components of liquid mixtures and such
type of deviation is generally attributed to dipole-dipole interactions and hydrogen bond
between unlike molecules [27] respectively. The factors that are mainly responsible for the
expansion of volume i.e. positive values of EVm are: (i) breaking one or both of the
components in a solution i.e. loss of dipolar association between the molecules (dispersion
forces). (ii) The geometry of molecular structures which does not favour the fitting of
molecules of one component into the voids created by the molecules of other component.
(iii) Steric hindrance of the molecules. The negative values of EVm are due to strong specific
interactions such as (iv) association of molecules through the formation of hydrogen bond
(or) association due to dipole-dipole interactions (or) association due to induced dipole -
dipole interactions (v) accommodation of molecules due to larger differences in molar
volumes.
The variation of excess molar volume in the present investigation is negative over the
entire mole fraction range. Both the components of the liquid mixtures studied are polar
molecules in nature. The observed negative EVm values are due to the interaction between
the proton of acid and lone pair of electrons on the nitrogen atom of aniline/resonant electron
density on benzene ring of substituted aniline. Due to the large difference in molar
volumes/masses of propanoic acid and substituted anilines accommodation of smaller
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molecules of one component into the voids created by the other component of molecules is
also responsible for observed negative EVm values. The above factors are responsible for the
negative values of EVm [28].
From the figures 5.A.3 and 5.A.4 it has been observed that as the temperature of the
systems increases the negative excess molar volumes decrease indicating the decrease of
interaction between the unlike molecules. The negative excess molar volumes follows the
order N,N-diethyl aniline > N,N-dimethyl aniline hence the strength of interactions as
follows, N,N-diethyl aniline > N,N-dimethyl aniline. The variations of excess Gibbs free
energy with mole fraction of propanoic acid at all temperatures for the binary systems are
shown in Figures 5.A.5 and 5.A.6. The ΔG*E are found to be positive for both the systems
and at all temperatures. These positive values are indicating the existing of strong
interactions between the components of unlike molecules. As temperature increases these
positive values are found to decrease which shows the decrease of interaction between
constituent molecules.
The values of deviation in viscosity and excess molar volume have been fitted to
Redlich-Kister type polynomial [29] equation. The R-K coefficients and the standard
deviations of both binary mixtures have been presented in Table 5.A.5. The smaller standard
deviation values show that the polynomial better fits the calculated properties.
The partial molar volumes ,1mV of component 1(PA) and ,2mV of component 2
(DMA/DEA) in the mixtures over the entire composition range are calculated. These values
are furnished in Table 5.A.6. From this table, the values of ,1mV and ,2mV for both the
components in the mixtures are lesser than their respective molar volumes in the pure state
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Table 5.A.5 Coefficients Ai of Redlich-Kister type polynomial equation (3.28) and the corresponding standard deviations, σ (3.29) of all the systems under investigation property A0 A1 A2 A3 A4 σ N,N-dimethyl aniline+propanoic acid
Table 5.A.6 Calculated values of partial molar volumes ( m,1V and m,2V ) with mole fraction of propanoic acid, x for all binary system at 303.15, 313.15 and 323.15 K N,N-dimethyl aniline+propanoic acid N,N-diethyl aniline+propanoic acid x m,1V / m,2V / x m,1V / m,2V / 10-6m3.mol-1 10-6m3.mol-1 10-6m3.mol-1 10-6m3.mol-
i.e contraction of volume takes place on mixing PA with DMA/DEA. Figures 5.A.7 and
5.A.8 represent the variation of excess partial molar volumes of PA and DMA/DEA in the
binary mixtures of PA+DMA and PA+DEA respectively. Examination of these figures
reveals that, indicating strong interactions exist between the unlike molecules. These figures
support the conclusions drawn from EmV values.
The dynamic viscosities of the binary liquid mixtures have been calculated using
various empirical relations like Grunberg and Nissan [30], Hind and Ubbelohde [31], Katti
and Chaudari [32], Heric and Brewer [33] and the corresponding interaction parameters are
also evaluated. Theoretical values of viscosity of the binary liquid mixtures of PA+DMA
and PA+DEA calculated using the above equations are given in Tables 5.A.7 and 5.A.8
respectively at all three temperatures. Table 5.A.9 presents the values of interaction
parameters along with the standard deviations, σ. The variation of these interaction
parameters with temperature or composition follows the order N,N-diethyl aniline > N,N-
dimethyl aniline at constant composition and temperature respectively. Further the
interaction parameter values are found to decrease with an increase of temperature for all the
systems studied. These results are in good agreement with the results derived from the
excess properties. Prolongo et al [34] reported positive values of interaction parameter
corresponding to systems with negative excess molar volumes. This is in good agreement
with our results. The estimated values of σ are smaller indicating that experimental values of
viscosities are well correlated by all the viscosity models.
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Table 5.A.7 Theoretical values of viscosities from eqn.s [(3.47) - (3.53)] with mole fraction of propanoic acid, x for N,N-dimethyl aniline+propanoic acid at 303.15, 313.15 and 323.15 K
Table 5.A.8 Theoretical values of viscosities from eqn.s [(3.47)-(3.53)] with mole fraction of propanoic acid, x for N,N-diethyl aniline+propanoic acid at 303.15, 313.15 and 323.15 K
Table 5.B.3 Experimental values of densities (ρ) and viscosities (η) with mole fraction of PA, x for (DMF+EOH)+PA binary system at 303.15, 313.15 and 323.15 K x T = 303.15 K T = 303.15 K T = 303.15 K
Table 5.B.4 Experimental values of densities (ρ) and viscosities (η) with mole fraction of PA, x for (DMF+POH)+PA binary system at 303.15, 313.15 and 323.15 K x T = 303.15 K T = 313.15 K T = 313.15 K
interactions are also present in the liquid mixtures investigated. In addition to these,
physical interaction such as geometrical fitting of
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smaller molecules into the voids created by the larger molecules is also favourable
for the present systems studied.
From figures 5.B.1 – 5.B.3 it is observed that, as the temperature of the
systems increases the negative excess molar volumes are found to decrease
indicating the decrease of interaction between the unlike molecules but the
interaction increases from MOH to POH. As the alkanol chain length increases,
decreasing the concentration of –OH groups in higher alkanols and thereby lowers
dipole moment in higher alkanols which causes weaker interactions. These are the
expected results, which we have observed that the strength of interaction increases as
we move from MOH to POH. This is due to the predomination of physical
interaction over chemical interaction between the unlike molecules, in other words,
geometrical fitting of smaller molecules into the voids created by the larger
molecules between the components of molecules of the liquid mixtures. Such similar
studies were reported by Harsha Kumar et al [46]. The strength of interactions in the
mixtures follows the order (DMF+MOH)+PA<
(DMF+EOH)+PA<(DMF+POH)+PA. The above discussion is also supported by the
observed positive values of Δη and ΔG*E.
Generally, negative values of Δη indicate the presence of dispersion forces or
mutual loss of specific interactions in like molecules operating in the systems arising
due to weak intermolecular interactions and positive values of deviation in viscosity
indicate the presence of strong interactions [25,26]. The sign and magnitude of Δη
depend on the combined effect of factors such as molecular size, shape, and
intermolecular forces. From the above observations it has been clear that as the
temperature increases the interaction between unlike molecules decreases.
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The deviation/excess properties have been fitted to Redlich-Kister type
polynomial [29] equation (3.28). The coefficients Ai (A0 to A4) are determined using
the least square method. The corresponding standard deviations ( )EY are
calculated using the relation 3.29. The coefficients, Ai and the standard deviations, σ
of all the liquid mixtures have been presented in Table 5.B.5.
The partial molar volumes ,1mV of component 1 (propanoic acid) and ,2mV of
component 2 (N,N-dimethyl formamide + methanol/ethanol/1-propanol) in the
mixtures over the entire composition range are calculated by using the relations 3.30
to 3.33 which are described in chapter 3. The excess partial molar volumes ,1EmV and
,2EmV are calculated using the relations 3.34 and 3.35. The values of ,1mV and ,2mV are
furnished in Table 5.B.6. From the above table, the values of ,1mV and ,2mV for both
the components in the mixtures are lesser than their respective molar volumes in the
pure state. The variation of excess partial molar volumes, ,1EmV (PA), ,2
EmV (Equimolar
mixture DMF+MOH/EOH/POH) with mole fraction of PA for (DMF+MOH)+PA,
(DMF+EOH)+PA and (DMF+POH)+PA mixtures are shown in Figures 5.B.10,
5.B.11 and 5.B.12 respectively. From these figures, it reveals that, the excess partial
molar volumes are almost negative over the entire composition range is studied. This
suggest that there is a contraction of volume occurs in the binary mixtures, indicating
the presence of strong interactions between the unlike molecules of the mixtures as
observed in EVm . The partial molar volumes, ,1mV
, ,2mV
and excess partial molar
volumes,,,1
EmV
, ,,2
EmV
of the components at infinite dilution are obtained using the
equations 3.36 and 3.37.
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Table 5.B.5 Coefficients Ai of Redlich-Kister type polynomial equation (3.28) and the corresponding standard deviations, σ (3.29) of all the systems under investigation property A0 A1 A2 A3 A4 σ (DMF+MOH)+PA