Binary Mixtures Of N-Methylformamide With O-Substituted Aniline

6.1 ABSTRACT
The densities (ρ) and viscosity (η) were reported for binary mixtures of N-methylformamide with O-substituted aniline (2-chloroaniline, 2-methylaniline and 2-methoxyaniline) over the entire composition range from 303.15 K to 318.15 K and at atmospheric pressure 0.1 MPa. These experimental data have been used to calculate excess volume (VE), deviation in viscosity (∆η) and excess Gibbs energy of activation of viscous flow (G*E). The variations in these properties with composition for all the binary mixtures suggest that loss of dipolar association, difference in size and shape of the component molecules, dipole-dipole interaction and hydrogen bonding between N-methylformamide with O-substituted aniline were observed. Furthermore,
On perusal of the data, negative deviations in κsE are observed for all the systems over the whole composition range and at all experimental temperatures studied. Negative deviations are attributed to the mesomeric effect / ortho effect (steric effect) and Basicity constants (Kb) of o-substituted aniline. Basic strength of o-substituted aniline falls in the order:
2-methoxyaniline > 2-methylaniline > 2-chloroaniline
From Table 3, the negative κsE values suggest that the structure-forming tendency dominant over to the structure-breaking tendency due to the hetero molecular interaction between the component molecules of the binary liquid mixtures.
The magnitude of sE shows the following the sequence:
2-methoxyaniline > 2-methylaniline >
As shown in Fig.2, the values of ∆ are positive over the entire composition range of the binary mixtures at temperature (T) of 303.15 - 318.15 K.
Positive values of deviation in viscosity show that heteroassociation in the mixtures is more prominent than the self association of pure components. The effect of temperature increase is to disrupt hetero and homo association of the molecules resulting in an increase in fluidity of the liquids giving higher η values at higher temperatures.
The deviation in viscosity values are found to be opposite to the sign of excess molar volumes for all binary mixtures, which is in agreement with the view proposed by Brocos et al. [24, 25].
The excess Gibbs energy of activation of viscous flow, like viscosity deviations, can be used to detect molecular interactions [26].The positive excess Gibbs energy of activation of viscous flow values are indicate of specific interactions between the molecules of binary liquid mixtures while negative values indicate of dispersive forces