Thermo acoustic and spectral investigations of charge transfer interaction between aromatic amine and ketones

Ultrasonic velocity (u), density (ρ) and coefficient of viscosity (η) were measured for ternary mixtures containing aniline (ANI) as common component and acetophenone (ACP), 4-chloroactophenone (ClACP) and 4-methylacetophenone (MACP) as other components in n-hexane medium in the concentration range 0.025–0.2 M. The measurements were made at four different temperatures, namely, 293, 298, 303 and 308 K and at atmospheric pressure. The experimental results have been used to calculate various acoustical parameters and excess parameters. The trend in these parameters with concentration establishes that (i) strong intermolecular interactions exist in these mixtures and (ii) formation of charge transfer complexes through hydrogen bonding between primary amine and aromatic ketones. The formation of complexes has also been confirmed by optical spectroscopy at 303 K. The formation constants of the charge transfer complexes determined using Benesi–Hildebrand equation (spectroscopic method) are comparable with those obtained using Kannappan equation (ultrasonic method). It is observed that the stability of the complexes is influenced by the structure of the component molecules. In order to assess the thermodynamic stability of the complexes, free energy of formation (ΔG), enthalpy of formation (ΔH) and entropy changes (ΔS) are computed.