Analysis of Molecular Interactions of Trimethylamine and Toluene in Liquid State at Certain Temperature (250C)

Abstract

The investigation of molecular interactions in binary liquid mixtures is essential for understanding the physicochemical behavior of solutions used in chemical processing, solvent extraction, and industrial applications. The present study focuses on the analysis of molecular interactions in the binary liquid mixture of trimethylamine and toluene at 25°C (298.15 K) through the determination of experimentally measured thermodynamic, acoustic, and transport properties. Parameters such as density, viscosity, ultrasonic velocity, refractive index, and related excess functions were evaluated over the entire composition range to characterize the nature of intermolecular forces operating between the constituent molecules. From the experimental data, important derived parameters including excess molar volume, isentropic compressibility, intermolecular free length, acoustic impedance, available volume, Rao's constant, Shear's relaxation time, and excess viscosity were calculated to assess deviations from ideal solution behavior. The observed excess functions reveal that the trimethylamine–toluene system exhibits moderate non-ideal characteristics resulting from weak intermolecular interactions. These interactions are primarily attributed to donor–acceptor (n→π) interactions between the lone pair electrons of the nitrogen atom in trimethylamine and the π-electron cloud of toluene, together with dipole-induced dipole and London dispersion forces. The variation of thermo-acoustic parameters with composition indicates changes in molecular packing efficiency, free volume, and structural organization within the liquid mixture. The absence of strong hydrogen bonding suggests that the observed deviations arise mainly from weak electronic interactions and steric effects associated with the molecular geometries of the two components. The experimental results were interpreted using established thermodynamic models to explain the composition-dependent behavior of the system. The present investigation provides valuable information on the molecular association and solution structure of trimethylamine–toluene mixtures and contributes useful thermophysical data for solvent selection, process optimization, molecular simulation, and the design of separation processes involving amines and aromatic hydrocarbons.