Determination of thermodynamic properties for protonation equilibrium between isomeric cresols and N,N-dimethylaniline in n-hexane medium

Abstract The formation of hydrogen bonded complexes of o -cresol (OC), m -cresol (MC) and p -cresol (PC) with N,N -dimethylaniline (DMA) in n -hexane solutions is investigated by ultrasonic velocity, density and dynamic viscosity measurements in the equimolar concentration of solutes ([cresol] = [DMA]) ranging from 0.05 to 0.22 mol kg − 1 at 293 K, 298 K, 303 K and 308 K and at atmospheric pressure. The variations in the acoustical and excess acoustical parameters with concentration in the three ternary systems establish the existence of strong solute–solute interactions, probably the formation of hydrogen bonded salts between tertiary amine and cresols. The formation constants (K) of the protonated species are determined using Kannappan equation. It is observed that the formation constant is influenced by the structure of cresol. K values are correlated with the molecular properties of cresols computed by B3LYP method. Thermodynamic parameters such as ΔG, ΔH and ΔS for the three equilibria are determined.