Thermodynamic studies on the interactions of phenyl salicylate in protic solvents at different temperatures

Phenyl salicylate (PS) is employed as a nervous system depressant as well as an intestinal antiseptic owing to its antibacterial activity upon hydrolysis in the small intestine. The study of changes in its physico-chemical properties in different solvents may be helpful in understanding the mechanism of the drug action at physiological body temperatures. The partial molar quantities, namely, apparent molar volume (Vϕ), partial molar volume (Vm°), thermal expansion coefficient (α2) and partial molar expansivity (E20) of phenyl salicylate in various protic solvents (i.e. methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and 2-butanol at T = 293.15 K-313.15 K have been determined. The density and viscosity data in a molality range of 9.4 × 10− 3-3.1 × 10− 2 mol/kg are obtained with the help of commercially available vibrating tube densimeter and viscometer, respectively. The variation in the volumetric parameters resulting due to changes in temperature and the nature of solvents are explained on the basis of the drug-solvent hydrogen bonding, dielectric constant and dipole moments of the solvents used. The viscosity data is analyzed by the Jones-Dole equation and the derived viscosity B-coefficient is interpreted in terms of drug-solvent interactions. The molar Gibbs free energy ∆G20#, enthalpy ΔH20# and entropy ΔS20# of activation for viscous flow in various protic solvents are determined using the transition state theory of solutions.