Thermodynamic Studies of Ion Association of s-Acetylthiocholine Halides and Perchlorate in Methanol Solutions

Abstract

Thermodynamic parameters (ΔH⁰, ΔG⁰, ΔS⁰) and the activation energy (ΔEs) were calculated to explain the limiting equivalent conductance (Λ₀) and ion association constant (K_A) of s-acetylthiocholine halides and perchlorate in methanol solutions at different temperatures by using conductance measurements. It has been evaluated by using Fuoss-Onsager equation. It is evident that the values of (Λ₀) increase regularly with increase in temperature. For all salts of s-acetylthiocholine, (Λ₀) indicates that higher mobility of the ions in all solvent systems studied. The free energy change ΔG⁰ values are negative for all salts (Br^-, I^- and ClO₄^-) in solvent systems studied. Clearly strengthening the interionic association at higher temperatures is largely caused by a decrease in the permitivity of the solvent. The positive values of (ΔH⁰) for three salts (Br^-, I^- and ClO₄^-) show that the association processes are endothermic in nature. Entropy change (ΔS⁰) values were positive for all salts because of decrease in solvation of ion-pair compared to that of the free ion. This may be attributed to increase in the degree of freedom upon association, mainly due to the release of solvent molecules.