Resumen

EL-HAMMAMY, Nasr Hussein; EL-HAMMAMY, Marwa Nasr  y  KAWANA, Aida Ibrahim. Thermodynamic Studies of Ion Association of s-Acetylthiocholine Halides and Perchlorate in Methanol Solutions. J. Mex. Chem. Soc [online]. 2014, vol.58, n.1, pp.11-15. ISSN 1870-249X.

Thermodynamic parameters (ΔH⁰, ΔG⁰, ΔS⁰) and the activation energy (ΔE_s) were calculated to explain the limiting equivalent conductance (Λ₀) and ion association constant (K_A) of s-acetylthio-choline 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 (ΔS ⁰) 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.

Palabras llave : s-acetylthiocholine salts; ion association; activation energy and thermodynamic functions.

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