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Thermodynamic parameters (∆Hº, ∆Gº, ∆Sº) and the activation energy (∆Es) were calculated to explain the limiting equivalent conductance (Λ0) and ion association constant (KA) of s-acetylthiocholine halides and perchlorate in acetonitrile 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 less solvation or higher mobility of the ions in all solvent systems studied. The free energy change ∆Gº values are negative for all salts (Br -, Iand ClO4 -). Clearly strengthening to interionic association at higher temperatures is largely caused by a decrease in the permitivity of the solvent. The positive values of (∆Hº) for three salts (Br -, Iand ClO4 -) show that the association processes are endothermic in nature. Entropy change (∆Sº) values are positive for all salts indicate the randomness of ions in all solvent systems studied.

The kinetics of alkaline hydrolysis of 2-chloro-3,5-dinitrobenzotrifluoride 1 and 1-chloro-2,4-dinitrobenzene 2 were studied in various acetonitrile-water (AN-H 2 O) mixtures (10-90% w/w) at different temperatures. Thermodynamic parameters H # and S # show great variation, whereas G # appears to vary little with the solvent composition presumably due to compensating variations. The results are discussed in terms of the solvent parameters such as preferential solvation, dielectric constant, polarity/polarizability, and hydrogen bond donor and acceptor parameters. It has been found that the factors controlling the reaction rates are the desolvation of OH − , the solvophobicity of the medium, and free water molecules in rich AN mixed solvent. The data showed that the solvatochromic parameters of (AN-H 2 O) mixed solvent are destroyed in the presence of excess OH − . C

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