• Archives of Pharmacal Research
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• v.16 no.3
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• pp.180-185
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• 1993

The acid dissociation constants of certain Schiff bases derived from isatin with p-substituted benzoyl hydrazines and somee amino acids of glycine, $\beta$-and $\alpha$-alanine, valine, $\beta$-phenyl-$\alpha$-alanine and anthranilic acid have been detemined potentiometrically at different temperatures in different aquo-organic solvent mixtures (ethnol, dioxane, dimethyl formamide, methanol, acetone and tetrahydrofurance). The pKa values were demonstrated on the light of the different electornic and steric effects of the substituents and the sovlent characteristics. In all the mixed media used, ionization of the compounds decreased by increasing the mole fraction of the organic cosolvent. Theemodynamic parameters $(\Delta{H}^\circ,\;\Delta{G}^\circ,\;\Delta{S}^\circ)$ were evaluated. The structural effects of the investigated compounds on these parameters were reported and discussed.