Determination of Dissociation Constants and Thermodynamic Parameters of 8-Aminoquinoline by Potentiometry in Aqueous and Mixed Organic-Water Solvent Systems

Abstract

The dissociation constant (pKa) and thermodynamic parameters (△G) of 8-­aminoquinoline are determined in aqueous and in mixed organic-water (dioxane, EtOH and MeOH) solvent systems. It is observed that ionization constant of 8-aminoquinoline in aqueous system increases with the increase of temperature. The curve is a parabolic one. It is to be noted that pKa values of this compound are lower than those of quinoline and some of its amino derivatives. For mixed organic-water solvent systems pKa M and pKaT values versus percent composition decrease slowly with increase in percent of EtOH, MeOH and dioxane. The curve of the pK. versus percent composition is a distorted parabola.The data have been obtained potentiometrically by titrating aqueous 8-aminoquinoline solution with hydrochloric acid. The values of dissociation constant were obtained from these data by a computer program written in GW-BASIC. From pKa values Gibb's free energies (△G) have also been calculated.