Determination of dissociation constants and thermodynamic parameters of 8-aminoquinoline by potentiometry in aqueous and mixed organic-water solvent systems

The dissociation constant (pK(a)) and thermodynamic parameters (DeltaG) of 8-aminoquinoline are determined in aqueous and in mixed organic-water (diox ane, EtOH and MeOH) Solvent systems. It is observed that ionization constan t of 8-aminoquinoline in aqueous system increases with the increase of temp erature. The curve is a parabolic one. It is to be noted that pK(a) values of this compound are lower than those of quinoline and some of its amino de rivatives. For mixed organic-water solvent systems pK(a)(M) and pK(a)(T) va lues versus percent composition decrease slowly with increase in percent of EtOH, MeOH and dioxane. The curve of the pK(a) versus percent composition is a distorted parabola. The data have been obtained potentiometrically by titrating aqueous 8-amino quinoline solution with hydrochloric acid. The values of dissociation const ant were obtained from these data by a computer program written in GW-BASIC . From pK(a) values Gibb's free energies (DeltaG) have also been calculated .