Determination of dissociation constant of some quinazoline derivatives at different temperatures in DMF–water medium

Abstract

The dissociation constant and some thermodynamic parameters of synthesized pyrazolo[5,1-b]quinazolines are determined by Calvin Bjerrum pH titration method in mixed organic-water (60:40v/v) solvent systems. The evaluated data are discussed in terms of the electron donating or electron withdrawing nature of side chain substitutions. The compound containing 4-flouro group is the most acidic whereas the methoxy containing compound is found to be the most basic. To determine factors which affect and control the dissociation process at three different temperatures, the thermodynamic analysis, such as enthalpy (∆H°), Gibb’s free energy (∆G°) and entropy (∆S°) of solutions are presented and discussed in the present study.