Determination of pKa values of azlactone dyes in non-aqueous media

4-Arylidene-2-aryl-5-oxazolone (azlactone) structures have wide range of applications arising from their promising photophysical and photochemical activities. Some of this class of dyes exhibit pH-dependent absorption and emission based response. For this reason, precise determination of the acidity constants (pKa) of the azlactone derivatives is necessary for further studies in different media. In this study, five different azlactone derivatives were chosen to obtain pKa values. The acidity constants were determined by using potentiometric titration method. The chosen derivatives were titrated with tetrabutylammonium hydroxide in solvents of dimethylformamide, tert-butanol, isopropanol, acetone and acetonitrile. A computerizable derivative method was used for a precise description of the end point and consequently the pKa values. All compounds exhibited stoichiometric and well shaped potentiometric titration curves.