Determination of acid dissociation constant values of some benzoxazolinone derivatives by using spectrophotometric, potentiometric, and capillary electrophoretic methods in aqueous buffered solution

Acid dissociation constant (pKa) values of fourteen structurally related 3-(2/4-pyridylethyl) benzoxazolinone derivatives have been found by using UV-Vis spectroscopy, and the results have been verified by using potentiometry and capillary electrophoresis methods. The position of the equilibrium reaction was suggested based on the experimental results. Under the light of data, the electro with-drawing groups (chlorine atom) on 6-benzoyl derivatives or on the main structure of benzoxazolinone ring showed more basic character in comparison with electron donating groups. Our results suggest that analgesic/anti-inflammatory activities of benzoxazolinones decreased when the pKa values and / or solubility of the compounds increased. Advantages and limitations of using UV-Vis spectroscopic, potentiometric, and capillary zone electrophoretic methods for determination of acid dissociation constants were discussed.