Experimental and computational study on the aqueous acidity constants of some new aminobenzoic acid compounds

The acidity constants of three new aminobenzoic acid derivatives were determined using potentiometric and spectrophotometric methods in 0.10 M aqueous potassium nitrate solution as supporting electrolyte. The potentiometric data and UV-Vis absorption spectra of solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, concentration distribution diagrams and number of components involved have been calculated. The relative pKa values for three acids were also calculated using ab initio quantum mechanical method at the HF/6-31G** level of theory in combination with CPCM continuum solvation method. The influence of substituents on the ionization constants of the studied molecular structures was investigated. The satisfactory agreement between the experimentally derived and theoretically calculated pKa values provides solid support for the acid-base reactions proposed in this work.