Spectrophotometric determination of acidity constants of 4-(2′–thiazolylazo)- resorcinol (TAR) in water–organic mixtures

The acidity constants of TAR in different water–organic solvent binary mixtures at 25 °C have been determined spectrophotometrically. DATa ANalysis (DATAN) program was used for calculations of the acidity constants and pure spectra of all formed species and their concentration distribution diagram in applied pH interval. Results show that there are a fairly inverse relationship between acidity constants and the mole fraction of the organic solvent in the binary mixtures. Effects of solvent composition on the pKas and pure spectrum of each component are also discussed.