Determination of Acidity Constants of 4-(2-Pyridylazo)resorcinol in Binary Acetonitrile + Water Mixtures

The acid−base properties of 4-(2-pyridylazo)resorcinol in binary mixtures of acetonitrile + water are studied by a multiwavelength spectrophotometric method. To evaluate the pH−absorbance data, a resolution method based on the combination of soft- and hard-modeling is applied. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model. The corresponding p K a values have been determined in all binary mixtures of acetonitrile + water. There is a linear relationship between acidity constants and the mole fraction of acetonitrile in the solvent mixtures. The effect of solvent properties on acid−base behavior is discussed.