SPECTROPHOTOMETRIC STUDY OF THE SOLUBILITY AND THE PROTOLYTIC PROPERTIES OF 1-(2-PYRIDYLAZO)-2-NAPHTHOL IN DIFFERENT ETHANOL-WATER SOLUTIONS

The solubility and the protolytic constants of 1-(2-pyridylazo)-2-naph thol (PAN) have been accurately determined at temperatures between 20. 0 and 30.0 degrees C in ethanol-water solutions with ethanol concentra tions ranging from 10.0% to 95.0% (v/v). The measurement of the protol ytic constants is based on the spectrophotometric determination of the concentrations of the corresponding conjugate acid-base pairs in etha nol-water solutions containing PAN and hydrochloric acid or sodium hyd roxide. The traditionally used pH measurements in such studies in non- aqueous solutions are thus avoided. The solubility and the protolytic constants of PAN in pure water have been calculated by extrapolating t he ethanol-water results to pure water where PAN is practically insolu ble. The determination of the thermodynamic data mentioned above is ne cessary for elucidating the interactions of PAN with various metal ion s in solutions and in cation-exchange membranes (e.g., Nafion(R)) used as PAN-based optodes. (C) 1998 Elsevier Science B.V.