Spectrophotometric and potentiometric study of the acid—base equilibria of indophenols in aqueous media

Abstract

Six indophenols, with redox and acid—base indicator properties, have been examined by spectrophotometric and potentiometric methods. By analysing the absorption spectra obtained at different pH values, three independent values were obtained for their K Ox dissociation constants, which are closely related to their properties as acid—base indicators. Three of the indophenols have also been examined by acid—base and redox potentiometric titrations. All K Ox and E° values agree well with polarographic values. The use of these substances as visual acid—base and redox indicators is discussed.