Association constants and enthalpies of formation of heteroassociates of anions of cresol red and thymol blue

Abstract

The tendency of anions of sulfophthaleine dyes to heteroassociation was studied in aqueous solutions of phenol red, cresol red, thymol blue, and non-substituted phenol red. It was spectrophotometrically determined that single (HAn−) and doubly charged anions (An2−) of sulfophthaleines can form stable heteroassociates of the composition Ct+ · HAn− and (Ct+)2 · An2− with cations (Ct+) of polymethine dyes, pinacyanol, and quinaldine red. The values of enthalpy formation of ions of dyes and heteroassociates were calculated semi-empirically and compared with experimentally determined values of the equilibrium association constants.