Interaction of sulfophthaleine anions with cationic dyes in aqueous solution

Abstract

An interaction between the singly and doubly charged anions (HAn− and An2−) of sulfophthaleines (phenol red and its derivatives: bromophenol blue, bromocresol green, bromocresol purple, and bromothymol blue), and singly charged cations (Ct+) of a polymethine (pinacyanol, quinaldine red), results in formation in an aqueous solution of heteroassociate with stoichiometric composition (Ct+)·HAn− and (Ct+)2·An2−. On the basis of spectrophotometric data the association constants were estimated. By quantum-chemical methods AM1 and PM3 the values of formation and reaction enthalpies of the species formed were calculated and the most probable structure of the heteroassociates was determined.