Study of Fuchsin Acid Fading in Micellar Media

Abstract

The rate constant of alkaline fading of fuchsin acid (FA 2− ) was measured in the presence of nonionic (TX-100), cationic (dodecltrimethylammonium bromide, DTAB), and anionic (sodium dodecyl sulfate, SDS) surfactants. FA 2− has three negatively charged substituents and one positive charge, and this makes the behavior of FA 2different from dyes such as bromophenol blue. It was observed that the reaction rate constant decreased in the presence of TX-100, DTAB, and SDS. Binding constants of FA 2− to TX-100, DTAB, and SDS and the related thermodynamic parameters were calculated by the stoichiometric (classical) model. The results show that the binding of FA 2− to SDS is endothermic in both regions, and the binding of FA 2− to DTAB and TX-100 is exothermic in one region and endothermic in another region of the used concentration range of these surfactants. Also, the binding constants of FA 2− to surfactant molecules of SDS/TX-100 and DTAB/TX-100 mixed micelles were obtained. C 2014 Wiley Periodicals, Inc. Int J Chem Kinet 46: 651-661, 2014

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