The rate constant of alkaline fading of methyl green (ME 2+ ) was measured in the presence of non ionic (TX-100), cationic (DTAB) and anionic (SDS) surfactants. ME 2+ hydrolyses and fades in neutral water and in this work we search the effects of surfactants on its fading rate. The rate of reaction showed remarkable dependence on the electrical charge of the used surfactants. It was observed that the reaction rate constant decreased in the presence of DTAB and SDS and increased in the presence of TX-100. Binding constants of ME 2+ to TX-100, DTAB and SDS and the related thermodynamic parameters were obtained by classical (or stoichiometric) model. The results show that binding of ME 2+ to TX-100 and DTAB are two-region and that of SDS is threeregion. Also, the binding constants of ME 2+ to surfactant molecules in DTAB/TX-100 and SDS/TX-100 mixed solutions and their stoichiometric ratios were obtained.

The rate constants of alkaline fading of a number of triphenylmethane (TPM) dyes including methyl green (ME2+), brilliant green (BG+), fuchsin acid (FA2−), and bromophenol blue (BPB2−) were obtained in aqueous binary mixtures of 2‐propanol (protic solvent) and dimethyl sulfoxide (DMSO) (aprotic solvent) at different temperatures. It was observed that the reaction rate constants of BG+ and ME2+ increased and those of FA2− and BPB2− decreased with an increase in weight percentages of aqueous 2‐propanol and DMSO binary mixtures. 2‐Propanol and DMSO interact with the used TPM molecules through hydrogen bonding and ion–dipole interaction, respectively, in addition to their hydrophobic interaction with TPM dyes. The fundamental rate constants of a fading reaction in these solutions were obtained by the SESMORTAC model. Also, the effect of electric charge and substituent groups of a number of TPM dyes on their alkaline fading rate was studied.

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