Kinetics of Fading of Some Triphenylmethane Dyes: Effects of Electric Charge,Substituent, and Aqueous Binary Mixtures of Dimethyl Sulfoxide and 2‐Propanol

The rate constants of alkaline fading of a number of triphenylmethane (TPM) dyes including methyl green (ME²⁺), brilliant green (BG⁺), fuchsin acid (FA^2?), and bromophenol blue (BPB^2?) 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 FA^2? and BPB^2? 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.