Oxidation of crystal violet and malachite green in aqueous solutions — a kinetic spectrophotometric study

The reactions of two triphenyl methane (TPM) dyes—crystal violet (CV⁺) and malachite green (MG⁺)—with N₃^? and OH^? radicals were studied by pulse radiolytic kinetic spectrophotometry. The rate constants for the reaction of the cationic dyes (D⁺) with N₃^? are (9.0±0.6)×10⁹ and (3.0±0.2)×10⁹ dm³ mol^?1 s^?1 respectively and those for the reaction with OH^? are obtained as (8.0±0.6)×10⁹ and (1.1±0.1)×10⁹ dm³ mol^?1 s^?1 respectively. The transient spectra resulting from the oxidation of the dyes were characterized. The time-resolved spectra indicate that the reaction with OH^? radicals initially generates an adduct which subsequently dissociates to form the radical dication D^?2+. The D^?2+ species decay by further reaction with the parent dye.