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

Abstract

The reactions of two triphenyl methane (TPM) dyes—crystal violet (CV +) and malachite green (MG +)—with N 3 • and OH • radicals were studied by pulse radiolytic kinetic spectrophotometry. The rate constants for the reaction of the cationic dyes (D +) with N 3 • are (9.0±0.6)×10 9 and (3.0±0.2)×10 9 dm 3 mol −1 s −1 respectively and those for the reaction with OH • are obtained as (8.0±0.6)×10 9 and (1.1±0.1)×10 9 dm 3 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.