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 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) X 10(9) and (3.0 +/- 0.2) X 10(9) dm(3) mol(-1) s(-1) respectively and those for the reaction with OH. are obtained as (8.0 +/- 0.6) x 10(9) and (1.1 +/- 0.1) X 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.