The kinetics of dye formation by pulse radiolysis of pararosaniline cyanide in aqueous organic solution

The radiation-induced conversion of the leucocyanide of pararosaniline dye [H₂N≤≥]₃≡C-CN, to the highly colored salt-isomer of the dye, [H₂N≤≥]₂=C=≤≥=NH⁺₂ + Cn^-, in acidic aqueous solution (wavelength of maximum absorption λ_max=540 nm) or polar organis soution (λ_max=550 nm),  takes place in two separate processes. The first is very fast (within <50ns), and the second much slower following first-order kinetics with a rate constant that varies from 4 x 10³ s^-1 to ∼ 10⁶ s^-1, as the acidity or concentration of an oxidizing agent increases. In oxygen-free acidic aqueous or organic solutions (argon saturated) there is an unstable transient species (λ_max=380 nm). When using O₂ og N₂O-saturated aqueous or organic solution, there is no intermediate absorption band at 380 nm, but the slow process of dye formation at 540 or 550 nm is still sequential to the initial fast process having somewhat faster kinetics than in Ar-saturated solution.