Photoinduced Reaction between Chlorine Dioxide and Iodine in Acidic Aqueous Solution

Photoinduced reaction between ClO 2 and I 2 has been discovered under illumination with 460 nm lightband. The photochemical reaction has a variable stoichiometry in acidic aqueous solution because the induced disproportionation of ClO 2 to ClO 3 - and Cl - competes with the oxidation of I 2 to IO 3 - by ClO 2 in the illuminated reaction mixture. The reaction rate depends on the light power of illumination and on the concentration of I 2, but it is independent of the concentration of ClO 2 . It is also independent of the pH in the range of 0−2.0 and of the ionic strength in the range of 0.01−1.0 M. Reversible dissociation of I 2 has been identified as the primary photochemical process and rate-determining step in the mechanism. Reactive I atoms are considered to initiate fast reaction steps, leading to the formation of products through reactive intermediates such as IClO 2, ClO, IO, and HOCl. This mechanism is proposed for explaining the photoresponses of the CDIMA oscillatory reaction system to the illumination with visible light.