2001 Volume 50 Issue 6 Pages 507-513
Hydrogen peroxide has been used in detergent products as a bleaching agent for many years owing to its oxidizing capacity. In bleaching, decoloration occurs through oxidative decomposition of colored stain with hydrogen peroxide. The mechanism for this process has been extensively studied but detailed aspects remain unclarified. This study was conducted to provide further clairfication of this mechanism using the anthraquinone dye, Alizarin Red S (ARS), as a model of colored stain. ESR was carried out for analysis of decomposition reactions of ARS. Four radical intermediates were noted to be formed through three elementary reactions. The first intermediate was to be a semiquione radical of ARS, suggesting oxidative decomposition initiated by one-electron transfer from the dye to hydrogen peroxide. This intermediate induced the second decomposition by attacking hydrogen peroxide anions to afford two second intermediates, is followed by formation of phthalic acid as the final product. Kinetic study indicated the formation of the first intermediate, i.e., electron transfer from hydrogen peroxide to the dye, to be the rate-determining step of oxidative decomposition.
