Mechanism of bleaching

Thompson KM, Spirito M, Griffith WP. Mechanism of bleaching by peroxides. Part 4—kinetics of bleaching of malvin chloride by hydrogen-peroxide at low pH and its catalysis by transition metal-salts. J Chem Soc Farad Trans 1996 92 2535. 

K.M. Thompson, W.P. Griffith, M. Spiro (1993). Mechanism of bleaching by peroxides. Part 2. Kinetics of bleaching of alizarin and crocetin by hydrogen peroxide at high pH. J. Chem. Soc., Faraday Trans., 89, 4035-4043. 

HG Hauthal, H Schmidt, HJ Scholz, J Hofmann, and W Pritzow. Studies concerning the mechanism of bleaching activation. Tenside Surfact. Del 27 187-193, 1990. 

Hypochlorites made thisway are used in huge quantities as bleaches. (See Section 18.5 under Bleaches for further details on the mechanism of bleaching.)... 

The hydrated electrons then react according to e + Cd Cd, and the Cd ions which have a strong absorption at 300 nm react with the colloidal particles after the pulse. It was observed that the same bleaching took place during this reaction as in the reaction of e with CkiS particles, and it was concluded from this result that Cd" transfers an electron to a CdS particle Cd" + (CdS), - Cd + (CdS) . These observations also are of interest for our understanding of the formation of Cd atoms in the photocathodic dissolution of CdS (see Sect. 3.4). Cd" cannot be the intermediate of the overall reaction 2e + Cd - Cd° as already pointed out in discussing the mechanism of Eqs. (35) and (36)... 

Thus the detailed mechanism of peroxide bleaching is not yet finally resolved. It should be borne in mind, however, that the work of Dannacher and Schlenker was carried out at 60 °C on tea-stained cotton, whereas Spiro and Griffith studied the decolorisation of individual colorants at 21-25 °C in the absence of a textile substrate. 

The mechanism of activation is believed to be as follows. In an alkaline medium, hydrogen peroxide yields the perhydroxide anion (Scheme 10.22), which reacts with TAED (10.86) to form diacetylethylenediamine (10.87) and the peracetate anion (10.88) as in Scheme 10.30 [244]. At pH 8-9, the peracetate anion is in equilibrium with free peracetic acid, as in Scheme 10.31 [244]. The peracetic acid reacts with the peracetate anion to form nascent oxygen which is the active bleaching agent, as in Scheme 10.32 [244]. Further possible activators suggested by Kleber [244] include ... 

The mechanism of hypochlorite bleaching appears to be considerably less controversial than peroxide bleaching. The pH-related active species in sodium hypochlorite are shown in Figure 10.29 and Scheme 10.33. The pH range 9-11 is the most suitable for hypochlorite bleaching. The active bleaching species is the hypochlorite anion CIO. In fact bleaching... 

Bleaching is thought to take place through the perhydroxyl free radical (Scheme 10.40) [223]. Various attempts have been made over the last decade to elucidate the mechanism and demonstrate the potential of peracetic acid in bleaching. Temperature and pH are critical parameters with regard to the rate and degree of bleaching on the one hand and the... 

---