Mechanism of peroxide bleaching

Though hydrogen peroxide is stable in acidic medium, but bleaching occurs by the addition of alkali or by increased temperature. Hydrogen peroxide liberates perhydroxyl ion (HO ) in aqueous medium and chemically behaves like a weak dibasic acid. The perhydroxyl is highly unstable and in the presence of oxidisable substance (coloured impurities in cotton), it is decomposed and thus bleaching action takes place. Sodium hydroxide activates hydrogen peroxide because ion is neutralised by alkali which is favourable for liberation of HO.  

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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. 

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