Interaction of oxidative bleach containing detergents with dyes.: Part 2:: Preparation and resistance of hydrazo dyes, derived from aryl diazonium salts and 1-hydroxynaphthalene-4-sulphonic acid, to oxidation by hydrogen peroxide and meta-chloroperbenzoic acid

Several variously substituted anilines were diazotised and coupled onto 1-hydroxy naphthalene-4-sulphonic acid. The resulting dyes were treated separately with hydrogen peroxide and meta-chloroperbenzoic acid, at 60degreesC and pH 9.8, in order to mimic the active bleaching species present in modern detergents, and pseudo first order rate constants for dye destruction were determined. Under the alkaline conditions employed the dyes were largely deprotonated and the pK(a) value of each was determined. The peracid was found to be much more effective than hydrogen peroxide in bringing about chromophore destruction: the free peracid, not the derived anion, being the active bleaching species. The introduction of either ortho- or para- electron withdrawing groups into the diazo component resulted in reduced rates of dye destruction, whereas an electron donating methoxy group in the para-position caused an increase in rate. Electron donating ortho- alkyl groups had minimal effect on stability towards the peracid. (C) 2003 Elsevier Ltd. All rights reserved.