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A series of red water soluble azo dyes were prepared by coupling variously substituted phenyldiazonium salts onto 1-aminonaphthalene-4-sulphonic acid. In order to mimic the conditions experienced during domestic laundering, in presence of an oxidative-bleach containing detergent, the dyes were then subjected, separately, to treatment with m-chloroperbenzoic acid and with hydrogen peroxide. Experiments were conducted under alkaline conditions (pH 9.8) and pseudo first order rate constants were determined for dye destruction. The m-chloroperbenzoic acid was much more effective than hydrogen peroxide in bringing about loss of colour. The introduction of electron donating groups into the diazo component of the dyestuff, which would be expected to lead to an increased propensity to undergo attack by electrophilic species, resulted in increased levels of bleaching by the peracid. Additionally reduction in pH caused an increase in the rate of bleaching in presence of peracid, the rate increasing approximately tenfold per unit drop in pH. These observations are consistent with attack by m-chloroperbenzoic acid, a highly electrophilic species, rather than m-chloroperbenzoate (the major species present at pH 9.8). |
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