STRUCTURE-REACTIVITY CORRELATIONS OF AZO REACTIVE DYES BASED ON H-ACID .4. INVESTIGATIONS INTO THE LIGHT FASTNESS IN THE DRY STATE, IN THE WET STATE, AND IN PRESENCE OF PERSPIRATION

In this paper we report on substituent effects on the light fading of azo reactive dyes based on H-acid on cellulose in the dry state, in the wet state, and in the presence of perspiration. Dyes containing strongly electron donating substituents tend to always fade oxidatively, while dyes with strongly electron withdrawing substituents prefer a reductive degradation pathway. In the dry state, a reductive fading mechanism prevails. In the presence of water, the fading becomes oxidative, while the fading of dyes containing electron donor substituents greatly enhanced. In the presence of artificial alkaline perspiration, the reductive fading is greatly accelerated. Thus, dyes containing an electron withdrawing substitution pattern have poor fastness properties to perspiration and light, while they fade reductively. The amino acid histidine, which is a component of perspiration, is concluded to be responsible for the enhanced reductive light fading in the presence of perspiration.