STRUCTURE REACTIVITY CORRELATIONS OF AZO REACTIVE DYES BASED ON H-ACID .2. DYE DEGRADATION BY HYPOCHLORITE

In this paper we report on substituent effects on the degradation of azo reactive dyes based on H-acid by hypochlorite in aqueous solution and on cellulosic substrates. Based on the pH dependence of the fading reaction, we establish a new perception which says that in the pH range above 5 only the dissociated form of the corresponding ortho-hydroxyazo dyes undergoes the degradation, and thus the dye's pKa value becomes a decisive criterion for the fastness to hypochlorite. With this background at hand, we use an expanded version of the Hammett equation, including the dyes' pKa values, to yield a linear free energy relationship. Also, the effect of dyestuff aggregation on the fading is investigated.