DESIGN OF CHLORINE-FAST REACTIVE DYES .1. THE ROLE OF SULFONATE GROUPS AND OPTIMIZATION OF THEIR POSITIONS IN AN ARYLAZONAPHTHOL SYSTEM

The effect on colour fastness to chlorinated water caused by incorporating a sodium sulphonate (SO3Na) group into the structure of reactive dyes based on arylazonaphthol has been investigated. The results of this study indicate that the SO3Na group can play a vital role in increasing the colour fastness of these dyes on cotton, and it is effective to arrange this group on each of the aryl and naphthol rings so that the azo group is surrounded from both sides. The most likely explanation for the effect lies in the ability of the two SO3Na groups to sterically protect the -NH-N= group of the hydrazone form which predominates in the arylazonaphthol system. A CO2Na group on the aryl ring exerts the same effect. The colour fastness is further affected by the position of an N-substituted amino group on the naphthol ring. The visible absorption spectra of these dyes are also described.