FEATURES OF A TYPICAL REACTIVE DYE MOLECULE

The four characteristic features of a typical reactive dye molecule are:

1. The chromophoric grouping, contributing the colour and much of the substantivity for cellulose;
2. the reactive system, enabling the dye to react with the hydroxy groups in cellulose;
3. a bridging group that links the reactive system to the chromophore;
4. one or more solubilising groups, usually sulphonic acid substituents attached to the chromophoric grouping.

In a few cases the reactive grouping is attached directly to the chromophore and most reactive systems contain a heterocyclic ring that contributes some substantivity for cellulose. The nature of the bridging group and other substituents on the heterocyclic ring greatly influences the reactivity and other dyeing characteristics of such dyes. The sulphatoethylsulphone precursor of the vinylsulphone reactive group contributes significantly to the aqueous solubility of reactive dyes of this type.

Many reagents can be used to acylate cellulose when it is partially ionized under alkaline conditions but in the production of reactive dyes of commercial interest numerous factors other than the chemistry of such reactions have to be taken into account.