In reactive dyes, the chromophore contains a substituent that can react with the substrate, because the dye molecules contain specific functional groups that can undergo addition or substitution reactions with the OH, SH and NH2 groups present in the fibers. Reactive dyes have good fastness properties due to the bonding during dyeing. Reactive dyes are most often used for the dyeing of cellulose, such as cotton or flax, and wool can also be dyed with reactive dyes. Reactive dyeing is the most important method of coloring cellulosic fibers. The first industrially important reactive dye system was developed for the coloring of wool and it utilized chloroacetylamino and the chloroethanesulfonyl groups. Vinylsulfonyl- and 2-sulfooxyethanesulfony are also found to be suitable for the dyeing of wool and cellulose.
Classification of Reactive Dyes
Mono-anchor dyes: Most mono-anchor dyes are derivatives of cyanuric chloride, which is a molecule with wide synthetic potential because the three chlorine atoms on the triazine ring differ in their reactivities. A wide variety of triazinyl dyes can be prepared by reactions. Condensation of cyanuric chloride with a chromophore containing an amino group yields the highly reactive dichlorotriazinyl dyes. These reactive dyes are sensitive to hydrolysis, and a suitable buffer is usually added to the powdered dye to increase its stability. When two of the chlorine atoms are substituted by functional groups, such as amino or alkoxyl groups, monochlorotriazinyl dyes are obtained. They are considerably less reactive, and hence react with cellulose in the exhaust dyeing process only at relatively high temperature, which are advantageous for printing.
Figure 1. Mono-anchor dyes
Double-anchor dyes: Since the 1980s, interest has been shown in strongly fixing reactive dyes, and the high fixation values have increasingly been achieved with the help of double anchors. Double-anchor dyes can be divided into two categories: those containing two equivalent reactive groups, and those with mixed-anchor systems.
Figure 2. Double-anchor dyes
Multiple-anchor dyes: Multiple-anchor dyes play a subordinate role in the world market. One example is a multiple-anchor system, in which cyanuric chloride is bound to an amine with two aliphatic 2-chloroethylsulfonyl chains:
Figure 3. Multiple-anchor dyes