Reactive dye

Reactive dye

The four characteristic features of a typical reactive dye molecule are the chromophoric group, the water solubilizing group(s) usually sulphonate (-SO3Na), the reactive group, and the bridging group that attaches the reactive group either
directly to the chromophore or to some other part of the dye molecule. Each of these structural groups has an effect on the physical properties of the dye molecule. The properties include color, molecular size, solubility, substantivity, ability to diffuse into fibres, migration within the fiber, colorfastness, and so on.


Typical reactive dye chromophores include the azo, triphenodioxazine,phthalocyanine, formazan and anthraquinone Most commercial ranges of reactive dyes have a comprehensive color gamut, many of which are particularly bright.

                                          Molecular structure of CI Reactive Red 1

The reactive groups can be divided into two distinct categories depending on the mechanism of formation of the dye-fibre bond, and the stability of this bond to subsequent treatments

Ø Nucleophilic substitution mechanism

Ø Nucleophilic addition mechanism


According to functional group

1. Monofunctional (above discussed )
2. Multifunctional

         a) Bifunctional (Homo & Hetero )

         b) Polyfunctional


Many of the reactive dyes available today are bifunctional with molecules having two identical or different reactive groups. Dyes with two identical reactive groups are known as homobifunctional reactive dyes and those with different groups as hetero-bifunctional. Technically, the bifunctional dyes have increased probability of reaction with the fibre. Thus, they give higher fixation yields and thus leave less colour in the dyehouseeffluent

A hetero-bifunctional dye possesses two different reactive groups and thus has two different extents of reactivity towards the cotton and two possible optimal temperature and pH conditions for dye-fibre reaction. Therefore, such a dye can give a more uniform degree of fixation over a wider range of fixation temperature and pH conditions than a homo-bifunctional dye. heterobifunctional reactive dyes were those capable of reacting with cellulose via both mechanisms, nucleophilicsubstitution and nucleophilic addition.


Incorporating more than two reactive groups into the dye molecule should theoretically increase the fixation efficiency. However, these additional reactive groups can have an impact on important dyeing properties such as substantivity and migration because they change the molecular size and alter the extent and mode of reactivity.