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The Development of Reactive Dye :
The idea of immobilizing a dye
molecule by covalent bond formation with reactive groups in a fibre originated
in the early 1900s. Various chemicals were found that reacted with the hydroxyl
groups of cellulose and ecentually converted into coloured cellulose
derivatives. The rather forceful reaction conditions for this led to the false
conclusion that cellulose was a relatively unreactive polymer. Possibly because
of this, a number of dyes now known to
be capable of covalent bond formation with groups in wool and cotton were not
initially considered as fibre-reactive dyes, despite the good fastness to
washing of their dyeing.
In 1955, Rattee and Stephen, working
for ICI in England, developed a procedure for dyeing cotton with fibre reactive
dyes containing dichlorotriazine groups.
They established that dyeing cotton
with these dyes under mild alkaline conditions resulted in a reactive chlorine
atom on the triazine ring being substituted by an oxygen atom from a
cellulose hydroxyl group. This is shown
in scheme 1 where Cell-OH is the
cellulose with a reactive hydroxyl group, Dye-Cl is the dye with its reactive
chlorine atom, and Cell-O-Dye the dye linked to the cellulose by a covalent
bond. The role of the alkali is to cause acidic dissociation of some of the
hydroxyl groups in the cellulose, and it is the cellulosate ion (Cell-O-) that
reacts with the dye.
Cell-OH + HO- => Cell-O- + H2O
Cell-O- + Dye-Cl => Cell-O-Dye + Cl-
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