Vinyl sulfone dyes
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Vinyl sulfone dyes are reactive dyes comprising a vinyl sulfone group as reactive group (a fiber-bonding site of the reactive dye, "reactive hook"). Due to the relatively high reactivity of the vinyl sulfone group with water (residual moisture, air humidity), it is present in many commercial products in a protected form. For protection, an ethylsulfonyl group is substituted with a leaving group. During the dyeing process under alkaline conditions, the vinyl sulfone group is released by an elimination reaction:
Formation of the vinyl sulfone group by alkaline elimination. R= alkyl or aryl radical, X=-OSO3H, -Cl
The vinyl sulfone reactive anchor is usually introduced into the reactive dye via an aromatic or aliphatic amine.
The oldest and most common intermediate is vinyl sulfone parabase ester (see image), an aniline substituted with a [2-(sulfooxy)ethyl]sulfonyl group. The vinyl sulfone parabase ester can be used as a diazo component in the preparation of azo dyes.[1] A further possibility is the condensation reaction of parabase ester with a chlorine or fluorotriazine residue, which in turn can be linked to any chromophore via a further amino group.
(2-[(4-Aminophenyl)sulfonyl]ethyl hydrogen sulfate)
Possible variations result from further substituents on the aromatic ring - usually hydroxy, methyl or methoxy groups - or from the position of the amino relative to the vinyl sulfone group. In addition to the para-substituted compound, also meta- and orthosubstituted vinyl sulfone anilines are used.[2]
ethoxy)ethanamine.svg)
If the vinyl sulfone group is introduced via a primary or secondary aliphatic amine, this is performed again by condensation with a halotriazine compound. An example is 2-[2-(2-chlorethylsulfonyl)ethoxy]ethanamine used in bifunctional reactive dyes in combination with a monofluoro or monochlorotriazine hook.[3]
Dyeing process
The vinylsulfone group reacts with the nucleophilic functional groups of the fibers by Michael addition to form a covalent ether bond:
Reaction of vinyl sulfone compounds with hydroxyl groups of cellulose (HO-CELL)
An unfavorable side reaction in the dyeing process is the conversion of the vinylsulfone group to the 2-(hydroxy)ethylsulfonyl group:[4]
Reaction of vinylsulfone compounds with water/OH− during dyeing
The hydroxylated, unreactive dye has to be washed out during the post-treatment.
