In the dye trade, "vinyl sulphone" usually means para base ester: 4-(beta-sulphatoethylsulphonyl)aniline. It is the intermediate that gives a large group of reactive dyes their reactive group, the part that forms a chemical bond with cellulose fibres such as cotton and viscose.
Dyes built on it are called vinyl sulphone reactive dyes. They are among the most widely used reactive dyes for cotton.
How it works on the fibre
The intermediate carries a sulphatoethylsulphonyl group. In the dyebath, alkali converts this group into a true vinyl sulphone group. That group then reacts with the hydroxyl groups of cellulose and forms a covalent bond.
Because the dye is chemically fixed to the fibre, wash fastness is good. Vinyl sulphone dyes usually fix at moderate temperatures, which suits exhaust dyeing and many printing processes.
The amino group on the other end of the molecule is diazotised and coupled to a chromophore. That is how the reactive anchor becomes part of a coloured dye.
Fixation is never complete. Some of the activated dye reacts with water instead of the fibre and forms hydrolysed dye, which must be washed off. Good intermediate quality and correct dyeing conditions keep that loss down.
Which dyes use it
Vinyl sulphone appears across the shade range. These are the main groups:
- Reactive blacks and navies, including Reactive Black 5, which is built from two units of para base ester coupled onto H-acid.
- Reactive oranges, reds and yellows, where para base ester is coupled with naphthalene or pyrazolone components.
- Bifunctional reactive dyes, which combine a vinyl sulphone group with a monochlorotriazine group to raise fixation.
- Some reactive blues, which use a related meta-substituted ester on an anthraquinone chromophore.
Points to check when you buy
Para base ester is made by a multi-step route, and the ester can hydrolyse if it is stored damp or warm. Hydrolysed material reacts poorly and gives weaker dyes. Ask the supplier for the assay method, usually nitrite titration, and limits on moisture, free acid and insolubles.
Also confirm the isomer you want. Para and meta esters are different products and are not interchangeable in a dye recipe. Store the ester dry and cool and use older lots first, since hydrolysis continues slowly in storage; see the shelf life of intermediates. Our article on what purity dye intermediates should have covers the wider specification.
Next step
If you make reactive dyes, a consistent ester supply protects your shade and fixation. We find and audit manufacturers, check samples against your specification and have lots tested before dispatch. To discuss your needs, book a free sourcing review.