Structures
The chemistry of acid dyes is quite complex. Dyes are normally very large aromatic molecules consisting of many linked rings. Acid dyes usually have a sulfo or carboxy group on the molecule making them soluble in water. Water is the medium in which dyeing takes place. Most acid dyes are related in basic structure to the following:
Anthraquinone type: Many acid dyes are synthesized from chemical intermediates which form anthraquinone-like structures as their final state. Many blue dyes have this structure as their basic shape. The structure predominates in the leveling class of acid dye.
Azo dyes: The structure of azo dyes is based on azobenzene, Ph-N=N−Ph (see image on right showing cis/trans isomers) Although azo dyes are a separate class of dyestuff mainly used In the dyeing of cotton (cellulose) fibers, many acid dyes have a similar structure, and most are red in color.
Triphenylmethane related: Acid dyes having structures related to triphenylmethane predominate in the milling class of dye. There are many yellow and green dyes commercially applied to fibers that are related to triphenylmethane.
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