On the basis or structure, dyes can be classified as:
(i) Nitro and Nitroso Dyes:
These are ancient known dyes. These dyes contain nitro or nitroso groups as the chromophores and -OH as Auxo chrome. A few Examples:
(ii) Diphenyl Methane Dyes:
These dyes have a basic structure of diphenylmethane.
Example:
Auramine – O is an important dye of this group which used to colour silk, wool, paper, jute etc.
(iii) Triphenyl Methane Dye:
These dyes are amino derivatives of triphenyl methane.
Example:
Malachite green which is used to colour woof and silk directly.
(iv) Phthalein Dyes:
The compounds formed by the combination of phthalic anhydride and phenolic compounds are known as phthalein. Xanthene ring structure can also be included in this group.
Example:
Phenolphthalein has phthalein as a ring structure and fluorescein is a xanthene derivative.
(v) Azo – Dyes:
It is the largest group of synthesized dyes which contain almost all the colours. Dyes characterised by the presence of an azo group (- N = N -) as the chromophore.
(vi) Indigo Dyes:
This is the most important group of natural dyes. The dyestuff is extracted from Indigofera tinctoria, a bush pea family.
(vii) Anthraquinone Dyes:
Dyes that have anthraquinone as their base and the carbonyl group (> C = O) as the chromophore. These dyes can be used with mordant dye where it gives different colours with different ions.
(viii) Heterocyclic dyes:
In these dyes at least one odd cyclic ring should be present. It is also a large group and new dyes are discovered.
