Direct Dyes
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Most of direct dyes are azo dyes (monoazo, disazo or bisazo, triazo and tetrakisazo dyes) containing one or more sulphonic acid (as sodium salt) groups to impart water solubility. These are made by diazotising an aromatic amine with or without a sulphonic acid group, and then coupling with an aromatic compound containing a hydroxy, amino or other group, which creates a coupling position. Polyazo dyes are made either from a diamine like benzidine, o-tolidine, o-dianisidine, or by diazotising an amine and coupling with another amino compound, the amino group of which may then be diazotised and further coupled with other suitable compounds.
