A novel reactive dye system based on diazonium salts

Azo dyes, possessing a primary aromatic amino group, on diazotisation in presence of cotton followed by treatment with soda ash at 60-65 °C were found to 'reactively' dye cotton with varying degrees of fixation depending on the chemical structure of the azo dye. Evidence of dye-fibre reaction is indirectly inferred from poor to fair colour values obtained in absence of added soda ash. Dyed cotton retained significant colour even after three treatments with boiling dimethyl formamide (DMF). Coloured cellulose precipitated when a solution of dyed cotton in 85% w/w phosphoric acid was diluted with dimethyl sulfoxide (DMSO). The phosphoric acid-DMSO mixture was colourless. These two tests prove the existence of a dye-fibre covalent bond. A new class of reactive dyes without an externally attached reactive system is therefore, in principle, available. It will have the advantage of reduced raw material and manufacturing costs.