Solvent Dyes
by : --
Most of these belong to azoic class in which an aromatic amino compound is diazotised and coupled with a suitable coupling component and the resulting azoic pigment is insoluble in water, but soluble in an organic solvent. They are soluble in oils and waxes. The aromatic amine is usually aniline, µ-naphthylamine, xylidine, toluidine, cresidine, anisidine etc. and the coupling component is dimethylaniline, µ- naphthol, b-naphthol, methyl phenyl pyrazolone, µ-naphylamine, phenol etc.
A typical solvent dye (Sudan Orange R) is made by diazotising aniline and coupling with b-naphtholIn actual practice, 1000 litres of water are charged in the diazo tub. It is cooled to 00C and 180 kg. aniline is added from a weighing tank. After cooling to —20C, 140 kg. solid sodium nitrite is added at less than 30C. This needs about 2,700 kg. ice. It is agitated for 2 hours, during which period, an excess of sodium nitrite is maintained. The contents are made up to 7,000 litres. The excess sodium nitrite is destroyed by sulphamic acid and the contents stirred for 3 hours.
