Process for the preparation of highly concentrated solutions of cationic azo dyes

A process for the preparation of a highly concentrated aqueous solution of a salt of a cationic azo dye, virtually free of chlorides, which comprises

• a) diazotising an amine of formula
• D--NH.sub.2 ( 1)
• wherein D is an unsubstituted or substituted radical of the benzene, thiazole, benzothiazole or thiadiazole series, in a solution which contains sulfuric acid, and subsequently
• b) coupling the diazotised amine with a coupling component of formula ##STR17## wherein R.sub.1 is hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, halogen or C.sub.1 -C.sub.4 alkanoylamino,
• R.sub.2 is hydrogen or C.sub.1 -C.sub.4 alkyl,
• n is an integer from 2 to 6,
• R.sub.3, R.sub.4 and R.sub.5 are each independently of one another unsubstituted or substituted alkyl or R.sub.3 and R.sub.4, together with the linking nitrogen atom, or R.sub.3, R.sub.4 and R.sub.5, together with the linking nitrogen atom, form a heterocyclic radical, or R.sub.3 and R.sub.4 are each C.sub.1 -C.sub.4 alkyl and R.sub.5 is amino, and An.sup..crclbar. is an anion, at a pH below 1.5 in the temperature range from -10.degree. to +30.degree. C. and subsequently heating the reaction mixture for 0.5 to 3 hours at 50.degree.-95.degree. C. and then
• c) washing the resultant azo dye with an aqueous solution of sulfuric acid which contains sodium sulfate,
• d) treating the precipitated dye in the form of its hydrogen sulfate with a water-soluble bicarbonate, and
• e) converting the dye bicarbonate with an organic acid into the dye salt of said acid.