Water-soluble disazo dyestuffs, prepared from unsymmetrical heterocyclic diamines

Disazo compound of the formula

• B.sub.1 -N.dbd.N-Z-N.dbd.N-B.sub.2
• wherein Z is ##STR36## wherein Y and M are the same or different and are methyl, ethyl, methoxy, ethoxy and halogen, a and b are 0, 1 or 2, X is ##STR37## --O-- or --S--, R.sub.1 is hydrogen, alkyl having one to 4 carbon atoms, phenyl or benzyl, B.sub.1 is a CH-acid coupling component of the acetoacetic acid arylamide series of the formula ##STR38## wherein R.sub.2 is ##STR39## benzimidazolon-5-yl, halogen substituted benzimidazolon-5-yl or alkyl-substituted benzimidazolon-5-yl having 1 to 2 carbon atoms in the alkyl moiety, wherein R.sub.10, R.sub.11 and R.sub.12 is independently from each other hydrogen, sulpho, carboxyl, nitro, amino, cyano, halogen, alkyl having 1 to 4 carbon atoms, hydroxyl, alkoxy having 1 to 4 carbon atoms or alkanoylamino having 1 to 4 carbon atoms in the alkanoyl moiety, R.sub.9 is sulpho, and s is 1, 2 or 3, and B.sub.2 is another coupling component radical which may be the same as B.sub.1 or different with the proviso that said disazo compound contains at least one sulpho group or carboxyl group in the dyestuff molecule and the alkali metal salt, alkaline earth metal salt or ammonium salt thereof.