Abstract: Azo dyestuffs, insoluble in water, are represented by the formula: ##STR1## wherein A represents the residue of a diazotizable benzene component carrying at least two substituents or the residue of a diazotizable heterocyclic component, R represents alkyl, B represents an unsubstituted or substituted alkyl group, and X represents hydrogen, chlorine, bromine, acylamino, benzoylamino, alkoxycarbonylamino, phenoxycarbonylamino, alkylsulfonylamino or phenylsulfonylamino, the dyestuff molecule being free of groups causing water solubility by formation of ions. These dyestuffs can be used for dyeing of hydrophobic fibers, in particular polyester fibers. Affinity is excellent and there are obtained bright, full-bodied shades very fast to wet tests, sublimation, abrasion and light.

Abstract: Process for the purification of mercaptobenzothiazole prepared according to known processes, characterized in that the crude product is treated with carbon tetrachloride or with 1,1,2,2-tetrachloroethylene.