Abstract: If highly concentrated aqueous solutions of azo dyes are prepared directly by diazotization and coupling reactions, appreciable difficulties generally result as a consequence of the fact that the diazotization and coupling reactions give rise to viscous phases which lead to stirring problems in the reaction apparatus used, which in turn results in an incomplete synthesis. The novel process for preparing concentrated aqueous dye solutions of an anionic dye in an aqueous medium overcomes this disadvantage by carrying out the diazotization of the aromatic amine diazo component and/or the coupling reaction between the diazonium salt and the coupling component in the presence of an auxiliary which exerts a viscosity-reducing effect on pasty phases. Examples of such auxiliaries are optionally alkyl-substituted naphthalenesulfonic acid-formaldehyde condensation products, ligninsulfonates, polyacrylates and copolymers of maleic anhydride and methacrylic acid or acrylic acid.

Abstract: Free radical heavy metal ions in water-soluble heavy metal complex dyestuffs are removed from the synthesis solution of the heavy metal complex dyestuff by means of a compound or several of the compounds mentioned below:(a) saturated and unsaturated fatty acids having about 8 to 18 carbon atoms and water-soluble salts thereof;(b) the monoesters and diesters of orthophosphoric acid and salts thereof corresponding to the general formula (1a) and (1b) ##STR1## in which R denotes a saturated or unsaturated aliphatic radical having about 8 to 18 carbon atoms and M stands for a hydrogen atom or a salt-forming, water-solubilizing metal;(c) aliphatic sulfonic acids and water-soluble salts thereof corresponding to the general formula (2)R--SO.sub.

Abstract: A process is described for separating sodium sulfate from aqueous solutions of certain fiber-reactive dyestuffs, which contain less than 2% by weight of chloride, by cooling down said solution to a temperature between +5.degree. C. and -15.degree. C. In the course of the cooling, the sodium sulfate precipitates in the form of the decahydrate and can be separated off in conventional manner, for example by filtration. The results obtained in this way are aqueous liquid low-salt preparations of these dyestuffs which contain less than 4% by weight of sodium sulfate.