Hoechst Aktiengesellschaft

Erhard Worfel

Josef Landler

Klaus Hunger

Konrad Opitz

Azo pigments are obtained by diazotizing a diazotizable aromatic amine without solubilizing groups in anhydrous dipolar aprotic water-miscible solvents with the stoichiometric amount or a small excess of nitrosylsulfuric acid or nitrosyl chloride, coupling the diazonium compound so obtained with a coupling component and isolating the pigment obtained in usual manner. This process is carried out in homogeneous solution and yields azo pigments the advantageous properties of which cannot be achieved by other methods, for example, the excellent purity, grain softness, narrow range of particle size distribution, excellent dispersibility in plastic materials and color lacquers, high gloss and excellent opacity in color lacquers.

Azo pigments obtained by diazotizing in a dipolar aprotic organic solvent

Process for the preparation of azo pigments by diazotizing in a dipolar

Concentrated dyeing compositions containing up to 45% by weight of one or more metal-free or metal complex azo dyestuffs containing one or more sulfo groups and one or more reactive groups, and containing buffer substances and having a pH of from 3 to 7, which may easily be prepared by diazotization and coupling of stoichiometrical amounts of a diazotizable amino compounds with a stoichiometrical amount of a nitrite and with a coupling component without addition of an acid but with the proviso that at least the diazo or coupling component contain at least one free acid group, such as sulfo group; these compositions are salt-free or practically salt-free and are very well suitable for the preparation of usual dyeing liquors and printing pastes useful in dyeing wool, silks, polyamide fibers and natural or regenerated cellulose.

Stable liquid aqueous composition of a water-soluble fiber-reactive azo

A new and very advantageous Process had been found for the preparation of azo dyestuffs by diazotation and coupling in which the synthesis is carried out without the hitherto usual addition of an acid, with the proviso that at least one of the diazo and coupling components contains at least one acid group. Besides the saving of reaction material and subsequently of alkali for neutralization of the reaction medium and isolation of the dyestuff, highly concentrated solutions of the dyestuff and salt-free or practically salt-free dyestuffs can be obtained, and waste-water is no longer charged with big amounts of salts.

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Hattersheim, Germany

Erhard Worfel