Hoechst Aktiengesellschaft

Edgar Vorwerk

Manfred Finke

Rudiger Lenz

The present invention relates to a process for the preparation of pure 3,3',4,4'-tetraaminobiphenyl in high yield by ammonolysis of 3,3,-dichlorobenzidine in the presence of copper powder and CuCl. After the crude product has been washed with ammonia water and water, the 3,3',4,4'-tetraaminobiphenyl, thus pretreated, is crystallized in water in the presence of 0 to 5% by weight of activated carbon and of about 1 to 2% by weight of a water-soluble reducing agent at temperatures of about 100.degree. to about 140.degree. C., under a protective gas atmosphere (redissolution). The water-soluble reducing agent is an alkali metal dithionite or alkali metal sulfite. The protective gas used can be nitrogen. The water used in the recrystallization (redissolution water) can be reused in whole or in part in the recrystallization.

Process for the production of pure 3,3',4,4'-tetraamino-biphenyl

Curing component (A) based on polyisocyanates for binders (B) which contain groups containing active hydrogen, wherein the curing component (A) is a product of the reaction of (a1) polyisocyanates with (a2) .alpha.-hydroxyalkylpyridines. Mixtures of (A) and (B), and also, if appropriate, diluents (C) and additives (D), are stable on storage and give, even at temperatures of 120.degree.-140.degree. C., curing products which are sufficiently solvent-stable. They are suitable, in particular, for surface-coating preparations.

Curing component for synthetic resins, curable mixtures containing the

The invention relates to a process for the preparation of 4,4'-dihydroxydiphenyl ether by dehydration of hydroquinone using sulfonic acids or sulfuric acid as catalysts at elevated temperatures. The dehydration product is stirred with an excess of water at 80.degree. to 110.degree. C. The higher condensed byproducts which are undissolved during this are separated off, and the ether desired is allowed to crystallize out of the filtrate obtained.

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Frankfurt am Main, Germany

Edgar Vorwerk