The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 10, 1993
Filed:
Jul. 08, 1992
Edgar Vorwerk, Kelkheim, DE;
Hoechst Aktiengesellschaft, Frankfurt am Main, DE;
Abstract
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.