Process for the purification of crude 3,4,3',4'-tetraaminodiphenyl

摘要

Crude 3,4,3',4'-tetraaminodiphenyl (TAD) prepared by ammonolysis of 3,3'-dichlorobenzidine in the presence of mainly Cu catalysts is purified by a process in which (a) after its isolation from the preparation process crude TAD is treated with an aqueous NH3 solution and, if desired, TAD thus treated is then (b) dissolved and reprecipitated in water in the presence of adsorbents and also of a water-soluble reducing agent. Compared with relevant processes of the state of the art, the process produces a higher yield of pure TAD and it is also simpler to carry out.