US Patent 7235694 Process for preparing 4-aminodiphenylamine

A process for preparing 4-aminodiphenylamine having the steps of reacting nitrobenzene and aniline in the presence of a complex base catalyst, hydrogenating the reaction mixture with hydrogen, a powdery composite catalyst, and a hydrogenation solvent; separating, recovering, and reusing the complex base catalyst and the powdery composite catalyst from the reaction mixture; separating, recovering, and reusing aniline, and optionally water, from the the reaction mixture; refining the reaction mixture to obtain 4-aminodiphenylamine. The complex base catalyst comprises tetraalkyl ammonium hydroxide, and tetraalkyl ammonium salt.