Identification of a toxic impurity in commercial diphenylamine

The impurity in commercial diphenylamine which induces polycystic kidney disease in rats has been identified as N,N,N'-triphenyl-p-phenylenediamine. The structure of the compound was confirmed by mass and proton magnetic resonance spectrometry and by comparison with a synthetic standard prepared by the Ullman coupling of iodobenzene and p-phenylenediamine or N,N-diphenyl-p-phenylenediamine. Laboratory studies with highly purified diphenylamine indicated that N,N,N'-triphenyl-p-phenylenediamine can be formed by heating diphenylamine.