Contaminants in commercial dapsone

Three contaminants commonly found in commercial dapsone were identified as 2,4'-sulfonylbis(benzeneamine), 4-(phenylsulfonyl)benzeneamine, and 4-(4'-chlorophenylsulfonyl)benzeneamine. The identities were based on the spectral analysis and unambiguous synthesis of each compound. Solvent-free, pure dapsone was prepared by recrystallization from chloroform.