1: hydroxylamine hydrochloride; pyridine / ethanol / 7 h / 60 °C 2: sodium nitrite; sulfuric acid / diethyl ether; water / |Inert atmosphere 3: 1,3-bis(3,5-bis(trifluoromethyl)phenyl)urea / 24 h / 70 °C / |Molecular sieve View Scheme

1,3-bis(3,5-bis(trifluoromethyl)phenyl)urea T=70°C; 24 h; Molecular sieve;