Benzene, 1,1'-methylenebis(4-nitro- → n-Hydroxy-1,1-bis(4-nitrophenyl)methanimine

The title compound was prepared by modification of procedures previously reported in the literature (Chapman and Fidler (1936) J. Chem. Soc, 448; Kulin and Leffek (1973) Can. J. Chem., 51: 687). A solution of chromic anhydride (20 g, 200 mmol) in 125 ml of H2O was added dropwise over 4 hours, to a suspension of bis(4-nitrophenyl)methane (25 g, 97 mmol) in 300 ml of acetic acid heated to reflux. The reaction mixture was heated at reflux for 1 hour, cooled to room temperature, and poured into water. The solid was collected by filtration, washed with H2O, 5% sodium bicarbonate, H2O , and air-dryed to provide a 1:1 mixture of bis(4-nitrophenyl)methane/4,4'-dinitrobenzophenone via 1H NMR. This material was oxidized with a second portion of chromic anhydride (20 g, 200 mmol), followed by an identical work-up procedure to provide the crude product. Trituration with 200 ml of benzene heated to reflux for 16 hours provided 4,4'-dinitrobenzophenone (20.8 g, 79%) as a yellow powder.