Azoxybenzene Explained

Azoxybenzene is organic compound with the formula C₆H₅N(O)NC₆H₅. It is a yellow, low-melting solid.^[1] The molecule has a planar C₂N₂O core. The N-N and N-O bond lengths are nearly the same at 1.23 Å.^[2]

Preparation

It can be prepared by partial reduction of nitrobenzene. This reaction is proposed to proceed via the intermediacy of phenylhydroxylamine and nitrosobenzene:^[1]

PhNHOH + PhNO → PhN(O)NPh + H₂O

Another option is the oxidation of aniline by hydrogen peroxide, in acetonitrile at 50 °C. In this reaction, the pH should be kept around 8, to activate the hydrogen peroxide and avoid too much oxygen evolution at the same time. First, the acetonitrile is oxidized, forming an imine hydroperoxide. Then, this intermediate oxidizes the aniline to azoxybenzene.^[3]

CH₃CN + H₂O₂ → [CH₃C(OOH)=NH]

2 PhNH₂ + 3 [CH₃C(OOH)=NH] → PhN(O)NPh + 3 CH₃C(O)NH₂ + 2 H₂O

PhNO2 + Na₃AsO₃/NaOH→ Ph−N⁺O⁻=N-Ph

References

1. Azoxybenzene . H. E. Bigelow . Albert Palmer . Organic Syntheses. 1931. 11. 16. 10.15227/orgsyn.011.0016.
2. Acta Crystallographica Section E. trans-Diphenyldiazene Oxide. 2007. o3639. 63. 8 . S. P. G. Martínez . S. Bernès . 10.1107/S1600536807035787.
3. Reactions of Hydrogen Peroxide. VII. Alkali-Catalyzed Epoxidation and Oxidation Using a Nitrile as Co-reactant . George B. Payne . Philip H. Deming . Paul H. Williams . The Journal of Organic Chemistry. 1961. 26. 3 . 659-663. 10.1021/jo01062a004.