Nitrosobenzene

Nitrosobenzene is the organic compound with the formula C₆H₅NO. The compound can be viewed as hybrid of singlet O₂ and azobenzene. This diamagnetic species exists in equilibrium with its dimer.

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Preparation

C₆H₅NO was first prepared by Adolf von Baeyer by the reaction of diphenylmercury and nitrosylbromide:^[1]

[C₆H₅]₂Hg + BrNO → C₆H₅NO + C₆H₅HgBr

The modern synthesis entails reduction of nitrobenzene to phenylhydroxylamine, C₆H₅NHOH, which is then oxidized by Na₂Cr₂O₇.^[2] C₆H₅NO can also be prepared by oxidation of aniline using peroxymonosulfuric acid, Caro's acid.^[3] It is usually purified by steam distillation, where it comes over as a green liquid that solidifes to a colorless solid.

Characteristic reactions

The monomer undergoes Diels-Alder reactions with dienes.^[4] Most characteristically nitrosobenzene condenses with "active" methylene and amine groups, e.g. of malonic esters. Condensation with anilines affords azobenzene derivatives (Mills reaction)^[5] and condensation with benzylcyanide PhCH₂CN the imine PhC(CN)=NPh (The Ehrlich-Sachs Reaction).^[6]

Reduction of PhNO produces C₆H₅NH₂.

See also

• Nitroso

References

1. ^ Baeyer, A. "Nitrosobenzol und Nitrosonaphtalin" Chemische Berichte 1874, volume 7, pp.1638–1640.
2. ^ G. H. Coleman, C. M. McCloskey, F. A. Stuart (1955). "Nitrosobenzene". Org. Synth.; Coll. Vol. 3: 668. 
3. ^ H. Caro, Z. angew. Chem., volume 11, p 845ff (1898).
4. ^ H. Yamamoto, N. Momiyama "Rich Chemistry of Nitroso Compounds" Chemical Communications 2005, pp.3514–3525.
5. ^ H. D. Anspon (1955). "p-Phenylazobenzoic Acid". Org. Synth.; Coll. Vol. 3: 711. 
6. ^ H. Feuer in S. Patai (ed.) "The Chemistry of the Nitro and Nitroso Groups Part 1," Wiley: New York. pp. 278-283