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Skeletal formula
Ball-and-stick model
CAS number 586-96-9 YesY
PubChem 11473
ChemSpider 10989 YesY
KEGG C06876 YesY
RTECS number DA6497525
Jmol-3D images Image 1
Molecular formula C6H5NO
Molar mass 107.11 g mol−1
Appearance Colorless solid
Melting point 65 to 69 °C (149 to 156 °F; 338 to 342 K)
Boiling point 59 °C (138 °F; 332 K) (at 18 mmHg)
Solubility in water Low
Solubility in other solvents Sol. in organic solvents
Molecular shape N is sp2
R-phrases R20/21R25
S-phrases S26S36/37S45
Main hazards toxic
Related compounds
Related compounds Nitrobenzene
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

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.


Nitrosobenzene was first prepared by Adolf von Baeyer by the reaction of diphenylmercury and nitrosyl bromide:[1]

(C6H5)2Hg + BrNO → C6H5NO + C6H5HgBr

The modern synthesis entails reduction of nitrobenzene to phenylhydroxylamine (C6H5NHOH) which is then oxidized by sodium dichromate (Na2Cr2O7).[2]

Nitrosobenzene 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[edit]

Nitrosobenzene undergoes Diels–Alder reactions with dienes.[4] Condensation with anilines affords azobenzene derivatives in a reaction known as the Mills reaction.[5] Reduction of nitrosobenzene produces aniline.

Most characteristically, nitrosobenzene condenses with active methylene groups, such as those of malonic esters and benzyl cyanide. For example, condensation with benzylcyanide (PhCH2CN) gives the imine (PhC(CN)=NPh) in a reaction known as the Ehrlich-Sachs Reaction:[6]

Ph–CH2-CN + Ph–NO → Ph–CH(CN)–N(OH)–Ph (oxyamination adduct) → PhC(CN)=N–Ph

Sometimes condensation with active methylene compounds could give products of O-nitroso-aldol reaction:[7]

R–CH2-CHO + Ph–NO → R–CH(CHO)–O–NHPh (aminoxylation adduct)


  1. ^ Baeyer, A. (1874). "Nitrosobenzol und Nitrosonaphtalin". Chemische Berichte 7: 1638–1640. doi:10.1002/cber.187400702214. 
  2. ^ G. H. Coleman, C. M. McCloskey, F. A. Stuart (1955), "Nitrosobenzene", Org. Synth. ; Coll. Vol. 3: 668 
  3. ^ H. Caro (1898). Z. angew. Chem. 11: 845ff. 
  4. ^ H. Yamamoto, N. Momiyama "Rich Chemistry of Nitroso Compounds" Chemical Communications 2005, pp.3514–25.
  5. ^ H. D. Anspon (1955), "p-Phenylazobenzoic Acid", Org. Synth. ; Coll. Vol. 3: 711 
  6. ^ H. Feuer. S. Patai, ed. The Chemistry of the Nitro and Nitroso Groups Part 1 (New York: Wiley). pp. 278–283. 
  7. ^ "Asymmetric O− and N− Nitroso Aldol Reaction – an efficient access to a-oxy and a-amino carbonyl compound".