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Skeletal formula
Ball-and-stick model
IUPAC name
3D model (JSmol)
ECHA InfoCard 100.008.721
RTECS number DA6497525
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 other solvents Sol. in organic solvents
-59.1·10−6 cm3/mol
N is sp2
Main hazards toxic
R-phrases (outdated) R20/21R25
S-phrases (outdated) S26S36/37S45
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Nitrosobenzene is the organic compound with the formula C6H5NO. 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 solidifies 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". Organic Syntheses. ; Collective Volume, 3, p. 668 
  3. ^ H. Caro (1898). Z. Angew. Chem. 11: 845ff.  Missing or empty |title= (help)
  4. ^ H. Yamamoto, N. Momiyama "Rich Chemistry of Nitroso Compounds" Chemical Communications 2005, pp.3514–25.
  5. ^ H. D. Anspon (1955). "p-Phenylazobenzoic Acid". Organic Syntheses. ; Collective Volume, 3, p. 711 
  6. ^ H. Feuer. S. Patai, ed. The Chemistry of the Nitro and Nitroso Groups Part 1. New York: Wiley. pp. 278–283.  Missing or empty |title= (help)
  7. ^ "Asymmetric O− and N− Nitroso Aldol Reaction – an efficient access to a-oxy and a-amino carbonyl compound" (PDF).