"Nitrosyl" redirects here. For the analogous concept in metalorganic chemistry, see metal nitrosyl complex.

In organic chemistry, nitroso refers to a functional group in which the nitric oxide (\sN\dO) group is attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds (e.g., nitrosoalkanes; R\sN\dO), S-nitroso compounds (nitrosothiols; RS\sN\dO), N-nitroso compounds (e.g., nitrosamines, RN(\sR’)\sN\dO), and O-nitroso compounds (alkyl nitrites; RO\sN\dO).

Synthesis

Main article: Nitrosation

Nitroso compounds can be prepared by the reduction of nitro compounds[1] or by the oxidation of hydroxylamines.[2] Ortho-nitrosophenols may be produced by the Baudisch reaction. In the Fischer–Hepp rearrangement, aromatic 4-nitrosoanilines are prepared from the corresponding nitrosamines.

Properties

Nitrosoarenes typically participate in a monomer–dimer equilibrium. The azobenzene N,N'-dioxide (Ar(–O)N+=+N(O–)Ar) dimers, which are often pale yellow, are generally favored in the solid state, whereas the deep-green monomers are favored in dilute solution or at higher temperatures. They exist as cis and trans isomers.[3] The central "double bond" in the dimer in fact has a bond order of about 1.5.[4]

When stored in protic media, primary and secondary nitrosoalkanes isomerize to oximes.[5] Some tertiary nitrosoalkanes also isomerize to oximes through C-C bond fission, particularly if the bond is electron-poor.[6] Nitrosophenols and naphthols isomerize to the oxime quinone in solution, but reversibly; nitrosophenol ethers typically dealkylate to facilitate the isomerization. Nitroso tertiary anilines generally do not dealkylate in that way.[7]

Due to the stability of the nitric oxide free radical, nitroso organyls tend to have very low C–N bond dissociation energies: nitrosoalkanes have BDEs on the order of 30–40 kcal/mol, while nitrosoarenes have BDEs on the order of 50–60 kcal/mol. As a consequence, they are generally heat- and light-sensitive. Compounds containing O–(NO) or N–(NO) bonds generally have even lower bond dissociation energies. For instance, N-nitrosodiphenylamine, Ph2N–N=O, has a N–N bond dissociation energy of only 23 kcal/mol.[8]

Organonitroso compounds serve as a ligands giving transition metal nitroso complexes.[9]

Reactions

Many reactions make use of an intermediate nitroso compound, such as the Barton reaction and Davis–Beirut reaction, as well as the synthesis of indoles, for example: Baeyer–Emmerling indole synthesis, Bartoli indole synthesis. In the Saville reaction, mercury is used to replace a nitrosyl from a thiol group.

C-nitroso compounds are used in organic synthesis as synthons in some well-documented chemical reactions such as hetero Diels-Alder (HDA), nitroso-ene and nitroso-aldol reactions.[10]

Nitrosyl in inorganic chemistry

Nitrosyls are non-organic compounds containing the NO group, for example directly bound to the metal via the N atom, giving a metal–NO moiety. Alternatively, a nonmetal example is the common reagent nitrosyl chloride (Cl\sN\dO). Nitric oxide is a stable radical, having an unpaired electron. Reduction of nitric oxide gives the nitrosyl anion, NO-:

NO + e- → NO-

Oxidation of NO yields the nitrosonium cation, NO+:

NO → NO+ + e-

Nitric oxide can serve as a ligand forming metal nitrosyl complexes or just metal nitrosyls. These complexes can be viewed as adducts of NO+, NO-, or some intermediate case.

See also

References

  1. ^ G. H. Coleman; C. M. McCloskey; F. A. Stuart (1945). "Nitrosobenzene". Org. Synth.. 25: 80. doi:10.15227/orgsyn.025.0080
  2. ^
  3. ^ Beaudoin, D. & Wuest, J. D. (2016). "Dimerization of Aromatic C-Nitroso Compounds". Chemical Reviews. 116 (1): 258–286. doi:10.1021/cr500520s. PMID 26730505
  4. ^ Williams, D. L. H. (1988). Nitrosation. Cambridge, UK: Cambridge University. p. 36. ISBN 0-521-26796-X.
  5. ^ Kirby, G. W. (1977). "Electrophilic C-nitroso-compounds". Chemical Society Reviews. 6: 2. doi:10.1039/CS9770600001 (Tilden lecture).
  6. ^ Williams 1988, p. 36.
  7. ^ Williams 1988, pp. 59–61.
  8. ^ Luo, Yu-Ran (2007). Comprehensive Handbook of Chemical Bond Energies. Boca Raton, FL: Taylor and Francis. ISBN 9781420007282.
  9. ^ Lee, Jonghyuk; Chen, Li; West, Ann H.; Richter-Addo, George B. (2002). "Interactions of Organic Nitroso Compounds with Metals". Chemical Reviews. 102 (4): 1019–1066. doi:10.1021/cr0000731. PMID 11942786
  10. ^ Bianchi, P. & Monbaliu, J. C. M. (2022). "Three decades of unveiling the complex chemistry of C-nitroso species with computational chemistry". Organic Chemistry Frontiers. 9: 223–264. doi:10.1039/d1qo01415c