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Concept
Nitroso
Résumé
In organic chemistry, nitroso refers to a functional group in which the nitric oxide () group is attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds (e.g., nitrosoalkanes; ), S-nitroso compounds (nitrosothiols; ), N-nitroso compounds (e.g., nitrosamines, ), and O-nitroso compounds (alkyl nitrites; ).
Nitroso compounds can be prepared by the reduction of nitro compounds or by the oxidation of hydroxylamines.
Ortho-nitrosophenols may be produced by the Baudisch reaction. In the Fischer–Hepp rearrangement aromatic 4-nitrosoanilines are prepared from the corresponding nitrosamines.
Nitrosoarenes typically participate in a monomer–dimer equilibrium. The dimers, which are often pale yellow, are often 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.
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 , while nitrosoarenes have BDEs on the order of . 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 . Organonitroso compounds serve as a ligands for transition metals.
Many reaction exists which make use of an intermediate nitroso compound, such as the Barton reaction and Davis–Beirut reaction, as well as in 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.
Nitrite can enter two kinds of reaction, depending on the physico-chemical environment.
Nitrosylation is adding a nitrosyl ion to a metal (e.g. iron) or a thiol, leading to nitrosyl iron (e.g., in nitrosylated heme = nitrosylheme) or S-nitrosothiols (RSNOs).
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