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Nitroso refers to a functional group in organic chemistry which has the NO group attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds (e.g., nitrosoalkanes; R−N=O), S-nitroso compounds (nitrosothiols; RS−N=O), N-nitroso compounds (e.g., nitrosamines, R1N(−R2)−N=O), and O-nitroso compounds (alkyl nitrites; RO−N=O).
Contents
- Chemistry and biology of n nitroso compounds cambridge monographs on cancer research
- Nitrosyl as a ligand
- Organonitroso compounds
- Nitrosation vs nitrosylation
- In food
- References
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−N=O).
Nitric oxide is a stable radical, having an unpaired electron.
Reduction of nitric oxide gives the hyponitrite anion, NO−:
NO + e− → NO−Oxidation of NO yields the nitrosonium cation, NO+:
NO → NO+ + e−Chemistry and biology of n nitroso compounds cambridge monographs on cancer research
Nitrosyl as a ligand
Nitric oxide can serve as a ligand in complexes. The resulting complexes are called metal nitrosyls, and can bond to a metal atom in two extreme modes: as NO+ and as NO−. It is generally assumed that NO+ coordinates linearly, the M−N−O angle being 180°, whereas NO− forms a bent geometry, with an M−N−O angle of approximately 120°. However, the results of many studies have shown that the ionic descriptions of the NO ligand do not correlate with metal–NO geometry. A more realistic description of electron-counting in metal–nitrosyl chemistry is given by the Enemark–Feltham notation.
Organonitroso compounds
Nitroso compounds can be prepared by the reduction of nitro compounds or by the oxidation of hydroxylamines. A good example is (CH3)3CNO, known formally as 2-methyl-2-nitrosopropane, or t-BuNO, which is prepared by the following sequence:
(CH3)3CNH2 → (CH3)3CNO2(CH3)3CNO2 → (CH3)3CNHOH(CH3)3CNHOH → (CH3)3CNO(CH3)3CNO is blue and exists in solution in equilibrium with its dimer, which is colorless, m.p. 80–81 °C.
In the Fischer–Hepp rearrangement aromatic 4-nitrosoanilines are prepared from the corresponding nitrosamines. Another named reaction involving a nitroso compound is the Barton reaction.
Organonitroso compounds serve as a ligands for transition metals.
Nitrosation vs. nitrosylation
Nitrite can enter two kinds of reaction, depending on the physico-chemical environment.
2 + H+ ⇌ HONOHONO + H+ ⇌ H2O + NO+C6H5NH2 + NO+ → C6H5N(H)NO + H+
Many primary alkyl N-nitroso compounds, such as CH3N(H)NO, tend to be unstable with respect to hydrolysis to the alcohol. Those derived from secondary amines (e.g., (CH3)2NNO derived from dimethylamine) are more robust. It is these N-nitrosamines that are carcinogens in rodents.
In food
In foodstuffs and in the gastro-intestinal tract, nitrosation and nitrosylation do not have the same consequences on consumer health.
2 (99%). Cured meat is also added with sodium ascorbate (or erythorbate or vitamin C). As demonstrated by S. Mirvish, ascorbate inhibits nitrosation of amines to nitrosamine, because ascorbate reacts with NO−
2 to form NO. Ascorbate and pH 5 thus favor nitrosylation of heme iron, forming nitrosylheme, a red pigment when included inside myoglobin, and a pink pigment when it has been released by cooking. It participates to the "bacon flavor" of cured meat: nitrosylheme is thus considered a benefit for the meat industry and for consumers.