Nitrosonium

Nitrosonium

Names
Preferred IUPAC name Nitrosonium
Systematic IUPAC name Iminooxidanium
Identifiers
CAS Number	14452-93-8
Abbreviations	NO(+)
ChEBI	CHEBI:29120
ChemSpider	76569
Gmelin Reference	456
Jmol interactive 3D	Image
PubChem	84878
InChI InChI=1S/NO/c1-2/q+1 Key: KEJOCWOXCDWNID-UHFFFAOYSA-N
SMILES N#[O+]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

The nitrosonium ion is NO⁺, in which the nitrogen atom is bonded to an oxygen atom with a bond order of 3, and the overall diatomic species bears a positive charge. This ion is usually obtained as the following salts: NOClO₄, NOSO₄H (nitrosylsulfuric acid, more descriptively written ONSO₃OH), and NOBF₄. The ClO−
4 and BF−
4 salts are slightly soluble in CH₃CN. NOBF₄ can be purified by sublimation at 200–250 °C and 0.01 mmHg (1.3 Pa).

NO⁺ is isoelectronic with CO, CN⁻ and N₂. It arises via protonation of nitrous acid:

HONO + H⁺ ⇌ NO⁺ + H₂O

Chemical Properties

Hydrolysis

NO⁺ reacts readily with water to form nitrous acid:

NOBF₄ + H₂O → HONO + HBF₄

For this reason, NOBF₄ must be protected from water or even moist air. With base, the reaction generates nitrite:

NOBF₄ + 2 NaOH → NaNO₂ + NaBF₄ + H₂O

As a diazotizing agent

NO⁺ reacts with aryl amines, ArNH₂, to give diazonium salts, ArN+
2. The resulting diazonium group is easily displaced (unlike the amino group) by a variety of nucleophiles.

Reaction of nitrosonium with aniline to form a diazonium salt.

As an oxidizing agent

NO⁺, e.g. as NOBF₄, is a strong oxidizing agent:^[1]

• vs. ferrocene/ferrocenium, [NO]⁺ in CH₂Cl₂ solution has a redox potential of 1.00 V (or 1.46–1.48 V vs SCE)
• vs. ferrocene/ferrocenium, [NO]⁺ in CH₃CN solution has a redox potential of 0.87 V vs. (or 1.27–1.25 V vs SCE)

NOBF₄ is a convenient oxidant because the byproduct NO is a gas, which can be swept from the reaction using a stream of N₂. Upon contact with air, NO forms NO₂, which can cause secondary reactions if it is not removed. NO₂ is readily detectable by its characteristic orange color.

Nitrosylation of arenes

Electron-rich arenes are nitrosylated using NOBF₄.^[2] One example involves anisole:

CH₃OC₆H₅ + NOBF₄ → CH₃OC₆H₄-4-NO + HBF₄

Nitrosonium, NO⁺, is sometimes confused with nitronium, NO+
2, the active agent in nitrations. These species are quite different, however. Nitronium is a more potent electrophile than is nitrosonium, as anticipated by the fact that the former is derived from a strong acid (nitric acid) and the latter from a weak acid (nitrous acid).

As a source of nitrosyl complexes

NOBF₄ reacts with some metal carbonyl complexes to yield related metal nitrosyl complexes.^[3] One must be careful that [NO]⁺ is transferred vs. electron transfer (see above).

(C₆Et₆)Cr(CO)₃ + NOBF₄ → [(C₆Et₆)Cr(CO)₂(NO)]BF₄ + CO

See also

• Nitronium

References

1. N. G. Connelly, W. E. Geiger (1996). "Chemical Redox Agents for Organometallic Chemistry". Chem. Rev. 96 (2): 877–910. doi:10.1021/cr940053x. PMID 11848774.
2. E. Bosch and J. K. Kochi, "Direct Nitrosation of Aromatic Hydrocarbons and Ethers with the Electrophilic Nitrosonium Cation" Journal of Organic Chemistry, 1994, volume 59, pp. 5573–5586.
3. T. W. Hayton, P. Legzdins, W. B. Sharp "Coordination and Organometallic Chemistry of Metal-NO Complexes" Chemical Reviews 2002, volume 102, pp. 935–991