Nitrosonium

Nitrosonium

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Names
IUPAC name Nitrilooxonium
Systematic IUPAC name Oxidonitrogen(1+)
Other names Nitrosonium Iminooxidanium
Identifiers
CAS Number	14452-93-8
3D model (JSmol)	Interactive image
Abbreviations	NO(+)
ChEBI	CHEBI:29120
ChemSpider	76569
ECHA InfoCard
E number
Gmelin Reference	456
PubChem CID	84878
CompTox Dashboard (EPA)	{{#property:P3117}}
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. It can be viewed as nitric oxide with one electron removed. 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 acetonitrile CH₃CN. NOBF₄ can be purified by sublimation at 200–250 °C and 0.01 mmHg (1.3 Pa).

Synthesis and spectroscopy

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

HONO + H⁺ ⇌ NO⁺ + H₂O

In its infrared spectrum of its salts, ν_NO is a strong peak in the range 2150–2400 cm⁻¹.

Chemical properties

See also: Nitrosation

Hydrolysis

NO⁺ reacts readily with water to form nitrous acid:

NO⁺ + H₂O → HONO + H⁺

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

NO⁺ + 2 NaOH → NaNO₂ + Na⁺ + 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.

File:Nitrosonium ion with amine reaction.png

Reaction of nitrosonium with aniline to form a diazonium salt

As an oxidizing agent

NO⁺, e.g. as NOBF₄, is a strong oxidizing agent:

• 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).

In organic chemistry, it selectively cleaves ethers and oximes, and couples diarylamines.

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. One example involves anisole:

CH₃OC₆H₅ + NOBF₄ → CH₃OC₆H₄NO + 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

Main article: Metal nitrosyl complex

NOBF₄ reacts with some metal carbonyl complexes to yield related metal nitrosyl complexes. In some cases, [NO]⁺ does not bind the metal nucleophile but acts as an oxidant.

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

See also

• Nitronium (NO₂⁺)
• Nitric oxide (NO)