Nitrosonium

Nitrosonium
Preferred IUPAC name Nitrosonium
Systematic name Iminooxidanium
Identifiers
Abbreviations	NO(+)
CAS number	14452-93-8
PubChem	84878 Y
ChemSpider	76569 Y
ChEBI	CHEBI:29120
Gmelin Reference	456
Jmol-3D images	Image 1
SMILES N#[O+]
InChI InChI=1S/NO/c1-2/q+1 Key: KEJOCWOXCDWNID-UHFFFAOYSA-N
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 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 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, NO₂⁺, 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 NO 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