Nitrosonium

The nitrosonium ion is , in which the nitrogen atom is bonded to an oxygen atom with a bond order of 3, and the overall diatomic species is cationic, bearing a positive charge. It can be viewed as nitric oxide with one electron removed. This ion is usually obtained as the following salts: , (nitrosylsulfuric acid, more descriptively written ) and . The and salts are slightly soluble in acetonitrile . NOBF₄ can be purified by sublimation at 200–250 Ã‚°C and .

Synthesis and spectroscopy

is isoelectronic with CO, and . 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}, indicating it is a loose cation rather than coordinated to another species.

Chemical properties

Hydrolysis

reacts readily with water to form nitrous acid:

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

As a diazotizing agent

reacts with aryl amines, , to give diazonium salts, . The resulting diazonium group is easily displaced (unlike the amino group) by a variety of nucleophiles.

As an oxidizing agent

, e.g. as , is a strong oxidizing agent:

• vs. ferrocene/ferrocenium, in solution has a redox potential of 1.00 V (or 1.46–1.48 V vs SCE),
• vs. ferrocene/ferrocenium, in 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.

is a convenient oxidant because the byproduct NO is a gas, which can be swept from the reaction using a stream of . Upon contact with air, NO forms , which can cause secondary reactions if it is not removed. 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, , is sometimes confused with nitronium, NO, 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. 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)

References