Nitrosonium

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The nitrosonium ion is NO⁺, the nitrogen atom is bonded to an oxygen atom with a bond order of 2, the overall diatomic species bearing a positive charge. This ion is usually obtained as the following salts: NOClO₄, NOSO₄H (nitrosyl sulfuric acid, more descriptively written ONSO₂OH), and NOBF₄. The ClO₄^- and BF₄^- salts are soluble in CH₃CN. NOBF₄ can be purified by sublimation at 200–250 °C/0.01 mmHg.

For NOBF₄: Selected data: density = 2.185 g cm–3.3 MW =116.82

NO⁺ is isoelectronic with CO and N₂.

Contents

1 Chemical Properties

1.1 Hydrolysis
1.2 As a diazotizing agent
1.3 As an oxidizing agent
1.4 Nitrosylation of arenes
1.5 As a source of NO complexes

2 Suppliers/Manufacturers of the tetrafluoroborate salt
3 See also
4 References

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 salt, ArN₂⁺.

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)

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. The 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. 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

Suppliers/Manufacturers of the tetrafluoroborate salt

[Aldrich]

References

N. G. Connelly, W. E. Geiger, "Chemical Redox Agents for Organometallic Chemistry" Chemical Reviews 1996, vol. 96, pp. 877-910.
T. W. Hayton, P. Legzdins, W. B. Sharp "Coordination and Organometallic Chemistry of Metal-NO Complexes" Chemical Reviews 2002, volume 102, pp. 935-991
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.
G. A. Olah, G. K. S. Prakash, Q. Wang,X.-Y. Li ”Nitrosylsulfuric Acid” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.

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