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).
|Systematic IUPAC name
3D model (JSmol)
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
NO+ 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:
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.
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.
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).
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).