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 bears 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 °C and 0.01mmHg.[1]
is isoelectronic with CO, and . It arises via protonation of nitrous acid:
HONO + H+ NO+ + H2O
In its infrared spectrum of its salts, νNO is a strong peak in the range 2150-2400 cm−1.[2]
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:
reacts with aryl amines,, to give diazonium salts, . The resulting diazonium group is easily displaced (unlike the amino group) by a variety of nucleophiles.
, e.g. as, is a strong oxidizing agent:[3]
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.
Electron-rich arenes are nitrosylated using NOBF4.[4] One example involves anisole:
CH3OC6H5 + NOBF4 → CH3OC6H4NO + HBF4Nitrosonium,, 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).
See main article: Metal nitrosyl complex. NOBF4 reacts with some metal carbonyl complexes to yield related metal nitrosyl complexes.[5] In some cases, [NO]+ does not bind the metal nucleophile but acts as an oxidant.
(C6Et6)Cr(CO)3 + NOBF4 → [(C<sub>6</sub>Et<sub>6</sub>)Cr(CO)<sub>2</sub>(NO)]BF4 + CO