The nitrosoniumionisNO+, 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 acetonitrileCH3CN. NOBF4 can be purified by sublimation at 200–250 °C and 0.01 mmHg (1.3 Pa).[2]
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
vs. ferrocene/ferrocenium, [NO]+inCH2Cl2 solution has a redox potential of 1.00 V (or 1.46–1.48 V vs SCE),
vs. ferrocene/ferrocenium, [NO]+inCH3CN 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.
Electron-rich arenes are nitrosylated using NOBF4.[5] One example involves anisole:
CH3OC6H5 + NOBF4 → CH3OC6H4NO + HBF4
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.[6] 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
^Olah, George A.; Surya Prakash, G. K.; Wang, Qi; Li, Xing-ya; Surya Prakash, G. K.; Hu, Jinbo (15 October 2004). "Nitrosonium Tetrafluoroborate". Encyclopedia of Reagents for Organic Synthesis: rn058.pub2. doi:10.1002/047084289X.rn058.pub2. ISBN0471936235.
^Sharp, D. W. A.; Thorley, J. (1963). "670. The Infrared Spectrum of the Nitrosonium Ion". Journal of the Chemical Society (Resumed): 3557. doi:10.1039/JR9630003557.
^Bosch, E.; Kochi, J. K. (1994). "Direct Nitrosation of Aromatic Hydrocarbons and Ethers with the Electrophilic Nitrosonium Cation". Journal of Organic Chemistry. 59 (19): 5573–5586. doi:10.1021/jo00098a015.
^T. W. Hayton, P. Legzdins, W. B. Sharp. "Coordination and Organometallic Chemistry of Metal-NO Complexes". Chemical Reviews 2002, volume 102, pp. 935–991.
