Science of Synthesis

Kubik, S., Science of Synthesis, (2010) 41, 509.

The standard method for the generation of diazonium ions is reaction of primary amines with nitrous acid, formed by protonation of nitrite salts such as sodium nitrite, in acidic aqueous solution.[‌24‌,‌25‌] The reaction involves initial formation of an N-nitrosoamine that decomposes to give the corresponding diazonium cation (‌Scheme 5‌). Depending on the reaction conditions, dinitrogen trioxide, the oxoammonium ion (H2NO+), or the nitrosonium ion acts as the nitrosation agent. As a proton source, aqueous hydrochloric acid or glacial acetic acid is commonly used. Since the reaction requires the simultaneous presence of both the free amine and free nitrous acid, it proceeds only in a relatively narrow pH window, between ca. 3 and 5. Diazotization can also conveniently be performed using stable nitrosonium salts such as the tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, hexafluoroarsenate, or hydrogen sulfate.[‌26‌]

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References