Chapter 1 - Reagents effecting nitrosation

Abstract

The most commonly used reagent for bringing about electrophilic nitrosation is nitrous acid, generated in aqueous acid solution from a nitrite salt, usually sodium nitrite, and used in situ. Pure nitrous acid has never been isolated, because decomposition occurs, giving various oxides of nitrogen as final products. Where decomposition is a problem, such as for slow nitrosation reactions, better quantitative work can be achieved by carrying out the reactions anaerobically. Another important fact is that apart from the generation of nitrosyl halides in low concentration in aqueous acid solutions of nitrous acid containing halide ions, the nitrosyl halides can be used in solution in a variety of non-aqueous solvents to bring about nitrosation. Also, alkyl nitrites or nitrite esters have been known for a long time and are, under many conditions, effective nitrosating agents. They are mostly colorless–yellow volatile liquids derived in the main from aliphatic alcohols. There has been an upsurge, in recent years, in the range of rather unusual nitrosating agents, which have been developed. Some do not appear to have major synthetic advantages over the reagents already discussed, but others might be appropriate reagents under certain circumstances. These include sodium nitrite under phase-transfer condition, oxyhyponitrite, various complexes of HalNO and N2O4, sodium nitrite on silica and silica chloride bases and N2O4 immobilized on polyvinylpyrrolidone.