Ch22: Nitrosation of amines

Chapter 22: Amines

Nitrosation of Amines nitrosation of primary amines

nitrosation of primary amines

nitrosation of secondary amines

Summary

Typical reagents : sodium nitrite and aq. HCl or H₂SO₄ (this mixture yields nitrous acid, HNO₂)
The most useful reactions are probably those of primary aryl amines, Ar-NH₂, which give aryl diazonium salts, Ar-N₂⁺which can then be used to prepare substituted benzenes (see next page)
The actual nitrosation reagent is the nitrosyl cation, NO⁺ which is formed in situ:

mechanism for the formation of the nitrosyl cation

The nature of the product depends on the nature of the initial amine
Primary alkyl or aryl amines yield diazonium salts (hence the diazotisation reaction)

primary amines form unstable N-nitrosoamines that lose H2O and form diazonium ions

Alkyl diazonium salts are very unstable and yield carbocation-derived products by loss of the very good leaving group, N₂:

decomposition of alkyl diazonium salts

Secondary alkyl or aryl amines yield N-nitrosoamines:

secondary amines give N-nitrosoamines

Tertiary alkyl amines do not react in a useful fashion.
Tertiary aryl amines undergo nitrosation of the ring (an electrophilic aromatic substitution reaction)

tertiary aryl amines can undergo electrophilic aromatic substitution

© Dr. Ian Hunt, Department of Chemistry