Although you can oxidize all amines, only tertiary amines give easily isolated products. The oxidation of a tertiary amine leads to the formation of an amine oxide.
Arylamines tend to be easily oxidized, with oxidation occurring on the amine group as well as in the ring.
Reaction with nitrous acid
Nitrous acid is unstable and must be prepared in the reaction solution by mixing sodium nitrite with acid.
Primary amines react with nitrous acid to yield a diazonium salt, which is highly unstable and degradates into a carbocation that is capable of reaction with any nucleophile in solution. Therefore, reacting primary amines with nitrous acid leads to a mixture of alcohol, alkenes, and alkyl halides.
Primary aromatic amines form stable diazonium salts at zero degrees.
Secondary aliphatic and aromatic amines form nitrosoamine with nitrous acid.
Tertiary amines react with nitrous acid to form N‐nitrosoammonium compounds.
Reactions of aromatic diazonium salts
Diazonium salts of aromatic amines are very useful as intermediates to other compounds. Because aromatic diazonium salts are only stable at very low temperatures (zero degrees and below), warming these salts initiates decomposition into highly reactive cations. These cations can react with any anion present in solution to form a variety of compounds. Figure 1 illustrates the diversity of the reactions.
Figure 1