Reactions of Amines

Due to the unshared electron pair, amines can act as both bases and nucleophiles.

Reaction with acids

When reacted with acids, amines donate electrons to form ammonium salts.




Reaction with acid halides

Acid halides react with amines to form substituted amides.





Aldehydes and ketones react with primary amines to give a reaction product (a carbinolamine) that dehydrates to yield aldimines and ketimines (Schiff bases).





If you react secondary amines with aldehydes or ketones, enamines form.




Reaction with sulfonyl chlorides

Amines react with sulfonyl chlorides to produce sulfonamides. A typical example is the reaction of benzene sulfonyl chloride with aniline.




The Hinsberg test

The Hinsberg test, which can distinguish primary, secondary, and tertiary amines, is based upon sulfonamide formation. In the Hinsberg test, an amine is reacted with benzene sulfonyl chloride. If a product forms, the amine is either a primary or secondary amine, because tertiary amines do not form stable sulfonamides. If the sulfonamide that forms dissolves in aqueous sodium hydroxide solution, it is a primary amine. If the sulfonamide is insoluble in aqueous sodium hydroxide, it is a secondary amine. The sulfonamide of a primary amine is soluble in an aqueous base because it still possesses an acidic hydrogen on the nitrogen, which can be lost to form a sodium salt.




Oxidation

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