Reactions of Aryl Amines

Aryl amines, like aliphatic amines and ammonia, are strong nucleophiles and will undergo an S_N2 reaction with alkyl halides (or alkyl groups with "good leaving groups") to give further substitution on the nitrogen, as described previously. They will also react with activated carbonyl compounds to undergo acyl transfer reactions; thus amides are readily formed by the reaction of amines with acid halides, acid anhydrides or carboxylate esters. The conversion of an aryl amine into an amide is a convenient method for limiting ring bromination to the para- position on the ring, the intermediate amide being simply hydrolyzed in a second step.

This intermediate step is necessary, since the free amine highly activates the ring to substitution, yielding tri-substitution.

Perhaps the most useful reactions of aryl amines involve the intermediate conversion into the corresponding diazonium salt by reaction with nitrous acid.

These diazonium salts undergo a series of replacement reactions, collectively known as the Sandelmyer Reaction to give aryl nitriles or aryl halides. A copper salt is generally required to catalyze the reaction, with the exception of iodination, which occurs spontaneously.

Aryl diazonium salts also undergo reduction to yield the arene on reaction with phosphorous acid (not phosphoric), and hydrolysis in the presence of aqueous acid to give the corresponding phenol. The cationic nitrogen of diazonium salts also adds to the para- position of highly activated aryl rings (generally aryl amines and phenols) to give coupling products, as shown below.