7.3 Reactions in which Nitrogen is Retained
The reaction of the terminal nitrogen of a diazonium salt with nucleophile affords a covalent azo-compound.
7.3.1 Reduction to Arylhyrazones
The reduction of aromatic diazonium salts can be accomplished with sodium sulfite or SnCl2 or electrolysis to provide arylhydrazines. In case of sodium sulfite based reduction, the diazonium ion with a sulfite anion may give a covalent azo-sulfite that, having a double bond conjugated to an electron-accepting group, may add to a second nucleophilic sulfite ion which on hydrolysis provides the hydrazine.
7.3.2 Coupling Reactions
Diazonium ions are weak electrophiles, however, they undergo coupling with activated aromatic nuclei such as aryl amines, phenols and aromatic heterocyclic compounds. For example, N,N-dimethylaniline reacts with diazonium ion almost at the para -position. However, the careful control of the pH of the reaction medium is necessary for the success of the process.
In case of primary and secondary aromatic amines, the reaction preferentially takes place at the nitrogen atoms of the diazonium ions. For example, aniline adds to the aromatic diazonium salt to give diazoaminobenzene.
