Diazotization reactions are important intermediate steps in the preparation of organic halides. They are also done in the Sandmeyer and Schiemann reactions, used in the preparation of organic amino groups.
Diazotization involves the nitrosation of primary aromatic amines using nitrous acid. Being a weak and monobasic acid, this nitrous acid is generated on site from the reversible reaction of sodium nitrite with a strong acid, such as hydrochloric or hydrofluoric acid. The nitrous acid is nucleophilic causing it to attack the amine. The resulting reprotonation by solvent hydrogen atoms leads to the double elimination of water, yielding a carbene or cabenoid.
Intermediates resulting from the diazotization of primary, aliphatic amines are unstable, causing them to rapidly convert to carbocations after giving up nitrogen. The resulting radicals undergo further substitution, elimination or rearrangement reactions to yield stable compounds.
Diazotization is a convenient, one-step process for the preparation of aromatic and heterocyclic iodides with high yields. The sequential diazotization and subsequent iodination of aromatic amines with potassium iodide, sodium nitride and p-toluenesulfonic acid in an acetonitrile solution at room temperature is an example of an iodide preparation reaction. Diazotization has also been used in the preparation of pure arenediazonium tosylates aryl azides, 2-amino acids and industrial azo-dyes.