Diazotation

Diazotation, also known as diazotization, is a chemical process in which primary amines are converted into diazonium salts, most commonly arenediazonium salts. The reaction typically uses nitrous acid generated in situ from sodium nitrite and a strong mineral acid in a cold aqueous solution. A representative example is the conversion of a primary aromatic amine such as aniline into arenediazonium chloride: Ar-NH2 + HNO2 + HCl → Ar-N2+ Cl− + 2 H2O. The diazonium cation Ar-N2+ is stabilized by the counter-anion (for example Cl− or BF4−) under cold conditions, allowing isolation or use of the diazonium salt in solution.

Stability and scope: Diazonium salts derived from aryl amines are relatively stable only at low temperatures and in acidic media; they are usually prepared and used in situ because they can decompose violently if heated or concentrated. Aliphatic primary amines form diazonium salts that are generally unstable and are not commonly isolated.

Applications: Diazonium salts are versatile intermediates in organic synthesis. They undergo Sandmeyer and related reactions to replace the diazo group with halides, cyanide, or other nucleophiles. Hydrolysis of diazonium salts affords phenols; azo coupling with activated aromatic rings or phenols yields azo dyes. Other transformations include reductions and various substitution reactions, enabling diverse functionalizations of the aryl moiety.

Safety: Diazotization produces nitrogen gas and, in some cases, energetic diazonium salts. Procedures are performed at low temperature, in well-ventilated hoods, and with attention to stability and scattering hazards.