The nitrosation of primary aromatic amines with nitrous acid (generated in situ from sodium nitrite and a strong acid, such as hydrochloric acid, sulfuric acid, or HBF4) leads to diazonium salts, which can be isolated if the counterion is non-nucleophilic.
Diazonium salts are important intermediates for the preparation of halides (Sandmeyer Reaction, Schiemann Reaction), and azo compounds. Diazonium salts can react as pseudohalide-type electrophiles, and can therefore be used in specific protocols for the Heck Reaction or Suzuki Coupling.
The intermediates resulting from the diazotization of primary, aliphatic amines are unstable; they are rapidly converted into carbocations after loss of nitrogen, and yield products derived from substitution, elimination or rearrangement processes.
Mechanism of Diazotisation
A convenient and general one-step preparation of aromatic and some heterocyclic iodides in good yields includes a sequential diazotization-iodination of aromatic amines with KI, NaNO2, and p-TsOH in acetonitrile at room temperature.
E. A. Krasnokutskaya, N. I. Semenischeva, V. D. Filimonov, P. Knochel, Synthesis, 2007, 81-84.
Sulfonic Acid Based Cation-Exchange Resin: A Novel Proton Source for One-Pot Diazotization-Iodination of Aromatic Amines in Water
V. D. Filimonov, N. I. Semenischeva, E. A. Krasnokutskaya, A. N. Tretyakov, H. Y. Hwang, K.-W. Chi, Synthesis, 2008, 185-187.
Unusually Stable, Versatile, and Pure Arenediazonium Tosylates: Their Preparation, Structures, and Synthetic Applicability
V. D. Filimonov, M. Trusova, P. Postnikov, E. A. Krasnokutskaya, Y. M. Lee, H. Y. Hwang, H. Kim, K.-W. Chi, Org. Lett., 2008, 10, 3961-3964.
Efficient Synthesis of 2-Amino Acid by Homologation of β2-Amino Acids Involving the Reformatsky Reaction and Mannich-Type Imminium Electrophile
R. Moumne, S. Lavielle, P. Karoyan, J. Org. Chem., 2006, 71, 3332-3334.