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What is Diazotization reaction?

When aniline is treated with sodium nitrite (NaNO2) and dilute hydrochloric acid (HCl) at ice cold temperature (0-50C), benzene diazonium chloride salt is obtained. This reaction is called diazotization reaction.

At first nitrous acid(HNO2) is obtained by the action of NaNO2 and dil.HCl and then the nitrous acid reacts with with aniline to give benzene diazonium chloride.

Diazotization reaction

Mechanism of diazotization reaction

Step-I : Nitrous acid (HNO2) is obtained by the action of NaNO2 and dil. HCl in-situ.
Diazotization reaction mechanism

Step-II : Protonation of nitrous acid followed by loss of water gives nitrosonium ion.

Step-III : Nucleophilic attack of aniline on nitrosonium ion gives nitrosoaniline.

Diazotization reaction mechanism

Step-IV : Protonation of the oxygen in the nitrosoaniline, followed by elimination of water gives diazonium ion ,which gets chloride ion and forms benzenediazonium chloride.

Diazotization reaction mechanism

Uses of Diazotization reaction

Diazotization reactions have several important uses in organic chemistry. Here are some of the main applications:

1. Synthesis of azo dyes: Diazotization reactions are widely employed in the production of azo dyes. Azo dyes are an important class of organic compounds used extensively in the textile, printing, and coloring industries. By diazotizing an aromatic amine and coupling it with a suitable coupling agent, various colored azo compounds can be synthesized.

Diazotization reaction uses

2. Preparation of aryl halides: Diazotization reactions can be used to convert aromatic amines into aryl halides, such as aryl chlorides or aryl bromides. The diazonium salt can be treated with a copper halide or cuprous salt, resulting in the replacement of the diazonium group with a halogen atom.

Sandmeyer application

Gattermann reaction

Some other uses are :

3. Pharmaceutical synthesis: Diazotization reactions are utilized in the synthesis of pharmaceutical compounds. The diazonium salts obtained can be reacted with a range of nucleophiles, such as phenols, amines, and thiols, to produce pharmaceutical intermediates or active pharmaceutical ingredients (APIs).

4. Formation of heterocyclic compounds: Diazotization reactions are employed in the synthesis of various heterocyclic compounds. The diazonium salt can react with compounds containing active methylene groups, such as β-ketoesters or malonates, leading to the formation of fused or isolated heterocyclic rings.

5. Preparation of aromatic fluorides: Diazotization reactions can also be used to produce aromatic fluorides. By reacting the diazonium salt with hydrogen fluoride (HF), the diazonium group is replaced by a fluorine atom, resulting in the formation of aryl fluorides.