[Chemistry Class Notes] on Diazotization Reaction Mechanism Pdf for Exam

The process of producing diazonium salts or diazonium compounds is called diazotization. It was 1^st given by Peter Griess. Thus, diazotization is the process used in the formation of diazonium salts through aromatic amines. 

What is Diazotization Reaction? 

Aromatic amine reacts with nitrous acid and mineral acid to form diazonium salt and produces water as a side product. This reaction is known as Diazotization Reaction. The reaction can be represented in words reaction form as follows – 

Word Reaction Form of Diazotization Reaction – It will help you to remember the reaction easily. 

Aromatic Amine + Nitrous Acid + Mineral Acid [rightarrow] Diazonium Salt + Water 

Compounds in which an amino or substituted amino group is bonded directly to an aromatic ring are known as aromatic amines. For example –

Nitrous acid is a weak and monobasic acid which is generally used in the gaseous phase. Its formula is HNO₂. 

Nitrous Acid Structure :

Mineral acids are inorganic acids that give hydrogen ions when dissolved with water. Examples of mineral acids are HCl, H₂SO₄, HBF₄ etc. 

We can write diazotization reaction in the following form as well –

[ArNH_2 + HNO_2 + HX rightarrow RN_2^+X^- + H_2O]

Aromatic Amine   Nitrous Acid  Mineral Acid  Diazonium salt  Water

Example of Diazotization Reaction 

Diazotization of Aniline 

It is done by treating aniline with sodium nitrate and HCl at a temperature of 273K.

The Reaction Involved is Given Below :

Diazotization Reaction Mechanism

The Diazotization mechanism can be explained in the following four steps – 

Step 1. Formation of Nitrosonium Ion – 

Nitrous acid reacts with mineral acid (mineral acid provides hydrogen ion) and forms nitrosonium ion. The reaction is given below-

Step 2. Formation of N-Nitrosamine – 

In this step, Nitrosonium ion reacts with the aromatic amine to give N-nitrosamine. When nitrosonium ion reacts with aromatic amine, its positive charge shifts on the nitrogen of aromatic amine as nitrogen attached with aromatic amine gives its lone pair of electrons to nitrosonium ion. As a result of this, a nitrogen-nitrogen bond is formed between aromatic amine and nitrosonium ions. Now deprotonation takes place which gives N-nitrosamine as a product. The reaction involved is given below –  

Step 3. Formation of Diazohydroxide by Protonation and Deprotonation of N-Nitrosamine 

Protonation of N-nitrosamine takes place followed by deprotonation of it. Which gives rise to diazohydroxide.

Step 4. Formation of Diazonium Ion by Protonation of Diazohydroxide

In this step protonation of diazohydroxide takes place which gives water and diazonium ion. Diazonium ion can be easily converted into diazonium salt.

Diazotization Titration 

Diazotization titration involves a diazotization reaction or formation of diazotization salt. In the diazotization titration process, we 1st weigh the sample and put it in the standard conical flask. Now conc. HCl and KBr are added to the flask and the rest of the volume is filled with distilled water. This resulting solution is a standard solution. Now the appropriate quantity of standard solution is pipette out in another conical flask for titration. The temperature is maintained at 0-5℃. Now the solution is titrated with the NaNO₂ solution until starch iodide paper turns blue. It indicates the endpoint. 

Uses of Diazonium Compounds 

Uses of Diazonium Compounds are as follows – 

• It is used in the dye and pigment industry. 

• It is used in document reproduction as these compounds are light-sensitive and break down under UV or violet light. 

• It is used in the synthesis of organic compounds. 

• These compounds are used in explosive materials as solid diazonium halides are explosive. 

• It is used in Fischer indole synthesis of triptan compounds and indomethacin. 

• It is used in nanotechnology to exfoliate the nanotubes. 

• It is used in the reaction called Meerwein Arylation which produces phenylated products.

Benefits of Diazonium Compounds in Nanotechnology:

• Diazonium Compounds are a key component in the realm of nanotechnology.

• Diazonium Compounds are combined with an ionic solvent in a mortar and pestle to exfoliate the nanotubes.

• Due to significant cohesive forces between the tubes, dizonium compounds prohibit the tubes from forming intimate bundles, which is a recurring difficulty in nanotube technology.

Conclusion

This article is all about introduction of  diazotization reaction, diazotization reaction mechanism, diazotization titration and uses of diazotization compounds.