Diazotization Reaction Mechanism

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Phenyldiazonium Tetrafluoroborate

What is Diazotization? 

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

In this article we will discuss diazotization reaction, diazotization reaction mechanism, diazotization titration and uses of diazotization compounds.

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 🡪 Diazonium Salt + Water 

Compounds in which 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 gaseous phase. Its formula is HNO2

Nitrous Acid Structure :

Mineral acids are inorganic acids which 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 –


Example of Diazotization Reaction 

Diazotization of Aniline 

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

The Reaction Involved is Given Below :


Diazotization Reaction Mechanism 

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. Reaction is given below-

   Nitrous Acid            Hydrogen ion from mineral acid                       Nitrosonium ion                                  

Step 2. Formation of N-Nitrosamine - 

In this step Nitrosonium ion reacts with 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 ion. Now deprotonation takes place which gives N-nitrosamine as a product. Reaction involved is given below –  

Aromatic Amine                 Nitrosonium ion

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 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 in the flask and the rest of the volume is filled with the 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 end point. 

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 in nature. 

  • 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.

Diazotization reaction mechanism is one of the important topics of CBSE Class 12 Chemistry. Generally, questions are asked related to this topic in the final board examination. So, you need to prepare the topic strongly. If you still have any doubts, you can download the free PDFs of NCERT solutions for Class 12 Chemistry and study material available on Vedantu by just registering yourself on Vedantu Online.