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Diazotization Reaction Mechanism

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Last updated date: 23rd May 2024
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What is Diazotization?

The process of producing diazonium salts or diazonium compounds is called diazotization. It was 1st 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 –


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


Nitrous Acid Structure :


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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 :


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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-


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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 –  


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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.


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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.


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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.

FAQs on Diazotization Reaction Mechanism

1. What is the meaning of Diazotization?

Diazotization refers to a chemical process which is used in converting a primary aromatic amine into the corresponding diazonium salt of the amine, this process is commonly referred to as diazotization. The reaction of an aromatic amine with nitrous acid in the presence of another acid is used to make these diazonium salts. The diazotization reaction starts with nitrous acid reacting with another acid to produce water and the nitrosonium ion. In 1858, Peter Griess, a German industrial chemist, was the first to report such a reaction. He went on to find a large number of other diazonium salt reactions.

2. List some of the common uses of Diazonium Compounds.

The following are some of the applications of Diazonium Compounds:

  • Diazonium compounds are common agents in chemical synthesis, particularly for aryl derivatives. Because diazonium salts are photosensitive, they degrade when exposed to UV or violet light.

  • In the dye and pigment industries, dizonium compounds are regarded as an important ingredient.

  • Diazonium salts are used to make water-fast coloured fabrics by immersing the cloth in a diazonium compound solution, followed by a coupler solution.

  • In the area of nanotechnology, dizonium salts are a critical component. They're useful for functionalizing single-walled nanotubes efficiently.

  • It's mainly used in the Meerwein Arylation procedure, which results in phenylated compounds.

  • It's a chemical that's utilised to make organic compounds.

  • Solid diazonium halides are explosive, hence these compounds are employed in explosive materials.

3. What are the properties of Diazonium Salts?

Diazonium Salts have the following properties:

  • They have an ionic nature.

  • They are soluble in water.

  • Colorless crystalline solids, aryl diazonium salts are aryl diazonium salts.

  • Water dissolves benzenediazonium chloride. However, it only reacts to it when it is warmed.

  • Water does not dissolve benzenediazonium fluoroborate. At room temperature, it is fairly stable.

  • It is water soluble and stable at room temperature, but when warmed, it reacts with water.

  • When dry, it has a tendency to erupt.

4. What is the process for preparation of diazonium salts?

The process of turning an organic chemical, usually primary aromatic amines, into diazonium salts is known as diazotization or dissociation. Diazonium groups are extremely unstable, thus they can't be stored. As a result, we usually use them right away after they've been prepared. The reaction of nitrous acid with aromatic amines is one of the most common ways to make diazonium salt.


The diazonium salt is formed by the interaction of aniline (aromatic amine) with nitrous acid. The benzene diazonium chloride is this salt. Nitrous acid is a very dangerous gas. As a result, it's usually made by reacting NaNO2 with a mineral acid throughout the reaction.