Method of Preparation of Diazonium Salts: An Overview and Properties

Animes are organic compositions that incorporate and are positioned on one or more atoms of nitrogen. Amines are constructed to resemble ammonia in which the nitrogen has the capability of bonding with upto three hydrogens. However, amines also do have their additional characteristics on the basis of their carbon connectivity. In an anime organic substituents for example, alkyl and aryl can replace one or more hydrogen atoms from ammonia. Another type of organic molecule containing nitrogen without being an anime is called amide. It has carboxylic acid derivatives containing trivalent ammonia in the ground state. Amines and amides are very different from one another in terms of its characteristics and compositions, hence understanding their differentiation is very essential. 

Key Terms: Carboxylic acid, amines, Diazonium Salts, benzene, organic, compounds, nitrogen, atoms, ammonia, amides

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What are Diazonium Salts? 

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Diazonium Salts are important Organic salts that are characterized by the presence of -N₂⁺X^- a group where X can be any organic or inorganic anion. Their name is 'Di-Azonium' because they contain two nitrogen atoms (N₂) in their cationic part. Chemically, they are represented as R-N₂⁺X^-, where R is any alkyl or aryl group. 

Some examples of of Diazonium Salts:

1. Benzene Diazonium Chloride

In this case, the R group is Benzene ring and Anion (X) is Cl^-

Benzene Diazonium Chloride

2. Benzene Diazonium Hydrogen Sulfate

Benzene Diazonium Hydrogen Sulfate

In this case, the R group is Benzene ring and the Anion (X) group is Hydrogen Sulfate (HSO₄^-). 

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How To Prepare Diazonium Salts?

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• The process of preparing Diazonium Salts is called diazotization. It is also sometimes called dissociation. 
• Generally, primarily aromatic Amines are used to prepare the Diazonium Salts. However, other types of organic compounds may also be used. 
• For converting Aromatic Amines into Diazonium Salts, the most common method is a diazotization reaction between the Aromatic Amine (acting as a base) and Nitrous Acid (acting as an acid). 

Lets study the preparation of Benzene Diazonium Chloride in detail to understand this reaction better. 

• To prepare Benzene Diazonium Chloride, Aniline (an Aromatic Amine) is reacted with Nitrous Acid. 
• For this reaction, the Nitrous Acid is prepared in situ as a part of the reaction itself. NaNO₂ is reacted with any mineral acid to produce Nitrous Acid. This is important because Nitrous Acid is a highly toxic gas, and so needs to be generated on site. 
• While preparing Diazonium Salts, Temperature must be kept below 5º C because most of the Diazonium Salts are stable in this temperature only. The variation in temperature will affect the production of the Diazonium Salt. 

The reaction is shown below. 

Preparation of Diazonium Salts

Note: In this reaction, the mineral acid used was HCl because we wanted to have Chloride as the Anion. We can change the mineral acid if we want a different Anion. 

For example, Benzene Diazonium Hydrogen Sulphate can be prepared using Sulphuric Acid as the mineral acid. 

Diazonium Hydrogen Sulphate can be prepared using Sulphuric Acid as the mineral acid

Formation of Benzene Diazonium Chloride Reaction Mechanism

Step 1: Formation of Nitrous Acid

Step 2: Reaction of Nitrous Acid with HCl to produce HNO₂ + NaCl

Step 3: Reaction of Aniline with the above formed products in the presence of HCl at 0 to 5 degree Celsius. 

Step 4: Formation of Benzene Diazonium Chloride. 

Formation of Benzene Diazonium Chloride Reaction Mechanism

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What are the Properties of Diazonium Salts? 

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Some of the important properties of Diazonium Salts are discussed below. 

• They are water soluble Salts, and are ionic in nature. 
• The Diazonium Salts have two nitrogen atoms, out of which only one is charged. 
• Diazonium Salts with an aryl R group exit in the form of colourless crystalline solids.
• The naming of the Diazonium Salts are on the basis of the Anion present in the Diazonium group and the R group. For example: If the R group is Benzene, and the Anion is Chloride, then the Diazonium Salt will be called Benzene Diazonium Chloride. 

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What is the Importance of Diazonium Salts?

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• They are an important raw material for dye and pigment industries where they are frequently used to make dyed fabrics. 
• They can be used to produce a large number of other organic compounds. 
• They are immensely useful in document reproduction. This is because they have an unique property of breaking down in the presence of ultraviolet lights. 
• Diazonium Salts can be used to produce cyanobenzene, which is otherwise very difficult to produce. 

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