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Benzene Diazonium Chloride

Last updated date: 23rd May 2024
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Diazonium Salts: An Overview

Amines are compounds and functional groups in chemistry, including a basic N atom with a lone pair. Amines are ammonia derivatives with one or more H atoms substituted by a substituent like an alkyl or aryl group. Diazonium salts are organic compounds with a formula $Ar-{{N_2}^{+}}-{{X}^{-}}$, where Ar is for an aromatic compound. Aryl diazonium salts are usually used as intermediates in chemical synthesis. The diazonium group is also easily replaced by a variety of functional groups, including –I, –OH, –F, –CN, and –H, that can't be directly substituted into the aromatic ring. Hence, the importance of compounds like Benzene Diazonium Chloride significantly increases in organic synthesis and in many industrial applications.

Benzene Diazonium Cation

Benzene Diazonium Cation

What are Diazonium Salts?

In “Diazonium salts”, the word di refers to two, aza stands for N, and the last term onium suggests the ionic nature of the compound. As a result, diazonium salts refer to ionic compounds containing Triple bonded N atoms.

Diazonium compounds are organic compounds with the molecular formula $R-{{N_2}^{+}}-{{X}^{-}}$, where R may be any alkyl or aryl group (generally aryl groups) and X are often halogens, hydrogen sulphate, or alternative organic compounds.

Examples of Diazonium Salts

Examples of Diazonium Salts

Properties of Diazonium Salt

The Physical Properties of Diazonium Compounds are as Follows:

  • Diazonium salts are colourless crystalline compounds that darken once exposed to air.

  • When heated, several diazonium salts of nitrates and perchlorates explode. As a result, these salts are not separated and are utilised in different synthetic preparations as soon as they're produced in situ.

  • At room temperature, however, diazonium and Zn chloride double salts, also diazonium and trifluoroborate double salts, are stable and are used as dye salts in the manufacture of naphthol-AS colouring material.

Preparation of Diazonium Salts

At 273–278K, aniline reacts with nitrous acid to get benzene diazonium chloride. Once sodium nitrite reacts with acid, nitrous acid is formed within the reaction mixture. The method of diazotization is the transformation of primary aromatic amines into diazonium ions. Because of its volatility, diazonium salt is rarely kept and is used right away when produced.

Preparation of Diazonium Cation

Preparation of Diazonium Cation

Benzene Diazonium Chloride

Benzenediazonium chloride could be a colourless solid and has numerous uses in chemistry. If the temperature is raised in aqueous benzene diazonium chloride, it decomposes to phenol. Therefore, benzene diazonium is prepared once it's needed for some purpose.

  • Benzene diazonium chloride exists in solid form.

  • There are no melting or boiling point values because it decomposes promptly.

Preparation of Benzene Diazonium Chloride

Benzene diazonium chloride is prepared by the reaction of aniline. Once aniline reacts with nitrous acid at low temperatures (0-50℃), benzene diazonium chloride is given as the product. If the temperature is raised, benzene diazonium chloride decomposes to phenol.

Preparation of Benzene Diazonium Chloride

Preparation of Benzene Diazonium Chloride

Reactions of Benzene Diazonium Chloride

We can categorise reactions of benzene diazonium chloride into two categories.

  1. Reactions of substituting diazonium group by another group

  2. Coupling reactions of diazonium ions

The Reaction of Substituting the Diazonium Group with Another Group

Benzene diazonium chloride is often converted to different aromatic compounds like chlorobenzene, phenol, bromobenzene, etc.

Chlorobenzene may be prepared with the help of benzene diazonium chloride. Benzene diazonium chloride is treated with CuCl (Copper(I) chloride). Rather than CuCl, you can use copper powder with HCl. During this reaction, Cu+ ions behave as a catalyst. Benzene may also be prepared by benzene diazonium chloride reacting with ${{H}_{3}}P{{O}_{2}}$, ethanol as the chemical agent.

Coupling Reaction of Diazonium Ions

Benzene diazonium chloride reacts with phenol, β-naphthol, aniline, and 2-methyl aniline to form group dyes. In these reactions, the HCl molecule is eliminated.

Aniline and Benzene Diazonium Chloride Reaction

A coupling reaction between benzene diazonium chlorides with aniline in an acidic medium takes place to give a yellow colour compound. In this reaction, the nitrogen in the diazonium ion is lost and forms the bridge between two benzene rings forming an electrophilic substitution reaction. As a result, para-aminobenzene is formed as a final product.

Formation of Para Amino Benzene

Formation of Para Amino Benzene

Importance of Diazonium Salts

Benzene diazonium chloride is used as a raw material in the production of dyes. They find application within the dye and pigment industries and are used to manufacture coloured fabrics.

  • Due to their property of breaking down near ultraviolet light, they're used in document reproduction, i.e., copying of papers.

  • They are useful in the synthesis of an outsized variety of organic compounds, particularly aryl derivatives.

  • Direct halogenation is not an appropriate methodology for preparing aryl iodides and fluorides. However, diazonium salts can simply be used to manufacture cyanobenzene.

  • It is impracticable to prepare substituted aromatic compounds by direct substitution in benzene. For these compounds, we tend to use the replacement of the diazo group in diazonium salts.

  • They are used as intermediates for introducing –F, –Br, –Cl, –I, –NO2, –OH, and –CN groups into the aromatic ring.

Interesting Fact

  • The German organic chemist Johann Peter Griess (1829–88), developed the diazotization of aryl amines.

  • Many diazonium salts are highly explosive and decompose violently once heated. Several diazonium salts are susceptible to displacement reactions by numerous substrates, generating nitrogen as a by-product.

Important Question

Q1. What is Sandmeyer's reaction?

Ans: $Ar-N_{2}^{+}-{{X}^{-}}\to Ar-X+{{N}_{2}}$

Cl or Br replaces the diazonium group once a freshly prepared diazonium salt solution is combined with cuprous chloride or cuprous bromide. N is slowly created at room or higher temperatures, and the aryl chloride or aryl bromide is often separated from the reaction mixture after several hours. A cuprous halide-based approach is known as the Sandmeyer reaction.


Diazonium salts are named by suffixing diazonium to the name of the parent organic compound (hydrocarbon) from which they're formed, followed by the name of anion like chloride, hydrogen sulphate, etc. The N2+ group is termed diazonium salt. Diazonium salts may also be used to create azo compounds by interacting with different aromatic molecules. Diazonium salts are formed by combining an alkyl or aryl primary amine with sodium nitrite in the presence of acid (HCl).

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FAQs on Benzene Diazonium Chloride

1. What is Gattermann's reaction?

Gattermann reaction in chemistry is named after the German chemist Ludwig Gattermann, which is additionally termed the Gattermann formylation and also the Gattermann salicylaldehyde synthesis. The Gattermann reaction, which employs copper powder and hydrogen halide to carry out the synthesis rather than cuprous halide, is often utilised. No cuprous halide or copper is needed to replace the diazonium group with I; the diazonium salt and KI are merely mixed together and allowed to react. $Ar-N_{2}^{+}-{{X}^{-}}\to ArI+{{N}_{2}}+{{X}^{-}}$

The Gattermann reaction is the formulation of aromatic ring compounds. Formylation is the method where the formyl group is connected to the hydrocarbon.

2. What is the synthesis of phenol from diazonium salt?

Diazonium salts react with water to form phenols.

$Ar-N_{2}^{+}-{{X}^{-}}+{{H}_{2}}O\to Ar-OH+{{N}_{2}}+{{H}^{+}}$

Benzene diazonium chloride on heating in the presence of an aqueous solution provides phenol as the main product and N gas as a byproduct. Benzene diazonium chloride is hydrolyzed to phenols by treating it with dilute acids. So, the preparation of phenol from benzene diazonium chloride involves a hydrolysis reaction. This reaction is sluggish in cold diazonium salt solutions, which is why diazonium salts are used straight soon after synthesis; it may be made the key reaction of diazonium salts at higher temperatures.

3. What are the physical properties of diazonium salt?

Diazonium salts are colourless crystalline compounds that get dark in colour once exposed to air. Once heated or dried, several diazonium salts of nitrates and perchlorates explode. As a result, these salts don't seem to be separated and are utilised in different synthetic preparations as soon as they're made in situ. Double salts of diazonium and Zn chloride, in addition to double Salts of diazonium and trifluoroborates, are stable at 298K. The melting point of diazonium salt is more than 124°C.