Benzene Diazonium Chloride
The general molecular formula of aryldiazonium salt is PhN2X (e.g., benzene diazonium chloride PhN2Cl). It is a colorless and crystalline solid which turns brown on exposure to air. It is extremely soluble in water, sparingly soluble in ethanol and glacial acetic acid, and completely insoluble in ether.
Preparation of Benzene Diazonium Chloride
Benzene diazonium chloride is prepared by the addition of one mole of a concentrated solution of sodium nitrite to one mole of aniline dissolved in three moles of HCl at 0-5°C.
IIT-JEE (Main) Shift-2 | Date: 23.1.2025
Number of sp3 hybridised carbon atoms in C is:
Solution:
Total 4 sp3 hybridised carbon atoms are present in C.
 Shift-2 Date:23.1.2025)
Chemical Properties of Benzene Diazonium Chloride
Aryl diazonium salts give two distinct types of reactions:
- 1. Replacement reactions: The -N2X group is replaced by another univalent atom or group with the dynamic liberation of nitrogen gas.
- 2. Retention reactions: The two nitrogen atoms are completely retained in the structured end product.
1. Replacement Reaction with the liberation of N2 gas
Replacement by Hydrogen
Aryl diazonium salts are reduced by hypophosphorous acid (H3PO2) in the presence of cuprous chloride; the corresponding hydrocarbon configurations are obtained.
Replacement by Chlorine or Bromine
When an aqueous solution of diazonium salts is heated with cuprous chloride or cuprous bromide, chlorobenzene or bromobenzene products are smoothly obtained.
Replacement by Iodine
When an aqueous solution of diazonium salts is heated along with potassium iodide, iodobenzene is isolated.
Replacement by Fluorine
Aryl fluoride is easily prepared by adding the diazonium salt solution to fluoroboric acid (HBF4), followed by washing and drying the resulting fluoroborate precipitate. This reaction process is widely designated as the Balz-Schiemann Reaction.
Replacement by Hydroxyl Group
When an aqueous solution of diazonium salt is gently heated, the diazonium group is replaced by an -OH group to produce phenol. This specific reaction path is safely conducted within an acidic medium environment to completely prevent the automatic coupling of formed phenol with any remaining unreacted diazonium salt.
Replacement by Cyano Group
The diazo group structure is strategically replaced by a -CN group to create phenyl cyanide or benzonitrile utilizing cuprous cyanide. This reaction sequence is standardly identified as the Sandmeyer Reaction.
Replacement by Alkoxy Group
When an aqueous solution of diazonium salt is heated with an excess volume of alcohol, the diazo group components are substituted by an alkoxy group layout to yield an alkyl aryl ether variant.
Replacement by Nitro Group
When diazonium salt setups are processed with fluoroboric acid, benzene diazonium fluoroborate is synthesized. If this intermediate fluoroborate is heated alongside aqueous sodium nitrite, the diazo group is replaced by an -NO2 component to produce clean nitrobenzene.
Replacement by Aryl Group
When a diazonium salt layout is efficiently treated alongside an aromatic hydrocarbon within the presence of NaOH, a diaryl arrangement is securely obtained.
2. Reactions Involving the Retention of N2 in the product
Reduction of Benzene Diazonium Chloride
When a diazonium salt is properly reduced with sodium sulfite, phenylhydrazine structures are established.
Coupling Reaction of Benzene Diazonium Chloride
When diazonium salts are reacted with the aromatic rings of phenols and tertiary amines, vibrant azo compounds are produced.
IIT-JEE (Main) Shift-1 | Date: 30.1.2024
Find B in the following reaction:
Solution:
A is aniline and B is p-hydroxy azobenzene.
Reaction of 1° and 2° Amines With Benzene Diazonium Chloride
When a diazonium salt is reacted with 1° and 2° aromatic amines, aminoazobenzene structures are generated.
Reaction of Alkali With Benzene Diazonium Chloride
When a diazonium salt undergoes a structural chemical reaction with an alkali solution, diazohydroxide variations are acquired.