Benzene Diazonium Chloride Preparation and Properties
Aryl Diazonium Salt Preparation and Properties
Benzene Diazonium Chloride
The general molecular formula of aryldiazonium salt is PhN
2X (e.g. benzene diazonium chloride PhN
2Cl) and is a colorless and crystalline solids which turns brown on exposour to air. It is extreamily soluble in water and sparingly soluble in ethanol and glacial aeteic acid and insoluble in ether.
Preparation of Benzene Diazonium Chloride
Benzene diazonium chloride is prepared by the addition of one mole concentrated solution of sodium nitrite to one mole of aniline dissolved in three moles of HCl at 0-5°C.
Chemical Properties of Benzene Diazonium Chloride
Aryl diazonium salts give two types of reactions-
1. -N2X is replaced by other univalent atom or group with the liberation of nitrogen gas.
2. Two nitrohen atoms are retained in the product.
1. Replacement Reaction with the liberation of N2 gas
Replacement by Hydrogen
Aryl diazonium salts is reduced by hypochlorous acid (H
3PO
2) in the presence of cuprous chloride, corresponding hydrocarbon are obtained.
Replacement by Chlorine or Bromine
When aquous solution of diazonium salts is heated with cuprous chloride or cuprous bromide, chlorobenzene or bromobenzene are obtained.
Replacement by Iodine
When aquous solution of diazonium salts is heated with potassium iodide, iodobenzene is obtained.
Replacement by Fluorine
Aryl fluoride is prepared by adding the diazonium salt solution to fluoroboric acid (HBF
4) followed by washed and dried the fluoroborate ppt.. This reaction is known as
Balz-Schiemann Reaction.
Replacement by Hydroxyl Group
When aqueous solution of diazonium salt solution is heated, the diazonium group is replaced by -OH group and produce phenol. This reaction is conducted in acidic medium to prevent the coupling of phenol with the unreacted diazonium salt.
Replacement by Cyano Group
Diazo group is replaced by -CN and produce phenylcyanide or benzonitrile with cuprous cyanide. This reaction is known as
Sandmeyer Reaction
Replacement by Alkoxy Group
When aqueous solution of diazonium salt is heated with excess of alcohol, the diazogroup is replaced by alkoxy group and produce alkyl aryl ether.
Replacement by Nitro Group
When diazonium salt is heated with fluoroboric acid, benzenediazonium fluoroborate is obtained. This fluoroborate is heated with aqueous sodium nitrite, the diazogroup is replaced by NO
2 group and produce nitrobenzene.
Replacement by Aryl Group
When diazonium salt is treated with aromatic hydrocarbon in the presence of NaOH, diaryl obtained.
2. Reactions Involving the Retention of N2 in the product
Reduction of Benzene Diazonium Chloride
When diazonium salt is reduced to sodium sulphite, phenylhydrazine obtained.
Coupling Reaction of Benzene Diazonium Chloride
When diazonium salt is reacts with aromatic ring of phenols and tertiary amines, azo compounds are formed.
Reaction of 1° and 2° Amines With Benzene Diazonium Chloride
When diazonium salt is reacts with 1° and 2° aromatic amines, aminoazo benzene is formed.
Reaction of Alkali With Benzene Diazonium Chloride
When diazonium salt is reacts with alkali, diazohydroxide is obtained.
