Diazonium Salt Properties

Chemical Properties of Diazonium Salt Preparation and Properties

The reactions of diazonium salts can be broadly divided into two categories :

• Reaction involving displacement of Nitrogen.
• Reaction involving retention of diazo group (Coupling reaction)

→ Nitrogen Substitution Reaction : In these reactions —N₂²Cl group is substituted by other atoni or group.

→ These group releases nitrogen gas from aromatic ring. Free nitrogen releases as a gas from the reaction mixture.

→ SynthesIs of aryl halide : When benzene diazonium chloride react with Cu₂Cl₂ and HCl or Cu₂ Br₂ and HBr then (—N₂Cl group) is replaced by —CI or —Br respectively. This reaction is called Sandmeyer reaction.

→ Gatterniann Reaction It is a form of Sandmeyer’s reaction in which aromatic diazonium salt reacts with Cu/HCl, in presence of halogen acid and Cu powder to form aryl halide.

→ When benzene diazonium chloride is treated with fluoroboric acid, then benzene diazonium fluoroborate is precipitated which decomposes on heating and give flourobenzene.

→ This reaction is known as Balz-Schiemann reaction. Benzene diazonium salt when boiled with potassium iodide solution forms iodobenzene.

→ Synthesis of Nitro Compounds : Benzene diazonium chloride reacts with aqueous sodium nitrite solution in the presence of copper and forms nitrobenzene.

→ Synthesis of Phenol : Benzene diazonium chloride on distillatión with steam gives phenol.

Synthesis of Cyano Compound : Benzene diazonium chloride reacts with cuprous cyanide to form cyanobenzene.

→ Synthesis of Thiol : Benzene diazonium chloride reacts with potassium hydrosuiphide, the thiophenol is formed.

→ Oxidation : Mild reducing agents like hypophosphor ous acid or ethanol oxidised benzene diazonium chloride to benzene.

→ Reduction Benzene diazomum chloride when reduced in the presence of SnCl₂ and HCl, it gives phenyl hydrazine.

→ If benzene diazonium chloride reduces with Zn and HCl then aniline is formed.

→ Synthesis of Dlphenyl : Benzene cliazonium chloride when treated with benzene in the basic medium gives diphenyl.

Coupling Reactions : The azo products obtained have an extended conjugate system having both the aromatic rings joined through the —N = N— bond.

These compounds are often coloured and are used as dyes.

These reaction are as follows :

→ Reaction with Aniline : Diazonium chloride reacts with aniline and form paraaminoazobenzene. It is an example of electrophobic reaction.

→ Reation with Phenol : Benzene diazonium chloride reacts with pheno’ to form para hydroxyazo benzene.

→ Reaction with β-Naphthol Diazonium chloride reacts with -naphtho1 to form red coloured phenylazo-β-naphthol dye.

→ Reaction with Dimethyl Aniline : Dimethyl aniline reacts with benzene diazonium chloride to form p-Dimethylamino azo benzene.

Chemistry Notes