In basic conditions, benzene diazonium chloride is converted in to diazohydroxide and diazoate as both of which are not electrophilic and do not couple with aniline. coupling of benzene diazonium chloride and aniline is done under acidic conditions (pH = 4-5) .

The Coupling Reaction of Aryldiazonium Chloride with Aniline

The coupling reaction of aryldiazonium chloride with aniline is an important organic reaction that is widely used in the synthesis of azo dyes. This reaction involves the formation of an azo compound, which is characterized by the presence of a diazo group (-N=N-) bonded to an aromatic ring.

Reaction Mechanism:
The reaction proceeds through a substitution mechanism, where the diazonium chloride reacts with aniline to form the azo compound. The mechanism can be explained in the following steps:

1. Formation of the diazonium salt: The aryldiazonium chloride is formed by the reaction of an arylamine with sodium nitrite and hydrochloric acid. This reaction is known as diazotization and involves the conversion of the amino group (-NH2) into a diazonium group (-N2+ Cl-).

2. Nucleophilic attack by aniline: In the presence of a base, such as sodium acetate or sodium carbonate, aniline acts as a nucleophile and attacks the diazonium ion. The nitrogen atom of aniline donates a pair of electrons to the diazonium ion, resulting in the formation of a new carbon-nitrogen bond.

3. Rearrangement and elimination: The initially formed azo compound is unstable and undergoes rearrangement to form a more stable isomer. This rearrangement is accompanied by the elimination of a molecule of nitrogen gas. The resulting compound is an azo dye, which is characterized by the presence of a diazo group (-N=N-) bonded to two aromatic rings.

Reaction Conditions:
The coupling reaction of aryldiazonium chloride with aniline is typically carried out under mild conditions. The key reaction conditions include:

1. Temperature: The reaction is usually carried out at room temperature or slightly elevated temperatures. Higher temperatures can lead to side reactions and decomposition of the reactants.

2. pH: The reaction is highly dependent on the pH of the reaction mixture. The addition of a base, such as sodium acetate or sodium carbonate, is necessary to maintain an alkaline pH. This facilitates the nucleophilic attack by aniline and enhances the reaction efficiency.

3. Solvent: The reaction is commonly carried out in an organic solvent, such as ethanol or water-ethanol mixture. The choice of solvent depends on the solubility of the reactants and the desired reaction rate.

Applications:
The coupling reaction of aryldiazonium chloride with aniline has several applications in the synthesis of azo dyes. Azo dyes are widely used in various industries, including textiles, paints, and printing. They exhibit vibrant colors and good lightfastness, making them suitable for dyeing and coloring materials.

In addition to the synthesis of azo dyes, the coupling reaction of aryldiazonium chloride with aniline can also be used for the functionalization of aromatic compounds. By varying the substituents on the arylamine and aniline, a wide range of azo compounds can be synthesized with different properties and functionalities.

Overall, the coupling reaction of aryldiazonium chloride with aniline is a versatile and important reaction in organic chemistry, with applications in the synthesis of azo dyes and the functionalization of aromatic compounds.