Question

Benzene diazonium chloride on reaction with phenol in weakly basic medium gives

• A. Azobenzene
• B. Benzene
• C. Chlorobenzene
• D. p-hydroxyazobenzene

Hint:

Coupling with Phenol gives an Orange dye (p-hydroxyazobenzene). Coupling with Aniline gives a Yellow dye (p-aminoazobenzene).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Diazonium salts undergo coupling reactions with activated aromatic compounds, such as phenols, in a weakly basic medium to form azo dyes. This reaction is commonly used in the synthesis of azo compounds, which have a wide variety of applications, particularly in dyeing and pigment industries.
Step 2: Detailed Explanation:
In a weakly basic medium (pH 9-10), phenol is deprotonated to form the phenoxide ion (\( C_6H_5O^- \)). The phenoxide ion is highly activating toward electrophilic aromatic substitution reactions because the negative charge on the oxygen atom delocalizes into the aromatic ring, making the ring more reactive towards electrophiles.
The diazonium cation (\( C_6H_5N_2^+ \)) acts as an electrophile and attacks the aromatic ring of the phenoxide ion, typically at the para position due to steric and electronic reasons. This results in the formation of a product where an azo group (-N=N-) is attached to the aromatic ring. The resulting product is an orange azo dye known as p-hydroxyazobenzene.
Step 3: Final Answer:
The product formed in this reaction is p-hydroxyazobenzene.