Question:
Identify the medium required for formation of p-Hydroxyazobenzene from benzene diazonium chloride and phenol.
Identify the medium required for formation of p-Hydroxyazobenzene from benzene diazonium chloride and phenol.
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Phenol must be in the form of the more reactive phenoxide ion for the coupling to occur.
Updated On: Nov 13, 2026
- Strong acidic
- Mild alkaline
- Alcoholic
- Ether
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept
Benzene diazonium chloride couples with phenol to form p-hydroxyazobenzene (an azo dye) through electrophilic substitution at the para position.
Step 2: Role of the Medium
In mild alkaline medium (pH about 9 to 10), phenol forms the phenoxide ion, which is much more reactive towards the weak electrophile.
Step 3: Conclusion
A strongly acidic medium suppresses phenoxide formation. A strongly basic medium destroys the diazonium ion. So mild alkaline medium is needed.
Final Answer:
The coupling needs a mild alkaline medium. \[ \boxed{\text{(B) }\text{Mild alkaline}} \]
Benzene diazonium chloride couples with phenol to form p-hydroxyazobenzene (an azo dye) through electrophilic substitution at the para position.
Step 2: Role of the Medium
In mild alkaline medium (pH about 9 to 10), phenol forms the phenoxide ion, which is much more reactive towards the weak electrophile.
Step 3: Conclusion
A strongly acidic medium suppresses phenoxide formation. A strongly basic medium destroys the diazonium ion. So mild alkaline medium is needed.
Final Answer:
The coupling needs a mild alkaline medium. \[ \boxed{\text{(B) }\text{Mild alkaline}} \]
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