Consider the following statements about the coupling reactions of benzenediazonium chloride.
(A) In coupling reactions, the diazo group is retained in the product.
(B) The azo products have an extended conjugate system in which both the aromatic rings are joined through the –N=N– bond.
(C) In the reaction of benzenediazonium chloride with phenol, the phenol molecule is coupled with the diazonium salt at its ortho position.
(D) The reaction of benzenediazonium chloride with aniline yields p-aminoazobenzene.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (B) and (D) only
In a coupling reaction the diazonium ion attacks an activated ring such as phenol or aniline as an electrophile. Nitrogen is not lost; the product is an azo compound, often coloured and used as a dye.
(A) In coupling reactions, the diazo group is retained in the product. — True. Coupling is the reaction of diazonium salts that involves retention of the diazo group, unlike the replacement reactions where nitrogen escapes.
(B) The azo products have an extended conjugate system in which both the aromatic rings are joined through the –N=N– bond. — True. This extended conjugation is why these compounds are coloured.
(C) In the reaction of benzenediazonium chloride with phenol, the phenol molecule is coupled with the diazonium salt at its ortho position. — False. Phenol is coupled at its para position, giving p-hydroxyazobenzene:
\( \displaystyle \ce{C6H5N2^+Cl^- + C6H5OH} \xrightarrow{\ce{OH^-}} \ce{C6H5-N=N-C6H4-OH + Cl^- + H2O} \)
(D) The reaction of benzenediazonium chloride with aniline yields p-aminoazobenzene. — True. Aniline also couples at its para position:
\( \displaystyle \ce{C6H5N2^+Cl^- + C6H5NH2} \xrightarrow{\ce{H^+}} \ce{C6H5-N=N-C6H4-NH2 + Cl^- + H2O} \)
NCERT (2026-27 edition):
9.9 Chemical Reactions – “B. Reactions involving retention of diazo group … 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. Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para position is coupled with the diazonium salt to form p-hydroxyazobenzene. This type of reaction is known as coupling reaction. Similarly the reaction of diazonium salt with aniline yields p-aminoazobenzene.”