Benzenediazonium chloride reacts with aniline in a mildly acidic medium. Which of the following is the product of this reaction?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → p-Aminoazobenzene
This is a coupling reaction, in which the diazo group is retained.
The diazonium ion acts as an electrophile and attacks the aniline ring at the para position to the –NH2 group (electrophilic substitution). The two rings are joined through an –N=N– bond:
\( \displaystyle \ce{C6H5N2^+Cl^- + C6H5NH2} \xrightarrow{\ce{H+}} \ce{C6H5-N=N-C6H4-NH2 + HCl} \)
The product, p-aminoazobenzene, is a yellow dye.
Why the other options are incorrect
Option (1) p-Hydroxyazobenzene — Incorrect. This orange dye is formed when the diazonium salt couples with phenol in alkaline medium, not with aniline.
Option (2) o-Aminoazobenzene — Incorrect. Coupling takes place at the para position of aniline, not the ortho position.
Option (4) Diphenylamine — Incorrect. Forming \( \ce{C6H5NHC6H5} \) would need the loss of nitrogen; in coupling the –N=N– unit stays in the product.
NCERT (2026-27 edition):
9.9 Chemical Reactions – “The azo products obtained have an extended conjugate system having both the aromatic rings joined through the –N=N– bond.” … “Similarly the reaction of diazonium salt with aniline yields p-aminoazobenzene. This is an example of electrophilic substitution reaction.”