The most suitable synthetic procedure involving various reactions to convert benzene to p-bromoaniline will be
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (i) Nitration (ii) Reduction of nitro group to amine (iii) Acetylation of amino group to form substituted amide (iv) Bromination of substituted amide (v) Deprotecting acetyl group from substituted amide.
The –\( \ce{NH2} \) group of aniline strongly activates the ring. Aniline reacts with bromine water even at room temperature and gives 2,4,6-tribromoaniline at once, so a mono-bromo product cannot be obtained directly.
To control this, the amino group is protected by acetylation. In acetanilide (–\( \ce{NHCOCH3} \)), the nitrogen lone pair is also shared with the adjacent C=O group by resonance, so the ring is only moderately activated. The bulky group also favours substitution at the para position. After bromination, the acetyl group is removed by hydrolysis.
\( \displaystyle \ce{C6H6} \xrightarrow{\text{conc. }\ce{HNO3/H2SO4}} \ce{C6H5NO2} \xrightarrow{\ce{Sn/HCl}} \ce{C6H5NH2} \)
\( \displaystyle \ce{C6H5NH2} \xrightarrow{\ce{(CH3CO)2O}} \ce{C6H5NHCOCH3} \xrightarrow{\ce{Br2/CH3COOH}} \ce{4-BrC6H4NHCOCH3} \)
\( \displaystyle \ce{4-BrC6H4NHCOCH3} \xrightarrow{\ce{H+}\text{ or }\ce{OH-}} \ce{4-BrC6H4NH2} \)
So the correct route is nitration, reduction, acetylation, bromination, then removal of the acetyl group.
Why the other options are incorrect
Option (1) — Incorrect. The acetyl group is removed before bromination, so the free –\( \ce{NH2} \) is brominated and gives 2,4,6-tribromoaniline; the protection serves no purpose.
Option (2) — Incorrect. Direct bromination of aniline gives 2,4,6-tribromoaniline, not the para mono-bromo product.
Option (3) — Incorrect. Benzene cannot be converted directly into aniline by “amination”; aniline is made by nitration and reduction. The bromination step would also give the tribromo product.
NCERT (2026-27 edition):
Bromination – “Aniline reacts with bromine water at room temperature to give a white precipitate of 2,4,6-tribromoaniline.”
“The main problem encountered during electrophilic substitution reactions of aromatic amines is that of their very high reactivity. Substitution tends to occur at ortho- and para-positions. … This can be done by protecting the -NH2 group by acetylation with acetic anhydride, then carrying out the desired substitution followed by hydrolysis of the substituted amide to the substituted amine.”
“… Hence, the lone pair of electrons on nitrogen is less available for donation to benzene ring by resonance. Therefore, activating effect of –NHCOCH3 group is less than that of amino group.”