In the following reaction, identify the product D.

Phenol with Zn dust gives A; A with CH3Cl and anhydrous AlCl3 gives B; B with K2Cr2O7 and H2SO4 gives C; C with H2SO4 and HNO3 gives D

Answer & explanation

Correct answer: option 4

The correct answer is Option (4) → m-Nitrobenzoic acid

The sequence converts phenol into benzene, puts a methyl group on the ring, oxidises it to –COOH and then nitrates the ring. The –COOH group is deactivating and meta-directing, so the nitro group enters the meta position.

First, phenol is reduced to benzene (A) by heating with zinc dust:

\( \displaystyle \ce{C6H5OH + Zn} \xrightarrow{\Delta} \ce{C6H6 + ZnO} \)

Benzene then undergoes Friedel–Crafts alkylation: anhydrous \( \ce{AlCl3} \) is the Lewis acid that pulls \( \ce{Cl-} \) away from \( \ce{CH3Cl} \) and gives the electrophile \( \ce{CH3+} \); the product is toluene (B):

\( \displaystyle \ce{C6H6 + CH3Cl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{C6H5CH3 + HCl} \)

Acidified potassium dichromate oxidises the side chain to a carboxyl group and gives benzoic acid (C):

\( \displaystyle \ce{C6H5CH3} \xrightarrow{\ce{K2Cr2O7/H2SO4}} \ce{C6H5COOH} \)

Finally, the nitrating mixture provides the nitronium ion, \( \ce{NO2+} \), and the –COOH group directs it to the meta position; the product is m-nitrobenzoic acid (D):

\( \displaystyle \ce{C6H5COOH + HNO3} \xrightarrow{\text{conc. }\ce{H2SO4}} \text{m-}\ce{O2N-C6H4-COOH + H2O} \)

Why the other options are incorrect

Option (1) o-Nitrobenzoic acid — Incorrect. An ortho product would need an ortho/para director on the ring, such as the –\( \ce{CH3} \) of toluene; by the nitration step that group has already been oxidised to –COOH.
Option (2) p-Nitrobenzoic acid — Incorrect. For the same reason, the para product would come from nitrating toluene first and oxidising afterwards, the reverse of the order given.
Option (3) o,p-Dinitrobenzoic acid — Incorrect. The –COOH group deactivates the ring and is meta-directing, so neither ortho nor para substitution occurs, let alone two of them.

NCERT (2026-27 edition):
Reaction of Phenol with Zinc Dust – “Phenol is converted to benzene on heating with zinc dust.”

NCERT (2026-27 edition):
Ring Substitution – “Aromatic carboxylic acids undergo electrophilic substitution reactions in which the carboxyl group acts as a deactivating and meta-directing group. They however, do not undergo Friedel-Crafts reaction (because the carboxyl group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group).”