Which of the following reactions are given by Phenols?
(A) Nitration
(B) Halogenation
(C) Oxidation
(D) Acetylation
Choose the correct answer from the options given above:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B), (C) and (D)
The –OH group of phenol releases electrons into the benzene ring by resonance, so the ring is strongly activated towards electrophilic substitution at the ortho and para positions. The –OH group itself can also react, and phenol is easily oxidised.
(A) Nitration — Correct. Even dilute nitric acid at low temperature nitrates phenol, giving a mixture of ortho and para nitrophenols; concentrated nitric acid gives picric acid.
\( \displaystyle \ce{C6H5OH + HNO3} \xrightarrow[\text{298 K}]{\text{dil.}} o\text{-}\ce{O2NC6H4OH}\ \text{and}\ p\text{-}\ce{O2NC6H4OH} + \ce{H2O} \)
(B) Halogenation — Correct. With bromine water phenol at once gives a white precipitate of 2,4,6-tribromophenol; in a solvent of low polarity such as \( \ce{CS2} \), monobromophenols are formed.
\( \displaystyle \ce{C6H5OH + 3Br2(aq) -> C6H2Br3OH v + 3HBr} \)
(C) Oxidation — Correct. Chromic acid oxidises phenol to benzoquinone; in air phenol slowly turns dark for the same reason.
\( \displaystyle \ce{C6H5OH} \xrightarrow[\text{oxidation}]{\ce{Na2Cr2O7/H2SO4}} p\text{-benzoquinone} \)
(D) Acetylation — Correct. The –OH group reacts with acetic anhydride or acetyl chloride to form an ester, phenyl acetate; a base such as pyridine takes up the acid formed.
\( \displaystyle \ce{C6H5OH + (CH3CO)2O} \xrightarrow{\ce{H+}} \ce{C6H5OCOCH3 + CH3COOH} \)
NCERT (2026-27 edition):
Electrophilic Aromatic Substitution – “In phenols, the reactions that take place on the aromatic ring are electrophilic substitution reactions (Unit 9, Class XI). The –OH group attached to the benzene ring activates it towards electrophilic substitution. Also, it directs the incoming group to ortho and para positions in the ring …”
“(i) Nitration: With dilute nitric acid at low temperature (298 K), phenol yields a mixture of ortho and para nitrophenols.”
“… (ii) Halogenation: On treating phenol with bromine, different reaction products are formed under different experimental conditions.”