Phenol can be prepared from each compound in List-I. Match the compound in List-I with the reagent or condition in List-II used for it.
| List-I (Starting compound) | List-II (Reagent or condition) |
|---|---|
| (A) Chlorobenzene | (I) Warming with water |
| (B) Benzenesulphonic acid | (II) Oxidation by air, then treatment with dilute acid |
| (C) Benzenediazonium chloride | (III) Fusion with NaOH at 623 K and 320 atm, then acidification |
| (D) Cumene | (IV) Heating with molten NaOH, then acidification |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-III, B-IV, C-I, D-II
Two of these routes use sodium hydroxide to give sodium phenoxide, which is then acidified; they differ in the conditions. The other two give phenol in a different way: a diazonium salt is hydrolysed, and cumene is oxidised.
(A) Chlorobenzene — This matches (III) Fusion with NaOH at 623 K and 320 atm, then acidification. The aryl halide needs this high temperature and pressure.
\( \displaystyle \ce{C6H5Cl} \xrightarrow[\text{623 K, 320 atm}]{\ce{NaOH}} \ce{C6H5O^-Na+} \xrightarrow{\ce{H+}} \ce{C6H5OH} \)
(B) Benzenesulphonic acid — This matches (IV) Heating with molten NaOH, then acidification. Benzenesulphonic acid, made by sulphonating benzene with oleum, gives sodium phenoxide on heating with molten NaOH.
\( \displaystyle \ce{C6H5SO3H} \xrightarrow[\Delta]{\text{molten }\ce{NaOH}} \ce{C6H5O^-Na+} \xrightarrow{\ce{H+}} \ce{C6H5OH} \)
(C) Benzenediazonium chloride — This matches (I) Warming with water. The diazonium salt is hydrolysed and nitrogen gas is given off.
\( \displaystyle \ce{C6H5N2^+Cl^- + H2O} \xrightarrow{\text{warm}} \ce{C6H5OH + N2 + HCl} \)
(D) Cumene — This matches (II) Oxidation by air, then treatment with dilute acid. Air gives cumene hydroperoxide, which dilute acid splits into phenol and acetone.
\( \displaystyle \ce{C6H5CH(CH3)2} \xrightarrow{\ce{O2}\text{ (air)}} \ce{C6H5C(CH3)2OOH} \xrightarrow{\ce{H+}/\ce{H2O}} \ce{C6H5OH + CH3COCH3} \)
NCERT (2026-27 edition):
7.4.2 Preparation of Phenols – “1. From haloarenes Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced (Unit 6, Class XII).”
“2. From benzenesulphonic acid Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.”
“3. From diazonium salts … Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids (Unit 9, Class XII).”
“4. From cumene … Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide. It is converted to phenol and acetone by treating it with dilute acid.”