Match List-I with List-II
|
List I (Conversion) |
List II (Reagent) |
| (A) Conversion of phenol to salicylaldehyde | (I) Zinc dust |
| (B) Conversion of phenol to benzene | (II) \(Na_2Cr_2O_7/H_2SO_4\) |
| (C) Conversion of phenol to benzoquinone | (III) \(NaOH\) and \(CO_2/H^+\) |
| (D) Conversion of phenol to o-hydroxybenzoic acid | (IV) \(CHCl_3 + \text{ aq. }NaOH\) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A)-(IV), (B)-(I), (C)-(II), (D)-(III)
Phenol undergoes several named and reagent-specific reactions: electrophilic substitution on the activated ring (Reimer-Tiemann: –CHO enters ortho; Kolbe: –COOH enters ortho through the phenoxide ion), removal of the –OH group (zinc dust) and oxidation of the ring (chromic acid).
(A) Conversion of phenol to salicylaldehyde — This matches (IV) CHCl3 + aq. NaOH. In the Reimer-Tiemann reaction the intermediate benzal chloride is hydrolysed by the alkali; acidification gives salicylaldehyde.
\( \ce{C6H5OH + CHCl3 + 3NaOH} \xrightarrow{\Delta} \text{o-}\ce{NaOC6H4CHO + 3NaCl + 2H2O} \xrightarrow{\ce{H+}} \text{o-}\ce{HOC6H4CHO} \)
(B) Conversion of phenol to benzene — This matches (I) Zinc dust. On heating with zinc dust the –OH group is removed.
\( \ce{C6H5OH + Zn} \xrightarrow{\Delta} \ce{C6H6 + ZnO} \)
(C) Conversion of phenol to benzoquinone — This matches (II) Na2Cr2O7/H2SO4. Oxidation with chromic acid gives the conjugated diketone p-benzoquinone.
\( \ce{C6H5OH} \xrightarrow{\ce{Na2Cr2O7/H2SO4}} \ce{O=C6H4=O} \) (p-benzoquinone)
(D) Conversion of phenol to o-hydroxybenzoic acid — This matches (III) NaOH and CO2/H+. In Kolbe’s reaction sodium phenoxide reacts with the weak electrophile \( \ce{CO2} \); acidification gives salicylic acid.
\( \ce{C6H5ONa + CO2} \xrightarrow{\text{400 K, 4-7 atm}} \text{o-}\ce{HOC6H4COONa} \xrightarrow{\ce{H+}} \text{o-}\ce{HOC6H4COOH} \)
NCERT (2026-27 edition):
Reimer-Tiemann Reaction – “On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of alkali to produce salicylaldehyde.”
Reaction of Phenol with Zinc Dust – “Phenol is converted to benzene on heating with zinc dust.”
Oxidation – “Oxidation of phenol with chromic acid produces a conjugated diketone known as benzoquinone.”
Kolbe’s Reaction – “Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is formed as the main reaction product.”