Match the chemical conversion in List I to the appropriate reagent in List II
| List I | List II |
| A. \(\text{Phenol } \longrightarrow \text{ Benzene}\) | I. \(Na_2Cr_2O_7\) in presence of \(H_2SO_4\) |
| B. \(CH_3CH_2OH \longrightarrow C_2H_5OC_2H_5\) | II. \(H_2SO_4\) at \(443 K\) |
| C. \(\text{Phenol } \longrightarrow \text{1,4-Benzoquinone}\) | III. \(Zn\) |
| D. \(CH_3CH_2OH \longrightarrow CH_2=CH_2\) | IV. \(H_2SO_4\) at \(413 K\) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-III, B-IV, C-I, D-II
Each conversion needs its own reagent: zinc dust removes –OH from phenol, chromic acid oxidises phenol, and with ethanol the temperature of the acid decides between ether (lower) and alkene (higher).
(A) Phenol → Benzene — This matches (III) Zn. Heating with zinc dust removes the –OH group.
\( \displaystyle \ce{C6H5OH + Zn} \xrightarrow{\Delta} \ce{C6H6 + ZnO} \)
(B) CH3CH2OH → C2H5OC2H5 — This matches (IV) H2SO4 at 413 K. At the lower temperature one ethanol molecule attacks a protonated ethanol molecule (SN2), giving ethoxyethane.
\( \displaystyle \ce{2C2H5OH} \xrightarrow{\text{conc. }\ce{H2SO4},\ \text{413 K}} \ce{C2H5OC2H5 + H2O} \)
(C) Phenol → 1,4-Benzoquinone — This matches (I) Na2Cr2O7 in presence of H2SO4. Chromic acid oxidises phenol to the conjugated diketone benzoquinone.
\( \displaystyle \ce{C6H5OH} \xrightarrow{\ce{Na2Cr2O7/H2SO4}} \ce{O=C6H4=O} \)
(D) CH3CH2OH → CH2=CH2 — This matches (II) H2SO4 at 443 K. At the higher temperature, elimination of water gives ethene.
\( \displaystyle \ce{C2H5OH} \xrightarrow{\text{conc. }\ce{H2SO4},\ \text{443 K}} \ce{CH2=CH2 + H2O} \)
NCERT (2026-27 edition):
Reaction of Phenol with Zinc Dust – “Phenol is converted to benzene on heating with zinc dust.”
By Dehydration of Alcohols – “Alcohols undergo dehydration in the presence of protic acids (H2SO4, H3PO4). The formation of the reaction product, alkene or ether depends on the reaction conditions. For example, ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K, ethoxyethane is the main product.”
Oxidation – “Oxidation of phenol with chromic acid produces a conjugated diketone known as benzoquinone. In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing quinones.”