Match List I with List II
| LIST I | LIST II |
| A. Rosenmund reduction | I. CrO2Cl2/CS2-H3O+ |
| B. Etard Reaction | II. CO, HCl/Anhyd. AlCl3/CuCl |
| C. Gattermann-Koch reaction | III. H2-Pd-BaSO4 |
| D. Clemmensen reduction | IV. Zn-Hg/HCl |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-III, B-I, C-II, D-IV
These named reactions either make aldehydes (Rosenmund, Etard, Gattermann-Koch) or reduce a carbonyl group to \( \ce{CH2} \) (Clemmensen); each is recognised by its reagent:
A. Rosenmund reduction — This matches III. H2-Pd-BaSO4. An acyl chloride is hydrogenated over palladium on barium sulphate (poisoned catalyst) and stops at the aldehyde.
\( \displaystyle \ce{RCOCl + H2} \xrightarrow{\ce{Pd/BaSO4}} \ce{RCHO + HCl} \)
B. Etard Reaction — This matches I. CrO2Cl2/CS2-H3O+. Chromyl chloride oxidises the methyl group of toluene to a chromium complex, which is hydrolysed to benzaldehyde.
\( \displaystyle \ce{C6H5CH3} \xrightarrow[\text{(ii) }\ce{H3O^+}]{\text{(i) }\ce{CrO2Cl2},\ \ce{CS2}} \ce{C6H5CHO} \)
C. Gattermann-Koch reaction — This matches II. CO, HCl/Anhyd. AlCl3/CuCl. Benzene treated with carbon monoxide and HCl in the presence of anhydrous \( \ce{AlCl3} \) or CuCl gives benzaldehyde.
\( \displaystyle \ce{C6H6} \xrightarrow[\text{anhyd. }\ce{AlCl3}/\ce{CuCl}]{\ce{CO},\ \ce{HCl}} \ce{C6H5CHO} \)
D. Clemmensen reduction — This matches IV. Zn-Hg/HCl. Zinc amalgam and concentrated HCl reduce the C=O group of aldehydes and ketones to \( \ce{CH2} \).
\( \displaystyle \ce{>C=O} \xrightarrow{\ce{Zn-Hg},\ \text{conc. }\ce{HCl}} \ce{>CH2 + H2O} \)
Shortcut: The pair A-III appears in Options (2) and (3), and B-I then leaves only Option (2).
NCERT (2026-27 edition):
From Acyl Chloride (Acid Chloride) – “Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction.”
By Oxidation of Methylbenzene – “… (a) Use of chromyl chloride (CrO2Cl2): Chromyl chloride oxidises methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde.
\( \ce{C6H5CH3} \xrightarrow[\text{(ii) }\ce{H3O^+}]{\text{(i) }\ce{CrO2Cl2},\ \ce{CS2}} \ce{C6H5CHO} \)
This reaction is called Etard reaction.”
By Gatterman – Koch Reaction – “When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous aluminium chloride or cuprous chloride, it gives benzaldehyde or substituted benzaldehyde.
\( \ce{C6H6} \xrightarrow[\text{anhyd. }\ce{AlCl3}/\ce{CuCl}]{\ce{CO},\ \ce{HCl}} \ce{C6H5CHO} \)
This reaction is known as Gatterman-Koch reaction.”
Reduction – “… (ii) Reduction to hydrocarbons: The carbonyl group of aldehydes and ketones is reduced to CH2 group on treatment with zinc-amalgam and concentrated hydrochloric acid [Clemmensen reduction] or with hydrazine followed by heating with sodium or potassium hydroxide in high boiling solvent such as ethylene glycol (Wolff-Kishner reduction).”