Q. Reaction by which benzaldehyde cannot be prepared
A) Toluene + CrO₂Cl₂ in CS₂ followed by H₃O⁺
B) Benzoyl chloride (C₆H₅COCl) + H₂ in presence of Pd–BaSO₄
C) Benzene + CO + HCl in presence of anhydrous AlCl₃
D) Benzoic acid (C₆H₅COOH) + Zn/Hg and conc. HCl
Explanation
[Solution from source] Etard reaction (toluene + CrO₂Cl₂), Rosenmund reduction (benzoyl chloride + H₂/Pd–BaSO₄) and Gattermann–Koch reaction (benzene + CO + HCl/AlCl₃) all give benzaldehyde. Zn/Hg with conc. HCl (Clemmensen conditions) does not convert benzoic acid into benzaldehyde. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.