NEET 2025 · ChemistryCarbonyl reductionPrevious Year Question
Identify the suitable reagent for the following conversion: \ce{C6H5COOCH3 -> C6H5CHO} (methyl benzoate to benzaldehyde)
- A.(A) (i) \ce{NaBH4}, (ii) \ce{H+/H2O}
- B.(B) \ce{H2/Pd-BaSO4}
- C.(C) (i) \ce{LiAlH4}, (ii) \ce{H+/H2O}
- D.(D) (i) \ce{AlH(iBu)2}, (ii) \ce{H2O}✓
Correct Answer
(D) (D) (i) \ce{AlH(iBu)2}, (ii) \ce{H2O}
Solution & Explanation
\textbf{Answer:} (D) (i) \ce{AlH(iBu)2}, (ii) \ce{H2O} \textbf{Solution:} An ester is selectively reduced only as far as the aldehyde stage by diisobutylaluminium hydride, DIBAL-H \ce{AlH(iBu)2}, at low temperature followed by aqueous work-up; hence methyl benzoate gives benzaldehyde. \ce{NaBH4} and \ce{H2/Pd-BaSO4} do not reduce esters, and \ce{LiAlH4} over-reduces the ester all the way to the primary alcohol (benzyl alcohol).
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