Identify the suitable reagent for the following conversion.

Question

Question

This question was previously asked in

NEET 2025 Official Paper (Held On: 04 May, 2025)

Answer 1

CONCEPT:

Reduction of Esters to Aldehydes using DIBAL-H

DIBAL-H (Diisobutylaluminum hydride, AlH(iBu)₂) is a selective reducing agent that reduces esters to aldehydes without further reducing the aldehyde to an alcohol.
In the reaction with esters, DIBAL-H (AlH(iBu)₂) reduces the ester (R-C=O-OR') to the aldehyde (R-C=O-H), stopping the reduction at the aldehyde stage.
This reaction is followed by hydrolysis with water (H₂O) to work up the reaction and form the aldehyde.

EXPLANATION:

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In this case, DIBAL-H selectively reduces the ester (R-C=O-OR') to an aldehyde (R-C=O-H) and the alcohol group (ROH) is released.
The correct reagent for the conversion is Option 2 (AlH(iBu)₂, H₂O). DIBAL-H reduces the ester to the aldehyde, and water (H₂O) is used to hydrolyze the intermediate to the final aldehyde product.

Why not the other options:

Option 1: LiAlH₄ (Lithium aluminium hydride) followed by H₂O:
- LiAlH₄ is a strong reducing agent that reduces esters to alcohols rather than aldehydes. It would not stop at the aldehyde stage, which makes it unsuitable for this transformation.
Option 3: NaBH₄ (Sodium borohydride) followed by H₂O:
- NaBH₄ is a milder reducing agent than LiAlH₄ and typically reduces aldehydes and ketones to alcohols, but it is not reactive enough to reduce esters to aldehydes.
Option 4: H₂/Pd-BaSO₄ (Hydrogen and palladium on barium sulfate):
- This is a catalytic hydrogenation method, typically used to reduce alkenes or aromatic compounds. It will reduce aldehydes to alcohols, so it would not be selective enough to stop at the aldehyde stage when reducing esters.

Therefore, the correct answer is AlH(iBu)₂, H₂O, which reduces the ester to an aldehyde selectively.