Identify the suitable reagent for the following conversion: methyl benzoate (C6H5COOCH3, an ester) benzaldehyde (C6H5CHO).

Question

Identify the suitable reagent for the following conversion:

methyl benzoate (C6H5COOCH3, an ester) benzaldehyde (C6H5CHO).

1. A. (i) LiAlH4, (ii) H^+/H2O
2. B. (i) AlH(iBu)2 (DIBAL-H), (ii) H2O (Correct answer)
3. C. (i) NaBH4, (ii) H^+/H2O
4. D. H2/Pd-BaSO4

Correct Answer

Option B — (i) AlH(iBu)2 (DIBAL-H), (ii) H2O

Detailed Solution & Explanation

The correct answer is (i) AlH(iBu)$_2$ (DIBAL-H), (ii) H$_2$O.

Key Points

• DIBAL-H (diisobutylaluminium hydride) is a mild reducing agent that reduces esters (and nitriles) to aldehydes, stopping at the aldehyde stage.
• LiAlH$_4$ and NaBH$_4$ would over-reduce the ester all the way to a primary alcohol.
• H$_2$/Pd-BaSO$_4$ (Rosenmund) reduces acid chlorides, not esters.