The best reagent for converting 2-phenylpropanamide into 2-phenylpropan-1-amine is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → LiAlH4 in ether
2-Phenylpropanamide and 2-phenylpropan-1-amine have the same carbon chain: the C=O of the amide only has to become CH2. Lithium aluminium hydride reduces an amide to an amine with no loss of carbon:
\( \displaystyle \ce{C6H5CH(CH3)CONH2} \xrightarrow[\text{(ii) }\ce{H2O}]{\text{(i) }\ce{LiAlH4}\text{, ether}} \ce{C6H5CH(CH3)CH2NH2} \)
Why the other options are incorrect
Option (1) Excess H2 — Incorrect. Hydrogen gas alone, with no catalyst, does not reduce the C=O group of an amide; the reagent used for this reduction is LiAlH4.
Option (2) Br2 in aqueous NaOH — Incorrect. This is the Hoffmann bromamide degradation, which gives an amine with one carbon atom less: 1-phenylethanamine, \( \ce{C6H5CH(CH3)NH2} \), not 2-phenylpropan-1-amine.
Option (3) Hydrogen iodide in the presence of red phosphorus — Incorrect. It is not a reagent for turning an amide into an amine; the amide-to-amine reduction is done with LiAlH4.
NCERT (2026-27 edition):
9.4 Preparation of Amines – “4. Reduction of amides
The amides on reduction with lithium aluminium hydride yield amines.”