What is the product of reduction of Nitriles with Lithium Aluminium Hydride?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Amines
Lithium aluminium hydride is a strong reducing agent that supplies hydride ions (\( \ce{H^{-}} \)). It adds four hydrogen atoms across the C≡N triple bond: the carbon becomes a \( \ce{CH2} \) group and the nitrogen an \( \ce{NH2} \) group. The product is a primary amine:
\( \displaystyle \ce{R-C#N} \xrightarrow[\text{(ii) }\ce{H2O}]{\text{(i) }\ce{LiAlH4}} \ce{R-CH2-NH2} \)
For example, ethanenitrile gives ethanamine: \( \ce{CH3CN -> CH3CH2NH2} \). Catalytic hydrogenation (\( \ce{H2} \)/Ni) does the same. Because the amine has one carbon more than the alkyl halide used to make the nitrile, the method is used for the ascent of the amine series.
Why the other options are incorrect
Option (1) Alcohols — Incorrect. \( \ce{LiAlH4} \) gives alcohols from aldehydes, ketones and carboxylic acids, which contain oxygen. A nitrile has no oxygen, so its reduction gives an amine, not an alcohol.
Option (2) Aldehyde — Incorrect. A nitrile gives an aldehyde only by partial reduction followed by hydrolysis, with stannous chloride and HCl (Stephen reaction) or with DIBAL-H. \( \ce{LiAlH4} \) reduces the nitrile all the way to the amine.
Option (4) Ketone — Incorrect. A ketone is made from a nitrile by treating it with a Grignard reagent and then hydrolysing; this is not a reduction.
NCERT (2026-27 edition):
Reduction of Nitriles
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | 03-06 S2 29-05 S2 | – | – | – |