Q.Write the name and formula of the product formed in the following reaction: CH3C≡N —[H2/Ni]→ ____ ____ ____
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Reduction of Nitriles to Amines
Reduction of Nitriles to Amines
Think of a nitrile as a molecule with a carbon atom triple-bonded to a nitrogen atom — that's the −C≡N group. That triple bond is packed with electrons and is quite polarised: the nitrogen is more electronegative, so it pulls electron density toward itself, leaving the carbon slightly positive. This makes the carbon a good target for a nucleophilic attack by a hydride ion (H−).
When you treat a nitrile with a strong reducing agent like lithium aluminium hydride (LiAlH4) or hydrogen gas with a metal catalyst (H2/Ni, Pd, or Pt), you are essentially adding hydrogen atoms across that triple bond. The reaction does not stop at an imine (a C=N intermediate) because the conditions are strongly reducing — it pushes all the way to a saturated C−N single bond.
The key structural change: the nitrile carbon becomes a methylene (−CH2−) group, and the nitrogen becomes an amino (−NH2) group. So a nitrile R−C≡N becomes a primary amine R−CH2−NH2.
Notice that the carbon chain has grown by exactly one carbon atom — the nitrile carbon is now part of the alkyl chain. This is a powerful method to extend a carbon skeleton by one unit while introducing an amine functionality.
R−C≡NLiAlH4or H2/catalystR−CH2−NH2
The mechanism in brief (for LiAlH4)
- A hydride ion (H−) attacks the electrophilic nitrile carbon, forming an imine anion intermediate: R−C−=N−.
- A second hydride adds to the imine carbon, giving a dianion: R−CH2−N2−.
- Aqueous work-up (adding water or dilute acid) protonates the nitrogen, yielding the free amine R−CH2−NH2.
A common mistake is to think the product is R−NH2 (an amine with the same number of carbons). It is not — the nitrile carbon is reduced and retained, so you always get one extra carbon in the chain. For example, CH3C≡N (acetonitrile) gives CH3CH2NH2 (ethylamine), not methylamine.
Catalytic hydrogenation …
Catalytic hydrogenation adds hydrogen across the triple bond of a nitrile in stages, fully reducing it all the way to the corresponding primary amine. …
Catalytic hydrogenation (H₂/Ni) reduces the nitrile CH₃–C≡N to the primary amine CH₃CH₂NH₂.
Nitriles (R–C≡N) are reduced to primary amines by catalytic hydrogenation using H₂ in the presence of a catalyst such as Ni, Pt or Pd, or by using LiAlH₄:
CH3−C≡N+2H2NiCH3−CH2−NH2 …
- CBSE 2026Set 56/2/11 markMCQQ.Identify the compound produced by the reduction of Ethanenitrile with Lithium aluminium hydride : (A) Ethylamine (B) Ethanal (C) Propylamine (D) Methylamine
›Reveal solutionSolution
Lithium aluminium hydride reduces nitriles by adding four hydrogens across the C≡N triple bond, converting it to a primary amine with the same carbon count. Ethanenitrile (CHX3CN) becomes ethylamine (CHX3CHX2NHX2).
Nitriles contain a carbon-nitrogen triple bond (C≡N), one of the most polar and reactive functional groups in organic chemistry. When you treat a nitrile with a powerful reducing agent like lithium aluminium hydride (LiAlHX4), you're forcing hydride ions (HX−) onto that electron-deficient carbon.
The key insight: LiAlHX4 is a strong enough reductant to break the C≡N triple bond completely and add hydrogen across it, but it stops at the amine stage—it doesn't break the C−N single bond. The carbon skeleton stays intact; you simply convert −C≡N into −CHX2−NHX2.
Let's trace what happens to ethanenitrile:
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Start with the structure of ethanenitrile
Ethanenitrile is CHX3−C≡N. It has two carbons: one methyl group attached to the nitrile carbon.
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The reduction mechanism (simplified)
LiAlHX4 delivers hydride ions in stages. The nitrile carbon is electrophilic, so HX− attacks it. After the first hydride addition and protonation, you get an imine intermediate (CHX3−CH=NH). A second hydride attack on that imine carbon, followed by aqueous workup, gives the primary amine.
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Count the carbons
Ethanenitrile has two carbons. Reduction doesn't add or remove carbons—it only converts the nitrile group to an amine. So the product must also have two carbons.
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Identify the product
CHX3−C≡NLiAlHX4CHX3−CHX2−NHX2
This is ethylamine, a two-carbon primary amine. …
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- CBSE 2026Set ANNUAL1 markMCQQ.Which one of the following reactions will not form primary amine?(a) CH3CONH2 --KOH, Br2-->(b) CH3CN --LiAlH4-->(c) CH3NC --LiAlH4-->(d) CH3CH2CONH2 --LiAlH4-->
›Reveal solutionSolution
Three of the four routes give a primary amine directly; only the reduction of an alkyl isocyanide (R-NC) yields a secondary amine, because the extra carbon from the isocyanide's -NC group becomes a methyl group bonded to the same nitrogen.
Checking each route:
- CH3CONH2 --KOH, Br2--> is the Hofmann bromamide degradation. It converts an amide to a primary amine with loss of one carbon: CH3CONH2 -> CH3NH2 (methanamine). Forms a primary amine.
- CH3CN --LiAlH4--> reduces a nitrile fully to a primary amine: CH3CN -> CH3CH2NH2 (ethanamine). Forms a primary amine. …
- CBSE 2024Set ANNUAL1 markQ.Complete the following reaction: C6H5CNLiAlH4?
›Reveal solutionSolution
Lithium aluminium hydride reduces the C≡N triple bond of a nitrile completely, adding four hydrogens to give a primary amine with one extra CH2 carbon relative to the nitrile carbon.
Benzonitrile, C6H5−C≡N, is reduced by the powerful hydride donor LiAlH4. The nitrile carbon accepts hydride and (after aqueous work-up) protons across both π bonds of the C≡N triple bond, converting it into a −CH2NH2 group:
C6H5−C≡N(i) LiAlH4(ii) H2OC6H5−CH2−NH2
…
- CBSE 2021Set A1 markMCQQ.CH3CN on reduction gives(a) CH4(b) CH3COOH(c) C2H5NH2(d) C2H5COOH
›Reveal solutionSolution
Nitrile + [H] (e.g. LiAlH4 or Na/alcohol) -> primary amine; CH3CN gives C2H5NH2.
Reduction of a nitrile R-C≡N adds four hydrogen atoms across the C≡N triple bond to give a primary amine R-CH2-NH2. For methyl cyanide (acetonitrile):
CH3-C≡N + 4[H] -> CH3-CH2-NH2 (ethylamine, C2H5NH2)
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