Select the reagents that reduce nitriles to primary amines

A. LiAlH₄,H2O
B. Sn+HCl
C. H₂/Ni
D. Na(Hg)/C₂H₅OH
E. Br₂/aq.NaOH

To determine which reagents convert a nitrile (R‑C≡N) into a primary amine (R‑CH₂NH₂), we examine the typical reaction pathways of each reagent.

Reagent A: LiAlH₄, H₂O
LiAlH₄ is a very strong hydride donor. In the presence of water it supplies four equivalents of H⁻, which attack the electrophilic carbon of the nitrile carbon‑nitrogen triple bond. The sequence is:

$R‑C\equiv N\; +\; 4 H⁻\; \to \; R‑CH₂NH₂\; +\; Al(OH)$₄⁻

The nitrile is reduced directly to a primary amine without forming an intermediate aldehyde or imine that escapes reduction. Hence LiAlH₄/H₂O works.

Reagent B: Sn + HCl
Tin metal in acidic solution is a modest reducing system. It typically reduces nitriles to aldehydes (the “Tin/ HCl” reduction) rather than to amines. The aldehyde can be further reduced only under stronger conditions. Therefore Sn/HCl does **not** give a primary amine.

Reagent C: H₂/Ni
Catalytic hydrogenation over nickel provides molecular hydrogen in a highly activated form. The nitrene‑like carbon of a nitrile undergoes successive hydrogen addition:

$R‑C\equiv N\; +\; 2 H₂\; \to \; R‑CH₂NH₂$

Both the C≡N bond and the resulting imine intermediate are fully hydrogenated, yielding the primary amine. Thus H₂/Ni is suitable.

Reagent D: Na(Hg)/C₂H₅OH
Sodium amalgam in ethanol is a classic “Birch‑type” single‑electron‑transfer reducer. It reduces nitriles by delivering electrons and protons from the solvent, ultimately forming a primary amine:

$R‑C\equiv N\; +\; 4 e⁻\; +\; 4 H⁺\; \to \; R‑CH₂NH₂$

This method is widely used for converting nitriles to primary amines, so D is effective.

Reagent E: Br₂/aq NaOH
Bromine in aqueous alkali performs an oxidative halogenation that converts nitriles into carboxylic acids via the “haloform‑type” pathway, not into amines. Consequently, E does not achieve the desired transformation.

Summarizing the above A, C and D only

To determine which reagents convert a nitrile (R‑C≡N) into a primary amine (R‑CH₂NH₂), we examine the typical reaction pathways of each reagent.

Reagent A: LiAlH₄, H₂O
LiAlH₄ is a very strong hydride donor. In the presence of water it supplies four equivalents of H⁻, which attack the electrophilic carbon of the nitrile carbon‑nitrogen triple bond. The sequence is:

$R‑C\equiv N\; +\; 4 H⁻\; \to \; R‑CH₂NH₂\; +\; Al(OH)$₄⁻

The nitrile is reduced directly to a primary amine without forming an intermediate aldehyde or imine that escapes reduction. Hence LiAlH₄/H₂O works.

Reagent B: Sn + HCl
Tin metal in acidic solution is a modest reducing system. It typically reduces nitriles to aldehydes (the “Tin/ HCl” reduction) rather than to amines. The aldehyde can be further reduced only under stronger conditions. Therefore Sn/HCl does **not** give a primary amine.

Reagent C: H₂/Ni
Catalytic hydrogenation over nickel provides molecular hydrogen in a highly activated form. The nitrene‑like carbon of a nitrile undergoes successive hydrogen addition:

$R‑C\equiv N\; +\; 2 H₂\; \to \; R‑CH₂NH₂$

Both the C≡N bond and the resulting imine intermediate are fully hydrogenated, yielding the primary amine. Thus H₂/Ni is suitable.

Reagent D: Na(Hg)/C₂H₅OH
Sodium amalgam in ethanol is a classic “Birch‑type” single‑electron‑transfer reducer. It reduces nitriles by delivering electrons and protons from the solvent, ultimately forming a primary amine:

$R‑C\equiv N\; +\; 4 e⁻\; +\; 4 H⁺\; \to \; R‑CH₂NH₂$

This method is widely used for converting nitriles to primary amines, so D is effective.

Reagent E: Br₂/aq NaOH
Bromine in aqueous alkali performs an oxidative halogenation that converts nitriles into carboxylic acids via the “haloform‑type” pathway, not into amines. Consequently, E does not achieve the desired transformation.

Summarizing the above analysis, the reagents that successfully reduce nitriles to primary amines are:

A (LiAlH₄/H₂O), C (H₂/Ni) and D (Na(Hg)/C₂H₅OH) only.