Nitrile To Amine Lialh4

Nitrile Reactions: Nitrile to Primary Amine with LiAlH4

LiAlH₄ (lithium aluminum hydride) reduces nitriles (R-C≡N) to primary amines (R-CH₂-NH₂) after aqueous workup. Unlike DIBAL-H which delivers only one hydride and stops at the aldehyde, LiAlH₄ delivers two hydrides to fully reduce the nitrile to an amine.

Quick Summary

Feature	Details
Transforms	R-C≡N → R-CH₂-NH₂
Reagents	1) LiAlH₄, ether 2) H₂O
Product	Primary amine
Key difference	LiAlH₄ gives amine (2 H⁻); DIBAL-H gives aldehyde (1 H⁻)

Mechanism (6 Steps)

The mechanism involves two sequential hydride transfers from LiAlH₄ to the nitrile carbon, followed by aqueous workup to release the free amine.

Step 1 - Lewis Acid Coordination

The nitrile nitrogen lone pair coordinates to the electrophilic aluminum of LiAlH₄, forming a Lewis acid-base complex.

Nitrile nitrogen coordinates to aluminum — **Step 1:** N lone pair coordinates to Al (Lewis acid-base).

Step 2 - First Hydride Transfer

A hydride from AlH₄⁻ attacks the nitrile carbon. The triple bond is reduced to a double bond (C=N), forming an imine-aluminum intermediate.

First hydride transfers to nitrile carbon — **Step 2:** First H⁻ attacks nitrile C; C≡N becomes C=N.

Step 3 - Second Hydride Transfer

A second hydride attacks the imine carbon. The double bond is reduced to a single bond (C-N), forming an amine-aluminum complex.

Second hydride transfers to imine carbon — **Step 3:** Second H⁻ attacks imine C; C=N becomes C-N.

Step 4 - Amine-Aluminum Complex

After two hydride additions, the carbon now has two new hydrogens and nitrogen remains bound to aluminum in an anionic complex.

Amine-aluminum complex formed — **Step 4:** Amine-aluminum complex (R-CH₂-N-Al).

Step 5 - Aqueous Workup

Water protonates the nitrogen and breaks the Al-N bond, releasing the amine.

Aqueous workup protonates nitrogen — **Step 5:** H₂O protonates N; Al-N bond cleaves.

Step 6 - Primary Amine Product

The final product is a primary amine (R-CH₂-NH₂).

Worked Examples

Example A reactant: benzonitrile — **Example A - Benzonitrile.** LiAlH₄ reduces benzonitrile to benzylamine (phenylmethanamine).

Reagent: LiAlH4 then H2O — **Example A - Benzonitrile.** LiAlH₄ reduces benzonitrile to benzylamine (phenylmethanamine).

Example B reactant: acetonitrile — **Example B - Acetonitrile.** The simplest nitrile gives ethylamine after LiAlH₄ reduction.

LiAlH₄ vs DIBAL-H: Key Comparison

	LiAlH₄	DIBAL-H
Hydrides delivered	2	1 (controlled by stoichiometry + cold temp)
Product from nitrile	Primary amine (R-CH₂-NH₂)	Aldehyde (R-CHO)
Conditions	Room temp or reflux, ether	1 equiv, −78 °C, then H₂O workup
Selectivity	Full reduction	Partial reduction (stops at imine)

Why DIBAL-H stops at aldehyde: At −78 °C with 1 equivalent, the bulky isobutyl groups and low temperature prevent a second hydride transfer. Warming or excess reagent → over-reduction to amine.

Exam tip: If the question asks for an aldehyde from a nitrile, use DIBAL-H (1 equiv, −78 °C). If it asks for an amine, use LiAlH₄.

Common Exam Traps

Wrong reagent selection - LiAlH₄ gives amine, not aldehyde. DIBAL-H gives aldehyde.
Forgetting workup - The mechanism requires aqueous workup to release the free amine.
Chemoselectivity - LiAlH₄ reduces many functional groups. If other reducible groups are present, they will also be reduced:
- Reduced: aldehydes → alcohols, ketones → alcohols, esters → alcohols, carboxylic acids → alcohols, amides → amines, epoxides → alcohols, acid chlorides → alcohols
- Not reduced: alkenes, alkynes, aromatic rings, ethers, simple halides
Protic solvent destruction - LiAlH₄ reacts violently with water/alcohols. Must use anhydrous ether solvents.

Product Prediction Checklist

Identify the nitrile: R-C≡N
Convert to amine: R-CH₂-NH₂
The nitrile carbon becomes a CH₂ group
Check for other LiAlH₄-reducible groups

Tips

"Nitrile carbon becomes CH₂" - quick way to predict connectivity
Count the hydrides: 2 H⁻ from LiAlH₄ = amine; 1 H⁻ from DIBAL-H = aldehyde
LiAlH₄ is not selective - it reduces almost everything

Interactive Toolbox

Mechanism Solver - Enter any nitrile and see the full 6-step mechanism for LiAlH₄ reduction to primary amine.
Reaction Solver - Provide a nitrile and the Solver predicts aldehyde vs amine outcomes based on your reagent inputs.
IUPAC Namer - Use it to name the amine products.

Study Tools