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Lithium Aluminum Hydride ($LiAlH_4$)

A comprehensive guide to one of organic chemistry's most powerful reducing agents.

By chemca Team • Updated Jan 2026

Lithium Aluminum Hydride ($LiAlH_4$), commonly abbreviated as LAH, is a highly reactive and powerful reducing agent widely utilized in modern organic synthesis. It transfers nucleophilic hydride ($H^-$) to electrophilic centers, effectively reducing various polar functional groups.

Crucial Safety Note: $LiAlH_4$ reacts violently with water, releasing highly flammable hydrogen gas ($H_2$) and significant heat, which can lead to spontaneous ignition. All reactions must be conducted in strictly anhydrous (water-free) conditions using aprotic solvents like diethyl ether or Tetrahydrofuran (THF).

1. Reduction of Aldehydes & Ketones

Formation of Primary & Secondary Alcohols

$LiAlH_4$ smoothly reduces aldehydes to primary alcohols and ketones to secondary alcohols.

A. Reduction of Aldehydes:

$$ R-CHO \xrightarrow{\text{1) } LiAlH_4 \text{, ether} \quad \text{2) } H_3O^+} R-CH_2OH $$

B. Reduction of Ketones:

$$ R-CO-R' \xrightarrow{\text{1) } LiAlH_4 \text{, ether} \quad \text{2) } H_3O^+} R-CH(OH)-R' $$

2. Reduction of Carboxylic Acids & Esters

Complete Reduction to Primary Alcohols

Unlike milder agents (like $NaBH_4$), $LiAlH_4$ is strong enough to reduce carboxylic acids completely to primary alcohols. Esters are cleaved in the process to yield two alcohol molecules.

A. Reduction of Carboxylic Acids:

$$ R-COOH \xrightarrow{\text{1) } LiAlH_4 \text{, ether} \quad \text{2) } H_3O^+} R-CH_2OH $$

B. Reduction of Esters:

$$ R-COOR' \xrightarrow{\text{1) } LiAlH_4 \text{, ether} \quad \text{2) } H_3O^+} R-CH_2OH + R'-OH $$

3. Reduction of Amides & Nitriles

Synthesis of Amines

Amides and nitriles are both effectively reduced to amines. Notice that for amides, the carbonyl oxygen is entirely removed rather than forming an alcohol.

A. Reduction of Amides:

$$ R-CONH_2 \xrightarrow{\text{1) } LiAlH_4 \text{, ether} \quad \text{2) } H_2O} R-CH_2NH_2 $$

B. Reduction of Nitriles:

$$ R-C \equiv N \xrightarrow{\text{1) } LiAlH_4 \text{, ether} \quad \text{2) } H_2O} R-CH_2NH_2 $$

Limitations and Selectivity

Because it is highly reactive, $LiAlH_4$ lacks chemoselectivity. If multiple reducible functional groups are present, it will typically reduce all of them. However, $LiAlH_4$ does not generally reduce isolated carbon-carbon double bonds (alkenes) or triple bonds (alkynes), unless they are conjugated with certain specific groups.

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