Lithium Aluminium Hydride
Formula: LiAlH4
Type: Strong hydride reducing agent
Common use: Reduction of carbonyl compounds and carboxylic acid derivatives.
Lithium aluminium hydride is usually abbreviated as LiAlH4 or LAH.
What it reduces
Section titled “What it reduces”LiAlH4 commonly reduces:
- aldehydes to primary alcohols
- ketones to secondary alcohols
- esters to primary alcohols
- carboxylic acids to primary alcohols
- acid chlorides to alcohols
- amides to amines
General workflow
Section titled “General workflow”LiAlH4 is normally used under dry conditions, followed by a controlled aqueous or acidic work-up.
The reagent reacts strongly with water and protic solvents, so the work-up is treated as a separate step.
Comparison with NaBH4
Section titled “Comparison with NaBH4”| Feature | NaBH4 | LiAlH4 |
|---|---|---|
| Strength | Mild | Strong |
| Typical solvent | Alcohols or aqueous alcohols | Dry ether-type solvents |
| Aldehydes/ketones | Yes | Yes |
| Esters | Usually no under standard conditions | Yes |
| Carboxylic acids | Usually no under standard conditions | Yes |
| Operational risk | Lower | Higher |
Mechanistic idea
Section titled “Mechanistic idea”LiAlH4 provides hydride to electrophilic carbonyl carbons.
For many carboxylic acid derivatives, the reaction proceeds through addition, leaving group collapse and further reduction of the aldehyde-level intermediate.
This is why esters often end as alcohols rather than stopping at aldehydes.
Safety and handling context
Section titled “Safety and handling context”LiAlH4 is moisture-sensitive and can release hydrogen during quench.
For real laboratory work, follow the local risk assessment, supervisor instructions and current SDS. This note is for study and documentation, not a substitute for lab-specific safety procedures.
Common exam traps
Section titled “Common exam traps”- Do not run LiAlH4 in water or methanol as the main reaction solvent.
- Do not stop ester reduction at an aldehyde unless a selective reagent is specified.
- Do not forget the work-up step when drawing the final alcohol.
- Do not treat LiAlH4 as interchangeable with NaBH4.
- For amides, the product is usually an amine, not an alcohol.
Related pages
Section titled “Related pages”Quick summary
Section titled “Quick summary”LiAlH4 is the strong hydride reagent used when NaBH4 is not enough.
The main decision is scope: if the substrate is an ester, carboxylic acid or amide, LiAlH4 is much more likely than NaBH4 to give reduction under standard teaching conditions.