Advanced Topic 869 of 1102 Organic Chemistry
Reduction of Carbonyls
Hydride reagents such as NaBH4 and LiAlH4 reduce aldehydes and ketones to alcohols.
In-depth explanation of Reduction of Carbonyls
Carbonyl compounds are reduced by hydride reagents, which deliver a hydride ion, H-, to the electrophilic carbonyl carbon, and the resulting alkoxide is protonated to give an alcohol. Sodium borohydride, NaBH4, is mild and selective, reducing aldehydes and ketones but not esters or acids, and it can be used in alcohol solvents. Lithium aluminium hydride, LiAlH4, is much stronger and also reduces esters, carboxylic acids and amides, but it reacts violently with water and must be used in dry ether.
Going deeper: Reduction of Carbonyls
Key ideas: NaBH4 (in alcohol or water) reduces aldehydes and ketones to alcohols but not esters, acids or amides. LiAlH4 (dry ether, then workup) reduces all carbonyls: acids and esters to primary alcohols, amides to amines, nitriles to amines. Catalytic hydrogenation also works. Wolff-Kishner (hydrazine, KOH, heat) and Clemmensen (Zn-Hg, HCl) fully reduce C=O to CH2. DIBAL at low temperature stops at aldehyde.
Common mistakes and connections: Students put LiAlH4 in water, which reacts violently. Another error is thinking NaBH4 reduces C=C or esters. Choose Clemmensen for base-sensitive and Wolff-Kishner for acid-sensitive substrates. Links to hydride transfer, alcohol synthesis and Friedel-Crafts acylation followed by reduction.
Visualization of Reduction of Carbonyls
A hydride ion from NaBH4 or LiAlH4 attacks the carbonyl carbon, and protonation gives the alcohol. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Reduction of an ester with lithium aluminium hydride gives two alcohols, one from each part of the ester.
Frequently asked questions about Reduction of Carbonyls
What is Reduction of Carbonyls?
Hydride reagents such as NaBH4 and LiAlH4 reduce aldehydes and ketones to alcohols.
Is Reduction of Carbonyls a beginner, intermediate or advanced topic?
Reduction of Carbonyls is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Reduction of Carbonyls?
Study these earlier topics in Organic Chemistry first: Alpha Hydrogen Acidity, Baeyer's Reagent, Williamson vs Elimination.
What comes after Reduction of Carbonyls?
The next topics in Organic Chemistry are Epoxides and Sharpless Epoxidation.
Can I practise Reduction of Carbonyls with quizzes?
Yes. The interactive lesson includes a self-check question on Reduction of Carbonyls, and the Organic Chemistry quiz draws on every topic in this area.
Where Reduction of Carbonyls fits in Organic Chemistry
Reduction of Carbonyls is topic 141 of 148 in Organic Chemistry.