Knoevenagel Condensation

Knoevenagel Condensation

Knoevenagel Condensation


Condensation of aldehydes or ketones with compounds having active methylene group in the presence of basic catalyst such as ammonia and its derivatives to form α, β-unsaturated carbonyl compounds. This reaction is known as Knoevenagel Condensation.
In other words, Knoevenagel condensation is a nucleophilic addition of an activated methylene compound to an aldehyde or ketone using an amine base (e.g., pyridine or piperidine) as a catalyst followed by a dehydration in which a molecule of water is eliminated (condensation) and an α,β-unsaturated carbonyl compound obtained.

Knoevenagel Condensation
Both aliphatic and aromatic aldehydes give this reaction. For steric and electronic effect, ketones are less reactive than aldehydes. Ketones can reacts only when active methylene group is very powerfull(e.g. cyanoacetic acid, ethylacetoacetate).

Mechanism of Knoevenagel Condensation

In the first step, an amine base removes the proton from active methylene group to form a carbanion. This carbanion then acts as a nucleophile and attaches to the carbonyl acceptor molecule to form an alkoxide ion, which can undergo the dehydration to form the α,β-unsaturated product.
Mechanism of  Knoevenagel Condensation

Examples of Knoevenagel Condensation

Examples of Knoevenagel Condensation