The Knoevenagel condensation reaction is an organic reaction named after Emil Knoevenagel. It is a modification of the aldol condensation.
A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated (hence condensation). The product is often an alpha, beta conjugated enone.
In this reaction the carbonyl group is an aldehyde or a ketone. The catalyst is usually a weakly basic amine. The active hydrogen component has the form
- Z-CH2-Z or Z-CHR-Z for instance diethyl malonate, Meldrum's acid, ethyl acetoacetate or malonic acid.
- Z-CHR1R2 for instance nitromethane.
where Z is an electron withdrawing functional group. Z must be powerful enough to facilitate hydrogen abstraction to the enolate ion even with a mild base. Using a strong base in this reaction would induce self-condensation of the aldehyde or ketone.
The Hantzsch pyridine synthesis, the Gewald reaction and the Feist-Benary furan synthesis all contain a Knoevenagel reaction step. The reaction also led to the discovery of CS gas.
Read more about Knoevenagel Condensation: Doebner Modification, Scope, Weiss–Cook Reaction
Famous quotes containing the word condensation:
“Entification begins at arm’s length; the points of condensation in the primordial conceptual scheme are things glimpsed, not glimpses.”
—Willard Van Orman Quine (b. 1908)