Ludwig Claisen – discoverer of Claisen condensation reaction

Ludwig Claisen – discoverer of Claisen condensation reaction

Article published by Data Research Analyst, Worldofchemicals
Ludwig Claisen

Biography & contributions

Ludwig Claisen (Rainer Ludwig Claisen) was a famous German chemist born on January 14, 1851 – died on January 05, 1930. Claisen is best known for his work with discovering Claisen condensation reaction and Calisen flask.

Claisen had done many significant contributions towards chemistry like deduced the condensation of aromatic aldehydes with aliphatic aldehydes or ketones i.e., Claisen-Schmidt condensation reaction in the year of 1881, discovered synthesis of cinnamates by reacting aromatic aldehydes with esters and thermally induced rearrangement of allyl phenyl ether in the year of 1912, synthesized the isatin in the year of 1879.

Facts about isatin

Isatin is an indole derivative compound formed from the oxidation of indigo dye by nitric acid and chromic acids. Isatin is prepared by Sandmeyer isonitrosoacetanilide Isatin Synthesis from cyclicizing the condensation product of chloral hydrate, aniline, and hydroxylamine in sulfuric acid. Isatin is used as an intermediate in the syntheses of diclofenac and pirquinozol.

Claisen condensation reaction

The Claisen condensation can be described as a carbon-carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a β-ketoester or a β-diketone. It is named after Rainer Ludwig Claisen.


In claisen condensation reaction first step α-proton is removed by a strong base, resulting in the formation of an enolate anion. Enolate anion can be made relatively stable by the delocalization of electrons. Next step is the carbonyl carbon of the second ester is nucleophilically attacked by the enolate anion. The alkoxy group is then eliminated and the alkoxide removes the newly formed doubly α-proton to form a new, highly resonance-stabilized enolate anion. Aqueous acids like sulfuric acid or phosphoric acid are added in the final step to neutralize the enolate and any base still present. The newly formed β-ketoester or β-diketone is then isolated.

Aldol condensation reaction

An aldol condensation is an organic reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by a dehydration to give a conjugated enone. An aldol condensation is a major organic synthesis which provides a good way to form carbon-carbon bonds.


The first part of aldol condensation reaction is an aldol reaction, the second part involves removal of a water molecule or an alcohol molecule. Dehydration may be accompanied by decarboxylation when an activated carboxyl group is present. The aldol addition product can be dehydrated either by a strong base like potassium t-butoxide, potassium hydroxide or sodium hydride in an enolate mechanism or in an acid-catalyzed enol mechanism.

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