Darzens condensation

What is Darzens condensation?

The Darzens condensation (also known as Darzens-Claisen reaction) is a chemical reaction that allows for the synthesis of compounds containing a carbonyl group. This reaction is named after the French chemist Georges Darzens, who first described it in 1894..

The Darzens condensation involves the reaction of a compound called a “glycidic ester” with an aldehyde or a ketone. The reaction is typically carried out in the presence of a base, such as sodium hydroxide, and a solvent, such as ethanol..

Darzens condensation - Darzens-Claisen reaction
Darzens condensation

One of the advantages of the Darzens condensation is its high yield and efficiency. It is a relatively simple reaction that can be carried out under mild conditions and does not require the use of expensive or specialized reagents..

The Darzens condensation has a wide range of applications in the synthesis of pharmaceuticals, fragrances, and other chemicals. It has also been used in the synthesis of natural products, such as flavonoids and terpenoids..

Summary

The Darzens condensation is a valuable tool for the synthesis of compounds containing a carbonyl group and has played an important role in the development of a number of important chemical compounds..

Example

An example of the Darzens condensation is the following:

Treatment of ethyl chloroacetate with sodium ethoxide in ethanol gives the corresponding enolate ion.
This enolate ion then reacts with benzaldehyde to give the β-chloroethylbenzene by Darzens condensation.
Overall reaction:
Benzaldehyde + Ethyl chloroacetate –> β-chloroethylbenzene

In this example, benzaldehyde acts as an aldehyde, and ethyl chloroacetate acts as an ester. The reaction is typically carried out in the presence of a base such as sodium ethoxide, which acts as a catalyst to form the enolate ion..

Mechanism of reaction

The Darzens condensation reaction mechanism involves several steps:

  • The first step is the formation of an enolate ion. The base (such as sodium ethoxide) abstracts a hydrogen atom from the carbonyl group of the ester or halide (such as ethyl chloroacetate) to form the enolate ion.
  • Next, the enolate ion nucleophilically attacks the electrophilic carbon atom of the aldehyde or ketone (such as benzaldehyde). This results in the formation of a tetrahedral intermediate.
  • In the final step, the tetrahedral intermediate collapses, releasing a molecule of the base and forming the β-chloroethylbenzene..

Overall, the mechanism of the Darzens condensation reaction can be summarized as:

  • Enolate formation
  • Aldol condensation
  • Deprotonation

It is important to note that the Darzens condensation is a type of aldol condensation. The reaction is similar to aldol condensation but in Darzens condensation, the aldehyde or ketone is not an electrophile but the ester or halide acts as an electrophile..

References

  • G. Darzens, Compt. Rend. Acad. Sci. Paris 139, 1214 (1904);
  • G. Darzens, Chem. Zentr. I, 346 (1905)
  • G. Darzens, Compt. Rend. Acad. Sci. Paris 141, 766 (1905)
  • G. Darzens, Chem. Zentr. I, 22 (1906)
  • G. Darzens, Compt. Rend. Acad. Sci. Paris 142, 214 (1906)
  • G. Darzens, Chem. Zentr. I, 669 (1906)
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