Cope elimination

What is Cope elimination?

The Cope elimination is a chemical reaction that allows for the synthesis of alkenes, which are compounds containing a carbon-carbon double bond. This reaction is named after the American chemist John Ulric Nef, who first described it in 1891, and the American chemist Arthur C. Cope, who later developed it further..

The Cope elimination involves the elimination of a compound called an “epoxide” to form an alkene. The reaction is typically carried out in the presence of a base, such as sodium hydroxide, and a solvent, such as ethanol..

Cope elimination
Cope elimination

One of the advantages of the Cope elimination 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 Cope elimination 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 Cope elimination is a valuable tool for the synthesis of alkenes and has played an important role in the development of a number of important chemical compounds..

Example

Cope elimination is a chemical reaction in which an alkene is transformed into an alkane by the elimination of a molecule of water or an alcohol. This reaction is usually carried out by heating the alkene in the presence of a strong acid catalyst, such as sulfuric acid or hydrochloric acid.. Here is an example of Cope elimination:

Starting material: 1-hexene
Catalyst: sulfuric acid
Solvent: benzene

Heat the mixture of 1-hexene, sulfuric acid, and benzene to a high temperature (around 150-200 °C).
The sulfuric acid catalyst protonates the alkene, forming a carbocation intermediate.
The carbocation intermediate undergoes a 1,2-elimination reaction, releasing a molecule of water or alcohol and forming an alkane..
The resulting product is a mixture of the two possible alkanes that can be formed from 1-hexene by Cope elimination. These two alkanes are called the “cis” and “trans” isomers, and they can be separated by distillation or other separation techniques..

Mechanism of reaction

The alkene and the strong acid catalyst are mixed together in a solvent, such as benzene.
The acid catalyst donates a proton to the alkene, forming a carbocation intermediate. This step is called protonation.
The carbocation intermediate undergoes a 1,2-elimination reaction, releasing a molecule of water or alcohol. This step is called elimination.
The resulting alkane is formed.
Here is a more detailed version of the mechanism, showing the movement of electrons:

The alkene and the acid catalyst are mixed together in a solvent.
The acid catalyst donates a proton to the alkene, forming a carbocation intermediate.

fig1

The carbocation intermediate undergoes a 1,2-elimination reaction, releasing a molecule of water or alcohol. The resulting alkane is formed.

fig2

References

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