Claisen Condensation Mechanism

Introduction

Claisen condensation mechanism was named after Rainer Ludwig Claisen, the German chemist after its discovery. This reaction is started with discharge of alpha proton, and happens by the action of the strong base and finally results in the formation of an enolate ion. This particular action needs a minimum of one reagent and it should possess an alpha proton $\mathrm{(\alpha\:-\:H)}$ with it. It generally forms the anion upon deprotonation.

What is Claisen Condensation?

This is one of the essential reactions in the fields of chemistry in which the special carbon- carbon bond formation is done in the presence of the strong base and the final product β- ketoester is formed effectively. This is a significant reaction because it holds an important value in biosynthesis of the fatty acid. It can also be mentioned that the formation of the catabolism of the fatty acid happens in the reverse Claisen condensation.

Claisen Ester Condensation: Requirements

There are certain requirements for this reaction to be carried out effectively. These are mentioned below −

• One reagent is essentially needed for the reaction to be taken place effectively. It particularly helps in the creation of the nucleophilic carbon centre.

• Alpha position of hydrogen in ester helps enolate in anion formation during the deprotonation process.

• During this reaction, the base needs to be inactive and it should not react to the nucleophilic substitution reactions.

• Sodium Alkoxide would be ideal for this reaction to successfully happen because it serves as one of the conjugate bases among alcohols.

• The alkoxy part of ester should work as a wonderful leaving group during the process of reaction to create methyl esters and ethyl.

Claisen Condensation: Reaction Mechanism

The mechanism of reaction is given below −

Step 1: Formation of enolate

During this reaction, a strong base helps to remove alpha proton from ester. The production of the enolate ion occurs in this specific type of reaction.

Figure 1 − Enolate formation

This particular enolate ion is comparatively stable because of the delocalization of the electrons which also possess negative charge particles because of the electrons.

Step 2: Nucleophilic attack

The nucleophilic attack is generally happed in this particular stage. Carbonyl carbon, which belongs to the second ester reactant, is targeted by the nucleophilic attack in this specific stage.

Figure 2 − Nucleophilic attack

The removal of the alkoxy group is happed in this step and the regeneration of the conjugated base of the particular alcohol is formed in this particular step. The double alpha proton is removed by alkoxide ion which is created during the process of the reaction. It further generates a newly formed anion and this anion is now completely resonance stabilized.

Step 3: Removal of the leaving group

In this step, the aqueous acid mainly Sulphuric or Phosphoric acid is added for the neutralization of the negative charge of the enolate anion.

Figure 3 − Removal of leaving group

If any base is still present is also removed by adding these acids. The creation of β- diketone or the β- keto ester is led by this reaction. These esters are immediately removed in this step.

Step 4: Deprotonation

The acidic quality of the beta keto esters is high or great enough for allowing them entirely deprotonated by the alkoxide bases for the formation of the second enolate.

Figure 4 − Deprotonation

The equilibrium of this particular step can be easily possible and it further helps the whole reaction to proceed and produce the final product as soon as possible.

Step 5: Protonation

Figure 5 − Protonation

An enolate is generally protonated in the specific acid workup to generate a neutral beta ketoester product.

Variations

Claisen Condensation generally denotes an organic coupling reaction that is responsible for the biosynthesis of the fatty acid. Some essentials variations of this reaction are mentioned below-

• One of the most classic variations of this reaction includes the specific reaction between two particles of an ester containing compound and here the enolizable.

• The reaction of Dieckmann condensation describes the intermolecular reaction of the two ester groups which belong to the similar molecule. This reaction generates β- keto ester and this type of ester is cyclic in nature.

• Crossed Claisen condensation further refers to the type of reaction when an enolizable ketone or ester is being used with the type of ester which is non- enolizable.

• There is another modification that this reaction process. Stobbe condensation reaction is proceeding with the comparatively weak bases. The diethyl ester which is generally prepared from Succinic acid is mainly used in this type of reaction.

Conclusion

The aldol condensation is greatly associated with the Claisen condensation reaction. Both of these reactions come under the organic reaction process. In the chemistry field, these reaction is most significant. Claisen condensation acts for the addition of the enolate to esters. In the biosynthesis process of the fatty acid, this reaction plays an important role.

FAQs

1. What are the several kinds of Claisen condensations that exist?

There are different types of Claisen conduction that can be food. These are classic crossed and Dieckmann condensation reactions.

2. What are the prominent products that are generally found from Claisen reactions?

The accepted products from this reaction include β-ketoesters. These esters are known as one the vital synthetic intermediates in the specific field of organic chemistry. In this type of reaction, the reaction of the ester enolate with another ester substance is found to create the desired products.

3. What would be the most important requirements needed for the conduction of Claisen condensation reaction?

One reagent is needed to be essentially enolizable. It must possess the α-proton for creation of an enolate ion.

4. What is the main difference between Claisen and aldol condensation?

In also condensation addition of the enolates from aldehydes, whereas in Claisen condensation the particular addition of an enolate to the esters happens.