What is a Coupling Reaction?
When two fragments are joined together with the help of a metal catalyst to form a variety of reactions, then such types of reactions are known as coupling reactions in the field of organic chemistry. Metal catalysts are used because they increase the rate of the reaction without disturbing the thermodynamics of the reaction as transition metals are good catalysts. Organic chemistry is the division of chemistry that contains compounds formed from carbon in the field of organic chemistry. Here, we will be discussing the concept of coupling reactions and also their various types and applications in organic chemistry.
Principle of Coupling Reaction
When two similar or dissimilar types of chemical species react together with a common intermediate with the help of a metal catalyst to get a new product, then this type of reaction is called a coupling reaction. Coupling reactions are of two types based on their chemical species which can either be of the same or different types. Coupled reactions are those reactions that contain a common intermediate and where energy is being transferred from one side to another side of the reaction. These reactions are done in the presence of metal catalysts. Metal catalysts are used because metals are a good catalyst as they take away electrons from other molecules. Catalyst is used in chemical reactions because when we add a catalyst in a chemical reaction, then without affecting the thermodynamics of the reaction, it eventually increases the rate of the reaction.
For Example:
Endogenic formation of ATP which is coupled for the dissipation of protein gradient.
ATP + Glucose \[\rightarrow\] ADP + glucose - 1- Phosphate
Glucose - 1 - phosphate + fructose \[\rightarrow\] sucrose + phosphate
Sucrose is obtained from glucose and fructose with the expansion of energy stored in the form of ATP.
Coupling Reaction Examples
When organic halide reacts with an organometallic compound with general formula R-M, it facilitates the formation of a new carbon–carbon bond.
Also if organic halide has general formula R-M, then the new compound formed will be R-R’. ( where R= organic fragment and M= main group).
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Here is an example of a coupling reaction below where R1 and R3 are alkanes, alkene, or an alkyl group and R2 is the hydrogen group.
Benzenediazonium Chloride + Phenol (Para Position) \[\rightarrow\] p-hydroxyazobenzene
Types of the Coupling Reaction
There are two types of coupling reactions based on their chemical species.
Homo - Coupling Reaction: Homo means similar or the same. When two similar types of chemical species are combined to form a new compound, then they are known as homo-coupling reactions.
For example, the Wurtz reaction, Glaser coupling.
The general formula for Wurtz reaction is as follows:
2R - X + 2Na \[\rightarrow\] R-R + 2(Na+X-)
Hetero - Coupling Reaction: Hetero means different or which are not similar. When two different types of chemical species are combined or they are reacted together to form a new product, then they are known as hetero-coupling reactions. Hetero-coupling reactions are also known as cross-coupling reactions.
For example, the Grignard reaction, Suzuki coupling.
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Hetero coupling reactions are also known as cross-coupling reactions. These reactions are done in the presence of a metal catalyst to increase the rate of the reaction.
Azo Dyne Coupling Reaction: An organic compound with functional group R−N=N−R′ where R and R' are aryl groups. They belong to the family of azo compounds. They are insoluble in water and other solvents. They are used for the preparation of textile, leather objects, and some food products.
The reaction of Azo dyne is as follows:
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Applications of the Coupling Reaction
There are various applications where coupling reactions are used. Some are listed below:
Coupling reactions are used for various treatments such as for the formation of pharmaceuticals, polymers, and some other natural products.
Coupling reactions are used for the formation of various conjugated polymers by using metal catalysts.
For the production of various natural products, coupling reactions are used.
Cross-coupling reactions are used for the preparation of monomers and polymers.
Also, the reaction of Suzuki is used for the production of synthetic complex compounds. For example, the production of caparratriene which is highly effective in the treatment of leukemia.
They are also used for the preparation of monomers. Pharmaceuticals used for medical purposes are also prepared with the help of coupling reactions.
Conclusion
In this article, we have learned about coupling reactions, their types, a few examples, and applications. We may carry on this learning process with more interesting topics of chemistry which will also help you in competitive exams like JEE and NEET.
FAQs on Coupling Reaction
1. State a few homo-coupling reaction examples.
When the same type of chemical species reacts together with a common intermediate in the presence of a metal catalyst, such types of reactions are said to be homo-coupling reactions. A metal catalyst is used because transition metal is a good catalyst and it increases the rate of the reaction.
For example, the Wurtz reaction and Ullman reaction are both examples of Homo-Coupling reactions.
In Wurtz's reaction, two similar alkyl groups react with alkane as shown in the given example.
2R-X + 2Na 🠆 R-R +2Na+X-
Another example of homo-coupling is Ullman's reaction. In this reaction, the same type of alkyl halide is treated with another group of an alkyl halide in the presence of copper as a catalyst.
2. Explain the examples of cross-coupling reactions?
When two different chemical species are joined together to obtain a single new product, then such types of reactions are known as hetero coupling or cross-coupling Reactions. The most important example of hetero coupling reactions is the Heck reaction where aryl halide and alkyl group are reacted together in the presence of Pd as a catalyst. The heck reaction is as follows:
Here, in this reaction, R is an alkyl group and X is an aryl halide group. Another example of a cross-coupling reaction is a Grignard reaction in which magnesium is treated with an alkyl halide group to form a Grignard reagent.
