Coupling Reaction: Definition, Types, Examples & Important Questions

A coupling reaction is a type of organic reaction that involves merging two chemical species with the help of a metal catalyst . In simple words, it is a reaction in which fragments are bonded together with the help of a metal catalyst. In this article, we will look at types, examples, and some sample questions from Coupling Reaction.

Key Terms: Coupling reactions, alkaline, benzene, ATP, energy, metal catalyst, organic reaction, thermodynamics, aromatic compounds, Electron

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Definition of Coupling Reaction

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• Coupling reactions are when a shared intermediate is present, and energy is transmitted from one side of the reaction to the other. Metal catalysts are used to catalyze these processes.
• Metal catalysts catalyze these processes. Metal catalysts are used because they remove electrons from other substances efficiently. Catalysts are used in chemical processes because they increase the reaction rate without affecting the reaction's thermodynamics.
• When diazonium salts react with aromatic compounds with an electronn-rich group, they produce azo compounds (e.g., OH, NH2, etc.). Because it involves an electrophilic substitution, this is referred to as a coupling reaction.
• Azo compounds are vividly colored dyes and indicators. The coupling reaction occurs when benzene diazonium chloride reacts with an alkaline phenol solution to form p-hydroxy azobenzene (orange dye).

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Types of Coupling Reaction

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Based on the chemical species involved, there are two types of coupling reactions.

• Homo-coupling Reaction: Homo-coupling reactions occur when two chemical species with comparable properties unite to generate a new molecule.
• Hetero-coupling Reaction: Hetero-coupling reactions occur when two different types of chemical species are joined or reacted together to produce a new product. Cross-coupling reactions are another name for hetero-coupling reactions. These are also known as cross-coupling reactions.

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Examples of Coupling Reactions

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When an organic halide combines with an organometallic molecule having the general formula R-M, a new carbon-carbon bond is formed. If the organic halide has the general formula R-M, the new compound produced will have the formula R-R'. (where R denotes an organic fragment and M denotes the major group)

• Ullman Reaction

The Ullmann Reaction ( homo-coupling) is a term that refers to two distinct transformations. The "classic" Ullmann Reaction is a copper-catalyzed coupling reaction that produces symmetric biaryls. Copper-catalyzed Nucleophilic Aromatic Substitution between various nucleophiles (e.g. substituted phenoxides) and aryl halides is one of the "Ullmann-type" reactions. The Ullmann Ether Synthesis is the most common of these.

• Wurtz Reaction

The Wurtz Coupling, which produces a simple dimer from two alkyl halide equivalents, is one of the earliest organic reactions. The intramolecular form of the reaction has also been used in the synthesis of strained ring compounds.

• Grignard Reaction

The addition of alkyl/vinyl/aryl magnesium halides to any carbonyl group in an aldehyde/ketone is explained by the Grignard reaction mechanism. The reaction is thought to be a useful technique for forming carbon-carbon bonds. Grignard reagents are magnesium halides that are alkyl, vinyl, or aryl.

• Suzuki coupling reaction

Suzuki coupling reaction is another name for an organic chemistry reaction that is used to make single-bonded carbon-carbon molecules. It's a coupling reaction, as the name implies. Because a metal catalyst is used in the process, it is classified as a cross-coupling reaction.

In the Suzuki coupling reaction, an organoboron species is coupled with an alkyl or aryl halide in the presence of Pd(0) and a base to form a carbon-carbon single bond.

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Applications of Coupling Reaction

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• In the production of medications, coupling reactions are frequently used.
• Various coupling processes can be used to make a variety of natural compounds. The Sonogashira cross-coupling reaction, for example, can be used to make benzylisoquinoline alkaloids.
• For the preparation of monomers and polymers, cross-coupling processes are utilized.
• Many conjugated polymers are made with the help of a metal catalyst in coupling reactions.
• It's employed in the manufacturing of caparratriene, a leukemia medication that's quite effective.

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Things to Remember

1. The coupling reaction is an organic process in which two chemical species are linked together by a metal catalyst. When benzene diazonium chloride combines with phenol, the para position of the phenol molecule couples with the diazonium salt to generate p-hydroxyazobenzene.
2. The coupling reaction is a sub-topic of Unit-13 i.e. amines. The total weightage of organic chemistry will be 28 marks.
3. Mechanisms of reactions like Wurtz Reaction, Grignard Reaction, and Suzuki Reaction are often asked in the exams and should be prepared thoroughly.
4. When an ATP molecule is hydrolyzed, high-energy phosphate bonds are broken, leading the exergonic form to release a large amount of energy. The linked response is required for the transformation of this energy into an endergonic state. The electricity, then, is not extracted by the machine as heat

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