Wurtz Reaction is a chemical reaction used to couple two alkyl halides, typically chlorides, bromides, or iodides, in the presence of sodium metal. This reaction leads to the formation of a new carbon-carbon bond, effectively joining two smaller alkane molecules into a larger one. It is named after the French chemist Charles-Adolphe Wurtz, who discovered it in 1855.
This article provides a detailed description of the Wurtz Reaction, including examples and its mechanism.
What is Wurtz’s Reaction?
The Wurtz reaction is a classic organic synthesis method discovered by Charles-Adolphe Wurtz in 1855. It is a coupling reaction that involves the formation of carbon-carbon bonds by combining two alkyl halides in the presence of reactive metals such as sodium. The reaction leads to the synthesis of symmetrical alkanes and sodium halide byproducts.
Wurtz Reaction Equation
The general form of the Wurtz reaction can be represented as follows:
2R-X + 2Na → R-R + 2NaX
In this equation:
- R-X represents an alkyl halide.
- Na represents sodium.
- R-R represents the desired alkane product, with a new carbon-carbon bond formed.
Read More about Haloalkane and Haloarenes.
Wurtz Reaction Example
Some common examples of Wurtz reaction are:
- Production of Ethane from Methyl Bromide
- Production of Butane from Ethyl Bromide
Let’s discuss these examples in detail.
Production of Ethane from Methyl Bromide
We can obtain ethane by reacting methyl bromide with sodium in the presence of anhydrous Ether.
The reaction is:
2CH3Br + 2Na → C2H6 +2NaBr
Here, a large alkane molecule (Ethane) is developed by joining two compounds of alkyl halide (Methyl Bromide) and eradicating the halogen atoms in the form of sodium halide (Sodium Bromide).
Production of Butane from Ethyl Bromide
Ethyl bromide and sodium can react to produce butane when anhydrous ether is present.
CH3-CH2-Br + 2Na + Br-CH2-CH3 → CH3-CH2-CH2-CH3 + 2NaBr
Mechanism of Wurtz Reaction
The mechanism of the Wurtz reaction involves a free radical species denoted by R• known as Alkyl Radical. The carbon-carbon bond is formed in this reaction mechanism can be broken down into the following 3 steps:
Step 1: In the first step, a metal halide is formed along with the alkyl radical.
R–X + Na → R• + Na+X–
Step 2: In the second step, an alkyl anion is formed when the alkyl radical accepts an electron from another metal (sodium) atom.
R• + Na → R−Na+
Step 3: In the final step, the halogen is removed from the carbon and a covalent bond is formed with the same carbon by the nucleophilic carbon of the alkyl anion through the SN2 reaction.
R–Na+ + R–X → R–R + Na+X–
Alkene formation could occur as a byproduct of this process due to its free radical mechanism.
Uses of Wurtz Reaction
Some uses of Wurtz reaction are as follows:
- Synthesizing symmetrical hydrocarbons, particularly alkanes, can be done easily with the Wurtz reaction.
- This reaction is used in closing small, especially 3 membered rings.
- Preparation of Bicyclobutane using the Wurtz coupling.
- This reaction gives alkenes as a product when the reactant is vicinal dihalide , and gives alkynes as a product if the reactant is Geminal dihalide.
Limitations of Wurtz Reaction
A few limitations of this reaction are listed below:
- Only symmetric alkanes can be synthesized via this method.
- Methane cannot be synthesized via the Wurtz reaction.
- Tertiary alkyl halides are less reactive in the Wurtz reaction due to steric hindrance.
- The Wurtz reaction is not effective for coupling aryl halides.
- The use of reactive metals like sodium poses safety concerns due to their reactivity with water and air.
- The byproducts of the Wurtz reaction, such as sodium halides, can contribute to environmental concerns.
Read More,
Wurtz Reaction: FAQs
1. Wurtz Reaction is Named after which Scientist?
The Wurtz reaction is named after the French chemist Charles-Adolphe Wurtz.
2. What is the Catalyst for the Wurtz Reaction?
The Wurtz reaction typically doesn’t use a catalyst but requires a strong base, usually sodium (Na) or sometimes potassium (K).
3. Wurtz Reaction is used to Prepare which Compounds?
Wurtz Reaction is used to prepare alkanes by coupling two alkyl halides.
4. What is Wurtz Reaction Reagent?
The key reagent in the Wurtz reaction is sodium metal, which facilitates the coupling of alkyl halides.
5. What is one Example of Wurtz Reaction?
An example is the reaction of two molecules of ethyl chloride (CH3CH2Cl) with sodium, yielding butane (CH3CH2CH2CH3) and sodium chloride.
6. How are Alkenes are Obtained by the Wurtz Reaction?
Alkenes are not typically obtained directly from the Wurtz reaction. This reaction is primarily for synthesizing alkanes. However, subsequent elimination reactions on the formed alkanes can yield alkenes.