Wurtz-Fittig Reaction - Wurtz Reaction Limitations, Mechanism, Fittig Reaction and Explanation

We use ethane in our daily life in many products. It is used in anti-freezing agents, plastics, detergents, and, majorly, it is present in CNG (compressed natural gas), which is used as fuel. Ethane is obtained as a product of the Wurtz reaction when methyl chloride is treated with sodium in the presence of dry ether. The Wurtz reaction is used in organic chemistry and organometallic chemistry to synthesize symmetrical alkanes and has many applications in industries.

So in this article, you will get a deep understanding of Wurtz's reaction.

TABLE OF CONTENT

• Wurtz Reaction
• Mechanism of Wurtz Reaction
• Limitation of Wurtz Reaction
• Fittig Reaction
• Wurtz-Fittig Reaction
• Practice Problems
• Frequently asked questions (FAQs)

Wurtz Reaction

Wurtz reaction is a coupling reaction in organic chemistry named after Charles Adolphe Wurtz. The Wurtz reaction leads to the preparation of higher alkanes. It is also beneficial in preparing alkanes with an even number of carbon atoms.

This reaction is named after Charles Adolphe Wurtz, a French chemist who also discovered the aldol reaction.

Metals such as silver, indium, activated copper, zinc, and iron, in addition to sodium, can be employed in the Wurtz reaction to produce alkanes.

The general form of the Wurtz reaction is

Where R is an alkyl group, and X is a halogen. This reaction takes place between two alkyl halides and sodium metals. In the presence of dry ether, this combination gives higher alkanes as a product. Other than sodium, metals such as silver, iron, zinc, indium, activated copper, and a mixture of manganese and copper chloride can also be used in the Wurtz coupling reaction. As the reaction involves a free radical mechanism, side reactions may take place and due to this, there is a possibility of the formation of alkene as a byproduct. A similar reaction involving aryl halides is known as the Wurtz-Fittig reaction.

Example:

Mechanism of Wurtz Reaction

The mechanism is initiated by the free radical species R and involves exchanging metal and halogen. It is also accompanied by the formation of a carbon-carbon bond.

A free radical species designated by R^*, which is a part of a halogen-metal exchange, is involved in the mechanism of the Wurtz reaction. The formation of Grignard reagents is comparable to this method. In this reaction mechanism, the carbon-carbon bond is formed through a nucleophilic substitution process, which can be broken down into three steps:

Step 1: Formation of free radical 

In this step, an electron is transferred from the metal(sodium) to the halogen atom in alkyl halide which leads to the formation of free radical, and sodium halide is also formed as a product.

Where R^* is alkyl radical and  Na⁺X^-  is metal halide.

Step 2: Formation of an alkyl anion

The alkyl free radical formed in step 1 will gain one electron from another sodium atom and get converted into an alkyl ion.

Where R ^-Na⁺ is the alkyl anion.

Step 3: Formation of Product 

The alkyl anion thus formed proceeds to displace the halide ion of another alkyl halide molecule. This reaction is known as the S_N2 reaction. It also forms a bond with another R which was initially bonded with the halogen. The reaction can be written as

As discussed, there is a possibility of a side reaction by which alkene is formed as a product.

Side Reaction:

As the reaction involves the formation of multiple side products, the yield of the main product is very low in the Wurtz reaction.

Limitations of Wurtz Reaction

Following are the limits of the Wurtz reaction:

1. Wurtz's reaction is of no use when forming low alkanes. Wurtz reaction requires a minimum of two carbon atoms to take place. Whereas, in the case of smaller or lower alkanes such as methane (CH₄), the Wurtz reaction cannot be applied since there is only one carbon atom in methane. Also, the Wurtz reaction is usually used to double the number of carbon atoms in every production. This means it does not support the formation of lower alkanes or alkanes with an odd number of carbon atoms.
2. As we know, the Wurtz reaction uses sodium, and the reaction cannot be carried out in moisture. Also, oxygen and moisture easily react with sodium and can catch fire.
3. Wurtz reaction always leads to the formation of symmetric alkanes. It does not prove useful while synthesizing asymmetric alkanes. If the Wurtz reaction is carried on two dissimilar alkyl halides, then it leads to the formation of products that only have a combination of alkanes. Products of such combinations are not easy to separate. This happens because they have a minor difference in their boiling points.

Wurtz's reaction always initiates side products. However, if the halides are bulky, they may form too many side reactions.

Fittig Reaction

A Fittig reaction is a chemical reaction where two aryl halides react in the presence of Sodium and dry ether. The product formed by the Fittig reaction consists of two aryl groups joined by a single bond.

Example:

Wurtz-Fittig Reaction

Wurtz - Fittig reaction is a chemical reaction taking place between an aryl halide and alkyl halide, thereby giving rise to an alkyl arene. Wutz - Fittig reaction takes place in the presence of dry ether and Sodium.

Example:

Practice Problems

Q1. When a mixture of 1-bromopropane and 2-bromopropane is reacted with sodium in the presence of ether, write the structural formulae and IUPAC designations of the various alkanes produced. What is the chemical reaction's name?

Solution:

Reaction of 1-bromopropane and 1-bromopropane gives hexane.

The reaction of 2-bromopropane and 2-bromopropane gives 2,3-Dimethylbutane.

The reaction of 1-bromopropane and 2-bromopropane gives 2-Methylpentane.

The name of the reaction is Wurtz Reaction.

Q2. Which of the following will not give Wurtz reaction?

A.

B.

 
C.

D.  None of the above

Solution: In the Wurtz reaction, two molecules of alkyl halides combine to produce higher alkanes containing an even number of carbon atoms on heating with sodium metal in presence of dry ether as a solvent.

Ethyl alcohol will not give Wurtz reaction.

So, the correct option is B

Q3. Which of the following cannot be formed as a single major product by Wurtz's coupling reaction of an alkyl halide?

Solution:

A)

B)

C)

D)

Option (A)

Option (B) has an odd number of carbon atoms in the parent chain, so that cannot be obtained by coupling of any alkyl halide.

Option (C)

Option (D)

So, the correct option is B.

Q4.  Na, dry ether is used in which of the following reaction?

A. Catalytic Hydrogenation
B. Kolbe’s Electrolysis
C. Wurtz reaction
D. Clemmensen Reduction

Solution:

Wurtz reaction is used for the preparation of higher alkanes containing an even number of carbon atoms. In this reaction, alkanes are prepared from alkyl halides by using Na, dry ether.

Hence, option (C) is the correct answer.

Frequently Asked Questions - FAQ

Question 1. Why isn't the Wurtz synthesis a good way to make propane?
Answer: Propane is made from two distinct alkyl halides (methyl chloride and ethyl chloride). As a result, three reactions could occur, resulting in a combination of ethane, butane, and propane.

Question 2. Why dry ether is used in Wurtz Reaction?
Answer: Dry ether is used as a solvent in the Wurtz reaction as alkanes are soluble in dry ether also it will not react with sodium and it is a nonpolar solvent which is required for the Wurtz reaction.

Question 3. Give a name of a reaction other than the Wurtz reaction to increasing the length of Carbon atoms?
Answer: Aldol condensation reaction and Grignard reaction increase the number of carbon atoms in a compound.

Question 4. Why Wurtz reaction is not suitable for unsymmetrical alkanes?
Answer: For the formation of unsymmetrical alkanes by the Wurtz reaction, different side products are formed, so it is not suitable for the preparation of an odd number of alkanes.

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