Problem 90 - A Complete Resource Book in Chemistry for JEE Main

Question

Wurtz reaction of methyl iodide yields an organic compound \(\mathrm{X}\). Which one of he following reactions also yields X? (a) \(\mathrm{CHCl}_{3} \stackrel{\text { Ag powder, } \triangle}{\longrightarrow}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{ONa} \longrightarrow\) (c) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{LiAlH}_{4} \longrightarrow\) (d) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{Mg} \frac{\text { Dry ether }}{\longrightarrow}\)

Step-by-Step Solution

Answer

Reaction (c) also yields ethane.

Step 1: Understand the Wurtz Reaction

The Wurtz reaction involves the coupling of two alkyl halides using sodium metal in dry ether, forming a new carbon-carbon bond. For example, when using methyl iodide (\(\text{CH}_3\text{I}\)), the product will be ethane (\(\text{C}_2\text{H}_6\)) as two methyl radicals couple to form the ethane molecule.

Step 2: Identify Product X

The organic compound \(X\) formed from the Wurtz reaction of methyl iodide is ethane (\(\text{C}_2\text{H}_6\)). This is because the reaction couples two methyl groups that form the ethane.

Step 3: Evaluate Reaction (a)

When \(\text{CHCl}_3\) is heated with silver powder, it can produce radicals, but the specific product of this reaction does not typically yield ethane.

Step 4: Evaluate Reaction (b)

The reaction \(\text{C}_2\text{H}_5\text{Cl} + \text{C}_2\text{H}_5\text{ONa} \rightarrow\) implies a nucleophilic substitution, but it would not result in ethane. The primary product would be an ether, not ethane.

Step 5: Evaluate Reaction (c)

In the reaction \(\text{C}_2\text{H}_5\text{Cl} + \text{LiAlH}_4 \rightarrow\), ethyl chloride would be reduced to ethane. Therefore, this reaction yields ethane, similar to the product of the Wurtz reaction with methyl iodide.

Step 6: Evaluate Reaction (d)

The reaction of \(\text{C}_2\text{H}_5\text{Cl}\) with \(\text{Mg}\) in dry ether produces a Grignard reagent, which will not yield ethane unless further reacted in a specific manner, such as with water, which is not specified here.

Key Concepts

Organic Synthesis

Organic synthesis is the process of constructing complex organic compounds from simpler entities. It's an essential aspect of chemistry that enables the creation of a wide array of organic molecules. One of the cornerstones of organic synthesis is understanding the different reactions and methods for forming desired compounds.
One common type of reaction used in organic synthesis is coupling reactions, where two molecules join to form a larger one. The Wurtz reaction is a classic example. It involves the coupling of two alkyl halides in the presence of sodium metal and dry ether to form a new carbon-carbon bond, resulting in the formation of an alkane.
This reaction is particularly useful for synthesizing symmetrical alkanes. For instance, using methyl iodide with the Wurtz reaction yields ethane, a simple alkane. This method is foundational to building more complex structures in organic chemistry.
Overall, mastering reactions like the Wurtz reaction means you can make purposeful, predictable changes to organic molecules—a skill essential for any chemist.

Alkyl Halides

Alkyl halides are important compounds in organic chemistry. They serve as key intermediates in various reactions, including the Wurtz reaction. Structurally, alkyl halides are hydrocarbons where one or more hydrogen atoms have been replaced with a halogen atom, such as chlorine (Cl), bromine (Br), or iodine (I).
In the context of synthesis, these halides are crucial because their structure's reactivity allows for different types of chemical transformations. They are highly reactive due to the polar carbon-halogen bond, making them suitable for substitution or elimination reactions.
A classic example is methyl iodide (\(CH_3I\) ), which reacts in a Wurtz reaction to produce ethane. The iodine atom leaves, creating a radical that combines with another radical to form a carbon-carbon bond. This makes alkyl halides versatile participants in organic synthesis by facilitating the formation of more complex structures.

Carbon-Carbon Bonding

Carbon-carbon bonding is at the heart of organic chemistry, allowing for the creation of a vast range of compounds with diverse properties. It's the formation of bonds between carbon atoms, which acts as the backbone for most organic molecules.
The ability to create carbon-carbon bonds is crucial in building extended carbon skeletons, key to molecular architecture. Reactions such as the Wurtz reaction play an essential role here by forming carbon-carbon bonds efficiently. This reaction combines two alkyl radicals to form a single molecule with a new carbon-carbon linkage.
For example, in the Wurtz reaction involving methyl iodide, each methyl group provides a carbon radical. These radicals join together to produce ethane, demonstrating simple yet powerful carbon-carbon bond formation.
Understanding and controlling the formation of carbon-carbon bonds is a fundamental aspect of designing and synthesizing new molecules, impacting everything from pharmaceuticals to materials science.