Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

Wurtz reaction involves the reduction of alkyl halide with (a) HI (b) \(\mathrm{Zn} / \mathrm{HCl}\) (c) Zn in an inert solvent (d) Na in ether

Step-by-Step Solution

Answer

The correct answer is (d) Na in ether.

Step 1: Understanding the Problem

The Wurtz reaction is a coupling reaction where two alkyl halides are reacted in the presence of sodium metal to form a longer alkane chain. This is typically carried out in an ether solvent. We need to identify which option involves such a chemical scenario.

Step 2: Option Analysis

Let's analyze each given option:- (a) HI: This would typically involve the formation of an alkyl iodide or similar, not a coupling reaction.- (b) \( \mathrm{Zn} / \mathrm{HCl} \): This setup is generally used for reductions but doesn't provide the conditions for coupling reactions.- (c) Zn in an inert solvent: This could be a reduction setup but not specifically for coupling.- (d) Na in ether: This is the classic setup for a Wurtz reaction, where sodium metal facilitates the coupling of alkyl halides in an ether solvent.

Step 3: Final Decision

Comparing all options, it is clear that option (d) corresponds to the Wurtz reaction setup. The presence of sodium in an ether solvent is essential to the Wurtz reaction as it promotes the coupling of alkyl halides into the longer alkane.

Key Concepts

alkyl halides

Alkyl halides, also known as haloalkanes, are organic compounds that contain one or more halogen atoms (such as chlorine, bromine, or iodine) attached to an alkyl group. They are versatile and reactive intermediates in organic chemistry.
These compounds are characterized by the presence of a carbon-halogen bond, which is typically polar due to the difference in electronegativity between the carbon and the halogen atoms. This polarity makes haloalkanes reactive and suitable for many chemical transformations.
Key properties of alkyl halides include:

• They serve as excellent substrates for substitution and elimination reactions.


• Their reactivity depends on the nature of the halogen (iodides are generally more reactive than bromides and chlorides).


• Alkyl halides can undergo nucleophilic substitution, making them important in the formation of various products in organic synthesis, such as alcohols, ethers, and more complex structures like alkanes when participating in reactions like the Wurtz reaction.

Understanding alkyl halides and their reactions can open the door to exploring more complex chemical syntheses and applications in creating larger and more complex molecules.

coupling reaction

A coupling reaction in chemistry involves the joining of two organic molecules, typically facilitated by a reagent or catalyst. These reactions are fundamental in constructing larger and more complex organic structures from simpler components. In the context of the Wurtz reaction, the coupling specifically involves alkyl halides.
The general mechanism for a coupling reaction includes:

• The generation of a reactive intermediate, often a free radical or an ion.


• The interaction of these intermediates, facilitated by the presence of a metal reagent like sodium in the Wurtz reaction.


• The formation of a new covalent bond, leading to the production of a larger organic molecule, such as a longer alkane in the case of the Wurtz reaction.

Coupling reactions are incredibly useful in organic chemistry because they allow for the expansion of carbon chains and the synthesis of more complex molecules. The Wurtz reaction, in particular, exemplifies this by converting two halide molecules into a single, longer alkane structure.

sodium metal

Sodium metal plays a crucial role in the Wurtz reaction as a powerful reducing agent. Its key function is to donate electrons, facilitating the conversion of alkyl halides to longer alkane chains through a coupling reaction.
When sodium metal is used in organic reactions:

• It serves as a source of electrons, generating reactive intermediates from alkyl halides.


• The metal's high reactivity helps in breaking the carbon-halogen bonds, forming free radicals or ions needed for coupling.


• In the presence of an ether solvent, sodium remains stable enough to effectively participate in the chemical conversion without unwanted side reactions.

This ensures efficient coupling, as seen in the Wurtz reaction where the metal's reactivity allows for the synthesis of longer alkanes. Understanding the role of sodium metal helps in appreciating its importance in various chemical syntheses beyond the Wurtz reaction.