Problem 111 - A Complete Resource Book in Chemistry for JEE Main

Question

Chloroethane reacts with magnesium in dry ether to form \(\mathrm{X}\). When \(\mathrm{X}\) is hydrolyzed, a carbon compound \(\mathrm{Y}\) and \(Z\) are formed. Which of the following is \(Y ?\) (a) \(\mathrm{C}_{2} \mathrm{H}_{4}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{2}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{6}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{6}\)

Step-by-Step Solution

Answer

The compound \(Y\) is ethane, \(\mathrm{C}_{2}\mathrm{H}_{6}\) (option c).

Step 1: Identify the Reaction Type

Chloroethane (\(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{Cl}\)) reacts with magnesium in dry ether to form a Grignard reagent, \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{MgCl}\). This is a type of organometallic reaction where a halide (chloroethane) and magnesium produce a Grignard reagent.

Step 2: Analyze the Grignard Reagent

The Grignard reagent \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{MgCl}\) can react with water during hydrolysis. These reagents are highly reactive and will do a nucleophilic attack on water to produce a new carbon compound and magnesium hydroxide.

Step 3: Hydrolysis of the Grignard Reagent

When the Grignard reagent \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{MgCl}\) is hydrolyzed, it reacts with water (\(\mathrm{H}_{2}\mathrm{O}\)) to form ethane\(\mathrm{C}_2\mathrm{H}_6\) (\(Y\)) and by-product, magnesium hydroxide \(\mathrm{Mg}(\mathrm{OH})_{2}\) (\(Z\)).

Step 4: Determine the Correct Option

After hydrolysis, the Grignard reagent produces ethane (\(\mathrm{C}_{2}\mathrm{H}_{6}\)). Comparing the options, the compound \(Y\) that matches \(\mathrm{C}_{2}\mathrm{H}_{6}\) is option (c).

Key Concepts

Chloroethane

Chloroethane, also known as ethyl chloride, is an organic compound with the chemical formula \( \mathrm{C}_2\mathrm{H}_5\mathrm{Cl} \). It's a colorless gas at room temperature, often used in the synthesis of other organic compounds.

A characteristic property of chloroethane is its ability to participate in organometallic reactions, particularly with magnesium, to form Grignard reagents. This conversion is fundamental in organic chemistry because it introduces the ability for the carbon in chloroethane to undergo further transformations.

In the presence of dry ether, a solvent that helps stabilize the reactive intermediate, chloroethane bonds with magnesium to form \( \mathrm{C}_2\mathrm{H}_5\mathrm{MgCl} \), a Grignard reagent:

• Chloroethane (\( \mathrm{C}_2\mathrm{H}_5\mathrm{Cl} \)) + Magnesium (Mg) → Grignard reagent (\( \mathrm{C}_2\mathrm{H}_5\mathrm{MgCl} \))

Understanding this reaction sets the stage for learning about organometallic reactions and their subsequent reactions such as hydrolysis.

Organometallic Reaction

Organometallic reactions are a fascinating area of chemistry, involving metal-carbon bonds. The reaction between chloroethane and magnesium is a prime example.

These reactions are characterized by the formation of an organometallic compound, here the Grignard reagent \( \mathrm{C}_2\mathrm{H}_5\mathrm{MgCl} \). In this reaction:

• A carbon-halogen bond in chloroethane breaks.
• Magnesium inserts itself into the carbon chain, forming a stable complex.

This process is central to creating nucleophiles that can attack other molecules, enabling the formation of new carbon-carbon bonds. It's a crucial step in synthetic chemistry, allowing the construction of complex organic compounds from simpler ones. The reactivity of these organometallic compounds makes them indispensable in many synthetic pathways.

Hydrolysis

Hydrolysis is an essential reaction that involves water breaking a compound into two or more products. For the Grignard reagent \( \mathrm{C}_2\mathrm{H}_5\mathrm{MgCl} \), hydrolysis plays a vital role in synthesizing new organic compounds.

When you add water to a Grignard reagent, such as \( \mathrm{C}_2\mathrm{H}_5\mathrm{MgCl} \), a reaction takes place resulting in:

• Ethane (\( \mathrm{C}_2\mathrm{H}_6 \)), a simple alkane.
• Magnesium hydroxide (\( \mathrm{Mg(OH)}_2 \)), as a by-product.

This hydrolysis step is crucial because it reverts the highly reactive Grignard reagent into a stable alkane and an inorganic by-product.

Understanding hydrolysis is essential for appreciating the full utility and transformation capability of organometallic chemistry, as it leads to workable end products in organic synthesis.