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) \(\mathrm{C}_{2} \mathrm{H}\) (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 (c) C₂H₆.

Step 1: Write the Reaction Equation

The reaction begins with chloroethane (C_2H_5Cl) reacting with magnesium (Mg) in the presence of dry ether to form a Grignard reagent. This reaction can be represented as: \[ \text{C}_2 ext{H}_5 ext{Cl} + ext{Mg} \xrightarrow[]{\text{dry ether}} \text{C}_2 ext{H}_5 ext{MgCl} \]The product formed \( \text{C}_2\text{H}_5\text{MgCl} \) is the compound \( \text{X} \).

Step 2: Hydrolysis of the Grignard Reagent

The Grignard reagent \( \text{C}_2\text{H}_5\text{MgCl} \) undergoes hydrolysis. During hydrolysis, the Grignard reagent reacts with water (H₂O) to produce ethane (C₂H₆) and magnesium hydroxide chloride (Mg(OH)Cl). The reaction is:\[ \text{C}_2\text{H}_5\text{MgCl} + \text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_6 + \text{Mg(OH)Cl} \]Here, ethane (C₂H₆) is the compound \( Y \), while \( Z \) is \( \text{Mg(OH)Cl} \).

Step 3: Identify the Compound Y

From the above reaction step, we identified that the hydrolysis of \( \text{C}_2\text{H}_5\text{MgCl} \) produces ethane (C₂H₆), which is the compound \( Y \). We can now proceed to match this with the options given in the problem.

Step 4: Match Y with Given Options

Compare the identified compound \( Y \), which is \( \text{C}_2\text{H}_6 \), with the provided options: - (a) \( \text{C}_2\text{H} \)- (b) \( \text{C}_2\text{H}_2 \)- (c) \( \text{C}_2\text{H}_6 \)- (d) \( \text{C}_6\text{H}_6 \)The correct match is option (c), \( \text{C}_2\text{H}_6 \).

Key Concepts

Organometallic Chemistry

Organometallic chemistry is a fascinating branch of research focusing on compounds where a chemical bond is formed between a carbon atom in an organic molecule and a metal. The Grignard reagent is a classic example of this type of compound. It is typically formed by the reaction of an alkyl or aryl halide with magnesium in an inert solvent like dry ether. This magical reaction opens doors to many synthetic possibilities. Grignard reagents are especially valuable in the organic chemistry toolkit, allowing the formation of carbon-carbon bonds.
Working with these reagents needs careful handling, as they are highly reactive and can be sensitive to moisture. They play a critical role in creating new molecules, supporting various industrial and pharmaceutical applications. Understanding how to create and use these organometallic compounds can significantly enhance a chemist's skill set in synthesis and reaction planning.

Reaction Mechanism

The formation of a Grignard reagent follows a well-defined reaction mechanism. The process starts with a halogenated hydrocarbon and magnesium metal in the presence of a solvent such as dry ether. The magnesium atom inserts itself between the carbon and halogen bond, creating a carbon-metal bond, resulting in the formation of the Grignard reagent.
This unique bond between carbon and magnesium gives the carbon anionic character, enabling it to act as a nucleophile in subsequent reactions. Nucleophiles are species that seek out positive centers, or electrophiles, in chemical reactions, creating new bonds. In simple terms, the Grignard reagent can attach carbon atoms to other molecules, effectively building bigger and more complex organic structures. Understanding these mechanisms provides essential insights for predicting reaction outcomes and developing new synthetic pathways.

Hydrolysis

Hydrolysis is a chemical process involving the breakage of bonds in a molecule using water. In the context of Grignard reagents, hydrolysis results in the transformation of the organomagnesium compound into a simpler organic molecule and a magnesium-based salt.
When a Grignard reagent like ethylmagnesium chloride (\(\text{C}_2\text{H}_5\text{MgCl}\)) reacts with water (\(\text{H}_2\text{O}\)), the product is ethane (\(\text{C}_2\text{H}_6\)) and magnesium hydroxide chloride (\(\text{Mg(OH)Cl}\)). This reaction is a straightforward hydrolysis because water is the reactant breaking down the chemical compound. Hydrolysis reactions are widespread in chemistry and biology, from digestion processes in the human body to the breakdown of polymers in industry. In the laboratory, understanding hydrolysis can help in predicting and controlling the outcome of synthetic reactions involving moisture-sensitive reagents.