Problem 131 - A Complete Resource Book in Chemistry for JEE Main

Question

The end product (b) in the following sequence of reactions \(\mathrm{CH}_{3} \mathrm{Cl} \stackrel{\mathrm{KCN}}{\longrightarrow}\) (a) \(\stackrel{\mathrm{H}^{\prime} / \mathrm{H}_{2} \mathrm{O}}{\longrightarrow}\) (b) is (a) \(\mathrm{HCOOH}\) (b) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{COOH}\) (d) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\)

Step-by-Step Solution

Answer

The end product (b) is (c) \( \mathrm{CH}_3\mathrm{COOH} \).

Step 1: Identifying Reaction 1

The first reaction involves the substitution of the chlorine atom in methyl chloride (\( \mathrm{CH}_3\mathrm{Cl} \)) with a cyano group using \( \mathrm{KCN} \). This reaction is a nucleophilic substitution, resulting in the product \( \mathrm{CH}_3\mathrm{CN} \), which is acetonitrile. This is compound (a).

Step 2: Identifying Reaction 2

The second reaction involves the hydrolysis of acetonitrile (\( \mathrm{CH}_3\mathrm{CN} \)) with water in the presence of acid \( \mathrm{H}^{+} \). This leads to the conversion of the nitrile group (\(-CN\)) into a carboxylic acid group (\(-COOH\)). Therefore, the product of this second reaction is acetic acid (\( \mathrm{CH}_3\mathrm{COOH} \)). This is compound (b).

Step 3: Matching with Options

According to the products of the reactions, compound (b) is \( \mathrm{CH}_3\mathrm{COOH} \), which matches option (c) \( \mathrm{CH}_3\mathrm{COOH} \). Thus, the end product is verified as acetic acid.

Key Concepts

Nucleophilic Substitution

In organic chemistry, nucleophilic substitution is a common type of reaction where a nucleophile, a molecule with a pair of electrons ready to donate, replaces a leaving group in a compound. This reaction is vital for transforming one functional group into another. In the exercise, the first part of the reaction sequence involves nucleophilic substitution. Here, methyl chloride ( \( \mathrm{CH}_3\mathrm{Cl} \)) undergoes nucleophilic attack by the cyanide ion ( \( \mathrm{CN}^- \)), which is a strong nucleophile.

• The chlorine atom serves as the leaving group; it detaches, making room for the cyano group to bond with the carbon atom.
• This results in the formation of acetonitrile ( \( \mathrm{CH}_3\mathrm{CN} \)), marking the successful completion of the nucleophilic substitution reaction.

This type of reaction is crucial for converting simpler molecules into more complex organic compounds.

Hydrolysis Reaction

Hydrolysis is a chemical process in which a compound reacts with water, leading to the breakdown of its bonds. In this specific exercise, a hydrolysis reaction follows the nucleophilic substitution stage.The acetonitrile ( \( \mathrm{CH}_3\mathrm{CN} \)) formed previously undergoes hydrolysis in an acidic environment. This reaction proceeds in several steps:

• The nitrile group ( \(-CN\)) reacts with water, with the help of protons ( \(\mathrm{H}^+ \)), to form an intermediate known as an imine.
• Subsequent reactions with more water ultimately transform this intermediate into a carboxylic acid due to the continuous addition and rearrangement of molecular groups.
• In this sequence, acetonitrile is converted to acetic acid ( \( \mathrm{CH}_3\mathrm{COOH} \)), a simple carboxylic acid.

Hydrolysis reactions are instrumental in breaking down complex molecules and form the backbone for many biochemical processes.

Acetonitrile Conversion

Acetonitrile conversion refers to the transformation of the molecule \( \mathrm{CH}_3\mathrm{CN} \) through chemical reactions to yield different products. In the exercise, acetonitrile is converted into acetic acid ( \( \mathrm{CH}_3\mathrm{COOH} \)) via a hydrolysis reaction, which we detailed earlier.Here's a closer look at this conversion process:

• Initially, the cyano group ( \(-CN\)) in acetonitrile is transformed step-by-step into a carboxyl group ( \(-COOH\)).
• This transformation is facilitated by water and acid, highlighting how conditions in the reaction environment influence the conversion.
• Overall, this conversion illustrates an essential method in organic chemistry to traverse from simple nitrile molecules to more complex acids and is used frequently in synthesis reactions.

Acetonitrile conversion demonstrates the practical application of nucleophilic substitution and hydrolysis, showcasing the importance of understanding radical transformations in organic chemistry.