Problem 53 - A Complete Resource Book in Chemistry for JEE Main

Question

What is the end product \(\mathrm{C}\) in this series? \(\mathrm{CH}_{3} \mathrm{CN} \stackrel{\mathrm{Na} / \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{OH}}{\longrightarrow} \mathrm{A} \stackrel{\mathrm{HNO}_{2}}{\longrightarrow} \mathrm{B}\) \(\stackrel{\mathrm{Cu} / 573 \mathrm{~K}}{\longrightarrow} \mathrm{C}\) (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NHOH}\) (c) \(\mathrm{CH}_{3} \mathrm{CONH}_{2}\) (d) \(\mathrm{CH}_{3} \mathrm{CHO}\)

Step-by-Step Solution

Answer

The end product \(\mathrm{C}\) is acetaldehyde, \(\mathrm{CH}_{3}\mathrm{CHO}\).

Step 1: Reduction of Nitrile

The first step involves conversion of methyl cyanide ( \(\mathrm{CH}_{3}\mathrm{CN}\)) in the presence of sodium (\(\mathrm{Na}\)) and ethanol (\(\mathrm{C}_{2}\mathrm{H}_{3}\mathrm{OH}\)) which results in the reduction of the nitrile group to an amine. The product is ethylamine (\(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{NH}_{2}\)), which is referred to as compound \(\mathrm{A}\).

Step 2: Reaction with Nitrous Acid

In the second step, ethylamine (compound \(\mathrm{A}\)) reacts with nitrous acid (\(\mathrm{HNO}_{2}\)). Primary amines such as ethylamine form alcohols when treated with \(\mathrm{HNO}_{2}\). This reaction converts ethylamine into ethanol (\(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH}\)), which is compound \(\mathrm{B}\).

Step 3: Oxidation of Ethanol to Acetaldehyde

In the final step, ethanol (compound \(\mathrm{B}\)) is oxidized using copper at a high temperature (573 K). This process oxidizes the alcohol to an aldehyde, resulting in acetaldehyde (\(\mathrm{CH}_{3}\mathrm{CHO}\)), which is compound \(\mathrm{C}\).

Key Concepts

Nitrile Reduction

Understanding the process of converting a nitrile to an amine is crucial in organic chemistry. The reduction of nitriles often involves converting the triple bond to a more reactive group, such as an amine. This transformation is typically conducted using metal catalysts and alcohols, like sodium (Na) and ethanol. In our scenario, methyl cyanide (\( \mathrm{CH}_{3}\mathrm{CN} \)) is reduced to ethylamine (\( \mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{NH}_{2} \)). The process can be understood through these streamlined steps:

• Sodium donates electrons, aiding in the breakdown of the nitrile bond.
• The hydrogen from ethanol (\( \mathrm{C}_{2}\mathrm{H}_{3}\mathrm{OH} \)) combines with the molecule to form the amine.
• The result is a transition from a nitrile group to a primary amine – ethylamine.

These reactions provide an efficient way to obtain amines from nitrile compounds, which are fundamental building blocks in various chemical processes.

Amines to Alcohols

Transitioning from amines to alcohols involves a fascinating reaction with nitrous acid (\( \mathrm{HNO}_{2} \)). Primary amines react with nitrous acid to form alcohols, nitrogen gas, and water. Ethylamine (\( \mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{NH}_{2} \)), when treated with nitrous acid, converts into ethanol (\( \mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{OH} \)). The essence of this reaction can be summed up as follows:

• The nitrous acid transforms the amine group into an unstable diazonium ion.
• Through hydrolysis, this ion then loses nitrogen gas, forming the corresponding alcohol.
• Ethanol emerges from this transformation, highlighting the delicate yet transformative nature of this reaction.

This method showcases a unique way to prepare alcohols from amine precursors, further expanding the range of potential compounds that can be synthesized in organic chemistry.

Alcohol Oxidation

Alcohol oxidation is a fundamental reaction where alcohols are converted into aldehydes or ketones. This transformation is particularly significant in creating value-added chemicals. In our outlined process, ethanol (compound \( B \)) is oxidized by copper at 573 K to produce acetaldehyde (\( \mathrm{CH}_{3}\mathrm{CHO} \)). The key steps in this reaction include:

• Copper acts as a catalyst to facilitate the removal of hydrogen from the alcohol.
• High temperatures increase reaction efficiency and speed.
• The end product is acetaldehyde, a simple and industrially crucial aldehyde.

Understanding alcohol oxidation helps chemists manipulate molecular structures to develop a wide array of functional products. It's a critical pathway not just in lab synthesis but also in larger-scale production of organic compounds.