Problem 17 - A Complete Resource Book in Chemistry for JEE Main

Question

An organic compound 'A' having molecular formula \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~N}\), on reduction gave another compound 'B'. Upon treatment with nitrous acid, 'B' gave ethyl alcohol. On warming with chloroform and alcoholic \(\mathrm{KOH}\), it formed an effensive smelling compound ' \(\mathrm{C}\) '. The compound ' \(\mathrm{C}^{\prime}\) is (a) \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{N}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~N} \equiv \mathrm{C}\)

Step-by-Step Solution

Answer

The compound 'C' is option (d) \( \text{CH}_3\text{CH}_2\dot{N} \equiv \text{C} \).

Step 1: Identify Compound 'A'

The molecular formula of compound 'A' is \( \text{C}_2\text{H}_3\text{N} \). This suggests that 'A' could possibly be a nitrile or an isocyanide. However, given the context of the problem, it is most likely to be a nitrile, specifically acetonitrile, \( \text{CH}_3\text{C} \equiv \text{N} \).

Step 2: Reduction of Compound 'A' to Obtain 'B'

When acetonitrile (\( \text{CH}_3\text{C} \equiv \text{N} \)) is reduced, it forms ethylamine (\( \text{CH}_3\text{CH}_2\text{NH}_2 \)), which is compound 'B'.

Step 3: React 'B' with Nitrous Acid

Ethylamine (\( \text{CH}_3\text{CH}_2\text{NH}_2 \)) reacts with nitrous acid (\( \text{HNO}_2 \)) to form ethyl alcohol (\( \text{CH}_3\text{CH}_2\text{OH} \)) and nitrogen gas.

Step 4: Formation of Compound 'C'

When compound 'B', ethylamine \( (\text{CH}_3\text{CH}_2\text{NH}_2) \), is treated with chloroform (\( \text{CHCl}_3 \)) and alcoholic \( \text{KOH} \), it undergoes a reaction to form an isocyanide. The product here, which has a foul odor, is ethyl isocyanide \( (\text{CH}_3\text{CH}_2\dot{N} \equiv \text{C}) \).

Step 5: Identify Compound 'C' in the Options

The compound \( \text{C} \), ethyl isocyanide, matches option (d) \( \text{CH}_3\text{CH}_2\dot{N} \equiv \text{C} \).

Key Concepts

Nitriles

Nitriles are organic compounds that contain a carbon triple-bonded to a nitrogen atom, denoted as \(... \text{C} \equiv \text{N} ...\).These compounds are noteworthy in organic chemistry due to their reactivity and diverse applications in synthesis.
Nitriles can be found in natural products and pharmaceuticals, and they serve as key intermediates in organic synthesis. In our exercise, the compound 'A', with the formula \(\text{C}_2\text{H}_3\text{N}\), is identified as a nitrile, specifically acetonitrile \(\text{CH}_3\text{C} \equiv \text{N}\).
Nitriles can be converted into a variety of other functional groups through different reactions, such as reduction, hydrolysis, and more. Their versatility makes them a valuable tool for chemists exploring new compound classes.

Reduction Reactions

Reduction reactions in organic chemistry involve gaining electrons or the removal of oxygen, commonly resulting in the addition of hydrogen atoms.
In the given exercise, the reduction of acetonitrile \(\text{CH}_3\text{C} \equiv \text{N}\) is a prime example. Through reduction, this nitrile forms compound 'B', ethylamine \(\text{CH}_3\text{CH}_2\text{NH}_2\).

• Reductions are often accomplished using reagents like LiAlH4 or hydrogen gas in the presence of a catalyst.
• Through reduction, nitriles can be transformed into primary amines, a crucial transformation in organic synthesis.

Understanding these reactions allows chemists to synthesize a wide array of amines, further expanding the toolkit for designing molecules with desired properties.

Ethylamine

Ethylamine is a simple and common type of amine, characterized by containing an ethyl group attached to an amine group (\(\text{NH}_2\)). The formula for ethylamine is \(\text{CH}_3\text{CH}_2\text{NH}_2\).
With its distinct properties and applications, ethylamine serves various roles:

• It can act as a building block in pharmaceuticals, such as local anesthetics.
• Ethylamine also engages in numerous reactions due to its basicity and nucleophilicity, participating in formations and substitutions.

In our exercise, reduction of acetonitrile yields ethylamine, which is then utilized to produce ethanol through reaction with nitrous acid, demonstrating its further transformation capabilities in chemical synthesis.

Isocyanides

Isocyanides, also known as isonitriles, are intriguing organic compounds characterized by the presence of the \(\text{--N} \equiv \text{C}\) group, where the nitrogen atom is directly attached to the rest of the molecule. These compounds exhibit unique bonding and properties, setting them apart:

• They have a notable pungent odor, which is often described as objectionable or foul.
• Isocyanides are important in synthesis, particularly in multi-component reactions known as the Passerini and Ugi reactions.

In the exercise, the compound 'C' formed from ethylamine using chloroform and potassium hydroxide is identified as an isocyanide, specifically ethyl isocyanide \(\text{CH}_3\text{CH}_2\dot{N} \equiv \text{C}\), displaying the conversion possibilities from common amine precursors.