Problem 160 - A Complete Resource Book in Chemistry for JEE Main

Question

In the chemical reactions, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}+\mathrm{CHCl}_{3}+3 \mathrm{KOH} \longrightarrow\) (a) \(+(\mathrm{b})+3 \mathrm{H}_{2} \mathrm{O}\) the compounds (a) and (b) are respectively: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CONH}_{2}\) and \(3 \mathrm{KCl}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{NC}\) and \(\mathrm{K}_{2} \mathrm{CO}_{3}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NC}\) and \(3 \mathrm{KCl}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{CN}\) and \(3 \mathrm{KCl}\)

Step-by-Step Solution

Answer

The correct answer is (c): \( \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NC} \) and \( 3 \mathrm{KCl} \).

Step 1: Analyze the Reaction

Begin by analyzing the reactants and their interactions. The equation involves the reaction of ethylamine \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2} \), chloroform \( \mathrm{CHCl}_{3} \), and potassium hydroxide \( \mathrm{KOH} \). This suggests a nucleophilic substitution reaction, possibly leading to the formation of an isocyanide or a cyanide.

Step 2: Consider Carbylamine Reaction

Recall the carbylamine reaction, a reaction where a primary amine, chloroform, and an alkali produce an isocyanide. The general formula for a carbylamine reaction is: \[\text{R-NH}_2 \ + \ \text{CHCl}_3 \ + \ 3\text{KOH} \ \rightarrow \ \text{R-NC} \ + \ 3 \text{KCl} \ + \ 3 \text{H}_2\text{O}\].

Step 3: Identify Product (a)

Based on the carbylamine reaction, the primary product \((a)\) is an isocyanide. In this case, the alkyl group \( \text{R} \) associated with the primary amine is \( \text{C}_2\text{H}_5 \), so the isocyanide is \( \text{C}_2\text{H}_5\text{NC} \).

Step 4: Identify Product (b)

Alongside the formation of the isocyanide, the chloroform interacts with \( 3 \text{KOH} \) to produce \( 3 \text{KCl} \) and water according to the balanced carbylamine reaction. Therefore, product \((b)\) is \( 3 \text{KCl} \).

Step 5: Match Products with Options

Compare the identified products with the available options: - Option (a): \( \text{CH}_3 \text{CH}_2\text{CONH}_2 \) and \( 3 \text{KCl} \) - Option (b): \( \text{C}_2\text{H}_3\text{NC} \) and \( \text{K}_2\text{CO}_3 \) - Option (c): \( \text{C}_2\text{H}_5\text{NC} \) and \( 3 \text{KCl} \) - Option (d): \( \text{C}_2\text{H}_5\text{CN} \) and \( 3 \text{KCl} \)The identified products \( \text{C}_2\text{H}_5\text{NC} \) and \( 3 \text{KCl} \) correctly correspond to option (c).

Key Concepts

Nucleophilic Substitution Reaction

Nucleophilic substitution reactions are a fundamental concept in organic chemistry. They take place when a nucleophile, a molecule or ion with a free pair of electrons, replaces a leaving group in a compound. In our exercise, the primary amine (\( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2} \)) acts as a nucleophile.
In the carbylamine reaction, the amine targets the carbon in chloroform (\( \mathrm{CHCl}_{3} \)).
What makes a compound a strong nucleophile is:

• The presence of a lone pair of electrons, allowing it to donate to an electron-deficient center.
• The tendency to form new bonds with substrates.

Here, the lone pair on the nitrogen in the amine attacks the carbon in chloroform. This is because the carbon is connected to electronegative chlorine atoms, making it electron-deficient. The reactions are facilitated by the presence of an alkaline medium provided by potassium hydroxide (\( \mathrm{KOH} \)). These elements create the perfect condition for a nucleophilic substitution reaction to occur efficiently.

Isocyanide Formation

The formation of isocyanides (also known as carbylamines) is a fascinating result of the carbylamine reaction. This transformation is crucial as it shows how primary amines can be converted into isocyanides with the help of chloroform and a strong base like \( \mathrm{KOH} \).
Here's what happens:

• Chloroform loses chlorine ions and gains hydroxide ions.
• This causes the formation of the highly reactive intermediate, dichlorocarbene (:CCl₂).

This intermediate is exceptionally reactive and attacks the nitrogen atom in the amine, leading to the formation of isocyanide (\( \mathrm{C}_2\mathrm{H}_5\mathrm{NC} \)) as the final product.

Characteristics of Isocyanides:

• They have a distinct odor, often described as 'offensive' or unpleasant.
• As intermediates, they have unique bonding where the carbon atom is triply bonded to the nitrogen atom, leaving the carbon less electronegative than normal.

Understanding isocyanide formation is essential, particularly for students exploring organonitrogen chemistry. It grapples with the nuances of nucleophilic substitution and the peculiar nature of carbylamines.

Chemical Reaction Analysis

Analyzing chemical reactions requires dissecting each element involved, understanding their interactions, and predicting product formation. This approach applies to the carbylamine reaction in our problem.
First, consider the reactants: ethylamine (\( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2} \)), chloroform (\( \mathrm{CHCl}_{3} \)), and potassium hydroxide (\( \mathrm{KOH} \)). We already understand that the nucleophilic substitution leads to isocyanide and salts like \( 3 \mathrm{KCl} \).

Steps to Reaction Analysis:

• Identify possible intermediates formed during the reaction.
• Predict the nature of the final products based on known chemical behavior and reactivity.

With the carbylamine process, understanding how chlorine ions are replaced by hydroxide ions is crucial. This replacement not only helps form isocyanide but also produces water as a part of the side reaction.

Key Observations:

• Reactivity is significantly influenced by the conditions, such as the basic environment set up by \( 3 \mathrm{KOH} \).
• The appearance of \( 3 \mathrm{KCl} \) explains the stoichiometric balance needed for reaction completion.

Delving into chemical reaction analysis helps students develop the skill of anticipating reaction progress and product outcomes, a vital tool in both academic and professional chemistry contexts.