Problem 181 - A Complete Resource Book in Chemistry for JEE Main

Question

In the following chemical reactions: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}+\mathrm{CHCl}_{3}+3 \mathrm{KOH} \longrightarrow(\mathrm{A})+(\mathrm{B})+3 \mathrm{H}_{2} \mathrm{O}\), the compounds (A) and (B) are respectively [2007] (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CONH}_{2}\) and \(3 \mathrm{KCl}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NC}\) 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 compounds (A) and (B) are (c) \(\mathrm{C}_2\mathrm{H}_5\mathrm{NC}\) and \(3\mathrm{KCl}\).

Step 1: Understanding the Reaction Type

The given reaction involves ethylamine reacting with chloroform and potassium hydroxide. This type of reaction is a known process called the Carbylamine reaction or Hoffmann's isocyanide synthesis.

Step 2: Analyzing Reactants and Expected Products

In a Carbylamine reaction, primary amines (like ethylamine) react with chloroform and potassium hydroxide to produce an isocyanide (also known as a carbylamine), potassium chloride, and water.

Step 3: Identifying the Product Structure and Components

From the analysis of Step 2, the expected major products will be an isocyanide formed from the ethyl group, specifically ethyl isocyanide (\(\mathrm{C}_2\mathrm{H}_5\mathrm{NC}\)), and three moles of potassium chloride (\(3\mathrm{KCl}\)).

Step 4: Matching with Given Options

Based on the expected products: ethyl isocyanide and potassium chloride, we compare with the given options to find that option (c), \(\mathrm{C}_2\mathrm{H}_5\mathrm{NC}\) and \(3\mathrm{KCl}\), matches the predicted products of this reaction.

Key Concepts

Ethylamine

Ethylamine is a primary amine represented by the formula \(\mathrm{CH}_3\mathrm{CH}_2\mathrm{NH}_2\). It is an organic compound that belongs to a group of chemicals called aliphatic amines. Non-toxic and pleasantly smelling, ethylamine is used in various chemical reactions, one of which includes the Carbylamine reaction.

• Structure: Ethylamine consists of an ethyl group \(\mathrm{CH}_3\mathrm{CH}_2\) attached to an amine group \(\mathrm{NH}_2\). This makes it a small molecule that acts as a nucleophile in reactions.
• Properties: It is a colorless liquid at room temperature with a base-like ammonia smell. Ethylamine is voluntarily soluble in water.

In reactions, ethylamine often serves as a building block due to its primary amine functional group. In the Carbylamine reaction, it reacts with chloroform and potassium hydroxide to produce ethyl isocyanide, showcasing its reactivity and utility in organic synthesis.

Isocyanide Synthesis

The Carbylamine reaction, also known as isocyanide synthesis, is significant in organic chemistry for producing isocyanides. This reaction is incredibly useful for chemists because it involves modifying a simple primary amine into a more complex compound.

• Mechanism: In this reaction, the primary amine, such as ethylamine, reacts with chloroform in the presence of an alkali like potassium hydroxide. The process involves several steps, including the formation of dichlorocarbene intermediary, which then reacts with the amine to form an isocyanide.
• Products: The main product of this synthesis from ethylamine is ethyl isocyanide (\(\mathrm{C}_2\mathrm{H}_5\mathrm{NC}\)). The formation of isocyanides can be confirmed by their characteristic, pungent odor. Additionally, potassium chloride and water are formed as byproducts.
• Uses: Isocyanides are not just renowned for their distinctive smell but also hold importance in pharmaceutical syntheses and the study of complex organic reactions.

Understanding the Carbylamine reaction widens a chemist's ability to synthesize unique compounds for various fields, from medicine to materials science.

Potassium Hydroxide Reaction

Potassium hydroxide (KOH) plays an essential role in the Carbylamine reaction. This strong base is a key player in facilitating the transformation of primary amines into isocyanides.

• Role of KOH: It assists in the deprotonation of the amine, generating a nucleophile that can react with chloroform. Moreover, KOH helps to generate dichlorocarbene from chloroform, an important intermediate in the reaction.
• Properties: Potassium hydroxide is a white, highly deliquescent solid at room temperature. It is soluble in water and readily dissociates to provide hydroxide ions \(\mathrm{OH}^-\), making it a strong base and excellent proton acceptor.
• Byproducts: Through its involvement, potassium chloride (\(3\mathrm{KCl}\)) and water are produced as secondary outcomes in the reaction. This underscores the role of KOH not just as a reactant, but also in shaping the final composition of the resulting mixture.

Utilizing potassium hydroxide in the Carbylamine reaction demonstrates how such chemical agents simplify the synthesis of complex organic products, further emphasizing their importance in industrial and laboratory settings.