Problem 140 - A Complete Resource Book in Chemistry for JEE Main

Question

On heating benzyl amine with chloroform and ethanolic KOH, the product obtained is (a) benzyl alcohol (b) benzaldehyde (c) benzonitrile (d) benzyl isocyanide

Step-by-Step Solution

Answer

The product is benzyl isocyanide.

Step 1: Identify the Reaction Type

The reaction of benzyl amine with chloroform and ethanolic KOH is known as the Carbylamine reaction. This reaction is a chemical test used to identify primary amines, and it results in the formation of isocyanides (or carbylamines).

Step 2: Write the Reaction Equation

The Carbylamine reaction can be written as: \[ C_6H_5CH_2NH_2 + CHCl_3 + 3KOH ightarrow C_6H_5CH_2NC + 3KCl + 3H_2O \]This equation represents the reaction of benzyl amine (C_6H_5CH_2NH_2) with chloroform (CHCl_3) in the presence of ethanolic KOH to yield benzyl isocyanide (C_6H_5CH_2NC).

Step 3: Analyze the Product

Based on the Carbylamine reaction, the product obtained is an isocyanide. For this reaction specifically using benzyl amine, the product formed is benzyl isocyanide.

Key Concepts

Primary Amines Identification

The Carbylamine reaction is a fascinating pathway primarily used to identify primary amines. Primary amines are organic compounds that contain one amino group (\(-NH_2\)). This test takes advantage of the unique chemical properties of primary amines, which react with chloroform and ethanolic KOH to form isocyanides.
These are usually characterized by their strong and distinct smell, making them easy to identify. Unlike secondary or tertiary amines, primary amines uniquely participate in this reaction, allowing chemists to use it as a diagnostic tool.
When performing the test, it's crucial to ensure that the amine involved is indeed primary. This specificity ensures that the test is both reliable and selective for identifying primary amines.

Benzyl Isocyanide Formation

In the Carbylamine reaction, benzyl isocyanide formation is a key process when benzyl amine reacts with chloroform and ethanolic KOH. This specific reaction results in the creation of benzyl isocyanide, a compound noted for its intense odor.
The reaction can be understood through the chemical equation: \[ C_6H_5CH_2NH_2 + CHCl_3 + 3KOH \rightarrow C_6H_5CH_2NC + 3KCl + 3H_2O \]This equation represents the transformation of benzyl amine (\(C_6H_5CH_2NH_2\)), assisted by the chloroform and KOH catalysts, into benzyl isocyanide (\(C_6H_5CH_2NC\)).
The mechanism is fascinating because it involves multiple steps starting with the deprotonation of chloroform and eventually leading to the formation of the isocyanide group. This transformation is significant in synthetic chemistry for constructing isocyanide compounds, vital in various chemical syntheses.

Chemical Test for Amines

A key application of the Carbylamine reaction is its role as a chemical test for primary amines. Chemists use it because of its simplicity and straightforward results. During this test, if a primary amine reacts, it yields an isocyanide, which is easily detectable due to its potent odor.
To conduct the test, the amine is heated with chloroform and ethanolic potassium hydroxide. If a primary amine is present, an isocyanide will form and can be quickly confirmed by the distinctive smell.
This method is not just a lab curiosity but a practical tool in organic chemistry to confirm the presence of primary amines, providing a rapid and direct way to test substances without complex apparatus or procedures. It helps researchers and students alike to determine the structure of unknown amines effectively.