Question

When a primary amine reacts with chloroform in ethanolic KOH, then the product formed is [2002] (a) an aldehyde (b) an isocyanide (c) an cyanide (d) an alcohol

Short answer

The product formed is (b) an isocyanide.

Step-by-step solution

Identify the Reaction Components

The key components of the reaction are a primary amine, chloroform, and ethanolic KOH. Understanding the role of each component is important in predicting the product.

Recognize the Reaction Type

The reaction of a primary amine with chloroform in the presence of a base like KOH is known as the Carbylamine reaction or Hofmann isocyanide synthesis. It is a classic method to synthesize isocyanides.

Understand the Reaction Mechanism

In the Carbylamine reaction, the primary amine reacts with chloroform under basic conditions. The base (KOH) deprotonates the amine, and the dichlorocarbene generated in situ from chloroform then reacts with the amine to form an isocyanide.

Identify the Product

Based on the Carbylamine reaction, the product formed is an isocyanide. This type of reaction specifically yields isocyanides when the right conditions are met.

Confirm by Answering the Question

Based on the understanding of the reaction, the correct answer to the question is (b) an isocyanide.

Key concepts

Primary Amine

Primary amines are organic compounds that contain an amino group ( H2N- ) attached to a single alkyl or aryl group. They are the building blocks in many organic reactions due to their reactive nature. Primary amines consist of a nitrogen atom bonded to one alkyl or aryl group and two hydrogen atoms.
In terms of nomenclature, the names of primary amines often end with "-amine". For example, methylamine has a chemical formula of CH3NH2.
Notably, primary amines can serve as nucleophiles due to the presence of the lone pairs on the nitrogen, which makes them highly reactive in different organic synthesis processes. In the context of the Carbylamine reaction, the role of the primary amine is crucial as it is responsible for the synthesis of the isocyanide.

Chloroform

Chloroform, or trichloromethane ( CHCl3 ), is a volatile liquid that is commonly used in laboratory synthesis. It is known for its characteristic sweet smell and dense properties. In organic chemistry, chloroform serves as a source of dichlorocarbene, especially when it reacts under basic conditions.
In the Carbylamine reaction, chloroform plays a pivotal role. When subjected to KOH, it produces dichlorocarbene, a highly reactive intermediate. This intermediate reacts with primary amines to facilitate the formation of isocyanides.
It's imperative to handle chloroform with caution, as it poses health risks when inhaled or absorbed through the skin. However, its essential role in many chemical reactions makes it indispensable in certain organic synthesis pathways.

Isocyanide Synthesis

Isocyanide synthesis is a fascinating aspect of organic chemistry that opens pathways to create compounds with distinct functional groups. One of the most widely known isocyanide syntheses is the Carbylamine reaction, also referred to as Hofmann isocyanide synthesis.
This reaction is particularly important for chemists seeking to create isocyanides from primary amines. The process involves the conversion of a primary amine into an isocyanide by reacting it with chloroform and a strong base like potassium hydroxide (KOH).
Isocyanides synthesized through this process are valuable in many chemical synthesis applications, including the formation of complex molecules for pharmaceuticals and specialty polymers. Due to their strong and often unpleasant odor, isocyanides synthesized in the lab should be handled with care.

Reaction Mechanism

The reaction mechanism in the Carbylamine reaction is intriguing and involves multiple key steps. It begins with the deprotonation of the primary amine using a strong base like KOH. This generates an amide ion nucleophile, which is essential for the subsequent steps.
The chloroform then reacts with the KOH to form dichlorocarbene, a reactive intermediate. This intermediate is crucial for the synthesis of the isocyanide.
The nucleophilic attack by the amide ion on the dichlorocarbene leads to the formation of an intermediate product. Finally, this intermediate rearranges to produce the isocyanide, which is the final product of the reaction.
Understanding the step-by-step mechanism is pivotal for grasping the intricacies of isocyanide synthesis and is a highlight in the study of organic reaction mechanisms.