Problem 114 - A Complete Resource Book in Chemistry for JEE Main

Question

The refluxing of the silver salt of the carboxylic acid in \(\mathrm{CCl}_{4}\) to form haloalkane or haloarene is called (a) Friedel-Crafts reaction (b) Wittig reaction (c) Hoffmann's bromamide reaction (d) Hunsdiecker reaction

Step-by-Step Solution

Answer

The correct answer is (d) Hunsdiecker reaction.

Step 1: Understanding the Question

The question describes a reaction where the silver salt of a carboxylic acid is refluxed in carbon tetrachloride (\(\mathrm{CCl}_4\)), which results in the formation of a haloalkane or haloarene. We need to identify which named reaction this process corresponds to from the given options.

Step 2: Identifying Reaction Components

Refluxing a silver salt of a carboxylic acid in the presence of carbon tetrachloride typically points towards a classical named reaction involving halogenation and decarboxylation.

Step 3: Analyzing Each Option

- Friedel-Crafts reaction is used for alkylation or acylation of arenes and does not involve silver salts. - Wittig reaction is for converting aldehydes or ketones into alkenes and not applicable here. - Hoffmann's bromamide reaction involves conversion of an amide to an amine, not relevant to haloalkane/arene formation. - Hunsdiecker reaction involves the conversion of a carboxylic acid to a haloalkane using silver salts.

Step 4: Concluding the Correct Reaction

The reaction described, where the silver salt of the carboxylic acid reacts in \(\mathrm{CCl}_4\) to form a haloalkane or haloarene, is best described by the Hunsdiecker reaction, which involves the formation of a halogenated compound by decarboxylation of silver salts.

Key Concepts

Halogenation

Halogenation is a fundamental reaction in organic chemistry where hydrocarbons are converted into haloalkanes or haloarenes by adding halogen atoms to them. This process is crucial for modifying organic molecules, increasing reactivity, or preparing compounds for further synthesis. The Hunsdiecker reaction is a perfect example of halogenation in action. Here, the process involves attaching a halogen to the hydrocarbon chain.
Fenstersatz

• Reactivity: Different halogens (like chlorine, bromine, or iodine) have varying reactivity and conditions required for halogenation.
• Selectivity: Depending on the conditions, halogenation can be selective, enabling the creation of specific compounds.

The halogenation in the Hunsdiecker reaction occurs simultaneously with decarboxylation, leading to a smooth conversion of carboxylic acids into halogenated compounds. By using silver salts of carboxylic acids in the presence of carbon tetrachloride (CCl₄), the reaction selectively forms haloalkanes or haloarenes.

Decarboxylation

Decarboxylation is a chemical reaction that involves the removal of a carboxyl group from an organic molecule, resulting in the release of carbon dioxide (CO₂). This reaction is a significant step in many organic processes, where it often simplifies complex molecules. In the context of the Hunsdiecker reaction, decarboxylation is crucial as it transforms carboxylic acids into hydrocarbons.
In this reaction:

• Mechanism: The silver salt of the acid decomposes, losing the carboxyl group as CO₂.
• Result: It leaves behind the corresponding alkyl or aryl halides, forming the target compound.

This efficient removal of the carboxyl group is what enables the Hunsdiecker reaction to transform a relatively inert carboxylic acid into a more reactive halogenated product, useful for a variety of applications in organic synthesis.

Named Reactions in Organic Chemistry

Named reactions are a cornerstone of organic chemistry, serving as handy tools for chemists to efficiently synthesize complex molecules. The Hunsdiecker reaction is one such named reaction that offers a unique example of combining halogenation with decarboxylation in a single step.
Named reactions often carry the name of their discoverers or developers, highlighting their unique contributions to the field. They are celebrated because they:

• Provide Reliability: Known conditions and outcomes allow chemists to predict the results of their reactions accurately.
• Simplify Complex Procedures: They streamline the synthesis processes by providing a clear protocol.
• Educational Value: Teaching named reactions helps students understand and predict reaction mechanisms effectively.

In a reaction like Hunsdiecker, recognizing it as a named reaction means you can understand that it specifically relates to transforming carboxylic acids into halogenated products using silver salts, making it a powerful technique in synthetic chemistry.