Problem 42 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Chromyl chloride oxidises toluene to benzaldehyde. This reaction is known as : (a) Rosenmund reaction (b) Wurtz reaction (c) Etard reaction (d) Fittig reaction

Step-by-Step Solution

Answer

The reaction is known as the Etard reaction.

Step 1: Understanding the Given Reaction

We are asked to identify the reaction in which chromyl chloride oxidizes toluene to benzaldehyde. Let's first understand what the reaction implies. In basic terms, during this chemical process, the methyl group in toluene is oxidized to a formyl group, converting it to benzaldehyde.

Step 2: Review List of Named Reactions

We have four options: Rosenmund reaction, Wurtz reaction, Etard reaction, and Fittig reaction. The task is to recall or look up each reaction to see which one matches the oxidation process of chromyl chloride with toluene.

Step 3: Identifying the Correct Reaction

The Etard reaction is the one where chromyl chloride is used to oxidize the methyl group in toluene to form benzaldehyde. This reaction does not match with the characteristics of the other listed reactions like Rosenmund (reduction of acyl chloride), Wurtz (coupling of alkyl halides), and Fittig (coupling of aryl halides).

Step 4: Confirming with Reaction Conditions

The Etard reaction utilizes chromyl chloride (\[\text{CrO}_2\text{Cl}_2\] ) in carbon tetrachloride (\[\text{CCl}_4\]) with toluene, which gets oxidized to benzaldehyde. This matches with the given reaction conditions, confirming our choice.

Key Concepts

Chromyl Chloride Oxidation

Chromyl chloride oxidation is a chemical process that involves the conversion of organic compounds using chromyl chloride (\( \text{CrO}_2\text{Cl}_2 \)). This process is particularly effective in oxidizing the methyl group of aromatic hydrocarbons into an aldehyde. In this reaction, chromyl chloride acts as the oxidizing agent, facilitating the conversion of toluene to produce benzaldehyde.

Here's a simple breakdown of this reaction:

• Chromyl chloride interacts with the methyl group attached to the benzene ring in toluene.
• The methyl group undergoes oxidation, transforming into a formyl group.
• As a result, toluene is converted into benzaldehyde.

Employing chromyl chloride for oxidation is beneficial because it is effective under milder conditions compared to other oxidizing agents. Additionally, due to its specificity, this method of oxidation is particularly useful for selective transformations in organic synthesis.

Toluene to Benzaldehyde

Converting toluene to benzaldehyde is a key reaction in organic chemistry. In this process, the ethyl group in toluene undergoes oxidation, ultimately forming benzaldehyde.

To achieve this transformation, the Etard reaction is used. Here are the significant points involved:

• Starting Material: Toluene, a simple aromatic hydrocarbon.
• Oxidizing Agent: Chromyl chloride is employed to selectively oxidize the methyl group.
• Product: The oxidation yields benzaldehyde, an important aldehyde with applications in chemical synthesis and perfumery.

The conversion from toluene to benzaldehyde is a showcase of how selective oxidation can lead to the formation of a functional group (here, an aldehyde) without drastically altering the molecular structure of the original compound. This reaction is particularly revered for its specificity and efficiency, demonstrating the precision of organic reactions.

Named Reactions in Organic Chemistry

Named reactions in organic chemistry are a collection of well-established chemical reactions which have been named after their discoverers. These reactions are valuable because they provide standardized procedures for obtaining specific chemical transformations.

In the context of the given exercise, several named reactions are presented:

• Etard Reaction: As detailed above, this involves the chromyl chloride oxidation of toluene to benzaldehyde. It is characterized by the mild oxidizing conditions and its selectivity for the oxidation of the methyl group.
• Rosenmund Reduction: Typically involves the reduction of acyl chlorides to aldehydes using hydrogen gas over a palladium-on-barium-sulfate catalyst.
• Wurtz Reaction: This is a coupling reaction that dimerizes alkyl halides to produce alkanes.
• Fittig Reaction: Similar to the Wurtz reaction, this involves the coupling of aryl halides.

Recognizing these reactions by name facilitates a deeper understanding of their mechanisms, benefits, and applications, leading to efficient and reliable chemical synthesis. Knowing which named reaction to apply under specific circumstances is a fundamental aspect of organic chemistry.