Question

In the given reactions identify the reagent A and reagent B

• A. \( A-\text{CrO}_3 \quad B-\text{CrO}_3\)
• B. \(A-\text{CrO}_3 \quad B-\text{CrO}_2\text{Cl}_2\)
• C. \(A-\text{CrO}_2\text{Cl}_2 \quad B-\text{CrO}_2\text{Cl}_2\)
• D. \(A-\text{CrO}_2\text{Cl}_2 \quad B-\text{CrO}_3\)

Answer 1

The Correct Option is B

To solve this problem, we need to identify reagents A and B in the given reactions. Let's analyze the reactions:

1. The first reaction shows the conversion of a methyl group on a benzene ring to an intermediate using reagent "A" with \((\text{CH}_3\text{CO})_2\text{O}\) at 273-283K. This suggests a common oxidation process.
2. In organic chemistry, \(\text{CrO}_3\) (chromium trioxide) is commonly used as an oxidizing agent for converting alkyl groups in aromatic compounds to carboxylic acids.
3. The second reaction shows the formation of an intermediate using reagent "B" with \(\text{CS}_2\) (carbon disulfide) and subsequent hydrolysis to form benzaldehyde. This indicates the involvement of a reagent that forms an aldehyde group.
4. \(\text{CrO}_2\text{Cl}_2\) (chromyl chloride) is known for converting methyl groups to an aldehyde group in aromatic rings.

From the reasoning above, it logically follows that:

• Reagent A should be \(\text{CrO}_3\) as it is responsible for the initial oxidation process.
• Reagent B should be \(\text{CrO}_2\text{Cl}_2\) as it facilitates the conversion to the aldehyde.

Given these considerations, the correct option is:

\(A-\text{CrO}_3 \quad B-\text{CrO}_2\text{Cl}_2\)

This option effectively explains the chemical transformation processes observed in the reaction scheme provided.

Answer 2

Step 1: The reaction starts with toluene, which is oxidized by reagent A (CrO₃) in acetic anhydride (CH₃CO)₂O. This oxidation step is known as the Etard reaction, where toluene is converted into benzylidene diacetate as an intermediate.

Step 2: The intermediate benzylidene diacetate is then treated with reagent B (CrO₂Cl₂), followed by hydrolysis (H₂O⁺) to yield benzaldehyde (C₆H₅CHO).

Thus, the correct reagents are A-CrO₃ and B-CrO₂Cl₂, which is represented by option (2).