In the given reactions identify the reagent A and reagent B
- \( A-\text{CrO}_3 \quad B-\text{CrO}_3\)
- \(A-\text{CrO}_3 \quad B-\text{CrO}_2\text{Cl}_2\)
- \(A-\text{CrO}_2\text{Cl}_2 \quad B-\text{CrO}_2\text{Cl}_2\)
- \(A-\text{CrO}_2\text{Cl}_2 \quad B-\text{CrO}_3\)
The Correct Option is B
Approach Solution - 1
To solve this problem, we need to identify reagents A and B in the given reactions. Let's analyze the reactions:
- 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.
- 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.
- 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.
- \(\text{CrO}_2\text{Cl}_2\) (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.
Approach Solution -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).
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