Question

Toluene on treatment with chromic oxide in presence of acetic anhydride at \( 273{-}283\,K \) gives compound (X). Compound (X) on hydrolysis with aqueous acid gives compound (Y). The compounds (X) and (Y) are respectively

• A. Benzylidene diacetate and phenol
• B. Benzyl alcohol and benzene
• C. Benzylidene diacetate and benzaldehyde
• D. Benzene and phenol
• E. Benzaldehyde and phenol

Hint:

Chromic oxide + acetic anhydride → protected aldehyde intermediate.

Answer 1

The Correct Option is C

Step 1: Understanding the Reaction:
This reaction is a method for the controlled oxidation of the methyl group of toluene to an aldehyde group. Strong oxidizing agents (like KMnO\(_4\)) would oxidize it all the way to a carboxylic acid (benzoic acid). Using chromic oxide (CrO\(_3\)) in acetic anhydride is a way to stop the oxidation at the aldehyde stage.
Step 2: Identifying Compound (X):
Reactants: Toluene (C\(_6\)H\(_5\)CH\(_3\)), Chromic oxide (CrO\(_3\)), and Acetic anhydride ((CH\(_3\)CO)\(_2\)O).
The role of acetic anhydride is to "protect" the aldehyde as it is formed. The aldehyde reacts with the anhydride to form a gem-diacetate (a compound with two acetate groups on the same carbon). This prevents the aldehyde from being further oxidized.
The intermediate compound formed (X) is benzylidene diacetate, which has the structure C\(_6\)H\(_5\)CH(OCOCH\(_3\))\(_2\).
\[ \text{C}_6\text{H}_5\text{CH}_3 \xrightarrow[\text{(CH}_3\text{CO})_2\text{O}]{\text{CrO}_3} \text{C}_6\text{H}_5\text{CH(OCOCH}_3)_2 \quad \text{(Compound X)} \] Step 3: Identifying Compound (Y):
Compound (X), the gem-diacetate, is then subjected to hydrolysis with an aqueous acid (like H\(_3\)O\(^+\)). Hydrolysis breaks the ester linkages of the diacetate, converting it back to the aldehyde and forming two molecules of acetic acid.
\[ \text{C}_6\text{H}_5\text{CH(OCOCH}_3)_2 \xrightarrow{\text{H}_3\text{O}^+} \text{C}_6\text{H}_5\text{CHO} + 2\text{CH}_3\text{COOH} \] So, compound (Y) is benzaldehyde.
Step 4: Final Answer:
Compound (X) is benzylidene diacetate and compound (Y) is benzaldehyde.