Find out compound B in the given reaction sequence:
\[
{C}_6{H}_6 + {CH}_3X \xrightarrow{{AlCl}_3} A \xrightarrow{{CrO}_3 { in } (CH_3CO)_2O / H_3O^+} B
\]
Show Hint
- {Acetophenone} ({C}_6{H}_5{COCH}_3)
- {Benzaldehyde} ({C}_6{H}_5{CHO})
- {Cyclohexyl carbaldehyde} ({C}_6{H}_{11}{CHO})
- {Benzoic acid} ({C}_6{H}_5{COOH})
The Correct Option is B
Solution and Explanation
Step 1: Identifying the first reaction. The first step involves Friedel-Crafts Alkylation, where \( {CH}_3X \) (an alkyl halide) reacts with benzene (\( {C}_6{H}_6 \)) in the presence of \( {AlCl}_3 \), forming toluene (A) (\( {C}_6{H}_5{CH}_3 \)). \[ {C}_6{H}_6 + {CH}_3X \xrightarrow{{AlCl}_3} {C}_6{H}_5{CH}_3 \]
Step 2: Oxidation of Toluene. - The second step involves oxidation using chromyl chloride (\({CrO}_2Cl_2\)), known as the Etard Reaction, which selectively oxidizes the methyl group (\(-{CH}_3\)) to an aldehyde (\(-{CHO}\)), forming benzaldehyde (B) (\({C}_6{H}_5{CHO}\)). \[ {C}_6{H}_5{CH}_3 \xrightarrow{{CrO}_3 { in } (CH_3CO)_2O / H_3O^+} {C}_6{H}_5{CHO} \]
Step 3: Eliminating incorrect Option.
- Acetophenone (A) (\({C}_6{H}_5{COCH}_3\)): Incorrect, as the oxidation of toluene in the Etard reaction leads to the formation of an aldehyde (\({C}_6{H}_5{CHO}\)) and not a ketone.
- Cyclohexyl carbaldehyde (C) (\({C}_6{H}_{11}{CHO}\)): Incorrect, as the reaction occurs on a benzene ring, not on a cyclohexane system, and no such transformation takes place.
- Benzoic acid (D) (\({C}_6{H}_5{COOH}\)): Incorrect, as oxidation of the methyl group (\(-{CH}_3\)) to a carboxyl group (\(-{COOH}\)) requires a stronger oxidizing agent such as alkaline \({KMnO}_4\) or acidic \({K}_2{Cr}_2{O}_7\) under reflux, which is not used in this reaction. 
Thus, the correct answer is (B) Benzaldehyde (\({C}_6{H}_5{CHO}\)).
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