Reaction Analysis: Identifying the End Product (C)

The given reaction sequence involves the transformation of a substituted benzene compound through specific organic reactions. Let's analyze the steps:

Step 1: Identify the Starting Compound and Reagents

The starting compound is a benzene ring with a methyl group (-CH₃) and a chlorine (Cl) substituent. The reagents used are:

KMnO₄ / KOH (Oxidizing agent)
H⁺ (Acidification)
SOCl₂ (Thionyl chloride)
H₂ / Pd-BaSO₄ (Catalytic hydrogenation with Lindlar's catalyst analogue)

Step 2: Understand Each Reaction Step

Step 2.1: Oxidation with KMnO₄/KOH followed by H⁺

KMnO₄/KOH is a strong oxidizing agent that converts alkyl side chains on benzene rings to carboxylic acid groups (-COOH). The methyl group (-CH₃) is oxidized to -COOH. The chlorine substituent remains unaffected as it is not oxidizable.

Intermediate product after oxidation: Benzene with -COOH and -Cl substituents.

Step 2.2: Reaction with SOCl₂

SOCl₂ (thionyl chloride) converts carboxylic acids (-COOH) to acid chlorides (-COCl).

R - COOH + SOCl 2 \to R - COCl + SO 2 + HCl

So, the -COOH group becomes -COCl.

Step 2.3: Reduction with H₂/Pd-BaSO₄

H₂/Pd-BaSO₄ is similar to Lindlar's catalyst, which is used for the partial reduction of alkynes to cis-alkenes. However, in this context, it is used to reduce the acid chloride (-COCl) group. Pd-BaSO₄ is a poisoned catalyst that reduces acid chlorides to aldehydes. This is known as the Rosenmund reduction.

R - COCl + H_{2} \overset{Pd - BaSO 4}{\to} R - CHO + HCl

Thus, the -COCl group is reduced to -CHO (aldehyde).

Step 3: Final Structure of Compound (C)

The final product is a benzene ring with two substituents:

-CHO (aldehyde group) from the oxidized and reduced methyl group
-Cl (chloro group) which remained unchanged throughout

The substituents are in the relative positions as in the starting compound. Since the starting compound is o-chlorotoluene (methyl and chlorine are ortho to each other), the final product is o-chlorobenzaldehyde.

Final Answer

The end product (C) is:

o-chlorobenzaldehyde

Related Topics

Oxidation of Alkylbenzenes
Conversion of Carboxylic Acids to Acid Chlorides
Rosenmund Reduction
Electrophilic Aromatic Substitution
Directing Effects of Substituents

Important Formulae and Theory

Oxidation of Alkyl Side Chains: Alkyl groups attached to benzene are oxidized to carboxyl groups by strong oxidizing agents like KMnO₄.

Ar - CH 3 \to Ar - COOH

Formation of Acid Chlorides: Carboxylic acids react with thionyl chloride (SOCl₂) to form acid chlorides.

RCOOH + SOCl 2 \to RCOCl + SO 2 + HCl

Rosenmund Reduction: Acid chlorides are reduced to aldehydes using hydrogen gas in the presence of palladium catalyst poisoned with barium sulfate.

RCOCl + H_{2} \overset{Pd / BaSO 4}{\to} RCHO + HCl