Question

An organic compound with the molecular formula C\textsubscript{8H\textsubscript{8}O forms 2,4-DNP derivative, reduces Tollen's reagent and undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1,2-benzenedicarboxylic acid. The organic compound is}

• A. 2-ethylbenzaldehyde
• B. 2-methylbenzaldehyde
• C. acetophenone
• D. 3-methylbenzaldehyde
• E. phenylacetaldehyde

Hint:

Vigorous oxidation of any alkyl group and the aldehyde group on a benzene ring turns them into carboxylic acid groups ($-COOH$). The name "1,2-benzenedicarboxylic acid" is the ultimate clue for an ortho relationship!

Answer 1

The Correct Option is B

Concept: This problem requires identifying a compound based on several diagnostic organic tests and its oxidation product.
• 2,4-DNP test: Indicates the presence of a carbonyl group (aldehyde or ketone).
• Tollen's reagent: A positive result (reduction) specifically identifies an aldehyde.
• Cannizzaro reaction: Indicates an aldehyde with no alpha-hydrogens ($\alpha$-H) on the carbon adjacent to the carbonyl. In aromatic aldehydes, the $-CHO$ group is attached directly to the benzene ring.
• Oxidation product: 1,2-benzenedicarboxylic acid (Phthalic acid) indicates that the benzene ring has two substituents at the ortho (1,2) positions.

Step 1: Analyze the structural requirements. - Molecular formula $C_8H_8O$ and the Tollen's test confirm it is an aromatic aldehyde with one extra carbon as a substituent ($C_6H_4(CHO)(CH_3)$). - Cannizzaro reaction is typical for benzaldehydes. - The formation of 1,2-benzenedicarboxylic acid upon vigorous oxidation proves that the $-CHO$ group and the other alkyl group ($CH_3$) must be at the 1 and 2 positions (ortho to each other).

Step 2: Identify the compound. The only compound that fits all criteria—being an ortho-substituted aromatic aldehyde with the correct carbon count—is 2-methylbenzaldehyde (o-tolualdehyde).