Question

An organic compound with the molecular formula \(C_8H_8O\) forms 2,4-DNP derivative, reduces Tollens’ reagent and undergoes Cannizzaro reaction. On vigorous oxidation it gives Benzene-1,2-dicarboxylic acid. Identify the compound and write the reactions of compound with 2,4-DNP and when it undergoes Cannizzaro reaction.

Hint:

Identification clues:

• 2,4-DNP test \(\Rightarrow\) Carbonyl compound.

• Tollens' test positive \(\Rightarrow\) Aldehyde.

• Cannizzaro reaction \(\Rightarrow\) Aldehyde without \(\alpha\)-hydrogen.

• Oxidation to phthalic acid \(\Rightarrow\) Ortho-substituted aromatic compound containing \(-CHO\) and \(-CH_3\) groups.
Hence, \[ \boxed{ o\text{-Methylbenzaldehyde} } \] is the only structure satisfying all the given conditions.

Answer 1

Step 1: Deduce the structure.
Positive Tollens' test confirms an aldehyde ($-CHO$). Cannizzaro reaction confirms no alpha-H (aromatic aldehyde). Vigorous oxidation gives phthalic acid (benzene-1,2-dicarboxylic acid), so the ring bears $-CHO$ and $-CH_3$ at ortho positions. The compound is o-methylbenzaldehyde.
Step 2: Reaction with 2,4-DNP reagent.
\[ C_6H_4(CH_3)CHO + H_2NNHC_6H_3(NO_2)_2 \rightarrow C_6H_4(CH_3)CH=NNHC_6H_3(NO_2)_2 + H_2O \] A yellow-orange crystalline hydrazone derivative is formed.
Step 3: Cannizzaro reaction.
In conc. NaOH, one molecule is oxidised (to carboxylate) and the other is reduced (to alcohol): \[ 2C_6H_4(CH_3)CHO + NaOH \rightarrow C_6H_4(CH_3)COONa + C_6H_4(CH_3)CH_2OH \] \[ \boxed{\text{Compound: } o\text{-Methylbenzaldehyde}} \]