Question

An aromatic compound ‘A’ with molecular formula C₈H₈O gives positive 2,4-DNP test. It gives yellow precipitate of compound ‘B’ on treatment with sodium hypoiodite. Compound ‘A’ does not react with Tollen’s or Fehling’s reagent; on drastic oxidation with KMnO₄ it forms a carboxylic acid ‘C’. Elucidate the structures of A, B, and C. Also give their IUPAC names.

Hint:

Positive 2,4-DNP and iodoform tests are diagnostic for identifying carbonyl and methyl ketone functional groups.

Answer 1

Compound A: Compound A is an aromatic ketone, phenyl methyl ketone (acetophenone), as it gives a positive 2,4-DNP test and does not respond to Tollen’s or Fehling’s reagents.

IUPAC Name: 1-phenylethanone

Compound B: Compound B is benzene with a carboxylic acid group (benzoic acid), formed on oxidation of acetophenone. Compound A reacts with NaOI (iodoform test) to form compound B, which is a yellow precipitate of iodoform. This confirms the methyl ketone group.

IUPAC Name: triiodomethane (Iodoform)

Compound C: Compound C is benzoic acid, formed upon drastic oxidation of acetophenone with KMnO4.

IUPAC Name: benzenecarboxylic acid