An aromatic carboxylic acid [A] which readily sublimes on heating, produces compound [B] on treatment with PCl₅. Compound [B], when reduced in the presence of Pd catalyst over BaSO₄ poisoned by sulphur in xylene solution gives compound [C]. When compound [C] is condensed in the presence of alcoholic KCN, it gives compound [D].
(Molecular formula of compound [D] is C₁₄H₁₂O₂)

Identify the compounds [A], [B], [C] and [D].

Solution