See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: The Perkin reaction involves the condensation of an aromatic aldehyde (or a compound that can generate one) with an acid anhydride in the presence of a base (the sodium salt of the corresponding acid, AcONa). Here, the starting material is o-cresol (2-methylphenol). Step 1: Identify the reagents and their roles. Acetic anhydride (Ac2O) and sodium acetate (AcONa) are the classic reagents for the Perkin reaction. AcONa acts as a mild base to generate the carbanion from the anhydride. Step 2: Mechanism. o-Cresol has an OH group and an ortho CH3 group on the benzene ring. Under Perkin reaction conditions, the phenol oxygen attacks the acetic anhydride to form a mixed ester intermediate (O-acetylation of phenol). The sodium acetate then deprotonates the methyl group (activated benzylic/ortho position), generating a carbanion which undergoes intramolecular Claisen-type condensation. This results in cyclization to form a lactone ring fused to the benzene ring. Step 3: Product identification. The intramolecular reaction of o-acetoxytoluene under basic conditions leads to cyclization forming coumarin (2H-chromen-2-one), which is a benzene ring fused with a lactone (alpha-pyrone) ring having the carbonyl at C2 and a C3=C4 double bond. This matches option (b). Step 4: Why other options fail. - Option (a): Chromone (4H-chromen-4-one) would require different starting material and conditions; Aldol condensation is not relevant here. - Option (c): The product shown is not consistent with Perkin conditions, and Cannizaro reaction requires an aldehyde with no alpha-H. - Option (d): This product (cinnamic acid derivative) is the intermolecular Perkin product from benzaldehyde, not from o-cresol cyclization. Also labeled incorrectly as Claisen-condensation. The reaction of o-cresol with Ac2O/AcONa followed by hydrolysis is the classic synthesis of coumarin via the Perkin reaction (specifically the intramolecular variant, sometimes called the Perkin synthesis of coumarin). Therefore, the correct answer is B.