See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: The starting material is diethyl 2,5-dioxocyclohexane-1,4-dicarboxylate. Treatment with H2O/Delta (aqueous acid or base hydrolysis followed by strong heating) involves two sequential processes: (i) saponification/hydrolysis of the ethyl ester groups to give the corresponding dicarboxylic acid, and (ii) decarboxylation upon strong heating. Step 2 - Hydrolysis: Under aqueous conditions, both ester groups (CO2Et) are hydrolyzed to carboxylic acids (CO2H), giving 2,5-dioxocyclohexane-1,4-dicarboxylic acid. This corresponds to option (a). Step 3 - Decarboxylation: The intermediate dicarboxylic acid (option a) has beta-keto acid functionality at both positions - each carboxylic acid is beta to a ketone carbonyl. Beta-keto acids readily undergo decarboxylation upon heating. Both carboxylic acid groups are lost as CO2, giving cyclohexane-1,4-dione (1,4-cyclohexanedione). Step 4 - Tautomerization/Aromatization: 1,4-Cyclohexanedione undergoes enolization. Under strong heating, the dienol tautomers of 1,4-cyclohexanedione can further tautomerize. The key point is that 1,4-cyclohexanedione can lose two molecules of water (through enolization and dehydration or tautomerism) to give hydroquinone (benzene-1,4-diol). This is a well-known transformation: 1,4-cyclohexanedione -> hydroquinone via double enolization and aromatization (or acid/base catalyzed tautomerism under heating). The driving force is the large thermodynamic stability of the aromatic ring. Step 5 - Why other options fail: - Option (a): This is only the hydrolysis product, not the final product after strong heating (decarboxylation has not yet occurred). - Option (b): 3-Hydroxycyclohex-2-en-1-one is an enol tautomer of 1,3-cyclohexanedione; it is not consistent with the 1,4-substitution pattern of this substrate. - Option (d): Cyclohexane-1,4-dicarboxylic acid would require reduction of the ketone groups, which does not occur under these conditions. The overall sequence is: diethyl 2,5-dioxocyclohexane-1,4-dicarboxylate -> (hydrolysis) -> 2,5-dioxocyclohexane-1,4-dicarboxylic acid -> (double decarboxylation, heating) -> 1,4-cyclohexanedione -> (double enolization/aromatization) -> hydroquinone (benzene-1,4-diol). Therefore, the correct answer is C.