See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: This reaction involves the alkylation (acylation) of an active methylene compound (malonate ester) under basic conditions using sodium metal, followed by acidic workup with AcOH. Step 1: Identify the starting material and product. Starting material: CH2(CO2Me)2 — dimethyl malonate, which has two ester groups flanking a CH2. Product: CH(CO2Me)3 — trimethyl methanetricarboxylate, which has THREE ester groups on a single carbon. Step 2: Determine what transformation is needed. The starting material CH2(CO2Me)2 needs to gain one additional CO2Me group on the same carbon. This means one of the two H atoms on the CH2 is replaced by a -CO2Me group. Step 3: Mechanism with Na and AcOH. Sodium (Na) deprotonates the active methylene of CH2(CO2Me)2 (pKa ~13) to form the stabilized carbanion/enolate: [CH(CO2Me)2]^-. This nucleophilic carbanion then attacks an electrophilic carbon source that can introduce a -CO2Me group. Step 4: Evaluate each option as the electrophile. (a) CH2(CO2Me)2 — another malonate ester; not electrophilic enough at carbon to react with the carbanion under these conditions. This would not introduce a single CO2Me group. (b) (CO2Me)2 — dimethyl oxalate; would introduce an oxalyl group, not a single CO2Me group directly. (c) Cl-CO2Me — methyl chloroformate (ClCO2Me); this is an acyl chloride with a methoxy group. The carbanion of dimethyl malonate attacks the electrophilic carbonyl carbon of ClCO2Me, displacing Cl^- and introducing the -CO2Me group onto the carbon. This gives CH(CO2Me)3 after workup. This is a straightforward C-acylation reaction. (d) COCl2 — phosgene; would introduce a -COCl group, not a -CO2Me group, and would likely give a different product (could react twice). Step 5: Why option C is correct. Methyl chloroformate (Cl-CO2Me) is the correct electrophile. The sodium enolate of dimethyl malonate attacks the carbonyl of methyl chloroformate, and after AcOH workup, the product is CH(CO2Me)3. This is a classic C-acylation of an active methylene compound. Why others fail: - (a) CH2(CO2Me)2 is not electrophilic at carbon under these conditions (no leaving group). - (b) (CO2Me)2 (dimethyl oxalate) would give a different carbon framework. - (d) COCl2 (phosgene) would not directly give the trimethyl ester product. Therefore, the correct answer is C.