See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents (RMgX) are strong bases as well as nucleophiles. When a beta-ketoester like ethyl acetoacetate (CH3-C(=O)-CH2-CO2Et) reacts with a Grignard reagent, the reaction pathway depends on the acidity of available protons and the nature of the Grignard reagent. Step 1: Identify the structure of ethyl acetoacetate. Ethyl acetoacetate is CH3-C(=O)-CH2-CO2Et. The methylene group (CH2) between the two carbonyl groups is highly acidic (pKa ~11) due to stabilization of the carbanion by two flanking carbonyl groups. Step 2: Determine the behavior of one mole of CH3MgI with ethyl acetoacetate. With only ONE mole of Grignard reagent, the Grignard reagent acts preferentially as a BASE rather than a nucleophile. It deprotonates the most acidic proton available. The alpha-CH2 protons between the ketone and ester carbonyls are the most acidic protons in the molecule. Step 3: The reaction. CH3MgI abstracts the acidic proton from the -CH2- group between the two carbonyls, forming CH4 (methane gas) and the magnesium enolate salt. The product is the carbanion/enolate stabilized by both carbonyl groups, with MgBr (from MgI, though shown as MgBr in option c) as the counterion on the carbon. This gives: CH3-C(=O)-CH(-)(MgBr+)-CO2Et, which corresponds to option (c). Step 4: Why other options fail. - Option (a): This is acetylacetone (2,4-pentanedione), which would result from a completely different reaction, not from Grignard reaction with ethyl acetoacetate. - Option (b): This would be the product of nucleophilic addition to the ketone carbonyl, which requires the Grignard to act as nucleophile. With one mole and the highly acidic CH2 present, deprotonation is favored over nucleophilic addition. - Option (d): This is a carbanion at the terminal CH2, which is not where the most acidic proton resides. Step 5: Conclusion. One mole of CH3MgI acts as a base and deprotonates the active methylene group of ethyl acetoacetate, yielding the stabilized carbanion-magnesium salt shown in option (c). Therefore, the correct answer is C.