RMgX + CO2 (dry ether) → Y → RCOOH (H3O+). What is Y in the above reaction?

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Question

RMgX + CO2 (dry ether) → Y → RCOOH (H3O+). What is Y in the above reaction?

Accepted Answer

Correct Answer: B - RCOOMgXStep-by-step Solution:When a Grignard reagent (RMgX) reacts with dry CO2, the carbon of CO2 acts as an electrophile. The carbanion (R-) from RMgX attacks the carbonyl carbon of CO2 in a nucleophilic addition reaction. This forms a magnesium carboxylate salt: RCOOMgX (or written as RCOO-Mg+X). This intermediate (Y) on acidic hydrolysis (H3O+) gives the carboxylic acid RCOOH.RMgX + CO2 → RCOOMgX (Y); RCOOMgX + H3O+ → RCOOH + Mg(OH)X.Why other options are incorrect: Option A [(RCOO)2Mg] would require 2 moles of Grignard per CO2, which is not the stoichiometry here. Option C would result from reaction with a ketone (not CO2). Option D is chemically unreasonable.Key Concepts:Grignard reagent + CO2 (dry ether) → magnesium carboxylate salt (RCOOMgX) → H3O+ → carboxylic acid. This is an important one-carbon elongation method.Grignard reagents react with CO2 to prepare carboxylic acids with one more carbon than the original alkyl/aryl halide.The reaction must be carried out in dry ether; moisture destroys the Grignard reagent (RMgX + H2O → RH + Mg(OH)X).

RMgX + CO2 (dry ether) → Y → RCOOH (H3O+). What is Y in the above reaction?

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RMgX + CO2 (dry ether) → Y → RCOOH (H3O+). What is Y in the above reaction?

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