Question

\(RMgX + CO_2 (\text{dry})→(\text{ether}) Y (H_3O^+)→ RCOOH\)
What is Y in the above reaction?

• A. \(RCOO-Mg+X\)
• B. \(R_3CO-Mg+X\)
• C. \(RCOO-X^+\)
• D. \((RCOO)_2Mg\)

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Grignard reagents (\(RMgX\)) are powerful nucleophiles. They react with the electrophilic carbon of carbon dioxide (\(CO_2\)) to form a magnesium carboxylate salt.
Step 2: Detailed Explanation:
1. Nucleophilic Attack: The alkyl or aryl group (\(R\)) of the Grignard reagent carries a partial negative charge. It attacks the electrophilic carbon atom of \(O=C=O\).
2. Bond Breaking: One of the \(\pi\) bonds in \(CO_2\) breaks, moving the electron pair to the oxygen atom.
3. Intermediate Formation: This results in a carboxylate anion (\(R-COO^-\)) which coordinates with the positive part of the Grignard reagent (\(Mg^+X\)).
The reaction is:
\[ R-MgX + O=C=O \xrightarrow{\text{dry ether}} R-C(=O)-O^-Mg^+X \]
This intermediate \(Y\) is known as a magnesium salt of a carboxylic acid.
4. Acidic Hydrolysis: In the second step, treatment with \(H_3O^+\) replaces the \(MgX\) group with a hydrogen atom to produce the final carboxylic acid (\(RCOOH\)).
Step 3: Final Answer:
The intermediate \(Y\) is \(RCOO^-Mg^+X\).