Identify "Y" in the following reaction:

The correct answer is Option (1) → RCOOH

Grignard reagents (R–Mg–X) are highly reactive organometallic compounds that act as strong nucleophiles.

When a Grignard reagent reacts with carbon dioxide (CO₂) in dry ether, the nucleophilic carbon of the Grignard reagent attacks the electrophilic carbon of CO₂ to form a magnesium carboxylate intermediate.

Reaction step:

R–MgX + CO₂ → RCOO⁻MgX

This intermediate is represented as X.

When the reaction mixture is treated with acidic hydrolysis (H₃O⁺), the magnesium salt is protonated to produce a carboxylic acid.

RCOO⁻MgX + H₃O⁺ → RCOOH

Thus, the final product Y is a carboxylic acid (RCOOH).

This reaction is commonly used in organic synthesis to increase the carbon chain length by one carbon atom.

Option-wise Explanation

Option 1: RCOOH

Correct. Grignard reagent reacts with CO₂ followed by acidic hydrolysis to give a carboxylic acid.

Option 2: RCHO

Incorrect. Aldehydes are typically formed when Grignard reagents react with formyl derivatives, not CO₂.

Option 3: RCOX

Incorrect. Acyl halides are not produced in this reaction sequence.

Option 4: ROH

Incorrect. Alcohols are formed when Grignard reagents react with carbonyl compounds such as aldehydes or ketones, not with CO₂.