Question

Which of the following statement(s) is/are correct about the given compound?

• A. It exhibits tautomerism.
• B. It does not react with metallic sodium.
• C. It gives reddish-violet coloration with FeCl$_3$ solution.
• D. It gives precipitate with 2,4-dinitrophenyl hydrazine solution.

Hint:

Using a simple frame or just bolding for the box
Key Points:
$\beta$-Keto esters (like ethyl acetoacetate) have acidic $\alpha$-hydrogens.
Compounds with $\alpha$-hydrogens adjacent to a carbonyl group can exhibit keto-enol tautomerism.
Active methylene compounds (acidic C-H) react with active metals like Na.
Enols typically give a positive FeCl$_3$ test (coloration).
Ketones (and aldehydes) react with 2,4-DNPH to form precipitates (hydrazones).

Answer 1

The Correct Option is A

Ethyl 3-oxobutanoate, or ethyl acetoacetate, is a β-keto ester. Examining each statement:

• (A) It exhibits tautomerism: This compound features α-hydrogens on the CH₂ group between the ketone and ester carbonyls. These acidic hydrogens enable keto-enol tautomerism. This statement is correct.
• (B) It does not react with metallic sodium: The α-hydrogens are significantly acidic (pKa ≈ 11) due to the electron-withdrawing carbonyls. Metals like sodium react with acidic hydrogens to release H₂. Ethyl acetoacetate *does* react with sodium; thus, this statement is incorrect.
• (C) It gives reddish-violet coloration with FeCl₃ solution: The FeCl₃ test is positive for phenols and enols. Ethyl acetoacetate's enol tautomer leads to a positive FeCl₃ test, usually producing a reddish or violet color. This statement is generally correct.
• (D) It gives precipitate with 2,4-dinitrophenyl hydrazine solution: 2,4-Dinitrophenylhydrazine (2,4-DNPH) reacts with aldehydes and ketones, forming solid precipitates. Ethyl acetoacetate contains a ketone group, which reacts with 2,4-DNPH. This statement is correct.

Statements (A) and (D) are correct, based on the analysis.