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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3co270

The beta-keto acid shown is heated gently, and the neutral product is then treated with excess /NaOH. Which statements are correct?

  1. ADecarboxylation gives butan-2-one (via a cyclic six-membered transition state and an enol)
  2. BThe decarboxylation product gives a positive iodoform test
  3. CThe organic acid obtained on acidifying the haloform mixture is propanoic acid
  4. DThe acid obtained on acidifying the haloform mixture is butanoic acid

Answer: A, B, C

The drawn compound is 2-methyl-3-oxobutanoic acid. Heating expels CO2 through a cyclic six-membered transition state to give an enol that tautomerises to butanone, CH3COCH2CH3. This methyl ketone gives CHI3 plus CH3CH2COO(-); acidification gives propanoic acid (3 carbons), not butanoic acid.
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