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JEE Advanced levelSingle correct optionDifficulty 3 of 3o1049

Cyclohexanone is converted into its ethylene glycol acetal using ethylene glycol and a catalytic amount of TsOH in refluxing benzene. Which modification would be LEAST helpful for a high yield of acetal?

  1. Aadding activated molecular sieves to the reaction flask
  2. Busing 50% aqueous ethylene glycol in place of benzene as the solvent
  3. Cusing a threefold excess of ethylene glycol
  4. Dadding a Dean-Stark trap to remove water azeotropically

Answer: B

Acetal formation is reversible and produces one mole of water per mole of acetal, so the yield is raised by removing water (Dean-Stark, sieves) or by excess diol (Le Chatelier). A large amount of water in the solvent shifts the equilibrium back toward ketone and diol, hydrolysing the acetal.
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