Identify ‘Y’?

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1 Answer
Jun 10, 2018

Answer:

The correct answer is (b).

Explanation:

Step 1. Grignard reaction

I m guessing that the starred #"O"# in your starting material is a radio-labelled oxygen atom.

The first step in the formation of #"X"# is the Grignard reaction of a lactone (a cyclic ester) to give a tertiary alcohol and a phenol.

Grignard

  • The Grignard reagent first converts the lactone to a phenyl ketone.

  • A second mole of the reagent then adds to the ketone to form a tertiary alcohol after acid workup.

  • The labelled oxygen remains on the original phenyl group.

Step 2. Acid-catalyzed formation of an ether

The formation of #"Y"# involves the acid-catalyzed condensation of a phenol and an alcohol to form an ether.

Mechanism

The steps in the mechanism are:

  • Sulfuric acid protonates the alcohol and converts it into a better leaving group.

  • The phenol displaces a water molecule from the water molecule and forms a protonated ether.

  • A molecule of excess alcohol deprotonates the ether

Again, note that the phenol oxygen stays attached to the ring.

Thus, we can represent the formation of #"Y"# as

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