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Alcohols and Phenols

Reactions of phenol and the iron(III) chloride test

  • 3 things to know
  • Component 2

Overview

Recall questions on the reaction of phenol with bromine water and with ethanoyl chloride, the observations and the equations, why phenol brominates so much more readily than benzene, the iron(III) chloride test and its result, and how phenol is distinguished from an alcohol.

What you need to know

Answer each one before you reveal it.

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Key term

Ethanol and phenol are each treated with neutral iron(III) chloride solution. State and explain the difference.

Key term

State what is seen when bromine water is added to an aqueous solution of phenol at room temperature.

Key term

Explain why phenol brominates readily in water when benzene needs a halogen carrier to brominate at all.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State what is seen when bromine water is added to an aqueous solution of phenol at room temperature.

    Model answer

    The orange colour disappears immediately and a white precipitate forms, accompanied by a sharp antiseptic smell.

  2. 2

    Name the precipitate formed when phenol reacts with bromine water and give the equation.

    Model answer

    It is 2,4,6-tribromophenol, formed by C₆H₅OH + 3Br₂ → C₆H₂Br₃OH + 3HBr.

  3. 3

    Explain why phenol brominates readily in water when benzene needs a halogen carrier to brominate at all.

    Model answer

    A lone pair on the oxygen atom is partly delocalised into the ring, which raises the electron density there so that the ring itself can polarise a bromine molecule and generate the electrophile unaided.

  4. 4

    At which positions on the ring does bromine substitute in phenol?

    Model answer

    At positions 2, 4 and 6, that is the two carbons either side of the hydroxyl group and the one directly opposite it.

  5. 5

    Name the type of reaction that takes place when phenol reacts with bromine water.

    Model answer

    It is an electrophilic substitution, with three hydrogen atoms of the ring replaced in turn.

  6. 6

    Both phenol and an alkene decolourise bromine water. How can the two be told apart in the test tube?

    Model answer

    Phenol also throws down a white precipitate, whereas the alkene gives a soluble colourless product and leaves the mixture clear.

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