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25.3 The chemistry of phenol

Sunday, 09 October 2016. 25.3 The chemistry of phenol. Phenols Phenols are organic chemicals containing a hydroxyl group (-OH (or alcohol) directly bonded on to a benzene ring. The simplest member of this group is phenol, C 6 H 5 OH. Draw phenol.

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25.3 The chemistry of phenol

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  1. Sunday, 09 October 2016 25.3 The chemistry of phenol

  2. Phenols Phenols are organic chemicals containing a hydroxyl group (-OH (or alcohol) directly bonded on to a benzene ring. The simplest member of this group is phenol, C6H5OH. Draw phenol

  3. Phenols and aromatic alcohols have some common reactions but they also have many different reactions because the proximity of the delocalised ring influences the -OH group. Production of phenol Past: C6H6 + H2SO4 + 2NaOH  C6H5OH + Na2SO3 + 2H2O Present: C6H6 + C3H6 + O2  C6H5OH + CH3COCH3 Future: C6H6 + N2O  C6H5OH + N2 Calculate the atom economy for each method

  4. How does the solubility of phenol compare to that of alcohols? Write an equation to show the dissociation of phenol in water

  5. Using the table, how does the acidity of phenol compare to alcohols and carboxylic acids? Explain in terms of Ka • Ethanol does not react with strong bases (e.g. sodium hydroxide) or weak bases (e.g. sodium carbonate). Carboxylic acids, like ethanoic acid, can react with both. What about phenol? • How could you use this information to distinguish phenol from a carboxylic acid?

  6. Write an equation to show the reaction between ethanoic acid and sodium hydroxide. • Write an equation to show the reaction between phenol and sodium hydroxide.

  7. Electrophilic substitution reactions of phenol Phenols are aromatic compounds so they undergo electrophilic substitution reactions. Phenol reactions take place under milder conditions and happen more readily than the reactions of benzene.

  8. Electrophilic substitution reactions of phenol Bromination Phenol reacts with aqueous bromine to form a white precipitate of 2,4,6-tribromophenol. Bromine water is decolourised. A halogen carrier is not required for this reaction and can be carried out at room temperature. Write the equation for this reaction.

  9. Electrophilic substitution reactions of phenol Nitration Phenol reacts readily with nitric acid to form two isomers, 2-nitrophenol and 4-nitrophenol. Write the equations for these reactions

  10. Phenol vs. Benzene Why do bromine and nitric acid react more readily with phenol than with benzene? For example phenol is nitrated with dilute nitric acid but benzene needs a mixture of concentrated nitric and sulfuric acids.

  11. Phenol vs. Benzene • The increased reactivity is caused by a lone pair of electrons from the oxygen p-orbital of the –OH group being donated to the π-system of phenol. • This increases the electron density of the benzene ring. • An increased electron density attracts electrophiles more strongly than with benzene.

  12. Phenol vs. Benzene • As a result the aromatic ring in phenol is therefore more susceptible to attack from electrophiles. • For bromine this means that the increased electron density in phenol is enough to polarise bromine molecule, so no halogen carrier is required.

  13. Homework clinic and PAG prep

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