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Phenol

Phenol. Aim: To introduce phenol and its properties To describe the reactions of phenol (i) With aqueous alkalis and sodium to form salts. (i) With bromine to form 2,4,6-tribromophenol. To explain the relative ease of bromination of phenol compared with benzene. What is phenol?.

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Phenol

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  1. Phenol • Aim: • To introduce phenol and its properties • To describe the reactions of phenol • (i) With aqueous alkalis and sodium to form salts. • (i) With bromine to form 2,4,6-tribromophenol. • To explain the relative ease of bromination of phenol compared with benzene.

  2. What is phenol? • Phenol is an aromatic alcohol. • The formula is C6H5OH • It has a sweet smell. • It is sparingly soluble in water. • It is extremely corrosive and causes white blisters on the skin.

  3. Solubility? • The OH group hydrogen bonds to water. • The ring can only form weak Van der Waal’s forces since it is a large hydrocarbon section of the molecule. • When a large mass of phenol is added to water 2 liquid layers form, one , the lower layer is a solution of water in phenol and the other, top layer is a solution of phenol in water.

  4. Reactions of Phenol • Phenol was originally called carbolic acid. • It is a weak acid- a proton donor. • Strength of acid? • Compare ethanol, water and phenol reactions with sodium metal. • All react to give off hydrogen gas in a similar reaction where the OH bond breaks.

  5. Comparing alcohols as acids

  6. Order of acidity? • Phenol>water>ethanol • Why? • Phenol a weak solution in ethanol so does not melt. • Wouldn’t want it to because if it was hot enough to melt it would ignite the ethanol. • Explain the observations.

  7. Water as an acid. • In the reaction : • 2Na +2H2O → 2NaOH + H2 • The water is behaving as H-OH. • The H-O bond breaks, producing H+ ions and OH- ions. • Reduction takes place: • 2Na + 2H+→ 2Na+ + H2 • When evaporated the OH- ions and Na+ ions form the ionic sodium hydroxide.

  8. Ethanol as an acid • Since ethanol also liberates hydrogen the reaction is the same. • H H • | | • H-C-C-O-H The O-H bond breaks . • | | • H H • This liberates H+ as before.

  9. Why is ethanol a weaker acid than water? • This is written as an equilibrium: • C2H5OH + H2O D C2H5O- + H3O+ • C2H5OH D C2H5O- + H+ • is the simpler alternative. • This equilibrium lies LEFT because there is a high electron density on the O- which attracts the proton back to recombine. • The ethoxide ion is a good base due to the +I effect of the chain.

  10. Phenol as an acid • Phenol is a stronger acid than water because, in the equilibrium the phenoxide ion is a weaker base than the OH- ion because it is a –I group. • The ion is stabilised by the partial delocalisation of the negative charge over the ring by the oxygen p orbitals interacting with the ring Π cloud. • This causes the equilibrium to lie RIGHT so that the H+ ion does not recombine. • The phenoxide ion is a weak base.

  11. C6H5OH D C6H5O- + H+ • However all three are weak acids compared with other weak acids ( e.g. ethanoic acid). • Only phenol will affect UI – but even then it has a pH of only 6.6.

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