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PHENOL PHENOL Before you start it would be helpful to… • know the functional groups found in organic chemistry • know the arrangement of bonds around atoms • recall and explain electrophilic substitution of aromatic rings PHENOL Structure phenol is an aromatic alcohol with formula C6H5OH the OH group is attached directly to the benzene ring it is an almost colourless crystalline solid PHENOL Structure phenol is an aromatic alcohol with formula C6H5OH the OH group is attached directly to the benzene ring it is an almost colourless crystalline solid Preparation You cannot put an OH group directly onto a benzene ring by electrophilic substitution, so phenol has to be synthesised in a multi-stage process PHENOL - REACTIONS OF THE OH GROUP Water phenol is a weak acid it dissolves very slightly in water to form a weak acidic solution it is a stronger acid than aliphatic alcohols the ring helps weaken the O-H bond and stabilises the resulting anion C6H5OH(aq) C6H5O¯(aq) + H+(aq) PHENOL - REACTIONS OF THE OH GROUP Water phenol is a weak acid (does not react with carbonates) it dissolves very slightly in water to form a weak acidic solution it is a stronger acid than aliphatic alcohols the ring helps weaken the O-H bond and stabilises the resulting anion C6H5OH(aq) NaOH C6H5O¯(aq) + H+(aq) phenol reacts with sodium hydroxide to form a salt - sodium phenoxide it is ionic and water soluble C6H5OH(aq) + NaOH(aq) ——> C6H5O¯ Na+(aq) + H2O(l) PHENOL - REACTIONS OF THE OH GROUP Water phenol is a weak acid it dissolves very slightly in water to form a weak acidic solution it is a stronger acid than aliphatic alcohols the ring helps weaken the O-H bond and stabilises the resulting anion C6H5OH(aq) NaOH C6H5O¯(aq) + H+(aq) phenol reacts with sodium hydroxide to form a salt - sodium phenoxide it is ionic and water soluble C6H5OH(aq) + NaOH(aq) ——> C6H5O¯ Na+(aq) + H2O(l) Sodium phenol reacts with sodium to form an ionic salt - sodium phenoxide hydrogen is also produced this reaction is similar to that with aliphatic alcohols such as ethanol 2C6H5OH(s) + 2Na(s) ——> 2C6H5O¯ Na+(s) + H2(g) PHENOL - REACTIONS OF THE AROMATIC RING We previously looked at methylbenzene and chlorobenzene. What did you discover about the effects of these groups on the benzene ring? PHENOL - REACTIONS OF THE AROMATIC RING We previously looked at methylbenzene and chlorobenzene. What did you discover about the effects of these groups on the benzene ring? PHENOL - REACTIONS OF THE AROMATIC RING ELECTROPHILIC SUBSTITUTION Bromine the OH group is electron releasing due to non-bonding pair donation it increases the electron density of the delocalised system it makes substitution much easier compared to benzene phenol reacts readily with bromine water WITHOUT A CATALYST it is so easy that multiple substitution takes place other electrophiles such as NO2+ react in a similar way PHENOL - REACTIONS OF THE AROMATIC RING ELECTROPHILIC SUBSTITUTION With dilute nitric acid Phenol reacts with dilute nitric acid at room temperature to give a mixture of 2-nitrophenol and 4nitrophenol. PHENOL - REACTIONS OF THE AROMATIC RING ELECTROPHILIC SUBSTITUTION With conc. nitric acid With concentrated nitric acid, more nitro groups substitute around the ring to give 2,4,6-trinitrophenol (old name: picric acid). Phenol-methanal plastics These are amongst the oldest plastics, Backland patenting the process in 1910. They are prepared from phenol and methanal on the addition of acid or alkali. Substitution Condensation The linear polymers linked via 2,6 positions then react further with more methanal molecules to form links through the 4 position also.