4 Phenols PAG7

Phenols In a phenol the OH group is directly attached to the benzene ring. In a phenol the lone pair of electrons on the oxygen is delocalised with the electron charge cloud of the arene ring. The delocalised bonding changes the reactivity of the OH group and the arene ring. OH CH2OH This is not a phenol, but is an alcohol because the OH group is attached to an alkyl group rather than the Phenols are very weakly acidic. They are weaker acids than carboxylic acids. benzene ring. Both phenols and carboxylic acids will react with sodium metal and sodium hydroxide. Only carboxylic acids will react with sodium carbonate as a phenol is not strong enough an acid to react. O – OH Na+ + Na + ½ H2 O – OH Na+ + NaOH + H2O sodium phenoxide The sodium phenoxide compound is more soluble than the original phenol. So the solid phenol dissolves on addition of NaOH Reaction with Bromine Phenol does not need a FeBr3 catalyst like benzene and undergoes multiple substitution whereas benzene will only add one Br. Reagents: Br2 Conditions: room temp OH OH Br Br Br + 3 HBr 2,4,6 –tribromophenol + 3 Br2 In phenol the lone pair of electrons on the oxygen (p- orbital) is partially delocalised into the ring. The electron density increases and the Br2 is more polarised The product in this reaction is a white solid Phenols are used in the production of plastics, antiseptics, disinfectants and resins for paints. N Goalby chemrevise.org 6 Reaction of Phenol with Nitric acid In comparison with benzene, phenol does not need concentrated nitric acid or the concentrated sulphuric acid catalyst With 4M HNO3 single substitution occurs (in comparison to the conc HNO3 needed for benzene) Reagent 4M HNO3 Conditions: room temp OH NO2 NO2 OH with 4M HNO3 or 2 -nitrophenol 4 -nitrophenol OH Effect of side groups on substitution Side groups on a benzene ring can affect the position on the ring of substitution reactions. Electron-donating groups such as OH, NH2 will force further substitutions to occur on the 2- and 4- positions of the ring OH NO2 NO2 OH with 4M HNO3 or 2 -nitrophenol 4 -nitrophenol OH Electron-withdrawing groups (such as NO2 ) will have a 3-directing effect of in electrophilic substitution of aromatic compounds