25.3 the chemistry of phenol

phenol as a week acid

• phenol is less soluble in water than alcohols due to the presence of the non-polar benzene ring

• when dissolved in water, phenol partially dissociates forming the phenoxide ion and a proton

• because of this ability to partially dissociate to produce protons, phenol is classed as a week acid

• it is more acidic than alcohols but less acidic than C.A so can only react with strong bases eg. sodium hydroxide

reaction of phenol with sodium hydroxide

phenol reactions with sodium hydroxide to form the salt, sodium phenoxide and water in a neutralisation reaction

bromination of phenol

• phenol reacts with bromine water to form a white precipitate of 2,4,6-tribromophenol 

• the reaction colourises the bromine water

• with phenol, a halogen carrier catalyst is not required and the reaction is carried out a room temperature   

nitration of phenol

• phenol reacts readily with dilute nitric acid at room temperature

• a mixture of 2-nitrophenol and 4-nitrophenol is formed

comparing the reactivity of phenol with benzene

• bromine and nitric acid react more readily with phenol than they do with benzene

• the increased reactivity is caused by a lone pair of electrons from the oxygen p-orbital of the -OH group being donated into the Pi system of phenol

• the electron density of the benzene ring in phenol is increased. This increased electron density attracts electrophiles more strongly than with benzene

• the aromatic ring in phenol is therefore more susceptible to attack from electrophiles than in benzene. For bromine, the electron density in the phenol ring structure is sufficient to polarise bromine molecules and so no halogen carrier is needed