- Created by: Kyra Mullarney
- Created on: 10-06-19 14:48
Phenols and phenol
- Type of organic chemical containing a hydroxyl group, -OH, bonded directly to an aromatic ring.
- The simplest phenol, C6H5OH, has the same name as the group, phenol.
- Although alcohols and phenols have some common reactions, many reactions are different as the proximity of the delocalised ring influences the -OH group.
Phenol as a weak acid
- Phenol is less soluble in water due to the presence of the non-polar benzene ring.
- When dissolved in water, phenol partially dissociates froming the phenoxide ion and a proton.
- Becasue of this ability to partially dissociate to produce protons, phenol is described as a weak acid.
- Phenol is more acidic than alcohols but less acidic than carboxylic acids.
- Ethanol does not react with sodium hydroxide (strong base) or sodium carbonate (weak base).
- Phenols and carboxylic acids react with solutions of strong bases such as aqueous sodium hydroxide.
- Only carboxylic acids are strong enough to react with the weak base, sodium carbonate.
- A reaction with sodium carbonate can be used to distinguish between a phenol and carboxylic acid - the carboxylic acid reacts with sodium carbonate to produce carbon dioxide, which is evolved as a gas.
Reaction of phenol with sodium hydroxide
- Reacts with sodium hydroxide to form the salt, sodium phenoxide, and water in a neutralisation reaction.
C6H5OH + NaOH ---> C5H5O-Na+ + H2O
Phenol + sodium hydroxide ---> sodium phenoxide + water
Electrophilic substitution reactions of phenol
- Phenols are aromatic compounds and they undergo electrophilic substitution reactions.
- The reactions take place under milder conditions and more readily than the reactions of benzene.
Bromination of phenol
- Reacts with an aqueous solution of bromine to form a white precipitate of 2,4,6-tribromophenol.
- The reaction decolourises the bromine water.
- A halogen carrier is not required and the reaction is carried out at room temperature.
C6H5OH + 3Br2 ---> C6H2Br3OH + 3HBr
Phenol + bromine ---> 2,4,6-tribromophenol + hydrogenbromide
Nitration of phenol
- Phenol reacts with dilute nitric acid at room temperature. A mixture of 2-nitrophenol and 4-nitrophenol is formed.
C6H5OH + HNO3 ---> C6H4NO2OH + H2O
Phenol + nitric acid ---> nitrophenol + water
Comparing reactivity of phenol and benzene
- Increased reactivity of phenol is caused by a lona pair of electrons from the oxygen p orbital of the -OH group being donated to the pi system of phenol.
- The electron density is increased. The increased electron density attracts electrophiles more readily than with benzene.
- The aromatic ring in phenol is more susceptible to attack from electrophiles than in benzene.