- Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure.
- Phenol is obtained by acidification of sodium phenoxide so produced
From Benzenesulphonic acid
- Benzene is sulphonated with oleum
- Benzenesulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide.
- Acidification of the sodium salt gives phenol.
From Diazonium salts
- A diazonium salt is formed by treating an aromatic primary amine with nitrous acid (NaNO2+HCl) at 273-278 K.
- Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids
- Cumene (isopropyl benzene) is oxidised in the presence of air to cumene hydroperoxide.
- It is converted to phenol and acetone by treating it with dilute acid
Boiling points of phenols are higher in comparison to other hydrocarbons due to the presence of intermolecular hydrogen bonding.
Solubility of phenols in water is due to their ability to form hydrogen bonds with water molecules
Acidic Character of Phenols
In alkoxide ion, the negative charge is localised on oxygen
- Phenol is more acidic than alcohols due to stabilisation of phenoxide ion through resonance
In phenoxide ion, the charge is delocalised.
- In substituted phenols, the presence of electron withdrawing groups enhances the acidic strength of phenol.
- This effect is more pronounced when such a group is present at ortho and para positions.
Electron releasing groups do not favour the formation of phenoxide ion resulting in decrease in acid strength
Electrophilic aromatic substitution
- The -OH group attached to the benzene ring activates it towards electrophilic substitution.
- It directs the incoming groups to ortho and para positions in the ring as these positions become electron rich due to the resonance effect caused by -OH group
With dilute nitric acid at low temperature, phenol yields a mixture of ortho and para nitrophenols.
With concentrated nitric acid, phenol is converted to 2,4,6-trinitrophenol or picric acid
When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2 and at low temperature, mono-bromophenols are formed.
When phenol is treated with bromine water, 2,4,6-tribromophenol is formed as white precipitate
On treating phenol with chloroform in the presence of sodium hydroxide, a -CHO group is introduced at the ortho position of benzene ring.
Reaction with zinc dust
Phenol is converted to benzene on heating with zinc dust.
Phenol gets oxidised by chromic acid to give a diketone known as benzoquinone.