Phenols are a type of organic compound containing a hydroxyl, -OH, functional group directly bonded to an aromatic ring.

The formula of phenol is C₆H₅OH.

The skeletal formula of phenol is:

React both with a metal carbonate such as sodium carbonate.

The carboxylic acid will react to produce carbon dioxide, which is evolved as a gas. Phenol is not acidic enough to react.

Acidity increases in the order: ethanol < water < phenol.

Phenol is a stronger acid than water because:

• The lone pairs of electrons on the oxygen atom in C₆H₅O^- overlap with the delocalised π-system on the benzene ring.
• C₆H₅O^- is more stable than OH^- because the negative charge of C₆H₅O^- is spread across the entire bezene ring.
• C₆H₅OH donates a proton (to form C₆H₅O^-) more readily than H₂O does (to form OH^-).

Ethanol is a weaker acid than water because:

• The ethyl group in C₂H₅O^- is electron-donating.
• C₂H₅O^- is less stable than OH^- because the negative charge of C₂H₅O^- is concentrated on the oxygen atom.
• C₂H₅OH donates a proton (to form C₂H₅O^-) less readily than H₂O does (to form OH^-).

Phenol is prepared by reacting phenylamine with nitrous acid (HNO₂) at a temperature below 10°C. The unstable diazonium salt produced is warmed in the aqueous solution to produce phenol.

Azo compounds are prepared by reacting an alkaline solution of phenol with a diazonium salt at a temperature below 10°C. A coupling reaction takes place in which the electrophilic diazonium ion substitutes into the benzene ring of phenol at the 4-position, directly opposite the -OH group.

1. Prepare nitrous acid (HNO₂) in situ. using sodium nitrite and hydrochloric acid:

NaNO₂ + HCl ➔ HNO₂ + NaCl

1. Add phenylamine to form a diazonium salt via a diazotisation reaction:

C₆H₅NH₂ + HNO₂ + HCl ➔ C₆H₅N≡NCl + 2H₂O

1. Warm the diazonium salt in aqueous solution to form phenol:

C₆H₅N≡NCl + H₂O ➔ C₆H₅OH + HCl + N₂

Phenol reacts with sodium hydroxide to form the salt, sodium phenoxide, and water in a neutralisation reaction.

C₆H₅OH + NaOH ➔ C₆H₅ONa + H₂O

Phenol neutralises other alkalis in the same way to form a salt and water.

Molten phenol reacts vigorously with sodium metal, forming sodium phenoxide and hydrogen gas.

2C₆H₅OH + 2Na ➔ 2C₆H₅ONa + H₂

Phenol reacts with an aqueous solution of bromine at room temperature to form a white precipitate of 2,4,6-tribromophenol. The reaction decolourises the bromine water.

In contrast to benzene, the halogenation of phenol does not require a halogen carrier.

Phenol reacts readily with dilute nitric acid at room temperature to form a mixture of 2-nitrophenol and 4-nitrophenol.

The lone pairs of electrons on the oxygen atom of the -OH group in phenol are donated into its π-system. This activates phenol's aromatic ring, making it more susceptible to electrophilic attack.

Phenol is nitrated with dilute nitric acid whereas benzene requires concentrated nitric and sulfuric acids.

Phenol is more reactive than benzene.

A lone pair of electrons from the oxygen p-orbital of the -OH group is donated into the π-system of phenol, increasing the electron density of the benzene ring, which attracts electrophiles more strongly compared to benzene.