Phenols

Chemical Formula

C₆H₅OH

Reactivity

Phenol is slightly more reactive than benzene due to having a higher electron density in the pi-ring.

This is due to the Oxygen from the -OH group donating a lone pair into the pi-ring.

Acidity

Due to the delocalisation of the lone pair of oxygen atom, phenol is a very weak acid, unlike regular alcohols, which are neutral.

Phenol (C₆H₅OH) is more acidic than alcohols but less acidic than carboxylic acids.

It partially ionizes in water:

Reactions of Phenol

Phenols react with alkalis but not with metal carbonates

Acid + Alkali —> Salt + Water ✅

Acid + Metal Carbonate —> Salt + Water + Carbon Dioxide ❌

This can be used to distinguish alcohols, acids, and phenols.

Phenol —> Bromo-phenol

Reaction: Nucleophilic Substitution

Conditions and Reagents: Br_{2 (aq)}

Other info:

• Phenol decolourises bromine.

• The 2-4-6-tribromophenol formed with a white precipitate.

• This distinguishes it from an alkane test.

Phenol —> Nitro-phenol

Reaction: Nucleophilic Substitution

Conditions and Reagents: Conc. / dilute HNO_{3 (aq)}

Other info:

Dilute nitric acid can be used to decrease the number of substitutions

Phenol —> Ester

Reaction: Nucleophilic Substitution

Conditions and Reagents: Acid chloride, RCOCl, at RT

Other info:

Steamy fumes of toxic HCl_(g) are produced

Fume cupboard required

Test for Phenol

1. Add aqueous FeCl₃ to the sample.

2. A positive test for phenol results in a colour change from yellow to a violet/purple complex forming.

Reaction:

• Phenol reacts with Fe³⁺ ions to form a coloured complex:

Observation:

• A purple or violet color indicates the presence of phenol or phenolic group