Mr Cole Chemistry

Phenol

Phenol

Aromatic Chemistry Worksheet

These questions are not relevant to AQA A-level Chemistry but are important for OCR A-level students.

1. Neutralisation of Phenol & Benzoic Acid

Phenol undergoes a different set of neutralisation reactions compared to benzene and benzoic acid.
a) Write the equation for the reactions of phenol and benzoic acid with sodium hydroxide.
Answer

Phenol: C6H5OH + NaOH → C6H5O–Na+ + H2O

Benzoic Acid: C6H5COOH + NaOH → C6H5COO–Na+ + H2O

b) Explain why phenol can react with sodium hydroxide whereas ethanol cannot.
Answer

Phenol is more acidic than ethanol.

When phenol loses a proton (H+), the resulting phenoxide ion (C6H5O–) is stabilised by delocalisation. The lone pair of electrons on the oxygen atom overlaps with the delocalised $\pi$-system of the ring, spreading the negative charge. Ethanol forms an ethoxide ion where the negative charge is concentrated on the oxygen, making it unstable and a very weak acid.

c) Write the equation for the reaction of benzoic acid with sodium carbonate.
Answer

2C6H5COOH + Na2CO3 → 2C6H5COO–Na+ + CO2 + H2O

d) Explain why sodium carbonate will react with benzoic acid but not phenol.
Answer

Benzoic acid is a stronger acid than phenol. It is strong enough to displace carbon dioxide from a carbonate (react with a weak base), whereas phenol is too weak to do so.

2. Reactivity & Mechanism

Phenol can undergo electrophilic substitution reactions in the same way as benzene.
a) Explain why phenol is more reactive than benzene.
Answer

The lone pair of electrons on the oxygen atom is delocalised into the benzene ring. This increases the electron density of the ring, making it more susceptible to attack by electrophiles (it can polarise electrophiles more effectively than benzene).

b) Copy and complete the table with the reactants and conditions for the reactions.
Arene Reaction with Bromine Reaction with Nitric Acid
Benzene
Phenol
Answer
Arene Reaction with Bromine Reaction with Nitric Acid
Benzene Bromine and FeBr3 (catalyst)
Warm		 Concentrated HNO3 and concentrated H2SO4 (catalyst)
50°C
Phenol Bromine water
Room temperature		 Dilute HNO3
Room temperature
c) Outline the mechanism for the reaction between benzene and bromine, with no catalyst present.
Answer

(Note: Benzene typically requires a catalyst. This question likely implies the mechanism for **Phenol**, which reacts without a catalyst, or asks for the general electrophilic substitution steps if a catalyst were assumed.)

Mechanism Image

3. Substitution Patterns

The presence of the alcohol group on the phenol impacts the position of the substitution.
a) i) Phenol reacts with nitric acid. Draw the product if a single nitro-group is substituted.
Answer

(Dilute HNO3) Forms a mixture of 2-nitrophenol and 4-nitrophenol.

2-nitrophenol OR 4-nitrophenol
a) ii) Phenol reacts with nitric acid. Draw the product if it is fully substituted.
Answer

(Conc. HNO3) Forms 2,4,6-trinitrophenol (Picric acid).

2,4,6-trinitrophenol
b) i) Phenol reacts with bromine. Draw the product if a single bromine is substituted.
Answer

(Br2 in non-polar solvent) Forms 2-bromophenol or 4-bromophenol.

2-bromophenol OR 4-bromophenol
b) ii) Phenol reacts with bromine. Draw the product if it is fully substituted.
Answer

(Bromine Water) Forms 2,4,6-tribromophenol (White precipitate).

2,4,6-tribromophenol
Return to Topic