The Chemistry Of Phenol

Question 1

What are phenols?

Answer 1

A type of organic chemical containing a hydroxyl functional group directly bonded to the aromatic ring.

Question 2

What is the simplest member of phenols?

Answer 2

C6H5OH.

Question 3

How can you differentiate between a phenol and an alcohol?

Answer 3

When the OH group is bonded to a carbon side-chain, rather than the OH group that is an alcohol not a phenol.

Question 4

What type of acid is phenol?

Answer 4

A weak acid.

Question 5

Why are phenols less soluble in water than in alcohols?

Answer 5

Due to the presence of the non-polar benzene ring.

Question 6

Why are phenols classed as weak acids?

Answer 6

When dissolved in water, phenol partially dissociates forming the phenoxide ion and a proton

Question 7

Are phenols more or less acidic than alcohols and carboxylic acids?

Answer 7

Phenols are more acidic than alcohols but less acidic than carboxylic acids.

Question 8

How can the comparison of acidity of phenols, alcohols and carboxylic acids be shown?

Answer 8

By comparing the acidic dissociation constant Ka of an alcohol with a phenol and a carboxylic acid.

Question 9

What are the 3 pieces of evidence that the acidic dissociation constant of Ka shows about the acidity of phenols, alcohols and carboxylic acids?

Answer 9

1. Ethanol does not react with sodium hydroxide (a strong base) or sodium carbonate (a weak base).
2. Phenols and carboxylic acids react with solutions of strong bases such as aqueous sodium hydroxide.
3. Only carboxylic acids are strong enough acids to react with the weak base, sodium carbonate.

Question 10

How can sodium carbonate be used to distinguish between the acidity of a phenol and a carboxylic acid?

Answer 10

The carboxylic acid reacts with sodium carbonate to produce carbon dioxide, which is evolved as a gas.

Question 11

What does phenol reacting with sodium hydroxide form?

Answer 11

Sodium phenoxide (salt) + H20 (in a neutralisation reaction).

Question 12

What type of reactions does phenol undergo?

Answer 12

Electrophilic substitution.

Question 13

What are 2 differences in electrophilic substitution reactions between phenols and benzene?

Answer 13

The reactions of phenol take place under milder conditions and more readily than the reactions of benzene.

Question 14

What happens in the bromination of phenol?

Answer 14

Phenol reacts with aqueous bromine solution (bromine water) to form a white precipitate of 2,4,6-tribromophenol.

Question 15

What are the 2 observations of bromination of phenol?

Answer 15

1. The reaction decolourises the bromine water from orange.
2. A white precipitate forms.

Question 16

What are the 2 conditions of bromination of phenol?

Answer 16

1. Carried out at room temperature.
2. A halogen carrier catalyst is not required.

Question 17

What is the skeletal mechanism for the bromination of phenol?

Answer 17

Phenol + 3Br2 FORMS a benzene ring with OH group at top and Br of 2,4,6 + 3HBr.

Question 18

What happens in the nitration of phenol?

Answer 18

Phenol reacts readily with dilute nitric acid at room temperature and a mixture of 2-nitrophenol and 4-nitrophenol is formed (two isomers).

Question 19

What is the skeletal mechanism for the nitration of phenol?

Answer 19

Phenol + HNO3 (dilute) FORMS 2-nitrophenol + H2O AND 4-nitrophenol + H2O.

Question 20

What are 2 differences in the electrophilic substitution reactions between phenol and benzene?

Answer 20

1. Bromine and nitric acid react more readily with phenol than they do with benzene.
2. Phenol is nitrated with dilute nitric acid rather than needing concentrated nitric acid and sulfuric acids with benzene.

Question 21

Why does phenol have an increased reactivity compared to benzene?

Answer 21

It is caused by a lone pair of electrons from the oxygen p-orbital of the -OH group being donated into the pi-system of phenol.

Question 22

How does the electron density differ in phenol and benzene? Therefore?

Answer 22

The electron density of the benzene ring in phenol is increased. The increased electron density attracts electrophiles more strongly than with benzene. Therefore, the aromatic ring in phenol is more susceptible to attack from electrophiles than in benzene. For bromine, the electron density in the phenol ring structure is sufficient to polarise bromine molecules and so no halogen carrier catalyst is required.