Phenols

Question 1

What is a phenol?

Answer 1

A phenol is a benzene ring with an -OH attached.

Question 2

How can phenols behave as a weak acid?

Answer 2

Phenols behave as a weak acid when a hydrogen ion on the OH transfers to a base.

C6H5OH + H2O ⇌ C6H5O- + H3O-

Phenol is able to lose a H+ ion because the phenoxide ion formed (C6H5O-) is fairly stable. The more stable an ion, the more likely it is to form.

Question 3

How is the phenoxide ion made stable when H+ ion removed from -OH group?

Answer 3

One of the lone pairs of electrons on the oxygen is delocalised with the electron cloud of the whole phenoxide ion.

Spreading the charge around makes the ion more stable than it would be if all the charge remained on the oxygen.

Question 4

Why does phenol only behave as a weak acid?

Answer 4

Oxygen is the most electronegative element on the ion and the delocalised electrons will be drawn towards it.
This means there will be a lot of charge around the oxygen which will tend to attract the hydrogen ion back again.

Question 5

Outline the reaction between phenol and alkali (NaOH)

Answer 5

Phenol acts as an acid by donating H+ ion to OH, forming H2O.
Na attaches to O-, forming sodium phenoxide salt.

C6H5OH + NaOH -> C6H5O-Na+ + H2O

Question 6

Outline the reaction between phenol and metal (Na)

Answer 6

Phenol reacts vigorously with reactive metals such as sodium.
A soluble salt is formed and hydrogen gas is given off.

2C6H5OH + 2Na -> 2C6H5O-Na+ + H2