How can phenol be obtained from sodium phenoxide?

Acidification

The correct answer is option 3. Acidification.

Sodium phenoxide (\( \text{C}_6\text{H}_5\text{ONa} \)) is the sodium salt of phenol (\( \text{C}_6\text{H}_5\text{OH} \)). The phenoxide ion is formed when a sodium ion (\( \text{Na}^+ \)) is attached to the oxygen atom of the phenol molecule.

Acidification Reaction:

When sodium phenoxide is treated with an acid, such as hydrochloric acid (\( \text{HCl} \)), the acid donates a proton (\( \text{H}^+ \)) to the oxygen atom in the phenoxide ion. This protonation results in the formation of phenol.

The chemical equation for the acidification reaction is:

Explanation:

1. Phenoxide Ion (\( \text{C}_6\text{H}_5\text{ONa} \)):
The phenoxide ion is a negatively charged species formed when a proton is removed from the hydroxyl group of phenol, leaving a lone pair of electrons on the oxygen atom. The sodium ion (\( \text{Na}^+ \)) is then attracted to the negatively charged oxygen, forming the sodium phenoxide salt.

2. Acidification:
When hydrochloric acid (\( \text{HCl} \)) is added, the acidic proton (\( \text{H}^+ \)) from the acid reacts with the phenoxide ion. The proton is accepted by the lone pair of electrons on the oxygen atom.

3. Formation of Phenol:
The acceptance of the proton results in the removal of the negative charge on the oxygen atom. The product of the reaction is phenol (\( \text{C}_6\text{H}_5\text{OH} \)), which is now neutral.

4. Formation of Sodium Chloride:
The sodium ion (\( \text{Na}^+ \)) originally present in the sodium phenoxide reacts with the chloride ion (\( \text{Cl}^- \)) from the hydrochloric acid to form sodium chloride (\( \text{NaCl} \)), which is a soluble salt.

In summary, acidification of sodium phenoxide involves the addition of an acid, resulting in the transfer of a proton to the phenoxide ion, ultimately yielding phenol and a corresponding salt. This process is a common way to regenerate phenol from its sodium salt in laboratory and industrial settings.