Benzyl alcohol is obtained from benzaldehyde by Cannizzaro's reaction.

Cannizzaro's reaction:
- Cannizzaro's reaction is a redox reaction in which an aldehyde is simultaneously oxidized and reduced.
- It involves the reaction of an aldehyde with a strong base, such as sodium hydroxide (NaOH), to give a salt and an alcohol.
- The aldehyde molecule acts as both a reducing agent and an oxidizing agent in this reaction.

Reaction mechanism:
The reaction mechanism of Cannizzaro's reaction involves two steps: the nucleophilic attack of the base and the transfer of a hydride ion.

1. Nucleophilic attack:
- In the first step, the hydroxide ion from the base attacks the carbonyl carbon of the aldehyde, forming a negatively charged intermediate called an alkoxide ion.
- The lone pair of electrons on the oxygen atom of the hydroxide ion attacks the partially positive carbon atom of the carbonyl group.
- This leads to the formation of a negatively charged alkoxide ion.

2. Hydride ion transfer:
- In the second step, a hydride ion (H-) is transferred from the aldehyde molecule to the alkoxide ion.
- The alkoxide ion acts as a strong base and abstracts a hydride ion from the aldehyde.
- This results in the reduction of one aldehyde molecule to an alcohol and the oxidation of another aldehyde molecule to a carboxylic acid.
- The hydride ion transfer step is responsible for the reduction process.

Benzyl alcohol formation:
- In the case of benzaldehyde, the Cannizzaro's reaction leads to the formation of benzyl alcohol and sodium benzoate.
- The hydroxide ion attacks the carbonyl carbon of benzaldehyde, forming an alkoxide ion.
- The alkoxide ion then abstracts a hydride ion from another benzaldehyde molecule, resulting in the reduction of one molecule to benzyl alcohol and the oxidation of another molecule to sodium benzoate.

Conclusion:
- Benzyl alcohol is obtained from benzaldehyde by Cannizzaro's reaction, which involves the simultaneous oxidation and reduction of the aldehyde.
- This reaction is useful for converting benzaldehyde into benzyl alcohol in the presence of a strong base like sodium hydroxide.