Benzaldehyde is an aromatic aldehyde with the formula C6H5CHO. It is a colorless liquid with a bitter almond odor. Benzaldehyde is a common flavoring agent and is also used in the production of perfumes, dyes, and other chemicals.

In the presence of air, benzaldehyde undergoes autoxidation to form benzoic acid. This reaction is catalyzed by the oxygen in the air, which acts as an oxidizing agent. The reaction proceeds through a free radical mechanism.

The first step in the reaction is the formation of a free radical by the abstraction of a hydrogen atom from the benzyl group by oxygen. This forms a benzyl radical and a hydroxyl radical.

The benzyl radical then reacts with oxygen to form a peroxy radical. The peroxy radical then reacts with another molecule of benzaldehyde to form a hydroperoxide and another benzyl radical.

The hydroperoxide then decomposes to form benzoic acid and a water molecule. The benzyl radical can then react with another molecule of oxygen to start the cycle again.

The overall reaction can be represented as follows:

2C6H5CHO + O2 -> 2C6H5COOH + H2O

The rate of autoxidation of benzaldehyde is increased by the presence of light, heat, and metal ions.