Benzoyl Peroxide - Synthesis, Structure, Physical Properties

Synthesis, Structure, Physical Properties

Benzoyl peroxide was the first organic peroxide prepared by intentional synthesis. It was prepared by treating benzoyl chloride with barium peroxide, a reaction that probably follows this stoichiometry:

2 C₆H₅C(O)Cl + BaO₂ → ₂O₂ + BaCl₂

Benzoyl peroxide is usually prepared by treating hydrogen peroxide with benzoyl chloride.

The oxygen-oxygen bond in peroxides is weak. Thus benzoyl peroxide readily undergoes homolysis (symmetrical fission), forming free radicals:

₂O₂ → 2 C₆H₅CO₂•

The symbol • indicates that the products are radicals; i.e., they contain at least one unpaired electron. Such species are highly reactive. The homolysis is usually induced by heating. The half-life of benzoyl peroxide is one hour at 92 °C. At 131 °C, the half-life is one minute.

Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which is significantly toxic. It is important to note that the safety of the decomposition products does not mean that the substance itself is safe, as it is benzoyl peroxide's action as an oxidizing agent that is of importance. Hydrogen peroxide can be corrosive due to its oxidizing properties, but decomposes to form water and oxygen. Sodium hypochlorite (commonly known as "bleach") also shares these properties, but disproportionates to form harmless products such as sodium chloride.