Does free radical halogenation only happen under application of UV?

1 Answer
Jun 10, 2015

No, free radical halogenation also happens under the application of heat.


The initiation step in a free radical halogenation involves the homolytic cleavage of a halogen molecule.

Breaking a bond requires an input of energy to the molecule

In the lab, the most convenient energy source is UV light.

Commercially, however, it is cheaper to use heat as the energy source.

The #"Cl-Cl"# bond dissociation energy is 239 kJ/mol, so a temperature of 250 to
300 °C is required to dissociate chlorine molecules fast enough to effectively initiate the chain reaction.

This temperature range is easily reached in an industrial process.