The halogenation of methane is a reaction that occurs with the formation of free radicals and involves the replacement of hydrogen by halogen.


Radical halogenations take place in three stages called: initiation, propagation and termination:

Initiation stage

In the first step of the reaction, the homolytic cleavage of the Cl-Cl bond occurs. This is achieved with heat or by absorbing light.


First stage of propagation

It is a slightly endothermic stage that consists of the subtraction of a hydrogen from methane by the chlorine radical formed in the previous stage, generating the methyl radical.


Second stage of propagation

During it, the methyl radical abstracts a chlorine atom from one of the initial molecules, giving chloromethane and a new chlorine atom. Said atom returns to the first stage of propagation and the whole process is repeated.


Termination stage

It takes place when the reagents are exhausted, then the radicals that are in the middle unite with each other.

mechanism-halogenation-05 and