Mechanism Of Free Radical Substitution Of Alkanes
Halogenation reactions occur via a mechanism called free radical substitution. There are three main steps in the free radical mechanism. They are:
The overall reaction of chlorination of methane.
CH4 + Cl2 ______> CH3Cl + HCl
This step involves the dissociation of the halogen molecule (e.g., chlorine molecule) into two chlorine atoms. Even though the total reaction is exothermic, initially energy should be supplied for the reaction to proceed.
- Propagation steps
During the propagation step, the hydrogen atom is abstracted from methane by a chlorine atom. This is followed by the reaction between the methyl radical and the chlorine molecule.
The termination steps involve the combination of the radicals.