Introduction:
Halogenation of alkanes is a chemical reaction where hydrogen atoms in an alkane are replaced by halogen atoms through a free radical mechanism.
This process is crucial in organic chemistry for the functionalization of alkanes and the synthesis of halogenated compounds.
Mechanism:
The reaction proceeds in three steps: initiation, propagation, and termination.
1. Initiation:
UV light or heat breaks the diatomic chlorine molecule into two chlorine radicals.
Cl2 + UV light/heat → 2Cl•Cl2 + UV light/heat → 2Cl•
2. Propagation:
A chlorine radical abstracts a hydrogen atom from the alkane, creating a carbon-centered radical and hydrochloric acid.
R-H + Cl• →R• + HClR-H + Cl• → R• + HCl
The carbon-centered radical reacts with another chlorine molecule, forming the chlorinated alkane and another chlorine radical.
R• + Cl2 → R-Cl + Cl•R• + Cl2 → R-Cl + Cl•
3. Termination:
The reaction stops when two radicals recombine to form a stable molecule.
Possible reactions include:
Two chlorine radicals forming a chlorine molecule.
A carbon-centered radical and a chlorine radical forming a chlorinated alkane.
Two carbon-centered radicals forming a new alkane.