Chemistry [[Module Three]] Alkanes: Chlorination

[[Chlorination]]

Alkanes do not react with chlorine at room temp but in the presence of UV light they react explosivly.

Process = Free Radical Substitution

-occurs in several steps

1) Inititaion
Cl2 ---> 2Cl*

The UV light provides activation energy by splitting a cholrine molecule into 2 chlorine free radicals.
This occurs first because Cl-Cl bond is weaker than the C-H bond in alkane.

2) Propagation

Cl* + CH4 --> CH3* + HCl

CH3* + Cl2 ---? CH3Cl + Cl*

A radical is used and a radical is formed, so it leads to a chain reaction.
Each step is exothermic

Overall equation: CH4 + Cl2 ---> CH3Cl + HCl

3) Termination
- two radicals combine to form a stable molecule and sequence of reations stop. Unpaired electrons form covalent bond.

Cl* + CH3* --> CH3Cl

CH3* + CH3* --> CH3CH3


Further Sunstitiution

-can occur to form

CH2Cl* --> CH2Cl2 and CHCl3

further substitution can be reduced if an excess of methane is used.