Question
What are the products of chlorination of methane ? Describe the mechanism of the formation of each?
Solution
Methane reacts with chlorine in diffused sunlight or ultraviolet light or at 600 K. Hydrogen atoms of methane are successively replaced by chlorine atoms.
Mechanism: It involves free radical mechanism and consists of three steps:
(i) Chain initiating step: The chlorine molecule takes up energy either from ultraviolet light or from heat to form two chlorine free radicals by homolysis.
(ii) Chain propagating step: The free radical Cl collides with methane molecule to form methyl free radical.
The above reaction is exothermic. The methyl free radical then attacks with chlorine molecule to form methyl chloride and chlorine free radicals.
Formation of other chlorinated products:
(iii) Chain terminating step: The reaction terminates when the free radical combines with each other.
Mechanism: It involves free radical mechanism and consists of three steps:
(i) Chain initiating step: The chlorine molecule takes up energy either from ultraviolet light or from heat to form two chlorine free radicals by homolysis.
(ii) Chain propagating step: The free radical Cl collides with methane molecule to form methyl free radical.
The above reaction is exothermic. The methyl free radical then attacks with chlorine molecule to form methyl chloride and chlorine free radicals.
Formation of other chlorinated products:
(iii) Chain terminating step: The reaction terminates when the free radical combines with each other.
