Question

How do you account for the formation of ethane during chlorination of methane? 

Answer 1

Chlorination of methane proceeds via a free radical chain mechanism. The whole reaction takes place in the given three steps. 

Step 1: Initiation: 

The reaction begins with the homolytic cleavage of Cl – Cl bond as: 

Step 2: Propagation: 

In the second step, chlorine free radicals attack methane molecules and break down the C–H bond to generate methyl radicals as: 

These methyl radicals react with other chlorine free radicals to form methyl chloride along with the liberation of a chlorine free radical. 

Hence, methyl free radicals and chlorine free radicals set up a chain reaction. While HCl and CH₃Cl are the major products formed, other higher halogenated compounds are also formed as: 

Step 3: Termination: 

Formation of ethane is a result of the termination of chain reactions taking place as a result of the consumption of reactants as: 

Hence, by this process, ethane is obtained as a by-product of chlorination of methane.