EXERCISES

 

Question 13.1:-

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


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:

                                          1.1

                                      

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:

                                  CH4+CIhνCH3+H-CI 

                                  Methane

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

              CH3+CI-CICH3-CI  +  Cl·

                                                     Methyl chloride                   

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:

                                          CH3Cl+CI·CH2CI+HCICH2CI+CI-CICH2CI2+CI·

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:

    CI·+CI·CI-CIH3C·+·CH3H3C-CH3

                                   (Ethane)

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