(a) Write the propagation steps leading to the formation of dichloromethane (CH2Cl2)from chloromethane.
(b) Explain why free-radical halogenation usually gives mixtures of products.
(c) How could an industrial plant control the proportions of methane and chlorine to favor production of CCl4? To favor CH3Cl?
Here, we are going to describe about the chain mechanism for the formation of dichloromethane from chloromethane.
Step 1: (a)
Cl2 molecule undergoes homolysis in presence of UV light for the formation of Cl. radical
One hydrogen atom is pulled off from chloromethane following by the formation of chloromethyl radical.
Step 2: (b)
Free radical halogenation reaction always substitutes the hydrogen atom by a halogen atom. It is even possible with a molecule having only one type of Hydrogen atom and that can also possible to substitute by a halogen to form a new compound.
Therefore Chlorination of methane molecule, can form different types of substituent compounds such as CH3Cl, CH2Cl2, CHCl3 and CCl4.
Thus, if a molecule contains different types of hydrogen atoms, then the chain reaction gives a mixture of possible products.