In the presence of UV light ethane react with chlorine to produce chloromethane

Question

, What is equation of the reaction
2, outline the mechanism of the reaction and state the role of the UV light .
3, Identify the organic product other than chloromethe which could be produce in a termination steps and write the equation to show the information

Answer 1

Hello Derick

 

Ethane cannot react with chlorine to form chloromethane as ethane is a 2-carbon alkane and methane is a 1-carbon alkane.  Therefore, there is some error in the question.

 

I will assume the starting alkane is METHANE, the product is chloromethane, and will answer the questions for you.

 

The overall reaction is:

 

CH₄ (g) + Cl₂ (g) → CH₃Cl (g) + HCl (g)

 

This reaction is called free-radical chlorination and the mechanism involves 3 main steps.  The first step is called the chain initiating step where the chlorine molecule splits into 2 chlorine radicals.  The splitting of the chlorine molecule into the 2 radicals requires UV light as this supplies the energy needed to break the covalent bond between the 2 chlorine atoms in the molecule.

 

A) Chain Initiating Step

 

Cl₂ + UV light → 2Cl•

 

B) Chain Propagating Step

 

Cl• + CH₄ → CH₃• + HCl

 

In the above reaction, the chlorine radical reacts with the first methane molecule to form a methyl radical and HCl.

 

CH₃• + Cl₂ → CH₃-Cl + Cl•

 

The methyl radical then reacts with a chlorine molecule to form one molecule of chloromethane and in the process generates another chlorine radical.  This Cl radical then reacts with another molecule of methane and the above 2 steps continue until either all the methane and/or chlorine molecules have reacted.

 

C) Chain Terminating Step

 

This can involve 3 separate reactions where any free radicals present in the reaction mixture can combine to end (or terminate) the reaction.

 

a) CH₃• + Cl• → CH₃-Cl

 

b) Cl• + Cl• → Cl₂

 

c) CH₃• + CH₃• → CH₃-CH₃

 

The combination of the two CH₃• radicals produces the alkane, ethane (C₂H₆), which is the "other organic product other than chloromethane formed in the terminating step."  (answer to part 3 of your questions above).

 

Hope the above was helpful!