Chlorination of methane is an example of which reaction


Chlorination of methane is an example of which reaction

Hint: The addition of chlorine to a molecule or a compound is known as chlorination. Chlorine can be added to a compound through addition or substitution. Methane is an organic compound having the chemical formula \[C{H_4}\]. It is the simplest hydrocarbon which is the compound of hydrogen and carbon.

Complete step by step answer:

In order to understand the chlorination of methane we have to identify the mechanism of chlorination. The chlorination of methane occurs in presence of light denoted by \[h\nu \] in a stepwise manner. The reaction consists of a radical mechanism to produce chlorinated methane. Three steps are involved in radical mechanism, initiation, propagation and termination. Let us understand the reaction mechanism step by step.Step\[1\]: Initiation:At first the chlorine radicals are generated by cleavage of the \[Cl - Cl\] bond.$Cl - Cl\xrightarrow{{h\nu }}2C{l^ \cdot }$Step\[2\]: Propagation:$C{H_4} + C{l^ \cdot }\xrightarrow{{}}C{H_3}^ \cdot + HCl$$C{H_3}^ \cdot + C{H_3}^ \cdot \xrightarrow{{}}C{H_3} - C{H_3}$ One hydrogen atom of methane is replaced by chlorine atom so it is a substitution reaction. The product is called chloromethane. Step\[3\]: Termination:The propagation step is stopped when a radical finds another radical. Three termination steps are possible for this reaction.$C{l^ \cdot } + C{l^ \cdot }\xrightarrow{{}}C{l_2}$ $C{H_3}^ \cdot + C{l^ \cdot }\xrightarrow{{}}C{H_3}Cl$ The radical mechanism indicates regeneration of radicals during the course of the reaction. It allows the reaction to propagate and lead to the desired product.

Hence option C is correct i.e. substitution.

Note: The radical reaction suffers through a major drawback. If the termination of radical does not occur, then the reaction gives a mixture of products. For this reaction there are several products possible like chloromethane, dichloromethane, trichloromethane, and tetrachloromethane. That is why the termination step is very important in radical reaction.

If a mixture of methane and chlorine is exposed to a flame, it explodes - producing carbon and hydrogen chloride. This is not a very useful reaction! The reaction we are going to explore is a more gentle one between methane and chlorine in the presence of ultraviolet light - typically sunlight. This is a good example of a photochemical reaction - a reaction brought about by light.

\[ CH_4 + Cl_2 \rightarrow CH_3Cl + HCl\]

The organic product is chloromethane. One of the hydrogen atoms in the methane has been replaced by a chlorine atom, so this is a substitution reaction. However, the reaction does not stop there, and all the hydrogens in the methane can in turn be replaced by chlorine atoms. Multiple substitution is dealt with on a separate page, and you will find a link to that at the bottom of this page.

The mechanism involves a chain reaction. During a chain reaction, for every reactive species you start off with, a new one is generated at the end - and this keeps the process going. The over-all process is known as free radical substitution, or as a free radical chain reaction.

  • Chain initiation: The chain is initiated (started) by UV light breaking a chlorine molecule into free radicals.

Cl2 \(\rightarrow\) 2Cl

Chlorination of methane is an example of which reaction

  • Chain propagation reactions : These are the reactions which keep the chain going.

CH4 + Cl\(\rightarrow\)CH3 + HCl

CH3 + Cl2\(\rightarrow\)CH3Cl + Cl

  • Chain termination reactions: These are reactions which remove free radicals from the system without replacing them by new ones.


CH3 + Cl \(\rightarrow\) CH3C l

CH3 + CH3\(\rightarrow\)CH3CH3


  • Jim Clark (