How do you write a stepwise mechanism that shows how a small amount of #CH_3CH_3# could form during the bromination of #CH_4?

1 Answer
Sep 7, 2016

Answer:

Bromination proceeds by a radical mechanism, in which #Br*# radicals are invoked. So let's see.

Explanation:

#"Initiation:"# #Br_2 +hnu rarr2Br*#

#"Propagation:"# #Br* +CH_4 rarr*CH_3 + H-Br#

#Br_2 +*CH_3 rarr BrCH_3 + Br*#

#"Termination:"# #Br* + Br* rarr Br_2#, i.e. the coupling of 2 radicals could occur, or the coupling of hydrocarbyl radicals made in the propagation step:

#H_3C*+*CH_3 rarr H_3C-CH_3#

And thus the coupling of 2 methyl radicals results in #C-C# bond formation.

Overall, the bromination rxn is:

#CH_4 + Br_2 rarr CH_3Br + H-Br#

The discovery of ethane in the reaction mixture is good evidence for the radical reaction as shown.