Question

How can alkyl halides be prepared from alkanes?

Answer 1

`"Free radical halogenation........."`

Explanation:

And the reaction scheme is generally constructed as:

`i.` `"Initiation: "X_2 + hnu rarr 2dotX`

`ii.` `"Propagation(i): "dotX + H_3CR rarr HX + H_2dotCR`

`"Propagation(ii): "H_2dotCR+ X_2rarr H_2XCR+ dotX`

`iii.` `"Termination: the coupling of two radical species,"`

`H_2dotCR+dotXrarrH_2CXR`

`2H_2dotCRrarrH_2RC-CH_2R`

The presence of small quantities of say ethane in the product mix of halogenation of methane is good evidence for the radical mechanism proposed.

The propagation step is a cascade type of process, in that the reaction of a radical species generates another radical species that can continue the chain of the reaction.