Question

Why haloalkane is generally not prepared from alkane

Plz guys it is urgent

Answer 1

Hi....
For production of alkyl halides, direct halogenation of alkanes is not suitable because they yield a mixture of different alkyl halides and the reaction is a chain reaction as for example the reaction of methane with chlorine forms various chlorides.

Answer 2

There is so many ways to prepare haloalkanes one of them being halogenation of alkanes.

In this process, in the presence of uv light an alkane is treated with halogen to form haloalkane and HCl.

CH4 +Cl2 ------------>CH3Cl + HCl

uv

But this is not a reliable method to prepare haloalkanes because of the following reasons:-

1. All the types of haloalkanes can be formed, like:-

When CH4 is treated with Cl2 in presence of uv light then CH3Cl will be formed along with CH2Cl2, CHCl3 and CCl4 due to the forrmation of free radicals.

2. Free radical mechanism is random so higher alkanes will also be from the lower one.

CH3• + CH3• ------> C2H6

3. Additional products will also be formed like:-

CH3• + Cl• ----------->CH3Cl

CH2Cl• + Cl• -------->CH2Cl2

CHCl2• + Cl•---------->CHCl3

CCl3• + Cl•-----------> CCl4

Cl• + Cl• --------------> Cl2

H• +H• --------------> H2

CH3• + H• ------------> CH4

The above mentioned products have almost comparable masses and thus they are difficult to separate.

Therefore this method is not suitable to prepare haloalkanes from alkanes but then also we use this method in organic conversions.