Understanding the Conversion of Alkanes to Haloalkanes: Free Radical Halogenation and Electrophilic Halogenation

Alkane to Haloalkane

Converting an alkane to a haloalkane involves the substitution of a hydrogen atom in the alkane with a halogen atom, such as chlorine (Cl), bromine (Br), or iodine (I)

Converting an alkane to a haloalkane involves the substitution of a hydrogen atom in the alkane with a halogen atom, such as chlorine (Cl), bromine (Br), or iodine (I). This substitution reaction is known as halogenation, and it can be carried out using different methods.

There are two common methods for converting an alkane to a haloalkane: free radical halogenation and electrophilic halogenation.

1. Free Radical Halogenation:
In this method, alkane molecules react with halogen molecules in the presence of ultraviolet (UV) light or heat. This process involves three steps: initiation, propagation, and termination.

Initiation: UV light or heat breaks the halogen molecule into two halogen atoms, forming highly reactive halogen radicals.
Cl2 ⟶ 2Cl•

Propagation: The alkane reacts with the halogen radical to form an alkyl radical and a hydrogen halide. This alkyl radical can further react with another halogen molecule to form a new halogen radical, and the process continues until all the alkane molecules have reacted.
CH4 + Cl• ⟶ CH3• + HCl
CH3• + Cl2 ⟶ CH3Cl + Cl•

Termination: The free radicals react with each other to form stable molecules, stopping the chain reaction.
Cl• + Cl• ⟶ Cl2

2. Electrophilic Halogenation:
In this method, alkane molecules react with halogen molecules in the presence of a Lewis acid catalyst, such as iron (Fe) or aluminum chloride (AlCl3). This process proceeds via an electrophilic substitution mechanism.

The catalyst first reacts with the halogen molecule to form an electrophilic halogen species.
Fe + Cl2 ⟶ FeCl3

The electrophilic halogen species then attacks the alkane molecule, displacing a hydrogen atom and forming a carbocation intermediate.
CH4 + Cl+ ⟶ CH3+ + HCl

Finally, a halide ion (e.g., Cl-) reacts with the carbocation to form the haloalkane.
CH3+ + Cl- ⟶ CH3Cl

Overall, the conversion of an alkane to a haloalkane involves the replacement of a hydrogen atom in the alkane with a halogen atom through either free radical halogenation or electrophilic halogenation. Both methods have their advantages and limitations, and the choice of method depends on the specific alkane and haloalkane desired.

More Answers: