Understanding the Free Radical Halogenation Process of Cyclohexane with Bromine in the Presence of Sunlight

Introduction

The reaction of cyclohexane with bromine in the presence of sunlight is a classic example of a free radical halogenation process. This reaction is a stepwise mechanism involving initiation, propagation, and termination. The free radicals play a crucial role in the formation of various brominated derivatives of cyclohexane.

The Mechanism of Cyclohexane Bromination in Sunlight

1. Initiation

In the presence of sunlight or UV light, the bromine molecules (Br}2) undergo homolytic cleavage, leading to the formation of bromine radicals (Br}}):

Br}2 xrightarrow light 2 Br}}

2. Propagation

The bromine radical can then react with cyclohexane (C}6H12) to abstract a hydrogen atom, resulting in the formation of a cyclohexyl radical (C}6H11H) and hydrogen bromide (HBr):

Br} C}6H12 rightarrow C}6H11H HBr}

The cyclohexyl radical can further react with another bromine molecule, leading to the formation of bromocyclohexane and regenerating the bromine radical:

C}6H11Br2 rightarrow C}6H11Br Br}

3. Termination

The reaction can terminate when two radicals combine to form stable products. Typical termination reactions include:

Br} Br} rightarrow Br2

C}6H11 C}6H11 rightarrow C12H22

Summary of the Reaction

The overall reaction can be summarized as:

C}6H12 Br}2 xrightarrow light C}6H11Br HBr}

Key Points

The reaction is initiated by the formation of bromine radicals due to UV light. The process involves radical intermediates and can lead to multiple products. The reaction cascade may produce various brominated cyclohexane derivatives, depending on the availability of radicals and bromine.

Frequently Asked Questions (FAQs)

Q: Is the reaction of cyclohexane with bromine in the presence of sunlight balanced?

Yes, the reaction is balanced as shown in the following equation:

C}6H12 Br}2 xrightarrow light C}6H11Br HBr}

Q: Why does cyclohexane react slowly with bromine under sunlight?

Cyclohexane is a cyclic alkane with no unsaturation; thus, it has no nucleophilic behavior. Therefore, it reacts slowly with bromine unless UV light or heat is applied, which initiates a free-radical substitution process.

Conclusion

The reaction of cyclohexane with bromine in the presence of sunlight exemplifies the free radical halogenation process. This mechanism highlights the role of UV light in initiating the reaction and the propagation steps through radical intermediates leading to various brominated derivatives of cyclohexane.