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Bromination

What is Bromination?

Bromination is a chemical reaction involving the reaction of a compound, and bromine results in bromine being added to the compound. The product formed after bromination will exhibit new properties from the initial reactant.

Table of Content

Types of Bromination

Bromination can occur in different ways, depending on the reactant.

  • A saturated compound undergoes bromination via a free radical mechanism.
  • An unsaturated hydrocarbon undergoes bromination via an addition reaction.
  • An aromatic compound undergoes bromination via an electrophilic substitution mechanism.

We will now briefly discuss types of bromination in detail.

Bromination via a Free Radical Mechanism

This type of reaction occurs in the saturated compound.

The mechanism for the reaction takes place in the following steps.

Initiation Step

The Br-Br bond of elemental bromine undergoes homolytic fission when irradiated under UV rays, and this process yields two bromine radicals.

Propagation Step

  • A bromine radical abstracts a hydrogen atom from ethane to produce the ethyl radical. In turn, the ethyl radical abstracts a bromine atom from a bromine molecule, and bromoethane is formed.
  • The second step also regenerates a bromine atom. These steps repeat many times until termination occurs.

Termination Step

Termination takes place when

  • A bromine atom reacts with another bromine atom to generate Br2.
  • A bromine atom reacts with ethyl radical to form bromoethane.
  • Two ethyl radicals can also combine to produce butane.

Bromination via an Addition Reaction

  • This type of reaction occurs in the unsaturated compound.
  • Bromination in unsaturated compounds proceeds through brominium ion intermediate.
  • This reaction is also used to check unsaturation.

Bromination via an Electrophilic Substitution Mechanism

  • Benzene reacts with bromine in lewis acid-like FeBr3 to form aryl bromide.
  • This reaction is known as the bromination of benzene.

Activation of Bromine by Lewis Acid

Bromine reacts with lewis acid FeBr3 to form a complex that makes the bromine more electrophilic.

Attack of Benzene

  • Benzene, being electron-rich, attacks electrophilic bromine.
  • This step produces cyclohexadienyl cation intermediate, destroying the aromaticity of benzene.

Deprotonation to generate Aromatic Ring

  • Proton is removed from sp3 Carbon bearing a Bromo group.
  • Aromaticity is retained.

Importance of Bromination

  • Bromination is used in many chemical industries as a suitable building block for numerous syntheses.
  • Bromination is used in agricultural, pharmaceuticals and chemical intermediates.

Frequently Asked Questions on Bromination

What is bromination?

Bromination is a chemical reaction involving the reaction of a compound, and bromine results in bromine being added to the compound.

The product formed after bromination will exhibit new properties from the initial reactant.

What is the nature of the mechanism of bromination of alkanes?

Alkane undergoes bromination via a free radical mechanism.

The mechanism for the reaction takes place in three steps.

  • Initiation Step
  • Propagation Step
  • Termination Step

What is the nature of the mechanism of bromination of the aromatic compound?

An aromatic compound undergoes bromination via an electrophilic substitution mechanism.

The mechanism for the reaction takes place in three steps.

  • Activation of bromine by lewis acid
  • Attack of benzene
  • Deprotonation to generate aromatic ring

What is the nature of the mechanism of bromination of the alkene?

Alkene undergoes bromination via an addition reaction.

  • This reaction is also used to check unsaturation.

What are the different types of bromination reactions?

Bromination can occur in different ways depending on the reactant.

  • A saturated compound undergoes bromination via a free radical mechanism.
  • An unsaturated hydrocarbon undergoes bromination via an addition reaction.
  • An aromatic compound undergoes bromination via an electrophilic substitution mechanism.

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