Question

what is dehalogenation?give an example?

Answer 1

The removal of a molecule of halogen ( I₂, Cl₂ or Br₂) from dihaloalkane compounds by the treatment of suitable regent, to give an alkene is known as dehalogenation reaction.
Halogen atom present in dihaloalkene could be vicinal or geminal.
1. Dehalgenation reaction of vicinal dihaloalkens ( halogen atoms present on adjacent carbon atoms)
Br-CH₂-CH₂-Br + Zn $\underset{\Delta }{\overset{C{H}_{3}OH}{\to }}$ CH₂=CH₂

2. Dehalogenation reaction of geminal dihaloalkanes ( both halogen atom present on same carbon )

CH₃-CH(Br)₂ + Zn ​$\underset{\Delta }{\overset{C{H}_{3}OH}{\to }}$ CH₂=CH₂

This is not an useful method for the preparation of alkene as dihaloalknes are generaly not avavilabe as starting material.