The halohydrin formation reaction
is a chemical reaction
in which a halogen
is added to an alkene
in aqueous solution
to form a halohydrin
. The reaction is a form of electrophilic addition
; it is similar to the halogen addition reaction
The basic chemical equation for this reaction is as follows:
- C=C + X2 + H2O → X-C-C-OH
(X represents a halogen, either Cl or Br).
The reaction occurs with anti addition, leaving the newly added X and OH groups in a trans configuration.
When bromination is desired, N-bromosuccinimide is preferable to bromine because fewer side-products are produced.
In the first step, the pi bond
of the alkene attacks the halogen. For the case where bromine is the halogen, three-membered C, C, Br ring; this is known as a bromonium
The addition of water, which provides the hydroxide anion, gives the desired halohydrin with high anti stereoselectivity in order to minimize the repulsion between the halogen and the hydroxide approaching group. Markovnikov's rule applies: the positive charge resides on the more-substituted carbon, hence the hydroxide anion adds here.