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Alkene Reactions: Chlorohydrin Formation using Cl2 and H2O

Chlorine (Cl2) in the presence of alkenes and water, react together form chlorohydrins:

Alkene Reactions: Chlorohydrin Formation using Cl2 and H2O image4.png

Chlorine reacts first with the alkene molecule, and ultimately resides on the least substituted carbon on the double bond (anti-Markovnikov). The water molecule (eventually OH) bonds with the most substituted carbon on the double bond (Markovnikov). The two functional groups are added in an anti addition where chlorine and OH are added to the opposite side of each other, giving 2 products that are enantiomers:

Anti Addition

Alkene Reactions: Chlorohydrin Formation using Cl2 and H2O image3.png

Partial anti Addition

Alkene Reactions: Chlorohydrin Formation using Cl2 and H2O image4.png

No stereocenters

Alkene Reactions: Chlorohydrin Formation using Cl2 and H2O image1.png

The reaction mechanism is depicted below:

Alkene Reactions: Chlorohydrin Formation using Cl2 and H2O image2.png

In the first step, electrons from the alkene bond react with the first chlorine to make a bond, and electrons from the first chlorine atom react with the other carbon to form another bond, forming a ring structure as an intermediate. The chlorine-chlorine bond is broken with electrons from the bond going to the second chlorine atom.

In the second step, water attacks the backside of the intermediate structure on the more substituted carbon, causing the bond between the more substituted carbon and chlorine to break, transferring the electrons to chlorine.

In the third step, another water molecule enters the reaction and the electrons from the oxygen atom in the water molecule react with one of the two hydrogens bonded to the oxygen on the alkane chain.

The reagents used for this reaction are Cl2 in a solution of H2O.