8.3a Hydration Acid Catalyzed Hydration

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ACID-CATALYZED HYDRATION
Less Substituted More Substituted
Two Groups Added H OH
Reagents Added H2SO4, H2O (i.e. H3O+)
Regioselectivity Markovnikov
Stereospecificity None
Other Characteristics Intermediate is a carbocation making rearrangements possible.

Acid-Catalyzed Hydration

Acid-catalyzed hydration results in the Markovnikov addition of a hydrogen (less substituted side) and a hydroxyl group (more substituted side) across an alkene forming an alcohol.  There is no stereospecificity associated with this reaction, but the intermediate is a carbocation so rearrangements are possible.  The reagents are water with a catalytic amount of strong acid most commonly sulfuric acid (H2SO4) though the reagents can also simply be listed as H3O+ as shown below.

Acid Catalyzed Hydration of an Alkene

Acid-Catalyzed Hydration Mechanism

Step 1: The pi electrons of the alkene attack a hydrogen of H3O+ resulting in carbocation formation.  The carbocation is a high energy intermediate making this the rate determining step (slow step) of the reaction.

 

Step 2: When there is no favorable rearrangement water carries out nucleophilic attack on the carbocation forming an oxonium ion.

 

Step 3: A water molecule deprotonates the oxonium intermediate yielding the product alcohol.

Acid Catalyzed Hydration of Alkene Mechanism