8.3a Acid Catalyzed Hydration of Alkenes
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|ACID CATALYZED HYDRATION|
| || |
|Two Groups Added|| || |
|Reagents Added||H2SO4, H2O (i.e. H3O+)|
|Other Characteristics||Intermediate is a carbocation making rearrangements possible.|
Acid Catalyzed Hydration of Alkenes
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 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.