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AdditionIntroductory
Acid-Catalyzed Hydration
Also known as: Markovnikov Hydration
General Equation
R-CH=CH₂ + H₂O → R-CH(OH)-CH₃
Description
Addition of water across a double bond following Markovnikov's rule. The OH group ends up on the more substituted carbon via carbocation intermediate. An alternative is oxymercuration-demercuration which avoids rearrangements.
Reaction Scheme
Reactants:
- • Alkene
Products:
- • Alcohol (Markovnikov regiochemistry)
Reagents:
- • H₂O
- • H₂SO₄ or H₃PO₄ (acid catalyst)
Conditions:
- • Aqueous acid, heat
Mechanism (3 steps)
1
Protonation of the alkene by H₃O⁺ to form the more stable carbocation (Markovnikov orientation).
Arrow: curvedR-CH⁺-CH₃
Proton adds to less substituted carbon
2
Water acts as nucleophile, attacking the carbocation.
Arrow: curvedR-CH(OH₂⁺)-CH₃
3
Deprotonation of the oxonium ion by water to give the alcohol product and regenerate H₃O⁺.
Arrow: curved
Acid is regenerated — catalytic
Key Points to Remember
- ✓Markovnikov regiochemistry (OH on more substituted C)
- ✓Equilibrium reaction — Le Chatelier drives with excess water
- ✓Carbocation rearrangements possible (use oxymercuration to avoid)
- ✓Reverse reaction = acid-catalyzed dehydration of alcohols
- ✓No stereocontrol (racemic at new stereocenter)
Examples
Reactant:
2-Methylpropene
Reagent:
H₂O, H₂SO₄
Product:
2-Methyl-2-propanol (t-butanol)
Yield: 80%
Reactant:
Cyclohexene
Reagent:
H₂O, H₃PO₄
Product:
Cyclohexanol
Yield: 75%
Synthetic Utility
Simple method to convert alkenes to Markovnikov alcohols. For rearrangement-free version, use oxymercuration-demercuration.
Limitations
- ⚠Carbocation rearrangements can give unwanted products
- ⚠Equilibrium process — requires excess water
- ⚠Competes with polymerization at higher concentrations
#addition#hydration#Markovnikov#alcohol#acid-catalyzed