E2 Elimination (Dehydrohalogenation)
C2H5Br + KOH → C2H4 + KBr + H2O
Overview
Strong base (KOH in ethanol) removes a beta-hydrogen and the halide leaves simultaneously in a concerted E2 elimination to form an alkene. The H and Br must be anti-periplanar (180 degrees) for the elimination to proceed. E2 competes with SN2, with bulky bases and secondary/tertiary substrates favoring elimination.
Participants
| Role | Substance | Coefficient | State |
|---|---|---|---|
| Reactant | Potassium Hydroxide KOH | 1 | (aq) |
| Product | Ethylene C₂H₄ | 1 | (g) |
| Product | Water H₂O | 1 | (l) |
Everyday Example
E2 elimination is used to prepare alkenes from easily available alkyl halides and is key to understanding organic reaction selectivity.
Industrial Importance
Dehydrohalogenation is used in the manufacture of vinyl chloride (from ethylene dichloride) and in producing various alkene monomers.
Properties
- Type
- Organic
- Reversible
- No
- Energy
- Exothermic
- ΔH
- -50.0 kJ/mol
Related Reactions
Aldol Condensation of Acetaldehyde
Amide Formation (Acetic Acid + Ammonia)
Baeyer-Villiger Oxidation
Beckmann Rearrangement (Cyclohexanone Oxime)
Bromination of Ethylene
Buchwald-Hartwig Amination
Cannizzaro Reaction of Formaldehyde
Catalytic Hydrogenation of Ethylene
Claisen Condensation (Ethyl Acetate)
Condensation Polymerization (Nylon 6,6)
Frequently Asked Questions
What is the equation for E2 Elimination (Dehydrohalogenation)?
The balanced equation is: C₂H₅Br + KOH → C₂H₄ + KBr + H₂O.
What type of reaction is E2 Elimination (Dehydrohalogenation)?
E2 Elimination (Dehydrohalogenation) is a organic reaction.
Is E2 Elimination (Dehydrohalogenation) exothermic or endothermic?
E2 Elimination (Dehydrohalogenation) is exothermic (releases energy). The enthalpy change (ΔH) is -50.0 kJ/mol.