Dehydration
Ethanol gives ethene through dehydration.
- Reagents
- Aluminium oxide catalyst
- Conditions
- Pass ethanol vapour over heated catalyst
- Reaction class
- Dehydration
- Equation
- C2H6O -> C2H4 + H2O
Overview
Ethanol gives ethene through dehydration.
Transformation
- Equation
- C2H6O -> C2H4 + H2O
- Reactants
- Ethanol
- Products
- Ethene + Water
- Reagents
- Aluminium oxide catalyst
- Environment
- Pass ethanol vapour over heated catalyst
- Reaction class
- Dehydration
- Mechanism
- dehydration
- Evidence level
- source-backed molecular example
Reference procedure
Ethanol dehydration over a heated catalyst
Ethanol vapour → ethene + water
Materials and quantities
- Ethanol on mineral wool
- Heated catalyst specified by the source
- Dilute unsaturation-test reagent
Apparatus
- Clamped heat-resistant reaction tube
- Gas delivery tube
- Water trough and collection tubes
Procedure
- Follow the source’s catalyst-heating and ethanol-vapour sequence.
- Collect gas over water and test a separate sample for unsaturation.
Work-up and isolation
- Record gas evolution and loss of the test reagent’s colour separately.
Critical controls
- Remove the delivery tube from water before stopping heating to prevent suck-back into hot glass.
- Air initially in the apparatus and possible entrained vapour limit purity claims.
- A bromine-water test is not a demonstration that a pure dibromoalkane has been isolated.
Scope and limitations
- Scope
- Named ethanol example; not a class-wide route prediction.
- Limitations
- This catalyst route is distinct from concentrated-acid dehydration; conditions are not interchangeable.
Related reactions
- Iodoform reaction: Ethanol → Triiodomethane products
Ethanol is oxidised and cleaved by alkaline iodine to give triiodomethane and methanoate.
- Partial oxidation: Ethanol → Ethanal
Ethanol is oxidised to ethanal.
- Oxidation: Ethanol → Ethanoic acid
Ethanol is oxidised to ethanoic acid.
- Reduction: Ethanal → Ethanol
Ethanal is reduced to ethanol.
- Esterification: Ethanol → Ethyl acetate
Ethanoic acid and ethanol combine reversibly to form ethyl acetate and water.
- Acid hydrolysis: Ethyl acetate → Ethanol
Ethyl acetate and water react reversibly to form ethanoic acid and ethanol.
- Hydration: Ethene → Ethanol
Ethene gives ethanol through hydration.
- Intermolecular dehydration: Ethanol → Diethyl ether
Protonation turns one ethanol OH group into a better leaving group. The oxygen of another ethanol molecule displaces water, and deprotonation gives diethyl ether; stronger dehydration conditions instead favour ethene.
- Hydrolysis: Bromoethane → Ethanol
Hydroxide attacks the saturated carbon bearing bromine while the C-Br bond breaks. This primary-substrate SN2 route replaces bromide with OH and preserves both carbon atoms; aqueous conditions favour this branch over elimination.
- Elimination: Bromoethane → Ethene
The base removes a hydrogen from the carbon next to bromine. The C-H electrons form the C=C pi bond as bromide departs, so elimination removes H and Br without changing the two-carbon skeleton.
- Acid hydrolysis: Ethyl butyrate → Ethanol
Water attack and proton transfers permit the ethoxy fragment to leave as ethanol. Re-forming the carbonyl produces butanoic acid on the other branch.
References
- Dehydration of alcoholsJim Clark · Chemguide · 2015
Named molecular transformation examples, checked 2026-09-08.
- Dehydration of ethanol to form etheneRoyal Society of Chemistry and Nuffield Foundation · RSC Education
Heated-catalyst dehydration, gas collection and unsaturation tests; emphasises suck-back prevention.