BRAINCAKEReaction with Alkali
Halogenoalkanes react with hydroxide ions from sodium hydroxide or potassium hydroxide, but the product depends on the solvent. Two reactions compete.
Aqueous alkali: substitution
Warmed under reflux with KOH(aq), the OH− acts as a nucleophile and replaces the halogen, giving an alcohol. (Details in the next lesson.)
Ethanolic alkali: elimination
Heated under reflux with KOH dissolved in ethanol, the OH− acts as a base. It removes an H+ from a carbon next to the C-X carbon, and the halide ion leaves. A C=C double bond forms, so the product is an alkene. A molecule of HX is eliminated overall:
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More in Halogenoalkanes
- Classifying Halogenoalkanes
- Reactivity of Halogenoalkanes
- Hydrolysis Reactions
- Comparing the Rates of Hydrolysis
- Nucleophilic Substitution
- Reaction with Aqueous Alkali
- Reaction with Ammonia
- Reaction with KCN
All 11 lessons in Halogenoalkanes · All Edexcel AS-level Chemistry topics