Dehydrohalogenation is an organic reaction from which an alkene is obtained from an alkyl halide [1]. It is also called a β-Elimination reaction and is a type of elimination reaction. Ethanolic potassium hydroxide when reacted with alkyl halide gives alkene.
In this reaction, the halogen on the carbon in the alkyl halide reacts with hydrogen present on the β-carbon releasing hydrogen chloride. Hence an alkene is formed due to formation of a double bond between the α- and β-carbon.
Contents |
Reactions
Here ethyl chloride reacts with potassium hydroxide dissolved in ethanol, giving ethene. Similarly 1-chloropropane and 2-chloropropane give propene.
Chlorobenzene does not react with potassium hydroxide due to the presence of the benzene ring which due to stabilization as a result of aromaticity does not give conventional elimination, as it would lead to a very unstable benzyne intermediate.
Promoting elimination
In general, the above reaction of haloalkane with potassium hydroxide would compete with an Sn2 nucleophilic substitution reaction (minor product) because OH- is a strong, sterically unhindered nucleophile. Perhaps a better reagent would be a deprotonated alcohol such as potassium tert-butoxide ([CH3]3CO- K+) or because it is an oxide anion and thus a strong base and nucleophile, potassium ethoxide (CH3CH2O- K+) and because of steric hindrance therefore promoting an elimination mechanism instead of a substitution mechanism.
See also
External links
References
- ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
