The removal of water or the
components of water, in the appropriate proportion, from a substance or
system or chemical compound is termed dehydration. Water's components can be
extracted from a single molecule or multiple molecules, as exemplified in the
dehydration of alcohol, where ethylene may be produced by the loss of water
elements from one molecule or ethyl ether by the loss of water elements from
two molecules:
CH3CH2OH → CH2=CH2 + H2O
2CH3CH2OH → CH3CH2OCH2CH3 + H2O
The latter reaction finds common
application in the production of ethers through the acidic dehydration of
alcohols. The traditional manufacturing process for ether involves the
dehydration of alcohol (denatured with ether) by sulfuric acid. The
anesthetic ether undergoes a special purification and packaging process.
Additionally, ether is obtained as a byproduct from the production of alcohol
from ethylene.
On an industrial scale, diethyl
ether and various other commercially available ethers are synthesized through the
acid-catalyzed dehydration of primary alcohols. For instance,
intermolecular dehydration of ethanol yields diethyl ether.
In Step 1, a proton is added:
A proton transfer from the acid
catalyst to the hydroxyl group results in an oxonium ion, which transforms –OH,
a less effective leaving group, into –OH2+, a more
efficient leaving group.
Step 2 involves:
Establishing a new bond between a
nucleophile and an electrophile while simultaneously breaking a bond to form
stable molecules or ions. Nucleophilic displacement of H2O by the OH
group of a second alcohol molecule leads to the formation of a new oxonium ion.
Step 3 entails taking a proton
away:
Proton transfer from the new
oxonium ion to H2O completes the reaction. It is noteworthy that the
acid serves as a catalyst in this reaction; one proton is utilized in Step 1,
but another is generated in Step 3.
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