Discuss the reaction and mechanism of acidic dehydration of ethyl alcohol to prepare ethene.

Explanation

Direct addition of `H_(2)O` to ethene in presence of an acid does not occur . Indirectly , ethene is first passed through conc . `H_(2)SO_(4)` , when ethyl hydrogen sulphate is foemed This on hydroiysis with boiling water gives ethanol .
Mechanism .
`H_(2)SO_(4)hArrH^(+)+OSO_(2)OH`
`underset("Ethene")(CH_(2)=CH_(2)+H^(+))tounderset("Ethylcarbocation")(CH_(3)-overset(+)(C)H_(2))underset("Fast")overset(""^(-)OSO_(2)OH)tounderset("Ethylhydrogen sulphate")(CH_(3)-CH_(2)-OSO_(2)OH)`
Ethyl hydrogen sulphate when boiled with water undergoes hydrolysis to form ethanol .