Question

Write the mechanism of acid catalysed dehydration of ethanol to give ethene.

Answer 1

Mechanism of acid catlaysed dehydration of ethanol:

Step 1: Protonation of ethanol

\[\begin{array}{cc}
\phantom{...............................}\ce{H}\\
\phantom{...............................}|\\
\ce{\underset{(Ethanol)}{CH3 - CH2 - \underset{\bullet\bullet}{\overset{\bullet\bullet}{O}}} - H ->[H - OSO3H] CH3 - CH2 - \underset{⊕}{O} - H + HS\overset{Θ}{O4}}
\end{array}\]

Step 2: Elimination of water molecule

\[\begin{array}{cc}
\ce{H}\phantom{....................}\\
|\phantom{....................}\\
\ce{CH2 - CH2 - O - H -> \underset{(Ethene)}{CH2 = CH2} + H2O + H^+}\\
|\phantom{................................................}\\
\ce{H}\phantom{................................................}
\end{array}\]