Question

Write the mechanism of the following reaction: \[ \text{CH}_3\text{CH}_2\text{OH} \xrightarrow{H^+ \, 443\, \text{K}} \text{CH}_2 = \text{CH}_2 \]

Answer 1

The acidic dehydration of ethanol (CH₃CH₂OH) to ethene (CH₂=CH₂) proceeds via the following stages:

Step 1: Protonation of Ethanol (Rapid)

Ethanol (CH₃CH₂OH) accepts a proton (H⁺) to yield the ethyl oxonium ion.

CH₃CH₂OH + H⁺ → CH₃CH₂OH⁺

Step 2: Carbocation Formation (Rate-Determining)

The ethyl oxonium ion loses a molecule of water, forming a carbocation in the slowest step.

CH₃CH₂OH⁺ → CH₃C⁺ + H₂O

Step 3: Ethene Formation via Deprotonation (Rapid)

The carbocation formed eliminates a proton to produce ethene.

Overall Reaction:

CH₃C⁺CH₂ → C₂H₄ (Ethene) + H⁺