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 mechanism for the dehydration of ethanol (CH₃CH₂OH) to ethene (CH₂=CH₂) under acidic conditions involves the following steps:

Step 1: Formation of protonated alcohol (Fast step)

Ethanol (CH₃CH₂OH) reacts with the proton (H⁺) to form the protonated alcohol (ethyl oxonium ion).

CH₃CH₂OH + H⁺ → CH₃CH₂OH⁺

Step 2: Formation of carbocation (Slow step)

The protonated alcohol undergoes the loss of water to form a carbocation, which is the rate-determining step.

CH₃CH₂OH⁺ → CH₃C⁺ + H₂O

Step 3: Formation of ethene by elimination of a proton (Fast step)

The carbocation formed in Step 2 loses a proton to form ethene.

Thus, the overall reaction is:

CH₃C⁺CH₂ → C₂H₄ (Ethene) + H⁺