Laboratory preparation of ethene

By dehydration of ethanol: heat ethanol with concentrated sulphuric acid at about 180 °C:

C₂H₅OH —(conc. H₂SO₄, 180 °C)→ CH₂=CH₂ + H₂O

It occurs in two steps:

1. CH₃CH₂OH + HOSO₃H → CH₃CH₂–OSO₃H (ethyl hydrogen sulphate) + H₂O
2. CH₃CH₂–OSO₃H (heat) → CH₂=CH₂ + H₂SO₄ (the acid is regenerated, so it acts as a catalyst/dehydrating agent)

Apparatus: flask with ethanol/acid mixture (sand or pumice stones added to prevent bumping) → delivery tube → wash bottle with NaOH solution (removes SO₂ and CO₂ formed in side reactions) → collect ethene over water. If the temperature is only 140 °C the product is diethyl ether instead (see alcohols).