BRAINCAKEMechanism of Dehydration
The acid-catalysed dehydration of an alcohol is an elimination reaction. With concentrated phosphoric or sulfuric acid, the mechanism has three steps.
Step 1: protonation. A lone pair of electrons on the oxygen of the -OH group forms a bond to an H+ ion from the acid. The alcohol becomes a protonated alcohol, with a positive charge on the oxygen.
Step 2: loss of water. The C-O bond breaks heterolytically, with both electrons going to the oxygen. A water molecule leaves, and a carbocation is formed.
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Key terms in this lesson
- carbocation
- A positively charged carbon atom formed as a reactive intermediate when a bond breaks heterolytically.
More in Alcohols
- Ethanol by Hydration of Ethene
- Biofuels and Carbon Neutrality
- Oxidation of Alcohols
- Oxidation of Primary Alcohols to Aldehydes and Carboxylic Acids
- Oxidation of Secondary Alcohols
- Distinguishing Aldehydes and Ketones
- Dehydration of Alcohols
- Reflux and Distillation
All 13 lessons in Alcohols · All AQA AS-level Chemistry topics