Chemistry · Interactive
Dehydration of Alcohols
Alcohol dehydration removes water from an alcohol to form an alkene. In this interactive example, ethanol becomes ethene and water: CH3CH2OH → CH2=CH2 + H2O. Drag the slider to watch the C-O and beta C-H bonds break, the C=C bond form, and every atom stay accounted for.
Drag the slider to follow ethanol dehydration into ethene and water. Open fullscreen ↗
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What is alcohol dehydration?
Alcohol dehydration is an elimination reaction in which an alcohol loses the elements of water and forms an alkene. In the ethanol example, concentrated sulfuric acid and heat convert CH3CH2OH into ethene and water. The acid activates the hydroxyl group so it can leave as water, while a neighboring hydrogen is removed to form the carbon-carbon double bond.
The ethanol dehydration equation
The overall equation is CH3CH2OH -> CH2=CH2 + H2O, usually written with concentrated H2SO4 and heat over the arrow. The same two carbon atoms remain connected, one hydrogen from the beta carbon joins the hydroxyl group to make water, and the C-C single bond becomes a C=C double bond in ethene.
Which bonds break and form?
In this simplified molecular animation, the C-O bond and one beta C-H bond break during elimination. A new O-H bond forms as water leaves, and the carbon-carbon bond gains pi-bond character to become the double bond of ethene. The animation keeps the same atoms throughout so the rearrangement is easy to track.
Why acid and heat are needed
The hydroxyl group in an alcohol is a poor leaving group on its own. Acid protonates the oxygen, turning it into water, which is a much better leaving group. Heating supplies the activation energy and favors elimination, so dehydration can proceed to the alkene product.
Alcohol dehydration steps
- Heat ethanol with concentrated acid so the hydroxyl group can be activated.
- Break the C-O bond and remove a beta hydrogen from the adjacent carbon.
- Form the C=C double bond of ethene while the removed hydrogen and hydroxyl group leave as water.
FAQ
What is formed when an alcohol is dehydrated?
An alkene and water are formed. For ethanol, dehydration gives ethene and water: CH3CH2OH -> CH2=CH2 + H2O.
What reagent is commonly used for dehydration of alcohols?
Concentrated sulfuric acid with heat is commonly used in school-level examples. Phosphoric acid or alumina can also be used depending on the reaction conditions.
Why does dehydration of ethanol make ethene?
Ethanol has two adjacent carbon atoms. When the hydroxyl group leaves from one carbon and a beta hydrogen is removed from the neighboring carbon, those two carbons form a double bond, giving ethene.
Is alcohol dehydration addition or elimination?
It is an elimination reaction. A small molecule, water, is removed from the alcohol, and a double bond forms in the organic product.
How do I use this alcohol dehydration animation?
Drag the reaction-progress slider to move from ethanol through the transition state to ethene and water. The 3D view highlights the bonds that break and form, the energy curve shows the activation barrier, and the atom counter confirms conservation of 2 C, 6 H, and 1 O.
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