Enol ether formation

Acid catalysed

Sn2

Enol ethers are sometimes called activated alkenes because of the oxygen lone pair conjugated to the double bond. This donates electrons to form a new double bonded resonance structure: an oxonium ion. Because of this special property, enol ethers are useful in many organic reactions.

Sn2

A usefull route to preparing enol ethers is to convert an aldehyde into an acetal, then to add a catalytic amount of acid and to remove the excess alcohol (EtOH) by distillation. In the animation methyl groups have been used in place of ethyl groups.

Background Colour:

Sn2

Click the structures and reaction arrows in sequence to view the 3D models and animations respectively

The start of the reaction almost looks like the hydrolysis of an acetal, however, there is no water to continue this process, so a proton is lost instead. In other words there is no suitable nucleophile for SN1 substitution, so E1 elimination takes place to form the enol ether.

 

 

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