Alcohols, Ethers, and Thiols - What Are Epoxides?

6 important questions on Alcohols, Ethers, and Thiols - What Are Epoxides?

How are epoxides synthesized?

On an industrial scale ethylene and oxygen are passed over a silver catalyst.
On lab scale most commonly used is peroxyacetic acid.

What stereoisomers are formed in epoxidation reactions?

The epoxidation reaction is stereoselective. Groups that are cis in the alkene will be cis in the epoxide.

Ethers normally don't react in the presence of an acid-catalyst, why do epoxides do?

The normal bond angle of a sp3 hybridized atom is 109.5o in epoxides the bond angle of the three-membered ring is 60o. Therefor epoxides undergo ring opening reactions with a variety of nucleophiles.

What product does the acid-catalyzed hydrolysis of epoxycycloalkane yield?

A trans-1,2-cycloalkanediol.

What are the steps in the SN2 mechanism of acid-catalyzed epoxide ring opening reactions?

1. addition of a proton to the oxygen
2. Reaction on an electrophile and a nucleophile (water) and the breaking of one of the C-O bonds.
3. Removal of a proton.

What are the three most important nucleophilic ring-opening reactions?

1. The addition of ammonia
2. The acid-catalyzed hydration
3. The reaction with a thiol salt.

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