18.5 Cyclic Ethers: Epoxides

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Objectives

After completing this section, you should be able to

identify two cyclic ethers which are commonly used as solvents.
write an equation to describe the industrial preparation of ethylene oxide.
list two important industrial uses of ethylene oxide.
write an equation to describe the normal laboratory preparation of an epoxide.
identify the epoxide produced from the reaction of a given alkene with a peroxyacid.
identify the alkene, the reagent, or both, needed to prepare a given epoxide.
write an equation to describe the preparation of an epoxide from an alkene via a halohydrin.
write the mechanism for the reaction of a halohydrin with a base to form an epoxide.

Key Terms

epoxide (oxirane)

Epoxides (also known as oxiranes) are three-membered ring structures in which one of the vertices is an oxygen and the other two are carbons.

The most important and simplest epoxide is ethylene oxide which is prepared on an industrial scale by catalytic oxidation of ethylene by air.

Oxacyclopropane synthesis by peroxycarboxylic acid requires an alkene and a peroxycarboxylic acid as well as an appropriate solvent. The peroxycarboxylic acid has the unique property of having an electropositive oxygen atom on the COOH group. The reaction is initiated by the electrophilic oxygen atom reacting with the nucleophilic carbon-carbon double bond. The mechanism involves a concerted reaction with a four-part, circular transition state. The result is that the originally electropositive oxygen atom ends up in the oxacyclopropane ring and the COOH group becomes COH.

example_rxn (1).png

Epoxides can also be synthesized by the treatment of a halohydrin with a base. This causes an intramolecular Williamson ether synthesis.

Contributors

Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University)
Prof. Steven Farmer (Sonoma State University)
William Reusch, Professor Emeritus (Michigan State U.), Virtual Textbook of Organic Chemistry

John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."