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Preparation of Epoxides

Preparation of Epoxides

Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...

Autoxidation of Ethers to Peroxides and Hydroperoxides

Autoxidation of Ethers to Peroxides and Hydroperoxides

Ethers represent a class of chemical compounds that become more dangerous with prolonged storage because they tend to form explosive peroxides when standing in the air. Autoxidation is the spontaneous oxidation of a compound in air. In the presence of oxygen, ethers slowly oxidize to form hydroperoxides and dialkyl peroxides.

Acid-Catalyzed Ring-Opening of Epoxides

Acid-Catalyzed Ring-Opening of Epoxides

Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...

Regioselective Formation of Enolates

Regioselective Formation of Enolates

As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are more stable. But the energy required to form kinetic enolates is less.

Base-Catalyzed Ring-Opening of Epoxides

Base-Catalyzed Ring-Opening of Epoxides

Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...

Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

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Related Experiment Video

Updated: Jan 4, 2026

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Published on: November 3, 2016

Thermalized Epoxide Formation in the Atmosphere.

Kristian H Møller¹, Theo Kurtén², Kelvin H Bates³

¹Department of Chemistry , University of Copenhagen , Universitetsparken 5 , DK-2100 Copenhagen Ø , Denmark.

The Journal of Physical Chemistry. A

|November 13, 2019

Summary

Atmospheric epoxide formation from hydroperoxy alkyl radicals is enhanced by hydrogen bonding. This mechanism is significant for biogenic hydrocarbon oxidation and peroxide decomposition, producing abundant isoprene oxidation products.

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Area of Science:

Atmospheric Chemistry
Organic Chemistry
Computational Chemistry

Background:

Epoxide formation from β-hydroperoxy alkyl radicals was previously thought to require excess energy.
The thermal reaction rate was considered too slow to compete with O2 addition.

Purpose of the Study:

To computationally investigate how substituents affect the epoxide formation rate coefficient of substituted β-hydroperoxy alkyl radicals.
To explore the conditions under which thermal epoxide formation becomes competitive with O2 addition.

Main Methods:

Computational investigation of substituted β-hydroperoxy alkyl radicals.
Analysis of reaction rate coefficients and substituent effects.

Main Results:

Thermal epoxide formation is competitive with O2 addition when the alkyl radical carbon has a hydroxyl (OH) group capable of hydrogen bonding.
This hydrogen bonding stabilizes the epoxide ring formation.
β-OOR alkyl radicals exhibit similar reactivity to β-OOH alkyl radicals, suggesting epoxide formation is a key pathway in ROOR peroxide oxidation.

Conclusions:

Substituent effects, particularly hydrogen bonding, significantly enhance thermal epoxide formation rates.
This pathway is relevant for the atmospheric oxidation of biogenic hydrocarbons and the decomposition of peroxides.
GEOS-Chem modeling indicates substantial production of isoprene dihydroxy hydroperoxy epoxide.