epoxidant

An epoxidant, or epoxidizing agent, is a chemical reagent that converts alkenes into epoxides (oxiranes) by transferring one oxygen atom across the carbon–carbon double bond. The transformation, known as epoxidation, is a fundamental reaction in organic synthesis and is typically stereospecific, preserving the relative geometry of the double bond.

Common epoxidants include peracids such as meta-chloroperbenzoic acid (m-CPBA) and peracetic acid. Hydrogen peroxide can serve as an epoxidant under catalytic conditions, notably with titanium-based catalysts (such as TS-1) or with chiral catalysts for asymmetric epoxidation (for example, tartrate-based systems in Sharpless epoxidation). Other reagents include urea–hydrogen peroxide and Oxone-based systems, as well as specialized reagents like dimethyl dioxirane.

Mechanistically, epoxidation proceeds via concerted transfer of electrophilic oxygen. It is usually stereospecific, with cis alkenes giving cis-epoxides and trans alkenes giving trans-epoxides. Regioselectivity is influenced by substitution and electronic effects; asymmetric epoxidation is possible with chiral catalysts to furnish enantioenriched epoxides.

Applications include production of epoxides for further transformations, epoxy resins for coatings and polymers, and numerous intermediates in pharmaceutical and agrochemical synthesis. Epoxide rings are reactive toward nucleophiles, allowing ring opening to vicinal diols, halohydrins, or alcohols under mild conditions.

Safety considerations: many epoxidants are strong oxidizers and reactive; peracids can be shock-sensitive; epoxides themselves can be irritants or harmful; appropriate storage, handling, and waste disposal are required, with attention to incompatibilities with bases, acids, or reductants.