epoxidationer

Epoxidation is a chemical transformation that converts alkenes into epoxides (oxiranes) by adding one atom of oxygen across the carbon–carbon double bond to form a strained three-membered ring. The reaction is often stereospecific and proceeds by a concerted, syn addition. When peroxide or peracid oxidants are used, the process is commonly referred to as a Prilezhaev epoxidation.

Common methods for epoxidation include the use of peracids such as meta-chloroperbenzoic acid (mCPBA) or peracetic acid, which transfer an electrophilic oxygen to the double bond. Hydrogen peroxide or organic hydroperoxides can also be employed, often with catalysts, to generate the active oxidizing species. These general approaches are used for a wide range of substrates, though unactivated alkenes can be challenging without specialized catalysts.

Catalytic asymmetric epoxidations expand the utility of epoxidation for enantioenriched products. Sharpless epoxidation, for allylic alcohols, uses titanium isopropoxide, diethyl tartrate, and tert-butyl hydroperoxide to give enantioenriched epoxides. Jacobsen–Katsuki epoxidation, based on Mn-salen catalysts, enables enantioselective epoxidation of many unactivated alkenes with peroxide oxidants. The Shi epoxidation employs a chiral fructose-derived ketone catalyst with Oxone or similar oxidants to achieve enantioselective epoxidation of electron-rich alkenes.

Industrial relevance includes the production of ethylene oxide and propylene oxide, key intermediates for polymers, solvents, and downstream chemicals. Epoxides are versatile intermediates that readily undergo ring-opening with nucleophiles to furnish alcohols, diols, amines, and other functional groups, making them central to pharmaceutical and materials synthesis.

Safety considerations are important, as epoxides and many oxidants are reactive and hazardous. Reactions require careful control of temperature and oxidant handling to prevent runaway reactions.