A DFT and kinetic study: Is it possible to prepare epoxides without catalysts using the in-situ generated peroxy radicals or peroxides by one-step method?

Abstract

DFT calculations and kinetic analysis have been employed to comprehensively explore the possibility to prepare epoxides by one-step method using the in-situ generated peroxy radicals or hydroperoxides as epoxidizing agents. Computational studies demonstrated that the selectivities for the reaction systems of O₂ /R2/R1, O₂ /CuH/R1, O₂ /CuH/styrene, O₂ /AcH/R1 were 68.2%, 69.6%, 100% and 93.3%, respectively. The in-situ generated peroxide radicals, such as HOO˙, CuOO˙ and AcOO˙, could react with R1 or styrene by attacking the CC double bond to form a CO bond and subsequently undergoing a cleavage of OO bond to yield epoxides. Peroxide radicals could abstract a hydrogen atom from methyl group on R1, forming unwanted by-products. It should be noted that the hydrogen atoms of HOO˙ is easy to be abstracted by CC double bond and simultaneously the oxygen atom is connected to the CH moiety to form an alkyl peroxy radical (Rad11), greatly limiting the selectivity. The comprehensive mechanistic studies provide a deep understanding on preparing epoxides by one-step method.

Keywords: epoxidation; in-situ-generated; olefins; peroxides; peroxy radicals.