Br^-/BrO^--mediated highly efficient photoelectrochemical epoxidation of alkenes on -Fe₂O₃

Epoxides are significant intermediates for the manufacture of pharmaceuticals and epoxy resins. In this study, we develop a Br-/BrO- mediated photoelectrochemical epoxidation system on alpha-Fe2O3. High selectivity (up to >99%) and faradaic efficiency (up to 82 +/- 4%) for the epoxidation of a wide range of alkenes are achieved, with water as oxygen source, which are far beyond the most reported electrochemical and photoelectrochemical epoxidation performances. Further, we can verify that the epoxidation reaction is mediated by Br-/BrO- route, in which Br- is oxidized non-radically to BrO- by an oxygen atom transfer pathway on alpha-Fe2O3, and the formed BrO- in turn transfers its oxygen atom to the alkenes. The non-radical mediated characteristic and the favorable thermodynamics of the oxygen atom transfer process make the epoxidation reactions very efficient. We believe that this photoelectrochemical Br-/BrO--mediated epoxidation provides a promising strategy for value-added production of epoxides and hydrogen. Alkene epoxidation, whose products are important intermediates for the manufacture of pharmaceuticals and epoxy resins, has attracted extensive attention. Unlike the conventional electrochemical Br-/Br-2-mediated epoxidation, here the authors report a photoelectrochemical Br-/BrO-- mediated system to achieve efficient epoxidation performance on alpha-Fe2O3.