Sulfate-modified iron oxide catalyzed epoxidation of styrene with CO2 activated hydrogen peroxide in water†

Abstract

Styrene oxide is a significant organic intermediate with promising applications in fine chemicals, pharmaceuticals and materials. In this study, we have developed a practical sulfate-modified iron oxide catalytic system promoting the epoxidation of styrene using hydrogen peroxide as the oxidant in a solvent-free environment. The sulfate-modified iron oxide has demonstrated significant enhancement of the styrene epoxidation process with the assistance of tetrabutylammonium, resulting in a more than 10-fold increase in the yield of styrene oxide compared to the unmodified one. Mechanistic studies have revealed that hydrogen peroxide is activated by carbon dioxide and the key intermediate singlet oxygen (¹O₂) has been detected by electron paramagnetic resonance. Sulfur, primarily present as chelated bidentate SO₄²⁻, acts synergistically with neighbouring coordinatively unsaturated iron atoms to promote the adsorption of ¹O₂ on the surface and facilitate oxygen atom transfer to styrene.