Highly Selective Epoxidation of Olefinic Compounds over TS-1 and TS-2 Redox Molecular Sieves Using Anhydrous Urea–Hydrogen Peroxide as Oxidizing Agent

Highly selective epoxidation of different olefinic compounds was carried out using urea–hydrogen peroxide adduct (UHP) as the oxidizing agent in the presence of TS-1 and TS-2 as redox catalysts. A considerable increase in the epoxide selectivity was observed for different unsaturated compounds, such as allylic (allyl alcohol, allyl chloride, allyl bromide, and methylallyl chloride), open-chain, and cyclic (1-hexene and cyclohexene) and aromatic (styrene and allylbenzene) olefinic compounds, when UHP and U+HP (urea and aqueous H2O2 added separately for the in situ formation of UHP) were used as oxidants instead of aqueous H2O2. The controlled release of anhydrous H2O2 from UHP is the main reason for enhanced epoxide selectivity. Direct spectroscopic evidences for the formation of different Ti-superoxo complexes by the solid–solid interaction between TS-1/TS-2 and urea–hydrogen peroxide adduct were obtained from the characteristic continuous absorption band in the UV–vis region (300–500 nm) and the anisotropic EPR spectra for the superoxide radical attached to Ti(IV) centers on TS-1 and TS-2.