Epoxidation of cyclohexene and indene with hydrogen peroxide in the presence of WO5 onto hydroxyapatite as catalyst Original Research Article

Epoxidation of cyclohexene and indene with hydrogen peroxide was performed with peroxotungstic species complexed with phosphate groups at the surface of hydroxyapatite. Hydroxyapatite (HAp) was prepared from calcium acetate, diammonium phosphate, and ammonia in water. Tungsten was deposited on HAp using two procedures. In procedure A, HAp was suspended in different volumes of peroxotungstic acid either at room temperature or in an autoclave at 90 or 120 °C. In the later case, the peroxo form was regenerated by heating the catalyst suspension with 30% H2O2 for 6 h at 60 °C. In procedure B, HAp was suspended in a solution of (AliQ+)2W2O11 in dichloromethane. The resulting materials were isolated by filtration, washed with CH2Cl2, and dried overnight under vacuum. Some of the catalysts were lipophilized and buffered by a partial exchange with R4N+ from NBu4Cl. The catalytic materials were characterized by adsorption–desorption isotherms of N2 at −196 °C, FT-IR, XRD, 31P CP/MAS NMR, and XPS. The stability of the catalysts was checked by leaching and recycling tests.