Highly active and green aminopropyl-immobilized phosphotungstic acid on mesocellular silica foam for the O-heterocyclization of cycloocta-1,5-diene with aqueous H2O2

Abstract

The heteropoly phosphotungstic acid, H₃PW₁₂O₄₀ (HPW), was successfully immobilized on the surface of MCF, SBA-15 and MCM-41 by means of chemical bonding to aminosilane groups. The as-obtained materials were characterized by N₂ sorption, TEM, XRD, FT-IR, ¹³C-, ²⁹Si-, ³¹P-MAS NMR and XPS. Characterization results suggest that the surface area decreased after grafting amino groups to silica. The as-prepared HPW-NH₂-MCF is highly efficient in the O-heterocyclization of cycloocta-1,5-diene (COD) to 2,6-dihydroxy-9-oxabicyclo[3.3.1] nonane (1) and 2-hydroxy-9-oxabicyclo [3.3.1] nonane-6-one (2) with a COD conversion of 100% and (1 + 2) selectivity up to 98%. It is worth mentioning that this material could be reused six times without any significant loss of activity and selectivity. The good stability can be attributed to the strong interaction between the amino groups on the surface of MCF and HPW anions.