Anionic iron(III) porphyrin immobilized on silanized kaolinite as catalyst for oxidation reactions

Abstract

Silanized kaolinite was used as a new inorganic support for immobilization of the anionic iron(III) porphyrin [(FeTDFSPP)Cl] 4− . The material (kaolinite-iron(III) porphyrin) was an efficient and selective catalyst for oxidation reactions. Kaolinite (KGa-2, standard poorly crystallized) was reacted with 3-aminopropyltriethoxysilane (3-APTS) (silanization reaction) after intercalation with urea and delamination under ultrasonic treatment. The silane groups were grafted partially on the layered kaolinite outer surface and aqueous treatment could hydrolyze the remaining ethoxy groups. The silanized kaolinite (compound 4 ) was used as a new inorganic support for immobilization of the anionic iron(III) porphyrin: 5,10,15,20-tetrakis(2,6-difluoro-3-sulfonatophenyl) porphyrinato iron(III) chloride [(FeTDFSPP)Cl] 4− (compound 3 ). It was found that compound 4 was an appropriated structure to immobilize the [(FeTDFSPP)Cl] 4− by electrostatic interactions. The obtained material (kaolinite-iron(III) porphyrin, compound 5 ) was characterized by different techniques such as UV-Vis and infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR), proton nuclear magnetic resonance ( 1 H NMR), atomic absorption spectrometry (AAS) and thermal analysis (simultaneous TG/DSC). Compound 5 was investigated in brand oxidation reactions using cyclooctene, heptane and cyclohexane. Iodosylbenzene (PhIO) was used as oxygen atom donor in different molar ratios of iron(III) porphyrin:PhIO. It was observed that compound 5 was an efficient and highly selective catalyst system for epoxidation of cyclooctene (97% of cyclooctene oxide) and hydroxylation of cyclohexane (90% cyclohexanol) after 1 h. The heptane hydroxylation gave 50% of heptanols. The hydrogen peroxide was also used as oxidant but moderate results were obtained. After reuse (3–5 times) the catalyst showed a higher conversion than the primary reactions.