Catalytic epoxidation of fatty acid methyl esters by modified metalloporphyrins with variable metals and electron-donating substituents

The catalytic efficiency of modified tetraphenylporphyrins with various metals (Mn, Fe, Co, Ni and Zn) and different electron-donating substituents (OCH₃, OH, N(CH₃)₂, SO₃Na) at the phenyl para-positions using hydrogen peroxide (H₂O₂, 30 wt%) as the oxidant has been researched in the epoxidation of unsaturated fatty acid methyl esters (FAMEs) under mild conditions. In the present system, the co-catalyst effect of inorganic salts had a crucial role in enhancing catalytic performance. According to the yields, the catalytic activities of metalloporphyrins were in the following order: Mn(TPP)Cl ≈ Fe(TPP)Cl > CoTPP > NiTPP > ZnTPP, and Mn (TPP)Cl > Mn(TMOPP)Cl ≈ Mn(THPP)Cl ≈ Mn(TDMPP)Cl > Mn(TPPS₄)Cl. Moreover, metalloporprhyrins after modification by electron-donating substituents displayed promoted thermolysis temperatures. Remarkably, the formation of intermediate porMn^V=O has also been indicated, which was verified by both a kinetic study of FAMEs epoxidation and UV-Vis spectroscopy.