Epoxidation Of Vegetable Oils Catalyzed By Non-metallic Carbonyl Compounds

As a kind of renewable resources, epoxidized vegetable oils are used for crucial environmental-friendly plasticizer nowadays. Comparing to the traditional metallic catalysts for the epoxidation of vegetable oils, the non-metallic carbohydrate derivatives are cheap and easy-preparing, they can catalyze the reaction in a mild condition, and will not cause the transition metals pollution, more in line with the trend of clean and low carbon production. So in this regard, here three non-metallic aldehyde and ketone catalysts for epoxidation of vegetable oils were synthesized and characterized by FT-IR and ¹H NMR.The non-metallic aldehyde and ketone catalysts successfully catalyzed the epoxidation of vegetable oils. The epoxidation reaction can proceed mildly with tert-butyl hydroperoxide as oxidant and CH3CN as co-catalyst, with no carboxylic acid and toxic metals involved. Aldehyde 1 was confirmed to have higher catalytic activity than the others, with the soybean oil conversion of 40.0 % and the epoxide selectivity of 52.7 % within 6 h at 50 oC in neutral condition. The reducing and disappearing process of double bond in soybean oil, and the forming frocess of orirane group in epoxidized soybean oil were verified by FT-IR,TG,¹H NMR.Both the electronic effect and stereohindrance effect tremendously impact on the catalytic properties. Generally, the contribution of substituent to catalytic activity is electron-donating group < H < electron-withdrawing group. It was found that the catalytic activity of carbohydrate derivatives significantly increased when the electron-withdrawing substituent groups were introduced into carbonyl carbon. A mechanism for soybean oil epoxidation was discussed and the possible pathway to form the active intermediate dioxiranes from carbonyl group was verified preliminarily by in-situ UV-vis spectra. Calculations on the catalytic cycle were carried out by Gaussian 03, and the reaction energy barrier of the proposed mechanism path was only 0.0178 a.u., owning a huge competitive advantage rather than the rest two paths. The mixture after reaction was detected by LC-MS, the fragment ions of CH₃CONH₂, which could be just generated accompanying with dioxirane 7 in the system, was found. The LC-MS data offered a strong evidence for the reliability of this mechanism. The results are encouraging and will open a novel clean pathway for the epoxidation of vegetable oils.