Mechanism of Propylene Epoxidation via O₂ with Co‐Oxidation of Aldehydes by Metalloporphyrins

Abstract

Propylene epoxidation by O2 plus acrolein in the presence of metalloporphyrins were investigated. According to the difference in initiation time and the reaction rate, a hypothesis metalloporphyrins or its center ion played a principal role in the initiation of reaction (redox reaction) rather than in the catalysis of PO generation reaction have been proposed, which was verified by the cyclic voltammogram of metalloporphyrins and UV/Vis spectra of samples in the time course study. Furthermore, the propylene epoxidation experiments using aldehydes easier to be initiated and corresponding blank control without metalloporphyrins were also investigated, and the results showed the same conclusion. On the other hand, the mechanism that the active species are peroxyacyl radical and peroxy acid was proposed through density function theory calculations, and in peroxyacyl radical path the intermediate generation process was the free radical addition of propylene by peroxyacyl radical. Moreover, optimum reaction paths were also carried out by computational calculations, the results showed that peroxyacyl radical was with higher activity than peroxy acid. As for peroxyacyl radical, the main addition site was the C1 of propylene, which was proved by the condensed Fukui function.

Continuous Flow Synthesis of Crotonic Acid from Crotonaldehyde

“…① Epoxidation reactions: the epoxidation reaction was easily triggered by the attack of peroxy radical on the double bond. There were several reports about the mechanism of double bond epoxidation. − In the beginning, the peroxycrotonate radical reacted with crotonaldehyde to form the epoxide 3-methyl epoxide-2-aldehyde ( 11 ) and further formed 3-methyl epoxide-2-carboxylic acid ( 12 ). Crotonic acid could also react with O 2 to form compound 12 .…”

Biomimetic Aerobic Epoxidation of Alkenes Catalyzed by Cobalt Porphyrin under Ambient Conditions in the Presence of Sunflower Seeds Oil as a Co-Substrate

“…Some successful biomimetic studies have been attempted to activate O 2 through in situ transformation to hydroperoxides in the presence of specific co-substrates, such as cumene and ethylbenzene. − However, current methods still require improvements in terms of high temperature, high pressure, and additional free-radical initiators. Aldehydes have successfully been used for epoxidation of alkenes through intermediates active oxygen species (peroxyacid or acylperoxy radical) under mild conditions (Mukaiyama mechanism). − However, the rapid exothermic reactions and high cost dramatically limited their further industrial applications …”