Catalytic oxygenation of dibenzothiophenes to sulfones based on FeIII porphyrin complex

FeIII porphyrin complexes as biomimetic catalysts display remarkable activity in the oxidation of dibenzothiophenes (DBTs) to the corresponding sulfones, in the absence of co-reductants or sacrificial agents, for deep desulfurization. The influence of the reaction conditions on the catalytic oxygenation was investigated. UV–vis spectra of FeIII porphyrin complexes under various reaction conditions revealed that temperature was a vital factor for the catalyst's lifetime. However, catalyst decomposition was not caused by thermal self-destruction but by oxygenation at high temperatures. The FeIII porphyrin complex was decomposed partly during the oxygenation, which was retarded by adding carbazole (CAR) to the reaction medium. FeIII porphyrins, substituted with electron-withdrawing groups (–Cl), showed higher efficiency than electron-donating groups (–OH). Radical scavenging experiments demonstrated that the oxygenation catalyzed by the FeIII porphyrin complex was not a free-radical reaction. Based upon the DBTs’ concentrations, obtained by gas chromatography, the catalytic oxygenation can be treated kinetically as a first-order reaction. Finally, a mechanism involving a two-step nucleophilic addition was proposed for the oxygenation.

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► FeIII porphyrins are particularly active in the oxygenation of dibenzothiophenes.
► These aerobic catalytic oxidations occur in non-polar hydrocarbons.
► The parameters influencing the stability of the porphyrin catalyst were studied.
► A mechanism involving a two-step process has been proposed.