Catalytic oxygenation of dibenzothiophenes to sulfones based on FeIII porphyrin complex

Fe-III 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 Fe-III 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 Fe-III porphyrin complex was decomposed partly during the oxygenation, which was retarded by adding carbazole (CAR) to the reaction medium. Fe-III 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 Fe-III 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. (C) 2011 Elsevier B.V. All rights reserved.