Oxidation of Aromatic Sulfur Compounds Catalyzed by Organic Hexacyanoferrates in Ionic Liquids with a Low Concentration of H₂O₂ as an Oxidant

A series of organic hexacyanoferrates were synthesized and employed as catalysts in ionic liquids (ILs) for catalytic oxidation of dibenzothiophene (DBT), benzothiophene (BT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). High activity was achieved using 1-butyl-3-methylimidazolium hexacyanoferrate ([C 4 mim] 3 Fe(CN) 6 ) as a catalyst and 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4 mim]BF 4 ) as an extractant in the presence of H 2 O 2 under mild conditions. It was interesting to find that the concentration of H 2 O 2 had a significant influence on desulfurization efficiency. The sulfur removal was 76.3% with 30 wt % H 2 O 2 as an oxidant, while it could reach 97.9% with 7.5 wt % H 2 O 2 . Electron spin resonance (ESR) spectroscopy measurements gave the evidence that the active oxygen species O 2 • – was generated in the catalytic oxidative desulfurization process, and gas chromatography–mass spectrometry (GC–MS) analysis indicated that the sulfur compounds were oxidized to the corresponding sulfones. The influence factors, such as reaction temperature, time, concentration, and dosage of H 2 O 2, amount of catalyst, catalytic system recycling, and different sulfur-containing compounds, were investigated. The kinetic investigations showed that oxidation of sulfur compounds presented a pseudo-first-order kinetic. Under the optimal conditions, the catalytic system could be recycled at least 4 times without a remarkable decrease in activity.