Superoxide Ion as Oxidative Desulfurizing Agent for Aromatic Sulfur Compounds in Ionic Liquid Media

The generation of superoxide (O 2 •– ) in ionic liquids (ILs) has been used to destroy hazardous materials. In this study, O 2 •– was used for the oxidative desulfurization of benzothiophene (BT) and dibenzothiophene (DBT) in two ILs as reaction media. The O 2 •– was released by dissolving potassium superoxide in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPyrr][TFSI] and n -methoxyethyl- n -methylmorpholinium bis(trifluoromethylsulfonyl)imide [MOEMMor][TFSI]. The highest conversion percentages for BT in [MOEMMor][TFSI] and [BMPyrr][TFSI] were 99.4 and 96.6%, respectively, and the highest conversion percentages for DBT in [MOEMMor][TFSI] and [BMPyrr][TFSI] were 98.3 and 94.3%, respectively. As the temperature was increased, the reaction of the O 2 •– with BT and DBT was enhanced significantly. The BT was converted easier than DBT due to the nucleophilic characteristic of the O 2 •– and the higher electron density of the sulfur atom in DBT than that in BT. In addition, the ILs had a clear effect on the oxidative desulfurization reaction, in which the O 2 •– demonstrated a higher conversion percentage in [MOEMMor][TFSI] than in [BMPyrr][TFSI]. This was the result of the stability of the O 2 •– in the ILs that were used in the study. In addition, the σ-potential obtained using the “Conductor-like Screening Model for Real Solvent” (COSMO-RS) indicated that [MOEMMor] + was a superior hydrogen bond donor and had a stronger affinity for the hydrogen bond acceptor than [BMPyrr] + . The reaction mechanism was reported, and no toxic byproducts were detected. This is the first study in which O 2 •– in ILs was used for the conversion of BT and DBT to nonhazardous compounds, and this technique can be used for other hazardous materials.