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

The generation of superoxide (O-2(center dot-)) in ionic liquids (ILs) has been used to destroy hazardous materials. In this study, O-2(center dot-). was used for the oxidative desulfurization of benzothiophene (BT) and dibenzothiophene (DBT) in two ILs as reaction media. The O-2(center dot-) 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][TESI] 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(center dot-) with BT and DBT was enhanced significantly. The BT was converted easier than DBT due to the nucleophilic characteristic of the O-2(center dot-) and the higher electron density of the sulfur atom in DBT than that in BT. In addition, the Its had a clear effect on the oxidative desulfurization reaction, in which the O(2)(center dot-)demonstrated a higher conversion percentage in [MOEMMor] [TFSI] than in [BMPyrr] [TFSI]. This was the result of the stability of the O-2(center dot-) in the Its that were used in the study. In addition, the a-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(center dot-) in ILs was used for the conversion of BT and DBT to nonhazardous compounds, and this technique can be used for other hazardous materials.