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

The generation of superoxide (O2•–) in ionic liquids (ILs) has been used to destroy hazardous materials. In this study, O2•– was used for the oxidative desulfurization of benzothiophene (BT) and dibenzothiophene (DBT) in two ILs as reaction media. The O2•– 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 O2•– with BT and DBT was enhanced significantly. The BT was converted easier than DBT due to the nucleophilic characteristic of the O2•– and the higher electron density of the sulfur atom in DBT than that in BT. In addition, the ILs had a clear effect o...