Generation of Superoxide Ion in Pyridinium, Morpholinium, Ammonium, and Sulfonium-Based Ionic Liquids and the Application in the Destruction of Toxic Chlorinated Phenols

Generation of superoxide ion (O₂^•–) was carried out in four ionic liquids (ILs) having the same anion, bis­(trifluoromethylsulfonyl)­imide [N­(Tf)₂]⁻, and different cations, N-hexylpyridinium [HPy]⁺, N-methoxyethyl-N-methylmorpholinium [MO1,1O2]⁺, N-ethyl-N,N-dimethyl-2-methoxyethylammonium [N112,1O2]⁺, and triethylsulfonium [S222]⁺. Cyclic voltammetry (CV) and chronoamperometry (CA) electrochemical techniques were used in this investigation. It was found that O₂^•– is not stable in the [HPy]⁺-based IL. On the other hand, CV showed that the electrochemically generated O₂^•– is stable in [MO1,1O2]⁺-, [N112,1O2]⁺-, and [S222]⁺-based ILs for the time duration of the experiment. The long-term stability of the generated O₂^•– was then investigated by dissolving potassium superoxide (KO₂) in dimethyl sulfoxide (DMSO) in the presence of the corresponding IL. It was found that ILs containing [MO1,1O2]⁺ and [N112,1O2]⁺ offer a promising long-term stability of O₂^•– for various reactions to be used for several applications. However, it was found that after 2 h, about 92.5% of the generated O₂^•– in [S222]⁺ based IL was consumed. The diffusion coefficient and solubility of O₂ in the studied ILs were then determined using CV and CA techniques simultaneously. It was found that diffusion coefficients and CA steady-state currents increase with temperature increases, while the solubility of O₂ decreased. To our best knowledge, this is the first time that morpholinium and sulfoniumbased ILs were utilized as media for chemical and electrochemical generation of O₂^•–. Additionally, the chemically generated O₂^•–, by dissolving KO₂, was then used for the destruction of 2,4-dichlorophenol (DCP) in [MO1,1O2]­[N­(Tf)₂] under ambient conditions. The destruction percentage was higher than 98%. This work represents a novel application of the chemically generated O₂^•– for the destruction of toxic chlorinated phenols in ILs media

Stability of Superoxide Ion in Phosphonium-Based Ionic Liquids

In this work the chemical generation of superoxide ion and determination of its stability in five phosphonium-based ionic liquids has been carried out. The stability of the generated superoxide ion depended on the anion. For the trihexyl­(tetradecyl)­phosphonium cation, the bis­(2,4,4-trimethylpentyl)­phosphinate anion (IL 104) has shown a relatively good stability with a rate constant of 3.34 × 10^–5 s^–1 for the reaction of the superoxide ion. Triisobutyl­(methyl)­phosphonium tosylate has also shown moderate stability (6.8 × 10^–5 s^–1). The order of stability, bis­(2,4,4-trimethylpentyl)­phosphinate > dicyanamide (6.97 × 10^–5 s^–1) > Br^– (7.72 × 10^–5 s^–1) > Cl^– (12.7 × 10^–5 s^–1), correlates well with the order of their respective ionic volumes. On application of the generated superoxide ion for the oxidation of two organic sulfur compounds, 15% conversion of thiophene was attained in 2 h while dibenzothiophene (DBT) was found to be unreactive to the ion in IL 104. This was attributed to higher electron density on the sulfur atom in DBT relative to thiophene and high nucleophilicity of the superoxide ion. Furthermore, the type of IL appears to slightly affect the conversion. The conversion of thiophene obtained was in the following order: IL 104 (15%) > [HMPyrr]­[TFSI] (8%) > [BMPyrr]­[TFSI] (7%) with the apparent differences in the magnitude of the alkyl chain length

Solubility of Thiophene and Dibenzothiophene in Anhydrous FeCl₃- and ZnCl₂‑Based Deep Eutectic Solvents

The solubilities of some common refractory-sulfur-containing compounds, namely thiophene and dibenzothiophene, were studied and measured in anhydrous FeCl₃- and ZnCl₂-based deep eutectic solvents (DES) at different temperatures under atmospheric pressure. The aim of this study is to explore the behavior of DESs toward solvation of sulfur-containing compounds so as to set a pace for the successful application of DESs into deep desulfurization of liquid fuels. The studied DESs were screened and prepared by the combination of anhydrous FeCl₃ and ZnCl₂ with different salts and hydrogen bond donors. High pressure liquid chromatography (HPLC) was employed for the quantitative measurements of solubilities of both thiophene and dibenzothiophene. It was found that FeCl₃ based DESs exhibited higher solubilities (from 17 wt % to above 90 wt %) for dibenzothiophene as compared to the ZnCl₂ based DESs (0.084–1.389 wt %). Moreover, FeCl₃ based DESs exhibited complete miscibility with thiophene while ZnCl₂ based DESs showed solubility values in the range of 1–10 wt % for thiophene. The experimental results obtained were further successfully modeled using the nonrandom two liquid (NRTL) model

Removal of Thiophene from Mixtures with <i>n</i>‑Heptane by Selective Extraction Using Deep Eutectic Solvents

This work investigates the use of deep eutectic solvents (DESs) to extract sulfur-based compounds from <i>n</i>-heptane as model diesel compounds. Four DESs were prepared by combining tetrabutylammonium bromide or methyltriphenylphosphonium bromide with ethylene glycol, triethylene glycol, or sulfolane. All DESs showed good ability to extract thiophene with the best extraction efficiency (35%) being observed for the sulfolane-based DES. The extraction efficiency can be further enhanced to reach 98% when five extraction cycles are performed. Moreover, the DESs were easily regenerated using rotary evaporation. In addition,¹H NMR analysis is used to elucidate the extraction mechanism. Finally, the COSMO-RS model was used to predict the ternary tie lines for the studied systems and the NRTL model allowed, correlating the experimental data with an average root-mean-square deviation of <2% for all DESs. These models can be utilized for further simulation analysis of the extraction process