How anion structure can affect the thiophene distribution between imidazolium-based ionic liquid and hydrocarbon phases? A theoretical QSPR study

In this study, the effects of different anion structures have been investigated on the thiophene distribution between ionic liquid (IL) and hydrocarbon phases in the ternary systems using quantitative structure–property relationship. The role of anion structures was investigated in the presence of different cations and hydrocarbons. In this regard, three different datasets were selected from the literature containing {([C_nMIM/anion]–thiophene–different hydrocarbon solvents): n = 2, 4, and 8} with 445 data points. It was found that the “E1v” descriptor of anions, belonging to the WHIM descriptor category, can take into account the effect of anion structures on the thiophene distribution for the systems containing the IL with the [C₂MIM] cation and different hydrocarbons. It was found that increasing the E1v values of anion structures leads to a decrease in the thiophene distribution coefficients. E1v reflects the unfilled space of the anion structure, which in turn affects the interactions of the anion and cation in the IL structure. More unfilled spaces of the anion structure lead to more powerful interaction with the cation, which in turn limit the cation interaction with thiophene and decrease the thiophene distribution coefficient. It was also found that the effect of the anion on the thiophene distribution is decreased by increasing the length of alkyl chains in the cation from [C₂MIM] to [C₄MIM] and [C₈MIM]. This finding can be attributed to the higher free volumes of [C₄MIM] and [C₈MIM] cations in comparison with that of [C₂MIM], which allows more efficient packing of thiophene in the IL structure.