How Anion Structures 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 {([CnMIM/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.