Theoretical study on interactions between ionic liquids and organosulfur compounds

Density functional theory has been used to investigate the interactions between dibenzothiophene, diphenylsulfide, diphenyldisulfide, benzene, tetralin and 1-methyl-3-methylimidazolium methyl sulfate ([MMIM][MeSO4]). The GGA/PW91 functional and DNP basis set were employed to optimize geometries. The interactions between [MMIM][MeSO4] and dibenzothiophene, diphenylsulfide, diphenyldisulfide, benzene, tetralin have been explained by NBO and AIM methods. The most stable gas-phase structure of [MMIM][MeSO4] ion pair indicates that hydrogen bonding interactions between oxygen atoms on [MeSO4] anions and the C2-hydrogen on the imidazolium ring play a dominating role in the formation of ion pair. Additional interactions are found between [MeSO4] anion and the hydrogen atoms on the adjacent methyl chains of [MMIM] cation. The [MeSO4] anion tends to be located near ring C2-proton, suggesting that dibenzothiophene, diphenylsulfide, diphenyldisulfide, tetralin, benzene adsorption on [MMIM][MeSO4] did not change the dominant interactions of [MMIM][MeSO4] pair. The π⋯π interactions, π⋯CH interactions and hydrogen bonding interactions occur between [MMIM][MeSO4] and dibenzothiophene, diphenylsulfide, or benzene. The π⋯CH interactions and hydrogen bonding interactions exist between [MMIM][MeSO4] and diphenyldisulfide or tetralin. The order of interaction energies between [MMIM][MeSO4] and molecules is dibenzothiophene > diphenyldisulfide > diphenylsulfide > tetralin > benzene, in agreement with the experimental conclusion.