The ability of ionic liquids to form hydrogen bonds with organic solutes evaluated by different experimental techniques. Part II. Alkyl substituted pyrrolidinium- and imidazolium-based ionic liquids

Abstract

© 2020 Elsevier B.V. This work is devoted to the study of hydrogen bond formation ability of ionic liquids. The proton donor abilities of pyrrolidinium-based ionic liquids with common anion bis(trifluoromethylsulfonyl)imide ([NTf2]) and a range of cations, i.e. 1-Methyl-1-ethylpyrrolidinium [MEPyr][NTf2], 1-Methyl-1-propylpyrrolidinium [MPrPyr][NTf2], 1-Methyl-1-butylpyrrolidinium [MBPyr][NTf2], 1-Methyl-1-octylpyrrolidinium [MOPyr][NTf2] were studied by FTIR spectroscopy. The proton acceptor abilities of several ionic liquids (1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [BMIM][NTf2], 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4], 1-butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM][TfO], 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], triethylsulfonium bis(trifluoromethylsulfonyl)imide [Et3S][NTf2], 1-butyl-3-methylimidazolium tricyanomethanide [BMIM][TCM], 1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM][BF4]) were studied by both FTIR and solution calorimetry techniques. The hydrogen bond enthalpies of pyrrole in various ionic liquids were calculated. A linear correlation between frequency shifts of H-bonded NH-group of pyrrole in ionic liquids and hydrogen bond enthalpies of pyrrole in the same ionic liquids was found. The obtained correlation for ionic liquids was compared with molecular organic solvents.