Effect of cation structure on the formation of hydrogen bond between ionic liquids and solute molecules

Abstract

In this work, we have studied the thermochemistry of the hydrogen bond formation between ionic liquids and solute molecules. The solution enthalpies of several organic compounds (benzene, acetone, 3-picoline dimethylsulfoxide, formamide, N-methylformamide, acetamide, N-methylacetamide) in the series of ionic liquids with common anion bis(trifluoromethanesulfonyl)imide and different cations (1-butyl-3-methylimidazolium [BMIM][NTf2], 1-butyl-1-methylpyrrolidinium [BMPYR][NTf2], 1-butylpyridinium [BPY][NTf2], 1-butyl-1-methylpiperidinium [BMPIP][NTf2], trimethylpropylammonium [TMPAm][NTf2]) were measured by solution calorimetry at infinite dilution. The enthalpies of hydrogen bond between solutes and ionic liquids were determined by the previously proposed approach. The hydrogen bond enthalpies were correlated with the proton acceptor ability of ionic liquids from the Kamlet-Abboud-Taft equation and the proton donor ability of amides from the Abraham model. The proton donor ability and hydrogen bond reorganization of studied ionic liquids was analyzed. The formation of the hydrogen bond complexes of linear amides with ionic liquids with different compositions was shown. The effect of the ionic liquid structure on the strength of the hydrogen bond of linear amides with ionic liquids has been established.