Hydrogen bonding of molecular solutes in protic and aprotic ionic liquids

Abstract

The thermochemical study of hydrogen bonding of organic solutes in 1-methylimidazolium bis(trifluoromethylsulfonyl)imide ([MIM][NTf2]) was carried out. Activity coefficients at infinite dilution of organic compounds in [MIM][NTf2] were measured by gas-liquid chromatography at different temperatures between 303.15 and 343.15 K. The solution enthalpies of organic solutes in [MIM][NTf2] were determined from the temperature dependence of activity coefficients in the same systems. Solution enthalpies of solutes (propanol-1, meta-cresol, acetone, acetonitrile, diethyl ether, tetrahydrofuran, dichloromethane, trichloromethane, pyrrole) in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][NTf2] were measured by using high-precision solution calorimetry. The hydrogen bond enthalpies of organic solutes in [MIM][NTf2] and [BMIM][NTf2] were calculated using a previously developed method. The hydrogen bond enthalpies of organic solutes in the protic ionic liquid [MIM][NTf2] were compared with the values in the aprotic ionic liquid [BMIM][NTf2], as well as with those in the molecular solvent pyrrole. The hydrogen bond enthalpies of proton acceptor molecules in [MIM][NTf2] differ significantly from zero unlike in [BMIM][NTf2]. Hydrogen bond enthalpies of proton acceptor molecules in [MIM][NTf2] and pyrrole are close.