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Absolute pKas of Sulfonamides in Ionic Liquids: Comparisons to Molecular Solvents
- Wang, Zedong, Li, Xin, Ji, Pengju, Cheng, Jin-Pei
- Journal of organic chemistry 2016 v.81 no.22 pp. 11195-11200
- acetonitrile, acidity, dimethyl sulfoxide, ionic liquids, organic chemistry, regression analysis, sulfonamides
- Absolute pKₐs of 25 sulfonamides in four ionic liquids (ILs) were measured spectroscopically with high precision and subsequently compared with those in conventional molecular solvents. It is found that the acidity order of these sulfonamides is as follows: in water > in DMSO > in ILs > in acetonitrile (ACN). The well-known solvent polarity index ε fails to explain the observed stronger bond-weakening effect of ILs in comparison to that of ACN, whose ε value is much greater. In addition, the regression analyses show that the pKₐs of sulfonamides determined in ILs linearly correlate with these in molecular solvents of distinct properties, but with various slopes. A rationale and related discussion on the effect of solvation in ILs are presented.