State Key Laboratory on Elemento-organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Department of Chemistry, Nankai University , Tianjin 300071, China.
J Org Chem. 2013 Dec 20;78(24):12487-93. doi: 10.1021/jo4021858. Epub 2013 Dec 11.
Equilibrium acidity (pKa) scales of 15 substituted benzoic acids in four room temperature ionic liquids (RTILs), BmimOTf, BmimNTf2, BmpyNTf2, and Bm2imNTf2, were established under standard conditions using a modified indicator overlapping method. The effect of homo hydrogen bonding on equilibrium acidity was calibrated, and the derived pKa values were evidenced to be free from ion-paring complication. Regression analyses demonstrated that all of the pKa scales obtained in four RTILs are linearly correlated to each other with an R value better than 0.996. These scales are also correlated well with the pKa values in DMSO and with the corresponding gas-phase acidities with regression coefficients of 0.993 and 0.992, respectively. In addition, both the cation and anion of the ionic liquids were found to play a role in affecting the acidity of carboxylic acid.
在标准条件下，使用改良的指示剂重叠法，建立了 15 种取代苯甲酸在四种室温离子液体（RTILs）中的平衡酸度（pKa）标度，BmimOTf、BmimNTf2、BmpyNTf2 和 Bm2imNTf2。校准了同质子氢键对平衡酸度的影响，得出的 pKa 值证明不受离子配对的影响。回归分析表明，在四种 RTILs 中获得的所有 pKa 标度彼此之间呈线性相关，相关系数 R 值优于 0.996。这些标度与 DMSO 中的 pKa 值以及相应气相酸度也很好地相关，回归系数分别为 0.993 和 0.992。此外，离子液体的阳离子和阴离子都被发现对羧酸的酸度有影响。
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