title: Standard and absolute pKa scales of substituted benzoic acids in room temperature ionic liquids.
abstract: 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.
authors.affiliation: State Key Laboratory on Elemento-organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Department of Chemistry, Nankai University , Tianjin 300071, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.forename: Hui
authors.initials: H
authors.lastname: Deng
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Pengju
authors.initials: P
authors.lastname: Ji
authors.forename: Jin-Pei
authors.initials: JP
authors.lastname: Cheng