Toward Prediction of the Chemistry in Ionic Liquids: An Accurate Computation of Absolute pKa Values of Benzoic Acids and Benzenethiols

In contrast to the great success of computational methodologies in molecular solvents, effective and accurate calculation of the fundamental bond energetic properties in ionic liquids (ILs) is essentially absent. This is largely due to the unusual complexity of handling solvation quantities of ILs and the lack of precisely determined bond parameters to serve as the authentic benchmark to calibrate the modeling methodology. Herein, we report the first accurate calculations of absolute pK(a) values in a commonly used IL, [Bmim][NTf2], with the carefully developed ion-biased cluster-continuum model. Experimental pK(a) values of benzoic acids and benzenethiols in [Bmim] [NTf2] were reproduced with mean unsigned errors of only 0.3 and 0.5 pK(a) units, respectively, which enables theoretical approaches with a suitable strategy as a powerful tool to handle complicated problems in ILs and to eventually realize the rational design of the IL chemistry.