title: Absolute Brønsted Acidities and pH Scales in Ionic Liquids.
abstract: Although receiving large interest over the last years, some fundamental aspects of Brønsted acidity in ionic liquids (ILs) have up to now been insufficiently highlighted. In this work, standard states, activity, and activity coefficient definitions for IL solvent systems were developed from general thermodynamic considerations and then extended to a general mixed solvent standard state. By using the bromide/bromoaluminate systems as representative ILs, formulae for thermodynamically consistent pH scales for ILs with simple (Br(-) ) and complex ([Aln Br3n+1 ](-) ) anions were derived on the basis of the chemical potential of the proton. Supported by quantum chemical [ccsd(t)/MP2/DFT/COSMO-RS] calculations, Gibbs solvation energies of the proton were calculated, which allowed the ILs to be ranked in absolute acidity, that is, pHabs or μabs (H(+) , IL), and additionally allowed their acidity to be compared with molecular Brønsted acid systems. It was shown that bromoaluminate ILs are suited for reaching superacidic conditions. The complexity of autoprotolysis processes in C6 MIM(+) [AlBr4 ](-) (C6 MIM=1-hexyl-3-methylimidazolium) with or without the addition of basic (i.e. Br(-) ) or acidic (AlBr3 and/or HBr) solutes was examined in detail by model calculations, and they indicated a large thermodynamic influence of small deviations from the exact stoichiometric composition.
authors: Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstrasse 19, 79104 Freiburg (Germany).
authors: Daniel
authors: D
authors: Himmel
authors: Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstrasse 19, 79104 Freiburg (Germany).
authors: Sascha K
authors: SK
authors: Goll
authors: Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstrasse 19, 79104 Freiburg (Germany).
authors: Franziska
authors: F
authors: Scholz
authors: Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstrasse 19, 79104 Freiburg (Germany).
authors: Valentin
authors: V
authors: Radtke
authors: Institute of Chemistry, University of Tartu, 14a Ravila Street, 50411 Tartu (Estonia).
authors: Ivo
authors: I
authors: Leito
authors: Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstrasse 19, 79104 Freiburg (Germany). krossing@uni-freiburg.de.
authors: Ingo
authors: I
authors: Krossing
keywords: acidity; ionic liquids; pH; quantum chemistry; thermodynamics