title: The Acidity of the HBr/AlBr3 System: Stabilization of Crystalline Protonated Arenes and Their Acidity in Bromoaluminate Ionic Liquids.
abstract: Bulk protonated mesitylene, toluene, and benzene bromoaluminate salts were stabilized and characterized in the superacidic system HBr/n AlBr3 with NMR spectroscopy and X-ray analysis of [HC6 H3 (CH3 )3 ](+) [AlBr4 ](-) (1), [HC6 H5 (CH3 )](+) [AlBr4 ](-) (2), and [C6 H7 ](+) [Al2 Br7 ](-) ⋅C6 H6 (3). Protonation attempts in bromoaluminate ILs led to a complete protonation of mesitylene, and a protonation degree of up to 15 % for toluene in the IL BMP(+) [Al2 Br7 ](-) . Benzene could only be protonated in the more acidic IL BMP(+) [Al3 Br10 ](-) , with a degree of 25 %. Protonation attempts on aromatics provide evidence that the bromoaluminate ILs tolerate superacidic environments. On the basis of the absolute Brønsted acidity scale, quantum chemical calculations confirmed the superacidic properties, and rank the acidities in ILs down to a pHabs value of 164 with an error of less than one pH unit compared with experimental findings. The neat AlBr3 /HBr system even may reach acidities down to pHabs 163.
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: Daniel
authors: D
authors: Himmel
authors: Lea
authors: L
authors: Eisele
authors: Wiebke
authors: W
authors: Unkrig
authors: Arthur
authors: A
authors: Martens
authors: Peter
authors: P
authors: Schlüter
authors: Ingo
authors: I
authors: Krossing
keywords: Lewis acids; ionic liquids; protonated arenes; quantum chemical calculations; superacids