is about -28. The following H0 values show that fluoroantimonic acid is stronger than other superacids. Increased acidity is indicated by smaller (in this case, more negative) values of H0. Fluoroantimonic acid (−23 < H0 < −28) Magic acid (H0 = −23) Carborane acid (H0 < −18) Fluorosulfuric acid (H0 = −15) Triflic acid (H0 = −15) Perchloric acid (H0 = -13) Of the above, only the carborane acids, whose H0 could not be directly determined due to their high melting points, may be stronger acids than fluoroantimonic acid. The H0 value measures the protonating ability of the bulk, liquid acid, and this value has been directly determined or estimated for various compositions of the mixture. The pKa on the other hand, measures the equilibrium of proton dissociation of a discrete chemical species when dissolved in a particular solvent. Since fluoroantimonic acid is not a single chemical species, its pKa value is not well-defined. The gas-phase acidity (GPA) of individual species present in the mixture have been calculated using density functional theory methods. (Solution-phase pKas of these species can, in principle, be estimated by taking into account solvation energies, but do not appear to be reported in the literature as of 2019.) For example, the ion-pair [H2F]+· was estimated to have a GPA of 254 kcal/mol. For comparison, the commonly encountered superacid triflic acid, TfOH, is a substantially weaker acid by this measure, with a GPA of 299 kcal/mol. However, certain carborane superacids have GPAs lower than that of [H2F]+·. For example, H(CHB11Cl11) has an experimentally determined GPA of 241 kcal/mol. Reactions Fluoroantimonic acid is so reactive that it is challenging to identify media with which it is unreactive. Materials compatible with fluoroantimonic acid as a solvent include SO2ClF, and sulfur dioxide; some chlorofluorocarbons have also been used. Containers for HF/SbF5 are made of PTFE. Fluoroantimonic acid decomposes when heated, generating free hydrogen fluoride gas and liquid antimony pentafluoride at a temperature of 40 °C. As a superacid, fluoroantimonic acid protonates nearly all organic compounds, often causing dehydrogenation, or dehydration. In 1967, Bickel and Hogeveen showed that 2HF·SbF5 will remove H2 from isobutane and methane from neopentane to form carbenium ions: (CH3)3CH + H+ → (CH3)3C+ + H2 (CH3)4C + H+ → (CH3)3C+ + CH4 It is also used in the synthesis of tetraxenonogold complexes. Safety HF/SbF5 is a highly corrosive substance that reacts violently with water. Heating fluoroantimonic acid