The Strongest Acid: Protonation of Carbon Dioxide

摘要

The strongest carborane acid, H(CHB11F11), protonates CO2 while traditional mixed Lewis/Bronsted superacids do not. The product is deduced from IR spectroscopy and calculation to be the proton disolvate, H(CO2)(2)(+). The carborane acid H(CHB11F11) is therefore the strongest known acid. The failure of traditional mixed superacids to protonate weak bases such as CO2 can be traced to a competition between the proton and the Lewis acid for the added base. The high protic acidity promised by large absolute values of the Hammett acidity function (H-0) is not realized in practice because the basicity of an added base is suppressed by Lewis acid/base adduct formation.