Gas-phase deprotonation energies of sulfuric acid, perchloric acid, chlorosulfuric acid and fluorosulfuric acid
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André H. Otto, Sigurd Schrader, Thomas Steiger and Matthias Schneider
Abstract
Gas-phase deprotonation energies (DEs) of sulfuric acid, perchloric acid, chlorosulfuric acid and fluorosulfuric acid have been calculated by applying the {MP2(fc)/6-311++G(d,p)//6-31+G(d)+ZPVE[6-31+G(d)]} abinitio MO level of calculation. The DEs obtained increase in the following order: H2SO4 > HClO4 > FSO3H > ClSO3H. Combining these results with experimental data and previous density functional theory (DFT) findings, we recommend for the DEs: 308 ± 3 kcal mol−1, 300 ± 3 kcal mol−1, 298 ± 3 kcal mol−1 and 295 ± 3 kcal mol−1, respectively. It is remarkable that chlorosulfuric acid is predicted to be a stronger acid in the gas phase than fluorosulfuric acid, in agreement with DFT and in contrast to previous supposition.