Gas-phase deprotonation energies of sulfuric acid, perchloric acid, chlorosulfuric acid and fluorosulfuric acid

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.