Shrinking of C–S bonds of organosulfonic acids in superacidic media—investigation of the protonation of methanesulfonic acid and benzenesulfonic acid and their limits

The reactions of methanesulfonic acid and benzenesulfonic acid in the binary superacidic systems HF/MF₅ (M = As and Sb) were investigated to explore the strengthening effects of protonation on the C-S bond and the limits of the protonability of sulfonic acids. Herein, we report the monoprotonated species of methanesulfonic acid and benzenesulfonic acid, respectively. The salts were characterized by low-temperature vibrational spectroscopy, single-crystal X-ray diffraction, and NMR spectroscopic measurements. The experimental data are discussed together with quantum chemical calculations at the B3LYP/aug-cc-pVTZ-level of theory.