Diprotonation of taurine: 2-[dihydroxy(oxo)sulfanyliumyl]ethanaminium bis[hexafluoroarsenate(V)].

Taurine is part of the cysteine cycle and is one of the few naturally occuring organosulfur-based molecules in the human body. As implied by modern studies, protonated taurine is of biological impact. The first attempts to isolate its protonated species in the binary superacidic system HF/SbF₅ were performed by Hopfinger, resulting in the isolation of monoprotonated taurine. Since the chosen conditions seemed rather harsh, investigations in less acidic systems were performed at room temperature to explore the involved protonated species. Herein, we present the structure of 2-[dihydroxy(oxo)sulfanyliumyl]ethanaminium bis[hexafluoridoarsenate(V)], [H₂O₃SC₂H₄NH₃][AsF₆]₂, the diprotonated form of 2-aminoethanesulfonic acid (taurine). It was synthesized in the binary superacidic system HF/AsF₅ and crystallizes as colourless needles. Diprotonated taurine was structurally characterized by single-crystal X-ray diffraction analysis, low-temperature vibrational spectroscopy and NMR spectroscopy.