Fluorosulfonic acid

Ball-and-stick model of fluorosulfonic acid. The white ball is hydrogen, the red balls are oxygen, the yellow ball is sulfur, and the yellow-green ball is fluorine.

Fluorosulfonic acid, also called fluorosulfuric acid, is a chemical compound related to sulfuric acid. It is an inorganic sulfonic acid where a fluorine atom replaces one of the −OH groups attached to the sulfur atom in sulfuric acid. The chemical formula of fluorosulfonic acid is HSO3F. It is a superacid and the strongest known simple Brønsted acid.

Properties

The fluorine atom is more electronegative than the group it replaced. This makes fluorosulfonic acid stronger than sulfuric acid. Acids stronger than sulfuric acid are called superacids. Fluorosulfonic acid can also be mixed with antimony pentafluoride to make an even stronger superacid called magic acid.

Fluorosulfonic acid is the mixed acid anhydride of H2SO4 and HF. As an anhydride, it is vulnerable to hydrolysis, and reacts violently with water to make sulfuric acid and hydrofluoric acid:

HS3OF + H2O → H2SO4 + HF

Preparation

Fluorosulfonic acid is made from sulfur trioxide and hydrogen fluoride. Because it reacts with water, anhydrous chemicals must be used. The chemical equilibrium

HSO3F ⇌ HF + SO3

means that there will always be small amounts of HF and SO3 in fluorosulfonic acid, which can damage glass containers by making hexafluorosilicic acid and silicon tetrafluoride.

References

  1. 1 2 3 George A. Olah, G. K. Surya Prakash, Arpad Molnar, and Jean Sommer (2009). "2.1.1.3 Fluorosulfuric Acid". Superacid Chemistry (2nd ed.). John Wiley & Sons, Inc. p. 37. ISBN 978-0-470-42154-3.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ↑ Olah, George A.; Schlosberg, Richard H. (1968). "Chemistry in super acids. I. Hydrogen exchange and polycondensation of methane and alkanes in FSO3H-SbF5 ("magic acid") solution. Protonation of alkanes and the intermediacy of CH5+ and related hydrocarbon ions. The high chemical reactivity of "paraffins" in ionic solution reactions". Journal of the American Chemical Society. 90 (10): 2726–2727. Bibcode:1968JAChS..90.2726O. doi:10.1021/ja01012a066.
  3. ↑ "Fluorosulfonic acid". PubChem. National Center for Biotechnology Information.