fluorosulfonic

Fluorosulfonic acid, with the chemical formula FSO3H (also written HSO3F), is a mineral acid and one of the strongest known non-oxidizing acids. It is a colorless to pale yellow, fuming liquid at room temperature and is highly hygroscopic, reacting vigorously with water.

Commercial fluorosulfonic acid is typically prepared by fluorinating sulfur-containing species such as sulfuric acid or sulfur trioxide with fluoride sources, and it is handled only under strictly anhydrous conditions. Because of its extreme reactivity with moisture, it can corrode many materials and must be kept away from water and protic substances. The hydrolysis of fluorosulfonic acid produces sulfuric acid and hydrogen fluoride, underscoring its high reactivity toward water.

In organic synthesis, fluorosulfonic acid is used as a superacid catalyst for reactions requiring very strong acidity. It enables certain dehydrations, activations, and fluorination-type transformations in dry organic media. Its high acidity can promote processes that are sluggish under ordinary mineral acids, but these reactions demand careful control of moisture, temperature, and compatible solvents and apparatus.

Safety and handling are essential due to its extreme corrosivity and reactivity. Contact with skin or eyes can cause severe burns; inhalation of vapors is dangerous. Hydrolysis can release hydrogen fluoride, which requires careful HF-handling precautions. The substance is stored in dry, inert conditions using compatible materials, often fluorinated polymers or other HF-resistant containers; glass and standard metals are generally unsuitable. Proper disposal and spill-response procedures should follow relevant regulations for strong fluorinated acids.