Sulfamic acid

Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, and sulfamidic acid, is a molecular compound with the formula H₃NSO₃. This colorless, water-soluble compound finds many applications.

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Sulfamic acid is a member of the following series of compounds: H₂SO₄ (sulfuric acid), H₃NSO₃ (sulfamic acid), H₄N₂SO₂ (sulfamide), H₅N₃SO (unknown), and H₆N₄S (unknown).

Structure and reactivity

First, it should be noticed that the compound is well described by the formula H₃NSO₃, not the tautomer H₂NSO₂(OH). The relevant bond distances are S=O, 1.44 and S-N 1.77 Å. The greater length of the S-N distance is consistent with a single bond. Furthermore, a neutron diffraction study located the hydrogen atoms, all three of which are 1.03 Å distant from nitrogen. The structures shown with this article are for the two main tautomers.

Sulfamic acid is a weak acid, K_a = 1.01 x 10⁻¹. Because the solid is non-hygroscopic, it is used as a standard in acidometry (quantitative assays of acid content). Double deprotonation can be effected in NH₃ solution to give [HNSO₃]²⁻.

Sulfamic acid melts at 205 °C before decomposing at higher temperatures to H₂O, SO₃, SO₂, and N₂.

With HNO₂, sulfamic acid reacts to give N₂, while with HNO₃, it affords N₂O.

The behavior of H₃NSO₃ resembles that of urea, (H₂N)₂CO, in some ways. Both feature amino groups linked to electron-withdrawing centers that can participate in delocalized bonding. Both liberate ammonia upon heating in water.

Applications

The most famous applicaton of sulfamic acid is in the synthesis of compounds that taste sweet. Reaction with cyclohexylamine followed by addition of NaOH gives C₆H₁₁NHSO₃Na, sodium cyclamate. Related compounds are also sweeteners, see acesulfame potassium.

Sulfamates (O-substituted-, N-substituted-, or di-/tri-substituted derivatives of sulfamic acid) have been used in the design of many types of therapeutic agents such as antibiotics, nucleoside/nucleotide human immunodeficiency virus (HIV) reverse transcriptase inhibitors, HIV protease inhibitors (PIs), anti-cancer drugs (steroid sulfatase and carbonic anhydrase inhibitors), anti-epileptic drugs, and weight loss drugs.

Sulfamic acid is used as an acidic cleaning agent, typically for metals and ceramics. It is a replacement for hydrochloric acid for the removal of rust. In households, it is often found as a descaling agent in detergents used for removal of limescale.

Sulfamic acid is used in the S.C. Johnson & Sons, Inc. "Scrubbing Bubbles™ Fizz-Its Toilet Tablets."

• Catalyst for esterification process
• Dye and pigment manufacturing
• Herbicide
• Ingredient in Denture Tablets
• Coagulator for urea-formaldehyde resins
• Ingredient in fire extinguishing media
• Pulp and paper industry as a chloride stabilizer
• Synthesis of nitrous oxide by reaction with nitric acid

References

• J. W. Bats, P. Coppens, T. F. Koetzle "The Experimental Charge Density in Sulfur-Containing Molecules: A Study of the Deformation Electron Density in Sulfamic Acid at 78 K by X-ray and Neutron Diffraction" Acta Crystallographica (1977). B33, pages 37-45.
• MSDS http://www.osha.gov [1]
• Sulfamates and their therapeutic potential. Med Res Rev. 2005 Mar;25(2):186-228. Review.
• R. J. Cremlyn “An Introduction to Organosulfur Chemistry” John Wiley and Sons: Chichester (1996). ISBN 0-471-95512-4
• Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.