Sulfamic acid

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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.

Sulfamic acid (H₃NSO₃) may be considered an intermediate compound between sulfuric acid (H₂SO₄), and sulfamide (H₄N₂SO₂), effectively - though see below - replacing an -OH group with an -NH₂ group at each step. This pattern can extend no further in either direction without breaking down the -SO₂ group.

Structure and reactivity[edit | edit source]

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.^[1] 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⁻.

<math>\mathrm{(NH_2)HSO_3 + NaOH \rightarrow NaNH_2SO_3 + H_2O}</math>

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.

<math>\mathrm{HNO_2 + (NH_2)HSO_3 \rightarrow H_2SO_4 + N_2 + H_2O}</math>

<math>\mathrm{HNO_3 + (NH_2)HSO_3 \rightarrow H_2SO_4 + N_2O + H_2O}</math>

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[edit | edit source]

The most famous application 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[edit | edit source]

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• 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
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External links[edit | edit source]

Wikimedia Commons has media related to Sulfamic acid.

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