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Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid, is a molecular compound with the formula H₃NSO₃. This colourless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to lớn water, sulfur trioxide, sulfur dioxide and nitrogen.^[2]

Sulfamic acid (H₃NSO₃) may be considered an intermediate compound between sulfuric acid (H₂SO₄), and sulfamide (H₄N₂SO₂), effectively replacing a hydroxyl (–OH) group with an amine (–NH₂) group at each step. This pattern can extend no further in either direction without breaking down the sulfonyl (–SO₂–) moiety. Sulfamates are derivatives of sulfamic acid.

Sulfamic acid is produced industrially by treating urea with a mixture of sulfur trioxide and sulfuric acid (or oleum). The conversion is conducted in two stages, the first being sulfamation:

OC(NH₂)₂ + SO₃ → OC(NH₂)(NHSO₃H)

OC(NH₂)(NHSO₃H) + H₂SO₄ → CO₂ + 2 H₃NSO₃

In this way, approximately 96,000 tonnes were produced in 1995.^[3]

The compound is well described by the formula H₃NSO₃, not the tautomer H₂NSO₂(OH). The relevant bond distances are 1.44 Å for the S=O and 1.77 Å for the S–N. The greater length of the S–N is consistent with a single bond.^[5] Furthermore, a neutron diffraction study located the hydrogen atoms, all three of which are 1.03 Å distant from the nitrogen.^[4] In the solid state, the molecule of sulfamic acid is well described by a zwitterionic size.

The crystalline solid is indefinitely stable under ordinary storage conditions, however, aqueous solutions of sulfamic acid slowly hydrolyse to lớn ammonium bisulfate, according to lớn the following reaction:

H₃NSO₃ + H₂O → [NH₄]⁺[HSO₄]⁻

Its behaviour resembles that of urea, (H₂N)₂CO. Both feature amino groups linked to lớn electron-withdrawing centres that can participate in delocalised bonding. Both liberate ammonia upon heating in water, with urea releasing CO₂ while sulfamic acid releases sulfuric acid.

Sulfamic acid is a moderately strong acid, K_a = 0.101 (pK_a = 0.995). Because the solid is not hygroscopic, it is used as a standard in acidimetry (quantitative assays of acid content).

H₃NSO₃ + NaOH → NaH₂NSO₃ + H₂O

Double deprotonation can be effected in liquid ammonia to lớn give the anion HNSO²⁻
₃.^[6]

H₃NSO₃ + 2 NH₃ → HNSO²⁻
₃ + 2 NH⁺
₄

With nitrous acid, sulfamic acid reacts to lớn give nitrogen:

HNO₂ + H₃NSO₃ → H₂SO₄ + N₂ + H₂O

while with concentrated nitric acid, it affords nitrous oxide:^[7]

HNO₃ + H₃NSO₃ → H₂SO₄ + N₂O + H₂O

The reaction of excess hypochlorite ions with sulfamic acid or a sulfamate salt gives rise reversibly to lớn both N-chlorosulfamate and N,N-dichlorosulfamate ions.^[8][9][10]

HClO + H₂NSO₃H → ClNHSO₃H + H₂O

HClO + ClNHSO₃H ⇌ Cl₂NSO₃H + H₂O

Consequently, sulfamic acid is used as hypochlorite scavenger in the oxidation of aldehydes with chlorite such as the Pinnick oxidation.

Upon heating sulfamic acid will react with alcohols to lớn size the corresponding organosulfates. It is more expensive phàn nàn other reagents for doing this, such as chlorosulfonic acid or oleum, but is also significantly milder and will not sulfonate aromatic rings. Products are produced as their ammonium salts. Such reactions can be catalyzed by the presence of urea.^[10] Without the presence of any catalysts, sulfamic acid will not react with ethanol at temperatures below 100 °C.

ROH + H₂NSO₃H → ROS(O)₂O⁻ + NH⁺
₄

An example of this reaction is the production 2-ethylhexyl sulfate, a wetting agent used in the mercerisation of cốt tông, by combining sulfamic acid with 2-ethylhexanol.

Sulfamic acid is mainly a precursor to lớn sweet-tasting compounds. Reaction with cyclohexylamine followed by addition of NaOH gives C₆H₁₁NHSO₃Na, sodium cyclamate. Related compounds are also sweeteners, such as acesulfame potassium.

Sulfamates 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), anticancer drugs (steroid sulfatase and carbonic anhydrase inhibitors), anti-epileptic drugs, and weight loss drugs.^[11]

Sulfamic acid is used as an acidic cleaning agent and descaling agent sometimes pure or as a component of proprietary mixtures, typically for metals and ceramics. For cleaning purposes, there are different grades based on application such as GP Grade, SR Grade and TM Grade. It is frequently used for removing rust and limescale, replacing the more volatile and irritating hydrochloric acid, which is cheaper. It is often a component of household descalant, for example, Lime-A-Way Thick Gel contains up to lớn 8% sulfamic acid and has pH 2.0–2.2,^[12] or detergents used for removal of limescale. When compared to lớn most of the common strong mineral acids, sulfamic acid has desirable water descaling properties, low volatility, and low toxicity. It forms water-soluble salts of calcium, nickel, and ferric iron.

Sulfamic acid is preferable to lớn hydrochloric acid in household use, due to lớn its intrinsic safety. If inadvertently mixed with hypochlorite based products such as bleach, it does not size chlorine gas, whereas the most common acids would; the reaction (neutralisation) with ammonia, produces a salt, as depicted in the section above.

It also finds applications in the industrial cleaning of dairy and brewhouse equipment. Although it is considered less corrosive phàn nàn hydrochloric acid, corrosion inhibitors are often added to lớn the commercial cleansers of which it is a component. It can be used as a descalant for descaling trang chủ coffee and espresso machines and in denture cleaners.

• Catalyst for esterification process
• Dye and pigment manufacturing
• Herbicide, as ammonium sulfamate
• Descalant for scale removal
• Coagulator for urea-formaldehyde resins
• Ingredient in fire extinguishing media. Sulfamic acid is the main raw material for ammonium sulfamate which is a widely used herbicide and fire retardant material for household products.
• Pulp and paper industry as a chloride stabilizer
• Synthesis of nitrous oxide by reaction with nitric acid
• The deprotonated size (sulfamate) is a common counterion for nickel(II) in electroplating.
• Used to lớn separate nitrite ions from mixture of nitrite and nitrate ions( NO₃⁻+ NO₂⁻) during qualitative analysis of nitrate by Brown Ring test.
• Obtaining deep eutectic solvents with urea^[13]

According to lớn the label on the consumer product, the silver cleaning product TarnX contains thiourea, a detergent, and sulfamic acid.

• "Chemical Sampling Information – Sulfamic Acid". Occupational Health & Safety Administration. 6 May 1997. Retrieved 17 November 2011.
• Cremlyn, R. J. (1996). An Introduction to lớn Organosulfur Chemistry. Chichester: John Wiley and Sons. ISBN 978-0-471-95512-2.
• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.