Sulfamic acid

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

H₃NSO₃ + H₂O → [NH₄]⁺[HSO₄]⁻

Its behaviour resembles that of urea, (H₂N)₂CO. Both feature amino groups linked to 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 give the anion HNSO²⁻
₃.[6]

H₃NSO₃ + 2 NH₃ → HNSO²⁻
₃ + 2 NH⁺
₄

With nitrous acid, sulfamic acid reacts to 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 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 form the corresponding organosulfates. It is more expensive than 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 cotton, by combining sulfamic acid with 2-ethylhexanol.

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 8% sulfamic acid and has pH 2.0–2.2,[12] or detergents used for removal of limescale. When compared to 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 hydrochloric acid in household use, due to its intrinsic safety. If inadvertently mixed with hypochlorite based products such as bleach, it does not form 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 than hydrochloric acid, corrosion inhibitors are often added to the commercial cleansers of which it is a component. It can be used as a descalant for descaling home coffee and espresso machines and in denture cleaners.

• Catalyst for esterification process
• Dye and pigment manufacturing
• Herbicide
• 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 form (sulfamate) is a common counterion for nickel(II) in electroplating.
• Used to 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 the label on the consumer product, the silver cleaning product TarnX contains thiourea, a detergent, and sulfamic acid.