 | |||
| |||
 | |||
| Names | |||
|---|---|---|---|
| IUPAC name Sulfamic acid | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
| ||
| ECHA InfoCard | 100.023.835 | ||
| EC Number |
| ||
| 25628 | |||
| RTECS number |
| ||
| UNII | |||
| UN number | 2967 | ||
| |||
| |||
| Properties | |||
| H3NSO3 | |||
| Molar mass | 97.10 g/mol | ||
| Appearance | white crystals | ||
| Density | 2.15 g/cm3 | ||
| Melting point | 205 °C (401 °F; 478 K) decomposes | ||
| Moderate, with slow hydrolysis | |||
| Solubility | |||
| Acidity (pKa) | 1.0[1] | ||
| Hazards | |||
| GHS labelling: | |||
 | |||
| Warning | |||
| H315,H319,H412 | |||
| P264,P273,P280,P302+P352,P305+P351+P338,P321,P332+P313,P337+P313,P362,P501 | |||
| Safety data sheet (SDS) | ICSC 0328 | ||
| Related compounds | |||
Othercations | Ammonium sulfamate | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Sulfamic acid, also known asamidosulfonic acid,amidosulfuric acid,aminosulfonic acid,sulphamic acid andsulfamidic 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 towater,sulfur trioxide,sulfur dioxide andnitrogen.[2]
Sulfamic acid (H3NSO3) may be considered an intermediate compound betweensulfuric acid (H2SO4), andsulfamide (H4N2SO2), effectively replacing ahydroxyl (–OH) group with anamine (–NH2) group at each step. This pattern can extend no further in either direction without breaking down thesulfonyl (–SO2–) moiety.Sulfamates are derivatives of sulfamic acid.
Sulfamic acid is produced industrially by treatingurea with a mixture ofsulfur trioxide andsulfuric acid (oroleum). The conversion is conducted in two stages, the first beingsulfamation:
In this way, approximately 96,000 tonnes were produced in 1995.[3]
The compound is well described by the formula H3NSO3, not thetautomer 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, aneutron 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 azwitterionic form.
The crystalline solid is indefinitely stable under ordinary storage conditions, however, aqueous solutions of sulfamic acid slowly hydrolyse toammonium bisulfate, according to the following reaction:
Its behaviour resembles that ofurea, (H2N)2CO. Both featureamino groups linked to electron-withdrawing centres that can participate indelocalised bonding. Both liberateammonia upon heating in water, with urea releasing CO2 while sulfamic acid releasessulfuric acid.
Sulfamic acid is a moderately strong acid,Ka = 0.101 (pKa = 0.995). Because the solid is nothygroscopic, it is used as a standard inacidimetry (quantitative assays of acid content).
Double deprotonation can be effected in liquidammonia to give the anionHNSO2−
3.[6]
Withnitrous acid, sulfamic acid reacts to givenitrogen:
while with concentratednitric acid, it affordsnitrous oxide:[7]
The reaction of excesshypochlorite ions with sulfamic acid or a sulfamate salt gives rise reversibly to bothN-chlorosulfamate andN,N-dichlorosulfamate ions.[8][9][10]
Consequently, sulfamic acid is used as hypochloritescavenger in the oxidation ofaldehydes withchlorite such as thePinnick oxidation.
Upon heating sulfamic acid will react with alcohols to form the correspondingorganosulfates. It is more expensive than other reagents for doing this, such aschlorosulfonic acid oroleum, but is also significantly milder and will not sulfonate aromatic rings. Products are produced as theirammonium salts. Such reactions can be catalyzed by the presence ofurea.[10] Without the presence of any catalysts, sulfamic acid will not react with ethanol at temperatures below 100 °C.
An example of this reaction is the production 2-ethylhexyl sulfate, a wetting agent used in themercerisation of cotton, by combining sulfamic acid with2-ethylhexanol.
Sulfamic acid is mainly a precursor to sweet-tasting compounds. Reaction withcyclohexylamine followed by addition ofNaOH gives C6H11NHSO3Na,sodium cyclamate. Related compounds are alsosweeteners, such asacesulfame potassium.
Sulfamates have been used in the design of many types of therapeutic agents such asantibiotics, nucleoside/nucleotidehuman immunodeficiency virus (HIV)reverse transcriptase inhibitors,HIV protease inhibitors (PIs), anticancer drugs (steroid sulfatase andcarbonic anhydrase inhibitors),anti-epileptic drugs, andweight loss drugs.[11]
Sulfamic acid is used as an acidiccleaning agent and descaling agent sometimes pure or as a component of proprietary mixtures, typically formetals andceramics. For cleaning purposes, there are different grades based on application such as GP Grade, SR Grade and TM Grade. It is frequently used for removingrust andlimescale, replacing the more volatile and irritatinghydrochloric 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] ordetergents used for removal oflimescale. When compared to most of the common strongmineral 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 asbleach, it does not formchlorine gas, whereas the most common acids would; the reaction (neutralisation) withammonia, 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 thanhydrochloric 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.
According to the label on the consumer product, the silver cleaning product TarnX containsthiourea, adetergent, and sulfamic acid.
