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

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

, sulfur trioxide,

sulfur dioxide Sulfur dioxide ( IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic ...

and

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

. Sulfamic acid (H₃NSO₃) may be considered an intermediate compound between sulfuric acid (H₂SO₄), and

sulfamide Sulfamide (IUPAC name: sulfuric diamide) is an organosulfur compound with the chemical formula and structure . Sulfamide is produced by the reaction of sulfuryl chloride with ammonia. Sulfamide was first prepared in 1838 by the French chemist ...

(H₄N₂SO₂), effectively replacing a

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

(–OH) group with an

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

(–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.

Production

Sulfamic acid is produced industrially by treating

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

with a mixture of sulfur trioxide and sulfuric acid (or

oleum Oleum (Latin ''oleum'', meaning oil), or fuming sulfuric acid, is a term referring to solutions of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid). Ol ...

). 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.

Structure and reactivity

The compound is well described by the formula H₃NSO₃, not the

tautomer Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hyd ...

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. Furthermore, a

neutron diffraction Neutron diffraction or elastic neutron scattering is the application of neutron scattering to the determination of the atomic and/or magnetic structure of a material. A sample to be examined is placed in a beam of thermal or cold neutrons to ob ...

study located the hydrogen atoms, all three of which are 1.03 Å distant from the nitrogen. In the solid state, the molecule of sulfamic acid is well described by a

zwitterionic In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively- and negatively-charged functional groups. : With amino acids, for example, in solution a chemical equilibrium w ...

form.

Hydrolysis

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 → H₄sup>+ SO₄sup>− Its behaviour resembles that of

, (H₂N)₂CO. Both feature

amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...

s linked to electron-withdrawing centres that can participate in delocalised bonding. Both liberate

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...

upon heating in water, with urea releasing CO₂ while sulfamic acid releases sulfuric acid.

Acid–base reactions

Sulfamic acid is a moderately strong acid, ''K''_a = 0.101 (p''K''_a = 0.995). Because the solid is not

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...

, it is used as a standard in acidimetry (quantitative assays of acid content). :H₃NSO₃ + NaOH → NaH₂NSO₃ + H₂O Double deprotonation can be effected in

solution to give the anion . :H₃NSO₃ + 2 NH₃ → + 2

Reaction with nitric and nitrous acids

With

nitrous acid Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents ...

, sulfamic acid reacts to give

: :HNO₂ + H₃NSO₃ → H₂SO₄ + N₂ + H₂O while with

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...

, it affords

nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has ...

: :HNO₃ + H₃NSO₃ → H₂SO₄ + N₂O + H₂O

Reaction with hypochlorite

The reaction of excess

hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ble ...

ions with sulfamic acid or a sulfamate salt gives rise reversibly to both ''N''-chlorosulfamate and ''N'',''N''-dichlorosulfamate ions. :HClO + H₂NSO₃H → ClNHSO₃H + H₂O :HClO + ClNHSO₃H Cl₂NSO₃H + H₂O Consequently, sulfamic acid is used as hypochlorite

scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...

in the oxidation of

aldehydes In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

with

chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chl ...

such as the Pinnick oxidation.

Reaction with alcohols

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 Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSO3Cl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic and ...

, but is also significantly milder and will not sulfonate aromatic rings. Products are produced as their

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternar ...

salts. Such reactions can be catalyzed by the presence of

. Without the presence of any catalysts, sulfamic acid will not react with ethanol at temperatures below 100 °C. :ROH + H₂NSO₃H → ROS(O)₂O⁻ + 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 2-Ethylhexanol (abbreviated 2-EH) is an organic compound with formula CHO. It is a branched, eight-carbon chiral alcohol. It is a colorless liquid that is poorly soluble in water but soluble in most organic solvents. It is produced on a large scale ...

Applications

Sulfamic acid is mainly a precursor to sweet-tasting compounds. Reaction with cyclohexylamine followed by addition of NaOH gives C₆H₁₁NHSO₃Na,

sodium cyclamate Cyclamate is an artificial sweetener. It is 30–50 times sweeter than sucrose (table sugar), making it the least potent of the commercially used artificial sweeteners. It is often used with other artificial sweeteners, especially saccharin ...

. Related compounds are also

sweetener {{Wiktionary, sweetener A sweetener is a substance added to food or drink to impart the flavor of sweetness, either because it contains a type of sugar, or because it contains a sweet-tasting sugar substitute. Many artificial sweeteners have be ...

s, such as acesulfame potassium. Sulfamates have been used in the design of many types of therapeutic agents such as

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...

s, nucleoside/nucleotide

human immunodeficiency virus The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immun ...

(HIV) reverse transcriptase inhibitors, HIV protease inhibitors (PIs), anticancer drugs (

steroid sulfatase Steroid sulfatase (STS), or steryl-sulfatase (EC 3.1.6.2), formerly known as arylsulfatase C, is a sulfatase enzyme involved in the metabolism of steroids. It is encoded by the ''STS'' gene. Reactions This enzyme catalyses the following chemi ...

and

carbonic anhydrase The carbonic anhydrases (or carbonate dehydratases) () form a family of enzymes that catalyze the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions). The active si ...

inhibitors), anti epileptic drugs, and weight loss drugs.

Cleaning agent

Sulfamic acid is used as an acidic

cleaning agent Cleaning agents or hard-surface cleaners are substances (usually liquids, powders, sprays, or granules) used to remove dirt, including dust, stains, bad smells, and clutter on surfaces. Purposes of cleaning agents include health, beauty, removi ...

and descaling agent sometimes pure or as a component of proprietary mixtures, typically for

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typi ...

s and

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelai ...

s. 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 Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), ...

and

limescale Limescale is a hard, chalky deposit, consisting mainly of calcium carbonate (CaCO3). It often builds up inside kettles, boilers, and pipework, especially that for hot water. It is also often found as a similar deposit on the inner surfaces of ol ...

, replacing the more volatile and irritating

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dig ...

, 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, or

detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are m ...

s used for removal of

. 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 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 Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...

gas, whereas the most common acids would; the reaction ( neutralisation) with

, 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

corrosion inhibitor In chemistry, a corrosion inhibitor or anti-corrosive is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy, that comes into contact with the fluid. The effectiveness ...

s 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.

Other uses

Catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

for

esterification In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glyceride ...

process *

Dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

and

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic comp ...

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

by reaction with nitric acid * The deprotonated form (sulfamate) is a common counterion for nickel(II) in

electroplating Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric cur ...

. *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

Kazachenko, Aleksandr S.; Issaoui, Noureddine; Medimagh, Mouna; Yu. Fetisova, Olga; Berezhnaya, Yaroslava D.; Elsuf'ev, Evgeniy V.; Al-Dossary, Omar M.; Wojcik, Marek J.; Xiang, Zhouyang; Bousiakou, Leda G. "Experimental and theoretical study of the sulfamic acid-urea deep eutectic solvent" (2022) Journal of Molecular Liquids, 363, art. no. 119859 DOI: 10.1016/j.molliq.2022.119859

Silver polishing

According to the label on the consumer product, the silver cleaning product TarnX contains

thiourea Thiourea () is an organosulfur compound with the formula and the structure . It is structurally similar to urea (), except that the oxygen atom is replaced by a sulfur atom (as implied by the '' thio-'' prefix); however, the properties of ur ...

, a

, and sulfamic acid.