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 a ...

sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...

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 activ ...

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 se ...

. Sulfamic acid (H₃NSO₃) may be considered an intermediate compound between

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

(H₂SO₄), and sulfamide (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 hydroxy ...

(–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 Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

(–NH₂) group at each step. This pattern can extend no further in either direction without breaking down the

sulfonyl In organosulfur chemistry, a sulfonyl group can refer either to a functional group found primarily in sulfones, or to a substituent obtained from a sulfonic acid by the removal of the hydroxyl group, similarly to acyl groups. Sulfonyl groups c ...

(–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 r ...

with a mixture of

and

(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). Ole ...

). The conversion is conducted in two stages, the first being

sulfamation In organic chemistry sulfamation is the installation of either of two related functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. Th ...

: :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 hydr ...

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 o ...

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 wil ...

form.

Hydrolysis

The crystalline solid is indefinitely stable under ordinary storage conditions, however, aqueous solutions of sulfamic acid slowly hydrolyse to

ammonium bisulfate Ammonium bisulfate, also known as ammonium hydrogen sulfate, is a white, crystalline solid with the chemical formula, formula (NH4)HSO4. This salt is the product of the half-neutralization of sulfuric acid by ammonia. Production It is commonly co ...

, 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 nitrogenous was ...

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

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 (chemistry), solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazoni ...

, 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 nitri ...

, 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 a ...

: :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 chlorous ac ...

such as the Pinnick oxidation.

Reaction with alcohols

Upon heating sulfamic acid will react with alcohols to form the corresponding

organosulfate Organosulfates are a class of organic compounds sharing a common functional group with the structure R-O-SO3−. The SO4 core is a sulfate group and the R group is any organic residue. All organosulfates are formally esters derived from alcohols ...

s. It is more expensive than other reagents for doing this, such as chlorosulfonic acid or

, 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 quaternary a ...

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 Mercerisation is a textile finishing treatment for cellulose fabric and yarn, mainly cotton and flax, which improves dye uptake and tear strength, reduces fabric shrinkage, and imparts a silk-like luster. Development The process was devise ...

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 (chemistry), alcohol. It is a colorless liquid that is poorly soluble in water but soluble in most organic solvents. It is prod ...

Applications

Sulfamic acid is mainly a precursor to sweet-tasting compounds. Reaction with

cyclohexylamine Cyclohexylamine is an organic compound, belonging to the aliphatic amine class. It is a colorless liquid, although, like many amines, samples are often colored due to contaminants. It has a fishy odor and is miscible with water. Like other amines, ...

followed by addition of

NaOH Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

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 been ...

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 bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

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 AIDS, acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the ...

(HIV)

reverse transcriptase inhibitor Reverse-transcriptase inhibitors (RTIs) are a class of antiretroviral drugs used to treat HIV infection or AIDS, and in some cases hepatitis B. RTIs inhibit activity of reverse transcriptase, a viral DNA polymerase that is required for replicati ...

HIV protease inhibitor Protease inhibitors (PIs) are medications that act by interfering with enzymes that cleave proteins. Some of the most well known are antiviral drugs widely used to treat HIV/AIDS and hepatitis C. These protease inhibitors prevent viral replicat ...

s (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 catalysis, catalyses the follow ...

and carbonic anhydrase inhibitors), anti

epileptic Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...

drugs, and

weight loss drug Anti-obesity medication or weight loss medications are pharmacological agents that reduce or control weight. These medications alter one of the fundamental processes of the human body, weight regulation, by altering either appetite, or absor ...

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, removin ...

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 typicall ...

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, porcelain ...

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 old ...

, 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 Acid strength is the tendency of an acid, symbol ...

, 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 more ...

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 Bleach is the generic name for any chemical product that is used industrially or domestically to remove color (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...

, it does not form

chlorine Chlorine is a chemical element with the Symbol (chemistry), 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 betwee ...

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. Glycerides ar ...

process * Dye 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 compo ...

manufacturing *

Herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...

* Descalant for scale removal * Coagulator for

urea-formaldehyde resin Urea-formaldehyde (UF), also known as urea-methanal, so named for its common synthesis pathway and overall structure, is a nontransparent thermosetting resin or polymer. It is produced from urea and formaldehyde. These resins are used in adhesive ...

s * Ingredient in fire extinguishing media. Sulfamic acid is the main raw material for

ammonium sulfamate Ammonium sulfamate (or ammonium sulphamate) is a white crystalline solid, readily soluble in water. It is commonly used as a broad spectrum herbicide, with additional uses as a compost accelerator, flame retardant and in industrial processes. Man ...

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 reduction of cations of that metal by means of a direct electric current. The part to be ...

. *Used to separate nitrite ions from mixture of nitrite and nitrate ions( NO₃⁻+ NO₂⁻) during qualitative analysis of nitrate by

Brown Ring test A Nitrate Test is a chemical test used to determine the presence of nitrate ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in ...

. * Obtaining

deep eutectic solvent Deep eutectic solvents or DESs are solutions of Lewis or Brønsted acids and bases which form a eutectic mixture. Deep eutectic solvents are highly tunable through varying the structure or relative ratio of parent components and thus have a wide va ...

s 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 urea ...

, a

, and sulfamic acid.