Cyanuric acid or 1,3,5-triazine-2,4,6-triol is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

(CNOH)₃. Like many industrially useful chemicals, this

triazine Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is . They exist in three isomeric forms, 1,3,5-triazines being common. Structure The triazines have planar six-membered benzene-like ring but ...

has many synonyms. This white, odorless solid finds use as a precursor or a component of

bleach Bleach is the generic name for any chemical product that is used industrially or domestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically t ...

es, disinfectants, and

herbicide Herbicides (, ), also commonly known as weed killers, 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 f ...

s. In 1997, worldwide production was 160 000

tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...

s.Klaus Huthmacher, Dieter Most "Cyanuric Acid and Cyanuric Chloride" Ullmann's Encyclopedia of Industrial Chemistry" 2005, Wiley-VCH, Weinheim. doi 10.1002/14356007.a08 191

Properties and synthesis

Properties

Cyanuric acid can be viewed as the cyclic trimer of the elusive

chemical species Chemical species are a specific form of chemical substance or chemically identical molecular entities that have the same molecular energy level at a specified timescale. These entities are classified through bonding types and relative abundance of ...

cyanic acid Isocyanic acid is a chemical compound with the structural formula HNCO, which is often written as . It is a colourless, volatile and poisonous gas, condensing at 23.5 °C. It is the predominant tautomer and an isomer of cyanic acid ''(a ...

, HOCN. The ring can readily interconvert between several

structures A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

via lactam–lactim tautomerism. Although the triol tautomer may have

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

character, the keto form predominates in solution. The

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) groups assume

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

ic character. Deprotonation with base affords a series of cyanurate

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

s: : (O)NHsub>3 ⇌ (O)NHsub>2 (O)Nsup>− + H⁺ (pK_a = 6.88)"Dissociation constants of organic acids and bases" CRC Handbook of Chemistry and physics, Internet Version 2005 (85th ed.) : (O)NHsub>2 (O)Nsup>− ⇌ (O)NH (O)Nsub>2²⁻ + H⁺ (pK_a = 11.40) : (O)NH (O)Nsub>2²⁻ ⇌ (O)Nsub>3³⁻ + H⁺ (pK_a = 13.5) Cyanuric acid is noted for its strong interaction with

melamine Melamine is an organic compound with the formula C3H6N6. This white solid is a trimer (chemistry), trimer of cyanamide, with a 1,3,5-Triazine, 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass, and its derivatives ha ...

, forming insoluble

melamine cyanurate Melamine cyanurate, also known as melamine–cyanuric acid adduct or melamine–cyanuric acid complex, is a crystalline complex formed from a 1:1 mixture of melamine and cyanuric acid. The substance is not a salt despite its non-systematic name '' ...

. This interaction locks the cyanuric acid into the tri-keto

tautomer In chemistry, 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 reloca ...

. Melamine cyanurate is cited as an example of

supramolecular chemistry Supramolecular chemistry refers to the branch of chemistry concerning Chemical species, chemical systems composed of a integer, discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from w ...

Synthesis

Cyanuric acid (CYA) was first synthesized by

Friedrich Wöhler Friedrich Wöhler Royal Society of London, FRS(For) HonFRSE (; 31 July 180023 September 1882) was a German chemist known for his work in both organic chemistry, organic and inorganic chemistry, being the first to isolate the chemical elements be ...

in 1829 by the thermal decomposition of

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

and

uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the Chemical formula, formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the meta ...

. The current industrial route to CYA entails the

thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition of a substance caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic ...

of urea, with release of

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

. The conversion commences at approximately 175 °C: : 3 H₂N-CO-NH₂ → (O)NHsub>3 + 3 NH₃ CYA crystallizes from water as the dihydrate. Cyanuric acid can be produced by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of crude or waste

followed by

crystallization Crystallization is a process that leads to solids with highly organized Atom, atoms or Molecule, molecules, i.e. a crystal. The ordered nature of a crystalline solid can be contrasted with amorphous solids in which atoms or molecules lack regu ...

. Acid waste streams from plants producing these materials contain cyanuric acid and on occasion, dissolved amino-substituted triazines, namely,

ammeline Ammeline (4,6-diamino-2-hydroxy-1,3,5-triazine) is a triazine derivative. It is the hydrolysis product of melamine. Synthesis Ammeline can be synthesized by the pyrolysis of urea or the condensation reaction among 2 moles of dicyandiamide and 1 ...

, ammelide, and melamine. In one method, an

ammonium sulfate Ammonium sulfate (American English and international scientific usage; ammonium sulphate in British English); (NH4)2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen a ...

solution is heated to the "boil" and treated with a

stoichiometric Stoichiometry () is the relationships between the masses of reactants and products before, during, and following chemical reactions. Stoichiometry is based on the law of conservation of mass; the total mass of reactants must equal the total m ...

amount of melamine, by which means the cyanuric acid present precipitates as

melamine-cyanuric acid complex Melamine cyanurate, also known as melamine–cyanuric acid adduct or melamine–cyanuric acid complex, is a crystalline complex formed from a 1:1 mixture of melamine and cyanuric acid. The substance is not a salt despite its non-systematic name '' ...

. The various waste streams containing cyanuric acid and

amino In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

-substituted

s may be combined for disposal, and during upset conditions undissolved cyanuric acid may be present in the waste streams.

Intermediates and impurities

Intermediates in the dehydration include both

isocyanic acid Isocyanic acid is a chemical compound with the structural formula HNCO, which is often written as . It is a colourless, volatile and poisonous gas, condensing at 23.5 °C. It is the predominant tautomer and an isomer of cyanic acid ''( ...

biuret Biuret ( ) is a chemical compound with the chemical formula . It is a white solid that is soluble in hot water. A variety of organic derivatives are known. The term "biuret" also describes a family of organic compounds with the chemical formula , ...

, and

triuret Triuret is an organic compound with the formula (H2NC(O)NH)2CO. It is a product from the pyrolysis of urea. Triuret is a colorless, crystalline, hygroscopic solid, slightly soluble in cold water or ether, and more soluble in hot water. It is a pla ...

: : H₂N-CO-NH₂ → HNCO + NH₃ : H₂N-CO-NH₂ + HNCO → H₂N-CO-NH-CO-NH₂ : H₂N-CO-NH-CO-NH₂ + HNCO → H₂N-CO-NH-CO-NH-CO-NH₂ As temperature exceeds 190 °C, other reactions begin to dominate the process. The first appearance of

occurs prior to 225 °C and is suspected also to occur from decomposition of biuret but is produced at a lower rate than that of CYA or ammelide. : 3 H₂N-CO-NH-CO-NH₂ → (O)sub>2(CNH₂)(NH)₂N + 2 NH₃ + H₂O Melamine, (NH₂)Nsub>3, formation occurs between 325–350 °C and only in very small quantities.

N-substituted isocyanurates from isocyanates

N-substituted isocyanurates can be synthesised by the trimerisation of

isocyanate In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...

s. This is utilised industrially in the formation of

polyisocyanurate Polyisocyanurate (), also referred to as PIR, polyol, or ISO, is a thermoset plastic typically produced as a foam and used as rigid thermal insulation. The starting materials are similar to those used in polyurethane (PUR) except that the proport ...

Applications

Cyanuric acid is used as a

chlorine Chlorine is a chemical element; it has 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 between ...

stabilizer / buffer in

swimming pool A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable Human swimming, swimming and associated activities. Pools can be built into the ground (in-ground pools) or built abo ...

s. It binds to free chlorine and releases it slowly, extending the time needed to deplete each dose of

sanitizer A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than s ...

. A chemical equilibrium exists between the acid with free chlorine and its chlorinated form.

Precursors to chlorinated cyanurates

Cyanuric acid is mainly used as a

precursor Precursor or Precursors may refer to: *Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), hypothesized genus of fossil birds that was composed of fossilized parts of unre ...

to ''N''-chlorinated cyanurates, which are used to disinfect water. The dichloro derivative is prepared by direct chlorination: : (O)NHsub>3 + 2 Cl₂ + 2 NaOH → (O)NClsub>2 (O)NH+ 2 NaCl + 2 This species is typically converted to its sodium salt,

sodium dichloro-s-triazinetrione Sodium dichloroisocyanurate (INN: sodium troclosene, ''troclosenum natricum'' or NaDCC or SDIC) is a chemical compound widely used as a cleansing agent and disinfectant.. It is a colorless, water-soluble solid, produced as a result of reaction of ...

. Further chlorination gives

trichloroisocyanuric acid Trichloroisocyanuric acid is an organic compound with the formula (CONCl)3. It is used as an industrial disinfectant, bleaching agent and a reagent in organic synthesis. This white crystalline powder, which has a strong "chlorine odour," is somet ...

, (O)NClsub>3. These ''N''-chloro compounds serve as disinfectants and algicides for swimming pool water. The aforementioned equilibrium stabilizes the chlorine in the pool and prevents the chlorine from being quickly consumed by

sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...

Precursors to crosslinking agents

Because of its trifunctionality, CYA is a precursor to crosslinking agents, especially for

polyurethane Polyurethane (; often abbreviated PUR and PU) is a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane term ...

resins and

thermoset plastics. The experimental antineoplastic drug teroxirone (triglycidyl isocyanurate) is formed by reacting cyanuric acid with 3 equivalents of

epichlorohydrin Epichlorohydrin (abbreviated ECH) is an organochlorine compound and an epoxide. Despite its name, it is not a halohydrin. It is a colorless liquid with a pungent, garlic-like odor, moderately soluble in water, but miscibility, miscible with most p ...

. It works by cross-linking DNA.

Analysis

Testing for cyanuric acid concentration is commonly done with a turbidometric test, which uses a reagent, melamine, to precipitate the cyanuric acid. The relative

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of both water clarity and wa ...

of the reacted sample quantifies the CYA concentration. Referenced in 1957, this test (dead link 8 April 2018) works because melamine combines with the cyanuric acid in the water to form a fine, white

precipitate In an aqueous solution, precipitation is the "sedimentation of a solid material (a precipitate) from a liquid solution". The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemic ...

of the insoluble complex

that causes the water to cloud in proportion to the amount of cyanuric acid in it. More recently, a sensitive method has been developed for analysis of cyanuric acid in

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

Animal feed

FDA permits a certain amount of cyanuric acid to be present in some

non-protein nitrogen Nitrogen's effects on agriculture profoundly influence crop growth, soil fertility, and overall agricultural productivity, while also exerting significant impacts on the environment. Nitrogen is an element vital to many environmental processes. N ...

(NPN) additives used in

animal feed Animal feed is food given to domestic animals, especially livestock, in the course of animal husbandry. There are two basic types: fodder and forage. Used alone, the word ''feed'' more often refers to fodder. Animal feed is an important input ...

and

drinking water Drinking water or potable water is water that is safe for ingestion, either when drunk directly in liquid form or consumed indirectly through food preparation. It is often (but not always) supplied through taps, in which case it is also calle ...

. Cyanuric acid has been used as NPN. For example,

Archer Daniels Midland The Archer-Daniels-Midland Company, commonly known as ADM, is an American multinational food processing and commodities trading corporation founded in 1902 and headquartered in Chicago, Chicago, Illinois. The company operates more than 270 p ...

manufactures an NPN supplement for cattle, which contains

, cyanuric acid and

2007 pet food recalls

Cyanuric acid is implicated in connection to the

2007 pet food recalls Beginning in March 2007, there was a widespread recall of many brands of cat and dog foods due to contamination with melamine and cyanuric acid. The recalls in North America, Europe, and South Africa came in response to reports of kidney failure i ...

, the contamination and wide recall of many brands of cat and dog foods beginning in March 2007. Research has found evidence that cyanuric acid, a constituent of urine, together with melamine forms poorly soluble crystals which can cause

kidney failure Kidney failure, also known as renal failure or end-stage renal disease (ESRD), is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney fa ...

(see Analysis section above).

Safety

Cyanuric acid is classified as "essentially nontoxic". The 50% oral median lethal dose ( LD₅₀) is 7700 mg/kg in rats. However, when cyanuric acid is present together with

(which by itself is another low-toxicity substance), it will form an

insoluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

and rather

nephrotoxic Nephrotoxicity is toxicity in the kidneys. It is a poisonous effect of some substances, both toxic chemicals and medications, on kidney function. There are various forms, and some drugs may affect kidney function in more than one way. Nephrotoxin ...

complex, as evidenced in dogs and cats during the 2007 pet food contamination and in children during the

2008 Chinese milk scandal The 2008 Chinese milk scandal was a significant food safety incident in China. The scandal involved Sanlu Group's milk and infant formula along with other food materials and components being adulterated with the chemical melamine, which resu ...

cases.

Natural occurrence

An impure copper salt of the acid, with the formula Cu(C₃N₃O₃H₂)₂(NH₃)₂, is currently the only known isocyanurate mineral, called

joanneumite Joanneumite, confirmed as a new mineral in 2012, is the first recognized isocyanurate mineral, with the formula Cu(C3N3O3H2)2(NH3)2. Its crystal structure is identical to the structure of its synthetic analogue bis(isocyanurato)diamminecopper(II). ...

. It was found in a

guano Guano (Spanish from ) is the accumulated excrement of seabirds or bats. Guano is a highly effective fertiliser due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. Guano was also, to a le ...

deposit in

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

. It is very rare.Mindat, http://www.mindat.org/min-42755.html

References

External links

*
Oregon Veterinary Medical Association (OVMA) Pet Food Contamination Page
{{Webarchive, url=https://web.archive.org/web/20081020030853/http://www.oregonvma.org/news/recallnews.asp , date=2008-10-20 – News and developments updated regularly Lactims Triazines Trimers (chemistry) Imides Isocyanuric acids