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 betwee ...

(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 (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...

es, disinfectants, and

herbicides 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 ...

. In 1997, worldwide production was 160 000

tonnes The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United States ...

.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 species

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 substance, with a boiling point of 23.5 °C. It is the predominant tautomer of cyanic acid (). ...

, 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 chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

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 called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...

ic character. Deprotonation with base affords a series of cyanurate

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

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 of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 67% nitrogen by mass, and its derivatives have fire retardant properties due t ...

, forming insoluble melamine cyanurate. This interaction locks the cyanuric acid into the tri-keto

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 ...

Synthesis

Cyanuric acid (CYA) was first synthesized by

Friedrich Wöhler Friedrich Wöhler () FRS(For) HonFRSE (31 July 180023 September 1882) was a German chemist known for his work in inorganic chemistry, being the first to isolate the chemical elements beryllium and yttrium in pure metallic form. He was the firs ...

in 1829 by the thermal decomposition of

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 ...

and

uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the 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 metabolic breakdown of ...

. The current industrial route to CYA entails the

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

of urea, with release of

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 ...

. 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 the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposi ...

. Acid waste streams from plants producing these materials contain cyanuric acid and on occasion, dissolved amino-substituted triazines, namely, ammeline, 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 refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equal ...

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 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 s ...

-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 substance, with a boiling point of 23.5 °C. It is the predominant tautomer of cyanic acid (). ...

, biuret, and triuret: : 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 ammeline occurs prior to 225 °C and is suspected also to occur from decomposition of biuret but is produced at a slower 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.

Applications

Cyanuric acid is used as a

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 ...

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 or other leisure activities. Pools can be built into the ground (in-ground pools) or built ...

s. It binds to

free chlorine Sodium hypochlorite (commonly known in a dilute solution as bleach) is an Inorganic chemistry, inorganic chemical compound with the chemical formula, formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may ...

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 st ...

. 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), a hypothesized genus of fossil birds that was composed of fossilized parts of unr ...

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 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 (C3Cl3N3O3). 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 s ...

, (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 a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...

Precursors to crosslinking agents

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

polyurethane Polyurethane (; often abbreviated PUR and PU) refers to 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, polyurethan ...

resins and

polyisocyanurate Polyisocyanurate (), also referred to as PIR, polyiso, 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 propor ...

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 miscible with most polar organi ...

. 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 water quality. Fluids can ...

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, insoluble, white

precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...

( melamine cyanurate) 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 in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...

Animal feed

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

non-protein nitrogen Non-protein nitrogen (or NPN) is a term used in animal nutrition to refer collectively to components such as urea, biuret, and ammonia, which are not proteins but can be converted into proteins by microbes in the ruminant stomach. Due to their lowe ...

(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 to ...

and

drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...

. 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, Illinois. The company operates more than 270 plants and 42 ...

manufactures an NPN supplement for cattle, which contains biuret, triuret, 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 ...

, 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 end-stage kidney disease, 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 failure is classified as eit ...

(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 solubil ...

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. Nephrotoxins ...

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 incidents in China, food safety incident in China. The scandal involved Sanlu Group, Sanlu Group's milk and infant formula along with other food materials and components being adultera ...

cases.

Natural occurrence

Impure copper salt of the acid, with the formula Cu(C₃N₃O₃H₂)₂(NH₃)₂, is currently the only known isocyanurate mineral, called joanneumite. It was found in a

guano Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...

deposit in

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

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

References

External links

* {{ICSC, 1313, 13
Oregon Veterinary Medical Association (OVMA) Pet Food Contamination Page
– News and developments updated regularly Lactims Triazines Imides Triketones Isocyanuric acids