Cyanuric acid

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Cyanuric acid
Cyanuric acid.png
Ball-and-stick model of the triol tautomer Cyanuric-acid-triol-3D-balls.png
Ball-and-stick model of the triol tautomer
Cyanuric (triol) tautomer
Ball-and-stick model of the trione tautomer Cyanuric-acid-from-xtal-3D-balls.png
Ball-and-stick model of the trione tautomer
Isocyanuric (trione) tautomer
Names
Preferred IUPAC name
1,3,5-Triazinane-2,4,6-trione [1]
Other names
1,3,5-Triazine-2,4,6(1H,3H,5H)-trione [1]
1,3,5-Triazinetriol
s-Triazinetriol
s-Triazinetrione
Tricarbimide
Isocyanuric acid
Pseudocyanuric acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.003.290 OOjs UI icon edit-ltr-progressive.svg
KEGG
PubChem CID
RTECS number
  • XZ1800000
UNII
  • InChI=1S/C3H3N3O3/c7-1-4-2(8)6-3(9)5-1/h(H3,4,5,6,7,8,9) Yes check.svgY
    Key: ZFSLODLOARCGLH-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C3H3N3O3/c7-1-4-2(8)6-3(9)5-1/h(H3,4,5,6,7,8,9)
    Key: ZFSLODLOARCGLH-UHFFFAOYAR
  • Cyanuric (triol) tautomer:Oc1nc(O)nc(O)n1
  • Isocyanuric (trione) tautomer:O=C1NC(=O)NC(=O)N1
Properties
C3H3N3O3
Molar mass 129.07 g/mol
Appearancewhite crystalline powder
Density 1.75 g/cm3
Melting point 320–360 °C (608–680 °F; 593–633 K) decomposes
0.27 g/100 ml (25 °C)
-61.5·10−6 cm3/mol
Hazards
Safety data sheet (SDS) ICSC 1313
Related compounds
Related triazines
Cyanuric fluoride
Cyanuric chloride
Cyanuric bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Cyanuric acid or 1,3,5-triazine-2,4,6-triol is a chemical compound with the formula (CNOH)3. Like many industrially useful chemicals, this triazine has many synonyms. This white, odorless solid finds use as a precursor or a component of bleaches, disinfectants, and herbicides. In 1997, worldwide production was 160 000 tonnes. [2]

Contents

Properties and synthesis

Properties

Cyanuric acid can be viewed as the cyclic trimer of the elusive chemical species cyanic acid, HOCN. The ring can readily interconvert between several structures via lactam-lactim tautomerism. Although the triol tautomer may have aromatic character, the keto form predominates in solution. [3] The hydroxyl (-OH) groups assume phenolic character. Deprotonation with base affords a series of cyanurate salts:

[C(O)NH]3 ⇌ [C(O)NH]2[C(O)N] + H+ (pKa = 6.88) [4]
[C(O)NH]2[C(O)N] ⇌ [C(O)NH][C(O)N]22− + H+ (pKa = 11.40)
[C(O)NH][C(O)N]22− ⇌ [C(O)N]33− + H+ (pKa = 13.5)

Cyanuric acid is noted for its strong interaction with melamine, forming insoluble melamine cyanurate. This interaction locks the cyanuric acid into the tri-keto tautomer.

Synthesis

Cyanuric acid (CYA) was first synthesized by Friedrich Wöhler in 1829 by the thermal decomposition of urea and uric acid. [5] The current industrial route to CYA entails the thermal decomposition of urea, with release of ammonia. The conversion commences at approximately 175 °C: [2]

3 H2N-CO-NH2 → [C(O)NH]3 + 3 NH3

CYA crystallizes from water as the dihydrate.

Cyanuric acid can be produced by hydrolysis of crude or waste melamine followed by crystallization. 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 solution is heated to the "boil" and treated with a stoichiometric amount of melamine, by which means the cyanuric acid present precipitates as melamine-cyanuric acid complex. The various waste streams containing cyanuric acid and amino-substituted triazines may be combined for disposal, and during upset conditions undissolved cyanuric acid may be present in the waste streams. [6] [7]

Intermediates and impurities

Intermediates in the dehydration include both isocyanic 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 lower rate than that of CYA or ammelide.

3 H2N-CO-NH-CO-NH2 → [C(O)]2(CNH2)(NH)2N + 2 NH3 + H2O

Melamine, [C(NH2)N]3, formation occurs between 325–350 °C and only in very small quantities. [8]

N-substituted isocyanurates from isocyanates

N-substituted isocyanurates can be synthesised by the trimerisation of isocyanates. This is utilised industrially in the formation of polyisocyanurates.

Applications

Cyanuric acid is used as a chlorine stabilizer / buffer in swimming pools. It binds to free chlorine and releases it slowly, extending the time needed to deplete each dose of sanitizer. A chemical equilibrium exists between the acid with free chlorine and its chlorinated form. [9]

Precursors to chlorinated cyanurates

Cyanuric acid is mainly used as a precursor to N-chlorinated cyanurates, which are used to disinfect water. The dichloro derivative is prepared by direct chlorination:

This species is typically converted to its sodium salt, sodium dichloro-s-triazinetrione. Further chlorination gives trichloroisocyanuric acid, [C(O)NCl]3. [2]

These N-chloro compounds serve as disinfectants and algicides for swimming pool water. [2] The aforementioned equilibrium stabilizes the chlorine in the pool and prevents the chlorine from being quickly consumed by sunlight. [9]

Precursors to crosslinking agents

Because of its trifunctionality, CYA is a precursor to crosslinking agents, especially for polyurethane resins and polyisocyanurate thermoset plastics.

The experimental antineoplastic drug teroxirone (triglycidyl isocyanurate) is formed by reacting cyanuric acid with 3 equivalents of epichlorohydrin. It works by cross-linking DNA. [10]

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 of the reacted sample quantifies the CYA concentration. Referenced in 1957, this test [11] works because melamine combines with the cyanuric acid in the water to form a fine, insoluble, white precipitate (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. [12]

Animal feed

FDA permits a certain amount of cyanuric acid to be present in some non-protein nitrogen (NPN) additives used in animal feed and drinking water. [13] Cyanuric acid has been used as NPN. For example, Archer Daniels Midland manufactures an NPN supplement for cattle, which contains biuret, triuret, cyanuric acid and urea. [14]

2007 pet food recalls

Cyanuric acid is implicated in connection to the 2007 pet food recalls, 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 (see Analysis section above).

Safety

Cyanuric acid is classified as "essentially nontoxic". [2] The 50% oral median lethal dose (LD50) is 7700 mg/kg in rats. [15]

However, when cyanuric acid is present together with melamine (which by itself is another low-toxicity substance), it will form an insoluble and rather nephrotoxic complex, [16] as evidenced in dogs and cats during the 2007 pet food contamination and in children during the 2008 Chinese milk scandal 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. It was found in a guano deposit in Chile. It is very rare. [17]

Related Research Articles

Urea, also called carbamide, is an organic compound with chemical formula CO(NH2)2. This amide has two amino groups joined by a carbonyl functional group. It is thus the simplest amide of carbamic acid.

<span class="mw-page-title-main">Melamine</span> Fire-resistant chemical used in dinnerware, insulation, and cleaning products

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 66% nitrogen by mass, and its derivatives have fire-retardant properties due to its release of nitrogen gas when burned or charred. Melamine can be combined with formaldehyde and other agents to produce melamine resins. Such resins are characteristically durable thermosetting plastic used in high pressure decorative laminates such as Formica, melamine dinnerware including cooking utensils, plates, plastic products, laminate flooring, and dry erase boards. Melamine foam is used as insulation, soundproofing material and in polymeric cleaning products, such as Magic Eraser.

In chemistry, a trimer is a molecule or polyatomic anion formed by combination or association of three molecules or ions of the same substance. In technical jargon, a trimer is a kind of oligomer derived from three identical precursors often in competition with polymerization.

<span class="mw-page-title-main">Triazine</span> Aromatic, heterocyclic compound

Triazines are a class of nitrogen-containing heterocycles. The parent molecules' molecular formula is C3H3N3. They exist in three isomeric forms, 1,3,5-triazines being common.

<span class="mw-page-title-main">Sulfamic acid</span> Chemical compound

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, sulfur trioxide, sulfur dioxide and nitrogen.

<span class="mw-page-title-main">Potassium cyanate</span> Chemical compound

Potassium cyanate is an inorganic compound with the formula KOCN. It is a colourless solid. It is used to prepare many other compounds including useful herbicide. Worldwide production of the potassium and sodium salts was 20,000 tons in 2006.

<span class="mw-page-title-main">Biuret</span> Chemical compound

Biuret is a chemical compound with the chemical formula HN(CONH2)2. 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 R1R2N−C(=O)−N(R3)−C(=O)−NR4R5, where R1, R2, R3, R4 and R5 are hydrogen, organyl or other groups. Also known as carbamylurea, it results from the condensation of two equivalents of urea. It is a common undesirable impurity in urea-based fertilizers, as biuret is toxic to plants.

<span class="mw-page-title-main">Isocyanic acid</span> Chemical compound (H–N=C=O)

Isocyanic acid is a chemical compound with the structural formula HNCO, which is often written as H−N=C=O. It is a colourless, volatile and poisonous substance, with a boiling point of 23.5 °C. It is the predominant tautomer and an isomer of cyanic acid (aka. cyanol).

<span class="mw-page-title-main">Azodicarbonamide</span> Chemical compound

Azodicarbonamide, ADCA, ADA, or azo(bis)formamide, is a chemical compound with the molecular formula C2H4O2N4. It is a yellow to orange-red, odorless, crystalline powder. It is sometimes called a 'yoga mat' chemical because of its widespread use in foamed plastics. It was first described by John Bryden in 1959.

1,3,5-Triazine, also called s-triazine, is an organic chemical compound with the formula (HCN)3. It is a six-membered heterocyclic aromatic ring, one of several isomeric triazines. S-triazine—the "symmetric" isomer—and its derivatives are useful in a variety of applications.

Monochloramine, often called chloramine, is the chemical compound with the formula NH2Cl. Together with dichloramine (NHCl2) and nitrogen trichloride (NCl3), it is one of the three chloramines of ammonia. It is a colorless liquid at its melting point of −66 °C (−87 °F), but it is usually handled as a dilute aqueous solution, in which form it is sometimes used as a disinfectant. Chloramine is too unstable to have its boiling point measured.

Carbamic acid, which might also be called aminoformic acid or aminocarboxylic acid, is the chemical compound with the formula H2NCOOH. It can be obtained by the reaction of ammonia NH3 and carbon dioxide CO2 at very low temperatures, which also yields ammonium carbamate [NH4]+[NH2CO2]. The compound is stable only up to about 250 K (−23 °C); at higher temperatures it decomposes into those two gases. The solid apparently consists of dimers, with the two molecules connected by hydrogen bonds between the two carboxyl groups –COOH.

<span class="mw-page-title-main">Melem</span> Chemical compound

In chemistry, melem is a compound with formula C
6
N
10
H
6
; specifically, 2,5,8-triamino-heptazine or 2,5,8-triamino-tri-s-triazine, whose molecule can be described as that of heptazine with the three hydrogen atoms replaced by amino groups. It is a white crystalline solid.

Non-protein nitrogen 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 lower cost compared to plant and animal proteins, their inclusion in a diet can result in economic gain, but at too high levels cause a depression in growth and possible ammonia toxicity, as microbes convert NPN to ammonia first before using that to make protein.

<span class="mw-page-title-main">Melamine cyanurate</span> Chemical compound

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 melamine cyanurate. The complex is held together by an extensive two-dimensional network of hydrogen bonds between the two compounds, reminiscent of the guanine–cytosine base pairs found in DNA. Melamine cyanurate forms spoke-like crystals from aqueous solutions and has been implicated as a causative agent for toxicity seen in the Chinese protein export contamination and the 2007 pet food recall.

<span class="mw-page-title-main">Triuret</span> Chemical compound

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 planar molecule. The central carbonyl is hydrogen-bonded to both terminal amino groups.

<span class="mw-page-title-main">Ureas</span>

In chemistry, ureas are a class of organic compounds with the formula (R2N)2CO where R = H, alkyl, aryl, etc. Thus, in addition to describing the specific chemical compound urea ((H2N)2CO), urea is the name of a functional group that is found in many compounds and materials of both practical and theoretical interest. Generally ureas are colorless crystalline solids, which, owing to the presence of fewer hydrogen bonds, exhibit melting points lower than that of urea itself.

<span class="mw-page-title-main">Cyanuric bromide</span> Chemical compound

Cyanuric bromide is a heterocyclic compound with formula C3N3Br3. It contains a six-membered ring of alternating nitrogen and carbon atoms, with a bromine atom attached to each carbon. It is formed by the spontaneous trimerisation of cyanogen bromide.

<span class="mw-page-title-main">Copper(II) cyanurate</span> Chemical compound

Copper(II) cyanurate (C3HCuN3O3) is an organic compound. It has very few uses, and is more often encountered accidentally, rather than actually synthesised.

<span class="mw-page-title-main">Bosch-Meiser process</span>

The Bosch–Meiser process is an industrial process, which was patented in 1922 and named after its discoverers, the German chemists Carl Bosch and Wilhelm Meiser for the large-scale manufacturing of urea, a valuable nitrogenous chemical.

References

  1. 1 2 Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 733. doi:10.1039/9781849733069-FP001. ISBN   978-0-85404-182-4.
  2. 1 2 3 4 5 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
  3. Pérez-Manríquez, Liliana; Cabrera, Armando; Sansores, Luis Enrique; Salcedo, Roberto (7 September 2010). "Aromaticity in cyanuric acid". Journal of Molecular Modeling. 17 (6): 1311–1315. doi:10.1007/s00894-010-0825-2. PMC   3102184 . PMID   20820829. Open Access logo PLoS transparent.svg
  4. "Dissociation constants of organic acids and bases" CRC Handbook of Chemistry and physics, Internet Version 2005 (85th ed.)
  5. Wöhler, F. (1829) "Ueber die Zersetzung des Harnstoffs und der Harnsäure durch höhere Temperatur," (On the decomposition of urea and uric acid at higher temperature), Annalen der Physik und Chemie, 2nd series, 15 : 619-630.
  6. "Process for preparing pure cyanuric acid". July 14, 1981. Retrieved 2007-12-10.
  7. "High pressure thermal hydrolysis process to decompose triazines in acid waste streams". March 22, 1977. Retrieved 2007-12-10.
  8. Shaber, Peter M.; et al. (August 1999). "Study of the thermal decomposition of urea (pyrolysis) reaction and importance to cyanuric acid production" (PDF). American Laboratory: 13–21. Archived from the original (PDF) on 2007-09-28. Retrieved 2007-05-08.
  9. 1 2 "What Is Pool Stabilizer". 2021-05-18. Retrieved 2022-07-27.
  10. M. Budnowski, Angew. Chem., 7, 827 (1968).
  11. "Merck Turbidity Test". Merck. June 6, 2003. Archived from the original on July 1, 2007. Retrieved 2007-05-06. (dead link 8 April 2018)
  12. Panuwet P, Wade EL, Nguyen JV, Montesano MA, Needham LL, Barr DB. Quantification of cyanuric acid residue in human urine using high performance liquid chromatography-tandem mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci 2010 878(28):2916-2922.
  13. "21CFR573.220 Feed-grade biuret". U.S. Food and Drug Administration. April 1, 2006. Retrieved 2007-05-06.
  14. "Roughage Buster Plus: ingredients". Archer Daniels Midland. Archived from the original on 2007-02-12. Retrieved 2007-05-06.
  15. U.S. Food and Drug Administration, "Interim Melamine and Analogues Safety/Risk Assessment; Availability", Archived December 16, 2007, at the Wayback Machine Federal Register: May 30, 2007 (Volume 72, Number 103). Accessed 2008-09-27.
  16. "Melamine and Cyanuric Acid Interaction May Play Part in Illness and Death from Recalled Pet Food" Archived May 18, 2007, at the Wayback Machine , American Veterinary Medical Association (AVMA), Press Release, May 1, 2007. Accessed 2008-09-27.
  17. Mindat, http://www.mindat.org/min-42755.html