Cyanuric acid
Encyclopedia
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 bleach
es, disinfectants, and herbicides. In 1997, worldwide production was 160 million kilograms.
of the elusive species cyanic acid, HOCN. The two structures
shown in the infobox readily interconvert; that is, they are tautomer
s. However, mixture with melamine
forms melamine cyanurate
, which locks cyanuric acid in the tri-keto tautomer and makes melamine cyanurate insoluble in water. The triol tautomer, which may have aromatic character, predominates in solution. The hydroxyl
(-OH) groups assume phenolic
character. Deprotonation with base affords a series of cyanurate salt
s:
in 1829 by the thermal decomposition of urea
and uric acid
. The current industrial route to CYA entails the thermal decomposition
of urea, with release of ammonia. The conversion commences at approximately 175 °C:
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.
, biuret
, and triuret:
One impurity in the production of CYA is ammelide
, especially as the reaction temperature exceeds 190 °C:
3 H2N-CO-NH-CO-NH2 → [C(O)]2(CNH2)(NH)2N + 2 NH3 + H2O
The first appearance of ammelamide 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.
Melamine
, [C(NH2)N]3, formation occurs between 325 and 350 °C and only in very small quantities.
This species is typically converted to its sodium salt, sodium dichloro-s-triazinetrione. Further chlorination gives trichloroisocyanuric acid, [C(O)NCl]3. These N-chloro compounds serve as disinfectants and algicides for swimming pool water. It stabilizes the chlorine in the pool and prevents the chlorine from being quickly consumed by sunlight.
This test 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.
(NPN) additives used in animal feed and drinking water. 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
.
, 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 renal failure (see Analysis section above).
The 50% oral median lethal dose (LD50) is 7700 mg/kg in rats.
However, when cyanuric acid is administered together with melamine
(which by itself is another low-toxicity substance), they may form extremely insoluble crystals, leading to formation of kidney stones and potentially causing kidney failure and death
-- as evidenced in dogs and cats during the 2007 pet food contamination
and in children during the 2008 Chinese milk scandal
cases.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
(CNOH)3. Like many industrially useful chemicals, this triazine
Triazine
A triazine is one of three organic chemicals, isomeric with each other, whose molecular formula is 333 and whose empirical formula is CHN.- Structure :...
has many synonyms. This white, odorless solid finds use as a precursor or a component of bleach
Bleach
Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...
es, disinfectants, and herbicides. In 1997, worldwide production was 160 million kilograms.
Properties
Cyanuric acid is the cyclic trimerTrimer (chemistry)
In chemistry, a trimer is a product derived from three identical precursors. Trimers are typically cyclic. Chemical compounds that often trimerise are aliphatic isocyanates and cyanic acids. Often, trimerization competes with polymerization....
of the elusive species cyanic acid, HOCN. The two structures
Chemical structure
A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as...
shown in the infobox readily interconvert; that is, they are tautomer
Tautomer
Tautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. This reaction commonly results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond...
s. However, mixture with melamine
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
forms melamine cyanurate
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 melamine cyanurate...
, which locks cyanuric acid in the tri-keto tautomer and makes melamine cyanurate insoluble in water. The triol tautomer, which may have aromatic character, predominates in solution. The hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
(-OH) groups assume phenolic
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
character. Deprotonation with base affords a series of cyanurate salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s:
- [C(O)NH]3
[C(O)NH]2[C(O)N]- + H+ (Ka = 10−7) - [C(O)NH]2[C(O)N]-
[C(O)NH][C(O)N]22- + H+ (Ka = 10−11) - [C(O)NH][C(O)N]22-
[C(O)N]33- + H+ (Ka = 10−14)
Synthesis
Cyanuric acid (CYA) was first synthesized by Friedrich WöhlerFriedrich Wöhler
Friedrich Wöhler was a German chemist, best known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, which belonged to aau...
in 1829 by the thermal decomposition of urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
and uric acid
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 created when the body breaks down purine nucleotides. High blood concentrations of uric acid...
. The current industrial route to CYA entails the thermal decomposition
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...
of urea, with release of ammonia. The conversion commences at approximately 175 °C:
- 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
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
followed by crystallization. Acid waste streams from plants producing these materials contain cyanuric acid and on occasion, dissolved amino-substituted triazines, namely, ammeline
Ammeline
Ammeline is a triazine. It is the hydrolysis product of melamine.-Synthesis:Ammeline can be synthesized by the pyrolysis of urea, or the condensation reaction amond 2 moles of dicyandiamide with 1 mole of biuret....
, ammelide
Ammelide
Ammelide is a triazine and the hydrolysis product of ammeline.-Synthesis:Ammelide can be obtained by heating dicyandiamide with aqueous ammonia at 160-170°C...
, and melamine
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
. In one method, an ammonium sulfate
Ammonium sulfate
Ammonium sulfate , 2SO4, is an inorganic salt with a number of commercial uses. The most common use is as a soil fertilizer. It contains 21% nitrogen as ammonium cations, and 24% sulfur as sulfate anions...
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.
Intermediates and impurities
Intermediates in the dehydration include both isocyanic acidIsocyanic acid
Isocyanic acid is an inorganic compound with the formula HNCO, discovered in 1830 by Liebig and Wöhler. This colourless substance is volatile and poisonous, with a boiling point of 23.5 °C...
, biuret
Biuret
Biuret is a chemical compound with the chemical formula H2NCNHCNH2. It is the result of condensation of two molecules of urea and is a problematic impurity in urea-based fertilizers. This white solid is soluble in hot water....
, 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
One impurity in the production of CYA is ammelide
Ammelide
Ammelide is a triazine and the hydrolysis product of ammeline.-Synthesis:Ammelide can be obtained by heating dicyandiamide with aqueous ammonia at 160-170°C...
, especially as the reaction temperature exceeds 190 °C:
3 H2N-CO-NH-CO-NH2 → [C(O)]2(CNH2)(NH)2N + 2 NH3 + H2O
The first appearance of ammelamide 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.
Melamine
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
, [C(NH2)N]3, formation occurs between 325 and 350 °C and only in very small quantities.
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:- [C(O)NH]3 + 2 Cl2 + 2 NaOH → [C(O)NCl]2[C(O)NH]
This species is typically converted to its sodium salt, sodium dichloro-s-triazinetrione. Further chlorination gives trichloroisocyanuric acid, [C(O)NCl]3. These N-chloro compounds serve as disinfectants and algicides for swimming pool water. It stabilizes the chlorine in the pool and prevents the chlorine from being quickly consumed by sunlight.
Precursors to crosslinking agents
Because of their trifunctionality, CYA is a precursor to crosslinking agents, especially for polyurethane resins.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 works because melamine combines with the cyanuric acid in the water to form a fine, insoluble, white precipitate (melamine cyanurate
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 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.
Animal feed
FDA permits a certain amount of cyanuric acid to be present in some non-protein nitrogenNon-protein nitrogen
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...
(NPN) additives used in animal feed and drinking water. Cyanuric acid has been used as NPN. For example, Archer Daniels Midland
Archer Daniels Midland
The Archer Daniels Midland Company is a conglomerate headquartered in Decatur, Illinois. ADM operates more than 270 plants worldwide, where cereal grains and oilseeds are processed into products used in food, beverage, nutraceutical, industrial and animal feed markets worldwide.ADM was named the...
manufactures an NPN supplement for cattle, which contains biuret
Biuret
Biuret is a chemical compound with the chemical formula H2NCNHCNH2. It is the result of condensation of two molecules of urea and is a problematic impurity in urea-based fertilizers. This white solid is soluble in hot water....
, triuret, cyanuric acid and urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
.
2007 pet food recalls
Cyanuric acid is implicated in connection to the 2007 pet food recalls2007 pet food recalls
The 2007 pet food recalls comprise the contamination and wide recall of many brands of cat and dog foods beginning in March 2007, and the ensuing developments involving the human food supply. The recalls in North America, Europe, and South Africa came in response to reports of renal failure in pets...
, 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
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
forms poorly soluble crystals which can cause renal failure (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 administered together with melamine
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
(which by itself is another low-toxicity substance), they may form extremely insoluble crystals, leading to formation of kidney stones and potentially causing kidney failure and death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
-- as evidenced in dogs and cats during the 2007 pet food contamination
2007 pet food recalls
The 2007 pet food recalls comprise the contamination and wide recall of many brands of cat and dog foods beginning in March 2007, and the ensuing developments involving the human food supply. The recalls in North America, Europe, and South Africa came in response to reports of renal failure in pets...
and in children during the 2008 Chinese milk scandal
2008 Chinese milk scandal
The 2008 Chinese milk scandal was a food safety incident in the People's Republic of China, involving milk and infant formula, and other food materials and components, adulterated with melamine....
cases.
External links
- Oregon Veterinary Medical Association (OVMA) Pet Food Contamination Page - News & developments updated regularly