Cyanuric acid or 1,3,5-triazine-2,4,6-triol is a chemical compound with the formula3. 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 million kilograms.
Cyanuric acid was first synthesized by Friedrich Wöhler 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.
Intermediates and impurities
Intermediates in the dehydration include both isocyanic acid, biuret, and triuret: One impurity in the production of CYA is ammelide, especially if the reaction temperature exceeds 190 °C: 3 H2N-CO-NH-CO-NH2 → 22N + 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, 3, formation occurs between 325 and 350 °C and only in very small quantities.
Applications
Cyanuric acid is used as a chlorine stabilizer in swimming pools. It binds to free chlorine and releases it slowly, extending the time needed to deplete each dose of sanitizer. The antineoplastic drug teroxirone, is formed by reacting cyanuric acid with 3 equivalents of epichlorohydrin.
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, 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 its trifunctionality, CYA is a precursor to crosslinking agents, especially for polyurethane resins and polyisocyanurate thermoset plastics.
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 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 nitrogen 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.
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.
Safety
Cyanuric acid is classified as "essentially nontoxic". The 50% oral median lethal dose is 7700 mg/kg in rats. However, when cyanuric acid is present together with melamine, it will form a insoluble and rather nephrotoxic complex, as evidenced in dogs and cats during the 2007 pet food contamination and in children during the 2008 Chinese milk scandal cases.
Natural occurrence
Impure copper salt of the acid, with the formula Cu22, is currently the only known isocyanurate mineral, called joanneumite. It was found in a guano deposit in Chile. It is very rare.
