Cyanuric acid

Cyanuric acid or 1,3,5-triazine-2,4,6-triol is an chemical compound with the formula (CNOH)3. Like many industrially useful chemicals, this triazine has many synonyms. This white solid is the cyclic trimer of cyanic acid, HOCN. It finds use as a precursor or a component of bleach, disinfectants, and herbicides.

Chemical and properties
Cyanuric acid is odorless, hygroscopic, and commonly used as a crystalline powder. On heating above 320 °C, the solid decomposes to toxic nitrogen oxides and cyanic acid.

The two chemical structures shown in the infobox readily interconvert: they are tautomers. The triol tautomer has aromatic character. Consequently, the hydroxyl (-OH) groups assume phenolic character, becoming more acidic than hydroxyl groups in typical alcohols. Deprotonation with base affords a cyanurate salt.

Synthesis
Cyanuric acid (CYA) was first synthesized by Wöhler in 1829 by the thermal decomposition of urea and uric acid. The current industrial route to CYA entails the thermal decomposition of urea (thermal decomposition). The production of CYA and ammelide commence simultaneously at approximately 175 °C, in the following two reactions involving both biuret and isocyanic acid as intermediates:
 * H2N-CO-NH-CO-NH2(m) + HNCO(g) → CYA(s) + NH3(g)
 * H2N-CO-NH-CO-NH2(m) + HNCO(g) → ammelide(s) + H2O(g)

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, by the following reaction:
 * H2N-CO-NH-CO-NH2(m) + HNCO(g) → ammeline + 2 H2O

The first appearance of melamine occurs between 325 and 350 °C and only in very small quantities.

Cyanuric acid can be produced by hydrolysis of crude or waste melamine and isolating the pure cyanuric acid product by crystallizing out and filtering off the cyanuric acid. 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 cyanurate. 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.

Applications
Cyanuric acid is used as a stabilizer in recreational water treatment to minimize the decomposition of hypochlorous acid by sunlight in outdoor swimming pools and hot tubs. It achieves this by absorbing UV radiation.

Chlorinated derivatives of cyanuric acid, such as trichloro-s-triazinetrione and sodium dichloro-s-triazinetrione, are used as algacides or microbiocides in swimming pool water and large scale water systems in industry.

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.

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. 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.

2007 pet food recalls
Cyanuric acid is implied 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 together with melamine forms poorly soluble crystals which can cause renal failure. The evidence is as yet inconclusive.