Cyanuric acid  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 million kilograms. Cyanuric acid can be viewed as the cyclic trimer of the elusive species cyanic acid, HOCN. The ring can readily interconvert between two structures via keto–enol tautomerism. 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 salts:  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. Cyanuric acid (CYA) 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 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 → [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.