Cyanuric and Isocyanuric Acids

Abstract Cyanuric acid has been known for over 200 years, but achieved commercial importance only in the mid‐1950s primarily via its derivatives. The chemistry of cyanuric acid is diversified because of multiple reaction sites. N ‐Chlorination of cyanuric acid produces chloroisocyanurates that are widely used as disinfectants, sanitizers, and bleaches. The triallyl‐ and tris(2‐hydroxyethyl) derivatives are employed as cross‐linking and curing agents, and tris(2,3‐epoxypropyl)isocyanurate is used in weather‐resistant powder coatings. Melamine cyanurate finds significant use as a fire retardant in plastics. Considerable interest has developed in the use of cyanuric acid for reduction of nitrogen oxides in exhaust gases from combustion of oil, gas, and coal. Nomenclature is based on the keto‐enol tautomers. The trihydroxy form is variously designated cyanuric acid, s ‐triazine‐2,4,6‐triol or 2,4,6‐trihydroxy‐ s ‐triazine. The trioxo structure, or s ‐triazine‐2,4,6(1 H ,3 H ,5 H )‐trione is the basis for the isocyanuric acid nomenclature. The triazine‐based system is preferred in the scientific literature and is used by government regulatory agencies; however, the less cumbersome (iso)cyanurate designations persist in commerce. The keto form normally predominates in cases of keto‐enol tautomerism. In alkaline solution, the anion formed is that of the hydroxy tautomer. Through common usage, both forms are collectively called cyanuric acid (CA).