Cyanuric acid chlorination

Cyanuric acid, chlorination, 58, 324 Cyanuric chloride, formation, use, 58,... 

In reahty the chemistry of breakpoint chlorination is much more complex and has been modeled by computer (21). Conversion of NH/ to monochloramine is rapid and causes an essentially linear increase in CAC with chlorine dosage. Further addition of chlorine results in formation of unstable dichloramine which decomposes to N2 thereby causing a reduction in CAC (22). At breakpoint, the process is essentially complete, and further addition of chlorine causes an equivalent linear increase in free available chlorine. Small concentrations of combined chlorine remaining beyond breakpoint are due primarily to organic chloramines. Breakpoint occurs slightly above the theoretical C1 N ratio (1.75 vs 1.5) because of competitive oxidation of NH/ to nitrate ion. Organic matter consumes chlorine and its oxidation also increases the breakpoint chlorine demand. Cyanuric acid does not interfere with breakpoint chlorination (23). 

Superchlorination typically refers to a dding FAC equal to 10 x ppm CAC, whereas shock treatment generally involves addition of 10 ppm FAC. The frequency of superchlorination or shock treatment depends on bather load and temperature. Calcium hypochlorite, because of its convenience, is widely used for superchlorination and shock treatment. Sodium hypochlorite, LiOCl, or chlorine gas are also used. Chloroisocyanurates are not recommended since their use would result in excessive cyanuric acid concentrations. 

Sta.bilizers. Cyanuric acid is used to stabilize available chlorine derived from chlorine gas, hypochlorites or chloroisocyanurates against decomposition by sunlight. Cyanuric acid and its chlorinated derivatives form a complex ionic and hydrolytic equilibrium system consisting of ten isocyanurate species. The 12 isocyanurate equilibrium constants have been determined by potentiometric and spectrophotometric techniques (30). Other measurements of two of the equilibrium constants important in swimming-pool water report significantly different and/or less precise results than the above study (41—43). A critical review of these measurements is given in Reference 44. 

A plot of species distribution for the cyanuric acid-available chlorine system at 25°C is shown in Figure 4. In the presence of excess cyanuric acid, the predominant chlorinated specie is the monochloroisocyanurate ion, HClCy where Cy represents the triisocyanurate anion. Therefore, the only significant equilibria in pool water are... 

At 25°C, pH 7.5, 1.5 ppm FAC, and 25 ppm cyanuric acid, the calculated HOCl concentration is only 0.01 ppm. Although the monochloroisocyanurate ion hydrolyzes to only a small extent, it serves as a reservoir of HOCl because of rapid hydrolysis. Indeed, this reaction is so fast that HClCy behaves like FAC in all wet methods of analysis. Furthermore, since HClCy absorbs uv only below 250 nm, which is filtered out of solar radiation by the earth s atmosphere, it is more resistant to decomposition than the photoactive C10 , which absorbs sunlight at 250—350 nm and represents the principal mode of chlorine loss in unstabilized pools (30). As Httie as 5 ppm of bromide ion prevents stabilization of FAC by cyanuric acid (23) (see also Cyanuric and ISOCYANURIC acids). 

Toxicity of Chlorine Sanitizers. Chlorine-based swimming-pool and spa and hot-tub sanitizers irritate eyes, skin, and mucous membranes and must be handled with extreme care. The toxicities are as follows for chlorine gas, TLV = 1 ppm acute inhalation LC q = 137 ppm for 1 h (mouse) (75). The acute oral LD q (rats) for the Hquid and soHd chlorine sanitizers are NaOCl (100% basis) 8.9 g/kg (76), 65% Ca(OCl)2 850 mg/kg, sodium dichloroisocyanurate dihydrate 735 mg/kg, and trichloroisocyanuric acid 490 mg/kg. Cyanuric acid is essentially nontoxic based on an oral LD q > 20 g/kg in rabbits. Although, it is mildly irritating to the eye, it is not a skin irritant. A review of the toxicological studies on cyanuric acid and its chlorinated derivatives is given in ref. 77. 

Stable A/-chloro compounds are formed by reaction of hypochlorous acid and appropriate N—H compounds. For example, HOCl, formed in situ via chlorine hydrolysis, converts di- or trisodium cyanurates to dichloro- and trichloroiso-cyanuric acids, respectively (114). Chloroisocyanurates can also be prepared from isocyanuric acid or monosodium cyanurate and preformed HOCl (115—117). Hydrolysis of chloroisocyanurates provide HOCl for use in swimming pool disinfection and in bleaching appHcations. 

Hypochlorous acid, preformed or generated in situ from chlorine and water, is employed in the manufacture of chlorohydrins (qv) from olefins, en route to epoxides, and in the production of chloramines (qv), especially chloroisocyanurates from cyanuric acid (see Cyanuric and isocyanuric acids). 

The equihbrium constant for the first reaction is 2.40 x 10 at 25°C (179). When cyanuric acid is used in conjunction with a hypochlorite for sanitising swimming pool water, the free available chlorine is kept in the 1 to 3 ppm range. 

Cyanuric acid is sold mainly in coarse granular form, >85% 2—0.15 mm (10 to 100 mesh). It is also available in powdered form. Typical analysis of commercial CA is CA >98.5% ammelide <1% water <0.6% pH of 1% slurry >2.8. Eor the chlorinated derivatives ... 

Direct bromination readily yields the 6-bromo derivative (111), just as with uracil. Analogous chlorination and iodination requires the presence of alkalies and even then proceeds in low yield. The 6-chloro derivative (113) was also obtained by partial hydrolysis of the postulated 3,5,6-trichloro-l,2,4-triazine (e.g.. Section II,B,6). The 6-bromo derivative (5-bromo-6-azauracil) served as the starting substance for several other derivatives. It was converted to the amino derivative (114) by ammonium acetate which, by means of sodium nitrite in hydrochloric acid, yielded a mixture of 6-chloro and 6-hydroxy derivatives. A modified Schiemann reaction was not suitable for preparing the 6-fluoro derivative. The 6-hydroxy derivative (115) (an isomer of cyanuric acid and the most acidic substance of this group, pKa — 2.95) was more conveniently prepared by alkaline hydrolysis of the 6-amino derivative. Further the bromo derivative was reacted with ethanolamine to prepare the 6-(2-hydroxyethyl) derivative however, this could not be converted to the corresponding 2-chloroethyl derivative. Similarly, the dimethylamino, morpholino, and hydrazino derivatives were prepared from the 6-bromo com-pound. ... 

A 500-ml three-necked flask is fitted with a mechanical stirrer, a thermometer, a gas outlet, and a gas inlet tube dipping into the solution. The flask is charged with a solution of cyanuric acid (15 g, 0.116 mole) dissolved in 300 ml of 5% aqueous potassium hydroxide solution. The flask is cooled in an ice-salt bath with stirring to 0° and irradiated with a mercury lamp. A rapid stream of chlorine is passed into the flask (approx. 5 ml/sec), whereupon a heavy white precipitate forms. The addition of gas is continued until the solid material no longer forms (approx. 2 hours). The flask is briefly flushed with air, the product is collected by suction filtration in an ice-cooled funnel, and the residue washed with several small portions of cold water. Since it undergoes slow hydrolysis, the product should be dried in a vacuum oven. The crude product has a variable melting point (195-225°) the yield is about 20 g (approx. 75%). 

Isocyanurate products are made by combining chlorine with cyanuric acid (CYA). The CYA acts as a chlorine stabilizer in preventing the rapid depletion of chlorine from the cooling system by ultraviolet (UV) light. 

Canelli E. Chemical, bacteriological and toxicological properties of cyanuric acid and chlorinated isocyanurates as applied to swimming pool disinfection. Am J Public Health 1974 62 155-162. 

Note Miscellaneous uses include cyanuric acid for chlorinated isocyanurates, crystalline adducts, deicing agents, pharmaceutical intermediates and sulfamic acid and its ammonium salt. 

Chloramines. This reagent chlorinates primary and secondary amines, but is most useful for chlorination of hindered amines. The reaction is carried out in water or benzene-water. The co-product, cyanuric acid, is removed by filtration. 

Among other electrophilic reagents ctq>able of twinging about the Pummerer rearrangement are halides of organic and inorganic acids. As these halides transform sulfoxides into a-chlorosulfides they complement the sulfide chlorination route to these compounds. Thionyl chloride reacts readily with sulfoxides and 3-keto sulfoxides methyl phenyl sulfoxide furnishes chloromethyl phenyl sulfide (equation 37). Benzoyl chloride and acetyl chloride behave similarly. d yanuric chloii is transformed into cyanuric acid by dimethyl sulfoxide, which in turn is transformed into methyl chloromethyl sulfide (equation 3g).54,S5... 

The synthesis of noncovalent hydrogen-bonded aggregates can often be accomplished simply by mixing the components in the correct molar ratio in an appropriate solvent (usually chlorinated hydrocarbons such as chloroform). In some cases, one of the components (usually the cyanuric acids) may be poorly soluble in chloroform in these cases it may be useful to dissolve the components in a more polar solvent or solvent mixture (e.g. chloroform-methanol), then remove this solvent and redissolve the residue in chloroform. This procedure can overcome kinetic limitations to formation of aggregates associated with solubilities. 

A powerful oxidizer. Forms an explosive product with cyanuric acid + sodium hydroxide. Potentially violent reaction with combustible materials. When heated to decomposition it emits very toxic fumes of Cr and NOx. Used to chlorinate swimming pools. 

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