Hypochlorites stabilization

There are two classes of chlorine commonly used in swimming pools referred to as unstabilized and stabilized. To protect hypochlorous acid from UV degradation cyanuric acid is added to the water. Whether the cyanuric acid is supplied endogenously by the product (stabilized) or whether the cyanuric acid must be added separately (unstabilized) distinguishes the classes. Unstabilized chlorine compounds are chlorine gas, sodium hypochlorite, calcium hypochlorite and lithium hypochlorite. Stabilized chlorine compounds are chlorinated forms of cyanuric acids, sodium dichloro-s-triazinetrione (dichlor) and trichloro-s-triazinetrione (trichlor). It is important to never mix stabilized and unstabilized chlorine products because they are not compatible and can be combustible when mixed as concentrates. 

The subject of hypochlorite stability in formulations containing oxidizable organic substrates, such as surfactants and fragrances, is complex. Stability will obviously be depen-... 

Hypochlorite is the most inexpensive and the most effective disinfectant known. Its activity is mainly due to the presence of hypochlorous acid (see Chapter 16). The strongest biocidal activity occurs at pH 6—8, where hypochlorous acid predominates because of the acid-base equilibrium, but products need a considerably higher pH in order to ensure hypochlorite stability. 

TABLE 64 Hypochlorite Stability Comparison with Various Surfactants... 

Calcium Hypochlorite. This chemical, marketed since 1928, is one of the most widely used swimming-pool water sanitizers. Calcium hypochlorite, a crystalline sofld, is a convenient source of available chlorine and is sold in granular or tablet form for use in home, semiprivate, and commercial pools. When dissolved in water, Ca(OCl)2 forms hypochlorous acid and hypochlorite ion similar to NaOCl. It contains small amounts of stabilizing Ca(OH)2, which has a very small effect on pool pH (7). Calcium hypochlorite has superior storage stabiUty and much higher available CI2 concentration than Hquid bleach, which reduces storage requirements and purchasing frequency. 

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. 

The ideal recommended cyanuric acid concentration is 30—50 ppm (Table 2). Although this range can be readily maintained when using hypochlorite sanitizers, it cannot be maintained when using chloroisocyanurates since they increase the cyanuric acid concentration. The NSPI recommends a maximum of 150 ppm cyanuric acid. Many health departments limit cyanuric acid to 100 ppm. No significant increase in stabilization occurs beyond 50—100 ppm, and since high levels of cyanuric acid slow down the rate of disinfection, the pool water should be partially drained and replaced with fresh water to reduce the cyanuric acid to below recommended maximum levels. Cyanuric acid is determined turbidimetricaHy after precipitation as melamine cyanurate. 

The stabilised nitrate may then be bleached with sodium hypochlorite, centrifuged to remove much of the water in which the polymer has been slurried and dehydrated by displacement with alcohol while under pressure in a press. It is interesting to note that in these processes approximately 35 000 gallons (160000 litres) of water are used for every ton of cellulose nitrate produced. Control of purity of the water is important in particular the iron content should be as low as 0.03 parts per million since iron can adversely affect both the colour and heat stability of the polymer. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Can catch fire when in contact with porous materials such as wood, asbestos, cloth, soil, or rusty metals Stability During Transport Stable at ordinary temperatures, however when heated this material can decompose to nitrogen and ammonia gases. The decomposition is not generally hazardous unless it occurs in confined spaces Neutralizing Agents for Acids and Caustics Flush with water and neutralize the resulting solution with calcium hypochlorite Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

The most stable solid hypochlorites are those of Li, Ca, Sr and Ba (see below). NaOCl has only poor stability and cannot be isolated pure KOCl is known only in solution, Mg yields a basic hypochlorite and impure Ag and Zn hypochlorites have been reported. Hydrated salts are also known. Solid, yellow, hydrated hypobromites Na0Br.xH20 (x = 5, 7) and K0Br.3H20 can be crystallized from solutions obtained by adding Br2 to cold cone solutions of MOH but the compounds decompose above 0°C. No solid metal hypoiodites have yet been isolated. 

Due to the -OCH2COOH group the ether carboxylic acids have a good chemical and thermal stability. Therefore they can be used in formulations containing oxidizing agents such as hypochlorite and peroxide [61,64]. 

Presumably the active chlorine of the chloramines formed by reaction with chlorine gas or hypochlorite reacts with TDM in the presence of acetic acid to yield dark blue, mesomerically stabilized quinoid reaction products that possibly rearrange to yield triphenylmethane dyestuffs. 

At low pH the existence of HOCl is favoured over OCl" (hypochlorite ion). The relative microbiocidal effectiveness of these forms is of the order of 100 1. By lowering the pH of hypochlorite solutions the antimicrobial activity increases to an optimum at about pH 5 however, this is concurrent with a decrease in stability of the solutions. This problem may be alleviated by addition of NaOH (see above equation) in order to maintain a high pH during storage for stability. The absence ofbuffer allows the pH to be lowered sufficiently for activity on dilution to use-strength. It is preferable to prepare use-dilutions of hypochlorite on a daily basis. 

Hypochlorite Salts., Hypochlorites are powerful oxidants and therefore may degrade polymeric chains. They are often used in combination with tertiary amines [1846]. The combination of the salt and the tertiary amine increases the reaction rate more than the application of a hypochlorite alone. A tertiary amino galactomannan may serve as an amine source [1062]. This also serves as a thickener before breaking. Hypochlorites are also effective for breaking stabilized fluids [1817]. Sodium thiosulfate has been proposed as a stabilizer for high-temperature applications. 

Methyl ketones are degraded to the next lower carboxylic acid by reaction with hypochlorite or hypobromite ions. The initial step in these reactions involves base-catalyzed halogenation. The a-haloketones are more reactive than their precursors, and rapid halogenation to the trihalo compound results. Trihalomethyl ketones are susceptible to alkaline cleavage because of the inductive stabilization provided by the halogen atoms. 

Unstabilized hypobromite solutions are even more unstable than hypochlorite. Hypobromite disproportionates to bromate (Br03), a toxic and potentially carcinogenic compound, in alkaline conditions. The stabilizer in STABREX inhibits that process as shown in Table3. 

Stability Unstable in air. Protect from water or moisture. Store away horn heat or ignition sources and sulfur compounds. Reacts with sulfur and sulfur compounds, producing highly toxic VX or VX-like compounds. It completely dissolves polymethylmethacrylate. It is incompatible with calcium hypochlorite (HTH), many chlorinated hydrocarbons, selenium, selenium compounds, moisture, oxidants, and carbon tetrachloride. 

---