Hypochlorous acid and hypochlorites

Cooling water pH affects oxidizing antimicrobial efficacy. The pH determines the relative proportions of hypochlorous acid and hypochlorite ion or, in systems treated with bromine donors, hypobromous acid and hypobromite ion. The acid forms of the halogens are usually more effective antimicrobials than the dissociated forms. Under some conditions, hypochlorous acid is 80 times more effective in controlling bacteria than the hypochlorite ion. Hypochlorous acid predominates below a pH of 7.6. Hypobromous acid predominates below pH 8.7, making bromine donors more effective than chlorine donors in alkaline cooling waters, especially where contact time is limited. 

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. 

Dichlorine monoxide, hypochlorous acid, and hypochlorites. Chlorous acid, chlorites, and chlorine dioxide. 

Chlora.tes. Sodium chlorate is produced by the electrolysis of sodium chloride at pH 6.5—7.5 in a one-compartment cell. DSA anodes and steel cathodes are generally used in chlorate cells. The electrolysis products, hypochlorous acid, and hypochlorite ions, react chemically to produce chlorate (eq. 

Hypochlorous acid and hypochlorite ion are known as free available chlorine. The chloramines are known as combined available chlorine and are slower than free chlorine in killing microorganisms. For identical conditions of contact time, temperature, and pH in the range of 6 to 8, it takes at least 25 times more combined available chlorine to produce the same germicidal efficiency. The difference in potency between chloramines and HOCl can be explained by the difference in their oxidation potentials, assuming the action of chloramine is of an electrochemical nature rather than one of diffusion, as seems to be the case for HOCl. 

J. A. WojTowicz, Dichlorine monoxide, hypochlorous acid and hypochlorites. Kirk-Othmer Encyclopedia of Chemical Technology, 4th edn., Wiley, New York, 1993, Vol. 5, pp. 932-68. J. J. Kaczur and D. W. Cawlfield, Chlorine dioxide, chlorous acid and chlorites, ibid., pp. 968-91. 

Pyrene is a common PAH contaminant and may occur in drinking water. Chlorination of water with or without bromide that may be present in coastal environments has been examined. Both chlorinated and brominated pyrenes with halogen substituents at the 1,3-, 1,6-, and 1,8-positions were found, and could putatively be produced by reaction of pyrene with hypochlorous acid and hypochlorite (Hu et al. 2006). 

Methods of determination of hypochlorous acid and hypochlorites are given in Ref 2, pp 292-296... 

CHLORINE OXYGEN ACIDS AND SALTS - DICHLORINE MONOX IDE, HYPOCHLOROUS ACID, AND HYPOCHLORITES] (Vol 5) Alkylketene dimers (AKD)... 

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