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|Molar mass||51.476 g mol−1|
−66 °C, 207 K, -87 °F
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Chloramines are derivatives of ammonia by substitution of one, two or three hydrogen atoms with chlorine atoms. Monochloramine is an inorganic compound with the formula NH2Cl. It is an unstable colourless liquid at its melting point of -66°C, but it is usually handled as a dilute aqueous solution where it is used as a disinfectant. The term chloramine also refers to a family of organic compounds with the formulas R2NCl and RNCl2 (R is an organic group). Dichloramine, NHCl2, and nitrogen trichloride, NCl3, are also well known.
Synthesis and chemical reactions
NH2Cl is a highly unstable compound in concentrated form. Pure NH2Cl decomposes violently above −40 °C. NH2Cl is, however, quite stable in dilute solution, and this considerable stability is the basis of its applications.
- NH3 + HOCl → NH2Cl + H2O
- NH2F + CaCl2 → NH2Cl + CaClF
Uses and chemical reactions
NH2Cl is a key intermediate in the traditional synthesis of hydrazine.
Uses in water treatment
Drinking water disinfection
NH2Cl is commonly used in low concentrations as a secondary disinfectant in municipal water distribution systems as an alternative to chlorination. This application is increasing. Chlorine (referred to in water treatment as free chlorine) is being displaced by chloramine—specifically monochloramine—which is much more stable and does not dissipate as rapidly as free chlorine. NH2Cl also has a very much lower, however still present, tendency than free chlorine to convert organic materials into chlorocarbons such as chloroform and carbon tetrachloride. Such compounds have been identified as carcinogens and in 1979 the United States Environmental Protection Agency began regulating their levels in U.S. drinking water.
Furthermore, water treated with chloramine lacks the distinct chlorine odour of the gaseous treatment and so has improved taste.
Some of the unregulated byproducts may possibly pose greater health risks than the regulated chemicals.
Adding chloramine to the water supply may increase exposure to lead in drinking water, especially in areas with older housing; this exposure can result in increased lead levels in the bloodstream which may pose a significant health risk.
Swimming pool disinfection
In swimming pools, chloramines are formed by the reaction of free chlorine with organic substances. Chloramines, compared to free chlorine, are both less effective as a sanitizer and, if not managed correctly, may be more irritating to the eyes of swimmers. Chloramines are also responsible for the reported "chlorine" smell of swimming pools. Pool test kits designed for use by homeowners are sensitive to both free chlorine and chloramines, which can be misleading. There is also evidence that exposure to chloramine can contribute to respiratory problems, including asthma, among swimmers. Respiratory problems related to chloramine exposure are common and prevalent among competitive swimmers.
Removing chloramines from water
Chloramines should be removed from water for dialysis, aquariums, hydroponic applications and homebrewing beer. Chloramines can interfere with dialysis, can hurt aquatic animals, and can give homebrewed beer a medicinal taste by forming chlorophenols. In hydroponic applications it will stunt the growth and fruit production of plants.
When a chemical or biological process that changes the chemistry of chloramines is used, it falls under reductive dechlorination. Other techniques use physical—not chemical—methods for removing chloramines.
Chloramine must be removed from the water prior to use in kidney dialysis machines, as it would come in contact with the bloodstream across a permeable membrane. However, since chloramine is neutralized by the digestive process, kidney dialysis patients can still safely drink chloramine-treated water.
The use of UV for chlorine or chloramine removal is an established technology that has been widely accepted in pharmaceutical, beverage, and dialysis applications. Ultraviolet light is also used at aquatic facilities.
Chloramine can be removed from tap water by treatment with superchlorination (10 ppm or more of free chlorine, such as from a dose of sodium hypochlorite bleach or pool sanitizer) while maintaining a pH of about 7 (such as from a dose of hydrochloric acid). Hypochlorous acid from the free chlorine strips the ammonia from the chloramine, and the ammonia outgasses from the surface of the bulk water. This process takes about 24 hours for normal tap water concentrations of a few ppm of chloramine. Residual free chlorine can then be removed by exposure to bright sunlight for about 4 hours.
Ascorbic acid and sodium ascorbate completely neutralizes both chlorine and chloramines but degrades in a day or two which only make it usable for short-term applications; SFPUC determined that 1000 mg of Vitamin C (tablets purchased in a grocery store, crushed and mixed in with the bath water) remove chloramine completely in a medium size bathtub without significantly depressing pH.
Activated carbon have been used for chloramine removal long before catalytic carbon became available; Standard activated carbon requires a very long contact time, which means a large volume of carbon is needed. For thorough removal, up to four times the contact time of catalytic carbon may be required.
Most dialysis units now depend on granular activated carbon (GAC) filters, two of which should be placed in series so that chloramine breakthrough can be detected after the first one, before the second one fails. Additionally, sodium metabisulfite injection may be used during circumstances.
Home brewers use reducing agents such as sodium metabisulfite or potassium metabisulfite (both proprietary sold as campden tablets) to remove chloramine from brewing fermented beverages. However, residual sodium can cause off flavors in beer so potassium metabisulfite is preferred.
Sodium thiosulfate is used to dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tap water requires between 0.1 grams and 0.3 grams of pentahydrated (crystalline) sodium thiosulfate per 10 liters of water. Many animals are sensitive to chloramine and it must be removed from water given to many animals in zoos.
Chloramine, like chlorine, can be removed by boiling and aging. However time required to remove the chloramine is much longer than that of chlorine. The time required to remove half of the chloramine (half life) from water by boiling is 26.6 hours, while the half life of free chlorine in boiling water is only 1.8 hours.
Reduction of organic chloramines
Chloramines are often an unwanted side product of oxidation reactions of organic compounds (with amino groups) with bleach. The reduction of chloramines back into amines can be carried out through a mild hydride donor. Sodium borohydride will reduce chloramines, but this reaction is greatly sped up with acid catalysis.
US EPA drinking water quality standards limit chloramine concentration for public water systems to 4 parts per million (ppm) based on a running annual average of all samples in the distribution system. In order to meet EPA regulated limits on halogenated disinfection by-products, many utilities are switching from chlorination to chloramination. While chloramination produces fewer regulated total halogenated disinfection by-products, it can produce greater concentrations of unregulated iodinated disinfection by-products and N-nitrosodimethylamine. Both iodinated disinfection by-products and N-nitrosodimethylamine have been shown to be genotoxic.
- Clause 2.4 Chloramines ISO 7393-2
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- "Controlling Chloramines in Indoor Swimming Pools". NSW Government. Retrieved 2013-02-15.
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- "QUESTIONS REGARDING CHLORINE AND CHLORAMINE REMOVAL FROM WATER". San Francisco Public Utilities Commission. Retrieved 19 April 2012.
- San Francisco Public Utilities Commission, "Questions Regarding Chlorine and Chloramine Removal From Water (Updated August 2010)"
- Handbook of Dialysis, page 81
- Brewing, Michael Lewis
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