Everything about Chloramine totally explained
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Chloramine (monochloramine) is a
chemical compound with the
formula NH
2Cl. It is usually used as a dilute solution where it's used as a
disinfectant. The term chloramine also refers to a family of
organic compounds with the formulas R
2NCl and RNCl
2 (R is an organic group).
Dichloramine, NHCl
2, and
nitrogen trichloride, NCl
3, are also well known.
Synthesis and chemical reactions
NH
2Cl is a highly unstable compound in concentrated form, much less as a pure liquid. Pure NH
2Cl decomposes violently above −40 °C. NH
2Cl is, however, quite stable in dilute solution, and this considerable stability is the basis of its applications.
NH
2Cl is prepared by the
chemical reaction between
ammonia and
hypochlorous acid under mildly alkaline conditions:
» NH
3 + HOCl → NH
2Cl + H
2O
The synthesis is conducted in dilute solution. In this reaction HOCl undergoes attack by the
nucleophile NH
3. At lower pH's, further chlorination occurs.
The above syntheses are useful but don't deliver NH
2Cl in pure form. The pure compound can be prepared by contacting
fluoroamine with
calcium chloride:
» NH
2F + CaCl
2 → NH
2Cl + CaClF
NH
2Cl is a key intermediate in the traditional synthesis of
hydrazine.
Monochloramine oxidizes sulfhydrals and disulfides in the same manner as HClO, but only possesses 0.4% of the biocidal effect of HClO.
Uses in water treatment
NH
2Cl is commonly used in low
concentrations as a
disinfectant in
municipal water systems as an alternative to
chlorination. This application is increasing.
Chlorine (sometimes referred to as
Free Chlorine) is being displaced by chloramine, which is much more stable and doesn't dissipate from the
water before it reaches consumers. NH
2Cl also exhibits less tendency to convert organic materials into
chlorocarbons such as
chloroform and
carbon tetrachloride. Such compounds have been identified as
carcinogens and in 1979 the U.S.
EPA 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.
Chloramine in tap water gives a greenish cast to the water in bulk, versus the normally bluish cast to pure water or water containing only free chlorine disinfectant. This greenish color may be observed by filling a white polyethylene bucket with chloraminated tap water and comparing it to chloramine-free water such as distilled water or a sample from a swimming pool.
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.
Situations where NH2Cl should be removed
Aquarium owners must remove the chloramine from their
tap water because it's
toxic to
fish. Aging the
water for a few days removes
chlorine but not the more stable chloramine, which can be neutralised using products available at pet stores.
Many animals are sensitive to chloramine and it must be removed from water given to many animals in zoos.
Chloramine must also 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.
Home brewers use reducing agents such as
sodium metabisulfite or
potassium metabisulfite to remove chloramine from brewing liquor as it, unlike
chlorine, can't be removed by boiling (A.J. DeLange). Residual sodium can cause off flavors in beer (See Brewing, Michael Lewis) so potassium metabisulfite is preferred.
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 more irritating to the eyes of swimmers. When swimmers complain of eye irritation from "too much chlorine" in a pool, the problem is typically a high level of chloramines, caused by too
little chlorine in relation to the amount of organic matter. Pool test kits designed for use by homeowners are sensitive to both free chlorine and chloramines, which can be misleading.
Organic chloramines
A variety of organic chloramines are known and proven useful in
organic synthesis. One example is
N-chloromorpholine ClN(CH
2CH
2)
2O,
N-chloro
piperidine, and
N-chloro
quinuclidinium chloride.
Safety
NH
2Cl is toxic in large quantities. US EPA regulations limit chloramine concentration to 4 parts per million (ppm). A typical target level in US public water supplies is 3 ppm.
Further Information
Get more info on 'Chloramine'.
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