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Chloramine

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Chloramine
Chloramine
Chloramine
Names
Other names Monochloramine
Chloramide
Chloroazane
Identifiers
CAS Number
3D model (JSmol)
ChemSpider
PubChem CID
InChI
  • InChI=1S/ClH2N/c1-2/h2H2Key: QDHHCQZDFGDHMP-UHFFFAOYSA-N
  • InChI=1/ClH2N/c1-2/h2H2Key: QDHHCQZDFGDHMP-UHFFFAOYAS
SMILES
  • ClN
Properties
Chemical formula NH2Cl
Molar mass 51.48 g/mol
Appearance colorless
Melting point −66 °C
Solubility in other solvents Soluble
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). checkY verify (what is  ?) Infobox references
Chemical compound

Chloramine (monochloramine) is an inorganic compound with the formula NH2Cl. It is a colourless liquid at room temperature, but it is usually handled as a dilute 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.

NH2Cl is prepared by the chemical reaction between ammonia and hypochlorous acid under mildly alkaline conditions:

NH3 + HOCl → NH2Cl + H2O

The synthesis is conducted in dilute solution. In this reaction HOCl undergoes attack by the nucleophile NH3. At a lower pH, further chlorination occurs.

Laboratory methods

The above syntheses are useful but do not deliver NH2Cl in pure form. For research purposes, the pure compound can be prepared by contacting fluoroamine with calcium chloride:

NH2F + CaCl2 → NH2Cl + CaClF

Uses and chemical reactions

NH2Cl is a key intermediate in the traditional synthesis of hydrazine.

Monochloramine oxidizes sulfhydryls and disulfides in the same manner as HClO, but only possesses 0.4% of the biocidal effect of HClO.

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.

Uses in water treatment

NH2Cl is commonly used in low concentrations as a secondary disinfectant in municipal water distribution systems as an alternative to free chlorine chlorination. This application is increasing. Chlorine (sometimes referred to as free chlorine) is being displaced by chloramine, which is much more stable and does not dissipate from the water before it reaches consumers. 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. 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. Pool test kits designed for use by homeowners are sensitive to both free chlorine and chloramines, which can be misleading.

New swimming pool initially filled with chloramine-treated tap water.

Chloramine-treated water has a greenish cast, the source of the colour is uncertain. Pure water by contrast normally is clear. 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.

Health risks

Adding chloramine to the water supply can increase exposure to lead in drinking water, especially in areas with older housing; this exposure can result in increased lead levels in the bloodstream and can pose a significant health risk.

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.

Chloramine use, together with chlorine dioxide, ozone, and ultraviolet, has been described as a public health concern and an example of the outcome of poorly implemented environmental regulation. These methods of disinfection decrease the formation of regulated byproducts, which has led to their widespread use. However, they can increase the formation of a number of unregulated cytotoxic and genotoxic byproducts, some of which pose greater health risks than the regulated chemicals, causing such diseases as cancer, kidney disease, thyroid damage,and birth defects..

Removing chloramine from water

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 is removed from water supplies

Many animals are sensitive to chloramine and it must be removed from water given to many animals in zoos. Aquarium owners remove the chloramine from their tap water because it is 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.

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, like chlorine, it can be removed by boiling, however boil time to reduce chloramine to a terminal measurement is longer. Residual sodium can cause off flavors in beer (See Brewing, Michael Lewis) so potassium metabisulfite is preferred.

Chloramine can be removed from bathwater and birthing tubs by adding 1000 mg of vitamin C (as the ascorbic acid form) to a medium size bathtub (about 40 gallons of water).

Organic chloramines

A variety of organic chloramines are known and proven useful in organic synthesis. One example is N-chloromorpholine ClN(CH2CH2)2O, N-chloropiperidine, and N-chloroquinuclidinium chloride.

Safety

NH2Cl is toxic in concentrated form. US EPA regulations limit chloramine concentration to 4 parts per million (ppm). A typical target level in US public water supplies is 3 ppm. In order to meet EPA regulated limits on halogenated disinfection by-products, many utilities are switching from chlorination to chloramination. While chloramination produces fewer total halogenated disinfection by-products, it produces 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.

References

  1. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  2. Fair, G. M., J. C. Morris, S. L. Chang, I. Weil, and R. P. Burden. 1948. The behavior of chlorine as a water disinfectant. J. Am. Water Works Assoc. 40:1051-1061.
  3. Jacangelo, J. G., V. P. Olivieri, and K. Kawata. 1987. Oxidation of sulfhydryl groups by monochloramine. Water Res. 21:1339-1344.
  4. Morris, J. C. 1966. Future of chlorination. J. Am. Water Works Assoc. 58:1475-1482.
  5. Marie Lynn Miranda et. al, "Changes in Blood Lead Levels Associated with Use of Chloramines in Water Treatment Systems", Environ Health Perspect., 2007 February; 115(2): 221–225.
  6. Bougault, Valérie, et. al, "The Respiratory Health of Swimmers", Sports Medicine, Vol. 39, No. 4, 2009, pp. 295-312(18).
  7. "The determinants of prevalence of health complaints among young competitive swimmers", International Archives of Occupational and Environmental Health, Vol. 80, No. 1, Oct. 2006.
  8. Stuart W. Krasner, "The formation and control of emerging disinfection by-products of health concern". Philosophical Transactions of the Royal Society A, Oct. 13, 2009, 367:4077-4095.
  9. By Dr. Winn Parker, "Chloramine Causes Collateral Health Damage"
  10. Choramine Info Center "What is Chloramine"
  11. "Experiments in Removing Chlorine and Chloramine From Brewing Water"
  12. San Francisco Public Utilities Commission, "Questions Regarding Chlorine and Chloramine Removal From Water (Updated August 2010)"
  13. Lindsay Smith, J. R.; McKeer, L. C.; Taylor, J. M. "4-Chlorination of Electron-Rich Benzenoid Compounds: 2,4-Dichloromethoxybenzene" Organic Syntheses, CollectedVolume 8, p.167 (1993)..http://www.orgsyn.org/orgsyn/pdfs/CV8P0167.pdf describes several N-chloramines
  14. Material Safety Data Sheet for Chloramine
  15. Occurrence of a New Generation of Disinfection Byproducts† Stuart W. Krasner,,, Howard S. Weinberg,, Susan D. Richardson,, Salvador J. Pastor,, Russell Chinn,, Michael J. Sclimenti,, Gretchen D. Onstad, and, Alfred D. Thruston, Jr. Environmental Science & Technology 2006 40 (23), 7175-7185 http://dx.doi.org/10.1021/es060353j
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