Chloramine

Chloramine
Other names Monochloramine Chloramide Chloroazane
Identifiers
CAS number	10599-90-3 Y
PubChem	25423
ChemSpider	23735 Y
KEGG	C19359 N
ChEMBL	CHEMBL1162370 Y
Jmol-3D images	Image 1
SMILES ClN
InChI InChI=1S/ClH2N/c1-2/h2H2 Y Key: QDHHCQZDFGDHMP-UHFFFAOYSA-N Y InChI=1/ClH2N/c1-2/h2H2 Key: QDHHCQZDFGDHMP-UHFFFAOYAS
Properties
Molecular formula	NH2Cl
Molar mass	51.48 g/mol
Appearance	colorless
Melting point	−66 °C
Solubility in other solvents	Soluble
Related compounds
Related compounds	Dichloramine Nitrogen trichloride
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Chloramines are derivatives of ammonia by substitution of one, two or three hydrogen atoms with chlorine atoms.^[1] Monochloramine is an inorganic compound with the formula NH₂Cl. It is an unstable colourless liquid at its melting point of -66° temperature, 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.^[2] 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^[3] 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,^[4] but only possesses 0.4% of the biocidal effect of HClO.^[5]

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

See also: Chloramination

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 (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.^{[citation needed]} Pool test kits designed for use by homeowners are sensitive to both free chlorine and chloramines, which can be misleading.^{[citation needed]}

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.^[6]

There is also evidence that exposure to chloramine can contribute to respiratory problems, including asthma, among swimmers.^[7] Respiratory problems related to chloramine exposure are common and prevalent among competitive swimmers.^[8]

Chloramine use, together with chlorine dioxide, ozone, and ultraviolet, have been described as public health concerns and an example of the outcome of poorly implemented environmental regulation.^{[citation needed]} These methods of disinfection decrease the formation of regulated byproducts such as alkyl chloroforms, which has led to their widespread adoption. However, they can increase the formation of a number of less regulated cytotoxic and genotoxic byproducts, some of which pose greater health risks than the regulated chemicals,^[9] causing such diseases as cancer, kidney disease, thyroid damage,^[10] and birth defects.^[11]

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 fermented beverages. Chloramine, like chlorine, can be removed by boiling. However the boiling time required to remove the chloramine is much longer than that of chlorine.^[12] 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).^[13]

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.^[14]

Safety

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.^[15][16] Both iodinated disinfection by-products and N-Nitrosodimethylamine have been shown to be genotoxic.^[16]

References

1. ^ Clause 2.4 Chloramines ISO 7393-2
2. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
3. ^ 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.
4. ^ Jacangelo, J. G., V. P. Olivieri, and K. Kawata. 1987. Oxidation of sulfhydryl groups by monochloramine. Water Res. 21:1339-1344.
5. ^ Morris, J. C. 1966. Future of chlorination. J. Am. Water Works Assoc. 58:1475-1482.
6. ^ 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.
7. ^ Bougault, Valérie, et. al, "The Respiratory Health of Swimmers", Sports Medicine, Vol. 39, No. 4, 2009, pp. 295-312(18).
8. ^ "The determinants of prevalence of health complaints among young competitive swimmers", International Archives of Occupational and Environmental Health, Vol. 80, No. 1, Oct. 2006.
9. ^ 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.
10. ^ By Dr. Winn Parker, "Chloramine Causes Collateral Health Damage"
11. ^ Choramine Info Center "What is Chloramine"
12. ^ "Experiments in Removing Chlorine and Chloramine From Brewing Water"
13. ^ San Francisco Public Utilities Commission, "Questions Regarding Chlorine and Chloramine Removal From Water (Updated August 2010)"
14. ^ 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
15. ^ Krasner, Stuart W.; Weinberg, Howard S.; Richardson, Susan D.; Pastor, Salvador J.; Chinn, Russell; Sclimenti, Michael J.; Onstad, Gretchen D.; Thruston, Alfred D. (2006). "Occurrence of a New Generation of Disinfection Byproducts". Environmental Science & Technology 40 (23): 7175–7185. doi:10.1021/es060353j. 
16. ^ ^{a b} Richardson, Susan D.; Plewa, Michael J.; Wagner, Elizabeth D.; Schoeny, Rita; DeMarini, David M. (2007). "Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: A review and roadmap for research". Mutation Research/Reviews in Mutation Research 636: 178–242. doi:10.1016/j.mrrev.2007.09.001. 

External links

• Chloramine FAQ from the San Francisco Public Utilities Commission
• "Chlorinated drinking water", IARC Monograph (1991)
• EPA Maximum Contaminant Levels
• WebBook page for NH2Cl
• Chlorine and chloramines in the freshwater aquarium