1. Water treatment
    Drinking water disinfection  Swimming pool disinfection 

2. Safety

3. Synthesis and chemical reactions
     Production    Decomposition    Reactions  

4. Removing from water
    Ultraviolet light  Ascorbic acid and sodium ascorbate  Activated carbon  Campden tablets  Sodium thiosulfate  Other methods 

5. Organic chloramines
    Reduction of organic chloramines 

6. See also

7. References

8. External links

Chloramines are derivatives of ammonia by substitution of one, two or three hydrogen atoms with chlorine atoms: monochloramine (chloroamine, NH₂Cl), dichloramine (NHCl₂), and nitrogen trichloride (NCl₃).^[1]{{full citation needed|date=May 2017}} The term chloramine also refers to a family of organic compounds with the formulas R₂NCl and RNCl₂ (where R is an organic group).

Monochloramine (chloramine) is an inorganic compound with the formula NH₂Cl. It is an unstable colorless liquid at its melting point of {{cvt|−66|°C}}, but it is usually handled as a dilute aqueous solution, in which form it is sometimes used as a disinfectant. Chloramine is too unstable to have its boiling point measured.^[2]

The wholesale cost in the developing world is about {{US$|link=yes}}13.80 to {{US$}}18.41 per 500 grams.^[3]

Water treatment

Chloramine is used as a disinfectant for water because it is less aggressive than chlorine and more stable against light than hypochlorites.^[4]

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—to be specific monochloramine—which is much more stable and does not dissipate as rapidly as free chlorine. NH₂Cl also has a much lower, but still active, 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.^[4]

Some of the unregulated byproducts may possibly pose greater health risks than the regulated chemicals.^[5]

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.^[6]

Swimming pool disinfection

In swimming pools, chloramines are formed by the reaction of free chlorine with amine groups present in organic substances, such as urine, sweat and shed skin cells. Chloramines, compared to free chlorine, are both less effective as a sanitizer and, if not managed correctly, more irritating to the eyes of swimmers. Chloramines are also responsible for the distinctive "chlorine" smell of swimming pools.^[7][8] Some pool test kits designed for use by homeowners are not able to distinguish free chlorine and chloramines, which can be misleading and lead to non-optimal levels of chloramines in the pool water.^[9]

There is also evidence that exposure to chloramine can contribute to respiratory problems, including asthma, among swimmers.^[10] Respiratory problems related to chloramine exposure are common and prevalent among competitive swimmers.^[11]

Safety

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 byproducts and N-nitrosodimethylamine.^[12][13] Both iodinated disinfection by-products and N-nitrosodimethylamine have been shown to be genotoxic.^[13]

Synthesis and chemical reactions

NH₂Cl is a highly unstable compound in concentrated form. Pure NH₂Cl decomposes violently above {{cvt|−40|°C}}.^[14] Gaseous chloramine at low pressures and low concentrations of chloramine in aqueous solution are thermally slightly more stable. Chloramine is readily soluble in water and ether, but less soluble in chloroform and carbon tetrachloride.^[15]

Production

In dilute aqueous solution, chloramine is prepared by the reaction of ammonia with sodium hypochlorite:^[15]

NH₃ + NaOCl → NH₂Cl + NaOH

This is also the first step of the Raschig hydrazine synthesis. The reaction has to be carried out in a slightly alkaline medium (pH 8.5–11). The acting chlorinating agent in this reaction is hypochlorous acid (HOCl), which has to be generated by protonation of hypochlorite, and then reacts in a nucleophilic substitution of the hydroxyl against the amino group. The reaction occurs quickest at around pH 8. At higher pH values the concentration of hypochlorous acid is lower, at lower pH values ammonia is protonated to form ammonium ions {{chem|NH|4|+}}, which do not react further.

The chloramine solution can be concentrated by vacuum distillation and by passing the vapor through potassium carbonate which absorbs the water. Chloramine can be extracted with ether.

Gaseous chloramine can be obtained from the reaction of gaseous ammonia with chlorine gas (diluted with nitrogen gas):

2 NH₃(g) + Cl₂(g) {{eqm}} NH₂Cl(g) + NH₄Cl(s)

Pure chloramine can be prepared by passing fluoroamine through calcium chloride:

2 NH₂F + CaCl₂ → 2 NH₂Cl + CaF₂

Decomposition

The covalent N−Cl bonds of chloramines are readily hydrolyzed with release of hypochlorous acid:^[16]

RR′NCl + H₂O {{eqm}} RR′NH + HOCl

The quantitative hydrolysis constant (K value) is used to express the bactericidal power of chloramines, which depends on their generating hypochlorous acid in water. It is expressed by the equation below, and is generally in the range 10⁻⁴ to 10⁻¹⁰ ({{val|2.8|e=-10}} for monochloramine):

In aqueous solution, chloramine slowly decomposes to dinitrogen and ammonium chloride in a neutral or mildly alkaline (pH ≤ 11) medium:

3 NH₂Cl → N₂ + NH₄Cl + 2 HCl

However, only a few percent of a 0.1 M chloramine solution in water decomposes according to the formula in several weeks. At pH values above 11, the following reaction with hydroxide ions slowly occurs:

3 NH₂Cl + 3 OH⁻ → NH₃ + N₂ + 3 Cl⁻ + 3 H₂O

In an acidic medium at pH values of around 4, chloramine disproportionates to form dichloramine, which in turn disproportionates again at pH values below 3 to form nitrogen trichloride:

2 NH₂Cl + H⁺ {{eqm}} NHCl₂ + {{chem|NH|4|+}}

3 NHCl₂ + H⁺ {{eqm}} 2 NCl₃ + {{chem|NH|4|+}}

At low pH values, nitrogen trichloride dominates and at pH 3–5 dichloramine dominates. These equilibria are disturbed by the irreversible decomposition of both compounds:

NHCl₂ + NCl₃ + 2 H₂O → N₂ + 3 HCl + 2 HOCl

Reactions

In water, chloramine is pH-neutral. It is an oxidizing agent (acidic solution: {{nowrap|1=E° = −1.48 V}}, in basic solution {{nowrap|1=E° = −0.81 V}}):^[15]

NH₂Cl + 2 H⁺ + 2 e⁻ → {{chem|NH|4|+}} + Cl⁻

Reactions of chloramine include radical, nucleophilic, and electrophilic substitution of chlorine, electrophilic substitution of hydrogen, and oxidative additions.

Chloramine can, like hypochlorous acid, donate positively charged chlorine in reactions with nucleophiles (Nu⁻):

Nu⁻ + NH₃Cl⁺ → NuCl + NH₃

Examples of chlorination reactions include transformations to dichloramine and nitrogen trichloride in acidic medium, as described in the decomposition section.

Chloramine may also aminate nucleophiles (electrophilic amination):

Nu⁻ + NH₂Cl → NuNH₂ + Cl⁻

The amination of ammonia with chloramine to form hydrazine is an example of this mechanism (the Raschig process):

NH₂Cl + NH₃ + NaOH → N₂H₄ + NaCl + H₂O

Chloramine electrophilically aminates itself in neutral and alkaline media to start its decomposition:

2 NH₂Cl → N₂H₃Cl + HCl

The chlorohydrazine (N₂H₃Cl) formed during self-decomposition is unstable and decomposes itself, which leads to the net decomposition reaction:

3 NH₂Cl → N₂ + NH₄Cl + 2 HCl

Monochloramine oxidizes sulfhydryls and disulfides in the same manner as hypochlorous acid,^[17] but only possesses 0.4% of the biocidal effect of HClO.^[18]

Removing from water

Chloramines should be removed from water for dialysis, aquariums, hydroponic applications, and homebrewing beer.{{Citation needed|reason=Citations needed for aquariums and homebrewing|date=April 2018}}. Chloramine must be removed from water prior to use in kidney dialysis machines because it can cause hemolytic anemia if it enters the blood stream.^[19] In hydroponic applications, chloramine stunts the growth of plants.^[20]

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.{{citation needed|date=November 2013}}

Ultraviolet light

The use of ultraviolet light for chlorine or chloramine removal is an established technology that has been widely accepted in pharmaceutical, beverage, and dialysis applications.^[21] UV is also used for disinfection at aquatic facilities ^[22].

Ascorbic acid and sodium ascorbate

Activated carbon

Activated carbon has been used for chloramine removal long before catalytic carbon, a form of activated carbon, became available{{Citation needed|reason=need evidence that "catalytic carbon" is any better than standard GAC|date=March 2018}}; 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.{{Citation needed|reason=chloramines are easily degraded into chloride and ammonia by activated carbon|date=March 2018}}

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.^[24] Additionally, sodium metabisulfite injection may be used in certain circumstances.^[25]{{full citation needed|date=May 2017}}

Campden tablets

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 sulfite can cause off flavors in beer^[26]{{full citation needed|date=May 2017}} so potassium metabisulfite is preferred.

Sodium thiosulfate

Sodium thiosulfate is used to dechlorinate tapwater for aquariums or treat effluent from wastewater treatments prior to release into rivers{{Citation needed|date=April 2018}}. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tapwater requires between 0.1 and 0.3 grams of pentahydrated (crystalline) sodium thiosulfate per 10 L of water{{Citation needed|date=April 2018}}. Many animals are sensitive to chloramine, and it must be removed from water given to many animals in zoos{{Citation needed|date=April 2018}}.

Other methods

Chloramine, like chlorine, can be removed by boiling and aging. However, time required to remove chloramine is much longer than that of chlorine. The time required to remove half of the chloramine (half-life) from {{convert|10|USgal}} of water by boiling is 26.6 minutes, whereas the half-life of free chlorine in boiling 10 gallons of water is only 1.8 minutes.^[27]{{better source|date=April 2018}}

Organic chloramines

A variety of organic chloramines are known and proven useful in organic synthesis. Examples include N-chloromorpholine (ClN(CH₂CH₂)₂O), N-chloropiperidine, and N-chloroquinuclidinium chloride.^[28]

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 accelerated with acid catalysis.{{citation needed|date=November 2013}}

See also

• Disinfection
• Disinfection by-products
• Water treatment
• Pathogen

References

External links

• [https://web.archive.org/web/20120512031418/http://monographs.iarc.fr/ENG/Monographs/vol52/volume52.pdf "Chlorinated drinking water", IARC Monograph (1991)]
• EPA Maximum Contaminant Levels
• WebBook page for NH₂Cl
• [https://web.archive.org/web/20120107235931/http://www.skepticalaquarist.com/chlorine-chloramine Chlorine and chloramines in the freshwater aquarium]

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