Chloramines are derivatives of ammonia by substitution of one, two or three hydrogen atoms with chlorine atoms. Monochloramine is an
inorganic compoundInorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the
formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
NH
2Cl. 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 compoundAn organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
s with the formulas R
2NCl and RNCl
2 (R is an organic group).
DichloramineDichloramine is a reactive inorganic compound. It has the formula . The yellow gas is unstable and reacts with many materials. It is formed by a reaction between ammonia and chlorine or sodium hypochlorite...
, NHCl
2, and
nitrogen trichlorideNitrogen trichloride, also known as trichloramine, is the chemical compound with the formula NCl3. This yellow, oily, pungent-smelling liquid is most commonly encountered as a byproduct of chemical reactions between ammonia-derivatives and chlorine .In pure form, NCl3 is highly reactive...
, NCl
3, are also well known.
Synthesis and chemical reactions
NH
2Cl is a highly unstable compound in concentrated form. 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 reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
between
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
and
hypochlorous acidHypochlorous acid is a weak acid with the chemical formula HClO. It forms when chlorine dissolves in water. It cannot be isolated in pure form due to rapid equilibration with its precursor...
under mildly alkaline conditions:
- NH3 + HOCl → NH2Cl + H2O
The synthesis is conducted in dilute solution. In this reaction HOCl undergoes attack by the
nucleophileA nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
NH
3. At a lower pH, further chlorination occurs.
Laboratory methods
The above syntheses are useful but do not deliver NH
2Cl in pure form. For research purposes, the pure compound can be prepared by contacting
fluoroamineFluoroamine is a chemical compound with formula NH2F. It is formed by the oxidation of the N−3 ion in ammonia to a N−1 ion. It is analogous to chloramine....
with
calcium chlorideCalcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...
:
- NH2F + CaCl2 → NH2Cl + CaClF
Uses and chemical reactions
NH
2Cl is a key intermediate in the traditional synthesis of
hydrazineHydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
.
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
bleachBleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...
. The reduction of chloramines back into amines can be carried out through a mild hydride donor.
Sodium borohydrideSodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...
will reduce chloramines, but this reaction is greatly sped up with acid catalysis.
Uses in water treatment
NH
2Cl is commonly used in low
concentrationIn chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
s as a secondary disinfectant in
municipal water distribution systemA water supply system or water supply network is a system of engineered hydrologic and hydraulic components which provide water supply. A water supply system typically includes:# A drainage basin ;...
s as an alternative to
chlorinationChlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
. This application is increasing.
ChlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
(sometimes referred to as
free chlorine) is being displaced by chloramine, which is much more stable and does not dissipate from the
waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
before it reaches consumers. NH
2Cl also has a very much lower, however still present, tendency than free chlorine to convert organic materials into chlorocarbons such as
chloroformChloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
and
carbon tetrachlorideCarbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
. Such compounds have been identified as
carcinogenA carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...
s 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.
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
asthmaAsthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, among swimmers. Respiratory problems related to chloramine exposure are common and prevalent among competitive swimmers.
Chloramine use, together with
chlorine dioxideChlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching....
,
ozoneOzone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
, and
ultravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
, have been described as public health concerns and an example of the outcome of poorly implemented environmental regulation. 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, 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.
AquariumAn aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
owners remove the chloramine from their
tap waterTap water is a principal component of "indoor plumbing", which became available in urban areas of the developed world during the last quarter of the 19th century, and common during the mid-20th century...
because it is toxic to
fishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
. Aging the
waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
for a few days removes
chlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
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 brewersHomebrewing is the brewing of beer, wine, sake, mead, cider, perry and other beverages through fermentation on a small scale as a hobby for personal consumption, free distribution at social gatherings, amateur brewing competitions or other non-commercial reasons...
use reducing agents such as
sodium metabisulfiteSodium metabisulfite or sodium pyrosulfite is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium...
or
potassium metabisulfitePotassium metabisulfite, K2S2O5, also known as potassium pyrosulfite, is a white crystalline powder with a pungent sulfur odour. The main use for the chemical is as an antioxidant or chemical sterilant. It is a disulfite and is chemically very similar to sodium metabisulfite, with which it is...
to remove chloramine from brewing fermented beverages. Chloramine, like
chlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, can be removed by boiling. However the boiling time required to remove the chloramine is much longer than that of chlorine. 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 synthesisOrganic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. One example is
N-chloromorpholine ClN(CH
2CH
2)
2O,
N-chloro
piperidinePiperidine is an organic compound with the molecular formula 5NH. This heterocyclic amine consists of a six-membered ring containing five methylene units and one nitrogen atom...
, and
N-chloro
quinuclidiniumQuinuclidine is an organic compound and a bicyclic amine and used as a catalyst and a chemical building block. It is a strong base with pKa of the conjugate acid of 11.0. This is due to greater availability of the nitrogen lone pair...
chloride.
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
chlorinationChlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
to
chloraminationChloramination is the treatment of drinking water with a chloramine disinfectant. Both chlorine and small amounts of ammonia are added to the water one at a time which react together to form chloramine , a long lasting disinfectant...
. While chloramination produces fewer total halogenated disinfection by-products, it produces greater concentrations of unregulated iodinated disinfection by-products and
N-NitrosodimethylamineN-Nitrosodimethylamine , also known as dimethylnitrosamine , is a semi-volatile organic chemical that is highly toxic and is a suspected human carcinogen. The US Environmental Protection Agency has determined that the maximum admissible concentration of NDMA in drinking water is 7 ng L−1...
. Both iodinated disinfection by-products and
N-NitrosodimethylamineN-Nitrosodimethylamine , also known as dimethylnitrosamine , is a semi-volatile organic chemical that is highly toxic and is a suspected human carcinogen. The US Environmental Protection Agency has determined that the maximum admissible concentration of NDMA in drinking water is 7 ng L−1...
have been shown to be genotoxic.
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