Monochloramine

Source: Wikipedia, the free encyclopedia.
Monochloramine
Stereo, skeletal formula of chloramine with all explicit hydrogens added
Spacefill model of chloramine
Names
Other names
  • Chloramine
  • Chloramide[1]
Identifiers
3D model (
JSmol
)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.031.095 Edit this at Wikidata
EC Number
  • 234-217-9
KEGG
MeSH chloramine
UNII
UN number 3093
  • InChI=1S/ClH2N/c1-2/h2H2 ☒N
    Key: QDHHCQZDFGDHMP-UHFFFAOYSA-N ☒N
  • NCl
Properties
NH
2Cl
Molar mass 51.476 g mol−1
Appearance Colorless gas
Melting point −66 °C (−87 °F; 207 K)
Acidity (pKa) 14
Basicity (pKb) 15
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Corrosive acid
Ingestion hazards
 Corrosive; nausea and vomiting
Inhalation hazards
 Corrosive
Eye hazards
 Irritation
Skin hazards
 Irritation
GHS labelling:
GHS07: Exclamation mark GHS08: Health hazard GHS05: Corrosive
Danger
H290, H314, H315, H319, H335, H372, H412
P234, P260, P261, P264, P270, P271, P273, P280, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P314, P321, P332+P313, P337+P313, P362, P363, P390, P403+P233, P404, P405, P501
NFPA 704 (fire diamond)
[2]
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard ACID: Acid
3
1
1
ACID
Lethal dose or concentration (LD, LC):
935 mg/kg (rat, oral)[2]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Monochloramine, often called chloramine, is the chemical compound with the formula NH2Cl. Together with dichloramine (NHCl2) and nitrogen trichloride (NCl3), it is one of the three chloramines of ammonia.[3] It is a colorless liquid at its melting point of −66 °C (−87 °F), 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.[4]

Water treatment

See also: Chloramination

Chloramine is used as a disinfectant for water. It is less aggressive than chlorine and more stable against light than hypochlorites.[5]

Drinking water disinfection

Chloramine is commonly used in low

chlorocarbons such as chloroform and carbon tetrachloride. Such compounds have been identified as carcinogens and in 1979 the United States Environmental Protection Agency (EPA) began regulating their levels in US drinking water.[6]

Some of the unregulated byproducts may possibly pose greater health risks than the regulated chemicals.[7]

Due to its acidic nature, 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. Fortunately, water treatment plants can add caustic chemicals at the plant which have the dual purpose of reducing the corrosivity of the water, and stabilizing the disinfectant.[8]

Swimming pool disinfection

In

sanitizer and, if not managed correctly, more irritating to the eyes of swimmers. Chloramines are responsible for the distinctive "chlorine" smell of swimming pools, which is often misattributed to elemental chlorine by the public.[9][10] Some pool test kits designed for use by homeowners do not distinguish free chlorine and chloramines, which can be misleading and lead to non-optimal levels of chloramines in the pool water.[11]
There is also evidence that exposure to chloramine can contribute to
swimmers.[12] Respiratory problems related to chloramine exposure are common and prevalent among competitive swimmers.[13]

Though chloramine's distinctive smell has been described by some as pleasant and even nostalgic,[14] its formation in pool water as a result of bodily fluids being exposed to chlorine can be minimised by encouraging showering and other hygiene methods prior to entering the pool,[15] as well as refraining from swimming while suffering from digestive illnesses and taking breaks to use the bathroom.[16][17]

Safety

US EPA

mutations which may lead to cancer.[19]

Lead poisoning incidents

In the year 2000,

Washington, DC switched from chlorine to monochloramine, causing lead to leach from unreplaced pipes. The number of babies with elevated blood lead levels rose about tenfold, and by one estimate fetal deaths rose between 32% and 63%.[20]

Trenton, Missouri made the same switch, causing about one quarter of tested households to exceed EPA drinking water lead limits in the period from 2017 to 2019. 20 children tested positive for lead poisoning in 2016 alone.[20] In 2023, Virginia Tech Professor Marc Edwards said lead spikes occur in several water utility system switchovers per year, due to lack of sufficient training and lack of removal of lead pipes.[20] Lack of utility awareness that lead pipes are still in use is also part of the problem; the EPA has required all water utilities in the United States to prepare a complete lead pipe inventory by October 16, 2024.[21]

Synthesis and chemical reactions

Chloramine is a highly unstable compound in concentrated form. Pure chloramine decomposes violently above −40 °C (−40 °F).[22] 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.[5]

Production

In dilute aqueous solution, chloramine is prepared by the reaction of ammonia with sodium hypochlorite:[5]

NH3 + NaOCl → NH2Cl + NaOH

This reaction is also the first step of the

ammonium ions
(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 + Cl2 ⇌ NH2Cl + NH4Cl

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:[23]

RR′NCl + H2O ⇌ RR′NH + HOCl

The quantitative

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 (2.8×10−10 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 

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+ ⇌ NHCl2 + NH+
4
3 NHCl2 + H+ ⇌ 2 NCl3 + 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: E° = +1.48 V, in basic solution E° = +0.81 V):[5]

NH2Cl + 2 H+ + 2 e− → 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 seen in the Olin 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

disulfides in the same manner as hypochlorous acid,[24] but only possesses 0.4% of the biocidal effect of HClO.[25]

See also

References

  1. ^ "CHLORAMINE". CAMEO Chemicals. NOAA.
  2. ^ a b "Chloramine T Trihydrate SDS". Fisher.[permanent dead link]
  3. ISBN 978-0-08-037941-8
    .
  4. ISBN 9780521782845
    .
  5. ^ a b c d Hammerl, Anton; Klapötke, Thomas M. (2005), "Nitrogen: Inorganic Chemistry", Encyclopedia of Inorganic Chemistry (2nd ed.), Wiley, pp. 55–58
  6. ^ "Govinfo" (PDF).
  7. PMID 19736234
    .
  8. PMID 17384768
    .
  9. ISBN 978-1-58011-533-9
    .
  10. ^ "Controlling Chloramines in Indoor Swimming Pools". NSW Government. Archived from the original on 2011-04-03. Retrieved 2013-02-15.
  11. ^ Hale, Chris (20 April 2016). "Pool Service Information". Into The Blue Pools. Retrieved 22 April 2016.
  12. S2CID 26017985
    .
  13. S2CID 21688495
    .
  14. ^ "The smell of chlorine: nostalgic or noxious?". Rheem Thermal Swimming Pool Heating. 2016-08-22. Retrieved 2020-11-22.
  15. ^ "Chloramines: Understanding "Pool Smell"". chlorine.americanchemistry.com. Retrieved 2020-11-22.
  16. ^ "The Chlorine Smell From Pools May Actually Indicate Bodily Fluids Mixed In The Water, According To The CDC". Bustle. Retrieved 2020-11-22.
  17. ^ "Chemical Irritation of the Eyes and Lungs | Healthy Swimming | Healthy Water | CDC". www.cdc.gov. 2019-05-15. Retrieved 2020-11-22.
  18. S2CID 41960634
    .
  19. ^
    PMID 17980649
    .
  20. ^ a b c Allison Kite (July 20, 2022). "'Time bomb' lead pipes will be removed. But first water utilities have to find them". NPR. Midwest Newsroom.
  21. ^ "Lead and Copper Rule Improvements". 4 May 2022.
  22. ISBN 0-12-352651-5
    .
  23. ISBN 978-3527306732
    .
  24. doi:10.1016/0043-1354(87)90007-8
    .
  25. doi:10.1002/j.1551-8833.1966.tb01719.x
    .

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Monochloramine&oldid=1218999698"