View source for Chlorine dioxide

{{short description|Chemical compound}}
{{Use mdy dates|date=March 2022}}
{{Distinguish|text=the [[chlorite]] ion or [[dichlorine dioxide]]}}
{{Redirect|E926|the furry-themed website e926|e621 (website)}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 476998061
| ImageFileL1 = Chlorine-dioxide.png
| ImageFileL1_Ref = {{Chemboximage|correct|??}}
| ImageNameL1 = Structural formula of chlorine dioxide with assorted dimensions
| ImageFileR1 = Chlorine-dioxide-3D-vdW.svg
| ImageFileR1_Ref = {{Chemboximage|correct|??}}
| ImageNameR1 = Spacefill model of chlorine dioxide
| ImageFile2 = Chlorine dioxide gas and solution.jpg
| ImageSize2 = 160
| IUPACName = Chlorine dioxide
| SystematicName = <!-- Dioxo-λ<sup>4</sup>-chlorane (substitutive) OR Dioxidochlorine(•) (additive) -->
| OtherNames = {{Unbulleted list|Chlorine(IV) oxide}}
|Section1={{Chembox Identifiers
| CASNo = 10049-04-4
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 24870
| ChemSpiderID = 23251
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 8061YMS4RM
| UNNumber = 9191
| EINECS = 233-162-8
| MeSHName = Chlorine+dioxide
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 29415
| RTECS = FO3000000
| Gmelin = 1265
| SMILES = O=[Cl]=O
| SMILES1 = O=Cl[O]
| StdInChI = 1S/ClO2/c2-1-3
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| InChI = 1/ClO2/c2-1-3
| StdInChIKey = OSVXSBDYLRYLIG-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| InChIKey = OSVXSBDYLRYLIG-UHFFFAOYAC}}
|Section2={{Chembox Properties
| Cl=1 | O=2
| Appearance = Yellow to reddish gas
| Odor = Acrid
| Density = 2.757 g dm<sup>−3</sup><ref>{{CRC91|page=4–58}}</ref>
| MeltingPtC = -59
| BoilingPtC = 11
| Solubility = 8&nbsp;g/L at 20&nbsp;°C
| SolubleOther = Soluble in alkaline solutions and [[sulfuric acid]]
| HenryConstant = {{val|4.01e-2|u=atm m<sup>3</sup> mol<sup>−1</sup>}}
| pKa = 3.0(5)
| VaporPressure = >1 atm<ref name=PGCH />
}}
|Section3={{Chembox Thermochemistry
| DeltaHf = 104.60 kJ/mol
| Entropy = 257.22 J K<sup>−1</sup> mol<sup>−1</sup>}}
|Section4={{Chembox Hazards
| MainHazards = Highly toxic, corrosive, unstable, powerful oxidizer
| ExternalSDS = [http://www.ercoworldwide.com/wp-content/uploads/SDSC-Chlorine-Dioxide-Solution.pdf Safety Data Sheet] [https://web.archive.org/web/20190725104307/http://www.ercoworldwide.com/wp-content/uploads/SDSC-Chlorine-Dioxide-Solution.pdf Archive].
| GHSPictograms = {{GHS flame over circle}}{{GHS corrosion}}{{GHS skull and crossbones}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|271|314|300+310+330|H372}}
| PPhrases = {{P-phrases|210|220|280|283|260|264|271|284|301+310|304+340|306+360|305+351+338|371+380+375|403+233|405|501}}
| NFPA-H = 3
| NFPA-F = 0
| NFPA-R = 4
| NFPA-S = OX
| LD50 = 94 mg/kg (oral, rat)<ref>{{cite book |last1=Dobson |first1=Stuart |last2=Cary |first2=Richard |title=Chlorine dioxide (gas) |publisher=World Health Organization. |page=4 |url=https://apps.who.int/iris/handle/10665/42421 |date =2002 | last3 =  International Programme on Chemical Safety|hdl=10665/42421 |isbn=978-92-4-153037-8 |access-date=17 August 2020}}</ref>
| LCLo = 260 ppm (rat, 2 hr)<ref name=IDLH>{{IDLH|10049044|Chlorine dioxide}}</ref>
| PEL = TWA 0.1 ppm (0.3 mg/m<sup>3</sup>)<ref name=PGCH>{{PGCH|0116}}</ref>
| IDLH = 5 ppm<ref name=PGCH />
| REL = TWA 0.1 ppm (0.3 mg/m<sup>3</sup>) ST 0.3 ppm (0.9 mg/m<sup>3</sup>)<ref name=PGCH />
}}
}}
'''Chlorine dioxide''' is a [[chemical compound]] with the formula ClO<sub>2</sub> that exists as yellowish-green [[gas]] above 11&nbsp;°C, a reddish-brown liquid between 11&nbsp;°C and −59&nbsp;°C, and as bright orange crystals below −59&nbsp;°C. It is usually handled as an aqueous solution.  It is commonly used as a [[bleach]]. More recent developments have extended its applications in [[food processing]] and as a [[disinfectant]].

== Structure and bonding ==
[[File:ClO2.svg|upright=0.8|thumb|left|The structure according to Pauling's ''General Chemistry'']]
[[File:Chlorine-dioxide solution-vs-gas.svg|thumb|left|Vapor-liquid equilibrium above an aqueous solution of chlorine dioxide at various temperatures]]
The molecule ClO<sub>2</sub> has an odd number of [[valence electron]]s, and therefore, it is a [[Paramagnetism|paramagnetic]] [[radical (chemistry)|radical]]. It is an unusual "example of an odd-electron molecule  stable toward dimerization" ([[nitric oxide]] being another example).<ref>{{Greenwood&Earnshaw2nd|page=845}}</ref>

[[File:ClO2 orthorhombic Pbca cmp-23207 computed.png|thumb|A unit cell of the orthorhombic ClO<sub>2</sub> crystal shown in an arbitrary direction.]]
ClO<sub>2</sub> crystallizes in the orthorhombic [[List of space groups|Pbca]] space group.<ref>{{Cite web |title=mp-23207: ClO2 (Orthorhombic, Pbca, 61) |url=https://materialsproject.org/materials/mp-23207/ |access-date=2022-11-03 |website=Materials Project}}</ref>

==History==
In 1933, [[Lawrence O. Brockway]], a graduate student of [[Linus Pauling]], proposed a structure that involved a [[three-electron bond]] and two single bonds.<ref>{{cite journal |doi=10.1073/pnas.19.3.303 |last=Brockway |first=L. O. |title=The Three-Electron Bond in Chlorine Dioxide |journal=Proceedings of the National Academy of Sciences |volume=19 |issue=3 |pages=303–307 |date=March 1933 |pmid=16577512 |pmc=1085967 |bibcode = 1933PNAS...19..303B |url=http://authors.library.caltech.edu/9165/1/BROpnas33b.pdf |doi-access=free }}</ref> However, Pauling in his ''General Chemistry'' shows a double bond to one oxygen and a single bond plus a three-electron bond to the other. The valence bond structure would be represented as the resonance hybrid depicted by Pauling.<ref name=Pauling>{{cite book |page=264|last=Linus Pauling |title=General chemistry |publisher=Dover Publications |location=Mineola, New York |year=1988 |isbn=0-486-65622-5 |url-access=registration |url=https://archive.org/details/generalchemistry00paul_0 }}</ref> The three-electron bond represents a bond that is ''weaker'' than the double bond. In [[molecular orbital theory]] this idea is commonplace if the third electron is placed in an anti-bonding orbital. Later work has confirmed that the [[HOMO|highest occupied molecular orbital]] is indeed an incompletely-filled antibonding orbital.<ref>{{Cite journal | doi = 10.1016/j.ijms.2005.12.046 | title = Core-level excitation and fragmentation of chlorine dioxide | year = 2006 | last1 = Flesch | first1 = R. | last2 = Plenge | first2 = J. | last3 = Rühl | first3 = E. | journal = International Journal of Mass Spectrometry | volume = 249-250 | pages = 68–76|bibcode = 2006IJMSp.249...68F }}</ref>

== Preparation ==
Chlorine dioxide was first prepared in 1811 by [[Sir Humphry Davy]].<ref>Aieta, E. Marco, and James D. Berg. "A Review of Chlorine Dioxide in Drinking Water Treatment." Journal (American Water Works Association) 78, no. 6 (1986): 62-72. Accessed April 24, 2021. http://www.jstor.org/stable/41273622</ref>

The reaction of chlorine with oxygen under conditions of flash photolysis in the presence of ultraviolet light results in trace amounts of chlorine dioxide formation.<ref>{{Cite journal |last1=Porter |first1=George |last2=Wright |first2=Franklin J. |date=1953 |title=Studies of free radical reactivity by the methods of flash photolysis. The photochemical reaction between chlorine and oxygen |url=http://xlink.rsc.org/?DOI=df9531400023 |journal=Discussions of the Faraday Society |language=en |volume=14 |pages=23 |doi=10.1039/df9531400023 |issn=0366-9033}}</ref>
: <chem>Cl2 + 2 O2 ->[\ce{UV}] 2 ClO2 ^</chem>'''.'''

Chlorine dioxide can decompose violently when separated from diluting substances. As a result, preparation methods that involve producing solutions of it without going through a gas-phase stage are often preferred.
=== Oxidation of chlorite ===
In the laboratory, ClO<sub>2</sub> can be prepared by oxidation of [[sodium chlorite]] with chlorine:<ref>{{cite book | last1 = Derby | first1 = R. I. | last2 = Hutchinson | first2 = W. S. | chapter = Chlorine(IV) Oxide | year = 1953 | title = Inorganic Syntheses | volume = 4 | pages = 152–158 | doi=10.1002/9780470132357.ch51| isbn = 978-0-470-13235-7 }}</ref>
{{block indent|{{chem2|NaClO2}} + {{frac|1|2}} {{chem2|Cl2 -> ClO2 + NaCl}}}}

Traditionally, chlorine dioxide for [[disinfectant|disinfection]] applications has been made from sodium [[chlorite]] or the sodium chlorite–[[hypochlorite]] method:
{{block indent|{{chem2|2 NaClO2 + 2 HCl + NaOCl -> 2 ClO2 + 3 NaCl + H2O}}}}
or the sodium chlorite–[[hydrochloric acid]] method:
{{block indent|{{chem2|5 NaClO2 + 4 HCl -> 5 NaCl + 4 ClO2 + 2 H2O}}}}
or the chlorite–[[sulfuric acid]] method:
{{block indent|{{chem2|4 ClO2(-) + 2 H2SO4 -> 2 ClO2 + HClO3 + 2 SO4(2-) + H2O + HCl}}}}

All three methods can produce chlorine dioxide with high chlorite conversion yield. Unlike the other processes, the chlorite–sulfuric acid method is completely chlorine-free, although it suffers from the requirement of 25% more chlorite to produce an equivalent amount of chlorine dioxide. Alternatively, [[hydrogen peroxide]] may be efficiently used in small-scale applications.<ref name="Vogt, H. 2010" />

Addition of sulfuric acid or any strong acid to [[chlorate]] salts produces chlorine dioxide.<ref name=Pauling/>
=== Reduction of chlorate ===
In the laboratory, chlorine dioxide can also be prepared by reaction of [[potassium chlorate]] with [[oxalic acid]]:
{{block indent|{{chem2|KClO3 + H2C2O4 ->}} {{frac|1|2}} {{chem2|K2C2O4 + ClO2 + CO2 + H2O}}}}

or with oxalic and sulfuric acid:
{{block indent|{{chem2|KClO3}} + {{frac|1|2}} {{chem2|H2C2O4}} + {{chem2|H2SO4 -> KHSO4 + ClO2 + CO2 + H2O}}}}

Over 95% of the chlorine dioxide produced in the world today is made by reduction of [[sodium chlorate]], for use in [[bleaching of wood pulp|pulp bleaching]]. It is produced with high efficiency in a strong acid solution with a suitable [[reducing agent]] such as [[methanol]], [[hydrogen peroxide]], [[hydrochloric acid]] or [[sulfur dioxide]].<ref name="Vogt, H. 2010">{{Ullmann|last1=Vogt|first1=H.|last2=Balej|first2=J.|last3=Bennett|first3=J. E.|last4=Wintzer|first4=P.|last5=Sheikh|first5=S. A.|last6=Gallone|first6=P.|last7=Vasudevan|first7=S.|last8=Pelin|first8=K.|date=2010|title=Chlorine Oxides and Chlorine Oxygen Acids|DOI=10.1002/14356007.a06_483.pub2}}</ref> Modern technologies are based on methanol or hydrogen peroxide, as these chemistries allow the best economy and do not co-produce elemental chlorine. The overall reaction can be written as:<ref>{{cite conference |url=http://www.tappi.org/Downloads/unsorted/UNTITLED---ipb96453pdf.aspx |title=Mechanism of the Methanol Based ClO2 Generation Process |first1=Y. |last1=Ni |first2=X. |last2=Wang |year=1996 |publisher=[[TAPPI]] |book-title=International Pulp Bleaching Conference |pages=454–462 }}{{dead link|date=July 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

{{block indent|chlorate + acid + reducing agent → chlorine dioxide + by-products}}

As a typical example, the reaction of [[sodium chlorate]] with [[hydrochloric acid]] in a single reactor is believed to proceed through the following pathway:
{{block indent|{{chem2|ClO3(-) + Cl(-) + H(+) -> ClO2(-) + HOCl}}}}
{{block indent|{{chem2|ClO3(-) + ClO2(-) + 2 H(+) -> 2 ClO2 + H2O}}}}
{{block indent|{{chem2|HOCl + Cl(-) + H(+) -> Cl2 + H2O}}}}

which gives the overall reaction 
{{block indent|{{chem2|ClO3(-) + Cl(-) + 2 H(+) -> ClO2}} + {{frac|1|2}} {{chem2|Cl2 + H2O}}.}}

The commercially more important production route uses [[methanol]] as the reducing agent and [[sulfuric acid]] for the acidity. Two advantages of not using the chloride-based processes are that there is no formation of elemental chlorine, and that [[sodium sulfate]], a valuable chemical for the pulp mill, is a side-product. These methanol-based processes provide high efficiency and can be made very safe.<ref name="Vogt, H. 2010"/>

The variant process using sodium chlorate, hydrogen peroxide and sulfuric acid has been increasingly used since 1999 for water treatment and other small-scale [[disinfectant|disinfection]] applications, since it produce a chlorine-free product at high efficiency, over 95%.{{cn|date=September 2022}}

=== Other processes ===
Very pure chlorine dioxide can also be produced by electrolysis of a chlorite solution:<ref name=white>{{cite book |last1=White |first1=George W. |first2=Geo Clifford |last2=White |title=The handbook of chlorination and alternative disinfectants |publisher=John Wiley |location=New York |year=1999 |isbn=0-471-29207-9 |edition=4th}}</ref>

{{block indent|{{chem2|NaClO2 + H2O -> ClO2 + NaOH}} + {{frac|1|2}} {{chem2|H2}}}}

High-purity chlorine dioxide gas (7.7% in air or nitrogen) can be produced by the gas–solid method, which reacts dilute chlorine gas with solid sodium chlorite:<ref name=white/>
{{block indent|{{chem2|NaClO2}} + {{frac|1|2}} {{chem2|Cl2 -> ClO2 + NaCl}}}}


== Handling properties ==
Chlorine dioxide is very different from elemental chlorine.<ref name="Vogt, H. 2010"/> One of the most important qualities of chlorine dioxide is its high water solubility, especially in cold water. Chlorine dioxide does not [[Hydrolysis|react with water]]; it remains a dissolved gas in solution. Chlorine dioxide is approximately 10 times more soluble in water than elemental chlorine<ref name="Vogt, H. 2010" /> but its solubility is very temperature-dependent.

At partial pressures above {{Convert|10|kPa|psi|abbr=on}}<ref name="Vogt, H. 2010" /> (or gas-phase concentrations greater than 10% volume in air at [[Standard Temperature and Pressure|STP]]) of ClO<sub>2</sub> may explosively [[Chemical decomposition|decompose]] into [[chlorine]] and [[oxygen]]. The decomposition can be initiated by light, hot spots, chemical reaction, or pressure shock. Thus, chlorine dioxide is never handled as a pure gas, but is almost always handled in an aqueous solution in concentrations between 0.5 to 10&nbsp;grams per liter. Its solubility increases at lower temperatures, so it is common to use chilled water (5&nbsp;°C, 41 °F) when storing at concentrations above 3&nbsp;grams per liter. In many countries, such as the United States, chlorine dioxide may not be transported at any concentration and is instead almost always produced on-site.<ref name="Vogt, H. 2010" /> In some countries,{{which|date=April 2022}} chlorine dioxide solutions below 3&nbsp;grams per liter in concentration may be transported by land, but they are relatively unstable and deteriorate quickly.

==Uses==
Chlorine dioxide is used for [[bleaching of wood pulp]] and for the [[disinfectant|disinfection]] (called [[Water chlorination|chlorination]]) of municipal drinking water,<ref>{{cite book| title = Inorganic Chemistry: An Industrial and Environmental Perspective| url = https://archive.org/details/inorganicchemist00swad_535| url-access = limited| first = Thomas Wilson | last = Swaddle| publisher = Academic Press| year = 1997| isbn = 0-12-678550-3| pages = [https://archive.org/details/inorganicchemist00swad_535/page/n199 198]–199
}}</ref><ref name="epa1999">{{citation |title=Alternative Disinfectants and Oxidants Manual, chapter 4: Chlorine Dioxide |publisher=US Environmental Protection Agency: Office of Water |url=https://www.epa.gov/safewater/mdbp/pdf/alter/chapt_4.pdf |date=April 1999 |access-date=2009-11-27 |url-status=dead |archive-url=https://web.archive.org/web/20150905194840/https://www.epa.gov/safewater/mdbp/pdf/alter/chapt_4.pdf |archive-date= 2015-09-05}}</ref>{{rp|4-1}}<ref name="block2001" /> treatment of water in oil and gas applications, disinfection in the food industry, microbiological control in cooling towers, and textile bleaching.<ref name="Simpson">{{cite book |last1=Simpson |first1=Gregory Deward |title=Practical Chlorine Dioxide |date=2005 |publisher=Greg D. Simpson & Associates |location=Colleyville, Texas |isbn=0-9771985-0-2 | edition=Volume 1 }}</ref> As a disinfectant, it is effective even at low concentrations because of its unique qualities.<ref name="Vogt, H. 2010" /><ref name="epa1999"/><ref name="Simpson"/>

=== Bleaching ===
Chlorine dioxide is sometimes used for bleaching of wood pulp in combination with chlorine, but it is used alone in ECF (elemental chlorine-free) bleaching sequences. It is used at moderately acidic [[pH]] (3.5 to 6). The use of chlorine dioxide minimizes the amount of [[Organochloride|organochlorine]] compounds produced.<ref name="eero">{{cite book
| first= E. |last=Sjöström
| title= Wood Chemistry: Fundamentals and Applications
| publisher= [[Academic Press]]
| year= 1993
| isbn= 0-12-647480-X
| oclc= 58509724}}</ref> Chlorine dioxide (ECF technology) currently is the most important [[bleach]]ing method worldwide. About 95% of all bleached [[kraft pulp]] is made using chlorine dioxide in ECF bleaching sequences.<ref>{{cite web|url=http://www.aet.org/science_of_ecf/eco_risk/2005_pulp.html|title=AET – Reports – Science – Trends in World Bleached Chemical Pulp Production: 1990–2005|access-date=2016-02-26|archive-url=https://web.archive.org/web/20170730101540/http://www.aet.org/science_of_ecf/eco_risk/2005_pulp.html|archive-date=2017-07-30|url-status=dead}}</ref>

Chlorine dioxide has been used to bleach [[flour]].<ref>{{cite journal | title = Maturing and Bleaching Agents in Producing Flour | first = C. G. | last = Harrel | journal = Industrial & Engineering Chemistry | date = 1952 | volume = 44 | issue = 1 | pages =  95–100 | doi = 10.1021/ie50505a030 }}</ref>

=== Water treatment ===
{{Further|Water chlorination|Portable water purification#Chlorine dioxide}}
The water treatment plant at [[Niagara Falls, New York]] first used chlorine dioxide for [[drinking water]] treatment in 1944 for destroying "taste and odor producing [[phenolic compounds]]."<ref name="epa1999" />{{rp|4-17}}<ref name="block2001" /> Chlorine dioxide was introduced as a drinking water disinfectant on a large scale in 1956, when [[Brussels]], Belgium, changed from chlorine to chlorine dioxide.<ref name="block2001" /> Its most common use in water treatment is as a pre-[[oxidant]] prior to chlorination of drinking water to destroy natural water impurities that would otherwise produce [[trihalomethane]]s upon exposure to free chlorine.<ref>{{Cite journal | doi = 10.1016/j.desal.2004.10.022 | title = Trihalomethane formation during chemical oxidation with chlorine, chlorine dioxide and ozone of ten Italian natural waters | year = 2005 | last1 = Sorlini | first1 = S. | last2 = Collivignarelli | first2 = C. | journal = Desalination | volume = 176| issue = 1–3| pages = 103–111 | bibcode = 2005Desal.176..103S }}</ref><ref>{{cite journal | pmid = 8758861 | title = A pilot study on trihalomethane formation in water treated by chlorine dioxide |lang=zh | last1 = Li |first1=J. | last2 = Yu |first2=Z. | last3 = Gao |first3=M. | journal = Zhonghua Yufang Yixue Zazhi (Chinese Journal of Preventive Medicine) | volume = 30 | issue = 1 | pages = 10–13 | year = 1996 }}</ref><ref name="volk2002">{{cite journal | title = Implementation of chlorine dioxide disinfection: Effects of the treatment change on drinking water quality in a full-scale distribution system | first1= C. J. |last1=Volk | first2 = R. |last2=Hofmann | first3 = C. |last3=Chauret | first4 = G. A. |last4=Gagnon | first5 = G. |last5=Ranger | first6 = R. C. |last6=Andrews | journal = Journal of Environmental Engineering and Science | volume = 1 | issue = 5 | pages = 323–330 | year = 2002 | doi = 10.1139/s02-026 | bibcode= 2002JEES....1..323V }}</ref> Trihalomethanes are suspected carcinogenic disinfection by-products<ref>{{cite journal | doi = 10.2307/3429432 | journal = Environmental Health Perspectives | year = 1982 | title = Trihalomethanes as initiators and promoters of carcinogenesis | first1= M. A. |last1=Pereira | first2 = L. H.|last2= Lin | first3 = J. M. |last3=Lippitt | first4 = S. L. |last4=Herren | volume = 46 | pmc = 1569022 | pages = 151–156 | pmid = 7151756 | jstor = 3429432 }}</ref> associated with chlorination of naturally occurring organics in raw water.<ref name="volk2002" /> Chlorine dioxide also produces 70% fewer halomethanes in the presence of natural organic matter compared to when elemental chlorine or bleach is used.<ref name=":1">{{Cite web|title=Guidelines for drinking-water quality, 4th edition, incorporating the 1st addendum|url=https://www.who.int/publications-detail-redirect/9789241549950|access-date=2021-11-29|publisher=[[World Health Organization]]|language=en}}</ref>

Chlorine dioxide is also superior to chlorine when operating above [[pH]] 7,<ref name="epa1999" />{{rp|4-33}} in the presence of ammonia and amines,<ref>{{Cite web|title=Chlorine dioxide as a disinfectant|url=https://www.lenntech.com/processes/disinfection/chemical/disinfectants-chlorine-dioxide.htm|access-date=2021-11-25|publisher=Lenntech}}</ref> and for the control of biofilms in water distribution systems.<ref name="volk2002" /> Chlorine dioxide is used in many industrial water treatment applications as a [[biocide]], including [[cooling towers]], process water, and food processing.<ref>{{Cite journal | first5 = D.| last5 = Park | first4 = R.| journal = Food Microbiology | volume = 19| pages = 261–267 | issue = 4| last4 = Grodner | first3 = R. | last1 = Andrews | year = 2002 | title = Chlorine dioxide wash of shrimp and crawfish an alternative to aqueous chlorine | first1 = L. | last2 = Key| last3 = Martin | first2 = A. | doi = 10.1006/fmic.2002.0493 }}</ref>

Chlorine dioxide is less corrosive than chlorine and superior for the control of ''[[Legionella]]'' bacteria.<ref name="block2001">{{cite book | title = Disinfection, Sterilization, and Preservation | first= Seymour Stanton |last=Block | edition = 5th | publisher = Lippincott, Williams & Wilkins | year = 2001 | isbn = 0-683-30740-1 | page = 215}}</ref><ref>{{cite journal | journal = Infection Control and Hospital Epidemiology | volume = 28 | issue = 8 | pages = 1009–1012 | year = 2007 | title = Safety and Efficacy of Chlorine Dioxide for ''Legionella'' control in a Hospital Water System | first1 = Zhe | last1 = Zhang | first2 = Carole | last2 = McCann | first3 = Janet E. | last3 = Stout | first4 = Steve | last4 = Piesczynski | first5 = Robert | last5 = Hawks | first6 = Radisav | last6 = Vidic | first7 = Victor L. | last7 = Yu | url = http://www.legionella.org/ZhangICHE07.pdf | access-date = 2009-11-27 | doi = 10.1086/518847 | pmid = 17620253 | s2cid = 40554616 | archive-date = 2011-07-19 | archive-url = https://web.archive.org/web/20110719125409/http://www.legionella.org/ZhangICHE07.pdf | url-status = dead }}</ref>
Chlorine dioxide is superior to some other secondary water disinfection methods, in that chlorine dioxide is not negatively impacted by pH, does not lose efficacy over time, because the bacteria will not grow resistant to it, and is not negatively impacted by [[silica]] and [[phosphate]]s, which are commonly used potable water corrosion inhibitors. In the United States, it is an [[Environmental Protection Agency|EPA]]-registered biocide.

It is more effective as a disinfectant than chlorine in most circumstances against waterborne pathogenic agents such as [[virus]]es,<ref>{{cite journal |last1=Ogata |first1=N. |last2=Shibata |first2=T. |title=Protective effect of low-concentration chlorine dioxide gas against influenza A virus infection |journal=Journal of General Virology |volume=89 |issue=pt 1 |pages=60–67 |date=January 2008 |pmid=18089729 |doi=10.1099/vir.0.83393-0 |doi-access=free }}</ref> [[bacteria]], and [[protozoa]] – including the [[Microbial cyst|cysts]] of ''[[Giardia lamblia|Giardia]]'' and the [[oocyst]]s of ''[[Cryptosporidiosis|Cryptosporidium]]''.<ref name="epa1999" />{{rp|4-20–4-21}}

The use of chlorine dioxide in water treatment leads to the formation of the by-product chlorite, which is currently limited to a maximum of 1 part per million in drinking water in the USA.<ref name="epa1999" />{{rp|4-33}} This EPA standard limits the use of chlorine dioxide in the US to relatively high-quality water, because this minimizes chlorite concentration, or water that is to be treated with iron-based coagulants, because iron can reduce chlorite to chloride.<ref>{{Cite web|title=Chlorine Dioxide & Chlorite {{!}} Public Health Statement {{!}} ATSDR|url=https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=580&toxid=108|access-date=2021-11-25|location=United States|publisher=[[Centers for Disease Control and Prevention]]}}</ref> The World Health Organization also advises a 1ppm dosification.<ref name=":1" />

=== Use in public crises ===
Chlorine dioxide has many applications as an oxidizer or disinfectant.<ref name="Vogt, H. 2010" /> Chlorine dioxide can be used for air disinfection<ref>{{cite journal|last1=Zhang|first1=Y.-L.|last2=Zheng|first2=S.-Y.|last3=Zhi|first3=Q.|year=2007|title=Air Disinfection with Chlorine Dioxide in Saps|url=http://www.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=07519213EN|journal=Journal of Environment and Health|volume=24|issue=4|pages=245–246}}</ref> and was the principal agent used in the decontamination of buildings in the United States after the [[2001 anthrax attacks]].<ref>{{cite web|url=http://www.epa.gov/opp00001/factsheets/chemicals/chlorinedioxidefactsheet.htm|title=Anthrax spore decontamination using chlorine dioxide|year=2007|location=United States|publisher=Environmental Protection Agency|access-date=2009-11-27}}</ref> After the disaster of [[Hurricane Katrina]] in [[New Orleans]], [[Louisiana]], and the surrounding Gulf Coast, chlorine dioxide was used to eradicate dangerous [[Mold (fungus)|mold]] from houses inundated by the flood water.<ref>{{cite journal|last1=Sy|first1=Kaye V.|last2=McWatters|first2=Kay H.|last3=Beuchat|first3=Larry R.|year=2005|title=Efficacy of Gaseous Chlorine Dioxide as a Sanitizer for Killing Salmonella, Yeasts, and Molds on Blueberries, Strawberries, and Raspberries|journal=Journal of Food Protection|publisher=International Association for Food Protection|volume=68|issue=6|pages=1165–1175|doi=10.4315/0362-028x-68.6.1165|pmid=15954703|doi-access=free}}</ref>

In addressing the COVID-19 pandemic, the [[United States Environmental Protection Agency|U.S. Environmental Protection Agency]] has posted a list of many [[Disinfectant|disinfectants]] that meet its criteria for use in environmental measures against the causative [[Coronavirus disease 2019|coronavirus]].<ref>{{Cite web|url=https://cen.acs.org/biological-chemistry/infectious-disease/How-we-know-disinfectants-should-kill-the-COVID-19-coronavirus/98/web/2020/03|title=How we know disinfectants should kill the COVID-19 coronavirus|website=Chemical & Engineering News|language=en|access-date=2020-03-28}}</ref><ref>{{Cite web|url=https://www.epa.gov/pesticide-registration/list-n-disinfectants-use-against-sars-cov-2|title=List N: Disinfectants for Use Against SARS-CoV-2|date=2020-03-13|location=United States|website=[[Environmental Protection Agency]]|language=en|access-date=2020-03-28}}</ref> Some are based on [[sodium chlorite]] that is activated into chlorine dioxide, though differing formulations are used in each product. Many other products on the EPA list contain [[sodium hypochlorite]], which is similar in name but should not be confused with sodium chlorite because they have very different modes of chemical action.

=== Other disinfection uses ===
Chlorine dioxide may be used as a fumigant treatment to "sanitize" fruits such as blueberries, raspberries, and strawberries that develop molds and yeast.<ref>{{cite journal
 | last = O'Brian
 | first = D.
 | title = Chlorine Dioxide Pouches Can Make Produce Safer and Reduce Spoilage
 | journal = AgResearch Magazine
 | publisher =USDA Agricultural Research Service
 | date = 2017
 | issue = July 
 | url = https://www.ars.usda.gov/news-events/news/research-news/2017/chlorine-dioxide-pouches-can-make-produce-safer-and-reduce-spoilage/
 | access-date = 2018-06-21
 }}</ref>

Chlorine dioxide may be used to disinfect poultry by spraying or immersing it after slaughtering.<ref>{{Cite web|url=https://www.bigissue.com/latest/the-truth-behind-the-chlorinated-chicken-panic/|title=The truth behind the chlorinated chicken panic|date=2019-05-29|website=The Big Issue|language=en|access-date=2020-02-05}}</ref>

Chlorine dioxide may be used for the disinfection of [[Endoscopy|endoscopes]], such as under the trade name Tristel.<ref>{{Cite journal | last1 = Coates | first1 = D. | title = An evaluation of the use of chlorine dioxide (Tristel One-Shot) in an automated washer/disinfector (Medivator) fitted with a chlorine dioxide generator for decontamination of flexible endoscopes | doi = 10.1053/jhin.2001.0956 | journal = Journal of Hospital Infection | volume = 48 | issue = 1 | pages = 55–65 | year = 2001 | pmid =  11358471}}</ref> It is also available in a trio consisting of a preceding pre-clean with [[surfactant]] and a succeeding rinse with [[deionized water]] and a low-level antioxidant.<ref>{{cite web |url=http://www.ethicalagents.co.nz/ProductPDF/Tristel-Trio-Wipe-System.pdf |title=Tristel Wipes System Product Information |website=Ethical Agents |access-date=2012-11-01 |archive-url=https://web.archive.org/web/20160415120703/http://www.ethicalagents.co.nz/ProductPDF/Tristel-Trio-Wipe-System.pdf |archive-date=2016-04-15 |url-status=dead }}</ref>

Chlorine dioxide may be used for control of [[zebra mussel|zebra]] and [[quagga mussel]]s in water intakes.<ref name="epa1999" />{{rp|4-34}}

Chlorine dioxide was shown to be effective in [[Bed bug|bedbug]] eradication.<ref>{{cite journal | pmid = 22476276 | doi=10.1086/665320 | volume=33 | issue=5 | title=Gaseous chlorine dioxide as an alternative for bedbug control | journal=Infection Control & Hospital Epidemiology | pages=495–9 | last1 = Gibbs | first1 = S. G. | last2 = Lowe | first2 = J. J. | last3 = Smith | first3 = P. W. | last4 = Hewlett | first4 = A. L.| s2cid=14105046 | year=2012 }}</ref>

For water purification during [[camping]], disinfecting tablets containing chlorine dioxide are more effective against pathogens than those using household bleach, but typically cost more.<ref>{{cite web |title= How to Treat Backcountry Water on the Cheap |last= Langlois |first= Krista |date= March 13, 2018 |work= Sierra |publisher= [[Sierra Club]] |url= https://www.sierraclub.org/sierra/how-treat-backcountry-water-cheap |access-date= 2021-02-10}}</ref><ref>{{cite web |title= A Guide to Drinking Water Treatment and Sanitation for Backcountry & Travel Use |date= April 10, 2009 |location=United States |publisher=[[Centers for Disease Control and Prevention]] |url= https://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html |access-date= 2021-02-10}}</ref>

=== Other uses ===
Chlorine dioxide is used as an oxidant for destroying [[phenols]] in [[wastewater]] streams and for odor control in the air scrubbers of animal byproduct (rendering) plants.<ref name="epa1999" />{{rp|4-34}} It is also available for use as a deodorant for cars and boats, in chlorine dioxide-generating packages that are activated by water and left in the boat or car overnight.

In dilute concentrations, chlorine dioxide is an ingredient that acts as an antiseptic agent in some [[mouthwash]]es.<ref name="pmid32410557">{{cite journal |vauthors=Kerémi B, Márta K, Farkas K, Czumbel LM, Tóth B, Szakács Z, Csupor D, Czimmer J, Rumbus Z, Révész P, Németh A, Gerber G, Hegyi P, Varga G |title=Effects of Chlorine Dioxide on Oral Hygiene - A Systematic Review and Meta-analysis |journal=Current Pharmaceutical Design |volume=26 |issue=25 |pages=3015–3025 |date=2020 |pmid=32410557 |pmc=8383470 |doi=10.2174/1381612826666200515134450}}</ref><ref name="pmid36634129">{{cite journal |vauthors=Szalai E, Tajti P, Szabó B, Hegyi P, Czumbel LM, Shojazadeh S, Varga G, Németh O, Keremi B |title=Daily use of chlorine dioxide effectively treats halitosis: A meta-analysis of randomised controlled trials |journal=PLOS ONE |volume=18 |issue=1 |pages=e0280377 |date=2023 |pmid=36634129 |pmc=9836286 |doi=10.1371/journal.pone.0280377|doi-access=free |bibcode=2023PLoSO..1880377S }}</ref>

== Safety issues in water and supplements ==
Potential hazards with chlorine dioxide include poisoning and the risk of spontaneous ignition or explosion on contact with flammable materials.<ref>{{Cite web|url=https://atsdr.cdc.gov/toxprofiles/tp160.pdf|title=Toxicological Profile for Chlorine Dioxide and Chlorite|publisher=Agency for Toxic Substances and Disease Registry, US HHS|url-status=dead|archive-url=https://web.archive.org/web/20190614173335/http://atsdr.cdc.gov/toxprofiles/tp160.pdf|archive-date=2019-06-14}}</ref><ref>{{Cite journal |last1=López |first1=María I. |last2=Croce |first2=Adela E. |last3=Sicre |first3=Juan E. |date=1994 |title=Explosive decomposition of gaseous chlorine dioxide |url=http://xlink.rsc.org/?DOI=FT9949003391 |journal=J. Chem. Soc., Faraday Trans. |language=en |volume=90 |issue=22 |pages=3391–3396 |doi=10.1039/FT9949003391 |issn=0956-5000}}</ref>

Chlorine dioxide is toxic, and limits on human exposure are required to ensure its safe use. The [[United States Environmental Protection Agency]] has set a maximum level of 0.8&nbsp;mg/L for chlorine dioxide in drinking water.<ref>{{cite web|title=ATSDR: ToxFAQs™ for Chlorine Dioxide and Chlorite|url=https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsLanding.aspx?id=581&tid=108}}</ref> The [[Occupational Safety and Health Administration]] (OSHA), an agency of the [[United States Department of Labor]], has set an 8-hour [[permissible exposure limit]] of 0.1&nbsp;ppm in air (0.3 [[milligram|mg]]/[[cubic meter|m<sup>3</sup>]]) for people working with chlorine dioxide.<ref>{{cite web |title=Occupational Safety and Health Guideline for Chlorine Dioxide |url=http://www.osha.gov/SLTC/healthguidelines/chlorinedioxide/recognition.html |access-date=2012-12-08 |archive-url=https://web.archive.org/web/20121204035804/http://www.osha.gov/SLTC/healthguidelines/chlorinedioxide/recognition.html |archive-date=2012-12-04 |url-status=dead }}</ref>

Chlorine dioxide has been fraudulently and illegally marketed as an ingestible cure for a wide range of diseases, including childhood autism<ref name=":0">{{Cite web|url=https://www.nbcnews.com/tech/internet/moms-go-undercover-fight-fake-autism-cures-private-facebook-groups-n1007871|title=Parents are poisoning their children with bleach to 'cure' autism. These moms are trying to stop it.|website=NBC News|date=May 21, 2019 |language=en|access-date=2019-05-21}}</ref> and [[COVID-19|coronavirus]].<ref>{{Cite web|url=https://www.detroitnews.com/story/news/nation/2020/01/31/fake-news-corona-virus/41121279/|title=Fake news: Chlorine dioxide won't stop coronavirus|website=Detroit News|language=en|access-date=2020-04-03}}</ref><ref>{{Cite news|last=Friedman|first=Lisa|url=https://www.nytimes.com/2020/04/03/climate/epa-fake-coronavirus-cleaners.html|title=E.P.A. Threatens Legal Action Against Sellers of Fake Coronavirus Cleaners|date=2020-04-03|work=The New York Times|access-date=2020-04-03|language=en-US|issn=0362-4331}}</ref><ref>{{Cite web|url=https://www.usatoday.com/story/news/health/2020/02/14/there-cure-coronavirus-no-do-not-drink-chlorine-dioxide/4751565002/|title=Those coronavirus 'cures' you're hearing about? They're fake. Don't drink chlorine dioxide.|last=Spencer|first=Sarnac Hale|website=USA TODAY|language=en-US|access-date=2020-04-03}}</ref> Children who have been given [[Enema|enemas]] of chlorine dioxide as a supposed cure for childhood autism have suffered life-threatening ailments.<ref name=":0" /> The [[Food and Drug Administration|U.S. Food and Drug Administration]] (FDA) has stated that ingestion or other internal use of chlorine dioxide, outside of supervised oral rinsing using dilute concentrations, has no health benefits of any kind, and it should not be used internally for any reason.<ref>{{Cite web|url=https://www.nbcnews.com/news/us-news/drinking-bleach-will-not-cure-cancer-or-autism-fda-warns-n1041636|title=Drinking bleach will not cure cancer or autism, FDA warns|website=NBC News|date=August 12, 2019 |language=en|access-date=2019-08-13}}</ref><ref name="FDA 2019"/>

=== Pseudomedicine ===
{{Main article|Miracle Mineral Supplement}}

On 30 July and 1 October 2010, the United States Food and Drug Administration warned against the use of the product "[[Miracle Mineral Supplement]]", or "MMS", which when prepared according to the instructions produces chlorine dioxide. MMS has been marketed as a treatment for a variety of conditions, including HIV, cancer, [[autism]], acne, and, more recently, [[COVID-19]]. Many have complained to the [[Food and Drug Administration|FDA]], reporting life-threatening reactions,<ref>{{cite web |url=https://abc7news.com/news/group-of-socal-parents-secretly-try-to-cure-kids-with-autism-using-bleach/1578833/ |title=Group of SoCal parents secretly try to cure kids with autism using bleach |first=Lisa |last=Bartley |date=2016-10-29 |work=ABC 7 News |publisher=[[American Broadcasting Company|ABC]] |access-date=2019-03-24 }}</ref> and even death.<ref>{{cite web |url=https://www.theguardian.com/society/2016/jul/13/fake-cures-autism-prove-deadly |title=The fake cures for autism that can prove deadly |first=Frances |last=Ryan |date=2016-07-13 |work=[[The Guardian]] |access-date=2019-03-24 }}</ref> The FDA has warned consumers that MMS can cause serious harm to health, and stated that it has received numerous reports of nausea, diarrhea, severe vomiting, and life-threatening low blood pressure caused by dehydration.<ref>{{cite web|archive-url=https://wayback.archive-it.org/7993/20170112005302/https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2010/ucm220747.htm|url=https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2010/ucm220747.htm|title=Press Announcements – FDA Warns Consumers of Serious Harm from Drinking Miracle Mineral Solution (MMS)|website=[[Food and Drug Administration]]|archive-date=2017-01-12}}</ref><ref>{{cite web|archive-url=https://wayback.archive-it.org/7993/20171101112353/https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm228052.htm|archive-date=2017-11-01|url=https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm228052.htm|title='Miracle' Treatment Turns into Potent Bleach|publisher=U.S. Food and Drug Administration|date=2015-11-20|access-date=2017-12-06|url-status=live}}</ref> This warning was repeated for a third time on 12 August 2019, and a fourth on 8 April 2020, stating that ingesting MMS is just as hazardous as ingesting bleach, and urging consumers not to use them or give these products to their children for any reason, as there is no scientific evidence showing that chlorine dioxide has any beneficial medical properties.<ref>{{cite web|url=https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm220747.htm|archive-url=https://web.archive.org/web/20110203232945/https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm220747.htm|url-status=dead|archive-date=2011-02-03|title=FDA Warns Consumers of Serious Harm from Drinking Miracle Mineral Solution (MMS)|location=United States|publisher=[[Food and Drug Administration]]|date=2011-02-03|access-date=2018-04-05}}</ref><ref name="FDA 2019">{{cite web|url=https://www.fda.gov/news-events/press-announcements/fda-warns-consumers-about-dangerous-and-potentially-life-threating-side-effects-miracle-mineral|title=FDA warns consumers about the dangerous and potentially life threatening side effects of Miracle Mineral Solution|location=United States|publisher=[[Food and Drug Administration]]|date=2019-08-12|language=en|archive-url=https://web.archive.org/web/20190814102219/https://www.fda.gov/news-events/press-announcements/fda-warns-consumers-about-dangerous-and-potentially-life-threating-side-effects-miracle-mineral|archive-date=2019-08-14|access-date=2019-08-16}}</ref>

==References==
{{reflist|30em}}

==External links==
*{{Commonscatinline|lcfirst=1}}

{{Chlorine compounds}}
{{Oxides}}
{{E number infobox 920-929}}
{{oxygen compounds}}
{{Authority control}}

[[Category:Chlorine oxides]]
[[Category:Bleaches]]
[[Category:Disinfectants]]
[[Category:Free radicals]]
[[Category:Gases with color]]
[[Category:Explosive gases]]
[[Category:Explosive chemicals]]