Chlorine dioxide

Source: Wikipedia, the free encyclopedia.

Not to be confused with the
dichlorine dioxide
.
Chlorine dioxide
Structural formula of chlorine dioxide with assorted dimensions
Structural formula of chlorine dioxide with assorted dimensions
Spacefill model of chlorine dioxide
Spacefill model of chlorine dioxide
Names
IUPAC name
Chlorine dioxide
Other names
  • Chlorine(IV) oxide
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
ECHA InfoCard
 100.030.135 Edit this at Wikidata
EC Number
  • 233-162-8
1265
MeSH Chlorine+dioxide
RTECS number
  • FO3000000
UNII
UN number 9191
  • InChI=1S/ClO2/c2-1-3 checkY
    Key: OSVXSBDYLRYLIG-UHFFFAOYSA-N checkY
  • InChI=1/ClO2/c2-1-3
    Key: OSVXSBDYLRYLIG-UHFFFAOYAC
  • O=[Cl]=O
  • O=Cl[O]
Properties
ClO2
Molar mass 67.45 g·mol−1
Appearance Yellow to reddish gas
Odor Acrid
Density 2.757 g dm−3[1]
Melting point −59 °C (−74 °F; 214 K)
Boiling point 11 °C (52 °F; 284 K)
8 g/L at 20 °C
Solubility Soluble in alkaline solutions and sulfuric acid
Vapor pressure >1 atm[2]
4.01×10−2 atm m3 mol−1
Acidity (pKa) 3.0(5)
Thermochemistry
257.22 J K−1 mol−1
Std enthalpy of
formation
(ΔfH⦵298)
 104.60 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Highly toxic, corrosive, unstable, powerful oxidizer
GHS labelling:
GHS03: OxidizingGHS05: CorrosiveGHS06: Toxic
Danger
H271, H300+H310+H330, H314, H372
P210, P220, P260, P264, P271, P280, P283, P284, P301+P310, P304+P340, P305+P351+P338, P306+P360, P371+P380+P375, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g. nitroglycerinSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
4
OX
Lethal dose or concentration (LD, LC):
94 mg/kg (oral, rat)[3]
260 ppm (rat, 2 hr)[4]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 0.1 ppm (0.3 mg/m3)[2]
REL (Recommended)
 TWA 0.1 ppm (0.3 mg/m3) ST 0.3 ppm (0.9 mg/m3)[2]
IDLH
(Immediate danger)
 5 ppm[2]
Safety data sheet (SDS) Safety Data Sheet Archive.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Chlorine dioxide is a chemical compound with the formula ClO2 that exists as yellowish-green gas above 11 °C, a reddish-brown liquid between 11 °C and −59 °C, and as bright orange crystals below −59 °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

Comparison of three-electron bond to the conventional covalent bond
The structure according to Pauling's General Chemistry
Vapor-liquid equilibrium above an aqueous solution of chlorine dioxide at various temperatures

The molecule ClO2 has an odd number of valence electrons, and therefore, it is a paramagnetic radical. It is an unusual "example of an odd-electron molecule which is stable towards dimerization" (nitric oxide being another example).[5]

In 1933,

highest occupied molecular orbital is indeed an incompletely-filled antibonding orbital.[8]

A unit cell of the orthorhombic ClO2 crystal shown in an arbitrary direction.

The crystal structure of ClO2 is orthorhombic, and displays the symmetry of the Pbca space group.[9]

Preparation

Chlorine dioxide was first prepared in 1811 by

Sir Humphry Davy.[10]

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.[11]

.

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, ClO2 can be prepared by oxidation of sodium chlorite with chlorine:[12]

NaClO2 + 1⁄2 Cl2 → ClO2 + NaCl

Traditionally, chlorine dioxide for disinfection applications has been made from sodium chlorite or the sodium chlorite–hypochlorite method:

2 NaClO2 + 2 HCl + NaOCl → 2 ClO2 + 3 NaCl + H2O

or the sodium chlorite–hydrochloric acid method:

5 NaClO2 + 4 HCl → 5 NaCl + 4 ClO2 + 2 H2O

or the chlorite–sulfuric acid method:

4 ClO−2 + 2 H2SO4 → 2 ClO2 + HClO3 + 2 SO2−4 + 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.[13]

Addition of sulfuric acid or any strong acid to chlorate salts produces chlorine dioxide.[7]

Reduction of chlorate

In the laboratory, chlorine dioxide can also be prepared by reaction of potassium chlorate with oxalic acid:

KClO3 + H2C2O4 → 1⁄2 K2C2O4 + ClO2 + CO2 + H2O

or with oxalic and sulfuric acid:

KClO3 + 1⁄2 H2C2O4 + 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 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.[13] 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:[14]

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:

ClO−3 + Cl− + H+ → ClO−2 + HOCl
ClO−3 + ClO−2 + 2 H+ → 2 ClO2 + H2O
HOCl + Cl− + H+ → Cl2 + H2O

which gives the overall reaction

ClO−3 + Cl− + 2 H+ → ClO2 + 1⁄2 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.[13]

The variant process using sodium chlorate, hydrogen peroxide and sulfuric acid has been increasingly used since 1999 for water treatment and other small-scale disinfection applications, since it produce a chlorine-free product at high efficiency, over 95%.[citation needed]

Other processes

Very pure chlorine dioxide can also be produced by electrolysis of a chlorite solution:[15]

NaClO2 + H2O → ClO2 + NaOH + 1⁄2 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:[15]

NaClO2 + 1⁄2 Cl2 → ClO2 + NaCl


Handling properties

At partial pressures above 10 kPa (1.5 psi)

which?
] chlorine dioxide solutions below 3 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 disinfection (called chlorination) of municipal drinking water,[16][17]: 4–1 [18] treatment of water in oil and gas applications, disinfection in the food industry, microbiological control in cooling towers, and textile bleaching.[19] As a disinfectant, it is effective even at low concentrations because of its unique qualities.[13][17][19]

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

kraft pulp is made using chlorine dioxide in ECF bleaching sequences.[21]

Chlorine dioxide has been used to bleach flour.[22]

Water treatment

Further information: Water chlorination and Portable water purification § Chlorine dioxide

The water treatment plant at

oxidant prior to chlorination of drinking water to destroy natural water impurities that would otherwise produce trihalomethanes upon exposure to free chlorine.[23][24][25] Trihalomethanes are suspected carcinogenic disinfection by-products[26] associated with chlorination of naturally occurring organics in raw water.[25] Chlorine dioxide also produces 70% fewer halomethanes in the presence of natural organic matter compared to when elemental chlorine or bleach is used.[27]

Chlorine dioxide is also superior to chlorine when operating above

cooling towers, process water, and food processing.[29]

Chlorine dioxide is less corrosive than chlorine and superior for the control of Legionella bacteria.[18][30] 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

EPA
-registered biocide.

It is more effective as a disinfectant than chlorine in most circumstances against waterborne pathogenic agents such as

oocysts of Cryptosporidium.[17]
: 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.[17]: 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.[32] The World Health Organization also advises a 1ppm dosification.[27]

Use in public crises

Chlorine dioxide has many applications as an oxidizer or disinfectant.

mold from houses inundated by the flood water.[35]

In addressing the COVID-19 pandemic, the

coronavirus.[36][37] 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.[38]

Chlorine dioxide may be used to disinfect poultry by spraying or immersing it after slaughtering.[39]

Chlorine dioxide may be used for the disinfection of

deionized water and a low-level antioxidant.[41]

Chlorine dioxide may be used for control of zebra and quagga mussels in water intakes.[17]: 4–34 

Chlorine dioxide was shown to be effective in

bedbug eradication.[42]

For water purification during camping, disinfecting tablets containing chlorine dioxide are more effective against pathogens than those using household bleach, but typically cost more.[43][44]

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.[17]: 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 mouthwashes.[45][46]

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.[47][48]

Chlorine dioxide is toxic, and limits on human exposure are required to ensure its safe use. The

m3) for people working with chlorine dioxide.[50]

Chlorine dioxide has been fraudulently and illegally marketed as an ingestible cure for a wide range of diseases, including childhood autism[51] and coronavirus.[52][53][54] Children who have been given enemas of chlorine dioxide as a supposed cure for childhood autism have suffered life-threatening ailments.[51] The 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.[55][56]

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 "

autism, acne, and, more recently, COVID-19. Many have complained to the FDA, reporting life-threatening reactions,[57] and even death.[58] 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.[59][60] 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.[61][56]

References

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External links

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