Chlorine dioxide
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| Names | |||
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IUPAC name
Chlorine dioxide
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| Other names
Chlorine(IV) oxide
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| Identifiers | |||
10049-04-4 
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| 3D model (Jmol) |
Interactive image Interactive image |
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| ChEBI |
CHEBI:29415
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| ChemSpider |
23251
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| ECHA InfoCard | 100.030.135 | ||
| EC Number | 233-162-8 | ||
| E number | E926 (glazing agents, ...) | ||
| 1265 | |||
| MeSH | Chlorine+dioxide | ||
| PubChem | 24870 | ||
| RTECS number | FO3000000 | ||
| UNII |
8061YMS4RM
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| UN number | 9191 | ||
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| Properties | |||
| ClO2 | |||
| Molar mass | 67.45 g·mol−1 | ||
| Appearance | Yellow to reddish gas | ||
| Odor | Acrid | ||
| Density | 2.757 g dm−3 | ||
| Melting point | −59 °C (−74 °F; 214 K) | ||
| Boiling point | 11 °C (52 °F; 284 K) | ||
| 8 g dm−3 (at 20 °C) | |||
| Solubility | soluble in alkaline and sulfuric acid solutions | ||
| Vapor pressure | >1 atm | ||
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Henry's law
constant (kH) |
4.01 x 10−2 atm-cu m/mole | ||
| Acidity (pKa) | 3.0(5) | ||
| Thermochemistry | |||
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Std molar
entropy (S |
257.22 J K−1 mol−1 | ||
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Std enthalpy of
formation (ΔfH |
104.60 kJ/mol | ||
| Hazards | |||
| Safety data sheet | ICSC 0127 | ||
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EU classification (DSD)
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 O C T+ N
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| R-phrases | R6, R8, R26, R34, R50 | ||
| S-phrases | (S1/2), S23, S26, S28, S36/37/39, S38, S45, S61 | ||
| NFPA 704 | |||
| Lethal dose or concentration (LD, LC): | |||
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LD50 (median dose)
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292 mg/kg (oral, rat) | ||
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LCLo (lowest published)
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260 ppm (rat, 2 hr) | ||
| US health exposure limits (NIOSH): | |||
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PEL (Permissible)
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TWA 0.1 ppm (0.3 mg/m3) | ||
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REL (Recommended)
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TWA 0.1 ppm (0.3 mg/m3) ST 0.3 ppm (0.9 mg/m3) | ||
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IDLH (Immediate danger)
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5 ppm | ||
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |||
Chlorine 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.
Chlorine dioxide is a neutral chlorine compound. It is very different from elementary chlorine, both in its chemical structure and in its behavior. One of the most important qualities of chlorine dioxide is its high water solubility, especially in cold water. Chlorine dioxide does not hydrolyze when it enters water; it remains a dissolved gas in solution. Chlorine dioxide is approximately 10 times more soluble in water than chlorine.
The molecule ClO2 has an odd number of valence electrons, and therefore, it is a paramagnetic radical. Its electronic structure has long baffled chemists because none of the possible Lewis structures is very satisfactory. In 1933, L. O. Brockway proposed a structure that involved a three-electron bond. Chemist Linus Pauling further developed this idea and arrived at two resonance structures involving a double bond on one side and a single bond plus three-electron bond on the other. In Pauling's view the latter combination should represent a bond that is slightly 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 is indeed an incompletely-filled orbital.
Chlorine dioxide is a compound that can decompose extremely 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. Arranging handling in a safe manner is essential.
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