Hypochlorite
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| Hypochlorite | |
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Hypochlorite |
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| Identifiers | |
| CAS number | 14380-61-1  |
| PubChem | 61739 |
| ChemSpider | 55632 |
| UN number | 3212 |
| ChEBI | CHEBI:29222 |
| Gmelin Reference | 682 |
| Jmol-3D images | Image 1 |
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 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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The hypochlorite ion, also known as chlorate(I) anion is ClO−. A hypochlorite compound is a chemical compound containing this group, with chlorine in oxidation state +1[1].
Hypochlorites are the salts of hypochlorous acid. Common examples include sodium hypochlorite (chlorine bleach or bleaching agent) and calcium hypochlorite (bleaching powder or swimming pool chlorination compound). Hypochlorites are frequently quite unstable — for example, sodium hypochlorite is not available as a solid, since removal of the water from NaClO solution converts it to a mixture of sodium chloride and sodium chlorate. Heating of NaClO solution also causes this reaction. Hypochlorites decompose in sunlight, giving chlorides and oxygen.
Due to their low stability, hypochlorites are very strong oxidizing agents. They react with many organic and inorganic compounds. Reaction with organic compounds is very exothermic and may cause ignition, so hypochlorites should be handled with care. They can oxidize manganese compounds, converting them to permanganates.
Covalent hypochlorites, such as methyl hypochlorite are also known, and are typically unstable.
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[edit] Preparation
The sodium salt of the hypochlorite ion, NaClO, is formed by the disproportionation of chlorine gas bubbled through dilute aqueous sodium hydroxide at room temperature:
- Cl2 (g) + 2 NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)
The reaction of chlorine with hot, concentrated sodium hydroxide forms chlorates of a higher oxidation state:
- 3 Cl2 (g) + 6 NaOH (aq) → 5 NaCl(aq) + NaClO3 (aq) + 3 H2O (l)
More commonly, though, hypochlorite is produced in unseparated chlor-alkali electrolysis maintained at neutral/basic pH. By this process, brine is electrolyzed to form Cl2 which dissociates in water to form hypochlorite. This reaction must be run in non-acidic conditions to prevent chlorine gas from bubbling out of solution:
- 2 Cl− → Cl2 + 2 e−
- Cl2 + H2O ↔ HClO + Cl− + H+
[edit] Chemistry
[edit] Acid reaction
Hypochlorites generate chlorine gas when mixed with dilute acids. Hypochlorite and chloride are in equilibrium with chlorine gas:
- 2 H+ (aq) + OCl− (aq) + Cl− (aq)
Cl2 (g) + H2O (l)
Therefore, by Le Chatelier's principle, a high pH drives the reaction to the left by consuming H+ ions, promoting the disproportionation of chlorine into chloride and hypochlorite, whereas a low pH drives the reaction to the right, promoting the release of chlorine gas.
[edit] Bleaching action
Hypochlorites are used as bleaches to remove dyes.
[edit] As an oxidising agent
Hypochlorite is the strongest oxidising agent of the generalized chlorates[citation needed]. For example, it oxidises Mn2+ to permanganate:
- 2 Mn2+ + 5 ClO− + 6 OH− → 2 MnO−
4 + 3 H2O + 5 Cl−
[edit] Metabolism
Hypochlorite is created in vivo when the human immune system destroys pathogens. Viruses and bacteria are engulfed into an intracellular vacuole, the phagosome, where they are digested. For this purpose, several proteases (e.g. elastase) are released into the phagosome from intracellular granules. In addition, there is also an enzyme-mediated ‘respiratory burst’, which results in the production of a set of reactive oxygen-derived compounds. Contact with a foreign particle causes the activation of membrane bound NADPH-oxidase, which produces superoxide in the phagosome. Superoxide dismutates to oxygen and hydrogen peroxide : the hydrogen peroxide formed is used as a substrate for the myeloperoxidase-catalysed reaction, which converts chloride to hypochlorite.[2]
[edit] Stability
Hypochlorite is the least stable of the chlorine oxyanions[citation needed]. Many hypochlorite compounds exist only in solution, as is also the case with hypochlorous acid (HClO) itself.
Hypochlorite is unstable with respect to disproportionation. Upon heating, it degrades to a mixture of chloride, oxygen and other chlorates:
- 2 OCl− (aq) → 2 Cl− (aq) + O2 (g)
- 3 OCl− (aq) → 2 Cl− (aq) + ClO−
3 (aq)
[edit] See also
[edit] References
- ^ Housecroft, C. E.; Sharpe, A. G. (2008). Inorganic Chemistry (3rd ed.). Prentice Hall. p. 186-189, 553-556. ISBN 978-0131755536.
- ^ http://www.colorado.edu/intphys/iphy3700/vitCHemila92.pdf
