Bleaching_powder

Calcium hypochlorite

Calcium hypochlorite

Chemical compound

Calcium hypochlorite is an inorganic compound with chemical formula Ca(ClO)2, also written as Ca(OCl)2. It is a white solid, although commercial samples appear yellow. It strongly smells of chlorine, owing to its slow decomposition in moist air. This compound is relatively stable as a solid and solution and has greater available chlorine than sodium hypochlorite.[1] "Pure" samples have 99.2% active chlorine. Given common industrial purity, an active chlorine content of 65-70% is typical.[2] It is the main active ingredient of commercial products called bleaching powder,[lower-alpha 1] used for water treatment and as a bleaching agent.[3]

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History

Charles Tennant and Charles Macintosh developed an industrial process in the late 18th century for the manufacture of chloride of lime, patenting it 1799.[4] Tennant's process is essentially still used today,[4][3] and became of military importance during World War I, because calcium hypochlorite was the active ingredient in trench disinfectant.[4]

Uses

Sanitation

Calcium hypochlorite is commonly used to sanitize public swimming pools and disinfect drinking water. Generally the commercial substances are sold with a purity of 65% to 73% with other chemicals present, such as calcium chloride and calcium carbonate, resulting from the manufacturing process. In solution, calcium hypochlorite could be used as a general purpose sanitizer,[5] but due to calcium residue (making the water harder), sodium hypochlorite (bleach) is usually preferred.

Organic chemistry

Calcium hypochlorite is a general oxidizing agent and therefore finds some use in organic chemistry.[6] For instance the compound is used to cleave glycols, α-hydroxy carboxylic acids and keto acids to yield fragmented aldehydes or carboxylic acids.[7] Calcium hypochlorite can also be used in the haloform reaction to manufacture chloroform.[8] Calcium hypochlorite can be used to oxidize thiol and sulfide byproducts in organic synthesis and thereby reduce their odour and make them safe to dispose of.[9] The reagent used in organic chemistry is similar to the sanitizer at ~70% purity.[10]

Production

Calcium hypochlorite is produced industrially by treating moist slaked lime (Ca(OH)2) with chlorine. The one-step reaction is shown below:[3]

2 Cl2 + 2 Ca(OH)2 → CaCl2 + Ca(OCl)2 + 2 H2O

Industrial setups allow for the reaction to be conducted in stages to give various compositions, each producing different ratios of calcium hypochlorite, unconverted lime, and calcium chloride.[3] In one process, the chloride-rich first stage water is discarded, while the solid precipitate is dissolved in a mixture of water and lye for another round of chlorination to reach the target purity.[2] Commercial calcium hypochlorite consists of anhydrous Ca(OCl)2, dibasic calcium hypochlorite Ca3(OCl)2(OH)4 (also written as Ca(OCl)2·2Ca(OH)2), and dibasic calcium chloride Ca3Cl2(OH)4 (also written as CaCl2·2Ca(OH)2).[11][12]

Reactions

Calcium hypochlorite reacts rapidly with acids producing calcium chloride, chlorine gas, and water:[citation needed]

Ca(ClO)2 + 4 HCl → CaCl2 + 2 Cl2 + 2 H2O

Safety

It is a strong oxidizing agent, as it contains a hypochlorite ion at the valence +1 (redox state: Cl+1).[citation needed]

Calcium hypochlorite should not be stored wet and hot, or near any acid, organic materials, or metals. The unhydrated form is safer to handle.[citation needed]

See also

References

  1. also chlorine powder, chloride of lime, chlorinated lime, "dry chlorine"
  1. [1]
    Gerald F. Connell. "Key operating strategies for chlorine disinfection operating systems" (PDF). Retrieved 19 October 2014.
  2. [2]
    "Calcium Hypochlorite - 3V Tech". www.3v-tech.com.
  3. [3]
    Vogt, H.; Balej, J; Bennett, J. E.; Wintzer, P.; Sheikh, S. A.; Gallone, P.; Vasudevan, S.; Pelin, K. (2010). "Chlorine Oxides and Chlorine Oxygen Acids". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a06_483.pub2. ISBN 978-3527306732. S2CID 96905077.
  4. [4]
    "Calcium hypochlorite". Chemistry World.
  5. [5]
    Chemical Products Synopsis: Calcium Hypochlorite (Technical report). Asbuiy Park, NJ: Mannsvile Chemical Products. 1987.
  6. [6]
    Nwaukwa, Stephen; Keehn, Philip (1982). "The oxidation of aldehydes to acids with calcium hypochlorite [Ca(ClO)2]". Tetrahedron Letters. 23 (31): 3131–3134. doi:10.1016/S0040-4039(00)88577-9.
  7. [7]
    Nwaukwa, Stephen; Keehn, Philip (1982). "Oxidative cleavage of α-diols, α-diones, α-hydroxy-ketones and α-hydroxy- and α-keto acids with calcium hypochlorite [Ca(ClO)2]". Tetrahedron Letters. 23 (31): 3135–3138. doi:10.1016/S0040-4039(00)88578-0.
  8. [8]
    Cohen, Julius (1900). Practical Organic Chemistry for Advanced Students. New York: Macmillan & Co. p. 63.
  9. [9]
    National Research Council (1995). Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. p. 161. doi:10.17226/4911. ISBN 978-0-309-05229-0.
  10. [10]
    "8.41799 Calcium hypochlorite for synthesis". Sigma-Aldrich. Assay (iodometric): 67.0 - 75.0 %
  11. [11]
    W.L Smith, Inorganic Bleaches, Production of Hypochlorite in Handbook of Detergents,Part F, (2009) Ed. U Zoller and Paul Sosis, CRC Press, ISBN 978-0-8247-0349-3
  12. [12]
    Aleksandrova, M.M.; Dmitriev, G.A.; Avojan, R.L. (1968). "The probable model of the crystal structure of the twobase calcium hypochlorite". Armyanskii Khimicheskii Zhurnal. 21: 380-386.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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