Calcium hypochlorite

Calcium hypochlorite is an inorganic compound with formula Ca(ClO)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]

Calcium hypochlorite
Calcium oxychloride
Names
Other names
Hypochlorous acid calcium salt, bleaching powder, chloride of lime
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.029.007
EC Number
  • 231-908-7
KEGG
RTECS number
  • NH3485000
UNII
UN number 1748 2208
  • InChI=1S/Ca.2ClO/c;2*1-2/q+2;2*-1 checkY
    Key: ZKQDCIXGCQPQNV-UHFFFAOYSA-N checkY
  • InChI=1S/Cacl.ClO/c;1-2/q+2;2*-1
    Key: ZKQDCIXGCQPQNV-UHFFFAOYAV
  • Cl[O-].[Ca+2].Cl[O-]
Properties
Ca(ClO)2
Molar mass 142.98 g/mol
Appearance white/gray powder
Density 2.35 g/cm3 (20 °C)
Melting point 100 °C (212 °F; 373 K)
Boiling point 175 °C (347 °F; 448 K) decomposes
21 g/100 mL at 25 °C
Solubility reacts in alcohol
Hazards
GHS labelling:
GHS03: OxidizingGHS05: CorrosiveGHS07: Exclamation markGHS09: Environmental hazard
Danger
H272, H302, H314, H400
P210, P220, P221, P260, P264, P270, P273, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P330, P363, P370+P378, P391, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
3
0
1
OX
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
850 mg/kg (oral, rat)
Safety data sheet (SDS) ICSC 0638
Related compounds
Other anions
 Calcium chloride
Other cations
 Sodium hypochlorite
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

History

Charles Tennant and Charles Macintosh developed an industrial process in the late 18th century for the manufacture of chloride of lime.[4] It was patented in 1799 and used heavily during World War I for disinfecting the trenches and wounds.

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 → Ca(ClO)2 + CaCl2 + 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(ClO)2, dibasic calcium hypochlorite Ca3(ClO)2(OH)4 (also written as Ca(ClO)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:

Ca(ClO)2 + 4HCl → CaCl2 + 2Cl2 + 2H2O

Safety

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

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

See also

References
  1. also chlorine powder, chloride of lime, chlorinated lime, "dry chlorine"
  1. Gerald F. Connell. "Key operating strategies for chlorine disinfection operating systems" (PDF). Retrieved 19 October 2014.
  2. "Calcium Hypochlorite - 3V Tech". www.3v-tech.com.
  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. "Calcium hypochlorite". Chemistry World.
  5. Chemical Products Synopsis: Calcium Hypochlorite (Technical report). Asbuiy Park, NJ: Mannsvile Chemical Products. 1987.
  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. 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. Cohen, Julius (1900). Practical Organic Chemistry for Advanced Students. New York: Macmillan & Co. p. 63.
  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. "8.41799 Calcium hypochlorite for synthesis". Sigma-Aldrich. Assay (iodometric): 67.0 - 75.0 %
  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. 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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