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,[a] used for water treatment and as a bleaching agent.[3]
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3D model (JSmol)
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| ECHA InfoCard | 100.029.007 |
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| UN number | 1748 2208 |
CompTox Dashboard (EPA)
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| Properties | |
| Ca(OCl)2 | |
| Molar mass | 142.98 g·mol−1 |
| 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 |
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| 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 | |
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| Flash point | Non-flammable |
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LD50 (median dose)
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850 mg/kg (oral, rat) |
| Safety data sheet (SDS) | ICSC 0638 |
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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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History
editCharles 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
editSanitation
editCalcium 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
editCalcium 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
editCalcium hypochlorite is produced industrially by reaction of moist slaked calcium hydroxide with chlorine gas. 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
editCalcium 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
editIt 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
editReferences
edit- ^ also chlorine powder, chloride of lime, chlorinated lime, "dry chlorine"
- ^ Gerald F. Connell. "Key operating strategies for chlorine disinfection operating systems" (PDF). Retrieved 19 October 2014.
- ^ a b "Calcium Hypochlorite - 3V Tech". www.3v-tech.com.
- ^ a b c d 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.
- ^ a b c "Calcium hypochlorite". Chemistry World.
- ^ Chemical Products Synopsis: Calcium Hypochlorite (Technical report). Asbuiy Park, NJ: Mannsvile Chemical Products. 1987.
- ^ 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.
- ^ 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.
- ^ Cohen, Julius (1900). Practical Organic Chemistry for Advanced Students. New York: Macmillan & Co. p. 63.
- ^ 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.
- ^ "8.41799 Calcium hypochlorite for synthesis". Sigma-Aldrich.
Assay (iodometric): 67.0 - 75.0 %
- ^ 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
- ^ 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.
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