Hypohalite

Hypohalites are chemical compounds containing the hypohalite ion, with the general formula XO⁻, where X is a halogen element from Group 17 of the periodic table (fluorine, chlorine, bromine, or iodine). Hypohalites are the conjugate bases of hypohalous acids (HOX) and represent the lowest oxidation state (+1) of halogens in their oxoanions. The pseudohalogen analogues are hypopseudohalites.

Hypohalites, especially hypochlorite and hypobromite, are commonly used as disinfectants. In human bodies, the animal heme-dependent peroxidases of the immune system produce hypohalites (OCl⁻, OBr⁻, OI⁻) and hypothiocyanite as a weapon.^[1]^[2] Hypohalites are also encountered in organic chemistry, often as acyl hypohalites (see the Hunsdiecker reaction). Sodium hypohalite is used in the haloform reaction as a test for methyl ketones.^[3] In human bodies, the generate hypohalites and hypopseudohalites are generated by ]

Structure

The hypohalite ion consists of a halogen atom covalently bonded to an oxygen atom, carrying an overall negative charge. The halogen is in the +1 oxidation state, and the oxygen is in the usual −2 state. The general formula is:

${\textstyle {\ce {XO-}}}$

${\ce {X}}$ is the halogen atom, and
${\ce {O}}$ is the oxygen atom

The Cl-O bond length in crystalline sodium hypochlorite pentahydrate, NaOCl·5H₂O, is 1.686 Å, while in sodium hypobromite pentahydrate, NaOBr·5H₂O, the Br–O bond length is 8% longer at 1.820 Å.^[4]

References

^ Moskwa P, Lorentzen D, Excoffon KJ, Zabner J, McCray PB, Nauseef WM, Dupuy C, Bánfi B (January 2007). "A Novel Host Defense System of Airways Is Defective in Cystic Fibrosis". Am. J. Respir. Crit. Care Med. 175 (2): 174–83. doi:10.1164/rccm.200607-1029OC. PMC 2720149. PMID 17082494.
^ Mayeno, A N; Curran, A J; Roberts, R L; Foote, C S (5 April 1989), "Eosinophils preferentially use bromide to generate halogenating agents", Journal of Biological Chemistry, 264 (10): 5660–8, doi:10.1016/S0021-9258(18)83599-2, PMID 2538427, archived from the original on 26 May 2009, retrieved 25 October 2009
^ Experimental Organic Chemistry: A Miniscale and Microscale Approach by John Gilbert Stephen Martin p. 863
^ Topić, Filip; Marrett, Joseph M.; Borchers, Tristan H.; Titi, Hatem M.; Barrett, Christopher J.; Friščić, Tomislav (2021). "After 200 Years: The Structure of Bleach and Characterization of Hypohalite Ions by Single-Crystal X-Ray Diffraction". Angew. Chem. Int. Ed. 60 (46): 24400–24405. doi:10.1002/anie.202108843. PMID 34293249. S2CID 236199263.

[pmid17082494-1] Moskwa P, Lorentzen D, Excoffon KJ, Zabner J, McCray PB, Nauseef WM, Dupuy C, Bánfi B (January 2007). "A Novel Host Defense System of Airways Is Defective in Cystic Fibrosis". Am. J. Respir. Crit. Care Med. 175 (2): 174–83. doi:10.1164/rccm.200607-1029OC. PMC 2720149. PMID 17082494.

[2] Mayeno, A N; Curran, A J; Roberts, R L; Foote, C S (5 April 1989), "Eosinophils preferentially use bromide to generate halogenating agents", Journal of Biological Chemistry, 264 (10): 5660–8, doi:10.1016/S0021-9258(18)83599-2, PMID 2538427, archived from the original on 26 May 2009, retrieved 25 October 2009

[3] Experimental Organic Chemistry: A Miniscale and Microscale Approach by John Gilbert Stephen Martin p. 863

[Friscic-4] Topić, Filip; Marrett, Joseph M.; Borchers, Tristan H.; Titi, Hatem M.; Barrett, Christopher J.; Friščić, Tomislav (2021). "After 200 Years: The Structure of Bleach and Characterization of Hypohalite Ions by Single-Crystal X-Ray Diffraction". Angew. Chem. Int. Ed. 60 (46): 24400–24405. doi:10.1002/anie.202108843. PMID 34293249. S2CID 236199263.

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