Bromide

A bromide ion is the negatively charged form (Br − ) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant materials, and cell stains. Although uncommon, chronic toxicity from bromide can result in bromism, a syndrome with multiple neurological symptoms. Bromide toxicity can also cause a type of skin eruption, see potassium bromide. The bromide ion has an ionic radius of 196 pm.

A bromide ion is the negatively charged form (Br − ) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant materials, and cell stains. Although uncommon, chronic toxicity from bromide can result in bromism, a syndrome with multiple neurological symptoms. Bromide toxicity can also cause a type of skin eruption, see potassium bromide. The bromide ion has an ionic radius of 196 pm. ==Natural occurrence== Bromide is present in typical seawater (35 PSU) with a concentration of around 65 mg/L, which is about 0.2% of all dissolved salts. Seafood and deep sea plants generally have higher levels than land-derived foods. Bromargyrite—natural, crystalline silver bromide—is the most common bromide mineral known but is still very rare. In addition to silver, bromine is also in minerals combined with mercury and copper. ==Formation and reactions of bromide== ===Dissociation of bromide salts=== Bromide salts of alkali metal, alkaline earth metals, and many other metals dissolve in water (and even some alcohols and a few ethers) to give bromide ions. The classic case is sodium bromide, which fully dissociates in water: NaBr → Na + + Br − Hydrogen bromide, which is a diatomic molecule, takes on salt-like properties upon contact with water to give an ionic solution called hydrobromic acid. The process is often described simplistically as involving formation of the hydronium salt of bromide: HBr + H 2 O → H 3 O + + Br − ===Hydrolysis of bromine=== Bromine readily reacts with water, i.e. it undergoes hydrolysis: Br 2 + H 2 O → HOBr + HBr This forms hypobromous acid (HOBr), and hydrobromic acid (HBr in water). The solution is called "bromine water". The hydrolysis of bromine is more favorable in the presence of base, for example sodium hydroxide: Br 2 + NaOH → NaOBr + NaBr This reaction is analogous to the production of bleach, where chlorine is dissolved in the presence of sodium hydroxide. ===Oxidation of bromide=== One can test for a bromide ion by adding an oxidizer. One method uses dilute HNO 3 . Balard and Löwig's method can be used to extract bromine from seawater and certain brines. For samples testing for sufficient bromide concentration, addition of chlorine produces bromine (Br 2 ): Cl 2 + 2 Br − → 2 Cl − + Br 2 ==Applications== Bromide's main commercial value is its use in producing organobromine compounds, which themselves are rather specialized. Organobromine compounds are commonly used as brominated flame retardants. Some organobromine flame retardants (not the bromide ion itself) were identified as persistent, bioaccumulative, and toxic to both humans and the environment and were suspected of causing neurobehavioral effects and endocrine disruption. Many metal bromides are produced commercially, including LiBr, NaBr, NH 4 Br, CuBr, ZnBr 2 and AlBr 3 . AgBr is used for the largely obsolete photographic gelatin silver process. ==Medicinal and veterinary uses== reactions to bromide, all except lower right ==Biochemistry== Bromide is rarely mentioned in the biochemical context. Some enzymes use bromide as substrate or as a cofactor. ===Substrate=== Bromoperoxidase enzymes use bromide (typically in seawater) to generate electrophilic brominating agents. Hundreds of organobromine compounds are generated by this process. Notable examples are bromoform, thousands of tons of which are produced annually in this way. The historical dye Tyrian purple is produced by similar enzymatic reactions. ===Cofactor=== In one specialized report, bromide is an essential cofactor in the peroxidising catalysis of sulfonimine crosslinks in collagen IV. This post-translational modification occurs in all animals and bromine is an essential trace element for humans. Eosinophils need bromide for fighting multicellular parasites. Hypobromite is produced via eosinophil peroxidase, an enzyme that can use chloride but preferentially uses bromide. The average concentration of bromide in human blood in Queensland, Australia, is and varies with age and gender. Much higher levels may indicate exposure to brominated chemicals. It is also found in seafood. ==Further reading== ===Encyclopedia articles and books=== Christe, K., and S. Schneider (2020), Bromine, Encyclopædia Britannica. Emerson, S., and J. Hedges (2011), Chemical Oceanography and the Marine Carbon Cycle, Cambridge University Press, Cambridge. Glasow, R. von, and C. Hughes (2014), Biogeochemical Cycles: Bromine, Encyclopedia of Atmospheric Sciences (Second Edition). Knight, J., and N. Schlager (2002), Real-life chemistry, Gale Group, Detroit, MI. Millero, F. J. (2013), Chemical oceanography, Taylor & Francis, Boca Raton. Newton D. E. (2010), Bromine (Revised), Chemical Elements: From Carbon to Krypton. Riley, J. P., G. Skirrow, and R. Chester (1975), Chemical Oceanography, Academic Press, London Ross, R. (2017), Facts About Bromine, LiveScience. Steele, J. H., S. A. Thorpe, and K. K. Turekian (2001), Encyclopedia of Ocean Sciences, Academic Press, San Diego. Steele, J. H., S. A. Thorpe, and K. K. Turekian (2009), Encyclopedia of Ocean Sciences, Academic Press, Boston. Watkins, T. (2011), Bromine, Environmental Encyclopedia. ===Peer-reviewed journal articles for bromine (Br)=== Wisniak, J. (2002), The history of bromine from discovery to commodity, NOPR. ===Peer-reviewed journal articles for bromide (Br − )=== Anbar, A. D., Y. L. Yung, and F. P. Chavez (1996), Methyl bromide: Ocean sources, ocean sinks, and climate sensitivity, AGU Journals. Foti, S. C., and Naval Ordnance Lab White Oak Md (1972), Concentration of Bromide Ions in Seawater by Isotopic Exchange with Mercurous Bromide, DTIC. Gribble, G. W. (2000), The natural production of organobromine compounds, Environmental Science and Pollution Research, 7(1), 37–49, . Leri A. (2012), The Chemistry of Bromine in Terrestrial and Marine Environments, Science Highlight. Magazinovic, R. S., B. C. Nicholson, D. E. Mulcahy, and D. E. Davey (2004), Bromide levels in natural waters: its relationship to levels of both chloride and total dissolved solids and the implications for water treatment, Chemosphere, 57(4), 329–335, . Pilinis, C., D. B. King, and E. S. Saltzman (1996), The oceans: A source or a sink of methyl bromide?, Geophysical Research Letters, 23(8), 817–820, . Stemmler, I., I. Hense, and B. Quack (2015), Marine sources of bromoform in the global open ocean – global patterns and emissions, Biogeosciences, 12(6), 1967–1981, . Suzuki, A., Lim, L., Hiroi, T., & Takeuchi, T. (2006, March 20). Rapid determination of bromide in seawater samples by capillary ion chromatography using monolithic silica columns modified with cetyltrimethylammonium ion. ==References==

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