Bromine

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Bromine (RP IPA: /ˈbrəʊmiːn/ OR /ˈbrəʊmaɪn/, GA /ˈbroʊmiːn/ OR /ˈbroʊmɪn/, Greek: βρῶμος, brómos, meaning "stench (of he-goats)" ^[1]), is a chemical element in the periodic table that has the symbol Br and atomic number 35. A halogen element, bromine is a red volatile liquid at standard room temperature which has a reactivity between chlorine and iodine. This element is corrosive to human tissue in a liquid state and its vapours irritate the eyes and throat. Bromine vapours are very toxic upon inhalation.

[edit] Notable characteristics

Bromine is the only liquid nonmetallic element at room temperature and one of six elements on the periodic table that are liquid at or close to room temperature. The pure chemical element has the physical form of a diatomic molecule, Br₂. It is a heavy, mobile, reddish-brown liquid, that evaporates easily at standard temperature and pressures in a red vapor (its color resembles nitrogen dioxide) that has a strong disagreeable odor resembling that of chlorine. Bromine is a halogen, and is less reactive than chlorine and more reactive than iodine. Bromine is slightly soluble in water, and highly soluble in carbon disulfide, aliphatic alcohols (such as methanol), and acetic acid. It bonds easily with many elements and has a strong bleaching action.

Bromine is highly reactive and is a powerful oxidizing agent in the presence of water. It reacts vigorously with amines, alkenes and phenols as well as aliphatic and aromatic hydrocarbons, ketones and acids (these are brominated by either addition or substitution reactions). With many of the metals and elements, anhydrous bromine is less reactive than hydrated bromine; however, dry bromine reacts vigorously with aluminium, titanium, mercury as well as alkaline earth metals and alkali metals.

Certain bromine-related compounds have been evaluated to have an ozone depletion potential or bioaccumulate in living organisms. As a result many industrial bromine compounds are no longer manufactured, are being restricted, or scheduled for phase out of manufacturing processes.

[edit] Chemistry

[edit] Electrophilic addition

Bromine undergoes electrophilic addition to the double-bonds of alkenes, via a cyclic bromonium intermediate. In non-aqueous solvents such as carbon tetrachloride, this gives the di-bromo product. For example, reaction with ethylene will produce 1,2-dibromoethane. When used as bromine water, the corresponding bromohydrin is formed instead.

Bromine also undergoes electrophilic addition to phenols and anilines, which are activated at the ortha and para positions. When added to either, the 2,4,6-tribromophenol or aniline product which is usually a white solid, will precipitate.

Apart from organic synthesis, bromine water is thus used as a qualitative test for alkenes, phenols, and anilines.

Bromine, sometimes with a catalytic amount of phosphorus, easily brominates carboxylic acids at the α-position. This is the Hell-Volhard-Zelinsky reaction.

[edit] Oxidation

Like the other halogens, bromine is an oxidizer, and it will oxidize iodide ions to elemental iodine, being itself reduced to bromide ions.

[edit] Free radical reaction

Like the halogens, bromine undergoes free radical reactions.

[edit] Bromine analogs

N-bromosuccinimide is commonly used as a substitute for elemental bromine, being easier to handle, and reacting more mildly and thus more selectively.

[edit] Applications

Elemental bromine is used to manufacture a wide variety of bromine compounds used in industry and agriculture. A common use of bromine was in the production of 1,2-dibromoethane which in turn was used as an anti-knock agent for leaded gasolines, but this application has been largely phased out due to environmental considerations.

Bromine is also used to form intermediates in organic synthesis, in which it is somewhat preferable over iodine due to its lower cost.

Bromine is used to make brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks.

Bromine is also used in the manufacture of:

• Fumigants
• Brominated flame retardants
• High refractive index compounds
• Water purification compounds
• Dyes
• Medicines
• Disinfectants

[edit] History

Bromine was discovered by Antoine Balard at the salt marshes of Montpellier in 1826, but was not produced in quantity until 1860. The French chemist and physicist Joseph-Louis Gay-Lussac suggested the name bromine due to the characteristic smell of the vapors.

[edit] Occurrence

Bromine occurs in nature as bromide salts in very diffuse amounts in crustal rock. Due to leaching, bromide salts have accumulated in sea water (85 ppm), and may be economically recovered from brine wells and the Dead Sea (up to 5000 ppm).

Approximately 500,000 metric tons (worth around US$350 million) of bromine are produced per year (2001) worldwide with the United States and Israel being the primary producers. The largest bromine reserve in the United States is located in Columbia and Union County, Arkansas. Israel's bromine reserves are contained in the waters of the Dead Sea. Bromine production has increased sixfold since the 1960s.

See also Halide minerals.

[edit] Safety

Elemental bromine is a strong irritant, oxidizing and, in concentrated form, will produce painful blisters on exposed skin and especially mucous membranes. Even low concentrations of bromine vapor (from 10 ppm) can affect breathing, and inhalation of significant amounts of bromine can seriously damage the respiratory system.

Accordingly, one should always wear safety goggles and ensure adequate ventilation when handling bromine.

A chronic overdose of bromides can lead to bromism (also called brominism) characterized by mental dullness, loss of muscular coordination, and possibly skin eruptions.

In laboratory settings, bromine should always be stored separately from acetone, as the two chemicals can react and create bromoacetone, a potentially hazardous lachrymatory agent.

[edit] Compounds

Aluminium bromide (AlBr₃), ammonium bromide (NH₄Br), bromine monofluoride (BrF), bromine pentafluoride (BrF₅), bromine trifluoride (BrF₃), ethidium bromide (C₂₁H₂₀BrN₃), tetrabromomethane (CBr₄), hydrobromic acid (HBr), iron(III) bromide (FeBr₃), lithium bromide (LiBr), phosphorus pentabromide (PBr₅), phosphorus tribromide (PBr₃), potassium bromide (KBr), potassium bromate (KBrO₃), silver bromide (AgBr), sodium bromide (NaBr), sodium bromate (NaBrO₃).

See also Bromine compounds.

[edit] See Also