Everything about Bromine totally explained
Bromine ( meaning "stench (of he-goats)" ), is a
chemical element with the symbol
Br and
atomic number 35. A
halogen element, bromine is a red
volatile liquid at
standard room temperature that's intermediate in reactivity between
chlorine and
iodine. Bromine vapours are
corrosive and
toxic. Approximately 730,000,000 kg was produced in 1993. The main applications for bromine are in
fire retardants and fine chemicals.
History
Bromine was discovered independently by two chemists
Antoine Balard and
Carl Jacob Löwig in 1825 and 1826.
Balard found bromide salts in the ash of sea weed from the
salt marshes of
Montpellier in
1826. The seaweed was used to produce iodine, but also contained bromine.
Carl Jacob Löwig working at the laboratory of
Leopold Gmelin produced elemental bromine by reacting mineral salts, which contained bromides, with chlorine gas. The publication of the results was delayed and Balard published his results first.
Bromine wasn't 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. Some also suggest that it may have been discovered by
Bernard Courtois, the man who discovered iodine.
Potassium bromide and
sodium bromide were used as anticonvulsants and sedatives in the late 19th and early 20th centuries, until it was gradually superseded by
chloral hydrate and then the
barbiturates.
Isotopes
Notable characteristics
Bromine is the only liquid
nonmetallic element at room temperature and one of only 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, Br
2. It is a dense, mobile, reddish-brown liquid, that evaporates easily at
standard temperature and pressures to give 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, like chlorine, is also used in pool maintenance.
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 phasing out.
Bromine is a powerful
oxidizing agent. It reacts vigorously with metals, especially in the presence of water, as well as most organic compounds, especially upon
illumination.
Bromine has no known role in human health. Organobromine compounds do occur naturally, a famous example being
Tyrian purple. Most organobromine compounds in nature arise via the action of
vanadium bromoperoxidase.
Occurrence and production
» See also .
The diatomic element Br
2 doesn't occur naturally. Instead, bromine exists exclusively as
bromide salts in diffuse amounts in
crustal rock. Due to
leaching, bromide salts have accumulated in sea water (85
ppm), but at a lower concentration than chloride. Bromine may be economically recovered from bromide-rich brine wells and from the
Dead Sea waters (up to 50000 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. Bromine production has increased sixfold since the 1960s. The largest bromine reserve in the United States is located in
Columbia and
Union County, Arkansas, U.S. Israel's bromine reserves are contained in the waters of the
Dead Sea. The bromide-rich brines are treated with chlorine gas, flushing through with air. In this treatment, bromide anions are oxidized to bromine by the chlorine gas.
» 2 Br
− + Cl
2 → 2 Cl
− + Br
2
Because of its commercial availability and long shelf-life, bromine isn't typically prepared. Small amounts of bromine can however be generated through the reaction of solid
sodium bromide with concentrated
sulfuric acid (H
2SO
4). The first stage is formation of
hydrogen bromide (HBr), which is a gas, but under the reaction conditions some of the HBr is oxidized further by the sulfuric acid to form bromine (Br
2) and
sulfur dioxide (SO
2).
» NaBr (s) + H
2SO
4 (aq) → HBr (aq) + NaHSO
4 (aq)
2 HBr (aq) + H
2SO
4 (aq) → Br
2 (g) + SO
2 (g) + 2 H
2O (l)
Similar alternatives, such as the use of dilute
hydrochloric acid with
sodium hypochlorite, are also available. The most important thing is that the
anion of the
acid (in the above examples,
sulfate and
chloride, respectively) be more
electronegative than bromine, allowing the
substitution reaction to occur.
Compounds
Organic chemistry
Organic compounds are brominated by either
addition or
substitution reactions. Bromine undergoes electrophilic addition to the double-bonds of
alkenes, via a cyclic bromonium intermediate. In non-aqueous solvents such as
carbon disulfide, this affords the di-bromo product. For example, reaction with
ethylene will produce
1,2-dibromoethane. Bromine also undergoes electrophilic addition to
phenols and
anilines. When used as bromine water, the corresponding
bromohydrin is formed instead. So reliable is the reactivity of bromine that bromine water is employed as a reagent to test for the presence alkenes, phenols, and anilines. Like the other halogens, bromine participates in
free radical reactions. For example hydrocarbons are brominated upon treatment with bromine in the presence of light.
Bromine, sometimes with a catalytic amount of
phosphorus, easily brominates
carboxylic acids at the α-position. This method, the
Hell-Volhard-Zelinsky reaction, is the basis of the commercial route to
bromoacetic acid.
N-Bromosuccinimide is commonly used as a substitute for elemental bromine, being easier to handle, and reacting more mildly and thus more selectively.
Organic bromides are often preferable relative to the less reactive chlorides and more expensive iodide-containing reagents. Thus,
Grignard and organolithium compound are most often generated from the corresponding bromides.
Inorganic chemistry
Bromine is an oxidizer, and it'll oxidize
iodide ions to iodine, being itself reduced to
bromide:
» Br
2 + 2 I
− → 2 Br
− + I
2
Bromine will also oxidize metals and metaloids to the corresponding bromides.
Anhydrous bromine is less reactive toward many metals than hydrated bromine, however. Dry bromine reacts vigorously with
aluminium,
titanium,
mercury as well as
alkaline earths and
alkali metals.
Applications
A wide variety of organobromine compounds are used in
industry. Some are prepared from bromine and others are prepared from
hydrogen bromide, which is obtained by burning
hydrogen in bromine. is the preparation of
1,2-Dibromoethane, the organobromine compound produced in the largest amounts:
» C
2H
4 + Br
2 → CH
2BrCH
2Br
Ethylene bromide is an additive in gasolines containing lead anti-
engine knocking agents. It scavenges lead by forming volatile lead bromide, which is exhausted from the engine. This application has declined since the 1970s due to environmental regulations. Ethylene bromide is also used as a fumigant, but again this application is declining.
Brominated flame retardants represent a commodity of growing importance. Specific compound used produced for this purpose include
tetrabromobisphenol A,
decabromodiphenyl ether, and
vinyl bromide.
The bromides of calcium, sodium, and zinc account for a sizable part of the bromine market. These salts form dense solutions in water that are used as
drilling fluids.
Miscellaneous uses:
Safety
Elemental bromine is toxic and
causes burns. As an
oxidizing agent, it's incompatible with most organic and inorganic compounds. Care needs to taken when transporting bromine, it's commonly carried in steel tanks lined with lead, supported by strong metal frames.
When certain ionic compounds containing Bromine are mixed with Potassium permanganate (KMnO
4), that'll form a pale brown cloud of Bromine gas. This gas smells like bleach and is very irritating to the mucus membranes. This form of Bromine will appear to diffuse slowly, but it'll suddenly disappear. Upon exposure, one should move to fresh air immediately. If symptoms arise, medical attention is needed.
Further Information
Get more info on 'Bromine'.
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