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Br, A. Jonathan Buhalis
BROMINE
by Jonathan Buhalis

History

Bromine has two independent discoverers. German chemist Carl Jacob Löwig in 1825 extracted a brown liquid from mineral water and suspected it to be a new substance. While his results remained unpublished, French chemist Antoine Balard in 1826 produced bromine from seaweed ash that was intended to be a source of iodine.

Bromine has been used in medicine, but much of this is in the past. Some bromine compounds were deployed as poison gas in World War I. Potassium bromide was used as a sedative and treatment for epilepsy in the 19th century and early 20th, but it has been replaced. Other uses are also being phased out because bromine contributes to ozone depletion.

Production

Bromine occurs naturally as water-soluble salts and so can most easily be extracted where it has been concentrated by water. Bromine is recovered from high-salinity brine pools, most notably the Dead Sea. Production of bromine in 2014 was about 600,000 tonnes, with the United States (33%), Israel (30%), and China (18%) the leaders.

Brines containing bromine are injected with chlorine gas. The two elements play similar roles in solution, but chlorine is more reactive, and so the bromine is forced into its liquid state.

Properties and Uses

bromine liquid and gas (Wikipedia), A. Jonathan BuhalisBromine is one of two elements, with mercury, that are liquids at room temperature. Bromine is a dark red liquid that evaporates into an orangish vapor (right). It has an unpleasant smell like chlorine.

Bromine is a halogen, less reactive than chlorine or fluorine, but more reactive than iodine. It reacts with most other elements and it acts as a bleach.

Recent research suggests that bromine may be a necessary trace element in humans and other mammals. In measurable amounts, though, elemental bromine builds up in the body and is toxic. As mentioned above, potassium bromide was once used as a sedative and anti-epileptic, but those uses have been generally phased out.

Bromine is introduced into plastics as a flame retardant. When a plastic containing bromine burns, molecules are released that interfere with the burning. This is the largest current use of bromine, in the manufacture of polyethylene, polyvinylchloride, and polypropylene.

A related use of bromine is in premium halogen fire extinguishers. Bromine halogens work better than chlorine halogens, but are more expensive. They are used in critical sealed environments such as submarines and spacecraft.

South Pole ozone hole, September 2013, courtesy NASA, A. Jonathan BuhalisFor general use, bromine halogens have fallen out of favor because they contribute to ozone depletion. Halogen gases are inert at sea level, but when they diffuse into the stratosphere, they are broken down by the sun's ultraviolet light into radicals that destroy protective ozone (right). Bromine radicals are particularly effective at this.

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Content by Jonathan Buhalis
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