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13 décembre 2011 2 13 /12 /décembre /2011 02:39

Laboratory methods of production

In the laboratory, because of its commercial availability and long shelf-life, bromine is not typically prepared. Small amounts of bromine can however be generated through the reaction of solid sodium bromide with concentrated sulfuric acid (H2SO4).Sony VAIO VPCW12S1E/W Battery

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 (Br2) and sulfur dioxide (SO2).

NaBr (s) + H2SO4 (aq) ? HBr (aq) + NaHSO4 (aq)

2 HBr (aq) + H2SO4 (aq) ? Br2 (g) + SO2 (g) + 2 H2O (l)Sony VAIO VPCW213AG/L Battery

Non oxidizing acid alternatives, such as the use of dilute hydrobromic acid with sodium hypobromite, are also available, as the hypobromous acid formed from them is unstable in the presence of bromide, being reduced by it according to the reaction:

2 OBr- (aq) + 4 HBr (aq) ? 2Br2 + 2H2O + 2BrSony VAIO VPCW213AG/P Battery

The reactions are the reverse of disproportionation reactions of elemental bromine in base, and are called comproportionation. A similar reaction happens with sodium hypochlorite, acid, and chloride, leading to elemental chlorine.Sony VAIO VPCW213AG/T Battery

Reactions involving an oxidizing agent, such as potassium permanganate or manganese dioxide, on bromide ions in the presence of an acid, also give bromine in the reactions analogous to the formation of elemental chlorine and iodine from an acid and oxidant.Sony VAIO VPCW213AG/W Battery

Like iodine, bromine is soluble in chloroform but only slightly soluble in water. In water, the solubility can be increased by the presence of bromide ions. Concentrated solutions of bromine are rarely prepared in the lab because of hazards.Sony VAIO VPCW215AG/L Battery

As is the case with chlorine solutions or iodine solutions, sodium thiosulphate(or any soluble thiosulphate) is an effective reagent for reducing bromine to colorless odorless bromide, thus dealing with stains and odor from the element in unwanted places. For the same reason, thiosulfate ("fixer's hypo") is used in photography to deal with free bromine in silver bromide film emulsions.Sony VAIO VPCW217JC Battery

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 yields the di-bromo product.Sony VAIO VPCW217JC/L Battery

For example, reaction with ethylene will produce 1,2-dibromoethane. Bromine also undergoes electrophilic addition to phenols and anilines. When used as bromine water, a small amount of the corresponding bromohydrin is formed as well as the dibromo compound.Sony VAIO VPCW217JC/P Battery

So reliable is the reactivity of bromine that bromine water is employed as a reagent to test for the presence of 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.Sony VAIO VPCW217JC/T Battery

Bromine, sometimes with a catalytic amount of phosphorus, easily brominates carboxylic acids at the ?-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.Sony VAIO VPCW217JC/W Battery

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.Sony VAIO VPCW218JC Battery

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.Sony VAIO VPCW218JC/L Battery

The Montreal Protocol mentions several organobromine compounds for this phase out.

Inorganic chemistry

Inorganic bromine compounds adopt a variety of oxidation states from ?1 to +7.

Bromine is an oxidizer, and it will oxidize iodide ions to iodine, being itself reduced to bromide:Sony VAIO VPCW218JC/P Battery

Br2 + 2 I? ? 2 Br? + I2

Bromine will also oxidize metals and metalloids 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.Sony VAIO VPCW218JC/T Battery

Dissolving bromine in alkaline solution gives a mixture of bromide and hypobromite:

Br2 + 2 OH? ? Br? + OBr? + H2O

This hypobromite is responsible for the bleaching abilities of bromide solutions. Warming of these solutions causes the disproportion reaction of the hypobromite to give bromate, a strong oxidising agent very similar to chlorate.Sony VAIO VPCW218JC/W Battery

3 BrO? ? BrO?3 + 2 Br?

In contrast to the route to perchlorates, perbromates are not accessible through electrolysis but only by reacting bromate solutions withfluorine or ozone.

BrO3? + H2O + F2 ? BrO?4 + 2 HF ,BrO3? + O3 ? BrO?4 + O2

Bromine reacts violently and explosively with aluminium metal, forming aluminium bromide:Sony VAIO VPCW219AJ/L Battery

2 Al + 3 Br2 ? 2 AlBr3

Bromine reacts with hydrogen in gaseous form and gives hydrogen bromide:

H2 + Br2 ? 2HBr

Bromine reacts with alkali metal iodides in a displacement reaction. This reaction forms alkali metal bromides and produces elemental iodine:Sony VAIO VPCW219AJ/P Battery

2 NaI + Br2 ? 2 NaBr + I2

2 KI + Br2 ? 2 KBr + I2

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.Sony VAIO VPCW219AJ/W Battery

Illustrative of the addition reaction is the preparation of 1,2-dibromoethane, the organobromine compound produced in the largest amounts:

C2H4 + Br2 ? CH2BrCH2Br

Flame retardant

Brominated flame retardants represent a commodity of growing importance, and represent the largest use of bromine.Sony VAIO VPCW21AAJ Battery

When the brominated material burns, the flame retardant produces hydrobromic acid which interferes in the radical chain reaction of theoxidation reaction of the fire. The mechanism is that the highly reactive hydrogen oxygen and hydroxy radicals react with hydrobromic acid and form less reactive bromine radicals (free bromine atoms).Sony VAIO VPCW21AKJ Battery

These also react with radicals in the first to help terminate the reaction.

The bromine-containing compounds can be placed in the polymers either during polymerization if a small amount of brominated monomer is added or the bromine containing compound is added after polymerization.Sony VAIO VPCW21AVJ Battery

Tetrabromobisphenol A can be added to producepolyesters or epoxy resins. Epoxy used in printed circuit boards (PCB) are normally made from flame retardant resins, indicated by the FR in the abbreviation of the products (FR-4 and FR-2. Vinyl bromide can be used in the production of polyethylene,polyvinylchloride or polypropylene.Sony VAIO VPCY115FGS Battery

Decabromodiphenyl ether can be added to the final polymers.

Gasoline additive

Ethylene bromide was an additive in gasolines containing lead anti-engine knocking agents. It scavenges lead by forming volatile lead bromide, which is exhausted from the engine.Sony VAIO VPCY115FX/BI Battery

This application accounted for 77% of the bromine use in 1966 in the US. This application has declined since the 1970s due to environmental regulations (see below).

Pesticide

Poisonous methyl bromide was widely used as pesticide to fumigate soil and to fumagate housing, by the tenting method.Sony VAIO VPCY115FXBI Battery

Ethylene bromide was similarly used. These volatile organobromine compounds are all now regulated as ozone depletion agents. The Montreal Protocol on Substances that Deplete the Ozone scheduled the phase out for the ozone depleting chemical by 2005,Sony VAIO VPCY118EC Battery

and organobromide pesticides are no longer used (in housing fumagation they have been replaced by such compounds as sulfuryl fluoride, which contain neither the chlorine or bromine organics which harm ozone). Prior to the Montreal protocol in 1991 (for example) an estimated 35,000 tonnes of the chemical were used to control nematodes, fungi, weeds and other soil-borne diseases.Sony VAIO VPCY118GX/BI Battery

Medical and veterinary

Use. Bromide compounds, especially potassium bromide, were frequently used as general sedatives in the 19th and early 20th century. Bromides in the form of simple salts are still used as anticonvulsants in both veterinary and human medicine, although the latter use varies from country to country.Sony VAIO VPCY119FJ/S Battery

For example, the U.S. Food and Drug Administration (FDA) does not approve bromide for the treatment of any disease, and it was removed from over-the-counter sedative products like Bromo-Seltzer, in 1975. Thus, bromide levels are not routinely measured by medical laboratories in the U.S.Sony VAIO VPCY11AFJ Battery

However, U.S. veterinary medical diagnostic testing laboratories will measure blood bromide levels on request, as an aid to treatment of epilepsy in dogs.

Toxicity. Long-term use of potassium bromide (or any bromide salt) can lead to bromism.Sony VAIO VPCY11AGJ Battery

This state of central nervous system depression causes the moderate toxicity of bromide in multi-gram doses for humans and other mammals. The very long half-life of bromide ion in the body (~12 days) also contributes to toxicity from bromide build-up in body fluids. Bromide ingestion may also cause a skin eruption resembling acne.Sony VAIO VPCY11AHJ Battery

Other uses

  • 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 sometimes called clear brine fluids.Sony VAIO VPCY11AVJ Battery
  • Bromine is also used in the production of brominated vegetable oil, which is used as an emulsifier in many citrus-flavored soft drinks (for example, Mountain Dew). After the introduction in the 1940s the compound was extensively used until the UK and the US limited its use in the mid 1970s and alternative emulsifiers were developed.Sony VAIO VPCY11M1E/S Battery
  • Soft drinks containing brominated vegetable oil are still sold in the US (2011).
  • Several dyes, agrichemicals, and pharmaceuticals are organobromine compounds. 1-Bromo-3-chloropropane, 1-bromoethylbenzene, and 1-bromoalkanes are prepared by the antimarkovnikov additionof HBr to alkenes. Ethidium bromide, EtBr, is used as a DNA stain in gel electrophoresis.Sony VAIO VPCY11S1E Battery
  • High refractive index compounds
  • Bromine, like chlorine, is used in maintenance of swimming pools, especially spas (hot tubs), where it is generated in situ from a bromide plus hydrogen peroxide. In spas, the high water temperatures render chlorinated water purification and buffering compounds unstable, and bromine compounds may improve the life of the free-halogen antimicrobial.Sony VAIO VPCY11V9E/S Battery
  • Water purification compounds, disinfectants and insecticides, such as tralomethrin (C22H19Br4NO3).
  • Potassium bromide is used in some photographic developers to inhibit the formation of fog (undesired reduction of silver).
  • Bromine vapor is used as the second step in sensitizing daguerreotype plates to be developed under mercury vapor. Bromine acts as an accelerator to the light sensitivity of the previously iodized plate.Sony VAIO VPCY218EC/BI Battery
  • Bromine is also used to reduce mercury pollution from coal-fired power plants. This can be achieved either by treating activated carbon with bromine or by injecting bromine compounds onto the coal prior to combustion.Sony VAIO VPCY218EC/G Battery
  • Bromine can also be artificially substituted for the methyl substituent in the nitrogenous base thymine of DNA, creating the base analog 5-bromouracil. When this base is incorporated into DNA its different hydrogen bonding properties may cause mutation at the site of that base pair. The compound 5-bromouracil is thus an artificial mutagen.Sony VAIO VPCY218EC/L Battery

Biological role

Bromine has no known essential role in human or mammalian health, but inorganic bromine and organobromine compounds do occur naturally, and some may be of use to higher organisms in dealing with parasites.Sony VAIO VPCY218EC/P Battery

For example, in the presence of H2O2 formed by the eosinophil, and either chloride or bromide ions, eosinophil peroxidase provides a potent mechanism by which eosinophils kill multicellular parasites (such as, for example, the nematode worms involved in filariasis); and also certain bacteria (such as tuberculosis bacteria).Sony VAIO VPCY21S1E/L Battery

Eosinophil peroxidase is ahaloperoxidase that preferentially uses bromide over chloride for this purpose, generating hypobromite (hypobromous acid).

Marine organisms are the main source of organobromine compounds. Over 1600 compounds were identified by 1999. Sony VAIO VPCY21S1E/P Battery

The most abundant one ismethyl bromide (CH3Br) with an estimated 56,000 tonnes produced by marine algae each year. The essential oil of the Hawaiian algaAsparagopsis taxiformis consists of 80% methyl bromide. Most of such organobromine compounds in the sea are made via the action of a unique algal enzyme, vanadium bromoperoxidase.Sony VAIO VPCY21S1E/SI Battery

Though this enzyme is the most prolific creator of organic bromides by living organisms, other bromoperoxidases exist in nature that do not use vanadium.

A famous example of a bromine-containing organic compound that has been used by humans since ancient times is the fabric dye Tyrian purple.Sony VAIO VPCZ110 Battery

The brominated indole indigo dye is produced by a medium-sized predatory sea snail, the marine gastropod Murex brandaris. The organobromine nature of the compound was not discovered until 1909 (see Paul Friedländer).

Safety

Elemental bromine is toxic and causes burns.Sony VAIO VPCZ110GB/BI Battery

As an oxidizing agent, it is incompatible with most organic and inorganic compounds. Care needs to be taken when transporting bromine; it is commonly carried in steel tanks lined with lead, supported by strong metal frames.

When certain ionic compounds containing bromine are mixed with potassium permanganate (KMnO4) and an acidic substance, they will form a pale brown cloud of bromine gas.Sony VAIO VPCZ112GD/S Battery

6 Br + 2 MnO4 + 8 H+ ? 3 Br2 + 2 MnO2 + 4 H2O

This gas smells like bleach and is very irritating to the mucous membranes. Upon exposure, one should move to fresh air immediately. If symptoms of bromine poisoning arise, medical attention is needed.Sony VAIO VPCZ112GX/S Battery

Krypton is a chemical element with the symbol Kr andatomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other rare gases in fluorescent lamps. Krypton is inert for most practical purposes.Sony VAIO VPCZ114GX/S Battery

Krypton, like the other noble gases, can be used in lighting and photography. Krypton light has a large number of spectral lines, and krypton's high light output in plasmas allows it to play an important role in many high-powered gas lasers (krypton ion and eximer lasers), which pick out one of the many spectral lines to amplify.\Sony VAIO VPCZ115 Battery

There is also a specific krypton fluoride laser. The high power and relative ease of operation of krypton discharge tubes caused (from 1960 to 1983) the official length of a meter to be defined in terms of the orange spectral line of krypton-86.Sony VAIO VPCZ115FC/B Battery

Krypton was discovered in Britain in 1898 by Sir William Ramsay, a Scottish chemist, and Morris Travers, an English chemist, in residue left from evaporating nearly all components of liquid air.Neon was discovered by a similar procedure by the same workers just a few weeks later.Sony VAIO VPCZ115FC/S Battery

William Ramsay was awarded the 1904 Nobel Prize in Chemistry for discovery of a series of noble gases, including krypton.

In 1960, an international agreement defined the meter in terms of wavelength of light emitted by the krypton-86 isotope (wavelength of 605.78 nanometers).Sony VAIO VPCZ116 Battery

This agreement replaced the longstanding standard meter located in Paris, which was a metal bar made of a platinum-iridium alloy (the bar was originally estimated to be one ten-millionth of a quadrant of the earth's polar circumference), and was itself replaced by a definition based on the speed of light — a fundamental physical constant.Sony VAIO VPCZ116GX/S Battery

In October 1983, the Bureau International des Poids et Mesures(International Bureau of Weights and Measures) defined the meter as the distance that light travels in a vacuum during 1/299,792,458 s.

Characteristics

Krypton is characterized by several sharp emission lines (spectral signatures) the strongest being green and yellow.Sony VAIO VPCZ117 Battery

It is one of the products of uranium fission. Solidified krypton is white and crystalline with a face-centered cubic crystal structure, which is a common property of all noble gases (except helium, with a hexagonal close-packed crystal structure).

Naturally occurring krypton is made of six stable isotopes.Sony VAIO VPCZ117FC/B Battery

In addition, about thirty unstable isotopes and isomers are known. 81Kr, the product of atmospheric reactions, is produced with the other naturally occurring isotopes of krypton. Being radioactive, it has a half-life of 230,000 years. Krypton is highly volatile when it is near surface waters but 81Kr has been used for dating old (50,000–800,000 years) groundwater.Sony VAIO VPCZ118 Battery

85Kr is an inert radioactive noble gas with a half-life of 10.76 years. It is produced by the fission of uranium andplutonium, such as in nuclear bomb testing and nuclear reactors. 85Kr is released during the reprocessing of fuel rods from nuclear reactors. Concentrations at the North Pole are 30% higher than at the South Pole due to convective mixing.Sony VAIO VPCZ118GC/B Battery

Chemistry

Like the other noble gases, krypton is chemically unreactive. However, following the first successful synthesis of xenoncompounds in 1962, synthesis of krypton difluoride (KrF2) was reported in 1963. In the same year, KrF4 was reported by Grosse, et al., but was subsequently shown to be a mistaken identification.Sony VAIO VPCZ118GX/S Battery

There are also unverified reports of a barium salt of a krypton oxoacid. ArKr+ and KrH+ polyatomic ions have been investigated and there is evidence for KrXe or KrXe+.

Compounds with krypton bonded to atoms other than fluorine have also been discovered.Sony VAIO VPCZ119 Battery

The reaction of KrF2 with B(OTeF5)3produces an unstable compound, Kr(OTeF5)2, that contains a krypton-oxygen bond. A krypton-nitrogen bond is found in the cation [HC?N–Kr–F]+, produced by the reaction of KrF2 with [HC?NH]+[AsF?6] below ?50 °C.HKrCN and HKrC?CH (krypton hydride-cyanide and hydrokryptoacetylene) were reported to be stable up to 40 K.Sony VAIO VPCZ119FJ/S Battery

Natural occurrence

The Earth has retained all of the noble gases that were present at its formation except for helium. Krypton's concentration in the atmosphere is about 1 ppm. It can be extracted from liquid air by fractional distillation.Sony VAIO VPCZ119GC/X Battery

The amount of krypton in space is uncertain, as the amount is derived from the meteoric activity and that from solar winds. The first measurements suggest an overabundance of krypton in space.

Applications

Krypton's multiple emission lines make ionized krypton gas discharges appear whitish, which in turn makes krypton-based bulbs useful in photography as a brilliant white light source.Sony VAIO VPCZ119L Battery

Krypton is thus used in some types of photographic flashes used in high speedphotography. Krypton gas is also combined with other gases to make luminous signs that glow with a bright greenish-yellow light.

Krypton mixes with argon as the fill gas of energy saving fluorescent lamps. This reduces their power consumption.Sony VAIO VPCZ119R/B Battery

Unfortunately this also reduces their light output and raises their cost. Krypton costs about 100 times as much as argon. Krypton (along with xenon) is also used to fill incandescent lamps to reduce filament evaporation and allow higheroperating temperatures to be used for the filament.Sony VAIO VPCZ119R/S Battery

A brighter light results which contains more blue than conventional lamps.

Krypton's white discharge is often used to good effect in colored gas discharge tubes, which are then simply painted or stained in other ways to allow the desired color (for example, "neon" type advertising signs where the letters appear in differing colors are often entirely krypton-based).Sony VAIO VPCZ11AFJ Battery

Krypton is also capable of much higher light power density than neon in the red spectral line region, and for this reason, red lasers for high-power laser light-shows are often krypton lasers with mirrors which select out the red spectral line for laser amplification and emission,Sony VAIO VPCZ11AGJ Battery

rather than the more familiar helium-neon variety, which could never practically achieve the multi-watt red laser light outputs needed for this application.

Krypton has an important role in production and usage of the krypton fluoride laser.Sony VAIO VPCZ11AVJ Battery

The laser has been important in the nuclear fusion energy research community in confinement experiments. The laser has high beam uniformity, short wavelength, and the ability to modify the spot size to track an imploding pellet.

In experimental particle physics, liquid krypton is used to construct quasi-homogeneous electromagnetic calorimeters.Sony VAIO VPCZ11CGX/X Battery

A notable example is the calorimeter of the NA48 experiment at CERN containing about 27 tonnes of liquid krypton. This usage is rare, since the cheaper liquid argon is typically used. The advantage of krypton over argon is a small Molière radius of 4.7 cm, which allows for excellent spatial resolution and low degree of overlapping.Sony VAIO VPCZ11DGX/SJ Battery

The other parameters relevant for calorimetry application are: radiation length of X0=4.7 cm, density of 2.4 g/cm3.

The sealed spark gap assemblies contained in ignition exciters used in some older jet engines contain a very small amount of Krypton-85 to obtain consistent ionization levels and uniform operation.Sony VAIO VPCZ11FHX/XQ Battery

Krypton-83 has application in magnetic resonance imaging (MRI) for imaging airways. In particular, it may be used to distinguish between hydrophobic and hydrophilic surfaces containing an airway.

Although xenon has potential for use in computed tomography (CT) to assess regional ventilation, its anesthetic properties limit its fraction in the breathing gas to 35%.Sony VAIO VPCZ11V9R/B Battery

The use of a breathing mixture containing 30% xenon and 30% krypton is comparable in effectiveness for CT to a 40% xenon fraction, while avoiding the unwanted effects of a high fraction xenon gas.

Precautions

Krypton is considered to be a non-toxic asphyxiant.Sony VAIO VPCZ11X9E/B Battery

Krypton has a narcotic potency seven times greater than air, so breathing a gas containing 50% krypton and 50% air would cause narcosis similar to breathing air at four times atmospheric pressure. This would be comparable to scuba diving at a depth of 30 m (100 ft) (seenitrogen narcosis) and potentially could affect anyone breathing it.Sony VAIO VPCZ11Z9E/B Battery

Nevertheless, that mixture would contain only 10% oxygen and hypoxia would be a greater concern.Sony VAIO VPCZ125GX/S Battery,Sony VAIO VPCZ127FC Battery,Sony VAIO VPCZ128GC Battery,Sony VAIO VPCZ12M9E/B Battery,Sony VAIO VPCZ13M9E/B Battery,Sony VAIO VPCZ13V9E/X Battery,Sony VAIO VPCZ13Z9E/X Battery,Sony VAIO VPCZZZHJ Battery,Sony VAIO VPZ117 Battery,Sony VAIO VPZ118 Battery

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