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21 décembre 2011 3 21 /12 /décembre /2011 02:20

Telluriumis a chemical element that has the symbol Teand atomic number 52. A brittle, mildly toxic, rare, silver-white metalloid which looks similar to tin, tellurium is chemically related toselenium and sulfur. It is occasionally found in native form, as elemental crystals. Tellurium is far more common in the universe than on Earth.Sony VAIO VGN-SZ58GN/C Battery

Its extreme rarity in the Earth's crust, comparable to that of platinum, is partly due to its high atomic number, but also due to its formation of a volatile hydride which caused the element to be lost to space as a gas during the hot nebular formation of the planet.Sony VAIO VGN-SZ58N Battery

Tellurium was discovered in Transylvania (today part of Romania) in 1782 by Franz-Joseph Müller von Reichenstein in a mineral containing tellurium and gold. Martin Heinrich Klaproth named the new element in 1798 after the Latin word for "earth", tellus. Gold telluride minerals (responsible for the name of Telluride, Colorado) are the most notable natural gold compounds.Sony VAIO VGN-SZ61MN/B Battery

However, they are not a commercially significant source of tellurium itself, which is normally extracted as by-product of copper and lead production.

Tellurium is commercially primarily used in alloys, foremost in steel and copper to improve machinability. Applications in solar panels and as a semiconductor material also consume a considerable fraction of tellurium production.Sony VAIO VGN-SZ61VN/X Battery

Tellurium has no biological function, although fungi can incorporate it in place of sulfur and selenium into amino acidssuch as telluro-cysteine and telluro-methionine.[3]In humans, tellurium is partly metabolized into dimethyl telluride, (CH3)2Te, a gas with a garlic-like odor which is exhaled in the breath of victims of tellurium toxicity or exposure.Sony VAIO VGN-SZ61WN/C Battery

Physical properties

When crystalline, tellurium is silvery-white and when it is in pure state it has a metallic luster. It is a brittle and easily pulverized metalloid. Amorphous tellurium is found by precipitating it from a solution of tellurous or telluricacid (Te(OH)6).Sony VAIO VGN-SZ640N/B Battery

ellurium is a semiconductor that shows a greater electrical conductivity in certain directions which depends on atomic alignment; the conductivity increases slightly when exposed to light (photoconductivity).[5]When in its molten state, tellurium is corrosive to copper, iron and stainless steel.Sony VAIO VGN-SZ645P3 Battery

Chemical properties

Tellurium adopts a polymeric structure, consisting of zig-zag chains of Te atoms. This gray material resists oxidation by air and is nonvolatile.

Naturally occurring tellurium has eight isotopes. Four of those isotopes, 122Te, 124Te, 125Te and 126Te, are stable.Sony VAIO VGN-SZ650N/C Battery

The other four, 120Te, 123Te, 128Te and 130Te, have been observed to be radioactive.[6][7]The stable isotopes make up only 33.2 % of the naturally occurring tellurium; this is possible due to the long half-lives of the unstable isotopes. They are in the range from 1013to 2.2 1024years (for 128Te).Sony VAIO VGN-SZ660N/C Battery

This makes 128Te the isotope with the longest half life among allradionuclides.,[8]which is approximately 160 trillion (1012) times the age of known universe.

There are 38 known nuclear isomers of tellurium with atomic masses that range from 105 to 142.Sony VAIO VGN-SZ670N/C Battery

Tellurium is among the lightest elements known to undergo alpha decay, with isotopes 106Te to 110Te being able to undergo this mode of decay.[6]The atomic mass of tellurium (127.60 g·mol?1) exceeds that of the following element iodine (126.90 g·mol?1).Sony VAIO VGN-SZ680ND Battery

Occurrence

With an abundance in the Earth's crust comparable to that of platinum, tellurium is one of the rarest stable solid elements in the Earth's crust. Its abundance is about 1 µg/kg.[10]In comparison, even the rarest of the lanthanides have crustal abundances of 500 µg/kg (see Abundance of the chemical elements).Sony VAIO VGN-SZ691N/X Battery

The extreme rarity of tellurium in the Earth's crust is not a reflection of its cosmic abundance, which is in fact greater than that of rubidium, even though rubidium is ten thousand times more abundant in the Earth's crust. The extraordinarily low abundance of tellurium on Earth is rather thought to be due to conditions in the Earth's formation,Sony VAIO VGN-SZ71E/B Battery

when the stable form of certain elements, in the absence of oxygen andwater, was controlled by the reductive power of free hydrogen. Under this scenario, certain elements such as tellurium which form volatile hydrides were severely depleted during the formation of the Earth's crust, through evaporation of these hydrides.Sony VAIO VGN-SZ71VN/X Battery

Tellurium and selenium are the heavy elements most depleted in the Earth's crust by this process.

Tellurium is sometimes found in its native (elemental) form, but is more often found as the tellurides of gold (calaverite, krennerite, petzite, sylvanite and others). Tellurium compounds are the most common chemical compounds of gold found in nature (rare non-tellurides such as gold aurostibite and bismuthide are known).Sony VAIO VGN-SZ71WN/C Battery

Tellurium is also found combined with elements other than gold, in salts of other metals. In contrast to selenium, tellurium is not able to replace sulfur in its minerals. This is due to the large difference in ion radius of sulfur and tellurium. In consequence, many sulfide minerals contain considerable amounts of selenium, but only traces of tellurium.Sony VAIO VGN-SZ74B/B Battery

In the gold rush of 1893, diggers in Kalgoorlie discarded a pyritic material which got in their way as they searched for pure gold. The Kalgoorlie waste was thus used to fill in potholes or as part of sidewalks. Three years passed before it was realized that this waste was calaverite, a telluride of gold that had not been recognized. This led to a second gold rush in 1896 which included mining the streets.Sony VAIO VGN-SZ750N/C Battery

Production

The principal source of tellurium is from anode sludges produced during the electrolytic refining of blister copper. It is a component of dusts from blast furnace refining of lead. Treatment of 500 tons of copper ore typically yields one pound (0.45 kg) of tellurium.Sony VAIO VGN-SZ75B/B Battery

Tellurium is produced mainly in the United States, Peru, Japan and Canada.[14]For the year 2006 the British Geological Survey gives the following numbers: United States 50 t, Peru 37 t, Japan 24 t and Canada 11 t.[15]

The anode sludges contain the selenides and tellurides of the noble metals in compounds with the formula M2Se or M2Te (M = Cu, Ag, Au).Sony VAIO VGN-SZ76 Battery

At temperatures of 500 °C the anode sludges are roasted with sodium carbonate under air. The metal ions are reduced to the metals, while the telluride is converted to sodium tellurite.

M2Te + O2+ Na2CO3? Na2TeO3+ 2 M + CO2

Tellurites can be leached from the mixture with water and are normally present as hydrotellurites HTeO3–in solution.Sony VAIO VGN-SZ770N/C Battery

Selenites are also formed during this process, but they can be separated by adding sulfuric acid. The hydrotellurites are converted into the insoluble tellurium dioxide while the selenites stay in solution.

HTeO3–+ OH–+ H2SO4? TeO2+ 2 SO42?+ 2 H2O

The reduction to the metal is done either by electrolysis or by reacting the tellurium dioxide with sulfur dioxide in sulfuric acid.Sony VAIO VGN-SZ77N Battery

TeO2+ 2 SO2+ 2H2O ? Te + SO42?+ 4 H+

Commercial-grade tellurium is usually marketed as 200-mesh powder but is also available as slabs, ingots, sticks, or lumps. The year-end price for tellurium in 2000 was US$14 per pound. In recent years, the tellurium price was driven up by increased demand and limited supply, reaching as high as US$100 per pound in 2006.Sony VAIO VGN-SZ780 Battery

Despite an expected doubling in production due to improved extraction methods, the United States Department of Energy (DoE) anticipates a supply shortfall of tellurium by 2025.

Compounds

Tellurium belongs to the same chemical family as oxygen, sulfur, selenium and polonium: the chalcogen family. Tellurium and selenium compounds are similar.Sony VAIO VGN-SZ78N Battery

It exhibits the oxidation states ?2, +2, +4 and +6, with the +4 state being most common.

Tellurides

Reduction of Te metal produces the tellurides and polytellurides, Ten2–. The ?2 oxidation state is exhibited in binary compounds with many metals, such as zinc telluride, ZnTe, formed by heating tellurium with zinc.Sony VAIO VGN-SZ791N/X Battery

Decomposition of ZnTe with hydrochloric acid yields hydrogen telluride (H2Te), a highly unstable analogue of the other chalcogen hydrides, H2O, H2S and H2Se:

ZnTe + 2 HCl ? ZnCl2+ H2Te

H2Te is unstable, whereas salts of its conjugate base [TeH]–are stable.Sony VAIO VGN-SZ84NS Battery

Halides

The +2 oxidation state is exhibited by the dihalides, TeCl2, TeBr2and TeI2. The dihalides have not been obtained in pure form,although they are known decomposition products of the tetrahalides in organic solvents, and their derived tetrahalotellurates are well-characterized:Sony VAIO VGN-SZ84PS Battery

Te + X2+ 2 X?? TeX2?4

where X is Cl, Br, or I. These anions are square planar in geometry. Polynuclear anionic species also exist, such as the dark brown Te2I2?6,[21]:283and the black Te4I2?14.[21]:285Sony VAIO VGN-SZ84S Battery

Fluorine forms two halides with tellurium: the mixed-valence Te2F4and TeF6. In the +6 oxidation state, the –OTeF5structural group occurs in a number of compounds such as HOTeF5, B(OTeF5)3, Xe(OTeF5)2, Te(OTeF5)4and Te(OTeF5)6.[22]The square antiprismatic anion TeF2?8 is also attested.Sony VAIO VGN-SZ84US Battery

The other halogens do not form halides with tellurium in the +6 oxidation state, but only tetrahalides (TeCl4, TeBr4and TeI4) in the +4 state, and other lower halides (Te3Cl2, Te2Cl2, Te2Br2, Te2I and two forms of TeI). In the +4 oxidation state, halotellurate anions are known, such as TeCl2?6 and Te2Cl2?10. Halotellurium cations are also attested, including TeI+3, found in TeI3AsF6.Sony VAIO VGN-SZ85NS Battery

Oxocompounds

Tellurium monoxide was first reported in 1883 as a black amorphous solid formed by the heat decomposition of TeSO3in vacuum, disproportionating into tellurium dioxide, TeO2and elemental tellurium upon heating.Sony VAIO VGN-SZ85S Battery

Since then, however, some doubt has been cast on its existence in the solid phase, although it is known as a vapor phase fragment; the black solid may be merely an equimolar mixture of elemental tellurium and tellurium dioxide.

Tellurium dioxide is formed by heating tellurium in air, causing it to burn with a blue flame.Sony VAIO VGN-SZ85US Battery

Tellurium trioxide, ?-TeO3, is obtained by thermal decomposition of Te(OH)6. The other two forms of trioxide reported in the literature, the ?- and ?- forms, were found not to be true oxides of tellurium in the +6 oxidation state, but a mixture of Te4+, OH?and O?2. Tellurium also exhibits mixed-valence oxides, Te2O5and Te4O9.Sony VAIO VGN-SZ94NS Battery

The tellurium oxides and hydrated oxides form a series of acids, including tellurous acid (H2TeO3), orthotelluric acid (Te(OH)6) and metatelluric acid ((H2TeO4)n).[26]The two forms of telluric acid form telluratesalts containing the TeO2–4 and TeO6?6 anions, respectively.Sony VAIO VGN-SZ94PS Battery

Tellurous acid forms telluritesalts containing the anion TeO2?3. Other tellurium cations include TeF2+8, which consists of two fused tellurium rings and the polymeric TeF2+7.

Zintl cations

When tellurium is treated with concentrated sulfuric acid, it forms red solutions containing the Zintl ion, Te2+4.Sony VAIO VGN-SZ94S Battery

The oxidation of tellurium by AsF5in liquid SO2also produces this square planar cation, as well as with the trigonal prismatic, yellow-orange Te4+6:4 Te + 3 AsF5? Te2+4(AsF?6)2+ AsF36 Te + 6 AsF5? Te4+6(AsF?6)4+ 2 AsF3 Other tellurium Zintl cations include the polymeric Te2+7 and the blue-black Te2+8, which consists of two fused 5-membered tellurium rings. The latter cation is formed by the reaction of tellurium with tungsten hexachloride:Sony VAIO VGN-SZ94US Battery

8 Te + 2 WCl6? Te2+8(WCl?6)2

Interchalcogen cations also exist, such as Te2Se2+6 (distorted cubic geometry) and Te2Se2+8. These are formed by oxidizing mixtures of tellurium and selenium with AsF5or SbF5.Sony VAIO VGN-SZ95NS Battery

Organotellurium compounds

Tellurium does not readily form analogues of alcohols and thiols, with the functional group –TeH and are called tellurols. The –TeH functional group is also attributed to using the prefix tellanyl-.Like H2Te, these species are unstable with respect to loss of hydrogen. Telluraethers (R-Te-R) are more stable as aretelluroxides.Sony VAIO VGN-SZ95S Battery

Tellurium (Latintellusmeaning "earth") was discovered in the 18th century in a gold ore from the mines in Zlatna, near what is now Sibiu, Transylvania. This ore was known as "Faczebajer weißes blättriges Golderz" (white leafy gold ore from Faczebaja) orantimonalischer Goldkies(antimonic gold pyrite), and, according to Anton von Rupprecht, was Spießglaskönig(argent molybdique), containing native antimony.Sony VAIO VGN-SZ95US Battery

In 1782 Franz-Joseph Müller von Reichenstein, who was then serving as the Austrian chief inspector of mines in Transylvania, concluded that the ore did not contain antimony, but that it was bismuth sulfide. The following year, he reported that this was erroneous and that the ore contained mostly gold and an unknown metal very similar to antimony.Sony VAIO VGN-TZ121 Battery

After a thorough investigation which lasted for three years and consisted of more than fifty tests, Müller determined the specific gravity of the mineral and noted the radish-like odor of the white smoke which passed off when the new metal was heated, the red color which the metal imparts to sulfuric acid, and the black precipitate which this solution gives when diluted with water.Sony VAIO VGN-TZ13 Battery

Nevertheless, he was not able to identify this metal and gave it the names aurum paradoxiumand metallum problematicum, as it did not show the properties predicted for the expected antimony.

In 1789, another Hungarian scientist, Pál Kitaibel, also discovered the element independently in an ore from Deutsch-Pilsen which had been regarded as argentiferous molybdenite, but later he gave the credit to Müller.Sony VAIO VGN-TZ130N/B Battery

In 1798, it was named by Martin Heinrich Klaproth who earlier isolated it from the mineral calaverite. The 1960s brought growth in thermoelectric applications for tellurium (as bismuth telluride), as well as its use in free-machining steel, which became the dominant use.Sony VAIO VGN-TZ131 Battery

Metallurgy

The largest consumer of tellurium is metallurgy, where it is used in iron, copper and lead alloys. When added to stainless steel and copper it makes these metals more machinable. It is alloyed into cast iron for promoting chill for spectroscopic purposes, as the presence of electrically conductive free graphite tends to deleteriously affect spark emission testing results.Sony VAIO VGN-TZ132/N Battery

In lead it improves strength and durability and decreases the corrosive action of sulfuric acid.

Semiconductor and electronic industry uses

Tellurium is used in cadmium telluride (CdTe) solar panels. National Renewable Energy Laboratory lab tests using this material achieved some of the highest efficiencies for solar cell electric power generation.Sony VAIO VGN-TZ132N Battery

Massive commercial production of CdTe solar panels by First Solar in recent years has significantly increased tellurium demand. If some of the cadmium in CdTe is replaced by zinc then (Cd,Zn)Te is formed which is used in solid-state X-ray detectors.

Alloyed with both cadmium and mercury, to form mercury cadmium telluride, an infrared sensitive semiconductor material is formed.Sony VAIO VGN-TZ150N/B Battery

Organotellurium compounds such as dimethyl telluride, diethyl telluride, diisopropyl telluride, diallyl telluride andmethyl allyl telluride are used as precursors for metalorganic vapor phase epitaxy growth of II-VI compound semiconductors. Diisopropyl telluride (DIPTe) is employed as the preferred precursor for achieving the low-temperature growth of CdHgTe byMOVPE.Sony VAIO VGN-TZ150N/N Battery

For these processes highest purity metalorganics of both selenium and tellurium are used. The compounds for semiconductor industry and are prepared by adduct purification.

Tellurium as a tellurium suboxide is used in the media layer of several types of rewritable optical discs, including ReWritable Compact Discs (CD-RW), ReWritable Digital Video Discs (DVD-RW) and ReWritable Blu-ray Discs.Sony VAIO VGN-TZ160CB Battery

Tellurium is used in the new phase change memory chips.[49]developed by Intel.[50]Bismuth telluride (Bi2Te3) and lead telluride are working elements ofthermoelectric devices. Lead telluride is used in far-infrared detectors.

Other uses

  • The strong increase in optical refraction upon the addition of selenides and tellurides into glass is used in the production of glass fibers for telecommunications. These chalcogenide glasses are widely used.
  • Mixtures of selenium and tellurium are used with barium peroxide as oxidizer in the delay powder of electric blasting caps.Sony VAIO VGN-TZ16GN/B Battery
  • Organic tellurides have been employed as initiators for living radical polymerization and electron-rich mono- and di-tellurides possess antioxidant activity.
  • Rubber can be vulcanized with tellurium instead of sulfur or selenium. The rubber produced in this way shows improved heat resistance.Sony VAIO VGN-TZ16N Battery
  • Tellurite agar is used to identify member of the corynebacterium genus, most typically Corynebacterium diphtheriae, the pathogen responsible for diphtheria.Biological role

Tellurium has no known biological function, although fungi can incorporate it in place of sulfur and selenium into amino acids such as telluro-cysteine and telluro-methionine.Sony VAIO VGN-TZ16N/B Battery

Organisms have shown a highly variable tolerance to tellurium compounds. Most organisms metabolize tellurium partly to form dimethyl telluride although dimethyl ditelluride is also formed by some species. Dimethyl telluride has been observed in hot springs at very low concentrations.Sony VAIO VGN-TZ17/N Battery

Precautions

Tellurium and tellurium compounds are considered to be mildly toxic and need to be handled with care, although acute poisoning is rare.[61]Tellurium is not reported to be carcinogenic.[61]

Humans exposed to as little as 0.01 mg/m3or less in air develop "tellurium breath", which has a garlic-like odor.Sony VAIO VGN-TZ170N/B Battery

The garlic odor that is associated with human intake of tellurium compounds is caused from the tellurium being metabolized by the body. When the body metabolizes tellurium in any oxidation state, the tellurium is converted into dimethyl telluride, (CH3)2Te, which is volatile and is the cause of the garlic-like smell.Sony VAIO VGN-TZ170N/N Battery

Even though the metabolic pathways of tellurium are not known, it is generally assumed that they resemble those of the more extensively studied selenium, because the final methylated metabolic products of the two elements are similar.

Iodineis a chemical element with the symbol Iand atomic number 53.Sony VAIO VGN-TZ17GN/B Battery

The name is pronounced  in both American[2]and British[3]English.[4]The name is from the Greek:????? iodes, meaning violet or purple, due to the color of elemental iodine vapor.

Iodine and its compounds are primarily used in nutrition, and industrially in the production of acetic acid and certain polymers.Sony VAIO VGN-TZ17N Battery

Iodine's relatively high atomic number, low toxicity, and ease of attachment to organic compounds have made it a part of many X-ray contrast materials in modern medicine. Iodine has only one stable isotope. A number of iodine radioisotopes are also used in medical applications.Sony VAIO VGN-TZ18/N Battery

Iodine is found on Earth mainly as the highly water-soluble iodide I-, which concentrates it in oceans and brine pools. Like the other halogens, free iodine occurs mainly as a diatomic molecule I2, and then only momentarily after being oxidized from iodide by an oxidant like free oxygen.Sony VAIO VGN-TZ180N/RC Battery

In the universe and on Earth, iodine's high atomic number makes it a relatively rare element, ranking 47th in abundance. However, its presence in ocean water has given it a role in biology. It is the heaviest essential element utilized widely by life in biological functions (only tungsten, employed in enzymes by a few species of bacteria, is heavier).Sony VAIO VGN-TZ185N/WC Battery

Iodine's rarity in many soils, due to initial low abundance as a crust-element, and also leaching of soluble iodide by rainwater, has led to many deficiency problems in land animals and inland human populations. Iodine deficiency affects about two billion people and is the leading preventable cause ofintellectual disabilities.Sony VAIO VGN-TZ18GN/X Battery

Iodine is required by higher animals, which use it to synthesize thyroid hormones, which contain the element. Because of this function, radioisotopes of iodine are concentrated in the thyroid gland along with nonradioactive iodine. The radioisotope iodine-131, which has a high fission product yield, concentrates in the thyroid, and is one of the mostcarcinogenic of nuclear fission products.Sony VAIO VGN-TZ18N Battery

Characteristics

Iodine under standard conditions is a bluish-black solid. It can be seen apparently sublimating at standard temperatures into a violet-pink gas that has an irritating odor. This halogen forms compounds with many elements, but is less reactive than the other members of its Group VII (halogens) and has some metallic light reflectance.Sony VAIO VGN-TZ190N/B Battery

Elemental iodine dissolves easily in most organic solvents such as hexane or chloroform owing to its lack of polarity, but is only slightly soluble in water. However, the solubility of elemental iodine in water can be increased by the addition of potassium iodide.Sony VAIO VGN-TZ190N/BC Battery

The molecular iodine reacts reversibly with the negative ion, generating the triiodide anion I3?inequilibrium, which is soluble in water. This is also the formulation of some types of medicinal (antiseptic) iodine, although tincture of iodine classically dissolves the element in aqueousethanol.Sony VAIO VGN-TZ191N/XC Battery

The colour of solutions of elemental iodine changes depending on the polarity of the solvent. In non-polar solvents like hexane, solutions are violet; in moderately polar dichloromethane, the solution is dark crimson, and, in strongly polar solvents such as acetone or ethanol, it appears orange or brown. This effect is due to the formation of adducts.Sony VAIO VGN-TZ195N/XC Battery

Iodine melts at the relatively low temperature of 113.7 °C, although the liquid is often obscured by a dense violet vapor of gaseous iodine.

Occurrence

Iodine is rare in the solar system and Earth's crust (47th in abundance); however, iodide salts are often very soluble in water.Sony VAIO VGN-TZ198N/RC Battery

Iodine occurs in slightly greater concentrations in seawaterthan in rocks, 0.05 vs 0.04 ppm. Minerals containing iodine include caliche, found in Chile. The brown algaeLaminariaand Fucusfound in temperate zones of the Northern Hemisphere contain 0.028–0.454 dry weight percent of iodine.Sony VAIO VGN-TZ250N/B Battery

Aside from tungsten, iodine is the heaviest element to be essential in living organisms, and iodine is the heaviest element thought to be needed by higher animals. About 19,000 tonnes are produced annually from natural sources.

Organoiodine compounds are produced by marine life forms, the most notable being iodomethane(commonly called methyl iodide).Sony VAIO VGN-TZ250N/N Battery

The total iodomethane that is produced by the marine environment, by microbial activity in rice paddies and by the burning of biological material is estimated to be 214 kilotonnes/year.[7]The volatile iodomethane is broken up in the atmosphere as part of a global iodine cycle.Sony VAIO VGN-TZ250N/P Battery

Structure and bonding

Iodine normally exists as a diatomic molecule with a I-I bond length of 270 pm,  one of the longest single bonds known. The I2molecules tend to interact via the weak van der Waals force called the London Forces, and this interaction is responsible for the higher melting point compared to more compact halogens, which are also diatomic. Since the atomic size of Iodine is larger, its melting point is higher.Sony VAIO VGN-TZ27/N Battery

The solid crystallizes as orthorhombic crystals. The crystal motif in the Hermann–Mauguin notation is Cmca (No 64), Pearson symbol oS8. The I-I bond is relatively weak, with a bond dissociation energy of 36 kcal/mol. In fact, most bonds to iodine tend to be weaker than for the lighter halides. One consequence of this weak bonding is the relatively high tendency of I2molecules to dissociate into atomic iodine.Sony VAIO VGN-TZ270N/B Battery

Production

Of the several places in which iodine occurs in nature, only two sources are useful commercially: the caliche, found in Chile, and the iodine-containing brines of gas and oil fields, especially in Japan and the United States. The caliche, found in Chile, contains sodium nitrate, which is the main product of the mining activities and small amounts of sodium iodate and sodium iodide.Sony VAIO VGN-TZ27N Battery

In the extraction of sodium nitrate, the sodium iodate and sodium iodide are extracted.[10]The high concentration of iodine in the caliche and the extensive mining made Chile the largest producer of iodine in 2007.

Most other producers use natural occurring brine for the production of iodine.Sony VAIO VGN-TZ28/N Battery

The Japanese Minami Kanto gas field east of Tokyoand the American Anadarko Basin gas field in northwest Oklahoma are the two largest sources for iodine from brine. The brine has a temperature of over 60°C owing to the depth of the source. The brine is first purified and acidified using sulfuric acid, then the iodide present is oxidized to iodine with chlorine.Sony VAIO VGN-TZ285N/RC Battery

An iodine solution is produced, but is dilute and must be concentrated.Air is blown into the solution, causing the iodine to evaporate, then it is passed into an absorbing tower containing acid wheresulfur dioxide is added to reduce the iodine. The hydrogen iodide (HI) is reacted with chlorine to precipitate the iodine. After filtering and purification the iodine is packed.Sony VAIO VGN-TZ28N Battery

2 HI + Cl2? I2? + 2 HCl

I2+ 2 H2O + SO2? 2 HI + H2SO4

2 HI + Cl2? I2? + 2 HCl

The production of iodine from seawater via electrolysis is not used owing to the sufficient abundance of iodine-rich brine. Another source of iodine was kelp, used in the 18th and 19th centuries, but it is no longer economically viable.Sony VAIO VGN-TZ290EAB Battery

Commercial samples often contain high concentrations of impurities, which can be removed by sublimation. The element may also be prepared in an ultra-pure form through the reaction of potassium iodide with copper(II) sulfate, which gives copper(II) iodide initially. That decomposes spontaneously to copper(I) iodide and iodine:

Cu2++ 2 I–? CuI2

2 CuI2? 2 CuI + I2

There are also other methods of isolating this element in the laboratory, for example, the method used to isolate other halogens: Oxidation of the iodide in hydrogen iodide (often made in situwith an iodide and sulfuric acid) by manganese dioxide (see below in Descriptive chemistry).Sony VAIO VGN-TZ290EAN Battery

Isotopes and their applications

Of the 37 known (characterized) isotopes of iodine, only one, 127I, is stable.

The longest-lived radioisotope, 129I, has a half-life of 15.7 million years. This is long enough to make it a permanent fixture of the environment on human time scales, but far too short for it to exist as a primordial isotope today.Sony VAIO VGN-TZ290EAP Battery

Instead, iodine-129 is an extinct radionuclide, and its presence in the early solar system is inferred from the observation of an excess of its daughter xenon-129. This nuclide is also newly-made by cosmic rays and as a byproduct of human nuclear fission, which it is used to monitor as a very long-lived environmental contaminant.Sony VAIO VGN-TZ295N/XC Battery

The next-longest-lived radioisotope, iodine-125, has a half-life of 59 days. It is used as a convenient gamma-emitting tag for proteins in biological assays, and a few nuclear medicine imaging tests where a longer half-life is required. It is also commonly used in brachytherapy implanted capsules, which kill tumors by local short-range gamma radiation (but where the isotope is never released into the body).Sony VAIO VGN-TZ298N/XC Battery

Iodine-123 (half-life 13 hours) is the isotope of choice for nuclear medicine imaging of the thyroid gland, which naturally accumulates all iodine isotopes.

Iodine-131 (half-life 8 days) is a beta-emitting isotope, which is a common nuclear fission product.Sony VAIO VGN-TZ33/B Battery

It is preferably administered to humans only in very high doses which destroy all tissues that accumulate it (usually the thyroid), which in turn prevents these tissues from developing cancer from a lower dose (paradoxically, a high dose of this isotope appears safer for the thryoid than a low dose).Sony VAIO VGN-TZ33/N Battery

Like other radioiodines, I-131 accumulates in the thyroid gland, but unlike the others, in small amounts it is highly carcinogenic there, it seems, owing to the high local cell mutation due to damage from beta decay. Because of this tendency of 131I to cause high damage to cells that accumulate it and other cells near them (0.6 to 2 mm away, the range of the beta rays),Sony VAIO VGN-TZ33/W Battery

it is the only iodine radioisotope used as direct therapy, to kill tissues such as cancers that take up artificially iodinated molecules (example, the compound iobenguane, also known as MIBG). For the same reason, only the iodine isotope I-131 is used to treat Grave's disease and those types of thyroid cancers (sometimes in metastatic form) where the tissue that requires destruction, still functions to naturally accumulate iodide.Sony VAIO VGN-TZ350N/B Battery

Nonradioactive ordinary potassium iodide (iodine-127), in a number of convenient forms (tablets or solution) may be used to saturate the thyroid gland's ability to take up further iodine, and thus protect against accidental contamination from iodine-131 generated by nuclear fission accidents,Sony VAIO VGN-TZ350N/N Battery

such as the Chernobyl disaster and more recently the Fukushima I nuclear accidents, as well as from contamination from this isotope in nuclear fallout from nuclear weapons.

Iodine was discovered by Bernard Courtois in 1811. He was born to a manufacturer of saltpeter (a vital part of gunpowder).Sony VAIO VGN-TZ350N/P Battery

At the time of the Napoleonic Wars,France was at war and saltpeter was in great demand. Saltpeter produced from French niter beds required sodium carbonate, which could be isolated from seaweedcollected on the coasts of Normandy and Brittany. To isolate the sodium carbonate, seaweed was burned and the ash washed with water.Sony VAIO VGN-TZ370N/B Battery

The remaining waste was destroyed by adding sulfuric acid. Courtois once added excessive sulfuric acid and a cloud of purple vapor rose. He noted that the vapor crystallized on cold surfaces, making dark crystals. Courtois suspected that this was a new element but lacked funding to pursue it further.Sony VAIO VGN-TZ37N/G Battery

Courtois gave samples to his friends, Charles Bernard Desormes (1777–1862) and Nicolas Clément (1779–1841), to continue research. He also gave some of the substance to chemist Joseph Louis Gay-Lussac (1778–1850), and to physicist André-Marie Ampère (1775–1836). On 29 November 1813, Dersormes and Clément made public Courtois's discovery.Sony VAIO VGN-TZ37N/P Battery

They described the substance to a meeting of the Imperial Institute of France. On December 6, Gay-Lussac announced that the new substance was either an element or a compound of oxygen. It was Gay-Lussac who suggested the name "iode", from the Greek word ????? (iodes) for violet (because of the color of iodine vapor).Sony VAIO VGN-TZ37N/R Battery

Ampère had given some of his sample to Humphry Davy (1778–1829). Davy did some experiments on the substance and noted its similarity to chlorine.[18]Davy sent a letter dated December 10 to the Royal Society of London stating that he had identified a new element.Sony VAIO VGN-TZ37N/X Battery

Arguments erupted between Davy and Gay-Lussac over who identified iodine first, but both scientists acknowledged Courtois as the first to isolate the element.

Catalysis

The major application of iodine is as a co-catalyst for the production of acetic acid by the Monsanto and Cativa processes.Sony VAIO VGN-TZ38N/X Battery

In these technologies, which support the world's demand for acetic acid, hydroiodic acid converts the methanol feedstock into methyl iodide, which undergoes carbonylation. Hydrolysis of the resulting acetyl iodide regenerates hydroiodic acid and gives acetic acid.Sony VAIO VGN-TZ398U/XC Battery

Animal feed

The production of ethylenediammonium diiodide (EDDI) consumes a large fraction of available iodine. EDDI is provided to livestock as a nutritional supplement.[6]

Disinfectant and water treatment

Elemental iodine is used as a disinfectant in various forms.Sony VAIO VGN-TZ50B Battery

The iodine exists as the element, or as the water-soluble triiodide anion I3-generated in situby adding iodide to poorly water-soluble elemental iodine (the reverse chemical reaction makes some free elemental iodine available for antisepsis). In alternative fashion, iodine may come from iodophors, which contain iodine complexed with a solubilizing agent (iodide ion may be thought of loosely as the iodophor in triiodide water solutions).Sony VAIO VGN-TZ90HS Battery

Examples of such preparations include:

  • Tincture of iodine: iodine in ethanol, or iodine and sodium iodide in a mixture of ethanol and water.
  • Lugol's iodine: iodine and iodide in water alone, forming mostly triiodide. Unlike tincture of iodine, Lugol's has a minimized amount of the free iodine (I2) component.
  • Povidone iodine (an iodophor)Sony VAIO VGN-TZ90NS Battery

Health, medical, and radiological use

In most countries, table salt is iodized. Iodine is required for the essential thyroxin hormones produced by and concentrated in the thyroid gland.

Potassium iodide has been used as an expectorant, although this use is increasingly uncommon.Sony VAIO VGN-TZ90S Battery

In medicine, potassium iodide is used to treat acute thyrotoxicosis, usually as a saturated solution of potassium iodide (SSKI). It is also used to block uptake of iodine-131 in the thyroid gland (see isotopes section above), when this isotope is used as part of radiopharmaceuticals (such as iobenguane) that are not targetted to the thyroid or thyroid type tissues.Sony VAIO VPC CW2MFX/PU Battery

Iodine-131 (in the chemical form of iodide) is a component of nuclear fallout and a particularly dangerous one owing to the thyroid gland's propensity to concentrate ingested iodine, where it is kept for periods longer than this isotope's radiological half-life of eight days.Sony VAIO VPC S11V9E/B Battery

For this reason, if people are expected to be exposed to a significant amount of environmental radioactive iodine (iodine-131 in fallout), they may be instructed to take non-radioactive potassium iodide tablets. The typical adult dose is one 130 mg tablet per 24 hours, supplying 100 mg (100,000 micrograms) iodine, as iodide ion.Sony VAIO VPCB119GJ/B Battery

(Note: typical daily dose of iodine to maintain normal health is of order 100 micrograms; see "Dietary Intake" below.) By ingesting this large amount of non-radioactive iodine, radioactive iodine uptake by the thyroid gland is minimized. See the main article above for more on this topic.Sony VAIO VPCB11AGJ Battery

Radiocontrast agent

Iodine, as a heavy element, is quite radio-opaque. Organic compounds of a certain type (typically iodine-substituted benzene derivatives) are, thus, used in medicine as X-ray radiocontrast agents for intravenous injection. This is often in conjunction with advanced X-ray techniques such as angiography and CT scanning. At present, all water-soluble radiocontrast agents rely on iodine.Sony VAIO VPCB11AVJ Battery

Other uses

Inorganic iodides find specialized uses. Hafnium, zirconium, titanium are purified by the van Arkel Process, which involves the reversible formation of the tetraiodides of these elements. Silver iodide is a major ingredient to traditional photographic film. Thousands of kilograms of silver iodide are consumed annually for cloud seeding.Sony VAIO VPCB11V9E Battery

The organoiodine compound erythrosine is an important food coloring agent. Perfluoroalkyl iodides are precursors to important surfactants, such as perfluorooctanesulfonic acid.

Iodine chemistry

Iodine adopts a variety of oxidation states, commonly ranging from (formally) I7+to I-, and including the intermediate states of I5+, I3+and I+.Sony VAIO VPCB11X9E Battery

Practically, only the 1- oxidation state is of significance, being the form found in iodide salts and organoiodine compounds.

Solubility

Being a nonpolar molecule, iodine is highly soluble in nonpolar organic solvents, including ethanol (20.5 g/100 ml at 15 °C, 21.43 g/100 ml at 25 °C), diethyl ether (20.6 g/100 ml at 17 °C, 25.20 g/100 ml at 25 °C), chloroform, acetic acid, glycerol,Sony VAIO VPCCW18FJ/P Battery

benzene (14.09 g/100 ml at 25 °C), carbon tetrachloride(2.603 g/100 ml at 35 °C), and carbon disulfide (16.47 g/100 ml at 25 °C). Elemental iodine is poorly soluble in water, with one gram dissolving in 3450 ml at 20 °C and 1280 ml at 50 °C. Aqueous and ethanol solutions are brown reflecting the role of these solvents as Lewis bases. Solutions in chloroform, carbon tetrachloride, and carbon disulfide are violet, the color of iodine vapor.Sony VAIO VPCCW18FJ/R Battery

One of the most distinctive properties of iodine is the way that its solubility in water is enhanced by the presence of iodide ions. The dissolution of iodine in aqueous solutions containing iodide (e.g., from hydroiodic acid, potassium iodide, etc.) results from the formation of the I3?ion. Dissolved bromides also improve water solubility of iodine.Sony VAIO VPCCW18FJ/W Battery

Redox reactions

In everyday life, iodides are slowly oxidized by atmospheric oxygen in the atmosphere to give free iodine. Evidence for this conversion is the yellow tint of certain aged samples of iodide salts and some organoiodine compounds.Sony VAIO VPCCW19FJ/W Battery

The oxidation of iodide to iodine in air is also responsible for the slow loss of iodide content iniodized salt if exposed to air.[23]Some salts use iodate to prevent the loss of iodine.

Iodine is easily oxidized and easily reduced. Most common is the interconversion of I-and I2. Molecular iodine can be prepared by oxidizing iodides with chlorine:Sony VAIO VPCCW1AFJ Battery

2 I?+ Cl2? I2+ 2 Cl?

or with manganese dioxide in acid solution:

2 I?+ 4 H++ MnO2? I2+ 2 H2O + Mn2+

Iodine is reduced to hydroiodic acid by hydrogen sulfide and hydrazine:Sony VAIO VPCCW1AHJ Battery

8 I2+ 8 H2S ? 16 HI + S8

2 I2+ N2H4? 4 HI + N2

When dissolved in fuming sulfuric acid (65% oleum), iodine forms an intense blue solution. The blue color is due to I+
2 cation, the result of iodine being oxidized bySO3:

2 I2+ 2 SO3+ H2SO4? 2 I+2 + SO2+ 2 HSO?
4

The I+
2 cation is also formed in the oxidation of iodine by SbF5or TaF5.Sony VAIO VPCCW1S1E Battery

The resulting I+2Sb2F?11 or I+2Ta2F?11 can be isolated as deep blue crystals. The solutions of these salts turn red when cooled below ?60°C, owing to the formation of the I2+4 cation:

2 I+2   I2+4

Under slightly more alkaline conditions, I2+4 disproportionates into I+3 and an iodine(III) compound. Excess iodine can then react with I+3 to form I+5 (green) and I3+15(black).Sony VAIO VPCCW1S1E/B Battery

Oxides of iodine

The best-known oxides are the anions, IO3–and IO4–, but several other oxides are known, such as the strong oxidant iodine pentoxide.

By contrast with chlorine, the formation of the hypohalite ion (IO–) in neutral aqueous solutions of iodine is negligible.Sony VAIO VPCCW1S1E/L Battery

I2+ H2O   H++ I?+ HIO   (K= 2.0×10?13)[24]In basic solutions (such as aqueous sodium hydroxide), iodine converts in a two stage reaction to iodide andiodate:

Organic derivatives of hypoiodate (2-Iodoxybenzoic acid, and Dess-Martin periodinane) are used in organic chemistry.Sony VAIO VPCCW1S1E/P Battery

Iodic acid (HIO3), periodic acid (HIO4) and their salts are strong oxidizers and are of some use in organic synthesis. Iodine is oxidized to iodate by nitric acid as well as by chlorates:

I2+ 10 HNO3? 2 HIO3+ 10 NO2+ 4 H2O

I2+ 2 ClO3?? 2 IO3?+ Cl2 Sony VAIO VPCCW1S1E/R Battery

Inorganic iodine compounds

Iodine forms compounds with all the elements except for the noble gases. From the perspective of commercial applications, an important compound is hydroiodic acid, used as a co-catalyst in the Cativa process for the production of acetic acid. Titanium and aluminium iodides are used in the production of butadiene, a precursor to rubber tires.Sony VAIO VPCCW1S1E/W Battery

Alkali metal salts are common colourless solids that are highly soluble in water. Potassium iodide is a convenient source of the iodide anion; it is easier to handle than sodium iodide because it is not hygroscopic. Both salts are mainly used in the production of iodized salt.Sony VAIO VPCCW21FX/B Battery

Sodium iodide is especially useful in the Finkelstein reaction, because it is soluble in acetone, whereas potassium iodide is less so. In this reaction, an alkyl chloride is converted to an alkyl iodide. This relies on the insolubility of sodium chloride in acetone to drive the reaction:Sony VAIO VPCCW21FX/L Battery

R-Cl (acetone) + NaI (acetone) ? R-I (acetone) + NaCl (s)

Despite having the lowest electronegativity of the common halogens, iodine reacts violently with some metals, such as aluminium:

3 I2+ 2 Al ? 2 AlI3

This reaction produces 314 kJ per mole of aluminum, comparable to thermite's 425 kJ. Yet the reaction initiates spontaneously, and if unconfined, causes a cloud of gaseous iodine due to the high temperature.Sony VAIO VPCCW21FX/R Battery

Interhalogen compounds

Interhalogen compounds are well known; examples include iodine monochloride and trichloride; iodine pentafluoride and heptafluoride.

Organic compounds

Many organoiodine compounds exist; the simplest is iodomethane, approved as a soil fumigant. Iodinated organic compounds are used as synthetic reagents.Sony VAIO VPCCW21FX/W Battery

Organic synthesis

Organoiodine compounds can be made in many ways. For example, methyl iodide can be prepared from methanol, red phosphorus, and iodine.[28]The iodinating reagent isphosphorus triiodide that is formed in situ:Sony VAIO VPCCW26EC Battery

3 CH3OH + PI3? 3 CH3I + [[H3PO3|Phosphorous acid]]

The iodoform test uses an alkaline solution of iodine to react with methyl ketones to give the labile triiodomethide leaving group, forming iodoform, which precipitates.Sony VAIO VPCCW26FX/B Battery

Aryl and alkyl iodides both form Grignard reagents. Iodine is sometimes used to activate magnesium when preparing Grignard reagents. Alkyl iodides such as iodomethane are good alkylating agents. Some drawbacks to use of organoiodine compounds in chemical synthesis are:

Sony AIO VPCCW28EC Battery

  • iodine compounds tend to be more expensive than the corresponding bromides and chlorides, in that order
  • iodides tend to be much stronger alkylating agents, and so are more toxic (e.g., methyl iodide is very toxic (T+).Sony VAIO VPCCW28FJ/P Battery
  • low-molecular-weight iodides tend to have a much higher equivalent weight, compared to other alkylating agents (e.g., methyl iodide versus dimethyl carbonate), owing to the atomic mass of iodine.

Analytical chemistry and bioanalysis

Iodine is a common general stain used in thin-layer chromatography. In particular, iodine forms an intense blue complex with the glucose polymers starch and glycogen. Several analytical methods rely on this property:Sony VAIO VPCCW28FJ/R Battery

  • Iodometry. The concentration of an oxidant can be determined by adding it to an excess of iodide, to destroy elemental iodine/triiodide as a result of oxidation by the oxidant. A starch indicator is then used as the indicator close to the end-point, in order to increase the visual contrast (dark blue becomes colorless, instead of the yellow of dilute triiodide becoming colorless).Sony VAIO VPCCW28FJ/W Battery
  • An Iodine test may be used to test a sample substance for the presence of starch. The Iodine clock reaction is an extension of the techniques in iodometry.
  • Iodine solutions are used in counterfeit banknote detection pens; the premise being that counterfeit banknotes made using commercially available paper contain starch.Sony VAIO VPCCW29FJ/W Battery
  • Starch-iodide paper are used to test for the presence of oxidants such as peroxides. The oxidants convert iodide to iodine, which shows up as blue. A solution of starch and iodide can perform the same function.
  • During colposcopy, Lugol's iodine is applied to the vagina and cervix.Sony VAIO VPCCW2AFJ Battery
  • Normal vaginal tissue stains brown owing to its high glycogen content (a color-reaction similar to that with starch), while abnormal tissue suspicious for cancer does not stain, and thus appears pale compared to the surrounding tissue. Biopsy of suspicious tissue can then be performed. This is called a Schiller's Test.Sony VAIO VPCCW2AHJ Battery

Clandestine synthetic chemical use

In the United States, the Drug Enforcement Agency (DEA) regards iodine and compounds containing iodine (ionic iodides, iodoform, ethyl iodide, and so on) as reagents useful for the clandestine manufacture of methamphetamine.Sony VAIO VPCCW2S1E Battery

Biological role

Iodine is an essential trace element for life, the heaviest element commonly needed by living organisms. Only tungsten, a component of a few bacterial enzymes, has a higher atomic number and atomic weight.

Thyroxines are iodine-containing hormones that justify the widespread use of iodised salt.Sony VAIO VPCCW2S1E/B Battery

Iodine's main role in animal biology is as a constituent of the thyroid hormonesthyroxine(T4) and triiodothyronine(T3). These are made from addition condensation products of the amino acid tyrosine, and are stored prior to release in an iodine-containingprotein called thyroglobulin. T4 and T3 contain four and three atoms of iodine per molecule, respectively.Sony VAIO VPCCW2S1E/L Battery

The thyroid glandactively absorbs iodide from the blood to make and release these hormones into the blood, actions that are regulated by a second hormone TSH from the pituitary. Thyroid hormones are phylogenetically very old molecules that are synthesized by mostmulticellular organisms, and that even have some effect on unicellular organisms.Sony VAIO VPCCW2S1E/P Battery

Thyroid hormones play a basic role in biology, acting on gene transcription to regulate the basal metabolic rate.[citation needed]The total deficiency of thyroid hormones can reduce basal metabolic rate up to 50%, while in excessive production of thyroid hormones the basal metabolic rate can be increased by 100%.Sony VAIO VPCCW2S1E/R Battery

T4 acts largely as a precursor to T3, which is (with minor exceptions) the biologically active hormone.

Iodine has a nutritional relationship with selenium. A family of selenium-dependent enzymes called deiodinases converts T4 to T3 (the active hormone) by removing an iodine atom from the outer tyrosine ring.Sony VAIO VPCCW2S1E/W Battery

These enzymes also convert T4 to reverse T3 (rT3) by removing an inner ring iodine atom, and convert T3 to 3,3'-diiodothyronine (T2) also by removing an inner ring atom. Both of the latter are inactivated hormones that are ready for disposal and have, in essence, no biological effects.Sony VAIO VPCCW2S5C CN1 Battery

A family of non-selenium-dependent enzymes then further deiodinates the products of these reactions.

Iodine accounts for 65% of the molecular weight of T4 and 59% of the T3. Fifteen to 20 mg of iodine is concentrated in thyroid tissue and hormones, but 70% of the body's iodine is distributed in other tissues, including mammary glands, eyes, gastric mucosa, the cervix, and salivary glands.Sony VAIO VPCF112FX/B Battery

In the cells of these tissues, iodide enters directly by sodium-iodide symporter (NIS). Its role in mammary tissue is related to fetal and neonatal development, but its role in the other tissues is unknown.


I2 + 2 OH? ? I? + IO? + H2O   (K = 30)
3 IO? ? 2 I? + IO3?   (K = 1020)

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