iodine

DescriptionIodine,I, is a nonmetallic element with an orthorhombic crystal structure, a violet to black color. This poisonous element sublimes readily and is easily purified in this manner. It is insoluble in water,but is soluble in common solvents such as alcohol, ether,and carbon tetrachloride. Iodine is used as a germicide, an antiseptic, in dyes,tinctures, and pharmaceuticals. It is also used in the production of vanadium metal in the McKechnie-Seybolt process, which is the reduction of vanadium pentoxide in the presence of iodine. Iodine is used in a similar manner in the production of high-purity zirconium. For many years, iodine tincture(3% to 7% dissolved in ethyl alcohol) has been an important antiseptic. The commercial tinctures also usually contain 5% potassium iodide to provide stability. This form produces a mild burning of the skin and stains both skin and fabrics. A milder preparation is available in which about 2% iodine is contained in an oil-water emulsion which also contains lecithin.

DescriptionIodine, (I), is a nonmetallic element of family seven, the halogens. It is heavy, grayish-black in color, has a characteristic odor, and is readily sublimed to a violet vapor. It has a vapor density of 4.98, which is heavier than air. It melts at 236°F (113.5°C), has a boiling point of 363°F (184°C), and is insoluble in water. Iodine is toxic by ingestion and inhalation, and is a strong irritant to eyes and skin. The TLV ceiling is 0.1 ppm in air. Iodine is used for antiseptics, germicides, x-ray contrast material, food and feed additives, water treatment, and medicinal soaps. The four-digit UN identification number for iodine is only for the compounds iodine monochloride and iodine pentafluoride, and they are 1792 and 2495, respectively. The DOT lists iodine monochloride as a Class 8 corrosive, and iodine pentafluoride carries an oxidizer and poison label. Iodine does not have an NFPA 704 designation.

OccurrenceIodine is the 64th most abundant element on Earth. It occurs widely over the Earth, butnever in the elemental form and never in high concentrations.It occurs in seawater where some species of seaweed and kelp accumulate the elementin their cells. It is also recovered from deep brine wells found in Chile, Indonesia, Japan,and Michigan, Arkansas, and Oklahoma in the United States. The iodine is recovered fromcremated ashes of seaweed. The ashes are leached with water to remove the unwanted salts.Finally, manganese dioxide (MnO2) is added to oxidize the iodine ions (I1-) to produceelemental diatomic iodine (I2). The following reaction takes place: 4I1- + MnO2 → MnI2 +I2 + 2O2-.Chilean saltpeter [potassium nitrate (KNO3)] has a number of impurities, includingsodium and calcium iodate. Iodine is separated from the impurities and, after being treatedchemically, finally produces diatomic iodine. Today, iodine is mostly recovered from sodiumiodate (NaIO3) and sodium periodate (NaIO4) obtained from Chile and Bolivia.

HistoryIodine was first discovered by Barnard Courtois, a French chemist in 1811 while extracting potassium and sodium from seaweed ash. When he accidentally added sulfuric acid, a violet colored cloud evolved from the mass. The resulting gas was condensed into dark crystals-the first occurrence of observed solid iodine.Courtois analyzed them and then gave some of them to a fellow chemist, Joseph Louis Gay-Lussac, for further study.Two years later, Gay-Lussac presented his study to the scientific community, announcing the discovery of a new element that he named "iodine," after the Greek word "ioeides" meaning violet colored.A Swiss physician by the name of J.F. Coindet had previously used burnt sponge and seaweed for the treatment of goiter (an enlargement of the thyroid gland). This treatment had been in use since 3600 B.C., when it appeared in Chinese medical writings, as well as writings by the Greek physician Hippocrates. Upon hearing of the work of Courtois and Gay-Lussac, Coindet suspected that iodine might be the active ingredient in seaweed that cured goiter. In 1819, he successfully tested a tincture of iodine on 150 patients, significantly reducing the size of their goiter within one week. As a result of these early studies, in the 1830s the medical community started advocating for iodine supplements to decrease the occurrence of goiter.

UsesOne of the most important uses of iodine is in the treatment of hypothyroidism, a conditionin which the thyroid gland is deficient in iodine. Iodine deficiency may lead to the formationof a goiter, wherein the gland that surrounds the windpipe in the neck becomes enlarged.There are other causes of goiter, including cancer of the thyroid gland. A deficiency of iodinecan also cause cretinism (infant hypothyroidism) in newborn babies, which can result inmental retardation unless the subject takes thyroid hormones for a lifetime. Green leafy foods,among other foods, contain iodine that when taken into the human body ends up in thethyroid gland. Some food grown in iodine-deficient soils do not contain adequate iodine forour diets. This is why iodine was added to table salt (about 0.01% potassium iodide) decadesago, specifically for people who live in regions with iodine-poor soils. The area around theGreat Lakes in the United States is one region with soil that is deficient in iodine. A healthydiet requires 90 to 150 micrograms of iodine each day that, in addition to being available iniodized salt, can be obtained from eating a balanced diet, including seafood.The isotope iodine-131 is an artificial radioisotope of iodine used as a tracer in biomedicalresearch and as a treatment for thyroid disease. I-131 has a half-life of about eight days, whichmeans it will be eliminated from the body in several weeks.In industry, iodine is used for dyes, antiseptics, germicides, X-ray contrast medium, foodand feed additives, pharmaceuticals, medical soaps, and photographic film emulsions and as alaboratory catalyst to either speed up or slow down chemical reactions.Iodine is also used as a test for starch. When placed on starch (a potato for example), iodineturns the starch a dark blue color. Silver iodide is used in the manufacture of photographicfilm and paper. It is also used to “seed” clouds because of its ability to form a large numberof crystals that act as nuclei upon which moisture in the clouds condenses, forming raindropsthat may result in rain.

UsesDyes (aniline dyes, phthalein dyes), alkylation and condensation catalyst, iodides, iodates, antiseptics and germicides, X-ray contrast media, food and feed additive, stabilizers, photographic film, water treatment, pharmaceuticals, medicinal soaps, unsat

UsesIodine is a halogen element extracted from chilean nitrate-bearing earth or from seaweed. it functions by its presence in the thyroid hormones. iodine deficiency is associated with goiter. sources are potassium and cuprous iodide and potassium and calcium iodate, of which the iodate form is preferred because of better stability. it is used as a food supplement.

PreparationIf extreme purification is unnecessary, commercial iodine or iodine regenerated from wastes can, according to a method described by Plotnikow, be sublimed, first over KI and then over BaO. It is then stored in ground glass containers placed in a desiccator over P2O5.

DefinitionA dark-violet volatile solid element belonging to the halogens (group 17 of the periodic table). It occurs in seawater and is concentrated by various marine organisms in the form of iodides. Significant deposits also occur in the form of iodates. The element is conveniently prepared by the oxidation of iodides in acid solution (using MnO2). Industrial methods similarly use oxidation of iodides or reduction of iodates to iodides by sulfur(IV) oxide (sulfur dioxide) followed by oxidation, depending on the source of the raw materials. Iodine and its compounds are used in chemical synthesis, photography, pharmaceuticals, and dyestuffs manufacture. Iodine has the lowest electronegativity of the stable halogens and consequently is the least reactive. It combines only slowly with hydrogen to form hydroiodic acid, HI. Iodine also combines directly with many electropositive elements, but does so much more slowly than does bromine or chlorine. Because of the larger size of the iodine ion and the consequent low lattice energies, the iodides are generally more soluble than related bromides or chlorides. As with the other halides, iodides of Ag(I), Cu(I), Hg(I), and Pb(II) are insoluble unless complexing ions are present. Iodine also forms a range of covalent iodides with the metalloids and non-metallic elements (this includes a vast range of organic iodides) but these are generally less thermodynamically stable and are more readily hydrolyzed than chlorine or bromine analogs.

DefinitionSymbol I. A dark violet nonmetallic element belonging to group 17 of the periodic table; a.n. 53; r.a.m. 126.9045;r.d. 4.94; m.p. 113.5°C; b.p. 184.35°C.The element is insoluble in water but soluble in ethanol and other organic solvents. When heated it gives a violet vapour that sublimes. Iodine is required as a trace element by living organisms;in animals it is concentrated in the thyroid gland as a constituent of thyroid hormones. The element is present in sea water and was formerly extracted from seaweed. It is now obtained from oil-well brines (displacement by chlorine). There is one stable isotope, iodine-127, and fourteen radioactive isotopes. It is used in medicine as a mild antiseptic(dissolved in ethanol as tincture of iodine),and in the manufacture of iodine compounds. Chemically, it is less reactive than the other halogens and the most electropositive (metallic)halogen. In solution it can bedetermined by titration using thiosulphate solution: I2 + 252O32-→ 2I- + SuO62-. The molecule forms an intense bluecomplex with starch, which is consequentlyused as an indicator. It was discovered in 1812 by Courtois.

DefinitionNonmetallic halogen element of atomic number 53; group VIIA of the periodic table; the least reactive of the halogens, aw 126.9045; valences = 1,3,5,7; no stable isotopes but many artificial radioactive isotopes.