DICTAPEDIAPreview
Open in TheBrain

Iodine

Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced  /ˈaɪ.ɵdaɪn/ ***eye**-o-dyne*,/ˈaɪ.ɵdɨn/ ***eye**-o-dən*, or /ˈaɪ.ɵdiːn/ ***eye**-o-deen* in both American[2] and British[3] English.[4] The name is from Greekἰοειδής ioeidēs, meaning violet or purple, due to the color of elemental iodine vapor.[5]

Iodine and its compounds are primarily used in nutrition, and industrially in the production of acetic acid and certainpolymers.

Iodine is a micronutrient and dietary mineral that is naturally present in the food supply in some regions, especially near sea coasts, but is generally quite rare in the Earth's crust, since iodine is a so-called "heavy" element with the highest atomic mass of any element needed by mammals for life), and abundance of chemical elements generally declines with greater atomic mass. Where natural levels of iodine in the soil are low and the iodine is not taken up by vegetables, iodine added to salt provides the small but essential amount of iodide needed by humans.

Iodide-treated table salt slowly loses its iodine content through the process of oxidation and iodine evaporation.

History

Iodine was discovered by Bernard Courtois in 1811.[14][15] He was born to a manufacturer of saltpeter (a vital part of gunpowder). 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 fromseaweed collected on the coasts of Normandy and Brittany. To isolate the sodium carbonate, seaweed was burned and the ash washed with water. 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.

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.

The major application of iodine is as a co-catalyst for the production of acetic acid by the Monsanto andCativa processes. In these technologies, which support the world's demand for acetic acid, hydroiodic acidconverts the methanol feedstock into methyl iodide, which undergoes carbonylation. Hydrolysis of the resulting acetyl iodide regenerates hydroiodic acid and gives acetic acid.[7]

[edit]Animal feed

The production of ethylenediammonium diiodide (EDDI) consumes a large fraction of available iodine. EDDI is provided to livestock as a nutritional supplement.[7]

[edit]Disinfectant and water treatment

Elemental iodine is used as a disinfectant in various forms. The iodine exists as the element, or as the water-soluble triiodide anion I3- generated in situ by 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). Examples of such preparations include:[21]

In most countries, table salt is iodized[citation needed]. 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. 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 targeted to the thyroid or thyroid type tissues.

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. 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. (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.[22]