Iodine

Iodine is a <a href="http://en.wikipedia.org/wiki/Chemical_element" title="Chemical element" >chemical element</a> with the symbol I and <a href="http://en.wikipedia.org/wiki/Atomic_number" title="Atomic number" >atomic number</a> 53. The name is pronounced <img alt="play" src="http://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Loudspeaker.svg/11px-Loudspeaker.svg.png" width="11" height="11" /> <a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Key" title="Wikipedia:IPA for English" >ˈaɪ.ɵdaɪn</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a> <a href="http://en.wikipedia.org/wiki/Wikipedia:Pronunciation_respelling_key" title="Wikipedia:Pronunciation respelling key" >eye-o-dyne</a>,<a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Key" title="Wikipedia:IPA for English" >ˈaɪ.ɵdɨn</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a> <a href="http://en.wikipedia.org/wiki/Wikipedia:Pronunciation_respelling_key" title="Wikipedia:Pronunciation respelling key" >eye-o-dən</a>, or <a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Key" title="Wikipedia:IPA for English" >ˈaɪ.ɵdiːn</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a> <a href="http://en.wikipedia.org/wiki/Wikipedia:Pronunciation_respelling_key" title="Wikipedia:Pronunciation respelling key" >eye-o-deen</a> in both American<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-1" >[2]</a> and British<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-2" >[3]</a> English.<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-3" >[4]</a> The name is from <a href="http://en.wikipedia.org/wiki/Ancient_Greek" title="Ancient Greek" >Greek</a>ἰοειδής ioeidēs, meaning violet or purple, due to the color of elemental iodine vapor.<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-4" >[5]</a>

Iodine and its <a href="http://en.wikipedia.org/wiki/Chemical_compound" title="Chemical compound" >compounds</a> are primarily used in <a href="http://en.wikipedia.org/wiki/Nutrition" title="Nutrition" >nutrition</a>, and industrially in the production of <a href="http://en.wikipedia.org/wiki/Acetic_acid" title="Acetic acid" >acetic acid</a> and certain<a href="http://en.wikipedia.org/wiki/Polymer" title="Polymer" >polymers</a>.

Iodine is a <a href="http://en.wikipedia.org/wiki/Micronutrient" title="Micronutrient" >micronutrient</a> and <a href="http://en.wikipedia.org/wiki/Dietary_mineral" title="Dietary mineral" >dietary mineral</a> 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 <a href="http://en.wikipedia.org/wiki/Atomic_mass" title="Atomic mass" >atomic mass</a> of any element needed by mammals for life), and <a href="http://en.wikipedia.org/wiki/Abundance_of_chemical_elements" title="Abundance of chemical elements" class="mw-redirect" >abundance of chemical elements</a> generally declines with greater atomic mass. Where natural levels of iodine in the <a href="http://en.wikipedia.org/wiki/Soil" title="Soil" >soil</a> 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.

<h2 >History</h2>

Iodine was discovered by <a href="http://en.wikipedia.org/wiki/Bernard_Courtois" title="Bernard Courtois" >Bernard Courtois</a> in 1811.<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-court-13" >[14]</a><a href="http://en.wikipedia.org/wiki/Iodine#cite_note-14" >[15]</a> He was born to a manufacturer of <a href="http://en.wikipedia.org/wiki/Potassium_nitrate" title="Potassium nitrate" >saltpeter</a> (a vital part of <a href="http://en.wikipedia.org/wiki/Gunpowder" title="Gunpowder" >gunpowder</a>). At the time of the <a href="http://en.wikipedia.org/wiki/Napoleonic_Wars" title="Napoleonic Wars" >Napoleonic Wars</a>, <a href="http://en.wikipedia.org/wiki/France" title="France" >France</a> was at war and saltpeter was in great demand. Saltpeter produced from French <a href="http://en.wikipedia.org/wiki/Niter" title="Niter" >niter</a> beds required <a href="http://en.wikipedia.org/wiki/Sodium_carbonate" title="Sodium carbonate" >sodium carbonate</a>, which could be isolated from<a href="http://en.wikipedia.org/wiki/Seaweed" title="Seaweed" >seaweed</a> collected on the coasts of <a href="http://en.wikipedia.org/wiki/Normandy" title="Normandy" >Normandy</a> and <a href="http://en.wikipedia.org/wiki/Brittany" title="Brittany" >Brittany</a>. To isolate the sodium carbonate, seaweed was burned and the ash washed with water. The remaining waste was destroyed by adding <a href="http://en.wikipedia.org/wiki/Sulfuric_acid" title="Sulfuric acid" >sulfuric acid</a>. 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 <a href="http://en.wikipedia.org/wiki/Toxicity" title="Toxicity" >toxicity</a>, and ease of attachment to <a href="http://en.wikipedia.org/wiki/Organic_compound" title="Organic compound" >organic compounds</a> have made it a part of many <a href="http://en.wikipedia.org/wiki/Radiocontrast" title="Radiocontrast" class="mw-redirect" >X-ray contrast</a> materials in modern medicine. Iodine has only one <a href="http://en.wikipedia.org/wiki/Stable_isotope" title="Stable isotope" >stable isotope</a>. A number of iodine <a href="http://en.wikipedia.org/wiki/Radionuclide" title="Radionuclide" >radioisotopes</a> are also used in medical applications.

The major application of iodine is as a co-catalyst for the production of <a href="http://en.wikipedia.org/wiki/Acetic_acid" title="Acetic acid" >acetic acid</a> by the <a href="http://en.wikipedia.org/wiki/Monsanto_process" title="Monsanto process" >Monsanto</a> and<a href="http://en.wikipedia.org/wiki/Cativa_process" title="Cativa process" >Cativa processes</a>. In these technologies, which support the world's demand for acetic acid, <a href="http://en.wikipedia.org/wiki/Hydroiodic_acid" title="Hydroiodic acid" class="mw-redirect" >hydroiodic acid</a>converts the <a href="http://en.wikipedia.org/wiki/Methanol" title="Methanol" >methanol</a> feedstock into methyl iodide, which undergoes <a href="http://en.wikipedia.org/wiki/Carbonylation" title="Carbonylation" >carbonylation</a>. Hydrolysis of the resulting acetyl iodide regenerates hydroiodic acid and gives acetic acid.<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-Ullmann-6" >[7]</a>

<h3 >[<a href="http://en.wikipedia.org/w/index.php?title=Iodine&action=edit&section=9" title="Edit section: Animal feed" >edit</a>]Animal feed</h3>

The production of <a href="http://en.wikipedia.org/wiki/Ethylenediammonium_diiodide" title="Ethylenediammonium diiodide" class="mw-redirect" >ethylenediammonium diiodide</a> (EDDI) consumes a large fraction of available iodine. EDDI is provided to livestock as a nutritional supplement.<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-Ullmann-6" >[7]</a>

<h3 >[<a href="http://en.wikipedia.org/w/index.php?title=Iodine&action=edit&section=10" title="Edit section: Disinfectant and water treatment" >edit</a>]Disinfectant and water treatment</h3>

Elemental iodine is used as a disinfectant in various forms. The iodine exists as the element, or as the water-soluble <a href="http://en.wikipedia.org/wiki/Triiodide" title="Triiodide" >triiodide</a> anion I3- generated in situ by adding <a href="http://en.wikipedia.org/wiki/Iodide" title="Iodide" >iodide</a> 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 <a href="http://en.wikipedia.org/wiki/Iodophor" title="Iodophor" >iodophors</a>, 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:<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-20" >[21]</a>

<ul >

<li ><a href="http://en.wikipedia.org/wiki/Tincture_of_iodine" title="Tincture of iodine" >Tincture of iodine</a>: iodine in ethanol, or iodine and <a href="http://en.wikipedia.org/wiki/Sodium_iodide" title="Sodium iodide" >sodium iodide</a> in a mixture of ethanol and water.</li>

<li ><a href="http://en.wikipedia.org/wiki/Lugol%27s_iodine" title="Lugol's iodine" >Lugol's iodine</a>: 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.</li>

<li ><a href="http://en.wikipedia.org/wiki/Povidone_iodine" title="Povidone iodine" class="mw-redirect" >Povidone iodine</a> (an <a href="http://en.wikipedia.org/wiki/Iodophor" title="Iodophor" >iodophor</a>)</li>

</ul>

In most countries, table salt is <a href="http://en.wikipedia.org/wiki/Iodized_salt" title="Iodized salt" class="mw-redirect" >iodized</a>[<a href="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed" >citation needed</a>]. Iodine is required for the essential thyroxin hormones produced by and concentrated in the thyroid gland.

Potassium iodide has been used as an <a href="http://en.wikipedia.org/wiki/Expectorant" title="Expectorant" class="mw-redirect" >expectorant</a>, although this use is increasingly uncommon. In medicine, <a href="http://en.wikipedia.org/wiki/Potassium_iodide" title="Potassium iodide" >potassium iodide</a> is used to treat acute <a href="http://en.wikipedia.org/wiki/Thyrotoxicosis" title="Thyrotoxicosis" class="mw-redirect" >thyrotoxicosis</a>, usually as a saturated solution of potassium iodide (SSKI). It is also used to block uptake of <a href="http://en.wikipedia.org/wiki/Iodine-131" title="Iodine-131" >iodine-131</a> in the thyroid gland (see isotopes section above), when this isotope is used as part of radiopharmaceuticals (such as <a href="http://en.wikipedia.org/wiki/Iobenguane" title="Iobenguane" >iobenguane</a>) that are not targeted to the thyroid or thyroid type tissues.

Iodine-131 (in the chemical form of iodide) is a component of <a href="http://en.wikipedia.org/wiki/Nuclear_fallout" title="Nuclear fallout" >nuclear fallout</a> 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 <a href="http://en.wikipedia.org/wiki/Micrograms" title="Micrograms" class="mw-redirect" >micrograms</a>) 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.<a href="http://en.wikipedia.org/wiki/Iodine#cite_note-21" >[22]</a>