Iodine

Iodine compounds are useful in organic chemistry and medicine.   Sodium iodide, NaI, is used to treat an iodine deficiency.   Potassium iodide, KI, is used to treat goiter.   When dissolved in alcohol, it is used as a disinfectant.   The radioactive isotope, I¹³¹, is used as a tracer in medicine and as a treatment for hyperthyroidism.   Silver iodide is used in photography.

Iodine is essential to life.  It is part of the thyroxime and triiodothyronine molecules located in the thyroid gland hormone that regulate body growth.   Sources: seafood, saltwater fish, seaweed, sea salt.   Lack of iodine in the body causes goiter (an enlarged thyroid gland), which can be cured by introducing iodine into the body, often through fortified salt, a medical preventative that was introduced in the U.S. in the 1920s. ^{Brody 187}   Iodine in large amounts is highly toxic.

In 1811, Bernard Courtois, a French chemist, accidently discovered iodine in an iodide compound while making potassium nitrate, KNO₃ from the potassium carbonate ("potash" = KCO₃) contained in seaweed.   Iodine can be obtained from seaweed which absorbs the iodides in sea water, from Chilean saltpeter, from iodates, NaIO₃ and KIO₃, and from nitrate-bearing earth, called caliche, from brines in old sea deposits, and from brackish water in petroleum and salt wells.   It can be obtained in ultrapure form from the reaction of potassium iodide with copper sulfate. ^{Lide 4-15}