Reviews F. C. Kpper, L. Kloo et al. DOI: 10.1002/anie.201100028 History of Iodine Chemistry Commemorating Two Centuries of Iodine Research: An Interdisciplinary Overview of Current Research Frithjof C. Kpper,* Martin C. Feiters, Berit Olofsson, Tatsuo Kaiho, Shozo Yanagida, Michael B. Zimmermann, Lucy J. Carpenter, George W. Luther III, Zunli Lu, Mats Jonsson, and Lars Kloo* Keywords: environmental chemistry · history of chemistry · iodine · Mçssbauer spectroscopy · X-ray spectroscopy Angewandte Chemie 11598 www.angewandte.org 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2011, 50, 11598 – 11620 Iodine Iodine was discovered as a novel element in 1811 during From the Contents the Napoleonic Wars. To celebrate the bicentennial anni- versary of this event we reflect on the history and highlight 1. Historic Background 11599 the many facets of iodine research that have evolved since 2. Characteristic Chemistry 11600 its discovery. Iodine has an impact on many aspects of life on Earth as well as on human civilization. It is accumu- 3. Supramolecular Interactions of Iodine, lated in high concentrations by marine algae, which are the Iodide, and Iodocarbons 11601 origin of strong iodine fluxes into the coastal atmosphere 4. Analytical Techniques for Iodine and its which influence climatic processes, and dissolved iodine is Compounds 11602 considered a biophilic element in marine sediments. Iodine is central to thyroid function in vertebrates, with 5. Organic Synthesis 11602 paramount implications for human health. Iodine can 6. Production and Industrial Applications 11605 exist in a wide range of oxidation states and it features a diverse supramolecular chemistry. Iodine is amenable to 7. Materials 11606 several analytical techniques, and iodine compounds have found widespread use in organic synthesis. Elemental 8. Solar Cells Based on the Conductance of iodine is produced on an industrial scale and has found a Polyiodides 11607 wide range of applications in innovative materials, 9. Medicine and Physiology 11610 including semiconductors—in particular, in solar cells. 10. Iodine Biochemistry 11611 1. Historic Background 11. Atmospheric Chemistry 11612 The goiter-preventing effects of iodine in seaweeds were 12. Marine Chemistry 11613 known to the legendary Chinese emperor Shen-Nung as early as around 3000 BC, and the knowledge of this treatment was 13. Geochemistry 11614 available in Greece by the time of Hippocrates.[1] Never- theless, iodine was not isolated and recognized as an element 14. Radiochemistry of Iodine 11615 until an early 19th century chemist, Bernard Courtois, explored brown seaweeds (Laminaria sp., Fucussp.; Figure 1) for their potential as an alternative feedstock to wood ashes for the production of saltpeter that was required Unfortunately, Courtois could not follow up on his for the Napoleonic war effort.[2] The addition of concentrated research of this new substance because of economic hardship. sulfuric acid to seaweed ashes did not only result in strong However, he managed to incite two of his chemist friends, corrosion of his copper vessels, he also noticed the emission of Charles Bernard Desormes and Nicolas Clment, to pursue a previously unobserved violet vapor through the reaction the studies—together with Andr M. Ampre and Jose- shown in Equation (1). ph Louis Gay-Lussac. Clment presented the findings on Courtois behalf to the Imperial Institute of France (Con- servatoire des Arts et Mtiers, where he held a professorship) À 2À 2I þ H2SO4 ! I2 þ SO3 þ H2O ð1Þ on November 29, 1813, which resulted in their original [*] Prof. F. C. Kpper Prof. M. B. Zimmermann Scottish Association for Marine Science ETH Zrich (Switzerland) Oban, Argyll, PA37 1QA, Scotland (UK) Prof. L. J. Carpenter E-mail: [email protected] Department of Chemistry, University of York (UK) Homepage: http://www.smi.ac.uk/frithjof-kuepper Prof. G. W. Luther III Dr. M. C. Feiters College of Earth, Ocean and Environment, University of Delaware, Dept. of Organic Chemistry, Institute for Molecules and Materials, Lewes (USA) Radboud University Nijmegen (The Netherlands) Dr. Z. Lu Prof. B. Olofsson Department of Earth Sciences, Syracuse University (USA) Organic Chemistry, Stockholm University, Arrhenius Laboratory Prof. M. Jonsson, Prof. L. Kloo (Sweden) Applied Physical Chemistry, Dept. of Chemistry, KTH Royal Institute Dr. T. Kaiho of Technology, SE-100 44 Stockholm (Sweden) Kanto Natural Gas Development Co., Ltd., Chiba (Japan) E-mail: [email protected] Prof. S. Yanagida Center for Advanced Science and Innovation, Osaka (Japan) Angew. Chem. Int. Ed. 2011, 50, 11598 – 11620 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 11599 Reviews F. C. Kpper, L. Kloo et al. Figure 1. Brown algae, especially of the genus Laminaria sp., are the strongest iodine accumulators among all living systems. They use iodide as a simple, inorganic antioxidant. At low tide, high iodide concentrations at the algal surface react with atmospheric oxidants, such as ozone, thereby resulting in strong fluxes of molecular iodine into the coastal atmosphere which contribute to the formation of aerosols. (Photograph: F.C.K., taken on the shore at Dunstaffnage, near Oban, Scotland, at low tide.) publication in the Annales de Chimie (Figure 2).[3] This paper already uses the name iode for the new substance, “due to the Figure 2. The front page of Courtois’ historic publication reporting the beautiful violet color of its vapor” (from the Greek iw´ dh& or discovery of iodine. ioeidh´&, that is, violet) and mentions the metal-like appear- ance of its solid, elemental state. Shortly afterwards, on December 6 and 20 of the same year, Gay-Lussac presented chlorine, but came to the conclusion that it was an element in his results on the compounds that this novel element formed its own right,[5] and competed for a while with Gay-Lussac with other elements.[4] It is amazing that despite the war, in over priority rights (even though both Davy and Gay-Lussac which most of Europe was embroiled at that time, scientific always acknowledged Courtois as the discoverer of iodine). exchange between opposing powers was still functioning. The Despite the scientific fame of the discovery and the rising eminent British chemist Sir Humphry Davy corresponded commercial interest in iodine, for example, for the treatment with his French peers (with mail taken back and forth of wounds, Courtois failed to capitalize on his discoveries and, between the hostile countries by smugglers and cartels), and sadly, died in poverty on September 27, 1838, aged only 62.[6] was given free passage to France (with Napoleon’s personal Iodine production from seaweeds became a major economic approval). Ampre gave him a sample of the new substance so activity in the coastal regions of Europe, in particular in parts that he could conduct his own research on iodine (Davy was of Brittany, Normandy, Ireland, and Scotland, and it features traveling with a portable chest for chemical experiments). in many historic and travel accounts of these places (for Initially, Davy believed that it was merely a compound of example, Ref. [7]). Frithjof C. Kpper was recently appointed to the Chair in Marine Biodiversity, a full 2. Characteristic Chemistry professorship at the University of Aberdeen. Until then, he was a Reader in Algal Iodine belongs to Group 17 of the Periodic Table, the Biochemistry at the Scottish Association for halogens, and thus shares many of the typical characteristics Marine Science. He obtained a joint French–German PhD with Bernard Kloareg of the elements in this group, such as high electronegativity nÀ1 (Roscoff) and Dieter G. Mller (Konstanz), (2.66 according to the Pauling scale) and a valence p and carried out postdoctoral research with configuration. These properties make iodine highly reactive Alison Butler (Santa Barbara). Leading an and prone to radical reactions. As a consequence of its high international consortium, his research has electronegativity it forms iodides with most elements, with resulted in the finding of iodide serving as an iodine possessing the formal oxidation state ÀI. Iodine is inorganic antioxidant in kelp, the first de- known in compounds with formal oxidation states ranging scribed from a living system. from ÀIto+ VII. The high formal positive oxidation states 11600 www.angewandte.org 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2011, 50, 11598 – 11620 Iodine are mainly found in compounds with the very electronegative elements oxygen and fluorine. However, since the polarizability of iodine is quite high, the chemical bonds also formed with the more electroposi- tive elements in the Periodic Table tend to contain a fair degree of covalency. This makes the structural chemistry of iodide compounds a bit more complex than for the other halogens. Just as for its halogen À congeners, molecular compounds Figure 3. Overview of the supramolecular chemistry of I2,I , and RI. are formed when the difference in electronegativity is small, but for larger differences chain- and layer-type of structures are also Grtzel-type solar cells (see Section 8).[10] Under favorable frequently observed, rather than simple ionic compounds circumstances, such as the stabilization provided to linear controlled only by ion electrostatics and ion size. Well-known polyiodides by the hydrophobic interior of a starch mole- [11] À and representative examples include AuI (chainlike struc- cule, I3 can associate with more I2 molecules to form À À ture), CdI2 (layered structure),