Purple Fumes: the Importance of Iodine

Chemistry 45 I

Science topics Science Issue 27 : Autumn 2013 Autumn Issue 27 : I Although Courtois suspected that Gay-Lussac went on to investigate his purple vapour was a new element, he did not have the financial means It was left to follow up his research. to his colleagues, including Joseph Gay-Lussac, to confirm his results and name the element iodine, from iodes, which means word the Greek purple or violet. the chemistry of iodine, and despite chemists found the French the war, with British ways to correspond chemists, notably Sir Humphry Davy. Davy believed the vapour Initially, to be a chlorine compound, but soon concluded that it was indeed a new element. Science in School Science in School - -

- century and the th ) for manufactur 3 The discovery of iodine can be Napoleonic wars. With the British im- Napoleonic wars. With ports, posing a blockade on European faced with shortages were the French (KNO of saltpetre from the Sun), prevents some congeni the Sun), prevents from tal abnormalities in humans, and has many industrial applications? traced back to the 19 trated sulphuric acid to seaweed ash and was surprised by the beautiful produced purple fumes that were 1). (figure ing gunpowder. So chemist Bernard So chemist Bernard ing gunpowder. Courtois investigated the potential algae, Laminaria of seaweed (brown for this sp.) as the potassium source substance. He added concen crucial - Purple fumes: Purple fumes: the importance of iodine Iodine, with its characteristic purple purple Iodine, with its characteristic applications has myriad vapours, to – from the familiar disinfectant cells. solar innovative

hat makes iodine so impor Not tant and interesting?

www.scienceinschool.org W By Frithjof C Küpper, C Küpper, By Frithjof Berit Olofsson, Martin C Feiters, Yanagida, Kaiho, Shozo Tatsuo B Zimmermann, Michael J Carpenter, Lucy W Luther III, Zunli Lu, George & Lars Kloo Mats Jonsson only does it sublimate into a dramatic many purple gas, but it also affects aspects of life on Earth and of human for exam- civilisation. Did you know, marine algae ple, that iodine protects oxidative damage (for example from Public domain image / Wikimedia Commons The front page of Courtois’ historic publication reporting the discovery of iodine Image courtesy of Frithjof Küpper Image courtesy of Frithjof

Sir Humphrey Davy

ain image / Wikim dom edia blic Co Pu mm o ns

Portrait of Joseph Louis Gay- Lussac, French physicist and chemist, by François Séraphin Delpech (1778–1825)

Chemistry history of science (the discovery of the elements), the Biology role of scientists in the development of weapons, or the Physics relationships between scientists of opposing countries History during wartime. Ages 13-18 Suitable comprehension questions include: In this concise update on the element iodine, the 1. From the article you can deduce that seaweeds authors guide the reader through the history and the accumulate iodine: many applications of this important element, from a) To oxidise atmospheric ozone medicine to industry and energy production. Sugges- tions for school laboratory experiments add interest b) To absorb atmospheric ozone and appeal to the topic. c) To produce atmospheric ozone Given the plain and clear style, I recommend this arti- d) To protect themselves from atmospheric ozone. cle not only to European science teachers but also to 2. If we do not receive enough iodine: their students aged 13-18. It could be used in lessons a) Our thyroid gland enlarges / atrophies on chemistry (the periodic table, halogens), biology b) Our anterior pituitary gland secretes less / more (endocrine glands, the thyroid and its diseases) and physics (isotopes, radioactivity and solar cells). There thyroid-stimulating hormone

REVIEW is also an interdisciplinary opportunity to address the Giulia Realdon, Italy

46 I Science in School I Issue 27 : Autumn 2013 www.scienceinschool.org Science topics

odi Squirmelia / y of J Flick rtes r ou e c ag With the help of X-ray absorption Im spectroscopy, we now know that seaweeds accumulate iodine as iodide (I-), which acts as an antioxidant to protect them against oxidative damage caused by atmospheric ozone

(O3). This goes some way to explain- ing why trace amounts of molecular iodine (I ) can be detected in the at- kelp forest, big Sur, Chemistry 2 California mosphere of coastal regions and why human iodine intake in these regions is dependent on seaweed abundance rather than proximity to the sea. For much of the next century, iodine continued to be extracted from seaweed. Today, however, it is removed from natural iodine-containing brines in gas and oil fields in Japan and the USA, or from Chilean caliches (nitrate Brown algae such as kelp are the strong- ores), which contain calcium iodate est iodine accumulators among living

(Ca(IO3)2). The iodine is supplied to systems. Photograph taken on the shore at the market as a purplish-black solid. Dunstaffnage, near Oban, Scotland, UK Iodine chemistry Iodine belongs to the halogens, and thus shares many of the typical characteristics of the elements in this group. Because of its high electron- Image courtesy of FCK egativity, iodine forms iodides with most elements in its formal oxidation state, -1. Many iodine-containing compounds are frequently used as reagents in organic synthesis – mainly for iodination, oxidation and C-C bond formation. Iodine in the atmosphere originates mostly from biological and chemical processes in the ocean – such as the iodide antioxidant system in seaweeds. Most iodine is ultimately removed from the atmosphere by cloud formation. In the ocean, iodine is mainly - dissolved and exists as iodate (IO3 , oxidised form) and iodide (I-, reduced form). In Earth’s outer layer (the litho- sphere), most iodine is in marine and terrestrial sediments; iodine levels are low in igneous rocks. The physiological importance of iodine Physiologically, iodine is an essential element, required for the synthesis www.scienceinschool.org Science in School I Issue 27 : Autumn 2013 I 47 Image courtesy of Eleanor A Merritt

s n o

r Iodine vapour

of thyroid hormones – triiodotyros- The thyroid hormones thyroxine (T4) ine and thyroxine (figure 3) – which and triiodotyrosine (T3) regulate growth, development and cell metabolism. The recommended dietary intake of iodine for adults is 150 µg/day, which can be obtained sive growth of the thyroid gland. But from dairy products, seaweed and the most damaging effect of a lack of iodised table salt. iodine is to the developing brains of The classic symptom of iodine defi- babies, leading to mental retardation. ciency is thyroid enlargement (goitre). Furthermore, severe iodine deficiency As iodine intake falls, the anterior during pregnancy is associated with a pituitary gland secretes increasing greater incidence of stillbirth, miscar- levels of thyroid-stimulating hormone riage and congenital abnormalities. in an effort to maximise the uptake of The most effective way to prevent available iodine; this leads to exces- Image courtesy of Michael Zimmermann iodine deficiency is to add potassium

48 I Science in School I Issue 27 : Autumn 2013 www.scienceinschool.org Science topics

iodide (KI) or potassium iodate (KIO3) cess) are used to catalyse the carbony Iodine in the energy industry lation of methanol. to table salt. This practice of salt Iodine is used in one of the most Silver iodide (AgI), used in early iodisation is carried out in around 120 promising solar cells on the market photographic plates, is used today countries, with more than 70% of the for the production of low-cost ‘green in cloud seeding to initiate rain and world population now having access energy’: the dye-sensitised titanium to control climate. Because AgI has a to iodised salt. oxide solar cell. Also known as the similar crystal structure to ice, it can Grätzel cell after one of its inventors, induce freezing by providing nuclea- Industrial uses of iodine it consists of polyiodide electrolytes as tion sites. This was done at the 2008 Iodine and its compounds are used the charge transport layer between the Chemistry Beijing Olympics to prevent rainfall in myriad products, from food and cathode and the anode (to learn more, during the opening and closing cer- pharmaceuticals, through to animal see Shallcross et al., 2009). emonies. feed and industrial catalysts (figure With its high atomic weight (126.9) Of the 37 known isotopes of io- 127 4). For instance, iodine is a potent an- and large number of electrons, iodine dine, all but one, I, are radioactive. timicrobial. For more than a century, is also an excellent X-ray absorber Most of these radioisotopes, which iodine tincture – a mixture of ethanol, and is used in X-ray contrast media. are produced via fission reactions in water, iodine and potassium iodide – These substances are generally safe to nuclear power plants and weapons, was used as an antiseptic for wounds. administer to humans and enable the are short-lived, which makes them This has now largely been replaced visualisation of soft tissues in X-ray useful as tracers and therapeutic by water-soluble ionophores (iodine examinations. agents in medicine. For example, io- complexed with surfactants), which A more everyday application of dine isotopes can be used to image the are less irritating to the skin. For iodine is in liquid-crystal displays for thyroid gland, which absorbs radioac- example, povidone iodine, a mixture TVs, computers and mobile phones, tive iodine when it is injected into the of polyvinylpyrrolidone and iodine, is which use polarising films to filter bloodstream. used widely as a surgical scrub. light. These films are commonly Unfortunately, radioactive 131I, In the industrial production of acetic made of polyvinyl alcohol layers released from nuclear accidents – such acid, iodine compounds such as rho- doped with iodine. Here, iodine acts as the disaster in Fukushima, Japan, in dium iodide (the Monsanto process) as a cross-linker and ensures that the 2011 – is also taken up by the thyroid. or iridium iodide (BP’s Cativa pro- structure is polarising. Because it is a high-energy β-particle

Image courtesy of Michael Zimmermann Image courtesy of: Wen-Yan King / Flickr

A 12-year-old boy with a goitre A Chinese man with a goitre due to hypothyroidism. Hypo- caused by iodine deficiency thyroidism can be caused by a deficiency in iodine that is easily preventable and treatable with just pinches of iodised salt. www.scienceinschool.org Science in School I Issue 27 : Autumn 2013 I 49 Image courtesy of Tatsuo Kaiho

Others Contrast media

15% 22% Herbicides 3%

Salt additives 4% 12% Antimicrobial agents Feed Additives 5%

7% 11% LCD 11% 10% Industrial catalyst

Stabilizers Pharmaceuticals

The major industrial uses of iodine

Commemorating two centuries of emitter, it damages cells and induces Acknowledgement iodine research: an interdiscipli- cancer. To counteract this effect, non- This article was adapted from a nary overview of current research. radioactive potassium iodide (KI) much longer publication in Angewand- tablets are ingested to saturate the Angewandte Chemie International Edi- te Chemie International Edition (Küpper thyroid’s ability to take up radioactive tion 50: 11598-11620. doi: 10.1002/ et al., 2011). iodine. anie.201100028 These are just a small sample of the References Shallcross D, Harrison T, Henshaw S, many applications of iodine. Clearly, Sellou L (2009) Looking to the heav- although the element has been known Küpper FC, Feiters MC, Olofsson B, ens: climate change experiments. for only two hundred years, it is well Kaiho T, Yanagida S, Zimmermann Science in School 12: 34-39. www. established in modern chemistry, MB, Carpenter LJ, Luther GW, scienceinschool.org/2009/issue12/ physics and medicine. Lu Z, Jonsson M, Kloo L (2011) climate

Iodine in the classroom

No doubt we are all familiar with the colourful ‘iodine • Potassium iodide can be used to detect the clock’ experiment between hydrogen peroxide, po- presence of starch in a range of foods. tassium iodide, starch and sodium thiosulphate – but • Various solutions, including aqueous sodium there are many other ways to introduce iodine practi- iodide, can be electrolysed and the products at the cally into the classroom. For example: electrodes identified. Students can then use their • When catalysed by water, aluminium and iodine practical experience and theoretical knowledge to react to produce spectacular clouds of purple construct simple ionic equations. iodine vapour. Details of these and many other school experiments • In a direct reaction between a metal and a non- can be downloaded from the Learn Chemistry web- metal, zinc powder reacts with a solution of iodine sitew1. in ethanol to form zinc iodide in an exothermic redox reaction. CLASSROOM ACTIVITY

50 I Science in School I Issue 27 : Autumn 2013 www.scienceinschool.org Science topics Chemistry

Image courtesy of Christian Jansky / Wikimedia

This Cessna 210 plane has two silver iodide generators on the sides for cloud seeding.

Web reference Berit Olofsson is a professor of or- Shozo Yanagida is a professor at ganic chemistry at Stockholm Univer- w1 – The Learn Chemistry website of the Center for Advanced Science and sity, Sweden. Her research focuses on the UK’s Royal Society of Chemistry Innovation, Osaka University, Japan. hypervalent iodine chemistry, which offers a wide range of download- His research focuses on dye-sensitised involves iodine compounds in high able resources to support the teach- solar cells. oxidation states. She has given several ing and learning of chemistry. See: Michael B Zimmermann MD is a popular scientific lectures to second- www.rsc.org/learn-chemistry professor of human nutrition at the ary-school students to stimulate their Swiss Federal Institute of Technology interest in chemistry. (ETH) in Zurich, Switzerland. His re- Dr Tatsuo Kaiho is the director of Frithjof C Küpper is a professor of search focuses on the disorders caused Nihon Tennen Gas Co Ltd, Japan. His marine biodiversity at the University by iodine deficiency. He teaches research interests are iodine produc- of Aberdeen, UK. His research focuses several courses on nutrition and tion and its novel applications. on the biochemistry and biodiversity metabolism at the University, at both of marine algae and microbes – in undergraduate and graduate level. particular, on halogen metabolism of seaweeds and its atmospheric impact. Image courtesy of the Pharmacie Centrale des Armées He is engaged in a range of scientific outreach activities, recently including the production of a filmed documen- tary (Immersed in the Arctic). Martin C Feiters is an associate professor in the Institute for Mol- ecules and Materials at the Radboud University Nijmegen, the Nether- lands. He has been involved in many spectroscopic and structural studies involving synchrotron radiation, and in chemistry demonstrations for Potassium iodide pills are distributed to people living within secondary-school students who are a radius of 10 km of each nuclear power plant in France, to interested in studying science further. prevent damage to their thyroid glands in case of an accident. www.scienceinschool.org Science in School I Issue 27 : Autumn 2013 I 51 Image courtesy of the AIEA /Wikimedia

The nuclear power plant at Tricastin, France, is situated close to a densely populated region. Approximately every five years, potassium iodide pills are distributed to the people who live nearby to prevent damage to their thyroid glands in case of a nuclear accident.

Lucy J Carpenter is a professor of specialises in geological cycling of atmospheric chemistry at the Univer- iodine. sity of York, UK. Her specialities are Mats Jonsson is a professor of nu- volatile halogens and their influence clear chemistry at the Royal Institute on atmospheric chemistry. of Technology, in Stockholm, Sweden. George W Luther is the Harrington Lars Kloo is a professor of inorganic Professor of Marine Chemistry at the chemistry and the head of applied School of Marine Science & Policy at physical chemistry at the Royal the University of Delaware, USA. He Institute of Technology (KTH), in explores biogeochemical processes in Stockholm, Sweden. He is often in- marine environments, emphasising volved with school teachers and their research that interfaces chemistry with classes, on the subject of solar energy biology with the view that chemistry in general and solar cells in particu- drives biology. He performs chemi- lar. Currently, he is involved in the cal magic shows for local schools Soljakten programme, jointly with the and outreach programmes, and takes Nobel Museum, in Stockholm, which high-school teachers on oceanograph- is aimed at final-year elementary- ic research cruises, including those school classes. studying hydrothermal vents. Zunli Lu is an assistant professor To learn how to use this code, see at Syracuse University, NY, USA, and page 53.

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modelling black holes in primary school

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