I2 color. Iodine (iodine) in nature. Application of iodine
Iodine was discovered in 1811 by a Parisian saltpeter manufacturer named Courtois in soda prepared from the ashes of coastal plants. In 1813, Gay-Lussac investigated a new substance and gave it a name based on the violet color of the vapor - iodine. It is derived from the Greek word - dark blue, violet. Then, when its similarity to chlorine was established, Davy proposed calling the element iodine (similar to chlorine); this name is still accepted in England and the USA.
Receipt:
The main source of iodine in the USSR is underground drilling water, which contains up to 10 - 50 mg/l of iodine. Iodine compounds are also present in sea water, but in such small quantities that their direct isolation from water is very difficult. However, there are some algae that accumulate iodine in their tissues. The ash of these algae serves as a raw material for the production of iodine. Iodine is also found in the form of potassium salts - iodate KIO 3 and periodate KIO 4, accompanying deposits of sodium nitrate (saltpeter) in Chile and Bolivia.
Iodine can be obtained similarly to chlorine by oxidation of HI with various oxidizing agents. In industry, it is usually obtained from iodides by treating their solutions with chlorine. Thus, the production of iodine is based on the oxidation of its ions, and chlorine is used as an oxidizing agent.
Physical properties:
Iodine at room temperature appears as dark purple crystals with a faint luster. When heated under atmospheric pressure, it sublimates (sublimates), turning into purple vapor; When cooled, iodine vapor crystallizes, bypassing the liquid state. This is used in practice to purify iodine from non-volatile impurities. Slightly soluble in water, well in many organic solvents.
Chemical properties:
Free iodine exhibits extremely high chemical activity. It interacts with almost all simple substances. The reactions of combining iodine with metals occur especially quickly and with the release of a large amount of heat.
It reacts with hydrogen only with sufficiently strong heating and not completely, since the reverse reaction begins to occur - the decomposition of hydrogen iodide:
H 2 + I 2 = 2HI - 53.1 kJ
It dissolves in solutions of iodides, forming unstable complexes. It disproportionates with alkalis, forming iodides and hypoiodites. It is oxidized by nitric acid to periodic acid.
If hydrogen sulfide water (aqueous solution of H 2 S) is added to a yellowish aqueous solution of iodine, the liquid becomes discolored and becomes cloudy from the released sulfur:
H 2 S + I 2 = S + 2HI
In compounds it exhibits oxidation states -1, +1, +3, +5, +7.
The most important connections:
Hydrogen iodide, gas, very similar in properties to hydrogen chloride, but has more pronounced reducing properties. Very soluble in water (425:1), a concentrated solution of hydrogen iodide smokes due to the release of HI, which forms a fog with water vapor.
In aqueous solution it is one of the strongest acids.
Hydrogen iodide, already at room temperature, is gradually oxidized by atmospheric oxygen, and under the influence of light the reaction is greatly accelerated:
4HI + O 2 = 2I 2 + 2H 2 O
The reducing properties of hydrogen iodide are noticeably manifested when interacting with concentrated sulfuric acid, which is reduced to free sulfur or even to H 2 S. Therefore, HI cannot be obtained by the action of sulfuric acid on iodides. Hydrogen iodide is usually obtained by the action of water on compounds of iodine with phosphorus - PI 3. The latter undergoes complete hydrolysis, forming phosphorous acid and hydrogen iodide:
PI 3 + ZN 2 O = N 3 PO 3 + 3HI
A solution of hydrogen iodide (up to 50% concentration) can also be obtained by passing H 2 S into an aqueous suspension of iodine.
Iodides, salts of hydroiodic acid. Potassium iodide is used in medicine - in particular, for diseases of the endocrine system, photoreagents.
Hydrous acid - HOI is an amphoteric compound in which the basic properties somewhat predominate over the acidic ones. Can be obtained in solution by reacting iodine with water
I 2 + H 2 O = HI + HOI
Hydrous acid - HIO 3 can be obtained by oxidizing iodine water with chlorine:
I 2 + 5Cl 2 + 6H 2 O = 2HIO 3 + 10HCl
Colorless crystals, quite stable at room temperature. Strong acid, energetic oxidizing agent. Salts are iodates, strong oxidizing agents in an acidic environment.
Iodine(V) oxide, iodic anhydride, can be obtained by carefully heating HIO 3 to 200°C, powder. When heated above 300°C, it decomposes into iodine and oxygen, exhibits oxidizing properties, in particular, it is used to absorb CO in the analysis:
5CO + I 2 O 5 = I 2 + 5CO 2
Periodic acid - HIO 4 and its salts (periodates) are well studied. The acid itself can be obtained by the action of HClO 4 on iodine: 2HCIO 4 + I 2 = 2HIO 4 + Cl 2
or by electrolysis of a solution of HIO 3: HIO 3 + H 2 O = H 2 (cathode) + HIO 4 (anode)
Periodic acid is released from solution in the form of colorless crystals with the composition HIO 4 2H 2 O. This hydrate should be considered a pentaprotic acid H5IO6(orthoiodine), since all five hydrogen atoms in it can be replaced by metals to form salts (for example, Ag 5 IO 6). Periodic acid is a weak, but stronger oxidizing agent than HClO 4.
Iodine (VII) oxide I 2 O 7 was not obtained.
Iodine fluorides, IF 5, IF 7- liquids hydrolyzed by water, fluorinating agents.
Iodine chlorides, ICl, ICl 3- Krist. substances that dissolve in chloride solutions to form complexes - and -, iodinating agents.
Application:
Iodine is widely used in the chemical industry (iodide refining of Zr and Ti) and for the synthesis of semiconductor materials.
Iodine and its compounds are used in analytical chemistry (iodometry) In medicine in the form of so-called iodine tincture (10% solution of iodine in ethyl alcohol), an antiseptic and hemostatic agent. Iodine compounds for the prevention (iodination of products) and treatment of thyroid diseases, radioactive isotopes are also used 125 I, 131 I, 132 I.
World production (without the USSR) is about 10 thousand tons/year (1976).
MPC is about 1 mg/m3.
See also:
P.A. Wallet. Ubiquitous iodine. "Chemistry" (addendum to the newspaper "1st September"), No. 20, 2005
Since childhood, a well-known assistant to all children and their parents for scratches, abrasions and cuts. It is a fast and effective means of cauterizing and disinfecting the wound surface. However, the scope of application of the substance is not limited only to medicine, since the chemical properties of iodine are very diverse. The purpose of our article is to get to know them in more detail.
Physical characteristics
The simple substance has the appearance of dark purple crystals. When heated, due to the peculiarities of the internal structure of the crystal lattice, namely the presence of molecules in its nodes, the compound does not melt, but immediately forms pairs. This is sublimation or sublimation. It is explained by the weak connection between the molecules inside the crystal, which easily break away from each other - a gaseous phase of the substance is formed. The number of iodine in the periodic table is 53. And its position among other chemical elements indicates that it belongs to non-metals. Let's look at this issue further.
Place of the element in the periodic table
Iodine is in the fifth period, group VII and, along with fluorine, chlorine, bromine and astatine, forms a subgroup of halogens. Due to the increase in nuclear charge and atomic radius, the non-metallic properties of halogen representatives weaken, therefore iodine is less active than chlorine or bromine, and its electronegativity is also lower. The atomic mass of iodine is 126.9045. A simple substance is represented by diatomic molecules, like other halogens. Below we will take a look at the atomic structure of the element.
Features of the electronic formula
Five energy levels and the last of them almost completely filled with electrons confirm the presence of pronounced non-metal characteristics in the element. Like other halogens, iodine is a strong oxidizing agent, taking away from metals and weaker non-metallic elements - sulfur, carbon, nitrogen - the electron missing to complete the fifth level.
Iodine is a nonmetal whose molecules contain a common pair of p-electrons that bind the atoms together. Their density at the point of overlap is greatest; the total electron cloud does not shift to any of the atoms and is located in the center of the molecule. A nonpolar covalent bond is formed, and the molecule itself has a linear shape. In the series of halogens, from fluorine to astatine, the strength of the covalent bond decreases. A decrease in the enthalpy value is observed, on which the decomposition of the molecules of the element into atoms depends. What consequences does this have for the chemical properties of iodine?
Why is iodine less active than other halogens?
The reactivity of nonmetals is determined by the force of attraction of foreign electrons to the nucleus of their own atom. The smaller the radius of an atom, the higher the forces of electrostatic attraction of its negatively charged particles of other atoms. The higher the number of the period in which an element is located, the more energy levels it will have. Iodine is in the fifth period, and it has more energy layers than bromine, chlorine and fluorine. This is why the iodine molecule contains atoms with a radius much larger than those of the previously listed halogens. This is why I 2 particles attract electrons less strongly, which leads to a weakening of their non-metallic properties. The internal structure of a substance inevitably affects its physical characteristics. Let's give specific examples.
Sublimation and solubility
A decrease in the mutual attraction of iodine atoms in its molecule leads, as we said earlier, to a weakening of the strength of the covalent nonpolar bond. There is a decrease in the resistance of the compound to high temperature and an increase in the rate of thermal dissociation of its molecules. A distinctive feature of halogen: the transition of a substance when heated from a solid state immediately to a gaseous state, i.e. sublimation is the main physical characteristic of iodine. Its solubility in organic solvents, such as carbon disulfide, benzene, ethanol, is higher than in water. Thus, only 0.02 g of the substance can dissolve in 100 g of water at 20 °C. This feature is used in the laboratory to extract iodine from an aqueous solution. By shaking it with a small amount of H 2 S, you can observe the violet color of hydrogen sulfide due to the transition of halogen molecules into it.
Chemical properties of iodine
When interacting with metals, the element always behaves the same. It attracts the valence electrons of the metal atom, which are located either in the last energy layer (s-elements such as sodium, calcium, lithium, etc.) or in the penultimate layer containing, for example, d-electrons. These include iron, manganese, copper and others. In these reactions, the metal will be a reducing agent, and iodine, whose chemical formula is I 2, will be an oxidizing agent. Therefore, it is precisely this high activity of a simple substance that is the reason for its interaction with many metals.
The interaction of iodine with water when heated deserves attention. In an alkaline environment, the reaction occurs with the formation of a mixture of iodide and iodic acids. The latter substance exhibits the properties of a strong acid and, upon dehydration, turns into iodine pentoxide. If the solution is acidified, then the above reaction products interact with each other to form the starting substances - free molecules of I 2 and water. This reaction is of the redox type; it exhibits the chemical properties of iodine as a strong oxidizing agent.
Qualitative reaction to starch
In both inorganic and organic chemistry, there is a group of reactions that can be used to identify certain types of simple or complex ions in interaction products. To detect macromolecules of a complex carbohydrate - starch - a 5% alcohol solution of I 2 is often used. For example, a few drops of it are dripped onto a cut of a raw potato, and the color of the solution turns blue. We observe the same effect when the substance comes into contact with any starch-containing product. This reaction, which produces blue iodine, is widely used in organic chemistry to confirm the presence of a polymer in a test mixture.
The beneficial properties of the product of interaction between iodine and starch have been known for a long time. It was used in the absence of antimicrobial drugs for the treatment of diarrhea, stomach ulcers in remission, and diseases of the respiratory system. Starch paste, containing approximately 1 teaspoon of an alcohol solution of iodine per 200 ml of water, has become widespread due to the low cost of ingredients and ease of preparation.
However, it must be remembered that blue iodine is contraindicated in the treatment of young children, people suffering from hypersensitivity to iodine-containing drugs, as well as patients with Graves' disease.
How do nonmetals react with each other?
Among the elements of the main subgroup of group VII, fluorine, the most active non-metal with the highest oxidation state, reacts with iodine. The process takes place in the cold and is accompanied by an explosion. I 2 reacts with hydrogen under strong heating, and not completely, the reaction product - HI - begins to decompose into the original substances. Hydroiodic acid is quite strong and, although its characteristics are similar to chloride acid, it still exhibits more pronounced signs of a reducing agent. As you can see, the chemical properties of iodine are due to its belonging to active non-metals, but the element is inferior in oxidizing ability to bromine, chlorine and, of course, fluorine.
The role of the element in living organisms
The highest content of I - ions is found in the tissues of the thyroid gland, where they are part of the thyroid-stimulating hormones: thyroxine and triiodothyronine. They regulate the growth and development of bone tissue, the conduction of nerve impulses, and metabolic rate. A lack of iodine-containing hormones in childhood is especially dangerous, since mental development may be delayed and symptoms of a disease such as cretinism may appear.
Insufficient secretion of thyroxine in adults is associated with water and food. It is accompanied by hair loss, swelling, and decreased physical activity. An excess of the element in the body is also extremely dangerous, as Graves’ disease develops, the symptoms of which are excitability of the nervous system, tremors of the limbs, and severe weight loss.
Distribution of iodides in nature and methods of obtaining pure substances
The bulk of the element is present in living organisms and the shells of the Earth - the hydrosphere and lithosphere - in a bound state. Salts of the element are present in sea water, but their concentration is insignificant, so extracting pure iodine from it is unprofitable. It is much more effective to obtain the substance from the ash of brown sargassum.
On an industrial scale, I 2 is isolated from groundwater during oil production processes. When processing some ores, for example, potassium iodates and hypoiodates are found in it, from which pure iodine is subsequently extracted. It is quite cost-effective to obtain I 2 from a solution of hydrogen iodide by oxidizing it with chlorine. The resulting compound is an important raw material for the pharmaceutical industry.
In addition to the already mentioned 5% alcohol solution of iodine, which contains not only a simple substance, but also a salt - potassium iodide, as well as alcohol and water, drugs such as "Iodine-active" and "Iodomarin" are used in endocrinology for medical reasons.
In areas with a low content of natural compounds, in addition to iodized table salt, you can use a remedy such as Antistrumin. It contains the active ingredient - potassium iodide - and is recommended as a prophylactic drug used to prevent the symptoms of endemic goiter.
The cat ran and waved its tail. This is not a fairy tale about the chicken Ryaba, but history of the discovery of iodine. It was discovered at a Paris plant that converts sodium nitrate into potassium nitrate. The first became damp in the air, and the second was in short supply.
The transformation took place using the ash remaining from burning algae. The method was invented in 1808, but they did not know what its secret was. The cat that the factory workers were chasing did not know this either. knocked over two vessels - with sulfuric acid and residual production salts.
Purple vapors shot into the air. The owner of the factory, Bernard Kurt, saw this. He conducted several experiments himself, then passed on the information to scientists. The result is that in 1814 the world learned about the existence of a new element. He became iodine.
Chemical and physical properties of iodine
Properties of iodine determined by its location in. The element is included in the 7th group. It contains halogens - the most active non-metals. Iodine, for example, has an easily polarizable electron shell.
That is, it doesn’t cost her any effort to separate in space. This allows cations of other elements to penetrate into the nonmetal atom, whose mass, by the way, is 127. “Guests” in the electron shell change it, making iodine the most covalent of all halogens.
Simply put, an element can form a greater variety of bonds with other atoms. Often iodine is positively polarized. This atom is the most active. What makes it stand out is its color, that same purple.
Iodine atom listed in the periodic table - a natural specimen. This is a stable isotope with atomic mass 127. Other atoms with numbers 125, 129, 131 have also been artificially obtained.
Each of them - radioactive iodine. Isotopes emit beta and gamma rays and are used in medicine. Radioactive iodine is obtained from the fission products of uranium. That is, nuclear reactors serve as laboratories.
Standard iodine is possible Compatible with most non-metals and approximately 40% metals. Noble people, and not only, do not react to the 53rd element. Interaction is also impossible with carbon, oxygen and all inert gases.
Is Yod study, or its compounds can be determined using water. The pure element is almost insoluble in it. Iodites, that is, compounds of a substance with alkali and alkaline earth atoms, are soluble. In its original form, the 53rd element disappears in water only with strong heating.
Iodine solution easy to obtain if you use organic matter. Glycerin, carbon disulfide, or carbon tetrachloride are suitable. If the solvent is oxygen-free, it will turn purple. If a liquid has oxygen atoms, iodine will make it .
In its pure form, at room temperature, iodine is purple-black. The luster of the substance is metallic, the state of aggregation is . They are dense - almost 5 grams per cubic centimeter.
Crystals are made up of molecules, each of which has 2 atoms. The substance enters the gaseous state at a temperature of 183 degrees. Getting iodine liquid is possible already at 114 Celsius.
Application of iodine
Iodine salts used in the glass industry. We are talking about car headlights and lamps with special effects. The main effect is that iodites serve as filters from oncoming light rays. Drivers know how important it is, sometimes, to neutralize them.
This process is called Polaroid and, in fact, was first used in photographic art. The author of the idea is the Englishman William Talbot. He was an outstanding chemist and physicist of the 19th century.
In the 21st century, digital technologies rule. However, to obtain a negative photo, the iodine variety is still used. In combination with gelatin, it produces an emulsion, which is coated with a glass substrate. Light hits the coating and release begins. More light - more metal. This is how the picture is made.
Iodine application found in metallurgy. Compounds of the element help produce high purity metals. By thermally decomposing iodites, industrialists extract, for example, vanadium and zirconium. These refractory elements are needed for many rocket alloys and nuclear reactor materials.
Can also be found in automotive bearings iodine. Which does it make sense? The element is added to the lubricant. It is recommended for titanium and stainless steel. The processing allows the parts to withstand a load 50 times greater than the standard one. This is despite the fact that there is only 1-2% iodine in the lubricant.
Without the 53rd element, medicine is unthinkable. Iodine in the body controls the functioning of the thyroid gland, is part of the hormones TSH, T3 and T4 produced by it. If there is a deficiency of the element, a goiter develops and cancer is possible.
At the same time, the body cannot produce the substance itself. Iodine comes exclusively from food, dietary supplements and medications. Of the latter, it’s easy to remember “ Iodomarin».
It is prescribed even to infants, especially in areas remote from the seas. In such areas, as a rule, there is a deficiency of the 53rd element, contained mainly in the waters of the oceans and their gifts.
One of the latest developments by doctors is blue iodine. Starch is added to it, which changes the color of the usual solution for external use. Starch also neutralizes the effects of alcohol and other harmful “additives”. Doctors allow this elixir for internal use and for rinsing with iodine. Although a mixture can handle the latter salt, soda, iodine.
Treatment with iodine is allowed not only in its stable, but also in its radioactive forms. So the 131st isotope is used to restore the functions of the thyroid gland. The procedures are strictly regulated, since an excess of radioactive iodine can cause cancer.
Iodine extraction
How much iodine mined per year? About 30,000 tons. World reserves of the element are estimated at almost 15,000,000 tons. Most of them are hidden in iodine compounds. It is rarely found in its pure form.
The method of isolating substances from natural reservoirs – algae – is still relevant. A ton of dried kelp contains 5 kilograms iodine.
(first electron)
(according to Pauling)
| I | 53 |
| 126,90447 | |
| 5s 2 5p 5 | |
| Iodine | |
Iodine, iodine(from ancient Greek ιώδης, iodes - “violet”) - an element of the main subgroup of the seventh group, the fifth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 53. Denoted by the symbol I (lat. Iodum). A chemically active non-metal, belongs to the group of halogens. The simple substance iodine (CAS number: 7553-56-2) under normal conditions is black-gray crystals with a violet metallic luster; it easily forms violet vapors with a pungent odor. The molecule of the substance is diatomic (formula I 2).
In medicine and biology, this substance is usually called iodine(for example, “iodine solution”), in the periodic table and chemical literature the name is used iodine.
Story
Iodine was discovered in 1811 by Courtois in seaweed ash, and in 1815 Gay-Lussac began to consider it as a chemical element.
Element symbol J was replaced by I relatively recently, in the 50s of the XX century.
Being in nature
It is found in large quantities in the form of iodides in sea water. It is also known in nature in free form, as a mineral, but such finds are rare - in the thermal springs of Vesuvius and on the island. Vulcano (Italy). Reserves of natural iodides are estimated at 15 million tons, 99% of reserves are located in Chile and Japan. Currently, intensive iodine mining is carried out in these countries, for example, the Chilean Atacama Minerals produces over 720 tons of iodine per year.
The raw material for the industrial production of iodine in Russia is oil drilling water, while in foreign countries that do not have oil fields, seaweed is used, as well as mother liquors of Chilean (sodium) nitrate, which makes the production of iodine from such raw materials much more expensive.
Physical properties
The vapors have a characteristic purple color, just like solutions in non-polar organic solvents such as benzene - in contrast to the brown solution in a polar alcohol. Iodine at room temperature appears as dark purple crystals with a faint luster. When heated at atmospheric pressure, it sublimates (sublimates), turning into violet vapor; When cooled, iodine vapor crystallizes, bypassing the liquid state. This is used in practice to purify iodine from non-volatile impurities.
Chemical properties
Chemically, iodine is quite active, although to a lesser extent than chlorine and bromine.
- When slightly heated, iodine reacts energetically with metals, forming iodides:
- Iodine reacts with hydrogen only when heated and not completely, forming hydrogen iodide:
- Elemental iodine is an oxidizing agent, less powerful than chlorine and bromine. Hydrogen sulfide H 2 S, Na 2 S 2 O 3 and other reducing agents reduce it to the I - ion:
- When dissolved in water, iodine partially reacts with it:
Application
Medicine
It is widely used in alternative (unofficial) medicine, but its use without a doctor’s prescription is generally poorly justified, and is often accompanied by various advertising statements.
see also
Battery production
Iodine is used as the positive electrode (oxidizing agent) in lithium-iodine batteries for electric vehicles.
Laser fusion
Some organoiodine compounds are used to produce high-power gas lasers using excited iodine atoms (laser fusion research and industry).
Radioelectronics industry
In recent years, the demand for iodine from manufacturers of liquid crystal displays has sharply increased.
Dynamics of iodine consumption
Toxicity
Iodine is a toxic substance. Lethal dose 2-3 g. Causes damage to the kidneys and cardiovascular system. When inhaling iodine vapor, a headache, cough, runny nose appears, and possibly pulmonary edema. Contact with the mucous membrane of the eyes causes lacrimation, eye pain and redness. If ingested, general weakness, headache, vomiting, diarrhea, brown coating on the tongue, heart pain and increased heart rate appear. After a day, the kidneys become inflamed and blood appears in the urine. If left untreated, the kidneys may fail within 2-3 days and myocarditis may occur. Without treatment, death occurs.
Iodine(lat. Iodum), I, a chemical element of group VII of the periodic system of Mendeleev, belongs to the halogens (the outdated name Iodine and the symbol J are also found in the literature); atomic number 53, atomic mass 126.9045; crystals of black-gray color with a metallic sheen. Natural iodine consists of one stable isotope with a mass number of 127. Iodine was discovered in 1811 by the French chemist B. Courtois. By heating the mother brine of seaweed ash with concentrated sulfuric acid, he observed the release of violet vapor (hence the name Iodine - from the Greek iodes, ioides - violet-like in color, violet), which condensed into dark shiny plate-like crystals. In 1813-1814, the French chemist J. L. Gay-Lussac and the English chemist G. Davy proved the elemental nature of iodine.
Distribution of iodine in nature. The average iodine content in the earth's crust is 4·10 -5% by mass. Iodine compounds are scattered in the mantle and magmas and in the rocks formed from them (granites, basalts and others); deep minerals of Iodine are unknown. The history of iodine in the earth's crust is closely related to living matter and biogenic migration. In the biosphere, processes of its concentration are observed, especially by marine organisms (algae, sponges and others). Eight supergene iodine minerals are known to form in the biosphere, but they are very rare. The main reservoir of iodine for the biosphere is the World Ocean (1 liter contains on average 5·10 -5 g of iodine). From the ocean, iodine compounds dissolved in drops of sea water enter the atmosphere and are carried by winds to the continents. (Areas remote from the ocean or fenced off from sea winds by mountains are depleted in iodine.) Iodine is easily adsorbed by organic matter in soils and marine silts. When these silts become compacted and sedimentary rocks form, desorption occurs and some of the iodine compounds pass into groundwater. This is how iodine-bromine waters used for the extraction of iodine are formed, especially characteristic of oil field areas (in some places, 1 liter of these waters contains over 100 mg of iodine).
Physical properties of Iodine. Iodine density is 4.94 g/cm 3, melting point 113.5°C, boiling point 184.35°C. The molecule of liquid and gaseous iodine consists of two atoms (I 2). A noticeable dissociation of I 2 = 2I is observed above 700 °C, as well as under the influence of light. Already at ordinary temperatures, iodine evaporates, forming a sharp-smelling purple vapor. When heated slightly, iodine sublimes, settling in the form of shiny thin plates; this process serves to purify iodine in laboratories and industry. Iodine is poorly soluble in water (0.33 g/l at 25 °C), well soluble in carbon disulfide and organic solvents (benzene, alcohol and others), as well as in aqueous solutions of iodides.
Chemical properties of Iodine. The configuration of the outer electrons of the Iodine atom is 5s 2 5p 5. In accordance with this, iodine exhibits variable valence (oxidation state) in compounds: -1 (in HI, KI), +1 (in HIO, KIO), +3 (in ICl 3), +5 (in HIO 3, KIO 3 ) and +7 (in HIO 4, KIO 4). Chemically, iodine is quite active, although to a lesser extent than chlorine and bromine. Iodine reacts vigorously with metals when slightly heated, forming iodides (Hg + I 2 = HgI 2). Iodine reacts with hydrogen only when heated and not completely, forming hydrogen iodide. Iodine does not combine directly with carbon, nitrogen, or oxygen. Elemental Iodine is an oxidizing agent, less powerful than chlorine and bromine. Hydrogen sulfide H 2 S, sodium thiosulfate Na 2 S 2 O 3 and other reducing agents reduce it to I - (I 2 + H 2 S = S + 2HI). Chlorine and other strong oxidizing agents in aqueous solutions convert it into IO 3 - (5Cl 2 + I 2 + 6H 2 O = 2HIO 3 H + 10HCl). When dissolved in water, iodine partially reacts with it (I 2 + H 2 O = HI + HIO); in hot aqueous solutions of alkalis, iodide and iodate are formed (3I 2 + 6NaOH = 5NaI + NaIO 3 + 3H 2 O). When adsorbed on starch, iodine turns it dark blue; it is used in iodometry and qualitative analysis for the detection of Iodine.
Iodine vapors are poisonous and irritate mucous membranes. Iodine has a cauterizing and disinfecting effect on the skin. Iodine stains are washed off with solutions of soda or sodium thiosulfate.
Obtaining Iodine. The raw material for the industrial production of iodine is oil drilling water; seaweed, as well as mother solutions of Chilean (sodium) nitrate containing up to 0.4% Iodine in the form of sodium iodate. To extract iodine from oil waters (usually containing 20-40 mg/l Iodine in the form of iodides), they are first treated with chlorine (2 NaI + Cl 2 = 2NaCl + I 2) or nitrous acid (2NaI + 2NaNO 2 + 2H 2 SO 4 = 2Na 2 SO 4 + 2NO + I 2 + 2H 2 O). The released iodine is either adsorbed by active carbon or blown out with air. Iodine adsorbed by coal is treated with caustic alkali or sodium sulfite (I 2 + Na 2 SO 3 + H 2 O = Na 2 SO 4 + 2HI). Free Iodine is isolated from the reaction products by the action of chlorine or sulfuric acid and an oxidizing agent, for example, potassium dichromate (K 2 Cr 2 O 7 + 7H 2 SO 4 + 6NaI = K 2 SO 4 + 3Na 2 SO 4 + Cr 2 (SO 4)S + 3I 2). When blown out with air, iodine is absorbed by a mixture of sulfur oxide (IV) with water vapor (2H 2 O + SO 2 + I 2 = H 2 SO 4 + 2HI) and then Iodine is replaced with chlorine (2HI + Cl 2 = 2HCl + I 2). Crude crystalline iodine is purified by sublimation.
Application of Iodine. Iodine and its compounds are used mainly in medicine and analytical chemistry, as well as in organic synthesis and photography.
Iodine in the body. Iodine is a microelement essential for animals and humans. In soils and plants of taiga-forest non-chernozem, dry steppe, desert and mountain biogeochemical zones, iodine is contained in insufficient quantities or is not balanced with some other microelements (Co, Mn, Cu); This is associated with the spread of endemic goiter in these areas. The average iodine content in soils is about 3·10 -4%, in plants about 2·10 -5%. There is little iodine in surface drinking waters (from 10 -7 to 10 -9%). In coastal areas, the amount of iodine in 1 m 3 of air can reach 50 mcg, in continental and mountainous areas it is 1 or even 0.2 mcg.
The absorption of iodine by plants depends on the content of its compounds in the soil and on the type of plant. Some organisms (so-called iodine concentrators), for example, seaweed - fucus, kelp, phyllophora, accumulate up to 1% Iodine, some sponges - up to 8.5% (in the skeletal substance spongin). Algae that concentrate iodine are used for its industrial production. Iodine enters the animal body with food, water, and air. The main source of iodine is plant products and feed. Iodine absorption occurs in the anterior sections of the small intestine. The human body accumulates from 20 to 50 mg of iodine, including about 10-25 mg in the muscles, and 6-15 mg in the thyroid gland. Using radioactive iodine (131 I and 125 I), it was shown that in the thyroid gland Iodine accumulates in the mitochondria of epithelial cells and is part of the diiodo- and monoiodotyrosines formed in them, which condense into the hormone tetraiodothyronine (thyroxine). Iodine is excreted from the body mainly through the kidneys (up to 70-80%), mammary, salivary and sweat glands, partly with bile.
In different biogeochemical provinces, the iodine content in the daily diet varies (for humans from 20 to 240 mcg, for sheep from 20 to 400 mcg). An animal's need for iodine depends on its physiological state, time of year, temperature, and the body's adaptation to the iodine content in the environment. The daily need for Iodine in humans and animals is about 3 mcg per 1 kg of body weight (increases during pregnancy, increased growth, and cooling). The introduction of Iodine into the body increases basal metabolism, enhances oxidative processes, tones muscles, and stimulates sexual function.
Due to a greater or lesser deficiency of Iodine in food and water, iodization of table salt is used, usually containing 10-25 g of potassium iodide per 1 ton of salt. The use of fertilizers containing iodine can double or triple its content in crops.
Iodine in medicine. Preparations containing iodine have antibacterial and antifungal properties, they also have an anti-inflammatory and distracting effect; They are used externally to disinfect wounds and prepare the surgical field. When taken orally, Iodine preparations affect metabolism and enhance thyroid function. Small doses of Iodine (microiodine) inhibit the function of the thyroid gland, affecting the formation of thyroid-stimulating hormone in the anterior pituitary gland. Since iodine affects protein and fat (lipid) metabolism, it has found application in the treatment of atherosclerosis, as it reduces cholesterol in the blood; also increases the fibrinolytic activity of the blood. For diagnostic purposes, radiopaque agents containing iodine are used.
With prolonged use of Iodine preparations and with increased sensitivity to them, iodism may appear - runny nose, urticaria, Quincke's edema, salivation and lacrimation, acne-like rash (iododerma), etc. Iodine preparations should not be taken in case of pulmonary tuberculosis, pregnancy, kidney disease, chronic pyoderma, hemorrhagic diathesis, urticaria.
Iodine is radioactive. Artificially radioactive isotopes of Iodine - 125 I, 131 I, 132 I and others are widely used in biology and especially in medicine to determine the functional state of the thyroid gland and treat a number of its diseases. The use of radioactive iodine in diagnostics is associated with the ability of iodine to selectively accumulate in the thyroid gland; use for medicinal purposes is based on the ability of β-radiation of iodine radioisotopes to destroy the secretory cells of the gland. When the environment is contaminated with nuclear fission products, radioactive isotopes of iodine quickly enter the biological cycle, ultimately ending up in milk and, consequently, in the human body. Their penetration into the body of children, whose thyroid gland is 10 times smaller than that of adults and also has greater radiosensitivity, is especially dangerous. In order to reduce the deposition of radioactive isotopes of iodine in the thyroid gland, it is recommended to use stable iodine preparations (100-200 mg per dose). Radioactive iodine is quickly and completely absorbed from the gastrointestinal tract and selectively deposited in the thyroid gland. Its absorption depends on the functional state of the gland. Relatively high concentrations of radioisotopes of Iodine are also found in the salivary and mammary glands and the mucous membrane of the gastrointestinal tract. Radioactive iodine not absorbed by the thyroid gland is almost completely and relatively quickly excreted in the urine.