Йод

Описание

Iodine was discovered in 1811 by Bernard Courtois, and is classed among the rarer elements. Iodine is found naturally in seaweed, and is considered and generally recognized as safe substance by the US Food and Drug Administration (FDA). Iodine is a required element by many species, including humans. It has been recognized as preventative against goiter since 1819, and is used in iodized salt for this purpose. Iodine is also used as a dough oxidizer in commercial bread making. Iodine is generally extracted from natural and oil field brines by means of oxidation of iodide with chlorine, then removal from solution with an airstream. Iodine is reabsorbed in solution and reduces to hidrotic acid with sulfur dioxide. The solution is then chlorinated to precipitate free iodine, and is further purified by treatment with concentrated sulfuric acid. Iodine is the heaviest essential element for most life, with tungsten being used by some bacteria.

Физические свойства

Bluish-black orthorhombic crystals; refractive index 3.34; density of solid4.933 g/cm3at 20°C; density of the element in liquid form at 120°C 3.96 g/cm3;melts at 113.6°C to a black mobile liquid; the solid can be sublimed to vaporbelow its melting point; vapor pressure of solid at 25°C 0.3075 torr; vaporpressure at 113.6°C 90.5 torr; the liquid boils at 184.3°C giving violet vapors;vapor density 6.75 g/L; critical temperature 545.8°C; critical pressure 48.9atm; critical volume 155 cm3/mol; dielectric constant of solid 10.3 at 23°C and liquid 11.08 at 118°C; resistivity 5.85 x 106ohm-cm at 25°C, and 1.10 x 105ohm-cm at 140°C; slightly soluble in water, 0.33 g/L at 25°C; soluble inethanol, carbon disulfide, benzene and chloroform, forming brown solutions;sulfur, selenium, metal iodides and many organic compounds dissolve in liq-uid iodine.

Использование

Iodine is used in the manufacture of manyiodine compounds; in photographic materi als; as an antiseptic, disinfectant, and germi cide; and as a reagent in analytical chemistry.It occurs in traces in seawater and in igneousrocks.

Методы производства

In the United States, the principal method used to recover iodine from oil brines involves the oxidation of iodide by chlorine, followed by removal of the volatile iodine from solution with an airstream. The iodine is reabsorbed in solution and reduced to hidrotic acid with sulfur dioxide. The solution is then chlorinated to precipitate free iodine, which is further purified by treatment with concentrated sulfuric acid. The same process is used to recover iodine from natural brines. In the recovery of iodine from Chilean nitrate deposits, solutions containing the iodates are reduced with sodium bisulfite to precipitate the iodine, which is then purified by sublimation.

Определение

ChEBI: Molecule comprising two covalently bonded iodine atoms with overall zero charge..

Биологические функции

Inhibition of the release of thyroid hormone by iodide is the basis for its use in hyperthyroidism. Iodide decreases the vascularity of the enlarged thyroid gland and also lowers the elevated BMR. It also has been suggested that excess iodide might change the conformation of thyroglobulin, making the protein less susceptible to thyroidal proteolysis.

Общее описание

Violet-black crystals with a metallic luster and a sharp odor. Mp: 133.5°C, bp: 185°C. Emits toxic vapor at room conditions; vapor becomes visibly purple when its concentration builds up in a confined space. Nearly insoluble in water but very soluble in aqueous solutions of iodides.

Профиль реактивности

Iodine is an oxidizing agent. Reacts vigorously with reducing materials. Incompatible with powdered metals in the presence of water (ignites), with gaseous or aqueous ammonia (forms explosive products), with acetylene (reacts explosively), with acetaldehyde (violent reaction), with metal azides (forms yellow explosive iodoazides), with metal hydrides (ignites), with metal carbides (ignites easily), with potassium and sodium (forms shock-senstive explosive compounds) and with alkali-earth metals (ignites). Incompatible with ethanol, formamide, chlorine, bromine, bromine trifluoride, chlorine trifluoride.

Опасность

Iodine vapors are an irritant to eyes, nose and mucous membranes.Inhalation can cause headache, irritation, and congestion of lungs. Oralintake can produce burning of the mouth, vomiting, diarrhea, and abdominalcramps. Skin contact can cause rashes.

Угроза здоровью

The acute toxicity of iodine by inhalation is high. Exposure may cause severe breathing difficulties, which may be delayed in onset; headache, tightness of the chest, and congestion of the lungs may also result. In an experimental investigation, four human subjects tolerated 0.57 ppm iodine vapor for 5 min without eye irritation, but all experienced eye irritation in 2 min at 1.63 ppm. Iodine in crystalline form or in concentrated solutions is a severe skin irritant; it is not easily removed from the skin, and the lesions resemble thermal burns. Iodine is more toxic by the oral route in humans than in experimental animals; ingestion of 2 to 3 g of the solid may be fatal in humans.
Iodine has not been found to be carcinogenic or to show reproductive or developmental toxicity in humans. Chronic absorption of iodine may cause insomnia, inflammation of the eyes and nose, bronchitis, tremor, rapid heartbeat, diarrhea, and weight loss.

Воспламеняемость и взрывоопасность

Iodine is noncombustible and in itself represents a negligible fire hazard when exposed to heat or flame. However, when heated, it will increase the burning rate of combustible materials.

Экологическая судьба

Iodine is released into the environment during nuclear explosions, as well as around any fuel rods, primarily spent. Due to iodine’s uses, it is frequently released into the environment, but adsorbs many minerals as well as organic masses, which inhibit transport.

хранилище

safety goggles and rubber gloves should be worn when handling iodine, and operations involving large quantities should be conducted in a fume hood to prevent exposure to iodine vapor or dusts by inhalation.

Методы очистки

It is usually purified by vacuum sublimation. Preliminary purifications include grinding with 25% by weight of KI, blending with 10% BaO and subliming, subliming with CaO, grinding to a powder and treating with successive portions of H2O to remove dissolved salts, then drying, and recrystallising from *benzene. Barrer and Wasilewski [Trans Faraday Soc 57 1140 1961] dissolved I2 in concentrated KI and distilled it, then steam distilled it three times and washed it with distilled H2O. Organic material is removed by sublimation in a current of O2 over platinum at about 700o, the iodine being finally sublimed under vacuum. HARMFUL VAPOURS.

Несовместимости

Iodine is stable under normal temperatures and pressures. Iodine may react violently with acetylene, ammonia, acetaldehyde, formaldehyde, acrylonitrile, powdered antimony, tetraamine copper(II) sulfate, and liquid chlorine. Iodine can form sensitive, explosive mixtures with potassium, sodium, and oxygen difluoride; ammonium hydroxide reacts with iodine to produce nitrogen triiodide, which detonates on drying.

Утилизация отходов

Excess iodine and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines. For more information on disposal procedures, see Chapter 7 of this volume.

Меры предосторожности

Students, users, and occupational workers should specially note iodine as: Poison, Danger, and Corrosive. Exposures cause severe irritation or burns to every area of contact. It may be fatal if ingested/swallowed/inhaled. The vapors cause severe irritation to the skin, eyes, and respiratory tract. Iodine is a strong oxidizer and contact with other material may cause fi re. Occupational workers should wear impervious protective clothing, boots, gloves, a lab- oratory coat, apron or coveralls, as appropriate, to prevent skin contact of iodine. Also, workers should use chemical safety goggles and/or a full-face shield where splashing is possible. Maintain an eye-wash fountain and quick-drench facilities in the work area.