Selenium hydrogen

Selenium heterocycles receive far less mention in the literature than do such homologs as oxazole, thiazole, or imidazole. In fact, preparative methods of selenium heterocycles are much more limited than for the other series, mainly because of manipulatory difficulties arising from the toxicity of selenium (hydrogen selenide is even more toxic) that can produce severe damage to the skin, lungs, kidneys, and eyes. Another source of difficulty is the reactivity of the heterocycle itself, which can easily undergo fission, depending on the reaction medium and the nature of the substituents. 

Selenium-hydrogen peroxide oxidation of hydroquinones (Table 10.32)... 

At constant pressure raise the temperature of a system which contains liquid selenium, hydrogen, and gaseous hydrogen selenide for the system in equilibrium the ratio X between the mass of sel nide formed and he possible mass of selenide varies as the temperature is raised this ra io incieases at fiist, passes through a maximum, then diminishes while the temperature continues to ripe. 

The system studied incloses, at constant volume, liquid sele nium, vap>ors of selenium, hydrogen, and selenhydric acid. 

We shall suppose the selenium, hydrogen and selenhydric acid enclosed in a tube where the temperature varies between a lower limit temperature of q the cold extremity) and a higher limit T temperature of the hot extremity). 

Other examples of the use of potassium bromate as an oxidant include the determination of various metals through bromination of anthranilic acid the determination of unsaturation As(III) Sb(III) Fe(II) in the presence of organic substances mixtures of iodide, bromide, and chloride hypophos-phite Cu(I) T1(I) selenium hydrogen peroxide and hydrazine. 

The selenium compounds that are most likely to be encountered in air in occupational settings are dusts of elemental selenium, hydrogen selenide, and selenium dioxide. Other volatile selenium compounds (e.g., dimethyl selenide, dimethyl diselenide) might be encountered in some naturally occurring situations. Because selenium is converted from one form to another, as in plant biosynthesis of selenoamino acids, it is not clear which specific forms may be encountered at hazardous waste sites. If a hazardous waste site specifically contains deposits of compounds of selenium, those compounds could be released off-site in dust or air. Toxicity data for exposures via inhalation are available for elemental selenium, selenium dioxide, selenium oxychloride, hydrogen selenide, and dimethyl selenide. Because there are few studies of inhalation of selenium of any single form, all available studies of inhalation exposures to selenium compounds will be included in this discussion. 

Characteristic Selenium Hydrogen selenide Selenic acid Selenious acid... 

CHEMICAL PROPERTIES very stable under ordinary conditions of use and storage thermally very stable hazardous polymerization will not occur practically inert to water hydrolyzes very slowly in cold water reaction with ammonia gas at 200°C (392°F) yields selenium, hydrogen fluoride, and nitrogen covalently saturated does not attack glass FP (not applicable) LFL/UFL (not applicable) AT (not applicable) HC (not applicable) HF (-1117.0 kJ/mol gas at 25°C). 

Hydrogen selenide solidifies at —64° and boils at —42 under atmospheric pressure. Pure hydrogen selenide is colorless however, in the presence of moisture, it is decomposed rapidly by oxygen, with deposition of red selenium. Hydrogen selenide burns with a blue flame. 

Recent work discusses the analysis of 23 elements in urine using ICP-MS with CCT. In this methodology by Heitland et al. different cell gases were employed for selenium (hydrogen) than for the other elements (helium). This work does not mention the capability of CCT gas switching mode where in theory it should be possible to purge one collision gas from the cell and introduce another. 

Sulphur is less reactive than oxygen but still quite a reactive element and when heated it combines directly with the non-metallic elements, oxygen, hydrogen, the halogens (except iodine), carbon and phosphorus, and also with many metals to give sulphides. Selenium and tellurium are less reactive than sulphur but when heated combine directly with many metals and non-metals. 

Hydrogen selenide (selenium hydride), HjSe, and hydrogen telluride (tellurium hydride), HjTe... 

Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions. 

Hydrogen selenide in a concentration of 1.5 ppm is intolerable to man. Selenium occurs in some solid in amounts sufficient to produce serious effects on animals feeding on plants, such as locoweed, grown in such soils. Exposure to selenium compounds (as Se) in air should not exceed 0.2 mg/m3 (8-hour time-weighted average - 40-hour week). 

Chromic(VI) acid Acetic acid, acetic anhydride, acetone, alcohols, alkali metals, ammonia, dimethylformamide, camphor, glycerol, hydrogen sulflde, phosphorus, pyridine, selenium, sulfur, turpentine, flammable liquids in general... 

Selenium is an essential element and is beneficial at low concentrations, serving as an antioxidant. Lack of selenium affects thyroid function, and selenium deficiencies have been linked to Keshan Disease (34). Selenium at high levels, however, is toxic. Hydrogen selenide (which is used in semiconductor manufacturing) is extremely toxic, affecting the mucous membranes and respiratory system. However, the toxicity of most organ oselenium compounds used as donor compounds for organic semiconductors is not weU studied. 

Laser isotope separation techniques have been demonstrated for many elements, including hydrogen, boron, carbon, nitrogen, oxygen, sHicon, sulfur, chlorine, titanium, selenium, bromine, molybdenum, barium, osmium, mercury, and some of the rare-earth elements. The most significant separation involves uranium, separating uranium-235 [15117-96-1], from uranium-238 [7440-61-1], (see Uranium and uranium compounds). The... 

Wet chlorination is performed by sparging slimes slurried either in water or hydrochloric acid using chlorine gas, or other oxidants such as sodium chlorate or hydrogen peroxide which Hberate chlorine from hydrochloric acid, at about 100°C. Under these conditions, selenium and selenides rapidly oxidize and dissolve. 

Selenides. Selenium forms compounds with most elements. Biaary compounds of selenium with 58 metals and 8 nonmetals, and alloys with three other elements have been described (55). Most of the selenides can be prepared by a direct reaction. This reaction varies from very vigorous with alkah metals to sluggish and requiring high temperature with hydrogen. 

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

Contact with elemental selenium does not injure the skin. Selenium dioxide, however, upon contact with water, sweat, or tears, forms selenous acid, a severe skin irritant. Selenium oxyhaHdes are extremely vesicant and cause bums when in contact with human skin (91,92). Hydrogen selenide affects the mucous membranes of the upper respiratory tract and the eyes (93). 

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