Of selenium compounds

This chapter is an attempt to present the important results of studies of the synthesis, reactivity, and physicochemical properties of this series of compounds. The subject was surveyed by Bulka (3) in 1963 and by Klayman and Gunther (4) in 1973. Unlike the oxazoles and thiazoles. there are few convenient preparative routes to the selenazoles. Furthermore, the selenium intermediates are difficult to synthesize and are often extremely toxic selenoamides tend to decompose rapidly depositing metallic selenium. This inconvenience can be alleviated by choice of suitable reaction conditions. Finally, the use of selenium compounds in preparative reactions is often complicated by the fragility of the cycle and the deposition of metallic selenium. 

The possibility of preconcentration of selenium in form of SeO by evaporation of low alkali water solution (for 20-1000 J.g/L) has been investigated. Considerable losses of selenium have been observed during evaporation of acidic and neutral solutions owing to volatility of selenium compounds. During evaporation of low alkali solutions at ph 9-10 there are no losses of selenium. Relative error of selenium determination is 1-2% for 1000 P-g/L solution and 3-5% for 20-100 p.g/L. Concentration factor is 10. 

The physiological properties of selenium compounds are similar to those of arsenic compounds. Any selenium dioxide solid or solution spilled on the skin should be removed immediately by washing under running water. 

In the case of selenium compounds in the presence of water, only gold selenide, AuSe, is formed (309). 

Not only propargyl precursors but also acceptor-substituted 1-methyleneallyl compounds such as 67, 71 or 74 can be used to produce the target allenes by sigmatropic reactions (Scheme 7.10). After oxidation of selenium compounds 67 followed by equilibration of the resulting selenoxides 68 and selenenic esters 69, hydrolysis... 

In a number of reproductive studies in mammals, using a variety of selenium compounds, adverse effects have only been seen at doses that are associated with maternal toxicity "... 

J. Gomez-Ariza, M.-A. Caro-de-la-Torre, I. Giraldez and E. Morales, Speciation analysis of selenium compounds in yeasts using pressurized liquid extraction and liquid chromatography-microwave-assisted digestion-hydride generation-atomic fluorescence spectrometry. Anal. Chim. Acta, 524(1-2), 2004, 305-314. 

Many toning processes in photography involve the use of selenium compounds.6 One such process recently recommended consists in treating the print or lantern slide, after developing, fixing and washing, with a solution containing about 1 per cent, of crystalline sodium sulphide and 1 per cent, of sodium selenite or selenious acid after twenty minutes or so in such a bath intense brown tones are obtained with chlorobromide papers, or brown-violet tones with pure bromide papers.7... 

By the action of hydrazine hydrate on a dilute solution of selenic acid, hydrazine hydrogen selenate may be obtained as a colourless compound which is not decomposed by boiling water, but which, when dry, explodes with great readiness when subjected to heat, to shock, or to fumes of hydrogen chloride. For this reason, before hydrazine hydrate is used in the analysis of selenium compounds (see p. 307), it is essential that selenic acid and selenates should be reduced to selenites by means of hydrochloric acid.3... 

After investigating the action of liquid ammonia on a variety of selenium compounds, Streeker and Claus 5 have come to the conclusion that the tetrahalides are the best initial materials for the preparation of selenium nitride. The action of liquid ammonia on selenium tetra-bromide in the presence of carbon disulphide gives a good yield of the nitride. 

Butyl hypochlorite, 55 of phenols to quinones Benzoyl /-butyl nitroxide, 28 2,3-Dichloro-5,6-dicyano-l, 4-benzoqui-none, 104 Periodic acid, 238 of phosphorus compounds Dimethyldioxirane, 120 of selenium compounds Potassium permanganate, 258 of sulfides to sulfoxides and sulfones /-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 ra-Chloroperbenzoic acid, 76, 112 Dimethyldioxirane, 120 of thiols to sulfur compounds Trimethylsilyl chlorochromate, 327... 

Pure selenium deficiency, wilhoui concurrent vitamin E deficiency, is not generally seen except in animals on experimental diets. In China, selenium deficiency in humans has been associated w ith Keshan disease, a cardiomyopathy seen in children and in women of child-bearing ages, and Kashin-Beck disease, an endemic osteoarthritis in adolescents. Selenium may have amicarcinogenic effects possibly because of the antioxidant properties of selenium compounds. 

Selenium TT assessment of selenium compounds and relationships with uptake in an invertebrate species. I (Maier and Knight, 1993)... 

G6mez-Ariza, J.L., J.A. Pozas, I. Giraldez et al. 1999. Use of solid phase extraction for speciation of selenium compounds in aqueous environmental samples. Analyst 124 75-78. 

Hydrogen selenide irritates the nose, eyes, and lung tissue, and disturbs the digestive and nervous systems. Solutions of selenium compounds may burn the skin and cause severe pain by skin absorption. Selenium dioxide dust irritates the respiratory system, eyes, and... 

The electron impact mass spectra of a series of selenazoles have been compared with those of their thiazole analogs. The results indicate that, in general, the mass spectrometric fragmentation patterns of the selenium heterocycles can be predicted by an examination of the corresponding sulfur analog. One of the characteristics of the mass spectra of selenium compounds is that they are rich in ions due to the presence of the six relatively abundant stable selenium isotopes (81JHC1335). 

M. T. Roberge, A. J. Borgerding, J. W. Finley, Speciation of selenium compounds from high selenium broccoli is affected by the extracting solution, J. Agric. Food Chem., 51 (2003), 4191D4197. 

M. Kotrebai, J. F. Tyson, E. Block, P. C. Uden, HPLC of selenium compounds utilizing perBuorinated carboxylic acid ion-pairing agents and inductively coupled plasma and electrospray ionization mass spectrometric detection, J. Chromatogr. A, 866 (2000), 51D63. 

J. Zheng, M. Ohata, N. Furuta, W. Kosmus, Speciation of selenium compounds with ion-pair reversed-phase liquid chromatography using inductively coupled plasma mass spectrometry as element-specific detection. J. Chromatogr. A, 874 (2000), 55-64. 

R. Lobinski, J. S. Edmonds, K. T. Suzuki, P. C. Uden, Species-selective determination of selenium compounds in biological materials (technical report), Pure Appl. Chem., 72 (2000), 447-461. 

P. Moreno, M. A. Quijano, A. M. Gutierrez, M. C. Perez-Conde, C. Camara, Fractionation studies of selenium compounds from oysters, and their determination by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 16 (2001), 1044-1050. 

E. P. Painter, The chemistry and toxicity of selenium compounds with special reference to the selenium problem, Chem. Rev., 28 (1941), 179-213. 

K. L. Yang, S. J. Jiang, Determination of selenium-compounds in urine samples by liquid chromatography-inductively coupled plasma-mass spectrometry with an ultrasonic nebuliser, Anal. Chim. Acta, 307 (1995), 109-115. 

J. Zheng, Y. Shibata, A. Tanaka, Study of the stability of selenium compounds in human urine and determination by mixed ion-pair reversed phase chromatography with ICP-MS detection, Anal. Bioanal. Chem., 374 (2002), 348-353. 

M. Stadlober, M. Sager, K. J. Irgoli , Effects of selenate supplemented fertilisation on the selenium levels in cereals D identiPcation and quantiPcation of selenium compounds by HPLC-ICP-MS, Food Chem., 73 (2001), 357 D366. 

Figure 3.46 Catalytic oxidation of aromatic aldehydes to phenols in the presence of selenium compounds and hydrogen peroxide.

Use and exposure Selenium is an essential trace element for human health. However, acute and prolonged periods of exposure to high concentrations of selenium compounds cause adverse health effects in humans. The symptoms include garlicky breath irritation of eyes, skin, nose, and throat visual disturbances headache nausea vomiting chills fever weakness violent cough bitter metallic taste in the mouth nose bleeds dyspnea bronchial spasms bronchitis pulmonary edema gastrointestinal tract disturbance ... 

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