The pyrazole precursors (149; X = NR) are conveniently obtained by reaction of the appropriate sydnone (148; X = NR) with dibenzoylacetylene 〈74JA4276〉. Method 2. 8.1. This procedure gives complex mixtures of phosphorus products when extended to the synthesis of other symmetrical tetra-alkyl selenopyrophosphates (42). The so-called cold-bluing process uses selenous acid, copper(II) nitrate, and nitric acid to change the color of the steel from silver-grey to blue-grey or black. 75 or 76) (Fig. The mass spectral data for compounds (198) and (199) are compared with their sulfur analogs and the spectral data show the high degree of stability of the three analogs studied. Lide, D.R. The approach suits the synthesis in good yields of simple R = R′ and mixed R ≠ R′ monoselenopyrophosphates. It had been shown that the toxicity of Se is largely due to changes that occur in the tertiary structure of proteins in cases where Se substitutes for S. However, oxidative stress [12, 13] and reactive oxygen species (ROS) may also be factors in Se toxicity [14, 15] associated with carcinogenesis, cytotoxicity, and genotoxicity [16, 17]. Alternatively, the same product can be obtained by treatment of the dioxime (165) with SCl2–DMF 〈75JOC2749〉. The major use is in protecting and changing the color of steel, especially steel parts on firearms. 8.2), HSeO3− and SeO32− are the main species in mild oxidizing environments (Fig. Tetraaryl derivatives (151; R1 and R2 = Ar) are obtained in good yield by thermal dimerization of arylazoethynylarenes (Ar1NNCCAr2) 〈74BCJ946〉. CRC Handbook of Chemistry and Physics. Selenous acid is the principal oxoacid of selenium. A number of methods for the treatment of high selenium levels in water, soils and sediments have been developed [25–30]. The dialkyl trimethylsilyl phosphites are obtained by silylation of dialkyl H-phosphonates (45). 8.2). The bis(dialkylphosphoryl) diselenide (1.5 mmol) in dichloromethane (5 ml) was added to a solution of the corresponding dialkyl trimethylsilyl phosphite (1.5 mmol) in dichloromethane (5 ml) at −100 to −95 °C. Many such salts are quite toxic; for example, about 5 mg of sodium selenate, Na2SeO4, is a fatal dose. Selenic acid, H2SeO4, has been obtained by the oxidation of selenous acid with strong oxidizing agents. Bis(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorinan-2-yl) selenide (55) (41). Geol. In the tellurium series the bis(2,4-dinitrophenylhydrazone) of 1,3-cyclopentadione and tellurium dioxide give only 2% of (208). This extremely exothermic reaction must be conducted at −100 to −95 °C under anhydrous conditions. The 31P NMR spectrum of product (56) confirmed the presence of two different phosphorus nuclei (δPO −22.9 ppm, δPSe 43.6 ppm). Symptoms of selenium poisoning can occur several hours after exposure, and may include stupor, nausea, severe hypotension and death. These remediation technologies are briefly described further. The compounds are gaseous, have vile odors, and are poisonous. Table 8.1. (ed.). Tellurium dioxide is known in several allotropic modifications, none of which is based upon discrete molecules. Table 6. Mp 164–169 °C. Speciation diagrams of selenite [SeO32−, Se(IV)] and selenate [SeO42−, Se(VI)] as a function of pH. The reaction mixture was worked up as described in the previous method. Salts corresponding to the replacement of both one and two hydrogen atoms are known, for example, NaHSeO4, Na2SeO4, Na(H5TeO6), Na2H4TeO6. Linear Formula H 2 SeO 3. 6.7.8). 8.2) [6, 7]. The reaction of phosphorus pseudohalogens with tricoordinate phosphorus compounds offers an alternative route to symmetrical monoselenopyrophosphates (47,48). Interestingly, bis(dialkylphosphoryl) diselenides (76) and (79) are obtained from an analogous reaction of the salts of O,O-dialkyl hydrogen phosphoroselenoates with bis(dialkylphosphoryl) disulfides (5). Red, amorphous selenium, originally known as α-selenium, is precipitated when H2Se is oxidized by air, when selenous acid is reduced, for example, with sulfur dioxide or when metal selenocyanates are reacted with acids. 6.7.7) (5). NACRES NA.22 It is moderately oxidizing in nature, but kinetically slow. The molecular ion is the most intense ion and its fragmentation starts with loss of one NO group followed by a second one. A selenium compound used as a source of SELENIUM, especially for patients that develop selenium deficiency following prolonged PARENTERAL NUTRITION. Here, as in the case of the arsenate and antimonate ions (see above), size factors are important. Both natural and anthropogenic sources contribute to Se contamination of the environment [1, 2]. In the market, selenious acid is available in the form of white crystalline powder by the chemical manufacturers and is offered mostly in the USP grade that makes it applicable for pharmaceutical applications. Selective reaction of dialkyl trimethylsilyl phosphites with O,O-dialkyl O-trimethylsilyl phosphoroselenonates and sulfuryl chloride provides tetra-alkyl monoselenopyrophosphates (58a–f) in excellent yields (Fig. Phosphonium salts (59) are the key intermediates and can transform via nucleophilic attack of the phosphoroselenoate anion on each of the phosphorus and carbon atoms of the phosphonium counter-ion, depending on the stereoelectronic properties of the surrounding substituents. Alternative procedures use copper sulfate and phosphoric acid instead. Treatment of the same salts with aqueous solutions of bis(dialkylphosphoryl) diselenides affords bis(dialkylphosphoryl) diselenides containing the same R groups as those in the salts (e.g. Table 7. The tellurium atom is large enough to bind six—OH groups in an octahedral fashion; the smaller selenium atom can accommodate only four oxygen atoms, and selenic acid, like sulfuric acid, has a tetrahedral molecular structure. The narrowest range is between dietary deficiencies (< 40 μg/day) and toxic levels (> 400 μg/day) [11]. Copyright © 2020 Elsevier B.V. or its licensors or contributors. Warming 5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorinane (2 mol) and selenous acid (1 mol) in benzene–methanol resulted in an exothermic reaction that had to be moderated by cooling in ice to avoid decomposition and formation of red selenium. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. 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