Selenium, carbonates

The lO-E-4 chalcogen(IV) species diphenylselenium(IV) dibromide (1, Fig. 1) and diphenyltellurium(IV) dibromide (2, Fig. 1) oxidize thiophenol to diphenyl disulfide in nearly quantitative yield as shown in equations (13) and (14). Tellurium(IV) dihalides 6-11 also oxidize thiophenol to diphenyl disulfide and benzene selenol to diphenyl diselenide. Similarly, the 12-Te-5 molecule dioxatellurapentalene 45 (Fig. 19) is a mild oxidant for ethylmercaptan, thiophenol, and benzene selenol giving diethyl disulfide, diphenyl disulfide, and diphenyl diselenide in essentially quantitative yield. As shown in equation (15), 1,1,5,5,9,9-hexachloro-1,5,9-tritelluracyclododecane oxidizes six molecules of thiophenol to diphenyl disulfide and 1,5,9-tritelluracyclododecane in 90% yield. In contrast, 12-Te-5 pertellurane 44 and 12-Se-5 perselenane 46 do not oxidize thiophenol to diphenyl disulfide. Instead, these molecules undergo a nucleophilic addition of thiophenol followed by cleavage of the tellurium-carbon or selenium-carbon bond. ... 

Support-bound organoselenium compounds have mainly been used as synthetic intermediates and linkers. The use of organoselenium compounds as linkers for solid-phase synthesis has been investigated by several groups [1-4]. The selenium-carbon bond is stable under a broad variety of reaction conditions, but can be selectively cleaved by tin radicals or by oxidants (see Sections 3.15.1 and 3.16.4). 

There were 37 distinct enzymes that contain molybdenum or tungsten known by the end of 1997. The enzymes are diverse in function, broadly distributed, and include oxidases, reductases, dehydrogenases, a transhydroxylase, and a hydratase. The Mo enzymes are found in eubacteria, archae, protista, fungi, plants, and animals (including humans) and are essential for respiration and carbon and nitrogen assimilation. Several of the enzymatic substrates and products are key components in the nitrogen, sulfur, selenium, carbon, and arsenic cycles and have major biological and environmental impact. 

Compounds with Selenium-Carbon Double Bonds 486... 

The nucleophilicity of selenolates is significantly higher than that of the corresponding thiolates. This property allows selenolates to be useful reagents in organic synthesis. Moreover, removal of the selenium moiety from the reaction products is easier because the selenium - carbon bond is weaker than the sulfur-carbon bond [3 b]. 

In Older to avoid the handling of poisonous hydrogen selenide, two other useful syntheses have been devised. One method uses the reaction of aromatic nitriles with aluminum selenide in the presence of pyridine, triethylamine and water (Scheme 24), while the other is performed by the reaction of nitriles with selenium, carbon monoxide and water in the presence of triethylamine (Scheme 25). These methods are exceedingly convenient in terms of manipulation without the isolation of hydrogen selenide for the preparation of selenoamides. Using these methods, a variety of aromatic and heterocyclic selenoamides can be obtained from the corresponding nitriles in high yields. 

Convenient one-pot syntheses of iV-substituted selenoamides from nitriles, metallic selenium, carbon monoxide, water and amines have been developed on the basis of an amino group exchange reaction between the IV-unsubstituted selenoamides formed in situ and the primary or secondary amines. Aromatic or aliphatic, and IV-mono- or IVA -di-substituted selenoamides can be obtained in good yields by this method (Scheme 27). 

In the cases of primary amines, the corresponding selenoamides have also been obtained from nitriles, selenium, carbon monoxide and excess primary amines by a single step mixing at the beginning of the reaction (Scheme 28). ... 

Miscellaneous components (maleic anhydride, aconitic acid, selenium, carbon disulfide)... 

Oligo mineral elements 0.5% (e.g., zinc, copper, selenium) Carbon hydrates 2.0% (mucopolysaccharides)... 

Krivdin and co-workers have performed four-component relativistic calculations of V(Se,C) spin-spin coupling constants in a series of 13 selenium heterocycles and their parent open-chain selenides. The authors concluded that relativistic effects play an essential role in the selenium-carbon coupling mechanism and could result in a contribution of as much as 15-25% of the total values of the V (Se,C). In the overall... 

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