Selenium, cyanates

Selen-verbindung, /. selenium compound, -wasserstoff, m, hydrogen selenide. -was-serstoffsaure, /. hydroselenic acid, -wismut-glanz, m. guanajuatite. -zelle, /. selenium cell, -zyanid, n. selenium cyanide seleno cyanate. -zyankalium, n. potassium selenocyanate. 

Cyanate condensation products of carbohydrazide, synthesis 11 Thiosemicarbazide, synthesis 12 Dithiocarbamates of selenium(II) and tellurium (II), synthesis 32 Aluminum phosphide, synthesis 7 Phosphorus(III) fluoride, synthesis 49... 

Selenocyanate groups can be linked to tellurium via the nitrogen or selenium atoms. In view of this uncertainty, cyanates, thiocyanates, and selenocyanates are discussed under diorgano dinitrogen compounds (page 639). 

A striking difference to the reactions with cyanate and thiocyanate [Eq. (95)] has been found with potassium selenocyanate. Elemental selenium is precipitated and cyanide ion is the reactive species in accordance with Eq. (86) (237). 

The cyanate ion has the ground-state electronic configuration lu , 2a, 3o , 4a, 6o, 6u , Itt the thiocyanate and subsequent ions are similar unless account is taken of the core electrons or empty d orbitals of sulfur, selenium, or tellurium which increase the complexity of the ground-state description. The most sophisticated calculations that have been carried out on these ions are those of McLean and Yoshimine 506) on NCO" and NCS . The calculated orbital energies are given in Table... 

The preceding sections have shown that the behavior of the thiocyanate and selenocyanate groups in homogeneous complex anions is identical in both cases the nitrogen atom coordinates to the class a metal, and the sulfur or selenium atoms coordinate to the class b metal. Although fewer comparable cyanate complexes are known, it is quite clear that the coordination of the cyanate group is not governed by the same factors. 

It may be concluded, therefore, that attempts to provide too detailed a comparison of the coordination behavior of the chalcogeno-cyanate ions are not useful until a better understanding is obtained of the differing effects of the cyano group on the atom X in NCX . Such an interaction may, and probably does, modify the comparative chemistry that might be expected for the oxygen, sulfur, or selenium... 

NIOSH REL TWA CL 5 mg/mVlOM SAFETY PROFILE Poison by intraperitoneal route. When heated to decomposition it emits very toxic fumes of NOx, CN", K2O, and Se. See also SELENIUM COMPOUNDS and CYANATES. 

Entries 1 and 2 in Table 8 are examples of an overall antarafacial 1,3-transposition of a hydroxy group by selenium compounds20,21. Treatment of the alcohols with 2-nitrophenyl seleno-cyanate in the presence of tributylphosphine gave the selenide with inversion of configuration. Oxidation with hydrogen peroxide led to the selenoxide, which rearranged suprafacially to the allylic alcohol. 

Most of the examples of seleniranes and telluriranes shown as the unstable intermediates in the organic synthesis are derived from oxiranes. As discussed previously in Section 1.07.6.2, seleno-cyanate anions react with epoxides at room temperature to deposit selenium via the selenirane intermediate and form the corresponding alkenes. On the other hand, triphenylphosphine selenide and trifluoroacetic acid constitute an effective and mild combination of reagents for carrying out the deoxygenation of epoxides (67) to alkenes via cyclic intermediate (68) (Scheme 12) <73CC253>. 

Salcomine, 360 Salicylaldehyde, 96, 217, 457 Sandmeyer reaction, 87 o-Santalene, 291 Schiff bases, 66, 249 Selenium dioxide, 93, 360-362 Selenium dioxide-Hydrogen peroxide, 362 Semicarbazide, 98 Semicarbazones, 65 Sensitizers, 285-286 L-Serine, 143 Serini reaction, 459, 460 Silica gels, 453 Silver acetate, 233, 362-363 Silver benzoate, 103 Silver carbonate, 363 Silver chlorate, 363-364 Silver cyanate, 224 Silver fluoride, 364-365 Silver fluoroborate, 365-366 Silver nitrate, 224, 240, 363, 366-368, 369, 371... 

Unprotected D-fructosamines react with isothio- or isoseleno-cyanates (Scheme 48) affording respectively 4-hydroxy-4-polyhydroxyalkylimidazolidine-2-thiones or -selones 95. " ° "" The latter were readily dehydrated to give the respective imidazo-line-2-thiones and -selones 96 and 97, which in effect are stable sulfur- and selenium-containing C-nucleosides. 

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