Selenides fluorination

Nitrogen and sodium do not react at any temperature under ordinary circumstances, but are reported to form the nitride or azide under the influence of an electric discharge (14,35). Sodium siHcide, NaSi, has been synthesized from the elements (36,37). When heated together, sodium and phosphoms form sodium phosphide, but in the presence of air with ignition sodium phosphate is formed. Sulfur, selenium, and tellurium form the sulfide, selenide, and teUuride, respectively. In vapor phase, sodium forms haHdes with all halogens (14). At room temperature, chlorine and bromine react rapidly with thin films of sodium (38), whereas fluorine and sodium ignite. Molten sodium ignites in chlorine and bums to sodium chloride (see Sodium COMPOUNDS, SODIUM HALIDES). 

The potentiostatic electrodeposition of iron selenide thin films has been reported recently in aqueous baths of ferric chloride (FeCb) and Se02 onto stainless steel and fluorine-doped TO-glass substrates [193], The films were characterized as polycrystalline and rich in iron, containing in particular a monoclinic FesSea phase. Optical absorption studies showed the presence of direct transition with band gap energy of 1.23 eV. 

An oxygen bound to a trifluoromethyl group has much less effect upon its chemical shift than a chlorine substituent. Thus, the fluorines of trifluoromethyl ethers (—58 ppm) are not as deshielded as those of CF3C1 (—28ppm). Those of CF3 sulfides and selenides are deshielded... 

In contrast to the cathodic reduction of organic tellurium compounds, few studies on their anodic oxidation have been performed. No paper has reported on the electrolytic reactions of fluorinated tellurides up to date, which is probably due to the difficulty of the preparation of the partially fluorinated tellurides as starting material. Quite recently, Fuchigami et al. have investigated the anodic behavior of 2,2,2-trifluoroethyl and difluoroethyl phenyl tellurides (8 and 9) [54]. The telluride 8 does not undergo an anodic a-substitution, which is totally different to the eases of the corresponding sulfide and selenide. Even in the presence of fluoride ions, the anodic methoxylation does not take place at all. Instead, a selective difluorination occurs at the tellurium atom effectively to provide the hypervalent tellurium derivative in good yield as shown in Scheme 6.12. 

The S- and Se-(perfluoroalkyl)dibenzothiophenium salts 17-27 were synthesized according to three methods (Eq. 4) (1) fluorination of the corresponding sulfide 1-6 or 8 or selenide 11 or 12 with F2 in the presence of an acid or a Lewis acid (2) fluorination with F2, followed by treatment with an acid or a Lewis acid and (3) treatment of sulfoxide 13, 14, or 15 or selenoxide 16 with triflic anhydride (Tf20). Sulfoxides 13-15 and selenoxide 16 were prepared by oxidation of the corresponding sulfides or selenide with m-chloroperbenzoic acid. 

Selenium atoms in organo-fluorine compounds are oxidized to higher oxidation states by the same or similar methods to those used for organosulfur compounds. Thus, fluoroalkyl selenides 1 are oxidized to higher oxidation state compounds 2 by rer(-butyl hypochlorite under mild conditions.215... 

Fluorination of diaryl sulfides, selenides, and tellurides leads to the formation of diarylsulfur, selenium, and tellurium difluorides, all of... 

The difluoroselenanes which are formed under mild reaction conditions in high yields after fluorination of selenides with xenon difluoride are more stable than the corresponding difluorosulfuranes115,116 (Scheme 49). 

Until recently, no selenium monohalide could be isolated only the short-lived radicals SeF, SeCl, and SeBr were identified in the gas phase. SeF, can be produced by reaction of fluorine atoms (by passing CF4 through a microwave discharge) with carbonyl selenide in a flow system. It has been detected by ESR spectroscopy and the Se-F bond length (1.742 A) is close to the value reported for SeF2 (1.69 A), deduced from infrared spectra. ... 

Silver and silver selenide thin films were prepared from a series of liquid silver precursors containing /3-diketonates and phosphite ligands (Table 5) as demonstrated by Shim and coworkers. In a typical deposition experiment, Ag(tfac)(P(OEt)3) produced very pure silver films under relatively mild conditions (170 °C) without any appreciable amount of fluorine, oxygen and phosphorus impurities. These films could easily be converted to Ag2Se by selenium vapor deposition . 

More recently, it has been reported [7] that similar properties were observed for Se-trifluoromethylated dibenzoselenonium salts. Se-(Trifluoromethyl) dibenzoselenophenium triflate (4) was successfully synthesized in high yield by the direct fluorination of an equimolar mixture of the selenide 5 and triflic acid (TfOH) with diluted molecular fluorine. The same salt was also obtained by cyclization of the selenoxide 6 with triflic anhydride (Tf2 0) - a reaction which probably occurs via the selenonium salt 7 (Scheme 1). 

Several oxaziridines related to (14) (eq 8) have been used, most notably in the enantioselective oxidation of sulfides to sulfoxides, of selenides to selenoxides, and of alkenes to oxiranes, It is also the reagent of choice for the hydroxylation of lithium and Grignard reagents and for the asymmetric oxidation of enolates to give a-hydroxy carbonyl compounds, - A similar chiral fluorinating reagent has also been developed, ... 

Anodic monofluorination of selenides bearing electron-withdrawing cyano and ester groups can be performed in an undivided cell, while the fluorination of a-selenoamide requires an anion-exchange membrane diaphragm [51] ... 

A fluorinated selenide linker for solid-phase synthesis of NPGs... 

EXPLOSION and FIRE CONCERNS combustible solid NFPA rating (NA) reacts to form explosive products with metal amides contact with acids may cause formation of poisonous hydrogen selenide gas incompatible or reacts violently with barium carbide, bromine pen-tafluoride, chromic oxide, fluorine, lithium carbide, lithium silicon, metals, nickel, sodium, nitric acid, nitrogen trichloride, oxygen, potassium, potassium bromate, rubidium carbide, zinc, silver bromate, uranium, strontium carbide, and thorium carbide toxic gases and vapors may be released in a fire involving selenium, sodium selenite, sodium selenate, and selenium dioxide use water for firefighting purposes. 

Fluorinated selenides were also used as the source of polyfluoroalkyl radicals. Homolytic decomposition of 22 and 23 under UV irradiation in the presence of furan gives 2-polyfluoroalkyl furans. 

The oxidation potentials of various fluoroalkyi sulfides, selenides, and tellurides have been determined by use of cyclic voltammetry. These substances exhibit irreversible multiple anodic waves. In Table 5 is summarized the first oxidation peak potentials ( p) of these substances together with those of some nonfluorinated and other electronegatively substituted chalcogeno compounds. In all cases, the fluorinated compounds are oxidized at more positive potentials than the corresponding nonfluorinated compounds because of the electron-withdrawing effects of fluoroalkyi groups. It should be noted... 

It should be noted that selenides 44d and 44e bearing an additional electron-withdrawing group (e.g., ester or chlorine atom) provide fluorinated selenides 45d and 45e in moderate yields, while a-alkyl-ated a-seleno-substituted ester 44f gives only a trace amount of the fluorinated product 45f (run 8). 

According to these results, the anodic fluorination reactions of selenides seem to involve fluoroselenonium ions L as a key intermediate in a manner similar to that seen in the case of sulfides. In fact, a... 

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