Selenium-Halogen Compounds

Selenium-Halogen Compounds.—Perfluoroethyl selenium trifluoride is produced, in almost 100% yield, by the reaction of bis(perfluoroethyl) di-selenide with chlorine monofluoride in a 1 6 ratio. Like SeF, CaFgSeFa forms 1 1 adducts with CsF and SbFg which are best formulated as Cs+C2F6SeFi and CgFsSeF SbFi , respectively. CypgSeFs is oxidized by QF, at ambient temperatures, according to the equation  

Several perfluoroalkyl derivatives of SF4 and SFg are known, but this appears to be the first report of the preparation of perfluoroalkyl derivatives of Sep4 and SeFg. 

The vibrational spectra of (a) selenium tetrafluoride in the vapour and solid phases, and isolated in inert-gas matrices, and (6) tellurium tetrafluoride, in both the solid and matrix-isolated condition, have been reported. The fundamental frequencies were assigned on the basis of the symmetry of discrete SeF4 and Tep4 molecules force constants, obtained by normal-coordinate analysis, showed that the axial bonds are weaker than the equatorial 

Desjardins, C. Lau, and J. Passmore, Inorg. Nuclear Chem. Letters, 1973, 9, 

A large number of new perfluoroalkyl derivatives of Sep4 and SeP have been prepared. The neutral perfluoroalkyl-selenium(iv) derivatives have structures based on a trigonal bipyramid, with the perfluoroalkyl group(s) preferentially occupying equatorial positions. The vibrational spectrum of CsF,C2p5SeF3 is consistent with an ionic formulation, and the spectra of the pentafluoride adducts suggest a substantial ionic contribution, with anion-cation interaction.  

The stabilization and characterization of the monochlorodiphenylselenonium ion, Ph2SeO, in the form of its adducts with SbCls and SnCL, has been reported. The adducts were assigned ionic structures on the basis of i.r. and conductance data. The PCls-SeCU phase diagram has been studied, and a 1 1 compound that is stable up to 280 C was found.  

Potassium fluoroselenate has been prepared by the reaction of selenium dioxide 

The solid-state reaction of SeOj with V2O5 has been studied by X-ray diffraction methods. In an inert atmosphere the reaction product was the dark red compound Se2V209, which is not isostructural with the corresponding tellurium analogue and which decomposes into its component oxides above 400 The formation of 1 1 complexes between Se02 and SeOCl2 and CP, Br , and I has been reported. The stability constants and nature of the complexes were correlated with those of SO2 and SOCI2, and the role of DMSO as solvent was discussed.  

Standard heats of formation of some gallium selenites and hydrogen selen-ites have been derived from heats of reaction of the salts with 20% HCl. 

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Since dioxiranes are electrophilic oxidants, heteroatom functionalities with lone pair electrons are among the most reactive substrates towards oxidation. Among such nucleophilic heteroatom-type substrates, those that contain a nitrogen, sulfur or phosphorus atom, or a C=X functionality (where X is N or S), have been most extensively employed, mainly in view of the usefulness of the resulting oxidation products. Some less studied heteroatoms include oxygen, selenium, halogen and the metal centers in organometallic compounds. These transformations are summarized in Scheme 10. We shall present the substrate classes separately, since the heteroatom oxidation is quite substrate-dependent. 

A novel class of chalcogen(II) halogen compounds was established recently by the preparation of the first simple binary mononuclear and oligomeric haloanions of divalent selenium and tellurium. The chemistry of these compounds is especially variable for selenium, and a number of highly interesting mono-, di-, tri, tetra- and pentanuclear anionic species with composition X Ym have been synthesized and characterized by structure analyses and spectroscopic studies up... 

Ferrocene organomercurials were also used to prepare a number of other derivatives, namely, halogen-, sulfur-, or selenium-containing compounds, biferrocenyl, or triphenylmethylferrocene [Nesmeyanov, Perevalova, 0. A. Nesmeyanova 258,259)]. Lithiation or sodium metalation provided even more versatile reagents, the reactions being used by other investigators as well. 

Compound classes, not previously described (eg. 5- and 6-membered heteroarenes) Compound classes, for which, in the meantime, significant improvements and progresses have been made, for example carbonic acid derivatives, carboxylic acids and carboxylic acid derivatives, aldehydes, carbonyl derivatives, halogen compounds, peroxides, sulfur, selenium, tellurium, nitrogen and phosphorus compounds. 

Selenium-oxygen bonds. The Se chemical shifts of some inorganic selenium-oxygen compounds are listed in the Tables 2 and 3. It is apparent that Se (Vl)-species are much more shielded (5 = 944-1076 Table 2) than the Se (IV)-species (5 = 1263-1559 Table 3). This holds as well for SeO3, the anhydride of selenic acid (H2SeO4), the halogen derivatives and its alkyl esters and amides. 

Synthesis, reactivity, and applications of sulphur- selenium-, and tellurium-halogen compounds electronic structure and bonding of hypervalent compounds of the heavy main group elements... 

Sihcon and boron bum ia fluorine forming siUcon tetrafluoride [7783-61-17, SiF, and boron trifluoride [7637-07-2] respectively. Selenium and tellurium form hexafluorides, whereas phosphoms forms tri- or pentafluorides. Fluorine reacts with the other halogens to form eight interhalogen compounds (see Fluorine compounds, inorganic-halogens). 

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). 

Chemical Properties. The most significant chemical property of L-ascorbic acid is its reversible oxidation to dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid has been prepared by uv irradiation and by oxidation with air and charcoal, halogens, ferric chloride, hydrogen peroxide, 2,6-dichlorophenolindophenol, neutral potassium permanganate, selenium oxide, and many other compounds. Dehydro-L-ascorbic acid has been reduced to L-ascorbic acid by hydrogen iodide, hydrogen sulfide, 1,4-dithiothreitol (l,4-dimercapto-2,3-butanediol), and the like (33). 

Reaction scheme for the formation of organo-selenium compounds (X = halogen). 

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