Pentafluoro-λ-sulfanyl (SF5) perfluoroalkyl iodides-synthesis and reaction with ethylene and tetrafluoroethylene : Crystal structure of SF5(CF2)4CH2CH2I

A series of reactions between SF₅CF₂CF₂I and SF₅(CF₂)₄I with F₂CCF₂ was carried out in an effort to find the most effective methods for chain-extension. Also, for the first time, SF₅(CF₂)₈I and SF₅(CF₂)₁₀I have been prepared and isolated. The reaction conditions for the addition of H₂CCH₂ were also investigated. A determination of the crystal structure of the SF₅(CF₂)₄CH₂CH₂I has been carried out: the crystal system is monoclinic, with space group P2(1)/n and a=23.465(5) Å; b=6.0971(12) Å; c=44.892(9) Å; α=90°; β=99.38(3)°; γ=90°; Z=20.     

Site directed synthesis of mono and disubstituted SF5-polyfluoroalkyl benzenes

A novel method for the preparation of o-, m-, p-SF₅CF₂CFYC₆H₄X (Y = Br, F and X = m-Br, p-Br, Cl, CH₃, CF₃, NO₂, o-NO₂, F, CF₃, CH(CH₃)₂) derivatives was devised by a two-step reaction: SF₅Br-addition to o-, m-, p-CF₂CFC₆H₄X followed by reaction of AgBF₄ with the o-, m-, p-SF₅CF₂CFBrC₆H₄X adducts. Additional studies have been carried out with several derivatives and includes the preparation of SF₅CF₂C(O)C₆H₅, p-CF₃CFBrC₆H₄NO₂, SF₅CF₂CF₂C₆H₃(NO₂)₂, SF₅CF₂CF₂C₆H₃(NH₂)₂, and an SF₅CF₂CF₂-containing polyimide and dye. The complete characterization (IR, NMR, and MS) of these compounds is given.     

Synthesis of SF5benzene (SF5C6H5) by the SF5halide method

Several significant and useful syntheses of pentafluorothiobenzene (SF₅C₆H₅) from SF₅halides (SF₅X, X=Cl, Br) and cyclohexene or derivatives of cyclohexene are presented.     

Halogen displacement chemistry with silver and alkali metal salts: Preparation of SF5-esters, alcohols, aliphatic olefins, acids and an iodide

It has been found that treatment of SF₅-alkyl halides, especially SF₅(CH₂)₂Br, with silver salts such as CH₃C(O)OAg, p-CH₃C₆H₄SO₃Ag, CF₃SO₃Ag and AgNO₃ provides convenient pathways for preparing the following ester compounds: SF₅CH₂CH₂R (R = CH₃COO, TosO, CF₃SO₃, NO₃), SF₅(CH₂)₃OTos, and SF₅(CF₂)₄(CH₂)₂OAc. Important derivatives prepared from these esters include SF₅(CH₂)₂OH; SF₅(CF₂)₄(CH₂)₂OH. Several alkenes SF₅C(Br)CH₂ and SF₅CH₂(COOCH₃)CCHC(O)OCH₃ are obtained using silver salts. The use of alkali metals salts with SF₅(CH₂)₃Br is studied and yields SF₅(CH₂)₃I; also, a pathway has been developed that extends for SF₅(CH₂)₃₋ the chain by two-carbon atoms and also produces the first SF₅-containing malonic acid.     

Novel sulfur-nitrogen-fluorine compounds : synthesis and properties of SF5NHF,SF5NClF and SF4NF

Using reactions developed for the synthesis of CF₂NF, CF₃NClF and CF₃NHF from ClCN, F₃SN can now be converted in high yield to the analogous sulfur compounds, SF₄NF, SF₅NClF and SF₅NHF. N-fluorotetrafluorosulfurimine is the simplest sulfur(VI) imine and is a rigid molecule. Details on the synthesis and properties of these novel compounds will be presented.     

The unusual chemical equilibria F3SSF ⇌ 2 SF2 and CF3SF2SCF3 ⇌ 2CF3SF

In order to understand more about the instability of sulfur difluoride, we have investigated the chemical interrelations between each of the monomers SF₂ and CF₃SF and the corresponding dimers F₃SSF and CF₃SF₂SCF₃. Thus we have found that SF₂ and CF₃SF exist in chemical equilibria with their dimers. These equilibria are unusual because they involve two different bonds (SF and SS). The equilibrium constants and dissociatíon enthalpies have been determined by i.r. and mass spectroscopic measurements.

The equilibrium between F₃SSF and SF₂ is disturbed by a decomposition reaction of these compounds yielding SF₄ and SSF₂. In both systems (1) and (2) the achievement of the equilibrium is comparatively slow at ?30 to 30 °C. The rates for dissociation and decomposition are strongly surface-dependent and the kinetics of the two processes have been studied separately. Under favorable conditions the half-lives at 298 K for the dissociation of F₃SSF and CF₃SF₂SCF₃ are found to be ca. 8.h and ca. 2 h, respectively, and for the decomposition of SF₂ to SF₄ and SSF₂ and CF₃SF to CF₃SF₃ and CF₃SSCF₃ (p?13 mbar) the values are ca. 10 h and 1 year respectively.     

Inner shell excitation of SF6 by 2.5 keV electron impact

The S 2p, S 2s and F 1s inner shell excitation spectra of SF₆ have been examined by small angle, inelastic scattering of 2.5 keV electrons. While the main features of the spectra are in agreement with previous photoabsorption spectra, a number of new features have been observed. A detailed investigation of the S 2p spectrum below the ionization limit has been performed. The weak Rydberg structure in this region has been interpreted on the basis of a comparison of the present electron energy loss results with previous photoabsorption studies. Part of the Rydberg structure in the electron impact spectrum has been identified as arising from electric quadrupole transitions.     

A convenient and efficient method for incorporation of pentafluorosulfanyl (SF5) substituents into aliphatic compounds

Both SF₅Cl and SF₅Br undergo smooth, high yield addition to alkenes and alkynes under the mild free radical chain reaction conditions of triethylborane initiation at low temperature, although the SF₅Br chemistry is somewhat limited by its competing high electrophilic reactivity with electron rich alkenes. The SF₅Cl addition reaction is relatively insensitive to a wide variety of non-allylic functionalities.     

Direct dynamics studies for the reactions of CF3CHFCF3 and CF3CF2CHF2 with H atoms

The rate constants of the hydrogen abstraction reactions of CF₃CHFCF₃ + H (R1) and CF₃CF₂CHF₂ + H (R2) have been calculated by means of the dual-level direct dynamics method. Optimized geometries and frequencies of stationary points and extra points along the minimum-energy path (MEP) are obtained at the MPW1K/6-311+G(d,p) level, and the classical energetic information is further corrected with the interpolated single-point energy (ISPE) approach by the G3(MP2) level of theory. Using the canonical variational transition state theory (CVT) with small-curvature tunneling corrections (SCT), the rate constants are evaluated over a wide temperature range of 200-2000 K. The calculated CVT/SCT rate constants are in good agreement with available experimental values. It is found that the variational effect is very small and almost negligible over the whole temperature region. However, the small-curvature tunneling correction plays an important role in the lower temperature range. Furthermore, the heats of formation of species CF₃CF₂CHF₂ (SC₁ or SC₂) and CF₃CF₂CF₂ are studied using isodesmic reactions to further elucidate the thermodynamic properties.     

Gas-phase reactions of SF5, SF2, and SOF with O(3 P): Their significance in plasma processing

Reactions of both SF₅ and SF₂ with O(³ P) and molecular oxygen have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For reactions with O(³ P), rate coefficients of (2.0±0.5)×10^–11 cm³ s^–1 and (10.8±2.0)×10^–11 cm³ s^–1 were obtained for SF₅ and SF₂ respectively. The rate coefficients for reactions with O₂ are orders of magnitude lower, with an estimated upper limit of 5×10^–16 cm³ s^–1 for both SF₅ and SF₂. Reaction of SF₂ with O(³ P) leads to the production of SOF which then reacts with O(³ P) with a rate coefficient of (7.9±2.0)×10^–11 cm³ s^–1. Both SO and SO₂ are products in the reaction sequence initiated by reaction between SF₂ and O(³ P). Although considerable uncertainty exists for the heat of formation of SOF, it appears that SO arises only from reaction between SOF and O atoms which is also the source of SO₂. These results are discussed in terms of a reaction scheme proposed earlier to explain processes occurring during the plasma etching of Si in SF₆/O₂ plasmas. A comparison between the results obtained here and those reported earlier for reactions of both CF₃ and CF₂ with O and O₂ shows that there is a marked similarity in the free radical chemistry which occurs in SF₆/O₂ and CF₄/O₂ plasmas.     

The application of novel methodology for the synthesis of o-, m-, and p-(SF5-perfluoroethyl) benzene derivatives

The reaction of o-, m-, and p-F₂CCFC₆H₄X with SF₅Br produces an intermediate adduct, F₅SCF₂CFBrC₆H₄X, which, on treatment with AgBF₄, affords the first useful, high yield preparation of o-, m-, and p-F₅SCF₂CF₂C₆H₄X.     

Electron impact ionization of CCl4 and SF6 embedded in superfluid helium droplets

Electron impact ionization of helium nano-droplets containing several 10⁴ He atoms and doped with CCl₄ or SF₆ molecules is studied with high-mass resolution. The mass spectra show significant clustering of CCl₄ molecules, less so for SF₆ under our experimental conditions. Positive ion efficiency curves as a function of electron energy indicate complete immersion of the molecules inside the helium droplets in both cases. For CCl₄ we observe the molecular parent cation CCl₄⁺ that preferentially is formed via Penning ionization upon collisions with He*. In contrast, no parent cation SF₆⁺ is seen for He droplets doped with SF₆. The fragmentation patterns for both molecules embedded in He are compared with gas phase studies. Ionization via electron transfer to He⁺ forms highly excited ions that cannot be stabilized by the surrounding He droplet. Besides the atomic fragments F⁺ and Cl⁺ several molecular fragment cations are observed with He atoms attached.     

Structures, electron affinities, and vibrational frequencies of the mono-, di-substituted SF6 radicals

Optimized molecular structures, electron affinities, and IR-active vibrational frequencies have been predicted using five different hybrid Hartree–Fock/density functional theory (DFT) methods for a series of mono-, di-substituted SF₆ compounds. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated [J.C. Rienstra-Kiracofe, G.S. Tschumper, H.F. Schaefer, S. Nandi, G.B. Ellison, Chem. Rev. 102 (2002) 231]. The equilibrium configurations of the anions and are found to be a zigzag geometry with ²A electronic state. Three different types of the neutral-anion energy separation reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities of the mono-, di-substituted SF₆ compounds obtained at the KMLYP function are 1.48 eV (SF₆), 3.20 eV (SF₅Cl), 3.49 eV (SF₅Br), 1.59 eV (SF₅CF₃), 3.21 eV (CF₃SF₄Cl), 3.59 eV (CF₃SF₄Br), 1.36 eV (CF₃SF₄CH₃), 2.32 eV (CF₃SF₄CF₃), respectively.     

Derivatives of trifluorovinylsulfur pentafluoride (SF5CFCF2) II

Trifluorovinylsulfur pentafluoride (SF₅CFCF₂) and carbonyl fluoride will add, in the presence of cesium fluoride and acetonitrile, to form SF₅CF(CF₃)C(O)F. This new acid fluoride serves as a source for preparing derivatives containing the SF₅CF(CF₃) - grouping. The following new compounds have been prepared and characterized: SF₅CF(CF₃)X where X = C(O)F, C(O)CH₃, C(O)OH, C(O)NH₂, CN. The dimer, (SF₅CFCF₂)₂, has also been prepared. Infrared, mass, and nmr spectra are presented in order to support their proposed structure.     

Isotopic selectivity in the sensitized dissociation of SF5Cl and CF3I by multiphoton excitation of SF6

The dissociation of SF₅Cl and CF₃I sensitized by multiphoton excitation of SF₆ by a pulsed CO₂ laser has been studied versus pressure, laser fluence, inert gas and optical frequency. Isotopic effects have been observed between ³²SF₅Cl/³³SF₅Cl and between ¹³CF₃I/¹²CF₃I and selectivity factors as high as α^?1_{$\text{33}\text{32}$} = 1.57 or α_{$\text{13}\text{12}$} = 1.23 obtained.     

The reaction of SF5Br with select 1,2-dihaloethylenes

SF₅Br reacts with 1,2-haloethylenes (F, Cl, Br) in distinct ways. In the case of F- and Cl-olefins, the expected addition occurs while with 1,2-dibromoethylene a metathetical reaction yielding in a clean reaction a 1:1 mixture of SF₅CHCHBr and CHBr₂CHBr₂ is found. The mechanism for this reaction is discussed.     

Ab initio quantum chemical studies on the reactions of CF3O2 with OH

The potential energy surface for the CF₃O₂ + OH reaction has been theoretically investigated using the DFT (B3LYP/6-311G(d,p)) level of theory. Both singlet and triplet potential energy surfaces are investigated. The reaction mechanism on the triplet surface is simple. However, the reaction mechanism on the singlet surface is more complicated. It is revealed that the formation of CF₃O + HO₂ is the dominant channel on the triplet surface. The potential energy surface (PES) for this reaction has been given according to the relative energies calculated at the DFT/B3LYP/6-311G(d,p) level. Because this reaction involves both triplet and singlet states, triplet–singlet intersystem crossing (ISC) crossing also have been investigated in this paper.     

Observation of Interference Effects in (e, 2e) Electron Momentum Spectroscopy of SF6 (cited: 1)

Two-dimensional electron density map (2D map) of binding energy and relative azimuthal angle (i.e., momentum) for the outer-valence molecular orbitals of SF₆ has been measured by a highly sensitive electron momentum spectrometer with noncoplanar symmetric geometry at the impact energy of 1.2 keV plus binding energy. The experimental electron momentum profiles for the relevant molecular orbitals have been extracted from the 2D map and interpreted on the basis of the quantitative calculations using the density functional theory with B3LYP hybrid functional. For the outermost F2p nonbonding orbitals of SF₆, the interference patterns are clearly observed in the ratios of the electron momentum profiles of molecular orbitals to that of atomic F2p orbital.     

Pressure-induced phase transitions in Al2(WO4)3

The high pressure behavior of aluminum tungstate [Al₂(WO₄)₃] has been investigated up to ∼18 GPa with the help of Raman scattering studies. Our results confirm the recent observations of two reversible phase transitions below 3 GPa. In addition, we find that this compound undergoes two more phase transitions at ∼5.3 and ∼6 GPa before transforming irreversibly to an amorphous phase at ∼14 GPa.     

Synthesis and reactions of 2-SF5-butadiene

A stable and storable precursor of 2-SF₅-butadiene, 3-SF₅-3-sulfolene, has been synthesized and its reactivity studied with several olefinic compounds. When SF₅Br is added to sulfolene, 3-bromo-4-SF₅-sulfolane is formed and when reacted further with silver tosylate forms 4-SF₅-2-sulfolene. The 4-SF₅-2-sulfolene undergoes rearrangement with silicic acid to give 3-SF₅-3-sulfolene and when heated forms 2-SF₅-butadiene; in the absence of a dienophile, dimerization does occur. The new 2-SF₅-butadiene is a reactive diene undergoing a Diels-Alder reaction with olefinic sytems such as maleic anhydride, p-naphthoquinone, and methyl acrylate.