- Temperature-enhanced electron detachment from C6F6- negative ions
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A method is described whereby photoelectrons generated by a short laser pulse at the cathode of a parallel-plate electrode arrangement are depleted by attachment to C6F6 molecules mixed with N2 in the interelectrode space as they drift to the anode under an externally applied electric field.The contribution of the initially produced (prompt) and the delayed (autodetached from C6F6-) electrons to the induced signal in the detector circuit is recorded as a function of time following the laser pulse and also as a function of gas number density, applied electric field, and gas temperature, T.Increases in T from ambient to 575 K enhance dramatically the autodetachment frequency, τd-1, for C6F6-.This heat-activated autodetachment correlates with the increase in the internal energy of the anion and has an activation energy of 0.477 eV.Electron attachment producing C6F6- initially increases slightly with increasing T below 500 K and subsequently decreases with further increases in T.
- Datskos, P. G.,Christophorou, L. G.,Carter, J. G.
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- Perfluorobarrelene
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The title fluorocarbon has been synthesized in three steps from cis-5,6-dichlorohexafluorocyclohexa-1,3-diene, a hexafluorobenzene synthon. Photolysis of perfluorobarrelene yields perfluorocyclooctatetraene. An extremely facile retro-Diels-Alder reaction is also described.
- Ralli, Philip,Zhang, Yin,Lemal, David M.
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- Laser Photodetachment Spectra of C6F6- in Nonpolar Liquids
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Aromatic anions absorb in the visible region of the spectrum and energetic considerations suggest that in solution photodetachment may be an important process at these wavelengths.This study reports electron photodetachment cross sections for C6F6- for wavelengths between 415 and 700 nm.The anion is generated by electron attachment to solute C6F6 during an X-ray pulse.Detachment is observed as a change in conductivity induced by a subsequent light pulse from a tunable dye laser.The threshold values are reported for tetramethylsilane, n-butane, cyclopentane, n-pentane, 2,2,4-trimethylpentane, 2,2-dimethylbutane, and neopentane.The thresholds are consistent with an electron affinity of 1.09 +/- 0.04 eV for the C6F6 molecule.Comparison of the data to the absorption spectrum of C6F6- shows that for proton energies above threshold the major process is photodetachment.The relationship of photodetachment data to other properties of the excess electrons in these solvents is discussed.
- Sowada, Ulrich,Holroyd, Richard A.
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- Progress toward an absolute gas-phase proton affinity scale
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The temperature dependence of the proton transfer equilibrium constants for approximately 80 pairs of bases ranging in proton affinity from N2 to tert-butylamine has been examined. These data provide the basis for formulation of a revised gas-phase proton affinity scale which now appears to have a firm basis. Excellent agreement with appearance energy determinations of proton affinities as well as ab initio calculated values is obtained. An important finding of this work is that the value of ΔHfo for the tert-butyl cation must be significantly higher than that derived from appearance energy measurements by Traeger which had formed the basis for the proton affinity assignment for isobutene, an important reference point in the proton affinity scale. The data obtained here would suggest that the proton affinity of isobutene must be revised downward by Δ4 kcal mol-1 with important consequence for all proton affinities in the vicinity of isobutene and above. In addition significant revisions are indicated for proton affinities between those of propene and isobutene. In contrast, however, the substantial upward revision of the proton affinity scale in the basicity region above ammonia which had been proposed by Mautner and Sieck (J. Am. Chem. Soc. 1991, 113, 4448) is not supported by the present experiments.
- Szulejko,McMahon
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- Ionizing reaction cross sections in the collision of argon atoms in high Rydberg states with various molecules
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Measurements of absolute ionizing reaction cross sections in collisions between argon atoms in high Rydberg states (HR) and CCl4, CCl3F, CH3I, CF6, C6F6, CF4, and CO are reported together with their dependence on the HR argon velocity (570-2100 m/sec).The identity of the positively and negatively charged reaction products has been investigated with a coincidence TOF mass spectrometer.A comparison of the present data with results of other bound and free electron experiments and theoretical predictions is given.
- Dimicoli, I.,Botter, R.
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- Ion-pair formation in the collision of high Rydberg argon atoms with SF6 and C6F6 and negative ion lifetimes
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The ion-pair formation in collision between argon atoms in high Rydberg states (HR) with SF6 and C6F6 has been investigated.The absolute cross sections are inversely proportional to the Ar(HR) velocity and increase monotonically with increasing principal quantum number n.Measurements of the negative ion lifetimes against autodetachment are reported and are above 20μsec for SF6- and ca 1μsec and above 20 μsec for C6F6-.The present data are reviewed in light of the theoretical predictions of "free electron" models and the results of free electron experiments.
- Dimicoli, I.,Botter, R.
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- Magnetic field effects on recombination fluorescence in liquid iso-octane
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The 123.6 nm photoionization of deuterated isooctane at -10 deg C in the presence of hexafluorobenzene has been studied by examining the effect of a magnetic field to alter the quantum yield of recombination fluorescence.This fiuorescence results from geminate recombination of hexafiuorobenzene anions with isooctane positive ions.The use of a deuterated as contrasted to a protonated alkane makes the intensity of the recombination fluorescence much more sensitive to the magnetic field and permits observation of two maxima in the fiuorescence yield at field strengths of 0 and 411 G and a possible third maximum at 822 G.The theory of the hyperfine induced spin evolution predicts these resonances at selected multiples of the C6F6- hyperfine constant of 137 G.Utilizing the diffusion theory of geminate recombination in a Coulomb field, the experimental magnetic field spectrum is found to be well predicted over most of the range of magnetic field strengths studied (up to 2.5 kG) by a simple, one parameter, exponential radial probability density of initial scavenged geminate pair separation distances.
- Saik, Vladimir O.,Ostafin, Agnes E.,Lipsky, Sanford
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- Single and double ionization of corannulene and coronene
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Electron-transfer processes that involve single and doubly charged cations of corannulene (C20H10) and coronene (C24H12) are examined by three different mass-spectrometric techniques. Photoionization studies give first-ionization energies of IE(C20H10) = 7.83 ± 0.02 eV and IE(C24H12) = 7.21 ± 0.02 eV. Photoionizations of the neutrals to the doubly charged cations occur at thresholds of 20.1 ± 0.2 eV and 18.5 ± 0.2 eV for corannulene and coronene, respectively. Energy-resolved charge-stripping mass spectrometry yields kinetic energy deficits of Qmin(C20H+10 = 13.8 ± 0.3 eV and Qmin(C24H+12 = 12.8 ± 0.3 eV for the transitions from the mono- to the corresponding dications in keV collisions. Reactivity studies of the C20H2+10 and C24H2+12 dications in a selected-ion flow-tube mass spectrometer are used to determine the onsets for the occurrence of single-electron transfer from several neutral reagents to the dications, affording two different monocationic products. With decreasing IEs of the neutral reagents, electron transfer to doubly charged corannulene is first observed with hexafluorobenzene (IE = 9.91 eV), while neutrals with lower IEs are required in the case of the coronene dication, e.g., NO2 (IE = 9.75 eV). Density-functional theory is used to support the interpretation of the experimental data. The best estimates of the ionization energies evaluated are IE(C20H10) = 7.83 ± 0.02 eV and IE(C24H12) = 7.21 ± 0.02 eV for the neutral molecules, and IE(C20H+10) = 12.3 ± 0.2 eV and IE(C24H+12) = 11.3 ± 0.2 eV for the monocations.
- Schroeder, Detlef,Loos, Jessica,Schwarz, Helmut,Thissen, Roland,Preda, Dorin V.,Scott, Lawrence T.,Caraiman, Doina,Frach, Maxim V.,Boehme, Dielhard K.
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- ELECTROPOLYMERISATION OF PERFLUOROCYCLO-ALKENES.
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Novel conducting materials are obtained by cathodic electropolymerisation of perfluoro-cyclobutene and -cyclopentene.
- Briscoe, Mark W.,Chambers, Richard D.,Silvester, Michael J.
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- Laser-Induced Fluorescence Studies of Large and Small Molecular Cations Produced by Using Electron Bombardment in a Free Jet Expansion
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Laser-induced fluorescence (LIF) excitation spectra have been obtained for a number of ions produced by electron impact in a free jet expansion.The ions observed include N2+, CO2+, C6F6+, C6F5H+, C6F3H3+, and C4H2+.In all cases "cold" laser excitation spectra have been obtained.For the simpler ions information about rotational distributions is available, while for the large ions the elimination of hot bands, sequence congestion, extensive rotational contours, etc., makes their spectra much easier to interpret.Under certain circumstances Penning ionization in the expansion effectively competes with direct ionization via electron impact.Some satellite structure is obtained in the C6F6+ spectrum which may be ascribed to C6F6+.Ar.
- Lester, Marsha Isack,Zegarski, B. R.,Miller, Terry A.
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- Stabilities and Structures of C6F6-(C6F6) and C6F6+(C6F6)
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The equilibria of clustering reactions C6F6+/- + C6F6 = C6F6+/-(C6F6) were studied with a pulsed electron beam high-pressure mass spectrometer.Thermochemical stabilities of the clusters C6F6-(C6F6) and C6F6+(C6F6) were determined.It was found that the bond energy of C6F6-(C6F6) is larger than that of C6F6+(C6F6).While C6F6+(C6F6) has the site-to-site type geometry, C6F6-(C6F6) has a stack form according to the ab initio MO calculation.
- Hiraoka, Kenzo,Mizuse, Susumu,Yamabe, Shinichi
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- Facile Synthesis of a Fully Fused, Three-Dimensional ?-Conjugated Archimedean Cage with Magnetically Shielded Cavity
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The synthesis of molecular cages consisting of fully fused, ?-conjugated rings is rare due to synthetic challenges including preorganization, large strain, and poor solubility. Herein, we report such an example in which a tris-2-aminobenzophenone precursor undergoes acid-mediated self-condensation to form a truncated tetrahedron, one of the 13 Archimedean solids. Formation of eight-membered [1,5]diazocine rings provides preorganization and releases the strain while still maintains weak ?-conjugation of the backbone. Thorough characterizations were performed by X-ray, NMR, and UV-vis analysis, assisted by theoretical calculations. The cage exhibits a rigid backbone structure with a well-defined cavity that confines a magnetically shielded environment. The solvent molecule, o-dichlorobenzene, is precisely encapsulated in the cavity at a 1:1 ratio with multiple ?···?, C-H···?, and halogen···πinteractions with the cage skeleton, implying its template effect for the cage closing reaction. Our synthetic strategy opens the opportunity to access more complex, fully fused, three-dimensional ?-conjugated cages.
- Han, Yi,Jiao, Tianyu,Li, Zhengtao,Ni, Yong,Wu, Jishan,Wu, Shaofei,Zhang, Qiuyu,Zhu, Jun
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p. 14314 - 14321
(2021/09/13)
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- Preparation method of hexafluorobenzene
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The invention relates to a preparation method of hexafluorobenzene, and belongs to the field of chemical production techniques. The preparation method of the hexafluorobenzene is characterized by comprising the following technologies: (1) mixing potassium fluoride with a nonprotic polar solvent, thus obtaining a mixed solution; (2) adding a reaction substrate, nitrobenzene and a phase transfer catalyst in the mixed solution, thus obtaining a reaction system, wherein the reaction substrate is chloropentafluorobenzene; (3) putting the reaction system obtained in the step (2) in a high-pressure kettle, sealing after discharging air in the high-pressure kettle, and reacting, thus obtaining a product; (4) rectifying the product after distilling, thus obtaining the hexafluorobenzene. According to the method disclosed by the invention, the energy consumption is lower, side effects are few, the reaction steps are simple, and the operation is easy; the solvent denaturation amount is less, separation and recycling are easy, and compared with other methods, and the method is greener and more environmental friendly.
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Paragraph 0024-0031
(2018/05/16)
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- Xenon(IV)-carbon bond of [C6F5XeF2]+; Structural characterization and bonding of [C6F5XeF2][BF4], [C6F5XeF2][BF4]·2HF, and [C6F5XeF2][BF4]· n NCCH 3 (n = 1, 2); And the fluorinating properties of [C6F5XeF2][BF4]
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The [C6F5XeF2]+ cation is the only example of a XeIV-C bond, which had only been previously characterized as its [BF4]- salt in solution by multi-NMR spectroscopy. The [BF4]- salt and its new CH3CN and HF solvates, [C6F5XeF2][BF4]·1.5CH3CN and [C6F5XeF2][BF4]·2HF, have now been synthesized and fully characterized in the solid state by lowerature, single-crystal X-ray diffraction and Raman spectroscopy. Crystalline [C6F5XeF2][BF4] and [C6F5XeF2][BF4]·1.5CH3CN were obtained from CH3CN/CH2Cl2 solvent mixtures, and [C6F5XeF2][BF4]·2HF was obtained from anhydrous HF (aHF), where [C6F5XeF2][BF4]·1.5CH3CN is comprised of an equimolar mixture of [C6F5XeF2][BF4]·CH3CN and [C6F5XeF2][BF4]·2CH3CN. The crystal structures show that the [C6F5XeF2]+ cation has two short contacts with the F atoms of [BF4]- or with the F or N atoms of the solvent molecules, HF and CH3CN. The lowerature solid-state Raman spectra of [C6F5XeF2][BF4] and C6F5IF2 were assigned with the aid of quantum-chemical calculations. The bonding in [C6F5XeF2]+, C6F5IF2, [C6F5XeF2][BF4], [C6F5XeF2][BF4]·CH3CN, [C6F5XeF2][BF4]·2CH3CN, and [C6F5XeF2][BF4]·2HF was assessed with the aid of natural bond orbital analyses and molecular orbital calculations. The 129Xe, 19F, and 11B NMR spectra of [C6F5XeF2][BF4] in aHF are reported and compared with the 19F NMR spectrum of C6F5IF2, and all previously unreported J(129Xe-19F) and J(19F-19F) couplings were determined. The long-term solution stabilities of [C6F5XeF2][BF4] were investigated by 19F NMR spectroscopy and the oxidative fluorinating properties of [C6F5XeF2][BF4] were demonstrated by studies of its reactivity with K[C6F5BF3], Pn(C6F5)3 (Pn = P, As, or Bi), and C6F5X (X = Br or I).
- Koppe, Karsten,Haner, Jamie,Mercier, Hlne P. A.,Frohn, Hermann-J.,Schrobilgen, Gary J.
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p. 11640 - 11661
(2015/01/16)
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- Interaction of the electrophilic bis(pentafluorophenyl)iodonium cation [(C6F5)2I]+ with the ambident pseudohalogenide anions [SCN]- and [CN]-
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The iodonium pseudohalide compounds, [(C6F5) 2I][X] (X = SCN and CN) were synthesized by means of fluoride substitution in [(C6F5)2I][F] with the Lewis acidic reagents (CH3)3Si-NCS and (CH3) 3Si-CN. The isolated iodonium pseudohalides are intrinsically unstable solids. Decomposition resulted in equimolar amounts of C 6F5I and C6F5SCN or C 6F5I and C6F5CN, respectively. In case of [(C6F5)2I][SCN] single crystals could be grown from CH2Cl2. The crystal structure revealed a dimer with an eight membered ring formed by two ambident anions bridging the iodine atoms of two cations by N and S coordination. The favored dimerization of [(C6F5)2I][SCN] and [(C6F 5)2I][CN] in the gas phase is supported by ab initio computations.
- Hirschberg, Markus E.,Barthen, Peter,Frohn, Hermann-Josef,Bl?ser, Dieter,Tobey, Briac,Jansen, Georg
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- Heterocyclic Compounds and the Use Thereof in Electronic and Optoelectronic Components
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The present invention relates to the use of heterocyclic compounds as the charge transport material, blocker material or light-scattering material in electronic, optoelectronic or electroluminescent components.
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- Bis(perfluoroorganyl)bromonium salts [(RF)2Br]Y (RF = aryl, alkenyl, and alkynyl)
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Bromonium salts [(RF)2Br]Y with perfluorinated groups RFC6F5, CF3CFCF, C 2F5CFCF, and CF3C≡C were isolated from reactions of BrF3 with RFBF2 in weakly coordinating solvents (wcs) like CF3CH2CHF2 (PFP) or CF3CH2CF2CH3 (PFB) in 30-90% yields. C6F5BF2 formed independent of the stoichiometry only [(C6F5)2Br][BF 4]. 1:2 reactions of BrF3 and silanes C6F 5SiY3 (Y = F, Me) ended with different products - C 6F5BrF2 or [(C6F5) 2Br][SiF5] - as pure individuals, depending on Y and on the reaction temperature (Y = F). With C6F5SiF3 at ≥-30 °C [(C6F5)2Br][SiF5] resulted in 92% yield whereas the reaction with less Lewis acidic C 6F5SiMe3 only led to C6F 5BrF2 (58%). The interaction of K[C6F 5BF3] with BrF3 or [BrF2][SbF 6] in anhydrous HF gave [(C6F5) 2Br][SbF6]. Attempts to obtain a bis(perfluoroalkyl) bromonium salt by reactions of C6F13BF2 with BrF3 or of K[C6F13BF3] with [BrF2][SbF6] failed. The 3:2 reactions of BrF3 with (C6F5)3B in CH2Cl2 gave [(C6F5)2Br][(C6F 5)nBF4-n] salts (n = 0-3). The mixture of anions could be converted to pure [BF4]- salts by treatment with BF3·base.
- Frohn, Hermann-Josef,Giesen, Matthias,Welting, Dirk,Bardin, Vadim V.
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experimental part
p. 922 - 932
(2010/10/03)
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- Extremely facile ring inversion and rearrangement in fluorobicyclo[2.1.0]pentanes
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cis-1,2,3,4,5,5-Hexafluorobicyclo[2.1.0]pentane and 1,2,4,5-tetrafluorobicyclo[2.1.0]pentane have been synthesized from hexafluorobenzene. The former hydrofluorocarbon, which exists entirely in the endo configuration, rearranges to cis-1,2,3,3,4,5-hexafluorocyclopentene below room temperature (Ea = 21.9 kcal/mol, log A = 13.4). The latter undergoes degenerate ring inversion with extraordinary ease (ΔG? = 6.8 ± 0.2 kcal/mol at -55 °C). Density functional calculations indicate that significant bonding between the bridgehead carbons is retained in the ring inversion transition state. Analogous calculations predict for hexafluorobicyclo[1.1.0]butane a considerably lower barrier for ring inversion and more 1,3-bonding in the transition state.
- Wei, Yanjun,Liu, Yufa,Wong, Terrence,Lemal, David M.
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p. 688 - 703
(2008/09/16)
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- Dehalogenative aromatization of perchlorofluoroalicyclic compounds C6Cl6F6, C10Cl8F8 and C5Cl4F5N in the vapour phase or in solution
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Dehalogenation of perhalogenated cyclohexanes C6Cl6F6, 1-azacyclohexenes C5Cl4F5N and bicyclo[4.4.0]dec-1(6)-enes C10Cl8F8 in the vapour phase over iron fil
- Bardin, Vadim V.,Trukhin, Dmitrii V.,Adonin, Nicolay Yu.,Starichenko, Vladimir F.
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p. 1431 - 1435
(2007/10/03)
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- Synergism in catalytic halogen-exchange fluorination of 4-chloronitro- and dichlorotetrafluorobenzenes
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Synergism was studied in catalytic halogen-exchange fluorination of 4-chloronitro- and dichlorotetrafluorobenzenes. The synergistic effect in the fluorination of chloroaromatic compounds with potassium fluoride was mainly attributed to separation of the activation functions of catalysts with respect to substrate molecules.
- Shipilov,Bykova,Elokhova,Igumnov
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p. 487 - 491
(2007/10/03)
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- The fluorine-pentafluorophenyl substitution reaction in anhydrous hydrogen fluoride (aHF): A new interesting methodical approach to synthesize pentafluorophenylxenonium salts
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In anhydrous hydrogen fluoride (aHF) (heterogeneous reaction) B(C6F5)3 transfers all the three aryl groups to XeF2 forming [C6F5Xe]+ salts. Upon addition of KF, the [C6F5Xe] [HF2] salt was isolated in 78.7% yield. [C6F5Xe] [HF2] dissolved in MeCN exhibits significant cation-anion interactions and decomposes within 14 days at 20°C. The acidity of the aHF solvent determines the nature of the products in the reaction of XeF2 with B(C6F5)3. The reaction path of this new methodical approach of fluorine-aryl substitution in aHF is discussed.
- Frohn, Hermann-Josef,Schroer, Thorsten
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p. 259 - 264
(2007/10/03)
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- C6F5XeCl and [(C6F5Xe)2Cl][AsF6]: The first isolated and unambiguously characterized xenon(II) chlorine compounds
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Xenon(II) chlorine compounds can be obtained as the isolable organo derivatives C6F5XeCl and [(C6F5Xe)2Cl][A5F6] (whose cation is depicted) in 85 and 91% yield, respectively. The
- Frohn, Hermann-Josef,Schroer, Thorsten,Henkel, Gerald
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p. 2554 - 2556
(2007/10/03)
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- Nucleophilic aromatic substitution with dialkoxycarbenes
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Dimethoxycarbene, generated at 110°C by thermolysis of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline, displaces fluoride from aromatic rings that are activated with electron-withdrawing groups. Intermolecular substitution on Sanger's reagent and on hexafluorobenzene are reported, together with intramolecular substitution by a dioxycarbene with a tethered aryl group.
- Ross, Joseph P.,Couture, Philippe,Warkentin, John
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p. 1331 - 1335
(2007/10/03)
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- Combined experimental and theoretical study of the protonation of polyfluorobenzenes [C6H(6-n)F(n)] (n = 0-6)
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In a recent high-pressure mass spectrometric revision to the gas-phase basicity scale (J. E. Szulejko and T. B. McMahon, J. Am. Chem. Sec. 115, 7839 (1993)), it was observed that the proton affinity for hexafluorobenzene was 24 kcal mol-1 (1 kcal = 4.184 kJ) lower than the accepted National Institute of Science and Technology (NIST) database value of 177.7 kcal mol-1 (S. G. Lias et al., J. Phys. Chem. Ref. Data 17, Suppl. 1 (1988)). Furthermore, the proton affinities for most other polyfluorobenzenes were also found to differ substantially from the NIST values. For many of the polyfluorobenzenes large protonation entropy changes were noted, which were substantially greater than then those expected from rotational symmetry number changes alone. In view of these observations, MP2/6-31G**/HF/6-31G** ab initio calculations were undertaken to investigate further the proton affinity and entropy changes with respect to the degree of fluorine substitution. The present proton affinity variations found for the polyfluorobenzenes (hexaflorobenzene excepted) can be interpreted with the aid of the ab initio results in terms of a simple additivity scheme. Each fluorine substituent para, meta, ortho or ipso to the ring protonation site will induce an incremental proton affinity change with respect to benzene of 1.5, -7.0, -1.5 and -19.0 kcal mol-1, respectively. This additivity scheme can also be used to rationalize the re-evaluated proton affinities for the polymethylbenzenes and m- and o-fluorotoluenes. The corresponding methyl increments are 7.5, 5.5, 2.5 and 1.0 kcal mol-l for para, meta, ortho and ipso protonation respectively. From the present ab initio statistical thermodynamic analysis of the various protonation entropy components, it was concluded that the low frequency vibrations are almost exclusively responsible for the large excess entropy changes observed experimentally. Ab initio calculated barriers for 1,2 proton shifts in arenium species available in the literature are concluded to be too large to allow the existence of a so-called dynamic proton. Large excess protonation entropies are noted from the literature for polymethylbenzenes, naphthalene and 1-methylnaphthalene.
- Szulejko,Hrusak,McMahon
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p. 494 - 506
(2007/10/03)
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- Fluorination of tetrafluorobenzenes C6HF4R with XeF2
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Replacement of hydrogen by fluorine and addition of fluorine atoms to the aromatic ring were found in the reaction of XeF2 with 1-R-2,3,4,5-tetrafluorobenzene (R = H, F, Br, NO2) or 1-R-2,3,4,6-tetrafluorobenzene (R = H, CF3) in HF or CH2Cl2-BF3·OEt2. Only fluorine addition took place in the case of 1-R-2,3,5,6-tetrafluorobenzenes (R = H, Br, CF3) or 1-Br-2,3,4,6-tetrafluorobenzene. The role of cation radicals as reactive intermediates is discusseed.
- Bardin,Shchegoleva,Frohn
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p. 153 - 159
(2007/10/03)
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- Mobilities of Radical Cations and Anions, Dimer Radical Anions, and Relative Electron Affinities by Times of Flight in n-Hexane
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The mobilities of several radical cations and anions are measured in n-hexane using a thin-sheet time-of-flight (TOF) technique.We observe the radical cations of N,N,N',N'-tetramethyl-p-phenylenediamine, zinc tetraphenylporphine, and pyrene and the radical anions of perfluorobenzene, p-benzoquinone, anthraquinone, chloranil, buckminsterfullerene (C60), and octafluoronaphthalene.For all electron acceptors but C60, the dependence of the anionic TOF on acceptor concentration reveals the appearance of the homodimer radical anion at sufficiently high concentrations.The equilibrium constant for the monomer anion/monomer acceptor association reaction is obtained from the concentration studies.A Born-Haber cycle is then applied to estimate the difference between the electron affinities of the monomer and dimer molecules in the gas phase.
- Lim, S. K.,Burba, M. E.,Albrecht, A. C.
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p. 9665 - 9675
(2007/10/02)
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- Thermal electron attachment to C6F5X and C6H5X (X - I, Br, Cl, and F)
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Rate constants have been measured for thermal electron attachment to C6F5X (X = I, Br, Cl, F, and H) and C6H5X (X = I, Br, Cl, and F) at room temperature in N2 buffer gas (1-100 Torr) using the pulse-radiolysis microwave cavity method.For all the compounds studied, the rate constants are of the two-body type.Unexpectedly, the values for C6F5X except C6F5H are all the same (ca. 2 x 10-7 cm3 molecule-1 s-1), which are higher than most of the previous values, while that for C6F5H, measured in Xe and Ar buffer gases, is very low (7 x 10-12 cm3 molecule-1 s-1).For C6H5X, the value decreases dramatically with varying X from I to Br to Cl as 1.0 x 10-8 to 6.5 x 10-12 to 3 x 10-14 cm3 molecule-1 s-1, and that for C6H5F must be much lower than 10-13 cm3 molecule-1 s-1.These results for the magnitude of the rate constant are rationalized by the variation in the energy of a transient negative-ion state of each molecule, which results from a combination of the electron affinities of constituents (halogen atom X and C6F5 radical) and the strength of the C6F5-X (or C6H5-X) bond.
- Shimamori, Hiroshi,Tatsumi, Yoshitsugu,Suanagawa, Takeyoshi
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p. 7787 - 7792
(2007/10/02)
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- INFRARED LASER INDUCED DECOMPOSITION OF HEXAFLUOROBENZENE AND SOME MONOSUBSTITUTED DERIVATIVES. INTERMEDIACY OF THE PENTAFLUOROPHENYL RADICAL.
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The infrared multiphoton laser induced reactions of hexafluorobenzene and related pentafluoro analogues (pentafluorobenzene, pentafluorochlorobenzene, pentafluorobromobenzene, and pentafluoroiodobenzene) have been investigated using a CO2 TEA laser.The study was carried out in order to define the decomposition products and to attempt to clarify their mode of formation.Thus, the products (relative yield, percent) of the irradiation of C6F6 (1027.3 cm-1; 0.73 J/cm2; 10 pulses; 25percent decomposition) were C2F4(64), C6F5CF3(28), C2F6(7), CF4(1) and that for C6F5H (949.4 cm-1; 0.80 J/cm2; 10 pulses; 25percent decomposition) was C2F4 and C6F5CF3.Increasing the number of pulses in the reaction with C6F6 decreased the amount of C2F4 and increased the amount of C6F5CF3 and C2F6 indicating secundary and tertiary reactions.Addition of halogen (X2, X = Cl, Br) to these reactions caused different products to be formed.Thus, the irradiation of a C6F6/Cl2 mixture (7.4/7 Torr; 1027.3 cm-1; 0.7 J/cm2; 35 pulses; 35percent reaction) afforded C6F5Cl(46); CF3Cl(24) and CF2Cl2(30).Irradiation of C6F5H/X2 mixtures afforded mainly C6F5X + HX.For example C6F5H/Br2 (10/40 Torr; 949.4 cm-1; 0.93 J/cm2; 10 pulses; 10percent reaction) gave C6F5Br and HBr exclusively.Irradiation of C6F5-X (X = Cl, Br, I) (977.2 cm-1; ca. 0.74 J/cm2; 200 pulses; 39-74percent reaction) gave C6F6 and a minor amount of decafluorobiphenyl , a radical combination product of the pentafluorophenyl radical (C6F5.).Increasing the fluence in these reactions gave similar products in most cases but in some instances increased the amount of C2F4 formed.The reactions and product distribution of the hydrogen substituted derivative (C6F5H) was examined in the presence of Br2 as a function of laser fluence and halogen concentration.It was found that the threshold for C6F5H decomposition was higher for the reaction involving Br2 (as compared with the reaction involving Cl2 or neat C6F5H).The presence of Br2 also decreased the amount of C6F5H that was decomposed, indicating a quenching process.The decomposition path with the lowest activation energie for these molecules is thought to be C6F5X -> C6F5. + X. and was accessible using a laser pulse with a fluence as low as 0.7 J/cm2.Using a higher laser fluence (ca. 1.2 J/cm2) di- and triatomic radicals were defined by spectroscopic identification of the and :CF2 species.These reactions are discussed in light of the formation of the C6F5. radical during a primary, laser induced, process.Subsequent decomposition to smaller fragments, combination with other radicals or scavenging by added reagents also takes place depending on the reaction conditions.
- Watanabe, Akio,Koga, Yoshinori,Sugawara, Ko-ichi,Takeo, Harutoshi,Fukuda, Kenzo,Matsumura, Chi
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p. 463 - 469
(2007/10/02)
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- STATE-DEPENDENT PHOTOCHEMISTRY OF HIGHLY FLUORINATED BICYCLOOCTA-2,4-DIENES
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A series of 1,2,3,4,5,6-hexafluorobicycloocta-2,4-dienes was subjected to direct irradiation with ultraviolet light and to triplet sensitization.While all of the dienes cyclized smoothly upon direct irradiation to tricyclo2,5>oct-3-enes, their behavior when triplet sensitized was strongly dependent upon the substituents in the 7- and 8-positions.Responses included no reaction, cyclization to tricyclooctene, and fragmentation to hexafluorobenzene plus olefin.Fragmentation occurred only when geminal chlorines were present at the 7-position.This observation is consistent with the view that the four-membered ring opens homolytically at the C6-C7 bond, and only if sufficient stabilization is available for a radical center at the 7-position.
- Roberts, Bryan E.,Goldman, Glenn D.,Lemal, David M.
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p. 353 - 360
(2007/10/02)
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- The First Compound with a Stable Xenon-Carbon Bond: 19F- and 129Xe-N.M.R. Spectroscopic Evidence for Pentafluorophenylxenon(II) Fluoroborates
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Pentafluorophenylxenon(II) fluoroborates have been synthesized by the reaction of xenon difluoride with tris(pentafluorophenyl)borane and characterized by 129Xe- and 19F-n.m.r. spectroscopy and by reaction with bis(pentafluorophenyl)tellurium and pentafluorophenyliodine to yield the novel cations (1+) and (1+), respectively.
- Naumann, Dieter,Tyrra, Wieland
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- Synthesis and Chemistry of Highly Fluorinated Bicyclohexenone
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A series of highly fluorinated bicyclo-5-hexen-2-ones (3) and their hydrates (4) have been prepared in two steps from hexafluoro Dewar benzene (1).Photolysis of exo-3H-pentafluorobicyclo-5-hexen-2-one (3d) at low pressure in the vapor phase gave 1H-pentafluorocyclopentadiene (8), but in solution the principal product was pentafluorophenol (9).Under Favorskii conditions, exo-3-bromo- and exo-3-chloropentafluorobicyclo-5-hexen-2-one (3a and 3b) ring opened stereospecifically to 2-cyclobutenecarboxylic acids 17 and 29, respectively.Treatment of these ketones with tert-butoxide under aprotic conditions effected stereospecific cleavage to tert-butyl methylenecyclobutenecarboxylates 25 and 30.The acid (27) corresponding to 25 was obtained both from bromohydrate 4a and the acid 17, again stereospecifically, by reaction with lithium diisopropylamide.Flash vacuum pyrolysis of the hydrate (4c) of of hexafluorobicyclo-5-hexen-2-one at 300 deg C gave hexafluoro-2,4-cyclohexadienone (12), which decarbonylated at higher temperatures to yield hexafluorocyclopentadiene (13).Similarly, flash vacuum pyrolysis of 3-chloropentafluorobicyclo-5-hexen-2-one (3b) at 650 deg C gave a mixture of 1- and 2-chloropentafluorocyclopentadienes.
- Soelch, Richard R.,McNierney, Edward,Tannenbaum, Gary A.,Lemal, David M.
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p. 5502 - 5511
(2007/10/02)
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- COMPETITION AMONG COLLISIONAL DEACTIVATION, IONIZATION, AND DISSOCIATION IN THE MULTIPHOTON EXCITATION OF OCTAFLUOROCYCLOOCTATETRAENE
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The gas-phase UV multiphoton induced chemistry and multiphoton ionization of octafluorocyclooctatetraene (OFCOT) have been examined as a function of laser pulse energy, laser wavelength, and background gas pressure.The production of hexafluorobenzene (HFB), tetrafluoroethylene (TFE), and tetrafluoromethane (TFM) as well as carbon has been observed.An intense fluorescence has also been recorded and attributed to the Swan bands of C2.The laser intensity dependent bulk kinetics of the OFCOT decomposition were found to be first order with a rate constant of 5.7 (+/-0.2)E3 s-1 at a (15 ns) pulse energy of 25 mJ and a sample pressure of 750 mTorr.Qualitative aspects of the photochemistry of HFB and TFE, under identical conditions, are also reported.The addition of N2 to the sample is shown to increase the rate of photolysis and decrease the MPI current.This observation is attributed to the competition between ionization and dissociation from the initially created valence state of the target molecule.The increase in the number of collisions results in a larger fraction of excited-state molecules undergoing relaxation to states which are either geometrically or energetically unfavorable with respect to ionization.The result, therefore, is an increase in the yield of the dissociation products.A simple kinetic rate equation model is in agreement with these observations.OFCOT appears to be a member of a unique group of large, organic molecules exhibiting this type of competition.
- BelBruno, Joseph J.,Greenfield, Scott R.,Carl, Richard T.,Hughes, Russell P.
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p. 2480 - 2484
(2007/10/02)
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- The Preparation and Characterization of Radical Cation Salts Derived from Perfluorobenzene, Perfluorotoluene, and Perfluoronaphthalene
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The salts C6F6+AsF6- (yellow), C6F5CF3- (lime green), and C10F8+AsF6- (dark green) may be prepared by electron oxidation of the appropriate perfluoro aromatic molecule with O2+AsF6-.Other O2+ salts can be similarly employed as can the more strongly oxidizing transition-metal hexafluorides, but salts of the latter are more labile than their AsF- relatives.C6F6+AsF6- is a convenient electron oxidizer (C6F6AsF6+C10F8 -> C10F8AsF6+C6F6) since that which remains from the reaction decomposes at room temperature to volatile products (2C6F6AsF6 -> C6F6+1,4-C6F8+2AsF5).Magnetic susceptibilities for C6F6AsF6 and C10F8AsF6 approximate to Curie law behavior, and g values are close to free-electron values.X-ray diffraction data (single crystal) show C6F6AsF6 to be primitive rhombohedral with a0=6.60 (1) Angstroem, α=106.0 (1) deg, V=246.1 Angstreom3, Z=1, probable space group R3, and (powder data) C10F8AsF6 to be tetragonal with a0=8.27 (5) Angstroem, c0=18.57 (s) Angstroem, V=1270 Angstoem3, Z=4.Salts derived from the monocyclic perfluoro aromatics are thermally unstable but can be kept below -15 deg C.The perfluoronapthalene salts are indefinitely stable at room temperatures.All hydrolyze rapidly.The products of thermal decomposition of the hexafluoroarsenates of the monocyclic cation salts parallel the products of the attack by F-.The latter reaction products are in the molar ratios indicated by the following equations: 2C6F6+ 2F- -> C6F6+ 1,4-C6F8; 2C6F5CF3+ ->2F- -> C6F5CF3+1,3-C6F7CF3.The 1,3-C6F7CF3 isomerizes to a 1:1 mixture with 1,4-C6F7CF3 over several days in the presence of fluoro acids.Mechanisms for the formation of the dienes are discussed.
- Richardson, T. J.,Tanzella, F. L.,Bartlett, Neil
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p. 4937 - 4943
(2007/10/02)
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- POLYFLUORO-COMPOUNDS BASED ON THE CYCLOHEPTANE RING SYSTEM. PART 5. OCTAFLUOROCYCLOHEPTA-1,3,5-TRIENE AND HEXAFLUOROTROPONE
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Decafluorocyclohepta-1,3-diene underwent reductive addition-elimination with sodium borohydride to give mainly 1H-nonafluorocyclohepta-1,3-diene, together with minor products, the 1H,4H-octafluoro-analogue and, most significantly, 5H-nonafluorocyclohepta-1,3-diene.Decafluorocyclohepta-1,4-diene, together with some 6H-nonafluorocyclohepta-1,4-diene and a trace of the 5H-1,3-diene.These last two dienes were important products, having hydrogen on allylic carbons.They could be dehydrofluorinated, either by bubbling through molten potassium hydroxide or, better, with powdered alkali in an inert medium.Unless special precautions were taken, such reactions yielded hexafluorotropone.With care however the primary product, octafluorocyclohepta-1,3,5-triene, could be isolated, but it was hydrolysewd rapidly, even by water, to give the tropone.Isomerizations and pyrolytic dehydrofluorinations of the major reduction products were carried out, but none yielded the triene or the tropone.It seemed that the triene was probably formed but decomposed to give perfluoroarenes.An interesting defluorination pathway was also operating, to give pentafluorobenzene. 2H-Nonafluorocyclohepta-1,3-diene was an isomerization product.Hexafluorotropone reacted with sodium methoxide in methanol to give 3,6-dimethoxytetrafluorotropone.
- Dodsworth, D. J.,Jenkins, C. M.,Stephens, R.,Tatlow, J. C.
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- FLUOROCYCLOHEXANES PART XV. DEHYDROFLUORINATIONS OF UNDECA- DECA- AND NONA- FLUOROCYCLOHEXANES
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An experimental modification has improved dehydrofluorinations of undeca- deca- and nona- fluorocyclohexanes, and enhanced the proportions of dienes and aromatics formed.
- Coe, Paul L.,Mott, Andrew W.,Tatlow, John Colin
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p. 167 - 172
(2007/10/02)
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- THE THERMAL ISOMERIZATION OF HEPTAFLUOROCYCLOHEXADIENES
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The evidence for the involvement of sigmatropic fluorine migrations in the isomerizations of fluorinated polyenes is reviewed and the difficulties inherent in providing satisfactory rationalizations are discussed.The thermal isomerizations of heptafluorocyclohexadienes under various reaction conditions are described.It is established that such isomerizations occur by a mechanism which does not involve catalysis by fluoride ion, however the exact mechanistic pathway remains uncertain.
- Feast, W. J.,Morland, J. B.
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- THE SIGMATROPIC MIGRATION OF FLUORINE
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Pyrolysis of polyfluorocyclohexadienes at 475-480 deg C over new quartz or Pyrex glass gave products derived from 1,5-sigmatropic migrations of fluorine; 1,3-migrations occurred to only a small degree.As the quartz or glass aged, other processes - 1,3-migrations and defluorinations to aromatics - began to occur; these appear to be due in some way to fluoride ion, since pyrolysis over sodium fluoride gave similar products.
- Burdon, J.,Childs, A.,Parsons, I. W.,Rimmington, T. W.
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- LA FLUORATION PAR KF DE PERHALOGENES ORGANIQUES AROMATIQUES EN PRESENCE DE FAIBLES QUANTITES DE SULFOLANE OU D'EAU. SPECTRES DE MASSES DES MELANGES OBTENUS EN SERIE BENZENIQUE
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The fluorinations of perhalogenated aromatic compounds with KF are carried out in sealed tubes in presence of inert gas.The addition of small quantities of aprotic solvent promotes the fluorination of pentachloropyridine above 180 deg C; these fluorinatio
- Hitzke, J.
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p. 101 - 116
(2007/10/02)
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- LA FLUORATION DE L'HEXACHLOROBENZENE ET DE LA PENTACHLOROPYRIDINE EN MILIEU DE FLUORURE DE POTASSIUM SOLIDE
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The fluorinations of hexachlorobenzene and pentachloropyridine were carried out in sealed tubes with KF in presence of inert gas; the fluorinated derivatives C6FxCly x + y = 6 0 - are investigated and compared; the molar yield varied from 45percent to 90percent.It is possible to get directly and selectively some fluorinated drivatives as C5Cl2F3N.The fluorinations in liquid KF-KCl and solid KF are compared.
- Hitzke, J.
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p. 103 - 128
(2007/10/02)
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