Vinyl Fluoride Research Articles

Carcinogenicity of 1,3-butadiene, ethylene oxide, vinyl chloride, vinyl fluoride, and vinyl bromide

Carcinogenicity of 1,3-butadiene, ethylene oxide, vinyl chloride, vinyl fluoride, and vinyl bromide

Adsorption of CH2CHF on the Anatase (101) Surface: A Quantum-Mechanical Study

The adsorption of CH2CHF on the anatase (101) surface has been studied by a periodic approach using hybrid-exchange density functional theory. The simulation was performed on the basis of a recently proposed experimental model for vinyl fluoride and chloride describing the adsorption of CH2CHX through the halogen atom rather than the CC double bond according to the infrared spectra. The adsorption has been investigated using different surface coverages and periodicities, and the energetics have been considered in terms of interaction, distortion, and binding energies. A simple model of nearest and next-nearest neighbors has been adopted to obtain the energies in the limit of an isolated adsorbed molecule and to quantify the lateral effects. The adsorbate−substrate interaction for the anatase surface resulted weaker than that for the rutile (110) one. The vibrational frequencies of the adsorbed molecule have been computed and found in agreement with the experimental ones thus supporting previous infrared interpretations.

Catalytic Arylations with Challenging Substrates: From Air-Stable HASPO Preligands to Indole Syntheses and C-H-Bond Functionalizations

The development of novel ligands and their applications to transition-metal catalysis performed in our laboratory are ­summarized. These studies include the use of air-stable, modular heteroatom-substituted secondary phosphine oxides (HASPO) in cross-coupling reactions of challenging substrates, such as aryl and vinyl chlorides, fluorides, and tosylates.

Electronic excitations of fluoroethylenes

Several lowest-lying singlet electronic states of vinyl fluoride, trans-, cis-, and 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene were investigated by using symmetry-adapted cluster configuration interaction theory. Basis sets up to Dunning's aug-cc-pVTZ augmented with appropriate Rydberg functions were utilized for the calculations. Calculated excitation energies show a good agreement with the available experimental values. Even in the troublesome pi-->pi(*) transitions, the excitation energies obtained in the present study agree well with the experimental values except in one or two fluoroethylenes. Strong mixing between different states was noticed in a few fluoroethylenes; especially the mixing is very strong between pi-pi(*) and pi-3ppi states in trifluoroethylene. No pure pi-sigma(*) excited state was found in almost all the fluoroethylenes. Several assignments and reassignments of features in the experimental spectra were suggested. The present study does not support the existing argument that the interaction between the pi-pi(*) and sigma-sigma(*) states is the reason behind the blueshift of around 1.25 eV in the pi-pi(*) excitation energy of tetrafluoroethylene. Possible reasons, including structural changes, for this shift are discussed in detail. Several low-lying triplet excited states were also studied.

Shock tube study of dissociation and relaxation in 1,1-difluoroethane and vinyl fluoride

This paper reports measurements of the thermal dissociation of 1,1-difluoroethane in the shock tube. The experiments employ laser-schlieren measurements of rate for the dominant HF elimination using 10% 1,1-difluoroethane in Kr over 1500-2000 K and 43 < P < 424 torr. The vinyl fluoride product of this process then dissociates affecting the late observations. We thus include a laser schlieren study (1717-2332 K, 75 < P < 482 torr in 10 and 4% vinyl fluoride in Kr) of this dissociation. This latter work also includes a set of experiments using shock-tube time-of-flight mass spectrometry (4% vinyl fluoride in neon, 1500-1980 K, 500 < P < 1300 torr). These time-of-flight experiments confirm the theoretical expectation that the only reaction in vinyl fluoride is HF elimination. The dissociation experiments are augmented by laser schlieren measurements of vibrational relaxation (1-20% C(2)H(3)F in Kr, 415-1975 K, 5 < P < 50 torr, and 2 and 5% C(2)H(4)F(2) in Kr, 700-1350 K, 6 < P < 22 torr). These experiments exhibit very rapid relaxation, and incubation delays should be negligible in dissociation. An RRKM model of dissociation in 1,1-difluoroethane based on a G3B3 calculation of barrier and other properties fits the experiments but requires a very large DeltaE(down) of 1600 cm(-1), similar to that found in a previous examination of 1,1,1-trifluoroethane. Dissociation of vinyl fluoride is complicated by the presence of two parallel HF eliminations, both three-center and four-center. Structure calculations find nearly equal barriers for these, and TST calculations show almost identical k(infinity). An RRKM fit to the observed falloff again requires an unusually large DeltaE(down) and the experiments actually support a slightly reduced barrier. These large energy-transfer parameters now seem routine in these large fluorinated species. It is perhaps a surprising result for which there is as yet no explanation.

Rotational spectroscopy and molecular structure of the 1,1-difluoroethylene-acetylene complex

Fourier transform microwave, rotational spectra in the 6-21 GHz region are obtained for the complex formed between 1,1-difluoroethylene and acetylene, including the normal isotopomer and each singly substituted (13)C species along with complexes derived from commercially available isotopic varieties of acetylene (HCCD, DCCD, and H(13)C(13)CH). Although two possible planar structures are consistent with the rotational constants derived from analysis of the spectra, ab initio calculations, as well as chemical intuition, support only one of the two as the structure of the complex. Nuclear quadrupole coupling constants for D-containing species show no evidence of electric field gradient perturbation and are consistent with the structures obtained from inertial data. The primary interaction between the two molecules is a 2.646(11) A hydrogen bond with acetylene as the donor and a 1,1-difluoroethylene fluorine as the acceptor that forms a 122.41(79) degrees C-Fcdots, three dots, centeredH angle. A secondary interaction between the acetylenic bond and the difluoroethylene hydrogen atom cis to the acceptor fluorine atom causes the hydrogen bond to deviate 53.25(24) degrees from linearity. Structural comparisons with the related complex, 1,1-difluoroethylene-hydrogen chloride [Z. Kisiel et al., J. Chem. Soc., Faraday Trans. 88, 3385 (1992)], suggest that the hydrogen bond in the acetylene complex is weaker, whereas comparisons with vinyl fluoride-acetylene [G. C. Cole and A. C. Legon, Chem. Phys. Lett. 369, 31 (2003)] indicate that the fluorine atoms in 1,1-difluoroethylene are less basic than the one in vinyl fluoride.

Photodissociation dynamics of vinyl fluoride (CH2CHF) at 157 and 193nm: Distributions of kinetic energy and branching ratios

Using photofragment translational spectroscopy and tunable vacuum-ultraviolet ionization, we measured the time-of-flight spectra of fragments upon photodissociation of vinyl fluoride (CH2CHF) at 157 and 193 nm. Four primary dissociation pathways--elimination of atomic F, atomic H, molecular HF, and molecular H2--are identified at 157 nm. Dissociation to C2H3 + F is first observed in the present work. Decomposition of internally hot C2H3 and C2H2F occurs spontaneously. The barrier heights of CH2CH --> CHCH + H and cis-CHCHF --> CHCH + F are evaluated to be 40+/-2 and 44+/-2 kcal mol(-1), respectively. The photoionization yield spectra indicate that the C2H3 and C2H2F radicals have ionization energies of 8.4+/-0.1 and 8.8+/-0.1 eV, respectively. Universal detection of photoproducts allowed us to determine the total branching ratios, distributions of kinetic energy, average kinetic energies, and fractions of translational energy release for all dissociation pathways of vinyl fluoride. In contrast, on optical excitation at 193 nm the C2H2 + HF channel dominates whereas the C2H3 + F channel is inactive. This reaction C2H3F --> C2H2 + HF occurs on the ground surface of potential energy after excitation at both wavelengths of 193 and 157 nm, indicating that internal conversion from the photoexcited state to the electronic ground state of vinyl fluoride is efficient. We computed the electronic energies of products and the ionization energies of fluorovinyl radicals.

Morphological, crystallization and plasticization studies on isomorphic blends of poly (vinyl fluoride) (PVF) and poly (vinylidene difluoride) (PVDF): using microhardness, XRD and SEM techniques

Property modification by blending of polymers has been the area of immense interest. In this paper, the isomorphic blends of two polymers poly (vinyl fluoride) (PVF) and poly (vinylidene difluoride) (PVDF) with different ratios were prepared using solution cast technique. The microhardness studies have been carried out on pure and polyblend specimens at various loads to test the plasticization and hardening effects using Vickers microhardness testing. The X-ray diffraction (XRD) study has been utilized to detect the crystalline and amorphous characteristics of specimens. Thus PVDF acts as plasticizer in the polyblend when the content of PVDF is relatively high as compare to PVF. When the PVF is major component in the polyblend, the microhardness of the blend specimen increases and the isomorphic blend specimens with 50:50 proportion of two polymers exhibit the maximum value of microhardness. Scanning electron microscopy (SEM) micrographs indicate complete chain formation with uniform texture, when the two polymers are blended in equal proportions. The findings of XRD and SEM have been correlated with the microhardness values.

Vinyl Fluorides in Cycloadditions

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Ab initio anharmonic force field and equilibrium structure of vinyl fluoride and vinyl iodide

The quadratic, cubic and semi-diagonal quartic force field of vinyl fluoride and vinyl iodide have been calculated at the MP2 level of theory employing a basis set of triple- ζ quality including a relativistic pseudopotential on iodine. A semi-experimental equilibrium structure has been derived from experimental ground state rotational constants and rovibrational interaction parameters calculated from the ab initio force field. This structure is in excellent agreement with the ab initio structure calculated at the CCSD(T) level of theory using a basis set of quadruple- ζ quality. Finally, the structure of different vinyl derivatives is compared.

Sample water removal method in volatile organic compound analysis based on diffusion through poly(vinyl fluoride) film

The humidity caught during air sampling or sample storage causes various problems during volatile organic compound (VOC) analysis and gives unreliable results. In this study, water vapour diffusion capacities through poly(vinyl fluoride) Tedlar, fluoroethylene propylene Teflon and Flex foil film were compared. A new approach to humidity removal has been tested for moderately polluted atmospheres. This approach consists in using the water vapour diffusion property of Tedlar film to remove humidity from bag samples containing a mixture of ten VOCs at 500 ppbv each in a 70% relative humidity atmosphere. The sampling bags were placed in a chamber flushed by a dry air stream at less than 5% relative humidity. After a few hours in the chamber, the samples in the Tedlar bags were dry (relative humidity <5%) and did not show significant VOC loss. This sample water removal (SWR) method is especially interesting as a pretreatment before air sampling on water sensitive adsorbents.

Effect of irradiation on the surface microhardness of pure poly(vinyl fluoride), poly(vinylidene fluoride) and their isomorphic blends

Many widely used polymers suffer main chain scission or crosslinking depending upon various physical parameters when exposed to radiation. Crosslinking and scission are two opposite consequences of irradiation. The preparation of pure Poly(vinyl fluoride) (PVF), Poly(vinylidene fluoride) (PVDF) and their isomorphic polyblends in different weight percentage proportion using solution cast technique is described. The effect of gamma irradiation on the surface microhardness of pure and polyblends of PVF and PVDF have been studied to detect radiation-induced crosslinking and radiational scissioning. The surface microhardness of the irradiated specimen was measured using Vickers method. The overall hardening of blend specimens at different dose level indicates occurrence of crosslinking. For lower radiation dose range of 0–1 Mrad and higher dose range of 1–25 Mrad, the maximum hardening is observed at 0.2 and 20 Mrad, respectively. However, beyond 15 Mrad, scissioning effect predominates in pure as well as polyblend specimens.

A Ring‐Closing Metathesis Pathway to Fluorovinyl‐Containing Nitrogen Heterocyles

AbstractThe synthesis of highly functionalized fluorinated piperidines is described. The key step in this synthesis is a ring‐closing metathesis reaction involving fluoride‐substituted olefins, which leads to the corresponding cyclic vinyl fluorides. Several sequences to arrive at differently substituted piperidines have been evaluated. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)

Determination of Aromatic Compounds in Exhalated from Human Skin by Solid-Phase Micro Extraction and GC/MS with Thermo Desorption System

An analytical method for the determination of aromatic compounds exhalated from hand skin has been proposed. The sampling of exhalated aromatic compounds was performed as follows: after the intake of aromatic compounds included in chewing gum or a capsule, exhalated skin gas was collected from a hand. The hand was covered with a sampling bag of poly vinyl fluoride (PVF) for 30 min. Then, the inner space of the sampling bag was sprayed with a 25% of ethanol aqueous solution. After removing the hand from the bag, the trapped solution containing skin gas was collected. The aromatic compounds in the trapped solution were extracted to the solid phase as Twister® (stir bar coated with poly dimethyl siloxane, Gerstel). Extracts were determined by gas-chromatograph mass spectrometry using a thermo desorption system and a selective ion mode. Linalool, citronellol and geraniol, which are the main components of rose essential oil, were detected from the skin of a hand after an oral intake of rose oil. The exhalated absolute amount of linalool, citronellol and geraniol increased in 30 to 60 min, and then decreased after intake. The recoveries of linalool, citronellol and geraniol were 53.5%, 66.7% and 55.1%, respectively. The correlation coefficient of the standard curves for linalool, citronellol and geraniol were 0.9977, 0.9994 and 0.9987, respectively. Each compound exahalated from the skin of a human body during 6 hours after intake was estimated to be, according to the amount of intake, 0.39%, 0.09% and 0.25%, respectively, for one subject. The absolute amount of geraniol exhalated from a hand increased significantly after oral intake for 8 subjects (P<0.025). This is the first report to present hard proof that an aromatic compound was exhalated from human skin after its intake as food.

A quantum-mechanical study of the vinyl fluoride adsorbed on the rutile TiO 2(1 1 0) surface

The adsorption of vinyl fluoride on the rutile TiO 2(1 1 0) surface has been simulated, on the basis of a recently proposed experimental model, using hybrid-exchange density functional theory. Different surface coverages have been considered and the lateral interaction between adsorbed vinyl fluoride molecules has been quantified through a simple model of nearest and next nearest neighbouring molecules. The vibrational frequencies of the adsorbed molecule have been calculated and are found to be in excellent agreement with those observed providing support for the proposed adsorption model. The effect of the adsorption on the electronic structure of the molecule and the surface have been characterised by computing electrostatic potential maps and the local density of states.

Cleavage of F–C(sp 2) bonds by MHR(CO)(P tBu 2Me) 2 (M = Os and Ru; R = H, CH 3 or Aryl): Product dependence on M and R

Both MH(Ph)(CO)L 2 (L = P t Bu 2Me; M = Ru and Os) react with vinyl fluoride to form M–F bonds; however, Ru eliminates benzene, while Os eliminates ethylene. In contrast, Ru(H) 2(CO)L 2 and Os(H) 2(CO)(1-butene)L 2 both react with vinyl fluoride to give ethylene and MHF(CO)L 2. Ethylene production from both dihydrides is attributed to β-F migration to M from an MCH 2CH 2F transient, while the unique behavior of RuH(Ph)(CO)L 2 (giving the C–F oxidative addition product Ru(η 1-vinyl)F(CO)L 2) is attributed to the difficulty of achieving Ru IV, and the ability of the strongly π-acidic vinyl fluoride to rapidly trigger reductive elimination of benzene. The products of reaction of RuH(Ar)(CO)L 2 with vinyl fluoride are redirected more towards ethylene formation when Ar carries fluorine substituents. The reaction products of OsH(R)(CO)L 2 with vinyl fluoride revert to R-H elimination when R is methyl. Finally, the more π-acidic H 2C CF 2 triggers very rapid CH 4 elimination from OsH(CH 3)(CO)L 2; cleavage of the second C–F bond yields the vinylidene OsF 2(CCH 2)(CO)L 2. All selectivity is rationalized via the fate of the adduct MH(R)(C 2H 4 − n F n )(CO)L 2.

Die Kinetik und Mechanismus der direkten Fluorinierung von Polyethylenen

Two types of low-density polyethylene (LDPE), five types of high-density polyethylene (HDPE), poly(vinyl fluoride) (PVF) and poly(vinylidene fluoride) (PVDF) were studied. The fluorination of LDPE and HDPE is a diffusion-controlled process and proceeds via a branched chain mechanism following an induction period. Initiation of the reaction takes place via the reaction of molecular fluorine with the C-H bond. The rate of fluorination of HDPE exceeds that of LDPE. PVDF cannot be fluorinated even at temperatures as high as 430K and/or under UV irradiation. The kinetics associated with the formation and termination of peroxy RO 2 • and fluorocarbon long-lifetime radicals was studied. It is mainly middle peroxy radicals that are formed at treatment conditions close to those used in industrial processes.

Chemical alteration of poly(vinyl fluoride) Tedlar® induced by exposure to vacuum ultraviolet radiation

Abstract In this study the chemical alteration of poly(vinyl fluoride) Tedlar® by vacuum ultraviolet radiation (VUV) (115–400 nm) has been examined using X-ray photoelectron spectroscopy (XPS). The initial F/C atom ratio of 0.34 decreases to 0.17 after a 2-h exposure. The F/C atom ratio is further reduced to a steady-state value of approximately 0.04 after a 24-h exposure. Similarly, the O/C atom ratio is reduced from 0.08 to 0.05 and then to 0.02 during these two exposures. As the F and O are removed by VUV exposure, the C concentration increases from 70.5 to 82.0 and then to 94.6 at.% thus forming a graphitic or amorphous carbon-like layer which erodes more slowly than the virgin Tedlar surface. Exposure of the VUV-damaged surface to O2 results in chemisorption of O, indicating that reactive sites are formed during the chemical erosion by VUV. Further exposure to VUV removes this chemisorbed oxygen but a subsequent exposure to air at atmospheric conditions causes a three-fold increase in O chemisorbed at the surface. Comparison of XPS data indicates that the mechanisms of chemical alteration by VUV radiation and hyperthermal (∼5 eV) atomic oxygen (AO) are similar.

Rotational spectrum, inversion, and geometry of 2,5-dihydrofuran⋯ethyne and a generalization about Z⋯H–C hydrogen bonds

The ground-state rotational spectra of nine isotopomers of a complex formed between 2,5-dihydrofuran and ethyne were recorded with a pulsed-jet, Fourier-transform microwave spectrometer. Rotational and centrifugal distortion constants were obtained for C4H6O...HCCH, C4H6O...DCCH, C4H6O...HCCD, C4H6O...DCCD, [3,4-D2]-C4H6O...HCCH, C4H6O...H13CCH, C4H6O...HC13CH, , and [3(13C]-C4H6O...HCCH. The substituted species were studied in their natural abundances. For the more abundant isotopomers, weak c-type transitions as well as strong a-type transitions were observed. The primary intermolecular binding was shown to consist of a hydrogen bond formed by the ethyne subunit acting as the proton donor and the O atom of 2,5-dihydrofuran as the proton acceptor. The complex has a plane of symmetry that includes the O atom and the ethyne subunit, with a pyramidal configuration at oxygen. A fit of the principal moments of inertia of all nine isotopomers under the assumption of unperturbed 2,5-dihydrofuran and ethyne geometries yielded the values r(O...H)=2.127(8) A, phi=57.8(18) degrees , and theta=16.2(32) degrees, where phi is the angle made by the HCCH subunit at O and theta is the angular deviation of the O...H-C nuclei from collinearity. This geometry is compared with those obtained by ab initio calculations conducted with a range of basis sets and with electron correlation taken into account at the MP2 (Møller-Plesset second order) level of theory. A small inversion doubling (approximately equal to 20-30 kHz) of c-type transitions, well resolved only for the parent isotopomer and [3HCCH, was attributed to a vibrational motion that inverts the configuration at oxygen. A one-dimensional model for this motion was used with a double minimum potential energy function of the type V(phi)=alphaphi(4)+betaphi(2) to estimate the observed separation DeltaE(01) of the lowest pair (v=0 and v=1) of associated energy levels. The predicted DeltaE(01) had the same magnitude as that deduced from the inversion doubling of the c-type transitions. The geometry of C4H6O...HCCH is compared with those other B...HCCH, where B is vinyl fluoride, oxirane, and thiirane. A rationalization of the angular geometries of various B...HX, where X=F, Cl, Br, or CCH, is presented.

Conformational properties of poly (vinyl Fluoride) based upon ab initio electronic structure calculations

The geometries and conformational energies of model segments of poly (vinyl fluoride) (PVF) are obtained from quantum chemistry calculations and used to determine the statistical weight parameters in a rotational isomeric state (RIS) model. The interaction energies show that the electrostatic interaction is important in the molecules containing high electronegative atoms. The calculated characteristic ratio is in agreement with available theoretical values by means of molecular mechanics (MM).