Estimating the PDMS-Coated, SPME-Fibre/Water- and Fibre/Gas-Partition Coefficients of Chlorinated Ethenes by Headspace-SPME

In this work, a simple, fast and reproducible method is presented for the determination of fibre/liquid-phase and fibre/gas-phase partition coefficients of five chlorinated ethenes on a poly-(dimethylsiloxane), PDMS-coated, solid-phase microextraction fibre, by employing a headspace HS-SPME coupled with gas chromatography. The partition coefficients were estimated by a numerical method using a Level-I fugacity method coupled with parameter-estimation software. Dimensionless partition coefficients between SPME fibre and liquid as well as gas phases were obtained at temperatures of 10 °C, 25 °C and 30 °C. The partition coefficients of the fibre and the gas phase, K _fg, increase with decreasing temperature by a factor of ≈2 to 6, and they are directly proportional to the linear slope of the regression line. The same tendency is observed for the partition coefficient of the fibre and liquid phase, K _fw, in a factor ≈1.2 to 2.0. The sorption enthalpy is higher in the gas phase; therefore, the sorption onto the fibre is favoured at lower temperatures. The correlation of the log K _ow versus log K _fw and log K _oa versus log K _fg shows a linear relationship with the number of chlorine atoms in the C = C molecule. Long-term experiments resulted in sorption to Teflon surfaces and possible losses in 43 mL vials, not observed in 250 mL Boston bottles.     

Statistical Spectral Analysis of liquid X-ray Diffraction Data

Abstract

The experimental procedure of determining the structure of a liquid by diffraction techniques is reformulated herein as a stochastic experiment subject to the data analysis formalism of statistical spectral analysis. Observed in such an experiment are averaged local microscopic fluctuations from the bulk density. The intensity function then represents a stochastic spectrum and it becomes necessary to statistically estimate a minimum bias, minimum variance covariance function which is the net radial distribution function. A low-pass tapered data window produces such an optimum estimate.     

Short communication: An alternative and effective catalyst for the silastannation of arylacetylenes with Me3SiSnBu3 at room temperature

The palladium‐catalyzed silastannation of acetylenes with tributyl(trimethylsilyl)stannane in the presence of triethylphosphite is reported for the first time. The reaction occurs at room temperature to give (Z)‐silyl(stannyl)ethenes in high yields. The protodemetallation of the resulting adducts with HCl–tetraethylammonium chloride is described first, which demonstrates that the reaction is governed only by the stability of a carbonium ion arising from the protonation to (Z)‐silyl(stannyl)ethenes rather than the hard and soft acid and base principle, i.e. the β‐cation stabilization effect (σ–π stabilization one) of a stannyl group in the carbonium ion is rather significant. Copyright © 2004 John Wiley & Sons, Ltd.     

Direction of protophilic hydrogen isotope exchange incis-1-ferrocenyl-2-(nitrophenyl)ethenes and calculation of atomic charges

Results of the calculation of atomic charges incis-1-ferrocenyl-2-(nitrophenyl)ethenes with the nitro group at positions 2 and 4 are in full agreement with the behavior of these compounds in the reaction of protophilic hydrogen isotope exchange.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1494–1495, August, 1993.     

Reaction of Polymer-supported Selenovinyl Bromide with Grignard Reagents： A Facile Route to the Synthesis of （E）-1, 2-Disubstituted Olefins

Polymer-supported selenovinyl bromide, easily prepared from polymer-supported selenenyl bromide with acetylene, reacts with different Grignard reagents using a step-by-step strategy to obtain （E）-1, 2-disubstituted ethenes in good yields.     

The13C/12C and 2H/1H Ratios of Trichloroethene,Tetrachloroethene and Their Metabolites

Abstract

Isotope ratios of technically and biologically produced halogenated hydrocarbons (HHC) are presented. Compared to the parent compounds, there is a significant enrichment of deuterium depending on the manner of production, whereas the carbon isotope ratio was only slightly influenced. Furthermore, there is nearly no alteration of the carbon isotope ratio due to biological degradation, so that the carbon fingerprint of the parent compounds is maintained in the metabolites. In contrast to this, the hydrogen isotope ratio of the metabolites reflects the ratio of the surrounding water. These results show that the isotopic fingerprint is a useful tool to distinguish between age, different charges of chemical dumping, and in addition to that, whether there is a contamination with technical products or residual metabolites.     

New tetrakis(4-aminophenyl)ethenes: synthesis and electrochemical investigations

Four novel functional conjugated tetraarylamines containing a tetraphenylenecore were synthesized via Ni-catalyzed aryl amination followed by McMurry olefination. Their electrochemical properties were studied by cyclic voltammetry, coulometry, and electrolysis monitored by UV-vis spectroscopy, and discussed with regard to those of the known tetrakis(dimethylaminophenyl)ethane.     

Photochromic dihetarylethenes. 10. Photochromic 1,2-bis[2-(benzothiazol-2-yl)-3-thienyl]- and 1,2-bis[2-(benzothiazol-2-yl)benzothiophen-3-yl]ethenes

Dithienylethenes containing the thiophene rings with benzothiazolyl substituents in position 2 were synthesized. 1,2-Bis[2-(benzothiazol-2-yl)benzothiophen-3-yl]hexafluorocyclopentene and 1,2-bis[2,5-di(benzothiazol-2-yl)-3-thienyl]hexafluorocyclopentene possess photochromic properties. The open forms of 1,2-bis(2-benzothiazolylhetaryl)ethenes fluoresce, but introduction of the benzothiazole rings into dihetarylethenes significantly lowers the fatigue resistance of photochromes and favors thermal reversibility.     

Synthesis and absorption spectral properties of substituted phenylfurylbenzothiazoles and their vinylogues

Summary A number of substituted 2-(5-aryl-2-furyl)benzothiazoles and their vinylogues were synthesized from corresponding 5-arylfurfurals by convenient methods. The yields of products and their UV/Vis spectroscopic properties are substituent-dependent.

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Synthese und absorptionspektroskopische Eigenschaften von substituierten Phenylfurylbenzthiazolen und ihren Vinylogen

Zusammenfassung Einige substituerte 2-(5-Aryl-2-furyl)benzthiazole und ihre Vinyloge wurden aus entsprechenden 5-Aryl-furfuralen synthetisiert. Die Ausbeuten an Produkten sowie ihre absorption-spektroskopischen Eigenschaften sind vom Substituenten abhängig.

     

Bamford-Stevens reaction assisted synthesis of styrene C-glycosides

Modification of carbohydrates and their analogs is hindered due to multi-step synthetic methodologies involving selective protection and deprotection of multiple hydroxyl groups present in the molecule. A highly efficient route for the synthesis of 1-phenyl-2-(β-D-glycopyranosyl)ethenes has been developed from native sugars, which neither requires protection/deprotection of the hydroxyl groups nor use of any metal/metal ions. The key step of the developed methodology is the use of Bamford-Stevens reaction which led to the formation of the desired compounds in moderate to high yields in three steps only.