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51.
Reactions of carboxylic acids with lead play an important role in the atmospheric corrosion of lead and lead-tin alloys. This is of particular concern for the preservation of lead-based cultural objects, including historic lead-tin alloy organ pipes. Two initial corrosion products, Pb(3)O(2)(CH(3)COO)(2)·0.5H(2)O (1) and Pb(2)O(HCOO)(2) (2), had been identified through powder diffraction fingerprints in the Powder Diffraction File, but their structures had never been determined. We have crystallized both compounds using hydrothermal solution conditions, and structures were determined using laboratory and synchrotron single-crystal X-ray diffraction data. Compound 1 crystallizes in P1, and 2 in Cccm. These compounds may be viewed as inorganic-organic networks containing single and double chains of edge-sharing Pb(4)O tetrahedra and have structural similarities to inorganic basic lead compounds. Bond valence sum analysis has been applied to the hemidirected lead coordination environments in each compound. Atmospheric exposure experiments contribute to understanding of the potential for conversion of these short-term corrosion products to hydrocerussite, Pb(3)(CO(3))(2)(OH)(2), previously identified as a long-term corrosion product on lead-rich objects. Each compound was also characterized by elemental analysis, thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), and Raman spectroscopy. 相似文献
52.
Supported liquid membrane (SLM) and solid phase extraction (SPE) have been applied as clean-up and/or enrichment techniques for a mixture of five benzimidazole anthelmintics compounds, namely albendazole, fenbendazole, mebendazole, oxibendazole, and thiabendazole. Two biological matrices, mainly urine and milk, and ultra high purity (UHP) water were spiked with a mixture of these five compounds. Waters Oasis® MCX and International Sorbent Technology (IST) HCX SPE sorbents were used. The liquid membrane used for clean-up and/or enrichment of these compounds was 5% tri-n-octylphosphine oxide (TOPO) dissolved in n-undecane/di-n-hexyl ether (1:1). The SLM extraction efficiencies and SPE percentage recoveries ranged between 60 and 100%. The detection limits (DLs) for different benzimidazole compounds by SPE/LC-ES-MS for thiabendazole, oxibendazole, and albendazole was 0.1 ng/L, for fenbendazole and mebendazole was 1 and 10 ng/L, respectively. Similarly, the detection limits of SLM/LC-ES-MS for thiabendazole, oxibendazole, and albendazole was 0.1 ng/L and for fenbendazole and mebendazole was 1 ng/L. The results of optimization of various parameters of the SLM method are reported. 相似文献
53.
Aebischer OF Aebischer A Tondo P Alameddine B Dadras M Güdel HU Jenny TA 《Chemical communications (Cambridge, England)》2006,(40):4221-4223
The self-assembled architectures in solution of a new HBC derivative bearing perfluoroalkylated side chains were investigated by optical excitation and emission spectroscopy and correlated to cryo-SEM, a new technique in organic chemistry. 相似文献
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Titus Niedermaier 《Fresenius' Journal of Analytical Chemistry》1962,187(6):415-425
Zusammenfassung An reinen Kaliumphosphat-Testlösungen mit bekannten Phosphorgehalten wurden die Einflüsse von Salzsäurekonzentration und Citronensäuremenge auf die Fällung des Phosphors als Chinoliniummolybdatophosphat untersucht und dabei Grenzwerte ermittelt, die nicht unterbzw. überschritten werden dürfen. Bei Düngemittelanalysen interessiert in vielen Fällen nur der für die Pflanze verfügbare Phosphorgehalt. Dieser Phosphoranteil wird nach vereinbarten Methoden meistens durch Extraktion mit alkalischer oder neutraler Ammoniumcitratlösung in Lösung gebracht. Diese relativ hohen Konzentrationen an Citronensäure, die die Phosphatlösung auf diese Weise zwangsläufig erhält, bringen es mit sich, daß für die Wahl des aliquoten Teils nicht mehr allein die für die Bestimmungsmethode maximal zulässige Phosphormenge maßgebend sein kann, sondern daß auch die Grenzen der zulässigen Citronensäuremenge berücksichtigt werden müssen.Weiter wurden Versuche angestellt, die auf eine Vereinfachung der Methode hinausliefen.Auf Grund unserer Untersuchungsergebnisse wurde eine von Perrin abweichende Arbeitsvorschrift zusammengestellt.Über einen großen Teil dieser Ergebnisse ist im Rahmen eines Vortrages am 27. September 1961 auf der Jahreshauptversammlung des Verbandes Deutscher Landwirtschaftlicher Untersuchungs- und Forschungsanstalten in Freiburg im Breisgau berichtet worden.Herrn Hugo Fay möchte ich auch an dieser Stelle für die sorgfältige Ausführung zahlreicher Bestimmungen vielmals danken. 相似文献
57.
Stefan Huber Peristera Stamouli Titus Jenny Reinhard Neier 《Helvetica chimica acta》1986,69(8):1898-1915
1,3-Butadienyl Thiocyanates in the Diels-Alder Reaction Followed by a [3,3]-Sigmatropic Shift (E)- and (Z)-1,3-Butadienyl thiocyanates 3 , 4 , and 12–15 have been synthesized selectively. Their use as dienes for Diels-Alder reactions followed by a [3,3]-sigmatropic shift to obtain an isomeric isothiocyanate has been studied. The butadienyl thiocyanates are, unfortunately, not very reactive in Diels-Alder reactions. This disadvantage can be overcome, if a trapping reaction with EtOH is added to the two-step sequence. This sequence allows to get good yields of the O-ethyl thiocarbamates 18–23 , even if the first two reactions have not favorable equilibrium constants. 相似文献
58.
The structure of triphenylselenonium chloride dihydrate has been determined by single-crystal X-ray diffraction techniques. Crystals of the compound C18H15Se+, Cl–, 2H2O are monoclinic, space groupC2/c, witha = 12.798(3),b = 13.802(1),c = 19.933(34) Å, = 9.0.0(1) ° andZ = 8. The structure was refined by full-matrix least-squares methods from 1444 diffraotometer intensities to a conventionalR of 0.067 and a weightedR of 0.072. The structure consists of pairs of triphenylselenonium cations which are weakly joined through pairs of bridging chloride ions. The water molecules are clustered in groups of four, separated by the triphenylselenonium chloride dimers. The hydrogen atoms of the water could not be positioned unambiguously, but it appears that hydrogen bonds link the four water molecules and the chloride ions together. 相似文献
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60.
Three-dimensional X-ray crystal structure analysis shows that the organotelluronium salt, triphenyltelluronium cyanate-chloroform(
), exists as a tetramer in the solid state with both end-to-end and terminally bridging NCO groups. The oligomer is predominantly ionic with tellurium—nitrogen and tellurium—oxygen distances significantly shorter than respective van der Waals distances. Refinement of the structure, based on 3817 reflections collected by automatic diffractometry, converged to a conventional R factor of 4.9% and a weighted R factor of 4.2%. Crystal data for Ph3Te(NCO) ·
CHCl3 are as follows: a = 12.083(6)Å, b = 12.900(12)Å, c = 13.878(10)Å, α = 95.83(7)°, β = 103.47(7)°γ = 98.87(6)°, V = 1901Å3 (temperature = 23°C) and Z = 4. 相似文献