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991.
992.
Bunyard WC Kadla JF DeYoung J DeSimone JM 《Journal of the American Chemical Society》2001,123(30):7199-7206
The thermal decomposition of the free-radical initiator bis(perfluoro-2-N-propoxyprionyl) peroxide (BPPP) was studied in dense carbon dioxide and a series of fluorinated solvents. For the fluorinated solvents, the observed first-order decomposition rate constants, k(obs), increased with decreasing solvent viscosity, suggesting a single-bond decomposition mechanism. The k(obs) values are comparatively larger in dense carbon dioxide and similar to the "zero-viscosity" rate constants extrapolated from the decomposition kinetics in the fluorinated solvents. The decomposition activation parameters demonstrate a compensation behavior of the activation enthalpy with the activation entropy upon change in solvent viscosity. Comparison of the change in activation parameter values upon change in solvent viscosity for BPPP with two additional initiators, acetyl peroxide (AP) and trifluoroacetyl peroxide (TFAP), further suggests that carbon dioxide exerts a very minimal influence on the decomposition mechanism of these initiators through solvent-cage effects. 相似文献
993.
An air-gap sulfide sensor is presented which operates on the basis of selective extraction of H2S from an acidified sample into a small alkaline electrolyte film containing the dicyanoargentate (I) complex. This complex is partly decomposed during the measurement by the absorbed sulfide, and the potential of a silver sulfide-based indicator electrode which is in direct contact only with the electrolyte, then depends on the sulfide concentration of the sample. Because of the extraction and dissociation equilibria, the sensor responds in the low sulfide concentration range with a slope four times larger than that of a normal sulfide electrode. The lower limit of linearity is 10?8 mol l?1, because sulfide accumulates in the electrolyte film. 相似文献
994.
995.
Acrylonitrole can be grafted in the bulk of PTFE films provided the monomer is allowed to diffuse into the grafted zones. For a given radiation dose, the amount of grafting is higher the lower the dose-rate. Even higher grafting efficiencies are reached under conditions of discontinuous irradiations, the reacting mixture being stored in the dark in a thermostat between successive irradiations. The grafting yield is higher the higher the storage temperature. The bulk grafting involves a progressive swelling of the grafted polyacrylonitrile branches by acrylonitrile monomer via a dipole-dipole association of the -CN groups of the monomer with the -CN groups in the polymer. 相似文献
996.
Vibrational and Electronic Spectra of Bond-Isomeric Hexakis(thiocyanato-isothiocyanato)ruthenates(III) Well resolved IR, Raman, and Electronic spectra of the bond isomeric complexes (TBA)3[Ru(NCS)n(SCN)6?n], n = 1–5, including the pairs of geometric isomers n = 2, 3, 4, are recorded at low temperatures (10 and 80 K). Characteristic vibrations of the N- or S-coordinated ambident ligand SCN? occur as listed: νCS(N): 810–850, νCS(S): 690–710, δNCS: 450–490, δSCN: 420–450, νRuN: 300–350, νRuS: 270–295 cm?1. The assignment of the complexes is based on stepwise increasing intensities of the νCS(N) modes with increasing number of N-coordinated ligands. Characteristic shifts and splittings in the spectra allow to distinguish the geometric bond isomers according to their different symmetries. Even the absorption spectra in the visible range show within the series of bond isomers and for the cis/trans pairs systematic alternations. 相似文献
997.
Summary The problems encountered in the development of ultra micro methods or trace methods of elemental analysis are generally discussed. It is shown that process analyses (e.g. titrations) are preferable to meet needs of accuracy and sensitivity. Moreover, continuous systems of chemical process analyses seem to give a solution to the generally stated problems.
Überlegungen zur Minimalisierung in der Ultramikroelementaranalyse
Zusammenfassung Die Probleme bei der Entwicklung von Ultramikro- oder Spurenmethoden in der Elementaranalyse werden allgemein diskutiert. Es wird gezeigt, daß Prozeßanalysen (z.B. Titrationen) den Anforderungen an Genauigkeit und Empfindlichkeit entsprechen. Darüber hinaus scheinen kontinuierliche Systeme chemischer Prozeßanalysen eine Lösung der aufgezeigten Probleme zu ermöglichen.
We thank the Czechoslovak Academy of Sciences, the Analytical Department of the Charles University of Prague and the High School for Chemical Technology of Pardubice for the possibility given to one of us (B.G.) to discuss with many colleagues in the SSR, the ideas presented in this article. 相似文献
998.
R. Belcher J. R. Majer W. I. Stephen I. J. Thomson P. C. Uden 《Analytica chimica acta》1970,50(3):423-431
Preparative details for perfluoroalkanoylpivalylmethanes and their lead chelates are given. Thermal analysis, gas chromatography and mass spectral studies all indicate high thermal stability, but strong column interaction makes successful quantitative gas chromatography difficult. The integrated ion-current technique is applied to determine lead heptafluorobutanoylpivalylmethanate in the range 10-9–10-7 g of lead, but a lower detection limit of ca. 10-14 g is indicated. 相似文献
999.
1000.
Yu. E. Pelcher A. K. Aren Z. A. Bomika G. Ya. Vanag 《Chemistry of Heterocyclic Compounds》1969,5(2):232-236
Intramolecular cyclization of the diamides and N,N-dimethylamides of -[indan-1,3-dion-2-yl]benzylmalonic acids (I) has given 1-aryl-2-carbamoyl-1,2,3,4-tetrahydro-4-azafluorene-3, 9-diones and 1-aryl-4-methyl-2-methylcarbamoyl-1,2,3,4-tetrahydro-4-azafluorene-3,9-diones (II). The structure of compounds II was shown by chemical methods: bromination, xanthylation, and hydrolysis in alkaline and acid media, and also by a study of IR and UV spectra. 相似文献