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991.
A conductometric method is proposed for the determination of quaternary ammonium salts (chloride or bromide), based on the poor solubility of the relative perchlorates. A comparison between expected and found values shows that the method is suitable, rapid, and easy for quantities in the range from 0.2 to 5 g. The error depends on the solubility of the relative perchlorate. The apparent and tentative solubility product of the studied compounds were calculated. The obtained values allowed to propose benzyltributyl ammonium chloride (BTBA Cl) as precipitant for the conductometric titration of perchlorate. This easy, rapid and accurate determination can be used to analyze the perchlorate ion even in concentrated solutions and to determine stability constants for complex formation in aqueous solutions. 相似文献
992.
Ivan panik Jan Krupcik Ivan Skacani Jaap De Zeeuw Mario Galli Pat Sandra 《Journal of separation science》1997,20(12):688-692
The separation of isomers and enantiomers of branched C10-C12 phenylalkanes by gas chromatography on fused silica capillary columns coated with some modified β- and γ-cyclodextrins was studied. It was shown that the separation of positional isomers of C10-C12 phynylalkanes on modified cyclodextrin capillary columns is not better than that on a column coated with modified polyethylene glycol. Differences were found in the enantioselectivity of modified β- and γ-cyclodextrins for the separation of C10-C12 secondary phenylalkane enantiomers. While alkylderivatives of β-CDs resolve enantiomers of 3-phenylalkanes, alkyl derivatives of γ-CD resolve enantiomers of 2-phenylalkanes. Since shape selectivity factors of modified cyclodextrins have indicated no inclusion of the considered solutes in cyclodextrin cavities, enantioselective interactions most probably occur on the outer sphere of cyclodextrins. 相似文献
993.
Focant JF Eppe G Scippo ML Massart AC Pirard C Maghuin-Rogister G De Pauw E 《Journal of chromatography. A》2005,1086(1-2):45-60
A comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC x GC-TOF-MS) experimental setup was tested for the measurement of seven 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs), ten 2,3,7,8-substituted polychlorinated dibenzofurans (PCDFs), four non-ortho-polychlorinated biphenyls (PCBs), eight mono-ortho-PCBs, and six indicator PCBs (Aroclor 1260) in foodstuff samples. A 40m RTX-500 (0.18mm I.D., 0.10 microm df) was used as the first dimension (1D) and a 1.5 m BPX-50 (0.10mm I.D., 0.10 microm df) as the second dimension (2D). The GC x GC chromatographic separation was completed in 45 min. Quantification was performed using 13C-label isotope dilution (ID). Isotope ratios of the selected quantification ions were checked against theoretical values prior to peak assignment and quantification. The dynamic working range spanned three orders of magnitude. The lowest detectable amount of 2,3,7,8-TCDD was 0.2 pg. Fish, pork, and milk samples were considered. On a congener basis, the GC x GC-ID-TOF-MS method was compared to the reference GC-ID high resolution mass spectrometry (HRMS) method and to the alternative GC-ID tandem-in-time quadrupole ion storage mass spectrometry (QIST-MS/MS). PCB levels ranged from low picogram (pg) to low nanogram (ng) per gram of sample and data compared very well between the different methods. For all matrices, PCDD/Fs were at a low pg level (0.05-3 pg) on a fresh weight basis. Although congener profiles were accurately described, RSDs of GC x GC-ID-TOF-MS and GC-QIST-MS/MS were much higher than for GC-ID-HRMS, especially for low level pork and milk. On a toxic equivalent (TEQ) basis, all methods, including the dioxin-responsive chemically activated luciferase gene expression (DR-CALUX) assay, produced similar responses. A cost comparison is also presented. 相似文献
994.
Treatment of methyl 2-chloro-2-phenylhydrazonoacetate (1) with 1-phenylsulphonylpropyne (3) in the presence of triethylamine gives pyrazole derivatives due to cycloadditions of a nitrile imine intermediate with 3 and with its rearranged product phenylsulphonylallene (4). 相似文献
995.
In this work we have studied the stabilizing effect of the lignin, obtained as a by-product of the acid hydrolysis of sugar cane bagasse, herein called sugar cane bagasse lignin, on the thermal and environmental degradation of butadiene rubber. This stabilizer was investigated in various concentrations in the pure form and as a substitute for a hindered phenol, in a commercially used formulation also containing a p-phenylene-diamine. For thermal degradation the stabilization level of the commercial sample is reached with 1·3% of pure lignin and the substitution of the hindered phenol in the commercial formulation increased the stabilization by a factor of 1·2. In the environmental ageing experiments the performance of the rubber stabilized with lignin was poorer than that of the commercial sample. This behaviour is assigned to the strong degradative effect of light on the rubber. 相似文献
996.
C. C. Van De Sande 《Journal of mass spectrometry : JMS》1976,11(2):121-129
The electron impact induced loss of a phenoxy radical from the molecular ions of α,ω-bis-aryloxy alkanes ΦO(CH2)nOΦ ( 1 n; n = 2–7) and F-p-C6H4(CH2)nOΦ(2n; n = 2?5) is the result of functional group interaction. Labelling data provide conclusive evidence for the O-aryl tetra-hydrofuranium and O-aryl tetrahydropyranium structures of the resulting decomposing species (lifetimes between 10?6 and 10?5 s) in the case of n = 4 and 5, respectively. Evidence is presented for the occurrence of phenyl participation in the loss of ΦOH from the molecular ions of the lower homologues of 1 n and 2n (n = 2, 3). 相似文献
997.
The gold(I) selenolate compound [Au(2)(SePh)(2)(mu-dppf)] (dppf = 1,1'-bis(diphenylphosphino)ferrocene) has been prepared by reaction of [Au(2)Cl(2)(mu-dppf)] with PhSeSiMe(3) in a molar ratio 1:2. This complex reacts with gold(I) or gold(III) derivatives to give polynuclear gold(I)-gold(I) or gold(I)-gold(III) complexes of the type [Au(4)(mu-SePh)(2)(PPh(3))(2)(mu-dppf)](OTf)(2), [Au(3)(C(6)F(5))(3)(mu-SePh)(2)(mu-dppf)], or [Au(4)(C(6)F(5))(6)(mu-SePh)(2)(mu-dppf)], with bridging selenolate ligands. The reaction of [Au(2)(SePh)(2)(mu-dppf)] with 1 equiv of AgOTf leads to the formation of the insoluble Ag(SePh) and the compound [Au(2)(mu-SePh)(mu-dppf)]OTf. The complexes [Au(4)(C(6)F(5))(6)(mu-SePh)(2)(mu-dppf)] and [Au(2)(mu-SePh)(mu-dppf)]OTf (two different solvates) have been characterized by X-ray diffraction studies and show the presence of weak gold(I)-gold(III) interactions in the former and intra- and intermolecular gold(I)-gold(I) inter-actions in the later. 相似文献
998.
Eduardo Corts Cortas Miryan Adaya Baos Olivia García‐Mellado De Corts 《Journal of heterocyclic chemistry》2004,41(2):277-280
A new synthesis to obtain eleven novel derivatives of 11‐[(o‐ m‐ and p‐substituted)‐phenyl]‐8‐chloro‐3,3‐dimethyl‐2,3,4,5,10,11‐hexahydro‐1H‐dibenzo[b,e][1,4]diazepin‐1‐ones with possible pharmacological activity in the central nervous system in two efficient steps has been developed. The final products were obtained by condensation and cyclization between 3‐[4‐chloro‐1,2‐phenylenediamine]‐5,5‐dimethyl‐2‐cyclohexenone with (o‐ m‐ and p‐substituted)benzaldehyde. The structure of all products was corroborated by ir, 1H‐nmr, 13C‐nmr and high resolution in ms. 相似文献
999.
Defoer N De Bo I Van Langenhove H Dewulf J Van Elst T 《Journal of chromatography. A》2002,970(1-2):259-273
The relationship between chemical concentrations (gas chromatography–mass spectrometry analysis) and odour concentrations (olfactometry) was studied for biofilter emissions from four aerobic vegetable, fruit and garden waste (VFG) composting plants and one animal rendering plant. For the VFG composting plants, the study revealed a good linear relationship of the odour concentration with the total volatile organic compounds (VOC) concentration (R2=0.97, n=16) as well as with the concentration of esters and ketones (R2=0.9, n=19). For biofilter emissions of the animal rendering plant, the total VOC concentration was a poor estimator for odour concentration. However, for this type of odour, concentrations of organic sulphur containing compounds correlated well with odour concentrations (R2=0.94, n=8). The results of the study also showed that the relationship between chemical and odour concentrations is specific for each type of odour and cannot be generalized. 相似文献
1000.
W. H. S. Brandão A. L. Aguiar L. A. Ribeiro D. S. Galvão J. M. De Sousa 《Chemphyschem》2021,22(7):701-707
Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( and ) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( ). Moreover, it was obtained that Young's modulus (YMod) (750–900 GPa) and ultimate strength (σUS) (120–150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. YMod values obtained for PopNTs are not significantly temperature-dependent. While the σUS values for the showed a quasi-linear dependence with the temperature, the exhibited no clear trends. 相似文献