In situ soft X-ray studies of ethylene oxidation mechanisms and intermediates on the Pt(111) surface

In situ studies of ethylene oxidation on Pt(111) have been performed using a powerful combination of fluorescence yield soft X-ray methods for temperatures up to 600 K and oxygen pressures up to 0.01 Torr. Absolute carbon coverages have been determined both in steady-state and dynamic catalytic conditions on the Pt(111) surface. Fluorescence yield near-edge spectroscopy (FYNES) and temperature-programmed fluorescence yield near-edge spectroscopy (TP-FYNES) experiments above the carbon K edge were used to identify the structure and bonding of the dominant surface species during oxidation. TP-FYNES experiments of preadsorbed ethylene coverages in oxygen pressures up to 0.01 Torr indicate a stable intermediate is formed over the 215-300 K temperature range. By comparing the intensity of the C-H sigma resonance at the magic angle with the intensity in the carbon continuum, the stoichiometry of this intermediate has been determined explicitly. Based on calibration with known C-H stoichiometries, the intermediate has a C(2)H(3) stoichiometry for oxygen pressures up to 0.01 Torr, indicating oxydehydrogenation occurs before skeletal oxidation. FYNES spectra at normal and glancing incidences were performed to characterize the structure and bonding of this intermediate. Using FYNES spectra of ethylene, ethylidyne, and acetylene as reference standard, this procedure indicates the oxidation intermediate is tri-sigma vinyl. Thus, oxidation of ethylene proceeds through a vinyl intermediate, with oxydehydrogenation preceding skeletal oxidation.     

Polynuclear nonfused bis(1,3,4-oxadiazole)-containing systems

Nonfused bis-1,3,4-oxadiazoles were synthesized by reaction of 5-substituted mono-and bis-tetrazoles with mono-and dicarboxylic acid chlorides. The results of kinetic studies showed that the transformation of tetrazoles into 1,3,4-oxadiazoles is accelerated by 1 to 2 orders of magnitude on addition of a catalytic amount of dimethylformamide, triethylamine, or pyridine.     

The effect of preparation procedure and composition of water-ethanol suspensions of amorphous silica on their aggregative stability and kinetics of coagulation

The method of flow ultramicroscopy is employed to study the effect of the composition and preparation procedure of dilute water-ethanol suspensions of two samples of amorphous silica (fractionated fused quartz and monodisperse amorphous silica) on the kinetics of their coagulation. It is revealed that all suspensions prepared by the addition of silica powders to water-ethanol mixtures with ethanol contents of 96 and 40 vol % are stable with respect to aggregation, as the suspensions prepared by the addition of aliquots of concentrated dispersions of the aforementioned silica samples in 96% ethanol aged for different time periods to water-ethanol mixtures containing 96 vol % ethanol. At a 40-vol % content of ethanol in the mixture, the coagulation whose character (including “superfast” coagulation) substantially depends on the time of aging of initial concentrated silica dispersions occurs. Furthermore, kinetic studies are performed for the coagulation of dilute silica suspensions prepared by the addition of silica powders to water-ethanol solutions containing 40 vol % of ethanol and traces (<1 ppm) of poly(ethoxysilane), poly(acrylic acid), and a supernatant prepared by the centrifugation of concentrated silica dispersion in 96% ethanol aged for more than 3 months. It is found that the addition of aliquots of the aforementioned ethanol solutions to silica suspensions in 40% ethanol, which are initially stable with respect to aggregation, causes their superfast coagulation.     

Contents and localization of heavy metals in human placentae

The placenta was used as an exposure index for the risk evaluation of prenatal fetal chemical exposure. Full-term placenta samples collected at maternity hospitals in 4 regions of different environmental pollutants and traffic density were examined for lead and cadmium contents using atomic absorption spectrometry (AAS). The results showed similar lead contents in placental samples from all selected regions, except for a small town with a lower traffic density. The findings may implicate traffic-related environmental lead pollution, rather than industrial sources. The highest concentration of cadmium was shown to be in the samples collected from the region with the highest proportion of smoking mothers (including passive smoking). Simultaneously, the placental samples were processed histochemically to determine the location of lead in the placental tissue (using light microscopy). The degree of placental metal contamination was done semiquantitatively, and the difference between the rural and industrial region was statistically compared. Parallel quantitative AAS analyses and semiquantitative histochemical lead analyses of human placental samples revealed analogous results regarding the level of placental contamination with metals. Received: 30 June 1997 / Revised: 21 December 1997 / Accepted: 30 December 1997     

Sorption properties of technical lignins. III. IR-spectral investigation of the sorption capacity of technical lignins and their derivatives in relation to bile acids

It has been established by IR-spectral investigations that the sorption of bile acids by technical lignins takes place through the formation of hydrogen bonds between the functional groups of thelignins and the bile acids, the form of these bonds being determined by nature of the lignins and acids concerned. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 240 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 545–547, July–August, 1998.     

Complexation of Ni (II) and Zn(II) ions by 3-(1-naphthyI)-2-mercaptopropenoic acid

The complexation equilibria between Ni(II) and Zn(II) metal ions with 3-(1-naphthyl)-2-mercaptopropenoic acid (H₂NMP) were studied by glass electrode potentiometry, at 25 °C and 1.0 mol·dm^–3 in NaClO₄ as constant ionic medium in 50% (v/v) water-ethanol solutions. Formation constants for the complexes Ni(NMP), Ni(NMP) ₂ ^2– , Zn(NMP) and Zn(NMP) ₂ ^2– , refined by the MINIGLASS program, are reported.     

The structure of the 1-1-difluoroethylene radical anion and the factors determining the hyperfine interaction with 19F

A structure with a pyramidal -CF₂ group is shown to desribe satisfactorily hyperfine interactions in CH₂CF_$\text{2}$ radical anions within the framework of the INDO method. The factors responsible for the substantial difference in the degree of spin density delocalization on F in CH₂CF_$\text{2}$ and C₂F_$\text{4}$ are analyzed.     

Molecular orbital study of gas phase basicities of carbofunctional derivatives of group IVB elements; stereochemical control

The gas phase basicities of a series of carbofunctional derivatives H₃M(CH₂)_nX (M = C, Si, Ge; X = NH₂, OH, F; n = 1–3) were investigated by the semiempirical CNDO/2 method. The calculations indicate that the electronic effects of silyl- and germyl-substituents differ greatly from the effect of simple alkyls. Moreover, in contrast to simple carbon derivatives, the overall nature of the electronic effects of siliyl- and germyl-substituents is crucially influenced by the molecular conformation.     

Nachweis von Oxoverbindungen. IV

Zusammenfassung Enolisierende Oxoverbindungen, die eine - CH₂-CO- oder eine- CO-NH-NH-Gruppe enthalten, geben mit Diazoniumsalz eine Farbreaktion. Formaldehyd, Benzaldehyd, Nitrobenzaldehyde, Benzoin, Benzophenon usw. reagieren dabei nicht. 1,3-Diketone geben mit diazotiertem p-Nitroanilin zweierlei Färbungen, bei geringer Diazoniumsalzkonzentration eine rote, bei großem Überschuß eine blaue oder grüne Färbung. Die Reaktionsgeschwindigkeit ändert sich auch nach der Art des Diazoniumsalzes. Mit dieser Methode wurden selektive Nachweise für Oxoverbindungen ausgearbeitet. Acetonspuren können in Äthanol bzw. in Wasser oder in Methyläthylketon mit diazotiertem Anilin, 10^–3 % Acetessigsäureäthylester in Äthylacetat mit diazotiertem p-Phenetidin, 10^–5 % Acetylaceton in Aceton mit diazotiertem p-Nitroanilin, außerdem Acetaldehyd neben Formaldehyd, Acetylphenylhydrazin neben Acetanilid, mbzw. o- neben p-Nitroanilin nachgewiesen werden. Nach dem Absorptionsspektrum erwies sich das Reaktionsprodukt von Aceton mit diazotiertem p-Nitroanilin als eine Azoverbindung.

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Detection of Oxocompounds. IV

Summary Enolizing oxo-compounds, that contain a -CH₂-CO- or a -CO-NH-NH-group, yield a color reaction with diazonium salt. Formaldehyde, benzaldehyde, nitrobenzaldehyde, benzoin, benzophenone etc. however do not show this reaction. 1,3-diketones yield two kinds of color reactions with diazotizedp-nitraniline; a slight diazonium salt concentration yields a red coloration, while a large excess gives a blue or green coloration. Selective detections for oxo-compounds were developed with this method. Traces of acetone may be detected in ethanol or water or in methylethyl ketone by means of diazotized aniline, 10^–3% of acetoacetic ester can be detected in ethyl acetate by means of diazotizedp-phenetidine, 10^–5% acetylacetone in aldehyde, acetylphenylhydrazine in the presence of acetanilide,m- oro- in the presence ofp-nitraniline. Judging from the absorption spectrum, the reaction product from acetone and diazotizedp-nitraniline is an azo compound.

     

2-arylfuro [2,3-b] quinoxalines

2-Arylfuro[2,3-b]quinoxalines were obtained by cyclization of 2-phenacyl-3-quinoxalones in the presence of polyphosphoric acid or a mixture of phosphorus oxychloride and phosphorus pentachloride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 259–260, February, 1973.