The reactions of phenolic reagents with α-bromo Michael acceptors in the K2CO3-acetone system. A stereospecific AdSNE process.

α-bromo Michael acceptors undergo ipso-substitution by phenol or benzenethiol in the K₂CO₃-acetone system, the reaction originating the (Z) isomers, via a stereospecific Ad_SNE process.     

Nucleophilic substitution of α-halo-ketones. XXIII. Acetolysis of 1-chloro-3-phenoxy-1-phenylthio-2-propanones. An intramolecular trans-acetylation involving phenoxide anion as the leaving group

The acetolyses of α-chloro-ketones1a-c,2a-c,9a and11a have been investigated parallely. Several aspects of the mechanisms involved in chlorine normal and cine substitution have been elucidated. Intramolecular trans-acetylation, ultimately leading to fragmentation of acetoxy-ketones3b,4a and4c, have been postulated to account for the formation of thiol ester6, aldehyde5a and ketone5c, respectively.     

Anodic stripping voltammetric determination of bismuth after solid-phase extraction using amberlite XAD-2 resin modified with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

A highly selective and sensitive anodic stripping differential pulse polarographic method has been developed for the determination of trace amount of bismuth in various samples after adsorption of its 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex on amberlite XAD-2 resin in the pH range of 2.0-3.0. The retained analyte on the resin recovered with 10.0 ml of 2 M hydrochloric acid and bismuth is determined by anodic stripping differential pulse polarography. In this case, 0.15 μg of bismuth can be concentrated in the column from 1100 ml of aqueous sample, where its concentration is as low as 0.14 ng ml⁻¹ and the linearity is maintained in the concentration range 0.05-160 μg ml⁻¹ in final solution with a correlation coefficient of 0.999 and relative standard deviation of ±1.2%. Various parameters such as the effect of pH, flow rate, and interference of number of metal ions on the determination of bismuth have been studied in detail to optimize the conditions for determination of bismuth in standard alloys: Nippon Keikinzoku Kogyo (NKK CRM No. 916 aluminum alloy); (NKK CRM No. 1021 Al, Si, Cu, Zn alloy); and (NKK CRM No. 920 aluminum alloy), biological samples: National Institute for Environmental Studies (NIES, No. 5 human hair; NIES, No. 7 tea leaves) and water samples: (spring water, river water; Kerman water; and Shiraz water).     

Studies of the mixed adsorption layer on a mercury electrode in the systemp-toluidine-polyethyleneglycol-1M NaClO4

Summary The properties of the mixed adsorption layer on a mercury electrode in the system 1M NaClO₄-p-toluidine-polyethyleneglycol (average molecular masses of polyethyleneglycols: 400 or 10000) are discussed. The parameters of theFrumkin and virial isotherms were determined in the range of strong adsorption potentials. In the range of more negative potentials, a mixed adsorption layer was found by investigating the kinetics of the reduction of Zn(II) ion as a pilot ion. Depending on the concentration ratio of the studied organic substances, inhibition, acceleration, or compensation of both with respect to Zn(II) electroreduction was observed. In the presence of polyethyleneglycol, the efficiency of the Zn(II) ion electroreduction increases due to a greater adsorption lability ofp-toluidine molecules on the mercury surface.

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Untersuchung der gemischten Adsorptionsschicht an einer Quecksilberelektrode im Systemp-Toluidin-Polyethyleneglycol-1M NaClO₄

Zusammenfassung Die Eigenschaften der gemischten Adsorptionsschicht an einer Quecksilberelektrode trode im System 1M NaClO₄-p-Toluidin-Polyethyleneglycol(durchschnittliche Molmassen der Polyethylenglycole: 400 bzw. 1000) werden diskutiert. Die Parameter derFrumkin- und Virialisotherme wurden im Bereich hoher Adsorptionspotentiale bestimmt. Im Bereich negativerer Potentiale wurde durch Untersuchung der Kinetik der Elektroreduktion von Zn(II)-Ionen als Pilotionen eine gemischte Adsorptionsschicht gefunden. In Abhängigkeit von der Konzentration der organischen Verbindungen beobachtet man bezüglich der Elektroreduktion von Zn(II) Hemmung, Beschleunigung oder eine gegenseitige Kompensation beider Effekte. In Gegenwart von Polyethyleneglycol nimmt die Effizienz der Elektroreduktion von Zn(II) aufgrund einer höheren Adsorptionslabilität derp-Toluidin-Moleküle an der Quecksilberoberfläche zu.

     

Preparation and characterization of novel PES‐(SiO2‐g‐PMAA) membranes with antifouling and hydrophilic properties for separation of oil‐in‐water emulsions

In the present study, modification of nanoparticles (NPs) was investigated to mitigate aggregation of SiO₂ nanoparticles and improve the polymeric membrane's performance. For this purpose, the surface of SiO₂ nanoparticles was activated with amine groups, and polymethacrylic acid (PMAA) was grafted on the surface of NPs by atom transfer radical polymerization. Modified NPs were characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) tests. Polyethersulfone (PES) membranes were fabricated with both SiO₂ and SiO₂‐g‐PMAA NPs via nonsolvent‐induced phase separation method. The fabricated membranes were characterized regarding their permeability, hydrophilicity, and porosity properties, and their separation efficiency was tested using the synthetic oil‐in‐water emulsion. The surface and cross‐sectional morphologies of membranes were observed by field emission scanning electron microscopy (FESEM). The experimental trials showed that modified NPs dispersed more uniformly in the structure of membranes and hydroxyl groups on the surface of NPs acted more effectively. Modification of NPs enhance the membrane performance in terms of permeate flux, hydrophilicity, and porosity. NPs modification improved the permeate flux about 46%. Oil rejection for all tested membranes was more than 98%, and modification of NPs did not reduce the rejection of membranes. The optimum concentration was obtained as 1 wt.% and 1.5 wt.% for SiO₂ and SiO₂‐g‐PMAA, respectively. Aggregation effect dominated at concentrations beyond the optimum values that decreased the permeate flux, consequently.     

Thin sums matroids and duality

Building on the recent axiomatisation of infinite matroids with duality, we present a theory of representability for infinite matroids. This notion of representability allows for infinite sums, and is preserved under duality.     

Flame atomic absorption spectrometric determination of trace amounts of lead, cadmium and nickel in different matrixes after solid phase extraction on modified multiwalled carbon nanotubes

The potential of modified multiwalled carbon nanotubes (a solid-phase extraction sorbent), for the simultaneous separation and preconcentration of lead, cadmium and nickel; has been investigated. Lead, cadmium and nickel, were adsorbed quantitatively; on modified multiwalled carbon nanotubes (in the pH range of 2–4). Parameters influencing, the simultaneous preconcentration of Pb(II), Ni(II) and Cd(II) ions (such as pH of the sample, sample and eluent flow rate, type and volume of elution solution and interfering ions), have been examined and optimized. Under the optimum experimental conditions, the detection limits of this method. for Pb(II), Ni(II) and Cd(II) ions, were 0.32, 0.17 and 0.04 ng mL⁻¹ in original solution, respectively. Seven replicate determinations, of a mixture of 2.0 μg mL⁻¹ lead and nickel, and 1.0 μg mL⁻¹ cadmium; gave a mean absorbance of 0.074, 0.151 and 0.310, with relative standard deviation 1.7%, 1.5% and 1.2%, respectively. The method has been applied, to the determination of trace amounts of lead, cadmium and nickel; in biological and water samples, with satisfactory results.