Kinetic-catalytic determination of traces of iron by the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline

A new kinetic-catalytic method by the initial rate procedure for the determination of nanogram level of iron(III) is developed, which is based on its catalytic effect on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with N,N-dimethylaniline (DMA) to form an indamine dye (λ_max=590 nm) in the presence of hydrogen peroxide. Iron(II) is also determined, being oxidized to iron(III) by hydrogen peroxide. Calibration graphs obtained by the initial rate method are linear in the range 1–1000 ng ml⁻¹ Fe and as low as 10⁻⁸ M Fe(II, III) can easily be determined. The relative standard deviations are 6.6, 2.5 and 1.5% for ten determinations of 1, 20 and 60 ng ml⁻¹ of Fe(III), respectively. The method is applicable to the determination of iron in natural waters without preconcentration and separation.     

Electronic influences on 3J(C,H) coupling constants via -S-, -S(O)- and -SO2-: their determination, calculation and comparison of detection methods

3J(C,H) coupling constants via a sulfur atom in two series of compounds, both including a sulfide, a sulfoxide and a sulfone, were detected experimentally and calculated by quantum mechanical methods. In the first series (1-3) the coupling between a hydrogen, bonded to an sp3 carbon, and an sp2 carbon is treated; the second series (4-6) deals with the coupling between a hydrogen, bonded to an sp3 carbon, and an sp3 carbon. Different pulse sequences (broadband HMBC, SelJres, 1D HSQMBC, J-HMBC-2, selective J-resolved long-range experiment and IMPEACH-MBC) proved to be useful in determining the long-range 3J(C,H) coupling constants. However, the dynamic behaviour of two of the compounds (4 and 6) led to weighted averages of the two coupling constants expected (concerning equatorial and axial positions of the corresponding hydrogens). DFT calculations proved to be useful to calculate not only the 3J(C,H) coupling constants but also the different contributions of FC, PSO, DSO and SD terms; the calculation of the Fermi contact term (FC) was found to be sufficient for the correct estimation of 3J(C,H) coupling constants.     

Untersuchungen an Hydriden im Bereich der Phase Ti2CO1—x Fe x (x=0–0,5)

The hydrogen absorption of the phase Ti₆₄Co_32–x Fe _x (x=0...16) and its influence on the magnetic properties have been investigated. Measurements of the vapour-pressure, wide-line NMR and magnetic susceptibility have been performed. Substitution of Co by Fe does not change the amount of absorbed hydrogen. However the reaction rate of hydriding process, the activation energy of diffusion and the magnetic quantities change upon this substitution.

     

Electron transfer from dibenzo[b,f]-1-azapentalene dianion: Attempted synthesis of dibenzo[b,f]-1-azapentalene

When dibenzo[b,f]-1-azapentalene dianion (3) was allowed to react with either iron (III) chloride or ethylene bromide, a one-electron transfer from3 took place readily to give the radical anion11. Further electron transfer from11 did not occur presumably due to the antiaromatic character of dibenzo[b,f]-1-azapentalene (1) that would have resulted. The radical anion11 underwent further transformation by hydrogen abstraction from the solvent to give 5,10-dihydroindeno[1,2-b]indole (2) and by dimerization to themeso and (R,S) isomers of 5,5,10,10-tetrahydro-10,10-biindeno[1,2-b]indole (4 a and4 b) respectively.

---

Elektronentransfer von Dibenzo[b,f]-1-azapentalen-Dianion: Ein Versuch zur Synthese von Dibenzo[b,f]-1-azapentalen

Zusammenfassung Die Reaktion von Dibenzo[b,f]-1-azapentalen-Dianion (3) mit Eisen (III) oder Ethylenbromid ergab einen Ein-Elektronentransfer zum Radikalanion11. Ein weiterer Elektronentransfer fand nicht statt, vermutlich wegen des antiaromatischen Charakters von Dibenzo[b,f]-1-azapentalen (1), das dabei entstehen müßte. Das Radikalanion11 ergab unter Wasserstoffentzug aus dem Lösungsmittel 5,10-Dihydroindeno[1,2-b]indol (2), das weiter zummeso- bzw. (R,S)-5,5,10,10-tetrahydro-10,10-biindeno[1,2-b]indol (4 a bzw.4 b) dimerisierte.

     

New method for determination of heats of thermal gas-phase reactions yielding intermediates

A new procedure for the determination of the heats of thermal gas-phase reversible reactions leading to intermediates in the framework of the adiabatic compression method is proposed. A model problem is solved, and the error of the method is evaluated (-1 %). The validity of the method was confirmed using the reversible formation of the I,2-biradical from tetrafluoroethylene as an example. Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 64–67, January, 1996.     

Quantum chemical studies on electrophilic addition

The geometries of the 2-aminoethyl cation and the isomeric protonated aziridine have been optimized using ab initio molecular orbital calculations employing the split-valence shell 4-31G basis set. The protonated aziridine is computed to be the more stable ion by 46.5 kcal/mole (4-31G level) and 44.9 kcal/mole (double-zeta basis set). The profile to interconversion is found to have a barrier of less than 15 kcal/mole (relative to the 2-aminoethyl cation) and this profile is compared with those computed for the similar ions XCH₂CH ₂ ⁺ where X=OH, F, SH and Cl.     

Hochselektive differentialpulspolarographische Spurenbestimmung von Uran (katalytische Nitratreduktion) nach Extraktionsabtrennung

Zusammenfassung Die polarographische Spurenbestimmung von Uran durch katalytische Reduktion des NO ₃ ^– ist eine sehr empfindliche Analysenmethode. Sie kann aber nur unter Ausschluß einer Reihe von störenden Kationen und Anionen durchgeführt werden und erfordert eine genau zusammengesetzte Grundlösung. Darum wurde für das Uran eine einfache und rasche Extraktionsabtrennungsmethode mit Triphenylarsinoxid in CHCl₃ ausgearbeitet. Die Rückextraktion aus der organischen Phase mit 0,02 N Na₂CO₃ und anschließendes definiertes Ansäuern mit HNO₃ ermöglichen die Überführung des Urans in eine für die differentialpulspolarographische Bestimmung geeignete, reproduzierbare Grundlösung. Über 60 untersuchte Kationen und 20 Anionen stören die Bestimmung in weiten Grenzen nicht, was eine vielseitige Anwendung erlaubt. Die Nachweisgrenze liegt bei 1 ppb Uran in wäßriger Lösung. Die relative Standardabweichung beträgt für 100 ppb Uran ±2%.

---

Highly selective trace determination of uranium by differential pulse polarography (catalytic nitrate reduction), following extraction separation

Summary The trace determination of uranium by differential pulse polarography, using the catalytic reduction of nitrate is known to be very sensitive, if certain interfering ions are excluded and if the composition of the base solution remains constant. In order to fulfil these conditions a simple and selective method for extracting uranium with triphenylarsine oxide in chloroform was developed. Back extraction with 0,02 N Na₂CO₃ and addition of HNO₃ lead to an appropriate base solution for the determination of uranium by differential pulse polarography. The influence of 60 cations and 20 anions was found to be negligible in a wide range. The limit of detection is about 1 ppb U and the standard deviation with 100 ppb U is ±2%.

Für die Überprüfung des Manuskripts möchte ich den Herren Dr. P. Baertschi und O. Antonsen herzlich danken.     

Spectrographic estimation of Ga, In and Tl in semiconductor grade selenium

Summary An emission spectrographic method for the estimation of Ga, In and Tl in semiconductor grade selenium at less than a ppm concentration has been developed. The impurities were separated from 1 g of selenium by volatilizing it from its solution in nitric acid and sulphuric acid. The residue containing the impurities was dissolved in small amounts of 6 M HCl and was loaded along with the washings on 10 mg mixture containing graphite (90%) and sodium chloride carrier (10%) in the electrode crater. The spectra were excited in a d.c. arc carrying 13 A current. The detection limits lie in the range of 0.0025–0.005 ppm. The precision of the method ranges from 7–12% for these elements. The recoveries of impurities from selenium were confirmed using radioactive tracers.

---

Spektrographische Bestimmung von Gallium, Indium und Thallium in Halbleiterselen

Zusammenfassung Eine 1 g-Probe wird in Salpeter- und Schwefelsäure gelöst und die Verunreinigungen durch Verflüchtigung des Selens isoliert. Sie werden in 6 M HCl gelöst und zusammen mit einem Graphit/NaCl-Gemisch (91) in die Elektrode eingebracht. Zur Anregung dient ein Gleichstrombogen (13 A). Die Nachweisgrenzen liegen im Bereich von 0.0025–0.005 ppm, der Variationskoeffizient bei 7–12%. Die Wiedergewinnung der Verunreinigungen wurde mit Hilfe von Radioindicatoren geprüft.

     

Numerische Ermittlung quasikonformer Abbildungen mit finiten Elementen

Summary In this note we consider so called p-analytic mappings of simply or doubly connected domains on rectangles or circular rings. Real and imaginary parts of the mappings can be described by minimal-principles. By minimizing the corresponding functionals in a class of linear or bilinear finite elements we obtain an approximation of the mapping and also upper and lower bounds for the p-module of a domain with polygonal boundary. Error bounds are given for smooth and for piecewise constant functionsp. We present numerical experiments.

     

Linear combination of concomitants of order statistics with application to testing and estimation

Summary Let (X ₁,Y ₁), (X ₂,Y ₂),…, (X _n,Y _n) be i.i.d. as (X, Y). TheY-variate paired with therth orderedX-variateX _rn is denoted byY _rn and terms the concomitant of therth order statistic. Statistics of the form are considered. The asymptotic normality ofT _n is established. The asymptotic results are used to test univariate and bivariate normality, to test independence and linearity ofX andY, and to estimate regression coefficient based on complete and censored samples.