Determination of lead and cadmium using a polycyclodextrin-modified carbon paste electrode with anodic stripping voltammetry

This work reports the use of and -cyclodextrin-modified carbon paste electrodes (CPE_-CD and CPE_-CD) to determine simultaneously Pb(II) and Cd(II) by means of the electrochemical technique known as anodic stripping voltammetry (ASV). Both modified electrodes displayed good resolution of the oxidation peaks of the said metals. Statistic analysis of the results strongly suggests that the CPE_-CD exhibited a better analytical response that the CPE_-CD, while the detection limits obtained for Pb(II) were 6.3×10^–7 M for the CPE_-CD and 7.14×10^–7 M for the CPE_-CD, whereas for Cd(II) they were 2.51×10^–6 M for the CPE_-CD and 2.03×10^–6 M for the CPE_-CD.     

Influence of additives on the structure and properties of polymers

Investigations into the transformation of hexagonal into monoclinic modification in isotactic polypropylene (iPP) were carried out. The hexagonal phase () was obtained by crystallization from a melt of iPP samples containing small molecular compounds (additives). A decline in the amount of-modification and changes of dimensions of ordering areas, perpendicular to the chain axes of iPP, was analysed at various temperatures and times of heating.The interdependence between the structure of additives and the amount of-phase occurring and also the stability of this modification during thermal treatment was observed.Obtained results indicated that only some additives play the role of moderating agents for the phase transition process.A preliminary report of this work has been presented at XIII Congress of the International Union of Crystallography (9–18 August 1984).     

A TPR study of SiO2-supported Ru?Ag catalysts

A H₂ chemisorption and TPR study of Ru–Ag/SiO₂ catalysts reveals that after oxidation at 373 K this systems behaves like Ru–Cu/SiO₂. High temperature oxidation, however, does not result in the separation of the metal like in the Ru–Cu case but in the redispersion of Ag on top of the Ru particles.

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H₂ Ru–Ag/SiO₂ , 373 Ru–Cu/SiO₂. , , , Ru–Cu, Ag Ru.

     

Thermoreversible gelation of polyacrylonitrile/dimethylformamide-solution

The thermoreversible gelation of semi-diluted atactic polyacrylnitrile (PAN)/dimethylformamide (DMF)-solutions has been studied. The structural features of PAN/DMF-gels, formed by supercooling have been investigated by DSC-, x-ray- and swelling measurements. A new structural model has been introduced to describe the morphology of the junction zones of PAN/DMF-gels and to also explain the gelation behavior of PAN/DMF-solutions as the structural features of PAN/DMF-gels. The junction zones of a PAN/DMF-gel have been defined as ordered junction zones.A gelation enthalpy of about H=–6 kJ/mol supports the idea that an ordered junction zone is formed by intermolecularly neighboring stereoregular parts of atactic PAN chains due to a nucleation process in the solution. It can be defined as a strongly distributed fringed micelle.     

Partitioning of <Emphasis Type="Italic">π</Emphasis> -electrons in rings of polycyclic conjugated hydrocarbons: Part 6. Comparison with other methods for estimating the local aromaticity of rings in polycyclic benzenoids

By adopting the convention that shared double bonds in polycyclic conjugated hydrocarbons contribute with one -electron and unshared ones with two -electrons, a partition of -electrons in each ring (-electron content, EC) can be obtained by averaging over all Kekulé structures, which are assumed to have equal weights. This affords a simple measure of local aromaticity that is comparable with other such local aromaticity indices in polycyclic benzenoids.     

Charge influence in semi-empirical calculations of heteroatomic ionic and neutral molecules

Iterative extended Hükel calculations for all valence electrons and iterative PPP calculations in the variable electronegativity formalism for -electrons were performed on benzene, pyridine, fluorobenzene, and the pyrylium ion. The charge distributions for all compounds were found more uniform and plausible with the iteration procedures than without. Polarization effects from the-electrons were found to be of importance for the -electrons. The lone-pair picture of the highest occupied MO in pyridine is preserved in the iterative extended Hückel method, and two lone-pairs were obtained on the fluorine atom of fluorobenzene. The results indicate that this atom is not hybridized.

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Zusammenfassung Benzol, Pyridin, Fluorbenzol und Pyriliumion wurden mit einer iterativen EH-Methode und einer iterativen PPP-VE-Methode berechnet. Es zeigte sich, daß Ladungsverteilungen bei Benutzung des Iterationsverfahrens besser beschrieben werden. Polarisationseffekte der-Elektronen auf die -Elektronen stellen sich als wichtig heraus. Auch in der IEH-Methode bleibt das oberste besetzte MO des Pyridins ein einsames Elektronenpaar. Am Fluoratom im Fluorbenzol werden zwei einsame-Elektronenpaare erhalten. Die Resultate führen zu der Annahme, daß dieses Atom nicht hybridisiert ist.

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Resumé Des calculs par les méthodes itératives de Hückel étendu pour tous les électrons de valence et de PPP avec électronégativité variable pour les électrons ont été effectués pour le benzène, la pyridine, le fluorobenzène et l'ion pyrylium. Les distributions de charge pour tons ces composés sont plus uniformes et plus plausibles avec les procédés itératis que sans. Les électrons ont un effet de polarisation important sur les électrons . La plus haute orbitale occupée dans la pyridine reste identifiable comme la paire libre dans la méthode de Hückel étendue, et l'on obtient deux paires libres sur l'atome de fluor du fluorobenzène. Cet atome n'est pas hybride.

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Sponsored in part by King Gustaf VI Adolfs 70-Years Fund for Swedish Culture, Knut and Alice Wallenberg's Foundation, and in part by the Swedish National Research Council.     

Bestimmung der HMO-Parameter von Nitrogruppen aus den UV-Absorptionsspektren von Nitroaromaten

Zusammenfassung Unter Benutzung der experimentellen Werte derK-Banden von Nitro-, m- und p-Dinitro- und sym-Trinitrobenzol wurden die Parameter der Resonanzintegrale der Nitrogruppe zu _CN=1,1 und _NO=1,6 bestimmt, die Parameter der Coulombintegrale auf Grund von Plausibilitätsbetrachtungen zu _O=1,5, _N=1,8 und _C=0,25 abgeschätzt. Die UV-Spektren der vier genannten Verbindungen wurden in Cyclohexan vermessen.Die erhaltenen Parameter werden zur Berechnung der Moleküldiagramme und Energieniveaus der vier Strukturen benutzt. Die Rechendaten stehen in guter Übereinstimmung mit den experimentellen Befunden, vor allem dann, wenn den weiterreichenden induktiven Effekten der Nitrogruppe in geeigneter Weise Rechnung getragen wird.

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Using the experimental values for theK bands of nitro-, m-and p-dinitro- and sym-trinitrobenzene, the parameters of the resonance integrals of the nitro group were calculated to be _CN=1,1 and _NO=1,6, and the parameters of the Coulomb integrals estimated as _O=1,5,_N=1,8 and _C=0,25 on the basis of plausibility considerations. The UV-spectra of the above compounds were measured in cyclohexane.The parameters obtained are used to calculate the molecular diagrams and energy levels. The calculated data are in good agreement with the experimental findings, above all when the more extensive inductive effects of the nitro group are suitably taken into account.

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Mit 7 Abbildungen     

Redox-induced η5 ⇔ η3 haptotropy of the fluorenyl ligand in 9-substituted η5-fluorenylmanganesetricarbonyl complexes

It has been shown by cyclic voltammetry in THF within the –90 to 40 °C temperature range that fluorenyl (⁵-9-R-C₁₃H₈)Mn(CO)₃ complexes (R=Bu^t (3) and Ph (4)) undergo two-electron reduction to form allyl type [(³-9-R-C₁₃H₈)Mn(CO)₃]^2– dianions as final products. At low temperatures complexes3 and4 are reduced in two one-electron steps according to the EEC-scheme. The first step is reversible and corresponds to the formation of 19-radical anions 3^–. and 4^–.. TheE ⁰ values for redox pairs3 ^0/–. and4 ^0/–. are –1.88 and –1.73 V, respectively. The further reduction of radical anions3 ^–. and4 ^–. at more negative potentials is accompanied by fast ^{5 3} haptocoordination of the fluorenyl ligand to form 18-dianions [(³-9-R-C₁₃H₈)Mn(CO)₃]^2–. These dianions obtained by the reduction of complexes3 and4 by the radical anion of pyrene are stable at –80 °C and are characterized by their IR spectra. At room temperature the ^{5 3} hapticity change is a fast and reversible process occurring at the step of 19-radical anions3 ^–. and4 ^–. and leading to the electron deficient 17-species [(³-9-R-C₁₃H₈)Mn(CO)₃]^–., which are reduced easier than the initial complexes. As a result, complexes3 and4 are reduced to the corresponding dianions [(³-9-R-C₁₃H₈)Mn(CO)₃]^2– at room temperature in one reversible two-electron step according to the ECE-scheme. Reactivities of 19e^–-species of the isomeric ⁵- and ⁶-fluorenylmanganesetricarbonyl complexes are compared.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1347–1353, July, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-05209) and the International Science Foundation (Grant No. REV 000).     

A differential scanning calorimetric study of phase transitions in Na2SO4

The results of a differential scanning calorimetric study of the transitions involving the various polymorphs of Na₂SO₄ are described. They are discussed in the light of their crystal structures and also in conjunction with more recently published data regarding these transitions.

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Zusammenfassung Die Ergebnisse einer mit Differentialabtastkalorimetrie durchgeführten Untersuchung der Übergänge verschiedener Polymorphe von Na₂SO₄ werden beschrieben. Sie werden im Hinblick ihrer Kristallstrukturen und im Zusammenhang mit verschiedenen unlängst veröffentlichten Daten bezüglich dieser Übergänge diskutiert.

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Résumé On décrit les résultats de l'étude, effectuée par analyse calorimétrique différentielle, des transitions mettant en jeu les diverses formes polymorphes de Na₂SO₄. Les résultats sont discutés en tenant compte des données récemment publiées sur ces transitions.

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. , .

     

Phytoecdysones ofSilene praemixta. II. Premixisterone

The structure of premixisterone (I) — a new ecdysteroid fromS. praemixta M. Pop. (Caryophyllaceae) — has been established. Compound (I) has the composition C₂₇H₄₄O₅, mp 110–112°C (from C₂H₅OH + H₂O), [] _D ²⁴ 0 ± 4° (c 0.85; MeOH), 202 nm (log 3.35), _max ^KBr 3415 cm^–1 (OH), 1710 cm^–1 (C=0), and does not contain the ⁷-6-keto grouping that is characteristic of natural ecdysteroids. The acetylation of (I) with (CH₃CO)₂ in Py gave the amorphous 3,22-diacetylpremixisterone (II), C₂₁H₄₈O₇. Compound (I) has the structure of 3,14,22R,25-tetrahydroxy-5-cholest-8-en-6-one. The IR, PMR, and mass spectra of (I) and (II) are given.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 797–799, November–December, 1979.     

1-Aryl-6-azauracile, 4. Mitt.: Die Synthese des 1-Phenyl-5-[5′-methyl-1′,2′,4′-oxdiazolyl-(3′)]-6-azauracils und einiger seiner Derivate

Zusammenfassung Arylhydrazon-cyanacetylcarbamidsäureäthylester (I) wurde durch Einwirkung einer Na₂CO₃-Lösung auf 1-Aryl-5-cyan-6-azauracile (II)^1,2 cyclisiert. Nitrile (II) wurden durch Addition von Hydroxylamin in entsprechende Amidoxime (III) übergeführt, welche durch Kochen mit Acetanhydrid die zugehörigen 1-Aryl-5-[5-methyl-1,2,4-oxdiazolyl(3)]-6-azauracile (IV) lieferten.

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Aryl hydrazone-cyanoacetylcarbamic acid ethyl esters (I) have been cyclized in Na₂CO₃ soln. yielding 1-aryl-5-cyano-6-azauraciles (II)^1,2. Addition of NH₂OH to the nitriles (II) gave the corresponding amidoximes (III), which by refluxing with Ac₂O were converted to the corresponding 1-aryl-5-[5-methyl-1, 2, 4-oxdiazolyl(3)]-6-azauraciles (IV).

     

Synthesis and Crystal Structures of Copper(I) Complexes with N-Allylhexamethylenetetraminium Chloride Obtained in Different Acidic Media

The crystals of [(CH₂)₆N₄(C₃H₅)]Cu₂Cl₃ (I), [(CH₂)₆N₄(C₃H₅)]Cu₂Cl₃ (II), and [(CH₂)₆N₄(C₃H₅)]CuCl₂ (III) complexes were electrochemically synthesized (ac) from CuCl₂ · 2H₂O and N-allylhexamethylenetetraminium chloride in ethanol solutions at pH 6, 4.5, and 3. Their structures were determined using X-ray diffraction analysis (DARCh diffractometer, MoK radiation, /2 scan mode). Complex Icrystallizes in the monoclinic system: space group A2/a, a = 24.812(6) Å, b = 8.855(3) Å, c = 12.080(2) Å, = 89.21(3)°, and Z = 8. Complex II crystallizes in the triclinic system: space group P , a = 7.618(2) Å, b = 7.048(2) Å, c = 13.150(3) Å, = 97.50(2)°, = 92.70(2)°, = 100.74(2)°, and Z = 2. The crystals of complex III are orthorhombic: space group Pmn2₁, a = 7.478(2) Å, b = 8.827(2) Å, c = 9.662(3) Å, Z = 2. The organic cation in complex I acts as a tridentate ,,-ligand; that in complex II, as a bidentate ,-ligand. In complex III, the organic cation is involved in coordination with the copper(I) atom only through one nitrogen atom.     

Study of the oxygen distribution in YBa2Cu3O7−x ceramics by (n, α) radiography technique

A technique to determine the oxygen distribution in high T_c superconducting YBa₂Cu₃O_7–x ceramics has been developed which is based on the (n, ) radiography method. The technique enables the non-destructive study of superconducting ceramics as well as monocrystal samples with spatial resolution not worse than 1 m at a relative standard deviation of 1.5%. This technique is used to study the influence of radiation-stimulated diffussion of oxygen on the formation of the superconducting phase in an yttrium ceramic. The oxygen distribution in the samples with a narrow transition (T1 K) and with a transition widened (T10 K) by thermal and thermo-radiative treatment is compared in the experiment. The oxygen distribution radiographs of irradiated and unirradiated samples provide strong evidence for the influence of irradiation on the ordering of superconducting ceramics structure.     

The thermal decomposition reactions of bis-(pyridine-2-aldoxime)-copper(II) complexes

The thermal properties of some complexes of copper(II) with pyridine-2-aldoxime (HPAO), where the ligand appears either as the ion (PAO^–) or as a neutral molecule, were determined in vacuo and in dynamic nitrogen and oxygen gas atmospheres. The study was carried out by thermoanalytical (TG, DTG. DTA), spectroscopic and spectrometric (UV-visible, IR, diffuse reflectance, mass) techniques.The initial decomposition temperature is influenced by the number of acid hydrogens in the complex; the thermal stability sequence in vacuo is: [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]The thermal decomposition reactions occur in several separate steps, the first of which gives rise to partial ligand decomposition, the reduction of copper(II) to copper(I), and the conversion of the residual pyridine-2-aldoxime into acid amide.

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Zusammenfassung Die thermischen Eigenschaften einiger Komplexe von Kupfer(II) mit Pyridin-2-aldoxim (HPAO), in denen der Ligand entweder als Ion (PAO^–) oder als neutrales Molekül vorliegt, wurden im Vakuum und in dynamischer N₂- und O₂-Atmosphäre ermittelt. Zur Untersuchung wurden thermoanalytische (TG, DTG, DTA) und spektrometrische (UV-sichtbar, IR, diffuse Reflektionsspektrophotometrie, Massenspektrometrie) Techniken herangezogen. Die Temperatur, bei der die Zersetzung beginnt, wird durch die Zahl der sauren Wasserstoffatome im Komplex beeinflußt; für die thermische Stabilität im Vakuum gilt die Reihenfolge [Cu(PAO)₂H]Cl > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂]. Die thermischen Zersetzurigsreaktionen verlaufen in mehreren diskreten Schritten, wobei der erste von diesen eine partielle Zersetzung des Liganden, die Reduktion von Kupfer(II) zu Kupfer(I) und die Konversion des verbleibenden Pyridin-2-aldoxims in das Säureamid in sich einschließt.

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-2- ( ), (-), . (, , ) , - , , - . , [Cu(PAO)₂H]CI > [Cu(PAO)₂H₂]Cl₂ > [Cu(PAO)₂] , , -2- .

     

Phenolate complexes of iron(III) in dimethylsulphoxide solution

Summary The formation of complexes between Fe³⁺ and 2,4-dinitrophenol, 4-nitrophenol and 4-methylphenol is studied in dimethylsulphoxide solution. The reaction proceeds almost to completion and the occurrence, in solution, of complexes with higher stoichiometry than 11 is reported for the first time. The following stability constants are determined (25 °C, 0.1 M KClO₄): Fe^III-2,4-dinitrophenolate ₁=1.8×10³, ₂=4.4×10⁵; Fe^III-4-nitrophenolate ₁=1.10×10⁷, ₂=2.5×10¹² ₃=3.9×10¹⁶; Fe^III-4-methylphenolate =1.7×10¹².The binding of a phenolate ligand to iron(III) strongly decreases its affinity for other phenolate ligands. The superior -donor, 4-methylphenolate (OC₆H₄Me)^–, only forms a 11 complex, Fe(OC₆H₄Me)²⁺. The e.s.r. spectrum of this species clearly prove it is a true iron(III) complex and does not contain iron(II), in opposition to recent claims. However, the complex Fe(OC₆H₄Me)²⁺ easily undergoes a ligand-to-metal electron transference. Addition of an excess of 1,10 phenanthroline yields the iron(II) complex [Fe(o-phen)₃]²⁺ instantaneously.     

Kinetics and mechanism of oxidation of triphenylphosphine by hydrogen peroxide

Kinetics of oxidation of triphenylphosphine (TPP) by hydrogen peroside has been investigated in 95 vol. % aqueous ethanol. The reaction is first-order each in TPP and hydrogen peroxide. A mechanism involving a bimolecular nucleophilic displacement of TPP on the peroxide molecule in the rate-determining step is proposed.

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() 95 .% . , H₂O₂. , , , H₂O₂ .

     

Photochemical reactions of anthraquinone with hydrocarbons in the presence and absence of oxygen: Trapping of radical intermediates

Radical intermediates formed at 25°C in the presence and absence of oxygen during the photolysis of anthraquinone in aromatic, cyclic and aliphatic hydrocarbon solvents were trapped by 2,6-dichloronitrosobenzene, 2,6-dibromonitrosobenzene and 2,4,6-tribromonitrosobenzene. The resulting nitroxide radicals have been characterized in situ by ESR spectra.

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: 2,6-, 2,6- 2,4,6-— , , 25°C. .

     

Relative reactivities of phosphites in reactions with hydrotrioxides

Studies of the interaction of hydrotrioxides ROOOH of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1,1-dimetoxyethane, 1,1-diethoxyethane, benzaldehyde and tetrahydrofuran with trimethyl triisopropyl, tributyl, triallyl, triphenyl and tri-o-chresyl phosphites (RO)₃P have revealed that in mild conditions ROOOH rapidly and selectively oxidizes (RO)₃P to the corresponding phosphates. The reaction stoichiometry has been established. Aromatic phosphites are shown to be of inferior reactivity to ROOOH as compared with aliphatic phosphites.

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, 1-, 2-, 1-, 2-, 1,1-, 1,1-, -, -, -, -, -, -, -- (RO)₃P. ROOOH (RO)₃P . . , ROOOH .