Etude calorimetrique et cinetique de la recristallisation du cuivre par analyse calorimetrique differentielle (DSC)

Résumé Du cuivre pur (99.999 %) avec différentes tailles de grains a été déformé par laminage (réduction d'épaisseur entre 30 et 90%).Les courbes DSC mettent en évidence le dégagement d'énergie au cours de la recristallisation et montrent que l'énergie emmagasinée par déformation n'est pas sensible à la dimension des grains qui, au contraire, agit sur les paramètres cinétiques de la recristallisation.Dans une région étroite des taux de déformation on observe une variation brutale de l'énergie emmagasinée, de la température du pic DSC et de l'énergie d'activation de la recristallisation.

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Pure copper (99.999 %) with various grain sizes was deformed by cold rolling (reduction in thickness 30–90%).DSC curves of energy evolution during recrystallization show that the stored energy of deformation does not depend on grain size, which on the contrary affects the kinetic parameters of recrystallization.Abrupt changes in stored energy, DSC peak temperature and activation energy of recrystallization are observed in a narrow range of deformation amounts.

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Zusammenfassung Reines Kupfer (99.999%) von sehr verschiedenen Korngrössen wurde durch Kaltwalzen deformiert (Herabsetzung der Stärke zwischen 30 und 90%).Die DSC-Kurven der Energieabgabe im Verlaufe der Rekristallisation zeigen, daß die durch Deformation entstandene Energiespeicherung gegenüber der Korngrösse nicht abhängig ist, jedoch die kinetischen Parameter der Rekristallisation beeinflußt.In einem engen Bereich der Deformationsgrössen kann eine jähe Änderung der gespeicherten Energie, der Temperatur des DSC-Peaks und der Aktivierungsenergie der Rekristallisation beobachtet werden.

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(99.999%) : ( 30–90%). , , . , .

     

Spectroscopic studies of purine. II. Properties of purine substituted at the second and sixth carbons

Abstract— Substitution of an amino group at the C2 carbon of purine causes the two main components of the X absorption band to be separated by 200–500 Å: primarily this reflects the Occurrence of the lowest-lying transition at much longer wavelengths than in purine since, except in deoxyguanosine, there is an appreciable absorption component at ? 2420 Å in these compounds. Unlike purine, the wavelength shifts produced by different solvents are not simply related to the dielectric constant or hydrogen bonding capacity of the solvents. In agreement with previous predictions thatπ-π*states should be the lowest-lying excited singlets, no phosphorescence is observed from 2–aminopurine—the fluorescence quantum yield is close to unity. Besides strong fluorescence very weak phosphoresence can be detected when another amino group is added at C6 and when an oxygen is attached to the sixth carbon (guanine) fluorescence and phosphorescence of comparable intensities are observed: the sum of the quantum yields for both types of emission is of the order of unity. Thus, the lowest-lying singlet transition must be a π-π*state. At room temperature themal quenching is the most important parameter in determining the fluorescence intensity of these molecules, however, at lower temperatures the intensity—similar to the wavelength—f this emission apparently also depends upon the ability of a given solvent to reorient and/or perturb Franck-Condon surfaces. Discrepancies observed between absorption and excitation spectra in deoxyguanosine and azaguanine appear to reflect emission caused respectively by aggregation of molecules and by keto-enol shifts.     

Beiträge zur Chemie des Phosphors. 167 [1, 2]. Konstitutions- und Konfigurationsisomere von Pentaphosphan(7), P5H7

Contributions to the Chemistry of Phosphorus. 167. Constitutional and Configurational Isomers of Pentaphosphane(7), P₅H₇ Phosphane mixtures containing 10—15 P-% of pentaphosphane(7), P₅H₇, are obtained by thermolysis of diphosphane, P₂H₄, or as residue from distillation of crude diphosphane [3]. According to the complete analysis of the ³¹P{¹H}-NMR spectrum on the basis of selective population transfer experiments, P₅H₇ exists as a mixture of three diastereomers of n-P₅H₇ — 1a (erythro, erythro), 1b (erythro, threo), 1c (threo, threo) — and of the constitutional isomer 2-phosphinotetraphosphane 2 (iso-P₅H₇, largest relative isomeric abundance). The correlation between the diastereomers and the observed spin systems results from the preferred gauche orientation of neighboring free electron pairs, the dependence of ¹J(PP) on dihedral angles, and the ³J(PP) long range couplings. From the ³¹P-NMR data of the phosphane molecules P_nH_n+2 with n = 1—5 general relationships for the δ(³¹P) values and the ¹J(PP) coupling constants of chain-type phosphorus hydrides as a function of their structural parameters are derived.     

Thermal decomposition of 4,4′-diaminodiphenylsulphone

The thermal decomposition of 4,4′-diaminodiphenylsulphone (DDS) was studied by thermogravimetry, differential scanning calorimetry and thermal volatilisation analysis. Solid residues, high-boiling and gaseous products of degradation were collected at each step of thermal decomposition and analysed by infrared spectroscopy and gas chromatography/mass spectrometry.

On programmed heating at normal pressure, DDS starts to evaporate at 250°C. Thermal decomposition, which probably proceeds through homolytic scission of the S-C bond is simultaneously observed. The resulting sulphonyl radicals provoke polymerisation and cross-linking of the solid residue which undergoes a limited degradation at 350°C with elimination of heteroatoms N and S as volatile moieties. Above 400°C, the residue undergoes a complex charring process leading to an aromatic char typical of carbonised aromatic polymers.     

Investigation of alkaloid N-oxides by secondary-ion mass spectrometry

An advantage of theSIMS method for investigating alkaloid N-oxides has been shown. In the case of N-oxides of steroid, diterpene, tropane, and pyrrolizidine alkaloids, fragments including the oxygen of the N-oxide group are revealed. The protonation of N-oxide molecules in a glycerol matrix takes place mainly through the negatively polarized oxygen atom of the N-oxide function. On fragmentation, theMH ⁺ ions of N-oxides of monoester tropane and pyrrolizidine alkaloids tend to form fragmentary ions of the protonated forms of the aminoalcohols (A+). The energies of the metastable transitionsMH ⁺ A⁺ have been calculated for the Noxides of the pyrrolizidine alkaloids viridif lorine, trachelanthamine, and echinatine.Institute of the Chemistry of Plant Substances [IKhRV], Academy of Sciences of the Republic of Uzbekistan [AN RUz], Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 833–837, November-December, 1995. Original article submitted February 20, 1995.     

Multi-step polymer-assisted solution-phase (PASP) library synthesis of functionalized diaminobenzamides

A parallel solution-phase library synthesis of functionalized diaminobenzamides is described. The four-step library synthesis is accomplished using polymer-assisted solution-phase (PASP) synthesis techniques. This high-yielding, multi-step sequence utilizes sequestering resins for the removal of reactants, reactant by-products, and employs a resin capture/release strategy as a key library synthesis step. Step one of the sequence relies on the displacement of an activated fluoro-group from the aromatic ring of 1a, b with a variety of primary amines to introduce the first diversity position. Step two is hydrolysis of the benzoate ester to a benzoic acid which is subsequently captured on a polyamine resin, washed, and released to give 4a, b in pure form. Step three utilizes PASP resins to mediate the amide coupling of a benzoic acid with a variety of primary amines to give the aminonitrobenzamides 5a, b and introduces the second diversity position. Step four is the parallel reduction of the aminonitrobenzamides 5a, b to the functionalized diaminobenzamides 6a, b. This library synthesis proceeds with high overall purities which average 80 % over the 4-step sequence.     

Light olefin production from CO/H2 over silica supported Fe/Mn/K catalysts derived from a bimetallic carbonyl anion, [Fe2Mn(CO)12]?

Fe/Mn/K catalysts derived from support of the anionic carbonyl, [Fe₂Mn(CO)₁₂]^– on silica were compared with catalysts prepared by aqueous impregnation methods, and found to be more selective for production of C₂–C₄ olefins. Addition of K had little effect, whereas variations in reaction conditions altered selectivity owing to secondary reactions of the alkene products.

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Fe/Mn/K, , [Fe₂Mn(CO)₁₂]^–, , , , C₂–C₄. , , .

     

Benzindoles

A large amount of structural similarity between 4,5-benzindole and naphthalene and between 6,7-benzindole and indole was detected on a basis of a comparison of the absorption, fluorescence, and phosphorescence spectra of isomeric benzindoles with the spectra of indole and naphthalene. A great analogy between indole and 6,7-benzindole as compared with 4,5-benzindole is also observed during the formation of hydrogen bonds, as indicated by the shift in the absorption band of the NH group in the IR spectra of the investigated compounds in the presence of various proton acceptors.     

Molecular vibrations of free and complexed ligands:symmetry coordinates for the Ni(PF3)4 model

Symmetry coordinates of molecular vibrations for the Ni(PF₃)₄ type model are deduced. They are classified as the coordinates for (a) ligand vibrations, (b) ligand-framework couplings, (c) framework vibrations, and finally (d) the redundant coordinates.     

Polyhydroxyoligothiophenes. 2. Hydrogen-Bonding-Oriented Solid State Conformation of 3,3'-Bis(2-hydroxyethyl)-2,2'-bithiophene and Regioselective Synthesis of the Corresponding Head-to-Head/Tail-to-Tail Quater- and Sexithiophene

This paper reports the X-ray structure of 3,3'-bis(2-hydroxyethyl)-2,2'-bithiophene (1), which is the building block for the synthesis of head-to-head/tail-to-tail 2-hydroxyethyl-substituted oligothiophenes. Contrary to all the bithiophenes reported so far, 1 exhibits a noncoplanar anti conformation and an inter-ring twist angle (67.5 degrees ) which is the largest ever measured for adjacent rings of alpha-conjugated oligothiophenes. This unusual conformation appears to be dictated by intermolecular hydrogen-bonding interactions involving the OH groups, which bind the molecule in close packed layers. The paper also describes the regioselective synthesis of the dimer and the trimer of 1, namely of 3,3',4",3"'-tetrakis(2-hydroxyethyl)-2,2':5',2":5",2"'-quaterthiophene (3c) and of 3,3',4",3"',4",3"'-hexakis(2-hydroxyethyl)-2,2':5',2":5",2"':5"',2":5",2"'-sexithiophene (4b). 3c And 4b were obtained through palladium(0)-catalyzed coupling of the mono- and distannanes of the tetrahydropyranyl derivative of 1 with the appropriate monobromo compound (Stille's reaction). Finally, the paper reports force-field calculations which suggest that the low lambda(max) values measured for 1, 3c, and 4b are also the result of intramolecular hydrogen-bonding interactions which favor highly twisted conformations in solution.