Pyridine Syntheses. II. Condensation Routes Toward Streptonigrin Ring C

Alternative complimentary syntheses of penta-substituted pyridine rings with full regiochemical control of substituents were studied as a method for the synthesis of Streptonigrin ( 1 ). Various α-substituted acetophenones 2 were reacted with enones 3 in acetic acid/ammonium acetate and air to afford penta-substituted pyridines 4 . α-Substituents that could provide a source of exocyclic nitrogen at position 3 of these Steptonigrin ring-C models proved to be the limiting factor. However, an inverse “3+2+1” cyclocondensation of α-cyanochalcone 5c with 2-furyl ethyl ketone ( 6b ) afforded the desired model 6-(2-furyl)-5-methyl2,4-diphenyl-3-pyridinecarbonitrile ( 4g ) in 75% yield.     

Capillary gas chromatographic analysis of highly brominated fire retardant compounds

We report the development of a capillary gas chromatographic method, superior to existing packed column methods, for the analysis of highly brominated additive fire-retardants, including decabromodiphenyl ether (1) and decabromodiphenoxyethane (II). Neither compound has been analyzed previously by capillary GC, and there are no published methods for (II). For (I), the new method is 5–10 times faster than an analogous packed column method, and it has 100 times lower detection limits and twice the precision of a gas chromatographic/mass spectrometric method. For (II), the capillary method is 30–50% faster than an unpublished liquid chromatographic method. The greater efficiency of the capillary method makes possible the complete resolution (R ≥ 1.25) of structurally very similar compounds (e.g. compound (II) and its Br₉Cl₁ and Br₈Cl₂ analogues). With the new method, commercial preparations of (I) and (II) can be rapidly analyzed, and samples from combustion and pyrolysis experiments can be evaluated for compositional changes.     

Alkyl ketoximes as analytical reagents. XIII

Summary The comparative effects of the distribution of 4-heptanone, 2–, and 4-methylcyclohexanone oximes between water and chloroform, the hydrolysis of the oximes and the solubilities of the corresponding palladium (II) chloride complexes in chloroform on the palladium extraction efficiency of the oximes are discussed. Steric effects were found to influence the relative extraction efficiency order to the greatest extent.The relative extraction efficiency order found using the outlined conditions was: 4-methylcyclohexanone oxime4-heptanone oxime 2-methylcyclohexanone oxime.

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Zusammenfassung Die Verteilung von 4-Heptanon-, 2- und 4-Methylcyklohexanonoxim zwischen Wasser und Chloroform, die Hydrolyse der Oxime und die Löslichkeit der entsprechenden Palladium(II)chloridkomplexe in Chloroform wurden hinsichtlich ihres Einflusses auf die Palladiumextraktion vergleichend diskutiert. Sterische Umstände beeinflussen die Extraktion in größtem Ausmaß. Unter den angeführten Bedingungen ergab sich folgende Reihenfolge der relativen Extraktionswirksamkeit: 4-Methylcyklohexanonoxim 4-Heptanonoxim 2-Methylcyklohexanonoxim.

     

Alkyl ketoximes as analytical reagents. XI

Summary The 4-heptanone oxime extraction procedure may be used for the quantitative separation of trace amounts of palladium from a noble-metals-bearing sulfide concentrate. An average palladium value of 0.335 oz/ton was obtained on a standard sample compared to the recommended value of 0.37 oz/ton.

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Zusammenfassung Für die quantitative Abtrennung von Palladiumspuren aus einem edelmetallhaltigen Sulfidkonzentrat eignet sich die Extraktion mit 4-Heptanonoxim. In einer Standardprobe, deren Palladiumgehalt mit 0,37 Unzen/Tonne angegeben war, wurden durchschnittlich 0,335 Unzen/Tonne gefunden.

     

Theory of angle-resolved photoemission from localised orbitals at solid surfaces

The theory of angle resolved photoemission from localised orbitals is reviewed and is cast in a form requiring the calculation of the purely outgoing wave emanating from an emitting atom, that describes the final state of the photoelectron, rather than using the more usual approach based on time reversed scattering states. An explicit expression is written down for the superposition of partial waves that results from emission from an atomic orbital, and it is pointed out that emission from more complex initial states such as localised bonds or Bloch and surface states, can be described by coherently combining such sets of partial waves. The effect of the crystal surface environment in damping and scattering the waves is described briefly. Model calculations are performed to investigate the major influences on the angular distribution of the photoelectrons. The profound effect of varying the polarisation direction of the incident light relative to the surface is discussed, with examples from the literature, showing how it can be used to determine the type of initial orbital. Emission from directed orbitals is studied and it is shown that scattering by the emitter potential can be an important effect, so that the radial wave function of the outgoing electron, which determines the amplitudes and phases of the outgoing waves, must be calculated with care. Different choices of these quantities lead in the model calculations to very different angular profiles, that sometimes bear little relation to the shape of the initial orbital. The consideration of emission from localised bonds shows that provided that bonds are not too strongly polarised, interference between waves from different centres is always significant at higher energies, and can also be important at energies of a few eV relative to the vacuum. Scattering by the ion cores of the surface region can strongly distort the angular distribution, or may have little effect. But it is generally difficult to decide a priori which influences are dominant for a particular case, so that the interpretation of angular profiles must be based on careful calculations including all these effects. The optimum energy range for the interpretation of experimental data is that from about 30 to 100 eV.     

A numerical technique for small-noise stochastic control problems

A numerical technique is described for solving approximately certain small-noise stochastic control problems. The method uses quantities computable from the optimal solution to the corresponding deterministic control problem. Numerical results are given for a two-dimensional linear regular problem with saturation and a time-optimal problem.     

Gravimetric determination of gold with di-2-thienylketoxime

Di-2-thienylketoxime may be used as a gravimetric reagent to determine gold. The error is of the order of ± 0.3%. There are few interfering ions and simple methods may be used to eliminate these.