Heterolytic cleavage of homoallylic alcohols—I: Fragmentation of 6-hydroxycamphene derivatives

Heterolytic fragmentation of homoallylic alcohols incorporated in a bicyclo[2,2,1]heptane system with electrophilic reagents or that of the corresponding epoxides with acids, is described. A short route, via this fragmentation, to synthon 25, potentially useful in the syntheses of cis-jasamone and prostanoids, is reported.     

Optimization of fermentation conditions for production of glycopeptide antibiotic vancomycin by Amycolatopsis orientalis

Glycopeptides produced by Streptomyces species are the drugs used against β-lactam drug-resistant staphylococcal infections, and vancomycin is important among them. Increased prevalence of resistant strains increased the usage of vancomycin worldwide and also promoted attempts for indigenous production. The optimum process conditions pH, temperature, inoculum size, agitation, and aeration for vancomycin production by Amycolatopsis orientalis were evaluated, statistically analyzed, and the response surface curves were constructed. The optimum process conditions were a pH of 7.6, a temperature of 29°C, an inoculum size of 4.5%, an agitation of 255 rpm, and an aeration of less than 1:10 medium-to-air ratio.     

Solid-phase synthesis of isoxazolines

The polymer-supported synthesis of isoxazolines is described via nitrile oxide intermediates, starting from primary nitroalkanes in a one-pot process.     

Heteroatom influence on the pi-facial selectivity of Diels-Alder cycloadditions to 1-oxa-4-thia-6-vinylspiro[4.5]dec-6-ene, 3-methoxy-3-methyl-2-vinylcyclohexene, and 3-methoxy-2-vinylcyclohexene

The facial selectivities of the Diels-Alder cycloadditions of several dienophiles to the title substrates were studied. The observed selectivities are interpreted as a consequence of the relative steric interactions offered by the substituents. The addition of dimethylacetylene dicarboxylate (DMAD) is influenced by the electrostatic repulsion arising from the interaction of an electron pair orbital on the acetal oxygen and the orthogonal pi-orbital of the acetylene unit in DMAD in the syn-to-oxygen addition of the latter. This repulsion is offset on coordination of Li+ to the said oxygen electron pair orbital, and the addition thus proceeds syn to oxygen. The enhanced and accelerated syn-to-oxygen addition in lithium perchlorate in nitromethane is interpreted as a consequence of the coordination of Li+ to both the acetal oxygen and a heteroatom in the dienophile that brings them in close proximity to facilitate a reaction. The Li+-oxygen combination, however, also exerts some steric effect that results in reduced syn-to-oxygen addition of dienophiles having large substituents such as N-phenylmaleimide.     

Self-similar analytical solutions for blast waves in inhomogeneous atmospheres with frozen-in-magnetic field

In the present paper, we have made an attempt to study the effects of the presence of a magnetic field on the cavity formation inside a blast wave propagating into a perfectly conducting gas with density varying as some power of distance from the plane or line of explosion. In order to obtain the closed form solutions for the flow variables inside the blast wave and to solve the problem of cavity formation analytically, a relation is taken between the ordinary pressure and the total pressure. It i s found that if the value of the inhomogeneity index is greater than a critical value (a function of M_A - Alfven Mach Number, - adiabatic index and i - wave geometry index), a contact discontinuity appears at some point inside the blast wave and the cavity formation occurs. The effect of the presence of magnetic field is found to increase the tendency of cavity formation.Received: 21 February 2003, Published online: 4 August 2003PACS: 47.40.-x Compressible flows; shock and detonation phenomena - 47.65.+a Magnetohydrodynamics and electrohydrodynamics     

Silicon-assisted ring opening of donor-acceptor substituted cyclopropanes. An expedient entry to substituted dihydrofurans

[reaction: see text]. (tert-butyldiphenylsilyl)methylcyclopropanes undergo ring opening to furnish substituted dihydrofurans in good to excellent yields on treatment with TiCl4 in dichoromethane. The silicon that assists the regioselective ring opening is retained in the product to allow further functional group manipulations.     

Diluted tributyl phosphate as an extraetant for silver

Summary A new method is devised for the rapid solvent extraction of silver with diluted tributyl phosphate. Thus 40% TBP in butanol quantitatively extracts silver (49.8g) from 1M nitric acid that is 2M in lithium nitrate as salting-out agent. Silver is stripped with dilute ammonia and is determined photometrically at 495 ran as its red-violet complex withp-diethylaminobenzylidenerhodanine. The effect of acidity, varying TBP concentration and salting-out agent was studied. The probable composition of the extractable species is thought to be AgNO₃·(TBP)₃ or HAg(NO₃)₂(TBP)₃. Silver can be extracted in presence of a large number of elements with which it is associated in alloys, minerals or fission products. The method is simple, selective and rapid and needs only 30 minutes for the separation and determination.

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Zusammenfassung Eine neue Methode der Silberextraktion mit verd. Tributylphosphat (TBP) wurde angegeben. Mit 40% TBP in Butanol wird Silber (49,8g) aus 1-m Salpetersäure, die 2 Mole Lithiumnitrat pro Liter als Aussalzmittel enthält, quantitativ extrahiert. Das Silber wird dann mit verd. Ammoniak abgeschieden und photometrisch bei 495 nm als rotvioletter Komplex mit p-Diäthylbenzylidenrhodanin gemessen. Der Einfluß der Acidität, verschiedener TBP-Konzentration und des Augsalzmittels wurde untersucht. Die extrahierbare Verbindung hat wahrscheinlich die Zusammensetzung AgNO₃·(TBP)₃ oder HA_g(NO₃)₂(TBP)₃. Silber kann in Gegenwart vieler Elemente extrahiert werden, mit denen es in Legierungen, Mineralen oder Spaltprodukten vergesellschaftet ist. Das Verfahren ist einfach, selektiv und rasch. Für Trennung und Bestimmung sind 30 Minuten erforderlich.

     

On Extended Hermite-Fezér interpolation based on the zeros of Laguerre polynomials

Szász [2] proved the existence of an interpolatory polynomial which interpolates a given function at given data with some extended points. He also gave its explicit representation. We study the uniform convergence of the same, interpolating at the zeros of Laguerre polynomials with one point (as origin) extension.     

Effect of thermal conductivity on ultrasonic attenuation in praseodymium monochalcogenides

The ultrasonic attenuation in intermetallic praseodymium monochalcogenides are evaluated in the temperature interval 100–500 K along the crystallographic directions 〈100〉, 〈110〉, and 〈111〉 for longitudinal and shear waves. A comparison has been made with lanthanum monochalcogenides and other similar materials. Ultrasonic attenuation at different temperatures is mainly affected by the lattice thermal conductivity values of the materials at these temperatures. Thermoelastic loss is very small in comparison to the attenuation due to phonon-phonon interaction mechanism at higher temperatures.