Hydrogen peroxide formation in the oxidation of carbonyl-containing compounds at β-CH bonds

The concepts of the selective inhibition of reactions with the participation of HO ₂^· radicals by nitrobenzene in accordance with a cyclic mechanism were supported using cyclohexanol oxidation as an example. It was demonstrated that the nitroxyl radical generated from nitrobenzene selectively reacts with HO₂ ^· to form hydrogen peroxide and nitrobenzene. A decrease in the rates of oxidation of esters, carboxylic acids, and ketones with specially chosen structures in the presence of nitrobenzene, as well as the detection of H₂O₂ and corresponding ,-unsaturated compounds among the reaction products, indicated that the degradation of -peroxyl radicals of the above compounds occurred under conditions of the liquid-phase oxidation of organic substances that result in the formation of the HO₂^· radical and an unsaturated compound.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 814–820.Original Russian Text Copyright © 2004 by Nepomnyashchikh, Nosacheva, Perkel.     

Molecular Structure of Samarium Dibromide

The molecular structure of samarium dibromide has been studied by electron diffraction at T _exp = 1250(50) K. The molecule has C_2v symmetry; the internuclear distance R_g(Sm–Br) = 274.5(5) pm; _g =131(6)°. The vibration frequencies were estimated from the experimental values of the mean square vibration amplitudes.     

Preparative gas-solid adsorption chromatography. Part II. Selection of optimal conditions for separation in preparative chromatography

Summary The paper discusses the effects of the flow rate and the nature of the carrier gas, and the value of the Henry temperature coefficient on the capacity and effciency of preparative gas-solid adsorption columns.The theoretical relationship between the height equivalent of a theoretical plate (HETP) and the experimental parameters under overloaded conditions was obtained byDe Wet andPretorius [1] and somewhat modified by us [2]. Although it was derived under the assumption that the sorption isotherm is linear, the equation was shown to be in qualitative agreement with the experimental results when the separation took place in a partition column.Consequently we investigated the applicability of this equation for separation on gas-solid adsorption columns containing modified silica, further the optimum characteristics of the adsorbents and the optimal separation conditions. The dependence of the capacity on the separation conditions, theoretically derived by us in an earlier paper [3] has also been studied.

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Präparative Adsorptions-Fest-Gas-Chromatographie. Teil II: Wahl der optimalen Trennbedingungen in der präparativen Chromatographie

Zusammenfassung Die Arbeit befaßt sich mit der Wirkung von Strömungsgeschwindigkeit und Art des Trägergases, sowie mit dem Wert des Temperatur-Koeffizienten nach Henry auf die Kapazität und Wirksamkeit von Adsorptionssäulen für die präparative Fest-Gas-Chromatographie. Die theoretische Beziehung zwischen Bodenzahl (HETP) und Versuchsbedingungen bei Überladung wurde vonDe Wet undPretorius [1] emittelt und von uns etwas abgewandelt [2]. Obwohl sie unter der Voraussetzung einer linearen Adsorptionsisotherme abgeleitet wurde, zeigte die Gleichung gute Übereinstimmungmit den experimentell erhaltenen Ergebnissen bei der Trennung in einer Verteilungssäule. Daraufhin untersuchten wir die Anwendbarkeit dieser Gleichung für Trennungen auf Adsorptionssäulen für die Gas-Fest-Chromatographie, die mit modifiziertem Silicagel gefüllt waren; weiterhin versuchten wir die optimalen Eigenschaften der Adsorbentien und die optimalen Trennbedingungen zu ermitteln. Die Abhängigkeit der Belastbarkeit von den Trennbedingungen, die in einer früheren Arbeit [3] von uns schon theoretisch abgeleitet worden war, wurde ebenfalls untersucht.

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Chromatographie d'adsorption gaz-solide prépartive. 2ème Partie: Sélection des conditions optimales de séparation en chromatographie préparative

Résumé Dans ce travail on étudie les effets de la vitesse, de la nature du gaz vecteur, ainsi que de la valeur du coefficient de température selon Henry, sur la capacité et l'efficacité de colonnes adsorbantes en chromatographie préparative gaz-solide. La relation théorique entre la hauteur équivalente d'un plateau théorique (HETP) et les paramètres expérimentaux, dans des conditions de surcharge, a été établie parDe Wet etPretorius [1] et légèrement modifiée par nous [2]. Bien que cette relation füt obtenue en supposant que l'isotherme d'adsorption est linéaire, on trouve une bonne concordance qualitative avec les résultats expérimentaux de la chromatographie de partage. Par conséquent nous avons étudié la validité de cette équation pour des séparations sur colonnes adsorbantes en chromatographie gaz-solide (silice modifié); en outre nous avons essayé d'établir les caractéristiques optimales des adsorbants et les conditions de séparation optimales. On a étudié la relation existant entre la capacité et les conditions de séparation, en tenant compte des équations théoriques établies par nous dans un travail antérieur [3].

     

New homochiralortho-palladated matrix bearing a bulky substituent at the carbon stereocenter

A new homochiral dimericortho-palladated complex bearing a bulkytert-butyl substituent at the carbon stereocenter was synthesized from optically activeN,N-dimethyl-α-tert-butylbenzylamine. Regioselective activation of only the aromatic C−H bond was shown to occur during the cyclometallation process proceeding under very mild conditions due to steric effects. Spectral characteristics of mononuclear derivatives of the new dimeric complex indicate that the five-membered palladacycle exists predominantly in one of two possible chiral conformations with the axial position of thetert-butyl substituent. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1375–1384, July, 1997.     

Reaction of K2PdCl4 with Synthetic and Natural Nucleic Acids

Circular dichroism was used to study reaction of K₂PdCl₄ with polydeoxyribonucleotides and calf thymus DNA. The optical and structural characteristics of the molecular components were determined to show that K₂PdCl₄ reacts with natural and synthetic acids, producing profound rearrangements in their structure.     

Diluent effects on the Debye-type dielectric relaxation in viscous monohydroxy alcohols

With the recognition that the Debye-type dielectric relaxation of liquid monohydroxy alcohols does not reflect the structural relaxation dynamics associated with the viscous flow and the glass transition, its behavior upon dilution is expected to differ from that of real alpha-processes. We have investigated the Debye-type dielectric relaxation of binary alcohol/alkane mixtures across the entire concentration range in the supercooled regimes. The focus is on 2-ethyl-1-hexanol in two nonpolar liquids, 3-methylpentane and squalane, which are more fluid and more viscous than the alcohol, respectively. The Debye relaxation is found to occur only for alcohol mole fractions x > 0.2 and is always accompanied by a non-Debye relaxation originating from the alcohol component. Prior to its complete disappearance, the Debye relaxation is subject to broadening. We observe that the Debye dynamics of 2-ethyl-1-hexanol is accelerated in the more fluid 3-methylpentane, while the more viscous squalane leads to longer Debye relaxation times. The present experiments also provide evidence that the breakdown of the Debye relaxation amplitude does not imply the absence of hydrogen-bonded structures.     

Total synthesis of kendomycin: a macro-C-glycosidation approach

Kendomycin, also known as (-)-TAN 2162, is a novel polyketide-derived ansamycin isolated from Streptomyces sp., which exhibits potent antagonist and agonist activities at the endothelin and calcitonin receptors, respectively. This bacterial metabolite also possesses a strong antibiotic activity against a range of gram-positive and -negative bacteria and cytostatic effects on the growth of human cancer cell lines. When a novel macroglycosidation reaction is employed as the key step, the first enantioselective total synthesis of kendomycin has been accomplished. A Friedel-Crafts-type ring closure of the acyclic precursor containing tetrahydropyran and benzofuran moieties produces the macrocycle as a single stereoisomer in good yield, thus establishing the aryl C-glycosidic linkage of the ansa core. This reaction requires a phenolic glycosyl acceptor and appears to proceed through a rapid O-glycosidation followed by a slow rearrangement to an aryl C-glycoside. The requisite secomacrocycle is prepared by the Pd(0)-catalyzed B-alkyl Suzuki-Miyaura cross-coupling of two subunits, which in turn can be expeditiously assembled from readily available building blocks in a modular fashion.     

Oxidation of 2,4-Dinitrotoluene with an Ozone-Oxygen Mixture

Oxidation of 2,4-dinitrotoluene to 2,4-dinitrobenzoic acid with an ozone-oxygen mixture in glacial acetic acid was studied.