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Preparation of wrapped carbon nanotubes poly(4-vinylpyridine)/MTO based heterogeneous catalysts for the oxidative desulfurization (ODS) of model and synthetic diesel fuel
No full textThe preparation of novel wrapped carbon nanotubes poly(4-vinylpyridine)/methyl trioxorhenium based heterogeneous catalysts has been reported by two different procedures: a) the wrapping by grinding of multiwall carbon nanotubes with pre-formed adducts, respectively, [poly(4-vinylpyridine)·methyltrioxorhenium] or [poly(4-vinylpyridine)-N-oxide·methyltrioxorhenium] and, b) the loading of methyltrioxorhenium on previously wrapped multiwall carbon nanotubes with poly(4-vinylpyridine) and poly(4-vinylpyridine)-N-oxide resins. The novel catalysts were characterized by SEM, TEM, ICP-MS and XPS analyses. Both types of catalysts were efficient systems in the oxidation of recalcitrant aromatic sulfur derivatives with H2O2, as representative models of oxidative desulfurization processes, affording the corresponding sulfones with yields ranging from moderate to quantitative. The oxidation of a complex model fuel oil and of synthetic diesel fuel, under optimal experimental conditions, is also reported. The performance of novel catalysts was dependent on the specific procedure applied for the immobilization of the active species, and was more efficient for both model oil and synthetic diesel fuel samples (with quantitative conversions and selectivities to the corresponding sulfones), than for isolated substrates
Hydroxypyridine/pyridone interconversions within ruthenium complexes and their application in the catalytic hydrogenation of CO<sub>2</sub>
No full textReaction of a new ligand 6-DiPPon (6-diisopropylphosphino-2-pyridone) with 0.5 equiv of [RuCl2(p-cymene)]2 resulted in the formation of a mixture of [RuCl2(p-cymene)(κ1-P-6-DiPPon)]2 (1) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]Cl ([2]Cl) (where 6-DiPPin = 6-diisopropylphosphino-2-hydroxypyridine). The ratio between the two products can be controlled by the nature of the solvent. The similar reaction between 6-DiPPon and [RuCl2(p-cymene)]2 in the presence of AgOTf and Na[BArF24] (where BArF24 = [{3,5-(CF3)2C6H3}4B]−) resulted in the formation of the complexes [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]OTf, ([2]OTf) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]BArF24 ([2]BArF24), respectively. Reactions between complex [2]Cl, [2]OTf, or [2]BArF24 and a base (either DBU or NaOMe) resulted in the deprotonation of the hydroxyl functional group to form a novel neutral orange-colored dearomatized complex, 3. The identity of complex 3 was confirmed as [RuCl(p-cymene)(κ2-P,N-6-DiPPon*)], where 6-DiPPon* is the anionic species (6-diisopropylphosphino-2-oxo-pyridinide), which contains the deprotonated moiety. The new 6-DiPPon ligand and its corresponding air stable half-sandwich derivative ruthenium complexes 1, [2]OTf, [2]BArF24, and 3 were all isolated in good yields and fully characterized by spectroscopic and analytical methods. The interconversions between the neutral and anionic forms of the ligands 6-DiPPon, 6-DiPPin, and 6-DiPPon* offer the potential for novel secondary sphere interactions and proton shuttling reactivity. The consequences for this have been explored in the activation of H2 and the subsequent catalytic hydrogenations of CO2 into formate salts in the presence of a base.</p
Ruthenium Arene Complexes with α-Aminoacidato Ligands: New Insights into Transfer Hydrogenation Reactions and Cytotoxic Behaviour
Get PDFThe RuII arene complexes [Ru(η6-p-cymene)(κ2N,O-aa)Cl] (aa = l-glutaminato, 1; l-homoserinato, 2; l-tyrosinato, 3; l-serinato, 4; l-prolinato, 5; trans-4-hydroxyl-l-prolinato, 6; l-threoninato, 7; glycinato, 8) were synthesized in high yields by the reactions of [Ru(η6-p-cymene)Cl2]2 with aa/MOH (M = Na, K). The salt [Ru(η6-p-cymene)(κ2N,O-l-serinato)(PPh3)][CF3SO3], 9[CF3SO3], was prepared in 68 % yield from 4 and AgSO3CF3/PPh3. All the products were fully characterized by analytical and spectroscopic methods, moreover the X-ray structures of 1 and 2 were elucidated by X-ray diffraction. Compounds 1–7 and 9[CF3SO3] were studied as catalytic precursors for the transfer hydrogenation reaction (THR) of acetophenone, using 2-propanol or sodium formate (in water) as hydrogen sources, under variable experimental conditions. The catalytic process was investigated also under microwave irradiation. In general, all the catalytic reactions selectively afforded 1-phenylethanol, and the best results were achieved with 5 and 6, in terms of both activity and enantioselectivity (enantiomeric excess up to 78 %). The in vitro cytotoxicity of 1, 4, 5 and 9[CF3SO3] was assessed towards the human pancreatic cancer cell line BxPC3 and the mouse embryo fibroblast Balb/3T3 Clone A31 cell line, all of the investigated compounds showing to be substantially inactive. The catalytic and biological results will be discussed in relation to the relevant chemical behaviour of the compounds in water solution
Dioxomolybdenum(VI) compounds with α-amino acid donor ligands as catalytic precursors for the selective oxyfunctionalization of olefins
Get PDFA series of cis-dioxomolybdenum(VI) α-amino acid containing compounds I–V has been investigated as potential catalyst precursors for the mild and selective oxyfunctionalization of conjugated or unconjugated olefins like styrene, α-methylstyrene, cis-β-methylstyrene, cyclohexene and cyclooctene, using tert-butyl hydroperoxide (TBHP) as main oxidant. All the I–V complexes behaved as active heterogeneous and recyclable catalysts, showing good to quantitative conversion values of the substrate. In all cases, high selectivity toward the corresponding epoxide formation was detected. No substantial difference in terms of efficiency has been observed among the different catalysts I–V, thus confirming that the different nature of the amino acidic side-chain does not strictly affect the catalytic process. Insights into mechanistic details and reaction free energy profile of catalytic oxidations by means of quantum chemical calculations have been discussed
Synthesis of 2-acylindoles via Ag- and Cu-catalyzed anti-Michael hydroamination of β-(2-aminophenyl)-α,β-ynones: Experimental results and DFT calculation
No full textβ-2-aminophenyl)-α,β-ynones afforded 3-unsubstituted 2-acylindoles in good yields in the presence of 20 mol% of AgOTf under MW heating. The use CuOTf as catalyst resulted in a similar reaction outcome, generally with a lower efficiency. This transformation represents the first example of 5-endo-dig cyclization of 2-alkynylanilines bearing an acyl group linked to the triple bond. By contrast with the previously reported gold-catalyzed reaction of β-2-aminophenyl)-α,β-ynones, that resulted in the formation of dibenzo[1,5]diazocines through a sequential process triggered by an intermolecular hydroamination, a selective intramolecular anti-Michael hydroamination was observed in the present study by mean of silver/copper catalysis. Density Functional Theory calculation on the Ag-catalyzed reaction revealed that the catalyst induces an electrostatic arrangement in the TS coherent with the experimentally observed cyclization
Iodoxybenzoic Acid Supported on Multi Walled Carbon Nanotubes as Biomimetic Environmental Friendly Oxidative Systems for the Oxidation of Alcohols to Aldehydes
No full textIodoxybenzoic acid (IBX) supported multi walled carbon nanotube (MWCNT) derivatives have been prepared as easily recyclable solid reagents. These compounds have been shown to be able to mimic the alcohol dehydrogenases and monooxygenases promoted oxidation of aromatic alcohols to corresponding aldehydes. Their reactivity was found to be dependent on the degree of functionalization of MWCNTs as well as from the chemical properties of the spacers used to bind IBX on the surface of the support. Au-decorated MWCNTs and the presence of longer spacers resulted in the optimal experimental conditions. A high conversion of the substrates and yield of desired products were obtained
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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