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Palladium-catalysed cross-coupling of styrenes with aryl methyl ketones in ionic liquids: a straight route to cyclopropanes
No full textAqueous choline acetate as reaction medium for the oxidation of kraft lignin with hydrogen peroxide
No full textRecently, choline-based ionic liquids (ILs), a class of biocompatible ILs, have been successfully employed in the pretreatment of lignocellulosic biomass. Nevertheless, their potential as solvents alternative to the more popular yet unfriendly imidazolium ILs in the oxidative depolymerization of lignin appears only marginally explored. In this study, aqueous cholinium acetate, [Ch][AcO], a readily available IL, was used as the reaction solvent for the oxidative depolymerization of Kraft lignin (KL) with H2O2/MoO3. Experimental optimization design was helpful to estimate optimal reaction parameters. Under reasonably mild conditions (H2O2 to KL weight ratio 0.33, 9.2% MoO3, 8% NaOH, 77 °C, 5 h), KL could be converted to 37% of depolymerization oil (KL_Oil), containing nearly 2.5% of aromatic monomers (ArMo), of which vanillin is the most abundant (up to 67%, yield 1.64%), and to 55% of oxidized lignin (OKL) solid fraction. When increasing H2O2/KL up to 1, ArMo yield decreased in favor of aliphatic acids (mainly, malonic acid), originating from ArMo over-oxidation, while OKL fraction enriched with carbonyl functional groups. Interestingly, in the absence of [Ch][AcO], lower ArMo yields (ArMo 1.68%) were observed, with vanillin selectivity dropping to 36% (yield 0.60%), hinting a possible stabilizing effect of the IL on reactive depolymerization intermediates and products. [Ch][AcO] could be regenerated, with <3% mass loss and unaltered chemical structure, and recycled without significant changes in product yields
Selective Palladium(II)‐Catalyzed Dimerization of Styrenes and Acrylates in Molten Tetrabutylammonium Acetate as an Ionic Liquid
Full text linkA method for the selective dimerization of styrenes and acrylates has been developed. The reaction is catalyzed by a very low amount of palladium acetate in molten tetrabutylammonium acetate without the need for any additional ligand. The use of this method enabled the coupling of substituted vinyl arenes in reasonable yields to give exclusively the (E,E)-1,4-diarylbutadiene motif within 7-10 h. Acrylates, on the other hand, exhibit higher reactivity, and the use of dibutyl acrylate resulted in the quantitative synthesis of dibutyl 2-methyleneglutarate in less than 2 h. This selectivity is unprecedented in the literature. The role of the ionic liquid and the different catalytic pathways involved in the two processes were also elucidated.The selective dimerization of styrenes and acrylates was possible with a very low amount of palladium acetate in molten tetrabutylammonium acetate. The coupling of substituted vinyl arenes gave exclusively the (E,E)-1,4-diarylbutadiene motif within 7-10 h, whereas butyl acrylate was converted into dibutyl 2-methyleneglutarate in less than 2 h. The catalytic pathways involved in the two processes were elucidated along with the role of the ionic liquid. imag
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Selective N-Alkylation of Arylamines with Alkyl Chloride in Ionic Liquids: Scope and Applications
No full textAn efficient N-selective alkylation of primary aromatic
amines in molten quaternary ammonium salts, as the solvent,
under relatively mild and base-free conditions is presented.
On the basis of the Kamlet–Taft parameters and the nucleophilicity
of the IL (ionic liquid) anions, the influence of the ionic liquid was evaluated. This protocol was validated on a
larger multigram scale and with the syntheses of bioactive
heterocycles (e.g., 1,4-benzothiazine and quinoxalines) and
new efficient MALDI matrixes
Ionic-Liquid-Assisted Metal-Free Oxidative Coupling of Amines To Give Imines
No full textAn oxidative coupling of amines to imines has been developed in ionic liquids (ILs) under metal-free aerobic conditions. The high efficiency achievable in ILs is mechanistically explained in terms of activation of the starting materials (benzylamine and molecular oxygen) by an initial electron transfer, which may be promoted by the ionic nature of the solvent. Reactivity data of variously para-substituted benzylamines show a general deactivating effect, which would imply a change in rate determining step within the same reaction mechanism
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