1,721,064 research outputs found
Pd(II)-Phosphine Catalysts for the Oxidative Carbonylation of Alkanols. Synthsis, Characterization, and Reactivity ofnew Carboalkoxy Complexes as Model Intermediates
No full textTrifluoroacetic Acid Hydroxylamine System as Organocatalyst Reagent in a One-Pot Salt Free Process for the Synthesis of Caprolactam and Amides of Industrial Interest
Full text linkIn this work we studied the reactivity of the Trifluoroacetic acid hydroxylamine system in the one step salt free synthesis of amides from ketones. A particular regards was paid to the caprolactam synthesis because of its industrial relevance. Synthesis, reactivity and characterization of the hydroxylamine trifluoroacetate is given. Fast oximation reaction of several ketones was gained at room temperature (1 h of reaction quantitative conversion for several ketones). In the same reactor, by raising the temperature at 383 K, the Beckmann rearrangement of the so obtained oximes is easily accomplished in the presence of three equivalent of TFA. The possibility of obtaining the trifluoroacetate of the hydroxylamine with a modified nitric acid hydrogenation reactions was verified, too. Reuse of solvent and trifluoroacetic acid is easily achieved by distillation. Graphical abstract: Salt free one-pot caprolactam and amides process catalyzed by CF3COOH, in the presence of NH2OH TFA as the oximation agent.[Figure not available: see fulltext.
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
Supported palladium metal as heterogeneous catalyst precursor for the methoxycarbonylation of cyclohexene
No full textThe methoxycarbonylation of cyclohexene has been carried out by using Pd metal deposited on a support as heterogeneous precursors instead of the homogeneous Pd(II) complexes usually proposed in literature. The two catalytic systems (homogeneous and heterogeneous) have been compared in methanol in the presence of free triphenylphosphine and p-toluenesulfonic acid as promoter. The precursor Pd on Amberlyst IRC 50 led to the best catalytic activity which is comparable to the activity obtained by using the homogeneous Pd(II)-catalyst. The leaching of the metal was negligible and the system has been efficiently recycled at least for three times. A reaction mechanism has been also proposed and discussed
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Pd/C Catalyzed selective hydrogenation of nitrobenzene to cyclohexanone oxime in the presence of NH2OH·HCl: Influence of the operative variables and insights on the reaction mechanism
No full textWe studied the influence of temperature, solvent, pressure, catalysts type on the selectivity of nitrobenzene hydrogenation to cyclohexanone oxime (COX) in the presence of NH2OH. The best reaction conditions are: pressure 0.8 MPa, temperature 333 K, solvent ethers, and catalyst Pd/C5%. Other hydrogenation metal catalysts did not give comparable results. The amount of Pd/C influences the yield in COX, which rises above to 90 % at the highest load. The reaction profile shows that aniline is the reaction intermediate. Indeed, aniline as a substrate gives COX, though in lower yield than that achieved employing nitrobenzene. The NH2OH parallel hydrogenation to NH4Cl, influences positively the selectivity to COX. It has been observed that COX, cyclohexanone and N-cyclohexylideneaniline are in equilibrium in the reaction solution and all likely derive from nucleophilic substitutions to a common imine intermediate formed on the Pd surface, whose high activity does not need any further metal catalyst
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