1,720,979 research outputs found
La Reazione di idroformilazione nella sintesi di fragranze
Full text linkIl nostro gruppo di ricerca si occupa già da alcuni anni della
preparazione per via catalitica di alcuni prodotti da destinare all’industria delle essenze e
dei profumi, in particolare sono stati preparati sia composti puri, partendo da semplici
substrati insaturi, sia miscele di prodotti partendo da estratti naturali
Idroformilazione selettiva del 1,3-diisopropenilbenzene per la sintesi del Florhydral®
Full text linkIl Florhydral®, 3-(3'-isopropenilfenil)butanal, è una fragranza di sintesi commercializzata a partire dal m-diisopropenilbenzene I ed il passaggio chiave dello schema di sintesi è rappresentato dall'idroformilazione di questa di olefina catalizzata da complessi di rodio.
L'oxosintesi, anche se altamente chemioselettiva, presenta però una selettività
piuttosto bassa verso la desiderata monoaldeide II, precursore del Florhydral®, fornendo
anche il prodotto dialdeidico III. Abbiamo pertanto effettuato uno studio più approfondito di
idroformilazione in presenza di vari sistemi catalitici sia omogenei che eterogenei con lo
scopo di ottenere selettivamente la monoaldeide, che viene convertita nel desiderato Florhydral® IV tramite idrogenazione catalitica del doppio legame alchilico utilizzando 10
atm di H2e Pd/C al 5% come catalizzatore
Hydrogenation of Imines Catalyzed by 2-(Aminomethyl)pyridine-Based Ruthenium and Osmium Complexes
No full textCNN pincer ruthenium(II) and osmium(II) complexes of general formula RuCl(CNN)(dppb) (1 a-c) and OsCl(CNN)(dppb) (2 a,b) (dppb=Ph2P(CH2)4PPh2, HCNN=[6-(p-tolyl)-2-pyridyl]methylamine (4), N-methyl-[6-(p-tolyl)-2-pyridyl]methylamine (7) and N,N-dimethyl-[6-(p-tolyl)-2-pyridyl]methylamine (8)) were prepared and assessed as catalysts in the hydrogenation of a variety of imines. Among the examined complexes, the Ru-complex 1 a, RuCl(4)(dppb), showed the best activity, reducing N-aryl and N-alkyl imines to the related amines in high yields (up to 100 %) with a catalyst loading of 0.1-1 mol% and under mild conditions (5 atm H2, 40-70 °C). The Os-complexes exhibited a lower activity than their ruthenium analogues. Despite this, the Os-complex 2 a, OsCl(4)(dppb), was successful in the reduction of N-benzylideneaniline at 70 °C, affording a rare example of application of osmium complexes in the catalytic hydrogenation of imines
Analisi di oli essenziali diCitrusdurante il periodo di maturazione del frutto
Full text linkGli oli essenziali del genereCitruscostituiscono un’importante classe di prodotti il cui utilizzo è molteplice. Nel campo alimentare sono utilizzati come aromatizzanti, nella profumeria per la formulazione di profumi con particolari “note di testa”, in campo farmaceutico come aromatizzanti. Vista l’importanza di questi oli abbiamo ritenuto interessante valutare la variabilità del loro contenuto in rapporto al grado di maturazione del frutto. La nostra indagine ha riguardato gli oli essenziali di due cultivar pigmentate: Moro e tarocco ed una cultivar bionda locale: San vito
Enantioseparation of organometallic compounds and metal complexes by liquid chromatographic techniques. A review
Full text linkChiral organometallic compounds and metal complexes, and more recently metal clusters, have attracted great interest for applications in chemical, biological, medical, and material sciences. In these fields, liquid chromatography has been widely used for fast chiral analysis to determine the enantiomeric purity of metal-containing chiral compounds prepared by asymmetric synthesis, for quality control of commercial chiral metal catalysts, for accessing enantioenriched or pure enantiomers of metal complexes for various applications, and often as test probe analytes for screening the enantioseparation capability of newly developed chiral columns and chromatographic systems. With the aim to show what was done in this field as a useful guide for new applications, in this review the evolution of methods and approaches used to separate the enantiomers of chiral metal-containing compounds is described, showing how this field have been changed over time, from the 1970s until most recent studies. For this purpose, representative applications of enantioselective liquid chromatography for the enantioseparation of chiral organometallic compounds and metal complexes will be presented and discussed, indicating chiral columns, mobile phases, and chromatographic conditions which have been used to obtain successful enantioseparations in this field
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
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
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