1,720,984 research outputs found
Avoiding hot-spots in Microwave-Assisted Pd/C catalysed reactions by using the biomass derived solvent γ-Valerolactone
Full text linkHerein, we report the use of γ-valerolactone as a new biomass-derived reaction medium for microwave assisted organic synthesis. The interaction of this solvent with microwaves and its heating profile under microwave irradiation has been fully characterized for the first time, demonstrating its stability and the applicability in microwave assisted Pd/C catalysed reactions avoiding the arcing phenomena frequently observed in these conditions. The use of γ-valerolactone demonstrated to be compatible with aliphatic and aromatic amines in the hydrogen transfer Pd/C mediated synthesis of benzimidazoles
Waste-minimized synthesis of C2 functionalized quinolines exploiting iron-catalysed C-H activation
No full textHerein we present an efficient and regioselective iron-catalyzed methodology for the external oxidant-free functionalization of quinoline-N-oxides. The protocol, based on the use of inexpensive and easily accessible FeSO4, showed broad applicability to a wide range of substrates. An additional green feature of this synthetic methodology is H2O being the only by-product. Experimental and computational investigations provide support to a mechanism based on a facile C-H activation event. The green efficiency of the process has also been carefully assessed using: (i) metrics related to the synthetic process (AE, Yield, 1/SF, MRP and RME); (ii) safety/hazard metrics (SHZI and SHI); and (iii) metrics related to the metal used as the catalyst (Abundance, OEL and ADP). In addition to the many advantages of this protocol related to the green iron catalyst used and the safety/hazard features of the process, an E-factor value of ca. 0.92 (84 to >99% reduction compared to known protocols) evidently confirms the sustainable efficiency of the procedure presented. Practical utility has also been demonstrated by performing the reaction efficiently on a multi-gram scale. This journal i
Chapter 6: Sustainable Approaches to C-H Functionalizations Through Flow Techniques
No full textC-H functionalization reactions have attracted great attention in recent years due to their promise of simplifying organic synthetic pathways. However, many reported protocols suffer from common limitations, such as the usually harsh reaction conditions, with the related safety issues, and the requirement of high catalyst loadings. Recent research efforts have demonstrated that the application of flow technologies to C-H functionalization reactions can significantly mitigate these issues, also resulting in more sustainable protocols. In this chapter we present selected examples of C-H functionalizations realized in flow conditions, highlighting the sustainability aspects effected by the application of flow techniques
Aerobic waste-minimized Pd-catalysed C-H alkenylation in GVL using a tube-in-tube heterogeneous flow reactor
No full textHerein we report the design and application of a tube-in-tube packed-bed flow reactor for the first time for the development of a heterogeneous palladium catalysed oxidative C-C bond formation process. In particular, we have defined an innovative tube-in-tube protocol for the Fujiwara-Moritani C-H alkenylation reaction in biomass-derived γ-valerolactone. Thanks to this novel flow system, the oxidative C-H activation process has been conducted using a sub-stoichiometric amount of an external organic oxidant (benzoquinone) in the presence of molecular oxygen as a benign sacrificial oxidant. The protocol features very limited metal leaching and high stability of the catalyst over time. In this study, the applicability of the protocol to a range of substituted acetanilides and N-methoxybenzamides and various electron-poor alkenes has been demonstrated. The practical utility of the tube-in-tube reactor has also been proved by performing the flow methodology on a multi-gram scale
Life cycle assessment of multistep benzoxazole synthesis: from batch to waste-minimised continuous flow systems
No full textIn this contribution we have focused on the progress of synthesis methods for the preparation of 2-aryl benzoxazoles as highly interesting materials with increasing relevance in the pharmaceutical industry as well as in optical applications. The traditional production methods of 2-aryl benzoxazoles clearly have some drawbacks related to the use of strong acids and/or toxic reagents leading to a large production of waste. Importantly, comprehensive analysis of the associated risk in terms of safety, environmental impact and disposal cost is lacking. In this regard, the life cycle assessment (LCA) methodology is herein applied to ultimately evaluate the environmental profile of the available routes to access 2-aryl benzoxazoles. Seven batch synthesis approaches and two continuous-flow (CF) approaches (small and large scale) are closely compared. The superiority of the CF technology is ultimately proven among the analysed environmental impact categories. The main finding is that the oxygen-flow chemistry intensification fortified the sustainability of the green chemistry principles (towards the catalyst/solvent) themselves by ensuring the regeneration of OMS catalysts and reduction of manganese leaching to the minimum by the CPME solvent, which also provided high solvent recyclability. In this way, it adds circularity in the sense of its 10R framework (e.g. R standing for recycle, repair, rethink, and refuse). As a result, for example, our flow approach reduces carbon emissions by 85% in comparison with our batch approach, the latter exhibiting lower environmental impact than the six batch approaches from the literature. In addition, our flow chemistry process has lower energy consumption and solvent load, whose share is up to 88% of the environmental impact
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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