1,721,422 research outputs found
Pd-Catalyzed Sequential Reactions Involving C–H Bond Activation: A Green and Sustainable Tool for Natural and Industrial Product Synthesis
No full textThe following sections are included:
Introduction: Green Chemistry and Sustainability
Sequential Reactions
C–H Activation
Relevant Selected Examples
Conclusion
Reference
Aliphatic Nitro Compounds as Key Precursors for the Eco-Friendly Synthesis of Fine Chemicals under Solvent-Free Conditions
No full textIn the last decades, there has been a phenomenal growth of the global economy and a continuous improvement of the living standards in industrialized countries. Sustainable development has consequently become an ideal goal. In the early 1990s, the concept of “green chemistry” was initiated in the United States as new paradigm, and since 1993 it has been promoted by the National Science Foundation (NSF) and the Environmental Protection Agency (EPA).
Sustainability has become an important issue in the wider context dealing with population, health, the environment, energy, technology, and renewable resources, and in the sciences, an integral part of the rapidly emerging field called green chemistry. This is a multidisciplinary field, requiring integrated study in the chemical, biological, and physical sciences. The 12 principles of green chemistry, as defined by Anastas and Warner, generally internationally accepted, cover complex issues, including minimization of waste, reduction in energy usage, and the use of renewable resources. In the chemical sciences, there is a need to develop benign synthetic pathways that, in addition to being high yielding (historically the most important measure of the success of a reaction), are simple, exhibit high atom efficiency, hence a reduced number of steps and no waste, are safe, and are environmentally acceptable. Further green metrics that are commonly used to quantify the “greenness” of a reaction are as follows: (1) the E-factor (environmental factor), which is the ratio of the mass of waste per mass of product (kilograms of waste/kilograms of product), and (2) the process mass intensity (PMI), that is the ratio of the total mass of materials used in the process to the mass of the isolated product, which, for pharmaceuticals, is typically >100. Removing organic solvents in chemical synthesis is important in the drive toward benign chemical technologies. Organic solvents are high on the list of toxic or otherwise damaging compounds because of the large volumes used in industry and difficulties in containing volatile compounds. Replacement reaction media include water, supercritical CO2, ionic liquid, and polyethylene or polypropylene glycol. Another alternative are the so-called solvent-free reactions (SFRs), which drastically minimize the environmental pollution, the exposure issues, and the E-factor. In fact, as reported by Tanaka and Toda, observing the natural phenomena, it could be obvious to say that conversion of one material into another occurs in the liquid state but not in the solid state (i.e., crushed grapes give wine by fermentation, but dried grapes do not result in wine, or shaking of milk gives cheese while dried milk can be kept unaltered) and, in this context, Aristotle summarized that no corpora nisi Fluida, which means “no reaction occurs in the absence of solvent.” Such philosophies had a big influence on the evolution of the modern sciences, and this
provides one historical reason to explain way most organic reactions have been studied in solution. On the contrary, often chemists still carry out their reaction in solution, even when the use of solvent is unnecessary. In this regard, aliphatic nitro compounds have demonstrated a great reactivity under neat conditions, mainly in the formation of new C–C bonds. Thus, the main focus of this report is to show the most important examples in which aliphatic nitro derivatives favor the reactivity under neat conditions and their application for preparing a variety of fine chemicals
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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