1,720,954 research outputs found
The study of N-heterocyclic carbenes (NHCs) in ionic liquids
Get PDFThe formation of N-heterocyclic carbenes (NHCs) from imidazolium based ionic liquids (ILs) has attracted great interest, especially for synthetic chemistry. Carbenes can be used as catalysts for C-C bond formation reactions, such as the benzoin condensation or Stetter reaction. In this project, ILs were used as the source of carbene in the benzoin condensation in neat conditions, which was successfully performed. The imidazolium acetate ILs proved to be useful catalysts as well as solvents for the benzoin condensation, with their activity likely arising from the in-situ formation of NHCs. For example, it was found that the reaction of benzaldehyde with 1-butyl-3-methylimidazolium acetate, [C4C1im][OAc] and 1-ethyl-3-methylimidazolium acetate [C2C1im][OAc] as catalysts produced benzoin with good to excellent yield. These results show that the acetate anion in the [C2C1im][OAc] can act as base in the reaction.
This result triggered us to investigate the reaction kinetics for the benzoin reaction using ILs. The results show that the reaction is a complex reaction which depends on a lot of parameters. The results also showed that the rate determining step is the second step, where the Breslow intermediate reacts with a second aldehyde. The first step is very fast. This result also brings another interesting question on the existence of NHCs in the reaction; did the NHC form during the reaction or did NHC is already exist in the ionic liquid. To investigate this, we have performed the kinetics of Breslow intermediate formation and isotope effect experiments were performed using deuterated C2 position of [C2C1im][OAc] with anisaldehyde and compared the rate of the reaction with normal [C2C1im][OAc]. The result showed no significant difference in the reaction rate. This suggests that the carbene already existed in ionic liquid rather than being form during the reaction.
The ability of ILs to react with the carbonyl group in cellulose is well established. A proposed method was performed to protect the aldehyde group from reacting with the ILs by using the diol compound as the protecting group. Two different methods were employed and the result showed that the protection group can prevent the ILs from reacting with the carbonyl group. As this result only used benzaldehyde as model compound, the applicability of the method in the actual cellulose compound remain question and further study is needed.Open Acces
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Review on Polyurethane Solubilization in Deep Eutectic Solvents (DES) for Plastic Recycling
Get PDFDeep eutectic solvents (DES) are a novel category of environmentally friendly solvents created by the interaction of hydrogen bond donors (HBDs) and acceptors (HBAs) in precise molar ratios, exhibiting unique physicochemical characteristics. DES have low volatility, non-flammability, and great stability, making them ecologically benign substitutes for traditional solvents. The essential physical qualities of DES, including density, viscosity, and thermal stability, are pivotal to its operation. These characteristics are affected by parameters like as temperature, component mix, and molar ratios, enabling customisation for particular purposes. DES have shown considerable promise in several domains, including electrochemistry, material synthesis, and environmentally friendly chemical processes, owing to their adaptability and safety. In the realm of polyurethane (PU) solubilisation, deep eutectic solvents (DES) have notable potential. The solubilization process is ascribed to the breakdown of the polymer’s hydrogen bonds and the dissolving of urethane connections by the DES components, helped by their strong hydrogen bond network. By customising DES characteristics, researchers may enhance the breakdown process for PU, offering a sustainable solution to plastic waste issues. The basic features, physical and chemical properties, wide range of uses, and potential for developing PU solubilisation technologies of DES are highlighted in this paper.Pelarut eutektik dalam (Deep Eutectic Solvents/DES) adalah kategori baru pelarut ramah lingkungan yang dibuat melalui interaksi antara donor ikatan hidrogen (hydrogen bond donors/HBDs) dan akseptor ikatan hidrogen (hydrogen bond acceptors/HBAs) dalam rasio molar tertentu, yang menunjukkan karakteristik fisikokimia unik. DES memiliki volatilitas rendah, tidak mudah terbakar, dan stabilitas tinggi, menjadikannya pengganti yang ramah lingkungan untuk pelarut konvensional. Sifat fisik utama DES, termasuk densitas, viskositas, dan stabilitas termal, sangat penting untuk fungsinya. Karakteristik ini dipengaruhi oleh parameter seperti suhu, komposisi komponen, dan rasio molar, sehingga memungkinkan penyesuaian untuk tujuan tertentu. DES telah menunjukkan potensi besar dalam berbagai bidang, termasuk elektrokimia, sintesis material, dan proses kimia ramah lingkungan, berkat kemampuan adaptasi dan keamanannya. Dalam bidang pelarutan poliuretan (polyurethane/PU), DES memiliki potensi yang signifikan. Proses pelarutan ini dikaitkan dengan penghancuran ikatan hidrogen dalam polimer dan pelarutan ikatan uretan oleh komponen DES, yang diperkuat oleh jaringan ikatan hidrogen yang kuat. Dengan menyesuaikan sifat-sifat DES, para peneliti dapat meningkatkan proses degradasi PU, menawarkan solusi berkelanjutan untuk masalah limbah plastik. Artikel ini menyoroti karakteristik dasar, sifat fisik dan kimia, berbagai aplikasi, serta potensi DES dalam pengembangan teknologi pelarutan PU
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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