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La modernità in tre mosse
No full textIl saggio delinea un'evoluzione del rapporto tra cinema italiano e modernità che conosce una prima significativa fioritura nella belle epoque (una modernità progettata dalle elite culturali e artistiche e che il cinema rende popolare) e si riassesta dandosi strutture, mezzi e strategie nel ventennio fascista (la modernità "immaginata" dai media, in un'Italia in buona parte arretrata), prima di esplodere con prepotenza nel secondo dopoguerra
PERCHLORATES AS POWERFUL CATALYSTS IN MANY IMPORTANT ORGANIC TRANSFORMATIONS
No full textFor long times, metallic perchlorates have been considered dangerous compounds[1] in that they function as explosives and as incontrollable oxidizers.
Therefore, the fear of the great hazard connected with their manufacture and uses had prevented an extensive use both in research laboratories and in industrial processes.[2]
However, recently it has been cleared that this bad reputation is due to the mistaken association of metallic perchlorates with the oxidizing potential of perchloric acid and the pyrotechnic performances of NH4ClO4.
In this conference, we report that Magnesium and Zinc perchlorates can be used as powerful Lewis acids in several organic transformations which are commonly employed both in laboratory and industrial processes.
As depicted in the Scheme, perchlorates are able to promote a series of reactions such as:
a) Acylation of alcohols[3,4]
b) Fisher esterification[5]
c) Synthesis of b–enamino esters[6]
d) Protection of the amino group as N-Boc derivative[7]
Moreover, they can act as specific catalysts for the development of a new organic transformations. In fact, the treatment of an alcohol or a phenol with Boc2O in the presence of Mg(ClO4)2 leads to the unexpected formation of the corresponding t-butyl ethers.[8] This represents the first general method to synthesize aromatic t-butyl ethers.
In an analogous manner, the treatment of phenols with diethyl dicarbonate results in a very efficient method to produce difficulty available aryl ethyl carbonates.
Several of the above mentioned transformations can be carried out in the absence of the solvent, and often the catalyst can be easily recovered and reused without an appreciable loss of activity.
Acknowledgement
Work carried out in the framework of the National Project “Stereoselezione in Sintesi Organica. Metodologie e Applicazioni” supported by MIUR, Rome, by the University of Bologna, in the framework of “Progetto di Finanziamento Pluriennale, Ateneo di Bologna”, and by National project FIRB “Progettazione, preparazione e valutazione biologica e farmacologica di nuove molecole organiche quali potenziali farmaci”
References
[1] Schumacher, J. C. Perchlorates-Their Properties, Manufacture and Uses, ACS Monograph Series, Reinhold: New York, 1960.Author. Title[J]. Name of the journal, Year, Volume(Issue): initial page and ending page (Optional).
[2] Long, J. Chemical Health & Safety, 2002, 9, 12.
[3] Bartoli, G.; Bosco, M.; Dalpozzo, R.; Marcantoni, E.; Massaccesi, M.; Rinaldi, S.; Sambri, L. Synlett, 2003, 39.
[4] Bartoli, G.; Bosco, M.; Dalpozzo, R.; Marcantoni, E.; Massaccesi, M.; Sambri, L. Eur. J. Org. Chem. 2003, 4611.
[5] a) Gooβen, L.; Döhring, A. Adv. Synth. Catal. 2003, 345, 943; b) Bartoli, G.; Boeglin, J.; Bosco, M.; Locatelli, M.; Massaccesi, M.; Melchiorre, P.; Sambri, L. Adv. Synth. Catal. 2005, 347, 33.
[6] Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Melchiorre, P.; Sambri, L. Synlett 2004, 239.
[7] Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Massaccesi, M.; Melchiorre, P.; Sambri, L. Synlett 2004, 1794.
[8] Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Melchiorre, P.; Sambri, L. Org. Lett., 2004, 7, 427
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
L'approccio endoscopico transnasosfenoidale per la decompressione del nervo ottico : uno studio anatomico
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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
APPLICATIONS OF PERCHLORATES IN ORGANIC SYNTHESIS. A NEW AND GENERAL ROUTE TO t-BUTYL ETHERS
No full textAPPLICATIONS OF PERCHLORATES IN ORGANIC SYNTHESIS. A NEW AND GENERAL ROUTE TO t-BUTYL ETHERS
Giuseppe Bartoli, Marcella Bosco, Manuela Locatelli, Paolo Melchiorre and Letizia Sambri
Dipartimento di Chimica Organica “A. Mangini”, v.le Risorgimento 4, Bologna, Italy
[email protected]
In the last few years, we were interested in the use of various metallic perchlorates as Lewis acid promoters in various organic transformations.1 In particular, perchlorate salts have shown a high ability to activate 1,3-dicarbonyl systems.
We surprisingly found that anhydrous Mg(ClO4)2 promotes the reaction of alcohols with t-butyl dicarbonate (Boc2O) to give t-butyl ethers.2 This reaction appears extremely interesting, as it represents a potential solution to a longstanding problem in organic synthesis namely, t-butyl ether formation. The t-butyl ether in fact is “one of the most underused alcohol protecting groups”,3 although it is one of the few ethers stable under strongly basic conditions.
We set up a new protocol for the synthesis of t-butyl ethers from a large variety of functionalized aromatic and aliphatic alcohols. Selective mono-protection of symmetric and asymmetric diols can also be achieved.
At the same time, a convenient deprotection protocol was set up. In fact, t-butyl ethers were easily reconverted in the corresponding alcohols by simple treatment with the CeCl3/NaI system.4
Scheme 1.
1. Bartoli, G.; Boeglin, J.; Bosco, M.; Locatelli, M.; Massaccesi, M.; Melchiorre, P.; Sambri, L. Adv. Synth. Catal. 2005, 347, 33-38. and references herein cited.
2. Bartoli, G.; Bosco, M.; Locatelli, M.; Marcantoni, E.; Melchiorre, P.; Sambri, L. Org. Lett. 2005, 7, 427-430.
3. Greene, T. W.; Wuts, P. G. M in Protective Groups in Organic Synthesis, Wiley, New York, 3rd Ed., 1999, pp. 65-67.
4. Bartoli, G.; Marcantoni, E.; Sambri, L. Synlett, 2003, 2101-2116
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
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