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Synthesis and reactivity of new transition metal-based catalytic systems in carbonylation reactions
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The aim of this PhD thesis was to explore the activity of new catalytic systems in some carbonylation reactions of organic substrates, like aromatic amines, olefins and/or iodoarenes which are transformed in isocyanates, ureas, esters, amides and polymers, interesting for the chemical industry.
In Chapter 1 the study of the synthesis of isocyanates and amides of industrial interest is reported. A catalytic system based on [PdCl2(dppf)]/FeCl3/O2 was studied for the synthesis of phenylisocyanate and N,N diphenylurea (DPU), by oxidative carbonylation of aniline. Also presented is a study of synthesis of cyclohexanoneoxime obtained by reduction of nitrobenzene in the presence of NH2OH.HCl with heterogeneous Pd catalysts, which by Beckmann rearrangement can lead to the formation of Caprolactam. A reactivity study of trifluoroacetate hydroxylamine (NH2OH.CF3COOH) for the synthesis of oximes and amides of industrial interest is also presented.
In Chapter 2, a study on the carbonylation of olefins with Pd-based heterogeneous pre-catalysts is presented. Through the study of methoxycarbonylation of cyclohexene these catalysts were compared to the activity of the homogeneous catalyst of [Pd(TsO)2(PPh3)2]. From a study of the reaction mechanism, the possibility of having a mixed homogeneous/heterogeneous catalysis is proposed.
In addition, a study of a new heterogeneous magnetic support obtained by decomposition of Fe(CO)5 is presented, which was suitably coated with a polyketone layer. Such a support was employed for the synthesis of a Pd-based heterogeneous catalyst (Pd/MIM) and successfully employed in methoxycarbonylation reaction of cyclohexene, methoxycarbonylation of iodobenzene and for nitrobenzene reduction reaction.
In conclusion, the hydration of olefins catalyzed by CF3COOH, which is commonly employed as an acidic promoter in palladium-catalyzed carbonylation reactions, was investigated to delineate possible eddy reactions for olefin carbonylation reactions for industrially employed two-phase systems.
In Chapter 3, a study was performed on the carbonylation of iodobenzenes. A new catalytic system based on [PdCl2(Xantphos)] was studied for alkoxycarbonylation reactions. In particular, the effects of some additives on the productivity of the reaction have been studied, defining as the best catalytic system the one formed by [PdCl2(Xantphos)] and the pair Ferrocene/ferrocenium.
In addition, a preliminary study of the amino-carbonylation reaction of iodobenzene is presented, the selectivity of the reaction is explored, and the possible competition of the base required for the catalytic cycle and the amine employed as a nucleophile.
In Chapter 4, the possibility of employing green surrogates for carbonylation reactions was investigated. A study was carried out on the generation of CO from formic acid, through the Morgan reaction, using heterogeneous acid catalysts. The best setup of the reactor has been studied to optimize the yield of carbon monoxide and avoid the mechanical degradation of acid resins used as catalysts.
A new multi-chamber reactor has also been designed to perform simultaneously several Palladium-catalyzed carbonylation reactions, employing CO generated by formic acid.
Finally, the first example of polymer obtained by catalytic carbonylation of ethylene (PK), employing CO generated by formic acid and acetic anhydride system, is presented. The HCOOH/CH3COO2 mixture plays both the role of solvent and carbon monoxide generator
Synthesis of phenyl isocyanate and derivates via oxidative carbonylation of aniline catalyzed by Pd(II)-based redox systems
No full textOne of the challenges in current day catalysis is to replace wasteful and dangerous industrial processes by more environmentally friendly and safer ones. An example of such a challenge is to replace the highly toxic and corrosive phosgene often used as carbonylating agent. An important example, from an industrial point of view, is represented by the synthesis of isocyanates, starting materials for the production of polyurethanes, actually performed by treating amines with phosgene. Among the numerous phosgene-free methods reported in the literature to produce isocyanates, carbamates and ureas, the reductive carbonylation of nitro compounds and the direct oxidative carbonylation of amines represents a valid alternative to the traditional methods. The Pd-catalyzed carbonylation of aniline to phenylisocyanate, phenylcarbamate or 1,3-diphenylurea has been deeply studied and appears particularly attractive from the standpoint of atom economy. In such a systems, the catalyst consists of a Pd(II) salt that, to form the desiderated products, is reduced to inactive Pd(0) species. The reoxidation of such species to Pd(II) active ones is a key step which permits the restarting of the catalytic cycle. As a matter of fact, the direct reoxidation of Pd(0) species by molecular oxygen is so slow that the precipitation of inactive palladium metal (palladium black) often competes with the reoxidation itself, making inefficient the catalysis. Several methods have been proposed and developed to circumvent this problem mainly based on two strategies which can work at the same time: 1) the stabilization of reoxidable Pd(0) complexes, avoiding the formation of Pd metal; 2) the increasing of the Pd(0) reoxidation rate. An interesting proposal widely adopted in literature is to increase the rate of Pd(0) reoxidation step by inserting an electron-transfer mediator (ETM) between the substrate-selective catalyst and O2 or H2O2 as terminal oxidant. This ETM would then carry the electrons from the metal to the oxidant along a low-energy pathway which would compete kinetically with side reactions of the reduced form of the metal (precipitation, decomposition). Actually, the ETM’s (redox cocatalysts) proposed in literature are mainly metal compounds of varying valences. Salts of Cu, Fe, Ag and heteropolyacids like H3PMo12O40 are the most frequently used cocatalysts, which are able to oxidize Pd(0) to Pd(II), allowing to restart the main reaction cycle. In the present work we synthesized directly phenyl isocyanate through the oxidative carbonylation of aniline catalyzed by a Pd(II)-based multistep redox system in which oxygen is used as terminal oxidant
The [PdCl2(Xantphos)] Complex Efficiently Catalyzed the Methoxycarbonylation of Iodobenzene to Methyl Benzoate
No full textThe [PdCl2(Xantphos)] complex, in comparison with several [PdCl2(P–P)] complexes having different diphosphine chelating ligands (P–P), is very active as a catalyst for the carbonylation of iodobenzene to methyl benzoate. The run conditions and the influence of several cocatalysts have been also studied to further improve the catalytic activity. The optimization of the catalytic system allowed to obtain TOFs of ca. 260,000 h−1. The addition of some additives able to reduce the possible catalyst deactivation allowed to increase the TOF of ca. 15%. The best positive results were obtained by adding reducing agents such as ferrocene, which leads to a TOF higher than 300,000 h−1
New Green Polymers for Applications in Cleaning Graffiti Vandalism on Cultural Heritage Stones
No full textThe coupling of carbon dioxide with ethene to produce acrylic acid sodium salt in one pot by using Ni(II) and Pd(II)-phosphine complexes as precatalysts
No full textThe use of CO2 as a feedstock for chemical synthesis is considered as a viable alternative option to some traditional processes. One of the most interesting challenge for the industry is represented by the CO2 coupling with olefins to produce acrylate. Only recently, with the choice of suitable ligands and the use of a sacrificial base, a selective catalytic reaction was established by using Ni(0)-based complexes. The one-pot reaction, which leads to the highest TON (107 mol/mol Ni, in 20 h) reported so far, was successfully developed starting from Ni(0)-based precursors in the presence of disphosphine ligands, a large excess of base and of finely powdered zinc. In the present paper, we carried out the catalytic synthesis of sodium acrylate from CO2 and ethene, in one-pot, by using Ni(II)-chloride and Pd(II)-chloride phosphine-complexes as precatalyst. \ud
The reaction occurs under basic conditions and without adding any external reductants. The Ni(II) complexes lead to higher TON than the respective Pd(II) precursors and the best results are obtained by using diphosphines having high bite angles. Such catalysis is favored by aprotic and polar solvents in which a TON of 290 mol/mol Ni is reached by using the [NiCl2 (dppp)] precursor in DMSO. Furthermore the TON could be increased by increasing the temperature, the base concentration and by using diphosphine ligands having high bite angle
Influence of Electron Transfer Mediators in the Pd(II)-Catalyzed Oxidative Carbonylation of Aniline
No full textCurrently, the most promising alternative to the use of the phosgenation reaction, for large-scale production of isocyanates, ureas, and carbamates, appears to be the Pd-catalyzed oxidative carbonylation of arylamines. During the reaction, the Pd(II) catalytic species are reduced to Pd(0) and the addition of sacrificial oxidizing agents is usually necessary to restart the catalytic cycle. Among these oxidizing agents, molecular oxygen is undoubtedly the more appealing, from an economical and green point of view, but it is not so efficient, whereas several metal salts (named cocatalysts) can be used, able to form redox couples with Pd(0) or to act as electron transfer mediators with oxygen itself. Testing several Pd(II) complexes, metal cocatalysts, and promoters, we have found that the [PdCl2(dppf)]/FeCl3/LiBr = 1/1200/200 (mol/mol) system efficiently catalyzes the carbonylation of aniline to form 1,3–diphenylurea selectively (100%) with a TOF of ca. 1177 h−1. On the other hand, the addition of oxygen to such a system strongly increases the aniline conversion (0.3 MPa of O2 increases the TOF at ca. 3930 h−1), but it moves the selectivity towards the phenyl isocyanate (65%, mol/mol)
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
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