Cerium(III) salts have recently gained increasing attention in the synthetic community, owing to the powerful features that are reviewed in detail in this tutorial. This review reports significant ...examples of cerium(III) promoted synthesis of heterocyclic structures, initially dealing with the synthesis of five- and six-membered ring nitrogen containing heterocycles, then describing the preparation of their oxygenated analogues and finally discussing the achievement of seven-membered rings and mixed heterocyclic motifs.
Microcrystalline Cellulose (MCC) is an isolated, colloidal crystalline portion of cellulose fibers, and it is a valuable alternative to non-renewable fossil-based materials. It is used for a large ...plethora of different fields, such as composites, food applications, pharmaceutical and medical developments, and cosmetic and material industries. The interest of MCC has also been driven by its economic value. In the last decade, particular attention has been driven to the functionalization of its hydroxyl groups to expand the field of applications of such biopolymer. Herein, we report and describe several pre-treatment methods that have been developed to increase the accessibility of MCC by breaking its dense structure allowing further functionalization. This review also collects the results that have appeared in the literature during the last two decades on the utilization of functionalized MCC as adsorbents (dyes, heavy metals, and carbon dioxide), flame retardants, reinforcing agents, energetic materials, such as azide- and azidodeoxy-modified, and nitrate-based cellulose and biomedical applications.
Cover boxes with inspection glass are generally used outdoors for photovoltaic systems. Sometimes these boxes break, during normal use. High temperature, thermal stress, cyclic stress, and cracking ...contribute to weakening the polymeric inspection “glass”. The study presents an interdisciplinary analysis to discover the mode of occurrence and causes of the failure. First, the material is accurately characterized. Then its mechanical behavior is characterized in a virtual scenario that reconstructs the real external environment. The goal is to build a new cover with inspection boxes that exhibits superior life cycle behavior when exposed to harsh weather conditions and atmospheric agents. The breaking phenomena of solar panels covering boxes in PMMA (Poly Methyl Methacrylate) are examined. Environmental stress is the main responsible for cracking. Styrene is employed in the polymerization process of Sheet Molding Compound (SMC); the diffusion of this material is the main responsible for cracking. Comprehensive engineering analysis shows how the thermoplastic component fails after being exposed to atmospheric agents. The PMMA “glass” is one of the polymers most sensible to the crazing phenomena.
SEM micrograph of PMMA composite.
The outbreak of SARS-CoV-2 has drastically changed our everyday life and the life of scientists from all over the world. In the last year, the scientific community has faced this worldwide threat ...using any tool available in order to find an effective response. The recent formulation, production, and ongoing administration of vaccines represent a starting point in the battle against SARS-CoV-2, but they cannot be the only aid available. In this regard, the use of drugs capable to mitigate and fight the virus is a crucial aspect of the pharmacological strategy. Among the plethora of approved drugs, a consistent element is a heterocyclic framework inside its skeleton. Heterocycles have played a pivotal role for decades in the pharmaceutical industry due to their high bioactivity derived from anticancer, antiviral, and anti-inflammatory capabilities. In this context, the development of new performing and sustainable synthetic strategies to obtain heterocyclic molecules has become a key focus of scientists. In this review, we present the recent trends in metal-promoted heterocyclization, and we focus our attention on the construction of heterocycles associated with the skeleton of drugs targeting SARS-CoV-2 coronavirus.
Abstract
In the scientific context, the environmental and healthy impact of polymers is more related to the residual monomer content rather than their macromolecular structure, due to the monomer ...capability to interact with membrane cells. For this a novel method to stabilize and quantify residual monomeric isocyanates in high thermal resistance polyamide resins (PAs) has been developed. This new analytical method resulted in an improvement concerning the quantification of residual aromatic diisocyanates in viscous polymeric matrices by using a simple and cheap technique like HPLC-VWD. Diisocyanate monomers were derivatized with dibutylamine, resulting in stable urea derivatives that were simultaneously analysed and quantified. The method was applied to solvent-based polyamide resins, used as primary electrical insulation, for avoiding additional step of solvent removing before the analysis. The quantification of residual monomers answers to the provisions imposed by European Regulation N. 1907/2006 (REACH) for polymer registration, and the necessity of an early evaluation of the occupational risk associated with the use of diisocyanates, due to their toxicity and high reactivity towards moisture.
A poly(urethane-acrylate) polymer (PUA) was synthesized, and a sufficiently high molecular weight starting from urethane-acrylate oligomer (UAO) was obtained. PUA was then loaded with two types of ...powdered ligno-cellulosic waste, namely from licorice root and palm leaf, in amounts of 1, 5 and 10%, and the obtained composites were chemically and mechanically characterized. FTIR analysis of final PUA synthesized used for the composite production confirmed the new bonds formed during the polymerization process. The degradation temperatures of the two types of waste used were in line with what observed in most common natural fibers with an onset at 270 °C for licorice waste, and at 290 °C for palm leaf one. The former was more abundant in cellulose (44% vs. 12% lignin), whilst the latter was richer in lignin (30% vs. 26% cellulose). In the composites, only a limited reduction of degradation temperature was observed for palm leaf waste addition and some dispersion issues are observed for licorice root, leading to fluctuating results. Tensile performance of the composites indicates some reduction with respect to the pure polymer in terms of tensile strength, though stabilizing between data with 5 and 10% filler. In contrast, Shore A hardness of both composites slightly increases with higher filler content, while in stiffness-driven applications licorice-based composites showed potential due to an increase up to 50% compared to neat PUA. In general terms, the fracture surfaces tend to become rougher with filler introduction, which indicates the need for optimizing interfacial adhesion.
The benzimidazole core is a common moiety in a large number of natural products and pharmacologically active small molecules. The synthesis of novel benzimidazole derivatives remains a main focus in ...medicinal research. In continuation of the efforts towards Ce(III) catalysts for organic transformations, we observed for the first time the activity of the iodide ion and copper cation in activating CeCl3·7H2O in the selective formation of prototypical 2-substituted benzimidazoles. The one-pot CeCl3·7H2O-CuI catalytic system procedure includes the cyclo-dehydrogenation of aniline Schiff's bases, generated in situ from the condensation of 1,2-phenylenediamine and aldehydes, followed by the oxidation with iodine, which works as a hydrogen sponge. Mild reaction conditions, good to excellent yields, and clean reactions make the procedure a useful contribution to the synthesis of biologically active fused heterocycles containing benzimidazoquinazolines.
A catalyst-free heterocyclization reaction of α-chloroglycinates with thiobenzamides or thioureas leading to 2,4-disubstituted-5-acylamino-1,3-thiazoles has been developed. The methodology provides ...straightforward access to valuable building blocks for pharmaceutically relevant compounds.
The effect of four lignocellulosic waste fillers on the thermal and mechanical properties of biocomposites was investigated. Powdered licorice root, palm leaf, holm oak and willow fillers were melt ...compounded with polypropylene at two different weight contents, i.e., 10 and 30, and then injection molded. A commercially available maleated coupling agent was used to improve the filler/matrix interfacial adhesion at 5 wt.%. Composites were subjected to chemical (FTIR-ATR), thermal (TGA, DSC, DMA) and mechanical (tensile, bending and Charpy impact) analyses coupled with a morphological investigation by scanning electron microscopy. Although similarities among the different formulations were noted, holm oak fillers provided the best combination of thermal and mechanical performance. In particular, at 30 wt.% content with coupling agent, this composite formulation displayed remarkable increases in tensile strength and modulus, flexural strength and modulus, of 28% and 110%, 58% and 111%, compared to neat PP, respectively. The results imply that all these lignocellulosic waste fillers can be used successfully as raw materials for biocomposites, with properties comparable to those featured by other natural fillers.
Functionalized polysubstituted oxazoles are an important class of five‐membered N,O‐heterocycles that occur widely in the structure of natural products and fine chemicals. They are also often used as ...building blocks in the synthesis ofheterocyclic molecules with more complex structures. Therefore, efficient synthetic protocols based on Lewis acid promoted reactions are desirable. In this context, we report that, under microwave irradiation, the CeCl3·7H2O/NaI/I2 system is capable of promoting a 5‐exo‐dig cyclization of propargyl amides with good functional group tolerance. The microwave reactor also provides a more convenient and safer method for heating the reaction. This methodology represents a straightforward CeCl3·7H2O/NaI/I2 promoted cyclization using microwave irradiation to accomplish the synthesis of polysubstituted oxazole derivatives.
After a wide‐ranging scientific investigation on the use of cerium(III) salts as promoters for useful organic transformations, we describe here a new, microwave‐assisted reaction involving the combinationof CeCl3·7H2O/NaI/I2 for the construction of N,O‐heterocycles. The study concerns the preparation of highly substituted oxazoles starting from N‐propargyl carboxamides.
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