硅系阻燃剂研究进展

从添加型硅系阻燃剂、含硅本质阻燃高聚物、聚合物／层状硅酸盐纳米复合阻燃材料等方面，阐述了硅系阻燃剂近几年的发展情况；介绍了有机硅系阻燃剂、无机硅系阻燃剂；评述了硅系阻燃剂具有高效、低毒、抑烟和促进成炭等优点；综述了含硅基团共聚物、含硅接枝共聚物及聚合物／层状硅酸盐纳米复合材料的结构和阻燃性能。     

Metal-catalyzed cross-coupling reactions with supported nanoparticles: Recent developments and future directions

The metal-catalyzed processes are ubiquitous in the modern organic synthesis toolbox. However, a continuous challenge has been related to the design of reactions from a sustainable viewpoint (e.g., easy recovery of the catalyst, ability to perform sequential steps in high yields, avoidance of high amounts of organic solvents). Supported nanocatalysts have prompted special interest because of the synergy involving eletronic and surface effects which can play key roles towards more sustainable processes. In this article, we comprehensively summarize the latest progress in cross-coupling reactions involving supported metal nanoparticles. A background to mechanisms and industrial application will also be presented.     

Optimal Sequential Tests for Two Simple Hypotheses

Abstract

A general problem of testing two simple hypotheses about the distribution of a discrete-time stochastic process is considered. The main goal is to minimize an average sample number over all sequential tests whose error probabilities do not exceed some prescribed levels. As a criterion of minimization, the average sample number under a third hypothesis is used (modified Kiefer–Weiss problem). For a class of sequential testing problems, the structure of optimal sequential tests is characterized. An application to the Kiefer–Weiss problem for discrete-time stochastic processes is proposed. As another application, the structure of Bayes sequential tests for two composite hypotheses, with a fixed cost per observation, is given. The results are also applied for finding optimal sequential tests for discrete-time Markov processes. In a particular case of testing two simple hypotheses about a location parameter of an autoregressive process of order 1, it is shown that the sequential probability ratio test has the Wald–Wolfowitz optimality property.     

The aza-Michael reaction as an alternative strategy to generate advanced silicon-based (macro)molecules and materials

Aza-Michael reaction is a simple and accessible addition reaction performed at moderate temperature, possibly without a catalyst and without releasing by-products. Its versatility allows designing specific structures thanks to the availability of a multitude of Michael acceptors and Michael donors. The reaction rate of the aza-Michael reaction can be improved by adding different co-reactants (polar protic solvents, catalysts) and/or adjusting the external energy sources (e.g. moderate to high temperatures or high pressures). Here, we show that this addition reaction is efficient for modifying or curing silicon-containing molecules, oligomers and polymers. The pros and cons of applying the aza-Michael reaction to silicon-containing molecules (including alkoxysilanes and PDMS) are highlighted. A large variety of intermediates such as coupling agents, reactive diluents, and sol-gel precursors prepared by the aza-Michael reaction are presented. Finally, applications of these, including products ranging from functional silicone intermediates to soft (unfilled) elastomers, are reported.     

Synthesis,characterization, thermal and flame-retardant properties of silicon-based epoxy resins

A new silicon-containing oxirane triglycidyl phenyl silane oxide (TGPSO) and its corresponding silicon-containing epoxy resins are synthesized and characterized. The activation energies of TGPSO curing reaction with various curing agents, including 4,4-diaminodiphenylmethane, 4,4-diaminodiphenylsulfone, and dicyanodiaminde, are found to be 180, 196.5, and 154 kJ/mol. The curing reaction of TGPSO with diamines is determined to be a first-order reaction through means of Arrhenius plots. The introduction of the silicon-containing group results in higher curing reactivity. This silicon-containing resin possesses higher char yield as well as higher limiting oxygen index (LOI = 35) than the commercial epoxy resins, confirming the usefulness of these silicon-containing epoxy resins as flame retardants. Char yields and LOI measurements demonstrate that incorporating silicon into epoxy resins is able to improve their flame retardancy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1231–1238, 1999     

Palladium-catalyzed Suzuki-Miyaura cross-coupling reactions employing dialkylbiaryl phosphine ligands

The cores of many types of polymers, ligands, natural products, and pharmaceuticals contain biaryl or substituted aromatic structures, and efficient methods of synthesizing these structures are crucial to the work of a broad spectrum of organic chemists. Recently, Pd-catalyzed carbon-carbon bond-forming processes, particularly the Suzuki-Miyaura cross-coupling reaction (SMC), have risen in popularity for this purpose. The SMC has many advantages over other methods for constructing these moieties, including mild conditions, high tolerance toward functional groups, the commercial availability and stability of its reagents, and the ease of handling and separating byproducts from its reaction mixtures. Until 1998, most catalysts for the SMC employed triarylphosphine ligands. More recently, new bulky and electron-rich phosphine ligands, which can dramatically improve the efficiency and selectivity of such cross-coupling reactions, have been introduced. In the course of our studies on carbon-nitrogen bond-forming reactions, we found that the use of electron-rich and bulky phosphines enhanced the rate of both the oxidative addition and reductive elimination processes; this was the beginning of our development of a new family of ligands, the dialkylbiarylphosphines L1-L12. These ligands can be used for a wide variety of palladium-catalyzed carbon-carbon, carbon-nitrogen, and carbon-oxygen bond-forming processes as well as serving as supporting ligands for a number of other reactions. The enhanced reactivity of these catalysts has expanded the scope of cross-coupling partners that can be employed in the SMC. With use of such dialkylbiarylphosphine ligands, the coupling of unactivated aryl chlorides, aryl tosylates, heteroaryl systems, and very hindered substrate combinations have become routine. The utility of these ligands has been successfully demonstrated in a wide number of synthetic applications, including industrially relevant processes. In this Account, we provide an overview of the use and impact of dialkylbiarylphosphine ligands in the SMC. We discuss our studies on the mechanistic framework of the reaction, which have allowed us to rationally modify the ligand structures in order to tune their properties. We also describe selected applications in the synthesis of natural products and new materials to illustrate the utility of these dialkylbiarylphosphine ligands in various "real-world" synthetic applications.     

Diaryl sulfides synthesis: copper catalysts in C–S bond formation

ABSTRACT

Diaryl sulfides play an important role in the synthesis of natural products, pharmaceutically and biologically molecules. The metal catalysts are powerful tools for C–S bonds formation. Despite the utility of palladium-catalyzed carbon–sulfur bond formation, copper complexes are fascinating catalysts for this transformation because copper is less toxic and inexpensive than palladium. In recent times, a large number of protocols using various copper catalysts to perform cross-coupling reactions leading to the synthesis of diaryl sulfides have been described. In this review, we summarized recent developments in the area of synthesis of diaryl sulfides based on using copper catalysts. Both the considerable advantages and drawbacks of these protocols are discussed.     

Prozesse der Reaktivdestillation

Reactive Distillation Processes Reactive distillation, i.e. the simultaneous implementation of reaction and distillation in a counter–current column, is a promising alternative to the conventional sequential processes. In a preceding paper the effective phase equilibrium of a reactive distillation was studied with a special focus on the determination of so–called reactive azeotropes. In this contribution, a knowledge of these thermodynamic fundamentals is applied to the conceptual design of reactive distillation processes. Furthermore, some process examples of technically important processes are presented.     

Using extraction and sorption processes to obtain nanosized powders of calcium silicates and functional materials on their basis

The review presents summary data on extracting agents and the application of sorption processes during the cycle of studies on the joint processing of calcium and silicon-containing raw materials on the production of calcium silicates and composite materials on their basis. It is found that, in processes of the production of synthetic calcium silicates from various types of calcium and silicon-containing raw materials, ionic and nonionic surfactants, including extractants, serve as structuring additives that hinder crystal growth and impede their agglomeration. The sorption properties of amorphous and crystalline nanopowders of calcium silicates and hydrosilicates synthesized from water-soluble materials are studied with respect to cations of base and rare metals. It has been found that the studied samples have high sorption capacity for cations of Eu3+, Pr³⁺, Tb³⁺, Er³⁺ and may be used as the basis for producing functional composite materials. The efficiency of applying the extraction-pyrolytic method has been shown to provide homogeneity and predetermined composition of the desired products, for the production of ceramic pigments and luminescent materials based on calcium silicates.     

锂离子电池硅基复合负极制备方法

硅（Si）被视为取代现有商业化石墨负极极具潜力的材料之一,然而硅基材料在充放电过程中巨大的体积变化严重影响电池的电化学性能和使用寿命,因此如何有效克服体积效应以提高其电化学性能成为亟待解决的问题。本文围绕硅基复合负极制备过程,从物理方法、化学方法、多种方法结合三个方面综述了目前在硅基负极改性方面的最新进展,重点对不同的制备方法及过程进行了简介、分类、比较和分析,总结了其优缺点,指出多种方法结合制备硅基复合负极最具优势。最后对未来高性能硅基复合负极的研究和开发进行了展望,以期为硅基负极性能优化及探索新型制备方法提供借鉴。     

Preparation and Characterization of Novel Polyimide/SiO2 Nano-hybrid Films by In Situ Polymerization

A silicon-based aromatic polyimide (PI) containing pendent aryl rings was synthesized by solution polycondensation of a silicon-containing diamine with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride. Its nano-hybrids with different colloidal SiO₂ concentrations were synthesized by in situ polymerization. The reactions were carried out in presence of 3-aminopropyltriethoxysilane as a coupling agent. The inclusion of the coupling agent in the polymer chain and its co-condensation with SiO₂ nanoparticles afforded a silica network that was interconnected chemically with the PI matrix. The chemical structure of the hybrid materials was analyzed by Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy. The morphology of the hybrid films and the surface roughness were characterized by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The results indicated that nanometer-scale inorganic particles were homogeneously dispersed throughout the PI matrix with 50–70 nm size range. The best results and favorable miscibility between polymer and silica phases in the nano-hybrids were obtained when up to 40 wt% nanoparticles were introduced into the backbone of PI matrix.     

Use of Fluorine-Containing Compounds for Modification of Polycaproamide

The possibility of increasing the fireproof characteristics of fluorine-containing PCA by additional incorporation of phosphorus- and phosphorus—silicon-containing flame retardants was investigated. Samples of modified PCA with an oxygen index of 28-29% were obtained with these flame retardants. It was found that polyfluorinated alcohol—T-2 fireproofing compound and polyfluorinated alcohol—microencapsulated T-2 fireproofing compound systems alter the direction of the processes that take place in the basic stage of thermal decomposition of the polymer by decreasing the amount and rate of liberation of volatile products and alter the composition of the carbonized residue.     

Gold Catalysis and Fluorine

Performing gold-catalyzed organic transformations in the presence of fluorinating reagents can lead to both fluorinated and non-fluorinated products. Gold(I) complexes can activate alkynes towards nucleophilic attack by fluoride leading to fluoroalkenes under mild conditions. Fluorinated products can also be prepared upon performing gold-catalyzed transformations in the presence of electrophilic sources of fluorine. In most cases, however, the combination of gold and electrophilic fluorinating reagents does not lead to fluorination but delivers products of oxidative homo- or cross-coupling. In these processes the “F⁺” source is likely acting as a sacrificial two-electron external oxidant performing the key oxidation of gold(I) to gold(III) in the redox cycle. Oxidative coupling is an emerging field of gold catalysis which, when combined with the well-established reactivity of gold as a soft π-acid, holds promise as a mild and efficient method for the construction of complex organic molecules.     

The Development of Alkoxide-Directed Metallacycle-Mediated Annulative Cross-Coupling Chemistry

Alkoxide-directed metallacycle-mediated cross-coupling is a rapidly growing area of reaction methodology in organic chemistry. Over the last decade, developments have resulted in more than thirty new and highly selective intermolecular (or “convergent”) C−C bond-forming reactions that have established powerful retrosynthetic relationships in stereoselective synthesis. While early studies were focused on developing transformations that forge a single C−C bond by way of a functionalized and unsaturated metallacyclopentane intermediate, recent advances mark the ability to employ this organometallic intermediate in additional stereoselective transformations. Among these more advanced coupling processes, those that embrace the metallacycle in subsequent [4+2] chemistry have resulted in the realization of a number of highly selective annulative cross-coupling reactions that deliver densely functionalized and angularly substituted carbocycles. This review discusses the early development of this chemistry, recent advances in reaction methodology, and shares a glimpse of the power of these processes in natural product synthesis.     

High-turnover aminopyridine-based Pd-catalysts for Suzuki–Miyaura reaction in aqueous media

A high-turnover catalytic system based on commercially available aminopyridines (L) and PdCl₂ has been developed for Suzuki–Miyaura reaction in aqueous media. Reactions of arylboronic acids with a wide range of aryl iodides, bromides and chlorides proceeded in the presence of these catalysts for a short time in aqueous media to afford the cross-coupling products in high yields. Furthermore, this protocol allows tolerating a wide range of functional groups.     

Possibilities of monitoring the polymerization process of silicon-based water repellents and consolidants in stones through infrared and Raman spectroscopy

The increasing use of Raman and infrared (IR) portable instruments for in situ diagnosis and characterization of materials and their conservation state in artworks, has led us to investigate in the laboratory the real possibilities that both vibrational spectroscopies could have for monitoring in situ and in real time the polymerization process of silicon-based water repellents and consolidants in stones, after application of the corresponding treatments. Initially, we took IR and Raman spectra of the selected conservation products deposited on inert surfaces along several weeks, in order to determine the spectral regions more sensitive to changes as polymerization proceeded. Afterwards, we tried to apply the same protocol to model stone specimens (Bateig stone widely used in the Spanish Architectural Heritage) impregnated with the conservation products. The stone was characterized, and weight recording, colour variation and SEM observations were carried out once a week during 6 weeks in order to complement the protocol. As far as silicon-based conservation treatments applied to calcite containing stones refer (as the Bateig one here employed), we do not foresee possibilities for in situ infrared reflectance spectroscopic monitoring of the corresponding polymerization processes. In the case of the Raman technique, stone fluorescence represented an additional problem. If it can be overcome, Raman data could provide some clues for assessing the polymerization state, especially for the consolidant case.     

Polymerase Synthesis of DNA Containing Iodinated Pyrimidine or 7-Deazapurine Nucleobases and Their Post-synthetic Modifications through the Suzuki-Miyaura Cross-Coupling Reactions

All four iodinated 2′-deoxyribonucleoside triphosphates (dNTPs) derived from 5-iodouracil, 5-iodocytosine, 7-iodo-7-deazaadenine and 7-iodo-7-deazaguanine were prepared and studied as substrates for KOD XL DNA polymerase. All of the nucleotides were readily incorporated by primer extension and by PCR amplification to form DNA containing iodinated nucleobases. Systematic study of the Suzuki-Miyaura cross-coupling reactions with two bulkier arylboronic acids revealed that the 5-iodopyrimidines were more reactive and gave cross-coupling products both in the terminal or internal position in single-stranded oligonucleotides (ssONs) and in the terminal position of double-stranded DNA (dsDNA), whereas the 7-iodo-7-deazapurines were less reactive and gave cross-coupling products only in the terminal position. None of the four iodinated bases reacted in an internal position of dsDNA. These findings are useful for the use of the iodinated nucleobases for post-synthetic modification of DNA with functional groups for various applications.     

The Slow-Release Strategy in Suzuki–Miyaura Coupling

Despite great advances in metal-catalyzed cross-coupling reactions, their efficacy is often compromised by side reactions, reducing the yield, or requiring a large excess of one component. Suzuki–Miyaura cross-coupling is no exception, as the boronic acid functionality can be susceptible to a range of undesired processes. A number of methods have been developed to mitigate these side reactions, and herein we focus on the “slow-release” strategy. These conditions involve deployment of a “masking” reagent that protects the vulnerable boronic acid functionality from degradation, particularly protodeboronation, whilst simultaneously facilitating controlled liberation of the active reagent into the catalytic milieu. Under suitably tailored conditions, this dual-action approach ensures that the concentration of the free boronic acid is minimized, thus attenuating its degradation but still facilitating transmetallation of the organoboron species with the key organopalladium intermediate.     

S-arylation of 2-mercaptobenzazoles: a comprehensive review

In recent years 2-arylthio-benzazoles (benzothiazoles, benzoxazoles, and benzimidazoles) have attracted more and more attention due to their diverse biological and pharmacological properties. Consequently, great efforts have been devoted to exploiting efficient strategies towards the synthesis of titled compounds. Among the different methods reported for the synthesis of 2-arylthio-benzazoles, the most general and applicable one consists of the C–S cross-coupling of corresponding 2-mercaptobenzazoles with various electrophilic coupling partners. This protocol has advantages of the easily accessible starting materials, satisfactory yield of products, broad substrate scope, and high generality which makes it a useful and attractive method for the construction of various 2-arylthio-benzazoles. In this review, we highlight the significant advances achieved in this field from 1987 to 2017, with special emphasis on the mechanistic aspects of the reactions.