Microwave-Assisted Synthesis of Disulfides

Abstract

A new microwave-assisted synthesis methodology for the preparation of substituted disulfide derivatives is presented. 4-Substituted sulfenimides were reacted with 4-substituted thiols under neat (to right doughy consistency) conditions in chloroform, with both microwave heating and conventional methods. The resulting 4-substituted disulfide derivatives were obtained at higher yields and in shorter reaction times with microwave heating. Their chemistry was confirmed by ¹H-NMR, ¹³C-NMR, infrared (IR), and elemental analysis.

GRAPHICAL ABSTRACT     

微波对碱式碳酸镁结晶过程的影响

在微波外场作用下,利用氯化镁和碳酸钠溶液反应结晶法直接合成碱式碳酸镁晶体。通过对比微波、水浴两种加热方式下镁离子变化曲线和产物的差异,XRD、FTIR,SEM等对相转移过程的物相分析表征,探索微波对反应的强化影响。结果表明,反应结晶直接合成碱式碳酸镁过程分为絮状物→出现晶体→完全转变为球状碱式碳酸镁3个阶段。微波对反应3个阶段中都有强化作用,促进絮状物的形成,加快相转变,提高反应转化率,微波加热条件下在粒径分布与组装方式与水浴加热方式均有不同,微波作用下较小颗粒是由纳米片层平行组装而成,而较大颗粒可能是无定形物在球状小颗粒表面继续转变,形成交错的表层纹理的大颗粒碱式碳酸镁。     

One-pot synthesis of N-substituted pantolactams from pantolactone

Rac-N-substituted pantolactams (5) are readily obtained in medium to good yields by reaction of rac-pantolactone (1) with primary amines under acid catalysis, whether at 250°C in a pressure reactor or under microwave irradiation. It appears that the amine can react with pantolactone at the carbonyl carbon atom to give a hydroxyamide (3) in a reversible way and at the methylene carbon atom to give a γ-amino acid (4). The last one on dehydration would give the corresponding pantolactam (5).     

A kinetic study of methane conversion by a dinitrogen microwave plasma

Conversion of CH₄ with a N₂ microwave plasma (2.45 GHz) is studied. The experiments cover the absorbed microwave power range 300–700 W with 17–62% of methane in the gas mixture, with pressures of 10–40 mbar and flow rates of 140–650 ml· min^–1. The yields of C₂ hydrocarbons and dihydrogen are analyzed by gas chromatography. The distance of methane addition downstream of the plasma plays an important role on the composition and the concentration of the products obtained. This distance mainly determines the energy concentrated in the active species of the plasma when they react with methane. Different behaviors for acetylene formation, on the one hand, and for ethane and ethene formation, on the other hand, have been observed, and this finding allows us to propose a kinetic mechanism for the decay of methane and for the formation of C₂ hydrocarbons.     

微波-超声复合场辅助水介质砜类化合物合成

发展了一种微波-超声复合场下绿色高效合成砜类化合物的简便方法。 以芳甲基氯和苯亚磺酸钠为原料,以水为反应介质,在微波-超声复合场辅助下合成了一系列芳甲基苯基砜。 通过考察微波功率、超声功率、原料投料比、溶剂体积和反应时间等因素的影响,得出了苄基氯与苯亚磺酸钠之间模型反应的最优反应条件:微波功率为40 W,超声功率为50 W,苄基氯与苯亚磺酸钠的摩尔配比为1:3,反应时间为5 min。 在此条件下合成的苄基苯基砜产率为83%。 相比常规油浴条件,在微波-超声复合场的强化下反应速率提升了约42倍。 该方法具有较好的底物适应性,成功合成了23种砜类化合物。     

High-pressure microwave dissolution of ceramics prior to trace metal determinations by microwave induced plasma atomic emission spectrometry

A commercial laboratory microwave acid digestion system was evaluated for the acid dissolution of ceramic powders (Al₂O₃, AlN, BN and Si₃N₄) prior to the determination of their trace element content by microwave induced plasma atomic emission spectrometry. Newly designed vessels, capable of withstanding internal pressures of over 110 bar, provide rapid and satisfactory results for sample dissolution. Sample preparation time was approximately 30 min (including the subsequent cooling time and preparation of the final solution). Results from conventional stainless-steel acid digestion vessel (Teflon bomb) dissolution are compared with the microwave bomb results of microwave plasma atomic emission spectrometry.     

Microwave-assisted saccharide coupling with n-pentenyl glycosyl donors

n-Pentenyl glycosides, armed and disarmed, and n-pentenyl orthoesters couple with acceptors, hindered and unhindered, within 25 min under microwave activation. The reaction takes place in acetonitrile under neutral conditions with N-iodosuccinimide as promotor, which are therefore ideal for use with reactants bearing acid-labile protecting groups.     

Microwave-Enhanced Hydrogenation of Carbon–Carbon Double Bonds in Single-Stranded Polymers by p-Tosylhydrazide

A rapid and efficient method for the hydrogenation of the backbones of various single-stranded polymers with p-tosylhydrazide is developed using microwave irradiation, through which the corresponding saturated and more flexible polymers are obtained in good to excellent yields.     

Microwave spectrum, centrifugal distortion, dipole moment and conformation of 2-methyl-1,3-dioxane

Microwave spectrum of 2-methyl-1,3-dioxane has been investigated in the frequency range 8–40 GHz. Rotational a-type and c-type transitions with J≤40 have been identified. Rotational constants A = 4658.122(2) MHz, B = 2503.221(1) MHz, C = 1783.950(1) MHz and centrifugal distortion constants for the ground vibrational state have been found. Dipole moment components μ_a = 1.43 ± 0.01 D, μ_c = 1.15±0.01 D and overall dipole moment μ = 1.84±0.02 D have been determined. The data obtained are in accord with the chair conformation of the molecule having equatorial arrangement of the methyl group. Original Russian Text Copyright ? 2006 by A. Kh. Mamleev, R. V. Galeev, L. N. Gunderova, M. G. Faizullin, and A. A. Shapkin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No.2, pp. 373–375, March–April, 2006.     

Measurement of electron densities by a microwave cavity method in 13.56-MHz RF plasmas of Ar,CF4, C2F6, and CHF3

Electron densit ies have been determined /or RF plasmas that were generated within a microwave resonant cavity by measuring the difference of the resonance frequencies with and without plasma. Since that method only yields a value of the electron density weighted ouer the microwave electric field distribution, to obtain real values an assumption on the spatial distribution of the electron density had to he made. Spatial profiles were taken of the emission of a 4s–5p Ar line at 419.8 not (with a small Ar admixture). The electron densities have been determined as a function of pressure and RF power in Ar, CF₄, C₂ F₆ and CHF, plasmas. The results indicate that the electron density for the last three gases decreases as a function of pressure above 50 m Torr. Typical values for the electron density for the investigated parameter range are 1–6 · 10³ cm^–3. Furthermore, the electron density is the lowest in gases with a high attachment cross .section.     

Microwave‐assisted Chemical Reactions

Microwave (MW) radiation has been used in chemical analysis and chemical synthesis. MW heating under controlled conditions offers distinct advantages over conventional heating. The reactions are carried out in environmentally clean and safe solvents and in many cases, reactions can be carried out under solvent‐free conditions. This method of synthesis has grown rapidly and found its use in various sectors. This paper reviews some of the reactions that have been accelerated with higher yields under MW irradiation. The application of MW‐assisted synthesis in the medicinal and pharmaceutical industries will be emphasized.     

Recent Progress in Iron-Based Microwave Absorbing Composites: A Review and Prospective

With the rapid development of communication technology in civil and military fields, the problem of electromagnetic radiation pollution caused by the electromagnetic wave becomes particularly prominent and brings great harm. It is urgent to explore efficient electromagnetic wave absorption materials to solve the problem of electromagnetic radiation pollution. Therefore, various absorbing materials have developed rapidly. Among them, iron (Fe) magnetic absorbent particle material with superior magnetic properties, high Snoek’s cut-off frequency, saturation magnetization and Curie temperature, which shows excellent electromagnetic wave loss ability, are kinds of promising absorbing material. However, ferromagnetic particles have the disadvantages of poor impedance matching, easy oxidation, high density, and strong skin effect. In general, the two strategies of morphological structure design and multi-component material composite are utilized to improve the microwave absorption performance of Fe-based magnetic absorbent. Therefore, Fe-based microwave absorbing materials have been widely studied in microwave absorption. In this review, through the summary of the reports on Fe-based electromagnetic absorbing materials in recent years, the research progress of Fe-based absorbing materials is reviewed, and the preparation methods, absorbing properties and absorbing mechanisms of iron-based absorbing materials are discussed in detail from the aspects of different morphologies of Fe and Fe-based composite absorbers. Meanwhile, the future development direction of Fe-based absorbing materials is also prospected, providing a reference for the research and development of efficient electromagnetic wave absorbing materials with strong absorption performance, frequency bandwidth, light weight and thin thickness.     

Plasma polymerization anda-C:H film ablation in microwave discharges in methane diluted with argon and hydrogen

Neutral hydrocarbons are observed from a microwave discharge in a fast flow of (A) 0.5–6% methane in argon, (B) 0.5–6% methane in hydrogen, and (C) hydrogen over a previously depositeda-C:H film. System (A) produces polyacetylenic and other hydrocarbons through C₈ by predominantly gas-phase reactions and deposits ana-C: H film. Reactions under conditions (B) and (C) produce hydrocarbon radicals and molecules with masses through 300 that in case (B) arise from both gas-phase reactions and film ablation, and in case (C) from film ablation alone. Proposals are made for the mechanisms of gas-phase polymerization, film deposition, and ablation. Hydrocarbon ions observed downstream from these discharges appear to arise from ionization of neutral species with a distribution determined by subsequent ion-molecule reactions and selective diffusion losses.Work supported by NSF Grant CHE-87-21744.     

Synthesis of novel amphiphilic pyridinylboronic acids

Novel 3‐alkoxy‐2‐pyridinylboronic acids bearing, in their 3‐position, linear alkoxy or perfluoroalkoxy chains with n carbon atoms (n = 6, 8, 10, 12 and 18) 2a – 2g are synthesized from 2‐bromo‐3‐pyridinol, which is the common starting product. Our alternative procedure for the synthesis of 3‐alkoxy‐2‐bromopyridine in a phase‐transfer catalysis system is to carry out the reaction in a solid–liquid medium in the presence of a quaternary ammonium salt under microwave irradiation. General and versatile synthetic methods have been developed for preparation of a large variety of new 2‐pyridinylboronic acids bearing two alkylated or perfluoroalkylated side chains with an ether junction in the 3‐position. Copyright © 2003 John Wiley & Sons, Ltd.     

微波有机合成反应的新进展

综述了近来微波辐射技术在有机合成应用中的新进展。着重介绍了微波有机合 成反应技术及其在重要有机合成反应中的应用。     

A simple non-invasive optical pyrometric method for plotting temperature—Time profiles of high temperature reactions in microwave ovens

A simple optical pyrometric method is described, based on a photocell with red and blue filters calibrated by the disappearing filament technique. The method, which is cheap, non-invasive and reproducible, is used for measurement of the rate of heating of solid materials such as coke, CuO or Fe₃O₄ in a microwave oven. All materials were heated under dinitrogen in a silica reaction vessel over 3 min in a 650 W oven. Coke (which contains graphitic phases) and magnetite heat smoothly to maximum temperatures of 1180 and 1050°C respectively. CuO heats erratically with plasma discharges from the surface, however when covered with a layer of coke the oxide heats smoothly achieving a maximum temperature of 1210°C. The observations are discussed.     

S2-控制剂对Ag纳米产物的形貌及光学性能的影响

采用改装的微波冷凝回流装置,以乙二醇作为还原剂和溶剂,在表面活性剂聚乙烯吡咯烷酮的保护下,添加Na2S与AgNO3反应生成Ag2S,对Ag2S进行热分解即可获得Ag纳米产物。保持其它参数(加热功率、加热时间、表面活性剂浓度和反应物溶液浓度等)不变的条件下,通过改变Na2S的浓度得到不同形貌的Ag纳米产物。利用扫描电子显微镜、X射线衍射仪和紫外-可见分析仪对所得Ag纳米产物的形貌、物相和光学性能进行分析表征,结果表明,在微波冷凝回流作用下,Na2S浓度的逐渐增大使银纳米产物经历了一个类球形-立方体-线形的形貌演变。此外,通过分析反应过程,对S2-如何影响Ag纳米产物的形貌及Ag纳米线的生长机理作了进一步研究探讨。     

Synthesis of nanosized silver colloids by microwave dielectric heating

Silver nanosized crystallites have been synthesized in aqueous and polyols viz., ethylene glycol and glycerol, using a microwave technique. Dispersions of colloidal silver have been prepared by the reduction of silver nitrate both in the presence and absence of stabilizer poly(vinylpyrolidone) (PVP). It was observed that PVP is capable of complexing and stabilizing Ag nanoparticles formed through the reduction of Ag⁺ ions in water and ethylene glycol. In the case of ethylene glycol, it has been shown that the use of PVP leads to particles with a high degree of stability. The colloids are stable in glycerol for months even in the absence of stabilizer.     

Rapid Microwave‐Promoted Synthesis of Polyurethanes from a Fluorene Unit‐Containing Diol and Diisocyanates

A fluorene diol derivative, 9,9‐bis[4‐(2‐hydroxyethoxy)phenyl]fluorene ( 1 ), reacted with diisocyanates such as 1,3‐bis(isocyanatomethyl)cyclohexane ( 2a ), 1,6‐diisocyanatohexane ( 2b ), and 1,3‐bis(isocyanatomethyl)benzene ( 2c ) under temperature‐controlled microwave irradiation to form the corresponding polyurethanes with being 30 000 to 60 000, measured by GPC with reference to polystyrene standards within 5 to 10 min at 160 to 200 °C. In the reactions of 2a and b , the molecular weights were 15 to 20 times higher than those obtained by conventional oil bath heating. For a solvent of the microwave‐promoted reaction, a hydrocarbon compound, decalin, is preferably used to undergo the polymerization cleanly without unfavorable coloration and/or gelation.

     

Direct Arylation of Adenine by Fluoro- and Chloronitrobenzenes: Effect of Microwaves

Direct arylation of adenine with fluoro- and chloronitrobenzenes leads to mixtures of N9 and N7 substituted adenines. After separation by column chromatography, the individual isomers can be efficiently hydrogenated on Pd to give the corresponding aminophenyladenines. A significant enhancement of the reaction rate by microwave irradiation was observed. This two-step procedure was found to be a feasible route to otherwise hardly available 7-aminophenyladenines. Correlation between calculated shielding constants and experimental values of chemical shifts in ¹³C and ¹⁵N NMR was used for assignment of the site of substitution.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]