Online Determination of Colloidal Properties of Tannin Solutions under Microwave Irradiation using a Modified Zetasizer

A rapid and exact method for the determination of the colloidal properties of tannin solutions following microwave irradiation was developed and validated using a modified zetasizer. The accuracy and feasibility online detection compared with the conventional method were characterized by the particle size and zeta potential of the tannin solutions treated with microwave irradiation using the optimized conditions, including the tannin concentration, microwave radiation time, and temperature. The results showed that the values determined by the online method presented a linear relationship at a tannin concentration of 4?g/L, microwave times of 30–90?min, and temperatures from 25 to 40?°C. These values were essentially unchanged using conventional detection. In addition, the online method is feasible for both hydrolyzable and condensed tannins. Ten parallel measurements had relatively small standard deviations, showing that the precision was within acceptable limits. Therefore, the online method is appropriate for the characterization of tannin colloidal properties treated with microwave radiation which may have practical applications.     

Silica nanoparticles obtained by microwave assisted sol–gel process: multivariate analysis of the size and conversion dependence

Silica nanoparticles were synthesized by the sol–gel method in alcoholic solution under microwave irradiation in the presence of an ammonium catalyst. The effect of the reaction time, the reaction temperature, water and ammonium concentrations on particle size and conversion (measured by light scattering and FTIR respectively) were analyzed using multivariate analysis. The results showed that water and ammonium concentrations are the main factors that control the particle size and the conversion. Both properties increase with water and ammonium concentration. Moreover, comparing with the results obtained using traditional heating, the microwave heating gave rise to higher reaction rate and narrower dispersion of the particle size.     

Microwave-Promoted Facile and Rapid Synthesis Procedure for the Efficient Synthesis of 5,5-Disubstituted Hydantoins

A fast, general, environmentally friendly, and facile method for preparation of 5, 5-disubstituted hydantoins from the reaction between ketone (or aldehyde) derivatives with KCN and ammonium carbonate under microwave irradiation is presented. The microwaves remarkably accelerated this reaction, the reaction times decreased dramatically, the reaction conditions were milder, and the yields were also greater. Also a comparative study of microwave versus classical conditions has been done. All the products were characterized by infrared, NMR, and CHN analysis, and their melting points are identical to those of the known compounds reported in the literature. This method might be useful in the future for the preparation of similar derivatives.

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

Microwave-assisted aqueous synthesis: a rapid approach to prepare highly luminescent ZnSe(S) alloyed quantum dots

In this paper, we present a new procedure for the rapid synthesis of luminescent ZnSe nanocrystals in aqueous phase by microwave irradiation with controllable temperature. The effects of microwave irradiation and experimental conditions on the synthesis of nanocrystals were investigated systematically. It was found that there were significant effects of pH value of reaction solutions, molar ratio of precursors, and heating time of microwave irradiation on the optical properties of the ZnSe nanocrystals. A series of nanocrystals with different size was prepared in 1 h, and the photoluminescence quantum yield reached up to 17% at the optimal reaction condition. The results of HRTEM and XRD showed that the as-prepared nanocrystals had high crystallinity. The characterizations of EDS spectra and elemental analysis showed that the sulfur content of nanocrystals increased with the growth of nanocrystals. We speculated that the structure of nanocrystals was an alloy ZnSe(S) shell on the surface of the ZnSe particles core. Furthermore, we found that the oxygen from air in the reaction vessel played an important role in the decomposition of the thiol group under microwave irradiation.     

微波辐照合成羟基功能化离子液体氯盐中间体

采用微波辐照法合成了4种羟基功能化离子液体中间体氯化1-甲基-3-羟乙基咪唑、氯化N-羟乙基吡啶、氯化1-甲基-3-(2,3-二羟基)丙基咪唑和氯化N-(2,3-二羟基)丙基吡啶,考察了微波功率、辐射方式和辐射时间对反应产率的影响。结果表明,利用常规加热方法合成这4种离子液体中间体耗时长达24～96h,而用微波方法只需110～390s,反应时间大大缩短,同时微波方法较常规加热方法产率也略有提高。     

微波辐射无皂乳液聚合制备聚氰基丙烯酸正丁酯微球

在微波辐射的"非致热效应"作用下,采用不含乳化剂的无皂乳液聚合,制备了聚氰基丙烯酸正丁酯(PBCA)微球。通过透射电子显微镜观察了微球的形态结构,利用激光光散射粒度测定仪测定了微球的粒径大小及其分布,探讨了柠檬酸浓度、氰基丙烯酸正丁酯(BCA)用量、微波辐射功率等对微球粒径的影响。研究结果表明,与常规无皂乳液聚合相比较,微波作用下的无皂乳液聚合反应时间缩短,得到的PBCA微球粒径更小,分散性更好。柠檬酸浓度增加,PBCA微球粒径逐渐增大;单体浓度增加,或微波功率增加,PBCA微球的粒径先减小后增大。当柠檬酸质量分数为0.005%、BCA体积分数为1.0%、微波功率为600W时,所制得的微球粒径最小,为200nm左右。     

微波作用下的多肽固相缩合反应及动力学研究

分别在微波作用以及传统加热两种方式下, 研究了Fmoc-Val-OH与NH₂-Tyr(t-Bu)-Wang树脂的固相缩合反应及其动力学. 测定了温度变化对反应速率的影响, 并获得了两种方式下的缩合反应的宏观动力学参数: 300 W微波作用下表观缩合反应级数为2.3, 活化能为104.7 kJ/mol; 传统方法中表观反应级数为2.9, 活化能为142.4 kJ/mol. 微波作用将常规条件下的连接率由68%提高到95%, 而所需时间降为常规条件的1/14.     

Microwave-Assisted Synthesis of Poly(ε-caprolactone)-block-poly(ethylene glycol) and Poly(lactide)-block-poly(ethylene glycol)

Summary: This study reported the preparation and characterization of PCL-b-mPEG (poly(ε-caprolactone)-block-poly(ethylene glycol)) and PLL-b-mPEG (poly(L-lactide)-block-poly(ethylene glycol)) diblock copolymers by microwave heating and comparison of resulted products the ones with prepared by conventional heating. Diblock copolymers were synthesized successfully by the microwave-assisted ROP in the presence of stannous octoate (SnOct₂) as catalyst under nitrogen atmosphere in different monomer ratios. Structural and functional characterization of copolymers were performed by FTIR, ¹H-NMR and DSC. Molecular weight values were determined by GPC and also calculated from ¹H-NMR. According to the results, microwave irradiation allowed to obtain polymers with very narrow size distribution in very short reaction time. Similar polymers prepared by conventional heating were also synthesized for comparison. Molecular weight and conversion of polymers were increased by irradiation time. This change was continued until a certain time point after which no more increase was observed. It was concluded that microwave irradiation is a succesful method to obtain these diblock copolymers in very short reaction time and with a similar conversion obtained by conventional method.     

Development of microwave-assisted derivatization followed by gas chromatography/mass spectrometry for fast determination of amino acids in neonatal blood samples

Analysis of amino acids in blood samples is an important tool for the diagnosis of neonatal amino acid metabolism disorders. In the work, a novel, rapid and sensitive method was developed for the determination of amino acids in neonatal blood samples, which was based on microwave-assisted silylation followed by gas chromatography/mass spectrometry (GC/MS). The amino acids were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) under microwave irradiation. The controlled reaction was carried out employing BSTFA under conventional heating at 120 degrees C for 30 min. Experimental results show that microwave irradiation can accelerate the derivatization reaction of amino acids with BSFTA, and much shorten analysis time. The method validations (linear range, detection limit, precision and recovery) were studied. Finally, the method was tested by determination of amino acids in neonatal blood by the measurement of their trimethylsilyl derivatives by GC/MS in electron impact (EI) mode. Two biomarkers of L-phenylalanine and L-tyrosine in phenylketonuria (PKU)-positive blood and control blood were quantitatively analyzed by the proposed method. The results demonstrated that microwave-assisted silylation followed by GC/MS is a rapid, simple and sensitive method for amino acid analysis and is also a potential tool for fast screening of neonatal aminoacidurias.     

微波相转移催化氧化法合成氯代苯甲酸

在相转移催化剂存在下，用微波辐射快速合成氯代苯甲酸。考察了微波辐射功率、辐射时间、相转移催化剂对反应的影响。实验证明：在455W的微波辐射下，以季铵盐A-1为相转移催化剂，反应3min，对氯苯甲酸、邻氯苯甲酸的产率分别达72．5％和71．8％。     

Synthesis of ring-contracted erythromycin A derivatives via microwave-assisted intramolecular transesterification

The synthesis of ring-contracted derivatives of erythromycin A via intramolecular transesterification under microwave irradiation of 8,9-anhydroerythromycin A 6,9-hemiketal and its derivatives is described. It was found that microwave irradiation could significantly improve the yields and shorten the reaction times under either solvent-containing (method A) or solvent-free (method B) conditions.     

Fast Microwave‐Mediated Bulk Polycondensation of d,l‐Lactic Acid

The polycondensation of D ,L ‐lactic acid upon microwave irradiation was studied. The results of polycondensation by means of microwave were compared to those obtained from conventional heating of lactic acid at 100°C, and it was found that the reaction proceeds with much higher rate upon microwave irradiation. The oligomer mixtures formed were investigated by means of matrix‐assisted laser desorption/ionization mass spectrometry (MALDI MS). The molecular mass of the poly(lactic acid) formed under microwave irradiation was found to increase with irradiation time, and the formation of cyclic oligomers after 20 min of reaction time was also revealed.     

Microwave Effects Due to Anionic or Cationic Initiators in Emulsion Polymerization Reactions

Summary: Emulsion polymerization reactions were performed under microwave irradiation and conventional heating using anionic or cationic initiators and surfactants. Microwave irradiation promoted higher reaction rates for both initiators and surfactants, in comparison with the conventional heating. The effect of high power microwave irradiation was studied using a method of cycles of heating and cooling, where rapid polymerization reactions were obtained. In the reactions with anionic initiator and surfactant, a decrease in the particle diameters was observed with microwave heating, and even smaller particles were obtained using high power microwave irradiation. Moreover, the decrease in the particle size was acompanied by an increase in the polymer molecular weight. On the other hand, these effects were not observed for reactions with cationic initiator and surfactant.     

Assessment of Microwave Effect on Polymerization Conducted under ARGET ATRP Conditions

A comprehensive kinetic model based on the method of moments is developed for understanding the kinetics of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) under microwave irradiation. Both the experimental data and the simulation results show that the polymerization under microwave irradiation is much faster than the thermal polymerization. Simulation results indicate that the acceleration of polymerization can be attributed to the increase of propagation rate coefficient and the radical generation by microwave irradiation. Kinetic behaviors, such as the effect of catalyst concentration and initial initiator, are investigated in detail. Results show that the catalyst concentration has negligible influence on polymerization rate while the initiator concentration can affect both the molecular weight and the reaction rate. In conclusion, this work thoroughly investigates the kinetic mechanism of ARGET ATRP under microwave irradiation, providing both theoretic and experimental supports to improve the product property of polymer materials.     

相转移催化与微波辐射合成三(2-氰乙基)胺

将微波辐射与相转移催化技术相结合,在加压密闭容器中,以氨水和丙烯腈合成了配位中间体三(2-氰乙基)胺,产率为61.2%,合成时间比传统方法缩短了8倍;在微波辐射下,产率为67.2%,合成时间缩短约90倍.对产物进行了元素分析,IR,¹H-NMR,ES-MS,及TG-DTA表征.     

Preparation and characterization of fluorinated acrylate copolymer latexes by miniemulsion polymerization under microwave irradiation

Fluoroacrylate copolymer miniemulsion was prepared by miniemulsion polymerization under microwave irradiation. The composition of the copolymer was determined by FTIR, DSC, ¹H NMR and ¹⁹F NMR. The morphology, size, and size distribution of the latex particles as well as changes in the size during polymerization were characterized by TEM and photon correlation spectroscopy (PCS). The effects of kinetic parameters on the polymerization were evaluated. The particle size of latex underwent almost no change during microwave irradiation polymerization. The diameters of latex particles prepared by microwave irradiation were smaller and more monodispersed than those prepared by conventional heating and the latex had good centrifugal stability. Polymerization under microwave irradiation had a higher reaction rate and higher conversion than traditional heating. By using 10 wt% fluoromonomer, the surface energy of the latex film could be reduced from 27.24 mJ/m² (latex film of fluorine-free) to 17.59 mJ/m² and the decomposition temperature increased by 25 °C.     

微波辐射活性炭负载磷钨酸催化合成季戊四醇双缩酮(醛)

在微波辐射下，以活性炭负载磷钨酸为催化剂，不用溶剂，合成了8种季戊四醇双缩酮（醛），以环己酮与季戊四缩的缩合为模型反应进行优化，其优化反应条件为：季戊四醇2．0g，催化剂0．3g，环己酮4．0mL，微波输出功率600W，辐射时间3min，产率达95．4％，该条件下的反应速度是常规加热反应速度的30倍，所得产物经元素分析，IR和1H NMR表征。     

The Microwave-Assisted Dehydrative Cyclization of Thiosemicarbazides Forming Substituted 1,2,4-Triazoles

Different types of 4,5-disubstituted 1,2,4-triazole-3-thiones were prepared by microwave irradiation as well as by a classical method. The beneficial effect of microwave irradiation on the dehydrative cyclization of thiosemicarbazides in different reaction media is described. Our results show that the effect of microwave irradiation on the reaction studied was the shortening of reaction times (from 2–9 h to 2–4 min) and a minor decrease (1–4%) in yields. The structure of the new compounds was established by FTIR, MS, and ¹H NMR spectral data.     

微波辅助制备CdS插层K2La2Ti3O10复合物及其光催化制氢的性能

采用微波辅助通过酸交换、胺柱撑、离子交换等步骤制备了CdS插层的K2La2Ti3O10(记做CdS-K2La2Ti3O10)复合光催化剂.利用X射线粉末衍射(XRD),场发射扫描电子显微镜(SEM),紫外-可见漫反射吸收光谱(UV-Vis)和光致发光光谱(PL)等对产物进行表征,考察了CdS-K2La2Ti3O10在紫外光及可见光下催化制氢活性.结果表明,微波辅助法与传统法制备的插层复合催化剂晶型结构相似,同时大大减少了离子交换反应时间,减少了对层间结构的破坏,拓展了催化剂的可见光吸收范围.微波辅助制备的催化剂在紫外光和可见光照射3 h后的产氢量分别为221.53 mmol/(g cat.)和3.23 mmol/(g cat.),并对光催化机理进行了分析.     

Microwave-assisted asymmetric organocatalysis. A probe for nonthermal microwave effects and the concept of simultaneous cooling

A series of five known asymmetric organocatalytic reactions was re-evaluated at elevated temperatures applying both microwave dielectric heating and conventional thermal heating in order to probe the existence of specific or nonthermal microwave effects. All transformations were conducted in a dedicated reactor setup that allowed accurate internal reaction temperature measurements using fiber-optic probes. In addition, the concept of simultaneous external cooling while irradiating with microwave power was also applied in all of the studied cases. This method allows a higher level of microwave power to be administered to the reaction mixture and, therefore, enhances any potential microwave effects while continuously removing heat. For all of the five studied (S)-proline-catalyzed asymmetric Mannich- and aldol-type reactions, the observed rate enhancements were a consequence of the increased temperatures attained by microwave dielectric heating and were not related to the presence of the microwave field. In all cases, in contrast to previous literature reports, the results obtained either with microwave irradiation or with microwave irradiation with simultaneous cooling could be reproduced by conventional heating at the same reaction temperature and time in an oil bath. No evidence for specific or nonthermal microwave effects was obtained.