微波技术在Suzuki反应中的应用

与传统的加热方式相比,微波加热具有加热速度快、热效率高、节约能源、洁净、操作简单等优点,已成为重要的有机合成工具之一。钯催化的Suzuki反应提供了一种合成各种联芳烃的温和方法,具有较高的选择性。本文综述了近年来微波技术在Suzuki反应中的应用研究进展,涉及到各种不同的反应体系,重点讨论了KF/Al2O3负载钯和聚合物负载钯等非均相催化体系,对于均相反应则着重讨论无过渡金属和超低含量钯催化的Suzuki反应体系,还讨论了连续流动的微波反应器及Suzuki反应在有机合成中的应用。     

微波技术在催化剂制备中的应用

微波作为一种独特的加热手段在化学领域已得到广泛应用。本文综述了微波技术在催化剂的合成、活性组分的负载等方面的研究应用,重点探讨了在分子筛催化剂的合成中微波技术所表现出的优越性,对微波合成催化剂的作用机理及影响因素作了评述,并展望了微波技术在催化领域的发展前景。     

微波在柴油机滤烟器催化再生中的应用 Ⅱ.滤烟器在含氧气氛中的微波加热催化再生

采用柴油机台架装置及微波加热装置,考察了柴油机催化滤烟器的微波加热再生效应．结果表明,过滤体上捕集的碳烟量对催化滤烟器在氧气中的微波加热燃烧再生至关重要,只有捕集的碳烟量超过某一下限值,滤烟器上的碳烟才有可能被微波加热至起燃温度; 但碳量也不可超过一上限值,否则滤烟器的微波加热催化再生可能失去控制,碳烟急剧燃烧产生的热量将使过滤基质烧结． 此碳烟上下限再生窗口随催化剂活性的差异而有所改变． 研究中还发现,在再生过程中,产物中ＣＯ和ＣＯ２ 的比率有较大波动．     

微波在柴油机滤烟器催化再生中的应用：Ⅱ.滤烟器在含氧气氛中的微波加热 ？

采用柴油机台架装置及微波加热装置,考察了柴油机催化滤烟器的微波加热再生效应。结果表明,过滤体上捕集的碳烟量对催化滤烟器在氧气中的微波加热燃烧再生至关重要只有捕集的碳烟量超过某一直限值,滤烟器上的碳烟才有可能被微波加热至起燃温度;但碳量也不可超过一上限值,否则滤烟器的微波加热催化再生可能失去控制,碳烟急剧燃烧产生的热量将使过滤基质烧结。     

铈锆固溶体的微波辅助法制备及表征

采用共沉淀法并结合不同的老化处理方式(室温陈化、常规加热回流和微波辅助加热回流)制备了Ce_0.6Zr_0.4O₂固溶体。利用SEM、N₂吸附、XRD、Raman光谱和H₂-TPR等技术对样品的形貌、比表面积、孔结构、晶相结构、高温热稳定性和还原性进行了表征,并考察了其对CO氧化反应的催化性能。结果表明,微波辅助加热回流老化处理所制备的固溶体属于立方萤石结构,颗粒的大小均匀,表面结构疏松,具有最大的比表面积和孔容、最高的热稳定性及最好的低温还原性。CO氧化实验表明微波辅助加热回流老化处理所制备的Ce_0.6Zr_0.4O₂固溶体具有最好的催化氧化活性。     

微波在柴油机滤烟器催化再生中的应用 Ⅰ.滤烟器在氮气中的微波加热温升行为

利用柴油机台架装置及微波加热装置考察了柴油机催化滤烟器的微波加热温升效应． 结果表明,过滤体上捕集的烟碳量对催化滤烟器在氮气中的微波加热温升至关重要,烟碳量的微小增加,可引起滤烟体温度的显著升高． 另外,当微波加热过程中隔离氧气时,滤烟体上出现了明显的金属氧化物催化剂被碳还原的现象．     

微波在柴油机滤烟器催化再生中的应用：Ⅰ.滤烟器在氮气中的微波加热温 …

利用柴油机台架装置及微波加热装置考察了柴油机催化滤烟器的微波加热温升效应。结果表明,过滤体上捕集的烟碳量对催化滤烟器在氮气中的微波加热温升至关重要,烟碳量的微小增加,可引起滤烟体温度的显著升高。另外,当微波加热过程中隔离氧气时,滤烟体上出现了明显的金属氧化物催化剂被碳还原的现象。     

微波条件下ZnCl2改性离子交换树脂催化改质生物油的研究

在微波加热条件下,以732型阳离子交换树脂和ZnCl2改性离子交换树脂为催化剂,添加乙醇为溶剂,对生物油进行催化酯化改质.比较研究了两种催化剂随催化剂用量、反应时间及反应温度改变对生物油改质效果的影响,同时考察了微波加热与传统水浴加热条件下催化剂的活性.结果表明,酯化过程中ZnC12改性离子交换树脂比732型树脂活性有...     

微波干法催化醛酮与胺的缩合反应

利用微波辐射和固体中性Al2 O3 载体催化醛酮与胺的缩合反应的方法合成了十六种亚胺 ,研究了微波功率、作用时间、产物提取方式等因素对反应的影响 ;与无微波作用的一般合成方法相比 ,该法明显地提高反应速度及产率 ;文中用低极性熔点递变物质灌装毛细管的方法观测微波作用下反应温度 ,探讨微波作用化学反应的机理 ,其机理除与微波加热作用有关外还与分子间氢键及分子的缔合性有关。     

微波辐照下泡沫陶瓷担载镍催化剂上CH4/CO2重整制合成气反应

制备了吸波性良好的泡沫陶瓷担载镍的甲烷／二氧化碳重整催化剂,并考察了催化剂在微波场中的升温行为;研究了微波加热与常规加热对甲烷／二氧化碳重整制合成反应的影响,发现微波辐照下能有效地消除反应积炭;同时,在达到相同转化率和选择性时,微波加热方式下催化剂床层的温度远低于常规加热方式下催化床床层的温度;在微波加热方式下,８００℃反应时产物中Ｈ２／ＣＯ体积比接近于１。     

Environmentally Friendly Methods for Syntheses of New Aromatic Bisesters

Two environmentally friendly methods, one in liquid and the other in solid phase, for preparation of phenyl bisesters (bearing alkylating groups) under microwave (MW) irradiation are presented. The MW remarkably enhanced the rate of acceleration for esterification: the reaction time decreased dramatically, the reaction conditions are milder, and the consumed energy decreased considerably. In the most cases, in the liquid phase under MW irradiation, the yields are better, in some cases substantially (almost 75%). In the solid phase under MW irradiation, the yields are moderate to good compared to the liquid phase but excellent compared to conventional heating. Both methods are fast, general, and facile, but because the solid-phase reactions are solvent-free, we consider this one to be the most suitable for synthetic chemistry. A comparative study of MW and conventional heating was done.     

微波辐射-酶耦合催化(MIECC)反应

将微波辐射用于非水相酶催化可以获得很多有别于常规加热下的反应结果。本文讨论了微波的非热效应在酶促反应中的表现,探讨了微波辐射对酶的结构、构象、活性及酶催化反应动力学的影响,以及微波辐射-酶耦合催化对反应的对映选择性、底物专一性、前手性选择性和区域选择性的影响。在大多数场合,适当的微波辐射不会损伤酶活而且可以提高反应速率,而对酶特异性的影响则不一而论。     

Dechlorination of poly(vinyl chloride) by microwave irradiation I: A simple examination using a commercial microwave oven

Poly(vinyl chloride) (PVC) was decomposed by microwave (MW) irradiation (2.45 GHz) using a commercial MW oven. The efficiency of dielectric absorption was evaluated quantitatively from the rate of temperature increase on MW irradiation. The efficiency of dielectric heating increased at temperatures above the glass transition temperature (T_g). The decomposition on MW irradiation, monitored using the weight, depended on the initial (preheating) temperature of the sample before irradiation. The degradation time profile with various initial temperatures was shifted along the time axis and was successfully superimposed on a single curve. A pure PVC film was subjected to heating at a constant temperature from 230 °C to 310 °C, and the rate of weight decrease on heating was measured. The apparent activation energy was 84.4 kJ/mol for a single monomer unit.     

Microwave-assisted synthesis of colloidal inorganic nanocrystals

Colloidal inorganic nanocrystals stand out as an important class of advanced nanomaterials owing to the flexibility with which their physical-chemical properties can be controlled through size, shape, and compositional engineering in the synthesis stage and the versatility with which they can be implemented into technological applications in fields as diverse as optoelectronics, energy conversion/production, catalysis, and biomedicine. The use of microwave irradiation as a non-classical energy source has become increasingly popular in the preparation of nanocrystals (which generally involves complex and time-consuming processing of molecular precursors in the presence of solvents, ligands and/or surfactants at elevated temperatures). Similar to its now widespread use in organic chemistry, the efficiency of "microwave flash heating" in dramatically reducing overall processing times is one of the main advantages associated with this technique. This Review illustrates microwave-assisted methods that have been developed to synthesize colloidal inorganic nanocrystals and critically evaluates the specific roles that microwave irradiation may play in the formation of these nanomaterials.     

微波诱导甲烷在活性炭/碳化硅上直接转化制C2烃

 在高功率脉冲微波辐照下甲烷可在常压条件下在活性炭/碳化硅和活性炭碳化硅等 三种催化剂上直接转化为C2烃。研究结果表明,当使用合适的微波作用条件时,微波加热与微波 等离子协同作用可使甲烷在多孔碳化硅担载的活性炭催化剂上以很高的转化率和选择性直接转化为乙炔,除单独的微波加热诱导作用和微波等离子催化作用外,转移反应机制可能是微波加热与微波等离子交互作用的具体表现形式,对促进甲烷向乙炔直接转化起了重要作用。     

Microwave Effect in the Fast Synthesis of Microporous Materials: Which Stage Between Nucleation and Crystal Growth is Accelerated by Microwave Irradiation?

Microporous materials, such as silicalite-1 and VSB-5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW-MW, MW-CE, CE-MW, and CE-CE (in the order of nucleation-crystal growth). In the case of synthesis by MW-CE or CE-MW, the heating modes were changed for the second step just after the appearance of X-ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW-MW相似文献   

Silver Nanoparticles Supported on CeO2‐SBA‐15 by Microwave Irradiation Possess Metal–Support Interactions and Enhanced Catalytic Activity

Metal–support interactions (MSIs) and particle size play important roles in catalytic reactions. For the first time, silver nanoparticles supported on CeO₂‐SBA‐15 supports are reported that possess tunable particle size and MSIs, as prepared by microwave (MW) irradiation, owing to strong charge polarization of CeO₂ clusters (i.e., MW absorption). Characterizations, including TEM, X‐ray photoelectron spectroscopy, and extended X‐ray absorption fine structure, were carried out to disclose the influence of CeO₂ contents on the Ag particle size, MSI effect between Ag nanoparticles and CeO₂‐SBA‐15 supports, and the strong MW absorption of CeO₂ clusters that contribute to the MSIs during Ag deposition. The Ag particle sizes were controllably tuned from 1.9 to 3.9 nm by changing the loading amounts of CeO₂ from 0.5 to 2.0 wt %. The Ag nanoparticle size was predominantly responsible for the high turnover frequency (TOF) of 0.41 min^?1 in ammonia borane dehydrogenation, whereas both particle size and MSIs contributed to the high TOF of 555 min^?1 in 4‐nitrophenol reduction for Ag/0.5CeO₂‐SBA‐15, which were twice as large as those of Ag/SBA‐15 without CeO₂ and Ag/CeO₂‐SBA‐15 prepared by conventional oil‐bath heating.     

Facile Synthesis of new 3,5‐Dispiro Substituted Piperidine Analogs via Microwave‐Assisted One Pot Multicomponent Reaction

An eco‐efficient one‐pot three component reaction for the synthesis of 3,5‐dispirosubstituted piperidines is reported by condensing of 2‐thiobarbituric acid, formaldehyde, and aromatic amines in the presence of a catalytic amount of p‐toluenesulfonic acid (1.0 equivalent) in dimethyl sulfoxide. The reactions were examined by two special methods such as classical heating and microwave (MW) irradiation. In general, improvements in rates and yields were observed when reactions were carried out under MW irradiation compared to the conventional method.     

微波与有机化学反应的选择性*

本文综述了微波辅助下有机化学反应的选择性,包括化学选择性、区域选择性、顺反选择性、非对映选择性、对映选择性,与传统加热条件下反应选择性的区别。讨论了微波对有机化学反应选择性的影响。从文献报道的结果来看,虽然观察到了一些反应在微波照射与加热条件下显示出不同的选择性,但绝大部分例子并不是在严格相同的条件下进行的对比,还有一些虽然做了对比研究,但却忽略了温度的影响。对于绝大多数例子,微波产生的选择性的差别似乎都可以用热效应来解释。可以认为微波辅助的反应中基本不存在特殊的"非热效应"。微波辅助技术可以通过改变反应温度来实现改变某些反应的选择性。希望本文对微波效应和微波对有机反应加速效应的本质的理解提供一些有用信息。     

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.