“热效应”或“非热效应”——微波加热反应机理探讨

微波辅助下有机反应是否存在"非热效应",是微波化学领域备受争议的研究热点。"非热效应"和"热效应"的支持者都通过大量实验和理论计算来验证自己的观点。本文总结了微波与物质的相互作用,探讨了准确测定反应温度在验证"热效应"和"非热效应"中的重要作用。大量的研究结果表明,在微波辐射下有机反应,"热效应"对反应时间、速率和收率作用重大。     

微波辅助有机合成中“非热效应”的研究方法

微波作为一种新颖的加热方式,极大地提高了有机合成的效率.对于微波促进有机合成反应机理,人们提出了它具有"非热效应".本文从微波对分子的影响、微波光量子对化学键的影响以及微波对化学反应的影响3个方面,对"非热效应"存在的理论依据进行了阐述;从理论、实验以及两者相结合的角度,对"非热效应"的研究方法与技术进行了综述.     

微波介电加热及其在化学中的应用

简要介绍了９０年代以来在微波介电加热及微波致热和非致热效应方面的研究、微波炉中测温控温技术上的新进展，以及微波技术在无机化学、有机化学、物理化学、放射化学等领域中的部分新应用。     

微波辅助合成菲并咪唑衍生物及微波非热效应

以1,10-邻菲啰啉5,6-二酮及苯甲醛(或取代苯甲醛)为原料, 在微波辐射条件下制备了一系列菲并咪唑类衍生物, 考察了温度、 时间以及投料比对微波辅助合成菲并咪唑类衍生物的影响, 并进一步探讨了微波非热效应的影响. 设计正交实验优化了反应条件; 使用SiC管作为反应容器屏蔽微波对反应的影响; 通过元素分析、 核磁共振波谱、 质谱及红外光谱等对化合物进行了表征. 结果表明, 微波辅助反应的最佳反应条件为: 1,10-邻菲啰啉-5,6-二酮与苯甲醛(或取代苯甲醛)的投料比为1: 1.5, 反应温度为100℃, 反应时间为20 min; 并且发现SiC管中反应的产率明显低于石英管反应容器. 与传统制备方法相比, 微波辅助合成方法可在更短时间内快速方便地制得菲并咪唑类衍生物; 反应温度、 反应时间以及投料比对微波辅助合成反应有明显影响; 微波非热效应有助于提高反应产率.     

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.     

微波化学温度模拟研究进展

在微波化学研究中,通过数学模拟分析微波作用在化学体系的温度分布及变化,有助于控制微波加热过程,了解微波与物质之间的相互作用机理.本文针对微波化学数值模拟的特点,系统介绍了各种方法及模拟过程,对数值模拟分析中的关键问题进行了讨论,综述了近年来数值模拟温度分布在微波化学中的应用,提出了目前的研究难点,并展望了发展趋势.     

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.     

微波频率下氯化钠溶液电导率的非线性特性

在微波频段研究了电磁场对氯化钠溶液电导率的影响. 运用不对称周期双阱势函数和Langvin方程描述了恒温条件下氯化钠溶液团簇结构中平均氢键的动力学行为, 由Bertolini公式建立团簇的平均氢键形成的概率变化与电导率变化的关系. 计算结果表明, 在恒温条件下, 当微波场的场强达到10 kV·m-1 时, 微波能会部分转化为团簇里分子间势能, 使得氯化钠溶液的电导率与电场强度有关, 这一结果与实验结果符合. 这种微波与氯化钠溶液的相互作用表现出强烈的非线性变化, 应该属于微波的非热效应范畴.     

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。     

微波热效应法合成Y_2O_3∶Eu~（3＋）荧光体

微波热效应法合成Ｙ_２Ｏ_３∶Ｅｕ~（３＋）荧光体李沅英，戴德昌，蔡少华（中山大学化学系，广州，５１０２７５）关键词微波热效应法，合成，荧光体，掺铕氧化钇掺铕（Ⅲ）氧化钇荧光体是阴极射线管（ＣＲＴ）、彩色投影电视和三基色节能荧光灯等领域的重要发光材料。?..     

Microwaves in organic synthesis. Thermal and non-thermal microwave effects

Microwave irradiation has been successfully applied in organic chemistry. Spectacular accelerations, higher yields under milder reaction conditions and higher product purities have all been reported. Indeed, a number of authors have described success in reactions that do not occur by conventional heating and even modifications of selectivity (chemo-, regio- and stereoselectivity). The effect of microwave irradiation in organic synthesis is a combination of thermal effects, arising from the heating rate, superheating or "hot spots" and the selective absorption of radiation by polar substances. Such phenomena are not usually accessible by classical heating and the existence of non-thermal effects of highly polarizing radiation--the "specific microwave effect"--is still a controversial topic. An overview of the thermal effects and the current state of non-thermal microwave effects is presented in this critical review along with a view on how these phenomena can be effectively used in organic synthesis.     

The analysis of “power window” induced by thermal effect during the microwave heating

The “windows” are often considered as the evidence of microwave non-thermal effect. Here, enzyme catalysis acrylonitrile reaction was carried out and the coupled multiphysics field equations were solved by finite difference time domain (FDTD) method. The temperature curves can be obtained under the different power. Then, the results calculated by chemical reaction kinetic show that the power window of product concentration can be induced by thermal effect. The power window cannot be a criterion of microwave non-thermal effects.     

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。     

A Critical Overview on the Effect of Microwave Irradiation in Organic Synthesis

Despite the great success of Microwave Assisted Organic Synthesis (MAOS) there is still a lack of knowledge about the interaction of the electromagnetic radiation with matter. In consequence, it has been very difficult to rationalize the effect of microwave irradiation in chemistry, to determine the existence of microwave effects (thermal and non‐thermal) and to develop predictive models on the characteristics required for a reaction to be improved under microwaves. This has been a handicap to develop new chemistry under microwave irradiation and the origin of many controversies. This personal account collects some new findings in this field and our work on the use of computational chemistry to develop predictive models and to determine parameters related to thermal and non‐thermal effects, with clear advantages over experimental methods where separation of these effect is almost impossible.     

Kinetic features of radical polymerization of styrene under microwave irradiation conditions

A comparative study of radical polymerization of styrene under thermal and microwave heating conditions has been carried out. The polymerization reaction orders with respect to the monomer and initiator concentrations and the polymerization rate constants have been determined. It has been found that non-thermal microwave effects are not manifested during styrene polymerization, because styrene is a weakly polar substance.     

Polymerizations of epoxides with microwave energy

The polymerization of the bisaliphatic epoxy resin, 3,4‐epoxycyclohexylmethyl, 3,4‐epoxycyclohexylcarboxylate initiated by diaryliodonium or triarylsulfonium salts under both microwave energy and conventional thermal heating, was investigated. DSC and FTIR methods to determine the extent of polymerization were established. Some polymerization phenomena such as polymerization selectivity, polymerization temperature shift, and polymerization temperature shift by microwave power setting in microwave fields compared to thermal fields were investigated. To explain the phenomena, a theory that a new partition function existed in microwave fields was proposed with statistical thermodynamics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4230–4246, 2004     

Microwave activation of the electro-oxidation of glucose in alkaline media

The oxidation of glucose is a complex process usually requiring catalytically active electrode surfaces or enzyme-modified electrodes. In this study the effect of high intensity microwave radiation on the oxidation of glucose in alkaline solution at Au, Cu, and Ni electrodes is reported. Calibration experiments with the Fe(CN)(6)(3-/4-) redox system in aqueous 0.1 M NaOH indicate that strong thermal effects occur at both 50 and 500 microm diameter electrodes with temperatures reaching 380 K. Extreme mass transport effects with mass transport coefficients of k(mt) > 0.01 m s(-1)(or k(mt) > 1.0 cm s(-1)) are observed at 50 microm diameter electrodes in the presence of microwaves. The electrocatalytic oxidation of glucose at 500 microm diameter Au, Cu, or Ni electrodes immersed in 0.1 M NaOH and in the presence of microwave radiation is shown to be dominated by kinetic control. The magnitude of glucose oxidation currents at Cu electrodes is shown to depend on the thickness of a pre-formed oxide layer. At 50 microm diameter Au, Cu, or Ni electrodes microwave enhanced current densities are generally higher, but only at Au electrodes is a significantly increased rate for the electrocatalytic oxidation of glucose to gluconolactone observed. This rate enhancement appears to be independent of temperature but microwave intensity dependent, and therefore non-thermal in nature. Voltammetric currents observed at Ni electrodes in the presence of microwaves show the best correlation with glucose concentration and are therefore analytically most useful.     

液相微波介电加热法制备纳米粒子的研究进展

随着纳米科技的飞速发展,合成纳米材料的新方法层出不穷。在这些新方法当中,液相微波介电加热法近年来得到了飞速的发展,引起了科学界越来越多的关注。本文介绍了近年来液相微波介电加热法制备纳米粒子的一些研究进展,主要是该方法在制备金属、过渡金属氧化物和金属硫族化合物纳米粒子中的应用,并且对该领域未来的发展作了一些展望。