Dudley Gregory B, Richert Ranko, Stiegman A E
Department of Chemistry and Biochemistry , Florida State University , Tallahassee , FL , USA . Email:
Department of Chemistry and Biochemistry , Arizona State University , Tempe , AZ , USA.
Chem Sci. 2015 Apr 1;6(4):2144-2152. doi: 10.1039/c4sc03372h. Epub 2015 Jan 16.
The use of microwave radiation to drive chemical reactions has become ubiquitous in almost all fields of chemistry. In all of these areas it is principally due to rapid and convenient heating resulting in significantly higher rates of reaction, with other advantages including enhanced product selectivity and control of materials properties. Although microwave heating continues to grow as an enabling technology, fundamental research into the nature of microwave heating has not grown at the same rate. In the case of chemical reactions run in homogeneous solution, particularly synthetic organic reactions, there is considerable controversy over the origins of rate enhancement, with a fundamental question being whether there exist microwave-specific effects, distinct from what can be attained under conventional convective heating, that can accelerate a reaction rate. In this Perspective, we discuss unique aspects of microwave heating of molecules in solution and discuss the origin and nature of microwave-specific effects arising from the process of "selective heating" of reactants in solution. Integral to this discussion is work from the field of dielectric relaxation spectroscopy, which provides a model for selective heating by Debye relaxation processes. The Perspective also includes a critical discussion of hypotheses of non-thermal effects (alternatively classified here as resonant processes) and an outline of specific reaction parameters for chemical systems in which microwave-specific Debye relaxation processes can result in observable reaction rate enhancement.
利用微波辐射驱动化学反应在几乎所有化学领域都已变得十分普遍。在所有这些领域中，这主要是由于快速便捷的加热方式能显著提高反应速率，其他优势还包括增强产物选择性以及对材料性质的控制。尽管微波加热作为一种辅助技术持续发展，但对微波加热本质的基础研究却未以相同速度跟进。在均相溶液中进行的化学反应，尤其是有机合成反应，关于反应速率提高的根源存在相当大的争议，一个基本问题是是否存在与传统对流加热不同的、能加速反应速率的微波特异性效应。在这篇综述文章中，我们讨论了溶液中分子微波加热的独特方面，并探讨了溶液中反应物“选择性加热”过程所产生的微波特异性效应的起源和本质。介电弛豫光谱领域的研究工作是此次讨论的核心内容，它为德拜弛豫过程的选择性加热提供了一个模型。这篇综述文章还对非热效应（在此也归类为共振过程）的假说进行了批判性讨论，并概述了化学体系中的特定反应参数，在这些体系中，微波特异性德拜弛豫过程能够导致可观测到的反应速率提高。
