Parameters Affecting the Microwave-Specific Acceleration of a Chemical Reaction
Parameters Affecting the Microwave-Specific Acceleration of a Chemical Reaction
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DOI：
10.1021/jo5011526
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发表时间：
2014-08-15
影响因子：
3.6
通讯作者：
Stiegman, A. E.
中科院分区：
文献类型：
--
作者：
Chen, Po-Kai;Rosana, Michael R.;Stiegman, A. E.
在适当的条件下，可以观察到有机化学反应的反应速率的显著微波特异性增强。具体而言，烯丙基对硝基苯基醚（ApNE）溶解在萘中的单分子Claisen重排反应进行了研究，在微波加热和常规对流（热）加热。在恒定的微波功率下，达到185 ° C的温度，在微波中观察到比使用对流加热的速率提高4倍;这意味着微波反应在202 ° C的有效温度下进行。相反，在恒温微波条件下（200摄氏度），可以忽略不计（类似于1.5倍）的微波特定的速率增强观察。当一系列300 W脉冲编程为145-175摄氏度和85-155摄氏度循环时，观察到最大的微波特定速率增强，其中分别观察到超过常规热加热预测的2倍和9倍速率增强。微波特定效应的假定起源是纯粹的热，并产生于选择性加热的ApNE，微波吸收反应物在非吸收溶剂。在这些条件下，过量的热量在ApNE溶质周围的区域中积累，使得其经历比本体介质的测量温度更高的有效温度，导致加速的单分子重排。
Under appropriate conditions, significant microwave-specific enhancement of the reaction rate of an organic chemical reaction can be observed. Specifically, the unimolecular Claisen rearrangement of allyl p-nitrophenyl ether (ApNE) dissolved in naphthalene was studied under microwave heating and conventional convective (thermal) heating. Under constant microwave power, reaching a temperature of 185 degrees C, a 4-fold rate enhancement was observed in the microwave over that using convective heating; this means that the microwave reaction was proceeding at an effective temperature of 202 degrees C. Conversely, under constant temperature microwave conditions (200 degrees C), a negligible (similar to 1.5-fold) microwave-specific rate enhancement was observed. The largest microwave-specific rate enhancement was observed when a series of 300 W pulses, programmed for 145-175 degrees C and 85-155 degrees C cycles, where 2- and 9-fold rate enhancements, over what would be predicted by conventional thermal heating, was observed, respectively. The postulated origins of the microwave-specific effect are purely thermal and arise from selective heating of ApNE, a microwave-absorbing reactant in a nonabsorbing solvent. Under these conditions, excess heat is accumulated in the domains around the ApNE solute so that it experiences a higher effective temperature than the measured temperature of the bulk medium, resulting in an accelerated unimolecular rearrangement.