Tiwari Shraeddha, Khupse Nageshwar, Kumar Anil
National Chemical Laboratory, Pune 411008, India.
J Org Chem. 2008 Nov 21;73(22):9075-83. doi: 10.1021/jo801802q. Epub 2008 Oct 24.
The present work aims at understanding the role of viscosity or solvent friction in ionic liquids for an intramolecular Diels-Alder (IMDA) reaction of (E)-1-phenyl-4-[2-(3-methyl-2-butenyloxy)benzylidene]-5-pyrazolone (1). The results have been analyzed on the basis of the current theoretical models, and their failure to account for the observed trends is discussed in terms of "effective" viscosity or microviscosity. The rates of the reaction decrease with the increasing viscosity of the ionic liquids. As evident from the anionic effect, the solute-solvent specific interactions play a role in governing the kinetics of the reaction. The lower viscosities of the bistrifluoromethanesulfonimide NTf2 based ionic liquids as compared to those based on tetrafluoroborate BF4 anion fail to result in a corresponding acceleration in the rates of the reaction. These contradictory results indicate that solvent microviscosity, rather than the bulk macroscopic viscosity, should be the criteria for selecting the ionic liquids as reaction media.
本研究旨在了解离子液体中的粘度或溶剂摩擦对（E）-1-苯基-4-[2-（3-甲基-2-丁烯氧基）亚苄基]-5-吡唑啉酮（1）的分子内狄尔斯-阿尔德（IMDA）反应的作用。已根据当前的理论模型对结果进行了分析，并从“有效”粘度或微观粘度的角度讨论了这些模型无法解释所观察到的趋势的原因。反应速率随离子液体粘度的增加而降低。从阴离子效应可以明显看出，溶质-溶剂的特定相互作用在控制反应动力学方面发挥着作用。与基于四氟硼酸根[BF4]-阴离子的离子液体相比，基于双三氟甲磺酰亚胺[NTf2]-的离子液体较低的粘度并未导致反应速率相应加快。这些相互矛盾的结果表明，溶剂微观粘度而非整体宏观粘度应作为选择离子液体作为反应介质的标准。
