Effect of Structure of Room Temperature Ionic Liquids on Organic Reactions Involving Electrochemically Generated Superoxide Ions

摘要：项目负责人：John W. Weidner, Michael a . Matthews和John Monnier机构：南卡罗莱纳大学提案号：0500032题目：室温离子液体结构对电化学生成超氧离子有机反应的影响项目概述：智力价值：该项目旨在为有机底物选择性部分氧化的新型可持续方法提供科学依据。该方法利用电化学手段在高导电性、不易挥发的室温离子液体（RTIL）溶剂中生成超氧离子（O2o-），然后利用O2o-进行后续均相反应。这项工作的前提是RTIL结构的合理设计将允许选择性控制O2o的形成和随后的部分氧化。因此，本项目的科学目标是确定在电化学生成的O2o-存在下稳定的RTILs，在广泛的RTILs中进行某些有机氧化反应，并将RTIL的阴离子和阳离子结构与这些反应的速率和产率联系起来。这将涉及识别反应产物和测量涉及O2o的选定有机反应的内在动力学。我们感兴趣的三类有机反应是：(1)分别由伯醇和仲醇氧化生成羧酸和酮；(2)在二氧化碳存在下分别由醇和胺产生的碳酸盐和氨基甲酸酯；(3)多卤芳烃（如多氯联苯）的氧化。所有这些反应的第一步是电化学生成O2o- in RTILs。在美国国家科学基金会（NSF）探索性资助的支持下，pi表明，只要控制RTIL的结构和纯度，就可以在RTIL中产生稳定的O2o-物种。此外，O2o-与苯甲醇、苯甲醇、二氧化碳和六氯苯反应形成所需产品。他们还表明，RTIL阳离子结构的微小变化会显著影响产物收率。此外，首选阳离子取决于反应。例如，在咪唑环的2号位置加入一个甲基，使苯并氢生成二苯甲酮的平均产率从50%提高到98%以上。同样重要的是，在这些高产量的同时，没有检测到RTIL的退化。O2o-与苯甲醇反应生成苯甲酸时，产率从23%下降到0.0%，表明RTIL对反应有抑制作用。迄今为止使用的PF6阴离子的长期稳定性也存在问题，因为它会受到电解和水解的影响，产生与O2o-反应的氢氟酸。虽然到目前为止的结果非常有希望，但是对于给定的反应，没有先验的方法可以知道哪种RTIL是合适的，更不用说最佳的了。为了使给定的反应与合适的RTIL相匹配，需要了解RTIL结构对均相反应速率和产率的影响。希望发现基本知识，以确定在O2o存在下具有长期稳定性和良好溶剂催化性能的RTILs。因此，pi计划将阴离子和阳离子结构与它们在产物收率和本征反应速率中的作用联系起来，用于本项目中三大类有机反应中的代表性反应。这将使对给定反应的RTIL的合理选择成为可能。更广泛的影响：这项工作将加速使用新颖的、潜在的环境友好型电有机化学合成策略。RTILs不仅是有前途的绿色溶剂，而且超氧化物电化学利用空气或氧气和室温下的电。因此，RTIL技术与电化学的结合促进了生产有机中间体或氯化芳烃修复的环保技术的发展。该项目将与一个通过斯隆基金会少数族裔博士奖学金招收少数族裔博士生的项目联系在一起，该项目已经实施了几年。南卡罗来纳大学（USC）的少数族裔博士生受益于南加州大学非裔美国人教授计划（AAPP），该计划将少数族裔学生和教师导师配对。南加州大学本科生将参加美国国家科学基金会资助的研究交流工作室（NSF EEC 0212244， PI博士Michael Matthews），该工作室提供技术出版和演示指导。来自其他大学的本科生将通过正在进行的化学工程系污染防治领域的美国国家科学基金会本科生研究经验（REU）计划（NSF- eec -0097695, PI Dr. John Weidner）参加。

ABSTRACTPI: John W. Weidner, Michael A. Matthews and John Monnier Institution: University of South CarolinaProposal Number: 0500032Title: Effect of Structure of Room Temperature Ionic Liquids on Organic Reactions Involving Electrochemically Generated Superoxide Ion Project Summary: Intellectual merit: This project is aimed at providing the scientific basis for a novel and sustainable approach for the selective, partial oxidation of organic substrates. The approach utilizes electrochemical means to generate the superoxide ion (O2o-) in highly conducting, non-volatile room-temperature ionic liquid (RTIL) solvents, and then utilizes O2o- to carry out subsequent homogeneous reactions. The premise of this work is that the rational design of RTIL structures will allow selective control of O2o- formation and subsequent partial oxidation. Therefore, the scientific objectives of this project are to identify RTILs that are stable in the presence of electrochemically generated O2o-, conduct certain organic oxidation reactions in broad classes of RTILs, and relate the structure of the anion and cation of the RTIL to the rate and yield of these reactions. This will involve identifying reaction products and measuring intrinsic kinetics of selected organic reactions involving O2o-. The three classes of organic reactions of interest are: (1) carboxylic acids and ketones, produced by oxidation of primary and secondary alcohols, respectively; (2) carbonates and carbamates, produced from alcohols and amines, respectively, in the presence of carbon dioxide; and (3) oxidation of polyhalogenated aromatics, (e.g. polychlorinated biphenyls). The first step in all these reactions is the electrochemical generation of O2o- in RTILs. With prior support from an exploratory NSF grant, the PIs showed that a stable O2o- species can be generated in RTILs as long as the structure and purity of the RTIL are controlled. Further, O2o- reacts with benzyl alcohol, benzhydrol, carbon dioxide, and hexachlorobenzene to form the desired products. They also showed that small changes in the structure of the RTIL cation dramatically affect product yield. In addition, the preferred cation depends on the reaction. For example, adding a methyl group in the position 2 of the imidazolium ring increased the average yield of benzhydrol to benzophenone from 50% to over 98%. Equally significant was that no degradation of the RTIL was detected along with these high yields. In contrast, the reaction of O2o- with benzyl alcohol to form benzoic acid decreased the yield from 23% to 0.0%, indicating reaction inhibition caused by the RTIL. There is also a problem with the long-term stability of the PF6 anion used to date since it is subject to electrolysis and hydrolysis, producing hydrofluoric acid that reacts with O2o-. While the results to date are very promising, there is no a priori way to know which RTIL is appropriate, much less optimal, for a given reaction. To match a given reaction with an appropriate RTIL, there is a need to understand the effect of RTIL structure on homogeneous reaction rates and yield. It is desired to discover the fundamental knowledge that will identify RTILs that have both long-term stability in the presence of O2o- and favorable solvent catalytic properties. Therefore, the PIs plan to relate anion and cation structure to their role in product yield and intrinsic reaction rates, for representative reactions within three important classes of organic reactions in this project. This will enable a rational choice of an RTIL for a given reaction. Broader impacts: This work will accelerate the use of novel and potentially environmentally friendly strategies for electro-organic chemical syntheses. Not only are RTILs promising green solvents, but superoxide electrochemistry utilizes air or oxygen and electricity at room temperature. Thus the combination of RTIL technology with electrochemistry promotes the development of an environmentally friendly technology for either the manufacturing of organic intermediates, or the remediation of chlorinated aromatics. The project will be linked with a program to recruit minority Ph.D. students through Sloan Foundation Minority Doctoral Fellowships that have been in place for several years. Minority Ph.D. students at the University of South Carolina (USC) benefit from the USC African American Professors Program (AAPP), which pairs minority students and faculty mentors. USC undergraduates will participate in the NSF-Sponsored Research Communications Studio (NSF EEC 0212244, PI Dr. Michael Matthews), which provides instruction in technical publishing and presenting. Undergraduates from other universities will participate through the ongoing NSF Research Experience for Undergraduate (REU) program in the Department of Chemical Engineering in the area of pollution prevention (NSF-EEC-0097695, PI Dr. John Weidner).