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

文章摘要：John W.Weidner，Michael A.Matthews和John Monnier研究所：南卡罗来纳大学提议编号：0500032标题：室温离子液体的结构对涉及电化学产生的超氧离子的有机反应的影响项目摘要：智力价值：该项目旨在为有机基质的选择性部分氧化提供一种新的和可持续的方法的科学基础。该方法利用电化学方法在高导电性、不挥发性的室温离子液体(RTIL)溶剂中生成超氧离子(O2O-)，然后利用O2O-进行后续的均相反应。这项工作的前提是，合理的RTIL结构设计将允许选择性地控制O2O的形成和随后的部分氧化。因此，该项目的科学目标是确定在电化学生成的O2O-存在下稳定的RTIL，在广泛的RTIL类别中进行某些有机氧化反应，并将RTIL的阴离子和阳离子的结构与这些反应的速度和产率联系起来。这将涉及识别反应产物和测量涉及O2O-的选定有机反应的本征动力学。这三类有机反应是：(1)分别由伯醇和仲醇氧化生成的羧酸和酮；(2)分别由醇和胺在二氧化碳存在下生成的碳酸盐和氨基甲酸酯；(3)多卤代芳香族化合物(如多氯联苯)的氧化。所有这些反应的第一步是在RTILs中电化学生成O2O-。在NSF探索性拨款的事先支持下，PI表明，只要RTIL的结构和纯度得到控制，RTIL中就可以产生稳定的O2O-物种。此外，O2O-与苯甲醇、苯甲醇、二氧化碳和六氯苯反应生成所需的产物。他们还表明，RTIL阳离子结构的微小变化极大地影响产品收率。此外，首选的阳离子取决于反应。例如，在咪唑环的2位添加甲基，可将苯并氢的平均收率从50%提高到98%以上。同样重要的是，在获得这些高产量的同时，没有检测到RTIL的降解。相反，O2O-与苯甲醇反应生成苯甲酸，产率从23%降至0.0%，表明RTIL对反应有抑制作用。目前使用的PF6阴离子的长期稳定性也有一个问题，因为它会被电解和水解，产生与O2O-反应的氢氟酸。虽然到目前为止，结果是非常有希望的，但没有一个先验的方法来知道对于给定的反应，哪种RTIL是合适的，更不是最优的。为了将给定的反应与适当的RTIL相匹配，需要了解RTIL结构对均相反应速率和产率的影响。人们希望发现基础知识，以确定在O2O存在下既具有长期稳定性又具有良好的溶剂催化性能的RTIL。因此，PI计划将阴离子和阳离子结构与它们在产物产率和本征反应速率中的作用联系起来，用于本项目中三类重要有机反应中的典型反应。这将使得能够针对给定的反应理性地选择RTIL。更广泛的影响：这项工作将加速使用新的和潜在的环境友好型策略，用于电-有机化学合成。RTIL不仅是很有前景的绿色溶剂，而且超氧化物电化学在室温下利用空气或氧气和电。因此，RTIL技术与电化学的结合促进了环境友好技术的发展，无论是制造有机中间体，还是修复氯代芳烃。该项目将与一个通过斯隆基金会少数民族博士奖学金招收少数民族博士生的计划联系在一起，该奖学金已经实施了几年。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。南加州大学的本科生将参加由国家科学基金会赞助的研究传播工作室(NSF EEC 0212244，PI Michael Matthews博士)，该工作室提供技术出版和演示方面的指导。来自其他大学的本科生将通过正在进行的美国国家科学基金会本科生研究经验(REU)项目，在污染预防领域的化学工程系(美国国家科学基金会-欧洲经济共同体-0097695，PI约翰·魏德纳博士)。

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).