CAS:Mechanochemical Activation Carriers and Mechanisms by in Situ Chemical Kinetics Monitoring

在化学(CHE)部的化学结构、动力学和机理B(CSDM-B)计划和材料研究部(DMR)的固态和材料化学(SSMC)计划的支持下，Old Dominion大学的Silvina Pagola博士将研究机械化学反应的基本方面及其机制。机械力化学是研究机械力引起的反应和机械能并入的化学领域。机械化反应在很大程度上减少或避免了反应溶剂的使用。它们是“绿色”的化学过程，越来越多地用于制备无机、有机和金属-有机材料。然而，机械化学反应的化学机制仍然知之甚少，这限制了它们的实施。这个项目将测试一个理论模型，该模型假设包含机械力化学反应的能量学和仅由热激活驱动的对应能量学之间的关键差异。将开发确定机械力化学反应活化势垒的方法。这些研究有可能为机械力化学开辟一个新的视角，并为机械力化学激活的定量建模提供新的方法。这种方法有可能成为其他寻求开发机械化学法的宝贵工具，作为现有化学工艺的更可持续的替代品，从而带来环境和经济利益。与该项目相关的教育活动包括对研究生和本科生的培训，以及纳入在STEM(科学、技术、工程和数学)领域任职人数不足的个人。还将组织利用免费分发的软件从X射线粉末衍射计算晶体结构的年度讲习班。这项研究试图开发方法来测量和解释机械力化学反应的活化势垒的意义。来自均相动力学和化学机理的知识将与最近开发的原位动力学监测技术和仪器的使用相结合，以测量机械力化学反应的活化势垒。对“应力增强热激活”理论模型的有效性和适用范围进行了研究。这个模型意味着机械力化学反应的吉布斯自由能比仅由热活化驱动的反应的吉布斯自由能降低，这是因为加入了一个唯象功项，该唯象功项是由沿反应坐标施加于反应物的外力产生的。这一效应与机械处理激发的振动模式相结合，协同降低了机械力化学激活势垒。将研究三种类型的机械力化学反应：(1)金属-有机骨架ZIF-6的机械合成；(2)两次Diels-Alder环加成(共价力化学)；(3)四硫富瓦烯和氯苯酸的机械力化学有机共结晶，以及导致离子和中性晶型的化学机理。等温动力学数据将在球磨机上使用拉曼光谱在非原位X射线粉末衍射的支持下进行现场测量。活化势垒将由Arrhenius和Eyring图计算。将分析几种研磨参数组合的激活值的吉布斯自由能的变化，从而导致总体机械能输入的系统增加。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms-B (CSDM-B) Program of the Chemistry (CHE) Division, and the Solid State and Materials Chemistry (SSMC) Program of the Division of Materials Research (DMR), Dr. Silvina Pagola at Old Dominion University will investigate fundamental aspects of mechanochemical reactions and their mechanisms. Mechanochemistry is the field of chemistry studying reactions induced by mechanical forces and the Incorporation of mechanical energy. Mechanochemical reactions largely reduce or avoid the use of reaction solvents. They are "green" chemical processes, increasingly used toward the preparation of inorganic, organic and metal-organic materials. However, the chemical mechanisms of mechanochemical reactions remain poorly understood, which limits their implementation. This project will test a theoretical model hypothetically embodying critical differences between the energetics of mechanochemical reactions and their counterparts driven only by thermal activation. Methods to determine the activation barriers of mechanochemical reactions will be developed. These studies have the potential to open up a new perspective on mechanochemistry, and new ways of quantitatively modeling mechanochemical activation. Such an approach has the potential to serve as a valuable tool for others seeking to develop mechanochemical approaches as more sustainable alternatives to existing chemical processes, with attendant environmental and economic benefits. Educational activities associated with this project include the training of graduate and undergraduate students, along with the inclusion of individuals underrepresented in STEM (science, technology, engineering and mathematics) fields. Yearly workshops on solving crystal structures from X-ray powder diffraction using freely distributed software will be also organized. This research seeks to develop methods to measure and interpret the meaning of the activation barriers of mechanochemical reactions. Knowledge from homogeneous-phase kinetics and chemical mechanisms will be combined with the use of recently developed in situ kinetics monitoring techniques and instrumentation to measure the activation barriers of mechanochemical reactions. The validity and scope of a “stress-augmented thermal activation” theoretical model will be investigated. This model implies a reduction in the Gibbs free energy of activation of mechanochemical reactions in comparison with reactions driven only by thermal activation, by incorporating a phenomenological work term resulting of an external force applied to the reactants along the reaction coordinate. This effect is coupled with the excitation of vibrational modes by the mechanical treatment, synergistically reducing the mechanochemical activation barriers. Three types of mechanochemical reactions will be investigated: (1) The mechanosynthesis of ZIF-6, a metal-organic framework; (2) two Diels-Alder cycloadditions (covalent mechanochemistry); (3) the mechanochemical organic co-crystallization of tetrathiafulvalene and chloranilic acid, and the chemical mechanisms leading to ionic and neutral polymorphs. Isothermal kinetic data will be measured in situ from a ball mill using Raman spectroscopy, supported by ex situ X-ray powder diffraction. The activation barriers will be calculated from Arrhenius and Eyring graphs. The variation of the Gibbs free energy of activation values will be analyzed for several combinations of milling parameters, leading to a systematic increase of the overall mechanical energy inputs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.