Flow Electrochemical Strategies for Carbon Feedstock Valorisation

化学废物的有价化对工业和社会都很有吸引力，因为它能够将原材料和污染物转化为可重复使用的产品。特别是，二氧化碳和其他挥发性有机化合物(挥发性有机化合物，如轻烯烃、炔烃和芳烃)是消耗化石燃料和几个工业过程不可避免的副产品。这些化合物作为温室气体对环境产生了深远的影响，因此为它们的再利用制定合成方案是可持续发展的关键。尽管最近取得了进展，但二氧化碳和不饱和碳氢化合物功能化的最新方法仍然严重依赖过渡金属催化剂的使用，因此引起了人们对它们的成本、毒性和有限的地壳可获得性的担忧。此外，二氧化碳和挥发性有机化合物的气态性质使这些试剂的处理变得复杂，从而阻碍了它们在间歇反应中的使用。该项目的目标是实施一个无金属合成平台，利用流动反应器将原料和高活性化学中间体转化为战略合成构件。为了实现这一点，我们将设计新的1，3-偶极类型的1，3-偶极-量身定制的氧化还原活性部分-它可以在1，3-偶极环加成反应中与挥发性有机化合物(如丙炔)、二氧化碳或芳烃物种接触-而不需要贵重过渡金属的中间体-来提供环加成产物(例如2-4)。氧化还原不稳定官能团的存在使得环加合物在电化学条件下容易被单电子转移(SET)激活-根据氧化还原活性部分的性质而定-通过还原或氧化，从而产生自由基中间体。后者的自由基裂解将产生高度功能化的精细化学品(即5-7)，这些精细化学品可以作为合成重磅炸弹药物的中间体，如Aubagio(R)、布洛芬和Otezla(R)。电化学方法已被选为最方便和有效的实验装置，以促进氧化还原活性中间体的SET还原/氧化；因为自由基碎裂过程只需要一个电子的调解。使用流动反应器--包括并联和串联--对于促进使用难以处理的试剂和反应物至关重要，如气体(二氧化碳和挥发性有机化合物)和高活性物质(芳烃)。此外，流动设置在效率(增加电极表面积、限制焦耳加热和改善能耗)、选择性(例如使用层流流动)、可伸缩性和实验简易性方面为电化学反应带来了明显的优势。在这里，克里森扎博士在自由基介导的催化过程和有机合成方面的知识，加上Dryfe小组在电化学和流动系统方面的专业知识，支持了这些研究努力的成功。

The valorisation of chemical waste is attractive to both industry and society since it enables the conversion of raw materials and pollutants into reusable products. In particular, carbon dioxide and other volatile organic compounds (VOCs, e.g. light-weight alkenes, alkynes and arenes) are inevitable byproducts of the consumption of fossil fuels and several industrial processes. These compounds have a profound impact on the environment - by acting as greenhouse gases - thus the development of synthetic protocols for their re-utilization is key to sustainability. Despite recent advances, state-of-theart methods for the functionalization of CO2 and unsaturated hydrocarbons still heavily rely on the use of transition metal catalysts, thus raising concerns over their cost, toxicity and limited Earth-crust availability. Furthermore, the gaseous nature of both CO2 and VOCs complicates the handling of these reagents, thus thwarting their use in batch reactions.This project targets the implementation of a metal-free synthetic platform to convert feedstock materials and highly-reactive chemical intermediates into strategic synthetic building blocks, using flow reactors. To realise this, we will design novel 1,3-dipoles of the type of 1 - tailored with a redox-active moiety - which can engage VOCs (such as propyne), CO2, or aryne species in 1,3-dipolar cycloadditions - without the intermediacy of precious transition metals - to deliver cycloadduct products (e.g. 2-4). The presence of a redox-labile functionality renders the cycloadducts prone to single electron transfer (SET) activation - either by reduction or oxidation, depending on the nature of the redox-active moiety -under electrochemical conditions, this generating radical intermediates. Radical fragmentation from the latter species will deliver highly functionalised fine chemicals (i.e. 5-7), which can serve as intermediates the synthesis blockbuster drugs - such as Aubagio(R), Ibuprofen, and Otezla(R). Electrochemical methods have been selected as the most convenient and efficient experimental settings to facilitate the SET reduction/oxidation of the redox-active intermediate; since the radical fragmentation process only requires the mediation of an electron. The use of flow reactors - both in parallel and in series - will be crucial to facilitate the use of difficult-to-handle reagents and reactants, such as gases (CO2 and VOCs) and highly-reactive species (arynes). Additionally, flow settings brings clear advantages to electrochemical reactions in terms of efficiency (enhanced electrode-surface area, limited Joule heating and improved energy consumption), selectivity (e.g. use of laminar flow streams),scalability and experimental ease.This project sits at the interface between synthetic chemistry, catalysis and chemical engineering. Here, the knowledge of Dr Crisenza in radical-mediated catalytic processes and organic synthesis, combined with the Dryfe group's expertise in both electrochemistry and flow-systems supports the success of these research endeavours.