Flow Electrochemical Strategies for Carbon Feedstock Valorisation

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.