Novel electrosynthetic methods: focus on carbon dioxide utilisation

2019-04-16T15:48:25Z (GMT) by Vlod Tabas
The release of CO2 into the earth's atmosphere has been increasing exponentially since the dawn of the industrial age. Mainly due to the burning of fossil fuels; needed for power generation this increased amount of CO2 has been a direct cause to the increased greenhouse effect which in turn brings about severe consequences. Various ways of limiting the release CO2 have been developed over the years, with varying degrees of efficiency and success. Carbon Dioxide utilisation (CDU) is a relatively new technique which utilises CO2 rather than storing it. The main challenges associated with this technique stem from a sustainability aspect, therefore research is placed into developing methods which are environmentally friendly as well as energy and cost efficient. Many research groups from around the world have developed various techniques and approaches to incorporate CO2 into a variety of organics ranging from haloalkanes to alkynes. These techniques have ranged from using standard chemical reactions, intricate photocatalysts to using electrochemical processes, all with the main goal of forming a stable C-C bond, however all these methods possess some form of shortcomings. This project addresses the shortcomings in electrochemical methods associated with CO2. The discovery of a novel electrochemical process using non-sacrificial carbon electrodes in the hydrocarboxylation of styrenes was achieved under mild conditions, (10 Volts, 1 atm CO2 pressure, room temperature, non-sacrificial electrodes) was achieved producing the corresponding mono-carboxylic acids in a highly regioselective manner in good to excellent yields (50-85%). The novel method also proved successful in incorporating CO2 in alkynes, dienes, and acrylates as well as the reducing of internal double bonds. Furthermore, mechanistic analysis was undertaken to deduce the mode of action, this included the use of deuterium labelled reagents, cyclopropyl traps as well as common radical traps. This work has shown the potential of non-sacrificial electrochemical cells, by-passing the environmental and efficiency issues attributed with common electrochemical cells. The bonus of high regioselectivity, robustness towards various functional groups and potential to apply to various starting materials further enhances the potential of this method in become a valuable tool in organic synthesis.