Evaluation of most promising options for the C1 to C2-coupling: alternative formate coupling

This thesis work contains an overview of potential alternative options to couple formate produced from CO2 with other coupling partners than formate itself. Ultimately, the intent is to produce high value chemicals from CO2 at a high selectivity and conversion, whilst keeping the required utility of electrons in the electrochemical CO2 conversion at a minimum. To select and find new coupling partners, a framework was developed upon which a broad variety of candidates were assessed and ranked. A multi-stage process was used to select first potential classes of molecules. For each class, a variety of commercially available compounds was analysed in depth for its potential suitability in the reaction with the active carbonite intermediate. This analysis has shown that a wide variety of factors come into play and especially the reactivity of the hydride catalyst poses a mayor challenge. The three major potential classes of compounds suitable for the coupling are carbon oxides (CO2 & CO), and aldehydes. As a second step the remaining options were ranked to identify which compound to test first. In this ranking the reactants sustainability, ease of commercial operation and commercial attractiveness of the compound were considered. The highest-ranking compounds that proposed the highest potential are CO2, benzaldehyde and para-formaldehyde. In proof-of-principle experiments CO2 could successfully be incorporated in the form of carbonate, oxalate and potentially formate. The overall incorporation efficiency based on the hydride consumption was shown to be 50%. It is suggested to continue this work with mechanistic studies to understand the reaction in detail as, based on further gained knowledge, the reaction can then be optimized towards optimal CO2 incorporation in the form of oxalate.