Elektrochemische Umsetzung biogener Carbonsäuren durch (Non-)Kolbe Elektrolyse

• Electrochemical conversion of biogenic carboxylic acids through (Non-)Kolbe electrolysis

Meyers, Jérôme; Palkovits, Regina (Thesis advisor); Waldvogel, Siegfried R. (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen Univerisity, 2022

Abstract

In this dissertation, one of the most important electro-organic reactions, the (Non-)Kolbe electrolysis, was investigated, adding valuable and sustainable additions to the substrate and product portfolio. The obtained results underline the potential of this reaction class, discovered more than 180 years ago, by application-related examples. With these innovations, (Non-)Kolbe electrolysis serves the currently increasing interest in energy storage technologies and sustainable biorefinery processes in view of the current climate crisis. Based on a study of the electrochemical conversion of the biologically derivable model substrate 3-hydroxydecanoic acid, a promising diesel fuel blend could be produced. In this work, an efficient protocol for the Non-Kolbe electrolysis of a β-hydroxy acid, a recurring element in biologically produced substances, was delivered with high yields of over 95%. The product composition of seven different C9-based oxygenates showed similar suitability to fossil diesel, providing a basis for high blending ratios with fossil or Fischer-Tropsch diesel. Further investigations in a simulated fermentation broth showed that in a dilute microbial environment, a similar product distribution of the mixture can be achieved despite reduced yield. In addition, the potential of this reaction system for future scale-up in continuous electrolysis cells (semi-batch and single-pass setups) was demonstrated. In another study, an alternative (Non-)Kolbe pathway was investigated that cannot be classified into either the classical Kolbe, or Non-Kolbe route. This method of synthesis of unsaturated compounds, an intramolecular biradical recombination, occurs during the electrochemical conversion of unprotected dicarboxylic acids. The feasibility of the reaction was first demonstrated using the example of methylsuccinic acid, which can be obtained from biogenic itaconic acid by electrochemical reduction. Here, the desired product was formed in excellent yields (up to 83 % propene). In a one-pot process starting from itaconic acid, 49 % propylene was obtained without membrane separation despite the additional reduction step required. The applicability and limitations of this consecutive oxidation, according to mechanistic studies, were demonstrated by a broad substrate spectrum. Here, for each dicarboxylic acid HO2C(CH2)nCO2H with n < 5 yields in the double-digit range could be achieved for alkenes, alkynes or even cycloalkanes. A promising synthetic route from an economic point of view was achieved in the intramolecular biradical recombination from the most produced amino acid glutamic acid. By protecting the amino group with a Boc-unit, the monomer allylamine could be sustainably produced. Finally, the focus was placed on the electrochemical production of nitrile-based valuable products starting from amino acids. By adapting a known multi-step process for the synthesis of adiponitrile, glutamic acid could be converted to acrylonitrile in the final reaction step by Non-Kolbe electrolysis. With this sustainable synthesis route, an alternative to the petroleum-based SOHIO process, a selectivity of up to 69.5% of the desired Non-Kolbe product acrylonitrile could be achieved. In addition, a promising one-step process to the anti-inflammatory, therapeutic agent 3-(methyl-sulfonyl)propanenitrile, or dapansutrile, which is highly traded in literature, was developed. The route involves an 8-electron transfer via indirect electrolysis of methionine with ammonium bro-mide as a mediator.