Homocoupling of Carboxylic Acids through Kolbe Electrolysis

Kolbe Electrolysis is a well-established electrochemical process, yet its adoption for chemical synthesis is slow compared to other methods, primarily due to its reliance on platinum electrodes. To explore more accessible alternatives, this study investigates carbon-based electrodes as substitutes for platinum in Kolbe Electrolysis. Reticulated Vitreous Carbon (RVC) is a promising candidate in preliminary research. Although Kolbe Electrolysis typically exhibits slow kinetics, it demonstrates favorable selectivity and yield during bulk electrolysis. This research also aims to explore sustainable alternatives for chemical manufacturing, mainly through biomass conversion into carbon-based molecules with carboxylic acids. The Kolbe Electrolysis mechanism is known to eliminate carboxylic acid groups, forming radicals that couple to produce longer-chain molecules; however, this mechanism has primarily been validated for linear alkane reactants. This study will investigate the feasibility of using various carboxylic acid-containing molecules with RVC electrodes in Kolbe Electrolysis to expand the understanding of its applications.

The present work investigated the Kolbe electrolysis of many carboxylic acid-containing molecules, including levulinic acid in an electrolyte comprised of acetonitrile, tetramethylammonium hydroxide (TMAH), and water. Two RVC electrodes were immersed in this solution and bulk electrolysis was performed by applying a constant current for a specified duration. Following the reaction, the reaction products were extracted and analyzed using gas chromatography-mass spectrometry (GC-MS). The resulting data was then examined to identify and quantify the products. Starting with levulinic acid, we observed the formation of 2,7-octanedione. By comparing the expected products to the measured products, we can also propose a reaction mechanism for Kolbe electrolysis on RVC electrodes that will guide future research.