Browsing by Author "Ding, Haoran"
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Item A Benign Synthesis Route to Terephthalic Acid via Two-Step Electrochemical Oxidation of P-xylene(Journal of The Electrochemical Society, 2024-05-31) Ding, Haoran; Orazov, Marat; Oliveira, Nicholas; Yan, YushanTerephthalic acid is conventionally synthesized through the AMOCO process under harsh conditions, making milder electrosynthesis routes desirable. Electrooxidation of p-xylene has been demonstrated but the degree of oxidation is limited, resulting in low terephthalic acid yields. Here, we demonstrate a process with two electrochemical steps enabling the complete oxidation of p-xylene into terephthalic acid. The first electrochemical step achieves C-H activation of p-xylene using electrochemically generated bromine as a mediator, while the second electrochemical step does alcohol oxidation of 1,4-benzenedimethanol into terephthalate on NiOOH. The divided cell in the first step simultaneously generates acid and base that are utilized subsequently, negating the need of external acid and base addition and thus offering a cost competitive synthesis route. The competing bromide oxidation in the second step is suppressed by using constant voltage electrolysis at 0.50 V, where an optimal yield of terephthalic acid of 81% is achieved.Item Anodically-Generated Alkyl Radicals Derived from Carboxylic Acids as Reactive Intermediates for Addition to Alkenes(ChemElectroChem, 2023-05-12) Ding, Haoran; Orazov, MaratElectrochemically driven C−C coupling has the potential to reduce the cost and environmental impact of some organic syntheses currently accomplished through thermochemical methods. Here, we use electrochemical oxidation of carboxylic acids as a source of reactive carbon-centered radicals that enable radical addition to alkenes in the anode boundary layer. We demonstrate an optimization of reaction conditions to suppress the thermodynamically favored, but synthetically undesirable radical self-coupling in favor of radical addition to styrene. In methanol solvent, 88 % selectivity and 72 % Faradaic efficiency for targeted functionalized benzenes are achieved. For low current densities, iridium anodes outperform platinum, gold, palladium, and glassy carbon anodes. With constant potential or constant current electrolyses, the deposition of organic by-products on the catalyst surface leads to anode passivation. We show that periodic cathodic current pulses effectively regenerate the catalyst. Lastly, we confirm the role of free radicals in the reaction mechanism with a radical trap. Graphical Abstract available at: https://doi.org/10.1002/celc.202201099 Electrochemically driven C−C coupling: High anodic current density favors the formation of the undesirable radical self-coupling product. Low anodic current density favors the formation of the target product, but also leads to more solvent oxidation. Solvent oxidation at low current density can be suppressed by multiple methods to achieve high Faradaic efficiency of the target product at high selectivity.