Finn Moeller

The selective oxidation of benzylic C-H bonds is a pivotal transformation in organic synthesis. Undoubtedly, achieving efficient and highly selective aerobic oxidation of methylarenes to benzaldehydes has been highly challenging due to the propensity of benzaldehyde to undergo overoxidation under typical aerobic conditions. Herein, we propose an innovative approach to address this issue by leveraging electrocatalytic processes, facilitated by ion-pair mediators [Ph3C]+[B(C6F5)4]-. By harnessing the power of electrochemistry, we successfully demonstrated the effectiveness of our strategy, which enables the selective oxidation of benzylic C-H bonds in benzylic molecules and toluene derivatives. Notably, our approach exhibited high efficiency, excellent selectivity, and compatibility with various functional groups, underscoring the broad applicability of our methodology.

Nature Communications, Published online: 04 April 2024; doi:10.1038/s41467-024-47220-9

Cross-dehydrogenative coupling (CDC) of C-H bonds is an ideal approach for C-C bond construction but suffers from low selectivity of similar C-H bonds. Here, the authors describe a highly selective paired electrocatalysis strategy towards CDC combining hydrogen evolution reaction catalysis with hydride transfer catalysis.

The Cover Feature shows that three steps are key in capturing p-hydroxybenzamide and converting it into paracetamol from a waste stream produced from the ammonia pretreatment of biomass, e.g., poplar trees or oil palm empty fruit bunches. The pretreated biomass is converted into renewably sourced fuels (e.g., isobutanol and sustainable aviation fuel). The p-hydroxybenzamide (yellow bottles) is converted in a continuous process to p-aminophenol (purple bottle), a precursor to paracetamol (red bottle), plastics, ink, and other products. This result is a portfolio of sustainably sourced commodity chemicals that could add value to a biorefinery. More information can be found in the Research Article by S. D. Karlen and co-workers.

Biomass valorisation during water electrolysis may serve as an alternative anode reaction for green H₂ production. For lignin oxidation to vanillin, a Ni−Fe catalyst composition selected with the help of scanning droplet cell screening was employed to investigate and optimise the pulse electrolysis parameters to mitigate vanillin overoxidation. In conjunction with thermolysis, significant improvement of the produced amount of vanillin from lignin was achieved.

Abstract

The electrification of the production of fine chemicals has received increased interest in combating petrochemical routes with a high carbon footprint. Oxidising biomass from waste streams with concomitant hydrogen production, such as the transformation of lignin to vanillin, would be a great asset. Here, we show the combination of activity screening using a scanning droplet cell on a thin-film Ni−Fe library and performance testing in a flow-through cell with pulse electrolysis. The identified optimal Ni−Fe material composition was prepared on Ni foam with a polymer/metal precursor spray method. Full factorial and Doehlert matrix designs were employed to better comprehend each parameter‘s effects on the complex system. The best conditions for the electrooxidation of Kraft lignin at room temperature were at E_1st=1.36 V vs RHE, t_1st=1 s for the first pulse and E_2nd=1.60 V vs RHE and t_2nd=15 s for the second pulse, leading to the significantly improved production of 2.15 μmols of vanillin at room temperature. Pulsed chronopotentiometry was demonstrated to be a cost-effective and robust technique with a simple setup for the valorisation of Kraft lignin. Combined with a subsequent thermolysis step, 8.05 μmols of vanillin were obtained.

We illustrate a sustainable and mild reaction process that efficiently transforms biomass-derived furfural directly into GVL. Combining the homogeneous catalyst Ru-MACHO-BH with H₃PO₄(aq) allows to transform furfural to GVL in 84 % yield at 100 °C. This demonstrates the feasibility of transforming a major polysaccharide component in lignocellulose (hemicellulose) to GVL in a one-pot direct approach without intermediate purification and isolation.

Abstract

Herein, we report the direct conversion of biomass-derived furfural to γ-valerolactone (GVL) in a one-pot system, using the combination of Ru-MACHO-BH and a Brønsted acid (H₃PO₄). A GVL yield of 84 % is achieved under mild reaction conditions using 1 mol% of Ru-MACHO-BH and 3.8 M H₃PO₄(aq) at 100 °C for 7 hours.