Search

We report a scalable hydrogenation method for nitriles based on cost-effective materials in a very simple two-electrode setup under galvanostatic conditions. All components are commercially and readily available. The method is very easy to conduct and applicable to a variety of nitrile substrates, leading exclusively to primary amine products in yields of up to 89% using an easy work-up protocol. Importantly, this method is readily transferable from the milligram scale in batch-type screening cells to the multi-gram scale in a flow-type electrolyser. The transfer to flow electrolysis enabled us to achieve a notable 20 g day−1 productivity of phenylethylamine at a geometric current density of 50 mA cm−2 in a flow-type electrolyser with 48 cm2 electrodes. It is noteworthy that this method is sustainable in terms of process safety and reusability of components. [ABSTRACT FROM AUTHOR]

The necessary separation of anodic and cathodic compartments in the electrochemical multicomponent synthesis of alkyl arenesulfonates in batch was overcome by the transfer of this reaction in an undivided electrochemical flow cell. The yield was increased from an initial 23 % to 67 % by optimization using Design of Experiments (DoE). The experiments were carried out using an automated experimental flow electrolysis setup controlled by the automation software LABS (Laboratory Automation and Batch Scheduling), an open‐source software that allows to plan and conduct experiments with an arbitrary, freely selectable experimental setup. The automated experimental setup turned out to be stable and provides reproducible results. In total, 6 examples are demonstrated with isolated yields up to 81 %. In addition, the robust scalability of the electrochemical reaction was demonstrated in a 10‐fold scale‐up. [ABSTRACT FROM AUTHOR]

The direct anodic conversion of alkali carbonates in aqueous media provides access to peroxodicarbonate, which is a safe to use and green oxidizer. Although first reports date back around 150 years, its low concentrations and limited thermal stability have consigned this reagent to oblivion. Boron-doped diamond anodes, novel electrolyser concepts for heat dissipation, and the mixed cation trick allow record breaking peroxodicarbonate concentrations >900 mM. The electrochemical generation of peroxodicarbonate was already demonstrated on a pilot scale. The inherent safety is ensured by the limited stability of the peroxodicarbonate solution, which decomposes under ambient conditions to oxygen and facilitates subsequent downstream processing. This peroxide has, in particular at higher concentrations, an unusual reactivity and seems to be an ideal reagent when peroxo-equivalents in combination with alkaline base are required. The conversions with peroxodicarbonate include the Dakin reaction, epoxidation, oxidation of amines (aliphatic and aromatic) and sulfur compounds, deborolative hydroxylation reactions, and many more. Since the base equivalents also represent the makeup chemical for pulping plants, peroxodicarbonate is an ideal reagent for the selective degradation of lignin to vanillin. Moreover, peroxodicarbonate can be used as a halogen-free bleaching agent. The emerging electrogeneration and use of this green platform oxidizer are surveyed for the first time. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of nitroarenes allows direct access to manifold nitrogen containing heterocycles. This work reports the simple and direct electro-organic synthesis of 18 different examples of 2H,4H-4-hydroxy-1,4-benzoxazin-3-ones in up to 81% yield. The scalability of the method was demonstrated on a gram-scale. [ABSTRACT FROM AUTHOR]

An intramolecular electrochemical dehydration reaction of dicarboxylic acids to their cyclic anhydrides is presented. This electrolysis allows dicarboxylic acids as naturally abundant, inexpensive, safe, and readily available starting materials to be transformed into carboxylic anhydrides under mild reaction conditions. No conventional dehydration reagent is required. The obtained cyclic anhydrides are highly valuable reagents in organic synthesis, and in this report, we use them in‐situ for acylation reactions of amines to synthesize amides. This work is part of the recent progress in electrochemical dehydration, which – in contrast to electrochemical dehydrogenative reactions for example – is an underexplored field of research. The reaction mechanism was investigated by 18O isotope labeling, revealing the formation of sulfate by electrochemical oxidation and hydrolysis of the thiocyanate‐supporting electrolyte. This transformation is not a classical Kolbe electrolysis, because it is non‐decarboxylative, and all carbon atoms of the carboxylic acid starting material are contained in the carboxylic anhydride. In total, 20 examples are shown with NMR yields up to 71 %. [ABSTRACT FROM AUTHOR]

Important improvements have been achieved in developing the coupling of electrochemical CO2 reduction to formate with its subsequent microbial conversion to polyhydroxybutyrate (PHB) by Cupriavidus necator. The CO2 based formate electrosynthesis was optimised by electrolysis parameter adjustment and application of Sn based gas diffusion electrodes reaching almost 80 % Faradaic efficiency at 150 mA cm−2. Thereby, catholyte with the high formate concentration of 441±9 mmol L−1 was generated as feedstock without intermediate downstream processing for semi‐automated formate feeding into a fed‐batch reactor system. Moreover, microbial formate conversion to PHB was studied further, optimised, and successfully scaled from shake flasks to semi‐automated bioreactors. Therein, a PHB per formate ratio of 16.5±4.0 mg g−1 and a PHB synthesis rate of 8.4±2.1 mg L−1 OD−1 h−1 were achieved. By this process combination, an almost doubled overall process yield of 22.3±5.5 % was achieved compared to previous reports. The findings allow a detailed evaluation of the overall CO2 to PHB conversion, providing the basis for potential technical exploitation. [ABSTRACT FROM AUTHOR]

A novel electrochemical approach to access alkyl alkenesulfonates via a multicomponent reaction was developed. The metal‐free method features easy‐to‐use SO2 stock solution forming monoalkylsulfites from alcohols with an auxiliary base in‐situ. These intermediates serve a dual role as starting materials and as supporting electrolyte enabling conductivity. Anodic oxidation of the substrate styrene, radical addition of these monoalkylsulfites and consecutive second oxidation and deprotonation preserve the double bond and form alkyl β‐styrenesulfonates in a highly regio‐ and stereoselective fashion. The feasibility of this electrosynthetic method is demonstrated in 44 examples with yields up to 81 %, employing various styrenes and related substrates as well as a diverse set of alcohols. A gram‐scale experiment underlines the applicability of this process, which uses inexpensive and readily available electrode materials. [ABSTRACT FROM AUTHOR]