Self-supported paired electrosynthesis of 2,5-dimethoxy-2,5-dihydrofuran using a thin layer flow cell without intentionally added supporting electrolyte

Nickel-Electrocatalyzed Synthesis of Bifuran-Based Monomers

Bifuran motifs can be accessed with nickel-bipyridine electrocatalyzed homocouplings of bromine-substituted methyl furancarboxylates, which, in turn, can be prepared from hemicellulose-derived furfural. The described protocol uses sustainable carbon-based graphite electrodes in the simplest setup - an undivided cell with constant current electrolysis. The reported method avoids using a sacrificial anode by employing triethanolamine as an electron donor.

Electrocatalytic hydrogenation of benzoic acids in a proton-exchange membrane reactor

The highly efficient chemoselective electrocatalytic hydrogenation of benzoic acids (BAs) to cyclohexanecarboxylic acids (CCAs) was carried out in a proton-exchange membrane reactor under mild conditions without hydrogenation of the carboxyl group. Among the investigated catalysts, the PtRu alloy catalyst was found to be the most suitable for achieving high current efficiencies for production of CCAs. An electrochemical spillover mechanism on the PtRu alloy catalyst was also proposed.

Application of an Electrochemical Microflow Reactor for Cyanosilylation: Machine Learning-Assisted Exploration of Suitable Reaction Conditions for Semi-Large-Scale Synthesis

Cyanosilylation of carbonyl compounds provides protected cyanohydrins, which can be converted into many kinds of compounds such as amino alcohols, amides, esters, and carboxylic acids. In particular, the use of trimethylsilyl cyanide as the sole carbon source can avoid the need for more toxic inorganic cyanides. In this paper, we describe an electrochemically initiated cyanosilylation of carbonyl compounds and its application to a microflow reactor. Furthermore, to identify suitable reaction conditions, which reflect considerations beyond simply a high yield, we demonstrate machine learning-assisted optimization. Machine learning can be used to adjust the current and flow rate at the same time and identify the conditions needed to achieve the best productivity.

Electrosynthesis in Laminar Flow Using a Flow Microreactor

Electrosynthesis and microflow synthesis have become essential tools in their own rights in modern organic synthesis. In this personal account, we summarize our works on the integrated use of these techniques, i. e., electrosynthesis in a flow microreactor. Our group has developed an electrochemical microflow system composed of a pair of electrodes that face each other to form a micrometer-scale gap for the flow path, through which solution passes in laminar flow. By the aid of laminar flow, unprecedented chemo- and electrochemical selectivity has been observed, which is not achievable with conventional batch-type electrochemical cells. In addition, we showcase various unique electrochemical systems and reactions achieved with the flow microreactor, including self-supported electrolysis, efficient paired electrolysis, in situ generation of active species and its flash use, the spaciotemporal control of electropolymerization, and combinatorial screening of the reaction conditions.

Towards a better understanding of the electrosynthesis of 2,5-dicarboxy-2,5-dihydrofurans: structure, mechanism and influence over stereochemistry

2,5-Dicarboxy-2,5-dihydrofurans are key constituents of a number of natural products and have roles as intermediates in the formation of other such compounds of interest. Typically, these species are synthesized using toxic Pb(IV) salts. Electrochemical syntheses of 2,5-diacetoxy-2,5-dihydrofuran that do not require the use of lead have been reported, but a general lack of experimental detail has prevented these procedures from being more widely adopted. Moreover, no electrochemical study has yet reported the ratio of cis and trans isomers produced. Herein, we compare the chemical, lead-based route to 2,5-diacetoxy-2,5-dihydrofuran with a fully described electrosynthesis method. In doing so, we have discovered that the cis and trans isomers of this compound were previously incorrectly assigned in the literature, an error that we correct by obtaining the crystal structure of cis-2,5-diacetoxy-2,5-dihydrofuran. This allows the ratios of the isomers as prepared by the chemical (2 : 1 cis : trans) and electrochemical (7 : 5 cis : trans) methods to be obtained. Through experimental and computational insights, we propose a mechanism for the electrochemical synthesis of 2,5-dicarboxy-2,5-dihydrofurans and go some way towards validating this mechanism by synthesizing 2,5-dibutoxy-2,5-dihydrofuran electrochemically for the first time. We hope that these findings will provide some greater clarity to the literature surrounding the electrosynthesis and potential applications of 2,5-dicarboxy-2,5-dihydrofurans.

Modern Electrochemical Aspects for the Synthesis of Value-Added Organic Products

The use of electricity instead of stoichiometric amounts of oxidizers or reducing agents in synthesis is very appealing for economic and ecological reasons, and represents a major driving force for research efforts in this area. To use electron transfer at the electrode for a successful transformation in organic synthesis, the intermediate radical (cation/anion) has to be stabilized. Its combination with other approaches in organic chemistry or concepts of contemporary synthesis allows the establishment of powerful synthetic methods. The aim in the 21st Century will be to use as little fossil carbon as possible and, for this reason, the use of renewable sources is becoming increasingly important. The direct conversion of renewables, which have previously mainly been incinerated, is of increasing interest. This Review surveys many of the recent seminal important developments which will determine the future of this dynamic emerging field.

An Easy-to-Machine Electrochemical Flow Microreactor: Efficient Synthesis of Isoindolinone and Flow Functionalization

Flow electrochemistry is an efficient methodology to generate radical intermediates. An electrochemical flow microreactor has been designed and manufactured to improve the efficiency of electrochemical flow reactions. With this device only little or no supporting electrolytes are needed, making processes less costly and enabling easier purification. This is demonstrated by the facile synthesis of amidyl radicals used in intramolecular hydroaminations to produce isoindolinones. The combination with inline mass spectrometry facilitates a much easier combination of chemical steps in a single flow process.

Expedient preparation of nazlinine and a small library of indole alkaloids using flow electrochemistry as an enabling technology

An expedient synthesis of the indole alkaloid nazlinine is reported. Judicious choice of flow electrochemistry as an enabling technology has permitted the rapid generation of a small library of unnatural relatives of this biologically active molecule. Furthermore, by conducting the key electrochemical Shono oxidation in a flow cell, the loading of electrolyte can be significantly reduced to 20 mol % while maintaining a stable, broadly applicable process.

Difluoro-and Trifluoromethylation of Electron-Deficient Alkenes in an Electrochemical Microreactor

Electrochemical microreactors, which have electrodes integrated into the flow path, can afford rapid and efficient electrochemical reactions without redox reagents due to the intrinsic properties of short diffusion distances. Taking advantage of electrochemical microreactors, Kolbe electrolysis of di-and trifluoroacetic acid in the presence of various electron-deficient alkenes was performed under constant current at continuous flow at room temperature. As a result, di-and trifluoromethylated compounds were effectively produced in either equal or higher yields than identical reactions under batch conditions previously reported by Uneyamas group. The strategy of using electrochemical microreactor technology is useful for an effective fluoromethylation of alkenes based on Kolbe electrolysis in significantly shortened reaction times.

Micro Reactors, Flow Reactors and Continuous Flow Synthesis

Dr Paul Watts is a reader in organic chemistry at The University of Hull and since graduating from the University of Bristol, where he completed a PhD in bio-organic natural product synthesis, he has led the Micro Reactor Group at Hull. In this role, he has published 90 papers, and he regularly contributes to the field by way of invited book chapters, review articles, and keynote lecturers on the subject of micro reaction technology in organic synthesis.

Dr Charlotte Wiles is the Chief Technology Officer at Chemtrix BV, and has been actively researching within the area of micro reaction technology for 10 years, starting with a PhD entitled Micro reactors in organic chemistry, which she obtained from The University of Hull in 2003. In the past decade, she has authored many scientific papers and review articles, recently co-authoring a book on the subject of micro reaction technology in organic synthesis. More recently, she has tailored her experience to the development and evaluation of commercially available continuous flow reactors, systems and peripheral equipment.

This review article explains the advantages of micro reactors and flow reactors as tools for conducting organic synthesis and describes how the technology may be used in research and development as well as production. A selection of examples is taken from the literature to illustrate how micro reactors enables chemists to perform their reactions more efficiently than when using batch processes.

A practical microreactor for electrochemistry in flow

A microreactor for electrochemical synthesis has been designed and fabricated. It has been shown that different reactions can be carried out successfully using simple protocols.

Green and sustainable chemical synthesis using flow microreactors

Several features that allow flow microreactors contribute to green and sustainable chemical synthesis are presented: (1) For extremely fast reactions, kinetics often cannot be used because of the lack of homogeneity of the reaction environment when they are conducted in batch macroreactors. Better controllability, by virtue of fast mixing based on short diffusion paths in microreactors, however, leads to a higher selectivity of the products, based on kinetics considerations. Therefore, less waste is produced. (2) Reactions involving highly unstable intermediates usually require very low temperatures when they are conducted in macrobatch reactors. By virtue of short residence times, flow microreactors enable performing such reactions at ambient temperatures, avoiding cryogenic conditions and minimizing the energy required for cooling. (3) By virtue of the precise residence time control, flow microreactors allow to avoid the use of auxiliary substances such as protecting groups, enabling highly atom- and step-economical straightforward syntheses. The development of several test plants based on microreaction technology has proved that flow microreactor synthesis can be applied to the green and sustainable production of chemical substances on industrial scales. (4) Microreactor technology enables on-demand and on-site synthesis, which leads to less energy for transportation and easy recycling of substances.

Theory and experiments of transport at channel microband electrodes under laminar flows. 2. Electrochemical regimes at double microband assemblies under steady state

The development of any particular analytical or preparative applications using electrochemical techniques in microfluidic devices requires integration of microelectrodes. This involves detailed predictions for optimizing the design of devices and selecting the best hydrodynamic conditions. For this purpose, we undertook a series of works aimed at a precise investigation of mass transport near electrodes with focus on analytical measurements. Part I of this series (Anal. Chem. 2007, 79, 8502-8510) evaluated the common case of a single microband electrode embedded within a microchannel under laminar flow. The present work (Part 2) investigated the case of a pair of microband electrodes operating either in generator-generator or generator-collector modes. The influence of the confining effect and flow velocity on the amperometric responses was examined on the basis of numerical simulations under steady-state regime. Several situations were identified, each of them corresponding to specific interactions taking place between the electrodes. Related conditions were extracted to establish a zone diagram describing all the situations. These predictions were systematically validated by experimental measurements. The results show that amperometric detections within microchannels can be performed at dual electrodes with higher analytical performances than at single ones.