Translating batch electrochemistry to single-pass continuous flow conditions: an organic chemist’s guide

Abstract

The recent renaissance of electrochemical methods for organic synthesis has also attracted increased interest towards flow electrochemistry as the most suitable scale-up strategy. Many electrochemical methods using flow cells are based on recirculation of the electrolyte solution. However, single-pass processing is very attractive as it permits integration of the electrochemical reaction with other synthetic or purification steps in a continuous stream. Translation of batch electrochemical procedures to single-pass continuous flow cells can be challenging to beginners in the field. Using the electrochemical methoxylation of 4methylanisole as model, this paper provides newcomers to the field with an overview of the factors that need to be considered to develop a flow electrochemical process, including advantages and disadvantages of operating in galvanostatic and potentiostatic mode in small scale reactions, and the effect of the interelectrode gap, supporting electrolyte concentration and pressure on the reaction performance. A comparison of the reaction efficiency in batch and flow is also presented.

Making electrochemistry easily accessible to the synthetic chemist

“…107 In addition, Cantillo and co-workers published a guide to translating batch electrochemistry into single-pass continuous flow conditions. 108 Continuous electrochemical cells are often used to recirculate batch solutions, however a single-pass layout offers the prospect of telescoping reaction solutions into subsequent reaction or purification steps. The authors also discussed the advantages and disadvantages of potentiostatic vs. galvanostatic conditions and the effects of interelectrode gap, electrolyte concentration, reaction pressure and steady state on the reaction outcome using the example of 4-methylanisole oxidation.…”

“…Cantillo and coworkers have discussed the advantages and disadvantages for galvanostatic and potentiostatic conditions for continuous reactions. 108 Is the reaction reproducible?. Similar to a traditional chemical reaction, an electrochemical reaction can only be reproducible if all reaction conditions are the same.…”

A Divergent Paired Electrochemical Process for the Conversion of Furfural Using a Divided‐Cell Flow Microreactor

“…The selectivity can be increased in such reactors due to the large electrode surface‐to‐volume ratio and due to a meticulous control over the residence time and the cell potential. Using such intensified reaction conditions, the reaction time is typically reduced significantly compared to batch cells and, thus, the products are only briefly exposed to the electrochemical conditions, efficiently avoiding undesired follow‐up reactions [27–29] . In this work, we show that a divergent paired electrochemical flow strategy enables the simultaneous production of 2(5 H )‐furanone via an anodic oxidation, and the generation of furfuryl alcohol and/or hydrofuroin via a cathodic reduction (Figure 1A).…”

Bridging Lab and Industry with Flow Electrochemistry

“…It would require time investment to learn and master the basics of electrochemistry, flow chemistry, and the combination of the two. Learning one and not the other would not suffice and one cannot directly jump to learning flow electrochemistry because flow chemistry itself is not a self-sufficient research area and an understanding of electrochemistry in batch is key ( Maljuric et al., 2020 ). So, for flow electrosynthesis to pick up better traction it has to be hand-in-hand with an improved appreciation of batch organic electrosynthesis.…”

“…Such segments might help reactions that need improved mass transfer by increasing turbulence in the liquid phase. However, gas does not conduct electricity and hence gas-liquid segments negatively affect the performance of the flow cell by increasing local current densities ( Maljuric et al., 2020 ; Cao et al., 2021 ). When it comes to scale-up, several electrochemical cells are stacked together in a filter-press arrangement.…”