Paired Electrolysis in the Simultaneous Production of Synthetic Intermediates and Substrates

Abstract

In electrochemical processes, an oxidation half-reaction is always paired with a reduction half-reaction. Although systems for reactions such as the reduction of CO can be coupled to water oxidation to produce O at the anode, large-scale O production is of limited value. One may replace a low-value half-reaction with a compatible half-reaction that can produce a valuable chemical compound and operate at a lower potential. In doing so, both the anodic and cathodic half-reactions yield desirable products with a decreased energy demand. Here we demonstrate a paired electrolysis in the case of the oxidative condensation of syringaldehyde and o-phenylenediamine to give 2-(3,5-dimethoxy-4-hydroxyphenyl)benzimidazole coupled with the reduction of CO to CO mediated by molecular electrocatalysts. We also present general principles for evaluating current-voltage characteristics and power demands in paired electrolyzers.

Electrifying Organic Synthesis

“…The generated hydrogen can potentially be directly employed for a coupled synthesis 146. One remarkable example is the N−N heteroatom coupling of carbazoles at a carbon anode, investigated by Baran and co‐workers as a pivotal step of the first total synthesis of dixiamycin B (Scheme 51).…”

Paired Electrochemical Reactions and the On‐Site Generation of a Chemical Reagent

“…[1,3,31] So,a na nodic reaction can in principle be paired with the generation of av ariety of chemical reagents and synthetic transformations.F or example,t he oxidative condensation reaction shown in Scheme 2h as been paired with the production of carbon monoxide. [29] Efforts to further expand the reactions along these lines are underway as part of al arger program to illustrate how the inclusion of an electrochemical reaction in as ynthetic sequence can be used to improve the sustainability of not only that particular reaction, but also av ariety of other non-electrochemical reactions in the sequence.…”

“…[19] Many other efforts have been dedicated as well, particularly in the general area of energy conversion. [20][21][22][23][24][25][26][27][28][29] However,inspite of the potential paired electrochemical reactions hold for running more sustainable processes and the impressive examples illustrating this potential, the technique remains primarily of interest to chemists specifically engaged in the development of new electrochemical methods.A number of factors contribute to this situation. These factors range from little need to consider the energy efficiencyo f synthetic methods conducted in an academic laboratory setting to the impression that paired electrochemical reactions require "carefully matched" oxidation and reduction reactions and hence have limited synthetic generality.W ith respect to the first point, academic chemists are becoming increasingly aware of the need for more sustainable synthetic methods and strategies.I nt hat context, it makes sense to examine methods that meet the challenge from both ap erspective of atom and energy economy.P aired electrolysis reactions offer such an opportunity.T he second point raised above represents ap otentially more significant barrier.…”

Elektrifizierung der organischen Synthese

“…[146] One remarkable example is the NÀNh eteroatom coupling of carbazoles at acarbon anode,investigated by Baran and co-workers as ap ivotal step of the first total synthesis of dixiamycin B( Scheme 51). [147] Thea uthors demonstrated that this reaction can be generally applied to substituted carbazoles and b-carbolines with yields of up to 66 %.…”