Manufacturing with the Power of Electricity: Organic Electrochemistry

Although the term "chemical manufacturing (synthesis)" may sound simple, it covers a very wide range, from inorganic compounds like ceramics and magnets to organic compounds like pharmaceuticals and electronic materials, and even polymeric compounds like plastics and rubber. In this column, I will focus on the synthesis of organic compounds and briefly introduce some of the recent research conducted in our laboratory.

When you hear about the synthesis of organic compounds, or "organic synthesis," many people probably imagine pouring reagents, the raw materials, into containers like beakers and flasks. However, it is rare to obtain the desired compound just by doing that; to make the reaction proceed, it is necessary to add special reagents (sometimes multiple types). In other words, to form new bonds, existing bonds must be activated with the help of special reagents. Without going into detail, wouldn't manufacturing that does not require such special reagents be ideal?

After that rather long introduction, this is where organic electrochemistry comes in. Organic electrochemistry, as the name implies, refers to organic chemistry combined with electrochemistry, and manufacturing that utilizes its concepts and methods is called organic electrosynthesis. In organic electrosynthesis, as shown in the schematic diagram in Figure 1 (A), the reaction is made to proceed by immersing two electrodes (a cathode and an anode) in a solution of the raw material (substrate) and applying a constant current or voltage. At this time, a reactive intermediate is formed through electron transfer between the electrode and the substrate, and this reactive intermediate is converted into the desired compound through a chemical reaction. In short, because organic electrosynthesis treats electrons themselves as if they were reagents, it can be considered a manufacturing method that does not require special reagents.

Using our recent research results shown in Figure 2 as an example, I will briefly introduce the appeal of organic electrosynthesis. In the reaction of oxidizing isoeugenol (substrate), a type of phenol, on the anode, changing the solvent used to dissolve the substrate yielded a completely different product. When methanol (MeOH) was used as the solvent, a compound called licarin A, which exhibits anti-inflammatory activity, was obtained as the main product. However, when hexafluoroisopropanol (HFIP) was used as the solvent, a compound called α-diisoeugenol, which exhibits diverse biological activities, was obtained as the sole product. We believe this is because the structure and stability of the reactive intermediate formed by the oxidation reaction on the anode are greatly influenced by the type of solvent. I believe that this dramatic change in product with only a slight alteration of reaction conditions is one of the greatest appeals of organic electrosynthesis.

Finally, I would like to conclude this column by touching on the past, present, and future of organic electrochemistry. Ushered in by the invention of the voltaic pile in 1800, organic electrochemistry has brought many developments to organic synthetic chemistry over the course of 200 years. And now, from the perspective of "green and sustainable chemistry," which supports the development of a sustainable society, the field of organic electrochemistry (organic electrosynthesis), which enables environmentally friendly manufacturing, is experiencing a renaissance. To ensure that this trend does not end as a mere boom, I intend to continue my research by confronting organic electrochemistry head-on, although my contribution may be small.