(Organic and Biological Electrochemistry Division Manuel M. Baizer Award, Digital Presentation) Electron-Transfer-Triggered Smart Reactions Boost a Better Anthropocene
Authors: Chiba Kazuhiro 
Published: July 2022

It is important that chemical reactions initiated by electron transfer associated with electrodes can be achieved by precise control of intramolecular and intermolecular electron transfer of organic compounds, which is difficult to achieve by general chemical methods. Expectations for a new production process that positively controls the electron transfer is also expanding dramatically. Here, the solvent that dissolves the substrate for reaction, the network structure of the ionic species in the solution, and the role of coexisting substances are exactly grasped, and the total energy consumption is controlled under milder conditions. If it is possible to develop a chemical process that reduces the consumption of substances such as reaction reagents to the utmost while significantly suppressing the above, it is expected that structural conversion of chemical substances based on the electron transfer process can be realized. This means that advanced control of the formation, stabilization, and subsequent reactions of active open-shell molecules opens the door to new chemical reactions that reduce excess reagent and energy consumption. There is a possibility that the atom economy will be dramatically enhanced by the electron transfer reaction process for the reagents that need to be charged. This achieves a chemical reaction that is regarded as "Electrons as Reagents", and it will be a core technology that will bring about innovation in the chemical substance manufacturing method that is currently produced with the production of a large amounts of unnecessary substances and energy consumption.

Research achievements: In such a background, K. Chiba pioneered original organic electrolytic reactions based on the research activities on chemical synthesis of biologically active natural compounds, and achieved various carbon skeleton formation, chemical synthesis of useful substances and biologically active natural substances. One of the notable results is the electrolytic synthesis reaction method using a unique electrolyte solution composed of lithium perchlorate / nitromethane. It was shown that the cation species generated by electrode electron transfer using this electrolyte solution are stabilized and can be applied to the formation of a wide variety of intermolecular carbon-carbon bonds. That is, numerous electrode process-triggered reactions such as varied (hetero)Diels-Alder reactions, [3+2], and [2+2] cycloaddition reactions have been achieved. In addition, the olefin metathesis without transition metal catalysis was successful for the first time. The importance of the role of the electrolyte solution in the organic electrolysis reaction was widely shown. The elucidation of these reaction mechanisms and new findings on the action of the reaction field have contributed to the rapid development of the field in recent years by utilizing and enhancing the functions of various electrolyte solutions.

In addition, the application of the new organic electrolysis method has widely developed chemical synthesis methods for natural and non-natural peptides, artificial nucleic acids, etc. It is noteworthy that it was successful in electrolytic synthesis of various aza-nucleosides by utilizing the cation species under the stabilizing action of the lithium perchlorate / nitromethane electrolyte solution. This basic skeleton paves the way for mass synthesis of nucleic acid derivatives, which are promising as therapeutic drug for covid-19.

Furthermore, K. Chiba achieved organic electrolytic reactions that mimic the electron transfer process in the living body. Inspired by the bio-mimic chemical reaction system, he proposed a chemical process based on biphasic solutions. The key technology is the introduction of a solution system that combines a highly polar electrolyte solution and a hydrophobic organic solvent. By controlling the temperature, phase-fusion and phase-separation can be repeated, so that the product, for example, can be taken out from the reaction system while reusing the electrolyte solution. By forming reverse micelles in a hydrophobic solvent, a continuous reaction system can be constructed, which has led to the proposal of an important method for industrial application of electrolytic reactions and of multi-step medium-size molecule syntheses reducing environmental load.

Outlook for the future: We must achieve a more efficient cycle of material, food and energy to support the world's population of 9 billion in the near future. For that purpose, it is extremely important to pay attention to and apply the functions of electrons involved in the production and decomposition of all chemical substances, including the elucidation and utilization of biological functions. The key technology of controlling electron transfer is indispensable for achieving a smart green society boosting a better Anthropocene.