Revisiting aromatic diazotization and aryl diazonium salts in continuous flow: highlighted research during 2001–2021

Aryl diazonium salts play an important role in chemical transformations; however their explosive nature limits their applications in batch. Continuous flow technology allows safer operation for diazotization and application of aryl diazonium salts. Moreover, the other characteristics of continuous flow, such as laminar flow, residence time control, flow reactors with a larger surface area-to-volume ratio, the flexibility of equipment, etc., have significantly improved the reaction efficiency and industrialization potential of diazotization and aryl diazonium salts in various types of chemical transformations. However, the transformation from batch to continuous flow is still accompanied by new challenges (e.g., solid management, automation, and process analytical technology). Therefore, the application of aryl diazonium salts in continuous flow systems is closely related to the upgrade of continuous flow technology. In this article, an overview of aromatic diazotization and applications of aryl diazonium salts in continuous flow systems was described in detail.