In-situ Mass Spectrometric Analysis of the Reactive Intermediates Generated in the Electrochemical Amidation Reactions

Abstract

Amide bond is a ubiquitous and crucial functional group that serves as the linchpin for constructing proteins, peptides, and is also the central site in numerous drug molecules. Consequently, it is crucial to investigate the strategies and mechanisms of amidation reactions. In recent years, the use of electrochemistry for amidation has gained significant attention due to its exceptional qualities such as increased selectivity and eco-friendliness. However, due to the complexities of the reaction processes and the scarcity of relevant analytical tools, the studys of in-situ monitoring and mechanistic investigations on these electrochemical amidation reactions are rare. In response to this challenge, a novel coupling device was designed in this study. The main component of the coupling device was a glass capillary tube with a metal cover. The metal coating on the tip's outer surface was connected to a high voltage power supply to drive the electrospray ionization process. Additionally, the metal coating inside the tip was also connected to the metal coating on the tip's outer surface and served as the working electrode for an electrochemical reaction. When high voltage was applied, both the electrospray process and the electrochemical reaction on the tip could be driven simultaneously. The substances produced by the electrochemical reaction in the capillary tip could be quickly transfered to spray droplets, ionized via desolvation process, and finally detected via mass spectrometry. Based on this technique, a series of aromatic primary amines amidation reactions were observed in situ while using triphenylphosphine as the condensing agent. Numerous important intermediates were also discovered during these reactions. Remarkably, this novel approach not only facilitated continuous real-time monitoring of these reactions but also empowered scientists to unambiguously identify an array of key intermediates, including the elusive short-lived free radical intermediates. The electrochemical-mass spectrometry coupling device has numerous advantages, including short analysis delays, the ethical use of sample resources, and uncomplicated, simple preparation processes. It's potential to revolutionize the field of electroorganic synthesis reactions. This cutting-edge technique is poised to become an invaluable tool for rapid screening and in-depth investigations into the complex mechanisms of driving amidation reactions. The coupling device represents an exciting improvement forward in the context of drug investigations, where precision and efficiency are critical. Additionally, as society places increasing emphasis on environmental sustainability and the demand for precise chemical processes intensifies, this breakthrough coupling device is expected to become a formidable instrument in investigating the mechanism of electrochemical reactions.

Keywords

• • amidation reactions
• radical intermediate
• in-situ mass spectrometry
• triphenylphosphine