Acid-Base Catalysis in the Mechanochemical Formation of a Reluctant Imine

Understanding the mechanism of action of catalytic amounts of additives on mechanochemical reactions is a growing and increasingly important topic in mechanochemistry, because it allows a significant level of control over the course and selectivity of mechanochemical reactions. Here, we investigate catalysis in the mechanochemical formation of an imine derived from p-nitrobenzaldehyde and p-nitroaniline, which did not occur by neat grinding at room temperature. Based on in situ reaction monitoring and DFT computations, we explain efficient catalysis observed for carboxylic acids, which suitably position the reacting partners and facilitate proton transfer. We also observe the formation of an aminal intermediate and conclude that the final elimination step in imine formation may proceed from either the hemiaminal or the aminal. Keywords: imine, mechanochemistry, acid-base catalysis, mechanism, Raman monitoring.