Mechanical energy or heat? Thermal modulation of the kinetics of a mechanically activated solvent-free organic transformation Patrick A. Julien, Tristan H. Borchers, Hatem M. Titi, Martin Etter, Christopher J. Barrett and Tomislav Friščić Department of Chemistry, McGill University, Canada Understanding the relative importance of mechanical energy and heat on the course of organic reactions remains an ongoing challenge of mechanochemical synthesis. While strong variations in reaction kinetics have been observed upon relatively minor changes of milling conditions for mechanochemical solid-state organic reactions, notable increases in reaction temperatures due to frictional heating have been reported when increasing milling frequencies. This complicates the development of a fundamental understanding of the roles of temperature and mechanical impact forces in mechanochemistry. To decouple impact and mixing forces from thermal effects and better understand the role of temperature in solid-state organic reactions, we applied variable temperature real- time measurements of pre-milled reaction mixtures. Comparing the kinetics of milling reactions with hot-stage Raman microscopy measurements of pre-milled reactants for the reaction of o- phenylenediamine and benzil allows for a better understanding of thermal effects on the kinetics of the reaction. The reaction temperature appears to dominate the mobility and kinetics of the transformation, highlighting the significance of small temperature differences in milling reactions. Lower conversions for thermal reactions relative to milling are likely due to sublimation and provide a justification of the use milling for these thermally sensitive reactions.
P30
© The Author(s), 2022
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